CA1178288A - Process for preparing anhydro polyol containing polyol mixtures - Google Patents
Process for preparing anhydro polyol containing polyol mixturesInfo
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- CA1178288A CA1178288A CA000402491A CA402491A CA1178288A CA 1178288 A CA1178288 A CA 1178288A CA 000402491 A CA000402491 A CA 000402491A CA 402491 A CA402491 A CA 402491A CA 1178288 A CA1178288 A CA 1178288A
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Abstract
ABSTRACT OF THE DISCLOSURE
A process for preparing polyol mixtures containing two or more polyols selected from the group consisting of C4-C6 sugar alcohols, C4-C6 monoanhydro polyols, and C4-C6 dianhydro polyols is disclosed. The process is carried out at elevated temperature and in the presence of a strongly acidic heterogeneous catalyst. Water content in the reaction mixture and reaction time are controlled to produce polyol mixtures having hydroxyl numbers in the range from 810 to 1800. The mixtures are useful as starting materials or as intermediates in chemical syntheses.
A process for preparing polyol mixtures containing two or more polyols selected from the group consisting of C4-C6 sugar alcohols, C4-C6 monoanhydro polyols, and C4-C6 dianhydro polyols is disclosed. The process is carried out at elevated temperature and in the presence of a strongly acidic heterogeneous catalyst. Water content in the reaction mixture and reaction time are controlled to produce polyol mixtures having hydroxyl numbers in the range from 810 to 1800. The mixtures are useful as starting materials or as intermediates in chemical syntheses.
Description
(~ ~
32~ 3259 PROCESS FOR PREPARING
.
ANHYDRO POLYOL CONTAINING POLYOL ~IIXTURES
BACKGROlJND OF THE INVENTION
Field of the Invention The present invention relates to a process for pre paring mixtures of polyols containing two or more polyols, selected from ~he ~roup consisting of C4-C6 sugar alcohols, C4-C6 monoanhydro polyols and C4-C6 dianhydro polyols.
The Prior Art _ Sugar alcohols such as, for example, hexitols, monoanh~dro-hexitols, dianhydrohexitols and mixtures thereof are generally known. They are used as basic materials or intermediates for chemical syntheses, especially o Eine chemicals, ester-based emulsiiers, polyester and alkyd resins~ and polyurethanes. An important criterion in the use o these polyols in the manufac-ture of synthetic resins, apart from the type of polyols or polyol mixturesr is their hydroxyl number, ~7hich theoretically may be varied from 1848 for pure hexitols to 768 for pure dianhydrohexitols.
Practically pure sugar alcohols may be obtained by cata-lytic hydrogenation of the respective sugar. However, the known processes for the production of anhydro polyols or of polyol mixtures containing such compounds by dehydration from sugar alcohols at elevated temperature in the presence of acidic catalysts merely yield mix~ures with a rather limited content of dianhydrosugar alcohol (about 66% maximum) and monoanhydrosugar alcohol (about 40~ maximum). These processes, moreover, do not permit the ratio in which the various polyols are pre~sent in the reaction mixture to be significan~ly changed for a given hydroxyl number. Only insignificant changes can be effected by selecting process parameters, especially catalyst, temperature, reaction medium and/or reaction time. This is especially so for ones in the range of medium and low hydroxyl numbers.
Another aspect of the prior art is that comparatively high di- and monoanhydrosugar alcohol yields may be obtained only if so called homogeneous catalysts, i.e., catalysts molecularly dispersed in the reaction system, like hydrochloric or sulfuric acid~ are used~ These are fairly corrosive and lead to the formation of by-products, especially of esters of the catalyst acid (e.g., halogenation products). Moreover, after the reaction, they require neutralization with subsequent desalting of the reaction mixture (Carbohydrate Chemistry, Vol. II, 191-193 (1963).
The use of organic solvents, which is well-known in this context, for removing t~e reaction water by azeotropic distillation results in only a small improvement in anhydro polyol yields Some o~ the disadvantages of the processes using acid catalysts dissolved in the reation mixture (e.g., the corrosion problem and the formation of excessive amounts o~ hard-to-separate esteri~ied by-products) may be avoided in a ~nown manner by the use of heterogeneous catalysts, such as cer-tain strongly acidic cation exchange resins. Unfortunately, this can result in several other disadvantages such as poorer anhydro polyol yields (up to 35%) and the need to use organic solvents as a reaction medium and entraining agents for the removal of water by azeotropic distillation. (See Ropuszynski et al~ in Przem. Chem. 1969, 48 (11), 665-8 and ~eisleder, et al. in Carbohydr. Res. _ ~ 133-141 ~1980).) As far as the need to use carefully selected organic solvents is concerned, it is mentioned in the last cited publication that in an assay carried out for comparison and aiming at the produc-tion of 1~4; 3,6-dianhydro-D-sorbitol from sorbitol by "dry distillation with the acidic resin" that a yield several times lower, i.e., only 5%, was obtained.
It is thus clear that the state of the art only per-mits a comparatively small segment out of the broad spectrum of relevant polyol mixtures to be produced as immediate re-action products. The majority of these mixtures, especially those with hydroxyl numbers in the mean and lower part of the theoretical range, can only be obtained from fractions enrichcd wit}l mono- and/or dianhydro polyols which are separated from the reactlon product mixtures by complicated separating procedures such as fractionating crystallization, distillation or chromatography. These mixtures are optionally blended to form polyol compositions of the desired hydroxyl numbers. Considering that the polyol mixtures are intended for use in the manufacture of synthetic resins, this pro-cedure is too complicated and costly.
It is an object of this invention to provide a process which overcomes the disadvantages of the prior art described above and which permits the production of a broad spectrum of polyol mixtures which in terms of hydroxyl number and ratio of sugar alcohol to monoanhydro polyol to dianhydrosugar alcohol almost completely covers the theoretical ranges.
Another object is to produce such `mixtures by an unc~mpli-cated and inexpensive process; directly by dehydration in the presence of acidic catalysts.
SUM~IARY OF THE INVEWTION
The objects o~ the invention have been accomplished on the basis of the surprising finding that water, ~hich in the known processes invariably has to be removed con-stantly and preferably completely, in reactions of the type in quest.ion not only ~ails to be disturbing but, on the contrary, even helps to obtain reaction product mixtures with higher contents of mono- ànd/or dianhydro polyols than had been possible according to the prior art reaction systems containing much smaller amounts of water. This is achieved by using heterogeneous catalysts and keeping the water concentration within the range defined below.
The polyols of the invention are selected from the group consisting of C4-C6 sugar alcohols, C4-C6 monoanhydro polyols and C4-C6 dianhydro polyols having the general formula~
.
R OH
>~~
R ~
where Rl is selected from the group consisting of hydroxyl and the ether oxygen atom of a second oxacyclopentane riny and ~2 is selected from the group consisting of hydrogen, hydroxymethyl, l,2-dihydroxyethyl and an alpha-hydroxyethylidelle radical t provided that when R2 is an alpha-hydroxyethylidene radical, Rl is an èther oxygen atom and the general ormula S of the polyol is as follows:
OE~
Y ':
OH
DETAILE~D DESCRIPTIOI~ OF THE INVENTION
The anhydro polyol containing polyol mixtures of the present invention are prepared by dehydrating sugar alcohols at elevated temperatures in the liquid phase and in the presence of a strongly acidic heterogeneous catalyst. Water content in the reaction mixture is controlled so that the maximum amount of water is 120% w/w by weight of sugar alcohols present~ The minimum amount is the reaction water liberated in the process.
