WO2006134299A1 - Method for making a gel-type compound, for treating effluent - Google Patents

Abstract

The invention concerns a method for making a gel-type compound, for treating effluent and/or preparing papermaking pulp, whereby said gel is obtained by crosslinking an untreated raw wheat flour with a crosslinking agent, within a reactor maintained under constant agitation, until a solid is obtained, after washing, purifying and filtering said solid then functionalizing same by chemical activation.

Description

PROCESS FOR PRODUCING A GEL-TYPE COMPOUND FOR THE TREATMENT OF EFFLUENT

The present invention is in the field of effluent treatment, in particular in the manufacture of effluent treatment means and the treatment of effluent by these means. The invention also falls within the field of paper formulation, particularly in the manufacture and use of binding agents or fixatives in paper pulps.

The invention relates more particularly to a process for producing a gel-type compound having adsorbent, chelating, complexing and binding properties, as well as the gel resulting from this process.

Effluent treatment occurs in several areas often related to solution recycling, such as pulp recycling or water treatment, but also in solution bleaching, adsorption of pollutants, and so on.

It is then necessary to use a product which will be used, as the case, adsorbent for pollutants of organic and / or metal type, flocculating agent, complexing, chelating, bleaching, binder or fixer.

Generally, the adsorbents are based on the use of activated carbons or synthetic chemical compounds, such as synthetic resins, which are modified to obtain the qualities and characteristics necessary for the treatment envisaged.

The most commonly used methods include activated carbons as adsorbent systems. However, the coals saturate very quickly and then require regeneration treatments, very expensive. In a known manner, another state of the art also envisages the use in a treatment process, in particular of effluent decolorization, of a compound constituted so as to allow the formation of a precipitate. In other processes, a soluble cationic coagulant is used, in combination or not with a polymer.

All these methods have the disadvantage of using chemicals, such as proteins, whose synthesis remains expensive and are rarely biodegradable, generating environmental pollution and additional costs of reprocessing or regeneration. In addition, activated carbons have a lack of selectivity for certain molecules and have little affinity for hydrophilic pollutants.

To overcome these drawbacks, it has been imagined to use natural polymers, such as polysaccharides (for example starch, cellulose, chitin, chitosan or the like), as adsorbent solids. These natural polymers have the advantage of being both effective and inexpensive.

For example, document FR 2 359 861 describes absorbent products obtained by polymerization of acrylonitrile with grafting on a flour comprising starch, for example wheat flour. Such a compound is useful for reducing the water content of emulsions and dispersions, for coating substrates to increase their water retention capacity, for solidification of liquid residues and as a thickening agent for aqueous systems. The process for preparing such an absorbent composition consists in polymerizing grafted acrylonitrile on a substrate containing starch and then saponifying the polymer resulting from this reaction in an aqueous sludge with an alkali and finally drying the product thus obtained. up to a moisture level making it insoluble in water. Document FR 2 761 365 discloses the preparation of products resulting from the polymerization and the crosslinking in an alkaline medium of a gel prepared from wheat flour in the presence of a crosslinking reagent chosen from formalin and anhydride. maleic. Such a compound will find particular use in the field of abrasive particles. Successive firings are reciprocally obtained, on the one hand, a gel from a cereal flour, a basic agent and a crosslinking agent and, on the other hand, a solid of glassy character and determined water content, said solid being ground to form abrasive particles of homogeneous particle size.

Another example of a use of crosslinked gelatinized starch is described in document FR 2 378 506. This patent discloses the manufacture of absorbent material for specific disposable absorbent products of the diaper, tampon or sanitary napkin type. The method of production and the product resulting therefrom are very precise, complex and are limited to ranges of degree of substitution of the crosslinking groups of between 0.001 and 0.04, as well as ionic groups, so as to confer a retention of urine of at least 6 g / g for the crosslinked starch derivative.

Another method, described in FR 1 601 483, is the etherification and gelatinization of the starch to form a textile warp finish to improve the strength of the fabric yarns. Such a process aims to obtain a low demand biochemical oxygen compound through complex and very precise reactions.

