Process for the preparation of a copper depressant 1-thioglycerol for copper-molybdenum ore flotation separation

Abstract

The present application relates to the technical field of mineral processing, and particularly relates to a preparation method of a copper inhibitor 1-thioglycerol for copper-molybdenum ore flotation separation. Sodium hydrosulfide is added into a mixed solvent of anhydrous ethanol and deionized water for dissolution; under the protection of a micro-positive pressure of nitrogen, the temperature is increased to 55-65 DEG C, and a mixed solution of 3-chloro-1,2-propanediol and anhydrous ethanol is added dropwise; the temperature is increased to 75-80 DEG C for reflux, and thin layer chromatography is monitored until the raw material 3-chloro-1,2-propanediol is completely consumed; the reaction solution is cooled, hydrogen sulfide is removed by nitrogen blowing, vacuum filtration is performed, the filter cake is washed with ethanol, the filtrate and the washing solution are combined, a composite antioxidant is added, and the solid residue is obtained by vacuum concentration under the nitrogen atmosphere, the vacuum environment and the water bath temperature of 25-28 DEG C; water is added, hydrochloric acid is used to adjust the pH to 3-4, and salt is added for salting out; n-butanol is extracted for multiple times, and the organic phase is collected; the organic phase is dried with anhydrous sodium sulfate, and n-butanol is removed under reduced pressure at the water bath temperature of 33-37 DEG C.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of mineral processing, and particularly relates to a preparation method of a copper inhibitor 1-thioglycerol for copper-molybdenum ore flotation separation. BACKGROUND

[0002] Copper-molybdenum separation is a core key process in the molybdenum ore dressing process, and the separation effect directly determines the final grade, recovery rate and economic value of the molybdenum concentrate. The copper inhibitors widely used in current industrial production mainly include cyanide, sulfide (sodium sulfide, sodium hydrosulfide) and mercaptoacetate, but each type of inhibitor has difficult-to-overcome technical defects: 1. Cyanide inhibitors: Although cyanide such as sodium cyanide and potassium cyanide has excellent copper inhibition effect, it is a highly toxic chemical, and there are significant safety and environmental risks in the whole process of storage, transportation, use and wastewater treatment, which seriously endangers the health of operating personnel and easily causes water and soil heavy metal pollution. At present, it has been restricted or prohibited in ore dressing in most countries in the world; 2. Sulfide inhibitors: Sodium sulfide and sodium hydrosulfide are the most widely used non-cyanide copper inhibitors at present, but they have the following outstanding problems: large dosage (usually 10-20 times that of cyanide), unstable inhibition effect (significantly affected by pulp pH, dissolved oxygen content and slime content), easy to be oxidized by air to lose effectiveness, poor operating environment (release of highly toxic H2S gas), and serious over-standard of COD and sulfide in ore dressing wastewater, and extremely high wastewater treatment cost; 3. Mercaptoacetate inhibitors: The copper inhibition capacity of this type of inhibitor is limited, and it has poor adaptability to high secondary copper sulfide content of refractory ores, and is expensive (about 8-10 times that of sodium hydrosulfide), so large-scale application will significantly increase the cost of ore dressing reagents, and it is difficult to promote the use in small and medium-sized mines.

[0003] 1-thioglycerol, also known as alpha-mercapto glycerol, has the following significant advantages: good inhibition selectivity, small dosage (only 1 / 10-1 / 20 of that of sodium hydrosulfide), stable inhibition effect, easy biodegradation, no toxicity, etc. It has a broad application prospect in the field of copper-molybdenum separation.

[0004] However, the existing synthesis technology of 1-thioglycerol still has many technical bottlenecks, which seriously restricts its large-scale industrial production and ore dressing application: (1) low reaction efficiency and large yield fluctuation: the existing process mostly uses pure ethanol or pure water solution system. In the pure ethanol system, the solubility of sodium hydrosulfide is low, and the dissociation degree is poor, the effective HS -(1) Reaction rate is slow due to insufficient ion concentration, reaction time is more than 5 hours, raw material conversion rate is low, and product yield is only 58%~92%; (2) Catalyst side effect is obvious: in order to improve the reaction rate, phase transfer catalysts such as tetrabutylammonium bromide are added in part of the process, but the catalysts promote the generation of polysulfides, oxidation of mercapto and other side reactions, resulting in a product yield of less than 74%, and the residual catalysts significantly affect the flotation selectivity of the product; (3) Hydrolysis side reaction is serious: if the water content is too high, the 3-chloro-1,2-propanediol raw material will undergo alkaline hydrolysis to generate glycerol and other by-products, the product yield will drop to less than 36%, and the product has deep color, low purity and strong odor, which cannot meet the quality requirements of flotation reagents; (4) High production cost: the existing process has large solvent consumption (about 160 mL / 0.1 mol of raw material), complex post-treatment process, high energy consumption for solvent recovery, and poor batch quality stability, resulting in high market price of 1-thioglycerol, which is difficult to fully replace traditional copper inhibitors.

[0005] Therefore, it is of great practical significance and industrial application value to develop a preparation method of 1-thioglycerol with high reaction yield, high product purity, short reaction time, less solvent consumption and suitable for industrial large-scale production, which can promote the green upgrading of copper-molybdenum ore flotation industry and replace traditional toxic and harmful inhibitors. SUMMARY

[0006] The present application provides a preparation method of 1-thioglycerol as a copper inhibitor for copper-molybdenum ore flotation separation.

