A diatomic catalyst, its preparation method and application in calcium carbide method vinyl chloride monomer production

Abstract

The application discloses a diatomic catalyst, a preparation method thereof and application of the diatomic catalyst in production of chloroethylene monomer by calcium carbide method. The diatomic in the diatomic catalyst refers to two types of atoms, wherein the first type of atom is mercury atom, and the second type of atom is one or more of potassium, zinc, calcium, barium, nitrogen, boron, sulfur and phosphorus. The preparation method of the diatomic catalyst comprises the following steps: (1) immersing a precursor aqueous solution containing the second type of atom into a defect-rich activated carbon, drying, and then performing heat treatment at 400-600 DEG C in an inert atmosphere to obtain carbon material A; the I D / I G value of the Raman spectrum of the defect-rich activated carbon is higher than 1.2; and (2) adsorbing gaseous mercuric chloride by the carbon material A in an inert atmosphere environment, and the adsorption temperature is higher than the volatilization temperature of the mercuric chloride to obtain the diatomic catalyst.

Description

Technical Field

[0001] This invention relates to the field of catalysts, specifically to a diatomic catalyst, its preparation method, and its application in the production of vinyl chloride monomer via the calcium carbide process. Background Technology

[0002] Polyvinyl chloride (PVC) is a general-purpose plastic. In some regions, PVC production is primarily based on the calcium carbide acetylene process in coal chemical industry, using activated carbon-supported mercuric chloride catalyst (HgCl2 / AC) as the industrial catalyst. However, mercuric chloride has extremely poor thermal stability and readily volatilizes into the environment during industrial use, posing a significant threat to human health and the environment. Further reducing mercury usage while maintaining performance can alleviate the pressure of mercury pollution control. Given the current lack of industrial applications of mercury-free catalysts, developing micro-mercury catalysts with a mercury content below 2 wt% is one of the key measures for the healthy development of the calcium carbide-based PVC industry.

[0003] In recent years, some enterprises and research institutions have conducted research on catalysts with ultra-low mercury content. However, this often requires the addition of a large number of secondary active centers. For example, patent applications CN105251531A and CN105413746A disclose the preparation of ultra-low mercury catalysts by adding large amounts of precious metals palladium and platinum. Although the amount of mercury used is reduced, the cost of the catalyst actually increases. Patent specification CN110833838A discloses a method for preparing ultra-low mercury catalysts using copper chloride as the secondary active center. However, copper chloride readily reacts with acetylene to produce flammable and explosive copper acetylide, posing a safety hazard during catalyst use and storage. Patent specification CN113131031A discloses a method for preparing ultra-low mercury catalysts by recycling waste batteries. This method achieves resource recovery and product upgrading through waste resources. However, it is rich in catalytic carbon depositing elements such as nickel and cobalt, which easily cause the catalyst to produce a large amount of carbon deposits covering the active centers, leading to rapid catalyst deactivation. The patent specification with publication number CN117000273A discloses a method for preparing a low-mercury catalyst by vapor deposition of selenium and mercuric chloride using elemental selenium as an anchoring agent. However, elemental selenium is a highly toxic chemical, and the vapor deposition temperature is high (>700℃), which will lead to resource waste and safety hazards in the production process.

[0004] Modifying the carbon support through heteroatom doping is also a method for preparing ultra-low mercury content catalysts. Patent specification CN111346662A discloses a method for preparing an ultra-low mercury catalyst supported on nitrogen-doped activated carbon. Nitrogen-doped activated carbon is prepared by impregnating activated carbon with amino resin, followed by loading with mercuric chloride and additives. This catalyst exhibits good catalytic performance, but the mercuric chloride loss rate remains relatively high, and its thermal stability needs further improvement.

[0005] In summary, although researchers have made some improvements to catalysts with ultra-low mercury content, problems such as high cost and serious mercury loss still exist. Furthermore, the activity and stability of mercury catalysts need to be improved due to the low mercury content. Summary of the Invention

[0006] In view of the above-mentioned technical problems and the shortcomings in the field, the present invention provides a method for preparing a diatomic catalyst, which further reduces the mercuric chloride content, improves catalytic activity and thermal stability, and greatly reduces the mercuric chloride loss rate of the catalyst during use, which can further alleviate the problems of mercury resource scarcity and environmental pollution.