The process of the invention permits the production of polyol mixtures with monoanhydro polyol contents of about 5 to 80% w/w and dianhydro polyol contents of about 90 to 5~ w/w (% ww referring to polyol solids). This is accomplished ~'7~
by a suitable selection of the reaction conditions, especially water concentration and reaction time.
The course of the reaction and the compositiOn o the re-action mixture depènd on a number of factors such as the composi-tion o the basic material, (apart from pure sugar alcohols it is possible to use sugar alcohol mixtures in the process of the invention) the catalyst, the reaction time and temperature, and especially the water content of the reaction mixture. Accordingly, a firm rule for selecting process conditions which would enable one skilled in the art to calculate optimum conditions for each individual case in advance in exact figures may not be given.
However, one skilled in the art will readily be able to determine the process conditions suitable or every desired polyol mixture within the scope of the invention by varying water content and reaction time based on some orienting tests and considering the following principles.
Reaction rates, as usual, increase rapidly with increas-ing temperatures. However, thermal stability of starting materials~ reaction products and/or catalysts set a limit to the acceleration of a reaction or, in other words, to the shortening of the reaction time by an increase in the reac-tion temperature. The reaction temperature, therefore, which can be from 60 to 200 C. r is generally kept within a range of 80 to 170 C. preferably 95 to 160 C. and most preferably z~
105 to 145 C~ As may be seen from the examples, temperatures from 120 to 145 C. have been found to be particularly suitable when polystyrene sulfonic acid cation exchanger resins in the H form, cross-linked with divinyl benzene (DVB), are used as catalysts.
Water in increasing concentrations slows down the reaction rate with respect to both the reaction of sugar alcohols to mono-anhydro polyols and the formation of dianhydro polyols from monoanhydro polyols. Surprisingly enough, the latter reaction is apparently retarded to a much greater extent than the former one. This is surprising because according to the prior art a prefera~ly complete removal, even of the reaction water, is indispensable for achieving at least fairly acceptable anhydro polyol yields. The reaction equilibrium neither regarding the reaction of sugar alcohols to monoanhydro polyols nor even with respect to the formation of dianhydro polyols by dehydration from monoanhydro polyols is shifted to the disadvantage of the compound with the lower water content to an extent large enough to prevent acceptable anhydro polyol yields from being obtained. On the contrary, the anhydro polyol yields achieved in the process of the invention in the presence of relatively high water concen-trations both for mono- (up to and over 80~ w/w) and especially for dianhydro polyols (up to and over about 90% w/w) clearly exceed the maximum values of about 40 and 66% w/w respectively (f ~
? ~J ~
which are given in the ~itera~ure for practically anhydrous systems. The effect on the process o the invention is that in reaction mixtures containing no or comparatively small amounts of added water of a few percentages, first the mono-and shortly afterwards also the dianhydro polyol content starts to increase rapidly. With increasiny reaction time the dianhydro polyo~ content continues to increase constantly and comparatively rapidly to ahout 90% w/w and even before the sugar alcohol has been widely consumed reaches remarkable valuesD The monoanhydro polyol content soon reaches a peak o~ about 4Q~ w/w and in the further course of the reaction fairly quickly drops to values around 5-10~ w/w (see Figure I).
In reaction mixtures containing larger amounts o~ added water, the forma-tion of anhydro polyol on the one hand is generally retarded and on the other hand is chansed in such a way that starting with an added water content of about 8 to 10% w/w the monoanhydro polyol content continues to increase constantly until the sugar alcohol has largely been consumed, reaching values up to and sometimes over 80% w/w~ Substantial amounts of dianhydro polyol start to form comparatively late (see e.g. Figure II).
The inference to be drawn from the above-~entioned course of reaction for the process of the invention is that for producing polyol mixtures with a comparatively low monoanhydro polyol content (at equal hydroxyl number) the reaction should most suitably be carried out in reaction systems containing no or only a small amount of added water, up to about 10~ w/w, while for the production of polyol mixtures with higher mono-anhydro polyol contents it is recommended to use larger amounts of added water~ more than about 10% w/w, especially if the desired hydroxyl number is situated ln the medium or lower section of the range of 810 to 1800 and if a monoanhydro polyol content over about 40 and es?ecially over 50% w/w is desired or the polyol mixture.
Normally amounts o added water of about 0.1 to 100, preferably 3 to 70 and r,lost preferably 8 to 50% w/w, with reference to the sugar alcohol weight, are appropriate.
The added water conten~ of the reaction mixture in the process of the invention may most suitably be kept constant by wor~ing under reflux conditions.
In certain cases, especially when polyol mixtures with extremely low sugar alcohol contents and hydroxyl numbers in the medium to lowex section of the range of 810 to 1800 or, in other words, with high contents of mono- and/or dianhydro polyols are to be produced, it is advisable to change the water content of the reaction mixture continuously or stepwise in the course of the reaction. Usually it is recommended to start the reac-tion with a relatively high water content, to lower the water concentration when the sugar alcohol content of the reaction mixture has dropped to a point close to the desired ultimate -- 10 -- .
value, and then to allow the reaction to continue at the reduced water content until the desired ratio of mono-to diahydro polyols is reached. This en~odiment oE the invention is advantageous mainly because it not only mades accessible polyol mixtures with monoanhydro polyol contents in the range of 35 to 90, preferably 40 to 85 and most preferably 50 to 80% w/w/ which normally and especially in those cases where a high ratio of mono- to diahydro polyols is equally desired require the presence of added water concentrations of 1 to 100, preferably 3 to 70 and most preferably 8 to 50~ w/w, reEerred to sugar alcohols, but compared to methods involvin~ constantly low or also high water concentrat.ions also permits a reduction in the thermal strain on the temperature-sensitive reaction mixture components and/or a reduction of the total reaction time.
The catalysts to be used in the invention in some cases show a rather limited thermal stability and it is therefore usually expedient to fully dry them before they are used.
However, the water introduced into the reaction system by moist catalysts is not detrimental, at least in the above-mentioned embodiment o~ the invention, even if polyol mixtures with extremely low sugar alcohol and extremely high dianhydro polyol contents are desired which are unobtainable with higher water contents, since this water may readily be removed as far as necessary in the course of the reaction, 7~3~
The same applies, by analogy, to excess water that may be introduced ~ith the sugar alcohol.
As already mentioned the process of the invention is advantageous for the production of polyol mixtures featuring hydroxyl numbers in the lower and in the medium section of the range of 810 to 1800 as well as sugar alcohol contents which have been greatly reduced compared to the starting material.
Therefore the reaction in the process of the invention is preferably allo~7ed to continue until the hydroxyl number of the resulting polyol mixture ranges between 1000 and 1600, preferably 1100 and 1500 and most preferably 1250 and 1400 and/or un~il the residual sugar alcohol content of the mixture reaches a maximum of 40, preferably less than 20 and most preerably less than 10% w/w-Reaction times in the process of the invention normally range between 0.1 and 50 hours. The optimum reaction time for each individual case is most suitably ascertained by preliminary trials. The narrower range of appropriate reac-tion times may usually be seen from the attached Figures I
or II in which the development of the reaction mixture compo-sition under conditions typical of the process of the invention (use of sorbitol as a starting material and of a strongly acidic macroporous polystyrene sulfonic acid cation exchanger resin in the H+ form as a catalyst as well as the presence of a reaction temperature of 125 C.~ has been shown graphically '7~
2t an added water concentration of 1% w/w (Fig. I) and 70%
w/w (Fig II) respectively.
