A method for preparing low-water magnesium chloride by reacting low-carbon small molecules with magnesium chloride for dehydration

Abstract

The present invention provides a method for preparing low-water magnesium chloride by reacting low-carbon small molecules with magnesium chloride for dehydration. The specific steps of the method are as follows: (1) using low-carbon small molecule gas as a raw material, and deoxygenating and dehydrating the low-carbon small molecule gas to obtain the treated low-carbon small molecule gas; (2) contacting the low-carbon small molecule gas treated in step (1) with magnesium chloride for reaction, and then cooling and taking out under a reaction atmosphere to obtain low-water magnesium chloride. The method provided by the present invention reduces the temperature of magnesium chloride dehydration, avoids the use of HCl gas and organic solvents, etc., realizes the controllable preparation of low-water magnesium chloride under milder conditions, reduces industrial energy consumption, solves environmental pollution and equipment corrosion problems, and provides a guarantee for the intrinsic safety of chemical processes.

Description

Technical Field

[0001] The invention relates to a method for preparing low-water magnesium chloride by dehydrating low-carbon small molecules from magnesium chloride. Background Art

[0002] Magnesium chloride usually refers to MgCl2 containing two or more (including two) crystal waters. The anhydrous / low-water (less than two crystal waters) magnesium chloride obtained by dehydration is the raw material for the preparation of magnesium metal and magnesium alloys, and is widely used in various fields of magnesium industry production. At present, the most common magnesium chloride dehydration process methods in domestic and foreign industries mainly include (1) HCl gas protection dehydration method; (2) organic solvent distillation and molecular sieve dehydration method; (3) ammonia complex dehydration method. However, these processes usually involve extreme conditions such as high temperature and HCl acid gas, which leads to stringent requirements on the high temperature resistance, corrosion resistance and sealing of key equipment in the actual production process; in addition, the use of expensive organic solvents is not only costly, but also has low dehydration efficiency, high energy consumption, and easy to cause environmental pollution. Although the domestic magnesium industry has conducted a lot of research on several traditional processes for dehydration of hydrochlorite, there are currently serious shortcomings: either the magnesium oxide and water content in the dehydrated water is too high, or there are serious environmental problems and high energy consumption. Therefore, it is of great significance to change the existing high-energy consumption and high-concentration corrosive gas protection anhydrous / low-water magnesium chloride preparation process. In addition, there is still a huge challenge in reducing preparation costs by optimizing production conditions. Summary of the invention

[0003] The present invention aims at the blank of preparing low-water magnesium chloride by dehydrating magnesium chloride under low temperature conditions, and provides a method for preparing low-water magnesium chloride by dehydrating low-carbon small molecules with magnesium chloride. This method greatly reduces the temperature of magnesium chloride dehydration, avoids the use of HCl gas and organic solvents, etc., realizes the controllable preparation of high-purity low-water magnesium chloride under milder conditions, reduces industrial energy consumption, solves the problems of environmental pollution and equipment corrosion, and provides a guarantee for the intrinsic safety of chemical processes.

[0004] The present invention provides a method for preparing low-water magnesium chloride by reacting low-carbon small molecules with magnesium chloride for dehydration, and the specific steps are as follows:

[0005] (1) Using low-carbon small molecule gas as raw material, and deoxygenating and dehydrating the low-carbon small molecule gas to obtain treated low-carbon small molecule gas;

[0006] (2) The low-carbon small molecule gas treated in step (1) is contacted with magnesium chloride for reaction, and then cooled and taken out under the reaction atmosphere to obtain low-water magnesium chloride.

[0007] Furthermore, in step (1), the low-carbon small molecule is selected from at least one of methanol, ethanol, propanol, butanol, methane, carbon monoxide, methyl chloride, dichloromethane, chloroform, carbon tetrachloride, ethyl chloride, dichloroethane, trichloroethane, tetrachloroethane, pentachloroethane and hexachloroethane, preferably at least one of methanol, methyl chloride, ethyl chloride, carbon monoxide, a mixture of carbon monoxide and methyl chloride, and a mixture of carbon monoxide and ethyl chloride.

[0008] Furthermore, in step (1), the deoxygenation and dewatering treatment steps specifically include first using a 401 manganese-based deoxidizer for deoxygenation, then using anhydrous calcium chloride and molecular sieves to remove water adsorbed in low-carbon small molecules, respectively, to achieve the purpose of deep water removal, and finally using color-changing silica gel to detect the degree of water removal until the color-changing silica gel does not change color.

[0009] Furthermore, in step (1), before the low-carbon small molecules are subjected to deoxygenation and dehydration treatment, if there are liquid low-carbon small molecules, they need to be heated and vaporized to obtain low-carbon small molecule gas.

