Study On Hydrate Based Biogas Decarburization Technology In The Presence Of TBAB And TEAB

As a clean,renewable and valuable resources in our country,biogas is significance to improve China’s energy structure,protect the environment,and achieve sustainable energy development.But the existence of high CO₂ content,low calorific value and other shortcomings of biogas,affecting its efficient use,it is necessary to capture CO₂ from the biogas.Hydrate based CO₂ capture method from biogas has the advantages of mild reaction conditions,low energy consumption and environmental friendly,and has attracted widely concerned by researchers.At present,there are some unsolved technical problems for hydrate based CO₂ capture technology,such as the poor selectivity,low formation velocity.In this paper,the effection of TBAB solution and the TEAB solution for hydrate equilibrium of CH₄,CO₂ and CH₄/CO₂ systems was studied by an isochoric pressure–search method;instead of the equilibrium separation method,a pressure recovery method was used for hydrate based CO₂ captured from biogas was investigated.The results provide the theoretical reference for the development of high efficiency,low energy consumption technology to capture CO₂ from biogas.The phase equilibrium temperature for TBAB solutions was ranged from 273.6 to 294.2 K,and the pressure was ranged from 0.54 to 14.57 MPa.TBAB solution with concentration of 1.76 wt% has a promotion effect when the pressure is lower than 3 MPa,and has no significant promotion effect when the pressure is higher than 3 MPa.The phase equilibrium conditions of TBAB semi–clathrate hydrate for CH₄/CO₂ mixed gas were mainly determined by the concentration of TBAB solution,independent of the concentration of CH₄/CO₂ mixed gas.The phase equilibrium temperature of TEAB solutions ranged from 274.1 to 288.2 K,pressure ranged from 2.75 to 12.18 MPa.When the concentration of TEAB solution is lower than 10.00 wt%,the hydrate phase equilibrium data is similar to the data in water.When the concentration of TEAB solution is higher than 10.00 wt%,TEAB functioned as hydrate inhibitor.The selectivity of CH₄ and CO₂ hydrate formation in TEAB solution is better than that in TBAB solution.The results of the separation experiments show that the pressure recovery method was functioned more effective for gas separation than the pressure unrecovery method,and when the operation pressure was 3 MPa,the effect of CO₂ capture for TBAB solution with concentration of 5.00 wt% is better than the concentration of 3.32 wt% and 14.00 wt%.The maximum concentration of CH₄ in the residual gas phase was 93.52 mol%,and obtained at the operating conditions of 1.14 MPa,5.00 wt% TBAB solution with pressure recovery method.The maximum CO₂ separation factor was 52.87,and the maximum CH₄ recovery factor was 2.050,which was obtained under pressure recovery method at 1.14 MPa and 1.76 wt% TBAB solution.The separation results of CH₄/CO₂ mixture gas in TEAB solution with mass fraction of 5wt% is better than the results of TBAB solution.The use of pressure recovery method can improve the separation effection from biogas in the presence of TEAB.