Bubble column reactor and device for preparing oligomer comprising same

Abstract

The invention provides a bubble tower reactor and a device comprising the same for preparing oligomer. The bubble tower reactor comprises a liquid area in which reaction occurs and a gas area located above the liquid area; a partition wall section that divides the liquid region into a first region and a second region in the longitudinal direction; the liquid level meter is connected to a second area of the liquid area and measures the liquid level of the second area; and a downstream pipe disposed on a side surface of a second region in the liquid region and discharging a liquid flow, in which the partition wall portion is disposed in the liquid region such that one end thereof is located at a boundary between the liquid region and the gas region and the other end thereof is located at a boundary between the gas region and the liquid region. The partition wall portion is disposed in the first region to store a flow of liquid of the first region overflowing above the partition wall portion in the second region.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to and the benefit of Korean Patent Application No. 10-2023-0188410, filed on December 21, 2023, which is hereby incorporated by reference in its entirety. Technical Field

[0003] The present disclosure relates to a bubble column reactor and an apparatus for preparing oligomers including the bubble column reactor, and more particularly, to a bubble column reactor capable of preventing pipe clogging by minimizing bubbles entrained in a liquid stream containing a reaction product, and an apparatus for preparing oligomers including the bubble column reactor. Background Art

[0004] α-olefins are important materials used in comonomers, detergents, lubricants, plasticizers, etc., and are widely used commercially. Among them, 1-hexene and 1-octene have been widely used as comonomers to control the density of polyethylene in the preparation of linear low-density polyethylene (LLDPE).

[0005] These α-olefins can be produced by oligomerization in the presence of a catalyst in a state where ethylene is dissolved in a solvent, and the oligomerization can be performed, for example, in a bubble column reactor.

[0006] The bubble column reactor allows the raw gas to flow into a liquid area containing a solvent, a catalyst, etc. through a distribution device installed at the lower part thereof (such as a distributor with multiple holes, a multi-tube, a nozzle, etc.), forming a large number of bubbles and dispersing them while rising in the form of bubbles, and performs oligomerization reaction by mixing the dispersed gas in the liquid area while generating turbulence.

[0007] In this case, the liquid level in the reactor should be kept constant because it affects the control of reaction conditions such as pressure and temperature, catalyst residence time, ethylene conversion, calorific value, etc. For this reason, it is very important to indicate the liquid height in the reactor.

[0008] Because the solvent, ethylene dissolved in the solvent, and liquid substances (oligomers) generated by ethylene conversion coexist in the liquid region of the reactor where the oligomerization reaction occurs, the composition of the liquid changes. Consequently, the density of the liquid after the reaction changes compared to the liquid before the reaction. In particular, the density of the entire liquid volume is significantly reduced due to the amount of gas bubbles (gas holdup) entrained in the liquid. Thus, this density is affected by the properties of the liquid substances in the reactor (temperature, pressure, composition, viscosity, etc.).

[0009] To measure the liquid level in the reactor during oligomer production, a differential pressure level transmitter (LT) is typically used. However, the density of the liquid changes with the reaction rate, which can lead to incorrect liquid level indications. When the differential pressure LT indicates a significant level error, it becomes difficult to maintain a constant actual liquid level within the reactor.

[0010] In addition, when a large amount of bubbles are entrained in the liquid material produced by the oligomerization reaction and transferred to the downstream pipe connected to the lower part of the reactor, severe blockage may occur due to the increase of two phases in the pipe. Summary of the Invention

[0011]

Technical Issues

[0012] The present disclosure is intended to solve the problems mentioned in the background art and provide a bubble column reactor capable of preventing pipe clogging by minimizing bubbles entrained in a liquid stream containing reaction products.

[0013]

Technical solution

[0014] In one general aspect, a bubble column reactor includes: a liquid region where a reaction occurs and a gas region located above the liquid region; a partition wall portion that divides the liquid region into a first zone and a second zone in a longitudinal direction; a liquid level gauge that is connected to the second zone of the liquid region and measures the liquid level of the second zone; and a downstream pipe that is arranged on a side of the second zone in the liquid region and discharges a liquid flow, wherein the partition wall portion is arranged in the liquid region so that one end thereof is located at the boundary between the liquid region and the gas region to store the liquid flow of the first zone overflowing above the partition wall portion in the second zone.

