Caesium-promoted catalyst

Caesium-promoted catalyst for sulphuric acid plant has a lower ignition temperature and can result in higher overall conversion of SO2 SO3 but is more costly. It can reduce consumption of alkali in tail gas scrubber as compared to conventional potassium-promoted catalyst. 

Use of better catalyst by loading caesium-promoted catalyst in the first and last passes of the converter, the conversion of SO2 to SO3 could be started at 390-395 °C in the first pass and higher equilibrium yield could be obtained in the last pass as it was operated at a lower temperature (400-405 °C). 

Use of caesium-promoted catalyst made it possible to operate the last pass of converter at a lower temperature (395-400 °C) as compared to 425-430 °C with conventional catalyst, and this could achieve a higher equiUbrimn conversion of SO2 to SO3. 

Manufacture of sulphuric acid by the modified 3 + 2 DCDA process (having three catalyst passes before interpass absorption tower and two passes after it) with caesium-promoted catalyst resulted in better conversion of SO2 to SO3 and negligible escape of SO2 from exit gases. An alkali scrubber for tail gases was provided for taking care of this. 

Strong function of the amount of alkali metal component and an optimum amount of this component exists. A sudden change in activation energy occurs at relatively higher temperatures as the caesium to Co/Mo ratio decreases. Then Berispek [4] continued the work of Overstreet and made some important conclusions. The WGS activity of the catalysts is strongly dependent on the Cs to Mo ratio. The K-promoted catalysts are quite active compared to the Li and Na impregnated catalysts. The caesium-promoted Zn-Mo catalyst is not active as Co-Mo catalyst. 

The catalyst shall promote the desired reactions at operation of the process at appreciably less temperatures, pressures, etc. Operation at lower temperature can increase overall equilibrium conversion in case of reversible exothermic reaction (oxidation of SO2 to SO3 in the presence of caesium-promoted vanadium pentoxide catalyst used in sulphuric acid plants). 

The evaluation of carriers and catalyst compositions showed that significantly higher SO2 oxidation activity could be achieved with Cs as a promoter under the operating conditions downstream the intermediate absorption tower as demonstrated by the results in Table 1, where the activity compared to the standard product is increased by more than a factor 2. This was clearly sufficient for the introduction of VK69 to the market as a new sulphuric acid catalyst. The activity results for different melt compositions were used to optimise the vanadium content and the molar ratios of K/V, Na/V. and Cs/V. However, the choice of Cs/V was not only a question of maximum activity, because of the significant influence of the Cs content on the raw material costs (the price of caesium is 50-100 times the price of potassium on a molar basis). Here, the economic benefits obtained by the sulphuric acid producer by the marginal activity improvement at high Cs content also had to be taken into account. 

Reactions of amines with alkenes have been reviewed298,299. Alkali metal amides are active homogeneous catalysts for the amination of olefins. Thus diethylamine and ethylene yield triethylamine when heated at 70-90 °C at 6-10 atm in the presence of lithium diethylamide and /V./V./V. /V -tetrarncthylcthylcncdiaminc. Solutions of caesium amide promote the addition of ammonia to ethylene at 100 °C and 110 atm to give mixtures of mono-, di- and triethylamines300. The iridium(I)-catalysed addition of aniline to norbomene affords the anilinonorbomane 274301. Treatment of norbomene with aniline... 

It should be noted that while enyne metathesis is considered incompatible with molybdenum catalyst 1, ruthenium catalysts other than the Grubbs type also promote the reaction. Semeril et al. [103] reported efficient enyne RCM with a catalyst conveniently generated in situ from [RuCl2(p-cymene)]2,1,3-bis(mesityl)imidazolium chloride and caesium carbonate. Interestingly the authors found that the in situ derived system gave better results than the isolated catalyst. One of the most impressive examples of the use of enyne RCM is the total synthesis of (-)-longithorone by Layton et al. [104]. Inspired by a pro-... 

Fischer s experiments with iron catalysts promoted with alkalies showed that they increased in efficiency with the strength of the base, with the exception of caesium. Working with catalysts prepared by calcining steel turnings with potassium hydroxide, Frolich and Lewis 1J7 showed that with a gas containing 40 per cent carbon monoxide passed into the reactor at a space velocity of 1250 at 200 atmospheres and 325° to 335° C. the best yields were obtained when the base comprised 2.2 per cent of the catalysts (calculated as K20). From this it appears that a strong base present in small amount with iron as the catalyst enables the best yields of liquid products to be obtained. This conclusion has been confirmed by the work of Audibert and Raineau. 

Caesium has no known biological value, but it can replace potassium, for which reason in excess amounts it can be toxic. There is approximately 0.6 mg of caesium in the body and the average daily intake is 0.03 mg through food and even through tea leaves (3 ppb). Caesium is used in industry as a catalyst promoter and is used to make optical glass. Caesium gel is widely used in Japan for skin rejuvenation, where it probably acts by boosting enzymes. 

---