Study On Removal Of Hydrogen Sulfide From Simulated Syngas By Modified Semi-cokes And Regeneration

Hydrogen sulfide is one of the toxic and harmful gas, which is the major reason that high-efficiency noble metal catalysts have been deactivation during the process of producing ammonia, methanol and methanation gas. In addition, the H2S of natural gas burns into SO2, forming acid rain, resulting in environmental pollution, metal corrosion etc.In this paper, raw semi-cokes from Inner Mongolia were as precursors of the desulphurizer. A series of H2S removal agents of modified semi-cokes were prepared from raw semi-cokes by means of hydrothermal method, HNO3 oxidation and heat treatment at high temperature as well as their combined modification, and then loading CuO on the surface of the semi-coke exhibiting best desulfurizer.Raw and modified semi-cokes were determined all kinds of physical and chemical properties, the results were as follows: Raw semi-cokes contained much highter volatile, little fixed carbon, few surface acid-base properties, little specific surface area and pore volume; The modified semi-coke by means of hydrothermal method included less volatile, more surface base functional groups; The semi-coke treated with HNO3 oxidation had led to reducing ash, rising more volatile, acid surface; The process of heat treatment at high temperature in the present of H2O and O2 could remarkably improved volatile and surface base properties; The combined modification processes, the best one, made total basic amount increased by 7 times, surface area and pore volume reach to 468.42m2·g-1 and 0.2467 m3·g-1, respectively.The capacity of H2S removal and effect of process operation condition on H2S removal activities for various semi-cokes were investigated in fixed bed reactor in simulated syngas. The results indicated that the H2S removal efficiency and capacity for raw semi-cokes were very low; The ability of desulfurization greatly enhanced, that is, firstly, raw semi-cokes treated with the hydrothermal method under high pressure. Secondly, it modified by 45% HNO3 oxidation for half and an hour, then water cleaning and drying. Thirdly, that was calcined for half and an hour at 700℃, the atmosphere of 1%O2, 45%H2O and the rest of nitrogen(volume fraction). With this method the sulfur capacity of the best desulfuring agent was up to 5.14% at 70℃, ~4% H2O, ~1.8% O2 and space velocity of 1100h-1; Modified semi-cokes dipped complex solution of copper and ammonia could significantly improve desulfurization performance. At the same experimental conditions, the sulfur capacity of the semi-coke with only 1.5% CuO could reach to 9.31%; The optimal conditions of H2S removal by modified semi-cokes were desulfurization temperature ~70℃, H2O content ~2%, O2 content~1.3%, meanwhile, space velocity had great influence to desulfurization performance. When space velocity was 800h-1, the sulfur capacity of the desulfurizer reaction could reach to 15.5%.The relationship between property of different desulfurizer and their physical parameters was analyzed. It was found that the modified semi-coke with high content of basic functional groups showed pretty well performance for H2S removal, but the desulfurizing capacity had no linear relationship with the content of basic group; The modified semi-coke with large specific surface area and pore volume was favorable to remove H2S, besides, while average pore diameter was the range of 20-23?, the increase of sulfur capacity was with higher pore diameter; SEM analyses indicated that modified and supported technologies were reasonable and feasible, in the meantime, the predictive mechanism of hydrogen sulphide removal was correct.Two methods, (NH4)2S regeneration and nitrogen regeneration, have been used for the deactivation modified semi-cokes which had removed H2S. The effect combined (NH4)2S with steam regeneration was the desirable process, which could make sulphur recovery rate and sulfur capacity regeneration rate reach to more than 90%, and was higher accumulative sulfur capacity, the optimal conditions of regeneration was that the concentration of (NH4)2S was 2.5mol·L-1 with 30℃and 60min,the temperature of water steam was about 450℃associated heating 2h. In nitrogen regeneration, sulfur capacity regeneration rate was rather low and was greatly affected by temperature, time and frequency of regeneration. The best result was found that sulfur capacity regeneration rate was only 79.7%, and quite difficult recovery of sulfur.