Preparation method of high-quality bio-based water glass

Abstract

The invention belongs to the technical field of inorganic materials, and particularly discloses a preparation method of high-quality bio-based water glass, which comprises the following steps: (a) putting a biomass raw material into an incinerator for combustion to obtain biomass ash and saturated steam; the excess air coefficient of combustion is 1.5-1.6, and the air ratio is 4: 6-6: 4; (b) carrying out acid pickling and impurity removal on the biomass ash, then mixing the biomass ash with alkali in deionized water, heating to a specified temperature, carrying out heat preservation for reaction, after the reaction is finished, cooling, and carrying out solid-liquid separation to obtain a water glass solution. The preparation method is efficient, economical and simple; the prepared product is water-white and controllable in modulus, and can be applied to a plurality of industrial fields such as white carbon black manufacturing, precision casting, refractory materials, environment-friendly coatings, detergents, silica gel and molecular sieves; meanwhile, the technical problems that in the prior art, when a biological silicate solution is prepared from biomass raw materials, a product is amber and the modulus is low are solved.

Description

Technical Field

[0001] This invention belongs to the field of inorganic materials technology and relates to the preparation of silicates, specifically to a method for preparing colorless, transparent or slightly water-white, high-modulus bio-based water glass. Background Technology

[0002] Silica (amorphous hydrated silica) is an important chemical filler and reinforcing agent, widely used in industries such as rubber, plastics, and coatings. Among its production methods, precipitated silica is widely used due to its lower cost. The further preparation of silica from water glass obtained from rice husks, an agricultural byproduct, aligns with the requirements of green, low-carbon, and sustainable development, and is currently a research hotspot.

[0003] The process typically begins by pretreating rice husks to obtain rice husk ash, which is then reacted with an alkaline solution to prepare water glass (sodium silicate). This water glass is then further processed through carbonization and other steps to produce silica. However, residual metallic impurities (such as iron and manganese) and organic matter in the rice husk ash can cause the water glass to develop a difficult-to-remove amber color during the high-temperature alkaline dissolution process. This color is unacceptable in industrial applications, as industrial-grade water glass is typically required to be water-white.

[0004] Existing technologies have attempted various decolorization methods, such as activated carbon filtration, zeolite treatment, ion exchange resins, the use of chelating agents (such as EDTA), or chlorine oxidation, but the results have been unsatisfactory or the costs too high. Patent CN1021038C proposes using the active carbonaceous substances inherent in bio-silica (such as rice husk ash) as an anti-discoloration agent, reducing or absorbing polyvalent metals and organic compounds and their analogues during the reaction process, thereby preventing the formation of amber color in water glass. However, this method has a significant drawback: to prevent discoloration, the reaction must be carried out at a relatively low temperature (<135℃) or for a short time, which directly results in a low modulus of water glass (less than 2.5), making it difficult to prepare high-modulus water glass (usually referring to a modulus greater than 3). High-modulus water glass is a key precursor for the production of high-quality silica.

[0005] Therefore, developing a new method that can obtain water-white water glass using rice husks as raw material while ensuring high reaction efficiency (i.e., fully reacting at higher temperatures to obtain high-modulus products) has significant industrial application value. In view of this, the present invention is proposed. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a method for preparing high-quality bio-based water glass. This method is efficient, economical, and simple; the resulting product is water-white with a controllable modulus, and can be used in multiple industrial fields such as silica manufacturing, precision casting, refractory materials, environmentally friendly coatings, detergents, silica gel, and molecular sieves. Furthermore, it solves the technical problems of amber color and low modulus in the preparation of biosilicates from biomass raw materials in existing technologies.

[0007] This invention is achieved through the following technical solution: A method for preparing high-quality bio-based water glass includes the following steps: (a) The biomass raw material is fed into an incinerator for combustion to obtain biomass ash and saturated steam; the excess air coefficient of the combustion is 1.5 to 1.6, and the air ratio is 4:6 to 6:4. (b) The biomass ash is acid-washed to remove impurities and then mixed with alkali in deionized water. The mixture is heated to a specified temperature and kept at that temperature to carry out the reaction. After the reaction is completed, the mixture is cooled and the solid and liquid are separated to obtain a water glass solution.

