Porous Carbons From Coffee Grounds: Study On The Shaping Process And Their Properties

Biomass is a natural resource,which is widely used as the precursor of carbon materials because of its wide distribution,low cost and easy availability.Biomass porous carbon has the advantages of easily regulated pore structure,rich surface functional groups,good stability and environmental friendliness.It is a potential porous solid adsorbent.The preparation process of biomass porous carbon generally needs to add binder to shape it and prepare it into a regular and uniform shape for storage,transportation and use.The addition of binder often changes the properties of porous carbon.Therefore,it is of great significance to explore a suitable binder to prepare high-performance biomass based molded porous carbon.This paper focuses on the preparation of columnar porous carbon materials,The pore structure and surface chemical properties of porous carbon were adjusted by adjusting the binder and activation process.The results are as follows:In order to obtain high specific surface area and high strength formed porous carbon,it was extruded with coffee grounds,sesbania and phosphoric acid.After carbonization,steam activation and water washing,columnar coffee grounds based porous carbon was prepared.By changing the temperature,time and flow rate of water vapor activation,the mechanism of water vapor activation was studied in detail,and a series of columnar coffee grounds based porous carbons with rich pore structure,high specific surface area and high strength were prepared.The optimum process conditions were selected according to the preparation cost and economic benefits.The carbonization yield was 26.03%,the mechanical strength was 287N/cm and the bulk density was 1.03 g/cm³;The specific surface area is 636 cm²/g and the total pore volume is 0.26 cm³/g.Further,it was modified by benzene deposition,the results show that the sample has the separation performance for N₂/O₂under the conditions of normal temperature and pressure and low flow rate（1 ml/min）.At the same time,the dynamic separation performance of CH₄/N₂was tested for the samples with large pore volume.Under the conditions of 298 K and 1.1 bar,it has a complete separation time of 6 minutes,the dynamic adsorption capacity of CH₄is 0.32 mmol/g,and the dynamic separation coefficient is1.7.In order to improve the mass transfer rate of porous carbon,mesoporous was introduced into porous carbon,it was extruded with coffee grounds,sesbania and sodium silicate.After carbonization,steam activation,alkali washing and water washing,columnar coffee grounds based mesoporous porous carbon was prepared.The pore structure and surface chemical properties of porous carbon were regulated by adjusting the amount of sodium silicate.The prepared representative samples have a specific surface area of 527 cm²/g,a total pore volume of 0.33 cm³/g and a mesoporous rate of 55%.The micropores are mainly concentrated at 0.48nm and the mesopores are mainly concentrated at 30-50 nm.At 298 K and 1 bar,the static adsorption capacity of CH₄is 0.87 mmol/g,and the IAST separation selectivity of CH₄/N₂（3/7）is 10.3.The dynamic penetration test results of the mixture confirmed that the material had excellent CH₄/N₂dynamic separation performance under atmospheric pressure and pressure,and the dynamic selectivity reached 10.4 and 17.9 at 298 K,1.1 bar and 5 bar,respectively.And it has good cycle performance and water vapor resistance.