Pilot scale semi-continuous autoclave process for alpha high strength gypsum

Abstract

This invention relates to a semi-continuous pressurized hydrothermal method for producing α-type high-strength gypsum on a pilot-scale basis. The method uses power plant desulfurization gypsum as raw material and employs a pilot-scale reaction apparatus including a 200 L reactor. After the hydrothermal reaction, the slurry is automatically transported to a dewatering device, effectively avoiding crystal degradation caused by temperature drops during intermittent dewatering. Experimental studies have determined the optimal process conditions for preparing α-type high-strength gypsum to be a reaction temperature of 130℃, a reaction time of 4 h, and a crystallization agent dosage of 0.2 wt%. The α-type high-strength gypsum obtained by this method conforms to the α25 standard in JC / T 2038-2010 "α-High-Strength Gypsum". This invention provides a feasible path for promoting the industrialization of pressurized hydrothermal preparation of α-type high-strength gypsum.

Description

Technical Field

[0001] This invention relates to the field of α-type high-strength gypsum manufacturing technology, specifically to a semi-continuous pressurized hydrothermal method for pilot-scale α-type high-strength gypsum production. Background Technology

[0002] Alpha-type high-strength gypsum is an important gelling material. It is produced by reacting calcium sulfate dihydrate (CaSO4•2H2O) with water in a certain ratio to form a suspension, adding an appropriate amount of crystal-transforming agent, and then reacting under certain conditions to obtain calcium sulfate hemihydrate (CaSO4•0.5H2O). This material has a variety of excellent properties, including high strength, short initial setting time, high porosity, dimensional stability, and non-toxicity. These properties enable alpha-type high-strength gypsum to be used to prepare products with high mechanical strength, good thermal stability, and excellent biocompatibility. Therefore, it has broad application prospects and high research value in the fields of building materials and medical materials (Tan Qi, Zhao Yi, Liu Yulin, et al., Preparation Technology and Application Fields of Alpha-type High-strength Gypsum [C], Beijing: National Building Materials Industry Technology Information Institute, 2016).

[0003] From a microscopic perspective, α-type high-strength gypsum exhibits a hexagonal prism shape. Referring to the JC / T 2038-2010 standard, the qualified dry compressive strength of α-type high-strength gypsum is ≥25 MPa, and its 2-hour flexural strength is ≥3.5 MPa, as shown in Table 1. These performance indicators ensure the reliability and durability of α-type high-strength gypsum in practical applications, providing an important basis for the quality assessment of α-type high-strength gypsum.

[0004] Table 1 Performance Indicators of Type α High-Strength Gypsum

[0005] In recent years, the preparation and application development of α-type high-strength gypsum has received widespread attention. Currently, the two most commonly used methods are pressurized hydrothermal method and autoclaving method.

[0006] Figure 1 The solubility curves of gypsum with different water of crystallization contents are shown (Yang Na, Hydrothermal Preparation and Stabilization Study of Calcium Sulfate Whiskers [D], Changsha: Hunan University, 2014). Figure 1 It is evident that products with lower solubility are more prone to precipitation. Alpha-type high-strength gypsum is a hemihydrate gypsum, therefore the preparation temperature must be above 100 ℃, at which point the solubility of hemihydrate gypsum is significantly lower than that of dihydrate gypsum. Since water boils at 100 ℃ under normal pressure, the preparation of alpha-type high-strength gypsum requires a pressurized environment. Depending on the amount of water used, the pressurization method can be divided into the pressurized hydrothermal method and the autoclaving method.

[0007] The pressurized hydrothermal method is a method for preparing α-type high-strength gypsum. This method involves mixing calcium sulfate dihydrate with a certain amount of crystal-changing agent in an aqueous solution to form a suspension, placing it in a sealed high-pressure reactor, stirring and heating it for a period of time, then filtering the product while it is still hot. The resulting filter residue is then dried and powdered to obtain α-type high-strength gypsum. The autoclaving method was the earliest method used in domestic industrial production (Sun Peng, Wang Xiaodong, Research and Development of α-type Hemihydrate Gypsum [J], Journal of Dandong Textile College, 2004, (03):36-40). The traditional autoclaving method involves mixing gypsum and water in a certain proportion to form blocks, reacting them under certain temperature and pressure conditions for a period of time, and then drying and powdering them to obtain α-type high-strength gypsum. This process is simple and suitable for large-scale industrial production, but it has high costs, high energy consumption, and requires excessively high temperatures. Furthermore, the raw materials are piled into blocks during production, resulting in uneven heating and large fluctuations in product quality.

[0008] In the laboratory research phase, the pressurized hydrothermal method was superior to the autoclaving method in terms of compressive strength, reaction time, and residual impurities in the product, whether for α-type high-strength gypsum. (1) In terms of strength, the compressive strength of α-type high-strength gypsum produced by autoclaving is generally around 30 MPa. After the autoclaving process is improved, α-type high-strength gypsum with a compressive strength of 62 MPa can be produced. The compressive strength of α-type high-strength gypsum produced by pressurized hydrothermal method is generally above 40 MPa, and can even reach 64.7 MPa. Therefore, in comparison, the compressive strength of α-type high-strength gypsum produced by pressurized hydrothermal method is the greatest. (2) Compared to time, the steaming method takes a long time, generally more than 5 hours. Reducing the thickness of the material or improving the preparation process can reduce the steaming time to a certain extent. The pressurized hydrothermal method is carried out in a water environment, and the material contact area is large, so the reaction time is shorter, generally less than 4 hours. Therefore, the time used by the pressurized hydrothermal method is more stable and relatively shorter. (3) In terms of post-processing, the autoclaving method produces no waste, but the impurities and crystallizing agents in the gypsum remain in the product, which will affect the strength of the product to some extent; while the pressurized hydrothermal method is carried out in a water environment, so both the impurities in the gypsum and the residual crystallizing agents remain in the mother liquor. Therefore, it is only necessary to treat the mother liquor to make it harmless.

