Method for measuring water content of anhydrous lithium hydroxide based on vacuum drying method

Abstract

The invention belongs to the technical field of chemical detection and analysis, and particularly relates to a method for determining the moisture content of anhydrous lithium hydroxide based on a vacuum drying method. According to the method for measuring the moisture content of anhydrous lithium hydroxide based on the vacuum drying method, drying treatment and cooling treatment are optimally selected under the vacuum condition on the basis of a traditional drying gravimetric method, a sample is prevented from being in contact with air, moisture absorption and carbonization are prevented, it is effectively guaranteed that the whole drying-cooling process is not affected by the outside world, and the detection accuracy is high. The stability of the to-be-detected sample is ensured, the moisture content of anhydrous lithium hydroxide can be rapidly and accurately determined, and the repeatability of a determination result is improved.

Description

Technical Field

[0001] This invention belongs to the field of chemical detection and analysis technology, specifically relating to a method for determining the moisture content of anhydrous lithium hydroxide based on vacuum drying. Background Technology

[0002] Anhydrous lithium hydroxide (LiOH), as a key lithium compound, has irreplaceable application value in new energy, aerospace, pharmaceuticals, and chemical industries. In the lithium-ion battery industry, anhydrous lithium hydroxide is a core raw material for preparing high-nickel ternary cathode materials. Its moisture content directly affects the crystallinity, morphology, and electrochemical performance of the cathode material. Excessive moisture content can lead to lithium volatilization and abnormal grain growth during sintering, thereby reducing the battery's energy density and cycle life. In the aerospace field, anhydrous lithium hydroxide is commonly used as a CO2 absorbent in spacecraft cabins; excessive moisture content significantly reduces its absorption efficiency and affects the stability of cabin environmental control. In the pharmaceutical field, anhydrous lithium hydroxide is used as an alkaline catalyst or raw material; fluctuations in moisture content can lead to decreased reaction rates and product purity, increasing production risks. Therefore, accurately controlling the moisture content of anhydrous lithium hydroxide is crucial for ensuring product quality and downstream application performance. Currently, the main methods for testing the moisture content of solid chemical products include the Karl Fischer method, gravimetric method, infrared spectroscopy, and gas chromatography.

[0003] The Karl Fischer method, due to its advantages of high sensitivity, good selectivity, and fast determination speed, is widely used for the determination of trace moisture in various organic and inorganic compounds, and is also one of the recommended methods for testing the moisture content of anhydrous lithium hydroxide in current national standards. However, in practical applications, existing testing methods still have insurmountable technical difficulties when dealing with samples such as anhydrous lithium hydroxide that are strongly alkaline, hygroscopic, and prone to side reactions with the test system. First, the Karl Fischer method requires small sample sizes: milligram-level sampling cannot represent the true moisture content of a whole batch of hygroscopic anhydrous lithium hydroxide samples with inconsistent homogeneity, resulting in poor data parallelism and low reliability. Secondly, the operating environment is harsh: the entire determination process requires strict isolation from air humidity, demanding extremely high operational skills and environmental conditions; even slight negligence can lead to significant deviations in results. Thirdly, there are reagent consumption and costs: specialized instruments and reagents are required, resulting in usage and maintenance costs.

[0004] The traditional gravimetric method (also known as the drying method) is the classic and fundamental method for determining the moisture content of substances. Its core principle is based on the quantitative relationship between the volatility of water and the total mass of the sample. By measuring the mass difference of the sample before and after drying, the proportion of water in the total mass of the sample is calculated. This method is applicable to most solid, liquid, or semi-solid substances, and is particularly accurate for samples without volatile components. However, for the determination of the moisture content of anhydrous lithium hydroxide, improper drying temperature may lead to the decomposition of lithium hydroxide or incomplete removal of moisture; moreover, the sample is exposed to air during the cooling process, making it prone to moisture absorption, resulting in higher results; and the entire process is not standardized, resulting in poor repeatability and low precision.

[0005] Therefore, the development of a simple, interference-resistant, and highly accurate method for testing the moisture content of anhydrous lithium hydroxide is of great significance. Summary of the Invention

[0006] Therefore, the technical problem to be solved by the present invention is to provide a method for determining the moisture content of anhydrous lithium hydroxide based on vacuum drying, which has the advantages of more stable results, stronger representativeness, and stronger anti-interference ability.

