Preparation method and application of a sulfur-containing molybdenum phosphide catalyst for medium- and low-temperature coal tar hydrogenation

Abstract

The present invention provides a preparation method and application of a sulfur-containing molybdenum phosphide catalyst for the hydrogenation of medium- and low-temperature coal tar. The method uses ammonium heptamolybdate as a molybdenum source, diammonium hydrogen phosphate as a phosphorus source, and silicon-surface-modified alumina as a carrier. After equal volume impregnation and drying and calcination, the catalyst is first sulfurized and then hydrogenated in a fixed-bed reactor to reduce the severity of the activation process of the molybdenum phosphide and simultaneously form a sulfur-doped molybdenum phosphide active structure to obtain a sulfur-containing molybdenum phosphide catalyst. Medium- and low-temperature coal tar is then directly introduced into the original fixed-bed reactor to carry out a medium- and low-temperature coal tar full-fraction hydrogenation refining reaction. The preparation of the sulfur-containing molybdenum phosphide catalyst and the in-situ activation in the reactor of the present invention can be completed completely within the preparation and reaction system of the existing transition metal sulfide catalyst, greatly reducing the difficulty of preparing and using the phosphating catalyst. Moreover, the sulfur-containing molybdenum phosphide catalyst prepared by the present invention can be used completely based on the existing hydrogenation system and exhibits good hydrogenation activity.

Description

Technical Field

[0001] The present invention belongs to the technical field of coal chemical industry, and in particular relates to the preparation and application of a sulfur-containing molybdenum phosphide catalyst for hydrogenation refining of medium- and low-temperature coal tar. Background Art

[0002] The efficient and clean conversion and utilization of coal is a pressing task. Hydrogenation of low- and medium-temperature coal tar, derived from coal pyrolysis, to produce clean, high-end oil products such as coal-based specialty fuels and naphthenic base oils is a key area of ​​focus. Compared to crude oil, low- and medium-temperature coal tar possesses many unique properties, including a lower hydrogen-to-carbon atomic ratio and a higher degree of unsaturation. In particular, its low sulfur, high nitrogen, high aromatics, and high asphaltene content are distinct from crude oil. The structural morphology of its colloids and asphaltenes is also significantly different from that of crude oil.

[0003] The existing medium and low temperature coal tar hydrogenation catalysts are mainly based on transition metal sulfide catalysts. Studies have found that transition metal phosphide catalysts are more active than sulfide catalysts in terms of hydrogenation denitrogenation and hydrogenation saturation, and are more suitable for processing medium and low temperature coal tar with low sulfur, high nitrogen and high aromatic content. In recent years, some research has been conducted on coal tar hydrogenation phosphide catalysts at home and abroad. These phosphide catalysts show higher activity than transition metal sulfide catalysts in the process of hydrogenation refining reaction. However, the preparation technology of phosphide catalysts has obvious shortcomings in the actual industrial application process: First, due to the strong interaction between the metal and the support, the temperature of phosphating activation of supported phosphide catalysts is usually above 650 ° C. The hydrogenation reactors that are currently in mature industrial operation cannot meet the harsh conditions of phosphating activation. When used as industrial catalysts, they need to be activated and passivated outside the reactor. The operation procedures are complicated and industrial application is difficult. Second, although the activation conditions of non-supported bulk phosphide catalysts are relatively mild, their specific surface area is often less than 1m 2 / g, which is much smaller than the 150-250m3 of traditional sulfide catalysts. 2 / g, the macroscopic hydrogenation activity is difficult to meet the industrial demand; thirdly, most phosphide catalysts require the use of highly toxic substances such as phosphine as a phosphorus source, which is difficult to operate and is not conducive to the large-scale industrial application of phosphide catalysts. For example, patent application CN 108686700 A discloses a medium- and low-temperature coal tar hydrotreating catalyst. This catalyst uses ammonium dihydrogen phosphate or diammonium hydrogen phosphate and nickel nitrate as precursors, supported on MCM-48 molecular sieve, and undergoes programmed reduction under hydrogen to form a Ni2P active component. However, this catalyst requires reduction in a hydrogen environment at 650°C, placing high demands on the reaction equipment. Patent CN 104941673 B provides a bulk sulfur-containing nickel phosphide catalyst for the selective hydrogenation of nitrobenzene compounds. The catalyst typically has a very small specific surface area, and the preparation process requires reaction, mixing, grinding, washing, and drying, making it difficult to prepare a supported porous catalyst. Therefore, it cannot be used for hydrorefining reactions of complex mixed oils. Patent CN 103386318 B provides a transition metal phosphide catalyst for coal tar hydrogenation. The catalyst uses phosphoric acid or a phosphate as the phosphorus source. After the catalyst precursor is prepared, it needs to be reduced in the presence of hydrogen at a high temperature of 700°C, placing high demands on the reaction equipment. Summary of the Invention

