Low acid value bio-gasoline and bio-diesel made from waste cooking oils using a fast pyrolysis process

Continuous stable and fast pyrolysis of waste cooking oil (WCO) under isothermal conditions was achieved using catalyst pellets with a binder (bentonite) loaded with 25 wt% active materials including: Al₂(SO₄)₃, Na₂CO₃, NaOH, and CaO. The experiments were carried out in an instant evaporator pyrolytic system with pyrolysis reactor temperatures ranging from 450 ^oCto 550 ^oC. The catalyst pellets were prepared by drying and calculating the extrudates made from the pastes of the active materials and the binder. Low acid value (AV < 0.5 mg KOH/g) pyrolytic oils (PO) were obtained using these base catalyst pellets. Long-term tests, performed with these base catalysts, showed that CaO pellets can produce a PO with a near zero AV in a cycle time of 12 h. The physical properties of the bio-gasoline oil (BGO) and the bio-diesel oil (BDO) when separated from the PO almost meets the specifications of commercial petroleum gasoline and diesel, except that the octane number of the BGO (76) was below the target (92). Soap-like matter, in addition to the coke, produced during the pyrolysis of WCO using the catalyst pellets (Na₂CO₃ and NaOH) plugged the pyrolytic reactor, thereby preventing further operation. This soap-like matter was not found using the CaO catalyst pellet, suggesting that CaO was the most suitable base catalyst for WCO pyrolysis. The basic CaO pellets, able to reduce the fatty acids derived from thermal radical cracking reactions of WCO to aldehydes and ketones, produced a minimum aromatic hydrocarbon content in PO (from WCO) with a higher content of saturated fatty acids than from fresh edible soybean oil containing a higher content of unsaturated fatty acids. The resulting environmental friendly PO with a near zero AV, produced from WCO using the CaO pellets, proved the utility of the simple and one-step continuous pyrolytic process presented here.