JPH0348891B2 - - Google Patents

Description

[Detailed description of the invention]

(Field of Application of the Invention) The present invention relates to a method for producing 1,3-butadiene, and more specifically, from a solution obtained by absorbing a mixed gas containing 1,3-butadiene with a solvent,
The present invention relates to a method for efficiently separating and recovering 1,3-butadiene. (Background of the Invention) As a method for producing 1,3-butadiene from n-butene (a mixture of 1-butene and 2-butenes, the same applies hereinafter), for example, n-butene or a mixture containing n-butene is heated with oxygen. and nitrogen, water vapor,
A method is known in which the mixture is mixed with a diluent gas that is substantially inert to the reaction, such as carbon dioxide gas, and gas phase catalytic oxidative dehydrogenation is carried out at a high temperature, for example, 300 to 500° C., in the presence of a catalyst.
If high-purity n-butene is used as a raw material in this method, the cost of refining the raw material will be high industrially, so a small amount of n-butane, isobutane,
N-butene mixed with C ₃ hydrocarbons, C ₅ hydrocarbons, etc. is often used. Note that isobutene is generally more reactive than n-butene, and since n-butene inhibits a smooth reaction, it is preferable that it is substantially not contained, for example, it needs to be removed to 0.5% by weight or less. In this method, in addition to the target butadiene, carbon monoxide, carbon dioxide, organic acids,
Aldehydes, hydrocarbons such as benzene, and furan are also produced as by-products. Therefore, the reaction product gas obtained by oxidative dehydrogenation of n-butene is a mixture containing oxygen, nitrogen, water vapor, butadiene, and the above-mentioned by-products and _C3 to _C5 hydrocarbons contained in the raw materials. It's gas. Various methods have been conventionally used to separate high-purity butadiene from such a mixed gas. First, by cooling the reaction product gas with an indirect or direct cooler, water vapor and organic substances such as high boiling point organic acids can be removed. It is also known that relatively water-soluble organic substances such as aldehydes can be removed by pressurizing this gas and then washing it with water (Japanese Patent Publication No. 17647/1983). In step 2 above, relatively high-boiling components and water-soluble components are removed, but other components remain contained in the mixed gas. As a method to further separate and recover C ₄ hydrocarbons including butadiene from such a mixed gas,
Methods of absorbing with a solvent are known (for example, Japanese Patent Publication No. 17647-1970, Japanese Patent Publication No. 922-1972, Japanese Patent Publication No. 48-1973).
-13082). Examples of the absorption solvent used in this case include organic solvents such as benzene, toluene, and vinylcyclohexane. An example of a conventional method for separating and recovering C ₄ hydrocarbons including butadiene using these absorption solvents is shown in FIG. The equipment system in FIG. 1 includes distillation columns 1 and 3, and distillation column 1.
It consists of a degassing tower 2 installed in front of the degassing tower 2. The degassing column 2 is generally provided to facilitate temperature control of the distillation column 1 and to prevent popcorn polymer formation in the distillation column. The rich solvent obtained by absorbing C ₄ hydrocarbons in the mixed gas with an absorption solvent in an absorption tower (not shown) is introduced into a degassing tower 2 through a conduit 4, where it is extracted with inorganic gases such as nitrogen and oxygen. is removed in advance, and then fed to the distillation column 1, where the absorption solvent and the fraction mainly composed of C ₄ hydrocarbons are separated by distillation. The fraction mainly composed of C ₄ hydrocarbons obtained from the top of the distillation column 1 includes C ₅ hydrocarbons,
Since it contains a small amount of impurities, such as furan, which have a boiling point higher than that of the C ₄ hydrocarbons, this fraction is further sent to the distillation column 3, where the impurity components are removed from the bottom of the column via line 8. On the other hand, a fraction containing butadiene as a main component is obtained from the top of the distillation column 3 via a conduit 7. Impurities in this fraction include C ₃ hydrocarbons, butane, butene, etc., and these components can be separated from butadiene by known methods such as extraction and extractive distillation. However, the conventional 1,3-
