JPS6353976B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention provides high purity butene from _C4 hydrocarbon fraction.
The present invention relates to a method for separating and purifying butene-1 and butene-2. High purity butene-1 is used as a comonomer in the polymerization of polyethylene, but the butene-1 used for this purpose is required to be of high purity as exemplified in Table 1. Moreover, polybutene-1 can also be obtained by polymerizing butene-1 itself. This polymer has excellent high temperature stress cracking resistance, high temperature cleaving resistance, and environmental stress cracking resistance, and is suitable as a material for hot water pipes for heating and the like. Table 1 Composition of butene-1 for polyethylene comonomer Butene-1 99.0% by weight or more Butene-2 0.5 Isobutene 0.5 N-butane 0.5 1,3-butadiene 150PPM or less Acetylenes 15 Water 10 Butene Although 2 is a good raw material for maleic anhydride, butadiene can also be synthesized from butene-2 by a catalytic oxidative dehydrogenation reaction using a catalyst containing molybdenum oxide or bismuth oxide as a main component.
For example, a document published by Mr. LMWelch of Petrotex Corporation (U.S.A.) (Hydrocarbon Processing
Nov. 1978, pp. 131-136), 1,3-
The selectivity to butadiene is said to be highest for cis-butene-2 and second for trans-butene-2. However, separating the C ₄ hydrocarbon fraction by the usual distillation method is difficult to separate the n-
Since the boiling points of butane and trans-butene-2 are close to each other, it is economically disadvantageous. According to the above literature, n-butane in butene-2 does not have any adverse effects such as a decrease in selectivity if the amount of n-butane mixed in is 14% or less, but since it flows into the reaction product unreacted, a large amount of n-butane is mixed in. This is not economical because it leads to an unnecessary increase in the size of the reactor and an inefficiency of the 1,3-butadiene separation device produced. Therefore, prior to the reaction, n
- It is preferable to remove butane as much as possible, and it is particularly preferable to limit it to 5% by weight or less. An object of the present invention is to provide butene-1 and butene-2 of high purity and substantially free of harmful impurities that can be used for the above-mentioned purposes in large quantities and at low cost. The C ₄ hydrocarbon fraction that is the subject of the present invention is the one obtained by removing 1,3-butadiene and isobutylene from the C ₄ hydrocarbons produced as a by-product from naphtha steam cracking equipment, or the one obtained by removing 1,3-butadiene and isobutylene from petroleum catalytic cracking equipment. This includes, but is not limited to, _C4 hydrocarbons with isobutylene removed. these
Removal of 1,3-butadiene from _C4 hydrocarbons is usually carried out by extraction using the CAA method (cuprammonium acetate method) or extractive distillation using polar extraction solvents (e.g. dimethylformamide, dimethylacetamide, N-methylpyrrolidone, acetonitrile). It can be removed by law. On the other hand, isobutylene can be removed by the long-established extraction method using sulfuric acid or the recently developed etherification method using aliphatic alcohol. For example, Italy
ASSORNI (ASSOSIATION for
SCIENTIFIC RESERCH of ENI GROUP
COMPANIES) by Mr. A. Clementi (Hydrocarbon Processing, Dec, 1979)
(pp. 109-113), isobutylene can be almost completely etherified by contacting a mixture of _C4 hydrocarbon fraction and methanol with an acid catalyst (e.g., an ion exchange resin with sulfonic acid groups).
The concentration remaining in _C4 hydrocarbons will be less than 0.1%. Table 2 illustrates the composition of the _C4 hydrocarbon fraction from which 1,3-butadiene and isobutylene have been removed.

