EP0807126A1

EP0807126A1 - Process for the alcaline oxidative degradation of reducer sugars and products thus obtained

Info

Publication number: EP0807126A1
Application number: EP95941763A
Authority: EP
Inventors: Guy Fleche; Pierrick Duflot
Original assignee: Roquette Freres SA
Current assignee: Roquette Freres SA
Priority date: 1995-12-05
Filing date: 1995-12-05
Publication date: 1997-11-19
Also published as: WO1997020860A1; FI973215A0; AU4307596A; NO973393D0; US5817780A; FI973215A; NO973393L

Abstract

The invention relates to a process for the alcaline oxidative degradation of an ose, an ulose, polymers or mixtures thereof in aqueous solution and in the presence of a redox couple comprised of a mixture of monosulfonic anthraquinone-2-acid and of hydrogen peroxide, characterized in that the oxidant gas is air and said air is stirred up and introduced into the reaction medium in agitation flow rate conditions and such that the dissolved oxygen saturation of the reaction medium gives a pink coloration of said reaction medium.

Description

PROCESS OF OXIDATIVE ALKALINE DEGRADATION OF REDUCING SUGARS AND PRODUCTS THUS OBTAINED

The present invention relates to an improved process for alkaline oxidative degradation of oses or uloses and their polymers.

By oses, uloses and their polymers, is meant any reducing carbohydrate or sugar of the polyhydroxyaldehyde or polyhydroxyketone type (or any compound derived therefrom such as ketoaldonic, uronic acids, acetylated, amino, alkyl, carboxymethylated derivatives, etc.) or polymers or polysaccharides capable of releasing these same compounds by hydrolysis.

A subject of the invention is also, as new industrial products, the dextrins or hydrolysates of native or modified starch thus degraded, but also the products obtained by alkaline oxidative degradation of the hydrolysates of polysaccharides or of polyholosides such as cellulose hydrolysates , dextrans, arabans, xylans, arabinoxylans, fructans, inulin, or hydrolysates of heteropolyholosides such as gums, hemicelluloses, mucilages, pectins, or also synthetic polymers obtained by polymerization various monomeric oses in the presence of acid and at high temperature, such as polydextrose which is a highly branched polymer of glucose.

One advantage of oxidatively degrading the oses, and especially their polymers in an alkaline medium, lies in obtaining hydroxylated molecules which become carriers of carboxylic groups. We know that such molecules show interesting properties sequestering.

These sequestering properties can be exploited in the field of cements, mortars and concretes where glucose syrups oxidized by bleach have already been proposed as setting retarders, for example in the British patent application GB 2,075,502.

They can also be used in the detergency field where glucose syrups, this time oxidized by a gas containing oxygen in the presence of a catalyst based on a noble metal, have been proposed for cleaning articles of glass or metal, or as additives for detergents as mentioned, for example, in European patent application EP 232.202.

The processes of alkaline oxidation described in these two patent applications have in common that they use weakly alkaline media, with a pH between 7.5 and 11 and that the oxidation of the reducing functions takes place. practically without carbon loss and therefore without degradation, namely that under the conditions described, the oxidation of the reducing function of a ose provides essentially aldonic acid of the same rank, therefore counting the same number of carbon atoms. The oxidized glucose syrups thus obtained are therefore essentially composed of gluconate from the oxidation of glucose, maltobionate from the oxidation of maltose, and more generally dextrins-gluconates from the oxidation of polysaccharides of higher degree of polymerization. .

However, neither of these two methods allows the total transformation of the reducing functions into carboxylic acid functions and the products thus obtained have always a significant residual reducing power. In the case of oxidation with bleach, there are even phenomena of oxidation leading to the creation of reducing ketone functions from the secondary alcohol groups of the oses. In the case of oxidation by oxygen, catalyzed by a noble metal, we do not witness these phenomena of overoxidation but although this oxidation reaction takes place at a low pH, we cannot avoid the appearance of ketone functions which are formed by alkaline isomerization of the hemiacetal functions and which are not oxidizable by the process employed.

Thus, in the case of a glucose syrup of 33 DE oxidized by bleach according to patent application GB 2,075,502, it is hardly conceivable to go down to residual reducing sugar contents expressed in glucose and measured by the Bertrand method, less than 4.5% and that in the case of European patent application EP 232.202, this content can hardly be lowered to values less than 1.7%. Although the products obtained by these processes demonstrate excellent complexing properties, they are not very compatible with washing formulations of high pH since the powders thus formulated become yellow over time by alkaline degradation of these residual reducing sugars.

In addition, the presence of chlorides brought by bleach or the cost of catalysts based on noble metals, are not elements which argue in favor of the use of these glucose syrups oxidized in cements, concretes and mortars.

Chlorides corrode the reinforcements metallic and the extremely low cost of hydraulic compositions does not allow to add them with expensive products.

British patent application GB 2,075,502 also describes a process for the degradation, in a non-oxidative alkaline medium this time, of glucose polymers, which also results in the formation of acids by degradation of the reducing ends of the monomers and polymers making up the syrups. glucose. Unlike the previous processes, this degradation of the reducing functions is carried out with a carbon loss, namely that under the conditions described in examples 4 and 5 of this patent application, the reducing oses are essentially transformed into carboxylic acids of ranks lower, having 1, 2, 3, 4 or 5 fewer carbon atoms than the dare that gave them birth.