[0007] To solve the above-mentioned technical problems, the present invention provides a method for determining the moisture content of anhydrous lithium hydroxide based on vacuum drying, comprising the following steps:

[0008] (1) Constant weight of container: Take the measuring container and dry it to constant weight, and record its mass m0;

[0009] (2) Sample weighing: Take anhydrous lithium hydroxide sample, mix well, weigh the sample to be tested and place it in the measuring container, and record the total mass m1 of the two;

[0010] (3) Vacuum drying: The sample to be tested, together with the measuring container, is subjected to a second drying under vacuum conditions;

[0011] (4) Vacuum cooling: The sample to be tested, together with the measuring container, is cooled to room temperature under vacuum conditions;

[0012] (5) Constant weight weighing: Weigh the sample to be tested and the measuring container again to constant weight, and record the total mass m2 of the two.

[0013] (6) Calculate the moisture content of the anhydrous lithium hydroxide sample according to the following formula:

[0014] Moisture content (%) = [(m1-m2) / (m1-m0)] × 100%.

[0015] Specifically, in the method for determining the moisture content of anhydrous lithium hydroxide based on vacuum drying, the measuring container in step (1) is an inert material container.

[0016] Specifically, in the method for determining the moisture content of anhydrous lithium hydroxide based on vacuum drying, the measuring container in step (1) includes a tetrafluoroethylene container or a quartz beaker.

[0017] Specifically, in the method for determining the moisture content of anhydrous lithium hydroxide based on vacuum drying, step (1) includes:

[0018] The temperature of the first drying step is 95-105℃; and / or,

[0019] The first drying step takes 1-2 hours.

[0020] Specifically, in the method for determining the moisture content of anhydrous lithium hydroxide based on vacuum drying, in step (2), the weight of the sample to be tested is 30±0.1g.

[0021] Specifically, in the method for determining the moisture content of anhydrous lithium hydroxide based on vacuum drying, step (3) includes:

[0022] The temperature of the second drying step is 150℃-155℃; and / or,

[0023] The vacuum degree of the second drying step is ≥ -0.08 MPa; and / or,

[0024] The second drying step takes 1-3 hours.

[0025] Specifically, in the method for determining the moisture content of anhydrous lithium hydroxide based on vacuum drying, in step (4), the vacuum degree of the vacuum cooling step is ≥-0.08MPa.

[0026] Specifically, in the method for determining the moisture content of anhydrous lithium hydroxide based on vacuum drying, the vacuum cooling step has the same vacuum level as the vacuum drying step.

[0027] Specifically, in the method for determining the moisture content of anhydrous lithium hydroxide based on vacuum drying, steps (1), (2), or (5) further include the step of repeatedly weighing until the mass difference is ≤0.002g.

[0028] This invention also discloses the application of the method for determining the moisture content of anhydrous lithium hydroxide based on vacuum drying in the field of moisture content detection of anhydrous lithium hydroxide.

[0029] The method for determining the moisture content of anhydrous lithium hydroxide based on vacuum drying described in this invention optimizes the drying and cooling processes under vacuum conditions, based on the traditional gravimetric drying method. This eliminates contact between the sample and air, preventing moisture absorption and carbonization, effectively ensuring that the entire drying-cooling process is unaffected by external factors, ensuring the stability of the sample, avoiding carbonization and moisture absorption during the measurement process, reducing the stringent requirements on the operating environment, and enabling rapid and accurate determination of the moisture content of anhydrous lithium hydroxide, thus improving the repeatability of the measurement results.

[0030] The method for determining the moisture content of anhydrous lithium hydroxide based on vacuum drying described in this invention optimizes the drying parameters, specifically the combination of a drying temperature of 150℃-155℃ and a vacuum degree of ≥-0.06MPa. This effectively balances drying efficiency and sample stability, ensuring complete evaporation of moisture without causing sample decomposition. The entire method exhibits good sample stability.

