DE3939058A1 - Prepn. of epimer-free sugar alcohol(s) for use as sweeteners - Google Patents

Abstract

The prepn. of epimer-free sugar alcohols (I) chosen from xylitol, sorbitol (D-glucitol), 4-O-beta-D-galactopyranosyl- D-glucitol and 4-O-alpha-D-gluco -pyranosyl-D-sorbitol comprises continuous catalytic hydrogenation of the corresp. sugar (II), -xylose, alpha-D-glucose, 4-O-beta-D-galactopyranosyl-alpha-Dm. glucopyranose or 4-O-alpha-D-glucopyranosyl -alpha-D-glucopyranose. The reaction is carried out in aq. soln. with hydrogen at a H2-pressure of 100-500 bar and 60-125 deg.C in fixed bed process in the reaction zone above a hydrogenation catalyst consisting of carrier-free moulded bodies of pressure resistance above 50N (esp. 100-400N) on the surface and an inner surface of 10-90 m2/g and consisting of one or more elements of the Fe gp. of the periodic table.

Description

The invention relates to a method for producing the Disaccharide alcohol 4-O-α-D-glucopyranosyl-D-sorbitol (Maltitol) from 4-O-α-D-glucopyranosyl-α-D-glucopyranose (Maltose) through continuous catalytic hydrogenation with hydrogen. The course of the reaction can be illustrate the following reaction scheme:

Maltitol is made in the human body by amylolytic Enzymes difficult to break down.

Hence maltitol is considered sugar Substitute for reduced calorie diet and for Suitable for diabetics (Ullmann’s Encyklopadie der technical chemistry, volume 24, Weinheim 1983, p. 771).

The sweetness of maltitol reaches the sweetness of Sucrose. Maltitol can be in liquid form with others sweet-tasting carbohydrates, such as Fruc tose, sorbitol, xylitol and others can be mixed. Especially recommended for use in the beverage industry because of its high sweetness and low Tendency to crystallize even in high concentrations ions.

To manufacture the so far not in nature Maltits is a discount from US 37 41 776 known process (batch process), in which a powdery nickel catalyst in a suspension tion process was used.

Batch processes have the disadvantage that their capacity, relative to the reaction volume, is very small is and therefore a need for large reaction apparatus doors and storage tanks. The energy consumption is uneconomical and staffing requirements are proportionate high.

Continuous powder catalyst process using several hydrogenation reactors connected in cascade avoid some of the disadvantages mentioned. It  remains the cumbersome way, the powdery way Targeted activation, pumping and to be filtered quantitatively from the reaction product. The Catalyst slurry pumps are subject to a high mecha African stress. The quantitative removal of the powdered catalyst is expensive (rough and Fine filtration apparatus in exchangeable version). Further there is a great risk that the catalyst will operations are relatively quick Loses activity (high catalyst consumption). It is therefore desirable to have the reaction over fixed Let catalysts run off, which have a high spe ought to have specific activity that also has a after a long period of 1 to several years should leave because frequent catalyst changes also Fixed bed reactions are expensive.

EP 1 52 779 describes a process for the hydrogenation of α-D Glucopyranosido-1,6-fructose on fixed kata known analyzers. However, this is a mixture two reduction products, namely α-D-gluco pyranosido-1,6-mannitol and α-D-glucopyranosido-1,6-sorbitol obtained, the ratio of which is approximately 1: 1.

It was therefore surprising that in the present process only one disaccharide alcohol from maltose, namely the Maltitol can not be obtained by one Epimization reaction or by an aldose-ketose iso relocation products caused by merization will be used directly as a dietetic can.  

A process for the preparation of 4-O-α-D-glucopyranosyl-D-sorbitol (maltitol) from 4-O-α-D-glucopyranosyl-α-D-glucopyranose (maltose) by catalytic hydrogenation in aqueous solution was used Hydrogen found under elevated pressure and at elevated temperature, which is characterized in that the hydrogenation is carried out continuously at a hydrogen pressure of 100-500 bar and temperatures of 60-120 ° C. in a fixed bed process in a reaction zone via unsupported shaped bodies serving as hydrogenation catalysts a compressive strength of more than 50 N, preferably 100-400 N, on the molded body surface and an inner surface of 10 to 90 m ² / g from metal powders of elements of subgroup 8 of the periodic table.

The maltitol is almost in the process of the invention quantitative yield obtained. This is special Significance because the removal (due to ether formation higher) or (by hydrogenolysis resulting) low-molecular disturbing impurities conditions from the reaction product by additional Cleaning processes, such as recrystallization from solutions means, usually a considerable ecological one Disposal effort required. That for Maltitol diastereomeric 4-O-α-D-glucopyranosyl-D-mannitol is not detectable in the reaction product.  

