GB2077753A - Process for extractive distillation of hydrocarbons - Google Patents
Process for extractive distillation of hydrocarbons Download PDFInfo
- Publication number
- GB2077753A GB2077753A GB8114421A GB8114421A GB2077753A GB 2077753 A GB2077753 A GB 2077753A GB 8114421 A GB8114421 A GB 8114421A GB 8114421 A GB8114421 A GB 8114421A GB 2077753 A GB2077753 A GB 2077753A
- Authority
- GB
- United Kingdom
- Prior art keywords
- extractive distillation
- column
- stage
- distillation column
- hydrocarbon
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
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Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D3/00—Distillation or related exchange processes in which liquids are contacted with gaseous media, e.g. stripping
- B01D3/34—Distillation or related exchange processes in which liquids are contacted with gaseous media, e.g. stripping with one or more auxiliary substances
- B01D3/40—Extractive distillation
-
- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C7/00—Purification; Separation; Use of additives
- C07C7/04—Purification; Separation; Use of additives by distillation
- C07C7/05—Purification; Separation; Use of additives by distillation with the aid of auxiliary compounds
- C07C7/08—Purification; Separation; Use of additives by distillation with the aid of auxiliary compounds by extractive distillation
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- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Engineering & Computer Science (AREA)
- Analytical Chemistry (AREA)
- Oil, Petroleum & Natural Gas (AREA)
- Water Supply & Treatment (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
- Vaporization, Distillation, Condensation, Sublimation, And Cold Traps (AREA)
Abstract
A relatively easily soluble hydrocarbon is separated from a hydrocarbon mixture by extractively distilling the hydrocarbon mixture in an extractive distillation apparatus composed of two stages of a unit consisting of an extractive distillation column DA or DE and a stripping column DC or DF using a polar extractive solvent, a first-stage extractive distillation column DA being operated at a higher bottom pressure than the bottom pressure of a second- stage extractive distillation column, a pre-stripping column DB being provided between the first-stage extractive distillation column DA and a first-stage stripping column DC and operated at a pressure equal to or lower than the bottom pressure of the first-stage extractive distillation column DA and equal to or higher than the bottom pressure of the second- stage extractive distillation column DE, a gas of the relatively easily soluble hydrocarbon generated in the pre-stripping column DE being directly sent to the second-stage extractive distillation column DE without going through the first-stage stripping column DC and a compressor K or pump. <IMAGE>
Description
SPECIFICATION
Process for extractive distillation of hydrocarbons
This invention relates to an improvement in a process for separating conjugated diolefin hydrocarbons such as 1 ,3-butadiene or isoprene which are relatively easily soluble hydrocarbons from a hydrocarbon mixture, especially a C4 hydrocarbon mixture or a C5 hydrocarbon mixture, by a two-step extractive distillation process using a polar extractive solvent. More specifically, it relates to an improvement in and relating to an extractive distillation process which comprises a first step of removing relatively difficultly soluble hydrocarbons such as paraffinic and olefinic hydrocarbons and a second step of removing more soluble hydrocarbons such as acetylenic hydrocarbons than conjugated diolefin hydrocarbons.
In the present invention, the terms "relatively difficultly soluble hydrocarbons" and "relatively easily soluble hydrocarbons", qualitatively express the differences in solubility of hydrocarbons in an extracting solvent. Paraffinic hydrocarbons and olefinic hydrocarbons are the relatively difficultly soluble hydrocarbons as compared with conjugated diolefin hydrocarbons, and acetylenic hydrocarbons are the relatively easily soluble hydrocarbons as compared with conjugated diolefin hydrocarbon.
Conjugated diolefin hydrocarbons, especially 1 ,3-butadiene and isoprene, are important starting materials for synthetic rubbers, fibers, resins, etc. These conjugated diolefin hydrocarbons are contained in relatively large amounts in C4 and C5 hydrocarbon fractions which occur as by-products in the production of ethylene, etc. by thermal cracking of LPG, naphtha, kerosene, etc. The conjugated diolefin hydrocarbons are also obtained by dehydrogenation of paraffinic or olefinic hydrocarbons or by other synthesizing methods. In any case, the conjugated diolefin hydrocarbons are obtained as a mixture of paraffinic hydrocarbons, olefinic hydrocarbons and conjugated diolefin hydrocarbons.To separate 1,3butadiene or isoprene from such a hydrocarbon mixture and purify it, one-step and two-step extractive distillation processes using an extractive solvent such as dimethyl formamide, N-methyl-pyrrolidone, furfural or acetonitrile are known.
