In the xylene isomerization process, a mixture of C aromatics such as ortho-, meta- and para-xylenes plus ethyl benzene is converted to p-xylene by isomerization and disporportionation.xylene isomerization catalyst The p-xylene component in the product effluent is of an amount at least approaching that in the xylene mixture produced at thermal equilibrium.
The isomerization reaction is induced by the application of hydrogen at a pressure in the range of 300 to 600 psig.xylene isomerization catalyst The reaction zone is operated at a temperature in the range of 340 to 400 deg C. A platinum-containing catalyst on a support of active alumina and mordenite is employed for the isomerization. The platinum-containing catalyst is plated with nickel to form an alloy. The catalyst is available from JSC PO Kirishineftorgsintez (SIE Neftehim, LLC) under the trademark IK-112. It has been used at a commercial ortoxylene and paraxylene recovery unit with excellent results, including a high p-xylene yield.
A major objective of the isomerization process is to convert a straight chain alkane to a branched alkane.xylene isomerization catalyst This is a fundamentally different objective than in cat cracking and alkylation processes which focus on changing the size of the molecule. The isomerization process aims to make the molecular structure more branched and more flexible, allowing it to be broken down by hydrogen.
The xylene isomerization reactor is designed to produce maximum quantities of p-xylene from the mixture of xylene isomers and ethyl benzene in a feed.xylene isomerization catalyst The isomerizer takes crystallizer effluent lean in p-xylene and converts the other xylene isomers to p-xylene, thereby reducing the ethyl benzene content of the product to an acceptable level.
It is important to control the ethyl benzene conversion in the isomerizer to ensure that the p-xylene concentration approaches or achieves thermal equilibrium, and it is also essential to minimize the amount of p-xylene lost during the isomerization reaction. The value of a p-xylene loss is measured by subtracting the p-xylene content of the fed mixture from that of the product effluent.
Typical oxylene isomerization reactions use a ZSM-5 zeolite loaded with 0.05 up to 1.5 weight percent of a metal such as zinc, cadmium, iron, barium and tin. In the isomerization reaction, the metals serve as an effective diluent for the xylene to allow it to diffuse more easily through mX than through oX or mX/pX. This results in a low oxylene isomerization reaction loss of less than 0.2 wt. % and a high ethyl benzene recovery.
In addition, the low ppm levels of hydrogen at which the Ha is applied in this process eliminates the need for frequent shutdowns to regenerate the catalyst, resulting in a continuous operation with a high PX yield. The high ethyl benzene yield and the low oxylene loss in the isomerization process are particularly beneficial to refiners and marketers of p-xylene. It is also advantageous to be able to operate with an oxylene content in the feed that is well below the thermal equilibrium point. This is especially desirable for use with oxylene-to-ethyl benzene (OB) ratios of 50 or less.
Tags:butene isomerization catalyst | ethylbenzene synthesis catalyst