[0007] The first object of the present application is to provide a preparation method of 1-thioglycerol as a copper inhibitor for copper-molybdenum ore flotation separation, which comprises the following steps: S1. Sodium hydrosulfide is dissolved in a mixed solvent of anhydrous ethanol and deionized water at room temperature; the volume ratio of anhydrous ethanol to deionized water in the mixed solvent is 100~200:1; S2. Under the protection of a slight positive pressure of nitrogen, the temperature is raised to 55~65℃, and a mixture of 3-chloro-1,2-propanediol and anhydrous ethanol is added dropwise, the dropwise adding time is 15~25 min; the temperature is raised to 75~80℃ for reflux, and thin layer chromatography is used to monitor until the raw material 3-chloro-1,2-propanediol is completely consumed, and the total reaction time is 3.5~4.5h; S3. After the reaction is completed, the reaction solution is cooled, hydrogen sulfide is removed by nitrogen blowing, sodium chloride solid is removed by vacuum filtration, the filter cake is washed with ethanol, and the filtrate and the washing liquid are combined to obtain a crude product mixture; S4. A composite antioxidant is added to the crude product mixture, and the mixture is concentrated under reduced pressure in a nitrogen atmosphere and an environment with a vacuum degree of-0.09~0.1Mpa at a water bath temperature of 25~28℃ to obtain a solid residue; S5. Dissolve the solid residue in water, adjust the pH to 3-4 with hydrochloric acid, and salt out the residue. Extract the organic phase multiple times with n-butanol and collect the organic phase. After drying the organic phase with anhydrous sodium sulfate, remove the n-butanol under reduced pressure at a water bath temperature of 33-37℃ to obtain high-purity 1-thioglycerol.

[0008] Preferably, a pretreatment step S0 is provided before step S1: a three-necked flask is used as the main reaction vessel, and the flask mouth is connected to a reflux condenser, a nitrogen gas delivery tube and a thermometer respectively; a sealed buffer balloon and a two-stage tail gas washing device are connected in series at the uppermost outlet of the reflux condenser; air is introduced into the high-purity nitrogen replacement device for 10~20 minutes, and the system is kept under a slight positive pressure of nitrogen to isolate oxygen throughout the process.

[0009] Preferably, the sodium hydrosulfide is industrial-grade sodium hydrosulfide with a purity of 70%; the addition ratio of the 3-chloro-1,2-propanediol and the mixed solvent is 0.1 mol: 60~90 mL.

[0010] Preferably, in step S2, a mixture of 3-chloro-1,2-propanediol and anhydrous ethanol is added dropwise through a constant pressure dropping funnel, and the dropping time is controlled to be 20 min; the ratio of 3-chloro-1,2-propanediol to anhydrous ethanol is 0.1 mol: 20 mL.

[0011] Preferably, thin-layer chromatography uses ethyl acetate:petroleum ether = 1:1 as the developing solvent and phosphomolybdic acid as the colorimetric reagent for raw material tracking; the total reaction time is 4 hours.

[0012] Preferably, the composite antioxidant is composed of sodium sulfite and ascorbic acid; for every 0.1 mol of 3-chloro-1,2-propanediol, 0.05~0.15 g of sodium sulfite and 0.02~0.08 g of ascorbic acid are added.

[0013] Preferably, step S5 specifically includes the following sub-steps: S51. Add deionized water at 35~45℃ to the concentrated solid residue, stir at 35~45℃ for 8~15min to completely dissolve the residue in water; under continuous stirring, slowly add hydrochloric acid solution with a concentration of 4~8mol / L to adjust the pH of the aqueous system to 3~4. S52. Add solid sodium chloride, stir to dissolve and complete salting out, let stand for 3-10 minutes to separate the layers; use n-butanol for three extractions, separate and combine the upper organic phases; S53. Add anhydrous sodium sulfate solid to the upper organic phase and stir and dry at room temperature for 25-35 min; transfer the dried and filtered organic phase to a rotary evaporator, maintain a vacuum of -0.098 MPa, and concentrate under reduced pressure at a water bath temperature of 33-37℃ to completely remove the n-butanol organic solvent, and obtain a colorless, transparent, oily high-purity 1-thioglycerol product.

[0014] Preferably, in step S52, the amount of solid sodium chloride added is 10-20g; 10-20mL of n-butanol is added for each extraction, and the mixture is vigorously shaken for 2min before standing to separate into layers. All organic phases obtained from the three extractions are combined and collected.

[0015] The second objective of this invention is to provide a copper inhibitor, 1-thioglycerol, for the flotation separation of copper-molybdenum ore. The 1-thioglycerol is prepared using a method for the flotation separation of copper-molybdenum ore; the purity of the 1-thioglycerol is ≥98.5%, and its appearance is a colorless, transparent, oily liquid.

[0016] Compared with the prior art, the present invention can achieve the following beneficial effects: (1) The product has excellent performance and can completely replace traditional toxic inhibitors: The 1-thioglycerol prepared by this invention has a strong selective inhibitory effect on copper minerals. The amount used is only 1 / 10 to 1 / 20 of sodium hydrosulfide to achieve the same inhibitory effect. Moreover, the inhibitory effect is not affected by the dissolved oxygen content in the slurry. The agent has a long action time, which can significantly improve the mineral processing operation environment and reduce the difficulty and cost of mineral processing wastewater treatment.

