Adsorption Separation Of Hydrogen And Methane From Coke Oven Gas

Coke oven gas, a byproduct of coking process, is one of the most potential hydrogen sources because it contains nearly 50% hydrogen and 30% methane. Therefore, recovering hydrogen from coke oven gas is a significant application. Hydrogen separation from coke oven gas is currently performed by activated carbon and zeolite 5A through pressure swing adsorption (PSA). Based on the characteristics of commerical adsorbents, in this work, activated carbons and zeolite 5A were modified to improve their adsorption performances. We also attempted to apply the new adsorbent ETS-4 in separating hydrogen and methane using its unique structure.The isotherms of CH4, H2, N2, CO and CO2 were measured by static volume on commerical adsorbents:activated carbon AC and zeolite 5A with temperature between 15 and 35℃and pressure below 1.0 MPa. The isosteric adsorption heats were obtained by the equation of Clausius-Claperyron. The breakthrough curves of simulated coke oven gas and the effects of pressure and feed gas flow on the adsorption were also investigated. The results show that the adsorption capacity of the five kinds of gas on the adsorbents is in the following sequence:CO2>CH4>CO>N2>H2, and that of CO2 is much larger than others. The capacities decrease with the increase of temperature and the isotherms of CO2, CH4, CO, N2 presents typeⅠ, while that of H2 presents linearity. The isosteric adsorption heat fluctuates with the change of adsorption capacity indicated that the surface of the adsorbents is energetically homogeneous and there is no interaction between adsorbed molecules. The breakthrough curves show that with the decrease of feed gas flow and the increase of adsorption pressure, the breakthrough time prolongs and the adsorption capacity increases.Activated carbons were prepared by subbituminous coal and the effects of preparation parameter such as KOH/coal ratio, activation temperature and activation time on the porous texture of carbons and their adsorption characteristics were discussed. When the pore diamater of prepared activated carbon was centralized in the range of 0.7-2 nm, the adsorption capacity of CH4 and the ideal equilibrium separation factor increased with the pore volume. The optimal conditions for preparing actived carbon for CH4 adsorption and separation of CH4/H2 are the of KOH/coal ratio of 5, activation temperature of 800℃and activation time of 90 min; and the optimal conditions for preparing actived carbon for H2 adsorption are the KOH/coal ratio of 4, activation temperature 800℃and activation time 60 min. The commerical activated carbon was modified by CH3(CH2)11SO3Na and MgO. The adsorption capacities of CH4 and H2 and the separation factor were investigated. After modification with CH3(CH2)11SO3Na and MgO, the adsorption capacities of CH4, H2 and ideal separation factor of CH4/H2 reached the maxmium when the concentration of CH3(CH)11SO3Na and Mg(NO3)2 was 2% and 0.5 mol/L, respectively.The submicron particle zeolite A with average particle size about 200-400 nm was synthesized using polyethyleneglycol (PEG-1000) as surfactant, and the hierarchical zeolite A was synthesized using [3-(trimethoxysilyl)propyl] octadecyldimethylammonium chloride (TPOAC) as mesopore directing agent. Both zeolites A were ion-exchanged with strontium nitrate. The prepared samples were characterized by XRD, nitrogen sorption, SEM, TEM and laser particle size analyzer and confirmed as submicron particle zeolite SrA and hierarchical zeolite SrA. The adsorption measurements of submicron SrA, hierarchical SrA and commercial 5A adsorbents were tested by static methods. The results show that both submicron SrA and hierarchical SrA have higher adsorption capacity of CH4 (and H2) and higher separation factor of CH4/H2 compared with commercial 5A. Submicron SrA shows the highest adsorption capacity of CH4 (and H2) and separation factor of CH4/H2.Microporous titanium silicate molecular sieve ETS-4 was prepared and then ion-exchanged with strontium nitrate. The SEM images show that the crystal has fiber-like aggregates morphologies and resembles two cauliflower heads attached to each other. The thermogravimetric analysis confirmed that the thermal stability was enhanced after ion-exchanged with Sr2+. The equilibrium and kinetics data of CH4 and H2 were obtained by concentration pulse chromatography. The effect of ion-exchanged with Sr2+ and temperature were also investigaed. After ion-exchanged with Sr2+, the Henry constant of CH4 and H2 increase and diffusion rates decrease. With the increase of dehydration temperature, the kinetic separation factor increases. When the temperature reached 310℃, the knietic separation factor increased to 8.91, indicating the the advantages of ETS-4 and its potential application in separation.