SK109995A3 - Method of production of monocarboxylic acids from saccharides, saccharides derivatives or primary alcohols and device for realization of this method - Google Patents

Abstract

In the method proposed for the production of monocarboxylic acids from carbohydrates, carbohydrate derivatives or primary alcohols, the carbohydrates, carbohydrate derivatives or primary alcohols are oxidized continuously in aqueous solution at concentrations between 0.1 and 60 % by oxygen or oxygen-containing gases, using noble-metal or mischmetal catalysts. The output flow of products thus formed is fed to an electrodialysis unit and the monocarboxylic acids removed and isolated. The device consists of a gassing step (10), oxidising step (30) and electrodialysis step, all of them put into series.

Description

Technical field

The invention relates to a process and an apparatus for producing monocarboxylic acids from sugars, sugar derivatives or primary alcohols.

BACKGROUND OF THE INVENTION

By various biochemical methods, it is possible to selectively oxidize sugars. However, these manufacturing processes have considerable disadvantages. In the first place is the multiplication of microorganisms or the production of biocatalysts, which are burdened with many drawbacks. The production methods mostly involve fermentation (for example during the production of gluconic acids), so that the use of nutrient salts in solution fermentation leads to considerable salt loads. Another disadvantage is the sterile mode of operation, which is often required in these processes, and therefore expensive equipment is required.

Of particular importance is attributed to the heterogeneity of the catalyzed oxidation of the noble metals of the eighth subgroup on suitable support materials. The oxidation of glucose to gluconic acid by atmospheric oxygen can be carried out chemically in this manner, for example on Pt / C catalysts. A disadvantage of this process, however, is the sharp reduction in the selectivity of the reaction and the rapid deactivation of the catalyst, see Ullmanns Enzyklopadie der Technischen Chemie, 4th New Revised Edition, Volume 24, p. 785, Verlag Chemie, 1983.

Similar problems arise in the oxidation of sucrose. Heyns and Paulsen investigated this reaction on platinum catalysts (K. Heyns, H. Paulsen, Adv. Carbohydr. Chem.,

17, 169 (1962), K. Heyns, W. D. Soldat, P. Koll, Chem. Ber., 3619 (1975). As the resulting products, they obtained mixtures of oxidized compounds for which no further data concerning the chemical composition and structure could be given due to the complexity involved.

In the process known from EP 0 040 709 B1 for the preparation of diacetone ketone gluconic acid, diacetone sorbose is partially oxidized and separated by dialysis. This is a batch process and due to the introduction of protecting groups the initial derivative has only one oxidizable group.

From DE 38 03 456 A1, DE 39 16 206 A1 and US-PS 4 985

Various intermittent processes are known which produce quantitatively unacceptable conversion amounts of product mixtures containing undesirable impurities with the starting compounds. In some cases, it is already suggested in the citations that the product be isolated by expensive purification methods.

The process described in EP 0 218 150 B1 for the catalytic oxidation of sucrose explicitly points out that in this way the multiply oxidized products are largely obtained in this way.

Attempts to oxidize selectively sucrose on only one primary OH group have so far been unsuccessful using conventional technologies.

In addition to the 3 possible monocarboxylic acids obtainable by oxidation of the primary OH groups, dicarboxylic and tricarboxylic acids are often also present in the resulting mixture. Furthermore, in the case of the described variants, cleavage products are formed which are not specified in detail, which leads to significant yield losses and significantly reduces the selectivity of the reaction with respect to the formation of monocarboxylic acids. (Les A. Edye, George V. Meehan, Geoffrey N. Richards, Platinum catalyst oxidation of sucrose, J. Carbohydrate Chemistry, 10 (1), 11-23 [1991]).

The same results were found in the case of saccharide reduction, as shown in palatinose assays (Dissertation by H. Puke, TU Braunschweig).

It is an object of the present invention to propose the oxidation of sugars, sugar derivatives and primary alcohols with better selectivity with respect to monooxidized products.

SUMMARY OF THE INVENTION

This object is achieved by continuously oxidizing sugars, sugar derivatives or primary alcohols in an aqueous solution and at a concentration of between 0.1 and 60% oxygen or oxygen-containing gases on noble metal or mixed metal catalysts, the bulk stream of products thus formed is fed to the electrodialysis stages and the obtained monocarboxylic acid is removed.

