FR2623194A1 - PROCESS FOR THE PURIFICATION OF AQUEOUS SOLUTIONS OF POLYSACCHARIDES AND THEIR DERIVATIVES, IN PARTICULAR SCLEROGLUCANE BY ADSORPTION - Google Patents

Abstract

Method for purification of an aqueous solution of viscous polysaccharide, having a high molecular mass and high viscosity, wherein the impurities are removed by treating the solution with activated charcoal, preferably at a temperature comprised between 50 and 130 DEG C. The method is particularly well adapted to the purification of scleroglucane.

Description

 The present invention relates to the purification of aqueous solutions of different polysaccharides and their derivatives, especially natural polymers, synthetic or produced by directed cultures of fungi or bacteria, in particular galactomannans, pectins, alginates, carrageenans, xanthan, scleroglucan, dextran , schyzophyllane and the like, It aims a process for the removal of various impurities of these solutions, including nitrogenous, phosphorus, sulfur, polar or ionic, may have acid functions and, possibly, ionic compounds, metal.

Aqueous solutions of polysaccharides have various industrial applications. One of them is currently of particular importance is the use of enhanced oil recovery. This technique involves moving oil trapped in the reservoir rocks by higher viscosity aqueous polymer solutions, thereby increasing the amount of oil extracted. Two criteria are decisive for the choice of polymer: a high viscosity and good filterability. Scleroglucan, a nonionic polysaccharide, obtained by fermentation using a mushroom of the type
Sclerotium Rolfsii (ATC 15206), is currently the most promising polymer in difficult operations, thanks to its good viscosity at high salinity and high temperature (900C or more) .However, these interesting properties are annihilated by the presence of impurities leading to the self-aggregation of the polymer, over time, making the solutions very heterogeneous, with micro-gel phases, which inevitably results in progressive clogging and loss of viscosity in the vicinity of the well injection. In addition, impurities create risks of biological degradation, including bacterial or enzymatic, chemical and / or thermal polysaccharide employed. Protein impurities play a particularly important role.

 The prior art, with respect to xanthan and its derivatives, is mainly directed towards the removal of proteins from aqueous solutions, before the use of these, so that an attempt has been made to apply a treatment with alkalis, bringing the pH of the solution above 11, while hot, as disclosed in US Pat. No. 3,729,460, but this method did not produce the desired result.Several authors have used proteases to remove the proteins from the polysaccharide solutions. pH 7.5 to 13 an improvement has been achieved by this means, but - to avoid clogging of oil wells - it is still necessary to filter the treated solution, in the end, these processes, including those of US Pat. 4,119,491 or 4,165,257, although useful, is very laborious and expensive. Progress was made by applying a polysaccharase or glucan hydrolase enzyme at a pH of 3 to 7, according to the patent publication. French 2,491,494, n In addition, this process requires a great deal of care and time, is relatively expensive, and does not apply to scleroglucan. With regard to adsorbent treatments, particularly with silica and adsorbent earths, their disappointing results have confirmed what the theory indicates that there is no reason for large protein molecules to preferentially adsorb to those polysaccharide which may be the same size or larger.

 However, contrary to what was foreseeable and to the negative results, given by the inorganic adsorbents, against all odds, according to the present invention it is possible to selectively remove the harmful impurities from the polysaccharide solutions by their adsorption on the activated carbon particles. , while clays, silica or alumina do not allow this purification.

 The process according to the invention is therefore characterized in that an aqueous solution of polysaccharide, containing impurities, is purified by contact with activated charcoal.

 This process makes it possible to eliminate, inter alia, impurities such as proteins, in particular enzymes, acids such as, for example, oxalic and lactic acids, metal salts, colored materials, and, in general, ionic or polar molecules, soluble or non-soluble ones. soluble in water.

 For the treatment to be carried out properly, the viscosity of the polysaccharide solution must not be too high: it is therefore preferably carried out with solutions having a dynamic viscosity at 200C of 0.01 to 10 Pa.s. and preferably 0.03 to 5 Ps.s.

