Shift, high temperature

This reaction is first conducted on a chromium-promoted iron oxide catalyst in the high temperature shift (HTS) reactor at about 370°C at the inlet. This catalyst is usually in the form of 6 x 6-mm or 9.5 x 9.5-mm tablets, SV about 4000 h . Converted gases are cooled outside of the HTS by producing steam or heating boiler feed water and are sent to the low temperature shift (LTS) converter at about 200—215°C to complete the water gas shift reaction. The LTS catalyst is a copper—zinc oxide catalyst supported on alumina. CO content of the effluent gas is usually 0.1—0.25% on a dry gas basis and has a 14°C approach to equihbrium, ie, an equihbrium temperature 14°C higher than actual, and SV about 4000 h . Operating at as low a temperature as possible is advantageous because of the more favorable equihbrium constants. The product gas from this section contains about 77% H2, 18% CO2, 0.30% CO, and 4.7% CH. ... 

Besides the effect of the presence of alkali on CO adsorption, there is also a stabilizing effect of adsorbed CO on the adsorption state of alkali. Within the high alkali coverage range the number of CO molecules adsorbed on promoted surface sites becomes practically equal to the number of alkali metal species and their properties are not dependent on the CO coverage. In this region CO adsorption causes also stabilization of the adsorbed alkali, as indicated by the observed high temperature shift of the onset of alkali desorption. 

Different types of gel materials, such as polysaccharides, proteins and synthetic polymers, are now used to entrap biocatalysts. Among them, photo-crosslinkable resin prepolymer ENTP-4000 as shown in Eig. 7 is more useful compared to others. Entrapment of biocatalysts should be carried out under the illumination of near ultraviolet hght within 3-5 min, by which high temperatures, shifts of pH to extremely alkahne or acidic sides are avoided. ENTP-4000, hydrophobic photo-crosslinkable resin prepolymer, is one of the most suitable prepolymers for entrapment of p-glucosidase. Molecular weight of its main chain is about 4000. 

Andreev and coworkers—promoting effect of Cu addition on Fe-Cr shift catalysts, and Raney Cu/Zn catalysis described by an associative mechanism. Andreev and coworkers240 added promoters to traditional high temperature shift Fe-Cr catalyst, and found that Cu and Co moved the maximum in the CO conversion curve to lower temperatures. No explanation was provided for the effect. 

Wheeler, Schmidt, and coworkers—kinetic model for Pt/Ce at short contact times over medium to high T range. In 2004, Wheeler and coworkers422 reported on the water-gas shift reaction over Pt/ceria at short contact times (0.008-0.05 sec) for temperatures between 300 and 1000 °C. The reactant composition for CO, H2, and H20 was 1/2/4. A Langmuir-Hinshelwood kinetic model was used to adequately fit the medium and high temperature shift data ... 

Querino, do Carmo Rangel, and coworkers—improvement in catalytic activity by doping Pt/zirconia with Ce. Querino et al.469 reported that doping of a fraction of approximately 0.1 Ce to Pt/Zr02 led to enhanced activity for the high temperature shift reaction. The catalyst was prepared using a sol-gel synthesis... 

Table 100 CO conversion rates as a function of steam/gas (S/G) ratio under high temperature shift conditions. Feed (dry basis) 10% CO, 10%CO2, 50% H2, 30% N2. WHSV = 42 h l. 33 mg of catalyst employed469...

E) Metal/a-Fe203 catalysts. Although Fe Cr and modified Fe-Cr-Cu catalysts have been used extensively in industry for high temperature shift applications, this section covers references only from 1993 to the present510-526 specifically dealing with metal/a-Fe203 catalysts for low temperature shift. 

Table 130 Rate enhancement observed after adding 1 %Pt to various oxides for high temperature shift carried out at 450 °C using a feed containing 9%CO, 9%HzO, balance N2 with flow rates ranging between 150 and 600 cm3/min538...

Certainly, water-gas shift has in the past been carried out using zeolites as supports for Rh (e.g., Rh/Y Zeolite and Rh/NaY Zeolite539), ZnO (Na/mordenite540), and Fe oxide (Na/mordenite540) in high temperature shift catalyst studies. More recent investigations are aimed at applying zeolites and related materials for use in low temperature shift catalysts. 

The reformate gas contains up to 12% CO for SR and 6 to 8% CO for ATR, which can be converted to H2 through the WGS reaction. The shift reactions are thermodynamically favored at low temperatures. The equilibrium CO conversion is 100% at temperatures below 200°C. However, the kinetics is very slow, requiring space velocities less than 2000 hr1. The commercial Fe-Cr high-temperature shift (HTS) and Cu-Zn low-temperature shift (LTS) catalysts are pyrophoric and therefore impractical and dangerous for fuel cell applications. A Cu/CeOz catalyst was demonstrated to have better thermal stability than the commercial Cu-Zn LTS catalyst [37], However, it had lower activity and had to be operated at higher temperature. New catalysts are needed that will have higher activity and tolerance to flooding and sulfur. 

