Elemental nitrogen balance, reaction kinetics and the effect of ethanol on the hydrothermal liquefaction of soy protein

Abstract

Hydrothermal liquefaction (HTL) is a thermochemical method to convert wet biomass and bio-waste into renewable crude and other valuable products. During HTL, water near critical point acts as a reaction medium and as a catalyst, breaking and hydrolysing bio-macromolecules into smaller compounds which interact and re-condense into different components and phases. Proteins as one of the key components in biomass plays a crucial role in the HTL process and products. Proteins are the source of nitrogen content in the HTL renewable crude, which generates environmental problems because of potential NOx emissions from combustion. Proteins also increases the pH of the aqueous phase, as over 60% of contained nitrogen is recovered in the aqueous phase as ammonia, nitrate, and soluble organic nitrogen compounds. However, the nitrogen reaction mechanism and equilibrium under HTL conditions have not been fully understood. In this study, the reaction kinetics for the product phases and nitrogen migration/transformation are elucidated by examining the yields and composition of the renewable crude and aqueous phases of HTL experiments run with a model compound soy protein, in a batch reactor at 250, 300 and 350 °C with 15% by mass feedstock. Furthermore, a co-solvent/homogeneous catalyst system has been included as a fully renewable solution to enhance the renewable crude yield, energy recovery, nitrogen content, and clarify the reaction mechanism and kinetic effects.