[0008] A further improvement to the present invention is as follows: The biomass raw material is straw or rice husk or a mixture of both.

[0009] Preferably, the straw is one or a mixture of two or more of corn straw, wheat straw, or rice straw; the husk is rice husk, wheat husk, or a mixture of both.

[0010] Furthermore, the incinerator is selected from biomass furnaces, cyclone furnaces, fluidized bed furnaces, gasifiers, rotary kilns, or steam furnaces.

[0011] Preferably, the incinerator is a fluidized bed furnace.

[0012] Furthermore, the alkali is sodium hydroxide or potassium hydroxide or a mixture of both.

[0013] Preferably, the alkali is sodium hydroxide.

[0014] Furthermore, the mass ratio of the biomass ash to the deionized water is 1:2 to 6; the mass ratio of the biomass ash (based on the amount of silicon dioxide) to the alkali is 3:2 to 5:2.

[0015] Furthermore, the reaction temperature is 140-260℃, and the holding time is 0.5-24 h.

[0016] Furthermore, the saturated steam can be used to provide a heat source for the reaction process, or it can be collected and reused.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention enables biomass raw materials to be sintered under specific conditions by adjusting the sintering process, thereby controlling the content of organic components in biomass ash and obtaining a water-white product that meets the requirements of industrial grade (GB / T 4209-2022), thus solving the core pain point of coloring when preparing water glass from biomass ash raw materials.

[0018] 2. This invention allows the reaction to be carried out at higher temperatures (140-260 ℃), which greatly improves the reaction rate and the modulus of water glass (modulus > 3), and solves the problem of low reaction rate and low modulus caused by low temperature.

[0019] 3. The present invention does not require decolorization equipment (such as ion exchange columns) or expensive chelating agents. The apparatus involved in the method provided is highly mature and easy to industrialize.

[0020] 4. This invention makes full use of agricultural waste. Apart from igniting biomass, no additional heat supply is required. At the same time, it utilizes the heat generated during the combustion process, resulting in low overall cost and high economic benefits. The entire process meets the requirements of green chemistry and circular economy. Attached Figure Description

[0021] Figure 1 Images of the water glass prepared in the embodiments and comparative examples of this invention; Figure 2 The infrared spectra of rice husk ash prepared in Comparative Examples 1-3 of this invention are shown. Figure 3 The images show the infrared spectra of rice husk ash prepared in Examples 1, 3, 4, 6, and 9 of this invention. Detailed Implementation

[0022] The present invention will now be described in detail with reference to specific embodiments.

[0023] In this invention, the excess air coefficient is the ratio of actual air volume to theoretical air volume; theoretical air volume refers to the minimum amount of air theoretically required for the complete combustion of a unit weight (or volume) of fuel; actual air volume is the total amount of air used in actual operation; since mixing cannot be absolutely uniform, there are always some dead zones or airflow short circuits, in order to ensure the complete combustion of fuel, the actual amount of air supplied must be greater than the theoretical air volume.

[0024] In this invention, the air ratio is a primary / secondary air ratio; the primary air is located at the bottom of the furnace, mainly to ensure the fluidization of the bed material and provide the oxygen required for the initial combustion of fuel in the bed; the secondary air is located near the middle of the furnace, mainly to enhance turbulence and disturbance, and to provide sufficient oxygen for the fuel suspended and burning in the upper part of the furnace, which is the most critical link to reduce the residual carbon content of fly ash; during stable operation, the primary and secondary air are turned on simultaneously for combustion.

[0025] In this invention, the modulus of water glass is determined by the method described in GB / T 4209-2022.

[0026] The infrared spectrum of rice husk ash was determined using the method described in GB / T 6040-2019 and detected using a Thermo Fisher iS5 infrared spectrometer.

[0027] The ash content of rice husk ash was determined according to the method described in GB / T 17664-2024.

[0028] Comparative Example 1 (a) Rice husks were sintered in a muffle furnace at 400 °C for 2 h to obtain rice husk ash with an ash content of 86.00%. The obtained rice husk ash was then acid-washed to remove impurities and dried. (b) Take 375 g of pretreated rice husk ash and put it into a reactor containing 1500 g of deionized water. Then, dissolve 107.5 g of sodium hydroxide in the reactor and keep it at 200 °C for 12 h. After the reaction is completed and cooled, solid-liquid separation is performed to obtain water glass solution.

