Method for preparing silicon dioxide from silicon rubber pyrolysis waste residue

Abstract

The application belongs to the technical field of silica processing, and particularly relates to a method for preparing silica from silicon rubber pyrolysis waste residue. The method comprises the following steps: (1) preheating the waste residue to the ignition point of coking substances; (2) combusting and gasifying the coking substances under aerobic conditions; and (3) water-gas gasifying the waste residue after combustion and gasification to obtain silica. In the method, the coking substances in the waste residue are preheated to the ignition point and then combusted, so that a large amount of heat is released, and then the waste residue is subjected to water-gas gasification, so that impurities can be effectively removed, and the target silica with a high BET is obtained. The silica product prepared by the method belongs to a nanoscale product, and can meet the basic requirements in the fields of rubber and waterproof sealant, and has a wide market application prospect. In addition, the preparation method fully utilizes the heat of the coking substances in the waste residue, has low comprehensive energy consumption, less pollutant emission, and easy absorption and treatment of acid gases, and is simple to operate, and is suitable for large-scale industrial production and application.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for preparing silicon dioxide from silicon rubber pyrolysis waste residue, which is a method for separating and purifying silicon dioxide from waste residue composed of silicon dioxide and pyrolysis coking material, and belongs to the technical field of industrial solid waste utilization and silicon dioxide processing. BACKGROUND

[0002] The preparation of methylsiloxane (DMC) from recycled silicon rubber pyrolysis has practical applications in industry, and industrial-grade DMC is usually recovered by catalytic pyrolysis and rectification purification. The most commonly used catalysts are sulfuric acid and sulfonic acid. A large amount of nanosilica is added to industrial silicon rubber as a functional filler for silicon rubber, so a large amount of silicon dioxide is produced as the main component of silicon rubber pyrolysis waste residue, which also contains silicon rubber pyrolysis coking material and residual catalyst. The above solid waste residue is black and powdery in appearance, and the content of coking material is usually 15-22%, and the content of SO3 is 11-16%, which cannot be directly used as industrial filler and other fields.

[0003] At present, the waste residue is usually treated by oxidation and calcination to remove impurities, but the obtained silicon dioxide often has low purity, or other property parameters such as specific surface area cannot meet the subsequent application requirements, which cannot be directly used in subsequent processes and needs to be treated before application, resulting in increased cost. Or on the basis of the foregoing, a surfactant or other substance is added for coating treatment to improve the specific surface area, such as the silicon rubber pyrolysis ash treatment process and system based on gas-solid heterogeneous continuous method in Chinese patent CN107718359A, but it still has the problems of high BET and solid phase temperature rising during combustion, and the introduction of other substances may lead to the appearance of new impurities or the increase of impurity content, which may even affect the subsequent application. Therefore, there is still a lack of an efficient technology for extracting silicon dioxide from silicon rubber pyrolysis waste residue in the field.

[0004] Therefore, the present application provides a method for preparing silicon dioxide from silicon rubber pyrolysis solid waste residue, which can meet the general requirements of industrial-grade nanoscale filler and is convenient for direct application in subsequent production processes, thereby effectively reducing the cost. SUMMARY

[0005] The present application aims to solve the problems in the prior art and provides a method for preparing silicon dioxide from silicon rubber pyrolysis waste residue, which uses a coking material and other impurity gasification separation method, and can consider comprehensive factors such as product performance, production cost and environmental protection, to prepare silicon dioxide that can meet the general requirements of industrial-grade nanoscale filler.

[0006] To achieve the above object, the present application provides the following technical solutions.

[0007] A method for preparing silicon dioxide from silicon rubber pyrolysis waste residue, comprising the following processes:

[0008] (1) preheating the waste residue to the ignition point of coking matter;

[0009] (2) burning and gasifying the coking matter under oxygen conditions;

[0010] (3) water-gas gasifying the waste residue after burning and gasification to obtain silicon dioxide.

[0011] By adopting the above technical solutions, the coking matter in the waste residue is preheated to the ignition point by preheating, and then the coking matter can burn as oxygen appears and increases in the reaction environment, a large amount of heat is quickly released, the gas phase temperature quickly rises, and then the waste residue after the foregoing burning is water-gas gasified, the residual coking matter in the waste residue is gasified by steam, impurities can be effectively removed, temperature control can be realized, and finally target silicon dioxide with a higher BET can be obtained.

