Sample pretreatment method and total carbon measurement method for titanium tetrachloride

Abstract

The invention discloses a sample pretreatment method and a total carbon measurement method for measuring total carbon in titanium tetrachloride, and belongs to the technical field of analytical chemistry. The sample pretreatment method is as follows: the whole process is carried out under the protection of inert gas, the titanium tetrachloride sample to be measured is added into a strong alkali solution containing a catalyst for sufficient hydrolysis, and the water is evaporated after hydrolysis to obtain the solid of the sample to be measured. The total carbon measurement method in titanium tetrachloride is as follows: the solid of the sample to be measured is made into a powder of the sample to be measured, the total carbon content of the powder of the sample to be measured is measured by a total carbon analyzer, and then the total carbon content in the titanium tetrachloride sample to be measured is obtained by conversion. The present invention can effectively solve the problems that the sample pretreatment of the existing total carbon determination in titanium tetrachloride is prone to volatilization and loss of some components, thereby resulting in a low final measurement result; and the overall determination method has harsh analysis conditions, high detection costs, and difficult quality control.

Description

Technical Field

[0001] The invention belongs to the technical field of analytical chemistry, and in particular relates to a sample pretreatment method for measuring total carbon in titanium tetrachloride and a total carbon measurement method. Background Art

[0002] Titanium tetrachloride (TiCl4) is the main product obtained by molten salt chlorination with titanium concentrate, petroleum coke and chlorine as reactants or boiling chlorination with high titanium slag, petroleum coke and chlorine as reactants. In the above chlorination process, in addition to the main reaction to produce titanium tetrachloride, there are also a large number of side reaction products such as vanadium trichloride (VOCl3), ferric chloride (FeCl3), silicon tetrachloride (SiCl4), aluminum chloride (AlCl3), tin tetrachloride (SnCl4), trichloroacetyl chloride (CCl3COCl), carbon dichloride (COCl2), carbon tetrachloride (CCl4), etc. These by-products are the key factors affecting the purity of titanium tetrachloride. At present, the national standard YS / T 655-2016 "Titanium Tetrachloride" strictly controls inorganic impurities such as SiCl4, FeCl3, VOCl3, AlCl3, SnCl4, and has corresponding measurement standards, but organic impurities are not included in the standard requirements. The main reason is that there are many types of organic impurities in titanium tetrachloride and their forms are complex. There are currently 10 types publicly reported (CCl3COCl (trichloroacetyl chloride), CHCl2COCl (dichloroacetyl chloride), CH2ClCOCl (monochloroacetyl chloride), COCl (carbon oxychloride), COCl2 (carbon oxychloride), COS (carbon oxysulfide), CO2 (carbon dioxide), CS2 (carbon disulfide), CHCl3 (trichloromethane), CCl4 (carbon tetrachloride)), and it is difficult to quantitatively detect these organic substances in titanium tetrachloride.

[0003] The main reasons for the difficulty in determining the above organic impurities in titanium tetrachloride are: First, sample pretreatment technology is one of the most critical links in determining accurate measurement, but titanium tetrachloride samples have special properties and sample pretreatment is difficult. Once titanium tetrachloride comes into contact with water, it will undergo a violent hydrolysis reaction to generate irritating and corrosive hydrogen chloride fumes, which will not only cause the measured components to decompose or volatilize, but also irritate the eyes, skin and respiratory tract of operators, and cause harm to the human body when ingested. Second, the organic impurities in titanium tetrachloride are complex and diverse, and there are currently no corresponding standard samples and quality control samples, making it difficult to control the accuracy of the measurement results.

[0004] Titanium tetrachloride is an important chemical raw material for magnesium thermal reduction to produce titanium sponge (metallic pure titanium), and titanium sponge is the main raw material for producing titanium alloys, and its purity will directly affect the quality of titanium sponge. According to the reaction principle of magnesium thermal method to produce titanium sponge, the impurity content in refined TiCl4 is enriched and transferred to titanium sponge at a ratio of 4. During the process of magnesium thermal reduction of titanium tetrachloride, the above-mentioned organic impurities in titanium tetrachloride will also be converted into carbides and retained in titanium sponge, thereby affecting the quality of titanium sponge, and then affecting the quality and performance of the final product titanium alloy. Because carbon is a harmful element to titanium alloy, it will directly affect the strength and plasticity of titanium alloy, reduce corrosion resistance, and affect welding performance and processing performance. Therefore, accurate determination of the total carbon content in titanium tetrachloride is crucial to controlling the quality of refined titanium tetrachloride and even titanium alloys.

[0005] Regarding the detection technology of the above 10 organic impurities in titanium tetrachloride, the academic papers and patents currently publicly reported at home and abroad are as follows.

