A method for preparing impregnating asphalt for nuclear graphite

Abstract

A method for preparing impregnating pitch for nuclear graphite comprises: subjecting raw oil to solid-liquid separation and distillation to obtain a hydrogenated precursor; subjecting the hydrogenated precursor to multi-stage serial hydrogenation and impurity removal to obtain distillate oil A; subjecting distillate oil A to vacuum distillation to obtain distillate oil C; subjecting distillate oil A to hydrocatalytic cracking to obtain distillate oil B; subjecting distillate oil B to vacuum distillation to obtain distillate oil D; subjecting distillate oil A to vacuum distillation to obtain distillate oil E, which is then subjected to an asphalting reaction to obtain refined asphalt; mixing distillates C and D with the refined asphalt and subjecting them to pressurized thermal polymerization to obtain nuclear-grade asphalt; extracting the nuclear-grade asphalt to obtain a low-quinoline-insoluble nuclear-grade high-softening-point asphalt; and using the low-quinoline-insoluble nuclear-grade high-softening-point asphalt directly as the impregnating pitch for nuclear graphite or subjecting it to component cutting and removal of light components to obtain the impregnating pitch for nuclear graphite. The impregnating pitch for nuclear graphite has a wide mesophase melting temperature range, which improves the rheological mechanical properties of the system.

Description

Technical Field

[0001] The invention belongs to the technical field of nuclear graphite raw material preparation, and in particular relates to a method for preparing asphalt as an impregnating agent for nuclear graphite. Background Art

[0002] As global fossil energy becomes increasingly scarce and its use generates large amounts of pollutants, accelerating ecological degradation, countries are urgently searching for new alternative energy sources. Nuclear energy, as one of the new energy sources, is becoming the preferred choice for future new energy development due to its abundant resources, long service life, clean and efficient operation.

[0003] Nuclear graphite, also known as nuclear reactor graphite, refers to carbonaceous graphite used in nuclear reactors. It primarily includes neutron moderators and reflectors for atomic reactors, hot column graphite for isotope production, and spherical and block graphite for high-temperature gas-cooled reactors. Nuclear graphite used in nuclear reactors is a high-purity synthetic graphite with a polycrystalline structure, in which filler particles are bonded together by coal tar pitch. Coke is the aggregate in nuclear graphite production, while coal tar pitch serves as a binder and impregnant, shaping and densifying the material. Nuclear graphite is produced through a series of processes, including kneading, crushing, grinding, vibratory vacuum charging, isostatic pressing, roasting, impregnation, graphitization, and machining. During the production of nuclear graphite, the content of impurities and heteroatoms must be strictly controlled, as most impurities and heteroatoms will affect its key physical properties. Nuclear graphite production faces four key challenges: high purity, high density, anisotropy, and machinability. Nuclear graphite requires a purity of 99.8% and a bulk density of ≥1.7 g / cm. 3 , the isotropy is less than 1.05. Therefore, it is very important to reduce the impurities in the material, improve the isotropy of the coke, and the wettability and coking value of the impregnating agent pitch when manufacturing nuclear graphite.

[0004] Traditional impregnants for nuclear graphite typically use coal tar pitch with low quinoline insolubles. Due to varying coal tar sources, coal tar pitches are numerous and complex in composition and structure. Furthermore, due to differences in processing techniques, different pitches exhibit varying softening points, TI (toluene insolubles), and QI (quinoline insolubles), resulting in varying carbon residues. The microstructures of these different coal tar pitches after carbonization vary significantly, leading to varying wettability on the graphite substrate. Consequently, this significantly impacts the performance of nuclear graphite materials.

[0005] Nuclear graphite, a key material in nuclear power plant construction, has yet to be domestically produced. One key reason for this is that the raw materials used in its production, such as isotropic coke, binder pitch, and impregnant pitch—materials that offer superior performance, reduce manufacturing costs, and shorten manufacturing cycles—are primarily imported. To accelerate the development of my country's nuclear power industry and achieve energy sustainability, the primary task is to independently address the raw material supply issues for nuclear graphite production, and ultimately, the supply of nuclear graphite itself. Therefore, it is imperative to research and develop nuclear-grade impregnant pitch, optimize the entire process from raw material selection to manufacturing, improve the performance of graphite products, reduce manufacturing costs, and rapidly provide industrial-grade raw materials for nuclear graphite production, while also developing and selecting graphite products with improved irradiation lifespans. Summary of the Invention

[0006] The present invention provides a method for preparing an impregnating pitch for nuclear graphite. The product is a nuclear graphite impregnating pitch characterized by low quinoline-insoluble content, high purity, and low heteroatom content. It also exhibits excellent high-temperature fluidity, permeability, wettability, and a high coking value. The impregnating pitch exhibits a wide mesophase melting temperature range, improving the rheological properties of the system while effectively controlling various parameters of the nuclear-grade pitch. This invention successfully addresses the challenges of nuclear graphite's raw material requirements, such as stability and low impurities, and provides a new process for the research, development, and preparation of nuclear-grade carbon materials.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] A method for preparing an impregnating agent pitch for nuclear graphite comprises the following steps:

[0009] 1) The raw oil is subjected to solid-liquid separation and distillation processes to obtain a hydrogenation precursor.

[0010] The raw oil is one of medium-low temperature coal tar, high temperature coal tar, petroleum residue or catalytic cracking slurry.

[0011] Solid-liquid separation is one of centrifugal separation, filter press separation or sedimentation separation.