[0017] (2) Significantly improved reaction yield and product purity: Under optimal process conditions, the product yield can reach 98.2% and the HPLC purity can reach 98.7%, which is 6-40% higher than the existing pure ethanol process, more than 60% higher than the water-addition process, and the purity is increased by 0.5-2.5%; (3) Production efficiency is significantly improved: the total reaction time is shortened from more than 5 hours in the existing process to less than 4 hours, the production cycle is shortened by more than 20%, the utilization rate of core equipment such as reactors is significantly improved, and the production capacity per unit time is increased by more than 25%; (4) Production costs are effectively reduced: The total amount of solvent used is reduced from 160 mL / 0.1 mol raw material in the existing process to 80 mL / 0.1 mol raw material, reducing solvent consumption by 50% and reducing solvent recovery energy consumption accordingly; no phase transfer catalyst is needed, further reducing raw material costs, and the overall production cost is reduced by about 30% compared with the existing process.

[0018] (5) Stable product quality: The product adopts a nitrogen protection system throughout the process and a composite antioxidant system, which effectively solves the problem of easy oxidation and discoloration of mercapto compounds. The product is a nearly colorless and transparent oily liquid with no obvious irritating odor, low impurity content, and batch-to-batch quality difference of less than 0.5%, which fully meets the quality requirements of flotation reagents.

[0019] (6) Green and safe process: The two-stage NaOH tail gas absorption device can completely absorb the trace amount of H2S gas generated during the reaction process, and the tail gas emission meets the national environmental protection standards; no highly toxic raw materials and catalysts are used, the amount of waste generated is small, and the sodium chloride salt generated during the post-treatment process can be recycled. The entire process is safe and environmentally friendly, with no major safety risks. Attached Figure Description

[0020] Figure 1 This is a flowchart of a method for preparing 1-thioglycerol, a copper inhibitor for the flotation separation of copper-molybdenum ore, according to an embodiment of the present invention.

[0021] Figure 2 The 1H NMR spectrum of the 1-thioglycerol product prepared according to the embodiments of the present invention in deuterated methanol is shown below. 1 (H NMR) image. Detailed Implementation

[0022] In the following description, embodiments of the invention will be described with reference to the accompanying drawings. In the description below, the same modules are denoted by the same reference numerals. Where the same reference numerals are used, their names and functions are also the same. Therefore, their detailed description will not be repeated.

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not constitute a limitation thereof.

[0024] This invention provides a method for preparing 1-thioglycerol, a copper inhibitor for the flotation separation of copper-molybdenum ore, specifically comprising the following steps: S0. Apparatus Setup and Pre-Deoxygenation Treatment: A three-necked flask is used as the main reaction vessel, equipped with a magnetic stirring system, a reflux condenser circulation device, a nitrogen-sealed protection pipeline, a temperature measuring mechanism, and a two-stage series hydrogen sulfide tail gas absorption device. The positions and connections of each component are as follows: A three-necked flask is fixed on the platform of an oil bath heated magnetic stirrer. A magnetic stir bar (preferably a PTFE magnetic stir bar) is placed at the bottom of the flask. A spherical reflux condenser tube is vertically fixed to the middle neck of the three-necked flask. Ambient temperature circulating cooling water is introduced into the jacket of the condenser tube, using a bottom-in, top-out circulation method. A sealed buffer balloon and a two-stage tail gas scrubbing device are connected in series via a rubber hose at the top outlet of the condenser tube. The buffer balloon balances the system pressure, prevents backflow of outside air, and temporarily accommodates the overflowing hydrogen sulfide gas. Each of the two-stage scrubbing devices contains 10% hydrogen sulfide gas by mass. A sodium hydroxide aqueous solution is connected to a gas inlet pipe that is inserted below the liquid surface. The two-stage series system completely absorbs the H2S tail gas produced by the reaction. The purified gas is vented from the top of the second-stage gas scrubbing device. A sealed rubber stopper with a through hole is installed on the left side of the three-necked flask. A glass nitrogen gas delivery tube runs through the rubber stopper, with the lower end of the delivery tube extending 1-2 cm below the liquid surface of the flask. This is used to continuously introduce high-purity nitrogen gas to maintain a slight positive pressure of nitrogen in the reaction system. A glass thermometer is inserted into the right side of the three-necked flask. The mercury section of the thermometer is completely immersed in the liquid phase material to monitor the internal temperature of the reaction system in real time. After all sealing and assembly are completed, open the nitrogen cylinder and control the nitrogen flow rate to 30~50mL / min. High-purity nitrogen is continuously introduced into the three-necked flask through the nitrogen delivery tube to continuously replace the air in the device for 15 minutes, thoroughly removing residual oxygen from the flask, condenser, connecting pipes, and gas washing device. After replacement, continue to introduce nitrogen, maintaining a slight positive pressure of nitrogen inside the device throughout the process to prevent air and oxygen from entering the system and causing side reactions of thiol oxidation.

[0025] S1. Preparation of sodium hydrosulfide mixed solvent solution: Add sodium hydrosulfide solid to a mixed solvent of anhydrous ethanol and deionized water, stir at room temperature until completely dissolved to obtain sodium hydrosulfide alcohol aqueous solution; the volume ratio of anhydrous ethanol to deionized water in the mixed solvent is 100~200:1; In some embodiments, 20g of industrial-grade sodium hydrosulfide with a purity of 70% (approximately 0.25mol of pure product) is selected as the sulfur source; a mixed solvent is prepared in advance, which is obtained by uniformly mixing 0.5mL of deionized water and 80mL of anhydrous ethanol.

