Method for recovering unreacted monomers

Abstract

The present invention provides a method for recovering unreacted monomers, the method including: (S1) a step for supplying a residue, including unreacted monomers that remain after a polymerization reaction in a reactor, to a gas separation column to separate the residue into an overhead stream including an unreacted monomer gas and a bottoms stream including a relatively high boiling point component; (S2) a step for compressing the overhead stream, discharged from the top of the gas separation column and including the unreacted monomer gas, in a compressor to form a compressed stream, supplying the compressed stream to a condenser, and cooling the compressed stream in the condenser to obtain a cooled stream; and (S3) a step for separating the cooled stream in a gas-liquid separator and recovering a liquid monomer fraction from the bottom of the gas-liquid separator and a gas-phase monomer fraction from the top of the gas-liquid separator, wherein the liquid monomer fraction recovered from the bottom of the gas-liquid separator is recycled to the reactor.

Description

Method for recovering unreacted monomer

[0001] Cross-citation with related applications

[0002] This application claims the benefit of priority to Korean Patent Application No. 10-2024-0108175, filed August 13, 2024, and Korean Patent Application No. 10-2025-0110343, filed August 11, 2025, the entire contents of which are incorporated herein by reference.

[0003] Technology field

[0004] The present invention relates to a method for recovering unreacted monomers, and more particularly, to a method for efficiently recovering unreacted monomers from a polymerization reaction solution while minimizing energy consumption.

[0005] Polymers such as polyolefin, polystyrene, and polyamide can be produced by polymerizing monomers that constitute repeating units of the polymer chain in the presence of an appropriate catalyst in an organic solvent.

[0006] For example, polyolefins can be produced by introducing a feed containing ethylene monomers and linear alpha olefin monomers such as 1-butene dissolved in a solvent such as hexane into a reactor and performing a polymerization reaction in the presence of a catalyst. In the polymerization reaction, a large amount of monomers are consumed to obtain a polymer solution in which polyolefins are produced, and the final polyolefin is obtained through a purification process in which unreacted monomers, used solvents, catalyst components, impurities, etc. are removed from the polymer solution discharged from the reactor, and the separated solvent and monomers can be recovered and reused.

[0007] The residue remaining after the purification process exists as a mixture of unreacted monomers, solvents, and impurities. A separation process is necessary to recover the unreacted monomers and organic solvents from the residue and reuse them as raw materials.

[0008] Figures 1 and 2 illustrate a conventional separation process for residues (mixed solutions of C2, C4 and C6) remaining in a polymerization reaction process (polyolefin manufacturing process).

[0009] Referring to Fig. 1, a mixed solution of C2, C4, and C6 can be supplied to a gas separation tower (10) to be separated into an upper stream containing low-boiling-point unreacted monomer (C2, C4) gas and a lower stream containing high-boiling-point components (C6). The high-boiling-point component (C6) discharged to the lower portion of the gas separation tower (10) can be recovered and reused as a solvent. Meanwhile, the low-boiling-point unreacted monomers (C2, C4) discharged to the upper portion of the gas separation tower (10) exist in a high-temperature gaseous state, so a process of liquefying them through ultra-high-pressure compression is required for their recovery. Therefore, depending on the process equipment situation, the low-boiling-point unreacted monomers (C2, C4) may be incinerated without recovery in consideration of utility costs, but in this case, problems of raw material loss and greenhouse gas emissions arise.

[0010] Referring to Fig. 2, a mixed solution of C2, C4 and C6 is supplied to a gas separation tower (10) to separate an upper stream containing low-boiling-point monomer (C2, C4) gas, and then this is compressed into an ultra-high pressure (e.g., 20 kg / cm) compressor (20). 2·g) and supplied to a gas purification tower (30), and a C2 monomer with a very low boiling point is separated into the upper part using an ultra-low temperature refrigerant in a condenser (21) provided on the upper part of the gas purification tower (30), and a C4 monomer with a higher boiling point is separated into the lower part, thereby recovering low-boiling-point unreacted monomers. In this case, there is a disadvantage in that the equipment cost increases due to the additional construction of a gas purification tower for separating C2 monomers and C4 monomers, and excessive operating conditions such as the use of an ultra-low temperature refrigerant must be accompanied, thereby increasing energy consumption. In addition, there is a difficulty in that the operating conditions of the gas purification tower must be frequently changed in order to achieve the specifications of the unreacted monomers to be recovered.

