Cooling catalysts

Propane was selected as solvent for the isobutene for experiments down to -145° the aluminium chloride was dissolved in ethyl chloride, for the work at lower temperatures a mixture of ethyl chloride and vinyl chloride was used. Although these catalyst solutions were made up at -78° they were yellow, and as stated above, they probably contained some hydrogen chloride and other catalytically active decomposition products. The polymerisations were carried out by running the cooled catalyst solution into the monomer solution. Polymer was formed, and came out of solution, almost immediately, and the reaction was very fast even at the lowest temperature (-185°) and lowest monomer concentration (0.6 mole/1). After the reaction was over, propanol at the reaction temperature was added to the reaction mixture to deactivate the catalyst. 

Fig. 3.8. Reactor trajectories in adiabatic and cooled catalyst beds...

Cool catalyst bed input gas gives high S02 oxidation efficiency in single and double contact acid plants. Low deactivation temperature Cs catalyst is beneficial in this respect, Chapters 8 and 12. 

Hot catalyst from the regenerator is introduced to the bottom of the catalyst cooler through a standpipe, while fluidization air flows upward with the catalyst, passing along the surfaces of the heat transfer elements and leaving the cooler at the top. The cooled catalyst and air are sent back to the dense bed of an ordinary regenerator or the middle zone of an FFB regenerator for continued utilization of 02. A typical assembly of an upflow catalyst cooler is shown in Fig. 8. 

Figure 99 is an example of modern ammonia synthesis loop (Krupp-Uhde) with a two-vessel converter system and three indirectly cooled catalyst beds producing 1500 t/d NH3 at 188 bar. 

Polymerization at —145° C. Experiments were run to determine the temperature range where the log DP (degree of polymerization) us. 1/T relation begins to become nonlinear. Cooled catalyst solutions were added to the monomer at various temperatures and the molecular weight of the polymer produced was determined. 

Fig. 1 High ( ) and low (o) activity states of Pd catalysts in m-xylene oxidation. Contact time 0.06 s temperature ramp 5 C min" T heating, i cooling. Catalyst catalyst (III) m-xylene concentration 0.065 vol. % oxygen concentration 40 vol. % (A) CO concentration.

This chapter examines oxidation of the SO2 in cooled catalyst bed exit gas - in a 2" catalyst bed. 

The H2SO4 making tower input gas (i.e. cooled catalyst bed exit gas) contains ... 

As the spherical catalyst is prepared by quencher in water or aqueous solution, there are some differences between the spherical catalyst and the irregular catalyst cooled indirectly (such as air-cooled or water jacket cooled catalyst) as follows ... 

For gas mixtures both Pr and Sc are on the order of 1, so that the temperature difference between gas and solid surface is approximately equal to the adiabatic temperature rise at complete conversion, compare eq. (5.7). For gaseous reaction mixtures this can be several hundred degrees Celsius. Indeed it is found that when an exothermic gas phase reaction takes place at a solid catalyst particle, the temperature at the particle surface will be much higher than in the gas. Even in cooled catalyst beds these very high temperatures may be found in one of the first particle layers, in the middle. These are called hot spots, and may lead to catalyst sintering or other forms of deactivation. The obvious way to avoid hot spots is by reducing the reactant concentration (dilution with an inert gas)... 

Fortunately, catalyst solidification and melting are reversible so that the catalyst reactivates when it is once again heated and remelted. However, care must be taken to avoid exposing the cooled catalyst to moist air. Catalyst absorbs moisture, which causes it to weaken and partially disintegrate (MFCS, 2011). 

Gas stronger than 13 volume% 8O2 must be diluted with air or recycled cooled catalyst bed exit gas before catalytic oxidation. Both increase gas flow and cost. 

One of the authors would specifically like to thank his son George Davenport and his nephew Andrew Davenport for their help with (i) wet sulfuric acid and (ii) cooled catalyst bed exit gas recycle calculations. 

Combinations of countercurrent cooled catalyst beds with adiabatic beds have been suggested by ICI [508], Uhde [509] and in [510, 511]. 

Ammonia synthesis converters with radial flow in tubular cooled catalyst beds have been suggested by Toyo Engineering Corp. [520] and in [502]. The Toyo concept has, so far, not been used industrially, while the concept described in [502] has, as mentioned above, been demonstrated in revamps of converters originally designed by SBA. It is claimed that the cross flow makes it possible -through proper design of the cooling tube bundles - to optimize the temperature profile so that it follows very closely the maximum reaction rate curve. It is furthermore reported that the heat transfer coefficients obtained in practice in... 

A fundamental role played by molecules in the interstellar medium is as one of the cooling catalysts for the star formation process. Molecular clouds that exceed the maximum stable mass for a cloud with only thermal support, known as the Jeans mass (see Section Al), are predicted to gravitationally collapse. In order for this collapse to proceed, molecules and dust are required to radiate away energy released by the gravitational collapse. Many of the stars formed will eventually produce novae and supernovae, which further eiuich the interstellar medium with molecules that can be used as catalysts to future star formation events. 

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