EP2920129A1

EP2920129A1 - Use of a water-soluble copolymer for preparing an aqueous lime suspension

Info

Publication number: EP2920129A1
Application number: EP13803147.1A
Authority: EP
Inventors: Jacques Mongoin; Fabrizio Belli; Angelo BERLENDIS
Original assignee: Coatex SAS
Current assignee: Coatex SAS
Priority date: 2012-11-19
Filing date: 2013-11-18
Publication date: 2015-09-23
Also published as: WO2014076437A1; FR2998195B1; CN104812719A; FR2998195A1; JP2016505356A; KR20150089041A; CN104812719B; RU2015123646A; BR112015009970A2

Abstract

The present invention concerns a suspension made from lime comprising a water-soluble copolymer as an additive, and a method for preparing such a suspension. Such suspensions are used, in particular, as chemical neutralising agents in industrial or domestic processes.

Description

USE OF A WATER-SOLUBLE COPOLYMER FOR PREPARING AQUEOUS LIME SUSPENSION

The present invention relates to the technical field of the preparation of aqueous suspensions of calcium dihydroxide. More specifically, the present invention relates to the use of a water-soluble copolymer for preparing a slurry based lime, as well as aqueous slurries of lime comprising such a polymer. Such suspensions are used in particular as a chemical neutralization agent in industrial or domestic processes.

Calcium dihydroxide Ca (OH) ₂ , also called slaked lime or hydrated lime, is obtained by hydration of calcium oxide CaO, also called quicklime, according to the following exothermic reaction: CaO + H ₂ O Ca (OH) ₂ in the context of the present invention is used to designate the Ca (OH) ₂ the terms "calcium hydroxide" or the terms "calcium hydroxide" it equivalently.

Calcium hydroxide products come in a variety of forms: in the form of powder (dry product in powder form), in the form of plastic pastes or in the form of aqueous suspensions / dispersions (milk of lime).

The present invention relates more particularly to a product based on calcium hydroxide which is in the form of an aqueous suspension. Such aqueous suspensions of slaked lime can be used as chemical neutralizing agents in many industrial processes. As an indication, the treatment of industrial effluents, for example gaseous effluents such as acid fumes, is given as an indication. We also mention the treatment of drinking water, used or industrial.

The aqueous suspensions of slaked lime are characterized in particular by their dry matter content (% by weight). Those skilled in the art typically seek to increase the dry matter content in aqueous suspensions of slaked lime, mainly for economic reasons: by increasing the dry matter content of aqueous suspensions of slaked lime, the cost relative to transportation is thus reduced. and at the handling per tonne of product. In addition, it reduces the nuisance due to the handling of powders (hygiene, handling) and facilitates the implementation.

In order to increase the dry matter content of the aqueous suspensions of slaked lime, it is possible in particular to use a dispersing agent.

The term "dispersing agent" means an agent which has the capacity to improve the dispersion state of the Ca (OH) ₂ particles in the aqueous suspension. Specifically, when these agents are used in the aqueous suspensions of mineral matter, they induce a decrease in viscosity. Thus, an aqueous suspension of mineral material comprising a dispersing agent will have a viscosity lower than that of the same aqueous suspension of mineral material not containing said dispersing agent. A number of prior art documents describe the use of dispersant.

EP 0 061 354 (Blue Circle) describes the use of anionic oligomeric polyelectrolytes, for example homopolymers of (meth) acrylic acid, carboxymethylcellulose or sulphonate, for producing aqueous dispersions of slaked lime.

The document FR 2 677 351 (Italcementi) describes a concentrated aqueous suspension of calcium hydrate, which contains at least 40% of solid hydrated lime obtained from hydrated powdered lime, slaked lime or quicklime, and a polymer water-soluble which may be an alkali metal or alkaline earth metal polyacrylate.

EP 0 594 332 (Rohm & Haas) describes the use of polymeric anionic dispersing agents to obtain aqueous dispersions of quicklime or slaked lime. These dispersing agents are chosen from homopolymers, copolymers and terpolymers having carboxylic acid, sulphonic acid or phosphonic acid functionalities. Monomers which confer such an acid functionality include, for example, acrylic acid, methacrylic acid, crotonic acid, maleic acid, maleic anhydride, itaconic acid, mesaconic acid, fumaric acid, citraconic acid, vinyl acetic acid, acryloxypropionic acid vinyl sulfonic acid, styrene sulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, allylsulfonic acid, allylphosphonic acid, vinylphosphonic acid, and vinylsulfonic acid. Document US 2008/0011201 (Ultimate Nominees) describes the combined use of a polycarboxylate dispersant and a carbohydrate dispersant to prepare a lime milk for applications in the field of food and drinking water. In particular, according to this document, the carbohydrate dispersant is a sugar, chosen in particular from the aldoses, saccharides, disaccharides and polysaccharides. Also, examples of polycarboxylate dispersant include styrene maleic anhydride copolymer salts or polyether polycarboxylate salts. This document notably describes the combined use of a comb-type copolymer, namely Ethacryl® G (polycarboxylate dispersant from Coatex) and a glucose syrup (carbohydrate dispersant) to prepare a suspension / dispersion of hydrated lime. at 50%.

EP 0 848 647 (Chemical Lime Company) discloses the use of an anionic polyelectrolyte dispersant in combination with an alkali metal hydroxide to prepare a suspension of lime which may be quicklime or slaked lime. The anionic polyelectrolyte is chosen from polyacrylic acid, polycarboxylic acid and polyphosphoric acid, copolymers of polyacrylic acid, polycarboxylic acid and polyphosphoric acid and their alkali metal salts.

