CA1185610A - Polyglycerol ester synthesis - Google Patents
Polyglycerol ester synthesisInfo
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- CA1185610A CA1185610A CA000405555A CA405555A CA1185610A CA 1185610 A CA1185610 A CA 1185610A CA 000405555 A CA000405555 A CA 000405555A CA 405555 A CA405555 A CA 405555A CA 1185610 A CA1185610 A CA 1185610A
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Abstract
ABSTRACT
Polyols, in particular polyglycerol, are esterified using a fatty acid at atmospheric pressure or under slight vacuum. The reaction is carried out under an inert atmosphere at high temperatures (220°C-260°C) using an alkaline catalyst. When the free fatty acid level decreases to less than 1%, the reaction mixture is stripped of substantially all the water by reducing the pressure within the vessel. The alkaline mixture is then neutralized using a mild acid, e.g. phosphoric acid, while maintaining the high temperature and reduced pressure. The mixture is rapidly cooled to below 177°C after the neutralization step. The polyglycerol or polyol esters prepared via this process are of consistently high quality and are not subject to compositional changes during the process or on storage.
Polyols, in particular polyglycerol, are esterified using a fatty acid at atmospheric pressure or under slight vacuum. The reaction is carried out under an inert atmosphere at high temperatures (220°C-260°C) using an alkaline catalyst. When the free fatty acid level decreases to less than 1%, the reaction mixture is stripped of substantially all the water by reducing the pressure within the vessel. The alkaline mixture is then neutralized using a mild acid, e.g. phosphoric acid, while maintaining the high temperature and reduced pressure. The mixture is rapidly cooled to below 177°C after the neutralization step. The polyglycerol or polyol esters prepared via this process are of consistently high quality and are not subject to compositional changes during the process or on storage.
Description
POLYGLYCEROL ESTER SYNTHESIS
Paul Seiden Ricky A. Woo Technical Field 5This invention relates to the synthesis of polyol esters, in particular, polyglycerol fatty acid esters.
Backqround of the Invention There are a number of processes available for synthesizing polyol esters. These include esterification with fatty acids with and without catalysis, as well 3S transesterification using triglycerides. Stenzel et al., Die Nah~ , 21, 429-441 ~1977) reviews a number of literature references on the synthesis of polyglycerol fatty acid esters and their use. Phosphoric acid was ~ound to be a favorable catalyst for esterification, as was potassium or sodium hydroxide.
One method for synthesizing polyol esters uses an ion exchange resin as a catalyst, see Canadian Patent 834,214, issued to Kuhrt et al. ~1970). This process is said to yield pure monoesters of various polyglycerols. However, not all ion exchange resins are ~0 approved for use in foods or for pr paring food additives.
Moreover, ion exchange resins are more expensive than alkaline catalysts. ~
` One of the problems wi~l polyol esters, in particular polyglycerol esters, is the inconsistent quality of the product.
The polyol starting material is a mixture of dimers, trimers, tetramers, etc. of the starting alcohol. When this material is esterified with the fatty acid, the fatty acid will react with any of the free hydroxyl groups within the molecule. Thus, the esterified polyol is a mixture of monoesters, diesters, triesters, etc. Upon cooling in the presence of a catalyst or moisture, these esters can rearrange r,ot only by changing the position of .` ' `~
the ester group within the molecule, but actual equilibration between diesters forming monoesters and triesters, etc. This equilibration chan3es the composition to a lower monoester content and increases the concentration of higher esters.
The degree of shift caused by interesterification is variableO The process herein eliminates the shift în composition and the batch-to-batch variations.
In general, the more hydrophilic type of polyglycerol esters are more functional. These polyglycerol esters have a greater number of free hydroxyl groups relative to the number of esterified hydroxyl groups.
The esterification reaction is carried out under an inert atmosphere to obtain good color7 filavor and odor characteristics.
However, unless the mixture is properly neu-tralized to remove the esterification catalyst, rearrangement will occur. That is, the polyglycerol ester will revert to polyol and higher esters (rearrangement).
.
After the esterification is completed the catalyst is neutralized with a mild acid at~~ Z5C. During the acid addition or the cooling step which follows, rearrangement occurs. The composition shiFts to a more lipophilic and therefore less functional product. The rearrangement releases free polyol which separates from the reaction mixture. The free polyol, if recycled into the product, contaminates the product and causes darkening of 2s the color. In particular, the recycle of polyglycerol results in additional undesirable polymerization of the glycerol. The polyol to fatty acid ratio also affects the ester composition but it is difficult to compensate for the shift caused by interesterification (i.e. rearrangement).
The process of this invention eliminates the uncontrolled interesterification and eliminates the need for polyol recycle.
The process permits one to produce the most hydrophilic, most functional esters at the lowest polyol to fatty acid ratio. Since polyol is always more expensive than fatty acid, this process is also more economical.
5~
Moreover, it has been found that the water from the reaction must be substantially removed before the neutrallzation of the catalyst to insure a product without reversion or random rearrangement.
S Therefore, it is an object of the present invention to provide a process for producing polyol esters of consistently good color, flavor and odor characteristics. It is a further object of this invention to produce polyol esters which do not revert or rearrange upon standing.
It is an additional object of this invention to provide a process which utilizes inexpenslve materials which are approved ~or preparation o~ food grade materîals.
These and other ob~ects will become apparent from reading the speci~lcation.
Unless specified herein, all percentages are by weight.
