Cesium in catalyst

Carbonyl fluoride, COF2, and oxygen difluoride react in the presence of cesium fluoride catalyst to give bis(trifluorylmethyl)trioxide [1718-18-9] CF OOOCF (31). CF OOF has been isolated from the reaction in the presence of excess OF2 (32). 

The oxidative dehydration of isobutyric acid [79-31-2] to methacrylic acid is most often carried out over iron—phosphoms or molybdenum—phosphoms based catalysts similar to those used in the oxidation of methacrolein to methacrylic acid. Conversions in excess of 95% and selectivity to methacrylic acid of 75—85% have been attained, resulting in single-pass yields of nearly 80%. The use of cesium-, copper-, and vanadium-doped catalysts are reported to be beneficial (96), as is the use of cesium in conjunction with quinoline (97). Generally the iron—phosphoms catalysts require temperatures in the vicinity of 400°C, in contrast to the molybdenum-based catalysts that exhibit comparable reactivity at 300°C (98). 

The performance of many metal-ion catalysts can be enhanced by doping with cesium compounds. This is a result both of the low ionization potential of cesium and its abiUty to stabilize high oxidation states of transition-metal oxo anions (50). Catalyst doping is one of the principal commercial uses of cesium. Cesium is a more powerflil oxidant than potassium, which it can replace. The amount of replacement is often a matter of economic benefit. Cesium-doped catalysts are used for the production of styrene monomer from ethyl benzene at metal oxide contacts or from toluene and methanol as Cs-exchanged zeofltes ethylene oxide ammonoxidation, acrolein (methacrolein) acryflc acid (methacrylic acid) methyl methacrylate monomer methanol phthahc anhydride anthraquinone various olefins chlorinations in low pressure ammonia synthesis and in the conversion of SO2 to SO in sulfuric acid production. 

The single absorption contact process for sulfuric acid is characterized by four main process steps gas drying, catalytic conversion of S02 to S03, absorption of S03, and acid cooling. The maximum S02 conversion for a single absorption plant is about 97.5-98 percent. By adding a second S03 absorber with one or two catalyst beds between absorbers, the S02 conversion can be increased to 99.5-99.8 percent or even as high as 99.9 percent with a cesium-promoted catalyst, resulting in lower S02 emis-... 

Fig. 12.7 also shows, however, that this problem can be overcome by feeding the gas at 660 K. This explains industrial use of low gas input temperature cesium-enhanced catalyst in 1st catalyst beds, Table 8.1. This catalyst can be fed with 660 K gas without falling below its de-activation temperature. 

In general, the catalysts contain varying quantities of the oxides of aluminum, potassium, calcium, magnesium, and silicon as promoters. Patents recommend adding sodium [243], beryllium [244], vanadium [245], uranium [246], or platinum [247]. Reference [248] describes cesium-containing catalysts. Catalysts patented by Lummus [249] and Ammonia Casale [250] contain cerium as additional promoter. ICI [251] has developed a cobalt-containing catalyst, as has Grande Paroisse [252]. 

In recent years heteropolycompounds have been studied for the oxidation of propane to acrylic acid and of isobutane to methacrylie aeid. Rohm Haas Company was the first in 1981 to claim the one-step oxidation of isobutane to methacrolein and methacrylie acid (55). Even though no reference is made to heteropolycompounds, the claimed catalyst compositions correspond to Keggin-type structures. In the patents later issued by Sumitomo (56,57) an important role was claimed to be played by vanadium (in an anionic position), by cesium (in a cationic position), as well as by an excess of phosphorus with respect to the stoichiometric composition. These catalysts gave selectivities to methacrylie acid plus methacrolein close to 70 %, with isobutane conversions in the 10 to 13 % range. Besides carbon oxides, acetic acid was the main by-product. 

This section of the review considers several recent developments in catalysts for low to medium pressure methanol synthesis that could be used in existing converters. These include the Raney copper-zinc catalysts, which have similar compositions and properties to co-precipitated catalysts, thorium-copper and cesium-copper intermetallics and supported noble metals... 

