Highly stable gasified straw slag as a novel solid base catalyst for the effective synthesis of biodiesel: Characteristics and performance

•A preparation-free gasified-straw slag as solid base catalyst for biodiesel production.•The catalyst shows superior stability and activity in 33-run test.•Three crystallites, quartz, åkermanite, and leucite are included in the catalyst.•Fixed-crystal-structure was responsible for the excellent stability.•Basic sites include low-coordination oxygen anions, OH groups, and metal-oxygen pairs.

A novel solid base catalyst derived from gasified straw slag for producing biodiesel was prepared by simple pulverization and sieving. This catalyst exhibited high stability, low leaching of the catalytic species, and good catalytic activity, caused by high-temperature melting in the biomass gasifier. SiO2, CaO, K2O, MgO, FeO, and Al2O3 were the common constituents (calculated as oxides) as per XRF analysis and EA. XRD and TEM-EDS analysis indicated that the catalyst comprises three crystallites: quartz, leucite, and åkermanite. The catalyst was strongly basic with a basic site concentration of 0.3974 mmol⋅g−1, including strongly basic low-coordination oxygen anions, moderately basic OH groups, and metal-oxygen pairs, as identified by CO2-TPD and IR. TGA results indicated that the catalyst is thermally stable up to 400 °C, which is greater than the typical reaction temperature. BET analysis results indicated that the slag exhibits a broad pore distribution with pore diameters of 5-15 and 45-75 nm. The catalyst exhibited high catalytic activity and stability, exhibiting a fatty acid methyl ester (FAME) conversion of 95% for transesterification conducted at 200 °C for 8 h with a catalyst dose of 20% and a methanol-oil molar ratio of 12:1. The FAME conversion remained greater than 85% even after reusing the catalyst for 33 reactions without any appreciable loss of catalytic activity. Small amounts of K and Mg (<10 ppm) leached into the product from the catalyst. These results indicated that the gasified straw slag catalyst demonstrates promise for producing biodiesel.

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