This corresponds, for most of the usual polysaccharides, to weight concentrations of 0.02 to 10% and especially 0.05 to 5% (500 to 50,000 ppm).

 Several qualities of activated carbon are commercially available: they differ in their specific surface, porosity, granulometry, surface activation, packaging (powder or granule), etc.

These coals can be of animal or vegetable origin; whatever quality is used, similar results are obtained by varying quality, contact time, and / or other parameters. However, in order to achieve the optimum treatment, it is preferable to have an active carbon with a specific surface area (BET, in m2 / g) of between 100 and 2000, preferably between 200 and 1500; macroporosity (cm 3 / g) between 0.5 and 3 or better between 0.6 and 1.8, and microporescence (cm 3 / g) between 0.05 and 2, preferably between 0.1 and 0.8. pH is between 3 and 10 and preferably between 6 and 9, In order to eliminate more easily the activated carbon particles after treatment, and to avoid the clogging of the filters, it is advisable to use a coal of average particle size greater than 10r, preferably greater than 20> 1m and density greater than 0.2, or better still greater than 93. If, in some cases, it is imperative to use active carbon of smaller particle size, it is desirable to make several filtrations successive with decreasing pore diameter filters.

 The treatment according to the invention can be carried out by dispersion, from 0.05 g to 50 g of active carbon, preferably 0.5 g to 10 g, per gram of polysaccharide.

The purified solution is then separated by centrifugation or filtration. The starting polysaccharide solutions may or may not contain biomass; Of course, the preliminary elimination of this biomass, c. to d. cell walls, microorganisms, etc. or any insoluble compounds in the solution, facilitates and improves the results.

 Under industrial purification conditions, it is often necessary to use filtration aids. These filtering agents must have a low density, between 0.2 and 0.4, and must be chemically inert with respect to the polysaccharide: there may be mentioned, for example, diatomaceous earth, expanded perlite or not , asbestos or cellulose fibers.

The activated carbon-treated solutions can be filtered in the presence of these filtering agents either directly on filters or on "precoatches" consisting of mixtures of different qualities of these filtering agents.

 In this embodiment, the precoatings are generally formed by aqueous dispersions containing by weight about 0.5 to 10% of diatomaceous earth or other filter aid, preferably from 1 to 3%. In conjunction with the activated carbon, an adjuvant is used, between 0 and 10% or better 1 to 3% by weight relative to the solution.

 Another procedure allows continuous operation: it consists of passing the impure solution through columns loaded with activated carbon granules. In this case, to avoid irreversible clogging of the columns, it is desirable for the polysaccharide solutions to be stripped of their biomass and of any insoluble particles, by prior filtration. It is understood that for each column, the "available" pore volume, the adequate flow rate of the pumps, are determined in order to have the necessary contact time for the purification, as well as the saturation volume where there is no more purification.

 It is advisable to use a battery of columns mounted in parallel, one of which operates, while in the others the active carbon is regenerated.

 In a particular preferred embodiment of the invention, an electrolyte is dissolved in the polysaccharide solution to be purified. This feature of the invention results from the unexpected finding that the presence of a salt in the solution contributes significantly to improving the adsorption of impurities by the activated carbon. The elimination of proteins is thus greatly promoted.

 The electrolytes, which are most suitable for carrying out the invention, are mono or divalent cation salts, the anion may also be mono- or divalent. Such salts are more particularly halides, sulphates, sulphites, nitrates; perchlorates etc. alkali, alkaline earth or ammonium metals. The chlorides, sulphates, sulphites, nitrates and / or perchlorates of Na, K, Li, Ca, Mg and NH4 are especially suitable.

 The usable concentrations of these salts in the polysaccharide solution; are approximately 0.008 to 2.5 M and especially 0.15 to 0.70 M. In the case of NaCl, which is naturally the most economical, these concentrations represent 0.5 to 130 g per liter, and preferably about 10 to 40 g / l.