Downstream of the reformer the CO is converted into hydrogen by two subsequent water-gas shift sections a high-temperature shift (HTS) followed by a low-temperature shift (LTS). This is done because the equilibrium of the WGS reaction lies at the product side at lower temperatures (around 200 °C), but the reaction kinetics are faster at increasing temperature. Therefore, to reach high CO conversions, most of the CO is converted in a HTS section and the remainder is converted within a LTS section. 

K-HTC is used more successfully for sorption-enhanced water-gas shift [27]. Breakthrough of CO occurs at the same time as breakthrough of CO2 [37] and the amount of steam necessary for desorption can be kept relatively low [27]. A commercial high-temperature shift catalyst can be used. During desorption in steam, the catalyst can be oxidized, so it is necessary to add some hydrogen to the purge steam [27]. 

For MCFC SOFC, no high temperature shift, low temperature shift, nor CO removal required. 

A conceptual design and selection of an ATR biodiesel processor for a vehicle fuel cell auxiliary power unit were reported by Specchia et al. [81]. Three processor options were compared for H2 production with respect to efficiency, complexity, compactness, safety, controllability and emissions. The ATR with both high-temperature shift (HTS) and low-temperature shift (LTS) reactors showed the most promising results. 

A high temperature water-gas shift reactor 400°C) typically uses an iron oxide/chromia catalyst, while a low temperature shift reactor ( 200°C) uses a copper-based catalyst. Both low and high temperature shift reactors have superficial contact times (bas on the feed gases at STP) greater than 1 second (72). 

On the basis of the calibration by melting points and phase transitions, a number of shift thermometers have been developed for solid-state NMR spectroscopy in various temperature ranges. Wehrle et al. 144), for example, used the line splitting in the N CP/MAS NMR spectrum of the organic dye molecule tetra-methyldibenzotetraaza annulene (TTAA) in the temperature range 123—405 K. A high-temperature shift thermometer for temperatures of up to 790 K was developed by van Moorsel et al. 40) on the basis of Sn MAS NMR spectroscopic... 

For the WGS reaction, the standard testing conditions were chosen as typical of the low-temperature shift inlet conditions imposed by conventional outlet high-temperature shift conditions, e.g., 200 °C 3% CO, 37% H2, 14% C02, 23% H20, Ar balance GSHV = 3000. 

M.-S. Xu, Z.-M. Du, X.-F. Gao, False transient method for determining effectiveness factors of high-temperature shift reaction catalyst B109, J. Chem. Ind. Eng. (China) 44 (1993) 465. 

Conventionally the reaction is performed in two stages, the so-called high- and low-temperature water-gas shift. In large-scale industrial processes, Fe203/Cr203 catalysts are applied for high-temperature shift (which is then performed between... 

Ndm3 (min gcal) Tests were performed for both low- and high-temperature water-gas shift. The feed was composed of simulated high-temperature shift product for low-temperature shift (3% CO, 14% C02, 25% HzO and 55% H2) and of a simulated steam reforming product for high-temperature water-gas shift (9% CO, 8% C02, 34% H20 and 49% H2). 

Temperature ramps were applied for testing, which were set to 300, 325 and 350 °C and held for 1 h each for low-temperature shift. For high-temperature shift testing, the temperature ramps were set to 350,375 and 400 °C for the same duration. These low reaction temperatures compared with industrial conditions for high-temperature shift (up to 450 °C) were applied because mostly precious metal catalysts were tested in the screening protocol, which are subject to coke formation at higher reaction temperatures. 

The shift from carbon monoxide to carbon dioxide generally occurs in two steps - first a High Temperature Shift Conversion and then a Low Temperature shift conversion. In some cases the two steps may be combined in one isothermal or adiabatic step called Medium Temperature Shift Conversion. When the feed gas to the CO conversion is not desulfurized, the CO conversion is called Sour Gas Shift and a special type of sulfur-resistant catalyst is used166. 

As shown above, Eq. (5.2) is exothermic, and high temperatures are unfavorable for complete conversion. In the High Temperature Shift (HTS) conversion, the synthesis gas is passed through a bed of iron oxide/chromium oxide catalyst at around 400°C and a pressure of 25 to 28 bar. The CO content of the gas is reduced to about 3% (on a dry gas basis), and this is limited by the shift equilibrium at the actual operating temperature. The catalyst is not... 

In 2001 Hyprotech and Synetix announced an ammonia plant simulation that can be used for modeling, on-line monitoring and optimization of the plant. The simulation includes Synetix reactor models, customized thermodynamic data and information to simulate the performance of a range of catalysts. The reactor models in the simulation include Primary and Secondary Reformers, High Temperature Shift converter, Low Temperature Shift Converter, Methanator and Ammonia Synthesis Converter80. 

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