Intensification of Biomass Thermal Deoxygenation via a Two-Stage Process

Abstract

Thermal deoxygenation (TDO) is a promising reaction scheme for producing low oxygen bio-oil from biomass carbohydrate. The primary step in bio-oil production involves pyrolysis of alkaline earth metal-neutralized biomass hydrolysates at 723 K yielding bio-oil, chars, carbonates, and light gases. Reactor scaling from bench to floor-scale, however, reduced carbon yields from 80% to 48% of theoretical, respectively. This paper details a two-stage process to intensify the TDO process, improving carbon yields to 79% of theoretical. The scheme involves a 523 K thermal pretreatment (stage I) to yield a polysalt and transition of a melt-phase. The resulting solid polysalt is reduced to powder to improve material handling and reaction rates during decomposition at 723 K (stage II). Resulting bio-oil yield is shown to improve from 0.082 to 0.16 kg-oil/kg-feed. A two-step reaction model is developed detailing the reaction rates and regimes which can guide continuous process design efforts.