Produção de etanol celulósico e resíduo lignocelulósico a partir da palha da cana-de-açúcar: eficiência, aspectos de saúde e segurança e alternativas para agregar valor à rota de segunda geração

Abstract

Currently, second-generation technology (2G) is the industrial route that is being developed with the potential to couple the demand for biofuels and bioproducts. The technology studied in this work is based on non-food biomass processing for sugar and lignocellulosic residue extraction, with sugars being used for cellulosic ethanol production, and residue used as fuel in boilers for steam and electricity production. However, the use of lignocellulosic residue only for the generation of steam and energy is limited in the face of many opportunities that this feedstock presents. Thus, it is necessary to define how it can be better utilized. This study had three objectives: 1) to compare the main results obtained from the production of cellulosic ethanol using sugarcane straw on an industrial scale to the literature, taking into account the following processes: pre-treatment, enzymatic hydrolysis and fermentation steps; 2) to characterize the lignocellulosic residue from sugarcane straw, the biochar obtained from its pyrolysis and evaluate the effects of final process temperature and heating rate on the yield of pyrolysis products, and 3) to identify the main process risks in a classified area of a 2G ethanol industry using the Hazard and Operability (HAZOP) Study. When compared to the literature, the industrial scale production of cellulosic ethanol from sugarcane straw revealed a global and per area efficiency similar to several studies related to the 2G route, with production of 200 liters of cellulosic ethanol per ton of processed biomass. The chemical characterization of lignocellulosic residue, performed by Fourier Transform Infrared Spectrometry, showed a spectrum compatible with the presence of phenolic and aliphatic hydroxyls, ketones, carbonyls, p-coumaric acid, ether, guaiacyl rings, synapyl and p-coumaril units and aromatic compounds. When considering temperature (500°C and 700°C) and heating rate (5°C/min and 15°C/min), the best yield of bio-oil (39.0% w/w) was obtained at 700°C and 15°C/min, showing that higher temperatures and heating rates are necessary for bio-oil production, when compared to the lower temperatures (500°C) and heating rates (5°C/min) used for the best yield of biochar (40.3% w/w). Finally, the HAZOP study revealed that even for the most critical process system (distillation of ethanol within its limits of explosiveness), only 6.5% of the scenarios were considered as "Moderate risk", compared to 93.5% classified as "Acceptable risk". In conclusion: 1) the production of 2G ethanol from sugarcane straw in industrial scale has shown potential for their commercial development; 2) higher temperatures and heating rates are necessary for best yield of bio-oil; and 3) the production of 2G ethanol, considering healthy and safety according to HAZOP, is considered safe. Continued investment in research is essential if full commercialization of 2G ethanol and lignocellulosic residue is to be achieving within the next decade.