JPS6118733A - Recovery of 1,3-butadiene - Google Patents

Abstract

PURPOSE:In the recovery of the titled compound, the carbonyl compounds included in the reaction mixture gas resulting from the oxidative dehydrogenation of olefins is absorbed in water and the water is subjected to decarbonylation and a part of the resultant water is recycled whereby waste water is reduced. CONSTITUTION:n-Butene or C4 fraction containing n-butene, oxygen source and dilution gas which is inert to the reaction are fed into the reactor 1 in the presence of a catalyst to effect oxidative dehydrogenation. The reaction product is compressed, sent to the first absorption column 5 to effect absorption of by-products into water, then the other remaining by-products are fed into the second absorption column 6 to effect absorption by feeding the bottom fraction of the first absorption column 5 to the middle and the aqueous solution from the decarbonylation process 7 to the top of the second absorption column 6. Thus, 1,3-butadiene free from carbonyl compounds is recovered from the top and the aqueous solution containing by-products from the bottom of the column 6 is fed to the decarbonylation process 7. Then, decarbonylated water is fed partially to absorption columns 5, 6.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Application of the Invention) The present invention relates to a method for recovering 1,3-butadiene, and more specifically to a method for recovering carbonyl compounds contained in a reaction product gas obtained by an oxidative dehydrogenation reaction of olefins. This invention relates to a method for recovering 1,3-butadiene, which facilitates the recovery of the main product.

(Background of the Invention) It is known that when olefins are subjected to an oxidative dehydrogenation reaction, trace amounts of carbonyl compounds (acetaldehyde, aqualein, benzaldehyde, etc.) are generated. Conventionally, as a method of separating and recovering these carbonyl compounds from the main product, a method of absorbing and removing them with water has been carried out (for example, Japanese Patent Publication No. 4.5-17647).

However, this method requires the use of a large amount of water in order to obtain a high-purity product, and the aqueous solution that has absorbed the carbonyl compound is
Because it contains about 00 ppm of carbonyl compounds,
The disadvantage is that wastewater treatment is required, resulting in high costs.

(Objective of the Invention) The object of the present invention is to provide a method capable of eliminating the drawbacks of the above-mentioned prior art, significantly reducing the amount of wastewater containing carbonyl compounds, and efficiently recovering <1,3-butadiene. It's about doing.

(Summary of the Invention) In order to achieve the above object, the present inventors have conducted various studies and found that a part of the aqueous solution obtained by decarbonylating an aqueous solution that has absorbed a carbonyl compound is returned to the absorption tower again.
The present invention has been achieved by discovering that scales can be used to remove carbonyl compounds from reaction gases, thereby significantly reducing the amount of wastewater containing carbonyl compounds and significantly reducing the cost of wastewater treatment.

The present invention provides (a) n-butene or a C4 containing the same;
A first absorption step in which the reaction product gas obtained by subjecting the fraction to an oxidative dehydrogenation reaction is compressed and then supplied to a first absorption tower to absorb by-products in water; (b) in the first absorption tower; After further compression of the reaction product gas containing unabsorbed by-products,
The second absorption tower is supplied with the bottom liquid of the first absorption tower from the middle stage, the aqueous solution obtained in the decarbonylation step described later from the upper stage, and fresh water from near the top of the tower as necessary. (c) a second absorption column step in which 1,3-butadiene substantially free of carbonyl compounds is recovered from the top of the column; A decarbonylation step of decarbonylating an aqueous solution containing the product, and a step of supplying a portion of the aqueous solution obtained in the decarbonylation step to a first absorption tower and/or a second absorption tower as an absorption liquid. This is a method for recovering 1,3-butadiene.

In the method of the invention, 0-butene means butene-1 and/or butene-2. Further, examples of the decarbonylation treatment include methods such as aeration and distillation.

Hereinafter, the present invention will be explained in detail with reference to the drawings. FIG. 1 is a process diagram showing an embodiment of the method of the present invention.

The method of the present invention mainly comprises a first absorption tower step for absorbing and removing carbonyl compounds from the gas after oxidative dehydrogenation reaction, a second absorption tower step, and a decarbonylation step. In the figure, first, n-butene or C containing n-butene
4 fraction, an oxygen source such as oxygen or air, water vapor and a diluent gas inert to the reaction such as nitrogen or carbon dioxide, for example M.