The degraded glucose syrups thus obtained are therefore composed of formate, acetate, lactate, saccharinate or arabinonate, but there are also found in significant amounts glycolate, dihydroxybutyrate, metasaccharinate,

1 isosaccharinate, deoxypentonate which are formed at the expense of degraded glucose. There are also dextrins-saccharinates or dextrins-aldonates including some dextrins-arabinonates which were formed at the expense of glucose polymers.

Degraded glucose syrups obtained in this way always contain at least 5% residual reducing sugars. They are also strongly colored, which immediately excludes them from the field of detergency. However, if they are produced relatively economically, and it is therefore possible to use them as setting retarders in hydraulic compositions, they do not provide reproducible results since slight variations in pH or in the degradation temperature lead to considerable variations in their composition, both from the point of view of the acids formed and of the length of the chains. residual polysaccharides which it is specified in this patent application that they are easily hydrolyzable, even in a slightly alkaline medium and at low temperature. This process, which is difficult to reproduce from one manufacturing batch to another, therefore does not make it possible to obtain products with repetitive performance, which is however highly desirable in an application such as setting retarders for cements, mortars and concretes, where taking too quickly during transport or too late during formwork can have extremely damaging consequences.

Another advantage of oxidatively degrading in an alkaline medium the polymers of dares and especially their monomers lies in obtaining the most exclusive possible of aldonic acids having only one carbon atom less than the dare which gave them birth.

Such methods have been known for a very long time and have been applied to alkaline oxidative degradation using oxygen monoses or monouloses, or even certain reducing disaccharides such as lactose, maltose, palatinose.

However, unlike the methods explained above and which only use weakly alkaline reaction media, with a pH of 11.0 at most, these other methods use very reaction media. strongly alkaline with a pH at least greater than 12.0 which are therefore liable to degrade the carbon skeleton of the polymers but which allow the almost total disappearance of the reducing sugars by lowering their content to residual values generally less than 0.5 %. They are indeed effective on ketone functions.

These processes, to the knowledge of the applicant, have however been used only on monomeric or dimeric reducing doses and are based on the process developed by NEF and perfected by SPENGLER and PFANNENSTIEL (Z. Wirtschafts-gruppe Zuckerindustrie, Tech Tl, 1935, 85, 546-552). These, by using gaseous oxygen to improve the NEF process which used air, managed to degrade oxidatively in strongly alkaline medium, glucose, fructose, mannose and arabinose with molar yields close to 75% essentially in arabinonic acid for the first three sugars and in erythronic acid for pentose.

This type of alkaline oxidative degradation process mainly results on the one hand in the degradation of sugar into aldonic acid comprising one carbon atom less than the initial reducing sugar and in formic acid on the other hand. It is in obtaining this aldonic acid of lower rank that their main interest lies. They allow access to shorter molecules which can serve as the basis for many chemical syntheses. Thus, the oxidation of L-sorbose according to these methods, makes it possible to obtain L-xylonic acid, the hydrogenation of the lactone of which provides xylitol. These molar yields of 75% of arabinonic acid are achieved with glucose in an aqueous medium and at atmospheric pressure on condition of using finely divided oxygen and using at least 3 moles of hydroxyl anion OH ^" per mole of glucose used. Under the same conditions of high alkalinity and oxidation by l pure oxygen at atmospheric pressure, SCHMIDT described in US Pat. No. 2,587,906, obtaining molar yields of 65% of potassium arabinonate crystallized from invert sucrose In the presence of certain promoters which may play a role in redox couple and in particular methylene blue, he managed to bring this yield to 82%, however, this yield dropped to 77.7% when the oxidation was carried out by air in place of oxygen.

This type of alkaline oxidative degradation, effective on both hemiacetal and ketone functions, also leads to the formation of by-products such as in particular carbonic, oxalic, glyceric, glycolic, lactic, erythronic and of course formic acids, obtained in a yield approximately 25% molar from glucose when the alkalinity conditions are such that they allow a yield of 75% of arabinonate. Formic acid is always produced with yields close to 100% of stoichiometry.

An excellent study of the SPENGLER-PFANNENSTIEL process can be found in the thesis of DUBOURG and NAFFA

(Bull. Soc. Chim. Fr., (1959) 1353-1362) which report the degradation by alkaline oxidative route in the presence of gaseous oxygen, arabinose, glucose, galactose and maltose. These authors had further noted that the presence in the reaction medium of methanol, or redox promoters such as hydroquinone or resorcin favored the oxidation to arabinonic acid of the glucose by increasing slightly the rate of oxidation and the yield of the reaction.

They have also shown that the use of amounts less than 3 moles of hydroxyl anions OH ^" per mole of reducing sugar used results in a drastic reduction in the yield of lower-ranking aldonate. For example, in the absence of promoter and even by carrying out the oxidation with pure oxygen, the use of 2 moles of potassium hydroxide per mole of glucose only allows the obtaining of 58% of arabinonate.