Brief SummarY of the Invention A process for esterifying a polyol comprising the stPps of:
reactihg fatty acid and polyol under an inert atmosphere of temperatures from about 220C to about 260C and an ; 20 absolute pressure of ~rom about 500 mm to about 900 mm o~
mercury, in the presence of an alkaline catalyst;
Paul Seiden Ricky A. Woo Technical Field 5This invention relates to the synthesis of polyol esters, in particular, polyglycerol fatty acid esters.
Backqround of the Invention There are a number of processes available for synthesizing polyol esters. These include esterification with fatty acids with and without catalysis, as well 3S transesterification using triglycerides. Stenzel et al., Die Nah~ , 21, 429-441 ~1977) reviews a number of literature references on the synthesis of polyglycerol fatty acid esters and their use. Phosphoric acid was ~ound to be a favorable catalyst for esterification, as was potassium or sodium hydroxide.
One method for synthesizing polyol esters uses an ion exchange resin as a catalyst, see Canadian Patent 834,214, issued to Kuhrt et al. ~1970). This process is said to yield pure monoesters of various polyglycerols. However, not all ion exchange resins are ~0 approved for use in foods or for pr paring food additives.
Moreover, ion exchange resins are more expensive than alkaline catalysts. ~
` One of the problems wi~l polyol esters, in particular polyglycerol esters, is the inconsistent quality of the product.
The polyol starting material is a mixture of dimers, trimers, tetramers, etc. of the starting alcohol. When this material is esterified with the fatty acid, the fatty acid will react with any of the free hydroxyl groups within the molecule. Thus, the esterified polyol is a mixture of monoesters, diesters, triesters, etc. Upon cooling in the presence of a catalyst or moisture, these esters can rearrange r,ot only by changing the position of .` ' `~
the ester group within the molecule, but actual equilibration between diesters forming monoesters and triesters, etc. This equilibration chan3es the composition to a lower monoester content and increases the concentration of higher esters.
The degree of shift caused by interesterification is variableO The process herein eliminates the shift în composition and the batch-to-batch variations.
In general, the more hydrophilic type of polyglycerol esters are more functional. These polyglycerol esters have a greater number of free hydroxyl groups relative to the number of esterified hydroxyl groups.
The esterification reaction is carried out under an inert atmosphere to obtain good color7 filavor and odor characteristics.
However, unless the mixture is properly neu-tralized to remove the esterification catalyst, rearrangement will occur. That is, the polyglycerol ester will revert to polyol and higher esters (rearrangement).
.
After the esterification is completed the catalyst is neutralized with a mild acid at~~ Z5C. During the acid addition or the cooling step which follows, rearrangement occurs. The composition shiFts to a more lipophilic and therefore less functional product. The rearrangement releases free polyol which separates from the reaction mixture. The free polyol, if recycled into the product, contaminates the product and causes darkening of 2s the color. In particular, the recycle of polyglycerol results in additional undesirable polymerization of the glycerol. The polyol to fatty acid ratio also affects the ester composition but it is difficult to compensate for the shift caused by interesterification (i.e. rearrangement).
The process of this invention eliminates the uncontrolled interesterification and eliminates the need for polyol recycle.
The process permits one to produce the most hydrophilic, most functional esters at the lowest polyol to fatty acid ratio. Since polyol is always more expensive than fatty acid, this process is also more economical.
5~
Moreover, it has been found that the water from the reaction must be substantially removed before the neutrallzation of the catalyst to insure a product without reversion or random rearrangement.
S Therefore, it is an object of the present invention to provide a process for producing polyol esters of consistently good color, flavor and odor characteristics. It is a further object of this invention to produce polyol esters which do not revert or rearrange upon standing.
It is an additional object of this invention to provide a process which utilizes inexpenslve materials which are approved ~or preparation o~ food grade materîals.
These and other ob~ects will become apparent from reading the speci~lcation.
Unless specified herein, all percentages are by weight.
Brief SummarY of the Invention A process for esterifying a polyol comprising the stPps of:
reactihg fatty acid and polyol under an inert atmosphere of temperatures from about 220C to about 260C and an ; 20 absolute pressure of ~rom about 500 mm to about 900 mm o~
mercury, in the presence of an alkaline catalyst;
(2) reducing the pressure to less than 127~of mercury when the free fatty acid level is less than 1~ to remove ~ubstantially all the water;
(3) neutralizing th~ alkaline catalyst with a weak acid under reduced pressure; and
(4) rapidly cooling the reaction mixture to less than 177C.
.
Detail~d Description of Invention The process herein is useful for the esterification nf many different polyols. Polyols are organic compounds oontaining more than one hydroxy group on the molecule. These include dihydroxyalkanes, glycerine, carbohydrates; sugar alcohols, polyglycerols, etc.
The most preferred polyol is polyglycerol which is prepared by the polymerization o~ glycerine in the presence of either acid or base. The polyglycerols can contain from 2 to 20 gl-ycerol moieties. Preferably, the polyglycerols will be those having from ~ to 15 glycerol moieties.
The polyglycerol compounds can be made by any synthetic method9 the method of their preparation is not critical to the esterification process. See for example, U.S. 3,968,169 issued to Seiden and Martin (1976). However, the purer the starting 10 polyglycerol? the purer the polyglycerol ester will be.
Additional polyols that may be used in the esterification reaction described herein are glycerine, sorbitol, xylitol, erythritol and pentaerythritol. These materials may be reacted with fatty acids to produce mono- or diglycerides9 sorbitol esters, xylitol esters, etc. The reaction is especially useful for polyols which are not soluble in the fatty acid and which are `~ not good solvents themselves.
