US3584068A - Process for c8 aromatic feed fractionation - Google Patents

Process for c8 aromatic feed fractionation Download PDF

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US3584068A
US3584068A US21627A US3584068DA US3584068A US 3584068 A US3584068 A US 3584068A US 21627 A US21627 A US 21627A US 3584068D A US3584068D A US 3584068DA US 3584068 A US3584068 A US 3584068A
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xylene
feed
zone
fractionation
column
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Steven B Jackson
Roger A Murray
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Fluor Corp
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Fluor Corp
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    • 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
    • C07C5/00—Preparation of hydrocarbons from hydrocarbons containing the same number of carbon atoms
    • C07C5/22—Preparation of hydrocarbons from hydrocarbons containing the same number of carbon atoms by isomerisation
    • C07C5/27—Rearrangement of carbon atoms in the hydrocarbon skeleton
    • C07C5/2702—Catalytic processes not covered by C07C5/2732 - C07C5/31; Catalytic processes covered by both C07C5/2732 and C07C5/277 simultaneously
    • C07C5/2708—Catalytic processes not covered by C07C5/2732 - C07C5/31; Catalytic processes covered by both C07C5/2732 and C07C5/277 simultaneously with crystalline alumino-silicates, e.g. molecular sieves
    • 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

Definitions

  • the feed may be depleted of mxylene prior to fractionation by chemically complexing the m-xylene into a separable form e.g. with HF-BF3.
  • the fractionation zone provides a predominantly ethylbenzene overhead stream, a predominantly o-xylene bottoms stream and a sidestream predominantly of m-xylene and/or p-xylene.
  • the sidestream may be processed to separate p-xylene as a product of the process, and/or to convert unwanted isomers to desired isomers, with such converter eluent being returned directly to the fractionation zone, or to the feed, 'for fractionation in common with the fresh feeds.
  • C8 feeds can 'be heat separated, that is, advantage may be taken of their different boiling points to fractionate the feed, with lower boiling materials e.g. ethylbenzene (B.P. 277 F.) and light ends passing overhead out of a fractionating zone and higher boiling materials e.g. o-xylene (B.P. 291 F.) and heavy ends withdrawn as bottoms from the zone.
  • the m-xylene and pxylene fractions may be withdrawn as overhead or bottoms depending on operation of .the zone. Generally, successive separations are carried out to isolate the different desired products.
  • p-Xylene for example, may be separated from m-xylene in a p-xylene crystallizing plant by freezing the p xylene (F.P. 55 F. and passing the m-xylene (F.P. 54 F.) out of the plant.
  • m-xylene has limited commercial usage, it is often isomerized, or converted, to p-xylene and/or oxylene, either preceding or following fractionation operations.
  • This invention is particularly concerned with a complex :fractionation process having low capital costs and low operating expense by virture of the separation of the ethylbenzene and o-xylene components from the m-xylene and p-xylene fractions ywith the same heat ow.
  • Various preliminary and subsequent operations -to the complex fractionation may be combined therewith to give extremely ilexible Ca processing abilities for maximum advantage in use of available feeds to satisfy product requirements.
  • o-Xylene and heavy ends in the conversion plant eilluent typically are passed with other xylenes to still another fractionator where they are separated from p-xylene as bottoms, the second o-xylene and heavy ends separation in this operation.
  • the p-xylene rich remainder can be returned directly to the crystallization plant .for processing with additional feed from the ethylbenzene fractionator.
  • the m-xylene component is chemically separated from the feed, and optionally converted to additional p-xylene and o-xylene, in advance of fractionation operations, but the fractionation of remaining components is effected in multiple steps with successive heatings and extensive handling of several streams.
  • One of the major objectives of the present invention is to achieve a variety of C8 products with fewer separate heating operations, thus to eliminate substantial capital expense and operating costs. This objective is met by separating one from another with a common heat flow in a fractionation zone, the major desired fractions, ethylbenzene, o-xylene and m-/p-xylene.
  • the present process for fractionating a predominantly C8 aromatic hydrocarbon mixture containing ethylbenzene and xylenes into component fractions which includes feeding a first C8 aromatics stream relatively rich in ethylbenzene into a multilevel fractionation zone at a first feed tray located intermediate the top and bottom of the zone, feeding a second C8 aromatics feed stream relatively rich in o-xylene into the zone at a second feed tray located intermediate the top and bottom of the zone and below the first feed tray, and heating both feed streams with a common heat fiow in said zone, and separating a predominantly ethylbenzene overhead stream, a predominantly o-xylene bottom stream and a xylene isomer sidestream at a level of the zone between the first and second feed trays.
