CN112239222A - Equipment and method for continuous hydrothermal production of magnesium hydroxide - Google Patents
Equipment and method for continuous hydrothermal production of magnesium hydroxide Download PDFInfo
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Abstract
The invention discloses equipment and a method for producing magnesium hydroxide by continuous hydrothermal, wherein a horizontal/vertical continuous hydrothermal reaction kettle provides a stable crystallization environment, energy consumption caused by frequent temperature rise and temperature drop operation of a single kettle in an intermittent process is greatly reduced, and simultaneously, magnesium hydroxide flame retardant products with regular appearance, controllable granularity and uniform particle size distribution can be produced by controlling a continuous production process, so that the application effect of the products is improved.
Description
Technical Field
The invention relates to the production of green inorganic flame retardant, in particular to novel equipment and a method for producing a hexagonal flaky magnesium hydroxide flame retardant by adopting a continuous hydrothermal treatment technology.
Background
The magnesium hydroxide fire retardant is one of important magnesium-based basic functional materials in the industrial chain of seawater desalination and comprehensive utilization at home and abroad. As a typical halogen-free flame retardant, the magnesium hydroxide flame retardant has three functions of flame retardance, smoke abatement and filling, does not generate secondary pollution in the combustion process, can generate synergistic action of various substances, is non-volatile, non-toxic, small in corrosivity and high in thermal stability, and is particularly suitable for being matched with polymers with higher processing temperature to prepare various flame-retardant composite materials. The magnesium hydroxide flame retardant product in developed countries has strong specificity, and different varieties can be selected according to different application fields. The major manufacturers include 3M (Martin Marietta Mag-nesia), Lonza, Solem, Morton, Ameribrom, etc. The high-quality magnesium hydroxide of 3M company has low production cost and strong market competitiveness, and the developed product mainly has three ranges of particle sizes, is uniform in particle size distribution and can be used for thermoplastic plastics, thermoelastic resin and resin for coating wires and cables; products with the grain diameter of 0.9-1.1 mu m developed by Lonza company can be used for flame retardance of materials such as polyolefin, PVC, nylon and the like, and the company is developing new varieties with nano-micron grain diameter. Solem company develops high-quality magnesium hydroxide flame retardant with good dispersibility and processing temperature up to 332 ℃.
Along with the emphasis on environmental protection and the increase of the demand on low-pollution flame retardants in China, the development and production investment of magnesium hydroxide flame retardants in China is also increased. However, the research and development of preparing the magnesium hydroxide fire retardant from seawater brine in China are relatively late, the reaction operation mode of the existing industrial production is intermittent operation, the production mode is mostly single-kettle hydrothermal or multi-kettle series hydrothermal, and the product has the problems of incomplete crystal form mixing of single-kettle products, wide particle size distribution, high energy consumption of multi-kettle series, large investment, poor product application effect and the like. In patent ZL2005100864739, a magnesium hydroxide product synthesized at normal temperature is subjected to hydrothermal modification by a single kettle, and is stirred at a constant temperature of 100-250 ℃ for 1-6 hours under the condition of adding a dispersing agent, but the process is an intermittent process, and a heating-heat preservation-cooling process needs to be repeatedly carried out during industrial production, so that continuous production cannot be carried out, the production efficiency is low, the process energy consumption is high, and equipment required under the same yield occupies a large area. The invention patent ZL2010105074802 adopts the mode that a plurality of hydrothermal kettles are connected in series to realize the gradual transfer of materials among the hydrothermal kettles, and the materials are finally cooled in a heat exchange mode, although the process is the hydrothermal process of magnesium hydroxide slurry in the plurality of kettles in series, a plurality of reaction kettles are still required to carry out sequential reaction, the number of devices and series pipelines are more, and the reaction environment in a single kettle is easy to have difference and higher pressure, so the stability of the hydrothermal and transfer processes of the materials is poor, and the energy consumption is higher; the final cooling of the material needs to exchange heat with a refrigerant through a heat exchange system, so that the equipment type, the occupied area and the production energy consumption are further increased.
In conclusion, the magnesium hydroxide fire retardant industry is an important part of the high-quality and high-value industrial chain for the comprehensive utilization of seawater, China has a great gap in research and development and production in the field, and the magnesium hydroxide fire retardant product with high quality is not effectively formed and developed yet and needs to be imported.
