Analytical pyrolysis of biomass using pyrolysis-gas chromatography/mass spectrometry

Analytical pyrolysis is currently showing tremendous potential for investigating biomass conversion into chemicals and biofuels, of which the most notable is the pyrolyzer coupled with the gas chromatography/mass spectrometry (Py-GC/MS) technique. This review aimed to summarize the different approaches (i.e., conventional pyrolysis, stepwise pyrolysis, and catalytic pyrolysis) conducted using Py-GC/MS, as well as the composition and distribution of resulting products. The basic plausible pyrolysis mechanisms were first summarized based on the analytic pyrolysis of typical chemical components, i.e., cellulose, hemicellulose, lignin, protein, and lipid. As for the conventional pyrolysis proceeded by using Py-GC/MS, the influence of biomass types and operation parameters was discussed, which indicated that biomass types and final temperature played a dominant role in regulating the composition and distribution of products. Subsequently, the product release behaviors at different stages were revealed and discussed via Py-GC/MS experiments using stepwise pyrolysis. The primary objectives of different stepwise pyrolysis approaches (torrefaction and pyrolysis, two-step pyrolysis, and multi-step pyrolysis) were to produce value-added chemicals or increase bio-oil quality. Furthermore, the catalytic effects of various catalysts, including soluble inorganic salts, metal oxides, microporous zeolites, and mesoporous zeolite, were also summarized and compared to elucidate the role of catalysts in catalytic pyrolysis for targeted product production. Based on the above, the potential practical implications and current limitations that exist in the application of analytical pyrolysis were also proposed, with the aim of improving the effectiveness of Py-GC/MS in future applications.