[0031] The method for determining the moisture content of anhydrous lithium hydroxide based on vacuum drying described in this invention addresses the strong hygroscopicity and easy reaction of anhydrous lithium hydroxide with carbon dioxide. By using large sample quantities at the gram level, the method can better reflect the moisture content of the entire batch of material. The gram-level sampling data has good parallelism and avoids the phenomenon of "fluctuations". It fundamentally solves the core problem of the Karl Fischer method, which is not representative due to small sample quantities. It also solves the defect of poor macroscopic uniformity of batches of anhydrous lithium hydroxide samples. The results are not only more stable but also more representative.

[0032] Previous research in this invention revealed that for the determination of moisture content in anhydrous lithium hydroxide, the error caused by uneven sampling is far greater than the weighing error. This method, through precise system design, effectively controls the operational errors that may arise from large sample volumes, thereby achieving a more accurate and reliable measurement of the overall true moisture content of the sample. Therefore, its "accuracy" lies in reflecting the true state of the batch sample, rather than in the precise measurement of a few milligrams of sample.

[0033] The method for determining the moisture content of anhydrous lithium hydroxide based on vacuum drying described in this invention does not pursue "precise" measurement of a few particles at the milligram scale, but rather achieves accurate assessment of the overall "average" moisture content of a batch of samples at the gram scale through precise control of mass changes and suppression of chemical processes. The method's RSD value is far lower than that of the Karl Fischer method, which is the most direct proof of its improved accuracy and precision.

[0034] The method for determining the moisture content of anhydrous lithium hydroxide based on vacuum drying described in this invention solves the representativeness problem with "gram-level sampling", achieves accurate measurement with "constant weight difference method", and ensures the specificity of measurement with "optimized drying and vacuum cooling parameters". The three are closely linked and together constitute a reliable method that can accurately reflect the true moisture content of batch samples of anhydrous lithium hydroxide.

[0035] The method for determining the moisture content of anhydrous lithium hydroxide based on vacuum drying described in this invention uses inert containers such as tetrafluoroethylene, which have the advantages of corrosion resistance and non-adhesion, improving weighing accuracy, and eliminating the need to purchase additional instruments and special chemical reagents, thus reducing detection costs.

[0036] The method for determining the moisture content of anhydrous lithium hydroxide based on vacuum drying described in this invention differs from traditional vacuum drying methods primarily in that it utilizes a large sample volume (approximately 30g), fundamentally solving the problem of unrepresentative measurement results caused by the hygroscopic nature and poor uniformity of anhydrous lithium hydroxide. Furthermore, this invention precisely optimizes drying parameters (150-155℃, vacuum degree ≥ -0.06MPa) and introduces a crucial "vacuum cooling" step after drying. This not only significantly improves drying efficiency but also thoroughly prevents the sample from absorbing moisture or reacting with carbon dioxide for decomposition during cooling. Therefore, while ensuring complete removal of moisture, it greatly enhances the accuracy, stability, and repeatability of the measurement results.

[0037] The method for determining the moisture content of anhydrous lithium hydroxide based on vacuum drying described in this invention further employs vacuum cooling after vacuum drying, which can effectively suppress carbonization: the change in lithium carbonate content after drying is minimal, directly verifying that the combination of specific temperature and vacuum cooling successfully avoids secondary moisture absorption and carbonization of the sample, effectively ensuring the detection accuracy of the entire method. Attached Figure Description

[0038] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings, wherein...

[0039] Figure 1 This is a flowchart of the method described in this invention. Detailed Implementation

[0040] The present invention provides a method for determining the moisture content of anhydrous lithium hydroxide based on vacuum drying in the following embodiments, comprising the following steps:

[0041] (1) Constant weight of container: Take the measuring container and dry it to constant weight, and record its mass m0;

[0042] (2) Sample weighing: Take anhydrous lithium hydroxide sample, mix well, weigh the sample to be tested and place it in the measuring container, and record the total mass m1 of the two;

[0043] (3) Vacuum drying: The sample to be tested, together with the measuring container, is subjected to a second drying under vacuum conditions;

[0044] (4) Vacuum cooling: The sample to be tested, together with the measuring container, is cooled to room temperature under vacuum conditions;

[0045] (5) Constant weight weighing: Weigh the sample to be tested and the measuring container again to constant weight, and record the total mass m2 of the two.

