CA1180301A - Process for separating relatively easily soluble hydrocarbons from a hydrocarbon mixture - Google Patents
Process for separating relatively easily soluble hydrocarbons from a hydrocarbon mixtureInfo
- Publication number
- CA1180301A CA1180301A CA000379589A CA379589A CA1180301A CA 1180301 A CA1180301 A CA 1180301A CA 000379589 A CA000379589 A CA 000379589A CA 379589 A CA379589 A CA 379589A CA 1180301 A CA1180301 A CA 1180301A
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- CA
- Canada
- Prior art keywords
- column
- stage
- extractive distillation
- hydrocarbon
- distillation column
- 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.)
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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
ABSTRACT
In a process for separating a specified relatively easily soluble hydrocarbon from a hydrocarbon mixture which 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, 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 pre-stripping 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 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 is directly sent to the second-stage extractive distillation column without going through the first-stage stripping column and a compressor or pump.
In a process for separating a specified relatively easily soluble hydrocarbon from a hydrocarbon mixture which 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, 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 pre-stripping 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 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 is directly sent to the second-stage extractive distillation column without going through the first-stage stripping column and a compressor or pump.
Description
i~8~3~
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 solu~le hydrocarbons from a hydrocarbon mixture, espec~ally ~ C4 hydrocarbon mixture or a C5 hydrocarbon mixture, by a two-step extractive distillation process using a polar ex-tractive solventO More specifically, it relates to an improvement in and relating to an ex-tractive distillation process which comprises a first step of removing relatively difficultly soluble hydro-carbons 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", ~ualitatively express the dif-ferences in solubility of hydrocarbons in an extracting solvent. Paraffinic hydrocarbons and olefinic hydro-carbons are the relatively difficultly soluble hydro-carbons as compared with conjugated diolefin hydrocarbons, and acetylenic hydrocarbons are the relatively easily soluble h~-drocarbons as compared with conjugated diolefin hydrocarbon~
Conjugated diolefin hydrocarbons, especially 1,3-butadiene c~nd isoprene, are important starting ma-terials ~or synthetic rubbers, fibers, resins, etc.
~ .
~ 3q?3~
These conjugated diolefin hydrocarbons are contained in relatively large amounts in C4 and C5 hydrocarbon frac-tions which occur as by-products in -the produc-tion of ethylene, etc~ by thermal cracking of ~PG, naphtha, kerosene, etcO ~he conjugated diolefin hydrocarbons are also obtained by dehydrogenation o~ para~finic or olefinic hyt~rocarbons or by other synthesiæing methods~
In any case, the conjugated diolefin hydrocarbons are obtained as a mixture of para~finic hydrocarbons, olefinic hydrocarbons and conjugated diolefin hydro-carbonsO ~o separate 1,3-butadiene or isoprene from such a hydrocarbon mixture and purify it, one-step and two-step extractive distillation processes using an ex-tractive solvent such as dimethyl formamide, ~-methyl-pyrrolidone, furfural or acetonitrile are known~
In the two-step extractive dis-tillation process, the extractive distilla-tion is carried out by using an apparatus composed of two stages of a unit consisting of an extractive distillation column and a s-tripping 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 completely 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 ex-tractive distillati~n 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 separa-ted by distilla-tlon in the presence of an extractive solvent Erom the conjugated dioleEin hydrocarbons such as 1,3-butadiene or isoprene. The conjuga-ted diolefin hydrocarbon is 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-s-tep ex-trac-tive distillation process which comprises separating a specified relatively easily soluble conjugated diolefin hydrocarbon from a mixture of C4 or C5 hydro-carbons using an extxactive distillation apparatus composed of two stages of a unit consisting of an extractive distillation column and a stripping column, the improvement wherein a first-s-tage extractive distilla-tion column is operated at a higher bottom pressure than the bottom pressure of a second-stage extrac-tive distillation column, and apre-stripping 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 conjugated diolefin hydrocarbon generated~in the pre-stripping column is directly sent to the second-stage extractive distillation column without going through the firs-t-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 ~B
3~
column and -the second-s-tage dis-tillation 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 strip-ped in the pre-stripping column results in minimiæation of the load on the subsequent stripping opera-tion in the firs-t-s-taye stripping column, and the load on the compressor for transporting -the relatively easily soluble hydro-carbon from -the first-stage stripping column to the second-stage extracti~Je distillation column or the load on the pump for liquid transportation. Accord-ingly, 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.
