A method for processing coal tar feedstock

Abstract

This invention discloses a method for processing coal tar raw materials, the method comprising the following steps: (1) pre-reacting the coal tar raw materials with alkali metals, wherein the water content in the coal tar raw materials is 0.8%~3.2% based on the weight of the coal tar; (2) mixing the pre-reacted material from step (1) with the alkali metals again for further reaction; (3) subjecting the mixture obtained after the reaction in step (2) to a solid-liquid separation unit to obtain the final coal tar. This method can solve the problems of complex processes, low liquid yield, high energy consumption, and equipment corrosion in existing technologies.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of coal chemical industry, and relates to a coal tar raw material pretreatment method, in particular to a method for treating full-range coal tar raw material by using an external pretreatment agent. BACKGROUND

[0002] Coal tar is a liquid product obtained in the process of coal dry distillation and gasification, and is a black viscous liquid at room temperature, mainly composed of polycyclic aromatic compounds. Coal tar is extremely complex in composition and difficult to process. In the traditional treatment method, phenolic oil and naphthalene are extracted by heat separation, and the remaining components are burned as heavy fuel oil, which causes serious environmental pollution and waste of resources.

[0003] In recent years, with the decrease of conventional oil resources and the increasing demand for clean fuel oil, coal tar hydrogenation to prepare clean fuel oil has attracted much attention, especially in Shaanxi, Inner Mongolia and Xinjiang, and coal tar hydrogenation technology has developed rapidly. Coal tar hydrogenation technology can be roughly divided into: coal tar cutting fraction fixed bed hydrogenation, coal tar full-range suspension bed / boiling bed hydrogenation technology. However, no matter what kind of technology, the coal tar needs to be pretreated before hydrogenation treatment.

[0004] The coal tar feedstock has high impurity content. A large amount of mechanical impurities and water are generated during the dry distillation and condensation of coal. The coal tar, as a byproduct of coal dry distillation, has high content of aromatic hydrocarbons, especially condensed ring aromatic hydrocarbons, mainly in the form of gum and asphaltene. The mechanical impurities in the coal tar mainly include coal powder, coke powder and pyrolysis carbon, etc. These substances have small particles and high content, and generally need to be removed by centrifugal treatment or static sedimentation, etc. However, the removal efficiency is not high, especially the particles smaller than 50 μm, which are difficult to remove. These small particles that are not removed will enter the catalyst bed with the stream, causing the bed void to be blocked, resulting in rapid increase of bed pressure drop and shortening of the operation cycle of the device. More than 90% of the metals in the coal tar feedstock are enriched in the heavy components of the coal tar. The heavy components carrying a large amount of metals enter the fixed bed hydrogenation reactor, which on the one hand is easy to form a scale layer at the top of the catalyst bed, causing the bed pressure drop to rise, and on the other hand, the heavy components are easy to carbonize on the surface of the catalyst, blocking the pores of the catalyst, causing the catalyst to be carbonized and deactivated. At present, the general pretreatment method for coal tar full-range feedstock is to set up pre-distillation and delayed coking, which can obtain purified coal tar feedstock by discarding 10% to 30% of the heavy components or converting the heavy components into low-value coke. However, both pretreatment processes have problems such as high energy consumption and low resource utilization rate. In addition, the coal tar feedstock usually contains about 3% of free water, which can seriously affect the stability of the device operation and the performance of the catalyst. Therefore, the coal tar pretreatment needs to be dehydrated to reduce the water content to below 300 μg / g to 500 μg / g. Dehydration is usually carried out by atmospheric dehydration, negative pressure dehydration, etc. Conventional dehydration has problems such as high energy consumption, high dehydration temperature, easy to cause coal tar coking, etc. In addition, the naphthenic acid, fatty acid and phenolic substances contained in the coal tar feedstock can cause corrosion of the equipment, which needs to be solved on the industrial device.

[0005] Patent CN105505453A introduces a method for removing water and metals from coal tar. Specifically, it discloses a method for removing water and metals from coal tar. The method includes the following steps in sequence: heating treatment, first agent addition and mixing, first stage solid-liquid separation, second agent addition and mixing, and second stage solid-liquid separation. The invention adds special additives to coal tar containing a large amount of impurities, and mixes them moderately, so that the impurities collide and coalesce with each other. Then, two-stage effective separation is carried out by using solid-liquid separation equipment, so as to obtain purified coal tar. The process flow is relatively complex, and the additive is mainly an acid, which causes the loss of heavy components such as asphaltene while removing metals.

