CSTR in Series

UNIVERSITI TEKNOLOGI MARA FAKULTI KEJURUTERAAN KIMIA PROCESS ENGINEERING LABORATORY 2 (CPE554) NAME

GROUP EXPERIMENT DATE PERFORMED SEMESTER PROGRAMME / CODE

No.

Title

Allocated Marks (%)

1 Abstract/Summary 2 Introduction 3 Aims 4 Theory 5 Apparatus 6 Methodology/Procedure 7 Results 8 Calculations 9 Discussion 10 Conclusion 11 Recommendations 12 Reference / Appendix TOTAL MARKS Remarks

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Checked by

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: MOHAMAD NOOR HADMAN B ADAM MOHD FIRDHAUS B OSMAN MOHAMAD FIRDAUS B MOHAMAD : GROUP 2 : CSTR IN SERIES : 2ND OCTOBER 2015 :4 : EH2414

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5 10 5 10 5 10 10 10 20 5 5 5 100

Marks

Abstract This experiment involves a continuous stirred tank reactor (CSTR) in series. The reactor system consists of three agitated, glass reactor vessels in series. The concentration is kept uniform for each reactor and it is observed that there is a change in concentration as fluids move from one reactor to the other reactor. This experiment is carried out to determine and observe the effect of step change input. CSTR is one kind of chemical reactor system with non-linear dynamics characteristics. The usage of this equipment is to study the reaction mechanism as well as the dynamics of reactor with various types of inputs. CSTR is widely used in water treatment and chemical and biological processes. The deionised water are filled in both tanks with the sodium chloride are diluted in one tank. Then the deionised water from the second tank will flow through to fill up the three reactors. The flow rate of the deionised water is set to 150 ml/min to prevent from over flow. The readings are taken at the time to after the conductivity readings showing stable enough. After that, the readings are continuously taken for every 3 minutes until to the point where the conductivity values for three reactors are equivalent. Based on the result obtained, the graph has been plotted between conductivity, Q (mS/cm) against time, t (min).

Aim To study the effect of step change input to the concentration.

Introduction In industrial chemical processes, a reactor is the most important equipment where the raw materials undergo a chemical reaction to form a desired product. The design and operation of chemical reactors are important criteria responsible for the whole success of the industrial operation. The stirred tank reactor present in the form of either single tank, or more often in series of tanks, particularly suitable for liquid phase reactions and widely used in chemical industry, for example, pharmaceutical for medium and large scale of production. It can form a

unit in a continuous process which giving more consistent product quality, easy to control and low man power requirement. The mode of operation of reactors can be in batch or continuous flow. In a batch flow reactor, the reactor is filled with reactant, mixed well and left to react at a certain length of time and finally the mixture will be discharged. A continuous flow reactor, the feed to reactor and the discharge from it are continuous. There are three types of continuous flow reactor, which is plug flow reactor, the dispersed plug flow reactor, and completely mixed or continuously stirred tank reactors (CSTR). CSTR consists of agitation tank that has a feed stream and discharge stream. Frequently, several CSTRs are aligned in series, to improve their conversion and performance. Complete mixing in a CSTR reactor produces the tracer concentration throughout the reactor to be the same as the effluent concentration. In other words, in an ideal CSTR, at any travel time, the concentration down the reactor is identical to the composition within the CSTR. It is also important to notice that the mixing degree in a CSTR is an extremely important factor, and it is assumed that the fluid in the reactor is perfectly mixed in this case, that is, the contents are uniform throughout the reactor volume. In practice, an ideal mixing would be obtained if the mixing is sufficient and the liquid is not too viscous. If the mixing is inadequate, there will be a bulk streaming between the inlet and the outlet, and the composition of the reactor contents will not be uniform. If the liquid is too viscous, dispersion phenomena will occur which will affect the mixing extent.

Theory The continuous flow stirred-tank reactor (CSTR), also known as vat- or backmix reactors, is a common ideal reactor type in chemical engineering. A CSTR often refers to a model 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. The behavior of a CSTR is often model by the Continuous Ideally Stirred-Tank Reactor (CISTR). All calculations performed with CISTRs assume perfect mixing. In a perfectly

mixed reactor, the output composition is identical to composition of the material inside the reactor, which is a function of residence time and rate of reaction. If the residence time is 5-10 times the mixing time, this approximation is valid for engineering purposes. The CISTR model is often used to simplify engineering calculations and can be used to describe research reactors. In practice it can only be approached, in particular in industrial size reactors. Assumption: Perfect or ideal mixing, as stated above Integral mass balance on number of moles Ni of species i in a reactor of volume V.

