KR101808248B1 - A continuous process for preparing neopentyl glycol - Google Patents

Abstract

The present invention relates to a process for the continuous production of neopentyl glycol. The continuous production process of neopentyl glycol according to the present invention enables the simplification of the subsequent process and the improvement of the yield of neopentyl glycol by extracting hydroxypivalic aldehyde with improved efficiency.

Description

TECHNICAL FIELD [0001] The present invention relates to a continuous process for producing neopentyl glycol,

The present invention relates to a process for the continuous production of neopentyl glycol with a high yield and a simplified process.

Neopentyl glycol (synonyms: 2,2-dimethyl-1,3-propanediol, hereinafter referred to as NPG) is an organic compound used in the synthesis of polyesters, paints, lubricants and plasticizers.

NPG is a hydroxypivalaldehyde (synonyms: 3-hydroxy-2,2-dimethylpropanal, hereinafter HPA) produced by aldol condensation reaction of isobutyraldehyde (synonyms: 2-methylpropanal) and formaldehyde Hydrogenation reaction.

The product of the aldol condensation reaction for obtaining HPA includes, in addition to HPA, an unreacted raw material compound, a catalyst, and a catalyst such as 2,2,4-trimethyl-1,3-pentanediol, neopentyl glycol hydroxy pivalate, neopentyl glycol isobutyl By-products such as rate are included. In particular, it is important to minimize the formation of by-products in the reaction to obtain HPA, since complex separation processes and equipment are required to separate the byproducts.

Particularly, formaldehyde among the raw materials for the production of HPA is difficult to recover because it is coexistent with water contained in the product of the aldol condensation process, and can act as a catalyst poison to the hydrogenation reaction of HPA. For this reason, the residue of formaldehyde should be minimized in the product of the aldol condensation process.

In this regard, the yield of HPA can be improved by adjusting the molar ratio of the reactants in the aldol condensation reaction or the composition of the catalyst, or by applying a plurality of continuous stirred-tank reactors (CSTR), and the yield of formaldehyde There have been attempts to minimize the amount of residues and by-products. Various purification processes have been proposed to obtain high purity NPG from the products of the aldol condensation process.

However, the methods proposed so far have a limitation in that the yield of HPA is still low, complicated processes are required until NPG is obtained due to ineffective purification, and excessive equipment cost and operation cost are accompanied.

U.S. Patent No. 3939216 (Feb. Korean Registered Patent No. 0231644 (Aug. 31, 1999)

The present invention is to provide a method for continuously producing NPG with a high yield and a simplified process.

According to the present invention,

An aldol condensation process for obtaining a product containing HPA through aldol condensation reaction of an aqueous solution of formaldehyde and isobutylaldehyde in the presence of a catalyst,

An extraction step of contacting the product of the aldol condensation step with an extraction solvent to obtain an extract containing HPA,

A low boiling point material separation step of distilling the extracted liquid to obtain a distilled liquid from which a low boiling point material having a boiling point lower than that of HPA is removed,

A hydrogenation step of hydrogenating the distillate from which the low boiling point material has been removed in the presence of a catalyst to obtain a product containing NPG, and

And a purification step of distilling the product of the hydrogenation step to obtain NPG;

Wherein the extraction process is performed in an extraction column having a plurality of stages partitioned by perforated trays.

Hereinafter, a method for continuously producing NPG according to an embodiment of the present invention will be described.

Prior to that, and unless explicitly stated throughout the present specification, the terminology is used merely to refer to a specific embodiment and is not intended to limit the present invention. And, the singular forms used herein include plural forms unless the phrases expressly have the opposite meaning. Also, as used herein, the term " comprises " embodies specific features, regions, integers, steps, operations, elements or components, and does not exclude the presence of other specified features, regions, integers, steps, operations, elements, It does not.

The feed of the extraction process is a liquid mixture containing a solute to be extracted, which is a mixture of a soluble solute with an extraction solvent and an inert material which is not soluble . When the extraction solvent is added to the feed, the solute is dissolved from the feed into the extraction solvent by mass transfer phenomenon. The extraction solvent, in which a significant amount of solute is dissolved, forms an extract solution, and the feed that has lost a significant amount of solute forms a raffinate solution.

On the other hand, as a result of continuous research by the present inventors, it has been confirmed that remarkable simplification of the subsequent process can be achieved when the efficiency of the extraction process for obtaining the extract containing HPA by contacting the product of the aldol condensation process with the extraction solvent is improved.

