Aproveitamento do bagaço de malte na produção de polpa celulósica e carboximetilcelulose

Abstract

Brewer’s spent grain represents 85% of solid waste generated in the brewing process that only in Brazil, corresponding to an annual output of 2.6 million tons, consisting mainly of cellulose (16-21%), hemicellulose (15-29%), lignin (19 - 28%) and protein (24 - 39%). This material is employed basically like animal feed. In this context, this work aimed to extract pulp from spent grain and employ it in the synthesis of carboxymethylcellulose utilizing microwave reactor. Initially BSG dry with a particle size less than or equal to 1 mm was subjected to alkaline treatment followed by bleaching in which it was evaluated, employing 23 factorial design with center point and response surface methodology, the influence of temperature (70- 80 ° C), time (3-4 h) and ratio of bleach solution/pulp (40/1- 50/1 (v / m)) the properties of pulps obtained. The synthesis of carboxymethylcellulose (CMC) was performed under heterogeneous conditions in two stages: the alkalization and etherification. In the alkalinization step, isopropanol was used and 40% NaOH solution at a ratio of 1.6 g of NaOH per g of pulp for 15 minutes. The etherification step was performed in a microwave reactor which it was evaluated, employing 23 factorial design with center point and response surface methodology, the effect of the ratio of monochloroacetic acid/pulp (g/g) (2.5-5), temperature (70-90 ° C) and time (2.5-7.5 min) in the average content of carboxymethyl group per anhydrous glucoside unit (degree of substitution). The degree of substitution and the distribution of carboxymethyl groups in carboxymethylcellulose samples were determined by proton nuclear magnetic resonance (RMN 1H). Principal component analysis was applied to group samples of carboxymethylcellulose with degree of substitution and distribution of carboxymethyl groups similar. The chemical modifications that occurred after the carboxymethylation of cellulose pulp were verified by Infrared Spectroscopy Fourier transform (FTIR). The optimum bleaching conditions were obtained using the relationship bleach solution/pulp (v/m) 50/1, temperature and time of 80 ° C and 3.66 h, respectively, resulting in bleached pulp with 93.80, 86.39, 3.40, 1.67% cellulose, α-cellulose, hemicellulose and lignin, respectively, and viscosity of 10.55 cP. The removal of non-cellulosic constituents was confirmed by infrared spectroscopy (FTIR), X-ray diffraction and thermal analysis. The optimum conditions for etherification were obtained with time 7.5 min., ratio of 5 g of monochloroacetic acid per gram of pulp and temperature of 70 °C, allowing the obtaining of carboxymethylcellulose with degree of substitution equal to 1.44. Synthesis of carboxymethylcellulose was confirmed by spectroscopy of RMN 1H and infrared. By employing principal component analysis of the three groups of samples was defined according to the degree of substitution and distribution pattern of carboxymethyl groups. Based on the presented results, it is concluded that the brewer’s spent grain has a potential for pulp production that can be employed in the synthesis of carboxymethylcellulose utilizing a microwave reactor.