Bioenergia a partir da pirólise de biomassas lignocelulósicas: uma revisão sistemática da literatura

Abstract

For many years, fossil fuels were used, which during burning release many gases that are harmful to the environment as they intensify the greenhouse effect and generate abnormal warming of the planet. Other energy sources have been studied to replace these finite fuels, such as lignocellulosic biomass. There are many processes to carry out this transformation of biomass into energy, one of the most important being pyrolysis, mainly because it is the initial stage of thermochemical transformations and because it generates three products that have added value (biochar, bio-oil and biogas). Therefore, in this work, a systematic literature review article was written to understand how the pyrolysis process works and how operational parameters (temperature, residence time, heating rate and particle size) can affect yield and quality of the products generated. For the review, 33 articles were selected from 542 available in the database using review software, StArt. As a result, it was possible to identify the main trends of the last 10 years to optimize the pyrolysis process; Among them, there is: the use of pre-treatments, different forms of heating (such as microwaves and solar energy), and co-pyrolysis, which is the use of two or more biomasses at the same time. According to articles studied, temperature was the most widely evaluated parameter. The authors observed that with its increase, the biochar yield decreases, the bio-oil reaches a maximum conversion at temperatures of 500°C and the biogas increases. Furthermore, it was observed that biochar characteristics such as surface area, pH, carbonaceous content and fixed carbon are changed with increasing temperature. Different uses for this product were highlighted, in addition to its use as a biofuel, such as sequestering carbon from the atmosphere and regulating soil pH. The second parameter most evaluated by the articles was the heating rate: with its increase, the biochar yield is reduced, and bio-oil and biogas are increased. With increasing particle size, biochar and bio-oil tended to increase, while biogas tended to decrease, mainly due to the fact that the larger the particle size, the greater the internal temperature gradient and, consequently, less volatile material will be released from the biomass. The increase in residence time causes a decrease in biochar yield, and an increase in bio-oil and biogas yield. Finally, other parameters were identified that can also affect the yield and quality of the products, including the carrier gas flow, humidity and type of reactor.