Preparation of Cellulose-Derived Solid Acid Catalyst and Its Use for Production of Biodiesel from Waste Oils with High Acid Value

A cheap cellulose-derived solid acid catalyst (Cellulose-SO3H), containing SO3H groups (1.69 mmol/g), was successfully prepared through sulfonation of incompletely carbonized cellulose. Various preparation variables exerted remarkable effects on the catalytic activity of the prepared catalyst, and the optimal preparation conditions were found as follows: carbonization at 400 oC for 15 h and subsequent sulfonation at 150 oC for 15 h. The resulting catalyst showed significantly higher activity for esterification of oleic acid with methanol than several typical solid acid catalysts (niobic acid, amberlyst-15, and sulfated zirconia). The Cellulose-SO3H catalyst was capable of efficiently catalyzing esterification of other higher fatty acids (palmitic acid and stearic acid) with methanol to the corresponding fatty acid methyl esters (biodiesel). Moreover, the conversion of waste oils containing 27.8% free fatty acids to biodiesel catalyzed by Cellulose-SO3H was investigated. It was found that the optimal molar ratio of methanol to oil, catalyst amount, reaction temperature, and reaction time were 25, 10% (based on the mass of waste oil), 85 °C, and 10 h, respectively. Under the optimal reaction conditions, the yield of biodiesel obtained catalyzed by Cellulose-SO3H was much higher than that by the above-mentioned three typical catalysts. Cellulose-SO3H still retained above 90% of its original catalytic activity even after 30 cycles of successive re-use, indicating excellent operational stability. It can be clearly seen that the Cellulose-SO3H catalyst displays tremendous potential for biodiesel production.