JPH0142249B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an improved method for producing 1,3-butadiene (hereinafter abbreviated as butadiene),
More specifically, the present invention relates to a method for producing butadiene from a hydrocarbon raw material having 4 carbon atoms (C ₄ ). Conventionally, it is well known to produce butadiene by dehydrogenating or oxidatively dehydrogenating 1-butene and/or 2-butene (hereinafter sometimes referred to as n-butenes) in the presence of a selective catalyst. Ori,
It is also implemented on an industrial scale. The n-butenes used as raw materials in this method are by-products from n-butane dehydrogenation, fluid catalytic cracking (FCC) equipment for heavy oil, and by-products from steam cracking equipment for naphtha, kerosene, light oil, etc. It is widely produced by methods such as extraction. Among these _C4 fractions, naphtha and other by-products from steam cracking equipment contain a large amount of butadiene (for example, 25 to 50% by weight), so the remaining fraction after extracting and separating butadiene ( Spent _C4 fraction) is used as a source of n-butenes. C ₄ fraction by-produced from the FCC equipment and spent from the steam cracking equipment
In addition to n-butenes, the _C4 fraction contains i-butane, i-
It is a mixture containing butene, n-butane, etc.
It is preferable that the raw material for producing butadiene by dehydrogenation or oxidative dehydrogenation reaction not only has a high concentration of n-butenes in the _C4 fraction but also substantially does not contain i-butene. For example, UOP,
1978 Technology Conference-H-11 states that the concentration of n-butenes as a raw material for butadiene production may be approximately 90% or more, but the concentration of i-butene is approximately 0.3.
% or less. As shown in Table 1, it is virtually impossible to separate and obtain specific components in the _C4 fraction by ordinary distillation because their boiling points are close to each other, and various methods have been researched and developed. There is.

【table】

【table】

[Table] Table 2 conceptually shows the separation status of C ₄ paraffins and olefins in the main separation methods for C ₄ hydrocarbons. Various types of _C4 that can be supplied
The fraction contains substantially no i-butene, which is used as a raw material for the production of butadiene by dehydrogenation or oxidative dehydrogenation, and most of the _C4 paraffins have been removed.
- There is no single method that can separate and obtain butenes in high yield; a combination of two or more methods is required. For example, in Petrochemical Industry Handbook (Asakura Shoten, 1962), p. 178, Figures 7 and 6B, the _C4 fraction is first treated with a sulfuric acid absorption device to remove i-butene, and then subjected to an extractive distillation device to remove n-butene. A process diagram for obtaining butenes is shown. Also Oil & Gas
Journal 55 (48), p. 87, states that the raw material _C4 fraction is sent to a raw material preparation process consisting of a sulfuric acid absorption device and an extractive distillation device to remove i-butene, i-butane, and n-butane. A fraction is obtained, and this fraction is then sent to a butadiene synthesis process consisting of a dehydrogenation device and a product gas treatment device to obtain a crude butadiene fraction, and this fraction is further sent to a butadiene purification process to obtain butadiene. Additionally, a method is described in which an unreacted _C4 fraction containing n-butenes as a main component is separated and recovered in a butadiene purification step and recycled to a butadiene synthesis step and/or a raw material preparation step. Further UOP, 1978, Technology
At Conference H-23, the ₄ fractions of raw material C were first subjected to a sulfuric acid absorption device to remove i-butene, and the remaining fraction was removed.
A process for removing butanes and obtaining n-butenes through a C ₄ CLEX apparatus is described. In the methods exemplified above, the sulfuric acid absorption method is used to remove i-butene, but
As is clear from Table 2, it can be easily inferred that the etherification method, gas phase adsorption method, and dimerization method can be used in place of the sulfuric acid absorption method. The entire process of combining these n-butene production processes (raw material preparation process) with a butadiene synthesis process by dehydrogenation or oxidative dehydrogenation and a butadiene purification process to obtain high-purity butadiene can be described in Oil & Gas Journal 55 ( 48), page 87, as shown in Figure 1. That is, the _C4 fraction raw material containing _C4 paraffins and olefins is first sent to the raw material preparation process,
Substantially all i-butene and most (or substantially all) _C4 paraffins are removed.
