JPS6353975B2 - - 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, and the butene-1 used for this purpose is required to be of high purity as exemplified in Table 1. Moreover, butene-1 can also be polymerized itself to obtain polybutene-1. This polymer is
It has excellent high-temperature stress cracking resistance, high-temperature creep resistance, and environmental stress cracking resistance, making it 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-2 is Although it 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 the 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, followed by trans-butene-2. However, separating the C ₄ hydrocarbon fraction by the usual distillation method is difficult as shown in Table 2.
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 it is mixed in an amount of 14% or less, but since it flows into the reaction product unreacted, large amounts of n-butane should not be 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 equipment produced. Therefore, prior to the reaction, n
It is preferable to exclude -butane, particularly preferably at a content of 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 subjected to extractive distillation using a polar solvent in step A 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, distillation is performed to obtain a fraction containing 1-butene and diolefin-based and acetylene-based hydrocarbons as main components from the top of the column, and a mixture of 2-cis-butene and 2-trans-butene from the bottom of the column.
In the next step C, the diolefin system entrained in the butene-1 from the previous step by the second step extractive distillation,
Removes acetylenic hydrocarbons. 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 create the lowest azeotropic point with butene-1.
1 is obtained from the bottom of the tower. 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 alone or 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 quenchers. A foaming agent 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 may be used alone or Two or more types can be used in combination.

【table】

[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 plates, and the polar solvent is fed through pipe 2 to several stages below the top of the column. A first stage extractive distillation is carried out. Isobutane and n-butane flow out from the top of the column via pipe 3. Inside the tower, the pressure is 1 to 15 atmospheres, and the bottom temperature is 100 to 180.
Can be operated at °C. Butene from the bottom of the tower
1, butene-2, diolefin type, and acetylene type hydrocarbons are taken out together with the solvent and fed through pipe 4 to the top of the first stripping column A-2, where they are separated into C ₄ hydrocarbons and polar solvents. There are usually 1 to 2 inside the tower.
The pressure and bottom temperature can be controlled by the boiling point of the solvent at that pressure. Butene-1 from the top of the tower,
Butene-2, diolefin hydrocarbons, and acetylene hydrocarbons are taken out through a pipe 5, pressurized by a compressor 6, and then supplied to a first distillation column B through a pipe 7. Only the polar solvent is taken out from the bottom of the column and circulated through pipe 8 to column A-1. The first distillation column B 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, diolefin hydrocarbons, and acetylene hydrocarbons are taken out from the top of the column via pipe 9 and supplied to the middle stage of the second extractive distillation column C-1. From the bottom of the column, cis- and trans-butene-2
is removed through pipe 10 along with small amounts of diolefinic and acetylenic hydrocarbons. A polar solvent is supplied through a pipe 11 to several stages below the top of the second extractive distillation column C-1, which has 100 stages, and contacts the butene-1 supplied to the middle stage to carry out the second stage of extractive distillation. be exposed. 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. High purity butene-1 is taken out from the top of the column via pipe 12 and fed to the middle stage of second distillation column D. 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 C-2 via pipe 13, where they are separated into diolefinic and acetylenic hydrocarbons and the solvent. The inside of the column is usually 1 to 2 atmospheres, and the bottom temperature can be controlled at the boiling point at that pressure. Diolefin and acetylene hydrocarbons are discharged from the top of the column via pipe 14, and only the solvent is taken out from the bottom of the column and recycled via pipe 15 to column C-1. 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.

【table】

[Table] In the middle stage of the 100-stage first extractive distillation column A-1, the fourth
Raw materials having the composition listed in the table were supplied at 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 operating at a tower bottom temperature of 139°C, the first stripping tower A
16.4 Kg/H of gas was obtained from the top of the -2 tower (outlet of process A). Most of the butanes were removed. This gas was pressurized into the middle stage of the 100-stage first distillation column B, with a reflux ratio of 9, a tower top pressure of 3.3 Kg/cm ² gauge, and a tower top temperature of 37°C.
As a result of distillation, butene-2 was released from the bottom of the column.
A mixture of 7.65 Kg/H was obtained. Their compositions are shown in Table 4. The total amount of gas containing butene-1 as the main component from the top of the column is sent to the middle stage of the second extractive distillation column C-1, which has 100 stages, and is extracted in the second stage using a polar solvent of 60 kg/H and a reflux liquid of 8 kg/H. Distillation was carried out. Tower top pressure 3.3
As a result of operating at a Kg/cm ² gauge, a tower top temperature of 37°C, and a tower bottom temperature of 145°C, butene-1 was obtained from the top of the tower substantially free of diolefin and acetylene hydrocarbons. The entire amount of butene-1 was sent to the middle stage of the 30-stage second distillation column D, and water was distilled off. As a result of operation at a tower top pressure of 3.3 Kg/cm ² , gauge, and tower top temperature of 37°C, butene-1 containing substantially no water 7.65
Kg/H was obtained from the bottom of the column. Their compositions are shown in Table 4. The polar solvent used was a mixture of anhydrous dimethylformamide, 0.1% by weight of nitrobenzene, and 0.05% by weight of sodium nitrite.

[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
represents the first stripping column, B the first distillation column, C-1 the second extractive distillation column, C-2 the second stripping column, and D 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) As step B (first distillation step), the step A is separated into
The extract from is sent to the first distillation column to obtain a fraction mainly containing butene-1 and diolefin-based and acetylene-based hydrocarbons at the top, and purified butene-2 at the bottom. (3) Step As C (second extractive distillation step), the fraction mainly composed of butene-1 and diolefin-based and acetylene-based hydrocarbons from step B is sent to the second extractive distillation column and treated with a polar solvent to remove butene-1. 1
is obtained as a ranenate, and separated into an extract containing diolefin and acetylenic hydrocarbons as main components, (4) as step D (second distillation step), step C
A method for separating and purifying high-purity butene-1 and butene-2, which comprises feeding butene-1 into a second distillation column, removing a trace amount of water from the top, and obtaining purified butene-1 from the bottom. 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.