[0006] In summary, under the "double carbon" target, it is necessary to consider how to maximize energy saving, reduce consumption, improve resource utilization rate and reduce equipment corrosion in the coal tar pretreatment process. Therefore, it is necessary to develop a new type of efficient coal tar full-range pretreatment technology, which can improve the liquid yield, purify the coal tar feedstock, provide high-quality raw materials for the downstream process, and reduce the corrosion of the equipment. SUMMARY

[0007] In view of the problems of complex process, low liquid yield, high energy consumption and corrosion equipment in the existing coal tar full-range feedstock pretreatment technology, the application provides a method for treating coal tar raw material. The application utilizes special additives to remove impurities such as metal, water and acidic substances in the coal tar raw material, maximizes the liquid yield, provides high-quality coal tar raw material for the downstream, and realizes efficient utilization of coal tar resources and long-period operation of subsequent processing devices.

[0008] The application provides a method for treating coal tar raw material, which comprises the following steps:

[0009] (1) The coal tar raw material is contacted with alkali metal for pre-reaction, and the mass content of water in the coal tar raw material is 0.8% to 3.2%, preferably 1.0% to 2.5%, and further preferably 1.2% to 2.0%, based on the weight of the coal tar;

[0010] (2) The material pre-reacted in step (1) is mixed with alkali metal again for reaction;

[0011] (3) The mixture obtained after the reaction in step (2) is subjected to a solid-liquid separation unit to obtain the final coal tar.

[0012] In the method, the mass ratio of the alkali metal used in step (1) to the alkali metal used in step (2) is 0.5 to 10:1, preferably 1 to 6:1, and further preferably 1.5 to 5:1.

[0013] In the method, the mechanical impurities in the coal tar raw material are 0.05% to 0.42%, preferably 0.08% to 0.30%, and further preferably 0.10% to 0.20%; the mechanical impurities include coke powder, pyrolysis carbon, coal powder and metal oxides such as iron oxide generated in the pyrolysis process.

[0014] In the method, the coal tar in step (1) is full-range coal tar, and the properties of the full-range coal tar are as follows: density 0.9800 g / ml to 1.0378 g / ml, sulfur 2000 μg / g to 5000 μg / g, and nitrogen 5000 μg / g to 10000 μg / g.

[0015] In the method, the alkali metal in step (1) is one or more of Li, Na, K, Ru, Cs and Fr.

[0016] In the method, the mass ratio of the alkali metal in step (1) to the coal tar raw material is 0.5 to 10:100, and preferably 1 to 5:100.

[0017] In the method, the alkali metal in step (1) is added to the coal tar raw material in a sealed condition in a solid or liquid form.

[0018] In the method, the alkali metal in step (1) is mixed with a solvent and then added to the coal tar raw material. The solvent is one or a mixture of several of naphtha, diesel oil, kerosene, wax oil and heavy oil, and the solvent can be derived from a petroleum-based raw material or a coal-based raw material. The mass ratio of the solvent to the alkali metal is 2:1 to 10:1, and preferably 3:1 to 8:1. The scheme of mixing the alkali metal with the solvent can further improve the reaction effect.

[0019] In the embodiment of the application, one non-limiting mixing process of the alkali metal and the solvent is as follows: the alkali metal and the solvent are mixed in a mixing device in a proper proportion, and are fully mixed and uniformly distributed. The operating conditions of the stirring in the mixing device are as follows: the rotating speed is 600 r / m to 3000 r / m, the stirring time is 10 min to 60 min, and the corresponding temperature of the mixture during stirring is 20℃ to 150℃; preferably, the rotating speed is 1000 r / m to 2500 r / m, the stirring time is 15 min to 40 min, and the corresponding temperature of the mixture during stirring is 40℃ to 110℃.

[0020] The mixing device can be a static mixer or a tank containing a static mixer. The static mixer can be one or several of an SV type static mixer, an SX type static mixer, an SL type static mixer, an SH type static mixer and an SK type static mixer. The static mixer mainly changes the shape and cross-sectional area of the fluid, and simultaneously makes the fluid rotate, so as to fully mix different fluids.

