WO2023139405A1

WO2023139405A1 - Method for forming dispersing agents in a colloidal clay aqueous suspension for the ceramic manufacturing industry

Info

Publication number: WO2023139405A1
Application number: PCT/IB2022/050450
Authority: WO
Inventors: Raúl Andrés BECERRA ARCINIEGAS
Original assignee: Becerra Arciniegas Raul Andres
Priority date: 2022-01-19
Filing date: 2022-01-19
Publication date: 2023-07-27

Abstract

The present invention relates to the manufacture of ceramic tiles from colloidal clay aqueous suspensions by using dispersing agents for their stabilisation and improvement of their rheological properties. The invention relates to a first subprocess of obtaining sodium or potassium silicate from the mixture of sand, caustic soda and water, heating and regulated pressure, favouring the formation of the β-crystalline structure in the product; a second subprocess of manufacturing polyacrylic acid with low molecular weight and low polydispersity; a third subprocess of neutralising the polyacrylic acid with the aforementioned dispersing agents; and a fourth subprocess of obtaining the deflocculant by mixing the alkaline silicate and the neutralised polyacrylate obtained with the dispersing/neutralising agents. The invention can be applied to dispersion systems of clay/water which must have a low viscosity and high density to be used in the manufacture of ceramic tiles, obtaining a low manufacturing cost and easy handling of the slip.

Description

PROCESS OF FORMATION OF DISPERSING AGENTS IN CLAY COLLOIDAL AQUEOUS SUSPENSION FOR THE CERAMIC MANUFACTURING INDUSTRY

OBJECT OF THE INVENTION.

The object of the present invention is a process for shaping dispersing agents in clayey colloidal aqueous suspension for the ceramic manufacturing industry.

Particularly, it is related to the synergy between dispersing agents in clayey colloidal aqueous suspensions used in the ceramic manufacturing industry.

It is also an object of the present invention to prepare shaped dispersing agents from a synergistic mixture of organic and inorganic compounds in the process of grinding clays in aqueous systems such as slip.

A no less important object of the present invention is to form dispersing agents in clayey colloidal aqueous suspension suitable for the handling, transport and processability of clays in the wet method in the manufacture of ceramic tablets.

From the present invention, the synergistic mixture between sodium and/or potassium silicate synthesized by the hydrothermal method, a polyacrylic acid with low polydispersity and the use of co-dispersing agents, generates a significant improvement in the behavior rheology of clay suspensions and also decreases the negative effect of thickening as a function of time of the slips (thixotropy), which results in a reduction in the cost of the product with excellent performance in the plant.

Other objects will become apparent to those skilled in the art from the present description.

FIELD OF THE INVENTION.

The present invention relates to the manufacture of ceramic tiles from clayey colloidal suspensions stabilized with dispersing agents.

More precisely, it initially provides for a first sub-process for obtaining sodium or potassium silicate from the mixture of sand, caustic soda and water, heating and regulated pressure in order to favor the formation of the silicate with the presence of a crystalline structure p in the product in any proportion; a second thread for the manufacture of low molecular weight and low polydispersity polyacrylic acid; a third thread that includes the neutralization of the polyacrylic acid; and, finally, a fourth sub-process that includes obtaining the deflocculant by mixing the alkaline silicate and the neutralized polyacrylate obtained with the co-dispersing/neutralizing agents in a stirred tank.

The invention is applicable to obtained clay dispersions that must have a low viscosity and high density to be used in the manufacture of ceramic tiles to obtain a low manufacturing cost and easy handling of the slip in the process.

The specific difference is the use of co-dispersing agents as neutralizers for low polydispersity polyacrylic acid. These allow to decrease the amount of polymer/co-dispersant within the deflocculant formulation which significantly reduces the cost of the deflocculant. as it is the most expensive component in the mix. In addition, this modification provides excellent performance as a deflocculant in wet grinding of clays for the ceramic sector, as shown in figure 1.

Additionally, we want to extend this concept to mixtures with alkaline silicates that contain L¡+, K+ and/or Na+ as counter ions.

In the same way, polyachlates containing L¡+, K+ and/or Na+ as counter ions. In a range of 1 -99% of the amount of these components.

BACKGROUND OF THE INVENTION.

Commercial deflocculants are generally a mixture of sodium silicate and sodium polyachlate in different proportions. Sodium silicate is obtained by reaction at high temperatures of approximately 1000 °C of sodium carbonate and sand, commonly known as furnace synthesis. This method presents the drawbacks of generating carbonaceous impurities and high ratios of silicon oxide/sodium oxide (SIO2/Na2Ü) between 2.0 -3.0. The sodium polyacrylates used in these formulations are regularly of low molecular weight, the products found on the market have a high polydispersity between macromolecules with a Mw/Mn> 2.6, this irregularity between polymer chains decreases the dispersing power of sodium polyacrylate. These drawbacks require a high demand for the sodium silicate/polyacrylate mixture to obtain good slip properties such as: low viscosity and high density.

