JPS5822133B2 - Method for treating by-products of acetaldehyde production - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating an aqueous solution containing mainly chloroacetaldehyde, which is produced as a by-product when acetaldehyde is produced from ethylene by the so-called Hoechst method (or Wallaker method).

Acetaldehyde is produced industrially by oxidizing ethylene in the presence of palladium chloride and a redox catalyst, but this process produces many types of by-products, including chloroacetaldehyde.

Therefore, acetaldehyde is taken out from the reaction system as hydrous crude acetaldehyde containing various by-products.

From this, acetaldehyde is distilled and by-products with a lower boiling point than acetaldehyde are distilled and separated, and then the distillate is distilled again to obtain acetaldehyde as an overhead fraction, while at the same time water is extracted from the bottom of the column and the by-products The chloroacetaldehyde is extracted as a side stream from the tower.

Since there is no suitable use for chloroacetaldehyde, it is detoxified and then disposed of, or it is incinerated and the chlorine content is recovered as hydrochloric acid, but the latter is usually adopted from the perspective of effective resource utilization. .

Since chloroacetaldehyde is a highly reactive substance, it easily polymerizes to form high boiling point Harz.

The generated Harz accumulates in the gaps between the trays or packing provided inside the rectification chamber, which not only reduces the rectification effect but also makes the distillation operation impossible.

In order to prevent this, a method has been proposed in which, when chloroacetaldehyde is extracted from an acetaldehyde rectification culture, it is extracted as a side stream containing a small amount of acetaldehyde (Japanese Patent Application Laid-open No. 54315-1983).

However, when the extracted side stream is incinerated to treat chloroacetaldehyde, it is disadvantageous if it still contains acetaldehyde, so it is necessary to recover the acetaldehyde in advance.

At this time, if the acetaldehyde content of the chloroacetaldehyde aqueous solution is reduced, the flammability will deteriorate.For example, if acetaldehyde is completely removed, the chloroacetaldehyde concentration will not be natural unless the concentration of chloroacetaldehyde is about 30 wt% or more, so the chloroacetaldehyde aqueous solution will be diluted. Incineration of fuel requires a considerable amount of combustion improver, making it extremely uneconomical.

Therefore, recovering acetaldehyde from said side stream;
There is a desire for a method to obtain an aqueous chloroacetaldehyde solution with as high a concentration as possible.

As a result of various studies on this problem, the present inventors first distilled the side stream liquid of the acetaldehyde rectification column (concentration distillation) to distill out the entire amount of acetaldehyde and most of the chloroacetaldehyde, and Recovery of acetaldehyde from the side stream and recovery of chloroacetaldehyde by distilling off the remainder and most of the water and then dividing the distillate by partial condensation into an acetaldehyde-rich gas phase and a chloroacetaldehyde-rich condensate. A method for concentrating acetaldehyde was investigated.

Although this method yielded satisfactory results in terms of concentrating chloroacetaldehyde, it was not necessarily sufficient in terms of recovering acetaldehyde.

Therefore, the present inventors have conducted further intensive studies, and as a result, have arrived at the present invention.

That is, an object of the present invention is to provide an industrially advantageous treatment method for recovering acetaldehyde from chloroacetaldehyde and an aqueous solution containing acetaldehyde, and obtaining an aqueous solution with a high concentration of chloroacetaldehyde. An aqueous solution containing chloroacetaldehyde and acetaldehyde obtained by distilling and purifying hydrous crude acetaldehyde obtained by reacting ethylene and oxygen in the presence of a catalyst is supplied to a concentration distillation column, and acetaldehyde is extracted from the top. ,
obtaining a distillate containing chloroacetaldehyde and water;
A dilute aqueous chloroacetaldehyde solution containing substantially no acetaldehyde is drawn out from the bottom of the column, and (b) the distillate is supplied to a recovery distillation column to distill and recover acetaldehyde, and a concentrated aqueous solution of chloroacetaldehyde is distilled out. , (/→ The gist of the present invention is a method for treating by-products of acetaldehyde production, which is characterized by incinerating the obtained concentrated aqueous chloroacetaldehyde solution.

Next, the present invention will be explained in detail.

The method of the present invention is mainly applied to an aqueous solution containing chloroacetaldehyde and containing 0.5 wt% or more of acetaldehyde.

More specifically, the present invention involves reacting ethylene with oxygen in the presence of a by-product of acetaldehyde production, that is, palladium chloride, and a redox catalyst, supplying the resulting hydrous crude acetaldehyde to a rectification column, and purifying the acetaldehyde from the top. It is applied to the aqueous solution obtained as a side stream when water is extracted from the bottom of the column.

The side stream liquid of the acetaldehyde rectification column depends on the operating conditions of the rectification column, but usually contains 5 to 30 wt of chloroacetaldehyde.
%, acetaldehyde 0.5 to 70 wt% (especially 3 to 3
0 wt%), 20 to 90 wt% water, and other trace components.