Document FR 6687396 (Lhoist) discloses meanwhile a calcium oxide-extinguishing process or magnesium oxide in the presence of ions S0 ₃ - ^", S0 ₄ ^2-" or Cl ^"and during the reaction or at the end of the reaction, a polymer or copolymer comprising monomers chosen from acrylic acid and its salts, methacrylic acid and its salts, vinylbenzylsulphonic acid and its salts, acrylamino-2-methylpropanesulfonic acid and its salts, 2-sulfoethyl methacrylate and its salts.

JP 09 122471 (Nippon Shokubai) discloses the use of copolymers consisting of a carboxylic monomer and a monomer of the polyalkylene glycol (meth) acrylate type as a dispersing agent which makes it possible to obtain aqueous dispersions of slaked lime having a low viscosity. This document illustrates the use for this purpose of copolymers whose molecular weight is less than 20 000 g / mol.

WO 2010/106111 (Lhoist) relates to compositions comprising slaked lime and / or quicklime and an organic polymer incorporated into the solid phase of slaked lime. The polymers described in this document can be nonionic, anionic, cationic or amphoteric and very varied in nature. They can be obtained from monomers chosen from anionic monomers having a carboxylic function or having a sulphonic acid function, the nonionic monomers (acrylamide, methacrylamide, N-vinylpyrrolidone, vinylacetate, vinyl alcohol, acrylate esters, allyl alcohol, N-vinyl acetamide, N-vinylformamide), the cationic monomers (ADAME, MADAME quaternized or salified, DADMAC, APTAC MAPTAC), optionally in combination with one or more hydrophobic monomer (s) preferably chosen from the group comprising the esters of (meth) acrylic acid with an alkyl, arylalkyl and / or ethoxylated chain, (meth) acrylamide derivatives containing an alkyl, arylalkyl or dialkyl chain, cationic allylic derivatives, anionic or cationic hydrophobic (meth) acryloyl derivatives or the monomers anionic and / or cationic derivatives of (meth) acrylamide bearing a hydrophobic chain.

Using the polymers of the prior art, the inventors nevertheless found a problem of sedimentation when the suspensions are kept without agitation for a period exceeding 3 days, especially during their transport. A paste is then formed at the bottom of the tanks containing the suspensions which makes it difficult or impossible to pump them. The inventors have further noted that this problem of sedimentation was due to a poorly adapted rheology of the currently available suspensions and bad deagglomeration of lime particles.

The dispersing agents available to date do not make it possible to obtain aqueous suspensions of lime giving complete satisfaction especially in terms of sedimentation and rheological properties.

An object of the present invention is to avoid the problem of sedimentation when lime slurries are kept without stirring.

Another object of the present invention is to provide aqueous lime suspensions as concentrated as possible and which have a rheology adapted to their uses in industrial processes. Unexpectedly, the inventors have demonstrated that by using a polymer of particular structure, it was possible to obtain concentrated and stable aqueous suspensions over time.

More specifically, a first subject of the present invention relates to the use of a water-soluble copolymer consisting of:

methacrylic acid monomers and / or any of its salts,

optionally acrylic acid monomers and / or any of its salts,

monomers of formula (I):

R - X - R '

(D

according to which:

R represents a polymerizable unsaturated functional group, in particular acrylate, methacrylate, methacrylurethane, vinyl or allyl,

R 'denotes hydrogen or an alkyl group having from 1 to 4 carbon atoms, X represents a structure comprising n unit (s) of ethylene oxide EO and m unit (s) of propylene oxide OP, arranged randomly or regularly,

m and n are 2 non-zero integers and between 1 and 150,

to prepare an aqueous suspension of calcium hydroxide from calcium hydroxide in powder form.

The subject of the present invention is also an aqueous suspension of calcium hydroxide, comprising at least one copolymer consisting of:

methacrylic acid monomers and / or any of its salts,

optionally acrylic acid monomers and / or any of its salts,

monomers of formula (I):

R - X - R '

(D

according to which: R represents a polymerizable unsaturated functional group, in particular acrylate, methacrylate, methacrylurethane, vinyl or allyl,

m and n are 2 non-zero integers and ranging from 1 to 150.

Indeed, the inventors have realized that in order for the aqueous suspensions to exhibit the stability properties in the expected time and concentration, it was necessary to disperse the calcium hydroxide particles in the presence of a water-soluble comb-type copolymer having a (meth) acrylic acid backbone and poly (alkylene glycol) side chains of particular structure. By "calcium hydroxide in powder form" is meant slaked lime particles. Slaked lime is a lime consisting of a set of solid particles, mainly calcium dihydroxide Ca (OH) ₂ which is the result of the reaction of quicklime particles with water, a reaction called hydration or extinction. The hydrated lime is also called hydrated lime. In general, the slaked lime may contain impurities, which are mainly derived from quicklime, for example magnesia, magnesium oxide, Al ₂ O ₃ , Fe ₂ O ₃ , MgO, S, SiO ₂ , MnO ₄ , silicates etc. The slaked lime can be in pulverulent form or in the form of an aqueous suspension, called lime milk. In the context of the present invention, slaked lime in the form of a powder is dispersed in an aqueous solution in order to obtain a lime milk that is concentrated and stable over time. For example, the starting material used is a slaked lime in the form of a commercially available powder. By way of example, mention is made of the slaked lime sold under the names Supercalco® 97, Supercalco® 97/20, Sorbacal® SP, Standard Hydrated Lime and MicroCal® HF.

The particular methacrylic copolymer according to the invention is a water-soluble comb-type copolymer having a methacrylic acid skeleton, and optionally acrylic acid, and poly (alkylene glycol) side chains. By "poly (alkylene glycol)" is meant a polymer of an alkylene glycol derived from an olefinic oxide.

