Method for preparing acesulfamide lithium through ion exchange

Abstract

The invention provides a method for preparing acesulfamide lithium through ion exchange, which comprises the following steps: mixing and dissolving ethanol and o-benzoyl sulfimide in a reaction kettle, adding lithium hydroxide into the ethanol to form turbid liquid, slowly adding the turbid liquid into the reaction kettle, controlling the temperature, slowly dropwise adding an ethanol solution of acesulfame potassium under stirring and temperature control, continuously stirring, and reacting for 2-3 hours to obtain the acesulfamide lithium salt. Filtering to remove precipitates, concentrating filtrate to remove ethanol, cooling and crystallizing after purifying, adding seed crystals, collecting acesulfamide lithium crystals, and drying in vacuum. According to the method disclosed by the invention, efficient and stable synthesis of acesulfamide lithium is realized, and the purity and yield of the product are improved.

Description

Technical Field

[0001] The invention relates to a method for producing a chemical raw material, and in particular to a method for preparing lithium acesulfame. Background Art

[0002] The mechanism of acesulfame as a battery additive mainly involves the chemical and electrochemical reactions it forms in the battery electrolyte.

[0003] As an electrolyte salt, lithium acetylsulfamate has important application prospects in lithium-ion battery electrolytes. However, the process of converting lithium acetylsulfamate through potassium acetylsulfamate has the problem of high potassium ions.

[0004] The preparation of lithium acesulfame requires the control of specific reaction conditions, such as temperature, pressure and reaction time. Slight changes in these conditions may have a significant impact on the purity and performance of the final product. The purity of the raw materials has an important impact on the purity and performance of the final product. Therefore, when preparing lithium acesulfame, it is necessary to ensure that the raw materials used have high purity. Some waste or pollutants may be generated during the preparation and use of lithium acesulfame. These waste or pollutants may have a certain impact on the environment.

[0005] As an electrolyte salt, lithium acesulfame has important application prospects in lithium-ion battery electrolytes. The process of converting lithium acesulfame through potassium acesulfame may involve complex chemical synthesis steps and environmental factors. Potassium ions, as part of the electrolyte salt, need to be removed during the preparation process. If they are not removed, the performance of the electrolyte may be affected to a certain extent. Summary of the invention

[0006] The present invention provides a method for preparing lithium acesulfame, comprising the following steps:

[0007] Step 1, reactant mixing: ethanol is added into a reaction kettle, and the stirrer is turned on to evenly distribute the ethanol; then o-benzoylsulfonyl imide is slowly added, and stirring is continued until it is completely dissolved;

[0008] Step 2, preparation and addition of lithium hydroxide suspension: In another container, lithium hydroxide is added to ethanol and stirred to form a uniform suspension, and then the suspension is slowly added to the reactor while maintaining stirring and controlling the temperature within a predetermined range;

[0009] Step 3, adding acesulfame potassium solution dropwise: preparing an ethanol solution of acesulfame potassium in another container, and then slowly adding the solution dropwise to the reactor under continuous stirring and temperature control;

[0010] Step 4, stirring and removing the precipitate: After the dropwise addition is completed, the reaction mixture is continued to be stirred for a period of time, and then the generated precipitate is separated from the reaction solution by a filtering device;

[0011] Step 5, filtrate concentration and crystallization: the filtered filtrate is concentrated to remove most of the ethanol; it is further purified before crystallization, and then the temperature is gradually lowered to the crystallization endpoint temperature, and seed crystals are added to promote crystallization;

[0012] Step 6, product collection and drying: collect the formed lithium acesulfame crystals by filtration, and dry them in a vacuum drying oven to constant weight.

[0013] In step 1, the amount of ethanol added is 1500-1700 L, and the amount of o-benzoylsulfonimide added is 500 mol.

[0014] In step 2, 500 mol of lithium hydroxide is added to 400-500 L of ethanol and stirred to form a uniform suspension, and then slowly added to the reactor at a rate of about 100 L per hour, and the temperature is controlled between 15 and 30°C.

[0015] In step 3, 500 mol of acesulfame potassium is dissolved in 5000L-6000L of ethanol, and the solution is slowly added dropwise to the reactor.

[0016] In step 4, after stirring the reaction mixture for 4-5.5 hours, the generated precipitate is separated from the reaction solution by a filtration device, and the filtration pressure is set between 0.2-0.4 MPa.

[0017] In step 5, the crystallization end point is a temperature of 6-10° C., and the cooling rate is 1-2° C. per hour; at the same time, lithium acesulfame powder with a purity of not less than 99.9% is added as a seed crystal, and the amount of the seed crystal added is 0.5% of the total mass of the reaction solution.

[0018] Ethanol was used as the main solvent and 5-10% deionized water was added as the auxiliary solvent.

