Two steps methanolysis and ethanolysis of olive pomace oil using olive-pomace-based heterogeneous acid catalyst

Olive pomace (OP) and olive pomace oil (OPO) are low-cost, non-edible, by-products of olive oil processing. Converting OPO into biodiesel by (trans-)esterification and olive pomace into a heterogeneous acid catalyst by sulfonation with sulfuric acid could promote waste-to-energy actions. OPO has a high fatty acid content of 126.39 mg_KOH/g_oil, which does not allow the use of base catalyst for biodiesel production. Homogeneous acid catalyst such as sulfuric acid could be used, however the wastewater should be neutralized and the catalyst could not be regenerated nor reused. The objective of this paper is to use the OP to produce a heteregeneous acid catalyst, that will be used in the esterification reaction of OPO to produce biodiesel. OP was pyrolyzed, activated with steam and sulfonized. Then OPO esterification was performed as at 60 °C and 65 °C for 5 h under agitation at 400 rpm using methanol and ethanol, respectively. The optimization of reaction was performed using an full factorial design by varying oil-to-methanol/ethanol molar ratio (1:3, 1:6, and 1:9) and catalyst loading (10 wt%, 15 wt%, and 20 wt%). The optimum esterification conditions were obtained at 1:9 oil-to-ethanol molar ratio and 20 wt% catalyst. Final products acidities reached 1.14 mg_KOH/g_oil and 3.89 mg_KOH/g_oil with methanol and ethanol, respectively. Work was then focused on ethanolysis and a second step of homogeneous alkali-catalyzed transesterification was performed. FAEE yield registered 95.7% using the products of optimized first step. The physical and chemical properties of final product were measured and they respect EN14214 requirements except glycerides contents that were slightly higher than the norm. It registered a viscosity of 3.38 mm²/s, a flash point of 168 °C, and a Cold Filter Plugging Point of 14 °C. Its Copper Strip Corrosion class (1a) respects EN14214. Solid catalyst was regenerated and reused up to 6 cycles before being mechanically degraded.