US patent US 4,125,559 to SCHOLZ and GOTSMANN recommends working under oxygen pressures of up to 40 bar and claims to obtain arabinonate yields of up to 98%.

In the example envisaged in this patent, the sodium hydroxide / glucose molar ratio is 3.5 and the oxygen pressure is 21.5 bars.

VUORINEN, HYPPANEN and SJOSTROM (Stârke, 43 Nr 5, s. 194-198; 1991) succeeded in oxidizing with a yield of 78% the glucose to arabinonate by using only 2.17 moles of soda per mole of glucose in 1 ' water and under an oxygen pressure of 26 bars (2.6 mega Pascal). This yield could be brought to 86% in the presence of a redox promoter: AMS, (sodium salt of 2-anthraquinone monosulfonic acid) with an alkali / sugar molar ratio of only 2.03, but in the presence 0.96 Kg of methanol per Kg of water in the final reaction medium, and this under a more reasonable oxygen pressure which amounted however to 6 bars (0.6 mega Pascal). The explanation for this good yield is, according to these authors, that in a methanolic environment, mass transfers are faster and the oxygen is more soluble, which allows a higher selectivity and a higher yield of the alkaline oxidative degradation reaction. It will also be noted that the presence of methanol in the reaction medium makes it possible to crystallize potassium arabinonate as it is formed and thus to favorably shift the direction of the reaction.

VUORINEN also, in PCT patent application 93/19030, example 7, demonstrates that it is possible to oxidize sorbose to xylonic acid with a molar yield of 69% by using only 2.06 mole of alkali per mole of sugar, but on condition that it operates under an oxygen pressure of 10 bars and in the presence of approximately 100 g of methanol per 200 g of water.

HENDRICKS, KUSTER and MARIN (Carb. Res, 214 (1991) 71-85) have shown that the selectivity and the rate of oxidative degradation of glucose, galactose and lactose can be considerably increased by the use, in the medium reaction, of a redox couple consisting of the sodium salt of 2-anthraquinone monosulfonic acid (AMS) and hydrogen peroxide, provided that oxygen is used at a pressure of 1 bar (0, 1 mega Pascal) to be saturated with the reaction medium (the AMS must remain in its colorless oxidized form while its reduced form is dark red). These authors also use very alkaline media, containing three moles of hydroxyl anions OH ^" per mole of reducing sugar used.

By this process, the yields of arabinonate reach 95 to 98% of theory from glucose. They are lower when a diholoside is used. works since they only reach 90 to 95% of galactopyranosyl 1-3 arabinonate from lactose. The authors explain this drop in selectivity by the alkaline hydrolysis of the beta 1 -> 4 osidic bond of this disaccharide, caused by the high pH at which the reaction takes place (13.8 to 14.5). They conclude, however, that they believe their process generally applicable to carbohydrates.

Whether considered together or separately, expedients consisting of:

- use pure oxygen

- to work under pressure

- to use excess alkalis

- to have recourse to solvents have had the incontestable result of helping to increase the selectivity and the yield of the processes of alkaline oxidative degradation of the monomeric or dimeric oses and uloses.

The use of promoters has made it possible to further improve these performances.

However, there is still no process at the present time which makes it possible to oxidize a reducing ose, an ulose or a diholoside in such a specific and complete manner that it practically only provides acid. corresponding aldonique of immediately lower rank (therefore having only one carbon atom less) and of course formic acid in equimolecular quantity and which does not call on these expensive, even dangerous expedients that are the use of oxygen pure, high pressures, excess of alkalis, organic solvents.

Similarly, it still does not exist today of a process which allows to oxidize in an almost exclusive way to polyholoside-aldonate, and more precisely to dextrin-aldonate, a polymer of dares or of uloses, and more preferentially a hydrolyzate of native or modified starch, until almost complete disappearance of reducing sugars and without shortening of the carbon skeleton of the polymer as a result of the hydrolysis of some of its osidic bonds. It is by limiting the oxygen saturation of the reaction medium and by going against the teachings of the prior art, by doing without all of the above-mentioned expedients, the usefulness of which now seemed to be beyond doubt. , that the Applicant Company, which has become aware of these problems and the need to provide a solution, has managed to develop a process for the alkaline oxidative degradation of oses or uloses and even of their polymers which is finally devoid of disadvantages already mentioned.

According to the invention, this process of alkaline oxidative degradation, which consists in oxidizing a ose, an ulose, their polymers or their mixtures, in aqueous solution in the presence of a redox couple consisting of a mixture of AMS and of peroxide of hydrogen, is characterized by the fact that the oxidizing gas is air and that this air is stirred and introduced into the reaction medium under stirring conditions and at a rate such that the oxygen saturation of the reaction medium leads to l 'obtaining a pink coloration of this reaction medium.

We know that the reduced hydroquinonic anion AMS (OH) ₂ develops an intense red-brown color while the oxidized molecule AMS0 ₂ quinone is strictly colorless. The pair made up of AMS quinone and its hydroquinone therefore also behaves like a colored indicator of redox allowing visually to estimate the level of saturation in dissolved oxygen of the reaction medium. Under these conditions of reduced oxygenation, however surprisingly sufficient, indicated by a pink coloration of the AMS, the Applicant Company noted that the reducing sugars were oxidized in an almost completely selective and total manner to the aldonic acid of rank immediately below and in formic acid without significant formation of other acids resulting from the non-oxidative alkaline degradation of these reducing sugars

(lactic, metasaccharinic, dihydroxybutyric etc ...).