In the two-step extractive distillation process, the extractive distillation is carried out by usi ig an apparatus composed of two stages of a unit consisting of an extractive distillation column and a stripping column. In this process, the extractive distillation column is operated at atmospheric or elevated pressures, and the stripping column is operated at atmospheric or lower pressures in order to strip relatively easily soluble hydrocarbons dissolved in the extractive solvent as complete!y as possible.
Usually, the relatively easily soluble hydrocarbons recovered from the top of the stripping column of the first extractive distillation step are liquefied and sent to the extractive distillation column in the second step, or are first compressed by a compressor to an elevated pressure and then transported to the second extractive distillation column, in order to purify them further. In the second step of the extractive distillation process, the easily soluble hydrocarbons are separated by distillation in the presence of an extractive solvent from the conjugated diolefin hydrocarbons such as 1 ,3-butadiene or isoprene. The conjugated diolefin hydrocarbon are recovered from the top of the extractive distillation column in the second step and withdrawn as a final product. Or to remove traces of impurities, they are subjected to a subsequent step.
According to this invention, there is provided in a two-step extractive distillation process which comprises separating a specified relatively easily soluble hydrocarbon from a hydrocarbon mixture using an extractive distillation apparatus composed of two stages of a unit consisting of an extractive distillation column and a stripping column, the improvement wherein a first-stage extractive distillation column is operated at a higher bottom pressure than the bottom pressure of a second-stage extractive distillation column, and a prestripping column is provided between the first-stage extractive distillation column and a first-stage stripping column, and by operating the pre-stripping column at a pressure equal to or lower than the bottom pressure of the first-stage extractive distillation column or equal to or higher than the bottom pressure of a second-stage extractive distillation column, a gas of the relatively easily soluble hydrocarbon generated in the pre-stripping column is directly sent to the second-stage extractive distillation column without going through the first-stage stripping column and a compressor or a pump.
According to the improved process of this invention, the electric power for the pump or compressor installed between the first-stage distillation column and the second-stage distillation column can be reduced, and the load on the first-stage stripping column can be decreased. In the present invention, maximization of the amount of the relatively easily soluble hydrocarbon stripped in the pre-stripping column results in minimization of the load oii the subsequent stripping operation in the first-stage stripping column, and the load on the compressor for transporting the relatively easily soluble hydrocarbon from the first-stage stripping column to the second-stage extractive distillation column or the load on the pump for liquid transportation.Accordingly, it is desirable in the present invention to provide in the pre-stripping column a reboiler for raising the temperature of the extractive solvent in the pre-stripping column in order to assist in the stripping operation in the pre-stripping column.
The invention is further described below by reference to the accompanying drawings.
This drawings show one example of a process for separating a conjugated diolefin hydrocarbons such as 1 3-butadiene or isoprene from a C4 hydrocarbon mixture or CB hydrocarbon mixture, and does not in any way limit the present invention.
Figure 1 shows a process of an extractive distillation in accordance with the process of this invention, and Figure 2 shows a conventional extractive distillation process.
Referring to Figures 1 and 2, a starting hydrocarbon mixture is fed into an intermediate portion of a first-stage extractive distillation column (DA) from a line (1). By extractive distillation, a relatively difficultly soluble hydrocarbon is concentrated at the top of the column, and all the difficultly soluble hydrocarbon is withdrawn from the system as a distillative via a line (2). The extractive solvent is fed to the top of the first-stage extractive distillation column (DA) through a line (3), and while flowing downwardly through the column, it becomes a solution rich in the relatively easily soluble hydrocarbon by the extractive distillation operation. Usually, the concentration of the solvent in the extractive distillation column should be maintained high.The amount of the solvent to be fed is determined by distillation calculation by roughly setting it at several times to several ten times the amount of the feed hydrocarbon as a standard. In the process of the invention, a polar solvent such as dimethyl formamide,
N-methyl pyrrolidone, furfural or acetonitrile, above all dimethyl formamide, is conveniently used.