3~, ~ he invention is fur-ther described below by reference to the accompanying drawingsO
Tllis drawings show one example of a process for separating a conjugated diolefin h-ydrocarbons such as 1,3-butadiene or isoprene from a CL~ hydrocarbon mixture or C5 hydrocarbon mixture, and does not in any way limit the presen-t invention~
Figure 1 shows a process of an extr~ctive dis-tillation in accordance with the process of this inven-tion, and ~igure 2 shows a conventional extractive dis-tillation processO
Re~erring to Figures 1 a~d 2, a star~ing hydro-carbon mixture is fed into an intermediate portion of a first-stage extractive distillation column (DA) from a 1~ line (1). By ex-tractive distil.la-tion, a relatively dif-ficultly soluble hydrocarbQn is concentrated a-t the top of the column, and all the difficultly soluble hydro-carbon is ~ithdrawn 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 columIl, it becomes a solution rich in the re]atively easily soluble hydrocarbon by the extractive distillation operationO Usually, the concentration of the solvent in the extractive distillation colu~l should be maintained higho ~he amo~m-t of the solvent to be fed is determined by distillation calculation by roughly setting it at ;'3~
several times -to several ten times the amount of the feed hydrocarbon as a standardO In the process of the inven-tion, a polar sol~ent such as dimethyl formamide, N_methyl pyrrolidone, furf-1ral or acetoni-trile, above all dime-thyl formamid~, is conveniently usedO
Usually, the first-stage extractive distilla-tion column is operated under a pressure in equilibrium at a temperature at which ~ rela-tively difficultly soluble hydrocarbon at the top of the column can be con-densed by cooling wa-ter, At the bottom of -the column, the pressure is higher than the top of the column by several atmospher~s owing to pressure drop in the columnO
A reboiler (EA) for supplying heat re~uired for the ex-tractive distillation is provided at the bottom of the first-stage extractive distillation colu~n. ~he reboiler also serves to control the amount of the relatively easily soluble hydrocarbon dissolved in the ex-tractive solvent withdrawn from the bottom of the columnO In other words, the concentration of the relatively easily soluble hydrocarbon in the extractive solvent wi-thdrawn from a line (4) is in equilibrium relation wi-th the con-centration of the hydrocarbon at the bottom of the columnO
~he solubility decreases at a high temperature and in-creases at a low temperature. Hence, the amount of the relatively easily soiuble hydrocarbon dissolved in the solvent can be increased or decreased by controlling the -temperatureO On the other hand, if the extractive solvent :for dissolving the rel~-tively easily soluble hydrocarbon is maintained at a high temperature above a certain limit, polymerization of a conjugated diene is accelerated, and the resul-ting pol~mer adheres -to the appara-tus to recluce the func-tion of a heat-exchanger, etc. Accordingly, -the upper limit of -the temperature of the co1um~bQttom is determined experi.men-tally or through experience~ Since in usual extrac-tive 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 hydro-carbon dissolved in the extractive solvent necessarily exceeds the optimum amount of the r~latively easily soluble hydrocarbon extracted from the bottom of the column~ ~hus, because of the need for keeping a material balance in the extractive di.stillation column~ the excess of the relatively easily soluble hydrocarbon dissolved is returned to .the::first-sta~e extracti~a distillation column (DA) by a line ~) via the first-stage stripping 2Q column (DC) and a compressor (K)o In the process of this inven-tion, -the extractive solvent containing the extracted material from the bottom of the first-stage extractive distillation column is sent to a pre-stripping col~n (DB) shown in Figure 1 via a line (4). A part of the relatively easily soluble hydro-carbon in the extrac-tive solvent is evaporated by operat-ing the pre-stripping column at a pressure equal to or ~ 33~)~
lower -than the pressure o~ the bottom of the ~irst-stage extractive distilla-tion column an~ equal to or higher than the pressure of the bot-tom o~ the second~stage ex-tractive distilla-tion colurlm. Pre~erably, heat required for evaporation of the relatively easily soluble hydro-carbon is supplied by the reboiler (EB) provided a-t the bottom of the pre--stripping coll~nO 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 reduce the stripping operation for the rela-tively easily soluble hydrocarbon in the fir~t-stage stripping column an~ the lo~d on the compresser ~or transporting the relatively easily soluble hydrocarbon l~ from the firs-t-s-tage s-tripping colu~n to -the second-stage extractive distillation colu~lnO An ernpty column or a kettle-type hea-t exchanger may be used as the pre-strip-ping column in this inventionO
