Study On Pyrolusis Mechanism Of Carbon And Oxidation-containing Chemical Groups In Sewage Sludge

Thermochemical conversion technology is considered to be an effective recyclable sludge energy technology.The conversion of energy contained in sludge into pyrolysis oil and synthetic natural gas with low calorific value by pyrolysis technology has been proved to be an environmentally friendly way of utilization.However,sludge pyrolysis is a multiphase chemical reaction between organic and inorganic substances in sludge,including the transformation between the interior of three-phase products and between three-phase products.In the pyrolysis process,the formation and distribution of the product are affected by many reaction conditions.On the other hand,due to the simultaneous and continuous thermochemical reactions of multiple components in the process of pyrolysis and pyrolysis make it difficult to advance the conversion mechanism of C and O in the process of sludge pyrolysis.In this study,X-ray photoelectron spectroscopy and Thermogravimetric analysis-Fourier transform infrared spectroscopy were used to characterize the oxygen and carbon-containing chemical groups of sludge.XPS spectral analysis showed that the most abundant elements on the surface of the sludge were C and O,and the carbon and oxygen-containing groups were mainly divided into C=C,O-C=O,R-OH,Ar-OH,-CHO and-C₆H₅.The evolution characteristics of thermal cracking volatiles in sludge under the influence of temperature were systematically studied by observing and measuring the distribution and content changes of different chemical groups in pyrolysis products under various important temperature nodes.The thermogravimetric analysis of sludge,acid demineralized sludge and mineral added sludge shows that the pyrolysis process can be divided into three stages:dehydration?<200°C?,devolatilization?200-550°C?,and residual coke formation?>550°C?.The organic matter mainly escapes in the second stage of thermal cracking,accounting for more than 80%.Simultaneously,the pyrolysis heating rate is an important parameter affecting the sludge pyrolysis process.It is found through research that with the increase of heating rate,the thermal hysteresis phenomenon becomes more and more obvious,but the thermal decomposition starting temperature of sludge is improved.Furthermore,the kinetic model of sewage sludge pyrolysis was constructed to study the weight loss characteristics of the pyrolysis process,which indicated that the main reaction stage of sludge pyrolysis?170-570°C?is the multi-step reaction.Pyrolysis temperature is the main influencing factor affecting the evolution of chemical groups in sludge.During the low temperature pyrolysis stage?<350°C?,the elevated temperature results in the largest decrease of O-C=O content,which is reduced by about 33%.In the mid-temperature pyrolysis process?350-550°C?,the contents of C=C,-CHO,-OH,-C₆H₅ increased significantly,while O-C=O decreased slowly,but its content was still high.In the higher temperature range?>550°C?,chemical activity of aliphatic hydrocarbon molecules is enhanced,and aromatization polycondensation reactions such as dehydration,decarboxylation,decarbonylation and aldol condensation occur.In addition,the thermal cracking of macromolecules such as proteins and lignin contained in the sludge causes-C₆H₅to become the main chemical group in the pyrolysis stage.Based on the above conclusions,the pyrolysis conversion pathways of organic acids such as acids,aldehydes,alcohols,phenols,olefins and their derivatives are proposed.In addition,X-ray diffraction?XRD?and pyrolysis-gas-chromatography/mass spectrometry?Py-GC/MS?were used to study the influence of main primary mineral components in sludge on the formation and transformation of carbon,oxygen-containing groups and their compounds in pyrolysis volatiles.The results show that the mineral inorganic compounds inherent in the sludge reduce the activation energy of the chemical reaction to a certain extent,thereby promoting the thermal cracking of the organic components and shortening the time required for the decomposition of the organic matter.Under medium and low temperature conditions?<550°C?,the minerals in the sludge promoted the formation of carbon and oxygen-containing groups during pyrolysis,while at high temperature?>550°C?,it showed a certain inhibition.