JPS60126235A - Production of butadiene - Google Patents

Abstract

PURPOSE:To recover butadiene, economically in an industrial scale, in the production of butadiene by the vapor-phase catalytic oxidative dehydrogenation of n-butene, by removing the aldehydes existing as by-products prior to the compression of the produced gas, and then absorbing the produced gas under pressure. CONSTITUTION:Butadiene is produced by the vapor-phase catalytic oxidative dehydrogenation of n-butene in the presence of a dilution gas containing >=30vol%, preferably >=50vol% off-gas recycled from the final off-gas treatment process. After the optional removal of heat from the produced gas, the gas is cooled (preferably with a quenching column) to separate the high-boiling by- products, and a small amount of aldehydes existing in the cooled gas is removed (to a residual amount of <=0.4mol%, especially <=0.2mol%). The refined produced gas is compressed to >=2atm gauge, and the 4C components containing butadiene and other 4C hydrocarbons are recovered from the compressed gas (usually by absorbing in a solvent and desorbing therefrom). The off-gas delivered from the recovery process and purified by this process is recycled as a diluent gas for the butadiene synthesis reaction.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing butadiene. More specifically, the present invention relates to an industrially advantageous process for producing butadiene by subjecting normal butene to gas phase catalytic oxidative dehydrogenation.

A method for producing butadiene by subjecting normal butene to gas phase catalytic oxidation dehydrogenation at high temperatures with molecular oxygen has already been carried out industrially. However, the known methods generally use a large excess of steam as a reaction diluting gas, which increases the cost of steam, and requires a large amount of cooling water during cooling.
Processing 1978 (11) 151
, The Oll and Gas , rourna
11973, 1j] 12) In addition, if an attempt is made to increase the conversion rate of normal butene by increasing the oxygen supply to the reaction process, the oxygen concentration present in the product gas after cooling will increase, creating a risk of explosion. It has been virtually impossible to perform industrially advantageous pressurized absorption when recovering butadiene and other 04 hydrocarbons from the produced gas.

The disadvantage of the former is that instead of steam, off-gas (i.e., waste gas from which harmful by-products such as butadiene and other 04 hydrocarbons, useful by-products such as furanbenzene, high-boiling substances, and aldehydes are removed from the reaction product gas) is used. This problem can be solved by using a gas) as a diluent, and the latter drawback can also be solved by using an off-gas to relatively reduce the oxygen concentration in the generated gas.

However, even in this method, if the conversion rate of normal butene is high (if the conversion rate of normal butene is high), butadiene and other components from the produced gas cannot be recovered by pressurized absorption. There is a problem that tar-like by-products are generated and adhere to the inside of the compressor and the discharge part, significantly interfering with normal operation. This tendency was remarkable when the remaining C4 fraction from which imbutene was extracted was used as the raw material.

Therefore, the present inventors have determined that even if the conversion rate of normal butene per one pass through the oxidative dehydrogenation reaction zone is high, and even if BBRR containing a trace amount of isobutyne or C6 fraction is used as the normal butene raw material, As a result of intensive studies aimed at making it possible to recover butadiene and other C6 hydrocarbons by pressure absorption, it was discovered that it is effective to remove aldehydes contained as by-products before pressurizing the produced gas, and the present invention has been made. I have reached the point where I have completed the .

Thus, according to the present invention, a reaction step (1) for producing butadiene by subjecting normal butene to gas phase catalytic oxidative dehydrogenation in the presence of a reaction diluent gas containing an off-gas recycled from step (6) described below; A cooling step (2) in which the produced gas is cooled and high-boiling byproducts contained in the produced gas is removed; an aldehyde removal step (3) in which a small amount of aldehydes contained in the cooled produced gas is removed; ), a compression step (4) to compress the derived produced gas, a C4 recovery step (sl c, refining the off-gas derived from the recovery step) to recover C4 components containing butadiene and other 04 hydrocarbons from the compressed produced gas There is provided a method for producing butadiene, which comprises an off-gas treatment step (6).

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

Normal butene, oxygen, reaction diluent gas, etc. are introduced into the reaction process through pipe 0). Nitrogen is usually used as the oxygen source, and off-gas is used as the reaction diluent gas.

At this time, other diluent gases such as steam and nitrogen may be used together as appropriate, but the off-gas content in the diluent gas is 30
It is appropriate that the content be at least 50 i% by volume, and more preferably at least 50 i% by volume.