Specifically, when the extraction process is performed in an extraction column having a plurality of stages partitioned by perforated plates, the HPA extraction efficiency of 99% or more can be secured and the water content can be significantly reduced. Accordingly, the low-boiling substance contained in the product of the aldol condensation process can be separated only by one step after the extraction process, and recycling is possible without further refining facilities for the separated low-boiling substance.

In addition, as a result of continuous research by the present inventors, an aldol condensation process for obtaining HPA was sequentially carried out in three or more continuously stirred reactors connected in series, and isobutylaldehyde in the raw material compound was added to each reactor at different ratios , And it was confirmed that HPA could be obtained in a remarkably improved yield when reactants of the aldol condensation reaction were allowed to react in different reactors under different residence times.

It has been confirmed through this aldol condensation process that not only the residual amount of unreacted formaldehyde can be remarkably lowered but also the production of by-products such as neopentyl glycol hydroxy pivalate can be effectively inhibited. Particularly, in the aldol condensation process, by sequentially decreasing the proportion of isobutyl aldehyde branching into each reactor and sequentially increasing the residence time of the reactants in each reactor, a further improved effect can be exhibited.

According to one embodiment of the invention,

An aldol condensation process for obtaining a product containing HPA through aldol condensation reaction of an aqueous solution of formaldehyde and isobutylaldehyde in the presence of a catalyst,

An extraction step of contacting the product of the aldol condensation step with an extraction solvent to obtain an extract containing HPA,

A low boiling point material separation step of distilling the extracted liquid to obtain a distilled liquid from which a low boiling point material having a boiling point lower than that of HPA is removed,

A hydrogenation step of hydrogenating the distillate from which the low boiling point material has been removed in the presence of a catalyst to obtain a product containing NPG, and

And a purification step of distilling the product of the hydrogenation step to obtain NPG;

Wherein the extraction process is performed in an extraction column having a plurality of stages partitioned by perforated plates.

In the accompanying drawings, FIG. 1 schematically shows a continuous production method of NPG according to an embodiment of the invention, and FIG. 2 schematically shows an aldol condensation process in the continuous production method of NPG.

1, the continuous production method of the NPG includes an aldol condensation reaction system 100, an extraction column 200, a low boiling point material separation column 300, a hydrogenation reaction system 400, a distillation column 500, And may be performed with a flow including the point material removal column 600.

Hereinafter, with reference to FIGS. 1 and 2, each process that can be included in the continuous production method of NPG will be described.

(One) Aldol Condensation  fair

The aldol condensation process is a process for obtaining an HPA-containing product through aldol condensation reaction of formaldehyde aqueous solution and isobutylaldehyde in the presence of a catalyst.

The aldol condensation process can be carried out in three or more, preferably three or five, more preferably three or four successive stirred reactors connected in series. Although the efficiency of the aldol condensation reaction can be expected to be improved by increasing the number of the continuously stirred reactors, it is preferable to determine the number of the reactors in consideration of the efficiency of the process and the complexity of the equipment.

2 schematically shows an embodiment of an aldol condensation reaction system 100 including three continuous stirred reactors.

Referring to FIG. 2, the aldol condensation process may be performed in an aldol condensation reaction system 100 comprising three continuous stirred reactors (R1, R2 and R3). In the aldol condensation reaction system 100, the catalyst (F0-TEA) to be used for the aldol condensation reaction and the starting compounds (F0-iBAL and F0-FA) are introduced into the first reactor (R1) Then, the reactants are sequentially transferred to the other reactors (R2 and R3) through the connection pipes (F1 and F2), and the reaction proceeds.

Particularly, in the aldol condensation process, isobutylaldehyde (F0-iBAL) in the raw material compound is added to the respective reactors (R1, R2 and R3) at different ratios (S1, S2 and S3) The reactants are reacted under different residence times in each reactor.

Preferably, the proportion of isobutylaldehyde added to each reactor in the aldol condensation process is sequentially decreased, and the residence time of the reactants in each reactor is sequentially increased. Here, the deceleration width of the isobutylaldehyde content added to the respective reactors and the increase width of the reactant retention time are not particularly limited.

