Method for purifying sodium fluoborate pyrolysis kettle residues

Abstract

The invention discloses a method for purifying sodium fluoborate pyrolysis kettle residues, which comprises the following steps: heating a sodium fluoborate pyrolysis kettle residue and water, cooling, crystallizing and centrifuging to obtain a sodium fluoride extract and a filtrate I; as the content of sodium fluoride in the sodium fluoborate pyrolysis residual kettle is in a range of 15-20%, the solubility of sodium fluoride can be improved by heating the sodium fluoborate pyrolysis residual kettle and water and dissolving sodium fluoborate, sodium fluoride and sodium chloride in water and in a sodium fluoborate solution, and then the solubility of sodium fluoride can be improved by cooling crystallization under the condition that the temperature is reduced. Sodium fluoride is separated out firstly, sodium fluoborate and sodium chloride are left in the solution, sodium fluoride is purified in a centrifugal mode, and the utilization rate of sodium fluoride is increased.

Description

Technical Field

[0001] The present application relates to the technical field of separation and purification, and in particular to a method for purifying sodium fluoroborate pyrolysis kettle residue. Background Art

[0002] When sodium fluoroborate is used to prepare boron trifluoride, a pyrolysis residue is obtained. The pyrolysis residue contains a large amount of sodium chloride, a small amount of sodium fluoride, and a trace amount of sodium fluoroborate. Since the solubility of sodium fluoride increases in the aqueous solution in the presence of sodium fluoroborate, it is difficult to purify the sodium fluoride in the pyrolysis residue, which limits the recycling rate of sodium fluoride. Summary of the Invention

[0003] The present application is made in view of the above-mentioned problems, and its purpose is to provide a method for purifying sodium fluoroborate pyrolysis kettle residue, so as to purify sodium fluoride in the sodium fluoroborate pyrolysis kettle residue.

[0004] In order to achieve the above-mentioned purpose, the present invention provides a method for purifying sodium chloride and sodium fluoroborate from the synthetic waste liquid of sodium fluoroborate.

[0005] In a first aspect, the present invention provides a method for purifying sodium fluoroborate pyrolysis reactor residue, comprising the following steps:

[0006] Heat the residual kettle of sodium fluoroborate pyrolysis with water, cool it down, crystallize it, and centrifuge it to obtain sodium fluoride extract and filtrate 1.

[0007] Therefore, in the technical solution of the embodiment of the present application, since there is a large amount of sodium chloride, a small amount of sodium fluoride, and a trace amount of sodium fluoride in the sodium fluoride pyrolysis residue, the solubility of sodium chloride in water at 25°C is 36.2g, and the solubility of sodium chloride in water at 100°C is 39.8g. The solubility of sodium fluoride in water at 25°C is 107g, and the solubility of sodium fluoride in water at 100°C is 210g. The solubility of sodium fluoride in water at 25°C is 4.14g, and the solubility of sodium fluoride in water at 100°C is 5.08g. Since the content of sodium fluoride in the sodium fluoborate pyrolysis residue is within the range of 15% to 20%, the sodium fluoborate pyrolysis residue can be heated with water to dissolve sodium fluoborate, sodium fluoride and sodium chloride in the water. This can increase the solubility of sodium fluoride in the sodium fluoborate solution. Then, by cooling and crystallizing, sodium fluoride is precipitated first when the temperature is lowered, while sodium fluoborate and sodium chloride remain in the solution. Sodium fluoride can be purified by centrifugation, thereby improving the utilization rate of sodium fluoride.

[0008] In any embodiment of the present application, the heating temperature is 70-90° C. Within this temperature range, it is beneficial to increase the amount of dissolved sodium fluoride, because increasing the temperature can promote the dissolution of each component into the solution, thereby increasing the yield of sodium fluoride; optionally, the heating temperature is 75-85° C., which can further increase the yield of sodium fluoride; and / or,

[0009] The crystallization temperature is 20-30°C. Within this temperature range, the sodium fluoride dissolved in the solution can be fully crystallized, which can improve the yield of sodium fluoride; optionally, the crystallization temperature is 23-27°C, which can further improve the yield of sodium fluoride; and / or,

[0010] The crystallization time is 0.5 to 3 hours. During this crystallization time, sodium fluoride can be fully crystallized from the solution, which is beneficial to improving the yield of sodium fluoride; optionally, the crystallization time is 0.5 to 1.5 hours, which can further improve the yield of sodium fluoride; and / or,

[0011] The crystallization process includes stirring crystallization, which can make the crystallization system more uniform and help improve the stability of crystallization separation.

[0012] In any embodiment of the present application, after heating the sodium fluoborate pyrolysis residue with water, cooling, crystallizing, and centrifuging to obtain a sodium fluoride extract and a first filtrate, the method further includes: heating and concentrating the first filtrate under vacuum conditions, cooling, crystallizing, and centrifuging to obtain a first filter residue and a second filtrate; rinsing and filtering the first filter residue to obtain a third filter residue and a second filter residue; and drying the second filter residue to obtain a sodium chloride extract. The first filter residue contains a large amount of sodium chloride, a small amount of sodium fluoborate, and a trace amount of sodium fluoride. By heating, concentrating, cooling, and crystallizing, most of the sodium chloride can be crystallized and precipitated. By centrifugation, the filter residue containing a large amount of sodium chloride can be separated. After rinsing, a small amount of sodium chloride, a trace amount of sodium fluoborate, and a small amount of sodium fluoride can be retained in the third filter residue, thereby purifying the sodium chloride.