[0011] The present invention is intended to solve the problems mentioned in the background technology of the above invention, and provides an efficient method for recovering unreacted monomers, which can minimize equipment / operating costs and energy consumption for recovering low-boiling-point unreacted monomers from unreacted residues generated in a polymer manufacturing process and ensure operational stability.

[0012] In order to solve the above problem, one aspect of the present invention provides a method for recovering unreacted monomers, comprising: (S1) supplying a residue containing unreacted monomers after a polymerization reaction in a reactor to a gas separation tower and separating the residue into an upper stream containing unreacted monomer gas and a lower stream containing relatively high-boiling components; and (S2) compressing an upper stream containing the unreacted monomer gas discharged from an upper portion of the gas separation tower in a compressor to form a compressed stream, supplying the compressed stream to a condenser, and cooling the compressed stream in the condenser to obtain a cooled stream; and (S3) separating the cooled stream in a gas-liquid separator to recover a liquid monomer fraction from a lower portion of the gas-liquid separator, and recovering a gaseous monomer fraction from an upper portion of the gas-liquid separator, wherein the liquid monomer fraction recovered from the lower portion of the gas-liquid separator is recycled to the reactor.

[0013] According to the present invention, by liquefying and recovering unreacted monomer gas separated from residue generated in a polymerization reaction process through low-pressure compression and cooling, equipment / operating costs and energy consumption can be minimized compared to a recovery method that performs a subsequent purification process after a conventional ultra-high-pressure compression.

[0014] In addition, in the present invention, by changing the composition of the unreacted monomer to be recovered in a manner of controlling the liquefaction temperature of the unreacted monomer stream in the low-pressure compression and cooling step, the specifications of the monomer raw material used in the polymerization reaction can be efficiently achieved.

[0015] Therefore, the gaseous and liquid monomer fractions contained in the cooled stream can be recycled to the compressor of the front stage or reused as raw materials for the polymerization reaction without going through a separate purification process, thereby reducing raw material costs and greenhouse gas emissions.

[0016] Figures 1 and 2 illustrate a conventional separation process for residues remaining in a polymerization reaction process.

[0017] FIG. 3 illustrates a process for recovering unreacted monomer gas from residue generated in a polymerization reaction process according to one embodiment of the present invention.

[0018] Figures 4 and 5 illustrate the composition of a liquid monomer fraction and the composition of a gaseous monomer fraction, respectively, according to the temperature of a stream cooled by low-pressure compression and cooling in a recovery method according to one embodiment of the present invention.

[0019] The terms or words used in the description and claims of the present invention should not be interpreted as limited to their usual or dictionary meanings, but should be interpreted as meanings and concepts that conform to the technical idea of ​​the present invention, based on the principle that the inventor can appropriately define the concept of the term to explain his or her own invention in the best way.

[0020] 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.

[0021] 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.

[0022] As used herein, the term "upper" means a point 0% to 20% below the top of the device, unless otherwise specified, and may specifically mean the top (top). In addition, the term "lower" means a point 80% to 100% below the top of the device, and may specifically mean the bottom (bottom).

[0023] Additionally, the “pressure” referred to herein means gauge pressure measured relative to atmospheric pressure.

[0024] Meanwhile, in the present invention, in devices such as separation towers and purification towers, the operating temperature of the device may refer to the temperature at the bottom of the device unless otherwise specified. In addition, the operating pressure of the device may refer to the pressure at the top of the device unless otherwise specified.

[0025] One embodiment of the present invention relates to a method for efficiently recovering unreacted monomer from residue generated in a polymerization reaction process while consuming minimal energy.

[0026] Hereinafter, the present invention will be described in detail with reference to the attached drawings.

[0027] FIG. 3 schematically illustrates a method for recovering unreacted monomer gas from residue generated in a polymerization reaction process according to one embodiment of the present invention, and the recovery method of the present invention can be performed in an equipment system including a gas separation tower (10), a compressor (20), a condenser (21), and a gas-liquid separator (22). In addition, the gas separation tower may be installed with a reboiler for heating the feed stream by transferring heat to it, and a condenser for converting the upper stream generated by the heating from a gas phase to a liquid phase, and valves for controlling the flow of the stream, pumps, sensors for measuring temperature, pressure, and density, etc. may be additionally installed and used in each device.

