25.3.4 Technical questions
1. Why is the chloral hydrate converter is fed with steam and water alternatively ?
Ans: The chloral hydrate conversion to chloral takes good amount of time and switch type heating and cooling is required. Heating only with steam will enable faster decomposition of chloral which is very reactive and unstable. Therefore, the switch type heating is enabled in this case.
2. Why is air is circulated in the DDT condensation unit ?
Ans: In the DDT condensation unit, two liquids need to be thoroughly mixed. For this purpose, air is sparged so that interfacial area of the reactants enhances drastically due to the sparging effect.
3. DDT is a solid but the organic layer from the DDT condensation unit does not have any solid. Why ?
Ans: DDT is soluble in most organic solvents but not in water. Therefore, upon drying, the liquid mass consisting of dissolved DDT in monochlorobenzene gets generated as a solid product.
4. Why are vapors released from the still despite knowing the fact that no HCl is produced from the still ?
Ans: Due to the high temperature of the still, it is possible that some chloral hydrate decomposes to unwanted compounds such as HCl, chloroform and ethanol. These compounds will be non-condensible at the condenser operating temperatures and therefore, these are vented out.
5. Discuss what technology you would adopt to recover the H2SO4 from the spent solutions ?
Ans: The sulphuric acid stream from the units will have higher concentrations of organics. Therefore, technology should be targeted that enables the recovery of these organics. Multiple effect evaporator appears to be suitable in this regard to concentrate the sulphuric acid as well as eliminate the organic impurities. The regenerated sulphuric acid with its regained original strength can be reused for the DDT condensation and chloral hydrate conversion operations.
References:
1. Dryden C. E., Outlines of Chemical Technology, East-West Press, 2008
2. Kirk R. E., Othmer D. F., Encyclopedia of Chemical Technology, John Wiley and Sons, 1999-2012