  • the complex fractionation zone may be operated at temperatures between 250 and 500 F., and pressures between 10 and 100 p.s.i.a.
  • the process in certain embodiments includes processing the xylene isomer sidestream to isolate p-xylene therefrom, andprocesing the resulting p-xylene depleted sidestream in a conversion zone to convert m-xylene isomer present therein to other xylene isomers, and returning the conversion zone effluent to the fractionation zone as the second feed stream relatively rich in o-xylene.
  • the conversion zone may be operated to convert m-xylene to o-xylene or p-xylene or both, with the common heat fiow in the fractionation zone being utilized to enable separation of the o-xylene and p-xylene produced in the conversion zone from one another.
  • the process may further include returning separated o-xylene to the conversion zone for conversion into p-xylene, or conversion of p-xylene to oxylene, as dictated by product requirements.
  • the amount of p-xylene isolated from the sidestream is at least equal to the amount of p-xylene present in the predominantly C8 aromatics mixture.
  • the present process further includes heating the predominantly C8 aromatic mixture in a preliminary fractionation zone, and separating the feed into an overhead portion relatively rich in ethylbenzene and a bottoms portion relatively rich in o-xylene, feeding the overhead portion into a multilevel fractionation zone at a first feed tray located intermediate the top and bottom of the zone, feeding the bottoms portion into the multilevel zone at a second feed tray located intermediate the top and bottom of the zone and below the first feed tray, and heating both feed streams with a common heat flow in the lmultilevel fractionation zone, and separating a predominantly ethylbenzene overhead stream, a predominantly oxylene bottom stream and a xylene isomer sidestream at a level of the multilevel zone between the first and second feed trays.
  • the preliminary fractionation typically is carried out at temperatures in the range of 250 and 600 F. and at pressures between 10 and 150 p.s.i.a.
  • the first stream, overhead, from the preliminary fractionation is heated incrementally in the multilevel fractionation zone to separate ethylbenzene and light ends from the p-xylene and m-xylene in the first stream.
  • Heat utilized in the prefractionation is advantageously transferred from the prefractionation zone to the multilevel fractionation zone as may be effected by cycling the preliminary fractionation zone overhead through the fractionation zone above the sidestream draw point or by reboiling hydrocarbons in the multilevel fractionation zone between the feed streams against condensation of the preliminary fractionation zone overhead vapors outside the multilevel fractionation zone.
  • the hydrocarbons for yreboiling may be drawn from the multilevel fractionation zone at or near the level of the sidestream, whereby preliminary fractionation zone heat is utilized in both stripping and rectification operations in the multilevel fractionating zone.
  • the foregoing embodiment of the present process may further include returning the efiiuent from the conversion zone processing of p-xylene depleted sidestream, fwherein m-xylene has been converted into o-xylene and/or pxylene, to the multilevel fractionation zone below the sidestream level.
  • m-Xylene may be depleted from the initial feed to the process in advance of fractionation in other embodiments of the process.
  • the present invention contemplates preliminarily depleting the C8 aromatic hydrocarbon mixture of m-xylene, feeding a m-xylene depleted mixture relatively rich in ethylbenzene into the multilevel fractionation zone as a first feed stream at a first feed tray located intermediate the top and bottom of the zone, feeding a second C8 aromatics feed stream relatively rich in o-xylene into the zone at a second feed tray located intermediate the top and bottom of the zone and below the first feed tray and heating both feed streams with a common heat flow in the multilevel fractionation zone, and seperating a predominantly ethylbenzene overhead stream, a predominantly o-xylene bottom stream and a xylene isomer side-stream at a level of the zone between the first and second feed trays.
  • the m-xylene may be depleted from the feed by chemical
  • the m-xylene initially depleted from the feed mixture may be heated to convert the separated m-xylene to o-xylene and/or p-Xylene, these conversion products then being fed to the multilevel fractionation zone for separation in common with other C8 aromatics in that zone.
  • the initial m-xylene depletion embodiment of the invention is similar to the embodiment described above and may include sidestream processing to isolate p-xylene and return of the p-xylene depleted stream to the multilevel fractionation zone or at least a portion thereof may be combined with fresh feed ahead of the m-xylene depletion zone, isolating at least the amount of p-xylene present in the first feed stream from the sidestream, converting separated o-xylene or isolated p-xylene to p-xylene or o-xylene respectively to be fed to the multilevel fractionation zone e.g. at a point above the sidestream level and also preliminarily fractionating the m-Xylene depleted feed mixture and utilizing the preliminary fractionation heat as described above in the multilevel fractionation zone.