A method of the state of the art also uses a biodegradable gel acting as a coagulant based on proteins, natural or vegetable, soy. A cationic monomer is added to quaternize said protein to give the gel its chemical properties.

However, these methods are not entirely satisfactory.

The object of the invention is to overcome the drawbacks of the state of the art by proposing a method of manufacturing a gel-like compound based on wheat flour. The invention also relates to the gel resulting from the preceding process.

The present invention therefore relates to a method for producing a gel-type compound, for the treatment of effluent and / or the formulation of paper pulp, wherein said gel is obtained by crosslinking a flour-based solution. raw wheat not treated with a crosslinking agent, in a reactor stirred continuously, until a solid, after washing, purification and filtration of said solid and then by functionalization by chemical activation of the latter.

Advantageously, the crosslinking step consists of:

suspend wheat flour in a solution of soda; add sodium borohydride; heat the solution for four hours; simultaneously adding dropwise a crosslinking agent and an ammonia solution; add paraffin; heating the resulting solution at 50 ° C for two hours; add acetone.

Preferably, the crosslinking agent is epoxy and consists of epichlorohydrin, 1,2-ethanediol-diglycidyl ether, 1,4-butane-diol-diglycidyl ether, or 1,3-diglycidylglycerol. In addition, the washing, filtering and purification consist in cooling the gel obtained, filtering it, washing it and purifying it with soxhlet and / or with ethanol, acetone and water.

Advantageously, the functionalization step consists of:

suspending said gel in a sodium hydroxide solution; add functionalization reagent; heat the resulting mixture at 50 ° C for twenty hours; cool the solution and neutralize it with hydrochloric acid; wash with ethanol, acetone, and water, and then dry the compound obtained.

Preferably, the functionalizing reagent is 2,3-epoxypropyltrimethylammonium chloride, chloroacetic acid or 2-chloroethylamine.

The invention also relates to a gel-type compound derived from the process according to any one of the preceding claims.

Other features and advantages of the invention will emerge from the following detailed description of non-limiting embodiments of the invention.

The present invention is in the field of effluent treatment, solution or the like. It is also in the field of paper formulation. In particular, the present invention relates to the synthesis of an amphiphilic and complexing gel type compound intended to act as an adsorbent for organic and / or metallic pollutants, a flocculating agent, a complexing agent, a binder, a bleaching agent and / or fixer.

A feature of the invention lies in the fact that this compound is a biopolymer based on wheat flour. In this respect, this flour is presented as a de-proteinated and starch-enriched agro-food by-product. This by-product does not require any pre-treatment and is used as is. Starch is a natural, renewable, cheap and biodegradable resource. However, modified, it is able to selectively adsorb efficiently polluting molecules such as heavy metals, dyes or aromatic derivatives.

The synthesis of such a compound resides essentially in two distinct steps carried out in a basic aqueous medium. The synthesis consists, on the one hand, in a chemical modification by crosslinking and, on the other hand, in a functionalization step by chemical activation.

Crosslinking is a bridging creation between macromolecular chains. This operation creates a three-dimensional amine network that gives the material both specific physicochemical and amphiphilic properties. Crosslinked networks are thus obtained comprising specific surfaces and having a variable basicity, in particular depending essentially on the amount of ammonia introduced, as well as swelling properties in water due to the hydrophilic nature of the gel. One advantage is a better diffusion of the pollutant in the gel and faster adsorption kinetics.

Functionalization by chemical activation consists of a grafting of active molecules. This step gives the surface of said gel an ion exchange character, thanks to its complexing and chelating properties. This exchange character will be associated with the hydrophilic and hydrophobic properties of the gel to allow better results in terms of adsorption capacity and / or fixing efficiency. This functionalization step depends on the end use of said gel and is a function of the effluent and the pollutant to be treated. She serves essentially: to increase the adsorbent and / or fixing properties of the previously crosslinked gel. The ion exchange character can be optimized from the experimental conditions.