[0006] (1) Fourier transform infrared absorption spectroscopy. This method is currently the most appropriate method for measuring organic impurities in titanium tetrachloride. The content of each organic component in titanium tetrachloride is measured by Fourier transform infrared spectrometer, converted into carbon content, and then summed to obtain the total carbon content in titanium tetrachloride (such as literature: 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). Although this method can simultaneously measure multiple impurity components in titanium tetrachloride, it also has the following shortcomings in actual use: First, titanium tetrachloride is extremely easy to hydrolyze in the air, and thick hydrochloric acid smoke is immediately produced when it comes into contact with air. The sample needs to be loaded in an absolutely dry or atmosphere-protected space, which has strict requirements on the operating environment. In practical applications, the equipment is usually placed at the production site, and the sample is introduced into the instrument sample pool by online sampling. The sample pool and pipeline also need special design and special anti-corrosion materials. At the same time, the production site environment is prone to equipment corrosion, which affects the service life of the equipment. Second, at present, the calibration standard sample is prepared by manually adding the pure substance of the measured organic impurities to the refined titanium tetrachloride. Since organic matter is volatile and there are many types of organic matter in titanium tetrachloride, the accuracy of the prepared artificial synthetic calibration standard substance is difficult to guarantee. Third, only the main components that have been detected can be detected, and the undetected components cannot be measured, resulting in incomplete detection of components. Fourth, when using a dedicated Fourier transform infrared spectrometer for measurement, the equipment investment is large and the detection cost is high.

[0007] (2) Infrared absorption spectroscopy. This method hydrolyzes the titanium tetrachloride sample with water at a volume ratio of 1:25, extracts the total oil in the hydrolysis solution with tetrachloroethylene, and quantitatively analyzes the total oil content in the refined titanium tetrachloride by external standard (such as literature: Wang Yanjiao, Zou Xiaonan, Zu Yue, et al. Determination of total oil in refined titanium tetrachloride by hydrolysis-infrared absorption spectroscopy [J]. Metallurgical Analysis, 2022, 42(08): 76-80. DOI: 10.13228 / j.boyuan.issn1000-7571.011702). This study has the following shortcomings: First, titanium tetrachloride is very easy to undergo hydrolysis reaction when in contact with water vapor, and the generated hydrogen chloride also has an infrared absorption peak, and the absorption peak wave number of hydrogen chloride and oil is close, causing hydrogen chloride to interfere with the infrared absorption spectroscopy method for determining the total oil content in the original titanium tetrachloride sample. Second, some organic matter in titanium tetrachloride (such as COS, COCl2) decomposes into carbon dioxide (volatilization) after hydrolysis, resulting in a low measurement result. Third, the hydrolysis of titanium tetrachloride is an exothermic reaction, and the solution temperature is high during hydrolysis, which may cause some organic matter to volatilize.

[0008] (3) Gas chromatography. This method involves hydrolyzing titanium tetrachloride in water, extracting organic matter from the hydrolyzate with an organic solvent such as n-heptane or n-hexane, and then measuring it with gas chromatography (e.g., Li Qing, Song Guanglin, Tan Hong, et al. Comparison of the extraction capacity of different extractants for the determination of trace carbon tetrachloride in titanium tetrachloride hydrolysis system by liquid-liquid extraction gas chromatography [J]. Metallurgical Analysis, 2014, 34(02): 15-19. DOI: 10.13228 / j.issn.1000-7571.2014.02.004). This method still involves hydrolyzing titanium tetrachloride in water, and there is also the problem of organic matter volatilization loss.

[0009] (4) CN 118533787 A discloses a device for detecting the oil impurity content of titanium tetrachloride. In the dedicated device, titanium tetrachloride is heated in a main chamber, and the oil impurities in the sample are introduced into a secondary chamber filled with tetrachloroethylene through a distillation tube. The distilled oil impurities are absorbed by tetrachloroethylene and then measured by infrared spectroscopy. This method provides a new idea for processing titanium tetrachloride samples, but when measuring by infrared spectroscopy, it also faces the problem of difficulty in obtaining calibration samples and quality control samples.

[0010] (5) CN 116046600A discloses a method for detecting the carbon content in titanium tetrachloride, wherein titanium tetrachloride is dissolved in dilute hydrochloric acid to form a test solution; sodium hydroxide solution is used to neutralize the test solution to a pH of 7 to 12; after neutralization, the neutralized residue is filtered, washed and dried, a certain amount of the neutralized residue is taken, and iron powder and tungsten powder are added to the carbon-sulfur analyzer for detection and analysis. This method has the following shortcomings: first, some organic matter (such as COS, COCl2) is decomposed into carbon dioxide (volatilized) after hydrolysis; second, some organic matter (such as CCl4) is not hydrolyzed in dilute hydrochloric acid, resulting in a low measurement result; third, the solution temperature is high during hydrolysis, which may cause some organic matter to volatilize, resulting in a low measurement result.

[0011] (5) CN 114778369A discloses a sample pretreatment method for detecting the carbon content of titanium tetrachloride by high-temperature burning. This method uses the principle of heating to carbonize organic matter, then filters the precipitated black carbide, and uses the weight method to determine the total carbon in titanium tetrachloride. This method has the following shortcomings: First, some organic matter (such as COS, COCl2) decomposes into carbon dioxide (volatilization) after hydrolysis and cannot be carbonized; second, some organic matter with a lower boiling point than titanium tetrachloride (such as COS, CO2, CS2, CHCl3, CCl4) will be distilled out in advance, or even form azeotropes with titanium tetrachloride and cannot be carbonized, resulting in low measurement results; third, the total carbon content in refined titanium tetrachloride is low, and the weight method has a large error.

