AU689101B2 - Method and device for producing monocarboxylic acids from carbohydrates, carbohydrate derivatives or primary alcohols - 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 betweeen 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.

Description

Description Method and apparatus for manufacturing monocarboxylic acids from carbohydrates, carbohydrate derivatives or primary alcohols The invention relates to a method and an apparatus for manufacturing monocarboxylic acids from carbohydrates, carbohydrate derivatives or primary alcohols.

It is possible with various biochemical processes to oxidize carbohydrates selectively. These manufacturing methods however possess considerable disadvantages. In the first place the breeding of microorganisms or the manufacture of biocatalysts is fraught with considerable difficulties. The production methods mostly involve fermentation during the manufacture of gluconic acids), so that the use of nutrient salts in the fermentation solution leads to considerable salt loads. A further disadvantage is the sterile method of operation often required with these processes, so that considerable equipment costs have to be allowed for.

Particular importance has been acquired by heterogeneously catalysed oxidation with noble metals of the 8th sub-group on suitable support materials. The oxidation of glucose to gluconic acid with atmospheric oxygen can be carried out chemically in this way, e.g. on Pt/C catalysts.

Disadvantageous with this method of procedure is however the sharply decreasing selectivity of the reaction and the rapid deactivation of the catalyst, cf. "Ullmanns Enzyklopddie der Technischen Chemie", 4th newly revised edition, Vol. 24, page 785, Verlag Chemie 1983.

Similar problems are observed with the oxidation of saccharose. Heyns and Paulsen have already investigated this reaction on platinum catalysts Heyns, H. Paulsen, Adv. Carbohydr. Chem. 17, 169 (1962); K. Heyns, W.D.

Soldat, P. K611, Chem. Ber. 3619 (1975). They cbtained as 1- I--II i,,

I

2 resulting products mixtures of oxidized compounds, on which no further data could be given regarding chemical structure and composition because of the complexity involved.

In a method known from EP 0 040 709 B1 for manufacturing diacetone ketogulonic acid, diacetone sorbose is partially oxidized and separated by means of electrodialysis. In this case a discontinuous method is involved and, due to the introduction of protective groups, the initial derivative possesses only one oxidizable group.

There are known from DE 38 03 465 Al, DE 39 16 206 Al and US-PS 4 985 553 various batch processes, which produce quantitatively unacceptable conversion figures or product mixtures containing unsatisfactory impurities with parent compounds. In some cases it is already proposed in the citations to undertake a product isolation with expensive purification methods.

A method described in EP 0 218 150 Bl for the catalytic oxidation of saccharose explicitly points out that with a discontinuous process multiply oxidized products are obtained on a large scale.

Attempts to oxidize saccharose selectively on only one primary OH group have had no success to date with the conventional techniques.

In addition to the 3 possible monocarboxylic acids obtainable by oxidation of the primary OH groups, the diand tricarboxylic acids also occur as compounds in the product mixture. There are moreover formed in the case of the variants described a number of cleavage products not specified in detail, which lead to considerable losses in yield and reduce considerably the selectivity of the reaction as regards the formation of monocarboxylic acids.

,(Les A. Edye, George V. Meehan, Geoffrey N. Richards, _I I I Platinum catalysed oxidation of sucrose. J. Carbohydrate Chemistry, 10 11-23 (1991)).

The same has also been observed in the case of reducing saccharides, as e.g. tests on palatinose show (Dissertation H. Puke, TU Braunschweig).

The object of the invention is conversely to propose an oxidation of carbohydrates, carbohydrate derivatives and primary alcohols with a better selectivity in terms of the monooxidized products.

This object is achieved by continuous oxidation of carbohydrates, carbohydrate S"derivatives or primary alcohols in aqueous solution and concentration between 0.1 15 and 60% with oxygen or oxygen-containing gases on noble metal or mixed metal catalysts, and feeding the volume flow of the products so formed to an electrodialysis stage for recovery of the monocarboxylic acid.

