Antifoaming magnesium hydroxide suspension

Description

Technical Field

[0001] The present invention relates to magnesium hydroxide suspensions and their uses, in particular in industrial processes requiring the use of alkaline agents and encountering foaming problems, such as agriculture, the food industry, textiles, inks and coatings, lubricants, the paper industry, biotechnologies and the water and gas treatment industry, more particularly in the field of municipal and industrial effluent treatment or the treatment of process water or wash water within an industrial process. This concerns in particular the field of gas wash water treatment within a wet or semi-wet flue gas desulfurization system and the treatment of effluents in a municipal or industrial wastewater treatment plant, in particular at the stages involving aeration (clarification, nitrification / denitrification, etc.), biological microorganisms (dephosphatation, biological, methanization, etc.) or the addition of chemicals such as polymers or disinfectants. Other applications of this suspension are, for example, industrial transformation processes or bioprocesses involving a fermentation process (vinification, beer production, etc.) or respiration. Finally, this suspension can also potentially be used during paper production, at all stages of its manufacture, from the production of paper pulp to its bleaching stage including the treatment of wastewater from the process or even for the recycling of the latter, particularly during the deinking stage. Prior art

[0002] The prior art contains various examples of formulation and use of magnesium hydroxide suspensions. These are generally concentrated suspensions of around 40 to 65% by mass of small particles per unit mass of suspension. Although there are many ways to formulate a suspension, two main production routes are distinguished in the state of the art: the suspension of solid particles of Mg(OH) 2 (or of previously hydrated MgO) in water or the method in which Mg(OH) 2 is directly precipitated from a magnesium salt.

[0003] Magnesium hydroxide suspensions are used in many applications as an alkali or alkaline agent (basic substance), such as neutralizing industrial acid waste, adjusting pH in wastewater treatment or gas scrubbing process water, or in pulp bleaching. Using a suspension, as opposed to using a powdered product, has several advantages. These include easier handling (dosing, transportation) and the assurance of using a product with consistent characteristics compared to a product formulated at the end user's site.

[0004] The performance of a magnesium hydroxide suspension is judged in light of two major criteria, its reactivity and its stability. These two parameters are intrinsically linked to the nature of the precursors and the method of preparation of the suspension, directly influencing the physicochemical parameters of the latter, the most important parameters being the concentration of solid matter as well as the size, shape and porosity of the particles.

[0005] The reactivity of a magnesium hydroxide suspension can be assimilated to the number of active sites per unit mass of the product and more broadly to the specific surface area (SSA) of the powder. Generally, we speak of reactivity under the cover of a kinetic approach. Mg(OH) 2 having by nature, a low solubility in water, a high reactivity is required for the suspension in all the aforementioned applications.

[0006] The stability of a magnesium hydroxide suspension encompasses several sub-criteria, the latter being almost exclusively linked to its implementation, use and handling including preparation, packaging, transport, flow, pumping, etc. The literature indicates that a suspension is pumpable when the viscosity level of the latter is such that its agitation (maintaining the suspension without sedimentation, re-homogenization, resuspension) and its movement (transport in pipe, pumping) are facilitated. Empirically, it has been determined that so-called pumpable magnesium hydroxide suspensions have a dynamic viscosity of less than 1000 mPa.s (measured using a Brookfield viscometer at 20°C at 1.7 s -1< ) ​​and preferably less than 700 mPa.s to be easily pumpable.

[0007] The rheological stability of a suspension is therefore generally reduced to its viscosity value. Generally speaking, the viscosity of a Mg(OH)2 suspension increases with an increase in the dry matter concentration of the suspension, with a decrease in the size of the Mg(OH)2 particles and an increase in their specific surface area.

[0008] Generally, the viscosity of magnesium hydroxide suspensions does not increase when the solids concentration remains below 40% by mass. In this case, the suspension behaves like a Newtonian fluid. However, the viscosity levels are not sufficient to keep the magnesium hydroxide particles suspended. The suspension then dephases very quickly and a bed of particles forms at the bottom of the container. This sediment is all the more coherent and difficult to disperse when the particles used are fine and reactive. Such a result is not possible because the suspension subsequently becomes unusable.

[0009] When the dry matter concentration exceeds 40% by mass, the viscosity increases abruptly and results in a non-Newtonian, shear-thinning and thixotropic fluid whose behavior is viscoelastic or even Binghamian. The behavior of these suspensions is linked to the existence of a 3D structure within the latter. When it is in place, it ensures sufficient viscosity so that the particles do not sediment too quickly. This structure is then destroyed by the application of a mechanical stress greater than the threshold stress of the material in order to cause flow. These transformations are reversible.

[0010] However, as the mineral load continues to increase, the interactions between the solid and the carrier liquid also continue to increase until a stage where the 3D structures created are no longer destructurable and structurable at will. The product then formed becomes very viscous and unusable. These changes in rheological behavior are the cause of many technical drawbacks, including the impossibility of stirring and transporting suspensions despite the application of high shear stresses.

[0011] In order to reduce these effects when increasing the amount of dry matter, the addition of a dispersing agent is a well-known practice in the state of the art. The addition of a dispersant leads to a decrease in viscosity by reducing the interactions between solid particles. Patent application US2017 / 0225961 discloses a list of dispersing agents that are particularly functional for magnesium hydroxide suspensions. These agents aim to reduce viscosity and therefore the negative effects linked to high viscosity values ​​so that the suspension can thus recover interesting rheological properties. These are the main rheological additives used in suspension formulations.

[0012] In some cases, it is also possible to add non-associative gelling agents or thickeners to increase viscosity at low speed gradients. The properties brought to the medium following this addition are, for example, an exacerbated and non-thixotropic shear-thinning behavior and a higher yield threshold. The advantage of these additives is that they do not have a high gradient effect. They are often used to improve storage stability. These agents include cellulose derivatives, xanthan gum, alginates, polyvinyl alcohols (PVA), polyethylene glycol (PEG) or polyoxyethylenes (POE), polyvinylpyrrolidones (PVP) or certain members of the acrylic (co)polymer (ASE) family.