These conditions of reduced oxygenation can be easily obtained, and this is a huge pecuniary advantage, without pure oxygen or without oxygen-enriched air and without the use of high pressures or alcohol promoting mass transfers. or increasing the solubility of oxygen in the reaction medium. Generally, in the context of the process which is the subject of the invention, it is sufficient for the air pressure to be sufficient to overcome the hydrostatic pressure created by the liquid column present in the reactor. It will also be taken with interest that the exhaust of the gases from the reactor takes place without constraint and at atmospheric pressure.

The Applicant Company believes that under the conditions described for the process of the invention, oxygen does not exist in sufficient quantities to directly oxidize the reducing sugars, or rather the enols which are formed under alkaline conditions. We know that this direct action of oxygen is not completely selective and that it brings, alongside aldonic acids of immediately lower rank, the production of acids resulting from an overoxidation of these reducing sugars into short-chain hydroxycarboxylic acids (oxalic , glycolic, glyceric, tartronic, etc ...), even carbonic.

The Applicant Company also believes that in the process according to the invention, the quantity of oxygen present in the reaction medium is in fact just sufficient to regenerate in its quinone form, with concomitant synthesis of hydrogen peroxide, anthraquinone

(AMS0 ₂ ), which has selectively oxidized the reducing sugar or more precisely its enediol to aldosulose, transforming into hydroquinonic form (AMS (OH) ₂ ). The hydrogen peroxide thus formed is immediately used to oxidize specifically, and practically without the formation of by-products, aldosulose to aldonic acid having a carbon atom of less on the one hand and to formic acid on the other hand.

For convenience in understanding these chemical reactions, reference may be made to the single figure of this booklet.

There is therefore also neither in the process of the invention, an excess of hydrogen peroxide in an amount such that it is capable of directly detectable oxidizing the reducing sugar to the state of formic acid and water by homolytic rupture of its carbon chain. This process would gradually lead to the total degradation of an aldose by successive and rapid shortening of its carbon chain, the aldose of departure being itself transformed into another aldose of immediately lower rank on the one hand and formic acid on the other hand. (HS ISBELL et al. Carbohydrate Research, 203 (1990) 287-289). This extreme selectivity of the alkaline oxidative degradation of the oses or of the uloses and of their polymers, obtained by the particular conditions of oxygen saturation of the process according to the invention makes it possible to reduce to the quasi-stoichiometric quantity, barely greater than 2 moles, the alkali to be used per mole of reducing sugar to be oxidized. Even under these conditions, the selectivities and yields obtained remain excellent.

This is only made possible by the quasi-absence of parasitic reactions resulting in the appearance of short chain acids and only one mole of formic acid and one mole of aldonic acid are to be neutralized per mole of reducing sugar. implemented.

Only a slight reserve of alkalinity is necessary to give the reaction medium until the end of the reaction a pH sufficiently alkaline to allow the formation of enediols which are the reactive entities.

This has many advantages, not the least of which is limited use of alkali.

Indeed, it is often necessary, at the end of the alkaline oxidative degradation reaction, to bring the pH of the reaction medium to about neutral and even more to acid pH when it is desired to distillate formic acid inevitably product. This therefore also results in an economy of acid and less production of the by-products that are the salts resulting from this neutralization or acidification. This restricted use of alkali also has the effect, when the oxidative alkaline degradation reaction according to the invention is carried out on polymers, of preserving this polymer backbone and of preserving the molecular weight of these polymers.

As a result, the process of the invention makes it possible to obtain, as new industrial products, acid derivatives of polysaccharides, that is to say polymers composed of at least three carbohydrate units, containing less than 1% of reducing sugars. residual and preferably less than 0.5% of residual reducing sugars characterized in that their terminal carbohydrate is an aldonic acid containing one carbon atom less than the reducing carbohydrate which gave rise to it. The process of the invention can therefore be carried out preferably with amounts of alkali less than three moles of hydroxyl anions OH ^" per mole of reducing sugar subjected to oxidation. Preferably these amounts of alkali are between 2.05 and 2.5 moles, and preferably between 2.2 and 2.4 moles.

The amounts greater than three moles of hydroxyl anions OH ^" per mole of reducing sugar used appear irrelevant since they are anti-economic and even appear harmful, in particular in the case of oxidative degradation carried out on polysaccharides. In this case, the polymeric backbone of the polysaccharides is observed and their molecular weight decreases. The amounts less than two moles of hydroxyl anions OH ^" per mole of the reducing sugar used no longer make it possible to obtain complete alkaline oxidative degradation and their use can be summarized by a reaction, admittedly selective, but incomplete, which results in the persistence at the end of the reaction of residual reducing sugars.

However, when this presence of residual reducing sugars does not constitute a handicap in the case of certain products obtained by the process of the invention, it is conceivable to use quantities of alkali lower than two moles of hydroxyl anions OH ^" per mole of reducing sugar used, this may in particular be the case when it is contemplated to purify the aldonate obtained, for example by crystallization.