[0009] However, the current industrial processes for continuous production of α-type high-strength gypsum mostly employ autoclaving because pressurized hydrothermal methods face numerous difficulties during scale-up. Therefore, identifying the key limitations on pressurized hydrothermal process scale-up, overcoming the scale-up challenges of pressurized hydrothermal methods, and developing a continuous hydrothermal high-strength gypsum preparation process are crucial for the large-scale production of high-quality α-type high-strength gypsum. Summary of the Invention

[0010] Power plant desulfurization gypsum is produced by a chemical reaction in power plants, in which calcium elements in the form of Ca(OH)2 react with SO2 in flue gas to generate CaSO3 and CaSO4.

[0011] Currently, in laboratory-scale preparation of α-type high-strength gypsum using the pressurized aqueous solution method, the dehydration process is intermittent, resulting in low production efficiency and hindering industrialization. This invention uses power plant desulfurization gypsum as raw material and, through equipment scaling up and modification, employs a pressurized hydrothermal method to prepare α-type high-strength gypsum. The main technical innovations are as follows: 1. Equipment scaling up and modification: By gradually expanding the pilot-scale reaction device from a 0.5 L reactor to a 10 L reactor, and further to a 200 L reactor, the heating, discharge methods, and filtration devices were modified to investigate factors limiting process scaling up; 2. Using the modified equipment to prepare α-type high-strength gypsum, the optimal process conditions of the improved reactor were investigated by changing the reaction temperature, reaction time, and crystallizing agent dosage. After the hydrothermal reaction, the slurry is automatically transported to the dehydration equipment, effectively avoiding crystal degradation caused by temperature drops during intermittent dehydration. The α-type high-strength gypsum obtained by this method conforms to the α25 standard in JC / T 2038-2010 "α-High-Strength Gypsum". This invention provides a feasible path for promoting the industrialization of the preparation of α-type high-strength gypsum by pressurized hydrothermal method.

[0012] This invention provides a semi-continuous pressurized hydrothermal method for the pilot-scale preparation of α-type high-strength gypsum, wherein the method uses a reaction apparatus including a 200 L reactor, the reaction apparatus comprising, as... Figure 4 As shown: The reactor includes an outer shell, a frame-type stirring paddle 4 located inside the reactor, a feed inlet 2 and an inert gas (nitrogen) inlet 3 located at the top of the reactor, a thermometer 5, a pressure gauge 6, and a pressure relief valve 14 located at the top of the reactor, and a discharge outlet 8 located at the bottom of the reactor. The filtration device includes a housing, a feed inlet in the middle, an internal agitator 11, a solid outlet 12 at the bottom, and a liquid outlet 13 at the bottom. A feed pipe 9, connected from the outlet 8 of the reactor to the inlet of the filter device, is used to transport the reaction products from the reactor to the filter device; and A steam jacket, which covers the reactor, feed pipe 9, and filter device, has a steam inlet 1, a steam channel 7, and a steam outlet 10, and is used to heat the reaction apparatus. The method includes the following steps: (1) Add demineralized water to the reactor, and add maleic acid and desulfurized gypsum while stirring; wherein, based on the weight of desulfurized gypsum, the amount of maleic acid is 0.15-0.25 wt%; (2) Turn on the steam and heat to 125-135℃ for 3.5-4.5 hours; (3) Introduce nitrogen gas to transfer the reactants from the reactor to the filter device, drain the water from the bottom outlet under stirring, and then take out the material from the discharge port.

[0013] In some embodiments, the blade diameter of the frame-type agitator in the reactor is 50% to 96% of the reactor's inner diameter, for example, 60%, 70%, 80%, 90%, 95%, etc., particularly 75% to 96%; the height is 20% to 70% of the reactor's height, for example, 25%, 30%, 35%, 40%, 45%, 50%, 65%, etc., particularly 25% to 50%. Here, the reactor's inner diameter refers to the diameter of the horizontal circular cross-section at the center of the reactor's cylinder, and the reactor's height refers to the distance between the center points of the upper and lower ends of the reactor's interior; the blade diameter of the frame-type agitator refers to the length of the uppermost horizontal frame of the agitator, and the height of the frame-type agitator refers to the distance between the center point of the lower section of the agitator and the center point of the uppermost horizontal frame.

[0014] In some embodiments, in step (1), the amount of maleic acid used is 0.18-0.22 wt%, for example 0.19 wt%, 0.20 wt% or 0.21 wt%, particularly 0.2 wt%, based on the weight of the desulfurized gypsum.

[0015] In some embodiments, in steps (1) and (2), the stirring speed is 40-60 Hz, preferably 45-55 Hz, and especially 50 Hz.

