Experimental Studies on the Reactive Extraction of Different Carboxylic Acids

Abstract

In modern society, organic acids are used in food, agriculture, medicine, pharmaceuticals and other fields. Caproic acid is used for manufacturing artificial flavors, elastic, colors, pharmaceutical products, etc. Effective uses of n-butyric acid are notable for cancer treatment, for the production of alternative energy sources such as butanol and in the food and pharmaceutical industries. Iso-butyric acid acts as the precursor to produce methacrylic acid used to manufacture transparent acrylic glass, water bottles, kitchen and housewares, and medical equipment. Valeric acid has wide use in pharmaceutical and solvent industries and as an intermediate in the production of perfumes, fungicides, plasticizers and lubricants, and is also used as the monomer in polymer industries. Major uses of propionic acid can be found as an artificial food flavoring agent in food industries, fungicides, herbicides and plasticizers in pharmaceutical industries.
Due to the quick depletion of petroleum crude soon, the fermentation of biomass will be the major source of carboxylic acid. The produced acids in the broth are present at a very low concentration level. Reactive extraction can be an effective technology for recovering the carboxylic acids from the fermenter broth due to the integration of the fermentation and separation processes together. In the current work, an attempt has been made to identify the microorganism friendly reactive extractant and diluent pairs for different carboxylic acid systems. The performances of the natural diluents were compared with the petrochemical-based diluents. The study conferred the effect of temperature in the range of 298K-318K and also analyzed the effect of the initial concentrations of the selected carboxylic acids and the reactive extractant. Important performance determining parameters, distribution coefficient, loading ratio, extraction efficiency etc. as well as thermodynamic data like enthalpy and entropy changes were estimated.
N-butyric acid was extracted using tri-octyl amine (TOA). In physical extraction, KD𝑑𝑖𝑙 and partition coefficient, 𝑃 decreased in the order of decanol > sunflower oil > soybean oil, whereas dimerization constant, 𝐷 showed an opposite trend. In chemical extraction, the extraction efficiencies were 85-90% for decanol, 82-88% for sunflower oil and 75-86% for soybean oil. In terms of the distribution coefficient, decanol was better diluent than sunflower oil followed by soybean oil. The achieved distribution coefficient and extraction efficiency using sunflower and soybean oils were found encouraging in bio-refinery industries. The reaction equilibrium constant, 𝐾𝐸(𝑚:𝑛) has the highest value at the lowest temperature (298 K) and decreased with temperature and has a value in the order of decanol > sunflower > soybean. Iso-butyric acid was extracted by using tri-octyl amine (TOA) in eight different diluents. In physical extraction, KD𝑑𝑖𝑙 decreased in the order of decanol > octanol > hexanol > MIBK > toluene > petroleum ether > sunflower oil > soybean oil. In chemical extraction, the extraction efficiencies were 82-93% in decanol, 80-88% in octanol 78-87% in hexanol, 76-86% in MIBK, 75-85% in toluene, 75-83% in petroleum ether, 73-82% in sunflower oil and 72-81% in soybean oil. The significantly high distribution coefficient and extraction efficiency using sunflower and soybean oils suggested their use in bio-refinery industries. The reaction equilibrium constant, 𝐾𝐸(𝑚:𝑛) has the highest value at the lowest temperature (298 K). The extraction of valeric acid (VA) using tri-butyl phosphate (TBP) as a reactive extractant was carried out. The high values of the distribution coefficient and extraction efficiency advocated for using sunflower and soybean oils in the bio-refinery industries. Sunflower oil appeared to be a better diluent than soybean oil. The higher values of 𝐾𝐸(𝑚:𝑛) occurred due to the higher stability of the VA-TBP complex in sunflower oil. Caproic acid was extracted using TBP in green and non-toxic diluents: sunflower and soybean oils. Current work has suggested using sunflower and soybean oil in the biorefinery industry for recovering the acid from the fermentation unit. The reactive extraction of propionic acid was carried out using both TBP and TOA as the extractant in non-toxic soybean and rice bran oil as the diluents. In physical extraction, soybean oil (maximum 𝐾𝐷𝑑𝑖𝑙 of 0.44 at 298 K) exhibited slightly better extraction performance than rice bran oil (maximum 𝐾𝐷𝑑𝑖𝑙 of 0.41 at 298 K). Using TBP as the extract, the overall distribution coefficient and extraction efficiency were found marginally higher in soybean oil (0.78) than in rice bran oil (0.72). Using TOA, soybean oil (maximum 𝐾𝐷𝑜𝑣𝑒𝑟𝑎𝑙𝑙 of 0.73 at 298 K,) showed better extraction performance than rice bran oil (maximum 𝐾𝐷𝑜𝑣𝑒𝑟𝑎𝑙𝑙 of 0.66 at 298 K). The performance of TBP as the extractant was found little better than TOA. 𝐾𝐸(𝑚:𝑛) appeared higher due to the stability of the PA-TOA complex in soybean oil than in rice bran oil.