Disclosure of Invention
The invention aims to overcome the defects of the prior art, and provides equipment and a method for producing magnesium hydroxide flame retardant products by continuous hydrothermal, aiming at the defects and defects of unstable product quality, too wide particle size distribution, high energy consumption and the like in the existing magnesium hydroxide flame retardant production process in China.
The technical purpose of the invention is realized by the following technical scheme.
An equipment for continuous hydrothermal production of magnesium hydroxide comprises a preheater, a continuous hydrothermal reaction kettle, a decompression kettle, a first heat exchanger and a second heat exchanger, wherein:
the magnesium hydroxide crude slurry storage tank and the alkali source storage tank are respectively connected with an inlet of a preheater through pipelines, an outlet of the preheater is connected with an inlet of the continuous hydrothermal reaction kettle through a pipeline, an outlet of the continuous hydrothermal reaction kettle is connected with an inlet of a pressure reduction kettle through a pipeline, a gas outlet of the pressure reduction kettle is connected with a first heat exchanger, and the first heat exchanger is connected with the magnesium hydroxide crude slurry storage tank; and a product outlet of the pressure reduction kettle is connected with a second heat exchanger, the second heat exchanger is connected with a filtering device, the filtering device is connected with a washing device, and the washing device is connected with a drying device.
Furthermore, a pump is provided in each line to provide operating power for the entire system.
And the first heat exchanger is arranged on a pipeline between the magnesium hydroxide crude slurry storage tank and the preheater so as to carry out heat treatment on the magnesium hydroxide crude slurry which does not enter the preheater.
Moreover, the preheater is a tube type or plate type preheater, and the heat source is heat-conducting oil.
Moreover, the first heat exchanger is a shell-and-tube or plate heat exchanger and adopts steam-water exchange.
And the second heat exchanger is a shell-and-tube or plate heat exchanger and adopts water-water exchange.
Moreover, the continuous hydrothermal reaction kettle is a horizontal/vertical continuous hydrothermal reaction kettle, and the temperature is controlled in a heat conduction oil jacket mode; the reaction kettle is in a continuous feeding and continuous discharging mode; the top of the reaction kettle is provided with a speed regulation stirrer, and the bottom of the reaction kettle is provided with a drain port.
The method for producing the magnesium hydroxide by using the device in the continuous hydrothermal mode comprises the steps of heating crude magnesium hydroxide slurry through the first heat exchanger, heating the crude magnesium hydroxide slurry and an alkali source in the preheater, reacting the crude magnesium hydroxide slurry and the alkali source in the continuous hydrothermal reaction kettle, discharging a reaction product to the pressure reduction kettle, reducing the pressure, flashing, cooling through the second heat exchanger, filtering, washing and drying to obtain a hexagonal flaky magnesium hydroxide flame retardant product with uniform particle size distribution.
Moreover, the magnesium hydroxide crude product is low-added-value magnesium hydroxide with irregular morphology, and the solid content of the slurry of the magnesium hydroxide crude product after pulping (the magnesium hydroxide crude product is dispersed in water) is 1-15 wt%, preferably 3-10 wt%.
And the alkali source is sodium hydroxide or potassium hydroxide or an aqueous solution of the sodium hydroxide and the potassium hydroxide, and the adding amount of the alkali source is that the hydroxide concentration in the raw material slurry consisting of the crude magnesium hydroxide slurry and the alkali source is 2-8 mol/L, preferably 5-8 mol/L.
And the washing liquid selected in the product washing process is deionized water.
And in addition, a high-temperature drying mode is selected in the drying process of the product, and the drying temperature is 100-140 ℃.
And the temperature of the secondary steam of the decompression flash evaporation is 100-105 ℃, and the secondary steam is recycled to the first heat exchanger to treat the crude magnesium hydroxide slurry so as to heat the crude magnesium hydroxide slurry to 90-100 ℃.
Furthermore, the raw slurry composed of crude slurry of magnesium hydroxide and alkali source is heated in a preheater to 160-180 deg.C, and then heated by 0.5-1 m3The flow of the reaction kettle per hour is continuously fed into a continuous hydrothermal reaction kettle for reaction.
