JPS58222037A - Method for recovering 1,3-butadiene - Google Patents

Abstract

PURPOSE:To recover 1,3-butadiene with a slight energy loss, by absorbing crude butadiene with an organic compound having a high boiling point as an absorption solvent, and distilling the absorption solvent together with an organic compound, e.g. benzene or butanol, etc. added to the distillation zone. CONSTITUTION:Crude butadiene is absorbed from a mixed gas containing the crude butadiene with an organic compound having >=170 deg.C boiling point, preferably a chemically stable aromatic hydrocarbon or 10-15C straight or branched chain hydrocarbon, as an absorption solvent, and the resultant absorption solvent containing the crude butadiene and an organic compound having 30-150 deg.C boiling point, preferably a 5-10C straight or branched chain hydrocarbon or aromatic hydrocarbon, e.g. propanol or xylene, are together or separately fed to a stripping step to separate and recover the crude butadiene. The absorption solvent and the organic compound after recovering the crude butadiene are preferably separated and circulated for reuse. The addition of the organic compound keeps the top temperature of the distillation column at a coolabl temperature, and the bottom temperature is controlled at a relatively low temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for recovering 1,3-butadiene. More specifically, C4 whose main component is 1,3-butadiene
This article relates to a method VC for producing butadiene from a mixed gas containing hydrocarbons (hereinafter abbreviated as crude butadiene).

1. One method for producing 3-butadiene is to add n-butene to a diluent gas that is substantially inert to the reaction, such as nitrogen, steam, or carbon dioxide gas, in the presence of a catalyst at a high temperature (e.g., 300 to 500 C). There is a method of producing 1,3-butadiene by carrying out a catalytic oxidative dehydrogenation reaction using molecular oxygen VC in the presence of VC.

In this case, the reaction product crude butadiene is obtained as a mixture with a large amount of other gases, and the crude butadiene is recovered using a suitable absorption solvent.

In this way, when crude butadiene is produced by the catalytic oxidative dehydrogenation method, the reaction product gas contains, in addition to 1,3-butadiene, unreacted 7L-butene, carbon dioxide, -carbon oxide, oxygen, Contains nitrogen, water vapor, and small amounts of by-product organic compounds. By cooling this reaction product gas9, most of the water vapor and by-product organic compounds with high boiling points can be condensed and removed.

The remaining reaction product gas contains, in addition to crude butadiene, inorganic scum such as VC1 carbon dioxide, -carbon oxide, oxygen, and nitrogen, and a small amount of by-produced low-boiling organic compounds.

As a method for recovering crude butadiene from the above mixed gas,
A method of recovering crude butadiene using a relatively low boiling point compound such as benzene or toluene as an absorption solvent is known. (Special Public Interest Publication 45-17647.% Published 48-1308
2. (Japanese Patent Publication No. 52-922) However, when crude butadiene is absorbed and recovered from the mixed gas using these methods, in the exhaust gas discharged from the absorption zone,
There is an absorbing bath agent that corresponds to the vapor pressure at absorption@operating temperature. 1- However, since the boiling point of the absorption solvent is relatively low, the amount of absorption solvent present in the exhaust gas is large, which leads to a loss of absorption solvent. For example, using benzene or toluene as an absorbing solvent,
When crude butadiene in a mixed gas is absorbed under the conditions of 0 atmosphere and 40C, the vapor pressure of the absorption solvent at 40 tl' is 183wH975I! Since it is DIIH9, the concentrations of benzene and toluene in the exhaust gas are about 2.4 vo1% and 1.0 vo1% VCf, respectively.
do. Therefore, when this method is implemented on an industrial scale,
A large amount of absorption solvent may be entrained in the exhaust gas. If this exhaust gas is disposed of in its own way, the loss of absorption solvent will increase the recovery cost of butadiene and also cause air pollution. , it is necessary to recover the absorption solvent in the exhaust gas.It is possible to absorb benzene and toluene in the exhaust gas using high-boiling point absorption oil, but after absorption, it is necessary to recover benzene and toluene at low concentrations.

It is necessary to separate it from the toluene-containing absorbed oil, which has the disadvantage of increasing equipment and operating costs.

