Evaluation of available adsorbents for the dry washing of the wasted frying oil based crude ethyl esters

Abstract

Russia's invasion of Ukraine strongly actualized the issue of liquid biofuels production. Ethyl esters biodiesel may be produced from widely available domestic Ukrainian oils and locally produced bioethanol. Dry washing with adsorbents is an advanced biodiesel purification technique. There is still a lack of information on the dry washing of alkaline ethanolysis products, especially concerning the removal of heavy contaminants, originating from partially polymerized waste oils. Current work deals with the investigation of available materials as adsorbents for the purification of crude ethyl esters (88% esters, 1.61% monoacylglycerols, 0.73% diacylglycerols, 0.19% tryacylglyceroles, 1.04% soaps, 0.12% fatty acids, 1.07% glycerol, and 0.17% ethanol). Esters were prepared via alkaline-catalyzed transesterification of wasted frying sunflower oil (2.46 mg KOH/g, 7.1% palmitic, 3.5% stearic, 27.7% oleic, and 59.3% linoleic acids). Activated anthracite, synthetic carbon Chemviron, colloidal silica, meta-kaolin, talc, and bentonite were evaluated as adsorbents. All samples provided the removal of the majority of soaps and glycerol, decreased the ethanol concentration, and, in most cases, acid value. Dry washing had almost no impact on the acylglycerols content. Activated carbons, characterized by a combination of developed micro- and mesoporosity, produced the greatest results, including a minor amount of monoacylglycerols removal. However, none of the adsorbents provided the removal of heavy oligomer contaminants, which is indirectly indicated by no higher than 90% esters content in treated samples. Improvement of these characteristics may be achieved by vacuum distillation.