The reaction process consists of a reactor (1) maintained at high temperature and filled with a catalyst, in which normal butene is oxidatively dehydrogenated to produce butadiene. The catalyst to be used may be selected as appropriate, and a specific example thereof may be a catalyst previously developed by the present inventors (for example, Japanese Patent Application Laid-open Nos. 56-140951 and 56-140951).
6-150025 Fireflies). Although there is no particular limit to the conversion rate per pass of normal butene, it is effective when the conversion rate is 504 or more, particularly 70 or more. Further, the supply of oxygen to the reaction process is appropriately determined in consideration of the explosion limit in the compression process described later.

When the conversion rate of normal butene is high, there is little unreacted normal butene and there is no need for recycling, so it is possible to use a BBRRf raw material that contains a large amount of butane that shows almost no reactivity to oxidative dehydrogenation reactions. In this case, a BBRR having a composition of 85% or less of normal butene and a total of 15% or more of normal butane and isobutane, which is commercially available at low cost, can be used.
It is advantageous to use

When BBRR is used as a raw material, BBRR generally contains trace amounts of isobutyne, C, and distillates as impurities.
Many of these are simultaneously oxidized in the oxidative dehydrogenation reaction zone to produce aldehydes as by-products. These aldehydes are removed in a later process, but if they are produced too much as a by-product, the load on the removal process increases, so the content of inbutene, Cl fraction, etc. that cause the generation of these aldehydes is preferably 7 parts or less. 5
% or less is appropriate.

The generated gas discharged from the reactor (1) is introduced into a heat removal process provided as necessary to remove heat from the generated gas. Industrially, this process is preferably carried out using a waste heat boiler (2). Here, the produced gas is cooled to 220-150C, preferably 200-170C, and the recovered waste heat is usually converted into steam and utilized. If the produced gas is excessively cooled in this step, a trace amount of high-boiling by-products contained in the produced gas will clog the precipitation tube, so care must be taken. In particular, when the butene conversion rate is high (or when a BBRR'ft raw material is used), the amount of high-boiling by-products produced increases significantly, so the cooling temperature is important.

The generated gas that has undergone the heat removal process in this way is introduced into a cooling system that removes trace amounts of high-boiling by-products contained in the generated gas and cools the generated gas through pipe (2). Although this step can be divided into a step of removing high-boiling byproducts and a step of cooling the produced gas, it is preferable to carry out both steps at the same time. Generally, a quench column (■) is used, but high-boiling byproducts precipitate in the quenching section, clogging the pipes and towers and causing many troubles, so it is necessary to take measures to prevent high-boiling byproducts from precipitating. .

In this step, a quenching method using an oil such as paraffin oil or naphthenic oil (for example, Japanese Patent Publication No. 49-6283) may be used, but a quenching method using water is industrially advantageous. However, in the case of quenching with water, precipitation of high-boiling byproducts tends to occur, so to prevent this,
To maintain the generated gas passing through the column above 130C, and to keep the generated gas passing through the quench column (1) at the inlet of the quench column
It is effective to maintain the temperature at 20C or higher and to sufficiently mix and contact the generated gas with 15 to 70[degrees] of spray water in the quench tower.

A small amount of the aldehydes contained in the produced gas is removed in the quench tower (2), but most of the aldehydes remain in the produced gas and are introduced into the aldehyde removal step through the pipe (2). This step may be carried out using any known method as long as it is capable of removing a small amount of aldehydes contained in the produced gas, but it generally consists of an aldehyde absorption tower (1) and an aldehyde stripping tower (0). The aldehydes in the generated gas derived from the aldehyde absorption tower (1) by countercurrent contact with the organic acid aqueous bath liquid in the aldehyde absorption tower are usually 0.4 molar or less, preferably 0.2 molar or less. separated until .

The aldehydes separated here are diffused in an aldehyde diffusion tower 0. The degree of organic acid contained in the organic acid aqueous solution may be appropriate, and the organic acid may be added from the outside if necessary, but organic acids (such as acetic acid, (acrylic acid, methacrylic acid, isobutyric acid, etc.) are used. In addition, water generally passes through pipe 0), where a portion of the moisture in the steam in the generated gas is condensed in column ①, so this condensed water is recycled and used, but if it is necessary to add more water, it is necessary to Water is introduced separately from the top of the tower. The aldehyde absorption tower (■) and the aldehyde stripping tower (0) are normally filled with a packed column or a plate column.
A polymerization inhibitor is introduced to prevent polymerization caused by aldehydes.

