Purification, adsorption refrigeration

Adsorption phenomena are of interest in several topics and find uses including purification technology, refrigeration technology [9]. The uptake of gases by charcoal was studied by Scheele in 1773 and further by Fontana in 1777. 

The solvent used to form the dope is evaporated during the extrusion process and must be recovered. This is usually done by adsorption on activated carbon or condensation by refrigeration. For final purification, the solvent is distilled. Approximately 3 kg of acetone, over 99%, is recovered per kg of acetate yam produced. Recovery of solvent from triacetate extmsion is similar, but ca 4 kg of methylene chloride solvent is needed per kg of triacetate yam extmded. 

Even though most chemical purification methods are not carried out at low temperatures, they are useful in several cryogenic gas separation systems. Ordinarily water vapor is removed by refrigeration and adsorption methods. However, for small-scale purification, the gas can be passed over a desiccant, which removes the water vapor as water of crystallization. In the krypton-xenon purification system, carbon dioxide is removed by passage of the gas through a caustic, such as sodium hydroxide, to form sodium carbonate. 

Helium gas purification systems. Where the concentration of moisture and atmospheric contaminants in the helium stream are very low, e.g., about 500 parts per million or less and where the system is operating at low pressure, the helium stream may be cooled to low temperatures inside the Norelco circulating cold gas head, and thence purified in a conventional adsorption system as illustrated by the process diagram, Figure 10. Calculations show that a refrigerator of this type has the capacity to purify about 4000 SCFH of helium of the aforenoted specifications. 

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