Method for synthesizing low-viscosity PAO from coal-based α-olefins

Abstract

The invention discloses a method for synthesizing low-viscosity PAO from coal-based alpha-olefins. The method comprises the following steps: S1, introducing Lewis acid gas BF3 into a coal-based alpha-olefin fraction section, carrying out a complex reaction between BF3 and oxygen-containing compounds in a coal-based alpha-olefin liquid fraction section at a pressure of 0.05 to 1 MPa to form a heterogeneous system of a BF3 complex and a coal-based alpha-olefin liquid, and then separating and removing the BF3 complex in the system to obtain a deoxidized coal-based alpha-olefin fraction section; S2, adding alcohol to the deoxidized coal-based alpha-olefin fraction section to carry out a polymerization reaction; and S3, separating the polymerization reaction mixture to obtain a polymer product and a BF3 complex, removing residual BF3 from the polymer product by flash evaporation and / or steam stripping, separating BF3 gas from the BF3 complex by gas-liquid separation, and returning the BF3 gas separated from the polymer product and the BF3 complex to step S1 for reuse.

Description

Technical Field

[0001] The invention belongs to the technical field of poly alpha-olefin preparation, and particularly relates to a method for synthesizing low-viscosity PAO from coal-based alpha-olefins. Background Art

[0002] Group IV lubricant base oils—poly alpha olefins (PAOs)—are long-chain paraffinic lubricant base oils produced by the polymerization and hydrogenation of alpha olefins over a catalyst. As an important synthetic lubricant base oil, PAOs offer advantages such as a high viscosity index, low volatility, excellent low-temperature fluidity, superior shear stability, and high-temperature oxidation resistance. Based on the kinematic viscosity at 100°C, PAOs below 10 cSt are conventionally classified as low-viscosity PAOs, including PAO2, PAO2.5 / 3, PAO4, PAO5, PAO6, PAO8, PAO9, and PAO10 (the numbers represent the kinematic viscosity at 100°C). Low-viscosity PAOs are currently the most in-demand Group IV base oil, primarily used in long-span, premium internal combustion engine oils, aircraft engine oils, and energy-efficient, full-life precision equipment oils. They account for over 80% of the total PAO market.

[0003] Catalysts used to synthesize PAO include AlCl3, BF3, Ziegler-Nata, chromium-based, and metallocene catalysts. Among these, the catalysts used to prepare low-viscosity PAO primarily include AlCl3, BF3, and metallocene catalysts. BF3 catalytic systems are widely used in the synthesis of low-viscosity PAO due to their advantages, including high catalytic conversion, high product yield, narrow product molecular weight distribution, and good selectivity. However, after the reaction, the BF3 catalyst typically needs to be removed from the product. Common removal methods involve washing with alkaline solutions such as sodium hydroxide solution or ammonia. This method generates wastewater that is difficult to dispose of, and the catalyst cannot be recycled, leading to serious environmental pollution and resource waste. CN112299940A proposes a method for the continuous synthesis of low-viscosity PAO using a BF3 catalyst. By recovering the BF3 from the material through gas-liquid separation and reusing it, the BF3 removal rate can reach over 80%, and the resulting polymer products are primarily trimers and tetramers.

[0004] The raw materials for PAO synthesis are primarily C8-C10 α-olefins, products of ethylene oligomerization. 1-decene is the most widely used, and the resulting PAO products offer the best performance. Currently, my country lacks production facilities for C8-C10 α-olefins, relying primarily on imported raw materials, which increases the cost of PAO synthesis. Fischer-Tropsch oil contains a significant amount of α-olefins, and coal-derived α-olefins with suitable carbon numbers can also be selected from these α-olefins as raw materials for PAO synthesis. Fischer-Tropsch oil is derived from coal, a resource abundant in my country. Its widespread availability and low cost facilitate lowering PAO production costs and expanding the PAO industry. Fischer-Tropsch oil is characterized by a continuous carbon number structure, primarily composed of linear alkanes and linear α-olefins. The product also contains a complex array of oxygenates, typically ranging from 5% to 15%, including alcohols, aldehydes, ketones, and acids of varying chain lengths. The presence of these oxygenates significantly impacts its quality and hinders further processing, necessitating a suitable method for their removal. CN105777467A proposes a method for separating oxygenates from Fischer-Tropsch synthetic oil products. After removing oxygenates in an extraction tower using two extractant feed operations, an oxygenate-rich stream is obtained, and the remaining oxygenates are further removed using a third extractant. Although this method simplifies and improves the extraction process, it has the disadvantages of a long process, high energy consumption, and more equipment. CN105885929B proposes a method for synthesizing low-viscosity PAO using a metallocene catalytic system using coal-based α-olefins as a raw material, wherein the oxygenates in the coal-based α-olefin raw material are removed by alkaline earth metals. This removal method can deeply remove oxygenates from coal-based α-olefins, but the process uses a large amount of alkaline earth metals and solid adsorbents, which will produce a large amount of waste residue.