; The polyols can be esterified with any fatty acid or interesterified with a fatty acid ester or fatty acid 20 triglyceride. The fatty acids can be saturated, unsaturated, or polyunsaturated. In particularg those having from 8 to 24 carbon atoms are preferred for use herein. For the preparation of emulsifiers, those having from about 10 carbons to about 22 carbons are preferred. These include decanoic acid, dodeca~oic 2s acid, stearic acid, palmitic acid, oleic acîd, behenic acid, and others. Triglycerides of these acids can also be used. Lower alkyl esters, in particular, methyl and ethyl esters of the fatty acids, can be used as fatty acid sources.
The polyol and fatty acid are mixed together with an alkaline 30 catalyst. The alkaline catalyst can be the hydroxide of any of the alkaline earth metals, for example sodium, potassium or lithium hydroxide. The order of addition is not critical to the process.
The mole ratio of the polyol to fatty acid can range ~rom 35 about 0.1:1 to about 3:1.
3s~
An amount of the alkaline catalyst effective to catalyze the reaction is used. Preferably, an amount in the range of from about û.01 to about 0.2 mole per mole of fatty acid used3 most preferably from about 0.04 to about 0.10 mole per mole of fatty acid.
The fatty acid, the polyol and the catalyst are added to a reaction vessel which is held under an inert atmosphere. The inert atmosphere can be maintained by sparging the mixture, or by simply passin3 a non-reactive gas through the vessel. Inert (non-reactive) gases include nitrogen, helium, argon, etc. Under some conditions, water or carbon dioxide can act as the inert gas.
In order to produce a final product which has a good color and less off-odor, effective agitation is necessary~ The agitation can be accomplished by any conventional means. This includes the use of a mechanical mixer as well as by inert gas spar3ing.
The esterification mixture is then heated to a temperature of from about 220C to about 260C, preferably from 225C to 235C.
The vessel is held under atmospheric pressure or at a slight vacuum (508 mm to 76û mm of mercury absolute) or at a slight positive pressure (760 to 900 mm of mercury absolute). During the esterification reaction, the water is distilled off. The water is not returned to the reaction vessel. The reaction is monitored by measuring the free fatty acid level in the reaction mixture.
The free fatty acid level can be determined by titrating the free acid in aliquot portions.
When the free fatty acid level has been reduced to less than 1%, and preferably less than 0.5%, the pressure in the mixing vessel is reduced to less than about 127 mm of mercury, preferably less than 12 mm of mercury. The temperature is maintained at about 204C to about 238C. This reduction in pressure further strips the water from the mixture. The removal of the water also deodorizes the polyol ester.
The reaction mixture is held at full vacuum until substantially ail of the water has been removed. The amount of time necessary to do this will, of course, depend on the size of . . .
the reaction vessel and the vacuum system ~e.g. pump or ejector systems). It can vary from 10 minutes to 4 hours. For example, a 68 kg. reaction mixture would be heid at less than 127 mm of mercury for about 15 minutes. It is extre,~ely important to eliminate the water or minimize the water content to control the interesterification and thus reversion to the more lipophilic estersO
The catalyst neutralization and the subsequent cooling steps also represent an improvement over the prior art.
After removal of the water, the catalyst is neutralized with a mild acid. For example3 phosphoric acid, sodium di-hydrogen phosphate, acetic acid, citric acid, and other carboxylic acids can be used~ Water can be present in the acid as water is readily removed because of the high temperatures and the vacuum.
The acid is added slowly to the reaction vessel. For examplet a rate of from about lOû g/minute is suitable for a 45 kg.
reaction batch. The pressure of less than 127 mm of H3 and the elevated temperatures (~04C to 238C) are maintained during the neutralization to remove any water present. For maximum 20 efficiency, the acid is added through the bottom oF the reaction vessel. The rate of acid addition is also a~fected by the water content in the acid and the effectiveness of the vacuum system.
Following the acid addition, the reaction mixture is cooled rapidly to less than 177C. ~referably, the mixture is cooled to 25 less than 160C. The rate of cooling should be at least 3C to 15C per minute, preferably 5C to 1~C/minute. Once the temperature has reached about 145C, the rate of cooling is no longer critical to the stability of the-product.
Rapid cooling can be accomplished using a heat exchanger, cooling coils or a water sparge. After the reaction mixture is cooled, any excess water is removed to minimize product deterioration during storage.
The minimizing of the water content before and during neutralization is critical to the formation of polyol esters which have good color odor and flavor characteristics and which are consistent in compos;tion on a batch to batch basis. The rapid cooling of the reaction mixture minimizes the interesterification nf the polyol esters Reversion, i.e. random rearrangement shifts in the composition, during and after processing can be detected by measuring the refractive index of the products or by analyzing the ; differential scanning calorimetry curve.
If a compositional shift has occurred in the product due to improper process control, the final refractive index reading will be sîgnificantly lower than the refractive index prior to neutralization and the peak height ratio of the differential scanning calorimeter curve will change. (Peak height ratio is defined below.) Table 1 illustrates the changes that can occur in the peak height ratio measurements and in the refractive indexO The seven samples, A through E, are all palmitic and stearic acid esters of hexapolyglycerol. They were prepared using about the same ratios of fatty acid, polyglycerol, sodium hydroxide, and phosphoric acid as in Example I. The scale of the reaction varied.
Samples C, D, E and G were prepared according to the process of this invention. Samples A and B were prepared using a process which was similar to that of Example I except that the pressure ; was not reduced prior to neutralization. The rearrangement that occurred in Samples A and B was a result of the high moisture conditions during this step of the process.
Sample F was prepared in the same manner as Sample G except that the reaction was cooled at the rate of about 1C per minute.
Because of this slow cooling, rearrangement occurred.
