Thermogravimetric Analysis and Kinetic Study on Catalytic Pyrolysis of Rice Husk Pellet using Its Ash as a Low-cost In-situ Catalyst

Abstract

The thermogravimetric behaviors and the kinetic parameters of uncatalyzed and catalyzed pyrolysis processes of a mixture of powdered raw rice husk (RRH) and its ash (RHA) in the form of pellets were determined by thermogravimetric analysis at three different heating rates, i.e., 5, 10, and 20 K/min, from 303 to 873 K. This research aimed to prove that the rice husk ash has a catalytic effect on rice husk pyrolysis. To investigate the catalytic effect of RHA, rice husk pellets (RHP) with the weight ratio of RRH:ARH of 10:2 were used as the sample. Model-free methods, namely Friedman (FR), Kissinger-Akahira-Sunose (KAS), and Flynn-Wall-Ozawa (FWO), were used to calculate the apparent energy of activation ( ). The thermogravimetric analysis showed that the decomposition of RHP in a nitrogen atmosphere could be divided into three stages: drying stage (303-443 K), the rapid decomposition stage (443-703 K), and the slow decomposition stage (703-873 K). The weight loss percentages of each stage for both uncatalyzed and catalyzed pyrolysis of RHP were 2.4-5.7%, 35.5-59.4%, and 2.9-12.2%, respectively. Using the FR, FWO, and KAS methods, the values of for the degrees of conversion (a) of 0.1 to 0.65 were in the range of 168-256 kJ/mol for the uncatalyzed pyrolysis and 97-204 kJ/mol for the catalyzed one. We found that the catalyzed pyrolysis led the to have values lower than those got by the uncatalyzed one. This phenomenon might prove that RHA has a catalytic effect on RHP pyrolysis by lowering the energy of activation.

Kinetics of In-Situ Catalytic Pyrolysis of Rice Husk Pellets Using a Multi-Component Kinetics Model

“…Besides that, the amount of hemicellulose, cellulose, and lignin in rice husk and the comparation from other studies are presented in Table 2. More complete information regarding the characterizations of rice husk can be seen in our previous report [10].…”

“…The value of di/dt in Equation ( 9) is calculated by the finite difference method. Furthermore, optimization of an objective function (OF) is carried out to obtain the values of the kinetic parameters based on initial guesses by minimizing the sum of the squared errors between the calculation results and the experimental data as follows [16,17,27]: (10) in which J is the data points (in the range of 1000-1600). Optimization is performed using the differential evolution method, which has advantages in terms of accuracy, efficiency, and reliability for complex and highly nonlinear objective function optimization.…”

“…The crystalline structure of the ash dominated by silica (SiO2) was analyzed using XRD (Figure 1(b)), which showed that the ash had an amorphous silica structure with a crystallinity index of 30% [10]. This structure could increase the surface area of the ash.…”

“…According to Shen [39], the high content of amorphous silica in rice husk ash contributes to CO2 adsorption and increases the hydrogen-rich gas yielded. More detailed information regarding the characterization of the ash can be seen in our previous report [10].…”

“…Biomass-ash-based catalysts, which are inexpensive, can also be used in the pyrolysis process. Rice husk ash, containing high amount of silica and having a large mesoporous surface area, can be added to rice husk and has the catalytic effect of decreasing the activation energy of pyrolysis [3,10]. It can also improve the yields and quality of liquid products [11].…”