S* This method is especially suitable for manufacturing monooxidized carbohydrates or carbohydrate derivatives and primary alcohols. The smooth, continuous reaction process and the simultaneous separation of the oxidation products by means of S• electrodialysis, leads to the recovery of virtually exclusively monocarboxy compounds from carbohydrates and carbohydrate derivatives or primary alcohols.

A high space-time yield is possible at the same time.

The specific functionalizing of saccharides and saccharide derivatives, which are numbered among the starting materials, is of great industrial interest as regards the synthesis of hydrophilic building blocks for the polymer and surfactant sector on a carbohydrate basis. Because of their ecologicially favourable properties, these raw I II I rm

I

materials possess considerable advantages compared with synthetic products.

It has proved particularly effective if the substances remaining after the electrodialysis stage and the removal of the monocarboxylic acids are passed to the oxidation stage once again. A continuous cycle and particularly effective working up of the starting materials are obtained in this way.

10 It is beneficial if the material flow is prior to entering the catalyst bed enriched with air, so that sufficient oxygen is available for the oxidation reaction.

The invention presented here describes a continuous method in which carbohydrates or carbohydrate derivatives can be converted selectivey to 15 monocarboxy derivatives by a combination of two method steps.

6 C The first method stage consists of a continuously operated oxidation on noble metal or mixed metal catalysts. The last-named are also suitable, but in view of their recyclability noble metal catalysts with a catalytically active element are to be 20 preferred.

The monocarboxylic acids formed during the oxidation are then, likewise continuously, removed from the reaction mixture by means of the second method step, an electrodialysis stage.

Said combination of first and second method steps, not described to date, of continuously operated oxidation with subsequent continuous removal of the oxidation products formed is suitable in a particular manner for manufacturing monocarboxylic acids from carbohydrates and their derivatives. Higher conversion rates are obtained with it than with the methods described to date and the selectivity, in terms of the formation of monocarboxylic acids is surpisingly above a I I The starting materials for use in the method of the invention are preferably reducing saccharides palatinoso, glucose, fructose and sorbose) and/or nonreducing saccharides saccharose and trehalose) and/or sugar alcohols (e.g.

palatinitol and sorbitol) and/or alkyl glycosides and alkyl polyglycosides e.g.

methyl glycoside and octyl glycoside) or similar mixtures and/or specially modified carbohydrate derivatives IIMF or GMF).

to* 0 be.

'00:0, a 6 to .0.0.

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The continuously operated oxidation is achieved in process engineering terms as follows: a) The reactor system consists of a gassing stage (agitator vessel) together with a tubular reactor in which the fixed bed catalyst is disposed. The gassing stage can in particular be an agitator vessel (agitator reactor). In the agitator reactor there takes place the oxygen enrichment, either by the introduction of air, or alternatively gaseous mixtures with higher oxygen partial pressures or pure oxygen as finely distributed bubbles or bubble-free via special gas introduction hoses, under pressure or pressureless. Said agitator reactor is connected to a tubular reactor disposed in parallel (up and down flow possible), in which the actual oxidation takes place in contact with a catalyst.

b) The oxidation can also be carried out with suspended catalysts (slurry method) in an agitator vessel, wherein the connection to the electrodialysis unit takes place via a separation stage. In the simplest case decanter centrifuges or cross-flow modules can be employed for this. A technological solution to this problem is also possible by the use of suitable retention systems such as filters with back-flushing unit, separators etc..

There are suitable as catalysts noble metal contacts or mixed metal catalysts, which can be used e.g. as extrudates oxides), fibres, tablets or powder. If noble metal catalysts are used, the metal portion should come to between 0.1 and 10%. Particularly good results were achieved with Pt catalysts which exhibited a platinum content of only 1% and were in powder form, wherei however the fines were removed by sizing. The part flow coming from the tubular reactor is then fed to the electrodialysis unit C I _I_ on the diluate side, so that the oxidized products migrate into the concentrate by application of a voltage and are then discharged from the reaction system. In order to maintain the equilibrium state of the continuously operated reaction system, the amount which is discharged out of the concentrate is dosed in controlled manner by the addition of educt solution to the agitator reactor.

o Mixed metal catalysts are for example ones such as those supplied by Degussa AG and described in an article by K.

