Process for separating and purifying a solution of water-soluble natural polymers containing salts

Abstract

A process for separating and purifying at least one water-soluble polysaccharide oxidized to dialdehyde from an aqueous solution comprising said polysaccharide and at least iodic acid or its salt, said process being carried out in an electrodialysis apparatus comprising a stack of cells, each cell consisting of two adjacent concentration (C) and dilution (D) compartments delimited alternately by cationic and anionic membranes, in which said aqueous solution is sent to said dilution compartments (D) to obtain an aqueous solution comprising at least one water-soluble polysaccharide oxidized to purified dialdehyde, and an aqueous effluent comprising at least iodic acid or its salt is recovered from said concentration compartments (C). Figure 1 to be published

Description

Title of the invention: Method for separating and purifying a solution of water-soluble natural polymers containing salts. Field of the invention

[0001] The invention relates to a process for preparing a bio-based additive for the cellulosic products industries, and in particular the paper industry. More specifically, the present invention relates to a process for preparing a bio-based additive based on a polysaccharide that can adsorb onto a cellulosic material as a reinforcing agent. Previous art

[0002] The use of functionalized polysaccharides as reinforcing agents for cellulosic materials, such as paper fibers or textile fibers, is well known in the prior art. Such additives have already been developed to give treated cellulosic materials good wet strength (WSE) and / or dry strength.

[0003] Application FR3085681 discloses a process for preparing a solution comprising a paper pulp strengthening agent based on a dialdehyde polysaccharide obtained from a water-soluble starting polysaccharide such as xyloglucan, glucomannan, mannan, and galactomannan, preferably xyloglucan. The process for preparing the dialdehyde polysaccharide includes an oxidation step of the starting polysaccharide with an oxidizing agent, preferably periodate, and more preferably sodium metaperiodate. This oxidation step yields a solution comprising the dialdehyde polysaccharide, as well as residual salts obtained after chemical oxidation of the starting polysaccharide with periodate. The purification of the dialdehyde polysaccharide solution is carried out by means of dialysis, which efficiently removes the salts contained in the dialdehyde polysaccharide solution.However, dialysis is a method that consumes a very high amount of water (relative to the production volumes of additives) and does not allow for the concentration of salts upstream of the dialysis stage, which makes the recycling of these salts impossible.

[0004] Indeed, it may be advantageous to be able to recycle the salts contained in the polysaccharide solution in order to regenerate the periodate-based oxidizing agent, given its significant cost. However, the dialdehyde polysaccharide must remain in the aqueous phase to retain its ability to adsorb onto a cellulosic material and to have the lowest possible salt content. For this, a separation step is necessary. To date, the separation techniques known to those skilled in the art do not These methods do not allow for the separation of a dialdehyde polysaccharide solution on one side and salts in sufficient concentration to make their regeneration and recycling upstream of the oxidation process technically and economically feasible. Furthermore, precipitation of the oxidized polysaccharide is generally used by those skilled in the art, but once precipitated, the dialdehyde polysaccharide is no longer water-soluble. Consequently, once precipitated, the polysaccharide can no longer adsorb onto a cellulosic material.

[0005] Application WO2008133847 discloses a process for preparing a dialdehyde polysaccharide in powder form, by a series of separation steps including a precipitation step of iodate salts, a separation step by filtration of the dialdehyde polysaccharide solution, and then a purification and precipitation step of the dialdehyde polysaccharide by solvent extraction. However, the disclosed process does not allow for the direct recycling of the iodate oxidant, due to its association with divalent cations or Ag+. Furthermore, filtration is difficult to perform due to the viscosity of the dialdehyde polysaccharide solution. Finally, the use of solvents is detrimental to the purity of the product, for environmental and energy reasons (solvent regeneration).Furthermore, the precipitation of oxidized dialdehyde polysaccharides is undesirable, because once precipitated or dried, it is difficult or even impossible to solubilize the resulting dialdehyde polysaccharide again, and therefore it loses all its properties of interest for paper pulp processing.

[0006] Application WO9512619 discloses a process for oxidizing starch using an acidic aqueous solution by coupling regeneration by electro-oxidation of the oxidant (periodate ion) and separating the suspended starch from the oxidized starch by filtration through a polysaccharide-impermeable membrane. In one embodiment, an electrodialysis step is mentioned to concentrate the ions from the oxidant (iodate, periodate) from a portion of the aqueous solution prior to the regeneration step.

[0007] In this process, the polysaccharide, in this case starch, is not in solution but in suspension, as is its oxidized form. The solution used in the optional electrodialysis step is free of polysaccharides in solution since the polysaccharides are separated by upstream filtration. The electrodialysis thus used focuses solely on concentrating the iodate and formate ions in the electrodialyzer to promote the subsequent oxidation of these anions and the elimination of formate ions as CO2, and not on separating a salt-free solution of oxidized polymer.

[0008] There is therefore a strong interest in providing a process for efficiently separating the dialdehyde polysaccharide from the residual salts obtained after oxidation, while keeping the polymer in aqueous solution to avoid deteriorating its properties of use, while concentrating the salts sufficiently in another aqueous solution to allow their recycling, which is essential for the viability of the process. Object of the invention

[0009] Surprisingly, the Applicant has developed a new process for separating and purifying a solution comprising a dialdehyde polysaccharide and at least iodic acid or a salt of iodic acid resulting from the oxidation of a starting polysaccharide with an oxidizing agent based on metaperiodic acid or its salt, using an electrodialyzer that keeps the dialdehyde polysaccharide in solution, while efficiently separating the iodic acid or its salt, and after separation, allows the iodic acid or its salt to be concentrated sufficiently to limit the volume of effluent to be treated, and thus allows its regeneration into metaperiodic acid or its salt for reuse in the oxidation step of the starting polysaccharide into dialdehyde polysaccharide.

[0010] According to a first aspect, the present invention relates to a process for separating and purifying at least one water-soluble polysaccharide oxidized to dialdehyde from an aqueous solution comprising said polysaccharide and at least iodic acid or a salt of iodic acid, said process being carried out in an electrodialysis apparatus comprising a stack of cells, each cell being made up of two adjacent concentration (C) and dilution (D) compartments delimited alternately by cationic membranes and anionic membranes, in which said aqueous solution is sent into said dilution compartments (D) to obtain an aqueous solution comprising at least one water-soluble polysaccharide oxidized to purified dialdehyde and an aqueous effluent comprising at least said iodic acid or said salt of iodic acid is recovered from said concentration compartments (C).

