Experimental Study On Purification Of Landfill Gas By Ammonia Modified Activated Carbon

China's biogas and landfill gas resources are abundant,but its utilization rate is low.The reasons are mainly due to the following two aspects: Firstly,the presence of carbon dioxide greatly reduces the calorific value of biogas.Therefore,direct combustion is limited in use.On the other hand,incineration will bring about environmental pollution,since the existence of S,H2 S and other substances in the biogas.In order to improve utilization,the gas needs to be purified.There is a lot of municipal rubbish produced in China every year,and so on abundant landfill gas.The main component of landfill gas is methane,carbon dioxide and nitrogen.How to purify landfill gas is also beginning to attract attention.However,in recent years the national research on the separation of methane and carbon dioxide has been deep enough,but little research on nitrogen remove.Gas separating by pressure swing Adsorption(PSA)method has been preliminarily industrialized because of its simplicity in operation,low energy consumption,non-corrosive and pollution,and simple process.However,there have been cases where the product gas recovery rate is low and the selectivity of the adsorbent is constant.Therefore,the key technology of removing carbon dioxide by pressure swing adsorption is the selection and development of high efficiency decarbonizing adsorbent.Activated carbon has a large pore structure and a large specific surface area,and the surface can be attached with special functional groups.These structural characteristics make activated carbon have a wide range of applications,and the research on activated carbon has also become a hot topic.In this paper,ammonia was used to modify activated carbon and CH4 and N2 were used as sample gas.The effects of modification temperature,modification time,and ammonia concentration(in terms of mass fraction)on the specific surface area,surface chemical structure and adsorption capacity of activated carbon were investigated.The change of activated carbon performance before and after modification was studied on the adsorption capacity and separation coefficient of modified activated carbon for methane and nitrogen,and the following conclusions were obtained:(1)Characteristics of the effect of ammonia concentration on the surface structure of activated carbon: The test uses activated carbon with a mass fraction of 25%,20%,15%,10%,and 5% ammonia for 25 hours at 25°C,and passes the scanning electron microscope,specific surface area Analytical instruments and infrared spectra were used to analyze the changes in the specific surface area,total pore volume,pore volume,absorption peak,and pore diameter of activated carbon before and after modification,and the following conclusions were reached: After activated carbon was modified with ammonia water with a mass fraction of 10%,activated carbon was used.Alkaline groups on the surface increased,the content of acidic groups decreased,the number of micropores on the surface of activated carbon increased,and the absorption peaked,increasing the adsorption of methane and nitrogen.(2)The effect of ammonia concentration on the adsorption performance of activated Carbon: The experiment was conducted on activated carbon 12 h at ambient temperature with mass fraction of 5%,10%,15%,20% and 25%,and gravimetric method was used to analyze the adsorption amount of methane on activated carbon.The following conclusion was drawn: At ammonia mass fraction of 10%,the adsorption peaked at a peak of 1.067 kg/mol,an increase of 2.49% compared to 1.046 kg/mole of the original activated carbon.Under this modified condition methane and nitrogen were The separation factor increased to 5.10,which was 1.796% higher than the 5.01 of the original activated carbon.In addition,the separation coefficient of mixed gas composed of nitrogen and methane by ammonia-modified activated carbon is generally improved.Among them,the separation coefficient of the two gases with the activated carbon modified with 5% by mass of ammonia has reached the maximum value.The maximum is 5.36.It is 6.98% higher than the original activated carbon.(3)Effect of modified temperature on adsorption performance of activated carbon: In the experiment,the ammonia solution with mass fraction of 5% was used for modification at different temperatures(20,30,40,50,60 ?)for 12 hours,and the adsorption capacity of activated carbon for methane was analyzed.The following conclusions are drawn: when the modified temperature was 50 ?,the methane adsorption amount reaches a peak value of 1.053 kg/mol.Compared with the original activated carbon and the modification temperature of 20°C,the adsorption amount is increased by 0.699% and 1.15% respectively.(4)The test was carried out with a 5% aqueous ammonia solution at 105 k Pa and 25°C for 3 hours,6 hours,9 hours,12 hours,and 24 hours respectively.The activated carbon is fully contacted with the gas in the shaker to react until the concentration of methane and nitrogen in the container is not changed.The residual gas concentration is measured to further calculate the amount of activated carbon adsorbed on methane and nitrogen.The following conclusions were reached: When the modification time was 12 h,both the methane adsorption amount and the separation coefficient of the two-component gas reached the optimum values.The peak adsorption amount of methane was 1.031 kg/mol compared with 0.989 kg/mol when the modification time was 3 h,which increased by 4.25%,and the separation factor was 5.36,which was 6.98% higher than 5.01 of the original activated carbon.