[0013] In any embodiment of the present application, the filtrate 1 is heated and concentrated under vacuum conditions, cooled, crystallized, and centrifuged to obtain a filter residue 1 and a filtrate 2, the filter residue 1 is rinsed and filtered to obtain a filtrate 3 and a filter residue 2, and the filter residue 2 is dried to obtain a sodium chloride extract: the vacuum pressure is -0.1 to -0.054 MPa. Within this pressure range, water can be gradually removed from the filtrate 1, and at the same time, sodium chloride gradually reaches supersaturation and gradually crystallizes and precipitates. Optionally, the vacuum pressure is -0.095 to -0.085 MPa, which can further improve the crystallization effect; and / or,

[0014] The heating and concentration temperature is 70-90° C. Within this temperature range, the water in the system is rapidly evaporated under vacuum, and sodium chloride gradually crystallizes out of the system. Due to the appropriate crystallization speed, the inclusion of sodium fluoroborate and sodium fluoride can be reduced, thereby improving the purity of sodium chloride. Optionally, the heating temperature is 70-75° C., the crystallization speed is more stable, and the purity of sodium chloride can be further improved; and / or,

[0015] The solid content of the heated concentrated solution is 50-70%. Within this solid content range, most of the sodium chloride is fully crystallized during the evaporation and cooling process. At this time, since the sodium fluoborate is just close to the saturation state, and the solubility of sodium fluoride in the system increases due to the affinity of sodium fluoborate, neither sodium fluoborate nor sodium fluoride will crystallize in large quantities. At this time, only trace amounts of sodium fluoborate and sodium fluoride are mixed in the crystals, which can improve the purity of the sodium chloride. Optionally, the solid content of the concentrated solution is 58%-62%, which can further improve the purity of the sodium chloride. And / or,

[0016] The crystallization temperature is 25-40° C. At this crystallization temperature, part of the sodium chloride that failed to crystallize during the evaporation process is further crystallized, which can increase the yield of sodium chloride; optionally, the crystallization temperature is 23-27° C., which can further increase the yield of sodium chloride; and / or,

[0017] The crystallization time is 0.5 to 3 hours. Under this crystallization time, sodium chloride can be fully precipitated. At the same time, due to the redissolution of the previously crystallized sodium borate and sodium fluoride by water, more sodium chloride crystals are formed, which can increase the yield of sodium chloride. Optionally, the crystallization time is 0.5 to 1.5 hours, which can further increase the yield of sodium chloride; and / or,

[0018] The crystallization process includes stirring crystallization. The stirring crystallization method can make the crystallization system more uniform, which is beneficial to improving the stability of the crystallization.

[0019] In any embodiment of the present application, the filtrate 1 is heated and concentrated under vacuum conditions, cooled, crystallized, and centrifuged to obtain a filter residue 1 and a filtrate 2, the filter residue 1 is rinsed and filtered to obtain a filtrate 3 and a filter residue 2, and the filter residue 2 is dried to obtain a sodium chloride extract:

[0020] The mass ratio of the filter residue to the flushing liquid is (1.7-2.5):1. Under this mass ratio, the crystalline sodium fluoride and sodium fluoroborate can be dissolved, and the dissolution of sodium chloride can be reduced, thereby improving the yield and purity of sodium chloride; and / or,

[0021] The drying temperature is 100-150°C. At this drying temperature, the water in the system is evaporated quickly, and the obtained crystals are relatively uniform in size, have good fluidity, and are easy to discharge. Optionally, the evaporation drying temperature is 110-130°C, which can further stabilize the evaporation drying effect; and / or,

[0022] The drying pressure is -0.1 to 0 MPa. The operating pressure is selected according to the drying temperature. When the drying temperature is 100 to 150° C., the operating pressure is at a point or range of -0.1 to -0.08 MPa, and the drying effect is good. Alternatively, when the drying temperature is 110 to 130° C., the operating pressure is at a point or range of -0.095 to -0.085 MPa, and the drying effect is more stable and better. And / or,

[0023] The drying time is 3 to 10 hours. Under this drying time, the moisture attached to the crystal surface and the moisture hidden in the crystal gaps can have more time to evaporate. The moisture attached to the crystal surface is easier to evaporate, so most of it will be removed in the early stage of drying. The moisture hidden in the crystal gaps has a strong binding ability for moisture due to the action of capillaries, and it takes a relatively longer time to force it to leave the crystal gaps. Therefore, the water removal is fast in the early stage of drying and slow in the later stage. Optionally, the drying time is 4 to 6 hours, which can improve production efficiency while meeting the moisture requirements.

[0024] In any embodiment of the present application, the step of heating and concentrating the filtrate 1 under vacuum conditions, cooling, crystallizing, and centrifuging to obtain a first filter residue and a second filter residue, washing and filtering the first filter residue to obtain a third filter residue and a second filter residue, and drying the second filter residue to obtain a sodium chloride extract further comprises:

[0025] Mix the filtrate 2 and the filtrate 3, and heat and evaporate them under vacuum conditions to obtain a mixed salt;

[0026] The mixed salt is mixed with the organic solvent and centrifuged to obtain a filter residue 3 and a filtrate 4;

[0027] The filtrate 4 was heated and evaporated under vacuum conditions to obtain a sodium fluoroborate extract.

[0028] Mixed salts contain a large amount of sodium chloride, a small amount of sodium fluoborate, and trace amounts of sodium fluoride. Using organic solvents to dissolve the specific component, sodium fluoborate, from the mixed salts, achieving separation. Ethylene glycol dimethyl ether has a good solubility for sodium fluoborate, while having little solubility for sodium chloride and sodium fluoride. Its solubility in sodium fluoborate measured at room temperature is 2.02g, allowing for the specific purification of sodium fluoborate, effectively resolving the technical challenge of extracting sodium fluoborate from mixed salts.

[0029] In any embodiment of the present application, the filtrate 2 and the filtrate 3 are mixed, heated and evaporated under vacuum conditions to obtain a mixed salt:

[0030] The vacuum pressure is -0.1 to 0 MPa. Within this pressure range, water can be gradually removed from the mixture of filtrate 2 and filtrate 3, and at the same time, the salts of each component in the mixture gradually reach supersaturation and gradually crystallize out. Optionally, the vacuum pressure is -0.095 to -0.085 MPa, which can further improve the yield of the mixed salt; and / or,

[0031] The heating temperature is 70-120°C. Within this temperature range, the water in the system is rapidly evaporated, the crystallization rate is more stable, and each component salt gradually crystallizes out of the system, thereby improving the yield of the mixed salt; optionally, the heating temperature is 80-100°C, the crystallization rate is more stable, and the yield of the mixed salt can be further improved; and / or,

[0032] The heating time is 1 to 10 hours. Under this heating time, the mixed solution can be fully evaporated to dryness and the mixed salt can be precipitated, thereby improving the yield of the mixed salt. Optionally, the heating time is 2 to 4 hours, which can further improve the yield of the mixed salt.