[0019] The invention is characterized in that the resistivity of the deionized water is not less than 18 MΩ·cm.

[0020] The potassium ion content in the lithium acesulfame crystals prepared by the method is less than 20 ppm.

[0021] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0022] The method of the invention manufactures a lithium acesulfame product with low potassium ion content. DETAILED DESCRIPTION

[0023] In order to make the technical problems solved by the present invention, the technical solutions adopted and the technical effects achieved clearer, the technical solutions of the embodiments of the present invention are further described in detail below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0024] The present invention relates to a method for preparing lithium acesulfame. The method uses the following equipment:

[0025] The reactor with a capacity of not less than 4000L is made of stainless steel and has heating, cooling and stirring functions. The reactor should be equipped with temperature sensors and pressure sensors to ensure temperature and pressure control during the reaction process.

[0026] High-speed agitator with adjustable speed ensures that the reactants are evenly mixed in the reactor.

[0027] A rotary evaporator or vacuum concentrator is used to remove most of the ethanol in the filtrate to complete the concentration.

[0028] A plate and frame filter press or vacuum filtration device is used to separate the precipitate and the filtrate to complete the filtration.

[0029] The vacuum drying oven has the functions of temperature and vacuum control and is used to dry lithium acesulfame crystals.

[0030] High performance liquid chromatography (HPLC), atomic absorption spectrometer (AAS), differential scanning calorimeter (DSC) and capillary melting point determination instrument are used for quality analysis of products.

[0031] The method uses the following raw materials:

[0032] Ethanol, with a purity of not less than 99.5%, is used to dissolve reactants and adjust the polarity of the solution.

[0033] Deionized water, with a resistivity of not less than 18 MΩ·cm, is used for cleaning equipment and preparing lithium hydroxide suspension.

[0034] Saccharin, with a purity of not less than 98%, is used as one of the reaction raw materials.

[0035] Lithium hydroxide, with a purity of not less than 98%, is used to prepare lithium hydroxide suspension.

[0036] Acesulfame potassium, with a purity of not less than 98%, for the preparation of acesulfame potassium solution.

[0037] High purity lithium acesulfame powder, as seed crystal, with purity not less than 99.9%, is used to promote the crystallization process.

[0038] In the first step, the reactants are mixed.

[0039] Clean the reactor. Use deionized water and ethanol to thoroughly clean the reactor, then blow it dry with dry air to ensure that there is no impurity or moisture inside the reactor. During the cleaning process, a soft brush or high-pressure airflow can be used to assist in cleaning.

[0040] Add ethanol. Add 1500L of ethanol to the reactor and turn on the agitator to ensure that the ethanol is evenly distributed. The stirring speed can be set to 30rpm and the stirring time should be no less than 10 minutes.

[0041] Add saccharin. Slowly add 500 mol of saccharin and continue stirring until it is completely dissolved. At this point, the solution should be clear and transparent with no solid residue. The stirring speed can be maintained at 30 rpm for no less than 30 minutes.

[0042] Step 2: Preparation and addition of lithium hydroxide suspension

[0043] Prepare lithium hydroxide suspension. In another container, add 500 mol lithium hydroxide to 500 L ethanol and stir to form a uniform suspension. The stirring speed can be set to 20-50 rpm, and the stirring time is not less than 20 minutes to ensure that the lithium hydroxide is completely dispersed in the ethanol.

[0044] Add lithium hydroxide suspension. Slowly add the prepared lithium hydroxide suspension into the reactor while stirring. During the addition process, the temperature should be controlled between 15 and 30 ° C to avoid local overheating. The addition speed can be controlled at about 100L per hour, and the stirring speed should be maintained at 30rpm.

[0045] The third step is to add acesulfame potassium solution dropwise.

[0046] Prepare acesulfame potassium solution. In another clean container, dissolve 500 mol acesulfame potassium in 6000 L ethanol and stir to form a uniform solution. The stirring speed can be set to 50 rpm and the stirring time should be no less than 30 minutes to ensure that the acesulfame potassium is completely dissolved.

[0047] Add acesulfame potassium solution dropwise. Under continuous stirring and temperature control, start adding acesulfame potassium solution dropwise. The addition speed needs to be strictly controlled. It is recommended to add about 5L per minute to avoid the formation of precipitation too quickly due to excessive local concentration. During the addition process, the changes in the reaction system should be closely observed to ensure that there are no abnormalities. The stirring speed is maintained at 30rpm and the addition time is about 2 hours.

[0048] The fourth step is subsequent stirring and precipitation removal.

[0049] After the addition is complete, the reaction mixture is stirred for 4 hours to ensure complete reaction. During the stirring process, the stirring speed can be appropriately adjusted to maintain between 30-40 rpm to maintain the uniformity of the reaction system.