[0029] Comparative Example 2 (a) Rice husks were sintered in a muffle furnace at 650 °C for 2 h to obtain rice husk ash with an ash content of 95.31%. The obtained rice husk ash was then acid-washed to remove impurities and dried. (b) Take 375 g of pretreated rice husk ash and put it into a reactor containing 1500 g of deionized water. Then, dissolve 119.14 g of sodium hydroxide in the reactor and keep it at 200 °C for 12 h. After the reaction is completed and cooled, solid-liquid separation is performed to obtain water glass solution.

[0030] Comparative Example 3 (a) Rice husks were sintered in a muffle furnace at 800 °C for 2 h to obtain rice husk ash with an ash content of 96.15%. The obtained rice husk ash was then acid-washed to remove impurities and dried. (b) Take 375 g of pretreated rice husk ash and put it into a reactor containing 1500 g of deionized water. Then, dissolve 120.19 g of sodium hydroxide in the reactor and keep it at 200 °C for 12 h. After the reaction is completed and cooled, solid-liquid separation is performed to obtain water glass solution.

[0031] Comparative Example 4 (a) Rice husks are put into an incinerator for combustion. The excess air coefficient is adjusted to 1.8 and the air ratio is 5:5, so that the bottom bed temperature is 740±20 ℃, and rice husk ash with an ash content of 91.68% is obtained. The obtained rice husk ash is then acid washed to remove impurities and dried. (b) Take 375 g of pretreated rice husk ash and put it into a reactor containing 1500 g of deionized water. Then, dissolve 114.6 g of sodium hydroxide in the reactor and keep it at 200 °C for 12 h. After the reaction is completed and cooled, solid-liquid separation is performed to obtain water glass solution.

[0032] Comparative Example 5 (a) Rice husks are put into an incinerator for combustion. The excess air coefficient is adjusted to 1.4 and the air ratio is 6:4, so that the bottom bed temperature is 860±20 ℃, and rice husk ash with an ash content of 93.24% is obtained. The obtained rice husk ash is then acid washed to remove impurities and dried. (b) Take 375 g of pretreated rice husk ash and put it into a reactor containing 1500 g of deionized water. Then, dissolve 116.55 g of sodium hydroxide in the reactor and keep it at 200 °C for 12 h. After the reaction is completed and cooled, solid-liquid separation is performed to obtain water glass solution.

[0033] Comparative Example 6 (a) Rice husks are put into an incinerator for combustion. The excess air coefficient is adjusted to 1.6 and the air ratio is 7:3, so that the bottom bed temperature is 870±20 ℃, and rice husk ash with an ash content of 95.78% is obtained. The obtained rice husk ash is then acid washed to remove impurities and dried. (b) Take 375 g of pretreated rice husk ash and put it into a reactor containing 1500 g of deionized water. Then, dissolve 119.73 g of sodium hydroxide in the reactor and keep it at 200 °C for 12 h. After the reaction is completed and cooled, solid-liquid separation is performed to obtain water glass solution.

[0034] Example 1 (a) Rice husks are put into an incinerator for combustion. The excess air coefficient is adjusted to 1.50 and the air ratio is 4:6, so that the bottom bed temperature is 860±15 ℃, and rice husk ash with an ash content of 99.30% is obtained. The obtained rice husk ash is then acid washed to remove impurities and dried. (b) Take 750 g of pretreated rice husk ash and put it into a reactor containing 1500 g of deionized water. Then, dissolve 331.00 g of sodium hydroxide in the reactor and keep it at 140 °C for 0.5 h. After the reaction is completed and cooled, solid-liquid separation is performed to obtain water glass solution.

[0035] Example 2 (a) Rice husks are put into an incinerator for combustion. The excess air coefficient is adjusted to 1.50 and the air ratio is 5:5, so that the bottom bed temperature is 855±15 ℃, and rice husk ash with an ash content of 98.72% is obtained. The obtained rice husk ash is then acid washed to remove impurities and dried. (b) Take 750 g of pretreated rice husk ash and put it into a reactor containing 1500 g of deionized water. Then, dissolve 246.80 g of sodium hydroxide in the reactor and keep it at 200 °C for 12 h. After the reaction is completed and cooled, solid-liquid separation is performed to obtain water glass solution.