[0033] In any embodiment of the present application, the mixed salt includes sodium fluoride, sodium chloride and sodium fluoroborate, and the sodium fluoroborate still residue contains a thermal cracking product of a mixture of sodium fluoroborate and sodium chloride, wherein the pyrolysis of sodium fluoroborate generates sodium fluoride and boron trifluoride, and boron trifluoride can react with sodium fluoride to generate sodium fluoroborate, and boron trifluoride can be discharged as a gaseous product, while sodium chloride does not participate in the reaction. Therefore, the pyrolysis still residue contains three components: sodium fluoride, sodium chloride and sodium fluoroborate. After the sodium fluoride and sodium chloride are extracted from the pyrolysis still residue, the sodium fluoride and sodium chloride still remain, and form a mixed salt with the unextracted sodium fluoroborate; and / or,

[0034] The organic solvent includes ethylene glycol dimethyl ether. By using this organic solvent, sodium fluoroborate in the mixed salt can be dissolved without dissolving other substances, and sodium fluoroborate can be selectively separated.

[0035] In any embodiment of the present application, the mixed salt is mixed with the organic solvent and centrifuged to obtain a filter residue three and a filtrate four:

[0036] The mass ratio of the mixed salt to the organic solvent is (0.22-0.28):1. At this mass ratio, a sufficient amount of solvent can be provided to dissolve and wash away the sodium fluoroborate in the mixed salt, thereby improving the yield of sodium fluoroborate. Optionally, the mass ratio of the mixed salt to the organic solvent is (0.24-0.26):1, which can further improve the yield of sodium fluoroborate.

[0037] In any embodiment of the present application, the mixed salt is mixed with the organic solvent and centrifuged to obtain a filter residue three and a filtrate four:

[0038] The mixing temperature is 20-30° C. At this temperature, ethylene glycol dimethyl ether has sufficient solubility for sodium fluoroborate in the mixed salt, which can reduce energy consumption; optionally, the mixing temperature is 23-27° C., which can further reduce energy consumption; and / or,

[0039] The mixing time is 0.5 to 3 hours. Under this mixing time, the sodium fluoborate in the mixed salt can be fully dissolved. First, the sodium fluoborate exposed on the crystal surface will be dissolved quickly, while the sodium fluoborate trapped inside the crystal will not be easily dissolved. After a period of stirring, friction and crushing will occur between the crystals, or the sodium fluoborate will be dissolved through slow migration in the crystal gap channel, thereby increasing the yield of sodium fluoborate. Optionally, the mixing time is 0.5 to 1.5 hours, which can improve the dissolution efficiency.

[0040] In any embodiment of the present application, the filtrate 4 is heated and evaporated under vacuum conditions to obtain the sodium fluoborate extract:

[0041] The vacuum pressure is -0.1 to 0 MPa. Within this pressure range, ethylene glycol dimethyl ether can be gradually removed from the filtrate 4. At the same time, sodium fluoroborate gradually reaches supersaturation and gradually crystallizes and precipitates, thereby increasing the yield of sodium fluoroborate. Optionally, the vacuum pressure is -0.095 to -0.085 MPa, which can further improve the stability of the evaporation operation and reduce energy consumption. And / or,

[0042] The temperature of the heating evaporation is 50-90°C. At this temperature, ethylene glycol dimethyl ether can be gradually removed from the filtrate 4. At the same time, sodium fluoroborate gradually reaches supersaturation and gradually crystallizes out. At a temperature of 50-85°C, reduced pressure evaporation should be adopted; at a temperature of 85-90°C, normal pressure evaporation can be adopted. Generally, reduced pressure evaporation has higher efficiency. Optionally, the heating evaporation temperature is 60-80°C, the crystallization speed is more stable, the obtained mixed salt particle size is more uniform and stable, and the evaporation effect can be further improved. DETAILED DESCRIPTION

[0043] The following specifically discloses embodiments of the method for purifying sodium fluoroborate pyrolysis still residue of the present application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repeated descriptions of substantially identical structures may be omitted. This is to avoid unnecessary length in the following description and to facilitate understanding by those skilled in the art. Furthermore, the following description is provided to enable those skilled in the art to fully understand the present application and is not intended to limit the subject matter recited in the claims.

[0044] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0045] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0046] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0047] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0048] When sodium fluoroborate is used to prepare boron trifluoride, a pyrolysis residue is obtained. The pyrolysis residue contains a large amount of sodium chloride (about 79%), a small amount of sodium fluoride (about 17%), and a trace amount of sodium fluoroborate (about 4%). Since the solubility of sodium fluoride increases in the aqueous solution containing sodium fluoroborate, it is difficult to purify the sodium fluoride in the pyrolysis residue, which limits the recycling rate of sodium fluoride.

[0049] Therefore, there is an endless stream of research on the purification of sodium fluoride. For example, a method for producing and extracting sodium fluoride and sodium chloride from acidic wastewater containing fluorine and chlorine comprises neutralizing the wastewater with sodium hydroxide to obtain a solution of sodium fluoride and sodium chloride, which is then concentrated, crystallized, centrifuged, and the filter cake is dried to obtain sodium fluoride. The mother liquor containing sodium fluoride and sodium chloride is reacted with calcium chloride to obtain calcium fluoride with minimal solubility. The calcium fluoride is then filtered and the filter cake is dried to obtain calcium fluoride. The mother liquor is then filtered and concentrated, crystallized, centrifuged, and the filter cake is dried to obtain sodium chloride. However, this method has the following problems with extracting sodium fluoride and sodium chloride: first, it requires the consumption of calcium chloride and produces a new by-product, calcium fluoride, making it difficult to obtain sodium fluoride.