[0015] In one general aspect, the present disclosure provides an apparatus for preparing oligomers including the bubble column reactor.

[0016] Beneficial effects

[0017] The bubble column reactor according to the present disclosure is provided with a partition wall portion that divides the lower liquid region where the reaction occurs into a first zone and a second zone at a height located at the boundary between the gas region and the liquid region. Therefore, the liquid flow in the first zone that has risen above the boundary height can be stored in the second zone. Because bubbles are removed by the partition wall portion, the liquid flow stored in the second zone can minimize density changes. Thereafter, the height of the liquid in the second zone of the liquid region where gas-liquid separation occurs is measured to control the amount of liquid flow discharged, thereby stably maintaining the liquid level of the reactor.

[0018] Furthermore, by suppressing the amount of bubbles in the liquid flow discharged from the second zone of the liquid area, the flow of the oligomer product in the downstream pipe can be smoothed, clogging can be prevented, and the emission of ethylene gas to the downstream flow can be reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is a diagram illustrating a bubble column reactor according to one embodiment of the present disclosure.

[0020] Figure 2 and Figure 3 This is a diagram showing a bubble column reactor used in Comparative Examples. DETAILED DESCRIPTION

[0021] The terms and words used in this specification and claims should not be interpreted as general or dictionary meanings, but should be interpreted as meanings and concepts that satisfy the technical spirit of the present disclosure based on the principle that inventors can appropriately define the concepts of terms in order to describe their inventions in the best way.

[0022] The terms "include" or "comprising" used herein specifically refer to specific attributes, regions, integers, steps, operations, elements or components, and do not exclude the existence or addition of other specific attributes, regions, integers, steps, operations, elements, components or groups thereof.

[0023] As used herein, the term "flow" may refer to the flow of a fluid in a process, and may also refer to the fluid itself flowing in a pipeline. Specifically, flow may refer to the flow of the fluid itself as well as the flow of the fluid flowing in the pipeline connecting each device. In addition, the fluid may include at least one component selected from the group consisting of a gas, a liquid, and a solid.

[0024] Unless otherwise specified, the term "upper" as used herein refers to a point at a height of 0 to 50% from the top of the device, and may specifically refer to the top (top of the tower). In addition, the term "lower" refers to a point at a height of 50 to 100% from the top of the device, and may specifically refer to the bottom (bottom of the tower).

[0025] In addition, the "pressure" mentioned in this article refers to the gauge pressure measured based on atmospheric pressure.

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

[0027] One embodiment of the present disclosure relates to a bubble column reactor for conducting oligomerization reactions and the like.

[0028] Reference Figure 1The bubble column reactor 100 according to the present disclosure includes an upper gas region 110 and a lower liquid region 120 where a reaction occurs, and the liquid region 120 is divided into a first zone D1 and a second zone D2 in a longitudinal direction by a partition wall portion 130, and a liquid level meter 20 and a downstream pipe 30 for discharging a liquid flow can be connected to the second zone D2.

[0029] The bubble column reactor 100 receives ethylene gas and a solvent from the liquid region 120 (specifically, the first zone D1) and performs an oligomerization reaction. For example, ethylene gas is supplied from a gas inlet pipe 122 to the liquid region 120, where a solvent is supplied along with a catalyst through a solvent inlet pipe 121. The ethylene gas rises in the form of bubbles and is dispersed by a distribution device (e.g., a distributor having multiple holes, a multi-tube, a nozzle, etc.) installed at the bottom of the liquid region 120. The bubbles are then dispersed to form a large number of bubbles, which are then mixed within the liquid region while generating turbulence, thereby performing an oligomerization reaction.

[0030] Oligomerization can refer to a reaction in which monomers are oligomerized. Depending on the number of monomers being oligomerized, the oligomerization reaction is referred to as trimerization or tetramerization, collectively referred to as polymerization. Alpha-olefins such as 1-hexene and 1-octene can be prepared, for example, by trimerization or tetramerization of ethylene.

[0031] The ethylene gas supplied to the bubble column reactor may be a stream comprising ethylene (C2) separated from the thermal cracking of naphtha.