The fixed bed catalysts to be used according to the invention tend to be in contrast to supported catalysts not to "bleed", i.e. H. not the transition from kata analyzer components in ionic or colloidal form in the solution phase of the substrate so that the substrate is not contaminated by heavy metals that nor sometimes also difficult, for example with Help from ion exchangers, with ecological effort can be removed from the substrate. The one setting catalysts can be used after can be easily worked up because the heavy metals are not cumbersome to be separated from a carrier material have to.

It is therefore possible in the method according to the invention the maltitol in a purity of over 99% in the To produce dry matter. The content of not vice versa set maltose reaches values of at most 0.1%. There the glycosidic ether bonds in maltose or are preserved in maltitol, the contents of Mono sugar alcohols mannitol or sorbitol only at 0.3% or below. The commercial specifications for Maltitol can therefore normally be used without further purification processes are fulfilled directly.

As a starting compound for the Ver pure maltose is used, which either in in liquid form or (in its β form) as crystalline Monohydrate can be present. The feed is in Dissolved oxygen-free deionized water so that a 15-45 wt .-%, preferably 35-40 wt .-% solution  arises, whose pH 5.5-10.5, preferably 6.5-7.5 is. Pure maltose shows dissolved in water with a pH of 7, a neutral or due to traces wise formation of sugar acid, a weakly acidic reak tion, but can in a manner known to those skilled in the art, for example by adding sorbic acid or ver thinned formic acid to the desired pH be put.

Pure water is used for the hydrogenation according to the invention used to a pressure of 100-500 bar, preferably 150-300 bar, is pre-compressed. The hydrie Fixed bed process takes place continuously catalysts described below by using the Solution to be hydrogenated either in cocurrent from below ascending together with the previously mixed what Hydrogen over the installed in a hydrogenation reactor Catalyst flows (direct current method) or but by taking the ascending to hydrie solution from the inflowing hydrogen counteracts (countercurrent method).

The hydrogenation reactor can either be a single high pressure pipe made of steel or a steel alloy, the completely or partially filled with the catalyst, with certain pipe cross sections also the application the catalyst on trays (wire baskets or similar) can be useful, or a coated high pressure tube bundle, the individual tubes with catalyst entirely or partially filled. Furthermore, instead of a  larger single-tube reactor an arrangement of several small single tube reactors in a row Cascade operated.

The unsupported catalysts are made from metal powders the elements of subgroup 8 of the periodic table, in particular nickel, cobalt and iron or mixtures of them, particularly preferably made of nickel or of minde at least 70% of mixtures consisting of nickel to form bodies processed. Here powder of each Metals or powdered alloys of the mentioned Me talle are used. The production of molded articles pern is made according to common methods by pressing the metal powder, for example on tableting or pelletizing machines, under high pressure, whereby for Improvement in the adhesion of the metal particles too Graphite and / or adhesives in amounts of 0.2-3% by weight, based on the total weight of the catalyst bil components that can be used. The The molded articles are produced in an oxygen free atmosphere to ver surface oxidations avoid. Examples of shaped bodies are tablets, spheres or granules with diameters of 3-7 mm. Tableted Moldings can continue to enlarge the outer Surface with an axial hole (hole core) be provided. Such moldings have macroscopic a smooth surface.

The catalysts to be used according to the invention as moldings formed from catalysts have to be produced in a manner known to the person skilled in the art so that the resulting moldings obtain compressive strengths above 50 N, preferably compressive strengths of 100-400 N, on the surface of the shaped body. This is important because lower compressive strengths lead to disintegration or erosive abrasion of the moldings, which would cause undesirable contamination of the reaction product with metal powder. The shaped catalyst bodies to be used according to the invention also have specific internal surfaces which are at values of 10-90 m ² / g. The inspection of molded articles on such inner surfaces and thus on usability for the process according to the invention are carried out by methods by FM Nelsen and FT Eggertsen, analyte. Chem. 30 (1958), 1387 or by SJ Gregg and SW Sing, Adsorption, Surface Area and Porosity, London 1967, chap. 2 and 8 have been described.

The hydrogenation is carried out at temperatures of 60-120 ° C. preferably carried out 70-115 ° C. Lower temperatures would long dwell times or the waiver of one largely quantitative sales of maltose. Higher temperatures lead to uncontrollable additions reactions such as caramelization, ether cleavage or hydrating cracking, which leads to discoloration and Can lead to the formation of unwanted by-products.

The hourly catalyst load is 25-100 g Maltose per liter of catalyst. If the ge mentioned reaction conditions are unexpectedly high kata  analyzer service life of 16,000 hours and more range, with specific catalyst consumption of at most 0.1% or less can be achieved. In order to are the technical advantages of the invention Procedure except in the by the almost quantitative Sales-related high yield and ecological Benefits derived from the purity of the manufactured Product result in the cost-saving continuous working method and the extremely low Kataly sator consumption.