The poly (alkylene glycol) chains of the copolymer according to the present invention contain a proportion of ethyleneoxy groups and a proportion of propyleneoxy groups. The poly (alkylene glycol) chains according to the present invention may for example comprise a major proportion of ethyleneoxy group in combination with a secondary proportion of propyleneoxy group. Specific examples of the alkylene glycol polymer include: polyalkylene glycols having an average molecular weight of 1,000, 4,000, 6,000, 10,000 and 20,000 g / mol; polyethylene polypropylene glycols having a percentage of ethylene oxide of between 20 and 80% by weight and a percentage of propylene oxide of between 20 and 80% by weight.

It should be noted that the ethyleneoxy groups and the propyleneoxy groups of the side chains of the copolymer may be arranged in a random manner, in a regular manner or in a block.

More specifically, the polymer according to the present invention consists of:

methacrylic acid monomers and / or any of its salts,

optionally acrylic acid monomers and / or any of its salts,

monomers of formula (I):

R - X - R '

(I)

according to which:

m and n are 2 non-zero integers and ranging from 1 to 150. Thus, the copolymer according to the invention has a skeleton consisting of methacrylic acid monomers, and optionally acrylic acid monomers. The inventors have indeed realized that the presence of methacrylic acid monomers in the backbone of the copolymer according to the invention was essential to solve the technical problem at the origin of the present invention.

According to one embodiment of the invention, the copolymer has a skeleton consisting exclusively of methacrylic acid monomers.

According to another embodiment of the invention, the copolymer has a skeleton consisting of methacrylic acid monomers and acrylic acid monomers.

Thus, it is excluded in the context of the present invention to use a copolymer having a skeleton consisting exclusively of acrylic acid monomers.

The inventors have further found that the use in the context of the present invention of the comb-type copolymer sold under the name Ethacryl® G (polycarboxylate dispersant from Coatex which does not contain methacrylic acid monomers) is not suitable. to solve the technical problem at the origin of the present invention. Said copolymer is obtained by the known methods of conventional free radical copolymerization in solution, in bulk, in bulk, in direct or inverted emulsion, in suspension or by precipitation in appropriate solvents, in the presence of known catalyst systems and transfer agents, or by controlled radical polymerization processes such as the method known as reversible addition-fragmentation chain transfer (RAFT), the method known as atom transfer radical polymerization (ATRP), the a process known as nitroxide-mediated polymerization (NMP), or the process known as cobaloxim-mediated radical polymerization. It is obtained in an acid form and optionally distilled. It may also be partially or totally neutralized with one or more neutralization agents chosen from hydroxides of sodium, calcium, magnesium and potassium and their mixtures or chosen from amines. According to one embodiment of the present invention, said copolymer is 100% neutralized with sodium hydroxide.

According to another embodiment of the present invention, said copolymer is partially neutralized with sodium hydroxide.

According to one embodiment, said aqueous calcium hydroxide suspension contains a concentration of water-soluble copolymer which ranges from 0.01 to 10% by weight, based on the total weight of calcium hydroxide particles in the suspension.

According to another embodiment, said aqueous calcium hydroxide suspension contains a water-soluble copolymer concentration which varies between 0.05 and 5% by weight, based on the total weight of calcium hydroxide particles in the suspension.

According to yet another embodiment, said aqueous suspension of calcium hydroxide contains a concentration of water-soluble copolymer which varies between 0.1 and 3.0% by weight, based on the total weight of calcium hydroxide particles in suspension.

According to another embodiment, said aqueous suspension of calcium hydroxide contains a concentration of water-soluble copolymer which varies between 0.2 and 2.0% by weight, based on the total weight of calcium hydroxide particles in the suspension.

According to another embodiment, the aqueous suspension according to the present invention is composed of an aqueous solution, for example optionally added water, calcium hydroxide particles and a copolymer according to the present invention. According to another embodiment, the aqueous suspension according to the present invention is composed of water, calcium hydroxide particles and a copolymer according to the present invention. According to this embodiment, the aqueous suspension does not comprise any additive other than the copolymer described in the present application, that is to say that it does not include, for example, another polymer or dispersant. According to one embodiment, the aqueous suspension is an aqueous suspension containing a dry content of at least 40% by weight, based on the total weight of the aqueous suspension. According to another embodiment, the aqueous suspension according to the present invention has a calcium hydroxide particle content of between 40 to 60% by weight, based on the total weight of the aqueous suspension.

The viscosity of said aqueous suspension measured by a Brookfield DVIII viscometer at 10 rpm is between 25 and 1000 mPa.s at 20 ° C, said suspension being obtainable by the method of the present invention.

According to another embodiment, the aqueous suspension according to the present invention has a calcium hydroxide particle content of between 45 to 55% by weight, based on the total weight of the aqueous suspension. According to one embodiment of the present invention, said copolymer has a molecular mass of between 30,000 and 200,000 g / mol as determined by size exclusion chromatography (CES).

According to another embodiment of the present invention, the copolymer has a molecular mass of between 30,000 and 160,000 g / mol as determined by size exclusion chromatography (CES).

According to one embodiment of the present invention, in said water-soluble copolymer, said monomer of formula (I) is such that n and m are two non-zero integers and n + m> 17.

According to one embodiment of the present invention, in said water-soluble copolymer, the R function of said monomer of formula (I) represents the methacrylate function.

According to one embodiment of the present invention, in said copolymer, the function R 'of said monomer of formula (I) represents H or C¾. According to one embodiment of the present invention, in said copolymer, said monomer of formula (I) consists of, expressed in percentage by weight of each of its constituents: 5 to 30% by weight of methacrylic acid monomers and / or any of its salts,

0 to 10% by weight of acrylic acid monomers and / or any of its salts,

- 70 to 95% by weight of monomers of formula (I).

According to one embodiment of the present invention, in said copolymer, said monomer of formula (I) consists of, expressed as a percentage by weight of each of its constituents:

- 7 to 22% by weight of methacrylic acid monomers and / or any of its salts,

0 to 5% by weight of acrylic acid monomers and / or any of its salts,

78 to 93% by weight of monomers of formula (I).

