Silicon dioxide for abrasive toothpaste and preparation method thereof

Abstract

The present invention relates to a preparation method of silicon dioxide for friction toothpaste, including: S1, adding sodium pyrophosphate solution, adding sodium silicate solution after heating; S2, adding phosphoric acid solution dropwise to pH 8-9.5 under stirring; S3, adding phosphoric acid solution and sodium silicate solution dropwise to react, keeping pH 8-9.5; S4, after the sodium silicate solution is added dropwise, phosphoric acid solution is continued to be added dropwise to pH 4-5.5, and then heat preservation and aging; S5, the reaction slurry after aging is filtered, washed, dried, and crushed to obtain silicon dioxide; S6, adjusting the pH of the recovered liquid composed of the filtered mother liquor and the washing water to 11.3-11.8, and then concentrating and crystallizing to obtain sodium phosphate salt. The preparation method of the present invention uses sodium silicate and phosphoric acid as raw materials, sodium pyrophosphate as a bottom liquid auxiliary agent, the reaction will not introduce other impurities, the reaction slurry is easy to filter, and zero discharge of production wastewater is achieved, and silicon dioxide and sodium phosphate salt for friction toothpaste can be obtained at the same time.

Description

Technical Field

[0001] The invention belongs to the technical field of daily chemical industry, and specifically relates to silicon dioxide for friction toothpaste and a preparation method thereof. Background Art

[0002] Silicon dioxide has stable physical and chemical properties, is resistant to acid, alkali and high temperature, has suitable hardness, particle size and good decontamination effect, is environmentally friendly, does not damage tooth tissue, is tasteless and odorless, and has good compatibility with the raw materials in toothpaste, ensuring that it does not affect the inherent fragrance of toothpaste. Therefore, it replaces other raw materials such as calcium carbonate as a toothpaste abrasive.

[0003] At present, the main process for producing silicon dioxide for toothpaste is the sulfuric acid method, which uses sulfuric acid and sodium silicate as raw materials and uses the precipitation method to prepare silicon dioxide for toothpaste. The technology is mature. However, with the rapid development of the times, increasingly stringent environmental protection requirements, and the deepening of the concept of making full use of resources to reduce costs and increase efficiency, the sodium element in the sulfuric acid method for preparing silicon dioxide has formed a low-value-added "sodium sulfate" byproduct, and the sewage is difficult to treat, resulting in poor economic benefits. Secondly, sulfuric acid is a strong acid with strong corrosiveness and high requirements for production equipment. In addition, the reaction is relatively violent and the operating conditions are difficult to control, resulting in rising production costs.

[0004] To this end, in view of the defects of the sulfuric acid method, the researchers used the phosphoric acid method to improve economic benefits and solve environmental pressure. For example: Chinese patent CN1686792A discloses a "method for preparing precipitated silica by phosphoric acid method". This method has certain limitations. Sodium chloride is used as a base liquid auxiliary agent in the preparation process to play the role of precipitating gel particles, but the chloride ions in sodium chloride are highly corrosive to the equipment, and the mother liquor contains chloride ions, which has a high separation cost, resulting in a decrease in the purity of the byproduct sodium phosphate salt, and it is impossible to achieve zero discharge of process water. Chinese patent CN101412514B discloses "a process for preparing white carbon black by phosphoric acid precipitation and directly producing sodium phosphate salt". This process adds nitric acid as a filter aid when producing silicon dioxide, which makes the reaction slurry easy to filter, but it also causes the sodium phosphate salt in the mother liquor to contain sodium nitrate salt, resulting in a decrease in the purity of the byproduct sodium phosphate salt.

[0005] Therefore, in order to solve the problems existing in the above-mentioned phosphoric acid method, it is necessary to develop a method for preparing silicon dioxide in which the reaction slurry is easy to filter and the main and by-products have high added value and purity. Summary of the invention

[0006] The purpose of the present invention is to provide a method for preparing silicon dioxide for abrasive toothpaste, wherein sodium silicate and phosphoric acid are used as raw materials, sodium pyrophosphate is used as a base liquid auxiliary agent, other impurity ions are not introduced into the reaction, the reaction slurry is easy to filter, and zero discharge of production wastewater is achieved. Not only silicon dioxide for abrasive toothpaste can be prepared, but also sodium phosphate salt can be obtained.