In order to solve the above-mentioned drawbacks, a method of using a high boiling point organic compound as an absorption solvent for crude butadiene can be considered. Therefore, the inventors investigated and found that the boiling point was 170
It has been found that if an organic compound with a molecular weight of t or more is used as an absorption solvent, the concentration of bath agent in the exhaust gas is extremely low, and the manipulation of the solvent from the exhaust gas becomes practically unfavorable. Furthermore, when an organic compound with a high boiling point is used as an absorption solvent VC, crude butadiene is absorbed from a mixed gas, and then the butadiene and absorption solvent are separated by distillation and when the butadiene is recovered, the difference in the boiling points of the two is very large. Because it is large, it is easy to separate it,
It has been found that this method is economically very advantageous compared to the method described above in which a compound with a relatively low boiling point is used as an absorption solvent. However, as the research progresses, K 1 This method V
(It has also become clear that there are some shortcomings, such as:

When separating a mixture of crude butadiene and an organic compound with a boiling point of 170 t or higher by industrial distillation, the top of the column consisting of 1,3-butadiene is separated using cooling water, which is available at low cost in industry. In order to condense the vapor, the temperature at the top of the column must be raised to about 40C or higher.The operating pressure of the distillation column at this time is 3.4 ηtn2 or higher, and the temperature at the bottom of the column consisting of the high-boiling absorbent is 200T: 'It is expected that it will be more than that.

Because distillation is carried out at a bottom temperature of 200C or higher, eζ requires high-pressure steam as a heating source, and the 1,3-
The loss due to thermal dimerization of butadiene and the formation of a polymer due to polymerization of 1,3-butadiene may cause blockage of the apparatus, making it impossible to continue operation. Of course, it is possible to condense the top vapor at a low temperature using a refrigerator or the like to perform distillation at a low operating pressure and, therefore, at a low bottom temperature, but this is difficult in terms of refrigeration equipment costs and energy costs. This results in an increase in the cost of recovering crude butadiene. That is, by using an organic compound with a high boiling point as an absorption solvent, the loss of the absorption solvent is reduced, but it is not advantageous from an economic point of view because it requires equipment and energy for refrigeration.

As a result of intensive studies to solve the above drawbacks, the present inventors found that
By supplying an appropriate amount of an organic compound with a boiling point of 30 to 150 C to the distillation zone, the temperature at the top of the column can be maintained at a temperature that can be cooled with the cooling water normally used in industry, and the temperature at the bottom of the column can be kept relatively low. We found that it is possible to suppress this. That is, an organic compound with a boiling point of 30 to 150c (hereinafter referred to as
If a medium boiling point solvent is not used, crude butadiene and an absorption solvent with a boiling point of 170C or higher (hereinafter referred to as a high boiling point solvent) are used.
Fig. 1 schematically shows the composition distribution within the distillation zone where the gas is separated. On the other hand, when a medium boiling point solvent is added to this, the composition distribution becomes VC as shown in Figure 2. That is, by removing the medium-boiling point solvent, the medium-boiling point solvent is present at the bottom of the column, and the bottom temperature of the column can be lowered. Therefore, the temperature difference between the top and the bottom of the tower is small, and the temperature at the bottom of the tower can be kept relatively low without using refrigeration equipment for condensing steam at the top of the tower. Loss due to thermal dimerization and clogging of the device due to polymerization can be prevented. Based on these findings, the present inventors have completed the industrially advantageous crude butadiene recovery method described below.

The present invention uses a crude butadiene-containing gas with a boiling point of 170
Using an organic compound of C or more as an absorption solvent, this is absorbed in the absorption step, and the absorption bath agent containing the crude butadiene is supplied to the dispersion step together with the organic compound with a boiling point of 30 to 150 C or separately, The present invention provides a method for recovering crude butadiene from a mixed gas containing crude butadiene, which is characterized by separating crude butadiene.

The mixed gas containing crude butadiene in the present invention is not particularly limited, but includes, for example, the reaction product gas generated when 1,3-butadiene is produced from looptene by gas phase catalytic oxidation dehydrogenation reaction. After removing water and high-boiling point organic compounds, the crude product is... Contains L diene,
This includes gases whose main component is thermal gas.

