Study On In Situ Study Of Pore Structure Changes Of Some Bituminous Coals During Carbonization By Synchrotron Radiation SAXS

Small angle X-ray scattering(SAXS),as an experimental characterization method of nanostructure characteristics,has been developed rapidly in the past decades.Especially since synchrotron radiation was used as X-ray source,SAXS technology has promoted the research progress in many scientific fields and made a lot of contributions.Small angle X-ray scattering can be used to study polymer materials,porous materials,mesoporous materials,biological macromolecules and other samples in situ with high intensity and high collimation synchrotron radiation X-ray source,so as to obtain the structural information of the material at the nanoscale.In fact,coal is the most abundant fossil fuel resource in the world.Since clean and efficient utilization of coal resources has important strategic significance and economic and social value,it is necessary to make full use of coal,and coal carbonization is one of the main ways.Raw coal and its solid products(char,coke or residual carbon)produced in the process of carbonization technology have very abundant and complex porous network structure.The complex pore structure has a very important impact on their performance and application.Such structure is very suitable for the study of synchrotron radiation SAXS method.Based on the integrated experimental platform of Beijing Synchrotron Radiation Facility1W2 A beamline small angle experimental station of Institute of high energy physics,Chinese Academy of Sciences,this paper mainly studies the changes of pore network structure of some bituminous coals in the process of high temperature carbonization through in-situ online data acquisition,and obtains the variation and development laws of fractal dimension,porosity,specific surface and pore size distribution with the increasing temperature.Then,the main characteristics and basic mechanism of pore structure change of bituminous coal during carbonization are analyzed and discussed.The main contents are as follows:(1)Carbonization of coking coal can greatly improve its utilization rate and realize the comprehensive utilization of coal to a great extent.The pore structure is the main physical structure of coking coal and its carbonization products char and coke,synchrotron radiation small angle X-ray scattering(SAXS)technology was used as the main characterization method to study in-situ the carbonization process of two kinds of coking coal(fat coal and coking coal)at high temperature(1200°C).The results show that the carbonization process of the two kinds of coal presents obvious stage characteristics,and the Porod curves of the two kinds of coal and their carbonization solid products are positively deviated.After correcting the deviation,the pore structure parameters including pore size distribution,porosity and specific surface area are calculated,and their variation characteristics and mechanism are compared and analyzed.(2)Non-cohesive coal is abundant in nature,and carbonization is an effective means to realize their comprehensive utilization.In this work,using synchrotron radiation SAXS technology as the primary experimental characterization method,the changes in pore structure of two kinds of Non-cohesive coals with different coal ranks,namely,the Matigou non-coking coal and Zhangcun lean coal,were studied during the progress of high temperature carbonization(1200°C),and the characteristics and mechanism of the carbon network structure changes during the process are analyzed and discussed.The pore structure parameters including pore size distribution,porosity and specific surface area were calculated after correction deviation.The results showed that there were characteristic pores in the two kinds of non-cohesive coal samples and their solid products,and the carbonization process also showed obvious stage characteristics.(3)Fat coal is the bituminous coal with strong caking property and medium degree of coalification,while lean coal is the bituminous coal with the highest degree of coalification and no caking property.The synchrotron radiation small angle X-ray scattering method was used to study in situ the fractal structure changes of high-rank bituminous coal,namely fat coal and lean coal,during the progress of high-temperature carbonization.The results show that the raw coal,char and residual carbon of lean coal exhibit surface fractal structure during the carbonization process,while the raw coal and its carbonization products of fat coal exhibit surface fractal structure in the temperature range of 25°C～600°C,the pore and mass fractal structure in the temperature range of700°C～1200°C,and the variation curve of fractal dimension of these two kinds of coal forms an interesting closed loop with the change of carbonization temperature.This work analyzes the main characteristics and basic mechanism of the corresponding fractal dimension changes.(4)Using synchrotron radiation small-angle X-ray scattering to study the in-situ fractal structure changes of non-caking coal during the progress of high temperature carbonization(1200℃).The results show that the non-caking raw coal and its solid products(char and residual carbon)during the carbonization process all present surface fractal structure.And the change law of fractal dimension with increasing temperature fully reflects the corresponding structure changes of non-caking coal at different temperature intervals during the carbonization process.In this work,the variation characteristics and mechanism of fractal dimension are analyzed and discussed.