A third object of the present invention also relates to the use of the aqueous suspension of slaked lime according to the invention in the following applications.

The suspensions can be used in the treatment of fumes from energy production plants using fuels (especially coal) containing for example sulfur and other impurities that generate acidic molecules (sulfur dioxide, sulfur trioxide, sulfuric acid, hydrochloric acid, hydrofluoric acid ...) or pollutants (mercury, heavy metals ...). They can also be used in household or industrial waste incineration plants that generate the same type of pollutants with dioxins as well. The use of lime in concentrated aqueous suspension, sprayed into the fumes, traps the pollutants which are then eliminated in the solid residues produced by the reaction with lime and the partial or total drying of these reaction products. The suspensions may be used as neutralizing agents for acidic reaction products, allowing their removal in solid and / or neutralized form or their use in the form of a calcium salt (such as, for example, neutralized sulphonates and phenates as lubricant additives). Non-exhaustively, mention may be made of the neutralization of acid sludges from the manufacture of titanium dioxide, the neutralization of acidic solutions produced during chemical manufacturing processes.

The aqueous suspensions of the present invention can be used as neutralizing agents for the mine effluents, with the aim of neutralizing the acidity and / or separating the heavy metals in solution before the discharge of the fluids in the natural environment or in the lagoon.

The suspensions can be used in water decarbonation processes, a method for reducing the temporary hardness of water (partial or total elimination of alkaline earth metal hydrogencarbonates). The water thus treated is intended to be used as drinking water or industrial water, possibly after a readjustment of the pH by means of carbon dioxide or any other acid suitable for the final application.

Treatment of drinking water purification, wastewater or industrial generate residues called sludge. These sludges are first separated from the purified water and then treated in order to stabilize and concentrate them. The sludge treatment process is generally called conditioning and uses organic and / or inorganic additives.

The present invention also relates to the use of the aqueous suspension of slaked lime according to the invention for the conditioning of sludge, from wastewater treatment plants. The suspended lime is used initially to promote the flocculation of the sludge and in a second time for the sterilization by the pH of said sludge by maintaining the sludge at a pH of 12 or more, for 24 to 72 hours or more . The suspensions may be used in the treatment of aggregates used in the bituminous mix production process. The adhesion of the bitumen emulsions to the aggregates is greatly improved when these aggregates are previously treated with lime. This better adhesion leads to bituminous coatings that are more resistant to wear, deformation and have a prolonged physical integrity.

The aqueous suspensions of the present invention can be used in the production of cellular concrete construction materials. The lime is mixed with cement, sand and aluminum powder. The high pH of the mixture causes off-gassing of hydrogen by attacking the aluminum and the aerated dough thus produced is molded and then autoclaved to produce pieces of cellular concrete.

The aqueous suspensions of the present invention can be used in the treatment of contaminated soils in order to neutralize the acidity of these sols, immobilize the pollutants by neutralization or flocculation and thus avoid the entrainment of said pollutants in the groundwater.

The aqueous suspensions of the present invention can be used in the treatment of soils in agriculture to correct the pH of these soils, amend said soils by providing a source of calcium or calcium and magnesium in the case of dolomitic lime and make these soils less impervious by flocculation of the clays they contain. The aqueous suspensions of the present invention can be used in the treatment of surface waters, lakes, ponds and rivers in order to adjust the pH of the water to reduce the impact of the acidification of these waters, acidification of rain or animal origin in the case of fish farms. The aqueous suspensions of the present invention can be used in the production of feed for cattle or poultry and among others as a source of calcium or calcium and magnesium. The aqueous suspensions of the present invention can be used in the paper industry, for example as a constituent of paper pulp.

They can still be used for refining sugar.

They can also be used for the production of precipitated calcium carbonate (PCC).

The present invention also relates to the use of the aqueous suspension of calcium hydroxide according to the invention for the treatment of industrial fumes, in particular for the desulfurization of fumes, or for the treatment of domestic wastewater, especially drinking water, or industrial.

The present invention also relates to a process for the treatment of gases or fumes comprising a step of injecting / spraying an aqueous suspension of slaked lime according to the invention in the gases or fumes to be treated so as to eliminate acid compounds, oxides sulfur, hydrochloric acid, etc.

Another subject of the present invention relates to a process for preparing an aqueous suspension of calcium hydroxide according to the invention.

More specifically, the present invention relates to a process for preparing an aqueous suspension of calcium hydroxide, comprising the steps according to which: a) an aqueous solution containing a copolymer according to the invention is prepared, and

b) mixing with said aqueous solution of step a) calcium hydroxide in powder form.

According to one embodiment, said method further comprises a step of subjecting the suspension to homogeneous shear.

In the context of the present invention, and according to this embodiment, a homogeneous shear has the effect of applying the same minimum mechanical stresses for all parts of the aqueous suspension thus treated. According to another embodiment, said method further comprises a step of subjecting the suspension to homogeneous shear with a degree of shear greater than 50,000 sec ^-1 .

Such a degree of shearing makes it possible to obtain a suspension having a high slaked lime content, which does not sediment and is stable over time. Applying such a degree of shear to the suspensions of slaked lime thus makes it possible, in combination with the use of a water-soluble copolymer of particular chemical structure, to achieve these objectives. The rheological properties of the resulting dispersion are thus significantly optimized over time.

According to one embodiment, homogeneous shear of shear degree greater than 60,000 s ^-1 , in particular greater than 70,000 s ^-1 , is applied.

The homogeneous shear required according to this embodiment of the present invention can be obtained in several variants.

According to a first variant, it is conceivable to subject the suspension to a constant shear rate.

However, the invention is not limited to this particular embodiment. For example, the shear rate can be distinct, at a given time, for two points of the suspension. Thus, by varying the geometry of the device used to generate the shear forces, it is possible to modulate the shear rate applied to said dispersion in time and / or space.