[0010] Furthermore, in step (2), the magnesium chloride refers to MgCl2 with more than two crystal waters; and the low-water magnesium chloride refers to MgCl2 with less than two crystal waters.

[0011] Furthermore, in step (2), when the treated low-carbon small molecule gas is contacted with magnesium chloride for reaction, the gas flow rate is 1 mL / min-1000 L / min, preferably 10 mL / min-120 mL / min, and the air velocity is 1200 ml / g MgCl2 / h -200000ml / g MgCl2 / h, the reaction time is 2-600h, preferably 2-12h.

[0012] Furthermore, in step (2), the concentration of the treated low-carbon small molecules is 1%-100%. When the concentration is less than 100%, the remaining gas is the balance gas, which is usually selected from N2 or an inert gas.

[0013] Furthermore, in step (2), before the treated low-carbon small molecule gas contacts the magnesium chloride, the magnesium chloride is pretreated at a pretreatment temperature of 50-150° C., preferably 70-100° C., for a time of 0.5-6 h.

[0014] Furthermore, in step (2), during the reaction process, programmed heating is adopted, the heating rate is 0.1-100°C / min, preferably 1-10°C / min, the reaction temperature is 50-500°C, preferably 100-200°C, and the reaction time is 4-40 h.

[0015] Furthermore, in step (2), during the reaction, the mixture is cooled to room temperature and then taken out.

[0016] Furthermore, in step (2), the mass fraction of crystal water in the obtained low-hydrated magnesium chloride is 0.001%-20%.

[0017] The beneficial effects of the present invention are:

[0018] The method for preparing low-water magnesium chloride by dehydrating low-carbon small molecules and magnesium chloride provided by the present invention is the first to catalyze the reaction between low-carbon small molecules and the crystal water in magnesium chloride hexahydrate to carry out synergistic dehydration, thereby realizing a new process for the efficient preparation of low-water magnesium chloride. Traditional high-temperature hydrogen chloride atmosphere protection, organic solvent distillation, and ammonia evaporation and other dehydration processes require a dehydration temperature of more than 360°C. The method provided by the present invention creatively utilizes catalytic reaction dehydration, rather than traditional thermal dehydration and coordination competition dehydration. Through this method, the temperature of magnesium chloride dehydration can be effectively reduced, and the use of excessive hydrogen chloride gas and organic solvents that cause environmental pollution can be avoided. While greatly reducing energy consumption, the corrosion resistance problem of equipment can also be solved, and it is expected to greatly reduce the cost of preparing low-water magnesium chloride. In addition, by utilizing the dehydration strategy of catalytic reaction between low-carbon small molecules and crystal water, it can be extended to other halides containing crystal water, further improving the economic benefits of anhydrous halide preparation, and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is the X-ray diffraction pattern of the product obtained in Example 1 of the present invention;

[0020] Figure 2 is a thermogravimetric diagram of the product obtained in Example 1 of the present invention;

[0021] Figure 3 is the mass spectrum of the product obtained in Example 1 of the present invention;

[0022] Figure 4 is the X-ray diffraction pattern of the product obtained in Example 4 of the present invention;

[0023] Figure 5 is a thermogravimetric diagram of the product obtained in Example 4 of the present invention;

[0024] Figure 6 is the mass spectrum of the product obtained in Example 4 of the present invention;

[0025] Figure 7 It is a schematic diagram of the process flow of the dehydration of low-carbon small molecules by reaction with magnesium chloride according to the present invention. DETAILED DESCRIPTION

[0026] In order to enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the method for preparing low-water magnesium chloride by reacting low-carbon small molecules with magnesium chloride for dehydration is further described below in conjunction with the accompanying drawings and through specific implementation methods.

[0027] In the present invention, the crystal structure of the solid phase product obtained in the embodiment is determined by X-ray diffractometer (XRD).

[0028] In the present invention, thermogravimetric-mass spectrometry (TG-MASS) is combined with Karl Fischer method to accurately calculate the amount of crystal water in the solid phase product obtained in the embodiment. Example 1

[0029] The specific steps of the method for preparing low-water magnesium chloride by reacting low-carbon small molecules with magnesium chloride for dehydration are as follows:

[0030] First, weigh 2 g of magnesium chloride hexahydrate and put it into an oven at 85 °C for 2 hours; then, weigh 0.50 g of pretreated magnesium chloride hexahydrate into a quartz tube, and pass chloromethane gas, and strictly dehydrate and deoxygenate before entering the tubular furnace reactor. First, use 401 manganese deoxidizer for deoxygenation, then use anhydrous calcium chloride and powder sieve to remove water adsorbed in low-carbon small molecules, respectively, to achieve the purpose of deep water removal, and finally use color-changing silica gel to detect the degree of water removal until the color-changing silica gel does not change color. The concentration of chloromethane gas is 10% CH3Cl / N2 (balance gas), the gas flow rate is 80 mL / min, and the air velocity is 9600ml / g MgCl2 / h; finally, the temperature was raised to 130 ℃ at a heating rate of 5 ℃ / min, the reaction time was 8h, and the reaction atmosphere was lowered to room temperature and taken out to obtain a low-hydrate magnesium chloride product.

