JPH0165A - Synthesis method of ε-caprolactam - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

BACKGROUND OF THE INVENTION The present invention relates to a method for the synthesis of ε-caprolactam (hereinafter referred to as caprolactam) and an apparatus particularly suitable for carrying out the synthesis.

In conventional plants, caprolactam is obtained by reaction of cyclohexane-oxime (hereinafter referred to as oxime) with excess oleum.

According to one method (the "low temperature" method), highly exothermic reactions in the presence of liquid sulfur dioxide are carried out at very low temperatures (approximately -8°C).
The sulfate ester of caprolactam having the formula (■)=0SO,H is thereby obtained.

The second method is a "high temperature" process in the absence of SO2 to form caprolactam sulfate of formula ():
Usually 40-150°C) method.

Previously available "low temperature" methods exhibit the drawback of requiring excessive amounts of liquid SO3 (for cooling only) and also require "high temperature"
The method exhibited the drawback that the free SO2 content of the oleum had to be fairly low (generally below 30% by weight) when the temperature was very high, about 100° C., thus making the oleum capacity too large.

The Applicant has, however, proposed a method (hereinafter referred to as the "Low High Temperature" method) or "
We developed a method called "mixed method".

This will be explained in detail below.

In its broader aspect, the present invention provides for the synthesis of caprolactone by the reaction of an oxime with excess oleum, in which the reaction is first performed in the presence of liquid sulfur dioxide. Only part of
or more (preferably 65% by weight),
The initial step of the "low temperature" reaction is completed in a separate (second) "high temperature" step by simultaneously adding another (second) portion of oxime and evaporating most of the residual SO.
It also relates to a method characterized in that the ratio of the other (second) part of the oxime to the first (first) part is in the range of 0.5 to 1.2.

Excellent results are obtained by adding a third (third) portion of oxime mixed with the recycle stream to the crude product of the second ("hot") step in a third (finishing) step; of the crude product is divided into a recycle stream and a final crude product which passes through other conventional processing equipment, and the weight ratio of the recycle stream to the third portion of oxime is in the range of 10 to 150, and the oxime is The molar ratio of the third part to sulfur dioxide (present at the start of the third step) is 0.
．． less than 3 (preferably from 0.05 to 0.3) and preferably in the range from 40 to 80.

The amount of unbound S Os is at least 20% by weight at the beginning of the third step, preferably 20-26% by weight (25% by weight on average).

According to a preferred embodiment of the invention, a third portion of the oxime is added to the recycle stream in the static mixer (which consists of a portion of the product of the third step and is subjected to pre-evacuation of the discharge 5Offi). When the wave turbulence (upstream and downstream of the point of oxime injection into the mixer) corresponds to a very high Reynolds number. The desired level of wave turbulence can be achieved, for example, by equipping the conduits carrying the reaction liquid (upstream and downstream of the injection point) with fixed helical ribs or other similar devices exhibiting a low pressure drop. Particularly effective devices will be described later.

As the oxime portion is mixed with the crude product of the first rearrangement step, the temperature is raised rapidly (from -80 °C to 0 °C) and, due to the heat of reaction, the
The temperature is constantly raised to a temperature in the range of 0°C (usually 50-100°C).

The process according to the invention reduces the amount of ammonium sulfate formed as a by-product after ammonia treatment of lactam sulfate esters and also reduces the consumption of oleum. In addition, the process allows the maximum possible homogenization of the reaction mixture and thereby makes it possible to eliminate the formation of so-called hot spots, which lead to the formation of undesired compounds with excessive exothermic values. Another advantage is that it reconciles in the most balanced manner two requirements previously considered to be in stark contrast to each other, thereby increasing the Reynolds number and also the level of homogenization of the mixture. One such requirement is a significant increase in reaction mixture velocity to minimize residence time and minimize equipment size.

A second, contrasting requirement is to minimize the pressure drop in the third stage mixer. This plays a critical and decisive role in the design and operation of this type of plant, but the specific mixer in the third step (discussed below) is associated with the operating temperature and pressure of the caprolactam ester.
derived from the use of In fact, the oxime is fed into an ester which has a temperature below the freezing temperature of the oxime itself. The ester can be fed under pressure without causing undesired side reactions in the oxime line, even when the flow is stopped (shutdown).

Due to the method according to the invention, even in existing plants, the consumption of oleum is greatly reduced by introducing very simple modifications. In the first step, for example, when using concentrated oleum containing 65% by weight of free S Os (possible only if all other critical parameters are concerned), the oxime rearrangement is given a more thorough and rapid catalysis. There is also a useful contraction in the specific volume of oleum.

Another less pronounced but important effect is the use of crude oximes mixed with only a small proportion of water, without the usual dangerous dehydration operations (oximes are very unstable below 2%). Additionally, the level of homogenization in the reaction zone is excellent and the pressure drop is very low.