The temperature at which the process of the invention is carried out is generally between 10 and 80 ° C. We prefer to work between 20 and 70 ° C and even more preferably between 25 and 60 ° C.

It should be noted that, as a general rule, the lowest temperatures make it possible to obtain the best selectivities but that this takes place at the expense of the reaction rate. Conversely, the higher temperatures make it possible to shorten the reaction times and can be used insofar as a slight degradation of a polymer or the obtaining of a few percent of carbonic, oxalic, glyceric, glycolic acids. , lactic, erythronic, metasaccharinic, dihydroxybutyric etc ... are not detrimental to the product obtained or the use that we intend to make of it.

However, a preferential implementation of this process, which makes it possible to combine both the specificity of the reaction and the rapid disappearance of all the sugars reducing agents, consists in initiating the alkaline degradation reaction at around 40 ° C and gradually or gradually increasing this temperature up to 60 ° C as these reducing sugars disappear as a result of their oxidation to aldonic acid of immediately lower rank. In general, it is preferable to allow the reaction to continue until a reducing sugar content, measured by the BERTRAND method, of less than 1%, preferably less than 0.5%, is obtained, and again more preferably less than 0.3%, this content being expressed as a percentage by weight of glucose equivalent on the sweet dry matter introduced into the reactor.

The concentration of dry matter at which the process according to the invention should be carried out is not critical and must above all be guided by economic principles. Concentrations of less than 50 g of dry matter per liter of reaction medium are generally not advantageous since they then mobilize too large a volume of reactor. Likewise, concentrations higher than 600 g / l cannot generally be envisaged since they then require aeration and stirring power such that the mechanical stresses which they impose cannot find a solution which is not expensive.

Here again, a practical implementation of the process of the invention consists in initiating this oxidative degradation in the presence of small quantities of reducing sugars, then in introducing these into the reactor continuously or in successive fractions, in the form of powder. or concentrated syrups, as they are disappearance and their transformation into aldonic acid of immediately lower rank.

The reactors making it possible to carry out the implementation of the process of the invention are the reactors allowing efficient mass and heat transfers and can be those which are used for the aerobic microbiological transformation of various liquid substrates either into biomass or into acids organic amino or not, either enzymes or antibiotics. The essence of the invention residing in the fact that the air is stirred and introduced into the reaction medium under stirring and aeration conditions such that this reaction medium has as long as possible a pink coloring, it is advisable to '' continuously adapt these conditions to the evolution of the reaction.

At constant temperature, the oxidation being faster at the start of the reaction than at the end of the reaction, the oxidation reaction should be started by stirring and / or aerating the reaction medium vigorously. Then, as this reaction progresses, care will be taken to maintain this pink coloration by reducing the aeration or stirring, taking care, however, that the reaction medium never becomes red.

With constant stirring and / or aeration, it will be possible to ensure that this pink coloration is maintained by acting on the temperature of the reaction medium. A rise in temperature has the effect of increasing the rate of oxidation and of decreasing the solubility of oxygen. When the reaction medium tends to become colorless, it is easy to return to the pink tint by increasing this temperature. Conversely, when the reaction medium becomes too red, we will lower this temperature.

To carry out the process of the invention, it is preferable to use an amount of AMS generally representing from 0.1 g to 5 g per mole of reducing sugar used and expressed in the form of glucose equivalent. Preferably, this amount of AMS is between 1 g and 4 g per mole of reducing sugar, and even more preferably between 2 g and 3 g per mole of reducing sugar.

The amount of hydrogen peroxide is used simultaneously with the AMS and in a substantially equimolecular amount. We therefore generally use from 0.03 ml to 1.6 ml, preferably from 0.3 ml to 1.2 ml and even more preferably from 0.5 ml to 1 ml of hydrogen peroxide at 110 volumes per kg of substrate to oxidize. AMS and hydrogen peroxide having a catalytic role, one can also play on their concentrations in the reaction medium to adapt the oxidation rates to the mechanical performance of the reactors used. If, for example, a reactor is used that has only a small installed power of aeration and agitation, it will be advantageous to use only the lowest doses of the pair of catalysts.

A preferred way of carrying out the alkaline oxidative degradation of the reducing sugars according to the process of the invention consists in introducing these sugars progressively into the reaction medium.

Thus, with constant stirring, aeration and temperature, it is possible to maintain the pink coloration of the AMS by adjusting the rate of introduction into the alkali solution, of reducing sugar. Too high feed rate will cause AMS to turn dark red while too low a flow rate will make the medium colorless.

The Applicant Company has noted that the best mode of implementing the process of the invention consists in first introducing into the reactor in the form of an aqueous solution a portion, generally less than 25%, preferably less than 15%, and even more preferably less than 10% of the reducing sugar or of the polymer which it is envisaged to oxidize, then to aerate under the aeration and stirring conditions determined by experience this dilute solution of sugar or polymer. It is convenient to take advantage of this period of saturation of the medium with dissolved oxygen to bring this "base stock" to the right temperature. After the end of this period, which generally does not exceed half an hour, it is preferable to add at once the dose of alkali necessary for the oxidative degradation reaction of the reducing sugar or of the polymer which it is intended to introduce. work, by calculating this dose so that it corresponds to approximately 2.3 moles of hydroxyl anions OH ^" per mole of reducing sugar. This alkali is calculated in slight excess so as to preserve a reserve of alkalinity sufficient to allow the formation of enediols, intermediates of this oxidation reaction. This alkali can also be added continuously or in portions during the reaction, but its utility is not well perceived oxidation of non-polymeric materials.

