Prepared And Performance Of Mn-based Mesoporous Sorbents With Wormlike-hole For Hot Coal Gas Desulfurization

In order to improve efficiency and reduce pollution emission, the clean coaltechnologies (CCT) are attracted more attention in the past decades. Power stationswith Integrated Coal Gasification Combined Cycle (IGCC) are promising technologyfor clean coal and efficient conversion. Unfortunately, about90%sulfur is convertedto H2S during the coal gasification process. H2S must be removed to preservedownstream equipment and minise emission to the environment. Compared with theconventional technique, the hot gas desulfurization (HGD) method is expected to be acrucial process in the IGCC system because it can utilize the thermal effectively. Thepure metal oxides sorbents, however, still suffered from several problems, such assintering, low duration and mechanical strength. In order to resolve theaforementioned problems, the mesoporous silica with wormhole-like channel wereselected as supports, a series of Mn-based sorbents with high sulfur capacity, highutilization and regeneration capacity was prepared. The following results andconclusions have been obtained in this dissertation:1. Effect of support on sorbent. A series of Mn2O3supported mesoporousMCM-41, HMS, and KIT-1sorbents with different frameworks were synthesized andtheir desulfurization performances were investigated at the range of600-850°C. Allmesoporous silica supported Mn2O3sorbents exhibited better desulfurizationperformance than Mn2O3/diatomite due to the high surface area and large pore volume,which could allow the rapid diffusion of gas molecules. The XRD and H2-TPR resultsconfirmed that both the surface area and the framework of support played animportant role in the desulfurization behavior of Mn2O3sorbents. The desulfurizationbehavior of KIT-1supported Mn2O3sorbent was better than Mn/MCM-41andMn2O3/HMS at high temperature due to the3D wormhole-like pore structure. Theresults of the eight consecutive desulfurization and regeneration cycles revealed thatthe Mn2O3/KIT-1was high stable with high sulfur capacity (160mg S/g sorbent). Thepresence of steam in hot coal gas has a very large influence on the desulfurizationperformance of Mn2O3/KIT-1.2. Fabrication and performance of xMnyCe/HMS sorbents. xMnyCe/HMSsorbents with wormhole like structure were synthesized. High sulphur capacity (121.7mg S/g sorbent) and utilization rate (82.4%) of4Mn1Ce/HMS sorbent at600°C could be achieved due to high-stable structure of wormhole-like mesoporous HMS andsynergetic effects of the manganese oxide and ceria oxide. The4Mn1Ce/HMS sorbentexhibited a complete regenerated ability and no obvious deactivation was observedafter eight consecutive desulfurization-regeneration cycles. The XRD patternsrevealed that in the4Mn1Ce/HMS sorbent, the active species of Mn3O4and CeO2were highly dispersed on the HMS support, and no MnSO4phase formed during thedesulfurization/regeneration cycles. The SAXRD, N2-adsorption, TEM, HRTEMshowed that the surface area of sorbent declined slightly after long term (8th)regeneration test, but the wormhole-like structure still remained in the4Mn1Ce/HMSsorbent.3. A series of xMnyMo/KIT-1sorbents with different Mn/Mo molar ratio weresynthesized and their desulfurization performances were investigated at the range of600-800°C. The results confirmed that textural properties as well as composition ofmixed metal oxide play an important role in H2S uptake. When the content of Mo waslow, the xMnyMo/KIT-1sorbents still have high surface area and large pore volume,and that structure could allow the rapid diffusion of gas molecules. The sulfurcapacity was increased due to the synergetic effects of Mn-Mo oxides. The90Mn10Mo/KIT-1exhibited a high sulfur capacity (168.4mg S/g sorbent) at700oC,and such behavior was maintained after five successive desulfurization-regenerationcycles. But when the molar ratio of Mn/Mo was50/50, the mixed oxides werecompletely formed MnMoO4phase with larger molar volume, which blocked thechannel more serious and the sulfur capacity declined remarkably. In addition, thesulfur capacity of90Mn10Mo/KIT-1declined significantly with the steam increment.4. Different loading percentages of Zn-Mn mixed oxides on mesoporous materialKIT-1with same Zn/Mn molar ratio (1/2) were synthesized. XRD results confirmedthat the mixed oxides were existed in ZnMn2O4. The ZnMn2O4with spinel structuresignificantly improved the vaporization of zinc at high temperature. Due to the highsurface areas and large pore volume, high sorbent utilization (85%) was achievedwhen the metal oxides content was lower than55wt%. Doping of CeO2(5wt%) intoZn-Mn/KIT-1sorbent could improve the dispersion of ZnMn2O4and decrease theparticle remarkably. The Ce-Zn-Mn/KIT-1sorbent exhibited a high sulfur capacity(171.7mg S/g sorbent) at550oC and this behavior was maintained in five successivedesulfurization-regeneration cycles. Because the ZnMn2O4with spinel structure wasinsensitive to steam during desulfurization, the sulfur capacity of Ce-Zn-Mn/KIT-1 sorbent was stability in different steam content.