Moreover, in a continuous hydrothermal reaction kettle, the reaction temperature is 160-220 ℃, and preferably 180-200 ℃; the stirring speed is 150-300 r/min, preferably 200-300 r/min; the reaction time is 1 to 10 hours, preferably 2 to 8 hours.
The invention provides equipment and a method for continuous hydrothermal production of hexagonal flaky magnesium hydroxide flame retardant products aiming at the defects and defects of unstable product quality, too wide particle size distribution, high energy consumption and the like in the existing production process of magnesium hydroxide flame retardants in China. Compared with the prior equipment and method for preparing the magnesium hydroxide flame retardant, the technical scheme of the invention has the following gain effects:
(1) compared with single kettle hydrothermal or multi-kettle series hydrothermal, the technical process has the characteristics that the continuous operation of the reaction kettle is realized in the process, and the process is stable;
(2) the whole process of the process is controllable, and the product quality is stable;
(3) the equipment is simple, the investment is low, and the occupied area is small;
(4) compared with single kettle or multi-kettle serial hydrothermal, the technical equipment can realize continuous hydrothermal production of products, the process energy consumption is low, and after liquid cooling and flashing are completed, secondary steam heat is recycled, so that the overall process energy consumption is further reduced.
Drawings
FIG. 1 is a process flow diagram of the continuous hydrothermal production of magnesium hydroxide flame retardant product of the present invention.
FIG. 2 is an SEM photograph of crude magnesium hydroxide as a raw material and magnesium hydroxide as a product in examples 1 to 5, wherein: a-a magnesium hydroxide crude product; b-magnesium hydroxide product of example 1; c-magnesium hydroxide product of example 2; d-example 3 magnesium hydroxide product; e-example 4 magnesium hydroxide product; f-example 5 magnesium hydroxide product.
FIG. 3 is an XRD spectrum diagram of crude magnesium hydroxide as a raw material and magnesium hydroxide as a product in examples 1 to 5.
FIG. 4 is a particle size distribution diagram of crude magnesium hydroxide as a raw material and magnesium hydroxide as a product in examples 1 to 5, wherein: a-a magnesium hydroxide crude product; b-magnesium hydroxide product of example 1; c-magnesium hydroxide product of example 2; d-example 3 magnesium hydroxide product; e-example 4 magnesium hydroxide product; f-example 5 magnesium hydroxide product.
Detailed Description
The technical scheme of the invention is further explained by combining specific examples.
As shown in the attached figure 1, the equipment for continuously and hydrothermally producing magnesium hydroxide comprises a preheater, a continuous hydrothermal reaction kettle, a decompression kettle, a first heat exchanger and a second heat exchanger, wherein: the magnesium hydroxide crude slurry storage tank and the alkali source storage tank are respectively connected with an inlet of a preheater through pipelines, an outlet of the preheater is connected with an inlet of the continuous hydrothermal reaction kettle through a pipeline, and an outlet of the continuous hydrothermal reaction kettle is connected with an inlet of a pressure reduction kettle through a pipeline; the gas outlet of the pressure reduction kettle is connected with a first heat exchanger, the first heat exchanger is connected with a magnesium hydroxide crude product slurry storage tank, the first heat exchanger is arranged on a pipeline between the magnesium hydroxide crude product slurry storage tank and the preheater so as to carry out heat treatment on the magnesium hydroxide crude product slurry which does not enter the preheater, and the magnesium hydroxide crude product slurry subjected to heat treatment and an alkali source are mixed in the pipeline and then enter the preheater; and a product outlet of the pressure reduction kettle is connected with a second heat exchanger, the second heat exchanger is connected with a filtering device, the filtering device is connected with a washing device, and the washing device is connected with a drying device.
Specifically, the preheater is a tube type or plate type preheater, and the heat source is heat conducting oil; the first heat exchanger is a shell-and-tube or plate heat exchanger and adopts steam-water exchange; the second heat exchanger is a shell-and-tube or plate heat exchanger and adopts water-water exchange; the continuous hydrothermal reaction kettle is a horizontal/vertical continuous hydrothermal reaction kettle, and the temperature is controlled in a heat conduction oil jacket mode; the reaction kettle is in a continuous feeding and continuous discharging mode; the top of the reaction kettle is provided with a speed-regulating stirrer, and the bottom of the reaction kettle is provided with a drain port; the filtering equipment is set by solid-liquid separation, and the washing equipment and the drying equipment are common equipment in the industry.
