阅读说明：本技术 一种大孔低密度块状复合凝胶及其生产工艺 (Macroporous low-density blocky composite gel and production process thereof ) 是由 申佳平 周强 于 2021-09-11 设计创作，主要内容包括：本发明属于硅胶的技术领域,具体涉及一种大孔低密度块状复合凝胶及其生产工艺。现有技术中常见的硅胶产品包括大孔硅胶及细孔硅胶,通常难以满足高比表面积及大孔容性能的同时实现。本发明在水洗过程中,加入扩孔剂并高温水洗相结合,对产品进一步扩孔。并在干燥过程中,低温干燥,延长干燥时间,有进一步进行扩孔。本发明制备的硅胶产品比表面积及孔径都显著高于现有技术。该制备工艺方法反应条件温和,操作过程安全、简便。(The invention belongs to the technical field of silica gel, and particularly relates to macroporous low-density blocky composite gel and a production process thereof. Common silica gel products in the prior art include macroporous silica gel and fine-pored silica gel, and the realization of high specific surface area and large pore capacity is difficult to meet at the same time. In the water washing process, the pore-expanding agent is added and the high-temperature water washing is combined, so that the pore-expanding agent can further expand pores of the product. And in the drying process, drying at low temperature, prolonging the drying time and further reaming. The specific surface area and the pore diameter of the silica gel product prepared by the method are obviously higher than those of the prior art. The preparation process has mild reaction condition and safe and simple operation process.)

1. A macroporous low-density blocky composite gel is characterized in that,

the pore size of the composite gel is 18-25 nm, the pore volume is 2.5-3.5 mL/g, and the specific surface area is 530-560 m²/g。

2. A process for the production of a gel according to claim 1, comprising the steps of:

step 1): taking a sulfuric acid aqueous solution with the mass concentration of 20-35% for later use;

step 2): taking 15-25% water glass by mass concentration for later use;

step 3): adding the sulfuric acid aqueous solution obtained in the step 1) into the water glass obtained in the step 2), controlling the pH value of a reaction system to be 7.5-8.0, and reacting at 35-50 ℃ to obtain a silicic acid gel;

step 4): aging the silicic acid gel obtained in the step 3) at 60-90 ℃ for 35-38 h;

step 5): after aging is finished, tapping the gel to obtain a gel block with the size of 5-15 mm;

step 6): transferring the wet silica gel block obtained in the step 5) into a washing tank with a built-in heating coil, adding washing liquid, and controlling the temperature to wash;

step 7): and (5) after the water washing is finished, replacing the washing liquid in the step 6), taking out the wet glue block, and performing vacuum drying to obtain the target product.

3. The production process according to claim 2, wherein the washing solution in the step 6) is an aqueous solution of 2-6% by weight of the pore-enlarging assistant.

4. The process of claim 3, wherein the pore-expanding aid is (NH)₄)₂HPO₄、(NH₄)₃PO₄And one or more of ammonium bicarbonate.

5. The production process according to claim 2, wherein the washing temperature in the step 6) is 70-75 ℃.

6. The production process of claim 2, wherein the washing operation in the step 6) comprises the steps of adding a washing solution into a washing tank, heating to a washing temperature, standing for 3-4 hours, and discharging the washing solution from the bottom of the tank; repeating the operation until no sulfate radical is detected in the washing liquid and finishing the washing.

7. The production process according to claim 2, wherein the replacement liquid in the step 7) is an aqueous ethanol solution with a volume fraction of 50-80%.

8. The production process according to claim 2, wherein the drying temperature in the step 7) is 25-35 ℃ and the drying time is 20-28 h.