  • the multilevel fractionation zone typically is operated at temperatures between 250 and 500 F. and at pressures between 10 and p.s.i.a., the preliminary fractionation, if any, at temperatures between 250 and 600 F. and pressures between 10 and 150 p.s.i.a.
  • the relatively ethylbenzene rich first feed stream typically may contain from 12 to 25 mol percent ethylbenzene whether derived from an available process stream or from the prefractionation overhead product of a predominantly C8 aromatic feed mixture stream.
  • the relatively o-xylene rich second feed stream may contain from 15 to 30 mol percent o-xylene and generally will contain at least 8 mol percent o-xylene whether derived from available process streams, from prefractionation bottoms, and/ or from converter efiiuent.
  • product quality specifications may require that the various products of the process be purified further to remove unwanted contaminants, which purications are effected by conventional methods not comprising an essential part of this invention.
  • the ethylbenzene is purified by distillation and/ or solvent extraction, the o-Xylene by distillation, and the p-xylene by re-crystallization and/or selective adsorption, generally incorporated within the p-xylene separation unit.
  • FIG. 1 is a schematic ow sheet of one embodiment of the present process
  • FIG. 2 is a schematic flow sheet of an embodiment of the process in which the xylene isomer sidestream is processed to effect p-xylene isomer separation and conversion and return of converter-effluent and/or other isomers to the fractionation zone and depicting ethylbenzene and o-xylene purification operations;
  • FIG. 3 is a schematic iiow sheet of an embodiment of the present process illustrating particularly the feed mixture prefractionation and intermediate reboiling of multilevel fractionation hydrocarbons against condensation of prefractionator overhead vapor;
  • FIG. 4 is a schematic flow sheet of an embodiment of the present process similar to FIG. 3, and particularly depicting another means of heat transfer from prefractionator to multilevel fractionator;
  • FIG. 5 is a schematic flow sheet of an embodiment of the present process generally similar to FIG. 4 and particularly depicting intermediate reboiling of multilevel fractionator hydrocarbons;
  • FIG. 6 is a schematic ow sheet of an embodiment of the present process, generally similar to FIG. 4, without special provision for heat transfer from prefractionator to multilevel fractionator;
  • FIG. 7 is a schematic flow sheet of an embodiment of the present process particularly depicting initial depletion of m-xylene from the feed mixture
  • FIG. 8 is a schematic fiow sheet of an embodiment of the present process generally similar to FIG. 7 with the addition of preliminary fractionation of the m-xylene depleted feed mixture.
  • a feed relatively rich in ethylbenzene such as a fresh reformate fraction from catalytically reformed naphtha
  • feed #1 a feed relatively rich in ethylbenzene
  • the fresh feed may be suitably at a temperature of about 360 F. and may flow directly from a toluene recovery fractionator (not shown).
  • This first feed stream composition may typically be: ethylbenzene 16 mol percent; p-xylene 17 mol percent; m-xylene 42 mol percent; o-xylene 20 mol percent; and other hydrocarbons 5 mol percent.
  • a feed relatively rich in o-xylene such as may be obtained as effluent from a xylene isomerization unit is introduced into the system through line 3 as a second feed stream (Feed #2) to the complex fractionation column 2, suitably at a temperature of about 400 F.
  • the second feed stream composition may typically be ethylbenzene 8 mol percent; p-xylene 21 mol percent; m-xylene 47 mol percent; o-xylene 21 mol percent; and other hydrocarbons 3 mol percent.
  • the complex fractionation zone in FIG. 1 is shown as a multilevel, plural tray column 2 which may alternatively be two or more interconnected sections. (See FIG. 2.)
  • the first feed stream line 1 enters the fractionator column 2 at a first feed tray 4 located intermediate the top and bottom of the column.
  • the second feed stream line 3 enters the fractionator column 2 at a second feed tray 5 also located intermediate the top and bottom of the column but below the first feed tray 4.
  • a multiple or complex fractionation is effected 1n column 2.
  • ethylbenzene and light ends are separated from m-xylene and p-xylene
  • oxylene and heavy ends are separated from m-xylene and p-xylene.
  • these two different separations are effected with a single or common heat flow in the column. 'Ihat is, heat input to the column 2 by passage of column bottoms through reboiler loop 6 having heat exchanger 7 to raise the column bottoms temperature to about 250 F.
  • desired column temperatures which comprises mainly o-xylene with heavy ends
  • o-xylene purification zone 16 wherein heaxy ends are separated through line 17 and the oxylene product is passed out in line 1'8.
  • the column 2 may comprise two or more interconnected sections and be coupled to ethylbenzene and o-xylene purification zone 12, and i16.
  • the column may further be connected to xylene isomer separators and/ or converters.