[0011] According to one or more embodiments of the invention, said aqueous solution comprises between 0.5% and 25% by mass of a water-soluble polysaccharide oxidized to dialdehyde relative to the total mass of said aqueous solution.

[0012] According to one or more embodiments of the invention, said salt of iodic acid is chosen from sodium iodate (NaIO3), potassium iodate (KIO3), or lithium iodate (LiIO3), preferably sodium iodate (NaIO3).

[0013] According to one or more embodiments of the invention, the content of iodic acid in said aqueous solution is between 0.015% and 50% by mass, or the content of said salt of iodic acid in said aqueous solution is between 0.015% and 14% by mass, relative to the total mass of said aqueous solution.

[0014] According to one or more embodiments of the invention, said aqueous solution further comprises formic acid or a salt of formic acid selected from sodium formate, potassium formate or lithium formate, preferably sodium formate.

[0015] According to one or more embodiments of the invention, the content of said salt of formic acid in said aqueous solution is greater than 0% and less than or equal to 2.5% by mass relative to the total mass of said aqueous solution.

[0016] According to one or more embodiments of the invention, the pH of said aqueous solution upstream of the separation and purification step is between 2 and 10.

[0017] According to one or more embodiments of the invention, said process is carried out in discontinuous mode.

[0018] According to one or more embodiments of the invention, the ratio between the volume of aqueous solution sent into the dilution compartments (D) of the electrodialysis device and the volume of aqueous effluent recovered in the concentration compartments (C) is greater than 1.

[0019] According to one or more embodiments of the invention, said process is carried out in continuous mode.

[0020] According to one or more embodiments of the invention, the ratio between the flow rate of the aqueous solution sent into the dilution compartments (D) of the electrodialysis device and the flow rate of the aqueous effluent recovered in the concentration compartments (C) is greater than 1.

[0021] According to one or more embodiments of the invention, the conductivity of said aqueous effluent comprising said iodic acid or said salt of iodic acid is between 2 and 200 mS / cm.

[0022] According to one or more embodiments of the invention, a current density of between 20 and 1000 mA / cm2, preferably between 30 and 200 mA / cm2, is applied in the electrodialysis device.

[0023] According to one or more embodiments of the invention, said process is carried out at a temperature between 5 and 80°C.

[0024] According to one or more embodiments of the invention, said water-soluble polysaccharide oxidized to dialdehyde is derived from natural water-soluble polysaccharides selected from glucans, such as dextran, starch, cellulose derivatives such as methylcellulose, ethylcellulose, carboxymethylcellulose, hemicelluloses, such as xylan, arabinoxylan, arabinan, glucomannan, galactomannan, galactogluco-mannan, mannan and xyloglucan, glycogen, fructans, such as inulin, levan, or alginates, chitosan, xanthan gums, amylopectin, pectins, glycosaminoglycans, carrageenans or peptidoglycans.

[0025] According to one or more embodiments of the invention, said water-soluble polysaccharide oxidized to dialdehyde is a derivative of xyloglucan, glucomannan, mannan or galactomannan, preferably of xyloglucan.

[0026] According to a second aspect, the invention relates to a process for preparing at least one water-soluble polysaccharide oxidized to dialdehyde comprising at least the following steps:

[0027] a) at least one charge comprising at least one water-soluble polysaccharide in aqueous solution is supplied;

[0028] b) said water-soluble polysaccharide in aqueous solution contained in said feed supplied in step a) is oxidized in the presence of at least metaperiodic acid or a salt of metaperiodic acid as an oxidizing agent to obtain an aqueous solution comprising a water-soluble polysaccharide oxidized to dialdehyde and at least iodic acid or a salt of iodic acid, taken alone or in mixture;

[0029] c) said aqueous solution obtained at the end of step b) is sent into a process according to the first aspect of the invention to obtain an aqueous solution of water-soluble polysaccharide oxidized to purified dialdehyde and an aqueous effluent comprising at least iodic acid or a salt of iodic acid.

[0030] According to one or more embodiments of the invention, said water-soluble polysaccharide is selected from glucans, such as dextran, starch, cellulose derivatives such as methylcellulose, ethylcellulose, carboxymethylcellulose, hemicelluloses, such as xylan, arabinoxylan, arabinan, glucomannan, galactomannan, galactogluco-mannan, mannan and xyloglucan, glycogen, fructans, such as inulin, levan, or alginates, chitosan, xanthan gums, amylopectin, pectins, glycosaminoglycans, carrageenans or peptidoglycans.

[0031] According to one or more embodiments of the invention, said water-soluble polysaccharide is selected from xyloglucan, glucomannan, mannan or galactomannan, preferably xyloglucan.

[0032] According to one or more embodiments of the invention, said salt of metaperiodic acid is chosen from sodium metaperiodate, potassium metaperiodate, or lithium metaperiodate, preferably sodium metaperiodate or potassium metaperiodate, more preferably sodium metaperiodate.

[0033] According to one or more embodiments of the invention, step b) is carried out at a temperature between 5°C and 95°C, and for a duration between 1 minute and 8 hours.

[0034] According to one or more embodiments of the invention, said salt of iodic acid is chosen from sodium iodate (NaIO3), potassium iodate (KIO3), or lithium iodate (LiIO3), preferably sodium iodate (NaIO3).

[0035] According to one or more embodiments of the invention, said process further comprises a step d) in which said salt of iodic acid contained in said aqueous effluent obtained at the end of step c) is converted at least in part to obtain an effluent comprising a regenerated oxidizing agent.

[0036] According to one or more embodiments of the invention, said step d) comprises the following substeps:

[0037] dl) an oxidation step of iodate ions in the presence of an oxidizing flux to obtain a precipitate based on sodium, potassium or lithium paraperiodate, preferably sodium paraperiodate;

[0038] d2) a step of separating the sodium paraperiodate-based precipitate, from potassium or lithium, preferably sodium paraperiodate;

[0039] d3) a solubilization step of said sodium paraperiodate-based precipitate, potassium or lithium, in the presence of a strong acid, to obtain sodium, potassium or lithium metaperiodate as a regenerated oxidizing agent.