[0004] In view of the problems in the prior art that bulk phosphating catalysts have a small specific surface area, supported phosphating catalysts have a high phosphating temperature, and poor preparation and activation operability, as well as unsatisfactory hydrorefining effects and poor sulfur and nitrogen removal effects of existing coal tar hydrorefining agents, the present invention provides a method for preparing a sulfur-containing molybdenum phosphide catalyst having mild phosphating process conditions and specifically for the hydrogenation of "low sulfur and high nitrogen" medium and low temperature coal tar, as well as a method for catalyzing the hydrogenation of medium and low temperature coal tar using the catalyst prepared by the method.

[0005] The preparation method of the sulfur-containing molybdenum phosphide catalyst of the present invention comprises the following steps:

[0006] Step 1: At room temperature, add ammonium heptamolybdate and diammonium hydrogen phosphate to deionized water, controlling the P / Mo molar ratio to 0.8-1.5:1, and adjust the pH to 2-5 with nitric acid to obtain a clear solution;

[0007] Step 2: According to the equal volume impregnation method, the aluminum oxide support treated with silicon surface modification is impregnated with the clarified solution obtained in step 1, and then dried in an air environment at 90-150°C, and then calcined in an air environment at 400-600°C for 2-5 hours to obtain a molybdenum phosphide catalyst precursor; the molybdenum phosphide catalyst precursor has a molybdenum oxide content of 18-25wt%, a phosphorus pentoxide content of 8-15wt%, a silicon oxide content of 2.5-3.5wt%, and an aluminum oxide content of 60-65wt%;

[0008] Step 3: The molybdenum phosphide catalyst precursor of step 2 is loaded into a fixed bed reactor, a mixture of hydrogen sulfide and hydrogen is introduced, the temperature is raised to 340°C to 400°C, and maintained for 2 to 10 hours; then the gas is switched to hydrogen, the temperature is raised to 450 to 550°C, and maintained for 1 to 8 hours to complete the catalyst activation, and finally a sulfur-containing molybdenum phosphide catalyst is obtained.

[0009] In step 2 above, after alumina is formed, the silicon-containing organic compound is loaded by an equal volume impregnation method. After impregnation and calcination, a silicon-surface-modified alumina support is obtained. The pores of the silicon-surface-modified alumina support exhibit a bimodal distribution. The silicon-containing organic compound is either ethyl orthosilicate or methyl orthosilicate.

[0010] In the above step 3, the molybdenum phosphide catalyst precursor of step 2 is preferably loaded into a fixed bed reactor, a mixture of hydrogen sulfide and hydrogen is introduced, and the temperature is increased to 360-400°C at a heating rate of 20-30°C / h, and maintained for 2-6 hours; then the gas is switched to hydrogen, and the temperature is increased to 450-550°C at a heating rate of 10-20°C / h, and maintained for 2-4 hours to complete the catalyst activation.

[0011] Furthermore, in the above step 3, the concentration of hydrogen sulfide in the mixed gas is 2000 to 20000 mL / m³.

[0012] The method for hydrogenating medium-low temperature coal tar provided by the present invention is as follows: the sulfur-containing molybdenum phosphide catalyst obtained after the catalyst activation in the above step 3 is cooled to below 200°C, the medium-low temperature coal tar is introduced and hydrogen is introduced to carry out catalytic hydrogenation reaction, the reaction temperature is controlled to be 300-360°C, the liquid phase space velocity is controlled to be 0.1-1.0h -1 , the hydrogen partial pressure is 10-18 MPa, and the volume ratio of hydrogen to medium and low temperature coal tar is 1000-2000:1.

