A control method for static crystallization process and its application

Abstract

The present invention discloses a control method for a static crystallization process and its application. The control method comprises: a crystallization process: the material to be crystallized is fed into a crystallization device, a first refrigerant is introduced into a heat exchange element inside the crystallization device, a first hot agent is introduced into an external jacket of the crystallization device, the temperature of the first hot agent is higher than the temperature of the material to be crystallized, the first refrigerant in the heat exchange element is controlled to gradually cool down, so that the material to be crystallized crystallizes and precipitates a crystal layer, and the mother liquor generated in the crystallization process is discharged; a sweating process: a second hot agent is introduced into the heat exchange element, the temperature of the second hot agent is controlled to be higher than the temperature of the crystal layer to perform sweating treatment on the crystal layer, so that impurities in the crystal layer are precipitated, and a second refrigerant is introduced into the external jacket, and the temperature of the second refrigerant is controlled to be lower than the temperature of the crystal layer. The present invention can increase the crystallization temperature, reduce the sweating temperature, and thus reduce energy consumption.

Description

Technical Field

[0001] The invention relates to the technical field of static crystallization, and in particular to a control method for a static crystallization process and application thereof. Background Art

[0002] The static crystallization process is a type of melt crystallization. Static crystallization refers to the gradual cooling and crystallization of the material in the static crystallizer, the crystal heating and sweating after the crystallization mother liquor is discharged, and the crystal heating and melting process. In the static crystallization process, there is no mechanical stirring, and there is no need to separate the crystals from the crystallization mother liquor by mechanical separation means such as centrifugation or filtration. The consumption of mechanical kinetic energy can be reduced, and the operation is simple. It can avoid the problems of material blockage, separation difficulties, product damage and loss when the high melting point system is separated from the solid in the suspension melt crystallization process. Therefore, the static crystallization process is particularly suitable for crystallization separation operations with high product quality requirements.

[0003] In recent years, with the rapid development of chemical industry, materials, medicine, new energy vehicles and other fields, the demand for high-end chemicals has also increased. Among them, high-purity glycolide can be used as a polymerization monomer to prepare biodegradable medical polymer materials; high-purity lactide can be used as a polymerization monomer to prepare medical polylactic acid and degradable agricultural mulch films; electronic grade ethylene carbonate can be used to prepare lithium battery electrolyte solutions for electric vehicles; high-purity 2,6-diisopropylnaphthalene, as an important basic organic chemical raw material, can be used to synthesize advanced polyester materials and liquid crystal polymers, such as polyethylene naphthalate (PEN) and polybutylene naphthalate (PBN) and liquid crystal polymers (LCP); durene, as an important fine chemical raw material, can be used to produce pyromellitic anhydride ( PMDA) and further produce polyimide (PI), and polyimide (PI) is widely used in aviation, aerospace, microelectronics, nano, liquid crystal, separation membrane, laser and other fields due to its excellent mechanical properties, high temperature resistance, chemical resistance and other properties; high-purity p-dichlorobenzene can be used as pesticides, preservatives, etc. in addition to organic synthesis; high-purity p-xylene, as an important basic organic chemical raw material, is mainly used to prepare terephthalic acid (PTA) and dimethyl terephthalate (DMT), and then produce polyethylene terephthalate (PET), which has excellent physical and mechanical properties in a wide temperature range and is widely used in thin films, engineering plastics and other fields. Due to its remarkable characteristics, the static crystallization process can be used in the separation and purification process of the above chemicals.

[0004] However, for the static crystallization process, the current focus is limited to how to improve the purity of the product as much as possible, and there is little research on how to reduce the energy consumption of the static crystallization process. At the same time, in order to obtain a product of target purity, multi-stage crystallization and sweating are often required. There are also few reports on the energy consumption optimization of the multi-stage static crystallization process.

[0005] CN108096872A relates to a plate-type crystallizer, including a box, a crystallization plate group, a cover plate, and a raw liquid inlet pipe. The crystallization plate group includes plates, cold and hot medium inlet and outlet pipes, a manifold and a connecting pipe. The plates are arranged at equal intervals along the length direction of the manifold, and at least one plate is arranged outside the end of the manifold to reduce the spacing between adjacent plates of two adjacent groups of crystallization plate groups. The plate is connected with a medium inlet and outlet pipe, which is fixed at the end of the manifold. The remaining plates are connected to the manifold through a connecting pipe, and the cold and hot medium inlet and outlet pipes are connected to the manifold. The technical scheme effectively reduces the spacing between the plates between groups, so that all the plates in the box can be kept at the same distance, avoiding the influence of different spacing on the overall crystallization speed in the box, greatly improving the overall crystallization speed, shortening the reaction time, reducing energy consumption, and improving production efficiency. It mainly improves the uniformity of the entire crystallization and sweating process, thereby improving product quality, and cannot directly reduce energy consumption.

