Continuous ethylene oligomerization system

Abstract

The invention discloses a continuous ethylene oligomerization system, and belongs to the technical field of ethylene polymerization. An ethylene pipeline is respectively connected with the venturi tube (5) and the secondary compressor (7), the venturi tube (5) and the secondary compressor (7) are both connected to the inlet end of the loop reactor (9), the outlet end of the loop reactor (9) is connected with the inlet of the reaction liquid gas-liquid separation tank (11), the gas phase outlet of the reaction liquid gas-liquid separation tank (11) is connected with the secondary compressor (7), and the gas phase outlet of the reaction liquid gas-liquid separation tank (11) is connected with the secondary compressor (7). A liquid phase outlet of the reaction liquid gas-liquid separation tank (11) is connected with a rectification separation unit (15), the rectification separation unit (15) is provided with outlets of recycled low-pressure ethylene (16), a recycled solvent (19), a target product (20) and a secondary product (21), and an outlet of the recycled low-pressure ethylene (16) is connected to a secondary compressor (7). The dispersion effect of the Venturi tube on monomers and solvents is utilized, and a new loop reactor is matched, so that wax deposition and attachment are avoided, and reaction heat removal is easy.

Description

Technical Field

[0001] The invention belongs to the technical field of ethylene polymerization, and in particular relates to a continuous ethylene polymerization system. Background Art

[0002] Linear α-olefins are an important class of chemical raw materials and intermediates, and are widely used in high-performance polyolefins, high-end lubricants, surfactants and other fields. In recent years, with the development of high-end PE, POE and other materials, the market demand for linear α-olefins, especially 1-hexene and 1-octene, has continued to grow. As one of the key technologies for oil conversion and oil-to-special conversion of refining enterprises, the technology of preparing α-olefins such as 1-hexene and 1-octene by ethylene selective polymerization has received high attention and has become a research and development hotspot. On the one hand, a variety of highly active and highly product-selective catalysts have been developed. On the other hand, there are also a lot of progress reports in process engineering development, such as the selection of reactor types and measures for long-term stable operation. But overall, there are still bottlenecks that need to be optimized in the industrial implementation of this technology such as engineering scale-up.

[0003] Even under the existing highly selective catalytic system, the products of ethylene polymerization will show a wide carbon number distribution. Although the yield of the target product 1-hexene and / or 1-octene can reach more than 85%, the generation of byproducts above C4 olefins and C14 olefins is difficult to avoid, but the byproduct yields of different systems are different. These byproducts include ethylene oligomers of different forms above C20. Although their yields are not high, even less than 0.1%, they are solid at 90°C and cannot be fully dissolved in the reaction liquid. As the reaction proceeds, it is easy to deposit and adhere to the inner surface of the reactor at a lower temperature, grow to form a wax layer, seriously affecting heat transfer and reaction heat removal, and greatly increasing the difficulty of controlling the reaction temperature; it will also deposit and form blockages in low-flow pipelines; the oligomers suspended in the reaction liquid will flow backward with the reaction liquid, and will also cause blockage of the filter screen and equipment, affecting the stable operation of the device. For continuous devices, the frequency of shutdown and maintenance will increase, affecting the operation cycle and production capacity of the device.

[0004] In the prior art, CN103896704B, CN104086350B, and CN104086349B disclose methods for producing alpha olefins by polymerization of ethylene. A reaction device in which an external container is connected to a loop reactor is proposed, wherein a portion of the pressurized ethylene monomer is continuously introduced into an external container filled with a reaction solvent for pre-dissolution, and then the reaction solvent containing the ethylene monomer is continuously introduced into the loop reactor from the external container; another portion of the pressurized ethylene monomer is directly introduced into the loop reactor filled with the reaction solvent; a liquid solvent distributor or a gas ethylene distributor is provided in the external container to improve the efficiency of pre-dissolving part of the ethylene in the solvent. It is said that it has the advantages of easily controlling the pressure of the reactor and avoiding blockage of the reactor.

[0005] CN113511949A removes the solid polymer in the reactor tube by cutting the loop reactor out of the reaction system and raising the reactor temperature. It solves the problem of wax deposition on the reactor wall by increasing the number of reactors and adopting the method of offline regeneration of spare reactors, which increases the investment and reduces the efficiency of the device relative to a certain scale of devices.