[0013] The addition of such agents in the formulation will give rise to new complex interaction mechanisms solvent / particles, particles / particles, particles / agent, agent / agent, agent / solvent. Thus, the determination of the optimal dose is generally a meticulous empirical work. The suspension is then said to be in equilibrium and stable with respect to the rheological changes that may occur during its successive manipulations, it is notably less sensitive to the aging phenomena observed with certain suspensions.

[0014] Indeed, the aging of magnesium hydroxide suspensions is generally linked to variations in the specific surface area or the crystalline system of the particles but also to the re-agglomeration of particles between them leading to their sedimentation. The stability of a magnesium hydroxide suspension is generally evaluated over time. A suspension that is not very dependent on aging sees its viscosity change little over time.

[0015] Suspension aging can take place under stationary (resting phase), dynamic (agitation phase) or mixed (alternating rest-agitation) conditions. Aging under stationary conditions is generally characterized by more or less rapid sedimentation depending on the particle size, generating areas where the dry matter concentration is higher.

[0016] The aging phases of suspensions reflect common industrial practices (alternating storage and transport cycles). During these phases, agitation prevents sedimentation, which is detrimental to product optimization. The more stable a suspension is (under the conditions defined above), the less energy it will require to overcome its sedimentation. Furthermore, the greater stability of a suspension will reduce the risk of clogging in areas of low turbulence, particularly in pump cavities or at bends encountered in the hydraulic path.

[0017] In conclusion, the formulation of a magnesium hydroxide suspension with high reactivity and stability requires perfect control of the formulation of said suspensions, particularly in terms of the selection of the raw material and additives, their quantity, the sequence of addition of the latter and all the physical treatments applied during suspension (agitation, grinding, dilution, etc.). The result of such an operation is a suspension in equilibrium where any disturbance linked to the addition of a post-production chemical compound can disturb this equilibrium and reduce the reactivity and / or stability performance of the product.

[0018] Foaming problems are frequently encountered in industry. The foams encountered can be of different nature (aqueous, organic or biological). In all cases, they are characterized by the dispersion of gas bubbles (O 2 , CO 2 , air, etc.) in a liquid. The balance between the arrival of new bubbles on the surface and their persistence determines whether an accumulation of bubbles is possible and therefore whether the formation of a foam is possible. The persistence of this foam is conditioned by the stability of the gas / liquid interface separating the bubbles from each other. Thermodynamically, foams are unstable. On the other hand, they can be metastable for a given period of time. The factors having a direct impact on the stability of foams are the following: A - Drainage of bubble surfaces by gravity; B - Diffusion of gas through bubbles; C - Balance of attractive and repulsive forces between bubbles; D - Transport of liquid by capillarity within gas / liquid interfaces.

[0019] Certain chemical compounds have the ability to increase the persistence of foams. These are called foaming agents. These agents can be of different physicochemical nature. There are three main families of foaming agents. Surfactants are molecules generally composed of a hydrophilic polar head and a hydrophobic polar tail (effect on A, B, C and D). Macromolecules can be polymers or organic molecules, they generally act on A and C in their capacity as electrolyte or viscosity modifier. Solid particles can reduce the surface tension of liquids and thus participate in the stabilization of the foam. The combination of gas, liquid and solid particles gives rise to foam. The particles adhere to the gas / liquid interfaces and thus participate in strengthening them against destructive forces that can lead to the coalescence of the foam or foam (mechanical agitation, injection of pressurized air, etc.). They also reduce the drainage of the interface, further contributing to the stabilization of the foam.

[0020] Foaming problems can have adverse consequences on the proper operation of an industrial process or treatment process. The most common problem is the overflow of reactors containing foaming liquid, causing safety issues (treatment of contaminated effluents) or loss of production (fermentation tanks). The subsequent cleanup associated with these overflows is often tedious.

[0021] In the context of treatment processes or industrial processes involving the use of an alkali (or alkaline agent) and more particularly within a process for treating gas washing water within an on-board wet or semi-wet flue gas desulfurization system, foaming problems can be solved in different ways.

[0022] Among the solutions that can be easily implemented, we can cite: the reduction of cascade operations, the sealing of leaks, the reduction of gas velocity, the incorporation of expansion vessels, etc. Other, more restrictive solutions can be considered, in particular by modifying the size of the equipment used to transport or contain the (potentially) foaming liquid or adding auxiliary structures such as overflow or retention basins.

[0023] Mechanical methods can also be implemented, such as installing a spray device, a vacuum deaeration device, centrifugation, a wave generator, or an electrostatic dust removal device. It is also possible to modify the liquid temperature. Indeed, an increase in the latter lowers the surface tension of the liquid. Finally, the injection of dry air is also a potential solution, provided that it is well controlled so as not to cause the generation of additional foam.

[0024] However, these methods can be difficult to implement and are not always sufficient to effectively and optimally address foaming problems, particularly in the field of gas washing water treatment processes within an on-board wet or semi-wet flue gas desulfurization system. Indeed, the majority of these systems have been sized without taking into account the potential foaming problems that may arise within the unit but so that gas treatment is optimized. Therefore, modifying the process parameters is not trivial.

[0025] Similarly, these units, installed on board merchant ships or cruise ships, are generally located in narrow and confined areas of the ship. The installation of auxiliary structures or physical devices to disrupt foam stabilization imposes excessive technical, logistical and economic constraints. The same applies to devices to control the foam level within the system and remedy foaming problems by the continuous or periodic injection of a defoaming agent.

[0026] Another solution is to add an antifoam agent directly into the process.