[0012] The conditions of the distillation process are as follows: the tower bottom temperature is controlled at 220~340℃, the tower top temperature is controlled at 130~230℃, and the vacuum degree is controlled at 0.01~0.09MPa.

[0013] The density of the hydrogenated precursor at 20°C is 0.9~1.1g / cm 3 , the content of oxygen-containing compounds in the form of phenol and its derivatives is ≤1%, the content of fractions above 350°C is ≤60%, and the content of quinoline insoluble matter is ≤0.03%.

[0014] 2) The hydrogenated precursor obtained in step 1) is subjected to a multi-stage serial hydrogenation and impurity removal process to obtain distillate oil A; wherein the first stage is a water-resistant hydrogenation catalyst, the second stage or multiple stages are mild hydrogenation refining catalysts, the reaction temperature of the first stage is 180-320°C, and the reaction temperature of the second stage or more stages is 220-400°C.

[0015] The multi-stage series hydrogenation impurity removal process is a boiling bed, fluidized bed or fixed bed multi-stage series hydrogenation impurity removal process. The distillate oil A is a full-range oil obtained by the hydrogenation precursor through the multi-stage series hydrogenation impurity removal process. Its density at 20℃ is 0.88~1.0g / cm 3 , the content of fractions below 350℃ is ≥60%; the content of fractions below 500℃ is ≥95%; the content of quinoline insoluble matter is ≤0.01%; the content of toluene insoluble matter is ≤1%; the content of sulfur is <0.3%; the content of nitrogen is <0.3%; the content of ash is <4.0×10 -4 %.

[0016] 3) The distillate oil A obtained in step 2) is subjected to vacuum distillation to obtain distillate oil C. Distillate oil C is the oil in the distillation range of 350-440° C. cut from distillate oil A by vacuum distillation.

[0017] 4) The distillate oil A obtained in step 2) is subjected to a hydrocatalytic cracking process to obtain distillate oil B; the hydrocatalytic cracking reaction temperature is 280-440° C. The hydrocatalytic cracking process is a fixed-bed catalytic hydrogenation process.

[0018] Fraction oil B is a full-range oil obtained by fixed-bed hydrocatalytic cracking of fraction oil A, wherein the content of fractions below 500° C. is ≥90%; the content of quinoline insolubles is ≤0.01%; and the content of toluene insolubles is ≤1%.

[0019] 5) Distillate oil B obtained in step 4) by vacuum distillation to obtain distillate oil D. Distillate oil D is the oil in the distillation range of 160-370° C. cut from distillate oil B by vacuum distillation.

[0020] 6) Distillate oil A obtained in step 2) is subjected to vacuum distillation to obtain distillate oil E, and distillate oil E is further subjected to an asphalting reaction to obtain refined asphalt; distillate oil E is the 350-500°C distillate oil cut from distillate oil A by vacuum distillation.

[0021] The asphaltization reaction is protected by inert gas or nitrogen replacement, using high-purity nitrogen or high-purity argon, etc. The initial pressure after replacement is 0.01~0.5MPa, the final reaction pressure is 0.3~2.0MPa, the reaction temperature is 260~400℃, the constant temperature time is 0.5~10h, and the heating rate is 0.5~5℃ / min.

[0022] The softening point of refined asphalt is 20~80℃, the content of toluene insoluble matter is 0.5~12%, the content of quinoline insoluble matter is ≤0.05%, the sulfur content is <0.3%, the nitrogen content is <0.3%, and the ash content is <4.0×10 -4 %.

[0023] 7) The distillate oil C obtained in step 3) and the distillate oil D obtained in step 5) are mixed with the refined asphalt obtained in step 6), and then subjected to pressurized thermal polymerization to obtain a nuclear-grade asphalt precursor; the thermal polymerization conditions are inert gas or nitrogen displacement protection, the initial pressure after displacement is 0.01-0.5 MPa, the final reaction pressure is 0.5-2.0 MPa, the reaction temperature is 300-450°C, the constant temperature time is 0.5-10 hours, and the heating rate is 0.5-5°C / min.

[0024] According to the mass ratio, distillate oil C: distillate oil D: refined asphalt = 1~10:1~10:1~10.

[0025] The softening point of the nuclear-grade asphalt precursor is 80~220℃, the toluene insoluble matter content is ≥15%, the quinoline insoluble matter content is ≤0.01%, the sulfur content is <0.3%, the nitrogen content is <0.3%, the ash content is <0.5%, and the neutron absorbing impurities are <2ppm.

[0026] 8) subjecting the nuclear-grade asphalt precursor obtained in step 7) to an extraction process to obtain nuclear-grade asphalt; the extraction process is an extraction and separation process;

[0027] The softening point of the nuclear grade asphalt is 60-180°C, the toluene insoluble matter content is 8-45%, the quinoline insoluble matter content is ≤0.01%, the sulfur content is <0.3%, the nitrogen content is <0.3%, and the ash content is <4.0×10 -4 %, neutron absorbing impurities <2ppm.

[0028] 9) By controlling the process indicators of the nuclear-grade pitch obtained in step 8), the nuclear-grade pitch obtained in step 8) can be directly used as an impregnating agent pitch for nuclear graphite, or the nuclear-grade pitch obtained in step 8) can be subjected to a component cutting process to remove light components to obtain an impregnating agent pitch for nuclear graphite.

[0029] The component cutting process uses a thin film evaporator.

