Method for measuring contents of total carbon, inorganic carbon and organic carbon in titanium tetrachloride

Abstract

The invention discloses a method for determining the content of total carbon, inorganic carbon and organic carbon in titanium tetrachloride, and belongs to the technical field of analytical chemistry. The determination method comprises the following steps: under inert atmosphere protection and a low-temperature environment, adding a titanium tetrachloride sample into an inorganic acid solution, fully hydrolyzing, and fixing the volume to obtain hydrolysate; analyzing the concentration of total carbon and inorganic carbon in the hydrolysate by using a TOC (Total Organic Carbon) analyzer; and calculating the contents of total carbon, inorganic carbon and organic carbon in the titanium tetrachloride sample according to the concentrations of total carbon and inorganic carbon in the hydrolysate. According to the method, inorganic carbon and total carbon in the hydrolysate can be directly measured, the content of organic carbon is calculated through a difference value method, and accurate typing of carbon forms is achieved. The method is simple to operate, short in detection period, high in efficiency and lower in cost. The method can effectively solve the problem that blind areas exist in impurity traceability and accurate control due to the fact that detection data of total carbon, inorganic carbon and organic carbon cannot be accurately separated through an existing method for measuring the carbon-containing compounds in titanium tetrachloride.

Description

Technical Field

[0001] The invention belongs to the technical field of analytical chemistry, and in particular relates to a method for determining the contents of total carbon, inorganic carbon and organic carbon in titanium tetrachloride. Background Art

[0002] Titanium tetrachloride is the core raw material for the production of titanium sponge, and its purity directly affects the performance of downstream titanium alloys. In the current preparation process, in addition to the generation of inorganic impurities such as vanadium trichloride and silicon tetrachloride, it also contains 11 types of carbon-containing compounds (including inorganic carbon such as carbon dioxide and phosgene, and organic carbon such as chlorinated hydrocarbons and hexachlorobenzene), and the control of total carbon content is particularly critical. The detection of carbon-containing compounds faces a double dilemma: the sample will hydrolyze violently when it comes into contact with water to produce corrosive fumes, which will cause the decomposition of components and endanger operational safety; at the same time, there is a lack of standard reference materials, and the complex form of organic impurities makes it difficult to verify the test results. Because carbon impurities will be enriched in titanium alloys at four times the concentration when sponge titanium is produced by the magnesium thermal method, causing the mechanical properties and processing properties (strength, plasticity, corrosion resistance, welding performance) of titanium alloys to deteriorate. Establishing a detection method that accurately distinguishes total carbon, inorganic carbon and organic carbon has become a core technical bottleneck to ensure product quality.

[0003] The detection technology of carbon-containing compounds in titanium tetrachloride is currently mainly carried out through spectroscopy and chromatography, but it still faces multiple technical bottlenecks. Mainstream methods such as Fourier transform infrared absorption spectroscopy can identify a variety of organic matter and calculate total carbon, but require an absolutely dry or atmosphere-protected sample loading environment, and there are no corresponding standards and quality control samples, the accuracy of the measurement results is difficult to control, and the equipment cost is high. Although infrared absorption spectroscopy and gas chromatography can extract and analyze oils or some carbon-containing compounds, the hydrolysis reaction causes hydrogen chloride interference and organic matter volatilization, and the data reliability is limited. In the patent technology, CN119198283A discloses a method for measuring total carbon in titanium tetrachloride. This method is easy to operate and control quality, but the drying link of the hydrolyzate is long and the timeliness is insufficient. CN118533787A discloses a detection device for the impurity content of titanium tetrachloride oil. This method can only measure the organic carbon of oils with a boiling point lower than titanium tetrachloride, and faces the problem that calibration samples and quality control samples are not easy to obtain. CN116046600A discloses a method for detecting the carbon content in titanium tetrachloride. This method has the problem that some organic matter decomposes and volatilizes after hydrolysis or does not undergo hydrolysis, resulting in low measurement results. CN114778369A discloses a sample pretreatment method for detecting the carbon content of titanium tetrachloride by high-temperature burning. This method has the problem that some organic matter is distilled out in advance and cannot be carbonized, resulting in low measurement results. In addition, the weight method has a large error when the total carbon content is low.

[0004] In response to the problem of carbon loss caused by high temperature during the hydrolysis of titanium tetrachloride, existing studies have explored low-temperature hydrolysis technology, but there are essential differences between its technical goals and carbon detection needs. For example, some studies focus on regulating the hydrolysis conditions to directly generate titanium dioxide (such as the literature: Xu Jing et al. prepared rutile nano-titanium dioxide by low-temperature hydrolysis of titanium tetrachloride); other technologies obtain stable titanium tetrachloride solutions for subsequent synthesis by inhibiting the hydrolysis reaction (such as the literature: Zhou Zhongcheng et al. used low-temperature hydrolysis to prepare nano-barium carbonate powder). Obviously, the core goal of existing low-temperature hydrolysis technology is to control product morphology or prepare intermediates, rather than directional conversion of carbon-containing compounds, and does not involve morphological detection and analysis of total carbon, inorganic carbon and organic carbon.