The present invention will, however, be illustrated by a series of drawings with respect to some of its features, but the scope of the invention itself is not limited thereby.

According to FIG. 1, the oxime stream (1), the oleum stream in excess of stoichiometric amount (2) and the liquid SO□ stream (3)
is fed into a first rearrangement step (4) operating at low temperature (approximately -8° C.) according to conventional techniques. The product (5) emerging from this step consists of caprolactam sulfate ester, free sulfur dioxide (not ester bound) and residual sulfur trioxide.

Another stream of oxime (7) is fed to the small device (6). The reaction mixture is then placed at low temperature (approximately 8° C.) in an evaporator/reactor (8) where residual SO□ is evaporated and excess SO□ is contacted (at “hot” conditions) with additional oxime feed. A second dislocation step associated with is carried out. Thus, there will be a multi-step process for oxime rearrangement. The first step is of the "low temperature" type and the subsequent steps are of the "high temperature" type.

The reaction mixture first falls onto a tray (heated by a heating coil not shown in the drawing) where it receives heat of dislocation (approximately 7
5°C), most of the residual SO□ is released. The same mixture is then passed through the recycle stream (11
) with another mixture (9) obtained by injecting a further (third) portion of oxime (IO).

The heat generated by the reaction of the oxime with S Os increases the temperature considerably, however, the temperature is lower than that of the coil system (1
2) appropriately maintained at an optimum level (usually 85-100°C) by a suitable thermal fluid (eg ethylene glycol) circulating therein; Once the conversion is complete, the product is transferred to the exhaust tank (
13), where the final traces of S02 are separated and recycled via line (14) back to the evaporator-reactor (8).

A vent (15) exhausts all the sulfur dioxide emitted by the entire system, e.g. a water-cooled heat exchanger (16).
lowers the temperature of the thermal fluid (17). Conversion of the oxime does not occur in the static mixer (18) (if it does, it is at a minimal rate); this vessel is exclusively
The oxime is dispersed in a very homogeneous manner in the recycle stream (11) containing the SO5 necessary for the rearrangement step.

The unrecycled product (11/a) is finally transferred to the neutralization zone and then to the ammonium sulfate separation zone. (For example, Italian Patent No. 1.144,91
No. 2 and Italian Patent Application Publication No. 22427A/82
and 20018A/84).

According to FIG. 2, the sulfuric acid recycle stream (11) leaving the device (8) and consisting of sulfuric acid esters is introduced into a flanged cylinder (18) into which the oxime stream (IO) is injected. Fixed helical fins (19) and (20) are arranged upstream and downstream of the injection point of the cylinder, respectively. The injection nozzle is covered with a heating jacket which is thermally stabilized by a flow (21) or another homogeneous thermal fluid, and the oxime inlet is connected to the surface of the sealing ring (24) by a spring (23) of suitably adjusted strength. It is closed by a sealing device (22) consisting of a check valve with an axially sliding tippered piston that is brought back into tight contact.

When the difference between the oxime pressure upstream of the check valve and the pressure downstream of the valve is higher than a predetermined value (usually 0.5 bar), the valve is lowered and oxime flows in. When the pressure drops, the valve is pulled back by the spring (23) to stop the flow;
This prevents the ester from flowing upward along the oxime duct, resulting in dangerous reactions involving partial carbonylation of the oxime and increased temperature. This device functions as a temperature-regulated supply nozzle and as a typical check valve,
This eliminates clogging of the supply ducts with carbonaceous residues. Therefore, if such a device is not used, there is a very high possibility that the clogging will occur particularly when the plant is shut down or when the entire plant is started.

Figures 3 and 4 illustrate structural details of the feed nozzle. In particular, consideration has been given to the stop bin (25)
It is.

The following examples merely illustrate some features of the invention:
It is not intended thereby to limit the scope of the invention in any manner.

Takumi-yu (comparison) According to Figure 1, molten cyclohexanone oxime (1) containing about 2% water by weight 1,333 parts, free 5 otss
% by weight and sufficient liquid 5a for synthesis heating (approximately -8°C)
2.034 parts by weight of oleum (2) containing t(3) was continuously fed to the first rearrangement step (4).

The effluent from the first step (5) was transferred to the device (6) along with another portion of the oxime (1,066 parts by weight).

The temperature was adjusted to 0℃ by measuring the liquid sulfur dioxide.The heat of reaction was adjusted to 75℃ by measuring the liquid sulfur dioxide.
The crude product is then pumped into the separation tank (13) and into the neutralization zone (using NH3) via the line (l/a). After this, it was transferred to a purification and recovery (for high purity caprolactam) zone of the type described in Italian Patent Publication 19737A/87. The highly pure final lactam had the following properties: Potassium permanganate number (3 wt% solution): 20,000 - Optical density (290 nanometers): 0.03
- Volatile base (milliequivalents/kg): 0.2 Selectivity of the rearrangement reaction (with respect to oximes) is >99%,
The amount of by-product (ammonium sulfate) is caprolactam 1k
It was about 1.35 kg per g. Regarding the definition of optical density and potassium permanganate value, Italian Patent No. 1.0
No. 98.009 and U.S. Pat. No. 3.914,217, please refer to them as necessary.

