A magnetic surfactant and its method for fly ash carbon, ash separation and recovery

Abstract

The application provides a magnetic surfactant and a method for separating and recycling coal cinder carbon and ash, wherein the magnetic surfactant is obtained by reacting a surfactant solution with a specific group of chelating groups or electrostatic binding groups with a metal ion solution with magnetic response. The magnetic surfactant of the application can reduce the surface tension under the action of a magnetic field, and enhance the carbon capturing capacity. After demagnetization, the magnetic surfactant can be separated and recycled from carbon, thereby avoiding the problem of high consumption of reagents in conventional flotation.

Description

Technical Field

[0001] This invention relates to a magnetic surfactant and a method for separating and recovering carbon and ash from coal slag, and particularly to a method for separating and recovering carbon from coarse and fine slag in a gasifier. Background Technology

[0002] In coal gasification, pulverized coal or coal slurry is mixed with oxygen through burners and enters the gasifier, where a gasification reaction produces syngas such as CO and H2. Due to the limited residence time of coal particles in the gasifier, some incompletely reacted carbon particles are discharged as coarse and fine slag. Both coarse and fine slag are mainly composed of carbon and ash. Taking a single-nozzle gasifier as an example, the carbon content of coarse slag is 10%-20%, and that of fine slag is 30%-40%. The ash in the slag is inorganic amorphous or crystalline minerals, while the carbon, after high-temperature roasting, has a more developed porosity and lower density. To address the land occupation and environmental problems associated with coal slag accumulation, the industry commonly outsources coarse and fine slag for use as building materials or landfills, resulting in low economic efficiency. Furthermore, the high carbon content of the slag increases the loss on ignition of building materials, affecting product quality. Decarbonization of coal slag can not only recover carbon to replace part of the raw coal, complying with carbon reduction policies, but also allow the remaining low-carbon slag to be used in the production of building materials or adsorbents, achieving resource reuse.

[0003] Patent CN112237786 discloses a method for separating residual carbon in coal gasification fine slag. The method involves mixing the fine slag slurry at the bottom of the settling tank with oil, and then using a coalescer to separate and recover carbon particles and oil. However, the recovery efficiency and product quality are not as good as conventional flotation. Furthermore, this patent only involves the recovery of fine slag. Coarse slag, due to its larger particle size and specific gravity, is not suitable for reuse by this method, which is not conducive to the overall recovery and reuse of residual carbon in coal slag.

[0004] Patent CN107641537 discloses a coal gasification slag purification process and a system for implementing the process, which separates the slag slurry according to ash concentration and sorts it by specific gravity difference, but does not recover the residual carbon in the high ash portion, and the flotation involved still has the problem of large reagent consumption. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a magnetic surfactant suitable for separating and recovering carbon and ash from coal slag, as well as a method for separation and recovery, avoiding the problem of high consumption of flotation reagents.

[0006] On one hand, the present invention provides a magnetic surfactant, which is obtained by reacting a surfactant solution having chelating groups or electrostatic binding groups with a metal ion solution having a magnetic response.

[0007] In this invention, the surfactant having a specific group is one or more of 1-tetradecane-3-methylimidazolium chloride, dodecyltrimethylammonium bromide (DTAB), octadecyltrimethylammonium bromide (STAB), and 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA), preferably 1-tetradecane-3-methylimidazolium chloride; the magnetically responsive metal ion is one or more of gadolinium trichloride, holmium trichloride, cerium trichloride, and dysprosium trichloride, preferably holmium trichloride.

[0008] In this invention, the solvent for the surfactant solution with specific groups and the metal ion solution with magnetic response is water.

[0009] In this invention, the reaction system of the magnetic surfactant further includes a solvent, which is one or more of methanol and ethanol, preferably methanol.

[0010] On the other hand, the present invention provides a method for preparing a magnetic surfactant, the steps of which are as follows:

[0011] (1) Prepare reaction raw materials, including surfactant solutions with specific groups, metal ion solutions with magnetic response, and solvents;

[0012] (2) The surfactant solution and the metal ion solution are mixed in stoichiometric ratio and heated together with the solvent to react;

[0013] (3) The reaction mixture obtained in step (2) is subjected to vacuum dehydration and desolventization to obtain a magnetic surfactant.