Melamine (2,4,6-triamino-l,3,5-triazine) is used with formaldehyde to produce resins for use in counter tops, dishes, and such. A third route reacts carbon dioxide with orthoesters or ketals using an iodide catalyst.35 The byproduct ketone can be reconverted to the ketal (2.11) and used in the next run, so that there is no waste. The selectivity was 86% at 94% conversion using a cesium iodide catalyst. 

However, the scmbber will not be required during steady running of the plant when a cesium promoted catalyst is used in adequate amounts in the last pass of the converter which is operated at 385-390 °C. 

A higher (10.0-10.5%) SO2 gas strength in the burner outlet gases will be possible due to use of a cesium promoted catalyst. This will also require lower volumes of gases to be handled, thus reducing power consumption. 

Using a DCDA process instead of SCSA and cesium promoted catalyst in the last pass of the converter. 

Use of cesium promoted catalysts in first and fourth/fifth passes. This would enable the start of conversion at about 385-390 °C earher than conventional catalysts having an ignition temperature of 410 °C, i.e., faster after any plant stoppage). This will improve the efficiency of conversion to as high as 99.9% instead of the 99.5% offered by DCDA (3 +1) systems. 

Cesium activated catalyst is used to reduce SO2 emissions below 200 ppm in the... 

In the case that the conventional process of conversion of sulfur dioxide is adopted, the conversion of sulfur to sulfur trioxide as described in Sect. 11.2 can be carried out at a pressure slightly above atmospheric pressure to overcome a pressure drop in conversion and absorption. However, due to the availability of pure sulfur dioxide using a cesium activated catalyst, a higher strength of sulfur trioxide cau be produced. This will reduce air flow and lower operating costs. 

The high stability of the block copolymer-colloid approach was also illustrated by the use of poly(A-vinyl-2-pyrrohdone) protected rhodium colloid (Rh-PVP) that was used as a catalyst for methanol carbonylation under elevated temperature (140 °C) and high pressure (5.4 MPa). During the reaction, the catalyst was still in a colloidal state as verified by TEM observations, even after repeated uses and a total TON reaching 19 700 cycles per atom of rhodium. Toshima and Shiraishi also demonstrated the possibility to enhance the catalytic activity of silver colloids (Ag-PVP) in the oxidation of ethylene by the addition of alkali metal ions such as cesium. Bimetallic catalysts in colloidal dispersions composed of two distinct metals also appeared in the literature with often better activity... 

In summary, modifications to the generally practiced DCDA process are primarily the use of cesium activated catalyst an additional fifth pass to increase conversion efficiency, the use of twin oleum tower system and replacing PHE s by special alloy steel heat exchangers, an efficient acid distribution system, and PTFE lined piping for acid circulation. 

Table 29.2 Industrial percent SO2 oxidation in a four pass double absorption acid plant. The feed gas contains 10 volume% SO2, 11 volume% O2, 4 volume% CO2, and 75 volume% N2. The catalyst bed inlet temperatures are as follows bed 1 420 °C, bed 2 435 °C, bed 3 440 °C, and bed 4 410 °C. Cesium-promoted catalyst is installed in bed 4. ...

Cesium-promoted catalysts and the new catalysts LEAPS (Christensen and Polk, 2011) and GEAR (Felthouse et al., 2011) are used to maximize SO2 oxidatimi. They are more costly than conventional catalysts (potassium promoted), but give appreciably better SO2 oxidation performance. Table 29.3 provides industrial design data which show the benefits of using cesium-promoted catalyst in a four pass single coti-tact type metallurgical acid plant. 

The feed gas contams 10 volume% SO2, 14 volmne% O2, and 76 volume% N2. In this example, the use of cesium-promoted catalyst results in a 21 % decrease in SO2 emissions. Case 1 uses all conventional (potassium promoted) catalyst. Defined below Table 28.1. 

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