250998 Extraction and Back-Extraction Studies of Picolinic Acid Using Tri-n-Octylamine Dissolved in 1-Decanol

Tuesday, October 30, 2012: 10:10 AM
404 (Convention Center )
Dipaloy Datta, Chemical Engineering, Birla Institute of Technology & Science, Pilani, Pilani, India and Sushil Kumar, Chemical Engineering, Birla institute of Technology and Science (BITS), Pilani, India

Extraction and Back-Extraction Studies of Picolinic Acid Using Tri-n-Octylamine Dissolved in 1-Decanol

Dipaloy Datta1 and Sushil Kumar2

Department of Chemical Engineering

Birla Institute of Technology and Science (BITS), PILANI – 333031 (Rajasthan), INDIA


1 E-mail: dipaloy@bits-pilani.ac.in; dipaloy@gmail.com

Homepage: http://universe.bits-pilani.ac.in/pilani/dipaloy/profile


2E-mail: skumar@bits-pilani.ac.in; sushilk2006@gmail.com

Phone : +91-1596-245073 Ext 215; Fax: +91-1596-244183

Homepage: http://universe.bits-pilani.ac.in/pilani/skumar/profile


The chemical industry has come under increasing pressure to make chemical production more eco-friendly due to its reliance on fossil resources, its environmentally damaging production processes and its toxic byproducts and waste. Within this framework, bio-based chemistry and biotechnologies offer great prospects. Microbial production of organic acids is a promising approach for obtaining building-block chemicals from renewable carbon sources (Hatti-Kaul et al., 2007). Picolinic acid acts as a bidentate ligand with two active groups such as a carboxyl group (-COOH) and a pyridinic nitrogen atom (-N). The acid is well known for its efficient chelating activity and can chelate metals like Cu, Fe, Ni, Zn, Cd, Pb, Mn, Cr, and Mo in the human body (Suzuki et al., 1957). 3-hydroxyanthranilic acid oxygenase enzyme can oxidize 3-hydroxyanthranilic acid by the catabolism of tryptophan through kynurenine to picolinic acid (Smith et al., 2007). A major drawback of fermentation is low acid product yield and concentration which leads to the difficulty in recovery of the product from the very dilute solution. To improve the biological production of picolinic acid, it is necessary to develop a cheap and environment friendly recovery method (Wang et al., 2005). Among the several separation processes,  reactive extraction using a suitable extractant has been found to be a most promising alternative to recover carboxylic acids from the fermentation broth and dilute aqueous solution. Tertiary amines especially tri-n-octylamine (TOA) are found to be effective extractant to recover different carboxylic acids by reactive extraction (Kertes and King, 1986; Tamada et al., 1990; Datta and Kumar, 2011).


Literature is widely available on the reactive extraction of different carboxylic acids from aqueous streams, but work on reactive extraction and back-extraction of picolinic acid is limited. Therefore, the present work is aimed to intensify the recovery of picolinic acid (0.01 to 0.05 kmol×m-3) using reactive extraction with TOA (= 0 to 0.344 kmol×m-3) using 1-decanol as active (polar) diluent. The experimental data are analyzed by calculating distribution coefficient (KD = Corg/Caq), degrees of extraction [E = KD / (1 + KD)] and loading ratios (Z =). In the experiment, equal volumes (20 ml) of organic and aqueous phases are equilibrated by shaking for 8 h at 298 K in a constant temperature water bath (Remi Labs, HS 250, India). After reaching equilibrium, the phases are allowed to settle for 2 h to have a clear separation of the phases. The aqueous phase is sampled by a pipette. Picolinic acid concentration in the aqueous phase (Caq) is measured by titration using NaOH solution of 0.01 N. Acid concentration in the organic phase (Corg) is calculated by a mass balance. The initial and equilibrium pH of aqueous solution are measured using a digital pH-meter (ArmField Instruments, PCT-40, UK). The back-extraction of picolinic acid is carried out by pure water (temperature swing regeneration) at 353 K with 1:4 volume ratio of phases.

