Apparatus and method for producing isovaleraldehyde as a byproduct from the oil phase of a condensation recycle column of a 2-propylheptanol production plant

Abstract

The application provides a device and method for producing isopentanal byproduct of oil phase of 2-propyl heptanol production device condensation circulating tower, and relates to the field of chemical industry.The device comprises a first rectifying tower and a second rectifying tower;the inlet of the first rectifying tower is communicated with the oil phase outlet of the overhead chromatograph of the 2-propyl heptanol condensation circulating tower, the bottom outlet of the first rectifying tower is communicated with the inlet of the second rectifying tower, and the bottom outlet of the second rectifying tower is communicated with the inlet of the 2-propyl heptanol condensation reactor.The method comprises the following steps: introducing materials from the oil phase outlet of the overhead chromatograph to the first rectifying tower, separating in the first rectifying tower, and obtaining a crude pentanal mixture at the bottom;the crude pentanal mixture is sent to the second rectifying tower for separation, crude n-pentanal is obtained at the bottom, and isopentanal product is obtained at the top.The device and method provided by the application simultaneously realize the production and separation of isopentanal, effectively reduce energy consumption, the equipment is simple, the production capacity is high, and large-scale industrial production is suitable.

Description

TECHNICAL FIELD

[0001] The present application relates to the chemical industry field, and particularly relates to a device and method for byproduct isovaleraldehyde in oil phase of condensation circulating column of 2-propyl heptanol production device. BACKGROUND

[0002] Isovaleraldehyde, also known as 2-methyl butyraldehyde, is an organic compound with a chemical formula of C5H 10 O, which is a colorless transparent liquid and slightly soluble in water, but miscible in ethanol, diethyl ether and the like. Isovaleraldehyde can be used as an intermediate in organic synthesis and pharmaceutical chemistry, and is mainly used for modification and synthesis of organic functional molecules. In addition, isovaleraldehyde can also be used as a flavorant and can be used in the production of food flavorants.

[0003] N-pentanal is a homologue of isovaleraldehyde, which is an important intermediate. After condensation and dehydration, hydrogenation can obtain 2-propyl heptanol, which is an important plasticizer raw material and also an important solvent for rubber and pharmaceutical products.

[0004] At present, the main production process of n-pentanal and isovaleraldehyde is butene low-pressure hydroformylation, that is, butene and synthesis gas are used as raw materials to synthesize pentanal under the action of rhodium catalyst and corresponding ligand, and then the unreacted carbon four hydrocarbons are separated out by a preliminary rectifying column. At present, the industrial device adopting the butene low-pressure hydroformylation method mainly aims to produce 2-propyl heptanol (2-PH), and n-pentanal and isovaleraldehyde are only intermediate products. The ratio of n-pentanal to isovaleraldehyde generated by reaction is often more than 15:1, and the content of isovaleraldehyde in the mixed pentanal product is far less than that of n-pentanal. The separation cost is high, and it is difficult to meet the strong demand for high-purity isovaleraldehyde product in the market at present. SUMMARY

[0005] In view of the problem that the content of isovaleraldehyde in the reaction product of butene hydroformylation in the existing mainstream 2-PH device is small, and the isovaleraldehyde is mainly used for the production of decanol by further condensation and hydrogenation, and the existing pentanal separation system cannot prepare high-purity n-pentanal and isovaleraldehyde products, and it is difficult to meet the market demand, the present application provides a device and method for byproduct isovaleraldehyde in oil phase of condensation circulating column of 2-propyl heptanol production device, so as to solve the above problems.

[0006] To achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0007] A device for byproduct isovaleraldehyde in oil phase of condensation circulating column of 2-propyl heptanol production device, comprising: a first rectifying column and a second rectifying column;

[0008] The inlet of the first rectifying column is communicated with the oil phase outlet of the top chromatograph of the condensation circulating column of the 2-propyl heptanol production device, the bottom outlet of the first rectifying column is communicated with the inlet of the second rectifying column, and the bottom outlet of the second rectifying column is communicated with the inlet of the condensation reactor of the 2-propyl heptanol production device.

