A coal tar pretreatment process

Abstract

The present invention provides a coal tar pretreatment process, which comprises the following contents: (1) pretreating the coal tar raw material, controlling the mass content of mechanical impurities in the pretreated coal tar to be 0.05% to 0.35% based on the weight of the coal tar, and controlling the water content to be 0.1% to 1.0%; (2) mixing the coal tar obtained after the pretreatment in step (1) with an alkali metal for reaction; (3) desolidifying the material after the reaction in step (2) to obtain the final coal tar. The method of the present invention can remove impurities such as metals from the coal tar raw material, while maximizing the liquid recovery, providing high-quality purified coal tar raw materials for the downstream, realizing efficient utilization of coal tar resources and long-term operation of subsequent processing equipment.

Description

Technical Field

[0001] The invention belongs to the field of coal chemical industry and relates to a coal tar pretreatment process, in particular to a pretreatment process which uses a full fraction of coal tar as a raw material and utilizes an external pretreatment agent to purify the full fraction of coal tar. Background Art

[0002] Coal tar is a liquid product obtained during coal distillation and gasification. At room temperature, coal tar is a black viscous liquid with a high density. It is mainly composed of polycyclic aromatic compounds. The composition of coal tar is extremely complex, and more than 500 species have been isolated and identified.

[0003] In recent years, with the reduction of conventional oil resources and the increasing demand for clean fuel oil, coal tar hydrogenation to prepare clean fuel oil has attracted much attention as a substitute for petrochemicals, and coal tar hydrogenation technology has made significant progress. In summary, it can be roughly summarized as: coal tar hydrorefining / hydroprocessing technology, delayed coking-hydrocracking combined process technology, coal tar fixed bed hydrocracking technology, coal tar suspended bed / ebullated bed / slurry bed hydrocracking technology.

[0004] Coal tar contains 1wt% to 3wt% mechanical impurities and moisture during the distillation and collection process. Coal tar contains a high content of aromatic hydrocarbons, especially polycyclic aromatic hydrocarbons, which mainly exist in the form of colloids and asphaltene. The mechanical impurities in coal tar are mainly coal powder, coke powder and pyrolytic carbon. These substances are small in particle size and high in content. They generally need to be removed by centrifugal treatment or static sedimentation, but the removal efficiency is not high. The current centrifuge mainly removes large particles larger than 50μm, and it is difficult to remove particles smaller than 50μm. Once these unremoved fine particles enter the fixed bed hydrogenation reactor, they are easy to deposit in the gaps of the catalyst bed, causing the bed pressure drop to increase rapidly and shortening the operation cycle of the device. The heavy components in coal tar are enriched with more than 90% of the metals in the coal tar raw materials. After entering the fixed bed hydrogenation reactor, the heavy components containing a large amount of metals are easy to form a scale layer on the top of the catalyst bed, which also causes the bed pressure drop to increase. The heavy components are easy to accumulate carbon on the catalyst surface, blocking the catalyst pores, causing the catalyst to be carbonized and deactivated. At present, the common pretreatment method for coal tar full-fraction raw materials is to set up pre-distillation and delayed coking. The purified coal tar raw materials are obtained by discarding 10%~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.

[0005] Patent CN105505453A introduces a method for anhydrous demetallization of coal tar, specifically discloses a

[0006] A method for anhydrous desalting and demetallizing of coal tar. The method comprises: 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 a special auxiliary agent to the coal tar containing a large amount of impurities, and stirs and mixes appropriately to make the impurities collide and agglomerate with each other, and then uses a solid-liquid separation device to perform two-stage effective separation, thereby obtaining purified coal tar. The process of this method is relatively complicated, and the auxiliary agent is mainly acid, which causes the loss of heavy components such as asphaltene while removing metals.