 The treatment according to the invention of an aqueous solution of polysaccharide can be carried out at different temperatures, the somewhat high temperatures being interesting because of the decrease in the viscosity which they comprise. The permissible upper temperatures are limited to that at which the polysaccharide has practically no viscosity since this limit is generally about 1300C, the temperature range is usually 5 to 1300C and especially 100 to 1200C.

 The regeneration of the activated carbon can be carried out in several ways: by passing an alkaline solution, especially sodium hydroxide and / or acid, such as hydrochloric or sulfuric. In some cases, an alcoholic solution, especially methanol or isopropanol, is preferable. These solutions degrade or desorb the impurities captured, and cause elution. If conditions permit, the regeneration can be carried out by a heat treatment between 5500 to 6500C in an oven. The charcoal is then washed by passage with water.

 Although the different kinds of commercially available activated carbons are suitable for the practice of the invention, it is preferable to subject them prior to the action of a sterilant. One method is to disperse them in an alcohol, methyl or ethyl. The dispersions are subjected to ultrasound.

After filtration, this charcoal is heated at 1500C for one hour so as to completely eliminate any possible microbial or fungal pollution.

 Given the modest prices of activated carbons and the simplicity of the operations according to the present invention, the treatment is very economical, while providing the desired benefits: the purified solutions obtained are perfectly colorless and transparent, homogeneous, presenting no micro-organisms. freezes, nor tend to form with time. In addition there is a better resistance to bacterial or enzymatic degradation, low temperature, and oxidizing at high temperature.

 The examples which follow are non-limiting and illustrate the invention.

 EXAMPLE 1: Elimination of proteins and metal traces 3 influence of salinity.

Starting from a commercial solution of (CSHL) of scleroglucan, freed from its biomass and containing 0.35% by weight of the polymer, two solutions diluted to 0.1% of polymer are prepared, one in water. distilled (solution A), the other in a 36 g / l aqueous solution of NaCl (solution B). To each of these solutions,
A and B, 5 g / l of activated carbon (Prolabo) with a particle size of between 30 and 50 μm and 20 g / l of infusorial earth (Prolabo) are added. The solutions are then dispersed by stirring for one hour, and each filtered with overpressure through three filters intercalated in the following manner: coarse paper filter (Watman) / filter
Millipore (5, u) / coarse paper filter (Watman). The purified solutions are quite clear and colorless whereas they were strongly stained initially.

The dosages of the solutions before and after the purification gave the following results:
Raw solution Purified solutions
(N 1) A (N 2) B (N 3) total protein 50 10 0 (1) (ppm BSA)
Fe (ppm) 1.2 0 0 total
Total acidity OOO (oxalic and lactic) (1) Bio-Rad method
It is seen that the presence of NaCl in solution B improved the elimination of proteins.

Example 2: Purification and filtration on diatomaceous earth.

 A solution B at 1000 ppm of scleroglucan is prepared and treated in the same manner as in Example 1.

The solution is then filtered on a layer of diatomaceous earth, of about 2 mm, previously formed on a sintered glass (porosity 4), under medium vacuum.

A perfectly colorless solution of the same characteristics as in Example 1 is obtained, the yield of which of the polymer by precipitation in lisopropanol gives less than 5% weight loss, thus showing very little retention of the polymer on the filtering layer.

Example 3 Purification of a fermentation must containing scleroglucan. Elimination of oxalic acid and biomass.

 From a direct sample of a fermentation must of Sclerotium rolfsii, a solution is prepared so as to obtain 0.1% by weight of polymer purified in water at 36 g / l NaCl. This solution contains, besides the biomass (the mycelium), all the impurities resulting from the fermentation.

The activated carbon treatment and the filtration are carried out under the same conditions as in Example 2. The solution obtained is perfectly colorless.

Assays before and after purification gave the following results.

Raw solution Purified solution
(NO 5) (No 6) total protein 400 <1 (ppm SAB)
Total Fe OO (ppm)
Total acidity 3000 0 (ppm) (oxalic and lactic)
EXAMPLE 4 Purification of Scleroglucan Mash Under Production Conditions

 In a stirred tank and controlled thermal regulation, to 200 1 of a diluted fermentation broth, containing about 0.5% of scleroglucan, 200 g of CaCl 2 and 200 g of NaCl are added. Stirring is maintained for 30 minutes.