[0007] The specific technical solution is as follows:

[0008] A method for preparing a diatomic catalyst, wherein the diatomic catalyst refers to two types of atoms, wherein the first type of atom is a mercury atom, and the second type of atom is one or more of potassium, zinc, calcium, barium, nitrogen, boron, sulfur, and phosphorus (for example, the second type of atom may be nitrogen and sulfur coexisting).

[0009] The preparation method includes the following steps:

[0010] (1) The precursor aqueous solution containing second-type atoms is impregnated onto defect-rich activated carbon, dried, and then heat-treated in an inert atmosphere at 400-600℃ (e.g., 420℃, 450℃, 480℃, 500℃, 520℃, 550℃, 580℃, etc., preferably 500℃) to obtain carbon material A with second-type atoms monolayer dispersed near the defect sites of the activated carbon carrier;

[0011] The Raman spectrum of the defect-rich activated carbon (I) D / I G Values ​​higher than 1.2;

[0012] (2) In an inert atmosphere, the carbon material A is used to adsorb gaseous mercuric chloride at an adsorption temperature higher than the volatilization temperature of mercuric chloride to obtain the diatomic catalyst.

[0013] This invention uses defect-rich activated carbon as a carrier. First, it utilizes the property that carbon defect sites facilitate the dispersion of type II atoms to prepare a carbon material A with highly dispersed type II atoms. Then, it leverages the tendency of these specific type II atoms to readily adsorb and anchor mercuric chloride, resulting in chemisorption between the highly dispersed type II atoms in carbon material A and gaseous mercuric chloride. This significantly enhances the interaction between the two and improves the thermal stability of mercuric chloride. The defect-rich activated carbon described in this invention can refer to any activated carbon material rich in framework defects, containing one or more of intrinsic defects, topological defects, etc.

[0014] The method of this invention first loads a second type of atom onto a defect-rich activated carbon support, allowing the second type of atom to be effectively dispersed monolayer near the defect sites of the activated carbon support. Then, the temperature is raised above the volatilization temperature of mercuric chloride to perform gas-phase adsorption of mercuric chloride, which allows the second type of atom to effectively anchor the mercuric chloride. This results in the anchored mercuric chloride exhibiting a monoatom dispersion, greatly improving the utilization efficiency of the active component mercuric chloride, inhibiting the volatilization of mercuric chloride during use, significantly reducing the loss rate of mercuric chloride in the catalyst, and improving the thermal stability of the catalyst.

[0015] In step (1), the precursor containing the second type of atom can be one or more of potassium chloride, zinc chloride, calcium chloride, barium chloride, melamine, urea, dicyandiamide, boric acid, sublimed sulfur, phosphoric acid, ammonium dihydrogen phosphate, and phytic acid. After high-temperature heat treatment, the aforementioned metal chloride precursors disperse near the defect sites and are activated by the defect sites to form energetic sites, readily forming chemical coordination with mercuric chloride. This effectively anchors mercuric chloride onto the carbon support A, improving the thermal stability of mercuric chloride in the diatomic catalyst. Similarly, metal-free precursors such as melamine and urea, after heat treatment, also accumulate near the defect sites, further altering the electron cloud distribution around the defect sites and forming energetic sites that can disperse and anchor mercuric chloride molecules, thus improving the dispersion and thermal stability of mercuric chloride in the diatomic catalyst.

[0016] In step (1), the amount of the precursor containing the second type of atoms can be 5%-15% of the mass of the diatomic catalyst.

[0017] In step (1), the impregnation can be an equal-volume impregnation.

[0018] In step (1), the immersion temperature can be 30-60℃ and the time can be 2-6h.

[0019] In step (1), the drying process is used to remove moisture. Specifically, the drying temperature can be 90-120℃, and the drying time can be 6-12 hours.

[0020] In step (1), the heat treatment time can be 1-5 hours, for example, 3 hours.

[0021] In some embodiments, in step (2), the adsorption temperature does not exceed 350°C; further, the adsorption temperature is greater than 150°C and does not exceed 350°C. Since the volatilization temperature of mercuric chloride is 120°C, the gas-phase adsorption temperature must be higher than its volatilization temperature for mercuric chloride to be captured by carbon material A in gaseous form. However, when the adsorption temperature is too high, mercuric chloride will decompose into zero-valent mercury at high temperatures, losing its catalytic activity. Simultaneously, excessively high temperatures can easily cause the adsorbed mercuric chloride to desorb from carbon material A and return to the gas phase, affecting the loading rate of mercuric chloride.