FREE FATTY REFRACTIVE INDEX* PEAK HEIGHT RATX0**
ACID ~e~ S~ple 2 Sample 1 Sample 2 A less than 0.3 58.9 53.3 0.55 0.41 a less than 0.5 55.4 49.9 0.62 0.36 C less than 0.2 59.1 58.9 0.79 0.78 D less than 0.1 59.0 58.7 0.68 0.71 E less than 0.1 59.9 59.8 1.28 1.25 F less than 0.2 60.2 52.0 - -G less than 0.5 60.9 60.0 - -*the butyro scale was used to measure the refractive index.
Sample 1 is the sample before neutralization, Sample 2 is the final sample.
**Ratio of peak heights from the differential scaling calorimeter. Sample 1 is taken before neutralization7 Sample 2 is taken at`ter final cooling.
A. Refractive Index Measurement Any refractometer can be used.
A Zeiss refractometer was used to measure the re-fractive index of the process samples. The refractometer is preheated and maintained at 6û'' + û.1C using a constant temperature water bath. Two samples are obtained from the reactor:
1. A sample prior to neutralization.
2. A sample 2fter the reaction has cooled rapidly to 60C to 82C.
Sarnple 1 which is taken from the reactor before neutralization is rapidly cooled to 60C and then the refractive index measured. Sample 2 is measured at~60C. The standard refractive index method for the instrument is used.
B. Differential Scannin~ Calorimetry Any differential scanning calorimeter can be used.
A duPont ~odel 990 thermal analyzer connected to a Model 910 dif~erential scanning calorimeter was used to measure the peak height ratios of the process samples.
3s 10.0 + 0.1 mg of solid ester is placed in the sample cup.
Most samples are more easily handled in their solid formO The lid is placed on the sample cup making sure that no material is on the sealing lip. The sample cup and lid are hermetically crimped using the sample crimper. ~ reference cell is prepared by crimping two lids on one empty sample cup.
The instrument controls are set as follows:
Control Setting X-Axis Zero Shift 0 X-Axis Scale 5C/in.
Y-Axis Zero Shift as required lo Y-Axis Scale (Sensitivity) 2 Base line slope 0 Program mode isothermal Temperature rate 5C/min~
Starting temp. lOûC
Allow tho instrument to heat to 110C to remove all the moisture in the cell. Reset the starting temperature to 20C and allow the instrument to cool to 20C ~changing to isothermal control cools).^ Remove the cell cover and the silver lid from the cell. Place the sample pan on the rear thermocouple and the 20 reference pan on the front thermocouple. The same reference is left in place for all the tests. Allow the cell to equiliorate for approximately 2 to 3 minutes. Using the Y-Axis Zero control, position the pen to the starting point on the chart paper and move the pen to the down position to begin recording. Switch the t 25 control program mode to Heat. It should take about 10 minutes to reach 70C. When the temperature reaches 70C, move the pen to the up position to stop recording and reset the starting temperature to 100C and change to the isothermal mode. When the temperature reaches 100C, remove the sample from the cell.
30 Repeat these same steps for the next sample.
Determination of the Peak Height Ratio The determination of the ratio of the two peaks produced by the instrument is done by first determining a base line. The base line is determined by extrapolating the line back from the 35 horizontal section of the curve tracing around the 60C to 70C
mark. This extrapolated line, going back to the 30C mark should ; be as straight and hor~zontal as possible. The height (number o~
blocks from base line to the top o~ the peak) o~ the first peak is divlded by the height of the second peak to arrive at the ratio.
Detennination of the peak teme~a ures The determination of the differential scanning calorimeter peak temperatures i5 done by reviewing the heating mode differential scanning calorimeter scale cell of the polyol ester.
The maximum point oF each peak apex is extrapolated vertically to 10 the temperature ax;s (X-Axis). These temperature points are the peak temperature for each curve, respectively.
EXAMPLE I
Synthesis of a mixed ester of hexapolyglycerol.
; A reaction vessel, sufficient to hold 50 kg. of reactant, is 15 used. The reaction vessel is fitted with a nitrogen spar~e and a propeller mixer, is adapted to run under vacuum, and is also equipped with a condenser to collect the water removed during the reaction. To t~is vessel is added 27.67 kg. of polyglycerol ; having an average chain length of 6. The polyglycerol is mixed 20 with 0.43 kg. of 50~ sodium hydroxide. The reaction mixture is then heated to about 115C under f`ull vacuum for about 15 minutes to remove the water from the sodium hydroxide polyglycerol mixture. Palmitic acid at a weight of 11.4 kg. (45.2 moles) and 6.12 kg. of stearic acid (21.S moles) are added to the reaction 25 mixture at atmospheric pressure. A partial vacuum is then pulled ` on the reaction vessel (about 5û8 rmm of mercury) and tne vessel heated to about 220C over the period of about an hour. The percent free fatty acid after an hour is about 6.3~. The vessel is then maintained at this partial pressure and at a temperature 30 of about 230C for an additional 20 minutes when the free fatty acid drops to less than 0.3~.
The pressure is then lowered to about 12 mm of mercury and held there about ~or 15 minutes. This removes substantially all of the water from the reaction mixture. The temperature is then 3s maintained at about 224C, the pressure maintained at 12 mm, and aeid is added from the bottom Over the period of about 5 minutes, 0.68 kg. ~f 75~ phosphoric acid is added. The mixture is then cooled by using a water sparge and a 4.5C eooling coil to a temperature of about 157C over a period of about 7 minutes.
During this cooling, the water distills out of the reaction mixture. The water sparge is then stopped, and the mixture cooled by the cooling coil to about 93C. The product is an opaque liquid which solidifies on further cooling.