The n-butene fraction thus obtained is sent to a butadiene synthesis step, and some n-butenes are converted to butadiene, which is sent as a crude butadiene fraction to a butadiene purification step. In the butadiene purification process, unreacted C ₄ fraction is separated from butadiene, and the former fraction is mainly recycled to the butadiene synthesis process. However, if the separation of C ₄ paraffins is insufficient in the raw material preparation process, _C4 paraffins are inactive in the reaction under the catalyst used for normal dehydrogenation or oxidative dehydrogenation of n-butenes, and they remain in the system as they are, gradually accumulating and causing a serious hindrance to operation. will come. For this reason, part or all of the recycle stream from the butadiene purification process is recycled to the raw material preparation process. However, obtaining n-butenes by combining these existing technologies not only complicates the process and increases equipment costs, but also increases operating diameter costs. Considering the competition between the butadiene produced by separating and refining the butadiene in the _C4 fraction, which is a by-product from steam cracking equipment such as naphtha, a major economic problem arises, and improvements are required. That was the reality. As a result of studies to solve the problems of these conventional techniques, the present inventors found that the raw material preparation process for producing butadiene by dehydrogenation or oxidative dehydrogenation is as follows:
Rather than looking at it independently, we can construct a more rational process by considering it in conjunction with the butadiene purification process, which has a common element in terms of separating each component in the _C4 fraction. As a result of intensive studies based on the idea that this might be the case, we found that the raw material _C4 fraction containing at least n-butenes (if it contains light fractions and/or heavy fractions other than _C4 , it is necessary to (removed in advance by distillation etc.), together with a C ₄ fraction containing butadiene obtained from the dehydrogenation or oxidative dehydrogenation step described below, or separately, directly feeding it to, for example, the middle stage of an extractive distillation column, A fraction containing C ₄ paraffins as a main component is distilled from the top of the column, while a stage for supplying a C ₄ fraction containing butadiene obtained from the dehydrogenation or oxidative dehydrogenation step and a column near the top of the column are distilled. A side stream rich in n-butenes is extracted as a vapor stream from a stage between the selective solvent supply stage and a selective solvent and a fraction mainly composed of butadiene are extracted _from the bottom of the column. The concentration of n is relatively reduced.
- It has been found that butenes are obtained as a side stream of an extractive distillation column and that by removing i-butene from this fraction by known methods, it can be used as a raw material for dehydrogenation or oxidative dehydrogenation (butadiene synthesis step),
This has led to the present invention. That is, in the present invention, a _C4 hydrocarbon fraction (D fraction) containing at least n-butenes is supplied to an extractive distillation column (B column), and distilled in an atmosphere of a selective solvent. At the top of the column, a fraction containing _C4 paraffins as the main component was obtained as a hydrocarbon component.
Mainly as a hydrocarbon component from the stage between the upper side of the G fraction supply stage and the lower side of the selective solvent supply stage, which will be described later.
The fraction containing _C4 olefins is extracted as a side stream, and the fraction is fed to the i-butene removal step (F step) to substantially remove the i-butene and make n-butenes the main component. A fraction is obtained, and the fraction is supplied to a dehydrogenation or oxidative dehydrogenation step (Step A) to convert n-butenes into 1,3-butadiene, containing the 1,3-butadiene thus obtained. C ₄
A hydrocarbon fraction (G fraction) is supplied alone or together with the D fraction to the B column, and from the bottom of the column, the hydrocarbon component mainly consists of 1,3-butadiene, and further selected Extract the fraction containing the solvent,
It is characterized by separating 1,3-butadiene from the fraction. In the present invention, the fraction consisting of hydrocarbons containing butadiene as a main component and a selective solvent obtained from the bottom of the extractive distillation column is obtained by a known method, e.g.
Encyclopedia of Chemical Processing and
Design, Vol. (Marcel Dekker, Inc.1977) No.