Then about 1.5 kg of active charcoal is dispersed
ACTICARBONE 3S - CECA for one hour.

Meanwhile, several precoat diatomaceous earth (CLARCEL-CECA) are deposited on the trays of a filter-press filtering device. After complete stabilization of the fines, the polymer solution is passed through.

A clear and colorless filtrate (NO 7 solution) is collected whose protein, Fe and total acidity levels are all negative.

Example 5: Improvement of the purification of a scleroglucan solution, under the production conditions, by raising the temperature.

 With the same type of apparatus and under the same conditions as in Example 4, it has been observed that the heating of the dispersion at 800 ° C., as well as the filtration at this temperature, greatly improves the filterability, in fact, the flow rate of filtration is at least doubled. The filtrate obtained (solution NO 8) is clear and colorless and retains viscosity levels comparable to those of the other techniques. The levels of impurities are zero.

Example 6 Essars of Various Samples of Activated Carbon

A solution is prepared from a fermentation must so as to have 0.5% final purified scleroglucan. The following activated carbon samples were tested compared to those of the previous examples (prolabo, milled and screened between 30 and 50 pm), under the conditions of Example 3.

Coal <SEP> Prolabo <SEP> Acticarbone <SEP> (CECA)
<tb> characteristics <SEP> CXV <SEP> 3S <SEP> BAG <SEP> 516 <SEP> GP <SEP> WNC
<tb> Surface <SEP> specific
<tb> (m2 / g) <SEP> BET <SEP> 1555 <SEP> 1674 <SEP> 1209 <SEP> 1501 <SEP> 613 <SEP> 1088
<tb> Microporous <SEP> Volume
<tb> (2)
<tb>(<SEP><<SEP> 5m <SEP>;<SEP> cm3 / g) <SEP> BET <SEP> 0.77 <SEP> 0.61 <SEP> 0.46 <SEP> 0, 11 <SEP> 0.15
<tb> Macroporous <SEP> Volume
<tb> (3)
<tb>(<SEP><<SEP> 5m <SEP>;<SEP> cm3 / g) <SEP> -.69 <SEP> 1.7 <SEP> 1.81 <SEP> 1.1 <SEP> 1.07 <SEP> 0.86
<tb> pressure <SEP> Hg
<tb> Porosity <SEP> total
<tb> (cm3 / g) <SEP> 1.46 <SEP> 2.31 <SEP> 2.27 <SEP> 1.76 <SEP> 1.18 <SEP> 1.01
<tb> Density <SEP> - <SEP> 0.33 <SEP> 0.33 <SEP> 0 <SEP> 0.50 <SEP> 0.58
<tb> pH <SEP> (surface) <SEP> - <SEP> 3-6 <SEP> 9 <SEP> - <SEP> 9 <SEP>
<SEP> average radius <SEP> of
<tb> grains <SEP> (10-4microns ~ <SEP> 24 <SEP> 21 <SEP> 29 <SEP> 4 <SEP> 22 <SEP> 21
<tb> Density and pH values are as indicated by the manufacturers.

 Whatever the quality of the coal, all the solutions obtained are clear and colorless. The protein and oxalic acid assays are negative, however, coals having a low macroporous volume and a high microporous volume are preferably used.

Coal Prolabo CXV 3S SAC516 GP WNC features solutions.

green (1) 20 25 15 10 3 (weight)% transmission (2) 90 80 95 70 98 98 (1)% loss: concentration of the crude solution (ppm)
concentration of purified solution (ppm) (2)% Transmission, measured on purified solutions
showing traces of activated carbon.

 For viscous scleroglucan solutions, in order to facilitate the removal of the coal and to reduce the polymer losses during the treatment, it is preferable to choose coals with small specific surface areas, average particle size, greater than or equal to 2 x 10- 3 microns and high densities.

Example 7
Determination of the dispersion of scleroglucan and comparison with the prior art.

