Construction Of Carbon-containing Functional Groups Model Compound Of Sewage Sludge And Study On Its Pyrolysis Mechanism

Sludge pyrolysis is currently one of the disposal and treatment technologies for the realization of sludge energy utilization.Sludge is rich in hydrocarbon organic compounds,and pyrolysis technology can be used to obtain gas and liquid derived fuels.Due to the complex organic and inorganic sludge composition,the mechanism of pyrolysis is not yet clear.Therefore,research on the pyrolysis mechanism of the carbon-containing functional groups of the main organic structure of sludge has important research significance and practical value for promoting targeted development and technological development of sludge pyrolysis products.In this paper,urban sewage sludge with a relatively high volatile content is taken as the research object.First,the existence and forms of functional groups in the sludge are detected by Fourier transform infrared spectroscopy?FTIR?and X-ray photoelectron spectroscopy?XPS?.Carbon-containing functional group content.The results showed that the sludge in the aromatic structure 700cm^-1900cm^-1,the main oxygen group 1000cm^-11800cm^-1,the hydrocarbon functional group range 1800cm^-13000cm^-1,hydroxyl functional group 3000cm The four infrared bands^-13600cm^-1 have obvious absorption peaks;the Peakfit coefficient is fitted to the correlation coefficient at R²>0.95,SE<0.01.It is determined that the main carbon-containing functional groups in the sludge are:Ether?COC?,carboxyl?-COOH?,benzene ring??-?*?and alkenyl?C=C?,the relative content ratio is about 14:5:7:24.Then,combined with the principle of the model compound construction and sewage chemical properties,the model compounds of the four carbon-containing functional groups of the sludge were:m-xylene,tetrahydrofuran,acetic acid and cyclopentene.The Pyrolysis Analyzer-Gas Chromatography-Mass Spectrometry?PY-GC-MS?was used to qualitatively and quantitatively analyze the carbon-containing functional groups of the pyrolysis products at different temperatures and at different temperatures for the five model compounds.The evolution mechanism of carbon functional groups.The results show that the formation and evolution of organic matter in the pyrolysis process of sludge can be divided into three stages.In the low temperature stage?250°C-450°C?,the organic matter in the sludge pyrolysis product is less,mainly carboxylic acid?-COOH?The peak area of the total ion chromatograms of the pyrolysis products accounted for 52.6%;the organic matter species in the pyrolysis products of the intermediate temperature stage?450°C-650°C?were more,and the proportion of the carboxylic acid substances was reduced to 7%.The mass ratio of aromatics and aliphatics was more than 10%,and the products of organic compounds in the high temperature stage?650°C-850°C?tended to be similar,and the peak values in the total ion current diagrams decreased.The functional groups in the pyrolysis products of the sludge at different temperatures were mainly benzene rings,of which aromatics accounted for more than 90%.The pyrolysis of the model compounds showed that the functional groups of meta-xylene remained almost unchanged during the pyrolysis of m-xylene.At high temperature pyrolysis,the proportion of alkenyl groups rose to 7%,and the ratio of benzene rings accounted for 90%.Tetrahydrofuran starts to be converted into unsaturated aliphatic compounds and aromatic compounds at the intermediate temperature stage.At high temperature,the functional groups were 18%of alkenyl groups and 78%of benzene rings.In acetic acid pyrolysis the carboxyl groups are converted from mesophilic to alkenyl and benzene rings with a small amount of ether linkages.When alkenyl was pyrolyzed,the alkenyl group was reduced to 15%at low temperatures,the intermediate temperature began to rise to a high temperature of 25%,and the benzene ring accounted for 68%.The distribution of functional groups in the pyrolysis products of the model compound according to the functional group ratio is consistent with the distribution trend of the functional groups of the pyrolysis products of the sludge.At last,the analysis of pyrolysis non-condensable gas and pyrolysis infra-red infrared analysis of the integrated sludge showed that the complex physical and chemical reactions of the carbon-containing functional groups of the sludge during the pyrolysis process include free radical generation reactions,aliphatic side chain cleavage reactions,and functional groups.Decomposition reaction,cleavage reaction,dehydrogenation reaction,hydrogenation reaction,condensationreaction,bridgingbondcleavagereaction,polycondensation reaction,aromatization reaction,and the like.This study reveals the mechanism of pyrolysis of carbon-containing functional groups in the pyrolysis process of sludge,which lays a theoretical foundation for the research and development of sludge pyrolysis technology and product target generation control of sludge pyrolysis products.