The total yield of the ester of the hexapolyglycerol is 40.6 kg. The weight of the distillate, including water collected during the reaction is 1.8 kg.9 approximately 0.9 kg. of this is water. The remainder is low molecular weight polyol. The saponification value is 98.74, and the hydroxyl value is 441.
; When this reaction is repeated using 27.66 kg. of the polyglycerol having an average chain length of 6, 11.6 kg.
palmitic acid, 6 kg. of stearic acid, essentially the sa~e results are obtained. This product has a saponification value of 99.98 and a hydroxyl yalue of 430.
EXA~PLE ll A reaction vessel sufficient to hold 680 kg of reactant is used. The reaction vessel is fitted with nitrogen sparge a propeller mixer is adapted to run under vacuum, and is - equipped with a condenser to collect the water removed during ; the reaction. To this ves;sel is added 394. 6 kg of polyglycerol having an average chain length of 6. l he polyglycerol is mixed with 6.3 kg of sodium hydroxide catalyst ~50% aqueous solution).
The reaction mixture is then heated to 110-116C under full vacuum for approximately lO to 15 minutes.
The vacuum is released and 285.8 kg of stearic and palmitic acid is added. The ratio of palmitic to stearic acid is 65:35.
~litrogen sparging is then started. The reaction is heated to about 229C.
Samples are removed from the reac-tion vessel periodically and titrated for free fatty acid. When the free fatty acid level is below l~, the pressure is lowered to a full vacuum ~about 12 mm.
of mercury) and held there for one hour. The vacuum is pulled slowly (to avoid foaming ancl excessive temperature drop).
Substantially all the water is removed from the reaction mixture.
Twenty pounds of phosphoric acid Is then slowly added to the
.
Detail~d Description of Invention The process herein is useful for the esterification nf many different polyols. Polyols are organic compounds oontaining more than one hydroxy group on the molecule. These include dihydroxyalkanes, glycerine, carbohydrates; sugar alcohols, polyglycerols, etc.
The most preferred polyol is polyglycerol which is prepared by the polymerization o~ glycerine in the presence of either acid or base. The polyglycerols can contain from 2 to 20 gl-ycerol moieties. Preferably, the polyglycerols will be those having from ~ to 15 glycerol moieties.
The polyglycerol compounds can be made by any synthetic method9 the method of their preparation is not critical to the esterification process. See for example, U.S. 3,968,169 issued to Seiden and Martin (1976). However, the purer the starting 10 polyglycerol? the purer the polyglycerol ester will be.
Additional polyols that may be used in the esterification reaction described herein are glycerine, sorbitol, xylitol, erythritol and pentaerythritol. These materials may be reacted with fatty acids to produce mono- or diglycerides9 sorbitol esters, xylitol esters, etc. The reaction is especially useful for polyols which are not soluble in the fatty acid and which are `~ not good solvents themselves.
; The polyols can be esterified with any fatty acid or interesterified with a fatty acid ester or fatty acid 20 triglyceride. The fatty acids can be saturated, unsaturated, or polyunsaturated. In particularg those having from 8 to 24 carbon atoms are preferred for use herein. For the preparation of emulsifiers, those having from about 10 carbons to about 22 carbons are preferred. These include decanoic acid, dodeca~oic 2s acid, stearic acid, palmitic acid, oleic acîd, behenic acid, and others. Triglycerides of these acids can also be used. Lower alkyl esters, in particular, methyl and ethyl esters of the fatty acids, can be used as fatty acid sources.
The polyol and fatty acid are mixed together with an alkaline 30 catalyst. The alkaline catalyst can be the hydroxide of any of the alkaline earth metals, for example sodium, potassium or lithium hydroxide. The order of addition is not critical to the process.
The mole ratio of the polyol to fatty acid can range ~rom 35 about 0.1:1 to about 3:1.
3s~
An amount of the alkaline catalyst effective to catalyze the reaction is used. Preferably, an amount in the range of from about û.01 to about 0.2 mole per mole of fatty acid used3 most preferably from about 0.04 to about 0.10 mole per mole of fatty acid.
The fatty acid, the polyol and the catalyst are added to a reaction vessel which is held under an inert atmosphere. The inert atmosphere can be maintained by sparging the mixture, or by simply passin3 a non-reactive gas through the vessel. Inert (non-reactive) gases include nitrogen, helium, argon, etc. Under some conditions, water or carbon dioxide can act as the inert gas.
In order to produce a final product which has a good color and less off-odor, effective agitation is necessary~ The agitation can be accomplished by any conventional means. This includes the use of a mechanical mixer as well as by inert gas spar3ing.
The esterification mixture is then heated to a temperature of from about 220C to about 260C, preferably from 225C to 235C.
The vessel is held under atmospheric pressure or at a slight vacuum (508 mm to 76û mm of mercury absolute) or at a slight positive pressure (760 to 900 mm of mercury absolute). During the esterification reaction, the water is distilled off. The water is not returned to the reaction vessel. The reaction is monitored by measuring the free fatty acid level in the reaction mixture.
The free fatty acid level can be determined by titrating the free acid in aliquot portions.
When the free fatty acid level has been reduced to less than 1%, and preferably less than 0.5%, the pressure in the mixing vessel is reduced to less than about 127 mm of mercury, preferably less than 12 mm of mercury. The temperature is maintained at about 204C to about 238C. This reduction in pressure further strips the water from the mixture. The removal of the water also deodorizes the polyol ester.