[0026] S2. Nucleophilic substitution reaction: The sodium hydrosulfide aqueous solution obtained in step S1 was transferred to a three-necked flask, and nitrogen gas was continuously introduced to maintain a slight positive pressure in the system. The temperature was raised to 55~65℃. A mixture of 3-chloro-1,2-propanediol and anhydrous ethanol was added dropwise at a uniform rate under stirring, and the dropping time was controlled to be 15~25 min. The temperature was raised to 75~80℃ and the reaction was refluxed. The reaction was monitored by thin-layer chromatography. The reaction was stopped after the starting material 3-chloro-1,2-propanediol was completely consumed. The total reaction time was 3.5~4.5 h. Specifically, a mixture of 3-chloro-1,2-propanediol and anhydrous ethanol was added dropwise using a constant-pressure dropping funnel, with the addition time controlled at 20 min; the ratio of 3-chloro-1,2-propanediol to anhydrous ethanol was 0.1 mol: 20 mL; the total volume of the mixed solvent used for each 0.1 mol of 3-chloro-1,2-propanediol was 60-90 mL, preferably 80 mL; no phase transfer catalyst was added; the developing solvent used for thin-layer chromatography was ethyl acetate: petroleum ether = 1:1, with phosphomolybdic acid as the colorimetric agent; the total reaction time was 4 h.

[0027] The equation for the substitution reaction in this step is as follows: ClCH2CH(OH)CH2OH+NaHS→HSCH2CH(OH)CH2OH+NaCl.

[0028] S3. Desalination by vacuum filtration: Stop the oil bath heating and allow the entire reaction apparatus to cool naturally to room temperature. Continuously purge with nitrogen gas and stir for 8-15 minutes. Use the nitrogen gas flow to purge and remove the free hydrogen sulfide gas dissolved in the liquid phase. The removed hydrogen sulfide gas is completely absorbed by a buffer balloon and a two-stage sodium hydroxide absorption bottle. Transfer all the reaction mixture in the three-necked flask to a vacuum filtration device and separate the sodium chloride solid filter cake generated by the reaction under vacuum. Wash the filter cake twice with 10 mL of anhydrous ethanol. Combine the two washing solutions with the filtrate to obtain a mixed filtrate containing crude 1-thioglycerol. Specifically, the stirring time is 10 minutes.

[0029] S4. Vacuum Concentration: Add a composite antioxidant to the mixed filtrate, transfer it to a rotary evaporator flask, continuously purge with nitrogen to maintain a slight positive pressure inside the flask to isolate oxygen, set the vacuum degree to -0.098MPa, concentrate under reduced pressure at a water bath temperature of 25~28℃ until no liquid distills out of the flask, and obtain concentrated solid residue. The entire process relies on the dual protection of antioxidant and nitrogen to avoid thiol oxidation and discoloration. Specifically, the compound antioxidant includes sodium sulfite and ascorbic acid, with the addition amount being 0.05~0.15g of sodium sulfite and 0.02~0.08g of ascorbic acid per 0.1mol of 3-chloro-1,2-propanediol; preferably, 0.1g of sodium sulfite and 0.05g of ascorbic acid; sodium sulfite preferentially consumes dissolved oxygen in the system, and ascorbic acid can reduce oxidized disulfides, and the synergistic effect of the two can effectively prevent thiol oxidation.

[0030] S5. Multi-stage extraction and purification: Dissolve solid residue in water, adjust pH to 3-4 with hydrochloric acid, and salt out; extract multiple times with n-butanol, collect the organic phase; dry the organic phase with anhydrous sodium sulfate, and remove n-butanol under reduced pressure at a water bath temperature of 33-37℃ to obtain high-purity 1-thioglycerol; specifically including: S51. Add deionized water at 35~45℃ to the concentrated solid residue, stir at 35~45℃ for 8~15min to completely dissolve the residue in water; under continuous stirring, slowly add hydrochloric acid solution with a concentration of 4~8mol / L to adjust the pH of the aqueous system to 3~4. S52. Add solid sodium chloride, stir to dissolve and complete salting out, let stand for 3-10 minutes to separate the layers; use n-butanol for three extractions, separate and combine the upper organic phases; Specifically, the amount of solid sodium chloride added is 10-20g; 10-20mL of n-butanol is added for each extraction, and the extraction is carried out by vigorous shaking for 2min each time. After each extraction, the mixture is allowed to stand and separate into layers. All organic phases obtained from the three extractions are combined and collected. S53. Add anhydrous sodium sulfate solid to the upper organic phase, stir and dry at room temperature for 25-35 min to remove trace amounts of moisture from the organic phase, and filter to remove the anhydrous sodium sulfate desiccant; transfer the dried and filtered organic phase to a rotary evaporator, maintain a vacuum of -0.098 MPa, and concentrate under reduced pressure at a water bath temperature of 33-37℃ to completely remove the n-butanol organic solvent, finally obtaining a colorless, transparent, oily high-purity 1-thioglycerol product; Specifically, the amount of anhydrous sodium sulfate solid added is 8~12g; the water bath temperature is 35℃.

