JPS60184029A - Purification of unsaturated hydrocarbon - Google Patents

Abstract

PURPOSE:To purify the titled compound produced by the oxidative dehydrogenation process, economically, by using the absorption step to remove the by-produced carbonyl compound using an aqueous solution of an organic acid as the absorption solvent, the recovering and recycling step of the accompanied hydrocarbons, and the recovering and recycling step of said solvent. CONSTITUTION:In the production of the titled compound by the oxidative dehydrogenation of stock hydrocarbons, the obtained reaction mixture gas 1 is made to contact with the absorption solvent 8 composed of an aqueous solution of an organic acid to absorb (A) the by-produced carbonyl compound in said solvent and separate the non-condensing components containing the objective compound as the gaseous component 2. The non-condensing components containing the objective compound is recovered (B) from the absorption solvent 3 delivered from the step A, and is circulated 6 to the reaction mixture gas 1. The by- product 7 is evaporated (C) from the absorption solvent 5 delivered from the step B, the absorption solvent is recovered, and at least a part 8 of the solvent is recycled to the step A. The loss of the hydrocarbon can be minimized, the by- product can be removed selectively, and the operation can be continued stably for a long period.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for removing carbonyl compounds from a reaction product gas, and more specifically, the present invention relates to a method for purifying a reaction product gas by a specific process when producing cine-saturated hydrocarbons by an oxidative dehydrogenation method. This invention relates to a method for removing by-product carbonyl compounds.

It is known that industrially useful unsaturated hydrocarbons, such as styrene, 1,3-butadiene, isoprene, etc., can be produced by oxidative dehydrogenation of less saturated hydrocarbons. This reaction is carried out by catalytically oxidizing raw material large hydrogen at high temperature in the coexistence of oxygen and a catalyst.In this case, in addition to the target unsaturated hydrocarbon, carbonyl compounds such as aldehydes, ketones, and carboxylic acids are By-products are inevitable.

Therefore, methods for removing such by-products have been studied for some time, such as a method of treating the reaction product gas with an absorption solvent containing a halide (U.S. Pat. No. 3,327,
001) and a method of treating the reaction product gas with an alkaline absorption solvent (Japanese Patent Publication No. 17646/1983).

However, when using an absorption solvent containing a halogenide as in the former method, there are problems in that it tends to corrode the equipment material and requires expensive special metals to withstand long-term use. On the other hand, when using an alkaline absorption solvent as in the latter method, it is an efficient method in terms of absorption of carbonyl compounds, but it is not effective for gases containing carbonyl compounds, such as methacrolein, which are relatively difficult to absorb in water. However, there is a problem in that the removal ability is low, and the condensation reaction of aldehydes proceeds due to the alkali catalyst in the absorption solvent, resulting in the formation of solid suspended matter, making stable operation difficult.

Therefore, the present inventors have conducted intensive studies on a method for removing industrially valuable carbonyl compounds that suppresses the loss of useful hydrocarbons as much as possible and enables stable operation for a long period of time.
The present invention has been completed based on the discovery that it is effective to remove carbonyl compounds using an absorption solvent containing an organic acid and to further recover a small amount of accompanying hydrocarbons.

Thus, according to the present invention, in a method for removing a carbonyl compound from a reaction mixture gas containing carbonyl compounds as a by-product produced by an oxidative dehydrogenation reaction of a raw material hydrocarbon, the purification step converts the reaction mixture gas into an organic acid. Absorption process (1) in which a carbonyl compound is brought into contact with an absorption solvent consisting of an aqueous solution to be absorbed into the absorption solvent and a non-condensable component containing the target unsaturated hydrocarbon is separated as a gas component; Recovery process 8 (2), which recovers non-condensable components including accompanying unsaturated hydrocarbons from the solvent and circulates them into the reaction mixture gas, after removing the carbonyl compound 1vIJ from the absorption solvent from which this step was derived, Step (3) of circulating at least a portion of the absorption solvent to the absorption step (1)
A method for purifying unsaturated hydrocarbons is provided.

