Please use this identifier to cite or link to this item: http://localhost:8081/xmlui/handle/123456789/910
Title: INTENSIFICATION OF RECOVERY OF CARBOXYLIC ACID BY REACTIVE EXTRACTION
Authors: Keshav, Amit
Keywords: CARBOXYLIC ACID;CHEMICAL INDUSTRY;ENERGY EFFICIENCY;CHEMICAL ENGINEERING
Issue Date: 2009
Abstract: Process intensification (PI) is a key strategy that the chemical industry is adopting for increasing energy efficiency and profitability. PI offers the benefits of smaller, safer and cheaper unit, small time to the market, less waste generation and low energy consumption, thus leading to a better company image. PI can be classified in methods and equipments. The basic philosophy of the PI methods is to choose the task in a manner such that the combination of operations lead to a better overall performance. Since any chemical process involves unit operations for reaction and separation, most of such task combinations fall under the umbrella of reactive separation processes. Reactive extraction links chemical sources and sink to enhance reaction rate, conversion and selectivity. For the last few decades, there has been intensive work on the reactive extraction for the recovery of carboxylic acid from waste water and fermentation broths. Reactive extraction being a clean, simple and cheap operation has created a lot of scope as an efficient recovery process. Propionic acid is an important carboxylic acid having wide uses in food, chemical and pharmaceutical industries. It can be prepared both by synthesis as well as fermentation route. Fermentation is advantageous over the former in view of being a clean process using low cost substrate material can be used as feed source. Also, the rapid price fluctuation andthe depleting petrochemical feed sources of synthesis route have created interest in the production of propionic acid using the bio-route. The challenge lying in the commercialization of the fermentation technology is the difficult downstream recovery of dilute concentrations of acid. In view of this, reactive extraction was selected as the technique for recovery of acid. The design of reactive extraction process requires the information about the chemical equilibria and physical conditions like effect of pH and temperature. Further, since the recovery of the acid is to be carried out from waste solutions and fermentation broths, which also contain various salts and substrates sources, it is desirable to study the effect of these parameters. Extraction of acid Intensification of Recovery of Carboxylic Acid by Reactive Extraction ii Abstract from model solutions is also desirable to study the performance of actual process. Some modified recovery reagents like mixed extractants and/or mixed diluents were also tried in order to explore even better recovery agent. Kinetic studies were made to see the progress of reaction and the reaction regime. Finally, the acid transferred to the recovery agent after extraction has to be recovered back for reuse. With these requirements, it has been decided to study the reactive extraction process for the recovery of propionic acid. The experimental results revealed the following. Physical extraction of propionic acid was studied using different diluents like aliphatic hydrocarbons (heptane, hexane, paraffin liquid, petroleum ether and kerosene), aromatic hydrocarbons (benzene, toluene), esters (butyl acetate, ethyl acetate), alcohols (1-octanol, 2- octanol, 1-decanol, 1-dodecanol, and oleyl alcohol) and ketone (MIBK). Distribution coefficients, partition coefficients and dimerization constants were evaluated. It was found that alcohols provide higher extractions than the other category of diluents. The reason for this is that alcohols are active diluents which interact with the acid by hydrogen bonding. The difference in extraction by different diluents was explained in terms of Ej parameter. Higher the ET value of particular diluent, higher is the extraction obtained. In general, it was found that the extraction using diluent alone were not high enough to be used successfully on commercial scale. Chemical extraction using different extractants: organophosphorous compounds (tri-nbutyl phosphate (TBP), tri-n-octylphosphine oxide (TOPO)), tertiary amine (tri-n-octylamine (TOA)) and quaternary amine (Aliquat 336) in different diluents were studied. In all cases, extraction was significantly enhanced by extractant. Higher extractions were obtained using TOA in alcohols and dipolar aprotic diluents with >94 % recovery of acid from aqueous solutions. Chemical extraction using TOA resulted in distribution coefficient (KD) values as high as 18.379 in comparison to TBP (maximum KD = 3.006) and Aliquat 336 (maximum KD = 2.841). In all cases, the stoichiometric loading ratio was less than 0.5, suggesting the formation of only (1:1) acid - extractant complexes. (1:1) extraction equilibrium complexation constant Intensification of Recovery of Carboxylic Acid by Reactive Extraction iii Abstract (KB) for TBP, TOA and Aliquat 336, vary in the range 0.591 - 2.249, 0.686 - 17.784 and 0.321 - 4.020 m3/kmol, respectively, in different diluents. Kinetics of extraction of propionic acid was studied. TBP in diluents: hexane, benzene, petroleum ether and 1-octanol; TOA in diluents: MIBK, 2-octanol and 1-decanol; and Aliquat 336 