FR2700973A1 - Carbon black-chitosan complex and its use in binding and extraction processes - Google Patents

Abstract

Carbon black-chitosan complex in the form of beads on which a chitosan gel is deposited. Use in processes for binding and/or extracting various components, in particular for the depigmentation of vegetable extracts or of algae extracts and/or for binding metals.

Description

 The present invention relates to a black carbon-chitosan complex and its use in fixing and extraction processes, in particular for depigmenting plant extracts or extracts of algae and fixing metals. The invention relates more particularly to the formulation of a chitosan-based support, especially suitable for fixing various compounds and the use of carbon black as a doping element of the chitosan polymer.

 The supports usually selected for such applications and having a high exchange surface are of various kinds. These may be films deposited on inactive substrates of various shapes such as beads, tubes or fibers. They may also be extended porosity gels or any other physicochemical system, such as emulsions, allowing close contact in a biphasic relationship.

 It has now been unexpectedly found that an activated carrier can be made for the reversible binding and / or extraction of various compounds using chitosan in the form of a gel deposited on the surface of carbon black particles. In particular, it has been found that such a gel preserves the valuable chitosan chelation and adsorption properties and further retains the important surface area of the carbon black particles and thereby increases the fixation kinetics.

 The present invention therefore has as its first object a complex of carbon black-chitosan, especially in the form of beads, in particular as described below, on which a chitosan gel is deposited.

 The invention furthermore relates to the use of such a complex in processes for fixing and / or extracting various elements, in particular for the depigmentation of plant extracts or extracts of algae and / or for fixing metals.

 The subject of the invention is also the use of such a complex for limiting contraction phenomena of the chitosan network, in particular those causing the impregnation of the surface of the polymer gel, so as to preserve the integrity of the this one.

 These and other objects will become more apparent from the following description, in which are detailed preferred embodiments of the invention, as well as variants thereof and the exemplifications of its implementation.

 Chitosan is a polysaccharide derived from the deacetylation of chitin, itself extracted from the skeleton of crustaceans and the endoskeleton of cephalopods. Chitin and chitosan are both unbranched linear copolymers of D-glucosamine and N-acetylated D-glucosamine linked together by ss (1-> 4) glucosidic bridges. From the point of view of their chemical constitutions, these compounds are differentiated only by their N-acetylation rate.

 Chitin is the polymer having an acetylation level greater than 50, even 60 and even 70%, when the distribution of the acetyl groups is statistical.

 Conversely, chitosan is the polymer having this same level below these values.

 Physically chitin is insoluble in aqueous acidic medium and chitosan is soluble in such a medium.

 Chitin is particularly useful: in medicine, for its regenerating and healing effects, as well as in the synthesis of proteins; in cosmetics, for its dermoprotective and moisturizing effects; in agriculture, for its ability to protect plants; and also for its chelating effect of metals.

 The physico-chemical properties of chitosan are closely related to the fact that this polymer is at the same time a natural polymer, a polysaccharide and a polyamine.

As:
- natural polymer, it can intervene directly or indirectly on many biological mechanisms and is completely biodegradable;
polysaccharide, it has interesting properties, such as that of generating hydrogen bonds or of giving high viscosities at low concentration. In addition, the P (1-> 4) glycosidic linkages linking the glucosamine units give it film-forming properties and the possibility of being spun with good mechanical properties in the dry state. It is also an excellent water retainer;
- polyamine, it has properties that largely depend on its acid-base behavior, in relation to the dissociation equilibrium:
-NH3 + <-> -NH2 + whose pRo value (intrinsic pKa) is close to 6.5.

 The NH 3 + form gives it the ability to selectively associate with anions and to form polyanion-polycation complexes with all polyanions, whether of the sulfate or carboxylate type, for example.

 The NH2 form gives it excellent chelating properties; it is home to a wide range of chemical modifications, in addition to those that can be classically performed on primary and secondary alcohol functions. It gives it the ability to adsorb or adsorb many substrates through a hydrogen bonding interaction.

 All of these properties make it a suitable compound to involve binding mechanisms, adsorption or chelation, or even extraction processes or chromatography techniques (adsorption, desorption).

 The choice of support and the physical form of the latter are therefore very important, since in these mechanisms the surface constituting the interface between the solution and the adsorbent (whether physisorption or chemisorption> manages the Exchange kinetics It is essential to maximize this area to optimize the effectiveness of the adsorbent.

 The black carbon-chitosan complex according to the present invention has been found to meet these conditions.