[0012] In summary, there are two main modes for the determination of total carbon in titanium tetrachloride. One is to use Fourier transform infrared absorption spectroscopy for direct online determination. Although this method is more direct and relatively accurate, it also has the disadvantages of harsh analysis conditions, high detection cost and difficult quality control. The second is to hydrolyze titanium tetrachloride in water or acid, and then extract the hydrolyzed solution with an organic solvent to transfer the organic matter in the hydrolyzed solution to the extractant, and then measure it with infrared spectroscopy or gas chromatography; or heat and distill the hydrolyzed solution to transfer the organic matter in the hydrolyzed solution to the distillation residue, and then measure it with an infrared carbon-sulfur analyzer. This sample pretreatment method of hydrolyzing titanium tetrachloride in water or acid also has the problem that some organic matter is decomposed into carbon dioxide after hydrolysis and some organic matter is easily volatilized and lost. It is not difficult to see from the above discussion that the total carbon in titanium tetrachloride is crucial to the quality control of titanium tetrachloride and subsequent titanium alloy products. Since it is difficult to directly determine the total carbon in titanium tetrachloride, there are always deficiencies in the existing technology for measuring the total carbon in titanium tetrachloride, resulting in the inability to accurately determine the total carbon in titanium tetrachloride. Therefore, developing a method for detecting total carbon in titanium tetrachloride that is simple to operate and has good measurement accuracy and repeatability is of great significance for further strengthening the quality control of titanium tetrachloride and improving its product quality. Summary of the invention

[0013] The technical problems to be solved by the present invention are: 1) the existing method for determining total carbon in titanium tetrachloride is prone to volatilization and loss of some components during sample pretreatment, thereby resulting in a low final measurement result; 2) the existing method for determining total carbon in titanium tetrachloride has the problems of harsh analysis conditions, high detection cost and difficult quality control.

[0014] The technical solution adopted by the present invention to solve its technical problem is:

[0015] In a first aspect, the present invention provides a sample pretreatment method for measuring total carbon in titanium tetrachloride: the entire process is carried out under the protection of an inert gas, the titanium tetrachloride sample to be tested is added to a strong alkaline solution containing a catalyst for sufficient hydrolysis, and the water is evaporated after hydrolysis to obtain a solid substance of the sample to be tested; the catalyst is a mixture of a transition metal and its oxide in a mass ratio of 1:1.

[0016] In the above sample pretreatment method, the amount of the titanium tetrachloride sample to be tested is 1-5 mL, the content of the catalyst is 0.15-0.75 g, the volume of the strong alkali solution is 20-60 mL, and the titanium tetrachloride sample to be tested and OH in the strong alkali solution are reacted. - The molar ratio is 1:4.

[0017] In the above sample pretreatment method, the strong alkaline solution is any one of lithium hydroxide solution, potassium hydroxide solution and sodium hydroxide solution.

[0018] In the above sample pretreatment method, the mixture of transition metals and their oxides is any one of a mixture of vanadium and vanadium oxide, a mixture of copper and copper oxide, a mixture of chromium and chromium oxide, a mixture of manganese and manganese oxide, a mixture of iron and iron oxide, a mixture of cobalt and cobalt oxide, a mixture of nickel and nickel oxide, and a mixture of zinc and zinc oxide.

[0019] In the above sample pretreatment method, the hydrolysis temperature is 75-95°C, the hydrolysis time is 5-20 minutes, and the evaporation temperature is 100-120°C.

[0020] In a second aspect, the present invention provides a method for measuring total carbon in titanium tetrachloride, comprising the following steps:

[0021] a. The solid sample to be tested is obtained by the sample pretreatment method for measuring total carbon in titanium tetrachloride described above, and ground into powder under inert gas protection to obtain a powdered sample to be tested and packaged for standby use;

[0022] b. Prepare synthetic calibration standards and quality control samples with spectrally pure titanium dioxide and high-grade pure carbonate, mix them evenly, select a high-frequency infrared carbon and sulfur analyzer for total carbon analysis, establish an analysis method and draw a calibration working curve;

[0023] c. Using the instrumental analysis method established in step b to measure the total carbon content in the sample powder obtained in step a, the total carbon content in the titanium tetrachloride sample to be tested is calculated based on the total carbon content in the sample powder to be tested.

[0024] In the above-mentioned measurement method, in step b, the high-grade pure carbonate is any one of lithium carbonate, sodium carbonate, potassium carbonate, magnesium carbonate, calcium carbonate, and barium carbonate.

[0025] In the above measurement method, in step b, the analysis method of the high-frequency infrared carbon and sulfur analyzer is: oxygen flow rate 3.5L / min, purge time 10s, integration delay 8s, analysis time 30s, comparator level 2%, combustion power 95%; high-purity oxygen is used as the carrier gas and combustion-supporting gas, nitrogen is used as the power gas, the carrier gas output pressure is adjusted to 0.25MPa, and the power gas pressure is 0.15MPa.

