Method for preparing oligomer

Abstract

The present invention provides a method for preparing an oligomer, the method comprising the steps of: (S1) performing an oligomerization reaction by supplying ethylene gas to a lower liquid region comprising a solvent in a reactor, and then discharging unreacted ethylene gas from an upper portion of the reactor and discharging a liquid stream comprising an oligomer product from a lower portion side of the reactor; (S2) supplying the liquid stream discharged from the lower portion side of the reactor to a separation tower and separating gas from the liquid stream so as to obtain a stream comprising an oligomer product; and (S3) supplying the gas discharged from the upper portion of the reactor to a compressor in which a recirculation pipe is installed, compressing the gas, and then recirculating the compressed gas to the reactor, wherein some of the compressed gas discharged from the compressor is branched, and the branched compressed gas is recirculated to a compressor supply line through a pressure control valve provided in the recirculation pipe of the compressor so as to control the pressure of the compressor supply line.

Description

Oligomer manufacturing method

[0001] Cross-citation with related applications

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

[0003] Technology field

[0004] The present invention relates to a method for producing an oligomer, and more particularly, to a method for producing an oligomer that can improve the safety of catalytic reaction and process operation by maintaining the pressure of a reactor constant during the recirculation process of unreacted gas.

[0005] Alpha-olefins are widely used commercially as important substances used as comonomers, detergents, lubricants, and plasticizers. In particular, 1-hexene and 1-octene are widely used as comonomers to control the density of linear low-density polyethylene (LLDPE) during the production of polyethylene.

[0006] These alpha olefins can be produced by performing an oligomerization reaction in a state where ethylene is dissolved in a solvent in the presence of a catalyst, and the oligomerization reaction can be performed, for example, in a bubble column reactor.

[0007] In the bubble column reactor, the raw material gas is introduced into a liquid region containing a solvent, catalyst, etc. through a distribution device installed at the bottom thereof, and is dispersed while rising in the form of bubbles, and the dispersed gas is mixed within the liquid region while generating turbulence, thereby performing an oligomerization reaction.

[0008] After the oligomerization reaction is performed, the stream from the liquid region within the reactor contains the oligomer product polymerized with ethylene, along with by-products, solvent, unreacted gas dissolved in the solvent, etc. Therefore, the discharge stream from the liquid region can be supplied to a separation tower to separate the unreacted gas, solvent, etc., thereby obtaining a purified oligomer product.

[0009] Meanwhile, a significant amount of unreacted gas among the raw material gas introduced into the bubble column reactor is discharged to the top of the reactor and then supplied back to the reactor to be used as raw material gas.

[0010] FIG. 1 illustrates a recycle loop of unreacted gas applied to a conventional oligomer manufacturing process, wherein unreacted gas discharged from the upper portion of a reactor (100) can be recycled to the reactor via a compressor (10). In addition, gas recovered from a separation tower (200) of an oligomer product can also be transported to the supply line of the compressor (10) and recycled back to the reactor through a recirculation process. At this time, if the design flow rate of the compressor (10) and the flow rate of the unreacted gas discharged from the reactor (100) are different, pressure fluctuations may occur in the compressor supply line. In addition, pressure fluctuations may also occur if the flow rate of the gas recovered from the separation tower (200) is combined with the compressor supply line.

[0011] If a pressure fluctuation occurs in the supply line of the compressor (10) through which the unreacted gas discharged from the above reactor (100) is transferred, it affects the differential pressure of the pressure control valve provided in the reactor in the front stage, making it difficult to maintain a constant pressure inside the reactor, and pressure fluctuation also occurs in the discharge line of the compressor, which may increase the instability of the flow rate (hunting) of the recirculated gas supplied to the reactor. Such an instability of the pressure change inside the reactor and the gas supply flow rate changes the liquid level inside the reactor, and as a result, the catalyst residence time changes, which affects the reaction productivity due to changes in the activity and selectivity of the catalytic reaction, and the heat removal operability may deteriorate due to changes in the calorific value.

