WO1997032903A1

WO1997032903A1 - Method for oxidizing polysaccharides using ozone in the presence of a halogenide-containing catalyst

Info

Publication number: WO1997032903A1
Application number: PCT/NL1997/000107
Authority: WO
Inventors: Ronald Peter Wilhelmus Kesselmans; Ido Pieter Bleeker
Original assignee: Coöperatieve Verkoop- En Productievereniging Van Aardappelmeel En Derivaten Avebe B.A.
Priority date: 1996-03-04
Filing date: 1997-03-04
Publication date: 1997-09-12
Also published as: NL1002527C2; AU2236397A; ID16115A

Abstract

The invention relates to a method for the oxidation of polysaccharides with ozone under the influence of a halogenide-containing catalyst in aqueous medium, wherein, depending on the catalyst and pH, the oxidation can be controlled in the direction of carbonyl or carboxyl groups. The polysaccharides can be selected, inter alia, from starch, cellulose and inulin. The catalyst that is used is a bromine or iodine compound.

Description

Title: Method for oxidizing polysaccharides using ozone in the presence of a halogenide-containing catalyst.

The invention relates to a method for oxidizing polysaccharides using ozone and in the presence of a halogenide-containing catalyst.

The oxidation of polysaccharides has been described in diverse variants. Known oxidizing agents for this purpose are periodic acid, peracetic acid, perborate, persulfate, potassium permanganate, lead(IV) salts, hydrogen peroxide, chlorite and hypochlorite.

The most conventional method for the oxidation of polysaccharides utilizes hypochlorites. This method has as a disadvantage that large amounts of salts are formed in the process, which causes problems in the processing of the waste water. Moreover, the yield of oxidized polysaccharides is often insufficient and long reaction times are necessary. Dutch patent specification 43493, European patent application 0 427 349 and international patent application 91/17189 disclose the oxidation of polysaccharides with a catalytic amount of bromide to form oxidized polysaccharides. The bromide is converted to hypobromite by hypochlorite or by electrochemical route. Using hypochlorite, relatively many salts are introduced, while the electrochemical regeneration is complicated, inter alia because of the use of different compartments and because of the soiling of the electrodes. It is also known that ozone can be used as an oxidizing agent for polysaccharides.

Angibeaud et al., for instance, in "Cellulose, Its Derivatives" ed. J.F. Kennedy, published by Horwood Chichester U.K. (1985) entitled "Cellulose and Starch Reactivity with Ozone" describe the use of ozone as an oxidizing agent for polysaccharides.

In the introduction of this article it is concluded that the use of ozone as oxidizing agent for polysaccharides, with starch being mentioned as an example, is impeded by the absence of selectivity. Both carbonyl and carboxyl groups are formed, while glycosidic bonds are broken. No details are given about any effect of catalysts on the oxidation with ozone.

Further, Szymanski, in the Journal of Applied Polymer Science 8 (1964), 1597-1606, describes a method for oxidizing maize starch utilizing ozone. The oxidation with ozone is carried out both under dry conditions and in aqueous suspension and in an organic solvent.

The aim of the study which is described in this article by Szymanski was the introduction of a large amount of aldehyde groups into the starch. Because in addition to the intended aldehyde groups a considerable amount of ketone groups was formed as well, the objective was not achieved according to the author.

In a part of this study the effect of the salts iron sulfate and manganese sulfate on the ozone oxidation of maize starch is described. The manganese salt led to a 38% increase as regards the carbonyl substitution, while the iron salt, by contrast, showed an inhibiting effect.

Furthermore, it is known from U.S. Patent 3,361,741 that starch in an aqueous suspension can be oxidized by tetravalent lead ions, these lead ions being obtained by oxidation of bi- or trivalent lead ions with ozone.

German Offenlegungsschrift 22 33 977 describes the oxidation of polysaccharides using an aqueous basic solution of a silver oxide system. In the presence of this silver oxide system the polysaccharides can be oxidized with a large number of agents, including ozone.

International patent application 93/01905 describes the oxidation of polysaccharides with periodate, this periodate being electrochemically regenerated in a separate reaction space. Such a method requires complicated equipment and a complicated process control.

Now, a method for the oxidation of polysaccharides has been found, in which only slight amounts of salt are used and which leads to a yield of more than 90% of desired products in short reaction times.