[0009] Preferably, the first rectifying column and the second rectifying column are float valve columns.

[0010] Preferably, the number of theoretical plates of the first rectifying column is 18-40.

[0011] The number of theoretical plates of the second rectifying column is 60-100, and the side line outlet position is the 4th-15th plate from the top of the column.

[0012] Preferably, the top of the second rectifying column is provided with a reflux tank, and the reflux tank is an oil-water separation reflux tank.

[0013] The application also provides a method for producing isopentanal byproduct from the oil phase of a condensation circulating column of a 2-propylheptanol production device, comprising:

[0014] Part or all of the material from the oil phase outlet of the top chromatograph of the condensation circulating column of the 2-propylheptanol production device is introduced into the first rectifying column, and separation is carried out in the first rectifying column, and a crude pentanal mixture is obtained at the bottom.

[0015] The crude pentanal mixture is sent into the second rectifying column for separation, and a crude n-pentanal is obtained at the bottom and returned to the condensation reactor of the 2-propylheptanol production device for further reaction, and the top product is separated by an oil-water separation reflux tank to obtain an isopentanal product.

[0016] In view of the problems of low isopentanal content in the hydroformylation reaction product of the mainstream 2-PH device using a low-pressure hydroformylation process at the present stage, and high separation cost, the oil phase outlet line of the top chromatograph of the condensation circulating column of the condensation unit is selected as the raw material.

[0017] Preferably, the operating pressure at the top of the first rectifying column is 4-6 bar, and the operating temperature is 45-55°C; the operating pressure at the top of the second rectifying column is 1-2 bar, and the operating temperature is 105-115°C.

[0018] Preferably, the operating pressure at the top of the first rectifying column is 4-5.5 bar, and the operating pressure at the top of the second rectifying column is 1.5 bar.

[0019] Preferably, the reflux ratio of the first rectifying column is 3-6, and the reflux ratio of the second rectifying column is 10-18.

[0020] Preferably, the reflux ratio of the first rectifying column is 3.5-4.5, and the reflux ratio of the second rectifying column is 13-16.

[0021] Preferably, the residence time of the material at the top of the second rectifying column in the oil-water separation reflux tank is 20-50 min, and preferably 30-40 min.

[0022] Compared with the prior art, the beneficial effects of the present application include:

[0023] The device and method for producing isopentanal byproduct from the oil phase of the condensation circulating column of the 2-propylheptanol production device provided by the present application can effectively produce isopentanal byproduct on the basis of the existing 2-propylheptanol device by adding a small amount of equipment and at a low cost, and the technology is relatively mature and easy to realize industrialization.

[0024] Meanwhile, the present application selectively uses the oil phase of the condensation circulating column of the 2-propylheptanol production device as raw material. The steric hindrance effect caused by the side chain of isopentanal in the condensation reactor makes the conversion rate of isopentanal much lower than that of n-pentanal, which leads to the content of unreacted isopentanal in the oil phase entering the condensation circulating column from the outlet of the condensation reactor and then entering the top chromatograph of the condensation circulating column being significantly higher than that of isopentanal in the original crude pentanal at the inlet of the condensation unit of the 2-propylheptanol production device, which means that the different reaction difficulties of n-pentanal and isopentanal in the condensation reaction have pre-concentrated the isopentanal content in the proposed purification raw material to a certain extent before the additional rectification operation is performed, thereby reducing the separation difficulty and energy consumption compared with directly using the crude pentanal raw material at the bottom of the C4 column of the 2-propylheptanol device. The purity of the obtained isopentanal product is more than 98 mol%, and the water content is less than 1 mol%, which is high in purity and can meet the market demand for isopentanal products. BRIEF DESCRIPTION OF DRAWINGS

[0025] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments. It should be understood that the following drawings only show some embodiments of the present application, and therefore should not be regarded as a limitation on the scope of the present application.

