engleski

Deep eutectic solvents in biodiesel production from sustainable feedstocks

This research aimed to develop and implement alternative purification solutions into the production of biodiesel from sustainable feedstocks. The goal was to use deep eutectic solvents (DESs) for extractive deacidification of waste acidic feedstocks and extractive purification of crude biodiesel. Feedstocks included in the work ranged from slightly acidic, such as waste coffee ground oils (WCGO) and waste cooking oils (WCO), to very acidic like waste animal fats of Category 1 and 2 (WAF1) and Category 3 (WAF2), according to the animal by- product categorisation. Biodiesel was produced via base-catalysed transesterification, which required feedstock purification before the reaction. The study started with eight DESs of various properties – ranging from acidic to basic, from slightly to highly viscous. Six were choline chloride-based, and two were based on potassium carbonate. DESs were used for the removal of free fatty acids (FFA) from feedstocks via extractive deacidification. The results demonstrated that purification efficiency depended on the solvent's pH value, with two basic, potassium carbonate- based DESs exhibiting the highest efficacy. This conclusion raised the question of whether the efficiency was due to extraction or neutralisation. Further experiments revealed that it depended on the DES to feedstock mass ratio. The extraction was occurring at low mass ratios, while neutralisation was observed only at high mass ratios. Potassium carbonate : ethylene glycol (1:10, mol.) DES was chosen as the most suitable for deacidification, at DES to feedstock mass ratios 0.1:1 and 0.25:1, depending on the initial FFA content. The research into feedstock purification was extended to metals and trace elements (Na, K, Ca, Mg, P, B and Fe) purification, and four DESs were used for that purpose. Two were based on choline chloride, and two on potassium carbonate, with ethylene glycol and glycerol as hydrogen bond donors. DESs were compared against two commercial adsorbents and proved more efficient for removing most of the investigated impurities. The initial feedstock impurities composition highly influenced the purification efficiency – with a lower driving force, the mass transfer was slower for all tested purification methods. Upon identifying the best feedstock purification solvent, the investigation proceeded to biodiesel synthesis and crude biodiesel purification. Transesterification was conducted with methanol in the presence of KOH or NaOH. KOH proved slightly better. The ratio of methanol and catalyst to oil was also varied, and their influence was almost negligible in the investigated range. Crude biodiesels were then purified with choline chloride : ethylene glycol (1:2.5 mol.) DES. The experiments were conducted to determine the optimal extraction duration and DES/biodiesel mass ratio. Results showed that the chosen DES was very effective for removal of free and total glycerol. Long extraction time or high mass ratios resulted in a slight decrease in fatty acid methyl ester (FAME) content, except in WAF1, leading to the conclusion that unsaturated FAME slightly dissolved in the DES, while saturated ones present in fat did not. Purification of WCGO biodiesel was also conducted in a continuous Karr column. Stabilisation was achieved after 15 minutes, and purified biodiesel satisfied the criteria for FAME, free glycerol and total glycerol content.

biodiesel ; deep eutectic solvents ; extraction ; free fatty acids ; feedstocks ; glycerides ; glycerol ; metals ; trace elements ; transesterification

Skandinavski model