EQUILIBRIUM AND KINETIC MODELING FOR THE ADSORPTIVE REMOVAL OF FURFURAL FROM AQUEOUS SOLUTION USING LOW-COST ADSORBENT

Abstract

Furfural is a colourless, readily volatile oily liquid, with a pungent aromatic odour. Besides being used in solvent extraction processes in the petroleum refining industry, furfural has wide variety of other uses e.g. as solvent, ingredient of phenolic resins, chemical intermediate, weed killer, fungicide and also as a flavouring agent. Evaporation condensate from sulfite pulping processes used in the pulp and paper industry is a major source of furfural contamination in the effluent water streams. Levels of furfural in sulfite evaporator condensate, which represents about 15% of the wastewater flow from pulp mills, have been reported in the range of 10-1280 mg/l. Synthetic rubber plant wastewater has been found to have 1.7 g/1 furfural. At the workplace, furfural may enter the body by the respiratory as well as the percutaneous route. Furfural is an irritant of the skin, mucous membranes and respiratory track. Concentration of 1.9 to 14 ppm produces symptoms of irritation in exposed persons. In large lube units, furfural contamination in effluent water streams may reach upto 2% (w/w) furfural. Solvent extraction may be used to recover furfural from wastewater, constraints affect the ease of solvent recovery and solvent solubility in the water streams. The polymeric adsorbent XAD-4 and XAD-7 have been used for removal of furfural from pretreated and hydrolyzed plant biomass. Biological treatments for the degradation of furfural which includes aerobic and anaerobic processes. However, these processes are costly and cannot be used by small industries to treat furfural-laden wastewater. Present study deals with equilibrium and kinetic modeling for the adsorptive removal of furfural from aqueous solution using low-cost adsorbent viz. bagasse fly ash (BFA) and to explore the possibility of bagasse fly ash as a low cost adsorbent for the removal of furfural from aqueous solution. The economic feasibility and adsorptive capacity of bagasse fly ash has been also compared with activated carbon commercial grade. Proximate analysis of adsorbents showed 32.90 and 77.82 % fixed carbon in BFA and ACC, respectively. Aqueous solutions of different furfural concentrations were prepared in laboratory, using double distilled water. Batch studies were performed to evaluate the influence of various experimental parameters viz. initial pH, adsorbent dose, contact time, initial concentration and temperature on the removal of furfural. iii Optimum initial pH (pHo) of aqueous solution for furfural removal was found to be pHo:----- 5.5 for furfural-BFA system, whereas, in furfural-ACC system, change in removal was insignificant with variation in pHo. Adsorbent dose (m) of 4 g/1 and 10 g/I were found for BFA and ACC, respectively. Equilibrium time as achieved 4 h and 6 h for BFA and ACC, respectively. The adsorption of furfural onto both the adsorbents, BFA and ACC followed pseudo-second-order kinetics. Equilibrium adsorption data was analyzed by Freundlich, Langmuir, Dubinin—Raduskevich, Redlich—Peterson and Temkin isotherm equations, using regression and error analysis. Redlich-Peterson isotherm was found to best represent the data for furfural adsorption onto both the adsorbents. Adsorption of furfural on BFA and ACC is favourably influenced by a decrease in the temperature of the operation. The high negative value of change in Gibbs free energy (AG) indicates the feasible and spontaneous adsorption of furfural on BFA and ACC. iv