MXPA96002768A - Procedure for the production of xili - Google Patents

Abstract

The present invention relates to a process for the production of xylitol, specifically, the process consists of two reaction steps, the first step is the conversion by fermentation of a hexose to pentitol, the second step is the catalytic chemical isomerization of pentitol a xylitol, optionally xylitol is separated from the other pentitol

Description

PROCEDURE FOR THE PRODUCTION OF XILITQL FIELD OF THE INVENTION The present invention describes a method for the production of a pentitol. The present invention relates to a method for the production of pentitols from hexases. Specifically, xylitol is obtained from glucose in a reaction comprising a sequence of only two separate steps. The glucose is fermented to form arabinitol and is chemically isomerized to form a mixture of pentitoles including xylitol.

BACKGROUND OF THE INVENTION Xylitol is produced on an industrial scale by xylcsa-hitiogenation. Xylose is not available as such and is obtained from plant materials that contain xylans. To obtain xylose, plant materials containing the xylan such as almond sheath, carous or birch wood are hydrolyzed in an acid medium at elevated temperatures. This hydrolysis has two disadvantages: a high load of waste material due to the low content of xylan in the aforementioned starting materials and a low purity and product yield due to the considerable formation of by-products under the extreme conditions of the hydrolysis that they use. To eliminate the excess acid and the strong color, extensive purification and refining is required. Subsequent crystallization of the xylose-free syrup suffers from the purity of the xylose syrup. Other hemicellulosic sugars also formed during hydrolysis have similar physicochemical properties and have to be eliminated quantitatively. To prevent the formation of galactitol, the galactose must be removed at an early stage, before catalytic hydrogenation. The application of xylitol in foods and related products requires the complete elimination of galactitol for reasons of human safety, for example, damage to the eye. For each kilogram of crystalline xylitol, 12 to 13 kg of almond sheath must be processed resulting in about 11 to 12 kg of solid waste. Apart from a contamination problem, there is also a logistical problem with this procedure in that large quantities of almond sheath have to be transported. Finally, the availability of material containing xylan can be a limiting factor. Therefore, it is of interest to consider alternative methods for the production of xylitol which do not have the aforementioned disadvantages. Chemical and iccobiological processes have been described for the production of? Ilitol. Recently, some reaction models have been published to produce xylitol, starting from readily available hexoses, in particular D-glucose and D-ga.lactose. All these models consist of a sequence of more than two reaction steps. In a first step hexase is subjected to a chain reduction reaction which produces an intermediate C ». This step is done either by fermentation or chemically. The subsequent procedure relates to the conversion of the intermediate Cs to xylitol, using a sequence of at least two steps of conversion by f rmation and / or chemistry. In documents EP l + 03 392 and EP ?? && Subsequently, arabinitol (intermediate Cß) is converted by means of bacteria (Acetobacter, Gluconobacter or Kletasiella) into D-xylulose. In the third step, xylulose is isolated in a xylose / cellulose mixture with glucose (xylose) isomerase. In the final step, the xylose is enriched by chromatography before hydrosgenation, or the xylulose / xylite mixture is directly subjected to higenation, followed by separation of the xylitol by chromatography. In WO 93/19030 the glucose, fructose or galactose or mixtures thereof (obtained by hydrolysis of the disaccharides, sucrose and lactose) are oxidatively decarboxylated to alkaline metal arabinonate and alkali, respectively. These intermediaries are first converted to the form of aldonic acid. Subsequently, the aldonic acids, which in the intermediates Cs, are transformed into xylitol. When L-sorbose is used, L-xylonate is obtained through the decarbaxy oxidative ion and this is converted to the aldonic acid form before being hydrogenated to xylitol. This last route seems simple; however, the reaction steps required to obtain the L-sarbose must be taken into account. L-sorbose is obtained mainly through the oxidative fermentation of sorbitol, which in turn is obtained from glucose by catalytic hydcogenation, resulting in a total of five reaction steps to obtain the final xylitol. Other chemical methods for the preparation of xylitol include elaborate reaction schemes that involve the use of protection groups. Due to the lack of economic possibilities, these reactions no longer dry considered here. (Helv. Chim. Acta 56, 1975, 311). Several routes have been published exclusively mit robiological; however, none of them is competitive due to the total yield which is too low. There is therefore a need for an economically valuable method for the production of pentitoles, especially xylitol, with a low level of impurities that is easily refinable, comprising a short reaction sequence and starting from readily available hexases, such as glucose (anhydrous) , monahidratada or syrups with high content of dextrose).