-It is supplied to a reactor 1 filled with a Bi-based solid catalyst, and an oxidative dehydrogenation reaction is carried out. The 1q reaction product gas is cooled in a quenching tower 2, and after removing fine powder by-products such as fume in a scrubber 3, it is introduced into a compressor TA4.

A two-stage or multi-stage compressor is used as the compressor. The gas compressed to 0.1 to 5 kg/cnlG in the first stage is supplied to the bottom of the first absorption tower 5, where carbonyl compounds and the like in the reaction gas are absorbed and removed. As the absorption liquid in the first absorption tower, the bottom liquid of the decarbonylation tower 7 described later is used. That is, the bottom liquid is brought into contact with the reaction product gas in the first absorption tower 5, and a portion of the carbonyl compound in the reaction product gas is absorbed. Next, the reaction product gas from which the carbonyl compound has been partially removed is introduced again into the compression Ia4 from the top of the first absorption tower 5, and is compressed at a rate of 3 to 9 kg/crA.
After being compressed to c, it is supplied to the bottom of the second absorption tower 6,
Furthermore, carbonyl compounds are absorbed and removed. The absorption liquid in the second absorption tower 6 includes (1) the bottom liquid of the first absorption tower (total amount), (2) the bottom ti of the decarbonylation tower 7 described later, (
(30 to 70% of the total amount) and (3) additionally supplied fresh water (00 to 50% of the total amount of liquid supplied to the second absorption tower 6). The supply location for these absorption liquids is the second
From the lower stage of the absorption tower, the liquid is supplied in this order: (1) the bottom liquid of the first absorption tower, (2) the bottom liquid of the decarbonylation tower, and fresh water that is additionally supplied near the top of the tower. It is preferable. The bottom liquid of the first absorption tower can be used as the absorption liquid of the second absorption tower because the operating pressure of the second absorption tower is 2 to 10 times the operating pressure of the first absorption tower.

In the second absorption tower 6, most of the carbonyl compounds in the reaction product gas are absorbed and removed, and from the top of the tower, the main raw acids 1,
3-Butadiene is obtained, which undergoes a recovery step (not shown)
sent to.

On the other hand, the aqueous solution containing the carbonyl compound obtained from the bottom of the second absorption tower 6 is supplied to the upper part of the decarbonylation tower 7 to perform a decarbonylation process, that is, decarbonylation treatment means such as aeration and/or decarbonization. The carbonyl compound is removed from the top of the column. On the other hand, a part of the bottom liquid of the decarbonylation tower 7 is supplied and recycled to the first and/or second absorption tower as an absorption liquid. The remainder of the bottom liquid of the decarbonylation column 7 is introduced into the vaporizer 8, where a part of it is vaporized to become almost pure water, which is used as a diluent for the reaction gas, and a concentrated liquid (water containing high-boiling carbonyls). ) is sent to a wastewater treatment process (not shown).

(Effects of the Invention) According to the method of the present invention, since the carbonyl compounds in the reaction gas are removed by the water recovered from the decarbonylation process, the amount of wastewater containing carbonyl compounds to be treated can be reduced compared to the conventional method. can be significantly reduced. Further, in the present invention, since the reaction product gas is compressed in multiple stages, there is also the advantage of preventing clogging in the compressor and related piping due to the carbonyl compound or its polymer contained in the reaction product gas.

(Example of the invention) Hereinafter, the present invention will be explained in more detail with reference to Examples.

Example The present invention was carried out according to the process diagram shown in FIG.

n-butene, air, and steam generated in the vaporizer 8 are mixed and supplied to the reactor 1 to form a Mo-Bi system.

The oxidative dehydrogenation reaction was carried out at 350:C using a solid catalyst. Next, the reaction product gas was quenched in a quenching bath 2 to remove organic acids, water, etc., and then by-products such as hume were removed in a scrubber 3.

Then the carbonyl compound 0.6544 m o 7! %
Reaction product gas containing 18.84 N rr? / Hr
is introduced into compressor 4, compressed to 3 kg/cnlG, and
After raising the temperature to 00°C, the first absorption tower 5 (column diameter 78.1
in, the number of perforated plate plates was 15) at the bottom of the column.

