摘要
Hexamethylene-1,6-diisocyanate (HDI) is one of the most significant aliphatic diisocyanates for polyurethane production. The thermal decomposition of dimethylhexane-1,6-dicarbamate (HDC) has been considered as a very attractive non-phosgene route for HDI synthesis to realize industrialization because HDC can be synthesized by reacting 1,6-hexanediamine (HDA) with a green component, dimethyl carbonate (DMC). In this study, the optimal separation process design for non-phosgene HDC synthesis is investigated. Three design strategies to separate reaction products are proposed here. In the first two strategies, the low-boiling mixture containing un-reacted DMC and byproduct methanol is almost completely withdrawn from a column top, while some amount of un-reacted DMC is deliberately designed to be drawn out from the column bottom in the third strategy. Optimal processes designed by these three strategies are further enhanced by heat integration to reduce energy consumption. Simulation results reveal that the processes designed by strategy 3 need the least total annual cost and much economic benefit is achieved by the technologies of internal and external heat integrations. The key cost saving from internal heat integration is attributed to fully take advantage of the characteristic of DMC–methanol azeotrope at high pressure, and the higher column top temperature rendering condenser duty totally utilized by column bottom.