BRIEF DESCRIPTION OF THE INVENTION The present invention provides said method. The present invention relates to a method for producing a pentitol from a hexose, characterized in that the method comprises the following steps, a) fermentation of a hexose to form a CB intermediate consisting mainly of a pentitol, b) iso erization of the pentitol of step a) in the presence of a chemical catalyst to form a corresponding mixture of pentitol, c) optionally the separation of the desired pentitol from the product of step b). The present invention can be summarized as follows. The invention describes the fermentation of CA carbohydrates which results in Cs polyols, the fermentation step is followed by chemical catalytic isolation. The starting material can be an easily available CA carbohydrate, the preferred substrate is glucose, anhydrous or mopohydrate, or in the form of a high dextrose syrup.

Starting with glucose, fermentation produces mainly arabinitol. The fermentation of the present invention is based on methods known in the art. To carry out a process according to the present invention, any yeast having the ability to produce D-arabinitol from glucose can be used. For example, the yeasts that belong to the genus Pichia.

Endomvcoosis Hansenul, Debarvomv s. ZvQosa charoniv s.

Saccharo vces. Candida and other yeasts belonging to the genus of Torulop i are suitable for this particular fermentation. The yield of D-arabinitol in the fermentation product is preferably greater than 20% (w / w), most preferably 0 (w / w) based on the initial hexose content. In general, with the use of osmophilic yeasts D-arabinitol is the only pentitol that is produced. D-arabinitol is subjected to catalytic isomerization by methods known in the art. D-arabinitol is treated at temperatures between 70 and 250 ° C, preferably at a temperature above 100 ° C, and at gaseous hydrogen pressures between 0.1 and 10 MPa, preferably between 1 and 6 MPa. The catalytic isolation is effected in the presence of catalysts which are known in the art for carrying out hydrogenation / dehydcogenation. Suitable catalysts include ruthenium, copper, palladium, platinum, rhodium, cobalt and nickel-based catalysts, or their oxides and mixtures thereof. Isolation of the polyol is effected accurately at different pH levels, and the addition of alkali or acid has an influence on the thermodynamic equilibrium of the pentitole mixture. The isoenzation reaction results in a product containing xylitol, ribitol and DL-arabinitol. Xylitol is present in these mixtures in more than 0.1%, preferably in more than 205S. The reaction product also contains some lower alditols, such as tetcols and triitols, reaching a maximum of 103%, preferably only 5% of the total content of alditol. The optionally isolating mixture is subjected to chromatography on cationic resins producing purified xylitol with a purity greater than 95 & Preferably the mixture is first dehydrated and then subjected to chromatography. The refining is suitably carried out using a strong cation exchange resin, for example Duolite C 2A, followed by a medium base anion exchange resin Duolite A 36 & Preferably1, this procedure is repeated once. On an industrial scale, the romatography is performed using suitable equipment, obtained for example from Mitsubishi, with Diaion UB-555 resin (in the form of Ca * 8"**). The other pentitols are optionally re-inoculated in the isomerization step of the polyol, resulting in an increased overall yield Fl xylitol can also be further purified by crystallization The advantage of this method compared to the processes described above, such as the process described in WO 93/19030 is that operations can be used well established units for & refining (classic syrup refining) and that known techniques and equipment for fermentation and catalytic isomerization can be used. The main advantage compared with other methods, such as those described in EP L03 392 and EP? + 2l &S > 2 and WO 93/19030, is that the overall reaction sequence is much shorter. The method of the present invention is illustrated schematically in diagram 1, wherein underlined steps are essential.

SCHEME 1 Hexose Fermentation 10 Pentitol 15 Laughter 20 Isolation 25 Recirculation of pentitoles Ref ination Separation Xilitol +0 The invention will be illustrated later with the following examples.

Example 1 Zyuosaccharomvces ba keci Y-222 was inoculated into a culture medium containing 30 (w / v) glucose, .0% (w / v) corn impregnation liquor, 0.1% (w / v) potassium phosphate , 0.05% (w / v) of magnesium sulfate, 0.01% (w / v) of calcium chloride, 0.01% (w / v) of sodium chloride, and cultivated at pH 6, (pH adjustment with hydroxide sodium) at 30 ° C poc. days. The following yield was obtained: * + < - > .1% arabinitol, 2% residual glucose, and 10.5% glycerol (as a percentage of glucose that has been converted). The reaction product was demineralized and refined on a double-pass ion exchange battery, followed by selective crystallization of the arabinitol. This results in crystals with a purity of 99%. Fl arabinitol is isomerized on the ruthenium catalyst < W% of catalyst on total dry matter) which was supported on silica (5% Ru on silica), applying a hydrogen pressure of? + MPa to a pecatura of 150 ° C. The isomerization of the polyol was completed in hours. The obtained ineralized isocyanate product obtained had the following composition of pentitols: arabinitol 60%, xylitol 22%, ribitol lfi%. Et xylitol was separated by chromatography on resin ti of cation exchange in the form of calcium, producing xylitol with a purity greater than 95%. Arabinitol and ribitol were recirculated for isomerization. The xylitol was crystallized to obtain crystals of 99.9% purity.