[0027] US 5,624,568, US 4,561,897 and EP 0 114 755 disclose antifoam agents comprising a silicone-based oil and its use in an aqueous suspension of magnesium hydroxide. 11

[0028] However, the inventors surprisingly discovered that it was possible to use the alkaline agent represented by the magnesium hydroxide suspension as an anti-foaming agent by preparing a particular magnesium hydroxide suspension having such a function without the latter losing its reactivity and / or stability performance. Statement of the invention

[0029] The present invention therefore relates to an aqueous suspension of magnesium hydroxide comprising: (a) at least 40% by mass, preferably at least 50% by mass, more preferably at least 53% by mass, relative to the total mass of the suspension, of magnesium hydroxide particles; b) from 0.001% to 5% by mass, advantageously from 0.01% to 4% by mass, more advantageously from 0.1% to 3% by mass, relative to the total mass of the magnesium hydroxide, of at least one dispersant, advantageously selected from the group consisting of homopolymers or copolymers of acrylic acid or methacrylic acid and their salts and a mixture thereof and lignosulfonates and their mixtures, in particular chosen from polycarboxylates, polyether polycarboxylates, polyacrylates, polyacrylate copolymers, acrylic and / or methacrylic copolymers, salts (in particular polyacrylate salts) and a mixture thereof, and c) from 0.001% to 5% by mass, advantageously from 0.005% to 1% by mass, more advantageously from 0.01% to 0.5% by mass,relative to the total mass of the suspension, of at least one anti-foaming agent, advantageously selected from the group consisting of organic oils, polyglycols, fatty acid esters or polyesters and their mixtures, said oils or polyglycols being able to contain organic or mineral particles in suspension, characterized in that the at least one anti-foaming agent does not comprise silicone oil.

[0030] The suspension according to the invention therefore comprises (a) magnesium hydroxide particles in a content of at least 40% by mass, advantageously at least 50% by mass, more advantageously at least 53% by mass, relative to the total mass of the suspension. The content of these particles (a) can even be up to 58% by mass and even up to 65-70% by mass.

[0031] In one embodiment, the magnesium hydroxide particles have a volume average size, specifically a volume average diameter, D 90 of less than 200 µm, preferably less than 100 µm, in particular less than 45 µm, more preferably less than 25 µm, even more preferably less than 15 µm, measured by a laser granulometer, specifically the Mastersizer 2000 from Malvern Instruments, more specifically obtained after dilution of the suspension to 20000 th and passage through the granulometer.

[0032] In another embodiment, the magnesium hydroxide particles have a volume average size, specifically a volume average diameter, D 50 of less than 40 µm, preferably less than 20 µm, in particular less than 7 µm, even more preferably less than 2.5 µm, measured by a laser granulometer, specifically the Mastersizer 2000 from Malvern Instruments, more specifically obtained after dilution of the suspension to 20000 th< and passage through the granulometer.

[0033] In another embodiment, the specific surface area of ​​the magnesium hydroxide particles is between 5 and 100m 2 < / g measured by multipoint BET method by N 2 adsorption, in particular with Micromeritics Gemini VII equipment.

[0034] The suspension according to the invention therefore further comprises (b) at least one dispersant, in a content of 0.001% to 5% by mass, advantageously from 0.01% to 5% by mass, in particular from 0.01% to 4% by mass, more advantageously from 0.1% to 5% by mass, in particular from 0.1% to 3% by mass, relative to the total mass of magnesium hydroxide.

[0035] In a particular embodiment, the at least one dispersant is selected from the group consisting of homopolymers or copolymers of acrylic acid or methacrylic acid and their salts and a mixture thereof and lignosulfonates and their mixtures, in particular chosen from polycarboxylates, polyether polycarboxylates, polyacrylates, polyacrylate copolymers, acrylic and / or methacrylic copolymers, salts (in particular polyacrylate salts), such as sodium salts (in particular sodium polyacrylates) and a mixture thereof. Specifically the at least one dispersant is a polyether polycarboxylate or a polyacrylate, in particular a polyether polycarboxylate or polyacrylate salt, in particular a polyacrylate salt, more particularly a sodium polyacrylate.The dispersant may be in the form of an aqueous solution, in particular having a solids content of 40% by mass relative to the total mass of the aqueous dispersant solution. Advantageously, the dispersant is not or does not comprise alkyl benzene sulfonate, more advantageously it is not isopropylamine dodecyl benzene sulfonate.

[0036] The suspension according to the invention further comprises (c) at least one anti-foaming agent, in a content of 0.001% to 5% by mass, advantageously from 0.005% to 1% by mass, more advantageously from 0.01% to 0.5% by mass, even more advantageously in a content of between 0.01% and 0.05% by mass, in particular in a content of between 0.01% and 0.04% relative to the total mass of the suspension, characterized in that the at least one anti-foaming agent does not comprise silicone oil.

[0037] Said at least one anti-foaming agent does not comprise silicone oil (such as polydimethylsiloxanes in particular marketed by the company Kurita or by the company ArrMaz) or silicone product or polydimethylsiloxanes or silicone-based product or silicone oil-based product, more particularly with or without silica particles, more advantageously the anti-foaming agent is not a silicone oil, with or without silica particles, even more particularly the anti-foaming agent is not a polydimethylsiloxane with or without silica particles.

[0038] In a particular embodiment, the at least one anti-foaming agent is selected from the group consisting of organic oils (such as hydrocarbon oils), polyglycols, fatty acid esters or polyesters (such as polyester polyols esterified with natural fatty acids, in particular marketed by the company ArrMaz, natural fatty acid esters, in particular marketed by the company ArrMaz, and polyether polyols esterified with natural fatty acids, in particular marketed under the name Flofoam ™ < H by the company SNF) and mixtures thereof, said oils or polyglycols possibly containing organic particles (such as wax particles) or mineral particles (such as silica dioxide particles) in suspension.

