Process for preparing oligomers

Abstract

The present invention provides a method for preparing an oligomer, comprising: (S1) supplying ethylene gas to a lower liquid zone containing a solvent in a reactor for an oligomerization reaction, discharging unreacted ethylene gas to the upper part of the reactor, and discharging a liquid stream containing an oligomer product to the lower side of the reactor; (S2) feeding the liquid stream discharged from the lower side of the reactor to a separation column and separating gas from the liquid stream to obtain a stream comprising an oligomer product; and (S3) supplying the gas discharged from the upper part of the reactor to a compressor equipped with a recirculation line to compress the gas, and then recirculating the compressed gas to the reactor, in which a portion of the compressed gas discharged from the compressor is shunted to the compressor, the shunted compressed gas is recirculated to the compressor supply line through a pressure regulating valve disposed in the compressor recirculation line to control the pressure in the compressor supply line.

Description

[0001] Cross - reference to related applications

[0002] This application claims priority to Korean Patent Application No. 10 - 2023 - 0128683, filed on September 26, 2023, and Korean Patent Application No. 10 - 2024 - 0099986, filed on July 29, 2024, the entire contents of which are incorporated herein by reference as part of the specification. Technical field

[0003] The present invention relates to a method for preparing oligomers, and more particularly, to a method for preparing oligomers that improves catalytic reaction and process operation safety by maintaining a constant pressure in a reactor during the process of recycling unreacted gas. Background art

[0004] α - Olefins are important raw materials for comonomers, detergents, lubricants, plasticizers, etc. and are widely used commercially. In particular, 1 - hexene and 1 - octene are often used as comonomers when preparing linear low - density polyethylene (LLDPE) to adjust the density of polyethylene.

[0005] α - Olefins can be prepared by oligomerization reaction in a state where ethylene is dissolved in a solvent in the presence of a catalyst, and the oligomerization reaction can be carried out in, for example, a bubble column reactor.

[0006] In a bubble column reactor, raw material gas is introduced into a liquid zone containing a solvent, a catalyst, etc. through a distribution device installed at the lower part, and is dispersed while rising in the form of bubbles. The dispersed gas is mixed in the liquid zone while generating turbulence, thereby carrying out an oligomerization reaction.

[0007] After the oligomerization reaction, in the material flow in the liquid zone in the reactor, in addition to the oligomer product formed by the polymerization of ethylene, it also contains by - products, solvents, unreacted gas dissolved in the solvent, etc. Therefore, the discharge flow of the liquid zone is supplied to a separation column to separate unreacted gas, solvent, etc., thereby obtaining a refined oligomer product.

[0008] At the same time, after discharging a large amount of unreacted gas in the raw material gas introduced into the bubble column reactor to the upper part of the reactor, it can be supplied to the reactor again and used as raw material gas.

[0009] Figure 1An unreacted gas recycle loop applied to a conventional oligomer preparation process is shown. The unreacted gas discharged from the upper part of the reactor 100 can be recycled to the reactor through the compressor 10. In addition, the gas recovered in the oligomer product separation column 200 can also be transported to the supply pipeline of the compressor 10 and recycled to the reactor again through the recycling process. Here, when the designed flow rate of the compressor 10 is different from the flow rate of the unreacted gas discharged from the reactor 100, pressure fluctuations may occur in the supply pipeline of the compressor. Additionally, even if the flow rate of the gas recovered in the separation column 200 is combined in the supply pipeline of the compressor, pressure fluctuations may still occur.

[0010] When pressure fluctuations occur in the supply pipeline of the compressor 10 that transports the unreacted gas discharged from the reactor 100, the pressure difference of the pressure regulating valve set in the reactor at the previous stage will be affected, making it difficult to maintain a constant internal pressure. Moreover, pressure fluctuations also occur in the discharge pipeline of the compressor. Therefore, the flow rate oscillation of the recycled gas supplied to the reactor may increase. The pressure fluctuations in the reactor and the flow rate oscillation of the gas supply change the liquid level in the reactor, resulting in a change in the residence time of the catalyst. Consequently, the reaction productivity will be affected by changes in catalytic reaction activity and selectivity, and the heat dissipation operability may deteriorate due to changes in the calorific value.