[0050] Based on this, the present application provides a method for purifying sodium fluoroborate pyrolysis kettle residue.

[0051] In a first aspect, the present invention provides a method for purifying sodium fluoroborate pyrolysis reactor residue, comprising the following steps:

[0052] Heat the residual kettle of sodium fluoroborate pyrolysis with water, cool it down, crystallize it, and centrifuge it to obtain sodium fluoride extract and filtrate 1.

[0053] Therefore, in the technical solution of the embodiment of the present application, since there is a large amount of sodium chloride, a small amount of sodium fluoride, and a trace amount of sodium fluoride in the sodium fluoride pyrolysis residue, the solubility of sodium chloride in water at 25°C is 36.2g, and the solubility of sodium chloride in water at 100°C is 39.8g. The solubility of sodium fluoride in water at 25°C is 107g, and the solubility of sodium fluoride in water at 100°C is 210g. The solubility of sodium fluoride in water at 25°C is 4.14g, and the solubility of sodium fluoride in water at 100°C is 5.08g. Since the content of sodium fluoride in the sodium fluoborate pyrolysis residue is within the range of 15% to 20%, the sodium fluoborate pyrolysis residue can be heated with water to dissolve sodium fluoborate, sodium fluoride and sodium chloride in the water. This can increase the solubility of sodium fluoride in the sodium fluoborate solution. Then, by cooling and crystallizing, sodium fluoride is precipitated first when the temperature is lowered, while sodium fluoborate and sodium chloride remain in the solution. Sodium fluoride can be purified by centrifugation, thereby improving the utilization rate of sodium fluoride.

[0054] In any embodiment of the present application, the heating temperature is 70 to 90° C. Within this temperature range, it is beneficial to increase the amount of dissolved sodium fluoride, because increasing the temperature can promote the dissolution of each component into the solution, thereby increasing the yield of sodium fluoride; the heating temperature can be 70° C., 75° C., 80° C., 85° C. or 90° C.; optionally, the heating temperature is 75 to 85° C., which can further increase the yield of sodium fluoride.

[0055] In any embodiment of the present application, the crystallization temperature is 20-30°C, and the sodium fluoride dissolved in the solution can be fully crystallized, which can improve the yield of sodium fluoride; optionally, the crystallization temperature is 23-27°C, which can further improve the yield of sodium fluoride. The crystallization temperature can be 20°C, 21°C, 22°C, 23°C, 24°C, 25°C, 26°C, 27°C, 28°C, 29°C or 30°C; optionally, the crystallization temperature is 23-27°C, which can further improve the yield of sodium fluoride.

[0056] In any embodiment of the present application, the crystallization time is 0.5 to 3 hours. During this crystallization time, sodium fluoride can be fully crystallized from the solution, which is beneficial to improving the yield of sodium fluoride. The crystallization time can be 0.5 hours, 1 hour, 1.5 hours, 2 hours, 2.5 hours, or 3 hours; optionally, the crystallization time is 0.5 to 1.5 hours, which can further improve the yield of sodium fluoride.

[0057] In any embodiment of the present application, the crystallization process includes stirring crystallization, which can make the crystallization system more uniform and help improve the stability of crystallization separation.

[0058] In any embodiment of the present application, after heating the sodium fluoborate pyrolysis residue with water, cooling, crystallizing, and centrifuging to obtain a sodium fluoride extract and a first filtrate, the method further includes: heating and concentrating the first filtrate under vacuum conditions, cooling, crystallizing, and centrifuging to obtain a first filter residue and a second filtrate; rinsing and filtering the first filter residue to obtain a third filter residue and a second filter residue; and drying the second filter residue to obtain a sodium chloride extract. The first filter residue contains a large amount of sodium chloride, a trace amount of sodium fluoborate, and a small amount of sodium fluoride. By heating, concentrating, cooling, and crystallizing, most of the sodium chloride can be crystallized and precipitated. By centrifugation, the filter residue containing a large amount of sodium chloride can be separated. After rinsing, a small amount of sodium chloride, a small amount of sodium fluoborate, and a trace amount of sodium fluoride can be left in the third filter residue, thereby purifying the sodium chloride.

[0059] In any embodiment of the present application, the filtrate one is heated and concentrated under vacuum conditions, cooled, crystallized, and centrifuged to obtain a filter residue one and a filtrate two, the filter residue one is rinsed and filtered to obtain a filtrate three and a filter residue two, and the filter residue two is dried to obtain a sodium chloride extract: the vacuum pressure is -0.1 to -0.054 MPa. Within this pressure range, water can be gradually removed from the filtrate one, and at the same time, sodium chloride gradually crystallizes and precipitates due to gradual supersaturation. Optionally, the vacuum pressure is -0.095 to -0.085 MPa, which can further improve the crystallization effect.

[0060] The heating and concentrating temperature is 70-90° C. Within this temperature range, water in the system is rapidly evaporated under vacuum, and sodium chloride gradually crystallizes out of the system. Due to the appropriate crystallization speed, the inclusion of sodium fluoroborate and sodium fluoride can be reduced, thereby improving the purity of the sodium chloride. The heating and concentrating temperature can be 70° C., 75° C., 80° C., 85° C. or 90° C.; optionally, the heating and concentrating temperature is 65-75° C., which can further improve the purity of the sodium chloride.

[0061] In any embodiment of the present application, the filtrate 1 is heated and concentrated under vacuum conditions, cooled, crystallized, and centrifuged to obtain a filter residue 1 and a filtrate 2, the filter residue 1 is rinsed and filtered to obtain a filtrate 3 and a filter residue 2, and the filter residue 2 is dried to obtain a sodium chloride extract: the solid content of the heated concentration is 50-70%. Within this solid content range, most of the sodium chloride is fully crystallized during the evaporation and cooling process. At this time, since the sodium fluoborate is just close to saturation, and the solubility of sodium fluoride in the system increases due to the affinity of sodium fluoborate, neither sodium fluoborate nor sodium fluoride will crystallize in large quantities. At this time, only trace amounts of sodium fluoborate and sodium fluoride are mixed in the crystals, which can improve the purity of the sodium chloride. The solid content of the heated concentration can be 50%, 55%, 60%, 65%, or 70%; alternatively, the solid content of the concentrate is 58%-62%, which can further improve the purity of the sodium chloride.

