The Study Of Preparation And Properties Of Coal Tar Based Carbon Foam

Shaanxi Province is rich in coal resources,of which 150 billion tons of low-rank coal can produce about 14.5 billion tons of tar.In view of the current technological level of coal pyrolysis and coal tar lightening,the output of tar is much higher than its processing consumption.Coal tar has the characteristics of high aromaticity and easy graphitization.Therefore,the preparation of high-quality carbon materials with coal tar as a precursor is explored to provide theoretical and technical support for the realization of industrial upgrading and sustainable development of environment and resources in the coal industry.In this paper,mesophase pitch was prepared from the heavy components of low temperature coal tar.Coal tar composition is changed by distillation.The effects of different components and reaction conditions of coal tar on the properties of the mesophase pitch were investigated.Styrene-butadiene-styrene block copolymer(SBS)was used to control the mesophase structural ordering of asphalt.The changes of SBS structure,S/B value and addition amount on the content and structure of the mesophase pitch were revealed.Coal tar and mesophase pitch were analyzed by polarized light microscope test,infrared spectrum test(FT-IR),nuclear magnetic resonance test(1H-NMR),gas chromatography test and family composition test.The mechanism of preparing mesophase pitch from coal tar was revealed from the perspectives of molecular structure,chemical bond and functional group.To clarify the relationship between the microphase structure and mesophase ordered structure of SBS and clarify the mechanism.Using mesophase pitch as raw material,carbon foam is prepared by self-foaming.The effects of reaction temperature,heating rate and reaction pressure on the properties of coal tar-based carbon foam were investigated.Revealing the correlation between mesophase ordered structure and carbon foam properties.The experimental results show that the formation process of mesophase pitch is the result of the combined effect of chemical reaction and physical regulation.Increasing the distillation temperature of coal tar is beneficial to prepare mesophase pitch with few alkyl substituents,short chain length and high degree of aromatic condensation.Using coal tar with a distillation temperature of 360℃ as the raw material,at a reaction temperature of 400℃ and holding the temperature for 12h,the asphalt mesophase content is high.The structure is mainly inlaid.SBS can regulate the order of mesophase pitch,and the linear SBS with large S/B value has a more obvious effect on promoting the order of mesophase pitch.With 4 wt.%SBS-792 as additive,the reaction temperature is 400℃,and a streamlined mesophase structure can be formed after 6h of reaction.The regulation of mesophase order by SBS mainly plays a role in two aspects.SBS undergoes chain scission reaction and participates in and promotes the polymerization of asphalt molecules.SBS can increase the soluble mesophase content.The reaction temperature had the greatest effect on the porosity of the carbon foam,and the heating rate had the least effect.The optimal value of carbon foam porosity is 72.8%,and the corresponding conditions are:temperature 559℃,pressure 0.48 MPa,and heating rate 9℃/min.The optimum thermal conductivity of carbon foam is 0.219 W·m-1·K-1.The reaction conditions were 549℃,2 MPa,3.9℃/min.The influencing factors are heating rate>pressure>temperature.By regulating the order of intermediate pitch by SBS,carbon foam materials with graphitization degree can be prepared at low temperature.It is proved that the ordered growth of carbonaceous mesophase has the effect of reducing the graphitization temperature.