Moreover, in this method for the oxidation of polysaccharides the halogenide-containing catalyst is regenerated in the same space as where the oxidation reaction occurs.

The present invention provides methods whereby polysaccharides such as starch can be selectively oxidized using ozone and in the presence of a catalyst. More particularly, the invention relates to a method wherein polysaccharides are treated with ozone in the presence of a halogenide-containing catalyst, while, depending on the choice of the catalyst and the reaction conditions, it can be set what oxidation product can be obtained or the product formation can be optimized within limits.

This object is achieved through the use of the method according to the invention, which is characterized in that polysaccharides are oxidized in the presence of a catalyst selected from the group consisting of bromine and iodine compounds, wherein ozone is passed through an aqueous suspension or solution of these polysaccharides.

Preferably, the bromine compounds are bromides or oxy bromides such as hypobromite, while the iodine compounds are iodides, oxy iodides and iodic acid compounds. Without wanting to be bound by any particular theories, it is supposed that the bromine and iodine compounds in the presence of ozone are converted to reactive oxidizing oxidants, such as hypobromite and periodic acid, which compounds oxidize the polysaccharides. In principle, only a small content of these reactive bromine and iodine compounds needs to be present in the reaction medium, since the compounds are continuously regenerated by ozone to form the active oxidants.

The bromine and iodine compounds already exhibit an effect in slight amounts. These catalysts are already active in concentrations from 0.05% by weight, as dry matter calculated on the starch. In the case of bromine compounds such as NaBr, C2 - C3- and C6-carboxyls and -carbonyls are formed. With an increasing amount of NaBr, to an increasing extent C2 - C3-carboxyl groups with respect to C6 are formed. In the case of iodine compounds such as HI0₃ substantially the C2 - C3- and C6-groups are oxidized to aldehydes. This has been demonstrated with a gas chromatography/mass spectrometry technique (Hewlett Packard, gas chromatograph GC 5890 series II and mass spectrometer MS 5989A).

In Dutch patent application 1002526 of the same filing date, the oxidation of starch with ozone in the absence of catalysts is described. The present inventors have found that if chlorine compounds such as hypochlorite are added to this ozone system, hardly any advantages or other effects are found. In fact, only a slight increase in the content of carboxyl and carbonyl groups was found. In this connection, reference is also made to Example 1 below. Without wanting to be bound by any particular theory, it is supposed that in the presence of ozone, chlorate ions are readily formed from chlorine compounds. Chlorate ions have little or no oxidizing power.

When instead of the chlorine compounds the bromine or iodine compounds according to the present invention are used, it is found that far fewer halogenide ions can suffice. For bromine compounds it has been found that only about a tenth of the amount by weight of chlorine compounds whose use was found to give any effect, are needed to obtain the desired results. Depending on the pH and the catalyst, an oxidized polysaccharide with any desired carbonyl/carboxyl ratio between 1:1000 and 20:1 can be obtained. With increasing pH, carboxyl groups are formed to an increasing extent. Accordingly, the invention makes it possible, by setting the pH, to form in one and the same reaction system, in the case of starch, an aldehyde starch or a carboxyl starch or an intermediate form, depending on the eventual application of the product. The products obtained by the method of the invention can be used in many different technical fields of application. For instance, carbonyl group containing starches have good utility in adhesives, in paper (for instance in coating layers and surface-sizing), and in textile (for instance as size). Starting products where the sugar ring has been oxidized open, which occurs, for instance, in C2-C3 starch oxidation, can be used as co-builders in detergents. Carbonyl groups formed according to the invention are interesting reaction centres and can be converted by conventional techniques to, for instance, amines, imines, acetals, and the like.

The pH is held constant by adding during the reaction a base or a solution thereof, for instance a solution of sodium hydroxide or potassium hydroxide. Buffer systems are less preferred because they are based on salts, and so introduce salts into the product. Moreover buffer systems are more expensive. The invention can be applied to polysaccharides such as starch, cellulose, inulin and derivatives thereof. The starches that are oxidized according to the invention can be of all types. Preferably, root starches (e.g. tapioca), tuber starches (e.g. potato) and waxy cereal starches (e.g. waxy maize, waxy rice) are used, because of their low content of contaminants. Physically and chemically modified polysaccharides, such as roller-dried polysaccharides, and etherified and esterified polymers, can also be oxidized in accordance with the invention. According to the above-mentioned method the polysaccharide is oxidized in aqueous suspension and after reaction the aqueous phase with catalyst can be separated from the reaction product in a simple and known manner and be recirculated. Optionally, bromine and/or iodine compounds can be captured using ion exchangers.