[0005] The common problems of various methods for determining carbon compounds in titanium tetrachloride are prominent: volatile components are easy to lose, there is a lack of standard material calibration, and the detection range is incomplete, which makes it difficult to meet the precise control needs of carbon compounds in titanium tetrachloride. The total carbon in titanium tetrachloride is crucial to the quality control of titanium tetrachloride and subsequent titanium alloy products. The accuracy and stability shortcomings of existing technologies have become the core obstacles to the quality upgrade of titanium tetrachloride. Therefore, it is urgent to develop a detection scheme that takes into account the convenience of operation, data accuracy, good repeatability, and controllable costs. Summary of the invention

[0006] The present invention aims to solve three major problems of the existing method for determining carbon-containing compounds in titanium tetrachloride: 1) some components are easily volatilized and lost during sample pretreatment, resulting in low measurement results; 2) the existing method has the disadvantages of strict analysis conditions, high detection cost, great difficulty in quality control, poor timeliness and high energy consumption; 3) the existing technology cannot accurately separate the detection data of total carbon, inorganic carbon and organic carbon, resulting in blind spots in impurity traceability and precise control.

[0007] In order to solve the above technical problems, the technical solution of the present invention is as follows.

[0008] The present invention provides a method for determining the contents of total carbon, inorganic carbon and organic carbon in titanium tetrachloride, comprising the following steps: S1. Under inert atmosphere protection and low temperature environment, add titanium tetrachloride sample to quantitative inorganic acid solution for full hydrolysis, make up to volume with inorganic acid solution of the same concentration to obtain hydrolyzate, and simultaneously prepare blank solution; S2. Prepare inorganic carbon calibration solution, organic carbon calibration solution, mixed calibration solution and quality control solution respectively; S3. Use a TOC analyzer (with total carbon / total organic carbon determination function) to measure the mixed calibration solution of step S2, establish a calibration working curve and determine the detection method; S4. Analyze the hydrolyzate and blank solution of step S1 using the detection method of step S3 to determine the total carbon and inorganic carbon concentrations; S5. Calculate the total carbon, inorganic carbon and organic carbon contents in the titanium tetrachloride sample based on the total carbon and inorganic carbon concentrations in the hydrolyzate.

[0009] In the above measurement method, in step S1, the inert atmosphere is argon or nitrogen.

[0010] In the above measurement method, in step S1, the low temperature environment is 0~5°C.

[0011] Furthermore, the above low temperature environment is achieved by an ice water bath.

[0012] In the above determination method, in step S1, the amount of titanium tetrachloride sample added is 1-2 mL.

[0013] In the above determination method, in step S1, the amount of inorganic acid solution added is 40-60 mL, and the H + The concentration is 1.5~2.5mol / L.

[0014] Furthermore, the inorganic acid solution is at least one of a hydrochloric acid solution, a nitric acid solution, and a sulfuric acid solution.

[0015] In the above determination method, in step S1, the preparation method of the blank solution is the same as the preparation method of the hydrolyzate except that no titanium tetrachloride sample is added.

[0016] In the above determination method, in step S2, high-grade pure carbonate is used to prepare an inorganic carbon calibration solution.

[0017] Furthermore, the above-mentioned high-grade pure carbonate is a water-soluble carbonate, specifically at least one of sodium carbonate, sodium bicarbonate, potassium carbonate and lithium carbonate.

[0018] In the above determination method, in step S2, high-grade pure phthalates are used to prepare an organic carbon calibration solution.

[0019] Furthermore, the above-mentioned high-grade pure phthalate is any one of potassium phthalate, sodium phthalate, potassium hydrogen phthalate, and sodium hydrogen phthalate.

[0020] In the above determination method, in step S2, according to the sample carbon concentration range, an inorganic carbon calibration solution and an organic carbon calibration solution are taken to prepare a mixed calibration solution and a quality control solution with a gradient concentration of total carbon (total carbon = inorganic carbon + organic carbon) for establishing a standard working curve and quality control.

[0021] In the above determination method, in step S5, the calculation formula for the total carbon content in the titanium tetrachloride sample is: ω TC ={[(C TC1 -C TC0 )×V1]÷(V2×1.73)}×10-6 ×100%, where: ω TC Indicates the mass fraction of the total carbon content in the carbon tetrachloride sample, %; C TC1 Indicates the total carbon concentration in the hydrolyzate measured in step S4, mg / L; C TC0 Indicates the total carbon concentration in the blank solution measured in step S4, mg / L; V1 represents the volume of the hydrolyzate (total volume after constant volume), mL; V2 represents the volume of titanium tetrachloride sample, mL; 1.73 represents the density of titanium tetrachloride, g / mL.