[0028] Referring to FIG. 3, a method for recovering unreacted monomers according to one embodiment of the present invention comprises the steps of: (S1) supplying a residue containing unreacted monomers after a polymerization reaction in a reactor to a gas separation tower and separating the residue into an upper stream containing unreacted monomer gas and a lower stream containing relatively high-boiling components; and (S2) compressing an upper stream containing the unreacted monomer gas discharged from an upper portion of the gas separation tower in a compressor to form a compressed stream, supplying the compressed stream to a condenser, and cooling the compressed stream in the condenser to obtain a cooled stream; and (S3) separating the cooled stream in a gas-liquid separator to recover a liquid monomer fraction from a lower portion of the gas-liquid separator, and recovering a gaseous monomer fraction from an upper portion of the gas-liquid separator, wherein the liquid monomer fraction recovered from the lower portion of the gas-liquid separator is recycled to the reactor. Specifically, in the method for recovering unreacted monomers according to the present invention, step (S1) includes a process of supplying a residue containing unreacted monomers after performing a polyolefin polymerization reaction in a reactor to the gas separation tower (10) and separating the residue into an upper stream containing unreacted monomer gas and a lower stream containing relatively high-boiling-point components.

[0029] The residue containing the unreacted monomer may refer to a residue obtained after purifying the polyolefin from the reaction product after performing a polymerization reaction to polymerize polyolefin in the reactor (40). The residue containing the unreacted monomer may contain unreacted monomers that have not reacted in the polymerization reaction, although the polyolefin has been largely removed. If the unreacted monomers are separated from the residue containing the unreacted monomers and supplied to the reactor (40) for reuse, the loss of unreacted monomers that are discarded can be reduced and costs can also be reduced. The polyolefin can be produced by introducing a raw material composition into a reactor and performing a polymerization reaction in the presence of a catalyst, and the raw material composition for the polymerization reaction may include, as a monomer, an ethylene monomer or a propylene monomer; and a linear alpha-olefin copolymerizable with the monomers (1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, etc.). In addition, the raw material composition may include a solvent for dissolving the monomer and linear alpha-olefin to be polymerized, and the solvent may be n-pentane, n-hexane, n-heptane, cyclohexane, methylcyclohexane, octane, cyclooctane, decane, or the like.

[0030] In addition, as a catalyst for promoting activity in the polymerization reaction, at least one selected from the group consisting of a transition metal catalyst, for example, 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 may be used.

[0031] In the above polymerization reaction, a large amount of monomer is consumed to obtain a polymerization solution in which polyolefin is produced, and the final polyolefin is obtained through a purification process in which unreacted monomers, used solvents, catalyst components, impurities, etc. are removed from the polymerization solution discharged from the reactor (40).

[0032] In this polyolefin manufacturing process, if the polyolefin is purified after the polymerization reaction, a residue containing unreacted monomers, solvents, and impurities can be obtained. For example, the residue containing the unreacted monomers may be an unreacted monomer of C2 to C4 and an unreacted monomer of C5 to C 12 It may be a mixed solution containing hydrocarbons.

[0033] The residue containing such unreacted monomers can be supplied to a gas separation tower (10) to be separated into an upper stream containing unreacted monomer gas and a lower stream containing relatively high boiling point components.

[0034] At this time, an upper stream containing unreacted monomer gases of C2 and C4 can be discharged from the upper portion of the gas separation tower (10). In addition, a lower stream containing relatively high boiling point components can be discharged from the lower portion of the gas separation tower (10), and the relatively high boiling point components are C5 to C 12 may contain hydrocarbons.

[0035] The above gas separation tower (10) may be, for example, a distillation tower.

[0036] Specifically, when the gas separation tower (10) is a distillation tower, the residue containing the unreacted monomer is supplied to the distillation tower and the distillation tower is heated to separate the components contained in the residue containing the unreacted monomer into a gaseous fraction containing unreacted monomers of C2 to C4 and a gaseous fraction containing unreacted monomers of C5 to C 12It can be separated into a liquid fraction containing hydrocarbons of C2 to C4. The gaseous fraction containing unreacted monomers of C2 to C4 is formed into a gaseous fraction containing components with relatively low boiling points, and C5 to C 12 The liquid fraction containing hydrocarbons can be formed into a liquid phase by including components with relatively high boiling points. The gaseous fraction containing unreacted monomers of C2 to C4 is discharged as an upper stream of the gas separation tower (10) and supplied to the compressor (20), and C5 to C 12 The liquid fraction containing hydrocarbons can be discharged as a bottom stream of the gas separation tower (10).

