CKB 20104 Reaction Engineering UniKL MICET Experiment 4: Reactor Test Rig full lab report

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1.0 SUMMARY PFR and CSTR are commonly used in industry to contain chemical reactions. Reactors are used to maximize net present value for a reaction. Energy changes in reactor usually are in the form of heating, pumping or cooling. In PFR, chemicals are usually pumped through a tube while in CSTR, the chemicals will be contained in a container to stirred. This experiment was conducted to found out the saponification reaction between NaOH and Et(Ac) by using PFR, 3 stage CSTR and single stage CSTR. The flow rate for this experiment was kept constant, at 200 ml/min. Then, the reaction between conversion and different type of reactors were observed, hence reaction rate is determined. Graph was then plotted to show the relationship between conductivity and concentration of NaOh. The results from the graph shows that 3-stages CSTR is the most effective reactor since it has the highest reaction rate and conversion and single CSTR is the the least effective. Theorically, the PFR is the most effective and followed by 3stages CSTR and lastly single CSTR. There are some recommendations need to be done to increase the efficiency of the reactors. During the experiment, make sure the solution used is measure correctly. The eyes must perpendicular to the measuring scale to avoid parallax error.

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3.0 ANALYSIS AND DISCUSSION From this experiment of reactor test rig,the main objective is to compare the performance of single reactor,3 CSTRs,and PFR.In order to start this experiment 50L sodium hydroxide (0.1M) and Ethyl acetate (0.1M) was mixed in receiving vessel B3 to prepare the general solutions to start the experiment.The experiment then was proceed to fulfill the objectives which to carry out a saponification NaOH and Et(Ac) using different types of reactors,to compare the reaction conversion between different types of reactors and to determine the reaction rate constant.

From the experiment that have been conducted,the value for the conversion,X % for each reactors have been identified.For single stage CSTR reactor the conversion obtained is 62.9834% at which the inlet and outlet conductivity (mS/cm) are at 6.53 and 4.94.From the calculation that have has been done the residence time τ (min) obtained is 0.011.For the 3 stage CSTRs the conversion,X % obtained is 99.99949% at which the inlet and outlet conductivity is at 9.12 and 4.92.The value of residence time τ (min) calculated is 0.005.For reactor type of PFR,the inlet and outlet conductivity are 11.64 and 0.0030 at which the conversion recorded is 94.5055%.From the PFR reactor,the value for residence time τ (min) obtained is 0.008.

From this results,it can be said that the conversion in a reactor depends on the average reaction rate as well as the residence time.A CSTR is well mixed, and the average reaction rate will be that of the conditions of the bulk mixture. The composition of the reactor product is also the same as that in the reactor. For most reactions (especially equilibrium reactions) the rate of reaction decreases with increasing concentrations of final product (and decreasing concentrations of reagent).In a plug flow reactor, the rate is not constant. In the first section of the reactor, the rates are high (high concentration of feed and low concentration of product). As the material goes through the reactor the rates drop. The average rate is still higher and hence the conversion for a given reactor volume is also better.

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Residence time is said to be directly proportional to system capacity but inversely proportional to the flow rate of the substance through the system.If the size of the system is changed, the residence time of the system will be changed as well. The larger the system, the larger the residence time, assuming the inflow and outflow rates are held constant. The smaller the system, the shorter the residence time will be, again assuming steady-state conditions.From this statement we can conclude that the bigger the system the lower the value of conversion for that reactor.As can been shown from the experimental result which the PFR has higher conversion compared to single stage of CSTR.

For the 3 stage of CSTR,the conversion,X % is higher compared to both reactor which the CSTR and PFR.This can be explained by adding more CSTR in series will improve the average rate and yields.Within each stage the ideal heat transfer conditions can be achieved by varying the surface to volume ratio or the cooling/heating flux. Thus stages where process heat output is very high either use extreme heat transfer fluid temperatures or have high surface to volume ratios (or both). By tackling the problem as a series of stages, extreme cooling/heating conditions to be employed at the hot/cold spots without suffering overheating or overcooling elsewhere. The significance of this is that larger flow channels can be used. Larger flow channels are generally desirable as they permit higher rate, lower pressure drop and a reduced tendency to block.