[0022] In the above determination method, in step S5, the calculation formula for the inorganic carbon content in the titanium tetrachloride sample is: ω IC ={[(C IC1 -C IC0 )×V1]÷(V2×1.73)}×10 -6 ×100%, where: ω IC Indicates the mass fraction of inorganic carbon content in carbon tetrachloride sample, %; C IC1 Indicates the concentration of inorganic carbon in the hydrolyzate measured in step S4, mg / L; C IC0 Indicates the concentration of inorganic carbon in the blank solution measured in step S4, mg / L; V1 represents the volume of the hydrolyzate (total volume after constant volume), mL; V2 represents the volume of titanium tetrachloride sample, mL; 1.73 represents the density of titanium tetrachloride, g / mL.

[0023] In the above determination method, in step S5, the calculation formula for the organic carbon content in the titanium tetrachloride sample is: ω TOC =ω TC -ω IC , where: ω TOC Indicates the mass fraction of organic carbon content in carbon tetrachloride sample, %; ω TC Indicates the mass fraction of the total carbon content in the carbon tetrachloride sample, %; ω IC Indicates the mass fraction of inorganic carbon content in carbon tetrachloride sample, %.

[0024] The beneficial effects of the present invention are: 1. The present invention hydrolyzes titanium tetrachloride in an inorganic acid system of 1.5-2.5 mol / LH⁺ under inert gas protection and low temperature (0-5°C), which can significantly inhibit the volatilization and thermal decomposition of organic matter (such as CCl4 and COCl2), and effectively solves the problem of low measurement results caused by carbon loss due to high temperature in the traditional hydrolysis process.

[0025] 2. The present invention establishes for the first time a morphological classification detection system for carbon impurities in titanium tetrachloride (organic carbon = total carbon - inorganic carbon), measures total carbon and inorganic carbon separately, and obtains organic carbon by difference calculation, breaking through the limitation of existing technologies that only detect part of the carbon components, and providing direct data support for the traceability of impurity carbon and process control in the industrial production of carbon tetrachloride.

[0026] 3. Compared with the traditional hydrolysis-separation method, the present invention significantly improves the accuracy by directly measuring the total carbon and inorganic carbon content of the hydrolyzate and combining it with the indirect calculation of organic carbon; compared with existing technologies such as Fourier transform infrared spectroscopy, the present invention eliminates the complicated sample pretreatment process, the detection method is simpler, the detection cycle is shorter, the efficiency is higher, and it does not require the support of high-cost moisture-proof equipment, so the cost is lower.

[0027] 4. The present invention uses high-grade pure carbonate and phthalate to prepare calibration samples and quality control samples, which are not easy to volatilize, easier to obtain and operate, and the prepared calibration samples and quality control samples are more stable, and the measurement results have better repeatability. DETAILED DESCRIPTION

[0028] The technical solution of the present invention can be specifically implemented in the following manner.

[0029] The present invention provides a method for determining the contents of total carbon, inorganic carbon and organic carbon in titanium tetrachloride, comprising the following steps: Step 1: In an inert atmosphere and low temperature environment (0~5℃), add 40~60mL of inorganic acid solution ([H + ]=1.5~2.5mol / L), slowly add 1~2mL of titanium tetrachloride sample to fully hydrolyze, and then make up to 100mL with inorganic acid solution of the same concentration to obtain a hydrolyzate.

[0030] In one embodiment of the present invention, the inert atmosphere is a nitrogen or argon atmosphere.

[0031] In one embodiment of the present invention, the low temperature environment is achieved by an ice-water bath, that is, the reaction container containing the inorganic acid solution is placed in an ice-water bath at 0-5°C, and then the titanium tetrachloride sample is added for full hydrolysis.

[0032] In one embodiment of the present invention, the above-mentioned inorganic acid solution is a hydrochloric acid solution, a nitric acid solution or a sulfuric acid solution; or, the inorganic acid solution is a mixed solution of hydrochloric acid and nitric acid, a mixed solution of hydrochloric acid and sulfuric acid, or a mixed solution of nitric acid and sulfuric acid; or, the inorganic acid solution is a mixed solution of hydrochloric acid, nitric acid and sulfuric acid.

[0033] Titanium tetrachloride is hydrolyzed to form Ti(OH) n ·Cl (4-n) (n=1,2,3,4) compounds, inorganic carbon compounds and organic carbon compounds in titanium tetrachloride undergo corresponding hydrolysis reactions to generate H2CO3 and organic acids. The main reaction equations are as follows: nH + +TiCl4=nHCl+Ti(OH) n ·Cl (4-n) (n=1,2,3,4); COS+2H2O=H2CO3+H2S; CO2+H2O=H2CO3; COCl2+2H2O=H2CO3+2HCl; CS2+3H2O=H2CO3+2H2S; CH2ClCOCl+H2O=CH2ClCOOH+HCl; CHCl2COCl+H2O=CHCl2COOH+HCl; CCl3COCl+H2O=CCl3COOH+HCl.