[0022] In step (2), the adsorption time can be 0.5-2h.

[0023] In some embodiments, step (2) may specifically include: placing mercuric chloride and the carbon material A at the upper and lower air inlets of a tubular furnace, respectively; heating the tubular furnace to a temperature greater than the volatilization temperature of mercuric chloride in an inert gas flow to allow the carbon material A to adsorb the gaseous mercuric chloride, thereby obtaining the diatomic catalyst. Further, in the tubular furnace, the distance between the mercuric chloride and the carbon material A may not exceed 20 cm.

[0024] The flow rate of the inert gas stream can be 1-10 mL / min. In this invention, the inert gas and the inert gas stream refer to gases and gas streams that do not participate in the reaction. The specific gas types can be one or more combinations of nitrogen, rare gases (such as argon, helium, etc.).

[0025] The heating rate can be 5-10℃ / min.

[0026] The volatilization temperature of mercuric chloride is 120℃. The carbon material A obtained in step (1) and mercuric chloride are placed in a tube furnace. When the tube furnace is heated above the volatilization temperature of mercuric chloride, the mercuric chloride at the upper air vent will gradually or even completely transform into a gaseous phase and flow through carbon material A under the influence of an inert gas flow. At this time, the strong adsorption sites centered on type II atoms in carbon material A can easily capture and anchor the gaseous mercuric chloride, forming a strong coordination structure between the type II atoms and the mercuric chloride. This results in the anchored mercuric chloride forming a single-atom dispersion, greatly improving the utilization efficiency of the active component mercuric chloride. After the tube furnace cools to room temperature, the diatomic catalyst is obtained.

[0027] The present invention also provides a diatomic catalyst prepared by the aforementioned preparation method.

[0028] In the preparation method and the diatomic catalyst described above, the mass of the mercury atom can account for 0.5%-1.5% of the total mass of the diatomic catalyst.

[0029] In the preparation method and the diatomic catalyst described above, the second type of atomic mass can account for 1%-10% of the total mass of the diatomic catalyst.

[0030] In the preparation method and the diatomic catalyst described above, the molar ratio of mercury atoms to the second type of atoms is 1:1-5, which is conducive to the full coordination between the two.

[0031] This invention also provides the application of the aforementioned diatomic catalyst in the production of vinyl chloride monomer using the calcium carbide process. The diatomic catalyst can be used to catalyze the hydrochlorination of acetylene to produce vinyl chloride monomer.

[0032] Compared with the prior art, the beneficial effects of this invention are as follows:

[0033] 1) The diatomic catalyst of this invention first utilizes defect sites to anchor and disperse second-type atoms, resulting in a monolayer dispersion on an activated carbon support. Based on this, the highly dispersed second-type atoms can better disperse and anchor mercuric chloride, enhancing the interaction between mercuric chloride and the support, and improving the thermal stability of mercuric chloride in the diatomic catalyst (mercuric chloride loss rate less than 0.8%).

[0034] 2) The second type of atoms introduced according to the method of the present invention can not only disperse mercuric chloride, but also synergistically improve the catalytic activity of the micro-mercury catalyst.

[0035] 3) It has expanded the preparation process of micro-mercury catalysts with ultra-low mercury content (mercuric chloride content less than 2wt%), which can further reduce the amount of mercuric chloride used in mercury catalysts and help promote environmental protection. Detailed Implementation

[0036] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Operating methods not specifically specified in the following embodiments are generally performed under conventional conditions or as recommended by the manufacturer.

[0037] The defect-rich activated carbon used in the following examples and comparative examples refers to the activated carbon with Raman spectra I. D / I G Activated carbon with a value higher than 1.2; ordinary activated carbon refers to activated carbon with an I value in its Raman spectrum. D / I G Activated carbon with a value not exceeding 1.2.

[0038] Example 1

[0039] 0.25 kg of potassium chloride was dissolved in 7 L of 10% hydrochloric acid solution. After complete dissolution, 10 kg of defect-rich activated carbon was added. The mixture was impregnated at 30°C for 5 hours, dried at 100°C for 8 hours, and then heat-treated in a tube furnace at 500°C under nitrogen for 3 hours. Natural cooling yielded carbon material A. 0.2 kg of mercuric chloride was then accurately weighed and placed in two separate quartz boats along with carbon material A. These boats were positioned at the upper and lower air vents of the tube furnace, respectively, with a distance of no more than 10 cm between them. The two quartz boats were heat-treated at 300°C under nitrogen flow for 2 hours, and then naturally cooled to room temperature, yielding a diatomic micro-mercury catalyst with approximately 2 wt% mercuric chloride and 2.5 wt% potassium chloride content.