General mol balance equation:

Assumption 1) Steady state therefore, dNA/dt = 0 2) Well mixed therefore rA is the same throughout the reactor ∫

∫

Rearranging the generation

In term if conversion

Reactors in Series Given -rA as a function of conversion, , -rA = f(X), one can also design any sequence of reactors in series provided there are no side streams by defining the overall conversion at any point.

Mol balance on Reactor 1 In – out + generation = 0 FA0 – FA1 + rA1V1 = 0

FA1 = FA0 – FA0X1

Mol balance on Reactor 2 In – out + generation = 0 FA1 – FA2 + rA2V2 = 0

FA2 = FA0 – FA0X2

Apparatus

1) Distilled water 2) Sodium chloride 3) Continuous reactor in series 4) Stirrer system 5) Feed tanks 6) Waste tank 7) Dead time coil 8) Stop watch

Experimental Procedure 1) The general start-up was performed by following the instruction of the manual given at the instrument. 2) Tank 1 and tank 2 was filled with 20 L feeds deionizer water. 3) 200g of Sodium Chloride was dissolved in tank 1 until the salts dissolve completely and the solution is homogenous. 4) Three way valve (V3) was set to position 2 so that deionizer water from tank 2 will flow into reactor 1. 5) Pump 2 was switched on to fill all three reactors with deionizer water. 6) The flow rate (Fl1) was set to 150 ml/min by adjusting the needles valve (V4). Do not use too high flow rate to avoid the over flow and make sure no air bubbles trapped in the piping. 7) The stirrers 1, 2 and 3 were switched on. The deionizer water was continued pumped for about 10 minute until the conductivity readings for all three reactors were stable at low values. 8) The values of conductivity were recorded at t=0. 9) The pump 2 was switched off after 5 minutes. The valve (V3) was switched to position 1 and the pump 1 was switched on. The timer was started. 10) The conductivity values for each reactor were recorded every three minutes. 11) The conductivity values were continuously recorded until reading for reactor 3 closed to reactor 1. 12) Pump 2 was switched off and the valve (V4) was closed. 13) All liquids in reactors were drained by opening valves V5 and V6.

Result The effect of step-change input FT : 150 ml/min

TT1 : 29.2 oC

TT2 : 29.9 oC

TT3 : -32768.0 oC

Time (min)

QT1 (mS)

QT2 (mS)

QT3 (mS)

0

3.280

0.428

0.063

3

10.370

3.280

0.113

6

17.760

8.240

4.010

9

19.620

14.290

4.560

12

22.600

17.370

11.880

15

22.400

18.780

14.180

18

22.200

21.600

16.560

21

23.200

15.190

18.040

24

22.800

22.500

19.390

27

23.200

23.100

21.400

30

23.200

23.100

21.800

33

23.400

23.100

22.000

36

23.300

23.400

22.900

39

23.300

23.300

23.000

Graph result based on data

CONDUCTIVITY, Q (mS)

Conductivity change in time for each reactor in pulse change 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 -1 0 -2

5

10

15

20

25

30

TIME (min) Reactor 1

Reactor 2

Reactor 3

35

40

45

Calculation Vi = FA0 (XAi – XAi-1)/(-rA)i Where Vi = volume of reactor i FAi = molal flow rate of A into the first reactor XAi = fractional conversion of A in the reactor i XAi+1 = fractional conversion of A in the reactor i-1

For the first order reaction, -rA = kCA1 = kCA0(1-XAi)

v = volumetric flow rate of A = 150 ml/min = 0.150 liter/min

For the first reactor: (V=20 liter) (-rA)1 = (kCA)1 = kCA1 = kCA0 (1-XA1) CA0 = FA0/v i.e. FA0 = vCA0 XAi+1 = XA0 = 0

Therefore, Tank 1 Vi = FA0 (XAi - XAi-1) / (-rA)i 20 = 0.150 (XA1 - 0) / (0.158 x (1 – XA1)) XA1 = 0.955

