Reaction equilibrium pressure

The heat-storage and heat-release reactions occur at different pressure levels. The low-temperature side has a higher reaction equilibrium pressure. The CHP, as studied earlier, operates as a batch system with a heat-storing step followed by a heat-releasing step. For example, hydration and carbonation reactions can be used on the high-temperature (600 to 1200 K) side reactor. Evaporation and condensation of the reactant media are often used on the low-temperature (273 to 523 K) side reactor. 

It is found that after the elapse of a sufficient time interval, all reversible reactions reach a state of chemical equilibrium. In this state the composition of the equilibrium mixture remains constant, provided that the temperature (and for some gaseous reactions, the pressure also) remains constant. Furthermore, provided that the conditions (temperature and pressure) are maintained constant, the same state of equilibrium may be obtained from either direction of a given reversible reaction. In the equilibrium state, the two opposing reactions are taking place at the same rate so that the system is in a state of dynamic equilibrium. 

Irimescu and Kato have recently described an interesting example of enzymatic KR in ionic liquids instead of organic solvents (Scheme 7.4) [12]. The resolution with CALB is based on the fact that the reaction equilibrium was shifted toward the amide synthesis by the removal of water under reduced pressure. Nonsolvent systems have been also employed in this enantioselective amidation processes, reacting racemic amines with aliphatic acids. The best reaction conditions for the conversion of acids to amides was observed using CALB at 90 °C under vacuum. Meanwhile, no... 

Annular flow reactors, such as that illustrated in Figure 3.2, are sometimes used for reversible, adiabatic, solid-catalyzed reactions where pressure near the end of the reactor must be minimized to achieve a favorable equilibrium. Ethylbenzene dehydrogenation fits this situation. Repeat Problem 3.7 but substitute an annular reactor for the tube. The inside (inlet) radius of the annulus is 0.1m and the outside (outlet) radius is 1.1m. 

One of the most important characteristics of IL is its wide temperature range for the liquid phase with no vapor pressure, so next we tested the lipase-catalyzed reaction under reduced pressure. It is known that usual methyl esters are not suitable for lipase-catalyzed transesterification as acyl donors because reverse reaction with produced methanol takes place. However, we can avoid such difficulty when the reaction is carried out under reduced pressure even if methyl esters are used as the acyl donor, because the produced methanol is removed immediately from the reaction mixture and thus the reaction equilibrium goes through to produce the desired product. To realize this idea, proper choice of the acyl donor ester was very important. The desired reaction was accomplished using methyl phenylth-ioacetate as acyl donor. Various methyl esters can also be used as acyl donor for these reactions methyl nonanoate was also recommended and efficient optical resolution was accomplished. Using our system, we demonstrated the completely recyclable use of lipase. The transesterification took place smoothly under reduced pressure at 10 Torr at 40°C when 0.5 equivalent of methyl phenylthioacetate was used as acyl donor, and we were able to obtain this compound in optically pure form. Five repetitions of this process showed no drop in the reaction rate (Fig. 4). Recently Kato reported nice additional examples of lipase-catalyzed reaction based on the same idea that CAL-B-catalyzed esterification or amidation of carboxylic acid was accomplished under reduced pressure conditions. ... 

When produced from natural gas the synthesis gas will be impure, containing up to 5 per cent inerts, mainly methane and argon. The reaction equilibrium and rate are favoured by high pressure. The conversion is low, about 15 per cent and so, after removal of the ammonia produced, the gas is recycled to the converter inlet. A typical process would consist of a converter (reactor) operating at 350 bar a refrigerated system to condense out the ammonia product from the recycle loop and compressors to compress the feed and recycle gas. A purge is taken from the recycle loop to keep the inert concentration in the recycle gas at an acceptable level. 

Equation (7) shows the reaction temperature corresponds to the reaction pressure in Equation (4) type gas-solid reaction system. Relationship between 1 IT and In K(= Th2o) is linear at a range in which changes of AH and AS are negligible, and is called as a reaction equilibrium line. 

The equilibrium conversion can be calculated from knowledge of the free energy, together with physical properties to account for vapor and liquid-phase nonidealities. The equilibrium conversion can be changed by appropriate changes to the reactor temperature, pressure and concentration. The general trends for reaction equilibrium are summarized in Figure 6.8. 

The left-hand side of the cell, the working electrode, has its Pq2 fixed by the Ni + NiO equilibrium pressure, while on the right-hand side the reference electrode has Po2 given by the air atmosphere. Alternatively, a buffer may be used on the reference electrode side. The left- and right-hand side half-cell reactions are respectively... 

Ammonia is in surface reaction equilibrium with an equilibrium pressure, p = P /KbPg. 

The shift reaction is independent of pressure, but the reforming reaction equilibrium is favored by low pressure. At lower pressures, the conversion of hydrocarbon to hydrogen is higher. 

This reaction quotient is a fraction. The numerator is the product of the chemical species on the right hand side of the equilibrium arrow, each one raised to the power of that species coefficient in the balanced chemical equation. The denominator is the product of the chemical species on the left hand side of the equilibrium arrow, each one raised to the power of that species coefficient in the balanced chemical equation. It is called Qc, in this case, since molar concentrations are being used. If this was a gas phase reaction, gas pressures could be used and it would become a Qp. 

The presence of water in synthesis gas mixtures along with light components, such as carbon monoxide or hydrogen, has the effect that phase separations may persist even under extreme conditions of temperature and pressure. The need exists to demonstrate that these phase separations, perhaps with simultaneous reaction equilibrium, can be described by models capable of some accuracy. 

Figure 3. Critical and reaction equilibrium points (a) critical pressure (b) critical temperature (c) conversion of CO...

SURFTHERM Coltrin, M. E. and Moffat, H. K. Sandia National Laboratories. SURFTHERM is a Fortran program (surftherm.f) that is used in combination with CHEMKIN (and SURFACE CHEMKIN) to aid in the development and analysis of chemical mechanisms by presenting in tabular form detailed information about the temperature and pressure dependence of chemical reaction rate constants and their reverse rate constants, reaction equilibrium constants, reaction thermochemistry, chemical species thermochemistry, and transport properties. 

Stander [23] concluded that slow movement of the phase boundary is the ratecontrolling step at pressures appreciably different from the equilibrium pressure. At pressures near the equilibrium pressure nucleation seems to play a role. The difference in activation energy for the two mechanisms cannot be regarded as being significant. Furthermore, as the reaction proceeds, nucleation will become less important. Eventually he concluded that nucleation is kinetically unimportant in the decomposition... 

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