[0006] In summary, the present invention aims to provide a control method that can reduce the energy consumption of the static crystallization process, so as to fundamentally increase the crystallization temperature of the crystallization process and reduce the sweating temperature of the sweating process, thereby reducing the energy consumption of the entire static crystallization process, which is of great significance for the promotion and application of the static crystallization process. Summary of the invention

[0007] In view of the above-mentioned problems existing in the prior art, the present invention provides a control method for a static crystallization process and an application thereof. The control method for a static crystallization process provided by the present invention avoids the defects of the prior art in high energy consumption caused by low crystallization temperature and high sweating temperature, and can increase the crystallization temperature and reduce the sweating temperature, thereby reducing energy consumption.

[0008] A first aspect of the present invention provides a method for controlling a static crystallization process, the method comprising:

[0009] Crystallization process: the material to be crystallized is fed into a crystallization device, a first refrigerant is introduced into a heat exchange element inside the crystallization device, a first hot agent is introduced into an outer jacket of the crystallization device, the temperature of the first hot agent is higher than the temperature of the material to be crystallized, the first refrigerant in the heat exchange element is controlled to gradually cool down, so that the material to be crystallized crystallizes and precipitates a crystal layer, and after crystallization, the remaining mother liquor of the crystallization process is discharged;

[0010] Sweating process: a second heat agent is introduced into the heat exchange element, and the temperature of the second heat agent is controlled to be higher than the temperature of the crystal layer to perform sweating treatment on the crystal layer, so that impurities in the crystal layer are precipitated, and a second coolant is introduced into the external jacket, and the temperature of the second coolant is controlled to be lower than the temperature of the crystal layer.

[0011] The inventors found in the research process that the traditional static crystallizer, whether it is a fin type or a tube type, only introduces heat exchange medium into the heat exchange element, and the outer surface of the crystallizer is not provided with a jacket, and only the static crystallizer is insulated and heat-insulated. During the crystallization process, with the addition of the refrigerant in the heat exchange element, the cold gradually diffuses outward from the heat exchange element and disperses into all the materials in the crystallizer, resulting in too large a supersaturation of the solution, and then the initial crystallization temperature and the terminal crystallization temperature are very low, and the energy consumption is very high. Similarly, during the sweating process, with the addition of the hot agent in the heat exchange element, the heat gradually diffuses outward from the heat exchange element, resulting in a small heat exchange temperature difference between the heat exchange element and the wall of the crystallizer, thereby requiring a higher sweating temperature to make the impurities entrained in the crystal "sweat" and seep out. That is to say, under the traditional static crystallizer and crystallization process, the crystallization process requires more cold, and the sweating process requires more heat to ensure the ideal product purity and recovery rate, resulting in a high overall energy consumption in the static crystallization process, which is more obvious in the multi-stage static crystallization process.

[0012] Moreover, even if a static crystallizer with an external jacket is used, it is also to avoid the interference of the external environment on the temperature of the material in the crystallizer, and the conventional operation is to control the jacket temperature to be equivalent to the temperature of the heat exchange medium in the heat exchange element. In this case, the crystallization temperature is often increased by adding seed crystals to control the product quality. However, in the static crystallization process, due to the absence of stirring operation, the addition of solid seed crystals is not convenient to operate, and the uniformity of addition to the crystallizer cannot be guaranteed, resulting in local crystallization and affecting product quality. However, when the seed crystals are added in the form of slurry, not only is it necessary to perform external refrigeration to prepare the slurry first, which consumes too much cold energy, but also requires a pump to circulate the crystallization raw materials and the slurry together, which consumes kinetic energy and causes cold energy loss, which undoubtedly increases the energy consumption of the entire crystallization process.

[0013] Based on this, the control method of the above-mentioned static crystallization process provided by the present invention can increase the temperature gradient between the heat exchange element and the wall of the crystallizer during the crystallization process by controlling the temperature of the heat exchange medium in the external jacket, so that the supersaturation of the material to be crystallized in the crystallizer is significantly reduced, so that the material to be crystallized can be crystallized at a higher temperature, which not only greatly reduces the amount of cooling required for the crystallization process, but also significantly improves the crystallization efficiency. The improvement of crystallization efficiency not only means an increase in sweating crystals, but also helps to improve the yield of the static crystallization process. More importantly, the improvement of crystallization efficiency can reduce the concentration of the crystallization mother liquor, so that the crystallization mother liquor consumes less cooling when further recrystallization or secondary crystallization is carried out, thereby greatly reducing the energy consumption of the entire crystallization process, which is particularly obvious for the energy consumption reduction effect of the multi-stage static crystallization process.

[0014] According to some embodiments of the control method of the present invention, the first coolant and the second heat agent are the same and are selected from at least one of water, ethanol, ethylene glycol and heat transfer oil.

[0015] According to some embodiments of the control method of the present invention, the first heat agent and the second coolant are the same and are selected from at least one of water, ethanol, ethylene glycol and heat transfer oil.

[0016] In different embodiments of the present invention, the specific types of the first coolant, the second coolant, the first hot agent, and the second hot agent are not limited, and the temperature control of the first coolant, the second coolant, the first hot agent, and the second hot agent is more important. Different heat exchange media can be selected according to different materials to be crystallized and different crystallization and sweating processes.