Preferably, the AMS is introduced into the reactor at the same time as the alkali and the hydrogen peroxide. It is preferable to introduce this AMS directly in the powder state into the reactor. The reaction medium then immediately takes on a dark red coloration which disappears in a few tens of seconds to return to pink.

We then start at this time, the continuous introduction or by small successive portions of the residue of reducing sugars, residue which can represent at least

75%, preferably at least 85% and even more preferably at least 90% of the reducing sugar or of the polymer which it is intended to oxidize. The flow rate to which this remainder of reducing sugars is added, which can be either in the form of a concentrated solution or of powder, is adjusted to be adapted to the stirring and aeration performance of the reactor and is generally such as the substrate to be oxidized or introduced entirely in 1 to 10 hours, preferably in 2 to 8 hours and even more preferably in 3 to 6 hours.

When all the substrate to be oxidized has been introduced into the reactor and the reaction has reached a sufficient degree of progress such that at least 90% of the reducing sugars introduced have been transformed into aldonic acid of immediately lower rank, it is possible to gradually increase the temperature of the reaction medium to complete this reaction as quickly as possible, while taking care to maintain this pink coloration of the reaction medium. The reaction is terminated when the content of reducing sugars has fallen below a sufficiently low value, less than 1% glucose equivalent in most cases.

Depending on its destinations or uses, the raw reaction medium thus obtained can undergo various types of treatment or purification.

Almost generally, it should be removed the AMS. This can be done in an extremely simple way by adsorption of this catalyst on vegetable or animal black. The best way to proceed consists in percolating the reaction medium on granular black columns after having brought the pH of this reaction medium to a value preferably less than 7.0.

If formic acid proves to be a discomfort in the products obtained by the process of the invention, it is convenient to eliminate the latter by distilling the reaction medium after having carried out its acidification with a strong acid and optionally with crystallization and elimination of the salt formed by this strong acid and the alkali used during the oxidation reaction.

Such purification is however not necessary when it is desired to use the aldonates or the polymer-aldonates obtained by the process of the invention in applications such as detergency or modifiers of fluidity or setting time for concrete, mortars and cements. This purification, consisting mainly of removing formic acid, may be necessary insofar as it is contemplated to proceed to the hydrogenation of the aldonic acids obtained in order to obtain the corresponding polyols. This can be for example the case of xylitol which can be obtained by hydrogenation of the lactone of xylonic acid, this acid can be produced under conditions of purity and economy without equal by the process of the invention in oxidizing L sorbose.

The following examples are intended to illustrate and better understand the invention. They cannot be limiting, in particular with regard to conditions for aeration or agitation of the reactors making it possible to implement the process of the invention.

In particular, the geometry and the size of the reactors used have a great influence on the invariants of similarity constituted in particular by the number of REYNOLDS, and therefore on the capacities of the apparatuses to transfer into the liquid medium the oxygen necessary for the process of invention.

Example 1:

Oxidation of a monomer: glucose.

In a glass tank fermenter, BIOLAFITTE brand, with a useful capacity of 15 liters, 7 liters of water and 338.60 grams of dextrose monohydrate (i.e. 1.71 mole of glucose) are introduced. This solution is aerated with an air flow corresponding to 20 liters per minute and with stirring of 650 revolutions / minute while bringing its temperature to 40 ° C. A 50% dry matter glucose solution is prepared extemporaneously, prepared using 1443.40 grams of dextrose monohydrate and 1181 grams of water, containing 7.29 moles of glucose, as well as a concentrated solution. 50% sodium hydroxide formulated from 840 g of dry sodium hydroxide and 840 g of water, ie 21 moles of sodium hydroxide.

24 g of sodium anthraquinone 2-sulfonate are weighed and 7.56 cm ³ of hydrogen peroxide at 110 volumes (30% in concentration) are prepared.

At time t = 0, corresponding to aeration for approximately 30 minutes of the glucose solution contained in the fermenter, the concentrated solution is added simultaneously soda, anthraquinone and hydrogen peroxide in the fermenter.

The reaction medium then immediately takes on a dark red coloration characteristic of the reduced form of AMS: AMS (OH) ₂ . This color disappears practically immediately by bringing the stirring to the speed of 800 revolutions per minute and the reaction medium becomes colorless, characterizing the oxidized form of AMS: AMS0 ₂ .

A pink color is immediately restored to the medium by lowering the stirring speed to 415 revolutions per minute, then the concentrated solution containing 50% glucose is introduced continuously into the reactor.

Care is therefore taken to ensure permanently until the end of the reaction a pink coloration of the reaction medium by continuously adjusting the appropriate stirring speed.

When the reducing sugar content of the reaction medium has fallen to a value close to 10 g / liter, which occurs after 180 minutes, the temperature is gradually increased to 60 ° C.