[0031] The core technical principle of this invention is as follows: By precisely controlling the polarity and solubility of the solvent system, using a specific ratio of anhydrous ethanol and trace amounts of water as a mixed solvent, without adding any phase transfer catalyst, the solubility and dissociation of sodium hydrosulfide in organic solvents are significantly improved, greatly increasing the concentration of the effective nucleophile HS- in the reaction system, thereby accelerating the nucleophilic substitution reaction process. Simultaneously, the water content of the system is strictly controlled within an extremely low range (volume ratio ≤1%), completely suppressing the alkaline hydrolysis side reaction of 3-chloro-1,2-propanediol. Combined with nitrogen protection throughout the process and a composite antioxidant system, thiol oxidation is effectively prevented, ultimately achieving high-yield, high-purity, low-cost, and green preparation of 1-thioglycerol. See the preparation flow chart. Figure 1 .

[0032] Example 1: This embodiment provides a method for preparing 1-thioglycerol, a copper inhibitor for the flotation separation of copper-molybdenum ore. The method utilizes a trace amount of water-ethanol mixed solvent system to prepare 1-thioglycerol, and specifically includes the following steps: S0. A three-necked flask is used as the main reaction vessel. A magnetic stir bar is added to the 250mL three-necked flask. A reflux condenser (with a sealed balloon at the top and a two-stage 10% NaOH tail gas absorption device), a thermometer, and a nitrogen gas delivery tube are installed. High-purity nitrogen is introduced and the air in the system is replaced for 15 minutes.

[0033] S1. Select 20g of industrial-grade sodium hydrosulfide with a purity of 70% (approximately 0.25mol of pure product) as the sulfur source; prepare a mixed solvent in advance, which is obtained by uniformly mixing 0.5mL of deionized water and 80mL of anhydrous ethanol; add the sodium hydrosulfide solid to the mixed solvent of anhydrous ethanol and deionized water, and stir at room temperature until completely dissolved to obtain an aqueous solution of sodium hydrosulfide; the volume ratio of anhydrous ethanol to deionized water in the mixed solvent is 160:1.

[0034] S2. Transfer the obtained sodium hydrosulfide aqueous solution to a three-necked flask, continuously purge with nitrogen to maintain a slight positive pressure in the system, and heat to 60°C; add a mixture of 3-chloro-1,2-propanediol and anhydrous ethanol dropwise through a constant pressure dropping funnel, with a ratio of 0.1 mol: 20 mL of 3-chloro-1,2-propanediol to anhydrous ethanol, and control the dropping time to 20 min; heat to 75-80°C and reflux the reaction, using thin-layer chromatography to monitor the reaction (using ethyl acetate: petroleum ether = 1:1 as the developing solvent, and phosphomolybdic acid as the colorimetric agent), and stop the reaction after the starting material 3-chloro-1,2-propanediol is completely consumed, with a total reaction time of 4 h.

[0035] S3. Stop the oil bath heating and allow the entire reaction apparatus to cool naturally to room temperature. Continuously purge with nitrogen gas and stir for 10 minutes. Use the nitrogen gas flow to purge and remove the free hydrogen sulfide gas dissolved in the liquid phase. The removed hydrogen sulfide gas is completely absorbed by passing through a buffer balloon and a two-stage sodium hydroxide absorption bottle in sequence. Transfer all the reaction mixture in the three-necked flask to a vacuum filtration device and separate the sodium chloride solid filter cake generated by the reaction under vacuum. Wash the filter cake twice with 10 mL of anhydrous ethanol. Combine the two washing solutions with the filtrate to obtain a mixed filtrate containing crude 1-thioglycerol.

[0036] S4. Add a composite antioxidant (including 0.1g sodium sulfite and 0.05g ascorbic acid) to the mixed filtrate, transfer it to a rotary evaporator flask, continuously purge with nitrogen to maintain a slight positive pressure inside the flask to isolate oxygen, set the vacuum degree to -0.098MPa, concentrate under reduced pressure at a water bath temperature of 25~28℃ until no liquid distills out of the flask, and obtain concentrated solid residue. The entire process relies on the dual protection of antioxidant and nitrogen to avoid thiol oxidation and discoloration.

[0037] S5. Multi-stage extraction, specifically including: S51. Add deionized water at 10℃ to the concentrated solid residue, keep warm and stir for 10 minutes to completely dissolve the residue in the water; under continuous stirring, slowly add hydrochloric acid solution with a concentration of 6mol / L to adjust the pH of the aqueous system to 3~4. S52. Add 15g of solid sodium chloride, stir to dissolve and complete salting out, let stand for 5min to separate the layers; use n-butanol for three extractions, add 15mL of n-butanol for each extraction, shake vigorously for 2min for each extraction, and let stand for separation. Combine and collect all organic phases obtained from the three extractions. S53. Add 1g of anhydrous sodium sulfate solid to the upper organic phase, stir and dry at room temperature for 30min; transfer the dried and filtered organic phase to a rotary evaporator, maintain a vacuum of -0.098MPa, concentrate under reduced pressure at a water bath temperature of 35℃ to completely remove n-butanol organic solvent, and finally obtain a colorless, transparent, oily high-purity 1-thioglycerol product. The molecular chemical structure of 1-thioglycerol is: .

[0038] The product yield of 1-thioglycerol was 98.2%, and the purity was 98.7% by HPLC external standard method. The product is a colorless, transparent, oily liquid with no obvious irritating odor.