Specifically, in the case of the aldol condensation reaction system 100 including three successive stirring reactors (R1, R2 and R3), it is preferable that the aldol condensation reaction system (100) comprises 89 to 94% by weight based on the total content of isobutylaldehyde Isobutylaldehyde is charged to the first reactor (R1), 5 to 10 wt% isobutylaldehyde is charged to the second reactor (R2), 1-3 wt% isobutylaldehyde is introduced to the third reactor (R3) Lt; / RTI > That is, it is preferable that at least 89 wt% of isobutylaldehyde is added to the first reactor (R1) in consideration of the aspect of activity represented by the catalyst and the overall efficiency of the aldol condensation reaction. In the third reactor (R3) % Or less of isobutyl aldehyde is preferably added.

Particularly, with the branching of the isobutylaldehyde, the residence time of the reactants in the three continuous stirred reactors is increased from 10 to 13 minutes in the first reactor (R1), from the second reactor R2 to 13 to 17 minutes, and in the third reactor R3 to 17 to 19 minutes.

Here, the residence time of the reactants in each reactor is determined by measuring the space velocity of the reactants, in particular the liquid hourly space velocity (LHSV) of the reactants in the aldol condensation reaction, ≪ / RTI >

In order to effectively stir the reactants in each reactor in the aldol condensation process, the Reynolds number, the linear velocity at the tip of the impeller, the linear velocity at the reactor wall, and the like Should be taken into account. Preferably, in the aldol condensation reactor system, the Reynolds number of each reactor is 50,000 or more, and the difference in the linear velocity between the impeller tip and the wall surface of the reactor is adjusted to 2 to 5 m / sec.

The aldol condensation reaction of formaldehyde aqueous solution and isobutylaldehyde is an exothermic reaction. Therefore, it is preferable to remove the reaction heat while circulating the reactants in the respective reactors to the outside of the reactor. Particularly, when the reactant is circulated to the outside, the reaction product is injected strongly into the reactor by using the injector equipped with the venturi nozzle, so that the improved reaction efficiency can be secured. That is, the aldol condensation process can be carried out in three or more continuously stirred reactors connected in series via a reactant circulating unit including a circulating pump, a heat exchanger and a reactant injector.

On the other hand, in the aldol condensation process, it is advantageous to use isobutylaldehyde having an isomer content of less than 0.5% by weight to inhibit the formation of by-products.

And, isobutylaldehyde can be used in a molar ratio of 1.1 to 1.5, preferably 1.1 to 1.2, per mole of formaldehyde. That is, in order to induce complete reaction of the formaldehyde used in the aldol condensation reaction, isobutylaldehyde can be used in an excess relative to the formaldehyde, preferably in a molar ratio of 1: 1.1 or more. However, when isobutylaldehyde is excessively used, the formation of by-products due to Tischchenko reaction may be increased. Therefore, isobutylaldehyde is preferably used in a molar ratio of formaldehyde to formaldehyde of 1: 1.5 or less.

In the aldol condensation process, it is advantageous to use formalin having a formaldehyde concentration of 35 to 45% by weight as an aqueous solution of formaldehyde in order to improve the reaction efficiency and reduce the generation of waste water. Generally, methanol is added to formaldehyde aqueous solution to prevent polymerization of formaldehyde, and its content is preferably 0.1 to 5% by weight based on the aqueous solution of formaldehyde.

In the aldol condensation process, the catalyst may include hydroxides such as LiOH, NaOH, KOH, and Ca (OH) ₂ ; Alkali metal carbonates such as NaCO ₃ , LiCO ₃ , KCO ₃ , Ca (CO ₃ ) ₂ and NH ₄ CO ₃ ; Tertiary amine compounds such as trimethylamine, triethylamine and tripropylamine may be used. Of these catalysts, tertiary amine compounds, especially triethylamine, can be more preferably used in terms of improving the efficiency of the aldol condensation reaction.

The catalyst may be used in a molar ratio of 0.01 to 0.5, preferably 0.15 to 0.25, and more preferably 0.18 to 0.22, per mole of formaldehyde. That is, in order to exhibit the catalytic effect, the catalyst may be used in a molar ratio of formaldehyde of 1: 0.01 or more. However, if the catalyst is used excessively, recovery of the catalyst may be required and production of by-products may be caused. Therefore, the catalyst is preferably used in a molar ratio of formaldehyde of 1: 0.5 or less.