The use of co-dispersing agents decreases the polymer requirement in the deflocculant mixture. In addition, the demand for deflocculant in the clay grinding process decreases, since in these the co-dispersant has the ability to adsorb between the laminar structure of the clays, promoting the distance between these laminas, eliminating swelling processes produced when interacting with water. Also The use of co-dispersing agents contributes to breaking the weak interactions between colloidal particles in the slip dispersion, as a consequence a decrease in the thixotropic effect of the slip is observed. The prior art technique also discloses the preparation of polyacrylic acids by free radical polymerization of the corresponding acid has been known for a long time and is carried out according to various processes (see Kirk-Othmer, "Encyclopedia of Chemical Technology", 2-edition, Interscience Public Publishers 1963, Volume I, p.306). A conventional method of the state of the art consists in polymerizing acrylic acid in aqueous solution or in an organic solvent medium, such as benzene. In general, the polymerization of acrylic acid is carried out in the aqueous phase in the presence of initiators, such as hydrogen peroxide, sodium persulfate or potassium persulfate, or organic peroxides, or the polymerization is initiated with a redox system composed, for example, of potassium persulfate and sodium thiosulfate. According to the traditional technique, it is convenient to carry out the polymerization, in aqueous solution, using solutions that have a monomer concentration of less than 25%, since, in the case of more concentrated solutions, the polymerization is difficult to control due to the high heat of polymerization, evolved.

A traditional method of controlling molecular weights is to introduce an agent to limit the length of the polymer chains, and US Patent No. 2,789,099 to Gagne describes the use for this purpose of a system composed of sodium hypophosphite and copper acetate. It is also possible to use alcohols as chain transfer agents, but the disadvantage of such a process is that partial esterification of the polyacrylic acid takes place, and this does not provide the desired objective. Accordingly, the technique requires improving the properties of the deflocculant. More precisely, it is required to form a Deflocculant that reduces the interaction between colloidal particles in aqueous suspension, which is achieved with a polymer that has a regular chain size and additives that generate a high surface charge density on the colloidal particle, producing low viscosity and high density in the slips used in the manufacture of ceramic tiles to obtain a low manufacturing cost and easy handling of the slip in the process.

The present invention meets these needs and provides other related advantages.

BRIEF DESCRIPTION OF THE FIGURES.

In order to further clarify the invention and its advantages compared to the known art, the possible forms of illustrative and non-limiting embodiments of the application of said principles are described below with the help of the attached drawings.

FIG. 1. Shows a comparative graph of the amount of deflocculant saved in a company in the ceramic manufacturing sector in Latin America, comparing the conventional flocculant vs. that obtained by the process according to the present invention.

DESCRIPTION OF THE INVENTION.

The present invention relates to the manufacture of ceramic tiles from colloidal aqueous suspensions that use dispersing agents as stabilizing agents of the colloidal system, in this case clay/water.

According to the invention, a sub-process for obtaining sodium or potassium silicate from the mixture of sand, caustic soda and water is initially foreseen, heating and regulated pressure in order to favor the formation of the crystalline structure p in the product; a second thread for the manufacture of low molecular weight and low polydispersity polyacrylic acid; a third thread that includes the neutralization of the polyacrylic acid; and, finally, a fourth subprocess that includes obtaining the deflocculant by mixing the alkaline silicate and the neutralized polyacrylate obtained with the co-dispersing/neutralizing agents in a stirred tank.

The product described in this patent is a highly efficient synergistic mixture of organic and inorganic compounds that acts as a deflocculant in the clay grinding process in aqueous systems (slip). The obtained clay dispersions must have a low viscosity and high density to be used in the manufacture of ceramic tiles to obtain a low manufacturing cost and easy handling of the slip in the process.

The synergistic mixture described according to the present invention improves the properties of the deflocculant, where the formulation described here differs from commercial products in the manufacturing method of some of its components, as well as the chemical composition of the deflocculant as described below.