[0039] Proton NMR spectroscopy was performed under the following conditions: deuterated methanol (400 MHz, CD3OD) as solvent, TMS as internal standard, and a test frequency of 400 MHz. The results are as follows: Figure 2 As shown. The spectral peaks are assigned as follows: 1. The multiple peaks in the δ2.5~2.7 region are attributed to the methylene (-CH2SH) hydrogen atoms directly bonded to the thiol group in the molecule. Since the electronegativity of sulfur atoms is much lower than that of oxygen atoms, their deshielding effect on the bonded hydrogens is weak, so the chemical shift of this group of hydrogens is at the highest field. At the same time, since the C2 position is a chiral center, the two hydrogens of this methylene group are diastereoisosonic hydrogens, which are coupled to the same carbon and also to the ortho-coupled hydrogen of the methylene group at the C2 position, thus exhibiting a complex multiple peak. 2. Multiplets in the δ3.5~3.7 region: These contain two sets of carbon skeleton hydrogen signals: First, the two hydrogen atoms of the terminal methylene group (-CH2OH) attached to the hydroxyl group at C3 are chemically shifted to the lower field due to the strong deshielding effect of the oxygen atom. Similarly, due to the chiral center at C2, the two hydrogen atoms are diastereoisospatial hydrogens, resulting in multiplets. Second, the one hydrogen atom of the methine group (-CH(OH)-) directly attached to the hydroxyl group at C2 is simultaneously deshielded by the oxygen atom and coupled with the four non-equivalent hydrogens at the adjacent C1 and C3 positions, splitting into complex multiplets that partially overlap with the terminal methylene group signal. 3. The quintet at δ~3.30 is the residual solvent peak of deuterated methanol (CHD2OD), which is coupled with two deuterium atoms according to the 2nI+1 coupling rule and splits into a quintet, and does not belong to the sample signal; the strong singlet at δ~4.83 is the residual water peak in deuterated methanol (HOD), which is the characteristic signal of trace water in the solvent and does not belong to the hydrogen in the sample itself. 4. Since deuterated methanol is a strong protic solvent, the active hydrogens of the thiol group (-SH) and the two hydroxyl groups (-OH) in the molecule will undergo rapid hydrogen-deuterium exchange with the deuterium in the solvent. Therefore, the signals of these three active hydrogens were not observed in the spectrum, which is completely consistent with the structural characteristics of 1-thioglycerol.

[0040] NMR analysis confirmed that the chemical structure of the synthesized product was completely consistent with the target molecule of 1-thioglycerol, with no obvious impurity peaks, indicating that the product structure was correct.

[0041] Comparative Example 1: This comparative example provides a method for preparing 1-thioglycerol. The solvent system uses 160 mL of pure anhydrous ethanol without adding water. Step S1 is as follows: 20 g of industrial-grade sodium hydrosulfide (approximately 0.25 mol of pure product) with a purity of 70% is selected as the sulfur source. The sodium hydrosulfide solid is added to 160 mL of anhydrous ethanol and stirred at room temperature until completely dissolved to obtain a sodium hydrosulfide alcohol solution. The total reaction time for step S2 is 5 hours; the remaining steps are the same as in Example 1.

[0042] Finally, 9.98g of pale yellow oily 1-thioglycerol product was obtained, with a yield of 92.3% and a purity of 98.1% by HPLC external standard method.

[0043] Comparative Example 2: This comparative example provides a method for preparing 1-thioglycerol. The solvent system uses 160 mL of pure anhydrous ethanol without adding water. Step S1 is as follows: 20 g of industrial-grade sodium hydrosulfide (approximately 0.25 mol of pure product) with a purity of 70% is selected as the sulfur source. 0.32 g of tetrabutylammonium bromide (0.001 mol, 0.01 eq) is added to 160 mL of anhydrous ethanol, followed by the addition of solid sodium hydrosulfide. The mixture is stirred at room temperature until completely dissolved to obtain an alcoholic solution of sodium hydrosulfide containing a phase transfer catalyst. The total reaction time for step S2 is 5 hours; the remaining steps are the same as in Example 1.

[0044] The final product yielded 7.99g of a dark yellow, oily 1-thioglycerol, with a yield of 73.9% and a purity of 97.5% by HPLC external standard method. The product had a distinct off-odor.

[0045] Comparative Example 3: This comparative example provides a method for preparing 1-thioglycerol. The solvent system is the same as in Example 1 (80 mL anhydrous ethanol + 0.5 mL deionized water). Step S1 is as follows: 20 g of industrial-grade sodium hydrosulfide with a purity of 70% (about 0.25 mol of pure product) is selected as the sulfur source. 0.32 g of tetrabutylammonium bromide (0.001 mol, 0.01 eq) is added to the mixed solvent of 80 mL anhydrous ethanol and 0.5 mL deionized water. Then, sodium hydrosulfide solid is added and stirred at room temperature until completely dissolved to obtain an aqueous solution of sodium hydrosulfide containing a phase transfer catalyst. The total reaction time for step S2 is 4.5 hours; the remaining steps are the same as in Example 1.

[0046] The final product was 10.59g of pale yellow oily 1-thioglycerol, with a yield of 97.9% and a purity of 98.4% by HPLC external standard method. It had no obvious irritating odor.

[0047] Comparative Example 4: This comparative example provides a method for preparing 1-thioglycerol. The solvent system uses 80 mL of pure anhydrous ethanol without adding water. Step S1 is as follows: 20 g of industrial-grade sodium hydrosulfide with a purity of 70% (about 0.25 mol of pure product) is selected as the sulfur source. The sodium hydrosulfide solid is added to 80 mL of anhydrous ethanol and stirred at room temperature until completely dissolved to obtain a sodium hydrosulfide alcohol solution. The total reaction time for step S2 is 5.5 hours; the remaining steps are the same as in Example 1.

