(429a) Kinetic Modeling of the Epoxidation of High Oleic Palm Oil Using Amberlite IR-120 As Catalyst

Steven A. Solarte, Alvaro Orjuela, Laura R. Conde.

Department of Chemical and Environmental Engineering, Universidad Nacional de Colombia, 111321, Bogotá D.C., Colombia

In recent years, the chemical industry has been actively integrating renewable raw materials as substitutes for conventional fossil feedstocks. Among these, vegetable oils have emerged as promising alternatives, particularly for sensitive applications like cosmetics, food products, pharmaceuticals, and biocompatible polymers. Their inherent properties, environmentally friendly composition, renewability, low toxicity levels, high lubricity, low boiling points, and notable biodegradability make vegetable oils invaluable sources of various chemical compounds. Oleochemical derivatives can effectively serve as direct or functional substitutes for many fossil-based products, either partially or entirely. This is of particular importance for products with significant negative environmental impacts such as fossil-based polymers.

Polymers play a crucial role in human development. However, the environmental pollution resulting from mismanagement at the end of their use, the health hazards associated with certain additives (such as phthalate-based plasticizers), and the high costs and complexity of recycling have fostered the development of renewable and biodegradable materials and additives for the polymer industry. Consequently, the biopolymer market reached a valuation of USD 11.5 billion in 2022. Within this market, biobased epoxides constitute a large portion, serving as fundamental components in the production of resins, polyols, polyurethanes, polyesters, polyethers, and as additives for different applications (including plasticizers, lubricants, thermal stabilizers, surface coatings, hydrogen chloride scavengers in PVC). Currently, most biobased epoxides correspond to epoxidized vegetable oils, primarily utilized as plasticizers for PVC, monomers in epoxy resins, and feedstock for polyols used in polyurethanes.

Epoxidized vegetable oils with high oxygen oxirane content, low remaining iodine values, and minimal acidity are considered superior raw materials within the biopolymer industry. Consequently, they are primarily derived from highly unsaturated oils such as linseed, soybean, sunflower, and canola. Nonetheless, such raw materials have higher costs compared to the predominant oil within the global market, namely palm oil. Despite its lower cost and widespread availability, palm oil is rarely used as a raw material for epoxides due to its low unsaturation content, which limits its theoretical maximum oxirane index in-between 3-3.5 g-O/100 g-oil. Recently, due to phytosanitary issues in palm cultivation, hybrid species have been extensively cultivated. Surprisingly, the oil extracted from the fruits of these hybrid palms exhibits a higher content of oleic acid chains in the triglycerides. This has facilitated the large-scale production of high oleic palm oil (HOPO), characterized by iodine values ≥75 g-I₂/100 g-oil. Using HOPO as feedstock, it would be possible to obtain epoxides with theoretical oxirane oxygen content ≥4% wt., making them suitable to produce plasticizers and polyols (2).

The quality of epoxidized oils and their oxirane oxygen content are significantly influenced by the synthesis method. Industrially, epoxidized vegetable oils are typically synthesized via the Prileschajew reaction using H₂O₂ as the oxidant, a percarboxylic acid as the oxygen carrier, and H₂SO₄ as the catalyst. Despite achieving high conversion, this process exhibits limited selectivity, resulting in productivity below 80%. This was confirmed in a recent study that experimentally optimized HOPO epoxidation using H₂SO₄ (1). The study revealed productivities up to 80% and epoxidized products with oxirane indexes ~3.5 g-O/100 g-oil. However, challenges arose due to the corrosiveness of sulfuric acid and the required downstream neutralization, leading to waste generation. Consequently, there is a need for more selective, less problematic, and more environmentally conscious processes and catalysts. Various studies have proposed the use of heterogeneous catalysts to overcome the limitations of traditional ones. Among these, ion exchange resins have shown promising results for large-scale implementation. Several ion exchange resins, including Amberlite IR-120, Amberlyst 39, Amberlyst 36, Indion 225, Seralite SRC-120, Dowex 50WX2, Zerolit 325, and Aquivon PW79S, have been explored. Particularly, gel-type Amberlite IR-120 stands out as a suitable catalyst for epoxidation due to its activity and stability. However, as HOPO only recently became commercially available, heterogeneously catalyzed epoxidation has not been explored, and there is a lack of available kinetic models, which are necessary for further process design and scale-up.

In this respect, Amberlite IR-120 was assessed as a catalyst in the epoxidation of HOPO with H₂O₂ via the in-situ peracetic acid process. A Box-Behnken experimental design was employed to investigate the effect of catalyst loading, acetic acid loading, temperature, and molar ratio of reactants on the selectivity and yield of the epoxidation reaction. The progress of the reaction was monitored by measuring the oxirane oxygen and iodine content using a greener and safer spectroscopic method (near-infrared spectroscopy). The obtained experimental data were used to correlate a kinetic model using a pseudo-homogeneous approach and considering ring opening as a side reaction. Based on literature reports, different kinetic models were evaluated (i.e. Power law, Eley-Rideal, LHHW), and their corresponding kinetic parameters were determined by regression. All models exhibited a relative error below 10%, indicating their suitability in describing the reaction kinetics. These models can be further employed for process design, kinetic optimization, and scale-up. Additionally, further experiments were conducted to assess the reusability of the catalyst. It was observed that Amberlite IR-120 enhanced both selectivity and productivity compared to traditional catalysts, and it could be reused for multiple cycles without significant loss of activity.

1.Bohórquez, W. F., Orjuela, A., Narváez Rincón, P. C., Cadavid, J. G., & García-Nunez, J. A. (2022). Experimental optimization during epoxidation of a high-oleic palm oil using a simplex algorithm. Industrial Crops and Products, 187 (Part A), 115321. https://doi.org/10.1016/j.indcrop.2022.115321.

2.Orjuela, Á., Bohórquez, W., Díaz, M. A., García, J. A., Narváez, P. C., Cadavid, J. G. (2022). Polioles grasos: producción, retos y oportunidades para el sector del aceite de palma. Bogotá. https://doi.org/10.56866/9789588360935