Biogas to methanol: techno-economic assessment of an alternative process configuration

In today’s economy, methanol is a crucial compound extensively used as a building block for producing intermediates and synthetic hydrocarbons, solvents, energy storage media, and fuels. This status is expected to improve in the coming years, making the task of producing it in a sustainable way crucial in terms of green chemistry. Methanol is commonly produced through three main steps: preparation of syngas, methanol synthesis, and downstream separation. The aim of this thesis is to explore a different raw material that can be independent from hydrocarbons. The project focuses on a plant that utilizes biogas for methanol production. Biogas is fed to a heat and power plant, which uses pure oxygen as an oxidant and where the energy content of methane is recovered. Carbon dioxide becomes the carbon source for methanol synthesis. The reducing agent is molecular hydrogen. To achieve a completely sustainable process, the hydrogen, which is normally obtained from syngas, is produced by water electrolysis, utilizing the electricity produced by the power plant. Finally, the production of methanol follows the latest technologies in terms of reactors and recovery plants, allowing for energy savings and ensuring the most profitable configuration. This type of process reaches the objective of reducing carbon dioxide emissions, with a production of only 0.04 kgCO2/kgMeOH. This configuration is able to produce 20 kton/year with a feedstock of 2000 m3/h of biogas. The energy recovery system (CHP) produces a net power of 4780 kW, reaching an efficiency for the combined cycle equal to 42%. The electrolysis cell (AWE) instead has an efficiency of 71%, with a total consumption of power equal to 22.5 MW. The total electricity consumption of the plant is 18.9 MW, and that is the main reason for the unprofitable of the process. In conclusion, in fact, due to the high cost of utilities, the NPV after 15 years is -159 M€.