[0007] The technical solution adopted by the present invention to solve the above problem is: a method for preparing silicon dioxide for abrasive toothpaste, comprising the following steps: S1. Preparation of reaction base liquid: add sodium pyrophosphate solution into the reaction kettle, then heat it to 75°C-95°C, and then add sodium silicate solution; S2, adding phosphoric acid solution dropwise while stirring to make the pH in the reactor 8-9.5; S3, neutralization reaction: add phosphoric acid solution and sodium silicate solution dropwise while stirring to react, and keep the pH value at 8-9.5 during the process; S4, acidification and aging: After the sodium silicate solution is added, phosphoric acid solution is continued to be added until the pH drops to 4-5.5, and then the mixture is kept warm and aged; S5. Filter, wash, dry and crush the reaction slurry after aging to obtain abrasive silicon dioxide for toothpaste.

[0008] S6. The pH value of the recovered liquid consisting of the filtered mother liquor and the washing water in step S5 is adjusted to 11.3-11.8 with sodium hydroxide, and then concentrated and crystallized under negative pressure to obtain sodium phosphate salt. The evaporated water generated in the concentration and crystallization can be recycled after condensation.

[0009] Preferably, in step S1, the mass percentage concentration of the sodium pyrophosphate solution is 1%-2%, and the mass percentage concentration of the sodium silicate solution is 35%-40%.

[0010] Preferably, the amount of the sodium silicate solution added in step S1 is 5%-10% of the mass of the sodium pyrophosphate solution.

[0011] Preferably, the mass percentage concentration of the phosphoric acid solution in step S2 is 10%-20%, and the temperature of the phosphoric acid solution is 75°C-95°C.

[0012] Preferably, in step S3, the mass percentage concentration of the phosphoric acid solution is 10%-20%, and the temperature of the phosphoric acid solution is 75°C-95°C; the mass percentage concentration of the sodium silicate solution is 13%-20%, and the temperature of the sodium silicate solution is 75°C-95°C.

[0013] More preferably, the preparation method of the phosphoric acid solution is specifically as follows: adding water to dilute concentrated phosphoric acid with a mass fraction of 85% to form a 10%-20% phosphoric acid solution, and heating it to 75°C-95°C; the preparation method of the sodium silicate solution is specifically as follows: adding water to dilute liquid sodium silicate with a modulus of 3.3-3.5 and a mass fraction of 35%-40% to form a solution with a concentration of 13%-20%, and heating it to 75°C-95°C.

[0014] Preferably, the reaction time in step S3 is 75-105 minutes.

[0015] Preferably, the heat preservation and aging time in step S4 is 30-50 minutes.

[0016] Preferably, step S5 specifically comprises: filtering the reaction slurry after aging, then beating and washing the filter cake until the pH value of the filtrate is 6.5-7.5, and drying the washed filter cake and then crushing it to meet the particle size requirements of silicon dioxide for toothpaste.

[0017] Another object of the present invention is to provide a friction type silica for toothpaste, wherein the friction type silica for toothpaste is prepared by the above-mentioned preparation method.

[0018] Compared with the prior art, the advantages of the present invention are: (1) In the method for preparing silica for friction toothpaste of the present invention, phosphoric acid and sodium silicate are used as raw materials, and sodium pyrophosphate is used as a base liquid auxiliary agent. Not only other impurity ions will not be introduced during the reaction process, but also sodium pyrophosphate can bring about a dispersing effect. The byproduct sodium phosphate salt produced during the reaction also plays a dispersing role, which greatly improves the dispersing effect, inhibits excessive agglomeration of silica particles, makes the product particle size distribution more uniform, and greatly simplifies the subsequent treatment process. The main and byproducts obtained are relatively pure, and silica for toothpaste and sodium phosphate salt can be obtained at the same time, which organically combines phosphorus chemical industry and silicon chemical industry to achieve high-value utilization of the three elements of "sodium, silicon and phosphorus".