This process is particularly suitable for the production of mono-oxidized sugars or sugar derivatives and primary alcohols. In fact, a smooth continuous reaction process and simultaneous separation of oxidation products by electrodialysis yields truly exclusive monocarboxylic compounds from sugars and sugar derivatives or from primary alcohols. At the same time, it is possible to obtain a high yield in real time and space.

The specific introduction of functional groups of carbohydrates and carbohydrate derivatives, which are numerous among the starting materials, is of great industrial importance in terms of the synthesis of hydrophilic building blocks for the polymer and sugar-based surfactant segment. Due to their ecologically advantageous properties, these raw materials have considerable advantages over synthetic products.

It has been found to be particularly effective when the substances remaining after the electrodialysis step and the removal of single crystal acids are allowed to return to the oxidation step. A continuous cycle and particularly efficient treatment of the starting materials is obtained by this process.

It is preferred that the material stream is enriched with air bubbles prior to entering the catalyst bed so that there is sufficient oxygen for the oxidation reaction.

The invention described herein describes a continuous process in which sugars or sugar derivatives can be converted selectively into monocarboxylic derivatives by a combination of two process steps. The first step consists in continuously carrying out the oxidation on noble metal or mixed metal catalysts. Mixed metals are also suitable, but with respect to the recyclability of the noble metal catalysts with the catalytically active element, the noble metal catalysts are more preferred.

The monocarboxylic acids formed during the oxidation are then similarly continuously removed from the reaction mixture by a second process step, which is an electrodialysis step.

This hitherto unwritten combination of continuous oxidation followed by continuous removal of the oxidation products formed is particularly suitable for the production of monocarboxylic acids from sugars and their derivatives. A higher conversion rate than the previously described methods is obtained and the selectivity with respect to the formation of monocarboxylic acids is surprisingly above 95%.

Continuously performed oxidations are achieved under progressive design conditions as follows:

(a) the reactor system consists of an uptake stage (mixing vessel) together with a tubular reactor in which a fixed catalyst layer is deposited. In particular, the absorber stage may be a mixing vessel (mixing reactor). In the mixing reactor, oxygen enrichment is carried out either by introducing air or alternatively gas mixtures with higher partial pressures or pure oxygen in the form of finely dispersed bubbles by means of special introducing hoses for the gas, under or without pressure. This mixing reactor is connected to a tubular reactor arranged in parallel (possible up and down flow) in which the actual oxidation is carried out in contact with the catalyst.

b) The oxidation can also be carried out with suspended catalysts (slurry process) in a mixing vessel, where the connection to the electrodialysis unit is carried out through a separation step. In the simplest case, settling centrifuges or cross-flow modules can be used for this purpose. Technological solutions to this problem are also possible using suitable retention systems such as backwash filters, separators and so on.

Suitable catalysts are noble metal contacts or mixed metal catalysts which can be used, for example, as extrudates (C, oxides), fibers, tablets or powders. When noble metal catalysts are used, the proportion of metal should be in the range of 0.1 to 10%. Particularly good results were obtained with Pt catalysts having a platinum content of only 1% and in powder form, but the fines were removed by separation. The stream exiting the tubular reactor is then fed to the electrodialysis unit on the diluate side so that the oxidized products migrate to the concentrate by applying voltage and then discharged from the reaction system. In order to maintain the equilibrium state of the continuous reaction system, the amount discharged from the concentrate is metered in a controlled manner by adding an educational solution to the mixing reactor.

Mixed metal catalysts are, for example, those supplied by Degussa AG and are described in an article by K. Deller and B. Despeyroux in Catalysis of organic reactions (1992).

A particularly preferred apparatus for carrying out the present invention is characterized in that it comprises a serially connected sorption stage, an oxidation stage and an electrodialysis stage.

In order to achieve particularly precise control of the amount of substances to be treated in individual cases, it is particularly advantageous if a branch line is provided parallel to the electrodialysis stage.

