KR20000022551A - Process for the separation of a ketoxime or aldoxime from an amide - Google Patents

Abstract

PURPOSE: A process for simply and directly separating a ketoxime or aldoxime from a ketoxime- or aldoxime-containing amide mixture is provided in which the ketoxime or aldoxime is separated from the amide mixture by means of distillation. CONSTITUTION: A process for separating a ketoxime or aldoxime from an amide comprises a steam distillation and a distillation under reduced pressure. The distillation is performed at 80-180°C, and can be divided into two stages and be put in theoretical trays. The pressure reduction is lower than 200Pa.

Description

How to separate ketoxime or aldoxime from amides

The present invention relates to a process for separating ketoxime or aldoxime from a ketoxime- or aldoxin-containing amide mixture, for example from a mixture obtained in a Beckman shift.

The process is described in GB-A-1286427 in which the oxime-containing lactam mixture is treated with sulfur dioxide. In the process, at least one mole of sulfur dioxide is added per mole of oxime. Excess sulfur dioxide is subsequently removed and caprolactam is obtained in pure form by distillation.

A disadvantage of this method is that foreign material is added to the reaction and must be removed from the reaction in the last step.

Moreover, this is a disadvantage because oximes, such as ketoxime or aldoxime, function as chain terminators in the polymerization of amides, for example when polymerizing caprolactam to nylon-6. It is therefore important to obtain the desired amide product in the purest form possible.

The object of the invention relates to a process for separating ketoxime or aldoxime from an amide in a simple, direct manner.

The above object can be achieved by separating ketoxime or aldoxim by distillation according to the present invention.

This is surprising because GB-A-1286427 states that the separation of oximes from lactams is simple, too expensive and impossible to be a simple physical separation. It is also surprising that ketoxime or aldoxime are not thermally stable. As an undesired by-product, for example, octahydrophenaxin (OHP) is expected to form upon distillation. OHP is a disadvantage in the final quality of caprolactam.

It is often known that amides, in particular lactams (eg -caprolactam) can be prepared, for example cyclohexanone oximes, by Beckman displacement of ketoxime or aldoxime. The displacement takes place using a solid acid or neutral catalyst. The shifting takes place in the gaseous or liquid phase.

Examples of solid acids or neutral catalysts include, for example, boric acid on a support such as silica or alumina and crystalline silica such as silicalite I (silicon-rich MFI) and silicalite II (silicon-rich MEL). Use; Optionally acid ion exchangers or (mixed) metal oxides are used.

The advantage of the catalyst according to the preparation method is that no by-products such as ammonium sulfate are formed in the typical case of Beckman displacement, which is treated with aldoxim or ketoxime with a strong acid such as sulfuric acid. The desired amide must then be recovered through neutralization of the reaction mixture by using ammonia water. However, by-products form large amounts of ammonium sulfate.

However, in Beckman displacement in the liquid or gas phase, an incomplete conversion of ketoxime or aldoxim occurs, such that a specific amount of ketoxime or aldoxim that has not reacted with the desired amide remains in the reactor. On the other hand, it is most preferred that the ketoxime or aldoxime be completely removed from the oxime-containing mixture by cleavage in the downstream process of the amide. Therefore, it is important to obtain the desired amide with high purity.

Examples of ketoximes or aldoxins in the ketoxime- or aldoxin-containing amide mixtures obtainable from Beckman repositioning are aliphatic ketoximes or aldoxins having 2-12 carbon atoms which are unsaturated and saturated, substituted or unsubstituted or As cyclic ketoxime, for example acetone oxime, acetaldehyde, benzal oxime, propane aldoxin, butane aldoxin, butanone oxime, 1-butene oxime, cyclopropanone oxime, cyclohexanone oxime, cyclooctanone Oxime, cyclododecanone oxime, cyclopentenone oxime, cyclododecenone oxime, 2-phenyl cyclohexanone oxime, cyclohexenone oxime.

Distillation techniques used in the practice of the present invention include steam distillation and distillation under reduced pressure. The temperature at which distillation can occur is between 80 ° C and 180 ° C. Preferred temperatures are between 100 ° C and 160 ° C.

Distillates containing ketoxime or aldoxim are returned to the reactor and are subsequently repositioned.

The distillation can be carried out in two stages, divided into theoretical trays, and the pressure drop is less than 200 Pa per theoretical tray. Pressure drops below 200 Pa relate to the measurement under standard conditions, ie the reaction of the cis-trans decalin mixture (50% cis and 50% trans) under full reflux at a pressure of 50 mbar and a vapor rate of 5.2 m / s.

