Methods for producing bioderived propylene glycol

Abstract

In the process of distilling a polyol product mixture including one or both of a biobased propylene glycol and a biobased ethylene glycol from the reaction of hydrogen with a biobased feed, it has been discovered that undesirable epoxides can form, and the present invention provides means for guarding against their formation, for removing epoxides which do form by particular methods of distilling, and for removing the epoxides from a finished, otherwise commercially acceptable biobased glycol product.

What is claimed is: 
     
         1 . A process for distilling a product mixture comprised of biobased propylene glycol, biobased ethylene glycol or comprising both of these, and which further comprises one or both of propylene oxide and glycidol, including separating out the propylene glycol and glycidol so that a distilled biobased glycol product is produced which is substantially free of both propylene oxide and glycidol. 
     
     
         2 . A process according to  claim 1 , wherein the product mixture is an aqueous reaction product from the reaction of hydrogen with an aqueous solution of biobased glycerol, and wherein the distillation of the product mixture includes:
 distilling low molecular weight alcohols inclusive of methanol, ethanol and any propanols overhead in a first column;   distilling substantially all of the water from the first column bottoms overhead in a second column;   modifying the pH of the second column bottoms with acid, and then removing substantially all of the components therein with higher boiling points than that of propylene glycol in the bottoms from a third column; and   distilling the overheads from the third column in a fourth column to produce the distilled biobased propylene glycol product as the bottoms, with removing any glycidol and propylene oxide contained in the third column overheads as the overheads from the fourth column.   
     
     
         3 . A process according to  claim 2 , further comprising distilling the third column bottoms to produce an ethylene glycol-rich diols mix overhead and a bottoms containing unreacted glycerol for recycle and reuse. 
     
     
         4 . A process according to  claim 1 , wherein the product mixture is an aqueous reaction product from the reaction of hydrogen with an aqueous solution of biobased glycerol, and wherein the distillation of the product mixture includes:
 modifying the pH of the product mixture by addition of an acid before distilling the product mixture in a first column to produce an overheads with lower molecular weight alcohols inclusive of methanol, ethanol and any propanols;   distilling overhead all but a small amount of the water in the first column bottoms, in a second column;   distilling the second column bottoms in a third column, to separate out unreacted glycerol for recycle in the third column bottoms and provide a distillate overhead comprised of ethylene glycol, propylene glycol, C 4  and higher diols, propylene oxide, glycidol and less than one percent of water;   distilling the third column overheads in a fourth column, to produce an ethylene glycol-rich bottoms and fourth column overheads; and   distilling the fourth column overheads to produce a distilled biobased propylene glycol product which is substantially free of both propylene oxide and glycidol as well as being substantially water-free, and an overheads comprised of propylene oxide, glycidol, residual water and C 4  and higher diols.   
     
     
         5 . A process according to  claim 1 , wherein the product mixture is an aqueous reaction product from the reaction of hydrogen with an aqueous solution of biobased glycerol, and wherein the distillation of the product mixture includes:
 modifying the pH of the product mixture by addition of an acid before distilling the product mixture in a first column to produce an overheads with lower molecular weight alcohols inclusive of methanol, ethanol and any propanols;   distilling overhead all but a small amount of the water in the first column bottoms, in a second column;   distilling the second column bottoms in a third column, to separate out unreacted glycerol for recycle in the third column bottoms and provide a distillate overhead comprised of ethylene glycol, propylene glycol, C 4  and higher diols, propylene oxide, glycidol and less than one percent of water;   distilling the distillate overhead from the third column to produce a fourth column overheads comprising propylene oxide, glycidol, C 4  and higher diols and residual water, and bottoms comprised of ethylene and propylene glycols;   distilling the fourth column bottoms in a fifth column, wherein a predominantly ethylene glycol bottoms is produced, a substantially propylene oxide-, glycidol- and water-free distilled propylene glycol product is recovered as a sidestream, and propylene glycol and residual propylene oxide are recovered overhead for being recycled back in a recycle loop to the feed for the third distillation column.   
     
     
         6 . A process for removing substantially all of the propylene oxide and glycidol from a finished, industrial or pharmaceutical grade biobased propylene glycol product, comprising the steps of determining the content of propylene oxide and glycidol impurities in the propylene glycol product and contacting the propylene glycol product with a strong acid ion exchange resin for a time and under conditions sufficient to reduce the levels of propylene oxide and glycidol present to below detection limits. 
     
     
         7 . A process according to  claim 6 , wherein the strong acid ion exchange resin is a food grade resin. 
     
     
         8 . A process according to  claim 6 , wherein one or both of propylene oxide and glycidol are present in the untreated biobased propylene glycol product at more than 100 parts per million, and after treatment have a corresponding concentration or concentrations of less than 100 parts per billion. 
     
     
         9 . A process according to  claim 6 , wherein the untreated biobased propylene glycol product is both substantially colorless and substantially odorless. 
     
     
         10 . A process for guarding against the formation of propylene oxide and glycidol in a biobased glycol product from the distillation of an aqueous product mixture comprised of biobased propylene glycol, biobased ethylene glycol or comprising both of these, comprising removing organic acid salts contained in the aqueous product mixture through ion exclusion chromatography. 
     
     
         11 . A process according to  claim 10 , wherein the aqueous product mixture is the result of the hydrogenolysis of a carbohydrate or a polyol. 
     
     
         12 . A process according to  claim 10 , wherein at about 85 percent of the salts are removed before the product mixture is distilled. 
     
     
         13 . A process according to  claim 12 , wherein at least about 90 percent of the salts are removed. 
     
     
         14 . A process according to  claim 13 , wherein at least about 96 percent of the salts are removed. 
     
     
         15 . A process according to  claim 10 , wherein the ion exclusion chromatography is accomplished in a simulated moving bed system. 
     
     
         16 . A biobased propylene glycol or ethylene glycol with no detectable amounts of oxiranes contained therein.