Gases altering equilibrium compositions

Therefore pressure changes will alter equilibrium composition only in reactions that involve a gas or variety of gases as products and/or reactants. Again, consider the ammonia example. 

No gas phase equilibrium exists between O2 and CO2 in the oxidant gas that could alter the composition or cathode potential. 

Some chemical operations, however, demand a supply of pure hydrogen these include ammonia synthesis and fat-hardening, and so it became necessary to find a way of altering the composition of water-gas to achieve this. Its gaseous components can be brought into equilibrium by the water-gas shift... 

The equilibrium composition of the product gas can be altered by choice of suitable temperature, pressure, and steam to feedstock ratio to produce a gas mixture consisting largely of methane or largely of hydrogen having varying proportions of carbon monoxide (qv). In each case, some carbon dioxide (qv)... 

One relevant aspect of gas recycling is its effect on the gas-liquid equilibrium in the reactor [61]. It is typical for most HOT units to operate with partially vaporized hydrocarbon feed. This effect alters gas composition and reaction rates. Increasing the H2/oil ratio can be useful for concentrating the heaviest and most refractory compounds (e.g., dibenzothio-phenes in gas oil feeds) in the liquid phase, providing them more contact time with the catalyst. However, special care must be taken with excess recycle rates because some of the species in the vaporized fraction may not have access to the active sites of the catalyst particle. 

The curve in Figure 21 represents S02 equilibrium conversions vs temperature for the initial S02 and 02 gas concentrations. Each initial S02 gas concentration has its own characteristic equilibrium curve. For a given gas composition, the adiabatic temperature rise lines can approach the equilibrium curve but never cross it. The equilibrium curve limits conversion in a single absorption plant to slightly over 98% using a conventional catalyst. The double absorption process removes this limitation by removing the S03 from the gas stream, thereby altering the equilibrium curve. 

We need to examine the effects of changes in temperature on the composition of a binary solution in equilibrium with the vapor phase. The situation is somewhat complicated because the composition of the two phases, as well as the total pressure, is altered with temperature changes. For, an increase in T favors the evaporation of the more volatile component, thereby enriching the gas phase and depleting the liquid phase of this component. Thus, both x,- and x/ are changed, even though the overall composition of the closed system remains the same. To simplify matters we impose the additional restriction that the total pressure remain fixed. This may be done in principle by use of a moveable piston. We now invoke the equilibrium constraint for each species /i,(g) = Mi(0. Then, according to Eqs. (2.4.15) and (2.5.1),... 

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