Study on microwave pyrolysis properties of bamboo by using activated carbon-supported iron catalyst

In the present work, the application of activated carbon(AC) supported iron catalyst(Fe/AC) into the microwave pyrolysis of bamboo was proposed based on the advantages of the activated carbon as catalyst support and its good microwave absorbing capacity. The influence of the catalyst on the microwave-assisted bamboo pyrolysis characteristics was revealed via the temperature-rising characteristics, the product distribution and the properties of the pyrolysis products. This work was helpful to the resource utilization of biomass. The catalysts were prepared via the incipient wetness method. About 30 g of the obtained AC was impregnated in the ferrous acetate (Fe(Ac)2) solution, with the following amounts of Fe(Ac)2: 0.01, 0.05, 0.10 and 0.15 mol, respectively. The dried activated carbon, containing Fe(Ac)2, were then heated in an electric furnace at 500℃ in the nitrogen atmosphere for 10 min. The obtained activated carbon catalysts were noted as Fe/AC-0.01, Fe/AC-0.05, Fe/AC-0.10 and Fe/AC-0.15, according to the addition amount of Fe(Ac)2, respectively. The bamboo raw materials and the bamboos mixed with AC, Fe/AC-0.01, Fe/AC-0.05, Fe/AC-0.10 and Fe/AC-0.15 were marked as PB, BC-0, BC-0.01, BC-0.05, BC-0.10 and BC-0.15, respectively. The catalysts were characterized by applying many ways, including an ICP-OES for the determining of the metal element contained in catalyst, Boehm method for the analysis of the acid functional group on the catalyst surface, a micromeritics instrument for analyzing the pore texture of the catalyst and an X-Ray Diffraction (XRD) for the components on the surface of the catalyst. The bio-oil compositions obtained from microwave pyrolysis of bamboo with and without catalysts were determined by using gas chromatograph-mass spectrometer (GC-MS). The compositions of the gaseous product were characterized by GC. The result indicated that the activated carbon supported iron catalyst could exert an effect on the microwave pyrolysis of bamboo to a certain extent. The addition of the catalyst increased the heating rates and the maximum reaction temperatures of bamboo under the microwave irradiation. In comparison to the bamboo raw material, the maximum temperature of samples with the addition of the Fe/AC-0.15 catalyst under microwave condition was increased by 54.38%. The bio-oil consisted mainly of acids, carbonyl compounds, phenols, furans and alcohols, and the percent of acid in bio-oil was accounting for 48%, so they were the dominant compositions of the bio-oil. After the addition of the catalysts, the contents of the acids and carbonyl compounds were increased accompanied with the increase in the contents of the phenols and furans, indicating the catalysts had a positive influence on the cracking of the ring compounds in bio-oil to form the linear-chain compounds. The contents of the acids and carbonyl compounds were increased with the increase in the loading amount of iron. The production of the gaseous products was promoted by the catalyst and the yields of the pyrolysis gas were increased with the increasing in the loading amount of iron. The maximal yield of the gas could reach up to 69.11% when the Fe/AC-0.15 catalyst was used. The catalyst was favorable to the formation of syngas and the contents of the syngas were increased with the loading amount of the iron. The maximum volumetric content and yield of the syngas (CO+H2) in pyrolysis gas could reach up to 77.24% and 17.5 mmol/g, respectively. © 2019, Editorial Department of the Transactions of the Chinese Society of Agricultural Engineering. All right reserved.