CA1232902A - Crystallization of fructose utilizing alcohols - Google Patents

Abstract

ABSTRACT
This invention describes the crystallization of fructose through the use of a mixture of at least two alcohols such as ethanol and isopropanol.

Description

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BACKGROUND (:)F THE INVENTION
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l. Field Of The Invention This invention relates to obtaining fructose in high yields with a high degree of purity.

2. Description Of The Art Practices Fructose may be viewed as one-half of a sucrose molecule with the other half being dextrose ~glucose~. Sucrose is, of cDurse, known commonly as table sugar and is widely used as a sweetener and structurant in many products from cake mixes to soft drinks. It has been determined that the fructose por-tion of the sucrose molecule has greater sweetening power on an equal weight basis than sucrose or dextrose. There~ore, if fruc~ose is substituted into formulations, ~he overal I cos~ may be lowered when compared to using sucrose. The use of fructose provides a higher degree of sweetening at a given weight level tt an suçrose. Thus, ~ewer calories are present in a fructosP-s~Neetened procluct at equal sweetening levels than when suçrose is used.

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Several routes have been utilized to isolate and separate fructose as a crystalline component. For the most part, fructose is prepared by isomeri~ing dextrose which is obtained through the refining of corn syrup.
The isomerization of dextrose is general Iy not a 100 conversion and therefore the fructose must be separated from the remaining saccharides, e.g. dextrose, and crystallized from the aqueous dispersion.
The separation of fructose from the syrup is complicated by ~he high degree of solubility of the fruc~ose in water. Therefore, the separation of fructose at acceptable purity and yield from an aqueous syrup i5 yet to be accomplished in a practical manner.
Il. S. Patent 3,607,392, issued September 21, 1 5 1 971, to i~uer , describes a process and apparatus for obtaining crystalline fructose through the use of methanol. Methanol has limits on its usage in food products which is the major market for crystalline fructose in the first instance, U.S. Patent 3,883,365, issued to Forsberg et al on May 13, 1975, describes a separation of fruct~se from giucose within a narrowly constrained pH range by ~ , , ~, .

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lowering the temperature of the reaction mixture. The disadvantage in this process is that it is not economical to refrigerate a syrup in a plant setting. That is, the syrup will be at least at an ambient temperature during 5 processing and the mechanics of cooling require the substantial expenditure of energy.
Yamauchi U.S. Patent 3,928,062, issued De-cember 23, 1975, discloses recovering fructose by seed-ing anhydrous fructose crystals into a super-10 saturated solution of fructose. U.S. Patent 4,371,402, issued February 1, 1983, to Kubota, describes the dehydration of fructose utilizing an organic solvent having azeotropic behavior with respect to water.
The teachings of Dwivedi et al in U . S . Patent 15 4,1g9,373, issued April 22, 1980, relate to anhydrous free-flnwing crystalline fructose obtained by allowing a seeded syrup to seand at low temperature and high relative humidity . United 5tates Patent 4,199,374, issued April 2?, 1980 also to Dwivedi et al suggests 20 seeding a syrup containing fructose and allowing it to stand foilowed by recovery of the fructose. U. S.
Patent 3,513,023 to Kush, issuecl May 19, 1970, discloses :

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the recovery of crystalline fructose over a broad pH
range, through concentratior~ an~ cooling, following . seeding of the mixture.
It therefore remains to effectively separale 5 fructose from an aqueous syrup in a high degree of purity and with a high yield. The present inven$i~n, as later described, deals with this problem effectively by using a mixture of two alcohols to separate the comp~
nents to a superior degree than when using a single 1 0 alcohol.
- Throughout the specificatiDn and claims, percentayes and ratios are by weight, temperatures are degrees C;elsius, and pressures are in KPascal over amhient unless otherwise indicated~

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A process for prepariny crys~alllne fructose from an aqueous dispersion containing fructose i5 de-scribed including:
~a~ obtaining an aqueous dispersion containing on a dry solids basis at least a~out 85% by weight fructose:
(b3 adding to the aqueous dispersion at le~st two a~cohols;
(c) mixing the aqueous dispersion and the akohols untii the weight rativ of the fructose to the alcohols is from aboL3t 1~:1 to 1:~;
(d) allowing crystallization to occl3r"
15 and, recovering the fructose.

