Recovering Ethanol with Sidestreams to Regulate C3+ Alcohols Concentrations

Abstract

This invention relates to purification and/or recovery of ethanol from a crude ethanol product obtained from the hydrogenation of acetic acid. Separation and purification processes of a crude ethanol mixture are employed to allow recovery of ethanol and remove impurities. In particular, the process involves one or more sidestreams to regulate C 3 + alcohols concentration in the recovered ethanol.

We claim: 
     
         1 . A process for producing ethanol, comprising:
 hydrogenating acetic acid in a reactor in the presence of a catalyst to form a crude ethanol product;   separating at least a portion of the crude ethanol product in a first distillation column to yield a first residue comprising acetic acid and water, wherein a substantial portion of the water in the crude ethanol product that is fed to the column is removed in the first residue, a first distillate comprising ethanol, ethyl acetate and water, and one or more sidestreams comprising one or more C 3 + alcohols;   removing water from at least a portion of the first distillate to yield an ethanol mixture stream comprising less than 10 wt. % water; and   recovering ethanol from the ethanol mixture stream.   
     
     
         2 . The process of  claim 1 , wherein said one or more C 3 + alcohols are selected from the group consisting of isopropanol, n-propanol, n-butanol, 2-butanol, isobutanol, tert-butanol, 2,2-dimethyl-1-propanol, 3-pentanol, 2-pentanol, 1-pentanol, 3-methyl-2-butanol, 2-methyl-2-butanol, a mixture thereof, and an azeotrope thereof. 
     
     
         3 . The process of  claim 1 , wherein said one or more sidestreams comprise one or more C 3  to C 6  alcohols, a mixture thereof, and an azeotrope thereof. 
     
     
         4 . The process of  claim 1 , wherein the first distillate comprises substantially none of said one or more C 3 + alcohols. 
     
     
         5 . The process of  claim 1 , wherein the first distillate comprises less than 1000 wppm of said one of more C 3 + alcohols. 
     
     
         6 . The process of  claim 1 , wherein water is removed from the first distillate using an adsorption unit, membrane, extractive column distillation, molecular sieve, or a combination thereof. 
     
     
         7 . The process of  claim 6 , wherein the adsorption unit is a pressure swing adsorption unit or a thermal swing adsorption unit. 
     
     
         8 . The process of  claim 1 , wherein the ethanol mixture stream comprises less than 6 wt. % water. 
     
     
         9 . The process of  claim 1 , further comprising separating a portion of the feed to a second distillation column to yield a second residue comprising ethanol and a second distillate comprising ethyl acetate. 
     
     
         10 . The process of  claim 1 , wherein the acetic acid is formed from methanol and carbon monoxide, wherein each of the methanol, the carbon monoxide, and hydrogen for the hydrogenating step is derived from syngas, and wherein the syngas is derived from a carbon source selected from the group consisting of natural gas, oil, petroleum, coal, biomass, and combinations thereof. 
     
     
         11 . A process for producing ethanol, comprising:
 providing a crude ethanol product;   separating at least a portion of the crude ethanol product in a first distillation column to yield a first residue comprising acetic acid and water, wherein a substantial portion of the water in the crude ethanol product that is fed to the column is removed in the first residue, a first distillate comprising ethanol, ethyl acetate and water, and one or more sidestreams comprising one or more C 3 + alcohols;   removing water from at least a portion of the first distillate to yield an ethanol mixture stream comprising less than 10 wt. % water; and   recovering ethanol from the ethanol mixture stream.   
     
     
         12 . The process of  claim 11 , wherein said one or more C 3 + alcohols are selected from the group consisting of isopropanol, n-propanol, n-butanol, 2-butanol, isobutanol, tert-butanol, 2,2-dimethyl-1-propanol, 3-pentanol, 2-pentanol, 1-pentanol, 3-methyl-2-butanol, 2-methyl-2-butanol, a mixture thereof, and an azeotrope thereof. 
     
     
         13 . The process of  claim 11 , wherein said one or more sidestreams comprise one or more C 3  to C 6  alcohols, a mixture thereof, and an azeotrope thereof. 
     
     
         14 . The process of  claim 11 , wherein the first distillate comprises substantially none of said one or more C 3 + alcohols. 
     
     
         15 . The process of  claim 11 , wherein the first distillate comprises less than 1000 wppm of said one of more C 3 + alcohols. 
     
     
         16 . The process of  claim 11 , wherein water is removed from the first distillate using an adsorption unit, membrane, extractive column distillation, molecular sieve, or a combination thereof. 
     
     
         17 . The process of  claim 16 , wherein the adsorption unit is a pressure swing adsorption unit or a thermal swing adsorption unit. 
     
     
         18 . The process of  claim 11 , wherein the ethanol mixture stream comprises less than 6 wt. % water. 
     
     
         19 . The process of  claim 11 , further comprising separating a portion of the feed to a second distillation column to yield a second residue comprising ethanol and a second distillate comprising ethyl acetate. 
     
     
         20 . The process of  claim 11 , wherein said one or more C 3 + alcohols are selected from the group consisting of isopropanol, n-propanol, n-butanol, and 2-butanol.