Optimized liquid-phase oxidation

Abstract

Disclosed is an optimized process and apparatus for more efficiently and economically carrying out the liquid-phase oxidation of an oxidizable compound. Such liquid-phase oxidation is carried out in a bubble column reactor that provides for a highly efficient reaction at relatively low temperatures. When the oxidized compound is para-xylene and the product from the oxidation reaction is crude terephthalic acid (CTA), such CTA product can be purified and separated by more economical techniques than could be employed if the CTA were formed by a conventional high-temperature oxidation process.

1 . A process comprising: 
 (a) introducing an oxidant stream comprising molecular oxygen into a reaction zone of a bubble column reactor;    (b) introducing a feed stream comprising an oxidizable compound into said reaction zone, wherein said feed stream is introduced into said reaction zone in a manner such that when said reaction zone is theoretically partitioned into 4 vertical quadrants of equal volume by a pair of intersecting vertical planes, not more than about 80 weight percent of said oxidizable compound enters said reaction zone in a common one of said vertical quadrants; and    (c) oxidizing at least a portion of said oxidizable compound in a liquid phase of a multi-phase reaction medium contained in said reaction zone.    
     
     
         2 . The process of  claim 1  wherein not more than about 60 weight percent of said oxidizable compound enters said reaction zone in a common one of said vertical quadrants.  
     
     
         3 . The process of  claim 1  wherein said reaction medium has a maximum width (W), wherein at least about 50 weight percent of said oxidizable compound enters said reaction zone within about 2.5 W of the lowest location where said molecular oxygen enters said reaction zone.  
     
     
         4 . The process of  claim 1  wherein not more than 40 weight percent of said oxidizable compound enters said reaction zone in a single one of said vertical quadrants, wherein said reaction medium has a maximum diameter (W), wherein at least 75 weight percent of said oxidizable compound enters said reaction zone within 5 W of the lowest location where said molecular oxygen enters said reaction zone.  
     
     
         5 . The process of  claim 1  wherein said reaction medium has a maximum diameter (W), wherein said feed stream enters said reaction zone via a plurality of feed openings, wherein at least two of said feed openings are vertically spaced from one another by at least about 1.5 W.  
     
     
         6 . The process of  claim 1  wherein at least a portion of said reaction zone is defined by one or more upright sidewalls of said reactor, wherein at least about 25 weight percent of said oxidizable compound enters said reaction zone at one or more locations spaced inwardly at least 0.05 D from said upright sidewalls, wherein said reaction zone has a maximum diameter (D).  
     
     
         7 . The process of  claim 6  wherein at least about 50 weight percent of said oxidizable compound enters said reaction zone at one or more locations spaced inwardly at least 0.05 D from said upright sidewalls.  
     
     
         8 . The process of  claim 1  wherein said reaction medium has a maximum height (H), a maximum width (W), and an H:W ratio of at least about 3:1.  
     
     
         9 . The process of  claim 8  wherein said H:W ratio is in the range of from about 8:1 to about 20:1  
     
     
         10 . The process of  claim 8  wherein a majority of said molecular oxygen enters said reaction zone within about 0.25 W of the bottom of said reaction zone.  
     
     
         11 . The process of  claim 8  wherein a majority of said molecular oxygen enters said reaction zone within about 0.2 W and about 0.02 H of the bottom of said reaction zone.  
     
     
         12 . The process of  claim 1  wherein said oxidizable compound is an aromatic compound.  
     
     
         13 . The process of  claim 1  wherein said oxidizable compound is selected from the group consisting of para-xylene, meta-xylene, para-tolualdehyde, meta-tolualdehyde, para-toluic acid, meta-toluic acid, acetaldehyde, and combinations of two or more thereof.  
     
     
         14 . The process of  claim 1  wherein said reaction medium is a three-phase reaction medium.  
     
     
         15 . The process of  claim 1  wherein said oxidizing causes the formation of solids in said reaction medium.  
     