Example 2 Pichia oh eci ATCC 20.209 was grown at 30 ° C in a medium containing 15% (w / v) glucose, 0.2 (w / v) yeast extract, 0.1% (w / v) potassium biphosphate and 0.1 % (w / v) of magnesium sulfate. After 6 days the reaction medium was filtered and demineralized on ion exchange resins. A yield of l + 0.5% arabinitol was obtained after crystallization. The arabinitol was isomerized on ruthenium catalyst (or% of the catalyst on the total dry substance) which was sustained on activated carbon (5% Ru sotare carbon). To isomerize the arabinitol, phosphoric acid syrup (1% on the total dry substance) was added. The reaction temperature was 150 ° C at a hydrogen pressure of < + MPa. A > + hours the isomerized syrup had the following composition: 90% of total pentitols (of which: arabinitol (t + 5%), xylitol (3i +%), ribitol (21%) and 10% of lower alditols. in a manner similar to that described in example 1.

Example 3 The fermentation of glucose to arabinitol was carried out using a culture medium of 10% (w / v) glucose, O.5% (w / v) yeast extract and 0.1% (w / v) urea. The medium was inoculated with a yeast strain of the genus Endomvcopsis chodati. After 72 hours of grinding, 5% arabinitol was obtained without significant amounts of glycecol (below! +%). After the ineralization and refining, the arabinital syrup was used directly for the isomerization of the polyol in the presence of Raney nickel (5% of the catalyst suspension on the total dry substance). The pH was increased to 11 with the addition of 0.5 M HCl. A hydrogen pressure of 4 MPa was applied at a temperature of 170 ° C and the isation reaction stopped after k hours, resulting in a mixture of pentitols of the following composition: arabinitol (90%), xylitol (6%), ribitol < ? +%).

Example The fermentation of glucose to arabinitol is carried out as described in eq. 1, except that a yeast belonging to the genus Candida, called Candida polv orpha ATCC 20 213, is used. We obtained! +. 5 g of D-arabinitol per 100 ml of fermentation solution. The subsequent isolating of polyol was carried out on a rutepium catalyst (4% of the catalyst "-on the substance e to total) which was supported on zeolite material (5% of Ru on zeolite). The reaction temperature is 135 ° C at a hydrogen pressure of 4 MPa. After 4 hours of reaction the polyol mixture had the following pentitol composition: arabinitol (73%), xylitol (13%), ribitol (14%). The xylitol was recovered as in example 1.

Claims (7)

NOVELTY OF THE INVENTION CLAIMS

1. A method for the production of a pentitol from a hexose characterized in that the method comprises the following steps: a) the fermentation of a hexose to produce an intermediate of Cs consisting mainly of a pentitol, b) the isomerization of pentitol from step a) in the presence of a chemical catalyst to produce the corresponding mixture of pentitoles, c) optionally the separation of the desired pentitol from the product of step b).

2. A method for the production of a pentitol from a hexose according to claim 1, further characterized in that the pentitol is refined after fermentation and / or of the isomer ion.

3. A method for the production of a pentitol from a hexose according to claim 1, further characterized in that the hexose is an easily available CA carbohydrate, preferably glucose (for example, the anhydrous, monocyanate or syrup with high dextrose content).

4. A method for the production of a pentitol from a hexase according to claim 1, further characterized in that step a) is an aerobic fermentation of glucose syrup to arabinitol carried out by an osmophilic yeast selected from the group consisting of of the following genres: Pichia. Endo vc opsis, Hansenula. Debaryomyce. ZvaosacL haromvces. Saccharo yces. Candida and Torulopsis. A method for the production of a pentitol from a hexcsa according to claim 1, further characterized in that the pentitol is selected from the group consisting of xylitol, ribitol and arabinitol. 6. A method for the production of a pentitol from a hexcsa according to claim 1, further characterized in that the isomerization is carried out in the presence of a hydrogen ion / thiamyrogenation catalyst promoted by the addition of alkaline material or acid, respectfully. 7. A method for the production of a pentitol from a hexose according to any of the preceding claims, further characterized in that the isomer i zac ion is conducted at a hydrogen pressure of between 0.1 and 10 MPa and at a temperature of between 70 and 250 ° C. 6. A method for the production of a pentitol from a hexose according to claim 7, further characterized in that the hydrogen pressure is preferably between 1 and & MPa. 9. A method for the production of a pentitol from a hexose according to claim 7, further characterized in that the temperature is preferable between 100 and 200 ° C. 10. A method for the production of a pentithal from a hexcsa according to claim 1 further characterized in that the separation of step c) is carried out using a cationic resin.