The synthesis of sodium and/or potassium silicate by hydrothermal method according to the present invention presents different advantages such as:

- Easy incorporation of different alkali metal ions such as Na+, K+ or L¡+; greater purity of sodium, potassium or lithium silicate, because sodium hydroxide NaOH (Soda caustica), potassium hydroxide KOH (Potash) or lithium hydroxide is used as a source of sodium oxide, eliminating the problem of the formation of carbonaceous by-products;

- Low greenhouse gas emissions during the synthesis process; low SÍO2/Na2Ü, SÍÜ2/K2O or S¡0 ₂ /L¡ ₂ 0 ratio between 1 - 2.4, where silicates with these ratios have a higher alkalinity which gives them a better buffer property adjusting the pH of the slips to a pH greater than 9 necessary for the formation of the characteristic electric double layer in colloidal dispersions generating an effective electrostatic repulsion between particles;

- The formation of the crystalline structure p is favored due to the strict control during the synthesis process of parameters such as pressure, temperature and cooling speed of the reactor after completion of the reaction. The p structure presents a greater chelating power compared to the other polymorphic structures of sodium silicate. This fact is a positive aspect because polyvalent cations such as aluminum, iron, copper, magnesium or calcium can be removed from the grinding water, which eliminates the flocculation process that these metallic cations generate in the slip.

For its part, the polyacrylic acid synthesized based on the present invention has a molecular weight range between 1000-5000g/mol, with a polydispersity of Mw/Mn < 2.5, which makes it highly efficient as a dispersant for clayey colloidal particles in aqueous systems, providing great stability due to the effect of spherical impediment.

The use of co-dispersing agents of a basic nature, thanks to laboratory tests, the inventors have found that the sodium ion does not have a strong dispersing activity in the slips and, therefore, to enhance the deflocculant mixture, basic compounds are used to neutralize the polyacrylic acid with dispersing power, known in the literature as co-dispersing agents.

Co-dispersing agents have been used in different industries, such as the manufacturing industry of paint and fluids for drilling muds in the oil sector, however, this concept has not been applied in the ceramic industry to date, which makes the present invention a pioneer in this area. Co-dispersing agents can partially or totally replace the use of caustic soda and/or potash in a range of 0-100% during acid neutralization. polyacrylic. Furthermore, mixtures of co-dispersing agents can be used in different proportions.

The advantages of using co-dispersing agents decrease the polymer requirement in the deflocculant mix. In addition, the demand for deflocculant in the clay grinding process decreases, since in these the co-dispersant has the capacity to adsorb between the laminar structure of the clays, promoting the distance between these laminas, eliminating swelling processes produced when interacting with water. The use of co-dispersing agents also contributes to breaking the weak interactions between colloidal particles in the slip dispersion, as a consequence a decrease in the thixotropic effect of the slip is observed.

Co-dispersing agents can be chemicals such as: 2-Amino-2-methyl-1-propanol, 2-Amino-2-ethyl-1,3-propanediol, 2-Dimethylamino-2-methylpropanol, 4-(2-hydroxyethylamine)cyclohexan-1-ol tris(hydroxymethyl)aminomethane, 2-n-butylaminoethanol, methylamine, dimethylamine, trimethylamine, heptaminol, morpholine. Short chain epoxidized amines of the N(H) _X (CH2-CH2-OH)3- _X type can be used where x can be from 0 to 3. Long chain epoxidized amines of the Methoxypolyethylene glycol amine type with molecular formula H2NCH2CH2(OCH2CH2) _n OCH3 can also be used where the degree of polymerization (n) can be between 1 and 100. Finally, a hydroxylated mines synthesized by reduction of amino acids, such as: Lysinol, Alaninol, Serinol, Glutaminol, Leucinol, Aspartol. Hydroxylated amines obtained by reaction between organic epoxides and nucleophiles such as ammonia, primary, secondary or tertiary amines may also be included. Pentasodium tripolyphosphate can also be used to neutralize polyacrylic acid since its dissolution tends to have a pH greater than 8. In addition, salts obtained from hydroxylated inorganic acids from the bisphosphonate family, such as alendronic acid, hsedronic acid, etidronic acid, pamidronic acid, Zoledronic acid obtained by total or partial neutralization with any of the aforementioned basic components. In addition to salts obtained from organic acids such as citric, sulfamic, maleic, itaconic, and sorbic acids, among others. The synergistic mixture between sodium and/or potassium silicate synthesized by the hydrothermal method, a polyacrylic acid with low polydispersity and the use of co-dispersing agents generates a significant improvement in the rheological behavior of clayey suspensions. In addition, it reduces the negative effect of thickening as a function of time of the slips (thixotropy). Which results in a decrease in the cost of the product with an excellent performance in the plant.