[0012] Preferably, the waste residue in step (1) is sieved through an 80-mesh screen to remove mechanical impurities and further enable the coking matter to fully contact oxygen and burn.

[0013] Preferably, the content of silicon dioxide in the waste residue in step (1) is not less than 60%.

[0014] Preferably, the preheating of the waste residue in step (1) can be performed by heating with high-temperature gas. The temperature of the high-temperature gas used for preheating is at least 350 DEG C or higher, and the waste residue is preheated to the ignition point. The maximum temperature of the gas is not particularly limited. More preferably, the waste residue preheating can be performed by directly heating with high-temperature gas in a packed bed, a rotary drum, a fluidized bed, a boiling bed, etc. More preferably, the high-temperature gas described above can be high-temperature gas after gasification, which effectively realizes comprehensive utilization of heat energy.

[0015] Preferably, the burning and gasification of the coking matter under oxygen conditions in step (2) means that the coking matter ignites at the ignition point under continuous introduction of oxygen-containing gas, a strong exothermic reaction occurs between the carbon-hydrogen substance and oxygen, the coking matter is gasified into CO2, H2O, etc., and a large amount of SO3 is released.

[0016] Preferably, the oxygen condition in the process of step (2) is achieved by introducing oxygen-containing gas, the oxygen content of which is not less than 18w%, so that the coking material can be ignited and combusted in the presence of oxygen; more preferably, the temperature of the oxygen-containing gas is not less than the ignition point temperature of the coking material, so as to avoid the introduction of gas with too low temperature, which can cause the temperature of the coking material to decrease below the ignition point, making it difficult to ignite; more preferably, the amount of the oxygen-containing gas introduced is controlled according to the gas phase temperature, and more preferably, it is 1.5-1.7 times the theoretical amount of oxygen, so that the coking material can be fully combusted.

[0017] Preferably, in the process of step (2), the temperature of the high-temperature section of the gasification gas phase is controlled to be 1050-1300°C, further preventing the temperature from being too high, which can cause the solid to sinter and thus reduce the BET of the product. More preferably, within the temperature range of the high-temperature section, the residence time of the material is at least 4s and at most 10s. If the residence time is too long, the silicon dioxide crystals can sinter and coagulate at high temperature, causing the specific surface area of the product to decrease rapidly. On the contrary, if the residence time is too short, a small amount of coking material remains, causing the whiteness of the final product to decrease. Higher temperature can cause more sintering. More preferably, in order to prevent the local temperature of the solid material from rising too high during the oxygen-containing gasification process of the coking material, it is better to use a fluidized bed or a boiling bed gasification method for oxygen-containing gasification. The fluidized bed is easy to control the temperature rise of the solid combustion material.

[0018] Preferably, the water-gas gasification process of the waste residue in step (3) refers to the introduction of water-containing gas, more preferably water vapor, or the introduction of water, but more preheating fuel is required, which can reduce the efficiency of the reactor and the oxygen concentration. The specific selection depends on the actual working conditions and economic conditions; the carbon in the high-temperature coking material reacts with water to produce carbon gasification reaction, etc.:

[0019] C+H2O→CO+H2

[0020] and the hydroxylation activation reaction of the silicon dioxide surface:

[0021] SiO2+H2O=H2SiO3

[0022] Hydroxylation of the silicon dioxide surface and conversion of the surface crystal state to amorphous state can not only effectively block the high-temperature coagulation of silicon dioxide crystals, but also effectively improve the surface activity or performance of the silicon dioxide product.

[0023] More preferably, the above two reactions in step (3) are endothermic processes, which will cause the temperature of the object material to drop sharply, resulting in incomplete gasification of the coking material. Therefore, the outlet temperature of the steam gasification section is controlled to be no less than 750°C. At a lower outlet temperature, the steam gasification reaction rate decreases, which may lead to incomplete reaction. More preferably, through heat balance calculation, the minimum concentration of residual oxygen in the outlet gas phase (dry basis) in the steam gasification process is no less than 7%, so that the steam gasification reaction products CO and H2 are completely combusted to maintain the temperature of the gasification.

