Preparation Of Porous Carbon Materials By Orientated Polymerization Of Biomass Pyrolysis Gas

Biomass pyrolysis is one of the most concerned methods of biomass utilization.However,the biomass structure is complex,and the large molecular pyrolysis gas generated during the pyrolysis process is difficult to be converted into small molecular components.The bio-oil obtained after condensation contains many heavy components,with high viscosity,poor fluidity,and difficult conversion and utilization.At present,the cost of quality-enhancing technology is high and the process is complicated,which has not yet achieved large-scale production.In addition,macromolecular pyrolysis gas is easy to polymerize and has many functional groups and high carbon contents,making it an ideal carbon source for preparing porous carbon materials.In recent years,porous carbon materials have been widely used in the fields of machinery,electronics,aviation,adsorption,catalysis,energy storage,and environmental treatment due to their excellent heat resistance,high thermal conductivity,good chemical inertness,and high electrical conductivity.Based on this,this paper put forward the idea of using biomass macromolecular pyrolysis gas as carbon source and using template method to prepare porous carbon materials in order to achieve high value utilization of biomass macromolecular pyrolysis gas before condensation and reduce coking to improve liquid quality.Aiming at this idea,this paper separately prepared hydrogen storage porous carbon materials with heavy components of bio-oil(off-line)and biomass macromolecular pyrolysis gas(on-line).The key factors affecting the yield and properties of porous carbon materials were explored,and the action mechanism of the template agent and the mathematical model of the carbonization process were proposed.The specific content and main conclusions are as follows:The heavy carbon components of bio-oil were used to prepare porous carbon materials and their hydrogen storage performance were tested.A variety of organic calcium salts(calcium acetate,calcium carbonate and calcium citrate)are used as template agents,and the heat-treated heavy bio-oil is used as a carbon source to prepare hydrogen storage porous carbon materials.Calcium citrate was selected as the optimal template.The effects of calcium citrate/bio-oil mass ratio and carbonization temperature on the properties of porous carbon materials were investigated.The results show that,under the condition that the mass ratio of bio-oil to template is 1,and the carbonization temperature is 800℃,the yield of porous carbon material prepared with calcium citrate as template is increased by about 8 times and the specific surface area increases about 12 times to reach 1688m~2/g compared with the direct carbonization of heavy components of bio-oil.The pore size distribution is more concentrated and the microporosity reaches 24.51%.The hydrogen storage capacity can reach 199.79 cm~3/g at 77K under 1 bar,which is better than metal complexes,etc..The carbonization mechanism of biomass macromolecular pyrolysis gas/calcium citrate mixture was studied.Based on in-situ diffuse reflectance infrared Fourier transform spectroscopy,the carbon formation mechanism and the template action mechanism during the carbonation process were proposed.The thermogravimetric analyzer was used to investigate the influence of different biomass to template mass ratio and reaction temperature on the carbon-containing precursor carbonization weight loss.The Gaussian method was used to simulate the weightlessness of carbonization.The results show that phenols,alcohols,etc.in the biomass pyrolysis gas macromolecular component/calcium citrate mixture undergo deoxygenation and dehydrogenation reactions during carbonization to produce water molecules.The pyrolysis gas and calcium citrate crack and polymerize,producing small molecular volatiles and large molecular polymers.The generated calcium oxide has a pore-forming effect,and the generated small molecule gas physically activates the carbonaceous material,increasing the porosity of the carbon material.During the carbonization of the mixture,polycondensation,cracking,dehydrogenation and deoxidization of pyrolysis gas macromolecules and thermal decomposition of calcium citrate mainly occur.According to the DTG curve of the mixture,a five-stage continuous virtual component reaction model is established by Gaussian method,and the fitting results are basically consistent with the experimental results.Biomass macromolecular pyrolysis gas was used to prepare porous carbon materials and study their characteristics.The effects of pyrolysis temperature,heating rate,reaction temperature and carrier gas flow rate on the yield,composition distribution and properties of carbon-containing precursors and condensed liquids for biomass pyrolysis were investigated.The results showed that with the increase of reaction temperature,the yield of carbon-containing precursor decreased from29.79%to 9.32%,and the yield of condensed liquid increased from 10.17%to 31.07%.When the reaction temperature is 50℃,the maximum acid content in the condensed liquid is about 32.69%.When the reaction temperature is 350℃,the maximum phenol content in the condensed liquid is about 49.1%.As the reaction temperature increases,the yield of carbon-containing precursors gradually decreases,and the yield of condensed liquid gradually increases.When the reaction temperature is low,the condensed liquid contains a large amount of acids;when the reaction temperature is high,the relative content of phenolic substances in the condensed liquid is significantly increased.Under the optimal working conditions,pyrolysis temperature 550℃,heating rate10℃/min,reaction temperature 200℃and carrier gas flow rate 0.4L/min,the porous carbon material was prepared and applied to hydrogen storage.The hydrogen storage capacity is about 170cm~3/g under 77K and 1 bar.