('The organic compound with a boiling point of 170C or higher used in the present invention is preferably one that is chemically stable in nature, does not react with Petaji≠Technology, is compatible with it, and is liquid at room temperature.For example, , aromatic hydrocarbons such as tetralin, methylnaphthalene, dimethylnaphthalene, ethylnaphthalene, diethylnaphthalene, polymethylnaphthalene, polyethylnaphthalene, triethylbenzene, diethylbenzene, alkylbenzene, cymene, alkyl-substituted biphenyls, and their substituted products, nitrobenzene, etc. Aromatic nitro compounds, aromatic carboxylic acid esters such as methyl benzoate, ethyl benzoate, carbon atoms 10-
15 linear or branched hydrocarbons, heptatools,
Alcohols such as octatool, ethylene glycol, as well as phenyl ether, quinoline, N-methyl-
Compounds such as 2-pyrrolidone, isophorone, acetonylacetone, gas oil, mixtures such as creosote oil, and mixtures of the above compounds. %, chemically rc-stable aromatic hydrocarbons and straight-chain or branched hydrocarbons having 10 to 15 carbon atoms are preferred. 'The upper limit of the boiling point is not specified, but if it is too high, a large amount of medium-boiling point solvent must be used and it is not economical, so it is practically preferable that it is 350C or less. Organic compounds (
(medium boiling point solvent) is chemically stable in nature, does not react with butadiene, and has a boiling point of 17
It is compatible with organic solvents of 0c or higher and is liquid at room temperature. For example, benzene, toluene, 0-xylene,
Aromatic hydrocarbons such as m-xylene, p-xylene, and ethylbenzene, aromatic halides such as chlorobenzene, linear or branched hydrocarbons having 5 to 1 carbon atoms, alcohols such as glopanol and butanol, acetic acid. There are mixtures containing the above compounds, such as esters such as propyl and butyl formate, as well as compounds such as triethylamine and propionitrile, and mixed xylenes. A preferable one can be selected in consideration of various conditions such as gas-liquid equilibrium and price. Special 1/(, product 1,
Since the contamination of oxygen-containing compounds into 3-butadiene is undesirable, in order to reduce the burden of the subsequent 1,3-butadiene purification step, straight-chain or branched hydrocarbons having 5 to 10 carbon atoms are added. It is preferable to use distilled or aromatic hydrocarbons.

Hereinafter, the present invention will be specifically described with reference to the drawings.

FIG. 3 shows a flow route showing the crude pushene recovery method of the present invention. For example, from a raw material containing looptene as the main component and a small amount of butanes, gas phase catalytic oxidation dehydrogenation reaction>
6. From vc, ■, When producing 3-butadiene &j
The resulting reaction product gas consisting of crude butadiene, oxygen, gas, carbon dioxide gas, carbon oxide, water vapor, and by-product organic compounds, etc., is cooled by cooling device 2.
Supply Vc and cool. This cooling device 2d1 is, for example, an indirect cooler or an IM indirect cooler with cooled water and/or condensate from the reaction products. In this way, the reaction product gas of the face is cooled, and most of the water vapor and
The Takasu point organic compound produced by the reaction is condensed, and the condensate is removed from the tube 3. The uncondensed mixed gas passes through the pipe 4 and, if necessary, is pressurized by the compressor 5 and then supplied to the absorption tower 7 via the pipe 6.

Apparatus used for absorbing Poutazier from a mixed gas d
Although a general absorption device may be used, it is preferable to use one that can efficiently bring the mixed gas and absorption solvent into contact with each other in countercurrent flow. For example, in order to increase the contact area, it is possible to fill an absorption column with a Raschig ring or the like, and use a plated column-type absorption zone such as a tray, a pulp tray, a sheep tray, etc. The absorption tower 7 preferably has O~80C10~20
ky/cm, more preferably 30~70c15~1
The system is operated at a temperature and pressure of 5 to 1/Cm2, and an absorption solvent having a boiling point of 1000 or more is supplied from a pipe 8. Add an appropriate amount of polymerization inhibitor (according to the required tζ) to this absorbent bath agent.
For example, t-butylcatechol... ”゛hereinafter T
BC) is added. In the absorption tower 7, the internal temperature rises due to the heat of absorption generated, which causes a decrease in absorption efficiency. Therefore, it is preferable to install one or several intercoolers 7a in the middle of the absorption tower. .

