Pirólise de cascas de grãos de girassol: determinação de parâmetros cinéticos, e influência da atmosfera (H2 ou He) e da catálise ex-situ (HZSM-5) na geração de vapores

Abstract

The growing population, along with societal modernization, presents numerous challenges. Among these challenges is the need to find alternatives to replace the primary source of energy and chemicals, petroleum, since it is fossil-based and unsustainable. Biomass plant residues emerge as a promising source of resources to meet some of this demand. There are several methodologies for converting biomass into energy and/or valuable chemicals. The thermochemical conversion process known as pyrolysis can generate these products in solid, liquid, and gaseous phases, and it exhibits a high level of selectivity depending on process conditions. This study aimed to perform the pyrolysis of sunflower seeds husks (SSH) in order to analyze the starting material and the reaction products. Additionally, a kinetic study to obtain triple parameters (activation energy, reaction model, and frequency factor) to better understand the pyrolysis process. The pyrolytic kinetics of SSH used previous activation energy data and, based on the so-called kinetic compensation effect, calculated a mean frequency factor value of 3.517x109 1/s; the two-dimensional reaction model (D2), based on diffusion phenomena, for which the mathematical representation is [-ln(1-α)]-1, was the one that best represented the pyrolysis of SSH; and the calculated kinetic parameters were efficient in predicting the experimental kinetic behavior, as their deviations showed low values, with a maximum magnitude of 6%. Analytical fast pyrolysis tests of SSH were conducted under four different conditions: pure SSH in a helium atmosphere (SHHe); pure CGG in a hydrogen atmosphere (SHHi); CGG with ex-situ zeolite in a helium atmosphere (SH-ZeHe); and SSH with ex-situ zeolite in a hydrogen atmosphere (SH-ZeHi). HZSM-5 zeolite was used as the catalyst. For each mentioned experimental condition, tests were conducted at temperatures of 450, 550, and 650 °C, and the pyrolytic vapors were analyzed in a Py-GC/MS system. The results demonstrated that the condition with the greatest effect, regarding the organic functions present in the volatiles and also the selectivity distribution, especially for hydrocarbon formation, was the use of the zeolitic catalyst. The catalyst promoted deoxygenation reactions of the pyrolytic volatiles, enabling the generation of improved vapors; in SH-ZeHi, the production of hydrocarbons with a maximum yield of 42 % peak area was achieved at 550 °C. The reaction temperature and gas atmosphere played secondary roles; the higher temperature (650 °C) resulted in greater quantities of volatiles; while the hydrogen atmosphere yielded results similar to the helium atmosphere. Based on the results, it is possible to affirm that the mathematical representations found for the studied pyrolytic reactions are efficient and that this lignocellulosic biomass residue (SSH) can be used as a source of energy and chemicals highly demanded by society, emerging as a cleaner and more sustainable alternative to the use of fossil resources. This study is pioneering in calculating the kinetic triple for SSH via the kinetic compensation effect, and in investigating hydropyrolysis and catalytic hydropyrolysis for the residues in question.