(242d) Reactive Extraction of Nicotinic Acid Using Tri-n-Octylphosphine Oxide (TOPO) Dissolved in a Binary Diluent Mixture

Reactive
Extraction of Nicotinic Acid using Tri-n-Octylphosphine Oxide (TOPO) Dissolved in a Binary Diluent Mixture

Sushil Kumar^1*  Dipaloy Datta¹ and
B V Babu²

¹Department
of Chemical Engineering

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

*Corresponding
Author:

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

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

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

Abstract

Nicotinic acid (pyridine-3-carboxilic
acid) is a water-soluble vitamin and precursor to coenzymes (NADH, NAD⁺,
NADP⁺, and NADPH) which serves an important role in the redox reactions taking place inside the human living cells
for the metabolism activity. Niacin helps in both DNA repair and formation of
steroid hormones in the adrenal gland. A deficiency of niacin can cause
pellagra, a serious disease that has paralyzed mankind for centuries. Also, a
mild deficiency slows down the metabolism of the body, causing decreased tolerance
to cold (Kumar and Babu, 2009). The production
of organic acids by biochemical fermentation route is comparatively a clean and
a green technology. The biosynthesis process produces nicotinic acid at a lower
rate and also the concentration of the acid in the fermentation
broth is found to be very low. Therefore, to make the fermentation route efficient
and effective, there is a need to develop novel fermentation processes and efficient
separation techniques. The reactive extraction with higher distribution
coefficient is proposed to be an efficient and eco-friendly primary separation
process (Kertes and King, 1986; Kumar and Babu,
2008).

Phosphorus-bonded, oxygen containing
extractants have a phosphoryl
group and a stronger Lewis basicity than those of carbon-bonded,
oxygen-containing extractants. Phosphorus-bonded, oxygen-containing extractants
can only co-extract small amounts of water and show low solubilities
in water. When organophosphorus extractants
are used, the solvation has a higher specificity (Kertes and King, 1986).
These extractants are dissolved
in organic diluents (ketones, alcohols, hydrocarbons) to provide appropriate
physical properties (density, viscosity, etc.,) to the extractant-diluent
system. The diluents are categorized in two groups based on their activity: (i) inactive (inert) diluents, and (ii) active diluents
(modifiers). The presence of polar functional groups in the modifiers enables
them to act as better solvation medium for the acid-extractant complex by the
formation of hydrogen bond. Also,
a modifier enhances the extracting power of organophosphoric
extractant as compared to an inert diluent in the
extraction of organic acids (Mariya et al.,
2005; Yankov et al., 2004).

The present work is aimed to
intensify the recovery of nicotinic acid using reactive extraction with tri-octyl
phosphine oxide (TOPO) in a diluent mixture
consisting of an active and an inactive diluent [MIBK + kerosene (1:1
v/v)]. The aqueous solutions of nicotinic acid are prepared in the concentration
range 0.02 to 0.12 mol/L
using distilled water. Organic solutions
are prepared by varying the concentration of TOPO (0.1 and 0.5 mol/L)
in the mixture of MIBK + kerosene (1:1 v/v). MIBK is used as the active diluent
(modifier). Kerosene is used as inactive diluent to control density and
viscosity of the organic phase. The extraction equilibrium
experiments are carried out with equal volumes (20 ml) of the aqueous and
organic solutions in conical flasks of 100 ml and shaken at 100 rpm for 8 hours
in a temperature controlled reciprocal shaker bath (HS 250, Remi
Labs, India) at constant temperature (298 K). After attaining equilibrium, the
mixture of aqueous and organic phases is kept for separation in separating
funnel (125 ml) for 2 hrs at 298 K. After separation of both phases, the
aqueous phase acid concentration is analyzed by titration using NaOH solution of 0.01 N with phenolphthalein as an
indicator and also by UV-Vis Spectrophotometer (Evolution 201, Merck, India at
262 nm). The acid concentration in the organic phase is calculated by mass
balance. The equilibrium pH values of
aqueous solution are measured by a digital pH-meter
(PCT 40, ArmField Instruments, UK).
The experimental data are analyzed by calculating distribution coefficient (K_D = C_org/C_aq),
degrees of extraction [E = K_D / (1 + K_D)] and loading ratios (Z = C_org/
).

