Formation, purification and recovery of phthalic anhydride
US4234494A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Aug 29, 1979 |
| Grant date | Nov 18, 1980 |
| Priority date | — |
| Expiry date | Aug 29, 1999 |
Classification
- Technology area (CPC C)Chemistry; Metallurgy
- CPC primaryC07C51/56
- WIPO fieldOrganic fine chemistry
- WIPO sectorChemistry
Abstract
Phthalic anhydride of commercially acceptable quality is recovered in high (94-96%) yields from a mixture containing, on a weight basis, from 70 to 90% o-phthalic acid, 1.5 to 21% water, 0.3 up to 13% benzoic acid, 0.2 up to 2% o-toluic acid, 0.2 to 1% 2-carboxybenzaldehyde, 0.1 up to 2% phthalide, from 1.3 up to 10% higher boiling materials, and from 0.05 up to 0.8% bromine by rapid dehydration of o-phthalic acid to its anhydride and rapid evaporation thereof followed by contact of the resulting vapor mixture with a noble metal catalyst to remove bromine and then with an inert reflux liquid in a fractionation zone to remove water and to provide a partial purification of the anhydride, removal of phthalide therefrom by only heating said partially purified anhydride in the presence of a catalytic amount of an alkali metal hydroxide having a molecular weight of at least 56 followed by fractionation of the phthalide-free mixture. Such process is more commercially attractive than melting said mixture containing 70 to 90% o-phthalic acid to dehydrate it to its anhydride and recovering the anhydride by fractionation because such apparently simple process cannot produce phthalic anhydride…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.