Suitable heterogeneous catalysts for the process of the invention, apart from strongly acidic cation exchanger resins, are normally all kno~7n strongly acidic, solid catalysts of adequate heat stability and especially "acidic" molecular sieves such as zeolites as well as the crack and/or hydrocrack catalysts commonly employed in the mineral oil industry.
Tne latter are attractive for the purpose o~ the invention chiefly because they are widely used in the manufacture of hexitols by catalytic hydrogenation of the respective sugars, thus opening up the road to integrated processes ~or the pro-duction of the subject polyol mixtures from sugars in one or a few steps.
The best results so ~ar have been obtained with strongly acidic synthetic cation exchanger resins or, more particulaL-ly, with polystyrene sulfonic acid cation exchanger resins cross-linked with divinyl benzene. Suitable in this context are so-cal7ed gel resins cross-linked with only a small amount, i.e., maximum 4%, of divinyl benzene as ~7ell as macroporous resins hich should most suitably be cross-linked with a large amount, i.e., at least 10~ of divinyl benzene.
The catalysts in the process o~ the invention are separated from the reaction product mixture by simple solid/liquid sepa-rating methods, e.g., filtration. They may be reused several times without re~uiring any previous treatment.
In the process of the invention it is recommended in cer-tain cases, i~e., especially when relatively high reaction temperatures and long reaction times are involved, to conduct the reaction in an inert gas atmosphere to avoid oxidation reactions. The inert gas is most suitabLy bubbled through the reaction mixture~
It is also possible in the process of the invention to optionally use organic (auxiliary) solvents which are at least partly miscible with water and/or are distillable azeo-trcpically. This is oten advisable in those cases where relatively small amounts of water are refluxed~
It is also pointed out that the process of the invention, while frequently being carried out batchwise ~or the manu~ac-ture of larger amounts of polyol mixtures of specific composi-tions, may easily be carried out also according to known continuous methods, a two- or multistep process being usually recommended~
The process of the invention, as already mentioned, leads to polyol mixtures which distinguish themselves by unusually high monoanhydro polyol contents of at least 43, preferably at least 50 and most preferably at least 55% w/w at hydroxyl numbers ranging from 1030 to 1600 and which it would have been impossible to obtain from the known processes as immediate reaction products.
The examples will more clearly illustrate the invention and the advantages obtained from it by reference to sorbitol. In the process of the invention, sorbitol is preferred as starting material because it is the only sugar alcohol presently available as an industrial product at acceptable prices in almost unlimited amounts and to C4-C6 sugar alcohol mixtures obtained by catalytic hydrogenation of hemicellulose hydrolysates which are additional starting materials from which polyol mixtures having valuable properties can be obtained~
Unless otherwise indicated, all figures in percentages refer to weight.
Example 1 In a l-liter, three-necked flask 250 g sorbitol and 20 g of a strongly acidic ion exchanger in the H+ form (macroporous polystyrene sulfonic acid resint cross-linked with 14% DVB) was stirred ~or one hour under reflux conditions at 125 C. The amount of water introduced by the reagents was a~out 2 g, corresponding to 0.8~ relative to sorbitolO ~fter the reaction solution was filtered from the catalyst and the reaction water distilled off, 233 g of a polyol mixture was obtained which con-tained 79~O sorbitol, 15o monoanhydrosorbitol and 6% dianhydro-sorbitol. The hydroxyl number of the mixture was 1711.
Example 2 Example 1 was repeated, except that filtration znd con-centration took place after a reaction time of 3 hours. 214 q of a polyol mixture of the following composition was obtained:
31% sorbi~ol~ 35% monoanhydrosorbitol, 33% dianhydrosorbitol.
The hydroxyl number was 1319.
Example 3 Example 2 was repeated with a reaction time extended to 4 hours. 206 g of a polyol mixture consisting of 10%
sorbitol, 40% monoanhydrosorbitol and 50% dianhydrosorbitol was obtained. The hydroxyl number of the mixture was 1116.
Example 4 Example 3 was repeated with a reaction time extended to 5 hours. After filtration and distillation, 197 g oE a mix-ture of 1% sorbitol, 28% monoanhydrosorbitol ana 71% dianhy-drosorbitol with the hydroxyl number 946 was obtainedO
Example 5 Example 4 was repeated with a reaction time extended to 7 hours. A polyol mixture, 192 g, consisting of 9% monoanhy-drosorbitol and 91% dianhydrosorbitol with a hydroxyl numberof 822 was obtained.
- 16 ~
~ 7~3 Ex~mple 6 In a l~ er, three-nec~ed flask 250 g sorbitol was reacted with 28 9 water and 20 g of the ion exchanger described in Example 1 and stirred fo~ 1 hour at 125 C. under reflux con-S ditions. Water content was 12%, relative to sorbitol. Theresulting product was filtered from the cata:Lyst and concen-trated. 227 9 of a polyol mixture of 55% sorbitol, 40% mono-anhydrosorbitol and 5% dianhydrosorbitol ~as obtained. The hydroxyl number of the mixture was 1602.
Example 7 Example G was repeated, except that filtration and con~
centration took place after a reaction time of 2 hours. 222 g of a polyol mixture of the following composition was obtained:
40~ sorbitol, 50~ monoanhydrosorbil:ol and 10% dianhydrosorbitol.
The hydroxyl number was lS00, Example 8 Example 7 was repeated with a reaction time extended to 3 hours. 216 9 of a polyol mixture consisting of 20%
sorbitol, 65% monoanhydrosorbitol and 15% dianhy~rosorbitol with a hydroxyl nurnber of 1374 was obtained.
Exam~le 9 Example 8 was repeated witl a reaction time extended to 4 hours. After filtration and distillation, 207 g of a `I ~ 17~2~3~
polyol mixture consis~ing o 5% sorbitol, 60% monoanhydro-sorbitol and 35~ dianhydro50rbitol with a hydroxyl number o~
1182 was obtained.
Example lQ
In a l-liter, three-necked flask 357 9 o~ a 70~ aqueous sorbitol solution was reacted with 20 g of the catalyst des-cribed in Example 1 and was stirred for 5 hours under reflux conditions at 125G C. Water content was 43%, relative to sorbitol. The resulting reaction mixture was filtered from the catalyst and concentrated. 232 g of a polyol mixture containing 70% sorbitol and 30~ monoanhydrosorbitol was ob-tained. The hydroxyl number was 1704.
Example 11 Example 10 was repeated, except that the stirring time at 125 C. under reflux conditions was 10 hours. After fil-tration and concentration, a polyol mixture of 45% sorbitol, 50~ monoanhydrosorbitol and 5% dianhydrosorbitol having a hydroxyl number of 1554 was obtained. The yield was 225 9.
Ex~mple 12 Example 11 was repeated with a reaction time of 15 hours. The resulting polyol mixture (221 g) consisted of 35~ sorbitol, 57~ monoanhydrosorbitol and 8~ dianhydrosor-bitol and showed a hydroxyl number of 1488.
E~ample 13 Example 12 was repeated with a reaction time of 20 hours.
217 g of a polyol mixture of 20~ sorbitol, 70~ monoanhydro-sorbitol and 10% dianhydrosorbitol having a hydroxyl number of 1404 was obtained.