[0030] The process indicators of the impregnating agent pitch for nuclear graphite are: softening point 120~240℃, toluene insoluble matter content ≥25%, quinoline insoluble matter content ≤0.01%, coking value ≥57%, sulfur content <0.3%, nitrogen content <0.3%, ash content <4.0×10 -4 %, neutron absorbing impurities <2ppm.

[0031] The percentage contents in the present invention are all by mass.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] 1) The impregnating agent pitch for nuclear graphite prepared by the method of the present invention has low quinoline insoluble matter content, high purity, low heteroatom content, and good high-temperature fluidity, permeability, wettability and high coking value.

[0034] 2) The impregnating agent pitch for nuclear graphite prepared by the method of the present invention has a wide melting temperature range of the mesophase, which improves the rheological mechanical properties of the system and effectively controls various indicators of the nuclear-grade pitch.

[0035] 3) As a raw material for nuclear graphite, it can achieve large-scale specifications, stable quality, good thermal stability and low thermal expansion coefficient of nuclear graphite in a cold state.

[0036] 4) This invention successfully solves the difficult problems of nuclear graphite's requirements for raw material stability and low impurities, and at the same time, provides a new process route for the research and development and preparation of nuclear-grade carbon materials. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the specific implementation methods of the present invention are further described below in conjunction with examples. The following examples are used to specifically illustrate the contents of the present invention. These examples are only general descriptions of the contents of the present invention and do not limit the contents of the present invention.

[0038] Example 1:

[0039] The medium-low temperature coal tar is heated to 50°C, centrifuged at a speed of 1000 rad / min, and a sieve mesh of 300 meshes to remove solid impurities to obtain a medium-low temperature coal tar centrifuge liquid. The medium-low temperature coal tar centrifuge liquid is passed through a vacuum distillation tower with the top temperature controlled at 140°C, the bottom temperature controlled at 250°C, and the vacuum degree controlled at 0.08 MPa to obtain a hydrogenated precursor at the bottom of the tower. The density of the hydrogenated precursor at 20°C is 0.98 g / cm 3 The content of oxygenated compounds in the form of phenol and its derivatives was 0.92%, the content of fractions above 350°C was 46.2%, and the content of quinoline insoluble matter was 0.02%. The hydrogenated precursor was subjected to two-stage hydrogenation and impurity removal in an ebullient bed to obtain distillate oil A, where the reaction temperature of the first stage was 180°C and the reaction temperature of the second stage was 320°C. The density of distillate oil A (20°C) was 0.93 g / cm 3 The content of fractions below 350℃ is 60.2%, the content of fractions below 500℃ is 96.8%, the content of quinoline insoluble matter is 0.01%, the content of toluene insoluble matter is 0.81%, the content of sulfur is 0.23%, the content of nitrogen is 0.20%, and the ash content is 3.9×10 -4%; Fraction A is distilled through a vacuum distillation tower, with the top temperature controlled at 320°C, the bottom temperature controlled at 420°C, and the vacuum degree controlled at 0.08MPa, and fraction C is obtained from the side of the tower; Fraction A is subjected to fixed-bed catalytic hydrogenation to obtain fraction B, with the reaction temperature being 380°C, the quinoline insoluble matter content of fraction B being 0.006%, the toluene insoluble matter content being 0.46%, and the fraction content below 500°C being 96%; Fraction B is distilled through a vacuum distillation tower, with the top temperature controlled at 140°C, the bottom temperature controlled at 340°C, and the vacuum degree controlled at 0.09MPa, and fraction D is obtained from the side of the tower; Fraction A is distilled through a vacuum distillation tower, with the top temperature controlled at 140°C, the bottom temperature controlled at 340°C, and the vacuum degree controlled at 0.09MPa, and fraction D is obtained from the side of the tower; The temperature was controlled at 320°C, the tower bottom temperature was controlled at 440°C, and the vacuum degree was controlled at 0.09 MPa. The distillate oil E was obtained from the tower side line. The distillate oil E passed through a polymerization reactor for asphaltification reaction. First, the reactor was replaced with high-purity nitrogen to make its initial pressure 0.05 MPa, and the pressure was increased by self-pressure. Then, the temperature was increased from room temperature to 360°C at a rate of 3°C / min, and the temperature was kept constant for 8 hours. The final pressure in the reactor was maintained at 0.45 MPa to obtain refined asphalt. The softening point of the refined asphalt was 36°C, the toluene insoluble matter content was 4.68%, the quinoline insoluble matter content was 0.03%, the sulfur content was 0.225%, the nitrogen content was 0.197%, and the ash content was 3.8×10 -4 %; Distillate C and distillate D were mixed with refined asphalt in a mass ratio of 1:1:1 and then introduced into a polymerization reactor. The reactor was replaced with high-purity nitrogen to an initial pressure of 0.05 MPa. The pressure was then increased automatically, and the temperature was raised from room temperature to 360°C at a rate of 3°C / min. The mixture was kept at a constant temperature for 8 hours, and the final pressure in the reactor was maintained at 0.65 MPa to obtain a nuclear-grade asphalt precursor. The nuclear-grade asphalt precursor had a softening point of 135°C, a toluene-insoluble matter content of 15%, a quinoline-insoluble matter content of 0.0035%, a sulfur content of 0.23%, a nitrogen content of 0.18%, and an ash content of 3.5×10 -4 %, and the neutron absorption impurities were 1.42ppm; the nuclear-grade asphalt precursor was extracted to obtain a soluble phase, and the soluble phase was then distilled under reduced pressure to recover the extract to obtain nuclear-grade asphalt, wherein the extract was quinoline, the extraction temperature was 238℃, and the extraction time was 2h; the softening point of the nuclear-grade asphalt was 128℃, the toluene insoluble matter content was 28%, the quinoline insoluble matter content was 0.01%, the coking value was 60%, the sulfur content was 0.23%, the nitrogen content was 0.18%, and the ash content was 3.2×10 -4 %, and the neutron absorbing impurities are 1.42ppm, which can be directly used as impregnating asphalt for nuclear graphite.