[0021] In the method, the coal tar raw material in step (1) can be mixed with the alkali metal in a batch reactor or a continuous reactor, and can be a kettle type reaction device or a pipe type reaction device.

[0022] In the method, the operating conditions of the reaction of the coal tar raw material with the alkali metal in step (1) are as follows: the reaction temperature is 80℃ to 180℃, the hydrogen partial pressure is 1.0 to 5.0 MPa, the reaction time or residence time is 5 min to 15 min, and the hydrogen / oil volume ratio is 50:1 to 400:1; and preferably, the reaction temperature is 90℃ to 120℃, the hydrogen partial pressure is 2.0 to 4.0 MPa, the reaction time or residence time is 6 min to 12 min, and the hydrogen / oil volume ratio is 80:1 to 200:1.

[0023] In the method, the alkali metal in step (2) is added to the coal tar pre-reacted in step (1) in a sealed condition in a solid or liquid form.

[0024] In the method, the alkali metal is mixed with the solvent and then added to the coal tar after pre-reaction in step (1). The solvent is one or a mixture of several of naphtha, diesel, kerosene, wax oil and heavy oil, which can be derived from petroleum-based raw materials or coal-based raw materials. The mass ratio of the solvent to the alkali metal is 2:1 to 10:1, preferably 3:1 to 8:1. The scheme of mixing the alkali metal with the solvent can further improve the reaction effect.

[0025] In the method, the operation conditions for adding the alkali metal for reaction in step (2) are as follows: reaction temperature: 140-300℃, hydrogen partial pressure: 4.0-10.0 MPa, reaction time or residence time: 5-60 min, hydrogen to oil volume ratio: 50:1-400:1, and preferred operation conditions: reaction temperature: 180-250℃, hydrogen partial pressure: 5.0-8.0 MPa, reaction time or residence time: 10-40 min, hydrogen to oil volume ratio: 80:1-200:1.

[0026] In the method, the solid impurities in step (3) are separated by using the principle that the density of the reaction generated metal sulfide, the gathered mechanical impurities and the attached elemental metal is different from that of the coal tar.

[0027] In step (3), the material desolidification can be carried out by one or several of centrifugal desolidification, static sedimentation separation, electric field purification, chemical separation, solvent extraction and cyclone separation; preferably, the mechanical separation method is used, and further preferably, the centrifugal separation method is used.

[0028] Compared with the prior art, the method for treating coal tar raw materials has the following advantages:

[0029] 1. In the coal tar raw material of the present application, appropriate water is retained, and a proper amount of alkali metal reacts with water in the coal tar to produce part of active hydrogen while removing water; at the same time, part of the alkali substance can react with the original acidic substance in the coal tar to improve the acid-base degree of the system, which is beneficial to the uniform dispersion of the subsequently added alkali metal and improves the reaction efficiency.

[0030] 2. The method can efficiently remove the metal and S impurities in the coal tar raw material by using the high reactivity of the alkali metal; at the same time, the method takes advantage of the characteristics of the coal tar raw material that the original mechanical impurities are more, and the existence of the micron-sized coal powder provides a carrier for the efficient dispersion of the alkali metal; the metal sulfide produced by the reaction and the removed elemental metal can be attached to the coal powder, avoiding the deposition on the reactor wall, and providing convenient conditions for the next solid-liquid separation.

[0031] 3, The coal tar full fraction raw material pretreatment technology disclosed by the application has good coal tar raw material purification effect, low impurity removal rate and high liquid yield. More than 80% of the sulfur in the coal tar raw material, more than 85% of the metal, 100% of the clear water, acidic substances and most of the solid particles are removed, the liquid yield reaches more than 97%, and the obtained coal tar raw material has excellent properties and can meet the feeding requirements of downstream fixed bed hydrogenation, ebullated bed hydrogenation and other hydrogenation devices.

[0032] 4, The technology reduces the requirement for water removal from the coal tar, avoids the problems of coal tar coking and high energy consumption caused by high heating temperature in the deep dewatering process of the traditional coal tar pretreatment technology, improves the stability of the pretreatment device operation, and reduces the energy consumption. DETAILED DESCRIPTION

[0033] The application will be further described below through specific embodiments, but the protection scope of the application is not limited. In the context of the application, "% " is the mass percentage unless otherwise specified.