Gas, free of crude butadiene, is discharged from line 9.

The absorption solvent that has absorbed the crude butadiene is supplied from the bottom of the absorption tower 7 to the stripping tower 11 via the pipe 1 (1).
In order to lower the bottom temperature of the stripping tower 11, a medium-boiling point absorbing solvent is fed to the stripping tower 1] through the pipe [2]. This absorption solvent VC may optionally contain a polymerization inhibitor (for example, TB).
An appropriate amount of C) is added. The stripping tower 11 has a pressure of 2.2~
It is preferable to operate at a pressure of 6.0 kηm2. When operating at a pressure lower than this pressure, it becomes difficult to condense the overhead vapor using the cooling water normally used in industry, and When operating at 1,3-butadiene pressure, the temperature inside the column increases, and high-pressure steam is not only required as a heating source for the tube bottom reboiler (not shown) industrially, but also the 1,3-butadiene The loss due to thermal difluorination (V) increases, and the production of polymer products makes the equipment unusable. The stripping tower 111C is supplied with a polymerization inhibitor (for example, TBC) as required.

梧'r, mainly consisting of crude butadiene, obtained via tube 13
J4 steam is condensed in cooler I4 and enters cypress 15.

Among the top vapors, gases that cannot be condensed in the cooler 14, such as inorganic gases such as acid, nitrogen, carbon dioxide, and carbon oxide, are removed through the pipe 16, but since they contain some crude butadiene, A cooler (not shown) is installed in the middle of the pipe 16 to improve the recovery rate of crude butadiene, and then the crude butadiene is discharged to the outside of the line and/or is refluxed to the suction side of the compressor 5. It is also possible to reduce the loss of butadiene. In addition, a degassing device (not shown) as described in Japanese Patent Publication No. 45-17647 is installed in front of the stripping tower 11,
If inorganic gases such as nitrogen, acid, carbon dioxide, and carbon oxide are removed in advance, the device 6 after the pipe 16, which is used to remove inorganic gases, may not be necessary.

From the tank 15, a part of the crude butadiene is refluxed to the cinnabar column 11 via a pipe 17, and the remaining crude butadiene flows out as an overhead distillate via a pipe 18, and is sent to a butadiene purification process (not shown). , pure 1,3-butadiene is O'/l JA! be done.

Most of the waste in the stripping tower 11 consists of high-boiling point absorbing bath agents and medium-boiling point absorbing solvents, and also sieve-boiling point organic compounds, residues, polymers, etc. produced as by-products in the butadiene production reaction. These pass through pipe 19 to the distillation column'll) I
The operating pressure on the distillation column side differs depending on the type of high-boiling point absorbing bath agent and medium-boiling point solvent Vζ, but it is condensed by top steam or cooling water used in normal industry. The overhead temperature is such that it is possible to
Above, more preferably, the temperature is 40C or higher, and the bottom temperature is a temperature at which low-pressure steam can be used as a heating temperature for the bottom reboiler (not shown), that is, preferably 190C or lower, and more preferably 190C or lower. It is operated at a pressure of 170C or less. Therefore, distillation column 20 is often operated under reduced pressure.

Top steam on the distillation column side (if mostly consisting of medium-boiling bath additives)
passes through the pipe 21 and is condensed in the cooler 22, resulting in t4m23
to go into. From 4423, a part passes through pipe 24 to distillation column 2.
However, if the difference in boiling point between the medium boiling point bath agent and the high boiling point solvent is large and separation is easy, the reflux may not be carried out at 8 degrees. The medium-boiling point absorption solvent that is not refluxed is extracted from the pipe 12 and supplied to the stripping tower 11 for circulation.