~he e~tractive solven-t withdrawn from the bot-tom of the pre~stripping column is sent to the firs-t-stage stripping column (DC) through a line (5). and the relatively easily soluble h~rdrocarbon is separated and recovered completely from the solvent in the first-stage stripping colu~mO ~he relatively easily soluble hydro-carbon thus stripped is introduced as a vapor into thecompressor (K) and pressurized to a pressure slightly higher than the pressure of the bottom of the ~irst-stage .~'3 ex-tractive distillation column, arld all or most of the comlpressed hydrocarbon gas is returned to the bottom of the ~irst-stage distillation column through a line (8)~
~he concentration o the relatively difficultly soluble hydrocarbons ln -the relati-vely easily soluble hydrocarbon at -the first-stage extractive distillation col~n can be controlled by eecli.ng a part of -the gas exhausted from the compressor to the second-stage extractive distilla-tion colum.n v a line (9)0 In the second-stage extractive distillation, a more easily soluble acetylenic hydrocarbon, etc~ are re-moved from the rela-tively easily soluble hydrocarbons separated in the irst-staDe extractive distillation step, by an extractive distillation method in the pre-sence of an extractive solventO In this step, there are used a second-stage extrac-tive distillation col~mn and a second-sta~e stripping column (DF) for stripping acety-lenic hydrocarbons from the extractive solvent containing the acetylenic hydrocarbons~ ~he rel~atively easil~
soluble hydrocarbons from the first distillation step are fed to the second-stag~ extraction distillation column (DE) through a line (lO)o ~he fed hydrocarbons counter-currently contact the extractive solvent from a line (12) to concentrate the acetylenic hydrocarbons, etcO, and the desired con~ugated diolefin hydrocarbon such as 1,3-butadiene or isoprene is recovered from the top o the second-s-ta~e extractive distillation column (DE) through ~13~
a line (13)D ~or removal of traces of impurlties, the recovered conjugated diolefin hydrocarbon is further subjected to several cycles of di.stilla-tion. and then taken out of the system as a flnal produc-t~
In the meantime. the solvent solution having absorbed -the ace-tylenic hydrocarbons, etcO is sent to ;,he top of the second-stage s-tripping col.umn (DF) from -the bottom of the second-s-tage distillation column ~D~) by a line (14)o The acetylenic hydrocarbons are with-drawn from a part near the center of the second-stage stripping column -through a line (17), an-l after recover-ing the entrained solvent, are used as a fuel, etcO
Since the gas at the top of the second-stage stripping column contains the conjugated diole~in hydrocarbon in a fairl~ high concentration, it is de~irably returned to the suction side of the compressor (K) through a line (15) for recovery~
~ he extr~ctive solvents not containing the con-jugated diolefin hydrocarbons and acetylenic hydrocarbons which are withdrawn from lines (11) and (16) from the bottoms~of the first-s-tage stripping column (DC) and a second-stage stripping~ colu~n (DF) are recycled to the first-stage extractive distillation column and the second-stage extrac-tive distillation column respectively after the heat possessed by the solvents has been recovered, the temperatures of the solvents are adjusted to prede-termined values by a water cooler (EG), and the flow t ~, rates of the solvents are controlledO
According to the process of this invention described hereinabove, a grea-ter por-tion of the relati-vely easily solubl.e hydrocarbons separated and recovered at the bottom of the ~irst-stage extractive distilla-tion colu~n can be fed to the second-stage extrac~tive disti]-lation column without going -tilrough -the firs-t-sta~e stripping column (DC) and the compressorO Accordingly, the load on the first~s-tage stripping column can be de-creased and the electric power of the compressor can bemarkedly reduced as compared with a conventional two-step extractive distillation processO
~ he following 5xample specifically illu~trate the present inventionO
Exa~ple Apparatuses of the types shown in Figure ~
