CEY Issue 3 Instruction Manual

PLUG FLOW REACTOR

Instruction Manual

CEY

ISSUE 3 December 2010

Table of Contents Copyright and Trademarks ...................................................................................... 1 Use with CEX Service Unit.......................................................................................... 2 General Overview ....................................................................................................... 3 Equipment Diagrams................................................................................................... 5 Important Safety Information....................................................................................... 6 Introduction.............................................................................................................. 6 Electrical Safety....................................................................................................... 6 Wet Environment ..................................................................................................... 6 Heavy Equipment .................................................................................................... 6 Chemical Safety ...................................................................................................... 7 Water Borne Hazards .............................................................................................. 7 Description .................................................................................................................. 9 Overview.................................................................................................................. 9 Flow of Material ..................................................................................................... 10 Installation ................................................................................................................. 14 Advisory................................................................................................................. 14 Installation Process ............................................................................................... 14 Operation .................................................................................................................. 18 Operating the Software.......................................................................................... 18 Operating the Equipment....................................................................................... 29 Equipment Specifications.......................................................................................... 34 Overall Dimensions ............................................................................................... 34 Connection to Drain............................................................................................... 34 Ventilation.............................................................................................................. 34 Environmental Conditions...................................................................................... 34 Routine Maintenance ................................................................................................ 36 Responsibility ........................................................................................................ 36 General.................................................................................................................. 36 RCD Test............................................................................................................... 36 ii

Table of Contents Temperature sensors Calibration .......................................................................... 36 Conductivity probe calibration ............................................................................... 37 Low conductivity Calibration (0-5 mS/cm) ............................................................. 37 Pipe work and connections.................................................................................... 38 Column packing..................................................................................................... 40 Static Premixer Packing ........................................................................................ 43 CEXC sensors fitting ............................................................................................. 44 Laboratory Teaching Exercises................................................................................. 46 Index to Exercises ................................................................................................. 46 Nomenclature ........................................................................................................ 46 Common Theory.................................................................................................... 47 Exercise A - Flow pattern characterisation - Step change ........................................ 49 Exercise B - Flow pattern characterisation - Pulse change....................................... 60 Exercise C - Conversion experiment......................................................................... 69 Contact Details for Further Information ..................................................................... 79

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Disclaimer This document and all the information contained within it is proprietary to Armfield Limited. This document must not be used for any purpose other than that for which it is supplied and its contents must not be reproduced, modified, adapted, published, translated or disclosed to any third party, in whole or in part, without the prior written permission of Armfield Limited. Should you have any queries or comments, please contact the Armfield Customer Support helpdesk (Monday to Friday: 0800 – 1800 GMT). Contact details are as follows: United Kingdom

International

(0) 1425 478781 (calls charged at local rate)

+44 (0) 1425 478781 (international rates apply)

Email: [email protected] Fax: +44 (0) 1425 470916

Copyright and Trademarks Copyright © 2009 Armfield Limited. All rights reserved. Any technical documentation made available by Armfield Limited is the copyright work of Armfield Limited and wholly owned by Armfield Limited. Brands and product names mentioned in this manual may be trademarks or registered trademarks of their respective companies and are hereby acknowledged.

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Use with CEX Service Unit This instruction manual describes the use of the CEY Plug Flow Reactor in conjunction with the CEXC Computer Controlled Service Unit. An alternative instruction manual is available from Armfield that describes the use of the CEY in conjunction with the CEX Service Unit. Please contact Armfield if a copy of this instruction manual is required. Contact details are included later in this document.

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General Overview This instruction manual should be used in conjunction with the manual supplied with the CEXC Computer Controlled Chemical Reactor Service Unit. This Manual provides the necessary information for operating the equipment in conjunction with the CEXC Computer Controlled Chemical Reactor Service Unit, and for performing a range of Teaching Exercises designed to demonstrate the basic principles of Chemical Reactors theory and use. Tubular reactors are often used when continuous operation is required but without back-mixing of products and reactants. In a tubular reactor, the feed enters at one end of a cylindrical tube and the product stream leaves at the other end. The long tube and the lack of provision for stirring prevent complete mixing of the fluid in the tube. Hence the properties of the flowing stream will vary from one point to another in both radial and axial directions. The Armfield CEY-Plug Flow Reactor is an example of an ideal tubular reactor specially designed to allow detailed study of this important process. It is one of five reactor types which are interchangeable on the Computer Controlled Reactor Service Unit (CEXC), the others being CEM MkII - Continuous Stirred Tank Reactor, CET MkII – Tubular Reactor, the new CEB MkIII – Transparent Batch Reactor and CEZ – Laminar flow reactor. Reactions are monitored by conductivity probe as the conductivity of the solution changes with conversion of the reactants to product. In addition, all the experiments are followed visually by means of the reactor transparency and the use of colour indicators in all the experiments.

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Armfield Instruction Manual

CEY Plug Flow Reactor

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Equipment Diagrams

Figure 1: Front View of Plug Flow Reactor Unit

Figure 2: Top View of Plug Flow Reactor Unit

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Important Safety Information Introduction All practical work areas and laboratories should be covered by local safety regulations which must be followed at all times. It is the responsibility of the owner to ensure that all users are made aware of relevant local regulations, and that the apparatus is operated in accordance with those regulations. If requested then Armfield can supply a typical set of standard laboratory safety rules, but these are guidelines only and should be modified as required. Supervision of users should be provided whenever appropriate. Your CEY Plug Flow Reactor Unit has been designed to be safe in use when installed, operated and maintained in accordance with the instructions in this manual. As with any piece of sophisticated equipment, dangers exist if the equipment is misused, mishandled or badly maintained.

Electrical Safety The equipment described in this Instruction Manual operates from a mains voltage electrical supply. It must be connected to a supply of the same frequency and voltage as marked on the equipment or the mains lead. If in doubt, consult a qualified electrician or contact Armfield. The equipment must not be operated with any of the panels removed. To give increased operator protection, the unit incorporates a Residual Current Device (RCD), alternatively called an Earth Leakage Circuit Breaker, as an integral part of this equipment. If through misuse or accident the equipment becomes electrically dangerous, the RCD will switch off the electrical supply and reduce the severity of any electric shock received by an operator to a level which, under normal circumstances, will not cause injury to that person. At least once each month, check that the RCD is operating correctly by pressing the TEST button. The circuit breaker MUST trip when the button is pressed. Failure to trip means that the operator is not protected and the equipment must be checked and repaired by a competent electrician before it is used.

Wet Environment The equipment requires a header tank containing water. During use it is possible that there will be some spillage and splashing. 

All users should be made aware that they may be splashed while operating the equipment, and should wear appropriate clothing and non-slip footwear.



‘Wet Floor’ warnings should be displayed where appropriate.



Electrical devices in the vicinity of the equipment must be suitable for use in wet environments or be properly protected from wetting.

Heavy Equipment This apparatus is heavy. 

The apparatus should be placed in a location that is sufficiently strong to support its weight, as described in the Installation section of the manual. 6

Important Safety Information 

Use lifting tackle, where possible, to install the equipment . Where manual lifting is necessary, two or more people may be required for safety, and all should be made aware of safe lifting techniques to avoid strained backs, crushed toes, and similar injuries.



Safety shoes and/or gloves should be worn when appropriate.

Chemical Safety Details of the chemicals intended for use with this equipment are given in the Operation section. Chemicals purchased by the user are normally supplied with a COSHH data sheet which provides information on safe handling, health and safety and other issues. It is important that these guidelines are adhered to. 

It is the user’s responsibility to handle chemicals safely.



Prepare chemicals and operate the equipment in well ventilated areas.



Only use chemicals specified in the equipment manuals and in the concentrations recommended.



Follow local regulations regarding chemical storage and disposal.

Specific Safety Guidelines: 

Indigo Carmine is dangerous and so should be used with the necessary safety procedures. When handling use of rubber gloves and protection glasses are strongly recommended.



Ethyl acetate is highly inflammable. Be careful with possible ignition sources, such as electric current, very hot surfaces or flames. Avoid breathing the ethyl acetate vapours.



Extreme care should be taken whilst handling either acetic acid or acetic anhydride. Both chemicals are highly corrosive and care should be taken to avoid contact or inhalation of vapour.