Various 1st to 2nd paragraphs listed on pages 144-154
It can be purified to high purity butadiene by stage extractive distillation. Hereinafter, the present invention will be explained in more detail with reference to the drawings. FIG. 2 is a flowchart showing the main steps of the present invention. The difference from the conventional process shown in FIG. C ₄ in the C ₄ hydrocarbon fraction containing the raw C ₄ hydrocarbon fraction and butadiene obtained from the butadiene synthesis process (dehydrogenation or oxidative dehydrogenation process)
Separation and removal of paraffins, recovery of _C4 olefins, and concentration and separation of butadiene are performed in one extractive distillation column. Furthermore, by passing the raw material _C4 hydrocarbon fraction through an extractive distillation column (butadiene purification step) before the i-butene removal step, it can be used as is even if the raw material contains butadiene in any proportion. Therefore, there is no need to process the _C4 fraction containing high concentrations of butadiene, which is produced as a by-product from naphtha and other steam cracking equipment, in a separate butadiene purification equipment before the i-butene removal process, and the C4 fraction is directly recycled into the main stream. It can be used as a raw material for inventions. Next, FIG. 3 is a flow sheet showing an example of the butadiene production method based on the present invention, and shows an example of a one-stage extractive distillation method as the butadiene purification process. In the figure, the C ₄ hydrocarbon fraction of the raw material is supplied via conduit 15 and/or the C ₄ fraction containing butadiene obtained by dehydrogenation or oxidative dehydrogenation from gas treatment device 10 is supplied via conduit 14. Both are supplied to the extractive distillation column 16 in the butadiene purification process. The supply position of the raw material supplied from the conduit 15 is appropriately selected to be higher, the same level, or lower than the supply position of the conduit 14, depending on its composition (mainly butadiene concentration). Conduits 15a, 15b, 15c, and 15d show piping to the appropriate stages. In addition, the raw material
If there are many C ₃ or less or C ₅ or more components in the C ₄ hydrocarbon fraction, after removing them in advance in a preliminary distillation step,
Preferably, it is supplied via conduit 15. In addition, if there is a large amount of i-butane in the raw material, remove part or all of it in advance in a preliminary distillation step, and then
It is also possible to reduce the load on the extractive distillation column 16 by supplying it to the extractive distillation column 16 via the column. A selective solvent is supplied from a conduit 17 near the top of the extractive distillation column 16 . Any selective solvent may be used as long as it can be used to separate butanes/butenes/butadiene, such as acetone, acetonitrile, dimethylformamide, N-methylpyrrolidone, furfural, etc. alone or in combination,
Alternatively, a mixed solvent with water is preferably used. From the top of the extractive distillation column 16, a vapor stream enters conduit 18.
After being concentrated in a condenser 19, it enters a reflux tank 20, where a portion is returned to the top of the column via a conduit 21 as reflux, and the remainder is sent out of the system via a conduit 22 as an overhead fraction. It is discharged. This column overhead fraction contains n-butane, i-butane, etc. as hydrocarbon components.
The main component is C ₄ paraffins, and operating conditions are selected to keep the loss of C ₄ olefins low. Also, depending on the type of selective solvent used, some of this may be entrained in the overhead fraction, so if necessary, recover the solvent by washing with water, etc., and remove the hydrocarbon fraction. Purification can be carried out. In the extractive distillation column 16, the gas treatment device 10
A vapor stream is withdrawn as a side stream via conduit 23 from the stage between the stage in which the C ₄ feed containing butadiene obtained from is fed and the selective solvent feed stage is fed to the bottom of the butene recovery column 24. Ru. On the other hand, a liquid stream is withdrawn from the bottom of the butene recovery column 24 via a conduit 25, and is supplied to a nearby stage, particularly preferably the same stage, from which the side stream of the extractive distillation column 16 was withdrawn. On the other hand, a mixture of a hydrocarbon component containing butadiene as a main component and a selective solvent is obtained from the bottom of the extractive distillation column 16 via a conduit 31, and is supplied to the middle stage of the radiant column 32. It is possible to make the hydrocarbon components in the bottom fraction substantially free of _C4 olefins by appropriately selecting operating conditions, but usually a small amount of 2-butene is added. is mixed in. Further, if the raw materials supplied from conduit 14 and conduit 15 contain C ₄ acetylenes, the entire amount thereof is mixed into the bottom fraction. The butene recovery column 24 consists of, for example, 5 to 20 trays, and is used to separate the selective solvent and hydrocarbon components. A vapor stream is withdrawn from the top of the column via conduit 26, condensed in a condenser 27 and then entered into a reflux tank 28, a portion of which is returned as reflux to the top of the butene recovery column 24 via conduit 29, and the remainder is fed as an overhead fraction to the i-butene removal unit 1 via conduit 30. Note that depending on the type of selective solvent used, this column overhead fraction may contain some of the entrained solvent, and in such cases, after removing the solvent by washing with water etc. The i-butene removal device 1 is supplied. The hydrocarbon component in the overhead fraction of the butene recovery column 24 obtained via the conduit 30 is mainly composed of C ₄ olefins and contains a small amount of C ₄ paraffins.
