Terry Rigdon

Ethanol (ethyl alcohol) Made from biomass such as corn or sugar Ethanol added to gasoline Benefits of ethanol over gasoline Brazil has introduced cars that are able to run using 100% ethanol Water must be removed by distillation Ethanol Fuel

Diffusion distillation is a vaporization-condensation process in the presence of a stagnant inert gas. Depending on the molar fluxes of components a condensate of composition different from the composition of the original mixture is formed and flows as a liquid film on the condensing surface. Diffusion Distillation

In a diffusion distillation process no auxiliaries are necessary and also there is no change of pressure in the system Diffusion distillation column Diffusion Distillation

1. The composition does not change along the length of the film 2. The annulus is regarded as a plane slot 3. The inert gas in the slot is stagnant and isobaric 4. Mass transfer is described by steady state molecular diffusion in a 1-D coordinate system; there is no transport by convection 5. The liquid mass transfer resistance in the falling film in negligible. 6. The liquid and vapor at the interface have their equilibrium composition Assumptions

This process is multicomponent, involving ethanol (1), water (2), and a stagnant inert gas (3) Diffusion is accurately described by the Stefan-Maxwell diffusion equation: Theory Boundary conditions are: and

The vapor composition on the vaporization and condensation side is described by: Theory The composition on the condensation side is given by: and

Differential section of diffusion distillation column Mass Balance

When we apply the total mass balance over the differential height dl at the vaporization side the following equation results: Mass Balance or The total mass balance at the condensation side over differential height dl provides:

The perimeter flow rate of ethanol at the vaporization side can be written as: Mass Balance Which on differentiation with respect to l provides:

The total mass balance equation provides: Mass Balance And the mass balance for component 1 provides:

To calculate the interface temperature on the condensation side energy balance is required: Energy Balance

or

Neetu Singh and Ram Prasad used the parameters: Experiments Selectivity and different inert gases

Selectivity can be defined as the difference between the mole fraction of ethanol on the vaporization side Represents a direct measure of the total molar flux which is equal to the condensate flow rate divided by the area of mass transfer For effective separation by diffusion distillation, higher selectivity as well as higher total molar flux is desirable Therefore, the vaporization temperature affects selectivity and total molar flux as well Results

It is prevalent that the higher selectivity is obtained at lower total molar flux and vice versa. Results

Conclusion

Questions