[0012] Additionally, the unreacted gas for reactor recirculation may include low-boiling-point products and reaction solvent. As shown in Fig. 2, a process may be added in which a condenser (20) is installed between the reactor and the compressor, and unreacted gas is supplied to the condenser to separate a liquid stream containing condensed low-boiling-point products and reaction solvent from a gaseous stream containing unreacted gas that has not been condensed. At this time, if a pressure fluctuation occurs in the compressor supply line, the amount and composition of the condensate obtained from the condenser may fluctuate, and the concentration of low-boiling-point products in the gas re-introduced into the reactor via the compressor may change, which may affect the reactivity within the reactor.

[0013] However, there is still no special device to prevent pressure fluctuations in the compressor supply line that occur during the reactor recirculation process of unreacted gas, which has resulted in limitations in that the pressure in the reactor fluctuates or the gas recovered from the separation tower cannot be stably fed into the compressor supply line.

[0014] The present invention is intended to solve the problems mentioned in the background technology of the above invention, and provides a method for producing an oligomer capable of improving the safety of catalytic reaction and process operation by controlling the pressure between a reactor and a compressor during the process of recirculating unreacted gas to the reactor to maintain the pressure of the reactor constant.

[0015] According to one aspect of the present invention for solving the above problem, a method for producing an oligomer is provided, comprising: (S1) supplying ethylene gas to a lower liquid region containing a solvent in a reactor to perform an oligomerization reaction, then discharging unreacted ethylene gas to the upper portion 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 tower and separating gas from the liquid stream to obtain a stream containing an oligomer product; and (S3) supplying the gas discharged from the upper portion of the reactor to a compressor having a recirculation pipe installed, compressing the gas, and then recirculating the gas to the reactor, and branching a portion of the compressed gas discharged to the compressor, and recirculating the branched compressed gas to a compressor supply line through a pressure regulating valve provided in the recirculation pipe of the compressor to control the pressure of the compressor supply line.

[0016] In the present invention, the pressure regulating valve provided in the recirculation pipe of the compressor can be maintained in a normally open state to continuously perform recirculation of the branched compressed gas.

[0017] According to the present invention, in an oligomer manufacturing process, after compressing unreacted ethylene gas in a compressor, a portion of the compressed gas discharged from the compressor is branched and recycled to the supply line of the compressor, thereby offsetting the pressure fluctuations in the compressor supply line even if the flow rate of the unreacted gas discharged from the reactor is less than the design flow rate of the compressor. In particular, a pressure control valve provided in the recirculation pipe of the compressor is designed to be sized appropriately for offsetting the pressure fluctuations and is continuously opened, so that even if a change in the flow rate of the unreacted gas discharged from the reactor occurs, the pressure in the compressor supply line can be maintained constant by appropriately controlling the flow rate of the compressed gas recirculated to the compressor supply line.

[0018] Through this, pressure fluctuations between the reactor and the compressor can be prevented during the reactor recirculation process of unreacted ethylene gas, and as a result, the internal pressure of the reactor is maintained constant, while at the same time, the instability (hunting) of the flow rate of the recirculated gas supplied to the reactor is minimized, thereby maintaining the liquid level and catalytic reaction in the reactor constant, thereby improving the operability of the catalytic reaction and process safety for oligomer production.

[0019] Figures 1 and 2 illustrate a recirculation loop of unreacted gas to a reactor applied in a conventional olefin production process.

[0020] Figures 3 to 6 illustrate a recirculation loop of unreacted gas to a reactor, including a structure in which recirculation pipes are installed in the supply line and discharge line of a compressor in an olefin production process according to one embodiment of the present invention.

[0021] As used herein, the terms “include” or “contain” specify a particular characteristic, area, integer, step, operation, element, or component, but do not exclude the addition of other particular characteristics, areas, integers, steps, operations, elements, or components.

[0022] The term 'copolymer' used herein means a copolymer composed of repeating units derived from two or more monomers.

[0023] The term "stream" as used herein may refer to the flow of fluid within a process, or may refer to the fluid itself flowing within a pipe. Specifically, the stream may refer to both the fluid itself flowing within the pipe connecting each device and the flow of the fluid. Furthermore, the fluid may include one or more components of gas, liquid, and solid.

[0024] The term "upper" as used herein, unless otherwise specified, means a point 0 to 50% in height downward from the top of the device, and may specifically mean the top (top). In addition, the term "lower" means a point 50 to 100% in height downward from the top of the device, and may specifically mean the bottom (bottom).

