Question

1. Why organic solvent is often used in liquid-liquid extraction?

2. Name the adverse effects which occur when a trayed absorption tower operates at too high and too low vapor flow rate?

3. Component separation involving two or more phases (regardless of technique) occurs because systems want to achieve equlibrium and as a result, mass transfer occurs. In a scenario where this mass transfer is particularly slow, would it be more accurate to model a system based on phase equlibrium or mass transfer? Explain.

Answer 1

1.

Choosing of a solvent in liquid-liquid extraction is very importent. Because, it should have suitable properties to soluble the desired solute. The compound which is to be extract, must be soluble in organic solvent and insoluble in water.

In most general solvent system would be water plus organic solvent. Since, water is polar and immiscible with organic solvent. So that, solute will come along with organic solvent as a extract from the liquid-liquid extraction equipment.

Distribution coefficient is a quantitative measure of the how an organic compount will distribute between aqueous and organic phases.

2.

When a trayed absorption tower operates at too high and too low vapor flow rates "Entrainment" and "Dumping" will taks place respectively.

Entrainment - At a high vapor flow rates, when the gas is discharged from the liquid some droplets of liquid will be carried out by the gas so that it reduces the efficiency of column.

Dumping - At a low vapor flow rates, non of the liquid will doesn't reach the down commer. All liquid comes down through the perforations. Extreme case of weeping is known as Dumping.

3.

Driving force for the mass transfer is difference in chemical potential. Mass transfer will continues until the chemical potential of both phases are equal. Rate of mass transfer will dependent upon the liquid phase resistance and gas phase resistance. As consideration of assumptions to calculate the mass transfer rate, it will vary from model to model.