[0013] In the above-mentioned method for hydrogenating medium- and low-temperature coal tar, the sulfur-containing molybdenum phosphide catalyst obtained after catalyst activation is preferably cooled to below 200°C at a rate of 10-30°C / h.

[0014] The beneficial effects of the present invention are as follows:

[0015] 1. The present invention uses ammonium heptamolybdate as a molybdenum source and diammonium hydrogen phosphate as a phosphorus source. The activation process severity of molybdenum phosphide is reduced by first sulfurizing and then hydrogen reduction phosphating. The phosphating activation temperature is reduced from above 650°C to below 550°C, which greatly reduces the high temperature resistance requirements of the phosphating activation equipment. At the same time, a sulfur-doped molybdenum phosphide active structure is formed. The obtained sulfur-containing molybdenum phosphide catalyst exhibits good hydrogenation activity in the medium- and low-temperature coal tar full-fraction hydrorefining reaction. During the coal tar hydrogenation process, the sulfur and nitrogen removal rates can be above 99%.

[0016] 2. The preparation of the sulfur-containing molybdenum phosphide catalyst of the present invention can be completed entirely in an existing industrial hydrogenation reactor. After in-situ activation, medium- and low-temperature coal tar can be directly introduced into the hydrogenation reactor for a hydrogenation refining reaction. No special catalyst preparation equipment is required, which greatly reduces the difficulty of preparing and using the catalyst. The preparation and activation conditions of the catalyst are relatively mild, and the sulfur-containing molybdenum phosphide catalyst prepared by the present invention can be used entirely in existing hydrogenation systems.

[0017] 3. The sulfur-containing molybdenum phosphide catalyst of the present invention uses ammonium heptamolybdate as the molybdenum source and diammonium hydrogen phosphate as the phosphorus source. The sulfurization system and technical solution of the transition metal sulfide catalyst can be fully used in the sulfurization process. The in-situ reduction after sulfurization does not use any additional highly toxic substances such as phosphine. The catalyst preparation and reduction are both environmentally friendly, reliable, and easy-to-operate technical paths and solutions. DETAILED DESCRIPTION

[0018] The present invention is further described in detail below with reference to the embodiments, but the protection scope of the present invention is not limited to these embodiments.

[0019] The silicon surface-modified alumina support used in the following examples was prepared by the following method:

[0020] Step 1: Mix 100g of macroporous pseudo-boehmite (alumina content 70±1%, produced by Shandong Silica Aluminum New Materials Co., Ltd.) with 6g of sesbania powder, and continue to add 100g of monodisperse polystyrene sphere solution with a diameter of 80nm and 6g40wt% nitric acid, wherein the polystyrene sphere content in the monodisperse polystyrene sphere solution is 10wt%. After kneading on a twin-screw extruder for 30 minutes, extrude it into φ1.9mm clover-shaped strips. After natural air drying for 8 hours, place it at 120℃ for 4 hours, continue to place it in a calcination furnace and heat it to 550℃ at 3℃ / min and calcine it at a constant temperature for 4 hours to obtain a formed alumina carrier.

[0021] Step 2: Use the equal volume impregnation method to impregnate the cyclohexane solution of tetraethyl orthosilicate on the alumina carrier formed in step 1. The amount of tetraethyl orthosilicate added is 17wt% of the formed alumina carrier. After impregnation, air dry at room temperature for 8 hours and then place it at 120℃ for 4 hours. Continue to place it in a roasting furnace and heat it at 5℃ / min to 450℃ for 4 hours to obtain a silicon surface modified alumina carrier with a bimodal pore size distribution. The specific surface area of ​​the obtained carrier is 173m 2 / g, pore volume 1.25mL / g, the pores present the most probable pore diameters at 13.2nm and 107.3nm, the pores with diameters of 5-20nm account for 43.6% of the total pore volume, and the pores with diameters of 70-500nm account for 32.4% of the total pore volume. Example

[0022] Step 1: Weigh 42.91 g of ammonium heptamolybdate and 25.69 g of diammonium hydrogen phosphate, respectively, at a P / Mo molar ratio of 0.8, dissolve them in 100 mL of deionized water with stirring, then add 0.5 mol / L nitric acid dropwise to adjust the pH to 2, and continue stirring until a clear solution is obtained;

