(234d) A Heat-Pump-Assisted Reactive Distillation Process for Methyl Lactate Hydrolysis

Reactive distillation (RD) is a prominent example of process intensification. From a thermodynamic perspective, continuous removal of product(s) from the reaction mixture allows the reaction equilibrium to shift in the forward direction, improving both the conversion and the selectivity of the process. From an economic perspective, combining reaction and separation in one physical equipment can significantly reduce both the capital investment and the operating expenses. However, because of the relatively low thermodynamic efficiency of conventional distillation superstructure, the conventional RD processes are still highly energy intensive. Many alternative designs have been reported in literature that can improve the overall process efficiency by reducing the thermodynamic losses in distillation columns.

In this study, we demonstrate the advantage of a heat-pump-assisted design over a conventional design for methyl lactate hydrolysis in an RD column. First, a rigorous simulation model is developed for the conventional RD column in Aspen Plus® and reference cost analysis is performed. Then, an alternative design based on mechanical vapor recompression (VRC) is developed and optimized for maximum energy savings. The optimized VRC system shows that the reboiler (that is, the hot utility) can be eliminated from the process. Overall, the VRC-based RD column offers 54–56% savings in direct operating/energy costs and, assuming a payback period of 3 years, 18–20% savings in the total annualized cost (TAC) relative to the conventional RD column.