     
         16 . The process of  claim 1  wherein said oxidizing causes at least about 10 weight percent of said oxidizable compound to form solids in said reaction medium.  
     
     
         17 . The process of  claim 1  wherein said reaction medium comprises in the range of from about 5 to about 40 weight percent solids.  
     
     
         18 . The process of  claim 1  wherein said oxidizing is carried out in the presence of a catalyst system comprising cobalt.  
     
     
         19 . The process of  claim 18  wherein said catalyst system further comprises bromine and manganese.  
     
     
         20 . The process of  claim 1  wherein said oxidizable compound is para-xylene, wherein said oxidizing is carried out in a manner such that when said reaction zone is theoretically partitioned into 30 horizontal slices of equal volume, a pX-max horizontal slice has the maximum para-xylene concentration of all of said 30 horizontal slices and a pX-min horizontal slice has the minimum para-xylene concentration of all the horizontal slices located above said pX-max horizontal slice, wherein said para-xylene concentration is measured in a liquid phase of said reaction medium on a time-averaged and volume-averaged weight basis, wherein the ratio of the para-xylene concentration of said pX-max horizontal slice to the para-xylene concentration of said pX-min horizontal slice is at least about 5:1.  
     
     
         21 . The process of  claim 20  wherein the ratio of the para-xylene concentration of said pX-max horizontal slice to the para-xylene concentration of said pX-min horizontal slice is at least about 20:1.  
     
     
         22 . A process comprising: 
 (a) introducing an oxidant stream comprising para-xylene into a reaction zone of a bubble column reactor;    (b) introducing a feed stream comprising an oxidizable compound into said reaction zone via a plurality of feed openings, wherein said reaction zone has a maximum diameter (D), wherein at least two of said feed openings are spaced from one another by at least about 0.5 D; and    (c) oxidizing at least a portion of said oxidizable compound in a liquid phase of a multi-phase reaction medium contained in said reaction zone to thereby form crude terephthalic acid particles.    
     
     
         23 . The process of  claim 22  wherein at least about 30 weight percent of said para-xylene enters said reaction zone within about 1.5 D of the lowest location where said molecular oxygen enters said reaction zone.  
     
     
         24 . The process of  claim 22  wherein at least two of said feed openings are vertically spaced from one another by at least about 1.5 D.  
     
     
         25 . The process of  claim 22  wherein at least about 25 wherein at least a portion of said reaction zone is defined by one or more upright sidewalls of said reactor, wherein at least about 25 weight percent of said oxidizable compound enters said reaction zone at one or more locations spaced inwardly at least 0.05 D from said upright sidewalls.  
     
     
         26 . The process of  claim 25  wherein at least about 50 weight percent of said oxidizable compound enters said reaction zone at one or more locations spaced inwardly at least 0.05 D from said upright sidewalls.  
     
     
         27 . The process of  claim 22  wherein said reaction medium has a maximum height (H), a maximum width (W), and an H:W ratio in the range of from about 7:1 to about 25:1.  
     
     
         28 . The process of  claim 22  wherein less than about 9 volume percent of said reaction medium has a time-averaged para-xylene concentration greater than 1,000 ppmw.  
     
     
         29 . A process for producing terephthalic acid, said process comprising: 
 (a) introducing an oxidant stream comprising molecular oxygen into a reaction zone of a bubble column reactor;    (b) introducing a feed stream comprising para-xylene into said reaction zone, wherein said para-xylene enters said reaction zone in a manner such that when said reaction zone is theoretically partitioned into 4 vertical quadrants of equal volume by a pair of intersecting vertical planes, not more than about 80 weight percent of said para-xylene enters said reaction zone in a single one of said vertical quadrants;    (c) oxidizing at least a portion of said para-xylene in a liquid phase of said reaction medium contained in said reaction zone to thereby form crude terephthalic acid; and    (d) oxidizing at least a portion of said crude terephthalic acid in a secondary oxidation reactor to thereby form purer terephthalic acid.    
     
     
         30 . The process of  claim 29  wherein not more than about 60 weight percent of said para-xylene enters said reaction zone in a single one of said vertical quadrants.  
     
