The Dow Chemical Company

Inca International S.p.a.

Sergio Schena

Luciano Piras

Christopher John Tucker

John Klier

Guo-shuh J Lee

Thomas H Kalantar

Kenneth A Burdett

Daniel Patrick Green

Michelle Chiarelli

Luigi Soro

The present invention pertains to an improved method of oxidizing substituted aromatic compounds (such as p xylene) to their corresponding aromatic acids (such as terephthalic acid). The improvement involves carrying out the oxidation reaction in an aqueous medium, wherein the aqueous medium contains at least 30 percent water, preferably up to 30 percent surfactant and preferably a low molecular weight material containing a hydrophilic end group as a co-surfactant. The reaction is carried out at a pH of less than 3.0.

Oxidation of alkyl aromatic compounds to aromatic acids in an aqueous medium

A process for the preparation of purified terephthalic acid which comprises first introducing a liquid slurry containing crystalized terephthalic acid with impurities into a high pressure rotary filter, then filtering the slurry with the high pressure rotary filter and collecting at least some of the solid portion. The filter typically consists of a case, pressurized at process pressure, and a drum covered by a filtering device such as, for example, a cloth or equivalent filtering device, pressurized at a pressure suitably lower than the case. The drum is ideally divided into three zones: first zone, where the mother liquor is removed; second zone, where the solid is washed; third zone, where the excess of washing liquor is removed and the solid is discharged. The solid portion is washed, onto the filter drum, with additional amounts of water. The washed solid portion is then transferred to a letdown zone, which is at a pressure less than the zone in which the solid portion was collected. After the solid portion is transferred into the letdown zone, the connection between the letdown zone and the collection zone is sealed, such that a change of pressure in the letdown zone will not effect the pressure in the collection zone. The pressure of the letdown zone is then gradually reduced and the solid removed. The letdown zone is then pressurized back up so that it is ready to accept additional solid from the rotary filter.

Process for the recovery of purified terephthalic acid (PTA)

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Mantova, Italy

Sergio Schena