[0019] (2) The method for preparing silica for abrasive toothpaste of the present invention adopts a method of first single feeding (single drop of phosphoric acid solution) and then double feeding (simultaneous addition of phosphoric acid solution and sodium silicate solution), and controls the pH of the slurry reaction in stages to avoid rapid agglomeration of silica, reduce the generation of gel during the reaction, and make the product slurry easy to filter.

[0020] (3) In the method for preparing silica for abrasive toothpaste of the present invention, the reaction slurry after aging is filtered and washed, and the filtered mother liquor water and washing water (containing sodium phosphate) are concentrated and reused to achieve zero discharge of sewage and reduce environmental pollution. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The process flow chart of silicon dioxide for abrasive toothpaste of the present invention is shown in FIG. DETAILED DESCRIPTION

[0022] The present invention is further described in detail below with reference to the accompanying drawings.

[0023] like Figure 1 As shown, this is a process flow chart of silicon dioxide for abrasive toothpaste of the present invention. Example 1

[0024] A method for preparing silicon dioxide for abrasive toothpaste comprises the following steps: S1. Add 690 g of sodium silicate solution with a modulus of 3.26 and a mass fraction of 35.5% and 228.7 g of 85% phosphoric acid solution into two 2L containers respectively, and then dilute with water to a mass fraction of 14.4% (sodium silicate solution) and 10% (phosphoric acid solution) respectively, and set aside; S2, prepare 855g of 2% sodium pyrophosphate aqueous solution and inject it into a 5L reactor, start stirring and heat to 95°C, then add 45g of 35.5% sodium silicate aqueous solution; S3, add the 10% phosphoric acid solution prepared in S1 dropwise (drop speed of 8.5 ml / min) to the reaction base solution in S2 until the pH reaches 9.5, stop the single dropwise addition, and then add the phosphoric acid solution and sodium silicate solution prepared in S1 dropwise at the same time, adjust the flow ratio of the phosphoric acid solution and the sodium silicate solution prepared in S1 to 1:2, so that the reaction pH is stabilized at 9.5 during the double dropwise addition, the reaction time is 105 minutes, and the reaction temperature is maintained at 95°C; S4. After the sodium silicate solution is added, continue to drop the phosphoric acid solution, and acidify the slurry to pH 4.5 in 25 minutes, and then continue to mature for 30 minutes, maintaining the reaction temperature at 95°C; S5. After the aging is completed, the slurry is filtered and washed with water until the pH of the filtrate reaches 6.5; S6. Dry the washed silica filter cake at 120° C. for 2 hours, and then crush it until the content of the material under a 325-mesh sieve is greater than 98%, thereby obtaining abrasive silica for toothpaste.

[0025] S7, recovering the filtered mother liquor and washing water in step S6, adjusting the pH of the recovered liquid to 11.5 with sodium hydroxide, concentrating and crystallizing under negative pressure to obtain sodium phosphate salt, and the evaporated water can be recycled after condensation and can be used for the preparation of dilute sodium silicate solution and dilute phosphoric acid solution in step S1. Example 2

[0026] A method for preparing silicon dioxide for abrasive toothpaste comprises the following steps: S1. Add 690 g of sodium silicate aqueous solution with a modulus of 3.26 and a mass fraction of 35.5% and 228.7 g of 85% phosphoric acid aqueous solution into two 2L containers respectively, and dilute them with water to a mass fraction of 15% (sodium silicate solution) and 20% (phosphoric acid solution) respectively, and set aside; S2, prepare 855g of 1% sodium pyrophosphate aqueous solution and inject it into a 5L reactor, start stirring and heat to 85°C, then add 60g of 35.5% sodium silicate aqueous solution; S3, add a single drop of the 20% phosphoric acid solution prepared in S1 to the reaction base solution in S2 until the pH reaches 9, stop the single drop addition, and then simultaneously add the phosphoric acid solution and the sodium silicate solution prepared in S1, adjust the flow ratio of the phosphoric acid solution and the sodium silicate solution so that the reaction pH is stabilized at 9 during the double drop addition process, the reaction time is 75 minutes, and the reaction temperature is maintained at 85°C; S4. After the addition is completed, continue to drop the phosphoric acid solution, and acidify the slurry to pH 4 in 25 minutes, and then continue to mature for 30 minutes, maintaining the reaction temperature at 85°C; S5. After the aging is completed, the slurry is filtered and washed with water until the pH of the filtrate reaches 6.8; S6. Dry the washed silica filter cake at 120° C. for 2 hours, and crush it until the content of the filter cake below a 325-mesh sieve is greater than 98%, thereby obtaining abrasive silica for toothpaste.