[0037] In addition, the gas separation tower (10) has a temperature of 60 to 100 ℃ or 70 to 90 ℃ and a pressure of 0.5 to 1.5 kg / cm 2 ·g or 0.6 to 1.2 kg / cm 2 · It can be operated at a pressure of g. When the above operating conditions are satisfied, the unreacted monomer with a low boiling point and the component with a higher boiling point can be effectively separated.

[0038] In the method for recovering unreacted monomer according to the present invention, step (S2) may be performed by compressing an upper stream containing unreacted monomer gas discharged from the upper portion of the gas separation tower (10) in a compressor (20) to form a compressed stream, and cooling the compressed stream in a condenser (21) to liquefy it, thereby obtaining a cooled stream.

[0039] The above compressor (20) can be any device known in the art that can compress a gas flow using electric energy, and can be applied as one or multiple devices connected in series depending on the capacity of the incoming gas flow.

[0040] In a conventional unreacted monomer recovery process, low-boiling-point unreacted monomers were discharged through the upper portion of a gas separation tower (10) in a high-temperature gaseous state, and this high-temperature gas was immediately liquefied through ultra-high-pressure compression to perform a purification process for the unreacted monomers. However, this conventional process, because it was performed under high-pressure and ultra-low-temperature conditions, resulted in increased energy consumption and facility costs.

[0041] In order to overcome these problems, in the present invention, a process of compressing and then condensing the upper stream containing the unreacted monomer gas discharged from the gas separation tower (10) is performed in stages. Specifically, the upper stream containing the unreacted monomer gas may be subjected to a low-pressure compression process in which the pressure is increased by 1.4 to 10 times, 2 to 8 times, or 2 to 5 times in the compressor (20), and a subsequent process of cooling and liquefying the compressed gas in the condenser (21) may be performed. More specifically, the upper stream containing the unreacted monomer gas discharged from the upper portion of the gas separation tower (10) may be compressed to a low pressure in the compressor (20) to form a compressed gaseous stream having a pressure of 1.4 to 10 times, 2 to 8 times, or 2 to 5 times the pressure of the upper stream containing the unreacted monomer gas. The pressure of the compressed stream compressed to a low pressure may be 1 to 10 kg / cm 2 ·g or 2 to 8 kg / cm 2 ·g may be. The compression pressure in the compressor (20) may be a lower pressure (low pressure) than the pressure for compressing the gas discharged from the gas separation tower (10) in a conventional process, thereby saving energy for compressing the upper stream containing the unreacted monomer gas, and by performing the subsequent condensation process together, the same effect as compressing at high pressure can be achieved, thereby effectively separating and recovering the unreacted monomer.

[0042] If the pressure of the compressed stream is less than 1.4 times the pressure of the upper stream containing the unreacted monomer gas, the pressure is high, making it difficult to control and process the compressed stream, and if it exceeds 10 times, it may result in excessive energy consumption and increased facility costs.

[0043] In addition, the temperature of the compressed stream may be higher than the upper stream containing the unreacted monomer gas, and may increase in proportion to the pressure compressed in the compressor (20). For example, the compressed stream discharged from the compressor (20) may be in a gaseous state exhibiting a temperature of 70 to 120°C or 80 to 100°C. If the temperature of the compressed stream is less than 70°C, gas-liquid separation through condensation may be difficult, and if it exceeds 120°C, it may exceed the equipment limit, resulting in unstable operation.

[0044] The compressed stream may be discharged from the compressor (20) and supplied to a condenser (21), and may be cooled by heat exchange with cooling water in the condenser (21). The compressed stream may be cooled in the condenser (21) and separated into a liquid monomer fraction and a gaseous monomer fraction. In the introduced compressed stream, unreacted monomer gas (e.g., C4 monomer) having a relatively high boiling point may be condensed by cooling to form a liquid monomer fraction, and unreacted monomer gas (e.g., C2 monomer) having a relatively low boiling point may not be condensed to form a gaseous monomer fraction. At this time, the stream cooled in the condenser (21) may be in a gas-liquid equilibrium state including the gaseous monomer fraction and the liquid monomer fraction.

