As a process engineer, your company has enlisted your expertise to design a reac

Question

As a process engineer, your company has enlisted your expertise to design a reactor for a new catalytic reaction that has just been devised by the R&D Q4. (a) (i) Upon closer study, you have found out that the reaction is highly exothermic. What are the possible consequences if a packed bed reactor (2 marks) were used for the highly exothermic reaction? (ii) Suggest a way to mitigate the above problem for the packed bed reactor (2 marks) (iii) What other types of reactor configuration are more suitable for this (4 marks) reaction? Provide your reasons. A venturi loop reactor is used to perform hydrogenation of unsaturated fats to produce saturated fats. Different sizes of nickel catalysts powder have been dosed into the reactor for the hydrogenation reaction. (b) (i) Describe the configuration of the venturi loop reactor with the help of a diagram. (6 marks) Table Q4 below shows the data gathered from the hydrogenation experiment with different operating conditions. What is the major resistance to the catalytic reaction? (ii) (The Henry's law for hydrogen H'PH2 CH2, H-0.00233 kmol H/atm. m) Table 04 RunH2 pat Catalyst size Catalyst charge H2 reaction rate atm ol/m3 s 25 25 50 50 100 100 0.05 0.02 0.0125 0.0016 0.00319 0.00040 0.4 0.8 0.8 (11 marks)

Explanation / Answer

Q.4 (a) If the reaction is highly exothermic in a packed bed reactor, then it will lead to the decrease in the conversion inside the reactor.

(b) To mitigate the problem of the decrease in conversion, we need to proceed in this way-

First carry out the reaction at a higher temperature because higher temperature leads to increase in the specific reaction rate which ultimately increase the rate of reaction. But then soon decrease the temperature as the reaction proceeds to keep the conversion high inside the reactor.

Or we can use interstage cooling inside the reactor to avoid the temperature rising too much high by the removal of heat evolved out due to exothermic reaction.

(C) The other reactor more suitable for this reaction ( where temperature control is very sensitive) is a fluidized bed multistage reactor because of the concentration gradient because in fixed bed we are using only one concentration through out that's why optimal utilisation of concentration is not there but here we have optimally utilised the concentration using points at each and every cross-section.

We can also use multistage reactor by maintaing high temperature in first reactor and progressively decreasing the temperature in the following reactors .

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