Methods and systems for purifying styrene feedstock comprising use of low palladium catalyst

Abstract

Apparatus, methods and systems useful for removing phenylacetylene from crude styrene feedstock are disclosed. Generally the processes and systems comprise the catalytic reduction of phenylacetylene to produce styrene via injection of a phenylacetylene reducing agent, such as hydrogen. A phenylacetylene reduction catalyst preferred Wherein comprises palladium on a calcium aluminate carrier, wherein the catalyst comprises less than 0.3 weight percent palladium.

We claim:  
     
         1 . A system for decreasing the level of a contaminant in a crude styrene feedstock, the system comprising: 
 a) a crude styrene supply comprising an initial level of contaminant X, a crude styrene input stream, and a crude styrene output stream, wherein said crude styrene input stream is arranged to receive crude styrene from an ethylbenzene dehydrogenation unit, wherein said crude styrene is produced by dehydrogenation of ethylbenzene in said dehydrogenation unit;    b) a hydrogen source arranged to inject a first portion of hydrogen into the crude styrene output stream to produce stream B;    c) a first catalyst bed arranged to receive stream B, wherein the first catalyst bed comprises a first catalyst bed output stream, wherein the first catalyst bed comprises a first catalyst having from about 0.01 to less than 0.3 weight percent palladium, and wherein said first catalyst bed output stream comprises a level of contaminant X less then said initial level.    
     
     
         2 . The system of  claim 1  further comprising: 
 d) a second hydrogen source arranged to inject a second portion of hydrogen into said first catalyst bed output stream to produce stream C; and,  
 e) a second catalyst bed arranged to receive stream C, wherein the second catalyst bed comprises a second catalyst bed output stream comprising a level of contaminant X less then said first catalyst bed output stream.  
 
     
     
         3 . The system of  claim 2  wherein the first hydrogen source is pure hydrogen, vent gas obtained from the ethylbenzene dehydrogenation unit, or a mixture of hydrogen and a diluent.  
     
     
         4 . The system of  claim 3  wherein the second hydrogen source is pure hydrogen, vent gas obtained from the ethylbenzene dehydrogenation unit, or a mixture of hydrogen and a diluent.  
     
     
         5 . The system of  claim 4  wherein the diluent is nitrogen.  
     
     
         6 . The system of  claim 4  wherein said second catalyst bed comprises a second catalyst comprising from about 0.01 to less than 0.3 weight percent palladium.  
     
     
         7 . The system of  claim 6  wherein said first and second catalysts each comprise from about 0.03 to about 0.05 weight percent palladium.  
     
     
         8 . The system of  claim 6  wherein said first and second catalyst beds are in a single reactor.  
     
     
         9 . The system of  claim 6  wherein said first and second catalyst beds are each in a separate reactor.  
     
     
         10 . The system of  claim 6  wherein said first and second catalysts are phenylacetylene reduction catalysts dispersed on a calcium aluminate carrier, and are the same catalyst.  
     
     
         11 . The system of  claim 19  wherein said contaminant X is phenylacetylene, and wherein said level of phenylacetlyene of said second catalyst bed output stream is less than 10 ppm.  
     
     
         12 . The system of  claim 11  wherein said first and second catalysts are in the shape of cylindrical pellets.  
     
     
         13 . A method for decreasing the level of a contaminant in a crude styrene feedstock, the method comprising the steps of: 
 a) admixing a portion of a first reducing agent together with a first portion of crude styrene to produce a stream A, wherein said crude styrene comprises an initial level of a contaminant X;    b) contacting stream A with a first catalyst bed comprising a first catalyst comprising from about 0.01 to less than 0.3 weight percent palladium to produce stream B, wherein stream B comprises a level of contaminant X less than the initial level of contaminant X.    
     
     
         14 . The method of  claim 13  further comprising the steps of: 
 c) admixing a portion of a second reducing agent together with stream B to produce stream C;  
 d) contacting stream C with a second catalyst bed comprising a second catalyst comprising from about 0.01 to less than 0.3 weight percent palladium to produce stream D, wherein stream D comprises a level of contaminant X less than that of stream B.  
 
     
     
         15 . The method of  claim 14  wherein said first and second catalysts each comprise from about 0.03 to about 0.05 weight percent palladium.  
     
     
         16 . The method of  claim 14  wherein said first portion of crude styrene is a stream of styrene, wherein said crude styrene is produced by dehydrogenation of ethylbenzene in an ethylbenzene dehydrogenation unit, and wherein said first and second reducing agents are obtained as vent gas from said dehydrogenation unit.  
     
     
         17 . The method of  claim 15  wherein said first and second reducing agents are hydrogen gas.  
     
     
         18 . The method of  claim 16  wherein said first and second catalyst beds are in the same reactor unit.  
     
     
         19 . The method of  claim 16  wherein said first and second catalyst beds are each in a separate reactor unit.  
     
     
         20 . The method of  claim 15  wherein said contaminant X is phenylacetlyene, and wherein said level of phenylacetylene of stream D is less than 10 ppm.