[0005] CN104560191B proposes a method for synthesizing low-viscosity PAO using a Fischer-Tropsch oil (FTO) catalyst using a BF3 catalyst. The FTO is composed of olefins, alkanes, and alcohols, and the alcohol provides an oxygen content of 0.2-2%. Comparative technologies have specific requirements for the composition and content of the raw materials, resulting in poor universal applicability. Other oxygen-containing impurities in the raw materials are not removed, which could affect subsequent polymerization. Furthermore, there is no subsequent BF3 catalyst treatment process.

[0006] In summary, BF3 catalyst remains the most widely used choice for low-viscosity PAO synthesis due to its numerous advantages. Regarding raw materials, coal-based α-olefins, replacing C8-C10 α-olefins as PAO feedstock, can effectively reduce PAO production costs. However, current methods for removing oxygenates from Fischer-Tropsch oil still suffer from lengthy processes, high energy consumption, and the generation of large amounts of waste liquids or solids. Summary of the Invention

[0007] Based on the above problems, the object of the present invention is to provide a method for synthesizing low-viscosity PAO from coal-based α-olefins.

[0008] To achieve the above object, the present invention provides a method for synthesizing low-viscosity PAO from coal-based α-olefins, comprising the following steps:

[0009] S1, introducing Lewis acid gas BF3 into the coal-to-α-olefin fraction section, causing BF3 to undergo a complex reaction with oxygen-containing compounds in the coal-to-α-olefin liquid fraction section at a pressure of 0.05 to 1 MPa to form a heterogeneous system of BF3 complex and coal-to-α-olefin liquid, and then separating and removing the BF3 complex in the system to obtain a deoxygenated coal-to-α-olefin fraction section;

[0010] S2, adding alcohol to the deoxygenated coal-based α-olefin fraction section to carry out a polymerization reaction;

[0011] S3, separating the polymerization reaction mixture to obtain a polymer product and a BF3 complex, removing residual BF3 from the polymer product by flash evaporation and / or steam stripping, and separating BF3 gas from the BF3 complex by gas-liquid separation, and returning the BF3 gas separated from the polymer product and the BF3 complex to step S1 for reuse.

[0012] In the method for synthesizing low-viscosity PAO from coal-based α-olefins of the present invention, the coal-based α-olefin fraction segment is a C5-C30 fraction segment, preferably a C8-C12 fraction segment.

[0013] In the method for synthesizing low-viscosity PAO from coal-based α-olefins of the present invention, the reaction temperature of the complexation reaction in step S1 is 0-50° C., and the reaction time is 0.5-2 h.

[0014] In the method for synthesizing low-viscosity PAO from coal-based α-olefins of the present invention, the separation method in step S1 and step S3 is sedimentation separation.

[0015] In the method for synthesizing low-viscosity PAO from coal-based α-olefins of the present invention, the alcohol is one or more of methanol, ethanol, propanol, glycerol, butanol, pentanol and hexanol.

[0016] The method for synthesizing low-viscosity PAO from coal-based α-olefins of the present invention is characterized in that the reaction temperature of the polymerization reaction in step S2 is 20-50° C. and the pressure is 0.05-1 MPa.

[0017] In the method for synthesizing low-viscosity PAO from coal-based α-olefins of the present invention, the flash temperature in step S3 is 30-150°C, and the stripping temperature is 80-150°C.

[0018] The method for synthesizing low-viscosity PAO from coal-based α-olefins of the present invention separates the BF3 complex into gas and liquid by thermal cracking at a thermal cracking temperature of 150-200°C.

[0019] In the method for synthesizing low-viscosity PAO from coal-based α-olefins of the present invention, the oxygen content of the coal-based α-olefin fraction is ≤1%.