Conditions are set such that the concentration of butadiene is kept low. The amount of C ₄ paraffins in the conduit 30 is desirably set to less than 50%, preferably less than 30%, of the amount of C ₄ paraffins in the stream supplied via conduits 14 and 15. This amount
When it is more than 50%, the concentration of C ₄ paraffins in the total hydrocarbons supplied to the butadiene synthesis step becomes high, which is not preferable in terms of butadiene synthesis. On the other hand, it is desirable to set the amount of butadiene in the stream withdrawn via conduit 30 to less than 10%, preferably less than 5%, of that supplied via conduits 14 and 15. If this amount exceeds 10%, i-
Not only will the amount lost by reaction etc. in the butene and/or butadiene synthesis step become excessive, but the processing cost will also increase. Incidentally, since the amount of heat necessary for operating the butene recovery column 24 is entirely supplied by the vapor flow from the conduit 23, a reboiler at the bottom of the column is usually not required. The top fraction of the butene recovery column 24 is sent to the i-butene removal device 1 through the conduit 30, and the known methods shown in Table 2 above can be used to remove the i-butene. It is. For example, the
Oil and Gas Journal, Dec.2, 1957, No. 87-95
The sulfuric acid absorption method, as described on page The Oil
and Sas Journal, pp. 68-71 (February 21, 1977)
The isomerization distillation method described in Hydrocarbon Processing, pp. 175-179 (May 1979);
A gas phase adsorption separation method that takes advantage of the difference in shape between straight-chain hydrocarbons and branched hydrocarbons, a method in which i-butene is dimerized and then separated by distillation, etc. can be used. Among these, in the sulfuric acid absorption method, for example, a 45 to 65% by weight hydrogen sulfate solution is used as an i-butene absorption solvent. For example, Petroleum Refiner,
Vol. 33(5), pages 156-159, contains an example using a 65% sulfuric acid aqueous solution, and Vol. 41(5), pages 119-123,
An example using a 50% by weight sulfuric acid aqueous solution is also reported in the same magazine.
Vol. 48(9), pages 195 to 198, describes an example using a 45% by weight aqueous sulfuric acid solution. By these methods, i-butene is absorbed into an aqueous sulfuric acid solution, separated from hydrocarbons mainly composed of n-butenes, and further stripped and discharged from the system through conduit 2. Incidentally, a part of i-butene is polymerized during the absorption-diffusion operation and changes into oligomers mainly composed of dimers, so the oligomers are discharged from the system through the conduit 4. The C ₄ hydrocarbon fraction containing n-butenes as a main component from which i-butene has been removed is supplied to a butadiene synthesis unit 7 via a conduit 5 . The isomerization distillation method involves isomerizing the stream in conduit 30 into 1-butene and 2-butene, which are then distilled. In the isomerization reactor, 1-butene is mostly converted to 2-butene and then fed to a distillation column, from the top of which are i-butene, unconverted 1-butene, and i-butane. (contained in stream 30 and some i- during the isomerization reaction)
A stream mainly composed of 2-butene (converted butene) is discharged from the system through conduit 2, while a stream mainly composed of 2-butene is obtained from conduit 5 as the bottom fraction of the distillation, etc. Flow is from butadiene synthesizer 7
is supplied to In addition, the i-butene contained in the flow of the conduit 30 may be reacted with an alcohol such as methanol using a cation exchange resin as a catalyst, for example, to react with an alcohol such as methanol.