[0011] In addition, the unreacted gas used for reactor recycling will also contain low-boiling products and reaction solvents. As Figure 2 shown, the following steps can be added: install a condenser 20 between the reactor and the compressor, supply the unreacted gas to the condenser, and separate the liquid flow formed by the condensation of low-boiling products and reaction solvents and the gaseous flow of uncondensed and unreacted gas. Here, when pressure fluctuations occur in the supply pipeline of the compressor, the amount and composition of the condensate obtained in the condenser will change, and the concentration of the low-boiling products in the gas re-added to the reactor through the compressor will change, which may affect the reactivity of the reactor.

[0012] However, there is currently no dedicated device to prevent pressure fluctuations in the supply pipeline of the compressor during the process of recycling unreacted gas to the reactor. Therefore, the limitation is that the pressure fluctuations in the reactor or the gas recovered in the separation column cannot be stably added to the supply pipeline of the compressor. Summary of the Invention

[0013]

Technical Problem

[0014] To solve the problems mentioned in the background art, the purpose of the present invention is to provide a method for preparing oligomers, which can improve the safety of catalytic reactions and process operations by controlling the pressure between the reactor and the compressor during the process of recycling unreacted gas to the reactor to maintain a constant pressure in the reactor.

[0015]

Technical Solution

[0016] In a general aspect, a method for preparing an oligomer includes: (S1) supplying ethylene gas to a lower liquid zone containing a solvent in a reactor to carry out an oligomerization reaction, discharging unreacted ethylene gas to the upper part of the reactor, and discharging a liquid stream containing an oligomer product to the lower side of the reactor; (S2) supplying the liquid stream discharged from the lower side of the reactor to a separation column, separating a gas from the liquid stream to obtain a stream containing an oligomer product; and (S3) supplying the gas discharged from the upper part of the reactor to a compressor equipped with a recirculation line to compress the gas, and then recycling the compressed gas to the reactor, wherein a part of the compressed gas discharged from the compressor is diverted to the compressor, and the diverted compressed gas is recycled to a supply line of the compressor through a pressure regulating valve provided in the compressor recirculation line to control the pressure in the compressor supply line.

[0017] In the present invention, the pressure regulating valve provided in the recirculation line of the compressor can be kept open to continuously recycle the diverted compressed gas.

[0018]

Advantageous Effects

[0019] According to the present invention, in the oligomer preparation process, unreacted ethylene gas is compressed in a compressor, and then a part of the compressed gas discharged from the compressor is diverted and recycled to the supply line of the compressor, so that even when the flow rate of the unreacted gas discharged from the reactor is lower than the design flow rate of the compressor, the pressure fluctuation in the compressor supply line can be compensated. In particular, through an appropriate size design suitable for pressure fluctuation compensation, the pressure regulating valve provided in the recirculation line of the compressor is continuously opened, so as to appropriately adjust the flow rate of the compressed gas recycled to the supply line of the compressor, so that even when the flow rate of the unreacted gas discharged from the reactor changes, a constant pressure in the compressor supply line can be maintained.

[0020] Thereby, pressure fluctuation between the reactor and the compressor can be prevented during the recycling of unreacted ethylene gas to the reactor, so that the flow rate oscillation of the recycled gas supplied to the reactor is minimized, and at the same time, the internal pressure of the reactor is kept constant, so as to keep the liquid level and catalytic reaction in the reactor constant, improving the catalytic reaction of oligomer production and the safety of process operation. Description of the Drawings

[0021] Figure 1 and Figure 2 shows a circulation loop of unreacted gas to a reactor applied to a conventional olefin preparation process.

[0022] Figures 3 to 6Shows a recycle loop of unreacted gas to the reactor in an olefin preparation process according to an exemplary embodiment of the present invention, including a structure in which a recycle line is installed in the supply line and the discharge line of a compressor. Detailed Embodiment

[0023] The terms and words used in the description and claims of the present invention should not be construed restrictively as having a general or dictionary meaning, but should be understood as having a meaning and concept consistent with the technical idea of the present invention based on the principle that the inventor can appropriately define the term concept so as to describe their own invention in the best way.

[0024] As used herein, "comprising" and "including" embody specific features, fields, integers, steps, actions, elements or components, and do not exclude the addition of other specific features, fields, integers, steps, actions, elements or components.

[0025] The term "block copolymer" used in this application refers to a copolymer in which repeating units derived from two or more monomers are arranged in block form. The "block copolymer" may include a diblock copolymer, a triblock copolymer or a multiblock copolymer.

