Water-gas shift high temperature

After the reforming reaction, the gas is quickly cooled down to about 350 450 °C before it enters the (high-temperature) water-gas shift reaction (CO shift). Here, the exothermic catalytic conversion takes place of the carbon monoxide formed with steam to hydrogen (H2) and carbon dioxide (C02) in the following reaction ... 

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). 

Iron oxide is an important component in catalysts used in a number of industrially important processes. Table I shows some notable examples which include iron molybdate catalysts in selective oxidation of methanol to formaldehyde, ferrite catalysts in selective oxidative dehyrogenation of butene to butadiene and of ethylbenzene to styrene, iron antimony oxide in ammoxidation of propene to acrylonitrile, and iron chromium oxide in the high temperature water-gas shift reaction. In some other reactions, iron oxide is added as a promoter to improve the performance of the catalyst. 

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). 

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Singh, C.P. Saraf, D.N. Simulation of High-Temperature Water-Gas Shift Reactors Ind. Eng. Chem. 

The exit from the secondary reformer contains about 10-12% CO, is cooled to about 350°C and fed to a high-temperature water gas shift (HTS) reactor. 

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. 

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Rhodes, C., Williams, B.P., King, F., and Hutchings, G.J. Promotion of Fe304/Cr203 high temperature water gas shift catalyst. Catalysis Communications, 2002, 3, 381. 

Qi, X. and Flytzani-Stephanopoulos, M. Activity and stability of Cu-Ce02 catalysts in high-temperature water-gas shift for fuel-cell applications. Industrial Engineering Chemistry Research, 2004, 43, 3055. 

Ma, D. and Lund, C.R.F. Assessing high-temperature water-gas shift membrane reactors. Industrial Engineering Chemistry Research, 2003, 42, 711. 

The most common industrial method to make ultra-pure hydrogen is by steam-methane reforming (SMR) using a catalyst at the temperature 890-950° C. The reformed gas is then subjected to a high temperature water gas shift (WGS) reaction at 300-400°C. The WGS reactor effluent typically contains 70-80% H2, 15-25% CO2, 1-3% CO, 3-6% CH4, and trace N2 (dry basis), which is fed to a PSA system at a pressure of 8-28 atm and a temperature of 20 0°C for production of an ultrapure (99.99+ mol%) hydrogen gas at the feed pressure. Various PSA systems have been designed for this purpose to produce 1-120 million cubic feet of H2 per day. 

The outlet from the secondary reformer contains about 10-14% CO (dry gas) which is fed to a high-temperature water gas shift (WGS) reactor (Fig. 2.2), typically loaded with Fe or Cr particulate catalyst at about 350°C. This further increase the H2 content lowering CO content to about 2% as governed by the thermodynamic and kinetics of the Eq. 2.3, that is an exothermic reaction. Water gas shift reaction equilibrium is sensitive to temperature with the tendency to shift towards products when temperature decreases. 

Mathematical Modelling of the High Temperature Water-Gas Shift Converter... 

K (440 °C), which is the upper temperature tolerated by commercial Fe304/ Cr203 high-temperature water-gas shift catalysts employed in the study [87]. Research goals were to test membranes under simulated high-temperature water-gas shift reactor conditions, 613-713 K (340-440 °C), and to resist differential pressures over 30 bar [81]. Palladium-based catalyst layers were approximately 400 nm on each side. 

Figure 4.7 Hydrogen flux upon exposure to various components of a high-temperature water-gas shift mixture. Steam and CO do not affect flux or catalysts relative to an ideal H / He mixture. Some loss in hydrogen flux occurs with addition of CO, but a flux of 150 mL min" cm" (STP) was achieved with over 1 bar CO in the mix at 693 K (420°C).

Both theoretical and experimental studies have been performed on palladium-based membrane reactors for the water-gas shift reaction. Ma and Lund simulated the performance achievable in a high temperature water-gas shift membrane reactor using both ideal membranes and catalysts [18]. By comparing the results obtained with those related to the existing palladium membrane reactors, they concluded that better membrane materials are not needed, and that higher performances mainly depend on the development of a water-gas shift catalyst not inhibited by CO2. Marigliano et al. pointed out how the equilibrium shift conversion in membrane reactors is an increasing function of the sweep factor (defined as the ratio between the flow rate of the sweep at the permeate side and the flow rate of CO at the reaction side) [19]. The ratio is an index of the extractive capacity of the system. 

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J. Dufour, C. Martos, A. Ruiz, F. J. Ayuela, Effect of the precursor on the activity of high temperature water gas shift catalysts, Int. J. Hydrogen Energy 38 (2013) 7647-7653. 

J. Y. Lee, D.-W. Lee, K.-Y. Lee, Y. Wang, Cr-free Fe-based metal oxide catalysts for high temperature water gas shift reaction of fuel processor using LPG, Catal. Today 146 (2009)... 

Q. Li, W. Ma, R. He, Z. Mu, Reaction and characterization studies of an industrial Cr-free iron-based catalyst for high-temperature water gas shift reaction, Catal. Today 106 (2005) 52-56. 

D.-W. Jeong, V. Subramanian, J.-O. Shim, W.-J. Jang, Y.-C. Seo, H.-S. Roh, J. H. Gu, Y. T. Lim, High-temperature water gas shift reaction over Fe/Al/Cu oxide based catalysts using simulated waste-derived synthesis gas, Catal. Lett. 143 (2013) 438-444. 

F. Meshkani, M. Rezaei, Mesoporous Ba-promoted chromium free Fe2Q3-Al203-Ni0 catalyst with low methanation activity for high temperature water gas shift reaction, Catal. Commun. 58 (2015) 26-29. 

J. Li, Z. Hongwei, R. Razzaq, C. Li, L. Zengxi, Effect of structural and lattice oxygen changes on the properties of CuO/Ce02 catalysts for high-temperature water-gas shift of H2-rich coal-derived synthesis gas, Z. Phys. Chem. 227 (2013) 371—387. 

I. Valsamakis, M. F. Stephanopoulos, Sulfur-tolerant lanthanide oxysulfide catalysts for the high-temperature water-gas shift reaction, Appl. Catal. B Environ. 106 (2011) 255-263. 

G. K. Reddy, K. Gunasekara, P. Boolchand, P. Smimiotis, Cr- and Ce-doped ferrite catalysts for the high temperature water-gas shift reaction TPR and Mossbauer spectroscopic study, J. Phys. Chem. C 115 (2011) 920-930. 

Z. Tang, S. J. Kim, G. K. Reddy, J. Dong, P. Smimiotis, Modified zeolite membrane reactor for high temperature water gas shift reaction, J. Membr. Sci. 354 (2010) 114-122. 

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