[0014] In this invention, the concentration of the surfactant solution with the specific group is 30-50%, preferably 35-45%; the concentration of the magnetically responsive metal ion solution is 5-10%, preferably 6-8%; and the solvent is of analytical grade or higher.

[0015] In this invention, the surfactant with a specific group in step (1) is one or more of 1-tetradecane-3-methylimidazolium chloride, dodecyltrimethylammonium bromide (DTAB), octadecyltrimethylammonium bromide (STAB), and 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA), preferably 1-tetradecane-3-methylimidazolium chloride; the magnetically responsive metal ion solution is one or more of gadolinium trichloride, holmium trichloride, cerium trichloride, and dysprosium trichloride, preferably holmium trichloride; and the solvent is one or more of methanol and ethanol, preferably methanol.

[0016] The molar ratio of the surfactant with specific groups to the magnetically responsive metal ions is 0.5-2:1, preferably 1:1.

[0017] In this invention, the reaction conditions in step (2) are: nitrogen atmosphere, stirring speed of 100-1000 rpm, preferably 300-500 rpm; temperature of 10-90℃, preferably 20-80℃; and reaction time of 12-50h, preferably 24-48h.

[0018] In this invention, the solvent removal temperature in step (3) is 70-90℃ and the time is 12-16h.

[0019] In another aspect, the present invention provides an application of a magnetic surfactant for the separation and recovery of carbon and ash in coal slag.

[0020] Finally, the present invention provides a method for separating and recovering carbon and ash from coal slag, comprising the following steps: carbon-containing coal slag is fed into a flotation device, and separation is achieved by utilizing the difference in hydrophobicity between carbon and ash to obtain low-carbon products and crude products; the crude products are fed into a solvent recovery device to obtain solvent and high-carbon products; the recovered solvent is returned to the flotation device; the flotation device is a flotation machine equipped with a magnetic field generating device, and the strength of the magnetic field is 0.5-3T; the flotation reagent in the flotation device is a magnetic surfactant.

[0021] Preferably, the carbonaceous coal slag further includes screening, gravity separation, and secondary screening processes before entering the flotation device.

[0022] In this invention, the screening process includes: coal slag first passing through a screening device to separate large particles (>1mm), medium particles (0.074-1mm), and small particles (<0.074mm). The large particles have a low carbon content and can be directly sold as building materials after dewatering. The medium particles enter a gravity separation device, and the small particles enter a flotation device.

[0023] In this invention, the gravity separation process includes: separating low-carbon products and high-carbon crude products under the action of centrifugal force, wherein the low-carbon products are also dehydrated and sold as building materials.

[0024] In this invention, the secondary screening process includes: feeding the high-carbon crude product obtained by gravity separation into a screening device, which can screen according to particle size to obtain high-carbon product and medium-carbon product, wherein the high-carbon product can be returned to the gasifier for use, and the medium-carbon product enters the flotation device.

[0025] In this invention, the screening device selects a stacked screen with appropriate screen openings based on the particle size distribution of the coal slag.

[0026] In this invention, the reselection device is one of a hydrocyclone or a spiral chute;

[0027] In this invention, the dewatering device is one of a settling tank and a filter press;

[0028] In this invention, the solvent recovery device is a combination of a vertical tank and a circulating pump. The tank is equipped with a screen and a heating device is installed outside the tank. After the crude product produced by the flotation device enters the recovery device, the surfactant is demagnetized at high temperature. The separation from the carbon solid is achieved by the action of the circulating pump and the screen. The surfactant solution is recycled back to the flotation device for reuse.

[0029] The present invention has the following beneficial effects:

[0030] The magnetic surfactant of this invention can reduce surface tension and enhance carbon capture ability under the action of a magnetic field. After demagnetization, it can be separated from carbon, recycled and reused, avoiding the problem of high reagent consumption in conventional flotation.

