Effective production of branched-chain biodiesel by the hydrolysis-esterification of castor oil using porous carbon-based solid acid

Abstract

Using Chinese fir sawdust as a carbon source, a porous carbon-based solid acid was successfully developed and utilized for the hydrolysis-esterification of castor oil to produce branched-chain biodiesel. A series of characterizations proved that the CPS-400–2 possessed a large specific surface area (1129.86 m²/g), high total acid density (5.03 mmol/g) and abundant -SO₃H density (1.68 mmol/g). The hydrolysis yield of castor oil reached 85.5 % under the conditions of hydrolysis temperature 160 °C, hydrolysis time 3 h, water/oil mass ratio 2:1, and catalyst dosage 6 wt%. Subsequent esterification of the resulting ricinoleic acid with isopropanol (molar ratio 18:1) at 160 °C for 2.5 h with catalyst dosage 5 wt% achieved 95.1 % esterification ratio. Combined with density functional theory calculations, a potential reaction pathway for the esterification of ricinoleic acid with isopropanol was proposed. And, the environmental assessment revealed that the hydrolysis-esterification process to produce the branched-chain biodiesel was an environmentally friendly technology. Finally, according to the LCC cost analysis results, using CPS-400–2 as the catalyst to product the biodiesel had relatively low cost.