Usually, the first-stage extractive distillation column is operated under a pressure in equilibrium at a temperature at which relatively difficultly soluble hydrocarbon at the top of the column can be condensed by cooling water. At the bottom of the column, the pressure is higher than the top of the column by several atmospheres owing to pressure drop in the column. A reboiler (EA) for supplying heat required for the extractive distillation is provided at the bottom of the first-stage extractive distillation column. The reboiler also serves to control the amount of the relatively easily soluble hydrocarbon dissolved in the extractive solvent withdrawn from the bottom of the column.In other words, the concentration of the relatively easily soluble hydrocarbon in the extractive solvent withdrawn from a line (4) is in equilibrium relation with the concentration of the hydrocarbon at the bottom of the column. The solubility decreases at a high temperature and increases at a low temperature. Hence, the amount of the relatively easily soluble hydrocarbon dissolved in the solvent can be increased or decreased by controlling the temperature. On the other hand, if the extractive solvent for dissolving the relatively easily soluble hydrocarbon is maintained at a high temperature above a certain limit, polymerization of a conjugated diene is accelerated, and the resulting polymer adheres to the apparatus to reduce the function of a heat-exchanger, etc. Accordingly, the upper limit of the temperature of a column bottom is determined experimentally or through experience.Since in usual extractive distillation, the temperature of the bottom of a first-stage extractive distillation column is maintained at below this upper limit, the amount of the relatively easily soluble hydrocarbon dissolved in the extractive solvent necessarily exceeds the optimum amount of the relatively easily soluble hydrocarbon extracted from the bottom of the column. Thus, because of the need for keeping a material balance in the extractive distillation column, the excess of the relatively easily soluble hydrocarbon dissolved is returned to the first-stage extractive distillation column (DA) by a line (8) via the first-stage stripping column (DC) and a compressor (K).
In the process of this invention, the extractive solvent containing the extracted material from the bottom of the first-stage extractive distillation column is sent to a pre-stripping column (DB) shown in
Figure 1 via a line (4). A part of the relatively easily soluble hydrocarbon in the extractive solvent is evaporated by operating the pre-stripping column at a pressure equal to or lower than the pressure of the bottom of the first-stage extractive distillation column and equal to or higher than the pressure of the bottom of the second-stage extractive distillation column. Preferably, heat required for evaporation of the relatively easily soluble hydrocarbon is supplied by the reboiler (EB) provided at the bottom of the pre-stripping column.By evaporating the largest possible amount of the relatively easily soluble hydrocarbon and transporting the generated gases directly to the second-stage extractive distillation column, it is possible to reduced the stripping operation for the relatively easily soluble hydrocarbon in the first-stage stripping column and the load on the compressor for transporting the relatively easily soluble hydrocarbon from the first-stage stripping column to the second-stage extractive distillation column. An empty column or a kettle-type heat exchanger may be used as the pre-stripping column in this invention.
The extractive solvent withdrawn from the bottom of the pre-stripping column is sent to the firststage stripping column (DC) through a line (5), and the relatively easily soluble hydrocarbon is separated and recovered completely from the solvent in the first-stage stripping column. The relatively easily soluble hydrocarbon thus stripped is introduced as a vapor into the compressor (K) and pressurized to a pressure slightly higher than the pressure of the bottom of the first-stage extractive distillation column, and all or most of the compressed hydrocarbon gas is returned to the bottom of the first-stage distillation column through a line (8). The concentration of the relatively difficultly soluble hydrocarbons in the relatively easily soluble hydrocarbon at the first-stage extractive distillation column can be controlled by feeding a part of the gas exhausted from the compressor to the second-stage extractive distillation column via a line (9).
In the second-stage extractive distillation, a more easily soluble acetylenic hydrocarbon, etc. are removed from the relatively easily soluble hydrocarbons separated in the first-stage extractive distillation step, by an extractive distillation method in the presence of an extractive solvent. In this step, there are used a second-stage extractive distillation column and a second-stage stripping column (DF) for stripping acetylenic hydrocarbons from the extractive solvent containing the acetylenic hydrocarbons. The relatively easily soluble hydrocarbons from the first distillation step are fed to the second-stage extraction distillation column (DE) through a line (10).The fed hydrocarbons countercurrently contact the extractive solvent from a line (12) to concentrate the acetylenic hydrocarbons, etc., and the desired conjugated diolefin hydrocarbon such as 1,3-butadiene or isoprene is recovered from the top of the second-stage extractive distillation column (DE) through a line (13). For removal of traces of impurities, the recovered conjugated diolefin hydrocarbon is further subjected to several cycles of distillation and then taken out of the system as a final product.
In the meantime, the solvent solution having absorbed the acetylenic hydrocarbons, etc. is sent to the top of the second-stage stripping column (DF) from the bottom of the second-stage distillation column (DE) by a line (14). The acetylenic hydrocarbons are withdrawn from a part near the center of the second-stage stripping column through a line (17), and after recovering the entrained solvent, are used as a fuel, etc. Since the gas at the top of the second-stage stripping column contains the conjugated diolefin hydrocarbon in a fairly high concentration, it is desirably returned to the suction side of the compressor (K) through a line (15) for recovery.
