Preparation process of calcium hydroxide with high specific surface area

Abstract

The invention discloses a preparation process of calcium hydroxide with high specific surface area, which comprises the following steps: by taking industrial-grade high-quality lime as a raw material, adding diethanolisopropanolamine into water to prepare a modifier solution, firstly putting the lime into a closed high-temperature still kettle, then adding the modifier solution, stirring, heating and preserving heat to maintain the pressure, and reacting for 2-4 hours; after the digestion is finished, obtaining a calcium hydroxide powder product with high specific surface area; a novel modifier with a remarkable effect is adopted, a common dry digestion process is improved by combining heating and pressure applying in a closed digestion device, the effect of improving the specific surface area of calcium hydroxide by the modifier is optimized, the method is a single-stage digestion process, the technological process is simple and convenient, consumed time is short, and the method is suitable for industrial production. The complex steps of a multi-stage digestion technology are omitted, no other waste is generated in the preparation process, and the method can be widely applied to production and preparation of calcium hydroxide with the high specific surface area and has great significance in improving the market competitiveness of the calcium-based desulfurizing agent.

Description

Technical Field

[0001] The invention belongs to the field of preparation of micro-nano inorganic powder materials (calcium hydroxide), and particularly relates to a preparation process of calcium hydroxide with a high specific surface area. Background Art

[0002] In the context of the currently emerging dry flue gas desulfurization process, calcium hydroxide (Ca(OH)2) is one of the most widely studied flue gas desulfurization materials in my country. Compared with the sodium bicarbonate (NaHCO3) desulfurizer commonly used in dry flue gas desulfurization systems, calcium hydroxide not only has a simple preparation process and low cost, but also does not generate new pollutants and waste during the desulfurization process. More importantly, the desulfurization end product of calcium hydroxide, gypsum (CaSO4), can be used as a cement retarder or gypsum board raw material to achieve 100% resource utilization, completely avoiding the problem of disposing of salt-containing solid waste generated by sodium-based desulfurizers. At present, calcium hydroxide has become the green desulfurization material with the most development potential in the field of dry desulfurization.

[0003] The desulfurization performance of calcium hydroxide is closely related to its specific surface area. Ordinary calcium hydroxide has poor uniformity and dispersion, and particles tend to agglomerate to form clumps, resulting in a specific surface area generally lower than 15m 2 / g, and high specific surface area calcium hydroxide has a specific surface area more than twice that of ordinary calcium hydroxide and a rich microporous structure. Therefore, it has a larger reaction contact area when reacting with some acidic pollutants and sulfur-containing flue gases, and thus has higher reaction activity when undergoing acid-base reactions and adsorption with them.

[0004] At present, when preparing calcium hydroxide with high specific surface area, it is often adopted to introduce chemical reagents such as alcohol, small molecule inorganic electrolytes and surfactants into the wet preparation process, and to prepare calcium hydroxide with high specific surface area by modifying the surface functional groups (such as introducing hydroxyl groups). However, this method is relatively tedious and complicated in preparation process, and the cost is relatively high, and the preparation process will produce a large amount of alkaline waste liquid. Although the ordinary dry preparation process has a simple preparation process and low cost, the modification effect of the modifier is poor, and the specific surface area and pore volume of the prepared calcium hydroxide are low. Therefore, a new high-efficiency modifier is used in the dry preparation process of calcium hydroxide, and the dry preparation process is improved, so as to prepare calcium hydroxide with high specific surface area, so that it has better physical and chemical properties and higher reaction activity, which is of vital importance for acid gas pollution treatment, sulfur-containing flue gas purification and related applications. Summary of the Invention

[0005] The present invention mainly solves the problems that the common calcium hydroxide products prepared by the existing dry process have a low specific surface area, resulting in poor desulfurization effect; and the process flow of high specific surface area calcium hydroxide products is cumbersome and complicated, and the price is high, resulting in ordinary small and medium-sized coking plants and power plants and other related enterprises with flue gas desulfurization needs being unable to afford the problem. A high specific surface area calcium hydroxide preparation process with a simple process flow is provided. Compared with other high specific surface area calcium hydroxide preparation processes, the process flow is relatively simple, the complex intermediate process of multi-stage digestion is omitted, the preparation process is greatly simplified, and energy consumption is reduced. The prepared product meets the basic indicators of high specific surface area calcium hydroxide while greatly reducing production costs, which is of great significance to improving the market competitiveness of calcium-based desulfurizers.