The bottoms (consisting mostly of #1 high-boiling absorption solvent) from the distillation column Δ) are extracted from a pipe 26, cooled in a cooler 27, passed through a pipe 8, and sent to an absorption tower 7 as an absorption solvent. Can be reused. Before supplying to the absorption tower 7, some or all of the bottoms are taken out through the tube side and sent to the absorption solvent purification section 29, where a small amount of VCC in the bottoms is removed and by-products are removed by the butadiene production reaction. "High-boiling organic compounds produced"? After removing some or all of the polymers and the like, the contaminants 1. In order to ensure continuous operation, favorable results can be achieved.

Next, examples of the present invention will be shown.

Example-1 In the process shown in Figure 3, four people poured the reaction product residue from the 1,3-butadiene manufacturing process from tube 1 into direct cooler 2 using chilled water, and cooled it to 40C. Most of the water vapor and high-boiling organic compounds produced as by-products in the process were condensed and removed through tube 3. Next, the pressure was increased at 9.8 kf/ctn in the two-stage compressor 5 with an intercooler.
When cooled to 43C (cooler not shown), the mixed gas had the following composition. That is, nitrogen 72.
2 ryal%, oxygen 3.5 mol%, carbon oxide 1.1 mol%, carbon dioxide 32rnol
%, water Q, f3 mo1%, n-butene 3.
l mol %, 1.3-butadiene 16.0 mol
% and other reaction by-products.

This mixed gas is passed through pipe 6 and passed through McMahon type packing 4.
575N1 to the lower part of the absorption tower 7 with an inner diameter of 36 mm filled with nt light.
It is supplied l- at a flow rate of /hr.

On the other hand, from pipe 8, a mixture of n-paraffins containing decane as a main component (NP-HC80 manufactured by Mikata Texaco Chemical Co., Ltd. 9. Supply paraffin (hereinafter abbreviated as heavy paraffin) at a flow rate of 16019Δ■.
Absorption of crude butadiene was carried out at a pressure of OkV/cm2. In addition, in order to keep the temperature inside the absorption tower low, the liquid inside was extracted from the bottom of the VC1 packed bed at a position of 1.5 m and 0,5 m, and after cooling to 40C using water, the liquid was released into the tower. I returned it to (Cooling reservoir piping, heat exchanger, etc. are not shown.) As a result of the above absorption operation, from the top of the absorption tower, 0.02 mol % of n-butyy, 7 L of 1,3-putadi
0. IQ mo1% and extremely small amount (0,01 mo
A gas containing heavy paraffin (l %) is supplied at a flow rate of 4
It was discharged at a rate of 66N/hr. Further, an absorption liquid containing 24% by weight of n-butene and 11.8 parts of 1,3-butadiene was obtained from the bottom of the column at a flow rate of 18,749/hr.

Next, this absorption liquid was placed at the 25th stage from the bottom of the stripping tower 11 equipped with 50 stages of sieve trays with an inner diameter of 5 cm.
Hebutane (containing a small amount of heavy paraffin) as a medium-boiling solvent was added at a flow rate of 3/hr and in the same position.
Feed 12 at a flow rate of 5099/hr, reflux ratio 5, pressure 2.
Distillation was carried out at 8 k〆〃L2. The overhead vapor was cooled and condensed using water in a heat exchanger 14. The gas that did not condense here is further cooled by OC in a t-co cooler (not shown).
It was cooled at f and discharged through tube 16.

The top temperature was 36C and the bottom temperature was 165C. Therefore, at a bottom temperature of this level, it is possible to heat even relatively low-pressure steam in an industrial-scale plant, and there is no loss due to polymerization of 1°3-butadiene and blockage of the equipment due to polymer formation. is also a successor. Medium boiling point solvent f: If crude butadiene is separated without using it, the bottom temperature is expected to be 300C or higher, and in fact,
The operating conditions are so severe that it seems impossible to carry out the operation.