The generated gas discharged from the aldehyde absorption tower is then transferred to the pipe
The produced gas is introduced into the compression process through which it is compressed. In this step, a compressor Q) is usually used. Here, the produced gas is usually compressed to a gauge pressure of 2 atmospheres or more, preferably 5 atmospheres or more.

The compressor performs compression in several stages as necessary, but it is preferable that the discharge temperature of each stage is 300C or less.

The oxygen concentration in the generated gas introduced into the compressor (?) is preferably 6 molar or less, more preferably 4 molar or less, to avoid the risk of explosion. The content of aldehydes in the produced gas is preferably 0.4 molar or less, more preferably 0.2 molar or less. A tar-like substance is generated and adheres to pipes, towers, etc., causing frequent troubles. The amount of carbon-like or tar-like substances generated is so small that it does not pose a particular problem during short-term operation of the plant, but it makes the operation extremely difficult when continuous operation is performed for a long period of 10 days or more. Any known compressor can be used.

The produced gas extracted from the compressor (2) is usually cooled in a direct cooling type and/or intercooled type heat exchanger [phase], and then C, containing butadiene and other C4 hydrocarbons are extracted from the produced gas.
It is introduced into the C6 recovery process to recover the components. The process is
Usually, there is a C4 absorption tower (i) that absorbs and separates the C4 component contained in the produced gas using an absorption solvent, a stabilizer 〇 that dissipates small amounts of oxygen, nitrogen, carbon dioxide, etc. absorbed at the same time as the C4 component, and a C4 component. It consists of a C1 stripping tower which separates the absorbent from the solvent.

The absorption solvent is C1-010 saturated hydrocarbons, c1-C,
Other commonly used aromatic hydrocarbons, butadiene dimer, etc. may be used. For C, absorption tower @, stabilizer ○, and C4 stripping tower 0, a packed tower, a plated tower, or other usual type of tower is used.

After the C6 component is absorbed and separated in the C4 absorption tower 0, the produced gas is sent as an off-gas to the off-gas treatment process through a pipe @.

In stabilizer 〇, most of the oxygen, nitrogen, carbon dioxide gas, etc. that are slightly absorbed in the absorption solvent and a part of the components are released, and this usually passes through the tube [phase] before the compression process. be introduced. The C4 component is dissipated in the C6 dispersion tower [phase],
It is passed through a tube [phase] to a butadiene purification step not shown in FIG.

The off-gas drawn out from the pipe @ contains an absorption solvent (Q, absorption solvent) for the C4 component of the vapor.

This strong C4 absorbing solvent is oxidized in the oxidative dehydrogenation reaction zone to produce products that are undesirable in the process, and are therefore removed in the off-gas treatment step. Although the process may be performed by any known method, the off-gas FIA drawn out from the 〇tube@, which usually consists of a C1 absorption solvent recovery column and its separation column [phase].
, - A treatment method in which the concentration of C4 absorption solvent in the off-gas is usually reduced to 1 molti or less in the absorbed agent recovery column [phase] can be selected as appropriate, but it is usually O, 7%-0. It is recovered by being brought into countercurrent contact with a solvent consisting of saturated hydrocarbons and the like.

In addition, the recovered solvent that has absorbed the C4 absorption solvent is separated in the separation column [C], the %C4 absorption bath agent is sent to the column [2], and the recovered solvent is sent to the column [3].
phase].

Other methods may be used instead of tower [phase] and tower [stock].

For example, instead of using a column [phase], or after passing through a column [phase], it may be possible to pass a catalyst zone in which the combustible substances contained in the off-gas are burned.

The thus treated off-gas is then introduced into one reaction step in the required amount as a reaction diluent gas.

Excess off-gas is disposed of.

The components and composition of the off-gas used as the reaction diluting gas, especially the concentration of oxygen, are calculated, and the sum of the air and oxygen introduced into the reaction process is calculated to suit the reaction conditions. Usually, the reaction conditions (oxygen production, normal butene concentration, etc.) can be freely set by controlling the dedicated air forging to suit the reaction conditions.

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 that shown in FIG.

According to the method of the present invention, an industrially safe, inexpensive, and continuously operable butadiene production process using off-gas as a diluent gas for each reaction can be achieved. In particular, since this is a process that uses steam as a diluent gas for the reaction using a known method, after the steam is condensed and removed, the concentration of C4 components and unreacted oxygen in the generated gas increases significantly, which is a part of the process. However, in the present invention, the produced gas is diluted with the reaction diluent gas and φ is reduced in all steps of the process except for the C4 component stripping tower. BBRR″t-i
It can also be used as a fee.