[0016] In some implementations, in step (2), the temperature is raised to 128-132°C, for example 129°C, 130°C or 131°C, especially 130°C.

[0017] In some implementations, in step (2), the reaction time is 3.75-4.25 hours, particularly 4 hours.

[0018] In some embodiments, step (3) is performed as follows: nitrogen gas is introduced to blow the material to transfer the reactants from the reactor to the filter device, the agitator of the filter device is turned on and rotated to the forward direction, the bottom outlet of the filter device is opened, and after the bottom outlet stops discharging water for three to five minutes, the nitrogen gas is turned off, the steam is turned off, the outlet of the filter device is opened, the agitator is rotated to the reverse direction and the material is taken out.

[0019] The α-type high-strength gypsum obtained by the method of this invention is a hexagonal prism crystal with a flexural strength of more than 3.5 MPa after 2 hours and a compressive strength of more than 25 MPa after drying, which meets the α25 standard in JC / T 2038-2010 "α High-Strength Gypsum".

[0020] Beneficial effects This disclosure has the following characteristics: 1. Utilize industrial equipment to reduce laboratory-like operating conditions, such as reducing ethanol washing processes and achieving the goal under low-speed conditions; 2. Energy conservation in the project process is achieved by reducing the raw material preheating stage and lowering the temperature during the test. 3. Optimizing the testing equipment process enables continuous production; 4. The obtained product quality is good, with a 2-hour flexural strength of 3.88 MPa and a dry compressive strength of 27.23 MPa; 5. It can turn desulfurization gypsum, a solid waste generated by power plants, into a valuable resource, which not only reduces the solid waste treatment costs of power plants but also achieves green and circular energy utilization. 6. Currently, the hydrothermal production process is not used domestically because it generates a large amount of wastewater, requiring the construction of a wastewater treatment system for later processing. This disclosure, through joint technical research between enterprises and universities, has achieved the ability to recycle the water from the three-in-one filter, reducing wastewater generation. Moreover, the small amount of wastewater generated during the production process can enter the factory's wastewater treatment system with minimal impact on the system.

[0021] It should be understood that the foregoing general description and the following detailed description are exemplary and illustrative only, and are not intended to limit the invention.

[0022] This invention document provides an overview of various implementations or examples of the techniques described herein, and is not a complete disclosure of the full scope or all features of the disclosed techniques. Attached Figure Description

[0023] Figure 1 The solubility curves of gypsum with different water of crystallization contents are shown, where AH is anhydrous gypsum; DH is dihydrate gypsum; and HH is hemihydrate gypsum.

[0024] Figure 2 The stirring paddles equipped with the reactors of Reference Examples 1, 2 and 3 are shown.

[0025] Figure 3 The following are SEM images of the α-type high-strength gypsum products obtained using different reactors in Examples 1-3: (a) product obtained in a 0.5 L reactor of Example 1; (b) product obtained in a 10 L reactor of Example 2; and (c) product obtained in a 10 L reactor of Example 3.

[0026] Figure 4This is a schematic diagram of an apparatus for preparing α-type high-strength gypsum using a pressurized hydrothermal method according to the present invention, wherein 1-steam inlet; 2-feed inlet; 3-nitrogen inlet; 4-frame-type stirring paddle; 5-thermometer; 6-pressure gauge; 7-steam channel; 8-discharge port; 9-feeding pipe; 10-steam outlet; 11-stirring paddle; 12-solid discharge port; 13-liquid discharge port; 14-pressure relief valve.

[0027] Figure 5 These are SEM images of α-type high-strength gypsum prepared at different reaction temperatures in Examples 1-3, where (a) 120℃; (b) 130℃; and (c) 140℃.

[0028] Figure 6 These are X-ray diffraction patterns of α-type high-strength gypsum prepared at different reaction temperatures in Examples 1-3.

[0029] Figure 7 These are SEM images of α-type high-strength gypsum prepared at different reaction times in Examples 1 and 4-5, where (a) 3 h; (b) 4 h; and (c) 5 h.

[0030] Figure 8 These are X-ray diffraction patterns of α-type high-strength gypsum prepared at different reaction times in Examples 1 and 4-5.

[0031] Figure 9 SEM images of α-type high-strength gypsum prepared under different amounts of crystallizing agent in Examples 1 and 6-9, where (a) 0 wt%; (b) 0.1 wt%; (c) 0.2 wt%; (d) 0.3 wt%; and (e) 0.4 wt%.

[0032] Figure 10 X-ray diffraction patterns of α-type high-strength gypsum prepared under different amounts of crystallizing agent in Examples 1 and 6-9. Detailed Implementation

[0033] The following detailed description of specific embodiments of the present invention is provided in conjunction with examples. However, the following examples are provided only for a more illustrative understanding of the present invention, and the scope of the present invention is not limited thereto.

[0034] Unless otherwise specified, the raw materials, reagents, and methods used in the embodiments are all conventional raw materials, reagents, and methods in the art.

[0035] reagents The desulfurized gypsum comes from Xingtai Gengcheng Energy Technology Co., Ltd. SEM image analysis shows that the microstructure of the desulfurized gypsum is monoclinic crystal; XRD analysis shows that the peaks of the desulfurized gypsum are in the same positions as those of CaSO4•2H2O, therefore the power plant desulfurized gypsum is CaSO4•2H2O.

