Separations Involving Phase Changes.pdf

Separations Involving Phase Changes Lecturer : Chong Arechkang, MSc Outline I. Volatization II. Distillation III. Lyophilization I. Volatilization Volatilization is the conversion of all or part of solid or a liquid to a gas. The gas may be produced by several methods: (I)...

Separations Involving Phase Changes Lecturer : Chong Arechkang, MSc Outline I. Volatization II. Distillation III. Lyophilization I. Volatilization Volatilization is the conversion of all or part of solid or a liquid to a gas. The gas may be produced by several methods: (I) by direct heating. such as heating NH4NO3 to form N2 and H2O; (2) by applying the principle that strong acids displace weaker acids and strong bases displace weaker bases; for example. the evolution of gaseous CO2, a weak acid, from solid CaCO3 by adding HCI, a strong acid. Or the removal of gascousNH3, a weak base, from solid (NH4)2SO4 by adding NaOH; (3) by oxidation such as burning a sulfide in air to produce SO2; or (4) by reduction, or converting the elements to hydrides such as AsH3 or H2Se. I. Volatilization A brief summary of how several of these can be obtained in a volatile form is shown below for the inorganic compounds. I. Volatilization I. Volatilization Moisture Determination  Moisture Determination An aluminum dish weighed 1.9593 g empty and 2.8410 g with sample. After the sample was brought to constant weight, the combination weighed 2.7555 g. What is the % moisture in this sample? II. Distillation Distillation is the process of producing a vapor from a liquid by heating the liquid in a vessel, then condensing the vapors and collecting them in another vessel. II. Distillation : simple distillation A simple distillation involves applying heat to vaporize a liquid and then cooling the vapor until it condenses as a liquid. The separation of water from the salts in sea water is one example. II. Distillation : fractional distillation What do you do if the mixture has two or more compounds that have appreciable vapor pressure? Fractional Distillation is used to separate miscible liquids that are volatile in nature. The boiling points of these liquids are close enough. A large surface area is needed so the process can be repeated several time along the length of the column. A column for this purpose is called a fractionating column and the process is called fractional distillation. II. Distillation : fractional distillation III. Distillation : vacuum distillation III. Distillation : vacuum distillation There are many times when distilling compounds that it becomes impossible at atmospheric pressure because they must be heated to such a high temperature that they may polymerize, react with other compounds in the mixture, explode, decompose to an unidentifiable mass or contain an azeotrope. A way to reduce the temperature of a distillation is to reduce the atmospheric pressure of the system. Any distillation below atmospheric pressure is called a vacuum distillation III. Distillation : vacuum distillation III. Distillation : vacuum distillation III. Lyophilization (freeze-drying) Sublimation is a process in which a solid becomes a gas without first becoming a liquid. III. Lyophilization (freeze-drying) Lyophilization is a process of drying materials by subliming the water from a frozen sample. This works well for materials that are heat sensitive and would be wholly or partially destroyed if dried at atmospheric drying conditions. The basic process is to first freeze the sample, then apply a vacuum so that the ice will sublime without melting- hence, the more common name freeze drying. III. Lyophilization (freeze-drying) From this it can be seen that water will sublime at any combination of temperatures below 0 oC and pressures below 4.57 torr. Commercially. freeze drying is considered to be any process of this type operating below 100 Pa (0.75 torr). III. Lyophilization (freeze-drying) From this it can be seen that water will sublime at any combination of temperatures below 0 oC and pressures below 4.57 torr. Commercially. freeze drying is considered to be any process of this type operating below 100 Pa (0.75 torr). III. Lyophilization (freeze-drying) III. Lyophilization (freeze-drying)