Example 14 In a 1 liter, three-nec~ed flask 250 9 sorbitol was stirred together witn 167 g water and 20 g of the catalyst mentioned in Example 1 for 10 hours under reflux conditions at :L25 C.
Water content was 67~ relative to sorbitol. The reaction mix-ture was filtered from the catalyst and evaporated under vacuum. 233 9 of a polyol mixture of 72% sorbitol and 28%
monoanhydrosorbitol having a hydroxyl number of 1714 was obtained.
Example 15 Example 14 was repeated with a reaction time of 20 hours.
After filtration and concentration, 225 g of a polyol mixture of 4~% sorbitol, 52% monoanhydrosorbitol and 4% dianhydrosorbi-tol was obtainedO The hydroxyl number was 1556.
Example 16 Example 15 was repeated with a reaction time of 30 hours.
218 g of a polyol mixture of 21% sorbitol, 72% monoanhydro-~ 7~
sorbitol and 7Q dianhydrosorbitol with a hydroxyl number of 1427 was obtained.
E~ample 17 Example 16 was repeated with a reaction time of 40 hours. 210 g of a polyol mixture of 86~ monoanhydrosorbi-tol and 14~ dianhydrosorbitol with a hydroxyl number of 1284 was obtained.
Exaniple 18 In a l-liter three-necked flask 250 9 of a catalytically hydrogenated hemicellulose hydrolysate obtained from corn shells and 20 g of a strongly acidic ion exchanger in the H+ orm tpolystyrene sulfonic acid-gel resin, 2 % DVB
cross-linked) were placed and stirred 2 hours at 130 C under refluxing.
The water content of the solution had been adjusted to 10 ~, The resulting melt was removed from the ion exchanger by filtering while hot, dissolved in water and treated with active carbon. After filtration and concentration 235 g of a product were obtained having a hydroxyl number of 1658 in comparison to a hydroxyl number of 1790 of the starting material.
~7~
A H LC-examination sho~ed that the polyols present in the ra~Y material (ca~ 75 g pentitol, from which more than 55 % con-sisted of xylitol, sorbitol and gallactitol) had been converted into anhydroderivatives in an extent of 22 gO~
Example 19 The above example was repeated wi~h a reaction time of 4 hours~ 197 g of the product having a hydroxyl number of 1115 were obtained. 85 % o the polyol had been converted to anhydro polyols~
Exam~le 20 The preceding example was repeated with a reaction time o~
6 hours. A gel resin being cross-linked with 10 % DV3 was used as catalyst~
193 g of the product having a hydroxyl number of 1080 were obtained.
A HPLC-examination showed that more than 9~ ~ of the pol~ols of the raw material have been converted to anhydropolyols.
Exam~le 21 ,.
The example 18 was repeated with the exception that a water content of the reaction solution o 19 % ~zs adjusted, and a macroporous polystyrene sulfonic acia resin cross-linked with 20 DVB was used as catalyst.
236 g o the product havlng a hydroxyl number of 1732 were obtained A HPLC-exarnination revealed a conversion of approximately 11 % of the polyols to anhydropolyols.
Example 22 The example 21 was repeated with a reaction time of 4 hours.
227 g of a product having a hydroxyl number of 1515 were ob-tained. 38 % of the polyols were conver~ed to anhydropoIyols.
Example 23 lQ The example 22 was repeated with a reaction time o 6 hours.
210 g of a product having a hydroxyl number of 13?7 were obtai.ned, 60 % of the polyols were converted to anhydropolyols.
Example 24 The example 22 was repeated with a reaction time of 8 hours, 191 g of a product having a hydroxyl number of 1113 were obtained, 87 ~ of the polyols were converted to anhydropolyols.
Having set forth the general nature and some specific examples of the present invention, the scope is now parti-cularly set forth in the appended claims.
32~ 3259 PROCESS FOR PREPARING
.
ANHYDRO POLYOL CONTAINING POLYOL ~IIXTURES
BACKGROlJND OF THE INVENTION
Field of the Invention The present invention relates to a process for pre paring mixtures of polyols containing two or more polyols, selected from ~he ~roup consisting of C4-C6 sugar alcohols, C4-C6 monoanhydro polyols and C4-C6 dianhydro polyols.
The Prior Art _ Sugar alcohols such as, for example, hexitols, monoanh~dro-hexitols, dianhydrohexitols and mixtures thereof are generally known. They are used as basic materials or intermediates for chemical syntheses, especially o Eine chemicals, ester-based emulsiiers, polyester and alkyd resins~ and polyurethanes. An important criterion in the use o these polyols in the manufac-ture of synthetic resins, apart from the type of polyols or polyol mixturesr is their hydroxyl number, ~7hich theoretically may be varied from 1848 for pure hexitols to 768 for pure dianhydrohexitols.
Practically pure sugar alcohols may be obtained by cata-lytic hydrogenation of the respective sugar. However, the known processes for the production of anhydro polyols or of polyol mixtures containing such compounds by dehydration from sugar alcohols at elevated temperature in the presence of acidic catalysts merely yield mix~ures with a rather limited content of dianhydrosugar alcohol (about 66% maximum) and monoanhydrosugar alcohol (about 40~ maximum). These processes, moreover, do not permit the ratio in which the various polyols are pre~sent in the reaction mixture to be significan~ly changed for a given hydroxyl number. Only insignificant changes can be effected by selecting process parameters, especially catalyst, temperature, reaction medium and/or reaction time. This is especially so for ones in the range of medium and low hydroxyl numbers.
Another aspect of the prior art is that comparatively high di- and monoanhydrosugar alcohol yields may be obtained only if so called homogeneous catalysts, i.e., catalysts molecularly dispersed in the reaction system, like hydrochloric or sulfuric acid~ are used~ These are fairly corrosive and lead to the formation of by-products, especially of esters of the catalyst acid (e.g., halogenation products). Moreover, after the reaction, they require neutralization with subsequent desalting of the reaction mixture (Carbohydrate Chemistry, Vol. II, 191-193 (1963).
The use of organic solvents, which is well-known in this context, for removing t~e reaction water by azeotropic distillation results in only a small improvement in anhydro polyol yields Some o~ the disadvantages of the processes using acid catalysts dissolved in the reation mixture (e.g., the corrosion problem and the formation of excessive amounts o~ hard-to-separate esteri~ied by-products) may be avoided in a ~nown manner by the use of heterogeneous catalysts, such as cer-tain strongly acidic cation exchange resins. Unfortunately, this can result in several other disadvantages such as poorer anhydro polyol yields (up to 35%) and the need to use organic solvents as a reaction medium and entraining agents for the removal of water by azeotropic distillation. (See Ropuszynski et al~ in Przem. Chem. 1969, 48 (11), 665-8 and ~eisleder, et al. in Carbohydr. Res. _ ~ 133-141 ~1980).) As far as the need to use carefully selected organic solvents is concerned, it is mentioned in the last cited publication that in an assay carried out for comparison and aiming at the produc-tion of 1~4; 3,6-dianhydro-D-sorbitol from sorbitol by "dry distillation with the acidic resin" that a yield several times lower, i.e., only 5%, was obtained.