[0020] Beneficial effects of the present invention:

[0021] 1. Selecting coal-based α-olefin raw materials, the introduction of BF3 simultaneously achieves complex deoxygenation and catalytic polymerization, reducing the raw material cost of the polymerization reaction. In addition, the deoxygenation process and polymerization process of coal-based α-olefin raw materials are connected in series through BF3 to achieve efficient utilization of BF3;

[0022] 2. The use of complexation to remove oxygenated compounds from coal-to-α-olefin raw materials has a short process flow, low energy consumption, and simple operation. It is an efficient method for removing oxygenated compounds;

[0023] 3. The obtained product material can be subjected to secondary separation, and the BF3 gas therein can be efficiently recovered and reused, thereby improving the utilization efficiency of BF3 and reducing the generation of waste liquid. DETAILED DESCRIPTION

[0024] Source of raw materials:

[0025] Raw material name Coal-to-α-olefin oil Raw material specifications Industrial grade, oxygen content 100~1000ppm Manufacturer Ningxia Coal, Lu'an Coal, Yanzhou Coal, low-temperature or high-temperature Fischer-Tropsch products

[0026] Evaluation and analysis methods: kinematic viscosity analysis, lubricant base oil pour point analysis, inductively coupled plasma atomic emission spectrometry (ICP-AES)

[0027] Example 1

[0028] A 2-liter reactor was charged with 1 liter of coal-based α-olefin liquid fraction, and BF3 was introduced into the reactor. The reaction was fully reacted at 20°C and 0.3 MPa for 1.5 hours. After sufficient settling, the reaction system was separated into layers to produce an upper layer of deoxygenated coal-based α-olefins and a lower layer of generated BF3 complexes. The lower layer of BF3 complexes was removed. Hexanol was then added to the deoxygenated coal-based α-olefins and the reaction was fully carried out at 20°C and 0.3 MPa for 2 hours. The reaction system was fully settled to produce an upper layer of polymerized product and a lower layer of BF3 complex system. The polymerized product was flash evaporated at 150°C to separate the residual BF3 gas. The BF3 complex system was thermally cracked at 170°C to separate the BF3 gas. The separated BF3 gas was recovered and recycled.

[0029] Example 2

[0030] A 2-liter reactor was charged with 1 liter of coal-based α-olefin liquid fraction, and BF3 was introduced into the reactor. The reaction was fully reacted at 30°C and 0.3 MPa for 1.5 hours. After sufficient settling, the reaction system was separated into layers to produce an upper layer of deoxygenated coal-based α-olefins and a lower layer of generated BF3 complexes. The lower layer of BF3 complexes was removed. Pentanol was then added to the deoxygenated coal-based α-olefins and the reaction was fully carried out at 30°C and 0.3 MPa for 2 hours. The reaction system was fully settled to produce an upper layer of polymerized product and a lower layer of BF3 complex system. The polymerized product was flash evaporated at 120°C to separate the residual BF3 gas. The BF3 complex system was thermally cracked at 170°C to separate the BF3 gas. The separated BF3 gas was recovered and recycled.

[0031] Example 3

[0032] A 2-liter reactor was charged with 1 liter of coal-based α-olefin liquid fraction, and BF3 was introduced into the reactor. The reaction was fully reacted at 40°C and 0.3 MPa for 1.5 hours. After sufficient settling, the reaction system was separated into layers to produce an upper layer of deoxygenated coal-based α-olefins and a lower layer of generated BF3 complexes. The lower layer of BF3 complexes was removed. Butanol was then added to the deoxygenated coal-based α-olefins and the reaction was fully reacted at 40°C and 0.3 MPa for 2 hours. The reaction system was fully settled to produce an upper layer of polymerized product and a lower layer of BF3 complex system. The polymerized product was flash evaporated at 90°C to separate the residual BF3 gas. The BF3 complex system was thermally cracked at 160°C to separate the BF3 gas. The separated BF3 gas was recovered and recycled.

[0033] Example 4

[0034] A 2-liter reactor was charged with 1 liter of coal-based α-olefin liquid fraction, and BF3 was introduced into the reactor. The reaction was fully reacted at 50°C and 0.3 MPa for 1.5 hours. After sufficient settling, the reaction system was separated into layers to produce an upper layer of deoxygenated coal-based α-olefins and a lower layer of generated BF3 complexes. The lower layer of BF3 complexes was removed. Glycerol was then added to the deoxygenated coal-based α-olefins and the reaction was fully carried out at 50°C and 0.3 MPa for 2 hours. The reaction system was fully settled to produce an upper layer of polymerized product and a lower layer of BF3 complex system. The polymerized product was flash evaporated at 60°C to separate the residual BF3 gas. The BF3 complex system was thermally cracked at 160°C to separate the BF3 gas. The separated BF3 gas was recovered and recycled.

