Preparation method of silicon dioxide

Abstract

The invention relates to a method for producing silica, in particular precipitated silica, in which a process gas comprising carbon dioxide is used, said gas being dispersed in an alkali metal silicate solution in a static mixer located outside the reaction vessel. The invention also relates to an apparatus for preparing precipitated silica, comprising a reaction vessel (1), a bypass section comprising a static mixer (5), a line (7), an optional metering point (6) and / or a pump (8), where the bypass section is located outside the reaction vessel and is connected to the vessel via a line, and wherein the static mixer is configured to circulate back to the reaction vessel via a line.

Description

Technical Field

[0001] The present invention relates to a method for producing silica, in particular precipitated silica, which uses a process gas containing carbon dioxide, and to its production apparatus. Background Art

[0002] Methods for producing precipitated silica in the liquid phase are well known in the art.

[0003] In recent years, there has been a growing interest in using emitted process gases in chemical production processes in order to support the environmental conversion cycle. In the method for producing precipitated silica, a process gas containing carbon dioxide is reacted with an alkali metal silicate.

[0004] The manner in which the process gas is dispersed into the alkali metal silicate solution may vary in each process, and those skilled in the art are seeking to achieve increased carbon dioxide / alkali metal silicate interaction. Enhanced interaction is achieved as follows: by increasing the carbon dioxide concentration in the reaction medium through purification of the process gas, or by better dispersing the gas into the solution using an air distributor, which subsequently results in increased yield of silica production and / or controlled silica particle size.

[0005] US2006225615(A1) discloses a method for producing precipitated silica, in which the gas is directly injected into the precipitation vessel after silica precipitation.

[0006] CN 212356558(A) discloses an apparatus for producing precipitated silica by carbon dioxide dispersion, in which carbon dioxide is dispersed in the reaction liquid by dispersion vanes, and the dispersion vanes are all arranged in the reaction kettle.

[0007] CN 104418332(B) discloses a method for producing silica by directly dispersing a process gas containing carbon dioxide into a reactor via an air distributor. The CO concentration is increased by process gas purification before the process gas is fed into the reaction medium, which requires additional process steps, and the particle size distribution is controlled by means of reaction vanes. 2 Concentration, which requires additional process steps, and the particle size distribution is controlled by means of reaction vanes.

[0008] All known methods in the art directly distribute the process gas into the liquid solution in the reactor, with or without prior gas purification. They attempt to better distribute CO by means of a mixer, a vane reactor, or by using a nozzle, an air distributor, or a pump. 2 However, none of these methods provides the required distribution of carbon dioxide gas into the alkaline solution.

[0009] In addition, conventional reactors cannot be properly used for silica production while using process gases and require special reactor designs.

[0010] Process gases typically have a low CO 2 concentration, and the CO 2 gas is not evenly dispersed in the silicate solution, resulting in an uneven particle size distribution (large aggregates or fine powder). Therefore, a powerful pump or air distributor is required to evenly disperse the CO 2 gas in the silicate solution. In some cases, gas purification is required to increase the reaction rate.

[0011] Therefore, a method is needed that can improve the yield of the silica production process while still using process gases, without the need for further process gas purification steps or the use of an air distributor that directly distributes the gas into the solution in the reactor medium. Summary of the Invention

[0012] The object of the present invention is to provide a method for better dispersing CO 2 into the sodium silicate solution during the production of precipitated silica, which brings improved silica yield with a shorter precipitation time by increasing the reaction rate in a timely manner. Overview of the Invention

[0014] The present invention provides a method for preparing silica (silica) using a process gas containing carbon dioxide according to the claims. The method of the present invention solves the problem of uneven particle size distribution without using an air distributor or similar type, and solves the problem of low yield by increasing the reaction rate without further gas purification.

[0015] It has surprisingly been found that when a process gas containing carbon dioxide is dispersed into the reaction medium via a bypass section containing a static mixer located outside the reactor and then recycled into the reaction kettle, no further gas purification step or further arrangement within the reactor vessel, such as using a nozzle / pump or air distributor, is required to achieve uniform dispersion / distribution of CO 2 into the liquid phase. Compared to a standard precipitation reactor with direct gas injection into the reactor, an increased CO 2 yield is obtained at the same process time.

[0016] An increased reaction rate is achieved through better interaction of CO 2 with the alkali metal silicate when forming precipitated silica. Since CO 2 is more effectively used to react with the same amount of silicate solution, a higher space / time yield of silica production can also be obtained.

[0017] The method can be carried out in a conventional reactor known in the art without the need for further arrangement inside the reactor. By using a bypass section, the need for a special reactor design for silica production while using process gas is thus overcome.

[0018] According to a first aspect, the present invention relates to a method for preparing precipitated silica as defined in claim 1.

[0019] The method for preparing precipitated silica comprises the following steps:

[0020] (a) Providing an alkali metal silicate solution in a reaction vessel (1);

[0021] (b) Transferring the alkali metal silicate solution from the reaction vessel (1) to a bypass section comprising a static mixer (5) and a pipeline (7), wherein the bypass section is located outside the reaction vessel (1) and is connected to the vessel via a pipeline;

[0022] (c) Dispensing a process gas containing carbon dioxide into the alkali metal silicate solution in the static mixer (5);

[0023] (d) Returning the alkali metal silicate solution reacted with the process gas to the reaction vessel;

[0024] (e) Precipitating silica, and then filtering, washing and drying to obtain precipitated silica.

