Production process of silicon dioxide with high light transmittance

Abstract

The invention belongs to the technical field of silicon dioxide production, and particularly relates to a high-light-transmittance silicon dioxide production process. The process comprises the following steps: mixing preheated low-iron solid water glass with process water containing sodium hydroxide, carrying out steam pressure-maintaining dissolution for 45-65 minutes, precipitating and deslagging, adding a nonionic surfactant, diluting into dilute water glass by using the process water, filtering, continuously adding the dilute water glass and concentrated sulfuric acid into a precipitation reaction kettle to obtain a silicon dioxide suspension with a certain solid content, and carrying out vacuum drying on the silicon dioxide suspension. And aging, washing, drying and ball-milling to obtain the product. The light transmittance of the silicon dioxide product prepared by the process is greater than 75%, and the silicon dioxide product has excellent properties such as BET 190-210 m < 2 > / g and the like; the dissolving process is optimized, the single-batch period is shortened, the energy consumption is reduced, and the cost is reduced by 0.3-0.8% per thousand jin; undissolved particles are reduced by repeatedly adding water and controlling the dissolving time, the dispersibility is improved by adding the surfactant, the continuous operation is realized, the solid content of the suspension is controlled, and the product consistency and the production stability are improved.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of silica production, in particular to a high-transmittance silica production process. BACKGROUND

[0002] Silica is an important reinforcing agent for silicone rubber, which can significantly improve the tensile strength, tear strength and wear resistance of the silicone rubber. Moreover, high-transmittance silica has great significance in the field of silicone rubber, which is uniformly dispersed in the silicone rubber and can significantly improve the transparency of the silicone rubber, thereby expanding the application of the silicone rubber in the fields of optical products, aerospace and medical equipment. The preparation methods of silica include the precipitation method, the sol-gel method and the gas phase method. The sol-gel method can realize high-purity preparation, but has the problems of complex process and long production cycle; the gas phase method can prepare high-purity silica, but has high equipment requirements and high energy consumption; the precipitation method has low cost, but the product purity and transparency are limited. At present, the preparation method of silica in the ton level is the precipitation method.

[0003] In the process of preparing silica by the precipitation method, the factors affecting the transparency of silica include the purity of raw materials, which directly determines the impurity content, or the improper control of reaction temperature and time, which easily leads to uneven particle size of silica, or the too fast deposition rate which causes particle agglomeration and destroys the structural uniformity. At present, the purity of raw materials is controlled by water glass purification and inorganic acid refining, and the reaction temperature and pH are automatically controlled, and the concentration of reactants and the feeding mode are also automatically controlled, so as to solve the above problems. At present, the transmittance of silica prepared by the ton-level precipitation method can reach 70%, but the production cost is also increased. Therefore, an optimized preparation method is developed to solve the problems of the prior art and realize the stable production of low-cost and high-transmittance silica. SUMMARY

[0004] The application aims to provide a high-transmittance silica production process which solves the problems of the prior art.

[0005] The application achieves the above-mentioned purpose by the following technical scheme:

[0006] A high-transmittance silica production process comprises the following steps:

[0007] (1) Preheated low-iron solid water glass is added into a reaction kettle, process water containing sodium hydroxide at 50-60 DEG C is first added, then steam is introduced for pressure maintaining and dissolution, and after the solid water glass is completely dissolved, the reaction kettle is placed in a buffer tank, and after sedimentation and deslagging, concentrated liquid water glass is obtained, wherein the mass concentration of sodium hydroxide in the process water is 5-10%, the process water is added into the reaction kettle in 1-3 times, and the time for completely dissolving the solid water glass is 45-65 min;

[0008] (2) Pump the concentrated liquid water glass into a preparation tank, and in the process of pumping, add a mixed liquid of non-ionic surfactant and process water, then add process water to the preparation tank at a temperature of 85-90 DEG C to prepare dilute water glass with pH=9.5-12, and then filter into a water glass circulating tank;

[0009] (3) Continuously and slowly add the prepared dilute water glass and concentrated sulfuric acid into a precipitation reaction kettle at the same time, adjust pH=3.0-4.0, and obtain a precipitated silica suspension with a solid content of 15-25wt%, pump the suspension into an aging tank, and after aging, filtering, washing, pulping, spray drying and crushing, obtain a silica product.

[0010] As a further improvement of the present application, in step (1), the low-iron solid water glass is preheated by using a silica washing liquid at 50-60 DEG C.

[0011] As a further improvement of the present application, in step (1), the volume ratio of the low-iron solid water glass to process water is 1:(1.8-2.4).

[0012] As a further improvement of the present application, in step (2), the non-ionic surfactant is one of polyoxyethylene type non-ionic surfactant, polyether type non-ionic surfactant or organic silicon type non-ionic surfactant.

[0013] As a further improvement of the present application, the concentration of the non-ionic surfactant is 0.05-0.5% based on the total system percentage of dilute water glass.