[0040] According to one or more embodiments of the invention, a step e) of recycling at least part of the regenerated oxidizing agent obtained at the end of step d) is carried out towards step b) of oxidation of the water-soluble polysaccharide in aqueous solution. Description of the figures

[0041] Fig. 1 schematically represents the process of separating and purifying a water-soluble polysaccharide oxidized to dialdehyde implemented in an electrodialysis device according to an embodiment of the invention.

[0042] Fig. 2 schematically represents a pair of dilution compartments (D) and concentration compartments (C) of the electrodialysis apparatus implemented in the process according to the invention as shown in Fig. 1.

[0043] Figure 3 schematically represents a process for preparing a water-soluble polysaccharide oxidized to dialdehyde according to an embodiment of the invention.

[0044] Figure 4 represents the time tracking of the electrodialysis according to the example according to the invention with "ol" the ionic conductivity of the aqueous solution circulating in the dilution circuit 3' (in mS / cm), "o2" the ionic conductivity of the aqueous solution circulating in the concentration circuit 7' (in mS / cm), "I" the current (in Amperes denoted A), "Q" the charge (in Coulombs denoted C); and "t" the time (in minutes denoted min). Detailed description 1. Definitions

[0045] In the following detailed description, many specific details are set forth to provide a more thorough understanding of the process. However, it will be apparent to those skilled in the art that the process can be implemented without necessarily including all of these specific details. In other cases, well-known features have not been described in detail to avoid unnecessarily complicating the description.

[0046] It is specified that, throughout this description, the expression "between ... and ..." should be understood as including the limits mentioned, unless otherwise specified.

[0047] In this description, the term "include" is synonymous with (means the same as) "comprise", "include", and "contain", and is inclusive or open and does not exclude other elements not mentioned. It is understood that the term "include" includes the exclusive and closed term "consist".

[0048] Furthermore, when used in this description, the terms "essentially" or "substantially" or "approximately" in relation to a reference value correspond to an approximation of ± 10%, preferably ± 5%, most preferably ± 2%, or even more preferably ± 1% of that reference value, which may be, for example, conductivity, current density, current, temperature, pressure, distance, speed, flow rate, compound content(s), etc.

[0049] In the sense of the present invention, the different embodiments presented can be implemented separately or in combination with each other, without limitation of combinations when this is technically feasible.

[0050] In the sense of the present invention, the different parameter ranges for a given step, such as pressure ranges and temperature ranges, can be used alone or in combination. For example, in the sense of the present invention, a preferred range of pressure values ​​can be combined with a more preferred range of temperature values. 2. Detailed description 2.1 Separation and purification process

[0051] The process for separating and purifying the water-soluble polysaccharide oxidized to dialdehyde (also referred to herein as PSOH or dialdehyde polysaccharide) is carried out using an aqueous solution comprising said polysaccharide and at least iodic acid or a salt of iodic acid. Said dialdehyde polysaccharide is advantageously obtained by oxidation of a starting polysaccharide using a oxidizing agent comprising at least metaperiodic acid or a salt of metaperiodic acid.

[0052] Advantageously, the starting polysaccharide is a water-soluble polysaccharide selected from glucans, such as dextran, starch, cellulose derivatives, such as methylcelluloses, ethylcelluloses, carboxymethylcelluloses, hemicelluloses, such as xylans, arabinoxylans, arabinanes, glucomannans, galactomannans, galactogluco-mannans, mannans and xyloglucans, glycogen, fructans, such as rinulin, levan, or alginates, chitosan, xanthan gum, amylopectin, pectins, glycosaminoglycans, carrageenans or peptidoglycans.

[0053] Preferably, the water-soluble polysaccharide is chosen from hemicelluloses, preferably chosen from xyloglucan, glucomannan, galactogluco-mannan, mannan, and galactomannan.

[0054] Preferably, the water-soluble polysaccharide is xyloglucan.

[0055] Said aqueous solution advantageously comprises between 0.5% and 25% by mass of a water-soluble polysaccharide oxidized to dialdehyde relative to the total mass of said aqueous solution, preferably between 1% and 15% by mass, more preferably between 1% and 10% by mass, and even more preferably between 1% and 5% by mass, in order to limit the viscosity of the solution while remaining sufficiently concentrated for economic reasons and those related to the final application. The concentration of the aqueous solution is adjusted according to the nature of the water-soluble polysaccharide oxidized to dialdehyde used in the process according to the invention.

[0056] When said aqueous solution comprises a salt of iodic acid, said salt of iodic acid is preferably chosen from sodium iodate (NaIO3), potassium iodate (KIO3), or lithium iodate (LiIO3), preferably said salt of iodic acid being sodium iodate. The presence of salts of iodic acid in the aqueous solution results from the reduction of periodate ions, which allows the oxidation of the starting polysaccharide to a dialdehyde polysaccharide.

[0057] The content of said salt of iodic acid in said aqueous solution, that is to say before sending the aqueous solution into the electrodialysis apparatus, is advantageously between 0.015% and 14% by mass in relation to the total mass of said aqueous solution, preferably between 0.015% and 9% by mass, more preferably between 0.03% and 5% by mass, and even more preferably between 0.03% and 0.5% by mass.

[0058] When said aqueous solution comprises iodic acid, its concentration is advantageously between 0.015% and 50% by mass relative to the total mass of said aqueous solution, preferably between 0.015% and 9% by mass, plus preferably between 0.03% and 5% by mass, and even more preferably between 0.03% and 0.5% by mass.

[0059] In an embodiment according to the invention, said aqueous solution may further comprise formic acid or a salt of formic acid. Preferably, said salt of formic acid is selected from sodium formate, potassium formate, or lithium formate. Preferably, said salt of formic acid is sodium formate. The presence of formic acid salts may result from the double oxidation of certain sugar units of the starting polysaccharide used to form the dialdehyde polysaccharide.

[0060] In an embodiment according to the invention, said aqueous solution comprises a salt of formic acid, in particular obtained from the oxidation of the starting polysaccharide. The content of said salt of formic acid in said aqueous solution, i.e. before it is sent to the electrodialysis device, may be greater than 0% and less than or equal to 2.5% by mass relative to the total mass of said aqueous solution, preferably between 0.005% and 1.5% by mass, more preferably between 0.005% and 1.0% by mass, and even more preferably between 0.005% and 0.5% by mass.