[0025] Preferably, the process gas contains carbon dioxide at a concentration of more than 10% by volume, preferably 20%, or 30%, or 40%, or 50%, or 60%, or 70%, or 80%, or 90%.

[0026] The process gas can enter the static mixer in the form of bubbles via a metering point.

[0027] Preferably, in step (a), the alkali metal silicate solution is mixed with water to obtain a solution with a pH higher than 8, preferably 9, preferably at a temperature between 50 - 95 °C.

[0028] According to the present invention, a further alkali metal silicate solution can be added to the reaction vessel to maintain the pH within the range of higher than 8 to 10.5.

[0029] Preferably, the process gas is metered in the pipeline before the static mixer, preferably near the static mixer, or in the static mixer.

[0030] According to the method of the present invention, the alkali metal silicate solution is metered from the reactor tank into the static mixer via a pipeline, and the process gas is preferably metered into the static mixer simultaneously with the alkali metal silicate solution.

[0031] In the present invention, the alkali metal silicate solution mixture can be circulated back to the reaction vessel from the reaction vessel through a bypass section at least once. Preferably, in step (d), the carried alkali metal silicate solution mixture after reacting with the process gas and transferred to the reaction vessel through the pipeline is circulated more than once.

[0032] According to a preferred embodiment of the present invention, the alkali metal silicate solution is a sodium silicate solution.

[0033] The filtered silica in step (e) is preferably dried under the condition of adding an inorganic acid, such as sulfuric acid, or with a process gas containing CO 2 or containing CO 2 to adjust the pH value between 4 and 9, preferably between 6 and 8.2.

[0034] According to a second aspect, the present invention relates to a device for preparing the precipitated silica material as defined in the claims.

[0035] The device includes a reaction vessel (1), a bypass section including a static mixer (5) and a pipeline (7), wherein the bypass section is located outside the reaction vessel and is connected to the vessel via a pipeline, and wherein the static mixer is configured to be circulated back to the reaction vessel via a pipeline.

[0036] Preferably, the bypass section further includes a metering point (6) for metering the process gas through the static mixer, and the process gas metering point is located before the static mixer in the flow direction, preferably near the static mixer, or on the static mixer.

[0037] Preferably, the metering point is located on the pipeline before the static mixer in the flow direction, more preferably near the static mixer.

[0038] The bypass section may include more than one static mixer, preferably located one after another on the pipeline.

[0039] Preferably, the reaction vessel includes a water metering point (3) and a silicate solution metering point (4), preferably located at the top or side of the reaction vessel.

[0040] Preferably, the reaction vessel includes an outlet (or suspension outlet) (9) preferably located at the bottom of the reactor to release the solution from the reactor.

[0041] The reaction vessel may further include dispersion blades or a stirrer.

[0042] By using this device arrangement, there is no need for spray nozzles, gas distributors or special high-pressure pumps to directly disperse the process gas in the reaction vessel.

[0043] The present invention also relates to the use of a static mixer for the production of precipitated silica. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] To better illustrate the advantages and performance of the claimed silica preparation method and the apparatus used in this method, the figures mentioned below are attached as non - limiting examples of the production method.

[0045] Figure 1 Showing the overall production apparatus for silica production having a reaction vessel and a static mixer. DETAILED DESCRIPTION OF THE INVENTION

[0047] The present invention provides an improved method for the production of silica, comprising the following steps:

[0048] (a) Providing an alkali metal silicate solution to a reaction vessel (1);

[0049] (b) Transferring the alkali metal silicate solution from the reaction vessel (1) to a bypass section comprising a static mixer (5) and a pipeline (7), wherein the bypass section is located outside the reaction vessel (1) and is connected to the vessel via a pipeline;

[0050] (c) Dispensing a process gas containing carbon dioxide into the alkali metal silicate solution in the static mixer (5);

[0051] (d) Returning the alkali metal silicate solution reacted with the process gas to the reaction vessel; and

[0052] (e) Precipitating silica, and then filtering, washing and drying to obtain precipitated silica.

[0053] The present invention also relates to an apparatus for preparing the precipitated silica, the apparatus comprising a reaction vessel (a), a bypass section comprising a static mixer (5) and a pipeline (7), wherein the bypass section is located outside the reaction vessel and is connected to the vessel via a pipeline, and the static mixer is configured to be recycled back to the reaction vessel via a pipeline.

[0054] The term "reaction vessel" refers to a reaction cup or container that facilitates the entire process. Terms such as reaction tank, reaction container or reactor can be used interchangeably.

[0055] The reaction vessel preferably comprises a water metering point (3) and a silicate solution metering point (4). The water and silicate solution metering points are preferably located at the top or side of the reaction vessel.

[0056] The reaction vessel may further comprise dispersion vanes or a stirrer, a pH sensor and a temperature sensor. Heating can be achieved by direct steam injection or a heating jacket. The dispersion vanes, pH sensor and temperature sensor can be arranged inside the reaction vessel.

[0057] Mixers and agitators can be arranged inside the reaction vessel. The device may also include dispersion vanes to disperse the reacted liquid in the silicate solution in the reaction vessel.