[0006] CN110639459A discloses a device and method for preparing 1-octene by continuous selective polymerization of ethylene. The process adopts a process of connecting a kettle reactor and a tubular reactor in series: ethylene is transported to the kettle reactor in low-temperature liquid phase, heated and gasified in the reactor, a part of the ethylene gas is sprayed into the reaction system through a distributor to participate in the reaction, and the other part of the ethylene is gasified as a heat transfer medium to absorb the reaction heat and recycled, the main catalyst a, ligand b and co-catalyst c are respectively mixed with a solvent and added to the kettle reactor, and the regulator d is directly fed into the reactor in gas phase; the reacted material is sent to the tubular reactor through a delivery pump, reacts with the quenching agent at high temperature in the tubular reactor, and the quenched material enters the separation system; ethylene is sprayed into the reaction liquid through the gas distribution holes at different positions on the coil in the reactor, so as to improve mass transfer, make the ethylene concentration distribution in the reaction liquid more uniform, avoid excessive generation of by-product oligomers due to excessive local concentration of ethylene, and at the same time, realize the scouring of the heat exchange tube wall surface, and slow down the adhesion of oligomers to the equipment. This method for preparing 1-octene has the advantages of high catalytic activity, high 1-octene selectivity, high quenching efficiency, and long operation cycle. However, the essence of this method is to dissolve the raw materials separately, improve the dispersibility of each raw material in the solvent, add more mixing devices and reaction vessels, and the cost is higher; it requires secondary mixing and two-stage reaction, and the operation cycle and reaction stability cannot be determined.

[0007] CN115894148B provides a method for continuous production of 1-octene by selective polymerization of ethylene, specifically, solvent, ethylene, catalyst and catalytic promoter are premixed, and then enter the first stage reactor together with hydrogen for reaction, part of ethylene directly participates in the reaction, and the other part of liquid ethylene is drawn out of the reaction after endothermic gasification in the upper part of the kettle, and then compressed and condensed and returned to the first stage reactor for recycling, and the liquid phase material obtained by the first stage reactor overflows into the second stage reactor for continuous reaction, and the temperature is higher than the temperature of the reaction in the first stage reactor, and the jacket temperature of the two stage reactors is higher than the material temperature in the kettle, and the obtained liquid phase product enters the separation system after quenching, recovers the unreacted ethylene, and obtains 1-octene product and 1-hexene product respectively. The method adopts a two-stage reactor series process to achieve better overall interaction, which can effectively improve the catalyst utilization rate, reduce the generation and wall adhesion of waxy polyethylene, reduce costs, and ensure the continuous and stable operation and production of the device. The method needs to pass through two stages of reaction vessels, gradually heat up, and requires ethylene gasification endothermic control temperature, which has high requirements for temperature control and is relatively complicated. Summary of the invention

[0008] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a continuous ethylene oligomerization system which can improve product selectivity and reaction efficiency, reduce oligomers, avoid wax deposition, and extend the operation cycle of the device.

[0009] The technical solution adopted by the present invention to solve the technical problem is: a wax inhibitor for ethylene polymerization, the component of which is one of dodecylnaphthalene and hydrogenated poly-1-decene or a mixture of the two in any proportion.

[0010] Hydrogenated poly-1-decene (PAO2, CAS No. 68037-01-4) is a by-product of the polymerization of raw materials containing 1-decene (such as FT synthetic light oil polymerization), also known as hydrogenated-(1-decene dimer), with a common viscosity of 1.5~3.5mPa·s at 100℃, a pour point less than -50℃, and a flash point greater than 60℃. Waxing inhibitors are hydrocarbons with a normal pressure boiling point greater than nC20. Like solvents such as cyclohexane and methylcyclohexane, they are stable inert components in the catalyst system of the polymerization reaction, and finally remain in the heavy residual oil and are discharged at the bottom of the tower of the product separation unit, without affecting the progress of the target reaction and the purity of the distillation product.

[0011] Through the action of van der Waals forces between oligomer molecules, a three-dimensional network structure is formed between dodecylnaphthalene and oligomers, which increases the solubility and fluidity of oligomers in the reaction solution and reduces the deposition of oligomers on the inner wall of the tube. Hydrogenated poly-1-decene has the characteristics of low pour point and "comb-like" structure, and has good similar compatibility with oligomers. It can also increase the fluidity of oligomers in the reaction solution and reduce their deposition on the inner wall of the tube, thereby playing an excellent role in inhibiting wax deposition and greatly delaying wax deposition on the inner wall of the reaction vessel.

[0012] After the waxing inhibitor delays the waxing on the inner wall of the reaction vessel, it can, firstly, extend the equipment operation cycle and reduce the frequency of shutting down the production equipment for wax removal; secondly, it can reduce the thermal resistance of the reactor wall, making it easier to remove heat using an external medium, making the radial temperature inside the vessel more stable and uniform, reducing the occurrence of side reactions caused by unstable and uneven temperature, and thus being more conducive to improving the reaction selectivity.

[0013] Preferably, the waxing inhibitor is a mixture of dodecylnaphthalene and hydrogenated poly-1-decene, and the mass ratio of dodecylnaphthalene to hydrogenated poly-1-decene is 1:2.5-4.4. Mixing the two in a specific ratio can more effectively delay waxing on the inner wall of the reactor.