[0040] Example 2:

[0041] The high-temperature coal tar was heated to 50°C and sent to a filter press by a centrifugal pump for separation treatment. The filter was pressed for 1.5 hours and the mesh size was 300 meshes to obtain a filtrate and a filter residue. The filtrate was used to remove solid impurities to obtain high-temperature coal tar. The high-temperature coal tar filtrate was passed through a vacuum distillation tower with the top temperature controlled at 130°C, the bottom temperature controlled at 260°C, and the vacuum degree controlled at 0.09 MPa. A hydrogenated precursor was obtained at the bottom of the tower. The density of the hydrogenated precursor (20°C) was 1.01 g / cm 3 The content of oxygenated compounds in the form of phenol and its derivatives was 0.71%, the content of fractions above 350°C was 45%, and the content of quinoline insoluble matter was 0.02%. The hydrogenated precursor was subjected to two-stage hydrogenation and impurity removal in an ebullient bed to obtain distillate oil A, where the reaction temperature of the first stage was 240°C and the reaction temperature of the second stage was 360°C. The density of distillate oil A (20°C) was 0.96 g / cm 3 The content of fractions below 350°C is 75%, the content of fractions below 500°C is 97%, the content of quinoline insoluble matter is 0.01%, the content of toluene insoluble matter is 0.7%, the content of sulfur is 0.14%, the content of nitrogen is 0.21%, and the ash content is 3.15×10 -4 %; Fraction A is distilled through a vacuum distillation tower, with the top temperature controlled at 300°C, the bottom temperature controlled at 415°C, and the vacuum degree controlled at 0.09 MPa, and fraction C is obtained from the side of the tower; Fraction A is subjected to fixed-bed catalytic hydrogenation to obtain fraction B, with the reaction temperature being 400°C. The quinoline insoluble matter content of fraction B is 0.051%, the toluene insoluble matter content is 0.85%, and the content of fractions below 500°C is 93.4%; Fraction B is distilled through a vacuum distillation tower, The top temperature of the tower was controlled at 120°C, the bottom temperature was controlled at 320°C, the vacuum was controlled at 0.09 MPa, and distillate oil D was obtained from the side line of the tower. Distillate oil A was subjected to a vacuum distillation tower with the top temperature controlled at 300°C, the bottom temperature controlled at 435°C, and the vacuum controlled at 0.09 MPa, and distillate oil E was obtained from the side line of the tower. Distillate oil E was passed through a polymerization reactor for asphaltification reaction. First, the reactor was replaced with high-purity nitrogen to an initial pressure of 0.05 MPa, and the pressure was increased by self-increase. Then, the temperature was increased from room temperature to 360°C at a rate of 3°C / min, and the temperature was kept constant for 4 hours. The final pressure in the reactor was maintained at 0.5 MPa to obtain refined asphalt. The softening point of the refined asphalt was 80°C, the toluene insoluble matter content was 11.6%, the quinoline insoluble matter content was 0.02%, the sulfur content was 0.13%, the nitrogen content was 0.19%, and the ash content was 3.0×10 -4%; Distillate C and distillate D were mixed with refined asphalt in a mass ratio of 3:1:2 and then introduced into a polymerization reactor. The reactor was replaced with high-purity nitrogen to an initial pressure of 0.05 MPa. The pressure was then increased automatically, and the temperature was raised from room temperature to 450°C at a rate of 3°C / min. The mixture was kept at a constant temperature for 3 hours, and the final pressure in the reactor was maintained at 0.4 MPa to obtain a nuclear-grade asphalt precursor. The softening point of the nuclear-grade asphalt precursor was 220°C, the toluene-insoluble matter content was 30%, the quinoline-insoluble matter content was 0.0045%, the sulfur content was 0.28%, the nitrogen content was 0.193%, and the ash content was 3.7×10 -4 %, and the neutron absorption impurities were 1.62ppm; the nuclear-grade asphalt precursor was extracted to obtain a soluble phase, and the soluble phase was then distilled under reduced pressure to recover the extract to obtain the nuclear-grade asphalt, wherein the extract was quinoline, the extraction temperature was 238℃, and the extraction time was 2h; the softening point of the nuclear-grade asphalt was 180℃, the toluene insoluble matter content was 35%, the quinoline insoluble matter content was 0.0021%, the coking value was 58%, the sulfur content was 0.14%, the nitrogen content was 0.21%, and the ash content was 3.15×10 -4 %, and the neutron absorbing impurities are 1.3ppm, which can be directly used as impregnating asphalt for nuclear graphite.