[0017] According to some embodiments of the control method of the present invention, the melting point of the crystal layer is lower than 25°C.

[0018] According to a preferred embodiment of the control method of the present invention, the temperature of the first heat agent in the external jacket is controlled to be constant.

[0019] According to a preferred embodiment of the control method of the present invention, the temperature of the first heat medium in the external jacket is controlled to be 7-25° C. higher than the initial temperature of the first coolant in the heat exchange element.

[0020] According to some embodiments of the control method of the present invention, the melting point of the crystal layer is lower than 25°C.

[0021] According to a preferred embodiment of the control method of the present invention, the temperature difference between the second coolant in the external jacket and the second hot agent in the heat exchange element is controlled to be 7-20°C.

[0022] According to some embodiments of the control method of the present invention, the melting point of the crystal layer is higher than 25°C.

[0023] According to a preferred embodiment of the control method of the present invention, the temperature difference between the first hot agent in the external jacket and the first cold agent in the heat exchange element is controlled to be 7-25°C.

[0024] According to some embodiments of the control method of the present invention, the melting point of the crystal layer is higher than 25°C.

[0025] According to a preferred embodiment of the control method of the present invention, the temperature of the second coolant in the outer jacket is controlled to be constant.

[0026] According to a preferred embodiment of the control method of the present invention, the temperature of the second refrigerant in the external jacket is controlled to be 7-20° C. lower than the temperature of the second hot medium in the heat exchange element.

[0027] In different embodiments of the present invention, the material to be crystallized may include a low melting point material whose melting point of the target product is lower than room temperature and a high melting point material whose melting point of the target product is higher than room temperature. That is, the material to be crystallized in the present invention may include a low melting point material whose melting point of the crystal layer is lower than 25°C and a high melting point material whose melting point of the crystal layer is higher than 25°C.

[0028] According to a preferred embodiment of the control method of the present invention, the melting point of the crystal layer is significantly lower than 25°C, especially lower than 0°C. The temperature of the first hot agent is controlled to be constant and the temperature difference between the second cold agent and the second hot agent is maintained at a certain level. This can avoid consuming more cooling energy in the jacket and is more conducive to energy saving of the device.

[0029] According to a preferred embodiment of the control method of the present invention, when the melting point of the crystal layer is significantly higher than 25°C, especially higher than 50°C, the first hot agent and the first cold agent are controlled to maintain a certain temperature difference, and the temperature of the second cold agent is controlled to be constant, which can avoid more heat consumption of the jacket and is more conducive to energy saving of the device.

[0030] According to some embodiments of the control method of the present invention, the low-melting-point material having a melting point lower than 25° C. in the crystal layer includes a liquid of para-xylene.

[0031] According to some embodiments of the control method described in the present invention, the high-melting-point material with a melting point higher than 25° C. in the crystal layer includes at least one of liquids of ethylene carbonate, glycolide, lactide, tetramethylene, p-dichlorobenzene, 2,6-diisopropylnaphthalene, etc.

[0032] According to some embodiments of the control method of the present invention, during the crystallization process, the temperature difference between the first heat agent in the external jacket and the temperature of the material to be crystallized is controlled to be 5-15°C.

[0033] In different embodiments of the present invention, during the crystallization process, by controlling the temperature difference between the first heat agent in the external jacket and the first coolant in the heat exchange element, the temperature difference between the first heat agent in the external jacket and the temperature of the material to be crystallized is 5-15°C, which can increase the crystallization temperature of the crystallization process by more than 3°C. In particular, for high-melting-point materials with a melting point of the crystal layer higher than 25°C, the crystallization temperature of the crystallization process can be increased by more than 8°C.

[0034] In the present invention, by increasing the temperature of the first heat agent in the external jacket to increase the temperature gradient between the heat exchange element and the wall of the crystallization device during the crystallization process, the supersaturation of the material to be crystallized in the crystallization device is significantly reduced, so that the material to be crystallized can be crystallized at a higher temperature, which not only greatly reduces the amount of cold required for the crystallization process, but also significantly improves the crystallization efficiency. In addition, the improvement of the crystallization efficiency not only means an increase in sweating crystals, but also helps to improve the yield of the static crystallization process. Furthermore, the improvement of the crystallization efficiency can reduce the concentration of the crystallization mother liquor, so that the crystallization mother liquor consumes less cold during recrystallization or secondary crystallization, thereby greatly reducing the energy consumption of the entire crystallization process, which is particularly effective in reducing the energy consumption of the multi-stage static crystallization process.

[0035] According to some embodiments of the control method of the present invention, during the sweating process, the temperature difference between the second refrigerant in the external jacket and the temperature of the crystal layer is controlled to be 5-20°C.

[0036] In different embodiments of the present invention, during the sweating process, by controlling the temperature difference between the second refrigerant in the external jacket and the second hot agent in the heat exchange element, the temperature difference between the second refrigerant in the external jacket and the temperature of the crystal layer is 5 to 20°C, which can reduce the sweating temperature of the sweating process by more than 1.5°C.