Water Borne Hazards The equipment described in this instruction manual involves the use of water, which under certain conditions can create a health hazard due to infection by harmful micro-organisms. For example, the microscopic bacterium called Legionella pneumophila will feed on any scale, rust, algae or sludge in water and will breed rapidly if the temperature of water is between 20 and 45°C. Any water containing this bacterium which is sprayed or splashed creating air-borne droplets can produce a form of pneumonia called Legionnaires Disease which is potentially fatal. Legionella is not the only harmful micro-organism which can infect water, but it serves as a useful example of the need for cleanliness. Under the COSHH regulations, the following precautions must be observed: 

Any water contained within the product must not be allowed to stagnate, ie. the water must be changed regularly.

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Armfield Instruction Manual 

Any rust, sludge, scale or algae on which micro-organisms can feed must be removed regularly, i.e. the equipment must be cleaned regularly.



Where practicable the water should be maintained at a temperature below 20°C. If this is not practicable then the water should be disinfected if it is safe and appropriate to do so. Note that other hazards may exist in the handling of biocides used to disinfect the water.



A scheme should be prepared for preventing or controlling the risk incorporating all of the actions listed above.

Further details on preventing infection are contained in the publication “The Control of Legionellosis including Legionnaires Disease” - Health and Safety Series booklet HS (G) 70.

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Description Where necessary, refer to the drawings in the Equipment Diagrams section.

Overview The reactor column is mounted on a stand to allow careful vertical alignment of the reactor. The CEY should be located close to the CEXC unit to allow connection to the instrumentation. The plug flow reactor is an acrylic column with a total volume of 1 L. It is packed with 3 mm glass beads to give plug flow with axial dispersion and improve flow distribution. At the bottom of the reactor a static premixer with a total volume of 1.6 ml is located. It is packed with glass beads of 1.2 mm in diameter to thoroughly mix the reactants before they enter the reactor. To avoid movement of the glass beads there are four meshes, which are located at the ends of the reactor column and the static premixer. The temperature of materials exiting the column is measured by temperature sensor (T1) which is fitted into the sensor block and is located at the top of the stand. The temperature value is displayed on the mimic screen of the CEXC software. An additional temperature sensor T2 is supplied with the CEXC and can be monitored. It is not necessary to use the Hot Water Circulator. The conductivity probe supplied with the CEXC unit is also fitted into this sensor block allowing the conductivity to be monitored at the exit of the reactor. The reactor is supplied with a Feed assembly, which is made up of a 6 port injection valve, PTFE pipe, silicone pipe with smaller diameter and two barbed connectors. The 6 port valve allows injection of a determined volume of liquid for tracer experiments. Sockets on the rear of the service unit provide connections for the conductivity probe and thermocouple plugs.

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Armfield Instruction Manual

Figure 1: CEY reactor

Flow of Material Reactants are pumped from the reagent bottles to the reactor passing through the 6 port injection valve. See Figure 2. At the exit of the reactor the stream enters the sensor block where conductivity and temperature values are monitored and then drained. See Figure 3.

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Description

Figure 2: Flow of material circuit

It is recommended to place the Plug flow reactor close to CEXC plinth in order to simplify the sensor connections and shorten the reactants path.

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Armfield Instruction Manual

Figure 3: Flow Exit Reactor

Injection valve operation The injection valve has 6 ports and two positions. In one position adjacent ports are linked together inside the valve so that there are 3 pairs of linked ports. Changing the position of the valve links the alternate port pair together (Figure 4.2). The function of the valve is to inject the tracer solution (colourful solution) in a defined volume ratio. This is achieved by using a tracer solution loop of defined lengths (230 cm for a volume of 10 ml). When the injection valve is in the load position (Figure 4.1) the tracer solution loop is filled. Tracer solution passes out of the injection valve and it is recirculated. Carrier liquid (water) is directed to the reactor. When the injection valve is switched to the injection position (Figure 4.2) the carrier liquid (water) picks up the volume of the tracer solution (dye) contained in the loop and passes it to the reactor.

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Description

Figure 4.1 and 4.2: Injection valve positions

Figure 5: Injection Flow Assembly (FIA)

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Installation Advisory Before operating the equipment, it must be unpacked, assembled and installed as described in the steps that follow. Safe use of the equipment depends on following the correct installation procedure.

Installation Process Locate the CEXC unit in the desired location, on a steady workbench.

Mount the 6 port injection valve assembly on to the CEXC using the two locating studs and the black thumbnuts. Position the valve on the left hand side of the base. Position the reagent bottles in the channel through the unit. Locate the CEY reactor unit close to the CEXC unit. Change the silicone tubing on both sides of the CEXC peristaltic pumps for the new Silicone tubing (smaller diameter). Tubing on the left side of each feed pump is fitted into the bottles as shown. Tubing on the right side is connected to the corresponding ports of the valve through the barbed connector supplied. If connections to the 6 port valve are necessary see below:

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Installation

Note: Changing the length of the Loop changes the volume of tracer injected into the column. Check that the two solutions follow two different circuits: Circuit 1(for water): Bottle 1- enter valve- exit valve- reactor. Circuit 2(Tracer): Bottle 2-enter valve – enter Loop (exit valve) – Exit Loop (enter valve) – Exit valve. Fit the CEXC conductivity sensor into the gland in the sensor block of the reactor unit (bottom channel of the sensor block). Fit the CEXC temperature sensor into the other gland on the sensor block (top channel of the sensor). Sensors should be inserted as described in CEXC sensors fitting.

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Armfield Instruction Manual

Connect the conductivity probe and temperature sensor (T1) plugs to the sockets at the rear of the service unit.

Check that the voltage specified on the equipment matches the supply voltage. Note: this unit must be earthed. Connect the power socket at the rear of the plinth to a suitable mains electricity supply. Ensure that the circuit breakers and RCD are switched to ON (up). The on/off switch for the apparatus is located on the orange panel on the front of the plinth. Switch on the apparatus. Connect CEXC to a PC using the USB cable supplied. Insert the CEY software CD-ROM into the CD-R drive of a suitable PC. The installation program should auto run. If it does not, select ‘Run...’ from your Start menu, type run d:\setup where d is the letter of your CD-ROM drive.

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Installation

Follow the instructions on screen. Run the software. The basic operation of the CEY has been confirmed. Refer to the Operation section for further information.

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Operation Where necessary, refer to the drawings in the Equipment Diagrams section. The apparatus must be set up in accordance with the Installation section. Additionally, ensure that you have read the Important Safety Information at the beginning of this manual.

Operating the Software Note: The diagrams in this section are included as typical examples and may not relate specifically to the individual product described in this instruction manual. The Armfield Software is a powerful Educational and Data Logging tool with a wide range of features. Some of the major features are highlighted below, to assist users, but full details on the software and how to use it are provided in the presentations and Help text incorporated in the Software. Help on Using the Software or Using the Equipment is available by clicking the appropriate topic in the Help drop-down menu from the upper toolbar when operating the software as shown:

Before operating the software ensure that the equipment has been connected to the IFD5 Interface (where IFD5 is separate from the equipment) and the IFD5 has been connected to a suitable PC using a USB lead. For further information on these actions refer to the Operation manual. Load the software. If multiple experiments are available then a menu will be displayed listing the options. Wait for the presentation screen to open fully as shown:

Before proceeding to operate the software ensure that IFD: OK is displayed at the bottom of the screen. If IFD:ERROR is displayed check the USB connection between 18

Operation the IFD5 and the PC and confirm that the red and green LED’s are both illuminated. If the problem persists then check that the driver is installed correctly (refer to the Operation manual).

Presentation Screen - Basics and Navigation As stated above, the software starts with the Presentation Screen displayed. The user is met by a simple presentation which gives them an overview of the capabilities of the equipment and software and explains in simple terms how to navigate around the software and summarizes the major facilities complete with direct links to detailed context sensitive ‘help’ texts. To view the presentations click Next or click the required topic in the left hand pane as appropriate. Click More while displaying any of the topics to display a Help index related to that topic. To return to the Presentation screen at any time click the View Presentation icon from the main tool bar or click Presentation from the dropdown menu as shown:

For more detailed information about the presentations refer to the Help available via the upper toolbar when operating the software.

Toolbar A toolbar is displayed at the top of the screen at all times, so users can jump immediately to the facility they require, as shown:

The upper menu expands as a dropdown menu when the cursor is placed over a name. The lower row of icons (standard for all Armfield Software) allows a particular function to be selected. To aid recognition, pop-up text names appear when the cursor is placed over the icon.

Mimic Diagram The Mimic Diagram is the most commonly used screen and gives a pictorial representation of the equipment, with continuously updated display boxes for all the various sensor readings, calculated variables etc. directly in engineering units.