[0007] In summary, from the perspective of energy conservation and consumption reduction and improving resource utilization, it is necessary to develop new and efficient coal tar full-fraction raw material pretreatment technology to maximize liquid recovery while removing impurities such as metals and sulfur in coal tar raw materials to provide high-quality raw materials for downstream processes. Summary of the invention

[0008] In view of the problems of complex process and low liquid yield in the existing coal tar full fraction raw material pretreatment technology, the present invention provides a coal tar full fraction pretreatment technology. The technology of the present invention uses special additives to remove impurities such as metals in coal tar raw materials, while maximizing liquid yield, providing high-quality purified coal tar raw materials for downstream, realizing efficient utilization of coal tar resources and long-term operation of subsequent processing equipment.

[0009] The present invention provides a coal tar pretreatment process, which comprises the following contents:

[0010] (1) Pretreating the coal tar raw material, controlling the mass content of mechanical impurities in the pretreated coal tar to be 0.05% to 0.35%, preferably 0.08% to 0.20%, more preferably 0.10% to 0.15% based on the weight of the coal tar; and controlling the water content to be 0.1% to 1.0%, preferably 0.2% to 0.8%, more preferably 0.3% to 0.5%;

[0011] (2) The coal tar obtained after the pretreatment in step (1) is mixed with an alkali metal to react;

[0012] (3) The material after the reaction in step (2) is desolidified to obtain the final coal tar.

[0013] In the process of the present invention, the pretreatment in step (1) is a dehydration treatment, and the dehydration treatment adopts one or more of the dehydration methods such as atmospheric pressure flash evaporation, negative pressure flash evaporation, centrifugal flash evaporation, etc. Desolidification treatment can be performed before or after the dehydration treatment, preferably, the desolidification treatment is performed first and then the dehydration treatment. The desolidification treatment is one or more of centrifugal desolidification, static sedimentation separation, electric field purification, chemical separation, solvent extraction, and cyclone separation.

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

[0015] In the process of the present invention, the alkali metal in step (2) is one or more of Li, Na, K, Ru, Cs, and Fr.

[0016] In the process of the present invention, the mass ratio of the alkali metal described in step (2) to the coal tar raw material is 0.5-10:100, preferably 1-5:100, calculated as a single substance.

[0017] In the process of the present invention, the alkali metal in step (2) is added in a solid or liquid form to the coal tar obtained after pretreatment in step (1) under sealed conditions.

[0018] In the process of the present invention, the alkali metal in step (2) is mixed with a solvent and then added to the coal tar raw material in step (1). The solvent is a mixture of one or more of naphtha, diesel, kerosene, wax oil and heavy oil, and the solvent can be derived from either 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, preferably 3:1 to 8:1. The solution of mixing the alkali metal with the solvent can further improve the reaction effect.

[0019] A non-limiting alkali metal and solvent mixing process used in the embodiment of the present invention is as follows: an appropriate proportion of alkali metal and solvent are mixed in a mixing device and fully mixed. The operating conditions of stirring in the mixing device are a rotation speed of 600r / m~3000r / m, a stirring time of 10min~60min, and a corresponding temperature of the mixture during stirring: 20℃~150℃; preferably a rotation speed of 1000r / m~2500r / m, a stirring time of 15min~40min, and a corresponding temperature of the mixture during stirring: 40℃~110℃.

[0020] The above-mentioned mixing equipment can be a static mixer, or a tank containing a static mixer. The static mixer can be one or more of SV type static mixer, SX type static mixer, SL type static mixer, SH type static mixer, and SK type static mixer. The main function of the static mixer is to change the shape and cross-sectional area of ​​the fluid, and at the same time make the fluid "rotate" to achieve the purpose of fully mixing different fluids.

[0021] In step (2) of the present invention, the coal tar obtained after the pretreatment in step (1) is mixed with the alkali metal for reaction, which can be carried out in a batch reactor or a continuous reactor, and can be a kettle reaction equipment or a tubular reaction equipment.