[0014] A continuous ethylene polymerization method, wherein a portion of fresh ethylene monomer is sucked into a venturi tube by a solvent for mixing and dissolution, and then continuously enters a loop reactor together with a catalyst system and the above-mentioned waxing inhibitor for polymerization reaction; the obtained reaction liquid is flash-evaporated to obtain a circulating gas phase and a liquid phase; the liquid phase is further rectified to obtain low-pressure ethylene, products, solvents and by-products; the circulating gas phase, low-pressure ethylene and another portion of fresh ethylene monomer are mixed and then circulated into the loop reactor for polymerization reaction; The part of fresh ethylene monomer and the other part of fresh ethylene monomer constitute the total amount of fresh ethylene monomer, and the weight ratio of the two parts of monomers is 1:0.7~2.4; the amount of wax inhibitor added accounts for 0.1%~5% of the total weight of the fresh ethylene monomer; the mass ratio of the circulating gas phase, low-pressure ethylene, and the total amount of fresh ethylene monomer is 0.2~0.6:0.2~0.6:1.

[0015] The product is one or a mixture of any proportion of 1-hexene, 1-octene and 1-decene, and is more suitable for continuous production of 1-octene through ethylene polymerization.

[0016] The total amount of fresh ethylene enters the loop reactor in two parts. One part is fully mixed, dispersed and dissolved in the total solvent through the venturi tube, and then cooperates with the waxing inhibitor to avoid excessive self-polymerization and waxing of the highly active fresh ethylene monomer in the initial reaction stage. Compared with the raw material tank dissolution in the prior art, the feeding efficiency is higher and the waxing inhibitor is quickly mixed and uniformly achieved. In addition, the higher proportion of pre-dissolved ethylene saves the power consumption of liquid pressurization of some fresh ethylene monomer raw materials from dissolution pressure to reaction pressure and increasing some gas compression.

[0017] The catalyst system comprises a catalyst, an alkylaluminoxane, an alkylaluminum and a solvent. The catalyst can be selected from one of iron-based, chromium-based, nickel-based and zirconium-based metal catalysts.

[0018] Preferably, the hydrogenated poly-1-decene is a byproduct of polymerization of a raw material containing 1-decene, has a viscosity (100°C) of 1.7 mPa·s to 2.5 mPa·s, a pour point of less than -60°C, and a flash point of greater than 60°C.

[0019] Preferably, the reaction pressure of the loop reactor is 4.5 MPa~5.5 MPa, the inlet and outlet pressure drops are 100 kPa~300 kPa, and the reaction temperature is 60°C~80°C.

[0020] The larger the circulation flow rate, the more violent the turbulence, the smaller the radial temperature gradient and concentration gradient of the annular tube reactor, the more favorable the reaction selectivity, and the slower the wax deposition on the inner wall of the tube. However, the greater the pressure drop, the greater the power consumed by the axial flow pump; in addition, when the circulation flow rate exceeds a certain amount, the effect of reducing the deposition of oligomers will not be significant.

[0021] Preferably, the total amount of fresh ethylene monomer is recorded as liquid at 0°C, and the volume space velocity in the loop reactor is 0.1h -1 ~1.0h -1 , the weight ratio of the total amount of fresh ethylene monomer to the solvent is 1:1~5.

[0022] By limiting the entry rate of the total amount of fresh ethylene monomer, the residence time of the reaction liquid in the loop reactor is controlled, that is, the reaction time is controlled. Under the optimal conditions, the highest reaction efficiency and the lowest wax deposition effect can be obtained, and the stable operation effect is the best.

[0023] Preferably, the flash separation pressure is 3.3 MPa~5 MPa, and the temperature is 30°C~50°C.

[0024] Preferably, the amount of wax inhibitor added is 0.3% to 3% by weight of the total weight of fresh ethylene monomer.

[0025] Preferably, the solvent can be cyclohexane and methylcyclohexane, or a mixture of the two in any proportion.

[0026] Preferably, a liquid flow enhancement unit is provided in the annular reactor, the length of the liquid flow enhancement unit is 5 to 20 times the inner diameter of the annular reactor, and a filler with a porosity of 85% to 99% is provided in the liquid flow enhancement unit. The radial temperature gradient and concentration gradient are reduced by means of the turbulence of the fluid in the annular tube to improve the selectivity of the reaction and reduce the deposition of oligomers. This avoids relying solely on increasing the power of the axial flow pump to increase the circulation flow of the reaction solution and reduce the deposition of oligomers.

[0027] A continuous ethylene polymerization system comprises a venturi tube, a loop reactor, a gas-liquid separation tank and a product separation unit comprising multiple distillation towers; an ethylene pipeline is respectively connected to the venturi tube and a secondary compressor, the venturi tube and the secondary compressor are both connected to the inlet end of the loop reactor, the outlet end of the loop reactor is connected to the inlet of a reaction liquid gas-liquid separation tank, the gas phase outlet of the reaction liquid gas-liquid separation tank is connected to the secondary compressor, the liquid phase outlet of the reaction liquid gas-liquid separation tank is connected to a distillation separation unit, the distillation separation unit is provided with outlets for recovered low-pressure ethylene, recovered solvent, target product and secondary product, and the outlet of the recovered low-pressure ethylene is connected to the secondary compressor.

