Thermal treatment of lignin, cellulose and hemicellulose in nitrogen and carbon dioxide

• Published in: Fuel (Guildford) 2020-07, Vol.271, p.117656, Article 117656
• Main Authors: Senneca, O., Cerciello, F., Russo, C., Wütscher, A., Muhler, M., Apicella, B.
• Format: Article
• Language: English
• Subjects: Acetone; Biomass fast pyrolysis; Carbon dioxide; Cellulose; Char; Chemical treatment; Chromatography; Depolymerization; Gas chromatography; Graphitization; Heat treatment; Hemicellulose; High temperature; Levoglucosan; Lignin; Mass spectrometry; Mass spectroscopy; Oxygenation; Primary products; Pyrolysis; Pyrolysis products; Raman spectroscopy; Scanning electron microscopy; Size exclusion chromatography; Soot; Strip; Tar; Thermogravimetric analysis; Vanillin; Volatile compounds; Volatiles; Volatilization; Xylan
• ISSN: 0016-2361; 1873-7153
• DOI: 10.1016/j.fuel.2020.117656

[Display omitted] •Analysis of primary products of fast pyrolysis of Lignin, Cellulose and Hemicellulose.•Tar always contains primary depolymerization products (Levoglucosan or Vanillin).•Temperature favors formation of Heavy tar and graphitization of the char.•Cellulose does not produce char. Hemicellulose produces an atypical solid residue.•CO2 limits the formation of very heavy tar compounds and graphitization of char. The paper explores the primary products from fast pyrolysis of biomass components: Lignin, Cellulose and Hemicellulose (Xylan). A heated strip reactor is employed at temperatures of 1573 K and 2073 K with N2 and CO2 atmospheres. Volatiles quench immediately after volatilization on a cold pyrex bridge, while char remains on the heated strip for 3 s. Tar, soot and char are collected and subject to chemical treatments and analyses, including gas chromatography-mass spectrometry and Size Exclusion Chromatography, Thermogravimetric analysis, Raman spectroscopy and Scanning Electron Microscopy. Fast pyrolysis of Lignin produces “Light tar” (soluble in acetone) and “Heavy tar” (soluble in NMP), char, a minor fraction of soot. The “Light tar” contains Vanillin, which can be considered the main primary depolymerization product, but also aliphatics and PAHs. Higher temperature enhances “Heavy tar” and graphitization of the char. Cellulose at 1573 K produces only “Light tar”, largely made of Levoglucosan, as the result of depolymerization. At higher temperature the tar becomes heavier. Hemicellulose has a peculiar behavior: it produces a “Light tar” which is chemically similar to that of Cellulose and, at high temperature also “Heavy tar”. Hemicellulose pyrolysis results also in the production of an atypical solid residue: swollen ad spongy at lower temperature, bright and glassy at higher temperature. CO2 affects the pyrolysis products, particularly those of Lignin, promoting tar cracking and oxygenation already at the stage of primary pyrolysis and hindering thermal annealing and structural ordering of the solid carbonaceous structure.