[0026] The term "flow" used in this application may refer to the fluid flow in a process or the fluid itself flowing in a pipeline. Specifically, the flow may refer to the fluid itself flowing in the pipeline connecting each device or the flow of the fluid. In addition, the fluid may include any one or more of gas, liquid and solid components.

[0027] Unless otherwise specified, the term "upper part" used herein refers to a point at 0 to 50% of the height from the top to the bottom of the device, and specifically, may refer to the top (top of the tower). In addition, the term "lower part" refers to a point at 50 to 100% of the height from the top to the bottom of the device, and specifically, may refer to the bottom (or bottom of the tower).

[0028] Unless otherwise specified, the term "side stream" used herein refers to a stream discharged at a height of 25 to 80% from the top to the bottom of the device, or a stream discharged at a height of 40 to 70%.

[0029] In addition, the "pressure" mentioned herein refers to the gauge pressure measured based on the atmospheric pressure.

[0030] The present invention will be described in detail below with reference to the accompanying drawings.

[0031] An exemplary embodiment of the present invention relates to a method for preparing an oligomer, which can improve the stability of the catalytic reaction and process operation by maintaining a constant reactor pressure during the process of recycling unreacted gas to the reactor.

[0032] Figures 3 to 6The flowchart of a method for preparing olefins according to an exemplary embodiment of the present invention is shown, and this method can be implemented in a system provided with an unreacted gas recycle loop. The system includes: a reactor 100, a separation column 200, and a compressor 10 equipped with a recycle pipeline. Additionally, in the separation column, a reboiler heated by heat transfer, a condenser for converting the flow generated by heating from the gas phase to the liquid phase, a gas-liquid separator for separating the condensed flow, valves for controlling the flow rate of each flow, pumps, sensors for measuring temperature and pressure, etc. can also be provided.

[0033] According to an exemplary embodiment of the present invention, first, ethylene gas is supplied to the lower liquid zone containing a solvent in the reactor 100 to carry out an oligomerization reaction, and a catalyst for activating the reaction can also be included in this liquid zone.

[0034] The reactor 100 can be a reactor capable of continuously carrying out an oligomerization reaction in the presence of a catalyst with ethylene dissolved in a solvent, and this reactor can include a continuous stirred tank reactor, a plug flow reactor, a bubble column reactor, etc.

[0035] For example, the raw material gas is introduced into the liquid zone containing a solvent, a catalyst, etc. through a distribution device installed at the lower part of the bubble column reactor, and is dispersed while rising in the form of bubbles. The dispersed gas is mixed in the liquid zone while generating turbulence, thereby carrying out an oligomerization reaction.

[0036] The oligomerization reaction can generate a target α-olefin product by supplying ethylene monomer gas to the reactor 100. Here, the oligomerization reaction takes place in the lower region of the reactor 100, and the oligomerization reaction of the monomer can be carried out in the liquid state where gaseous ethylene monomer is dissolved in the solvent.

[0037] The oligomerization reaction can refer to the reaction of monomer oligomerization. According to the number of polymerized monomers, the oligomerization reaction can be called a trimerization reaction and a tetramerization reaction, and these are collectively referred to as a polymerization reaction. For example, α-olefins such as 1-hexene and 1-octene can be prepared through the trimerization reaction or tetramerization reaction of ethylene.

[0038] The ethylene gas supplied to the reactor 100 can be a stream containing ethylene (C2) separated from naphtha cracking.

[0039] The solvent for dissolving ethylene gas can include one or more selected from n-pentane, n-hexane, n-heptane, cyclohexane, methylcyclohexane, octane, cyclooctane, decane, dodecane, benzene, xylene, 1,3,5-trimethylbenzene, toluene, ethylbenzene, chlorobenzene, dichlorobenzene, trichlorobenzene. If necessary, the solvent can be used in a combination of two or more. Therefore, ethylene gas can be liquefied at a higher temperature, and the dissolution rate of ethylene gas dissolved in the solvent can be increased.

