Raw Gas Treatment and Conditioning for Methanol Production from Biomass and Waste Gasification

Biomass and waste gasification offer a renewable pathway to methanol via syngas, yet the stringent impurity limits required by commercial methanol catalysts make syngas cleaning a critical step in the process. In this review, we first define the optimal syngas composition for economical methanol production based on literature data. It then establishes a systematic link between gasification conditions, raw gas (RG) composition, and downstream cleaning requirements. Unlike previous reviews that mainly focus on individual gas cleaning technologies, this work integrates impurity specifications required for methanol synthesis with gasification conditions, downstream cleaning strategies, and recent advances in gasification and cleaning process modeling. The influences of feedstock composition, gasifier type, and gasification medium on RG composition and impurity levels, including tars, particulates, sulfur species, halides, nitrogen compounds, and trace metals, are examined as factors determining the design and severity of downstream cleaning trains and necessary gas conversions. Key cleaning technologies, including high-temperature filtration, tar removal, desulfurization, and removal of halides and nitrogen species, are evaluated with emphasis on integrated systems. Emerging approaches such as novel catalysts and sorbents, as well as advanced strategies like molten-salt-based gasification or cleaning, are also reviewed. Recent advances in process modeling, including kinetic and equilibrium models, Aspen Plus simulations, and physics-informed machine learning, are highlighted for optimizing gasification-cleaning chains. Additionally, a decision-tree flowchart is proposed to guide the selection of appropriate gas-cleaning strategies for efficient methanol production. The review shows that integrated cleaning strategies tailored to gasifier type, combined with advanced modeling tools, have strong potential to reduce purification costs and improve the economic feasibility of methanol synthesis from biomass and waste.