[0058] The dispersion vanes or mixers can be equipped with gas outlet holes communicating with the internal parts of the reaction vessel and also with a gas source to directly feed process gas into the reaction vessel through these gas outlet holes.

[0059] In a preferred embodiment of the present invention, the reaction vessel can be a gas - liquid phase reactor, which can be a stirred tank reactor or a liquid / liquid phase reactor.

[0060] The bypass section according to the present invention includes a bypass section comprising a static mixer (5) and a pipeline (7). The bypass section is located outside the reaction vessel (1) and is connected to the vessel via a pipeline. Preferably, the pipeline extends from the lower part of the reaction vessel to the upper part of the reaction vessel, more preferably from the bottom of the reaction vessel to the top of the reaction vessel, or from the bottom of the reaction vessel to the middle or above of the reaction vessel.

[0061] The bypass section is connected to the reaction vessel via a pipeline to be referred to / used as a bypass system in silica production.

[0062] The bypass section preferably further includes a metering point (6).

[0063] Preferably, the metering point is on the pipeline before the static mixer in the flow direction, more preferably near the static mixer.

[0064] Alternatively, the metering point can be located on the static mixer.

[0065] The metering point can be formed by at least one gas hole, and the diameter of the metering point can vary depending on the reactor size, the length of the static mixer, and all other flow parameters.

[0066] Optionally, the bypass section can include a pump to pump the alkali metal silicate solution through the bypass section via the pipeline. Preferably, the pump is arranged between the bottom of the reaction vessel and the static mixer.

[0067] The reaction vessel (1) is connected to one end of the bypass section via a pipeline, and the pipeline extends back from the other end of the bypass section to the reaction vessel to circulate the alkali metal silicate solution.

[0068] According to the present invention, preferably, the process gas flows / presses on the silicate solution at the metering point very close to the static mixer.

[0069] Preferably, the process gas mass flow rate (kg / h) is from 400 g / min for a 2m 3 reactor vessel to for a 160m3 32700 g / min for the reactor vessel. The mass rate depends on the final reactor size.

[0070] The bypass section in the device may contain more than one static mixer. In this case, the process gas is metered into the alkali metal silicate solution before the first static mixer, and then the mixture moves from the first static mixer to further static mixers for further reaction and mixing, and to achieve sufficient mixing of CO 2 gas with the alkali metal silicate solution and better CO 2 distribution.

[0071] The length of the static mixer will also depend on the reactor size and the pipeline diameter. The larger the reactor, the longer the pipeline must be to connect all structures. Generally, the pipeline should not be longer than necessary.

[0072] A static mixer is a device for continuously mixing fluid materials without moving components. Generally, the fluids to be mixed are liquids, but static mixers can also be used to mix gas streams, disperse gases into liquids, or blend immiscible liquids. The energy required for mixing comes from the pressure loss when the fluid flows through the static mixer, or from inserts that direct the flow of the liquid / gas in a turbulent manner when the liquid / gas flows through. Static mixers are well known in the art for different uses in chemical processing.

[0073] In the present invention, different types of static mixer designs can be used, such as plate-type mixers or device types consisting of mixer elements contained in a cylindrical (tube) or square housing. Horizontal or vertical static mixers can be used. Without relying on any specific model or source, static mixers from Sulzer are versatile and can be effectively used in the present invention.

[0074] Any known construction materials for static mixer components can be used, including stainless steel, polypropylene, Teflon, PVDF, PVC, CPVC, and glass-lined steel, preferably PVDF or stainless steel.

[0075] By using a process gas containing carbon dioxide instead of other known inorganic acids such as sulfuric acid, the environmental impact of acid consumption is reduced, and since it is recycled into the silica production process, the amount of CO 2 released via the process gas is also reduced. These two beneficial effects both directly support a sustainable method for producing silica.

[0076] In addition, by using a bypass section containing a static mixer, further purification of the process gas is eliminated because CO 2It is evenly distributed into the solution by means of a static mixer in the bypass section, which also improves the yield of silica production with a uniform particle size distribution in a shorter time period. The static mixer in the bypass section enables very good dispersion of CO 2 gas into the silicate solution, which is then recycled to the reaction kettle to be mixed with the alkali metal silicate solution.

[0077] By using this device arrangement, there is no need for a spray nozzle, a gas distributor or a special high-pressure pump to directly disperse the process gas in the reaction kettle, although they can be used or present in the reaction kettle.

[0078] The alkali metal silicate solution is well known in the art and is a combination of an alkali metal oxide (e.g., Na 2 O), silica and water, or a combination of an alkali metal silicate and water.

[0079] Although other alkali metals such as lithium or potassium can be used, the alkali metal silicate solution is preferably a sodium silicate solution, also known as water glass. The sodium silicate solution can be produced under a wide range of compositions and is distinguished by the ratio of silica to the alkali metal, with the general formula (Na 2 O) x ·(SiO 2 ) y ·(H 2 O) z , where x, y, z are molar ratios.

[0080] Preferably, water and the alkali metal silicate solution are added to the reaction kettle in step (a) to make the pH higher than 8, more preferably higher than 9. Preferably, the pH is maintained below 10.5. During the process of the alkali metal silicate solution circulating through the pipeline section, the pH range is kept constant by adding additional alkali metal silicate solution.