[0028] Preferably, it also includes a primary compressor, the outlet of the recovered low-pressure ethylene is connected to the primary compressor (17), and the primary compressor is connected to the secondary compressor.

[0029] Preferably, the annular tube reactor is provided with 1 to 10 liquid flow enhancement units along the length direction of the annular tube, the length of the liquid flow enhancement unit is 5 to 20 times the inner diameter of the annular tube reactor, and the liquid flow enhancement unit is provided with structured packing, random packing or spiral ribbon packing with a porosity of 85% to 99%.

[0030] Compared with the prior art, the present invention has the following beneficial effects: utilizing the dispersing effect of the venturi tube on the monomer and the solvent, as well as the coordinated effect of the wax deposit inhibitor and the new loop reactor, thereby avoiding wax deposit adhesion, facilitating reaction heat removal, controlling temperature more accurately, improving product selectivity and reaction efficiency, and extending the operation cycle of the device. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 The present invention is a schematic flow diagram of a continuous ethylene polymerization system.

[0032] Figure 2 Schematic diagram of the process of the ethylene oligomerization system used in the comparative example.

[0033] Among them, 1. total fresh ethylene monomer feedstock; 1-1. a portion of ethylene feedstock pre-dissolved with solvent; 1-2. another portion of ethylene feedstock mixed with circulating gas; 2. high-pressure solvent; 3. catalyst system; 4. waxing inhibitor; 5. venturi tube; 5A. solvent ethylene dissolved flow booster pump; 6. solvent ethylene dissolved flow; 6A. boosted flow; 7. secondary compressor; 8. secondary compressor outlet gas; 9. loop reactor; 9A. loop reactor without liquid flow intensification unit; 9-1. loop Jacket on the outer wall of the tube; 9-2, liquid flow intensification unit; 9-3, differential pressure gauge; 9-4, axial flow pump; 10, reactor discharge; 11, reaction liquid gas-liquid separation tank; 12, circulating gas phase; 13, secondary compressor inlet gas; 14, separation tank liquid phase; 15, distillation separation unit; 16, recovered low-pressure ethylene; 17, primary compressor; 18, pressurized low-pressure ethylene; 19, recovered solvent; 20, target product; 21, secondary product; 22, heavy residual oil; 22A, heavy residual oil without wax inhibitor. DETAILED DESCRIPTION

[0034] Embodiment 7 is the best embodiment of the present invention, and the following is combined with the attached Figure 1 The present invention is further described.

[0035] Refer to the attached Figure 1A continuous ethylene polymerization system comprises a venturi tube 5, a loop reactor 9, a primary compressor 17, a secondary compressor 7, a reaction liquid gas-liquid separation tank 11 and a rectification separation unit 15; the total fresh ethylene monomer raw material 1 is divided into a part of ethylene raw material 1-1 pre-dissolved with a solvent and another part of ethylene raw material 1-2 mixed with a circulating gas phase, wherein a part of the ethylene raw material 1-1 pre-dissolved with a solvent and a high-pressure solvent 2 are mixed and dissolved in the venturi tube 5 to form a solvent ethylene dissolved flow 6, a catalyst system 3, and a waxing inhibitor 4 to enter the loop reactor 9, and another part of the ethylene raw material 1-2 mixed with the circulating gas phase and the circulating gas phase 12 are pressurized by the secondary compressor 7 and the outlet gas 8 from the secondary compressor also enters the loop reactor 9, and a selective polymerization reaction occurs under certain temperature, pressure and catalyst system conditions. The generated series of α-olefin products are mixed with the solvent and unreacted ethylene to form a reactor discharge 10, and the α-olefin products contain a small amount of macromolecular oligomers. In the prior art, oligomers will deposit wax on the inner wall of the reaction tube, gradually increase the thermal resistance of the reaction tube to remove heat, and significantly affect the control of the reaction temperature and the operation cycle of the device.

[0036] The reaction liquid is driven by the axial flow pump 9-4 to form a certain amount of circulating flow in the annular tube of the annular tube reactor 9; the pressure drop caused by the reaction liquid flowing in the reaction tube is displayed by the differential pressure gauge 9-3, which is approximately equal to the inlet and outlet pressure difference of the axial flow pump 9-4; the larger the circulation flow rate, the more violent the turbulence, the smaller the radial temperature gradient and concentration gradient, the more favorable the selectivity of the reaction, and the slower the deposition of wax on the inner wall of the tube. However, the greater the pressure drop, the greater the power consumed by the axial flow pump; in addition, when the circulation flow exceeds a certain amount, the effect of reducing the deposition of oligomers will not be significant. The outer wall of the annular tube reactor 9 is provided with an annular tube outer wall jacket 9-1, and under normal working conditions, a cold medium is passed into the jacket to remove the reaction heat to maintain a normal reaction temperature. Several groups of liquid flow enhancement units 9-2 are also provided in the annular tube reactor 9. The interior of the annular tube of unit 9-2 is filled with fillers, which are used to enhance the turbulence of the fluid in the tube and reduce the radial temperature gradient and concentration gradient. The provision of the liquid flow enhancement unit 9-2 can also increase the pressure drop of the differential pressure gauge 9-3. The pressure drop value represents the effect of fluid turbulence. Increasing the pressure drop within a certain range will enhance the fluid turbulence, which is beneficial to slowing down the deposition of wax on the inner wall of the tube.