The reaction mixture is held at full vacuum until substantially ail of the water has been removed. The amount of time necessary to do this will, of course, depend on the size of . . .
the reaction vessel and the vacuum system ~e.g. pump or ejector systems). It can vary from 10 minutes to 4 hours. For example, a 68 kg. reaction mixture would be heid at less than 127 mm of mercury for about 15 minutes. It is extre,~ely important to eliminate the water or minimize the water content to control the interesterification and thus reversion to the more lipophilic estersO
The catalyst neutralization and the subsequent cooling steps also represent an improvement over the prior art.
After removal of the water, the catalyst is neutralized with a mild acid. For example3 phosphoric acid, sodium di-hydrogen phosphate, acetic acid, citric acid, and other carboxylic acids can be used~ Water can be present in the acid as water is readily removed because of the high temperatures and the vacuum.
The acid is added slowly to the reaction vessel. For examplet a rate of from about lOû g/minute is suitable for a 45 kg.
reaction batch. The pressure of less than 127 mm of H3 and the elevated temperatures (~04C to 238C) are maintained during the neutralization to remove any water present. For maximum 20 efficiency, the acid is added through the bottom oF the reaction vessel. The rate of acid addition is also a~fected by the water content in the acid and the effectiveness of the vacuum system.
Following the acid addition, the reaction mixture is cooled rapidly to less than 177C. ~referably, the mixture is cooled to 25 less than 160C. The rate of cooling should be at least 3C to 15C per minute, preferably 5C to 1~C/minute. Once the temperature has reached about 145C, the rate of cooling is no longer critical to the stability of the-product.
Rapid cooling can be accomplished using a heat exchanger, cooling coils or a water sparge. After the reaction mixture is cooled, any excess water is removed to minimize product deterioration during storage.
The minimizing of the water content before and during neutralization is critical to the formation of polyol esters which have good color odor and flavor characteristics and which are consistent in compos;tion on a batch to batch basis. The rapid cooling of the reaction mixture minimizes the interesterification nf the polyol esters Reversion, i.e. random rearrangement shifts in the composition, during and after processing can be detected by measuring the refractive index of the products or by analyzing the ; differential scanning calorimetry curve.
If a compositional shift has occurred in the product due to improper process control, the final refractive index reading will be sîgnificantly lower than the refractive index prior to neutralization and the peak height ratio of the differential scanning calorimeter curve will change. (Peak height ratio is defined below.) Table 1 illustrates the changes that can occur in the peak height ratio measurements and in the refractive indexO The seven samples, A through E, are all palmitic and stearic acid esters of hexapolyglycerol. They were prepared using about the same ratios of fatty acid, polyglycerol, sodium hydroxide, and phosphoric acid as in Example I. The scale of the reaction varied.
Samples C, D, E and G were prepared according to the process of this invention. Samples A and B were prepared using a process which was similar to that of Example I except that the pressure ; was not reduced prior to neutralization. The rearrangement that occurred in Samples A and B was a result of the high moisture conditions during this step of the process.
Sample F was prepared in the same manner as Sample G except that the reaction was cooled at the rate of about 1C per minute.
Because of this slow cooling, rearrangement occurred.
FREE FATTY REFRACTIVE INDEX* PEAK HEIGHT RATX0**
ACID ~e~ S~ple 2 Sample 1 Sample 2 A less than 0.3 58.9 53.3 0.55 0.41 a less than 0.5 55.4 49.9 0.62 0.36 C less than 0.2 59.1 58.9 0.79 0.78 D less than 0.1 59.0 58.7 0.68 0.71 E less than 0.1 59.9 59.8 1.28 1.25 F less than 0.2 60.2 52.0 - -G less than 0.5 60.9 60.0 - -*the butyro scale was used to measure the refractive index.
Sample 1 is the sample before neutralization, Sample 2 is the final sample.
**Ratio of peak heights from the differential scaling calorimeter. Sample 1 is taken before neutralization7 Sample 2 is taken at`ter final cooling.
A. Refractive Index Measurement Any refractometer can be used.
A Zeiss refractometer was used to measure the re-fractive index of the process samples. The refractometer is preheated and maintained at 6û'' + û.1C using a constant temperature water bath. Two samples are obtained from the reactor:
1. A sample prior to neutralization.
2. A sample 2fter the reaction has cooled rapidly to 60C to 82C.
Sarnple 1 which is taken from the reactor before neutralization is rapidly cooled to 60C and then the refractive index measured. Sample 2 is measured at~60C. The standard refractive index method for the instrument is used.
B. Differential Scannin~ Calorimetry Any differential scanning calorimeter can be used.
A duPont ~odel 990 thermal analyzer connected to a Model 910 dif~erential scanning calorimeter was used to measure the peak height ratios of the process samples.
3s 10.0 + 0.1 mg of solid ester is placed in the sample cup.
Most samples are more easily handled in their solid formO The lid is placed on the sample cup making sure that no material is on the sealing lip. The sample cup and lid are hermetically crimped using the sample crimper. ~ reference cell is prepared by crimping two lids on one empty sample cup.
The instrument controls are set as follows:
Control Setting X-Axis Zero Shift 0 X-Axis Scale 5C/in.
Y-Axis Zero Shift as required lo Y-Axis Scale (Sensitivity) 2 Base line slope 0 Program mode isothermal Temperature rate 5C/min~
Starting temp. lOûC
Allow tho instrument to heat to 110C to remove all the moisture in the cell. Reset the starting temperature to 20C and allow the instrument to cool to 20C ~changing to isothermal control cools).^ Remove the cell cover and the silver lid from the cell. Place the sample pan on the rear thermocouple and the 20 reference pan on the front thermocouple. The same reference is left in place for all the tests. Allow the cell to equiliorate for approximately 2 to 3 minutes. Using the Y-Axis Zero control, position the pen to the starting point on the chart paper and move the pen to the down position to begin recording. Switch the t 25 control program mode to Heat. It should take about 10 minutes to reach 70C. When the temperature reaches 70C, move the pen to the up position to stop recording and reset the starting temperature to 100C and change to the isothermal mode. When the temperature reaches 100C, remove the sample from the cell.