It has become clear that the butadiene recovery method has the following drawbacks. That is, when ordinary industrial water is used as the refrigerant in the top condenser of distillation column 1 to condense the distillate from the top of the column, the top pressure must be kept quite high, and as a result, the bottom temperature will decrease. As a result, polymerization of easily polymerizable substances such as furan and butadiene may cause clogging of the equipment, and industrially, it is necessary to use a high-temperature heat source, which is high-quality energy, as the heat source for the distillation column 1. There is a drawback that it requires In this case, if the pressure in the distillation column 1 is kept low by cooling the top gas of the distillation column 1 using, for example, a refrigerator without using industrial water commonly used in the industry, Although it is possible to lower the tower low temperature, this method is also not a preferable method considering the energy cost for operating the refrigerator. Another method is to compress the top gas with a compressor to keep the pressure in the distillation column 1 low and to make it possible to use normal industrial water, but this method also uses a compressor. Considering the increase in equipment costs and operating costs due to installation, this is not a preferable method. (Object of the Invention) The object of the present invention is to eliminate the drawbacks of the prior art, reduce the pressure of the distillation column and the low temperature of the column, and efficiently convert 1,3-butadiene from a mixed gas containing 1,3-butadiene. - To provide a method for separating and recovering butadiene. (Summary of the Invention) As a result of intensive research to achieve this objective, the present inventors have discovered that when separating an absorption solvent from other components, C ₄ hydrocarbons, C ₅ hydrocarbons and/or furan are separated into a distillation column. The present invention was achieved by discovering that the pressure inside the distillation column can be lowered by withdrawing it from an intermediate stage as a side stream of the distillation column, and therefore the temperature can also be lowered. The present invention has 1,3-butadiene as a main component,
A rich solvent obtained by absorbing a mixed gas containing a small amount of C ₅ hydrocarbons and/or furans with an absorption solvent having a boiling point higher than that of the C ₅ hydrocarbons and/or furans is mixed with the absorption solvent and other components. When separating the two by distillation, a gas mainly composed of inorganic gas etc. dissolved in a small amount in the rich solvent is allowed to flow out from the top of the first distillation column, and a gas consisting essentially of the absorbed solvent is allowed to flow out from the bottom of the column. The poor solvent is removed, and a fraction containing C ₄ hydrocarbons is extracted as a side stream from an intermediate stage of the first distillation column, and a relatively C ₅ hydrocarbon and / or a furan-rich fraction is withdrawn and these fractions are fed to separate distillation columns, with C ₄ hydrocarbons from the former and C ₅ hydrocarbons and/or furans from the latter being fed to the respective columns. This is a method for producing 1,3-butadiene, which is characterized in that it is distilled as an overhead fraction, and the bottom liquid of each column is returned to the first distillation column. In this method, a fraction containing _C4 hydrocarbons is extracted in liquid form as a side stream from a first distillation column,
It is also preferred to feed this fraction to a distillation column operated at a higher pressure than the first distillation column. Furthermore, the present invention provides a method for absorbing a mixed gas containing 1,3-butadiene as a main component and a small amount of C ₅ hydrocarbons and/or furans using an absorption solvent having a boiling point higher than that of the C ₅ hydrocarbons and/or furans. When the rich solvent obtained by absorption is separated into the absorbed solvent and other components by distillation, a gas whose main component is an inorganic gas dissolved in a small amount in the rich solvent flows out from the top of the first distillation column. In addition, a poor solvent consisting essentially of the absorbing solvent is withdrawn from the bottom of the column, and a side stream is withdrawn from an intermediate stage of the first distillation column, and this is transferred to a second distillation column.
C ₄ hydrocarbons and C ₅ hydrocarbons and/or furan are distilled from the top of the second distillation column, while the bottom fraction of the second distillation column is fed to the first distillation column. and the top fraction of the second distillation column is further supplied to a third distillation column, so that the C ₄ fraction is fed from the top of the third distillation column, and the C ₅ and/or furan is removed from the bottom of the third distillation column. This is a method for recovering 1,3-butadiene. In this process as well, it is preferred to withdraw a side stream in liquid form from the first distillation column and to feed it to a second distillation column which is operated at a higher pressure than the first distillation column. The mixed gas used in the present invention is not particularly limited; High boiling point substances such as fatty acids are further absorbed with water to remove carbonyl compounds, resulting in _C4 hydrocarbons mainly composed of 1,3-butadiene, small amounts of _C5 hydrocarbons, furan and Examples include gases containing inorganic gases. The absorption solvent used in the present invention is not particularly limited as long as _it is highly compatible with C ₄ hydrocarbons and has a boiling point higher than that of C ₅ hydrocarbons and/or furan. In view of entrainment loss of the absorption solvent to the inorganic gas in the separation from furan and absorption steps, those having a boiling point of 50 to 16°C (for example, toluene) are preferably used. In the recovery method of the present invention, C ₄