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4.0 CONCLUSIONS AND RECOMMENDATIONS This experiment was conducted to found out the saponification reaction between NaOH and Ethyl Acetate by using PFR, 3 stage CSTR and single stage CSTR. The flow rate for this experiment was kept constant, at 200 ml/min. Then, the reaction between conversion and different type of reactors were observed, hence reaction rate is determined. The results from the graph shows that PFR is the most effective reactor since it has the highest reaction rate and conversion and single CSTR is the least effective. From the theory, the conversion reaction for every reactor should be in increasing. Thus, the 3 stages CSTR is good compared to single CSTR because it takes a little time of a fluid to mixed well in the reactor. Both PFR and 3 stages CSTR has a higher conversion reaction than single CSTR. From the result, it can be said that PFR is the most effective reactor since the conversion is the highest. It follows with 3 stages CSTR and lastly single CSTR. There are a few recommedations that needed to be applied. During the experiment, make sure the solution used is measure correctly. The eyes must perpendicular to the measuring scale to avoid parallax error. The stirrer should be opened earlier when the solution has reached to the half of the reactor to make sure the solution is mixed well. Both valve V9 and V10 should be adjusted at 200 ml/min to give the accurate value of conductivity.

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TUTORIAL

1. Write differences between 3 reactors: single CSTR, 3-stages CSTR and Tubular (PFR) reactor. Discuss advantages and disadvantages for each configuration. i.

Differences between 3 reactors Single CSTR  Open system  A steady-state

  

3-stages CSTR  Open system  A steady-state

operation, hence no

operation, hence no

operation, hence no

accumulation and

accumulation and

accumulation and

unvarying product

unvarying product

unvarying product

quality Mixing Short reaction time Constant volumetric

quality Mixing Shorter reaction time Constant volumetric

quality Not mixing Shortest reaction time Not constant

flow rates

ii.

Tubular (PFR)  Open system  A steady-state

  

flow rates

  

volumetric flow rates

Advantages and disadvantages each configuration

Advantages

Single CSTR  Cheap to

3-stages CSTR  Flexible

Tubular (PFR)  Mechanically

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simple, reactant and products can

temperature



compact Greater biological

through Tubes easy to

control Good 

control Easily adapts

   

construction Easy to clean Low

stability Potentially throughputs

clean, no moving





parts High volumetric unit conversion

optimal

rate per reactor Run for long

conditions Greater ability to cope with

cost Fast response

feedstock



periods without 

maintenance Low pressure



drops Suitable for fast reaction mainly

volume and

used for gas

quality

conditions Easy to clean and maintain

of reactor to



due to

fluctuating

Single CSTR  Conversion

easily flow

higher

operating

to operating

Disadvantages

Te s t

More

runs Good control Simple



Reactor



to two phase



4

construct Good

temperature 

Experiment

3-stages CSTR  Expensive  More



phase reaction. Continuous



Operation Good heat



transfer Very efficient

Tubular (PFR)  Maintenance 

more expensive Temperatures are

product per

complex

volume of

control and

hard to control

reactor is

operational

which can result

small

requirements

in undesirable

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compared to

temperature

other flow

gradients and

reactors. Lowest

vary the

conversion

product Hot spots may

composition of 

per unit 

Te s t

volume By-passing

occur within

and

for exothermic

channeling

reactions

PFR when used

possible with poor agitation

•

2. Write a one-paragraph summary of any journal article that studies chemical reaction in a multiple stages CSTR. The article must have been published within last 5 years. Explain on PFR reactor used in the study and its significance to the study done.

i. Title:

Journal article title: Bio-hydrogen

production

multistage stirred tank reactor,

during

acidogenic

fermentation

in

a

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Estela Tapia V., Juan Esteban R., Andres Donoso B., Lorena J., Jean Phillipe S. and