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Armfield Instruction Manual

To view the Mimic Diagram click the View Diagram icon from the main tool bar or click Diagram from the View drop-down menu as shown:

A Mimic diagram is displayed, similar to the diagram as shown:

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Operation

The details in the diagram will vary depending on the equipment chosen if multiple experiments are available.

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Armfield Instruction Manual In addition to measured variables such as Temperature, Pressure and Flowrate (from a direct reading flowmeter), calculated data such as Motor Torque, Motor Speed and Discharge / Volume flowrate (from pressure drop across an orifice plate) are continuously displayed in data boxes with a white background. These are automatically updated and cannot be changed by the user. Manual data input boxes with a coloured background allow constants such as Orifice Cd and Atmospheric Pressure to be changed by over-typing the default value, if required. The data boxes associated with some pressure sensors include a Zero button alongside. This button is used to compensate for any drift in the zero value, which is an inherent characteristic of pressure sensors. Pressing the Zero button just before starting a set of readings resets the zero measurement and allows accurate pressure measurements to be taken referenced to atmospheric pressure. This action must be carried out before the motor is switched on otherwise the pressure readings will be offset. The mimic diagram associated with some products includes the facility to select different experiments or different accessories, usually on the left hand side of the screen, as shown:

Clicking on the appropriate accessory or exercise will change the associated mimic diagram, table, graphs etc to suit the exercise being performed.

Control Facilities in the Mimic Diagram A Power On button allows the motor to be switched off or on as required. The button always defaults to off at startup. Clicking this button switches the power on (1) and off (0) alternately. A box marked Motor Setting allows the speed of the motor to be varied from 0 to 100% either stepwise, by typing in values, or using the up / down arrows as appropriate. It is usual to operate the equipment with the motor initially set to 100%,

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Operation then reduce the setting as required to investigate the effect of reduced speed on performance of the equipment. When the software and hardware are functioning correctly together, the green LED marked Watchdog Enabled will alternate On and Off. If the Watchdog stops alternating then this indicates a loss of communication between the hardware and software that must be investigated. Details on the operation of any automatic PID Control loops in the software are included later in this section.

Data Logging Facilities in the Mimic Diagram There are two types of sampling available in the software, namely Automatic or Manual. In Automatic logging, samples are taken regularly at a preset but variable interval. In Manual logging, a single set of samples is taken only when requested by the operator (useful when conditions have to be changed and the equipment allowed to stabilize at a new condition before taking a set of readings). The type of logging will default to manual or automatic logging as appropriate to the type of product being operated. Manual logging is selected when obtaining performance data from a machine where conditions need to stabilize after changing appropriate settings. To record a set of set of data values from each of the measurement sensors click the main toolbar. One set of data will be recorded each time the

icon from the icon is clicked.

Automatic logging is selected when transients need to be recorded so that they can be plotted against time. Click the the

icon from the toolbar to start recording, click

icon from the toolbar to stop recording.

The type of logging can be configured by clicking Configure in the Sample dropdown menu from the upper toolbar as shown:

In addition to the choice of Manual or Automatic sampling, the parameters for Automatic sampling can also be set. Namely, the time interval between samples can be set to the required number of minutes or seconds. Continuous sampling can be selected, with no time limit or sampling for a fixed duration can be set to the required number of hours, minutes or seconds as shown:

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Armfield Instruction Manual

Tabular Display To view the Table screen click the View Table icon click Table from the View dropdown menu as shown:

from the main tool bar or

The data is displayed in a tabular format, similar to the screen as shown:

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Operation

As the data is sampled, it is stored in spreadsheet format, updated each time the data is sampled. The table also contains columns for the calculated values. New sheets can be added to the spreadsheet for different data runs by clicking the icon from the main toolbar. Sheets can be renamed by double clicking on the sheet name at the bottom left corner of the screen (initially Run 1, Run 2 etc) then entering the required name. For more detailed information about Data Logging and changing the settings within the software refer to the Help available via the upper toolbar when operating the software.

Graphical Display When several samples have been recorded, they can be viewed in graphical format. from the main To view the data in Graphical format click the View graph icon tool bar or click Graph from the View drop-down menu as shown:

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Armfield Instruction Manual The results are displayed in a graphical format as shown:

(The actual graph displayed will depend on the product selected and the exercise that is being conducted, the data that has been logged and the parameter(s) that has been selected). Powerful and flexible graph plotting tools are available in the software, allowing the user full choice over what is displayed, including dual y axes, points or lines, displaying data from different runs, etc. Formatting and scaling is done automatically by default, but can be changed manually if required. To change the data displayed on the Graph click Graph Data from the Format dropdown menu as shown:

The available parameters (Series of data) are displayed in the left hand pane as shown:

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Operation

Two axes are available for plotting, allowing series with different scaling to be presented on the same x axis. To select a series for plotting, click the appropriate series in the left pane so that it is highlighted then click the appropriate right-facing arrow to move the series into one of the windows in the right hand pane. Multiple series with the same scaling can be plotted simultaneously by moving them all into the same window in the right pane. To remove a series from the graph, click the appropriate series in the right pane so that it is highlighted then click the appropriate left-facing arrow to move the series into the left pane. The X-Axis Content is chosen by default to suit the exercise. The content can be changed if appropriate by opening the drop down menu at the top of the window. The format of the graphs, scaling of the axes etc. can be changed if required by clicking Graph in the Format drop-down menu as shown:

For more detailed information about changing these settings refer to the Help available via the upper toolbar when operating the software.

PID Control Where appropriate, the software associated with some products will include a single or multiple PID control loops whereby a function on the product can be manually or

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Armfield Instruction Manual automatically controlled using the PC by measuring an appropriate variable and varying a function such as a heater power or pump speed. The PID loop can be accessed by clicking the box labelled PID or Control depending on the particular software:

A PID screen is then displayed as shown:

The Mode of operation always defaults to Manual control and 0% output when the software is loaded to ensure safe operation of the equipment. If appropriate, the operator can retain manual operation and simply vary the value from 0 to 100% in the Manual Output box, then clicking Apply. Alternatively, the PID loop can be changed to Automatic operation by clicking the Automatic button. If any of the PID settings need to be changed from the default values then these should be adjusted individually before clicking the Apply button.

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Operation The controller can be restored to manual operation at any time by clicking the Manual button. The value in the Manual Output box can be changed as required before clicking the Apply button. Settings associated with Automatic Operation such as the Setpoint, Proportional Band, Integral Time, Derivative Time and Cycle Time (if appropriate) can be changed by the operator as required before clicking the Apply button. Clicking Calculations displays the calculations associated with the PID loop to aid understanding and optimization of the loop when changing settings as shown:

Clicking Settings returns the screen to the PID settings. Clicking OK closes the PID screen but leaves the loop running in the background. In some instances the Process Variable, Control variable and Control Action can be varied to suit different exercises, however, in most instances these boxes are locked to suit a particular exercise. Where the variables can be changed the options available can be selected via a drop-down menu.

Advanced Features The software incorporates advanced features such as the facility to recalibrate the sensor inputs from within the software without resorting to electrical adjustments of the hardware. For more detailed information about these advanced functions within the software refer to the Help available via the upper toolbar when operating the software.

Operating the Equipment Switching on the Unit The unit is switched on using the switch on the front of the unit. The circuit breakers and RCD device located at the rear of the unit should be turned on beforehand. Both the temperature controller and conductivity display should illuminate. 29

Armfield Instruction Manual

Filling the feed bottles Lift the feed bottle lids and pour solutions in from above.

Operation of Data Logger and Software The Tubular Reactor is controlled using the CEY software supplied, which allows real-time monitoring and data logging of all sensor outputs and control of the heater unit and pumps. Recorded results can be displayed in tabular and graph format. The software runs on a WindowsTM PC which connects to the CEXC using a USB interface. Installation of the software is described in the Installation Guide, and the software must be installed before connecting the PC to the CEXC. The software may then be run from the Start menu (Start > Programs > Armfield Chemical Reactor Software > CEY). Operation of the software is described in a walkthrough presentation within the software, and also in the online Help Text accessible via the software Help menu. Operation and setting of specific controls is also provided within the experiments described in this manual.

Mimic Diagram and software The equipment is usually controlled from the Mimic Diagram screen in the software. This shows all the sensor outputs, and controls for the pumps. There is an extra temperature sensor ‘T3’ and ‘Low conductivity’ plugs with outputs on the software for extra connections made by the user.