The continuous production of the magnesium hydroxide material is carried out on the basis of the equipment, and the specific embodiment is as follows:
example 1:
the method for continuously producing hexagonal flaky magnesium hydroxide (serving as a flame retardant) by using crude magnesium hydroxide as a raw material and sodium hydroxide as an alkali source through hydrothermal reaction comprises the following steps:
(1) preparing raw material slurry: pulping the crude magnesium hydroxide, wherein the solid content is 3 wt%, heating the pulp to 100 ℃ by using flash secondary steam of a pressure reduction kettle through a first heat exchanger, and adding an alkali source to obtain the pulp, wherein the concentration of sodium hydroxide in the pulp is 2 mol/L;
(2) preheating: injecting the raw material slurry into a preheater by using a metering pump, preheating to 180 ℃, and then adding 1m3Continuously feeding the slurry into a continuous hydrothermal reaction kettle at the flow rate of/h, wherein the reaction temperature is 200 ℃, and the reaction residence time is 4 hours, so that the slurry is continuously discharged from the reaction kettle to a pressure reduction kettle;
(3) and (3) after the slurry is decompressed and cooled to 100 ℃ in the decompression kettle, decompressing and flashing secondary steam (100-105 ℃) is recycled to the first heat exchanger to finish the heating process in the step (1), and the flashed slurry is cooled to below 60 ℃ through the second heat exchanger, and then is subjected to solid-liquid separation, washing and drying to produce high-purity magnesium hydroxide flame retardant powder with uniform particle size distribution and regular appearance.
(4) The SEM of the product is shown in figure 2(B), and compared with the irregular shape of the raw material, the product is in a regular hexagonal sheet shape and has clear edges; the XRD diffraction peak of the product is detailed in figure 3, compared with the raw material, the diffraction peak intensity of the product is increased, the peak shape is sharper, and meanwhile, according to the XRD characteristic peak intensity ratio in the table 1, the I of the product001/I101More than 1, compared with the raw material I001/I101The method is greatly improved, and proves that the process and the equipment are favorable for improving the crystallinity, and simultaneously reduce the surface polarity of the product, so that the product is easier to be mixed and melted with organic materials, and the using effect is improved; the particle size analysis is detailed in figure 4(B) and table 2, and compared with the raw materials, the particle size of the product is uniform and concentrated in distribution, which is beneficial to subsequent product application. The above results show that the process and equipment of the invention can realize continuous production of magnesium hydroxide flame retardant products with higher quality.
Example 2:
the method for continuously producing the hexagonal flaky magnesium hydroxide flame retardant by using the crude magnesium hydroxide as a raw material and potassium hydroxide as an alkali source through hydrothermal reaction comprises the following steps:
(1) preparing raw material slurry: pulping the crude magnesium hydroxide, wherein the solid content is 12%, heating the pulping by a first heat exchanger by using flash secondary steam of a decompression kettle at 100 ℃, and adding an alkali source to obtain the pulp with the potassium hydroxide concentration of 4 mol/L;
(2) preheating: injecting the raw material slurry into a preheater by using a metering pump, preheating to 160 ℃, and then adding 1m3Continuously feeding the slurry into a continuous hydrothermal reaction kettle at the flow rate of/h, wherein the reaction temperature is 180 ℃, and the reaction retention time is 4 hours, so that the slurry is continuously discharged from the reaction kettle to a pressure reduction kettle;
(3) and (3) after the slurry is decompressed and cooled to 100 ℃ in the decompression kettle, decompressing and flashing secondary steam (100-105 ℃) is recycled to the first heat exchanger to finish the heating process in the step (1), and the flashed slurry is cooled to below 60 ℃ through the second heat exchanger, and then is subjected to solid-liquid separation, washing and drying to produce high-purity magnesium hydroxide flame retardant powder with uniform particle size distribution and regular appearance.
