Process for production of biodiesel from high acid feed

Abstract

Biodiesel fuels are produced efficiently and at low cost from waste oil feeds containing high concentrations of fatty acids. By first producing an ester of a water immiscible alcohol, water of reaction from the esterification can be easily stripped out with and separated from the alcohol, which is recycled to the esterification reaction. Subsequent transesterification with glycerin produces a feed with a sufficiently low acid value to allow methanolysis using a basic catalyst to proceed rapidly without consumption of large quantities of catalyst or organic acid salt formation.

1 . A process for producing biodiesel comprising, 
 providing a feed stream comprising glycerides of at least one fatty acid and at least 1 weight percent of free fatty acids;    adding a water immiscible alcohol to the feed stream to form a first reaction mixture, wherein the alcohol is added in a molar excess relative the amount of free fatty acids in the feed stream;    forming an ester of the free fatty acids and alcohol by heating the first reaction mixture in the presence of an acidic catalyst and stripping water and some of the water immiscible alcohol from the first reaction mixture;    adding glycerol to the ester thus produced to form a second reaction mixture;    forming glycerides of the free fatty acids by heating the second reaction mixture and stripping the water immiscible alcohol from the second reaction mixture;    adding at least one C 1 -C 4  alcohol to the glycerides thus produced to form a third reaction mixture;    forming an ester of the fatty acids and at least one C 1 -C 4  alcohol, and a glycerol byproduct, by heating the third reaction mixture in the presence of a catalyst comprising a sodium or potassium alkoxide of the at least one C 1 -C 4  alcohol.    
     
     
         2 . The process according to  claim 1 , wherein the water immiscible alcohol is added to the feed stream in a 20 to 100 percent molar excess relative to the amount of free fatty acids in the feed stream.  
     
     
         3 . The process according to  claim 1 , wherein the glycerol is added to the first reaction mixture in an equimolar or greater amount relative to the amount of water immiscible alcohol added to the feed stream.  
     
     
         4 . The process according to  claim 1 , further comprising sparging the first reaction mixture and second reaction mixture with nitrogen.  
     
     
         5 . The process according to  claim 1 , wherein the step of forming a glyceride of the free fatty acids is conducted so that a portion of the ester from the first reaction mixture remains in the second reaction mixture.  
     
     
         6 . The process according to  claim 1 , further comprising sparging the first reaction mixture with nitrogen and heating the second reaction mixture under vacuum such as to vaporize out most of the alcohol, and condensing the alcohol for recycle.  
     
     
         7 . The process according to  claim 1 , wherein the water immiscible alcohol is hexanol, heptanol, isononanol, or 2-ethylhexanol.  
     
     
         8 . The process according to  claim 1 , further comprising separating a bottom stream from the third reaction mixture comprising the glycerol byproduct and recycling the glycerol byproduct to the second reaction mixture either as is or following purification.  
     
     
         9 . The process according to  claim 1 , wherein the stripped water and water immiscible alcohol are separated after stripping and the stripped water immiscible alcohol is returned to the first reaction mixture.