Abstract
Toray has developed two new processes for p-xylene production. The one is the Aromax process, in which p-xylene is separated from a mixture of xylene isomers by adsorption and the other is the Isolene process, in which the residual xylene isomers are converted to p-xylene by means of isomerization.
The first commercial Isolene and Aromax units have been successfully on stream in Toray's Kawasaki Plant since September, 1971 and March, 1973, respectively. Distinguished features of Aromax and Isolene processes proved in commercial operation are as follows:
1. Aromax Process
(1) p-Xylene yield per pass can be more than 90% against about 60% in crystallization process.
(2) Higher one pass yield causes lower flow rate of xylene feedstock and smaller investment in downstream plant for isomerization.
(3) In crystallization process, complicated mechanical separation of p-xylene crystal from slurry is required while Aromax is operated under milder conditions which make operation and maintenance much easier.
(4) Material of construction can be carbon steel throughout the unit.
2. Isolene Process
(1) One-pass yields of C8 hydrocarbon are as high as 97∼98% including ethylbenzene conversion to xylenes.
(2) Regeneration of the catalyst is required only once or twice a year under normal operating conditions.
(3) Hydrogen consumption is low.
(4) Operating conditions are mild.
(5) No corrosive chemicals are needed, eliminating special alloys for the unit.
