Single Stage Separation

Consider the liquid mixture illustrated in Figure 1. If this liquid mixture is partially vaporized then the vapour becomes richer in the more volatile components (i.e. those with the lower boiling points) than the liquid phase. The liquid becomes richer in the less volatile components (i.e. those with the higher boiling points). If we allow the system in Figure 1 to come to equilibrium conditions, then the distribution of the components between the vapour and liquid phases is

Figure 1 Partial vaporization of a liquid mixture creates a separation.

dictated by thermodynamic vapour-liquid equilibrium considerations. All components can appear in both phases. However, involatile components will tend to stay in the liquid phase.

Rather than partially vaporize a liquid, as shown in Figure 1, we could have started with a mixture of components in the vapour phase and partially condensed the vapour. We would still have had a separation, as the liquid which was formed would be richer in the less volatile components, while the vapour would have become depleted in the less volatile components. Again, the distribution of components between the vapour and liquid is dictated by thermo-dynamic vapour-liquid equilibrium considerations if we allow the system to come to equilibrium. Any noncondensable components present in the vapour will tend to stay in the vapour phase.

For each component in the mixture, thermody-namic equilibrium is given by the condition when the vapour and liquid fugacities are equal:

These equations can be combined to give an expression for the constant, K:

x pv

This expression provides the basis for vapour-liquid equilibrium calculations based on equations of state (e.g. Peng-Robinson equation). Alternatively:

This expression provides the basis for vapour-liquid equilibrium calculations based on liquid-phase activity coefficient models (e.g. Wilson equation). At moderate pressures:

Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

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