(4) The SEM of the product is shown in figure 2(C), and compared with the irregular shape of the raw material, the product is in a regular hexagonal sheet shape and has clear edges; the XRD diffraction peak of the product is detailed in figure 3, compared with the raw material, the diffraction peak intensity of the product is increased, the peak shape is sharper, and meanwhile, according to the XRD characteristic peak intensity ratio in the table 1, the I of the product001/I101More than 1, compared with the raw material I001/I101The method is greatly improved, and proves that the process and the equipment are favorable for improving the crystallinity, and simultaneously reduce the surface polarity of the product, so that the product is easier to be mixed and melted with organic materials, and the using effect is improved; the particle size analysis is detailed in figure 4(C) and table 2, compared with the raw material, the particle size of the product is uniform and concentrated in distribution, and the subsequent product application is facilitated. The above results show that the process and equipment of the invention can realize continuous production of magnesium hydroxide flame retardant products with higher quality.
Example 3:
the method for continuously producing the hexagonal flaky magnesium hydroxide flame retardant by using the crude magnesium hydroxide as a raw material and sodium hydroxide as an alkali source through hydrothermal reaction comprises the following steps:
(1) preparing raw material slurry: pulping the crude magnesium hydroxide, wherein the solid content is 8%, heating the pulp to 100 ℃ by using flash secondary steam of a decompression kettle through a first heat exchanger, and adding an alkali source to obtain the pulp with the concentration of 8mol/L of sodium hydroxide;
(2) preheating: injecting the raw material slurry into a preheater by using a metering pump, preheating to 180 ℃, and then feeding the slurry to a feed pump with a feed pump diameter of 0.5m3Continuously feeding the slurry into a continuous hydrothermal reaction kettle at the flow rate of/h, wherein the reaction temperature is 220 ℃, and the reaction residence time is 6 hours, so that the slurry is continuously discharged from the reaction kettle to a pressure reduction kettle;
(3) and (3) after the slurry is decompressed and cooled to 100 ℃ in the decompression kettle, decompressing and flashing secondary steam (100-105 ℃) is recycled to the first heat exchanger to finish the heating process in the step (1), and the flashed slurry is cooled to below 60 ℃ through the second heat exchanger, and then is subjected to solid-liquid separation, washing and drying to produce high-purity magnesium hydroxide flame retardant powder with uniform particle size distribution and regular appearance.
(4) The SEM of the product is shown in figure 2(D), and compared with the irregular shape of the raw material, the product is in a regular hexagonal sheet shape, and the edge is clear; the XRD diffraction peak of the product is detailed in figure 3, compared with the raw material, the diffraction peak intensity of the product is increased, the peak shape is sharper, and meanwhile, according to the XRD characteristic peak intensity ratio in the table 1, the I of the product001/I101More than 1, compared with the raw material I001/I101The method is greatly improved, and proves that the process and the equipment are favorable for improving the crystallinity, and simultaneously reduce the surface polarity of the product, so that the product is easier to be mixed and melted with organic materials, and the using effect is improved; the particle size analysis is detailed in figure 4(D) and table 2, and compared with the raw materials, the particle size of the product is uniform and concentrated in distribution, which is beneficial to subsequent product application. The above results show that the process and equipment of the invention can realize continuous production of magnesium hydroxide flame retardant products with higher quality.
Example 4:
the method for continuously producing the hexagonal flaky magnesium hydroxide flame retardant by using the crude magnesium hydroxide as a raw material and sodium hydroxide as an alkali source through hydrothermal reaction comprises the following steps:
(1) preparing raw material slurry: pulping the crude magnesium hydroxide, wherein the solid content is 15%, heating the pulp to 100 ℃ by using flash secondary steam of a decompression kettle through a first heat exchanger, and adding an alkali source to obtain the pulp with the concentration of 6mol/L of sodium hydroxide;
(2) preheating: injecting the raw material slurry into a preheater by using a metering pump, preheating to 160 ℃, and then feeding the slurry to a feed pump with a feed pump diameter of 0.5m3Continuously feeding the slurry into a continuous hydrothermal reaction kettle at the flow rate of/h, wherein the reaction temperature is 180 ℃, and the reaction retention time is 8 hours, so that the slurry is continuously discharged from the reaction kettle to a pressure reduction kettle;
(3) and (3) after the slurry is decompressed and cooled to 100 ℃ in the decompression kettle, decompressing and flashing secondary steam (100-105 ℃) is recycled to the first heat exchanger to finish the heating process in the step (1), and the flashed slurry is cooled to below 60 ℃ through the second heat exchanger, and then is subjected to solid-liquid separation, washing and drying to produce high-purity magnesium hydroxide flame retardant powder with uniform particle size distribution and regular appearance.
