Simulation Of Hydrogen Purification By Fixed-bed Adsorption And Preparation Of Shaped ZIF-8 With Determination Of Its Adsorption Performance

Hydrogen is regarded as the the most promising clean energy due to its abundant sources,green and low carbon characteristics.The sources of hydrogen in China mainly include reforming of fossil fuels,by-product hydrogen from refining and chemical industries,electrolysis of water.Among them,the by-product hydrogen comes from a wide range of sources and contains a considerable number of light hydrocarbons and hydrogen.If the hydrogen in it can be effectively recovered,it will provide a source of hydrogen for the refinery and market.This paper focuses on fixed-bed adsorption separation,with the goal of recovering high-purity hydrogen from hydrogen-containing tail gas,simulates the process of the 2-bed 6-step pressure swing adsorption with traditional double-layer fixed adsorbent.The performance of shaped ZIF-8 forhydrogen purification is also investigated to explore the potential of ZIF-8 for industrial scale application in the field of adsorption and separation.The propane dehydrogenation tail gas containing H2/CH4/CO/CO2/N2 is used as the feed.The adsorption bed is filled with a double-layer adsorbent of activated carbon and5 A molecular sieve,and a 2-bed 6-step of pressure swing adsorption process is designed.The effects of operating and equipment parameters such as adsorption time,adsorption pressure,adsorbents height,and feed to purge ratio on the process are analyzed.Hydrogen product with the purity of 99.908 mol% and recovery of 69.70% is obtained under the optimal conditions of 120 s adsorption time,2.5 MPa adsorption pressure of,adsorbent height ratio of activated carbon: 5A molecular sieve = 4:6,and feed to purge ratio of 0.15.The corresponding energy consumption per unit product is calculated as 552.05 kg standard oil/t hydrogen product.To investigate the potential of ZIF-8 in the industrial fixed-bed adsorption process,shaped ZIF-8 in different additives ratios with methylcellulose and deionized water is prepared.It is applied to the adsorption and separation of CH4/H2 mixed gas.The characterization results of the shaped material show that the microporous structure of the ZIF-8 is blocked or covered with the increasing of the ratio of the additive,,which reduces the adsorption capacity of the ZIF-8,but its particle strength is greatly improved.The optimum proportion of shaping additive is 10 wt% methylcellulose,and pure gas adsorption isotherm experiments and mixed gas separation experiments are carried out.The results show that the saturated adsorption capacities of pure CH4 and H2 on the shaped ZIF-8 are significant difference,and the average isosteric adsorption heats are 26.55 k J/mol and 12.29 k J/mol respectively.Compared with the original ZIF-8,the separation selectivity of the shaped ZIF-8 added with 10 wt% methylcellulose decreased by 35.09%,and the unit adsorption capacity of CH4 decreased by 23.7%.