Method for producing hollow spherical glass particles

Abstract

The present invention relates to a method for producing hollow spherical glass particles comprising at least SiO2, Al2O3, and an alkali metal oxide, the method comprising: producing precursor particles comprising at least SiO2, Al2O3, and an alkali metal oxide by mixing starting materials, slurrying the starting materials with water, and subsequently spray-drying the particles; and heat-treating the resulting precursor particles at a temperature of 1000°C to 1800°C, preferably 1300°C to 1600°C, by contacting the precursor particles with at least one open flame.

Description

[Technical Field]

[0001] The present invention relates to a method for producing hollow spherical glass particles comprising at least SiO, AlO, and an alkali metal oxide, the method comprising: mixing starting materials, slurrying the starting materials with water, and subsequently spray-drying the mixture to produce precursor particles comprising at least SiO, AlO, and an alkali metal oxide; and heat-treating the precursor particles thus obtained at a temperature of 1000°C to 1800°C, preferably 1300°C to 1600°C, by contacting the precursor particles with at least one open flame. [Background technology]

[0002] Hollow spherical glass particles, also known as hollow glass microspheres, are used as fillers for materials in various application fields. The specific gravity of these hollow spherical glass particles is significantly lower than that of other fillers, while maintaining high physical properties such as heat resistance, pressure resistance, and impact resistance. Therefore, hollow spherical glass particles are widely used as fillers for weight-reducing articles containing molded resin or metal parts, such as automobile parts, household goods, sealing materials, or building materials. Examples of such hollow spherical glass particles and their production are described, for example, in U.S. Pat. Nos. 3,699,050, 4,336,338, 5,176,732, and U.S. Patent Application Publication No. 2002 / 0004111 A1.

[0003] The methods known in the art for producing hollow spherical glass particles usually involve dispersing fine glass powder in a hot gas, where the glass is heated to a melt, reducing the viscosity of the molten material (melting starts from the outer layer). At the same time, gas is generated by vaporization of the expansion agent present in the composition of the precursor particles. Therefore, due to surface tension, the shape of the resulting particles is spherical, and at the same time, the particles are hollow due to the gas formed inside the particles.

[0004] Regarding the chemical composition of hollow spherical glass particles, borosilicate glass is widely used due to its chemical and mechanical resistance. For example, Japanese Patent Application Laid-Open No. 58-156551 discloses a method for forming hollow borosilicate glass microspheres from starting materials such as SiO2, H3BO3, CaCO3, Na2CO3, NH4H2PO4, and Na2SO4. However, due to regulatory requirements, the application of hollow non-spherical glass particles that do not contain boron is preferred. Furthermore, boron can make the particles brittle.

[0005] WO 2017 / 108831 discloses a method for preparing boron-free hollow spherical alumosilicate glass particles using Al2O3, SiO2, and at least one alkali metal oxide as starting materials. The starting materials are mixed with water and the mixture is spray-dried to obtain precursor particles having an average particle size of 80 μm to 400 μm and a residual moisture content of 1% to 10%. The precursor particles are then fed into a heating device at a temperature ranging from 1500°C to 1800°C, allowing the dried mixture to fall through the heating device for about 1 second to about 10 seconds, thereby producing hollow spherical glass particles preferably having a particle size of 10 μm to 600 μm. The heating device is a tube furnace including an outer heating mantle.

[0006] Our earlier application, WO 2020 / 020921, discloses boron-free hollow spherical glass particles containing at least 30% by weight of Al2O3, at least 35% by weight of SiO2, and at least 18% by weight of at least one alkali metal oxide, and having a particle size of greater than 20 μm to 75 μm. This application further discloses a method for producing such particles, which comprises providing a composition containing at least 30% by weight of Al2O3, at least 35% by weight of SiO2, and at least 18% by weight of at least one alkali metal oxide, wherein these components are present as fine particles having a particle size of ≦10 μm, mixing the particles with water and optionally an organic binder, spray-drying the particles, and feeding the dried particles into a heating device, such as a tube furnace, to blow the particles upward while maintaining a temperature above 1000°C, thereby obtaining hollow spherical glass particles. Alternatively, two heating devices connected in series can be used, or at least a portion of the particles are circulated back into the heating device.The tube furnace described includes an outer heating mantle.

[0007] Japanese Patent Application Laid-Open Publication No. 7-277768 discloses a method for producing hollow glass spheres. The starting material is a mixture of glass powder and an inorganic material, preferably a carbonate or sulfate powder, which decomposes at higher temperatures and generates gas. This mixture is converted into granules, for example, by a spray dryer. The granules are then exposed to an air stream at a temperature sufficient to decompose the inorganic material and generate gas. Preferably, the heat treatment is carried out in an air stream at approximately 1200-1600°C for 5-1000 milliseconds. In Example 1, glass powder (55% SiO, 14% Al, 8% B, 1% MgO, 21% CaO, and 1% BaO; by weight) is mixed with CaSO·2H, and water to obtain a slurry, which is then spray-dried to obtain granules with an average particle size of 50 μm. The granules are then fed into a gas burner air stream at a maximum temperature of 1500°C, heat treated for about 100 milliseconds, and then collected in a cyclone. This example does not teach that the granules are contacted with the open flame of a gas burner, only that the granules are fed into the hot air stream generated by the gas burner. No details are disclosed regarding the apparatus used to heat the granules in the hot air stream.

[0008] Tube furnaces containing external heating mantles for heat treating materials at temperatures above 1000°C may be suitable if the tube diameter is not excessively large. However, as the tube diameter increases, as may be necessary in a production plant, heat transfer into the tube becomes increasingly difficult. Summary of the Invention [Problem to be solved by the invention]

[0009] An object of the present invention is to provide an improved method for producing hollow spherical glass particles, which method also makes it possible to produce hollow spherical glass particles using a heating device with a large inner diameter. [Means for solving the problem]

[0010] Accordingly, a method for producing hollow spherical glass particles comprising at least SiO2, Al2O3, and an alkali metal oxide has been found, the method comprising at least the following steps: (I) Producing precursor particles by a method comprising at least the following substeps: (I-1) providing a starting composition containing particles of at least one starting compound for forming a glass containing at least SiO2, Al2O3, and an alkali metal oxide; (I-2) mixing the starting composition with a liquid, thereby obtaining a slurry; and (I-3) spray-drying the obtained slurry to obtain precursor particles; and (II) heat-treating the precursor particles at a temperature of 1000°C to 1800°C by passing the precursor particles through a heating device, thereby obtaining hollow spherical glass particles; Here, at least one open flame fed by a combustible gas burns inside the heating device, and the heat treatment is carried out by bringing the precursor particles into contact with the one or more open flames.

[0011] Preferably, the hollow spherical glass particles to be produced contain at least 30 wt. % of SiO, at least 25 wt. % of AlO, and at least 18 wt. % of alkali metal oxides, based on the total weight of the hollow spherical glass particles, and do not contain boron, and the hollow spherical glass particles have an average diameter of 20 μm to 200 μm. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic diagram showing a vertical (upright) heating apparatus for adding precursor particles to a combustible gas. [Figure 2] FIG. 2 is a schematic diagram showing a heating device including multiple flames. [Figure 3] FIG. 3 is a schematic diagram showing a distributor for combustible gases including eight burner nozzles. [Figure 4]FIG. 4 is a schematic diagram showing a vertical heating apparatus for adding precursor particles to a non-flammable carrier gas. [Figure 5] FIG. 5 is a schematic diagram showing a horizontal (transverse) heated apparatus adding precursor particles to a non-flammable carrier gas, with an additional inlet for gas to cool the reactor walls. [Figure 6] FIG. 6 is a schematic diagram showing a vertical heating apparatus for adding precursor particles to a non-flammable carrier gas. [Figure 7] FIG. 7 is a process flow diagram of a plant including exhaust gas recirculation. [Figure 8] FIG. 8 is a schematic diagram showing a rotary kiln in which precursor particles are added to a combustible gas. [Figure 9] FIG. 9 is a schematic diagram showing a rotary kiln adding precursor particles to a combustible gas, with an additional inlet for gas to cool the reactor walls. [Figure 10] FIG. 10 is a schematic diagram showing the front of a rotary kiln where precursor particles are added to a combustible gas and a non-combustible gas is also introduced. [Figure 11] FIG. 11 is a schematic diagram showing the front of a rotary kiln where precursor particles are added to a non-flammable carrier gas. DETAILED DESCRIPTION OF THE INVENTION

[0013] The present invention can be specifically explained as follows.

[0014] hollow spherical glass particles The composition of glasses is often expressed in terms of their content of SiO2, Al2O3, alkali metal oxides, and optionally further oxides. This description of composition is also used for the purposes of the present invention.

[0015] The hollow spherical glass particles produced by the method of the present invention comprise at least SiO2, Al2O3, and an alkali metal oxide, preferably Na2O. Optionally, further components may be present.

[0016] Preferably, the hollow spherical glass particles produced by the method of the present invention contain at least 30 wt. % SiO, at least 25 wt. % AlO, and at least 18 wt. % alkali metal oxide, preferably NaO, based on the total weight of the hollow spherical glass particles.

[0017] In one embodiment of the present invention, the hollow spherical glass particles contain 30 wt % to 55 wt % SiO2, 25 wt % to 45 wt % Al2O3, and 18 wt % to 40 wt % alkali metal oxide, preferably Na2O, based on the total weight of the hollow spherical glass particles. In yet another embodiment of the present invention, the hollow spherical glass particles contain 30 wt % to 40 wt % SiO2, 25 wt % to 35 wt % Al2O3, and 30 wt % to 40 wt % Na2O, based on the total weight of the hollow spherical glass particles.