[0032] The solvent for dissolving ethylene gas can include one or more selected from normal pentane, normal hexane, normal heptane, cyclohexane, methylcyclohexane, octane, cyclooctane, decane, dodecane, benzene, dimethylbenzene, 1,3,5-trimethylbenzene, toluene, ethylbenzene, chlorobenzene, dichlorobenzene and trichlorobenzene. In some cases, a mixture of two or more of the above-mentioned solvents can be used as solvent. Therefore, ethylene gas can be liquefied at a higher temperature, and the dissolution rate of ethylene gas dissolved in the solvent can be improved.

[0033] In the oligomerization reaction of ethylene, a compound containing a transition metal can be used as a catalyst to improve the reaction activity. For example, the catalyst can be a compound selected from chromium (III) acetylacetonate, chromium (III) tetrahydrofuran chloride, chromium (III) 2-ethylhexanoate, chromium (III) tris(2,2,6,6-tetramethyl-3,5-heptanedione), chromium (III) benzoyl acetonate, chromium (III) hexafluoro-2,4-pentanedione, chromium (III) acetate hydroxide, chromium (III) acetate, chromium (III) butyrate, chromium (III) valerate, chromium (III) laurate, and chromium (III) stearate.

[0034] In addition, a co-catalyst can be used to improve the activity of the above catalyst. The co-catalyst can include one or more selected from, for example, trimethylaluminum, triethylaluminum, triisopropylaluminum, triisobutylaluminum, sesquiethylaluminum chloride, diethylaluminum chloride, ethylaluminum dichloride, methylaluminoxane, modified methylaluminoxane and borate.

[0035] The oligomerization reaction may be performed under conditions commonly used in the related art, and may be performed, for example, at a temperature of 30 to 150° C. or 50 to 120° C. and a pressure of 20 to 65 bar or 20 to 40 bar.

[0036] When the oligomerization reaction is carried out, a liquid stream containing oligomer products polymerized with ethylene, by-products, a solvent, unreacted gas dissolved in the solvent, etc. may exist in the lower liquid region 120 of the bubble column reactor 100, and unreacted ethylene gas that is not dissolved in the solvent and thus does not participate in the oligomerization reaction may rise to the upper gas region 110.

[0037] The density of the liquid stream present in the liquid region 120 of the bubble column reactor may vary depending on the amount of liquid oligomer product produced by ethylene conversion and the amount of bubbles originating from unreacted gas dissolved in the solvent, and when false indications occur during liquid level measurement due to density variations, it may be difficult to maintain a stable liquid level within the reactor.

[0038] To overcome these problems, in the present disclosure, a partition wall portion 130 serving as a weir is installed in the liquid region 120 of the bubble column reactor in the longitudinal direction, and the liquid level after gas-liquid separation is measured in a space storing a liquid flow having passed through the partition wall portion.

[0039] Specifically, the partition wall portion 130 can be configured so that one end is located at the boundary between the liquid region 120 and the gas region 110, while dividing the liquid region 120 into a first zone D1 and a second zone D2 in the longitudinal direction, and is not particularly limited as long as it has a shape that can confine the liquid flow within the liquid region 120.

[0040] For example, Figure 1 As shown, the partition wall portion 130 can restrict the liquid flow in the following form: the partition wall portion 130 has a vertical wall along the longitudinal direction and a horizontal plate extending horizontally from the lower end of the vertical wall and contacting the side of the second zone of the liquid area, and the horizontal plate can be adjacent to or spaced apart from the lowest surface of the liquid area 120.

[0041] As another example, the partition wall portion 130 may restrict the liquid flow in the form of a vertical wall extending upward from the lowermost surface of the liquid region 120. In this case, in the liquid region 120 divided by the partition wall portion 130, the lower portion of the first zone D1 may be configured to open a distribution device (e.g., a distributor having a plurality of holes, a multi-tube, a nozzle, etc.) to allow the ethylene gas supplied from the gas inlet pipe 122 to be dispersed to the first zone D1, while the lower portion of the second zone D2 may be configured to be blocked to prevent the ethylene gas from passing through.

[0042] As another example, the partition wall portion 130 may be configured in the form of a vertical tube having an annular edge and a blocked lower portion to restrict liquid flow, and the annular partition wall portion may be disposed at various positions, such as the center or edge of the liquid region 120 .

