ABSTRACTOn the 30th or March 2015, an experiment on Continuous Stirred Tank Reactor was carried out in a group. The model used for the simulation of this experiment is MODEL: BP 143 which is the 40L Continuous Stirred Tank Reactor. The purpose of conducting this experiment was to determine the effect of residence time of the reaction in a Continuous Stirred Tank Reactor. To summarize the whole experiment, it was started likewise in all experiments, which is the general start-up procedure. After the general start-up procedure was carried out and the equipment was set to a desired setting, the solution of tank 1 and tank 2 were allowed to flow in the tank with the highest flow rate as possible. Next, as soon as the reactor has been filled up, the flow rate was adjusted to 0.1 L/min at both pumps. The stirrer was turned on and equipment was left for a few minutes to ensure a steady state condition. Then, the initial conductivity value was recorded and 50mL sample was collected to be titrated to determine the concentration of sodium hydroxide in the reactor and the extent of conversion. The experiment was then repeated by adjusting the flow rates of sodium hydroxide and ethyl acetate to 0.15, 0.20, 0.25 and 0.30 L/min. Results that were obtain was calculated and tabulated further.

INTRODUCTIONContinuous Stirred Tank Reactor is a type reactor that is commonly used in the industrial chemical processes. It is also known as CSTR, vat or back mix reactor. Basically, in this reactor, the reactants and products are continuously feed in and withdrawn. Thus, hydraulic agitation is needed to achieve uniform composition and temperature, which is the alternative that strongly influenced by process considerations.CSTR is used mostly for liquid phase reactions. As for the operations, it is usually operated at steady state and the reaction is assumed to be perfectly mixed. As a result, there is no dependence in time or position dependence of the temperature, the concentration, also the reaction rate in the reactor.Due to the compositions of mixtures leaving the reactor, the reaction driving forces, normally the reactant concentrations, is necessarily low. Thus, excluding the reaction for zero order and negatives, CSTR requires big amount of volume of the reactor types to get desired conversions.In addition, in CSTR every of the variables are the same at every points. This is due to the concentration and temperature in the exit streams is similar everywhere within the reactions vessel. This will lead to the temperature and concentration in the exit stream is modeled as being similar as those in the reactor.It is important to understand the behavior of on how the reactors function to know the correct way in handling and controlling the reaction system. There are two main groups of reactors, batch reactors and continuous flow reactors. In CSTR, to obtain good result, divide a single vessel into compartments while minimizing back mixing and short circuiting. The bigger number of CSTR stages, the closer the performance approaches that of a tubular plug flow reactor. (H.S. Fogler, 2006)In this experiment, the model used is CSTR (Model: BP143) which has been designed suitable for student to run the experiment on chemical reactions in liquid phase under both conditions; isothermal and adiabatic. The unit is completely came with jacketed glass reactor, constant temperature water circulating unit, vapor condenser; individual reactant feed tanks and pumps, temperature sensors, conductivity measuring sensor and data acquisition system.OBJECTIVEThere are a few objectives for this experiment: To carry out saponification reaction between sodium hydroxide and ethyl hydroxide, To determine the effect of residence time onto the extent of conversion, To determine the reaction rate constant.THEORYRate of Reaction and Rate LawRate at which the given chemical reaction proceeds can be articulate either as the rate of disappearance of the reactants or the rate of formation of products.The rate equation, for an example the rate law, for rj is an algebraic equation that is solely a function of the properties of the reacting materials and reaction conditions (eg. Temperature, pressure or type of catalyst if it does exist at any point in the system). The rate equation is then classified as independent of the type of reactor in which the reaction is carried out.For an instant,

Where in the equation, A and B are the reactants, C and D are the products. Meanwhile, a,b,c and d are the stoichiometric coefficients for the respective species.Similarly, the rate of reaction can also be represented by the rate of disappearance of another species, such as rB instead of -rA. Also, the rate of formation of a product, such as rC or rD In an equation, it can be written as;

The rate law is essentially an algebraic equation involving concentration. It may be linear function of concentration or maybe some other types of algebraic equations. One of the common equations is;

ConversionTaking species A as the basis, the reaction expression can be divided through the stoichiometric coefficient of species A, in order to arrange the reaction expression as the following :

Conversion is a better way to quantify how much the reaction has moved, or how many moles of products are formed for every mole of A has consumed. Conversion XA is the number of moles of A that have reacted per mole of A fed to the system.