[0061] The pH of the aqueous solution is advantageously between 2 and 10, preferably between 5 and 8, and more preferably between 6 and 7.5.

[0062] According to an essential aspect of the invention, the separation and purification process is implemented in an electrodialysis apparatus comprising a stack of cells, each cell consisting of two adjacent concentration (C) and dilution (D) compartments delimited alternately by cationic membranes and anionic membranes.

[0063] The electrodialysis technique allows the extraction of ions present in a solution. It is carried out using an electrodialyzer, or electrodialysis cell, composed of a plurality of compartments separated by anionic and cationic membranes. Generally, the electrodialyzer comprises alternating anionic and cationic membranes, forming multiple electrodialysis cells, which are positioned between two electrodes allowing the migration of ions under the effect of an electrical potential difference.

[0064] Anionic membranes comprise resins with positively charged cationic groups, allowing the passage of anions from the solution, which can then migrate through the membrane under the influence of the electric field. Conversely, cationic membranes are composed of negatively charged anionic groups, thus allowing the migration of cations under the influence of the electric field and repelling anions by electrostatic repulsion.

[0065] The cations, which migrate in the direction of the electric current towards the negatively charged cathode, exit the first compartment by crossing the cationic membrane and are blocked in a second compartment by the anionic membrane.

[0066] The negatively charged anions also exit the first compartment by migrating through the anionic membrane towards the positively charged anode. They are then blocked in a second compartment by the cationic membrane.

[0067] Consequently, the salt concentration in the first compartment decreases. This is why it is called the dilution compartment. Conversely, in the second compartment, the concentration of dissolved ions increases; this is called the concentration compartment (the "brine" compartment).

[0068] The electrodialysis device therefore comprises an alternation of dilution compartments (D) and concentration compartments (C).

[0069] Electrodialysis as used in the invention makes it possible to generate two directly usable streams: a solution of polysaccharide dialdehyde in the dilution compartments (D) and a solution of salts in the concentration compartments (C) in sufficient concentration to allow their regeneration and recycling in the process.

[0070] Indeed, in the process according to the invention, the aqueous solution comprising the water-soluble polysaccharide oxidized to dialdehyde and at least iodic acid or a salt of iodic acid is sent into the dilution compartments (D) of the electrodialysis apparatus to obtain an aqueous solution comprising at least one water-soluble polysaccharide oxidized to purified dialdehyde and an aqueous effluent comprising at least iodic acid or the salt of iodic acid is recovered in the concentration compartments (C).

[0071] In an embodiment according to the invention, the conductivity of said aqueous effluent comprising iodic acid or the salt of iodic acid is between 2 and 200 mS / cm, preferably between 0.5 and 16 mS / cm.

[0072] In an embodiment according to the invention, a current density of between 20 and 1000 mA / cm2, preferably between 30 and 200 mA / cm2, is applied in the electrodialysis device.

[0073] Advantageously, said process is carried out at a temperature between 5 and 80°C, preferably between 15 and 60°C, and more preferably between 20 and 40°C.

[0074] In one embodiment according to the invention, the process for separating and purifying the dialdehyde polysaccharide is carried out in batch mode. In this embodiment, the ratio between the volume of the aqueous solution sent to the dilution compartments (D) of the electrodialysis unit and the volume of the aqueous effluent recovered in the concentration compartments (C) is advantageously greater than 1, preferably between 1 and 5, and even more preferably between 1 and 3. Such a ratio allows the salt concentrations in compartments (C) to increase beyond the initial concentration present in the load of compartments (D).

[0075] In another embodiment of the invention, the process for separating and purifying the dialdehyde polysaccharide is carried out in continuous mode. In this embodiment, the ratio between the flow rate of the aqueous solution sent to the dilution compartments (D) of the electrodialysis unit and the flow rate of the aqueous effluent recovered in the concentration compartments (C) is advantageously greater than 1, preferably between 1 and 5, and even more preferably between 1 and 3. Such a ratio makes it possible to increase the salt concentrations in the compartments (C) beyond the initial concentration present in the feed of the compartments (D).

[0076] Advantageously, the process of separating and purifying the dialdehyde polysaccharide is carried out until a conductivity in the aqueous solution comprising said water-soluble polysaccharide oxidized to purified dialdehyde is obtained of less than 1000 pS / cm, preferably less than 500 pS / cm, more preferably less than 100 pS / cm and even more preferably less than 50 pS / cm.

[0077] In one embodiment of the invention, the aqueous solution comprising at least one water-soluble polysaccharide oxidized to purified dialdehyde is sent to an optional additional purification step to remove the last traces of remaining anions, such as iodate and formate anions. Advantageously, an anionic resin is used for this purpose. This resin is regenerated with a basic solution or brine to exchange the adsorbed anions again for hydroxide or chloride ions, respectively. Preferably, the regeneration is carried out with sodium hydroxide. The regeneration effluent is advantageously mixed with the aqueous effluent comprising at least iodic acid or the salt of iodic acid, from the concentration compartment (C) of the electrodialysis unit to maximize iodate recovery.

[0078] In order to better understand the invention, the following description, by way of example of application, relates to a process for separating and purifying a water-soluble polysaccharide oxidized to dialdehyde, implemented in an electrodialysis apparatus, as schematically illustrated in [Fig. 1]. In this embodiment, the water-soluble polysaccharide oxidized to dialdehyde is obtained by oxidizing xyloglucan, as the starting water-soluble polysaccharide, with a sodium metaperiodate oxidizing agent.