[0026] Figure 1 The schematic diagram of the device for producing isopentanal byproduct from the oil phase of the condensation circulating column of 2-propylheptanol provided by the embodiments of the present application is shown in the figure.

[0027] Figure 2 The schematic diagram of the circulating device provided for Comparative Example 1 is shown in the figure.

[0028] Figure 3 The schematic diagram of the reaction and separation device provided for Comparative Example 2 is shown in the figure.

[0029] Reference signs:

[0030] 1 - first rectification column; 2 - second rectification column; 3 - condensation reactor of 2-propylheptanol production device; 4 - condensation circulating column of 2-propylheptanol production device; 5 - top chromatograph. DETAILED DESCRIPTION

[0031] As used herein:

[0032] "Prepared from" is synonymous with "comprising". The terms "comprising", "including", "having", "containing", or any other variations thereof as used herein are intended to cover non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that includes the listed elements is not necessarily limited to those elements, but may include other elements not expressly listed or elements inherent to such composition, step, method, article, or apparatus.

[0033] The conjunction "composed of..." excludes any unspecified elements, steps, or components. If used in a claim, this phrase makes the claim closed, excluding materials other than those described, except for associated conventional impurities. When the phrase "composed of..." appears in a clause of the body of a claim rather than immediately following it, it limits only the elements described in that clause; other elements are not excluded from the claim as a whole.

[0034] When a quantity, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pair of any upper or preferred value with any lower or preferred value, regardless of whether the range is disclosed individually. For example, when the range “1–5” is disclosed, the described range should be interpreted as including ranges “1–4”, “1–3”, “1–2”, “1–2 and 4–5”, “1–3 and 5”, etc. When numerical ranges are described herein, unless otherwise stated, the range is intended to include its endpoints and all integers and fractions within that range.

[0035] In these embodiments, unless otherwise specified, the portions and percentages are expressed in molar fractions.

[0036] "Mole fraction" is a basic unit of measurement used to express the mass ratio of multiple components. One part can represent any unit mass, such as 1g or 2.689g. If we say that component A has 'a' parts by mass and component B has 'b' parts by mass, it means the mass ratio of component A to component B is a:b. Alternatively, it can mean that the mass of component A is aK and the mass of component B is bK (where K is any number representing a multiplier). It is important to understand that, unlike parts by mass, the sum of the mass parts of all components is not limited to 100 parts.

[0037] "And / or" is used to indicate that one or both of the described situations may occur, for example, A and / or B includes (A and B) and (A or B).

[0038] The implementation schemes of this application will be described in detail below with reference to specific embodiments. However, those skilled in the art will understand that the following embodiments are only for illustrating this application and should not be regarded as limiting the scope of this application. Unless otherwise specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments used without specified manufacturers are all conventional products that can be purchased commercially.

[0039] Example 1

[0040] like Figure 1 As shown, this embodiment provides an apparatus for producing isovaleraldehyde as a byproduct of the oil phase in a condensation circulation tower of a 2-propylheptanol production unit. The apparatus includes a first distillation tower 1 and a second distillation tower 2. The condensation reactor 3 of the 2-propylheptanol production unit is an upstream unit that performs the condensation reaction to obtain a mixture of condensation product and pentaldehyde. A condensation circulation tower 4 of the 2-propylheptanol production unit is located downstream of the condensation reactor 3. The inlet of the first distillation tower 1 is connected to the oil phase outlet of the top-column analyzer 5 of the condensation circulation tower 4. The bottom outlet of the first distillation tower 1 is connected to the inlet of the second distillation tower 2. The bottom outlet of the second distillation tower 2 is connected to the inlet of the condensation reactor 3 of the 2-propylheptanol production unit.

[0041] In another optional embodiment, a reflux tank is provided at the top of the second distillation column 2. The reflux tank is an oil-water separation reflux tank (not shown in the figure) used to separate the oil and water of the top product of the second distillation column 2.

