https://doi.org/10.15255/KUI.2019.031
Published: Kem. Ind. 68 (9-10) (2019) 397–405
Paper reference number: KUI-31/2019
Paper type: Original scientific paper
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Deep Eutectic Solvents for Purification of Waste Animal Fats and Crude Biodiesel

A. Petračić, A. Sander, M. Ćurić, D. Furač, A. Šimičević and J. Parlov Vuković

Abstract

Given the fact that biodiesel produced from oil used in the food industry is not competitive with fossil-based diesel, it is necessary to use cheaper raw materials for its production. Thereby, waste edible oil, by-products of the manufacturing process of edible oils, inedible oils, and waste animal fat are considered the economically acceptable raw materials. The goal of this work was to investigate the applicability of deep eutectic solvents for extractive deacidification of waste animal fats and removal of glycerol and glycerides from crude biodiesel. Extractive deacidification of waste animal fat was conducted using deep eutectic solvent potassium carbonate – ethylene glycol (1 : 10, mol.), and it was used in mass ratio 1 : 4 (solvent : fat), at 60 °C for 30 min. Total acid number was reduced from 26.63 to 1.1 mg KOH/g fat. After purification of the feedstock, biodiesel was synthesised with different catalysts (KOH and NaOH), and KOH exhibited better conversion; therefore it was chosen for further experiments. In order to define the optimal reaction conditions, the influence of mass ratio catalyst : methanol : fat on the conversion of triglycerides into fatty acid methyl esters was investigated. At all reaction conditions, high quality biodiesel was obtained, i.e., the ester content was above the EN 14214 limit (96.5 %). The influence of catalyst load was greater than of methanol. At the highest concentration of catalyst, neutralisation of free fatty acids occurred. Biodiesel synthesised at 1 : 40 : 100 (KOH : methanol : fat) was chosen as the best, and was used for further experiments – extraction of glycerol and glycerides from crude biodiesel. For that purpose, deep eutectic solvent choline chloride – ethylene glycol (1 : 2.5, mol.) was used. The influence of mass ratio solvent : biodiesel and extraction duration was investigated. Increase in mass ratio and extraction duration resulted in a slight increase in ester content. To confirm the removal of glycerol and unreacted glycerides, samples of biodiesel before and after extraction were analysed by gas chromatography. Three samples after extraction were chosen – one at the lowest and one at the highest mass ratio of solvent to biodiesel, and one at the highest duration of extraction. Crude biodiesel contained too high concentrations of free and total glycerol. After extraction for 90 min, a significant reduction was observed – the extraction efficiencies for free glycerol, diglycerides, triglycerides, and total glycerol were: 90.77 %, 13.19 %, 10.43 %, and 21.59 %, respectively. The content of glycerol and glycerides after extraction was well below the EN 14214 limit. Density and viscosity of biodiesel were within the range defined by the European standard EN 14214.

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Keywords

biodiesel, extraction, natural deep eutectic solvents, deacidification, waste animal fats