[0042] Example 3:

[0043] The petroleum residue was heated to 60°C, centrifuged at a speed of 1200 rad / min, and a sieve mesh of 400 mesh to remove solid impurities to obtain a petroleum residue centrifuge liquid. The petroleum residue centrifuge liquid was passed through a vacuum distillation tower with the top temperature controlled at 140°C, the bottom temperature controlled at 260°C, and the vacuum degree controlled at 0.07 MPa to obtain a hydrogenated precursor at the bottom of the tower. The density of the hydrogenated precursor (20°C) was 0.93 g / cm 3 The content of oxygenated compounds in the form of phenol and its derivatives was 0.31%, the content of fractions above 350°C was 42%, and the content of quinoline insoluble matter was 0.01%. The hydrogenated precursor was subjected to two-stage hydrogenation and impurity removal in an ebullient bed to obtain distillate oil A, where the reaction temperature of the first stage was 180°C and the reaction temperature of the second stage was 320°C. The density of distillate oil A (20°C) was 0.89 g / cm 3 The content of fractions below 350°C is 70.5%, the content of fractions below 500°C is 98%, the content of quinoline insolubles is 0.01%, the content of toluene insolubles is 0.38%, the content of sulfur is 0.16%, the content of nitrogen is 0.14%, and the ash content is 2.8×10 -4%; Fraction A is distilled through a vacuum distillation tower, with the top temperature controlled at 290°C, the bottom temperature controlled at 400°C, and the vacuum degree controlled at 0.08MPa, and fraction C is obtained from the side of the tower; Fraction A is catalytically hydrogenated through a fixed bed to obtain fraction B, with the reaction temperature being 280°C. The quinoline insoluble matter content of fraction B is 0.01%, the toluene insoluble matter content is 0.56%, and the fraction content below 500°C is 98.6%; Fraction B is distilled through a vacuum distillation tower, with the top temperature controlled at 290°C, the bottom temperature controlled at 400°C, and the vacuum degree controlled at 0.08MPa, and fraction C is obtained from the side of the tower; Fraction A is catalytically hydrogenated through a fixed bed to obtain fraction B, with the reaction temperature being 280°C, the quinoline insoluble matter content of fraction B is 0.01%, the toluene insoluble matter content is 0.56%, and the fraction content below 500°C is 98.6%; The top temperature was controlled at 120°C, the bottom temperature was controlled at 320°C, the vacuum was controlled at 0.07 MPa, and distillate oil D was obtained from the side line of the tower. Distillate oil A was subjected to a vacuum distillation tower, the top temperature was controlled at 290°C, the bottom temperature was controlled at 420°C, the vacuum was controlled at 0.09 MPa, and distillate oil E was obtained from the side line of the tower. Distillate oil E was passed through a polymerization reactor for asphaltification reaction. First, the reactor was replaced with high-purity nitrogen to make its initial pressure 0.05 MPa, and the pressure was increased by itself. Then, the temperature was increased from room temperature to 320°C at a rate of 3°C / min, and the temperature was kept constant for 4 hours. The final pressure in the reactor was maintained at 1.0 MPa to obtain refined asphalt. The softening point of the refined asphalt was 45°C, the toluene insoluble content was 6.5%, the quinoline insoluble content was 0.01%, the sulfur content was 0.15%, the nitrogen content was 0.12%, and the ash content was 2.6×10 -4 %; Distillate C and distillate D were mixed with refined asphalt in a mass ratio of 3:2:4 and then introduced into a polymerization reactor. The reactor was replaced with high-purity nitrogen to an initial pressure of 0.05 MPa. The pressure was then increased automatically, and the temperature was raised from room temperature to 380°C at a rate of 3°C / min. The mixture was kept at a constant temperature for 8 hours, and the final pressure in the reactor was maintained at 0.6 MPa to obtain a nuclear-grade asphalt precursor. The softening point of the nuclear-grade asphalt precursor was 140°C, the toluene-insoluble matter content was 22.6%, the quinoline-insoluble matter content was 0.05%, the sulfur content was 0.16%, the nitrogen content was 0.14%, and the ash content was 3.0×10 -4 %, and neutron absorbing impurities were 1.2ppm; the nuclear-grade asphalt precursor was extracted to obtain a soluble phase, and the soluble phase was then distilled under reduced pressure to recover the extract to obtain the nuclear-grade asphalt, wherein the extracting liquid was pyridine, the extraction temperature was 160℃, and the extraction time was 2h; the softening point of the nuclear-grade asphalt was 120℃, the toluene insoluble matter content was 17.9%, the quinoline insoluble matter content was 0.0031%, the coking value was 57.6%, the sulfur content was 0.16%, the nitrogen content was 0.14%, the ash content was 0.15%, and the neutron absorbing impurities were 1.2ppm; the nuclear-grade asphalt was passed through a thin film evaporator to remove the light components before 280℃ to obtain the impregnating agent asphalt for nuclear graphite, which had a softening point of 140℃, a toluene insoluble matter content of 32%, a quinoline insoluble content of 0.001%, a coking value of 61.2%, a sulfur content of 0.16%, a nitrogen content of 0.14%, and an ash content of 2.8×10 -4 %, and the neutron absorbing impurities are 1.2ppm.