[0006] To solve the related technical problems, the technical solution adopted by the present invention is: a preparation process of calcium hydroxide with high specific surface area, comprising the following steps:

[0007] Step 1: crushing and screening the lump lime raw material with a crusher and a vibrating screen to obtain granular powdered quicklime raw material within a specific raw material particle size range, and placing it into an autoclave;

[0008] Step 2: Add a modifier to water weighed at a specific water-to-lime ratio to prepare a modifier solution of a certain concentration, in accordance with a certain proportion of the mass of the lime raw material in the previous step;

[0009] Step 3: Add the modifier solution into the autoclave to digest with lime, keep the autoclave in a closed state, and digest for a certain time at a certain stirring speed;

[0010] Step 4: The pressure in the autoclave during the digestion process in the previous step is regulated by heating and maintaining the pressure under closed conditions and releasing the pressure with the exhaust valve to control the pressure within a positive pressure range;

[0011] Step 5: The product digested in step 4 is taken out through the discharge port and dried to obtain a calcium hydroxide product with a high specific surface area.

[0012] The autoclave used in step 2 of the present invention is an FCF-30L high-temperature autoclave produced by Zhengzhou Yuda Instrument Technology Co., Ltd. The sealed autoclave is cylindrical and equipped with stirring blades. The outer layer of the autoclave is wrapped with a resistance insulation heating layer, which can insulate the interior of the autoclave and increase the air pressure in the autoclave by heating during the lime digestion process. First, a fixed amount of lime raw material is added to the autoclave, and then the prepared modifier solution is quickly added to the autoclave. The autoclave is kept sealed, and the air pressure in the autoclave is subsequently regulated by an exhaust valve, a heating device, and a pressure gauge. After the addition of the modifier solution, the lime is digested under high temperature and positive pressure. After digestion is completed, the autoclave exhaust valve is opened to release air and cool the powder. The powder is then discharged through a discharge device at the bottom of the autoclave to obtain a uniform high-specific surface area calcium hydroxide powder with a moisture content of approximately 0.5%. Since lime expands in volume after reacting with water, and the resulting powder is relatively dry, the prepared powder will appear fluid and rotate evenly under the drive of the stirring blades in the autoclave, so that the heat and moisture are evenly distributed, the digestion is relatively complete, and there is no sedimentation and agglomeration caused by uneven digestion.

[0013] Preferably, the lime in the first step is industrial grade high-quality lime, with a main calcium oxide content of 94% to 95% by weight, an effective calcium content of 93.5% by weight, and an activity of 400ml.

[0014] Preferably, the crusher in the first step is a jaw crusher, and the vibrating screen is a shock-type dual-purpose vibrating screen.

[0015] Preferably, the particle size of the lime raw material after crushing and screening in the first step is less than 1.25 mm.

[0016] Preferably, the modifier solute in the modifier solution in step 2 is an organic compound containing single or multiple hydroxyl groups, such as diethanol monoisopropanolamine (DEIPA), triethanolamine (TEA), ethylene glycol (EG), isopropyl alcohol (IPA), etc., the amount of the modifier used is 0.6% to 5.4% by weight of the lime raw material, and the amount of digestion water used is 45% by weight of the lime raw material.

[0017] Preferably, the stirring speed in step 3 is 200 r / min and the digestion time is 30 min.

[0018] Preferably, the air pressure in the autoclave in step 4 is controlled at 0.3-0.6 MPa.