[0034] Other extremely small amounts of organic carbon compounds such as oil compounds (CH hydrocarbon compounds), CCl4 (carbon tetrachloride), C6Cl6 (hexachlorobenzene), and C=O (carbonyl compounds) are difficult to hydrolyze in inorganic acids and exist in the hydrolyzate. After stirring, a water-in-oil mixed solution containing a relatively low concentration will be formed.

[0035] The present invention uses a low-temperature inorganic acid hydrolysis system to convert carbon-containing compounds in titanium tetrachloride into detectable H2CO3 and organic acids, and disperses some difficult-to-hydrolyze organic carbon liquid in the form of a detectable water-in-oil emulsion in the hydrolyzate. The inorganic carbon and total carbon in the hydrolyzate are directly measured using a TOC analyzer, and the organic carbon is obtained by the difference method to achieve accurate carbon morphology classification. Compared with the existing technology (such as the strong base full conversion method used in CN119198283A), although the total carbon can be measured, its alkaline hydrolysis environment completely converts organic impurities into organic salts and carbonates, resulting in inorganic / organic carbon data overlap, and the initial form of impurity carbon cannot be traced.

[0036] The invention controls the reaction temperature by an ice-water bath, thereby suppressing local overheating caused by the violent hydrolysis of titanium tetrachloride; the inert atmosphere can prevent the interference of moisture and oxygen in the air on the hydrolysis of titanium tetrachloride; the purpose of using the same concentration of inorganic acid solution to fix the volume is to prevent the acidity of the solution from decreasing after dilution, and titanium tetrachloride from being hydrolyzed into titanium dioxide, resulting in turbidity or precipitation of the hydrolyzed solution.

[0037] The total carbon mass fraction in refined titanium tetrachloride is generally 0.0001~0.01%, the lower limit of measurement of TOC carbon meter is generally 0.00001%, and the optimal measurement range is 0.0001~1.0%. If the concentration is too high, the sample solution needs to be diluted before measurement. Therefore, the present invention limits the addition amount of titanium tetrachloride to 1~2mL according to the total carbon content in titanium tetrachloride and the lower limit of instrument measurement and the optimal measurement range. At the same time, in order to achieve the purpose of energy conservation and emission reduction, the acid consumed in the experiment and the waste liquid generated are controlled to be as small as possible, and the present invention limits the addition amount of inorganic acid solution to 40~60mL.

[0038] Due to the low total carbon content in titanium tetrachloride, when the titanium tetrachloride sample volume is less than 1mL, the total carbon concentration in the hydrolyzate is lower than the optimal measurement range of the instrument due to the small sample volume, resulting in poor stability of the measurement results and increased errors; at the same time, if the volume of the hydrolyzate is too small (less than 30mL), after titanium tetrachloride is added to the hydrolyzate, since hydrolysis is an exothermic reaction, it is easy to cause the local temperature of the hydrolyzate to be too high, causing the decomposition of some carbon compounds (such as H2CO3), and titanium tetrachloride is not easily hydrolyzed completely, and the total carbon measurement result is low. When the titanium tetrachloride sample volume is greater than 2mL, since titanium tetrachloride is added slowly, it will increase the time consumption, and the volume of the hydrolyzate will also increase accordingly. Although the increase in the volume of the hydrolyzate is conducive to controlling the temperature of the hydrolyzate system, too much hydrolyzate will increase the consumption of acid, and the waste liquid generated at the end of the experiment will also increase, which is not conducive to energy conservation and emission reduction. The experiment found that when the titanium tetrachloride sample volume is selected as 1~2mL, the hydrolyzate is selected as 40~60mL, and the volume is fixed to 100mL after hydrolysis, the result concentration is just within the optimal measurement range of the instrument.

[0039] In one embodiment of the present invention, while preparing the hydrolyzate, a blank control test is performed simultaneously, and except that the titanium tetrachloride sample is not added, the remaining operations are consistent with step 1 to obtain a blank solution. The present invention accurately corrects the background carbon interference introduced by the reagent and the environment through the blank control test to ensure the traceability and accuracy of the test results.

[0040] Step 2: Use high-grade pure carbonate to prepare inorganic carbon calibration solution, and use high-grade pure phthalate to prepare organic carbon calibration solution; according to the carbon concentration range of the sample, take inorganic carbon calibration solution and organic carbon calibration solution to prepare mixed calibration solution and quality control solution with total carbon gradient concentration for establishing standard working curve and quality control.

[0041] In a specific embodiment of the present invention, the above-mentioned high-grade pure carbonate is at least one of sodium carbonate, sodium bicarbonate, potassium carbonate and lithium carbonate.

[0042] In a specific embodiment of the present invention, the above-mentioned high-grade pure phthalate is any one of potassium phthalate, sodium phthalate, potassium hydrogen phthalate, and sodium hydrogen phthalate.