[0035] Example 5

[0036] A 2-liter reactor was charged with 1 liter of coal-based α-olefin liquid fraction, and BF3 was introduced into the reactor. The reaction was fully reacted at 0°C and 0.05 MPa for 2 hours. After sufficient settling, the reaction system was separated into layers to produce an upper layer of deoxygenated coal-based α-olefins and a lower layer of generated BF3 complexes. The lower layer of BF3 complexes was removed. Propanol was then added to the deoxygenated coal-based α-olefins and the reaction was fully carried out at 30°C and 0.05 MPa for 3 hours. The reaction system was fully settled to produce an upper layer of polymerized product and a lower layer of BF3 complexes. The polymerized product was stripped at 150°C with nitrogen to separate the BF3 gas. The BF3 complex system was thermally cracked at 150°C to separate the BF3 gas. The separated BF3 gas was recovered and recycled.

[0037] Example 6

[0038] A 2-liter reactor was charged with 1 liter of coal-based α-olefin liquid fraction, and BF3 was introduced into the reactor. The reaction was fully reacted at 10°C and 0.5 MPa for 1 hour. After sufficient settling, the reaction system was separated into layers to produce an upper layer of deoxygenated coal-based α-olefins and a lower layer of generated BF3 complexes. The lower layer of BF3 complexes was removed. Ethanol was then added to the deoxygenated coal-based α-olefins and the reaction was fully carried out at 30°C and 0.5 MPa for 1.5 hours. The reaction system was fully settled to produce an upper layer of polymerized product and a lower layer of BF3 complexes. The polymerized product was stripped at 120°C with nitrogen to separate the BF3 gas. The BF3 complex system was thermally cracked at 180°C to separate the BF3 gas. The separated BF3 gas was recovered and recycled.

[0039] Example 7

[0040] A 2-L reactor was charged with 1 L of coal-based α-olefin liquid fraction, and BF3 was introduced into the reactor. The reaction was fully reacted at 20°C and 0.7 MPa for 0.8 h. After sufficient settling, the reaction system was separated into layers to produce an upper layer of deoxygenated coal-based α-olefins and a lower layer of generated BF3 complexes. The lower layer of BF3 complexes was removed. Methanol was then added to the deoxygenated coal-based α-olefins and the reaction was fully reacted at 30°C and 0.7 MPa for 1 h. The reaction system was fully settled to produce an upper layer of polymerized product and a lower layer of BF3 complexes. The polymerized product was flash evaporated at 30°C and stripped at 100°C with nitrogen to separate the BF3 gas. The BF3 complex system was thermally cracked at 190°C to separate the BF3 gas. The separated BF3 gas was recovered and recycled.

[0041] Example 8

[0042] A 2-L reactor was charged with 1 L of coal-based α-olefin liquid fraction, and BF3 was introduced into the reactor. The reaction was fully reacted at 30°C and 1.0 MPa for 0.5 h. After the reaction, the system was allowed to settle and separated into layers, yielding an upper layer of deoxygenated coal-based α-olefins and a lower layer of generated BF3 complexes. The lower layer of BF3 complexes was removed. Methanol was then added to the deoxygenated coal-based α-olefins and the reaction was fully reacted at 30°C and 1.0 MPa for 0.5 h. The system was allowed to settle fully, yielding an upper layer of polymerized product and a lower layer of BF3 complexes. The polymerized product was flash evaporated at 30°C and stripped at 80°C with nitrogen to separate the BF3 gas. The BF3 complex system was thermally cracked at 200°C to separate the BF3 gas. The separated BF3 gas was recovered and recycled.

[0043] Comparative Example 1

[0044] The same as Example 1, except that the raw materials are not deoxygenated by BF3 and the polymerization reaction is directly carried out.

[0045] Comparative Example 2

[0046] Same as Example 1, except that the pressure for complexation removal of oxygen-containing compounds is 0.02 MPa.