[0037] In the method and device for preparing 1-hexene and / or 1-octene and / or 1-decene by selective polymerization of ethylene, a liquid flow enhancement unit is arranged in the reactor annular tube, which enhances the turbulence of the fluid in the tube and reduces the radial temperature gradient and concentration gradient, thereby improving the selectivity of the reaction and further reducing the deposition of oligomers. Adding a waxing inhibitor to the reaction feed can improve the solubility and fluidity of the oligomers in the reaction solution, more effectively reduce the deposition of oligomers on the inner wall of the tube, and extend the operation cycle of the device. By arranging a venturi tube, part of the ethylene raw material is sucked in and mixed and dissolved with the ethylene raw material by the suction force generated by a large amount of high-pressure solvent in the venturi tube, thereby saving part of the power consumption.

[0038] The reactor discharge 10 is discharged from the reactor and enters the reaction liquid gas-liquid separation tank 11 for separation to obtain a circulating gas phase 12 and a separation tank liquid phase 14. The circulating gas phase 12 is mixed with part of the ethylene feedstock and pressurized low-pressure ethylene 18 to form a secondary compressor inlet gas 13, which is pressurized by the secondary compressor 7 to obtain a secondary compressor outlet gas 8.

[0039] The liquid phase 14 of the separation tank enters the distillation separation unit 15 for separation in sequence to obtain recovered low-pressure ethylene 16, recovered solvent 19, target products 20 such as 1-hexene and / or 1-octene and / or 1-decene, byproducts 21 such as C4 and C12~C18, and heavy residual oil 22 containing hydrocarbons of C20 and above, waxing inhibitor, catalyst system and terminator residues. The recovered low-pressure ethylene 16 is compressed by the primary compressor 17 and then pressurized into low-pressure ethylene 18, which is circulated back to the reaction system; the recovered solvent 19 is pressurized by the solvent pump and then returned to the reaction system to merge with a small amount of supplementary solvent to form a high-pressure solvent 2 (omitted in this figure).

[0040] In some embodiments of the present invention, preferably, the mass concentration of the wax inhibitor based on the total fresh ethylene monomer feedstock is 0.1%-5%, for example, 0.1%, 0.2%, 0.3%, 0.5%, 1.0%, 2.0%, 3.0%, 5%, and any value in the range consisting of any two values, preferably 0.3%-3%. When the above mass concentration range is met, the purpose of extending the device operation cycle is achieved by inhibiting the deposition of the inner wall of the oligomer tube. When the mass concentration is greater than the above mass concentration range, the effect of further extending the device operation cycle will not be obvious, and the operating cost will increase significantly.

[0041] Based on the attached Figure 1 The continuous ethylene polymerization system shown is a continuous ethylene polymerization method: a portion of fresh ethylene monomer, solvent, catalytic system and wax inhibitor are continuously introduced into the loop reactor 9 for polymerization reaction to obtain reaction liquid, wherein a portion of fresh ethylene monomer and solvent are mixed and dissolved in the form of being simultaneously sucked in through the venturi tube 5; the reaction liquid enters the reaction liquid gas-liquid separation tank 11, and a circulating gas phase and a liquid phase are obtained through gas-liquid separation, and the liquid phase is further distilled to obtain low-pressure ethylene, products, solvents and by-products; the circulating gas phase, low-pressure ethylene and another portion of fresh ethylene monomer are mixed and circulated into the loop reactor 9 to participate in the polymerization reaction again, and the circulating gas phase and another portion of fresh ethylene monomer are returned to the loop reactor 9 through the primary compressor 17, and the low-pressure ethylene returns to the loop reactor 9 after passing through the primary compressor 17 and the secondary compressor 7.

[0042] The present invention is further described below by specific examples. The examples are all based on a production capacity of 50,000 tons / year. In actual applications, the production capacity can be adjusted according to the process as it changes. The specific feed amount in the examples cannot limit the scope of protection of the present invention. The "number of days of stable operation of the device" recorded in the examples and comparative examples refers to the time when the actual measured reaction temperature in the loop reactor 9 deviates from the set temperature by 3°C while maintaining the temperature, pressure and output of the process stable, thereby requiring the interval time for the loop reactor 9 to be offline for dewaxing. Example 1

[0043] The continuous ethylene polymerization method and system is a 50,000 ton / year ethylene selective polymerization method and system for preparing 1-octene; the loop reactor 9 and accessories are 2 sets (sets) connected in parallel, the inner diameter of the loop is 380 mm, and the total length of the loop is 175 meters; each tube is equipped with 8 groups of liquid flow enhancement units 9-2, the length of the liquid flow enhancement unit 9-2 is 2 meters, and the liquid flow enhancement unit 9-2 is filled with spiral ribbon structured packing, and the porosity of the packing is 90%. The circulation flow rate of the reaction liquid in the loop reactor 9 is 2000 t / h, the pressure drop is 280 kPa, and the loop reactor 9 uses the outer sleeve to remove heat from the reaction.