(invention~ and 2 ~prior art) were usedO ~he number of trays in each col~n was as follows~
First extractive distillation column 140 First stripping column 15 Pre-stripping col~ln empty column Second extractive distillation column 60 Second stripping col~ln 20 A material having the followihg composition was 25 fed at a rate of 1~o29 N m3/hr to a middle stage of the first extractive distilla-tion colur.n, and a dimet'n.-yl .,8~D3 ~ 12 -formamide as a solvent was fed from the top of the column at a rate of 275 liters/hrO The starting material was thus extrac-tively dis-tilled in -this columnO
(Composition of a CL~ hydrocarbon mixture) ~elatively difficulty soluble h~droc~rbons % b~
Butanes 2 l-Butene 18.0 i-Bu-tene 24~7
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 solu~le hydrocarbons from a hydrocarbon mixture, espec~ally ~ C4 hydrocarbon mixture or a C5 hydrocarbon mixture, by a two-step extractive distillation process using a polar ex-tractive solventO More specifically, it relates to an improvement in and relating to an ex-tractive distillation process which comprises a first step of removing relatively difficultly soluble hydro-carbons 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", ~ualitatively express the dif-ferences in solubility of hydrocarbons in an extracting solvent. Paraffinic hydrocarbons and olefinic hydro-carbons are the relatively difficultly soluble hydro-carbons as compared with conjugated diolefin hydrocarbons, and acetylenic hydrocarbons are the relatively easily soluble h~-drocarbons as compared with conjugated diolefin hydrocarbon~
Conjugated diolefin hydrocarbons, especially 1,3-butadiene c~nd isoprene, are important starting ma-terials ~or synthetic rubbers, fibers, resins, etc.
~ .
~ 3q?3~
These conjugated diolefin hydrocarbons are contained in relatively large amounts in C4 and C5 hydrocarbon frac-tions which occur as by-products in -the produc-tion of ethylene, etc~ by thermal cracking of ~PG, naphtha, kerosene, etcO ~he conjugated diolefin hydrocarbons are also obtained by dehydrogenation o~ para~finic or olefinic hyt~rocarbons or by other synthesiæing methods~
In any case, the conjugated diolefin hydrocarbons are obtained as a mixture of para~finic hydrocarbons, olefinic hydrocarbons and conjugated diolefin hydro-carbonsO ~o separate 1,3-butadiene or isoprene from such a hydrocarbon mixture and purify it, one-step and two-step extractive distillation processes using an ex-tractive solvent such as dimethyl formamide, ~-methyl-pyrrolidone, furfural or acetonitrile are known~
In the two-step extractive dis-tillation process, the extractive distilla-tion is carried out by using an apparatus composed of two stages of a unit consisting of an extractive distillation column and a s-tripping 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 completely 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 ex-tractive distillati~n 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 separa-ted by distilla-tlon in the presence of an extractive solvent Erom the conjugated dioleEin hydrocarbons such as 1,3-butadiene or isoprene. The conjuga-ted diolefin hydrocarbon is 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-s-tep ex-trac-tive distillation process which comprises separating a specified relatively easily soluble conjugated diolefin hydrocarbon from a mixture of C4 or C5 hydro-carbons using an extxactive distillation apparatus composed of two stages of a unit consisting of an extractive distillation column and a stripping column, the improvement wherein a first-s-tage extractive distilla-tion column is operated at a higher bottom pressure than the bottom pressure of a second-stage extrac-tive distillation column, and apre-stripping 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 conjugated diolefin hydrocarbon generated~in the pre-stripping column is directly sent to the second-stage extractive distillation column without going through the firs-t-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 ~B
3~
column and -the second-s-tage dis-tillation 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 strip-ped in the pre-stripping column results in minimiæation of the load on the subsequent stripping opera-tion in the firs-t-s-taye stripping column, and the load on the compressor for transporting -the relatively easily soluble hydro-carbon from -the first-stage stripping column to the second-stage extracti~Je distillation column or the load on the pump for liquid transportation. Accord-ingly, 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.