Deller and B. Despeyroux in: "Catalysis of organic reactions" Ed W.E. Pascoe, Marcel Dekker, Inc., New York (1992).

A particularly suitable apparatus for carrying out the method according to the invention is characterised in that it comprises, connected in series, a gassing stage, an oxidation stage and an electrodialysis stage.

In order to achieve a particularly accurate control of the substance amounts processable in individual cases, it is particularly preferable if a branch line is provided parallel to the electrodialysis stage.

There is obtained with this additional parallel line a kind of bypass line parallel to the electrodialysis stage.

Together with corresponding flow control units or pumps it is possible for amounts of substance fed out of the catalyst or the upstream gassing stage to be fed to the electrodialysis stage only to the extent that they can be processed there and for non-processable amounts to be returned directly into the gassing stage once again by means of the bypass line. In each of the stages, therefore, exactly the optimal amount of substance is processed.

R The names of the three possible saccharose-monocarboxylic Z acids are used only in abbreviated form in this k vr A _1 application. The full names, together with those of two other products also mentioned below, are:

C

6 -saccharose monocarboxylic acid: l-0-(B-D-fructofuranuronyl)-a-D-glucopyranoside C.-saccharose monocarboxylic acid: 2-keto-2-0-(a-Dglucopyranosyl-B-D-glucofuranonic acid C,,-saccharose monocarboxylic acid: -D-fructofuranosyl)-a-D-glucopyranuronide C,-oxidized GMF: 5- (-D-glucopyr-inosyl-oxymethyl)-furan-2carboxylic acid

C

6 ,-oxidized GMF: 5-(a-D-gluco; rranuronyl-oxymethyl)furfural An apparatus for carrying out the method will be explained in detail below from drawings, as will some particularly preferred parameters.

Fig. 1 shows a preferred embodiment of the invention; Fig. 2 a graph of the method in a first example; Fig. 3 a graph of the method in a second example; Fig. 4 an alternative embodiment to Fig. 1.

The diagrammatic representation in Fig. 1 shows an agitator vessel or a tank 10 with an agitator 11 and a motor 12 for the agitator 11. There is introduced into the vessel 10 at the educt, at 17 a pH controller is provided diagrammatically, at 18 data are outputted to a thermostat and at 19 inputted from the latter. In addition air (N,/0 2 is fed to the tank 10 at 21.

I I I r-

I

8 After the intermixing in the agitator vessel the pHcontrolled educt, for instance a carbohydrate, which is enriched and intermixed with oxygen, is fed via one of the pumps labelled P to the oxidation stage 30. Said oxidation stage 30 contains a noble metal or mixed metal catalyst, in this case a Pt/C supported catalyst. In the oxidation stage there takes place a continuous oxidation of the starting material; the latter is after this passed via the next of the pumps labelled P to an electrodialysis stage 40. The latter, an ED stack or an electrodialysis cell, is likewise shown only diagrammatically. In it the monocarboxylic acid is drawn off continuously out of the partially oxidized mixture, namely along the path marked 41, in which a conductivity cell 42, additionally labelled is also located.

The non-monooxidized carbohydrates etc. are conversely returned along the path 43 again into the tank 10 for further processing additionally to the educt 15, to which they in any case correspond chemically.

The monocarboxylic acids are after passage through the conductivity cell 42 fed into a tank 50 and concentrated there. In the tank 50 there takes place constantly a pH measurement indicated at 51. The product is withdrawn here at 52, while at 53 non-discharged product is returned once again into the electrodialysis stage via a pump P.