[0014] As a further improvement of the present application, in step (2), the M of dilute water glass is 2.8-3.2, and the mass concentration of sodium silicate is 20-35%.

[0015] As a further improvement of the present application, in step (3), the mass concentration of the concentrated sulfuric acid is 98%.

[0016] As a further improvement of the present application, in step (3), the temperature of the aging is 60-65 DEG C, and the time is 0.8-1.2h.

[0017] As a further improvement of the present application, the crushing is ball milling crushing, 2-5mm silica balls, ball-to-material ratio 6:1-8:1, and rotation speed 100r / min-120r / min.

[0018] As a further improvement of the present application, the parameters of the silica product are: light transmittance >75%, BET 190-210m 2 / g, CTAB 140-180m 2 / g, oil absorption value 2.4-2.6ml / g, and particle size 8-12μm.

[0019] The present application has the advantages of:

[0020] (1) The parameters of the silica product prepared by the process of the present application are: light transmittance >75%, BET 190-210m 2 / g, CTAB 140-180m 2 / g, oil absorption value 2.4-2.6ml / g, particle size 8-12μm, narrow distribution (D90 / D10<2) scattering regularity uniform, light transmittance more stable. And the production cycle of single batch product is shortened, and the energy consumption of single batch is reduced, and the cost can be reduced by 0.3-0.8% per thousand jin.

[0021] (2) In the process of the present application, by adding process water containing sodium hydroxide for multiple times and strictly controlling the dissolution time, the solid water glass is fully and uniformly dissolved, the undissolved particles are reduced to hinder the light, and the non-ionic surfactant is added during the pumping process, which can improve the dispersibility and stability of the water glass solution, avoid the formation of agglomerates in the subsequent reaction, and further ensure the light transmittance of the product.

[0022] (3) In the process of the present application, the dissolution link of solid water glass is optimized, the preheated low-iron solid water glass is used, and the process water containing sodium hydroxide is added for 1-3 times, the dissolution efficiency is improved, and the time for completely dissolving the solid water glass is controlled within 45-65min, compared with the traditional process, the time required for dissolution is shortened, the process cycle is shortened, and the consumption of energy such as steam is reduced.

[0023] (4) The process of the present application uses non-ionic surfactant and continuous reaction operation, which helps to reduce the interference of external factors on the reaction. In the precipitation process, the solid content of the precipitated silica suspension is controlled to be 15-25wt%, which ensures the stability of the production process. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 is the flow chart of the silica production process of the present application. DETAILED DESCRIPTION

[0025] The subject matter described herein will now be discussed with reference to example implementations. It should be understood that the discussion of these implementations is merely meant to provide a better understanding of the subject matter described herein and changes to the function and arrangement of the elements discussed can be made without departing from the scope of the content of this specification.

[0026] In at least one embodiment of the present application, a high light transmittance silica production process is disclosed, as shown in Figure 1 , comprising the following steps:

[0027] (1) The preheated low-iron solid water glass is added into the reaction kettle, first adding process water containing sodium hydroxide at 50-60°C, then passing steam to keep pressure and dissolve, after the solid water glass is completely dissolved, it is put into a buffer tank, after the residue is precipitated and removed, the concentrated liquid water glass is obtained, wherein the mass concentration of sodium hydroxide in the process water is 5-10%, the process water is added into the reaction kettle in 1-3 times, and the time for the solid water glass to be completely dissolved is 45-65 min;

[0028] (2) The concentrated liquid water glass is pumped into a preparation tank, in the pumping process, a mixed liquid of non-ionic surfactant and process water is added, then process water is added to the preparation tank at a temperature of 85-90°C to prepare dilute water glass with pH = 9.5-12, and then filtered into a water glass circulating tank;

[0029] (3) The prepared dilute water glass and concentrated sulfuric acid are simultaneously and continuously slowly added into a precipitation reaction kettle, the pH is adjusted to 3.0-4.0, and a precipitated silica suspension with a solid content of 15-25 wt% is obtained, the suspension is pumped into an aging tank, after aging, filtration, washing, pulping, spray drying and crushing, a silica product is obtained.

[0030] In step (1), the low-iron solid water glass can be preheated by using the silica washing liquid at 50-60°C in step (3), and the waste heat is utilized.

[0031] In step (1), the volume ratio of low-iron solid water glass to process water is 1:(1.8-2.4).

[0032] In step (2), the non-ionic surfactant is one of polyoxyethylene type non-ionic surfactant, polyether type non-ionic surfactant or organosilicon type non-ionic surfactant.

[0033] The concentration of non-ionic surfactant is 0.05-0.5% based on the total system percentage of dilute water glass.

[0034] In step (2), the M of dilute water glass is 2.8-3.2, and the mass concentration of sodium silicate is 20-35%.

[0035] In step (3), the mass concentration of concentrated sulfuric acid is 98%.