[0043] Step 3: Measure the mixed calibration solution by a TOC analyzer, establish a standard working curve and determine the detection method; use the detection method to analyze the hydrolyzate and blank solution of step S1 to determine their total carbon and inorganic carbon concentrations; calculate the total carbon, inorganic carbon and organic carbon contents in the titanium tetrachloride sample based on the total carbon and inorganic carbon concentrations in the hydrolyzate solution.

[0044] In a specific embodiment of the present invention, the TOC analyzer has the total carbon / total organic carbon determination function and is suitable for the detection and analysis of oil, grease and lubricating oil.

[0045] Example

[0046] 1. Implementation of the determination method of total carbon, inorganic carbon and organic carbon content in titanium tetrachloride 1. Reagent preparation: (1) Preparation of inorganic acid solution: Take a certain volume of concentrated hydrochloric acid, slowly add it into a certain volume of carbon dioxide-free ultrapure water, mix it to the fixed volume, and prepare [H + ] 0.5mol / L, 1.0mol / L, 1.5mol / L, 2.0mol / L, 2.5mol / L, and 3.0mol / L hydrochloric acid solutions are available for use.

[0047] Take a certain volume of concentrated nitric acid, slowly add it into a certain volume of carbon dioxide-free ultrapure water, mix it to a fixed volume, and prepare [H + ] 0.5mol / L, 1.0mol / L, 1.5mol / L, 2.0mol / L, 2.5mol / L and 3.0mol / L nitric acid solutions are available for use.

[0048] Take a certain volume of concentrated sulfuric acid, slowly add it into a certain volume of carbon dioxide-free ultrapure water, mix it to a fixed volume, and prepare [H + ] are 0.5mol / L, 1.0mol / L, 1.5mol / L, 2.0mol / L, 2.5mol / L and 3.0mol / L sulfuric acid solutions for use.

[0049] (2) Preparation of organic carbon calibration solution: Accurately weigh 2.5221 g of potassium phthalate dried at 105°C into a 1000 mL volumetric flask, dissolve and dilute to volume with carbon dioxide-free ultrapure water, shake well, and prepare an organic carbon calibration solution with a mass concentration of 1000 mg / L.

[0050] (3) Preparation of inorganic carbon calibration solution: Accurately weigh 8.8262 g of sodium carbonate dried at 105°C into a 1000 mL volumetric flask, dissolve and dilute to volume with carbon dioxide-free ultrapure water, shake well, and prepare an inorganic carbon calibration solution with a mass concentration of 1000 mg / L.

[0051] (4) Preparation of mixed calibration solution and quality control solution: Use a pipette or pipette with an appropriate range to take 10.00 mL of organic carbon calibration solution and inorganic carbon calibration solution respectively and place them in a 100 mL volumetric flask, make up to volume with carbon dioxide-free ultrapure water, shake well, and obtain a mixed calibration intermediate solution with a mass concentration of 100 mg / L.

[0052] According to the contents shown in Table 1, take different volumes of mixed calibration intermediate solution to prepare a series of mixed calibration solutions and quality control solutions with concentration gradients, make up to volume with carbon dioxide-free ultrapure water, and shake well. The calibration solution range can be appropriately adjusted according to the sample content range.

[0053] Table 1. Preparation of mixed calibration solutions and quality control solutions

[0054] 2. The determination of total carbon, inorganic carbon and organic carbon content in titanium tetrachloride specifically comprises the following steps: (1) Under the protection of argon atmosphere, add 40 mL of inorganic acid solution into a 200 mL hydrolysis cup, and place the hydrolysis cup in an ice water bath at a temperature of 0-5 °C. Under electromagnetic stirring, slowly add 1.0 mL of titanium tetrachloride sample into the hydrolysis cup and stir for 5 min to fully hydrolyze carbon tetrachloride. Then transfer the hydrolyzate to a 100 mL volumetric flask and make up the volume with the same concentration of inorganic acid solution. Shake well to obtain the hydrolyzate for use.

[0055] (2) Simultaneously carry out a blank control experiment. Under the protection of argon atmosphere, add 40 mL of inorganic acid solution into a 200 mL hydrolysis cup, and place the hydrolysis cup in an ice water bath at a temperature of 0-5 °C. Stir electromagnetically for 5 min, then transfer the blank hydrolyzate to a 100 mL volumetric flask, make up the volume with the same concentration of inorganic acid solution, shake well, and obtain a blank solution for use.

[0056] (3) The mixed calibration solution was analyzed using a Multi N / C 3100 high-performance total organic carbon analyzer (Analytik Jena AG, Germany), a standard working curve was established, and the detection method was determined. The analysis method of the instrument was as follows: combustion temperature 850°C, integration time 300 s, and injection volume 0.50 mL.

