The Adsorption Equilibria Of Natural Gas On Graphene Sheets

From 1980 s,the theory and technology of adsorption natural gas(ANG)become more and more mature.Their hard studies have made obvious progresses in adsorption field,such as exploiting new adsorbents,researching adsorption theory and adsorption equilibria by the way of computer simulations and calculation.As a new adsorbent in carbon family,graphene sheets(GS)possess large theoretical surface area to 2630 m2/g and been provided with excellent adsorption capacity,which made become popular object of extensive theoretical and experimental investigations in recent years.Currently,most adsorption studies on GS mainly focus on the heavy metal ions,organic pollutants or the computer simulations or calculation of gas adsorption.However,the experimental data about gas adsorption on GS is still rare,it is inevitable and indispensible to experimentally focus on the research of adsorption of gas on GS.In this paper,GS were made by oxidation-reduction method,the characterization result shows the surface area of GS is 805 m2/g and pore volume of GS is 1.03 cm3/g.The adsorption isotherms on GS of CH4 at 0-6 MPa,C2H6 at 0-1.6 MPa,C3H8 at 0-0.3 MPa and C4H10 at 0-0.05 MPa from natural gas were measured using a volumetric method..Five temperatures were chosen as the experimental temperatures and they were 263.15 K,273.15 K,283.15 K,293.15 K and 303.15 K.Moreover,Langmuir model,Langmuir-freundlich(L-F)model and vacancy solution model were used to fit the adsorption equilibria data.The result showed that the isotherms were describe well by these three models,but L-F and vacancy solution were better than Langmuir ? The isosteric heats were calculated in the range of 0.3mmol/g to 2.1mmol/g with the interval of 0.3mmol/g for CH4,C2H6 and C3H8,and for C4H10 the adsorption amount range to get isosteric heat is 0.1mmol/g to 0.7mmol/g with the interval of 0.1mmol/g.The extreme heats were also calculated when the pressure were low enough.The result showed that the isosteric heat of adsorption values decreased in the order C4H10> C3H8> C2H6> CH4 and the extreme heat of adsorption values decreased in the order C4H10> C3H8> C2H6> CH4 which means they were consistent with each other.This suggests that the interactions between C1-C4 and the graphene layers decreased in the order C4H10> C3H8> C2H6> CH4.To investigate the influences of the hydrophilic functional groups in GS on the adsorption of CH4 hydrate,the adsorption isotherms of CH4 hydrate on GS were compared before and after the GS were carbonized.The result indicated that the surface areas of carbonized GS is larger than that of GS without carbonization about 100 m2/g,and the pore volume is a little bigger than that before.The maximum adsorption amount of CH4 hydrate on carbonized GS is twice than that on GS without carbonization.