[0036] The desalinated water is manufactured in-house by Xuyang Group, with a conductivity of less than or equal to 50 μS / cm.

[0037] Maleic acid, 99%, CAS: 110-16-7, purchased from Shanghai Maclean Biochemical Technology Co., Ltd. (M813429-500g).

[0038] Test methods SEM measurements were performed using a MIRA LMS scanning electron microscope manufactured by TESCEN in the Czech Republic.

[0039] X-ray diffraction was measured using an XRD-6100 X-ray diffractometer manufactured by Shimadzu Instruments Co., Ltd. in Japan.

[0040] Standard consistency water consumption: measured using a building gypsum consistency meter according to standard GB / T 17669.4-1999.

[0041] Fineness: According to standard JC / T 2038-2010, a square-hole sieve with a sieve aperture side length of 0.125 mm is used for measurement.

[0042] 2-hour flexural strength and 24-hour compressive strength: measured according to standard GB / T 17669.3-1999 using a YAW-300D microcomputer-controlled constant stress compressive and flexural strength testing machine manufactured by Lechter Technology Co., Ltd.

[0043] Setting time: determined according to standard GB / T 17669.4-1999.

[0044] Reference Example 1: Laboratory-scale preparation of α-type high-strength gypsum First, α-type high-strength gypsum was prepared using a 0.5 L laboratory-scale reaction apparatus.

[0045] The laboratory-scale reaction apparatus includes a 0.5 L reactor manufactured by Yantai Songling Chemical Equipment Co., Ltd., comprising the reactor body, reactor lid, and a detachable electric heater, along with an anchor-type agitator and a floating agitator located inside the reactor (structure as follows). Figure 2 (as shown in (a)) The thermometer, pressure gauge and pressure relief valve are located on the top of the reactor; filtration is performed using a Buchner funnel, a vacuum flask and a circulating water vacuum pump.

[0046] The optimal reaction conditions were obtained by changing the concentration of the crystallizing agent and the reaction time. The optimal reaction process is as follows: The crystallizing agent (0.27 wt% relative to the amount of desulfurized gypsum) was dissolved in 240 g of tap water to prepare a crystallizing agent solution. Then, 60 g of desulfurized gypsum was added to prepare a slurry with a concentration of 20 wt%. After mixing evenly, the mixture was poured into a 0.5 L reactor. The electric heating mantle was turned on, and the temperature was set to 130 ℃, the reaction time to 6 h, and the stirring speed to 250 r / min for hydrothermal reaction. After the reaction time was completed, the slurry was quickly poured out and filtered while hot. The slurry was then poured into a Buchner funnel for vacuum filtration to separate the solid and liquid. The slurry was immediately washed twice with boiling water and then rinsed once with anhydrous ethanol. The filter cake was then quickly transferred to an electric thermostatic drying oven at 110 ℃ and dried to constant weight to obtain α-hemihydrate gypsum.

[0047] The obtained SEM images of the products are as follows Figure 3 As shown in (a), it has a good crystal form and morphology.

[0048] Reference Example 2: Laboratory-scale preparation of α-type high-strength gypsum α-type high-strength gypsum was prepared using a 10 L laboratory-scale reaction apparatus.

[0049] The laboratory-scale reaction apparatus includes a 10 L reactor manufactured by Weihai Chaoyang Chemical Machinery Co., Ltd., comprising a reactor body (with an internal electric heating jacket), a reactor lid, and a removable inner liner. A propeller-type agitator is connected to the reactor lid (structure as follows). Figure 2 (b) shown), temperature sensor, pressure gauge and pressure relief valve; filtration uses a vacuum filter.

[0050] The optimal reaction conditions were obtained by changing the concentration of the crystallizing agent and the reaction time. The optimal reaction process is as follows: The crystallizing agent (0.27 wt% relative to the amount of desulfurized gypsum) was dissolved in 4800 g of tap water to prepare a crystallizing agent solution. Then, 1200 g of desulfurized gypsum was added to prepare a slurry with a concentration of 20 wt%. After mixing evenly, the mixture was poured into a 10 L reactor. The temperature was set at 130 ℃, the reaction time at 4 h, and the stirring speed at 250 r / min for hydrothermal reaction. After the reaction time was completed, the slurry was quickly removed, filtered while hot, and poured into a 10 L vacuum filter (Zhengzhou Zhuocheng Instrument Technology Co., Ltd.) for solid-liquid separation. The slurry was immediately washed twice with boiling water. The filter cake was quickly transferred to an oven at 110 ℃ and dried to constant weight to obtain α-hemihydrate gypsum.

[0051] The obtained SEM images of the products are as follows Figure 3 As shown in (b), not only is the product morphology uneven, but the aspect ratio is also too large, which does not meet the requirements of α-type high-strength gypsum.

[0052] Reference Example 3: Laboratory-scale preparation of α-type high-strength gypsum In addition to adding an anchor-type agitator to the agitator of the reactor in Reference Example 2 (see the final agitator morphology), Figure 2 Except for (c)), the other reaction apparatus is the same as in Reference Example 2.