[0039] In another particular embodiment, the at least one anti-foaming agent is selected from the group consisting of organic oils (such as hydrocarbon oils), fatty acid esters or polyesters (such as polyester polyols esterified with natural fatty acids, in particular marketed by the company ArrMaz, natural fatty acid esters, in particular marketed by the company ArrMaz, and polyether polyols esterified with natural fatty acids, in particular marketed under the name Flofoam ™ < H by the company SNF) and mixtures thereof, said oils possibly containing organic particles (such as wax particles) in suspension.

[0040] In yet another particular embodiment, the at least one anti-foaming agent is selected from the group consisting of organic oils (such as hydrocarbon oils), polyether polyols esterified by natural fatty acids (for example having a viscosity at 20°C of 200 mPa.s, and / or a density at 20°C of 0.92 g / cm 3< , in particular marketed under the name Flofoam ™< H by the company SNF, and mixtures thereof, said oils possibly containing organic particles (such as wax particles) in suspension.

[0041] In yet another particular embodiment, the at least one anti-foaming agent is a dispersion of organic particles, in particular wax, in an organic oil, in particular a hydrocarbon oil, advantageously a dispersion of wax particles in a hydrocarbon oil. More particularly, the at least one anti-foaming agent has a viscosity at 20°C of 350 mPa.s, and / or a density at 20°C of 0.855 g / cm 3< , and may be commercially available under the name Flofoam ™< D from the company SNF.

[0042] The aqueous suspension of magnesium hydroxide according to the invention therefore advantageously comprises water (d) as the sole solvent.

[0043] The suspension according to the invention may optionally also contain a non-associative thickener or gelling agent, in particular as described above (for example cellulose derivatives, xanthan gum, alginates, polyvinyl alcohols (PVA), polyethylene glycol (PEG) or polyoxyethylenes (POE), polyvinylpyrrolidones (PVP) or certain members of the acrylic (co)polymer (ASE) family), alkali salts (for example magnesium acetate, potassium nitrate), and acid conditioners (for example acetic acid, citric acid) or a mixture thereof.

[0044] In an advantageous embodiment, the aqueous suspension of magnesium hydroxide according to the invention consists essentially of, in particular of, the particles of magnesium hydroxide (a), the dispersant (b), the anti-foaming agent (c) and water (d) in the contents indicated above.

[0045] In one embodiment, the viscosity of the aqueous suspension of magnesium hydroxide according to the invention, measured at 1.7 s -1< at 20°C with a Brookfield viscometer, is less than 1000 mPa.s, preferably less than 700 mPa.s, in particular less than 300 mPa.s. In an advantageous embodiment, the aqueous suspension of magnesium hydroxide according to the invention is stable in the resting phase at room temperature. Advantageously, the result of its “7th day 2nd for test” is at least 90%.

[0046] The state of the art such as patent application US2017 / 0225961 indicates that the stability of a Magnesium Hydroxide suspension can be assessed using the Pour test method. This is a method that allows the mass quantity of product that can be extracted from a given container after 7 days or 14 days to be assessed.

[0047] In this test, 50 g of magnesium hydroxide suspension sample is poured into a 60 mL PP (polypropylene) or HDPE (high-density polyethylene) bottle. The total weight of the entire container is then measured, along with the height of the suspension's meniscus relative to the base of the container. The sample is then left to stand for 7 or 14 days.

[0048] After 7 or 14 days, the sediment level is located and the sediment height is measured relative to the base. Then, the container is opened and the product is allowed to flow for 30 seconds. Then the sample is resealed and the residual mass is evaluated. The resulting mass corresponds to the mass of the "7th day or 14th day - 1st for test". It is then compared to the initial mass of the sample and the extraction percentage is then calculated. Then the container is reacted and the product is again allowed to flow for 30 seconds. The sample is resealed and the residual mass is evaluated. The resulting mass corresponds to the mass of the "7th day or 14th day 2nd for test" and is then compared to the initial mass of the sample. The result is then expressed as the ratio (in %) between the mass of the “7th day or 14th day 2nd day for test” and the initial mass of the sample.

[0049] The present invention further relates to the use of the aqueous suspension of magnesium hydroxide according to the invention for the treatment of gas washing water within an on-board wet or semi-wet flue gas desulfurization system, the treatment of effluents in a municipal or industrial wastewater treatment plant, in particular at the stages involving aeration (clarification, nitrification / denitrification, etc.), biological microorganisms (dephosphatation, biological, methanization, etc.) or the addition of chemical products such as polymers or disinfectants, in industrial transformation processes or bioprocesses involving a fermentation process (vinification, beer production, etc.) or breathing or in the paper production process, in particular at all stages of its manufacture, from the production of the paper pulp to its bleaching stage including the treatment of wastewater from the process or even for the recycling of the latter, in particular during the deinking stage, or even in agriculture. In particular, this use is as an alkaline anti-foaming agent. Thus, advantageously, the aqueous suspension of magnesium hydroxide according to the invention is used in the fields of agriculture, the food industry, textiles, inks and coatings, lubricants, the paper industry, biotechnologies and the water and gas treatment industry, more particularly in the field of the treatment of municipal and industrial effluents or the treatment of process water or wash water within an industrial process.

[0050] The present invention will be better understood upon reading the description of the figures and examples which follow, which are given for informational purposes only, without limitation. Brief description of the drawings

[0051] There figure 1 represents the pH curve as a function of time of acidified water in which a standard magnesium hydroxide suspension (MH1, MH2 and MH3) or a magnesium hydroxide suspension according to the invention (MH1AM4, MH2AM4 and MH3AM4) is added to neutralize the effluent under the conditions of Example 2.1. figure 2 represents a schematic diagram of an on-board desulfurization system. EXAMPLES Example 1 : testing of different anti-foam agents

[0052] The tests were carried out in such a way as to come as close as possible to the foaming conditions encountered within an on-board wet or semi-wet flue gas desulfurization system.