[0026] In the above-mentioned measurement method, in step c, the measurement method is specifically as follows: a ceramic crucible specially used for carbon-sulfur analysis is calcined in a muffle furnace at 1150-1250° C. for 4-5 hours, taken out and placed in a dryer for cooling for standby use; 0.30-0.50 g of high-purity iron particles are added to the cooled ceramic crucible, and then 0.20-0.40 g of the sample powder to be tested obtained in step a is weighed and placed in the ceramic crucible, and then 1.00-1.50 g of a tungsten-tin mixed flux is added; measurement is performed according to the analysis method of the above-mentioned high-frequency infrared carbon-sulfur analyzer, and the measurement result is the mass fraction of the total carbon in the sample powder to be tested obtained in step a.

[0027] In the above measurement method, in step c, the calculation formula for the total carbon content in the titanium tetrachloride sample to be measured is: TC =[(V×1.73) / m]×ω1, where:

[0028] ω TC Indicates the mass fraction of the total carbon content in the carbon tetrachloride sample to be tested, %;

[0029] V represents the amount of titanium tetrachloride sample added during pretreatment, mL;

[0030] m represents the mass of the sample powder obtained in step a, g;

[0031] ω1 represents the mass fraction of total carbon in the sample powder to be tested obtained in step a, %;

[0032] 1.73 represents the density of titanium tetrachloride, g / mL.

[0033] The beneficial effects of the present invention are:

[0034] 1. The present invention proposes for the first time a method for treating samples by directly hydrolyzing titanium tetrachloride in a strong alkaline solution under the protection of an inert gas, which effectively solves the problems that during hydrolysis in water or acid, some organic matter (such as COS, COCl2, etc.) decomposes into carbon dioxide and volatilizes after hydrolysis, and the high solution temperature during hydrolysis causes some organic matter to volatilize, thereby causing low measurement results.

[0035] 2. The present invention particularly uses transition metals and their oxides (such as copper and copper oxide, etc.) as catalysts, which can effectively increase the hydrolysis rate of non-polar organic matter such as carbon tetrachloride in a strong alkaline solution system, so that the organic matter in titanium tetrachloride is completely hydrolyzed, ensuring that the total carbon in titanium tetrachloride is accurately measured.

[0036] 3. The method of the present invention can convert volatile organic matter in titanium tetrachloride into non-volatile organic acid salts or inorganic salts, which can minimize the loss of organic matter in titanium tetrachloride and more accurately reflect the total carbon content in titanium tetrachloride.

[0037] 4. The present invention uses spectrally pure titanium dioxide and high-grade pure carbonate to prepare artificially synthesized calibration samples and quality control samples. Since they are all inorganic substances, they are not easy to volatilize, are easier to obtain and operate, and the prepared calibration samples and quality control samples are more stable, and the measurement results have better repeatability.

[0038] 5. The entire titanium tetrachloride sample pretreatment process of the present invention is carried out under the protection of argon inert gas, which minimizes the harm to operators caused by hydrochloric acid mist generated when titanium tetrachloride contacts water in the air for hydrolysis, and is more environmentally friendly and healthy. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 Schematic diagram of the experimental device of the pretreatment method in the embodiment of the present invention.

[0040] In the figure: 1 is an inert gas operation box, 2 is a precision peristaltic pump (with flow control), 3 is a magnetic stirrer (with heating function), 4 is a sample cup, 5 is a hydrolysis cup, 6 is a peristaltic pump display control panel, 7 is a peristaltic pump shaft, 8 is a magnetic stirrer display control panel, 9 is a magnetic stirrer adjustment control key, 10 is a pressure indicator, 11 is an exhaust port, 12 is a protective gas outlet, 13 is a protective gas inlet, and 14 is a peristaltic pump tube. DETAILED DESCRIPTION

[0041] The technical solution of the present invention can be specifically implemented in the following manner.

[0042] The present invention provides a sample pretreatment method for determining total carbon in titanium tetrachloride, which is carried out under inert gas protection throughout the process and specifically comprises the following steps:

[0043] A. Add 1-5 mL of the titanium tetrachloride sample to be tested into 20-60 mL of a strong alkaline solution containing 0.15-0.75 g of a catalyst, and fully hydrolyze at 75-95°C for 5-20 min;

[0044] B. After the hydrolysis is completed, heat to 100-120°C to evaporate the free water in the hydrolyzate to obtain the solid sample to be tested.

[0045] When the amount of titanium tetrachloride sample to be tested is less than 1mL, the amount of sample is too low, resulting in a low content of organic hydrolysis products, which is further manifested as poor stability of the measured carbon content data; when the amount of titanium tetrachloride sample to be tested is greater than 5mL, the volume of the corresponding strong alkali solution will also increase, and too much liquid will lead to increased time and energy consumption during subsequent heating and evaporation of the hydrolyzate, which is not conducive to improving work efficiency. Therefore, in the sample pretreatment method of the present invention, the amount of titanium tetrachloride sample to be tested is limited to 1-5mL, and the volume of the strong alkali solution is limited to 20-60mL. With the titanium tetrachloride addition amount and the strong alkali solution volume defined by the present invention, there will be no situation where the titanium tetrachloride is not completely hydrolyzed due to too little solution and unsmooth stirring; there will be no problem that the time taken to evaporate the hydrolyzate becomes longer due to too much solution, the work efficiency is reduced, and the energy consumption is increased.

