Experimental Study On The Dissociation Of Covalent Bonds In Oil Shale During Pyrolysis

With the rapid development of China’s economy,energy consumption continues to increase,and the external dependence of energy also increases year by year,so it is urgent to find new alternative energy.The same is true of fossil fuels around the world,where consumption is high,demand is high and reserves are worrying.Energy storage,utilization and exploration are the main problems we face.As an alternative energy source,shale oil and shale gas can be obtained by pyrolysis and redistillation.The study on the chemical structure and pyrolysis mechanism of oil shale is helpful to the comprehensive utilization of oil shale and alleviate the problem of energy shortage.The essence of chemical reaction is the change of atomic bond relationship,which starts from the break of covalent bond.Therefore,interpreting the pyrolysis process of oil shale from the perspective of covalent bond can effectively understand the change of chemical structure of oil shale,and provide reference for the control of oil generation process.Based on this,the pyrolysis process of organic matter in oil shale from huadian,Fushun,Wangqing and Beipiao areas was studied from the perspective of covalent bond by using thermogravimetry,solid-phase Fourier transform Infrared spectroscopy and GC-MS.Using hydrochloric acid and hydrofluoric acid pickling processing of oil shale,removing most of the carbonate and silicate components,mainly organic component of oil shale samples,and using Fourier infrared spectrum（solid phase）of the components in the sample before and after the pickling change has carried on the simple analysis,confirmed that the organic matter content in the samples meet the expected requirements.The weight loss rule of organic matter pyrolysis of oil shale was obtained through TG-DTG experiments.It was found that the weight loss mainly occurred between 300℃and 600℃,and the phenomenon of rapid weight loss occurred between 400℃and 500℃.Then,PY-GC-MS experiments with preset temperatures of 400℃,500℃and 600℃,reaction time of 10s and residence time of 5 min were carried out for the four kinds of oil shale kerogen,and the distribution of the products was analyzed.It was found that the products were dominated by aliphatic alkane/olefin structure and their relative content increased with the increase of temperature.In the pyrolysis process,there are alcohols,acids,aldehydes,esters and other groups that do not participate in the reaction,and there is no ring-opening reaction.Fourier infrared spectroscopy（solid phase）was used to detect the pyrolytic semi-coke obtained at eight final pyrolysis temperatures ranging from 300℃to 600℃with a temperature interval of 50℃,and Peak Fit was used to perform Gaussian peak fitting on the obtained spectra.Area normalization method was used to analyze the relative contents of each bond structure in the semi-coke.Based on the above experimental results,the bond breaking rules of C_al-C_al,C_ar-C_al,-OH,-CHO,O=C-O-and other structures during pyrolysis were obtained,and the influence of organic matter structure on bond breaking during pyrolysis was also analyzed.It is found that a small part of oxygen-containing functional group participates in the reaction to generate CO₂and CO in the early stage of pyrolysis,and most of them escape with complete group structure along with the rupture of C-C bond.The aromatic structure will not be destroyed,only escape with the rupture of C-C bond.Moreover,the generation of organic pyrolysis products of the whole oil shale mostly depends on the rupture of aliphatic hydrocarbon C_al-C_albond and C_ar-C_albond.The length of the aliphatic chain can determine the temperature at which small molecules fall off,while the change of other functional groups during pyrolysis is not affected by the structure of organic matter,but only related to its own properties.