[0053] The material used is: acidified seawater (pH = 2) (EDMA); a suspension of magnesium hydroxide (MH1) containing: 53% by mass relative to the total mass of the suspension of magnesium hydroxide particles with a particle size distribution D 10 = 0.67µm, D 50 = 2.18 µm and D 90 = 10.34 µm (measured by the Mastersizer 2000 laser granulometer from Malvern Instruments after dilution of the suspension to 20,000th and passage through the granulometer), and 0.25% by mass relative to the mass of particles of a Polyether polycarboxylate dispersant in aqueous solution having a solids content of 40%;a suspension of standard magnesium hydroxide (MH2) containing: 58% by mass relative to the total mass of the suspension of magnesium hydroxide particles with a particle size distribution D 10 = 2.36µm, D 50 = 16.2µm and D 90 = 66.4µm (measured by the Malvern Instruments Mastersizer 2000 laser granulometer after dilution of the suspension to 20,000th and passage through the granulometer), and 2.3% by mass relative to the mass of particles of a sodium polyacrylate dispersant in aqueous solution having a solids content of 40%;a suspension of magnesium hydroxide (MH3) containing: 53% by mass relative to the total mass of the suspension of magnesium hydroxide particles with particle size distribution D 10 = 0.96 µm, D 50 = 4.86 µm and D 90 = 37.42 µm (measured by the Mastersizer 2000 laser granulometer from Malvern Instruments after dilution of the suspension to 20000 th< and passage through the granulometer), and 5.0% by mass relative to the mass of particles of a dispersant belonging to the category of lignosulfonates and their mixtures in aqueous solution having a solid content of 40%; 5 different anti-foaming agents; Plastic stirring container filled to ¼: Volume: 80 mL Cylinder height: h = 8.3 cm.;

[0054] The shape of the container and the quantity of liquid added were selected to accentuate the foaming phenomena.

[0055] The different anti-foaming agents used are shown in Table 1 below. Table 1 - the anti-foaming agent AM7 is not according to the invention Anti-foam agent Supplier Chemical family AM1 ArrMarz (USA) Polyester polyol(s) esterified with natural fatty acids AM4 SNF (FR) (Flofoam D) Hydrocarbon dispersion of organic components AM5 ArrMarz (USA) Polyester polyol(s) esterified with natural fatty acids AM6 SNF (FR) (Flofoam H) Mixtures of polyether polyols esterified with natural fatty acids AM7 Kurita (FR) Polydimethylsiloxanes

[0056] The test methodology is as follows: 1. 20 mL of EDMA is added to the container. 2. A quantity of 6 to 24 mg / L of magnesium hydroxide suspension is then added to neutralize the water to a pH of 6. 3. A quantity of 5 ppm relative to the amount of liquid present in the antifoam agent medium is then added to the system. 4. The container is sealed and then manually agitated for 30 seconds. 5. The height of the foam formed is measured in % relative to the total height of the cylinder. 6. A second dose of 15 ppm relative to the amount of liquid present in the antifoam agent medium is then added and steps 4 and 5 are repeated. 7. A third dose of 30 ppm relative to the amount of liquid present in the antifoam agent medium is then added and steps 4 and 5 are repeated.

[0057] The results are collected in the following Table 2. Table 2 Suspension Anti-foam agent total dosage in ppm relative to the quantity of liquid present in the medium residual foam height in % Comments MH1 AM1 5 8,3 Low unstable foam - Very rapid coalescence MH1 AM1 15 0 No foaming MH1 AM4 5 0 No foaming MH1 AM5 5 8,3 Light, uneven foam - Rapid coalescence MH1 AM5 15 0 No foaming MH1 AM6 5 0 No foaming MH1 AM7 5 8,3 Light, uneven foam - Medium coalescence MH1 AM7 15 8,3 Light, uneven foam - Medium coalescence MH1 AM7 30 0 No foaming MH2 AM4 5 0 No foaming MH3 AM4 5 0 No foaming

[0058] Much more antifoam agent AM7 (30 ppm) is required to achieve an absence of foaming. Agent AM7 is not according to the invention. It is therefore the least effective antifoam agent. Although all other antifoam agents have an effect, antifoam agents AM4 and AM6 demonstrated optimal effectiveness in this test. Indeed, they prevent the appearance of foaming for the minimum dose added to the effluent. Therefore, the experiments with these agents were repeated using process water (pH = 5, presence of sulfates and residues from incomplete combustion of heavy fuel oil) previously acidified to evaluate whether the effectiveness of these agents is maintained in a context closer to reality. The results are summarized in Table 3 below. Table 3 Suspension Anti-foam agent total dosage in ppm relative to the quantity of liquid present in the medium residual foam height in % Comments MH1 AM4 5 0 No foaming MH1 AM6 5 5 Light peripheral foam - Fairly rapid coalescence MH2 AM4 5 0 No foaming MH3 AM4 5 0 No foaming

[0059] It therefore appears that the antifoam agent AM4 is the agent with the greatest antifoaming power for the system in question. The other examples were carried out with this antifoam agent. Example 2 : reactivity and stability tests of the suspension according to the invention containing the anti-foam AM4

[0060] These tests aim to evaluate the antifoaming properties of the suspension according to the invention containing the antifoam AM4 while quantifying the impact of the addition of this antifoam on its reactivity and stability. Example 2.1: Suspension reactivity