[0022] In step (2) of the present invention, the coal tar obtained after pretreatment in step (1) is mixed with an alkali metal for reaction under the following operating conditions: reaction temperature: 140°C to 300°C, hydrogen partial pressure: 4.0 to 10.0 MPa, reaction time or residence time: 5 min to 60 min, hydrogen to oil volume ratio: 50:1 to 400:1. The preferred operating conditions are: reaction temperature: 180°C to 250°C, hydrogen partial pressure: 5.0 to 8.0 MPa, reaction time or residence time: 10 min to 40 min, hydrogen to oil volume ratio: 80:1 to 200:1.

[0023] In step (3) of the present invention, the desolidification utilizes the difference in density between solid impurities and coal tar to separate the metal sulfides produced by the reaction, the accumulated mechanical impurities and the metal elements attached thereto.

[0024] In step (3) of the present invention, the material can be desolidified by centrifugal desolidification, static sedimentation separation, electric field purification, chemical separation, solvent extraction, cyclone separation or more. Preferably, mechanical separation is used, and more preferably, centrifugal separation is used.

[0025] Compared with the prior art, the coal tar pretreatment process of the present invention has the following advantages:

[0026] 1. The inventors surprisingly found during the research that the appropriate mechanical impurity content in coal tar is retained during the pretreatment process, and the mechanical impurities dispersed in the coal tar are used as carriers to efficiently disperse the alkali metal, thereby improving the utilization rate of the alkali metal and the reaction effect; in the material system after the reaction, the metal sulfide produced after the reaction and the removed metal element can be aggregated into large particles with the fine particles in the coal tar that are difficult to remove, providing convenient conditions for the next step of solid-liquid separation;

[0027] 2. The coal tar whole fraction raw material pretreatment technology of the present invention has mild operating conditions. The slag removal and dehydration are completed by using the currently mature technologies in the market. The removal of impurities such as metals and solid powders is completed by using specific solvents. The solvents are widely available, cheap and easy to obtain, easy to operate, and have mild conditions. Compared with traditional pretreatment technologies, the operating severity is greatly reduced.

[0028] 3. The coal tar full fraction raw material pretreatment technology of the present invention has good purification effect on coal tar raw materials, low impurity removal rate and high liquid yield. More than 80% of sulfur, more than 85% of metals and most of the solid particles in the coal tar raw materials are removed, and the liquid yield reaches more than 97%. The coal tar raw materials after purification have excellent properties and can meet the feed requirements of downstream fixed bed hydrogenation, ebullating bed hydrogenation and other hydrogenation units. DETAILED DESCRIPTION

[0029] The present invention is further described below by specific embodiments, but the protection scope of the present invention is not limited. In the present invention, "%" refers to mass percentage unless otherwise specified.

[0030] The properties of the coal tar raw materials described in the examples and comparative examples of the present invention are shown in Table 1. The alkali metal used is metallic sodium, and the solvent used is coal-based diesel.

[0031] In the pretreatment technology described in the present invention, the coal tar raw material is first centrifuged through a three-phase centrifuge or similar equipment to control the content of mechanical impurities in the treated coal tar. The coal tar after centrifugation is then dehydrated by flash evaporation at normal pressure to control the content of mechanical impurities in the treated coal tar. The desolidified and dehydrated coal tar raw material is then mixed with a prepared solvent. The mixed materials enter a reaction device for reaction to obtain treated coal tar and solid insoluble matter. The reaction is performed again by a centrifuge for liquid-solid separation to finally obtain coal tar and solid insoluble matter. The coal tar is used as a downstream deep processing raw material, and the metals therein are recovered from the solid insoluble matter.

[0032] Example 1

[0033] The medium and low temperature coal tar listed in Table 1 is used as raw material and the pretreatment technology described in the patent of the present invention is adopted.