[0050] Precipitation removal. The generated potassium o-benzoylsulfonyl imide precipitate is separated from the reaction solution by a filtration device. During the filtration process, the filtration speed should be controlled to avoid precipitation loss. The filtration pressure can be set between 0.2-0.4MPa, and the filtration time depends on the amount of precipitation.

[0051] The fifth step is concentration and crystallization of the filtrate.

[0052] Filtrate transfer and concentration. Transfer the filtered filtrate to another clean container and prepare for concentration. Use a concentration device to remove most of the ethanol. During the concentration process, the temperature and pressure should be controlled to avoid ethanol volatilization too quickly and cause product loss. The concentration temperature can be set between 60-70℃, the vacuum degree is maintained above -0.08MPa, and the concentration time depends on the amount of filtrate.

[0053] Preparation for crystallization. Before crystallization, remove particulate impurities in the solution by filter pressing to ensure the purity of the crystallization solution. The initial temperature is 40°C, and the temperature is gradually lowered at a rate of 2°C per hour until the crystallization endpoint temperature of 10°C is reached. During this process, an appropriate amount of deionized water (5-10% by volume) can be added to change the solubility or distribution of potassium ions in the solution. At the same time, 300-mesh high-purity lithium acesulfame powder is added as a seed crystal, and the amount of seed crystal added is 0.5% of the total mass.

[0054] Crystallization process. The total crystallization time is 24 hours. After reaching the crystallization temperature, keep warm to promote uniform growth of crystals. During the insulation period, the speed of the agitator should be kept between 20-30rpm to ensure uniformity during the crystallization process. At the same time, an appropriate amount of acid or alkali (such as lithium hydroxide or acetic acid) can be added to adjust the pH value of the solution to 7.5-8 during the crystallization process to change the existence state of potassium ions in the solution, making it easier to separate from lithium acesulfame.

[0055] Step 6: Product collection and drying.

[0056] Product collection. Collect the formed lithium acesulfame crystals by filtering again. During the filtration process, the filtration speed should be controlled to avoid crystal loss. The filtration pressure can be set between 0.1-0.3MPa, and the filtration time depends on the amount of crystals.

[0057] Product drying. The collected lithium acesulfame crystals are placed in a vacuum drying oven and dried to constant weight at an appropriate temperature. The drying temperature can be set between 60-80°C, the vacuum degree is maintained below -0.1MPa, and the drying time is determined according to the initial moisture content of the crystals, generally not less than 12 hours.

[0058] Quality analysis. The dried product should be subjected to quality analysis, including purity testing, melting point determination, etc., to verify the product's eligibility. Purity testing can be performed by high performance liquid chromatography (HPLC) or atomic absorption spectrometry (AAS), and melting point determination can be performed by differential scanning calorimetry (DSC) or a capillary melting point tester.

[0059] After the above steps, lithium acesulfame was prepared. The content of potassium ion (K+), ferrous ion (Fe2+) and calcium ion (Ca2+) was detected by atomic absorption spectroscopy (AAS). The potassium content in the finished product was less than 20ppm and the yield was close to 90%. This technical effect is due to the following aspects:

[0060] Solvent selection: Use ethanol as the main solvent and add 5-10% deionized water as the auxiliary solvent. This solvent combination helps to change the solubility or distribution of potassium ions in the solution, making it easier to separate from lithium acesulfame. At the same time, the volatility of ethanol also facilitates its removal during the concentration process, further reducing the residual potassium ions in the crystals.

[0061] Temperature control: Through precise temperature control, the temperature is gradually lowered at a rate of 2°C per hour until the crystallization endpoint temperature is reached. This slow temperature change helps the uniform growth of crystals and may promote the diffusion of potassium ions from the surface or interior of the crystals into the solution, thereby reducing their inclusion in the crystals.

[0062] pH adjustment: The pH of the solution during the crystallization process is adjusted to 7.5-8 by adding appropriate amounts of acid and alkali. This pH condition changes the state of potassium ions in the solution, making it easier to separate from lithium acesulfame. At the same time, a stable pH value also helps to reduce side reactions during crystal growth, thereby improving the purity and crystallinity of the product.

[0063] Stirring and seeding: Appropriate stirring speed and the addition of seeding can help the uniform growth of crystals and reduce impurity inclusions. Stirring too fast may cause crystal breakage, while stirring too slow may cause uneven crystal growth. The addition of seeding can induce the formation of crystals, improve crystallization efficiency and product purity.

[0064] Filtration and drying: Through the filtration and drying steps, impurities and residual solvents in the product can be further removed to improve the purity and stability of the product. During the filtration process, pay attention to controlling the filtration speed and pressure to avoid product loss. During the drying process, pay attention to controlling the temperature and vacuum degree to avoid product deterioration or decomposition.

[0065] The following are examples of the present invention.