This complex is basically composed of a gel deposited on the surface of carbon black particles, whose significant surface area contributes to increase the kinetics of fixation and / or extraction.

 According to a preferred embodiment, for the sake of convenience of use, the gel is advantageously produced in the form of beads obtained preferably according to the process for the preparation and control of the size of the beads which are the subject of the application for French parallel patent, filed today in the name of the same applicant and entitled "Method and device for the manufacture of beads of biopolymers or proteins", which can be usefully referenced.

 Advantageously, the concentration of chitosan in this complex is between about 0.1 and 20% by weight, and preferably is close to 3% by weight, while the concentration of carbon black is between about 0.3 and 10%. by weight, and preferably is close to 0.5% by weight.

 For the preparation of this complex according to the invention it is recommended to operate according to the method described in the above-mentioned French patent application.

 In general terms this process for the manufacture of beads of biopolymers or proteins by dripping, especially for the manufacture of such beads, the particle size of which can be modulated at will between about 10 mm and about 10 μm, while the sphericity of particles is retained, comprises the implementation of a flow of gas sent to the outlet of the injection system so that it acts around each drop created or in the immediate environment thereof, preferably by pushing said drop at the moment of its fall from the injection system.

 As for the equipment recommended for the implementation of this method, it is preferably as described in this same parallel French patent application mentioned above.

 This apparatus essentially comprises equipment for feeding the solution forming beads by dripping, injectors for the formation of drops and equipment for the creation of a gas flow, in particular a compressed air flow, at the exit of injectors, and advantageously a condensation vessel.

 The beads obtained are spherical particles of defined sizes, preferably between 0.1 and 0.5 mm in diameter.

 The drip solution from which the above spherical particles are formed is preferably a chitosan solution having a concentration of between about 0.5 and 5% by weight in a suitable solvent or mixture of solvents, when the chitosan has a degree of polymerization (DP) greater than 100,000, and having a concentration greater than about 5%, preferably between 15 and 20% by weight, when the chitosan has a DP less than 100,000.

 Preferably, the oligomers of chitosan thus used according to the present invention are obtained by hydrolysis with a hydrohalic gas, as described in the patent application No. 9300513 in the name of the same applicant and entitled Process for the hydrolysis of chitin and and / or chitosan and oligomers of D-glucosamine hydrochloride obtained.

 It is advantageous that the deacetylation rate of chitosan is greater than about 75%, with a more pronounced preference for a level equal to or greater than about 90%.

 Said solution may contain a heavy solvent, in order to increase the density thereof and also to facilitate its implementation.

 The amounts of carbon black used can vary within wide limits and can in practice be up to about 2% by weight. Above this value, the material produced becomes friable and no longer has the same mechanical strength. However, it is not excluded to carry the carbon black content beyond the aforesaid value; in practice, this concentration of carbon black may be even greater than 10% by weight, if desired.

 The condensation solution in which the beads are formed is as defined in the parallel patent application, filed today in the name of the same applicant and entitled "Method and device for the manufacture of beads of biopolymers or proteins", to which we can usefully refer.

 It is in practice composed of a solution of caustic soda with a concentration always at least equal to 1.5 times the amount necessary for the neutralization of the drip solution and having a density lower than that of said drip solution.

This density can, if necessary, be corrected by a light solvent supply.

 The synergy which has thus been found to result from the combination of chitosan and carbon black in the complex according to the invention gives rise to a certain number of particularly advantageous industrial results.

 It must be remembered that chitosan gels are adsorbents described in the literature.

They are used as such in applications as diverse as the recovery of metals (by chelation and chemisorption), the deaerization of coffee (by chemisorption) and the fixation of dyes or tannins, among others. However, for these applications, chitosan is generally employed in the form of beads or on fiber-type supports (for example cellulose). When reactive or non-reactive binding mechanisms are involved, the chitosan has a tendency to contract and to correlatively undergo a significant decrease in its porosity, this being particularly true when using this compound in a gel form. This results in a waterproofing of the surface of the polymer of chitosan, which can go in extreme cases until a total loss of activity thereof.

 Although not wishing to be bound by any theory, it is believed that the black carbon-chitosan complex according to the invention singularly limits this phenomenon because it ensures a physical maintenance of the structure of chitosan, and by creating this that can be called a doped three-dimensional network.

 However, the use of carbon black poses many problems at the industrial production stage. Thus, for example, because of its fine powder structure, carbon black requires suitable filtration and, despite its high depigmenting activity due to its high specific surface area, can not be used without causing difficulties that limit notably its possibilities of industrial applications.

