Effect Of Functional Groups On Pyrolysis Characteristics Of Biomass

The total amount of biomass waste in China is increasing year by year,and as a"zero CO₂emission"fuel,the issue of harmless treatment and efficient use of biomass is gaining more and more attention.Biomass pyrolysis is one of the most efficient ways to utilise biomass resources.The structure of functional groups in biomass can effectively reflect its chemical characteristics,but there is a lack of in-depth understanding of the evolutionary differences and common patterns of different functional groups in biomass pyrolysis.In this thesis,we investigate the correlation between the properties of biomass functional groups and pyrolysis using a combination of experimental and numerical methods,taking biomass with different functional group properties as the object of study.Pyrolysis products of three biomasses,namely maize straw,wood chips and palm shells,were obtained using a fixed bed pyrolysis unit at four end temperatures of200°C,400°C,600°C and 800°C.The biochar,tar and gaseous products were examined by FT-IR,GC-MS and GC.The functional groups of biochar at different end temperatures were characterized by peak fitting using FT-IR spectrograms,and the properties of the functional group classification on the product yield and components were analysed semi-quantitatively by calculating the structural parameters of the functional groups.The results showed that:hydroxyl groups prolong the preheating time of pyrolysis;unbroken phenolic and alcohol hydroxyl groups are present in the tar fraction,and broken hydroxyl groups form H₂and CO in the late stage of pyrolysis;methyl content is the determining factor for the concentration of hydrocarbon gases released;weakly bound oxygen-containing groups,such as C=O and carboxyl groups in aldehyde groups,decompose in the high temperature region leading to the release of CO₂and CO;strongly bound oxygen-containing groups,such as carbonyl and ether bonds.The rate of CO and CO₂release is increased at 600-800°C;the hydrogen bonding content directly affects the H₂concentration.It was also found that the aromaticity of biochar further increases as the pyrolysis temperature increases;the content of unstable structural functional groups in the tar fraction decreases and the content of aromatic structures increases.The biomass pyrolysis process was modelled using a biomass chemical permeation devolatilisation model,referred to as the Bio-CPD model,to further clarify the pyrolysis component yields during the pyrolysis process.The kinetic and chemical structure parameters were obtained by linear fitting method and three-component weighted average method,and brought into the Bio-CPD model for yield prediction.The results show that the oxygen-containing functional groups increase the required temperature for pyrolysis,the aromatic structure contributes to the reaction time of pyrolysis and the aliphatic hydrocarbons reduce the starting temperature of the pyrolysis reaction.The simulation method was also compared and found to be suitable for predicting the rapid pyrolysis process of biomass at high temperatures.