[0019] In the technical solution of the present invention, the lime raw material is preliminarily processed from the raw material stage. Under the premise that it can be implemented on a large scale in actual industry, the lime with the required composition is crushed and screened into a specific raw material particle size range to maximize the reaction activity of the lime during digestion. When using an autoclave for digestion, the advantages of its simple industrial process for preparing high-specific surface area calcium hydroxide, rapid production process, no new pollutants generated in the production process, and low cost of process equipment are highlighted. The single-stage digestion method is used to eliminate multiple steps in the multi-stage digestion process, greatly simplifying the preparation process and reducing energy consumption. A product that meets the basic performance requirements of high-specific surface area calcium hydroxide is prepared to meet the use needs of small and medium-sized power plants and coking plants. The high-specific surface area calcium hydroxide product prepared by this process has a moderate moisture content (about 0.5%), good powder uniformity (325 mesh sieve pass rate of 92.6%, calcium hydroxide mass fraction of 92% to 93%), high specific surface area and rich internal pore structure (BET specific surface area can reach up to 32.8787m 2 / g, and the pore volume can reach up to 0.1662cm 3 / g). BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The accompanying drawings are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the accompanying drawings:

[0021] Figure 1 Shown is a process flow chart for preparing high specific surface area calcium hydroxide of the present invention;

[0022] Figure 2 Shown is a particle size distribution curve of the high specific surface area calcium hydroxide powder prepared in Example 3 of the present invention;

[0023] Figure 3 Shown is the SEM image of ordinary calcium hydroxide;

[0024] Figure 4 Shown is a SEM image of high specific surface area calcium hydroxide prepared in Example 2; DETAILED DESCRIPTION

[0025] In order to enable those skilled in the art to better understand the present invention, the present invention is further described in conjunction with embodiments.

[0026] Example 1

[0027] After industrial-grade high-quality lime (effective calcium content of about 93.5% and activity of about 400ml) is crushed and sieved to <1.25mm, 1000g is taken and placed in an autoclave, followed by weighing 6g of diethanol monoisopropanolamine (DEIPA), adding it to 450g of water to form a modifier solution, and then quickly adding it to the autoclave. The air pressure in the autoclave is controlled at 0.5MPa by the exhaust valve, barometer, and heating device, and the stirring blade speed is set at 200r / min. The solution is digested for 30min. After digestion, calcium hydroxide powder is obtained.

[0028] Example 2

[0029] After industrial-grade high-quality lime (effective calcium content of about 92-93% and activity of about 400ml) is crushed and sieved to <1.25mm, 1000g is taken and placed in an autoclave, 30g of diethanol monoisopropanolamine (DEIPA) is subsequently weighed and added to 450g of water to form a modifier solution, which is then quickly added to the autoclave. The air pressure in the autoclave is controlled at 0.5MPa by an exhaust valve, a barometer, and a heating device. The stirring blade speed is set at 200r / min and the mixture is digested for 30min. After digestion, calcium hydroxide powder is obtained.

[0030] Example 3

[0031] Industrial-grade high-quality lime (effective calcium content of about 92-93% and activity of about 400ml) is crushed and sieved to <1.25mm. 1000g is then placed in an autoclave. 54g of diethanol monoisopropanolamine (DEIPA) is then weighed and added to 450g of water to form a modifier solution. The solution is then quickly added to the autoclave. The air pressure in the autoclave is controlled at 0.5MPa using an exhaust valve, a barometer, and a heating device. The stirring blade speed is set at 200r / min and digested for 30min. After digestion, calcium hydroxide powder is obtained.

[0032] Example 4

[0033] Industrial-grade high-quality lime (effective calcium content of about 92-93% and activity of about 400ml) is crushed and sieved to less than 1.25mm. 1000g is then placed in an autoclave. 30g of triethanolamine (TEA) is then weighed and added to 450g of water to form a modifier solution, which is then quickly added to the autoclave. The pressure in the autoclave is controlled at 0.5MPa using an exhaust valve, a barometer, and a heating device. The stirring blade speed is set at 200r / min and digested for 30min. After digestion, calcium hydroxide powder is obtained.