[0042] It should be noted that both the first distillation column 1 and the second distillation column 2 are valve-fed columns. The theoretical number of trays in the first distillation column 1 is 18-40.

[0043] The theoretical number of trays in the second distillation column 2 is 60-100, and the side stream is drawn from the 4th to the 15th trays from the top of the column.

[0044] In actual production, the actual number of trays can be selected within the above range as needed, and the location of the side stream extraction can also be adjusted and confirmed according to the actual situation.

[0045] It should be noted that the core focus of the apparatus provided in this application lies in the inlet connection location of the first distillation column 1, that is, the location where the raw material for the first distillation column 1 is selected. The reason for this is that: Figure 2As shown, the current process flow of the condensation unit of the 2-PH (2-propyl heptanol) production device is as follows: the crude pentanal (in which the ratio of n-pentanal to iso-pentanal is about 15-20:1) from the upstream hydroformylation unit enters the condensation reactor, and the condensation reaction between pentanal and pentanal occurs in the presence of sodium hydroxide solution to generate decenal, and then the reaction product enters the condensation circulating column for separation. The generated decenal is mainly enriched in the bottom of the column due to its heaviness, and after being separated from the water phase, it enters the subsequent hydrofining unit. The light components such as unreacted pentanal and a small amount of hydrocarbons contained in the condensation reaction raw material are mainly enriched in the top of the column, and after being separated from the water phase in the top chromatograph, the oil phase is recycled to the inlet of the condensation reactor. Due to the steric hindrance effect caused by the side chain in the molecular structure of iso-pentanal, the single-pass conversion rate of iso-pentanal in the condensation circulating column is significantly lower than that of n-pentanal, which results in that the content of iso-pentanal (generally about 30%) in the oil phase of the top chromatograph of the condensation circulating column is much higher than the content of iso-pentanal (4-5%) in the original pentanal stream from the upstream hydroformylation unit after the device is stably operated.

[0046] Therefore, the oil phase extraction and recycling line of the top chromatograph of the condensation circulating column is used as the iso-pentanal by-product raw material, and the separation difficulty is lower than that of directly separating the crude pentanal introduced from the hydroformylation unit, which is more energy-saving and investment-saving. At the same time, the iso-pentanal extracted from the extraction line can also reduce the proportion of by-product of the condensation reaction of pentanal in the condensation reaction, and finally improve the content of 2-PH in the 2-PH product obtained by hydrofining, and the product is more competitive.

[0047] Example 2

[0048] The present embodiment provides a method for producing iso-pentanal by-product from the oil phase of the condensation circulating column of the 2-propyl heptanol production device, which is operated by using the device provided in Example 1, and includes the following steps:

[0049] S1. All or part of the material from the oil phase outlet of the top chromatograph 5 of the condensation circulating column 4 of the 2-propyl heptanol production device is introduced into the first rectifying column 1, and separation is performed in the first rectifying column 1 to obtain a crude pentanal mixture at the bottom.

[0050] S2. The crude pentanal mixture is sent to the second rectifying column 2 for separation, and the crude n-pentanal at the bottom is returned to the condensation reactor 3 of the 2-propyl heptanol production device for further reaction, and the overhead product is separated by an oil-water separation reflux tank to obtain an iso-pentanal product.

[0051] The specific parameters are as follows:

[0052] 2-Propylheptanol production device condensation circulating tower 4 overhead chromatograph 5 oil phase production of isopentanal content will be reduced to 11.9%, n-pentanal accounted for 64.1%, moisture about 4.6%, carbon four, carbon five hydrocarbons about 16.2%, while the mass flow rate is also reduced to about 0.52t / h. Pressurized to 0.6MPa and heat transfer to the first rectifying column 1, the overhead operating pressure 4.8bar, reflux ratio 4.5, the number of theoretical plates is 36, the overhead is mainly carbon four, carbon five hydrocarbons about 0.065t / h, the bottom of the mixed pentanal 0.45t / h, of which n-pentanal accounted for 78.4%, isopentanal accounted for 14.3%, moisture about 3.9%, the rest is carbon ten enal and the like.