Fig. 4 shows a layout conforming in almost all particulars to that of Fig. 1. There is provided in addition a line a bypass line between the outlet of the oxidation stage and the return line 43 from the electrodialysis stage into the tank This line 60 is purely diagrammatic here; it can contain additional tanks, measuring stages and devices, pumps and flow control elements.

-re~ II 9 The pumps P already mentioned, which are also contained in the embodiment according to Fig. 1, are capable alone or with said elements above-mentioned of transferring from the oxidation stage 30 into the electrodialysis stage 40 only those amounts of substance which can also be optimally processed there. Surplus amounts can be returned via the bypass line, the line 60, again into the gassing stage or the tank 10, together with the non-monooxidized carbohydrates from the electrodialysis stage 40 along the path 43.

As an example let there be discussed, as a non-reducing disaccharide, saccharose, which can be converted selectively to its monocarboxylic acids in the apparatus shown by the method described Although three primary hydroxy groups are capable of reacting per molecule, the oxidation took place on only one of these groups in each case, so that exclusively monooxidized saccharose derivatives are obtained. The selectivity to these products comes to at least 95% and the possible formation of the di- or tricarboxylic acid is not observed with the use of this continuous method.

In addition to the high selectivity there can be observed with this continuous method of operation, in comparison with the discontinuous method, a considerable rise in the reaction velocity. The advantages of the method according to the invention in terms of the reactivity are documented for glucose and saccharose, compared with the discontinuous method, in Figs 2 and 3.

In Figures 2 and 3 there is plotted in each case horizontally the time in minutes; vertically the conversion rate in per cent. There is shown graphically in each case -o with the symbol a discontinuous test, in Fig. 2 for glucose reaction, in Fig. 3 for saccharose reaction. There 1 rll is shown in dotted lines a continuous test, once again in Fig. 2 for glucose reaction and in Fig. 3 for saccharose reaction; in Fig. 3 in addition a continuous test with pure oxygen (02).

A further rise in the reaction velocity with regard to the formation of monocarboxylic acids can be achieved by increasing the oxygen partial pressure in the solution, e.g. by the introduction of pure oxygen (instead of air or oxygen/nitrogen mixtures).

A further technical advantage of this method of operation according to the invention is that a deactivation of the catalyst, such as generally occurs with discontinuous operation (comparison: K. Heyns, H. Paulsen (see above); H.

Puke, Dissertation TU Braunschweig) is not observed. Even on the introduction of the pure oxygen no deactivation of the catalyst surprisingly takes place. This advantage has not been described to date in the relevant literature and also proves to be a great advance from a technological point of view during the selective derivatization of carbohydrates.

The method can be applied without difficulty to reducing sugars, such as e.g. palatinose and glucose.

The selectivity to particular monooxidation products can be controlled by the choice of suitable catalysts, either by the use of particular supports or mixed metal contacts, or by means of the pH value.

In the case of palatinose it is moreover possible, by the use of particular noble metal catalysts Pt/A1 2 0, (1% Pt) Aldrich), in which A1 2 0 3 is used as support, to oxidize the primary OH group in 6' position to the maximum extent.

4 11 In this case it is found that, despite the possibility of the formation of the dicarboxylic acid, exclusively only the monocarboxylic acid is obtained. Furthermore it can be observed that with this method the selectivity can be influenced in such a way, through the choice of the catalyst, that the oxidation surprisingly leads in the main to only one oxidation product.

Tests with other catalysts also showed that not only the selectivity to the mono-acids, but also the selectivity to a desired product, can be controlled with this method. The method is not only suitable for the oxidation of saccharides, but it is also possible to convert sugar alcohols isomalt) into the corresponding mono-acids.

Furthermore it is possible to oxidize carbohydrate derivatives, such as e.g. glucopyranosylmethylfurfural, wherein on the one hand the 6' position and on the other hand the aldehyde function is converted into the corresponding monocarboxylic acid.

