The elucidation of reaction kinetics for hydrothermal liquefaction of model macromolecules

Abstract

Conversion of waste to energy via the hydrothermal liquefaction (HTL) of biomass in hot compressed water is an emerging technology. In order to efficiently design and optimise industrial scale HTL processes, it is necessary to be able to predict the quantity and composition of the products. Various biomass feedstocks are being considered as feedstock for the HTL process and they are composed of different combinations of carbohydrate, lignin, lipid, protein and inorganic compounds, which react very differently under HTL to form distinctive products. The yields of the products from HTL, including renewable crude oil, gaseous, solid and aqueous phases, have been quantified via multivariate experiments in this work for four model compounds: cellulose, alkaline lignin, sunflower oil and bovine serum albumin (BSA). Simulated distillation via thermogravimetric analysis (TGA) has been used to find the hydrocarbon fractions of the renewable crude products. A bulk kinetic reaction model has been established for each of the four model compounds in order to develop a general model which can predict the HTL products of various feedstocks. For temperatures of 250, 300 and 350 °C and residence times from 0 to 60 min in a HTL batch reactor, higher reaction temperatures and longer reaction times generally resulted in lower renewable crude yields containing higher proportions of the more preferable diesel-like petroleum fractions.