3~, ~ he invention is fur-ther described below by reference to the accompanying drawingsO
Tllis drawings show one example of a process for separating a conjugated diolefin h-ydrocarbons such as 1,3-butadiene or isoprene from a CL~ hydrocarbon mixture or C5 hydrocarbon mixture, and does not in any way limit the presen-t invention~
Figure 1 shows a process of an extr~ctive dis-tillation in accordance with the process of this inven-tion, and ~igure 2 shows a conventional extractive dis-tillation processO
Re~erring to Figures 1 a~d 2, a star~ing hydro-carbon mixture is fed into an intermediate portion of a first-stage extractive distillation column (DA) from a 1~ line (1). By ex-tractive distil.la-tion, a relatively dif-ficultly soluble hydrocarbQn is concentrated a-t the top of the column, and all the difficultly soluble hydro-carbon is ~ithdrawn 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 columIl, it becomes a solution rich in the re]atively easily soluble hydrocarbon by the extractive distillation operationO Usually, the concentration of the solvent in the extractive distillation colu~l should be maintained higho ~he amo~m-t of the solvent to be fed is determined by distillation calculation by roughly setting it at ;'3~
several times -to several ten times the amount of the feed hydrocarbon as a standardO In the process of the inven-tion, a polar sol~ent such as dimethyl formamide, N_methyl pyrrolidone, furf-1ral or acetoni-trile, above all dime-thyl formamid~, is conveniently usedO
Usually, the first-stage extractive distilla-tion column is operated under a pressure in equilibrium at a temperature at which ~ rela-tively difficultly soluble hydrocarbon at the top of the column can be con-densed by cooling wa-ter, At the bottom of -the column, the pressure is higher than the top of the column by several atmospher~s owing to pressure drop in the columnO
A reboiler (EA) for supplying heat re~uired for the ex-tractive distillation is provided at the bottom of the first-stage extractive distillation colu~n. ~he reboiler also serves to control the amount of the relatively easily soluble hydrocarbon dissolved in the ex-tractive solvent withdrawn from the bottom of the columnO In other words, the concentration of the relatively easily soluble hydrocarbon in the extractive solvent wi-thdrawn from a line (4) is in equilibrium relation wi-th the con-centration of the hydrocarbon at the bottom of the columnO
~he solubility decreases at a high temperature and in-creases at a low temperature. Hence, the amount of the relatively easily soiuble hydrocarbon dissolved in the solvent can be increased or decreased by controlling the -temperatureO On the other hand, if the extractive solvent :for dissolving the rel~-tively easily soluble hydrocarbon is maintained at a high temperature above a certain limit, polymerization of a conjugated diene is accelerated, and the resul-ting pol~mer adheres -to the appara-tus to recluce the func-tion of a heat-exchanger, etc. Accordingly, -the upper limit of -the temperature of the co1um~bQttom is determined experi.men-tally or through experience~ Since in usual extrac-tive 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 hydro-carbon dissolved in the extractive solvent necessarily exceeds the optimum amount of the r~latively easily soluble hydrocarbon extracted from the bottom of the column~ ~hus, because of the need for keeping a material balance in the extractive di.stillation column~ the excess of the relatively easily soluble hydrocarbon dissolved is returned to .the::first-sta~e extracti~a distillation column (DA) by a line ~) via the first-stage stripping 2Q column (DC) and a compressor (K)o In the process of this inven-tion, -the extractive solvent containing the extracted material from the bottom of the first-stage extractive distillation column is sent to a pre-stripping col~n (DB) shown in Figure 1 via a line (4). A part of the relatively easily soluble hydro-carbon in the extrac-tive solvent is evaporated by operat-ing the pre-stripping column at a pressure equal to or ~ 33~)~
lower -than the pressure o~ the bottom of the ~irst-stage extractive distilla-tion column an~ equal to or higher than the pressure of the bot-tom o~ the second~stage ex-tractive distilla-tion colurlm. Pre~erably, heat required for evaporation of the relatively easily soluble hydro-carbon is supplied by the reboiler (EB) provided a-t the bottom of the pre--stripping coll~nO 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 reduce the stripping operation for the rela-tively easily soluble hydrocarbon in the fir~t-stage stripping column an~ the lo~d on the compresser ~or transporting the relatively easily soluble hydrocarbon l~ from the firs-t-s-tage s-tripping colu~n to -the second-stage extractive distillation colu~lnO An ernpty column or a kettle-type hea-t exchanger may be used as the pre-strip-ping column in this inventionO
~he e~tractive solven-t withdrawn from the bot-tom of the pre~stripping column is sent to the firs-t-stage stripping column (DC) through a line (5). and the relatively easily soluble h~rdrocarbon is separated and recovered completely from the solvent in the first-stage stripping colu~mO ~he relatively easily soluble hydro-carbon thus stripped is introduced as a vapor into thecompressor (K) and pressurized to a pressure slightly higher than the pressure of the bottom of the ~irst-stage .~'3 ex-tractive distillation column, arld all or most of the comlpressed hydrocarbon gas is returned to the bottom of the ~irst-stage distillation column through a line (8)~
