Synthesis of Biodiesel Using Alkali Ion Conductive Ceramic Membranes

Abstract

Methods and apparatus for synthesizing biodiesel using alkali alkoxide generated on-site using an electrochemical process are disclosed. The apparatus and methods are disclosed to converting alkali salts of glycerine into glycerine and thereby facilitate the separation of clean glycerine from biodiesel. These methods are enabled by the use of alkali ion conductive ceramic membranes in electrolytic cells.

1 . A method for producing biodiesel, comprising: 
 (a) obtaining a first electrolytic cell comprising a first alkali ion conductive ceramic membrane configured to selectively transport alkali ions, the ceramic membrane separating a first anolyte compartment configured with an electrochemically active first anode and a first catholyte compartment configured with an electrochemically active first cathode;    (b) introducing an alkali hydroxide solution into the first anolyte compartment;    (c) introducing alcohol and a triglyceride into the first catholyte compartment;    (d) applying an electric current to the first electrolytic cell thereby: 
 i. oxidizing hydroxide anions in the first anolyte compartment to form oxygen, gas and water;  
 ii. causing alkali ions to pass through the alkali ion conductive ceramic membrane from the first anolyte compartment to the first catholyte compartment; and  
 iii. reducing the alcohol in the presence of alkali ions in the first catholyte compartment to form an alkali alkoxide and hydrogen gas; and  
 iv. reacting the alkali alkoxide and the triglyceride to form a mixture of biodiesel and C 3 H 5 (OM) 3 , wherein M is an alkali metal;  
   (e) obtaining a second electrolytic cell comprising a second alkali ion conductive ceramic membrane configured to selectively transport alkali ions, the ceramic membrane separating a second anolyte compartment configured with an electrochemically active second anode and a second catholyte compartment configured with an electrochemically active second cathode;    (f) removing the mixture of biodiesel and C 3 H 5 (OM) 3  from the first catholyte compartment and introducing the mixture into the second anolyte compartment;    (g) introducing hydrogen gas into the second anolyte compartment;    (h) introducing water into the second catholyte compartment;    (i) applying an electric current to the second electrolytic cell thereby: 
 i. oxidizing hydrogen gas in the second anolyte compartment to form hydrogen ions and thereby facilitate the following reaction: C 3 H 5 (OM) 3 +3H + →C 3 H 5 (OH) 3 +3M + ;  
 ii. causing alkali ions (M + ) to pass through the alkali ion conductive ceramic membrane from the second anolyte compartment to the second catholyte compartment; and  
 iii. decomposing water in the presence of alkali ions in the second catholyte compartment according to the following reaction: M + +H 2 O+e 31 →MOH +½H 2 ; and  
   (j) removing biodiesel and glycerine (C 3 H 5 (OH) 3 ) from the second anolyte compartment.    
   
   
       2 . A method for producing biodiesel according to  claim 1 , further comprising the step of separating the glycerine and biodiesel.  
   
   
       3 . A method for producing biodiesel according to  claim 1 , wherein the alcohol comprises a straight chain, lower alkyl alcohol, C 1  to C 6 , that may contain more than one hydroxyl moiety.  
   
   
       4 . A method for producing biodiesel according to  claim 1 , wherein the alcohol comprises methanol.  
   
   
       5 . A method for producing biodiesel according to  claim 1 , wherein the alcohol is selected from methanol, ethanol, propanol, isopropanol, hexanol, butanol, ethylene glycol, and propylene glycol.  
   
   
       6 . A method for producing biodiesel according to  claim 1 , wherein the triglyceride comprises vegetable oil.  
   
   
       7 . A method for producing biodiesel according to  claim 1 , wherein the triglyceride comprises animal fat.  
   
   
       8 . A method for producing biodiesel according to  claim 1 , wherein hydrogen gas produced in the first catholyte compartment is introduced into the second anolyte compartment.  
   
   
       9 . A method for producing biodiesel according to  claim 1 , wherein hydrogen gas produced in the second catholyte compartment is introduced into the second anolyte compartment.  
   
   
       10 . A method for producing biodiesel according to  claim 1 , wherein the second anode comprises a catalyst to facilitate oxidation of hydrogen gas into hydrogen ions.  
   
