Adsorption And Separation Of CO₂/CH₄ Of Landfill Gas On Organic Amine Alkali Metal Ion Modified Silica Gel Adsorbent

In recent years,the environmental pollution caused by the greenhouse effect has become increasingly serious,and most countries around the world have begun to pay attention to these problems.Carbon dioxide and methane are greenhouse gases,and the main components of landfill gas are CO₂ and CH₄.Landfill gas contains 40-60%CH₄,20-30%CO₂ and 10-20%trace element gas.Now landfill gas has been developed as secondary energy in the world,and the process of separating and recovering CO₂ and CH4 from landfill gas involves the treatment of CO₂/CH₄ mixture system.Based on the analysis of the performance of the original silica gel adsorbent,this paper discusses the characterization of silica gel before and after modification,the adsorption and separation effect of CO₂/CH₄ mixture and the actual performance of simulated landfill gas treatment by alkali metal ion modification,organic amine modification and organic amine alkali metal ion combination modification,and discusses the moisture content and regeneration of silica gel It can be analyzed and discussed.The main conclusions are as follows:（1）The adsorption isotherms of CO₂ and CH₄ on silica gel at 25℃,35℃and45℃were measured by static volume method.The adsorption isotherms were fitted by Langmuir model,sips model and Freundlich model.The maximum saturation and adsorption capacity of CO₂ and CH₄ were calculated.The results show that the adsorption capacity of the two gases decreases with the increase of temperature.According to the correlation coefficients and average relative errors of the three models,the results show that the sips model is the best for the adsorption isotherms of CO₂ and CH₄.Therefore,sips model is used to fit the experimental data.（2）Silica gel was modified by chloride solution of potassium,calcium,magnesium and barium,which was favorable for CO₂ adsorption.The order of adsorption performance of silica gel modified by different kinds of alkali metal ions is:Ba Cl₂>KCl>Ca Cl₂>Mg Cl₂,among which barium chloride modified silica gel is the best.After comparing the adsorption capacity of silica gel modified with different barium chloride concentration and the separation effect of CO₂/CH₄,the best modified concentration of barium chloride solution is 0.1 mol/L.The results of sips model fit show that the optimal adsorption capacity of the modified silica gel for CO₂ is 2.51mmol/g at 25℃,which is about 18.96%higher than the original activated carbon.The separation ratio of CO₂/CH₄ is 9.92,which is 23.84%higher than that of silica gel.（3）Using ethanolamine,diethanolamine and diethylenetriamine to modify silica gel,the most obvious effect is ethanolamine modified silica gel,its adsorption capacity of CO₂ is 84.83%higher than the original silica gel.However,the adsorption of CH₄on organoamine modified silica gel is similar to that of the original silica gel.The effect of silica gel modified by different kinds of organic amines on the separation of the mixture was:MEA>DEA>DETA.Through the study of the influence of different concentration of ethanolamine modified silica gel on the adsorption and separation of CO₂ and CH₄,it is found that when the ratio of ethanolamine and methanol is 1:6,the static saturated adsorption capacity of the modified silica gel for CO₂ reaches 3.90mmol/g,which is84.83%higher than the original silica gel,and the separation effect of CO₂/CH₄mixture is the best,the separation ratio is 8.51,which is 6.25%higher than the original silica gel under the same condition.（4）Barium chloride and ethanolamine were used to modify silica gel.The surface morphology of modified silica gel combines the characteristics of barium chloride modified silica gel and ethanolamine modified silica gel.The saturated adsorption capacity of barium chloride ethanolamine modified silica gel is 4.19mmol/g,which is about 98.57%higher than that of the original silica gel;the saturated adsorption capacity of CH₄ is 0.49mmol/g,which is about 63.33%higher than that of the original silica gel.The separation ratio of barium chloride ethanolamine modified silica gel to CO₂/CH₄ is 9.92,which is about 23.84%higher than the original silica gel.（5）In this paper,barium chloride ethanolamine combined with modified silica gel was used as adsorbent to test the adsorption and separation effect of the adsorbent on simulated landfill gas under different process parameters.The results showed that the best adsorption pressure of the silica gel adsorbent was 0.2MPa,and the best adsorption flow rate was 800ml/min.under this condition,the adsorption capacity of CH₄ and CO₂was 0.51mmol/g and 4.3mmol/g respectively,and the separation ratio was 10.38.With the increase of water content of modified silica gel,the adsorption capacity of CO₂increased,and the separation ratio of mixture increased obviously.However,if the water content is too high,the penetration time of CO₂ will be shortened.The regeneration experiment shows that the regeneration performance of the adsorbent is better,but it is slightly lower than the original silica gel.