9. The production process according to claim 2,

step 1): taking a sulfuric acid aqueous solution with the mass concentration of 30% for later use;

step 2): taking 20% water glass by mass concentration for later use;

step 3): adding the sulfuric acid aqueous solution obtained in the step 1) into the water glass obtained in the step 2), controlling the pH value of a reaction system to be 7.5-8.0, and reacting at 35-50 ℃ to obtain a silicic acid gel;

step 4): aging the silicic acid gel obtained in the step 3) at 60-90 ℃ for 36 h;

step 5): after aging is finished, tapping the gel to obtain a gel block with the size of 5-10 mm;

step 6): transferring the wet silica gel block obtained in the step 5) into a washing tank with a built-in heating coil, adding an aqueous solution of ammonium bicarbonate with the mass fraction of 3%, heating to the temperature of 70-75 ℃, standing for 3-4 hours, and discharging a washing liquid from the bottom of the tank; repeating for 3 times, and detecting no sulfate radical;

step 7): and (3) after the water washing is finished, replacing the washing liquid in the step 6) with 75% ethanol water solution by volume fraction, taking out the wet glue block, and drying in vacuum at the drying temperature of 30 ℃ for 24 hours to obtain the target product.

Technical Field

The invention belongs to the technical field of silica gel, and particularly relates to macroporous low-density blocky composite gel and a production process thereof.

Background

Silica gel is a typical high-activity porous adsorption material, is nontoxic and tasteless, has stable chemical properties, hardly reacts with any substance except strong alkali and hydrofluoric acid, and has a microporous structure. The silica gel has a large specific surface area due to the three-dimensional space reticular porous structure, and in addition, a plurality of silanol groups are attached to the surface of the silica gel, so that the silica gel has strong adsorption performance and can be used as a drying agent, an adsorbent, a catalyst and a catalyst carrier. The adsorption performance of the silica gel is closely and inseparably related with the rich pore structure and the high specific surface area.

The silica gel forms different skeleton structures due to different production processes and preparation methods, and the existing silica gel products are commonly macroporous silica gel and fine-pore silica gel, wherein the macroporous silica gel has larger pore volume but smaller specific surface area, and the fine-pore silica gel has better specific surface area but smaller pore volume. The inventor believes that it is of great productive interest to develop a silica gel product having both a large pore volume and a high specific surface area. The research of Zhao Xipeng provides a preparation method of silica gel with large pore volume and high specific surface area, sodium silicate and inorganic acid are used as raw materials to prepare the silica gel with large pore volume and high specific surface area by a chemical precipitation method, and the silica gel has shallow adsorption capacity and is suitable for producing advertisement and office paper such as winding drum spray paper, color spray paper, photographic paper and the like. Quichhang et al reported the effect of drying on the performance of the carrier silica gel, and according to the results of their studies, different drying methods had significant effects on the surface area, pore volume and average pore size of the silica gel.

The existing production method of the silica gel with large pore volume needs steaming, adopts salt soaking and calcination for some of the silica gels, adopts organic solvent replacement and other preparation methods, generally has the problems of large energy consumption and high production cost, and some organic solvents are difficult to completely recycle in the production process and pollute the environment. For example: chinese patent CN103159220A discloses a preparation method of macroporous silica gel in 2013, 6/19/h, which takes silicate, inorganic acid, alkaline medium, fatty alcohol or fatty alcohol amine as raw materials, and comprises the following reaction steps: 1) contacting alkaline medium with inorganic acid at 20-50 deg.C for 10-30 min; 2) adding fatty alcohol or fatty alcohol amine, and reacting at 30-70 deg.C for 10-60 min; 3) gradually adding silicate solution with the concentration of 1.0-3.0mol/L at the speed of 2.0-5.0 mL/min; 4) adding fatty alcohol or fatty alcohol amine again, and reacting at 30-70 deg.C for 10-30 min; 5) then adding silicate solution gradually at the speed of 2.0-5.0mL/min, and then adjusting the pH value of the solution to 6-8 by using inorganic acid; 6) heating to 60-90 deg.C, maintaining for 1-7h, acidifying, washing, and drying to obtain silica gel. Because the preparation method of the macroporous silica gel uses fatty alcohol or fatty alcohol amine twice, the fatty alcohol or fatty alcohol amine belongs to an organic solvent, and the fatty alcohol or fatty alcohol amine is used, on one hand, the macroporous silica gel can be removed only by high-temperature drying or activating treatment in the later production process, so that the energy consumption is large, and the production cost is high; on the other hand, the organic solvents are difficult to completely recycle in the production process, and environmental pollution is caused. Chinese patent CN103387239A proposes a method for washing silica gel with seawater, which improves the washing rate through the weak alkalinity of seawater, but the weak alkalinity of seawater easily damages the inner microstructure of silica gel, which causes the unreasonable pore size of silica gel, and affects the subsequent water absorption effect of silica gel, and the seawater transportation equipment and investment cost are high, and thus cannot be applied in large scale.