   
       11 . A method for producing biodiesel according to  claim 1 , wherein alkali hydroxide produced in the second catholyte compartment is removed and introduced into the first anolyte compartment.  
   
   
       12 . A method for producing biodiesel according to  claim 1 , wherein water produced in the first anolyte compartment is removed and introduced into the second catholyte compartment.  
   
   
       13 . A method for producing biodiesel according to  claim 1 , wherein the triglyceride has the general formula [C 3 H 5 O 3 ] [OCR] 3 , where R is a C 14  to C 24  hydrocarbon chain.  
   
   
       14 . An apparatus for producing biodiesel comprising: 
 a first electrolytic cell comprising: 
 a first anolyte compartment comprising an electrochemically active first anode having a source of aqueous alkali hydroxide in which hydroxide ions are oxidized to form oxygen gas and water;  
 a first catholyte compartment comprising an electrochemically active first cathode separated from the first anolyte compartment by a first alkali ion conductive ceramic membrane configured to selectively transport alkali ions (M + ) into the first catholyte compartment, wherein the first catholyte compartment has a source of alcohol and a triglyceride, in which the alcohol is reduced in the presence of alkali ions to form alkali methoxide and hydrogen gas and wherein the alkali alkoxide and the triglyceride react to form a mixture of biodiesel and C 3 H 5 (OM) 3 , wherein M is an alkali metal;  
   a second electrolytic cell comprising: 
 a second anolyte compartment comprising an electrochemically active second anode having a source of hydrogen gas and C 3 H 5 (OM) 3  in which hydrogen gas is oxidized to form hydrogen ions to thereby facilitate the following reaction: C 3 H 5 (OM) 3 +3H +→C   3 H 5 (OH) 3 +3M + ;  
 a second catholyte compartment comprising an electrochemically active second cathode separated from the second anolyte compartment by a second alkali ion conductive ceramic membrane configured to selectively  
 transport alkali ions (M + ) into the second catholyte compartment, wherein the second catholyte compartment has a source of water, in which the water is decomposed in the presence of alkali ions to form alkali hydroxide and hydrogen gas;  
   a fluid path for transporting a portion of the biodiesel and C 3 H 5 (OM) 3  from the first catholyte compartment to the second anolyte compartment; and    a fluid path for removing biodiesel and glycerine (C 3 H 5 (OH) 3 ) from the second anolyte compartment.    
   
   
       15 . An apparatus for producing biodiesel according to  claim 14 , further comprising a settling tank to separate the glycerine and biodiesel.  
   
   
       16 . An apparatus for producing biodiesel according to  claim 14 , wherein the alcohol comprises a straight chain, lower alkyl alcohol, C 1  to C 6 , that may contain more than one hydroxyl moiety.  
   
   
       17 . An apparatus for producing biodiesel according to  claim 14 , wherein the alcohol comprises methanol.  
   
   
       18 . An apparatus for producing biodiesel according to  claim 14 , wherein the alcohol is selected from methanol, ethanol, propanol, isopropanol, hexanol, butanol, ethylene glycol, and propylene glycol.  
   
   
       19 . An apparatus for producing biodiesel according to  claim 14 , wherein the triglyceride comprises vegetable oil.  
   
   
       20 . An apparatus for producing biodiesel according to  claim 14 , wherein the triglyceride comprises animal fat.  
   
   
       21 . An apparatus for producing biodiesel according to  claim 14 , further comprising a fluid path for transporting hydrogen gas produced in the first catholyte compartment to the second anolyte compartment.  
   
   
       22 . An apparatus for producing biodiesel according to  claim 14 , further comprising a fluid path for transporting hydrogen gas produced in the second catholyte compartment to the second anolyte compartment.  
   
   
       23 . An apparatus for producing biodiesel according to  claim 14 , wherein the second anode further comprising a catalyst to facilitate oxidation of hydrogen gas into hydrogen ions.  
   
   
       24 . An apparatus for producing biodiesel according to  claim 14 , further comprising a fluid path for transporting alkali hydroxide produced in the second catholyte compartment to the first anolyte compartment.  
   