[0079] Referring to Figures 1 and 2, an aqueous solution 3 comprising a water-soluble polysaccharide oxidized to dialdehyde (PSOH) and a sodium iodate salt (NaIO3) resulting from the oxidation of a starting water-soluble polysaccharide, such as the Xyloglucan, diluted with sodium metaperiodate, is introduced into an electrolyzer X3 via a reservoir 26 and circulates in a dilution circuit 3' through the dilution compartments (D), i.e., between pairs of oppositely polarized membranes, namely a cation exchange membrane 24 and an anion exchange membrane 25. The circuit 3' includes at least one circulation pump (not shown in the figure). Under the effect of a sufficient voltage applied to the electrodes (anode 21 and cathode 22) of the electrolyzer X3, a polarization-induced flow of ions occurs across the membranes. The selectivity of the membranes allows the separation of the cationic and anionic ions contained in the aqueous solution, which migrate across the membranes to reach the concentration compartments (C).The cations (C+) present in the aqueous solution, typically Na+ cations, migrate through the cation exchange membranes 24, attracted by the cathode, while the anions (A) present in the aqueous solution, typically iodate (IO3), formate (HCOO) anions and possibly residual periodate (IO4) ions, migrate through the anion exchange membranes 25. This results in a progressive concentration of salts in the concentration compartments (C) contained in the concentration circuit 7' and a progressive depletion of salts in the dilution compartments (D) contained in the circuit 3'. The concentration circuit 7' includes a reservoir 27, into which top-up with water 5 or partially recycled wastewater 10 can be carried out, and at least one circulation pump (not shown in [Fig. 1]).

[0080] At the ends of the electrolyzer X3, the water contained in the aqueous electrolyte 23 undergoes electrolysis, with oxidation at the anode 21 and reduction at the cathode 22. The electrolyte 23 is a conventional aqueous saline solution for this type of application. The addition of electrolyte 28 may be considered. The presence of salts is necessary both for ionic conductivity and for the circulation of ions through the exchange membranes. The salt typically used for this application is sodium sulfate (Na2SO4). Since the electrolyte 23 also circulates between the cathode 22 and the anode 21, its composition remains relatively stable during electrolysis.

[0081] At the end of electrodialysis, an aqueous solution is recovered comprising at least one water-soluble polysaccharide oxidized to purified dialdehyde (PSOH) 6 and an aqueous effluent 7 enriched in sodium iodate salt (NaIO3) and sodium formate salt (HCOONa).

[0082] 2.2 Process for preparing a water-soluble polysaccharide oxidized to dialdehyde (PSOH)

[0083] Another object according to the invention relates to a process for preparing at least one water-soluble polysaccharide oxidized to dialdehyde comprising at least the following steps:

[0084] a) at least one charge comprising at least one water-soluble polysaccharide in aqueous solution is supplied;

[0085] b) said water-soluble polysaccharide contained in said feed supplied in step a) is oxidized in the presence of an oxidizing agent comprising at least metaperiodic acid or a salt of metaperiodic acid to obtain an aqueous solution comprising a water-soluble polysaccharide oxidized to dialdehyde and at least iodic acid or a salt of iodic acid;

[0086] c) said aqueous solution obtained at the end of step b) is sent into a separation and purification process of at least one water-soluble polysaccharide oxidized to dialdehyde according to the invention to obtain an aqueous solution of water-soluble polysaccharide oxidized to purified dialdehyde and an aqueous effluent comprising at least iodic acid or the salt of iodic acid;

[0087] d) Optionally, at least part of the iodic acid or the salt of iodic acid in said aqueous effluent obtained at the end of step c) is converted to obtain an effluent comprising a regenerated oxidizing agent.

[0088] The steps are described in detail below. Other optional steps are also described below. Step a)

[0089] According to step a) of the preparation process, a feed comprising at least one water-soluble polysaccharide in aqueous solution is supplied. Advantageously, the water-soluble polysaccharide is selected from glucans, such as dextran, starch, cellulose derivatives, such as methylcelluloses, ethylcelluloses, carboxymethylcelluloses, hemicelluloses, such as xylans, arabinoxylans, arabinanes, glucomannans, galactomannans, galactogluco-mannans, mannans and xyloglucans, glycogen, fructans, such as rinulin, levan, or alginates, chitosans, xanthan gums, amylopectin, pectins, glycosaminoglycans, carrageenans or peptidoglycans.

[0090] Preferably, the water-soluble polysaccharide is chosen from hemicelluloses, preferably from xyloglucan, glucomannan, galactoglucomannan, mannan, and galactomannan. Most preferably, the water-soluble polysaccharide is xyloglucan.

[0091] Preferably, the concentration of water-soluble polysaccharide contained in the filler is between 0.5 and 25% by mass relative to the total mass of the filler, preferably between 1 and 15% by mass, preferably between 1 and 10% by mass, and more preferably between 1 and 5% by mass.

[0092] The charge according to step a) of the preparation process can be prepared by any treatment known to those skilled in the art aimed at concentrating the starting polysaccharide content in aqueous solution, with a possible de-oiling step to facilitate separation operations. Examples include hot water extractions, extractions in a basic medium, and extractions with solvents including alcohols and ethers. When the starting polysaccharide is xyloglucan, the latter can be extracted from tamarind powder according to a protocol such as that described in the article by Trung Thanh Nguyen, Weerachet Jittanit and Warangkana Srichamnong: “Production of xyloglucan component extracted from tamarind (Tamarindus indica) seeds using microwave treatment for seed decortication”, Journal of Food Processing and Preservation, Volume 43, Issue 8 e 14055 or in the article by Kumar CS, Bhattacharya S.Tamarind seed: “Properties, processing and utilization”, Critical Reviews in Food Science and Nutrition, 2008, 48(1): 1-20. doi:10.1080 / 10408390600948600. PMID: 18274963. . Step b)

[0093] According to step b) of the preparation process, the water-soluble polysaccharide in aqueous solution contained in the feed supplied in step a) is oxidized in the presence of an oxidizing agent comprising at least metaperiodic acid or a salt of metaperiodic acid to obtain an aqueous solution comprising a water-soluble polysaccharide oxidized to dialdehyde and at least iodic acid or a salt of iodic acid.

[0094] When the oxidizing agent is a salt of metaperiodic acid, said salt is preferably chosen from sodium metaperiodate, potassium metaperiodate, or lithium metaperiodate. Preferably, the oxidizing agent is sodium metaperiodate.

[0095] Preferably, the temperature of step b) is between 5°C and 95°C, preferably between 10°C and 80°C, and even more preferably between 15°C and 60°C.

[0096] Preferably, the duration of step b) is between 1 minute and 8 hours, preferably between 10 minutes and 4 hours, more preferably between 10 minutes and 2 hours.

[0097] The pH of the aqueous solution during the oxidation reaction is adjusted with a strong base, preferably sodium hydroxide, to neutralize the formic acid generated. Indeed, the presence of formic acid results from the double oxidation of certain sugar units of the starting polysaccharide used to form the dialdehyde polysaccharide. Preferably, the pH of the aqueous solution during step b) is between 5 and 14, more preferably between 5 and 13.5, and even more preferably between 6 and 13.