[0066] Embodiment 1:

[0067] (I) Mixing of reactants:

[0068] First, the reactor was cleaned thoroughly with deionized water and ethanol, and then blown dry with dry air to ensure that there was no impurity or moisture inside the reactor.

[0069] Add 1500 L of ethanol to the reactor and turn on the agitator to ensure that the ethanol is evenly distributed.

[0070] Slowly add 500 mol of o-benzoylsulfonyl imide (Saccharin) and continue stirring until it is completely dissolved. At this point, the solution should be clear and transparent with no solid residue.

[0071] (II) Preparation and addition of lithium hydroxide suspension:

[0072] In another container, add 500 mol of lithium hydroxide into 500 L of ethanol and stir to form a uniform suspension.

[0073] Slowly add the prepared lithium hydroxide suspension into the reactor while keeping stirring and controlling the temperature between 15 and 30° C. During the addition process, pay attention to observe the changes in the reaction system to ensure that there is no local overheating.

[0074] (III) Add acesulfame potassium solution:

[0075] In another clean container, dissolve 500 mol of acesulfame potassium in 6000 L of ethanol and stir to form a uniform solution.

[0076] Under continuous stirring and temperature control, start dripping acesulfame potassium solution. The dripping speed needs to be strictly controlled. It is recommended to drip about 5L per minute to avoid the precipitation caused by excessive local concentration. During the dripping process, closely observe the changes in the reaction system to ensure that there are no abnormal phenomena.

[0077] As acesulfame potassium is gradually added, o-benzoylsulfonyl potassium precipitate begins to form in the reaction system. This process is a key step in the synthesis of acesulfame lithium, and the formation of the precipitate indicates the progress of the reaction.

[0078] (IV) Subsequent stirring and precipitation removal:

[0079] After the addition is complete, the reaction mixture is stirred for 4 hours to ensure complete reaction. During the stirring process, the stirring speed can be appropriately adjusted to maintain the uniformity of the reaction system.

[0080] The generated potassium o-benzoylsulfonyl imide precipitate is separated from the reaction solution by a filtration device. During the filtration process, pay attention to controlling the filtration speed to avoid precipitate loss.

[0081] (V) Filtrate concentration and crystallization:

[0082] Transfer the filtered filtrate to another clean container for concentration.

[0083] Use a concentration device (such as a rotary evaporator) to remove most of the ethanol. During the concentration process, pay attention to controlling the temperature and pressure to avoid ethanol volatilization too quickly and causing product loss.

[0084] Crystallization preparation: Before crystallization, remove particulate impurities in the solution by filter pressing to ensure the purity of the crystallization solution. The initial temperature is 40°C, and the temperature is gradually reduced at a rate of 2°C per hour until the crystallization end temperature of 10°C is reached. Continue to use ethanol as the main solvent and add 5-10% deionized water as an auxiliary solvent to change the solubility or distribution of potassium ions in the solution. Use 300 mesh high-purity lithium acesulfame powder as a seed crystal, and the amount of seed crystal added is 0.5% of the total mass. Set the agitator speed to 20-30rpm to ensure uniformity during the crystallization process.

[0085] Crystallization process: The total crystallization time is 24 hours. After reaching the crystallization temperature, keep warm to promote uniform growth of crystals. Add appropriate amount of acid or alkali (such as lithium hydroxide or acetic acid) to adjust the pH value of the solution to 7.5-8 during the crystallization process to change the existence state of potassium ions in the solution, making it easier to separate from lithium acesulfame.

[0086] (VI) Product collection and drying:

[0087] The formed lithium acesulfame crystals were collected by filtering again. During the filtering process, the filtering speed was controlled to avoid crystal loss.

[0088] The collected lithium acesulfame crystals are placed in a vacuum drying oven and dried at an appropriate temperature to a constant weight. During the drying process, the temperature and vacuum degree are carefully controlled to avoid crystal deterioration or decomposition.

[0089] Embodiment 2:

[0090] Example 2 made some adjustments to the reaction conditions of Example 1. The specific steps are as follows:

[0091] (I) Mixing of reactants:

[0092] First, the reactor is thoroughly cleaned with deionized water and ethanol, and then dried with dry air to ensure that there is no impurity and moisture inside the reactor. 1600L ethanol (increased by 100L compared with Example 1) is added to the reactor, and the agitator is turned on, and the speed is set to 40rpm to ensure that the ethanol is evenly distributed. 500mol of o-benzoylsulfonyl imide is slowly added and continued to stir for 2 hours until completely dissolved. At this point, the solution should be clear and transparent, with no solid residue.

