Synergetic effect and primary reaction network of corn cob and cattle manure in single and mixed hydrothermal liquefaction

Abstract

Agricultural waste is a good choice to produce biofuels because of its abundance and environmental friendliness. In this work, corn cob and cattle manure were studied by hydrothermal liquefaction (HTL) in a batch reactor with reaction temperatures from 300 °C to 360 °C alone and in mixtures. HTL products, including bio-oil, aqueous phase, and gas were comparatively analyzed. The maximum bio-oil yields were 22.2% at 300 °C for corn cob and 19.3 % at 360 °C for cattle manure, respectively. Besides, the bio-oil from cattle manure had lower oxygen, higher H/C ratios, and higher HHVs than that from corn cob. N-Heterocycles could be taken as the characteristic compounds of bio-oils from cattle manure, yet organic acids and aldehydes were only detected from corn cob. Although benzenediols and N-heterocycles were major products in water-soluble organic matter (WSOM) for both two feedstocks, the pH values of aqueous phase products are acidic for corn cob and alkali for cattle manure, respectively. This is attributed to the generation of some ammonia from the decomposition of protein in cattle manure pyrolysis. The synergistic effect in mixtures could promote the decomposition of lignin by generating more phenols and benzenediols that improved the quality of bio-oil and increased the yields of WSOM. It could also affect the product of protein decomposition and transfer more N into the aqueous phase. The major component in the gaseous product was all CO2. These results indicate that different compositions could not only react with each other but also change the pH values of the reaction environment and further affect the reaction pathways of other compositions. A predicted primary reaction network of different components from corncob and cattle manure in the HTL was also proposed.