[0045] Specifically, the C2 monomer or C4 monomer may be present mixed in the liquid monomer fraction and the gaseous monomer fraction depending on the temperature of the cooled stream. For example, when the temperature of the cooled stream is 10°C to 60°C, the liquid monomer fraction and the gaseous monomer fraction contained in the cooled stream may exist in a gas-liquid equilibrium state. In other words, the C2 monomer is mostly present in the gaseous monomer fraction, but some may be present in the liquid monomer fraction due to the gas-liquid equilibrium, and the C4 monomer is mostly present in the liquid monomer fraction, but some may be present in the gaseous monomer fraction due to the gas-liquid equilibrium. This means that the above-mentioned gaseous monomer fraction and liquid monomer fraction are not separated only into the gaseous monomer fraction and the C4 monomer into the liquid monomer fraction depending on the boiling point of the hydrocarbon, but the C2 monomer and the C4 monomer can be mixed and exist in the gaseous monomer fraction and the liquid monomer fraction. However, the ratio of the C2 monomer and the C4 monomer in the gaseous monomer fraction and the liquid monomer fraction can be controlled by controlling the temperature of the cooled stream. By using this characteristic, for example, the C2 monomer and the C4 monomer included in the liquid monomer fraction can be supplied directly to the reactor (40) without a separate monomer mixing process by controlling the temperature of the condenser (21) to adjust the ratio of the C2 monomer and the C4 monomer to a ratio suitable for the polymerization reaction.

[0046] The compressed stream may be condensed by heat exchange with cooling water in the condenser (21), and at this time, the condenser (21) may be operated so that the temperature of the stream cooled by cooling is controlled in the range of 10 to 60° C., or 10 to 20° C., or 20 to 60° C. The composition of the unreacted monomer contained in the cooled stream may be adjusted according to the temperature. In other words, the temperature of the cooled stream formed in the condenser (21) may be 10 to 60° C., and the composition ratio of the C2 monomer or C4 monomer contained in the gaseous monomer fraction and the liquid monomer fraction may be adjusted according to the temperature of the cooled stream.

[0047] The cooling water supplied to the above condenser (21) for heat exchange may have a temperature of 5 to 50°C or 10 to 35°C.

[0048] The flow rate of cooling water that exchanges heat with the compressed stream in the condenser (21) can be controlled within an appropriate range by measuring the temperature of the cooled stream using a temperature controller (T) provided at the rear end of the condenser. Specifically, when the temperature of the cooled stream is to be increased, the temperature of the cooled stream discharged from the condenser (21) is measured, and the temperature of the cooled stream can be controlled by supplying less cooling water in proportion to the desired temperature increase and the flow rate of the compressed stream supplied to the condenser (21). By controlling the temperature of the cooled stream using this simple control method, the composition ratio of unreacted monomers included in the gaseous monomer fraction and the liquid monomer fraction can be changed.

[0049] Figures 4 and 5 illustrate the composition of a liquid monomer fraction and the composition of a gaseous monomer fraction, respectively, according to the temperature of a stream cooled by low-pressure compression and cooling in a recovery method according to one embodiment of the present invention.

[0050] Referring to FIGS. 4 and 5, the higher the temperature of the cooled stream, the more the proportion of C4 monomer gas in the gaseous monomer fraction may increase, and the lower the temperature of the cooled stream, the more the proportion of C2 monomer in the liquid monomer fraction may increase.

[0051] As an example, when the temperature of the cooled stream is controlled to 10 to 20° C., the gaseous monomer fraction may contain 50 to 60 wt% of C2 monomer gas and 40 to 50 wt% of C4 monomer gas based on its weight, and the liquid monomer fraction may contain 5 to 10 wt% of C2 monomer and 90 to 95 wt% of C4 monomer based on its weight.

[0052] Meanwhile, when the temperature of the cooled stream is controlled to be between 20°C and 60°C, the gaseous monomer fraction may contain 20 to 40 wt% of C2 monomer gas and 60 to 80 wt% of C4 monomer gas, and the liquid monomer fraction may contain 1 to 5 wt% of C2 monomer and 95 to 99 wt% of C4 monomer.

