Chemical and Biochemical Engineering

Biography

Biography: Jian Yu

Abstract

Carbon dioxide (CO₂) is a prime green-house gas emission from industrial processes. It can be converted into bio-oil by microalgae via conventional photosynthesis. The CO₂ fixation rate, however, is quite low and affected by the intermittent solar radiation. Cupriavidus necator, a hydrogen-oxidizing bacterium, was grown on CO₂ and H₂ in dark gas fermentation to produce single cell proteins and Polyhydroxybutyrate (PHB). Sunlight is captured by photovoltaic modules and immediately converted to H₂ as a stable energy source via water electrolysis. The clean H₂ and O₂ are used by C. necator in CO₂ assimilation. Under the chemolithotrophic conditions, the average CO₂ uptake rate was 1.2 kg m^-3 h^-1. The molar ratios of H₂/CO₂ was 7.3 and the biomass/H₂ yield was 1.4 g g^-1. The overall energy efficiency from H₂ to biomass was 22.4%. Under nutrient control, the PHB content of dry cell mass was 65 wt%. The polymer productivity was 1.87 g L^-1 d^-1, 14 times higher than oil productivity by a typical bio-oil-producing microalga. PHB is a biodegradable thermoplastic that can find various environmentally friendly applications. The biopolyester can also be converted into small functional chemicals (C3-C4). Specifically, PHB was degraded and deoxygenated on a solid phosphoric acid catalyst, generating a hydrocarbon oil (C6-C18) from which a gasoline-grade fuel (77 wt% oil) and a biodiesel-grade fuel (23 wt% oil) were obtained via distillation. Aromatics and alkenes were the major compounds, depending on the reaction conditions. This work demonstrated a bioprocess through which bioplastics and high-grade liquid fuels can be directly produced from carbon dioxide. The novel bioprocess can be continuously operated regardless the intermittency of renewable powers.