[0031] Figure 1 is the X-ray diffraction pattern of the low-water magnesium chloride product prepared in Example 1. Figure 1 It can be seen that the X-ray diffraction pattern of low-hydrated magnesium chloride obtained by the method of the present invention is consistent with the characteristic peaks in the PDF card of standard monohydrate magnesium chloride, so it is determined that the generated product is monohydrate magnesium chloride, and the purity is> 99%. Figure 2 This is the thermogravimetric diagram of low-water magnesium chloride prepared in Example 1; Figure 3 This is the mass spectrum of water released during thermogravimetric analysis. Figure 2 and Figure 3 It shows that the product of the weight loss process in area A and area B is mainly water. According to the weight loss ratio combined with the Karl Fischer method, the product is determined to be magnesium chloride with 1.01 crystal water. Figure 1 The XRD results are consistent with those of Example 2

[0032] The specific steps of the method for preparing low-water magnesium chloride by reacting low-carbon small molecules with magnesium chloride for dehydration are as follows:

[0033] First, 2 g of magnesium chloride hexahydrate was weighed and placed in an oven at 85 °C for 2 h; then, 0.50 g of the pretreated magnesium chloride hexahydrate was weighed into a quartz tube, and CO gas was introduced, and strict water removal and deoxygenation were performed before entering the tubular furnace reactor. The treatment steps were the same as in Example 1. The concentration of CO gas was 10% CO / N2 (balance gas), the gas flow rate was 80 mL / min, and the space velocity was 9600 ml / g MgCl2 / h,; finally, the temperature was raised to 130 ℃ at a heating rate of 5 ℃ / min, the reaction time was 8h, the reaction atmosphere was lowered to room temperature and taken out to obtain a low-hydrate magnesium chloride product.

[0034] The X-ray diffraction pattern, thermogravimetric pattern and water mass spectrum of the product obtained in Example 2 are similar to those in Example 1. According to the characterization results, Example 2 obtains high-purity magnesium chloride monohydrate (MgCl2×H2O) with a purity of >99%. Example 3

[0035] The specific steps of the method for preparing low-water magnesium chloride by reacting low-carbon small molecules with magnesium chloride for dehydration are as follows:

[0036] First, weigh 2 g of magnesium chloride hexahydrate and put it into an oven at 85 ° C for 2 hours; then, weigh 0.50 g of pretreated magnesium chloride hexahydrate into a quartz tube, and pass dichloromethane (need to be heated and vaporized) gas, and strictly remove water and oxygen before entering the tubular furnace reactor. The treatment steps are the same as in Example 1. The concentration of dichloromethane is 10% CH2Cl2 / N2 (balance gas), the gas flow rate is 80 mL / min, and the space velocity is 9600 ml / g MgCl2 / h,; finally, the temperature was raised to 130°C at a heating rate of 5°C / min, the reaction time was 8h, the reaction atmosphere was lowered to room temperature and the reaction mixture was taken out to obtain a low-hydrate magnesium chloride product.

[0037] The X-ray diffraction pattern, thermogravimetric pattern and water mass spectrum of the product obtained in Example 3 are similar to those in Example 1. According to the characterization results, Example 3 obtains high-purity magnesium chloride monohydrate (MgCl2×H2O) with a purity of >99%. Example 4

[0038] The specific steps of the method for preparing low-water magnesium chloride by reacting low-carbon small molecules with magnesium chloride for dehydration are as follows:

[0039] First, weigh 2 g of magnesium chloride hexahydrate and put it into an oven at 85°C for 2 hours; then, weigh 0.50 g of the pretreated magnesium chloride hexahydrate into a quartz tube, and pass methyl chloride gas, and strictly remove water and oxygen before entering the tubular furnace reactor. The treatment steps are the same as in Example 1. The concentration of methyl chloride gas is 10% CH3Cl / N2 (balance gas), the gas flow rate is 80 mL / min, and the space velocity is 9600 ml / g MgCl2 / h; finally, the temperature was raised to 160°C at a heating rate of 5°C / min, the reaction time was 8h, the reaction atmosphere was lowered to room temperature and the reaction mixture was taken out to obtain a low-water magnesium chloride product.