[0046] (6) Calculate the moisture content of the anhydrous lithium hydroxide sample according to the following formula:

[0047] Moisture content (%) = [(m1-m2) / (m1-m0)] × 100%.

[0048] As an exemplary implementation, such as Figure 1 The flowchart shown illustrates the following embodiments of the present invention, where the method for determining the moisture content of anhydrous lithium hydroxide based on vacuum drying specifically includes the following steps:

[0049] (1) Constant weight of container: Use a PTFE beaker, watch glass or quartz beaker, dry at 95℃-105℃ for 1-2 hours, cool and weigh, repeat until constant weight (mass difference ≤0.002g), record mass m0;

[0050] (2) Sample weighing: Mix the anhydrous lithium hydroxide sample evenly, and crush it if necessary; weigh about 30g of the sample into a constant weight beaker and record the total mass m1.

[0051] (3) Vacuum drying: Place the above samples (anhydrous lithium hydroxide sample and container) into a vacuum drying oven and dry for 2-3 hours at 150℃-155℃ and vacuum degree ≥-0.08MPa;

[0052] (4) Vacuum cooling: Continue to cool the above samples to room temperature under vacuum in the drying oven;

[0053] (5) Constant weight weighing: Weigh immediately after taking it out, and repeat drying, cooling and weighing until constant weight (mass difference ≤ 0.002g), and record the mass m2;

[0054] (6) Calculate the moisture content of the anhydrous lithium hydroxide sample according to the following formula:

[0055] Moisture content (%) = [(m1-m2) / (m1-m0)]×100%; where m0 is the mass of the container after constant weight, m1 is the total mass of the sample and container before drying, and m2 is the total mass of the sample and container after constant weight after drying.

[0056] Example 1

[0057] In this embodiment, the water content of anhydrous lithium hydroxide samples was determined using the method described above.

[0058] In this embodiment, the method for determining the moisture content of anhydrous lithium hydroxide based on vacuum drying specifically includes the following steps:

[0059] (1) Constant weight of container: Use a tetrafluoroethylene beaker, watch glass or quartz beaker, dry at 100℃ for 2 hours, cool and weigh, repeat until constant weight (mass difference ≤ 0.002g), and record the mass m0;

[0060] (2) Sample weighing: Mix the anhydrous lithium hydroxide sample evenly, and crush it if necessary; weigh about 30g of the sample into a constant weight beaker and record the total mass m1.

[0061] (3) Vacuum drying: Place the above samples (anhydrous lithium hydroxide sample and container) into a vacuum drying oven and dry for 2 hours at 150℃ and a vacuum degree of -0.06MPa;

[0062] (4) Vacuum cooling: Continue to cool the above sample to room temperature in the drying oven while maintaining a constant vacuum level;

[0063] (5) Constant weight weighing: Weigh immediately after taking it out, and repeat drying, cooling and weighing until constant weight (mass difference ≤ 0.002g), and record the mass m2;

[0064] (6) Calculate the moisture content of the anhydrous lithium hydroxide sample.

[0065] In this embodiment, the moisture content was detected using the conventional method of existing technology. Five parallel measurements were performed on the same homogeneous sample, and the results are shown in Table 1 below.

[0066] Table 1 Sample test data

[0067]

[0068]

[0069] It is evident that when the method of the present invention measures the same batch of anhydrous lithium hydroxide samples, the RSD value of the entire method (3.96%) is much lower than that of the Karl Fischer method (25.8%).

[0070] This directly proves that by using large sample volumes at the gram level, the fluctuation of the results when repeatedly measuring the same batch of samples is much smaller than that of the Karl Fischer method, which significantly improves the precision, stability and reliability of the measurement results and solves the core defects pointed out in the background art.

[0071] The method described in this invention involves vacuum drying at 150℃-155℃ and a vacuum degree ≥-0.06MPa. This efficiently removes the water of crystallization from the sample, significantly increasing the relative percentage of its main component, LiOH. Meanwhile, the lithium carbonate content shows only a very slight change. This indicates that the optimized drying conditions effectively prevent the decomposition and carbonization of lithium hydroxide (2LiOH+CO2→Li2CO3+H2O), ensuring the accuracy of the measurement process and high sample stability.