[0046] In a specific embodiment of the present invention, in step A of the sample pretreatment method, the titanium tetrachloride sample to be tested is reacted with OH in a strong alkaline solution. - The molar ratio of is 1:4; the strong base solution is any one of lithium hydroxide solution, potassium hydroxide solution and sodium hydroxide solution; the catalyst is a mixture of transition metals and their oxides in a mass ratio of 1:1.

[0047] The present invention limits the volume of the strong alkaline solution and also limits the volume of the titanium tetrachloride sample to be tested and the OH in the strong alkaline solution. - The purpose is to control the concentration of the strong alkaline solution. - The strong alkali solution is prepared at a molar ratio of , which can not only ensure that there is enough strong alkali to fully hydrolyze the titanium tetrachloride, but also prevent the strong alkali from being excessively evaporated and remaining in the hydrolysis product. The residual strong alkali absorbs carbon dioxide in the air to form carbonate, causing the measured carbon content data to be too high.

[0048] In a specific embodiment of the present invention, the catalyst is any one of a mixture of vanadium and vanadium oxide, a mixture of copper and copper oxide, a mixture of chromium and chromium oxide, a mixture of manganese and manganese oxide, a mixture of iron and iron oxide, a mixture of cobalt and cobalt oxide, a mixture of nickel and nickel oxide, and a mixture of zinc and zinc oxide.

[0049] In the sample pretreatment method of the present invention, titanium tetrachloride is hydrolyzed in a strong alkaline solution, wherein titanium tetrachloride is hydrolyzed to form titanium hydroxide (Ti(OH)4) precipitate, and organic impurities in titanium tetrachloride are hydrolyzed to form corresponding organic acid salts or carbonates. Taking potassium hydroxide hydrolysis solution as an example (similar hydrolysis reaction also occurs in lithium hydroxide or sodium hydroxide hydrolysis solution), the main reaction equation is as follows:

[0050] 4KOH+TiCl4=4KCl+Ti(OH)4↓;

[0051] CH2ClCOCl+KOH=CH2ClCOOK+KCl+H2O;

[0052] CHCl2COCl+2KOH=CHCl2COOK+KCl+H2O;

[0053] CCl3COCl+2KOH=CCl3COOK+KCl+H2O;

[0054] COCl+4KOH=HCOOK+2KCl+2H2O;

[0055] COCl2+4KOH=K2CO3+2KCl+2H2O;

[0056] COS+4KOH=K2CO3+K2S+2H2O;

[0057] CS2+KOH=K2CS3+H2O;

[0058] 2KOH+CS2=K2COS2+H2O;

[0059] CHCl3+4KOH=HCOOK+3KCl+2H2O;

[0060] CCl4+6KOH=4KCl+K2CO3+3H2O.

[0061] According to the above hydrolysis reaction equation, it can be seen that their hydrolysis products in the strong alkaline solution are organic acid salts and carbonates. Based on this, those skilled in the art can reasonably infer that other organic impurities in titanium tetrachloride that have not yet been discovered can also undergo similar hydrolysis reactions to generate corresponding organic acid salts or carbonates. Based on this hydrolysis principle, it can be seen that the sample pretreatment method of the present invention can convert volatile organic matter in titanium tetrachloride into non-volatile organic acid salts or inorganic salts, which can minimize the loss of organic matter in titanium tetrachloride.

[0062] The present invention also provides a method for measuring total carbon in titanium tetrachloride, comprising the following steps:

[0063] a. The solid sample to be tested is obtained by the sample pretreatment method for the determination of total carbon in titanium tetrachloride, which is ground into powder under inert gas protection to obtain a sample powder to be tested and packaged for standby use;

[0064] b. Prepare synthetic calibration standards and quality control samples with spectrally pure titanium dioxide and high-grade pure carbonate, mix them evenly, select a high-frequency infrared carbon and sulfur analyzer for total carbon analysis, establish an instrumental analysis method, and draw a calibration working curve;

[0065] c. Using the instrumental analysis method established in step b to measure the total carbon content in the sample powder obtained in step a, the total carbon content in the titanium tetrachloride sample to be tested is calculated based on the total carbon content in the sample powder to be tested.

[0066] In a specific embodiment of the present invention, in step b of the above method for measuring total carbon in titanium tetrachloride, the high-grade pure carbonate is any one of lithium carbonate, sodium carbonate, potassium carbonate, magnesium carbonate, calcium carbonate and barium carbonate.

[0067] In a specific embodiment of the present invention, in step b of the above method for measuring total carbon in titanium tetrachloride, a high-performance total carbon-total nitrogen analyzer can also be selected to perform total carbon analysis.