[0043] Meanwhile, the first and second zones D1 and D2 of the liquid region divided by partition wall 130 may have an area ratio of 100:1 to 5:1. When the area ratio is outside this range, i.e., when the area of ​​second zone D1 is less than 1% of the area of ​​first zone D1, insufficient space is available to control the liquid level, resulting in a reduced residence time of the liquid in second zone D2 and difficulty in accurately controlling the liquid level. When the area of ​​second zone D1 exceeds 20% of the area of ​​first zone D1, the residence time of the liquid in second zone D2 increases excessively, leading not only to additional side reactions but also to an increase in the overall size of the reactor, potentially increasing equipment costs.

[0044] With this structure, when an oligomerization reaction is performed in the liquid region 120 of the bubble column reactor, the liquid flow of the first zone D1, which has risen above the boundary height between the gas region 110 and the liquid region 120, can overflow over the partition wall portion 130 and be stored in the second zone D2. That is, due to the difference in boiling points between the liquid and the gas at the boundary between the liquid and the gas, the ethylene gas passes through the first zone D1 of the liquid region 120 in the form of bubbles, passes through the gas region 110, and is then discharged through the upper pipe 111, while the liquid is transferred to the second zone D2 through the partition wall portion 130. The liquid stored in the second zone D2 can suppress the entrainment of bubbles.

[0045] In this way, since the liquid flow stored in the second zone D2 of the liquid area is in a state where bubbles are removed by the partition wall portion 130, gas-liquid separation is achieved, and therefore, there is no need to install a separate gas-liquid separator outside the reactor.

[0046] The prior art produces olefins by oligomerizing ethylene in the liquid zone of a bubble column reactor. Unreacted gases are separated by discharging the olefin-containing liquid stream from the reactor and transferring the discharged liquid stream to an external gas-liquid separator. However, this process suffers from a problem in which the temperature decreases depending on the residence time of the liquid during the process, leading to precipitation of byproducts such as polymers. To prevent this, the prior art requires additional equipment to maintain the temperature of the gas-liquid separator. However, the present disclosure allows gas-liquid separation to be performed within the bubble column reactor, preventing byproduct precipitation due to temperature drops without requiring additional equipment, thus offering advantages in terms of facility and maintenance costs.

[0047] The flow of the liquid from which the gas is separated in the second zone D2 of the liquid area 120 is measured by the liquid level meter 20 connected to the second zone D2.

[0048] The liquid level meter may be a differential pressure liquid level transmitter (LT) commonly used in the related art, but is not limited thereto.

[0049] The liquid stored in the second area D2 of the liquid region 120 does not experience a significant density change because bubbles are removed and the composition of the liquid does not change. Therefore, unlike the first area D1 where the liquid composition changes, the possibility of false indication when measuring the liquid level in the second area D2 is low.

[0050] Therefore, the height of the liquid with suppressed density variation is measured using the liquid level meter 20 connected to the second zone D2, and the liquid flow in the second zone D2 is discharged according to the signal of the liquid level meter 20, so that the liquid level of the bubble column reactor can be stably maintained.

[0051] The liquid flow in the second zone D2 of the liquid area 120 can be discharged through the downstream pipe 30 connected to the second zone D2. In this case, the amount of the discharged liquid flow can be controlled by controlling the opening and closing of the control valve CV provided in the downstream pipe 30 according to the signal of the liquid level meter 20.

[0052] Additionally, by minimizing the amount of bubbles in the liquid stream discharged from the second zone D2 of the liquid region 120, the oligomer product can flow smoothly in the pipeline, preventing blockage and reducing the emission of ethylene gas to the downstream stream.

[0053] The present invention also provides a device for preparing oligomers, comprising the bubble column reactor.

[0054] The liquid stream discharged through the downstream pipe 30 in the bubble column reactor may be supplied to a separation column (not shown), and unreacted gas, solvent, etc. may be further separated in the separation column to obtain a purified oligomer product.

[0055] Example

[0056] Below, the present disclosure will be described in more detail by way of examples. However, the following examples are provided to illustrate the present disclosure, and it will be apparent to those skilled in the art that various modifications and changes may be made without departing from the scope and spirit of the present disclosure, and the scope of the present disclosure is not limited to these examples.

[0057] Comparative Example 1:

[0058] like Figure 2 As shown, in a bubble column reactor including an upper gas region 110, a lower liquid region 120, a liquid level meter 20 and a downstream pipe 30, a solvent and a catalyst are supplied to the lower liquid region 120 through a solvent inlet pipe 121, and ethylene gas is supplied through a gas inlet pipe 122 to carry out an oligomerization reaction.