【table】

[Table] The present inventors conducted two extractive distillation processes using a polar solvent, particularly dimethylformamide (DMF), and a conventional distillation process on a _C4 hydrocarbon fraction with a composition similar to that exemplified in Table 2. By employing a combined process for treatment, butene is substantially free of diolefins, acetylene hydrocarbons, water, etc. that are harmful when used as a comonomer for polyethylene polymerization or a monomer for polybutene polymerization. 1, and at the same time a suitable cis-
We have found a separation method to obtain a mixture of 2-butene and 2-trans-butene. According to the method of the present invention, the _C4 hydrocarbon fraction is first removed in step A by extractive distillation using a polar solvent to remove isobutane, n-butane, butene-1, cis-
A mixture of 2-butene, 2-trans-butene, and impurities of diolefinic and acetylenic hydrocarbons is obtained. Next, in step B, the extract from the previous step A is subjected to extractive distillation using a polar solvent to obtain raffinate containing butene-1 and butene-2 as main components from the top of the column, and diolefin and acetylene hydrocarbons from the bottom of the column. to obtain a mixture of In the next step C, the raffinate from the second stage of extractive distillation is distilled to obtain butene-1 from the top of the column and purified butene-2 from the bottom of the column. In the final step D, a trace amount of water remaining in the butene-1 is removed by distillation. At this time, water is distilled from the top of the column to form the lowest azeotropic point with butene-1, and purified butene-1 is obtained from the bottom of the column. The polar solvent used in the present invention is _a 1,3-
Polar solvents used as solvents for extractive distillation of butadiene can be used. The N-alkyl substituted lower fatty acid amides in the polar solvent include dimethylformamide, diethylformamide, dimethylacetamide, etc. All of these have excellent solubility, specific volatility, and moderate boiling point when used in an anhydrous state. Therefore, it is a preferred solvent suitable for the purpose of the present invention. Table 3 shows the specific volatility of C ₄ hydrocarbons in various polar solvents. Among these, dimethylformamide is the most preferred because it has a suitable boiling point and excellent specific volatility. These polar solvents can be used not only alone but also in combination of two or more, and can also be used as polymerization inhibitors to prevent the polymerization of diolefin and acetylene hydrocarbons, as well as antioxidants and antifoaming agents. Agents can also be used in combination. Various polymerization inhibitors can be used as long as they have polymerization prevention and/or chain transfer effects, and in particular, t-butylcatechol, sulfur, sodium nitrite, furfural, benzaldehyde, and aromatic nitro compounds can be used alone. Alternatively, two or more types can be used in combination.

[Table] Preferred embodiments of the present invention are shown below using the drawings. The _C4 hydrocarbon fraction containing butene-1 and butene-2 is fed to the middle stage of the first extractive distillation column A-1, which has 100 stages, and the polar solvent is supplied to the pipe 2 several stages below the top of the tower.
The first step is extractive distillation. Isobutane and n-butane flow out from the top of the column via pipe 3. The pressure inside the tower is 1 to 15 atm, and the bottom temperature is
Can be operated at 100-180℃. Butene-1, butene-2, diolefin-based hydrocarbons, and acetylene-based hydrocarbons are taken out together with the solvent from the bottom of the tower, and are supplied to the top of the first stripping tower A-2 through pipe 4, where they are fed to the top of the first stripping tower A-2.
Separated into _C4 hydrocarbon and polar solvent. The pressure inside the column is usually 1 to 2 atmospheres, and the temperature at the bottom of the column can be controlled at the boiling point of the solvent at that pressure. Butene-1, butene-2, diolefin-based, and acetylene-based hydrocarbons are taken out from the top of the tower via pipe 5 and sent to compressor 6.
After increasing the pressure at , it is supplied to the second extractive distillation column B-1 via tube 7. Only the solvent is taken out from the bottom of the tower and pipe 8
is recycled to column A-1. A polar solvent is supplied through pipe 9 to several stages below the top of the second extractive distillation column B-1, which has 100 stages.
Butene-1, butene-1, which was supplied to the middle stage through
2. The second stage of extractive distillation is carried out by contacting with diolefin and acetylene hydrocarbons. The inside of the column can be operated at a pressure of 1 to 15 atm and a bottom temperature of 100 to 160°C. From the top of the tower, butene-1 and butene-1
2 is removed via pipe 10 and sent to the first distillation column C.
It is supplied to the middle row of. Diolefinic and acetylenic hydrocarbons are taken out from the bottom of the column along with the solvent, and are supplied to the top of the second stripping column B-2 through pipe 11, where they are separated into diolefinic and acetylenic hydrocarbons and a polar solvent. The inside of the tower is usually 1 to 2 atmospheres,
The bottom temperature operates at the boiling point at that pressure.
Diolefin and acetylene hydrocarbons are discharged from the top of the column via pipe 12, and only the solvent is taken out from the bottom of the column and circulated via pipe 13 to column B-1. The first distillation column C having 100 stages can be operated at a pressure of 1 to 15 atmospheres inside the column and at a boiling point at that pressure. Butene-1 is taken out from the top of the column via pipe 14 and fed to the middle stage of the second distillation column D.
The purified cis- and trans-butene-2 is removed from the bottom of the column via line 15. The inside of the second distillation column D having 30 stages can be operated at a pressure of 1 to 15 atm, and the temperature inside the column can be set to the boiling point at that pressure. A very small amount of water flows from the top of the tower into pipe 1.
6, and high purity butene-1 product is taken out from the bottom of the column via pipe 17. EXAMPLE The following experiment was conducted using the apparatus shown in the drawings. A raw material having the composition shown in Table 4 was fed into the middle stage of the 100-stage first extractive distillation column A-1 at a rate of 22.5 kg/H, and extractive distillation was performed using a polar solvent of 225 Kg/H and a reflux liquid of 22 Kg/H. Tower top pressure 3.5Kg/cm ² gauge, tower top temperature 45
As a result of operation at a bottom temperature of 139°C, 16.4 kg/H of gas was obtained from the top of the first stripping column (outlet of process A-2). Most of the butanes were removed.