For convenience, the following table shows, as a function of time, the values of the temperatures and the stirring speeds employed in carrying out this example. The approximate rate of introduction of the concentrated glucose solution into the fermenter has also been indicated in this table: TABLE 1

time temperature stirring flow rate in minutes ° C. ; revolutions / min) glucose solution ml / min

0 38.7 4 41 155 1 100,, 11

5 38.7 4 41 155 1 100,, 11

14 39.1 4 42 200 1 100,, 11

20 39.7 4 43 300 1 100,, 11

30 40 4 44 455 1 100,, 11

40 40 4 46 655 1 100,, 11

41 40 1 133,, 33

45 40 4 47 755 1 133,, 33

70 40 4 47 755 1 133,, 33

74 40 5 50,000 1,133., 33

79 40 5 52 200 1 133,, 33

170 40 5 59 900 ffiinn ddee ll''aaddddiittiioonn

180 45 7 72 255

188 45 7 77 755

50 8 89 900

50 8 85 555

50 8 83 355

212 50 8 80 000 216 50 7 76 655 219 50 7 73 355 220 50 6 69 955 225 50 6 63 300 229 50 5 59 955 234 50 5 55 500 250 50 4 44 455 255 50 4 43 300 257 50 4 40 055 265 50 3 38 800 280 50 3 33 355 310 55 5 50,000 312 60 3 35,500 320 60 2 25,500 355 60 2 22,200

In this example, where the alkali / sugar ratio was established at 21/9 moles, ie 2.33 moles of hydroxyl anions per mole of reducing sugar used, and where the sugar used at the start of the reaction represented 19% of the total amount subjected to oxidation, it has been possible to oxidize the glucose to arabinonic acid with a molar yield of 84.7% .

Only 2% of the molar yield of glyceric acid and 6.4% of the molar yield of glycolic acid were obtained.

As a comparative example, it will be noted that VUORINEN et al. (Stârke, 43 Nr 5, s. 194-198), proceeding with the oxidation of glucose without methanol, had to use a pressure of pure oxygen of 26 bars to obtain a yield of arabinonic acid of only 78% with respectively 3.5% and 6.5% of impurities constituted by glyceric and glycolic acids.

In the present example, at time t = 280 min, the concentration of reducing sugars in the reaction medium amounted to 3.4 g / 1, it was only 0.5 g / 1 at time t = 355 min when the reaction was terminated, which represents approximately 2.2% and 0.32% respectively of residual reducing sugars relative to the glucose used, knowing that the total reaction volume at the end of oxidation was 10.5 liters.

At the end of the reaction, this reaction medium was neutralized using 40 ml of concentrated sulfuric acid to reach a pH of 5.80. The solution obtained then takes on a green color.

The medium thus neutralized is then percolated on a column of granular black which makes it perfectly colorless and eliminates the AMS thereof.

A simple concentration to a dry matter greater than 30% makes it possible to crystallize sodium arabinonate.

The complete dehydration of this reaction medium thus purified makes it possible to obtain a powder which can be used as a "co-builder" in detergent formulations. Its very low content of residual reducing sugars does not cause any coloration of the formulas over time ...

Example 2: Oxidation of a polymer: glucose syrup.

In the same equipment as that described in Example 1, 9.190 liters of water and 481 g of an aqueous solution of a 37 DE glucose syrup consisting of 1532.6 g of this glucose syrup are introduced. 78.5% dry matter and 873.7 g of water. This solution is aerated for 30 minutes with an air flow rate fixed at 20 1 / rrvn and with stirring of 650 revolutions / minute while bringing its temperature to 40 ° C.

Extemporaneously, a 50% sodium hydroxide solution formulated with 217.6 g of sodium hydroxide and as much water is prepared.

At time t = 0, corresponding to aeration for 30 minutes of the glucose syrup solution, the sodium hydroxide solution, 6.6 g of AMS and 2.2 cm ³ of sodium hydroxide are added simultaneously to the fermenter. hydrogen peroxide at 110 volumes. The reaction medium then immediately takes on a blood-red coloration for a few seconds and then discolours.

The stirring is then lowered to the speed of 400 revolutions / minute to bring a pink coloration to the reaction medium.

After ten minutes of reaction, the remainder is introduced glucose solution at a rate such that this addition takes place in 3 hours.

During the whole course of the reaction, the stirring speed is continuously adjusted to maintain the pink coloration of the medium.

After 3 hours and 20 minutes of reaction, the temperature of the reaction medium is increased to 50 ° C. and after five hours of reaction, it is increased to 60 ° C. Finally, the reaction is stopped after 6 hours 40 minutes. The content of reducing sugars in the reaction medium then fell to 0.36 g / 100 g of dry matter of glucose syrup.

In this example where the alkali / reducing sugar molar ratio was established at 2.2, it was possible to oxidize all the glucose syrup to arabinonate and dextrin-arabinonate while retaining the degree of polymerization of the glucose syrup subjected to oxidation, c ' is to say without a detectable hydrolysis of the sugar bonds appearing. This new product is obtained in a completely reproducible manner and does not color, even when placed in a strongly alkaline medium.