[0040] Example 2

[0041] 0.5 kg of zinc chloride was dissolved in 7 L of 10% hydrochloric acid solution. After complete dissolution, 10 kg of defect-rich activated carbon was added. The mixture was impregnated at 30°C for 5 hours, dried at 100°C for 8 hours, and then heat-treated in a tube furnace at 500°C under nitrogen for 3 hours. Natural cooling yielded carbon material A. 0.2 kg of mercuric chloride was then accurately weighed and placed in two separate quartz boats along with carbon material A. These boats were positioned at the upper and lower air vents of the tube furnace, respectively, with a distance of no more than 10 cm between them. The two boats were heat-treated at 300°C under a nitrogen atmosphere for 2 hours, and then naturally cooled to room temperature, yielding a diatomic micro-mercury catalyst with approximately 2 wt% mercuric chloride and 5 wt% zinc chloride content.

[0042] Example 3

[0043] 0.4 kg of calcium chloride was dissolved in 7 L of 10% hydrochloric acid solution. After complete dissolution, 10 kg of defect-rich activated carbon was added. The mixture was impregnated at 30°C for 5 hours, dried at 100°C for 8 hours, and then heat-treated in a tube furnace at 500°C under nitrogen for 3 hours. After natural cooling, carbon material A was obtained. 0.2 kg of mercuric chloride was then accurately weighed and placed in two separate quartz boats along with carbon material A. These boats were positioned at the upper and lower air vents of the tube furnace, respectively, with a distance of no more than 10 cm between them. The two boats were heat-treated at 300°C under a nitrogen atmosphere for 2 hours, and then naturally cooled to room temperature to obtain a diatomic micro-mercury catalyst with approximately 2 wt% mercuric chloride and 4 wt% calcium chloride content.

[0044] Example 4

[0045] 0.6 kg of barium chloride was dissolved in 7 L of 10% hydrochloric acid solution. After complete dissolution, 10 kg of defect-rich activated carbon was added. The mixture was impregnated at 30°C for 5 hours, dried at 100°C for 8 hours, and then heat-treated in a tube furnace at 500°C under nitrogen for 3 hours. Natural cooling yielded carbon material A. 0.2 kg of mercuric chloride was then accurately weighed and placed in two separate quartz boats along with carbon material A. These boats were positioned at the upper and lower air vents of the tube furnace, respectively, with a distance of no more than 10 cm between them. The two boats were heat-treated at 300°C under a nitrogen atmosphere for 2 hours, and then naturally cooled to room temperature, yielding a diatomic micro-mercury catalyst with approximately 2 wt% mercuric chloride and 6 wt% barium chloride content.

[0046] Example 5

[0047] 0.5 kg of urea was dissolved in 7 L of 10% hydrochloric acid solution. After complete dissolution, 10 kg of defect-rich activated carbon was added. The mixture was impregnated at 30°C for 5 hours, dried at 100°C for 8 hours, and then heat-treated in a tube furnace at 500°C under nitrogen for 3 hours. After natural cooling, carbon material A was obtained. 0.2 kg of mercuric chloride was then accurately weighed and placed in two separate quartz boats along with carbon material A. These boats were positioned at the upper and lower air vents of the tube furnace, respectively, with a distance of no more than 10 cm between them. The two quartz boats were heat-treated at 300°C under a nitrogen flow for 2 hours, and then naturally cooled to room temperature to obtain a diatomic micro-mercury catalyst with approximately 2 wt% mercuric chloride and 2 wt% nitrogen content.

[0048] Example 6

[0049] 1 kg of phytic acid was dissolved in 7 L of 10% hydrochloric acid solution. After complete dissolution, 10 kg of defect-rich activated carbon was added. The mixture was impregnated at 30°C for 5 hours, dried at 100°C for 8 hours, and then heat-treated in a tube furnace at 500°C under nitrogen for 3 hours. After natural cooling, carbon material A was obtained. 0.2 kg of mercuric chloride was accurately weighed and placed in two separate quartz boats along with carbon material A. These boats were positioned at the upper and lower air vents of the tube furnace, respectively, with a distance of no more than 10 cm between them. The two quartz boats were heat-treated at 300°C under a nitrogen flow for 2 hours, and then naturally cooled to room temperature to obtain a diatomic micro-mercury catalyst with approximately 2 wt% mercuric chloride and 1.2 wt% phosphorus content.