[0053] The optimal reaction conditions were obtained by changing the concentration of the crystallizer and the reaction time. Except for the optimal amount of crystallizer, which was 0.2 wt%, the other reaction processes and conditions were the same as in Reference Example 2.

[0054] The obtained SEM images of the products are as follows Figure 3 As shown in (c), it has a good crystal form and morphology.

[0055] In Reference Examples 1-3, (1) Reference Examples 1 and 2 both use rotary impellers, and the size of the impeller increases with the increase of the reactor capacity; (2) Similarly, rotary impellers (such as...) are used. Figure 2 As shown in a): When the reactor capacity is small (0.5L), the suspension can be mixed evenly to obtain a product with a better morphology, such as Figure 3 As shown in (a); however, when the reactor capacity is large (10L), the stirring effect is poor, which affects the product morphology, such as Figure 3 As shown in (b); (3) The original rotary agitator of the 10L reactor (such as Figure 2 Based on (as shown in a), add an anchor-type stirring paddle (such as...) Figure 2 As shown in b), more uniform stirring enhances mass transfer and results in a more uniform product morphology, such as... Figure 3 As shown in (c).

[0056] Referring to Examples 1-3, (1) with the increase of reactor capacity and the change of impeller type, the optimal reaction conditions are slightly different: the reaction temperature is 130 ℃, the stirring speed is 250 rpm, the reaction time is between 4 and 6 h, and the amount of crystallizing agent is between 0.2 and 0.3 wt%. (2) The impeller configuration is the key factor determining the product morphology. In a 0.5 L reactor, a combination of upper propeller and lower anchor impeller (refer to Example 1) can make the suspension mixed evenly and obtain a product with good morphology. When the reactor is scaled up to 10 L, if only a propeller impeller is used (refer to Example 2), the stirring effect will decrease significantly, resulting in uneven product morphology, such as Figure 3 As shown in (b). Therefore, the original propeller in the 10 L vessel ( Figure 2 Based on (b), an anchor-type mixing paddle is added. Figure 2 (c), referring to Example 3), enhances the stirring and mass transfer effect, thereby obtaining a product with a more uniform morphology, such as Figure 3As shown in (c). (3) After the reactor is expanded by 20 times, the difficulty of hot filtration increases, so the filtration equipment needs to be enlarged and the steps simplified accordingly: the anhydrous ethanol rinsing is cancelled, and only two boiling water washings are retained, so as to balance the temperature maintenance and efficiency improvement in the intermittent operation.

[0057] As can be seen from the results of Examples 1-3, although products meeting the morphological requirements of α-type high-strength gypsum were successfully prepared in the laboratory using both 0.5 L and 10 L reactors, the mechanical properties could not be measured due to insufficient yield. In order to prepare products sufficient for mechanical property measurement, a scale-up process for preparing α-type high-strength gypsum using a 200 L reactor was explored based on the process conditions explored in the 10 L reactor.

[0058] The inventors discovered two key factors when preparing α-type high-strength gypsum in the laboratory using 0.5 L and 10 L reactors: 1. the type of agitator; 2. hot filtration. Therefore, these two factors also need to be considered during scale-up from 10 L to 200 L. The inventors made the following modifications to the original pilot-scale reactor and filtration device.

[0059] (1) Stirring device As can be seen from Example 2, when a propeller-type agitator is used in a 10 L reactor, it is impossible to produce a product with good crystal form and morphology after multiple experiments.

[0060] After several attempts, the inventors added an anchor-type agitator to the propeller-type agitator and successfully prepared a product with good crystal form and morphology after another test. See Example 3.

[0061] Based on the above improvements made in the laboratory, the inventors repeatedly selected the reactor and finally chose a 200 L reactor equipped with a frame-type stirring paddle.

[0062] (2) Heating method The advantages of electric heating are precise temperature control, rapid response, and cleanliness and environmental friendliness; the disadvantages are high energy consumption, low heating efficiency, and short equipment lifespan. In the laboratory, it takes 90 minutes to raise the temperature of a 10 L reactor to 130 ℃ using electric heating. If electric heating is used to heat a 200 L reactor, the time required would be too long.

[0063] Therefore, after scaling up the reactor to a 200 L vessel, the inventors changed the heating method to jacketed steam heating. Experiments showed that the initial heating process of the reactor only required 20 minutes, a change that significantly reduced the heating time and improved reaction efficiency. Furthermore, steam heating, when applied to continuous production in chemical reactors, offers advantages such as rapid heating and low cost.

[0064] (3) Discharge method The 10 L reactor used in the laboratory requires heat insulation equipment during the discharge and filtration process. The inner liner of the reactor is removed and poured into the filter while it is still hot.

[0065] The inventors discovered that continuing to manually transfer and filter the material from a 200 L reactor was an extremely laborious and dangerous operation. Therefore, in the scale-up modification, the reactor outlet was connected to the filter inlet, and steam was used to maintain a constant temperature during the discharge process. This improvement significantly reduced the risk and operational difficulty. Simultaneously, the pressure generated during the reaction process could be utilized for filtration, reducing the filtration time; nitrogen could also be used for purging, minimizing product loss and increasing yield.

[0066] (4) Filtration device Depend on Figure 1 It is known that if the temperature is successfully controlled during the reaction stage, but the temperature drops during the filtration stage, the product will still be in an aqueous environment. At temperatures below 100°C, the solubility of dihydrate gypsum will be lower than that of hemihydrate gypsum, resulting in the product being dihydrate gypsum. Therefore, hot filtration is crucial.

