Equilibration of lower alkyl substituted polyalkyl aromatic hydrocarbons with reduced disproportionation

Abstract

Disproportionation losses in the isomerization of C 8 aromatic hydrocarbons are reduced by the use of silica-alumina catalyst composites with high surface areas and having .[.pore.]. .Iadd.most of its pore volume from pores of .Iaddend. radii .[.in the main.]. above about 45° A.

What is claimed is: 
     
       1. The process for the catalytic isomerization of an alkyl substituted polyalkyl aromatic hydrocarbon feed which comprises contacting the feed with a silica-alumina isomerization catalyst at a temperature in the range from about 700° F. to 1000° F., at a liquid hourly space velocity in the range from about 0.1 to 10, and at a pressure below about 200 p.s.i.g., wherein said catalyst consists essentially of a silica and alumina composite having a surface area in the range from about 250 to 400 square meters per gram, wherein at least 40 percent of the catalyst .Iadd.pore volume is from .Iaddend.pores .[.have.]. .Iadd.having .Iaddend.a radius greater than about 45 A., said feed having an aromatic carbocyclic carbon atom content below about 13, and having from 2 to about 4 of the same or different lower alkyl substituent groups; and said composite having a silica to alumina weight ratio in the range from about 70-90 to about 10-30, respectively. 
     
     
       2. The process as in claim 1 further characterized in that the feed is a polymethylbenzene, in that the surface area is in the range from about 270-350 square meters per gram, and in that at least about 70 percent of the .Iadd.pore volume is from .Iaddend.pores .[.have.]. .Iadd.having .Iaddend.a radius greater than 45 A. 
     
     
       3. The process as in claim 2 further characterized in that less than about 10 percent of the .Iadd.pore volume is from .Iaddend.pores .[.have.]. .Iadd.having .Iaddend.a radius less than 45 A. 
     
     
       4. The process as in claim 2 further characterized in that the composite contains, in addition to the silica and alumina, an amount in the range from about 5 to 15 parts by weight of an oxide selected from the group consisting of magnesia, zirconia, thoria and beryllia. 
     
     
       5. The process as in claim 4 further characterized in that the oxide is magnesia and in that the silica to alumina weight ratio is about 80 to 20, respectively. 
     
     
       6. The process as in claim 1 further characterized in that the composite contains, in addition to the silica and alumina, an amount in the range from about 5 to 15 parts by weight of an oxide selected from the group consisting of magnesia, zirconia, thoria, and beryllia. 
     
     
       7. The process as in claim 5 further characterized in that the feed is a p-xylene reduced C 8  aromatic hydrocarbon mixture. 
     
     
       8. The process as in claim 1 further characterized in that the pore radius is greater than 50 A. 
     
     
       9. The process as in claim 1 further characterized in that the temperature is in the range from about 750° F. to 900° F.