Valorisation of corncob residues to functionalised porous carbonaceous materials for the simultaneous esterification/transesterification of waste oils

Green Chemistry (Impact Factor: 6.85). 09/2011; 13(11):3162-3167. DOI: 10.1039/C1GC15908A

ABSTRACT Functionalised porous carbonaceous materials prepared from the controlled pyrolysis of corncobs were found to provide excellent activities in the simultaneous esterification/transesterification of highly acidic waste oils to biodiesel-like mixtures. Materials carbonised at 600 °C (mostly microporous) containing –SO3H groups (ca. 1 wt% S, 0.16 mmol g−1 –SO3H) exhibited the optimum yields (>95%) to fatty acid methyl esters after 6 h of reaction.

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    ABSTRACT: Multifunctional mesoporous solid acids were prepared by the sulfonation of carbonized de-oiled seed waste cake (DOWC), a solid waste from biodiesel production. Detailed structural characterization of the materials by elemental analysis, FT-IR, Raman, XRD, XPS, TGA, NH3-TPD and N2-physisorption showed that they were structurally different from the carbohydrate and resin based sulfonated carbon catalysts. In addition to the typical –OH, –COOH and –SO3H groups they contain several N species (pyridinic, pyrrolic etc) incorporated in their carbon frameworks. The basic structural unit of these materials is a flexible carbon nitride sheet which is extensively functionalized with acidic groups. Our results show distinct effects of raw material composition and preparation methods (activation, sulfonating agent etc) on structure, stability, surface acidity and textural properties. Here, catalyst –SO3H density and porosity (pore size, pore volume and surface area) had a direct effect on activity. Also, H2SO4 was less useful than 4-BDS (4-benzenediazoniumsulfoante) as a sulfonating agent. The best catalysts with mesoporous structure (average pore diameter 3.9-4.8 nm, pore volume 0.28-0.46 cm3g-1) and –SO3H density (0.70-0.84 mmol/gcat) were obtained by 4-BDS sulfonation of chemically activated DOWCs. In contrast, hydrothermal H2SO4 sulfonation of DOWC produced a non-porous catalyst with high –SO3H density while those obtained by H2SO4 treatment of activated biomass (AC) had a porous structure with low –SO3H density (0.19 mmol/gcat). Furthermore, the reported catalysts show excellent activity in two reactions of interest in biomass conversion: cellulose saccharification (glucose yield 35-53%) and fatty acid esterification (conversion upto 97%) outperforming H2SO4, conventional solid acids (zeolites, ion-exchange resins etc) as well as sulfonated carbons reported earlier works, confirming their potential as alternative environmentally benign solid catalysts for sustainable, carbon efficient biorefining.
    Applied Catalysis B Environmental 03/2015; DOI:10.1016/j.apcatb.2015.03.005 · 6.01 Impact Factor

Rick Arneil Arancon