[0062] In any embodiment of the present application, the filtrate 1 is heated and concentrated under vacuum conditions, cooled, crystallized, and centrifuged to obtain a filter residue 1 and a filtrate 2, the filter residue 1 is rinsed and filtered to obtain a filtrate 3 and a filter residue 2, and the filter residue 2 is dried to obtain a sodium chloride extract: the crystallization temperature is 25 to 40°C. At this crystallization temperature, part of the sodium chloride that failed to crystallize during the evaporation process further crystallizes, which can increase the yield of sodium chloride. The crystallization temperature can be 25°C, 30°C, 35°C or 40°C; optionally, the crystallization temperature is 23 to 27°C, which can further increase the yield of sodium chloride.

[0063] In any embodiment of the present application, the filtrate 1 is heated and concentrated under vacuum conditions, cooled, crystallized, and centrifuged to obtain a filter residue 1 and a filtrate 2, the filter residue 1 is rinsed and filtered to obtain a filtrate 3 and a filter residue 2, and the filter residue 2 is dried to obtain a sodium chloride extract: the crystallization time is 0.5 to 3 hours. At this crystallization time, sodium chloride can be fully precipitated. At the same time, due to the redissolution effect of water on the previously crystallized sodium fluoroborate and sodium fluoride, more sodium chloride crystals are obtained, which can improve the yield of sodium chloride. The crystallization time can be 0.5 hours, 1 hour, 1.5 hours, 2 hours, 2.5 hours or 3 hours; optionally, the crystallization time is 0.5 to 1.5 hours, which can further improve the yield of sodium chloride.

[0064] In any embodiment of the present application, the filtrate 1 is heated and concentrated under vacuum conditions, cooled, crystallized, and centrifuged to obtain a filter residue 1 and a filtrate 2, the filter residue 1 is rinsed and filtered to obtain a filtrate 3 and a filter residue 2, and the filter residue 2 is dried to obtain a sodium chloride extract: the crystallization process includes stirred crystallization. The use of stirred crystallization can make the crystallization system more uniform, which is beneficial to improving the stability of the crystallization.

[0065] In any embodiment of the present application, the filtrate 1 is heated and concentrated under vacuum conditions, cooled, crystallized, and centrifuged to obtain a filter residue 1 and a filtrate 2, the filter residue 1 is rinsed and filtered to obtain a filtrate 3 and a filter residue 2, and the filter residue 2 is dried to obtain a sodium chloride extract: the mass ratio of the filter residue 1 to the rinsing liquid is (1.7 to 2.5):1. At this mass ratio, the crystallized sodium fluoride and sodium fluoroborate can be dissolved and the dissolution of sodium chloride can be reduced. The mass ratio of the filter residue 1 to the rinsing liquid can be 1.7:1, 1.8:1, 1.9:1, 2.0:1, 2.1:1, 2.2:1, 2.3:1, 2.4:1 or 2.5:1.

[0066] In any embodiment of the present application, the filtrate 1 is heated and concentrated under vacuum conditions, cooled, crystallized, and centrifuged to obtain a filter residue 1 and a filtrate 2, the filter residue 1 is rinsed and filtered to obtain a filtrate 3 and a filter residue 2, and the filter residue 2 is dried to obtain a sodium chloride extract: the drying pressure is -0.1 to 0 MPa, and the operating pressure is selected according to the drying temperature. When drying, 100 to 150°C is used, and the operating pressure is in the range of -0.1 to -0.08 MPa, and the drying effect is good; when drying, 110 to 130°C is used, and the operating pressure is in the range of -0.095 to -0.085 MPa, and the drying is more stable and the effect is better.

[0067] In any embodiment of the present application, the filtrate 1 is heated and concentrated under vacuum conditions, cooled, crystallized, and centrifuged to obtain a filter residue 1 and a filtrate 2, the filter residue 1 is rinsed and filtered to obtain a filtrate 3 and a filter residue 2, and the filter residue 2 is dried to obtain a sodium chloride extract: the drying temperature is 100-150°C. At this drying temperature, the water in the system is rapidly evaporated, and the obtained crystal particle size is relatively uniform, the fluidity is good, and it is easy to discharge. The drying temperature can be 100°C, 110°C, 120°C, 130°C, 140°C or 150°C; optionally, the drying temperature is 110-130°C, which can further stabilize the effect of evaporation and drying.

[0068] In any embodiment of the present application, the filtrate 1 is heated and concentrated under vacuum conditions, cooled, crystallized, and centrifuged to obtain filter residue 1 and filtrate 2, the filter residue 1 is rinsed and filtered to obtain filtrate 3 and filter residue 2, and the filter residue 2 is dried to obtain sodium chloride extract: the drying time is 3 to 10 hours. Under this drying time, the moisture attached to the crystal surface and the moisture hidden inside the crystal gap can have more sufficient time to evaporate. The moisture attached to the crystal surface is easier to evaporate, so most of it will be removed in the early stage of drying. The moisture hidden in the crystal gap has a strong binding ability for moisture due to the capillary effect, and it takes a relatively longer time to force it to leave the crystal gap, so the water removal is fast in the early stage of drying and slow in the later stage; optionally, the drying time is 4 to 6 hours, which can improve production efficiency while meeting the moisture requirements.

[0069] In any embodiment of the present application, the step of heating and concentrating the filtrate 1 under vacuum conditions, cooling, crystallizing, and centrifuging to obtain a first filter residue and a second filter residue, washing and filtering the first filter residue to obtain a third filter residue and a second filter residue, and drying the second filter residue to obtain a sodium chloride extract further comprises:

[0070] Mix the filtrate 2 and the filtrate 3, and heat and evaporate them under vacuum conditions to obtain a mixed salt;

[0071] The mixed salt is mixed with the organic solvent and centrifuged to obtain a filter residue 3 and a filtrate 4;

[0072] The filtrate 4 was heated and evaporated under vacuum conditions to obtain a sodium fluoroborate extract.