[0025] The term 'side stream' as used herein may mean a stream discharged from the top of the device at a height of 25 to 80% or from 40 to 70% downwards, unless otherwise specified.

[0026] Additionally, the “pressure” referred to herein means gauge pressure measured relative to atmospheric pressure.

[0027] Hereinafter, the present invention will be described in detail with reference to the attached drawings.

[0028] One embodiment of the present invention relates to a method for producing an oligomer capable of improving catalytic reaction and process operation stability by maintaining the pressure of a reactor constant during the process of recirculating unreacted gas to the reactor.

[0029] Figures 3 to 6 illustrate a process of a method for producing olefins according to one embodiment of the present invention, and the method can be performed in a system equipped with a recirculation loop for unreacted gas, including a reactor (100), a separation tower (200), and a compressor (10) equipped with a recirculation pipe. In addition, the separation tower may be additionally equipped with a reboiler for heating by transferring heat, a condenser for converting a stream generated by heating from a gas phase to a liquid phase, a gas-liquid separator for separating the condensed stream, a valve for controlling the flow of each stream, a pump, a sensor for measuring temperature and pressure, etc.

[0030]

[0031] According to one embodiment of the present invention, first, an oligomerization reaction is performed by supplying ethylene gas to a lower liquid region containing a solvent in a reactor (100), and the liquid region may additionally include a catalyst for reaction activation.

[0032] The above reactor (100) may be a reactor capable of continuously performing an oligomerization reaction in a state where ethylene is dissolved in a solvent in the presence of a catalyst, and such reactor may include a continuous stirred-tank reactor, a plug flow reactor, a bubble column reactor, etc.

[0033] For example, a raw material gas is introduced into a liquid region containing a solvent, catalyst, etc. through a distribution device installed at the bottom of a bubble column reactor, and is dispersed while rising in the form of bubbles, and the dispersed gas is mixed within the liquid region while generating turbulence, so that an oligomerization reaction can be performed.

[0034] The above oligomerization reaction can produce a desired alpha olefin product by supplying ethylene monomer gas to a reactor (100) and undergoing an oligomerization reaction. At this time, the oligomerization reaction is performed in the lower region of the reactor (100), and the oligomerization reaction of the monomer can be performed in a liquid state in which the gaseous ethylene monomer is dissolved in a solvent.

[0035] The above oligomerization reaction may refer to a reaction in which monomers are oligomerized. Depending on the number of monomers polymerized, it is called trimerization or tetramerization, and these are collectively called multimerization. For example, alpha olefins such as 1-hexene and 1-octene can be produced through trimerization or tetramerization of ethylene.

[0036] The ethylene gas supplied to the above reactor (100) may be a stream containing ethylene (C2) separated from naphtha thermal cracking.

[0037] The solvent for dissolving the above ethylene gas may include at least one selected from the group consisting of n-pentane, n-hexane, n-heptane, cyclohexane, methylcyclohexane, octane, cyclooctane, decane, dodecane, benzene, xylene, 1,3,5-trimethylbenzene, toluene, ethylbenzene, chlorobenzene, dichlorobenzene, and trichlorobenzene. In some cases, two types of the above solvents may be mixed and used. Through this, the ethylene gas can be liquefied at a higher temperature, and the dissolution rate of the ethylene gas in the solvent can be improved.

[0038] In the above ethylene oligomerization reaction, a compound including a transition metal catalyst may be used as a catalyst to promote reaction activity. For example, the catalyst may be a compound including at least one selected from the group consisting of chromium (III) acetylacetonate, chromium (III) chloride tetrahydrofuran, chromium (III) 2-ethylhexanoate, chromium (III) tris(2,2,6,6-tetramethyl-3,5-heptaneindionate), chromium (III) benzoylacetonate, chromium (III) hexafluoro-2,4-pentaneindionate, chromium (III) acetate hydroxide, chromium (III) acetate, chromium (III) butyrate, chromium (III) pentanoate, chromium (III) laurate, and chromium (III) stearate.

[0039] In addition, a cocatalyst may be additionally used to increase the activity of the catalyst, and for example, the cocatalyst may include at least one selected from the group consisting of trimethyl aluminum, triethyl aluminum, triisopropyl aluminum, triisobutyl aluminum, ethylaluminum sesquichloride, diethylaluminum chloride, ethyl aluminum dichloride, methylaluminoxane, modified methylaluminoxane, and borate.