This additional parallel line provides a bypass line parallel to the electrodialase stage. Together with the corresponding current controllers or pumps, the amount of the substance led from the catalyst or from the end of the uptake stage may be used so that it is fed to the electrodialysis stage only to an extent that could be processed and unprocessed to be returned to the uptake stage through this bypass line. In this way, exactly the optimum amount of the substance is processed in each of the steps.

baths of three possible monocarboxylic acids of sucrose are given in abbreviated form only in the following description. Úpinp names together with two other also mentioned products are:

^ yl monuKarL acid sucrose _Q C: 1-0- (β-D-fruktofuranuronyl) -α-D-glucopyranoside, saccharose monocarboxylic acid: 2-keto-2-0- (D-glucopyranosyl) -β-D-glukofuranónová acid C ₆ sucrose monocarboxylic acid: 1-O- (β-D-fructofuranosyl) -α-D-glucopyranuronide

C 6 oxidized GMF: 5- (α-D-glucopyranozyloxymethyl) furan-2-carboxylic acid,

Oxidθ oxidized GMF: 5- (α-D-glucopyranuronyloxymethyl) furfural.

BRIEF DESCRIPTION OF THE DRAWINGS

The apparatus for carrying out this method will be explained in detail in the drawings with particularly advantageous parameters of the apparatus.

Fig. 1 shows a preferred embodiment of the present invention; FIG. 2 is a graph of the method in the first exemplary embodiment; FIG. 3 is a graph of the method of the second exemplary embodiment; FIG. 4 is an alternative embodiment with respect to FIG. First

The schematic representation of FIG. 1 shows the mixing vessel or tank 10 with the stirrer 11 and the stirrer motor 12. The starting material is introduced into the vessel 10 via line 15, and also the pH controller 17 is shown schematically, reference numeral 18 is given for the thermostat outlet and 19 for the inlet. Additional air (N ₂ / O ₂ ) is directed to vessel 10 at 21.

After mixing in the mixing vessel, the pH-controlled feedstock, for example sugar, which is enriched and mixed with oxygen, is metered into one of the oxidation stages 30 via one of the P-marked pumps. This oxidation stage 30 contains a noble metal or mixed metal catalyst, in the case of a Pt / C supported catalyst. In the oxidation stage 30, a continuous oxidation of the starting material takes place. This material is then fed to an electrodialysis stage 40 by means of a further pump, designated P. This stage, the ED shaft or electrodialysis cell, is shown only schematically. In it, the monocarboxylic acid is discharged continuously outwardly in the partially oxidized mixture, by the route indicated by 41, in which the conducting cell 4.2 is also stored, additionally indicated by the letter L.

The non-monoxidized sugars and other substances, on the other hand, are returned via route 43 again to the tank 10 for further processing simultaneously with the feed substance 15, which in each case corresponds chemically.

The monocarboxylic acids are passed through the conductive cell 42 into the tank 50 and concentrated there. In the tank 50, a pH measurement, indicated at 51, is carried out continuously. The product is taken here at point 52 while at 53 the product not returned is returned to the electrodialysis stage by means of a pump P.

Fig. 4 shows an arrangement corresponding to almost all details of FIG. In addition, there is a conduit 60, a bypass conduit between the outlet of the oxidation stage 30 and the return line 43 from the electrodialysis stage to the tank.

This line 60 is pure schematic. It may contain additional tanks, measuring stages and equipment, pumps and flow control elements.

The pumps P already mentioned are also included in the embodiment of FIG. 1 and are capable of passing alone or in conjunction with the above-mentioned elements from the oxidation stage 30 to the electrodialysis stage 40 only those amounts of substance which can also be optimally processed there. Excess amounts can be returned via the branch line, line 60 again to the uptake stage or tank 10 together with non-monoxide sugars from the electrodialysis stage 40 through line 43.

By way of example, the non-reducing disaccharide sucrose will be discussed herein, which can be converted selectively to its monocarboxylic acids in this apparatus, in the manner described.

Although three primary hydroxyl groups are capable of reacting in the molecule, oxidation is carried out on only one of these groups in each case, so that only mono-oxidized sucrose derivatives are obtained. The selectivity of these products is at least 95% and the possible formation of di- or tricarboxylic acid has not been established using this continuous process.