[0059] A differential pressure level transmitter (LT) is used as a liquid level gauge 20 to measure the height of a liquid stream containing the oligomer product obtained by the reaction, a solvent, and unreacted ethylene gas dissolved in the solvent. The liquid stream is discharged through a downstream pipe 30 of the reactor. In this case, the amount of the discharged liquid stream is controlled by a control valve CV based on the liquid level measurement value to maintain the liquid level in the reactor. At the same time, a gas stream containing unreacted ethylene gas is discharged through an upper pipe 111 of the gas zone 110.

[0060] Comparative Example 2:

[0061] like Figure 3 As shown, in a bubble column reactor including an upper gas region 110, a lower liquid region 120, and an overflow pipe 20 connected to a boundary position of the gas region and the liquid region, a solvent and a catalyst are supplied to the lower liquid region 120 through a solvent inlet pipe 121, and ethylene gas is supplied through a gas inlet pipe 122 to carry out an oligomerization reaction.

[0062] The liquid stream containing the oligomer product obtained by the reaction, the solvent, and the unreacted ethylene gas dissolved in the solvent is discharged through the overflow pipe 10 when it rises above the boundary position between the gas region 110 and the liquid region 120, thereby maintaining the liquid level in the reactor. At the same time, the gas stream containing the unreacted ethylene gas is discharged through the upper pipe 111 of the gas region 110.

[0063] Example 1:

[0064] like Figure 1As shown, in a bubble column reactor including an upper gas region 110, a lower liquid region 120, a partition wall portion 130 arranged at a height located at a boundary between the gas region and the liquid region and dividing the liquid region 120 into a first zone D1 and a second zone D2, a liquid level meter 20 and a downstream pipe 30, a solvent and a catalyst are supplied to the first zone D1 of the lower liquid region 120 through a solvent inlet pipe 122, and ethylene gas is supplied through a gas inlet pipe 121, thereby carrying out an oligomerization reaction.

[0065] During the reaction, the liquid flow of the first zone D1, which has risen above the boundary height between the gas region 110 and the liquid region 120, overflows over the partition wall portion 130 and is stored in the second zone D2. In this case, due to the difference in boiling points between the liquid and the gas at the boundary between the liquid and the gas, the ethylene gas passes through the first zone D1 of the liquid region 120 in the form of bubbles, passes through the gas region 110, and is then discharged through the upper pipe 111, while the liquid is transferred to the second zone D2 through the partition wall portion 130 while removing the bubbles.

[0066] Thereafter, in the second zone D2 of the liquid region 120, the liquid level of the liquid stream from which bubbles have been removed (i.e., from which gas has been separated) is measured using a differential pressure LT connected to the second zone D2 as a liquid level gauge 20, and the liquid stream is discharged through a downstream pipe 30 provided in the second zone D2. In this case, the amount of the discharged liquid stream is controlled based on the liquid level measurement value using a control valve CV provided in the downstream pipe 30 to maintain the liquid level in the reactor. Simultaneously, a gas stream containing unreacted ethylene gas is discharged through the upper pipe 111 of the gas region 110.

[0067] The results of liquid level measurement and liquid maintenance of the reactors according to the above-described Examples and Comparative Examples are shown in Table 1 below.

[0068] [Table 1]

[0069]

[0070] As can be seen from Table 1 above, in Example 1, the partition wall portion, which divides the lower liquid region 120 into a first zone D1 where the reaction occurs and a second zone D2 where the liquid flow from which bubbles have been removed is stored, is positioned at a height located at the boundary between the gas and liquid regions. This allows the liquid flow in the first zone, which has risen above the boundary height, to be stored in the second zone while gas-liquid separation is performed by the partition wall portion. The liquid level is then measured. This results in virtually no density changes in the second zone liquid due to bubbles, minimizing false indications from the differential pressure LT. Consequently, the amount of liquid discharged is controlled by a liquid level control valve CV connected to the differential pressure LT, ultimately maintaining a constant liquid level in the reactor.

