Method of preparing a dialkyl carbonate, and its use in the preparation of diaryl carbonates and polycarbonates

Abstract

Unexpected corrosion of downstream sections of a dialkyl carbonate manufacturing apparatus has been traced to alkyl chloroformate impurities, which slowly decompose to yield hydrochloric acid. An improved process and apparatus for dialkyl carbonate synthesis reduce corrosion by physically removing or chemically decomposing the alkyl chloroformate impurities within the corrosion-resistant upstream sections of the apparatus.

1 . A method of preparing dimethyl carbonate, comprising: reacting methanol, oxygen, carbon monoxide, and a catalyst to form a mixture comprising dimethyl carbonate, methyl chloroformate, hydrochloric acid, water, carbon dioxide, and carbon monoxide; and subjecting said mixture to conditions comprising a water concentration ([H 2 O]), a methanol concentration ([MeOH]), a temperature (T), and a residence time (t), such that a parameter X calculated according to the expression X=exp{−[(2.09×10 9 )e (−6381/T) [H 2 O]+(4.14×10 10 )e (−7676/T) [MeOH]]t} has a value less than about 0.9, wherein said water concentration and said methanol concentration are expressed in moles per milliliter, said temperature is expressed in degrees Kelvin, and said residence time is expressed in minutes.  
     
     
         2 . The method of  claim 1 , wherein said parameter X has a value less than about 0.2.  
     
     
         3 . The method of  claim 1 , wherein said parameter X has a value less than about 0.1.  
     
     
         4 . The method of  claim 1 , wherein said parameter X has a value less than about 0.05.  
     
     
         5 . The method of  claim 1 , wherein said parameter X has a value less than about 0.01.  
     
     
         6 . The method of  claim 1 , wherein said water concentration is about 0.1 to about 50 moles per liter.  
     
     
         7 . The method of  claim 1 , wherein said methanol concentration is about 1 to about 25 moles per liter.  
     
     
         8 . The method of  claim 1 , wherein said temperature is about 30° C. to about 130° C.  
     
     
         9 . The method of  claim 1 , wherein said residence time is about 0.5 hour to about 10 hours.  
     
     
         10 . The method of  claim 1 , further comprising removing hydrochloric acid from said mixture.  
     
     
         11 . The method of  claim 10 , wherein said removing hydrochloric acid comprises reducing the concentration of said hydrochloric acid to less than about 1×10 −3  moles per liter.  
     
     
         12 . A method of preparing dimethyl carbonate, comprising: reacting methanol, oxygen, carbon monoxide, and a catalyst to form a mixture comprising dimethyl carbonate, methyl chloroformate, hydrochloric acid, water, carbon dioxide, and carbon monoxide; 
 subjecting said mixture to conditions comprising an initial concentration of methyl chloroformate ([MCF] t=0 ), a water concentration ([H 2 O]), a methanol concentration ([MeOH]), a temperature (T), and a residence time (t), such that a parameter Z calculated according to the expression Z=[MCF] t=0 exp{−[(2.09×10 9 )e (−6381/T) [H 2 O]+(4.14×10 10 )e (−7673/T) [MeOH]]t} has a value less than about 5×10 −6 , wherein said initial concentration of methyl chloroformate, said water concentration, and said methanol concentration are expressed in moles per milliliter, said temperature is expressed in degrees Kelvin, and said residence time is expressed in minutes.    
     
     
         13 . The method of  claim 12 , wherein said initial concentration of methyl chloroformate is about 5×10 −6  to about 5×10 −4  moles per liter.  
     
     
         14 . The method of  claim 12 , further comprising removing hydrochloric acid from said mixture.  
     
     
         15 . A method of preparing a dialkyl carbonate, comprising: reacting methanol, oxygen, carbon monoxide, and a catalyst to form a mixture comprising dimethyl carbonate, methyl chloroformate, hydrochloric acid, water, carbon dioxide, and carbon monoxide; and maintaining said mixture at a temperature of about 50° C. to about 80° C. for about 1 hour to about 10 hours.  
     
     
         16 . The method of  claim 15 , further comprising removing hydrochloric acid from said mixture.  
     
     
         17 . A method of preparing dimethyl carbonate, comprising: reacting methanol, oxygen, carbon monoxide, and a catalyst to form a mixture comprising dimethyl carbonate, methyl chloroformate, hydrochloric acid, water, carbon dioxide, and carbon monoxide; and subjecting said mixture to conditions comprising an initial dimethyl carbonate concentration ([DMC] t=0 ), an initial water concentration ([H 2 O] t=0 ), an initial methanol concentration ([MeOH] t=0 ), an initial hydrochloric acid concentration ([HCl] t=0 ), a temperature (T), and a residence time (t), such that a parameter X calculated according to the expression X=exp {−[(2.09×10 9 )e (−6381/T) [H 2 O] t=0 +(4.14×10 10 )e (−7676/T) [MeOH] t=0 ]t} has a value less than about 0.9, and a parameter Y calculated according to the expression  
           Y={ 1−[H 2 O] t=0 ([ DMC ]) t=0 }/{(1−([H 2 O] t=0 ([ DMC ]) t=0 )(exp((6.6×10 10 )(exp(−− 6636   /T ))[HCl] t=0   [DMC]   t=0 ([H 2 O] t=0 ([ DMC ]) t=0 −1) t )))} has a value of at least about 0.9, wherein said initial dimethyl carbonate concentration, said initial water concentration, said initial methanol concentration, and said initial hydrochloric acid concentration are expressed in moles per milliliter, said temperature is expressed in degrees Kelvin, and said residence time is expressed in minutes.    
     
     
         18 . The method of  claim 17 , wherein said parameter Y has a value of at least about 0.95.  
     
     
         19 . The method of  claim 17 , wherein said parameter Y has a value of at least about 0.99.  
     
     
         20 . The method of  claim 17 , wherein said initial dimethyl carbonate concentration is about 0.5 to about 10 moles per liter.  
     
     
         21 . The method of  claim 17 , wherein said initial hydrochloric acid concentration is about 1×10 −3  to about 2×10 −1  moles per liter.  
     
     
         22 . The method of  claim 17 , further comprising removing hydrochloric acid from said mixture.  
     
     
         23 . A method of preparing dimethyl carbonate, comprising: reacting methanol, oxygen, carbon monoxide, and a catalyst to form a mixture comprising dimethyl carbonate, methyl chloroformate, hydrochloric acid, water, carbon dioxide, and carbon monoxide; and 
 subjecting said mixture to conditions comprising a water concentration ([H 2 O]), a methanol concentration ([MeOH]), a temperature (T), and a residence time (t), such that a parameter X′ calculated according to the expression        X′= 1/[1+[(2.09×10 9 ) e   (−6381/T) [H 2 O]+(4. 14×10 10 ) e   (−7676/T) [MeOH]]t]   has a value less than about 0.5, wherein said water concentration and said methanol concentration are expressed in moles per milliliter, said temperature is expressed in degrees Kelvin, and said residence time is expressed in minutes.