 Chitosan combined with the carbon black according to the present invention provides the latter with the physical support necessary for its support. In the variant corresponding to its use in the form of beads, moreover, it retains compared to other compacted forms an interesting activity, without its implementation presents difficulties.

 In addition, the combination in the form of a complex according to the invention of carbon black and chitosan provides a compound having not only an interest because of its ease of use, but also having a synergistic activity in the fixing processes, especially in those aimed at depigmentation applications.

 The invention is more specifically illustrated in the following examples, which do not limit it in any way and in which parts and percentages are by weight, unless otherwise indicated.

The tests of the examples which follow were made from beads having the following compositions:
BO reference balls
BOl B02 B03
Chitosan 1% 3% 10%
Carbon black 0% 0% 0%
Size of the balls 3 mm 3 mm 3 mm
Characteristics of the balls according to the invention
B01 B02 B03 B04 B05 B06 B07
Chitosan (%) 1 1 3 3 3 10 10
Carbon black (%) 0.5 1 0.5 5 0.5 0.5 0.5
Size of the balls (mm) 3 1 3 3 1 3 1
In order to test the activity of the BO-Bn supports under conditions corresponding to depigmentation, metal chelation and other applications, these supports were impregnated with solvent from the solution of the substrate when it was a solution. not completely aqueous, or it was stabilized with an appropriate amount of potassium sorbate when it was an aqueous solution.

Examples
Series 1
The various depigmentation examples were carried out on glycolic or glycolic extracts of brown algae, whose material characteristics and other usually significant parameters were initially known.

Glycolic extract of Fucus vesiculosus
This extract was obtained by slow passage of 120 liters of propylene glycol through a bed of 100 kg of Fucus vesiculosus freshly harvested and previously dried at low temperature (60 ° C.) and then milled to a particle size of less than 1 mm. The recovered extract (100 liters) was then filtered.

Example la
100 liters of the above glycolic extract at 10.5 dry matter were placed on a static bed of 25 liters of resin beads B3 and all was left to rest for several days.

 Regular sampling allowed to follow the kinetics of adsorption on the chitinous support.

 After three weeks, the initial intense brown stain had faded to leave a colorless extract containing only 7.0% dry matter.

Example lb
10 liters of the same extract as that described in Example 1a were stirred in the presence of a quantity of carbon black identical, in all respects, to that used in the beads of Example 1a, ie 60 g.

No depigmentation was found after three weeks. The variation in dry matter was not significant for the 5% threshold of the dry residual extract.

Example lc
10 liters of the same extract as that described in Example 1a were deposited on a bed of 2.5 liters of resin B02 resin as standard reference. This support being tanslucide, a slow migration of the algal pigments inside the beads could be observed.

But the depigmentation obtained was not complete even after three weeks. It was comparable to that obtained according to the example at the end of seven weeks and it was also accompanied by a flocculation within the solution, due to the polysaccharides of the algae which could not penetrate the gel of chitosan hemi-impermeable by the formation on the surface of polyanion-polycation complexes.

Example 2
Following the procedure of Example 1a with B1 beads, depigmentation comparable to that obtained in Example 1a was obtained, but after only nine weeks.

Example 3
Following the procedure of Example 1a with B6 beads, depigmentation comparable to that of Example 1a was obtained after two weeks.

 The results obtained in Examples 1a and 2 indicate that the rate of depigmentation increases with concentration, but not linearly.

Example 4
B2 beads were used according to the procedure of Example la and gave in equal mass proportion a result similar to that of Example 1a. On a diffusion time of three weeks the size of the balls intervened little.

Series 2
The extract of Fucus vesiculosus was made under conditions different from those of series 1.

 On 100 kg of undried fresh seaweed and placed in a 400 liter tank 40 liters of propylene glycol were poured. This solution was allowed to stand for two weeks, while the extraction juices were removed every two days and returned to the top of the algae bed. At the end of this period of time, the 40 liters were withdrawn and replaced by twice 30 liters in the week that followed. The 100 liters of extract were collected and then filtered to give a light yellow-orange juice with a dry matter equal to 9.3%. This solution has been used in the series of examples below.

Example 5
20 liters of the extract described above were deposited on a bed of 10 liters of B3 beads to give a total depigmentation after four days. The concentration of polyphenols responsible for the coloring was indeed lower in the solutions resulting from the extraction of fresh brown algae because of the higher water content in the final solutions (around 40% against 5 to 10% in the solutions described about the first series). Bleaching hydroalcoholic solutions of brown algae was therefore faster.