Third addition of oxime where the Takumi-Yu product was accumulated and 15.000 parts by weight of the product was injected via lines (11) and (9) into the static mixer (18) via line (IO). things (35
Example 1 was repeated with continuous recirculation to the reactor-evaporator (8) along with 0 parts by weight). After reaching the desired operating temperature in the third step (90 °C in the lower part of the reactor-evaporator thermally stabilized with ethylene glycol) -
The combined product was separated for transfer to the neutralization operation and subsequent operation (11a).

The high purity final caprolactam showed the same physical and chemical properties as Example 1, but the amount of by-product (ammonium sulfate) was 1
．． The weight decreased to 17 kg/kg. In other words, if the third step had not been carried out, the amount of by-products would have increased by more than 13%. Furthermore, it must be pointed out that the oxime (350 parts) in the third step was replaced with the oxime (1,0 parts) in the second step.
66 parts) would create an abnormal thermal imbalance, resulting in a dangerous increase in viscosity and an unacceptable loss of quality in the final product.

From the above, it will be appreciated how critical the third step is under conditions of high oxime dilution (and, with respect to the second step, higher temperature).

Takumi-1 The amount of oxime (pipe 10) in the third step was 680 parts by weight, the weight ratio R [recirculated flow (pipe 11)/oxime (pipe IO)] was maintained at about 40, and the steady temperature ( Example 2 was repeated by adjusting the temperature (at the bottom of the reactor-evaporator) to about 100°C.

High purity caprolactam of excellent quality was obtained and unexpectedly the amount of by-products was reduced to 1.07 kg/kg of caprolactam.

If such a third step had not been applied, the amount of by-products would have been higher than about 21%, as can be easily calculated.

fLL4 (comparison) Example 2 was repeated using 2.125 parts by weight of highly diluted (45% by weight S O3) oleum in place of the concentrated oleum and reducing the oxime concentration in the third step to 200 parts by weight. After neutralization and purification, caprolactam of very poor quality was obtained, with a synthesis selectivity (with respect to oxime) in the range of 97-98%. This test shows how critical the use of significantly increased concentrations of oleum is in the initial "cold" process.

[Brief explanation of drawings]

Figure 1 is a flow sheet schematically illustrating the entire process; Figures 2, 3 and 4 are static mixers used in the third step of the "mixing process" according to the invention; and Figure 5 shows the viscosity of the recycle stream (approximately 20 wt% free S Oa, 1% S Ot) which is mixed with oxime in the same third step. It is a graph. The main parts in the figure are as follows: 1.7.10... Oxime flow, 2... Oleum flow, 3... Liquid SO2 flow 4... First rearrangement step, 8... Evaporation vessel-reactor, 11...recirculated stream, 11/a...non-circulated product 18...static mixer or flanged cylinder, 19 and 20...helical fin, 25...
Stop bin Δ-Δ Procedural amendment (method) July 11, 1988 Director General of the Japan Patent Office Yoshi 1) Indication of the case of Takeshi Moon 1988 Patent application No. 55864 Title of invention - Amendment to the method of synthesizing cabrilactam person who does

Claims (6)

[Claims] (1) Cyclohexanone-oxime carried out according to conventional "cold" techniques with an amount of free SO_3 in the oleum in the first step using a first portion of oxime in the presence of liquid SO_2 at 50% by weight or more. A process for the synthesis of caprolactam by reaction of oxime with excess oleum, in which the "low temperature" step is completed in a separate (second) high temperature step by adding another (second) portion of the oxime, and the oxime is A method characterized in that the ratio of the other (second) part to the first (first) part is in the range 0.5 to 1.2. (2) The crude product of the second "hot" step is mixed with a further (third) oxime in the recycle stream in a subsequent (third) step.
), and the crude product of the third step is divided into the recycle stream and the final crude product stream, the weight ratio of the recycle stream and the third portion of oxime is from 10 to 150, and the oxime and the unbound S present at the start of the third step.
The molar ratio with O_3 is less than 0.30 (preferably 0.05
~0.30) and the weight ratio (recycle stream + final crude product)/(third portion of oxime) is in the range from 10 to 150. Method. 3. A process according to claim 2, wherein the weight ratio (recycle stream + final crude product)/(third portion of oxime) is in the range of 40 to 80. (4) The method according to claim 2, wherein the temperature in the third step is higher than the temperature in the step. 5. A method as claimed in claim 2, in which the third portion of oxime is injected into the recirculating stream in a static mixer, preferably provided with fixed helical blades (fins, ribs or baffles). (6) The method of claim 5, wherein the third portion of the oxime is injected through a temperature-controlled nozzle with a check valve.