With this educt also no doubly oxidized products are obtained. Despite the existence of a more readily oxidizable aldehyde function, products are likewise isolated which bear a carboxyl function exclusively in C 6 position. The aldehyde function is retained with these compounds.

Likewise alkyl glycosides or mixtures, such as e.g. alkyl polyglycosides, can be oxidized with this method.

The examples show that the method described here is suitable for the oxidation of aldehyde and primary hydroxy functions in order to obtain monooxidized products. The 'R'R 4\/educts used, which come here mainly from the carbohydrate ector, must be soluble in water or in mixtures of water 7\ nd organic solvents water/isopropanol mixtures) and

I

-I I not volatilize under the test conditions used. In the case also of educts from the "non-carbohydrate sector" the method is suitable for manufacturing monooxidized products propanol to propionic acid), provided they are (even partly) soluble in the media described.

The oxidation may be conducted at temperatures between 0 and 0 C. Preferred temperatures are between 20 and 60 0 C. The educt concentrations can vary between 0.1 and 60%, but are for preference kept in the range from 3 to 20%. The pH values can be adjusted in the range from 1 to 13 during the oxidation by the addition .of Na 2

CO

3 NaHCO 3 or NaOH or other 0 "alkalizing agents".

For the isolation of the monocarboxylic acids, ion exchange membranes can be used in the electrodialysis. In this case, however, the free acids can be obtained only at low pH values. Despite a neutral method of operation, however, mostly the Na salts of the monocarboxylic acids are u isolated in this case.

If the ED is carried out with bipolar membranes, the neutralizing agent can be recovered again and in addition the free monocarboxylic acids of the corresponding educts be obtained. Although higher investment costs have to be calculated for bipolar membranes, the economic factor must nevertheless be checked on a case-to-case basis in terms of the processing involved in subsequent operations.

Comparison tests with a non-continuous method of operation (batch) show clearly the advantages of the method described here. With the batch tests the reaction velocities are significantly slower. The selectivity in the case of the comparison tests to the monocarboxy compounds decreases sharply and subsidiary products occur on a considerable scale, which have not been identified in detail.

Y -1 M In the case of the continuous method of operation no deactivation of the catalyst was observed with the method described here even after a period of 2 months. With the batch method of operation inactivation of the catalyst occurs after only a short time, as has already also been described in the literature.

For the carrying out of the oxidation, the circulation apparatus described in Fig. 1 is used. The gassing takes place in an agitatable cylindrical double-walled agitator reactor (500 ml) above a frit base. A glass insert is used as relaxation zone, from which a part flow is conveyed by a centrifugal pump through the catalyst bed, which is located in a glass column sealed with 2 frits. After passing through the fixed bed this part flow reaches the electrodialysis unit and, after separation of the oxidation products, is then returned again into the agitator reactor.

The product is discharged via the concentrate cycle of the electrodialysis unit and the equivalent amount of educt solution is dosed into the agitator reactor in controlled manner by means of a hose pump. The solution lost during the concentrate cycle is replaced with distilled water.

Example 1 Continuous oxidation of palatinose at 35 °C.

Using the apparatus described, 20 g of platinum/activated carbon catalyst Pt/C; particle size 40 100 gm, Degussa) and 1000 ml of a 0.1 molar palatinose solution are charged into the circulation apparatus and the diluate cycle of the electrodialysis unit. Distilled water is used for the concentration cycle and 1 M Na 2 SO, as electrode rinsing.

The temperature is held at 35 °C by means of a circulation thermostat, the gas supply (N 2 /0 2 4 1) can be set by 14 pressure reducing valves and needle valves and the gas volume flow rate measured with a rotameter, so that the gassing rates of 100 cm 3 /min 02 and 400 cm/min N 2 are adhered to. The pH value is held constant at 6.5 by titration of the acid obtained with 1 M NaHCO,. The electrodialysis unit (Bel III, Berghof GmbH Labortechnik) is equipped with 6 AMV/CMX membrane pairs (effective membrane area 360 cm 2 and is operated at a voltage of to 6 V. On attainment of the equilibrium state the course of the reaction is monitored by means of HPLC measurements.