[0034] First, the whole fraction coal tar raw material is desolidified and dehydrated. The desolidification operation conditions are centrifuge speed 3500r / min, normal pressure, centrifugal temperature 100℃, centrifugal time 10min, dehydration operation conditions are flash temperature 125℃, flash pressure normal pressure, and the mechanical impurity content of the desolidified and dehydrated coal tar is 0.10%, and the water content is 0.3%. Then, the sodium metal and coal-based diesel are crushed and mixed under the action of a shearing machine at a mass ratio of 1:3. The shearing machine speed is 1000r / min, the shearing time is 15min, and the shearing temperature is 40℃ to obtain a slurry pretreatment agent. The solvent and alkali metal mixing mass ratio is 8:1, and the mixing ratio of coal tar and sodium metal is 100:1). They are mixed evenly in a mixer, and then heated to 200℃ and pumped into the processing equipment for reaction. The operating conditions in the processing equipment are: reaction temperature: 180℃, hydrogen partial pressure: 5.0MPa, reaction time 10min, and hydrogen-oil volume ratio 80:1. Finally, a centrifuge was used to perform centrifugal deslagging treatment again to obtain purified coal tar and solid insoluble matter. The reaction results are shown in Table 2.

[0035] Example 2

[0036] The medium and low temperature coal tar listed in Table 1 is used as raw material, and the pretreatment technology described in the present invention is adopted. First, the whole fraction coal tar raw material is desolidified and dehydrated. The desolidification operation conditions are centrifuge speed 3800r / min, normal pressure, centrifugal temperature 110℃, centrifugal time 10min, and dehydration operation conditions are flash temperature 135℃, flash pressure normal pressure, and the mechanical impurity content of the coal tar after desolidification and dehydration is 0.13%, and the water content is 0.4%. Then, metallic sodium and coal-based diesel are crushed and mixed under the action of a shearing machine at a mass ratio of 1:6, with a shearing machine speed of 1800r / m, a shearing time of 25min, and a shearing temperature of 70℃ to obtain a slurry pretreatment agent. The mass ratio of the solvent to the alkali metal is 5:1, and the ratio of the coal tar to the metallic sodium is 100:2.5). The mixture is evenly mixed in a mixer, and then heated to 240°C and pumped into a treatment device for reaction. The operating conditions in the treatment device are: reaction temperature: 215°C, hydrogen partial pressure: 6.0MPa, reaction time 25min, and hydrogen-to-oil volume ratio 140:1. Finally, a centrifuge is used for centrifugal deslagging to obtain purified coal tar and solid insolubles. The reaction results are shown in Table 2.

[0037] Example 3

[0038] The medium and low temperature coal tar listed in Table 1 is used as raw material, and the pretreatment technology described in the present invention is adopted. First, the whole fraction coal tar raw material is desolidified and dehydrated. The desolidification operation conditions are 3300r / min, normal pressure, centrifugal temperature 90℃, centrifugal time 10min, and the dehydration operation conditions are flash temperature 115℃, flash pressure normal pressure, and the mechanical impurity content of the coal tar after desolidification and dehydration is 0.15% and the water content is 0.5%. Then, the metallic sodium and coal-based diesel are crushed and mixed under the action of a shearing machine at a mass ratio of 1:8, the shearing machine speed is 2500r / m, the shearing time is 40min, and the shearing temperature is 110℃ to obtain a slurry pretreatment agent. The mass ratio of the solvent to the alkali metal is 3:1, and the ratio of the coal tar to the metallic sodium is 100:5. The mixture is evenly mixed in the mixer, and then heated to 300°C and pumped into the treatment equipment for reaction. The operating conditions in the treatment equipment are: reaction temperature: 250°C, hydrogen partial pressure: 8.0MPa, reaction time 40min, and hydrogen-oil volume ratio 200:1. Finally, a centrifuge is used for centrifugal deslagging to obtain purified coal tar and solid insolubles. The reaction results are shown in Table 2.