The equilibrium isotherms are drawn between organic and aqueous phase concentrations of picolinic acid at four initial acid concentrations and three concentrations of TOA in Figure 1. It is observed that the distribution coefficients ( << 1) of picolinic acid in 1-decanol alone are not sufficiently high. Also the degree of extraction is very low. Physical extraction of picolinic acid with 1-decanol has been found unsuitable. The hydrophilic nature of picolinic acid [dipole moment, μ = 4.42 D (Kulkarni et al., 1978); log P = -0.97 (Leo et al., 1971)] makes it poorly extractable by common organic solvents. Therefore, the equilibrium chemical extraction experiments for the recovery of picolinic acid are also carried out with TOA (0.115 - 0.344 kmol·m-3) dissolved in 1-decanol and isotherms are shown in Figure 1. Improved extraction efficiency in terms of KD is observed when an extractant is used with diluent as compared to that of diluent alone. The maximum value of KD in the chemical extraction is found to be 7 with TOA (0.344 kmol·m-3) at 0.01 kmol·m-3 of picolinic acid initial concentration. The distribution coefficients are found to be higher at lower concentration of acid (0.01 kmol·m-3). It can be observed that at a fixed concentration of picolinic acid, the distribution coefficient increases with an increase in the TOA (0.115 to 0.344 kmol·m-3) concentration, whereas upon varying the acid concentration for a fixed extractant concentration, KD values decrease (Figure 2). The maximum removal of picolinic acid is 87.5% with TOA (0.344 kmol·m-3) in 1-decanol at 0.01 kmol·m-3 of picolinic acid initial concentration. The distribution coefficient increases from 3 to 7 when the amount of TOA is increased from 0.115 to 0.344 kmol·m-3. The effect of loading ratio (Z) on the extraction efficiency is shown in Figure 3. It can be seen that loading ratio decreases with increasing concentration of TOA at a fixed concentration (0.01 kmol·m-3) of acid. The same trend is observed for other concentrations of acid. Also, at higher acid concentration, the organic phase is more loaded with the acid molecule compared to low acid concentration. The extraction mechanism of picolinic acid also depends on the pH and the pKa of acid. In the present study, the values of equilibrium pH are found to be in the range of 3.55 to 4.11 which is in between the pKa's of the acid (pKa1 = 1.01, pKa2 = 5.29; John, 1972).

Figure 1. Equilibrium isotherms of picolinic acid (0.01 to 0.05 kmol·m-3) for different concentrations of TOA (0.115 to 0.344 kmol·m-3) dissolved in 1-decanol

Figure 2. Effect of initial acid and extractant concentration on KD

Figure 3. Effect of initial acid and extractant concentration on Z

An equation is derived using mass action law to relate KD with m, n and equilibrium constant (KE) of equilibrium reaction as:



The values of m, n and KE are estimated by optimizing the error between the experimental and predicted values of KD using Eq. (1). The estimated values of m are found to be near about one with TOA imply that there are mainly formation of (1:1) acid-TOA complex in the organic phase (Table 1). The higher values of KE are found at lower extractant concentration which shows faster mass transfer of the solute into the organic phase.


Table 1. Values of m, n and KE

TOA (kmol·m-3)
















In the back-extraction of picolinic acid (Figure 4), it can be seen that with an increase in the concentration of TOA, the slope of the isotherm decreases i.e. distribution coefficient of back-extraction (KD′ = Caq/Corg) of picolinic acid is reduced. Though, at higher concentration of TOA may provide higher extraction of acid but would make the regeneration process difficult. The regeneration of the extractant loading with high concentration of acid (Cin = 0.05 kmol·m-3) will be easier (Z = 0.297 at  = 0.115 kmol·m-3) and higher distribution of acid (KD′ = 4.037) can be achieved. Less loading of the extractant with the acid (Z = 0.122 at = 0.344 kmol·m-3) results in lower distribution of acid (KD′ = 0.714) and incomplete regeneration of the extracting agent.

Figure 4. Back-extraction isothermal curve of picolinic acid using TOA in 1-decanol



Datta, D.; Kumar, S. Reactive Extraction of Glycolic Acid Using Tri-n-Butyl Phosphate and Tri-n-Octylamine in Six Different Diluents: Experimental Data and Theoretical Predictions. Ind. Eng. Chem. Res. 2011, 50, 3041-3048.

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