It is thus clear that the state of the art only per-mits a comparatively small segment out of the broad spectrum of relevant polyol mixtures to be produced as immediate re-action products. The majority of these mixtures, especially those with hydroxyl numbers in the mean and lower part of the theoretical range, can only be obtained from fractions enrichcd wit}l mono- and/or dianhydro polyols which are separated from the reactlon product mixtures by complicated separating procedures such as fractionating crystallization, distillation or chromatography. These mixtures are optionally blended to form polyol compositions of the desired hydroxyl numbers. Considering that the polyol mixtures are intended for use in the manufacture of synthetic resins, this pro-cedure is too complicated and costly.
It is an object of this invention to provide a process which overcomes the disadvantages of the prior art described above and which permits the production of a broad spectrum of polyol mixtures which in terms of hydroxyl number and ratio of sugar alcohol to monoanhydro polyol to dianhydrosugar alcohol almost completely covers the theoretical ranges.
Another object is to produce such `mixtures by an unc~mpli-cated and inexpensive process; directly by dehydration in the presence of acidic catalysts.
SUM~IARY OF THE INVEWTION
The objects o~ the invention have been accomplished on the basis of the surprising finding that water, ~hich in the known processes invariably has to be removed con-stantly and preferably completely, in reactions of the type in quest.ion not only ~ails to be disturbing but, on the contrary, even helps to obtain reaction product mixtures with higher contents of mono- ànd/or dianhydro polyols than had been possible according to the prior art reaction systems containing much smaller amounts of water. This is achieved by using heterogeneous catalysts and keeping the water concentration within the range defined below.
The polyols of the invention are selected from the group consisting of C4-C6 sugar alcohols, C4-C6 monoanhydro polyols and C4-C6 dianhydro polyols having the general formula~
.
R OH
>~~
R ~
where Rl is selected from the group consisting of hydroxyl and the ether oxygen atom of a second oxacyclopentane riny and ~2 is selected from the group consisting of hydrogen, hydroxymethyl, l,2-dihydroxyethyl and an alpha-hydroxyethylidelle radical t provided that when R2 is an alpha-hydroxyethylidene radical, Rl is an èther oxygen atom and the general ormula S of the polyol is as follows:
OE~
Y ':
OH
DETAILE~D DESCRIPTIOI~ OF THE INVENTION
The anhydro polyol containing polyol mixtures of the present invention are prepared by dehydrating sugar alcohols at elevated temperatures in the liquid phase and in the presence of a strongly acidic heterogeneous catalyst. Water content in the reaction mixture is controlled so that the maximum amount of water is 120% w/w by weight of sugar alcohols present~ The minimum amount is the reaction water liberated in the process.
The process of the invention permits the production of polyol mixtures with monoanhydro polyol contents of about 5 to 80% w/w and dianhydro polyol contents of about 90 to 5~ w/w (% ww referring to polyol solids). This is accomplished ~'7~
by a suitable selection of the reaction conditions, especially water concentration and reaction time.
The course of the reaction and the compositiOn o the re-action mixture depènd on a number of factors such as the composi-tion o the basic material, (apart from pure sugar alcohols it is possible to use sugar alcohol mixtures in the process of the invention) the catalyst, the reaction time and temperature, and especially the water content of the reaction mixture. Accordingly, a firm rule for selecting process conditions which would enable one skilled in the art to calculate optimum conditions for each individual case in advance in exact figures may not be given.
However, one skilled in the art will readily be able to determine the process conditions suitable or every desired polyol mixture within the scope of the invention by varying water content and reaction time based on some orienting tests and considering the following principles.
Reaction rates, as usual, increase rapidly with increas-ing temperatures. However, thermal stability of starting materials~ reaction products and/or catalysts set a limit to the acceleration of a reaction or, in other words, to the shortening of the reaction time by an increase in the reac-tion temperature. The reaction temperature, therefore, which can be from 60 to 200 C. r is generally kept within a range of 80 to 170 C. preferably 95 to 160 C. and most preferably z~
105 to 145 C~ As may be seen from the examples, temperatures from 120 to 145 C. have been found to be particularly suitable when polystyrene sulfonic acid cation exchanger resins in the H form, cross-linked with divinyl benzene (DVB), are used as catalysts.
Water in increasing concentrations slows down the reaction rate with respect to both the reaction of sugar alcohols to mono-anhydro polyols and the formation of dianhydro polyols from monoanhydro polyols. Surprisingly enough, the latter reaction is apparently retarded to a much greater extent than the former one. This is surprising because according to the prior art a prefera~ly complete removal, even of the reaction water, is indispensable for achieving at least fairly acceptable anhydro polyol yields. The reaction equilibrium neither regarding the reaction of sugar alcohols to monoanhydro polyols nor even with respect to the formation of dianhydro polyols by dehydration from monoanhydro polyols is shifted to the disadvantage of the compound with the lower water content to an extent large enough to prevent acceptable anhydro polyol yields from being obtained. On the contrary, the anhydro polyol yields achieved in the process of the invention in the presence of relatively high water concen-trations both for mono- (up to and over 80~ w/w) and especially for dianhydro polyols (up to and over about 90% w/w) clearly exceed the maximum values of about 40 and 66% w/w respectively (f ~
? ~J ~
which are given in the ~itera~ure for practically anhydrous systems. The effect on the process o the invention is that in reaction mixtures containing no or comparatively small amounts of added water of a few percentages, first the mono-and shortly afterwards also the dianhydro polyol content starts to increase rapidly. With increasiny reaction time the dianhydro polyo~ content continues to increase constantly and comparatively rapidly to ahout 90% w/w and even before the sugar alcohol has been widely consumed reaches remarkable valuesD The monoanhydro polyol content soon reaches a peak o~ about 4Q~ w/w and in the further course of the reaction fairly quickly drops to values around 5-10~ w/w (see Figure I).
In reaction mixtures containing larger amounts o~ added water, the forma-tion of anhydro polyol on the one hand is generally retarded and on the other hand is chansed in such a way that starting with an added water content of about 8 to 10% w/w the monoanhydro polyol content continues to increase constantly until the sugar alcohol has largely been consumed, reaching values up to and sometimes over 80% w/w~ Substantial amounts of dianhydro polyol start to form comparatively late (see e.g. Figure II).
The inference to be drawn from the above-~entioned course of reaction for the process of the invention is that for producing polyol mixtures with a comparatively low monoanhydro polyol content (at equal hydroxyl number) the reaction should most suitably be carried out in reaction systems containing no or only a small amount of added water, up to about 10~ w/w, while for the production of polyol mixtures with higher mono-anhydro polyol contents it is recommended to use larger amounts of added water~ more than about 10% w/w, especially if the desired hydroxyl number is situated ln the medium or lower section of the range of 810 to 1800 and if a monoanhydro polyol content over about 40 and es?ecially over 50% w/w is desired or the polyol mixture.
Normally amounts o added water of about 0.1 to 100, preferably 3 to 70 and r,lost preferably 8 to 50% w/w, with reference to the sugar alcohol weight, are appropriate.
The added water conten~ of the reaction mixture in the process of the invention may most suitably be kept constant by wor~ing under reflux conditions.