[0061] The material used is: acidified drinking water to pH = 3; a suspension of standard magnesium hydroxide (MH1) containing: 53% by mass relative to the total mass of the suspension of magnesium hydroxide particles with particle size distribution D 10 = 0.67µm, D 50 = 2.18 µm and D 90 = 10.34 µm (measured by the Mastersizer 2000 laser granulometer from Malvern Instruments after dilution of the suspension to 20,000th and passage through the granulometer), and 0.25% by mass relative to the mass of particles of a Polyether polycarboxylate dispersant in aqueous solution having a solids content of 40%;a magnesium hydroxide suspension according to the invention (MH1AM4) containing: 53% by mass relative to the total mass of the suspension of magnesium hydroxide particles with a particle size distribution D 10 = 0.67µm, D 50 = 2.18 µm and D 90 = 10.34 µm (measured by the Mastersizer 2000 laser granulometer from Malvern Instruments after dilution of the suspension to 20,000th and passage through the granulometer), 0.25% by mass relative to the mass of particles of a Polyether polycarboxylate dispersant in aqueous solution having a solids content of 40% and 1000 ppm of anti-foaming agent AM4;a suspension of standard magnesium hydroxide (MH2) containing: 58% by mass relative to the total mass of the suspension of magnesium hydroxide particles with a particle size distribution D 10 = 2.36µm, D 50 = 16.2µm and D 90 = 66.4µm (measured by the Malvern Instruments Mastersizer 2000 laser granulometer after dilution of the suspension to 20,000th and passage through the granulometer), and 2.3% by mass relative to the mass of particles of a sodium polyacrylate dispersant in aqueous solution having a solids content of 40%;a magnesium hydroxide suspension according to the invention (MH2AM4) containing: 58% by mass relative to the total mass of the suspension of magnesium hydroxide particles with a particle size distribution D 10 = 2.36 µm, D 50 = 16.2 µm and D 90 = 66.4 µm (measured by the Mastersizer 2000 laser granulometer from Malvern Instruments after dilution of the suspension to 20,000 th and passage through the granulometer), and 2.3% by mass relative to the mass of particles of a sodium polyacrylate dispersant in aqueous solution having a solids content of 40% and 1000 ppm of anti-foam agent AM4;a suspension of standard magnesium hydroxide (MH3) containing: 53% by mass relative to the total mass of the suspension of magnesium hydroxide particles with distribution D 10 = 0.96 µm, D 50 = 4.86 µm and D 90 = 37.42 µm (measured by the Mastersizer 2000 laser granulometer from Malvern Instruments after dilution of the suspension to 20,000 th and passage through the granulometer), and 5.0% by mass relative to the mass of particles of a dispersant belonging to the category of lignosulfonates and their mixtures having a solids content of 40%;a magnesium hydroxide suspension according to the invention (MH3AM4) containing: 53% by mass relative to the total mass of the suspension of magnesium hydroxide particles with a particle size distribution D 10 = 0.96 µm, D 50 = 4.86 µm and D 90 = 37.42 µm (measured by the Mastersizer 2000 laser granulometer from Malvern Instruments after dilution of the suspension to 20,000 th and passage through the granulometer), and 5.0% by mass relative to the mass of particles of a dispersant belonging to the category of lignosulfonates and their mixtures having a solids content of 40% and 1000 ppm of anti-foaming agent AM4; a pH meter. ;

[0062] The test methodology is as follows: A dose of 1700 mg / L of magnesium hydroxide suspension is added to neutralize the effluent. The evolution of the pH of the solution is monitored over time and plotted.

[0063] The results are represented in the figure 1. In view of the results, the reactivity of a suspension according to the invention containing 1000 ppm of anti-foam agent AM4 is little impacted by its presence. The kinetic behavior of the two suspensions becomes identical again after 3.5 minutes of reaction. The times allowed for alkalis to react within an industrial system are of a greater order of magnitude. Example 2.2: Suspension stability

[0064] The material used is: a suspension of standard magnesium hydroxide (MH1) as described in Example 2.1; a suspension of magnesium hydroxide according to the invention (MH1AM4) containing: 53% by mass relative to the total mass of the suspension of magnesium hydroxide particles with a particle size distribution D 10 = 0.67 µm, D 50 = 2.18 µm and D 90 = 10.34 µm (measured by the Mastersizer 2000 laser granulometer from Malvern Instruments after dilution of the suspension to 20,000 th and passage through the granulometer), 0.25% by mass relative to the mass of particles of a Polyether polycarboxylate dispersant in aqueous solution having a solids content of 40% and from 200 to 500 ppm of anti-foaming agent AM4; a suspension of standard magnesium hydroxide (MH2) as described in Example 2.1; a magnesium hydroxide suspension according to the invention (MH2AM4) containing: 58% by mass relative to the total mass of the suspension of magnesium hydroxide particles with a particle size distribution D 10 = 2.36 µm, D 50 = 16.2 µm and D 90 = 66.4 µm (measured by the Mastersizer 2000 laser granulometer from Malvern Instruments after dilution of the suspension to 20,000 th and passage through the granulometer), and 2.3% by mass relative to the mass of particles of a sodium polyacrylate dispersant in aqueous solution having a solids content of 40% and 200 to 500 ppm of anti-foam agent AM4; a standard magnesium hydroxide suspension (MH3) as described in Example 2.1; a suspension of magnesium hydroxide according to the invention (MH3AM4) containing: 53% by mass relative to the total mass of the suspension of magnesium hydroxide particles with a particle size distribution D 10 = 0.96 µm, D 50 = 4.86 µm and D 90 = 37.42 µm (measured by the Mastersizer 2000 laser granulometer from Malvern Instruments after dilution of the suspension to 20,000 th and passage through the granulometer), and 5.0% by mass relative to the mass of particles of a dispersant belonging to the category of lignosulfonates and their mixtures having a solids content of 40% and 200 to 500 ppm of anti-foaming agent; Brookfield “RV series” viscometer.