[0093] (II) Preparation and addition of lithium hydroxide suspension:

[0094] In another container, add 500 mol of lithium hydroxide to 450 L of ethanol (50 L less than in Example 1), and stir to form a uniform suspension. Slowly add the prepared lithium hydroxide suspension to the reactor while stirring, and control the temperature between 18 and 28 ° C to further reduce the occurrence of side reactions. During the addition process, pay attention to the changes in the reaction system to ensure that there is no local overheating.

[0095] (III) Add acesulfame potassium solution:

[0096] In another clean container, dissolve 500 mol of acesulfame potassium in 5500 L of ethanol and stir to form a uniform solution. Under continuous stirring and temperature control, begin to drip the acesulfame potassium solution. Adjust the dripping speed to about 4 L per minute to avoid the formation of precipitation too quickly due to excessive local concentration. During the dripping process, closely observe the changes in the reaction system to ensure that there are no abnormalities.

[0097] (IV) Subsequent stirring and precipitation removal:

[0098] After the addition is complete, the reaction mixture is stirred for 5 hours to ensure that the reaction is more complete. During the stirring process, the stirring speed is adjusted in time according to the specific conditions of the reaction system to maintain the uniformity of the reaction system. The generated o-benzoylsulfonyl imide potassium precipitate is separated from the reaction solution by a filtering device. During the filtering process, it is noted to control the filtering speed to avoid precipitation loss. Meanwhile, the precipitate is washed with deionized water to remove impurities attached to the precipitate.

[0099] (V) Filtrate concentration and crystallization:

[0100] Transfer the filtered filtrate to another clean container and prepare for concentration. Use a concentration device (such as a rotary evaporator) to remove most of the ethanol. During the concentration process, control the temperature between 50 and 60°C and the pressure at a moderate level to avoid ethanol volatilization too quickly and cause product loss. Stop concentrating when the concentration reaches 1 / 6 of the original volume.

[0101] Before crystallization, the particulate impurities in the solution are further removed by filter pressing to ensure the purity of the crystallization solution. The initial temperature is 38°C, and the temperature is gradually reduced at a rate of 1.5°C per hour until the crystallization end temperature of 8°C is reached. Ethanol is used as the main solvent, and 8% deionized water is added as an auxiliary solvent to optimize the solubility or distribution of potassium ions in the solution. 400-mesh high-purity lithium acesulfame powder is used as a seed crystal, and the amount of seed crystal added is 0.6% of the total mass. Set the agitator speed to 25rpm to ensure uniformity during the crystallization process.

[0102] The crystallization time is 26 hours, and the temperature is kept for 2 hours after reaching the crystallization temperature to promote the full growth of crystals. During the crystallization process, an appropriate amount of lithium hydroxide or acetic acid is added in time to adjust the pH value of the solution to 7.8 to further improve the separation effect of potassium ions and lithium acesulfame.

[0103] (VI) Product collection and drying:

[0104] Collect the formed lithium acesulfame crystals by filtering again. During the filtration process, pay attention to controlling the filtration speed to avoid crystal loss. Place the collected lithium acesulfame crystals in a vacuum drying oven and dry them at 65°C to constant weight. During the drying process, regularly check the vacuum degree and crystal state to avoid crystal deterioration or decomposition.

[0105] Embodiment 3:

[0106] Example 3 further optimizes the reaction conditions and operating steps to improve the purity and yield of the product and reduce the production cost. The specific steps are as follows:

[0107] (I) Mixing of reactants:

[0108] First, the reactor was thoroughly cleaned with deionized water and ethanol, and dried with nitrogen to ensure that there were no impurities, moisture, and oxygen inside the reactor. 1700 L of ethanol was added to the reactor, and the agitator was turned on and set to 30 rpm to ensure that the ethanol was evenly distributed. 500 mol of o-benzoylsulfonyl imide was slowly added and stirred for 2.5 hours until it was completely dissolved.

[0109] (II) Preparation and addition of lithium hydroxide suspension:

[0110] In another container, add 500 mol of lithium hydroxide to 400 L of ethanol and stir to form a uniform suspension. Slowly add the prepared lithium hydroxide suspension to the reactor through a constant flow pump while keeping stirring and controlling the temperature between 20 and 26 ° C to reduce the occurrence of side reactions. During the addition process, use an online pH meter to monitor the pH value of the reaction system in real time to ensure that there is no local overheating or abnormal pH value.

[0111] (III) Add acesulfame potassium solution:

[0112] In another clean container, 500 mol of acesulfame potassium was dissolved in 5000 L of ethanol and stirred to form a uniform solution. Under continuous stirring and temperature and pH control, acesulfame potassium solution was added dropwise through a precision dropping device. The dropping speed was precisely controlled to drop about 3.5 L per minute to ensure a smooth reaction. During the dropping process, an online infrared spectrometer was used to monitor the composition changes of the reaction system in real time to ensure that there were no abnormalities.