Between the crosslinking synthesis and the functionalization step, the gel undergoes a purification step by soxhlet extraction. The gel is thus cooled, filtered and washed with soxhlet and / or with ethanol, acetone and water.

It should be noted that the synthesis of the gel is carried out in a reactor, in particular in a double wall reactor which makes it possible to maintain the temperature constant. In addition, constant stirring is maintained inside said reactor, in particular through mechanical stirring means or the like.

Under these conditions, the synthesis by crosslinking begins with the suspension of the wheat flour in a sodium hydroxide solution. The concentration of sodium hydroxide may be of the order of 40%. For a solution of 50 ml of 40% sodium hydroxide, 10 g of flour should be mixed.

In this respect, the proportions mentioned in the remainder of the description will be in adequacy with the previously mentioned dosage.

Sodium borohydride, of chemical formula NaBH4, is added to the solution. Proportionally, 50 mg of NaBH4 should be added.

The solution is then brought to 50 ^° C. and then stirred for four hours.

A crosslinking agent and an ammonia solution are simultaneously: added drop by drop. This addition is carried out while maintaining vigorous stirring at 50 ^° C. The crosslinking agent is of the epoxy type and may be composed of epichlorohydrin, 1,2-ethanediol-diglycidyl ether or 1,4-butanediol. diglycidyl ether, or 1,3-diglycidylglycerol. The amount of crosslinking agent is 70 ml while the ammonia solution is 94 ml.

Paraffin is added, especially in an amount of 50 ml, before continuing to heat the mixture at 50 ° C for two hours.

Under the same conditions, a solution of acetone, in particular 150 ml, is added.

Stirring is further maintained for one hour before cooling the resulting mixture and the steps of filtration, washing and grinding.

The product resulting from this process of synthesis by crosslinking is then in the form of a slightly yellowish powder.

The material can be chemically activated by the grafting of ligands which will give the gel ion exchange properties. This functionalization step consists, firstly to put the gel obtained in suspension in a sodium hydroxide solution at room temperature. The content of this solution can be 20%.

The mixture obtained is then stirred at room temperature for four hours, before the addition of the functionalization reagent which may be 2,3-epoxypropyltrimethylammonium, chloroacetic acid or 2-chloroethylamine. It is advisable: then to heat the mixture for twenty hours at 50 ° C.

After this period, the solution is cooled and neutralized with hydrochloric acid.

The filtrate obtained is finally washed with ethanol, with acetone, and with water and then dried.

Claims

A method of making a gel-like compound for the treatment of effluent and / or the formulation of paper pulp, wherein said gel is obtained by crosslinking a solution of non-crude wheat flour treated with a crosslinking agent, in a reactor maintained under constant stirring, until a solid is obtained, after washing, purification and filtration of said solid and then by functionalization by chemical activation of the latter.

2. Method according to claim 1, characterized in that the crosslinking step consists of:

suspend wheat flour in a solution of soda; add sodium borohydride; heat the solution for four hours; simultaneously adding dropwise a crosslinking agent and an ammonia solution; add paraffin; heating the resulting solution at 50 ° C for two hours; add acetone.

3. Method according to claim 2, characterized in that the crosslinking agent is epoxy and consists of epichlorohydrin, 1,2-ethanediol-diglycidyl ether, 1,4-butane-diol-diglycidyl ether , or 1,3-diglycidylglycerol.

4. Method according to any one of the preceding claims, characterized in that the washing, filtering and purification consist in cooling the gel obtained, filtering it, washing it and purifying it with soxhlet and / or with ethanol, acetone and water.

5. Method according to any one of the preceding claims, characterized in that the functionalization step consists of:

suspending said gel in a sodium hydroxide solution; add functionalization reagent; heat the resulting mixture at 50 ° C for twenty hours; cool the solution and neutralize it with hydrochloric acid; wash with ethanol, acetone, and water, and then dry the compound obtained.

6. Method according to claim 5, characterized in that the functionalizing reagent is 2,3-epoxypropyltrimethylammonium chloride, chloroacetic acid or 2-chloroethylamine.

7. Gel-type compound from the process according to any one of the preceding claims.