It can also be removed using tertiary butyl ether (MTBE) or the like. This method generates
MTBE is attracting attention because of its excellent performance as a gasoline octane number improver. MTBE produced in MTBE synthesis reactor
is separated from other C ₄ hydrocarbons by distillation and discharged from the system via conduit 2. In addition, if you want to recover it in the state of i-butene, for example,
It is also possible to recover it as i-butene from conduit 2 by co-locating a device for decomposing MTBE in the presence of a catalyst as described in Hydrocarbon Prcoessing, pages 101-106 (August 1981). . On the other hand, methanol is partially dissolved and entrained in the hydrocarbon fraction mainly composed of n-butenes from which i-butene is removed as MTBE.
After being removed by water washing, it is extracted through a conduit 5 and supplied to a butadiene synthesis device 7. Although a dehydrogenation reaction or an oxidative dehydrogenation reaction is performed in the butadiene synthesis apparatus 7, it is preferable to use an oxidative dehydrogenation method in view of the reaction yield. Here, oxidative dehydrogenation will be explained as an example. The hydrocarbon fraction from the conduit 5 or (and) the fraction containing 2-butene as a main component extracted from the bottom of the butadiene purification column 34 (described later) is supplied to the butadiene synthesis apparatus 7 via the conduit 41. Further, via a conduit 6, oxygen (usually air) as an oxidizing agent and an inert gas (usually steam) such as steam, nitrogen or carbon dioxide as a diluent are supplied. Note that it is also possible to use a non-condensable gas after recovering the hydrocarbon fraction from the reaction product gas as a diluent. For butadiene synthesis equipment and gas treatment equipment using the oxidative dehydrogenation method, for example, Industrial
and Engineering Chemistry, Vol.62, No.5, No.
pp. 42-47 (1970), The Oil and Gas
Journal, pp. 60-61 (August 2, 1971),
Hydrocarbon Processing, pp. 133-135 (1974
(June 1978), the same magazine, pp. 131-136 (November 1978). In the butadiene synthesis device 7, the reaction of producing butadiene from n-butenes by oxidative dehydrogenation is an exothermic reaction of approximately 30 kcal/mol, and some n-butenes are further oxidized to CO and _CO2. The heat generated by this cannot be ignored, and therefore temperature control is extremely important in order to allow the reaction to proceed smoothly. It is also possible to use an adiabatic reactor by diluting a large amount of hydrocarbons supplied to the reactor with steam or the like to reduce the unit calorific value of the reaction gas, but in this case, the temperature of the reactor outlet gas is much higher than the inlet temperature. Therefore, using a fixed bed multitubular reactor or a fluidized bed reactor not only maintains catalyst performance but also increases the concentration of n-butenes in the gas supplied to the reactor. This method is preferable from the viewpoint that the reaction product gas can be easily treated. Examples of oxidative dehydrogenation catalysts for n-butenes include ferrite, P-Sn, and Sn-Sb.
Known materials such as Mo-Bi system, Mo-Bi system, etc. are used.
In particular, Mo-Bi catalysts show extremely excellent performance. Oxidative dehydrogenation reaction is usually 250-600℃, 1-
The reaction is generally carried out under conditions of 5 atma and a space velocity of 500 to 3000 hr ^-1 , but it goes without saying that the optimum reaction conditions vary depending on the catalyst. The reaction product gas leaving the butadiene synthesizer 7 is
For example, after the heat is recovered in a heat generating boiler, it is supplied to the gas treatment device 10 via a conduit 8. The gas treatment device 10 is configured to process non-condensable gases such as nitrogen, oxygen, CO, and CO ₂ generated in the butadiene synthesis device 7, water vapor, various hydrocarbons mainly composed of C ₄ including butadiene, small amounts of oxygen-containing organic compounds, etc. It is used to recover hydrocarbon fractions from streams consisting of
Chemistry, Vol. 62, No. 5, pp. 42-47 (May 1970), The Oil and Gas Journal, pp. 60-61 (August 2, 1971). Can be adopted. The above gas treatment device 1
Water is introduced from the conduit 9 into the reactor 0, and a small amount of oxygen-containing organic compound contained in the reaction product gas is washed away with water. This water is combined with the steam supplied from the conduit 6 and the condensed steam generated by the reaction, and is discharged out of the system via the conduit 12 as waste water. For the stream obtained by condensing and removing steam from the reaction product gas, for example, after separating the non-condensable gas and the hydrocarbon fraction using an aromatic absorption oil, the non-condensable gas is discharged from the system through the conduit 11. be done. On the other hand, after the hydrocarbon fraction was separated from the absorbed oil, heavy components generated in the butadiene synthesis device 7 or the gas treatment device 10 were separated as necessary, and this was discharged outside the system through the conduit 13. Thereafter, it is supplied to the middle stage of the extractive distillation column 16 via a conduit 14. The stripping column 32 may be provided with a condenser and a reflux tank at the top of the column like the columns 16 or 24, and may be an independent column. 34 is preferable from the viewpoint of energy saving.
