Carbon, activated bead, solvent

PuraSiv HR A process for removing solvent vapors from air by adsorption on beaded activated carbon contained in a combined fluidized moving bed. For water-soluble solvents, the gas used for desorption is nitrogen and the process is known as PuraSiv HR, Type N (not to be confused with PuraSiv N) for chlorinated hydrocarbons, steam stripping is used and the process is known as PuraSiv HR, Type S. Developed by Kureha Chemical Company and now marketed by the Union Carbide Corporation. The process was originally known as GASTAK because it was developed by the Taiyo Kaken Company, subsequently acquired by Kureha Chemical Company. It is also marketed by Daikin Industries under the name Soldacs. 

These Deloxan beads have an inert siloxane matrix which is advantageous over other adsorbents such as activated carbon or organic polymer-based resins and fibers because (1) valuable API product is not adsorbed and lost as is the case when activated carbons are used and (2) they are chemically resistant to most solvents and stable over a wide pH range (0-12). 

Active ester formation by the mixed anhydride method is accompanied by the side reaction of esterification at the carbonate moiety of mixed anhydride 51 which generates mixed carbonate 52 (Scheme 12).This decreases the yields, but is more of a nuisance than an obstacle as the side products do not interfere with crystallization of the esters as the former are soluble in the crystallizing solvent. More mixed carbonate is formed from derivatives of the hindered amino acids and proline none is formed from a-unsubstituted acids. A-Hy-droxysuccinimide gives rise to much less byproduct than 4-nitrophenol other phenols generate intermediate amounts. Less byproduct is generated when the reagent is isopropyl chloroformate. The impurity can be readily removed from a solution of the ester by adsorption of the compounds on reverse-phase chromatography beads followed by separation by selective displacement. ... 

The polymeric resins are substantially more hydrophobic than activated carbon. The non-wetting types are subjected to the pre-wetting procedure described above (i.e., wetting wi a solvent, such as methanol, followed by aqueous solution). The pores are presumably wetted (completely) upon this treatment. Undoubtedly, the mesopores (i.e., voids between the microspheres within each bead) are wetted. It is not clear, however, whether the micropores within each microsphere are completely wetted by this procedure. 

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