[0081] According to the present invention, it is preferred to suck the alkali metal silicate solution from the bottom of the reaction kettle and send it to the static mixer (5) via the pipeline (7), optionally with the aid of a pump (8) arranged on the surface of the pipeline located between the bottom of the reaction kettle and the static mixer (5).

[0082] In one aspect of the present invention, the reaction between the alkali metal silicate solution and CO 2 gas mainly occurs in the static mixer, and the alkali metal silicate solution in which the process gas containing carbon dioxide is dispersed is recycled to the reaction kettle via the pipeline. Therefore, no additional process gas or CO 2 gas is pumped / sent into the reactor itself.

[0083] In another aspect of the present invention, dispersing the process gas containing carbon dioxide through the bypass section may not require the installation of an air distributor or a pump inside the reactor to distribute additional process gas.

[0084] The alkaline solution mixture should stay in the static mixer for the time required for the reaction to occur. If the gas is introduced into the mixer in the form of bubbles, the goal is to reduce the bubble size in the static mixer as much as possible. When the alkaline solution mixture is released from the static mixer, the goal is to have very small bubbles or no bubbles. It goes without saying that the longer the static mixer, the longer the alkaline solution mixture will stay in the static mixer.

[0085] CO 2 is mainly converted to carbonic acid in the static mixer and enters the reaction vessel via a pipeline for continuous precipitation in the reaction vessel. There may be a possibility that some precipitation may also occur in the static mixer or the pipeline.

[0086] In a preferred embodiment of the present invention, the alkali metal silicate solution reacts with CO 2 in a static mixer on a pipeline located outside the reactor as part of the bypass section, and the dispersed solution is then recycled to the reactor at least once or more.

[0087] This new dispersion method within the present invention enables CO 2 to be more evenly dispersed into the liquid phase, so as to better react with sodium silicate to form precipitated silica. Therefore, a higher space-time yield is achieved for precipitating silica with CO 2

[0088] The process gas can be any waste gas containing carbon dioxide. It can be exhaust gas, tail gas containing carbon dioxide, or waste gas from biomass. The process gas can also be, for example, carbon dioxide gas captured during a calcination or wastewater recycling process.

[0089] The above-mentioned process gas may contain at least 10% by volume of carbon dioxide concentration. The process gas preferably contains more than 10% by volume, preferably more than 20% or 30% or 40%, or 50%, or 60%, or 70%, or 80%, or 90% of carbon dioxide concentration. The process gas may further contain carbon monoxide, hydrogen, nitrogen, oxygen, sulfur or its oxides.

[0090] In a preferred embodiment of the present invention, the process gas containing carbon dioxide is pressurized at the metering point and uniformly dispersed into the alkali metal silicate solution in the form of fine bubbles.

[0091] The gas pressure at the metering point is preferably 2.5 to 4.5 bar.

[0092] Preferably, the alkali metal silicate solution is metered from the reactor tank via a pipeline into the static mixer, and the process gas is preferably metered into the static mixer simultaneously with the alkali metal silicate solution to keep the value of the pH or the Alkaline Number (the type of which depends on the formulation) constant.

[0093] The precipitation reaction temperature is generally 50 °C to 95 °C, and the reaction time for precipitating silica is between 40 minutes and 150 minutes and at atmospheric pressure, which depends on the specific components.

[0094] Heating can be achieved by direct steam injection or a heating jacket.

[0095] By using this type of static mixer and optionally flowing the process gas over the silicate solution via a metering point in this mixer section and then recycling it to the reaction kettle, the process gas and the silicate solution can be fully mixed and reacted, so that no further reaction occurs in the reaction kettle, which increases the reaction rate and the yield of silica production.

[0096] In a preferred embodiment of the present invention, the reaction of the alkali metal silicate solution with CO in the process gas 2 is terminated by re-acidifying the solution preferably with CO 2 and a process gas containing CO 2 to precipitate, and then filtered to obtain filtered silica.

[0097] In an embodiment of the present invention, the filtered silica is then dried by rotary flash drying with the addition of an inorganic acid such as sulfuric acid to reach a final pH of 6.5.

[0098] In an embodiment of the present invention, in the drying step, a silica slurry is obtained by mixing the obtained filtered silica with water and adding sulfuric acid to obtain a pH of 6.5, and then it is sent to a spray dryer. Any drying method known in the art can also be used, such as spray drying and / or rotary flash drying and / or rotary dryer.

[0099] In a preferred embodiment of the present invention, the alkali metal silicate solution is recycled from the reaction kettle back to the reaction kettle via the static mixer at least once.

[0100] In a preferred embodiment of the present invention, additional CO 2 or a process gas containing CO 2 is added to the solution in step (e) to precipitate silica at a pH above 8.

[0101] In a preferred embodiment of the present invention, after precipitation, CO 2 or a process gas containing CO2 The process gas and the solution are re-acidified by adding an acid during the drying step.

[0102] In a preferred embodiment of the present invention, the filtered silica in step (e) is dried by adding an inorganic acid, such as sulfuric acid, to adjust the pH value between 4 and 9, preferably between 6 and 8.2, wherein the concentration of sulfuric acid is 50% or higher.

[0103] The dried silica particles can then be granulated or ground.