Since the dispersion is fluid when subjected to shear, each part thereof can be subjected to a shear rate that varies over time. The shear is said to be homogeneous when, irrespective of the variation in time of the shear rate, it passes through a minimum value which is the same for all the parts of the dispersion, at a given moment which may differ from one place to the other of dispersion.

It is conceivable to introduce the aqueous suspension of lime in the shearing device in the form of a total aqueous suspension (the entire suspension is introduced into the device) or in the form of a primary aqueous suspension (only a part suspension is introduced into the device). The shearing device can have various configurations. The exact configuration is not essential according to the invention since at the output of this device the entire dispersion has been subjected to the same minimum shear.

By way of illustration but not limitation of the devices that can be implemented according to the invention, to apply a homogeneous shear, mention may be made in particular of the IKA® Magic Lab mixer and the Dispax Reactor® DR2000.

According to one embodiment of the present invention, a rotor-stator type mixer is used to achieve said homogeneous shear, for example with a shear rate greater than 50,000 s ^-1 .

According to another embodiment, a mixer consisting of several rotor-stator pairs in direct series is used. According to one embodiment of the present invention, a mixer consisting of cylindrical pieces which have a tangential speed greater than 40 m / sec is used. A rotor-stator type mixer generally consists of two concentric disks defining an enclosure in which the primary dispersion circulates. One of the disks is immobile (stator) and the other animated with a uniform rotation around its axis (rotor). Such a device comprises a product supply pipe (in this case suspension of lime) which passes through the upper disk to open into the central part of the enclosure. The suspension passes through the gap formed between the stator and the rotor. The rotor (part of the device driven by a motor) and the stator (fixed part) are respectively constituted, on their outer ring, slots which allow the circulation of lime slurry to shear. Such a device also comprises an outlet pipe connected to a reservoir for receiving the suspension thus sheared.

The shearing device may comprise a recirculation loop which makes it possible to multiply the passages in the shearing device.

Thus, according to one embodiment, the device used to perform said homogeneous shear is equipped with a recirculation loop. According to one embodiment, a device configured for an energy expenditure of at least 1000 W / m is used to produce said homogeneous shear.

EXAMPLES

In all of the tests that follow the suspensions are evaluated using the parameters described below. The viscosity (expressed in mPa.s) of each suspension is measured at 20 ° C. with a Brookfield DVIII type viscometer. The indicated viscosity values are measured before stirring or after stirring, at a speed of 10 rpm and 100 rpm, and at different storage times. The viscosity values after 1 month of storage and after stirring of the suspension (by means of equipment of the Rayneri type, for example) are particularly relevant in order to evaluate the characteristics of the invention (influence of the polymer, influence of equipment, influence of the minimum degree of shear) with regard to the use of suspensions in industrial processes.

The sedimentation of each suspension is evaluated by measuring the height of the deposit in the container. The sedimentation values are expressed as, ie, the ratio of a deposition height to the total height of the suspension in the vessel multiplied by 100.

EXAMPLE 1

This example illustrates the use of different polymers (prior art, invention, except invention) in a process for preparing an aqueous suspension of calcium hydroxide (slaked lime) according to the invention. Several aqueous suspensions of calcium hydroxide, each having a solids content of 48 ± 1, are prepared in this example. 503 g of water and a quantity of a polymer corresponding to 1.41% by dry weight (based on the total weight of the solids in the suspension) are introduced into a container, said polymer being a polymer of prior art or a polymer of the present invention. Then 485 g of slaked lime (Supercalco® 97, Carmeuse) are stirred into the vessel.

A mixer of type IKA® Magic Lab adjusted to produce a shear of 82 000 s ^"1 is then fed by the mixture obtained in the previous step A recirculation loop allows several passages in the gap constituted by the rotor and the stator of the IKA mixer.

Once sheared, the suspension is stored for evaluation of these viscosity parameters, sedimentation and stability at 1 month. The polymers used in Example 1 have the following characteristics:

Trial 1-1:

This test illustrates the use, in a process according to the invention, of a homopolymer outside the invention, commercially available under the name Rheosperse® 3010, Coatex, France and consisting of acrylic acid monomers, 100% neutralized with sodium hydroxide (molecular weight: 4000 g / mol).

Test 1-2:

This test illustrates the use, in a process according to the invention, of a copolymer outside the invention, available commercially and consisting of acrylic acid monomers and macromonomers of vinyl-PEG structure ₂ ooo, ie Monomers having 46 units of ethylene oxide.

Thus, this comb structure polymer does not comprise, on the one hand, methacrylic acid monomers and, on the other hand, propylene oxide units on its macromonomers.

Test 1-3:

This test illustrates the use, in a process according to the invention, of a commercially available copolymer outside the invention consisting of 15% by weight of monomers acrylic acid and methacrylic acid monomers, as well as 85% by weight. macromonomers of MPEG ₅₀₀₀ (i.e. methoxy (EO) n _{3 units} ).

Thus this comb structure polymer does not comprise propylene oxide units on its macromonomers. Trials 1-4 to 1-8: copolymers of particular structure, according to the invention or outside the invention

These tests illustrate the use of water-soluble copolymers, according to the invention or outside the invention, having:

a negatively charged backbone composed of randomly polymerized acrylic acid and / or methacrylic acid monomers, and

uncharged side chains consisting of poly (alkylene glycol) units.

* Test 1-4: Excluding the invention

The copolymer has the following composition (in% by weight relative to the total weight of the copolymer):

12.8% of acrylic acid monomers,

87.2% of monomers of formula (I): R - X - R 'in which R represents a methacrylate function, R' denotes hydrogen, X represents a structure comprising

46 units of ethylene oxide EO and 15 units of propylene oxide OP, arranged randomly.

