Studies On Removing Minor Content Of Hydrogen Sulfide In Gas By Pressure Swing Sorption

Removal of the toxic gas, H2S, is becoming more and more important as the requirement of environmental protection increases. Regeneration of conventional adsorbents or sorbents commonly used for trace H2S removal is often very difficult, which remains to be a big problem, and on the other side, most new methods still need further modification to be widely used. This work demonstrates that a pressure swing sorption (PSS) process operated at the ambient temperature can be used to remove the trace hydrogen sulfide impurity by using a porous solid coated with a solvent as the sorbent.The sorbent regeneration is achieved by pressure reduction and back-purge with a part of the purified gas.The process has a broad prospect for industry application, for its'easy operation, compact device and cheap sorbent.First part of this work is the fundermental study of the process, including characterization of the sorbents and the breakthrough experiments of the CH4 gas containing 190ppm H2S. Results showed that the dual modes of absorption and adsorption of hydrogen sulfide by the solvent and the solid adsorbent provide a higher capacity for its sorption than the solvent and adsorbent alone. The sorbent regeneration could be achieved by pressure reduction and back-purge at ambient temperature in short time and it's capacity remains stable after many cycles of breakthrough and regeneration just as the liquid film, which proved the feasibility of the PSS process using this new sorbent.Then factors influencing the performance of the process, such as the solid and solvent species, solvent loading rate, pressure, sorbent length, gas flow rate and temperature, were studied. Silica gel loading 26% triethanolamine(TEA) was chosen as the appropriate sorbent, 0.43MPa as the operating pressure and 0.021m/s as the gas flow rate.PSS process was conducted under the chosen condition. Cycle sequence including the times for sorption, pressure equalization, blow down and purge, the propriate purge gas velocity and purging ratio were determined. The purging ratio is 0.25 if the permissible hydrogen sulfide content in natural gas is 5 ppm. Even less purging ratio is possible if the kinetics of mass transfer could be improved. Continuous operation test demonstrated that the expected characters of the processcan be achieved rapidly and remained stable in long-time, which proves the industrial applicability of the new technology.At last, a breakthrough model of the the process containing parameters of axial diffusion and absorbing mass transfer was established based on the double-film theory. Results showed that simulated breakthrough curves fit the experimental ones well, and the process mass transfer was proved to be gas film diffusion controlled which could be promoted by increasing the bed porosity or reducing the sorbents diameters.