Example 6
Similar results were obtained after replacement of the B3 bile with B5 beads in Example 5; the size of the balls is not, in these examples, and subject to scale, significant.

Examples 7 to 9
In these examples, the beads B01, B02 and B03 respectively replaced, at equal proportions of chitosan, the beads B3 of Example 5, which was followed by the procedure. The depigmentation results obtained were similar in all three cases, although a decreasing rate of fixation from B01 to
B03, which could be attributed in part to a lower porosity of the balls.

 Under these conditions the bleaching was comparable in 14 (B01), 20 (B02) and 30 days (B03).

Examples 10 and 11
Following the procedure of Example 5, but replacing the beads B3 with beads B6 and B7 respectively, it was noted in both cases a depigmentation time of 10 days to obtain results comparable to those of the Example 5

Series 3
The examples of this series were carried out on extracts of Laminaria digitata obtained by the same method as that used for the extract of Fucus vesiculosus of series 1. The dry matter content obtained was 7.5%. This brown alga had, unlike the Fucus, the particularity of giving depigmentable extracts to carbon black.

Example 12
The Laminaria digitata extract described above was depigmented with carbon black. For depigmentation to occur, the solution of Laminaria extract should be stirred with carbon black. The quantities used were dependent on the quality of the initial algae, they varied according to the oxidation in the air, the time of the harvest, the temperatures of extraction, etc.

 For the extract described above, a quantity of 2% of carbon black made it possible to depigment the solution.

After decantation, then filtration, a clear solution was obtained, which served as a reference for the examples of this series.

Example 13
100 liters of Laminaria digitata extract with a very deep dark green-brown color were placed on a static bed of 25 liters of B3 resin beads and left standing for several days.

 After a period of ten days, the color had faded to leave room for a colorless extract comparable to that of Example 12 and containing only 4.5% dry matter.

 This technique allowed to recover the extract without additional filtration.

 The amount of carbon black used in this example was close to 0.1% and was significantly less than that required by Reference Example 12.

Example 14
By following the procedure of Example 13, but replacing the beads B3 with B02 beads, it was possible to obtain a depigmentation comparable to that of Example 12 after ten weeks. This was accompanied by a flocculation in the solution. This isolated floc was then identified as having a high percentage of polysaccharide (alginate). This decrease in the rate of fixation was probably due to a semi-waterproofing of the membrane by formation of polyanion-polycation complexes. This resulted in ionic destabilization of the medium, causing flocculation of the alginates in solution.

Series 4
This series was produced on extracts from
Fucus vesiculosus. In these examples the extraction solution used was an aqueous solution containing 0.2% of methyl parahydroxybenzoate. The extraction process differed from the previous processes because of the water uptake of the dehydrated algae and it consisted in this case to pass through a bed of Fucus vesiculosus placed in a suitable column and equipped with a Bottom bleed valve, the aqueous solution, percolation. The extraction was terminated when the amount of extract withdrawn at the bottom of the column was equal to the mass quantity of Fucus vesiculosus. The extract was then treated by any suitable method allowing 0.2 μm filtration and conditioning.

The dry matter obtained was 6%.

 The beads used in the following examples were impregnated with an aqueous solution of the same composition as the initial extraction solution.

Example 15
On the aqueous extract of Fucus vesiculosus described above was carried out the same experiment as that illustrated in Example 12 and from beads
B3. The coloring evolved over time from a thick black to a bright red, then slowly faded to a yellow hue and faded after five to six weeks.

Example 16
By the same procedure as that described in Example 15, the stirring carbon black was found to be inactive.

Example 17
When the beads used were of B02 type (= without carbon black), the formation of polyanion-polycation complexes resulted in the formation of an impermeable membrane on the surface of the beads which tinted bright red (by superficial adsorption of pigments). The beads then lost their volume and contracted strongly under the effect of osmotic forces. As the porosity of the chitosan network is greatly reduced, adsorption kinetics in the three-dimensional mass have also dropped. A cut of the pearls made it possible to see the section, from where it was able to note that the coloration had been made only on the periphery.

Series 5
This series was carried out on a sargasse extract, Sargassum multicum, obtained by the same method as that used in series 2. The water content of the final product was close to 40%. Dry matter accounted for about 3.2%.

Examples 18 and 19
Following the procedure of Examples 5 and 6 respectively, total depigmentation was achieved in two days.

Series 6
Examples in this series were algae
Himanthalia. The extract was made under conditions similar to those for obtaining the extracts of series 2 and 5.