[0113] (IV) Subsequent stirring and precipitation removal:

[0114] After completion of the dropwise addition, the reaction mixture was stirred for 5.5 hours to ensure complete reaction. During the stirring process, the stirring speed was adjusted in a timely manner according to the specific conditions of the reaction system, and an appropriate amount of nitrogen was introduced to protect the reaction system from oxygen. By an automatic filtering device, the generated o-benzoylsulfonylimide potassium precipitate was separated from the reaction solution. During the filtering process, nitrogen was used to purge the filter to remove impurities attached to the precipitation and the filter.

[0115] (V) Filtrate concentration and crystallization:

[0116] Transfer the filtered filtrate to another clean container and prepare for concentration. Use a concentration device (such as a molecular distillation instrument) to remove most of the ethanol. During the concentration process, control the temperature between 52 and 58°C and keep the pressure at a low level to reduce the volatilization loss of ethanol. Stop concentrating when the concentration reaches 1 / 7 of the original volume.

[0117] Before crystallization, the particulate impurities and trace organic matter in the solution are further removed by an ultrafiltration device to ensure the purity of the crystallization solution. The initial temperature is 36°C, and the temperature is gradually reduced at a rate of 1°C per hour until the crystallization end temperature of 6°C is reached. Ethanol is used as the main solvent, and 10% deionized water is added as an auxiliary solvent to further optimize the solubility or distribution of potassium ions in the solution. 500-mesh high-purity lithium acesulfame powder is used as a seed crystal, and the amount of seed crystal added is 0.7% of the total mass. Set the agitator speed to 30rpm to ensure uniformity during the crystallization process.

[0118] The crystallization time is 28 hours, and the temperature is kept for 3 hours after reaching the crystallization temperature to promote the full growth and perfection of the crystals. During the crystallization process, according to the change of the pH value of the solution, an appropriate amount of lithium hydroxide or acetic acid is added in time to adjust the pH value of the solution to keep the pH value of the solution between 7.6 and 7.9.

[0119] (VI) Product collection and drying:

[0120] The formed lithium acesulfame crystals are collected by an automatic filtering device. During the filtering process, nitrogen is used to purge the filtering device to reduce the loss of crystals. The collected lithium acesulfame crystals are placed in a vacuum drying oven and dried at 70°C to constant weight. During the drying process, nitrogen is used to protect the drying oven to prevent the crystals from coming into contact with oxygen or moisture in the air and deteriorating.

[0121] The inventors also conducted a number of comparative experiments, and the specific experimental results are as follows:

[0122] Comparative Example 1:

[0123] The specific steps of this comparative example are as follows:

[0124] 1. Mixing of reactants and formation of precipitate: According to the steps of Example 1, the reactants are mixed, a lithium hydroxide suspension is prepared and added, and a potassium acesulfame solution is added dropwise to form a potassium o-benzoylsulfonyl imide precipitate.

[0125] 2. Subsequent stirring and precipitate removal: After the dropwise addition is completed, the reaction mixture is stirred for 4 hours, and the precipitate is separated from the reaction solution by a filtration device.

[0126] 3. Filtrate concentration and crystallization: The filtered filtrate is transferred to another container and a concentration device is used to remove most of the ethanol. Before crystallization, the particulate impurities in the solution are removed by filter pressing. Then, the temperature is gradually reduced at a rate of 2°C per hour to a crystallization end point temperature of 10°C, but deionized water is not added as an auxiliary solvent. Use 300 mesh high-purity lithium acesulfame powder as a seed crystal, and set the agitator speed to 20-30rpm.

[0127] 4. Crystallization process and product collection: The total crystallization time is 24 hours, and the temperature is kept after reaching the crystallization temperature. Add appropriate amounts of acid and alkali to adjust the pH value of the solution to 7.5-8 during the crystallization process. Finally, the formed lithium acesulfame crystals are collected by filtration and placed in a vacuum drying oven to dry to constant weight.

[0128] Comparative Example 2:

[0129] The specific steps of this comparative example are as follows:

[0130] The steps of Example 1 were followed to carry out mixing of reactants, formation of precipitate, subsequent stirring and removal of precipitate, concentration of filtrate and preparation for crystallization. During the crystallization process, the temperature was gradually reduced at a rate of 5° C. per hour to a crystallization end point temperature of 10° C. Other conditions such as solvent composition, amount of seed crystals added, stirring speed and pH adjustment were the same as those in Example 1.

[0131] Comparative Example 3:

[0132] The specific steps of this comparative example are as follows:

[0133] The steps of Example 1 were followed to carry out the mixing of reactants, the formation of precipitates, the subsequent stirring and removal of precipitates, the concentration of filtrate and the preparation for crystallization. During the crystallization process, no acid or alkali was added to adjust the pH value of the solution, but it was kept in a natural state. Other conditions such as solvent composition, temperature change rate, amount of seed crystals added and stirring speed were the same as those in Example 1.