[0050] Example 7

[0051] 0.5 kg of sublimed sulfur was dissolved in 7 L of 10% hydrochloric acid solution. After complete dissolution, 10 kg of defect-rich activated carbon was added. The mixture was impregnated at 30°C for 5 hours, dried at 100°C for 8 hours, and then heat-treated in a tube furnace at 500°C under nitrogen for 3 hours. After natural cooling, carbon material A was obtained. 0.2 kg of mercuric chloride was then accurately weighed and placed in two separate quartz boats along with carbon material A. These boats were positioned at the upper and lower air vents of the tube furnace, respectively, with a distance of no more than 10 cm between them. The two boats were heat-treated at 300°C under a nitrogen flow for 2 hours, and then naturally cooled to room temperature to obtain a diatomic micro-mercury catalyst with a mercuric chloride content of approximately 2 wt% and a sulfur content of approximately 1.0 wt%.

[0052] Example 8

[0053] 0.2 kg of boric acid was dissolved in 7 L of 10% hydrochloric acid solution. After complete dissolution, 10 kg of defect-rich activated carbon was added. The mixture was impregnated at 30°C for 5 hours, dried at 100°C for 8 hours, and then heat-treated in a tube furnace at 500°C under nitrogen for 3 hours. After natural cooling, carbon material A was obtained. 0.2 kg of mercuric chloride was then accurately weighed and placed in two separate quartz boats along with carbon material A. These boats were positioned at the upper and lower air vents of the tube furnace, respectively, with a distance of no more than 10 cm between them. The two quartz boats were heat-treated at 300°C under a nitrogen flow for 2 hours, and then naturally cooled to room temperature to obtain a diatomic micro-mercury catalyst with approximately 2 wt% mercuric chloride and 0.4 wt% boron content.

[0054] Example 9

[0055] 0.125 kg of potassium chloride was dissolved in 7 L of 10% hydrochloric acid solution. After complete dissolution, 10 kg of defect-rich activated carbon was added. The carbon was impregnated at 30°C for 5 hours, dried at 100°C for 8 hours, and then heat-treated in a tube furnace at 500°C under nitrogen for 3 hours. Natural cooling yielded carbon material A. 0.1 kg of mercuric chloride was then accurately weighed and placed in two separate quartz boats along with carbon material A. These boats were positioned at the upper and lower air vents of the tube furnace, respectively, with a distance of no more than 10 cm between them. The two boats were heat-treated at 300°C under nitrogen flow for 2 hours, and then naturally cooled to room temperature, yielding a diatomic micro-mercury catalyst with approximately 1 wt% mercuric chloride and 1.25 wt% potassium chloride content.

[0056] Comparative Example 1

[0057] 0.25 kg of potassium chloride was dissolved in 7 L of 10% hydrochloric acid solution. After complete dissolution, 10 kg of ordinary activated carbon was added. The mixture was impregnated at 30°C for 5 hours, dried at 100°C for 8 hours, and then heat-treated in a tube furnace at 500°C under nitrogen for 3 hours. After natural cooling, carbon material B was obtained. 0.2 kg of mercuric chloride was then accurately weighed and placed in two separate quartz boats along with carbon material B. These boats were positioned at the upper and lower air vents of the tube furnace, respectively, with a distance of no more than 10 cm between them. The two quartz boats were heat-treated at 300°C under nitrogen flow for 2 hours, and then naturally cooled to room temperature to obtain a micro-mercury catalyst with a mercuric chloride content of approximately 2 wt% and a potassium chloride content of approximately 2.5 wt%.

[0058] Comparative Example 2

[0059] Weigh 10 kg of defect-rich activated carbon and accurately weigh 0.2 kg of mercuric chloride. Place both in two separate quartz boats, one at the top air vent and the other at the bottom air vent of a tube furnace, with a distance of no more than 10 cm between the two boats. Heat-treat the two boats at 300°C for 2 hours under a nitrogen atmosphere, then allow them to cool naturally to room temperature to obtain a micro-mercury catalyst with a mercuric chloride content of approximately 2 wt%.