In addition to the high selectivity, a considerable increase in the reaction rate can be observed in this continuous mode of operation compared to the discontinuous method. The advantages of this method of the invention in terms of reactivity are documented for glucose and sucrose as compared to the discontinuous method in FIG. 2 and 3.

In FIG. 2 and 3 is plotted in each case horizontal time in minutes, vertical conversion rate in percent. There is a graphical representation of the discontinuous test in each case; 2 for the glucose reaction, FIG. 3 for the sucrose reaction. The continuous test is shown by dotted lines, again in FIG. 2 for the glucose reaction; and FIG. 3 for the sucrose reaction. In FIG. 3 is the addition of the continuous test of pure oxygen (0 _2).

A further increase in the reaction rate for the formation of monocarboxylic acids can be achieved by increasing the partial pressure of oxygen in the solution, for example by introducing pure oxygen (instead of air or oxygen / nitrogen mixture).

Another technical advantage of this process according to the invention is that catalyst deactivation, which generally occurs in discontinuous operation (see K. Heyns, H. Paulsen [cited above], H. Puke, Dissertation TU Braunschweig), has not been found. Surprisingly, even when introducing pure oxygen, no catalyst deactivation occurs. This advantage has not hitherto been described in the corresponding literature, and even this is a great technological advantage during the selective derivatization of sugars.

This method can be used without difficulty to reduce sugars such as palatinose and glucose.

The selectivity to the respective monoxidation products can be controlled by the choice of suitable catalysts either using the appropriate mixed metal supports or contacts or by means of the pH value.

In the case of palatinose, moreover, the use of appropriate noble metal catalysts (e.g. Pt / Al ₂ O ₃ (1% Pt [Aldrich]) in which Al ₂ O ₃ is used as carrier _{) can} be used to oxidize the primary OH group at the 6 'position to the maximum extent possible.

In this case, it has been found that, in contrast to the possibility of dicarboxylic acid formation, only the monocarboxylic acid is obtained. It has further been found that in this process the selectivity can be influenced by the choice of the catalyst such that the oxidation surprisingly leads mainly to only one oxidation product.

Tests with other catalysts have also shown that not only selectivity to monoacids, but also selectivity to the desired product can be controlled in this way. This process is not only suitable for the oxidation of carbohydrates, but also possible for the conversion of alcoholic sugars (e.g. isomaltoses) into the corresponding monoacids.

Furthermore, it is possible to oxidize sugar derivatives such as glucopyranosylmethylfurfural, where, on the one hand, the 6 'position and on the other hand the aldehyde functionality is converted to the corresponding monocarboxylic acid.

No doubly oxidized products are also obtained with this starting material. Despite the existence of a more readily oxidizable aldehyde group, like the isolated products which carry a carboxyl group as the C _g. The aldehyde group is retained for these compounds.

Similarly, alkyl glycosides or mixtures such as alkyl polyglycosides can be oxidized in this manner.

The examples show that the process described herein is suitable for oxidizing aldehyde or primary hydroxyl groups to obtain mono-oxidized products. The feed materials used, which come mainly from the sugar field, must be soluble in water or in mixtures of water and organic solvents (for example water / isopropanol mixtures) and non-volatile under the test conditions used. Also in the case of feedstocks from the non-sugar region, this process is suitable for the production of mono-oxidized products (e.g. propanol to propionic acid), provided that they are (at least partially) soluble in the described environment.

The oxidation is carried out at temperatures between 0 ° C to 80 ° C, but preferably between 20 ° C to 60 ° C. The concentrations of the starting materials may vary between 0.1% to 60%, but it is preferable to maintain the concentrations in the range of 3% to 20%. The pH may be adjusted in the range of 1 to 13 during oxidation by addition of Na ₂ CO ₃ , NaHCO ₃ or NaOH or other alkalizing agents.

Ion-exchange membranes in electrodialysis may be used to isolate monocarboxylic acids. In this case, however, free acids can only be obtained at low pH values. In spite of the neutral mode of operation, however, the sodium salts of monocarboxylic acids are isolated in this case.

