Comparative Study of the Economic Analysis and Energy Requirements of a Non-Phosgene Process for Manufacture of Isocyanates with That of the Traditional Phosgenation Route

Isocyanates are commonly used as monomers to make polymers, such as polyurethanes which find significant application in the manufacture of rigid and flexible foams. Polyurethanes are also used in the production of adhesives, elastomers, and coatings. Isocyanates are currently manufactured by the phosgenation route which involves reacting an amine with phosgene. This process requires handling of hazardous chemicals and is also environmentally malignant due to issues related to disposal of the hydrochloric acid, formed as a byproduct.

McGhee et al have previously worked on a route to manufacture isocyanates from primary amine, carbon dioxide, a nitrogenous base and an electrophilic dehydrating agent. We modified this route by eliminating the use of the nitrogenous base and hence reducing the salt formed. Also by maintaining either moderately high pressure of carbon dioxide or extremely low temperatures it is possible to maintain huge excess of carbon dioxide in the reaction mixture. In excess of carbon dioxide, the zwitterion intermediate of the primary amine is formed which on reaction with a dehydrating agent forms isocyanate without any salt as byproduct. We have studied the effect of different solvents, dehydrating agents and varying temperature and pressures on the overall yield of isocyanate with the aim of maximizing the isocyanate content. The energy requirements of the process at different operating conditions for the non-phosgene route are compared with the traditional phosgenation route by simulating a plant for isocyanate manufacture using ASPEN. The economic analysis for project financing and operating cost for the two routes is presented using ASPEN – Icarus Process Evaluator.

McGhee, W.D., Paster M.D., Riley D.P., Ruettimann K.W., Solodar J.A, Waldman T.E, U.S. Patent # 5,451,697, 1995