[0134] Comparative Example 4:

[0135] The specific steps of this comparative example are as follows:

[0136] The steps of Example 1 were followed to carry out the mixing of reactants, the formation of precipitates, the subsequent stirring and removal of precipitates, the concentration of filtrate and the preparation for crystallization. In the crystallization process, 300-mesh high-purity lithium acesulfame powder was used as a seed crystal, but the amount of seed crystal added was increased to 2% of the total mass. Other conditions such as solvent composition, temperature change rate, pH adjustment and stirring speed were the same as those in Example 1.

[0137] For the above embodiments and comparative examples, the inventors used the following method to detect the experimental results:

[0138] Ion chromatography (IC) is an efficient and sensitive ion separation and detection technique, particularly suitable for the detection of constant to trace ions in liquid samples. In the embodiments and comparative examples, the content of potassium ions in the filtrate after the dissolution of lithium acesulfame crystals can be detected by ion chromatography. Using appropriate eluents (such as methanesulfonic acid) and cation chromatographic columns (such as IonPac CS12A), high-sensitivity detection of potassium ions can be achieved.

[0139] Operation steps: dissolve lithium acesulfame crystals in deionized water to prepare a test solution; use an ion chromatograph to inject the test solution into a chromatographic column for separation; detect and record the peak area or peak height of potassium ions, and calculate the concentration of potassium ions using a standard curve.

[0140] Inductively coupled plasma mass spectrometry (ICP-MS) is a highly sensitive multi-element analysis technique suitable for the detection of trace elements. ICP-MS can be used to detect the potassium ion content in lithium acesulfame crystals, especially when testing high-purity products.

[0141] Operation steps: dissolve lithium acesulfame crystals in a suitable acid (such as nitric acid) to prepare a test solution; use an ICP-MS instrument to introduce the test solution into plasma for ionization; detect and record the mass spectrometry signal of potassium ions, and calculate the concentration of potassium ions by an internal standard method or an external standard method.

[0142] Atomic absorption spectrophotometry (AAS) can be used to measure the potassium ion content in lithium acesulfame crystals, especially for lower purity samples or rapid screening.

[0143] Operation steps: dissolve lithium acesulfame crystals in an appropriate solvent (such as water or acid) to prepare a test solution; use an atomic absorption spectrophotometer to select the characteristic absorption wavelength of potassium ions and measure the absorbance; calculate the concentration of potassium ions using a standard curve.

[0144] Spectrophotometry is an analytical method based on the principle of selective absorption of light by matter and is suitable for the detection of major to trace elements.

[0145] Operation steps: dissolve lithium acesulfame crystals in an appropriate solvent and add a color developer for reaction; use a spectrophotometer to measure the absorbance at a specific wavelength; calculate the concentration of potassium ions using a standard curve.

[0146] The following are the test results of the potassium ion content in the lithium acesulfame crystals in Examples 1-3 and Comparative Examples 1-4 according to the above analysis method.

[0147]

[0148]

[0149] illustrate:

[0150] The results of ion chromatography (IC) were expressed in milligrams per liter (mg / L) with a detection limit of 0.1 mg / L.

[0151] Inductively coupled plasma mass spectrometry (ICP-MS) results are expressed in parts per million (ppm).

[0152] The results of atomic absorption spectrophotometry (AAS) are expressed in milligrams per liter (mg / L).

[0153] The results of spectrophotometry are expressed in milligrams per liter (mg / L), with a detection limit of 0.1 mg / L, and are determined after reaction with a specific color developer.

[0154] According to the methods of Examples 1-3, the potassium ion content detected by different methods in each example is different. Specifically, IC is less than 0.15, especially less than 0.1; ICP-MS is less than 10ppm, especially 5ppm; AAS is less than 0.25, because it is 0.15; Spectrophotometry is less than 0.2.

[0155] From the examples and comparative examples,

[0156] The addition of deionized water in the examples plays an important role. Deionized water can change the solubility or distribution of potassium ions in the solution, which helps to reduce the residual potassium ions in the lithium acesulfame crystals. In contrast, in Comparative Example 1, only pure ethanol is used as a solvent, resulting in a higher residual amount of potassium ions in the crystals.

[0157] A slow rate of temperature change contributes to uniform growth of crystals. In the embodiment, reducing the rate of temperature change by 2° C. per hour ensures that the crystals have enough time to grow in an orderly manner, thereby reducing the encapsulation of potassium ions. However, in Comparative Example 2, the rate of temperature change is too fast, resulting in faster crystal growth but poor uniformity, and potassium ions are more easily encapsulated in crystals. Therefore, the potassium ion content in Comparative Example 2 is higher.