[0034] Example 5

[0035] Industrial-grade high-quality lime (effective calcium content of about 92-93% and activity of about 400ml) is crushed and sieved to less than 1.25mm. 1000g of the lime is then placed in an autoclave. 30g of ethylene glycol (EG) is then weighed and added to 450g of water to form a modifier solution, which is then quickly added to the autoclave. The air pressure in the autoclave is controlled at 0.5MPa via an exhaust valve, a barometer, and a heating device. The stirring blade speed is set at 200r / min and the mixture is digested for 30min. After digestion, calcium hydroxide powder is obtained.

[0036] Example 6

[0037] Industrial-grade high-quality lime (effective calcium content of about 92-93% and activity of about 400ml) is crushed and sieved to less than 1.25mm. 1000g of the lime is then placed in an autoclave. 30g of isopropyl alcohol (IPA) is then weighed and added to 450g of water to form a modifier solution, which is then quickly added to the autoclave. The air pressure in the autoclave is controlled at 0.5MPa via an exhaust valve, a barometer, and a heating device. The stirring blade speed is set at 200r / min and the mixture is digested for 30min. After digestion, calcium hydroxide powder is obtained.

[0038] Example 7

[0039] After industrial-grade high-quality lime (effective calcium content of about 92-93%, activity of about 400ml) is crushed and sieved to <1.25mm, 1000g is taken and placed in an autoclave, 30g of diethanol monoisopropanolamine (DEIPA) is subsequently weighed, added to 450g of water to be configured to a modifier solution, and then quickly added to the autoclave. The air pressure in the autoclave is controlled at 0.3MPa by an exhaust valve, a barometer, and a heating device. The stirring blade speed is set at 200r / min and digested for 30min. After digestion, calcium hydroxide powder is obtained.

[0040] Example 8

[0041] After industrial-grade high-quality lime (effective calcium content of about 92-93% and activity of about 400ml) is crushed and sieved to <1.25mm, 1000g is taken and placed in an autoclave, 30g of diethanol monoisopropanolamine (DEIPA) is subsequently weighed and added to 450g of water to form a modifier solution, which is then quickly added to the autoclave. The air pressure in the autoclave is controlled at 0.6MPa by an exhaust valve, a barometer, and a heating device. The stirring blade speed is set at 200r / min and the mixture is digested for 30min. After digestion, calcium hydroxide powder is obtained.

[0042] In order to more clearly and intuitively distinguish the differences in process parameters between the various embodiments, detailed statistics are provided in Table 1. Table 1 shows the process parameters of the preparation processes in Examples 1 to 8 of the present invention, where the amount of modifier added is the percentage of the weight of the lime raw material.

[0043] Table 1 Process parameters of each embodiment

[0044]

[0045]

[0046] The calcium hydroxide powder samples prepared in Examples 1 to 8 were tested and calculated for moisture content, calcium hydroxide mass fraction, and lime conversion rate, and their BET specific surface area and pore volume were detected using an ASAP 2460 fully automatic specific surface area and porosity analyzer. Calcium hydroxide powder digested in a conventional manner was selected as a control group and compared with the samples prepared by the preparation process of the present invention. The results are shown in Table 2.

[0047] Table 2 Performance indicators of calcium hydroxide powder under each embodiment

[0048]

[0049]

[0050] The Mastersizer 2000 laser particle size analyzer was used to analyze the particle size of the high specific surface area calcium hydroxide sample prepared in Example 2 to understand its particle size distribution range and characteristics. The particle size analysis results are as follows: Figure 2 The micromorphology of the high specific surface area calcium hydroxide and ordinary calcium hydroxide samples prepared in Example 2 was characterized by using a Zeiss UltraPlus field emission scanning electron microscope to observe the changes in their micromorphology. The SEM images are shown in FIG. Figure 3 shown.

