Separation of n-heptane/isobutanol via eco-efficient vapor recompression-assisted distillation: process optimization and control strategy

In this study, vapor recompression and heat integration assisted distillation arrangements with either the low or high pressure in the reflux drum are proposed to reduce and/or eliminate the application of the costly refrigerant for the separation of n-heptane and isobutanol mixture. The high-pressure arrangement with vapor recompression and heat integration is the most attractive among these four intensified configurations since it can reduce total annual cost by 18.10%, CO2 emissions by75.01% based on natural gas（78.78% based on heavy oil fuel）, and second-law efficiency by 61.20% compared to a conventional refrigerated distillation system. Furthermore,exergy destruction in each component is calculated for the heat integration configurations and is shown in pie diagrams. The results demonstrate that the high-pressure configuration presents unique advantages in terms of thermodynamic efficiency compared to the low-pressure case. In addition, dynamic control investigation is performed for the economically efficient arrangement and good product compositions are well controlled through a dual-point temperature control strategy with almost negligible product offsets and quick process responses when addressing 20% step changes in production rate and feed composition. Note that there are no composition measurement loops in our developed control schemes.