Study On Hydrate-based CO₂/H₂ Separation With 13X Molecular Sieve Supported Tetrabutylammonium Bromide Solution

The rising of CO₂ concentrations in the atmosphere may cause global warming and seawater acidification.Thus,it's has received much attention from human being.Thermal power plants are one of the main sources of CO₂ emissions.Therefore,CO₂ separation technology in thermal power plants is an important research direction.Hydrate-based carbon dioxide capture and separation provide a novel and feasible approach for green gas control.As an emerging CO₂ capture technology,hydrate method has been widely accepted as a research focus owing to the environmental protective characteristic,mild separation conditions,high separation selectivity and simplified approach.However,a group of key issues involving slow formation rate and low gas storage which caused by the relatively low speed of gas-liquid transfer remain to be solved.Therefore,13X molecular sieve is used as the carrier of TBAB solution in this paper to improve the gas-liquid mass transfer in the process of gas hydrate formation.The strengthening mechanism of 13X molecular sieve supported TBAB solution for separation of CO₂/H₂ mixture by hydrate-based carbon dioxide capture method is studied from various angles.And the effects of TBAB concentration,experimental pressure,experimental temperature and solution saturation of 13X molecular sieve on the formation kinetics and separation effect of CO₂/H₂ separation by hydrate method were studied.In addition,the hydrate formation and decomposition characteristics of TBAB/CO₂/H₂ system were studied by high pressure differential scanning calorimetry?DSC?.The formation heat and decomposition heat of TBAB/CO₂ hydrate were measured,which provided references for subsequent research.The following research results were obtained:?1?The first part of this work is the mechanism study on the effect of 13X molecular sieve coupled TBAB solution for hydrate formation.The kinetics process and hydrate formation process morphology in 13X molecular sieve/TBAB/CO₂/H₂ system were studied.Due to the dispersion of the 13X molecular sieve on the TBAB solution,the gas-liquid contact area is increased.Thereby the gas diffusion resistance is decrease and gas uptake increase.The outcome of this study indicated that compared with the hydrate formation process in TBAB solution by agitation,13X molecular sieve coupled TBAB can significantly enhance the rate of pressure drop and the gas uptake of hydrate.According to the SEM and Raman analysis,during the hydrate formation process,TBAB/CO₂ hydrate is found to adhere the surface of 13X molecular sieve and 13X molecular sieve don't change the crystal formation direction of TBAB/CO₂ hydrate.What else,CO₂ is present in 5¹²6² and 5¹²6³ cages,while there is no H₂ in the cage structure of the hydrate.?2?The second part of this work is the effect of 13X molecular sieve coupled TBAB solution for separation of CO₂/H₂ mixture gas process.Based on the characteristics of 13X molecular sieve coupling TBAB promoter at 276.15-280.65k and 3.0-6.0Mpa,the study explores the pressure drop curve,gas uptake and S.Fr.in the formation process of CO₂/H₂ hydrate?39.8%CO₂/60.2%H₂?.For 13X molecular sieve/TBAB/CO₂/H₂ system,0.6mol%?1.Omol%TBAB,277.15K?278.15K and 25%?50%water saturation is the best condition for hydrate-based CO₂ separation.The initial pressure has a great influence on the separation of CO₂/H₂,and the gas uptake of the mixture is positively correlated with the initial pressure.?3?The third part of this work is the thermal decomposition characteristics of TBAB/CO₂ hydrate formation.The heat flow curve of TBAB/CO₂ hydrate formation under different pressure conditions was measured by high pressure DSC,and the hydrate formation decomposition characteristics were analyzed.The hydrate decomposition temperature,hydrate decomposition heat,hydrate formation subcooling and hydration were obtained.The results show that increasing the pressure of CO₂/H₂ mixed gas can improve the formation conditions of TBAB/CO₂ hydrate,and can increase the amount of hydrate formation and the stability of hydrate.The mixed gas pressure increased from 0.8MPa to 4.5MPa,the required subcooling of TBAB/CO₂ hydrate decreased from 18.06K to 12.57K,the relative production increased from 0.43 to 1.09,and the decomposition temperature increased from 262.62K to 269.73K.