   
       25 . An apparatus for producing biodiesel according to  claim 14 , further comprising a fluid path for transporting water produced in the first anolyte compartment to the second catholyte compartment.  
   
   
       26 . An apparatus for producing biodiesel according to  claim 14 , wherein the triglyceride has the general formula [C 3 H 5 O 3 ] [OCR] 3 , where R is a C 14  to C 24  hydrocarbon chain.  
   
   
       27 . An apparatus for producing biodiesel comprising: 
 a first electrolytic cell comprising: 
 a first anolyte compartment comprising an electrochemically active first anode having a source of aqueous alkali hydroxide in which hydroxide ions are oxidized to form oxygen gas and water;  
 a first catholyte compartment comprising an electrochemically active first cathode separated from the first anolyte compartment by a first alkali ion conductive ceramic membrane configured to selectively transport alkali ions (M + ) into the first catholyte compartment, wherein the first catholyte compartment has a source of methanol and a triglyceride, in which the methanol is reduced in the presence of alkali ions to form alkali methoxide and hydrogen gas and wherein the alkali alkoxide and the triglyceride react to form a mixture of biodiesel and C 3 H 5 (OM) 3 , wherein M is an alkali metal, and wherein the triglyceride comprises vegetable oil;  
   a second electrolytic cell comprising: 
 a second anolyte compartment comprising an electrochemically active second anode having a source of hydrogen gas and C 3 H 5 (OM) 3  in which hydrogen gas is oxidized to form hydrogen ions to thereby facilitate the following reaction: C 3 H 5 (OM) 3 +3H + →C 3 H 5 (OH) 3 +3M + , wherein the second anode comprising a catalyst to facilitate oxidation of hydrogen gas into hydrogen ions;  
 a second catholyte compartment comprising an electrochemically active second cathode separated from the second anolyte compartment by a second alkali ion conductive ceramic membrane configured to selectively transport alkali ions (M+) into the second catholyte compartment, wherein the second catholyte compartment has a source of water, in which the water is decomposed in the presence of alkali ions to form alkali hydroxide and hydrogen gas;  
   a fluid path for transporting a portion of the biodiesel and C 3 H 5 (OM) 3  from the first catholyte compartment to the second anolyte compartment;    a fluid path for removing biodiesel and glycerine (C 3 H 5 (OH) 3 ) from the second anolyte compartment;    a settling tank to separate the glycerine and biodiesel; 
 a fluid path for transporting hydrogen gas produced in the first catholyte compartment or the second catholyte compartment to the second anolyte compartment;  
 a fluid path for transporting alkali hydroxide produced in the second catholyte compartment to the first anolyte compartment; and  
 a fluid path for transporting water produced in the first anolyte compartment to the second catholyte compartment.  
   
   
   
       28 . A method for converting alkali salts of glycerine into glycerine comprising: 
 (a) obtaining an electrolytic cell comprising an alkali ion conductive ceramic membrane configured to selectively transport alkali ions, the ceramic membrane separating a anolyte compartment configured with an anode and a catholyte compartment configured with a cathode;    (b) introducing C 3 H 5 (OM) 3  into the anolyte compartment;    (c) introducing hydrogen gas into the anolyte compartment;    (d) introducing water into the catholyte compartment;    (e) applying an electric current to the electrolytic cell thereby: 
 i. oxidizing hydrogen gas in the anolyte compartment to form hydrogen ions and thereby facilitate the following reaction: C 3 H 5 (OM) 3 +3H + →C 3 H 5 (OH) 3 +3M + ;  
 ii. causing alkali ions (M + ) to pass through the alkali ion conductive ceramic membrane from the anolyte compartment to the catholyte compartment; and  
 iii. decomposing water in the presence of alkali ions in the catholyte compartment according to the following reaction: M + +H 2 O+e − →MOH+½H 2 ; and  
   (f) removing glycerine (C 3 H 5 (OH) 3 ) from the anolyte compartment.    
   
   
       29 . A method for converting alkali salts of glycerine into glycerine according to  claim 28 , wherein the anode comprises a catalyst to facilitate oxidation of hydrogen gas into hydrogen ions.