In certain cases, especially when polyol mixtures with extremely low sugar alcohol contents and hydroxyl numbers in the medium to lowex section of the range of 810 to 1800 or, in other words, with high contents of mono- and/or dianhydro polyols are to be produced, it is advisable to change the water content of the reaction mixture continuously or stepwise in the course of the reaction. Usually it is recommended to start the reac-tion with a relatively high water content, to lower the water concentration when the sugar alcohol content of the reaction mixture has dropped to a point close to the desired ultimate -- 10 -- .
value, and then to allow the reaction to continue at the reduced water content until the desired ratio of mono-to diahydro polyols is reached. This en~odiment oE the invention is advantageous mainly because it not only mades accessible polyol mixtures with monoanhydro polyol contents in the range of 35 to 90, preferably 40 to 85 and most preferably 50 to 80% w/w/ which normally and especially in those cases where a high ratio of mono- to diahydro polyols is equally desired require the presence of added water concentrations of 1 to 100, preferably 3 to 70 and most preferably 8 to 50~ w/w, reEerred to sugar alcohols, but compared to methods involvin~ constantly low or also high water concentrat.ions also permits a reduction in the thermal strain on the temperature-sensitive reaction mixture components and/or a reduction of the total reaction time.
The catalysts to be used in the invention in some cases show a rather limited thermal stability and it is therefore usually expedient to fully dry them before they are used.
However, the water introduced into the reaction system by moist catalysts is not detrimental, at least in the above-mentioned embodiment o~ the invention, even if polyol mixtures with extremely low sugar alcohol and extremely high dianhydro polyol contents are desired which are unobtainable with higher water contents, since this water may readily be removed as far as necessary in the course of the reaction, 7~3~
The same applies, by analogy, to excess water that may be introduced ~ith the sugar alcohol.
As already mentioned the process of the invention is advantageous for the production of polyol mixtures featuring hydroxyl numbers in the lower and in the medium section of the range of 810 to 1800 as well as sugar alcohol contents which have been greatly reduced compared to the starting material.
Therefore the reaction in the process of the invention is preferably allo~7ed to continue until the hydroxyl number of the resulting polyol mixture ranges between 1000 and 1600, preferably 1100 and 1500 and most preferably 1250 and 1400 and/or un~il the residual sugar alcohol content of the mixture reaches a maximum of 40, preferably less than 20 and most preerably less than 10% w/w-Reaction times in the process of the invention normally range between 0.1 and 50 hours. The optimum reaction time for each individual case is most suitably ascertained by preliminary trials. The narrower range of appropriate reac-tion times may usually be seen from the attached Figures I
or II in which the development of the reaction mixture compo-sition under conditions typical of the process of the invention (use of sorbitol as a starting material and of a strongly acidic macroporous polystyrene sulfonic acid cation exchanger resin in the H+ form as a catalyst as well as the presence of a reaction temperature of 125 C.~ has been shown graphically '7~
2t an added water concentration of 1% w/w (Fig. I) and 70%
w/w (Fig II) respectively.
Suitable heterogeneous catalysts for the process of the invention, apart from strongly acidic cation exchanger resins, are normally all kno~7n strongly acidic, solid catalysts of adequate heat stability and especially "acidic" molecular sieves such as zeolites as well as the crack and/or hydrocrack catalysts commonly employed in the mineral oil industry.
Tne latter are attractive for the purpose o~ the invention chiefly because they are widely used in the manufacture of hexitols by catalytic hydrogenation of the respective sugars, thus opening up the road to integrated processes ~or the pro-duction of the subject polyol mixtures from sugars in one or a few steps.
The best results so ~ar have been obtained with strongly acidic synthetic cation exchanger resins or, more particulaL-ly, with polystyrene sulfonic acid cation exchanger resins cross-linked with divinyl benzene. Suitable in this context are so-cal7ed gel resins cross-linked with only a small amount, i.e., maximum 4%, of divinyl benzene as ~7ell as macroporous resins hich should most suitably be cross-linked with a large amount, i.e., at least 10~ of divinyl benzene.
The catalysts in the process o~ the invention are separated from the reaction product mixture by simple solid/liquid sepa-rating methods, e.g., filtration. They may be reused several times without re~uiring any previous treatment.
In the process of the invention it is recommended in cer-tain cases, i~e., especially when relatively high reaction temperatures and long reaction times are involved, to conduct the reaction in an inert gas atmosphere to avoid oxidation reactions. The inert gas is most suitabLy bubbled through the reaction mixture~
It is also possible in the process of the invention to optionally use organic (auxiliary) solvents which are at least partly miscible with water and/or are distillable azeo-trcpically. This is oten advisable in those cases where relatively small amounts of water are refluxed~
It is also pointed out that the process of the invention, while frequently being carried out batchwise ~or the manu~ac-ture of larger amounts of polyol mixtures of specific composi-tions, may easily be carried out also according to known continuous methods, a two- or multistep process being usually recommended~
The process of the invention, as already mentioned, leads to polyol mixtures which distinguish themselves by unusually high monoanhydro polyol contents of at least 43, preferably at least 50 and most preferably at least 55% w/w at hydroxyl numbers ranging from 1030 to 1600 and which it would have been impossible to obtain from the known processes as immediate reaction products.
The examples will more clearly illustrate the invention and the advantages obtained from it by reference to sorbitol. In the process of the invention, sorbitol is preferred as starting material because it is the only sugar alcohol presently available as an industrial product at acceptable prices in almost unlimited amounts and to C4-C6 sugar alcohol mixtures obtained by catalytic hydrogenation of hemicellulose hydrolysates which are additional starting materials from which polyol mixtures having valuable properties can be obtained~
Unless otherwise indicated, all figures in percentages refer to weight.
Example 1 In a l-liter, three-necked flask 250 g sorbitol and 20 g of a strongly acidic ion exchanger in the H+ form (macroporous polystyrene sulfonic acid resint cross-linked with 14% DVB) was stirred ~or one hour under reflux conditions at 125 C. The amount of water introduced by the reagents was a~out 2 g, corresponding to 0.8~ relative to sorbitolO ~fter the reaction solution was filtered from the catalyst and the reaction water distilled off, 233 g of a polyol mixture was obtained which con-tained 79~O sorbitol, 15o monoanhydrosorbitol and 6% dianhydro-sorbitol. The hydroxyl number of the mixture was 1711.
Example 2 Example 1 was repeated, except that filtration znd con-centration took place after a reaction time of 3 hours. 214 q of a polyol mixture of the following composition was obtained:
31% sorbi~ol~ 35% monoanhydrosorbitol, 33% dianhydrosorbitol.
The hydroxyl number was 1319.
Example 3 Example 2 was repeated with a reaction time extended to 4 hours. 206 g of a polyol mixture consisting of 10%
sorbitol, 40% monoanhydrosorbitol and 50% dianhydrosorbitol was obtained. The hydroxyl number of the mixture was 1116.
Example 4 Example 3 was repeated with a reaction time extended to 5 hours. After filtration and distillation, 197 g oE a mix-ture of 1% sorbitol, 28% monoanhydrosorbitol ana 71% dianhy-drosorbitol with the hydroxyl number 946 was obtainedO
Example 5 Example 4 was repeated with a reaction time extended to 7 hours. A polyol mixture, 192 g, consisting of 9% monoanhy-drosorbitol and 91% dianhydrosorbitol with a hydroxyl numberof 822 was obtained.
- 16 ~
~ 7~3 Ex~mple 6 In a l~ er, three-nec~ed flask 250 g sorbitol was reacted with 28 9 water and 20 g of the ion exchanger described in Example 1 and stirred fo~ 1 hour at 125 C. under reflux con-S ditions. Water content was 12%, relative to sorbitol. Theresulting product was filtered from the cata:Lyst and concen-trated. 227 9 of a polyol mixture of 55% sorbitol, 40% mono-anhydrosorbitol and 5% dianhydrosorbitol ~as obtained. The hydroxyl number of the mixture was 1602.
