Effects of Na-containing salts on releasing and kinetic characteristics of gas phase products during corn stover pyrolysis

As a renewable energy source that is expected to replace fossil fuels, biomass energy is attracting more and more attention. Pyrolysis is considered to be one of the cutting-edge technologies for converting biomass energy into high value-added products such as gas, tar and biochar, but because of the low energy density of biomass energy, it needs to be pretreated prior to pyrolysis reaction to improve the quality of the products. The products are often regulated by adding catalysts during biomass pyrolysis, among which alkali metal salt catalysts are widely concerned due to their advantages of high efficiency and low cost. In view of the serious air pollution caused by corn stover burning in the northeast of China recently, in this work corn stover was obtained, and the influence of Na2CO3 and NaCl on the pyrolysis characteristics and gaseous products releasing kinetics were studied in a micro-fluidized bed reactor coupled with mass spectrometer (MFBR-MS), with the conditions of with and without Na2CO3 or NaCl addition at 550, 600, 650, 700 and 750 ℃, respectively. The purpose of this work was to grasp the catalytic process of Na2CO3 and NaCl on the gaseous products during corn stover pyrolysis and to better play its catalytic role to obtain the products desired. Besides, in order to obtain the reaction kinetic parameters of different gaseous products accurately, the kinetic parameters of single-component gas were calculated by using the Isothermal Model Fitting Method. The results showed that under the same temperature, the conversion rates of CO, CO2 and CH4 during corn stover pyrolysis with Na2CO3 addition increased significantly, which indicated that Na2CO3 significantly promoted the generation of carbonaceous gaseous products. However, the conversion rate of H2 during corn stover pyrolysis with NaCl addition increased significantly. When the temperature increased, all the amount of each gas phase product increased, especially the CO amount increasing most. Meanwhile, each gas phase product tended to release simultaneously, indicating that the Na-containing salts could promote the reaction. Among them, the releasing rates of CO, CO2 and CH4 all increased with Na2CO3 addition, indicating that it promoted the generation of carbonaceous gaseous products. Besides, the releasing rate of H2 increased with NaCl addition, indicating that NaCl promoted the generation of H2. The results of activation energies of different gas phase products during corn stover pyrolysis showed that the activation energies for different gaseous products were different, and the activation energies for CO and CO2 were generally smaller than that of CH4 and H2, which indicated that CO and CO2 were easier to generate than CH4 and H2. For CO and CO2, the addition of Na2CO3 and NaCl generally reduced the activation energies. The above results showed that during the corn straw pyrolysis, the conversion rates of carbonaceous gaseous products or H2 could increase with Na2CO3 or NaCl addition significantly. We hope the method of converting corn stover into combustible gases via pyrolysis discussed here could provide a method for the treatment of corn stover.