[0053] The pentanal mixture obtained at the bottom is introduced into the second rectifying column 2 again, the overhead operating pressure is 1.5bar, the number of theoretical plates is 90 plates, the reflux ratio is 17.6 (the ratio of the reflux mass flow rate to the side line production), the side line production is about 54kg / h, of which n-pentanal accounts for 1.0%, isopentanal accounts for 98.9%, and moisture accounts for about 0.09%. The crude n-pentanal is obtained at the bottom, about 389kg / h, of which n-pentanal accounts for 93.2%, isopentanal accounts for 2.8%, and the rest is mainly carbon ten enal and the like, which is introduced back to the inlet of the condensation reactor 3 of the 2-propylheptanol production device to continue to react with the upstream feed. The water tank water discharge sewage is about 3.7kg / h, of which the water content is 99.2%. Equivalent to 10,000 tons / year 2-PH device can by-product isopentanal about 432 tons / year.

[0054] Example 3

[0055] The present embodiment provides a method for producing isopentanal by using the oil phase of the condensation circulating tower of the 2-propylheptanol production device, which is operated by using the device provided in Example 1, comprising the following steps:

[0056] S1. All or part of the material from the oil phase outlet of the overhead chromatograph 5 of the condensation circulating tower 4 of the 2-propylheptanol production device is introduced into the first rectifying column 1, and separation is carried out in the first rectifying column 1, and a crude pentanal mixture is obtained at the bottom;

[0057] S2. The crude pentanal mixture is sent to the second rectifying column 2 for separation, and the crude n-pentanal is returned to the condensation reactor 3 of the 2-propylheptanol production device for further reaction, and the overhead product is separated by the oil-water separation reflux tank to obtain isopentanal product.

[0058] The specific parameters are as follows:

[0059] 2-Propylheptanol production device condensation circulating column 4 top layer chromatograph 5 oil phase production of isopentanal content will be reduced to 11.9%, n-pentanal accounted for 64.1%, water about 4.6%, carbon four, carbon five hydrocarbons about 16.2%, while the mass flow rate is also reduced to about 0.52t / h. Pressurized to 0.6MPa and heat after sending to the first rectifying column 1, the top operating pressure 4.8bar, reflux ratio 4.5, the number of theoretical plates for 20 blocks, the top of the light carbon four, carbon five hydrocarbons about 0.065t / h, the bottom of the mixed pentanal 0.45t / h, wherein n-pentanal accounted for 72.4%, isopentanal accounted for 12.1%, water about 3.9%, butene accounted for 5.2%, the rest is carbon ten enal and so on.

[0060] The pentanal mixture obtained at the bottom of the column is introduced into the second rectifying column 2 again, the top operating pressure is 1.5bar, the number of theoretical plates is 90 plates, the reflux ratio is 17.6 (the ratio of the reflux mass flow rate to the side line extraction amount), the side line extraction is about 54kg / h, wherein n-pentanal accounts for 0.9%, isopentanal accounts for 94.5%, water accounts for about 0.09%, butene accounts for 5.5%. Crude n-pentanal is obtained at the bottom, about 389kg / h, wherein n-pentanal accounts for 93.2%, isopentanal accounts for 2.8%, and the rest is mainly carbon ten enal and the like, which is introduced back to the inlet of the condensation reactor 3 of the 2-propylheptanol production device to continue to participate in the reaction with the upstream feed. The water tank water at the top of the reflux tank discharges sewage about 3.7kg / h, which contains 99.2% water.

[0061] Due to the change of the number of theoretical plates of the rectifying column 1, the purity of isopentanal product decreases.