[0018] In one embodiment of the present invention, the hollow spherical glass particles do not contain boron. As used herein, the terms "boron-free" or "boron-free" do not exclude the presence of a small amount of boron. Specifically, the amount of boron contained in the hollow spherical glass particles, if any, is preferably 1.0 wt. % or less, more preferably 0.1 wt. % or less, even more preferably 0.01 wt. % or less, for example, 0.001 wt. % or less, based on the total weight of the hollow spherical glass particles.

[0019] In one embodiment of the present invention, the hollow spherical glass particles have an average particle size of 20 to 200 μm, for example, 20 μm to 150 μm, or 20 μm to 70 μm. This value relates to a number average, which can be measured, for example, by microscopy.

[0020] In one embodiment of the present invention, the wall thickness of the hollow spherical glass particles is 0.1 to 15 μm, in particular 0.2 to 12 μm.

[0021] Furthermore, the hollow spherical glass particles according to the present invention preferably have a pressure collapse strength value in the range of 120 to 150 MPa. To measure the pressure collapse strength value, the hollow spherical glass particles are transferred to a closed-bottom cylinder and pressure is applied to the top using a punch. The hollow spherical glass particles are pressed by the punch, as in a press. The filling height of the hollow spherical glass particles in the cylinder depends on the particle size. The cylinder is placed in a tension / compression testing device that controls the piston force. A predetermined normal force or surface pressure is thus generated. Depending on the particle size, the results are evaluated by measuring the percentage of broken hollow spherical glass particles using microscopic or visual inspection. The cylinder used for this procedure has an inner diameter of 20 mm and an internal length of 80 mm. The filling height was 20 mm. This criterion is based on 80% intact hollow spherical glass particles of the appropriate diameter.

[0022] The bulk density of the hollow spherical glass particles is 0.4 to 1.2 g / cm 3 in the range of 0.5 to 1.0 g / cm 3 and even more preferably in the range of 0.6 to 0.9 g / cm 3 range, e.g., 0.7-0.8g / cm 3 It is preferable that the range is:

[0023] Method for producing hollow spherical glass particles The method for producing hollow spherical glass particles according to the present invention comprises at least two steps.

[0024] In a first step (I), precursor particles containing suitable glass-forming components are produced, and in a second step (II), the precursor particles are heat-treated using an open flame at temperatures between 1000°C and 1800°C, thereby obtaining hollow spherical glass particles.

[0025] Step (I)—Preparation of Precursor Particles Step (I) includes at least three substeps: (I-1), (I-2), and (I-3). In step (I-1), a starting composition for producing precursor particles is provided. In step (I-2), the starting composition is mixed with a liquid to obtain an aqueous slurry of the starting material, and in step (I-3), the obtained aqueous slurry is spray-dried to obtain precursor particles.

[0026] Step (I-1) The starting composition for preparing the precursor particles comprises particles of at least SiO, AlO, and at least one starting material for forming a glass comprising an alkali metal oxide, preferably NaO. Preferably, a mixture of at least two different starting materials is used.

[0027] Starting materials for forming glasses comprising at least SiO2, Al2O3, and an alkali metal oxide, preferably Na2O, are basically known in the art. The starting materials can comprise all of the SiO2, Al2O3, and alkali metal oxide components, or only two of these, or only one of these.

[0028] Examples of starting materials suitable for use in the present invention include alkali metal carbonates, especially sodium carbonate, silicon dioxide, silicates, alumosilicates, for example zeolites such as zeolite A, clays, for example kaolinite, mica, or mixtures thereof.

[0029] The starting composition can release a gas upon heat treatment in step (II). Such a gas may be, in particular, carbon dioxide and / or water. Preferably, the starting material for forming the glass itself is capable of releasing this gas, although in other embodiments, additional expansion additives can be used for this purpose. Examples of starting materials that release a gas upon heat treatment include alkali metal carbonates, such as sodium carbonate, which release CO2 upon heating. Further examples include starting materials containing water containing chemically bound water, such as silicates and / or alumosilicates. For example, starting materials of the general formula: M2 / z O·Al2O3·xSiO2·yH2O, where M is an alkali or alkaline earth metal cation, z is the charge of the cation, x is from about 1.8 to 12, and y is from 0 to about 8. Specific examples include zeolites of the formula: Na 12 ((AlO2) 12 (SiO2) 12 )·27H2O. Further examples include clays, such as kaolinite. Gas released from the starting components during heat treatment causes the hollow spheres to expand.

[0030] In one embodiment of the invention, the starting composition comprises at least a zeolite, for example zeolite A.

[0031] In another embodiment of the invention, the starting composition comprises at least a zeolite, such as zeolite A, and an alkali metal carbonate, especially sodium carbonate, preferably zeolite A and sodium carbonate.

[0032] In another embodiment of the invention, the starting composition comprises at least a zeolite, such as zeolite A, and a clay mineral, such as kaolin or kaolinite, preferably zeolite A and kaolin and / or kaolinite.

[0033] In yet another embodiment of the present invention, the starting composition comprises at least a zeolite, such as zeolite A, a clay mineral, such as kaolin or kaolinite, and an alkali metal carbonate, in particular sodium carbonate, preferably zeolite A, kaolin and / or kaolinite, and sodium carbonate.

[0034] In one embodiment of the present invention, the starting composition is boron-free, the term "boron-free" having already been defined above.

[0035] The types and amounts of starting materials in the starting composition are adjusted according to the intended composition of the glass, keeping in mind that the above-mentioned gases, or other volatile components that may be present, will be released from the composition during the heat treatment in step (II). Thus, although the ratios of SiO, AlO, and alkali metal oxides in the starting composition are the same as in the glass, their absolute percentages in the starting composition may be lower due to mass loss during the heat treatment.

[0036] The particles of the starting material can be obtained by grinding. In one embodiment of the present invention, the method includes a step of grinding the starting material. Grinding can be carried out before mixing the starting materials or after mixing the starting materials. The grinding process can be dry or wet. In one embodiment of the present invention, the grinding process is carried out so that the average particle size of the particles in the starting composition is 10 μm or less, preferably 7 μm or less. Particle size refers to the number average, which can be measured by microscopy.

[0037] Step (I-2) In step (I-2), the starting composition comprising particles of the starting material prepared in step (I-1) is mixed with a liquid, thereby obtaining a slurry of particles of the starting composition in the liquid.

[0038] The liquid may be a single component or may comprise a mixture of different components. Preferably, the liquid comprises water, i.e., is an aqueous liquid. In one embodiment, water is used alone as the liquid to slurry the particles.

[0039] The slurry can contain up to about 80.0% by weight of the starting composition, for example, from about 50 to about 75% by weight.

[0040] In addition, the slurry may contain further additives.

[0041] In one embodiment, the slurry may further comprise a dispersant. Examples of suitable dispersants include polymeric dispersants such as polyvinylpyrrolidone, polyacrylate, polyacrylate copolymers, or mixtures thereof.

[0042] In another embodiment, a binder can be used. Such a binder can aid in the formation of the precursor particles. Examples of binders include inorganic binders, such as water glass, or organic binders, such as glycerin, glycol, xylitol, sorbitol, erythritol, starch, polyvinyl alcohol, or mixtures thereof.

[0043] Step (I-3) In step (I-3), the slurry obtained in step (I-2) is spray-dried to obtain precursor particles.

[0044] Equipment for spray drying is known in the art and commercially available. In one embodiment of the present invention, the slurry is spray dried at a temperature of 150°C to 250°C, which is related to the inlet temperature of the spray dryer. The precursor particles resulting from spray drying are spherical, or at least essentially spherical.

[0045] Each precursor particle contains multiple primary particles of the starting material. The particle size of the precursor particles is adjusted according to the intended particle size of the hollow spherical glass particles to be produced. Generally speaking, as the particle size of the precursor particles increases, the particle size of the hollow spherical glass particles also increases. How to adjust particle size by process parameters during the spray drying process is known in the art. In one embodiment of the present invention, the particle size of the precursor particles is adjusted to 20 μm to 250 μm. Particle size refers to a number average, which can be measured by microscopy.

[0046] Optionally, the precursor particles obtained in step (I-3) can be screened, for example by sieving, to select only a specific fraction of precursor particles for heat treatment in step (II), for example to separate out very coarse and / or very fine precursor particles.

[0047] Step (II) - Heat treatment of precursor particles overview In step (II), the precursor particles obtained in step (I) are heat-treated at a temperature of 1000°C to 1800°C, preferably 1300°C to 1600°C, to obtain hollow spherical glass particles. The heat treatment is carried out by passing the precursor particles through a heating device, in which at least one open flame is burning inside the heating device, and the precursor particles are heat-treated by contacting one or more open flames. The flame is supplied by a combustible gas emitted from at least one burner nozzle arranged inside the heating device. Preferably, the heating device includes multiple burner nozzles, so that multiple flames are burning inside the heating device. The contact time of the particles in the flame is short, for example, 0.001 seconds to 1 second.

[0048] Essentially, any type of heating device that is heated by at least one open flame burning inside it can be used.

[0049] Preferably, the heating device comprises an elongated reaction chamber, where precursor particles are introduced at one end (front end) of the elongated reaction chamber and hollow spherical glass particles are removed at the other end (rear end) of the elongated reaction chamber, such that the particles are transported from one end to the other through the elongated reaction chamber while being chemically transformed.

