Favourable equilibrium

The reactor is run initially as a batch reactor (F = 0) under adiabatic conditions (Fco = 0) to obtain a high initial rates of reaction. At time TIMEON the cooling flow rate is set to FCON and the reaction temperature reduced to obtain favourable equilibrium conditions. 

The maximum conversion of reactants which can be achieved in an isothermal batch reactor is determined by the position of thermodynamic equilibrium. If this conversion is regarded as unsatisfactory, the use of a simple batch reactor may be abandoned in favour of a reactor which permits removal of products from the reaction mixture. Alternatively, the reactor temperature may be changed to obtain a more favourable equilibrium however, this may result in an unacceptable reduction in the net reaction rate. Such conflicts are often resolved by the use of optimisation procedures (see Sect. 8). 

The more favourable equilibrium constants for the addition of thiols to the carbonyl group of aldehydes and ketones compared to those for the addition of alcohols are well documented (Jencks, 1964 Lienhard and Jencks, 1966 Kanchuger and Byers, 1979), if not fully understood. There appears to be a similar tendency for thiols to add to the carbonyl (or thiocarbonyl) group of esters (or thioesters) and several tetrahedral intermediates with one or more... 

Normally, Oppenauer oxidations are performed employing Al3+ cations as catalyst because aluminium alkoxides possess a good balance of a desired high hydride transfer capability versus a low propensity to promote undesired base-induced reactions, like aldol condensations and Tischtschenko reactions. In the reaction, as originally described by Oppenauer, aluminium t-butoxide is used as catalyst,4 because its high basicity allows a very favourable equilibrium towards the formation of the aluminium alkoxide of the alcohol whose oxidation is desired. However,... 

Scheme 4.331 provides a further illustration of the power of enzymatic methods for the selective synthesis of either member of an enantiomeric pair on a preparative scale.621-622 Pseudomonas cepacia lipase (PCL) hydrolysed the meso-diacetate 331.1 to give (25,3/ )-2 3-0-cyclohexylidene-erythritol monoacetate (331 4) in 91% chemical yield and >99% ee whereas transesterification using vinyl acetate accomplished the conversion of the diol 3313 to the (2/ ,35)-antipode 331.4 in diminished yield (78%) but comparable ee. Vinyl or propenyl acetate ensures a favourable equilibrium owing to tautomerisation of the enol generated during the transesterification.623 624... 

Clayton proposes a graphical analysis of the breakthrough curve under favourable equilibrium conditions which states ... 

Favourable Equilibrium If the ion exchange equilibrium is very favourable (. [ 1, >> 1) the exchange zone maintains a... 

K is known as the equilibrium constant and in this case it has the value 2000. An equilibrium constant greater than unity suggests that equilibrium lies to the right-hand side and the forward reaction is favoured. Equilibrium constants vary with temperature, but not with concentration if the concentrations have been correctly expressed in terms of activities. 

In recent years, new concepts to produce hydrogen by methane SR have been proposed to improve the performance in terms of capital costs reducing with respect to the conventional process. In particular, different forms of in situ hydrogen separation, coupled to reaction system, have been studied to improve reactant conversion and/or product selectivity by shifting of thermodynamic positions of reversible reactions towards a more favourable equilibrium of the overall reaction under conventional conditions, even at lower temperatures. Several membrane reactors have been investigated for methane SR in particular based on thin palladium membranes [14]. More recently, the sorption-enhanced steam methane reforming (Se-SMR) has been proposed as innovative method able to separate CO2 in situ by addition of selective sorbents and simultaneously enhance the reforming reaction [15]. 

The less reactive ketones can be persuaded to react with other, usually non-enolisable, carbonyl compounds as in the reaction of cyclohexanone 5 with diethyl carbonate to give the P-keto-ester 7. This reaction is really under thermodynamic control as the favourable equilibrium between the product 7 and its stable enolate 8 more than compensates for the unfavourable equilibrium between 5 and its unstable enolate 6. This stable enolate 8 is a specific enolate. 

In Indirect sequence, the first split is much easier (35 trays), and the amount of entrainer is lower (0.08). In the second split, however, the situation is less favourable. Equilibrium diagram y-x shows difficult separation of pure acetone, because very low relative volatility with respect to benzene. However, the same high purity of 99.8% acetone can be obtained. It is important to note that the feed should be placed near to the reboiler, so that the second column is practically a stripper. The recycled entrainer benzene may contain a small amount acetone, which helps to get high purity products. The energetic consumption is slightly below the direct sequence, because low amount of entrainer. Hence, contrary to expectations, the indirect sequence has better indices, both as hardware and energetic consumption. 

A methanol process intended exclusively to produce fuel methanol was also launched by Messrs. Wentworth Brothers, Inc., Cincinatti, in 1982 [3.34] it is based on experience gained with the high-pressure process which has become classical under the name Vulcan Cincinnati. Contrary to the rules of thermodynamics, the attempt to operate with low temperatures at the end of the reaction and thus under favourable equilibrium conditions was not always consequently made. As opposed to this one appears, at least in intermediate sections of reaction control, to aim at as high an end temperature as possible in order to be able to utilize the effective part of the reaction heat at the highest possible temperature level to generate high-pressure steam and probably also to improve the conversion of CO2. 

TAS giving more favourably equilibrium. Hence, the steam reforming reaction is entropy-driven. 

Structure and bears a reactive -SH group that combines with acyl groups to form thiol esters. These are energy-rich compounds that can take part in reactions which would not be possible but for the favourable equilibrium established by cleavage of the thiol ester bond. 

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