(4) The SEM of the product is shown in figure 2(E), and compared with the irregular shape of the raw material, the product is in a regular hexagonal sheet shape and has clear edges; the XRD diffraction peak of the product is detailed in figure 3, compared with the raw material, the diffraction peak intensity of the product is increased, the peak shape is sharper, and meanwhile, according to the XRD characteristic peak intensity ratio in the table 1, the I of the product001/I101More than 1, compared with the raw material I001/I101The method is greatly improved, and proves that the process and the equipment are favorable for improving the crystallinity, and simultaneously reduce the surface polarity of the product, so that the product is easier to be mixed and melted with organic materials, and the using effect is improved; the particle size analysis is detailed in figure 4(E) and table 2, and compared with the raw materials, the particle size of the product is uniform and concentrated in distribution, which is beneficial to subsequent product application. The above results show that the process and equipment of the invention can realize continuous production of magnesium hydroxide flame retardant products with higher quality.
Example 5:
the method for continuously producing the hexagonal flaky magnesium hydroxide flame retardant by using the crude magnesium hydroxide as a raw material and potassium hydroxide as an alkali source through hydrothermal reaction comprises the following steps:
(1) preparing raw material slurry: pulping the crude magnesium hydroxide, wherein the solid content is 4%, heating the pulp to 100 ℃ by using flash secondary steam of a decompression kettle through a first heat exchanger, and adding an alkali source to obtain the pulp with the potassium hydroxide concentration of 6 mol/L;
(2) preheating: injecting the raw material slurry into a preheater by using a metering pump, preheating to 180 ℃, and then feeding the slurry to a feed pump at a feed rate of 0.8m3Continuously feeding the slurry into a continuous hydrothermal reaction kettle at the flow rate of/h, wherein the reaction temperature is 200 ℃, and the reaction residence time is 6 hours, so that the slurry is continuously discharged from the reaction kettle to a pressure reduction kettle;
(3) and (3) after the slurry is decompressed and cooled to 100 ℃ in the decompression kettle, decompressing and flashing secondary steam (100-105 ℃) is recycled to the first heat exchanger to finish the heating process in the step (1), and the flashed slurry is cooled to below 60 ℃ through the second heat exchanger, and then is subjected to solid-liquid separation, washing and drying to produce high-purity magnesium hydroxide flame retardant powder with uniform particle size distribution and regular appearance.
(4) The SEM of the product is shown in figure 2(F), and the product is in a regular six-shape form compared with the irregular shape of the raw materialThe edges are clear; the XRD diffraction peak of the product is detailed in figure 3, compared with the raw material, the diffraction peak intensity of the product is increased, the peak shape is sharper, and meanwhile, according to the XRD characteristic peak intensity ratio in the table 1, the I of the product001/I101More than 1, compared with the raw material I001/I101The method is greatly improved, and proves that the process and the equipment are favorable for improving the crystallinity, and simultaneously reduce the surface polarity of the product, so that the product is easier to be mixed and melted with organic materials, and the using effect is improved; the particle size analysis is detailed in figure 4(F) and table 2, and compared with the raw materials, the particle size of the product is uniform and concentrated in distribution, so that the subsequent product application is facilitated. The above results show that the process and equipment of the invention can realize continuous production of magnesium hydroxide flame retardant products with higher quality.
TABLE 1 XRD Peak intensity ratios (I) of crude materials and examples 1-5001/I101) Summary of the invention
Injecting: i is001/I101Can be used to determine the surface polarity, I, of magnesium hydroxide products001/I101The non-polar surface exposure is higher proved by more than 1, which is favorable for mixing and dissolving with organic materials
TABLE 2 summary of particle size analysis characteristics of crude raw materials and examples 1-5
Injecting: d10、D50、D90The standard deviation can be used to judge the uniformity of the particle size distribution, and the lower the standard deviation, the more uniform the particle size distribution.
The invention also discloses a regulation and control process condition to realize the control of product quality, namely when the equipment is used for preparing magnesium hydroxide, the adjustment is carried out on the alkali source, the continuous hydrothermal reaction temperature and the reaction time to realize the control of product quality.