[0036] In step (3), the aging temperature is 60-65°C, and the time is 0.8-1.2 h.

[0037] The crushing is ball milling crushing, 2-5 mm silica balls, ball to material ratio 6:1-8:1, and rotation speed 100 r / min-120 r / min.

[0038] The parameters of the silica product are that the light transmittance is >75%, and the BET is 190-210 m2 / g, CTAB 140-180m 2 / g, oil absorption value 2.4-2.6ml / g, particle size 8-12μm.

[0039] The following further describes the present application in conjunction with examples and comparative examples. It is necessary to point out that the following specific examples are only used to further illustrate the present application and cannot be understood as limiting the scope of protection of the present application. Those skilled in the art can make some non-essential improvements and adjustments to the present application according to the above application content.

[0040] The low-iron solid water glass in the present application has an iron element content of ≤50ppm.

[0041] The process water in the present application is tap water which is sequentially subjected to ion exchange equipment and disinfection filtration equipment to remove impurities in the water, and has a conductivity of 50-55μs / cm.

[0042] The polyoxyethylene type nonionic surfactant in the present application includes but is not limited to fatty alcohol polyoxyethylene ether, fatty acid polyoxyethylene ester. The polyoxyethylene type nonionic surfactant in the following examples is fatty acid polyoxyethylene ester (S-40);

[0043] The polyether type nonionic surfactant includes but is not limited to polyoxyethylene-polyoxypropylene block copolymer, siloxane-polyether copolymer. The polyether type nonionic surfactant in the following examples is polyoxyethylene-polyoxypropylene block copolymer (L61).

[0044] The organosilicon type nonionic surfactant includes but is not limited to silane glycerol ether, amino-modified polyether silane, silane fatty acid ester. The organosilicon type nonionic surfactant in the following examples is silane glycerol ether (Dow Corning 5200 series).

[0045] The methods used in the present application are conventional methods known to those skilled in the art, and the reagents and other materials used are commercially available products, and the instruments used are conventional instruments known to those skilled in the art, unless otherwise specified.

[0046] Example 1

[0047] The silica production process in the present embodiment includes the following steps:

[0048] (1) The preheated low-iron solid water glass (about 50°C) is added to the reaction kettle, first adding process water containing sodium hydroxide at 55±5°C, then dissolving by passing in steam, and after the solid water glass is completely dissolved in about 50 minutes, it is put into a buffer tank, and after sedimentation and slag removal, a concentrated liquid water glass is obtained. The volume ratio of low-iron solid water glass to process water is 1:2.4, the mass concentration of sodium hydroxide in the process water is 5%, and the process water is added to the reaction kettle in three times with a volume ratio of 4:3.5:2.5;

[0049] (2) The concentrated liquid water glass is pumped into a preparation tank, and in the pumping process, a mixed liquid of fatty acid polyoxyethylene ester and process water is added, and then process water is added to the preparation tank to prepare a dilute water glass at a temperature of 85-90°C, pH=10.5(±1.5), M=3.2 of the dilute water glass, and the mass concentration of sodium silicate is 29%, and then filtered into a water glass circulating tank; wherein the concentration of non-ionic surfactant is 0.2%;

[0050] (3) The prepared dilute water glass and concentrated sulfuric acid with a mass concentration of 98% are simultaneously and continuously slowly added to a precipitation reaction kettle, the pH is adjusted to 3.5±0.5, and a precipitated silica suspension with a solid content of 25wt% is obtained. The suspension is pumped into an aging tank, the aging temperature is 65°C, and the aging time is 1.2h, and then after filtration, washing, pulping, spray drying and ball milling, a silica product is obtained; wherein the ball milling parameters are 2-5mm silica balls, the ball-to-material ratio is 8:1, and the rotation speed is 120r / min.

[0051] Example 2

[0052] The silica production process in this example includes the following steps:

[0053] (1) The preheated low-iron solid water glass (about 50°C) is added to the reaction kettle, first adding process water containing sodium hydroxide at 55±5°C, then dissolving by passing in steam, and after the solid water glass is completely dissolved in about 45 minutes, it is put into a buffer tank, and after sedimentation and slag removal, a concentrated liquid water glass is obtained. The volume ratio of low-iron solid water glass to process water is 1:2.4, the mass concentration of sodium hydroxide in the process water is 10%, and the process water is added to the reaction kettle in one time;

[0054] (2) The concentrated liquid water glass is pumped into a preparation tank, and in the pumping process, a mixed liquid of fatty acid polyoxyethylene ester and process water is added, and then process water is added to the preparation tank to prepare a dilute water glass at a temperature of 85-90°C, pH=10.5(±1.5), M=2.8 of the dilute water glass, and the mass concentration of sodium silicate is 32%, and then filtered into a water glass circulating tank; wherein the concentration of non-ionic surfactant is 0.2%;

[0055] (3) The prepared dilute water glass and concentrated sulfuric acid with a mass concentration of 98% are simultaneously and continuously slowly added into the precipitation reactor, the pH is adjusted to 3.5±0.5, a precipitated silica suspension with a solid content of 20wt% is obtained, the suspension is pumped into an aging tank, the aging temperature is 62℃, the time is 1.0h, then after filtration, washing, pulping, spray drying and ball milling, a silica product is obtained; wherein the ball milling parameters are 2-5mm silica balls, the ball-to-material ratio is 8:1, and the rotation speed is 110r / min.

