Study On Adsorption Properties Of Typical Components In Landfill Gas

The main components of landfill gas are methane(CH4,about 50%),carbon dioxide(CO2,about 40%),nitrogen and oxygen.Methane is the major energy source of landfill gas.However,it is reported that the existed CO2,N2 and O2 had significantly negative impacts on the quality of landfill gas.Therefore,it is necessary to remove CO2,N2 and O2 during purification process of landfill gas.Adsorption is widely used in gas separation since the simple process and low cost.More specifically,the high efficient adsorbents development is the vital idea of the adsorption technology.According to literatures of landfill gas purification,it is mainly focused on adsorption and separation among CO2,CH4 and N2.By contrast,there are few studies about separations among CO2,CH4 and O2-The effects of trace gases(eg.VOCs)on adsorbents efficiency have not been studied yet.In this paper,the main aim is to find suitable adsorbents for different gases separations in landfill gas purification.In this paper,several adsorbents have been studied,namely zeolite molecular sieves,carbon-based adsorbents and some other types of molecular sie-ves.The adsorption capacity,selectivity and adsorption kinetics of CO2,CH4,N2 and O2 have been compared.Meanwhile,the influences of five typical VOCs and water vapor on adsorbents have been researched.The main conclusions are as follows:The adsorption isotherms of CO2,CH4,N2 and O2 are as similar as type I.The results shown that 13X,5A and USY-1 had higher CO2 adsorption capacities and lower adsorption capacities of CH4,N2 and O2,when the pressure is 100kPa and temperature is 303K.The CO2 adsorption capacities of 13X,5A and USY-1 are 2.07,1.66 and 0.94 mmol/g,respectively.Two different activated carbons show high adsorption capacities for CO2 and CH4,and AC-2 shows significantly higher CH4 adsorption capacity than others.The TS-1 has higher CO2 adsorption capacity,which is similar to activated carbon and 5A.ETS-10 has similar adsorption capacities between CO2 and CH4,whereas low adsorption capacities for N2 and O2:In this paper,the ideal separation coefficients of five mixed gases models(C02/N2,CO2/CH4,CH4/N2,CO2/O2 and CH4/O2)on the different adsorbents are discussed.It is manifested that there is a good CO2/N2 separation for 13X,5A and USY-1 with the ideal separation coefficients at 45.95,14.23 and 18.53 respectively(experimental condition:P=100kPa and T=303K).Due to the pressure independent,USY-1 can apply to distinctive pressure conditions.For CO2/CH4 system,13X and USY-1 show better separation performance with the separation coefficients at 7.2 and 6.9 respectively.ETS-10,13X and AC-2 show good separation performance in CH4/N2 system.For CO2/O2 system,13X and 5 A have higher ideal separation coefficients than others,which are 33.6 and 51.4.In CH4/O2 system,5A and ETS-10 show better separation performance rather than others.To sum up,13X,5A and USY-1 have higher CO2 adsorption capacity and selectivity,which can be used as adsorbents for decarburization during landfill gas purification process.Moreover,as the strengths of ETS-10,it is a promising adsorbent for CH4,N2 and O2 separation.13X and AC have a high adsorption capacity for five typical VOCs,while only small amount of VOCs desorbed under vacuum operation.Hence,the adsorbents are fouling with adsorbed VOCs during adsorption-desorption cycles,resulting in negative impact on CO2 adsorption capacity.The pore size of 5A is smaller than the typical VOCs,therefore,it has low adsorption capacity for VOCs.There are significantly decreases of adsorption capacity on 13X and AC,whereas 5 A has slight decrease.It is illustrated a positive correlation between the decrease of CO2 adsorption capacity and the VOCs adsorption capacity.The VOCs in landfill gas have greater impact on CO2 adsorption of 13X and AC instead of 5 A.13X and 5 A have higher adsorption capacities of water vapor than carbon-based adsorbents.The CO2 adsorption capacities of 13X,5 A and USY declined after water vapor adsorption,which are 99%,90%and 83%,respectively.As the higher Si-Al ratio of USY,there is less impact of water vapor on CO2 adsorption capacity.For AC,the CO2 adsorption capacity has been slightly influenced by water vapor.13X,5A and USY are sensitive to water vapor,which can make these adsorbents almost lose the CO2 adsorption capacity.In contrast,water vapor causes little effect on AC.In conclusion,13X,5A and USY can be used for CO2 removal since the good CO2 adsorption capacity and selectivity.If 13X is selected as a decarburization adsorbent,the severe dehydration and de-VOCs process is a prerequisite.5A and USY are sensitive to water vapor,but 5A has good resistance to VOCs,so a strict dehydration process is necessary if 5A and USY are used as adsorbents before decarburization process.