[0057] (4) The hydrolyzate and blank solution prepared in step (1) and step (2) are loaded into an analytical instrument respectively to measure the total carbon and inorganic carbon concentrations in the hydrolyzate and the blank solution; and the total carbon, inorganic carbon and organic carbon contents in the titanium tetrachloride sample are calculated based on the total carbon and inorganic carbon concentrations.

[0058] (5) For batch samples, after testing 5 batches, use quality control solution to monitor the calibration curve and instrument status to ensure that the instrument status is stable and the data is accurate.

[0059] 2. Study on the influence mechanism of process parameters on test results 1. Different H + Effect of concentration on carbon measurements in hydrolysate: With inorganic acid (hydrochloric acid, nitric acid or sulfuric acid) and its H + Concentration (0.5 mol / L, 1.0 mol / L, 1.5 mol / L, 2.0 mol / L, 2.5 mol / L, 3.0 mol / L) was a single variable. The contents of total carbon, inorganic carbon and organic carbon in the same titanium tetrachloride sample were measured according to the above experimental steps. The test results are shown in Table 2.

[0060] Table 2. Different H + Determination results of total carbon, inorganic carbon and organic carbon in titanium tetrachloride samples at concentrations

[0061] Comparing the data in Table 2, it can be found that when the concentration of hydrogen ions in the inorganic acid is lower than 1.5 mol / L, the liquid after the titanium tetrachloride sample is dissolved is milky white (hydrated titanium dioxide formed after the hydrolysis of titanium ions). At this time, the measured values ​​of total carbon, organic carbon, and inorganic carbon are significantly reduced. This may be because the titanium dioxide produced after hydrolysis adsorbs some carbon-containing compounds or blocks the injection system, resulting in low measurement results. + As the concentration increases, the sample solution after hydrolysis gradually becomes clear. + When the concentration is greater than 1.5 mol / L, the hydrolysis solution is relatively clear, and the measured values ​​of total carbon, inorganic carbon and organic carbon in the hydrolysis solution also tend to be stable.

[0062] Since the higher the hydrogen ion concentration, the stronger the acidity of the sample solution after hydrolysis, and the stronger the corrosion to the instrument injection system, the experiment found that when H +When the concentration is greater than 3.0 mol / L, the corrosion of the sample solution after hydrolysis to the instrument injection system is significantly accelerated. + The concentration is 1.5~2.5mol / L.

[0063] In addition, it can be seen from Table 2 that when titanium tetrachloride is hydrolyzed, it reacts with H + The concentration is directly related to the type of inorganic acid used, so the control of H + Concentration is the key condition of the test.

[0064] 2. The influence of different hydrolysis temperatures on the carbon measurement value in the hydrolyzate: Since the hydrolysis reaction of titanium tetrachloride is an exothermic reaction, the test found that without any cooling measures, the temperature of the hydrolysis solution can reach up to 105°C. According to the physical and chemical properties of the carbon-containing compounds in titanium tetrachloride, it can be seen from the hydrolysis reaction that at this temperature, carbon tetrachloride (boiling point 76.7°C) and some small molecular carbonyl compounds, such as: acetaldehyde (boiling point 20.2°C), propionaldehyde (boiling point 20.2°C), butyraldehyde (boiling point 20.2°C), acetone (boiling point 20.2°C), butanone (boiling point 20.2°C), formic acid (boiling point 20.2°C), carbonic acid (decomposed at room temperature), etc., have volatilized at this time. Therefore, in order to reduce the volatilization loss of the above carbon-containing compounds in the hydrolysis product, the hydrolysis environment temperature must be controlled.

[0065] The temperature of the ice water bath (0℃, 5℃, 10℃, 15℃, 20℃) is used as a single variable, and the temperature error of each section is controlled within ±2℃. + The hydrochloric acid solution with a concentration of 1.5 mol / L is an inorganic acid solution. The contents of total carbon, inorganic carbon and organic carbon in the same titanium tetrachloride sample are measured according to the above experimental steps. The test results are shown in Table 3.

[0066] Table 3. Total carbon, inorganic carbon and organic carbon determination results of titanium tetrachloride samples at different ambient temperatures

[0067] From the measurement data in Table 3, it can be seen that when the ambient temperature is between 0 and 5 °C, there is no significant difference in the measured values ​​of each carbon content. As the hydrolysis ambient temperature increases, the total carbon, inorganic carbon, and organic carbon show a downward trend. The main reason is that as the ambient temperature increases, some low-boiling carbon compounds volatilize, resulting in low measurement results. Therefore, the test uses an ice water bath to control the hydrolysis ambient temperature at 0-5 °C, at which time the loss of each carbon compound in the hydrolysis product is minimal.

