US3299158A - Production of pure aromatic hydrocarbons - Google Patents

Production of pure aromatic hydrocarbons Download PDF

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US3299158A
US3299158A US396801A US39680164A US3299158A US 3299158 A US3299158 A US 3299158A US 396801 A US396801 A US 396801A US 39680164 A US39680164 A US 39680164A US 3299158 A US3299158 A US 3299158A
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solvent
aromatics
column
aromatic
extract
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Wirth Hans
Eisenlohr Karl-Heinz
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GEA Group AG
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Metallgesellschaft AG
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    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10G—CRACKING HYDROCARBON OILS; PRODUCTION OF LIQUID HYDROCARBON MIXTURES, e.g. BY DESTRUCTIVE HYDROGENATION, OLIGOMERISATION, POLYMERISATION; RECOVERY OF HYDROCARBON OILS FROM OIL-SHALE, OIL-SAND, OR GASES; REFINING MIXTURES MAINLY CONSISTING OF HYDROCARBONS; REFORMING OF NAPHTHA; MINERAL WAXES
    • C10G21/00—Refining of hydrocarbon oils, in the absence of hydrogen, by extraction with selective solvents
    • C10G21/02—Refining of hydrocarbon oils, in the absence of hydrogen, by extraction with selective solvents with two or more solvents, which are introduced or withdrawn separately
    • C10G21/04—Refining of hydrocarbon oils, in the absence of hydrogen, by extraction with selective solvents with two or more solvents, which are introduced or withdrawn separately by introducing simultaneously at least two immiscible solvents counter-current to each other
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C7/00—Purification; Separation; Use of additives
    • C07C7/005—Processes comprising at least two steps in series
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C7/00—Purification; Separation; Use of additives
    • C07C7/10—Purification; Separation; Use of additives by extraction, i.e. purification or separation of liquid hydrocarbons with the aid of liquids
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10G—CRACKING HYDROCARBON OILS; PRODUCTION OF LIQUID HYDROCARBON MIXTURES, e.g. BY DESTRUCTIVE HYDROGENATION, OLIGOMERISATION, POLYMERISATION; RECOVERY OF HYDROCARBON OILS FROM OIL-SHALE, OIL-SAND, OR GASES; REFINING MIXTURES MAINLY CONSISTING OF HYDROCARBONS; REFORMING OF NAPHTHA; MINERAL WAXES
    • C10G21/00—Refining of hydrocarbon oils, in the absence of hydrogen, by extraction with selective solvents
    • C10G21/06—Refining of hydrocarbon oils, in the absence of hydrogen, by extraction with selective solvents characterised by the solvent used
    • C10G21/12—Organic compounds only
    • C10G21/20—Nitrogen-containing compounds