To obtain sodium or potassium silicate, a reactor that supports pressures of up to 20 bars is used, completely closed batch type, which includes an access gate and a cooling column through which water circulates at room temperature. The reactor is made with a 2.54 cm carbon steel sheet, internally jacketed with a stainless steel sheet to prevent corrosion due to the hydroxides used during the reaction. The steam used during the synthesis can be injected both from the top and from the bottom of the reactor. The steam necessary to activate the reaction is generated in a Clayton® brand tubular steam generator manufactured in Mexico.

For the manufacture of low molecular weight and low polydispersity polyacrylic acid, a reactor made from stainless steel is required, which has a half-round heating system around the reactor. In addition, the reactor comprises an internal cooling system in a stainless steel tube and an access hatch. In addition, it has an adjustable agitation system between 1 and 100 rpm

According to the present invention the process comprises: i. A first thread for the synthesis of silicate comprises: a) Generate the mixture of sand, caustic soda and water under continuous agitation, having stabilized it is hermetically passed to the high pressure reactor. b) Verify that all entrances and exits of the reactor are closed. With the help of steam pressure, which enters the bottom of the reactor, the temperature and pressure are increased to start the reaction between soda and sand. For this, it is verified that the internal pressure generated inside the reactor reaches 16 Bars of pressure. c) When the reaction reaches 16 bars of pressure, the temperature is controlled around 200 °C by means of a cooling tower for 1 hour and 30 minutes, then a rapid cooling of the synthesized silicate is carried out that lasts around 30 minutes in order to favor the formation of the p crystalline structure in the product.

The synthesis procedure for potassium or lithium silicate is the same with the difference that instead of caustic soda, potash or lithium hydroxide are used, respectively.

Yo. A second sub-process for the manufacture of low molecular weight and low polydispersity polyacrylic acid comprises: a) Heating reaction water to 70°C, this must not have hardness for which it has been treated prior to synthesis. b) Acrylic acid, a chain transfer agent and a polymerization initiator are added rigorously over 4 hours. c) After 4 hours of polymerization, an oxidizing mixture is added to ensure complete conversion of the monomers to the desired product and to oxidize some by-products formed during the reaction. iii. A third sub-process for the neutralization of polyacrylic acid, where the polyacrylic acid is totally or partially neutralized with alkali metal hydroxides such as NaOH or KOH and to complete a total neutralization, the co-dispersing/neutralizing agents mentioned above are used and for use in the final mixture the polyachlate comprises a pH between 6.5 and 14. iv. A fourth thread that includes the manufacture of the deflocculant as a final product that includes the mixture of the alkaline silicate and the neutralized polyachlate with the co-dispersing/neutralizing agents in a tank with agitation at a speed between 30-70 rpm where the amount of polyachlate used can vary between 1 and 99% depending on the requirements of the clays in which this product will be used.

After manufacturing the product, quality control is carried out such as fluidity measurement in a Ford cup number 4 and density. Additionally, deflocculation tests are carried out on the clays in which the deflocculant will be used.

The specific difference is the use of co-dispersing agents as neutralizers for low polydispersity polyacrylic acid. These allow the amount of polymer/co-dispersant within the deflocculant formulation to be decreased which significantly reduces the cost of the deflocculant since it is the most expensive component in the mix. In addition, this modification provides excellent performance as a deflocculant in clay grinding in the wet grinding process for the ceramic sector.

Additionally, we want to extend this concept to alkaline silicate mixtures that contain L¡+, K+ and/or Na+ as counter ions. Similarly, polyachlates containing L¡+, K+ and/or Na+ as counterions in a range of 1 -99% of the amount of these components. From the present invention a synergy is obtained between dispersing agents in clayey colloidal aqueous suspensions used in the ceramic manufacturing industry.

For the development of the process of the present invention, a bibliographic review of other co-dispersing agents used in aqueous suspensions must be made; a qualitative analysis of different clayey formulations used in ceramic manufacturing companies, in order to determine about them:

Plastic character of the clay. - Hardness of the recirculated water used in the grinding process

Determination of ions Al ⁺³ , Fe ⁺² , Ca ⁺² among others.

Once established, laboratory experimentation of the rheological behavior of these formulations is carried out when interacting with the formulation obtained from the process of the invention and followed by scaling the process to a pilot plant (in batches of 40Kg) in which the standardized process is reproduced and refined in the experimental part. In this scaling process, a representative sample is obtained as expected in the industrial process, this is used to be sent to the client in order to be tested in his processes or products. This sample can also be sent to laboratories that certify the properties of the product.