[0040] In the oligomerization reaction of ethylene, a compound including a transition metal-based catalyst can be used as a catalyst to promote the reaction activity. For example, the catalyst can be a compound including at least one selected from chromium(III) acetylacetonate, chromium(III) chloride tetrahydrofuran, chromium(III) 2-ethylhexanoate, chromium(III) tris(2,2,6,6-tetramethyl-3,5-heptanedionate), chromium(III) benzoylacetone, chromium(III) hexafluoro-2,4-pentanedionate, chromium(III) acetate hydroxide, chromium(III) acetate, chromium(III) butyrate, chromium(III) valerate, chromium(III) laurate, and chromium(III) stearate.

[0041] In addition, a cocatalyst that can enhance the catalytic activity can also be used. For example, the cocatalyst can include at least one selected from trimethylaluminum, triethylaluminum, triisopropylaluminum, triisobutylaluminum, sesquiethylaluminum chloride, diethylaluminum chloride, dichloroethylaluminum, methylaluminoxane, modified methylaluminoxane, and borate.

[0042] The oligomerization reaction can be operated under conditions commonly applied in the art. For example, it can be carried out at a temperature of 30 °C to 150 °C or 50 °C to 120 °C and a pressure of 20 bar to 65 bar or 20 bar to 40 bar.

[0043] When carrying out the oligomerization reaction, in the reactor 100, a liquid stream containing oligomer products and by-products generated by ethylene polymerization, a solvent, unreacted gases dissolved in the solvent, etc. will exist in the lower region, while unreacted ethylene gas that is not dissolved in the solvent and does not participate in the oligomerization reaction will exist in the upper region.

[0044] The liquid stream can be discharged through a discharge pipeline connected to the lower side of the reactor 100 and transported to the separation column 200.

[0045] The liquid stream can be supplied to the separation column 200, and component separation can be carried out according to the boiling point to separate a gaseous upper discharge stream containing unreacted ethylene monomer and a liquid lower discharge stream containing oligomer products, by-products, and a solvent. The oligomer products and solvent contained in the lower discharge stream of the separation column 200 can be supplied to an additional separation column (not shown) to separate the solvent therefrom, thereby obtaining a refined oligomer product. The separation column 200 and the additional separation column can be operated under conditions commonly used in the art, without special limitations.

[0046] Meanwhile, the unreacted ethylene gas that does not participate in the oligomerization reaction in the reactor 100 can be discharged to the upper part of the reactor and then recycled to the reactor 100 through the compressor 10 to reuse the gas as a raw material gas.

[0047] The compressor 10 supplies electrical energy to the unreacted ethylene gas delivered from the reactor 100 to increase the pressure by compression, and the temperature of the gaseous stream can rise proportionally with the amount of electrical energy.

[0048] As Figures 3 to 6 shown, in the present invention, a circulation pipe provided with a pressure regulating valve 11 is connected to the supply pipe 10a of the compressor for delivering the unreacted gas and the discharge pipe 10b through which the compressed gas flowing out of the compressor passes. A part of the compressed gas can be diverted and recycled in the compressor discharge pipe 10b, thereby preventing pressure fluctuations from occurring in the supply pipe 10a of the compressor.

[0049] That is, even if the flow rate of the unreacted gas discharged from the reactor 100 is lower than the design flow rate of the compressor 10, a part of the compressed gas discharged from the compressor 10 can be used as a source for maintaining the pressure in the supply pipe 10a of the compressor to compensate for pressure fluctuations. Thus, the change in the pressure difference of the pressure regulating valve provided in the reactor at the previous stage can be minimized to keep the pressure in the reactor constant, and the pressure fluctuation of the compressor discharge pipe 10b can be prevented to minimize the flow rate oscillation of the recycled gas supplied to the reactor 100. Thereby, the liquid level and the catalyst reaction in the reactor are kept constant, thereby improving the oligomer productivity and the process operation stability.

[0050] In addition, it is preferable that the pressure regulating valve 11 provided in the recirculation line of the compressor 10 remains open. Because generally, the pressure regulating valve provided in the recirculation line of the compressor only controls the pressure in the line from dropping below a certain value by the function of only opening the pressure regulating valve when the surge phenomenon of the gas not being introduced into the compressor occurs and closing the pressure regulating valve when returning to normal operation, pressure oscillations may occur in the supply line of the compressor. However, in the present invention, the capacity of the compressor is designed to be greater than the sum of the flow rate of the gas discharged from the reactor and the flow rate of the gas discharged from the separation column, and the pressure regulating valve 11 provided in the recirculation line of the compressor is designed to maintain a constant opening in response to the fluctuations of the flow rate of the gas discharged from the reactor and the flow rate of the gas discharged from the separation column, thereby regulating the flow rate of the diverted compressed gas and keeping the pressure in the supply pipe 10a of the compressor constant.