To determine the physical
extraction parameters (partition coefficient = P and dimerization
constant = D), the following equation is fitted linearly in the Origin
8.0 (software package).

                                                                                           (1)

The values of
of nicotinic acid with diluent mixture are found to be
in the range of 0.074 to 0.149 which are less than one.  The values of P and D are obtained as
0.0598 and 115.66, respectively. The use of non-polar solvents such as kerosene
in the extraction of carboxylic acid at higher initial acid concentration may also
lead to the formation of a stable emulsion and dimer
in the organic phase. Therefore, a modifier (active diluent) is generally added
with the inert diluent to avoid the formation of a stable emulsion and dimer in the organic phase.

The equilibrium chemical
extraction experiments for the recovery of nicotinic acid is carried out using
TOPO dissolved in MIBK + kerosene (1:1 vv). The extraction
degree decreases with an increase in acid concentration in the aqueous phase.
This may be due to the lower amount of TOPO used in the initial organic phase,
and TOPO concentration is found to be a limiting parameter for the extraction. Generally,
for a high initial acid concentration, the
distribution coefficient (K_D)
may decrease with an increase in the acid concentration in aqueous solution using
TOPO with diluent mixture. The
distribution coefficients (K_D) and degree of extraction (E)
are found to increase with an increase in TOPO concentration (0.10
to 0.50 mol/L). TOPO/diluent
system favors the formation of ?not overloaded' complexes of polar acid-TOPO
structures with the Z factors restricted mainly between 0.032 and 0.684. With TOPO (0.365 mol/L) dissolved in MIBK + kerosene
(1:1 v/v), the maximum value of K_D
is to be 4.168 for an acid concentration of 0.02 mol/L.

The experimental results are also
interpreted in terms of the distribution coefficient of acid by chemical
extraction (
) with extractants (TBP and
TOA) dissolved in diluent mixtures and given by Eq. (2).

                                                                                             (2)

where ν is the volume fraction of
diluent mixture.

The overall distribution coefficient (
) by physical and chemical extraction is obtained from
the following equation.

                                                                                            (3)

The Z values less than 0.5 indicate a formation of
(1:1) acid-TOPO complex in the organic phase. Therefore, with assumption of (1:1) acid-extractant complexes in the
organic phase, the following model equations of reactive extraction mechanism
are developed incorporating the effect of physical extraction.

                       (4)

The m is the
loading of acid in organic phase by diluent mixture.

                                                                                                                 (5)

The plots of
 versus [HC] yield
a straight line with a slope representing the corresponding K_E value of the reactive
extraction. The equilibrium
complexation constants (K_E)
predicted by the Eq. (4) are presented with the coefficient of
determination (R²) and
standard deviation (SD). The model
predicted values of K_E are
showing good correlation with R²
> 0.98 and maximum value of SD =
0.092. The highest value of K_E
is found for lower acid and extractant concentration which shows a faster mass
transfer of solute into the organic phase.

References

(1)  
Kertes, A. S.;
King, C. Extraction Chemistry of Fermentation Product Carboxylic Acids. Biotechnol. Bioeng. 1986,
28, 269-282.

(2)   Kumar, S.; Wasewar, K.L.; Babu, B.V. (2008) Intensification of
Nicotinic Acid Separation using Organophosphorous
Solvating Extractants: Reactive Extraction. Chem. Eng. Technol. 31, 1584-1590.

(3)   Kumar, S., Babu, B.V.
(2008) Process intensification for separation of carboxylic acids from
fermentation broths using reactive extraction, J. Fut. Eng. Technol. 3, 19.

(4)  
Kumar, S.; Babu B. V. Process
Intensification of Nicotinic Acid Production via Enzymatic Conversion using
Reactive Extraction. Chem. Biochem. Eng. Q. 2009, 23, 367-376.

(5)  
Mariya, M., Albet, J., Molinier, J., Kyuchoukov, G. Specific Influence of the Modifier
(1-Decanol) on the Extraction of Tartaric Acid by Different Extractants. Ind. Eng. Chem. Res. 2005, 44, 6534-6538.

Figure 1. Physical equilibria for extraction of
nicotinic acid at 298 K

Figure 2. Equilibrium complexation constant (KE)
determination for extraction of nicotinic acid at 298 K with TOPO in MIBK +
kerosene (1:1 v/v)