[0068] 3. Comparative Analysis with Existing Technologies 1. The influence of different hydrolysis methods on the carbon measurement value in the hydrolyzate: For the same titanium tetrachloride sample, the hydrolyzate was prepared according to the following hydrolysis methods: (1) Take two 1.0 mL titanium tetrachloride samples (1# and 2#) in parallel, add them into 40 mL water respectively, and hydrolyze them at room temperature (refer to "Determination of total oil in refined titanium tetrachloride by hydrolysis-infrared absorption spectrometry [J]. Metallurgical Analysis, 2022, 42(8): 76-80. DOI: 10.13228 / j.boyuan.issn 1000-7571.011702."), and obtain a hydrolyzate; (2) Take two 1.0 mL portions of titanium tetrachloride samples (#3 and #4) in parallel, add them into 40 mL of dilute hydrochloric acid (1:1), and hydrolyze them at room temperature (refer to CN116046600A “A method for detecting carbon content in titanium tetrachloride”) to obtain a hydrolyzate; (3) Take two 1.0 mL portions of titanium tetrachloride samples (#5 and #6) in parallel, add them into 40 mL of potassium hydroxide solution (1.82 mol / L) containing 0.3 g of copper-copper oxide catalyst, and hydrolyze them at room temperature (refer to CN119198283A "Sample pretreatment method and total carbon measurement method for total carbon in titanium tetrachloride") to obtain a hydrolyzate; (4) Take two 1.0 mL portions of titanium tetrachloride sample (#7 and #8) and add them into 40 mL of hydrochloric acid solution ([H + ]=1.5mol / L), and hydrolyzed according to the method of the present invention to obtain a hydrolyzate.

[0069] Methods (1), (2), (4): The total carbon (TC), inorganic carbon (IC), and total organic carbon (TOC) contents in the hydrolyzate were measured using a Multi N / C 3100 high-performance total organic carbon analyzer (Analytik Jena AG, Germany). The results are shown in Table 4.

[0070] Method (3): Since the hydrolysis product after hydrolysis according to this method is in the form of a white emulsion and cannot be analyzed using a TOC analyzer, the hydrolysis product is completely evaporated to dryness according to the method described in CN119198283A and then the total carbon (TC), inorganic carbon (IC) and total organic carbon (TOC) contents are determined using a high-frequency infrared carbon-sulfur analyzer. The results are shown in Table 4.

[0071] Table 4. Determination results of total carbon, inorganic carbon and organic carbon of titanium tetrachloride samples under different hydrolysis methods

[0072] From the comparative experimental results in Table 4, we can see that: First, when titanium tetrachloride is hydrolyzed in water and dilute hydrochloric acid, its organic carbon component is only partially converted into inorganic carbon, and the test results show that the organic carbon content is significantly higher than the inorganic carbon, indicating that most of the organic impurities remain in the hydrolysis system in their original unhydrolyzed form and are not fully hydrolyzed.

[0073] Second, by comparing the determination data of total carbon, inorganic carbon and organic carbon under different hydrolysis methods, it was found that the total carbon was the lowest when hydrolyzed in water, followed by dilute hydrochloric acid. This difference is attributed to the fact that in the conventional hydrolysis process, part of the organic matter decomposes into CO2 and volatilizes, and the hydrolysis exotherm intensifies the volatilization of low-boiling organic matter, resulting in a systematic low carbon recovery rate; while the low-temperature inorganic acid hydrolysis technology (7#, 8# data) of the present invention suppresses volatilization and thermal decomposition, making the total carbon detection value closer to the actual content.

[0074] Third, although the use of strong alkaline solution hydrolysis can achieve complete hydrolysis of organic matter, it causes complete overlap of inorganic carbon and organic carbon data, and only the total carbon parameters can be obtained. It is impossible to analyze the independent contents of inorganic carbon and organic carbon originally contained in the titanium tetrachloride sample, and the impurity traceability capability is lost.

[0075] 2. Comparison experiment with Fourier transform infrared spectroscopy For the same crude titanium tetrachloride and refined titanium tetrachloride samples, the total carbon content in titanium tetrachloride was measured according to the following test methods: (1) The content of each single component of organic matter in the sample was measured by Fourier transform infrared spectrometer, converted into carbon content, and then summed to obtain the total carbon content in titanium tetrachloride (refer to "Wang Lijuan, Liu Zhenghong, Li Yi, et al. Research on online detection technology of oxygen and carbon impurities in refined titanium tetrachloride [J]. Progress in Titanium Industry, 2022, 39(1): 32-35. DOI: 10.13567 / j.cnki.issn1009-9964. 2022.01.007"). The test results are shown in Table 5.

[0076] (2) H + The hydrochloric acid solution with a concentration of 1.5 mol / L is an inorganic acid solution. The total carbon content in the sample is measured according to the experimental steps of the present invention. The test results are shown in Table 6.