The product range of the substances obtained has the following composition in the concentrate: (-D-glucopyranuronyl)-D-fructofuranose

(C

6 ,-acid): 2-keto-6-0(a-D-glucopyranosyl-D-arabino-hexonic acid acid): 42.5% acid (GPA acid): Selectivity to the monocarboxylic acids: 96% The substances were able to be separated on a preparative scale and characterised by means of NMR and mass spectrometry.

Example 2 Oxidation of palatinose at 42.5% Analogously to Example 1, palatinose is oxidized at a reaction temperature of 42.5 OC. The product mixture obtained in the concentrate has the following composition: C,,-acid: 50.0%

C

1 -acid: 42.5% GPA acid: Selectivity to mono-acids: 96.5% II at ri Ci I Batch comparison test 1 Oxidation of palatinose The carrying out of the batch oxidation likewise takes place in the circulation reactor system, but without electrodialysis and educt dosing.

36 g of palatinose are dissolved in 1000 ml distilled water and oxidized at 35 OC. There is used as catalyst a platinum/ activated carbon type Pt, Degussa, 40 100 pm).

With a palatinose reaction rate of 80% the test is terminated after 4 days and non-oxidized products separated by means of chromatography.

The product obtained has the following composition: C ,-acid: 50.6% C,-acid: 23.5% Di-acid: 8.1% together with a considerable proportion of non-identifiable products. The selectivity with regard to the formation of monocarboxylic acids comes in this case to only 74.1%.

Example 3 Oxidation of glucose The oxidation of glucose took place in the apparatus described in Example 1, with a pH value of 6.5 (addition of NaHCO3) and at a temperature of 35 The continuously obtained product solution has the following composition here: ~II 1-i I_ 16 Gluconic acid Na-salt: 92% Glucuronic acid Na-salt: 7% The selectivity referred to the mono-acids is 99%.

Batch comparison test 2 The conversion of glucose at 35 oC, a pH value of 6.5 and use of the platinum/activated carbon catalyst Pt, Degussa, 40 100 pm) led after 3 days to a conversion rate of approx. The main products oxidized are: Gluconic acid Na-salt: Glucuronic acid Na-salt: Glucaric acid Na-salt: together with 15% of products not identified in detail.

The selectivity with regard to the mono-acids come to b re.

The graphic representation in Fig. 2 shows reaction curves for the continuous and the batch-wise oxidation of glucose.

The reactivity of the continuous method of operation is significantly higher and deactivation of the catalyst cannot be observed.

Example 4 Oxidation of glucose at pH 3 The oxidation took place as described in Example 3, but no firm pH adjustment by addition of NaHCO 3 takes place. After the start-up phase the pH value comes to 3 as a result of the acids formed.

la, I I II I 17 There forms under these reaction conditions from gluconic acid the gluconic acid 6-lactone, which is however convertible into gluconic acid once again by raising of the pH value.

Product composition: Gluconic acid: Gluconic acid 6-lactone: Glucuronic acid: Example 4a Mixed metal catalysts are noble metal catalysts which contain two or more catalytically active metals together with promoters such as e.g. bismuth. A problem with these catalysts in the batch test is that despite longer reaction times they are not so selective. Consequent reactions with the monocarboxylic acids are involved in this case, however, so that considerable amounts of subsidiary products are obtained. This disadvantage can be overcome by the use of the method according to the invention. The products formed are removed by electrodialysis immediately after their formation and therefore no longer come into contact with the catalyst.

This was demonstrated in a practical comparison test with a Pt/Pd/Bi mixed metal catalyst (Degussa) from the oxidation of glucose to gluconic acid or glucuronic acid.