In a preferred embodiment, in the aqueous reaction medium a surface tension reducing agent is present, which provides that the ozone-containing gas bubbles can become smaller. Thus the starch molecules are contacted more intimately with the oxidizing agent. Suitable surface tension reducing agents include acetic acid, tertiary butanol and surface-active compounds such as octanols, known anti-foaming agents such as block polymers of ethylene oxide and propylene oxide (for instance Pluronic L61). The acetic acid can be used in concentrations from 0.1 to 10%, preferably from about 0.2 to 2 %; tertiary butanol in concentrations of 0.1 to 15%; anti-foaming agents in concentrations of 0.01 to 5%, preferably from about 0.05 to 2.5%. These percentages are based on the amount of dry starch subjected to the reaction for treatment.

The pH during the reaction may not be higher than 10.5 because ozone decomposes at higher pH values; and not lower than 1 in connection with hydrolysis of the polysaccharides. The pH is preferably between 4 and 10.5 when bromine compounds are used as catalyst and preferably between 2.5 and 7.0 when iodine compounds are used as catalyst. The polysaccharide concentration of the reaction mixture can vary from 1 to 45% (based on dry matter) and is preferably between 10 and 40%.

As a source and as a carrier gas for the ozone, oxygen, air or any other oxygenous gas can be used. In addition, ozone can be generated directly from water. When a gas is used, preferably oxygen is used.

The reaction can be carried out at temperatures of from 0 to 60°C, preferably between 5 and 40°C. The reaction time is between 10 minutes and 20 hours and depends on the desired degree of oxidation.

By applying the above-mentioned method, the intrinsic viscosity of polysaccharides can be reduced. This renders the polysaccharides suitable for various applications for which polysaccharides with a reduced viscosity are of importance. The intrinsic viscosity can be set inter alia with the reaction pH, the amount of catalyst, reaction temperature, reaction time, addition of surface tension reducing agents. The intrinsic viscosity of a substance is understood to mean the extent to which one molecule of that substance in solution can increase the viscosity and is determined by measuring the hydrodynamic volume of that substance. The intrinsic viscosity is expressed in dl/g. in the preferred embodiment of the above-mentioned method, wherein polysaccharide is oxidized in aqueous suspension with ozone under the influence of a catalyst, after reaction the aqueous phase with catalyst can be separated from the reaction product in a simple manner and the reaction medium can be used again. If desired, the bromine and iodine compounds can be recovered from the reaction mixture.

The invention will be further illustrated in and by the following non-limiting examples. The oxidation products are analyzed in the following manner.

The content of carboxyl groups (DScooh) is expressed in the number of moles of carboxyl per mole anhydroglucose unit (DScooh) and is determined titri etrically. To that end, the sample material is brought into the H⁺ form with 1 N HC1; and titrated to pH 8.6 with 0.1 M NaOH. The titration is carried out in 0.5 M NaCl.

The content of carbonyl groups (DSc=o) is expressed in the number of moles of carbonyl per mole anhydroglucose unit (DSc=o) and is determined by determining the dextrose equivalent (in mg/g) of the sample material with the Luff- Schoorl method, followed by conversion, as follows: (DS_C=0) = DE/(1000-DE).

The intrinsic viscosity (IV) is determined in a known manner with a Viscotek Y501B with 1 M NaOH as solvent and expressed in g/dl. Examples

Oxidation conditions and standard work-up procedure

Unless specified otherwise, the experiments were carried out in a glass 1-litre batch reactor provided with an agitator, a gas inlet and a pH meter having coupled thereto an automatic titrator having therein 4.4 wt.% NaOH solution. The partial overpressure was 0.1 bar. Ozone was generated, unless specified otherwise, by passing about 250 1 oxygen gas per hour through an ozone generator (Fischer, type 502). The ozone production at this flow rate was 8 g/hour. The ozone containing gas was passed through the reaction mixture. Upon completion of the reaction the product was worked up by adjusting to pH 5.5 in aqueous suspension with 6 M sulfuric acid or with 4.4 wt.% NaOH solution. Then the product was filtered off and washed with a 10-fold - based on the weight of the starch - amount of water. The product loss and the physical data were determined after the products were dried. The amount of an addition is expressed in percent by weight of the amount of starch, calculated on a dry matter basis. In all experiments demineralized water was used.