[0065] The viscosity of the suspensions tested is measured at 1.7 s -1< and at 20°C. The results are presented in Table 4 below. Table 4 N° Suspension AM 4 dose (ppm) Viscosity (mPa.s) Comments 1 MH1 0 180 Original MH1 standard suspension 2 MH1AM4 200 180 No macroscopic changes visible to the naked eye 3 MH1AM4 300 170 No macroscopic changes visible to the naked eye 4 MH1AM4 400 150 No macroscopic changes visible to the naked eye 5 MH1AM4 500 150 No macroscopic changes visible to the naked eye 6 MH2 0 130 Standard suspension original MH2 7 MH2AM4 200 130 No macroscopic changes visible to the naked eye 8 MH2AM4 300 120 No macroscopic changes visible to the naked eye 9 MH2AM4 400 120 No macroscopic changes visible to the naked eye 10 MH2AM4 500 120 No macroscopic changes visible to the naked eye 11 MH3 0 100 Original MH3 standard suspension 12 MH3AM4 200 100 No macroscopic changes visible to the naked eye 13 MH3AM4 300 110 No macroscopic changes visible to the naked eye 14 MH3AM4 400 110 No macroscopic changes visible to the naked eye 15 MH3AM4 500 110 No macroscopic changes visible to the naked eye

[0066] The viscosity of the suspension according to the invention remains within the preferred viscosity scale obtained after formulation. Example 2.3: Foaming test with the antifoaming agent incorporated into the suspension

[0067] The material used is: 1L beaker; High shear mixer; a standard magnesium hydroxide suspension (MH1) as described in Example 2.1; a magnesium hydroxide suspension according to the invention (MH1AM4) containing: 53% by mass relative to the total mass of the suspension of magnesium hydroxide particles with a particle size distribution D 10 = 0.67µm, D 50 = 2.18µm and D 90 = 10.34µm (measured by the Malvern Instruments Mastersizer 2000 laser granulometer after dilution of the suspension to 20,000th and passage through the granulometer), 0.25% by mass relative to the mass of particles of a Polyether polycarboxylate dispersant in aqueous solution having a solids content of 40% and 300 ppm of AM4 antifoaming agent;a suspension of magnesium hydroxide without dispersant (MH1') containing: 53% by mass relative to the total mass of the suspension of magnesium hydroxide particles with particle size distribution D 10 = 0.67µm, D 50 = 2.18 µm and D 90 = 10.34 µm (measured by the Mastersizer 2000 laser granulometer from Malvern Instruments after dilution of the suspension to 20000 th< and passage through the granulometer); a dispersant solution (D1) containing Polyether polycarboxylate in concentrated aqueous solution at 2% by mass relative to the mass of water; a standard magnesium hydroxide suspension (MH2) as described in Example 2.1;a magnesium hydroxide suspension according to the invention (MH2AM4) containing: 58% by mass relative to the total mass of the suspension of magnesium hydroxide particles with a particle size distribution D 10 = 2.36 µm, D 50 = 16.2 µm and D 90 = 66.4 µm (measured by the Mastersizer 2000 laser granulometer from Malvern Instruments after dilution of the suspension to 20,000 th and passage through the granulometer), and 2.3% by mass relative to the mass of particles of a sodium polyacrylate dispersant in aqueous solution having a solids content of 40% and 300 ppm of anti-foam agent AM4; a dispersant solution (D2) containing sodium polyacrylate in aqueous solution concentrated at 2% by mass relative to the mass of water; a suspension of standard magnesium hydroxide (MH3) as described in Example 2.1;a magnesium hydroxide suspension according to the invention (MH3AM4) containing: 53% by mass relative to the total mass of the suspension of magnesium hydroxide particles with a particle size distribution D 10 = 0.96 µm, D 50 = 4.86 µm and D 90 = 37.42 µm (measured by the Mastersizer 2000 laser granulometer from Malvern Instruments after dilution of the suspension to 20,000 th and passage through the granulometer), and 5.0% by mass relative to the mass of particles of a dispersant belonging to the category of lignosulfonates in aqueous solution having a solids content of 40% and 300 ppm of anti-foam agent AM4; a dispersant solution (D3) containing sodium lignosulfonate in concentrated aqueous solution at 4% by mass relative to the mass of water. ;

[0068] The test methodology is as follows: Dilution of the suspension evaluated by 10. The pH of this solution is such that: pH = 10; 400 mL of suspension or solution are stirred vigorously for 10 minutes; The incremental volume rate is measured and determined in % volume. The change in incremental volume after the end of stirring is evaluated qualitatively

[0069] The results are presented in Table 5 below. Table 5 N° Essay typology Volume increment (%) Evolution of foam 1 Diluted MH1 standard suspension 8 % Stable foam Slow coalescence 3 MH1 standard suspension aged for one year 7,5 % Stable foam Slow coalescence 4 Dispersant Solution D1 2 % Light foaming Fairly rapid coalescence 5 MH1' suspension without diluted dispersant 0 % No foaming 6 MH1AM4 suspension according to the invention diluted 2 % Unstable foam Rapid coalescence 7 MH1AM4 suspension according to the invention aged for 2 months diluted 2 % Unstable foam Rapid coalescence 8 Diluted MH2 standard suspension 4% Light foaming Fairly rapid coalescence 9 Dispersant Solution D2 2 % Light foaming Fairly rapid coalescence 10 MH2AM4 suspension according to the invention diluted 0% No foaming 11 Diluted MH3 standard suspension 4% Light foaming Fairly rapid coalescence 12 Dispersant Solution D3 2% Light foaming Fairly rapid coalescence 13 MH3AM4 suspension according to the invention diluted 0% No foaming

[0070] The results show that the antifoam agent AM4 is effective in reducing the foaming phenomenon caused by the simultaneous presence of solid particles and dispersant molecules in a system which could correspond to a situation of overdose in suspension of magnesium hydroxide.

[0071] Furthermore, there is no aging effect on the anti-foaming properties of the suspension according to the invention during the first 2 months. Example 3: full-scale test of the suspension according to the invention containing the anti-foam AM4

[0072] The protocol is as follows: Vessel A is a container ship 400 m long and 60 m wide. Consuming heavy fuel oil (> 2% by mass of Sulphur), it complies with the regulations of the International Maritime Organisation (IMO) by carrying out a scrubbing of its exhaust gases, a wet desulphurisation with Close Loop operating cycles.