[0104] Once the alkali metal silicate solution is moved to the static mixer, the process gas required for silica production is metered into the static mixer. In this way, CO 2 has been dispersed into the solution before entering the reactor. The reaction between the alkali metal silicate solution and CO 2 gas occurs in the static mixer, where almost all the gas is dispersed in the alkali metal silicate solution mixture. It can be expected that a small amount of unreacted CO 2 gas may be carried through the pipeline into the reactor.

[0105] By returning the alkali metal silicate solution via a pipeline to the reactor in which CO 2 has been dispersed, there is no need for a spray nozzle, a gas distributor or a special high-pressure pump to directly feed CO 2 into the reactor.

[0106] When needed, the dispersed carbon dioxide can be uniformly dispersed in the reaction liquid by recirculation and is beneficial to the production of silica.

[0107] The silica produced according to the present invention can be used in any suitable application, including rubber products, such as tires, industrial belts, hoses, gaskets, rubber sheets, threshing rubber drums for grain processing, rubber shoes and other rubber industrial products.

[0108] Measurement method

[0109] CO 2 Yield calculation:

[0110] Based on the stoichiometry of the reaction, the required CO 2 yield is determined. Theoretical calculations show that in order to completely neutralize, 421 grams of CO 2 are required per kilogram of SiO 2 . This calculation is based on the Na 2 O neutralization reaction. In order to evaluate the CO 2 consumption, the CO 2 bottles are weighed before and after the reaction here, taking into account the CO 2and any remaining unreacted CO 2 Alternatively, CO can also be used 2 The mass flowmeter measures CO 2 consumption.

[0111] Measure the pH with a pH meter.

[0112] Abbreviation

[0113] WGL / WG = water glass or sodium silicate Detailed Description of the Invention

[0114] Examples

[0115] The present invention will be further illustrated in detail below with reference to examples and comparative examples.

[0116] Standard water glass contains approximately 8% Na 2 O and 27% SiO 2 - Thus having a modulus of 3.45, which means that the SiO in solid sodium silicate 2 / Na 2 O weight ratio is approximately 3.45. Assuming a 100% CO 2 yield (which means the CO consumption / usage in this reaction, using all the calculated CO 2 )). Therefore, for such WGL, for 1 kg / min WGL, 113.6 g / min of CO should be metered in 2 . If the CO 2 consumption is less than 100%, a higher CO 2 metering addition may be required to keep the pH value constant. The water glass source can also be different, and the range can also be different accordingly. For example, for water glass containing approximately 21% SiO 2 and 6.3% Na 2 O (modulus 3.45), the CO 2 metering addition needs to be adjusted accordingly to achieve a higher yield. 2

[0117] The same standard water glass containing approximately 8% Na 2 O and 27% SiO 2 is used for all comparative examples and examples of the present invention disclosed herein, and is as follows.

[0118] After precipitating silica, for the remaining examples, the same filtration and drying steps as described in Comparative Example 1 are followed. In the examples according to the present invention, CO 2 can be used instead of sulfuric acid during the drying step.

[0119] In the comparative example, a conventional reactor was used, where the conventional reactor can refer to any known type of reactor suitable for silica precipitation and known in the art. The conventional reactor arrangement does not include a pipeline section with a static mixer as described in the present invention.

[0120] Example 1 - Comparison

[0121] A sodium silicate solution (solid sodium silicate and water) was metered into a 2 m conventional reactor containing a turbine and a stirrer with a metering spray gun in the reactor. 3 In the conventional reactor.

[0122] The reaction was carried out at a stirrer speed of 80 rpm while adding water to the alkali metal silicate solution to reach a pH of 9. The solution reached 1400 L while maintaining the temperature at approximately 82 °C.

[0123] Precipitation of silica:

[0124] CO 2 was metered into the sodium silicate solution at a pressure of 4 bar (measured in the pipeline), and the metering addition mass rate / flow rate of CO 2 was 316 g / min. Another sodium silicate was metered in at a rate of 4 kg / min and a total of 500 kg was metered in.

[0125] There was a metering spray gun in the reactor and CO 2 was metered in using the first and / or second metering spray guns in the reactor. The end of the metering spray gun was above the reactor turbine and CO 2 was metered onto it.

[0126] Then, re-acidification was started by stopping the additional sodium silicate metering feed and continuing the CO 2 metering feed. The CO 2 pressure was maintained at 4 bar, and the CO 2 metering feed rate remained 316 g / min.

[0127] When the pH reached 8, the re-acidification was stopped. The total reaction time including the re-acidification step was approximately 240 min.

[0128] Then, the resulting suspension was pumped to a filter press, washed (to remove residual salts) and dewatered. After filtering out the precipitate with the filter press and washing, a transparent, impurity-free liquid sodium silicate was obtained.

[0129] Then, the resulting filtered silica was dried by a rotary flash dryer. During the drying step, sulfuric acid was metered onto the filtered silica to reach a final pH of approximately 6.5 in the silica. Then, the powder was optionally granulated by conventional means.

[0130] For the remaining embodiments, the same filtration, drying and optional granulation steps are followed.

[0131] Total CO 2 The yield is calculated as 75%, meaning that 75% of the CO 2 calculated & fed in the reaction is consumed / used during the precipitation process, while the remaining 25% CO 2 is either released to the environment or not precisely distributed and reacted within the reaction medium. This means that the method will require adding more CO 2 and even increasing the precipitation time for total silicate conversion to increase the SiO 2 precipitation amount.