Continuous Stirred Tank ReactorsCSTR is sort of reactors that commonly used in industrial processing which required a stirred tank operated continuously. It runs normally at steady state and usually operated so as to be quite well mixed. In CSTR there a few kinds of phases presents; liquid phase, qas-liquid reactions, and solid-liquid reactions. The usages are when agitation is required and for series configurations for different concentration streams.The advantages of CSTR are it runs for continuous operation, has good temperature control, it easily adapts to two phase runs, a good control, simplicity of construction, low operating cost and it is easy to clean. How there are few disadvantages too. The contras are it has lowest conversion per unit volume and its by-passing and channeling possible with poor agitation.When general mole balance is applied to species A in a CSTR operated at steady state, in which there are no spatial variations in the rate of reaction, and the equation based on that is;

The familiar form known as the design equation for a CSTR is,

Usually, the conversion will increase with time the reactants spend in the reactor. As for continuous flow systems, time usually increases with growing reactor volume. As a result, the conversion X is a function of reactor volume V.Let FA0 is the molar flow rate of species A fed to a system operated at steady state, the molar flow rate at which species A is reacting within the entire system will be [ FA0 X ]. The molar feed rate of A to the system subtract rate of reaction of A within the system equals the molar flow rate of A leaving the system, FA0. Mathematically,

Molar flow rate which enter, FA0 is just the product of the entering concentration CA0 and the entering volumetric flow rate v0,

Combining both of the previous equation,

Since the exit composition from the reactor is identical to the composition inside the reactor, the rate of reaction is evaluated at the exit condition.

APPARATUS

Model: BP 143 40L Continuous Stirred Tank Reactor (CSTR)Solvent used: 1. 0.1 M sodium hydroxide, NaOH2. 0.1 M ethyl acetate, Et (Ac)3. 0.25 M hydrochloric acid, HCl3. De-ionized water, H2O4. Phenolphthalein

PROCEDURESGeneral Start-Up Procedures1. The following solutions were prepared;a) 40 L of sodium hydroxide, NaOH (0.1M)b) 40 L of ethyl acetate, Et(Ac) (0.1M)c) 1 L of hydrochloric acid, HCl (0.25M), for quenching.2. All the valves are ensured initially closed.3. The feed vessels were charged as follows;a) The charge port caps were open for vessels B1 and B2.b) The NaOH was carefully poured into vessel B1 and the Et(Ac) solution into vessel B2.c) The charge port caps were closed for both caps.4. The power was turned on for the control panel.5. The thermostat T1 tank was check for sufficient water. Refill if necessary.6. The overflow tube was adjusted to give a working volume of 10L in the Reactor R1.7. Valves V2, V3, V7, V8 and V11 were opened.8. The unit is then ready for the experiment.General Shut-Down Procedures1. The cooling water valve V13 was kept open to allow the cooling water to continue flowing.2. Both pumps P1 and P2 were switched off. Stirrer M1 was switched off.3. Thermostat T1 was switched off. The liquid in the reaction vessel R1 was let to cool down to room temperature.4. Cooling water valve 13 was closed.5. Valves V2, V3, V7 and V8 were closed. Valves V4, V9 and V12 were opened to drain any liquid from the unit.6. The power for the control panel was turned off.