[0037] In the present invention, by lowering the temperature of the second refrigerant in the external jacket to increase the radial temperature difference between the heat exchange element and the wall of the crystallization device during the sweating process, the difficulty of sweat exudation caused by insufficient temperature difference between the two is avoided, so that the sweating process can be carried out at a lower sweating temperature and obtain the same sweating effect, significantly improving the sweating efficiency and reducing the energy consumption of the sweating process. At the same time, the improvement of the sweating efficiency ensures the quality of the product, and can avoid the need for an additional stage of crystallization and sweating when the product quality is unqualified due to insufficient sweating efficiency, and the resulting large amount of energy waste. Therefore, the above-mentioned sweating process plays a positive role in reducing the energy consumption of the entire static crystallization process.

[0038] According to some embodiments of the control method of the present invention, after the sweating process, the method further includes: introducing a third heat agent into the heat exchange element, wherein the temperature of the third heat agent is higher than the temperature of the second heat agent, so that the crystal layer on the heat exchange element is completely melted.

[0039] According to some embodiments of the control method of the present invention, the third heat agent is the same as the first coolant and the second heat agent, and can be selected from at least one of water, ethanol, ethylene glycol and heat transfer oil.

[0040] In different embodiments of the present invention, if necessary, the crystals after the sweating treatment are further subjected to secondary or more levels of static crystallization and sweating treatment to further improve the purity of the product to meet the product quality requirements, that is, the above-mentioned crystallization steps and sweating steps are repeated multiple times. At the same time, the crystallization mother liquor and sweating liquid produced after each level of static crystallization are subjected to secondary crystallization to further improve the yield of the product, that is, the above-mentioned crystallization steps are repeated. It can be foreseen that the more times of crystallization and sweating treatment involved in the entire static crystallization process, the more obvious the energy saving effect.

[0041] According to some embodiments of the control method of the present invention, the mass concentration of the component to be crystallized in the material to be crystallized is 15-99.5% based on the total weight of the material to be crystallized.

[0042] According to a preferred embodiment of the control method of the present invention, when the mass concentration of the component to be crystallized in the material to be crystallized is lower than 50%, the material to be crystallized is subjected to two-stage or multi-stage crystallization treatment and then to sweating treatment.

[0043] According to a preferred embodiment of the control method of the present invention, when the mass concentration of the component to be crystallized in the material to be crystallized is higher than 70%, the mother liquor after primary crystallization and sweating is mixed with sweat for secondary crystallization, thereby reducing the energy consumption of multi-stage crystallization and sweating process.

[0044] For the above-mentioned treatment process, on the one hand, the crystallization and sweating processes are optimized according to the difference in the concentration of the raw material components, thereby avoiding the energy waste caused by multiple sweating treatments of low-concentration raw material components and realizing the reasonable allocation and utilization of energy. More importantly, for the multi-stage static crystallization process, the efficiency of the previous stage crystallization and sweating process is improved by controlling the previous stage crystallization and sweating process, so that the concentration of the feed liquid entering the next stage crystallization process is lower, and the purity of the crystals entering the next stage sweating process is higher, thereby reducing the energy consumption of the next stage static crystallization process and improving the quality of the product.

[0045] In different embodiments of the present invention, for the crystallization process, the higher the concentration of the component to be crystallized in the material to be crystallized, the smaller the temperature difference between the first heat agent in the external jacket and the first coolant in the heat exchange element is controlled. For the sweating process, the higher the concentration of the crystal layer after crystallization, the smaller the temperature difference between the second coolant in the external jacket and the second heat agent in the heat exchange element is controlled.

[0046] For the above process, during the crystallization process, the higher the concentration of the component to be crystallized in the material to be crystallized, the smaller the supersaturation range of the material to be crystallized itself. At this time, the smaller temperature difference between the first hot agent in the external jacket and the first cold agent in the heat exchange element can achieve the purpose of reducing the supersaturation and realizing crystallization, avoiding excessive consumption of heat in the external jacket and achieving energy saving. In the sweating process, the higher the concentration of the crystal layer, the fewer impurities entrained in the crystal layer. At this time, the smaller temperature difference between the second cold agent in the external jacket and the second hot agent in the heat exchange element can ensure the sweating and exudation of impurities, avoiding excessive consumption of cold in the external jacket and achieving energy saving.

[0047] According to some embodiments of the control method of the present invention, the temperature of the material to be crystallized when it is fed into the crystallization device is 0.5-2° C. higher than the initial crystallization material of the material to be crystallized.

[0048] According to some embodiments of the control method of the present invention, the external jacket of the crystallization device includes an external cylinder jacket of the crystallization device, that is, a single jacket.

[0049] According to some embodiments of the control method of the present invention, the external jacket of the crystallization device includes an external barrel jacket of the crystallization device and a bottom barrel jacket of the crystallization device, that is, a double jacket.