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Operation

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Armfield Instruction Manual

Feed pump speeds are controlled using up/down arrows or typing the flow rate in a value between 0 and the maximum ml/min. Click on the appropriate POWER ON symbol to start up the pumps. Concentration values must be typed in on each experiment so that the software will carry out the subsequent calculations. Conductivity and temperature values will be monitored on the screen and the data logged when ‘GO’ is clicked. The software also automatically generates a series of ‘Watchdog’ pulses, required by the plc, ensuring that the hardware shuts down safely in case of a software or communications failure.

Operating Plug Flow Reactor There are two modes of operation with the CEY Plug flow reactor: tracer experiment and conversion experiment operation. The type of experiment performed defines the operational layout. When tracer experiments take place, one solution is injected into the reactor after another. However, when conversion experiment takes place two solutions are injected into the reactor at the same time so that a T- connector is necessary. When performing experiments follow the experimental layouts described in each exercise.

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Operation

Operational Layout for tracer experiments

Overall Process Having reviewed the components of the CEY it is worthwhile considering the process as a whole. The feed pump delivers the feed to the injection valve assembly. All the connections should be set so that each solution passes through the correct port of the injection valve and is delivered to the reactor or back to the vessel. In the teaching exercises section each experiment fully describes the required connections.

Air bubbles in the reactor column Bubbles should not be allowed to enter the reactor column since this will have a negative effect on performance. Care should be taken not to pump any bubbles into the column. If any bubbles enter the column before the tracer solution is injected, continue flowing water into the reactor until all bubbles are gone. However, if a bubble enters the reactor when the tracer solution has been injected, the experiment has to be restarted since flow distribution will be affected and so will conductivity values.

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Equipment Specifications Overall Dimensions Reactor Unit: Height:

1381 cm

Width:

859 cm

Depth:

330 cm

Reactor dimensions: Reactor column: Total length:

1044 mm

Internal diameter:

34 mm

External diameter:

40 mm

Total volume column: 0.919 dm3 Pre mixer cylinder: Length

42 mm

Diameter internal

8.65 mm

Diameter external

20 mm

Connection to Drain Water exiting the equipment should be directed to a suitable drain capable of accepting volumes of up to 90 ml/min at temperatures not greater than room temperature. The chemical solutions used in each experiment at the required concentration should be directed to a suitable drain capable of accepting volumes of up to 90 ml/min at room temperature.

Ventilation For optimum results it is advisable to operate the reactor column in a ventilated environment at a room temperature up to 25ºC.

Environmental Conditions This equipment has been designed for operation in the following environmental conditions. Operation outside of these conditions may result reduced performance, damage to the equipment or hazard to the operator. a. Indoor use; b. Altitude up to 2000 m; c. Temperature 5 °C to 40 °C;

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Equipment Specifications d. Maximum relative humidity 80 % for temperatures up to 31 °C, decreasing linearly to 50 % relative humidity at 40 °C; e. Mains supply voltage fluctuations up to ±10 % of the nominal voltage; f.

Transient over-voltages typically present on the MAINS supply; NOTE: The normal level of transient over-voltages is impulse withstand (overvoltage) category II of IEC 60364-4-443;

g. Pollution degree 2. Normally only nonconductive pollution occurs. Temporary conductivity caused by condensation is to be expected. Typical of an office or laboratory environment

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Routine Maintenance Responsibility To preserve the life and efficient operation of the equipment it is important that the equipment is properly maintained. Regular maintenance of the equipment is the responsibility of the end user and must be performed by qualified personnel who understand the operation of the equipment.

General The equipment should be disconnected from the electrical supply when not in use. After use the feed bottles, reactor vessel, sump tray and pipework should be washed through with water to remove chemical residues, and then drained.

RCD Test Test the RCD by pressing the TEST button at least once a month. If the RCD button does not trip when the Test button is pressed then the equipment must not be used and should be checked by a competent electrician.

Temperature sensors Calibration The temperature sensors are calibrated before delivery and should not require recalibration. However, should calibration become necessary use the following procedure. This should only be done once the unit has fully warmed up. Connect CEXC service unit to a PC and start up the Armfield software. Open mimic diagram screen where T1, T2 and T3 windows are displayed. The temperature conditioning circuit (which provides the reading from the thermocouples supplied with the CEXC service unit) is located on a printed circuit board (PCB) inside the plinth on the right-hand side. However, should re-calibration become necessary the appropriate calibration potentiometers can be located using the diagram given in the CEXC manual (Routine Maintenance). Ensure the equipment has been connected to the electrical supply and switched on for at least 20 minutes. Start up the Armfield software for the specific reactor. To access the PCB remove the panel on the right hand side of the plinth by removing the four fixing screws. If a thermocouple calibrator is available: Connect Thermocouple calibrator simulator to T1 input socket, located at the rear of the plinth. Set to 25ºC and adjust VR1 (T1 ZERO) and VR2 (T1 SPAN) on the PCB to give 25ºC displayed on PC. Check accuracy at 15º and 40ºC. Repeat the same procedure for T2 by adjusting VR3 (T2 ZERO) and VR4 (T2 SPAN) on the PCB to give 25ºC displayed on PC, and VR5 (T3 ZERO) and VR6 (T3 SPAN) for T3 (if an extra thermocouple is used). If a thermocouple calibrator is not available: Temperature sensor T1, T2 and T3 should be dipped into crushed ice, and then adjust the ZEROS to give 0ºC, then sensors should be dipped into boiling water and then adjust the SPANS to 100ºC.

36

Routine Maintenance When the conditioning circuit has been re-calibrated, replace the front panel of the electrical console and re-install the sensors in the appropriate place on the CEXC service unit.

Conductivity probe calibration The conductivity conditioning circuit (which provides the reading from the conductivity probe supplied with the CEXC service unit) is located on a printed circuit board inside the plinth on the right-hand side. This circuit is calibrated before despatch and should not require re-calibration. However, should re-calibration become necessary the appropriate calibration potentiometers can be located using the diagram given in the CEXC manual (Routine Maintenance). Ensure the equipment has been connected to the electrical supply and switched on for at least 20 minutes. Start up the Armfield software for the specific reactor. To access the PCB remove the panel on the right hand side of the plinth by removing the four fixing screws. Disconnect the conductivity probe from the socket at the back of the plinth. Connect an AC Voltmeter (Range AC mV) to pins 1 and 2 of the vacant socket and adjust potentiometer VR10 on the PCB to give a reading of 50 mV (RMS) on the Voltmeter (probe excitation voltage). Disconnect the Voltmeter then reconnect the probe to the socket having removed the probe from the appropriate reactor fitted to the CEXC. Note that there are two, ‘High Cond’ and ‘Low Cond’ sockets. Connect the probe to the one which is going to be calibrated and read the conductivity value in the right window on the software.

High conductivity Calibration (0-20 mS/cm) Fill a small beaker with a Conductivity standard solution (e.g. 0.1M KCI giving a conductivity of 12.88 mS at 25°C) and measure the temperature of the standard solution using a suitable thermometer. From the table supplied determine the actual conductivity of the solution at the measured temperature. Immerse the probe into the Conductivity standard solution in the beaker then adjust potentiometer VR7 to give a reading of the standard solution in the ‘High conductivity’ box on the software to match the conductivity.

Low conductivity Calibration (0-5 mS/cm) Fill a small beaker with a Conductivity standard solution (e.g. 0.01M KCI giving a conductivity of 1.41mS at 25°C) and measure the temperature of the standard solution using a suitable thermometer. From the table supplied determine the actual conductivity of the solution at the measured temperature. Immerse the probe into the Conductivity standard solution in the beaker then adjust potentiometer VR8 to give a reading of the Standard solution in the ‘Low conductivity’ box on the software. When the conditioning circuit has been re-calibrated replace the panel and re-install the probe in the appropriate reactor on the CEXC service unit.