The reaction product gas to be treated in the present invention is obtained when producing simodiolefin or conjugated diolefin by oxidative dehydrogenation reaction, and specifically, carbon gas such as n-butene, isoamylene, ethylbenzene, etc. Examples include reaction product gases obtained in a method for producing 1,3-butadiene, isoprene, styrene, etc. by oxidative dehydrogenation of hydrocarbons of numbers 4 to 8. Among these, reaction product gas during the production of 1,3-butadiene is particularly suitable. Such a reaction product gas is usually produced by catalytically oxidizing raw material hydrocarbons, oxygen, and water vapor or an inert gas added as needed at about 300 to 700°C in the presence of an oxidation-dehydrogenation reaction, and then passing through a cooling process to usually It is obtained by cooling to 80°C or lower, preferably 80°C or lower.

Such a reaction gas mixture usually contains gas components such as nitrogen, argon, helium, carbon oxide, carbon dioxide, and oxygen (collectively referred to as non-condensable components) in an amount of 50 to 95% by volume, preferably 65 to 90% by volume. % of unreacted raw material hydrocarbons and target unsaturated hydrocarbons is 5 to 40%, preferably 10 to 40%.
30% by volume and water vapor from 1 to 20% by volume, preferably 3
Contains ~15%.

Carbonyl compounds as by-products include aldehydes such as formaldehyde, acetaldehyde, gropioaldehyde, butyraldehyde, enantaldehyde, invaleraldehyde, benzaldehyde, acrolein, methacrolein, crotonaldehyde, incrotonaldehyde, acetone, and methyl vinyl ketone. , diacetyl, methyl ethyl ketone, 3.3-dimethy/l/
Ketones such as -2-butanone, 2,4-dimethyl-3-pentanone, etc., acetic acid, propionic acid,
It exists in the form of carboxylic acids such as isobutyric acid, valeric acid, acrylic acid, methacrylic acid, benzoic acid, maleic acid, fluoric acid, and oxalic acid, and the amount thereof is
Usually, the amount of carbonyl compound removed from the mixed gas is 0.0 to 0.2 mole per mole of unsaturated hydrocarbon.

One of the essential features of the present invention is to use an absorption solvent consisting of an aqueous organic acid solution. Examples of the organic acids used include @ acid, acetic acid, propionic acid, butyric acid,
Included are aliphatic or aromatic carboxylic acids such as isobutyric acid, valeric acid, acrylic acid, methacrylic acid, benzoic acid, maleic acid, fumaric acid, phthalic acid, oxalic acid, and the like.

The concentration of the organic acid aqueous solution is usually 0.1 to 10%, preferably 0.4 to 5%; if the organic acid concentration is too low, the absorption capacity for carbonyl compounds will decrease, and if it is too high, on the contrary , the loss of organic acids into the purified gas cannot be ignored.

The pH of such an absorbing solvent is usually 5 or less, preferably [fk]
4-1 to 3. This absorption solvent may be freshly supplied from outside the system, but it is preferable to prepare it from acid and water produced as by-products in the oxidative dehydrogenation reaction and use it.

An example of the method of the present invention is shown in FIG. 1 as follows.

A reaction mixture gas containing a carbonyl compound is introduced into the absorption tower A through the tube (2), and an absorption solvent consisting of an aqueous solution of an organic acid is introduced through the tube (2) so as to be in countercurrent contact with the gas. If necessary, an aldehyde polymerization inhibitor is added to the organic acid aqueous solution.

Regarding the operating conditions of absorption tower A, generally speaking, the lower the pressure and the lower the temperature, the lower the absorption efficiency. However, it is important to operate above a temperature and below a pressure that does not condense the hydrocarbons in the reaction gas mixture.

These degrees and pressures vary depending on the type of target hydrocarbon and +iW&W in the mixed gas, but usually -0.5
kg/dG to 4 Yu/dG, preferably -0,2 Yu/i
G to 2 to 9/ff1G, and usually 10 to 70°C, preferably 20 to 50°C.

The amount of absorption solvent used varies depending on the operating temperature, pressure, and tower height, but is determined from the general design method of absorption towers. Typically 5 to 500 tons of trays are used per ton of gas fed to the absorption tower.

There are generally no particular restrictions on the structure of the tower as long as it absorbs trace components in the gas. Examples include perforated plate towers, grid towers, bubble bell towers, spray towers, and packed towers. Adding a cooling device as an accessory to the tower is effective in increasing the absorption efficiency of carbonyl compounds.

Furthermore, water is introduced from ・a(4) as necessary.