[0056] Example 3

[0057] The silica production process in this example includes the following steps:

[0058] (1) The preheated low-iron solid water glass (about 50℃) is added into the reactor, first 55±5℃ process water containing sodium hydroxide is added, then steam is introduced for pressure preservation and dissolution, after the solid water glass is completely dissolved for about 51min, it is put into a buffer tank, after precipitation and slag removal, a concentrated liquid water glass is obtained, wherein the volume ratio of low-iron solid water glass to process water is 1:1.8, the mass concentration of sodium hydroxide in process water is 8%, and the process water is added into the reactor in three times with a volume ratio of 4:3.5:2.5;

[0059] (2) The concentrated liquid water glass is pumped into a preparation tank, in the pumping process, a mixed liquid of fatty acid polyoxyethylene ester and process water is added, then process water is added to prepare dilute water glass in the preparation tank at a temperature of 85-90℃, the pH is 10.5(±1.5), the M of the dilute water glass is 3.0, and the mass concentration of sodium silicate is 30%, then it is filtered into a water glass circulating tank; wherein the concentration of nonionic surfactant is 0.2%;

[0060] (3) The prepared dilute water glass and concentrated sulfuric acid with a mass concentration of 98% are simultaneously and continuously slowly added into the precipitation reactor, the pH is adjusted to 3.5±0.5, a precipitated silica suspension with a solid content of 20wt% is obtained, the suspension is pumped into an aging tank, the aging temperature is 62℃, the time is 1.0h, then after filtration, washing, pulping, spray drying and ball milling, a silica product is obtained; wherein the ball milling parameters are 2-5mm silica balls, the ball-to-material ratio is 8:1, and the rotation speed is 110r / min.

[0061] Example 4

[0062] The silica production process in this example includes the following steps:

[0063] (1) The preheated low-iron solid water glass (about 50°C) is added to the reaction kettle, first adding process water containing sodium hydroxide at 55±5°C, then dissolving by passing in steam, and after the solid water glass is completely dissolved in about 51 min, it is put into a buffer tank, and after precipitation and slag removal, a concentrated liquid water glass is obtained. The volume ratio of low-iron solid water glass to process water is 1:1.8, the mass concentration of sodium hydroxide in the process water is 8%, and the process water is added to the reaction kettle in three times according to the volume ratio of 4:3.5:2.5;

[0064] (2) The concentrated liquid water glass is pumped into a preparation tank, and in the pumping process, a mixed liquid of fatty acid polyoxyethylene ester and process water is added, and then process water is added to the preparation tank to prepare a dilute water glass at a temperature of 85-90°C, pH=10.5(±1.5), M=3.0 of the dilute water glass, and the mass concentration of sodium silicate is 30%, and then filtered into a water glass circulating tank; wherein the concentration of non-ionic surfactant is 0.2%;

[0065] (3) The prepared dilute water glass and concentrated sulfuric acid with a mass concentration of 98% are simultaneously and continuously slowly added to a precipitation reaction kettle, the pH is adjusted to 3.5±0.5, and a precipitated silica suspension with a solid content of 18wt% is obtained. The suspension is pumped into an aging tank, the aging temperature is 60°C, and the aging time is 0.9h, and then after filtration, washing, pulping, spray drying and ball milling, a silica product is obtained; wherein the ball milling parameters are 2-5mm silica balls, the ball-to-material ratio is 8:1, and the rotation speed is 100r / min.

[0066] Example 5

[0067] The silica production process in this embodiment includes the following steps:

[0068] (1) The preheated low-iron solid water glass (about 50°C) is added to the reaction kettle, first adding process water containing sodium hydroxide at 55±5°C, then dissolving by passing in steam, and after the solid water glass is completely dissolved in about 52 min, it is put into a buffer tank, and after precipitation and slag removal, a concentrated liquid water glass is obtained. The volume ratio of low-iron solid water glass to process water is 1:1.8, the mass concentration of sodium hydroxide in the process water is 8%, and the process water is added to the reaction kettle in three times according to the volume ratio of 4:3.5:2.5;

[0069] (2) The concentrated liquid water glass is pumped into a preparation tank, and in the pumping process, a mixed liquid of fatty acid polyoxyethylene ester and process water is added, and then process water is added to the preparation tank to prepare a dilute water glass at a temperature of 85-90°C, pH=10.5(±1.5), M=3.0 of the dilute water glass, and the mass concentration of sodium silicate is 30%, and then filtered into a water glass circulating tank; wherein the concentration of non-ionic surfactant is 0.2%;