[0071] In addition, by minimizing the amount of bubbles in the liquid flow in the second zone D2 of the liquid area 120, the flow of the oligomer product in the downstream pipeline can be smoothed, clogging can be prevented, and the amount of ethylene gas recovered from the pipeline can be reduced.

[0072] In contrast, in Comparative Example 1, due to direct measurement of the liquid containing bubbles in reactor 100, an erroneous indication of a decreased LT value occurred at the same liquid level. This is because ethylene gas supplied from the lower portion of the reactor is contained in the liquid as bubbles as it passes through it. Since oligomer products are present after the reaction, and the gas retention space increases compared to the liquid containing only solvent at the start of the reaction, the liquid density decreases. Consequently, even if the liquid level remains at the same height, the pressure differential decreases, and the LT value appears as a decrease in the liquid level. Due to this erroneous indication, the control valve is closed to control the liquid level, and the actual liquid level in the reactor ultimately rises. As the liquid level rises, the catalyst residence time in the reactor increases, limiting the control of product quantity and calorific value. Polymer blockage occurs in the liquid discharge pipe, and the amount of ethylene recovered from the pipe increases.

[0073] Meanwhile, in Comparative Example 2, since the liquid level in the reactor 100 was controlled by discharging the liquid containing bubbles that had risen above the boundary height through the overflow pipe 10 at the boundary between the gas region and the liquid region, without separately measuring the liquid level in the reactor 100, a large amount of gas flow containing unreacted ethylene in the gas region was discharged together with the liquid flow through the overflow pipe 10. As a result, it was difficult to predict the ethylene content discharged through the overflow pipe, and clogging occurred due to the increase in the liquid-gas two-phase flow in the pipe.

[0074] [reference numerals]

[0075] 100: Bubble column reactor

[0076] 110: Gas area

[0077] 111: Air discharge pipe

[0078] 120: Liquid area (D1: first zone, D2: second zone)

[0079] 121: Solvent inlet pipe

[0080] 122: Intake pipe

[0081] 130: Partition wall

[0082] 10: Overflow pipe

[0083] 20: Liquid level gauge

[0084] 30: Downstream pipe

[0085] CV: Liquid Level Control Valve

Claims

1. A bubble column reactor comprising: a liquid region where the reaction occurs and a gas region located above the liquid region; a partition wall portion that divides the liquid region into a first area and a second area along a longitudinal direction; a liquid level gauge connected to the second zone of the liquid region; as well as a downstream pipe disposed on the side of the second zone in the liquid region and discharging the liquid flow, The partition wall portion is provided in the liquid region such that one end thereof is located at a boundary between the liquid region and the gas region, so that the liquid flow of the first region overflowing over the partition wall portion is stored in the second region.

2. The bubble column reactor according to claim 1, wherein the liquid zone receives ethylene gas and a solvent to perform an oligomerization reaction. 3 . The bubble column reactor according to claim 1 , comprising an upper pipe for discharging a gas flow containing unreacted gas from the gas region.

4. The bubble column reactor according to claim 1, wherein the partition wall portion is provided with a vertical wall in a longitudinal direction and a horizontal plate extending laterally from a lower end of the vertical wall and contacting a side surface of the second zone of the liquid region. The bubble column reactor according to claim 1 , wherein the horizontal plate of the partition wall portion is adjacent to or spaced apart from the lowest surface of the liquid region. 6 . The bubble column type reactor according to claim 1 , wherein the partition wall portion is in the form of a vertical wall extending upward from the lowest surface of the liquid region. 7 . The bubble column reactor according to claim 1 , wherein the partition wall portion is in the form of a vertical tube having a circular ring edge and a blocked lower portion. 8 . The bubble column reactor according to claim 1 , wherein the first zone and the second zone in the liquid region are divided at an area ratio of 100:1 to 20:

1.

9. The bubble column reactor according to claim 1, wherein the liquid stream stored in the second zone of the liquid region is a stream subjected to gas-liquid separation. 10 . The bubble column reactor according to claim 1 , wherein the liquid level meter measures a liquid level of the liquid stream after gas-liquid separation in the second zone of the liquid region.

11. The bubble column reactor according to claim 1, wherein a downstream pipe connected to a lower portion of the second zone in the liquid area includes a valve that controls a liquid discharge amount according to a signal from the liquid level meter. 12 . An apparatus for preparing oligomers, comprising the bubble column reactor according to claim 1 .

Images