HANOI UNIVERSITY OF MINING AND GEOLOGY
ADVANCED PROGRAM IN CHEMICAL ENGINEERING
ADECH04- MID 1
Duong Van Dai K4- 10/2017
Problem 1 : Suggest a block diagram for a balanced chlorination – oxychlorination vinyl chloride plant. Do you have comment if both oxychlorination and pyrolysis EDC occur in the same reactor and vinyl chloride is obtained in one stage ?
Solution
Block diagram for balanced chlorination – oxychlorination vinyl chloride plant :
O2
Oxychlorination HCl recycle
C2H4 EDC purification EDC pyrolysis VC purification C2H3Cl
Direct chlorination
Cl2
EDC mode
The process chosen for vinyl chloride production is a combination of 2 process direct chlorination and oxychlorination. This process is referred to as the balanced process. Direct chlorination itself is a process that operate at lower temperature and produces fewer by – products when compared with oxychlorination. Oxychlorination is used in vinyl chloride production because it consumes the HCl. Currently, ≈ 95% of the world’s supply is produced using the balanced process.
The main reactions in this process are :
Direct chlorination : 𝐶
𝐻
2
𝐶
𝐻
2 + 𝐶
𝑙
2→ 𝐶𝑙𝐶
𝐻
2
𝐶
𝐻
2
𝐶𝑙
Oxychlorination : 𝐶
𝐻
2
𝐶
𝐻
2+2𝐻𝐶𝑙
1
2
𝑂
2→𝐶𝑙𝐶
𝐻
2
𝐶
𝐻
2
𝐶𝑙
𝐻
2
𝑂
EDC pyrolysis : 2𝐶𝑙𝐶
𝐻
2
𝐶
𝐻
2
𝐶𝑙→2𝐶
𝐻
2
𝐶𝐻𝐶𝑙+2𝐻𝐶𝑙
Overall reaction : 2𝐶
𝐻
2
𝐶
𝐻
2+𝐶
𝑙
2
1
2
𝑂
2→2𝐶
𝐻
2
𝐶𝐻𝐶𝑙
𝐻
2
𝑂
The oxychlorination and pyrolysis EDC should not occur in the same reactor. Because oxychlorination is better performed in PFR or CSTR reactor with good temperature control. And it is exothermic reaction while pyrolysis EDC is endothermic reaction. Pyrolysis EDC is performed in PFR reactor so they should be performed in the different reactor.
Problem 2 :
In direct hydration of ethylene to produce ethanol, the conversion of ethylene is very small. Base on thermodynamic characteristic of the reaction ( the lecture, chp2 ) , do you have suggest in order to increase the conversion.
Calculate the raw material costs for ethanol manufacture by (i) indirect hydration of ethylene and (ii) direct hydration of ethylene, assuming yield of 90% in indirect hydration and 95% in direct hydration and an ethylene cost of 512USD/ton. Comment on your result.
Solution
Ethanol is manufactured by the direct catalytic hydration of ethene. The reaction is reversible and exothermic :

𝐶
2
𝐻
4
𝑔
𝐻
2
𝑂
𝑔
𝐶
2
𝐻
5
𝑂𝐻
𝑔

ΔH = -45 kJ/mol
In order to increase the conversion, the conditions are low temperature, high pressure and high steam concentration. A temperature 500K is used in the presence of the catalyst. Increasing the pressure pushes the reaction to the product side. High pressure also increases capital and operating costs. The process is generally under pressure of 60-70 atm. High ethene conversion can be obtained using an excess of water ( stream). A mole ratio of water : ethene around 0.6-1 is commonly used. Unreacted ethene is separated from the liquid products and recycle
It is possible to raise overall 95% conversion.
The formation of ethanol exothermic. Only 4% of ethylene is converted into ethanol at each pass.By reforming the ethanol from the equilibrium mixture and recycling the ethylene. It is possible to raise overall 95% conversion.



Cool
Gas

Liquid
Ethanol
Ratio of ethene to steam
Equation ratio is .Steam is cheap but we cannot use excess steam because catalyst is phosphoric acid coated on solid silicon support, more steam will dilute catalyst.
Temperature : reaction is exothermic , we should lower temperature to 300 C to get higher conversion.
Rate : low temperature gives low rate, we may use gas phase to get higher rate.
Pressure : there are 2 mol on LHS, 1mol on RHS. If we increase pressure, equilibrium shift to right . That is what we prefer. But we should not use very high pressure to avoid ethene polymerization and waste of energy to increase very high pressure.
Catalyst : use to get high rate.


Problem 3 :
Interpretation of flow diagram of isoprene manufacture.
Solution
Block 1: Dimerization –separation – recycle
Propylene and propylene recycle is pumped into the propylene purification tower and propane is obtained from the bottom, the light products with C1, C2 from the top.
The mixture is mixed with aluminum tripropyl , then compress to 150-200°C then goes to the dimerization reactor in liquid phase.
The dimenization reactor is CSTR with cooling jacket to remove heat from exothermic reaction.
After the reaction occurs, the liquid stream is subjected to flash