[0024] Preferably, in the steam gasification process of the waste residue in step (3), the humidity in the gas phase in the reaction system is ≥0.066 kg of water vapor / kg of dry gas, and the residence time is ≥2 s. At excessively low humidity and excessively short residence time, the coking material is not completely gasified, which will lead to a decrease in the whiteness of the product.

[0025] More preferably, the steam gasification process of the coking material of the waste residue in step (3) is preferably carried out in a fluidized bed or a boiling bed. The fluidized bed is easy to control the flying temperature of the solid phase combustion material. It is preferably carried out in the same reactor as the oxygen gasification in step (2). Considering that the residence times required in steps (2) and (3) are different, the horizontal cross-sectional area of the two bed layers can be adjusted, or the height distribution of the two sections can be adjusted. At the connection between the two bed layers, the water or steam required in step (3) and the oxygen-containing gas that may need to be supplemented are introduced.

[0026] Preferably, the residence time in the present application refers to the average residence time calculated according to the volume of the corresponding reactor and the average flow rate (m 3 / s) of the gas phase in the reactor.

[0027] Preferably, after the steam gasification in step (3), a post-treatment process of the recovered silica powder is carried out. More preferably, the post-treatment process of the recovered material is adapted to different application fields and contains, but is not limited to, at least one of the following:

[0028] A) Screening and packaging of the silica powder;

[0029] B) Dispersing and packaging of the silica powder;

[0030] C) Further impurity removal and purification treatment of the silica powder.

[0031] More preferably, in the above post-treatment process, the dispersing of the silica powder is the breaking and deagglomeration of the agglomerated particles therein. A negative pressure airflow cyclone mill can be used, and the powder after the mill is collected by a bag collector to collect the powder product;

[0032] The purpose of the purification treatment of silica powder is to further remove any water-soluble inorganic salts that may be present, including but not limited to water wetting, neutralizing residual acid with an alkaline solution, dewatering using a filter press, or further washing the filter cake in the filter press with water after dewatering, followed by drying the filter cake to obtain the final silica powder product. The water is at room temperature and has a conductivity of <500 μS / cm.

[0033] Compared with the prior art, the beneficial effects of the present invention are: the specific surface area of ​​the silica powder product prepared by the present invention is not less than 70m². 2 The silica product prepared by this invention has the following characteristics: silica content ≥90%, loss on heating at 105℃ <0.5%, loss on ignition <3.5%, water-soluble matter <2.5%, and other indicators also meet the requirements of "Precipitated Hydrated Silica in Rubber Compounding Agents" (HG / T3061-2009). The silica product prepared by this invention is a nanoscale product, which can meet the basic requirements of rubber, waterproof sealants, and other fields. It has broad market application prospects.

[0034] The preparation method using the technical solution of this invention fully utilizes the calorific value of the coking material in the waste residue, resulting in low overall energy consumption, minimal pollutant emissions, and easy absorption and treatment of acidic gases. Furthermore, it is simple to operate and suitable for large-scale industrial production applications. Attached Figure Description

[0035] Appendix Figure 1 The thermal analysis curve of raw material A is shown in the example.

[0036] Appendix Figure 2 The diagram shows the fluidized bed used in Example 1. The equipment 1 to 6 in the diagram are as follows: 1 is a raw material metering screw feeder, 2 is an air blower, 3 is a natural gas burner, 4 is the first fluidized bed, 5 is the second fluidized bed, and 6 is a cyclone separator.

[0037] Appendix Figure 3 The diagram shows the fluidized bed used in Example 3. The equipment 1 to 10 in the diagram are as follows: 1 is a raw material metering screw feeder, 2 is an air blower, 3 is a natural gas burner, 4 is the first fluidized bed, 5 is the second fluidized bed, 6 is a cyclone separator, 7 is a rotary dryer, 8 is a screw feeder, 9 is a heat exchanger, and 10 is a high-temperature fan. Detailed Implementation

[0038] For the convenience of understanding, the technical solutions and embodiments of the present application are further clearly, completely and specifically described below by means of specific examples in combination with the drawings. It should be understood that the described examples are implemented on the premise of the technical solutions of the present application, and detailed embodiments and specific operation processes are given, but only a part of the examples, not all the examples, of the present application. The specific embodiments are only used to illustrate and explain the present application, and do not limit the present application. Based on the examples in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0039] The experimental methods used in the following examples are conventional methods, and the materials, reagents and the like used in the examples are commercially available unless otherwise specified.

