Resumo:
This work aimed to synthesize an expanded polyurethane (EPU) based on crude glycerol (CG), and another based on a mixture of vegetable oil (70%) and pure glycerin (PG) (30%), as an alternative to petroleum-derived polyol, and to evaluate its efficiency as an adsorbent of the anionic dye amaranth from aqueous solution. CG was obtained from a biodiesel plant and was characterized by Fourier Transform Infrared Spectrophotometer (FT-IV), determination of the hydroxyl number (IOH) and free glycerol content in the crude waste. The IOH and free glycerol values found for CG were, respectively, 505 mg KOH/g and 32.0±0.29%. EPUs were synthesized and characterized by apparent density, FT-IV, thermogravimetry (TGA) and zeta potential (pHpcz). The EPU synthesized with CG (EPU-CG) presented higher apparent density (130.80 Kg m-3) in relation to EPU synthesized with the mixture of vegetable oil and PG (EPU-Mist) (29.7 Kg m-3), and proved to be less thermally stable. However, EPU-CG showed better performance in the adsorption tests, with more than 90% removal of amaranth (6 mg L-1) at pH 3 and room temperature, while EPU-Mist obtained 52.7% removal under the same conditions of study. The pHpcz values found were, respectively, 6.27 and 7.15 for EPU-Mist and EPU-CG. During the adsorption tests, the influence of pH, contact time and initial dye concentration were evaluated, and both EPUs obtained the best removal percentage at pH 2 and the lowest initial dye concentrations. The data obtained experimentally in the tests were adjusted to mathematical models of isotherm and adsorption kinetics. Both EPUs showed better fit to the Langmuir isotherm and to the pseudo-second order kinetics model. The maximum adsorption capacity (qmax) calculated for EPU-CG and EPU-Mist was 0.866 and 0.303 mg g-1, respectively. The reuse tests showed good performance for five consecutive cycles for EPU-CG and for three cycles for EPU-Mist. The results obtained suggest that glycerol is a raw material with great potential to replace petroleum-derived polyols in the synthesis of polyurethanes. However, its large-scale application still requires broader studies, in addition to the need for adjustments in the polyurethane formulation to increase the adsorption capacity.
