Chemical reaction engineering

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Chemical reaction engineering

  1. 1. ABSTRACT This experiment to study the effects of temperature on saponification reaction of ethyl acetate and sodium hydroxide in batch reactor. The batch reactor is the generic term for a type of vessel widely used in the process industries. In the first experiment, the calibration curve for calibration versus conductivity has been plotted by preparing 1 L of 0.1 M sodium hydroxide (NaOH) solution and 1 L of 0.1 M sodium acetate (Na(Ac)) solution. From the curve, the conductivity have been determined in 100 ml of deionised water for 0%, 25%, 50%, 75% and 100% conversions. In the second experiment, 2 L of 0.1 M of acetyl acetate and 2 L of 0.1 M sodium hydroxide was prepared. Then, the reactants were put into the jacketed reactor via the opening that are located at the top of the reactor. For the first part, the temperature of the water was set at 30°C that will be the same as the reactor and reactant temperature. Then, the stirrer was switched on. After that, the stirrer speed was set to the minimum speed. After 30 minutes later, conductivity was observed. The reading was recorded and the steps were repeated for temperature of 50°C after we collected the mixture in a beaker. Last but not least, after finishing all the steps in the experiments, mixture inside the reactor was drained off and the reactor was clean properly. All liquid waste (mixture) was dispose immediately after each experiment. Lastly, 4 L of deionised water was filled into the tank for cooling process. From the data that obtained by conducting this experiment, the temperature in term of conversion which was have the lower conductivity will made the high conversion. For example, at temperature 40oc have lower conversion and high conductivity which is 8.15 mS/cm. To increase the efficiency batch reactor, there are some recommendation, firstly, oversize the reactor discharge pumps to drive the external recirculation through a static mixer into the highly mixed zones. Secondly is a use a jacketed pump for steam or hot oil ensures consistent temperature through the loop and a better end product. 1
  2. 2. INTRODUCTION First of all, as concerned, the experiment was conducted to study the effect of temperature on saponification reaction of ethyl acetate and sodium hydroxide in batch reactor. A batch reactor was a reactor which characterized by its operation. This means the reactor reached steady state was called batch reactor. The Batch reactor was a generic term for a type of vessel widely used in the process industries. The vessels of this type were used for a variety of process operations such as solids dissolution, product mixing, chemical reactions, batch distillation, crystallisation, liquid or liquid extraction and polymerisation. In some cases, they were not referred to as reactors but have a name which reflects the role they perform There were many types of batch reactor such as FED batch rector, stirred batch reactor, and semi batch reactor. Besides, the reactants and the catalyst in batch reactor were placed in the reactor which was then closed to transport of matter. The reaction was allowed to proceed for a given time where upon the mixture of unreacted material together with the product is withdrawn. Besides that, provision for mixing may be required. Next, in batch reactor, all the reactants are loaded at once, the concentration then varies with time, but at any one time it was uniform throughout. Somehow, agitation served to mix separate feeds initially and to enhance heat transfer. In addition, batch reactors were popular in practice because of their flexibility with respect to reaction time and to the kinds and quantities of reactions that can be performed. Batch reactor 2
  3. 3. The above picture was the example of image or sketched batch reactor vessels. The characteristics of a batch reactor were that the total mass of each batch was fixed, each batch was a closed system, and the reaction time for all elements of fluid was the same. Apart from that, this reactor was less preferred because it involves high cost of operation and the product quality more variable than with continuous operation. Hence, the high cost of operation was an example of disadvantage of batch reactor. For further information, a batch reactor was used in chemical processes for small scale operation which were for testing new processes that have not been fully developed, for the manufacture of expensive products, and for processes that are difficult to convert into continuous operations. Other than that, the main advantage of a batch reactor was high conversion, which can be obtained by leaving the reactant in the reactor for long periods of time, but it also has the disadvantages of high labor costs per batch and the difficulty of large scale production. In a batch reactor, all the reactants were loaded at once. The concentration then varies with time, but at any one time it is uniform throughout. Agitation serves to mix separate feeds initially and to enhance heat transfer. Besides, these reactors were popular in practice because of their flexibility with respect to reaction time and to the kinds and quantities of reactions that can be performed. As this experiment involved the saponification process, hence, the term saponification will be defined. The term of saponification was the name given to the chemical reaction that occurs when a vegetable oil or animal fat that was mixed with a strong alkali. The products of the reaction are two which was soap and glycerin. Water was also present, but it does not enter into the chemical reaction. The water was only a vehicle for the alkali, which was otherwise a dry powder. At last but not least, the oils used in modern handmade soap were carefully chosen by the soap maker for the character they impart to the final soap. Coconut oil creates lots of glycerin, makes big bubbly lather, and was very stable. Olive oil has natural antioxidants and its soap makes a creamier lather. Tallow, or rendered beef fat, makes a white, stately bar that was firm and created abundant lather. Many other oil can be used, each one for a specific reason. The alkali used in modern soap was either potassium hydroxide that was used to make soap or liquid soap because of its greater solubility, or sodium hydroxide that was used to make bar soap. 3