37

Armfield Instruction Manual

12.88 mS/cm at 25ºC 0.1 M KCl ºC

mS/cm

ºC

mS/cm

5

8.22

20

11.67

10

9.33

21

11.91

15

10.48

22

12.15

16

10.72

23

12.39

17

10.95

24

12.64

18

11.19

25

12.88

19

11.43

26

13.13

1.413 mS/cm at 25ºC 0.01 M KCl ºC

mS/cm

ºC

mS/cm

5

0.896

20

1.278

10

1.02

21

1.305

15

1.147

22

1.332

16

1.173

23

1.359

17

1.199

24

1.386

18

1.225

25

1.413

19

1.251

26

1.441

Pipe work and connections The CEY pipework is mainly hard walled Teflon tubing (4 mm o.d., 2.5 mm i.d.). However for peristaltic pumps soft walled tubing is used. Two basic types of connectors are used: reducing connectors for soft walled tubing connected to hard walled tubing (see below) and silicone pipe to connect barbed connector from 6-port injection valve to Teflon pipe. This allows simple connection and disconnection as required.

38

Routine Maintenance

Connecting hard walled to soft walled tubing

The CEY is supplied with all pipework and connections in place, however there may be an instance when the user wishes to alter the arrangement. The barbed adaptors used on the 6-port injection valve remain connected. The only connection that maybe required is Teflon pipe with the injection valve, and this must be done using a piece of silicone pipe (see below).

Pipework connections with Injection valve

Any extra connection between hard walled Teflon tubing can be done using a piece of silicone tube with the same inner diameter as that provided with the equipment.

Connection to reactor fittings Quick connectors are found in every connection between Teflon pipe and reactor unit. These connections are located at the inlet and outlet of the column reactor, and at the inlet and outlet of the sensor block.

39

Armfield Instruction Manual

Column quick connectors

These connectors are made up of two parts; the body, which is screwed into the reactor, and cap which is connected to the Teflon pipe. Two steps comprise the connection; 1. Push cap against body until it clicks 2. Screw cap connector until sealed

Connections with quick connectors

Column packing CEY column should be provided already packed. However, if packing or unpacking should be necessary follow the below procedure.

40

Routine Maintenance

Plug flow reactor assembly

Unpacking 1. Disconnect CEXC unit from the electrical supply 2. Disconnect pipe and sensors from CEXC unit which are connected to the reactor unit (PTFE tubing, T1 and Conductivity plugs) so that the reactor unit can be moved 3. Disconnect pipe which goes from the reactor exit to sensor block 4. Unscrew the head screw so that the top bracket will come loose from the stand and also the top of the reactor. Do not unscrew the 6 screws from the top reactor 5. Unscrew the six screws from the bottom and do not take the lid off from the column until required 6. Keeping the lid on to avoid dropping glass beads, turn the reactor around so that the bottom becomes the top of the reactor and vice versa 7. Remove the lid, the mesh and the O-ring and keep them safe. See below. 8. Empty the reactor

41

Armfield Instruction Manual

Packing column

Initial procedure if column is not packed 1. Follow the same procedure as described above until point 4 2. Unscrew the six bottom screws and remove the lid 3. Turn the reactor around so that the bottom becomes the top and vice versa. See Packing Column above.

Packing: 4. Once initial procedure has been done, fill the reactor with water blocking the other end so that it does not drain. The glass beads will gently settle. 5. Once column is filled with water, start filling in with the 3 mm glass beads. Then, start the reassembly: 6. Unblock lower part of the reactor emptying the water 7. Replace the mesh and o-ring 8. Replace the lid and hold it close to the reactor so as not to spill glass beads 9. Turn the reactor down to its normal position 42

Routine Maintenance 10. Place it over the bottom bracket matching the holes of the reactor column and lid 11. Tighten the six bottom screws so that the bottom part of the reactor is fixed 12. Tighten the head screw so that the top part of the reactor is fixed

Static Premixer Packing

Static Premixer

Packing/unpacking 1. Disconnect pipe connected to the premixer from the reactor column 2. Remove the premixer the reactor 3. Remove the o-ring 4. Unscrew the fitting which connects the reactor column with the premixer 5. Remove the mesh 6. Make sure that at the bottom of the premixer there is a small mesh 7. Fill up the premixer with water keeping the other side blocked so that it does not drain 8. Fill the premixer with 1.3 mm diameter glass beads and leave sufficient room to fit the quick connector 9. Replace the mesh and refit the quick connector

43

Armfield Instruction Manual 10. Replace the o-ring and refit the premixer into the bottom of the reactor column

CEXC sensors fitting

Sensor block parts and fitting

It is recommended to place the CEY reactor close to CEXC plinth in order to simplify the sensor connections and shorten the reactants path. Note that CEXC is supplied with two temperature sensors. T1 is usually fitted in each reactor, and T2 is fitted in the Hot water Circulator (HWC). However the HWC is not required for the experiments with this reactor.

Temperature sensor (T1) connection The procedure for fitting the sensor is as follows: 

Unscrew gland T1



Handling carefully the temperature sensor, pass it through the gland and fit it into its corresponding hole.



Push the sensor down to the end of the channel so that the detecting part is in the flow path.



Then pull the probe back a few mm to allow the flow to pass through the path.



Re-tighten the gland in order to seal.

Conductivity sensor (CS) connection Be careful handling the conductivity probe since the glass part is very fragile. When fitting sensor use following procedure:

44



Unscrew cable gland CS



Handling the conductivity sensor carefully, pass it through the cable gland and fit it into its corresponding channel so that the two holes at the end of the

Routine Maintenance probe are positioned inline with entrance and exit of the sensor block and not towards the walls. For experiments described in this manual, high conductivity values are monitored (020mS/cm). However if other solutions are used with lower conductivity values (0-5 mS/cm), connect the conductivity probe to ‘Low cond.’ socket and monitor the reading on the ‘Low cond’ window. It is IMPORTANT to fit the probe into the sensor block as described above so that the two holes of the conductivity probe will be open to the flow. Otherwise the flow will be blocked by the conductivity probe and the conductivity values will not be accurate. Once the conductivity sensor is correctly positioned then retighten the gland in order to seal.

45

Laboratory Teaching Exercises Index to Exercises Exercise A - Flow pattern characterisation - Step change Exercise B - Flow pattern characterisation - Pulse change Exercise C - Conversion experiment

Nomenclature Symbol

Name

Unit

C NaOH0

sodium hydroxide initial conc. in (mol/dm3) mixed feed

C NaOH (t)

sodium hydroxide conc. in reactor at time t

(mol/dm3)

sodium hydroxide conc. in reactor after time

(mol/dm3)

C0

Tracer concentration

k

specific rate constant

L

overall length of tubular reactor (cm)

A

cross sectional area of tubular reactor

r

reaction rate

tR

residence time

(s)

t

elapsed time

(s)

T

reactor temperature

(K)

V

volume of reactor

(dm3)

Pe

Peclet number



Tau, space time

X NaOH

conversion of sodium hydroxide conductivity at time t

(cm2)

(s)

(Siemens/cm)

initial conductivity

46

Laboratory Teaching Exercises

conductivity at

time

sodium hydroxide conductivity Ă

Arrhenius frequency factor

Ea

activation energy

(J/mol)

R

gas constant

(J/mol K)

E(t)

residence time distribution function

M

Initial mixing proportion = C B0 /C A0

D ax

Axial dispersion

Common Theory The Armfield CEY Plug flow reactor is designed to demonstrate the mechanism of chemical reactions in continuous flowing systems and also to obtain the flow pattern by using tracer experiments. A tubular reactor packed with glass beads has a Residence Time Distribution that is very similar to that of a plug flow reactor, but with some axial dispersion. Two experiments demonstrate the flow pattern by means of tracer techniques and the calculation of the RTD. Another experiment demonstrates the steady state conversion of a second order reaction in a tubular reactor packed with glass beads. Although it may be possible to carry out demonstrations using other chemicals it is not advisable without first contacting Armfield as the materials of construction of the reactor may not be compatible.

DILUTION OF POTASSIUM CHLORIDE AND INDIGO CARMINE FOR USE WITH TRACER TECHNIQUES 

0.1M solution of Potassium Chloride containing 0.01% w/w of Indigo carmine

This should be made by dissolving potassium chloride as follows:

Mass of Indigo Carmine =

47

Armfield Instruction Manual Then, weight 7.459 g. of KCl and 0.1 g of IC and dissolve it in distilled water up to 1 litre 

Follow the same procedure for 1 M solution:

If the necessary volume is 150 cm3,

For Indigo Carmine solution at determined % (w/w) respect to the potassium chloride solution, make up as follows:

Then, weight 11.18gr of KCl and 0.15 gr of IC and dissolve it in distilled water up to 150 cm3

DILUTION OF ETHYL ACETATE AND SODIUM HYDROXIDE FOR USE WITH REACTION EXPERIMENT 

0.25 M solution of Ethyl Acetate containing 0.01% w/w of IC

This should be made by diluting concentrated Ethyl Acetate as follows:

As explained before, the indigo carmine at determined concentration C% (w/w) respect to the concentrate should be diluted as follows:



1 L of 0.2 M solution of 1 M Sodium Hydroxide

Then, in order to obtain a solution 0.2 M from a 1M NaOH solution, measure 0.2 litres of 1M NaOH and add distilled water until 1 litre. 48

Exercise A - Flow pattern characterisation - Step change Objective The aim of this practical exercise is to study the flow pattern characterisation of a tubular reactor packed with glass beads. This characterisation will be performed using a model considering a plug-flow reactor with axial dispersion and by determination of the Residence Time Distribution, RTD.