[0051] From the detailed description of the above Examples 1 to 8, it can be seen intuitively and clearly that the present invention eliminates the tedious intermediate steps of multi-stage digestion, greatly simplifies the production process, reduces energy consumption in the production process, saves costs, and no other pollutants are generated in the preparation process. The product prepared after digestion can be directly used for desulfurization. The high specific surface area calcium hydroxide powder prepared in Example 2 has a moderate moisture content (a moisture content of about 0.5%), a median particle size D50 of 6.441 μm, and a cumulative distribution of particles below 10 μm accounting for 69.89%. The mass fraction of calcium hydroxide is 92% to 93%, which proves that the powder is very fine and has good uniformity, and the lime digestion is relatively complete. In addition, the high specific surface area calcium hydroxide prepared in Example 2 has a small average particle size, is relatively dispersed between particles, has no large agglomerates, has good overall uniformity, is closely arranged between particles, and contains more microporous structures (the BET specific surface area can reach up to 32.8787 m 2 / g, and the pore volume can reach up to 0.1662cm 3 / g), which meets the basic index requirements of high specific surface area calcium hydroxide and can be applied to the flue gas desulfurization needs of small and medium-sized power stations and coking plants.

[0052] It should be understood that the above embodiments are merely exemplary embodiments used to illustrate the principles of the present invention, but the present invention is not limited thereto. Persons skilled in the art will readily appreciate that various modifications and improvements are possible without departing from the spirit and substance of the present invention, and such modifications and improvements should fall within the scope of protection of the present invention.

Claims

1. A process for preparing calcium hydroxide with a high specific surface area, using industrial-grade high-quality lime of a specific raw material particle size and a modifier solution as raw materials, digesting under specific pressure, stirring speed and digestion time, characterized in that: The following steps are involved: Step 1: crushing and screening the lump lime raw material with a crusher and a vibrating screen to obtain granular powdered quicklime raw material within a specific raw material particle size range, and placing it into an autoclave; Step 2: Add a modifier to water weighed at a specific water-to-lime ratio to prepare a modifier solution of a certain concentration, in accordance with a certain proportion of the mass of the lime raw material in the previous step; Step 3: Add the modifier solution into the autoclave to digest with lime, keep the autoclave in a closed state, and digest for a certain time at a certain stirring speed; Step 4: The pressure in the autoclave during the digestion process in the previous step is regulated by heating and maintaining the pressure under closed conditions and releasing the pressure with the exhaust valve to control the pressure within a positive pressure range; Step 5: The product digested in step 4 is taken out through the discharge port and dried to obtain a calcium hydroxide product with a high specific surface area.

2. The method for preparing a high specific surface area calcium hydroxide according to claim 1, wherein: The lime in the first step is industrial grade high-quality lime, with a main calcium oxide content of 94% to 95% by weight, an effective calcium content of 93.5% by weight, and an activity of 400ml.

3. The preparation method of high specific surface area calcium hydroxide according to claim 1, wherein: The crusher in the first step is a jaw crusher, and the vibrating screen is a shock-type dual-purpose vibrating screen.

4. The preparation process of a high specific surface area calcium hydroxide according to claim 1, wherein: The particle size of the lime raw material after crushing and screening in the first step is less than 1.25 mm.

5. A preparation technology for high specific surface area calcium hydroxide according to claim 1, characterized in that: The modifier solute in the modifier solution of the second step is an organic compound containing single or multiple hydroxyl groups, such as diethanol monoisopropanolamine (DEIPA), triethanolamine (TEA), ethylene glycol (EG), and isopropyl alcohol (IPA). The amount of the modifier used is 0.6% to 5.4% by weight of the lime raw material, and the amount of digestion water used is 45% by weight of the lime raw material.

6. A process for preparing high specific surface area calcium hydroxide according to claim 1, wherein: The stirring speed of the third step is 200 r / min, and the digestion time is 30 min.

7. A process for preparing high specific surface area calcium hydroxide according to claim 1, wherein: The air pressure in the autoclave in step 4 is controlled at 0.3-0.6 MPa.

8. A process for preparing high specific surface area calcium hydroxide according to claim 1, wherein: The calcium hydroxide sample prepared by the method according to claims 1 to 5 has a water content of about 0.5%, a calcium hydroxide mass fraction of 92% to 93% by weight, and a BET specific surface area of up to 32.8787 m 2 / g, and the pore volume can reach up to 0.1662cm 3 / g.

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