Production of biodiesel and hydrogen from plant oil catalyzed by magnetic carbon-supported nickel and sodium silicate

Abstract

A novel magnetic carbon-based nickel and sodium silicate catalyst (Na₂SiO₃@Ni/C) was prepared by the precipitation of Ni(OH)₂ on bamboo powders, pyrolysis and the loading of Na₂SiO₃, and was used in the co-production of biodiesel and hydrogen. The catalyst had strong magnetism (magnetic saturation, Ms of 15.7 Am² kg⁻¹) from the Ni and basicity (3.18 mmol g⁻¹) from the Na₂SiO₃ for magnetic separation and biodiesel production. In the presence of Na₂SiO₃@Ni/C, a biodiesel yield of 98.1% was achieved from soybean oil under the best conditions (9/1 methanol/oil molar ratio, 7 wt% catalyst, 65 °C for 100 min), optimized by single-factor experiments. The catalyst was cycled 4 times with biodiesel yields >93%, but the yield dropped to 80.9% with a 85.3% catalyst recovery rate in the fifth cycle. The deactivated catalyst, after 5 cycles, catalyzed the hydrothermal gasification of a biodiesel by-product (crude glycerol) at 350 °C for 5 min with a gasification rate of 80.1% and 82.7% H₂ purity. The role of Ni is to catalyze the H₂ production while the role of Na₂SiO₃ is to absorb CO₂ to achieve high H₂ concentrations. After gasification, the structure of the Ni/C changed slightly and can still be cycled to load Na₂SiO₃ for biodiesel production and subsequent gasification.