Study of the operational conditions for ethyl esters production using residual frying oil and KF/clay catalyst in a continuous system

The transesterification of residual frying oil (RFO) with pressurized ethanol was carried out in a continuous reactor containing KF/clay as a heterogeneous catalyst. In the experiments, different oil:ethanol mass ratios were evaluated at 275 and 300 ºC and 20 MPa. In the sequence, the operational stability of the catalyst was evaluated for 8 hours, as well as the conduct of the reaction in two steps (testing new and recycled catalyst). An esters yield of ~90% was achieve at 275 ºC, for15 min and at 1:1.5 oil:ethanol mass ratio. Under these conditions, the catalyst provided a stable yield in the first 3 hours of operation, and a total decrease of 29% after 8 hours. This result can be attributed mainly to the leaching of the K+ cations for the reactions in which the catalyst was exposed to long operating times. The two-step reaction served to increase the RFO conversion to esters, with low thermal decomposition.