[0132] The CO 2 consumption is calculated by stoichiometry. Theoretically, 421 g of CO 2 / kg of SiO 2 is required for neutralization. The basis for yield calculation is the neutralization reaction of Na 2 O. By weighing the CO 2 bottles before and after the reaction, considering the CO 2 fed to the reactor and the remaining / unreacted CO 2 , the CO 2 consumption is determined. In addition, the CO 2 consumption can also be measured with a CO 2 mass flowmeter. The same calculation is used for the remaining embodiments.

[0133] Example 2 - Comparison

[0134] The sodium silicate solution (solid sodium silicate and water) is metered into a 2 m 3 conventional reactor equipped with a metering lance tube and containing a turbine and a stirrer inside the reactor.

[0135] The reaction is carried out at a stirrer speed of 80 rpm while adding water to the alkali metal silicate solution to reach pH 9. The solution reaches 1400 L while maintaining the temperature at approximately 75 °C.

[0136] Precipitation of silicon dioxide:

[0137] The CO 2 is metered into the sodium silicate solution at a pressure of 4 bar (measured in the pipeline), and the CO 2 is metered in at a mass rate / flow of 324 g / min. Another sodium silicate is metered in at a rate of 4 kg / min and metered in a total of 500 kg.

[0138] Similar to the above, the CO2 。The end of the metering spray gun is above the reactor turbine and CO 2 is metered onto it.

[0139] Then, re-acidification is started by stopping the additional metering of sodium silicate and continuing the CO 2 metering. The CO 2 pressure is maintained at 4 bar and the CO 2 metering rate remains at 324 g / min.

[0140] When pH 8 is reached, re-acidification is stopped. The total reaction time including the re-acidification step is approximately 240 min.

[0141] The total CO 2 yield is calculated to be 82%, meaning that 82% of the CO 2 calculated and fed into the reaction is consumed / used during the precipitation process, while the remaining 18% of the CO 2 is either released into the environment or not precisely distributed and reacted within the reaction medium. This means that the method will require adding more CO 2 , and even increasing the precipitation time for the total silicate conversion to increase the amount of SiO 2 precipitation.

[0142] Example 3 - The present invention

[0143] The sodium silicate solution (solid sodium silicate and water) is metered into a 2 m Figure 1 reactor as shown in the present invention with an outlet at the bottom of the reactor (herein referred to as the suspension outlet). 3 in the reactor.

[0144] There is a circulation pump in the pipeline, which pumps the suspension through a static mixer via a pipeline (with a pipe diameter of 84.3 mm). The static mixer is 250 mm long and has PVDF inserts. This pipeline returns the suspension to the reactor at a position in the middle of the reactor below the liquid level.

[0145] The reaction is carried out at a stirrer speed of 95 rpm while adding water to the alkali metal silicate solution to reach pH 9. The solution reaches 1400 L while maintaining the temperature at approximately 75 °C.

[0146] Precipitation of silicon dioxide:

[0147] CO is metered in via the metering point 2 , where the metering point is kept before the static mixer and the CO 2 metering point has a diameter of 10 mm.

[0148] The CO 2Metered addition to the sodium silicate solution under a pressure of 4 bar (measured in the pipeline), CO 2 The metered addition mass rate / flow rate is 325 g / min. Another sodium silicate is metered in at a rate of 4 kg / min and a total of 500 kg is metered in.

[0149] The suspension circulation pump attached to the pipeline section has a pump speed of 2800 revolutions per minute (rpm).

[0150] Then start re-acidification by stopping the additional WGL metered feed and continuing the CO 2 metered feed.

[0151] CO 2 The pressure is 4 bar, CO 2 The metered addition rate remains 325 g / min.

[0152] When the pH reaches 8, stop re-acidification. The total reaction time including the re-acidification step is approximately 189 min.

[0153] Total CO 2 The yield is calculated to be 92%, meaning that 92% of the CO calculated & fed into the reaction is consumed / used during the precipitation process, and only 8% of the remaining CO 2 is either released into the environment or not precisely distributed and reacted within the reaction medium. The CO consumption is calculated again by stoichiometry. It is determined by weighing the CO 2 bottles before and after the reaction, taking into account the CO fed into the reactor 2 and the remaining / unreacted CO 2 and the remaining / unreacted CO. 2 and the remaining / unreacted CO 2 to determine.

[0154] Example 4 - The present invention

[0155] The sodium silicate solution (solid sodium silicate and water) is metered into a 2000 mL reactor with an outlet at the bottom (here called suspension outlet 9) as shown in the present invention Figure 1 in the reactor.

[0156] There is a circulation pump on the pipeline, which pumps the suspension through a static mixer via the pipeline (with a pipe diameter of 12 mm).

[0157] In this setup, two static mixers are used one after the other. Each static mixer is 1 m long, so a total of 2 m of static mixer length is used, with stainless steel inserts. The pipeline returns the suspension from the top of the reactor below the liquid level back to the reactor.

[0158] The reaction was carried out at a stirrer speed of 300 rpm while adding water to the alkali metal silicate solution to reach a pH of 9. The solution reached 1205 mL and contained 11 g of WGL while maintaining the temperature at approximately 70 °C.

