Sulfonated porous carbon catalysts for biodiesel production: Clear effect of the carbon particle size on the catalyst synthesis and properties

Sulfonated porous carbons (PCs-SO₃H) are prepared by the sol-gel reaction of resorcinol and formaldehyde. The porosity is maintained during drying using a cationic polyelectrolyte as pore stabilizer. It was found that varying the Resorcinol/Na₂CO₃ molar rate, different resins are produced which, after pyrolysis, give carbonaceous materials with different textural properties. It seems that a Resorcinol/Na₂CO₃ molar ratio of 200:1 was the optimal condition to produce a well-developed porous structure. Both resins and carbon materials are sulfonated by treatment with sulphuric acid. The relation between the carbon particles size, the sulfonation efficiency and its performance as a catalyst is studied. The higher amount of sulfonic groups, and thermal stability, as well as better catalytic performance, was obtained when smaller porous carbon particles were chosen by sieving. PCs-SO₃H exhibited high efficiency for the esterification reaction and high performance for biodiesel production. The catalysts can be recycled several times with a minimal loss of activity. Thermal analysis evidenced stability up to ca. 200 °C, allowing the use of this catalyst at high temperature. The simple synthesis and low cost of the PCs-SO₃Hs make them promising catalysts for the synthesis of biodiesel.