[0053] In this way, the upper stream containing the unreacted monomer gas is sequentially compressed and cooled (condensed), and the composition of the monomer component to be recovered can be secured through cooling temperature control, and the unreacted monomer recovered in this way can be immediately reused as a raw material by being fed into the reactor (40) without an additional purification process.

[0054] Therefore, by sequentially applying compressors and condensers, the desired recovery specifications for unreacted monomers can be achieved with minimal energy consumption, eliminating the need for gas purification towers, which were problematic in prior technologies. Furthermore, while using gas purification towers often necessitated frequent changes to their operating conditions, this difficulty can be overcome by sequentially applying compressors and condensers.

[0055] In step (S3) of the recovery method according to the present invention, the cooled stream is supplied to a gas-liquid separator (22) for separation, and a liquid monomer fraction is recovered from the lower portion of the gas-liquid separator and a gaseous monomer fraction is recovered from the upper portion of the gas-liquid separator.

[0056] The stream cooled through compression and cooling in the previous step exists in a gas-liquid equilibrium state including a gaseous monomer fraction and a liquid monomer fraction, and can be separated into a liquid monomer fraction and a gaseous monomer fraction in the gas-liquid separator (22) and recovered.

[0057] At this time, the gas-liquid separator (22) can be operated without additional heat supply according to the compressed pressure conditions in the compressor of the front stage. In other words, the gas-liquid separator (22) can separate the cooled stream, which is a stream discharged through the compressor (20) and the condenser (21), into a gaseous monomer fraction and a liquid monomer fraction by utilizing the temperature and pressure of the cooled stream.

[0058] For example, the gas-liquid separator (22) may be a flash drum. The cooled stream may be separated in the flash drum, and the gaseous monomer fraction may be discharged to the upper portion of the flash drum, and the liquid monomer fraction may be discharged to the lower portion of the flash drum and recovered.

[0059] Meanwhile, the gaseous monomer fraction can be recovered from the upper portion of the gas-liquid separator (22), and a portion of the gaseous monomer fraction can be recycled to the compressor (20) of the step (S2), and the remainder can be discharged and incinerated. The compressor (20) needs to continuously supply a certain amount of gas or more for stable operation, and a portion of the gaseous monomer fraction can be recycled to the compressor (20) to maintain this flow. If the gas supplied to the compressor (20) is insufficient, the gaseous flow of the shear column may be pulled, which may prevent the pressure conditions of the shear column from being maintained, or may affect the compression pressure of the compressor (20) itself, making the compression process unstable. For example, the flow rate recycled to the compressor may be 10 to 90 wt% or 30 to 80 wt% of the total gaseous monomer fraction flow rate.

[0060] Meanwhile, the liquid monomer fraction recovered from the lower portion of the gas-liquid separator may be transferred to a storage tank for use in the raw material composition of the polymerization reaction, or may be supplied directly to the reactor without being transferred to the storage tank. In this case, since the composition of the C2 and C4 unreacted monomers contained in the liquid monomer fraction is identical to the composition required for the reactor to which it is supplied, there is no need for separate monomer purification and mixing processes, thereby reducing the energy required for the process equipment and process.

[0061] In this way, the gaseous and liquid monomer fractions contained in the cooled stream can be recycled to the compressor of the front stage or reused as raw materials for the polymerization reaction without going through a separate purification process, thereby reducing raw material costs and greenhouse gas emissions.

[0062] 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.

[0063] The following examples and comparative examples simulate the method according to the present invention using the commercial process simulation program Aspen Plus. The constants required for the simulations were values ​​built into the program and values ​​described in the literature.

[0064] Example 1:

[0065] According to the process flow diagram shown in Fig. 3, the recovery process of unreacted monomers was simulated.

[0066] First, the residue generated in the polyolefin manufacturing process (a mixed solution containing unreacted monomers of C2 ethylene and C4 butene and a C6 hexane solvent) was supplied to a gas separation tower (10) and separated into an upper discharge stream containing C2 and C4 gases and a lower discharge stream containing high-boiling components higher than C6. At this time, the operating conditions of the gas separation tower (10) were a lower temperature of 86°C and an upper pressure of 0.7 kg / cm. 2 ·g was applied.

[0067] The upper discharge stream of the above gas separation tower (10) is compressed to low pressure in a compressor (20) to 81°C and 5 kg / cm 2 ·The compressed gas of g was discharged, and the compressed gas was cooled by heat exchange with 5°C cooling water in a condenser (21) to obtain a cooled stream (10°C).