[0067] In the laboratory, to maintain the temperature of the product in a 10 L reactor, rapid filtration is required, and hot water must be added during the filtration process to maintain the product temperature.

[0068] To achieve rapid, hot filtration of products from a 200 L reactor, the inventors added a jacketed steam heater to the filtration device during scale-up modifications. This ensures that the product temperature remains above 100 ℃ during filtration. Simultaneously, to improve filtration efficiency, a stirrer was added to the filtration device, enabling faster and more uniform filtration.

[0069] Thus, the inventors obtained an apparatus for preparing α-type high-strength gypsum using a pressurized hydrothermal method, such as... Figure 4 As shown, the device includes: The reactor includes an outer shell, a frame-type stirring paddle 4 located inside the reactor, a feed inlet 2 and an inert gas (nitrogen) inlet 3 located at the top of the reactor, a thermometer 5, a pressure gauge 6, and a pressure relief valve 14 located at the top of the reactor, and a discharge outlet 8 located at the bottom of the reactor. The filtration device includes a housing, a feed inlet in the middle, an internal agitator 11, a solid outlet 12 at the bottom, and a liquid outlet 13 at the bottom. A feed pipe 9, connected from the outlet 8 of the reactor to the inlet of the filter device, is used to transport the reaction products from the reactor to the filter device; and A steam jacket, which covers the reactor, feed pipe 9 and filter device, has a steam inlet 1, a steam channel 7 and a steam outlet 10, and is used to heat the reactor.

[0070] The apparatus for preparing α-type high-strength gypsum of the present invention may further include a control device for controlling the temperature and pressure of the reaction vessel, a drive device and control device for driving and controlling the stirring paddle, and a drying device for drying the reaction products, etc.

[0071] Example 1: Preparation of α-type high-strength gypsum Clean the reactor thoroughly, close all valves except for the feed inlet. Add 120 kg of demineralized water to the reactor, turn on the agitator, add 24 g of maleic acid (0.2 wt% relative to the desulfurized gypsum), and add 12 kg of desulfurized gypsum. Close the feed inlet. Turn on steam and maintain the temperature at 130°C for 4 hours. After the reaction is complete, open the nitrogen inlet valve to purge nitrogen into the reactor. Turn on the agitator of the filter and rotate it forward. Open the bottom outlet of the filter and wait for water to stop flowing for three to five minutes before turning off the nitrogen and steam. Open the outlet of the filter, reverse the agitator, and remove the material. Place the material in an oven at 110°C to dry.

[0072] Example 2-3 Effect of reaction temperature on the preparation of α-type high-strength gypsum Except for changing the reaction temperature from 130℃ to 120℃ or 140℃ respectively, α-type high-strength gypsum was prepared according to the method of Example 1.

[0073] Table 1 Experimental procedures at different reaction temperatures

[0074] SEM images, X-ray diffraction patterns, standard consistency water consumption, fineness, 2-h flexural strength, 24-h compressive strength, and setting time of the α-type high-strength gypsum prepared in Examples 1-3 were tested.

[0075] (1) Microscopic morphology Scanning electron microscope images of the products at different reaction temperatures are shown below. Figure 5 As shown. By Figure 5 It can be seen that when the reaction temperature is 120℃ (Figure a), the product exhibits a morphology of large, regular pieces and small, irregular pieces; when the reaction temperature is 130℃ (Figure b), the product exhibits a uniform hexagonal prism morphology; and when the reaction temperature is 140℃ (Figure c), the product exhibits a morphology of small, regular pieces and large, irregular pieces. Based on the comprehensive analysis of the product's microstructure, the product prepared at a reaction temperature of 130℃ yields better results.

[0076] (2) Phase composition X-ray diffraction patterns of the products at different reaction temperatures are shown below. Figure 6 As shown. By Figure 6It was found that the product was CaSO4·0.5H2O at different reaction times. When the reaction temperatures were 130℃ and 140℃, the relative peak values ​​of the product spectrum were similar to those of the standard spectrum; however, when the reaction time was 120℃, the peak value at 31.8° was too low, which is consistent with the inconsistent SEM images of the product. In summary, the spectra at reaction times of 130℃ and 140℃ were most similar to the standard spectrum, resulting in a better product.

[0077] (3) Physical properties The physical properties of α-type high-strength gypsum prepared at different reaction temperatures are shown in Table 2. Table 2 shows that the setting time increases with increasing reaction temperature. Regarding fineness, only when the reaction temperature is 130℃ does it meet the requirement of a sieve residue of no more than 5% in JC / T 2038-2010 "α-High-Strength Gypsum". Regarding mechanical properties, because the setting time of the product at 120℃ is too fast, its standard consistency water requirement cannot be effectively measured; therefore, the standard consistency water requirement at 130℃ is used as a reference to determine the product's strength. In terms of 2-hour flexural strength, both the products at 120℃ and 130℃ meet the α25 standard in JC / T 2038-2010 "α-High-Strength Gypsum", while the 2-hour flexural strength at 140℃ is close to the α40 standard. However, in terms of 24-hour compressive strength, the product at 130℃ has significantly higher strength than the other two, reaching 16.81 MPa. Based on a comprehensive analysis of fineness and mechanical properties, the product prepared at a reaction temperature of 130 ℃ yielded better results.

