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Steam Reforming
Published in Martyn V. Twigg, Catalyst Handbook, 2018
Acidity in the support is known to facilitate the reaction A, but it will also promote cracking (E) and polymerization (C), again producing carbon. This problem was solved by ICI by introducing an alkali metal component into the catalyst. This accelerates the carbon–steam reaction (D) and at the same time the alkali neutralizes the acidity in the catalyst support, so retarding cracking and polymerization. The most effective alkali was found to be K2O (potash), and most reformers today running on naphtha feedstocks use the alkalized catalyst system. This is the basis of ICI’s 46–1 series of catalysts. The potassium is effective by being mobile on the catalyst surface. Accurate formulation combines the potassium as a complex potassium alumina-silicate (e.g. Kalsilite, K2O.Al2O3.SiO2) and monticellite (CaO.MgO.SiO2). The potassium is liberated at a very slow rate as involatile K2CO3 which is hydrolysed as fast as it is formed, producing KOH, which is very mobile on the catalyst surface and is the effective carbon-removing agent. Potassium is therefore slowly lost from the catalyst into the product gases, but the rate of evolution is very slow, being kinetically controlled by its release from the Kalsilite compounds. The higher the temperature and the higher the feedstock throughput, the more rapid is the potassium depletion. Careful formulation of the catalyst ensures that lives of several years are obtained in most reformers.
Hydrogen Production by Catalytic Hydrocarbon Steam Reforming
Published in Deniz Uner, Advances in Refining Catalysis, 2017
Peter Broadhurst, Jumal Shah, Raimon Perea Marin
One of the major concerns during the life of steam methane reforming catalyst is deactivation via carbon formation. Thus, catalysts should be designed to minimize the rate of carbon deposition and maximize the rate of carbon gasification. Thermal cracking reactions are promoted by surface Lewis acid sites, whereas the carbon gasification is promoted by the alkali sites and is proportional to the surface coverage of OH–. It may therefore be necessary to increase the alkalinity of the catalyst, especially for the inlet section of the SMR tube where the risk of carbon formation is greater. Besides calcium and magnesium, potassium is the preferred promoter to increase the catalyst alkalinity, reduce the formation of carbon, and induce carbon gasification. For heavy feeds, potassium is effective due to its mobility on the catalyst surface. Complex phases such as kalsilite (K2O·Al2O3·SiO2) convert slowly under reaction conditions to release potassium, which catalyzes the carbon gasification. The range of Johnson Matthey KATALCOJM catalysts with different levels of potassium promotion is given in Table 8.4.13
Effect of kaolin addition on alkali capture capability during combustion of olive residue
Published in Combustion Science and Technology, 2019
Ozge Batir, Nevin Selçuk, Gorkem Kulah
XRD analyses of ashes of olive residue and olive residue-kaolin mixtures were also carried out in order to identify the mineral phases formed by the interaction between potassium in olive residue and kaolin. As shown in Figure 4, the structure of olive residue ash was mainly amorphous with small peaks of kalsilite and huntite crystals. With kaolin addition, the intensity of kalsilite significantly increased. However, at 8% kaolin content, the kalsilite peak intensity dramatically decreased and that of quartz crystal became dominant. This was considered to be due to the presence of abundant amount kaolin, more than the amount required to capture the available potassium. Although the reaction between potassium and meta-kaolinite can produce both kalsilite and leucite crystals, only kalsilite was observed in the XRD pattern. This was considered to be due to the fact that the molar ratio of Si to Al is 1 for kalsilite and 2 for leucite, indicating that kalsilite formation was more favourable, in agreement with a previous finding (Glazer (2007)).
Effect of potassium-containing sulfates on high-temperature mineral transformation and coal ash fusibility
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2020
Haiping Xiao, Hao Shi, Xinyao Li, Yanfei Jiang, Jian Li
In the actual system, potassium is primarily in the form of microcline near 900°C. It is then converted into leucite at around 1150°C. Kalsilite occurs if the potassium-containing sulfates content exceeds 10% and temperature is over 1100°C. Due to the low melting point, potassium-containing aluminosilicate melts in large quantities over 1100°C.