Experiment 7 - Batch Reactor

Abstract This experiment is done to study the effects of temperature on saponification reaction of ethyl acetate and sodium hydroxide in batch reactor. A batch reactor is a reactor which the reactant is feed and left in the tank. The product is only removed from the tank when the reaction is completed. In this experiment, ethyl acetate and sodium hydroxide is mixed in the tank. The temperature is manipulated and the time taken for the conductivity values to achieve a steady state for each flow rate is monitored and recorded. From the results obtained, it was found that as the temperature increases, the rate of reaction increases. Overall, the conductivity increase with the increase of time and temperature. Introduction A simple batch reactor is a reactor which the feed is charged via two holes in the top of the tank. While the reaction is carried out, there is nothing else to be put in or taken out from the tank until the reaction is completed. The tank is easily heated or cooled by cooling jacket. Batch reactor has the advantage of high conversion that can be obtained by leaving the reactant for a long period of time. There are several factors that affect the rate of reaction in the batch reactor. For this experiment, the objective is being study the effect of temperature on saponification reaction of ethyl acetate and sodium hydroxide in a batch reactor. Assumption made was the conductivity decreased with time but increased with the increment of temperature. Methodology: First of all, 2.5L of 0.1M sodium hydroxide solution, 500mL of 0.1M sodium acetate solution and 2.0L 0.1M ethyl acetate is prepared. Next to prepare calibration curve, 100mL of deionised water is mixed with each set of chemical mixture (a. 100mL NaOH for 0% conversion, 75mL NaOH + 25mL Na(Ac) for 25% conversion, 50mL NaOH + 50mL Na(Ac) for 50% conversion, 25mL NaOH + 75mL Na(Ac) for 75% conversion, and 100mL Na(Ac) for 100% conversion). To perform reaction at 30°C, the temperature is set at 30°C for both reactor and reactant. 1L of 0.1M ethyl acetate is added into the jacketed reactor through the opening at the top of the reactor. The stirrer is switched on and set at the minimum speed. Once the temperature is uniform, 1L of 0.1M NaOH is added into the reactor and stop watch is started immediately. Then the product is collected every 5mins and its conductivity is tested and recorded until its conductivity remain constant. After that, the reactant in the reactor is drained out. The steps are repeated by increase the reactor and reactant’s temperature until 50°C. Result:

No Conversion, % Conductivity 1 0 17.99 2 25 14.76 3 50 11.76 4 75 7.76 5 100 4.74 Table 1: Calibration data

Conversion versus Conductivity 120 100

f(x) = - 7.45x + 134.92 R² = 1

80 Conversion (%)

60

Conversion, % Linear (Conversion, %)

40 20 0 4

6

8 10 12 14 16 18 20 Conductivity

Graph 1: Calibration curve of conversion versus conductivity According to the calibration curve, the higher the conductivity, the lower the conversion. Conductivity is caused by the ionic solution such as sodium hydroxide and sodium acetate. Sodium hydroxide has a higher conductivity compared to sodium acetate. Therefore, when sodium hydroxide is used to produce sodium acetate; the concentration of the strong sodium hydroxide ions decreases, thus causing the conductivity to decrease as well. Based on the best line obtained, the relationship between conversion and conductivity can be expressed in the equation of

y=−7.4476 x+134.92 .

No .

Time (min)

Conductiv ity

Conversion, %

1

0

15.00

23.21

2

5

13.12

37.21

3

10

12.30

43.31

4

15

11.77

47.26

5

20

11.06

52.55

6

25

10.92

53.59

7

30

10.81

54.41

8

35

10.81

54.41

Table 2: Data for reaction at 30°C

Conversion / Conductivity versus Time 60.00 50.00 40.00 Conversion (%) / Conductivity

Conductivity

30.00

Conversion, %

20.00 10.00 0.00 0 10203040 Time (min)

Graph 2: Graph of Conversion/ Conductivity versus Time for the reaction at 30°C

No .

Time (min)

Conductiv ity

Conversion, %

1

0

14.14

29.61

2

5

10.71

55.16

3

10

10.53

56.50

4

15

10.66

55.53

5

20

10.65

55.60

6

25

10.53

56.50

7

30

10.53

56.50

8

35

10.53

56.50

Table 3: Data for reaction at 50°C

Conversion / Conductivity versus Time 60.00 50.00 40.00 Conversion (%) / Conductivity

Conductivity

30.00

Conversion, %

20.00 10.00 0.00 0 10203040 Time (min)

Graph 3: Graph of Conversion/ Conductivity versus Time for reaction at 50°C

Based on graphs 2 and 3, as the reaction time increases the rate of conversion increases until a state of equilibrium has achieved and the reaction has ended. The graph also shows that the conductivity decreases over time. This supports the theory that sodium hydroxide has a higher conductivity than sodium acetate and when sodium hydroxide is reacted to form sodium acetate in the saponification reaction, the conductivity decreases. The conductivity decreases faster and the rate of conversion in graph 3 is higher than graph 2 because the temperature is higher for the experiment in graph 3 than graph 2. A reaction in a higher temperature occurs faster because as the temperature increases, the particles vibrate and move faster, causing them to collide more with each other. This causes a higher rate of effective collisions and minimum activation energy is needed to get the reaction started.

Application of batch reactor in chemical process industries There are many types of batch reactors in chemical process industries a sequential batch reactor is one of those reactors in industries. It is used mostly in water treatment. Secondly is the FED batch reactor. It is mostly used in fermentation processes. Thirdly is the semi-batch reactor which is operated with both continuous and

batch input outputs. That means a semi-batch reactor can also function as a continuously stirred tank reactor. This type of reactor is used in chlorinations. Way to improve efficiencies of batch reactor Cleaning and maintenance should be regularly done to improve the efficiency of batch reactors. Flushing out precipitations and cleaning reactors may allow reactors to perform more efficiently without regular breakdowns and the total life-span of a reactor can be increased. Conclusion As a conclusion, sodium hydroxide contributes stronger conductivity compare to sodium acetate. Thus, as the time increase, the concentration of sodium hydroxide decrease and the conductivity decrease. At the same time, the concentration of sodium increase and cause the conversion increase. Besides, as the temperature increase, the conversion increase as well. There are a few suggested steps to obtain more accurate result. Firstly, make sure the concentrations of the reactants are accurately prepared. Next, make sure that the conductivity meter is well calibrated. Last but not least, safety precaution must be followed such as wear glove while handling chemical.

References 1. Control and Monitoring of Chemical Batch Reactors; 2011; Fabrizio Caccavale, Francesco Pierri, Mario Iamarino, Vincenzo Tufano; page 2 &page 3. 2. Element of Chemical Reaction Engineering; Forth edition; 2006; H. SCOTT FOGLER , Ame and Catherine Vennema Professor of Chemical Engineering, The University of Michigan, Ann Arbor; page 10 3. http://www.engin.umich.edu/~cre/asyLearn/bits/batch/index.htm