[0068] Example

[0069] 1. Sample pretreatment method for total carbon measurement in titanium tetrachloride and implementation of total carbon measurement method in titanium tetrachloride

[0070] 1. Sample preparation for total carbon measurement in titanium tetrachloride

[0071] (1) Experimental setup:

[0072] The sample pretreatment process in this embodiment is as follows Figure 1 The operation is carried out in the inert gas operation box 1 shown, which contains a precision peristaltic pump 2 with flow control, a magnetic stirrer 3 with heating function, a sample cup 4, a hydrolysis cup 5, a pressure indicator 10, an exhaust port 11, a protective gas outlet 12, and a protective gas inlet 13.

[0073] The precision peristaltic pump 2 comprises a peristaltic pump display control panel 6, a peristaltic pump shaft 7 and a peristaltic pump tube 14. One end of the peristaltic pump tube 14 extends into the sample cup 4 and the end of the pump tube is always below the liquid surface. The other end of the peristaltic pump tube 14 extends into the hydrolysis cup 5 and the end of the pump tube is always 1 to 2 cm above the liquid surface.

[0074] The magnetic stirrer 3 comprises a magnetic stirrer display control panel 8 and a magnetic stirrer adjustment control key 9 , and the hydrolysis cup 5 is placed on the magnetic stirrer 3 .

[0075] (2) Preparation of strong alkaline hydrolysis solution: Weigh 20.4 g of potassium hydroxide and slowly add it into 200 mL of carbon dioxide-free water to dissolve it to prepare a 1.82 mol / L potassium hydroxide hydrolysis solution.

[0076] (3) A sample pretreatment method for measuring total carbon in titanium tetrachloride comprises the following steps:

[0077] A. Open the inert gas operation box 1, put the titanium tetrachloride sample to be tested into the sample cup 4, put 40mL 1.82mol / L potassium hydroxide solution and 0.3g copper-copper oxide mixture into the hydrolysis cup 5, and then seal the inert gas operation box 1;

[0078] B. Open the shielding gas outlet 12 and shielding gas inlet 13 of the sealed inert gas operation box 1, pass argon gas to empty it, close the shielding gas outlet 12, continue to pass argon gas until the pressure indicator 10 shows 0.05MPa (control the reading to 0.02-0.05MPa, keep the air pressure in the operation box at a slightly positive pressure), and then close the shielding gas inlet 13;

[0079] C. Turn on the precision peristaltic pump 2 and set the pump speed to 5.0 mL / min, add 2.0 mL of the titanium tetrachloride sample to be tested into the hydrolysis cup 5, then turn off the precision peristaltic pump 2, turn on the magnetic stirrer 3 and start stirring, set the heating temperature to 85°C, and allow the reaction to fully react for 10 minutes. Stop stirring after the organic matter in the carbon tetrachloride is fully hydrolyzed;

[0080] D. Setting the heating temperature of the magnetic stirrer 3 to 105° C. to evaporate the water in the hydrolysis cup 5 to obtain the solid sample to be tested;

[0081] E. Open the exhaust port 11 and the protective gas inlet 13, replace the gas in the inert gas operation box 1 with argon gas and exhaust it into the laboratory fume hood.

[0082] 2. The method for measuring total carbon in titanium tetrachloride specifically comprises the following steps:

[0083] (1) Under the protection of inert gas, the solid sample to be tested obtained by the above pretreatment is transferred to an agate mortar and ground into powder to obtain the sample powder to be tested and packaged for later use.

[0084] (2) Prepare synthetic calibration standards and quality control samples using spectrally pure titanium dioxide and high-grade pure potassium carbonate according to the ratio in Table 1, mix well, and set aside.

[0085] Table 1 Composition and carbon content of calibration samples

[0086] Serial number Calibration standard and quality control sample composition / g Carbon content / % Remark 1 50.00g Titanium dioxide 0 Calibration Blank 2 50.00g titanium dioxide + 0.0222g potassium carbonate 0.0050 Calibration point 1 3 50.00g titanium dioxide + 0.0444g potassium carbonate 0.0100 Calibration point 2 4 50.00g titanium dioxide + 0.0888g potassium carbonate 0.0201 Calibration point 3 5 50.00g titanium dioxide + 0.1328g potassium carbonate 0.0300 Calibration point 4 6 50.00g titanium dioxide + 0.1775g potassium carbonate 0.0401 Calibration point 5 7 50.00g titanium dioxide + 0.2218g potassium carbonate 0.0500 Calibration point 6 8 50.00g titanium dioxide + 0.0624g potassium carbonate 0.0141 Quality Control Sample 1 9 50.00g titanium dioxide + 0.1115g potassium carbonate 0.0252 Quality Control Sample 2 10 50.00g titanium dioxide + 0.2012g potassium carbonate 0.0454 Quality Control Sample 3

[0087] (3) Measure the calibration samples shown in Table 1, establish the instrumental analysis method of the high-frequency infrared carbon and sulfur analyzer, and draw a calibration working curve; the instrumental analysis method is: oxygen flow rate 3.5L / min, purge time 10s, integration delay 8s, analysis time 30s, comparator level 2%, combustion power 95%; high-purity oxygen is used as carrier gas and combustion-supporting gas, nitrogen is used as power gas, and the carrier gas output pressure is adjusted to 0.25MPa, and the power gas pressure is 0.15MPa.