[0072] In summary, the method of this invention verifies the reliability of the moisture determination results by accurately analyzing the changes in main and secondary components before and after drying. This data indicates that the method is specifically designed for anhydrous lithium hydroxide, maximizing the preservation of the sample's chemical stability while removing moisture, and demonstrating high accuracy.

[0073] Example 2

[0074] In this embodiment, the method for determining the moisture content of anhydrous lithium hydroxide based on vacuum drying specifically includes the following steps:

[0075] (1) Constant weight of container: Use a tetrafluoroethylene beaker, watch glass or quartz beaker, dry at 95°C for 3 hours, cool and weigh, repeat until constant weight (mass difference ≤ 0.002g), and record the mass m0;

[0076] (2) Sample weighing: Mix the anhydrous lithium hydroxide sample evenly, and crush it if necessary; weigh about 30g of the sample into a constant weight beaker and record the total mass m1.

[0077] (3) Vacuum drying: Place the above samples (anhydrous lithium hydroxide sample and container) into a vacuum drying oven and dry for 2 hours at 155℃ and a vacuum degree of -0.08MPa;

[0078] (4) Vacuum cooling: Continue to cool the above samples to room temperature under vacuum in the drying oven;

[0079] (5) Constant weight weighing: Weigh immediately after taking it out, and repeat drying, cooling and weighing until constant weight (mass difference ≤ 0.002g), and record the mass m2;

[0080] (6) Calculate the moisture content of the anhydrous lithium hydroxide sample.

[0081] Example 3

[0082] In this embodiment, the water content of anhydrous lithium hydroxide samples was determined using the method described above.

[0083] In this embodiment, the method for determining the moisture content of anhydrous lithium hydroxide based on vacuum drying specifically includes the following steps:

[0084] (1) Constant weight of container: Use a tetrafluoroethylene beaker, watch glass or quartz beaker, dry at 105℃ for 2 hours, cool and weigh, repeat until constant weight (mass difference ≤ 0.002g), record mass m0;

[0085] (2) Sample weighing: Mix the anhydrous lithium hydroxide sample evenly, and crush it if necessary; weigh about 30g of the sample into a constant weight beaker and record the total mass m1.

[0086] (3) Vacuum drying: Place the above samples (anhydrous lithium hydroxide sample and container) into a vacuum drying oven and dry for 2 hours at 150℃ and a vacuum degree of -0.04MPa;

[0087] (4) Vacuum cooling: Continue to cool the above samples to room temperature under vacuum in the drying oven;

[0088] (5) Constant weight weighing: Weigh immediately after taking it out, and repeat drying, cooling and weighing until constant weight (mass difference ≤ 0.002g), and record the mass m2;

[0089] (6) Calculate the moisture content of the anhydrous lithium hydroxide sample.

[0090] Example 4

[0091] This embodiment is based on the scheme of Example 1 and further verifies the effectiveness of the whole method. Three batches of anhydrous lithium hydroxide samples with known components were measured, and the measurement results are shown in Table 2 below.

[0092] Table 2 Results of Method Validation

[0093]

[0094] In this embodiment, by measuring moisture content and simultaneously analyzing the chemical composition before and after drying, taking sample #1 as an example, the LiOH content increased from 99.50% to 99.69%. After moisture removal, the total mass of the sample decreased, while the absolute mass of LiOH remained essentially unchanged, thus its mass fraction increased accordingly. The increase in LiOH content after drying (+0.19%) is reasonably consistent with the measured moisture content (0.20%) in terms of numerical trend. The entire detection result forms a self-consistent chain of evidence, indicating that the moisture determination result is consistent with the mass conservation relationship of the main components. The detection results of samples #2 and #3 also demonstrate the rationality and accuracy of the method described in this invention.

[0095] Example 3

[0096] This embodiment is based on the scheme of Example 1, and tests the effect of different drying temperatures (105, 120, 150, 180℃) on the moisture content of anhydrous lithium hydroxide.