In order to separate hydrocarbons, C ₅ hydrocarbons and furans, the fraction containing them is withdrawn as a side stream from an intermediate stage of the distillation column. This side stream may be extracted from two locations as two side streams: a side stream for separating C ₄ hydrocarbons and a side stream for separating C ₅ hydrocarbons and furan. It is also possible to withdraw C ₄ hydrocarbons, C ₅ hydrocarbons and/or furans as a side stream from only one point in the distillation column.
It is also possible to separate the C ₄ hydrocarbons from the C ₅ hydrocarbons and/or furans in a separate distillation column. In addition, the extraction position of the side stream in the distillation column is lower than the rich solvent supply stage, and when the extraction of the side stream is carried out from two locations, the extraction position for C ₄ hydrocarbon separation is as follows. It is located above the extraction position for _C5 hydrocarbon and furan separation. In addition, the gas flowing out from the top of the distillation column contains a small amount of C ₄ hydrocarbons in addition to inorganic gas.
It is economically preferable not to release the waste as it is, but to recycle it to a process that does not pose a problem in the recovery process, for example, before the absorption process. (Embodiments of the Invention) The present invention will be described in detail below with reference to the drawings. For the sake of clarity, most of the pumps, heat exchangers, containers, etc. that are not particularly necessary for the explanation are omitted from the drawings, and only the main parts are shown. FIG. 2 is a system diagram illustrating an embodiment of the invention in which side streams are withdrawn from two locations in a distillation column. In the figure, a rich solvent (absorbing solvent) that has absorbed a mixed gas obtained by removing water, organic acids, carbonyl compounds, etc. from the reaction product gas generated by the oxidative dehydrogenation reaction of n-butene by a known method is introduced from a conduit 11. It is supplied to the top of the first distillation column 12. At the top of the first distillation column 12, an inorganic gas containing small amounts of C ₄ hydrocarbons and absorption solvent exits via line 13. This stream is typically recycled to an absorption step (not shown) and reprocessed. On the other hand, the first
From the bottom of the distillation column 12, an absorption solvent substantially free of _C4 hydrocarbons is obtained via line 14, which is also recycled to the absorption stage. In addition, in order to separate C ₄ hydrocarbons, a portion of the liquid in the first distillation column 12 is extracted as a side stream via the conduit 15 and is supplied to the bottom of the C ₄ recovery column 16 via the preheater 26. . Some of the C ₄ hydrocarbons in the side stream are transferred to conduit 1 as an overhead distillate of C ₄ recovery column 16.
8. The top gas of the _C4 recovery tower 16 is
It is condensed in a condenser 17, and a part of it is returned to the C ₄ recovery column 16 via a conduit 19 as reflux. on the other hand,
From the bottom of the C ₄ recovery tower 16, a liquid containing a lower proportion of C ₄ hydrocarbons than the liquid composition in the conduit 15 is obtained.
This liquid passes through the conduit 20 to the pipe 15 of the first distillation column 12.
is returned to a stage near it, preferably one stage below it. Further, for the separation of C ₅ hydrocarbons and furans, a portion of the gas or liquid of the first distillation column 12 is transferred to the side stream from a stage closer to the bottom than the side stream withdrawal stage of the first distillation column 12. It is extracted as This side stream is fed via conduit 21 to the bottom of C ₅ recovery column 22 . The overhead gas of the C ₅ recovery column 22 is condensed by a condenser 23, a part of which is obtained as an overhead distillate through a conduit 24, and the remainder is refluxed and converted into C ₅
It is returned to the recovery tower 22. The overhead distillate of the C ₅ recovery column 22 consists essentially of C ₅ hydrocarbons and/or furans. On the other hand, a liquid containing a relatively reduced concentration of _C5 hydrocarbons and/or furan is obtained from the bottom of the _C5 recovery column 22, and is passed through the conduit 25 to the vicinity of the tube 21 of the first distillation column 12. It is returned to the tier, preferably to the tier one level below. Therefore, it is preferable that the side stream drawn out from the conduit 21 is drawn out as a gaseous phase flow, and when drawn out as a liquid phase stream, there is a disadvantage that the amount of heat required in the distillation column 22 increases. Although not shown in FIG. 2, a reboiler is usually provided at the bottom of the first distillation column 12 and the C ₄ recovery column 16, but a reboiler is usually not required for the recovery column 22. It is. According to the above embodiment, a fraction containing C ₄ hydrocarbons is extracted from an intermediate stage of the first distillation column 12, and a fraction containing C ₅ hydrocarbons is extracted as a side stream from a lower stage near the bottom of the column. , mainly C ₅ in the C ₅ recovery tower 22