[0034] The coal tar raw material properties disclosed by the application are shown in Table 1, the alkali metal used is sodium, and the solvent used is coal-based diesel oil, and the reaction results are shown in Table 2.

[0035] In the method for treating the coal tar raw material disclosed by the application, the coal tar raw material is reacted with the alkali metal in steps, the obtained material after the reaction is subjected to liquid-solid separation by a centrifuge, and finally the coal tar is obtained, the coal tar is used as a downstream deep processing raw material, the solid insoluble substance is used as heavy fuel, and the metal therein is recovered. A three-phase horizontal screw centrifuge is used for solid-liquid treatment, the centrifuge speed is 3000 r / m, the centrifugation time is 30 min, and the centrifugation temperature is 80℃.

[0036] Example 1

[0037] The low-temperature coal tar corresponding to Example 1 in Table 1 is used as the raw material, and the method for treating the coal tar raw material disclosed by the application is used. The sodium metal is directly added to the coal tar raw material for pre-reaction, and the mixing mass ratio of the sodium metal and the coal tar raw material is 1:100, and the reaction conditions are as follows: reaction temperature: 90℃, hydrogen partial pressure: 2.0 MPa, reaction time: 6 min, hydrogen / oil volume ratio: 80:1; after the reaction, the sodium metal is continuously added for reaction, and the mass ratio of the sodium metal in step (1) to the sodium metal in step (2) is 5:1, and the reaction conditions are as follows: reaction temperature: 180℃, hydrogen partial pressure: 5.0 MPa, reaction time: 10 min, hydrogen / oil volume ratio: 80:1. After the reaction, the material is subjected to centrifugal treatment by a centrifuge to obtain the final coal tar.

[0038] Example 2

[0039] The low-temperature coal tar corresponding to Example 2 in Table 1 is used as a raw material, and the method for treating the coal tar raw material is used. Sodium metal is directly added to the coal tar raw material for pre-reaction, and the mass ratio of sodium metal to the coal tar raw material is 2.5:100. The reaction conditions are as follows: the reaction temperature is 105°C, the hydrogen partial pressure is 3.0 MPa, the reaction time is 9 min, and the hydrogen / oil volume ratio is 140:1. After the reaction is completed, sodium metal is continuously added for reaction. The mass ratio of sodium metal in step (1) to sodium metal in step (2) is 3:1. The reaction conditions are as follows: the reaction temperature is 215°C, the hydrogen partial pressure is 6.5 MPa, the reaction time is 25 min, and the hydrogen / oil volume ratio is 140:1. After the reaction, the material is centrifuged to obtain the final coal tar.

[0040] Example 3

[0041] The low-temperature coal tar corresponding to Example 3 in Table 1 is used as a raw material, and the method for treating the coal tar raw material is used. Sodium metal is directly added to the coal tar raw material for pre-reaction, and the mass ratio of sodium metal to the coal tar raw material is 5:100. The reaction conditions are as follows: the reaction temperature is 120°C, the hydrogen partial pressure is 4.0 MPa, the reaction time is 12 min, and the hydrogen / oil volume ratio is 200:1. After the reaction is completed, sodium metal is continuously added for reaction. The mass ratio of sodium metal in step (1) to sodium metal in step (2) is 1.5:1. The reaction conditions are as follows: the reaction temperature is 250°C, the hydrogen partial pressure is 8.0 MPa, the reaction time is 40 min, and the hydrogen / oil volume ratio is 200:1. After the reaction, the material is centrifuged to obtain the final coal tar.