[0159] Precipitation of silica:

[0160] CO 2 The metering point is before the static mixer and CO 2 The metering point has a diameter of 5 mm.

[0161] CO 2 was metered into the sodium silicate solution at a pressure of 2.5 bar (measured inside the pipeline). CO 2 The metering addition mass rate / flow rate was 0.42 g / min. Another sodium silicate was metered in at a rate of 6 g / min and metered in a total of 555 g.

[0162] The suspension circulation pump attached to the pipeline section had a suspension flow rate of 667 mL / min.

[0163] Then, by stopping the additional WGL metering feed and continuing the CO 2 metering feed, re-acidification was started.

[0164] CO 2 The pressure was 2.5 bar, and CO 2 The metering addition rate remained 0.42 g / min.

[0165] When the pH reached 8, the re-acidification was stopped. The total reaction time including the re-acidification step was approximately 115 min.

[0166] Total CO 2 The yield was calculated to be 100%, meaning that all the CO calculated and fed into the reaction 2 was consumed / used up during the precipitation process. Again, the CO consumption was calculated by stoichiometry 2 consumption. It was determined by weighing the CO 2 bottles before and after the reaction, taking into account the CO fed into the reactor 2 and the remaining / unreacted CO 2 to measure.

[0167] Example 5 - The present invention

[0168] The sodium silicate solution (solid sodium silicate and water) was metered into a 2000 mL reactor with an outlet at the bottom of the reactor (herein referred to as suspension outlet 9) as shown in the present invention. Figure 1

[0169] ​There is a circulation pump in the line which pumps the suspension via a line (with a tube diameter of 12 mm) through the static mixer.

[0170] In this setup, two static mixers were used right after each other. Each static mixer was 1 m long, so a total of 2 m static mixer length was used, with a stainless steel insert. The line brought the suspension from the top of the reactor back to the reactor below the liquid level.

[0171] The reaction was carried out at a stirrer speed of 300 rpm while water was added to the alkali metal silicate solution to reach pH 9, the solution reaching 1200 mL containing 11 g of WGL while the temperature was maintained at approximately 70°C.

[0172] Precipitation of Silica:

[0173] CO 2 The metering point is before the static mixer and the CO 2 The metering point has a diameter of 5 mm.

[0174] CO 2 At a pressure of 2.5 bar (measured in the pipeline), CO 2 The metering mass rate / flow rate was 0.6 g / min. Further sodium silicate was metered in at a rate of 8.3 g / min and a total of 555 g was metered in.

[0175] The suspension circulation pump attached to the pipeline section had a suspension flow rate of 667 mL / min.

[0176] Then, by stopping the additional WGL dosing and continuing the CO 2 Dosing was done to start reacidification.

[0177] CO 2 The pressure is 2.5 bar, CO 2 The metering rate was still 0.6 g / min.

[0178] Reacidification was stopped when pH 8 was reached. The total reaction time including the reacidification step was approximately 90 min.

[0179] Total CO 2 The yield was calculated to be 100%, meaning that the CO fed in the reaction was calculated to be 2 All consumed / used during precipitation. Again, CO is calculated from stoichiometry 2 Consumption. This is achieved by converting CO before and after the reaction. 2 Bottle weighing, taking into account the CO delivered to the reactor 2 and remaining / unreacted CO 2 To determine.

[0180] Example 6 - The present invention

[0181] The sodium silicate solution (solid sodium silicate and water) is metered into a 2000 mL reactor as shown in Figure 1 the present invention, which has an outlet (herein referred to as the suspension outlet 9) at the bottom of the reactor.

[0182] There is a circulation pump in the pipeline, which pumps the suspension through a static mixer via a pipeline (with a pipe diameter of 12 mm).

[0183] In this setup, two static mixers are used in succession. Each static mixer is 1 m long, so a total of 2 m of static mixer length is used, with stainless steel inserts. The pipeline returns the suspension from the top of the reactor below the liquid level back to the reactor.

[0184] The reaction is carried out at a stirrer speed of 300 rpm while adding water to the alkali metal silicate solution to reach a pH of 9. The solution reaches 1200 mL, which contains 11 g of WGL, while maintaining the temperature at approximately 67 °C.

[0185] Precipitation of silica:

[0186] CO 2 The metering point is before the static mixer and CO 2 The metering point has a diameter of 5 mm.

[0187] CO 2 is metered into the sodium silicate solution at a pressure of 2.5 bar (measured inside the pipeline). The metering addition mass rate / flow rate of CO 2 is 0.3 g / min. Another sodium silicate is metered in at a rate of 4.1 g / min and a total of 500 g is metered in.

[0188] The suspension circulation pump attached to the pipeline section has a suspension flow rate of 667 mL / min.

[0189] Then, re-acidification is started by stopping the additional WGL metering feed and continuing the CO 2 metering feed.

[0190] CO 2 The pressure is 2.5 bar and the metering addition rate of CO 2 remains 0.3 g / min.

[0191] When the pH reaches 8, the re-acidification is stopped. The total reaction time including the re-acidification step is approximately 147 min.