Definitions

  • the present invention relates to a process of producing pure aromatic hydrocarbons from mixtures containing aromatic and paraffinic hydrocarbons employing a selective solvent, a mixture of N-methyl-pyrrolidone and more than water.
  • this invention is directed to obtaining pure aromatic hydrocarbons from hydrocarbon mixtures, especially coke oven benzene, low temperature carbonization benzene, reformates from petroleum prodnets, and cracked benzine resulting from cracking of petroleum fractions, by extraction with a selective solvent consisting of N-methyl-pyrrolidone with more than 10% and as much as up to 40% water, specifically 35% water.
  • the starting hydrocarbon mixture may be purified in a preliminary step, for example, by catalytic hydrorefining in which polyunsaturated hydrocarbons are selectively hydrogenated and may be treated with bleaching earth or other known agents.
  • Pure aromatics as employed herein means aromatic hydrocarbons which are usable as starting materials directly in chemical synthesis and conversions which are sensitive to impurities and also means those which comply with the customary purity requirements for these raw materials.
  • the purity requirements for aromatics differ somewhat from country to country and according to the purpose for which the aromatics are to be used. However, certain minimum requirements or standards exist.
  • Pure C aromatics are frequently not used in the form of single individual components, that is the ortho, meta, and para xylene and ethylbenzene are not separated individually, but rather employed as pure xylene or a C cut.
  • the usual specifications or purity requirements for this pure xylene or C cut originated at a time when the xylene was recovered from coal tar and therefore was by nature free from non-aromatics. Accordingly, the provision of a boiling range of, for example, 135145 C. was suflicient to obtain the then desired purity.
  • the starting mixture containing non-aromatics was not suflicient for work up to the individual components, as, for example, ortho xylene for the production of phthalic anhydride, para xylene for the production of terephthalic acid and ethyl benzene for the production of styrene, since the non-aromatic content could not be reduced to about 0.05 to 0.1%.
  • olefines have been separated from diolefines with good efficiency employing N-methyl pyrrolidone containing 1-15% water, preferably 37% water, as the selective solvent.
  • Lactones, particularly butyrolactone have been suggested for separating aromatics from hydrocarbon mixtures. It is known, for example, to obtain a relatively high concentration of toluene from a toluene-heptane mixture employing butyrolactone having a water content of 25 or to recover a concentrated extract containing up to about 98% aromatics from a light hydroformate by means of butyrolactone having a water content of 10%.
  • the cyclohexane content of benzene may be no higher than 0.2% if the benzene is not to have a melting point below 5.4 C. If the benzene must have a melting point of 55 C, then the cyclohexane content may not even exceed 0.01%.
  • the ratio with the corresponding impurities in toluene and Xylenes is different, but is effected in the same manner.
  • the solvent employed for extraction must therefore be extremely selective with regard to the separation of benzene and cyclohexane in order to obtain an extract substantially completely free of cyclohexane since subsequent separation of benzene through rectification is extremely expensive due to the very close vapor pressures of these two components.
  • a column having 60 theoretical plates and a reflux of 150 times is necessary calculated on removal of the desired compounds as an azeotrope which must be removed in an amount of about 2.5%.
  • the viscosity of the solvent be as low as possible. If the viscosity is too high then the exchange of materials occurring in the extraction column, as, for example, in a column filled with screen bodies, a column having rotating disk contactors, a spray column or the like, is considerably reduced. In order to force this a battery of special mixer-separators is necessary. In such a case separation of the two phases into individual compounds presents practically insurmountable difficulties. Therefore the use of a solvent having a viscosity which is too high must be offset by an increase in temperature which brings with it other difiiculties such as the lowering of selectivity, increasing of decomposition and corrosion processes and the necessity of using pressure resistant apparatus.
  • the one group of solvents which was used with some success heretofore for recovery of an extract suited for further processing to pure aromatics from aromatic rich hydrocarbon mixtures is the lower polyethylene glycols, especially di-, triand tetraethylene glycol. These have suitable selectivity for aromatics and against olefines and naphthenes in order to achieve an adequately pure extract in the usual number of stages.
  • NMP N-methyl-pyrrolidone
  • hydrocarbon mixtures such as olefines and naphthenes
  • the resulting mixture of NMP and water has a selectivity which is at least equivalent to an if desired exceeds that of polyethylene glycols.
  • the viscosity is lower and the absolute chargeability, that is the amount of aromatics able to be dissolved in the solvent mixture of the invention, is higher than that of polyethylene glycols.
  • cyclohexane has a viscosity of 4.2 cs. contrasted to 43.5 cs. for tetraethylene glycol at the same temperature. Therefore with a mixture of NMP and 15% water as the extraction agent, for example, 2.5% cyclohexane can be separated from a mixture containing 25% benzene, 25% toluene, 10% xylene and 40% non-aromatics, that is a cyclohexane content corresponding to 10% of the benzene content, using an extraction apparatus having 22 theoretical plates.
