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- Novel sour water gas shift catalyst (SWGS) for lean steam to gas ratio applications
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Dry powder coal gasification is emerging as one of the most energy efficient methods for coal conversion. However, the low steam content, high temperature and high content of CO in the raw syngas make it difficult for a conventional sour water gas shift catalyst to be directly used for syngas conditioning. Conventional sour water gas shift takes place at very high steam to carbon monoxide ratio (H2O/CO), often 2 or above, but the H2O/CO ratio from a dry powder coal gasifier is often less than 0.8. To develop a sour water gas shift catalyst suitable for the lean steam raw syngas, we have prepared a series of MgAl2O4 spinel modified alumina supported CoMoOx catalysts by changing the content of K2O in the promoter, and tested them under lean steam to carbon monoxide (H2O/CO) ratio conditions for sour water gas shift process. Our results show that the addition of potassium into the catalyst increases the catalyst water gas shift activity at a lean steam to gas ratio, and that catalyst activity increases with the K2O content increase in 0-10 wt.% range; the potassium additive helps to increase the dispersion of MoO3 and improves catalyst strength and surface area. The increase of K2O content leads to higher catalyst activity for the CO shift reaction with little methane yield, reducing the hot spot formation in the catalyst bed. This may be due to the high K2CO3 content in the catalyst enhancing the surface affinity to steam in the syngas, and the basicity of K2CO3 depresses methane formation over the MoS2 active site. The 10.0 wt.% of K2O-containing SWGS catalyst showed the highest stability even in the absence of H2S in the feed gas for up to 90 min, and little H2S is released from the catalyst (reverse sulfurization) under such conditions. The optimized K2O-containing SWGS catalyst, e.g., QDB-5-10 has been used in an industrial plant for 2 years in a coal to methanol plant and showed stable and unique performance under the lean steam conditions, allowing the 1st stage SWGS reactor to be well within control. The potassium carbonate included in the catalyst is stable and little leachate occurred even after 2-years of use time on stream.
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- FDCDU15 - Catalytic Dehydrogenation of Propane by Carbon Dioxide : A Medium-Temperature Thermochemical Process for Carbon Dioxide Utilisation
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The dehydrogenation of C3H8 in the presence of CO2 is an attractive catalytic route for C3H6 production. In studying the various possibilities to utilise CO2 to convert hydrocarbons using the sustainable energy source of solar thermal energy , thermodynamic calculations were carried out for the dehydrogenation of C3H8 using CO2 for the process operating in the temperature range of 300-500℃. Importantly, the results highlight the enhanced potential of C3H8 as compared to its lighter and heavier homologues (C2H6 and C4H10,respectively ). To be utilised in this CO2 utilisation reaction The Gibbs Free Energy (∆_r G_m^θ) of each reaction in the modelled, complete reacting system of the dehydrogenation of C3H8 in the presence of CO2 also indicate that further cracking of C3H6 will affect the ultimate yield and selectivity of the final products. In a parallel experimental study, catalytic tests of the dehydrogenation of C3H8 in the presence of CO2 over 5wt%-Cr2O3/ZrO2 catalysts operating at 500℃, atmospheric pressure, and for various C3H8 partial pressures and various overall GHSV (Gas Hourly Space Velocity) values. The results showed that an increase in the C3H8 partial pressure produced an inhibition of C3H8 conversion but, importantly, a promising enhancement of C3H6 selectivity. This phenomenon can be attributed to competitive adsorption on the catalyst between the generated C3H6 and inactivated C3H8, which inhibits any further cracking effect on C3H6 to produce by-products. As a comparison, the increase of the overall GHSV can also decrease the C3H8 conversion to a similar extent, but the further cracking of C3H6 cannot be limited.