The extractive solvents not containing the conjugated diolefin hydrocarbons and acetylenic hydrocarbons which are withdrawn from lines (11) and (16) from the bottoms of the first-stage stripping column (DC) and a second-stage stripping column (DF) are recycled to the first-stage extractive distillation column and the second-stage extractive distillation column respectively after the heat possessed by the solvents has been recovered, and temperatures of the solvents are adjusted to predetermined values by a water cooler (EG), and the flow rates of the solvents are controlled.
According to the process of this invention described hereinabove, a greater portion of the relatively easily soluble hydrocarbons separated and recovered at the bottom of the first-stage extractive distillation column can be fed to the second-stage extractive distillation column without going through the first-stage stripping column (DC) and the compressor. Accordingly, the load on the first-stage stripping column can be decreased and the electric power of the compressor can be markedly reduced as compared with a conventional two-step extractive distillation process.
The following Example specifically illustrate the present invention.
EXAMPLE Apparatuses of the types shown in Figure 1 (invention) and 2 (prior art) were used. The number of trays in each column was as follows:
First extractive distillation column 140
First stripping column 15
Pre-stripping column empty column
Second extractive distillation column 60
Second stripping column 20
A material having the following composition was fed at a rate of 1 5.29 N m3/hr to a middle stage of the first extractive distillation column, and a dimethyl formamide as a solvent was fed from the top of the column at a rate of 276 liters/hr. The starting material was thus extractively distilled in this column.
(Composition of a C4 hydrocarbon mixture)
Relatively difficultly
soluble hydrocarbons % by weight
Butanes 2.5
1-Butene 18.0
i-Butene 24.7
2-Butenes 9.6
1,3-Butadiene 43.6
Methylacetylene 0.1
1,2-Butadiene 0.2
Ethylacetylene 0.2
Vinylacetylene 0.6
C5 hydrocarbons 0.5
The operating conditions in the first-stage extractive distillation column, the second-stage extractive distillation column and the pre-stripping column were as tabulated below. The amount of gases sucked by the compressor each time was 7.1 Nm3/hr.
For comparison, in the case of the prior art (Figure 2), the amount of gases sucked by the compressor under the same operating conditions was 11.4 Nm3/hr.
In the process of this invention and the prior art, the concentration of 1,3-butadiene in the relatively difficultly soluble hydrocarbons in the top of the first extractive distillation column was 0.2% by weight, and the purity of 1,3-butadiene recovered from the second-stage extractive distillation column was 96.5% by weight
First extractive Second extractive distillation Pre-stripping distillation column column column Amount of C4 hydrocarbon mixture fed (Nm3/hr) 15s29 ~ 7.8 Amount of the extractive solvent fed 276 367 27 (liters /hr) i (including C4 hydrocarbons) Column operating pressure (kg /cm2 G) Column top 3,5 3,0 Column bottom 4.5 3.5 3.4 Operating temperature ('C) Column top 35 ~ 40 Column bottom 115 135 130
Claims (6)
1. A process for separating a specified relatively easily soluble hydrocarbon (as defined herein) from a hydrocarbon mixture containing said relatively easily soluble hydrocarbon and relatively difficultly soluble hydrocarbon (as defined herein), which process comprises extractively distilling the hydrocarbon mixture in an extractive distillation apparatus composed of two stages of a unit consisting of an extractive distillation column and a stripping column using a polar extractive solvent, wherein a firststage extractive distillation column is operated at a higher bottom pressure than the bottom pressure of a second-stage extractive distillation column, a pre-stripping column is provided between the first-stage extractive distillation column and a first-stage stripping column, and the pre-stripping column is operated at a pressure equal to or lower than the bottom pressure of the first-stage extractive distillation column and equal to or higher than the bottom pressure of the second-stage extractive distillation column, a gas of the relatively easily soluble hydrocarbon generated in the pre-stripping column being sent directly to the second-stage extractive distillation column without going through the first-stage stripping column and a compressor or pump.
2. A process according to claim 1 wherein the polar extractive solvent is dimethyl formamide.
3. A process according to claim 1 or 2 wherein 1,3-butadiene as the relatively easily soluble hydrocarbon is separated from a C4 hydrocarbon mixture as the hydrocarbon mixture.
4. A process according to claim 1 or 2 wherein isoprene as the relatively easily soluble hydrocarbon is separated from a C5 hydrocarbon mixture as the hydrocarbon mixture.