[0050] According to a preferred embodiment of the control method of the present invention, the crystal layer is a high melting point crystal material with a melting point higher than 25°C, and preferably a crystallization device with the above double jacket structure is used. In addition, during the sweating process, a fourth heat agent is introduced into the bottom jacket of the bottom cylinder of the crystallization device, and the temperature of the fourth heat agent is 0 to 5°C higher than the end point sweating temperature of the crystal layer.

[0051] According to a preferred embodiment of the control method of the present invention, the crystal layer is a high melting point crystal material with a melting point higher than 25°C, and preferably a crystallization device with the above double jacket structure is used. In addition, during the sweating process, a fourth heat agent is introduced into the bottom jacket of the bottom cylinder of the crystallization device, and the temperature of the fourth heat agent is controlled to be 0-5°C higher than the melting point of the crystal layer.

[0052] According to some embodiments of the control method of the present invention, the fourth thermal agent is selected from at least one of water, ethanol, ethylene glycol and thermal oil.

[0053] For the above process, since the melting point of the high-melting-point crystallization material is relatively high, it is preferred to use a crystallization device with the above-mentioned double jacket structure. While the cylinder jacket controls the temperature difference between the heat exchange element and the wall during sweating to improve the sweating effect, the temperature of the cylinder bottom jacket is controlled to ensure that the higher concentration of sweat and high-purity crystal layer products in the later stage of sweating can be smoothly discharged from the crystallization device after melting.

[0054] The second aspect of the present invention provides an application of the above-mentioned static crystallization process control method in crystallization purification. Preferably, it is applied in the crystallization purification of ethylene carbonate, durene, p-dichlorobenzene, 2,6-diisopropylnaphthalene, glycolide, lactide and p-xylene. But it is not limited thereto.

[0055] Beneficial effects of the present invention:

[0056] (1) The control method of the static crystallization process provided by the present invention reduces the supersaturation of the crystallization process by controlling the temperature of the first hot agent in the external jacket to be higher than the temperature of the first cold agent in the heat exchange element during the crystallization process, thereby significantly improving the crystallization temperature and crystallization efficiency of the material to be crystallized and reducing the energy consumption of the crystallization process.

[0057] (2) During the sweating process, by controlling the temperature of the second coolant in the external jacket to be lower than the temperature of the second hot agent in the heat exchange element, the radial temperature difference between the heat exchange element and the wall of the crystallization device is increased, the sweating temperature of the crystal layer to be sweated is significantly reduced, and the energy consumption of the sweating process is reduced.

[0058] (3) The improvement of crystallization efficiency and sweating efficiency can not only further reduce the amount of cooling consumed by the crystallization mother liquor during recrystallization or secondary crystallization, but also reduce the number of stages in the static crystallization process, greatly reducing the energy consumption and cost of the entire static crystallization production process. DETAILED DESCRIPTION

[0059] In order to make the present invention more easily understood, the present invention will be described in detail below in conjunction with embodiments. These embodiments are only for illustration and are not intended to limit the application scope of the present invention.

[0060] [Example 1]

[0061] Crystallization process: A crude lactide solution with a mass concentration of 16.5% and a temperature of 34°C is sent to the crystallization device, and the first refrigerant ethylene glycol aqueous solution is introduced into the heat exchange element inside the crystallization device, and the first hot agent water is introduced into the outer jacket of the crystallization device. The water in the outer jacket is controlled to be constant at 45°C, and then gradually cooled from 45°C to 30°C after the crystallization point appears. The ethylene glycol aqueous solution in the heat exchange element is controlled to gradually cool down, and the material to be crystallized is also gradually cooled down. When the temperature of the ethylene glycol aqueous solution is 20°C and the temperature of the material to be crystallized is 32.84°C, crystals begin to precipitate on the surface of the heat exchange element. When the temperature of the ethylene glycol aqueous solution is 5°C and the temperature of the material to be crystallized is 20.50°C, the uncrystallized crystallization mother liquor is discharged from the bottom of the crystallization device. According to weight analysis, the crystallization rate (i.e., the weight percentage of crude crystals / raw materials) is 68.09%.

[0062] Sweating process: the second hot agent ethylene glycol aqueous solution is introduced into the heat exchange element, the second cold agent water is introduced into the outer cylinder jacket, and the fourth hot agent water is introduced into the bottom cylinder jacket. The temperature of the water in the outer cylinder jacket is controlled at 22°C, the temperature of the ethylene glycol aqueous solution in the heat exchange element is controlled to gradually rise from 30°C to 37°C, the temperature of the water in the outer cylinder bottom jacket is controlled at 40°C, and the corresponding crystal layer temperature is gradually raised from 29.15°C to 36.60°C. Impurities are discharged from the bottom of the crystallization device along with sweat. According to weight analysis, the sweating rate (percentage by weight of sweat / coarse crystals) is 58.02%.

[0063] After the sweating process is completed, the third heat agent ethylene glycol aqueous solution is continuously introduced into the heat exchange element, so that all the crystals remaining on the heat exchange element are melted and discharged from the bottom of the crystallization device.

[0064] [Example 2]

[0065] The operating procedure is the same as that of Example 1, except that the crude lactide solution raw material is replaced by ethylene carbonate raw material, wherein all the heating agents and cooling agents are water, and the specific temperature control conditions are shown in Table 1 below.

