Organic compounds -- part of the class 532-570 series – Organic compounds – Fatty compounds having an acid moiety which contains the...
Reexamination Certificate
2001-06-19
2002-03-19
Carr, Deborah D. (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Fatty compounds having an acid moiety which contains the...
Reexamination Certificate
active
06359157
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a process for obtaining fatty-acid esters from fat and/or oil of biological origin by transesterification.
Transesterification reactions as such are known; they represent a commercially important class of industrial organic reactions. In the course of a transesterification reaction an ester is converted into another ester by exchange of the acid groups or by exchange of the alcoholic groups. If the transesterification is carried out by exchange of the alcoholic groups, one speaks of so-called alcoholysis (also alkanolysis). In the case of alcoholysis the alcohol is added in excess in order to obtain a high yield of desired ester. In connection with the generation of diesel fuel from renewable raw materials the production of alkyl esters, particularly of methyl esters, by alcoholysis of vegetable oils (e.g. rapeseed oil) has recently gained considerably in topicality.
2. Description of the Related Art
Transesterification is an equilibrium reaction which, as a rule, is already triggered by mixing the reactants. However, the reaction proceeds so slowly that a catalyst is required for commercial implementation of the reaction. Conventionally use is made of strong acids or strong bases by way of catalysts.
Fats and oils of biological origin consist predominantly of glycerides (monoglycerides, diglycerides and triglycerides). In the course of the transesterification of such fats and oils the component glycerin can be substituted by low-molecular monohydric alcohols. In practice the method according to Bradshaw (described in U.S. Pat. Nos. 2,271,619 and 2,360,844) is frequently adopted for this purpose. The reaction is carried out in an open container which may consist of ordinary carbon steel. The fat or oil has to be dry (anhydrous), clean and, above all, neutral, i.e. the content of free fatty acids must be negligibly small (acid value no higher than 1.5). The initial product is heated to about 80° C., then commercial anhydrous methanol (99.7 wt. %), which contains 0.1 to 0.5 wt. % sodium hydroxide or potassium hydroxide in dissolved form, is added in excess (about 1.2 to 1.6 times the stoichiometric quantity). After addition of the alcohol the mixture is stirred for a few minutes and then allowed to stand. The glycerin begins to settle immediately. Since it is practically free from water and much heavier than the other liquids, it settles readily and forms a layer on the bottom of the container. The reaction of an oil with methanol to form methyl ester is usually 98% complete after one hour. The bottom layer (lower layer) contains not less than 90% of the glycerin originally present in the fat. The upper layer is composed of methyl esters, unconverted alcohol and alkali, the remaining glycerin, and a very small amount of soap. These various contaminants are washed out of the esters by repeated washing with small quantities of warm water. The method is advantageous, because methyl esters or ethyl esters can be obtained from the fat directly without any intermediate step, the reaction temperature is low and no items of apparatus made of special corrosion-resistant material are required.
With the method according to Bradshaw the methyl esters that are obtained are subsequently used in a continuous process for the production of anhydrous soap. For this purpose the esters are saponified at low temperature by means of sodium hydroxide and potassium hydroxide and the readily volatile methanol that is released in the process is recovered.
Feuge and Gros studied the transesterification of peanut oil with ethanol (J. Am. Chem. Soc. 26 [1949] 97-102). They found that the optimal temperature for the reaction lies in the vicinity of 50° C. A higher yield of glycerin was obtained at this temperature than at 30° C. or 70° C.
Toyama et. al. (Y. Toyama, T. Tsuchiya and T. Ishikava, J. Soc. Chem. Ind. Japan, 36 [1933] 230-232B) showed that the equilibrium between methanol or ethanol and fats in the presence of sodium hydroxide is attained at room temperature within two hours. In order to take the reaction as far as complete conversion of the fat into monoester, the glycerin that is released has to be removed.
In a paper 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 exact conditions for the alcoholysis of fats with methanol and ethanol were investigated in detail. Moreover, a report is given by the authors about experiments on alcoholysis with other monohydric alcohols. It is stated that the alcoholysis as described above, which is catalysed with alkali, is only completely successful when the fat is virtually free from free fatty acids and the reaction mixture is free from water. If one of these conditions is not satisfied, saponification occurs, which results in a loss of alkalinity and the formation of a gel structure which prevents or slows down the separation and settling of the glycerin.
Difficulties arise in the course of ethanolysis if the content of free fatty acids in the fat amounts to more than about 0.5 wt. %. If 30 parts of ethanol, 100 parts of cottonseed oil and 0.5 wt. % sodium hydroxide are caused to react, the yield of glycerin is diminished considerably by virtue of 0.3 wt. % water in the reaction mixture. However, the effect of the moisture can be partly compensated by adding further alkali and/or alcohol. If the catalyst content is doubled or the quantity of alcohol is increased to 40 parts, the water content in the reaction mixture may amount to up to 0.6 wt. %.
Similarly, it is shown by Wright et. al. that the rate of the overall reaction is fundamentally limited by the time that the glycerin requires for separation by gravity. A continuous separation by centrifuging at 65° C. with a dwell-time of about 5 minutes yielded a rather good result of approximately 85% of the theoretical value. The statement by Bradshaw and Meuly that less alcohol is needed in the case of stepwise addition of the alcohol and removal of the glycerin arising was confirmed for methanolysis but not for ethanolysis, in the case of which this procedure leads to gelling.
Various problems arise in particular when use is made of sodium compounds and potassium compounds by way of catalysts in the course of the transesterification of triglycerides with methanol and ethanol. For instance, by reason of the emulsion that has formed in the reaction, after the transesterification reaction has taken place the two phases separate at such a slow rate that the separation is very prolonged and large reaction volumes are necessary. In addition, even after the phase separation very fine droplets of glycerin still remain suspended in the monoester phase, which have to be washed out with water. Furthermore, the catalyst, which is distributed in both phases, has to be removed at least from the monoester phase after the reaction has been concluded. Depending on the further use of the glycerin, it is furthermore necessary to remove the dissolved catalyst also from the glycerin phase. It is regarded as an additional problem that the reaction sometimes does not set in immediately after the mixture has been produced.
A number of processes have been proposed with a view to solving the stated problems. For instance, in U.S. Pat. No. 2,383,614 a process for the continuous alcoholysis of fat is described in which a partial esterification of the fat or oil is carried out, optionally in several steps, and deposition of the glycerin is also undertaken in several stages. According to U.S. Pat. No. 2,383,580, after completion of the reaction firstly the catalyst that is used is inhibited by neutralisation of the reaction mixture and then the excess alcohol is removed by distillation. The remaining reaction mixture is distilled in a vacuum. In the process the condensate separates into a layer of glycerin and a layer of fatty-acid alkyl ester.
According to the method proposed in U.S. Pat. No. 4,164,506, in a two-stage process firstly the fr
Ganswindt Ruth
Neuner Hans-Peter
Peter Siegfried
Weidner Eckhard
Carr Deborah D.
Webb Ziesenheim Lodgson Orkin & Hanson, P.C.
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