[0051] In an exemplary embodiment of the present invention, as long as the compressor 10 is a device capable of compressing an air stream, various devices known in the art can be used without limitation, and one compressor or a plurality of compressors connected in series can be adopted according to the compression ratio of the supplied unreacted gas.

[0052] Reference Figure 3, The unreacted ethylene gas recovered in the separation column 200 can be transported to the supply pipeline 10a of the compressor for recycling to the reactor. Even though the flow rate of the unreacted gas discharged from the reactor and the flow rate of the gas discharged from the separation column are combined in the supply pipeline 10a of the compressor, increasing the possibility of pressure fluctuations, in the present invention, part of the compressed gas discharged from the compressor is diverted and recycled through the pressure regulating valve 11 provided in the recycle pipeline of the compressor 10, thereby controlling the pressure within the supply pipeline 10a of the compressor to minimize the differential pressure change of the pressure regulating valve provided in the reactor at the front stage of the compressor, thereby maintaining a constant pressure within the reactor.

[0053] The capacity of the compressor 10 can be selected considering the total flow rate of the unreacted gas discharged from the reactor, the gas recovered in the separation column, and the compressed gas recycled in the discharge pipeline of the compressor that can be combined in the supply pipeline 10a of the compressor.

[0054] Meanwhile, the flow rate of the compressed gas diverted from the discharge pipeline 10b of the compressor and recycled through the pressure regulating valve 11 can be adjusted by measuring the pressure in the supply pipeline 10a of the compressor, and can be, for example, in the range of 5 to 50 wt%, particularly 10 to 30 wt% of the total flow rate of the compressed gas discharged from the compressor 10. When the flow rate of the recycled compressed gas is less than 5 wt%, there are limitations in compensating for the pressure fluctuations occurring in the supply pipeline 10a of the compressor, making it difficult to maintain a constant pressure in the reactor 100. When the flow rate of the recycled compressed gas exceeds 50%, although the pressure fluctuations occurring in the supply pipeline 10a of the compressor can be fully controlled, the power consumption in the compressor 10 will increase, which is disadvantageous in terms of energy.

[0055] See Figure 4 , The unreacted gas discharged from the reactor and the gas recovered in the separation column can pass through the condenser 20 located at the front stage of the compressor 10 to condense the low-boiling components containing ethylene dimer and solvent, and then the gas stream of the unreacted ethylene monomer from which the condensate has been separated in the gas-liquid separator is supplied to the compressor 10 for recycling. Here, a part of the compressed gas whose temperature has increased after passing through the compressor 10 is recycled to the supply pipeline 10a of the compressor in a constant quantity range, for example, 5 to 50 wt% of the total flow rate of the compressed gas discharged from the compressor, thereby preventing the unreacted ethylene monomer stream discharged from the gas-liquid separator from condensing in the pipeline due to temperature changes of external air, etc. Thus, regardless of the composition of the gas discharged through the condenser and the gas-liquid separator, no condensate (liquid component) is supplied to the compressor, and thus the unreacted gas can be stably recycled to the reactor while maintaining a constant pressure within the reactor.

[0056] Refer to Figure 5 and 6, the unreacted ethylene gas recovered in the separation column 200 can be pre-compressed in a separate compressor 30 and then recycled to the reactor 100 together with the compressed gas discharged from the compressor 10. In this case, in the present invention as well, a part of the compressed gas is shunted and recycled through the pressure regulating valve 11 provided in the recycle line of the compressor 10, thereby directly controlling the pressure in the supply line 10a of the compressor (i.e., in the upper part of the reactor) to maintain a constant pressure in the reactor. At the same time, the unreacted gas discharged from the reactor is pressurized in the compressor and then recycled to the lower part of the reactor again.