[0036] Example 3 (a) Rice husks are put into an incinerator for combustion. The excess air coefficient is adjusted to 1.50 and the air ratio is 6:4, so that the bottom bed temperature is 850±15 ℃, and rice husk ash with an ash content of 98.36% is obtained. The obtained rice husk ash is then acid washed to remove impurities and dried. (b) Take 750 g of pretreated rice husk ash and put it into a reactor containing 1500 g of deionized water. Then, dissolve 196.72 g of sodium hydroxide in the reactor and keep it at 260 °C for 24 h. After the reaction is completed and cooled, solid-liquid separation is performed to obtain a water glass solution.

[0037] Example 4 (a) Rice husks are put into an incinerator for combustion. The excess air coefficient is adjusted to 1.55 and the air ratio is 4:6, so that the bottom bed temperature is 855±15 ℃, and rice husk ash with an ash content of 99.14% is obtained. The obtained rice husk ash is then acid washed to remove impurities and dried. (b) Take 375 g of pretreated rice husk ash and put it into a reactor containing 1500 g of deionized water. Then, dissolve 99.14 g of sodium hydroxide in the reactor and keep it at 140 °C for 12 h. After the reaction is completed and cooled, solid-liquid separation is performed to obtain water glass solution.

[0038] Example 5 (a) Rice husks are put into an incinerator for combustion. The excess air coefficient is adjusted to 1.55 and the air ratio is 5:5, so that the bottom bed temperature is 850±15 ℃, and rice husk ash with an ash content of 98.75% is obtained. The obtained rice husk ash is then acid washed to remove impurities and dried. (b) Take 375 g of pretreated rice husk ash and put it into a reactor containing 1500 g of deionized water. Then, dissolve 165.23 g of sodium hydroxide in the reactor and keep it at 200 °C for 24 h. After the reaction is completed and cooled, solid-liquid separation is performed to obtain water glass solution.

[0039] Example 6 (a) Rice husks are put into an incinerator for combustion. The excess air coefficient is adjusted to 1.55 and the air ratio is 6:4, so that the bottom bed temperature is 845±15 ℃, and rice husk ash with an ash content of 98.37% is obtained. The obtained rice husk ash is then acid washed to remove impurities and dried. (b) Take 375 g of pretreated rice husk ash and put it into a reactor containing 1500 g of deionized water. Then, dissolve 122.96 g of sodium hydroxide in the reactor and keep it at 260 °C for 0.5 h. After the reaction is completed and cooled, solid-liquid separation is performed to obtain water glass solution.

[0040] Example 7 (a) Rice husks are put into an incinerator for combustion. The excess air coefficient is adjusted to 1.6 and the air ratio is 4:6, so that the bottom bed temperature is 850±15 ℃, and rice husk ash with an ash content of 98.93% is obtained. The obtained rice husk ash is then acid washed to remove impurities and dried. (b) Take 250 g of pretreated rice husk ash and put it into a reactor containing 1500 g of deionized water. Then, dissolve 82.44 g of sodium hydroxide in the reactor and keep it at 140 °C for 24 h. After the reaction is completed and cooled, solid-liquid separation is performed to obtain water glass solution.

[0041] Example 8 (a) Rice husks are put into an incinerator for combustion. The excess air coefficient is adjusted to 1.6 and the air ratio is 5:5 so that the bottom bed temperature is 845±15 ℃, and rice husk ash with an ash content of 98.40% is obtained. The obtained rice husk ash is then acid washed to remove impurities and dried. (b) Take 250 g of pretreated rice husk ash and put it into a reactor containing 1500 g of deionized water. Then, dissolve 65.60 g of sodium hydroxide in the reactor and keep it at 200 °C for 0.5 h. After the reaction is completed and cooled, solid-liquid separation is performed to obtain water glass solution.