[0077] Table 5. Results of Fourier measurement of total carbon in titanium tetrachloride

[0078] Table 6. Results of the method of the present invention for measuring total carbon in titanium tetrachloride

[0079] By comparing the data in Table 5 and Table 6, it can be seen that there is no statistically significant difference between the total carbon determination values ​​of this method and Fourier infrared spectroscopy, but the precision index is significantly better than the latter; for crude titanium tetrachloride samples, the values ​​measured by this method are higher than those by Fourier method. It is speculated that the reason is that the complex organic components in the crude product are not effectively identified by Fourier infrared spectroscopy, resulting in slightly lower data. The experimental data verified that this method has the significant advantages of both high accuracy and high repeatability in the detection of total carbon in titanium tetrachloride.

Claims

1. A method for determining the content of total carbon, inorganic carbon and organic carbon in titanium tetrachloride, characterized in that: The steps include: S1. Under inert atmosphere protection and low temperature environment, add titanium tetrachloride sample to quantitative inorganic acid solution for full hydrolysis, make up to volume with inorganic acid solution of the same concentration to obtain hydrolyzate, and simultaneously prepare blank solution; S2. Prepare inorganic carbon calibration solution, organic carbon calibration solution, mixed calibration solution and quality control solution respectively; S3. Use a TOC analyzer to measure the mixed calibration solution of step S2, establish a calibration working curve and determine the detection method; S4. Analyze the hydrolyzate and blank solution of step S1 using the detection method of step S3 to determine the total carbon and inorganic carbon concentrations; S5. Calculate the total carbon, inorganic carbon and organic carbon contents in the titanium tetrachloride sample based on the total carbon and inorganic carbon concentrations in the hydrolyzate.

2. The measuring method according to claim 1, characterized in that: In step S1, the low temperature environment is 0-5°C; the amount of titanium tetrachloride sample added is 1-2 mL; the amount of inorganic acid solution added is 40-60 mL, and the H + The concentration is 1.5~2.5mol / L.

3. The assay method according to claim 2, characterized in that: In step S1, the inorganic acid solution is at least one of a hydrochloric acid solution, a nitric acid solution, and a sulfuric acid solution; the inert atmosphere is argon or nitrogen; and the low temperature environment is achieved by an ice water bath.

4. The measuring method according to claim 1, characterized in that: In step S1, the preparation method of the blank solution is the same as the preparation method of the hydrolyzate solution except that the titanium tetrachloride sample is not added.

5. The assay method according to claim 1, wherein: In step S2, an inorganic carbon calibration solution is prepared using high-grade pure carbonate; and an organic carbon calibration solution is prepared using high-grade pure phthalate.

6. The assay method according to claim 5, characterized in that: The high-grade pure carbonate is at least one of sodium carbonate, sodium bicarbonate, potassium carbonate and lithium carbonate; the high-grade pure phthalate is any one of potassium phthalate, sodium phthalate, potassium hydrogen phthalate and sodium hydrogen phthalate.

7. The assay method according to claim 1, characterized in that: In step S2, according to the carbon concentration range of the titanium tetrachloride sample, an inorganic carbon calibration solution and an organic carbon calibration solution are taken to prepare a mixed calibration solution and a quality control solution with a total carbon gradient concentration for establishing a calibration working curve and quality control.

8. The assay method according to claim 1, characterized in that: In step S5, the total carbon content in the titanium tetrachloride sample is calculated as follows: TC ={[(C TC1 -C TC0 )×V1]÷(V2×1.73)}×10 -6 ×100%, where: ω TC Indicates the mass fraction of the total carbon content in the carbon tetrachloride sample, %; C TC1 Indicates the total carbon concentration in the hydrolyzate measured in step S4, mg / L; C TC0 Indicates the total carbon concentration in the blank solution measured in step S4, mg / L; V1 represents the volume of the hydrolyzate, mL; V2 represents the volume of titanium tetrachloride sample, mL; 1.73 represents the density of titanium tetrachloride, g / mL.

9. The assay method according to claim 1, characterized in that: In step S5, the calculation formula for the inorganic carbon content in the titanium tetrachloride sample is: IC ={[(C IC1 -C IC0 )×V1]÷(V2×1.73)}×10 -6 ×100%, where: ω IC Indicates the mass fraction of inorganic carbon content in carbon tetrachloride sample, %; C IC1 Indicates the concentration of inorganic carbon in the hydrolyzate measured in step S4, mg / L; C IC0 Indicates the concentration of inorganic carbon in the blank solution measured in step S4, mg / L; V1 represents the volume of the hydrolyzate, mL; V2 represents the volume of titanium tetrachloride sample, mL; 1.73 represents the density of titanium tetrachloride, g / mL.

10. The determination method according to claim 1, characterized in that: In step S5, the calculation formula for the organic carbon content in the titanium tetrachloride sample is: TOC =ω TC -ω IC , where: ω TOC Indicates the mass fraction of organic carbon content in carbon tetrachloride sample, %; ω TC Indicates the mass fraction of the total carbon content in the carbon tetrachloride sample, %; ω IC Indicates the mass fraction of inorganic carbon content in carbon tetrachloride sample, %.

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