Experiment Procedures1. The general start up procedures was performed.2. Both pumps P1 and P2 were switched on simultaneously and valves V5 and V10 were opened to obtain the highest possible flow rate into the reactor.3. The reactor was let to fill up both solutions until it is just about to overflow.4. The valves V5 and V10 were readjusted to give a flow rate of about 0.1 L/min. Both flow rates were ensured the same. The flow rate was recorded.5. The stirrer M1 was switched on and the speed was set to about 200 rpm.6. The conductivity at QI-401 was start monitored until it does not change over time. This was to ensure the reactor has reached its steady state.7. The steady state conductivity value was recorded and the concentration of NaOH was found in the reactor and extent of conversion from the calibration curve.8. Sampling valve 12 was opened and 50mL sample was collected. A titration was carried out back to manually determine the concentration of NaOH in the reactor and extent of conversion.9. The experiment was repeated from step 6 to 9 for different residence times by adjusting the feed flow rates of NaOH and Et(Ac) to about 0.15, 0.20, 0.25 and 0.30 L/min. The both flow rates were ensured the same.

RESULTSFlowrate of NaOH, (L/min)0.100.150.200.250.30

Flowrate of Et(Ac), (L/min)0.100.150.200.250.30

Volume of NaoH titrated, V1 (mL) 30.3630.3834.0038.7344.77

Residence time, (min)200133.33100.0080.0066.67

Volume of unreacted quenching HCl, V2 (mL)12.14412.51213.615.49217.908

Volume of HCl reacted with NaOH , V3 (mL)-2.122-2.512-3.60-5.492-7.908

Conversion of NaOH in the reactor, X (%)121.44123.32136154.92179.08

RateConstant,k(M-1s-1)2.64193.40162.09881.28410.8590

Rate of reaction, -rA (M/s)2.42 x 10-4

3.53 x 10-46.80 x 10-49.68 x 10-41.34 x 10-4

Table 1: Table of result

Flowrate of NaOH, (L/min)0.100.150.200.250.30

Flowrate of Et(Ac), (L/min)0.100.150.200.250.30

Volume of NaoH titrated, V1 (mL)2724221917

Residence time, (min)200133.33100.0080.0066.67

Volume of unreacted quenching HCl, V2 (mL)10.89.68.87.66.8

Volume of HCl reacted with NaOH , V3 (mL)-0.80.41.22.43.4

Conversion of NaOH in the reactor, X (%)10896887668

RateConstant,k(M-1s-1)16.87590.012.223.391.992

Rate of reaction, -rA (M/s)2.7x10-43.6x10-44.4x10-44.7x10-45.1x10-4

Table 2: Table of result obtained from another group as reference

SAMPLE CALCULATIONSCalculation for flow rate = 0.10 L/minVolume of sample,Vs= 50 mLConcentration of NaOH in the feed vessel, CNaOH,f = 0.1 MVolume of HCl for quenching, VHCl,s = 10 mLConcentration of HCl in standard solution, CHCl,s = 0.25 mol/LVolume of NaOH titrated, V1 = 30.36 mol/LConcentration of NaOH used for titration, CNaOH,s = 0.1 mol/LConcentration of NaOH entering the reactor, CNaOH,0 = (1/2)(0.1) = 0.05 mol/L

Volume of unreacted quenching HCl, V2 = (CNaOH,s /CHCl,s) x V1 = (0.1/0.25) x 30.36 = 12.144 mLVolume of HCl reacted with NaOH in sample, V3 = VHCl,s - V2 = 10 12.144 = -2.144 mLMoles of HCl reacted with NaOH in sample, n1 = (CHCl,s x V3)/1000 = (0.25 x -2.144) / 1000 = -0.000536 molMoles of unreacted NaOH in sample, n2 = n1 = -0.000536 molConcentration of unreacted NaOH in the reactor, CNaOH = n2/ Vs x 1000 = x 1000 = -0.01072Conversion of NaOH in the reactor, X = x 100% = x 100% = 121.44 %Residence time, = VCSTR/F0 = 40 L/ (0.10 + 0.10) L/min = 200 min

Rate constant, = = 2.6419 M-1s-1Rate of reaction, -rA = kCA2 = 2.6419 (-0.01072)2 = 3.036 x 10-4 M/s