[0044] The total fresh ethylene monomer feed rate is 7200 kg / h, of which 2880 kg / h goes to the venturi tube 5, and the other part of the fresh ethylene monomer flow rate is 4320 kg / h. The volume space velocity of the total fresh ethylene monomer feed (liquid at 0°C) in the loop reactor 9 is 0.4 h / min. -1 ; The circulating gas flow rate is 2350kg / h, the low-pressure ethylene flow rate is 2100kg / h, the solvent is methylcyclohexane, and the total solvent flow rate is 12600kg / h (the amount of solvent used for the preparation of the catalyst system and the sealing of the axial flow pump is small and can be ignored). The amount of wax inhibitor added accounts for 1.3% of the total mass of fresh ethylene monomer, of which dodecylnaphthalene accounts for 0.3% and hydrogenated poly-1-decene accounts for 1%. Hydrogenated poly-1-decene is a by-product of the polymerization of 1-decene raw materials, with a viscosity (100℃) of 2.0mPa·s, a pour point of -63℃, and a flash point greater than 60℃. The catalyst system is a chromium catalyst (the concentration in terms of chromium is 0.5mo1 / L·Cr).

[0045] The reaction pressure was 5.0 MPa, the reaction temperature was 70°C, the pressure of the gas-liquid separation tank 11 was 4.1 MPa, and the temperature was 40°C. The final product 1-octene was 4154 kg / h, and the secondary product (mixed C6 containing 1-hexene) was 2198 kg / h. The device operated stably for 85 days. Example 2

[0046] A continuous ethylene polymerization method and system, based on the continuous ethylene polymerization method and system of Example 1: each loop reactor 9 is replaced with 4 groups of liquid flow intensification units, and the reactor pressure drop is 200kPa.

[0047] The remaining conditions were the same, and the final product 1-octene was 4152 kg / h, and the secondary product (mixed C6 containing 1-hexene) was 2200 kg / h. The device operated stably for 75 days. Example 3

[0048] A continuous ethylene polymerization method and system, based on the continuous ethylene polymerization method and system of Example 1: each loop reactor 9 is replaced with 12 groups of liquid flow intensification units, and the reactor pressure drop is 360kPa.

[0049] The remaining conditions were the same, and the final product 1-octene was 4156 kg / h, and the secondary product (mixed C6 containing 1-hexene) was 2195 kg / h. The device operated stably for 91 days. Example 4

[0050] A continuous ethylene polymerization method and system, based on the continuous ethylene polymerization method and system of Example 1: no liquid flow enhancement unit is provided in each loop reactor 9, and the pressure drop of the reactor is 120 kPa.

[0051] The remaining conditions were the same, and the final product 1-octene was 4151 kg / h, and the secondary product (mixed C6 containing 1-hexene) was 2204 kg / h. The device operated stably for 65 days. Example 5

[0052] A continuous ethylene oligomerization method and system, based on the continuous ethylene oligomerization method and system of Example 1: the amount of wax inhibitor added is set to 2.7% of the total mass of fresh ethylene monomer, of which dodecylnaphthalene accounts for 0.5% and hydrogenated poly-1-decene accounts for 2.2%.

[0053] The remaining conditions were the same, and the final product 1-octene was 4156 kg / h, and the secondary product (mixed C6 containing 1-hexene) was 2196 kg / h. The device operated stably for 95 days. Example 6

[0054] A continuous ethylene oligomerization method and system, based on the continuous ethylene oligomerization method and system of Example 1: the amount of wax inhibitor added is set to 3.5% of the total mass of fresh ethylene monomer, of which dodecylnaphthalene accounts for 1.0% and hydrogenated poly-1-decene accounts for 2.5%.

[0055] The remaining conditions were the same, and the final product 1-octene was 4156 kg / h, and the secondary product (mixed C6 containing 1-hexene) was 2196 kg / h. The device operated stably for 96 days. Example 7

[0056] A continuous ethylene polymerization method and system, based on the continuous ethylene polymerization method and system of Example 1: each loop reactor 9 is replaced with 4 groups of liquid flow intensification units; the amount of wax inhibitor added is set to 2.7% of the total mass of fresh ethylene monomer, of which dodecylnaphthalene accounts for 0.5% and hydrogenated poly-1-decene accounts for 2.2%.