[0192] Total CO 2The yield was calculated to be 100%, meaning that the CO fed in the reaction was calculated to be 2 All consumed / used during precipitation. Again, CO is calculated from stoichiometry 2 Consumption. This is achieved by converting CO before and after the reaction. 2 Bottle weighing, taking into account the CO delivered to the reactor 2 and remaining / unreacted CO 2 To determine.

[0193] Table 1

[0194]

[0195] result

[0196] The last column in Table 1 reflects CO 2 Yield, refers to CO 2 Total utilization for acidification.

[0197] Therefore, Table 1 reflects the increased CO at reduced precipitation temperature. 2 consumption, while the third column reflects the higher solid SiO obtained after precipitation 2 content.

[0198] When comparative example 1 or 2 is compared with example 3 of the present invention, the method of the present invention can achieve the upgrading of the existing silicon dioxide precipitation reactor. 2 As an acidulant, a higher space / time yield is obtained. 2 The conventional reactors of Comparative Examples 1 and 2 of the metering device were compared with the process using a reactor with a bypass section in which the static mixer was installed outside the reactor. 2 The solid content g / L has a longer precipitation time (240 / 214 vs. 189 minutes).

[0199] CO 2 The yield is significantly increased, which means that the embodiments of the present invention use almost all the CO fed 2 , without releasing too much to the outside / environment or leaving any unreacted CO in the reaction medium 2 In particular, Examples 4-6 of the present invention exhibit excellent CO 2 Yield, where all CO 2 Be reacted.

[0200] As can be seen from Table 1, higher SiO 2Solid / precipitated silica. The reason for this increased yield is due to the use of up to 100% CO in the reaction medium 2 , which enables a higher conversion of silica from silicate materials.

[0201] By using this new method and reaction setup, there is no need to meter in a higher amount of CO 2 , nor is there a need to purify the gas mixture to obtain a higher amount of CO therein 2 . Example 3 of the present invention is provided as a control example to show that even if the metered addition amount of CO 2 is equivalent to that of Comparative Examples 1 and 2, a higher amount of CO is consumed 2 .

Claims

1. A method for preparing precipitated silica, comprising the following steps: (a) providing an alkali metal silicate solution into a reaction vessel (1); (b) transferring the alkali metal silicate solution from the reactor (1) to a bypass section comprising a static mixer (5) and a pipeline (7), wherein the bypass section is located outside the reactor (1) and connected to the reactor via a pipeline; (c) dispersing the process gas comprising carbon dioxide into the alkali metal silicate solution in the static mixer (5); (d) returning the alkali metal silicate solution after reacting with the process gas to the reaction vessel; and (e) Silica is precipitated, and then filtered, washed and dried to obtain precipitated silica.

2. The method according to claim 1, wherein the process gas comprises carbon dioxide in a concentration of greater than 10%, preferably 20%, or 30%, or 40%, or 50%, or 60%, or 70%, or 80%, or 90% by volume.

3. A process according to claim 1 or 2, wherein in step (a) the alkali metal silicate solution is mixed with water to obtain a solution having a pH above 8, preferably 9, preferably at a temperature between 50-95°C.

4. A process according to any one of the preceding claims, wherein further alkali metal silicate solution is added to the reactor to maintain the pH in the range from above 8 to 10.

5. 5 . The process according to claim 1 , wherein the process gas is metered in a line upstream of the static mixer, preferably in the vicinity of the static mixer, or in the static mixer.

6. The process according to any of the preceding claims, wherein the alkali metal silicate solution is metered into the static mixer via a pipeline from the reactor and the process gas is preferably metered into the static mixer simultaneously with the alkali metal silicate solution.

7. The process according to any one of the preceding claims, wherein the alkali metal silicate solution mixture is circulated from the reactor via a bypass section back to the reactor at least once.

8. The method according to any one of the preceding claims, wherein the alkali metal silicate solution is a sodium silicate solution.

9. The process according to any one of the preceding claims, wherein the filtered silica in step (e) is dried under the addition of a mineral acid, such as sulfuric acid, or with CO2 or a process gas containing CO2, to adjust the pH value to between 4 and 9, preferably between 6 and 8.

2.

10. An apparatus for preparing precipitated silica according to the method according to any one of the preceding claims, comprising a reactor (1), a bypass section comprising a static mixer (5) and a pipeline (7), wherein the bypass section is located outside the reactor and connected to the reactor via a pipeline, wherein the static mixer is configured to circulate an alkali metal silicate solution back to the reactor via the pipeline.

11. The device according to claim 10, wherein the bypass section further comprises a metering point (6) for metering the process gas through the static mixer, and the process gas metering point is located in the pipeline before the static mixer in the flow direction, preferably near the static mixer, or on the static mixer.

12. The device according to any one of claims 10 or 11, characterized in that The bypass section comprises more than one static mixer (5), preferably located one after another in the pipeline.

13. The device according to any one of claims 10 to 12, characterized in that The reactor comprises a water metering point (3) and a silicate metering point (4), which are preferably located at the top or side of the reactor.

14. The device according to any one of claims 10 to 13, characterized in that The reactor comprises an outlet / suspension outlet (9), which is preferably located at the bottom of the reactor, to release the alkali metal silicate solution from the reactor.

15. The device according to any one of claims 10 to 14, characterized in that The reactor comprises a dispersing blade or a stirrer.

16. Use of a static mixer for preparing precipitated silica.

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