[0044] Example 4:

[0045] The high-temperature coal tar was heated to 65°C, centrifuged at a speed of 1100 rad / min, and the mesh size was 400 to remove solid impurities and obtain a high-temperature coal tar centrifuge liquid. The high-temperature coal tar centrifuge liquid was passed through a vacuum distillation tower with the top temperature controlled at 140°C, the bottom temperature controlled at 250°C, and the vacuum degree controlled at 0.08 MPa. A hydrogenated precursor was obtained at the bottom of the tower. The density of the hydrogenated precursor (20°C) was 1.1 g / cm 3 The content of oxygen-containing compounds in the form of phenol and its derivatives is 0.6%, the content of fractions above 350°C is 60%, and the content of quinoline insolubles is 0.03%. The hydrogenated precursor is subjected to two-stage hydrogenation and impurity removal in an ebullient bed to obtain distillate oil A, where the reaction temperature of the first stage is 280°C and the reaction temperature of the second stage is 400°C. The density of distillate oil A (20°C) is 0.99 g / cm 3 The content of fractions below 350°C is 60.5%, the content of fractions below 500°C is 96%, the content of quinoline insolubles is 0.01%, the content of toluene insolubles is 0.88%, the content of sulfur is 0.12%, the content of nitrogen is 0.11%, and the ash content is 3.12×10 -4 %; Fraction A is distilled through a vacuum distillation tower, with the top temperature controlled at 290°C, the bottom temperature controlled at 400°C, and the vacuum degree controlled at 0.08MPa, and fraction C is obtained from the side of the tower; Fraction A is catalytically hydrogenated through a fixed bed to obtain fraction B, with the reaction temperature being 420°C. The quinoline insoluble matter content of fraction B is 0.01%, the toluene insoluble matter content is 0.76%, and the fraction content below 500°C is 95.6%; Fraction B is distilled through a vacuum distillation tower, with the top temperature controlled at 290°C, the bottom temperature controlled at 400°C, and the vacuum degree controlled at 0.08MPa, and fraction C is obtained from the side of the tower; Fraction A is catalytically hydrogenated through a fixed bed to obtain fraction B, with the reaction temperature being 420°C, the quinoline insoluble matter content of fraction B is 0.01%, the toluene insoluble matter content is 0.76%, and the fraction content below 500°C is 95.6%; The top temperature was controlled at 120°C, the bottom temperature was controlled at 320°C, the vacuum was controlled at 0.07 MPa, and distillate oil D was obtained from the side line of the tower. Distillate oil A was subjected to a vacuum distillation tower, the top temperature was controlled at 290°C, the bottom temperature was controlled at 420°C, the vacuum was controlled at 0.09 MPa, and distillate oil E was obtained from the side line of the tower. Distillate oil E was passed through a polymerization reactor for asphaltification reaction. First, the reactor was replaced with high-purity nitrogen to make its initial pressure 0.05 MPa, and the pressure was increased by itself. Then, the temperature was increased from room temperature to 360°C at a rate of 5°C / min, and the temperature was kept constant for 4 hours. The final pressure in the reactor was maintained at 1.0 MPa to obtain refined asphalt. The softening point of the refined asphalt was 60°C, the toluene insoluble content was 9.5%, the quinoline insoluble content was 0.03%, the sulfur content was 0.11%, the nitrogen content was 0.09%, and the ash content was 3.11×10 -4%; Distillate C and distillate D were mixed with refined asphalt in a mass ratio of 2:2:3 and then introduced into a polymerization reactor. The reactor was replaced with high-purity nitrogen to an initial pressure of 0.05 MPa. The reactor was pressurized at 5°C / min and then heated from room temperature to 450°C. The reactor was kept at this temperature for 6 hours, and the final pressure in the reactor was maintained at 1.0 MPa to obtain a nuclear-grade asphalt precursor. The softening point of the nuclear-grade asphalt precursor was 180°C, the toluene-insoluble matter content was 26%, the quinoline-insoluble matter content was 0.008%, the sulfur content was 0.12%, the nitrogen content was 0.11%, the ash content was 0.2%, and the neutron-absorbing impurities were 1.1 ppm. The nuclear-grade asphalt precursor was extracted to obtain a soluble phase, and the soluble phase was then recovered by vacuum distillation to obtain nuclear-grade asphalt. The extracting liquid was quinoline, the extraction temperature was 240°C, and the extraction time was 1.5 hours. The softening point of the nuclear-grade asphalt was 120, the toluene-insoluble matter content was 16.1%, the quinoline-insoluble content was 0.0051%, the coking value was 58%, the sulfur content was 0.12%, the nitrogen content was 0.11%, and the ash content was 3.6×10 -4 %, and the neutron absorption impurities were 1.1ppm; the nuclear-grade pitch was passed through a thin film evaporator to remove the light components before 290°C to obtain the impregnating agent pitch for nuclear graphite. The softening point of the impregnating agent pitch for nuclear graphite was 143°C, the toluene insoluble matter content was 30.6%, the quinoline insoluble matter content was 0.0032%, the coking value was 63.2%, the sulfur content was 0.12%, the nitrogen content was 0.11%, and the ash content was 3.12×10 -4 %, and the neutron absorbing impurities are 1.2ppm.