~he concentration o the relatively difficultly soluble hydrocarbons ln -the relati-vely easily soluble hydrocarbon at -the first-stage extractive distillation col~n can be controlled by eecli.ng a part of -the gas exhausted from the compressor to the second-stage extractive distilla-tion colum.n v a line (9)0 In the second-stage extractive distillation, a more easily soluble acetylenic hydrocarbon, etc~ are re-moved from the rela-tively easily soluble hydrocarbons separated in the irst-staDe extractive distillation step, by an extractive distillation method in the pre-sence of an extractive solventO In this step, there are used a second-stage extrac-tive distillation col~mn and a second-sta~e stripping column (DF) for stripping acety-lenic hydrocarbons from the extractive solvent containing the acetylenic hydrocarbons~ ~he rel~atively easil~
soluble hydrocarbons from the first distillation step are fed to the second-stag~ extraction distillation column (DE) through a line (lO)o ~he fed hydrocarbons counter-currently contact the extractive solvent from a line (12) to concentrate the acetylenic hydrocarbons, etcO, and the desired con~ugated diolefin hydrocarbon such as 1,3-butadiene or isoprene is recovered from the top o the second-s-ta~e extractive distillation column (DE) through ~13~
a line (13)D ~or removal of traces of impurlties, the recovered conjugated diolefin hydrocarbon is further subjected to several cycles of di.stilla-tion. and then taken out of the system as a flnal produc-t~
In the meantime. the solvent solution having absorbed -the ace-tylenic hydrocarbons, etcO is sent to ;,he top of the second-stage s-tripping col.umn (DF) from -the bottom of the second-s-tage distillation column ~D~) by a line (14)o The acetylenic hydrocarbons are with-drawn from a part near the center of the second-stage stripping column -through a line (17), an-l after recover-ing the entrained solvent, are used as a fuel, etcO
Since the gas at the top of the second-stage stripping column contains the conjugated diole~in hydrocarbon in a fairl~ high concentration, it is de~irably returned to the suction side of the compressor (K) through a line (15) for recovery~
~ he extr~ctive solvents not containing the con-jugated diolefin hydrocarbons and acetylenic hydrocarbons which are withdrawn from lines (11) and (16) from the bottoms~of the first-s-tage stripping column (DC) and a second-stage stripping~ colu~n (DF) are recycled to the first-stage extractive distillation column and the second-stage extrac-tive distillation column respectively after the heat possessed by the solvents has been recovered, the temperatures of the solvents are adjusted to prede-termined values by a water cooler (EG), and the flow t ~, rates of the solvents are controlledO
According to the process of this invention described hereinabove, a grea-ter por-tion of the relati-vely easily solubl.e hydrocarbons separated and recovered at the bottom of the ~irst-stage extractive distilla-tion colu~n can be fed to the second-stage extrac~tive disti]-lation column without going -tilrough -the firs-t-sta~e stripping column (DC) and the compressorO Accordingly, the load on the first~s-tage stripping column can be de-creased and the electric power of the compressor can bemarkedly reduced as compared with a conventional two-step extractive distillation processO
~ he following 5xample specifically illu~trate the present inventionO
Exa~ple Apparatuses of the types shown in Figure ~
(invention~ and 2 ~prior art) were usedO ~he number of trays in each col~n was as follows~
First extractive distillation column 140 First stripping column 15 Pre-stripping col~ln empty column Second extractive distillation column 60 Second stripping col~ln 20 A material having the followihg composition was 25 fed at a rate of 1~o29 N m3/hr to a middle stage of the first extractive distilla-tion colur.n, and a dimet'n.-yl .,8~D3 ~ 12 -formamide as a solvent was fed from the top of the column at a rate of 275 liters/hrO The starting material was thus extrac-tively dis-tilled in -this columnO
(Composition of a CL~ hydrocarbon mixture) ~elatively difficulty soluble h~droc~rbons % b~
Butanes 2 l-Butene 18.0 i-Bu-tene 24~7
2-Butenes 9.6 1,3-P,utadiene L~, 6 Methylacetylene Ool 1,2~-Butadiene 002 :Ethylacetylene 0~2 ~inylacetylene 006 C5 hydrocarbons 005 The operating conditions in the first-stage extractive distillation colwmn~ the second-stage extrac-tive distillation column and the pre-stripping column were as tabulated below. The amo~Lnt of gases sucked by the compressor each time was 7.1 ~Tm3/hrO
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 ll~L~ Nm3/hrO
In the process of -this invention and the prior art, the concentration of 1,3-butadiene in the relatively difficultly soluble hydrocar~ons in the top o~ the first ex-tractive distilla-tion column was 002% by w~ight, and the purity of l,3-butadiene recovered from -the second~
sta~e extractive distillation column was 9605% by weightn _ _ _ _ ~ . __ Firs-t Pre- Second ~x-tractive s-tripping extractive distilla- column distilla-tion tion column column . _ _ _ . . _. ~
Amount of C4 hydro-carbon mixture fed 15029 _ 708 (.Nm3/hr) ~ . ._ .