[0050] Examples of such heating devices include heating devices with cylindrical reaction chambers, although other shapes are possible, for example reaction chambers with square or hexagonal cross sections. Preferably, the heating device is a cylindrical heating device.

[0051] The diameter of the longitudinal reaction chamber, preferably the cylindrical reaction chamber, can be selected as needed by those skilled in the art. Since the heating device is internally heated by one or more open flames, there is no problem with heat transfer into the reaction chamber, and therefore the inner diameter of the longitudinal reaction chamber can be advantageously made very large. The inner diameter may be, for example, 0.1 to 3 m, e.g., 1 to 3 m, but these figures do not limit the present invention.

[0052] The term "diameter" in this context refers to the hydraulic diameter d h = 4A / P, where A is the area of the cross section and P is the circumference of the heating device. In the case of a cylindrical heating device, i.e. a heating device with a circular cross section, d h is 4πr 2 / 2πr = 2r, where r is the radius of the circle. For a heating device with a square cross section, d h is 4a 2 / 4a=a, where a is the side length of the square. The hydraulic diameter of reaction chambers having other shapes can be easily calculated by one skilled in the art.

[0053] The diameter of the reaction chamber may be constant or may vary along its length. As an example, the heating device may include a portion having a constant diameter, e.g., a cylindrical portion, and the diameter decreases toward the rear end.

[0054] The longitudinal reaction chamber may be oriented horizontally or vertically or in any other direction. In one embodiment of the present invention, the longitudinal reaction chamber may be vertical (upright) or essentially vertical, where precursor particles are introduced at the bottom end and the formed hollow spherical glass particles are removed at the top end.

[0055] In one embodiment of the present invention, the heating device includes a stationary reaction chamber oriented horizontally, vertically, or in any other direction. The heating device, including the stationary longitudinal reaction chamber, is equipped with at least one inlet for a flammable gas, which is connected to at least one burner nozzle inside the reaction chamber. Flammable gases are known in the art. Examples include hydrogen and hydrocarbons, such as methane, ethane, or propane. There are several possibilities for mixing the flammable gas with oxygen or air for combustion. In a specific embodiment of the present invention, the burner nozzle is a one-component nozzle, and oxygen or air or any other gas required for combustion is mixed with the flammable gas before it exits the burner nozzle, for example, before the flammable gas enters the heating device. In another embodiment, the burner nozzle used is a two-component nozzle, such as a ring nozzle, from which separate flows of oxygen or air and the flammable gas exit. For this purpose, the heating device is provided with separate inlets for air or oxygen and, between the two-component nozzle and this inlet, separate pipes for the combustible gas and the oxygen or air.

[0056] The precursor particles can be contacted with one or more flames by dispersing them in the combustible gas itself, so that the combustible gas stream containing the precursor particles exits one or more burner nozzles. In this embodiment, the precursor particles pass through the entire flame and are converted into hollow spherical glass particles. After passing through the open flame, the hollow spherical glass particles thus formed are cooled at least to a degree that the glass particles become solid and are transported by the exhaust gas stream produced by combustion through the heating unit toward an outlet, from which the hollow spherical glass particles can be collected. Cooling can be achieved, for example, by cooling the walls of the heating device downstream of the one or more flames and / or by introducing a non-combustible gas, such as air or cooled recycled gas from the process itself at ambient temperature, into the heating device downstream of the one or more flames. Separation of the hollow spherical glass particles from the exhaust gas can be achieved, for example, by a cyclone. A heat exchanger in the line connecting the heating device and the device for separation can be used to further cool the stream.

[0057] Optionally, a non-flammable gas can be added to the reaction chamber, for example, at a location upstream of the one or more open flames. Such additional non-flammable gas assists in transporting the hollow spherical glass particles toward the outlet and helps to prevent backmixing. Examples of non-flammable gases include air, carbon dioxide, or recovered exhaust gas.

[0058] In another embodiment, the precursor particles can be dispersed in a separate non-flammable gas that acts as a carrier gas for the precursor particles, and the non-flammable gas stream containing the precursor particles can be introduced into a heating device at a location upstream of one or more open flames, thereby contacting the precursor particles with one or more flames. In this embodiment, the precursor particles do not pass through the center of one or more flames, but pass through the outer region of one or more flames. As in the first embodiment, the non-flammable gas helps transport the hollow spherical glass particles toward the outlet and helps prevent backmixing. Of course, these two methods can also be combined, i.e., the precursor particles can be added to both the flammable gas and the non-flammable gas.

[0059] In another embodiment, the heating device is a rotary kiln. A rotary kiln includes a reaction chamber that is a cylindrical, rotating tube, typically oriented horizontally or slightly tilted toward its rear end. Contact of the precursor particles with one or more flames can be achieved in the same manner as described above, i.e., by adding the precursor particles to a combustible or non-combustible gas. The rotational motion of the cylindrical reaction chamber typically at least assists in transporting the particles through the reaction chamber.

[0060] In one embodiment of the present invention, the longitudinal reaction chamber, preferably a cylindrical reaction chamber, of the heating device described above comprises a combustion zone (a) and a cooling zone (b). The cooling zone (b) is located downstream of the combustion zone (a). That is, precursor particles are introduced into the combustion zone (a), where they are converted into hollow spherical glass particles, and the hollow spherical glass particles thus obtained are transported through the cooling zone (b) and removed at the end of the cooling zone (b).

[0061] The combustion zone (a) is heated by at least one open flame, preferably by a plurality of open flames, which preferably extend over the entire cross section of the cylindrical reactor. Advantageously, the inner walls of the reaction chamber in the combustion zone (a) are protected by a refractory material to withstand the high temperatures. Suitable refractory materials are known in the art. Examples include ceramic materials based on aluminum and / or silicon oxide, or carbide materials, such as silicon carbide. OCMC (oxide ceramic matrix composite) materials may also be used. In one embodiment, the entire cylindrical reaction chamber is made of a refractory material.

[0062] A cooling zone (b) is provided downstream of the combustion zone (a), which allows the formed hollow spherical glass particles to be cooled at least to a temperature at which the walls of the hollow spherical glass particles become solid when they leave the flame(s). Therefore, cooling does not necessarily mean cooling to room temperature, but only requires that the above minimum requirements be met. As is known in the art, the melting point of a glass strongly depends on its composition. Generally, it is sufficient to cool the hollow spherical glass particles to a temperature about 500°C below their respective melting temperatures, although the present invention is not limited to this range.

[0063] Cooling has already begun as soon as the particles are no longer in contact with the flame(s). Further cooling can be achieved by introducing a gas, such as air, nitrogen, or recycled exhaust gas at ambient temperature, into the heating device at a location downstream of the flame(s). In this embodiment, the reaction chamber includes a suitable means, such as an inlet pipe, that allows the cooling gas to enter the cooling zone (b). Preferably, the inlet pipe can be arranged so that part of the gas flow is directed toward its interior and part flows essentially parallel to the wall. This arrangement helps prevent the hollow spherical glass particles from sticking to the wall. In one embodiment, there can be two, three, or even more cooling zones, allowing for gradual cooling. Cooling can be further assisted, for example, by cooling the walls of the cooling zone (b). The walls can be cooled by using a double-wall material for the cooling zone (b) and introducing a cooling medium into the hollow space between the two walls. To protect the walls of the combustion zone (a), in one embodiment, the walls of the combustion zone (a) can also be cooled. For cooling, a gas flow at ambient temperature is preferably blown into the hollow space through the inlet and hot gas can be removed through the outlet. The gas can be fresh gas, such as air or nitrogen, or recycled gas from the process itself.

[0064] The heat treatment results in a flow of hollow spherical glass particles in the exhaust gas stream and optionally additional non-combustible gas. Separation of the hollow spherical glass particles from the exhaust gas can be carried out, for example, by a cyclone or by a filter.

[0065] Detailed Description In one particular embodiment of the present invention, The heating device used for step (II) comprises at least: Inlet for flammable gases, Inlet for non-flammable gas, a longitudinal reaction chamber comprising at least two distinct zones (a) and (b) of: (a) a combustion zone capable of being heated by at least one open flame; wherein at least one burner nozzle connected to a combustible gas inlet is disposed in the combustion zone; and (b) cooling zone; and Outlets for hollow spherical glass particles, non-flammable gases, and waste; and Step (II) is carried out as follows: (II-1) introducing a flammable gas stream through the inlet, transferring the flammable gas stream to one or more burner nozzles, and igniting at least one open flame; (II-2) introducing a non-combustible gas stream into the combustion zone (a) through the inlet and moving the non-combustible gas stream to an outlet through the cooling zone (b); (II-3) Adding precursor particles into a heating device by at least one method selected from the following, and contacting the precursor particles with one or more open flames in a combustion zone (a), thereby obtaining hollow spherical glass particles, exhaust gas generated by the combustion of a combustible gas, and a stream of non-combustible gas; Adding precursor particles to the combustible gas stream, and / or adding precursor particles to a non-flammable gas stream; (II-4) cooling the formed hollow spherical glass particles, exhaust gas, and non-combustible gas by passing them through a cooling zone (b); and (II-5) Separating hollow spherical glass particles from exhaust gases and non-combustible gases.