[0046] Example 5

[0047] The high-temperature coal tar was heated to 55°C, centrifuged at a speed of 1000 rad / min, and the mesh size was 300 to remove solid impurities and obtain a high-temperature coal tar centrifuge liquid. The high-temperature coal tar centrifuge liquid was passed through a vacuum distillation tower with the top temperature controlled at 130°C, the bottom temperature controlled at 260°C, and the vacuum degree controlled at 0.09 MPa. A hydrogenated precursor was obtained at the bottom of the tower. The density of the hydrogenated precursor (20°C) was 1.07 g / cm 3 The content of oxygenated compounds in the form of phenol and its derivatives was 0.78%, the content of fractions above 350°C was 56%, and the content of quinoline insoluble matter was 0.03%. The hydrogenated precursor was subjected to two-stage hydrogenation and impurity removal in an ebullient bed to obtain distillate oil A, where the reaction temperature of the first stage was 300°C and the reaction temperature of the second stage was 400°C. The density of distillate oil A (20°C) was 1.0 g / cm 3 The content of fractions below 350°C is 65.5%, the content of fractions below 500°C is 95.6%, the content of quinoline insolubles is 0.01%, the content of toluene insolubles is 0.89%, the content of sulfur is 0.23%, the content of nitrogen is 0.18%, and the ash content is 2.7×10-4 %; Fraction A is distilled through a vacuum distillation tower, with the top temperature controlled at 290°C, the bottom temperature controlled at 400°C, and the vacuum degree controlled at 0.09 MPa, and fraction C is obtained from the side of the tower; Fraction A is subjected to fixed-bed catalytic hydrogenation to obtain fraction B, with the reaction temperature being 440°C. The quinoline insoluble matter content of fraction B is 0.005%, the toluene insoluble matter content is 0.76%, and the content of fractions below 500°C is 91.6%; Fraction B is distilled through a vacuum distillation tower, The top temperature of the tower was controlled at 120°C, the bottom temperature was controlled at 320°C, and the vacuum degree was controlled at 0.09 MPa. Distillate oil D was obtained from the side line of the tower. Distillate oil A was subjected to a vacuum distillation tower with the top temperature controlled at 290°C, the bottom temperature controlled at 420°C, and the vacuum degree controlled at 0.09 MPa. Distillate oil E was obtained from the side line of the tower. Distillate oil E was passed through a polymerization reactor for asphaltification reaction. First, the reactor was replaced with high-purity nitrogen to an initial pressure of 0.05 MPa, and the pressure was increased by self-pressure. Then, the temperature was increased from room temperature to 380°C at a rate of 5°C / min, and the temperature was kept constant for 6 hours. The final pressure in the reactor was maintained at 0.8 MPa to obtain refined asphalt. The softening point of the refined asphalt was 60°C, the toluene insoluble content was 9.5%, the quinoline insoluble content was 0.038%, the sulfur content was 0.215%, the nitrogen content was 0.175%, and the ash content was 2.6×10 -4 %; Distillate C and distillate D were mixed with refined asphalt in a mass ratio of 1:2:4 and then introduced into a polymerization reactor. The reactor was replaced with high-purity nitrogen to an initial pressure of 0.05 MPa. The reactor was pressurized and then heated from room temperature to 420°C at a rate of 3°C / min. The reactor was kept at a constant temperature for 6 hours, and the final pressure in the reactor was maintained at 0.6 MPa to obtain a nuclear-grade asphalt precursor. The softening point of the nuclear-grade asphalt precursor was 150°C, the toluene-insoluble matter content was 30.6%, the quinoline-insoluble matter content was 0.003%, the sulfur content was 0.23%, the nitrogen content was 0.18%, the ash content was 0.08%, and the neutron-absorbing impurities were 1.1 ppm. The nuclear-grade asphalt precursor was extracted to obtain a soluble phase, and the soluble phase was then recovered by vacuum distillation to obtain nuclear-grade asphalt. The extracting liquid was quinoline, the extraction temperature was 238°C, and the extraction time was 2 hours. The softening point of the nuclear-grade asphalt was 140°C, the toluene-insoluble matter content was 28.9%, the quinoline-insoluble content was 0.0021%, the coking value was 63.6%, the sulfur content was 0.23%, the nitrogen content was 0.18%, and the ash content was 2.9×10 -4 %, and the neutron absorption impurities were 1.1ppm; the nuclear-grade pitch was passed through a thin film evaporator to remove the light components before 280°C to obtain the impregnating agent pitch for nuclear graphite. The softening point of the impregnating agent pitch for nuclear graphite was 180°C, the toluene insoluble matter content was 34.2%, the quinoline insoluble matter content was 0.0017%, the coking value was 64.2%, the sulfur content was 0.23%, the nitrogen content was 0.18%, and the ash content was 2.7×10 -4The performance of the nuclear-grade asphalt prepared in Example 5 has met the requirements for use as an impregnating agent for nuclear graphite of the present invention. After the nuclear-grade asphalt is further treated by a thin film evaporator, the performance index of the impregnating agent for nuclear graphite obtained is even better, and the application performance will be even better.