[0057] The remaining conditions were the same, and the final product 1-octene was 4154 kg / h, and the secondary product (mixed C6 containing 1-hexene) was 2198 kg / h. The device operated stably for 93 days. Example 8

[0058] A continuous ethylene oligomerization method and system, based on the continuous ethylene oligomerization method and system of Example 1: each loop reactor 9 is not provided with a liquid flow enhancement unit, and the reactor pressure drop is 120 kPa. The amount of wax inhibitor added is set to account for 2.7% of the total weight of fresh ethylene monomer, of which dodecylnaphthalene accounts for 0.5% and hydrogenated poly-1-decene accounts for 2.2%.

[0059] The remaining conditions were the same, and the final product 1-octene was 4153 kg / h, and the secondary product (mixed C6 containing 1-hexene) was 2200 kg / h. The device operated stably for 76 days. Example 9

[0060] A continuous ethylene oligomerization method and system, based on the continuous ethylene oligomerization method and system of Example 1: the wax inhibitor added in equal amounts includes 0.7% dodecylnaphthalene and 0.6% hydrogenated poly-1-decene.

[0061] The remaining conditions were the same, and the final product 1-octene was 4153 kg / h, and the secondary product (mixed C6 containing 1-hexene) was 2199 kg / h. The device operated stably for 78 days.

[0062] Comparative Example 1 A continuous ethylene oligomerization method and system, based on the continuous ethylene oligomerization method and system of Example 1: no wax inhibitor is added.

[0063] The remaining conditions were the same, and the final product 1-octene was 4150 kg / h, and the secondary product (mixed C6 containing 1-hexene) was 2200 kg / h. The device operated stably for 43 days.

[0064] Comparative Example 2 A continuous ethylene oligomerization method and system, based on the continuous ethylene oligomerization method and system of Example 1: Venturi tube 5 is replaced by a logistics booster pump 5A, a portion of fresh ethylene monomer is first dissolved with the solvent in a pre-dissolution tank at a mass ratio of 1:1, and then pumped into a loop reactor 9A without a liquid flow enhancement unit through the logistics booster pump. The loop reactor 9A without a liquid flow enhancement unit is not provided with a liquid flow enhancement unit and a waxing inhibitor is not added.

[0065] The remaining conditions were the same, and the final product 1-octene was 4147 kg / h, and the secondary product (mixed C6 containing 1-hexene) was 2207 kg / h. The device operated stably for 17 days.

[0066] Comparative Example 3 A continuous ethylene polymerization method and system, based on the continuous ethylene polymerization method and system of comparative example 2: the circulation flow rate of each loop reactor 9 is set to 3000t / h, and the reactor pressure drop is set to 270kPa.

[0067] The remaining conditions were the same, and the final product 1-octene was 4151 kg / h, and the secondary product (mixed C6 containing 1-hexene) was 2204 kg / h. The device operated stably for 27 days.

[0068] Comparative Example 4 A continuous ethylene polymerization method and system, based on the continuous ethylene polymerization method and system of comparative example 2: the circulation flow rate of each loop reactor 9 is set to 4000t / h, and the reactor pressure drop is set to 480kPa.

[0069] The remaining conditions were the same, and the final product 1-octene was 4153 kg / h, and the secondary product (mixed C6 containing 1-hexene) was 2203 kg / h. The device operated stably for 29 days.

[0070] Performance Testing The experimental results of the above embodiments and comparative examples are summarized, and the specific results are shown in Table 1.

[0071] Table 1 Performance test results Flow Enhancement Unit, Group Waxing inhibitor,% Circulation volume, t / h Mixed C6, kg / h 1-octene, kg / h Device operation time, days Total energy consumption increase, kW Example 1 8 1.3 2000 2198 4154 85 155 Example 2 4 1.3 2000 2200 4152 75 73 Example 3 12 1.3 2000 2195 4156 91 238 Example 4 0 1.3 2000 2204 4151 65 -10 Example 5 8 2.7 2000 2196 4156 95 155 Example 6 8 3.5 2000 2196 4156 96 155 Example 7 4 2.7 2000 2198 4154 93 73 Example 8 0 2.7 2000 2200 4153 76 -10 Example 9 8 1.3 2000 2198 4154 78 155 Comparative Example 1 8 0 2000 2200 4150 43 155 Comparative Example 2 - - 2000 2207 4147 17 0 (baseline) Comparative Example 3 - - 3000 2204 4151 27 155 Comparative Example 4 - - 4000 2203 4153 29 372 According to the performance test results in Table 1, considering the operation stability of the device, product selectivity and energy consumption, the technical solution with the best energy efficiency ratio is Example 7.

[0072] Adding wax inhibitors to the raw materials can effectively reduce the deposition of oligomers on the inner wall of the tube and extend the running time or operation cycle of the device; however, if the addition amount exceeds 3%, the effect of further extending the running time of the device is not obvious.

