Process for the production of diaryl carbonates and treatment of alkalichloride solutions resulting therefrom

Abstract

Processes comprising: (a) reacting phosgene and a monohydroxyl aryl compound in the presence of a suitable catalyst to form a diaryl carbonate and a solution comprising an alkali chloride; (b) separating the diaryl carbonate from the solution; (c) adjusting the pH of the solution to a value of less than or equal to 8 to form a pH-adjusted solution; (d) treating the pH-adjusted solution with an adsorbent to form a treated solution; (e) subjecting at least a portion of the treated solution to electrochemical oxidation to form chlorine and an alkali hydroxide solution; and (f) recycling at least a portion of one or both of the chlorine and the alkali hydroxide solution.

1 . A process comprising: 
 (a) reacting phosgene and a monohydroxyl aryl compound in the presence of a suitable catalyst to form a diaryl carbonate and a solution comprising an alkali chloride;    (b) separating the diaryl carbonate from the solution;    (c) adjusting the pH of the solution to a value of less than or equal to 8 to form a pH-adjusted solution;    (d) treating the pH-adjusted solution with an adsorbent to form a treated solution;    (e) subjecting at least a portion of the treated solution to electrochemical oxidation to form chlorine and an alkali hydroxide solution; and    (f) recycling at least a portion of one or both of the chlorine and the alkali hydroxide solution.    
     
     
         2 . The process according to  claim 1 , wherein recycling at least a portion of the chlorine comprises feeding the portion to a reaction with carbon monoxide to form at least a portion of the phosgene reacted with the monohydroxyl aryl compound.  
     
     
         3 . The process according to  claim 1 , wherein recycling at least a portion of the alkali hydroxide solution comprises feeding the portion to the reaction of the phosgene and the monohydroxyl aryl compound.  
     
     
         4 . The process according to  claim 1 , further comprising subjecting one or more of the solution, the pH-adjusted solution and the treated solution to a separation to remove an amount of residual solvent.  
     
     
         5 . The process according to  claim 4 , wherein the separation comprises steam stripping.  
     
     
         6 . The process according to  claim 1 , wherein the electrochemical oxidation is carried out with a cathode comprising a gas diffusion electrode.  
     
     
         7 . The process according to  claim 1 , further comprising feeding a portion of the treated solution to a brine circuit of a membrane electrolysis process.  
     
     
         8 . The process according to  claim 1 , further comprising adding additional alkali chloride to the electrochemical oxidation.  
     
     
         9 . The process according to  claim 1 , wherein the pH of the solution is adjusted to a value of less than or equal to 7.  
     
     
         10 . The process according to  claim 1 , wherein adjusting the pH of the solution comprises adding hydrogen chloride.  
     
     
         11 . The process according to  claim 1 , wherein the treated solution prior to electrochemical oxidation has an alkali chloride concentration of 100 to 280 g/L.  
     
     
         12 . The process according to  claim 1 , wherein the alkali hydroxide solution has an alkali hydroxide concentration of 13 to 33 wt. %.  
     
     
         13 . The process according to  claim 1 , wherein separating the diaryl carbonate from the solution comprises: (i) separating a diaryl carbonate-containing organic phase and an aqueous alkali chloride-containing waste water solution; and (ii) washing the diaryl carbonate-containing organic phase at least once and separating the wash liquid.  
     
     
         14 . The process according to  claim 1 , wherein the electrochemical oxidation is carried out using an ion exchange membrane having a water transport value greater than 4 moles H 2 O per mole of alkali chloride.  
     
     
         15 . The process according to  claim 1 , wherein the electrochemical oxidation is carried out using an ion exchange membrane having a water transport value of 5.5 to 6.5 moles H 2 O per mole of alkali chloride.  
     
     
         16 . The process according to  claim 1 , wherein the electrochemical oxidation is carried out at a current density of 2 to 6 kA per m 2  of membrane.  
     
     
         17 . The process according to  claim 15 , wherein the electrochemical oxidation is carried out at a current density of 2 to 6 kA per m 2  of membrane.  
     
     
         18 . The process according to  claim 1 , wherein the electrochemical oxidation is carried out at a temperature of 70 to 100° C.  
     
     
         19 . The process according to  claim 1 , wherein the electrochemical oxidation is carried out at an absolute pressure of 1.0 to 1.4 bar.  
     
     
         20 . The process according to  claim 1 , wherein the electrochemical oxidation is carried out at a differential pressure between an anode compartment and a cathode compartment of 20 to 150 mbar.  
     
     
         21 . The process according to  claim 1 , wherein the electrochemical oxidation is carried out using an anode having a coating comprising ruthenium oxide and a compound of an element selected from the group consisting of Group 4 elements, Group 7 elements, Group 8 elements, and combinations thereof.  
     
     
         22 . The process according to  claim 1 , wherein the electrochemical oxidation is carried out using an electrolysis cell having an anode and a membrane, and wherein the anode has a surface area greater than a surface area of the membrane.  
     
     
         23 . The process according to  claim 1 , wherein the electrochemical oxidation is carried out at a current density of 2 to 6 kA per m 2  of membrane; a temperature of 70 to 100° C.; an absolute pressure of 1.0 to 1.4 bar; and a differential pressure between an anode compartment and a cathode compartment of 20 to 150 mbar.  
     
     
         24 . The process according to  claim 1 , wherein the monohydroxyl aryl compound comprises a phenol compound of the general formula (I):  
       
         
           
           
               
               
           
         
       
       wherein each R independently represents a substituent selected from the group consisting of hydrogen, halogens, C 1-9  alkyl groups, C 1-9  alkoxy groups, C 1-9  carbonyl groups, and C 1-9  alkoxycarbonyl groups; and n represents an integer of 0 to 5.  
     
     
         25 . A process comprising: 
 (a) reacting phosgene and a phenol compound of the general formula (I) in the presence of a suitable catalyst to form a diaryl carbonate and a solution comprising an alkali chloride;                          wherein each R independently represents a substituent selected from the group consisting of hydrogen, halogens, C 1-9  alkyl groups, C 1-9  alkoxy groups, C 1-9  carbonyl groups, and C 1-9  alkoxycarbonyl groups; and n represents an integer of 0 to 5;    (b) separating the diaryl carbonate from the solution;    (c) adjusting the pH of the solution with hydrogen chloride to a value of less than or equal to 7 to form a pH-adjusted solution;    (d) treating the pH-adjusted solution with an adsorbent to form a treated solution;    (e) subjecting at least a portion of the treated solution to electrochemical oxidation to form chlorine and an alkali hydroxide solution; and    (f) recycling at least a portion of one or both of the chlorine and the alkali hydroxide solution;    wherein recycling at least a portion of the chlorine comprises feeding the portion to a reaction with carbon monoxide to form at least a portion of the phosgene reacted with the monohydroxyl aryl compound; wherein recycling at least a portion of the alkali hydroxide solution comprises feeding the portion to the reaction of the phosgene and the monohydroxyl aryl compound; and wherein the electrochemical oxidation is carried out at a current density of 2 to 6 kA per m 2  of membrane; a temperature of 70 to 100° C.; an absolute pressure of 1.0 to 1.4 bar; and a differential pressure between an anode compartment and a cathode compartment of 20 to 150 mbar.