Influence of cross-linking modification of coal tar pitch on carbon structure
The microstructure of pitch-based carbon products is highly dependent on the properties of precursor pitch.While using chemi-cal cross-linking to modify asphalt,although all the reaction mechanism of chemical cross-linking operates via electrophilic substitution reaction,the degree of such modification fluctuates based on the type of cross-linking agent and catalyst utilized,which in turn impacts the structure of resulting carbon products.Using medium and low temperature coal tar pitch as raw materials,the effects of three cross-linking agents:terephthalyl alcohol(PXG),benzaldehyde(BA),p-phenylenediamine chloride(TPC),coupled with five catalysts:p-toluenesulfonic acid,concentrated sulfuric acid,concentrated nitric acid,concentrated hydrochloric acid,and boric acid on the structure of carbon products after asphalt crosslinking modification were explored.The thermal stability and functional group changes of cross-link-ing modified pitch through TG-DTG and FT-IR were studied.XRD and Raman were used to characterizethe microstructural differences of modified pitch carbon products.The results show that the presence of cross-linking agents and catalysts facilitate occurrence of molecu-lar crosslinking in pitch,effectively curbing the volatilization of light components during thermal conversion,and substantially enhancing pitch's coking value,softening point,and thermal stability among other metrics.When PXG serves as a cross-linking agent,the methyl-ene H on the branched chain within the cross-linked product is not easily replaced.Conversely,when boric acid functions as the catalyst,the methyl H at the branch chain's end is more prone to replacement.Utilizing BA as cross-linking agent,the position of hydrogen substi-tution predominantly occurs on the aromatic ring.When TPC is used as the cross-linking agent and concentrated sulfuric acid is used as-the catalyst,the content of C=O functional groups in the cross-linked product increases,indicating that TPC participates more in the re-action under this combination.Irrespective of the cross-linking agent used,when concentrated hydrochloric acid is employed as a catalyst,the crosslinking reaction substantially promotes the substitution of C-H bonds on the benzene ring and branch chains.After cross-link-ing modification,the strong π-π interactions among molecules in pitch's carbonization process are weakened,effectively hindering the formation of ordered carbon structures,thereby increasing ID/IG values.Simultaneously,the interlayer spacing d002 of carbon microcrystals significantly expands,while the Lc value demonstrates a declining trend and the number of aromatic layers reduces,indicating that chemi-cal cross-linking not only disrupts the arrangement of ordered carbon structures,but also restrains the development of carbon microcrys-tals.When boric acid isused as a catalyst,the catalytic effect is more ideal.The resultant carbon product's d002 exhibits the highest per-formance amongst its group.When PXG and boric acid collectively cross-link with pitch,the d002 of the achieved carbon material extends to 0.377 nm.In conclusion,this study lays a robust practical basis for the further targeted regulation and construction of pitch-based car-bon materials.
mid-low temperature coal tar pitchcross-linking modificationcatalyzercarbon microstructurelayer-spacing
万方数据
维普