[0040] The determination of the silica content in the products of the following examples is carried out according to Rubber Compounding Ingredients - Determination of Silica Content in Dried Sample of Precipitated Hydrated Silica (HG / T 3062); the determination of the water-soluble content is carried out according to Rubber Compounding Ingredients - Determination of Water-soluble Content in Precipitated Hydrated Silica - Cold Extraction Method (HG / T 3748); the specific surface area determination is carried out according to the method of Carbon Black - Determination of Total Surface Area and External Surface Area - Nitrogen Adsorption Method (GB / T 10722), and the instrument used is a specific surface area and pore size analyzer BK400 produced by Beijing Jeol Highbo Science and Technology Co., Ltd.; the determination of the heating loss is carried out according to Rubber Compounding Ingredients - Determination of Heating Loss of Precipitated Hydrated Silica (HG / T 3065); the determination of the ignition loss is carried out according to Rubber Compounding Ingredients - Determination of Ignition Loss of Dried Sample of Precipitated Hydrated Silica (HG / T 3066); the determination of the SiO2 and SO3 contents in the waste residue is carried out by X-ray fluorescence spectrometer quantitative analysis; the waste residue is subjected to a thermal gravimetric test method, and the instrument used is a comprehensive thermal analyzer HZ1500 produced by Shanghai Yingnuo Precision Instrument Co., Ltd., and the thermal gravimetric curve of the typical raw material A is shown in FIG. 2, and the analysis test results of the typical raw material are shown in Table 1 (except for the heating loss, the rest is the mass percentage of the 105℃ dried substance). Figure 1

[0041] Table 1 Composition analysis of two raw materials (waste residue) used in the examples

[0042]

[0043]

[0044] Example 1

[0045] The fluidized bed flow chart is shown in FIG. 1. Figure 2 ​The devices 1-6 in the figure are as follows: 1 is a raw material metering screw feeder, 2 is an air blower, 3 is a natural gas burner, 4 is a first-stage fluidized bed, 5 is a second-stage fluidized bed, and 6 is a cyclone separator.

[0046] The raw material A in Table 1 was used in the test. The raw material A was sieved through an 80-mesh screen to remove mechanical impurities and was fed into the reactor (attached Figure 2 to the first-stage fluidized bed 4) by the metering screw feeder 1 at a feeding speed of 1503 kg / h. High-temperature flue gas was provided by the liquefied gas burner 3 for preheating and then oxidation gasification, and air was provided by the air blower 2 to provide oxygen, and the air temperature was normal temperature;

[0047] Subsequently, the powder entered the second-stage fluidized bed 5 with the gas flow, and metered 0.63 MPa steam was introduced. The powder was separated from the gas in the cyclone separator 6 and was collected. The high-temperature tail gas from the cyclone separator 6 was first passed through a heat exchanger to recover heat, and the heat transfer medium used was heat-conducting oil. After cooling, the tail gas was passed through a bag-type collector to further collect fine powder. The collected fine powder was combined with the coarse powder collected by the cyclone dust collector 6 to obtain the silicon dioxide powder product. The acidic tail gas extracted from the bag-type collector was discharged after flue gas treatment. The amounts of raw material, air, liquefied gas fuel, steam, and the corresponding reactor control parameters after the system reached parameter stability are shown in Table 2. Table 2 also lists the properties of the obtained silicon dioxide product under the corresponding operating conditions. The heat value of the liquefied gas used was 11228 kcal / kg, and the humidity of the ambient air was 0.010 kg / kg of dry gas. According to the product technical index analysis, the key indicators of the product met the requirements specified in the “Rubber Compounding Agent Precipitated Hydrated Silica” (HG / T 3061-2009).