[0027] S7, recovering the filtered mother liquor and washing water in step S5, adjusting the pH of the recovered liquid to 11.7 with sodium hydroxide, concentrating and crystallizing under negative pressure to obtain sodium phosphate salt, and the evaporated water can be recycled after condensation and can be used for the preparation of dilute sodium silicate solution and dilute phosphoric acid solution in step S1. Example 3

[0028] A method for preparing silicon dioxide for abrasive toothpaste comprises the following steps: S1. Add 690 g of sodium silicate aqueous solution with a modulus of 3.26 and a mass fraction of 35.5% and 179.5 g of 85% phosphoric acid aqueous solution into two 2L containers respectively, and then dilute them with water to a mass fraction of 15% (sodium silicate) and 10% (phosphoric acid) respectively, and set aside; S2, prepare 855g of 2% sodium pyrophosphate aqueous solution and inject it into a 5L reactor, start stirring and heat to the reaction temperature of 75°C, and then add 85.5g of 35.5% sodium silicate aqueous solution; S3, add a single drop of the 10% phosphoric acid solution prepared in S1 to the reaction base solution in S2 until the pH drops to 8.5, stop the single drop addition, and then simultaneously add the phosphoric acid solution and sodium silicate solution prepared in S1, adjust the flow ratio of phosphoric acid and sodium silicate so that the reaction pH is stabilized at 8.5 during the double drop addition process, the reaction time is 90 minutes, and the reaction temperature is maintained at 75°C; S4. After the addition is completed, phosphoric acid is continued to be added dropwise to acidify the slurry until the pH value reaches 5.5 in 25 minutes, and then the aging is continued for 30 minutes, maintaining the reaction temperature at 75°C; S5. After the aging is completed, the slurry is filtered and washed with water until the pH of the filtrate reaches 7; S6. Dry the washed silica filter cake at 120° C. for 2 hours, and then crush it until the content of the filter cake below a 325-mesh sieve is greater than 98%, thereby obtaining silica for toothpaste.

[0029] S7, recovering the filtered mother liquor and washing liquid in step S5, adjusting the pH of the recovered liquid to 11.5 with sodium hydroxide, concentrating and crystallizing under negative pressure to obtain sodium phosphate salt, and the evaporated water can be recycled after condensation and can be used for the preparation of dilute sodium silicate solution and dilute phosphoric acid solution in step S1.

[0030] Comparative Example 1 Compared with Example 3, the only difference is that the base solution in step S2 does not contain sodium pyrophosphate, and other parameters and operating steps are the same as Example 3.

[0031] Comparative Example 2 Compared with Example 3, the only difference is that in step S3, a double dropping operation is performed directly instead of a single dropping operation, and other parameters and operation steps are the same as those in Example 3.

[0032] Comparative Example 3 Compared with Example 3, the only difference is that the reaction temperature in steps S1 and S3 is changed from 75° C. to 65° C., and the other parameters and operating steps are the same as those in Example 2.

[0033] The physical and chemical properties of the silicon dioxide and sodium phosphate prepared in Examples 1 to 3 and Comparative Examples 1 to 3 were measured according to the industry standard QB / T 2346-2015 and GB 1886.338-2021, respectively. The results are shown in Table 1: Table 1 shows the physical and chemical properties of silicon dioxide in Examples 1 to 3 and Comparative Examples 1 to 3

[0034] It can be seen from the above table that the physical and chemical properties of the sodium phosphate salts prepared in Examples 1 to 3 and Comparative Examples 1 to 3 all meet the standard GB 1886.338-2021, and can be used as food-grade trisodium phosphate. The physical and chemical properties of the silicon dioxide prepared in Examples 1 to 3 all meet the indicators of the friction series in the enterprise standard QB / T 2346-2015, and can be used as friction-type silicon dioxide for toothpaste. In Comparative Example 1, not adding sodium pyrophosphate as an auxiliary agent will reduce the density of silicon dioxide and increase the water absorption value, which does not meet the standard. In Comparative Example 2, not adopting the feeding method of single drop followed by double drop will reduce the density of silicon dioxide and does not meet the standard. In Comparative Example 3, lowering the reaction temperature will cause the water absorption value of silicon dioxide to be larger and does not meet the standard.

