Medium-temperature shift

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. 

Substituting the HT and LT shift with an isothermal Medium Temperature shift with a typical exit temperature of 260 °C would produce results similar to those provided by the combination of HTS and LTS. It is obvious that only a relatively expensive feed and a cheaper fuel would justify the additional investment needed to supplement the HT shift with a LT shift or install an isothermal MT shift in place of both of them225. 

The Medium Temperature Shift conversion normally takes place in an isothermal system, but it may also be accomplished in an adiabatic reactor with an exit temperature around 300°C. A copper-zinc catalyst is used for this... 

In an autothermal reforming process, lOOOkmol/h of methane at 20°C is compressed to 10 bar, mixed with 2500 kmol/h of saturated steam and reacted with pure oxygen to give 98% conversion of the methane. The resulting products are cooled and passed over a medium-temperature shift catalyst that gives an outlet composition corresponding to equilibrium at 350°C. 

Produced required amount of Catalytica Energy System s autothermal reformer (ATR) catalyst. Produced required amount of NexTech platinum (Pt)/ceria medium-temperature-shift (MTS) catalyst. Obtained Eos Alamos National Eaboratory preferential oxidation (PROX) reactor. 

The catalyst scheme is summarized in Table 3. The required amount of Catalytica Energy Systems ATR catalyst was produced and installed in the reactor. The required amount of NexTech shift catalyst was produced and installed in the first stage shift reactor. The NexTech shift catalyst is a medium-temperature shift catalyst that remains active in the oxidized or reduced state and is less sensitive to condensed moisture [2]. All catalysts are currently in pellet form however, noble metal wash coating on monolith substrates is existing technology. Therefore, once the catalyst and system performance are verified, it will be straightforward to convert these catalysts to monoliths. The reactors... 

MTS Medium Temperature Shift OEM Original Equipment Manufacturer... 

Recent developments in shift catalyst formulations allow the combination of high temperature and low temperature shift reactors in a single medium temperature step. The medium temperature shift catalyst is a copper-based catalyst that operates in the range of 260-280°C (500-540 F). Carbon monoxide conversion is improved, resulting in an overall savings on feed and fuel of 0.3% to 0.8% [2]. The medium temperature shift reactor has been commercially proven with isothermal tubular reactors, however, the use of an adiabatic reactor with intercooling is also possible. 

Maleic anhydride, 130, 206, 211, 213-215 Mannich base salt, 246, 248 Medium temperature shift, 61 Melt transesterification reaction, 233 Membrane air separation ... 

Depending on the operating conditions, three different types of WGS processes are applied [232] [303] [391]. High-temperature shift (300— 500°C) over a robust catalyst is used for primary conversion. Medium temperature shift (200—330 C) is used for special purposes. Low-temperature shift (185—250 C) is used to achieve maximum conversion. Sour gas shift (350 C) is used to operate under high sulphur eonditions and low H2/CO (raw coal gas, etc)... 

Dokupil et al. [542] described monolithic water-gas shift reactors operated at a gas hourly space velocity of20 000 h for medium temperature shift and 10 000h for low temperature shift. The adiabatic temperature rise in the medium temperature reactor operated at 300 ° C amounted to 68 K, in the low temperature reactor operated at 280 °C a temperature rise of only 15 K was determined. 

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 ... 

Low Temperature Shift 2-5% 1-3% Increase No Change Increase Medium Steam Purity... 

Relatively less attention has been given to the desulfurization of steam-containing gas mixtures with low H2S at medium temperature suitable for desulfurization of reformate from the reforming, where the temperature of the fuel gas at the outlet of the steam reforming is about 700 °C and at the inlet of high-temperature water-gas shift (HTWGA) is about 400 °C. 

Irrespective of the chosen apparatus, the equipment must be set up and handled in a way that both minimises the variability of the dissolution and avoids artefacts. The most common source to such variability or artefacts is hydrodynamic factors, but unwanted chemical reactions or temperature shifts could also occur. Alterations of hydrodynamics, as well as changes of temperature, can both affect the dissolution of a drug substance and the release of a substance from the dosage form. Chemical reactions in the test medium may cause degradation of the drug substance or some formulation excipient which may affect the dissolution, or may lead to misinterpretation of the results. Examples of different sources to variability for the USP apparatuses are summarised below ... 

The emission lifetimes of Ir(ppy)2(bpy)2 + and Ir(ppyXbpy)2 + are comparable in 77 K ethanol/methanol glasses (5.0 and 6.8 /is, respectively) and in fluid room temperature methanol solutions (0.35 and 1.1 /is, respectively). The positions of the emission energies of the two complexes were found to be dependent upon the solvent medium (blue shifts in more polar solvents). The magnitude of the luminescence lifetimes and the solvent dependence of the emission spectra are indicative of 3MLCT luminescence [99]. 

Medium-temperature (Fe-Cr) and low-temperature (Cu) catalysts were used for a decrease in CO content by shift reaction (see Fig. 3). The use of these catalysts allowed reducing CO concentration in synthesis gas for the test of polymeric fuel cell stack. Electric capacity of this stack can be up to 400 W. In this case, complete conversion of natural gas and CO is reached. 

C. Galletti, S. Specchia, G. Saracco, V. Specchia, Gold-supported catalysts for medium temperature-water gas shift reaction. Top. Catal. 52 (2009) 688-692. 

As a rule, the molecular weights obtained in these syntheses are not particularly high because, on the one hand, the use of relatively elevated temperatures shifts the equilibrium in favour of a growing contribution of the retro-DA reaction (viz. depolymerization) and on the other, polymers tend to lose their solubility as their DP increases, thus precipitating out of the reaction medium. 

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