Cleaner Process and Entrainer Screening for Bioethanol Dehydration by Heterogeneous Azeotropic Distillation

Abstract

Greenhouse gas footprint of fuels is due to both the burning fuel and its production process. Bioethanol is a sustainable biofuel but it is obtained diluted in water and its dehydration consumes large amounts of energy. Heterogeneous azeotropic distillation is a well-known suitable option for dehydration of bioethanol (separation of ethanol from water). Many entrainers for this process are studied in literature but unfortunately, there is no critical comparison in terms of the corresponding process efficiency. The distillation efficiency assessment is necessary as it has a great impact on the energy consumption and sustainability of bioethanol production. The process scheme and entrainer are screened following a fast-to-rigorous procedure: feasibility checking using the infinite/infinite analysis, screening based on the Distillation Sequence Efficiency (DSE) method and rigorous simulation using AspenPlus®. Different process schemes are assessed taking into account also that some gasoline additives, used as entrainers, could remain in bioethanol, which is to be included in the gasoline formulation. Some examples of commonly used ethers as gasoline additives are methyl tert-butyl ether (MTBE), ethyl tert-butyl ether (ETBE), diisopropyl ether (DIPE) and tert-amyl methyl ether (TAME). The study shows that when the entrainer is a gasoline additive, collecting the distillation product as a mixture of ethanol and additive consumes 27 % less energy than collecting pure ethanol. Performing the ethanol dehydration and gasoline additive mixing together in the same process leads to a 27 % decreasing of CO2 emissions.