By sipping water, it is possible to prevent the organic acid from scattering, and it is also possible to replenish the amount corresponding to the water in the substances discharged from tubes 1 and 2.

In the absorption tower, 95 to 99.9% of the carbonyl compounds in the reaction mixture gas can be easily removed, and the purified reaction mixture gas, which usually has a carbonyl compound content of 0.2 mol% or less, is passed from tube (1). can get.

Further, an absorption solvent containing carbonyl metals, a small amount of non-condensable components, and hydrocarbons is led out from the bottom tube of the absorption tower A, and introduced into the hydrocarbon recovery tower B. The amount of hydrocarbons entrained in the absorption solvent is usually 0.05-2% of the hydrocarbons in the reaction mixture.

In the hydrocarbon recovery column B, the non-condensable components and unsaturated hydrocarbons entrained in the absorption solvent are separated from the absorption solvent and returned in gaseous form from the tube 1 to the reaction mixture gas tube 11X). The operating temperature +X of the hydrocarbon recovery tower is 40 to 90°C1 -
The temperature is 70-85°C. If the temperature is low, the recovery of hydrocarbons will not be sufficient, and if the temperature is high, the carbonyl compounds will dissipate significantly, and at the same time aldehydes will polymerize, causing operational troubles due to the precipitation of solids. The operating pressure is typically between -0.5 kg/crl G and 0.5 kg/crl G.
5 kIiI/crl G.

Through such operations, it is possible to minimize the amount of hydrocarbons lost along with carbonyl compounds! can.

The shape of the column may be any device that can evaporate hydrocarbons, which are low-boiling substances. For example, flash tower,
Included are wet wall columns, spray columns, tray columns, packed columns or combinations thereof.

The absorption solvent from which non-condensable components and unsaturated hydrocarbons have been liberated is led out from pipe (1) and introduced into stripping column (C).

In the stripping tower C, the carbonyl compound is released from the absorption solvent. There are no particular restrictions on the structure of the tower. A mixture of low-boiling substances such as aldehydes, ketones, acids, and water is led out from the tube (2) at the top of the column, and is discarded after undergoing deoxidation treatment such as combustion. A high-boiling point acid and water 75 (are extracted from the bottom of the tower and introduced directly into the absorption tower A through pipe (2), and a portion is led out of the system through pipe (2) as necessary.

Dissipation methods include steam stripping, distillation, and gas stripping using air or waste gas. Among these, the distillation method is preferred. The operating conditions for a distillation column are usually an operating pressure of -0.9 to 0.1 at 9/cdG, a temperature at the top of the column of 25 to 50°C, and a temperature at the bottom of the column 60 to 90°C. . Particularly when the temperature is 90°C or higher, precipitation of tar and solid substances is observed, making stable operation difficult.

A polymerization inhibitor is introduced into the carbonyl compound-absorbing solvent to prevent polymerization caused by diodialdehydes.

Although an example of the method of the present invention has been shown above with reference to FIG. 1, the present invention is not limited to FIG. 1 in any way.

According to the present invention, it is possible to minimize the amount of loss of hydrocarbons, which are useful components in the reaction product gas, and selectively reduce carbonyl compounds such as formaldehyde and acetic acid. Furthermore, carbonyl compounds in hydrocarbons can be virtually eliminated, and aldehydes, which easily become tar and solid matter, can be suppressed from forming and operational troubles can be prevented. It can operate stably for a long period of time. Furthermore, the removed carbonyl compound is obtained in a form that can be easily rendered harmless.

Therefore, compared to the conventional method, the amount of organic matter in the wastewater separated from the reaction product gas can be significantly reduced, and as a result, the wastewater treatment can be facilitated.

The present invention will be explained in more detail with reference to Examples below.