30 Repeat these same steps for the next sample.
Determination of the Peak Height Ratio The determination of the ratio of the two peaks produced by the instrument is done by first determining a base line. The base line is determined by extrapolating the line back from the 35 horizontal section of the curve tracing around the 60C to 70C
mark. This extrapolated line, going back to the 30C mark should ; be as straight and hor~zontal as possible. The height (number o~
blocks from base line to the top o~ the peak) o~ the first peak is divlded by the height of the second peak to arrive at the ratio.
Detennination of the peak teme~a ures The determination of the differential scanning calorimeter peak temperatures i5 done by reviewing the heating mode differential scanning calorimeter scale cell of the polyol ester.
The maximum point oF each peak apex is extrapolated vertically to 10 the temperature ax;s (X-Axis). These temperature points are the peak temperature for each curve, respectively.
EXAMPLE I
Synthesis of a mixed ester of hexapolyglycerol.
; A reaction vessel, sufficient to hold 50 kg. of reactant, is 15 used. The reaction vessel is fitted with a nitrogen spar~e and a propeller mixer, is adapted to run under vacuum, and is also equipped with a condenser to collect the water removed during the reaction. To t~is vessel is added 27.67 kg. of polyglycerol ; having an average chain length of 6. The polyglycerol is mixed 20 with 0.43 kg. of 50~ sodium hydroxide. The reaction mixture is then heated to about 115C under f`ull vacuum for about 15 minutes to remove the water from the sodium hydroxide polyglycerol mixture. Palmitic acid at a weight of 11.4 kg. (45.2 moles) and 6.12 kg. of stearic acid (21.S moles) are added to the reaction 25 mixture at atmospheric pressure. A partial vacuum is then pulled ` on the reaction vessel (about 5û8 rmm of mercury) and tne vessel heated to about 220C over the period of about an hour. The percent free fatty acid after an hour is about 6.3~. The vessel is then maintained at this partial pressure and at a temperature 30 of about 230C for an additional 20 minutes when the free fatty acid drops to less than 0.3~.
The pressure is then lowered to about 12 mm of mercury and held there about ~or 15 minutes. This removes substantially all of the water from the reaction mixture. The temperature is then 3s maintained at about 224C, the pressure maintained at 12 mm, and aeid is added from the bottom Over the period of about 5 minutes, 0.68 kg. ~f 75~ phosphoric acid is added. The mixture is then cooled by using a water sparge and a 4.5C eooling coil to a temperature of about 157C over a period of about 7 minutes.
During this cooling, the water distills out of the reaction mixture. The water sparge is then stopped, and the mixture cooled by the cooling coil to about 93C. The product is an opaque liquid which solidifies on further cooling.
The total yield of the ester of the hexapolyglycerol is 40.6 kg. The weight of the distillate, including water collected during the reaction is 1.8 kg.9 approximately 0.9 kg. of this is water. The remainder is low molecular weight polyol. The saponification value is 98.74, and the hydroxyl value is 441.
; When this reaction is repeated using 27.66 kg. of the polyglycerol having an average chain length of 6, 11.6 kg.
palmitic acid, 6 kg. of stearic acid, essentially the sa~e results are obtained. This product has a saponification value of 99.98 and a hydroxyl yalue of 430.
EXA~PLE ll A reaction vessel sufficient to hold 680 kg of reactant is used. The reaction vessel is fitted with nitrogen sparge a propeller mixer is adapted to run under vacuum, and is - equipped with a condenser to collect the water removed during ; the reaction. To this ves;sel is added 394. 6 kg of polyglycerol having an average chain length of 6. l he polyglycerol is mixed with 6.3 kg of sodium hydroxide catalyst ~50% aqueous solution).
The reaction mixture is then heated to 110-116C under full vacuum for approximately lO to 15 minutes.
The vacuum is released and 285.8 kg of stearic and palmitic acid is added. The ratio of palmitic to stearic acid is 65:35.
~litrogen sparging is then started. The reaction is heated to about 229C.
Samples are removed from the reac-tion vessel periodically and titrated for free fatty acid. When the free fatty acid level is below l~, the pressure is lowered to a full vacuum ~about 12 mm.
of mercury) and held there for one hour. The vacuum is pulled slowly (to avoid foaming ancl excessive temperature drop).
Substantially all the water is removed from the reaction mixture.
Twenty pounds of phosphoric acid Is then slowly added to the
5 reaction vessel at the rate of about one pound/minute.
Two to three minutes after the addition of the phosphoric ackl, the vacuum is released and the system pressure reaches atmospheric. Nitrogen sparging is continuous. Water is injected into the vessel at the rate of 6.35 kg/minute over a 10 minute 10 period. This allows the reactor temperature to rapidly drop from 235C to about 1 49C. The cooling rate is about 8. 5C/minute.
Once the product reaches 300~F, a vacuum (12 mmHg) is then pulled on the system and the system continues to cool at a reduced rate to 82 . 2C .
The product has the following characteristics:
Refractive index6û . 5 ~butyro scale at 60C) Saponi~ication value101 Hydroxyl value 418 pH 7 Free fatty acid content 296
Two to three minutes after the addition of the phosphoric ackl, the vacuum is released and the system pressure reaches atmospheric. Nitrogen sparging is continuous. Water is injected into the vessel at the rate of 6.35 kg/minute over a 10 minute 10 period. This allows the reactor temperature to rapidly drop from 235C to about 1 49C. The cooling rate is about 8. 5C/minute.