[0048] Table 2 Operating conditions of Example 1 and properties of the product

[0049]

[0050]

[0051] Example 2

[0052] The same raw material and system as in Example 1, except that the raw material feeding speed was 1344 kg / h, and the residence time of the oxidation stage was increased. The other operating parameters and product technical indicators are shown in Table 2. According to the product technical index analysis, the key indicators of the product met the requirements specified in the “Rubber Compounding Agent Precipitated Hydrated Silica” (HG / T 3061-2009). The X-ray fluorescence analysis (XRD) results of the product are shown in Table 3:

[0053] Table 3 XRD analysis results of the product of Example 2

[0054]

[0055]

[0056] Comparative Example 1

[0057] The same raw materials and system as in Example 1 were used, except that the air flow and the amount of fuel for preheating were increased, and the amount of steam was reduced. The other operating parameters and product technical indicators are shown in Table 2. Analysis of the product technical indicators shows that the key indicator, the silica content, is lower than the requirements specified in the "Precipitated Hydrated Silica for Rubber Compounds" (HG / T 3061-2009), and the ignition loss is also higher.

[0058] Comparative Example 2

[0059] The same raw materials and system as in Example 2 were used, except that the air and steam were reduced. The other operating parameters and product technical indicators are also shown in Table 2. Analysis of the product technical indicators shows that the key indicator, the BET value, cannot meet the requirements specified in the "Precipitated Hydrated Silica for Rubber Compounds" (HG / T 3061-2009).

[0060] Example 3

[0061] A fluidized bed process diagram is shown in the accompanying Figure 3 Figure. In the figure, devices 1-10 are as follows: 1 is a raw material metering screw feeder, 2 is an air blower, 3 is a natural gas burner, 4 is a first-stage fluidized bed, 5 is a second-stage fluidized bed, 6 is a cyclone separator, 7 is a rotary dryer, 8 is a screw feeder, 9 is a heat exchanger, and 10 is a high-temperature fan.

[0062] The test raw material is Raw Material B shown in Table 1. Raw Material B is sieved through an 80-mesh screen to remove mechanical impurities, and is fed into the rotary dryer 7 using a metering screw 1. The material is dried and preheated using waste heat gas, and after drying, the material is fed from the rotary dryer 7 into the feed screw 8, and is continuously fed into the bottom of the reactor. The feed speed of the metering screw 1 is 1454 kg / h, and the powder is preheated to 380°C before being fed into the first-stage fluidized bed 4 using the screw feeder 8. The liquid gas burner 3 provides supplemental heating at the bottom of the first-stage fluidized bed 4 and is used as a backup during startup. The air blower 2 feeds in air, which is oxidized and gasified in the first stage. The powder is carried by the gas stream into the second-stage fluidized bed 5, where 0.63 MPa steam is introduced. The powder is separated from the gas in the cyclone separator 6 and is collected. The high-temperature tail gas from the cyclone separator 6 is first passed through the heat exchanger 9 to recover heat. The recovered heat can be used to preheat the next batch of raw material using the high-temperature fan 10, achieving comprehensive energy recovery and utilization. The heat exchange medium used is heat-conducting oil. After cooling, the tail gas is further collected in a bag-type collector 1. The fine powder collected in the bag-type collector is combined with the coarse powder collected in the cyclone separator 6 to obtain the silica powder product. The acidic tail gas extracted from the bag-type collector is treated and discharged.

[0063] The tail gas of the rotary dryer 7 is discharged and separated from the raw material dust in the bag collector 2, and the dust is sent to the raw material powder bin, and the gas is sent to the tail gas treatment system. The preheating temperature of the preheated powder discharged from the dryer is set from the control system and adjusted by the preheating gas temperature entering the dryer and the gas flow control. The amounts of raw materials, air, liquefied gas fuel, steam and corresponding reactor control parameters after the system reaches parameter stability are shown in the table. Table 4 also lists the properties of the obtained silicon dioxide product under the corresponding operating conditions. The heat value of the liquefied gas used is 11228 kcal / kg, and the humidity of the ambient air is 0.010 kg / kg dry gas. According to the analysis of the product technical indicators, the key indicators of the product meet the requirements specified in “Rubber Compounding Agent Precipitated Hydrated Silica” (HG / T3061-2009).

