Study On Removal Of Hydrogen Sulfide From Raw Gas By Modified Semi-coke

High-efficiency or noble metal catalysts have always been used during the process of producing ammonia, methanol and methanation gas when coal, petroleum and natural gas are as raw materials. Poisoning of sulfur complexes from raw gas is the major reason of the catalyst deactivation. The minim hydrogen sulphide (e.g, the H2S content is 0.1ppm) can make catalysts deactivate completely.In this paper, activated semi-coke in Inner Monogolia is as precursor of desulphurizer based on activated carbon. A series of H2S removal agents of activated semi-coke are prepared from activated semi-coke by means of hydrothermal method, HNO3 oxidation and heat treatment at high temperature as well as their combined modification. The composition and surface acid-base properties for semi-coke and activated semi-coke samples are characterized by means of acid-base titration methods. The analytical results show that raw semi-coke is higher in oxygen-containing functional groups content and fixed carbon content. Its contents of surface acidic and basic functional groups are lower, but the contents of basic functional groups are higher than that of acidic functional groups. The hydrothermal chemical modification can decrease the surface oxygen-containing acidic functional groups and raise the content of surface basic functional groups. HNO3 oxidation modification can increase the contents of oxygen-containing and nitrogen-containing functional groups of modified semi-coke. The de-ash capacity of HNO3 oxidation modification increases obviously. The basic functional of the surface of semi-coke can be increased by calcining at high temperature when oxygen or water is existent. The highest content of surface basic functional groups of modified semi-coke is by calcining at moistening and ventilating oxygen. The capacity of H2S removal and effect of process operation condition on H2S removal activities for raw semi-coke and the activated semi-coke are investigated in fixed bed reactor in simulated raw gas. The results indicate that the H2S removal efficiency and capacity for raw semi-cokes are very low, the hydrothermal method, HNO3 oxidation and heat treatment modification of the activated semi-cokes all can increase the H2S removal efficiency and capacity, that is, firstly, activated semi-coke treated by the hydrothermal method under high pressure. Secondly, activated semi-coke treated by HNO3 oxidation for half and an hour, then water cleaning and drying. Thirdly, it is calcined for half and an hour at 720℃, the atmosphere of 1%O2, 45%H2O and the rest of nitrogen. With this method the best desulfuring agent P270HN45NOHO720 with higher sulfur capacity and longer breakthrough time is prepared. The optimal conditions of H2S removal by activated semi-coke are desulfurization temperature 75℃, H2O content of 8-10%, O2 content from3% to 5%, and space velocity of 900h-1. The desulfurization reaction is controlled by diffusion at space velocity lower than 900h-1, while it is controlled by surface reaction at space velocity higher than 900h-1.The relationship between desulfurization property of different activated semi-coke and their physical parameters is analyzed. It is found that the activated semi-coke with high content of basic functional groups shows pretty well performance for H2S removal, but the desulfurizing capacity has no linear relationship with the content of basic groups. The activated semi-coke with large specific surface area shows desirable performance for H2S removal, but the desulfurizing capacity has no linear relationship to the specific surface area. The specific surface area of activated semi-coke is not the key factor for desulfurizing activity. XRD analyses indicate that there is CuO on the surface of desulfurizer which is prepared by dipping Cu(NO3)2 solution containing 4% CuO, calcining at 550℃a nd 720℃, and there is CuS on the surface of the spent carbon.Two methods, solvent regeneration and gas regeneration, have been used for the spent activated semi-cokes which had removed H2S. The solvents utilized is HNO3, it shows that HNO3 can regenerate the activated carbon by oxidation. The gases utilized are N2, 20%O2 in N2, the principles of regenerated activated semi-coke are thermal regeneration, oxidation, respectively. The best results are found as 65%HNO3, 20%O2 in N2, respectively. They can remove sulfur from the pore canal of carbon up to 66.70% and 85.93% of the total during the first regeneration cycle.The principle of H2S removal by activated semi-coke and effect of different factors on desulfurization property are clearly seen through above research work. So it can accumulate basic data for further industrial application.