  4. 4. LITERATURE REVIEW The usual agitator arrangement is a centrally mounted shaft with an overhead drive unit. Impeller blades are mounted on the shaft. A wide variety of blade designs are used and typically the blades cover about two thirds of the diameter of the reactor. Where viscous products are handled, anchor shaped paddles are often used which have a close clearance between the blade and the vessel walls.(Christe John Geankoplis. Transport Process and Separation Process Principle) Most batch reactors also use baffles. These are stationary blades which break up flow caused by the rotating agitator. These may be fixed to the vessel cover or mounted on the side walls. Despite significant improvements in agitator blade and baffle design, mixing in large batch reactors is ultimately constrained by the amount of energy that can be applied. On large vessels, mixing energies of more than 5 Watts per litre can put an unacceptable burden on the cooling system. High agitator loads can also create shaft stability problems. Where mixing is a critical parameter, the batch reactor is not the ideal solution. Much higher mixing rates can be achieved by using smaller flowing systems with high speed agitators, ultrasonic mixing or static mixers. (H. Scott Fogler, Elements of Chemical Reaction Engineering) A batch reactor is used for small-scale operation, for testing new processes that have not been fully develop, for the manufacture of expensive products, and for processes that are difficult to convert to CSTR. The reactor can be charged throught the holes at the top. A batch reactor has neither inflow nor outflow of reactants or products while the reaction is being carried out: Fjo = Fj = 0. In – Out + Generation = Accumulation V FA 0 FA rA dV dN A dt V dN A dt rA dV 4
  5. 5. (H. Scott Fogler, Elements of Chemical Reaction Engineering) There are some advantage and disadvantage for using batch reactor. For advantages: production of high cell densities due to extension of working time (particularly important in the production of growth-associated products) controlled conditions in the provision of substrates during the fermentation, particularly regarding the concentration of specific substrates as for ex. the carbon source control over the production of by-products or catabolite repression effects due to limited provision of substrates solely required for product formation the mode of operation can overcome and control deviations in the organism's growth pattern1 as found in batch fermentation allows the replacement of water loss by evaporation alternative mode of operation for fermentations leading with toxic substrates (cells can only metabolize a certain quantity at a time) or low solubility compounds increase of antibiotic-marked plasmid stability by providing the correspondent antibiotic during the time span of the fermentation no additional special piece of equipment is required as compared with the batch fermentation mode of operation For Disadvantages: It requires previous analysis of the microorganism, its requirements and the understanding of its physiology with the productivity. It requires a substantial amount of operator skill for the set-up, definition and development of the process. 5
  6. 6. In a cyclic fed-batch culture, care should be taken in the design of the process to ensure that toxins do not accumulate to inhibitory levels and that nutrients other than those incorporated into the feed medium become limiting, Also, if many cycles are run, the accumulation of non-producing or low-producing variants may result. The quantities of the components to control must be above the detection limits of the available measuring equipment. (H. Scott Fogler, Elements of Chemical Reaction Engineering) OBJECTIVE Firstly, the purpose of this experiment was to study the effects of temperature on saponification reaction of ethyl acetate and sodium hydroxide in batch reactor. In this experiment, two difference temperatures was used to measure the values of conductivity which is directly proportional to the concentration of reactants inside the tanks. Hence, the time required for completed reaction can be known when the values of conductivity become constant. 6
  7. 7. METHODOLOGY 5.1 Materials/Apparatus a) 2 L Fermenter b) Dissolve oxygen probe c) Ruler d) Caliper e) 2 L Distilled water f) N2 and O2 supply g) 2 g NaCl h) 5 ml cooking oil (antifoam) 5.2 Geometric of Stirred Tank Bioreactor Dimension of components Liter/mm Dimension of components Liter/mm Operating volume 2L Ratio of P/D 0.38 Liquid height (L) 15.0cm Ratio of B/D 0.07 Tank or vessel diameter (D) 21.0cm Impeller height (I) 180mm Ratio 0f L/D 57.74 Ratio of I/D 0.86 Impeller diameter (P) 80mm Number of impeller 2 Baffle width (B) 15mm 7
