Reactive extraction of cis,cis-muconic acid from aqueous solution using phosphorus-bonded extractants, tri-n-octylphosphineoxide and tri-n-butyl phosphate: Equilibrium and thermodynamic study

Highlights

• The muconic acid extraction by TOPO and TBP have been done firstly in the literature.

• Different solvents used to solve TOPO and TBP.

• Kinetic studies of the extraction mucconic acid was studied firstly in the literature.

Abstract

cis,cis-Muconic acid falls under the category of carboxylic acids and finds application mostly in biodegradable polymers, agrochemicals, and the food industry. Owing to the high thermal reactivity based upon the two-terminal carboxylic groups present in their structure, the chemical industry has widely used carboxylic acids. The major obstacle encountered during the production of carboxylic acids is their recovery from aqueous solutions and fermentation media. Therefore, the recovery of HccMA by reactive extraction as a particular product capture method, using tri-n-octylphosphine oxide (TOPO) and tri-n-butyl phosphate (TBP) in organic diluents such as 1-butanol, isoamyl alcohol, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), diisobutyl ketone, isobutanol, n-hexane, dimethyl glutarate, ethyl propionate, and diethyl carbonate (DEC) was executed in this study. This method was experimentally conducted to explore the most proper extractant and diluent combination. Extraction experiments were also conducted with pure diluents alone to examine the extractant effect on the extraction system. The important extraction parameters like distribution coefficient (K_D), extraction efficiency (E %), loading ratio (Z), dimerization constant (D), partition coefficient (P), and complexation constant (K_E11) were determined. Mass action law model interpreted the obtained results. For HccMA/TOPO extraction system, the maximum extraction efficiency was found 93.19% in the presence of n-hexane as a diluent. For HccMA/TBP extraction system, the maximum extraction efficiency was found 90.37% in the presence of ethyl propionate as a diluent. Thermodynamic studies at variable temperatures were also carried out to estimate ΔH, ΔS, and ΔG of the process. To investigate the feasibility of designing a counter-current liquid–liquid extraction column, the number of theoretical stages (NTS) were assessed by theodified Kremser equation and found between 3 and 5 to et the desired extraction efficiency.

Introduction

Carboxylic acids are typically consumed on a broad scale through the pharmaceutical and chemical industries. cis,cis-Muconic acid (HccMA) is a two-carbon double-bonded dicarboxylic acid (shown in Fig. 1). It is chiefly used in biodegradable polymers, food, pharmaceuticals, and related industries [1].

Additionally, HccMA is an intermediate platform chemical for manufacturing the commodity important compounds (adipic and terephthalic acid) used in nylon 6,6 and polyester production [2]. Several ways have been described in the literature to obtain HccMA through microbial approaches [3], [4], from biorefinery process intermediates [5], fermentation medium [6], and so on [7], [8].

Global warming, limited oil reserves, and international resource competition have oriented chemical industries to search for environmentally sustainable and economical production processes for alternatives to fossil-derived fuel resources. There has been a considerable increase in the number of the chemical industries devising alternative courses based upon sustainable sources. Extensive efforts in this area were implemented in an attempt to generate carboxylic acids. Green-generation of carboxylic acids avoiding fossil fuels as a resource has already been achieved with fermentation technique. It became applicable for industrial applications. Due to the recent enhancements in strain engineering fermentation technique has been able to be more competitive with their petrochemical counterparts. In stu removal of toxic metabolite and cell recycling from effluents tolerate the inhibitory metabolite produced, leading to a successful production yield. Aerobic and anaerobic treatments are fermentation pathways applied depending on the cell growth conditions, energy consumption and carbon source requirements. Whilst the production of carboxylic acids has been accomplish successfully by fermentation technique,

the uptake of carboxylic acids remains to be unaddressed. Numerous techniques for separating carboxylic acids have been examined in the literature viz. nanofiltration [9], [10], adsorption [11], [12], crystallization [13], [14], and membrane [15].