[0066] The crystallization rate of the obtained ethylene carbonate was 80.64%, and the sweating rate of the ethylene carbonate crystals was 49.98%.

[0067] [Example 3]

[0068] The operating procedure is the same as that of Example 1, except that the crude lactide solution raw material is replaced by glycolide raw material, and all the heating agents and cooling agents are heat transfer oils. The specific temperature control conditions are shown in Table 1 below.

[0069] The crystallization rate of the obtained glycolide was 70.22%, and the sweating rate of the glycolide crystals was 49.50%.

[0070] [Example 4]

[0071] The operating procedure is the same as that of Example 1, except that the crude lactide solution raw material is replaced by 2,6-diisopropylnaphthalene raw material, and all the heating agents and cooling agents are thermal oils. The specific temperature control conditions are shown in Table 1 below.

[0072] The crystallization rate of the obtained 2,6-diisopropylnaphthalene was 74.16%, and the sweating rate of the 2,6-diisopropylnaphthalene crystals was 49.15%.

[0073] [Example 5]

[0074] The operation procedure is the same as that of Example 1, except that the crude lactide solution raw material is replaced by durene raw material, wherein all the heating agents and cooling agents are heat transfer oils, and the specific temperature control conditions are shown in Table 1 below.

[0075] The crystallization rate of the obtained durene was 64.97%, and the sweating rate of the durene crystals was 55.24%.

[0076] [Example 6]

[0077] The operating procedure is the same as that of Example 1, except that the crude lactide solution raw material is replaced by p-dichlorobenzene raw material, wherein all the heating agents and cooling agents are water, and the specific temperature control conditions are shown in Table 1 below.

[0078] The obtained crystallization rate of p-dichlorobenzene was 61.73%, and the sweating rate of p-dichlorobenzene crystals was 51.33%.

[0079] Table 1

[0080] Example 2 Example 3 Example 4 Example 5 Example 6 Material concentration% 99.5 80 98 78 94 Raw material temperature ℃ 38 67 68.5 65.5 52 Crystallization process The first heat agent temperature of the jacket ℃ 42→24 80→64 72→59 78→58 58→50 Heat exchange element first refrigerant temperature ℃ 35→17 57→41 65→52 60→40 47→39 Initial crystallization temperature of the material 36.31 65.09 66.90 64.97 50.88 End point crystallization temperature of material 18.91 52.43 53.85 47.06 44.92 Crystallization rate % 80.64 70.22 74.16 64.97 61.73 Sweating process Second coolant temperature of cylinder jacket ℃ 28 60 56 62 40 The second heat medium temperature of the heat exchange element ℃ 35→36.8 75→80 63→67 72→77 49→52.5 The fourth heat agent temperature of the bottom jacket of the cylinder ℃ 39 85 71 80 54 Initial sweating temperature of crystal layer ℃ 34.41 74.04 61.82 71.28 48.35 Crystalline layer end point sweating temperature ℃ 36.73 79.11 66.49 76.22 52.08 Sweating rate% 49.98 49.50 49.15 55.24 51.33

[0081] [Example 7]

[0082] Crystallization process: a p-xylene solution with a mass concentration of 82% and a temperature of 12.5°C is fed into the crystallization device, a first refrigerant ethylene glycol aqueous solution is introduced into the heat exchange element inside the crystallization device, and a first hot agent anhydrous ethanol is introduced into the outer jacket of the crystallization device. The temperature of the anhydrous ethanol in the outer jacket is controlled at 15°C, and the temperature of the ethylene glycol aqueous solution in the heat exchange element is controlled to gradually decrease, and the temperature of the material to be crystallized is also gradually decreased. When the temperature of the ethylene glycol aqueous solution is 5°C and the temperature of the material to be crystallized is 9.90°C, crystals begin to precipitate on the surface of the heat exchange element. When the temperature of the ethylene glycol aqueous solution is -10°C and the temperature of the material to be crystallized is 0.95°C, the uncrystallized crystallization mother liquor is discharged from the bottom of the crystallization device. According to weight analysis, the crystallization rate (i.e., the weight percentage of coarse crystals / raw materials) is 60.40%.

[0083] Sweating process: a second hot agent, ethylene glycol aqueous solution, is introduced into the heat exchange element, and a second cold agent, anhydrous ethanol, is introduced into the external jacket; the temperature of the anhydrous ethanol in the external jacket is controlled to gradually rise from 0°C to 5°C, and the temperature of the ethylene glycol aqueous solution in the heat exchange element is controlled to gradually rise from 10°C to 12.5°C, and the corresponding crystal layer temperature gradually rises from 9.37°C to 12.14°C. Impurities are discharged from the bottom of the crystallization device along with sweat. After weight analysis, the sweating rate (weight percentage of sweat / coarse crystals) is 50.33%.

[0084] After the sweating process is completed, the third heat agent ethylene glycol aqueous solution is continuously introduced into the heat exchange element, so that all the crystals remaining on the heat exchange element are melted and discharged from the bottom of the crystallization device.