When ED (electrodialysis) is performed with bipolar membranes, the neutralizing agent can be recovered and, in addition, free monocarboxylic acids of the corresponding starting materials can be obtained. Although higher investment costs for bipolar membranes have to be calculated, the economic factor has to be controlled on a case-by-case basis for processing in subsequent operations.

Comparative tests with a non-continuous method of operation (batch) clearly show the advantages of the method described herein. In batch tests, reaction rates are significantly lower. The selectivity in the comparative tests for monocarboxylic compounds decreases sharply and by-products occur to a significant extent which are not identified in detail.

In the case of a continuous process, no catalyst deactivation was found in the process described, even after 2 months. In a batch process, catalyst inactivation occurs after a short time, as described in the literature.

The circulation apparatus described in FIG. 1. Gas uptake is performed by stirring allowing a two-wall stirred tank reactor (500 mL) above the frit base. The glass insert is used as a release zone, from which a portion of the current is passed through a centrifugal pump through a catalyst layer which is placed in a glass column sealed by two frits. After passing through the stationary layer, a portion of the stream is fed to the electrodialysis unit and then returned to the mixing reactor after separation of the oxidation products. The product is discharged via the concentration cycle of the dialysis unit, and an equivalent amount of feed solution is fed to the mixing reactor in a controlled manner using a hose pump. The solution losses during the concentration cycle are replaced by distilled water.

Examples of the invention

Example 1

Continuous oxidation of palatinose at 35'C

Using the described apparatus, 20 g of platinum / activated carbon catalyst (5% Pt / C, particle size 40-100 micrometers, Degussa) and 1000 ml of a 0.1 molar palatinose solution are charged to the circulation apparatus and the dilution cycle of the electrodialysis unit. For the concentration cycle, distilled water and IM Na ₂ SO _{4 are used} to elute the electrode.

The temperature is maintained at 35 ° C by means of a circulating thermostat, the gas supply (N ₂ / O ₂ ) can be adjusted by pressure reducing valves and the gas volumetric rate is measured with an associated rotameter, thus maintaining gas velocities of 100 cm ³ per minute 02 up to 400 cm ³ per minute N 2. The pH is kept constant at 6.5 by titration of the obtained IM NaHCO ₃ acid. The electrodialysis unit (Bel III, Berghof GmbH Labortechnik) is equipped with 6 AMV / CMX membrane pairs (effective membrane area = 360 cm- ⁵⁾ and operates at a voltage of 5 to 6 V. To achieve equilibrium, the progress of the reaction is monitored by HPLC measurement. The following ingredients are present in the concentrate:

6-O- (α-D-glucopyranuronyl) -D-fructofuranose (C ₆ , -acid): 50%,

2-keto-6-O- (α-D-glucopyranosyl) -D-arabinohexonic acid (C 1 -acid): 42.5%,

5-O- (α-D-glucopyranosyl) -D-arabonic acid (GPA acid):

3.5%

Selectivity for monocarboxylic acids: 96%.

The compounds were capable of separation to a preparative extent and were determined by NMR and mass spectrometry.

Example 2

Oxidation of palatinose at 42.5 ° C

Analogously to Example 1, palatinose is oxidized at a reaction temperature of 42.5 ° C. The resulting mixture in the concentrate has the following composition:

Cg, -acid 50.0% Cj-acid 42.5% GPA acid 4.0% selectivity to monoacids 96.5%

Continuous comparative test

Oxidation of palatinose

The batch oxidation is performed similarly in a circulating reactor system, but without electrodialysis and feedstock dosing.

g of palatinose was dissolved in 1000 ml of distilled water and oxidized at 35 C. The operation is ^much catalyst is platinum / activated carbon (5% Pt, particle size 40 to 100 microns, Degussa). With a reaction amount of 80% palatinose, the assay was terminated after days and the unoxidized products were separated by chromatography.

The product obtained has the following composition:

Cg, acid C11-acid diacid 50.6% 23.5% 8.1%

together with a significant proportion of unidentifiable products. The selectivity with respect to the formation of monocarboxylic acids in this case is 74.1%.