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

Example Butadiene was produced according to the present invention in the following manner.

(1) Reaction step; A catalyst was prepared according to the method described in Example 1 of JP-A-56-140931. This catalyst 600ml has an inner diameter of 1
The mixture was filled into a stainless steel reaction tube with a length of 2 m and heated to 365 C using night starch.

A gas mixture consisting of air, BBRR and offgas from the offgas treatment step was passed through it. The component composition of the mixed gas is 867.51 os of nitrogen and 1 os of oxygen per unit time.
, o-e, argon 10. s, e, co.

1B, 1g, Co 5.7-e, isobutane and normal butane 62.14. Normal butene 122.4-g, other Q
, ~cl hydrocarbons 7.31 (all gaseous, NT
In addition to P standards), trace amounts of xylene and the like contained in the off-gas were also included.

As a result, the normal butene conversion rate per passage of the catalyst layer was 8.
The butadiene yield was 76.5 mol, and the butadiene selectivity was 91.2%. Other by-products include CO and CO, as well as formaldehyde, acetaldehyde, furan, acetone, acrolein, methacrolein, and benzene.

Small amounts of methyl vinyl ketone, acetic acid, inbutyric acid, acrylic acid, methacrylic acid, maleic acid 6, etc. are produced.

A small amount of high-boiling byproducts were also produced.

The product gas thus obtained was 621 mol of nitrogen and 2 mol of oxygen.
．． 3 molti, argon, COI and co, total s, 7
Mol%, water 10.2 mol, butane 4.8 mol, normal butene t 5 mol%, butadiene 14 mol.

It consisted of 0.73 mole of aldehydes and 0.05 mole of organic acids, and also contained trace amounts of furan, acetone, benzene, methyl vinyl ketone, and high-boiling by-products. The product gas was produced at approximately 1.3 m'' (NTP standard).The product gas temperature at the reactor outlet was 365C.

(2) Cooling step: After the product gas thus obtained was cooled to 18.0 U, it was introduced into the quench tower through a tube with an inner diameter of 12 mm that was kept sufficiently warm. The generated gas temperature just before the quench tower entrance is 15
The quench tower was a spray tower in which an empty can with an internal diameter of 3 inches and a length of 120 m was suspended at the bottom of a nitrogen cylinder pipe with an internal diameter of 1 inch and a length of 1 m. I installed the tube. The can part was kept sufficiently warm. By introducing the product gas, the temperature of the inner wall surface of the can can be increased to 152
It was kept at C.

A spray nozzle was attached to the top of the column and 36 C water was circulated at 15 e/hr. The water in the tower gradually increased due to condensation of some of the water in the produced gas, so the amount of water in the tower increased and was continuously extracted.

The produced gas derived from the top of the tower has a temperature of about 40 to 45C,
The composition of the generated gas is 0.69 molt of aldehydes,
The resulting gas contained 0.02 mol of organic acid, and was substantially the same as the product gas introduced into the quench tower. In addition, fine furan, acetone, benzene, and methyl vinyl ketone were contained essentially in the same manner as the produced gas introduced into the quench tower, but high-boiling byproducts were removed in the quench tower and were not observed at all. .

(3) Aldehyde removal step: The generated gas discharged from the cooling step tS was introduced into the aldehyde absorption tower through a tube with an inner diameter of 1211 mm. The aldehyde absorption tower is a packed tower with an inner diameter of 3 inches and a length of 3 m, and the inside is filled with cylindrical Raschig rings of 5mm diameter x 5mm diameter.

From the top of the column, an aqueous organic acid solution from which aldehydes had been diffused was cooled to 20 ml and fed at a rate of 15 i/hr. The organic acid contained in the organic acid aqueous solution is a dissolved organic acid contained in the generated gas, and the organic cR concentration is appropriate. The product gas introduced into the column is brought into countercurrent contact with this solution. As a result, the aldehydes contained in the product gas are absorbed and separated, and 0.11 mol. contained aldehydes. Furthermore, almost no organic acid, acetone, or methyl vinyl ketone was observed in the generated gas. Other compositions.

The composition was substantially the same as that of the produced gas introduced into the aldehyde absorption tower. Part of the organic acid aqueous solution drawn out from the bottom of the aldehyde absorption tower is treated as waste water, and the remainder is introduced into the aldehyde stripping tower, where most of the absorbed aldehydes, acetone, and methyl vinyl ketone are released, and then the aldehyde is absorbed. Circulated into the tower.

