steam distillation of lemon grass oil
Steam Distillation of Lemongrass Oil
I. Introduction
When a mixture of cyclohexane and toluene is distilled, the boiling point of these two miscible liquids is between the boiling points of each of the pure components. By contrast, if a mixture of benzene and water (Immiscible liquids) is distilled, the boiling point of the mixture will be found below the boiling point of each pure component. Since the two liquids are essentially insoluble in each other, the benzene molecules in a droplet of benzene are not diluted by water molecules from nearby water droplets, and hence the vapor pressure exerted by the benzene is the same as that of benzene alone at the existing temperature. The same is true of the water present. Because they are immiscible, the two liquids independently exert pressures against the common external pressure, and when the sum of the two partial pressures equals the external pressure, boiling occurs. Benzene has a vapor pressure of 760 mm Hg at 80°C, and if it is mixed with water, the combined vapor pressure must equal 760 mm Hg at some temperature below 80°C. This temperature, the boiling point of the mixture, can be calculated from known values of the vapor pressure of the separate liquids at that temperature. Vapor pressures found for water and benzene in the range 50 to 80°C are plotted in the figure to the right. The dotted line cuts the two curves at points where the sum of the vapor pressures is 760 mm Hg; hence this temperature is the boiling point of the mixture
(69.3°C).
Practical use can sometimes be made of the fact that many water-insoluble liquids and solids behave as benzene does when mixed with water, volatilizing at temperatures below their boiling points. Thus naphthalene, a solid, boils at 218°C but distills with water at a temperature below 100°C. Since naphthalene is not very volatile, considerable water is required to entrain it, and the conventional way of conducting the distillation is to pass steam
I. Introduction
When a mixture of cyclohexane and toluene is distilled, the boiling point of these two miscible liquids is between the boiling points of each of the pure components. By contrast, if a mixture of benzene and water (Immiscible liquids) is distilled, the boiling point of the mixture will be found below the boiling point of each pure component. Since the two liquids are essentially insoluble in each other, the benzene molecules in a droplet of benzene are not diluted by water molecules from nearby water droplets, and hence the vapor pressure exerted by the benzene is the same as that of benzene alone at the existing temperature. The same is true of the water present. Because they are immiscible, the two liquids independently exert pressures against the common external pressure, and when the sum of the two partial pressures equals the external pressure, boiling occurs. Benzene has a vapor pressure of 760 mm Hg at 80°C, and if it is mixed with water, the combined vapor pressure must equal 760 mm Hg at some temperature below 80°C. This temperature, the boiling point of the mixture, can be calculated from known values of the vapor pressure of the separate liquids at that temperature. Vapor pressures found for water and benzene in the range 50 to 80°C are plotted in the figure to the right. The dotted line cuts the two curves at points where the sum of the vapor pressures is 760 mm Hg; hence this temperature is the boiling point of the mixture
(69.3°C).
Practical use can sometimes be made of the fact that many water-insoluble liquids and solids behave as benzene does when mixed with water, volatilizing at temperatures below their boiling points. Thus naphthalene, a solid, boils at 218°C but distills with water at a temperature below 100°C. Since naphthalene is not very volatile, considerable water is required to entrain it, and the conventional way of conducting the distillation is to pass steam