Reactive separation of p-nitro phenol (PNP) from aqueous solution using tri-n-butyl phosphate: equilibrium and COSMO-RS studies

ABSTRACT

The present study is aimed to optimized diluent type, tri-n-butyl phosphate (TBP) composition and temperature for the reactive extraction of p-nitro phenol (PNP) in two different PNP concentration ranges [(0.00036–0.00646) kmol·m⁻³ and (0.00646–0.01437) kmol·m⁻³] as found in industrial effluents. 1-Octanol is investigated as the best diluent with TBP based on COSMO-RS theory. Equilibrium study based on mass action law is performed to find the insights of extraction mechanisms, equilibrium constant (K = 295.12 k·mol⁻¹) and stoichiometry (m:n = 1:1) as also confirmed by FTIR. Thermodynamic parameters, enthalpy (ΔH°), and entropy (ΔS°) are determined 27.51 K J mol⁻¹ and −50.21 J mol⁻¹ K⁻¹, respectively.

KEYWORDS:

• p-Nitro phenol (PNP)
• reactive extraction
• equilibria
• COSMO-RS and thermodynamics

Nomenclature

PNP	=	p-nitro phenol
TBP	=	tri-n- butyl phosphate
% E	=	degree of extraction
K	=	equilibrium constant
n	=	Complex ratio
(Emisfit)	=	hydrogen bonding free energy
(EHB)	=	Van der Waals energy
${\sigma }^{\prime }$	=	coefficient for electrostatic misfit interactions
$a_{eff}$	=	effective contact area between two surface segments
CHB	=	Coefficient for hydrogen bond strength
${\sigma }_{HB}$	=	threshold for hydrogen bonding
${\tau }_{vdw}$	=	element-specific vdws coefficient
${\tau }_{vdw}^{\prime }$	=	element-specific vdws coefficient
ΔH°	=	change in enthalpy
ΔS°	=	change in entropy
HPh	=	concentration of undissociated PNP in aqueous phase
$\overline{HPh}$	=	concentration of PNP in organic phase
$\overline{TBP}$	=	TBP concentration in organic phase
Ka	=	dissociation constant
pKa	=	acidic strength of phenol
p	=	partition coefficient
KD	=	distribution coefficient
φ	=	volume fraction of solvent
Z	=	loading ratio
R	=	universal gas constant, 8.314 J−1mol·K
T	=	temperature in K
H- bond	=	hydrogen bond

Acknowledgments

The authors thank director, Motilal Nehru National Institute of Technology, for providing the research facility to carry out the experiments. The authors also thank Ewing Christian College, Allahabad University, for providing the FTIR facility.

Conflict of interest

The authors declare no conflict of interest.

Correction Statement

This article has been republished with minor changes. These changes do not impact the academic content of the article.