Study on phase equilibrium of separation and purification for gas with high CO2 concentration based on hydrate method

The determination of the phase equilibrium of high-concentration CO2 gas hydrate is a key issue in the uiliation of gas drainage based on gas hydratio n separation technology. Using the visual gas hydrate phase equilibrium device ,combined with the constant volume temperature search method and the observation met hod,the phase equilibrium conditions of three high-concentration CO2 gas samples at different temperatures and pressures were first measured,and the high-concentrat ion CO2 gas was proposed on the basis of the experiment.Then,a mathematical formula was fitted to describe the relation of phase equlibrium temperature and pressur e. In addition,the difference in hydrate phase eqilbrium between high-concentration CO2 gas samples and pure CO2 and pure CH4 gas samples is compared. The res ults show that the conditions for the formation of high-concentration CO2 gas hydrates are relatively mild. Specically,the phase equilibrium pressure in this test range i s the lowest at a temperature of 0.44 °C,which is 1.58 MPa; the phase equllibrium temperature and pressure of high-concentration CO2 gas hydrates are in a binomial r elationship; the phase equilibrium curve of CO2 gas hydrate lies between the phase equilibrium curve of pure CH4 and pure CO2 hydrate,and is closer to the phase equ ilibrium curve of pure CO2; at lower temperature and pressure( 0.44 ~ 4.94 。C,1.58 ~ 2.80 MPa),the gas increasing CO2 concentration in the sample can reduce the p hase equlibrium pressure of high-concentration CO2 gas hydrate and improve its phase equlibrium conditions. At higher temperature and pressure( 4.94~ 7.80 °C,2.80 ~ 4.02 MPa),the change of CO2 concentration in the gas sample has an effect on hydration. The phase equlibrium conditions have lttle effect; the difference between t he calculated value of the pressure obtained from the relationship between the phase eqilibrium temperature and pressure of high-concentration CO2 gas hydrate and the actual measured value is small,and the average relative error is 2.33%,which can accurately predict high concentrations CO2 gas hydrate phase equllibrium conditio ns. Phase equlibrium measurement results of coal mine gas with high CO2 concentration provide experimental reference and theoretical basis for the selection of temp erature and pressure in the gas separation and CO2 capture and sequestration technology based on the hydrate method.