The aqueous solution of maltitol leaving the reactor can after the relaxation, in which one over the intercept hydrogen and after the successful Compression and supplementation with additional hydrogen can be used again directly as Sugar substitute in liquid form Use fin the.

The water of this solution can also be used on ver different ways, for example via spray dryers, Remove drying rollers or freeze drying. As the colorless and crystal clear solution of maltitol in a falling film evaporator or a similar device on a sugar alcohol concentration of about 80 to 100 wt .-% to concentrate trieren and, if necessary, then after another Evaporation in a vacuum crystallizer Cooling for partial or complete crystallization to bring. The crystals can be by downstream grinding process and possibly screening bring a uniform grain size.  

Anhydrous maltitol can be made from solutions in absolute Ethanol can be obtained as an amorphous powder. It melts at 146 ° C-148 ° C and is hygroscopic (Helv. Chim. Acta 20, (1937), 86-90).

example 1

A vertical, heat-insulated high-pressure pipe made of stainless steel of 45 mm inner diameter and 1 m long was filled with 1.4 l of a hydrogenation catalyst produced by tableting nickel powder, which had a compressive strength of 174 at a cylinder height of 5 mm and a diameter of 5 mm N had on the cylinder surface and an inner surface of 33 m ² / g. Through this tube together with the five-fold molar amount of high-purity hydrogen under a pressure of 300 bar, 250 ml of a 40% solution of 4-O-α-D-glucopyranosyl-α-D-glucopyranose in deionized oxygen-free hourly Drinking water with a pH of 7.0 is pumped continuously, from the bottom upwards.

Aqueous solution and hydrogen were previously shared passed through a heat exchanger and so high he heats them up in the high pressure pipe at a temperature of 80 ° C occurred. The one leaving the high pressure pipe Mixture of aqueous solution and excess water fabric was placed in a separator via a cooler leads from where the hydrogen after replacing the ver needed again together with fresh 4-O-α-D- Glucopyranosyl-α-D-glucopyranose in the preheater and from there it was pumped again into the high pressure pipe.

The colorless and clear aqueous solution was let down and in a falling film evaporator on a sugar alcohol  concentration of approx. 80% and then after further evaporation in a vacuum crystallizer with cooling and, if necessary, addition of Seed crystals brought to crystallization. The crystalline 4-O-α-D-glucopyranosyl-D-sorbitol showed a purity of 99.6%. The content of not hydrogenated 4-O-α-D-glucopyranosyl-α-D-glucopyranose was 0.1%. The sorbitol content was 0.3%. Mannitol could not be detected. The Ni Content was <1 ppm. The catalyst was also after with a running time of 6200 hours.

Example 2

Through a high-pressure tube, as used in Example 1, the hydrogen was at a temperature of 85 ° C and a hydrogen pressure of 150 bar, the hydrogen in the reverse reaction flow, as described in Example 1, based on the rising solution of 4-O-α-D- Glucopyranosyl-α-D-glucopyranose counteracted, with an equal amount of 40% aqueous solution of 4-O-α-D-glu copyranose-α-D-glucopyranose as in Example 1 being hydrogenated every hour, which has a pH of 6.5. The catalyst was manufactured by tableting nickel powder. With a cylinder height of 5 mm and a diameter of 5 mm, the tablets had a compressive strength of 149 N on the cylinder surface and an inner surface area of 62 m ² / g.

After a running time of 2500 hours with undiminished Efficacy was the content of 4-O-α-D-glucopyranosyl D-sorbitol to dry in a rotary evaporator evaporated reaction mixture at 99.4%. The salary on non-hydrogenated 4-O-α-D-glucopyranosyl-α-D-gluco pyranose was 0.1%. The sorbitol content was included 0.3%. The Ni content was <1 ppm.

Example 3

In a high-pressure tube, as used in Example 1, an equal amount of a 40% aqueous solution of 4-O-α- was hourly at a temperature of 80 ° C and a hydrogen pressure of 300 bar in the same way as in Example 1 D-glucopyranosyl-α-D-gluco pyranose hydrogenated, which had a pH of 7.5. The catalyst was obtained by tableting a powdered nickel-iron alloy. The alloy contained 15% iron in nickel. With a cylinder height of 5 mm and a diameter of 5 mm, the tablets had a compressive strength of 137 N on the surface of the cylinder and an inner surface of 83 m ² / g. The 4-O-α-D-glucopyranosyl-α-D-sorbitol obtained in a vacuum evaporator had a purity of 99.3%. The content of unreacted 4-O-α-D-glucopyranosyl-α-D-glucose was 0.1%. The sorbitol content was 0.3%. Ni and Fe contents were <1 ppm. The catalyst was still effective after a running time of 4200 hours.