 The solutions of Example 1 (Nos. 1 to 3) were compared with a solution (No. 1 bis) obtained by the enzymatic treatment according to FR 2 491 494 of the crude solution (No. 1) of this example. This treatment was carried out using an alkalase (NOVO) in the manner described in Example 1, pages 14-16, of the aforementioned patent application.

For each of the four solutions, Nos. 1, 1 bis, 2 and 3, the coefficient K 'of HUGGINS was measured, in a manner known per se, by studying the slope of the intrinsic viscosity as a function of the concentration. This coefficient gives the measurement of the state of aggregation of the polymer in solution.

On the other hand, on each of the four solutions was carried out filterability tests at 200 c, through a Millipore membrane 47 cm in diameter, pore 5pm; the flow rate Q was 20 ml / h, the interpolysaccharide concentration 1000 ppm and the NaCl content of the solution 36 g / l.

The following table gives the HUGGINS coefficients k 'and the pressure differences #P characterizing the filterability according to the DARCY law: aP = KQn / k (K = constant, k filter permeability, n viscosity).

N <SEP> solution <SEP> N <SEP> 1 <SEP> N <SEP> 1 <SEP> bis <SEP> N <SEP> 2 <SEP> N <SEP> 3
<tb> characteristics <SEP> Example <SEP> 1 <SEP>: <SEP> Processing <SEP> Example <SEP> 1 <SEP>: <SEP> Example <SEP> 1 <SEP>:
<tb> solution <SEP> gross <SEP> according to <SEP> art <SEP> treats <SEP> at <SEP> charcoal <SEP> active
<tb> earlier. <SEP> coal <SEP> active. <SEP> in <SEP> presence
<tb> of <SEP> NaCl
<tb> [n]. <SEP> (cm3 / g) <SEP> 6000 <SEP> 6000 <SEP> 6100 <SEP> 6100
<tb> k1 <SEP> 1.35 <SEP> 2.6 <SEP> 0.8 <SEP> 0.6
<tb>#P<SEP> (1) <SEP> clogging <SEP> clogging <SEP> clogging <SEP> 20
<tb> n <SEP> (mPa.s) <SEP> to <SEP> 0.1s-1 <SEP> 178 <SEP> 145 <SEP> 160 <SEP> 150
<tb> to <SEP> 10s-1 <SEP> 52 <SEP> 34 <SEP> 50 <SEP> 46
<tb> (1) On a perfectly filterable solution, the figure corresponds to the final value of the landing.

 the values of k 'found prove a considerable improvement, provided by the coal treatment, according to the invention; in fact, 0.6 or 0.8 practically indicate the absence of aggregation, unlike the high figures 1.35 and 2.6 respectively corresponding to the solution before the treatment and to this same solution after the enzymatic treatment of FR 2 491,494.

As regards filterability, the solution N 3, i.e. test with electrolyte in scleroglucan solution, represents a remarkable progress with = P = 20, without any clogging.

Similar determinations were made for the solutions of Examples 3, 4 and 5. Their results are summarized in the table below.

N <SEP> Solution <SEP> N 5 <SEP> N <SEP> 6 <SEP> N <SEP> 7 <SEP> N <SEP> 8
<tb> Characteristics <SEP> Example <SEP> 3 <SEP>: <SEP> Example <SEP> 3 <SEP>: <SEP> Example <SEP> 4 <SEP>: <SEP> Example <SEP> 5 <SEP >:
<tb> Solution <SEP> Raw <SEP> Solution <SEP> Solution <SEP> Solution
<tb> purified. <SEP>. <SEP> purified. <SEP> purified.
<Tb>

[not]. <SEP> (cm3 / g) <SEP> 16 <SEP> 000 <SEP> 15 <SEP> 000
<tb> k1 <SEP> 1.1 <SEP> 0.4
<tb>#P<SEP> (mb) <SEP> clogging <SEP> 60 <SEP> 65
<tb> n <SEP> (mPa.s) <SEP> to <SEP> 0.1s-1 <SEP> 2 <SEP> 600 <SEP> 1 <SEP> 600 <SEP> 1 <SEP> 270 <SEP > 10s-1 <SEP> 50 <SEP> 49 <SEP> 53 <SEP> 50
<Tb>
These results show that the purification method, implemented according to the invention, makes it possible to have totally disaggregated and perfectly filterable solutions at 200 ° C., and that there is no degradation of the macromolecular chain during the treatment. .