[0057] According to the present invention described above, during the oligomer preparation process, the unreacted ethylene gas is compressed in the compressor, and then a part of the compressed gas discharged from the compressor is shunted and recycled to the supply line of the compressor, so that even when the flow rate of the unreacted gas discharged from the reactor is less than the designed flow rate of the compressor or there is a fluctuation in the flow rate of the unreacted gas discharged from the reactor, the pressure fluctuation in the supply line of the compressor can be compensated. In particular, the pressure regulating valve provided in the recycle line of the compressor appropriately adjusts the flow rate of the compressed gas recycled to the supply line of the compressor while remaining continuously open, thereby maintaining a constant pressure in the previous stage (i.e., the supply line of the compressor). For example, the pressure fluctuation in the supply line of the compressor can be controlled within the range of -1 bar to 1 bar, especially -0.2 bar to 0.2 bar, or -0.1 bar to 0.1 bar.

[0058] In this way, pressure fluctuations between the reactor and the compressor can be prevented during the recycling of the unreacted ethylene gas, thereby maintaining a constant pressure inside the reactor. For example, in the present invention, the pressure fluctuation inside the reactor operating during the oligomer preparation process can be controlled within the range of -0.5 bar to 0.5 bar, especially -0.1 bar to 0.1 bar, and more especially -0.02 bar to 0.02 bar, so that the reactor can operate stably.

[0059] In addition, the flow oscillation of the recycled gas supplied to the reactor is minimized to maintain the liquid level and the catalyst reaction in the reactor constant, thereby improving the oligomer productivity and the process operation stability.

[0060] Examples

[0061] The present invention will be described in more detail below by way of examples. However, the following examples are provided only for illustrative purposes of the present invention, and those skilled in the art can obviously make various modifications and changes without departing from the scope and spirit of the present invention, and the scope of the present invention is not limited thereto.

[0062] In the following Examples and Comparative Examples, the method according to the present invention was simulated using a commercial process simulation program (HYSYSD ANAMICS). The constants required for the simulation were the values embedded in the program, the values described in the literature, etc.

[0063] Comparative Example 1:

[0064] The oligomer preparation process was carried out according to the Figure 1 process flow chart shown.

[0065] (Step 1)

[0066] In reactor 100, ethylene gas was supplied to the lower liquid zone containing a solvent and a catalyst to carry out an oligomerization reaction. The unreacted ethylene gas (G) was discharged to the upper part of reactor 100, and the liquid stream (L) containing the oligomer product was discharged to the lower side of the reactor.

[0067] (Step 2)

[0068] The liquid stream (L) discharged from the lower side of reactor 100 was supplied to separation column 200, and gas was separated from the liquid stream to obtain a stream containing the oligomer product.

[0069] (Step 3)

[0070] The unreacted ethylene gas discharged from the upper part of reactor 100 was supplied to compressor 10, and the capacity of the compressor was designed to be 30% larger than the capacity of the compressor supply line. In addition, the gas separated and recovered in separation column 200 was transported to compressor 10 and compressed in compressor 10 together with the unreacted gas discharged from the reactor.

[0071] The compressed gas discharged from compressor 10 was recycled to reactor 100 and used again as the feed gas.

[0072] Comparative Example 2:

[0073] As Figure 2 shown, except that the unreacted gas discharged from the reactor and the unreacted gas discharged from the separation column were supplied to condenser 20 to separate a liquid stream containing low-boiling components containing ethylene dimer and condensed solvent and a gaseous stream containing uncondensed unreacted gas, and then the uncondensed unreacted gas was supplied to compressor 10 and the condensed liquid phase was transported to refining column 200 again, the process was carried out in the same manner as in Comparative Example 1.

[0074] Example 1:

[0075] As Figure 3 shown, the oligomer preparation process was carried out according to the process flow chart, and the structure included a recycle line provided with pressure regulating valves in the supply line and the discharge line of the compressor.

[0076] (Step 1)

[0077] Ethylene gas is supplied to a lower liquid zone containing a solvent and a catalyst in the reactor 100 to perform an oligomerization reaction, and then unreacted ethylene gas (G) is discharged to an upper portion of the reactor 100, and a liquid stream (L) containing oligomer products is discharged to a lower side of the reactor.

[0078] (Step 2)

[0079] The liquid stream (L) discharged from the lower side of the reactor 100 is supplied to the separation tower 200, and unreacted ethylene gas is separated and discharged from the liquid stream to obtain a stream containing oligomer products.

[0080] (Step 3)

[0081] The unreacted ethylene gas discharged from the upper part of the reactor 100 is supplied to the compressor 10 . At this time, the gas separated and recovered in the separation tower 200 is also supplied to the compressor 10 and compressed in the compressor 10 together with the unreacted gas discharged from the reactor.

