Energy-efficient and sustainable methanol distillation: Exploring diluted alcohol strategies, multi-effect heat integration, and heat pump-based electrification for carbon reduction

Abstract

Industrial methanol distillation systems typically use a fusel oil side-draw to maintain product purity; however, fusel oil is a hazardous byproduct that poses significant safety risks. This study proposes an alternative strategy that processes diluted alcohol instead of fusel oil to mitigate safety concerns and meet regulatory requirements. Four configurations were evaluated, combining forward and backward multi-effect heat integration schemes with fusel oil side-draw and diluted alcohol strategies. A simultaneous optimization algorithm was employed to optimize process parameters and heat integration structures. The results show that the diluted alcohol strategy outperforms fusel oil side-draw configurations in terms of total annual cost and methanol recovery rates, demonstrating its economic and operational advantages. Furthermore, the optimized configurations achieved lower unit steam consumption than values reported in the literature, highlighting the energy efficiency of the proposed approach. To enhance decarbonization potential, heat pump-based electrification strategies were assessed, including mechanical vapor recompression (MVR), flash vapor circulation (FVC), and FVC combined with bottom flashing (FVC-BP). Despite their low coefficient of performance, these strategies offer significant carbon reduction potential, achieving up to 95.5 % emission reductions in countries with low grid carbon intensity, such as Norway, and 54.3 % in countries with high grid carbon intensity, such as China.