Example 4

In a high-pressure tube, as used in Example 1, was at a temperature of 100 ° C and a hydrogen pressure of 200 bar in the same manner as in Example 1, an equally large amount of a 30% aqueous solution of 4-O-α-D -Glucopyranosyl-α-D-glucopyranose hydrogenated, which had a pH of 6.5. The catalyst was obtained by tableting cobalt powder. With a cylinder height of 5 mm and a diameter of 5 mm, the tablets had a compressive strength of 225 N on the surface of the cylinder and an inner surface of 19 m ² / g. The 4-O-α-D-glucopyranosyl-α-D-sorbitol obtained in a vacuum rotary tube had a purity of 99.1%. The content of unreacted 4-O-α-D-glucopyranosyl-α-D-glucopyranose was 0.1%. The sorbitol content was 0.2%. The Co content was <1 ppm. The catalyst was still undiminished after a running time of 1000 hours.

Example 5 (comparative example)

Through a high pressure tube, as used in Example 1, was at a temperature of 100 ° C and a hydrogen pressure of 300 bar in the same way as in Example 1 in the same time an equally large amount of a 40% aqueous solution of 4-O -α-D-glucopyranosyl-α-D-glucopyranose hydrogenated, which had a pH of 7.0. The catalyst had been prepared by applying an aqueous nickel salt solution on an inert spherical Al ₂ O _{3 support} (ball diameter: 5 mm) and then converting the nickel into the metallic state by reducing it in a hydrogen stream. The nickel content of the catalyst was 20%. The inner surface of the catalyst was 148 m ² / g. The 4-O-α-D-glucopyranosyl-α-D-sorbitol obtained in a vacuum evaporator had a purity of 92.9%. The content of unreacted 4-O-α-D-glucopyranosyl-α-D-glucopyranose was 1.4%. The sorbitol content was 3.6%. In addition, unknown impurities were found at a level of 2.1%, so that the 4-O-α-D-glucopyranosyl-α-D-sorbitol obtained in this way could not be used as a sugar substitute in this production form without ecologically complex cleaning procedures. Furthermore, a decrease in catalyst activity was observed after a running time of 700 hours. By increasing the reaction temperature from 100 to 120 ° C, the proportion of unreacted 4-O-α-D-glucopyranosyl-α-D-glucopy ranose could be reduced to a value of 0.2%, but increased at the same time the proportion of sorbitol to a value of 4.2%. In addition, the reaction product was contaminated with 48 ppm Ni.

Example 6 (comparative example)

Through a high pressure tube, as used in Example 1, was at a temperature of 100 ° C and a hydrogen pressure of 300 bar in the same way as in Example 1 an equally large amount of a 40% aqueous solution of 4-O-α -D-Glucopyranosyl-α-D-gluco pyranose hydrogenated, which had a pH of 6.5. The catalyst had been prepared by applying aqueous nickel and iron salt solutions to an inert, spherical Al ₂ O _{3 support} (ball diameter: 5 mm) and then converting the nickel and iron into the metallic state by reducing them in a stream of hydrogen. The nickel content of the catalyst was 16%, the iron content 4%. The inner surface of the catalyst was 151 m ² / g. The 4-O-α-D-glucopyranosyl-α-D-sorbitol obtained by evaporation in a rotary evaporator had a purity of 93.4%. The content of unreacted 4-O-α-D-glucopyranosyl-α-D-glucopyranose was 1.0%. The sorbitol content was 4.3%. In addition, unknown organic contaminants of 1.3% and Ni impurities of 31 ppm and Fe impurities of 12 ppm were found, so that the sugar alcohol obtained could not be used as a sugar substitute without ecologically complex cleaning measures.

Claims (4)

1. Process for the preparation of 4-O-α-D-glucopyranosyl-D-sorbitol from 4-O-α-D-glucopyranosyl-α-D-glucopyranose by catalytic hydrogenation in aqueous solution with hydrogen under elevated pressure and at elevated pressure Temperature, characterized in that the hydrogenation is carried out continuously at a hydrogen pressure of 100 to 500 bar and temperatures of 60 to 120 ° C in a fixed bed process in a reaction zone over unsupported shaped bodies serving as hydrogenation catalysts with a compressive strength of more than 50 N, preferably 100 to 400 N, on the shaped body surface and an inner surface of 10 to 90 m ² / g of metal powders of elements of the 8th subgroup of the periodic system. 2. The method according to claim 1, characterized in that that the moldings are those from Me tall powders of nickel, cobalt, iron or their Mixtures or alloys made with macroscopically smooth surface. 3. The method according to claim 1, characterized in that the hydrogenation catalysts are cylindrical or spherical shaped bodies with a diameter of 3-7 mm.   4. The method according to claim 1, characterized in that the hydrogenation of the 4-O-α-D-glucopyranosyl α-D-glucopyranose in 15 to 45% aqueous solution solution under a pH of 3.5 to 7.0 leads.