The side stream liquid may be used as it is in the method of the present invention, but if it contains a large amount of acetaldehyde, some amount of it may be distilled and recovered in advance and then used illegally.

FIGS. 1 and 2 are process diagrams showing aspects of the treatment method according to the present invention.

In FIG. 1, A represents a rectification column, B a concentration distillation column, and C a recovery distillation column.

Hydrous crude acetaldehyde obtained in the aldehyde production process is sent to rectification column A through conduit 1, product acetaldehyde is distilled from the top of the column through conduit 2, and water is discharged from the bottom of the column through conduit 3. Ru.

In this case, a chloroacetaldehyde fraction containing a certain concentration of acetaldehyde is drawn off as a side stream through line 4.

In the process of the invention, the side stream is first fed to the concentrating distillation column B.

Concentration in the concentration distillation column B is performed by distilling substantially all of the acetaldehyde in the side stream liquid and most of the chloroacetaldehyde from the top of the column, and obtaining a dilute aqueous chloroacetaldehyde solution containing substantially no acetaldehyde as the bottom liquid. Usually, a distillation column with 5 to 30 theoretical plates is used, and the bottom side of the column is kept at normal pressure to 2.5. Okg/cI? LG is operated at a top temperature of 95-120°C.

In FIG. 1, the side stream liquid is supplied to the vicinity of the top of the column, but if it is desired to increase the concentration of the side stream liquid, it is preferable to supply the side stream liquid to the middle stage of the concentrating column to obtain reflux.

The dilute aqueous chloroacetaldehyde solution withdrawn from the bottom of the column via conduit 6 is normally utilized as process water.

Acetaldehyde has a normal pressure boiling point of 21° C. and is very volatile, so it can be easily distilled and recovered, but chloroacetaldehyde is relatively difficult to distill.

In order to increase the recovery rate of chloroacetaldehyde, when the residence time in the column is lengthened, chloroacetaldehyde polymerizes.

In order to prevent polymerization, if the residence time in the tower is shortened and the recovery rate of chloroacetaldehyde is lowered, the amount of chloroacetaldehyde remaining in the dilute aqueous chloroacetaldehyde solution obtained as the tower bottom liquid increases, and the tower bottom liquid is used as process water. If used, it is not preferable because it causes clogging of aldehyde rectification towers and the like.

Therefore, the recovery rate of chloroacetaldehyde is 50~
99%, preferably about 70 to 90% as a practical range.

Note that polymerization of chloroacetaldehyde is more likely to occur at higher concentrations, but less likely to occur at lower temperatures, so the pressure within the concentrating distillation column should be kept as low as possible within the above range, and the bottom temperature should be maintained at 130°C or below. It is desirable to do so.

The top distillate of the concentration distillation column B is mainly composed of acetaldehyde and chloroacetaldehyde and contains a small amount of water vapor. Thereafter, it is supplied to the middle stage of the recovery distillation column C.

In the recovery distillation column C, high-purity acetaldehyde is distilled out and extracted through conduit 8, and a concentrated aqueous chloroacetaldehyde solution is taken out and sent to the incineration system through conduit 7. In order to prevent polymerization of chloroacetaldehyde, it is preferable to carry out the distillation operation so that 0.5 wt % or more of acetaldehyde remains in the bottoms.

When the top temperature of the recovery distillation column C is 43° C. or higher, it is difficult to separate impurities (for example, dichloromethane) having physical properties similar to those of acetaldehyde.

The temperature at the top of the column can be lowered by lowering the operating pressure of the recovery distillation column, but if the pressure is too low, it becomes difficult to recover (liquefy) the distilled acetaldehyde.

Therefore, the operating conditions for the recovery distillation column are usually 0.
5-1,5 ky/cI? LG, bottom temperature 90-110
℃, and the tower top temperature is selected from the range of 39 to 42°C to adjust the reflux amount and tower bottom heating.

In the method of the present invention, in order to reduce the distillation load on the recovery distillation column, the distillate from the concentrating distillation column B is introduced into the partial condenser as shown in Figure 2, and the gaseous phase rich in acetaldehyde is After separation into a chloroacetaldehyde-rich condensate and a chloroacetaldehyde-rich condensate, the gaseous phase is passed through a conduit 11 to a recovery distillation column C.
may be introduced.

If the gas phase temperature of the partial condenser is too low, the recovery rate of acetaldehyde will be low; if it is too high, the recovery rate of acetaldehyde will be good, but separation of by-products with physical properties similar to acetaldehyde will be poor.

Therefore, it is desirable that the gas phase temperature of the dephlegmator be in the range of 90 to 110°C.

The condensate from the fractionator is sent to the incineration system together with the bottoms from the recovery distillation column C.

At this time, a part of the condensate from the partial condenser may be refluxed to the concentration distillation column B through the conduit 10 as a reflux liquid.