[0082] A portion of the compressed gas is diverted from the compressor discharge line 10b and recycled to the compressor supply line 10a. At this time, the capacity of the compressor is designed so that the flow rate of the compressed gas diverted and recycled in the compressor discharge line 10b is 5% by weight of the total compressed gas flow rate. In addition, the regulating valve provided in the compressor recirculation line is kept in a normally open state to continuously recirculate the diverted compressed gas.

[0083] Meanwhile, the remaining compressed gas discharged from the compressor 10 is recycled to the reactor 100 and used again as a raw material gas.

[0084] Embodiment 2:

[0085] like Figure 4 As shown, the process is carried out in the same manner as Example 1, except that the unreacted gas discharged from the reactor and the gas recovered in the separation tower are supplied to the condenser 20 to separate a liquid stream containing low-boiling components containing ethylene dimer and a condensing solvent and a gaseous stream containing uncondensed unreacted gas, and then the uncondensed unreacted gas is supplied to the compressor 10, and the condensed liquid phase is transported to the refining tower 200 again.

[0086] Embodiment 3:

[0087] like Figure 5As shown, except that in Step 3, the gas recovered in the separation column 200 is pre-compressed separately in the compressor 30 and then recycled to the reactor 100 together with the compressed gas discharged from the compressor 10 to directly control the pressure at the upper part of the reactor. Meanwhile, a part of the compressed gas is diverted through the pressure regulating valve 11 provided in the recycle line of the compressor 10 and recycled to the supply line of the compressor, the process is carried out in the same manner as in Example 1.

[0088] Example 4:

[0089] As Figure 6 shown, except that in Step 3, the gas recovered in the separation column 200 is pre-compressed separately in the compressor 30 and then recycled to the reactor 100 together with the compressed gas discharged from the compressor 10 to directly control the pressure at the upper part of the reactor. Meanwhile, a part of the compressed gas is diverted through the pressure regulating valve 11 provided in the recycle line of the compressor 10 and recycled to the supply line of the compressor, the process is carried out in the same manner as in Example 2.

[0090] Example 5:

[0091] Except that in Step 3, the compressor capacity is designed such that the flow rate of the compressed gas diverted and recycled in the compressor discharge line 10b is 10% of the total compressed gas flow rate, the process is carried out in the same manner as in Example 1.

[0092] Example 6:

[0093] Except that in Step 3, the compressor capacity is designed such that the flow rate of the compressed gas diverted and recycled in the compressor discharge line 10b is 30% of the total compressed gas flow rate, the process is carried out in the same manner as in Example 1.

[0094] Example 7:

[0095] Except that in Step 3, the compressor capacity is designed such that the flow rate of the compressed gas diverted and recycled in the compressor discharge line 10b is 50% of the total compressed gas flow rate, the process is carried out in the same manner as in Example 1.

[0096] Example 8:

[0097] Except that in Step 3, the compressor capacity is designed such that the flow rate of the compressed gas diverted and recycled in the compressor discharge line 10b is 3% of the total compressed gas flow rate, the process is carried out in the same manner as in Example 1.

[0098] The pressure fluctuations of the reactor 100 and the compressor supply line 10a in the comparative example and the examples were calculated by simulation (using the HYSYSD ANAMICS program), and the results are shown in Table 1 below.

[0099] [Table 1]

[0100]

[0101] As can be seen from Table 1, in Comparative Examples 1 and 2, the capacity of the compressor is designed to be more than 30% larger than the capacity of the compressor supply line, and there is no compressor recirculation line. As a result, when the pressure in the compressor supply line decreases, the compressor is shut down by the interlocking device set to protect the compressor. The pressure in the compressor supply line is thereby increased, and then the compressor is operated again. As the process is repeated, the pressure difference of the pressure regulating valve located at the upper part of the reactor changes greatly, resulting in reactor pressure oscillation. In addition, due to the large pressure change in the compressor supply line, the separation tower recovery gas transported by the pressure difference in the separation tower is not supplied smoothly, and the pressure in the separation tower cannot be adjusted. That is, in Comparative Examples 1 and 2, the compressor is shut down due to the pressure difference with the compressor supply line, and large pressure fluctuations occur in the compressor supply line and in the reactor until the compressor is operated again.