[0023] Step 2: According to the equal volume impregnation method, 100 g of the silicon surface-modified alumina support was impregnated with the clarified solution obtained in step 1, dried in an air environment at 110° C. for 12 hours, and then calcined in an air environment at 450° C. in a muffle furnace for 2 hours to obtain a molybdenum phosphide catalyst precursor; the molybdenum phosphide catalyst precursor had a molybdenum oxide content of 23.5 wt%, a phosphorus pentoxide content of 9.3 wt%, a silicon oxide content of 3.1 wt%, and an aluminum oxide content of 64.1 wt%;

[0024] Step 3: The molybdenum phosphide catalyst precursor of step 2 is loaded into a fixed bed reactor, and then a mixture of hydrogen sulfide and hydrogen is introduced (wherein hydrogen sulfide can be obtained by reacting a liquid organic sulfur substance with hydrogen at a temperature of 180 to 220°C, and the liquid organic sulfur substance can be selected from carbon disulfide, dimethyl disulfide, etc., which are well known to technicians in this industry), and the temperature is increased to 360°C at a heating rate of 20°C / h. After maintaining for 3 hours, the concentration of hydrogen sulfide in the mixed gas is controlled to be 5000mL / m³; after the molybdenum phosphide catalyst precursor is sulfurized, the mixture of hydrogen sulfide and hydrogen is switched to hydrogen, and the temperature is increased to 550°C at a heating rate of 15°C / h, and maintained for 1 hour to complete the catalyst activation, thereby finally obtaining a sulfur-containing molybdenum phosphide catalyst. Example

[0025] Step 1: Weigh 42.91 g of ammonium heptamolybdate and 38.53 g of diammonium hydrogen phosphate, respectively, at a P / Mo molar ratio of 1.2, dissolve them in 100 mL of deionized water with stirring, then add 0.5 mol / L nitric acid dropwise to adjust the pH to 3. Continue stirring until a clear solution is obtained.

[0026] Step 2: According to the equal volume impregnation method, 100 g of the silicon surface-modified alumina support was impregnated with the clarified solution obtained in step 1, dried in an air environment at 120° C. for 8 hours, and then calcined in an air environment at 500° C. in a muffle furnace for 3 hours to obtain a molybdenum phosphide catalyst precursor; the molybdenum phosphide catalyst precursor had a molybdenum oxide content of 22.5 wt%, a phosphorus pentoxide content of 13.3 wt%, a silicon oxide content of 3.0 wt%, and an aluminum oxide content of 61.2 wt%;

[0027] Step 3: The molybdenum phosphide catalyst precursor of step 2 is loaded into a fixed bed reactor, and then a mixture of hydrogen sulfide and hydrogen is introduced, and the temperature is raised to 360°C at a heating rate of 30°C / h. After maintaining for 2 hours, the concentration of hydrogen sulfide in the mixed gas is controlled to 8000mL / m³; after the molybdenum phosphide catalyst precursor is sulfurized, the mixture of hydrogen sulfide and hydrogen is switched to hydrogen, and the temperature is raised to 500°C at a heating rate of 20°C / h, and maintained for 4 hours to complete the catalyst activation, and finally a sulfur-containing molybdenum phosphide catalyst is obtained. Example

[0028] Step 1: Weigh 45 g of ammonium heptamolybdate and 33.67 g of diammonium hydrogen phosphate, respectively, at a P / Mo molar ratio of 1.0, dissolve them in 100 mL of deionized water with stirring, then add 0.5 mol / L nitric acid dropwise to adjust the pH to 3, and continue stirring until a clear solution is obtained;

[0029] Step 2: According to the equal volume impregnation method, 100 g of the silicon surface-modified alumina support was impregnated with the clarified solution obtained in step 1, dried in an air environment at 120° C. for 6 hours, and then calcined in an air environment at 500° C. in a muffle furnace for 4 hours to obtain a molybdenum phosphide catalyst precursor; the molybdenum phosphide catalyst precursor had a molybdenum oxide content of 23.7 wt%, a phosphorus pentoxide content of 11.7 wt%, a silicon oxide content of 3.0 wt%, and an aluminum oxide content of 61.6 wt%;