Tank 2 Vi = FA0 (XAi - XAi-1) / (-rA)i 20 = 0.1597 (XA2 – 0.955) / (0.158 x (1 – XA2)) XA2 = 0.998 Tank 3 Vi = FA0 (XAi - XAi-1) / (-rA)i 20 = 0.1597 (XA3 – 0.998) / (0.158 x (1 – XA3)) XA3 = 1

Discussion In this experiment, we carried out an experimental procedure to determine the effect of step change input on the concentration of the salt solution used in the experiment which is sodium chloride, NaCl. The first step in the experiment was filling the reactor tanks with 20L of deionized water. In the experiment of CSTR in series, there are two main objectives to observe; effect of step-change input and effect of pulse input. But in this discussion, we are only focusing on the effect of step-change input. The difference between these two methods are that step-change input means we are continuously feeding the salt solution NaCl into the reactor throughout the experiment and through the time the salt solution will fill all three reactors until the first reactor and third reactor will have an equal value of conductivity. As for the effect of pulse input, we feed the reactor with 3 minutes worth of salt solution and then continuing the experiment feeding the reactors with deionized water spreading the salt solution equally through all three reactors. The feed is flowed through the reactors at roughly 150 ml/min and the system is running isothermally with each reactor’s temperature at around 29 0C. In this experiment we took readings of the conductivity of each reactor every 3 minutes. The experiment ends when the conductivity of the first reactor and the third reactor are equal and constant for the few last readings. The first reading of the reactors are as follows; QT1 is 3.280 mS, QT2 is 0.428 mS, and QT3 is 0.0633 mS. The results can be observed in the results section of the report. As observed from the results of the experiment, the conductivity of the mixture increases as time passes on as more and more salt solution is fed into the reactors. And at the 33rd minute we can see that the conductivity of the reactors are starting to slowly get equal and finally after some time at the 39th minute, the value reads QT1, QT2 and QT3 are 23.300 mS. Reactor in series is designed to provide there are no side streams by defining the overall conversion at any point. Reactors in parallel will have the same conversion for each reactor but in series the conversion is modified to be improved. In the sample calculation it shows that the results for fractional conversion Xi for each reactor. The results shows that the fractional conversion is increased where X1,X2 and X3 are 0.955, 0.998 and 1.0 where the conversion from reactor 1 to 3 change from 95.5% to 100% conversion. In a scientific research, there are always unknown variables that could disrupt us from obtaining the best results possible. During the recording of the data, there were some problems that occurred to the computer that recorded the data. The computer froze for a few

seconds and thus it did not record accurately every 3 minutes. Because the data was not very accurate, the plotting of the graph was affected and not very smooth. Conclusion As a conclusion, based on the aim of the experiment, we can say that the step-change input affected the concentration at the reactor. It can be seen from the graph plotted. If we compare our graph with a theorized graph, the graph is almost the same. But because of the error during recording of the data, there are some difference compared to the theory and a less smooth graph was obtained. It is safe to say that based on the results of the experiment, the experiment was a success as the objective was achieved.

Recommendation It is in our biggest interest to acquire the best results off of the experimental procedures but little do we know that most of the time the methodology is always incomplete in a sense that precautionary steps are rarely given. There is significant amount of external disturbances that can affect the results of the experiment. To prevent from any inaccuracy, it is advised that the precautionary steps are to be mentioned. For example in this experiment, make sure that the reactors are properly cleaned before starting the experiment because we don’t want any salt residue in the reactors that could affect the readings later on. The flow rate must be always at 150 ml/min to avoid disturbance or to the reading. Just to be on the safe side, the best way to have a precise outcome is to prepare the proper and complete procedures for the experiment.

References 1. Elements of Chemical reaction Engineering, Fourth Edition H. Scott Fogler, Pearson International Edition, 2006 Pearson Education, Inc 2. Perry, R.H., and D. Green, Perry’s Chemical Engineering Handbook, 6th Edition,McGraw-Hill, 1984. 3. Fluid Mixing Manual, Faculty of Chemical Engineering, Mara University of Technology (2014). 4. (2015). 12 October 2015, from 2. http://www.solution.com.my/pdf/bp107(a4).pdf

Appendix

CSTR (s) Solteq model BP107

CSTR (s) front image

CSTR (s) back image