In the aldol condensation step, the reaction temperature may be maintained at 70 to 100 ° C, preferably 70 to 85 ° C. In order to ensure the yield of the reaction, the reaction temperature is preferably 70 ° C or higher. However, if the reaction temperature is too high, the production of by-products may be accelerated, so that the reaction temperature is preferably 100 ° C or lower. The aldol condensation reaction may be carried out under pressure in order to ensure the yield.

The aldol condensation process carried out under the above-mentioned conditions can maximize the mixing efficiency with respect to the raw material compound, thereby improving the efficiency of the aldol condensation reaction and minimizing the formation of unreacted formaldehyde residues and by-products. Specifically, through the aldol condensation process, a high HPA yield of 99% or more and a low residual formaldehyde concentration of 2000 ppm or less can be secured.

(2) Extraction process

The extraction step is a step of contacting the product of the aldol condensation step with an extraction solvent to obtain an extract containing HPA.

In particular, in the present invention, the extraction process is performed in an extraction column having a plurality of stages partitioned by perforated plates. Accordingly, the extraction process can secure a significantly improved HPA extraction efficiency and simplify the subsequent low boiling point material separation process.

In the extraction step, an extraction column 200 of an excellent agitation system having a stage partitioned by perforated plates performing up-and-down repetitive movement as an extraction column according to a liquid-liquid contact method can be preferably applied. Specifically, the extraction column 200 may be a Kuhni column, a Karr type reciprocating plate column, a rotary-disk contactor, a Scheibel column, a spray extraction column ), A packed extraction column, a pulsed packed column, etc. may be used.

And, in order to allow sufficient extraction efficiency to be exhibited under the extraction column, the extraction process can be performed in an extraction column having 20 or more stages, preferably 20 to 30 stages, partitioned by perforated plates. At this time, the height of one end of the extraction column may be 300 to 500 mm, which is advantageous for improving the extraction efficiency. However, the number of stages and the height of the stage of the extraction column may be limited to the pilot column, and may be extended to an appropriate range for the commercialization process.

In the extraction process, the product of the aldol condensation process supplied to the extraction column 200 is contacted with the extraction solvent to produce an extract solution in which a significant amount of HPA is dissolved and a raffinate solution in which a substantial amount of HPA is lost Respectively. At this time, the extract liquid, which is a relatively light phase, is obtained through the upper outlet of the extraction column 200, and the additional balance, which is a relatively heavy phase, is obtained through the lower outlet of the extraction column 200.

In the above-mentioned extraction step, as the extraction solvent, it is possible to use solubility to HPA, preferably octanol.

The extraction solvent may be used in a weight ratio of 1: 0.3 to 1: 0.7, preferably 1: 0.4 to 1: 0.6, to the product of the aldol condensation process supplied to the extraction column 200. That is, in order to ensure sufficient extraction efficiency, the extraction solvent is preferably used in a weight ratio of 1: 0.3 or more to the product. Even if the weight ratio of the extraction solvent is more than 1: 0.7, the extraction efficiency may be improved. However, in the subsequent low boiling point material separation process, the loss amount of HPA may increase, and the reflux flow of the azeotropic solvent Which is undesirable.

And, if the temperature is excessively low, the HPA may be cured, so that the temperature of the extraction step is preferably maintained at 40 ° C or higher. However, when the temperature is excessively high, the extraction liquid may not be phase separated. Therefore, the temperature of the extraction step is preferably kept at 90 ° C or lower.

According to an embodiment of the invention, more than 99% of the HPA extraction efficiency can be secured through the above-described extraction process. That is, the extract obtained through the extraction process may contain 99 wt% or more of the HPA contained in the product of the aldol condensation process. In addition, as the water contained in the product of the aldol condensation process is mostly discharged as residual water, the extract contains 3% by weight or less of water.

As more than 99 wt% of the HPA obtained in the aldol condensation process is extracted through the extraction process, the loss of HPA in the extraction process can be minimized. The extraction process can lower the equipment burden and energy consumption of the subsequent low-boiling point material separation process.

(3) Low boiling point  Material separation process

The step of separating the low boiling point material is a step of distilling the extracted liquid to obtain a distilled liquid from which a low boiling point material having a lower boiling point than HPA is removed.

In addition to HPA, the extract contains unreacted isobutyl aldehyde, aldol condensation reaction catalyst, water contained in aqueous formaldehyde solution, and a low boiling point substance such as methanol. Such low-boiling substances can be separated from the extract by distillation.