Example 7 Example G was repeated, except that filtration and con~
centration took place after a reaction time of 2 hours. 222 g of a polyol mixture of the following composition was obtained:
40~ sorbitol, 50~ monoanhydrosorbil:ol and 10% dianhydrosorbitol.
The hydroxyl number was lS00, Example 8 Example 7 was repeated with a reaction time extended to 3 hours. 216 9 of a polyol mixture consisting of 20%
sorbitol, 65% monoanhydrosorbitol and 15% dianhy~rosorbitol with a hydroxyl nurnber of 1374 was obtained.
Exam~le 9 Example 8 was repeated witl a reaction time extended to 4 hours. After filtration and distillation, 207 g of a `I ~ 17~2~3~
polyol mixture consis~ing o 5% sorbitol, 60% monoanhydro-sorbitol and 35~ dianhydro50rbitol with a hydroxyl number o~
1182 was obtained.
Example lQ
In a l-liter, three-necked flask 357 9 o~ a 70~ aqueous sorbitol solution was reacted with 20 g of the catalyst des-cribed in Example 1 and was stirred for 5 hours under reflux conditions at 125G C. Water content was 43%, relative to sorbitol. The resulting reaction mixture was filtered from the catalyst and concentrated. 232 g of a polyol mixture containing 70% sorbitol and 30~ monoanhydrosorbitol was ob-tained. The hydroxyl number was 1704.
Example 11 Example 10 was repeated, except that the stirring time at 125 C. under reflux conditions was 10 hours. After fil-tration and concentration, a polyol mixture of 45% sorbitol, 50~ monoanhydrosorbitol and 5% dianhydrosorbitol having a hydroxyl number of 1554 was obtained. The yield was 225 9.
Ex~mple 12 Example 11 was repeated with a reaction time of 15 hours. The resulting polyol mixture (221 g) consisted of 35~ sorbitol, 57~ monoanhydrosorbitol and 8~ dianhydrosor-bitol and showed a hydroxyl number of 1488.
E~ample 13 Example 12 was repeated with a reaction time of 20 hours.
217 g of a polyol mixture of 20~ sorbitol, 70~ monoanhydro-sorbitol and 10% dianhydrosorbitol having a hydroxyl number of 1404 was obtained.
Example 14 In a 1 liter, three-nec~ed flask 250 9 sorbitol was stirred together witn 167 g water and 20 g of the catalyst mentioned in Example 1 for 10 hours under reflux conditions at :L25 C.
Water content was 67~ relative to sorbitol. The reaction mix-ture was filtered from the catalyst and evaporated under vacuum. 233 9 of a polyol mixture of 72% sorbitol and 28%
monoanhydrosorbitol having a hydroxyl number of 1714 was obtained.
Example 15 Example 14 was repeated with a reaction time of 20 hours.
After filtration and concentration, 225 g of a polyol mixture of 4~% sorbitol, 52% monoanhydrosorbitol and 4% dianhydrosorbi-tol was obtainedO The hydroxyl number was 1556.
Example 16 Example 15 was repeated with a reaction time of 30 hours.
218 g of a polyol mixture of 21% sorbitol, 72% monoanhydro-~ 7~
sorbitol and 7Q dianhydrosorbitol with a hydroxyl number of 1427 was obtained.
E~ample 17 Example 16 was repeated with a reaction time of 40 hours. 210 g of a polyol mixture of 86~ monoanhydrosorbi-tol and 14~ dianhydrosorbitol with a hydroxyl number of 1284 was obtained.
Exaniple 18 In a l-liter three-necked flask 250 9 of a catalytically hydrogenated hemicellulose hydrolysate obtained from corn shells and 20 g of a strongly acidic ion exchanger in the H+ orm tpolystyrene sulfonic acid-gel resin, 2 % DVB
cross-linked) were placed and stirred 2 hours at 130 C under refluxing.
The water content of the solution had been adjusted to 10 ~, The resulting melt was removed from the ion exchanger by filtering while hot, dissolved in water and treated with active carbon. After filtration and concentration 235 g of a product were obtained having a hydroxyl number of 1658 in comparison to a hydroxyl number of 1790 of the starting material.
~7~
A H LC-examination sho~ed that the polyols present in the ra~Y material (ca~ 75 g pentitol, from which more than 55 % con-sisted of xylitol, sorbitol and gallactitol) had been converted into anhydroderivatives in an extent of 22 gO~
Example 19 The above example was repeated wi~h a reaction time of 4 hours~ 197 g of the product having a hydroxyl number of 1115 were obtained. 85 % o the polyol had been converted to anhydro polyols~
Exam~le 20 The preceding example was repeated with a reaction time o~
6 hours. A gel resin being cross-linked with 10 % DV3 was used as catalyst~
193 g of the product having a hydroxyl number of 1080 were obtained.
A HPLC-examination showed that more than 9~ ~ of the pol~ols of the raw material have been converted to anhydropolyols.
Exam~le 21 ,.
The example 18 was repeated with the exception that a water content of the reaction solution o 19 % ~zs adjusted, and a macroporous polystyrene sulfonic acia resin cross-linked with 20 DVB was used as catalyst.
236 g o the product havlng a hydroxyl number of 1732 were obtained A HPLC-exarnination revealed a conversion of approximately 11 % of the polyols to anhydropolyols.
Example 22 The example 21 was repeated with a reaction time of 4 hours.
227 g of a product having a hydroxyl number of 1515 were ob-tained. 38 % of the polyols were conver~ed to anhydropoIyols.
Example 23 lQ The example 22 was repeated with a reaction time o 6 hours.
210 g of a product having a hydroxyl number of 13?7 were obtai.ned, 60 % of the polyols were converted to anhydropolyols.
Example 24 The example 22 was repeated with a reaction time of 8 hours, 191 g of a product having a hydroxyl number of 1113 were obtained, 87 ~ of the polyols were converted to anhydropolyols.
Having set forth the general nature and some specific examples of the present invention, the scope is now parti-cularly set forth in the appended claims.
Claims (17)
1. A process for preparing polyol mixtures containing two or more polyols having different molecular weights selected from the group consisting of C4-C6 sugar alcohols, C4-C6 monoanhydro polyols and C4-C6 dianhydro polyols wherein said polyols have the general formula:
where R1 is selected from the group consisting of hydroxyl and the ether oxygen atom of a second oxacyclopentane ring and R2 is selected from the group consisting of hydrogen, hydroxymethyl, 1,2-dihydroxyethyl and an alpha-hydroxyethylidene radical, provided that when R2 is an alpha-hydroxyethylidene radical, R1 is an ether oxygen atom and the general formula is as follows:
comprising dehydrating C4-C6 sugar alcohols in the liquid phase and in the presence of a strongly acidic heterogeneous catalyst wherein the reaction is carried out (a) in the presence of water in an amount which corres-ponds to at least the amount of reaction water liberated in the reaction up to a maximum of 120%
w/w of added water by the weight of the polyols, (b) at a temperature between 60 and 200° C., and (c) with a reaction time which is selected so that the hydroxyl number of the polyol mixture obtained is from 810 to 1800.
where R1 is selected from the group consisting of hydroxyl and the ether oxygen atom of a second oxacyclopentane ring and R2 is selected from the group consisting of hydrogen, hydroxymethyl, 1,2-dihydroxyethyl and an alpha-hydroxyethylidene radical, provided that when R2 is an alpha-hydroxyethylidene radical, R1 is an ether oxygen atom and the general formula is as follows:
comprising dehydrating C4-C6 sugar alcohols in the liquid phase and in the presence of a strongly acidic heterogeneous catalyst wherein the reaction is carried out (a) in the presence of water in an amount which corres-ponds to at least the amount of reaction water liberated in the reaction up to a maximum of 120%
w/w of added water by the weight of the polyols, (b) at a temperature between 60 and 200° C., and (c) with a reaction time which is selected so that the hydroxyl number of the polyol mixture obtained is from 810 to 1800.