Molecular weight: 38,000 - 52,000 g / mol

Partial neutralization NaOH; pH: 3-4.5.

This copolymer containing no methacrylic acid monomers is a copolymer outside the invention.

* Test 1-5: According to the Invention The copolymer has the following composition (in% by weight relative to the total weight of the copolymer):

7.44% of methacrylic acid monomers,

92.56% of monomers of formula (I): R - X - R 'in which R represents a methacrylate function, R' denotes hydrogen, X represents a structure comprising 46 ethylene oxide units EO and units of propylene oxide OP, arranged randomly.

Molecular weight: 110,000 - 150,000 g / mol

Partial neutralization with NaOH; pH: 3-4.5. Test 1-6: according to the invention

19.8% of methacrylic acid monomers,

3% of acrylic acid monomers, and

77.2% of monomers of formula (I): R - X - R 'in which R represents a methacrylate function, R' denotes hydrogen, X represents a structure comprising 46 ethylene oxide units EO and 15 units of propylene oxide OP, arranged randomly.

Molecular weight: 34,000 - 44,000 g / mol

Total neutralization NaOH; pH: 7.7.

* Test 1-7: according to the invention

12.5% of methacrylic acid monomers,

87.5% of monomers of formula (I): R - X - R 'in which R represents a methacrylate function, R' denotes hydrogen, X represents a structure comprising

Molecular weight: 60,000 - 95,000 g / mol

Total neutralization NaOH; pH: 6.7-7.7.

* Test 1-8: Excluding the invention

24% of methacrylic acid monomers,

- 4.3% of acrylic acid monomers, and

- 71.7% of monomers of formula (I): R - X - R 'in which R represents a methacrylate function, R' denotes H, X represents a structure comprising 46 ethylene oxide units OE.

Neutralization: 100% NaOH Molecular weight: 17,900 g / mol

This copolymer, the monomers of formula (I) of which do not comprise propylene oxide units, is a copolymer outside the invention. The sedimentation results and various viscosity measurements are presented in Table 1 below:

Table 1

AANT: prior art

HINV: except invention

INV: invention

Apag: after agitation

Avag: before stirring

It is found first of all that the polymers of tests 1-1 (homopolymers of acrylic acid) and 1-8 (copolymers having no propylene oxide in its side chains) do not prevent sedimentation. The use of these polymers therefore does not solve the technical problem at the origin of the present invention.

The measurement of the viscosity at 10 rpm after stirring and at T0 shows that the polymers of tests 1-2 and 1-3 do not make it possible to obtain suspensions of slaked lime having rheological characteristics allowing their use in industrial processes, in particular rheological characteristics pumping suspensions. The suspension obtained in test 1-2 using a polymer of the prior art indeed has a viscosity of 9,840 mPa.s at T0 after stirring. The suspension obtained in test 1-3 using another polymer of the prior art has a viscosity of 1,940 mPa.s at T0 after stirring. These values, outside the range of claimed viscosities (between 25 and 1000 mPa.s at 20 ° C) are incompatible with the use of the expected suspensions. The measurement of the viscosity 10 rpm after stirring at T0 + 1 month shows that the polymer of the test 1-4 does not make it possible to obtain a concentrated suspension of lime which has a suitable viscosity. Indeed, this viscosity amounts to 16,460 s ^-1 .

The rheological profiles of the lime suspensions of the tests 1-5, 1-6 and 1-7 (use of a copolymer according to the invention) are in line with the use of suspensions in industrial processes.

EXAMPLE 2 This example illustrates the use of shearing equipment, which may be identical or different, optionally adjusted to different degrees of shear to prepare an aqueous suspension of calcium hydroxide (slaked lime) containing a copolymer according to the invention. A first series of three aqueous suspensions of calcium hydroxide (tests 2-1 to 2-3), each having a solids content of 48 ± 1, are prepared by introducing into a container of 503 g of water, and an amount of a polymer which corresponds to 1.41% by dry weight (based on the total weight of the solids in the suspension). Said polymer is that of test 1-5. Then, 485 g of slaked lime (Supercalco® 97, Carmeuse) are introduced with stirring into the container. A second series of three aqueous suspensions of calcium hydroxide (tests 2-4 to 2-6), each having a solids content of 48 ± 1, are prepared by feeding into a 503 g container of water and water. an amount corresponding to 1.41% by dry weight of a polymer (based on the total weight of the solids in the suspension), said polymer being that of test 1-6. Then, 485 g of slaked lime (Supercalco® 97, Carmeuse) are introduced with stirring into the container.

Tests 2-1 and 2-4 An ultraturax® type mixer (rotor-stator type) set to produce a shear of about 40,000 s ^-1 and which provides homogeneous shear according to the definition of the present invention is fed by the mixture obtained in the previous step.

A recirculation loop allows several passages in the mixer. The recirculation time is set at 15 minutes.

Tests 2-2 and 2-5

A Rayneri® type mixer set to produce a shear of about 3000 s ^-1 (which does not provide homogeneous shear as defined by the present invention) is fed by the mixture obtained in the previous step.

A recirculation loop allows several passages in the mixer. The recirculation time is set at 15 minutes. Tests 2-3 and 2-6

A mixer of the IKA® Magic Lab type set to produce a shear of 82,000 s ^-1 and which provides homogeneous shear as defined by the present invention is then fed with the mixture obtained in the previous step.

A recirculation loop allows several passages in the gap constituted by the rotor and the stator of the IKA mixer. The recirculation time is set at 15 minutes.

Once sheared, the suspensions are stored for evaluation of viscosity, sedimentation and stability parameters at 1 month. The sedimentation results and various viscosity measurements are presented in Table 2 below:

Table 2

HINV: except invention

INV: invention

Apag: after agitation

Avag: before stirring

It is firstly noted that the degree of shearing used in tests 2-1 and 2-4 (Ultraturax® set at 40,000 s ^"1 ) and tests 2-2 and 2-5 (3000 s mixer ^{" 1} ) does not prevent sedimentation.

