Aconitic acid recovery from sugar-cane stillage: From the modeling of the anion-exchange step to the conception of a novel combined process

ABSTRACT

Sugarcane stillage is rich in tri-carboxylic aconitic acid. To study its purification through anion-exchange, selectivity coefficients between aconitate and the major competing minerals were determined on a weak-base resin for different pH. Simulation of solutes separation in the column, using mass conservation equations and equilibrium theory, confirmed that resin in sulfate form and pH = 4.5 led to the best separation performances, and showed that a preliminary chloride removal up to 0.5 g L⁻¹ was the most profitable to increase the ionic exchange capacity for aconitic acid. Demineralization of a real stillage by conventional electrodialysis followed by the optimized ion-exchange step led to an aconitic acid-rich extract.

KEYWORDS:

• Sugarcane stillage
• aconitic acid
• ion-exchange
• low-pressure chromatography
• electrodialysis

Nomenclature and units

BV	=	resin Bed Volume (in liter of resin or LR)
Ci	=	mass concentration of i in solution (g L−1)
Ci0	=	initial mass concentration of i in solution, for batch experiments (g L−1)
CF i	=	mass concentration of i in the column feed (g L−1)
Dax	=	axial dispersion coefficient in the column (m2 s−1)
DM	=	dry matter content (% w/w)
ɛ	=	Resin bed porosity (-)
FB	=	Free Base form
Kx i/j	=	Rational selectivity coefficient, considering i/j pair of anions (-)
L	=	column length (m)
m	=	resin dry mass in the column or in the closed flasks (gR) $N=\sum \left[\mathrm{i}\right]\left(\mathrm{e}\mathrm{q}{\mathrm{L}}^{-1}\right)$
P	=	aconitic acid purity with respect to DM (% w/w)
Papp	=	aconitic acid apparent purity with respect to global anions content analyzed in the solution (% w/w)
qi	=	mass retention capacity of solute i on the resin (g LR−1 or g gR−1)
qmax Aaco	=	maximal mass retention capacity of aconitic acid on the resin (g LR−1 or g gR−1)
qtot = $\sum \left[\mathrm{R}-\mathrm{i}\right]$	=	total ionic exchange capacity of the resin (eq LR−1 or eq gR−1)
RAaco	=	Aconitic acid recovery rate in elution fractions (%)
u	=	linear velocity of the fluid assumed uniform on a section of the column (m s−1)
V	=	volume of solution for equilibrium measurements in closed flasks (L)
V0	=	void volume in the column (L)
Vsi	=	stoichiometric or average breakthrough volume for the solute i (L)
Vsat	=	saturation volume passed until having at the column outlet C = 0.95 CF (L)
$x_i$	=	ionic fraction of solute i in solution (-)
$y_i$	=	ionic fraction of solute i in the resin (-)
YAaco	=	Aconitic acid regeneration yield during elution step in column (%)
YSat Aaco	=	Aconitic acid yield during saturation phase (%)
[i]	=	solute i concentration in solution (eq L−1)
[R-i]	=	solute i concentration in resin phase (eq LR−1 or eq gR−1)

Acknowlegments

Authors wish to thank Tereos, eRcane for their financial and technical support especially for HPIC analyses.