[0047] Table 1 Oxygenate removal effect

[0048] Example Manufacturer Source Distillation section Raw material oxygen content / ppm Oxygen content after removal / ppm Deoxidation rate / % Example 1 Yanzhou Coal Mining C5~C16 1000 24.0 97.6 Example 2 Lu'an C6~C12 600 20.4 96.6 Example 3 Ningxia Coal C8~C12 400 18.4 95.4 Example 4 Lu'an C8~C10 200 14.4 92.8 Example 5 Ningxia Coal C10~C16 400 34.8 91.3 Example 6 Ningxia Coal C16~C24 400 8.4 97.9 Example 7 Yanzhou Coal Mining C16~C30 1000 8.0 99.2 Example 8 Yanzhou Coal Mining C8~C20 1000 5.0 99.5 Comparative Example 1 Yanzhou Coal Mining C5~C16 1000 - - Comparative Example 2 Yanzhou Coal Mining C5~C16 1000 705 29.5

[0049] Table 2 Composition distribution of polymerization products

[0050]

[0051] The low-viscosity polymer products synthesized in Examples 1 to 8 were blended to obtain PAO products of three viscosity grades: PAO4, PAO6, and PAO8. The product properties are shown in the following table.

[0052] Table 3 PAO product properties

[0053] Viscosity grade Viscosity at 40°C Viscosity at 100℃ Viscosity Index Pour point / ℃ PAO4 17.7 4.0 125 -57 PAO6 32.5 6.0 132 -54 PAO8 47.1 7.9 138 -51

[0054] Of course, the present invention may have many other embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art may make various corresponding changes and modifications based on the present invention, but these corresponding changes and modifications should all fall within the scope of protection of the claims of the present invention.

Claims

1. A method for synthesizing low-viscosity PAO from coal-based α-olefins, characterized in that: The following steps are involved: S1, introducing Lewis acid gas BF3 into the coal-to-α-olefin fraction section, causing BF3 to undergo a complex reaction with oxygen-containing compounds in the coal-to-α-olefin liquid fraction section at a pressure of 0.05-1 MPa to form a heterogeneous system of BF3 complex and coal-to-α-olefin liquid, and then separating and removing the BF3 complex in the system to obtain a deoxygenated coal-to-α-olefin fraction section; S2, adding alcohol to the deoxygenated coal-based α-olefin fraction section to carry out a polymerization reaction; S3, separating the polymerization reaction mixture to obtain a polymer product and a BF3 complex, removing residual BF3 from the polymer product by flash evaporation and / or steam stripping, and separating BF3 gas from the BF3 complex by gas-liquid separation, and returning the BF3 gas separated from the polymer product and the BF3 complex to step S1 for reuse.

2. The method for synthesizing low-viscosity PAO from coal-based α-olefins according to claim 1, characterized in that: The coal-based α-olefin fraction section is a C5-C30 fraction section.

3. The method for synthesizing low-viscosity PAO from coal-based α-olefins according to claim 2, characterized in that: The coal-based α-olefin fraction section is a C8~C12 fraction section.

4. The method for synthesizing low-viscosity PAO from coal-based α-olefins according to claim 1, characterized in that: The reaction temperature of the complexation reaction in step S1 is 0-50° C., and the reaction time is 0.5-2 h.

5. The method for synthesizing low-viscosity PAO from coal-based α-olefins according to claim 1, characterized in that: The separation method in step S1 and step S3 is sedimentation separation.

6. The method for synthesizing low-viscosity PAO from coal-based α-olefins according to claim 1, characterized in that: The alcohol is one or more of methanol, ethanol, propanol, glycerol, butanol, pentanol and hexanol.

7. The method for synthesizing low-viscosity PAO from coal-based α-olefins according to claim 1, characterized in that: The reaction temperature of the polymerization reaction in step S2 is 20-50° C., and the pressure is 0.05-1 MPa.

8. The method for synthesizing low-viscosity PAO from coal-based α-olefins according to claim 1, characterized in that: In step S3, the flash temperature is 30-150°C, and the stripping temperature is 80-150°C.

9. The method for synthesizing low-viscosity PAO from coal-based α-olefins according to claim 1, characterized in that: The BF3 complex is separated into gas and liquid by thermal cracking at a temperature of 150~200℃.

10. The method for synthesizing low-viscosity PAO from coal-based α-olefins according to claim 1, characterized in that: The oxygen content of the coal-based α-olefin fraction section is ≤1%.

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