[0098] In one embodiment, a separation step is carried out after step b) and before step c) to remove any non-water-soluble solids that may be contained in the aqueous solution obtained at the end of step b). The separation step can be carried out by pressure filtration through a filter element that accumulates solids, vacuum filtration, or centrifugation, to obtain an aqueous solution advantageously comprising a residual solid content of less than 1% by mass relative to the total mass of the aqueous solution, preferably less than 0.5% by mass and very preferably less than 0.1% by mass. Step c)

[0099] In step c), the aqueous solution obtained at the end of step b), or the aqueous solution obtained after the optional separation step, is sent to a separation and purification process of at least one water-soluble polysaccharide oxidized to dialdehyde according to the invention to obtain an aqueous solution of purified water-soluble polysaccharide oxidized to dialdehyde and an aqueous effluent comprising at least iodic acid or the salt of iodic acid. A detailed description of this step has been given in section 2.1 above.

[0100] At the end of step c), an aqueous solution of water-soluble polysaccharide oxidized to purified dialdehyde is recovered, and an aqueous effluent comprising at least iodic acid or the salt of iodic acid. Step d) (optional)

[0101] According to step d), the iodic acid or the salt of iodic acid contained in said aqueous effluent obtained at the end of step c) is at least partially converted to obtain an effluent comprising a regenerated oxidizing agent. This oxidation step can be carried out by any means known to those skilled in the art.

[0102] In the embodiment in which the aqueous effluent comprises at least one salt of iodic acid selected from sodium iodate (NaIO3), potassium iodate (KIO3), or lithium iodate (LiIO3), preferably sodium iodate, said step d) comprises the following substeps:

[0103] dl) an oxidation step of iodate ions in the presence of an oxidizing flux to obtain a precipitate based on sodium, potassium or lithium paraperiodate, preferably sodium paraperiodate;

[0104] d2) a step of separating the sodium paraperiodate-based precipitate, from potassium or lithium, preferably sodium paraperiodate;

[0105] d3) a solubilization step of said precipitate based on sodium paraperiodate, of potassium or lithium, in the presence of a strong acid, to obtain sodium, potassium or lithium metaperiodate as a regenerated oxidizing agent.

[0106] Step dl) is carried out in the presence of an oxidizing flux, typically ozone, sodium hypochlorite, or sodium persulfate. The oxidation step dl) can be carried out by any technique for oxidizing iodate ions to paraperiodate known to those skilled in the art, and in particular ozonation, oxidation with sodium hypochlorite, or with sodium persulfate. The oxidation step is preferably carried out at a pH between 9 and 13. When the aqueous effluent contains at least one sodium iodate salt or potassium iodate salt, the presence of Na+ or K+ cations promotes the precipitation of the regenerated periodate in an alkaline medium as sodium or potassium paraperiodate, which is very sparingly soluble in aqueous solution. In all cases of oxidation of iodate ions, potentially present formate ions are also oxidized in the form of bicarbonate or carbonate (depending on the pH).

[0107] Step d2) can be carried out by any means that yields a solid composed of paraperiodate, preferably sodium paraperiodate, potassium paraperiodate, or lithium paraperiodate, more preferably sodium paraperiodate or potassium paraperiodate, and a residual aqueous solution. This separation step can be carried out by filtration, centrifugation, or any conventional method known to those skilled in the art. Obtaining periodate in the form of paraperiodate, due to its low solubility in water and its spontaneous precipitation, allows for its selective isolation from other salts, thus avoiding the concentration and precipitation of other salts.

[0108] Step d3) is a solubilization step of said precipitate based on sodium, potassium, or lithium paraperiodate, preferably sodium paraperiodate, in the presence of a strong acid, preferably selected from sulfuric acid, hydrochloric acid, or formic acid, more preferably hydrochloric acid or sulfuric acid, to obtain sodium, potassium, or lithium metaperiodate, preferably sodium metaperiodate, as a regenerated oxidizing agent. Step e) (optional)

[0109] In an embodiment according to the invention, a step e) is carried out of recycling at least part of the regenerated oxidizing agent obtained at the end of step d) to step b) of oxidation of the water-soluble polysaccharide in aqueous solution.

[0110] In order to better understand the invention, the description given below by way of example of application relates to a process for preparing a water-soluble polysaccharide oxidized to dialdehyde, as schematically shown in [Fig.3].

[0111] Referring to [Fig. 3], a feed 1 comprising at least one water-soluble polysaccharide in aqueous solution (also referred to herein as PS) is supplied. The feed 1 is sent to a stirred oxidation reactor XI in which oxidation by a An oxidizing agent 14 occurs, yielding a water-soluble dialdehyde oxidized polysaccharide (PSOH). In the embodiment described in [Fig. 3], the oxidizing agent is sodium metaperiodate (NaIO4). During this reaction, formic acid (HCOOH) is formed, and the periodate is reduced to iodate to obtain sodium iodate (NaIO3). Thus, the oxidation reaction produces an aqueous stream 2 comprising, in particular, the water-soluble dialdehyde oxidized polysaccharide (PSOH), but also a fraction of unreacted water-soluble polysaccharide (PS), solids, iodate ions, formate ions in aqueous solution, and possibly chlorides or sulfates of alkali metals (Na+, K+, Li+).

[0112] The aqueous stream 2 can then be sent into a device X2 for separating solids 4 and liquids, such as pressure filtration through a filter element accumulating solids, vacuum filtration, or centrifugation, to obtain an aqueous solution 3 advantageously comprising a residual solid content of less than 1% by mass relative to the total mass of the aqueous solution 3, preferably less than 0.5% by mass and very preferably less than 0.1% by mass.

[0113] The aqueous solution 3 is then sent to an electrodialysis unit X3 as described above and as described according to an exemplary embodiment in [Fig. 1]. At the outlet of the electrodialysis unit X3, a water-soluble polysaccharide oxidized to purified dialdehyde 6 and an aqueous effluent 7 comprising at least one sodium iodate salt (NaIO3) are recovered.