  • a pure benzene that is one having a melting point of at least 5.5 C. corresponding to a purity of at least 99.99% can be obtained from the resulting mixture directly by a simple distillation.
  • This high purity according to the invention is however not obtained by increasing costs or significant reduction of yield because benzene having the above purity can be obtained in yields of 99.5% based on the benzene content of the starting mixture.
  • NMP is not corrosive and is thermally and chemically stable and can be produced on a large scale at a practical price, all the disadvantages of extraction solvents employed heretofore are overcome by the solvent mixture of the invention. Also the essentially higher boiling point of 204 C.
  • the limits of dilution of the NMP according to the invention lie between a water content of over 10% and up to a maximum of 40%.
  • NMP having a water content up to about 10% has the disadvantages of all other known extraction solvents in that, with increased charge in aromatics from a mixture containing non-aromatics the nonaromatics are taken up equally as well as the non-aromatics whereby the charge may be increased in non-aromatics even more strongly in aromatics.
  • NMP with a water content of more than 10% is used as a solvent.
  • the change in the separation into the counterparts occurs initially above a water content of 10%, that is, after exceeding a critical aromatic content of the extract phase decreasing amounts of nonaromatics are absorbed, if the charge of the extract phase with aromatics is increased.
  • the limits of the water content of the solvent and the aromatic content of the extract, where this sudden reversal in absorbing properties occurs depends on several factors, such as the exact composition of the aromatic and non-aromatic constituents in the starting mixture and above all the operating temperature.
  • the selectivity for aromatics over non-aromatics and also over cycloparaffins and olefins increases further by increasing the addition of water while the capacity of the selective mixture according to the invention decreases only slightly.
  • the first strong decrease in capacity or chargeability occurs when the water content exceeds 40%.
  • the critical limits of the water content of selective solvent according to the invention are above and up to 40%, specifically about to 35%.
  • Usable starting mixtures are all hydrocarbons stemming from the purification of solid and volatile combustible materials, especially coke oven benzene and low temperature carbonization benzine, as well as reformates of petroleum products and cracked benzines resulting from cracking of petroleum fractions to produce olefines.
  • the starting material can also be purified in known ways, for example, by catalytic hydrorefining and treated with bleaching earth or other known agents.
  • FIGURE 1 is a schematic diagram of an apparatus suitable for separating aromatic hydrocarbons from a hydrocarbon mixture containing aromatic and non-aromatics;
  • FIGURE 2 is a schematic diagram of an apparatus suitable for separating aromatic hydrocarbons according to the invention wherein an 'antisolvent is employed to increase the selectivity of the solvent mixture;
  • FIGURE 3 is a three component diagram for a mixture of benzene, hexane and N-methyl pyrrolidone containing 25% water at C. showing the results of tests for equilibrium;
  • FIGURE 4 is a graph showing a comparison of known solvents with solvent mixtures according to the invention.
  • the process of the invention comprises feeding the starting hydrocarbon mixture into a multistage extractor, for example, into about the middle of an extraction column, feeding NMP containing more than 10% and up to about 40% water as the selective solvent into one end of the extractor and part of the resulting extract into the other end of the extractor.
  • the rafiinate phase, freed extensively of aromatics, is removed from the extractor at the end into which the selective solvent is fed and the extract phase, practically free of non-aromatics, from the nd into which the extract recycle or the anti-solvent is It is especially advantageous if an anti-solvent is passed through the extractor countercurrent to the fiow of the selective solvent at the same time and an extract recycle is employed since thereby the charge of the solvent with aromatics is shifted in the area in which the absorption capability for non-aromatics surprisingly declines again.
  • the simultaneous use of an anti-solvent and an extract recycle makes is possible to employ both supplemental materials together in smaller amounts than was necessary With each alone.
  • This special feature of the invention permits use of an essentially lower solvent ratio in comparison to other processes and also processing to the highest purity of aromatics under that with other processes.
  • the purest benzene having a melting point of 5.5 C. is recovered according to the invention using a solvent ratio of only 5-7 parts by weight solvent for each part by weight of aromatics contained in the starting mixture.
  • This preferred embodiment of the invention is effected simply by introducing the extract recycle along with the anti-solvent into the extractor at the end from which the extract phase is removed. In this case it is advantageous to strip the extract phase by dis tillation such that the extract results which is practically free of anti-solvent but an anti-solvent is produced still containing essential amounts of extract.
  • Test 1 was carried out using a mixture of by volume benzene and 30% by volume n-hexane while Test 2 was carried out employing a prepared mixture of 92% by volume benzene and 8% by volume n-hexane.
  • NMP containing 25% by volume water served as the selective solvent and was introduced in an amount of 1 part by volume selective solvent, i.e., NMP containing 25 water, to each part.
  • the concentration data is based on the solvent free mixture.