[0073] Mixed salts contain a large amount of sodium chloride, a small amount of sodium fluoborate, and trace amounts of sodium fluoride. Using organic solvents to dissolve the specific component, sodium fluoborate, from the mixed salts, achieving separation. Ethylene glycol dimethyl ether has a good solubility for sodium fluoborate, while having little solubility for sodium chloride and sodium fluoride. Its solubility in sodium fluoborate measured at room temperature is 2.02g, allowing for the specific purification of sodium fluoborate, effectively resolving the technical challenge of extracting sodium fluoborate from mixed salts.

[0074] In any embodiment of the present application, the filtrate two and the filtrate three are mixed and heated and evaporated under vacuum conditions to obtain a mixed salt: the vacuum pressure is -0.1 to 0 MPa. Within this pressure range, water can be gradually removed from the mixture of filtrate two and filtrate three, and at the same time, the salts of each component in the mixture gradually reach supersaturation and gradually crystallize and precipitate; optionally, the vacuum pressure is -0.095 to -0.085 MPa, which can further improve the yield of the mixed salt.

[0075] In any embodiment of the present application, the filtrate two and the filtrate three are mixed and heated and evaporated under vacuum conditions to obtain a mixed salt: the heating temperature is 70 to 120°C. Within this temperature range, the water in the system is rapidly evaporated, and the crystallization rate is more stable. The salt components gradually crystallize out from the system, thereby improving the yield of the mixed salt. The heating temperature can be 70°C, 80°C, 90°C, 100°C, 110°C or 120°C; optionally, the heating temperature is 80 to 100°C, the crystallization rate is more stable, and the yield of the mixed salt can be further improved.

[0076] In any embodiment of the present application, the second filtrate and the third filtrate are mixed and heated and evaporated under vacuum conditions to obtain a mixed salt: the heating time is 1 to 10 hours. Under this heating time, the mixed solution can be fully evaporated to dryness to precipitate the mixed salt, thereby improving the yield of the mixed salt; the heating time can be 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, or 10 hours. Optionally, the heating time is generally 2 to 4 hours, which can further improve the yield of the mixed salt.

[0077] In any embodiment of the present application, the mixed salt includes sodium fluoride, sodium chloride and sodium fluoroborate, and the sodium fluoroborate still residue contains a thermal cracking product of a mixture of sodium fluoroborate and sodium chloride, wherein the pyrolysis of sodium fluoroborate will generate sodium fluoride and boron trifluoride, and boron trifluoride can react with sodium fluoride to generate sodium fluoroborate, and boron trifluoride can be discharged as a gaseous product, while sodium chloride does not participate in the reaction. Therefore, the pyrolysis still residue contains three components of sodium fluoride, sodium chloride and sodium fluoroborate. After the sodium fluoride and sodium chloride are extracted from the pyrolysis still residue, the sodium fluoride and sodium chloride still remain, and form a mixed salt with the unextracted sodium fluoroborate.

[0078] In any embodiment of the present application, the filtrate two and the filtrate three are mixed, heated and evaporated under vacuum conditions to obtain a mixed salt: the organic solvent includes ethylene glycol dimethyl ether. By using this organic solvent, the sodium fluoroborate in the mixed salt can be dissolved without dissolving other substances, and the sodium fluoroborate can be selectively separated.

[0079] In any embodiment of the present application, the mixed salt is mixed with the organic solvent and centrifuged to obtain the filter residue three and the filtrate four: the mass ratio of the mixed salt to the organic solvent is (0.22-0.28):1. At this mass ratio, a sufficient amount of solvent can be provided to dissolve and wash away the sodium fluoborate in the mixed salt, thereby improving the yield of sodium fluoborate; the mass ratio of the mixed salt to the organic solvent can be 0.22:1, 0.23:1, 0.24:1, 0.25:1, 0.26:1, 0.27:1 or 0.28:1. Optionally, the mass ratio of the mixed salt to the organic solvent is (0.24-0.26):1, which can further improve the yield of sodium fluoborate.

[0080] In any embodiment of the present application, the mixed salt is mixed with an organic solvent and centrifuged to obtain a filter residue three and a filtrate four: the mixing temperature is 20 to 30°C. At this temperature, ethylene glycol dimethyl ether has sufficient solubility for sodium fluoroborate in the mixed salt, which can reduce energy consumption. The mixing temperature can be 20°C, 23°C, 25°C, 27°C or 30°C; optionally, the mixing temperature is 23 to 27°C, which can further reduce energy consumption.

[0081] In any embodiment of the present application, the mixed salt is mixed with the organic solvent and centrifuged to obtain a filter residue three and a filtrate four: the mixing time is 0.5 to 3 hours. Under this mixing time, the sodium fluoborate in the mixed salt can be fully dissolved. First, the sodium fluoborate exposed on the surface of the crystal will be quickly dissolved, while the sodium fluoborate trapped inside the crystal will not be easily dissolved. After a period of stirring, friction and crushing will occur between the crystals, or the sodium fluoborate will be dissolved through slow migration of the crystal gap channel, thereby increasing the yield of sodium fluoborate. The mixing time can be 0.5 hours, 1 hour, 1.5 hours, 2 hours, 2.5 hours or 3 hours; optionally, the mixing time is 0.5 to 1.5 hours, which can improve the dissolution efficiency.

[0082] In any embodiment of the present application, the filtrate four is heated and evaporated under vacuum conditions to obtain a sodium fluoborate extract: the vacuum pressure is -0.1 to 0 MPa. Within this pressure range, ethylene glycol dimethyl ether can be gradually removed from the filtrate four. At the same time, as the sodium fluoborate gradually reaches supersaturation, it gradually crystallizes and precipitates, thereby increasing the yield of sodium fluoborate; optionally, the vacuum pressure is -0.095 to -0.085 MPa, which can further improve the stability of the evaporation operation and reduce energy consumption.