[0114] In order to regenerate the iodate ions into metaperiodate, the aqueous effluent 7 is first introduced into an oxidation reactor X4 in the presence of an oxidizing flux 8, typically ozone, sodium hypochlorite or sodium persulfate to obtain a regeneration effluent 9. This oxidation step can be carried out by any technique for oxidizing iodate ions into paraperiodate known to those skilled in the art, and in particular ozonation, oxidation by sodium hypochlorite, or by sodium persulfate. The oxidation step is preferably carried out at a pH between 9 and 13. The presence of Na+ cations promotes the precipitation of the regenerated periodate in an alkaline medium as sodium paraperiodate, which is very poorly soluble in the regeneration effluent. In all cases of oxidation of iodate ions, the potentially present formate ions are also oxidized as bicarbonate or carbonate (depending on the pH).The regeneration effluent 9 is then sent to a separation device X5 to obtain a solid composed of sodium paraperiodate 11 and a residual aqueous solution 10. This separation step can be carried out by filtration, centrifugation, or any conventional method known to those skilled in the art. It should be noted that obtaining regenerated periodate under... The paraperiodate form exiting the oxidation reactor X4, due to its low solubility in water and spontaneous precipitation, allows for its selective isolation from other salts, thus avoiding the concentration and precipitation of other salts. The residual aqueous solution 10 from the separation device X5 can be purged (flow 15) or partially reused in the electrodialysis unit X3. The recycling of the residual aqueous solution 10 and the addition of water 5 are then adjusted to obtain an initial salt concentration upstream of the electrodialysis step X3 of between 1 and 100 mmol / L, preferably between 10 and 40 mmol / L. The sodium paraperiodate solid 11 can then be sent to a solubilization reactor X6 to regenerate the metaperiodate as an oxidizing agent 14.The regenerated sodium metaperiodate can be obtained by a solubilization step in a reactor X6 between sodium paraperiodate 11 and a strong acid 12, such as sulfuric acid, hydrochloric acid, or formic acid, preferably hydrochloric acid or formic acid, before being at least partially recycled to the oxidation reactor XI. Preferably, the concentration of sodium metaperiodate in reactor X6 is between 0.2 g / L and 160 g / L, preferably between 0.2 and 100 g / L, more preferably between 0.4 and 60 g / L, and even more preferably between 0.4 and 30 g / L. A top-up 13 of sodium metaperiodate can also be carried out.

[0115] In a variant of the invention, not shown in the figures, the oxidation reactor X4 is replaced by an electrochemical reactor where the iodate ions are oxidized to periodate by electrochemical oxidation at the anode. The electrochemical reactor is preferably a compartmentalized electrolyzer whose anodic and cathodic compartments are separated by an ion-exchange membrane, either a cation-exchange membrane, an anion-exchange membrane, or a bipolar membrane. The anode is selected from a lead dioxide electrode, a boron-doped diamond (BDD) electrode, or a titanium iridium electrode, preferably a boron-doped diamond electrode. As in other oxidation cases, any formate ions present are electrochemically oxidized to bicarbonate or carbonate (depending on the pH).At the cathode, water reduction is typically used with cathodes known to those skilled in the art. Generally, a filtration system is employed on the anolyte circulation to separate the paraperiodate formed and prevent deposits in the electrolyzer. In this case, the electrochemical reactor and the X5 separation device are coupled.

[0116] The following example illustrates the invention according to an embodiment of the invention, without limiting its scope. Examples

[0117] In this example, PSOH is produced by the oxidation of tamarind xyloglucan in the presence of sodium metaperiodate. The references correspond to those in [Fig. 1].

[0118] An electrodialyzer X3 composed of 50 pairs of membranes (a cation exchange membrane 24 and an anion exchange membrane 25). The membranes are separated from each other by spacers, which consist of a sealing frame and a mesh in the active zone. This mesh is filled with electrolyte and prevents the membranes from touching. Channels are formed from the holes in the spacers and are arranged to form two different channel systems, namely a concentrating circuit 7' passing through the concentrating compartments (C) and a diluting circuit 3' passing through the diluting compartments (D). The electrodes at the ends of the electrolyzer are made of Pt / Ir for the cathode 22 and Ti coated with mixed metal oxide (MMO) for the anode 23, respectively. The active surface area of ​​the electrodes and membranes is 200 cm².25 litres of an aqueous solution 3 comprising PSOH and salts are introduced into the reservoir 26 integrated into the dilution circuit 3'. The composition and pH of the aqueous solution 3 are shown in Table 1 below.

[0119] [Tables 1] Xyloglucan (% mass) 1.57% NaIO4 concentration (mmol / L) 0 NaIO3 concentration (mmol / L) 58.3 NaHCO2 concentration (mmol / L) 29.5 PH 7.6

[0120] 25 liters of deionized water 5 are introduced into the reservoir 27 integrated into the concentration circuit 7'. The electrolyte 23 across the cathode 22 and the anode 21 is a 50 mmol / L aqueous solution of Na2SO4. After circulating the aqueous solution 3 through the dilution circuit 3' and the deionized water 5 through the concentration circuit 7' at a flow rate of 3 L / min, the electrolyzer is switched on to a voltage of 36 V. Figure 4 shows the time evolution of the electrodialysis. A conductivity meter is used to monitor the progress of the electrodialysis. The initial conductivity of the aqueous solution is 5.05 mS / cm. We observe that the current increases at start-up, which corresponds to the increase in conductivity of the liquid circulating in the concentration compartments (C) via the concentration circuit 7', reaches a maximum, then decreases as the aqueous solution is desalinated.After 170 minutes, the residual conductivity of the aqueous solution circulating in the . Dilution compartments (D) via the dilution circuit 3' is 51 pS / cm. An iodine assay performed after electrodialysis of the aqueous solution containing purified PSOH 6 indicates a residual sodium iodate / periodate content of 48 ppm mass relative to the total weight of the purified PSOH aqueous solution.

Claims

Demands

1. A process for separating and purifying at least one water-soluble polysaccharide oxidized to dialdehyde from an aqueous solution comprising said polysaccharide and at least one iodic acid or the salt of iodic acid, said process being carried out in an electrodialysis apparatus comprising a stack of cells, each cell consisting of two adjacent concentration (C) and dilution (D) compartments delimited alternately by cationic membranes and anionic membranes, in which said aqueous solution is sent into said dilution compartments (D) to obtain an aqueous solution comprising at least one water-soluble polysaccharide oxidized to purified dialdehyde and an aqueous effluent comprising at least said iodic acid or said salt of iodic acid is recovered from said concentration compartments (C).

