Phthalic anhydride vapor pressure

According to the present method of operation, the products from the converter are passed continuously to a condenser where phthalic anhydride is first condensed in a relatively pure condition. The impurities having higher vapor pressures must be cooled further and condense in later sections. Without shutting down the converter the products are periodically... 

In this way the components of the mixture may be separated according to their vapor pressure/8 The naphthols, however, have a vapor pressure very nearly that of phthalic anhydride and would be difficult to separate from the pure product. Although occurring in only small amounts during improper operation, the formation of naphthols must be guarded against by insuring proper air ratios, temperatures and times of contact.40... 

The impurities in phthalic anhydride obtained in the vapor phase oxidation process may he caused to condense or polymerize by heating either with or without the addition of special agents. The vapor pressure of these materials is so lowered by this treatment that subsequent sublimation of tlu- mass results in pure product, the condensed materials remaining in the retort. 

The small amount of benzoic acid that forms with the phthalic anhydride during the oxidation of naphthalene represents a waste when not recovered. Methods have been proposed for the separation of the two acids which depend on differences in solubility and vapor pressure. Thus, an aqueous dispersion of the two acids is subjected to the leaching action of a solvent for the benzoic acid, such as gasoline or benzene. The solvent is subsequently separated from the water layer and the acids recovered... 

At these equilibrium conditions of 70°C and 1,034 torr, the partial pressure of phthalic anhydride in the vapor is (0.005/99.005)1,034 = 0.05 torr, which is equal to its vapor pressure. The partial pressure of water in the vapor is (4.25/99.005)1,034 = 44.4 torr, which is well below its vapor pressure of 234 torr at 70°C. Thus, water does not condense at these conditions. The amount of solids in the table above corresponds to a 99.5% desublimation of phthalic anhydride. At 85°C the percent desublimation is only 98%, while at 96.4 C it is only 95%. Thus, the recovery of phthalic anhydride from the reactor effluent is sensitive to the desublimation condenser temperature. 

Unit 700 now produces about 80,000 metric tons/yr of phthalic anhydride. The feeds are essentially pure naphthalene and excess air. These are pressurized, heated and vaporized (naphthalene), and reacted in a fluidized bed with a vanadium oxide on silica gel catalyst. The reactions are as follows. 

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