[0066] Preferably, the longitudinal reaction chamber is a cylindrical reaction chamber. In one embodiment, the longitudinal reaction chamber is oriented vertically, with the combustion zone (a) at the lower end of the longitudinal reaction chamber and the cooling zone (b) at the upper end of the longitudinal reaction chamber.

[0067] Figure 1 shows a schematic representation of a particular embodiment of a heating device suitable for use in the method of the present invention. The heating device comprises a vertical cylindrical reaction chamber, and precursor particles are added to a combustible gas. The reaction chamber (1) is cylindrical and comprises two distinct zones: a combustion zone (a) and a cooling zone (b). A flame (2) burns in the combustion zone (a). The flame is fed by combustible gas exiting a burner nozzle (3). The heating device further comprises one inlet (4) for the combustible gas.

[0068] Details regarding the combustible gas, the burner nozzle, and the mixing of the combustible gas with air or oxygen have already been disclosed above. In the embodiment of FIG. 1, a one-component nozzle is shown, and therefore the combustible gas premixed with oxygen or air must be introduced through the inlet (4). The diameter of the reaction chamber can be selected as needed by those skilled in the art. As mentioned above, the term "diameter" refers to the hydraulic diameter of the reaction chamber. This diameter may be, for example, 0.1 to 3 m, e.g., 1 to 3 m, but these figures are not intended to limit the invention.

[0069] In another embodiment of the present invention, multiple burner nozzles and multiple flames are used. Preferably, the multiple nozzles are arranged so that multiple flames are present across the entire cross-section of the combustion zone (a). An embodiment including multiple burner nozzles is shown schematically in FIG. 2. FIG. 3 shows a schematic top view of the burner nozzles, i.e., eight burner nozzles (3) arranged in a circular configuration within a cylindrical reaction chamber. Combustible gas enters the inlet (4) into a ring line (11), supplying all of the burner nozzles with combustible gas. The nozzles are arranged vertically as shown in FIG. 3, but may be slightly tilted toward the center of the ring and / or in other directions. The purpose of this nozzle arrangement is to provide multiple flames across the entire cross-section of the combustion zone. In one embodiment, the nozzles can be tilted at an angle of 1 to 30 degrees from the vertical centerline.

[0070] The heating device further includes an inlet (5) for a non-flammable gas as shown in Figure 1. Such additional non-flammable gas assists in transporting the hollow spherical glass particles toward the outlet and helps to avoid backmixing. Examples of non-flammable gases include air, carbon dioxide, or recycled gas from the process itself.

[0071] The inner walls of the reaction chamber in the combustion zone (a) are preferably protected by a refractory material to withstand high temperatures. Suitable refractory materials are known in the art. Examples include ceramic materials based on aluminum and / or silicon oxide, or carbide materials, such as silicon carbide. OCMC (oxide ceramic matrix composite) materials may also be used. In one embodiment of the present invention, the refractory material is cooled. This can be achieved by using a reaction chamber with a double wall, at least in the combustion zone (a). In another embodiment, the cooling zone (b) can also be equipped with a double wall for cooling purposes. For cooling, a gas flow at ambient temperature can be preferably injected into the hollow space through an inlet, and hot gas can be removed through an outlet. The hollow space between the two walls can be divided into several sections, each of which includes an inlet and an outlet for a coolant, preferably for the gases outlined above, so that the walls of different zones of the reaction chamber can be cooled independently of each other.

[0072] FIG. 1 shows a schematic representation of a heating device with a reaction chamber containing three different zones (6) for cooling the walls.

[0073] The heating device further includes an outlet (7) which serves to remove the hollow spherical glass particles formed during the heat treatment from the reaction chamber, and which also serves to remove the non-combustible gases injected into the reaction chamber as well as the exhaust gases formed during combustion from the reaction chamber.

[0074] The heating device further comprises a means for separating the hollow spherical glass particles from the exhaust gas and non-combustible gas. Such a device may be a cyclone (8). The gas is removed through an outlet (9), and the hollow spherical glass particles are removed through another outlet (10). Of course, other devices for separation may also be used, such as a filter.

[0075] During step (II), the precursor particle stream is introduced into a heating device, thereby obtaining hollow spherical glass particles. Step (II) includes at least five substeps: (II-1), (II-2), (II-3), (II-4), and (II-5).

[0076] During step (II-1), a combustible gas stream is introduced through an inlet (4), travels through a tube to one or more burner nozzles (3) located in the combustion zone (a), and ignites a flame (2).

[0077] During step (II-2), a non-combustible gas stream is introduced into the combustion zone (a) through the inlet (5) and moves through the cooling zone (b) to the outlet (7). Thus, the flow of gas and particles is unidirectional, from the inlet (5) to the outlet (7).

[0078] During step (II-3), precursor particles are added into a heating device and brought into contact with one or more open flames in a combustion zone (a), thereby obtaining hollow spherical glass particles, exhaust gases generated by the combustion of combustible gases, and a stream of non-combustible gases.

[0079] In a first embodiment of the present invention, precursor particles are added to a combustible gas stream. Methods for adding solids to a gas stream and transporting the solids in the gas stream are essentially known in the art. For example, the particles can be added to a swirl chamber through which at least a portion of the combustible gas stream flows.

[0080] In a second embodiment, the non-combustible gas acts as a carrier gas for the precursor particles and adds the precursor particles to the non-combustible gas stream.

[0081] Of course, the precursor particles can be added to both combustible and non-combustible gas streams, and other methods of adding precursor particles into the combustion zone and contacting the precursor particles with one or more open flames can also be applied.

[0082] The first embodiment is shown schematically in Figure 1. Precursor particles are dispersed in a combustible gas, and a flow of combustible gas and precursor particles is added through an inlet (4) and transported through a tube to one or more burner nozzles (3). The precursor particles pass through a flame and are converted within the flame into hollow spherical glass particles.

[0083] The hollow spherical glass particles thus formed are transported through the heating unit toward the outlet (7) by the exhaust gas flow generated by the combustion. Furthermore, a non-combustible gas is introduced into the reaction chamber through the inlet (5) at a position upstream of the one or more open flames. The purpose of using such a non-combustible gas is to avoid backmixing and to assist the transport of the hollow spherical glass particles toward the outlet.

[0084] A second embodiment is shown schematically in FIG. 4. The heating device shown in FIG. 4 is similar to that shown in FIG. 1. The heating device is heated by multiple flames (2) fed by combustible gases admitted into the heating device through an inlet (4). A non-combustible gas stream is admitted through an inlet (5), and precursor particles are added to this non-combustible gas stream. The non-combustible gas and precursor particle streams are introduced into the reaction chamber upstream of one or more open flames, so that the streams pass through the flames, thereby forming hollow spherical glass particles. As shown in FIG. 4, the use of multiple flames is advantageous, ensuring that the flames are present across essentially the entire cross section of the combustion zone (a). This arrangement ensures good contact between the flames and the precursor particles, thus enabling high process efficiency. The heating device shown in FIG. 4 further includes a mixing chamber (12) in which the precursor particles (13) and the non-combustible gas stream (14) are premixed. This premix is then transferred into the main line through which the flow of non-combustible gas and precursor particles is transported to the reaction chamber (1).

[0085] In the method of the present invention, the contact time between the precursor particles and the flame(s) is short. In one embodiment, this is between 0.001 and 1 second. The contact time depends primarily on the length of the flame. The flame speed is also high. In one embodiment, the flame speed may be, for example, between 5 and 100 m / s.

[0086] During step (II-4), the hollow spherical glass particles, exhaust gas, and non-combustible gas are passed through a cooling zone (b), whereby the hollow spherical glass particles are cooled. In the cooling zone (b), the hollow spherical glass particles formed in the combustion zone can be cooled to a temperature at least at which the walls of the hollow spherical glass particles become solid. Generally, it is sufficient to cool the hollow spherical glass particles to a temperature about 500°C lower than their respective melting temperatures, but the present invention is not limited to this range.

[0087] Cooling has already begun as soon as the particles are no longer in contact with the flame(s). In one embodiment of the invention, cooling can be assisted by introducing a non-combustible gas, such as air, nitrogen, carbon dioxide, or recycled exhaust gas, preferably at ambient temperature, into the cooling zone. In this embodiment, the reaction chamber is equipped with suitable means, such as an intake pipe, that allow the cooling gas to enter the cooling zone (b).

[0088] Preferably, the inlet pipe can be arranged so that part of the inlet gas flow is directed into the interior of the reaction chamber and part of the inlet gas flow flows essentially parallel to the walls. Such an arrangement helps to prevent the formed hollow spherical glass particles from sticking to the walls. Cooling the walls, as already outlined above, can assist in cooling.

[0089] FIG. 5 shows a schematic representation of one embodiment of a heating device for introducing non-combustible gas into the cooling zone (b). The heating device shown in FIG. 5 is horizontal (horizontal type). It includes elements of the heating device already shown in FIGS. 1 and 4. Precursor particles are added to the non-combustible gas stream. In addition, the cooling zone (b) is equipped with an inlet (16) for the non-combustible gas. The inlet is positioned so that the cooling gas flows downstream along the reactor wall, thereby cooling it. FIG. 5 also shows two optional elements that can be used: in the combustion zone (a), the inner wall of the reaction chamber is protected, preferably with a refractory material (17), to withstand high temperatures. Furthermore, the heating device is equipped with a flow straightener (18), which helps to avoid backmixing.