2. The process of claim 1 wherein the reaction is con-tinued until the hydroxyl number of the resulting polyol mix-ture is from 1000 to 1600.
3. The process of claim 1 wherein the reaction is con-tinued until the hydroxyl number of the resulting polyol mix-ture is from 1100 to 1500.
4. The process of claim 1 wherein the reaction is con-tinued until the hydroxyl number of the resulting polyol mix-ture is from 1150 to 1400.
5. The process of claim 1 wherein the reaction is con-tinued until the hexitol content of the resulting polyol mix-ture is from about 5% to about 40% w/w.
6. The process of claim 1 wherein the reaction is car-ried out in the presence of water in an amount which corres-ponds to the amount of reaction water plus 0.1 to 100% W/W
added water relative to polyols present.
added water relative to polyols present.
7. The process of claim 1 wherein the reaction is per-formed at a temperature ranging from 80 to 170° C.
8. The process of claim 1 wherein the reaction is per-formed at a temperature ranging from 105 to 145° C.
9. The process of claim 1 wherein the catalyst is selected from the group consisting of a strongly acidic cation exchanger resin, strongly acidic inorganic molecular sieve, and an acidic crack or hydrocrack catalyst.
10. The process of claim 9 wherein a polystyrene sul-fonic acid cation exchanger resin in the H+ form, cross-linked with divinyl benzene, is used as the catalyst.
11. The process of claim 1 characterized in that the reaction is carried out in an inert gas atmosphere, the inert gas being bubbled through the reaction mixture.
12. The process of claim 1 wherein the reaction is carried out at least partly under reflux conditions.
13. The process of claim 1 wherein an organic sol-vent is used, which is at least partly miscible with water and is distillable azeotropically.
14. The process of claim 1 wherein the starting mate-rial is selected from the group consisting of sorbitol or a sorbitol-containing hexitol mixture.
15. The process of claim 1 wherein the reaction mix-ture has been adjusted to a water content corresponding to an added water concentration of 1 to 100% w/w relative to polyols present and is allowed to react for a period suffi-ciently long to ensure that its monoanhydrohexitol content, relative to polyol solids, amounts to between 35 and 90% w/w and the weight ratio of mono- to dianhydrohexltol ranges from 9:1 to 1:2.8.
16. The process of claim 1 wherein the reaction is per-formed continuously in two or more steps.
17. The process of claim 1 wherein the starting materials are selected from the group consisting of sorbitol, a sorbitol containing hexitol mixture, at least two different C4-C6 sugar alcohols and a hydrogenated hemicellulose hydrolysate.
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Cited By (10)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US6407266B2 (en) | 2000-05-26 | 2002-06-18 | E. I. Du Pont De Nemours And Company | Continuous process for the manufacture of anhydro sugar alcohols and reactor useful therefor |
US7615652B2 (en) | 2006-01-26 | 2009-11-10 | Battelle Memorial Institute | Two-stage dehydration of sugars |
US7649099B2 (en) | 2006-01-26 | 2010-01-19 | Battelle Memorial Institute | Method of forming a dianhydrosugar alcohol |
US7728156B2 (en) | 2006-01-26 | 2010-06-01 | Battelle Memorial Institute | Method of performing sugar dehydration and catalyst treatment |
US7772412B2 (en) | 2006-01-26 | 2010-08-10 | Battelle Memorial Institute | Methods for dehydration of sugars and sugar alcohols |
US8008477B2 (en) | 2001-11-20 | 2011-08-30 | Roquette Freres | Method for preparing a composition containing at least one internal dehydration product for a hydrogenated sugar |
US9598325B2 (en) | 2013-05-02 | 2017-03-21 | Roquette Freres | Method for stabilizing a composition containing at least one product of internal dehydration of a hydrogenated sugar, resulting composition and uses thereof |
WO2017158303A1 (en) | 2016-03-16 | 2017-09-21 | Roquette Freres | Method for producing dianhydrohexitol with a step of distillation on a thin-film evaporator |
US10526340B2 (en) | 2016-04-25 | 2020-01-07 | Roquette Freres | Process for manufacturing dianhydrohexitol crystals with a step of evaporative crystallization of the first crystallization mother liquors |
WO2023006250A1 (en) | 2021-07-28 | 2023-02-02 | Roquette Freres | Oxidation-stable dianhydrohexitol composition containing gallic acid ester |
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1982
- 1982-05-07 CA CA000402491A patent/CA1178288A/en not_active Expired
Cited By (13)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US6407266B2 (en) | 2000-05-26 | 2002-06-18 | E. I. Du Pont De Nemours And Company | Continuous process for the manufacture of anhydro sugar alcohols and reactor useful therefor |
US8008477B2 (en) | 2001-11-20 | 2011-08-30 | Roquette Freres | Method for preparing a composition containing at least one internal dehydration product for a hydrogenated sugar |
US7615652B2 (en) | 2006-01-26 | 2009-11-10 | Battelle Memorial Institute | Two-stage dehydration of sugars |
US7649099B2 (en) | 2006-01-26 | 2010-01-19 | Battelle Memorial Institute | Method of forming a dianhydrosugar alcohol |
US7728156B2 (en) | 2006-01-26 | 2010-06-01 | Battelle Memorial Institute | Method of performing sugar dehydration and catalyst treatment |
US7772412B2 (en) | 2006-01-26 | 2010-08-10 | Battelle Memorial Institute | Methods for dehydration of sugars and sugar alcohols |
US9598325B2 (en) | 2013-05-02 | 2017-03-21 | Roquette Freres | Method for stabilizing a composition containing at least one product of internal dehydration of a hydrogenated sugar, resulting composition and uses thereof |
WO2017158303A1 (en) | 2016-03-16 | 2017-09-21 | Roquette Freres | Method for producing dianhydrohexitol with a step of distillation on a thin-film evaporator |
US10533017B2 (en) | 2016-03-16 | 2020-01-14 | Roquette Freres | Method for producing dianhydrohexitol with a step of distillation on a thin-film evaporator |
EP4219505A1 (en) | 2016-03-16 | 2023-08-02 | Roquette Freres | Method for producing dianhydrohexitol with a step of distillation on a thin-film evaporator |
US10526340B2 (en) | 2016-04-25 | 2020-01-07 | Roquette Freres | Process for manufacturing dianhydrohexitol crystals with a step of evaporative crystallization of the first crystallization mother liquors |
WO2023006250A1 (en) | 2021-07-28 | 2023-02-02 | Roquette Freres | Oxidation-stable dianhydrohexitol composition containing gallic acid ester |
FR3125684A1 (en) | 2021-07-28 | 2023-02-03 | Roquette Freres | COMPOSITION OF OXIDATION-STABLE DINAHYDROHEXITOLS AND CONTAINING A GALLIC ACID ESTER |
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