The oxidation took place as described in Example 3, apart from the use of the Pt/Pd/Bi mixed metal catalyst.

Product composition: Gluconic acid Na-salt: 94% ,Glucuronic acid Na-salt: 4% I II IIIIL IL The selectivity with regard to the mono-acids comes to 98% Example Oxidation of saccharose Saccharose can be converted into the corresponding monocarboxylic acids according to the procedure described in Example 1.

The oxidation takes place at a pH value of 6.5 and a temperature of 35 OC, wherein a mixture of three monocarboxylic acids is obtained as product: C,,-saccharose monocarboxylic acid:

C

6 -saccharose monocarboxylic acid: C,-saccharose monocarboxylic acid: 46.5% 43.7% 4.9% The selectivity is over Batch comparison test 3 Oxidation of saccharose The discontinuous oxidation at 35 oC and a pH value of led after 6 days with a reaction rate of 90% to the following product range: C,,-saccharose carboxylic acid: C,-saccharose carboxylic acid: C,-saccharose carboxylic acid: 40.0% 31.0% of which approx. 10% di-acid 8.8% The selectivity to the monocarboxy compounds comes to approx. 'L Y I~ =I 19 The graphical representation in Fig. 3 shows the advantages of the continuous method of operation, in relation to the reaction velocity.

Example 6 Oxidation of glucopyranosyl-methyl-furfural (GMF) The continuous oxidation of GMF takes place according to the same procedure as that described under Example 1.

At a temperature of 35 °C and a pH value of 7 there is obtained: C,,-oxidized GMF: 33% C,-oxidized GMF: 66% The selectivity to the monooxidized products come to 99%.

Example 7 The oxidation of saccharose takes place in the apparatus described in Example 1, at a pH value of 6.5 and with a temperature of 35 oC. Instead of the oxygen-nitrogen mixture, pure oxygen is introduced, whereby the formation of oxidized products is accelerated accordingly (Fig. 3).

The main products oxidized are: C,-saccharose carboxylic acid: 43.0% C,-saccharose carboxylic acid: 43.0% C,-saccharose carboxylic acid: The selectivity comes to over To sum up, the invention relates to a method and an apparatus for manufacturing monooxidized products from 111~ llsllI carbohydrates, carbohydrate derivatives and primary alcohols. The starting materials are fed to a continuously operated oxidation stage containing noble metal or mixed metal catalysts. The flow containing the monocarboxylic acids formed on the catalysts is fed to an electrodialysis stage, wherein the monocarboxylic acids are removed and obtained continuously.

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Claims (23)

1. Method for manufacturing monocarboxylic acids from carbohydrates, carbohydrate derivatives or primary alcohols, characterised in that carbohydrates, carbohydrate derivatives or primary alcohols are fed to an oxidation stage and oxidized continuously in aqueous solution and concentrations between 0.1 and 60% (by weight) with oxygen or oxygen- 10 containing gases on noble metal or mixed metal catalysts, .0 the volume flow of the products so formed is fed to an electrodialysis stage Sand the monocarboxylic acids are recovered.

2. Method according to claim 1, characterised in that 15 non-oxidised educts are after the removal of the monocarboxylic acids fed to the oxidation stage once again. .4

3. Method according to claim 1 or 2, characterised in that S. the flow of material is prior to entering the catalyst bed enriched with oxygen.

4. Method according to claim 3, characterised in that in the oxidation stage first of all a reactor is passed through, in which oxygen enrichment takes place by the introduction of air, of gaseous mixtures with higher oxygen partial pressures or pure oxygen as finely-distributed bubbles or bubble-free under pressure or pressureless, and that from the reactor a parit f the flow is pumped through a tubular reactor together with the catalysts.

5. Method according to claim 3, characterised in that in the oxidation stage a slurry method with suspended catalysts takes place in an agitator vessel.