[0040] Figure 4 is the X-ray diffraction pattern of the product prepared in Example 4. Figure 4 It can be seen that the X-ray diffraction pattern of the product obtained by the method of the present invention is consistent with the characteristic peaks in the standard PDF card of anhydrous MgCl2 and the standard PDF card of MgCl2·0.3H2O with 0.3 crystal waters, so it is determined that the generated product is a mixed phase of anhydrous MgCl2 and MgCl2·0.3H2O. Figure 5 This is the thermogravimetric diagram of the low-water magnesium chloride prepared in Example 4; Figure 6 This is the mass spectrum of water released during thermogravimetric analysis. Figure 5 and Figure 6 It shows that the product in the weight loss process of area A and area B is mainly water. According to the weight loss ratio and Karl Fischer method, the product is determined to be low-water magnesium chloride (a mixture of anhydrous MgCl2 and MgCl2·0.3H2O), which is consistent with the XRD results. Example 5

[0041] The specific steps of the method for preparing low-water magnesium chloride by reacting low-carbon small molecules with magnesium chloride for dehydration are as follows:

[0042] First, weigh 2 g of magnesium chloride hexahydrate and put it into an oven for drying at 85°C for 2 hours; then, weigh 0.50 g of the pretreated magnesium chloride hexahydrate into a quartz tube, and pass a mixture of CO and chloromethane into it, and strictly remove water and oxygen before entering the tubular furnace reactor. The treatment steps are the same as in Example 1. The ratio of CO and chloromethane mixture is 1:1, 10% CO / 10% CH3Cl / N2 (balance gas), the gas flow rate is 80 mL / min, and the space velocity is 9600 ml / g MgCl2 / h; finally, the temperature was raised to 160°C at a heating rate of 5°C / min, the reaction time was 8h, the reaction atmosphere was lowered to room temperature and the reaction mixture was taken out to obtain a low-hydrate magnesium chloride product.

[0043] The X-ray diffraction pattern, thermogravimetric pattern and water mass spectrum of the product obtained in Example 5 are similar to those in Example 4. According to the characterization results, it is shown that Example 5 obtains a mixed phase of anhydrous MgCl2 and MgCl2·0.3H2O. Example 6

[0044] The specific steps of the method for preparing low-water magnesium chloride by reacting low-carbon small molecules with magnesium chloride for dehydration are as follows:

[0045] First, weigh 2 g of magnesium chloride hexahydrate and put it into an oven at 85°C for 2 hours; then, weigh 0.50 g of the pretreated magnesium chloride hexahydrate into a quartz tube, and pass a mixture of CO and ethyl chloride (needs to be heated and vaporized), and strictly remove water and oxygen before entering the tubular furnace reactor. The treatment steps are the same as in Example 1. The ratio of CO and ethyl chloride is 1:1, 10% CO / 10% CH3CH2Cl / N2 (balance gas), the gas flow rate is 80 mL / min, and the space velocity is 9600 ml / g MgCl2 / h; finally, the temperature was raised to 160°C at a heating rate of 5°C / min, the reaction time was 8h, the reaction atmosphere was lowered to room temperature and the mixture was taken out to obtain a low-hydrate magnesium chloride product.

[0046] The X-ray diffraction pattern, thermogravimetric pattern and water mass spectrum of the product obtained in Example 6 are similar to those in Example 4. According to the characterization results, Example 6 obtains a mixed phase of anhydrous MgCl2 and MgCl2·0.3H2O.

[0047] The applicant declares that the above is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention shall fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing low-water magnesium chloride by reacting low-carbon small molecules with magnesium chloride for dehydration, the specific steps are as follows: (1) Using low-carbon small molecule gas as raw material, and deoxygenating and dehydrating the low-carbon small molecule gas to obtain treated low-carbon small molecule gas; (2) contacting the low-carbon small molecule gas treated in step (1) with magnesium chloride to react, and then cooling and taking out in a reaction atmosphere to obtain low-water magnesium chloride; In step (1), the low-carbon small molecule is selected from at least one of methanol, ethanol, propanol, butanol, methane, carbon monoxide, methyl chloride, dichloromethane, chloroform, carbon tetrachloride, ethylene monochloride, dichloroethane, trichloroethane, tetrachloroethane, pentachloroethane and hexachloroethane; In step (2), the mass fraction of crystal water in the low-hydrated magnesium chloride is 0.001%-20%; In step (2), when the treated low-carbon small molecule gas contacts and reacts with magnesium chloride, the gas flow rate is 10mL / min-120mL / min, and the air velocity is 1200mL / g MgCl2 / h -9600mL / g MgCl2 / h, reaction time is 2-12h; In step (2), during the reaction process, programmed heating is adopted, the heating rate is 1-10 °C / min, the reaction temperature is 100-200 °C, and the reaction time is 4-40 h.

2. The method according to claim 1, characterized in that In step (2), before the treated low-carbon small molecule gas contacts the magnesium chloride, the magnesium chloride is pretreated at a temperature of 50-150° C. for a time of 0.5-6 h.

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