The previous step allows the process to be passed to an industrial scale of approximately 6000Kg, where it is expected that this process can already be commercialized. As illustrated in Figure 1, the specific difference is the use of co-dispersing agents as neutralizers for low polydispersity polyacrylic acid. These allow the amount of polymer/co-dispersant within the deflocculant formulation to be decreased which significantly reduces the cost of the deflocculant since it is the most expensive component in the mix. In addition, this modification grants an excellent Performance as a deflocculant in wet grinding of clays for the ceramic sector.

Only some preferred embodiments of the invention have been illustrated by way of example. In this regard, it will be appreciated that the process of shaping dispersing agents for the stabilization of clayey colloidal aqueous suspensions, as well as the shaping arrangements can be chosen from a plurality of alternatives without departing from the spirit of the invention according to the following claims.

Claims

CLAIMS Process for shaping dispersing agents for the stabilization of colloidal aqueous suspensions of clays, where the process is characterized by comprising: i. a first sub-process for the synthesis of silicate comprising: a) generating a mixture of sand, caustic soda and water under continuous agitation and once it has been stabilized, it is hermetically passed to the high-pressure reactor; b) verify that all entrances and exits of the reactor are closed. With the help of steam pressure, which enters the bottom of the reactor, the temperature and pressure are increased to start the reaction between soda and sand. For this, it is verified that the internal pressure generated inside the reactor reaches 16 Bars of pressure; and c) where when the reaction reaches 16 bars of pressure, the temperature is controlled around 200 °C by means of a cooling tower for 1 hour and 30 minutes, subsequently a rapid cooling of the silicate formed is carried out, which lasts around 30 minutes in order to favor the formation of the crystalline structure p in the product,

Yo. a second sub-process for the manufacture of low molecular weight and low polydispersity polyacrylic acid comprising: a) heating reaction water to 70°C without hardness and treated prior to synthesis; b) rigorously adding over 4 hours acrylic acid, a chain transfer agent and a polymerization initiator; c) after 4 hours of polymerization, an oxidizing mixture is added where the conversion of the monomers to the desired product is completed and the by-products formed during the reaction are oxidized; iii. a third polyacrylic acid neutralization sub-process, where the polyacrylic acid is neutralized with alkali metal hydroxides selected from NaOH or KOH and complete the total neutralization with co-dispersing/neutralizing agents and with a pH between 6.5 to 14; and, iv. a fourth thread that includes the manufacture of the deflocculant as a final product that includes the mixture of the alkaline silicate and the neutralized polyacrylate with the co-dispersing/neutralizing agents in a tank with agitation at a speed between 30-70 rpm where the amount of polyacrylate used varies between 1 and 99% based on the clay requirement. Proceso de conformación de agentes dispersantes según la reivindicación 1 caracterizado porgue los agentes co-dispersantes son productos químicos seleccionados de 2-amino-2-metil-1 - propanol, 2-amino-2-etil-1 ,3-propanodiol, 2-Dimetilam¡no-2- metilpropanol, 4-(2-hidroxiet¡lam¡no) ciclohexan-1 -ol tris (hidroximetil) aminometano, 2-n-butilaminoetanol, metilamina, dimetilamina, thmetilamina, heptaminol, morfolina, aminas epoxidadas de cadena corta del tipo N(H) _X (CH2-CH2-OH)3- _X donde x puede ser de 0 a 3, aminas epoxidadas de cadena larga del tipo Metoxipolietilen glicol amina con fórmula molecular H2NCH2CH2(OCH2CH2) _n OCH3 donde el grado de polimerización (n) puede estar entre 1 y 100 y aminas hidroxiladas sintetizadas por reducción de aminoácidos, tales como: lisinol, alaninol, serinol, glutaminol, leucinol y aspartol. Process for shaping dispersing agents according to claim 1, characterized in that the co-dispersing agents are chemical products selected from hydroxylated amines obtained by reaction between organic epoxides, nucleophiles such as ammonia, primary, secondary or tertiary amines and salts obtained from hydroxylated inorganic acids of the bisphosphonate family such as alendronic acid, risedronic acid, etidronic acid, pami acid dronic acid and zoledronic acid obtained by total or partial neutralization with any of the aforementioned basic components, as well as salts obtained from organic acids such as citric, sulfamic, maleic, itaconic, and sorbic acids. Process for shaping dispersing agents according to claim 1, characterized in that in the third sub-process (iii), the polyacrylic acid is neutralized with pentasodium tripolyphosphate where the solution tends to a pH greater than 8. Process for shaping dispersing agents according to claims 1 and 2, characterized in that in the first sub-process (i) for the synthesis of potassium silicate, it comprises addition of potash. Process for shaping dispersing agents according to claims 1 and 2, characterized in that the first sub-process (i) of lithium synthesis comprises addition of lithium hydroxide.