[0039] Example 4

[0040] Example 4 The desolidification, dehydration and reaction conditions were the same as those in Example 1, except that the metallic sodium was not mixed with the solvent. During the implementation, the metal was directly mixed with the semi-purified coal tar. The mixing ratio of the metallic sodium to the coal tar raw material was 1.0:100, and the two were mixed before reacting. The reaction results are shown in Table 2.

[0041] Example 5

[0042] Example 5 The desolidification, dehydration and reaction conditions were the same as those in Example 2, except that the metallic sodium was not mixed with the solvent. During the implementation, the metal was directly mixed with the semi-purified coal tar. The mixing ratio of the metallic sodium to the coal tar raw material was 2.5:100, and the two were mixed before reacting. The reaction results are shown in Table 2.

[0043] Comparative Example 1

[0044] The method is basically the same as Example 1, except that the pretreatment technology introduced in patent CN201610028928 is used to treat the whole fraction of coal tar. The raw material is heated to 150°C, 3000ppm of X additive is added, wherein dicarboxylic acid accounts for 40% and organic phosphoric acid accounts for 60%, and the materials are stirred for 30 minutes to fully mix; then solid-liquid separation is performed, and 1000ppm of Y additive is added, wherein diol polymer accounts for 65% and quaternary ammonium salt accounts for 35%, and the mixture is stirred for 20 minutes, and secondary solid-liquid separation is performed to obtain purified coal tar. The reaction results are shown in Table 2.

[0045] Comparative Example 2

[0046] The method is basically the same as Example 1, except that the pretreatment technology introduced in patent CN201610028928 is used to treat the whole fraction of coal tar. The raw material is heated to 150°C, 2000ppm of X additive is added, wherein dicarboxylic acid accounts for 40% and organic phosphoric acid accounts for 60%, and the material is stirred for 30 minutes to fully mix the material; then solid-liquid separation is performed, and then 800ppm of Y additive is added, wherein diol polymer accounts for 65% and quaternary ammonium salt accounts for 35%, and the mixture is stirred for 20 minutes, and secondary solid-liquid separation is performed to obtain purified coal tar. The reaction results are shown in Table 2.

[0047] Table 1 Properties of full fraction coal tar raw materials

[0048]

[0049] Table 2 Reaction results

[0050]

[0051] Through the above description and comparative analysis of the embodiments and comparative examples, it is found that after the coal tar raw material is treated with the coal tar full fraction pretreatment technology recommended by the patent of the present invention, compared with the fresh coal tar raw material and the purified coal tar raw material treated by the comparative pretreatment technology, whether from the density, residual carbon, asphaltene content of the purified coal tar, or from the impurities such as S and metal content, the transportation properties of the purified coal tar treated by the patent of the present invention are greatly improved, which has obvious technical advantages and is an important treatment method for realizing the efficient conversion of unconventional resources such as coal tar.

Claims

1. A coal tar pretreatment process, characterized in that: The pretreatment process includes the following contents: (1) Pre-treating the coal tar raw material, controlling the mass content of mechanical impurities in the pre-treated coal tar to be 0.05%~0.35% based on the weight of the coal tar; and the water content to be 0.1%~1.0%; (2) The coal tar obtained after the pretreatment in step (1) is mixed with an alkali metal to react; (3) Desolidifying the materials after the reaction in step (2) to obtain final coal tar; In step (2), the coal tar obtained after pretreatment in step (1) is mixed with an alkali metal for reaction under the following operating conditions: reaction temperature: 140°C to 300°C, hydrogen partial pressure: 4.0 to 10.0 MPa, reaction time or residence time: 5 min to 60 min, and hydrogen to oil volume ratio: 50:1 to 400:

1.

2. The process according to claim 1, characterized in that: The pretreatment process includes the following contents: (1) Pre-treating the coal tar raw material, controlling the mass content of mechanical impurities in the pre-treated coal tar to be 0.08% to 0.20% based on the weight of the coal tar; and the water content to be 0.2% to 0.8%; (2) The coal tar obtained after the pretreatment in step (1) is mixed with an alkali metal to react; (3) The material after the reaction in step (2) is desolidified to obtain the final coal tar.