[0158] The adjustment of pH value has an important influence on the existence state of potassium ions in the solution and the crystal growth environment of lithium acesulfame. In the embodiment, by adjusting the pH value of the solution, the separation effect of potassium ions and lithium acesulfame can be improved, and the residual potassium ions in the crystal can be reduced. However, in Comparative Example 3, the pH value was not adjusted, resulting in a poor separation effect of potassium ions and lithium acesulfame, and a high potassium ion content.

[0159] The appropriate amount of seed addition contributes to the uniform growth of crystals. In the embodiment, 0.5% of seed addition can obtain a more uniform product particle size distribution while ensuring the crystal growth rate. However, in Comparative Example 4, too much seed addition provides more growth points, resulting in more intense competition during crystal growth, faster crystal growth rate but wider particle size distribution, and possible mixing of impurities or formation of irregular crystal morphology. Therefore, the potassium ion content in Comparative Example 4 is also relatively high.

[0160] The washing of the precipitation is an important step to remove impurities attached to the precipitation. In the embodiment, the precipitation is washed with deionized water, and potassium ions and other impurities attached to the precipitation are effectively removed, thereby reducing the residual potassium ions. The washing process is not mentioned in the comparative example, which may result in the precipitation still containing more potassium ions and other impurities.

[0161] The crystallization endpoint temperature and the holding time have an important influence on the growth and perfection of the crystal. In the embodiments, by controlling the crystallization endpoint temperature and the appropriate holding time, the uniform growth and perfection of the crystal are promoted, which helps to reduce the residual potassium ions. The crystallization endpoint temperature and the holding time are not specifically described in the comparative examples, which may cause imperfect crystal growth or defects, thereby affecting the content of potassium ions.

[0162] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing lithium acesulfame by ion exchange, characterized in that The following steps are involved: Step 1, mixing reactants: adding ethanol to a reactor and turning on a stirrer to evenly distribute the ethanol; then slowly adding o-benzoylsulfonyl imide and continuing to stir until it is completely dissolved; Step 2, preparation and addition of lithium hydroxide suspension: In another container, lithium hydroxide is added to ethanol and stirred to form a uniform suspension, and then the suspension is slowly added to the reactor while maintaining stirring and controlling the temperature within a predetermined range; Step 3, adding acesulfame potassium solution dropwise: preparing an ethanol solution of acesulfame potassium in another container, and then slowly adding the solution dropwise to the reactor under continuous stirring and temperature control; Step 4, stirring and removing the precipitate: after the dropwise addition is completed, the reaction mixture is continued to be stirred for a period of time, and then the generated precipitate is separated from the reaction solution by a filtering device; Step 5, filtrate concentration and crystallization: the filtered filtrate is concentrated to remove most of the ethanol; Further purification is performed before crystallization, and then the temperature is controlled to be gradually lowered to the crystallization endpoint temperature, and seed crystals are added to promote crystallization; Step 6, product collection and drying: collect the formed lithium acesulfame crystals by filtration, and place them in a vacuum drying oven to dry to constant weight.

2. The method for preparing lithium acesulfame according to claim 1, characterized in that: In step 1, the amount of ethanol added is 1500-1700 L, and the amount of o-benzoylsulfonimide added is 500 mol.

3. The method for preparing lithium acesulfame according to claim 1, characterized in that In step 2, 500 mol of lithium hydroxide is added to 400-500 L of ethanol and stirred to form a uniform suspension, and then slowly added to the reactor at a rate of about 100 L per hour, and the temperature is controlled between 15 and 30°C.

4. The method for preparing lithium acesulfame according to claim 1, characterized in that: In step 3, 500 mol of acesulfame potassium is dissolved in 5000L-6000L of ethanol, and the solution is slowly added dropwise to the reactor.

5. The method for preparing lithium acesulfame according to claim 1, characterized in that: In step 4, after stirring the reaction mixture for 4-5.5 hours, the generated precipitate is separated from the reaction solution by a filtration device, and the filtration pressure is set between 0.2-0.4 MPa.

6. The method for preparing lithium acesulfame according to claim 1, characterized in that: In step 5, the crystallization end point is a temperature of 6-10° C., and the cooling rate is 1-2° C. per hour; at the same time, lithium acesulfame powder with a purity of not less than 99.9% is added as a seed crystal, and the amount of the seed crystal added is 0.5% of the total mass of the reaction solution.

7. The method for preparing lithium acesulfame according to claim 6, characterized in that: Ethanol was used as the main solvent and 5-10% deionized water was added as the auxiliary solvent.

8. The method for preparing lithium acesulfame according to claim 7, characterized in that: Features The resistivity of the deionized water is not less than 18 MΩ·cm.

9. The method for preparing lithium acesulfame according to any one of claims 1 to 8, characterized in that The potassium ion content in the lithium acesulfame crystals prepared by the method is less than 20 ppm.

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