[0064] Table 4 Operating conditions of example 3 and properties of its product

[0065]

[0066] Example 4

[0067] The same raw materials and system as in example 1, except that the raw material feeding speed is 2189 kg / h, the residence time of the oxidation section is increased, and other operating parameters and product technical indicators are shown in table 4. According to the analysis of the product technical indicators, the key indicators of the product meet the requirements specified in “Rubber Compounding Agent Precipitated Hydrated Silica” (HG / T3061-2009).

[0068] Comparative example 3

[0069] The same raw materials and system as in example 4, except that the steam flow is reduced, and other operating parameters and product technical indicators are shown in table 4. According to the analysis of the product technical indicators, the key indicators of the product, such as BET value and silicon dioxide content, are lower than the requirements specified in “Rubber Compounding Agent Precipitated Hydrated Silica” (HG / T3061-2009).

[0070] Comparative example 4

[0071] The same raw materials and system as in example 3, except that the preheated powder temperature is increased to 400℃, and the air consumption is reduced, and other operating parameters and product technical indicators are also listed in table 4. According to the analysis of the product technical indicators, the key indicator of the product, such as BET value, cannot meet the requirements specified in “Rubber Compounding Agent Precipitated Hydrated Silica” (HG / T3061-2009).

[0072] Example 5

[0073] The product 1000 g obtained in Example 1 was added to 1500 ml of stirred deionized water at room temperature, the initial conductivity of the water was 430 μS / cm, after the powder was added, the stirring was continued for 30 min, then vacuum filtration was performed, the filter cake was washed with 500 ml of deionized water in three times, finally the filter cake was dried, the filter cake was transferred to a stainless steel tray, and dried in an oven at 100°C for 4 h, the dried product was collected, crushed by a rotary blade crusher, and sieved through a 200 mesh screen, 988 g of powder was obtained, the properties of the treated heat silica product were as follows:

[0074] Silica content: 93.0%

[0075] BET: 123 m 2 / g

[0076] 105°C heating loss: 2.2%

[0077] ignition loss: 0.34%

[0078] Calcium and magnesium oxides: 1.3%

[0079] Al2O3 content: 0.7%

[0080] Water-soluble content: 0.5%

[0081] pH value: 6.5

[0082] The above-described examples are only the preferred schemes of the present application, and do not limit the present application in any form, and other variations and modifications can be made without departing from the technical scheme recited in the claims.

Claims

1. A method for producing silicon dioxide from silicon rubber pyrolysis waste, characterized by, It comprises the following steps: (1) preheating the waste residue to the ignition point of coking matter; (2) burning and gasifying the coking matter under oxygen condition; (3) water-gas gasifying the waste residue after burning and gasification to obtain silicon dioxide; In the step (3), the outlet temperature of the water-gas gasification section is controlled to be not lower than 750℃.

2. The method for preparing silica from silicone rubber pyrolysis waste residue according to claim 1, characterized in that, In the step (1), the content of silicon dioxide in the waste residue is not lower than 60%.

3. The method for preparing silica from silicone rubber pyrolysis waste residue according to claim 1, characterized in that, In the step (2), the oxygen condition is realized by introducing oxygen-containing gas, and the oxygen content in the oxygen-containing gas is not lower than 18w%.

4. The method for preparing silica from silicone rubber pyrolysis waste residue according to claim 1, characterized in that, In the step (2), the temperature of the gasification gas phase high-temperature section is controlled to be 1050-1300℃.

5. The method for preparing silica from silicone rubber pyrolysis waste residue according to claim 4, characterized in that, In the high-temperature section, the residence time of the material is 4-10s.

6. The method for preparing silicon dioxide from silicon rubber pyrolysis waste residue according to claim 1, characterized in that, In the step (3), the humidity in the gas phase during the water-gas gasification of the waste residue is ≥0.066 kg water gas / kg dry gas, and the residence time is ≥2s.

7. The method for preparing silica from silicone rubber pyrolysis waste residue according to claim 1, characterized in that, In the step (3), water-containing gas is introduced during the water-gas gasification of the waste residue. 8.The method for preparing silicon dioxide from silicon rubber pyrolysis residues according to claim 1, characterized in that, The steps (2) and (3) are both carried out in a fluidized bed.

9. The method for preparing silica from silicone rubber pyrolysis waste residue according to claim 1, characterized in that, In the step (3), after the water-gas gasification, a post-treatment process of recovering the silicon dioxide powder is further carried out.

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