[0040] The above oligomerization reaction can be operated under conditions commonly applied in the field, for example, 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.

[0041] When this oligomerization reaction is performed, a liquid stream containing ethylene polymerized oligomer products, by-products, solvent, unreacted gas dissolved in the solvent, etc. may exist in the lower region of the reactor (100), and unreacted ethylene gas that is not dissolved in the solvent and thus does not participate in the oligomerization reaction may exist in the upper region.

[0042] The above liquid stream can be discharged through a discharge line connected to the lower side of the reactor (100) and transferred to a separation tower (200).

[0043] The above separation tower (200) can receive a liquid stream and perform component separation according to boiling point, thereby separating the liquid stream into a gaseous upper discharge stream containing unreacted ethylene monomer and a liquid lower discharge stream containing oligomer products, byproducts, and a solvent. The oligomer products and solvent contained in the lower discharge stream of the separation tower (200) can be supplied to an additional separation tower (not shown) to separate the solvent, thereby obtaining a purified oligomer product. The separation tower (200) and the additional separation tower can be operated under conditions commonly applied in the relevant field, and there are no special limitations.

[0044] Meanwhile, unreacted ethylene gas that did not participate in the oligomerization reaction in the reactor (100) may be discharged to the upper part of the reactor and then recycled to the reactor (100) via the compressor (10) to be reused as raw material gas.

[0045] The compressor (10) supplies electric energy to the unreacted ethylene gas transferred from the reactor (100) to compress it and increase the pressure, and the temperature of the gaseous stream can also increase in proportion to the amount of electric energy.

[0046] As illustrated in FIGS. 3 to 6, in the present invention, a recirculation pipe equipped with a pressure control valve (11) is connected to a compressor supply line (10a) through which unreacted gas is transported and a discharge line (10b) through which compressed gas passes through the compressor and is discharged, and a portion of the compressed gas is branched off from the compressor discharge line (10b) and recirculated, thereby preventing the occurrence of pressure fluctuations in the compressor supply line (10a).

[0047] That is, by using a portion of the compressed gas discharged from the compressor (10) as a source for maintaining the pressure of the compressor supply line (10a), even if the flow rate of the unreacted gas discharged from the reactor (100) is less than the design flow rate of the compressor (10), the pressure fluctuation can be offset. Through this, the pressure differential change of the pressure control valve provided in the reactor of the front stage can be minimized, so that the pressure inside the reactor can be kept constant, and further, the pressure fluctuation in the compressor discharge line (10b) can be prevented, so that the instability (hunting) of the flow rate of the recirculated gas supplied to the reactor (100) can be minimized. As a result, by maintaining the liquid level and catalytic reaction inside the reactor constant, the oligomer productivity and the stability of process operation can be improved.

[0048] In addition, it is preferable that the pressure regulating valve (11) provided in the recirculation pipe of the compressor (10) be maintained in an open state. The pressure regulating valve provided in the recirculation pipe of a general compressor has a function of opening the pressure regulating valve only when a surge phenomenon occurs in which gas does not flow into the compressor, and closing the pressure regulating valve when normal operation is restored. Since it only controls the pressure inside the pipe from decreasing below a certain value, pressure instability (hunting) may occur in the compressor supply line. In contrast, in the present invention, the capacity of the compressor is designed to be greater than the sum of the flow rates of the gas discharged from the reactor and the flow rates of the gas discharged from the separation tower, and the pressure regulating valve (11) provided in the compressor recirculation pipe is designed to be able to respond to fluctuations in the flow rates of the reactor exhaust gas and the flow rates of the separation tower exhaust gas, thereby being maintained open at all times, thereby controlling the flow rate of the branched compressed gas and maintaining a constant pressure in the compressor supply line (10a).

[0049] In one embodiment of the present invention, the compressor (10) may be any device known in the art that can compress a gaseous flow, and may be applied as one or multiple devices connected in series depending on the compression ratio of the supplied unreacted gas.