[0073] Ship A therefore needs an alkaline agent to neutralize the acidity caused by the absorption of SO2 in its wash water. The alkaline agent chosen is a suspension of magnesium hydroxide.

[0074] During operation, an overflow of the washing solution storage tank (labeled "holding tank") was observed on the diagram of the figure 2The origin of the causes of this overflow was investigated and determined. Indeed, the storage tank is equipped with vents allowing the depressurization of the tank following the arrival of air in the latter due to the transport in pipes not completely submerged. The extraction capacity of these vents is such that they are capable of extracting foam, much less dense than the carrier liquid, towards the outside of the tank. This foam overflows and is deposited on the deck of the ship. Once deposited, it coalesces and leaves room for a polluted liquid presenting a risk to passengers and personnel on board.

[0075] Before using a magnesium hydroxide suspension according to the invention as a means of remediation, several solutions were investigated without giving conclusive results. These solutions correspond to modifications of the on-board desulfurization system: Changed the water level setting within the tank. Reduced the velocity of the washing solution arriving within the tank while ensuring the treatment efficiency is maintained. Changed the regulation algorithm at the pH threshold level to minimize overdosing problems.

[0076] Although the implementation of these solutions yielded encouraging results, they were not sufficient to eliminate the foaming problem in all scenarios of use of the on-board desulfurization system. Overflow problems were still observed when the main scrubber treated the exhaust gases from the main engine when the latter was operating at more than 20% of its maximum speed.

[0077] Thus, the use of a magnesium hydroxide suspension with anti-foaming properties was considered, said suspension containing: 53% by mass relative to the total mass of the suspension of magnesium hydroxide particles with particle size distribution D 10 = 0.67µm, D 50 = 2.18 µm and D 90 = 10.34 µm (measured by the Mastersizer 2000 laser granulometer from Malvern Instruments after dilution of the suspension to 20000 th and passage through the granulometer), 0.25% by mass relative to the mass of particles of a dispersant (Polyether polycarboxylate in aqueous solution) having a solids content of 40% and 300 ppm of anti-foam agent AM4. Test results

[0078] The use of the magnesium hydroxide suspension according to the invention made it possible to eliminate the foaming problem not only for previously problematic operating conditions (engine load > 20%) but also in extreme main engine stress scenarios (up to engine load > 65%).

[0079] Additionally, the use of this suspension had no significant impact on: The quantity of magnesium hydroxide suspension consumed; The pH levels reached in the tank; The effectiveness of the desulfurization process and The proper conduct of post-use water treatment operations.

[0080] It is therefore possible to conclude that the magnesium hydroxide suspension according to the invention effectively addresses the problem of foaming during the treatment of gas washing water within an on-board wet or semi-wet flue gas desulfurization system.

Claims

1. An aqueous magnesium hydroxide suspension comprising: a) at least 40 wt.%, advantageously at least 50 wt.%, more preferably at least 53 wt.%, relative to the total weight of the suspension, of magnesium hydroxide particles; b) from 0.001 to 5 wt.%, advantageously from 0.01 to 4 wt.%, more advantageously from 0.1 to 3 wt.%, relative to the total weight of the magnesium hydroxide, of at least one dispersant, advantageously selected from the group consisting of homopolymers or copolymers of acrylic acid or methacrylic acid and their salts and a mixture thereof and lignosulfonates and mixtures thereof, in particular selected from polycarboxylates, polyether polycarboxylates, polyacrylates, polyacrylate copolymers, acrylic and / or methacrylic copolymers, salts and a mixture thereof, and c) from 0.001 to 5 wt.%, advantageously from 0.005 to 1 wt.%, more advantageously from 0.01 to 0.5 wt.%, relative to the total weight of the suspension, of at least one anti-foaming agent, advantageously selected from the group consisting of organic oils, polyglycols, fatty acid esters or polyesters and mixtures thereof, said oils or polyglycols possibly containing organic or mineral particles in suspension characterized in that the at least one anti-foaming agent does not comprise silicone oil.

2. The aqueous suspension according to claim 1, characterized in that the at least one dispersant is a polyether polycarboxylate or a polyacrylate, in particular a polyether polycarboxylate or polyacrylate salt, more particularly a sodium polyacrylate.

3. The aqueous suspension according to any one of claims 1 or 2, characterized in that the at least one anti-foaming agent is a dispersion of organic particles, in particular of wax, in an organic oil, in particular a hydrocarbon oil, advantageously a dispersion of wax particles in a hydrocarbon oil.

4. The aqueous suspension according to any one of claims 1 to 3, characterized in that the magnesium hydroxide particles have a volume average size D90 less than 200 µm, preferably less than 45 µm, even more preferably less than 15 µm, measured by a laser particle size analyzer.

5. The aqueous suspension according to any one of claims 1 to 4, characterized in that the magnesium hydroxide particles have a volume average size D50 less than 40 µm, preferably less than 7 µm, measured by a laser particle size analyzer.

6. The aqueous suspension according to any one of claims 1 to 5, characterized in that its viscosity measured at 1.7 s-1 at 20°C with a Brookfield viscometer, is less than 1000 mPa.s, preferably less than 700 mPa.s.

7. The aqueous suspension according to any one of claims 1 to 6, characterized in that it is stable in the rest phase at room temperature, in particular the result of its "7th day 2nd pour test" is at least 90%.

8. The aqueous suspension according to any one of claims 1 to 7, characterized in that the specific surface area of the magnesium hydroxide particles is comprised between 5 and 100 m2 / g.

9. A use of the aqueous suspension according to any one of claims 1 to 8 for the treatment of gas washing water in an on-board wet or semiwet flue gas desulfurization system, the treatment of effluent at a municipal or industrial wastewater treatment plant, in industrial transformation processes or bioprocesses involving a fermentation or respiration process or in the paper production process or in agriculture.

10. The use according to claim 9 as an alkaline anti-foaming agent.