[0088] (4) Measuring the total carbon content in the sample powder obtained in step (1), specifically:

[0089] 1) Place a special ceramic crucible for carbon and sulfur analysis (inner diameter 25 mm × 25 mm) in a muffle furnace and burn it at 1200°C for 4 hours, take it out and cool it in a desiccator for later use;

[0090] 2) Add 0.50 g of high-purity iron particles, 0.40 g of the sample powder to be tested, and 1.50 g of tungsten-tin mixed flux into a ceramic crucible, and perform measurement according to the instrumental analysis method in step (3). The measurement result is the mass fraction (ω1) of the total carbon in the sample powder to be tested obtained in step (1);

[0091] 3) For batch samples, after testing 5 batches, use the quality control samples in Table 1 to monitor the calibration curve and instrument status to ensure that the instrument status is stable and the data is accurate.

[0092] (5) According to the formula ω TC =[(V×1.73) / m]×ω1 to calculate the total carbon content in the titanium tetrachloride sample, where: ω TC represents the mass fraction of the total carbon content in the carbon tetrachloride sample to be tested, %; V represents the amount of titanium tetrachloride sample to be tested added during pretreatment, mL; m represents the mass of the sample powder to be tested obtained in step a, g; ω1 represents the mass fraction of the total carbon in the sample powder to be tested obtained in step a, %; 1.73 represents the density of titanium tetrachloride, g / mL.

[0093] 3. Measurement results: The total carbon content in the crude titanium tetrachloride and refined titanium tetrachloride samples was measured according to the above experimental steps. The results are shown in Table 2.

[0094] Table 2 Results of measuring total carbon in titanium tetrachloride using this method

[0095]

[0096] 2. Comparative experiment on total carbon content measurement in titanium tetrachloride

[0097] 1. Measurement of total carbon in titanium tetrachloride hydrolyzate

[0098] The same titanium tetrachloride sample was placed in water and dilute hydrochloric acid for hydrolysis to prepare hydrolyzate, and the hydrolyzate obtained by the sample pretreatment method of the present invention was used as a control, specifically:

[0099] (1) Take two portions (1# and 2#) of 1.0 mL of titanium tetrachloride sample in parallel, add them into 25 mL of water respectively for hydrolysis (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.”) to obtain a hydrolyzate;

[0100] (2) Taking two 1.0 mL portions of titanium tetrachloride samples (#3 and #4) in parallel, adding them to 25 mL of dilute hydrochloric acid for hydrolysis (refer to CN 116046600A “A method for detecting carbon content in titanium tetrachloride”) to obtain a hydrolyzate;

[0101] (3) Taking two portions (#5 and #6) of 1.0 mL of titanium tetrachloride sample in parallel, adding each portion into 25 mL of water, and hydrolyzing the sample according to the sample pretreatment method of the present invention to obtain a hydrolyzate.

[0102] The contents of total carbon (TC), inorganic carbon (IC) and total organic carbon (TOC) in the obtained hydrolyzate were measured using an organic carbon analyzer (model: multi N / C, Jena Analytical Instruments AG, Germany). The results are shown in Table 3.

[0103] Table 3 Distribution of carbon content in hydrolyzate when titanium tetrachloride is hydrolyzed in water and dilute hydrochloric acid

[0104]

[0105] From the comparative experimental results in Table 3, we can see that:

[0106] First, when titanium tetrachloride is hydrolyzed in water and dilute hydrochloric acid, the hydrolysis products of organic matter in titanium tetrachloride include inorganic carbon (mainly trichloroacetic acid, dichloroacetic acid, formic acid, etc.) and organic carbon (mainly carbon tetrachloride, carbon disulfide, etc.), and the content of organic carbon is higher than that of inorganic carbon, which indicates that when the organic matter in titanium tetrachloride is hydrolyzed in water or dilute hydrochloric acid, most of it exists in the form of unhydrolyzed organic matter; while in the method of the present invention, the contents of total carbon and inorganic carbon are very close, indicating that under the conditions of the method of the present invention, the organic matter in titanium tetrachloride is completely hydrolyzed in the strong alkaline solution, and the organic matter is converted into organic acid salts and carbonates that are not volatile after hydrolysis.

[0107] Second, comparing the total carbon measurement data under the three pretreatment methods, the total carbon is lowest when hydrolyzed in water, followed by dilute hydrochloric acid. The reason for this result is that when titanium tetrachloride is hydrolyzed in water or dilute hydrochloric acid, some organic matter (such as COS, COCl2) decomposes into carbon dioxide and then evaporates; when hydrolyzed in water, the solution temperature is high, and some organic matter (such as CCl4) evaporates, resulting in a low measurement result.