Particularly, in the present invention, since the HPA extraction efficiency of 99% or more is secured in the extraction process, it is possible to separate the low boiling point material by only a single distillation after the extraction process. And, the isobutylaldehyde and the catalyst among the separated low-boiling substances can be recycled to the aldol condensation process.

In the low boiling point material separation step, the extracted liquid supplied to the low boiling point material separation column 300 is contacted with an azeotropic solvent and distilled by evaporation and condensation while being heated to an appropriate temperature.

At this time, in order to efficiently separate the HPA contained in the extract from the low boiling point material, the low boiling point material separation process is preferably performed by an azeotropic distillation method. As the solvent to be applied to the above azeotropic distillation method, an azeotropic mixture with the above-mentioned low-boiling point substance can be achieved, and a conventional one having a boiling point lower than that of HPA can be applied.

(4) Hydrogenation process

The hydrogenation step is a step of hydrogenating the distillate from which the low boiling point material has been removed in the presence of a catalyst to obtain a product containing NPG.

As the catalyst for the hydrogenation reaction, a conventional nickel catalyst may be used. The catalyst may be used in an amount of 2 to 10% by weight based on the HPA contained in the distillate.

The hydrogenation reaction is a gas-liquid reaction. Therefore, in order to increase the contact efficiency of the reactants, a hydrogenation reaction system 400 having a venturi nozzle for injecting the HPA-containing distillate into the reaction system may be used in the hydrogenation reaction.

The hydrogenation reaction is preferably carried out at a hydrogen pressure of 100 to 1500 psig and a temperature of 100 to 200 ° C in view of the yield.

(5) Purification process

The purification step is a step of distilling the product of the hydrogenation step to obtain NPG.

The product of the hydrogenation process may include unreacted HPA, dimer of HPA, high boiling point material, etc. in addition to crude NPG. Accordingly, the product of the hydrogenation process can be distilled in the distillation column 500 to obtain high-purity NPG.

If necessary, a process of separating the high boiling point material may be performed by supplying the material separated from the NPG through the distillation to the high boiling point material removing column 600.

The continuous production process of NPG according to the present invention enables extraction of HPA with improved efficiency, thereby simplifying the subsequent process and improving the yield of NPG.

FIG. 1 schematically shows a method for continuously producing NPG according to an embodiment of the present invention.
2 schematically shows an aldol condensation process in a continuous production method of NPG according to an embodiment of the present invention.

Hereinafter, preferred embodiments of the present invention will be described in order to facilitate understanding of the present invention. However, the following examples are intended to illustrate the present invention without limiting it thereto.

Example

An apparatus having the same configuration as in Fig. 1 was prepared. In the aldol condensation process, an aldol condensation reaction system 100 including three continuously stirred reactors (R1, R2 and R3) connected in series as shown in FIG. 2 was used. As the extraction column 200 in the extraction process, a Kuhni column (one height of 400 mm) having a total of 24 stages, which is divided by the perforated plates which are repeatedly moved up and down, was used.

An aqueous solution of isobutylaldehyde and formaldehyde (containing 42 wt% of aldehyde and 1 wt% of methanol) was prepared as a raw material compound for the aldol condensation process. Triethylamine (TEA) was prepared as a catalyst.

Formaldehyde: isobutylaldehyde: Triethylamine was used in a molar ratio of 1: 1.1: 0.2. Formaldehyde aqueous solution and catalyst were added to the first reactor. Then, based on the total content of isobutylaldehyde, 91 wt% of isobutylaldehyde was added to the first reactor (R1), 7.5 wt% of isobutylaldehyde was added to the second reactor (R2), 1.5 wt% of isobutyl The aldehyde was added to the third reactor (R3), respectively. At the same time, the residence time of the reactants in each reactor was controlled as shown in Table 1 below.

Reactor Reactor Volume
(M3) Reactant Liquid Flow Rate (㎥ / hr) LHSV Reactant
Retention time (minutes) R1 2.41 12.62 5.23 11.47 R2 3.23 12.378 3.83 15.65 R3 3.74 12.293 3.29 18.23

The aldol condensation process was continuously carried out at a temperature of 72-78 캜 and under a pressure of 3 atm, thereby obtaining a product containing HPA (conversion rate: 89.8%, residual formaldehyde concentration in the product: 2000 ppm, HPA yield 99.20%).

