Study Of Sorption Enhanced Reforming Process Of Methanol For Hydrogen Production

In this paper, methanol as raw material was studied by using CO2 sorption enhanced reforming process （SERP-MeOH） to obtain high-purity H2 direactly, which has a siginifcant impact on proton exchange membrane fuel cells （PEMFC）, chemical process, oil refinery and metallurgy process.Theomodynamic model of SERP-MeOH was established to simulate the trend of methanol conversion and hydrogen content changed with the CO2 remove ratio and reaction temperature. At the same methanol conversion, SERP-MeOH can lower the reaction temperature by 50℃and obtains high-purity H2 directly. When the sorption ratio of CO2 increased to 95%, the product gas of SERP-MeOH contains 32.81 ppm CO and 98.36% H2. While the sorption ratio of CO2 increased to 99%, the product gas contains no CO by thermodynamic simulation. This demonstrated the feasibility of sorption enhanced steam methnol reforming for direct high-purity H2 prodcution.The Mg-Al hydrotalcites （HT1c） as CO2 adsorbent was modified by impregnating 22wt% K2CO3 and evaluated by a thermogravity analyzer and by a fixed-bed reactor. The experimental results show that the 22wt% K2CO3 promoted-HT1c has a sortption capacity of 0.31mol/kg in TGA and fixed-bed reactor.22wt% K2CO3 modified Mg-Al hydrotalcites has a high CO2 adsorption capacity, fast adsorption rate with high stability compared with original hydrtalcite. These evaluation results demonstrated that 22wt% K2CO3 promoted HT1c can be used in the SERP-MeOH as CO2 adsorbent.On the basis of thermodynamic simulation and adsorbent evaluation, the SERP-MeOH was studied on a fixed-bed reactor loaded with physical mixture of industrial CuO/ZnO/Al2O3 catalyst and 22wt% K2CO3 promoted-HT1c adsorbent. The effects of temperature, steam-to-methanol molar ratio, space velocity and asorbent-to-catalyst mass ratio on SERP-MeOH were studied. Under the reaction temperature of 180 ℃, the H2 purity is 99.63%, much higher than 74.47%, the H2 content obtained by conventional steam methanol reforming. Besides, even though the temperature increased to 280 ℃, the product gas still contains 99.37%H2 obtained by SERP-MeOH. Moreover, the methanol conversion under sorption-enhanced regime at temperature of 230 ℃ is almost equaled to the methanol conversion under 280 ℃ without sorption-enhanced, which demonstrated the sorption-enhancement can decrease the reaction temperature by 50 ℃ at the same methanol conversion. Under steam/methanol molar ratio of 6, the CO concentration in the sorption-enhanced regime is nearly one sixth of that obtained by conventional steam methanol reforming. With the adsorbent-to-catalyst mass ratio of 4, the methanol conversion in the sorption-enhanced regime is 21.51% higher than that without sorption-enhanced. The H2 purity is higher that 99.17%, with space velocity increased from 4595h-1 to 6433h-1. All these experiments demonstrated the advantages of SERP-MeOH process that can directly obtain high-purity H₂ with low temperature and high methanol conversion.A prelimary research on the kinetic behavior of the SERP-MeOH process revealed that an apparent activation energy decrease of 44.5kJ/mol compared with 74.0kJ/mol, the apparent activation energy of conventional steam methanol reforming. This explained the reason that high methanol conversion can be obtained with lower temperature by using SERP-MeOH process.Regeneration of the adsorbent was also studied and optimized. An optimized gas compostion of 3%H2 with 97% steam was found can maintain the acitivity of the copper reforming catalyst. Optimized steam flow rate is 400mL/min with duration of 75-100 min. And the adsorbent’s regeneration ratio was around 80% obtained by steam regeneration. These demonstrated the feasibility of steam regeneration of 22wt% K2CO3 promoted hydrotalcite, which can be used in further studies or industrial scale-up.