[0050] Referring to FIG. 3, unreacted ethylene gas recovered from the separation tower (200) can be transferred to the compressor supply line (10a) for recirculation to the reactor. Even if the possibility of pressure fluctuation increases due to the addition of the flow rate of the separation tower discharge gas to the flow rate of the reactor discharge unreacted gas in the compressor supply line (10a), in the present invention, a portion of the compressed gas is branched and recirculated through a pressure regulating valve (11) provided in the recirculation pipe of the compressor (10), thereby controlling the pressure of the compressor supply line (10a) to minimize the differential pressure change of the pressure regulating valve provided in the reactor upstream of the compressor, thereby maintaining the internal pressure of the reactor constant.

[0051] The capacity of the above compressor (10) can be selected by considering the total flow rate of the reactor discharge unreacted gas, the separation tower recovery gas, and the compressed gas recycled in the compressor discharge line that can be combined in the compressor supply line (10a).

[0052] Meanwhile, the flow rate of the compressed gas branched from the compressor discharge line (10b) and recirculated through the pressure regulating valve (11) can be controlled by measuring the pressure of the compressor supply line (10a), and may be, for example, in the range of 5 to 50 wt%, specifically 10 to 30 wt%, of the total compressed gas flow rate discharged from the compressor (10). When the flow rate of the recirculated compressed gas is less than 5 wt%, there is a limit to offsetting the pressure fluctuation occurring in the compressor supply line (10a), making it difficult to maintain a constant pressure in the reactor (100). When the flow rate of the recirculated compressed gas exceeds 50 wt%, the pressure fluctuation occurring in the compressor supply line (10a) can be sufficiently controlled, but the amount of electricity consumed in the compressor (10) increases, which is disadvantageous in terms of energy.

[0053] Referring to FIG. 4, the unreacted gas discharged from the reactor and the gas recovered from the separation tower are passed through a condenser (20) arranged in front of the compressor (10) to condense low-boiling-point components including ethylene dimers and solvents, and then the gaseous stream of unreacted ethylene monomer separated from the condensate in the gas-liquid separator can be supplied to the compressor (10) for recirculation. At this time, by recirculating a portion of the compressed gas, the temperature of which has increased by passing through the compressor (10), to the compressor supply line (10a) at all times in a constant range, for example, 5 to 50 wt% of the total compressed gas flow rate, the unreacted ethylene monomer stream discharged from the gas-liquid separator can be prevented from condensing within the pipe due to temperature changes such as outside air. Through this, regardless of the composition of the gas discharged through the condenser and gas-liquid separator, the condensate (liquid component) is prevented from being supplied to the compressor, protecting the compressor, while recirculating the unreacted gas to the reactor stably, thereby maintaining the pressure of the reactor constant.

[0054] Referring to FIGS. 5 and 6, the unreacted ethylene gas recovered from the separation tower (200) may 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). Even in this case, in the present invention, a portion of the compressed gas is branched and recycled through a pressure control valve (11) provided in the recirculation pipe of the compressor (10), thereby directly controlling the pressure in the compressor supply line (10a), i.e., the upper pressure of the reactor, thereby maintaining the internal pressure of the reactor constant, and at the same time, the unreacted gas discharged from the reactor can be pressurized in the compressor and then recycled back to the lower portion of the reactor.

[0055] According to the present invention as described above, in the oligomer manufacturing process, after compressing unreacted ethylene gas in a compressor, a portion of the compressed gas discharged from the compressor is branched and recycled to the supply line of the compressor, so that even if the flow rate of the unreacted gas discharged from the reactor is less than the design flow rate of the compressor or the flow rate instability (hunting) of the unreacted gas discharged from the reactor occurs, the pressure fluctuation of the compressor supply line can be offset. In particular, the pressure control valve provided in the recirculation pipe of the compressor can continuously open and appropriately control the flow rate of the compressed gas recycled to the compressor supply line, thereby maintaining the pressure of the compressor front end, i.e., the supply line, constant. For example, the pressure fluctuation in the compressor supply line can be controlled within a range of -1 bar to 1 bar, specifically, -0.2 bar to 0.2 bar or -0.1 bar to 0.1 bar.

[0056] In this way, pressure fluctuations between the reactor and the compressor can be prevented during the recirculation process of unreacted ethylene gas, thereby maintaining the internal pressure of the reactor at a constant level. For example, in the present invention, the internal pressure fluctuations of the reactor operated in the oligomer manufacturing process are controlled within a range of -0.5 bar to 0.5 bar, specifically -0.1 bar to 0.1 bar, and more specifically -0.02 bar to 0.02 bar, thereby enabling stable operation of the reactor.