[0030] Step 3: The molybdenum phosphide catalyst precursor of step 2 is loaded into a fixed bed reactor, and then a mixture of hydrogen sulfide and hydrogen is introduced, and the temperature is increased to 390°C at a heating rate of 20°C / h. After maintaining for 6 hours, the concentration of hydrogen sulfide in the mixed gas is controlled to be 12000mL / m³; after the molybdenum phosphide catalyst precursor is sulfurized, the mixture of hydrogen sulfide and hydrogen is switched to hydrogen, and the temperature is increased to 550°C at a heating rate of 15°C / h, and maintained for 3 hours to complete the catalyst activation, and finally a sulfur-containing molybdenum phosphide catalyst is obtained. Example

[0031] Step 1: Weigh 40 g of ammonium heptamolybdate and 32.92 g of diammonium hydrogen phosphate, respectively, at a P / Mo molar ratio of 1.1, dissolve them in 100 mL of deionized water with stirring, then add 0.5 mol / L nitric acid dropwise to adjust the pH to 4, and continue stirring until a clear solution is obtained;

[0032] Step 2: According to the equal volume impregnation method, 100 g of the silicon surface-modified alumina support was impregnated with the clarified solution obtained in step 1, dried in an air environment at 130° C. for 4 hours, and then calcined in an air environment at 480° C. in a muffle furnace for 3 hours to obtain a molybdenum phosphide catalyst precursor; the molybdenum phosphide catalyst precursor had a molybdenum oxide content of 21.7 wt %, a phosphorus pentoxide content of 11.8 wt %, a silicon oxide content of 3.1 wt %, and an aluminum oxide content of 63.4 wt %;

[0033] Step 3: The molybdenum phosphide catalyst precursor of step 2 is loaded into a fixed bed reactor, and then a mixture of hydrogen sulfide and hydrogen is introduced, and the temperature is increased to 360°C at a heating rate of 28°C / h. After maintaining for 6 hours, the concentration of hydrogen sulfide in the mixture is controlled to be 20,000 mL / m³; after the molybdenum phosphide catalyst precursor is sulfurized, the mixture of hydrogen sulfide and hydrogen is switched to hydrogen, and the temperature is increased to 450°C at a heating rate of 10°C / h, and maintained for 8 hours to complete the catalyst activation, and finally a sulfur-containing molybdenum phosphide catalyst is obtained. Example

[0034] Step 1: Weigh 35 g of ammonium heptamolybdate and 41.64 g of diammonium hydrogen phosphate, respectively, at a P / Mo molar ratio of 1.3, dissolve them in 100 mL of deionized water with stirring, then add 0.5 mol / L nitric acid dropwise to adjust the pH to 3, and continue stirring until a clear solution is obtained;

[0035] Step 2: According to the equal volume impregnation method, 100 g of the silicon surface-modified alumina support was impregnated with the clarified solution obtained in step 1, dried in an air environment at 100° C. for 10 hours, and then calcined in an air environment at 500° C. in a muffle furnace for 3 hours to obtain a molybdenum phosphide catalyst precursor; the molybdenum phosphide catalyst precursor had a molybdenum oxide content of 19.4 wt%, a phosphorus pentoxide content of 12.5 wt%, a silicon oxide content of 3.2 wt%, and an aluminum oxide content of 64.9 wt%;

[0036] Step 3: The molybdenum phosphide catalyst precursor of step 2 is loaded into a fixed bed reactor, and then a mixture of hydrogen sulfide and hydrogen is introduced, and the temperature is increased to 340°C at a heating rate of 30°C / h. After maintaining for 6 hours, the concentration of hydrogen sulfide in the mixture is controlled to be 10000mL / m³; after the molybdenum phosphide catalyst precursor is sulfurized, the mixture of hydrogen sulfide and hydrogen is switched to hydrogen, and the temperature is increased to 550°C at a heating rate of 10°C / h. It is maintained for 4 hours to complete the catalyst activation, and finally a sulfur-containing molybdenum phosphide catalyst is obtained.

[0037] Comparative Example 1

[0038] For the sake of comparison, a commercially used sulfurized transition metal catalyst was used. The nickel oxide content, molybdenum oxide content, and tungsten oxide content of the catalyst were 3 wt%, 8 wt%, and 16 wt%. The catalyst was sulfurized and activated using the conventional industrial wet sulfurization method.

