Recovery of lactic acid from aqueous solutions by reactive extraction using vegetable oils and trioctylamine

In the recent years, separation of carboxylic acids from various media has gained a great importance with the increase in their usage areas and production costs. Lactic acid (LA) is one of the most widely used carboxylic acids in industry and therefore, the studies on its recovery and purification have a great academic and industrial importance. Several methods have been tested to reach the aim and reactive extraction technique has been shown as more advantageous compared to the others due to its practicality, high efficiency, low cost, and low energy demand. However, due to the high toxic effect of the chemicals used in the process, the exploration of the alternative organic phase diluents is required. In this MS thesis, recovery of lactic acid by reactive extraction using various environmentally-friendly diluents and trioctylamine (TOA) extractant was studied. The results were compared with those obtained with 1-octanol. Eight different vegetable oils (sunflower, safflower, almond, hazelnut, canola, corn, soybean, sesame oils) were tested in the study and the highest recovery values were obtained with safflower oil. It was observed that the system reached the equilibrium by 45 minutes and the separation efficiencies decreased with the increase in the solution pH and temperature. The recovery percentages increased with the increase in LA and TOA concentrations in the experiments safflower oil was used as the organic phase diluent. Concentration effect varied depends on the initial concentrations of the acid and amine when 1-octanol was used as the diluent. The highest recovery efficiencies were 83.1% (KD=4,905) and 96.9% (KD=31,49) with safflower oil and 1-octanol, respectively. At high LA concentrations, the efficiencies obtained with two different diluents were observed to be very close to each other. In the following studies, more than 99% of the lactic acid in the organic phase was extracted into the second aqueous phase. The highest back extraction efficiency was reached with NaOH among the back extractants studied. This MS thesis clearly showed that vegetable oils can be used as the organic phase diluents instead of toxic conventional organic diluents during the reactive extraction of lactic acid.