(1) Alkali source
In the aspect of alkali source selection, sodium hydroxide and potassium hydroxide are easily available monobasic strong base, and can provide high-concentration OH in a material system of a reaction kettle-So that the crystal form of the crystal form can be regulated and controlled, and the generation of a hexagonal flaky crystal form can be promoted. In the aspect of the concentration of the alkali source, the concentration of the alkali source has positive influence on the crystal form and the particle size distribution of the product. Under the same other conditions, with the increase of the concentration of the alkali source (namely the increase of the concentration of hydroxide ions), the product presents hexagonal flaky morphology and simultaneously has the XRD characteristic peak intensity ratio (I)001/I101) The standard deviation value determining the uniformity of the particle size distribution of the product is reduced (the lower the standard deviation value, the more uniform the particle size distribution).
(2) Continuous hydrothermal reaction temperature
The magnesium hydroxide is a dissolution-recrystallization process in the hydrothermal treatment process, and the temperature has positive change to the crystal form molding of the product. The improvement of the temperature of the hydrothermal process system can improve the dispersion performance of the product and improve the stability of the hexagonal platelet crystal structure of the magnesium hydroxide. Along with the rise of the temperature, the relative intensity of the characteristic diffraction peak of the magnesium hydroxide is obviously changed, the 001 surface of the weak polar surface is more exposed, the 101 surface of the strong polar surface is inhibited, namely the XRD characteristic peak intensity ratio (I) of the product001/I101) The product is in an elevated state, and the appearance of the product can be in a hexagonal flaky crystal appearance.
(3) Hydrothermal reaction residence time (i.e., reaction time) the influence of hydrothermal reaction residence time on the product is mainly reflected in the degree of uniformity of the particle size of the product and the thickness of the crystals of the product. If uniform hexagonal flaky crystals are generated, the hydrothermal time is about 6 hours, which is a more appropriate time, and at this time, the product can form more regular hexagonal flaky crystals, and the particle size distribution is more uniform. The hydrothermal time is short, the product is not recrystallized completely, the fine particle size is not dissolved completely, the particle size distribution of the product is widened, and if the hydrothermal time is less than 2 hours, the product can not even form regular hexagonal plate crystals. When the hydrothermal time is more than 6 hours, the thickness of the product is obviously increased, and the product is different from flake magnesium hydroxide in the application field.
The adjustment of the process parameters according to the invention enables the preparation of magnesium hydroxide products, which exhibit properties substantially identical to those of the invention. The invention has been described in an illustrative manner, and it is to be understood that any simple variations, modifications or other equivalent changes which can be made by one skilled in the art without departing from the spirit of the invention fall within the scope of the invention.
Claims (10)
1. The equipment for producing the magnesium hydroxide by continuous hydrothermal is characterized by comprising a preheater, a continuous hydrothermal reaction kettle, a decompression kettle, a first heat exchanger and a second heat exchanger, wherein:
the magnesium hydroxide crude slurry storage tank and the alkali source storage tank are respectively connected with an inlet of a preheater through pipelines, an outlet of the preheater is connected with an inlet of the continuous hydrothermal reaction kettle through a pipeline, an outlet of the continuous hydrothermal reaction kettle is connected with an inlet of a pressure reduction kettle through a pipeline, a gas outlet of the pressure reduction kettle is connected with a first heat exchanger, and the first heat exchanger is connected with the magnesium hydroxide crude slurry storage tank; and a product outlet of the pressure reduction kettle is connected with a second heat exchanger, the second heat exchanger is connected with a filtering device, the filtering device is connected with a washing device, and the washing device is connected with a drying device.
2. The plant for continuous hydrothermal production of magnesium hydroxide according to claim 1, wherein the first heat exchanger is disposed on a pipeline between the crude magnesium hydroxide slurry storage tank and the preheater to thermally treat the crude magnesium hydroxide slurry that has not entered the preheater.
3. The equipment for continuous hydrothermal production of magnesium hydroxide according to claim 1 or 2, wherein the preheater is a tubular or plate preheater, and the heat source is heat conducting oil; the first heat exchanger is a shell-and-tube or plate heat exchanger and adopts steam-water exchange; the second heat exchanger is a shell-and-tube or plate heat exchanger and adopts water-water exchange.
