Cost saving schemes for biomethanol purification

Biosynthesis gas (bio-syngas) is a gas rich in CO and H2 obtained by gasification of biomass, which can be used for the production of biomethanol, as substitute to the one produced from natural gas. Biomass sources are preferable for biomethanol than for bioethanol because bioethanol is a high-cost and low-yield product (Demirbas, 2008). Biomethanol can be used as a clean biofuel or as a chemical feedstock. Its production process includes a section of its purification downstream the conversion unit, which is is generally carried out by distillation, with relevant energy consumption that may significantly impact on the costs of the whole process. This work aims at studying different configurations for the methanol purification section, so to determine the best one which allows for a reduction of the energy consumptions and thus of the operating costs. The base scheme is composed of two main sections, one for removing the low boiling impurities present in the mixture mainly composed of methanol and water and the second one for separating water and other components so to increase the concentration of methanol to the required high purity. Simulations have been carried out by using the commercial software ASPEN Plus®, by using the thermodynamic method Non-Random-Two-Liquid (NRTL), suitable for this system and for the low pressure conditions, and by considering a rate-based approach for the simulation of the columns. On the basis of the obtained results, the scheme which favor a reduction of the operating costs of the plant has been determined.