Current methods for aerogel production typically include supercritical drying and atmospheric drying methods. Supercritical drying is to heat and pressurize the solution in the gel pore canal to a supercritical state, in which the interface of the liquid and the gas disappears and the capillary force does not exist. The gel is decompressed and dried in a supercritical state, the original structure of the gel can be well maintained, but the pressure and the temperature of the supercritical point of the common liquid are higher, for example, the supercritical point of methanol is just 239.4 ℃ and nearly 81 atmospheric pressures, so that the high pressure and the high temperature cause the aerogel preparation equipment to be expensive, difficult to operate and high in cost, and meanwhile, the risk of explosion leakage exists.

The normal pressure drying method does not need high temperature and high pressure, and has safe operation and low cost. The normal pressure drying firstly uses a low surface tension solvent (such as n-hexane) to replace an original high surface tension solvent (such as water) in a gel pore channel by solvent exchange, and simultaneously performs inert modification on groups on the surface of the gel pore channel to modify hydroxyl with higher activity on the surface of the gel pore channel into chemically inert silicon methyl, so that the hydroxyl condensation caused by gel volume shrinkage in the drying process can be prevented. The aerogel material prepared by drying under normal pressure by the method can achieve supercritical drying on the structure and the performance. Because the traditional normal pressure drying needs several steps of solvent exchange of gel pore channels and surface hydrophobization treatment, the preparation period is long, the operation is complex, the waste water and waste liquid formed by multiple solvent replacements can cause serious environmental pollution, and the preparation cost of the aerogel is also increased.

The freeze-drying method fully utilizes the characteristics of the solvent, when the solvent is frozen into a solid state, the volume of the solvent expands, so that the original mutually close gel particles are properly separated, and the phenomenon of drying shrinkage is favorably overcome. However, freeze-drying has many disadvantages, such as long drying period, freezing expansion of the pore solvent to some extent causing damage to the network structure, and the like.

At present, the specific surface area and the pore diameter of a silica gel product prepared in the prior art and a preparation process are remarkably poor, and the preparation process has a plurality of problems. The specific surface area and the pore diameter are greatly higher than those of the silica gel product in the prior art and the process for preparing the silica gel product are urgently needed.

Disclosure of Invention

Aiming at the problems of the gel and the production process thereof in the prior art, the invention provides a macroporous low-density blocky composite gel and a production process thereof. The specific surface area and the pore diameter of the prepared product are obviously higher than those of the prior art; the preparation process has mild reaction condition, safe and simple operation process, and the prepared target product has larger aperture and higher specific surface area.

The invention is realized by the following technical scheme:

the macroporous low-density blocky composite gel has the pore size of 18-25 nm, the pore volume of 2.5-3.5 mL/g and the specific surface area of 530-560 m²/g。

The production process of the gel comprises the following steps:

step 1): taking a sulfuric acid aqueous solution with the mass concentration of 20-35% for later use;

step 2): taking 15-25% water glass by mass concentration for later use;

step 3): adding the sulfuric acid aqueous solution obtained in the step 1) into the water glass obtained in the step 2), controlling the pH value of a reaction system to be 7.5-8.0, and reacting at 35-50 ℃ to obtain a silicic acid gel;

step 4): aging the silicic acid gel obtained in the step 3) at 60-90 ℃ for 35-38 h;

step 5): after aging is finished, tapping the gel to obtain a gel block with the size of 5-15 mm;

step 6): transferring the wet silica gel block obtained in the step 5) into a washing tank with a built-in heating coil, adding washing liquid, and controlling the temperature to wash;

step 7): and (5) after the water washing is finished, replacing the washing liquid in the step 6), taking out the wet glue block, and performing vacuum drying to obtain the target product.