[0042] Example 4

[0043] The low-temperature coal tar corresponding to Example 1 in Table 1 is used as a raw material, and the method for treating the coal tar raw material is used. First, sodium metal and coal-based diesel are mixed in a mixer at a mass ratio of 1:3, the stirring speed is 1000 r / m, the stirring time is 15 min, and the stirring temperature is 40°C to obtain a mixed slurry of sodium metal and coal-based diesel. The mixed slurry is added to the coal tar raw material for pre-reaction at a mass ratio of 1:100. The reaction conditions are as follows: the reaction temperature is 90°C, the hydrogen partial pressure is 2.0 MPa, the reaction time or residence time is 6 min, and the hydrogen / oil volume ratio is 80:1. The slurry is continuously added to the material for reaction. The reaction conditions are as follows: the reaction temperature is 180°C, the hydrogen partial pressure is 5.0 MPa, the reaction time or residence time is 10 min, the hydrogen / oil volume ratio is 80:1, and the mass ratio of sodium metal introduced in the first step to sodium metal introduced in the second step is 5:1. After the reaction, the material is centrifuged to obtain the final coal tar.

[0044] Example 5

[0045] The medium-low temperature coal tar corresponding to example 2 listed in table 1 is used as raw material, and the method for treating coal tar raw material is used. First, the metal sodium and the coal-based diesel are mixed in a mixer at a mass ratio of 1:6, the stirring speed is 1800 r / m, the stirring time is 27 min, and the stirring temperature is 75 DEG C, to obtain a mixed slurry of metal sodium and coal-based diesel. The mixed slurry is added to the coal tar raw material for pre-reaction at a mass ratio of 2.5:100 of alkali metal to coal tar raw material, and the reaction conditions are as follows: the reaction temperature is 105 DEG C, the hydrogen partial pressure is 3.0 MPa, the reaction time or residence time is 9 min, and the hydrogen oil volume ratio is 140:1. The slurry mixture is continuously added for reaction, and the reaction conditions are as follows: the reaction temperature is 215 DEG C, the hydrogen partial pressure is 6.5 MPa, the reaction time or residence time is 25 min, and the hydrogen oil volume ratio is 140:1. The mass ratio of the metal sodium introduced before and after is 2.5:1. After the reaction, the material is treated by centrifugation to obtain the final coal tar.

[0046] Example 6

[0047] The medium-low temperature coal tar corresponding to example 3 listed in table 1 is used as raw material, and the method for treating coal tar raw material is used. First, the metal sodium and the coal-based diesel are mixed in a mixer at a mass ratio of 1:8, the stirring speed is 2500 r / m, the stirring time is 40 min, and the stirring temperature is 110 DEG C, to obtain a mixed slurry of metal sodium and coal-based diesel. The mixed slurry is added to the coal tar raw material for pre-reaction at a mass ratio of 5:100 of alkali metal to coal tar raw material, and the reaction conditions are as follows: 120 DEG C, hydrogen partial pressure: 4.0 MPa, reaction time: 12 min, hydrogen oil volume ratio: 200:1; the slurry mixture is continuously added for reaction, and the reaction conditions are as follows: reaction temperature: 250 DEG C, hydrogen partial pressure: 8.0 MPa, reaction time: 40 min, hydrogen oil volume ratio: 200:1, the mass ratio of the metal sodium introduced before and after is 1.5:1. After the reaction, the material is treated by centrifugation to obtain the final coal tar.

[0048] Comparative example 1

[0049] The same as example 1, except that the pretreatment technology introduced in patent CN201610028928 is used to treat the whole fraction of coal tar raw material. The raw material is heated to 150 DEG C, the X additive is added at an amount of 2500 ppm, the binary carboxylic acid accounts for 50%, and the organic phosphoric acid accounts for 50%, the material is mixed fully by stirring for 45 min; then solid-liquid separation is carried out, the Y additive is added at an amount of 1200 ppm, the diol polymer accounts for 60%, and the quaternary ammonium salt accounts for 40%, stirring is carried out for 20 min, and secondary solid-liquid separation is carried out, to obtain the purified coal tar, and the reaction results are shown in table 2.

[0050] Comparative example 2

[0051] The same as example 1, except that the pretreatment technology introduced in patent CN201610028928 is used to treat the coal tar full fraction raw material. The raw material is heated to 150 DEG C, and X additive is added in an amount of 1500 ppm, wherein dicarboxylic acid accounts for 40%, and organic phosphoric acid accounts for 60%, and the material is mixed fully by stirring for 30 minutes; then solid-liquid separation is carried out, Y additive is added in an amount of 1000 ppm, diglycol polymer accounts for 60%, and quaternary ammonium salt accounts for 45%, stirring is carried out for 20 minutes, and secondary solid-liquid separation is carried out, to obtain purified coal tar, and the reaction results are shown in Table 2.