4. The equipment for continuous hydrothermal production of magnesium hydroxide according to claim 3, wherein the continuous hydrothermal reaction kettle is a horizontal/vertical continuous hydrothermal reaction kettle, and the temperature is controlled by means of a heat-conducting oil jacket; the reaction kettle is in a continuous feeding and continuous discharging mode; the top of the reaction kettle is provided with a speed regulation stirrer, and the bottom of the reaction kettle is provided with a drain port.
5. The method for continuous hydrothermal production of magnesium hydroxide by using the device according to any one of claims 1 to 4, wherein the crude magnesium hydroxide slurry is heated by a first heat exchanger, and then enters a preheater with an alkali source for heating, the raw material slurry consisting of the crude magnesium hydroxide slurry and the alkali source enters a continuous hydrothermal reaction kettle for reaction, the reaction product is discharged to a decompression kettle for decompression and flash evaporation, and then is cooled by a second heat exchanger, and then is filtered, washed and dried to obtain a hexagonal flaky magnesium hydroxide flame retardant product with uniform particle size distribution; wherein the magnesium hydroxide crude product is low-added-value magnesium hydroxide with irregular morphology, and the solid content of the slurry of the magnesium hydroxide crude product after pulping (the magnesium hydroxide crude product is dispersed in water) is 1-15 wt%; the alkali source is sodium hydroxide or potassium hydroxide or an aqueous solution of the sodium hydroxide and the potassium hydroxide, and the addition amount of the alkali source is that the concentration of hydroxyl in raw material slurry consisting of the magnesium hydroxide crude product slurry and the alkali source reaches 2-8 mol/L; in a continuous hydrothermal reaction kettle, the reaction temperature is 160-220 ℃, the stirring speed is 150-300 r/min, and the reaction time is 1-10 hours.
6. The method for continuous hydrothermal production of magnesium hydroxide according to claim 5, wherein the slurry of crude magnesium hydroxide has a solid content ranging from 3 to 10 wt%; the amount of the alkali source added is such that the hydroxide concentration in the raw slurry consisting of the crude magnesium hydroxide slurry and the alkali source reaches 5 to 8 mol/L.
7. The method according to claim 5, wherein the washing liquid used in the washing of the product is deionized water; the drying process of the product adopts a high-temperature drying mode, and the drying temperature is 100-140 ℃.
8. The method for continuous hydrothermal production of magnesium hydroxide according to claim 5, wherein the secondary steam temperature of the reduced pressure flash evaporation is 100-105 ℃, and the secondary steam is recycled to the first heat exchanger to treat the crude magnesium hydroxide slurry so as to heat the crude magnesium hydroxide slurry to 90-100 ℃; heating the raw slurry consisting of crude magnesium hydroxide slurry and alkali source in a preheater to 160-180 deg.C, and adding 0.5-1 m3The flow of the reaction kettle is continuously fed into a continuous hydrothermal reaction kettle for reaction; in a continuous hydrothermal reaction kettle, the reaction temperature is 180-200 ℃; the stirring speed is 200-300 r/min; the reaction time is 2-8 hours.
9. Use of an apparatus according to claim 1 or a method according to claim 5 for conducting a continuous hydrothermal production of magnesium hydroxide for conditioning the product magnesium hydroxide.
10. The use of claim 9, wherein the XRD characteristic peak intensity ratio (I) of the product exhibits hexagonal plate-like morphology with increased alkali source concentration (i.e. increased hydroxide ion concentration)001/I101) The standard deviation value which determines the uniform degree of the particle size distribution of the product is reduced along with the rising situation; along with the rise of the temperature, the relative intensity of the characteristic diffraction peak of the magnesium hydroxide is obviously changed, the 001 surface of the weak polar surface is more exposed, the 101 surface of the strong polar surface is inhibited, namely the XRD characteristic peak intensity ratio (I) of the product001/I101) The product is in an elevated state, and the appearance of the product can be in a hexagonal flaky crystal appearance; the hydrothermal time is about 6h, the product can form regular hexagonal plate-shaped crystals, the particle size distribution is uniform, the hydrothermal time is less than 2h, the product even can not form regular hexagonal plate-shaped crystals, when the hydrothermal time is more than 6h, the thickness of the product is obviously increased, and the thick plate-shaped magnesium hydroxide is obtainedIs distinguished from flaky magnesium hydroxide.
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