Gonzalo

Ruiz

F.,

Bio-Hydrogen

Production

during

Acidogenic

Fermentation in a Multistage Stirred Tank Reactor, Vol. 38, Elsevier Publications, Netherlands, 2012, p2185-2190. The objective of this study was to evaluate the production of hydrogen in a multi-stage continuous stirred-tank reactor (CSTR) system where both reactors having the same volume and compare its performance with a conventional one-stage process. The lab-scale multi-stage and one-stage systems were operated at five pHs and five hydraulic retention time (HRTs). The maximum volumetric hydrogen productivity and yield obtained with the two-stage system were 5.8 mmol L−1 h−1 and 2.7 mol H2 mol glucose−1, respectively, at an HRT of 12 h and pH 5.5. Overall, the multi-stage system showed, at steady state, a better performance that the one-stage system for all the evaluated pHs. However, a comparison between the one-stage system, operating at 6 h of HRT, and the first reactor of the multi-stage system at the same HRT did not show any significant difference, highlighting the positive impact of having a multi-stage process. The determination of the ratio between the experimental measured H2 in the gas phase and the theoretical H2 generated in the liquid phase indicated that an important part of the hydrogen produced in the first reactor was transferred into the second reactor instead of being desorbed in the headspace. Therefore, the improving of hydrogen production in the multi-stage system is rather attributed to the increased transfer of hydrogen from liquid to gas than an actual total hydrogen production increase.

The CSTR is a process in which the reactants are fed to the reactor and the products or byproducts are withdrawn in between while the reaction is still progressing. For example, Haber Process for the manufacture of Ammonia. Continuous production will normally give lower production costs as compared to batch production, but it faces the limitation of lacking the flexibility of batch production. Continuous reactors are usually preferred for large scale production. In a CSTR, one or more fluid reagents are introduced into a tank reactor equipped with an impeller while the reactor effluent is recovered. The impeller stirs the reagents to ensure proper mixing. Therefore, it can be seen that in these reactors, reactants are continuously fed to

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the first vessel, they overflow through the others in succession, while being thoroughly mixed in each vessel. Though the composition is uniform in individual vessels, but a stepped concentration gradient exists in the system as a whole. The average amount of time spent by a discrete quantity of reagent inside the tank or the residence time can be obtained by simply dividing the volume of the tank by the average volumetric flow rate through the tank. The expected completion rate of the reaction, in percent can be calculated using chemical kinetics. A large commercial fluidized bed reactor is a nearly uniform temperature, but the flow patterns consist of mixed and plug flow and in-between zones. The CSTR model is used to estimate the key unit operation variables when using a continuous agitated tank reactor to reach a specified output. The mathematical model works for all fluids: liquids, gases and slurries. Perfect Mixing: This is a fair assumption due to the fact that it merely requires the region of variable composition at the inlet area is very small when compared to the entire reactor contents and the time required to mix tank contents is very small when compared to the residence time of the reactor. This is required due to the strong dependence of the reaction rate on the concentration of the reagent species.

ii.

Explain on PFR reactor used in the study and its significance to the study done. Plug Flow Reactor (PFR) is also known as continuous tubular reactors (CTR) or piston

flow reactor, consist of a cylindrical pipe with openings on each end for reactants and products which are continually consumed and obtained, respectively as they flow down through the length of reactor which the reactor is usually have plug flow, operated at steady-state and constant density (reasonable for liquids but a 20% error for polymerizations, valid for gases only if there is no pressure drop, no net change in the number of moles, or large temperature change) and a

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single reaction occurring in the bulk of the fluid (homogeneously). PFR has spatial variation in axial direction but not in radial direction (there is a changes in reactor in terms of concentration and temperature along axis direction). PFR is an ideal reactor which have real reactor that can be modeled as combinations of multiple of plug flow. Real reactor of PFR are tubular, tubular exchanger, fixed bed, radial-flow, fired heater, serpentine tubular and serpentine fluidized-bed reactor. A material balance on the differential volume of a plug, on species i of axial length dx between x and x+dx gives: [in]-[out]+[generation]-[consumption] = [accumulation] where accumulation is 0 under steady state, therefore, above mass balance can be written as follows:

Fi(x) - Fi(x+dx) + (At.dx.vi.r) = 0

PFR are used to describe chemical reactions in continuous, flowing systems of cylindrical pipes and predict the behavior of chemical reactors of such design, so that key reactor variables like dimensions of the reactor, can be estimated. Fluid going through PFR as a series of infinitely thin coherent ‘plugs’ each with a uniform composition, traveling in the axial direction of the reactor, with each plug having a different composition from the ones before and after it and it represent a variety of engineered or natural conduits through which liquids or gases flow (e.g. pipelines).Water at a controlled temperature is circulated through the tank to maintain constant reactant temperature. Any plug that enters the reactor at time will exit the reactor at time , where is the residence time of the reactor. The residence time distribution function is therefore a dirac delta function at . PFR has a residence time distribution that is a narrow pulse around the mean residence time distribution. PFR are used to carry out the process of Suzuki reaction, Hoffmann reaction, Grignard reaction, Oxidation reaction, biocatalyst, hydrogenation, Bourne reaction, emulsion polymerization, nano particle synthesis and counter current extraction. The significance of PFR to the study done is it is suitable for large-production, slow reactions, homogeneous or heterogeneous reactions, continuous production and high-temperature reactions and commonly used in industrial processing such as pharmaceutical, oil and gas and

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food and drinks. The functions of reactors are to describe chemical reactions in continuous, flowing systems and predict behavior chemical reactors of such design so that key reactor variables such as dimensions can be estimated. PFR is commonly used in industrial processing which works well for liquids, gases and slurries, which is used more often for gas phase reaction and are used to carry out the process of Suzuki reaction, Hoffmann reaction, Grignard reaction, Oxidation reaction, biocatalyst, hydrogenation, Bourne reaction, emulsion polymerization, nano particle synthesis and counter current extraction. PFR usually used in gasoline production, oil cracking, synthesis of ammonia from its elements, and the oxidation of sulfur dioxide to sulfur trioxide. PFR used in research on the oxidation of nitrogen compounds. In oil and gas industry of production of algae, PFR can also be used as bioreactors or for small scale production. The PFR bioreactor shown below is used for the production of algae. The algae is then compressed and dried and can be used as feed for a biodiesel reactor. A portable system and method for producing biofuel from algae are disclosed. In the portable system, a chemostat and a PFR formed from plastic bladders are interconnected. Further, an algae separator is in fluid communication with the PFR for removing algae cells. Also, the system includes a device for processing biofuel from the algae cells. Importantly, the system includes a temperature controller to maintain desired temperatures in the chemostat and PFR for algae growth and intracellular algae production. In process oil refining cracker of high quality of gasoline in industry oil and gas, the reactant and product flow regimes in the riser is modeled as plug flow assumptions. Plug flow is that reactor regime in which fluid moves in form of plugs. And along the length of riser there is variation in composition. That is there are axial variations. Fluid composition is changing. However radial variations are not present. Along each cross section the composition with respect to spatial and time domains is constant. Plug flow assumption is very useful in modeling the riser since there is no back mixing. Back mixing is condition where the reactor products catalyst etc is moved to rector influent. There they mix with reactant. And also back mixing leads to condition of mixed flow reactor. And in mixed flow reactor there is always a less conversion as compared to plug flow. And in our case we are requiring higher conversion. Back mixing with bring catalyst with the reactant and product to influent. In our case of fluidized catalytic cracking the feed is vacuum gas oil and its cracked products gasoline, coke and lights gases.