Claims

1. A method for preparing an impregnating pitch for nuclear graphite, characterized in that: The method comprises the following steps: 1) The raw oil is subjected to solid-liquid separation and distillation processes to obtain a hydrogenation precursor; 2) subjecting the hydrogenated precursor obtained in step 1) to a multi-stage serial hydrogenation and impurity removal process to obtain distillate oil A; wherein the reaction temperature of the first stage of the multi-stage serial hydrogenation and impurity removal process is 180-320° C., and the reaction temperature of the second stage or more than the second stage is 220-400° C.; 3) distilling the distillate oil A obtained in step 2) under reduced pressure to obtain distillate oil C; 4) The distillate oil A obtained in step 2) is subjected to a hydrocatalytic cracking process to obtain distillate oil B; the hydrocatalytic cracking reaction temperature is 280-440°C; 5) distilling the distillate oil B obtained in step 4) under reduced pressure to obtain distillate oil D; 6) distilling the fraction A obtained in step 2) under reduced pressure to obtain fraction E, and then subjecting the fraction E to asphaltification to obtain refined asphalt; 7) mixing the distillate oil C obtained in step 3) and the distillate oil D obtained in step 5) with the refined asphalt obtained in step 6), and subjecting the mixture to pressurized thermal polymerization to obtain a nuclear-grade asphalt precursor; the thermal polymerization conditions are inert gas displacement protection, an initial pressure after displacement of 0.01-0.5 MPa, a final reaction pressure of 0.5-2.0 MPa, a reaction temperature of 300-450° C., a constant temperature time of 0.5-10 h, and a heating rate of 0.5-5° C. / min; 8) extracting the nuclear-grade asphalt precursor obtained in step 7) to obtain nuclear-grade asphalt; 9) Based on the process specifications of nuclear-grade asphalt, the nuclear-grade asphalt is directly used as an impregnating asphalt for nuclear graphite, or the nuclear-grade asphalt obtained in step 8) is subjected to a component cutting process to remove light components to obtain an impregnating asphalt for nuclear graphite; In the above step 7), the mass ratio of distillate oil C: distillate oil D: refined asphalt is 1-10:1-10:1-10; The nuclear-grade asphalt precursor has a softening point of 80-220°C, a toluene-insoluble matter content ≥15%, a quinoline-insoluble matter content ≤0.01%, a sulfur content <0.3%, a nitrogen content <0.3%, an ash content <0.5%, and neutron-absorbing impurities <2ppm.

2. The method for preparing an impregnating pitch for nuclear graphite according to claim 1, wherein: In the above step 1), the raw oil is one of medium-low temperature coal tar, high temperature coal tar, petroleum residue or catalytic cracking slurry; The solid-liquid separation is one of centrifugal separation, filter press separation or sedimentation separation; The distillation process conditions are as follows: the tower bottom temperature is controlled at 220-340°C, the tower top temperature is controlled at 130-230°C, and the vacuum degree is controlled at 0.01-0.09 MPa; The density of the hydrogenated precursor at 20°C is 0.9-1.1 g / cm 3 , the content of oxygen-containing compounds in the form of phenol and its derivatives is ≤1%, the content of fractions above 350°C is ≤60%, and the content of quinoline insoluble matter is ≤0.03%.

3. The method for preparing an impregnating pitch for nuclear graphite according to claim 1, characterized in that: The multi-stage series hydrogenation impurity removal process in step 2) is a fluidized bed, fluidized bed or fixed bed multi-stage series hydrogenation impurity removal process, and the density of distillate oil A at 20°C is 0.88~1.0g / cm 3 , the content of fractions below 350℃ is ≥60%; the content of fractions below 500℃ is ≥95%; the content of quinoline insoluble matter is ≤0.01%; the content of toluene insoluble matter is ≤1%; the content of sulfur is <0.3%; the content of nitrogen is <0.3%; the content of ash is <4.0×10 -4 %.

4. The method for preparing an impregnating pitch for nuclear graphite according to claim 1, characterized in that: The distillate oil C in the above step 3) is the 350-440° C. distillation range oil of the distillate oil A cut by vacuum distillation.

5. The method for preparing an impregnating pitch for nuclear graphite according to claim 1, characterized in that: The hydrocatalytic cracking process in step 4) is fixed-bed catalytic hydrogenation; The distillate oil B has a content of fractions below 500° C. of ≥90%; a content of quinoline insoluble matter of ≤0.01%; and a content of toluene insoluble matter of ≤1%.

6. The method for preparing an impregnating pitch for nuclear graphite according to claim 1, characterized in that: The distillate oil D in the above step 5) is the oil in the distillation range of 160-370° C. cut from the distillate oil B by vacuum distillation.

7. The method for preparing an impregnating pitch for nuclear graphite according to claim 1, characterized in that: The distillate oil E in the above step 6) is the 350-500°C distillate oil cut from the distillate oil A by vacuum distillation; The asphaltification reaction adopts inert gas replacement protection. The initial pressure after replacement is 0.01~0.5MPa, the final reaction pressure is 0.3~2.0MPa, the reaction temperature is 260~400℃, the constant temperature time is 0.5~10h, and the heating rate is 0.5~5℃ / min. The refined asphalt has a softening point of 20-80°C, a toluene insoluble matter content of 0.5-12%, a quinoline insoluble matter content ≤0.05%, a sulfur content <0.3%, a nitrogen content <0.3%, and an ash content <4.0×10 -4 %.

8. The method for preparing an impregnating pitch for nuclear graphite according to claim 1, characterized in that: In the above step 8), the extraction process is an extraction and separation process; The softening point of the nuclear grade asphalt is 60-180°C, the toluene insoluble matter content is 8-45%, the quinoline insoluble matter content is ≤0.01%, the sulfur content is <0.3%, the nitrogen content is <0.3%, and the ash content is <4.0×10 -4 %, neutron absorbing impurities <2ppm.

9. An impregnating pitch for nuclear graphite prepared by the method for preparing an impregnating pitch for nuclear graphite according to any one of claims 1 to 8, characterized in that: The softening point is 120~240℃, the toluene insoluble matter content is ≥25%, the quinoline insoluble matter content is ≤0.01%, the coking value is ≥57%, the sulfur content is <0.3%, the nitrogen content is <0.3%, and the ash content is <4.0×10 -4 %, neutron absorbing impurities <2ppm.