Reactive extraction is a single-stage liquid–liquid extraction method relying on the acid-base formation in the organic phase. Reactive extraction with fermentation possesses intrinsic advantages such as reduced processing load and process cost, properly recovering the fermentation product in a single stage, and ease in acid removal. Additionally, depending on the continuous acid generation, the acidity of fermentation broth is increased which may pose a danger to the organisms. Removing acid produced regularly by an extractant has been a sensible approach to maintain appropriate pH in the fermentation broth [16]. Most of the extractants possess a high viscous characteristic. Since high viscosity brings lower solvation ability to complex, extractants are used along with solvents to support their physical properties by enhancing the extraction power. There has been an intensive research on the reactive extraction of levulinic [17], [18], [19], citric [20], [21], [22], propionic [23], [24], succinic [25], [26], lactic [27], caproic [28], nicotinic acid [29], [30] etc. The extraction equilibrium study of propionic acid by TBP with various solvents such as petroleum ether, n-heptane, and toluene was investigated by Keshav et al. The findings were assessed in terms of the equilibrium constant, distribution coefficient, extraction efficiency, and stoichiometric loading factor. The maximum recovery was achieved using a TBP + toluene combination with a distribution coefficient value of 3.444 [31]. Liquid-liquid equilibria of nicotinic acid by TOPO and TBP in n-heptane, n-decane, kerosene, methyl isobutyl ketone, and 1-decanol was studied by Kumar et al. to indicate the possible effect of the solvent, initial acid concentration, extractant type, and extractant proportion on the efficiency. The most prominent nicotinic acid extraction was achieved with TOPO dissolved in methyl isobutyl ketone at 0.10 kg.mol⁻¹ nicotinic acid concentration [32]. Wasewar et al. investigated the distribution of acrylic acid between water and tri-n-butyl phosphate dissolved in paraffin liquid, toluene, and butyl acetate. A comparative study based on the physical properties of diluents was performed. They reported that TBP in inert diluents, toluene and paraffin liquid allows the possibility to reach higher distribution coefficients [33]. Keshav et al. studied the physical and chemical extraction of gallic acid by TBP in octanol, n-hexane, toluene, and ethyl acetate at isothermal conditions. Gallic acid extraction by TBP dissolved in n-hexane was found to be at maximum with a distribution coefficient value of 24; when TBP utilized at 1.516 kg.mol⁻¹ concentration [34]. When it comes to the studies on the separation of HccMA from aqueous media or fermentation broth, there are only a few researches that have been described in the literature. Yoshikawa and the group developed a downstream process for the separation of HccMA including filtration, adsorption, precipitation, ion-exchange chromatography, and sedimentation stage. The results were achieved in high purity (95%) and high yield (90%). However, the high cost caused by the increased processing load was the primary drawback of a feasible downstream process for HccMA [35]. Zeiner et al. studied the reactive extraction of HccMA by water-insoluble and non-insoluble amines. They reported the high affinity of water-soluble amines to water may lead to bonds breaking between extracting agents and amines. Re-extraction of acid to the aqueous phase could result in a third phase formation. They suggested that modifiers like alcohols should be used in the extraction system to overcome a third phase formation by increasing the polarity of the organic phase [36].

Within this study, we aimed to search for a feasible downstream processing alternative to contribute to the separation of HccMA from fermentation media, resulting in an effective extraction system. Amines and organophosphorous compounds have been primarly extractants utilized for carboxylic acid separation from aqueous solutions that have been described in the literature. Considering their lower toxic effect on living beings, and their potantial to be more cost effective than amines, organophosphorous compounds have been utilized as extracting agent in this current study. This study focused on the reactive extraction of HccMA using organophosphorus compounds tri-n-octylphosphine oxide (TOPO) and tri-n-butyl phosphate (TBP) in organic solvents (alcohols, ketones, esters, and an aliphatic diluent), which has been undiscussed up to now. This study will be the first to investigate the effect of organophosphorousextractants on HccMA separation. TOPO and TBP were used as extractants to investigate the equilibria due to their high extraction capability and low solubility in water.