[Table] Outlet gas of first extractive distillation (process A) 16.4Kg/H
was pressurized into the middle stage of the 100 stage second extractive distillation column B-1, and the second stage extractive distillation was carried out using 110 kg/h of polar solvent and 16 kg/h of reflux liquid. As a result of operation at a column top pressure of 3.3 kg/cm ² gauge, a column top temperature of 40°C, and a column bottom temperature of 150°C, butene-1 and butene-1, which are substantially free of diolefin and acetylenic hydrocarbons, were produced from the top of the column. 15.3 kg/h of 2 mixtures were obtained. The entire amount of this mixture was sent to the middle stage of the 100-stage first distillation column C, and distillation was carried out at a reflux ratio of 9, a column top pressure of 3.3 Kg/cm ² , and a column top temperature of 37°C. As a result, butene was extracted from the bottom of the column. -2 7.2
Kg/H was obtained. Butene-1 8.0Kg/
H was obtained, and the entire amount was sent to the second distillation column D to distill off water. As a result of operation at a column top pressure of 3.3 Kg/cm ² gauge and a column top temperature of 37° C., highly pure butene-1 containing substantially no water was obtained. Their compositions are shown in Table 4. The polar solvent is anhydrous dimethylformamide, 0.1% by weight of nitrobenzene, and 0.05% by weight of sodium nitrite.
A mixture of these was used.

[Brief explanation of drawings]

The drawing is a flow diagram showing the separation and purification method of the present invention. Here, A-1 is the first extractive distillation column, A-2
is the first stripping column, B-1 is the second extractive distillation column, B-2
represents the second stripping column, C represents the first distillation column, and D represents the second distillation column.

Claims (1)

[Claims] 1 Contains at least isobutane, n-butane, 1-butene, 2-butene, and at least one diolefinic or acetylenic hydrocarbon.
A method for separating butene-2 and butene-1 substantially free of diolefinic and acetylenic hydrocarbons from a _C4 hydrocarbon fraction, comprising: (1) as step A (first extractive distillation step), _C4
The hydrocarbon fraction is treated with a polar solvent in the first extractive distillation column to produce raffinate containing isobutane and n-butane as main components, butene-1 and butene-1.
(2) In step B (second extractive distillation step), the extract from step A is sent to the second extractive distillation column. (3) Step C (first distillation) As step), the step B
The raffinate from is sent to the first distillation column to obtain butene-1 from the top and purified butene-2 from the bottom. (4) As step D (second distillation step), the above step C
A high-purity butene-1 characterized in that the butene-1 from the column is sent to a second distillation column, a trace amount of water is removed from the top, and purified butene-1 is obtained from the bottom.
1 and butene-2 separation and purification method. 2. The method according to claim 1, wherein an N-alkyl-substituted lower fatty acid amide is used as the polar solvent in the first and second extractive distillation steps.