Recovery and regeneration of carboxylic acids from aqueous solutions using process intensification
Creators: name: Eda, Sumalatha
Publisher: name: RMIT University
Year: 2024
Subjects: classificationCode: 400403
subject: Chemical engineering design
classificationCode: 400409
subject: Separation technologies
classificationCode: 400499
subject: Chemical engineering not elsewhere classified

description: Recovery and regeneration of value added carboxylic acids using process intensification, i.e. reactive extraction is a promising technique to recover carboxylic acids from dilute fermentation broths. The study is divided into three parts. In the first part of the work, the reactive extraction of levulinic and succinic acids are studied individually using tri-n-octylamine (TOA) in methyl isobutyl ketone (MIBK) and 1-decanol, respectively. In the second part of the work, the regeneration of levulinic acid from the loaded-organic phase using 4 different techniques is studied. The third part of the work is the recovery of multi-acids (volatile fatty acids) by reactive extraction. Equilibrium and kinetic studies were conducted in the reactive extraction of levulinic acid. Physical equilibrium studies of levulinic acid were carried out with MIBK at various temperatures (293-333 K). Partition () and dimerization () coefficients were estimated at different temperatures to represent the physical equilibrium. The distribution coefficient () at physical equilibrium was found to be very low. Chemical equilibrium studies conducted at different concentrations of TOA showed that the highest values of the distribution coefficient () and the extraction efficiency () achieved 58.0 and 98%, respectively for 0.1 kmol m-3 of levulinic acid and 0.678 kmol m-3 of tri-n-octylamine at 293 K. Chemical equilibrium was also found to lead to the formation of 2:1 complexes. Taguchi mixed design multivariate approach ((61 32)) was used to optimise the process variables and the ratio (larger-is better) criterion was adopted to optimise the performance parameters. The optimum combination of variables was found to be an acid concentration () of 0.3 kmol m-3, a TOA concentration () of 0.678 kmol m-3 and a temperature () of = 293 K. Kinetic studies performed at optimum parameters showed that the overall order of the reaction was second order with respect to levulinic acid and tri-n-octylamine. Based on the Hatta number the reaction regime was found to be instantaneously occurring in the film of the organic phase. The reactive extraction of succinic acid using TOA in 1-decanol at different temperatures (298-333 K) was studied by employing a response surface methodology to explore the reaction kinetics in a stirred cell. Extraction efficiency (), a response function, was optimized by using three process parameters: initial succinic acid concentration (), TOA composition (), and temperature (). In conjunction with response surface methodology, a central composite design consisting of twenty experimental runs was also employed to optimise the reactive extraction of succinic acid. A statistical second order polynomial quadratic model predicted an extraction efficiency () of 93.75% with the optimum parameter values of 0.2 kmol m-3 succinic acid concentration, TOA composition of 33 (v/v), and a temperature of 305.5 K. The actual extraction efficiency obtained at optimum conditions was 91%. Kinetic studies were carried out to analyze the process. An interfacial area () correlation was derived based on the droplet radius. The mass transfer coefficients of succinic acid, TOA, and the 1:1 acid-amine complex in 1-decanol were determined using a water/acetic acid/kerosene system. Based on the Hatta number, the reaction regime was found to be instantaneously occurring in the film. The second part of the study, the regeneration of carboxylic acids from the loaded-organic phase, is an essential step to complete the reactive extraction process. A study on the regeneration of levulinic acid from the loaded-organic phase (MIBK +TOA +levulinic acid) was carried out using various techniques including the NaOH, temperature swing, diluent swing, and tri-methylamine methods. Equilibrium data obtained show that among all the methods, the recovery of acid is the highest for the tri-methylamine method when the molar ratio of tri-methylamine to levulinic acid concentrations is greater than 1. Kinetic studies performed for the tri-methylamine method showed that there are no changes in the specific rate of extraction with changes in stirrer speed rate and phase volume ratio (, and the overall order of reaction is 1.5. Based on the effects of stirrer speed and phase volume ratio on the specific rate of extraction, the reaction was found to occur in the fast regime. Also, about 80% of acid was recovered by the evaporation of the tri-methylamine phase at 104–140 0C. A detailed economic evaluation for the recovery of levulinic acid using reactive extraction with a feed rate of 2 m3 h-1 shows that the payback period for recovering the capital investment is 0.49 years. The third part of the study, the recovery of volatile fatty acids (multi-acids) from fermentation broth has been investigated by adopting an intensified approach using extractants TOA and tri-butyl phosphate (TBP) dissolved in 1-decanol and MIBK. The effects on the distribution coefficient () and extraction efficiency () were studied by varying the operating conditions of temperature (293.15–323.15 K), pH (2.5, 3.5, and 4.5), and composition of extractant (10, 20, and 30 %). Taguchi () orthogonal design with five factors, (diluents, extractant type, composition, temperature, and pH), was employed for the multivariate optimisation of the reactive extraction of volatile fatty acids. In the Taguchi approach, a “larger is better” criterion was adopted to maximise and. Statistical analysis indicated that the degree of influence on by the experimental variables follows the following trend: extractant type () &gt; pH () &gt; diluent type () &gt; temperature () &gt; extractant concentration (). The trend for observed is as follows: extractant type () &gt; pH () &gt; temperature () &gt; extractant concentration () &gt; diluent type (). The combination of optimum parameters were obtained as = 1-decanol, = tri-n-octylamine, = 20 %, = 293.15 K, and = 3.5. A confirmation run was conducted using these parameters and and values from this run were determined to be 8.65 and of 89.64 %, respectively, which were very close to the predicted values = 10.36 and = 91.26 %.