[0090] FIG. 6 shows a schematic representation of another embodiment for introducing cooling gas into the cooling zone. The reaction chamber includes an opening (22) through which external air is drawn into the reaction chamber, and this air is drawn in the form of a flow along the reactor wall. Multiple such openings can be arranged in a circumferential manner. In one embodiment, the opening (22) can be located at the beginning of the cooling zone (b) as shown in FIG. 6, but it can also be located further downstream. Of course, multiple such openings can also be located at different distances in the flow direction from one or more flames. Furthermore, FIG. 6 shows a further embodiment of the invention, namely, a two-component nozzle (23) supplying separate flows of air (21) and combustible gas (20).

[0091] During step (II-5), hollow spherical glass particles are separated from the exhaust gas stream. Such separation can be carried out by conventional techniques. In one embodiment of the present invention, a cyclone is used. Figures 1, 4 and 5 show a schematic representation of a heating device equipped with a cyclone (8) for separating the hollow spherical glass particles. The gas is removed through an outlet (9), and the hollow spherical glass particles are removed through another outlet (10). Of course, other devices, such as filters, can also be used for separation. The gas may contain residual amounts of fine particles, which can be separated using an additional filter, such as an electrofilter.

[0092] Figure 7 is a process flow diagram illustrating one embodiment of a plant for producing hollow spherical glass particles according to the method of the present invention. The diagram shows the reaction chamber (1) detailed above, in which hollow spherical glass particles are produced as described above. The resulting product stream, comprising exhaust gas and hollow spherical glass particles, is transferred through an outlet (7) to a cyclone (8), where the hollow spherical glass particles are separated from the gas stream and removed through an outlet (10). A heat exchanger (38) is provided in the line between the outlet and the cyclone to further reduce the temperature of the stream comprising exhaust gas and hollow spherical glass particles before it enters the cyclone (8). The exhaust gas stream (9) is transferred through an electric filter (26) to remove the remaining solid fraction from the exhaust gas stream. The exhaust gas stream (9) can be removed through outlet (27) and / or recycled to the reactor by compressor (25). Fresh non-combustible gas can be admitted through inlet (23). The exhaust gas and / or fresh gas stream is split, and a partial stream (24) is introduced into the mixing chamber (12). The second partial stream (28) flows directly through inlet (5). Precursor particles (13) are also admitted into the mixing chamber (12) and mixed with the partial gas stream (24). The resulting concentrated stream of precursor particles and exhaust gas and / or fresh gas is admitted into the second partial stream (28), and the combined stream is admitted into the reaction chamber through inlet (5). A portion of the exhaust gas stream (39) can be branched off, cooled by one or more heat exchangers (38), and admitted into the reaction chamber for the cooling purposes outlined above. The plant shown in FIG. 7 can be operated with fresh non-combustible gas admitted through inlet (23). In another embodiment, only a portion of the exhaust gases formed during the reaction is removed through outlet (27), while another portion is recycled and re-entered into the reaction chamber.

[0093] In another embodiment of the present invention, The heating device used for step (II) comprises at least: Inlet for flammable gases, Optionally, an inlet for non-flammable gas, a cylindrical rotatable reaction chamber, the ends of which are rotatably attached to a fixed front unit and a fixed rear unit; wherein the rotatable cylindrical reaction chamber is disposed horizontally or inclined toward the rear end of the reaction chamber, and the rotatable cylindrical reaction chamber comprises at least two distinct zones (a) and (b): (a) a combustion zone capable of being heated by at least one open flame; wherein at least one burner nozzle connected to an inlet for a combustible gas is disposed in the combustion zone; and (b) cooling zone; a fixed front unit comprising at least a fitting for a cylindrical rotatable reaction chamber, an inlet for a flammable gas flow connected with the arrangement of burner nozzles of zone (a), and optionally an inlet for a non-flammable gas; a fixed rear unit comprising at least a mounting for a cylindrical rotatable reaction chamber, an outlet for hollow spherical glass particles, and an outlet for exhaust gases, and a drive device for rotating the cylindrical rotatable reaction chamber about its longitudinal axis; and Step (II) is carried out as follows: (II-0') rotating a cylindrical rotatable reaction chamber about its longitudinal axis; (II-1') introducing a flammable gas stream through an inlet, transferring the flammable gas stream to one or more burner nozzles, and igniting at least one open flame; (II-2') optionally introducing a non-flammable gas stream through the inlet and moving the non-flammable gas stream to the outlet; (II-3') Adding precursor particles into a heating device and contacting the precursor particles with one or more open flames in a combustion zone (a), thereby obtaining hollow spherical glass particles in an exhaust gas stream by: Adding precursor particles to the combustible gas stream, and / or adding precursor particles to a non-flammable gas stream; (II-4') Cooling the hollow spherical glass particles in the exhaust gas stream by passing the hollow spherical glass particles through a cooling zone (b) by a rotational motion o; and (II-5') Removing the hollow spherical glass particles through the hollow spherical glass particle outlet of the fixed rear unit and / or separating the hollow spherical glass particles from the exhaust gas stream exiting through the exhaust gas outlet.

[0094] Figure 8 shows a schematic diagram of a specific embodiment of such a heating device. The heating device comprises a fixed front part (30) and a fixed rear part (31). A cylindrical rotatable reaction chamber (29) is rotatably attached at its ends to the front unit (30) and the rear unit (31). The inner diameter of the cylindrical reaction chamber may be, for example, 0.1 to 3 m, e.g., 1 to 3 m, but the present invention is not limited to these figures.

[0095] The rotatable reaction chamber comprises a combustion zone (a) heated by at least one open flame (3), preferably several flames, and a cooling zone (b). Details have already been given above, see the corresponding section above. The inner walls of the reaction chamber in the combustion zone (a) are preferably protected by a refractory material to withstand high temperatures. Suitable refractory materials have already been given above.

[0096] The stationary front unit (30) includes a mounting (32) for rotatably mounting at least a cylindrical reaction chamber and an inlet for a combustible gas (4), which inlet is connected to a burner nozzle (3), or preferably multiple burner nozzles, located in zone (a). Thus, the burner nozzle or nozzles (3) are not connected to the rotatable reaction chamber but extend from the stationary front unit into zone (a). As detailed above, the burner nozzle may be a one-component or two-component nozzle. The stationary front unit (30) may optionally include an inlet for a non-combustible gas.

[0097] The stationary rear unit also includes a mounting (32) for at least a cylindrical, rotatable reaction chamber, and an outlet (35) for hollow spherical glass particles (34) and at least an outlet for exhaust gas (35), through which at least a portion of the hollow spherical glass particles can also be removed from the heating unit. The outlet (34) is preferably located at the bottom of the stationary rear unit, so that the hollow spherical glass particles can be removed by gravity. The outlet (35) can optionally be connected to a unit for separating the hollow spherical glass particles from the exhaust gas stream, such as the filter or cyclone described above.

[0098] The heating unit further comprises means (33) for rotating the cylindrical rotatable reaction chamber about its longitudinal axis.

[0099] 9 shows a schematic representation of another embodiment of a heating unit comprising a rotatable reaction chamber, in which the inner walls of the combustion zone (a) are protected by a layer of refractory material (36) and further comprise an air inlet (37) for cooling the walls of the cooling zone (b).

[0100] The rotatable cylindrical reaction chamber is arranged horizontally or inclined toward its rear end. When the reaction chamber is inclined, the inclination angle of the cylindrical rotatable reaction chamber may be greater than 0° to 20°, preferably greater than 0° to 10°. The transport of the hollow spherical glass particles can be achieved by rotating the cylindrical reaction chamber alone, particularly in combination with the inclination of the reaction chamber. In another embodiment, the cylindrical rotatable reaction chamber includes a device for assisting the transport of materials, such as a screw, therein. Of course, the exhaust gas flow and, optionally, an additional non-flammable gas flow can also assist the transport of the product through the rotatable reaction chamber.

[0101] Figures 10 and 11 show diagrammatically embodiments in which the fixed front unit of the heating unit is additionally provided with an inlet (5) for a non-combustible gas: in Figure 10, precursor particles are added to the combustible gas stream, and in Figure 11, precursor particles are added to the non-combustible gas.

[0102] Step (II) of the embodiment of the present invention using a heating unit comprising a rotatable reaction chamber comprises at least five substeps (II-0'), (II-1'), (II-3'), (II-4'), and (II-5'). Optionally, the process can additionally comprise step (II-2').

[0103] During step (II-0'), the cylindrical rotatable reaction chamber is rotated around its longitudinal axis at a rotation speed that can be selected by those skilled in the art and may be, for example, 0.5 to 10 revolutions per minute (rpm).

[0104] During step (II-1'), a combustible gas stream is introduced through an inlet (4), travels through a tube to one or more burner nozzles (3) located in the combustion zone (a), and ignites a flame (2).

[0105] During step (II-3'), precursor particles are added into a heating device and brought into contact with one or more open flames in a combustion zone (a), thereby obtaining hollow spherical glass particles, exhaust gases produced by the combustion of combustible gases, and a stream of non-combustible gases.

[0106] In a first embodiment of step (II-3'), precursor particles are added to the combustible gas stream. Details regarding the addition of precursor particles to the combustible gas stream have already been described above. Methods for adding solids to the gas stream have already been described above. For example, the mixing chamber described above can be used. Such an embodiment is shown schematically in Figures 8, 9, and 10. In one embodiment, shown schematically in Figure 10, an additional non-combustible gas stream is admitted through inlet (5). As described above, such additional non-combustible gas can help avoid backmixing and assist in the transport of the hollow spherical glass particles towards the outlet.

