CHAPTER 2 MANUFACTURING PROCESS
2.1 Manufacturing Processes:Literature indicates numerous methods of synthesis of Divinylbenzene (DVB).The methods are as follows:1. Reaction of methyl magnesium bromide with phthaladehyde, followed by dehydration. 2. Another long synthesis utilizes reaction between benzyl chloride, paraformaldehyde and zinc chloride. 3. It is synthesized s ynthesized using pyrolysis pyrolysis of diisopropylbenzene in the presence of hydrogen or steam. 4. By far most commonly used and commercially preferred method of DVB preparation is catalytic dehydrogenation of Diethylbenzene Diethylbenzene (DEB).
2.2 Comparison between Processes:Although only of DVB preparation by catalytic dehydrogenation dehydrogenation of Diethylbenzene (DEB) is commercially used because:1. Overall conversion of all the methods except “4” has conversion of less than 60% and product purity is as low as 26 %. 2. In pyrolysis process temperature is above 700 °C which damages zeolite catalyst used and also expensive as costlier MOC is required to survive the required process conditions. 3. .In DVB preparation preparation by catalytic dehydrogenation of of Diethylbenzene (DEB),conversion is about 79-80% and product purity attainable is 90% and also catalyst used is iron-oxide based which is cheaper than zeolite and also MOC of reactor is Carbon steel as process conditions are less severe so the process is overall cheaper and productive.
2.3 Selected Process:By comparison with various methods and by commercial survey, I have selected, DVB PREPARATION BY CATALYTIC DEHYDROGENATION OF DEB.
2.4 Introduction to selected process:First high purity iron oxide based EB plant, based on technology developed by UOP & ABB Lummus Global started up in 1990. Technology Supplier: UOP & ABB Lummus Global Raw Material: Diethylbenzene Product quality achievable: 90 wt% pure DVB can be produced, but the project discusses preparation of DVB grade 55,so the product contains 55 wt% DVB.
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Catalyst: FeO Material of construction: Carbon Steel Process Effluents: Inert component of polyethylbenzene feed such as ethylene, benzene, ethylbenzene which will appear as distillation column vent.
2.5 Process Chemistry:1.Raw material for DVB is DEB which is usually obtained by Friedel-Craft alkylation of benzene producing diethylbenzenes, collectively termed pol yethylene benzene (PEB) Benzene + Ethylene → EB (Ethylbenzene) EB + Ethylene →DEB (Diethylbenzene) (Die thylbenzene) 2.DVB is produced from catalytic dehydrogenation dehydrogenation of DEB resulting in mixtures of DVB & Figure 1 Ethylvinylbenzene Ethylvinylbenzene (EVB) isomers.
2.6 Process Description:The dehydrogenation reaction for the preparation of divinylbenzene from diethylbenzene can be carried out by bringing diethylbenzene together with steam into contact with a dehydrogenation dehydrogenation catalyst, for example, iron oxide containing catalyst, in the vapour phase. The process of this invention is effective when the dehydrogenation reaction is carried out at a conversion of 70% or more, preferably 80% to 90%, and particularly so when the selectivity of divinylbenzene in the dehydrogenation reaction is 40% by weight or more. The other conditions for the dehydrogenation dehydrogenation reaction may be in the ranges in the t he public knowledge. It is desirable to conduct the reaction under the conditions where the temperature is 600.degree. to 700.degree. C., the steam/diethylbenzene ratio (by weight) is 5 to 8, and the pressure is normal or reduced. As the dehydrogenation reaction of diethylbenzene is carried out at 600.degree. 600.degree. to 700.degree. 700.degree. C., the reaction product flowing out of the reactor is gaseous gaseous and the reaction product gas is condensed, separated into oil and water, and recovered as dehydrogenation oil.
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A condenser to be used for the condensation of the reaction product gas is not specified. It can be of any shape and a known heat exchanger may be used as condenser. According to a knowledge gained by the present i nventors, the polymerization is observed to take place extensively at places where gas changes changes into liquid and it is most important to prevent the polymerization at these places, it is prevented by maintaining appropriate steam to divinylbenzene ratio (weight basis) around 2.4.This prevents addition of polymerisation inhibitors such as Cu 2Cl2 initially, so easy separation and high purity product is obtained. Process Flow diagram (PFD):-
Figure 2
1. The process is best described by the flow diagram. A polyethylbenzene (PEB) feed (F1) is passed through the flash drum at 50 °C to remove volatile ethylene present in the feed, all of ethane is removed from top of flash drum via stream F2. 2.Stream F3 containing benzene,ethylbenzene,die benzene,ethylbenzene,diethylbenzene thylbenzene (DEB) is then passed through distillation column D-1 at around 80 °C and 1atm to remove benzene and ethylbenzene via stream F4,thus stream F5 contains only Diethylbenzene which is reactant t o the process. 3. Diethylbenzene enters reactor which is basically a dehydrogenator via stream F5,Reactor temperature is maintained at 600 °C and and pressure 1 atm, & the vapour reaction process process is isothermal. Along with the reactant superheated steam at 350 °C in steam to DEB ratio of 2.4 (% weight basis) is added at inlet. 4. The product obtained contains mixture of DVB & EVB at conversion level of 80% and along with it hydrogen, steam & unconverted DEB.All the product obtained in stream F7 is in vapour state and is required to be condensed. 5.Stream F7 is then passed through a condenser that separates mainly hydrogen & water vapour, and remaining mixture in liquid state is obtained from condenser is denoted by stream F8. 10
6. Stream F8 is then passed through vacuum distillation column at 1mmHg and 50 °C to separate a part of EVB and required grade DVB-55 is obtained as bottom product, when then sent to Storage. Plant capacity taken here is 1350 tons/year. According to:
Current demand and supply data for DVB
As well as other capacities of other Ethyl benzene operating plants
These points are discussed in chapter 1 topics 1.5 & 1.6.
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