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In pharmaceutical industry which PFR is used to produce penicillin-V which the design and operation of an industrial penicillin-V deacylation reactor is simulated, using a kinetic expression and mass transport parameters for the immobilized enzyme particles. It is desirable to use a series of equalized PFR with pH control at the entrance to each reactor, and with a possibility of recycling reactant in each reactor. Higher pumping costs and lower productivity are unavoidable drawbacks of an operation mode where the separation costs for the product mixture are desired to be low. In production of an aerosol, which is a process for the manufacture of 1-chloro-3,3,3trifluoropropene (HCFC-1233zd) at commercial scale from the reaction of HCC-240 and HF is disclosed. In one embodiment, HCC-240fa and HF are fed to a reactor operating at high pressure. Several different reactor designs useful in this process include; a stirred-tank reactor (batch and/or continuous flow); a PFR, a static mixer used as a reactor; at least one of the above reactors operating at high pressure; optionally combined with a distillation column running at a lower pressure; and combinations of the above; and/or with a distillation column. The resulting product stream consisting of 1233zd, HCl, HF, and other byproducts is partially condensed to recover HF by phase separation. The recovered HF phase is recycled to the reactor. The HCl is scrubbed from the vapor stream and recovered as an aqueous solution. The remaining organic components including the desired HCFC-1233zd are scrubbed, dried and distilled to meet commercial product specifications.

In environmental industry of sewage ponds water treatment, fixed-film or attached growth secondary treatment bioreactors are similar to a PFR model circulating water over surfaces colonized by biofilm, while suspended-growth bioreactors resemble a PFR keeping microorganisms suspended while water is being treated. Secondary treatment bioreactors may be followed by a physical phase separation to remove biological solids from the treated water. In industrial of production process of saponification that utilized plug flow reactor in its process is sequencing plug flow reactor treatment of industry wastewaters. Actually sequencing plug flow reactor technology has been widely applied for the treatment of industrial wastewater.

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However, treatment applications for highly polluted wastewaters are rather limited. Settling characteristic was good, but suspended solids' concentration in the effluent was high. High loaded systems proved to be as effective as low organic loadings in terms of COD removal. In production styrene monomer, PFR reactors in its process is in the dehydrogenation of ethylbenzene for the production of styrene monomer. It applies as fixed bed reactors (particles in one bed). The reactor incorporates a fixed-bed of solid particles of catalyst; that is particles do not move. The reacting fluid moves through the void space around the particles. It may be thought at first such an apparently tortuous flow path would be inconsistent with the occurrence of plug flow but provided certain conditions are met, such need not be the case; in any event, the departure from plug flow can be investigated experimentally ((Ronald W. Missen; Introduction to Chemical Reaction Engineering and Kinetics, (Toronto), 1928). It is for adiabatic operation. It is most practical for large-scale, relatively slow reactions not involving large heat generation or consumption. The fluid moves downward through the reactor in nearly plug flow. In this reactor, reactants while passing through the reactor get converted into polymers without back mixing.

6.0

REFERENCES 1. Estela Tapia V., Juan Esteban R., Andres Donoso B., Lorena J., Jean Phillipe S. and Gonzalo Ruiz F., Bio-hydrogen production during Acidogenic fermentation in a multistage stirred tank reactor, Vol. 38, Elsevier Publications, Netherlands, 2012, p21852190. 2. Lanny D.S., The Engineering of Chemical Reactions, Oxford University Press, New York, 1998.

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3. Plug Flow Reactor Model. (2005) Wikipedia. [Online]. [Accessed 27th February, 2016]. Available from World Wide Web: https://en.wikipedia.org/wiki/Plug_flow_reactor_model 4. Plug Flow Reactors. (2013) Encyclopedia Of Chemical Engineering Equipment. [Online] [Accessed 26th February, 2016]. Available from World Wide Web: http://encyclopedia.che.engin.umich.edu/Pages/Reactors/PFR/PFR.html 5. Plug Flow Reactors. (2000) University of Michigan’s Education Portal. [Online] [Accessed 28th February, 2016]. Available from World Wide Web: http://www.umich.edu/~elements/5e/asyLearn/bits/pfrfinal/index.htm 6. Octave Levenspiel, Chemical Reaction Engineering, 3rd Edition, John Wiley & Sons, Inc, United States of America, 1999, p72 7. Reactor Test Rig .(1990) Fresenius Chemistry Bulletin. [Online]. [Accessed 28th February, 2016]. Available from World Wide Web: http://www.informaworld.com/index/9069.pdf 8. Mark E. Davis and Robert J. Davis, Fundamentals of Chemical Reaction Engineering, Mc Graw-Hill, New York, 2003, p65 and p84