[0107] In a second embodiment of step (II-3'), the stationary front unit further comprises an inlet (5) for a non-flammable gas, as shown in Figure 11, and the process includes step (II-2'). In step (II-2'), a non-flammable gas stream is introduced into the heating device through the inlet (5) and moves through the rotating reaction chamber (29) to the outlet (35). Precursor particles are added to the non-flammable gas stream. Thus, in this embodiment, the non-flammable gas acts as a carrier gas.

[0108] In step (II-4'), the hollow spherical glass particles, exhaust gas, and optionally a non-combustible gas flow through the cooling zone (b), thereby cooling the hollow spherical glass particles. As already described in detail above, the cooling zone (b) allows the hollow spherical glass particles formed in the combustion zone (a) to be cooled at least to a temperature at which the walls of the hollow spherical glass particles become solid. In one embodiment of the present invention, cooling is assisted by introducing a non-combustible gas, such as air or nitrogen, preferably at ambient temperature, into the cooling zone. In this embodiment, the reaction chamber comprises a suitable means, such as an intake pipe, for allowing the cooling gas to enter the cooling zone (b). Preferably, the intake pipe can be arranged so that the injected gas flow is essentially parallel to the wall. This arrangement helps to prevent the formed hollow spherical glass particles from sticking to the wall.

[0109] During step (II-5'), the hollow spherical glass particles are removed from the heating device through outlet (34) of the stationary rear unit and / or separated from the exhaust gas flow, or optionally from the exhaust gas and additionally injected non-combustible gas flow exiting through outlet (35). As mentioned above, for such separation, for example, a filter unit or a cyclone can be used.

[0110] Apparatus for carrying out the method In another embodiment, the present invention relates to a heating apparatus for heat treating precursor particles comprising SiO, AlO, and alkali metal oxides at a temperature of 1000-1800°C, thereby obtaining hollow spherical glass particles, comprising at least: a longitudinal reaction chamber comprising at least two distinct zones (a) and (b) of: (a) a combustion zone capable of being heated by at least one open flame; wherein at least one burner nozzle connected to a combustible gas inlet is disposed in the combustion zone; and (b) cooling zone; Inlet for flammable gases, an inlet for introducing a non-combustible gas into the combustion zone (a); A means for adding precursor particles containing SiO2, Al2O3, and alkali metal oxides to a combustible gas and / or a non-combustible gas, and An outlet for removing hollow spherical glass particles, non-flammable gas, and waste from the cooling zone (b).

[0111] Details of such a heating device, including preferred embodiments, have already been disclosed above, and reference is made to the respective sections of the above specification.

[0112] In yet another embodiment, the present invention relates to a heating apparatus for heat treating precursor particles comprising SiO, AlO, and alkali metal oxides at a temperature of 1000-1800°C, thereby obtaining hollow spherical glass particles, comprising at least: Inlet for flammable gases, Optionally, an inlet for non-flammable gas, a cylindrical rotatable reaction chamber, the ends of which are rotatably attached to a fixed front unit and a fixed rear unit; wherein the rotatable cylindrical reaction chamber is disposed horizontally or inclined toward the rear end of the reaction chamber, and the rotatable cylindrical reaction chamber comprises at least two distinct zones (a) and (b): (a) a combustion zone capable of being heated by at least one open flame; wherein at least one burner nozzle connected to an inlet for a combustible gas is disposed in the combustion zone; and (b) cooling zone; a fixed front unit comprising at least a fitting for a cylindrical rotatable reaction chamber, an inlet for a flammable gas flow connected with the arrangement of burner nozzles of zone (a), and optionally an inlet for a non-flammable gas; a fixed rear unit comprising at least a mounting for a cylindrical rotatable reaction chamber, an outlet for hollow spherical glass particles, and an outlet for exhaust gases, and A drive for rotating the cylindrical rotatable reaction chamber about its longitudinal axis.

[0113] Details of such a heating device, including preferred embodiments, have already been disclosed above, and reference is made to the respective sections of the above specification.

[0114] Use of hollow spherical glass particles The present invention relates to the use of hollow spherical glass particles comprising at least SiO2, Al2O3, and an alkali metal oxide as a filler for high temperature products, molten metals, injection molding composite materials, fire retardant insulating foams, cement slurries, mortars, concrete, and oil field applications, wherein the hollow spherical glass particles are produced by the above-described method.

[0115] In yet another embodiment, the present invention relates to the use of hollow spherical glass particles comprising at least SiO, AlO, and an alkali metal oxide as an additive to a molten metal having a melting point of at least 500°C, wherein the hollow spherical glass particles are produced by the method described above.

[0116] Details of the hollow spherical glass particles, including preferred embodiments thereof, and details of the method, including preferred embodiments thereof, have already been disclosed above, and reference is made to the respective sections of the above specification.

[0117] Preferably, the hollow spherical glass particles used as described above contain at least 30 wt. % SiO, at least 25 wt. % AlO, and at least 18 wt. % alkali metal oxide, preferably NaO, based on the total weight of the hollow spherical glass particles, and are boron-free. Furthermore, the hollow spherical glass particles used preferably have an average diameter of 20 μm to 200 μm, as described above.

[0118] In the method for producing such particles used as described above, it is preferred to use a starting composition containing at least zeolite, clay, and alkali metal carbonate, and to heat treat at a temperature of 1300°C to 1600°C.

[0119] Advantages of the Invention The above-described method according to the invention of heat treating precursor particles by contacting them with at least one open flame to obtain hollow spherical glass particles has advantages over the prior art.

[0120] Because the heating device is internally heated by one or more open flames and the heat treatment is carried out by contacting the precursor particles with these one or more open flames, there are no problems with heat transfer into the heating device, and thus the cylindrical heating device can advantageously have a very large inner diameter. This inner diameter can be, for example, 0.1 to 3 m, e.g., 1 to 3 m, but these figures are not intended to limit the invention. The possibility of such large diameters significantly facilitates the construction of high-capacity production plants. Scale-up from a laboratory or pilot production plant is easily achieved by simply increasing the number of burner nozzles and the diameter of the reaction chamber. The invention disclosed herein includes the following aspects: [1] A method for producing a film of at least SiO 2 , comprising at least the following steps: 2 、Al 2 O 3 1. A method for producing hollow spherical glass particles comprising: (I) Producing precursor particles by a method comprising at least the following substeps: (I-1) At least SiO 2 、Al 2 O 3 and providing a starting composition comprising particles of at least one starting compound for forming a glass comprising an alkali metal oxide; (I-2) mixing the starting composition with a liquid to obtain a slurry; and (I-3) spray-drying the obtained slurry to obtain the precursor particles; and (II) heat-treating the precursor particles at a temperature of 1000°C to 1800°C by passing the precursor particles through a heating device, thereby obtaining hollow spherical glass particles; wherein at least one open flame supplied by a combustible gas is burning inside the heating device, and the heat treatment is carried out by contacting the precursor particles with one or more of the open flames. A method for producing hollow spherical glass particles. [2] The hollow spherical glass particles each contain at least 30% by weight of SiO 2 based on the total weight of the hollow spherical glass particles. 2 , at least 25 wt. % Al 2 O 3 and at least 18 wt. % of an alkali metal oxide. [3] The alkali metal oxide is Na 2 The method according to [1] or [2] above, wherein O [4] The method according to any one of the above [1] to [3], wherein the hollow spherical glass particles do not contain boron. [5] The method according to any one of the above [1] to [4], wherein the hollow spherical glass particles have an average diameter of 20 μm to 200 μm. [6] The method according to any one of the above [1] to [5], wherein the starting composition contains at least a zeolite. [7] The method according to any one of the above [1] to [5], wherein the starting composition contains at least a zeolite, a clay, and an alkali metal carbonate. [8] The method according to any one of the above [1] to [7], wherein the temperature of the heat treatment is 1300°C to 1600°C. [9] The method according to any one of [1] to [8] above, wherein the contact time with one or more of the flames is 0.001 seconds to 1 second.

[10] The method according to any one of the above [1] to [9], wherein the heating device has a longitudinal reaction chamber.

[11] The method according to

[10] above, wherein the reaction chamber is cylindrical.

[12] The method according to

[10] or

[11] above, wherein the inner hydraulic diameter of the longitudinal reaction chamber is 0.1 to 3 m.

[13] The method according to any one of the above [1] to

[12] , wherein the precursor particles are dispersed in the combustible gas that supplies one or more of the flames to the heating device.

[14] The method according to any one of [1] to

[12] above, wherein the precursor particles are dispersed in a non-flammable gas added to the heating device at a position upstream of one or more of the flames.

[15] The method according to any one of the above [1] to

[14] , wherein after contact with one or more of the open flames, the obtained hollow spherical glass particles are cooled in at least one cooling zone by at least one method selected from the following: introducing a gas into the reaction chamber; and Cooling the walls of the reaction chamber.

[16] The method according to

[15] above, wherein the reaction chamber comprises at least two cooling zones.