On the other hand, the shear rate of tests 2-3 and 2-6 (IKA set at 82,000 s ^-1 ), combined with the use of a particular structural polymer, not only avoids the problem of sedimentation, but also to obtain suspensions whose rheological profile is adapted to the expected use. EXAMPLE 3

This example illustrates the use of two polymers according to the invention in a process for preparing an aqueous suspension of calcium hydroxide (slaked lime) with a high dry matter content (> to 50% by weight).

Two aqueous suspensions of calcium hydroxide, each having a solids content of 50 to 51%, are prepared in this example. 478 g of water and a quantity corresponding to 1.41% by dry weight of a polymer, based on the total weight of the solids in the suspension, are introduced into a container. Then, 505 g of slaked lime (Supercalco® 97, Carmeuse) are introduced with stirring into the container.

Once sheared, the suspension is stored for evaluation of its viscosity, sedimentation and stability parameters at 1 month.

The polymers used in this example have the following characteristics:

Test 3-1: according to the invention The copolymer has the following composition (in% by weight relative to the total weight of the copolymer):

7.44% of methacrylic acid monomers,

Molecular weight: 110,000 - 150,000 g / mol

Partial neutralization with NaOH; pH: 3-4.5. Test 3-2: according to the invention

19.8% of methacrylic acid monomers,

3% of acrylic acid monomers, and

Molecular weight: 34,000 - 44,000 g / mol

Total neutralization NaOH; pH: 7.7.

The sedimentation results and various viscosity measurements are presented in Table 3 below:

Table 3

Apag: after agitation

Avag: before stirring

The results demonstrate that it is possible, according to the process of the present invention, and using water-soluble copolymers of particular structure, to prepare high concentration slaked lime suspensions that remain stable over time. EXAMPLE 4

This example illustrates the use of two polymers according to the invention in a process for preparing an aqueous suspension of calcium hydroxide from two different types of starter lime, namely a lime having an average particle diameter. between 4 and 5 μιη (Supercalco® 97, Carmeuse) and a lime having an average particle diameter of between 2 and 3 μιη (Supercalco® 97/20, Carmeuse).

Several aqueous suspensions of calcium hydroxide, each having a solids content of 48 ± 1, are prepared in this example. 503 g of water and a quantity corresponding to 1.41% by dry weight of a polymer (based on the total weight of the solids in the suspension) are introduced into a container. Then, 485 g of slaked lime, specifically Supercalco® 97 (Carmeuse) in tests 4-1 and 4-3, or Supercalco® 97/20 (Carmeuse) in tests 4-2 and 4-4 are introduced with stirring into the recipient.

An IKA® Magic Lab type mixer set to produce a shear of 82,000 s ^-1 is then fed with the mixture obtained in the previous step.

A recirculation loop allows several passages in the gap constituted by the rotor and the stator of the IKA mixer.

Once sheared, the suspension is stored for evaluation of these viscosity, sedimentation and stability parameters at 1 month. The polymers used in this example have the following characteristics:

Tests 4-1 and 4-2: according to the invention

7.44% of methacrylic acid monomers,

92.56% of monomers of formula (I): R - X - R 'in which R represents a methacrylate function, R' denotes hydrogen, X represents a structure comprising 46 units of ethylene oxide EO and 15 units of propylene oxide OP, arranged randomly.

Molecular weight: 110,000 - 150,000 g / mol

Partial neutralization with NaOH; pH: 3-4.5.

Trials 4-3 and 4-4: according to the invention

19.8% of methacrylic acid monomers,

3% of acrylic acid monomers, and

Molecular weight: 34,000 - 44,000 g / mol

Total neutralization NaOH; pH: 7.7.

The sedimentation results and various viscosity measurements are presented in Table 4 below:

Table 4

Apag: after agitation

Avag: before stirring The results demonstrate that it is possible, according to the process of the present invention, by using water-soluble copolymers of particular structure, to prepare slurried suspensions of high concentration which remain stable over time, irrespective of the starting granulometry of slaked lime.

EXAMPLE 5

This example is intended to illustrate the levels of organic carbon (TOC or Total Organic Carbon) present in the aqueous phase of lime suspensions dispersed with the polymers of the prior art or with the polymers of the invention, and thus of determine the free polymer concentrations in the aqueous phase.

This example also makes it possible to illustrate the contents of soluble Ca ²⁺ ions present in the aqueous phase of lime suspensions dispersed with the polymers of the prior art or with the polymers of the invention.

Process for the preparation of suspensions

Several aqueous suspensions of calcium hydroxide, each having a solids content of 48 ± 1, are prepared in this example. 503 g of water and an amount corresponding to 1.41% by dry weight of a polymer (based on the total weight of the solids in the suspension) are introduced into a container, said polymer being according to the art. prior art or according to the present invention. Then, 485 g of slaked lime (Supercalco® 97, Carmeuse) are introduced with stirring into the container.

A mixer of type IKA® Magic Lab adjusted to produce a shear of 82 000 s ^"1 is then fed by the mixture obtained in the previous step A recirculation loop allows several passages in the gap constituted by the rotor and the stator of the mixer Dca.

Test 5-1

The copolymer has the following composition (in% by weight relative to the total weight of the copolymer): 7.44% of methacrylic acid monomers,

Molecular weight: 110,000 - 150,000 g / mol

Partial neutralization with NaOH; pH: 3-4.5.

Test 5-2

The copolymer has the following composition (in% by weight relative to the total weight of the copolymer): 12.8% of acrylic acid monomers,

87.2% of monomers of formula (I): R - X - R 'in which R represents a methacrylate function, R' denotes hydrogen, X represents a structure comprising 46 ethylene oxide units EO and units of propylene oxide OP, arranged randomly.