Calculation for flow rate = 0.15 L/minVolume of sample,Vs= 50 mLConcentration of NaOH in the feed vessel, CNaOH,f = 0.1 MVolume of HCl for quenching, VHCl,s = 10 mLConcentration of HCl in standard solution, CHCl,s = 0.25 mol/LVolume of NaOH titrated, V1 = 30.83 mol/LConcentration of NaOH used for titration, CNaOH,s = 0.1 mol/LConcentration of NaOH entering the reactor, CNaOH,0 = (1/2)(0.1) = 0.05 mol/LVolume of unreacted quenching HCl, V2 = (CNaOH,s /CHCl,s) x V1 = (0.1/0.25) x 30.83 = 12.332 mLVolume of HCl reacted with NaOH in sample, V3 = VHCl,s - V2 = 10 12.332 = -2.332 mLMoles of HCl reacted with NaOH in sample, n1 = (CHCl,s x V3)/1000 = (0.25 x -2.332) / 1000 = -0.000583 molMoles of unreacted NaOH in sample, n2 = n1 = -0.000583 mol

Concentration of unreacted NaOH in the reactor, CNaOH = n2/ Vs x 1000 = x 1000 = -0.01166Conversion of NaOH in the reactor, X = x 100% = x 100% = 123.32 %Residence time, = VCSTR/F0 = 40 L/ (0.15 + 0.15) L/min = 133.33 minRate constant, = = 3.4016 M-1s-1Rate of reaction, -rA = kCA2 = 3.4016 (-0.01166)2 = 4.6247 x 10-4 M/s

DISCUSIONRecalling the objectives of this experiment, which are to carry out the reaction between sodium chloride and ethyl acetate in a Continuous Stirred Reactor, to determine the effect of residence time onto the reaction extent of conversion and to determine the reaction rate constant of the reaction, were yet to be achieved. In this experiment, five different flow rates of sodium hydroxide and ethyl acetate were manipulated; ranging from 0.1 L/min to 0.30 L/min with 0.05 L/min in difference respectively. The volume of sample was constant, 50mL, collected from the CSTR to be titrated. From that, the volume of NaOH titrated were collected and recorded.Flow rate (L/min)0.10.150.20.250.30

Vol. of NaOH titrated, V130.6330.8334.0038.7344.77

Table 3: Table of volume of NaOH titratedBy referring to the result table above, to the volume of sodium hydroxide used titrate the samples can be seen. The result obtained was then tabulated further by using some equations in order to enable the conversion, rate constant and rate of reaction to be calculated. From the tabulated data, which can be seen below, the volume of hydrochloric acid that reacted with sodium hydroxide in the sample, v3, calculated is to be negative in value which is not acceptable because the volume should not exceed the volume of hydrochloric acid added to the sample, vHCl,s which is 10 mL. The maximum volume that can be used in order to achieve an accurate result should be less than 27 ml. Flow rate (L/min)0.10.150.20.250.30

Vol. of HCl reacted with NaOH in sample, V3-2.122-2.512-3.60-5.492-7.908

Table 4: Table of volume of HCl reacted with NaOH in sample.

The following objectives will be further discussed:1. To carry out a saponification reaction between sodium hydroxide and ethyl acetate in a continuous stirred tank reactor.Saponification is a continuous reaction process used to produce soap. In order to stop the reaction, hydrochloric acid is used for quenching to stop the reaction after the sample was taken. The reaction is highly dependent of temperature. In the mixture of the solution containing sodium hydroxide and ethyl acetate, it is said to undergo a decrement in its conductivity with time. The reason for this occurrence is because hydroxyl ion, which is a highly conductive ion, is replaced with a poor conductive acetate ion during the reaction. Thus, that explains the decreasing in the conductivity value in this experiment.CH3COOC2H5 + Na+ + OH- CH3COO- + Na+ + C2H5OH2. To determine the effect of residence time onto the reaction extent of conversion.Residence time is the time taken for a substance to remain in the system. It depends highly on the conversion, x, of the reaction.

Figure 2: Graph of conversion against residence time from the other group as reference.

