Study of alternative configurations for methanol purification

Methanol is a relevant clean fuel and is considered an important chemical feedstock. Its production is usually obtained by catalytic conversion also starting from removed carbon dioxide and could significantly contribute to the reduction of direct CO2 emissions to the atmosphere. Despite a number of technologies for its synthesis have been developed, post-production treatment is fundamental for obtaining a high purity methanol stream and is generally carried out by distillation, with relevant energy consumption. The raw product exiting from the methanol production section is mainly composed of methanol and water, with traces of other components and is fed to the purification section. This one is composed of two separation units. The first unit aims at removing the low boiling impurities which exit from the top and the second one, the most energy demanding, treats the heavier stabilized methanol-rich stream to increase its concentration in methanol for obtaining a product with high-purity. This work focuses on the optimization of the process, with the study of possible modifications for obtaining energy saving and the selection of the best one on the basis of a techno-economic analysis. Simulations have been carried out by using the commercial software ASPEN Plus®. The thermodynamic method based on the Non-Random-Two-Liquid (NRTL) model, suitable for this system and for the low pressure conditions, has been employed and a rate-based approach has been considered for simulating the columns. The alternative configurations favour a reduction of the relevance of the methanol purification section on the total costs of the production plant.