Síntese de uma espuma composta de poliuretano/quitosana para adsorção do corante vermelho n° 40 em batelada e leito fixo

Abstract

Polyurethane foams (PU) may be used as the immobilization matrix for chitosan, in order to overcome/minimize the disadvantages with respect to chitosan as an adsorbent. However, the polyurethane and chitosan foams synthesized to date use conventional reagents, most of which are highly costly and non-renewable. In this context, the present study aims at the synthesis of a foam composed of polyurethane/chitosan based on a polyol derived from castor oil and its application in the removal of Food red 17 dye in batch system and fixed bed. The adsorbent was characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), mechanical tests (shear force and degree of swelling) and color analysis. Firstly, adsorption tests were performed to evaluate the effect of the amount of chitosan on PU synthesis, the effect of the amount of adsorbent (0.1 - 1 g) and the effect of pH (2 - 10). The batch adsorption study was performed through equilibrium isotherms, kinetic curves and thermodynamic parameters. In the fixed bed adsorption study, the rupture curves were constructed at different flow rates and bed heights and these parameters were optimized using the response surface methodology (RSM). The characterization indicated that the polyurethane/chitosan composite foam presented more adequate characteristics and adsorption potential than PU. In addition, the material presented a semi-crystalline structure, with adequate functional groups, high porosity and good mechanical properties. The Pseudo-second order model was suitable to represent the adsorption kinetics and the Sips model was appropriate to represent the equilibrium isotherms. The maximum adsorption capacity was 267.24 mg g-1, obtained at 328 K. The adsorption process was spontaneous, favorable and endothermic. Using identical adsorption conditions, the PU/chitosan composite foam was able to remove more than 98% of the dye from the solution, while the PU removed only 40%. The adsorption was favored at pH 2, using 1 g of adsorbent. Models for the forward curves, including Thomas, Yoon-Nelson and Bed Depth Service Time (BDST) were fitted to the experimental data. The optimum experimental condition for the adsorption of Food red 17 dye in fixed bed using PU/chitosan composite foam was 15 mL min-1 and bed height 6 cm. In this condition, the treated effluent volume was 2175 mL and the adsorption capacity of the column was 108.1 mg g-1. The results also showed that the Yoon-Nelson and BDST models accurately adjusted the experimental data under the optimal condition. The results showed that polyurethane foams are able to withstand chitosan, resulting in an adsorbent with better mechanical characteristics and high potential for removal of anionic dyes in aqueous media.