At this time, the vapor flow from the top of the stripping tower 32 to the conduit 33
is extracted from the butadiene purification column 34 and supplied as it is to the middle stage of the butadiene purification column 34
4, a liquid stream is withdrawn as a side stream from a stage adjacent to, preferably the same as, the supply stage of conduit 33, and
5 and is supplied to the top of the column as reflux to the stripping column 32. A stream consisting essentially of the selective solvent is withdrawn from the bottom of the stripping column 32 and cooled to a suitable temperature through a heat exchanger and a cooler (not shown) for heat recovery, and then passed through the pipe 17. is recycled to the extractive distillation column 16. Note that heavy components gradually accumulate in selective solvents during cyclic use, which can cause problems in operation, so a portion of the circulating flow is extracted and purified in a solvent purification process (not shown) before being recycled. It is preferable to return it to the system. A vapor stream is withdrawn from the top of the butadiene purification column 34 through a conduit 36, condensed in a condenser 37, and then entered into a reflux tank 38, and a portion is passed through a conduit 39 as reflux to the top of the butadiene purification column 34. The remainder is discharged outside the system via conduit 40 as an overhead fraction. This fraction essentially consists of butadiene, and can usually be used as a product butadiene as is, but if this fraction contains a large amount of acetylenes, it may be further deacetylated by extractive distillation, etc. After that, the product was made into butadiene. On the other hand, a fraction mainly consisting of 2-butene containing a small amount of butadiene is obtained from the bottom of the butadiene purification column 34 via a conduit 41 and is normally recycled to the butadiene synthesis apparatus 7, but the concentration of 2-butene is If the weight is low and the heavy content is large, it can be discharged out of the system through the conduit 41'. In addition, in FIG. 3, columns 16, 32 and 34
Although not shown in the figure, a reboiler or the like is provided to supply the heat necessary for the operation of the tower as necessary. Also, valves and the like provided in each piping system are omitted from illustration. Hereinafter, the present invention will be explained in more detail with reference to specific examples. Example 1 The present invention was carried out according to the flow shown in FIG. 3 using a C ₄ hydrocarbon fraction containing substantially no butadiene as a raw material. 23,131 kg/hr of _C4 hydrocarbon fraction having the composition shown in Table 3 is transferred from conduit 15 to conduit 15.
8571 Kg/hr of a butadiene-containing C ₄ hydrocarbon fraction obtained from the position shown in a and having the composition shown in Table 3 obtained from the oxidative dehydrogenation process was introduced into conduit 14.
These were respectively supplied to the extractive distillation column 16. In addition, a solvent 166265 consisting of 92% by weight of acetonitrile and 8% by weight of water as a selective solvent was placed near the top of the column.
Kg/hr was fed through conduit 17 at a temperature of 53°C. The extractive distillation column 16 has a top pressure of 5.0 atm and a top temperature of 5.0 atm.