[0068] The above-mentioned cooled stream was supplied to a gas-liquid separator (22) to separate a liquid monomer fraction and a gaseous monomer fraction, thereby recovering unreacted monomers in the polyolefin manufacturing process. Among these, the liquid monomer fraction was supplied to an appropriate reactor (40) depending on the composition of unreacted monomers contained in the liquid monomer fraction.

[0069] Examples 2 to 6:

[0070] The same process as Example 1 was performed except that the cooling temperature of the compressed gas in the condenser was changed to the conditions shown in Table 1, and the unreacted monomer was recovered.

[0071] Comparative Example 1:

[0072] According to the process flow diagram shown in Fig. 2, the recovery process of unreacted monomers was simulated.

[0073] First, the residue generated in the polyolefin manufacturing process (a mixed solution containing unreacted monomers of C2 ethylene and C4 butene and a C6 hexane solvent) was supplied to a gas separation tower (10) and separated into an upper discharge stream containing C2 and C4 gases and a lower discharge stream containing high-boiling-point components higher than C6. At this time, the operating conditions of the gas separation tower (10) were as follows: a lower temperature of 86°C and an upper pressure of 0.7 kg / cm 2 ·Applied as g.

[0074] The upper discharge stream of the above gas separation tower (10) is compressed at ultra-high pressure in a compressor (20) to -9°C and 20 kg / cm 2 ·g of cooled stream was obtained.

[0075] The above cooled stream was supplied to the gas purification tower (30), and C2 with a very low boiling point was separated into the upper part, and C4 with a higher boiling point was separated into the lower part. At this time, the gas purification tower (30) used an ultra-low temperature refrigerant of -20°C in the condenser provided at the upper part thereof, and the lower part temperature was 100°C and the upper part pressure was 20 kg / cm 2·g's driving conditions were applied.

[0076] The process conditions applied in the above examples and comparative examples and the results of recovery of unreacted monomers according to the conditions are shown in Table 1 below. In Table 1, among the liquefaction conditions of unreacted monomer gas, the compression pressure and cooling temperature refer to the pressure and temperature of the cooled stream.

[0077] Additionally, the composition of the liquid monomer fraction and the composition of the gaseous monomer fraction of the cooled stream obtained by changing the cooling temperature of the compressed gas in the examples are shown in FIGS. 4 and 5, respectively.

[0078] Energy consumption for construction of a gas purification tower for liquefaction of unreacted monomer gas 1) Composition of the final recovered unreacted monomer (wt%) Compression (kg / cm) 2 ·g) Cooling (℃) Gas phase monomer fraction Liquid phase monomer fraction Example 1510X30.6C2 / C4(60 / 40)C2 / C4(7 / 93) Example 2520X30.6C2 / C4(45 / 55)C2 / C4(5 / 95) Example 3530X30.6C2 / C4(39 / 61)C2 / C4(4 / 96) Example 4540X30.6C2 / C4(25 / 75)C2 / C4(3 / 97) Example 5550X30.6C2 / C4(21 / 79)C2 / C4(2 / 98) Example 6560X30.6C2 / C4(17 / 83)C2 / C4(1 / 99) Comparative example 120-9○193.1C2(100)C4(100)1) Energy consumption was calculated as the sum of the energy consumed in the compressor and reboiler among the entire facility.

[0079] From the above Table 1, it can be confirmed that Examples 1 to 6 showed a significant reduction in energy consumption compared to Comparative Example 1, which performed a purification process using a gas purification tower after ultra-high pressure compression by compressing the unreacted monomer gas containing C2 and C4 separated from the residue containing unreacted monomers generated in the polyolefin manufacturing process at a low pressure in a compressor and then cooling it in a condenser. That is, in the Examples, the energy required for compression and cooling can be reduced by compressing at a much lower pressure than in the Comparative Examples and cooling at a temperature higher than the cooling temperature in the Comparative Examples, and the unreacted monomer having a desired composition can be recovered without using a gas purification tower with high energy consumption. This can save energy and cost and also simplify the equipment required to stagnate and mix the unreacted monomers. In addition, Examples 1 to 6 can change the composition of the unreacted monomers to be recovered by controlling the cooling temperature of the stream containing the unreacted monomers of C2 and C4, i.e., the cooled stream. Referring to Table 1, it can be seen that as the cooling temperature increases in the examples, the C2 composition in the gaseous monomer fraction and the liquid monomer fraction decreases and the C4 composition increases.

