Lignin is one of the major components of lignocellulosic biomass. It is considered a low-cost natural resource with potential industrial use, from which biofuels and high value-added products can be obtained.
IMDEA Energy has investigated and published* the thermochemical valorization by means of thermal and catalytic fast pyrolysis of a high lignin content residue from a steam explosion pretreatment and enzymatic hydrolysis. Firstly, a study of the effect that temperature has on the different fractions obtained from pyrolysis (solid or biochar fraction, liquid or bio-oil fraction and gas fraction) has been carried out, with the aim of maximizing bio-oil production, being 600ºC the optimum temperature. The next objective was to improve the characteristics of the bio-oil, for which a nanocrystalline catalyst ZSM-5 modified with ZrO2 and agglomerated with attapulgite (ZrO2/n-ZSM-5/ATP) was used, obtaining an improved bio-oil with lesser oxygen amount. A study on the catalyst / lignin ratio was also carried out, and it was observed that this parameter strongly affected the mass and energy yields of the different fractions. A significant decrease in bio-oil yield was also observed, in exchange for an improved composition, with a reduction in oxygen content from 30 to 10% by weight. When comparing the ZSM-5 zeolite with the technical catalyst, the latter provided a bio-oil production with lower oxygen content and a higher proportion of aromatic compounds. Additionally, the ZrO2/n-ZSM-5-ATP technical catalyst increased the conversion of heavy molecules and, thus, the concentration in bio-oil of the compounds most valuable as chemical products. Among the molecules formed, phenolic derivatives stand out, key in the production of bisphenol-A (BPA), resins, polycarbonates, fuel additives or reagents in fine chemicals, among others. Interestingly, these remarkable results are obtained despite working under mild catalytic conditions (450 ºC, catalyst / lignin ratio = 0.2 g / g).
(*) A. Lago, H. Hernando, J.M. Moreno, D.P. Serrano, J. Fermoso, Valorisation of a lignin-rich residue via catalytic pyrolysis over ZrO2/ZSM-5 technical catalyst, Fuel Process. Technol. 215 (2021). https://doi.org/10.1016/j.fuproc.2021.106746
More information: Adrián Lago, Predoctoral Researcher of the Thermochemical Processes Unit, firstname.lastname@example.org
Technical catalyst (ZrO2/n-ZSM-5-ATP) allows increasing the concentration of the most valuable compounds for commercial applications (e.g. oxygenated aromatics) by a factor of 2.5 regarding the thermal test and under mild catalytic conditions (450ºC, catalyst/lignin = 0.2 g/g)