  8. 8. 5.3 Determination of KLa at different air flow rate 1. The agitation of bioreactor is set to 300 rpm. 2. Oxygen concentration of the solution is lowered by gassing the liquid out with N2 at 9 L/min until saturated and the flow is stopped. 3. O2 is supplied to the bioreactor at flow rate of 1.0 L/min until saturated, then the flow is stopped. 4. CL value is obtained at constant time interval during aeration. 5. Steps 2-4 are repeated for different oxygen flow rate (1.5 and 2 L/min). 6. The KLa of stirred tank reactor is determined at different air flow rate. 5.4 Determination of KLa at different agitation speed 1. The agitation of bioreactor is set to 200 rpm. 2. Oxygen concentration of the solution is lowered by gassing the liquid out with N2 at 9 L/min until saturated and the flow is stopped. 3. O2is supplied to the bioreactor at flow rate of 1 L/min until saturated, and then the flow is stopped. 4. CL value is obtained at constant time interval during aeration. 5. Steps 1-4 are repeated for different agitation speed (400 and 600 rpm). 6. The KLa of stirred tank reactor is determined at different agitation speed. 8
  9. 9. RESULTS Molar mass of ethyl-acetate = 88.11g/mol Molar mass of sodium hydroxide = 40 g/mol Density of ethyl-acetate =0.895 g/ml At T = 400C Time (min) Conductivity 5 9.92 10 8.90 15 8.50 20 8.42 25 8.20 30 8.15 At T = 600C Time (min) Conductivity 5 8.0 10 7.9 15 7.7 20 6.2 25 5.9 30 5.2 9
  10. 10. Calculation For NaOH, NaOH = 9 mL 120 mL NaOH = 20 L 1.5 L NaOH = ? 1.5 x 6 = 9 mL For EtAC, = 10.17 M1V1 = M2V2 (10.17)V1 = (0.1)(1.5) V1 = 15 mL Conversion + 100 ml DI water Conductivity,(mS/cm) 100 ml NaOH for 0% conversion 35.8 75 ml NaOH + 25 ml Na(Ac) for 25% conversion 30.3 50 ml NaOH + 50 ml Na(Ac) for 50% conversion 24.9 25 ml NaOH + 75ml Na(Ac) for 75% conversion 19.5 100 ml Na(Ac) for 100 % conversion 14.55 10
  11. 11. DISCUSSIONS Plot the calibration curve of conversion vs. conductivity and discuss relationship between these parameters. Graph calibration curve of conversion,X versus conductivity,mS/cm 120 Conversion,x(%) 100 80 60 40 y = -4.688x + 167.2 R² = 0.999 20 0 0 -20 5 10 15 20 25 30 35 Conductivity, (mS/cm) From the graph, the conversion is increase when the conductivity is decrease. Slope=m y=-4.6887x + 167.27 m=-4.6887 11 40
  12. 12. Plot a graph of conductivity / conversion vs. temperature. Compare the result for each temperature in term of conversion etc. 9 8 Conductivity,ms/cm 7 6 5 4 3 2 1 0 0 10 20 30 40 50 60 70 Temperature,(o C) 1) Temperature (40 oc) Conductivity-8.15 mS/cm 2) Temperature(60 oc) Conductivity-5.2 mS/cm From the graph, we can compare the result for temperature in term of conversion which the lower the conductivity, the higher the conversion. For example, at temperature 40oc have lower conversion and high conductivity which is 8.15 mS/cm. 1. Give 3 examples on the application of batch reactor in chemical process industries. i. Fermentation ii. Intermediate or one shot production iii. Pharmaceutical 12
  13. 13. iv. Small scale production 2. Suggest a method or way to improve the efficiencies of batch reactor. Oversize the reactor discharge pumps to drive the external recirculation through a static mixer into the highly mixed zones. A jacketed pump for steam or hot oil ensures consistent temperature through the loop and a better end product. Using multiple injection points with nozzles at the tank entrances will increase velocity for better mixing. However, these flow restrictions will increase horsepower requirements compared to simple recirculation. 13
  14. 14. CONCLUSION AND RECOMMENDATION CONCLUSION From this experiment, we can conclude that the conductivity is inversely proportional to temperature. Based on the result, for temperature in term of conversion which the lower the conductivity, the higher the conversion as for example, at temperature 40oc that has lower conversion will have high conductivity which is 8.15 mS/cm. Particles can only react when they collide. If a substance heat up, the particles move faster and so collide more frequently. Apart from that, it is obviously that from the result we obtained, the objective of this experiment successfully achieved. RECOMMENDATION 1. Oversize the reactor discharge pumps to drive the external recirculation through a static mixer into the highly mixed zones. 2. Used a jacketed pump for steam or hot oil ensures consistent temperature through the loop and a better end product. 3. Using multiple injection points with nozzles at the tank entrances will increase velocity for better mixing. However, these flow restrictions will increase horsepower requirements compared to simple recirculation. 4. Before start the experiment all the apparatus must be clean up and dry before pour any chemical solution.. 14
  15. 15. REFERENCES H. Scott Fogler, Elements of Chemical Reaction Engineering (Third Edition), Prentice Hall, International Series. Transport Process and Separation Process Principle (Include Unit Operations), 4th edition, Christe John Geankoplis. Optimisation of Batch Reactor Operation. Retrieved on 22 February 2011 from http://www.strath.ac.uk/Other/cpact/Project5/project5sum.htm. Batch Reactor. Retrieved on 22 February 2011 from http://www.scribd.com/doc/22995623/Batch-Reactors. Fed-Batch Fermentations. Retrieved on 22 February 2011 from http://userpages.umbc.edu/~gferre1/fedbatch.html#Some%20examples%20of%20fedbatch%20use%20in%20industry. Improve Batch Reactor Temperature Control. Retrieved on 22 February 2011 from http://www.chemicalprocessing.com/articles/2008/088.html. 15

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