[0057] In addition, by minimizing the instability (hunting) of the flow rate of the recirculating gas supplied to the reactor, the liquid level and catalytic reaction within the reactor are maintained constant, thereby improving oligomer productivity and process operation stability.

[0058] Hereinafter, the present invention will be described in more detail by way of examples. However, the following examples are intended to illustrate the present invention, and it will be apparent to those skilled in the art that various changes and modifications are possible within the scope and technical spirit of the present invention, and the scope of the present invention is not limited to these examples alone.

[0059] The following examples and comparative examples simulate the method according to the present invention using a commercial process simulation program (HYSYS DANAMICS). The constants required for the simulation used values ​​built into the program and values ​​described in the literature.

[0060]

[0061] Comparative Example 1:

[0062] The oligomer manufacturing process was performed according to the process flow diagram shown in Fig. 1.

[0063] (Step 1)

[0064] After performing an oligomerization reaction by supplying ethylene gas to the lower liquid region containing a solvent and a catalyst in the reactor (100), unreacted ethylene gas (G) was discharged to the upper part of the reactor (100) and a liquid stream (L) containing an oligomer product was discharged to the lower side of the reactor.

[0065] (Step 2)

[0066] The liquid stream (L) discharged from the lower side of the above reactor (100) was supplied to a separation tower (200), and gas was separated from the liquid stream to obtain a stream containing an oligomer product.

[0067] (Step 3)

[0068] Unreacted ethylene gas discharged from the upper portion of the reactor (100) was supplied to a compressor (10), and the capacity of the compressor was designed to be 30% greater than the flow rate of the compressor supply line. In addition, the gas separated and recovered in the separation tower (200) was also transported to the compressor (10) and compressed in the compressor (10) together with the unreacted gas discharged from the reactor.

[0069] The compressed gas discharged from the compressor (10) was recycled to the reactor (100) and used again as raw material gas.

[0070]

[0071] Comparative Example 2:

[0072] As shown in Fig. 2, in step 3, the reactor discharge unreacted gas and the separation tower discharge unreacted gas are supplied to a condenser (20) to separate a liquid stream in which low-boiling-point components and solvent including ethylene dimer are condensed and a gaseous stream of unreacted gas that has not been condensed, and then the same process as in Comparative Example 1 is performed except that the unreacted gas that has not been condensed is supplied to a compressor (10) and the condensed liquid is transferred back to a purification tower (200).

[0073]

[0074] Example 1:

[0075] As shown in Fig. 3, the oligomer manufacturing process was performed according to a process flow diagram including a structure in which a recirculation pipe equipped with a pressure regulating valve is installed in the supply line and discharge line of the compressor.

[0076] (Step 1)

[0077] After performing an oligomerization reaction by supplying ethylene gas to the lower liquid region containing a solvent and a catalyst in the reactor (100), unreacted ethylene gas (G) was discharged to the upper part of the reactor (100) and a liquid stream (L) containing an oligomer product was discharged to the lower side of the reactor.

[0078] (Step 2)

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

[0080] (Step 3)

[0081] Unreacted ethylene gas discharged from the upper portion of the reactor (100) was supplied to the compressor (10), and at this time, the gas separated and recovered in the separation tower (200) was also transported 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 branched from the compressor discharge line (10b) and recirculated to the compressor supply line (10a). At this time, the compressor capacity is designed so that the flow rate of the compressed gas branched from the compressor discharge line (10b) and recirculated is 5 wt% of the total compressed gas flow rate. In addition, the control valve provided in the compressor recirculation pipe is kept in a normally open state to continuously perform recirculation of the branched compressed gas.

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

[0084]

[0085] Example 2:

[0086] As shown in Fig. 4, in step 3, the unreacted gas discharged from the reactor and the gas recovered from the separation tower were supplied to a condenser (20) to separate a liquid stream containing low-boiling-point components and solvents including ethylene dimers into a condensed liquid stream and a gaseous stream of unreacted gas that was not condensed, and then the same process as in Example 1 was performed, except that the unreacted gas that was not condensed was supplied to a compressor (10) and the condensed liquid phase was transferred back to a purification tower (200).

