Thermodynamic traps

Thermodynamic traps utilize the heat energy in hot condensate and steam to control the opening and closing of the trap. They therefore respond to the difference in thermodynamic properties between steam and condensate. 

In some well-known reactions, the quantity of catalyst (or catalytic reagent) required is so large that it does affect the thermodynamic properties of reactants and products. 

A particularly misleading situation can occur when a reaction product forms a complex with the catalytic material. Thus the Gatterman-Koch reaction of benzene and carbon monoxide to produce benzaldehyde is thermodynamically unfavourable, but reaction proceeds under pressure in the presence of at least 1 mole AlCls/mole benzene. However, the benzaldehyde-AICI3 complex formed must be cleaved chemically, with water for example, to liberate the product. Surprisingly, the similar conversion of toluene to p-tolualdehyde (p-methylbenzaldehyde) is favourable, and separation from the catalyst system can be achieved by simple distillation workers with Mitsubishi in Japan have used BFa/HF.  

The above examples are from an area of traditional chemistry. However, in seeking to translate organometallic chemistry into catalytic processes, we may often find products or intermediates in the desired process scheme as ligands on the metal. In such circumstances, it is important to recognize that their formation confirms that a mechanistic pathway exists, but does not imply that the formation of the free product or intermediate is necessarily feasible under the conditions used. 

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The results supported the proposal of Glu-165 as the general base and suggested the novel possibility of neutral histidine acting as an acid, contrary to the expectation that His-95 was protonated [26,58]. The conclusion that the catalytic His-95 is neutral has been confinned by NMR spectroscopy [60]. The selection of neutral imidazole as the general acid catalyst has been discussed in terms of achieving a pX, balance with the weakly acidic intermediate. This avoids the thermodynamic trap that would result from a too stable enediol intermediate, produced by reaction with the more acidic imidazolium [58]. 

Researchers at Sunesis pharmaceuticals have developed a fragment-based drug discovery method termed tethering [25]. The approach, which is illustrated in Scheme 2.6, shares a number of features with DCC. Whereas protein-directed DCLs equilibrate small molecules via disulfide formation, say, in the presence of a protein that acts as a thermodynamic trap, tethering uses a cysteine residue on the protein surface to reversibly capture small-molecule thiol fragments from solution. Tethering is designed... 

The sizing of thermodynamic traps is more critical than for other types. Size a trap too small and it will back up condensate too large, eind it will waste steam. Excessive oversizing will cause the trap to destroy itself. This occurs when the trap cannot get enough condensate to fulfill its energy requirements and, therefore, begins to cycle more rapidly partly on live steam. This causes an... 

Sizing to include potential startup loads leads to oversizing in thermodynamic traps. A thermodynamic trap will handle a great deal more cold condensate than hot condensate and if a still greater rate is desired, the line can be manually blown down. For applications other than steam tracing, careful consideration should be given before introducing any startup allowance, especially if the addition requires an increase in trap size. 

Steam traps install trap below condensate exit (or with a water seal if the trap is elevated), use a strainer before all traps, use a check valve for bucket traps. Slant pipes to the trap. Use a downstream check valve for each trap discharging to a common header. Pipe diameter > trap inlet pipe diameter. Prefer to install auxiliary trap in parallel instead of a bypass. Do not group thermodynamic traps because of their sensitivity to downstream conditions. 

The steam coils should be tested by hydraulic pressure 1.5 times the working pressure and the steam traps should be providedfor rapid removal of the condensate— as soon as it is formed—to maintain rate of evaporation. Thermodynamic traps should be used and the hot condensate should be recovered for use as boiler feed water after testing its acidity. 

The chemistry of the 2-propenyl (aUyl) cation is subject to both thermodynamic and kinetic control. Nucleophilic trapping may occur more rapidly at an internal carbon that bears relatively more positive charge, giving the thermodynamically less stable product. The kinetic product may rearrange to its thermodynamic isomer by dissociation followed by eventual thermodynamic trapping. 

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