According to the method of the present invention, most of the water is removed from an aqueous solution containing chloroacetaldehyde and acetaldehyde, more specifically, a side stream liquid from an acetaldehyde rectification column in a concentrating distillation column, and acetaldehyde and chloroacetic acid are removed in a recovery distillation column. Since it separates into acetaldehyde, it is possible to recover acetaldehyde in the side stream liquid, which was conventionally incinerated together with chloroacetaldehyde, and it is also possible to reduce the amount of combustion improver by increasing the concentration of chloroacetaldehyde in the incineration liquid. can.

Next, specific embodiments of the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to the following Examples unless the gist thereof is exceeded.

Example 1 Side stream liquid of acetaldehyde rectification column (acetaldehyde 6
．． 5wt% chloroacetaldehyde 8.0wt%, water 8
4.0wt%, other 1.5wt%) with an inner diameter of 0.75m
150 per hour to the top stage of a concentrating distillation column with 9 theoretical plates.
Introduced at a rate of 0 kg, tower top pressure 1.5 kg/iG1
Distillation was carried out at a bottom temperature of 129°C.

The composition of the distillate is 23.1 wt% acetaldehyde, 24.1 wt% chloroacetaldehyde, and 51.0 wt% water.
t%, others 1.8wt%, and this distillate was
．． It was introduced into the second stage of a recovery distillation column with a length of 48 m and a number of theoretical plates of 4. Oky/iG, bottom temperature 102°
Distilled at C.

Acetaldehyde 92 ky/H with a purity of 100 wt% was distilled out from the top of the recovery distillation column, which means that 94% of the acetaldehyde in the charged side stream liquid was recovered.

The composition of the bottoms extracted from the bottom of the recovery distillation column at 350 kg/H was 29.1 wt% of chloroacetaldehyde;
The content was 1.5 wt% acetaldehyde, 67.2 wt% water, and 2.2 wt% others, and was sufficiently self-combustible.

Example 2 Side stream liquid of acetaldehyde rectification column (acetaldehyde 6
．． 5 wt%, chloroacetaldehyde 8.0 wt%, water 84.0 wt%, other 1.5 wt%) with an inner diameter of 0.75
m, 1 hourly to the 6th plate of a concentrating distillation column with 9 theoretical plates.
Introduced at a rate of 500kg, and the top of the tower is 1.5kg/=G
Distillation was carried out at a reflux ratio of 1.0 and a bottom temperature of 129°C.

The composition of the distillate is 23.9 wt% acetaldehyde, 30.1 wt% chloroacetaldehyde, and 44.2 wt% water.
, and others were 1°8 wt%.

This distillate was directly introduced into a dephlegmator and cooled to a gas phase temperature of 100°C.

A gaseous phase portion consisting of acetaldehyde with a purity of 34.4 wt % was extracted from the dephlegmator and introduced into the second stage of the recovery distillation column, where it was distilled at a top rate of 1.0 kg/iG and a bottom temperature of 102°C.

47 kg/I- of acetaldehyde with a purity of 100 wt% was distilled from the top of the recovery distillation column, which means that 48% of the acetaldehyde in the charged side stream liquid was recovered.

A part of the condensate from the demultiplexer was refluxed to the concentration distillation column, and a concentrated aqueous solution of chloroacetaldehyde was extracted so as to have a concentration of 35oky/H together with the distillation column bottoms.

The composition was 29.1 wt% of chloroacetaldehyde, 14.5 wt% of acetaldehyde, 541 wt% of water, and 2.3 wt% of others, and was sufficiently self-combustible.

[Brief explanation of drawings]

FIGS. 1 and 2 are process diagrams showing an embodiment of the method of the present invention. A: rectification column, B: concentration distillation column, C: recovery distillation column D: dephlegmation column.

Claims (1)

[Scope of Claims] 1. An aqueous solution containing chloroacetaldehyde and acetaldehyde obtained by distilling and purifying hydrous crude acetaldehyde obtained by reacting ethylene with oxygen in the presence of palladium chloride and a redox catalyst. ) is supplied to the concentration distillation column, and acetaldehyde,
obtaining a distillate containing chloroacetaldehyde and water;
A dilute aqueous chloroacetaldehyde solution containing substantially no acetaldehyde is drawn out from the bottom of the column, and (b) the distillate is supplied to a recovery distillation column to distill and recover acetaldehyde, and a concentrated aqueous solution of chloroacetaldehyde is distilled out. , (c) A method for treating by-products of acetaldehyde production, characterized in that the obtained concentrated aqueous chloroacetaldehyde solution is incinerated. 2. In the method for treating by-products of acetaldehyde production as set forth in claim 1, the distillate of the concentrating distillation column is fed to a partial condenser, and a gas phase rich in acetaldehyde and a condensate rich in chloroacetaldehyde are separated. A method characterized by separating the gaseous phase into a recovery distillation column, and incinerating the condensate.