[0060] Comparative Example 3

[0061] Weigh 0.25 kg of potassium chloride and 0.2 kg of mercuric chloride and dissolve them in 7 L of 10% hydrochloric acid solution. After complete dissolution, add 10 kg of defect-rich activated carbon, impregnate at 30°C for 5 h, dry at 100°C for 8 h, and then heat-treat in a tube furnace at 500°C under nitrogen for 3 h. After natural cooling to room temperature, a two-component micro-mercury catalyst with a mercuric chloride content of about 2 wt% and a potassium chloride content of about 2.5 wt% is obtained.

[0062] Comparative Example 4

[0063] Weigh 0.4 kg of mercuric chloride and dissolve it in 7 L of 10% hydrochloric acid solution. After it is fully dissolved, add 10 kg of defect-rich activated carbon, impregnate at 30°C for 5 h, and then dry at 100°C for 8 h to obtain a low-mercury catalyst with a mercuric chloride content of 4 wt%.

[0064] Comparative Example 5

[0065] Weigh 0.25 kg of potassium chloride and dissolve it in 7 L of 10% hydrochloric acid solution. After it is fully dissolved, add 10 kg of defect-rich activated carbon, impregnate at 30°C for 5 h, dry at 100°C for 8 h, and then heat-treat in a tube furnace at 500°C under nitrogen for 3 h. After naturally cooling to room temperature, a catalyst with a potassium chloride content of about 2.5 wt% is obtained.

[0066] Comparative Example 6

[0067] Weigh 0.25 kg of potassium chloride and 0.2 kg of mercuric chloride and dissolve them in 7 L of 10% hydrochloric acid solution. After complete dissolution, add 10 kg of defect-rich activated carbon, impregnate at 30°C for 5 h, dry at 100°C for 8 h, and then heat-treat in a tube furnace at 300°C under nitrogen for 3 h. After natural cooling to room temperature, a two-component micro-mercury catalyst with a mercuric chloride content of about 2 wt% and a potassium chloride content of about 2.5 wt% is obtained.

[0068] The results of parameter measurements for different catalysts in each embodiment and comparative example are shown in Table 1. Table 1 shows that the mercuric chloride loss rate of the diatomic micro-mercury catalysts with a mercuric chloride content of approximately 2 wt% in Examples 1-8 is generally less than 0.8%, and the acetylene conversion rate exceeds 35%. In contrast, the mercuric chloride loss rate of the catalyst in Comparative Example 2, which only supports mercuric chloride and does not contain type II atoms, is approximately 1.83%, and the acetylene hydrochlorination conversion rate is 17.2%. The acetylene hydrochlorination conversion rate of the catalyst in Comparative Example 5, which only supports type II atoms and does not support mercuric chloride, is only 2.1%. This indicates that the type II atoms introduced according to the method of the present invention can not only effectively anchor HgCl2, improve the thermal stability of HgCl2 and reduce its loss rate, but also that the type II atoms and mercuric chloride in the catalyst system prepared according to the method of the present invention have a strong interaction, synergistically promoting the acetylene conversion rate of the diatomic catalyst.

[0069] Comparative Example 1 used ordinary activated carbon as a support. The mercuric chloride loss rate of the prepared diatomic micro-mercury catalyst was much higher than that of the samples in Examples 1-8, and the acetylene conversion rate was much lower than that of Examples 1-8. This indicates that the defect sites in the carbon material play a key role in anchoring type II atoms and affecting the adsorption behavior of HgCl2. However, if HgCl2 and type II atom precursors are mixed and impregnated on defect-rich activated carbon and then heat-treated, the high heat treatment temperature destroys the interaction between the two, causing some HgCl2 to volatilize and affecting the HgCl2 content in the catalyst, thus affecting the catalytic performance, as in Comparative Example 3. When the mixture impregnated with the two precursors is calcined at a low temperature (<500℃), such as in Comparative Example 6, although HgCl2 can be retained on the carbon material due to the low temperature, the interaction between the type II atom precursor and the support is too weak, making it difficult to disperse uniformly on the support and easily forming agglomerates, increasing the loss rate of HgCl2 and reducing the acetylene conversion rate. Comparative Example 4 illustrates a low-mercury catalyst with a mercuric chloride content of 4 wt% prepared by the conventional impregnation method. Its mercuric chloride loss rate is approximately 2.81%, and its acetylene hydrochlorination conversion rate is 21.9%.