     
         31 . The process of  claim 29  wherein said reaction medium has a maximum width (W), wherein at least about 50 weight percent of said para-xylene enters said reaction zone within about 2.5 W of the lowest location where said molecular oxygen enters said reaction zone.  
     
     
         32 . The process of  claim 29  wherein not more than 40 weight percent of said para-xylene enters said reaction zone in a single one of said vertical quadrants, wherein said reaction medium has a maximum diameter (W), wherein at least 75 weight percent of said oxidizable para-xylene enters said reaction zone within 5 W of the lowest location where said molecular oxygen enters said reaction zone.  
     
     
         33 . The process of  claim 29  wherein said reaction medium has a maximum diameter (W), wherein said feed stream enters said reaction zone via a plurality of feed openings, wherein at least two of said feed openings are vertically spaced from one another by at least about 1.5 W.  
     
     
         34 . The process of  claim 29  wherein said oxidizing in said secondary oxidation reactor decreases the average concentration of 4-CBA present in said crude terephthalic acid by at least about 200 ppmw to thereby form said purer terephthalic acid.  
     
     
         35 . The process of  claim 29  wherein said crude terephthalic acid has an average 4-CBA concentration of at least about 400 ppmw and said purer terephthalic acid has an average 4-CBA concentration of less than about 400 ppmw.  
     
     
         36 . The process of  claim 29  wherein said oxidizing in said secondary oxidation reactor decreases the average concentration of 4-CBA in said crude terephthalic acid by at least about 400 ppmw to thereby form said purer terephthalic acid, wherein said crude terephthalic acid has an average 4-CBA concentration of at least about 800 ppmw and said purer terephthalic acid has an average 4-CBA concentration of less than about 250 ppmw.  
     
     
         37 . The process of  claim 29  wherein said oxidizing in said secondary oxidation reactor is carried out at an average temperature at least about 10° C. greater than the average temperature of said oxidizing in said bubble column reactor.  
     
     
         38 . The process of  claim 29  wherein said oxidizing in said bubble column reactor is carried out at an average temperature in the range of from about 125 to about 200° C., wherein said oxidizing in said secondary oxidation reactor is carried out at an average temperature in the range of from about 160 to about 240° C.  
     
     
         39 . The process of  claim 29  wherein said oxidizing in said secondary oxidation reactor is carried out at an average temperature in the range of from about 20 to about 80° C. greater than the average temperature of said oxidizing in said bubble column reactor, wherein said oxidizing in said bubble column reactor is carried out at an average temperature in the range of from about 140 to about 180° C., wherein said oxidizing in said secondary oxidation reactor is carried out at an average temperature in the range of from about 180 to about 220° C.  
     
     
         40 . The process of  claim 29  wherein a substantial portion of said crude terephthalic acid exists as solid crude terephthalic acid particles having an average BET surface area of at least about 0.6 meters squared per gram.  
     
     
         41 . The process of  claim 40  wherein said solid crude terephthalic acid particles have an average particle size in the range of from about 20 to about 150 microns.  
     
     
         42 . The process of  claim 41  wherein a substantial portion of said solid crude terephthalic acid particles are formed of a plurality of agglomerated sub-particles having an average particle size in the range of from about 0.5 to about 30 microns.  
     
     
         43 . The process of  claim 42  wherein said solid crude terephthalic acid particles have an average particle size in the range of from about 30 to about 120 microns, wherein said sub-particles have an average particle size in the range of from about 1 to about 15 microns.  
     
     
         44 . The process of  claim 29  wherein said process further comprises recovering an initial slurry comprising a mother liquor and said crude terephthalic acid from said bubble column reactor, wherein said process further comprises replacing at least about 50 weight percent of said mother liquor in said initial slurry with a replacement solvent to thereby provide a solvent-exchanged slurry comprising said replacement solvent and said crude terephthalic acid, wherein said process further comprises introducing said solvent-exchanged slurry into said secondary oxidation reactor.