Example 1 Nitrogen 72.6 mol%, oxygen 2.1 mol%, argon, c
o and CO2 total 2.4 mol%, water - 9.6 mol%,
Butane 3.5 mol%, normal butene 1.5 mol%, Ptazi:
r-77.0 mol%, aldehydes (mainly pormaldehyde, a7taldehyde, acrolein, methacrolein) 0.66 mol%, aeO, oz mol%, and a small amount of furan, acetone, The reaction mixture gas containing methane, methyl vinyl ketone, and high-boiling byproducts is fed through tube A to absorption column A at a rate of about 1.24 rn' per hour (based on N TP). 3
It is a packed tower with a length of 3 m and a height of 5 m inside.
A circular Raschig ring of X 5 zg is filled. An aqueous organic acid solution from which aldehydes had been diffused was cooled to 20° C. and fed through tube (1) at a rate of 251/hr. The organic acid contained in the organic acid aqueous bath liquid is the dissolved organic acid contained in the reaction mixture gas.Acetic acid O, a i amount%, acrylic acid 0.4% by weight, manic acid 0.2% by weight %, oxalic acid 0.1% by weight, isolafic acid,
It contains small amounts of methacrylic acid and formic acid. The pressure inside the column was maintained at 0.05 to 0.1 kfJ/cry G, and the reaction mixture gas introduced into the column was brought into countercurrent contact with the organic acid water bath liquid. As a result, the carbonyl compound contained in the reaction mixture gas was absorbed and separated, and the mixed gas discharged from the absorption tower contained 0.01 mol % of aldehydes. Furthermore, organic acids, acetone, and methyl vinyl ketone were hardly observed in the gas. The other component compositions were substantially the same as the component composition of the reaction mixture gas introduced into the absorption tower.

The organic acid aqueous solution that has absorbed the carbonyl compound is taken out from the bottom of the absorption tower, heated to 70°C, and then introduced into the hydrocarbon recovery tower B through pipe (1). The hydrocarbon recovery tower is an empty tower with an inner diameter of 12 inches and a length of 0.5 m. Pipe (1) is installed in the gas layer at the top of the tower, pipe (6) is installed at the top of the tower, and pipe (5) is installed at the bottom of the tower. has been done. The temperature in the recovery column is maintained at 70°C and the pressure at 0.15 k#/, iG.

Nitrogen, oxygen, argon,
Water, total 84,0 mol% of CO and CO2, butane,
A gas consisting of a total of 15.2 mol% of butene and butadiene and 0.8 mol% of aldehydes is generated at approximately 0.01 fT per hour.
1' (based on NTP) and returned to absorption tower A. An organic acid aqueous solution containing only traces of hydrocarbons is drawn out from the bottom of the recovery tower through pipe (2) and introduced into stripping tower (C).

The stripping tower is a packed tower with an inner diameter of 3 inches and a length of 1.5 m.
The inside of the distillation column was filled with cylindrical piping rings of 5 sizes x 5 cages, and had a heating device at the bottom, a cooling device and a rapid flow device at the top. The pressure inside the tower is approximately 200mmH
g (absolute pressure), the temperature at the top of the column is maintained at 30°C, and the reduction at the bottom of the column is maintained at 75°C.

An aqueous organic acid solution containing only traces of aldehydes was recovered from the bottom of the stripping tower. Most of the aqueous solution is returned to the absorption tower A via the cooling device.

Emitted aldehydes, a small amount of hydrocarbons, a small amount of acid and water were discharged from the top pipe (2).・The amount of hydrocarbons in the liquid was approximately 1 g.

Through this operation, 98.5% of carbonyl compounds in the reaction mixture gas were removed. Moreover, the loss of hydrocarbons in the reaction mixture gas was 0.3% or less.

[Brief explanation of drawings]

FIG. 1 is a flow sheet showing one embodiment of the present invention, A: Absorption tower B: Hydrocarbon recovery tower C: Stripping tower Patent applicant Nippon Shichion Co., Ltd. Figure 1 L3

Claims (1)

[Claims] 1. In a method for removing carbonyl compounds from a reaction mixture gas containing carbonyl compounds as by-products produced by the oxidative dehydrogenation reaction of feedstock hydrocarbons, the purification step involves converting the reaction mixture gas into an absorption solvent consisting of an aqueous organic acid solution. Absorption step (1) in which the carbonyl compound is absorbed into the absorption solvent by contact and the non-condensable component containing the target unsaturated hydrocarbon is separated as a gas component; A recovery step (2) in which non-condensable components including hydrocarbon bulk are recovered and recycled into the reaction mixture gas, and after removing carbonyl compounds from the absorption solvent from which this step was derived, at least a portion of the absorption solvent is Absorption process (1
) A method for producing bulk unsaturated hydrocarbons, characterized by comprising step (3) of circulating the unsaturated hydrocarbon to