[0070] (3) the prepared dilute water glass and concentrated sulfuric acid with a mass concentration of 98% are simultaneously and continuously slowly added into a precipitation reactor, pH is adjusted to 3.5±0.5, a precipitated silica suspension with a solid content of 24wt% is obtained, the suspension is pumped into an aging tank, the aging temperature is 65℃, the aging time is 1.2h, then after filtration, washing, pulping, spray drying and ball milling, a silica product is obtained; wherein the ball milling parameters are 2-5mm silica balls, the ball-to-material ratio is 8:1, and the rotating speed is 120r / min.

[0071] Example 6

[0072] The silica production process in this example includes the following steps:

[0073] (1) the preheated low-iron solid water glass (about 50℃) is added into a reactor, process water containing sodium hydroxide is first added, steam is then introduced for pressure maintaining and dissolution, after the solid water glass is completely dissolved for about 52min, it is put into a buffer tank, and after precipitation and residue removal, a concentrated liquid water glass is obtained, wherein the volume ratio of the low-iron solid water glass to the process water is 1:1.8, the mass concentration of sodium hydroxide in the process water is 8%, and the process water is added into the reactor in three times according to a volume ratio of 4:3.5:2.5;

[0074] (2) the concentrated liquid water glass is pumped into a preparation tank, in the pumping process, a mixed liquid of polyoxyethylene-polyoxypropylene block copolymer and process water is added, process water is further added at a temperature of 85-90℃ to prepare dilute water glass in the preparation tank, pH is 10.5(±1.5), M of the dilute water glass is 3.0, the mass concentration of sodium silicate is 32%, and then filtration is performed to a water glass circulating tank; wherein the concentration of the non-ionic surfactant is 0.2%;

[0075] (3) the prepared dilute water glass and concentrated sulfuric acid with a mass concentration of 98% are simultaneously and continuously slowly added into a precipitation reactor, pH is adjusted to 3.5±0.5, a precipitated silica suspension with a solid content of 20wt% is obtained, the suspension is pumped into an aging tank, the aging temperature is 62℃, the aging time is 1.0h, then after filtration, washing, pulping, spray drying and ball milling, a silica product is obtained; wherein the ball milling parameters are 2-5mm silica balls, the ball-to-material ratio is 8:1, and the rotating speed is 110r / min.

[0076] Example 7

[0077] The silica production process in this example includes the following steps:

[0078] (1) The preheated low-iron solid water glass (about 50°C) is added into the reaction kettle, first adding process water containing sodium hydroxide at 55±5°C, then passing steam to keep pressure and dissolve, and after the solid water glass is completely dissolved in about 52 min, it is put into a buffer tank, and after sedimentation and slag removal, a concentrated liquid water glass is obtained, wherein the volume ratio of low-iron solid water glass to process water is 1:1.8, the mass concentration of sodium hydroxide in the process water is 8%, and the process water is added into the reaction kettle in three times according to the volume ratio of 4:3.5:2.5;

[0079] (2) The concentrated liquid water glass is pumped into a preparation tank, and in the pumping process, a mixed liquid of silane glycerol ether active agent and process water is added, and then process water is added to the preparation tank to prepare a dilute water glass at a temperature of 85-90°C, pH=10.5(±1.5), M=3.0 of the dilute water glass, and the mass concentration of sodium silicate is 32%, and then filtered into a water glass circulating tank; wherein the concentration of nonionic surfactant is 0.08%;

[0080] (3) The prepared dilute water glass and concentrated sulfuric acid with a mass concentration of 98% are simultaneously and continuously slowly added into a precipitation reaction kettle, the pH is adjusted to 3.5±0.5, and a precipitated silica suspension with a solid content of 20wt% is obtained, the suspension is pumped into an aging tank, the aging temperature is 62°C, and the aging time is 1.0h, and then after filtration, washing, pulping, spray drying and ball milling, a silica product is obtained; wherein the ball milling parameters are 2-5mm silica balls, the ball-to-material ratio is 6:1, and the rotation speed is 110r / min.

