(576f) Deacidification of Used Cooking Oil: Modeling and Validation of Free Fatty Acid Ethanolic Extraction in a Liquid-Liquid Film Contactor

Used cooking oils (UCOs) or waste cooking oils (WCOs) are widely generated urban residues because of food preparation at households, restaurants, hosteling sites, and industry. Despite UCOs are highly contaminated with components of different nature, they are mainly composed of triacylglycerols of fatty acids, which can be used as raw materials for the oleochemical industry. However, a significant challenge in the valorization of UCOs is their high content of free fatty acids (FFA), which can lead to equipment corrosion, deactivate alkaline catalysts during transesterification reactions and reduce yields in various processes. To address these issues, it is necessary to reduce the acidity of UCOs. Industrially, this is typically achieved through high-energy and materials-intensive processes such as low vacuum distillation and neutralization (Noriega et al., 2022). For this reason, alternative processes such as alcoholic extraction have proven to be very effective, exhibiting lower energy consumption, reduced residue generation, and the potential to utilize the recovered free fatty acids (FFAs) through further esterification with the solvent.

In recent studies it was verified that FFAs could be removed from acid vegetable oils and/or UCOs by using ethanolic extraction in a high surface area liquid-liquid contactor under continuous operation (Cárdenas et al., 2022; Noriega et al. 2022). This equipment seeks to maximize the contact area between liquid phases using a semi structural packing, which in turn allows the equipment to operate under laminar regime reducing dispersion and facilitating downstream decantation. In a previous experimental exploration (Cárdenas et al., 2022) it was found that in a single stage contactor of 1.07m, it was possible to reduce UCO’s acidity by 51%, whereas using acidified palm oil (Noriega et al., 2022) it was possible to reduce acidity below 0.1 wt.%. In both cases, separation was carried out in a single stage contactor under a fixed ethanol-to-oil ratio.

In this regard, this work was aimed to develop and correlate a mathematical model to describe the operation of a liquid-liquid film contactor in the FFAs extraction from UCOs. In previous research (Noriega et al., 2022), it was established that mass transfer in the oil phase was the primary resistance affecting the overall process. Accordingly, the developed model proposes a rigorous description of the liquid-liquid mass transfer in the oil phase based upon previously validated phase equilibria data and reported physicochemical properties of the mixture. Subsequent stochastic and deterministic optimization algorithms were applied to regress model parameters using reported data from deacidification experiments carried out under different UCO flowrates, ethanol to UCO mass flow ratios and contactor lengths (Cárdenas et al., 2022). The obtained parameter allows the computation of triacylglycerol, free fatty acids and ethanol mass fractions in the oil phase with 8,46% of average relative deviation. Once the parameters were regressed and validated, the liquid-liquid extraction model was used to determine the best operating conditions and configuration to carry out the deacidification of UCOs. It was found that a cascade configuration comprised of three 1,07m liquid-liquid film contactors in series were required to reduce UCO’s acidity below the specifications of oleochemical feedstocks for biodiesel production (< 1 wt.%). Each contactor is operated at 70°C and with a 2:1 ratio between ethanol and used cooking oil. This arrangement intensified the mass transfer process in comparison with traditional configurations of mixed tank contactors with settlers.

1. Cárdenas J, Montañez MA, Orjuela A, Narváez PC, Katryniok B. Deacidification of used cooking oils by solvent extraction under lab scale and in a falling film contactor. Eng. Process. - Process Intensif. 181: 109089 (2022) https://doi.org/10.1016/j.cep.2022.109089
2. Noriega MA, Figueroa LA, Narváez PC. Fatty acid solvent extraction from palm oil using liquid–liquid film contactor: Mathematical model including mass transfer effects. Food Bioprod. Process. 133:16–24 (2022) https://doi.org/10.1016/j.fbp.2022.02.004