[0070] Example 9 presents a diatomic micro-mercury catalyst with a mercuric chloride content of approximately 1 wt%, in which the mercuric chloride loss rate is further reduced to 0.24% and the acetylene conversion rate is 27.3%. Its performance is superior to that of the low-mercury catalyst prepared by the conventional impregnation method given in Comparative Example 4, demonstrating the advanced nature of the diatomic micro-mercury catalyst preparation strategy proposed in this invention.

[0071] Table 1

[0072]

[0073] Note: [a] The mercuric chloride content in the catalyst was determined by copper reagent titration; [b] The content of type II atoms or their composition was analyzed by X-ray photoelectron spectroscopy; [c] The mercuric chloride loss rate of the mercury catalyst was determined according to GB / T 31530-2015; [d] The catalyst was tested at 180℃ with an acetylene space velocity of 1000 h⁻¹. -1 Evaluation was conducted under the condition that V(HCl) / V(C2H2) = 1.1.

[0074] Furthermore, it should be understood that after reading the above description of the present invention, those skilled in the art can make various alterations or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims.

Claims

1. A method for preparing a diatomic catalyst, characterized in that, The diatomic catalyst refers to two types of atoms, wherein the first type of atom is a mercury atom, and the second type of atom is one or more of potassium, zinc, calcium, barium, nitrogen, boron, sulfur, and phosphorus. The preparation method includes the following steps: (1) The precursor aqueous solution containing second-type atoms is impregnated onto defect-rich activated carbon, dried, and then heat-treated at 400-600℃ in an inert atmosphere to obtain carbon material A with second-type atoms monolayer dispersed near the defect sites of the activated carbon carrier. The Raman spectrum of the defect-rich activated carbon (I) D / I G Values ​​higher than 1.2; (2) In an inert atmosphere, the carbon material A is used to adsorb gaseous mercuric chloride at an adsorption temperature higher than the volatilization temperature of mercuric chloride to obtain the diatomic catalyst.

2. The preparation method according to claim 1, characterized in that, In step (1), after drying, the product is heat-treated at 500°C in an inert atmosphere.

3. The preparation method according to claim 1, characterized in that, In step (1): The precursor containing the second type of atom is one or more of potassium chloride, zinc chloride, calcium chloride, barium chloride, melamine, urea, dicyandiamide, boric acid, sublimed sulfur, phosphoric acid, ammonium dihydrogen phosphate, and phytic acid. The amount of the precursor containing the second type of atoms is 5%-15% of the mass of the diatomic catalyst.

4. The preparation method according to claim 1, characterized in that, In step (1): The impregnation is an equal-volume impregnation; The impregnation temperature is 30-60℃, and the time is 2-6 hours.

5. The preparation method according to claim 1, characterized in that, In step (1), the drying temperature is 90-120℃ and the time is 6-12 h.

6. The preparation method according to claim 1, characterized in that, In step (1), the heat treatment time is 1-5 hours.

7. The preparation method according to claim 1, characterized in that, In step (2): The adsorption temperature does not exceed 350℃; The adsorption time is 0.5-2 h.

8. The preparation method according to claim 7, characterized in that, In step (2), the adsorption temperature is greater than 150°C and does not exceed 350°C.

9. The preparation method according to claim 1, 7, or 8, characterized in that, Step (2) specifically includes: Mercuric chloride and the carbon material A were placed at the upper and lower air inlets of a tube furnace, respectively. In an inert gas flow, the tube furnace was heated to a temperature greater than the volatilization temperature of mercuric chloride to allow the carbon material A to adsorb the gaseous mercuric chloride, thereby obtaining the diatomic catalyst. In the tubular furnace, the distance between mercuric chloride and carbon material A shall not exceed 20 cm; The gas flow rate of the inert gas stream is 1-10 mL / min; The heating rate is 5-10℃ / min.

10. The diatomic catalyst prepared by the preparation method according to any one of claims 1-9.

11. The diatomic catalyst according to claim 10, characterized in that, The mercury atoms constitute 0.5%-1.5% of the total mass of the diatomic catalyst; The second type of atom accounts for 1%-10% of the total mass of the diatomic catalyst; The molar ratio of the mercury atoms to the second type of atoms is 1:1-5.

12. The application of the diatomic catalyst according to claim 10 or 11 in the production of vinyl chloride monomer by the calcium carbide method, characterized in that, The diatomic catalyst is used to catalyze the hydrochlorination of acetylene to produce vinyl chloride monomer.

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