[0085] [Comparative Example 1]

[0086] Crystallization process: A crude lactide solution with a mass concentration of 16.5% and a temperature of 34°C is fed into the crystallization device, and the first refrigerant ethylene glycol aqueous solution is introduced into the heat exchange element inside the crystallization device. The ethylene glycol aqueous solution in the heat exchange element is controlled to gradually cool down. When the temperature of the ethylene glycol aqueous solution is 2°C and the temperature in the cavity of the device body is 16.92°C, crystals begin to adhere to the heat exchange element. The temperature is continuously lowered. When the temperature of the ethylene glycol aqueous solution is -5°C and the temperature in the cavity of the device body is 12.37°C, the mother liquor is discharged. According to gravimetric analysis, the crystallization rate of crude lactide is 55.46%.

[0087] Sweating process: The temperature of the ethylene glycol aqueous solution in the heat exchange element is gradually increased from 30°C to 37°C. After the sweating process is completed, the sweating rate of the crude lactide crystals is 48.35% according to weight analysis. Moreover, at the same sweating rate, the sweating temperature is continued to increase. When the terminal sweating temperature is 40.9°C, the sweating rate of the crude lactide crystals is 57.98%.

[0088] [Comparative Example 2]

[0089] The operating procedure is the same as that of Comparative Example 1, except that the crude lactide solution raw material is replaced by ethylene carbonate raw material, wherein all the heating agents and cooling agents are water, and the specific temperature control conditions are shown in Table 2 below.

[0090] The crystallization rate of the ethylene carbonate obtained in this comparative example is 73.25%, and the sweating rate of the ethylene carbonate crystals is 40.39%. When the sweating temperature is further increased and the terminal sweating temperature is 38.4°C, the sweating rate of the ethylene carbonate crystals is 49.97%.

[0091] [Comparative Example 3]

[0092] The operating procedure is the same as that of Comparative Example 1, except that the crude lactide solution raw material is replaced by glycolide raw material, and all the heating agents and cooling agents are heat transfer oils. Please see Table 2 below for specific temperature control conditions.

[0093] The crystallization rate of glycolide obtained in this comparative example is 61.70%, and the sweating rate of glycolide crystals is 39.97%. When the sweating temperature is further increased and the terminal sweating temperature is 82°C, the sweating rate of glycolide crystals is 49.44%.

[0094] [Comparative Example 4]

[0095] The operating procedure is the same as that of Comparative Example 1, except that the crude lactide solution raw material is replaced by 2,6-diisopropylnaphthalene raw material, and all the hot agents and cold agents are heat transfer oils. Please see Table 2 below for specific temperature control conditions.

[0096] The crystallization rate of 2,6-diisopropylnaphthalene obtained in this comparative example is 64.09%, and the sweating rate of 2,6-diisopropylnaphthalene crystals is 41.23%. When the sweating temperature is further increased and the terminal sweating temperature is 70°C, the sweating rate of 2,6-diisopropylnaphthalene crystals is 49.08%.

[0097] [Comparative Example 5]

[0098] The operating procedure is the same as that of Comparative Example 1, except that the crude lactide solution raw material is replaced by durene raw material, wherein all the hot agents and cold agents are heat transfer oils, and the specific temperature control conditions are shown in Table 2 below.

[0099] The crystallization rate of durenyl obtained in this comparative example is 54.14%, and the sweating rate of durenyl crystals is 47.62%. When the sweating temperature is further increased and the terminal sweating temperature is 78.9° C., the sweating rate of durenyl crystals is 55.20%.

[0100] [Comparative Example 6]

[0101] The operating procedure is the same as that of Comparative Example 1, except that the crude lactide solution raw material is replaced by p-dichlorobenzene raw material, wherein all the heating agents and cooling agents are water, and the specific temperature control conditions are shown in Table 2 below.

[0102] The crystallization rate of p-dichlorobenzene obtained in this comparative example is 50.56%, and the sweating rate of p-dichlorobenzene crystals is 43.58%. When the sweating temperature is further increased and the terminal sweating temperature is 54° C., the sweating rate of p-dichlorobenzene crystals is 51.29%.

[0103] [Comparative Example 7]

[0104] The operating procedure is the same as that of Comparative Example 1, except that the crude lactide solution raw material is replaced by p-xylene raw material, wherein all the hot agents and cold agents are ethylene glycol aqueous solutions, and the specific temperature control conditions are shown in Table 2 below.

[0105] The crystallization rate of p-xylene obtained in this comparative example is 50.13%, and the sweating rate of p-xylene crystals is 41.45%. When the sweating temperature is further increased and the terminal sweating temperature is 14°C, the sweating rate of p-xylene crystals is 50.30%.