Method The study of the flow pattern in a reactor is usually done by using tracer techniques which consist of injecting several perturbations in the inlet reactor and waiting for its response. The commonly used perturbations in a plug flow reactor are a Pulse change and Step change. Coloured tracer solution is used in order to make the propagation of the concentration wave visible. In this exercise the Step change as a perturbation is studied.

Equipment Required Armfield service unit CEXC Armfield Plug Flow reactor unit CEY Compatible PC with Armfield software

Chemicals Distilled water Potassium Chloride Indigo carmine

Theory The flow characterisation of a reactor is done by the determination of the RTD, which is obtained using tracer techniques. The RTD curve allows us to obtain the permanence of each fraction of volume of fluid inside the reactor and also to demonstrate its behaviour, ideal or not ideal. Tracer techniques use several perturbations in the inlet of the reactor and wait for the reactor response. The most common perturbations used in a plug flow reactor are the named Step change and Pulse change. The perturbations use tracer solutions containing a detectable solution which can be detected and therefore followed. This allows the full comprehension of the reactor behaviour. In this experiment the tracer solution is made up of a salt, therefore detectable by conductivity measurement, and a dye, which allows it to be followed visually.

Step change Step input or step change consists of an instant change in concentration of the tracer from one concentration to another.

49

Armfield Instruction Manual

The response of the reactor is mathematically represented by the following function: C(t) = C 0 [1-H(t-0)]

(1)

(H) = Heaviside function The RTD equation for plug flow with axial dispersion, considering a semi infinite reactor;

(2) Integration of these equations gives the curve named Danckwerts curve P(t), reactor response to a Step change of C(t) = C 0 [1-H(t-0)] at the inlet concentration:

(3) for a plug flow reactor,

(4) C: concentration at the reactor outlet C 0 : the initial concentration (tracer concentration) Pe: Peclet number δ: Dirac delta function Then, by this change in concentration, experimentally, one has access to the P curve which allows the determination of the RTD:

50

Exercise A

(5) For an ideal reactor in general, closed to the diffusion and in steady state conditions, and for an axially-dispersed plug flow reactor in particular, the mean residence time, , is equal to the space-time, , i.e., the ratio between the useful reactor volume V and the feed flow rate follows:

. Therefore, equation (2) can be written as

(6) The axially-dispersed plug flow model has two parameters in the E(t) curve: , Pe. Peclet number is a parameter used to measure the behaviour of a chemical reactor. It is used as a correlation parameter which takes into account the axial dispersion model. When Pe = ∞ axial dispersion does not exit and the reactor behaves as an ideal plug flow reactor. When Pe number decreases some axial dispersion appears. When the tendency is Pe = 0 the residence time distribution (RTD) is wider and the reactor behaves as stirred tank reactor. Those two parameters are obtained by minimising the square of the residuals relative to the experimental curve. This is explained in detail in the results treatment section The normalisation of the concentration C/C 0 is obtained experimentally by recording the conductivity values during experiment, since conductivity of a solution varies linearly with the concentration.

Experiment set up Re-arrange the experimental assembly in accordance with the following:

51

Armfield Instruction Manual

Layout Step experiment

Verify the directional process of the six port injection valve by following the labels. Ensure there is enough volume of solutions made to the correct concentrations and they are well mixed. Ensure pumps are calibrated and they give the right flow rate The T connector supplied with the reactor unit is used in this case. Connect it to the entrance of the reactor. The PTFE pipe, which comes with the T connector, has to be connected to the right port of the injection valve. See Installation section for valve connections. Temperature and conductivity sensors have to be correctly fitted in accordance with CEXC sensors fitting section and plugged in the right socket at the rear of the CEXC service Unit. As the experiment involves the collection and storage sensors data, the USB port located on the right hand side of the plinth must be connected to the Armfield IFD data logger. This will enable data logging of conductivity, flow rates and temperature at selected time intervals over a selected period.

Procedure Make up 1 litre of 0.1 M Potassium Chloride containing 0.01% of Indigo Carmine. The procedure on how to make the solutions is given in the introduction of this section. IMPORTANT: It is essential when handling these chemicals to wear protective clothing, gloves and safety spectacles. Remove the lids of the reagent bottles and carefully fill bottle 1 with the tracer solution, and bottle 2 with 2 litres of water. Refit the lids. Arrange the experimental assembly in accordance with Experiment set up above. 52

Exercise A Set data collection of conductivity at 3 seconds on the software. Collection of data should continue until steady state conditions are reached in the reactor. This takes approximately 30 minutes. Take the feed pipe from the reagent bottle 2 and introduce it into reagent bottle 1, so that both pumps pump the same solution into the reactor. Type the flow rate in the software 50 ml/min in each window for each pump so that the total flow rate of the solution entering the reactor will be 100 ml/min. Switch on the pumps by pressing POWER ON and instigate the data logger program (or begin taking readings if computer is being used) by pressing ‘GO’. Take note of the time the solution takes to reach the reactor (column) and the time taken from the exit of the reactor solution takes until detector. The recorded times will allow estimation of the reactor space time and the space time in the connection tubes. Check whether the solution conductivity corresponds to its concentration and start the conductivity data acquisition, otherwise try to identify and solve the problem. Start the conductivity data acquisition in the computer. Turn off the peristaltic pump and change the tubes from vessel 1 to vessel 2 with water and turn on the pump again, taking note of the time at which this change has been done. Take note of the temperature at the exit stream at the beginning, in the middle, and the end of the experiment. Solution is pumped from reagent bottles to injection valve and hence to the reactor. At the exit the solution is directed to the sensor block where conductivity probe is fitted and conductivity values are continuously registered. When the conductivity logged is 0.00 mS/cm2, stop the experiment and the pump. Flow more distilled water to clean the reactor. Empty the reactor by means of inverting the pump tubes and connected the pumps will suck the water out from the reactor. Notes: 1. Check if the peristaltic pumps tubes have the flexibility and position required to a keep a constant flow rate. It is recommended to check the flow rate sometimes by measuring it at the exit of the conductivity probe. 2. Rinse the feed bottles with distilled water and pump the water through the reactor to rinse out the chemicals. The reactor can be left with water in the coil ready for the next experiment.

Results treatment 

Make up a table with the values of your experiment as follows:

53

Armfield Instruction Manual Useful volume reactor (ml)

372

Flowrate (ml/s)

1.76

Residence time (s) Pe tau (V/Fr) (s)

210.00

Tubes time (s)

16.63

SQD

Flowrate and reactor volume are parameters of the experiment. The “tubes time” as explained on the experimental procedure is the time taken by the solution travelling through the connection tubes before and after reactor column until it reaches the conductivity cell. This time must be calculated before or during the experiment at the flow rate of the experiment. The calculations are best carried out using a spreadsheet such as EXCEL so that the results can be displayed in tabular and graphical form. Using the Armfield data logger, a set of readings of conductivity against time are stored in the computer. At this point, this data can be transferred onto the spreadsheet. Start the spreadsheet program. 

Plot the dimensionless concentration curve C/C 2 along time with the experimental data

Dimensionless concentration curve (column C) 

54

Eliminate from column C those values relating to the connection tubes (column D)

Exercise A



Plot a column with equation (2), although the t r and Pe are unknown and without taking into account the integration:

Pe and t r numbers will be found through the model equation using the solver function.

In order to obtain the integral of the equation (4), perform as follows:



Plot the “mean point” column of E column:

(Column F)

55

Armfield Instruction Manual



Plot the “accumulative sum” of the last one, using the following excel function: SUM(F i ,F i + 1 ,…)



(Called column G)

Then plot the final “model equation” (equation 4): 1-G i (called column H)

In order to use the solver function, set in the SQD cell of your table the function SUMXMY2 selecting column D and H, which means will sum the squares of the differences between these two columns; experimental and model curves.