[0087]

[0088] Example 3:

[0089] As shown in Fig. 5, the gas recovered from the separation tower (200) in step 3 was pre-compressed in a separate compressor (30) and then recycled to the reactor (100) together with the compressed gas discharged from the compressor (10), and a portion of the compressed gas was branched through a pressure control valve (11) provided in the recirculation pipe of the compressor (10) and recycled to the compressor supply line, while directly controlling the upper pressure of the reactor, the same process as in Example 1 was performed.

[0090]

[0091] Example 4:

[0092] As shown in Fig. 6, the gas recovered from the separation tower (200) in step 3 was pre-compressed in a separate compressor (30) and then recycled to the reactor (100) together with the compressed gas discharged from the compressor (10), and a portion of the compressed gas was branched through a pressure control valve (11) provided in the recirculation pipe of the compressor (10) and recycled to the compressor supply line, while directly controlling the upper pressure of the reactor, the same process as in Example 2 was performed.

[0093]

[0094] Example 5:

[0095] In step 3, the same process as in Example 1 was performed, except that the compressor capacity was designed so that the flow rate of compressed gas branched from the compressor discharge line (10b) and recycled was 10 wt% of the total compressed gas flow rate.

[0096]

[0097] Example 6:

[0098] In step 3, the same process as in Example 1 was performed, except that the compressor capacity was designed so that the flow rate of compressed gas branched from the compressor discharge line (10b) and recycled was 30 wt% of the total compressed gas flow rate.

[0099]

[0100] Example 7:

[0101] In step 3, the same process as in Example 1 was performed, except that the compressor capacity was designed so that the flow rate of compressed gas branched from the compressor discharge line (10b) and recirculated was 50 wt% of the total compressed gas flow rate.

[0102]

[0103] Example 8:

[0104] In step 3, the same process as in Example 1 was performed, except that the compressor capacity was designed so that the flow rate of compressed gas branched from the compressor discharge line (10b) and recycled was 3 wt% of the total compressed gas flow rate.

[0105]

[0106] In the above comparative examples and examples, the pressure fluctuations in the reactor (100) and the compressor supply line (10a) were calculated through simulation (using the HYSYS DANAMICS program), and the results are shown in Table 1 below.

[0107] Branching / recirculation of compressed gasBranching ratio of compressed gas 1)Variation range of compressor supply line pressure during the entire process Variation range of reactor internal pressure during the entire process Electrical energy consumption in the compressor (KW) Comparative example 1X-± 5 bar exceeds ± 3 bar 10.02 Comparative example 2X-± 5 bar exceeds ± 3 bar 9.70 Example 1○5%± 0.2 bar± 0.05 bar 8.11 Example 2○5%± 0.2 bar± 0.05 bar 7.85 Example 3○5%± 0.05 bar± 0.05 bar 7.85 Example 4○5%± 0.05 bar± 0.05 bar 7.59 Example 5○10%± 0.1 bar± 0.02 bar 8.56 Example 6○30%± 0.1 bar± 0.02 bar 11.01 Example 7○50%± 0.1bar± 0.02bar15.41Example 8○3%± 1.0bar± 0.50bar7.941) Indicates the flow rate (weight %) that is branched and recirculated based on the flow rate of the entire compressed gas.

[0108] In the above Table 1, Comparative Examples 1 and 2 were designed without a compressor recirculation pipe and with a compressor capacity 30% larger than the compressor supply line flow rate. As a result, the compressor was stopped due to the interlock set to protect the compressor as the pressure in the compressor supply line decreased. As a result, the pressure in the compressor supply line increased until the compressor was restarted, and as this process was repeated, the differential pressure of the pressure regulating valve located at the top of the reactor changed significantly, causing the reactor pressure to become instable (hunting). In addition, as the pressure in the compressor supply line fluctuated significantly, the separation tower recovery gas, which was transported by the pressure difference in the separation tower, could not be supplied smoothly, and the pressure of the separation tower could not be controlled. In other words, in Comparative Examples 1 and 2, the compressor was stopped due to the pressure difference with respect to the compressor supply line, and a large pressure fluctuation occurred in the compressor supply line and the internal pressure of the reactor until the compressor was restarted.