  • Test 1 Composition of the refining phase:
  • the hydrocarbon mixture which was separated consisted of 50% non-aromatics having a boiling range of from 50 to 160 C., 23% benzene, 15% toluene, 18% xylene and 4% higher aromatic substances.
  • the solvent mixture used in the separating process consisted of 78.5% of N-rnethyl-pyrrolidone and 21.5% of water.
  • extraction column 1 has an efiiciency of 20 theoretical stages.
  • the hydrocarbon mixture to be separated was introduced through supply line 2 to a central stage of column 1.
  • the solvent was introduced into column 1 at the upper end thereof through the solvent supply line 3 and was enriched with aromatic substances as it proceeded downwardly through the column. 300 parts of the solvent were added for each 100 parts of starting mixture.
  • the solvent which contained dissolved aromatics free from non-aromatic hydrocarbons was discharged through line 4 at the lower end of column 1.
  • the non-aromatic hydrocarbons were discharged from the top of column 1 umn 8.
  • the aromatics were separated from the solvent by a direct flow of steam which entered the column through line 26.
  • a mixture of aromatics and water vapor was discharged from the stripper column at 9. This mixture was then condensed in the cooler 10 and flowed into the separator 11 within which it was separated into water and an aromatic phase.
  • the resulting aromatic substances which were discharged from the separator 11 through line 11A were taken off at the point 12 and discharged through line 13.
  • the non-aromatic substances which were discharged through line from column 1 contained a small quantity of solvent.
  • This solvent was separated from the nonaromatic substances in column 18 by a flow of steam introduced through line 27.
  • the non-aromatic substances were introduced into column 18 through line 19 and were discharged from the column through line 20, which conveyed them to cooler 21 and separator 22 wherein the substances were separated from water.
  • the non-aromatic substances were then discharged through line 25. Small quantities of water were discharged from separator 22 through line 24.
  • the solvent free from non-aromatic substances was discharged from column 18 through line 23 and recirculated through column 1 together with the solvent withdrawn from column 8 through line 17.
  • Example 2 The same starting mixture as employed in Example 1 was processed in the apparatus as described in FIGURE 2 with a solvent consisting of 85% NMP and 17% water.
  • the apparatus employed in the example consisted of a ZO-stage extractor 31 into which the starting mixture was introduced at one of the central stages through line 32.
  • the solvent comprising NMP and water was introduced through line 33 in the ratio of 360 parts of solvent per 100 parts of star-ting mixture.
  • the solvent was discharged from the column through line 34 together with aromatic substances.
  • a hydrocarbon mixture having a boiling point below 50 C. and comprising primarily pentane was introduced as an anti-solvent into the extractor 31 through line 35.
  • the pentane passed upwardly through column 31 countercurrent to the fiow of NMP and was discharged from the column through line 36 together with non-aromatic substances carried along therewith.
  • the aromatic substances and water were discharged from column 38 through line 40, subsequently condensed in cooler 41 and separated into an aqueous phase and a hydrocarbon phase in separator 42.
  • the required amount of water was introduced into the solvent through line 43 and the remaining water was discharged through line 44.
  • the aromatic substances were then discharged through line 45 into distillation column 46 in the upper part of which pure benzene was obtained at 47.
  • the pure benzene was discharged through line 48.
  • the solvent withdrawn from column 31 still contained small quantities of pentane with which it was in contact in the column.
  • the pentane was distilled in and removed from the top of column 46 through line 49 and recirculated into column 31 through cooler 50 and line 51.
  • the major portion of the anti-solvent was discharged from the extractor column at 36 together with some nonaromatic substances and was passed through line 52 into distillation column 53.
  • the small quantity of NMP which was carried along with these non-aromatic substances was withdrawn from column 53 through line 54 and introduced into the recycled solvent through line 33.
  • the pentane was distilled and removed from column 52 through line 55, condensed in cooler 56 and recirculated through lines 51 and 35.
  • Stripping steam was introduced into the column 38 through line 60.
  • column 53 the substances therein were heated by means of a heater coil 61 within which steam was circulated.
  • the column 46 was similarly indirectly heated by a heater coil 62.
  • the residue resulting from column 46 consisted of toluene, xylene and higher aromatic substances and was discharged therefrom at 63. This residue can be introduced into another system of columns not shown in order to obtain the individual constituents in their pure condition.
  • a process for separating pure aromatic hydrocarbons boiling at about to C. from a starting hydrocarbon mixture consisting essentially of aromatic and non-aromatic hydrocarbons comprising intimately contacting the said hydrocarbon mixture with a selective solvent consisting essentially of N-methyl-pyrrolidone with more than 10% by weight and up to 40% by weight water whereby the aromatic hydrocarbons are dissolved in the selective solvent to form an extract, and passing a mixture consisting essentially of a non-aromatic hydrocarbon anti-solvent boiling below the aromatic hydrocarbons in combination with recycled extracted aromatics countercurrently through the resulting extract and recovering the aromatic hydrocarbons dissolved in the extract in pure form.