in diluents: MIBK, hexanol and 2-octanol, were used for the studies. Stirred cell was employed for experimental kinetic studies. The method of discerning mechanism, discussed by Doraiswamy and Sharma (1984), were adopted to obtain the reaction regime, order of reaction and rate constant. In all the cases (except in Aliquat 336 + MIBK), the reaction was found to be fast reaction occurring in the diffusion film. In the system Aliquat 336 + MIBK, the reaction was found to be a slow reaction. Kinetic parameters have been evaluated and tabulated. Effect of temperature (313-333K) on reactive extraction of propionic acid was studied. In all the studied cases, increase in temperature was found to lower the extraction. This was due to exothermic nature of reactive extraction process. Enthalpy and entropy of reaction were also evaluated. However, in general it was found that increasing temperature from 305-313 K (the usual range of production of acid in fermentation broth) there is only marginal decrease in extraction. The extraction of propionic acid using extractants in binary diluents was studied with the aim to find a better recovery system. Binary diluent mixtures were obtained by mixing an active diluent (modifier) and an inert diluent. Presence of modifier was found to enhance the extraction in most of the cases studied. With the aim to search for the synergistic effect, mixed extractants, TBP+ Aliquat 336; TOA + Aliquat 336 and TOA + TBP, were employed for the recovery of propionic acid from aqueous solutions. It was found that the presence of one extractant enhances the performance of the other. Though, mixed systems (binary diluents or binary extractants) provide higher KD values, yet, the increase in extraction was not very large. Further, other factors like increase in complexity of the recovery system, requirement of additional step for separating the binary mixture, and the difficulty it could bring in the design of the process, become more important factors of concern. Intensification of Recovery of Carboxylic Acid by Reactive Extraction IV Abstract Fermentation broths contain various salts and substrate sources. With this aim, the effect of salts (NaCl, Na2S04 and K2HP04) on reactive extraction of propionic acid (using TOA (40%) in diluents: MIBK, 2-octanol and 1-decanol) were studied. The concentrations of salts used were kept as observed in actual fermentation broth. Each salt was found to have different hindrance effect on extraction of the acid. NaCl has greater effect in comparison to Na2S04 and K2HPO4. Since, there is no complete conversion of feed material in the fermentation broth and the unconverted residual feed may affect the separation process, it was decided to study the influence of residual feed material i.e. lactose and dextrose on reactive extraction of propionic acid. Concentrations of these sources were varied from 10 to 60 g/1 as these are normally present in this range in a commercial fermentation broth. Results indicated that these substrate sources have negligible effect on the efficency of reactive extraction process. Extraction of propionic acid from model solutions constituting salts and substrate source were also studied. Concentration of substrate source (20 g/1 each) and NaCl were fixed in all model solutions. It was found that compared to extraction from aqueous solutions, about 10% decrease in extraction was observed in the case of TOA + MIBK and about 20% decrease in extraction observed in the case of TOA + alcohols (2-octanol and 1-decanol) using model solutions. Further, since bioreactors operate at temperatures close to 313 K, the effect of temperature on reactive extraction of propionic from model solutions were also presented. In the selected temperature range (305 - 333 K), no significant effect of temperature on the extraction of propionic acid from model solutions was found. The linear solvation energy relationship (LSER) model was used to obtain the correlation of KD and KE with various solvatochromic parameters of the diluents used. LSER model predicted a close resemblance to the experimental data. Model equations have been generated and presented. For a successful reactive extraction process, the solvent must be regenerated for reuse. Hence, the back extraction of propionic acid from loaded organic phases of TOA + MIBK, Intensification of Recovery of Carboxylic Acid by Reactive Extraction v Abstract TOA + 1-decanol and TOA + 2-octanol waere studied using various regeneration methods. These methods include the use of NaOH, trimethyl amine (TMA) or using temperature and diluent swing regeneration operations. Employing NaOH and TMA has resulted in 100% recovery of the acid from the organic phase. Among the above two methods, TMA is more advantageous to use as TMA being a volatile amine can be easily separated by heating. Kinetics of back-extraction was also studied. The back-extraction reaction between acid and TMA, was found to be a fast reaction. This signifies that the back extraction process is fast enough for the sustainable operation.
URI: http://hdl.handle.net/123456789/910
Other Identifiers: Ph.D
Research Supervisor/ Guide: Wasewar, Kailas L.
Chand, Shri
metadata.dc.type: Doctoral Thesis
Appears in Collections:DOCTORAL THESES (ChemIcal Engg)

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