Example 1

Oxidation of potato starch with ozone under the influence of different catalysts (NaBr, NaCl, Nal, HIθ₃) at constant temperature and pH.

la Control reaction with 5% NaBr without ozone 250 g (200 g dry matter) potato starch was suspended in a solution of 10 g NaBr in 750 ml water. Then for 7.5 hours at 35°C oxygen was passed via a pipe into a porous stone and thus into the reaction system.

During the reaction the pH was maintained at 9.0 with the aid of 4.4 % NaOH and an automatic titrator combination. After reaction the product was filtered off, washed and dried.

lb Oxidation with ozone without catalyst 250 g (200 g dry matter) potato starch was suspended in 750 ml water. Then for 7.5 hours at 35°C ozone-containing oxygen was passed through via a porous stone.

lc Oxidation with ozone with 5% NaBr as catalyst 250 g (200 g dry matter) potato starch was suspended in a solution of 10 g NaBr in 750 ml water. Further carried out as lb.

Id Oxidation with ozone with 5% NaCl as catalyst 250 g (200 g dry matter) potato starch was suspended in a solution of 10 g NaCl in 750 ml water. Further carried out as lb.

le Oxidation with ozone with 12.5% Nal as catalyst 250 g (200 g dry matter) potato starch was suspended in a solution of 25 g Nal in 750 ml water. Further carried out as lb.

If Oxidation with ozone with 12.5% HIO3 as catalyst

250 g (200 g dry matter) potato starch was suspended in a solution of 25 g HIO3 in 750 ml water.

Further carried out as lb. Table 1

Ozone oxidation with different catalysts

The addition of chlorine ions does not show any catalytic effect.

Example 2

Oxidation of potato starch with ozone with increasing amounts of NaBr as catalyst;

0% - 0.05% - 0.5% - 5% - 50% NaBr

in five tests 250 g (200 g dry matter) potato starch was suspended in 750 ml water, in the presence of increasing amounts of NaBr: 0; 0.05; 0.5 ; 5, and 50%, respectively. Then for 7.5 hours at 35°C ozone-containing oxygen was passed through via a porous stone. During the reaction the pH was maintained at 10.5 with the aid of 4.4% NaOH and an automatic titrator combination. After reaction the product was filtered off, washed and dried. Table 2

Oxidation of potato starch with ozone in the presence of increasing amounts of NaBr

NaBr DScooh DSC=0 IV

0% 0.001 < 0 . 003 2 . 13

0.05% 0.001 < 0 .003 2 .02

0.5% 0.010 < 0 .003 0.46

5% 0.010 0.003 0.46

50% 0.014 0 .003 0.41

Example 3a

Oxidation of potato starch with ozone at different pHs: 6.6 - 7.5 - 9.0 - 10.5 with 5% NaBr as catalyst

250 g (200 g dry matter) potato starch was suspended in a solution of 10 g NaBr in 750 ml water. Then for 7.5 hours at 35°C ozone-containing oxygen was passed through via a porous stone.

During the reaction the pH was kept constant with the aid of

4.4% NaOH and an automatic titrator combination.

After reaction the product was filtered off, washed and dried. The reaction at pH 6.6 was started at pH 6.0. After a short time the pH stabilized at 6.6 without addition of NaOH.

Table 3a

Oxidation with ozone at different pHs

PH DScooh DSc=o IV

6.6 0.038 0.057 0.09

7.5 0.056 0.047 0.10

9.0 0.060 0.010 0.15

10.5 0.010 0.003 0.46

Example 3b

Oxidation of potato starch at different pHs: 3.0 - 4.5 with 1% HIO3 as catalyst

470 g (400 g dry matter) potato starch was suspended in 1530 g water. To this suspension was added 4.0 g HIO₃, whereafter the pH was adjusted with a 4.4% NaOH solution to 3.0 and 4.5, respectively. Then for 8 hours at 30°C ozone- containing oxygen was passed through via a porous stone (about 3% ozone; flow rate 100 1/h). During the reaction the pH was maintained at 3.0 and 4.5, respectively, with 4.4% NaOH and an automatic titrator combination. After reaction the product was filtered off and washed with 2 1 water.

