HEAT-INTEGRATED ETHANOL DEHYDRATION FLOWSHEETS

A theoretical evaluation of heat-integrated heterogeneous-azeotropic e thanol-water distillation flowsheets is presented. Simulations of two column flowsheets using several different hydrocarbon entrainers revea l a region of potential heat integration and substantial reduction in operating energy. In this paper, methods for comparing hydrocarbon ent rainers are shown. Two aspects of entrainers are related to operating and capital costs. The binary azeotropic composition of the entrainer- ethanol mixture is related to the energy requirements of the flowsheet . A temperature difference in the azeotropic column is related to the size of the column and overall process staging requirements. Although the hydrophobicity of an entrainer is essential for specification of s taging in the dehydration column, no substantial increase in operating energy results from an entrainer that has a higher water content. Lik ewise, liquid-liquid equilibria between several entrainer-ethanol-wate r mixtures have no substantial effect on either staging or operation. Rather, increasing the alcohol content of the entrainer-ethanol azeotr ope limits its recovery in the dehydration column, and increases the r ecycle and reflux streams. These effects both contribute to increasing the separation energy requirements and reducing the region of potenti al heat integration. A cost comparison with a multieffect extractive d istillation flowsheet reveals that the costs are comparable; however, the extractive distillation flowsheet is more cost effective as operat ing costs increase.