Promoters potassium

The typical SEA process uses a manganese catalyst with a potassium promoter (for solubilization) in a batch reactor. A manganese catalyst increases the relative rate of attack on carbonyl intermediates. Low conversions are followed by recovery and recycle of complex intermediate streams. Acid recovery and purification involve extraction with caustic and heat treatment to further decrease small amounts of impurities (particularly carbonyls). The fatty acids are recovered by freeing with sulfuric acid and, hence, sodium sulfate is a by-product. 

Oxychlorination of Ethylene to Dichloroethane. Ethylene (qv) is converted to dichloroethane in very high yield in fixed-bed, multitubular reactors and fluid-bed reactors by reaction with oxygen and hydrogen chloride over potassium-promoted copper(II) chloride supported on high surface area, porous alumina (84) ... 

R.A. DePaola, J. Hrbek, and F.M. Hoffmann, Potassium promoted C-0 bond weakening on Ru(001). I. Through-metal interaction at low potassium precoverage, J. Chem. Phys. 82(5), 2484-2498 (1985). 

Figure 7.21. Fraction of unoccupied sites, and of sites occupied by atomic nitrogen and NH, as a function of reactor length on a potassium-promoted iron ammonia catalyst at 673 K,...

Figure 7.22. NH3 concentration as a function of reactor length in the synthesis of ammonia with a potassium-promoted iron catalyst. The exit concentration is 19 % and corresponds to...

This XPS investigation of small iron Fischer-Tropsch catalysts before and after the pretreatment and exposure to synthesis gas has yielded the following information. Relatively mild reduction conditions (350 C, 2 atm, Hg) are sufficient to totally reduce surface oxide on iron to metallic iron. Upon exposure to synthesis gas, the metallic iron surface is converted to iron carbide. During this transformation, the catalytic response of the material increases and finally reaches steady state after the surface is fully carbided. The addition of a potassium promoter appears to accelerate the carbidation of the material and steady state reactivity is achieved somewhat earlier. In addition, the potassium promoter causes a build up on carbonaceous material on the surface of the catalysts which is best characterized as polymethylene. 

Secondly, the activation energy for the reaction is unchanged by the addition of sulfur in agreement with studies on supported systems (26,27). This suggests that although the rate is slowed, the mechanism of the reaction is fundamentally unchanged. A similar conclusion was reached In studies of the role of potassium promoters on a Nl(lOO) catalyst (28), although the effect of sulfur and potassium on the individual steps of the reaction are likely quite different (1J, , 28). 

Fig. 9. Invariant cycling state temperature profiles for a three-stage, 800 mm diameter pilot plant S02 converter with interstage cooling. Profiles were measured just before switching of the flow direction and are for S02 at 7.6 vol% and a superficial velocity of 0.07 m/s. Catalyst was a commercial potassium-promoted vanadia, Type S101. (Figure adapted from Xiao and Yuan, 1996, with permission of the authors.)...

Campbell, C. T., and Goodman, D. W. 1982. A surface science investigation of the role of potassium promoters in nickel catalysts for carbon monoxide hydrogenation. Surf. Sci. 123 413-26. 

Luo, M., O Brien, R.J., Bao, S., and Davis, B.H. 2003. Fischer-Tropsch synthesis Induction and steady-state activity of high-alpha potassium promoted iron catalysts. Appl. Catal. A Gen. 239 111-20. 

Arakawa, H., and Bell, A.T. 1983. Effects of potassium promotion on the activity and selectivity of iron Fischer-Trospch catalysts. Ind. Eng. Chem. Res. Process. Des. Dev. 22 97-103. 

The UPS spectra of Fig. 3.20 indicate that heating of CO on clean Fe(l 10) to 390 K leads mainly to desorption only a fraction of the CO dissociates. Substantially less CO desorbs from the potassium-promoted surface, however, and, after heating to 500 K, all CO on the surface has dissociated. Thus, potassium enhances CO bonding to the surface and promotes its dissociation. We discuss promoter effects in more detail in Chapter 9 and in the Appendix. 

Janssens et al. [38, 40] used photoemission of adsorbed noble gases to measure the electrostatic surface potential on the potassium-promoted (111) surface of rhodium, to estimate the range that is influenced by the promoter. As explained in Chapter 3, UPS of adsorbed Xe measures the local work function, or, equivalently, the electrostatic potential of adsorption sites. The idea of using Kr and Ar in addition to Xe was that by using probe atoms of different sizes one could vary the distance between the potassium and the noble gas atom. Provided the interpretation in terms of Expression (3-13) is permitted, and this is a point the authors checked [38], one thus obtains information about the variation of the electrostatic potential around potassium promoter atoms. 

Figure 9.11 Promoter-induced binding energy shifts of Ar, Kr and Xe photoemission peaks with respect to adsorption on the clean metal as a function of the distance of the adsorption site to the nearest potassium atom on a potassium-promoted Rh( 111) surface. These curves reflect the variation of the surface potential (or local work function) around an adsorbed potassium atom. Note the strong and distance-dependent local work function at short distances and the constant local work function, which is lower than that of clean Rh( 111) at larger distances from potassium. The lowering at larger distances depends on the potassium coverage. The averaged distances between the potassium atoms are 1.61, 1.32 and 1.20 nm for coverages of 2.7, 4.1 and 5.0% respectively, vertical lines mark the half-way distances. Lines are drawn as a guide to the eye (adapted from Janssens et al. [38]).

Figure 9.14 Thermal desorption spectra of CO from clean (left) and potassium-promoted Ni (110) (middle and right) mea-sured at a heating rate of 13 K/s. The spectra exhibit two desorption states for CO on promoted surfaces and indicate that CO binds more strongly to sites adjacent to potassium (from Whitman and Desorption Temperature (K) Ho [46]).

As a starting point, we will try to quantify the required activity of a new catalyst by simulating the S02 emission from a double absorption plant as a function of 4th bed catalyst activity for a feed gas with 11% S02 and 10% 02 and a 3+1 converter with fixed bed volumes, cf. Fig. 4. With a conventional potassium-promoted catalyst such as VK38 from Haldor Topsoc (relative activity 1), a typical requirement in the 1990ies of minimum 99.7% S02 conversion corresponding to 395 ppm S02 in the stack gas can be achieved in this plant at a 4th bed inlet temperature of 430-435°C. With a 2-3 times more active catalyst in bed 4, the S02 emission in this plant can be reduced to below 200 ppm at a lower optimum inlet temperature. 

The highest formation rate for C2 hydrocarbons was found over the K promoted catalysts. The ratio of oxygen conversion to methane conversion at equal residence times revealed an increased amount of oxygen utilized by both Li and Na catalysts over MnMo04, while the oxygen consumption for the potassium promoted catalyst decreased below that of MnMo04 catalyst (Fig. 4c). 

Selective partial oxidation of hydrocarbons poses considerable challenges to contemporary research. While by no means all, most catalytic oxidations are based on transition-metal oxides as active intermediates, and the oxidative dehydrogenation of ethylbenzene to styrene over potassium-promoted iron oxides at a scale of about 20 Mt/year may serve as an example [1]. Despite this... 

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