5. A process according to claim 1 substantially as described in the Example.
6. A process according to claim 1 substantially as described with reference to Figure 1 of the accompanying drawings.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP7834680A JPS574926A (en) | 1980-06-12 | 1980-06-12 | Separation of relatively easily soluble hydrocarbon from hydrocarbon mixture |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB2077753A true GB2077753A (en) | 1981-12-23 |
| GB2077753B GB2077753B (en) | 1983-09-21 |
Family
ID=13659421
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB8114421A Expired GB2077753B (en) | 1980-06-12 | 1981-05-12 | Process for extractive distillation of hydrocarbons |
Country Status (11)
| Country | Link |
|---|---|
| JP (1) | JPS574926A (en) |
| AR (1) | AR242624A1 (en) |
| AT (1) | AT375330B (en) |
| AU (1) | AU541746B2 (en) |
| CA (1) | CA1180301A (en) |
| GB (1) | GB2077753B (en) |
| HU (1) | HU187335B (en) |
| IN (1) | IN152086B (en) |
| MX (1) | MX159551A (en) |
| NO (1) | NO156447C (en) |
| YU (1) | YU113481A (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP1083160A1 (en) * | 1998-04-07 | 2001-03-14 | Nippon Zeon Co., Ltd. | Apparatus for separation and purification of saturated hydrocarbon and method for separation and purification |
| WO2005037396A1 (en) * | 2003-10-20 | 2005-04-28 | Polski Koncern Natfowy Orlen Spolka Akcyjna | Butadiene recovery process |
| US8080140B2 (en) | 2007-04-18 | 2011-12-20 | Exxonmobil Chemical Patents Inc. | Process for debottlenecking a system for the separation of a conjugated diolefin |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP5246027B2 (en) * | 2009-05-12 | 2013-07-24 | Ｊｓｒ株式会社 | Method for producing butadiene |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4134795A (en) * | 1978-04-05 | 1979-01-16 | The Goodyear Tire & Rubber Company | Acetylenes removal from diolefin streams by extractive distillation |
-
1980
- 1980-06-12 JP JP7834680A patent/JPS574926A/en active Granted
-
1981
- 1981-05-04 YU YU01134/81A patent/YU113481A/en unknown
- 1981-05-06 AR AR81285219A patent/AR242624A1/en active
- 1981-05-08 AU AU70300/81A patent/AU541746B2/en not_active Ceased
- 1981-05-11 HU HU811276A patent/HU187335B/en not_active IP Right Cessation
- 1981-05-12 IN IN498/CAL/81A patent/IN152086B/en unknown
- 1981-05-12 GB GB8114421A patent/GB2077753B/en not_active Expired
- 1981-06-11 NO NO811982A patent/NO156447C/en unknown
- 1981-06-11 CA CA000379589A patent/CA1180301A/en not_active Expired
- 1981-06-11 MX MX187764A patent/MX159551A/en unknown
- 1981-06-12 AT AT0264881A patent/AT375330B/en not_active IP Right Cessation
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP1083160A1 (en) * | 1998-04-07 | 2001-03-14 | Nippon Zeon Co., Ltd. | Apparatus for separation and purification of saturated hydrocarbon and method for separation and purification |
| EP1083160A4 (en) * | 1998-04-07 | 2003-03-12 | Nippon Zeon Co | Apparatus for separation and purification of saturated hydrocarbon and method for separation and purification |
| WO2005037396A1 (en) * | 2003-10-20 | 2005-04-28 | Polski Koncern Natfowy Orlen Spolka Akcyjna | Butadiene recovery process |
| US8080140B2 (en) | 2007-04-18 | 2011-12-20 | Exxonmobil Chemical Patents Inc. | Process for debottlenecking a system for the separation of a conjugated diolefin |
Also Published As
| Publication number | Publication date |
|---|---|
| JPS6212769B2 (en) | 1987-03-20 |
| AR242624A1 (en) | 1993-04-30 |
| AU541746B2 (en) | 1985-01-17 |
| MX159551A (en) | 1989-07-03 |
| IN152086B (en) | 1983-10-15 |
| ATA264881A (en) | 1983-12-15 |
| GB2077753B (en) | 1983-09-21 |
| YU113481A (en) | 1983-12-31 |
| JPS574926A (en) | 1982-01-11 |
| NO156447B (en) | 1987-06-15 |
| AT375330B (en) | 1984-07-25 |
| AU7030081A (en) | 1981-12-17 |
| HU187335B (en) | 1985-12-28 |
| NO811982L (en) | 1981-12-14 |
| NO156447C (en) | 1987-09-23 |
| CA1180301A (en) | 1985-01-02 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PCNP | Patent ceased through non-payment of renewal fee |
Effective date: 20000512 |