[0042] Example 9 (a) Rice husks are put into an incinerator for combustion. The excess air coefficient is adjusted to 1.6 and the air ratio is 6:4, so that the bottom bed temperature is 840±15 ℃, and rice husk ash with an ash content of 98.23% is obtained. The obtained rice husk ash is then acid washed to remove impurities and dried. (b) Take 250 g of pretreated rice husk ash and put it into a reactor containing 1500 g of deionized water. Then, dissolve 109.14 g of sodium hydroxide in the reactor and keep it at 260 °C for 12 h. After the reaction is completed and cooled, solid-liquid separation is performed to obtain water glass solution.

[0043] The results of ash content, water glass color, and modulus of rice husk ash in Comparative Examples 1-6 and Examples 1-9 are as follows:

[0044] The results of comparative examples 1-3 show that the prepared water glass all appear blackish-red. Figure 1With the increase of ash content in rice husk ash, and the infrared spectrum ( Figure 2 The weakening of absorption peaks at 3400 cm⁻¹ and 1600 cm⁻¹ in the water glass indicates that the color of the water glass gradually lightens. This phenomenon suggests that the color of the water glass is likely caused by residual organic components in the rice husk ash. Compared with Comparative Examples 4-6, the water glass modulus of the products prepared in Examples 1-9 is all >2.5, and the modulus of the water glass prepared in Examples 2, 3, 4, 6, 7, and 8 is >3.0. Furthermore, the water glass obtained in all examples is water-white or near-water-white in color. In addition, excessively high excess air coefficients and primary air ratios, as well as excessively low excess air coefficients, can lead to lower ash content and higher organic matter content in the sintered rice husk ash. Figure 2 and 3 This process gives the water glass its amber color. Only by using the method of this invention, employing a suitable incinerator, and controlling appropriate sintering parameters to obtain rice husk ash with high ash content and low organic components as the raw material for water glass, can we obtain water-white water glass that meets industrial requirements. Other methods are not as effective as those of this invention.

[0045] The above description of the embodiments is only for illustrating the technical concept and features of the present invention. Its purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly. Those skilled in the art can obviously easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative effort. Therefore, the above embodiments should not be used to limit the scope of protection of the present invention. All improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing high-quality bio-based water glass, characterized in that, Includes the following steps: (a) The biomass raw material is fed into an incinerator for combustion to obtain biomass ash and saturated steam; the excess air coefficient of the combustion is 1.5 to 1.6, and the air ratio is 4:6 to 6:

4. (b) The biomass ash is acid-washed to remove impurities and then mixed with alkali in deionized water. The mixture is heated to a specified temperature and kept at that temperature to carry out the reaction. After the reaction is completed, the mixture is cooled and the solid and liquid are separated to obtain a water glass solution.

2. The method for preparing high-quality bio-based water glass according to claim 1, characterized in that: The biomass raw material is straw or rice husk or a mixture of both.

3. The method for preparing high-quality bio-based water glass according to claim 2, characterized in that: The straw is one or a mixture of two or more of corn straw, wheat straw, or rice straw; the husk is rice husk, wheat husk, or a mixture of both.

4. The method for preparing high-quality bio-based water glass according to claim 1, characterized in that: The incinerator is selected from biomass furnaces, cyclone furnaces, fluidized bed furnaces, gasifiers, rotary kilns, or steam furnaces.

5. The method for preparing high-quality bio-based water glass according to claim 4, characterized in that: The incinerator is a fluidized bed furnace.

6. The method for preparing high-quality bio-based water glass according to claim 1, characterized in that: The alkali is sodium hydroxide or potassium hydroxide or a mixture of both.

7. The method for preparing high-quality bio-based water glass according to claim 6, characterized in that: The alkali is sodium hydroxide.

8. The method for preparing high-quality bio-based water glass according to claim 1, characterized in that: The mass ratio of the biomass ash to the deionized water is 1:2 to 6; the mass ratio of the biomass ash (based on the amount of silicon dioxide) to the alkali is 3:2 to 5:

2.

9. The method for preparing high-quality bio-based water glass according to claim 1, characterized in that: The reaction temperature is 140-260℃, and the holding time is 0.5-24 h.

10. The method for preparing high-quality bio-based water glass according to claim 1, characterized in that: The saturated steam can be used to provide a heat source for the reaction process and / or be collected and reused.

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