[0081] Comparative Example 1

[0082] The silica production process in the present comparative example includes the following steps:

[0083] (1) The low-iron solid water glass is added into the reaction kettle, process water at 55±5°C is added, steam is passed to keep pressure and dissolve, and after the solid water glass is completely dissolved in about 62 min, it is put into a buffer tank, and after sedimentation and slag removal, a concentrated liquid water glass is obtained, wherein the volume ratio of low-iron solid water glass to process water is 1:2.4, and the process water is added into the reaction kettle in three times according to the volume ratio of 4:3.5:2.5;

[0084] (2) The concentrated liquid water glass is pumped into a preparation tank, and in the pumping process, a mixed liquid of silane glycerol ether active agent and process water is added, and then process water is added to the preparation tank to prepare a dilute water glass at a temperature of 85-90°C, pH=10.5(±1.5), M=3.0 of the dilute water glass, and the mass concentration of sodium silicate is 32%, and then filtered into a water glass circulating tank; wherein the concentration of nonionic surfactant is 0.08%;

[0085] (3) The prepared dilute water glass and concentrated sulfuric acid with a mass concentration of 98% are simultaneously and continuously slowly added into the precipitation reactor, the pH is adjusted to 3.5±0.5, a precipitated silica suspension with a solid content of 20wt% is obtained, the suspension is pumped into an aging tank, the aging temperature is 80℃, the time is 2h, then after filtration, washing, pulping, spray drying and ball milling, a silica product is obtained; wherein the ball milling parameters are 2-5mm silica balls, the ball-to-material ratio is 12:1, and the rotation speed is 200r / min.

[0086] Comparative Example 2

[0087] The silica production process in the present comparative example includes the following steps:

[0088] (1) The preheated low-iron solid water glass (about 50℃) is added into the reactor, first 55±5℃ process water containing sodium hydroxide is added, then steam is introduced for pressure preservation and dissolution, after the solid water glass is completely dissolved for about 52min, it is put into a buffer tank, after precipitation and slag removal, a concentrated liquid water glass is obtained, wherein the volume ratio of low-iron solid water glass to process water is 1:1.8, the mass concentration of sodium hydroxide in process water is 8%, and the process water is added into the reactor in three times according to the volume ratio of 4:3.5:2.5;

[0089] (2) The concentrated liquid water glass is pumped into a preparation tank, process water is added to prepare dilute water glass at a temperature of 85-90℃, the pH is 10.5(±1.5), the M of the dilute water glass is 3.0, and the mass concentration of sodium silicate is 32%, then it is filtered into a water glass circulating tank;

[0090] (3) The prepared dilute water glass and concentrated sulfuric acid with a mass concentration of 98% are simultaneously and continuously slowly added into the precipitation reactor, the pH is adjusted to 3.5±0.5, a precipitated silica suspension with a solid content of 20wt% is obtained, the suspension is pumped into an aging tank, the aging temperature is 75℃, the time is 2h, then after filtration, washing, pulping, spray drying and ball milling, a silica product is obtained; wherein the ball milling parameters are 2-5mm silica balls, the ball-to-material ratio is 10:1, and the rotation speed is 150r / min.

[0091] Comparative Example 3

[0092] The silica production process in the present comparative example includes the following steps:

[0093] (1) The preheated low-iron solid water glass (about 50°C) is added into the reaction kettle, first adding process water containing sodium hydroxide at 55±5°C, then passing steam to maintain pressure for dissolution, and after the solid water glass is completely dissolved in about 52 min, it is put into a buffer tank, and after the residue is precipitated, the concentrated liquid water glass is obtained, wherein the volume ratio of low-iron solid water glass to process water is 1:1.8, the mass concentration of sodium hydroxide in the process water is 8%, and the process water is added into the reaction kettle in three times according to the volume ratio of 4:3.5:2.5;

[0094] (2) The concentrated liquid water glass is pumped into a preparation tank, and process water is added to prepare dilute water glass in a temperature environment of 85-90°C, pH=10.5 (±1.5), M=3.0 of the dilute water glass, and the mass concentration of sodium silicate is 32%, and then filtered into a water glass circulating tank;

[0095] (3) The prepared dilute water glass and concentrated sulfuric acid with a mass concentration of 98% are simultaneously and continuously slowly added into a precipitation reaction kettle, the pH is adjusted to 3.5±0.5, and a precipitated silica suspension with a solid content of 20wt% is obtained, the suspension is pumped into an aging tank, 0.1% silane glycerol ether active agent is added, the aging temperature is 70°C, and the time is 1.5h, then after filtration, washing, pulping, spray drying and ball milling, the silica product is obtained; wherein the ball milling parameters are 2-5mm silica balls, the ball-to-material ratio is 8:1, and the rotation speed is 120r / min.

[0096] The parameters of the silica production processes of Examples 1-7 and Comparative Examples 1-3 are summarized in Tables 1-3:

[0097] Table 1. Dissolution process parameters

[0098]

[0099] Table 2. Preparation process parameters

[0100]

[0101]

[0102] Table 3. Reaction and post-treatment process parameters

[0103]

[0104] As can be seen from Table 1, the addition of process water containing sodium hydroxide can accelerate the dissolution of solid water glass, which is a conventional operation in the industry, therefore, the addition ratio and number of times of process water are designed in combination, and it is found that this operation can further reduce the water consumption from 1:2.4 to 1:1.8.

