Avaliação ambiental dos processos de obtenção de nanocristais de celulose a partir de fibras de dendê

Abstract

In order to add value to the biofuel chain, palm fiber represents a potential source of crystalline nanocellulose (NCC), which has physicochemical properties that are very promising for application in new materials. The purpose of this study is to assess the environmental impacts of obtaining 1g of NCC, in laboratory scale, from palm pressed fiber by two different macroprocesses: 1 - pre-treatment with acetosolv pulping and 2 – pre-treatment with ethanosolv pulping. The study was conducted based on the ISO 14041 and 14044 approach for Life Cycle Assessment (LCA), using ReCiPe Hierarchist Midpoint for the following impact categories: climatic changes, terrestrial acidification, water depletion, human toxicity and freshwater and marine eutrophication. The production of NCC palm oil covers the processes of grinding, sieving, steam blasting, acetosolv pulping (acetic acid catalyzed with hydrochloric acid) or ethanosolv pulping (ethyl alcohol catalyzed with sodium hydroxide), bleaching with hydrogen peroxide, hydrolysis with sulfuric acid, centrifugation/ultrasound and dialysis. It was observed that in obtaining NCC by process 1 (with acetosolv pulping), the most environmentally impacting single process for freashwater eutrophication and human toxicity was bleaching, due to the energy consumption and use of hydrogen peroxide, respectively. For marine eutrophication, the palm cracking was the most significant step due to cultivation process. Regarding climatic changes, the most striking process was the centrifugation due to the high energy consumption, for terrestrial acidification was the hydrolysis by the use of sulfuric acid and for water depletion, the dialysis due to its high consumption of water. In obtaining NCC by process 2 (with ethanosolv pulping), the most environmentally impacting single process for all six assessed categories was bleaching due to the high energy and water demand and reagent consumption. The comparison of both macroprocesses reveals that obtaining NCC by the ethanosolv pulping method (process 2) is more impacting for all assessed categories than the same process carried out with acetosolv pulping (process 1). The acetosolv pulping is a quite strong process but also a very efficient one, so the subsequent steps can be carried out in tender conditions without compromising the quality of the final NCC obtained, reducing its environmental impacts. Meanwhile, ethanosolv pulping is a milder but less efficient process, so post-ethanosolv steps should be much longer and much more severe than post-acetosolv steps to ensure a NCC of similar properties and quality, increasing its environmental impacts. Thus, obtaining NCC by process 1 (with acetosolv pulping) is less harmful to the environment than by process 2 (with ethanosolv pulping).