[0052] Table 1

[0053]

[0054] Table 2

[0055]

[0056] Through the comparative analysis of the above description and examples and comparative examples, it is found that after the coal tar raw material is treated by using the coal tar full fraction pretreatment technology recommended by the patent, whether from the density, carbon residue, asphaltene and water content of the purified coal tar, or from the S and metal content and other impurities, the properties of the purified coal tar treated by the patent are greatly improved, and the patent has obvious technical advantages, and the device has a longer running period, and is an important treatment means for realizing the efficient conversion of unconventional resources such as coal tar.

Claims

1. A method of processing a coal tar feedstock, characterized by: The method comprises the following steps: (1) the coal tar raw material is contacted with alkali metal for pre-reaction, the mass content of water in the coal tar raw material is 0.8%~3.2% based on the weight of coal tar; (2) the pre-reaction material in step (1) is mixed with alkali metal again for reaction; (3) the mixture obtained after the reaction in step (2) is subjected to solid-liquid separation to obtain the final coal tar; In step (1), the mass ratio of the alkali metal used in step (1) to the alkali metal used in step (2) is 0.5~10:1; the pre-reaction operation conditions of the coal tar raw material with alkali metal in step (1) are as follows: reaction temperature: 80℃~180℃, hydrogen partial pressure: 1.0~5.0MPa, reaction time or residence time 5min~15min, hydrogen oil volume ratio 50:1~400:1; the reaction operation conditions of the pre-reaction material with alkali metal in step (2) are as follows: reaction temperature: 140℃~300℃, hydrogen partial pressure: 4.0~10.0MPa, reaction time or residence time 5min~60min, hydrogen oil volume ratio 50:1~400:

1.

2. The method of claim 1, wherein: In step (1), the mass content of water in the coal tar raw material is 1.0%~2.5% based on the weight of coal tar; the mass ratio of the alkali metal used in step (1) to the alkali metal used in step (2) is 1~6:

1.

3. The method of claim 2, wherein: In step (1), the mass content of water in the coal tar raw material is 1.2%~2.0% based on the weight of coal tar; the mass ratio of the alkali metal used in step (1) to the alkali metal used in step (2) is 1.5~5:

1.

4. The method of claim 1, wherein: In step (1), the mechanical impurities in the coal tar raw material are 0.05wt%~0.42wt%.

5. The method of claim 1, wherein: In step (1), the coal tar is full-range coal tar, and the properties of the full-range coal tar are as follows: density at 20℃ 0.9800g / ml~1.0378g / ml, sulfur 2000μg / g~5000μg / g, nitrogen 5000μg / g~10000μg / g.

6. The method of claim 1, wherein: In step (1), the alkali metal is one or more of Li, Na and K.

7. The method of claim 1, wherein: In step (1), the mass ratio of the alkali metal to the coal tar raw material is 0.5~10:100 based on the elemental substance.

8. The method of claim 1, wherein: In step (1), the alkali metal is mixed with a solvent before being added to the coal tar raw material, the solvent is a mixture of one or more of naphtha, diesel oil, kerosene, wax oil and heavy oil, and the mass ratio of the solvent to the alkali metal is 2:1~10:

1.

9. The method of claim 1, wherein: In step (1), the pre-reaction operation conditions of the coal tar raw material with alkali metal are as follows: reaction temperature: 90℃~120℃, hydrogen partial pressure: 2.0~4.0MPa, reaction time or residence time 6min~12min, hydrogen oil volume ratio 80:1~200:

1.

10. The method of claim 1, wherein: In step (2), the reaction operation conditions of the pre-reaction material with alkali metal are as follows: reaction temperature: 180℃~250℃, hydrogen partial pressure: 5.0~8.0MPa, reaction time or residence time 10min~40min, hydrogen oil volume ratio 80:1~200:

1.

11. The method of claim 1, wherein: In step (3), the solid-liquid separation is performed by one or more of centrifugal separation, static sedimentation separation, electric field purification, solvent extraction, and cyclone separation.

12. The method of claim 1, wherein: In step (3), the solid-liquid separation is performed by chemical separation.

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