Organic compounds -- part of the class 532-570 series – Organic compounds – Fatty compounds having an acid moiety which contains the...
Reexamination Certificate
1999-12-03
2001-04-03
Carr, Deborah (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Fatty compounds having an acid moiety which contains the...
C554S169000
Reexamination Certificate
active
06211390
ABSTRACT:
The invention concerns a method for producing fatty acid esters and in particular a method wherein fatty acid esters are obtained by transesterification of fats and oils of animal or vegetable origin.
The production of alkyl esters and in particular of methyl esters by alcoholysis of fats and oils has recently been the subject of a lively discussion with a view to the production of diesel fuels from renewable raw materials.
The glycerol component of fats and oils can, even at low temperatures, be substituted with low-molecular weight monovalent alcohols. Alcoholysis is catalysed by acids or alkalis. In technology, the Bradshaw method is frequently employed for the transesterification of fats with methanol (U.S. Pat. Nos. 2,271,619 and 2,360,844). Herein the fat which should not have an acid number in excess of 1.5 is stirred briefly at 80° C. with excess methanol in the presence of 0.1 to 0.5% sodium hydroxide. When left to rest, the glycerol separates out practically free from water at the bottom of the vessel.
The method is remarkable not only with respect to the production of methyl esters or ethyl esters directly from the fat, without an intermediate hydrolysis step, but also because of the lower reaction temperature and because special corrosion resistant equipment is not required.
If methanol is used, the reaction unfolds along the following pattern, wherein R represents a fatty acid radical:
C
3
H
5
(R)
3
+3CH
3
OH→C
3
H
5
(OH)
3
+3CH
3
R
The reaction is carried out in an open tank which may consist of common carbon steel. The fat must be dry, clean and above all neutral. It is heated to approx. 80° C., and commercially available, water-free methanol (99.7%) having 0.1 to 0.5% sodium hydroxide or potassium hydroxide dissolved in it is added. An amount of alcohol corresponding to about 1.6 times the theoretically required amount is recommended. The alcohol can, however, be reduced to about 1.2 times the theoretical amount if the process is performed in three steps. An amount in excess of 1.75 times the theoretical amount does not accelerate the reaction and hampers subsequent removal of the glycerol by gravity.
After adding the alcohol, the mixture is stirred for several minutes and then left to rest. The glycerol starts to separate out fairly immediately. As it is practically free from water and much heavier than the other liquids, it readily settles to form a layer at the tank bottom. Reaction of the oil into methyl ester is usually 98% complete after one hour.
The bottom layer contains not less than 90% of the glycerol originally present in the fat. The top layer is comprised of methyl esters, the major portions of the unreacted alcohol and alkali, the remaining glycerol, and a very small proportion of soap. These various impurities are removed from the esters by repeated washing with small amounts of warm water.
In the Bradshaw method the obtained methyl esters are utilized in a continuous process for producing water-free soap. The esters are readily saponified by sodium hydroxide or potassium hydroxide at a low temperature, and the highly volatile methanol is liberated and recovered for reusing.
The described method should, however, also be suited for producing monoesters for fractionation and thus custom-made fats and oils. The methyl esters and ethyl esters of the fatty acids are liquid and relatively stable, not corrosive and low-boiling, and are therefore frequently preferred to the free acids, in particular when fractionating must be carried out at elevated temperatures as is the case in distillation.
Transesterification of peanut oil with ethanol was studied in detail by Feuge and Gros, J. Am. Oil Chem. Soc. 26 (1949) 97-102. They found that the optimum temperature for the reaction is in the vicinity of 50° C. At this temperature a higher glycerol yield was obtained than at 30° C. or 70° C.
The described alcoholysis of triglycerides generally does, however, not only yield in free glycerol and monoester, but moreover monoglycerides and diglycerides and partial esters of the respective alcohol are formed.
Toyama et al. (Y. Toyama, T. Tsuchiya and T. Ishikawa, J. Soc. Chem. Ind. Japan, 36 (1933) 230-232B) demonstrated e.g. that in the presence of sodium hydroxide, equilibrium between methanol or ethanol and fats is reached within two hours at room temperature. In order to have the reaction continue until complete transformation of the fat into the monoester, it is necessary in this method to separate the released glycerol from the reaction mixture.
In a study by Wright et al. (H. J. Wright, J. B. Segur, H. V. Clark, S. K. Coburn, E. E. Langdon and R. N. DuPuis, Oil & Soap, 21 (1944) 145-148) the precise conditions for the alcoholysis of fats with methanol and ethanol are investigated in detail. It furthermore reports about experiments on alcoholysis with other monohydroxy alcohols. It is pointed out that the above described alcoholysis, catalysed by alkali, is only entirely successful if the fat is practically free from free fatty acids and if the reaction mixture is free from water. Where one of these conditions is not met, saponification ensues, resulting in a loss of alkalinity and formation of a gel structure which prevents or slows down separation and settling of the glycerol. Difficulties occur in ethanolysis if the content of free fatty acids in the fat is in excess of about 0.5%. When 30 parts ethanol, 100 parts cottonseed oil and 0.5% sodium hydroxide are made to react, the glycerol yield is considerably reduced by 0.3% water in the reaction mixture. The effect of moisture can, however, be partly compensated by the addition of further alkali and/or alcohol. The water tolerance of the above mixture is raised to 0.5 to 0.6% by doubling the catalyst content or by raising the quantity of alcohol to 40 parts.
It was also demonstrated by Wright et al. that the rate of the overall reaction is basically limited by the time required for separation of the glycerol by gravity. Continuous centrifugal separation at 65° C. with a dwell time of about 5 minutes yielded a rather good result of approx. 85% of the theoretical value. Bradshaw's and Meuly's allegation that less alcohol is required in stepwise addition and glycerol removal was confirmed for methanolysis, however not for ethanolysis inasmuch as this method results in gelling.
Particularly if sodium and potassium compounds are used as catalysts, various problems are encountered in converting the triglycerides with methanol and ethanol. The catalyst which is distributed to both phases must be removed after the reaction is completed. Separation of the two phases following the reaction develops at such a low rate that large reaction volumes become necessary. In the monoester very fine glycerol droplets remain suspended and have to be washed out with water. Depending on the further use of the glycerol it is necessary to remove the dissolved catalyst. The required separation of the emulsion formed in the reaction is extremely tedious. It is considered an additional problem that the reaction at times does not immediately start up.
Owing to the described drawbacks, the above method is frequently not well suited for producing fatty acid esters under practical conditions. It is an object of the invention to provide a method for producing fatty acid esters from fatty acid triglycerides, which can be carried out simply and economically and furnishes maximum yield of the desired reaction product. The method should moreover permit for a continuous reaction process at minimum possible reaction volumes.
This object is attained by the method according to claim
1
. Further embodiments result from the dependent claims.
It was surprisingly found that separation of the glycerol from the reaction mixture may be accelerated considerably by extracting the formed fatty acid ester with a near-critical extractant from the reaction mixture. Thereby the reaction rate is slowed down only insignificantly. When a liquid flow of the extractant is made to pass through the reaction mixture, phase separation is accele
Ganswindt Ruth
Peter Siegfried
Weidner Eckhard
Carr Deborah
Klauber & Jackson
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