In the first absorption tower 5, an aqueous solution containing a carbonyl compound (cOD 350 ppm) is supplied from the upper part of the tower through a conduit.
It was supplied at 0° C. and 10j2/Hr, and was brought into contact with the reaction product gas to absorb the carbonyl compound in the reaction product gas. The reaction product gas from which carbonyl compounds have been partially removed is discharged from the top of the column at 50°C, but this gas is again introduced into the compressor 4 and compressed to 9 kg/crA.
It is compressed to G and heated to 100°C and then supplied to the bottom of the second absorption tower 6 (column diameter: 78, 1 m, number of perforated plates: 40).

In the second absorption tower 6, the reaction product gas is supplied from the lower stage of the second absorption tower, and the bottom liquid (7
0°C) cooled to 40°C 10.3 A/Hr
and is further supplied from the upper stage,
Decarbonylation column 7 (column diameter 78° 1 ml, number of perforated plates 4)
0 stage) tower bottom liquid (40°C) IQ j! /Hr, and further contacted with water (25'C)3j2/Hr which is additionally supplied via a conduit from a stage near the top of the column, and the carbonyl compound is almost completely removed.

A reaction product gas containing 1,3-butadiene as a main component is discharged from the top of the second absorption tower 6 at 50° C. and sent to a 1,3-butadiene recovery step (not shown).

On the other hand, an aqueous solution containing 1.35 W t% of a carbonyl compound (7
0°C) 234/Hr is fed to the upper part of the decarbonylation column 7. In the decarbonylation tower 7, air (2
Most of the carbonyl compounds are discharged from the top of the column (60°C) together with air and sent to a carbonyl compound recovery step (not shown).

On the other hand, the aqueous solution containing the carbonyl compound discharged from the bottom of the decarbonylation column 7? Ii (cOD350ppm)
23j2/Hr, most of it is in the first absorption tower 5 and/or
Alternatively, it is supplied to the second absorption tower 6 as an absorption liquid through the conduit and M, respectively, and the remaining 37+/Hr is supplied to the vaporizer 8 (120°C). The 2.5 A/Hr of the aqueous solution vaporized at 120°C has its high-boiling carbonyl compounds removed, becomes almost pure water, and is supplied to the reactor 1 as a diluent. On the other hand, a high-boiling carbonyl compound (cOD2,10
Water containing 100 pp (L 20 'C) 0.51!
/Hr is sent to a wastewater treatment process (not shown).

Table 1 shows the composition of components in each conduit in the process of the method of the present invention.

According to the above example, the amount of aqueous solution entering the wastewater treatment process could be reduced by, for example, about 97% compared to the conventional one-stage absorption without using a decarbonylation column. In addition, there is almost no clogging caused by carbonyl compounds and their polymers in the compressor and related piping.
For example, continuous operation for three months was possible.

[Brief explanation of the drawing]

FIG. 1 is a process diagram showing one embodiment of the present invention. ■... Reactor, 2... Quenching tower, 4... Compressor, 5
... first absorption tower, 6 ... second absorption tower, 7 ... decarbonylation tower, 8 ... vaporizer.

Claims (1)

[Claims] 1. (a) After compressing the reaction product gas obtained by subjecting n-butene or the C_4 fraction containing it to an oxidative dehydrogenation reaction, it is supplied to the first absorption tower, and the by-products are absorbed in water. (b) After further compressing the reaction product gas containing by-products that are not absorbed in the first absorption tower,
The bottom liquid of the first absorption tower is supplied to the absorption tower, and the bottom liquid of the first absorption tower is supplied from the middle stage.
a second absorption tower step in which an aqueous solution obtained in the decarbonylation step described below is supplied from the upper stage to absorb byproducts, and 1,3-butadiene substantially free of carbonyl compounds is recovered from the top of the tower; c) A decarbonylation step in which the aqueous solution containing by-products obtained from the bottom of the second absorption tower is decarbonylated, and a part of the aqueous solution obtained in the decarbonylation step is transferred to the first absorption tower and/or the second absorption tower. 2. A method for recovering 1,3-butadiene, comprising the steps of supplying it as an absorption liquid to an absorption tower.