Análise cinética e termodinâmica da conversão térmica e termocatalítica do óleo de palma na presença de carbonatos e óxidos metálicos

Abstract

Considering the application of low-cost and easily obtained catalysts in the catalytic pyrolysis of triglyceride biomass to produce renewable hydrocarbons, this work aimed to evaluate, through thermogravimetric studies, the kinetic and thermodynamic parameters involved in the thermal and thermocatalytic conversion of palm oil using carbonate salts (Na2CO3, CaCO3 and K2CO3) and metal oxides (NiO, Al2O3 and Nb2O5). In the carbonate-catalyzed processes, the occurrence of two mass loss events during palm oil degradation was observed, suggesting that the salts act through sequential reactions, which can be attributed to alkaline hydrolysis and thermal cracking mechanisms. In contrast, in the processes catalyzed by the metal oxides, palm oil cracking occurred in a single thermal degradation event, indicating that the reactions promoted by the oxides take place simultaneously in a single reaction step. The most efficient catalysts were Na2CO3, K2CO3 and Nb2O5, which reduced the initial palm oil degradation temperature from 325 °C to 250 °C. The kinetic studies showed that the activation energy (Ea) of the non-catalytic process was concentrated in the range of 129 to 154 kJ mol–1 for the conversion range of 10% to 90%. When Na2CO3 was added to the pyrolysis process, a reduction in Ea values was observed up to 55% conversion, but after that point, Ea values increased, reaching values higher than 175 kJ mol–1. The K2CO3 and Nb2O5, when compared to the process without catalyst, reduced the Ea values throughout the conversion range studied, demonstrating a higher catalytic activity. Moreover, the thermodynamic studies indicated that the reactions promoted by K2CO3 and Nb2O5 occurred in a more controlled manner compared to the non-catalytic process, leading to the formation of structures with a higher degree of ordering and providing a lower energy expenditure in the palm oil cracking and deoxygenation reactions. Thus, the results showed that potassium carbonate and niobium oxide present potential to be used in the conversion of triglyceride biomass into biofuels and/or industrially applicable products.