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This invention also describes a process for preparing crystalline fructose from an aqueous dispersion containing fructose including:
la) obtaining an aqueous dispersion containing on a dry solids basis at least about 85~ by weight fructose;
(b) adding to the aqueous dispersion ethanol and isopropanol in a re-spective weight ratio of the alco-hols of 250:1 to 1:250;
(c) mixing the aqueous dispersion and the alcohois until the weight ratio of the fructose to the alcohols is from about 4:1 to 1:4;
(d) allowing crystallization to occur;
and, recovering the fructose.
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DETAILED DESCRIPTION OF THE INVENTION
The first component of the present invention is the aqueous dispersion (syrup~ from which the fructose is to be crystallized. While the aqueous dispersion could 5 consist essential Iy of fructose and water, it is more likely that other saccharides and various materiais ob-~ained in the processing of corn syrups will be presen~.
Nameiy, dextrose is typically present at from 3~ to 10%
by weight in the syrup. The foregoing is stated as it 10 may be desirable in some circumstances, where highly pure fructose is desired, that crystalline fructose be redissolved in water and recrystallized according to the present invention. In any event, the amount of fructose in the syrup as described in the Summary is preferably 15 from about ~iB% to about 97~ by weigh~ fructose and most preferably from about 93% to about 96% by weight on a dry solids basis (dsb). The preferred fructose source is from corn syrup, however, any source of fructose such as from inulin or other sources such as cane or 20 beet may be employed.
The conditions for the aqueous dispersion prior to the addition of the later described alcohols are such that the pH should be from about 3.0 to about 5.U, ,,~., , ' -, ~Z3Z~Z

preferably from about 3 . 5 to about 4 . 8 . The tempera-ture of the syrup and alcohol mixture prior to the crystall ization step should be from about 40C to about 8ûC, preferably from ab~ut 50C to about 70C.
The alcohols utilized herein are preferably obtained in their anhydrous state. This condition is imposed as any additional water in the system will de-crease the yield of fructose due to its solubility in water. The two alcohols (minimurn) used to obtain crystalline fructose are conveniently selected from ethanol, methanol, propanol, isopropanol, n-butanol, and sec-butanol. The alcohols are desirably monohydric.
The alcohols preferably employed herein are ethanol and isopropanol. The weight ratio of one alcohol to each 15 other alcohol is convenientiy from 250:1 to 1:250; more preferably 200:1 to 1:200.
It is preferred that ethanol be the predominant alcohol in the mixture of the alcohols. It is also pre-ferred that isopropanol also be present in the mixture of alcohols. The weight ratio of the ethanol to the isop~opanol is desirably from about 80:2û to about 98:2 preferably from about 85: 15 to about 97: 3 and most preferably from about 90:10 to about 96:4.

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It has been determined that within the forego-ing ranges that the mixture of ethanol and isopropanol gives a higher yield and purity of the fructose obtained when compared to either of th~e alcohols utilized alone.
5 The alcohols may be added to the syrup separately or by premixing of the alcohols. The ethanol, as it is a regulated material, may be denatured with a suitable denaturant sueh as methanol. Methanol is conveniently used to denature ethanol at from 1% to 1 û~6, particularly 10 at 5~ as in 3A alcohol. Thus ternary and higher mix-tures of alcohols are eontemplated herein.
The weight ratio of the fructose in the aque-ous dispersion to the alcohols is from about 4:1 to about 1:4; preferably from about 3:1 to about 1:3. The 15 alcohol ratio to the fructose in the aqueous dispersion is important in that an insufficient amount of alcohol does not allow the fructose to be effectively separated.
The rnixing of the aqueous dispersion and the alcohols is conducted as near ~o ideal as possible. The 20 mixing should also be continued during ~he crystal-lization step which is preferably induced by using a suitable fo~-grade seeding material. The preferred : :~

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, , - , .: . , seeding material is crystalline fructose which may be initially ob~ained from a commercial source. Any other suitable sugar or saccharide may be employed, however, as the goal is to obtain a high fructose content with as 5 high a degree of purity as possible, it is desirable to use pure fructose for the seeding. t)f course, after the process is started, a portion of the product which has been crystallized as fructose may be recovered and utilized for further initiation of seeding.
The mixing of the aqueous dispersion as previously noted allows an in~imate mixing of the alcohols thereby selectively extracting the fructose such that the solution structure of the water, fructose and alcohol molecules bring abvut favorable conditions for crystal-15 lization. Thus, when the seeding is initiated, crystal-lization of the dispersed fructose is extremely rapid.
The use of two alcohols also reduces the viscosity of the syrup thereby facilitating mixing.
The present process may be run on a continu-20 ous basis by introducing a fresh feed stream into the mixing tank, seeding, and removing crystalline fructose slurry from the bottom of the tank. The crystallized : :

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fructose can then be drawn of~, filtered, recovered as a semi-solid, and dried. Other suitable methods of re-covering the fructose from the slurry can also be em-ployed .
The present invention as described above allows for the recovery of crystalline fs uctose particles which average between 100 and 1,000 preferably 15û
and 500 micrvns. Larger granules are also possible if desired, The product is of high purity when seeded with fructose and is generally suitable for all applica-tions in which crystalline fructose is desired.
The ~ollowing are suggested exemplifications of the present invention.