[17] The method according to any one of the above [1] to [9], The heating device used for step (II) comprises at least: Inlet for flammable gases, Inlet for non-flammable gas, a longitudinal reaction chamber comprising at least two distinct zones (a) and (b) of: (a) a combustion zone capable of being heated by at least one open flame; wherein at least one burner nozzle connected to the inlet for the flammable gas is disposed in the combustion zone; and (b) cooling zone; and an outlet for the hollow spherical glass particles, non-flammable gas, and waste; and Step (II) is carried out as follows: (II-1) introducing the combustible gas stream through the inlet, transferring the combustible gas stream to one or more of the burner nozzles, and igniting at least one open flame; (II-2) introducing the non-combustible gas stream into the combustion zone (a) through the inlet and moving the non-combustible gas stream through the cooling zone (b) to the outlet; (II-3) Adding the precursor particles into the heating device by at least one method selected from the following, and contacting the precursor particles with one or more of the open flames in the combustion zone (a), thereby obtaining hollow spherical glass particles, exhaust gas generated by combustion of the combustible gas, and a stream of non-combustible gas: adding said precursor particles to said combustible gas stream; and / or adding the precursor particles to the non-flammable gas stream; (II-4) cooling the formed hollow spherical glass particles, exhaust gas, and non-combustible gas by passing them through the cooling zone (b); and (II-5) Separating the hollow spherical glass particles from the exhaust gas and the non-combustible gas.

[18] The method according to

[17] , wherein the longitudinal reaction chamber is oriented vertically, the combustion zone (a) is at a lower end of the reaction chamber, and the cooling zone (b) is at an upper end of the reaction chamber.

[19] The method according to

[17] or

[18] above, wherein the inner wall of the reaction chamber in the combustion zone (a) is protected by a refractory material.

[20] The method according to

[19] above, wherein the refractory material is cooled.

[21] The method according to any one of the above

[17] to

[20] , wherein the combustion zone (a) comprises a plurality of nozzles for the combustible gas.

[22] The method according to

[21] above, wherein the plurality of nozzles are arranged so that a flame is present across the entire cross section of the combustion zone (a).

[23] The method according to any one of

[17] to

[22] above, wherein the cooling zone (b) is provided with a means for additionally introducing cooling gas into the cooling zone.

[24] The method according to any one of the above

[17] to

[23] , wherein the wall of the cooling zone (b) is cooled by a non-flammable gas.

[25] The method according to any one of

[17] to

[24] above, wherein the reaction chamber includes at least two cooling zones and cooling is carried out in at least two steps.

[26] The method according to any one of the above

[17] to

[25] , wherein step (II-5) is carried out using a cyclone.

[27] The method according to any one of

[17] to

[26] above, wherein at least a portion of the mixture of the exhaust gas formed during the combustion and the non-combustible gas separated during step (II-5) is recycled.

[28] The method according to any one of [1] to [9] above, The heating device used for step (II) comprises at least: Inlet for flammable gases, Optionally, an inlet for non-flammable gas, a cylindrical rotatable reaction chamber, the ends of which are rotatably attached to a fixed front unit and a fixed rear unit; wherein the rotatable cylindrical reaction chamber is disposed horizontally or inclined toward the rear end of the reaction chamber, and the rotatable cylindrical reaction chamber comprises at least two distinct zones (a) and (b): (a) a combustion zone capable of being heated by at least one open flame; wherein at least one burner nozzle connected to the inlet for the combustible gas is disposed in the combustion zone; and (b) cooling zone; a fixed front unit comprising at least a fitting for said cylindrical rotatable reaction chamber, an inlet for a flammable gas flow connected with said arrangement of burner nozzles of zone (a), and optionally an inlet for a non-flammable gas; a fixed rear unit comprising at least a mounting for the cylindrical rotatable reaction chamber, an outlet for the hollow spherical glass particles, and an outlet for the exhaust gas; and a drive for rotating the cylindrical rotatable reaction chamber about its longitudinal axis; and Step (II) is carried out as follows: (II-0') rotating the cylindrical rotatable reaction chamber about its longitudinal axis; (II-1') introducing the combustible gas stream through the inlet, transferring the combustible gas stream to one or more of the burner nozzles, and igniting at least one open flame; (II-2') optionally introducing a non-combustible gas stream into the combustion zone (a) through the inlet and moving the non-combustible gas stream through the cooling zone (b) to the outlet; (II-3') Adding the precursor particles into the heating device and contacting the precursor particles with one or more of the open flames in the combustion zone (a), thereby obtaining hollow spherical glass particles in the exhaust gas stream by: adding said precursor particles to said combustible gas stream; and / or adding the precursor particles to the non-flammable gas stream; (II-4') cooling the hollow spherical glass particles in the exhaust gas stream by passing the hollow spherical glass particles through the cooling zone (b) by a rotational motion o; and (II-5') Removing the hollow spherical glass particles through the hollow spherical glass particle outlet of the fixed rear unit, and / or separating the hollow spherical glass particles from the exhaust gas flow that has exited through the exhaust gas outlet.

[29] The method according to

[28] above, wherein the inclination angle of the cylindrical rotatable reaction chamber is greater than 0° and less than 10°.

[30] The method according to

[28] or

[29] above, wherein the inner wall of the reaction chamber in the combustion zone (a) is protected by a refractory material.

[31] The method according to any one of the above

[28] to

[30] , wherein the combustion zone (a) comprises a plurality of nozzles for the combustible gas.

[32] The method according to

[31] above, wherein the plurality of nozzles are arranged so that a flame is present across the entire cross section of the combustion zone (a).

[33] The method according to any one of

[28] to

[32] above, wherein the cooling zone (b) is provided with a means for introducing a cooling gas into the reaction chamber.

[34] The method according to any one of the above

[28] to

[33] , wherein step (II-5') is carried out using a cyclone.

[35] The method according to any one of the above

[28] to

[34] , wherein a mixture of the exhaust gas formed during the combustion and the non-combustible gas separated during step (II-5') is recycled.

[36] SiO 2 、Al 2 O 3 and an alkali metal oxide, and a heating device for heat-treating precursor particles containing the precursor particles at a temperature of 1000 to 1800°C to obtain hollow spherical glass particles, the heating device comprising at least the following: a longitudinal reaction chamber comprising at least two distinct zones (a) and (b) of: (a) a combustion zone capable of being heated by at least one open flame; wherein at least one burner nozzle connected to a combustible gas inlet is disposed in the combustion zone; and (b) cooling zone; an inlet for said flammable gas; an inlet for introducing a non-combustible gas into said combustion zone (a); SiO 2 、Al 2 O 3 and a means for adding precursor particles comprising an alkali metal oxide to the combustible gas and / or the non-combustible gas; and an outlet for removing hollow spherical glass particles, non-combustible gas, and waste products from said cooling zone (b);

[37] The heating device according to

[36] above, wherein the inner wall of the reaction chamber in the combustion zone (a) is protected by a refractory material.

[38] The heating device according to

[37] above, wherein the heating device is provided with means for cooling the refractory material.

[39] The heating device according to any one of the above

[36] to

[38] , wherein the combustion zone (a) comprises a plurality of nozzles for the combustible gas.

[40] The heating device described in

[39] above, wherein the plurality of nozzles are arranged so that a flame is present across the entire cross section of the combustion zone (a).

[41] The heating device according to any one of the above

[36] to

[40] , wherein the cooling zone (b) is provided with a means for additionally introducing cooling gas into the cooling zone.

[42] The heating device according to any one of the above

[36] to

[41] , wherein the wall of the cooling zone (b) is double-walled and has at least an inlet and an outlet for cooling gas.

[43] The heating device according to any one of the above

[36] to

[42] , wherein the heating device is provided with a cyclone connected to the outlet.

[44] SiO 2 、Al 2 O 3 and a heating device for heat-treating precursor particles containing an alkali metal oxide at a temperature of 1000 to 1800°C to obtain hollow spherical glass particles, the heating device comprising at least the following: Inlet for flammable gases, Optionally, an inlet for non-flammable gas, a cylindrical rotatable reaction chamber, the ends of which are rotatably attached to a fixed front unit and a fixed rear unit; wherein the rotatable cylindrical reaction chamber is disposed horizontally or inclined toward the rear end of the reaction chamber, and the rotatable cylindrical reaction chamber comprises at least two distinct zones (a) and (b): (a) a combustion zone capable of being heated by at least one open flame; wherein at least one burner nozzle connected to the inlet for the combustible gas is disposed in the combustion zone; and (b) cooling zone; a fixed front unit comprising at least a fitting for said cylindrical rotatable reaction chamber, an inlet for a flammable gas flow connected with said arrangement of burner nozzles of zone (a), and optionally an inlet for a non-flammable gas; a fixed rear unit comprising at least a mounting for the cylindrical rotatable reaction chamber, an outlet for the hollow spherical glass particles, and an outlet for the exhaust gas; and A drive for rotating said cylindrical rotatable reaction chamber about its longitudinal axis.

[45] The heating device according to

[44] above, wherein the inclination angle of the cylindrical rotatable reaction chamber is greater than 0° and less than 10°.

[46] The heating device according to

[44] or

[45] above, wherein the inner wall of the reaction chamber in the combustion zone (a) is protected by a refractory material.

[47] The heating device according to any one of the above

[44] to

[46] , wherein the combustion zone (a) comprises a plurality of nozzles for the combustible gas.

[48] The heating device described in

[47] above, wherein the plurality of nozzles are arranged so that a flame is present across the entire cross section of the combustion zone (a).

[49] The heating device according to any one of the above

[44] to

[48] , wherein the cooling zone (b) is provided with a means for introducing a cooling gas into the reaction chamber.

[50] The heating device according to any one of

[44] to

[49] above, wherein the heating device comprises a cyclone connected to the outlet for exhaust gas.