Once the product reaches 300~F, a vacuum (12 mmHg) is then pulled on the system and the system continues to cool at a reduced rate to 82 . 2C .
The product has the following characteristics:
Refractive index6û . 5 ~butyro scale at 60C) Saponi~ication value101 Hydroxyl value 418 pH 7 Free fatty acid content 296
Claims (19)
1. A process for esterifying a polyol comprising the steps of:
(1) reacting fatty acid and polyol under an inert atmos-phere at temperatures of from about 220°C to about 260°C and an absolute pressure of from about 500 mm to about 900 mm of mercury, in the presence of an effective amount of alkaline catalyst;
(2) reducing the pressure to less than 127 mm of mercury when the free fatty acid level is less than 1% to remove substantially all the water;
(3) neutralizing the alkaline catalyst by slow addition of weak acid under reduced pressure and at a temperature of about 204°C to about 238°C; and (4) rapidly cooling the reaction mixture to less than 177°C, at the rate of at least 3°C per minute, at reduced pressure of less than 127 mm of mercury.
(1) reacting fatty acid and polyol under an inert atmos-phere at temperatures of from about 220°C to about 260°C and an absolute pressure of from about 500 mm to about 900 mm of mercury, in the presence of an effective amount of alkaline catalyst;
(2) reducing the pressure to less than 127 mm of mercury when the free fatty acid level is less than 1% to remove substantially all the water;
(3) neutralizing the alkaline catalyst by slow addition of weak acid under reduced pressure and at a temperature of about 204°C to about 238°C; and (4) rapidly cooling the reaction mixture to less than 177°C, at the rate of at least 3°C per minute, at reduced pressure of less than 127 mm of mercury.
2. A process according to Claim 1 wherein the mole ratio of polyol to fatty acid is from about 0.1:1 to about 3:1.
3. A process according to Claim 2 wherein the reaction step (1) is at a temperature of from 225°C to 235°C and a pressure of from about 500 mm to 760 mm and step 2 is at a pressure less than 13 mm of mercury.
4. A process according to Claim 3 wherein the alkaline catalyst is selected from the group consisting of potassium hydroxide, sodium hydroxide and lithium hydroxide.
5. A process according to Claim 4 wherein the mixture is cooled at the rate of at about 5°C to about 12°C per minute.
6. A process according to Claim 5 wherein the mixture is rapidly cooled in step (4) to a temperature of less than 160°C under reduced pressure.
7. A process according to Claim 4 wherein the amount of alkaline catalyst is from about 0.01 to about 0.2 moles per mole of fatty acid.
8. A process according to Claim 3 wherein the polyol is a polyglycerol.
9. A process according to Claim 8 wherein the poly-glycerol has from about 2 to about 15 glycerol moieties.
10. A process according to Claim 9 wherein the alkaline catalyst is selected from the group consisting of potassium hydroxide, sodium hydroxide and lithium hydroxide.
11. A process according to Claim 9 wherein the pressure is reduced in step (2) when the fatty acid level is less than 0.5%.
12. A process according to Claim 9 wherein the amount of alkaline catalyst is from about 0.01 to about 0.2 moles per mole of fatty acid.
13. A process according to Claim 12 wherein the alkaline catalyst is neutralized with phosphoric acid, acetic acid, or citric acid.
14. A process according to Claim 13 wherein the mixture is rapidly cooled in step (4) to a temperature of less than 160°C.
15. A process according to Claim 14 wherein the mixture is cooled at the rate of at least 3°C per minute.
16. A process according to Claim 3 wherein the polyol is selected from the group consisting of glycerol and sorbitol.
17. A process according to Claim 7 wherein the polyol is selected from the group consisting of glycerol and sorbitol.
18. A process according to Claim 3 wherein the resulting esters are glyceride esters, sorbitol esters and sorbitan esters.
19. A process according to Claim 7 wherein the resulting esters are glyceride esters, sorbitol esters and sorbitan esters.
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US27609181A | 1981-06-22 | 1981-06-22 | |
| US276,091 | 1981-06-22 | ||
| US36939782A | 1982-04-19 | 1982-04-19 | |
| US369,397 | 1982-04-19 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1185610A true CA1185610A (en) | 1985-04-16 |
Family
ID=26957766
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000405555A Expired CA1185610A (en) | 1981-06-22 | 1982-06-21 | Polyglycerol ester synthesis |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1185610A (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5585506A (en) * | 1994-07-22 | 1996-12-17 | Lonza Inc. | One phase production of polyglycerol esters |
| US7151186B2 (en) | 1999-10-15 | 2006-12-19 | Danisco Cultor America, Inc. | Method for the direct esterification of sorbitol with fatty acids |
| CN111670175A (en) * | 2018-12-11 | 2020-09-15 | Ioi油脂化学品有限责任公司 | Process for preparing polyglycerol fatty acid ester |
-
1982
- 1982-06-21 CA CA000405555A patent/CA1185610A/en not_active Expired
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5585506A (en) * | 1994-07-22 | 1996-12-17 | Lonza Inc. | One phase production of polyglycerol esters |
| US7151186B2 (en) | 1999-10-15 | 2006-12-19 | Danisco Cultor America, Inc. | Method for the direct esterification of sorbitol with fatty acids |
| CN111670175A (en) * | 2018-12-11 | 2020-09-15 | Ioi油脂化学品有限责任公司 | Process for preparing polyglycerol fatty acid ester |
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