[0039] Comparative Example 2

[0040] In step 3 of Example 5, the molybdenum phosphide catalyst precursor from step 2 was loaded into a fixed-bed reactor, and hydrogen was then introduced. The temperature was raised to 700°C at a rate of 10°C / h and maintained for 6 hours. The remaining steps were the same as in Example 5 to obtain a sulfur-containing molybdenum phosphide catalyst. Example

[0041] The catalysts obtained in Examples 1 to 5, Comparative Example 1 and Comparative Example 2 were cooled at a rate of 20°C / h to below 200°C, and medium-low temperature coal tar was introduced into the fixed bed reactor and hydrogen was introduced to evaluate the hydrorefining reaction performance. The properties of the medium-low temperature coal tar are shown in Table 1. The reaction temperature was controlled to be 360°C, and the liquid phase space velocity was 0.3h -1 The hydrogen partial pressure is 15.5 MPa, and the volume ratio of hydrogen to medium and low temperature coal tar is 2000:1. Since sulfur is relatively easy to remove, the removal rates of nitrogen, residual carbon, and asphaltene were examined in the evaluation process. The hydrogenation performance of medium and low temperature coal tar is shown in Table 2.

[0042] Table 1 Properties of medium and low temperature coal tar

[0043]

[0044] Table 2 Hydrogenation performance of medium and low temperature coal tar

[0045]

[0046] As can be seen from Table 2, compared with commercial sulfurized transition metal catalysts, under the same process conditions, the use of the sulfur-containing molybdenum phosphide catalyst of the present invention can better remove nitrogen, residual carbon and asphaltenes from medium- and low-temperature coal tar, thereby improving the quality of the medium- and low-temperature coal tar full-fraction hydrogenation product.

Claims

1. A method for preparing a sulfur-containing molybdenum phosphide catalyst for medium- and low-temperature coal tar hydrogenation, characterized in that: The steps include: Step 1: At room temperature, add ammonium heptamolybdate and diammonium hydrogen phosphate to deionized water, controlling the P / Mo molar ratio to 0.8-1.5:1, and adjust the pH to 2-5 with nitric acid to obtain a clear solution; Step 2: After forming alumina, an equal volume impregnation method is used to load a silicon-containing organic matter. After impregnation and calcination, a silicon-surface-modified alumina carrier is obtained. The pores of the silicon-surface-modified alumina carrier are bimodal, and the silicon-containing organic matter is any one of ethyl orthosilicate and methyl orthosilicate. According to the equal volume impregnation method, the silicon-surface-modified alumina carrier is impregnated with the clarified solution obtained in step 1, dried in an air environment at 90-150° C., and then calcined in an air environment at 400-600° C. for 2-5 hours to obtain a molybdenum phosphide catalyst precursor; the molybdenum phosphide catalyst precursor has a molybdenum oxide content of 18-25wt%, a phosphorus pentoxide content of 8-15wt%, a silicon oxide content of 2.5-3.5wt%, and an aluminum oxide content of 60-65wt%; Step 3: The molybdenum phosphide catalyst precursor of step 2 is loaded into a fixed bed reactor, and a mixture of hydrogen sulfide and hydrogen is introduced, wherein the concentration of hydrogen sulfide in the mixture is 2000-20000 mL / m³, and the temperature is raised to 360-400°C at a heating rate of 20-30°C / h, and maintained for 2-6 hours; then the gas is switched to hydrogen, and the temperature is raised to 450-550°C at a heating rate of 10-20°C / h, and maintained for 2-4 hours to complete the catalyst activation, and finally obtain a sulfur-containing molybdenum phosphide catalyst.

2. A method for hydrogenating medium and low temperature coal tar, characterized in that: The sulfur-containing molybdenum phosphide catalyst obtained after catalyst activation in step 3 of claim 1 is cooled to below 200° C., medium-low temperature coal tar is introduced and hydrogen is introduced to carry out catalytic hydrogenation reaction, and the reaction temperature is controlled to be 300-360° C. and the liquid phase space velocity is 0.1-1.0 h -1 , the hydrogen partial pressure is 10-18 MPa, and the volume ratio of hydrogen to medium and low temperature coal tar is 1000-2000:

1.

3. The method for hydrogenating medium and low temperature coal tar according to claim 2, characterized in that: The sulfur-containing molybdenum phosphide catalyst obtained after catalyst activation is cooled to below 200° C. at a rate of 10 to 30° C. / h.

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