engleski

Extractive deacidification of coffee oil with deep eutectic solvents

Used coffee grounds make an excellent feedstock for biodiesel production, containing around 10 % of oil that would otherwise go to waste if not extracted and used for transesterification. For the purpose of this work, used coffee grounds were collected from a café bar. Wet coffee grounds were dried in a convective dryer and then the oil was extracted in a Soxhlet extractor using n-hexane as a solvent. After extraction, solvent was evaporated in a rotary evaporator under vacuum. The obtained oil was a dark brown liquid under room conditions and its total acid number was around 5 mg KOH/g oil, due to the presence of free fatty acids. For base- catalysed transesterification, total acid number of oil should be below 2 mg KOH/g oil, therefore it was necessary to purify the oil. Deep eutectic solvents (DESs) were used for the extraction of free fatty acids from coffee oil. Eight different deep eutectic solvents were used for the extraction and their properties (pH value, electrical conductivity, viscosity and refractive index) were measured. The solvents consisted of choline chloride, malic acid, citric acid, fructose, glycerol, ethylene glycol and potassium carbonate. The extraction was carried out for three hours, at 60 °C and the mass ratio of DES to oil was 1:1. It was found that the DESs with higher pH were more effective for oil deacidification. DES containing potassium carbonate and ethylene glycol (molar ratio 1:10) was chosen as the best solvent for free fatty acid removal due to its high pH value and low viscosity. More experiments were carried out, searching for the optimal extraction conditions such as process duration, temperature and mass ratio of DES to oil and it was found that even after 15 minutes of extraction under room temperature with mass ratio of DES to oil 0.1:1 the total acid number was below 2 mg KOH/g oil.

biodiesel ; coffee oil ; deacidification ; deep eutectic solvents ; extraction

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