Process for preparing furan-2,5-dicarboxylic acid

Abstract

A process for preparing furan-2,5-dicarboxylic acid is disclosed. The process includes the following steps: preparing or providing a starting mixture including 5-(hydroxy-methyl)furfural (HMF), 5,5′-[oxy-bis(methylene)]bis-2-furfural (di-HMF), and water; subjecting said starting mixture to oxidation conditions in the presence of an oxygen-containing gas and a catalytically effective amount of a heterogeneous catalyst including one or more noble metals on a support so that both HMF and di-HMF react to give furane-2,5-dicarboxylic acid in a product mixture also including water and oxidation by-products. The use of a catalyst is also disclosed, the catalyst including one or more noble metals on a support as an heterogeneous oxidation catalyst for catalyzing in an aqueous starting mixture the reaction of both HMF and di-HMF to furane-2,5-dicarboxylic acid.

The invention claimed is: 
     
       1. Process for preparing furane-2,5-dicarboxylic acid comprising the following steps:
 (a) preparing or providing a starting mixture comprising
 5-(hydroxymethyl)furfural (HMF), 
 5,5′-[oxy-bis(methylene)]bis-2-furfural (di-HMF), and 
 water, 
 wherein a total amount of water in the starting mixture is at least 50 wt.-%, based on a total weight of the starting mixture and 
 wherein a pH of the starting mixture is in a range of from 4.0 to 7.0, 
 
 (b) subjecting said starting mixture to oxidation conditions in the presence of an oxygen-containing gas and a catalytically effective amount of a heterogeneous catalyst comprising one or more noble metals on a support so that both HMF and di-HMF react to give furane-2,5-dicarboxylic acid in a product mixture also comprising water. 
 
     
     
       2. The process according to  claim 1 , wherein the starting mixture has a molar ratio of HMF to di-HMF in the range of from 100 to 0.8, and/or a total weight of HMF and di-HMF in the starting mixture is in a range of from 0.1 to 50 wt.-%, based on the total weight of the starting mixture. 
     
     
       3. The process according to  claim 1 , wherein a pH of the product mixture is below 7. 
     
     
       4. The process according to  claim 1 , wherein said starting mixture at a temperature in a range of from 70° C. to 200° C., is subjected to said oxidation conditions in the presence of said oxygen-containing gas and said catalytically effective amount of a heterogeneous catalyst comprising one or more noble metals on a support, so that both HMF and di-HMF react to give furane-2,5-dicarboxylic acid in the product mixture also comprising water and oxidation by-products. 
     
     
       5. The process according to  claim 1 , wherein said starting mixture is subjected to said oxidation conditions in a pressurized reactor, wherein an oxygen partial pressure in the reactor at least temporarily is in a range of from 1 to 100 bar, during the reaction of both HMF and di-HMF to furane-2,5-dicarboxylic acid. 
     
     
       6. The process according to  claim 1 , wherein a total amount of acetate ions and acetic acid in said starting mixture is below 10 wt.-%, wherein a total amount of carboxylic acid ions and carboxylic acid in the starting mixture is below 10 wt.-%. 
     
     
       7. The process according to  claim 1 , wherein the step of preparing said starting mixture comprises
 (a1) preparing or providing a material mixture comprising
 one, two or more compounds selected from the group consisting of hexoses, oligosaccharides comprising hexose units, and polysaccharides comprising hexose units, and 
 
 (a2) subjecting said material mixture to reaction conditions so that a mixture results comprising
 HMF, 
 di-HMF, and 
 water. 
 
 
     
     
       8. The process according to  claim 1 , wherein in said heterogeneous catalyst comprising one or more noble metals on a support
 (i) at least one of said noble metals is selected from the group consisting of gold, platinum, iridium, palladium, osmium, silver, rhodium and ruthenium, and/or 
 (ii) said support is selected from the group consisting of carbon, metal oxides, metal halides, and metal carbides. 
 
     
     
       9. The process according to  claim 1 , wherein in said heterogeneous catalyst comprising one or more noble metals on a support
 at least one of said noble metals is selected from the group consisting of platinum, iridium, palladium, osmium, rhodium and ruthenium, 
 and 
 said support is carbon. 
 
     
     
       10. The process according to  claim 1 , wherein in said heterogeneous catalyst comprising one or more noble metals on a support
 said one or one of said more noble metals is platinum and said support is carbon, 
 and 
 a content of platinum on the support is in a range of from 0.1 to 20 wt.-%, based on a total weight of the heterogeneous catalyst comprising one or more noble metals on a support. 
 
     
     
       11. The process according to  claim 1 , wherein in said heterogeneous catalyst comprising one or more noble metals on a support
 a molar ratio of said one or one of said more noble metals to a total amount of HMF and di-HMF is in a range of from 1:1 000 000 to 1:10. 
 
     
     
       12. The process according to  claim 1 , wherein the product mixture obtained in step (b) comprises furan-2,5-di carboxylic acid in dissolved form. 
     
     
       13. A catalyst comprising one or more noble metals on a support as an heterogeneous oxidation catalyst for accelerating in an aqueous starting mixture a conversion of both HMF and di-HMF to furane-2,5-dicarboxylic acid, wherein a pH of the starting mixture is in a range of from 4.0 to 7.0. 
     
     
       14. The process according to  claim 7 , wherein the step of preparing said starting mixture further comprises
 (a3) subjecting the mixture resulting from step (a2) to additional treatment conditions, without adding a carboxylic acid and/or without adding an acidic solvent for dissolving HMF and di-HMF, 
 so that said starting mixture results. 
 
     
     
       15. The process according to  claim 3 , wherein the pH of the product mixture is in a range of from 1 to 4. 
     
     
       16. The process according to  claim 4 , wherein said starting mixture is at a temperature in a range of from 100° C. to 135° C. 
     
     
       17. The process according to  claim 5 , wherein the oxygen partial pressure in the reactor at least temporarily is in a range of from 1 to 20 bar. 
     
     
       18. The process according to  claim 9 , wherein at least one of said noble metals is platinum. 
     
     
       19. The process according to  claim 10 , wherein in the content of platinum on the support is in a range of from 1 to 10 wt.-%. 
     
     
       20. The process according to  claim 12 , wherein the product mixture obtained in step (b) does not comprise furan-2,5-dicarboxylic acid in solid form.