By removing the distillate and furan, the pressure inside the distillation column can be lowered, which lowers the bottom temperature of the column, and prevents troubles such as pipe clogging due to the formation of polymerizable substances. FIG. 3 is a system diagram illustrating an embodiment of the invention in which a side stream is withdrawn from a single point in the distillation column. In the figure, a rich solvent absorbs a mixed gas obtained by removing water, organic acids, carbonyl compounds, etc. by a known method from a reaction product gas generated by the oxidative dehydrogenation reaction of n-butene, for example, and is passed through a conduit 31 to the first distillation stage. It is fed to the top of column 32. From the top of the first distillation column 32, a small amount of C ₄
Inorganic gases containing hydrocarbons and absorption solvents are distilled out. This stream is typically recycled to an absorption step (not shown) and reprocessed. On the other hand, from the bottom of the first distillation column 32, an absorption solvent substantially free of C ₄ hydrocarbons is obtained via a conduit 34, which is also recycled to the absorption stage. Further, a side stream is extracted from the middle stage of the first distillation column 32 via a conduit 35 and is supplied to the bottom of the second distillation column 36 via a preheater 48 . Here, the side stream from the first distillation column 32 is preferably withdrawn in liquid form, and the second distillation column 3 to which this side stream is supplied
6 is preferably operated at a higher pressure than the first distillation column 32. From the top of the second distillation column 36, a vapor stream substantially free of absorption solvent and consisting of C ₄ hydrocarbons, C ₅ hydrocarbons and/or furans is withdrawn via conduit 37 and in a condenser 38. After being condensed, a portion is returned as reflux to the top of the second distillation column 36 via a conduit 40, and the remainder is supplied to the middle stage of the third distillation column 42 via a conduit 39. On the other hand, the second distillation column 36
A liquid containing a reduced concentration of hydrocarbons and furan is withdrawn from the bottom of the column via conduit 41 and transferred to an adjacent stage, preferably one stage below, from which the side stream of first distillation column 32 was withdrawn. be returned. Further, from the top of the third distillation column 42, a stream mainly consisting of C ₄ hydrocarbons is withdrawn as a vapor stream via a conduit 43, passes through a condenser 44, and a part of it passes through a conduit 46 as reflux to the third distillation column. 42 is returned to the top of the column, and the remainder is discharged to the outside of the system via a conduit 45. Purified 1,3-butadiene is obtained by treating this effluent stream in known manner. on the other hand,,
From the bottom of the third distillation column 42, a stream consisting mainly of C ₅ hydrocarbons and/or furans is passed through conduit 4.
It is extracted after 7. Although not shown in FIG. 3, the first distillation column 3
2. A reboiler is normally provided at the bottom of the second distillation column 36 and the third distillation column 42, but if the amount of heat supplied to the second distillation column 36 by the preheater 48 is sufficient, the second distillation column 36 is equipped with a reboiler. Sometimes a boiler is not installed. (Effects of the Invention) According to the method of the present invention, when separating the absorption solvent from other components, C ₄ hydrocarbons and C ₅ hydrocarbons and/or furan are collected as a side stream of the distillation column from an intermediate stage. By extracting it, the pressure inside the distillation column can be lowered, and therefore the bottom temperature of the distillation column can be lowered. As a result, various drawbacks of the conventional 1,3-butadiene recovery method,
In other words, blockage of the equipment due to polymerization of easily polymerizable substances,
The drawbacks such as the necessity of using a high-temperature heat source can be eliminated, and excellent technical effects can be achieved. (Examples of the invention) Example 1 After substantially removing water, organic acids, and carbonyl compounds from the reaction product gas obtained by oxidizing and dehydrogenating a hydrocarbon mixed gas containing n-butene as a main component, The rich solvent obtained by absorption with toluene was treated according to the system diagram in FIG. The operating conditions in distillation columns 12, 16 and 22 are shown in Table 1.

