Continuous Transesterification Reaction of Residual Frying Oil with Pressurized Ethanol Using KF/Clay as Catalyst

Abstract

The efficiency of a heterogeneous potassium fluoride (KF)/clay catalyst in continuous ester production from residual frying oil using pressurized ethanol is evaluated. Reactions without catalysts are conducted to determine the effect of the catalyst on ester yield. To verify the performance of the catalyst, the reactions are conducted for 3 h with determination of the ester yield every 30 min and characterization of the catalyst after each reaction. The influence of the temperature, catalyst mass used in the catalytic bed, and the residence time are evaluated. KF/clay is found to be efficient in ester synthesis and provides better results compared with non-catalytic reactions and the formation of esters is favored on increasing the temperature. The ester yields remain stable over time at 275 and 300°C but at 225 and 250°C the yields decrease by 48.42% and 38.40%, respectively. This may be due to the lower diffusion coefficient at these temperatures, implying that the reaction occurs preferentially at the catalyst surface. There is an increase in yield with an increase in the catalyst mass up to 2 g. The catalyst maintains its morphological characteristics after the reaction and the average mass loss in each reaction is <8%. Practical Applications: Transesterification at high temperature under pressurized conditions has great potential in biodiesel production, due to the efficiency in obtaining esters in short reaction times. In addition, the use of inexpensive and easily obtained clay-based catalysts contributes to higher yields and allows milder operating conditions. These factors make it possible to obtain biodiesel using a low-cost raw material (residual frying oil), under pressurized conditions, which will be of interest worldwide due to the various benefits linked to its use.

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

“…The substrates used were residual frying oil obtained from a local restaurant (Umuarama -PR) and ethanol (Panreac, 99.9% purity). The composition of the RFO was previously reported by Zempulski et al (2020), and its free fatty acid and water contents were 1.16 wt% and 0.16 wt%, respectively. For the preparation of the catalyst, Brazilian sodium smectite clays were used from deposits located in the states of Paraná and Paraíba, and potassium fluoride KF.2H 2 O (Synth, 98% purity).…”

“…The use of KF/clay catalyst in a pressurized medium for the synthesis of ethyl esters was reported in a previous study (Zempulski et al, 2020) in which the performance of the catalyst was verified for 3 h of operation in 225 to 300 °C, verifying low variation in the ester yield at 275 and 300 °C. Moreover, after the transesterification, it was verified that the potassium resulting from the impregnation remained in the catalyst, and that the roughness of the particles and agglomerates of the catalyst were not affected by the experimental conditions employed.…”

“…The tests were conducted using a catalyst mass of 2 g in the catalyst bed (these conditions correspond to an oil-to-catalyst ratio of 8:1, 6.4:1 and 5.4:1, respectively) at 275 and 300 °C. The catalyst mass and temperatures were defined based on the results obtained by Zempulski et al (2020), which provided the experiments the highest ester content and in the case of the selected temperature range did not show any loss in catalytic activity (in 3 h of reaction). The pressure was maintained at 20 MPa based on previous studies (Gonzalez et al 2013;Trentini et al 2018), and the residence times evaluated were 15, 30 and 45 min.…”

“…The experimental apparatus where the reactions were performed was previously described (Zempulski et al, 2020), and operated in continuous mode. The reaction mixture (RFO + ethanol) was kept under constant stirring (mechanical stirrer, IKA RW20) and pumped into the system using an isocratic pump (Waters 515 HPLC).…”

Effect of Different Parameters on Catalytic Production of Biodiesel from Different Oils

“…The heterogeneous catalysts can be efficiently separated from the reaction mixture. Thus, they are not corrosive, are environmentally friendly, have fewer disposal problems, are recyclable with higher selectivity, and have longer catalyst life 85, 104–106. Acid catalysts are not sensitive to the presence of FFAs and water.…”