Study Of Manganese-based Mid-temperature Desulfurizer Prepared By Supercritical Water Impregnation Method

In recent years, supercritical fluids, especially water, have received considerable attention due to its high density, high diffusivity, low viscosity as well as the ability to control its properties by varying the pressure and temperature conditions. One of the applications of supercritical water is hydrothermal synthesis reactions. It is not needed to use the toxic or noxious solvents and pretreat samples such as calcination during preparation catalyst by supercritical water impregnation. Thus, supercritical water impregnation, a solvent-free and environmentally benign procedure, would be expected as a new preparation method for supported catalysts.Gasification technology obviously raises the utilization efficiency of coal. The desulphurization purification of coal gas at mid-temperature is one of the key technologies of the large scale application of coal gasification technology. The mid-temperature desulfurizer must possess both good sulfidation performance and stable maintenance in hot coal gas. Therefore the improving of the mechanical strength and anti-pulverization ability of desulfurizer at mid-temperature is very important. Various metal oxides and their mixtures have been investigated as desulfurizers to remove H2S from hot coal gas. It is shown that the sulfidation reactivity of manganese oxide was higher than that of CaO, ZnO and other metal oxides in mid-temperature H2S removal and its thermodynamics and kinetics were also favorable.Based on these studies, a novel approach of preparing mid-temperature desulfurizers was explored to improve the performance of desulfurizer. A series of manganese-based sorbent supported onγ-Al2O3 carrier were prepared by supercritical water impregnation method. And the effects of preparation and sulfidation conditions on the sulfidation performance of manganese-based sorbent was investigated in a fixed-bed reactor under simulative coal gas. The products were analyzed by X-ray diffraction (XRD), scanning electron microscope (SEM) and atomic absorption spectrophotometer (AAS). The conclusions are as follows:1)The active components prepared by supercritical water impregnation method is almost completely and uniformly uploaded onγ-Al2O3 carrier.2)The desulfurizers prepared at 350oC, 30min, 100ml volume of precursor solution possess the best combination of high attrition resistance and sulfidation reactivity, sulfur removal efficiency in the moderate temperature of 400oC. 3)The mechanical strength of fresh and sulfided Mn-based desulfurizer is better than that of carrier and they are also stable in sulfidation–regeneration cycle.4)In five continuous cycles of sulfidation and regeneration, the efficiency of hydrogen sulfide removal is decreased slowly. But regeneration performance is relatively good, although desulfurization performance is slightly lower than fresh desulfurizer after regeneration. With the increase of regeneration operating cycle, desulfurization performance was still stabilized, which is conducive to realize industrialization.5)Desulfurization temperature has greater impact on the desulfurization activity. When the desulfurization temperature is increased from 300oC to 550oC, the sulfur capacity and time of break-through is significantly increased from 1.5g S/100g sorbent to 2.5g S/100g sorbent.6)Increase of space velocity can limitly improve the sulfur capacity of desulfurizer, but too high space velocity causes the decrease of desulfurization efficiency and the space velocity of 3000h-1 is optimal.7)The addition of copper in Mn-based desulfurizer can significantly improved the efficiency of hydrogen sulfide removal.