(383ay) Modelling and Assessment of Deacidification of Used Cooking Oils Using Ethanol Extraction in a Liquid-Liquid Film Contactor

Used cooking oils (UCOs) or waste cooking oils (WCOs) are widely generated urban residues that result from food preparation at households, restaurants, hosteling sites, and industry. Generally, in most urban areas worldwide UCOs are mishandled by disposal through sewage and solid residues causing a cascade of problems like infrastructure damage, water and soil pollution, vectors proliferation, etc. Despite UCOs are highly contaminated with components of different nature, they are mainly composed of triacylglycerols, which can be used as raw materials for the oleochemical industry. Among the variety of oleochemical derivatives, UCOs can be used for the production of plasticizers, asphalt/pavement binders, lubricants, epoxidizes, polyols, surfactants, bio-monomers, among others (Orjuela & Clark, 2020). Nonetheless, a main drawback for UCO’s valorization is the high content of free fatty acids (FFA) because they cause corrosion of equipment, deactivation of alkaline catalysts during transesterification reactions and reduction of yields in different processes. In order to overcome such problems, there is need to remove acidity of UCOs. Industrially this is carried out by mean of 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 has demonstrated lower energy consumption, minor residue generation, and potential recovery of FFAs via esterification with the solvent.

In recent studies it was verified that FFAs could be removed from acidified 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 maximizes 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. A simplified scheme of the equipment is presented in Figure 1. 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, and despite it was not verified, it was stated that a multiple contactor operation under a cascade or counter-current configuration would enable to obtain a better performance.

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. The model involved a rigorous description of the liquid-liquid mass transfer based upon previously validated phase equilibria data and reported physicochemical properties of the mixture. The two-film model was implemented to account for the convective mass transfer at the interface, and experimental data were used to estimate film thickness. Additionally, mass transfer parameters were adjusted by using reported data from deacidification experiments carried out under different operating conditions (Cárdenas et al., 2022). It was confirmed that the mass transfer in the oil phase was the controlling resistance of the overall process, making the accurate modelling of the oil phase crucial for the study of the operation and for further process design and scale up. Once regressed and validated, the liquid-liquid extraction model was optimized to determine the best operating conditions and configuration to carry out the deacidification of UCOs. It was found that a multistage configuration was required to reduce UCO’s acidity below the specifications of oleochemical feedstocks (< 0.5 wt.%), and that the contactor enabled to intensity the mass transfer process in comparison with traditional configurations of mixed tank contactors with settlers.

References

Cárdenas, J. Montañez, M. A., Orjuela, A., Narváez, P. C., Benjamin Katryniok, B.

(2022). Desacidificación de aceites vegetales usados mediante el método de extracción con solventes. Chemical Engineering and Processing - Process Intensification 181, 109089. https://doi.org/10.1016/j.cep.2022.109089

Orjuela, A., & Clark, J. (2020). Green chemicals from used cooking oils: Trends, challenges, and opportunities. In Current Opinion in Green and Sustainable Chemistry (Vol. 26). Elsevier B.V. https://doi.org/10.1016/j.cogsc.2020.100369

Noriega, M. A., Figueroa, L. A., & Narváez, P. C. (2022). Fatty acid solvent extraction from palm oil using liquid–liquid film contactor: Mathematical model including mass transfer effects. Food and Bioproducts Processing, 133, 16–24. https://doi.org/10.1016/j.fbp.2022.02

Figure 1. Simplified flow diagram of free fatty acid removal from waste cooking oil in the liquid-liquid film contactor