56

Exercise A



Then, go to the Solver function and in “set target cell” select SDQ cell; in “Equal to” select “Min” with value 0, which means will minimize this value. In “by changing cells” select the cells of residence time and Pe number on the table built.

Note: The smaller value of SDQ the better match between curves and therefore between residence time distribution and space time.



Press Solve bottom, Pe and residence time numbers will be found, as well as the unknown columns.

57

Armfield Instruction Manual



Plot Experimental and Model columns, columns D and H, and compare them.

Normalised potassium chloride concentration at the reactor outlet along time.

Repeat the experiment changing some variables, like flow rate and tracer concentration, to understand how significantly these parameters affect the residence time distribution. Study the different Pe numbers and the curves obtained. Repeat the same experiment without static premixer and compare the difference.

58

Exercise A

Reactor responses for the plug flow reactor with axial dispersion model

Conclusion One of the possible causes of the difference between model and experimental curve can be the error on the reading of the conductivity because of dead or stagnant volumes. Compare the reactor space time, obtained from tracer experiment.

, with the mean residence time,

,

A significant difference between both values, beyond the experimental errors, may indicate the presence of dead volumes or stagnant regions when presence of short circuits when

, or the

, or even other anomalies.

As experimental errors are common, make a sensible analysis to determine where the experimental errors affect the results more significantly. For example: does 1 sec error in the reading of the time required to fill graduated cylinder, used in the flow rate measurement, significantly affect the space time calculation?

59

Exercise B - Flow pattern characterisation - Pulse change Objective The aim of this practical exercise is to study the flow pattern characterisation in a tubular reactor packed with glass beads. This characterisation will be performed using a model considering a plug-flow reactor with axial dispersion and by determination of the RTD.

Method The study of the flow pattern in a reactor is usually done using tracer techniques which consist of introducing several perturbations at the inlet of the reactor and monitoring the effect in the reactor. The commonly used perturbations in a plug flow reactor are a Pulse change and Step change. A coloured tracer solution is used to make the propagation of the concentration wave visible. In this exercise the pulse change perturbation will be studied.

Equipment Required Armfield service unit CEXC Armfield Plug Flow Reactor CEY Feed assembly

Optional Equipment Compatible PC with Armfield software

Chemicals Distilled water Potassium Chloride Indigo Carmine

Theory The flow characterisation of a reactor is done by the determination of the RTD, which is obtained using tracer techniques. This curve enables the permanence of each fraction of volume of fluid inside the reactor to be determined and also to show if its behaviour is ideal or non ideal and how it differs. Tracer techniques use several perturbations at the inlet of the reactor and wait for the reactor answer. The most common perturbations used in a plug flow reactor are a Pulse input and Step input.

60

Exercise B

Pulse input

Pulse input consists of an instantaneous injection of a small quantity of tracer solution and it is mathematically represented by the following function: C(t) = C 0 [H(t-0)-H(t-Δt)]

(1)

H: Heaviside function Δt:duration of the perturbation And the response of the reactor is:

(2) Taking into account that for a plug-flow reactor the RTD is:

(3) δ(t) : Dirac delta function  : space time t r : Residence time The response of a plug flow reactor with axial dispersion to a pulse input in the inlet concentration is:

(4) For a sufficiently small pulse,

: 61

Armfield Instruction Manual

(5) Then, equation (4), for plug flow with axial dispersion, is simplified:

(6) For infinitesimal pulses, Equation 5 predicts that the maximum concentration appears at t = . For finite pulses, the maximum concentration comes out at t =  + Δt/2. Thus, in these circumstances, equation 5 is given by:

(7)

Experimental set up Re-arrange the experimental assembly in accordance with the following: .

Layout Pulse experiment

Verify the directional position of the six port injection valve so that water is pumped into the reactor and coloured solution (tracer) is being recirculated. The loop will contain the coloured solution. See Injection valve operation. Ensure there is sufficient volume of solutions and that they are well mixed. Ensure pumps are calibrated and they give the right flow rate 62

Exercise B T connector supplied with the unit is not necessary in this case since just one solution is injected into the reactor at a time. Connect the single PTFE tube to the reactor through the quick connector. Temperature and conductivity sensors have to be correctly fitted in accordance with CEXC sensors fitting section and plugged in the correct sockets at the rear of the unit. As the experiment involves the collection and the storage of sensors data, the data USB port on the right hand side of the service unit must be connected to the Armfield IFD data logger and the computer as detailed in the instruction leaflet supplied with the interface. This will enable data logging of the conductivity, flow rates and temperature values at selected time intervals over a selected period.

Procedure Make up the tracer solution with 250 cm3 of 1 M Potassium Chloride solution containing 0.1% of Indigo Carmine. IMPORTANT: It is essential when handling these chemicals to wear protective clothing, gloves and safety spectacles. Rearrange the experimental assembly in accordance with Experimental set up above. Pour about 250cm3 of tracer solution in bottle 1, and about 1 litre of distilled water in bottle 2. Start the software using option Pulse Experiment. Ensure that the injection valve is in the loading position (L position). When switching the injection valve from one position to another, turn the handle of the valve until it clicks so it is sure that connections between ports have been done properly. Otherwise, ports will be blocked, pressure will increase and pipe will split splashing with the solution contained. Once the loop has been loaded with tracer it is RECOMMENDED to stop the pump, so if blockage occurs during switch pressure will not increase on the tracer channel. Type flow rates in the software for each solution and press ‘POWER ON’ to start up the pumps. Note that the flow rate of the tracer solution is not important as it will be recirculated all the time. Take note of the time required for the water to reach the reactor entrance (after static premixer), the time spent in the reactor column, and the time spent between the exit reactor and the detector. The total time will help to obtain the space time spent in the connection tubes and to predict the reactor space time. To make sure air does not get inside the conductivity cell, take out conductivity sensor and as the water is exiting the reactor and overflows through the cell, fit the sensor back into the cell and screw until sealing. Then, start data acquisition by pressing ‘GO’. At the same time switch the injection valve position to injection position (I), and take note of the time at which this has been done. The solution inside the loop (tracer) will be injected into the reactor.

63

Armfield Instruction Manual Once the tracer is injected, change the valve position to loading position (L). Finish the experiment when the conductivity is approximately 0.01 mS/cm. Click again ‘POWER ON’ to finish the experiment. Stop data logging. At the end, empty and wash the reactor column with distilled water. Flow distilled water through the continuous flow electrode to remove any potassium chloride residues.

CEY in the Pulse injection experiment

Results The calculations are best carried out using a spreadsheet such as Microsoft EXCEL so that the results can be displayed in tabular and graphical form. On conclusion of the experiment using the Armfield data logger, a set of readings of conductivity with time will be stored in the computer. At this point, this data can be transferred onto the spreadsheet. Start the spreadsheet program.

64

Exercise B 

Make up a table as follows: 1.76

Flowrate (ml/s) Residence time (s) Pe tau (V/Fr) (s)

210.00

Tubes time (s)

16.63

SQD



With the values of time and conductivity obtained from the experiment plot the dimensionless concentration curve along time: C/C 0 against time,

Dimensionless concentration curve Eliminate from C(t) curve, those values relating to the connection tubes. (See Column C) The following step is to determine the Peclet number and Residence time. It will be necessary to use the solver function. 

Plot a column with the following equation:

(Column D) as t r and Pe are unknown, it is likely that nonsensical values will appear.



Then plot the final “model curve” ,

(Column E)

65

Armfield Instruction Manual

In order to use the solver function, set in the SQD cell the function SUMXMY2 selecting column C and E. This will sum the squares of the differences between these two columns, to minimise the difference.

66



Then, go to solver and in “set target cell” select SDQ cell, in “Equal to” select “Min” with value 0, which will minimize this value. And in “by changing cells” select the cells of residence time and Pe number on the table.



Press Solve button Pe and residence time numbers will be found, and also the two columns (model and equation).

Exercise B



Then plot C (t) column (C) and model equation column (H), and compare them

Normalised potassium chloride concentration at the reactor outlet, along time.

Repeat the experiment changing some variables; flow rate, tracer concentration or amount tracer injected. Study Peclet number and compare the different curves obtained. This will help to understand the concepts explained on this section.