2. A process according to claim 1, wherein said aqueous solution comprises between 0.5% and 25% by mass of a water-soluble polysaccharide oxidized to dialdehyde relative to the total mass of said aqueous solution.

3. A method according to any one of claims 1 or 2, wherein said salt of iodic acid is selected from sodium iodate (NaIO3), potassium iodate (KIO3), or lithium iodate (LiIO3), preferably sodium iodate (NaIO3).

4. A method according to any one of the preceding claims, wherein the content of iodic acid in said aqueous solution is between 0.015% and 50% by mass, or the content of said salt of iodic acid in said aqueous solution is between 0.015% and 14% by mass, relative to the total mass of said aqueous solution.

5. A method according to any one of the preceding claims, wherein said aqueous solution further comprises formic acid or a salt of formic acid selected from sodium formate, potassium formate or lithium formate, preferably sodium formate.

6. A process according to claim 5, wherein the content of said salt of formic acid in said aqueous solution is greater than 0% and less than or equal to 2.5% by mass relative to the total mass of said aqueous solution.

7. A method according to any one of the preceding claims, wherein the pH of said aqueous solution upstream of the separation and purification step is between 2 and 10.

8. A method according to any one of the preceding claims, wherein said method is carried out in batch mode.

9. A method according to claim 8, wherein the ratio between the volume of aqueous solution sent to the dilution compartments (D) of the electrodialysis apparatus and the volume of aqueous effluent recovered in the concentration compartments (C) is greater than i

10. 1. A method according to any one of claims 1 to 7, wherein said method is carried out in continuous mode.

11. A method according to claim 10, wherein the ratio between the flow rate of the aqueous solution sent to the dilution compartments (D) of the electrodialysis apparatus and the flow rate of the aqueous effluent recovered in the concentration compartments (C) is greater than i

12. 1. A method according to any one of the preceding claims, wherein the conductivity of said aqueous effluent comprising said iodic acid or said salt of iodic acid is between 2 and 200 mS / cm.

13. A method according to any one of the preceding claims, wherein a current density of between 20 and 1000 mA / cm2, preferably between 30 and 200 mA / cm2, is applied in the electrodialysis apparatus.

14. A method according to any one of the preceding claims, wherein said method is carried out at a temperature between 5 and 80°C.

15. A process according to any one of the preceding claims, wherein said water-soluble polysaccharide oxidized to dialdehyde is derived from selected natural water-soluble polysaccharides from glucans, such as dextran, starch, cellulose derivatives such as methylcellulose, ethylcellulose, carboxymethylcellulose, hemicelluloses, such as xylan, arabinoxylan, arabinan, glucomannan, galactomannan, galactogluco-mannan, mannan and xyloglucan, glycogen, fructans, such as inulin, levan, or alginates, chitosan, xanthan gums, amylopectin, pectins, glycosaminoglycans, carrageenans or peptidoglycans.

16. A process according to claim 15, wherein said water-soluble polysaccharide oxidized to dialdehyde is a derivative of xyloglucan, glucomannan, mannan or galactomannan, preferably xyloglucan.

17. A process for preparing at least one water-soluble polysaccharide oxidized to dialdehyde comprising at least the following steps: a) supplying at least one feed comprising at least one water-soluble polysaccharide in aqueous solution; b) oxidizing said water-soluble polysaccharide in aqueous solution contained in said feed supplied in step a) in the presence of at least metaperiodic acid or a salt of metaperiodic acid as an oxidizing agent to obtain an aqueous solution comprising a water-soluble polysaccharide oxidized to dialdehyde and at least iodic acid or a salt of iodic acid, alone or in mixture; c) sending said aqueous solution obtained at the end of step b) to a process according to any one of claims 1 to 16 to obtain an aqueous solution of purified water-soluble polysaccharide oxidized to dialdehyde and an aqueous effluent comprising at least iodic acid or a salt of iodic acid.

18. A process according to claim 17, wherein said water-soluble polysaccharide is selected from glucans, such as dextran, starch, cellulose derivatives such as methylcellulose, ethylcellulose, carboxymethylcellulose, hemicelluloses, such as xylan, arabinoxylan, arabinan, glucomannan, galactomannan, galactogluco-mannan, mannan and xyloglucan, glycogen, fructans, such as inulin, levan, or alginates, chitosan, xanthan gums, amylopectin, pectins, glycosaminoglycans, carrageenans or peptidoglycans.

19. A method according to claim 18, wherein said water-soluble polysaccharide is selected from xyloglucan, glucomannan, mannan or galactomannan, preferably xyloglucan.

20. A method according to any one of claims 17 to 19, wherein said salt of metaperiodic acid is selected from sodium metaperiodate, potassium metaperiodate, or lithium metaperiodate, preferably sodium metaperiodate or potassium metaperiodate, more preferably sodium metaperiodate.

21. A method according to any one of claims 17 to 20, wherein step b) is carried out at a temperature between 5°C and 95°C, and for a duration between 1 minute and 8 hours.

22. A method according to any one of claims 17 to 21, wherein said salt of iodic acid is selected from sodium iodate (NaIO3), potassium iodate (KIO3), or lithium iodate (LiIO3), preferably sodium iodate (NaIO3).

23. A process according to any one of claims 17 to 22, comprising a step d) in which said salt of iodic acid contained in said aqueous effluent obtained at the end of step c) is converted at least in part to obtain an effluent comprising a regenerated oxidizing agent.

24. A process according to claim 23, wherein said step d) comprises the following substeps: d1) a step of oxidizing iodate ions in the presence of an oxidizing flux to obtain a precipitate based on sodium, potassium or lithium paraperiodate, preferably sodium paraperiodate; d2) a step of separating the precipitate based on sodium, potassium or lithium paraperiodate, preferably sodium paraperiodate; d3) a step of solubilizing said precipitate based on sodium, potassium or lithium paraperiodate, in the presence of a strong acid, to obtain sodium, potassium or lithium metaperiodate as a regenerated oxidizing agent.

25. A process according to any one of claims 23 or 24, wherein a step e) of recycling at least part of the regenerated oxidizing agent obtained at the end of step d) is carried out to step b) of oxidation of the water-soluble polysaccharide in aqueous solution.

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