Syngas Purification by Porous Amino-Functionalized Titanium Terephthalate MIL-125

Abstract

The adsorption equilibrium of carbon dioxide (CO2), carbon monoxide (CO), nitrogen (N-2), methane (CH4), and hydrogen (H-2) was studied at 303, 323, and 343 K and pressures up to 7 bar in titanium-based metal-organic framework (MOF) granulates, amino-functionalized titanium terephthalate MIL-125(Ti)_NH2. The affinity of the different adsorbates toward the adsorbent presented the following order: CO2 > CH4 > CO > N-2 > H-2, from the most adsorbed to the least adsorbed component. Subsequently, adsorption kinetics and multicomponent adsorption equilibrium were studied by means of single, binary, and ternary breakthrough curves at 323 K and 4.5 bar with different feed mixtures. Both studies are complementary and aim the syngas purification for two different applications, hydrogen production and H-2/CO composition adjustment, to be used as feed in the Fischer-Tropsch processes. The isosteric heats were calculated from the adsorption equilibrium isotherms and are 21.9 kJ mol(-1) for CO2, 14.6 kJ mol(-1) for CH4, 13.4 kJ mol(-1) for CO, and 11.7 kJ mol(-1) for N-2. In the overall pressure and temperature range, the adsorption equilibrium isotherms were well-regressed against the Langmuir model. The multicomponent breakthrough experimental results allowed for validation of the adsorption equilibrium predicted by the multicomponent extension of the Langmuir isotherm and validation of the fixed-bed mathematical model. To conclude, two pressure swing adsorption (PSA) cycles were designed and performed experimentally, one for hydrogen purification from a 30/70% CO2/H-2 mixture (hydrogen purity was 100% with a recovery of 23.5%) and a second PSA cycle to obtain a light product with a H-2/CO ratio between 2.2 and 2.4 to feed to Fischer-Tropsch processes. The experimental cycle produced a light stream with a H-2/CO ratio of 2.3 and a CO2-enriched stream with 86.6% purity as a heavy product. The CO2 recovery was 93.5%.