Optimized production of aromatic dicarboxylic acids

Abstract

Disclosed is an optimized process and apparatus for more efficiently and economically producing aromatic discarboxylic acids. The process reduces costs associated with hydrogenation by forming a final composite product containing unhydrogenated acid particles

1 . A process comprising: 
 (a) providing a quantity of crude acid particles;    (b) subjecting a first portion of said crude acid particles to hydrogenation treatment, thereby producing a hydrogenation-treated acid; and    (c) combining a second portion of said crude acid particles that has not been subjected to hydrogenation treatment with at least a portion of said hydrogenation-treated acid, thereby producing a composite acid.    
     
     
         2 . The process of  claim 1  wherein said crude acid particles are particles of crude terephthalic acid, wherein said hydrogenation-treated acid is purified terephthalic acid.  
     
     
         3 . The process of  claim 1  wherein said process further comprises substantially dissolving said first portion of said crude acid particles in a solvent and subjecting the resulting solution to said hydrogenation treatment.  
     
     
         4 . The process of  claim 1  wherein said process further comprises forming solid particles of a purified acid from at least a portion of said hydrogenation-treated acid, wherein said combining of step (c) includes combining at least a portion of said crude acid particles and at least a portion of said purified acid particles, thereby forming said composite acid.  
     
     
         5 . The process of  claim 4 , wherein said hydrogenation treatment includes liquid-phase hydrogenation, wherein said purified acid particles are formed by crystallization.  
     
     
         6 . The process of  claim 5  wherein said liquid-phase hydrogenation is carried out at a temperature in the range of from about 200 to about 375° C., wherein said crystallization is carried out at a temperature in the range of from about 100 to about 200° C.  
     
     
         7 . The process of  claim 1  wherein said providing of step (a) includes oxidizing an aromatic compound in an oxidation reactor to thereby form said crude acid particles.  
     
     
         8 . The process of  claim 7  wherein said aromatic compound is para-xylene.  
     
     
         9 . The process of  claim 1  wherein the weight ratio of said crude acid particles to said hydrogenation-treated acid in said composite acid is at least about 0.01:1.  
     
     
         10 . The process of  claim 1  wherein the weight ratio of said crude acid particles to said hydrogenation-treated acid in said composite acid is in the range of from about 0.05:1 to about 2:1.  
     
     
         11 . The process of  claim 1  wherein the 4-carboxybenzaldehyde (4-CBA) content of said hydrogenation-treated acid is less than about 100 ppmw, wherein said crude acid particles have a 4-CBA content of at least about 600 ppmw.  
     
     
         12 . The process of  claim 1  wherein the para-toluic acid (p-TAc) content of said hydrogenation-treated acid is less than 500 ppmw, wherein said crude acid has a p-TAc content of at least about 150 ppmw.  
     
     
         13 . The process of  claim 1  wherein the combined 4-CBA and p-TAc content of said hydrogenation-treated acid is less than 600 ppmw, wherein said crude acid has a combined 4-CBA and p-TAc content of at least about 700 ppmw.  
     
     
         14 . The process of  claim 1  wherein the B* value of said hydrogenation-treated acid is less than about 3.0, wherein said crude acid has a B* value of at least about 3.0.  
     
     
         15 . The process of  claim 1  wherein said crude acid particles are particles of crude terephthalic acid having a combined 4-CBA and p-TAc content of at least about 850 ppmw and a B* value of at least about 3.5.  
     
     
         16 . The process of  claim 15  wherein said hydrogenation-treated acid is formed of particles of purified terephthalic acid, wherein the combined 4-CBA and p-TAc content of said purified terephthalic acid particles is less than about 300 ppmw, wherein the B* value of said purified terephthalic acid particles is less than about 2.0.  
     
     
         17 . The process of  claim 16  wherein the weight ratio of said crude terephthalic acid particles to said purified terephthalic acid particles in said composite acid is in the range of from about 0.05:1 to about 2:1.  
     
     
         18 . The process of  claim 1  wherein said process further comprises splitting said crude acid particles into said first portion and said second portion.  
     
     
         19 . The process of  claim 18  wherein the weight ratio of said second portion to said first portion is in the range of from about 0.01:1 to about 4:1.  
     
     
         20 . An apparatus comprising: 
 an oxidation reactor having a reactor outlet;    a solid/liquid separator having a separator inlet, a separated solids outlet, and a separated liquids outlet, wherein said separator inlet is coupled in communication with said reactor outlet;    a splitter having a splitter inlet, a first splitter outlet and a second splitter outlet, wherein said splitter inlet is coupled in communication with said separated solids;    a hydrogenation system having a hydrogenation system inlet and a hydrogenation system outlet, wherein said hydrogenation system inlet is coupled in communication with said first splitter outlet; and    a combining zone having a hydrogenated solids inlet, an unhydrogenated solids inlet, and a composite solids outlet, wherein said hydrogenated solids inlet is coupled in communication with said hydrogenation system outlet, wherein said unhydrogenated solids inlet is coupled in communication with said second splitter outlet.    
     
     
         21 . The apparatus of  claim 20  further comprising a crystallization system having a crystallization system inlet and a crystallization system outlet, wherein said crystallization inlet is coupled in communication with said hydrogenation system outlet, wherein said crystallization system inlet is coupled in communication with said hydrogenation system outlet.  
     
     
         22 . The apparatus of  claim 21  further comprising a second solid/liquid separator having a second separator inlet, a hydrogenated solids outlet, and hydrogenated liquids outlet, wherein said second separator inlet is coupled in communication with said crystallization system outlet, wherein said hydrogenated solids outlet is coupled in communication with said hydrogenated solids inlet.