[0097] In this embodiment, the moisture measurement results and sample state results at different temperatures are shown in Table 1 below, the sample composition change analysis (comparison before and after drying) and energy consumption assessment results at different temperatures are shown in Table 2 below, and the repeatability test results are shown in Table 3 below.

[0098] Table 1. Moisture content determination results and sample condition at different temperatures.

[0099]

[0100] Table 2: Analysis of sample composition changes at different temperatures (comparison before and after drying) and energy consumption assessment

[0101]

[0102]

[0103] Table 3. Repeatability test results (RSD%, n=5)

[0104]

[0105] As can be seen from the technical effects in Example 3, under a specific vacuum of ≥-0.06MPa, the boiling point of water is reduced, making it possible to remove moisture rapidly at 150℃-155℃, effectively ensuring that the impact on the entire drying process is minimized.

[0106] As can be seen, this invention tests the moisture content of anhydrous lithium hydroxide using vacuum drying technology. Addressing the unique technical challenges of moisture determination in anhydrous lithium hydroxide samples—a material with poor representativeness—and its extreme sensitivity to moisture and carbon dioxide in the air during cooling, this invention further selects a heating system far exceeding the 105°C typically used in atmospheric pressure drying methods, choosing a high-temperature drying range of 150°C-155°C. This aims to rapidly and thoroughly remove water of crystallization, effectively solving the shortcomings of traditional Karl Fischer methods and ordinary drying methods in systematically addressing external influences.

[0107] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for determining the moisture content of anhydrous lithium hydroxide based on a vacuum drying method, characterized by, The method comprises the following steps: (1) container constant weight: taking a measuring container to perform first drying to constant weight, and recording the mass m0 thereof; (2) sample weighing: taking a lithium hydroxide anhydrous sample, uniformly mixing the sample, taking a sample to be measured and placing the sample in the measuring container, and recording the total mass m1 of the two; (3) vacuum drying: performing second drying on the sample to be measured together with the measuring container under vacuum conditions; (4) vacuum cooling: cooling the sample to be measured together with the measuring container to room temperature under vacuum conditions; (5) constant weight weighing: weighing the sample to be measured and the measuring container to constant weight again, and recording the total mass m2 of the two; (6) calculating the moisture content of the lithium hydroxide anhydrous sample according to the following formula: Moisture content (%) = [(m1-m2) / (m1-m0)]x100%.

2. The method for determining the moisture content of anhydrous lithium hydroxide according to claim 1, wherein In the step (1), the measuring container is an inert material container.

3. The method of determining the moisture content of anhydrous lithium hydroxide according to claim 2, wherein In the step (1), the measuring container comprises a tetrafluoroethylene container or a quartz beaker.

4. The method for determining the moisture content of anhydrous lithium hydroxide according to any one of claims 1 to 3, characterized in that, In the step (1): the temperature of the first drying step is 95-105℃; and / or, the time of the first drying step is 1-2h.

5. The method for determining the moisture content of anhydrous lithium hydroxide according to claim 1, wherein In the step (2), the weighing weight of the sample to be measured is 30±0.1g.

6. The method for determining the moisture content of anhydrous lithium hydroxide according to claim 1, wherein In the step (3): the temperature of the second drying step is 150℃-155℃; and / or, the vacuum degree of the second drying step is ≥-0.08MPa; and / or, the time of the second drying step is 1-3h.

7. The method for determining the moisture content of anhydrous lithium hydroxide according to claim 1, wherein In the step (4), the vacuum degree of the vacuum cooling step is ≥-0.08MPa.

8. The method of determining the moisture content of anhydrous lithium hydroxide according to claim 7, wherein The vacuum degree of the vacuum cooling step is the same as that of the vacuum drying step.

9. The method for determining the moisture content of anhydrous lithium hydroxide according to claim 1, wherein In the steps (1), (2) or (5), the method further comprises the step of repeatedly weighing to a mass difference ≤0.002g.

10. The application of the method for determining the moisture content of lithium hydroxide anhydrous based on vacuum drying method according to any one of claims 1-9 in the field of detecting the moisture content of lithium hydroxide anhydrous.

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