It was operated at a temperature of 42° C. and a bottom temperature of 109° C., and 11,754 kg/hr of a C ₄ paraffin-based fraction having the composition shown in Table 3 was obtained as an overhead fraction via conduit 22. Further, from the bottom of the extractive distillation column 16, a stream of 171,512 kg/hr consisting of a hydrocarbon component mainly composed of butadiene and a selective solvent was extracted through a conduit 31 and supplied to the center of the stripping column 32. Although not shown in FIG. 3, a small amount of water-rich phase was separated in the reflux tank 20, so this was separated into layers and discharged to the outside of the system at a flow rate of 653 kg/hr. This stream was an aqueous solution containing 7% by weight acetonitrile. Further, since the flow extracted from the conduit 22 contained a considerable amount of acetonitrile, the acetonitrile was washed away with water in a water washing tower (not shown) and then discharged to the outside of the system. A side stream from an intermediate stage of the raw material-supplied stages of the extractive distillation column 16 (via conduits 14 and 15a) is extracted as a vapor stream through conduit 23 and fed to the bottom of the butene recovery column 24, while the butene A bottom fraction of 38,222 Kg/hr from the recovery column 24 was supplied via a conduit 25 to the same stage from which it was extracted as the side stream. The butene recovery column 24 is operated at a top pressure of 4.5 atm and a top temperature of 48°C, and thus a top fraction of 13,815 kg/hr is obtained, which is mainly composed of C ₄ paraffins having the composition shown in Table 3. was extracted through conduit 30. Since this stream contained a considerable amount of acetonitrile, the acetonitrile was washed away with water in a water washing tower (not shown) and then fed to the i-butene removal apparatus 1. Although not shown in the figure, a small amount of water-rich phase separates into the reflux tank 28, so
This was separated into layers and discharged to the outside of the system at a flow rate of 233 Kg/hr. This stream was an aqueous solution containing 4% by weight acetonitrile. In isobutene removal equipment 1, a 65% sulfuric acid aqueous solution is
- The method of using butene as an absorption solvent was adopted.
In this way, 9573 kg/hr of a fraction mainly composed of n-butenes having the composition shown in Table 3 is obtained from conduit 5, and this stream is obtained from the bottom of distillation column 34 through conduit 41. It was combined with a fraction of 106 Kg/Hr and supplied to the oxidative dehydrogenation reactor 7. Oxidation dehydrogenation reactor (butadiene synthesis equipment) 7
24249Kg/Hr of air and steam from conduit 6
3998Kg/Hr was supplied. The oxidation dehydrogenation reactor is a multitubular reactor composed of tubes with an inner diameter of 28 mm, and inside the tubes, as described in Japanese Patent Publication No. 53-41648,
The composite oxide of Mo-Bi-Fe-Co-Sb (trivalent) and Sb (pentavalent) was supported on an α-alumina carrier with a particle size of 4 mm, and a spherical catalyst with a particle size of about 5 mm was filled. Molten salt is circulated outside (inlet temperature 335°C) to control the reaction temperature. When the reaction was carried out with the pressure at the reactor inlet set to 1.7 atm, the n supplied to the reactor
-85% of the butenes were reacted, of which 90% was converted to butadiene. The reaction product gas leaving the oxidation dehydrogenation device 7 is transferred to the conduit 8
The gas is supplied to the gas processing device 10 through the. The gas processing device 10 performs operations such as quenching and compressing the reaction product gas, washing and removing oxygen-containing organic compounds produced by the reaction with water, and recovering hydrocarbon fractions from the non-condensable gas using absorbed oil. While 31,553 Kg/Hr of washing water for removing oxygen-containing organic compounds and washing with water is supplied to the system from conduit 9, wastewater containing acid-containing organic compounds
38684Kg/Hr from conduit 12, and 38Kg/Hr of heavy
Hr is discharged from the conduit 13 and a flow of 22186 Kg/Hr mainly composed of non-condensable gases is discharged from the system from the conduit 11, and thus a C ₄ fraction containing butadiene of 8541 Kg/Hr is obtained from the conduit 14. This stream was fed to extractive distillation column 16 as described above. The stripping tower 32 has a top pressure of 5.2 atm, a top temperature of 47°C,
The column was operated at a bottom temperature of 134° C., and a vapor stream of 22,903 Kg/Hr was extracted from the top of the column through conduit 33 and fed to the center of the butadiene purification column 34. On the other hand, a liquid stream of 16,297 Kg/Hr was extracted through a conduit 35 from the same stage to which the conduit 33 was connected to the butadiene purification column 34, and was supplied to the top of the stripping column 32 as reflux. From the bottom of the stripping tower 32, 164,906 Kg/Hr of solvent that does not contain hydrocarbons is extracted and transferred to the conduit 1.