As described above, as a result of operating the stripping tower 11, a small amount of n-t (0.01% by weight or less) of n-
Crude butadiene containing hebutane and no heavy paraffin was obtained at a flow rate of 200 g/hr. Also, tube 1
From No. 6, a gas containing 25.3 mol % of crude butadiene and whose main component is an inorganic gas is obtained from No. 6. It is discharged at a flow rate of 1N1A, and from the bottom of the column, 68.5% by weight of n-hebutane and 3
Made of heavy paraffin of 1.5 army M, fine #(0,
01, bottoms containing about 5% by weight of crude butadiene
It was obtained at a flow rate of 1109/hr. The bottoms were fed as they were to the top stage of the distillation column, which had an inner diameter of 5 ctn and 20 sieve trays] 5. Distillation was carried out at a pressure of 90wH9 without reflux. The overhead vapor was cooled [7] and condensed using water. The tower top temperature was 39C and the tower bottom temperature was 165C.

As a distillate, η-hebutane containing 0.4% by weight and 1t% of heavy paraffin was obtained from pipe 5 at a rate of 35099/hr. Further, from the bottom of the column, 9-heptane with a weight ratio of 0.03 and heavy paraffin containing a trace amount of heavy components were obtained at a flow value of 16019Δ■.

As a result of continuous operation for 24 hours using the above method, the recovery rate of crude butadiene was 97.4 hours.

Although this was not done in this example, it is possible to further increase the recovery rate by returning the crude butadiene-containing gas discharged from the pipe 16 to the t-absorption tower 7.

Comparative Example-1 Absorption of lubutene and 1,3-butadiene in a mixed gas having the same composition as in Example 1 was carried out using exactly the same equipment and method as in Example 1, except that toluene was used as an absorption bath agent. .

In other words, the mixed gas is fed to the bottom of the absorption tower at 575 NJ/
Supply at a flow rate of br] 2. Upper V of absorption tower (40C toluene, 13509/amount 1r) @kt Te supply L%
Absorption was carried out at a pressure of 9.0 kl/cm. the result,
An absorption liquid containing a total of 16.6 weight tons of n-butene and butadiene could be obtained from the bottom of the column at a flow rate of 15969/hr, but K in the exhaust gas from the top of the column was 1.0 mol.
% of toluene is included, and the exhaust gas flow value is 470%.
Nj! /hr, so 19.3 per hour
This means that 9 toluene was lost. In other words, 1.43% of the toluene supplied to the absorption tower escaped into the exhaust gas.

When absorption is carried out industrially in the manner described above, the loss of the absorption solvent is an economical VC + not negligible. Therefore, in order to recover toluene in the exhaust gas, VCl, an absorption tower, a distillation tower, etc. are required, and it is clear that the process is more complicated than in Example 1.

[Brief explanation of drawings]

Figure 1 is a composition distribution diagram in the distillation zone that separates butadiene and absorption solvent when a medium-boiling point absorption solvent is not introduced into the distillation zone, and Figure 2 is a composition distribution diagram in the case where a medium-boiling point absorption solvent is introduced into the distillation zone. FIG. 3 is a flow sheet of an embodiment of the method of the present invention. 2-...Cooler, 5...Compressor, 7...
...Absorption tower, 11...Emission tower, addition...
・Distillation column, 15, 23... Cypress, 7 a,
14, 22, 27...Cooler, 1.3, 4, 6
, 8, 9. ■, 12, 13, 16, 1? . +8. +9, 21, 24, 2.5, 2(i
, 28, 30-Piping, 4... Purification equipment. Figure 1 Figure 2

Claims (2)

[Claims] (1) Using an organic compound with a boiling point of 170C or more as an absorption solvent, in the absorption process, a mixed gas containing C4 hydrocarbons (hereinafter abbreviated as crude butadiene) mainly composed of 3 to butadiene is absorbed, and the crude A method for recovering crude butadiene from a crude butadiene-containing mixed gas, characterized by separating crude butadiene by supplying an absorption solvent containing butadiene together with an organic compound with a boiling point of 30 to 150 C or separately to a diffusion step. . (2) In the above diffusion step, crude butadiene is separated and recovered.1. Afterwards, an absorption solvent with a boiling point of 1701Z' or higher and a boiling point of 3
2. The method according to claim 1, wherein the organic compound having a temperature of 0 to 150 C is fractionally distilled, and the former is recycled to the absorption step K and the latter to the diffusion step.