Examples 20,21 and 22,23
These examples were identical to Examples 5 and 6, and 18 and 19. The depigmentation was complete in two days.

Series 7
As regards the field of activity of the carbon black-chitosan beads according to the invention, it has also been possible to estimate that their depigmenting action is also exerted on plant extracts, in particular extracts of ivy and / or horsetail.

Series 8
Numerous quantitative results seem to indicate that the adsorption of metals on chitosan, among others that of di- and trivalent metals, is somewhat faster than when using the black carbon-chitosan complex resin; this can be explained by the fact that chitosan is indeed also a polyamine whose -NH2 form gives it excellent chelating properties.

Series 9
This series of examples concerns the demonstration of the reversibility of the adsorption phenomenon (chemi- or physisorption) on the black carbonechitosan resin.

 In order to carry out the examples of this series, the B3 beads of compound to be adsorbed by multiple passages of the Fucus vesiculosus extract were saturated, as described in series 1. The total extraction time was then three weeks for the first pass and one week for the second, third and fourth passes. A fifth and sixth passage did not seem to give different results. The bead attachment sites have at this stage been considered saturated. These were then subjected to appropriate treatments.

 The beads were then drained and then thoroughly rinsed with water.

Example 24
120 ml (100 g) of saturated B3 beads (0.02 mol) were added to 100 ml of 1% sodium hydroxide solution (0.25 mol). After 24 hours, the tinted solution of the red pigment that had desorbed was replaced with a distilled water solution. This operation was renewed three times every two hours. The 500 ml recovered were pooled, neutralized to pH 7 and concentrated by evaporation in vacuo. 3 g of dry and strongly colored product containing the various pigments of the
Fucus vesiculosus.

Example 25
500 ml (400 g) of saturated B3 beads placed on a suitable chromatography column were slowly eluted with solutions of increasing concentrations of sodium hydroxide. The adsorbed elements on the chitosan were found unhooked and thus isolated, they could be dried and identified.

Example 26
The saturated B3 beads, then regenerated as described in Example 24 and impregnated with a solution of propylene glycol, were again used for pigment extraction under the same conditions as those indicated in Example 1a, all proportioned. .

The results obtained were similar to those of this example la. The regeneration could be carried out up to five times without damage for the support of carbon black-chitosan and without the pollution inherent to this type of process being detectable.

Series 10
Desorption of metals
Example 27
B3 beads from a saturation of the attachment sites by soaking them in a solution of cupric chloride were soaked in a hydrochloric acid solution of concentration greater than 3N and preferably equal to 10N.

 After twenty minutes all the copper was in solution. The beads were then washed with three to five concentrated hydrochloric acid baths, then washed five times with 2N sodium hydroxide solution (without passage with distilled water) and then washed with distilled water until a medium was obtained. neutral. This process regenerated the beads, which could be reused for the chelation of heavy metals.

 All of these examples and the experiments they relate allow to accredit the hypothesis of a synergy between chitosan and carbon black in fixation phenomena. Without wishing to be bound by any theory, we can consider that this may be true synergy (according to which the global effect is greater than the sum of the isolated effects), which is the in the case of depigmentation of the aqueous extracts of Fucus, or of an additive effect synergy, which occurs in the case of the depigmentation of Laminaria.

Claims (6)

 1. Complex of carbon black-chitosan, in the form of beads, on which is deposited a chitosan gel.  2. Complex according to claim 1, characterized in that the concentration of chitosan in this complex is between about 0.1 and 20% by weight, and preferably is close to 3% by weight, while the concentration of black of carbon is between about 0.3 and 10% by weight, and preferably is about 0.5% by weight.  3. Complex according to one of claims 1 or 2, characterized in that said beads obtained are spherical particles of sizes between 0.1 and 0.5 mm in diameter.  4. Complex according to any one of claims 1 to 3, characterized in that the drip solution from which the above spherical particles are formed is a solution of chitosan having a concentration ranging between about 0.5 and 5% by weight. weight in a suitable solvent or mixture of solvents, when the chitosan has a degree of polymerization (DP) greater than 100,000, and having a concentration greater than about 5%, advantageously between about 15 and 20% by weight, when the chitosan has a DP less than 100,000.  5. Use of a complex according to any one of claims 1 to 4 in processes for fixing and / or extraction of various elements, in particular for the depigmentation of plant extracts or extracts of algae and / or for fixing metals.  6. Use of a complex according to any one of claims 1 to 4 for limiting contraction phenomena of the chitosan network, in particular those causing the waterproofing of the surface of the polymer gel.