6. Method according to claim 5, characterised in that the oxidation products of the oxidation stage and the products of the f R W, electrodialysis stage are separated by a separation unit. r I- i I- Cc

7. Method according to any one of the preceding claims, characterised in that there are used as catalysts noble metals of the 8th sub-group of the Periodic Table of the Elements.

8. Method according to claim 7, charac, ;sed in that the catalysts are selected from Pt supported catalysts with platinum contents between 0.1 and 10% (by weight) and Pt/C powder catalysts with Pt contents between 0.1 and 10% (by weight) with the fines removed.

9. Method according to any one of the preceding claims, characterised in that reducing saccharides and/or non-reducing saccharides and/or sugar alcohols a "nd/or alkyl glycosides and alkyl polyglycosides or similar mixtures and/or 15 specially modified carbohydrate derivatives are used as starting substances and monooxidized.

10. Method according to claim 9, characterised in that the reducing saccharides are selected from palatinose, glucose, fructose and sorbose.

11. Method according to claim 9, characterised in that the non-reducing saccharides are selected from saccharose and trehalose.

12. Method according to claim 9, characterised in that the sugar alcohols are selected from palatinitol and sorbitol.

13. Method according to claim 9, characterised in that the alkyl glycosides are selected from methyl glycoside and octyl glycoside.

14. Method according to claim 9, characterised in that the specially modified carbohydrate derivatives are selected from HMF and GMF. III 23 Method according to any one of the preceding claims, characterised in that water or mixtures of water and secondary alcohols. are used as solvents for the starting substances.

16. Method according to claim 15, characterised in that the secondary alcohol is isopropanol.

17. Method according to any one of the preceding claims, in which the oxidation and the electrodialysis take place in the pH range from 1 to 13.

18. Method according to any one of the preceding claims, characterised in that the temperature for the oxidation lies between 0 and 800 C. 19, Method according to claim 18, characterised in that the temperature is between 20 and 60' C.

20. Method according to any one of the preceding claims, characterised in that the carbohydrates, carbohydrate derivatives or primary alcohols are used in concentrations between 3 and 20% (by weight). 5 21. Method according to any one of the preceding claims, characterised in that Na 2 CO 3 or NaHCO, or NAOH or other alkalizing agents are used for adjusting the pH of the flow.

22. Method according to any one of the preceding claims,characterised in that by the use of a Pt/A1203 supported catalyst selectively only the 6-positions on non-reducing glycopyranosyl units are oxidized.

23. Method according to any one of the preceding claims, characterised in that a branch line (60) is used and the flow of material coming from the oxidation stage is uncoupled from the flow of material of the electrodialysis stage. I 9

24. Apparatus when used in a method according to any one of the preceding claims, characterised in that it comprises, connected in series, a gassing stage an oxidation stage (30) and an electrodialysis stage Apparatus according to claim 24, characterised in that in addition a line (41) to a tank (50) and a return line (43) to the gassing stage S 10 (10) are provided.

26. Apparatus according to claim 24 or 25, characterised in that 0 the gassing stage (10) is an agitator vessel. 15 27. Apparatb's according to any one of claims 24 to 26, characterised in that ion exchange or bipolar membranes are used in the electrodialysis stage

28. Apparatus according to any one of claims 24 to 27, characterised in that a branch line (60) is provided parallel with the electrodialysis stage 0* SDated this nineteenth day of January 1998. SUDZUCKER AKTIENGESELLSCHAFT Patent Attorneys for the Applicant: F B RICE CO II LILI-I Abstract In a method for manufacturing monocarboxylic acids from carbohydrates, carbohydrate derivatives or primary alcohols, carbohydrates, carbohydrate derivatives or primary alcohols are oxidized continuously in aqueous solution and concentrations between 0.1 and 60% with oxygen or oxygen-containing gases on noble metal or mixed metal catalysts. The volume flow of the products so formed is fed to an electrodialysis stage and the monocarboxylic acids are removed and obtained. I- r Now