[0031] The recycling process of this invention covers both coarse and fine slag, comprehensively recovering unreacted carbon residue in the gasifier and maximizing profits. Attached Figure Description

[0032] Figure 1 This is a process flow diagram, where 1 is screening device 1; 2 is gravity separation device; 3 is screening device 2; 4 is flotation device; 5 is solvent recovery device; and 6 is dewatering device. Detailed Implementation

[0033] The present invention will be further described below with reference to embodiments. Figure 1 This is a process flow diagram, where 1 is screening device 1; 2 is gravity separation device; 3 is screening device 2; 4 is flotation device; 5 is solvent recovery device; and 6 is dewatering device.

[0034] Unless otherwise specified, the percentages mentioned below are by mass percentages.

[0035] Preparation of magnetic surfactant-1

[0036] A 50% aqueous solution of 96% 1-tetradecane-3-methylimidazolium chloride was prepared, and a 10% aqueous solution of 99% holmium trichloride was prepared. 100 g of the 1-tetradecane-3-methylimidazolium chloride solution was added to a 1 L three-necked flask, along with 200 g of methanol solvent. The temperature was set to 60 °C, and the stirring speed was 300 rpm under a nitrogen atmosphere for 15 min. Subsequently, 580 g of holmium trichloride solution was added, and the stirring speed was increased to 500 rpm. The mixture was stirred for 48 h to obtain the reaction product. The product was then vacuum dried at 80 °C for 12 h to obtain the magnetic surfactant.

[0037] Preparation of magnetic surfactant-2

[0038] A 50% aqueous solution of dodecyltrimethylammonium bromide (DTAB) (99%) and a 10% aqueous solution of cerium trichloride (99%) were prepared. 100 g of the DTAB solution was added to a 1 L three-necked flask, along with 200 g of methanol solvent. The temperature was set to 70 °C, and the stirring speed was 300 rpm under a nitrogen atmosphere for 15 min. Subsequently, 520 g of cerium trichloride solution was added, and the stirring speed was increased to 500 rpm. The mixture was stirred for 48 h to obtain the reaction product. The product was then vacuum dried at 80 °C for 12 h to obtain magnetic surfactant-2.

[0039] Preparation of magnetic surfactant-3

[0040] A 50% aqueous solution of octadecyltrimethylammonium bromide (STAB) (99%) and a 10% aqueous solution of gadolinium trichloride (99%) were prepared. 100 g of the STAB solution was added to a 1 L three-necked flask, along with 200 g of methanol solvent. The mixture was stirred at 60 °C and 300 rpm under a nitrogen atmosphere for 15 min. Subsequently, 440 g of gadolinium trichloride solution was added, and the stirring rate was increased to 500 rpm. The mixture was stirred for 48 h to obtain the reaction product. The product was then vacuum-dried at 80 °C for 12 h to obtain magnetic surfactant-3.

[0041] Preparation of carbonaceous coal slag

[0042] A 20% coal slag aqueous solution was sieved using a screening device to obtain three particle sizes: >1mm, 0.074-1mm, and <0.074mm. Particles >1mm had an ash content exceeding 98% and low recycling value; after dewatering, they were sold directly as building materials. Particles of 0.074-1mm entered a gravity separation unit (single unit feed flow rate 10m³ / h). 3 The process involves separating a product with an ash content of over 95% and a coarse product with an ash content of 50% (at a pressure of 1.5 barg and 4 spiral layers per hour). The product with over 95% ash content is dewatered and sold as building material. The coarse product with 50% ash content enters a screening device to obtain a product with 30% ash content and a medium-carbon product with 60% ash content. The 30% ash product can be mixed with coal slurry and returned to the gasifier. The medium-carbon product with 60% ash content enters the flotation device along with particles <0.074 mm.