[0083] In any embodiment of the present application, the filtrate four is heated and evaporated under vacuum conditions to obtain a sodium fluoborate extract: the heating and evaporation temperature is 50-90°C. At this temperature, ethylene glycol dimethyl ether can be gradually removed from the filtrate four. At the same time, as the sodium fluoborate gradually reaches supersaturation, it gradually crystallizes and precipitates. At a temperature of 50-85°C, reduced pressure evaporation is adopted; at a temperature of 85-90°C, normal pressure evaporation can be adopted. Generally, reduced pressure evaporation is more efficient. Optionally, the heating and evaporation temperature is 60-80°C, the crystallization rate is more stable, and the obtained mixed salt particle size is more uniform and stable, which can further improve the evaporation effect.

[0084] The technical solutions of the present invention are further described in detail below in conjunction with specific embodiments. It should be understood that the following embodiments are only used to explain the present invention and are not used to limit the present invention.

[0085] Example 1

[0086] A method for purifying sodium fluoroborate pyrolysis reactor residue comprises the following steps:

[0087] The sodium fluoroborate pyrolysis residue was mixed with water in a mass ratio of 1:2.4 at 80°C, cooled, stirred at 25°C for 1 hour, and centrifuged to obtain a sodium fluoride extract and a filtrate. The purity of the obtained sodium fluoride was 91.9%, and the yield was 13.9%.

[0088] Example 2

[0089] A method for purifying sodium fluoroborate pyrolysis reactor residue comprises the following steps:

[0090] The sodium fluoroborate pyrolysis kettle residue and water were heated at 80°C in a mass ratio of 1:2.4, cooled, stirred and crystallized at 25°C for 1 hour, and centrifuged to obtain a sodium fluoride extract and a filtrate.

[0091] Filtrate 1 was heated and concentrated at -0.092 MPa and 70°C to a solid content of 60%. The mixture was cooled, stirred and crystallized at 32°C for 1 hour, and centrifuged to obtain residue 1 and filtrate 2. Residue 1 was rinsed with water at a mass ratio of 0.5:1 and filtered to obtain filtrate 3 and residue 2. Residue 2 was dried at -0.092 MPa and 120°C for 4 hours to obtain a sodium chloride extract. The resulting sodium fluoride had a purity of 92.0% and a yield of 13.7%. The purity of sodium chloride was 98.8% and the yield was 53.0%.

[0092] Example 3

[0093] A method for purifying sodium fluoroborate pyrolysis reactor residue comprises the following steps:

[0094] The residual kettle of sodium fluoroborate pyrolysis was heated with water at a mass ratio of 1:2.4 at 80°C, cooled, stirred and crystallized at 25°C for 1 hour, and centrifuged to obtain sodium fluoride extract and filtrate 1;

[0095] The filtrate 1 was heated and concentrated at -0.092 MPa and 70°C to a solid content of 60%, cooled, stirred and crystallized at 32°C for 1 hour, and centrifuged to obtain a filter residue 1 and a filtrate 2. The filter residue 1 was washed with water at a mass ratio of 0.5:1, and filtered to obtain a filtrate 3 and a filter residue 2. The filter residue 2 was dried at -0.092 MPa and 120°C for 4 hours to obtain a sodium chloride extract.

[0096] Mix the filtrate 2 and the filtrate 3, and heat and evaporate them at -0.092 MPa and 100°C for 1 h to obtain a mixed salt;

[0097] Mix the mixed salt and ethylene glycol dimethyl ether at a mass ratio of 0.25:1 at 25°C for 1 hour, and centrifuge to obtain residue 3 and filtrate 4;

[0098] The filtrate was heated and evaporated at -0.093 MPa and 90°C to obtain a sodium fluoroborate extract. The purity of the obtained sodium fluoride was 91.8%, and the yield was 13.7%. The purity of the sodium chloride was 98.7%, and the yield was 52.7%. The purity of the sodium fluoroborate was 97.8%, and the yield was 2.7%.

[0099] The differences between Examples 4 to 19 and Example 3 are shown in Table 1.

[0100] Table 1 Parameters of Examples 4 to 19

[0101]

[0102] Comparative Example 1

[0103] The difference between Comparative Example 1 and Example 1 is that no heating is performed.

[0104] Because Comparative Example 1 was not heated, the easily soluble sodium fluoroborate and sodium chloride exposed on the crystal surface dissolved, while the sodium fluoroborate and sodium chloride encapsulated within the pyrolysis residual still crystals did not dissolve completely, forming peritectic crystals, which reduced the purity of the sodium fluoride. The sodium fluoride yield and purity in Comparative Document 1 were 80.9% and 15.1%, respectively.

[0105] Performance Testing

[0106] Purity test: by testing the anion and cation concentration of the sample, and then calculating based on the anion and cation test data. The details are as follows:

[0107] 1) ICP detection of cations:

[0108] Instrument model: ICAP-7000;

[0109] Carrier gas: argon;

[0110] Concentration range: 0.1~8ppm;

[0111] Na + Absorption wavelength: 589.592nm;

[0112] 2) Anions are detected by ion chromatography:

[0113] Instrument model: 930 Compact IC Flex;

[0114] Chromatographic column model: Metrosep A Supp5-250 / 4.0;

[0115] Mobile phase: 3.2 mmol / L Na2CO3 aqueous solution;

[0116] Detection column temperature: 30℃;

[0117] 3) Calculation of purity of each component:

[0118] P i =w i ×M i / M i - ;

[0119] Among them, P i Represents the purity of a salt, expressed as a percentage; w i Indicates the percentage of a certain ion; M i Indicates the molar mass of a salt; M i - Indicates the molar mass of an ion.

[0120] The cation data were used to compare the reliability of the anion data.

[0121] 4) Yield test:

[0122] Y i =G i / (G×S)×100%;

[0123] Among them, Y i Represents the yield of a certain salt, expressed as a percentage; G i It represents the mass of a salt obtained in a batch of experiments, in g; G represents the total mass of raw materials used in a batch of experiments, in g; S represents the solid content of the raw materials, expressed as a percentage.