3. The process according to claim 1, characterized in that: The pretreatment in step (1) is a dehydration treatment, and the dehydration treatment adopts one or more of the atmospheric pressure flash evaporation, negative pressure flash evaporation, and centrifugal flash dehydration methods.

4. The process according to claim 3, characterized in that: Desolidification is performed before or after dehydration, and the desolidification is one or more of centrifugal desolidification, static sedimentation separation, electric field purification, solvent extraction, and cyclone separation.

5. The process according to claim 3, characterized in that: Before or after the dehydration treatment, a desolidification treatment is performed, and the desolidification treatment is chemical separation.

6. The process according to claim 1, characterized in that: The coal tar in step (1) is full-fraction coal tar, and the properties of the full-fraction coal tar are as follows: density at 20°C: 0.9800 g / ml-1.0378 g / ml, sulfur: 2000 μg / g-5000 μg / g, and nitrogen: 5000 μg / g-10000 μg / g.

7. The process according to claim 1, characterized in that: The alkali metal in step (2) is one or more of Li, Na, K, Ru, Cs, and Fr.

8. The process according to claim 1, characterized in that: The mass ratio of the alkali metal described in step (2) to the coal tar raw material is 0.5-10:100 on a simple basis.

9. The process according to claim 8, characterized in that: The mass ratio of the alkali metal described in step (2) to the coal tar raw material is 1-5:100 on a simple basis.

10. The process according to claim 1, characterized in that: In step (2), the alkali metal is added in solid or liquid form to the coal tar obtained after pretreatment in step (1) under sealed conditions.

11. The process according to claim 1, characterized in that: The alkali metal in step (2) is mixed with a solvent and then added to the coal tar raw material in step (1), wherein the solvent is one or a mixture of naphtha, diesel, kerosene, wax oil and heavy oil, and the mass ratio of the solvent to the alkali metal is 2:1 to 10:

1.

12. The process according to claim 11, characterized in that: In step (2), the mass ratio of the solvent to the alkali metal is 3:1 to 8:

1.

13. The process according to claim 11, characterized in that: The alkali metal and solvent mixing process is as follows: the alkali metal and the solvent in an appropriate proportion are mixed in a mixing device and are fully mixed. The stirring operating conditions in the mixing device are a rotation speed of 600r / m~3000r / m, a stirring time of 10min~60min, and a corresponding temperature of the mixture during stirring: 20℃~150℃.

14. The process according to claim 13, characterized in that: In the process of mixing the alkali metal and the solvent, the stirring operating conditions in the mixing equipment are a rotation speed of 1000 r / m~2500 r / m, a stirring time of 15 min~40 min, and a corresponding temperature of the mixture during stirring: 40°C~110°C.

15. The process according to claim 13, characterized in that: The mixing device is a static mixer, and the static mixer is one or more of SV type static mixer, SX type static mixer, SL type static mixer, SH type static mixer, and SK type static mixer.

16. The process according to claim 1, characterized in that: In step (2), the coal tar obtained after the pretreatment in step (1) is mixed with the alkali metal for reaction using a batch reactor or a continuous reactor, a kettle reaction equipment or a tubular reaction equipment.

17. The process according to claim 1, characterized in that: In step (2), the coal tar obtained after pretreatment in step (1) is mixed with an alkali metal for reaction under the following operating conditions: reaction temperature: 180°C to 250°C, hydrogen partial pressure: 5.0 to 8.0 MPa, reaction time or residence time: 10 min to 40 min, and hydrogen to oil volume ratio: 80:1 to 200:

1.

18. The process according to claim 1, characterized in that: In step (3), the material is desolidified by one or more of centrifugal desolidification, static sedimentation separation, electric field purification, solvent extraction, and cyclone separation.

19. The process according to claim 1, characterized in that: In step (3), the material is desolidified by chemical separation.

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