[0043] Example 1

[0044] Carbon-containing coal slag and 3 kg / t (carbon-containing coal slag) of magnetic surfactant-1 are added to a flotation device equipped with a magnetic field generator. The magnetic field strength is set to 1T and the stirring speed is 1500 r / min. This yields a product with an ash content of over 90% and a crude product solution with an ash content of 20%. The product with an ash content of over 90% is dehydrated and sold as a building material. The crude product solution with an ash content of 20% is heated to 80℃ in a solvent recovery device to separate the magnetic surfactant from the carbon product and return it to the flotation device for reuse. The carbon product is mixed with coal slurry to prepare a coal slurry concentration of 60%-62% and returned to the gasifier for use.

[0045] Example 2

[0046] Based on Example 1, the surfactant from the solvent recovery device was reused (1-50 times) and added to a flotation device equipped with a magnetic field generator. The magnetic field strength was set to 1T and the stirring speed to 1500r / min. The resulting products are shown in the table below. After 50 reuses, a carbon product with an ash content of about 20% can still be obtained, and the carbon recovery rate is maintained above 80%, indicating that the surfactant reuse effect is good and avoids continuous consumption of reagents.

[0047] Number of times of reuse 1 10 20 30 40 50 High ash product 1 ash content 92％ 92％ 91％ 90％ 88％ 87％ Ash content of crude products 19％ 19％ 19％ 19％ 20％ 21％ carbon recovery rate 90％ 90％ 88.4％ 86.8％ 82％ 80％

[0048] Example 3

[0049] In this embodiment, coal slag is directly added to the flotation device for processing, eliminating the need for screening and gravity separation devices. Coal slag and 5 kg / t (of coal slag) of magnetic surfactant are added to a flotation device equipped with a magnetic field generator. The magnetic field strength is set to 1T, and the stirring speed to 1500 r / min. This yields a product with an ash content of over 90% and a crude product solution with an ash content of 21%. The product with over 90% ash is dehydrated and sold as building material. The crude product solution with 21% ash enters a solvent recovery device heated to 80°C to separate the magnetic surfactant from the carbon product. This separated product is then returned to the flotation device for reuse. The carbon product is mixed with coal slurry to a concentration of 60%-62%, and then returned to the gasifier for use.

[0050] Example 4

[0051] Carbon-containing coal slag and 3 kg / t (carbon-containing coal slag) of magnetic surfactant-2 are added to a flotation device equipped with a magnetic field generator. The magnetic field strength is set to 1T and the stirring speed is 1500 r / min. This yields a product with an ash content of over 89% and a crude product solution with an ash content of 19%. The product with an ash content of over 89% is dehydrated and sold as building material. The crude product solution with an ash content of 19% is fed into a solvent recovery device heated to 80℃ to separate the magnetic surfactant from the carbon product. The separated product is then returned to the flotation device for reuse. The carbon product is mixed with coal slurry to prepare a coal slurry concentration of 60%-62%, which is then returned to the gasifier for use.

[0052] Example 5

[0053] Carbon-containing coal slag and 3 kg / t (carbon-containing coal slag) of magnetic surfactant-3 were added to a flotation device equipped with a magnetic field generator. The magnetic field strength was set to 1T and the stirring speed to 1500 r / min. A product with 91% ash and a crude product solution with 21% ash were obtained. The 91% ash product was dehydrated and sold as building material. The crude product solution with 21% ash was fed into a solvent recovery device heated to 80℃ to separate the magnetic surfactant from the carbon product. The solution was then returned to the flotation device for reuse. The carbon product was mixed with coal slurry to prepare a coal slurry concentration of 60%-62%, which was then returned to the gasifier for use.

[0054] Comparative Example 1

[0055] This comparative example illustrates the effectiveness of conventional kerosene as a flotation reagent. Carbonaceous coal slag and 3 kg / t (of slag) of kerosene were added to a flotation unit equipped with a magnetic field generator. The magnetic field strength was set to 1 T, and the stirring speed to 1500 r / min. This yielded a product with an ash content of over 70% and a crude product solution with an ash content of 20%. The product with over 70% ash was dehydrated and sold as building material. The crude product solution with 20% ash entered a solvent recovery unit with a magnetic field direction opposite to that of the flotation unit, at a magnetic field strength of 1 T. Since the kerosene and carbonaceous product remained tightly bound and could not be separated, it was directly mixed with coal slurry to a concentration of 60%-62%, and then returned to the gasifier. The solution returned to the flotation unit required the addition of 3 kg / t (of slag) of kerosene for further flotation.