[0078] Table 2 Physical properties of products at different reaction temperatures

[0079] Effect of reaction time on the preparation of α-type high-strength gypsum in Examples 4-5 Except for changing the reaction time from 4h to 3h or 5h respectively, α-type high-strength gypsum was prepared according to the method of Example 1.

[0080] SEM images, X-ray diffraction patterns, standard consistency water content, fineness, 2-h flexural strength, 24-h compressive strength, and setting time of the α-type high-strength gypsum prepared in Examples 1 and 4-5 were tested.

[0081] Table 3 Experimental schemes at different reaction times

[0082] (1) Microscopic morphology Scanning electron microscope images of the products at different reaction times are shown below. Figure 7 As shown. By Figure 7It can be seen that when the reaction time is 3 h (Figure a), the product exhibits a large, regular shape with small, irregular shapes; when the reaction time is 4 h (Figure b), the product is mostly uniform hexagonal prisms; and when the reaction time is 5 h (Figure c), the product exhibits varying sizes and irregular shapes. Based on a comprehensive analysis of the product's microstructure, the product prepared with a reaction time of 4 h yields better results.

[0083] (2) Phase composition X-ray diffraction patterns of the products at different reaction times are shown below. Figure 8 As shown. By Figure 8 It was found that the product was CaSO4·0.5H2O at different reaction times. When the reaction time was 3 h and 4 h, the relative peak values ​​of the product spectrum were similar to those of the standard spectrum; however, when the reaction time was 5 h, the peak value at 31.8° was too large, which is consistent with the inconsistent bias of the product's SEM images. In summary, the spectra obtained at reaction times of 3 h and 4 h were most similar to the standard spectrum, and the resulting product showed better performance.

[0084] (3) Physical properties The physical properties of α-type high-strength gypsum prepared with different reaction times are shown in Table 4. Table 4 shows that the setting time increases with increasing reaction time. In terms of fineness, only when the reaction time is 4 h does it meet the requirement of a sieve residue of no more than 5% in JC / T 2038-2010 "α-High-Strength Gypsum". Regarding mechanical properties, when the reaction time is 3 h, the 2-hour flexural strength meets the α30 standard in JC / T 2038-2010 "α-High-Strength Gypsum"; the reaction times of 4 h and 5 h both meet the α25 standard. The 24-hour compressive strength of the product prepared with a reaction time of 4 h is significantly higher than the other two, reaching 16.81 MPa. Based on a comprehensive analysis of fineness and mechanical properties, the product prepared with a reaction time of 4 h exhibits better results.

[0085] Table 4 Physical properties of the products at different reaction times

[0086] Effects of crystallizing agent dosage on the preparation of α-type high-strength gypsum in Examples 6-9 Except for changing the amount of maleic acid, the crystallization agent, from 0.2 wt% to 0 wt%, 0.1 wt%, 0.3 wt%, or 0.4 wt%, respectively, α-type high-strength gypsum was prepared according to the method of Example 1.

[0087] Table 5 Experimental schemes for different amounts of crystal-changing agent

[0088] SEM images, X-ray diffraction patterns, standard consistency water content, fineness, 2-h flexural strength, 24-h compressive strength, and setting time of the α-type high-strength gypsum prepared in Examples 1 and 6-9 were tested.

[0089] (1) Microscopic morphology Scanning electron microscope images of the products with different amounts of crystallizing agent are shown below. Figure 9 As shown. By Figure 9 As can be seen, without the addition of a crystal-transforming agent (Figure a), the product generally exhibits a long columnar shape with many fragmented columnar components; with a crystal-transforming agent dosage of 0.1% (Figure b), the product generally exhibits a short columnar shape, but the product length is uneven; with a crystal-transforming agent dosage of 0.2% (Figure c), the product is mostly uniformly hexagonal prism-shaped; with a crystal-transforming agent dosage of 0.3% (Figure d), the product is cubic with low yield and uneven size; with a crystal-transforming agent dosage of 0.4% (Figure e), the product is cubic with uneven size distribution. Comprehensive analysis of the product's microstructure shows that the product prepared with a crystal-transforming agent dosage of 0.2% yields better results.

[0090] (2) Phase composition XRD patterns of products at different crystallizer concentrations, such as Figure 10 As shown. By Figure 10 It can be seen that the product is CaSO4·0.5H2O regardless of the concentration of the crystallizer. When the crystallizer dosage is 0.1% and 0.2%, the relative sizes of the peaks at 15° and 29° are similar to those in the standard spectrum. When the dosage is 0.3% and 0.4%, the peaks at 15° and 29° are very weak, while the peak at 31.8° is very strong. By referring to the graph, it can be seen that the peak at 31.8° corresponds to the (-114) plane, which is consistent with the result that the SEM image of the product is a cube rather than a hexagonal prism. In summary, when the crystallizer dosage is 0.1% and 0.2%, the spectrum is most similar to the standard spectrum, and the product obtained is better.

