Transesterification of cotton oil with ethanol for biodiesel using a KF/bentonite solid catalyst

•Bentonite impregnated with KF was used to the production of biodiesel with ethanol.•The reaction of cottonseed oil with ethanol and clay catalyst have conversion of 95%.•The clay catalyst has high activity at moderate temperature (120 to 140 °C).•The clay catalyst can be reused and the conversion in the second cycle was 89%.•The product of the reaction has chemical and physical characteristics compatible with biodiesel. Conventional biodiesel production uses an alkaline homogeneous catalyst and alcohols of small molecules for the transesterification of vegetable and animal oils. Recent studies have shown that heterogeneous catalysts have some advantages over homogeneous catalysts for biodiesel production. Most previous studies have failed to achieve adequate conversion for these catalysts for ethyl transesterification at low temperatures and pressures. This work aims to investigate some aspects of the ethyl transesterification reaction of cottonseed oil using a Brazilian bentonite treated with potassium fluoride as a catalyst. The bentonite and the catalysts, produced using this clay, were characterized by X-ray fluorescence spectroscopy, X-ray diffraction and infrared spectroscopy. Batch transesterification experiments were performed taking into account the reaction temperature, the concentration and type of catalyst and the reaction time. The reaction conversion was estimated by gas chromatography. The characterization of the clay indicates that it is rich in montmorillonite and kaolinite, and the characterization of the catalyst indicates that the bentonite treated with potassium fluoride enhances the alkalinity and improves the transesterification reaction. The results of the transesterification tests show that at a reaction temperature of 120 °C and using 6% (w/w) of catalyst, the conversion of the cottonseed oil into esters is 95% with a catalytic activity of 4.0 g/g.h, which is high for this system. The product of the reaction has several characteristics of biodiesel, such as calorific value, density and kinematic viscosity. The stability of the catalyst can be demonstrated by the fact that the reaction conversion in the second reaction cycle was 89%, which is as high as the conversion in the first reaction cycle.