[0073] By adopting the method provided by the present invention, a liquid flow enhancement unit is set in the loop reactor, which can also reduce oligomer deposition and extend the device operation cycle, but the effect is not as significant as adding a waxing inhibitor. In addition, adding too many units significantly increases the energy consumption of the device, and the effect of further extending the device operation time is not obvious.

[0074] From Comparative Examples 2 to 4, it can be seen that regulating the circulation volume of the annular pipe by an axial flow pump is also effective in reducing oligomer deposition and extending the operating time, but the effect is not as significant as that of the wax inhibitor and the liquid flow enhancement unit. In addition, the energy consumption of the device is significantly increased.

[0075] The above is only a preferred embodiment of the present invention, and does not limit the present invention in other forms. Any technician familiar with the profession may use the above disclosed technical content to change or modify it into an equivalent embodiment with equivalent changes. However, any simple modification, equivalent change and modification made to the above embodiment according to the technical essence of the present invention without departing from the technical solution of the present invention still belongs to the protection scope of the technical solution of the present invention.

Claims

1. A continuous ethylene oligomerization system, characterized in that: The invention comprises a venturi tube (5), a loop reactor (9), a gas-liquid separation tank (11) and a distillation separation unit (15); an ethylene pipeline is connected to the venturi tube (5) and the secondary compressor (7) respectively; the venturi tube (5) and the secondary compressor (7) are both connected to the inlet end of the loop reactor (9); the outlet end of the loop reactor (9) is connected to the inlet of the reaction liquid gas-liquid separation tank (11); the gas phase outlet of the reaction liquid gas-liquid separation tank (11) is connected to the secondary compressor (7); the liquid phase outlet of the reaction liquid gas-liquid separation tank (11) is connected to the distillation separation unit (15); the distillation separation unit (15) is provided with outlets for recovered low-pressure ethylene (16), recovered solvent (19), target product (20) and secondary product (21); and the outlet of the recovered low-pressure ethylene (16) is connected to the secondary compressor (7); When performing continuous ethylene polymerization, a portion of fresh ethylene monomer is sucked into a venturi tube (5) by a solvent for mixing and dissolution, and then continuously enters a loop reactor (9) together with a catalyst system and a wax inhibitor for polymerization reaction; the obtained reaction liquid is flash-evaporated to obtain a circulating gas phase and a liquid phase; the liquid phase is further rectified to obtain low-pressure ethylene, products, solvents and by-products; the circulating gas phase, low-pressure ethylene and another portion of fresh ethylene monomer are mixed and then circulated into the loop reactor (9) for polymerization reaction; The sum of the part of fresh ethylene monomer and the other part of fresh ethylene monomer is the total amount of fresh ethylene monomer, and the mass ratio of the two parts of monomers is 1:0.7-2.4; the amount of wax inhibitor added accounts for 0.1%-5% of the total weight of the fresh ethylene monomer; the mass ratio of the circulating gas phase, low-pressure ethylene, and the total amount of fresh ethylene monomer is 0.2-0.6:0.2-0.6:1; The waxing inhibitor is a mixture of dodecylnaphthalene and hydrogenated poly-1-decene, and the mass ratio of dodecylnaphthalene to hydrogenated poly-1-decene is 1:2.5-4.

4.

2. The continuous ethylene oligomerization system according to claim 1, characterized in that: It also includes a primary compressor (17), the outlet of the recovered low-pressure ethylene (16) is connected to the primary compressor (17), and the primary compressor (17) is connected to the secondary compressor (7).

3. The continuous ethylene oligomerization system according to claim 1, characterized in that: The annular tube reactor (9) is provided with 1 to 10 liquid flow enhancement units in the direction of the length of the annular tube, the length of the liquid flow enhancement unit is 5 to 20 times the inner diameter of the annular tube reactor (9), and the liquid flow enhancement unit is provided with structured packing, random packing or spiral ribbon packing with a porosity of 85% to 99%.

4. The continuous ethylene oligomerization system according to claim 1, characterized in that: The reaction pressure in the annular tube reactor (9) is 4.5 MPa to 5.5 MPa, the inlet and outlet pressure drops are 100 kPa to 360 kPa, and the reaction temperature is 60° C. to 80° C.

5. The continuous ethylene oligomerization system according to claim 1, characterized in that: The total amount of fresh ethylene monomer is recorded as liquid at 0°C, and the volume space velocity in the loop reactor (9) is 0.1h -1 ~1.0h -1 , the mass ratio of the total amount of fresh ethylene monomer to the solvent is 1:1~5.

6. The continuous ethylene oligomerization system according to claim 1, characterized in that: The flash separation pressure is 3.3MPa~5MPa, and the temperature is 30℃~50℃.

7. The continuous ethylene oligomerization system according to claim 1, characterized in that: The amount of wax inhibitor added is 0.3% to 3% of the total weight of fresh ethylene monomer.

8. The continuous ethylene oligomerization system according to claim 1, characterized in that: The solvent is cyclohexane and methylcyclohexane or a mixture of the two in any proportion.

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