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EXAMPLE I
Corn syrup containing 96 . 8% fructose on a dry solids basis is adjusted to a pH of 4. 5 and evaporated under vacl~um to a solids content 91.6~ by weight. The 5 remaining components in the mixture include dextrose and water.
The evaporated product in an amount of 208 parts is dissolved in 89 . 6 parts of an alcohol mixture which is 95:5 by weight ethanol to isopropanol. Both 10 alcohols were essentially anhydrous prior to introduction into the system. The alcohol is adcled incrementally to the aqueous mixture. The resulting combination of the aqueous mixture and the alcohols is mixed vigorously at 55C to obtain a clear solution.
I.g~5 parts of crystalline fructose is then mixed with the solution and stirring continued while the mixture is cooled to 22C over a period of 4 hours.
The seeded mixture is then filtered and washed with three separate, 24 part aliquots of the 20 previously described alcohol mixture at 0C. The fructose product so recovered is air-dried to obtain 147 parts of ~he product which is a white crystalline powder having a purity of 99.4% by weight.

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Substantialiy similar results are obtained by varying the alcohol mixture used above within the range as described in the Summary of the Invention. The pH
of the aqueous dispersion may be varied between about 3 5 and about 5 with substantially similar results.

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EXAMPLE I I
Several comparative tests of various alcohols and alcohol mixtures are conducted according to the process described in Example 1. The results are report-ed in Table I below.

TABLE i Alcohol Product Purity1 ~ Yield2 1009t IPA 94.6 ~gummy) 90 100% EToH4 98.9 - 99.8 73 100% MEClH5 99. 5 55 5% MEOH/95% ETOH 99~7 63 10% MEOHt90% ETOH 99.3 51 1596 MEQHI35~ ETOH 99.5 611 15 5% I PAt9596 ETOH 99. 4 81 7% IPA/93% ETOH 98.9 88 10% IPA/90% ETOH 98.9 91 15% IPA/85~g ETOH 98.3 87 1. 9g fructose in product.
2. Yields of fructose.

3. IPA is isopropanol.

4. ETOH is ethanol.

5. MEOH is methanoi.

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The tests conducted show the mixtures of IPA
and ETOH are most effective in increasing the purity and yield of crystailine fructose.
A similar run using 1 part isopropanol to 99 5 parts ethanol increased the yield of crystalline fructose by greater than 14% by weight over a comparative run using ethanol alone.

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Claims (13)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:-

1. A process for recovering crystalline fructose from an aqueous fructose containing dispersion comprising providing an aqueous fructose containing dispersion having a fructose content of at least 85 percent by weight dry solids basis, admixing with said dispersion ethanol and isopropa-nol in an amount sufficient to provide a fructose to total alcohol weight ratio of between about 4:1 and about 1:4, the weight ratio of ethanol to isopropanol being be-tween about 80:20 and about 98:2, crystallizing fructose from the dispersion alcohol mixture, and recovering crystalline fructose.

2. The process of claim 1 wherein the aqueous dis-persion contains from about 5% to about 15% by weight water.

3. The process of claim 1 wherein the fructose is present in the aqueous dispersion at from about 88% to about 97% by weight dry solids basis.

4. The process of claim 1 wherein the aqueous disper-sion also contains dextrose.

5. The process of claim 1 wherein the recovery of the fructose is enhanced by seeding the dispersion.

6. The process of claim 5 wherein the seeding is accomplished using a saccharide.

7. The process of claim 6 wherein the seeding is accomplished utilizing crystalline fructose,

8. The process of claim 1 wherein the weight ratio of the fructose to the alcohols is from about 3:1 to about 1:3.

9. The process of claim 1 wherein the weight ratio of the ethanol to the isopropanol is from about 85:15 to about 97:3.

10. The process of claim 1 wherein the mixing is continued during crystallization.

11. The process of claim 1 wherein the pH of the aqueous dispersion is between about 3.0 and about 5Ø

12. The process of claim 1 wherein the alcohols include methanol.

13. The process of claim 1 wherein the disper-sion alcohol mixture is maintained between about 40°C
and 80°C prior to the crystallization.