Example 8 Storage Stability at Room Temperature (Biological Degradations).

 The solutions of Example 1, crude solution NO 1 and purified solution NO 3 are stored at room temperature, in the presence of a bacteriostatic (50 ppm Kathon 886 MW, Rohm & aas). After 6 months, there is a slight haze and a loss of about 60% of the initial viscosity of the NO 1 solution, while the NO 3 solution has hardly changed.

Example 9: Thermal stability at 105 OC.

 In 2 reactors of 500 ml, perfectly sealed, solutions 1 and 3 of Example 1 are deoxygenated by bubbling with argon: less than 0.05 ppm of 2 dissolved was detected by "Chemetrics kit". After one month at 105 ° C., solution 1 completely lost its initial viscosity1 while solution 3 retains 90% of its initial value.

Example 10: Regeneration of coal-active columns.

1) Chemical way
Several volumes of a mixture of 1 volume of methanol with 1 volume of water, containing 4 g of NaOH per liter, and then an acidic aqueous solution of 0.1 HCl are passed.

The column is then rinsed with water until the pH neutrality of the eluate.

2) Physical path
The water is removed from the column by a nitrogen overpressure.

The column is then calcined in an oven at 5500-6500C for several hours.
After cooling, the column is rinsed with several volumes of water or eluate used.

Claims (14)

claims  A method for purifying an aqueous polysaccharide solution, characterized in that the impurities are removed by treating the solution with activated charcoal.  2. Process according to claim 1, characterized in that the treatment is applied to a solution containing 0.02 to 10% by weight, and preferably 0.05 to 5%, of polysaccharide.  3. Process according to claim 1 or 2, characterized in that 0.05 to 50 g of active carbon are used per g of polysaccharide and preferably 0.5 to 10 g.  4. Method according to one of the preceding claims, characterized in that the activated carbon is in the form of grains of at least 10 μm and preferably at least 20 μm of an apparent density greater than 0.2.  5. Method according to one of the preceding claims, characterized in that the activated carbon has a specific surface area (BET) of 100 to 2000 m / g, a macroporosity of 0.5 to 3 ml / g and a microporosity of 0.05 to 2 ml / g.  6. Process according to claim 5, characterized in that the specific surface area is 200 to 1500m / g, the macroporosity 0.6 to 1.8 ml / g and the microporosity 0.1 to 0.8 ml / g.  7. Method according to one of the preceding claims, characterized in that, together with the activated carbon is used an adsorbent earth, in an amount of between 0 and 10% by weight relative to the solution, and preferably 1 to 3%.  8. Method according to one of the preceding claims, characterized in that the polysaccharide solution to be purified contains at least one electrolyte.  9. Process according to claim 8, characterized in that the electrolyte is an alkali metal, alkaline earth or ammonium salt, in particular halide, sulphate, sulphite, nitrate or perchlorate, present at a concentration of 0.008 M to 2 , 5M, and preferably 0.15 to 0.7M.  10. A method according to claim 7, characterized in that the coal and the earth are placed in the same layer, or in two successive layers, and that the solution to be purified firstly on the adsorbent earth and then on activated carbon.  11. Method according to one of the preceding claims, characterized in that the spent active carbon is regenerated by treatment with a basic aqueous solution and / or acid.  12. Method according to one of the preceding claims, characterized in that the activated carbon is pretreated with alcohol and is then heated.  13. Method according to one of the preceding claims, characterized in that the polysaccharide is scleroglucan.  14. Method according to one of the preceding claims, characterized in that the treatment of the polysaccharide solution takes place at a temperature of 50 to 1300 C, preferably between 100 and 1200C and better around 800C.