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  • Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Oil, Petroleum & Natural Gas (AREA)
  • Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • General Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Water Supply & Treatment (AREA)
  • Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
  • Production Of Liquid Hydrocarbon Mixture For Refining Petroleum (AREA)
US396801A 1960-06-04 1964-09-08 Production of pure aromatic hydrocarbons Expired - Lifetime US3299158A (en)

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Application Number Priority Date Filing Date Title
DEM45554A DE1153738B (de) 1960-06-04 1960-06-04 Verfahren zur Trennung aromatischer von nichtaromatischen Kohlenwasserstoffen durch Extraktion mit N-Methylpyrrolidon enthaltenden Loesungsmitteln

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3434936A (en) * 1966-12-19 1969-03-25 Koppers Gmbh Heinrich Method of separating aromatic compounds from hydrocarbon mixtures containing the same by extractive distillation with an n-substituted morpholine
US3503875A (en) * 1966-12-06 1970-03-31 Doru Grigoriu Solvent extraction of aromatic hydrocarbons with epsilon-caprolactam
FR2485562A1 (fr) * 1980-06-27 1981-12-31 Texaco Development Corp Procede de raffinage de fractions d'huiles lubrifiantes a forte teneur en aromatiques

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE1276615B (de) * 1961-12-23 1968-09-05 Koppers Gmbh Heinrich Verfahren zur Gewinnung von Reinstaromaten
DE1232575B (de) * 1964-03-06 1967-01-19 Basf Ag Verfahren zur Gewinnung von Cyclopentadien

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2799627A (en) * 1953-08-17 1957-07-16 Universal Oil Prod Co Process for obtaining concentrated aromatic hydrocarbons
US2840620A (en) * 1954-07-12 1958-06-24 Universal Oil Prod Co Segregation and recovery of naphthenic hydrocarbon concentrates
GB812114A (en) * 1956-11-08 1959-04-15 Esso Engineering And Res Compa Solvent extraction process
US2886610A (en) * 1954-04-28 1959-05-12 American Oil Co Solvent recovery system
US2933448A (en) * 1954-12-06 1960-04-19 Ohio Oil Company Separation of aromatic hydrocarbons from non-aromatic hydrocarbons utilizing a lactam-water solvent

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2799627A (en) * 1953-08-17 1957-07-16 Universal Oil Prod Co Process for obtaining concentrated aromatic hydrocarbons
US2886610A (en) * 1954-04-28 1959-05-12 American Oil Co Solvent recovery system
US2840620A (en) * 1954-07-12 1958-06-24 Universal Oil Prod Co Segregation and recovery of naphthenic hydrocarbon concentrates
US2933448A (en) * 1954-12-06 1960-04-19 Ohio Oil Company Separation of aromatic hydrocarbons from non-aromatic hydrocarbons utilizing a lactam-water solvent
GB812114A (en) * 1956-11-08 1959-04-15 Esso Engineering And Res Compa Solvent extraction process

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3503875A (en) * 1966-12-06 1970-03-31 Doru Grigoriu Solvent extraction of aromatic hydrocarbons with epsilon-caprolactam
US3434936A (en) * 1966-12-19 1969-03-25 Koppers Gmbh Heinrich Method of separating aromatic compounds from hydrocarbon mixtures containing the same by extractive distillation with an n-substituted morpholine
FR2485562A1 (fr) * 1980-06-27 1981-12-31 Texaco Development Corp Procede de raffinage de fractions d'huiles lubrifiantes a forte teneur en aromatiques
US4333824A (en) * 1980-06-27 1982-06-08 Texaco Inc. Refining highly aromatic lube oil stocks

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GB958898A (en) 1964-05-27
DK108970C (da) 1968-03-04
DE1153738B (de) 1963-09-05

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