67

Armfield Instruction Manual

Conclusions As experimental errors are common, make a sensible analysis to determine which experimental errors affect the results most significantly. For example: does a sec error in the reading of the time that water takes to reach entrance reactor significantly affect the space time calculation? One of the possible causes of the difference between the model and the experimental curve can be the error on the reading of the conductivity because of stagnant volumes. Comparing the reactor space time, , and the mean residence time, t r , a significant difference between both values, may indicate the presence of dead volumes or stagnant regions. When t r < , this is a sign of stagnant regions and when t r > , this can be a sign of short circuits.

68

Exercise C - Conversion experiment Objective The specific goal of this practical work is the determination of the steady state conversion, for a second order reaction between sodium hydroxide and ethyl acetate, in a tubular reactor packed with glass beads.

Method The steady state conversion of the packed flow reactor is usually done by a reaction in a steady state condition. In this case, it will be a study of a second order reaction at 25ºC considering that the model of this reactor is Plug flow axially dispersed since this was demonstrated in the previous experiment.

Equipment Required Armfield service unit CEXC Armfield Plug Flow Reactor CEY Feed assembly

Optional Equipment Compatible PC with Armfield software

Chemicals Sodium hydroxide Ethyl Acetate Indigo Carmine Distilled water

Theory In the previous experiments the flow pattern in the tubular reactor packed with glass beads was characterised. In the present work we intend to determine the steady state conversion in the same tubular reactor, at room temperature. If we assume that the flow pattern in the reactor is described by the plug axially dispersed model, the steady state conversion for a second order reaction should be obtained from the reactor steady state mass balance: The steady state conversion for a second order reaction should be obtained from the reactor steady state mass balance:

(1) where u es the superficial velocity, x A is the conversion of the limiting reactant A, z is the axial coordinate, k is the reaction kinetic constant, C A0 is the concentration of species A at the reactor inlet, M = C B0 /C A0 ≥ 1, B being the second reactant, and D ax is the axial dispersion. Previous expression can be written in dimensionless form: 69

Armfield Instruction Manual

(2) where z* = zL and L is the length of the reactor. Introducing now the dimensionless Peclet number, Pe = uL/D ax , and the space time  = L/u:

(3) Once the residence time distribution is known, the steady state conversion can be determined by;

(4) replacing the C NaOH (t)/C NaOH0 for a second order reaction, yields:

(5) Finally,

(6) For an ideal plug flow reactor state conversion:

, an analytical solution exists for the steady

(7) for M >1, and for M=1:

(8) The kinetic constant and activation energy are data which can be obtained with a batch reactor at different temperatures. Once k 0 and Ea are known obtain the kinetic constant at the temperature of the experiment through:

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Exercise C If this information can not be obtained, use Figure C2 data as necessary:

Figure C1: Conversion of the NaOH at different temperatures

Figure C2: Linearization of NaOH conversion

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Armfield Instruction Manual

being

Ea (kJ/mol) = 29.4

(11)

k 0 (m3/mol s) = 12.5 m = slope M = C B0 /C A0 For example, for a C A0 = 0.1, C B0 = 0.125 and at these different temperatures: K (17ºC) = 6.40E-05 m3mol-1s-1 K (22ºC) = 8.00E-05 m3mol-1s-1 K (27ºC) = 9.60E-05 m3mol-1s-1

Experiment set up Re-arrange the experimental assembly in accordance with Figure C3. Verify the directional process of the six port injection valve so that solutions, sodium hydroxide and ethyl acetate with indigo carmine, are injected into the reactor. See Injection valve operation as necessary. Fit the T-connector into the reactor inlet. Then connect PTFE tubing to the injection valve as detailed in the Installation section. Temperature and conductivity sensors have to be correctly fitted in accordance with CEXC sensors fitting section and plugged into the correct socket of the control console. As the experiment involves the collection and the storage of the conductivity data, the data output port on the right hand side of the service unit must be connected to Armfield IFD data logger and the computer as detailed in the instruction leaflet supplied with the interface. This will enable data logging of the conductivity, flow rates and temperature at selected time intervals over a selected period.

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Exercise C

Figure C3: Layout Conversion experiment

Procedure Make up 1 L of sodium hydroxide of approximately 0.2 M but of rigorous titre and 1 L of ethyl acetate 0.25 M with Indigo Carmine at 0.01% w/w. IMPORTANT: It is essential when handling these chemicals to wear protective clothing, gloves and safety spectacles. Fill one bottle with 0.2M NaOH and the other one with the other solution; 0.25M ethyl acetate (with 0.01% w/w indigo carmine), and connect the corresponding tubes in each vessel. Bottles should be closed to protect from air. Set same flow rates as used in the pattern characterisation experiment (Exercise A and B), by filling the right value in the software. Set data collection at 3 seconds on the software. Start the data acquisition by pressing ‘GO’, and wait until the continuous flow reactor reaches the steady state. This should take about 5 minutes. It is recommended to check flow rate and temperature at the beginning, in the middle and at the end of the experiment. Pay attention to the colour change between reactor inlet and outlet, and try to relate it with the pH of the medium and with the sodium hydroxide conversion. The reactor inlet should be yellowish, whereas the outlet nearly dark blue. When solutions are almost finished, stop data logging and turn off the peristaltic pumps, drain the remainder into a flask and fill reagent vessels with distilled water. Empty the reactor by disconnecting tubes from the bottom and put a flask underneath to collect the solution inside.

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Armfield Instruction Manual Then, reconnect the tubes and start pumping distilled water into the reactor and sensor block to eliminate the residues of the experiment. Check that the conductivity values have reached the values corresponding to distilled water.

Results The calculations are best carried out using a spreadsheet such as Microsoft EXCEL so that the results can be displayed in tabular and graphical form. 

Make up a table as follows:

V

ml

Pe

[NaOH]

0.2

M

Tau

[EtAC]

0.25

M

k

K0

mS/cm2

K final

mS/cm2

Q

1.76

M

1.25

[NaOH] 0

0.1

ml/sec

Peclet number and space time should be obtained from the last experiment. Therefore, the flow rate should be the same in both experiments. Kinetic constant, k, depends on the temperature, therefore obtain that value at the temperature of the experiment. See kinetics data above as necessary. IMPORTANT: It is necessary to take into account the following considerations: C NaOH0 : Concentration of NaOH in the mixture (in this case 0.2/2 = 0.1) K0: conductivity of NaOH K∞: Final conductivity

Obtention of K 0 , K∞: Pour 100 cm3ml of the sodium hydroxide prepared into a flask and add 100 ml of distilled water mix it and take note of the conductivity value which corresponds to the sodium hydroxide 0.1 M (K 0 ). Measure again 100 cm3 ml of the prepared sodium hydroxide solution and pour it into a flask or glass reactor. Add 100 cm3 of the prepared 0.25 M ethyl acetate solution (with 0.01% w/w IC) and start the magnetic stirrer. Colour changes go from dark green to light and later on to blue at the end of the reaction. Take note of the conductivity when reaction is complete, K∞.

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Exercise C If those values can not be obtained by experimental method, apply the following equations: K 0 = 0.195[1+0.0184(T-294)] C NaOH 0

T ( ºK )

C NaOH 0 ( mol/cm3)

K∞ = 0.070[1+0.0284(T-294)] C NaOH 0

T ( ºK )

C NaOH 0 ( mol/cm3)

For C

NaOH 0

< C EtAc 0

since NaOH is limiting reagent

Once parameters are obtained, continue as follows: 

Plot the following equation (column D) to obtain C NaOH :

(12) 

Plot conversion column (column E)

(13) 

Plot same columns for Ethyl acetate (column F and G): (14)

(15) The following experimental results do not intend to be real, they are a demonstration of the data required and mathematical treatment must be done. The operating conditions are presented in the following table:

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Armfield Instruction Manual

Figure C4: Steady state conversions along time. Operation temperature = 20 ºC

Now, obtain the steady state conversion from the model equation and compare with the experimental value.

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

Plot equation (6) without apply the integration, using Pe, Tau numbers from tracer experiment. (Column H)



Then, plot the mean point of this column :

Exercise C



Finally, plot the SUM of the last column so that the integration is complete.

Perform the steady state conversion experiment at different flow rate, different temperature, and different Ethyl acetate concentrations. Compare and analyse what happens and why.

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Armfield Instruction Manual Perform the experiment without pre mixer and it will observe a segregation phenomenon.

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US Office:

Armfield Inc. 436 West Commodore Blvd (#2) Jackson, NJ 08527 Tel: (732) 928 3332 Fax: (732) 928 3542 Email: [email protected]

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