[0105] From the examples 1-3 and comparative example 1 in table 2, it can be found that adding sodium hydroxide will change the modulus of sodium silicate, and too high alkalinity (high OH- concentration) can affect the polymerization state or colloidal behavior of silicate ions, so that the content of "water glass glue" in the liquid water glass produced by dissolution increases, which can cause the viscosity to increase and the flowability to decrease. Therefore, in order to avoid affecting the removal of impurities in the precipitation deslagging, a non-ionic surfactant is added when pumping out, which can reduce the internal friction of the water glass solution, provide hydrophilicity and improve compatibility, and the non-ionic surfactant can inhibit agglomeration by dispersion stabilization and nucleation regulation in the reaction stage, and can optimize the pore structure by template effect and steric hindrance in the aging stage, so as to realize precise control of parameters such as specific surface area and pore size distribution. As can be seen from table 3, this operation can further reduce the energy consumption of aging and shorten the aging period, and can also reduce the parameters of the crushing process and reduce energy consumption. Compared with the traditional process of adding surfactant in the aging stage and adding non-ionic surfactant in the preparation stage, the effect is greater, and the amount is also reduced.

[0106] According to the known national standards or industry standards for testing silica, the related performance of the silica produced in examples 1-7 and comparative examples 1-3 is shown in table 4:

[0107] Table 4. Performance data of silica products

[0108]

[0109] As can be seen from the example and comparative example data, the light transmittance is significantly related to parameters such as BET specific surface area, particle size distribution and oil absorption value. In the present application, precise control of the process steps is the core to achieve high light transmittance:

[0110] In the examples, the process water temperature is controlled at 50-60℃, the sodium hydroxide concentration is 5-10%, and the reaction kettle is added in 1-3 times, so that the solid water glass is completely dissolved within 45-65 min. Under this condition, the polymeric degree of the concentrated water glass generated is moderate, which can avoid the residual impurities caused by incomplete dissolution (such as iron ion content > 50 ppm, which can absorb visible light and reduce light transmittance). In comparative examples 1-3, the BET value is low (175 m 2 / g), which may be caused by insufficient dissolution temperature (< 50℃) leading to insufficient silicon-oxygen bond breakage, forming a dense structure, while the BET value of examples 2-4 is 197-210 m 2 / g, corresponding to a light transmittance of 76-79%, which shows that moderate dissolution conditions can balance the specific surface area and light transmittance.

[0111] The CTAB value (165-178 m 2 / g) in examples 3-7 is significantly higher than that in comparative examples (130-155 m 2 / g), attributed to the surfactant adsorbed on the silica surface under alkaline conditions, inhibiting particle agglomeration by steric hindrance. For example, the D90 / D10 = 1.63 (15.5 / 9.5) in Example 7, the lowest among all groups, corresponds to a light transmittance of 80%, demonstrating that the dispersion of surfactant can reduce the particle size distribution range and reduce light scattering loss (Mie scattering theory shows that the narrower the particle size distribution, the higher the consistency of light scattering).

[0112] The D50 = 10.8 μm and BET = 210 m 2 / g, but the light transmittance is still 79%, because the acidic environment inhibits the disordered growth of particles, while the D50 = 6.5 μm in Comparative Examples 1-3 leads to secondary agglomeration of particles due to improper pH control (e.g., > 4.5), D90 / D10 > 3, and light transmittance is only 70-72%. In addition, the temperature and time of the aging stage affect the pore structure, and the oil absorption value of Example 3 is 2.7 ml / g, which is higher than that of Comparative Example 2, 2.8 ml / g, but because the aging time is moderate (4-6 h), a structure with a higher proportion of mesopores is formed, reducing the reflection of light by macropores.

[0113] The BET values of Examples 1-7 are 192-210 m 2 / g, and the light transmittance is 75-80%, while the BET of Comparative Examples 1-2 is 175 m 2 / g, and the light transmittance is as low as 70-72%, breaking the conventional understanding that the lower the specific surface area, the higher the light transmittance. This is because the BET in the examples is mainly contributed by mesopores (2-50 nm) (CTAB / BET ratio 0.75-0.90), while there are a large number of micropores (< 2 nm) in the comparative examples, although the BET is low, but the diffuse reflection of light by the inner surface of the micropores is stronger. For example, in Example 6, CTAB = 165 m 2 / g, and the BET = 197 m 2 / g, CTAB / BET = 0.84, mesopore proportion is high, and the light transmittance is as high as 78%, verifying that mesoporous structure is more conducive to light transmission than microporous structure.

[0114] The D90 / D10 in the examples are all < 2, and in Example 7, the D10 = 9.5 μm, the D90 = 15.5 μm, the ratio is 1.63, and the light transmittance is the highest (80%). This is because when the particle size distribution is narrow, the scattering wavelength of light by particles is consistent, and the total scattering intensity is reduced. In contrast, the D10 = 7.5 μm and the D90 = 18.5 μm in Comparative Example 3, the ratio is 2.47, and the wide distribution leads to different scattering wavelengths of 400-760 nm visible light by particles of different sizes, and the light transmittance is reduced to 75%. In addition, the D50 and the light transmittance are weakly correlated, the D50 = 11.0 μm (the largest) in Example 5, and the light transmittance is 75%, which is flat with Example 1 (D50 = 9.8 μm), indicating that the uniformity of particle size distribution is more critical than the average particle size.