In the distillation according to the invention, various evaporators can be used, for example falling film evaporators. As filler for the distillation column, the filler is suitable to give a pressure drop of less than 200 pa per theoretical tray. Such fillers are usually commercially available, e.g., Intalox metal fillers (described in Chemical Engineering Progress, March 86, 1979, pages 86-91), Sulzer BX (trade name). (See Chemie Ingenieur Technik, Vol. 37, p. 322, 1965) and Sulzer Mellapak (tradename) (Chemical Engineering Progress, described on Nov. 1977, pages 71-77). Preferred fillers can be the use of the aforementioned Melapak®, for example, where the pressure drop is less than 100 Pa per theoretical tray. The required number of theoretical trays in the rectification column is 1-15, preferably 5-12, in particular between 8-12. The purified caprolactam-oxime mixture is charged to the top of the column or to the column itself. As a rule, reflux ratios between 3 and 8 are used. The purity of the bottom product obtained according to the invention is usually> 99%.

The rectifying column is preferably operated at a bottom pressure of 500-3000 Pa and a bottom temperature between 120 and 160 ° C.

The invention will now be described with reference to the following examples which do not limit the invention.

Example 1

A mixture of 700 g of water, 4.57 g of cyclohexanone oxime and 16 g of caprolactam is fed to a 1 l vessel. The temperature of the vessel is raised to 100 ° C. and steam is passed through the mixture. The gaseous stream is cooled and six distillate fractions are collected throughout. In each fraction obtained at the same time and in each sample of the residue, the cyclohexanone oxime content and caprolactam content are measured by gas chromatography on an HP gas chromatograph equipped with a CP wax 52CB column. Detection is performed using a FID detector. The results are shown in Table 1 below.

Fraction + accumulation weight Distillate, oxime in accumulator (g) Oxime in residue (g) Lactam in distillate, cumulative (g) Lactam in residue (g) Fraction 128.7 g 0.53 4.04 0.0035 16.10 Fraction 2175g 1.95 2.62 0.029 15.93 Fraction 3265 g 3.03 1.53 0.08 15.86 Fraction 4420g 3.90 0.66 0.15 15.82 Fraction 5950g 4.52 0.05 1.54 14.31 Fraction 61000 g 4.57 0.003 3.3 12.67

In Table 1 above, it was found that minimal loss of lactam in the upper distillate and substantially pure lactam at the bottom of the distillate were substantially recovered, combined with substantially eliminating the unwanted oxime.

Example 2

Vacuum distillation preparation consists of a 30 cm column (Widmer) with 10-15 theoretical trays. The reflux ratio is five. The reflux ratio is defined as the reflux stream relative to the product stream. At the top of the column, the pressure is 5 mm Hg and the temperature is 130 ° C. At the bottom of the column, the temperature is 151 ° C. The composition of the starting material obtained from Beckman displacement is as follows:

Recrystallized twice with 40 g of caprolactam flakes and 10 g of cyclohexanone oxime, toluene to obtain> 99% pure cyclohexanone oxime.

The starting material is delivered to the bottom of the column at one time. The distilled fraction obtained as the top product of the column is analyzed by gas chromatography as described in Example 1. After completion of the distillation, the residue obtained at the bottom of the column is also analyzed. The results are shown in Table 2. The distilled fraction is returned to the vessel and Beckman displacement takes place. Large amounts of oximes are found in the pipes by condensation and solidification and are not included in the various distillate fractions.

% Oxime Oxime g G of lactam Distillate Fraction 14.01g 30.4 1.22 2.79 Distillate Fraction 22.10g 58 1.22 0.88 Distillate Fraction 33.26 g 11.6 0.38 2.88 Residue 32g - <100 ppm 32 Residues remaining in the exhaust gas and pipes 86.4 6.91 1.09

Claims (11)

A method for separating ketoxime or aldoxime from a ketoxime- or aldoxime-containing amide mixture, Separation method of ketoxime or aldoxime, characterized in that the ketoxime or aldoxim is distilled off from the amide mixture. The method of claim 1, The distillation is carried out under reduced pressure. The method of claim 1, The distillation is steam distillation. The method according to any one of claims 1 to 3, The distillation is carried out at a temperature between 80 ° C and 180 ° C. The method of claim 4, wherein The distillation is carried out at a temperature between 100 ° C and 160 ° C. The method according to any one of claims 1 to 5, The distillation is carried out in a column with 1-15 theoretical trays. The method of claim 6, The distillation is carried out in a column with 5-15 theoretical trays. The method of claim 7, wherein The theoretical pressure drop per tray is less than 200 pa. The method according to any one of claims 1 to 8, The ketoxime or aldoxime obtained by said distillation is recycled to the reactor for the production of the corresponding amide. The method according to any one of claims 1 to 9, The distillation is carried out in two steps. Method described in the detailed description and examples.