Investigation of in situ and ex situ catalytic pyrolysis of lignocellulosic biomass waste for the production of de-oxygenated C8-C18 range enhanced liquid fuel precursor - reaction mechanisms and optimization

Abstract

Pyrolysis oil derived from lignocellulosic biomass waste is considered a viable alternative to fossil fuels. Nonetheless, organic acids and other oxygenated components render it unsuitable for direct fuel uses. A feasible option for utilizing pyrolysis oil is to process it with refinery feedstock, leveraging existing infrastructure. The adaptability of pyrolysis oil for co-processing can be enhanced by decreasing the acidity, generating the oil within a C₈-C₁₈ carbon range, and reducing high concentrations of phenols and aromatics. Catalytic pyrolysis represents a viable method for producing high-quality biooil. Currently, the catalysts are expensive, and their recovery poses a significant concern, incurring additional costs. The study uses various metal-impregnated eggshell catalysts to examine lignocellulosic biomass waste pyrolysis under in situ and ex situ configurations. The study indicates that both catalytic methods yield pyrolysis oil within the C₈-C₁₈ carbon number range, with diminished organic acid levels and lower concentrations of aromatics and phenols. The GC-MS NMR, and GC analysis of pyrolysis products suggested that ex situ catalysis exhibited improved selectivity for C₈-C₁₈ products, increasing from 48.12 % to 98.56 %. A substantial decrease in oxygenated compounds was observed, declining from 93.1 % to 72.3 %. The acid content of pyrolysis oil decreased from 37.1 % to negligible levels. Among the various metal-impregnated catalysts tested, CaO-Cu and CaO-Fe impregnated catalysts showed a significant improvement in the quality of pyrolysis oil. The study on the reaction mechanisms indicates that the presence of the catalyst substantially modifies the pyrolysis mechanism, validating the alterations in the product distribution. The study demonstrates the preparation of an economically viable metal-impregnated catalyst that efficiently produces deoxygenated, acid-free pyrolysis oil from biomass. The catalyst recoverability and reusability in the ex situ catalytic pyrolysis process enhance the sustainability and cost effectiveness.