Production of biodiesel from triglycerides via a thermal route

Abstract

A method is presented for producing biodiesel from a triglyceride feedstock. The feedstock is first thermally cracked to remove contaminants and convert triglycerides to form a middle distillate fraction rich in fatty acids. The middle distillate fraction is then esterified the in the presence of an alcohol and a catalyst to produce a biodiesel stream. The biodiesel stream can be treated with a basic solution to convert unesterified free fatty acids to non-foaming metallic soaps, which can be removed by centrifugation, filtering or a combination thereof. A method is also provided for producing a biodiesel/naphtha mixture, in which a triglyceride feedstock is thermally cracked to produce a middle distillate fraction, a naphtha stream and a gas stream. The naphtha stream and the middle distillate fraction are then esterified to produce a mixed biodiesel/naphtha stream, which can be treated with a basic solution to convert unesterified free fatty acids to non-foaming metallic soaps. The basic salts are removed by known means.

1 . A method of producing biodiesel from a triglyceride feedstock, the method comprising: 
 a. pretreating the triglyceride feedstock by thermal cracking to remove contaminants and convert triglycerides to form a middle distillate fraction rich in free fatty acids;    b. esterifying the middle distillate fraction in the presence of an alcohol and a catalyst to produce a biodiesel stream;    c. treating the biodiesel stream with a basic solution to convert unesterified free fatty acids to non-foaming metallic soaps; and    d. removing the non-foaming metallic soaps by centrifugation, filtering or a combination thereof.    
   
   
       2 . The method of  claim 1  wherein the basic solution is an aqueous solution of a compound selected from the group consisting of lithium hydroxide (LiOH), potassium hydroxide (KOH), magnesium hydroxide (Mg(OH) 2 ), and calcium hydroxide (Ca(OH) 2 ).  
   
   
       3 . The method of  claim 2  wherein the basic solution is an aqueous solution of calcium hydroxide or lithium hydroxide.  
   
   
       4 . The method of  claim 1  wherein the triglyceride feedstock is selected from the group consisting of restaurant trap grease, rendered animal fats, waste greases, low-quality vegetable oils and combinations thereof.  
   
   
       5 . The method of  claim 1  wherein thermal cracking is conducted at a temperature of from 390° C. to 460° C.  
   
   
       6 . The method of  claim 1  wherein thermal cracking is conducted at a temperature of from 410° C. to 430° C.  
   
   
       7 . The method of  claim 1  wherein the middle distillate fraction is esterified in the presence of methanol as the alcohol.  
   
   
       8 . The method of  claim 7  wherein esterifying is conducted at a temperature of from 70° C. to 120° C.  
   
   
       9 . The method of  claim 8  wherein esterifying is conducted at a temperature of from 85° C. to 110° C.  
   
   
       10 . The method of  claim 1 , wherein the middle distillate fraction is esterified in the presence of an acid catalyst.  
   
   
       11 . The method of  claim 10  wherein the acid catalyst is selected from the group consisting of sulphuric acid (H 2 SO 4(l) ), sulphamic acid (H 2 NSO 3 H (l) ), formic acid (HCO 2 H (l) ), acetic acid (CH 3 CO 2 H (l) ), propionic acid (CH 3 CH 2 CO 2 H (l) ), hydrochloric acid (HCl (l) ), phosphoric acid (H 3 PO 4(l) ), sulphated metal oxides such as sulphated zirconia, and styrene divinylbenzne copolymers having SO 3 H functional groups.  
   
   
       12 . The method of  claim 11  wherein the acid catalyst is a styrene divinylbenzene copolymer having an SO 3 H functional group.  
   
   
       13 . The method of  claim 1 , further comprising filtering the triglyceride feedstock before thermal cracking to remove macroscopic contaminant particles.  
   
   
       14 . A method of producing a biodiesel/naphtha mixture from a triglyceride feedstock, the method comprising: 
 a. pretreating the triglyceride feedstock by thermal cracking to remove contaminants and convert triglycerides to produce a middle distillate fraction rich in free fatty acids, a naphtha stream and a gas stream;    b. esterifying the naphtha stream and middle distillate fraction in the presence of an alcohol and a catalyst to produce a mixed biodiesel/naphtha stream;    c. treating the mixed biodiesel/naphtha stream with a basic solution to convert unesterified free fatty acids to non-foaming metallic soaps; and    d. removing the non-foaming metallic soaps by centrifugation, filtering or a combination thereof.