(4) Compression process: 8 tons of aldehyde removal process - The generated gas is
It was introduced into compressor 1 through my friend's pipe. It was a compressor company diaphragm type, and was compressed to a gauge pressure of 10 atmospheres FJ: by two-stage compression with a raw S: gas line. Discharge gas ore of each stage about ao
It was cooled to a temperature of C.

The thus pressurized product gas was further cooled to 35C by countercurrent contact with water.

(151C4 component recovery step: The generated gas compressed in the compression step and cooled to 35C was first introduced into a C4 absorption tower to absorb the C4 component^5.

The C4 absorption tower is a packed tower with an inner diameter of 2 inches and a length of 6 m, and the inside is filled with cylindrical Raschig rings measuring 5 mm φ x 5 mm. From the top of the tower, the mixed xylene after the C6 component was diffused in a C6 stripping tower was cooled to 8C and fed at a rate of 4) per hour. The produced gas introduced from the bottom of the column is brought into countercurrent contact with this xylene, and 99% of the C4 component contained in the produced gas is
．． 5% was absorbed.

The remaining aldehydes contained in the produced gas are all absorbed into xylene together with furan and benzene, are dissipated together with the C9 component in the C4 removal column, and are then separated in the subsequent butadiene purification step. Ru. The off gas that does not contain C4 components and is led out of the C4 absorption tower is then sent to the off gas treatment process.The xylene that has absorbed the OC4 components is 0
4 It is led out from the bottom of the absorption tower and enters the stabilizer, where nitrogen, oxygen, CO, and a part of the C4 components dissolved in xylene are released (34 The absorbed C3 components are introduced into the stripping tower After dissipating aldehydes, furan, benzene, etc., it was circulated again to the C4 absorption tower.0(6) Off-gas treatment process; The off-gas derived from the C4 component recovery process was introduced into the xylene recovery tower through a pipe with an inner diameter of 12 mm. The xylene recovery tower is a packed tower with an inner diameter of 2 inches and a length of 1 m.
From the top of the O tower, which is filled with a cylindrical Raschig ring measuring 1,5Ilφ×51+1, light oil mainly composed of decane after xylene has been released is cooled to 20C and cooled down to 1% per hour. The off-gas introduced from the bottom of the tower is brought into countercurrent contact with light oil, and substantially all of the xylene contained in the off-gas is absorbed. , used in circulation. Traces of xylene and decane were present in the off-gas discharged from the xylene recovery tower, but the amount was negligible.

The composition of the off-gas thus obtained was 91.3% nitrogen, 6.5% nitrogen, and 1.1% argon.

3.1%, 000.9%, C4 component 01 ratio (all mol%), of which 609% (gaseous, wTy standard)
was recycled to the reaction process again as a reaction diluent gas, and the remainder was discarded.

(7) Operation results: A series of processes from steps (1) to i61 were operated continuously for 62 days under substantially the same conditions. As a result, during the operation period, butadiene could be produced stably without any troubles caused by the use of off-gas or troubles related to the precipitation of carbon-like or tar-like substances.

[Brief explanation of the drawing]

FIG. 1 is a flow sheet showing one embodiment of the present invention. ■・・・Reactor ■・・・Quench tower■・
...Aldehyde absorption tower■ ...Compressor O.
... C4 absorption tower Q ... C4 loss tower [phase] ... Absorption solvent recovery tower [phase] ... Separation tower patent applicant Nippon Zeon Co., Ltd.

Claims (1)

[Claims] 1. A reaction step (1) for producing butadiene tS by subjecting normal butene to gas phase catalytic oxidative dehydrogenation in the presence of a reaction diluent gas containing off-gas recycled from the below-mentioned step (6). ), a cooling step (2) in which the product gas derived from the reaction process is cooled and high-boiling byproducts contained in the product gas are removed; aldehyde removal to remove small amounts of aldehydes contained in the cooled product gas; Step (5), compression step (4) of compressing the derived product gas, recovering C4 components including butadiene and other C4 hydrocarbons from the compressed product gas;
A method for producing butadiene, comprising a recovery step (5) and an off-gas treatment step (6) for refining the off-gas derived from the C4 recovery step. 2. The method according to claim 1, wherein the content of off-gas in the reaction dilution gas is 50 volumes or more.