Example 3:

Oxidation of a ketosis: sorbose.

The oxidation of L-sorbose was carried out by introducing into the reactor used in the previous examples 7470 g of water which was aerated for 30 minutes at 25 ° C.

768 g of a 50% aqueous sodium hydroxide solution (9.6 mol), 4 cm ³ of hydrogen peroxide at 110 volumes and 12 g of AMS were then added thereto.

Finally added to the contents of this reactor 1440 g 50% sorbose solution (4 moles). The soda / sugar molar ratio was therefore 2.4. This sorbose solution was added at a rate of 6 g / min. All of the sugar was therefore introduced in 4 hours, at the end of which the temperature was increased to 50 ° C. The reaction was stopped after 8 hours. During all this time, the reactor had been aerated with an air flow rate of 20 liters / min and the agitation was varied between 800 and 190 revolutions / minute so as to always observe a pink coloration of the medium. At the end of the reaction, a residual reducing sugar content of 0.17% was obtained and a yield of sodium xylonate of 75 mol% was observed.

Example 4: Oxidation of a modified starch hydrolyzate: a carboxymethylated starch.

An enzymatic hydrolysis was carried out of a carboxymethylated wheat starch with a degree of substitution of 0.22 using 1% of alpha-amylase TERMAMYL 120 LS marketed by the company NOVO until obtaining an equivalent dextrose of 25.6.

After filtration and discoloration of this syrup according to conventional methods, its oxidation was carried out in the same equipment as that described in Example 1. After aerating and bringing to 40 ° C., 5124 g of water in the reactor, 768 g of a 50% aqueous sodium hydroxide solution (9.6 moles) were added thereto, as well as 12 g of AMS and 4 cm ³ of oxygenated water at 110 volumes. Was then introduced at a rate of 13.7 ml / min, 4320 cm ³ of a 50% aqueous solution of 1 hydrolyzate of carboxymethylated starch containing 2808 g dry of this product at 25.6 DE (i.e. 4 moles of reducing sugars expressed in glucose).

Throughout the reaction which lasted ten hours, care was taken to maintain the coloring of the medium.

At the end of the reaction, a residual reducing sugar content of 0.1% was observed and no change in the average degree of polymerization of the starch hydrolyzate.

After rectification of the pH to 6.0 then purification on a granular black column to remove the AMS and finally atomization of the product, it was used to replace the polyacrylates in a washing formula by substituting 1 part of polyacrylates for 2 parts new carboxymethylated and oxidized starch hydrolyzate according to the invention.

Not only, the powders obtained do not color in storage, but they show very interesting washing qualities since after having carried out 25 consecutive washes of cotton and cotton / polyester fabric samples, the whiteness indices obtained prove superior to the polyacrylate control. In addition, the rate of organic tissue encrustations is found to be significantly lower.

Claims

1 - Method of alkaline oxidative degradation of a ose, an ulose, their polymers or their mixtures, in aqueous solution and in the presence of a redox couple consisting of a mixture of monosulfonic acid-2-anthraquinone and hydrogen peroxide, characterized in that the oxidizing gas is air and that this air is stirred and introduced into the reaction medium under stirring conditions and at a rate such as the saturation of dissolved oxygen in the reaction medium lead to obtaining a pink coloration of this reaction medium.

2 - Process according to claim 1, characterized in that it is implemented with amounts of alkali less than three moles of hydroxyl anions OH ^" per mole of reducing sugar used.

3 - Process according to claims 1 or 2, characterized in that the amounts of alkali are between 2.05 and 2.5 and preferably between 2.2 and 2.4 moles of alkali per mole of reducing sugar implemented.

4 - Method according to claims 1, 2 or 3, characterized in that it is conducted at a temperature between 10 and 80 ° C, preferably between 20 and 70 ° C, and even more preferably between 25 and 60 ° C.

5 - Process according to any one of the preceding claims, characterized in that the alkaline oxidative degradation is initiated in the presence of small amounts of reducing sugars and then continued by introducing these into the reactor continuously or in successive fractions, under powder or syrup form concentrated, as they disappear and transform into aldonic acid of immediately lower rank.

6 - Method according to any one of the preceding claims, characterized in that

Monosulfonic-2-anthraquinone acid is used at a concentration representing from 0.1 g to 5 g per mole of reducing sugar used and expressed in the form of glucose equivalent, preferably from 1 g to 4 g per mole of reducing sugar, and more preferably still from 2 g to 3 g per mole of reducing sugar.

7 - Process according to any one of the preceding claims, characterized in that the hydrogen peroxide is used simultaneously with one monosulfonic acid-2-anthraquinone and in a substantially equimolecular amount.

8 - Acid derivatives of polysaccharides, characterized in that their terminal carbohydrate is an aldonic acid containing one carbon atom less than the reducing carbohydrate which gave rise to it and that they contain less than 1%, and preferably less than 0.5% of residual reducing sugars.

9 - Acid derivatives of polysaccharides according to claim 8, characterized in that the polysaccharides consist of a native or modified starch hydrolyzate.

10 - Acid derivatives of polysaccharides according to claim 9, characterized in that the oxidized polysaccharide is a hydrolyzate of carboxymethylated starch.