[0062] Comparative Example 1

[0063] The device shown in Figure 2 is used as a control, and its operating state is as follows:

[0064] The crude pentanal sent out by the upstream hydroformylation unit is about 1.57t / h, wherein n-pentanal accounts for 87.8% (molar fraction, the same below), isopentanal accounts for 5.4%, water accounts for about 3.5%, carbon four, carbon five hydrocarbons account for about 3.1%, and the rest is heavy substances and other impurities. After mixing with the oil phase extraction of the top layer chromatograph of the circulating column and the sodium hydroxide aqueous solution, it is introduced into the condensation reactor for reaction, and part of n-pentanal and isopentanal is converted into carbon ten enal. Subsequently, the reaction product enters the condensation circulating column, the top pressure is about 0.2MPa, the oil phase extraction of the top layer chromatograph is about 0.65t / h, wherein n-pentanal accounts for 51.2%, isopentanal accounts for 30.2%, water accounts for about 3.7%, carbon four, carbon five hydrocarbons account for about 13.3%, and the rest is carbon ten enal and the like. It is returned to the inlet of the condensation reactor to continue to participate in the reaction.

[0065] Under such operation, although the device connection relationship is simple, the proportion of isoamyl aldehyde in the oil phase of the top chromatograph is very high, and after mixing with the crude amyl aldehyde mixture sent from the upstream, the proportion of isoamyl aldehyde is still very high, thereby affecting the progress of the condensation reaction, not only reducing the purity of the final 2-PH product, but also failing to effectively utilize isoamyl aldehyde, a chemical substance with relatively high added value.

[0066] Comparative Example 2

[0067] With the device shown in Figure 3 as a control, the importance of selecting the inlet connection position of the first rectifying tower 1 in the present application is proved.

[0068] As shown in Figure 3 , according to the usual thinking, if isoamyl aldehyde in the reaction raw material is not conducive to the progress of the condensation reaction, then people will separate the crude amyl aldehyde mixture output after the falling film evaporator system after the reaction of the hydroformylation system, so that the material input into the condensation reactor is mainly n-pentyl aldehyde.

[0069] However, there are many disadvantages in separating at this node:

[0070] 1. The ratio of n-pentyl aldehyde to isoamyl aldehyde in the crude amyl aldehyde mixture output from the falling film evaporator system is about 15-20:1, and the proportion of isoamyl aldehyde is very low. In addition, n-pentyl aldehyde and isoamyl aldehyde belong to the same isomer, making it very difficult to separate the two; 2. Based on the first point, as shown in Figure 3 , multiple separations are needed to meet the needs, which not only increases the cost of equipment investment, site investment, etc., but also greatly increases the energy consumption required for separation; 3. Due to the very low proportion of isoamyl aldehyde, the separation efficiency is also very low, and the amount of crude amyl aldehyde mixture that needs to be treated to separate a unit amount of isoamyl aldehyde is much larger than the treatment amount of the device and method provided by the present application, further causing high energy consumption, high cost, and relatively low income.

[0071] In contrast, the device and method provided by the present application select the oil phase of the top chromatograph as the raw material for rectification and separation, the proportion of isoamyl aldehyde in the amyl aldehyde mixture is very high, the difficulty of rectification and separation is greatly reduced, and only two rectifying towers in series are needed to efficiently separate n-pentyl aldehyde and isoamyl aldehyde, thereby reducing the energy consumption required for separation and improving the separation efficiency; at the same time, the proportion of n-pentyl aldehyde in the amyl aldehyde mixture input into the condensation reactor is greatly improved, which is conducive to the progress of the condensation reaction, thereby further improving the yield of the final product 2-propyl heptanol; and a relatively high-purity isoamyl aldehyde can be output to meet the market demand. In the case of producing the same scale of isoamyl aldehyde product, if the crude amyl aldehyde mixture output from the falling film evaporator system is used as the raw material, the raw material treatment amount is increased by about 3 times (the isoamyl aldehyde content in the raw material is reduced), and the unit raw material treatment energy consumption is increased by 10% (the separation difficulty is increased).