Since the data obtain from the experiment cannot be used, a reference data will be used to further discuss this part of the objective. Judging from the graph plotted, it can be seen clearly that both of the parameters do depend on each other. The highest conversion, which is 96%, took about 133.33 minutes to be achieved. As for the lowest conversion, 68%, only took about 66.67 minutes. Thus, it can be concluded that, the longer the residence time, the higher the conversion of the reaction.3. To determine the reaction rate constant.The reaction rate constant, k, varies with the flow rates used for the pumps. From the unit obtained from the tabulated result, the reaction falls on the second order reaction. A graph of rate constant was plotted to see the relationship between both variables.

Figure 3: Graph of rate constant against total volume flow obtained from the result.

Figure 4: Graph of rate constant against total volume flow from reference result.Two graphs of rate constant against total volume flow rate was plotted in order to compare the value of the rate constant obtained. From both graphs, it can be clearly seen that there is an unusual peak at the 200 L/min flow rates. It might be caused by some interference during the reaction. Neglecting point at the 200 L/min, the pattern of the rate constant seems to be decreasing as the flow rates increases. It can be verified by the equation used to calculate the reaction rate constant below:Residence time, = VCSTR/F0 Rate constant, From the equations above, residence time, total volume of flow rates and the reaction rate constant do have a relationship against each other. Hypothetically, the greater the residence time, the lower the flow rates, the greater the rate constant.

The result of this experiment might be more accurate if precaution were to be taken in counter. There are a few reasons that contribute to this failure to obtain a more accurate result. Firstly, during the titration, 3 samples were taken to be titrated. Therefore, the average reading is taken in order to obtain a more accurate result. Unfortunately, this experiment requires the samples to be titrated as fast as possible. As a result, there is a huge range volume of hydrochloric acid used to titrate the first sample and the third sample so when the average volume was calculated, the value obtained was abruptly high. Secondly, due to the large consumption of sodium hydroxide, the burette needs to be filled constantly after each sample. Thus, this will surely take some time. As mentioned earlier, this experiment requires the sample to be titrated immediately. This explains why the volume of sodium hydroxide used increases. In other words, the longer the sample is left before it is titrated, the greater the volume of sodium hydroxide used for titration, the lower the accuracy of the data obtained. Lastly, due to limited amount of fume chamber, two groups need to share one fume chamber. If there are more fume chambers, the titration might be able to be done faster without the needs to wait for first sample to be completed. However, a reference result from the other group was used to be discussed in this part of the report.

CONCLUSIONAs a conclusion, this experiment is a failure as the value obtained deviate from the limit. Even so, the objectives are able to be achieved but not completely accurate. As the residence time increases, the conversion increases, the reaction rate constant increases with it too and so does the total volume flow rates.

RECOMMENDATION1. The timing to get the sample must be correct. Reduce the extension of time. Try to minimize the time wasted in taking the samples.2. Do not directly get the first flow out of the samples. Blow it first then only take the samples to be titrated.3. Check for any leaking in the pipes of the instrument. In case there is, do report to the lab technician.4. Control the speed from time to time, as well the flow rate, do not let it increase or drop rapidly for a long time of period.5. For every samples taken, let the system run for at least 5 minutes for stability then only read and recorded the data needed.6. For the calculation, if possible standardize the decimal points. Take at least 4 decimal points to get the more precise valuesREFERENCES1. Fogler, H.S (2006). Elements of Chemical Reaction Engineering (3rd Edition). Prentice Hall.2. Levenspiel, O. (1999). Chemical Reaction Engineering (3rd Edition). John Wiley.3. Continuous Stirred Tank Reactor, University of Minnesota Duluth, Department of Chemical Engineering. (Retrieved from http://www.d.umn.edu/~dlong/excstr.pdf on the 1st October 2013)4. W.H. Green (2007). Continuous Stirred Tank Reactor CSTRs. (Retrieved from http://ocw.mit.edu/courses/chemical-engineering/10-37-chemical-and-biological-reaction-engineering-spring-2007/lecture-notes/lec05_02212007_g.pdf on the 1st October 2013)