Process for Preparing Dialkyl Carbonate and Diol Products

Abstract

Dialkyl carbonate and diol products are prepared in an integrated process performed by reacting an alkylene oxide with carbon dioxide in the presence of a non-halide-containing homogeneous carbonation catalyst in a first reaction zone to form a crude cyclic carbonate product. The crude cyclic carbonate product is introduced along with an aliphatic monohydric alcohol to a second reaction zone containing a transesterification catalyst. The transesterification catalyst is comprised of a strongly basic Type I ion exchange resin in gel having a particular form. The cyclic carbonate product and monohydric alcohol are reacted to form the dialkyl carbonate and diol products. In another aspect, dialkyl carbonate and diol products are prepared in an integrated process wherein a halide-containing homogeneous carbonation catalyst is used to form a crude cyclic carbonate product that is then used in a transesterification reaction. The transesterification catalyst is regenerated to accommodate the effects of the halide-containing catalyst.

We claim: 
     
         1 . A method of preparing a dialkyl carbonate and diol products in an integrated process comprising:
 (a) reacting an alkylene oxide with carbon dioxide in the presence of a halide-containing homogeneous carbonation catalyst in a first reaction zone to form a crude cyclic carbonate product, the crude cyclic carbonate product containing amounts of the carbonation catalyst;   (b) introducing the crude cyclic carbonate product from the first reaction zone along with an aliphatic monohydric alcohol to a second reaction zone containing a transesterification catalyst comprised of an ion exchange resin and allowing the cyclic carbonate product and monohydric alcohol to react under reaction conditions to form the dialkyl carbonate and diol products until the ion exchange resin catalyst has deactivated to a selected degree; and   (c) regenerating the deactivated ion exchange resin of the second reaction zone by washing the ion exchange resin with water and contacting the washed ion exchange resin with a regeneration solution containing regenerating ions before continuing step (b).   
     
     
         2 . The method of  claim 1 , wherein:
 the halide-containing homogeneous carbonation catalyst is a C 1  to C 5  organic halide compound.   
     
     
         3 . The method of  claim 1 , wherein:
 the alkylene oxide has the formula   
       
         
           
           
               
               
           
         
       
       wherein R 1  and R 2  are independently from one another a —(CH 2 ) m — group, wherein m is an integer of from 1 to 3, more particularly 1 to 2. 
     
     
         4 . The method of  claim 1 , wherein:
 the aliphatic monohydric alcohol is a C 1  to C 5  aliphatic monohydric alcohol.   
     
     
         5 . The method of  claim 1 , wherein:
 the alkylene oxide is ethylene oxide.   
     
     
         6 . The method of  claim 1 , wherein:
 the monohydric alcohol is methanol.   
     
     
         7 . The method of  claim 1 , wherein:
 the alkylene oxide is ethylene oxide and the aliphatic monohydric alcohol is methanol, and wherein the dialkyl carbonate includes dimethyl carbonate and the diol includes monoethylene glycol.   
     
     
         8 . The method of  claim 1 , wherein:
 the halide-containing homogeneous catalyst is selected from at least one of alkali halide salts, quaternary ammonium halide compounds, organic amine halide compounds, and phosphine halide compounds.   
     
     
         9 . The method of  claim 1 , wherein:
 the halide-containing homogeneous catalyst is used in an amount of from about 0.01% to about 5% by weight of alkylene oxide that is introduced into the first reaction zone.   
     
     
         10 . The method of  claim 1 , wherein:
 the molar ratio of aliphatic monohydric alcohol to the crude cyclic carbonate product introduced into the second reaction zone is from about 1.5:1 to about 3:1.   
     
     
         11 . The method of  claim 1 , wherein:
 the ion exchange resin is a strongly basic Type I ion exchange resin in gel form of polystyrene crosslinked with divinyl benzene having from about 4% to about 8% crosslinking, and from about 40% to about 60% water retention, the ion exchange resin including at least one of quaternary ammonium groups or quaternary phosphonium groups, the transesterification catalyst being configured as substantially spherical beads having a particle size of from about 0.2 mm to about 1.5 mm.   
     
     
         12 . The method of  claim 11 , wherein:
 the ion exchange resin includes an anion selected from the group consisting of bicarbonate, bisulfite, metalate, carboxylate, and halide.   
     
     
         13 . The method of  claim 1 , further comprising:
 removing unreacted alkylene oxide, unreacted carbon dioxide, or both, from said crude cyclic carbonate product of step (a) prior to introducing the crude cyclic carbonate product to the second reaction zone in step (b).