Example 3

The glucose oxidation is carried out in the apparatus described in Example 1 at a pH of 6.5 (addition of NaHCO 3) and at a temperature of 35 ° C. The continuously obtained product solution has the following composition:

sodium gluconic acid 92% sodium glucuronic acid 7%

The selectivity based on the monoacids is 99%.

Continuous comparative test

Conversion of glucose at 35C and pH 6.5 and using a platinum / activated carbon catalyst (5% platinum, Degussa, 40 to 100 microns) resulted in a conversion rate of about 80% after three days.

The main oxidation products are:

Sodium gluconic acid salt 60% Sodium glucuronic acid salt 15% Sodium glucuronic acid salt 10% together with 15% products not detailed in detail.

The selectivity with respect to the monoacids is 75%.

The graphical representation of FIG. 2 shows the reaction curves for continuous and batch oxidation of glucose. The reactivity of the continuous mode of operation is significantly higher and no catalyst deactivation was found.

Example 4

Glucose oxidation at pH 3

The oxidation is carried out as described in the example

3, but no direct pH adjustment was made by addition of NaHCO ₃ . After the start-up phase, the pH stabilized at 3 as a result of the acid formed. Under these reaction conditions, gluconic acid delta-lactone is formed from gluconic acid, which is, however, convertible again into gluconic acid by increasing the pH.

Product composition:

gluconic acid 60% delta-lactone gluconic acid 20% glucuronic acid 15%

Example 4a

Mixed metal catalysts are noble metal catalysts containing 2 or more catalytically active metals together with promoters such as bismuth. The problem with the catalysts in the batch test is that they are not as active apart from longer reaction times. In this case, subsequent reactions with the monocarboxylic acids are included, but such that significant amounts of by-products are obtained.

This disadvantage can be overcome by using the method of the invention. The product formed is removed by electrodialysis immediately after its formation and therefore no longer comes into contact with the catalyst.

This has been demonstrated in a practical comparative test with a P / Pd / Bi mixed metal catalyst (Degussa) in the oxidation of glucose to gluconic acid or glucuronic acid.

The oxidation was carried out as described in Example 3 with respect to the use of a Pt / Pd / Bi mixed catalyst.

Product composition:

sodium gluconic acid%

sodium glucuronic acid 4%

The selectivity for the acids is 98%.

Example 5

Oxidation of sucrose

Sucrose can be converted to the corresponding monocarboxylic acids by the procedure described in Example 1.

The oxidation is carried out at a pH of 6.5 and a temperature of 35 ° C to give a mixture of 3 monocarboxylic acids:

monocarboxylic acid, C _g, C -sucrose monocarboxylic acid -sucrose _{g of} monocarboxylic acid C-sucrose

46,5%

43.7%

4.9%

The selectivity is greater than 95%.

Batch Comparison Test

Oxidation of sucrose

Discontinuous oxidation at 35 ° C and pH

6.5 resulted in the following products at a reaction rate of 90% after six days:

carboxylic acid, C _g, C -sucrose carboxylic acid -sucrose _{g of} carboxylic acid C ^ -sucrose

40.0%

31.0% of which about 10% was diacid

8.8%.

The selectivity for the monocarboxylic compounds was approximately 70%.

The graphical representation of FIG. 3 shows the advantages of a continuous mode of operation in relation to the reaction rate.

Example 6

Oxidation of glucopyranosylmethylfurfural (GMF)

Continuous oxidation of GMF was carried out in the same manner as in Example 1.

At a temperature of 35 ° C and a pH of 7, the following were obtained:

Cg, -oxidized GMF 33%

C - ^ - oxidized GMF 66%

The selectivity of the mono-oxidized products is 99%.

Example 7

The oxidation of saccharose is carried out in the apparatus described in Example 1 at pH 6.5 and at 35 ^e C.

Pure oxygen was introduced in place of the oxygen-nitrogen mixture, thereby accelerating the formation of oxidized products (Fig. 3).

The main oxidized products are:

carboxylic acid Cg-sucrose carboxylic acid Cg-sucrose carboxylic acid Cg-sucrose

43.0%

43.0%

9.5%

The selectivity is above 95%.