Table 3b Oxidation with ozone at different pHs

_PH DScooh DSc=o IV

3.0 0.013 0.045 0.15

4.5 0.002 0.015 0.39 Example 4

Oxidation of potato starch with ozone under the influence of a surface-active substance, Pluronic L61 with NaBr as catalyst

490 g (400 g dry matter) potato starch was suspended in 1510 g water. To this suspension was added 2.0 g NaBr, whereafter the pH was adjusted with a 4.4% NaOH solution to 7.5. Then for 5 hours at 25°C ozone-containing oxygen was passed through via a porous stone (about 3% ozone; flow rate 100 1/h). During the reaction the pH was maintained at 7.5 with 4.4 % NaOH and an automatic titrator combination. After reaction the product was filtered off and washed with 2 1 water.

The above reaction was repeated again with addition of 1.0 g Pluronic L61 (0.25%).

Table 4 Oxidation of potato starch under the influence of Pluronic L61

Pluronic DScooh DSc=o IV not present 0.012 0.042 0.15

0.25 % 0.015 0.060 0.12

Example 5

Oxidation with ozone of different starches under equal conditions (pH*7.5; 25°C, 0.5% NaBr)

5a Potato starch (AM)

490 g (400 g dry matter) potato starch was suspended in 1510 g water. With 4.4% NaOH the pH was adjusted to 7.5. Then for 5 hours ozone-containing oxygen was passed through via a porous stone (about 3% ozone; flow rate 100 1/h). During the reaction the pH was maintained at 7.5 with 4.4% NaOH and an automatic titrator combination.

5b Amylopectin potato starch (AAZM)

488 g (400 g dry matter) amylopectin potato starch was suspended in 1510 g water. Further carried out as 5a.

5c Waxy maize starch (WM)

449 g (400 g dry matter) waxy maize starch was suspended in 1550 g water, to which was added 4 g Pluronic L61 to prevent foaming. Further carried out as 5a.

5d Tapioca starch (TZ)

459 g (400 g dry matter) tapioca starch was suspended in 1550 g water, to which was added 4 g Pluronic L61 to prevent foaming. Further carried out as 5a.

Table 5

Ozone oxidation of different starches

starch DScooh DSc=o

AM 0.015 0.050

AAZM 0.008 0.027

WM 0.011 0.023

TZ 0.021 0.076 Example 6

Ozone oxidation of other polysaccharides; inulin and cellulose

6a Reaction with inulin with 6% NaBr as catalyst 82 g (75 g dry matter, 0.46 mol) Inulin (from chicory root) was suspended in a solution of 5 g NaBr in 669 ml water. The suspension was heated to 35°C whereafter the pH was adjusted to 9.0 with NaOH. Then for 6.5 hours 8 g/hour ozone was passed through. After reaction the pH was adjusted with 6 M hydrochloric acid to pH 3.0, whereafter the product was flocculated in ethanol. The flocculated material was dried in the air.

6b Reaction with cellulose with 8% NaBr as catalyst 138 g (129 g dry matter, 0.80 mol) Avicel PH102 was suspended in a solution of 10 g NaBr in 750 ml AD. The suspension was heated to 35°C whereafter the pH was adjusted to 9.0 with NaOH. Then for 7.5 hours 8 g/hour ozone was passed through. After reaction the pH was adjusted to 5.5 with 6 M HC1. Then the product was included in 1 1 AD and isolated by centrifugation. This washing procedure was repeated twice more.

Oxidation with ozone of inulin and cellulose

substrate DScooh DSc=o inulin 0.036 0.022 cellulose 0.027 0,004

Claims

Chilis

1. A method for oxidizing polysaccharides in the presence of a catalyst selected from the group consisting of bromine and iodine compounds, wherein ozone is passed through an aqueous suspension or solution of these polysaccharides.

2. A method according to claim 1, wherein the polysaccharide is starch or a derivative thereof.

3. A method according to claim 1, wherein the polysaccharide is cellulose or a derivative thereof.

4. A method according to claim 1, wherein the polysaccharide is inulin or a derivative thereof.

5. A method according to any one of claims 2-4, wherein the polysaccharide is present in aqueous suspension.

6. A method according to any one of claims 1-5, wherein the pH is maintained at a constant value.

7. A method according to claims 1-6, wherein surface tension reducing substances are added.

8. A method according to claim 7, wherein the surface tension reducing substances are selected from acetic acid, tert.butanol, octanol and anti-foaming agents.