[0106] Table 2

[0107] Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 Comparative Example 7 Raw material temperature ℃ 38 67 68.5 65.5 52 12.5 Crystallization process Initial crystallization point The first heat transfer medium temperature ℃ 26 42 53.5 45 39 1 Temperature inside the device ℃ 28.19 52.68 57.47 52.36 42.52 6.74 Crystallization endpoint The first heat transfer medium temperature ℃ 7 30 41 28 27 -15 Temperature inside the device ℃ 10.85 43.93 45.74 37.52 34.33 -4.06 Crystallization rate % 73.25 61.70 64.09 54.14 50.56 50.13 Sweating process Initial sweating temperature ℃ 35 75 63 72 49 10 End point sweating temperature 36.8 80 67 77 52.5 12.5 Sweating rate% 40.39 39.97 41.23 47.62 43.58 41.45 End point sweating temperature 38.4 82 70 78.9 54 14 Sweating rate% 49.97 49.44 49.08 55.20 51.29 50.30

[0108] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this field, under the technical enlightenment provided by the present invention, as common knowledge in the field, other equivalent variations and improvements can also be made, which should also be regarded as the protection scope of the present invention.

Claims

1. A control method for a static crystallization process, the control method comprising: Crystallization process: the material to be crystallized is fed into a crystallization device, a first refrigerant is introduced into a heat exchange element inside the crystallization device, a first hot agent is introduced into an outer jacket of the crystallization device, the temperature of the first hot agent is higher than the temperature of the material to be crystallized, the first refrigerant in the heat exchange element is controlled to gradually cool down, so that the material to be crystallized crystallizes and precipitates a crystal layer, and the remaining mother liquor of the crystallization process is discharged after crystallization; Sweating process: a second heat agent is introduced into the heat exchange element, the temperature of the second heat agent is controlled to be higher than the temperature of the crystal layer, and the crystal layer is sweated to precipitate impurities in the crystal layer; the external jacket of the crystallization device includes an external cylinder jacket of the crystallization device and a bottom jacket of the bottom cylinder of the crystallization device, a second coolant is introduced into the external cylinder jacket of the crystallization device, the temperature of the second coolant is controlled to be lower than the temperature of the crystal layer, a fourth heat agent is introduced into the bottom jacket of the bottom cylinder of the crystallization device, the temperature of the fourth heat agent is 0 to 5°C higher than the end sweating temperature of the crystal layer and / or the temperature of the fourth heat agent is 0 to 5°C higher than the melting point of the crystal layer.

2. The control method according to claim 1, characterized in that: The first coolant and the second heat agent are the same and are selected from at least one of water, ethanol, ethylene glycol and heat transfer oil; and / or, The first heat agent and the second coolant are the same and are selected from at least one of water, ethanol, ethylene glycol and heat transfer oil.

3. The control method according to claim 1 or 2, characterized in that: The melting point of the crystalline layer is lower than 25°C.

4. The control method according to claim 3, characterized in that: Crystallization process: controlling the temperature of the first heat agent in the outer jacket to be constant; and / or, Sweating process: Control the temperature difference between the second refrigerant in the outer cylinder jacket of the crystallization device and the second hot agent in the heat exchange element to be 7-20°C.

5. The control method according to claim 4, characterized in that: Crystallization process: Control the temperature of the first hot agent in the external jacket to be 7-25° C. higher than the initial temperature of the first cold agent in the heat exchange element.

6. The control method according to claim 1 or 2, characterized in that: The melting point of the crystalline layer is higher than 25°C.

7. The control method according to claim 6, characterized in that: Crystallization process: controlling the temperature difference between the first heat medium in the outer jacket and the first coolant in the heat exchange element to be 7-25° C.; and / or, Sweating process: Control the temperature of the second refrigerant in the outer cylinder jacket of the crystallization device to be constant.

8. The control method according to claim 7, characterized in that: Sweating process: Control the temperature of the second coolant in the outer cylinder jacket of the crystallization device to be 7-20° C. lower than the temperature of the second hot agent in the heat exchange element.

9. The control method according to claim 1 or 2, characterized in that: During the crystallization process, the temperature difference between the first heat agent in the external jacket and the temperature of the material to be crystallized is controlled to be 5-15°C.

10. The control method according to claim 1 or 2, characterized in that: During the sweating process, the temperature difference between the second refrigerant in the outer cylinder jacket of the crystallization device and the temperature of the crystal layer is controlled to be 5 to 20°C.

11. The control method according to claim 1 or 2, characterized in that: After the sweating process, the method further includes: introducing a third heat agent into the heat exchange element, wherein the temperature of the third heat agent is higher than the temperature of the second heat agent, so that the crystal layer on the heat exchange element is completely melted.

12. The control method according to claim 1 or 2, characterized in that: The mass concentration of the component to be crystallized in the material to be crystallized is 15 to 99.5% based on the total weight of the material to be crystallized; and / or, The temperature of the material to be crystallized when it is fed into the crystallization device is 0.5-2° C. higher than that of the initial crystallization material of the material to be crystallized.

13. Use of the static crystallization process control method according to any one of claims 1 to 12 in crystallization purification.

14. The use according to claim 13, characterized in that The application is application in the crystallization and purification of ethylene carbonate, durene, p-dichlorobenzene, 2,6-diisopropylnaphthalene, glycolide, lactide and p-xylene.