[0056] Comparative Example 2

[0057] This comparative example illustrates the effect of the flotation device without a magnetic field. 3 kg / t (coal slag) of magnetic surfactant was added to the flotation device, and the stirring speed was 1500 r / min. This yielded a product with 40% ash and a crude product solution with 20% ash. The separation effect was poor, with most of the carbon remaining in the product, resulting in low recovery value.

[0058] Comparative Example 3

[0059] This comparative example illustrates the effect of the solvent recovery device without heating. 3 kg / t (coal slag containing carbon) of magnetic surfactant was added to a flotation unit equipped with a magnetic field generator. The magnetic field strength was set to 1T, and the stirring speed to 1500 r / min. This yielded a product with over 90% ash and a crude product solution with 20% ash. The product with over 90% ash was dehydrated and sold as building material. The crude product solution with 20% ash entered the solvent recovery unit. At room temperature, some of the magnetic surfactant remained tightly bound to the carbon product, preventing complete separation. This solution was directly mixed with coal slurry to a concentration of 60%-62%, and then returned to the gasifier. The solution returned to the flotation unit required the addition of 1.5 kg / t (coal slag) of magnetic surfactant for further flotation.

Claims

1. A method for separating and recovering carbon ash from coal cinder, characterized by, The method comprises the following steps: The carbon-containing coal residue is introduced into a flotation device to realize separation by using the difference in hydrophobicity of carbon and ash, to obtain a low-carbon product and a crude product, the crude product is introduced into a solvent recovery device to obtain a solvent and a high-carbon product, and the recovered solvent is returned to the flotation device; the flotation device is a flotation machine with a magnetic field generating device, the strength of the magnetic field is 0.5-3T; the flotation reagent in the flotation device is a magnetic surfactant, the magnetic surfactant is obtained by reacting a surfactant solution with specific groups having chelating groups or electrostatic binding groups with a metal ion solution with magnetic response, the surfactant with specific groups is one or more of 1-tetradecane-3-methyl imidazolium chloride, dodecyltrimethylammonium bromide, octadecyltrimethylammonium bromide, 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid; and / or, the metal ion with magnetic response is one or more of gadolinium trichloride, holmium trichloride, cerium trichloride, and dysprosium trichloride.

2. The method of separating and recovering the carbon ash from the coal cinder according to claim 1, wherein, The reaction system of the magnetic surfactant further comprises a solvent, and the solvent is one or more of methanol and ethanol.

3. The method of separating and recovering the carbon ash from the coal cinder according to claim 1 or 2, characterized in that, The preparation method of the magnetic surfactant comprises the following steps: (1) preparing reaction raw materials, including a surfactant solution with specific groups, a metal ion solution with magnetic response, and a solvent; (2) mixing the surfactant solution and the metal ion solution in a stoichiometric ratio, and reacting with the solvent under heating; (3) vacuum dewatering and desolventizing the reaction mixture obtained in step (2) to obtain the magnetic surfactant.

4. The method of separating and recovering the coal cinder carbon ash according to claim 3, characterized in that, The concentration of the surfactant solution with specific groups is 30-50%, the concentration of the metal ion solution with magnetic response is 5-10%, and the solvent is analytical pure or above.

5. The method of separating and recovering the coal cinder carbon ash according to claim 3, characterized in that, The reaction conditions in step (2) are: nitrogen atmosphere, stirring rate of 100-1000 rpm, temperature of 10-90℃, and reaction time of 12-50h; and / or, the desolventizing temperature in step (3) is 70-90℃.

6. The method of separating and recovering carbon ash from coal cinder according to claim 1 or 2, characterized in that, The carbon-containing coal residue further comprises a process of screening, gravity separation, and secondary screening before being introduced into the flotation device.

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