On the other hand, the product of the aldol condensation process was introduced into the extraction column 200. At this time, 50% by weight of octanol relative to the product was introduced into the extraction column 200 as an extraction solvent. The extraction of HPA was carried out by vigorous stirring in the extraction column, and the composition of the organic layer in the extract obtained through this was shown in Table 2 below.

Subsequently, the extract was distilled in a low boiling substance separation column 300 to separate low boiling substances such as isobutyl aldehyde, triethylamine, water and methanol. The separated low boiling point material was discharged to the upper part of the low boiling point material separation column 300 and recycled to the aldol condensation reaction system 100. The composition of the low-boiling substance is shown in Table 2 below.

The distillate from which the low boiling point material was removed was continuously introduced into the hydrogenation reaction system 400, and the hydrogenation process was carried out in the presence of a nickel catalyst. The product of the hydrogenation process was continuously introduced into the distillation column 500 to be refined, and NPG was finally obtained.

Of the aldol condensation process
The product (% by weight) The organic layer
(weight%) Low-boiling substance
(weight%) HPA 57.3 45.4 4 water 23.8 2.7 5 Octanol 0.4 37.4 2 Isobutylaldehyde 4.1 3.2 21 Formaldehyde 0.3 0.2 2 Methanol 2.0 1.5 7 TEA 11.4 9.0 59 Neopentyl glycol
Isobutyrate 0.8 0.6 0

Referring to Table 2, it was confirmed that the extract obtained through the extraction process contained about 99.7% by weight of the HPA contained in the product of the aldol condensation process. And, the extract contained 3% by weight or less of water. As described above, the extraction process showed excellent HPA extraction efficiency of 99% or more.

R: raw material compound
100: Aldol condensation reaction system
200: extraction column
300: low boiling point material separation column
400: Hydrogenation reaction system
500: distillation column
600: High boiling point material removal tower
E: Extraction solvent
H: hydrogen
NPG: neopentyl glycol
HB: High boiling point material
F0-iBAL: isobutylaldehyde feed line
F0-FA: Formaldehyde aqueous solution supply line
F0-TEA: Catalyst feed line
S0: Dispenser
S1, S2, S3: Isobutylaldehyde branch feed line
R1, R2, R3: continuously stirred reactor

Claims (11)

An aldol condensation process for obtaining a product containing hydroxypivalaldehyde through aldol condensation reaction of an aqueous solution of formaldehyde and isobutylaldehyde in the presence of a catalyst,
An extraction step of contacting the product of the aldol condensation step with an extraction solvent to obtain an extract containing hydroxypivaloaldehyde,
A low-boiling-point separation step of distilling the extract to obtain a distillate from which a low-boiling substance having a boiling point lower than that of hydroxypivalaldehyde is removed,
A hydrogenation step of hydrogenating the distillate from which the low boiling point material has been removed in the presence of a catalyst to obtain a product containing neopentyl glycol, and
And a purification step of distilling the product of the hydrogenation step to obtain neopentyl glycol;
The aldol condensation process is carried out in three successive stirred reactors connected in series. The proportion of isobutylaldehyde added to each reactor is sequentially decreased and the residence time of the reactants in each reactor is sequentially increased.
Wherein the extraction step is performed in an extraction column having 20 to 30 stages of stages partitioned by 300 to 500 mm in height of one stage by means of perforated plates.
delete delete The method according to claim 1,
Wherein the extraction solvent is octanol and is used in a weight ratio of 1: 0.3 to 1: 0.7 with respect to the product of the aldol condensation process.
The method according to claim 1,
Wherein the extract obtained through the extraction step contains at least 99 wt% of the hydroxypivalic aldehyde contained in the product of the aldol condensation reaction process.
The method according to claim 1,
Wherein the extract obtained through the extraction step contains not more than 3% by weight of water.
delete delete delete The method according to claim 1,
Based on the total content of isobutylaldehyde charged to the three continuously stirred reactors, 89 to 94 wt.% Of isobutylaldehyde is charged to the first reactor, and 5 to 10 wt.% Of isobutylaldehyde is fed to the second reactor And 1 to 3% by weight of isobutylaldehyde is fed into the third reactor.
The method according to claim 1,
Wherein the residence time of the reactants in said three continuous stirred reactors is from 10 to 13 minutes in the first reactor, from 13 to 17 minutes in the second reactor and from 17 to 19 minutes in the third reactor.

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