[51] A method for producing a cellulose ester resin containing at least SiO 2 as a filler for high temperature products, molten metals, injection molding synthetic materials, fire retardant insulation foams, cement slurries, mortars, concrete, and oil field applications. 2 、Al 2 O 3 and an alkali metal oxide, wherein the hollow spherical glass particles are produced by the method described in any one of [1] to

[35] above.

[52] As an additive to molten metals with a melting point of at least 500°C, 2 、Al 2 O 3 and an alkali metal oxide, wherein the hollow spherical glass particles are produced by the method described in any one of [1] to

[35] above.

Claims

1. At least SiO ２ , Al ２ O ３ 1. A method for producing hollow spherical glass particles comprising: (I) Producing precursor particles by a method comprising at least the following substeps: (I-1) At least SiO ２ , Al ２ O ３ and providing a starting composition comprising particles of at least one starting compound for forming a glass comprising an alkali metal oxide; (I-2) mixing the starting composition with a liquid to obtain a slurry; and (I-3) spray-drying the obtained slurry to obtain the precursor particles; and (II) heat-treating the precursor particles at a temperature of 1000°C to 1800°C by passing the precursor particles through a heating device, thereby obtaining hollow spherical glass particles; wherein at least one open flame supplied by a combustible gas is burning inside the heating device, and the heat treatment is carried out by contacting the precursor particles with one or more of the open flames; dispersing the precursor particles in the combustible gas supplying the one or more flames to the heating device and / or dispersing the precursor particles in a non-combustible gas added to the heating device at a location upstream of the one or more flames; the starting composition does not contain boron, and The amount of boron contained in the hollow spherical glass particles is 1.0 wt % or less, based on the total weight of the hollow spherical glass particles. A method for producing hollow spherical glass particles.

2. The method of claim 1 , wherein the heating device comprises a longitudinal reaction chamber.

3. The method of claim 2 , wherein the reaction chamber is cylindrical.

4. 4. The method according to claim 1, wherein after contact with one or more open flames, the obtained hollow spherical glass particles are cooled in at least one cooling zone by at least one method selected from the following: - introducing a gas into the reaction chamber; and Cooling the walls of the reaction chamber.

5. 10. The method of claim 1, The heating device used for step (II) comprises at least: - inlets for flammable gases, - inlet for non-flammable gas, A longitudinal reaction chamber comprising at least two distinct zones (a) and (b): (a) a combustion zone capable of being heated by at least one open flame; wherein at least one burner nozzle connected to the inlet for the flammable gas is disposed in the combustion zone; and (b) a cooling zone; and an outlet for the hollow spherical glass particles, non-flammable gas, and waste; and Step (II) is carried out as follows: (II-1) introducing the flammable gas flow through the inlet, transferring the flammable gas flow to one or more of the burner nozzles, and igniting at least one open flame; (II-2) introducing the non-combustible gas stream into the combustion zone (a) through the inlet and moving the non-combustible gas stream through the cooling zone (b) to the outlet; (II-3) Adding the precursor particles into the heating device by at least one method selected from the following, and contacting the precursor particles with one or more of the open flames in the combustion zone (a), thereby obtaining hollow spherical glass particles, exhaust gas generated by combustion of the combustible gas, and a stream of non-combustible gas: adding the precursor particles to the combustible gas stream; and / or adding said precursor particles to said non-combustible gas stream; (II-4) cooling the formed hollow spherical glass particles, exhaust gas, and non-combustible gas by passing them through the cooling zone (b); (II-5) Separating the hollow spherical glass particles from the exhaust gas and the non-combustible gas.

6. 6. The method of claim 5, wherein the reaction chamber comprises at least two cooling zones and the cooling is performed in at least two steps.

7. 10. The method of claim 1, The heating device used for step (II) comprises at least: - inlets for flammable gases, Optionally, an inlet for a non-flammable gas; a cylindrical rotatable reaction chamber, the ends of which are rotatably attached to a fixed front unit and a fixed rear unit; wherein the rotatable cylindrical reaction chamber is disposed horizontally or inclined toward the rear end of the reaction chamber, and the rotatable cylindrical reaction chamber comprises at least two distinct zones (a) and (b): (a) a combustion zone capable of being heated by at least one open flame; wherein at least one burner nozzle connected to the inlet for the combustible gas is disposed in the combustion zone; and (b) a cooling zone; a fixed front unit comprising at least a fitting for said cylindrical rotatable reaction chamber, an inlet for a combustible gas flow connected with said arrangement of burner nozzles of zone (a), and optionally an inlet for a non-combustible gas; a fixed rear unit comprising at least a mounting for the cylindrical rotatable reaction chamber, an outlet for the hollow spherical glass particles, and an outlet for the exhaust gas; and a drive for rotating the cylindrical rotatable reaction chamber about its longitudinal axis; and Step (II) is carried out as follows: (II-0') rotating the cylindrical rotatable reaction chamber about its longitudinal axis; (II-1') introducing the combustible gas flow through the inlet, transferring the combustible gas flow to one or more of the burner nozzles, and igniting at least one open flame; (II-2') optionally, introducing a non-combustible gas stream into the combustion zone (a) through the inlet and moving the non-combustible gas stream through the cooling zone (b) to the outlet; (II-3') Adding the precursor particles into the heating device and contacting the precursor particles with one or more open flames in the combustion zone (a), thereby obtaining hollow spherical glass particles in an exhaust gas stream by: adding the precursor particles to the combustible gas stream; and / or adding said precursor particles to said non-combustible gas stream; (II-4') cooling the hollow spherical glass particles in the exhaust gas stream by passing the hollow spherical glass particles through the cooling zone (b) by a rotational motion; and (II-5') Removing the hollow spherical glass particles through the hollow spherical glass particle outlet of the fixed rear unit, and / or separating the hollow spherical glass particles from the exhaust gas flow that has exited through the exhaust gas outlet.

8. 8. The method of claim 7, wherein the combustion zone (a) comprises a plurality of nozzles for the combustible gas.

9. 9. The method of claim 8, wherein the plurality of nozzles are arranged so that a flame is present across the entire cross section of the combustion zone (a).

10. 10. The method according to any one of claims 7 to 9, wherein the mixture of exhaust gases formed during combustion and non-combustible gases separated during step (II-5') is recycled.

11. SiO ２ , Al ２ O ３ and an alkali metal oxide, at a temperature of 1000 to 1800°C to obtain hollow spherical glass particles. A longitudinal reaction chamber comprising at least two distinct zones (a) and (b): (a) a combustion zone capable of being heated by at least one open flame; wherein at least one burner nozzle connected to a combustible gas inlet is disposed in the combustion zone; and (b) a cooling zone; an inlet for said combustible gas; an inlet for introducing a non-combustible gas into said combustion zone (a); SiO ２ , Al ２ O ３ and a means for adding precursor particles containing an alkali metal oxide to the combustible gas and / or the non-combustible gas. wherein the precursor particles are dispersed in the combustible gas supplying the one or more flames to the heating device and / or the precursor particles are dispersed in a non-combustible gas added to the heating device at a location upstream of the one or more flames; an outlet for removing hollow spherical glass particles, non-combustible gas, and waste from said cooling zone (b); Here, the amount of boron contained in the hollow spherical glass particles is 1.0 wt % or less based on the total weight of the hollow spherical glass particles.

12. 12. The heating device according to claim 11, wherein the wall of the cooling zone (b) is double-walled and is provided with at least an inlet and an outlet for cooling gas.

13. SiO ２ , Al ２ O ３ and a heating device for heat-treating precursor particles containing an alkali metal oxide at a temperature of 1000 to 1800°C, thereby obtaining hollow spherical glass particles, the heating device comprising at least: - inlets for flammable gases, Optionally, an inlet for a non-flammable gas; a cylindrical rotatable reaction chamber, the ends of which are rotatably attached to a fixed front unit and a fixed rear unit; wherein the rotatable cylindrical reaction chamber is disposed horizontally or inclined toward the rear end of the reaction chamber, and the rotatable cylindrical reaction chamber comprises at least two distinct zones (a) and (b): (a) a combustion zone capable of being heated by at least one open flame; wherein at least one burner nozzle connected to the inlet for the combustible gas is disposed in the combustion zone; and (b) a cooling zone; a fixed front unit comprising at least a fitting for said cylindrical rotatable reaction chamber, an inlet for a combustible gas flow connected with said arrangement of burner nozzles of zone (a), and optionally an inlet for a non-combustible gas; a fixed rear unit comprising at least a mounting for the cylindrical rotatable reaction chamber, an outlet for the hollow spherical glass particles, and an outlet for the exhaust gas; and a drive for rotating the cylindrical rotatable reaction chamber about its longitudinal axis; Here, the amount of boron contained in the hollow spherical glass particles is 1.0 wt % or less based on the total weight of the hollow spherical glass particles.

14. 14. The heating device of claim 13, wherein the combustion zone (a) includes a plurality of nozzles for a combustible gas.

15. 15. The heating device of claim 14, wherein the plurality of nozzles are arranged so that a flame is present across the entire cross section of the combustion zone (a).

16. as a filler for high temperature products, molten metals, injection molding synthetic materials, fire retardant insulation foams, cement slurries, mortars, concrete, and oil field applications. ２ , Al ２ O ３ and an alkali metal oxide, wherein the hollow spherical glass particles are produced by the method according to any one of claims 1 to 10.

17. At least SiO as an additive to molten metals with a melting point of at least 500°C ２ , Al ２ O ３ and an alkali metal oxide, wherein the hollow spherical glass particles are produced by the method according to any one of claims 1 to 10.

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