[0080] The unreacted monomers recovered in this way can be recycled to the compressor of the front stage or reused in the reactor as raw materials for the polymerization reaction without going through a separate purification process, thereby reducing raw material costs.

[0081] [Explanation of symbols]

[0082] 10: Gas separation tower

[0083] 20: Compressor

[0084] 21: Condenser

[0085] T: Temperature controller

[0086] P: Pressure controller

[0087] 22: Gas-liquid separator

[0088] 30: Gas purification tower

[0089] 40: Reactor

Claims

1. (S1) A step of supplying the residue containing unreacted monomer after the polymerization reaction in the reactor to a gas separation tower and separating it into an upper stream containing unreacted monomer gas and a lower stream containing relatively high boiling point components; and (S2) a step of compressing an upper stream containing the unreacted monomer gas discharged from the upper portion of the gas separation tower in a compressor to form a compressed stream, supplying the compressed stream to a condenser, and cooling the compressed stream in the condenser to obtain a cooled stream; and (S3) A step of separating the cooled stream in a gas-liquid separator, recovering a liquid monomer fraction from the lower portion of the gas-liquid separator, and recovering a gaseous monomer fraction from the upper portion of the gas-liquid separator. A method for recovering unreacted monomers by recycling the liquid monomer fraction recovered from the lower portion of the above-described gas-liquid separator to the above-described reactor.

2. In paragraph 1, The residue supplied to the above gas separation tower is C2 to C4 unreacted monomer and C5 to C 12 A method for recovering unreacted monomers from a mixed solution of hydrocarbons.

3. In paragraph 1, A method for recovering unreacted monomer, wherein the pressure of the compressed stream is 1.4 to 10 times the pressure of the upper stream containing the unreacted monomer gas.

4. In paragraph 1, The pressure of the above compressed stream is 1 to 10 kg / cm 2 ·g, and a method for recovering unreacted monomer at a temperature of 70 to 120°C.

5. In paragraph 1, A method for recovering unreacted monomers in which the condenser cools the compressed stream by heat exchange with cooling water, and the temperature of the cooling water is in the range of 5 to 50°C.

6. In paragraph 1, A method for recovering unreacted monomers, wherein the temperature of the cooled stream is 10 to 60°C.

7. In paragraph 1, A method for recovering unreacted monomers, wherein the higher the temperature of the cooled stream, the higher the proportion of C4 monomer gas contained in the gaseous monomer fraction recovered from the upper portion of the gas-liquid separator.

8. In paragraph 1, A method for recovering unreacted monomers, wherein the lower the temperature of the cooled stream, the higher the proportion of C2 monomers contained in the liquid monomer fraction recovered from the lower portion of the gas-liquid separator.

9. In paragraph 1, The temperature of the above cooled stream is 10 to 20°C, The gaseous monomer fraction recovered from the upper portion of the gas-liquid separator contains 50 to 60 wt% of C2 monomer gas and 40 to 50 wt% of C4 monomer gas based on its weight, A method for recovering unreacted monomers, wherein the liquid monomer fraction recovered from the lower portion of the above-described gas-liquid separator contains 5 to 10 wt% of C2 monomers and 90 to 95 wt% of C4 monomers based on the weight thereof.

10. In paragraph 1, The temperature of the above cooled stream is between 20°C and 60°C, The gaseous monomer fraction recovered from the upper portion of the gas-liquid separator contains 20 to 40 wt% of C2 monomer gas and 60 to 80 wt% of C4 monomer gas, A method for recovering unreacted monomers, wherein the liquid monomer fraction recovered from the lower portion of the above-described gas-liquid separator contains 1 to 5 wt% of C2 monomers and 95 to 99 wt% of C4 monomers.

11. In paragraph 1, A method for recovering unreacted monomers, wherein at least a portion of the gaseous monomer fraction recovered from the upper portion of the gas-liquid separator is recycled to the compressor of step (S2).

12. In paragraph 1, A method for recovering unreacted monomers, wherein the liquid monomer fraction recovered from the lower portion of the above-described gas-liquid separator is supplied as a raw material for the above-described polymerization reaction.

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