Preferably, the washing solution in the step 6) is an aqueous solution of a pore-enlarging assistant with a mass fraction of 2% -6%.

Preferably, the pore-enlarging aid is (NH)₄)₂HPO₄、(NH₄)₃PO₄And one or more of ammonium bicarbonate.

Preferably, the washing temperature in the step 6) is 70-75 ℃.

Preferably, the washing operation in the step 6) comprises the steps of adding washing liquid into a washing tank, heating to the washing temperature, standing for 3-4 hours, and discharging the washing liquid from the tank bottom; repeating the operation until no sulfate radical is detected in the washing liquid; finishing washing;

preferably, the replacement liquid in the step 7) is ethanol water solution with volume fraction of 50-80%.

Preferably, the drying temperature in the step 7) is 25-35 ℃, and the drying time is 20-28 h.

In a preferred embodiment, the process for producing the gel comprises the following steps:

step 1): taking a sulfuric acid aqueous solution with the mass concentration of 30% for later use;

step 2): taking 20% water glass by mass concentration for later use;

step 3): adding the sulfuric acid aqueous solution obtained in the step 1) into the water glass obtained in the step 2), controlling the pH value of a reaction system to be 7.5-8.0, and reacting at 35-50 ℃ to obtain a silicic acid gel;

step 4): aging the silicic acid gel obtained in the step 3) at 60-90 ℃ for 36 h;

step 5): after aging is finished, tapping the gel to obtain a gel block with the size of 5-10 mm;

step 6): transferring the wet silica gel block obtained in the step 5) into a washing tank with a built-in heating coil, adding an aqueous solution of ammonium bicarbonate with the mass fraction of 3%, heating to the temperature of 70-75 ℃, standing for 3-4 hours, and discharging a washing liquid from the bottom of the tank; repeating for 3 times, detecting no sulfate radical, and finishing washing;

step 7): and (3) after the water washing is finished, replacing the washing liquid in the step 6) with 75% ethanol water solution by volume fraction, taking out the wet glue block, and drying in vacuum at the drying temperature of 30 ℃ for 24 hours to obtain the target product.

The invention has the beneficial effects that:

1) the product prepared by the invention has larger aperture and specific surface area.

2) Through the pore-expanding agent and the temperature rise in the washing process, the sulfate can be effectively washed, the pore-expanding effect is further realized, and the application of reagents such as ammonia water and the like is effectively avoided.

3) A drying stage, replacing with ethanol water solution, and vacuum drying at low temperature; the defects caused by freeze drying and supercritical drying in the prior art are avoided, and the ethanol water solution and low-temperature long-time drying effectively play a role in reaming in the process.

4) The process has mild reaction conditions, safe and simple operation process and is suitable for industrialization.

Detailed Description

The invention is further illustrated by the following examples, which should be properly understood: the examples of the present invention are merely illustrative and not restrictive, and therefore, the present invention may be modified in a simple manner without departing from the scope of the invention as claimed.

In the following examples, various procedures and methods not described in detail are conventional methods well known in the art.

Example 1

A production process of macroporous low-density blocky composite gel comprises the following steps:

step 1): taking a sulfuric acid aqueous solution with the mass concentration of 30% for later use;

step 2): taking 20% water glass by mass concentration for later use;

step 3): adding the sulfuric acid aqueous solution obtained in the step 1) into the water glass obtained in the step 2), controlling the pH value of a reaction system to be 7.8, and reacting at 40 ℃ to obtain silicic acid gel;

step 4): aging the silicic acid gel obtained in the step 3) at 80 ℃ for 36 h;

step 5): after aging is finished, tapping the gel to obtain a gel block with the size of 5-10 mm;

step 6): transferring the wet silica gel block obtained in the step 5) into a washing tank with a built-in heating coil, adding an aqueous solution of ammonium bicarbonate with the mass fraction of 3%, heating to the temperature of 70-75 ℃, standing for 3.5 hours, and discharging a washing solution from the tank bottom; repeating for 3 times, detecting no sulfate radical, and finishing washing;

step 7): and (3) after the water washing is finished, replacing the washing liquid in the step 6) with 75% ethanol water solution by volume fraction, taking out the wet glue block, and drying in vacuum at the drying temperature of 30 ℃ for 24 hours to obtain the target product.