[0035] In addition to the above embodiments, the present invention also includes other implementation modes. Any technical solutions formed by equivalent transformation or equivalent replacement should fall within the protection scope of the claims of the present invention.

Claims

1. A method for preparing silicon dioxide for abrasive toothpaste, characterized in that: The following steps are involved: S1. Add sodium pyrophosphate solution into the reactor, then heat it to 75°C-95°C, and then add sodium silicate solution; S2, adding phosphoric acid solution dropwise while stirring to make the pH in the reactor 8-9.5; S3, adding phosphoric acid solution and sodium silicate solution dropwise while stirring to react, maintaining the pH value at 8-9.5 during the process; S4. After the sodium silicate solution is added dropwise, phosphoric acid solution is continued to be added dropwise until the pH drops to 4-5.5, and then the mixture is kept warm for aging; S5, filtering, washing, drying and crushing the reaction slurry after aging to obtain abrasive toothpaste silica; S6. The pH value of the recovered liquid consisting of the filtered mother liquor and the washing water in step S5 is adjusted to 11.3-11.8 with sodium hydroxide, and then concentrated and crystallized under negative pressure to obtain sodium phosphate salt. The evaporated water generated in the concentration and crystallization can be recycled after condensation.

2. The method for preparing abrasive toothpaste silicon dioxide according to claim 1, characterized in that: The mass percentage concentration of the sodium pyrophosphate solution in step S1 is 1%-2%, and the mass percentage concentration of the sodium silicate solution is 35%-40%.

3. The method for preparing abrasive toothpaste silicon dioxide according to claim 1, characterized in that: The amount of the sodium silicate solution added in step S1 is 5%-10% of the mass of the sodium pyrophosphate solution.

4. The method for preparing abrasive toothpaste silicon dioxide according to claim 1, characterized in that: The mass percentage concentration of the phosphoric acid solution in step S2 is 10%-20%, and the temperature of the phosphoric acid solution is 75°C-95°C.

5. The method for preparing abrasive toothpaste silicon dioxide according to claim 1, characterized in that: In step S3, the mass percentage concentration of the phosphoric acid solution is 10%-20%, and the temperature of the phosphoric acid solution is 75°C-95°C; the mass percentage concentration of the sodium silicate solution is 13%-20%, and the temperature of the sodium silicate solution is 75°C-95°C.

6. The method for preparing abrasive toothpaste silicon dioxide according to claim 5, characterized in that: The specific method for preparing the phosphoric acid solution is: adding water to dilute concentrated phosphoric acid with a mass fraction of 85% to a 10%-20% phosphoric acid solution, and heating it to 75°C-95°C; the specific method for preparing the sodium silicate solution is: adding water to dilute liquid sodium silicate with a modulus of 3.3-3.5 and a mass fraction of 35%-40% to a solution with a concentration of 13%-20%, and heating it to 75°C-95°C.

7. The method for preparing abrasive toothpaste silicon dioxide according to claim 1, characterized in that: The reaction time in step S3 is 75-105 minutes.

8. The method for preparing silicon dioxide for abrasive toothpaste according to claim 1, characterized in that: The heat preservation and aging time in step S4 is 30-50 minutes.

9. The method for preparing silicon dioxide for abrasive toothpaste according to claim 1, characterized in that: Step S5 specifically comprises: filtering the reaction slurry after aging, beating and washing the filter cake until the pH value of the filtrate is 6.5-7.5, drying the washed filter cake and then crushing it to meet the particle size requirements of silicon dioxide for toothpaste.

10. A friction type silicon dioxide for toothpaste, characterized in that: The silicon dioxide for abrasive toothpaste is prepared by the preparation method described in any one of claims 1-9.

Images