[0102] In contrast, in Examples 1-8, since the unreacted ethylene gas is compressed in the compressor and a portion of the compressed gas discharged from the compressor is diverted and recycled to the supply line of the compressor to adjust the flow rate of the recycled compressed gas and control the pressure in the compressor supply line, it was confirmed that even if the flow rate of the unreacted gas discharged from the reactor changes, the pressure change inside the reactor is small.

[0103] In particular, in Example 6, since the flow rate of the compressed gas was 30%, the flow rate of the compressor supply line was increased by 30% to correspond to the compressor capacity of Comparative Examples 1 and 2, but the pressure fluctuation was controlled without a significant increase in power consumption. This is the result of adjusting the recirculation flow rate of the compressed gas diverted by constantly opening the pressure regulating valve provided in the compressor recirculation line to maintain a constant pressure in the compressor supply line.

[0104] Meanwhile, in Example 7, the flow rate of the compressed gas is 50%. Although the pressure fluctuation occurring in the compressor supply line is sufficiently controlled, the energy used is increased compared to that in Example 6.

[0105] Example 8 is an example of an instantaneous increase in the gas flow rate discharged from the top of the reactor or an instantaneous increase in the gas flow rate recovered at the top of the separation tower. Since the margin of the compressor capacity is small, the pressure in the compressor supply line increases, which affects the reactor pressure regulation, and thus the pressure fluctuation inside the reactor increases.

[0106] [reference numerals]

[0107] 100: Reactor

[0108] 200: Separation tower

[0109] 10, 30: Compressor

[0110] 11: Pressure regulating valve of the compressor recirculation pipeline

[0111] 20: Condenser

Claims

1. A method for preparing an oligomer, the method comprising: (S1) supplying ethylene gas to a lower liquid zone containing a solvent in a reactor to carry out an oligomerization reaction, discharging unreacted ethylene gas to an upper portion of the reactor, and discharging a liquid stream containing oligomer products to a lower side of the reactor; (S2) supplying a liquid stream discharged from the lower side of the reactor to a separation tower, and separating a gas from the liquid stream to obtain a stream containing oligomer products; and (S3) supplying the gas discharged from the upper part of the reactor to a compressor equipped with a recirculation pipeline to compress the gas, and then recycling the compressed gas to the reactor, Part of the compressed gas discharged from the compressor is diverted to the compressor, and the diverted compressed gas is recirculated to the compressor supply line through a pressure regulating valve arranged in the compressor recirculation pipeline to control the pressure in the compressor supply line.

2. The method for preparing an oligomer according to claim 1, wherein The gas separated in the separation column is recovered and sent to the compressor feed line.

3. The method for preparing an oligomer according to claim 1, wherein: The gas supplied to the compressor is obtained by separating the condensed low-boiling point components and the solvent in a condenser provided at the front stage of the compressor.

4. The method for preparing an oligomer according to claim 3, wherein: The low boiling point components and the solvent condensed in the condenser are sent to a separation column after separation.

5. The method for preparing an oligomer according to claim 1, wherein: The pressure regulating valve disposed in the compressor recirculation line is kept normally open to continuously recirculate the diverted compressed gas.

6. The method for preparing an oligomer according to claim 1, wherein: The flow rate of the compressed gas recirculated to the compressor feed line is 5 to 50% by weight of the total flow rate of the compressed gas discharged from the compressor.

7. The method for preparing an oligomer according to claim 6, wherein: The flow rate of the compressed gas recirculated to the compressor feed line is 10 to 30% by weight of the total flow rate of the compressed gas discharged from the compressor.

8. The method for preparing an oligomer according to claim 1, wherein: The gas separated in the separation tower is recovered and pre-compressed before being sent to the compressor discharge line.

9. The method for preparing an oligomer according to claim 1, wherein: The pressure fluctuation in the compressor feed line is controlled within the range of -1 bar to 1 bar.

10. The method for preparing an oligomer according to claim 9, wherein: The pressure fluctuation in the compressor feed line was controlled within the range of -0.2 bar to 0.2 bar.

11. The method for preparing an oligomer according to claim 1, wherein: The pressure fluctuation during the operation of the reactor was controlled within the range of -0.5 bar to 0.5 bar.

12. The method for preparing an oligomer according to claim 11, wherein The pressure fluctuation during the operation of the reactor was controlled within the range of -0.1 bar to 0.1 bar.

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