[0124] The purity and yield of the substances purified by the methods of purifying sodium fluoroborate pyrolysis reactor residue in Examples 1 to 19 were measured, and the test results are shown in Table 1.

[0125] From the data in Table 1, we can see that

[0126] (1) The first heating temperature is within the range of 65-90°C, which can improve the purity of sodium fluoride.

[0127] (2) The second heating temperature is within the range of 55-80°C, which can improve the purity and yield of sodium chloride.

[0128] (3) The solid content of the second heating is within the range of 55-75%. The higher the solid content of the second concentrated liquid, the more disadvantageous it is to the purity of sodium chloride, but the more favorable it is to increase the yield of sodium chloride. Therefore, weighing the pros and cons, the optimal point should be selected;

[0129] (4) The mass ratio of filter residue to flushing liquid is within the range of 0.38:1 to 0.5:1, which can improve the purity of sodium chloride;

[0130] (5) The third heating temperature is within the range of 60-120°C, which can improve the purity of sodium fluoroborate.

[0131] The above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Those skilled in the art will readily appreciate that the present invention is susceptible to various modifications and variations. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of the present invention.

Claims

1. A method for purifying sodium fluoroborate pyrolysis reactor residue, characterized in that: The following steps are involved: Heat the residual kettle of sodium fluoroborate pyrolysis with water, cool it down, crystallize it, and centrifuge it to obtain sodium fluoride extract and filtrate 1.

2. The method for purifying sodium borofluoride pyrolysis reactor residue as claimed in claim 1, wherein: The heating temperature is 70-90°C; and / or, The crystallization temperature is 20-30°C; and / or, The crystallization time is 0.5 to 3 hours; and / or, The crystallization process includes stirred crystallization.

3. The method for purifying sodium fluoroborate pyrolysis kettle residue as claimed in claim 1 or 2, characterized in that, The method further comprises heating the sodium fluoroborate pyrolysis kettle residue with water, cooling, crystallizing, and centrifuging to obtain a sodium fluoride extract and a filtrate: The filtrate 1 is heated and concentrated under vacuum conditions, cooled, crystallized, and centrifuged to obtain a filter residue 1 and a filtrate 2. The filter residue 1 is rinsed and filtered to obtain a filtrate 3 and a filter residue 2. The filter residue 2 is dried to obtain a sodium chloride extract.

4. The method for purifying sodium fluoroborate pyrolysis kettle residue as claimed in claim 3, wherein: The filtrate 1 is heated and concentrated under vacuum conditions, cooled, crystallized, and centrifuged to obtain a filter residue 1 and a filtrate 2. The filter residue 1 is rinsed and filtered to obtain a filtrate 3 and a filter residue 2. The filter residue 2 is dried to obtain a sodium chloride extract: The vacuum pressure is -0.1 to -0.054 MPa; and / or, The heating and concentrating temperature is 70-90°C; and / or, The solid content after heating and concentration is 50-75%; and / or, The crystallization temperature is 25 to 40°C; and / or, The crystallization time is 0.5 to 3 hours; and / or, The crystallization process includes stirred crystallization.

5. The method for purifying sodium fluoroborate pyrolysis reactor residue as claimed in claim 3 or 4, characterized in that: The filtrate 1 is heated and concentrated under vacuum conditions, cooled, crystallized, and centrifuged to obtain a filter residue 1 and a filtrate 2. The filter residue 1 is rinsed and filtered to obtain a filtrate 3 and a filter residue 2. The filter residue 2 is dried to obtain a sodium chloride extract: The mass ratio of filter residue to flushing liquid is (1.7-2.5):1; and / or, The drying pressure is -0.1 to 0 MPa; and / or, The drying temperature is 100-150°C; and / or, The drying time is 3 to 10 hours.

6. The method for purifying sodium fluoroborate pyrolysis kettle residue as claimed in claim 3, wherein: The method further comprises heating and concentrating the filtrate 1 under vacuum conditions, cooling, crystallizing, and centrifuging to obtain a filter residue 1 and a filtrate 2, washing and filtering the filter residue 1 to obtain a filtrate 3 and a filter residue 2, and drying the filter residue 2 to obtain a sodium chloride extract. Mix the filtrate 2 and the filtrate 3, and heat and evaporate them under vacuum conditions to obtain a mixed salt; The mixed salt is mixed with the organic solvent and centrifuged to obtain a filter residue 3 and a filtrate 4; The filtrate 4 was heated and evaporated under vacuum conditions to obtain a sodium fluoroborate extract.

7. The method for purifying sodium fluoroborate pyrolysis kettle residue as claimed in claim 6, wherein: The filtrate 2 and the filtrate 3 are mixed, heated and evaporated under vacuum conditions to obtain a mixed salt: The pressure is -0.1 to 0 MPa; and / or, The heating temperature is 70 to 120° C.; and / or, The heating time is 1 to 10 hours.

8. The method for purifying sodium fluoroborate pyrolysis kettle residue as claimed in claim 6 or 7, characterized in that: The mixed salt includes sodium fluoride, sodium chloride and sodium fluoroborate; and / or, The organic solvent includes ethylene glycol dimethyl ether.

9. The method for purifying sodium fluoroborate pyrolysis reactor residue according to any one of claims 6 to 8, characterized in that: The mixed salt is mixed with ethylene glycol dimethyl ether and centrifuged to obtain a filter residue three and a filtrate four: The mass ratio of the mixed salt to ethylene glycol dimethyl ether is (0.22-0.28):

1.

10. The method for purifying sodium fluoroborate pyrolysis reactor residue according to any one of claims 6 to 9, characterized in that: The mixed salt is mixed with the organic solvent and centrifuged to obtain a filter residue three and a filtrate four: The mixing temperature is 20-30°C; and / or, The mixing time is 0.5 to 3 hours.

11. The method for purifying sodium fluoroborate pyrolysis reactor residue according to any one of claims 6 to 10, characterized in that: The filtrate 4 is heated and evaporated under vacuum conditions to obtain the sodium fluoroborate extract: The vacuum pressure is -0.1 to -0.08 MPa; and / or, The heating and evaporation temperature is 50 to 90°C.

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