Example 2

A production process of macroporous low-density blocky composite gel comprises the following steps:

step 1): taking 20% sulfuric acid by mass concentration for later use;

step 2): taking water glass with the mass concentration of 15% for later use;

step 3): adding the sulfuric acid obtained in the step 1) into the water glass obtained in the step 2), controlling the pH value of a reaction system to be 7.5, and reacting at 35 ℃ to obtain silicic acid gel;

step 4): aging the silicic acid gel obtained in the step 3) at 60 ℃ for 35 h;

step 5); after aging is finished, tapping the gel to obtain a gel block with the size of 5-10 mm;

step 6): transferring the wet silica gel block obtained in the step 5) into a washing tank with a built-in heating coil, adding an aqueous solution of ammonium bicarbonate with the mass fraction of 2%, heating to the temperature of 70-75 ℃, standing for 3h, and discharging a washing solution from the bottom of the tank; repeating for 4 times, detecting no sulfate radical, and finishing washing;

step 7): and (3) after the water washing is finished, replacing the washing liquid in the step 6) with an ethanol water solution with the volume fraction of 50%, taking out the wet glue block, and performing vacuum drying at the drying temperature of 25 ℃ for 28h to obtain the target product.

Example 3

A production process of macroporous low-density blocky composite gel comprises the following steps:

step 1): taking 35% sulfuric acid water solution for later use;

step 2): taking 25% water glass by mass concentration for later use;

step 3): adding the sulfuric acid aqueous solution obtained in the step 1) into the water glass obtained in the step 2), controlling the pH value of a reaction system to be 8.0, and reacting at 50 ℃ to obtain silicic acid gel;

step 4): aging the silicic acid gel obtained in the step 3) at 90 ℃ for 38 hours;

step 5): after aging is finished, tapping the gel to obtain a gel block with the size of 5-10 mm;

step 6): transferring the wet silica gel block obtained in the step 5) into a washing tank with a built-in heating coil, adding 6% ammonium bicarbonate aqueous solution by mass, heating to 70-75 ℃, standing for 4h, and discharging washing liquid from the tank bottom; repeating for 5 times, detecting no sulfate radical, and finishing washing;

step 7): and (3) after the water washing is finished, replacing the washing liquid in the step 6) with an ethanol water solution with the volume fraction of 80%, taking out the wet glue block, and performing vacuum drying at the drying temperature of 35 ℃ for 20 hours to obtain the target product.

Example 4

A production process of macroporous low-density blocky composite gel comprises the following steps:

step 1): taking a sulfuric acid aqueous solution with the mass concentration of 30% for later use;

step 2): taking 20% water glass by mass concentration for later use;

step 3): adding the sulfuric acid aqueous solution obtained in the step 1) into the water glass obtained in the step 2), controlling the pH value of a reaction system to be 7.8, and reacting at 40 ℃ to obtain silicic acid gel;

step 4): aging the silicic acid gel obtained in the step 3) at 80 ℃ for 36 h;

step 5): after aging is finished, tapping the gel to obtain a gel block with the size of 5-10 mm;

step 6): transferring the wet silica gel block obtained in the step 5) into a water washing tank with a built-in heating coil, and adding (NH) with the mass fraction of 3%₄)₂HPO₄Heating the aqueous solution to 70-75 ℃, standing for 3.5 hours, and discharging the washing solution from the bottom of the tank; repeating for 3 times, detecting no sulfate radical, and finishing washing;

step 7): and (3) after the water washing is finished, replacing the washing liquid in the step 6) with 75% ethanol water solution by volume fraction, taking out the wet glue block, and drying in vacuum at the drying temperature of 30 ℃ for 24 hours to obtain the target product.