- Related item:
- Dry reforming of methane over ZrO2-supported Co-Mo carbide catalyst
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The process of dry reforming of methane has the potential to be an effective route for CO2 utilization via syn-gas production. In the present study, ZrO2-supported Co–Mo bimetallic carbide catalysts were prepared via a coprecipitation method through a combined reduction and carburization procedure employing a CH4/H2 (20/80 %) mixture. All of the as-synthesized materials were tested at 850C, under atmospheric pressure and a CO2:CH4 ratio of 1. The importance of the ZrO2 support became immediately apparent when it exhibited a higher conversion than the corresponding low-surface-area bulk Mo2C catalyst, which we attribute to lewis acid and base active sites on the surface of ZrO2. From catalytic tests and pre-and postreaction X-ray diffraction (XRD) patterns, we observed that different dispersions of the monometallic carbides, caused by varying the pre-heating temperatures on ZrO2, did not significantly affect conversion or yield. In contrast, incorporation of cobalt atoms into the Mo2C lattice significantly enhanced the conversion, yield and stability of the catalysts. Post-reaction XRD patterns indicated that the bimetallic carbide had enhanced the resistance to the oxidation effect that is known to deactivate Mo2C catalysts. In addition, increasing the Co loading in the mixed metal carbides was seen to enhance the resistance of the catalyst to the reverse water gas shift reaction, leading to improved stability of the H2 yields.
- Related item:
- Effect of Titania Addition on the Performance of CoMo/Al2O3 Sour Water Gas Shift Catalysts under Lean Steam to Gas Ratio Conditions
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CoMo/Al2O3 sour water gas shift catalysts with and without TiO2 modification have been tested in parallel industrial reactors under lean steam/gas conditions for two years, and part of catalyst samples was taken out each year during the maintenance period. The catalyst samples have been characterized using temperature programmed sulfurization (TPS), X-ray diffraction (XRD), and laser Raman and BET surface area measurements. The results have shown that adding TiO2 to the catalyst makes the active components, e.g., Mo and Co, easier to be sulfurized with higher sulfur capacity in the catalyst itself. This may be the main reason why the TiO2 modified CoMo catalyst to be active even at low H2S gas stream. The results from industrial operation showed that adding TiO2 to the shift catalyst increases the catalyst activity and stability, presents the higher shift activity in a broader range of H2S content, depresses the aggregating of the molybdenum oxide, and reduces carbon deposition. In addition, the TiO2 additive in the catalyst also helps to maintain the physical properties of the shift catalysts. In the freshly prepared catalyst, the active components e.g., MoO3 is mainly present in the internal surface or sublayer of the catalyst, but it gradually migrates to the catalyst surface with the time on stream. In summary, the CoMo/Al2O3 based sour water gas shift catalyst showed stable shift performance under the lean steam/gas conditions, adding TiO2 to the catalyst significant improves the catalyst activity and resulting into stable operation in the industrial reactor operation in a wide range of H2S concentrations.
- Related item:
- The effect of lanthanum addition on the catalytic activity of γ-alumina supported bimetallic Co–Mo carbides for dry methane reforming
- Description:
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The effect of lanthanum addition to c-alumina supported bimetallic carbides has been studied for the reaction of dry methane reforming using four different lanthanum loading levels of 1, 5, 10 and 15 wt% of lanthanum. It has been demonstrated that the addition of lanthanum to supported bimetallic carbides at low loading levels (1 wt%) results in smaller carbide crystallite sizes compared to catalysts containing either no lanthanum or higher lanthanum loading levels (5–15 wt%). Increased lanthanum loading results in increased carbon dioxide desorption at 500–700 _C. Reactions indicated that increased lanthanum loading resulted in significantly reduced product yields due to increased reverse water–gas shift activity. All materials exhibited degrees of sintering during the reaction. It was found that cobalt reacted with lanthanum species to form a LaCoO3 phase. The 1 wt% catalyst possessed superior catalytic properties for dry methane reforming and was tested for 100 h. After an initial loss of activity, the catalyst appeared to stabilise, however, a decrease of *3 % in the H2:CO ratio, evidence of carbide crystallite growth and carbon deposition, indicated that a shift in the side reactions had occurred during the reaction.