[0108] 2. Comparative experiment between the present invention and Fourier transform infrared spectroscopy

[0109] The single component content of each organic matter in the crude titanium tetrachloride and refined titanium tetrachloride samples same as those in the embodiment of the present invention 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 4.

[0110] Table 4 Results of Fourier measurement of total carbon in titanium tetrachloride

[0111]

[0112] By comparing the data in Table 2 and Table 4, it can be seen that: first, there is no significant difference between the measurement results of the method of the present invention and the Fourier transform infrared spectroscopy, but from the comparison of precision, the method is significantly better than the Fourier transform infrared spectroscopy. Secondly, for crude titanium tetrachloride, the measured value of this method is slightly higher than that of the Fourier transform infrared method. This may be because the organic components in crude titanium tetrachloride are more complex and diverse, and this part of organic matter is not measured by the Fourier transform infrared spectroscopy, resulting in slightly lower data. In summary, it can be seen that the accuracy and precision of the total carbon content in titanium tetrachloride measured by the method of the present invention are good.

Claims

1. A sample pretreatment method for measuring total carbon in titanium tetrachloride, characterized in that: The whole process is carried out under the protection of inert gas, the titanium tetrachloride sample to be tested is added to a strong alkaline solution containing a catalyst for full hydrolysis, and the water is evaporated after hydrolysis to obtain a solid sample to be tested; the catalyst is a mixture of transition metals and their oxides in a mass ratio of 1:1; The amount of the titanium tetrachloride sample to be tested is 1-5 mL, the content of the catalyst is 0.15-0.75 g, the volume of the strong alkali solution is 20-60 mL, and the molar ratio of the titanium tetrachloride sample to be tested to OH- in the strong alkali solution is 1:4; The hydrolysis temperature is 75-95°C, the hydrolysis time is 5-20 minutes, and the evaporation temperature is 100-120°C.

2. The sample pretreatment method for measuring total carbon in titanium tetrachloride according to claim 1, characterized in that: The strong alkaline solution is any one of lithium hydroxide solution, potassium hydroxide solution and sodium hydroxide solution.

3. The sample pretreatment method for measuring total carbon in titanium tetrachloride according to claim 1, characterized in that: The mixture of transition metals and their oxides is any one of a mixture of vanadium and vanadium oxide, a mixture of copper and copper oxide, a mixture of chromium and chromium oxide, a mixture of manganese and manganese oxide, a mixture of iron and iron oxide, a mixture of cobalt and cobalt oxide, a mixture of nickel and nickel oxide, and a mixture of zinc and zinc oxide.

4. A method for measuring total carbon in titanium tetrachloride, characterized in that: The steps include: a. A solid sample to be tested is obtained by the sample pretreatment method for measuring total carbon in titanium tetrachloride according to any one of claims 1 to 3, and ground into powder under inert gas protection to obtain a powdered sample to be tested and packaged for standby use; b. Prepare synthetic calibration standards and quality control samples with spectrally pure titanium dioxide and high-grade pure potassium carbonate, mix them evenly, select a high-frequency infrared carbon and sulfur analyzer for total carbon analysis, establish an analysis method and draw a calibration working curve; c. Using the instrumental analysis method established in step b to measure the mass fraction of the total carbon in the sample powder obtained in step a, the mass fraction of the total carbon content in the titanium tetrachloride sample to be tested is calculated based on the mass fraction of the total carbon in the sample powder to be tested.

5. The method for measuring total carbon in titanium tetrachloride according to claim 4, characterized in that: In step b, the analysis method of the high-frequency infrared carbon and sulfur analyzer is: oxygen flow rate 3.5L / min, purge time 10s, integration delay 8s, analysis time 30s, comparator level 2%, combustion power 95%; high-purity oxygen is used as carrier gas and combustion-supporting gas, nitrogen is used as power gas, and the carrier gas output pressure is adjusted to 0.25MPa and the power gas pressure is 0.15MPa.

6. The method for measuring total carbon in titanium tetrachloride according to claim 5, characterized in that: In step c, the measuring method is specifically as follows: a ceramic crucible specially used for carbon-sulfur analysis is calcined in a muffle furnace at 1150-1250° C. for 4-5 hours, taken out and placed in a dryer for cooling for standby use; 0.30-0.50 g of high-purity iron particles are added to the cooled ceramic crucible, and then 0.20-0.40 g of the sample powder to be tested obtained in step a is weighed and placed in the ceramic crucible, and then 1.00-1.50 g of a tungsten-tin mixed flux is added.

7. The method for measuring total carbon in titanium tetrachloride according to claim 4, characterized in that: In step c, the calculation formula for the mass fraction of the total carbon content in the titanium tetrachloride sample to be measured is: TC =[(V×1.73) / m]×ω1, where: ω TC Indicates the mass fraction of the total carbon content in the carbon tetrachloride sample to be tested, %; V represents the amount of titanium tetrachloride sample added during pretreatment, mL; m represents the mass of the sample powder obtained in step a, g; ω1 represents the mass fraction of total carbon in the sample powder to be tested obtained in step a, %; 1.73 represents the density of titanium tetrachloride, g / mL.

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