7 and then recycled to the extractive distillation column 16. This circulating solvent flow accumulates heavy oil during use and interferes with smooth operation, so 165
Kg/Hr (corresponding to 1% of the recycle stream) was withdrawn and treated in a solvent purification section (not shown) before being returned to the solvent recycle stream. The acetonitrile aqueous solution recovered by washing the streams in the conduits 22 and 30 with water, and the aqueous layer separated from the hydrocarbon layer in the reflux tanks 20 and 28 are collectively processed to concentrate and recover acetonitrile, and the solvent circulation system It was shown to. The butadiene purification column 34 is operated at a top pressure of 4.4 atm and a top temperature of 41 degrees centigrade and a bottom temperature of 50 degrees centigrade, and fractions having the compositions shown in Table 3 as top and bottom fractions are passed through conduit 40 and 6413 each via conduit 41
Kg/Hr and 106 Kg/Hr were obtained. The former stream is further purified if necessary, but when using the oxidative dehydrogenation catalyst system shown in this example,
Since the production of C ₄ acetylenes was extremely small, a highly pure butadiene product could be obtained without the need for further purification. Meanwhile, the latter stream was recycled to the oxidative dehydrogenation unit 7.

【table】

[Table] Example 2 According to the flow shown in Figure 3, a C ₄ hydrocarbon fraction containing a considerable amount of butadiene (a C ₄ fraction produced by steam cracking of naphtha) was processed in a selective hydrogenation unit. except that a C ₄ hydrocarbon fraction having the composition shown in Table 4 was supplied from conduit 15 from the position shown in conduit 15b. Example 1
The present invention was carried out in the same manner. Flow compositions and flow rates in the main conduits are shown in Tables 4 and 5. The fraction obtained via conduit 40 could be made into a high purity butadiene product without the need for further purification.

【table】

【table】

[Table] As described above, according to the present invention, i-butene is not removed from the _C4 hydrocarbon raw material and is directly sent to the extractive distillation process (butadiene purification process), where butenes are recovered and paraffins are separated. In addition to simultaneously removing and concentrating butadiene, butenes are removed in the i-butene removal step, and then
Since it is sent to the butadiene synthesis process and the same purification process, the paraffin removal process that was conventionally placed before the butadiene synthesis process is no longer necessary, simplifying the process and reducing equipment costs and operating costs. Furthermore, since the raw material is directly supplied to the extractive distillation process without removing i-butene, etc., it is possible to use raw materials containing high concentrations of butanes, butadiene, etc., increasing the versatility of the process. Can be done.

[Brief explanation of drawings]

Figure 1 is a flowchart showing the conventional manufacturing process of 1,3-butadiene, Figure 2 is a flowchart showing the main steps of the present invention, and Figure 3 is a flowchart showing the specific manufacturing process of an embodiment of the present invention. This is a flowchart. 1... Isobutene removal device, 7... Butadiene synthesis device, 10... Gas processing device, 16... Extractive distillation column, 24... Butene recovery column, 32... Stripping column, 34... Butadiene rectification column.

Claims (1)

[Claims] 1. 4 carbon atoms containing at least n-butenes
The ( _C4 ) hydrocarbon fraction (D fraction) is supplied to the extractive distillation column (B column), where it is distilled in an atmosphere of a selective solvent, and from the top of the column, mainly _C4 paraffins are extracted as hydrocarbon components. A fraction containing mainly C ₄ olefins as a hydrocarbon component is obtained as a side stream from a stage between the upper side of the G-fraction supply stage and the lower side of the selective solvent supply stage, which will be described later. This fraction is then supplied to the i-butene removal step (F step) to substantially remove the i-butene to obtain a fraction mainly composed of n-butenes, and the fraction is subjected to dehydrogenation or The n-butenes are supplied to the oxidative dehydrogenation step (A step) to convert 1,3
- A C ₄ hydrocarbon fraction (G fraction) containing 1,3-butadiene obtained in this way is supplied to the B column either alone or together with the D fraction, and An improved 1. Method for producing 3-butadiene. 2 In claim 1, when a fraction containing mainly C ₄ olefins as a hydrocarbon component is pushed out as a side stream and supplied to the F process, the extracted side stream is passed through another distillation column (E A hydrocarbon fraction in which C ₄ olefins are further concentrated is obtained as an overhead fraction of the E column.
1. A method for producing 1,3-butadiene, which comprises returning the bottom fraction of column E to a stage near the stage from which the side stream such as B was withdrawn at the same time as being supplied to the process.