[0048] The final product was 6.31g of yellow oily 1-thioglycerol, with a yield of 58.3% and a purity of 97.8% by HPLC external standard method.

[0049] Comparative Example 5: This comparative example provides a method for preparing 1-thioglycerol. The solvent system uses 30 mL of anhydrous ethanol and 30 mL of deionized water. Step S1 is as follows: 20 g of industrial-grade sodium hydrosulfide with a purity of 70% (about 0.25 mol of pure product) is selected as the sulfur source. The sodium hydrosulfide solid is added to a mixed solvent of 30 mL of anhydrous ethanol and 30 mL of deionized water and stirred at room temperature until completely dissolved to obtain a sodium hydrosulfide alcohol aqueous solution with high water content. In step S2, 3-chloro-1,2-propanediol was diluted with 10 mL of anhydrous ethanol and 10 mL of deionized water and then added dropwise. The total reaction time was 3.5 h. In step S5, the extraction operation was changed to extraction twice with 50 mL of n-butanol. The remaining steps were the same as in Example 1.

[0050] The final product was 3.85g of brownish-yellow oily 1-thioglycerol, with a yield of 35.6% and a purity of 96.2% by HPLC external standard method. The product had a strong, pungent odor.

[0051] The process conditions and product yields of the products prepared in Example 1 and Comparative Examples 1-5 were compared, and the comparison results are shown in Table 1.

[0052] Table 1 Comparison of results under different synthesis process conditions

[0053] As shown in Table 1, the trace water-ethanol mixed solvent system (Example 1) used in this invention achieved the best synthesis effect. Without adding any phase transfer catalyst, it achieved the highest product yield (98.2%) and purity (98.7%), with a reaction time of only 4 hours and a solvent consumption reduced by 50% compared to traditional processes. The pure ethanol system suffers from long reaction times and low yields, especially the small-volume pure ethanol system, where the yield is only 58.3%. While adding a phase transfer catalyst can shorten the reaction time to some extent, it triggers side reactions, leading to a significant decrease in yield and catalyst residue. Excessive water content causes severe hydrolysis of the raw materials, resulting in a sharp drop in yield to 35.6% and a significant deterioration in product quality. The above comparison fully verifies the scientific nature and superiority of the solvent system design in this invention.

[0054] The 1-thioglycerol product prepared in Example 1 was subjected to industrial flotation tests on a mixed copper-molybdenum concentrate at a large copper-molybdenum mine beneficiation plant. The mixed copper-molybdenum concentrate had a molybdenum grade of 1.88% and a copper grade of 13.85%. The copper-molybdenum separation operation adopted a process flow of "one roughing, five cleaning, and three scavenging". Sodium hydrosulfide, sodium mercaptoacetate, and the product of this invention were used as copper inhibitors, respectively. Comparative tests were conducted under the conditions of grinding fineness of -200 mesh (65%) and pulp pH of 10. The results are shown in Table 2 below.

[0055] Table 2 Comparison of Flotation Effects of Different Copper Depressants

[0056] As shown in Table 2, the industrial test results of the 1-thioglycerol prepared by this invention, with a dosage of only 500 g / t (1 / 15 of the dosage of sodium hydrosulfide), achieved a molybdenum concentrate grade of 45.36%, a molybdenum recovery rate of 88.67%, and a copper content in the molybdenum concentrate reduced to 0.42%. All indicators are significantly better than those of traditional sodium hydrosulfide and sodium thioglycolate inhibitors, demonstrating excellent flotation performance and high industrial application value.

[0057] The key technical points and advantages of this invention are as follows: (1) Innovative solvent system: The significant promoting effect of trace amounts of water-ethanol mixed solvent on this nucleophilic substitution reaction was proposed and verified for the first time. By precisely controlling the water content in the range of 0.5-1% (volume ratio), a very small amount of water is used to increase solvent polarity, promote the dissolution and dissociation of sodium hydrosulfide, and significantly increase the effective HS-H2O. - The concentration is high, the reaction process is accelerated, and the side reaction of raw material hydrolysis caused by excessive water is strictly avoided, thus breaking through the technical contradiction of traditional methods that hydrolyze when water is added and are difficult to dissolve without water. (2) Catalyst substitution innovation: Systematic comparative experiments have confirmed that phase transfer catalysts such as tetrabutylammonium bromide have a negative effect on this reaction, promoting side reactions such as polysulfide formation and thiol oxidation, and reducing product yield and purity. This invention completely replaces the phase transfer catalyst by optimizing the solvent system, which simplifies the post-processing process, reduces production costs, and avoids the adverse effects of catalyst residue on product flotation performance.

[0058] (3) Antioxidant technology innovation: A complete antioxidant system with full nitrogen micro-positive pressure protection and sodium sulfite-ascorbic acid composite antioxidant was established. Sodium sulfite preferentially removes dissolved oxygen in the system, and ascorbic acid reduces oxidized disulfides. The synergistic effect of the two completely solves the common industry problem of easy oxidation and discoloration and generation of dimer impurities in the synthesis and concentration of thiol compounds, and significantly improves product purity and appearance quality.

[0059] It should be understood that the various forms of processes shown above can be used to reorder, add, or delete steps. For example, the steps described in this invention disclosure can be executed in parallel, sequentially, or in different orders, as long as the desired result of the technical solution disclosed in this invention can be achieved, and this is not limited herein.