Table 2 shows the flow rate of each component in the main conduits after treatment under the above conditions.

Comparative Example The rich solvent used in Example 1 was fed via conduit 4 to degassing column 2 and then passed through columns 1 to 3 for treatment according to the system diagram in FIG. The operating conditions in columns 2, 1 and 3 are shown in Table 3.

[Table] The conduits shown in Table 4 correspond to each other in Example 1 and Comparative Example (Table 4).

[Table] When treated under the above conditions, a liquid or gas having a composition similar to that of Example 1 was obtained from the conduit corresponding to Example 1. However, as is clear from Tables 1 and 3, the bottom temperature of distillation column 1 in the comparative example was 180°C.
compared to 164°C in the first distillation column 12 of Example 1.
The temperature has risen by 16℃. Furthermore, the top pressure of distillation column 1 in the comparative example is 4.0Kg/cm ² ·G, while the top pressure of distillation column 12 in Example 1 is 2.8Kg/cm ² ·G.
It's getting quite low. This is because in Example 1, the side stream was extracted from the distillation column 12.
This is because the distillation column 12 can be operated at low pressure, and as a result, the temperature at the bottom of the column can be lowered. Example 2 In the process shown in FIG.
A liquid having the same composition as the rich solvent supplied from 1 is supplied to conduit 31.
The distillation column 32 was supplied from the distillation column 32. Towers 32, 36, 42
The operating conditions were as shown in Table 5.

[Table] Note that in Example 1 and Example 2, the conduits shown below correspond to each other.

[Table] When the absorption liquid was separated in the process shown in FIG. 3, a liquid or gas having a composition similar to that of Example 1 was obtained from the conduit corresponding to Example 1. It was also found that the bottom temperature of column 32 was 164°C, which was kept 16°C lower than the bottom temperature of column 1 in the comparison column. Therefore, it is clear that the method shown in FIG. 3 also has the same effect as the process shown in FIG. 2.

[Brief explanation of drawings]

FIG. 1 is a system diagram showing an example of a conventional 1,3-butadiene recovery method, and FIGS. 2 and 3 are system diagrams showing an example of the 1,3-butadiene recovery method of the present invention. 12, 32...first distillation column, 16... _C4 recovery column, 22... _C5 recovery column, 36...second distillation column,
42... Third distillation column, 26, 48... Preheater, 1
7, 23, 38, 44... Condenser.

Claims (1)

[Claims] 1 1,3-butadiene as the main component, with a small amount of
A rich solvent obtained by absorbing a mixed gas containing C ₅ hydrocarbons and/or furans with an absorption solvent having a boiling point higher than that of the C ₅ hydrocarbons and/or furans is mixed with the absorption solvent and other components. During separation by distillation, a gas mainly composed of inorganic gas etc. dissolved in a small amount in the rich solvent is allowed to flow out from the top of the first distillation column, and a poor solvent consisting essentially of the absorbed solvent is allowed to flow out from the bottom of the column. and a fraction containing C ₄ hydrocarbons as a side stream from an intermediate stage of the first distillation column,
A relatively C ₅ hydrocarbon and/or furan-rich fraction is also withdrawn as a side stream from the stages located below, and each of these fractions is fed to a separate distillation column, from which the C 5 ₄ hydrocarbons,
1,3- characterized in that C ₅ hydrocarbons and/or furan are distilled off from the latter as an overhead fraction of each column, and the bottom liquid of each column is returned to the first distillation column. Method for producing butadiene. 2. A fraction containing C ₄ hydrocarbons is withdrawn in liquid form from the first distillation column as a side stream, and this fraction is transferred to the first distillation column.
2. A process according to claim 1, characterized in that the distillation column is fed to a distillation column which is operated at a higher pressure than the distillation column. 3 Main component is 1,3-butadiene, with a small amount of
A mixed gas containing C ₅ hydrocarbons and/or furans is absorbed by an absorption solvent with a boiling point higher than that of the C ₅ hydrocarbons and/or furans, and the resulting rich solvent is distilled into the absorption solvent and other components. During separation, a gas mainly composed of inorganic gas dissolved in a small amount in the rich solvent is allowed to flow out from the top of the first distillation column, and a poor solvent consisting essentially of the absorbed solvent is extracted from the bottom of the column. , and a side stream is withdrawn from an intermediate stage of the first distillation column and fed to a second distillation column to produce C ₄ hydrocarbons and C ₅ hydrocarbons and/or furan from the top of the second distillation column. Meanwhile, the bottom fraction of the second distillation column is returned to the first distillation column, and the top fraction of the second distillation column is further supplied to a third distillation column to carry out the third distillation. from the top of the tower
1. A method for producing 1,3-butadiene, which comprises recovering C ₅ and/or furan from a C ₄ fraction from the bottom of the column. 4. Claim 3, characterized in that a side stream is withdrawn in liquid form from the first distillation column and is fed to a second distillation column operated at a higher pressure than the first distillation column. the method of.