Preparation And Performance Of Shaped Biomass-derived Porous Carbon Materials

Porous carbon materials are widely used in the fields of adsorption,catalysis,electrochemistry due to their advantages such as high specific surface area,developed pore structure and adjustable surface chemical properties.Compared with powdered porous carbons,the shaped porous carbons have a uniform size and shape,higher bulk density and mechanical strength,which facilitates the storage and use of porous carbons.Biomass is considered to be a suitable carbon precursor because of its abundant sources and low price.However,most of biomass-derived porous carbon materials exist in powder form,which often limits their practical application.Therefore,the preparation of high-performance shaped porous carbons using biomass as the carbon precursor is the current research hotspot and difficulty.In this thesis,waste coffee ground was used as the carbon precursor to prepare the shaped porous carbons by using extrusion molding method,the main research conclusions are as follows:（1）A series of microporous shaped porous carbons with high mechanical strength were synthesized by using coffee ground as the carbon precursor,phosphoric acid as the binder,and sesbania powder as the extrusion aid through the extrusion molding,carbonization and steam activation.By investigating the amount of phosphoric acid,steam activation temperature,steam activation time and the amount of sesbania powder,the optimal molding process conditions were determined.The shaped porous carbon prepared under this process conditions has a higher carbonization-activation yield（24%）,mechanical strength(220 N cm^-1),bulk density(0.86 g cm^-3),surface area(909 m² g^-1),total pore volume(0.42 cm³ g^-1)and microporosity（79%）.The dynamic breakthrough measurement showed that the CO₂ dynamic adsorption capacity of the shaped porous carbon was 0.60 mmol g^-1 for the CO₂/N₂ mixture gas separation at 298 K/1.1bar.N₂ was basically not adsorbed.The shaped porous carbon can achieve complete separation of the mixture gas and have excellent recycling stability and moisture resistance.（2）In order to improve the proportion of mesopores of the shaped porous carbons and enhance the mass transfer capacity of the substance.We prepared the porous carbons by using the extrusion molding method,coffee ground as the carbon precursor,sodium silicate as the binder,sesbania powder as the extrusion aid and microcrystalline cellulose as the enhancer.A series of mesoporous shaped porous carbons with high mechanical strength were prepared by investigating the process parameters such as the amount of sodium silicate,the sequence of steam activation and silica removal,the amount of microcrystalline cellulose.The shaped carbon prepared under the optimum process conditions has a higher yield（23%）,mechanical strength(226 N cm^-1),bulk density(0.80 g cm^-3),surface area(537 m² g^-1),total pore volume(0.39 cm³ g^-1)and mesoporosity（60%）,the pore size concentrated at about 25 nm.The CO₂adsorption capacities of the representative sample are 3.30 mmol g^-1 at 273 K/1 bar and 2.42mmol g^-1 at 298 K/1 bar.The isosteric heat of adsorption is in the range of 25-30 kJ mol^-1,it belongs to a typical physical adsorption process,which is beneficial to the regeneration of the shaped carbon adsorbent.