Example 5

A production process of macroporous low-density blocky composite gel comprises the following steps:

step 1): taking a sulfuric acid aqueous solution with the mass concentration of 30% for later use;

step 2): taking 20% water glass by mass concentration for later use;

step 3): adding the sulfuric acid aqueous solution obtained in the step 1) into the water glass obtained in the step 2), controlling the pH value of a reaction system to be 7.8, and reacting at 40 ℃ to obtain silicic acid gel;

step 4): aging the silicic acid gel obtained in the step 3) at 80 ℃ for 36 h;

step 5): after aging is finished, tapping the gel to obtain a gel block with the size of 5-10 mm;

step 6): transferring the wet silica gel block obtained in the step 5) into a water washing tank with a built-in heating coil, and adding (NH) with the mass fraction of 3%₄)₃PO₄Heating the aqueous solution to 70-75 ℃, standing for 3.5 hours, and discharging the washing solution from the bottom of the tank; repeating for 3 times, detecting no sulfate radical, and finishing washing;

step 7): and (3) after the water washing is finished, replacing the washing liquid in the step 6) with 75% ethanol water solution by volume fraction, taking out the wet glue block, and drying in vacuum at the drying temperature of 30 ℃ for 24 hours to obtain the target product.

Comparative example 1

A production process of macroporous low-density blocky composite gel comprises the following steps:

step 1): taking a sulfuric acid aqueous solution with the mass concentration of 30% for later use;

step 2): taking 20% water glass by mass concentration for later use;

step 3): adding the sulfuric acid aqueous solution obtained in the step 1) into the water glass obtained in the step 2), controlling the pH value of a reaction system to be 7.8, and reacting at 40 ℃ to obtain silicic acid gel;

step 4): aging the silicic acid gel obtained in the step 3) at 80 ℃ for 36 h;

step 5): after aging is finished, tapping the gel to obtain a gel block with the size of 5-10 mm;

step 6): transferring the wet silica gel block obtained in the step 5) into a washing tank with a built-in heating coil, adding purified water, heating to 70-75 ℃, standing for 3.5 hours, and discharging washing liquid from the tank bottom; repeating for 3 times, detecting no sulfate radical, and finishing washing;

step 7): and (3) after the water washing is finished, replacing the washing liquid in the step 6) with 75% ethanol water solution by volume fraction, taking out the wet glue block, and drying in vacuum at the drying temperature of 30 ℃ for 24 hours to obtain the target product.

Comparative example 2

A production process of macroporous low-density blocky composite gel comprises the following steps:

step 1): taking a sulfuric acid aqueous solution with the mass concentration of 30% for later use;

step 2): taking 20% water glass by mass concentration for later use;

step 3): adding the sulfuric acid aqueous solution obtained in the step 1) into the water glass obtained in the step 2), controlling the pH value of a reaction system to be 7.8, and reacting at 40 ℃ to obtain silicic acid gel;

step 4): aging the silicic acid gel obtained in the step 3) at 80 ℃ for 36 h;

step 5): after aging is finished, tapping the gel to obtain a gel block with the size of 5-10 mm;

step 6): transferring the wet silica gel block obtained in the step 5) into a washing tank with a built-in heating coil, adding an aqueous solution of ammonium bicarbonate with the mass fraction of 3%, heating to the temperature of 70-75 ℃, standing for 3.5 hours, and discharging a washing solution from the tank bottom; repeating for 3 times, detecting no sulfate radical, and finishing washing;

step 7): and (3) after the water washing is finished, replacing the washing liquid in the step 6) with a pure water solution, taking out the wet rubber block, and drying in vacuum at the drying temperature of 30 ℃ for 30 hours to obtain the target product.

Performance testing of the products of the above examples:

table 1 results of performance testing

Examples	Average pore diameter (nm)	Pore volume (mL/g)	Specific surface area (m)2/g）
				Example 1	25.0	3.5	560
Example 2	18.6	2.5	537
				Example 3	24.2	3.3	546
Example 4	20.3	2.7	532
				Example 5	22.5	3.0	534
Comparative example 1	10.8	1.0	370
				Comparative example 2	16.3	1.2	295