[0109] In contrast, in Examples 1 to 8, after compressing unreacted ethylene gas in a compressor, a portion of the compressed gas discharged from the compressor is branched and recycled to the supply line of the compressor, and the flow rate of the recycled compressed gas is controlled to control the pressure of the compressor supply line, so that it can be confirmed that the internal pressure change of the reactor is small even if the flow rate of the unreacted gas discharged from the reactor changes.

[0110] In particular, in Example 6, the flow rate of the compressor supply line increased by 30% as the branching ratio of the compressed gas was 30%, corresponding to the compressor capacity of Comparative Examples 1 and 2, and pressure fluctuations were controlled without a significant increase in electricity consumption. This is the result of maintaining the pressure of the compressor supply line constant by controlling the recirculation flow rate of the branched compressed gas by constantly opening the pressure regulating valve provided in the compressor recirculation pipe.

[0111] Meanwhile, Example 7 had a branching ratio of compressed gas of 50 wt%, sufficiently controlling the pressure fluctuation occurring in the compressor supply line, but the energy consumption increased somewhat compared to Example 6.

[0112] Example 8 is an example in which the flow rate of the exhaust gas from the upper part of the reactor increased instantaneously or the flow rate of the gas recovered from the upper part of the separation tower increased instantaneously. As the margin of compressor capacity was small, the pressure in the compressor supply line increased, affecting the reactor pressure control, and thus the pressure fluctuation within the reactor increased somewhat.

[0113]

[0114] [Explanation of symbols]

[0115] 100: Reactor

[0116] 200: Separation tower

[0117] 10, 30: Compressor

[0118] 11: Pressure regulating valve of compressor recirculation pipe

[0119] 20: Condenser

Claims

1. (S1) A step of supplying ethylene gas to a lower liquid region containing a solvent in a reactor to perform an oligomerization reaction, then 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) a step of 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 an oligomer product; and (S3) A step of supplying the gas discharged from the upper part of the reactor to a compressor equipped with a recirculation pipe, compressing the gas, and then recirculating it to the reactor, An oligomer manufacturing method for controlling the pressure of a compressor supply line by branching a portion of the compressed gas discharged from the compressor and recirculating the branched compressed gas to a compressor supply line through a pressure regulating valve provided in a recirculation pipe of the compressor.

2. In paragraph 1, An oligomer manufacturing method comprising recovering the separated gas from the above separation tower and transporting it to the supply line of the above compressor.

3. In paragraph 1, A method for producing an oligomer, wherein the gas supplied to the compressor is separated from the low-boiling-point components and solvent condensed in a condenser placed at the front end of the compressor.

4. In paragraph 3, A method for producing an oligomer in which the low-boiling-point component and solvent condensed in the above condenser are separated and then transferred to the above separation tower.

5. In paragraph 1, A method for manufacturing an oligomer in which a pressure control valve provided in the recirculation pipe of the above compressor is kept in a normally open state to continuously perform recirculation of the branched compressed gas.

6. In paragraph 1, A method for producing an oligomer, wherein the flow rate of compressed gas recycled to the compressor supply line is 5 to 50 wt% of the total flow rate of compressed gas discharged from the compressor.

7. In paragraph 6, A method for producing an oligomer, wherein the flow rate of compressed gas recycled to the compressor supply line is 10 to 30 wt% of the total flow rate of compressed gas discharged from the compressor.

8. In paragraph 1, An oligomer manufacturing method comprising recovering a gas separated from the above separation tower, pre-compressing it, and then transporting it to the discharge line of the above compressor.

9. In paragraph 1, A method for producing an oligomer in which pressure fluctuations in the compressor supply line are controlled within a range of -1 bar to 1 bar.

10. In paragraph 9, A method for producing an oligomer, wherein the pressure fluctuation in the compressor supply line is controlled within a range of -0.2 bar to 0.2 bar.

11. In paragraph 1, A method for producing an oligomer in which the pressure fluctuation during operation of the above reactor is controlled within a range of -0.5 bar to 0.5 bar.

12. In paragraph 11, A method for producing an oligomer in which the pressure fluctuation during operation of the above reactor is controlled within a range of -0.1 bar to 0.1 bar.

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