Comparison of coal-to-ethanol product separation strategies

Given China's energy structure and the limitations of bioethanol, the coal-to-ethanol (CTE) pathway, from dimethyl ether to ethanol (DMTE) via carbonylation and hydrogenation, is highly anticipated. Ethanol, methanol, methyl acetate, and ethyl acetate are the crude hydrogenation products that need to be purified, requiring at least an eight-column scheme. However, the optimization of the existing separation strategy with ethanol as the priority is unfavorable in the following aspects: it is usually plagued by tedious rules of thumb and, due to the large scale of the process, is prone to falling into local minima; pre-designed heat integration inevitably neglects the interaction of parameter optimization and heat integration; reports on alternative feasible distillation sequences are scarce in publications, let alone comparisons amongst these counterparts. Therefore, four viable separation strategies are proposed in this paper to compare with this faulted separation strategy. A self-adapting dynamic differential evolution (SADDE) algorithm, which is accelerated by parallel computation, is used to search for optimal column parameters of all the configuration options and facilitates simultaneous heat integration structure synthesis. Two strategies stand out after 3000 generations of evolution. Splitting methanol outperforms in specific steam consumption (SSC) of ethanol (1.8177), much better than the benchmark (2.4840), and splitting ethyl acetate with ethyl acetate priority has the most competitive total annual cost (TAC), 23.98% lower than the benchmark. In summary, this paper provides a reference for optimizing complex distillation systems like CTE product separation, or more specifically, the DMTE route, before the appearance of the most suitable separation strategy in demand. Furthermore, it will also serve for the CTE superstructure to further explore the optimal distillation sequence.