Amount of the 276 3~7 27 extractive solvent (including fed (liters/hr) C~ h~dro-carbons) . ._ _ . _ _ .
Column op~ratin~
pressure (kg/cm G) Col~n top 3~5 300 Column bottom 407 3~5 3o4 . ___ ............ . _ _ . .
Operating tempera~ure (C) Col.umn top 35 _ 40 . Column bottom 115 135 130
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 ll~L~ Nm3/hrO
In the process of -this invention and the prior art, the concentration of 1,3-butadiene in the relatively difficultly soluble hydrocar~ons in the top o~ the first ex-tractive distilla-tion column was 002% by w~ight, and the purity of l,3-butadiene recovered from -the second~
sta~e extractive distillation column was 9605% by weightn _ _ _ _ ~ . __ Firs-t Pre- Second ~x-tractive s-tripping extractive distilla- column distilla-tion tion column column . _ _ _ . . _. ~
Amount of C4 hydro-carbon mixture fed 15029 _ 708 (.Nm3/hr) ~ . ._ .
Amount of the 276 3~7 27 extractive solvent (including fed (liters/hr) C~ h~dro-carbons) . ._ _ . _ _ .
Column op~ratin~
pressure (kg/cm G) Col~n top 3~5 300 Column bottom 407 3~5 3o4 . ___ ............ . _ _ . .
Operating tempera~ure (C) Col.umn top 35 _ 40 . Column bottom 115 135 130
Claims (4)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. In a process for separating a specified relatively easily soluble conjugated diolefin hydrocarbon from a mixture of C4 or C5 hydrocarbons which 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, 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 pre-stripping 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 and equal to or higher than the bottom pressure of the second-stage extractive distillation column, a gas of the relatively easily soluble con-jugated diolefin 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 pump.
2. The process of claim 1 wherein the polar extractive solvent is dimethyl formamide.
3. The process of 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. The process of claim 1 or 2 wherein isoprene as the relatively easily soluble hydrocarbon is separated from a C5 hydrocarbon mixture as the hydro-carbon mixture.
Applications Claiming Priority (2)
| 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 |
| JP78,346/80 | 1980-06-12 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1180301A true CA1180301A (en) | 1985-01-02 |
Family
ID=13659421
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000379589A Expired CA1180301A (en) | 1980-06-12 | 1981-06-11 | Process for separating relatively easily soluble hydrocarbons from a hydrocarbon mixture |
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) |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP4134391B2 (en) * | 1998-04-07 | 2008-08-20 | 日本ゼオン株式会社 | Separation and purification apparatus and method for separation and purification of unsaturated hydrocarbons |
| PL201117B1 (en) * | 2003-10-20 | 2009-03-31 | Polski Koncern Naftowy Orlen S | Method for releasing butadiene |
| US8080140B2 (en) | 2007-04-18 | 2011-12-20 | Exxonmobil Chemical Patents Inc. | Process for debottlenecking a system for the separation of a conjugated diolefin |
| 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
Also Published As
| Publication number | Publication date |
|---|---|
| GB2077753A (en) | 1981-12-23 |
| 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 |
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