[0060] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A method for preparing 1-thioglycerol, a copper inhibitor for flotation separation of copper-molybdenum ore, characterized in that: Includes the following steps: S1. Dissolve sodium hydrosulfide in a mixed solvent of anhydrous ethanol and deionized water at room temperature; the volume ratio of anhydrous ethanol to deionized water in the mixed solvent is 100~200:

1. S2. Under nitrogen micro-positive pressure protection, heat to 55~65℃, add dropwise a mixture of 3-chloro-1,2-propanediol and anhydrous ethanol over 15~25 min; heat to 75~80℃ and reflux, monitor by thin-layer chromatography until the starting material 3-chloro-1,2-propanediol is completely consumed, with a total reaction time of 3.5~4.5 h; S3. After the reaction is complete, the reaction solution is cooled, nitrogen is purged to remove hydrogen sulfide, sodium chloride solid is removed by vacuum filtration, the filter cake is washed with ethanol, and the filtrate and washing liquid are combined to obtain a crude product mixture. S4. Add a composite antioxidant to the crude product mixture, and concentrate under reduced pressure in a nitrogen atmosphere and a vacuum of -0.09~0.1Mpa at a water bath temperature of 25~28℃ to obtain a solid residue. S5. Dissolve the solid residue in water, adjust the pH to 3-4 with hydrochloric acid, and salt out the residue. Extract the organic phase multiple times with n-butanol and collect the organic phase. After drying the organic phase with anhydrous sodium sulfate, remove the n-butanol under reduced pressure at a water bath temperature of 33-37℃ to obtain high-purity 1-thioglycerol.

2. The method for preparing 1-thioglycerol, a copper inhibitor for flotation separation of copper-molybdenum ore, according to claim 1, is characterized in that: Before step S1, there is a pretreatment step S0: a three-necked flask is used as the main reaction vessel, and the flask mouth is connected to a reflux condenser, a nitrogen gas delivery tube and a thermometer respectively; a sealing buffer balloon and a two-stage tail gas washing device are connected in series at the uppermost outlet of the reflux condenser; air is introduced into the high-purity nitrogen replacement device for 10-20 minutes, and the system is kept under a slight positive pressure of nitrogen to isolate oxygen throughout the process.

3. The method for preparing 1-thioglycerol, a copper inhibitor for flotation separation of copper-molybdenum ore, according to claim 1, is characterized in that: The sodium hydrosulfide is industrial-grade sodium hydrosulfide with a purity of 70%; the addition ratio of 3-chloro-1,2-propanediol and the mixed solvent is 0.1 mol: 60~90 mL.

4. The method for preparing 1-thioglycerol, a copper inhibitor for flotation separation of copper-molybdenum ore, according to claim 1, is characterized in that: In step S2, a mixture of 3-chloro-1,2-propanediol and anhydrous ethanol is added dropwise through a constant pressure dropping funnel, with the dropping time controlled at 20 min; the ratio of 3-chloro-1,2-propanediol to anhydrous ethanol is 0.1 mol: 20 mL.

5. The method for preparing 1-thioglycerol, a copper inhibitor for flotation separation of copper-molybdenum ore, according to claim 4, is characterized in that: The thin-layer chromatography used ethyl acetate:petroleum ether = 1:1 as the developing solvent and phosphomolybdic acid as the colorimetric reagent for raw material tracking; the total reaction time was 4 hours.

6. The method for preparing 1-thioglycerol, a copper inhibitor for flotation separation of copper-molybdenum ore, according to claim 1, is characterized in that: The composite antioxidant is composed of sodium sulfite and ascorbic acid; for every 0.1 mol of 3-chloro-1,2-propanediol, 0.05~0.15 g of sodium sulfite and 0.02~0.08 g of ascorbic acid are added.

7. The method for preparing 1-thioglycerol, a copper inhibitor for flotation separation of copper-molybdenum ore, according to claim 1, is characterized in that: Step S5 specifically includes the following sub-steps: S51. Add deionized water at 35~45℃ to the concentrated solid residue, stir at 35~45℃ for 8~15min to completely dissolve the residue in water; under continuous stirring, slowly add hydrochloric acid solution with a concentration of 4~8mol / L to adjust the pH of the aqueous system to 3~4. S52. Add solid sodium chloride, stir to dissolve and complete salting out, let stand for 3-10 minutes to separate the layers; use n-butanol for three extractions, separate and combine the upper organic phases; S53. Add anhydrous sodium sulfate solid to the upper organic phase and stir and dry at room temperature for 25-35 min; transfer the dried and filtered organic phase to a rotary evaporator, maintain a vacuum of -0.098 MPa, and concentrate under reduced pressure at a water bath temperature of 33-37℃ to completely remove the n-butanol organic solvent, and obtain a colorless, transparent, oily high-purity 1-thioglycerol product.

8. A method for preparing 1-thioglycerol, a copper inhibitor for flotation separation of copper-molybdenum ore, according to claim 7, characterized in that: In step S52, the amount of solid sodium chloride added is 10-20g; 10-20mL of n-butanol is added for each extraction, and the mixture is vigorously shaken for 2min before standing to separate into layers. All organic phases obtained from the three extractions are combined and collected.

9. A copper inhibitor, 1-thioglycerol, for the flotation separation of copper-molybdenum ore, characterized in that: The copper inhibitor 1-thioglycerol for flotation separation of copper-molybdenum ore, as described in claim 1, is prepared by a method for preparing the copper inhibitor 1-thioglycerol with a purity ≥ 98.5% and an appearance of a colorless, transparent, oily liquid.

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