In summary, the invention relates to a method and apparatus for producing monocarboxylic products from sugars, sugar derivatives, and primary alcohols. The starting materials are fed to a continuous oxidation stage comprising a noble metal catalyst or a mixed metal catalyst. The stream containing the monocarboxylic acids formed on the catalysts is fed to an electrodialysis step, wherein the monocarboxylic acids are continuously removed and recovered.

Claims (21)

Method for producing monocarboxylic acids from sugars, sugar derivatives or primary alcohols, characterized in that sugars, sugar derivatives or primary alcohols are continuously oxidized in aqueous solution and at concentrations between 0.1 and 60% oxygen or oxygen-containing gases on catalysts from precious metals or mixed metals, the bulk product stream thus generated is fed to the electrodialysis step and the monocarboxylic acids are removed and recovered. Process according to claim 1, characterized in that the non-oxidized starting materials are returned to the oxidation stage after the removal of the monocarboxylic acids. Method according to claim 1 or 2, characterized in that the material stream is enriched with oxygen bubbling before entering the catalyst layer. Method according to claim 3, characterized in that in the oxidation stage the stream first passes through a reactor in which oxygen enrichment is carried out by introducing air, gas mixtures with higher partial oxygen pressures or pure oxygen in the form of finely divided bubbles or free bubbles under pressure; without pressure, a part of the stream is pumped from the reactor through a tubular reactor arranged in parallel with the catalysts. Process according to claim 3, characterized in that in the oxidation step a slurry process is carried out with slurry catalysts in a mixing vessel. Method according to claim 5, characterized in that the oxidation stage and the electrodialysis stage are separated by a separation unit. Process according to any one of the preceding claims 1 to 6, characterized in that noble metals of the 8th subgroup on supports are used as catalysts. Process according to claim 7, characterized in that Pt catalysts are used in particular on supports having a platinum content between 0.1% and 10%, in particular Pt / C powder catalysts with a Pt content between 0.1% and 10% with fines removed. Method according to any one of the preceding claims 1 to 7, characterized in that reducing saccharides such as palatinose, glucose, fructose, sorbose and / or non-reducing saccharides such as sucrose, trehalose and / or sugar alcohols are used, such as palatinol, sorbitol and / or alkyl glycosides and alkyl polyglycosides such as methyl glycoside, octyl glycoside or the like, and / or specially modified sugar derivatives such as HMF or GMF as starting materials that are monooxidized. Process according to any one of the preceding claims 1 to 9, characterized in that water or mixtures of water and secondary alcohols, preferably isopropanol, are used as solvents for the starting materials. Process according to any one of the preceding claims 1 to 10, characterized in that the oxidation and electrodialysis are carried out in a pH range of 1 to 13. 12. A method according to any one of claims 1 to 11, characterized in that the temperature for the oxidation is in the range of O'C to 80C, preferably in the range of 20 C to 60 C ^e Method according to any one of the preceding claims 1 to 12, characterized in that the starting materials are used in a concentration between 3% and 20%. Method according to any one of the preceding claims 1 to 13, characterized in that Na ₂ CO ₃ or NaHCO ₃ or NaOH is used to adjust the pH or other alkalinizing agents are used. A process according to any one of the preceding claims 1 to 14, characterized in that only the 6-position on the non-reducing glycopyranosyl units are selectively oxidized using the supported Pt / Al ₂ O ₃ catalyst. Method according to any one of the preceding claims 1 to 15, characterized in that a lateral guide is used and the material stream coming from the oxidation stage is isolated from the material stream of the electrodialysis stage. Apparatus for carrying out the method according to any one of claims 1 to 16, characterized in that it comprises a serially connected absorption stage (10), an oxidation stage (30) and an electrodialysis stage (40). Device according to claim 17, characterized in that it is additionally provided with a guide (41) to the tank (50) and a return guide (43) to the absorption stage (10). Apparatus according to claim 17 or 18, characterized in that the absorber stage (10) is a mixing vessel. Device according to any one of claims 17 to 19, characterized in that the ion exchange or bipolar membranes are used in the electrodialysis stage (40). Device according to any one of claims 17 to 20, characterized in that the lateral guide (60) is formed parallel to the electrodialysis stage (40).