Molecular weight: 38,000 - 52,000 g / mol

Partial neutralization NaOH; pH: 3-4.5.

Trial 5-3

The polymer used is a homopolymer outside the invention, commercially available under the name Rheosperse® 3010, Coatex, France and consisting of acrylic acid monomers, 100% neutralized with sodium hydroxide (molecular weight: 4000 g / mol).

The suspensions obtained are filtered.

A sample of the filtrate is taken and analyzed according to the methods described below. TOC measurement

Total Organic Carbon (TOC) is measured using a Shimadzu TOC-V CSH, using a method based on a catalytic combustion oxidation method at 680 ° C.

The carbon atoms of the samples are oxidized to C0 ₂ . The eluent gas pushes C0 ₂ into a system that allows the removal of H ₂ 0 molecules and halogenated compounds. An IR (infrared) detector measures the C0 ₂ concentration. A calibration curve makes it possible to determine the carbon concentration in the sample.

Ion dosing:

The ion content is evaluated by means of ion chromatography using equipment of the type Metrohm 761 Compact IC. The separation of ions and polar molecules is based on their charge.

The results of TOC measurements and free Ca ²⁺ ion contents are given in Table 5 below:

Table 5

HINV: except invention

INV: invention

AANT: prior art First, it can be seen that the contents of free Ca ions vary considerably depending on the nature of the polymer used. This content of free Ca ²⁺ ions in a suspension of lime dispersed with a homopolymer of acrylic acid (test 5-3) is low compared to that of an aqueous suspension of lime dispersed with a copolymer having an acid skeleton (meth) acrylic and poly (alkylene glycol) side chains (tests 5-1 and 5-2).

In addition, although the amounts of starting polymer (1.41% dry weight) are identical for each of the suspensions, it is noted that the polymer concentrations in the filtrate of each slurry vary significantly depending on the polymer used. When the polymer used is a homopolymer of acrylic acid, the concentration of soluble polymer in the aqueous phase is almost zero.

In addition, less free copolymer remains in the filtrate of the lime slurry when using a copolymer according to the invention. Without being bound by any theory, it may be thought that the particular structure of the copolymer according to the invention is adapted to the chemical nature of the lime, which improves the chemical interactions between the copolymer and the Ca (OH) ₂ particles. Less free copolymer is found in the lime slurries prepared according to the process of the invention using a particular structural copolymer since more of it is adsorbed on the surface of the slaked lime particles.

It is thus demonstrated that subjecting a concentrated aqueous suspension of lime to a shearing operation under specific conditions in the presence of a copolymer according to the invention makes it possible to obtain a suspension of concentrated, stable lime which is novel with respect to the suspensions of lime of the prior art, because of the particular chemical interactions between the copolymers and the lime particles.

Claims

1. Use of a water-soluble copolymer consisting of:

methacrylic acid monomers and / or any of its salts,

optionally acrylic acid monomers and / or any of its salts,

monomers of formula (I):

R - X - R '

(D

according to which:

m and n are 2 non-zero integers and between 1 and 150,

2. An aqueous suspension of calcium hydroxide, comprising at least one copolymer consisting of:

methacrylic acid monomers and / or any of its salts,

optionally acrylic acid monomers and / or any of its salts,

monomers of formula (I):

R - X - R '

(D

according to which:

R 'denotes hydrogen or an alkyl group having from 1 to 4 carbon atoms, X represents a structure comprising n unit (s) of ethylene oxide EO and m unit (s) of propylene oxide OP, arranged randomly or in a regular manner,

m and n are 2 non-zero integers and ranging from 1 to 150.

3. Use according to claim 1 or suspension according to claim 2, wherein said suspension has a dry content of at least 40% by weight.

Use or suspension according to any one of the preceding claims, wherein the viscosity of said aqueous suspension measured by a Brookfield DVIII viscometer at 10 rpm is between 25 and 1000 mPa.s at 20 ° C.

Use or suspension according to any one of the preceding claims, wherein the copolymer has a molecular weight of between

30,000 and 200,000 g / mol as determined by size exclusion chromatography (CES).

6. Use or suspension according to any one of the preceding claims, wherein said monomer of formula (I) is such that n and m are two non-zero integers and n + m> 17.

7. Use or suspension according to any one of the preceding claims, wherein the R function of said monomer of formula (I) represents the methacrylate function.

8. Use or suspension according to any one of the preceding claims, wherein the R 'function of said monomer of formula (I) represents H or CH ₃ .

9. Use or suspension according to any one of the preceding claims, wherein said monomer of formula (I) consists of, expressed as a percentage by weight of each of its constituents: 5 to 30% by weight of methacrylic acid monomers and / or any of its salts,

0 to 10% by weight of acrylic acid monomers and / or any of its salts,

- 70 to 95% by weight of monomers of formula (I).

10. Use of the aqueous suspension of calcium hydroxide according to any one of claims 1, 3 to 9, for the treatment of industrial fumes, especially for the desulfurization of fumes, or for the treatment of domestic wastewater, including drinking water. , or industrial.

A process for preparing an aqueous suspension of calcium hydroxide according to any one of claims 2 to 9, comprising a step of subjecting the suspension to homogeneous shear.

12. The method of claim 11, wherein a homogeneous shear of shear greater than 50,000 s ^-1 is applied.

13. The method of claim 11 or 12, wherein a rotor-stator type mixer is used to effect said homogeneous shear.

14. Method according to any one of claims 11 to 13, wherein the device used to perform said homogeneous shear is equipped with a recirculation loop.

15. Method according to any one of claims 11 to 14, wherein is used to achieve said homogeneous shear a device configured for an energy expenditure of at least 1000 W / m.