Analysis of the pyrolysis characterization of biogas residue based on TG-FTIR-MS coupling technique

Pyrolysis characteristics of biogas residue can provide some ideas for resource utilization. In this study, the industrial and elemental analyses were conducted on five types of biogas residue raw materials, in order to explore the basic properties of biogas residue. The results showed that there was a high ash content of CMBR, whereas, the volatile content reached over 60% in the other types of biogas residue, except for CMBR. It infers that a higher proportion of biological oil and pyrolysis gas generated during the pyrolysis process. Then, TG-FTIR-MS was used to further evaluate the characteristics of different types of biogas residue raw materials. The experimental results show that the pyrolysis was divided into three stages: adsorption water evaporation (25-220 ℃), volatile evaporation (220-450 ℃), and carbonization (450 to 800 ℃). The weight loss rate was ranked in the order of STBR, SBR, FTBR, PTBR, CMBR, and the maximum weight loss rate was STBR, SBR, PTBR, FTBR, CMBR, due to the different internal components of five types of biogas residues. The comprehensive pyrolysis characteristic index D value demonstrated that the thermal stability was ranked as the CMBR, PTBR, FTBR, SBR, STBR. The STBR presented the lower thermal stability more conducive to the preparation of carbon materials as some soil amendments and heavy metal adsorbents. The volatile matter was gradually precipitated after 220 ℃ to reach the peak at the highest pyrolysis weight loss rate. Then, the volatile matter content decreased to the lowest, as the temperature gradually increased to the final temperature. There was a relatively complex composition of volatile components generated by pyrolysis, particularly with the multiple peaks within the range of 1 000-4 000 cm⁻¹. Volatility analysis showed that most of them occurred within about 10 minutes of pyrolysis. The pyrolysis range of the five types of biogas residues was between 220 and 450 ℃, indicating the highest production of H₂O. The other types of small molecule gases were also produced, depending on the type of material. The SBR contained a large amount of cellulose, hemicellulose, and lignin. The pyrolysis of cellulose first underwent depolymerization and dehydration reactions to form dehydrated sugar, and then decompose to form the other compounds after a series of reactions. As a result, the output of released gases was followed by the output of CO₂, CO, H₂. The output was reduced in turn, while the output of CH₄ was the smallest. The remaining part was non-biodegradable material, and the pyrolysis process mainly involved a decarbonization reaction, as most of the organic matter was consumed in the anaerobic fermentation process of CMBR. There was no hydrogen and methane that generated throughout the entire pyrolysis process. Kitchen waste PTBR, FTBR, and STBR produced a certain amount of CH₄, due to the high proportion of C and H in organic substances, such as protein, fat, and starch in the substrate after anaerobic fermentation. Interestingly, there was a relatively high production in the total available gas of food and kitchen waste PTBR, FTBR and STBR. Therefore, the food and kitchen waste can still be used for secondary gas production and secondary utilization after anaerobic fermentation.