Desenvolvimento de material adsorvente do resíduo da casca da acácia negra (Acacia mearnsii De Wild) para o branqueamento de óleo de arroz

Abstract

Black wattle (Acacia mearnsii De Wild) is a plant species that stands out economically in the state of Rio Grande do Sul. Its cultivation is related to the extraction of wood and tannin, activities that generate a high amount of solid waste, which end up being destined for composting or disposed of in landfills. Also in the state of Rio Grande do Sul, rice cultivation is a prominent activity, representing about 70% of all national production. In the processing of this grain for the production of white rice, bran is generated as a residue, which is the raw material for the extraction of crude rice oil. However, crude rice oil has impurities in its composition, which must be removed during refining. Among the refining steps, there is bleaching, which aims to remove compounds that affect the color and quality of rice oil, where adsorbent substances such as activated earth and activated carbon are used. In this context, the objective of the present work was the production of adsorbents from the ground and dried black wattle bark residue, chemically treated with NaOH and modified to activated carbon through pyrolysis in a nitrogen atmosphere, which were applied in the process bleaching of neutralized rice oil. The adsorbents produced were characterized in terms of real density and bulk, particle diameter, porosity of the particle bed, immediate analysis (moisture content, ash, volatiles and fixed carbon), TGA, DRX and specific surface area (BET). The neutralized oil and bleached oils were characterized in terms of peroxides, acidity, carotenoids, color and ɣ-oryzanol. As a result, the characterizations by TGA and DRX demonstrated that both NaOH and pyrolysis caused the degradation of hemicellulose and cellulose of the acacia bark, causing a more amorphous structure. The treatments also reduced the particle diameter from 121.7 µm for the fresh shell to 41.7 µm for the activated carbon produced. The specific surface area obtained for activated carbon was 204.9 m² / g. As for the fixed carbon content, there was an increase of 9.89% in the ground and dried acacia bark to 39.97% for activated carbon. It was found that in the bleaching tests, all the adsorbents produced showed a reduction for the percentage of peroxides, acidity, carotenoids, ɣ oryzanol and color. Acacia bark activated with NaOH was the adsorbent that obtained the highest percentage of reduction for carotenoids (69.43%), acidity (19.80%) and color, with the lowest loss for the content of ɣ-oryzanol (17, 5%). As for the peroxide index, the coal produced was the one that provided the highest percentage of reduction among the tested adsorbents (43.04%). From the results obtained, it is concluded that the residue of the black wattle bark from the extraction of tannins has favorable characteristics to be used as raw material in the production of adsorbent material to be used in the bleaching stage of rice oil.