[0115] Oil absorption value reflects the pore volume of the material, the oil absorption value of example 7 is 2.5ml / g (the lowest), the light transmittance is the highest, because the low oil absorption value means that the proportion of large pores is reduced, and the reflection path of light in the particle is shortened. But too low oil absorption value (such as <2.0ml / g) will lead to insufficient specific surface area, in the example, when the oil absorption value is 2.5-2.7ml / g, the mesopore volume is 0.6-0.7cm 3 / g, the specific surface area and light transmittance are considered. The oil absorption value of comparative examples 1-2 is 2.8ml / g, because there are too many large pores (pore size >50nm), the light is reflected multiple times at the interface of large pores, and the light transmittance is reduced instead.

[0116] The parameters of the silica product prepared by the process of the application are: light transmittance >75%, BET 190-210m 2 / g, CTAB 140-180m 2 / g, oil absorption value 2.4-2.6ml / g, particle size 8-12μm, narrow distribution (D90 / D10<2) scattering rule uniform, light transmittance is more stable. And shorten the production cycle of single batch product, and reduce the energy consumption of single batch, the cost can reduce 0.3-0.8% per thousand jin.

[0117] The above examples only express several embodiments of the application, which are described in more detail and in detail, but it cannot be understood as the limitation of the scope of the patent of the application. It should be pointed out that for ordinary skilled in the art, without departing from the concept of the application, a number of variations and improvements can be made, which belong to the protection scope of the application.

Claims

1. A process for producing silicon dioxide with high light transmittance, characterized in that: The following steps are involved: (1) Preheating low-iron solid water glass is added to a reactor, and process water containing sodium hydroxide at 50-60° C. is first added, and steam is introduced to maintain pressure to dissolve. After the solid water glass is completely dissolved, it is placed in a buffer tank, and concentrated liquid water glass is obtained after precipitation and slag removal. The mass concentration of sodium hydroxide in the process water is 5-10%, and the process water is added to the reactor 1-3 times. The time for the solid water glass to be completely dissolved is 45-65 minutes; (2) Pumping concentrated liquid water glass into the preparation tank, adding a mixture of non-ionic surfactant and process water during the pumping process, then adding process water to the preparation tank to make dilute water glass, and then filtering it into the water glass circulation tank; (3) The prepared dilute water glass and concentrated sulfuric acid are added simultaneously and slowly to a precipitation reactor, and the pH is adjusted to 3.0-4.0 to obtain a precipitated silica suspension with a solid content of 15-25 wt%. The suspension is pumped into an aging tank, and after aging, filtering, washing, pulping, spray drying, and crushing, a silica product is obtained.

2. The process for producing silicon dioxide with high light transmittance according to claim 1, wherein: In step (1), low-iron solid water glass is preheated using a 50-60° C. silica washing solution.

3. The process for producing silicon dioxide with high light transmittance according to claim 1, wherein: In step (1), the volume ratio of the low-iron solid water glass to the process water is 1:(1.8-2.4).

4. The process for producing silicon dioxide with high light transmittance according to claim 1, wherein: In step (2), the nonionic surfactant is one of a polyoxyethylene nonionic surfactant, a polyether nonionic surfactant or a silicone nonionic surfactant.

5. The process for producing silicon dioxide with high light transmittance according to claim 4, characterized in that: Calculated based on the total system percentage of the dilute water glass, the concentration of the nonionic surfactant is 0.05-0.5%.

6. The process for producing silicon dioxide with high light transmittance according to claim 1, wherein: In step (2), the M of the dilute water glass is 2.8-3.2, and the mass concentration of sodium silicate is 20-35%.

7. The process for producing silicon dioxide with high light transmittance according to claim 1, wherein: In step (3), the mass concentration of the concentrated sulfuric acid is 98%.

8. The process for producing silicon dioxide with high light transmittance according to claim 1, wherein: In step (3), the aging temperature is 60-65° C. and the aging time is 0.8-1.2 h.

9. The process for producing silicon dioxide with high light transmittance according to claim 1, wherein: The pulverization is performed by ball milling, with 2-5 mm silica balls, a ball-to-material ratio of 6:1-8:1, and a rotation speed of 100 r / min-120 r / min.

10. The process for producing silicon dioxide with high light transmittance according to any one of claims 1 to 9, characterized in that: The parameters of the silica product are: light transmittance>75%, BET 190-210m 2 / g, CTAB 140-180m 2 / g, oil absorption value 2.4-2.6ml / g, particle size 8-12μm.

Images