[0072] It should be noted that the above-mentioned embodiments are merely used to illustrate the technical solutions of the present application, rather than limit the present application; although the present application has been described in detail with reference to the above-mentioned embodiments, those skilled in the art should understand that the technical solutions recorded in the foregoing embodiments can be modified or equivalent replacements can be made to some or all of the technical features; and the modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present application.

[0073] Furthermore, those skilled in the art could understand that, although some embodiments herein include certain features rather than other features included in other embodiments, the combination of features of different embodiments means to be within the scope of the present application and form different embodiments. For example, in the above claims, any one of the claimed embodiments can be used in any combination. The information disclosed in the Background section is merely intended to deepen the understanding of the overall background of the present application, and should not be regarded as acknowledging or implying in any form that the information constitutes the prior art known to those skilled in the art.

Claims

1. A method for producing isovaleraldehyde as a byproduct from the oil phase of a condensation recycle column of a 2-propylheptanol production plant, characterized by, The device for producing isopentanal byproduct from oil phase of condensation circulating column of 2-propylheptanol production device comprises a first rectifying column and a second rectifying column. The inlet of the first rectifying column is communicated with the oil phase outlet of the overhead chromatograph of the condensation circulating column of the 2-propylheptanol production device, the bottom outlet of the first rectifying column is communicated with the inlet of the second rectifying column, and the bottom outlet of the second rectifying column is communicated with the inlet of the condensation reactor of the 2-propylheptanol production device. The method comprises: Part or all of the material from the oil phase outlet of the overhead chromatograph of the condensation circulating column of the 2-propylheptanol production device is introduced into the first rectifying column, and separation is carried out in the first rectifying column, so that a crude pentanal mixture is obtained at the bottom; The crude pentanal mixture is sent into the second rectifying column for separation, so that crude n-pentanal is obtained at the bottom and returned to the condensation reactor of the 2-propylheptanol production device for continuous reaction, and the overhead product is separated by an oil-water separation reflux tank to obtain isopentanal product; The operating pressure at the top of the first rectifying column is 4-6 bar, and the operating temperature is 45-55℃; the operating pressure at the top of the second rectifying column is 1-2 bar, and the operating temperature is 105-115℃; the reflux ratio of the first rectifying column is 3-6, and the reflux ratio of the second rectifying column is 10-18; the number of theoretical plates of the first rectifying column is 36-40; the number of theoretical plates of the second rectifying column is 60-100, and the side-drawing position is the 4th-15th plate from the top.

2. The method for producing isovaleraldehyde as a byproduct from the oil phase of a condensation circulating column of a 2-propylheptanol production apparatus according to claim 1, characterized by, The first rectifying column and the second rectifying column are float valve columns.

3. The method for producing isovaleraldehyde as a byproduct from the oil phase of a condensation circulating column of a 2-propylheptanol production apparatus according to claim 1, characterized by, The top of the second rectifying column is provided with a reflux tank, which is an oil-water separation reflux tank.

4. The method for producing isovaleraldehyde as a byproduct from the oil phase of a condensation circulating column of a 2-propylheptanol production apparatus according to claim 1, characterized by, The operating pressure at the top of the first rectifying column is 4-5.5 bar, and the operating pressure at the top of the second rectifying column is 1.5 bar.

5. The method for producing isovaleraldehyde as a byproduct from the oil phase of a condensation circulating column of a 2-propylheptanol production apparatus according to claim 1, characterized by, The reflux ratio of the first rectifying column is 3.5-4.5, and the reflux ratio of the second rectifying column is 13-16.

6. The method of producing isovaleraldehyde as a byproduct from the oil phase of a condensation recycle column of a 2-propylheptanol production plant according to any one of claims 1 to 5, characterized in that, The residence time of the overhead material of the second rectifying column in the oil-water separation reflux tank is 20-50 min.

7. The method according to claim 6, characterized in that, The residence time of the overhead material of the second rectifying column in the oil-water separation reflux tank is 30-40 min.

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