[0091] (3) Physical properties The physical properties of α-type high-strength gypsum prepared with different amounts of crystallizing agent are shown in Table 6. Table 6 shows that the standard viscosity water requirement decreased significantly after adding the crystallizing agent maleic acid; the setting time decreased with increasing dosage. Regarding fineness, only when the crystallizing agent dosage was 0.1% and 0.2% did it meet the requirement of no more than 5% sieve residue in JC / T 2038-2010 "α-High-Strength Gypsum". Regarding mechanical properties, when the crystallizing agent dosage was 0.1%, the 2-hour flexural strength met the α30 standard in JC / T 2038-2010 "α-High-Strength Gypsum", while the dosages of 0.2%, 0.3%, and 0.4% all met the α25 standard. The 24-hour compressive strength of the product with a dosage of 0.2% was significantly higher than the other types, reaching 16.81 MPa. Based on a comprehensive analysis of fineness and mechanical properties, the product prepared with a crystallization agent dosage of 0.2% showed better results.

[0092] Table 6 Physical properties of products with different crystallization agent dosages

[0093] Conclusion: Optimal reaction conditions: The optimal reaction conditions in the reaction apparatus including a 200 L reactor according to the present invention were determined by combining the 24-hour compressive strength with other properties. These conditions were those of Example 1: reaction temperature 130 °C, reaction time 4 h, and maleic acid content of 0.2 wt%. Under these conditions, the 24-hour compressive strength was 16.81 MPa. The product strips were further dried to constant weight, and their compliance with the α25 standard was tested. Table 7 shows the compressive strength of the product strips at different drying times.

[0094] Table 7. Effect of product drying time on the compressive strength of α-type high-strength gypsum.

[0095] As shown in Table 7, when the product strips are dried to constant weight at 40 ℃, the compressive strength of the product meets the α25 standard in JC / T2038-2010 "α High Strength Gypsum".

[0096] In summary, through experimental investigation, the optimal process conditions for preparing α-type high-strength gypsum in the reaction apparatus including a 200 L reactor according to the present invention are: reaction temperature 130 °C, reaction time 4 h, and crystallization agent dosage 0.2 wt%. The optimal microstructure of the obtained α-type high-strength gypsum is as follows: Figure 5 As shown in b, the product is a hexagonal prism crystal with a 2-hour flexural strength of 3.88 MPa and a dry compressive strength of 27.23 MPa. These results demonstrate that a product conforming to the α25 standard in JC / T 2038-2010 "α High-Strength Gypsum" was successfully prepared using the modified 200 L equipment.

Claims

1. A method for preparing α-type high-strength gypsum, characterized in that, The method uses a reaction apparatus including a 200 L reactor, the reaction apparatus comprising: The reactor includes an outer shell, a frame-type stirring paddle inside the reactor, a feed inlet and a nitrogen inlet at the top of the reactor, a thermometer, a pressure gauge, and a pressure relief valve at the top of the reactor, and a discharge outlet at the bottom of the reactor. The filtration device includes a housing, a feed inlet in the middle, an internal agitator, a solid outlet at the bottom, and a liquid outlet at the bottom. A feed pipe, connecting the outlet of the reactor to the inlet of the filtration device, is used to transport the reaction products from the reactor to the filtration device; and A steam jacket, which covers the reactor, feed pipe and filter device, has a steam inlet, a steam channel and a steam outlet, and is used to heat the reaction device; The method includes the following steps: (1) Add demineralized water to the reactor, and add maleic acid and desulfurized gypsum while stirring; wherein, based on the weight of desulfurized gypsum, the amount of maleic acid is 0.15-0.25 wt%; (2) Turn on the steam and heat to 125-135℃ for 3.5-4.5 hours; (3) Introduce nitrogen gas to transfer the reactants from the reactor to the filter device, drain the water from the bottom outlet under stirring, and then take out the material from the discharge port.

2. The method according to claim 1, characterized in that, The diameter of the frame-type agitator blade in the reactor is 50% to 96% of the reactor's inner diameter; the height is 20% to 70% of the reactor's height.

3. The method according to claim 1, characterized in that, The diameter of the frame-type agitator blade in the reactor is 75% to 96% of the reactor's inner diameter; the height is 25% to 50% of the reactor's height.

4. The method according to claim 1, characterized in that, In step (1), the amount of maleic acid used is 0.18-0.22 wt%, based on the weight of the desulfurized gypsum. In step (2), the temperature is raised to 128-132℃ and the reaction is carried out for 3.75-4.25 hours.

5. The method according to claim 1, characterized in that, In step (1), the amount of maleic acid used is 0.2 wt% based on the weight of the desulfurized gypsum. In step (2), the temperature is raised to 130°C and the reaction is carried out for 4 hours.

6. The method according to claim 1, characterized in that, In steps (1) and (2), the stirring speed is 40-60 Hz.

7. The method according to claim 1, characterized in that, In steps (1) and (2), the stirring speed is 45-55 Hz.

8. The method according to claim 1, characterized in that, In steps (1) and (2), the stirring speed is 50 Hz.

9. The method according to claim 1, characterized in that, Step (3) is as follows: Nitrogen gas is introduced to blow the material so that the reactants are transferred from the reactor to the filter device. The agitator of the filter device is turned on and rotated to the forward direction. The bottom outlet of the filter device is opened. After the bottom outlet stops discharging water, the nitrogen gas is turned off and the steam is turned off. The outlet of the filter device is opened, the agitator is rotated to the reverse direction and the material is taken out.

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