  • a fiow scheme is shown for processing a feed relatively rich in ethylbenzene, such as Feed #1 in the just described embodiment, introduced in the fractionation zone as the first feed stream.
  • the second feed is obtained from a xylenes converter and is relatively rich in o-xylene.
  • the first feed stream enters the system through line 1 at the complex fractionation zone defined by a multisection, plural tray column 2 having three interconnected sections, a lower section 2a, an intermediate section 2b and an upper section 2c.
  • the first feed line 1 enters the intermediate section 2b at a feed-tray 4.
  • Within section 2b an interior temperature is provided which drives the light ends and ethylbenzene components of the feed upward to be carried from the intermediate section along line 21 to the bottom of upper section 2c.
  • the overhead from intermediate section 2b is further fractionated so that the predominantly ethylbenzene overhead stream, containing the light ends of the feed is taken off overhead and passed into reflux loop ⁇ 8 through condenser 9l and accumulator 10 and into line 11 for separation of the ethylbenzene.
  • the bottoms from upper section 2c are returned along line 22 to the intermediate section 2b.
  • the bottoms in intermediate section 2b, following passage overhead of light ends and ethylbenzene and comprising primarily m-xylene, p-xylene, o-xylene and heavy ends are passed along line 23 from the intermediate section for further fractionation. A portion of these bottoms is taken as a sidestream. along line 24 for processing outside of the fractionation column 2 to isolate the p-xylene in a manner to be described, and the remainder is passed along line 23 to the top of lower section 2a.
  • the sidestream may be taken from any location in the fractionation column 2 below the entry point of first feed stream line 1 into the column (feed tray 4), with accompanying variation in the o-xylene content of the sidestream within the compositional o-xylene limits of the two feeds to the column, for increased fiexibility of product mix.
  • the bottoms are passed continually through reboiler loop 6 and reboiler 7 to maintain section temperature at desired levels.
  • a portion of the bottoms, including o-xylene and heavy ends, is taken off along line 15 out of the fractionation column 2 for separation of o-xylene.
  • the remainder of the lower section 2a feed, comprising primarily m-xylene and p-xylene is passed overhead along line 25 to the bottom of intermediate section 2b.
  • the three sections 2a, b, c are arranged to act as a single column with ethylbenzene and light ends taken out as overhead, o-xylene and heavy ends taken out as bottoms and m-xylene and p-xylene separated as a sidestream.
  • the predominantly ethylbenzene overhead stream in line 11 is conventionally processed in the ethylbenzene purification zone 12 to strip light ends, as necessary, for recovery of the desired purity ethylbenzene.
  • the overhead in line 11 may be processed by extraction or extractive distillation methods, as required when close-boiling non-aromatic contaminants are present.
  • the overhead stream is passed along line 11 to column 26 wherein light ends are distilled overhead to line 27 and partially returned as reux to column 26y through cooling loop 28, including condenser 29 and accumulator 30 and passed to waste or preferably to return to the naphtha reformer or toluene recovery column (not shown) for recovery of toluene or other values.
  • the column 26 bottoms, predominantly ethylbenzene is cycled through reboiler loop 31 having heat exchanger 32 and a portion is passed to line 14 for recovery as a product of the process.
  • the bottoms from fractionation column section 2a in line is conventionally processed in the o-xylene separation zone 16 to separate the o-xylene from the heavy ends.
  • the bottoms stream is passed along line 15 to column 35 wherein o-xylene is distilled overhead for recovery through line 18, as a product of the process, from retluxing loop 37 having condenser 38 and accumulator 39.
  • the heavy ends from the column 35 are taken off as bottoms through reboiler loop 40 having reboiler 41 to line 17, to Waste or further processing.
  • the sidestream taken from the intermediate section 2b of the fractionation column 2 is passed along line 24 to the p-xylene isolation zone.
  • the p-xylene is conventionally isolated from its mixture with m-xylene e.g. by cooling in p-xylene separation zone 42 to crystallize the higher melting p-Xylene component, and separating the p-xylene along line 43.
  • the p-xylene can be selectively adsorbed or otherwise separated in zone 42.
  • the liquid remaining, high in m-xylene is passed through line 44 to the converter 4S.
  • the nonp-xylene isomers may be converted to p-Xylene.
  • the pxylene rich effluent from converter 45 unlike prior processes is not recycled for immediate recovery of p-Xylene, following removal of heavy ends. Rather, the converter effluent is passed along line 3 as the second feed to the fractionation column 2 used to fractionate fresh feed.
  • the line 3 enters the fractionator 2 at feed tray 5 in the lower section 2a and below the sidestream take-out line 23 from intermediate section 2b.
  • the side dra'w line 23 is between the two feed lines, i.e. between line 1 carrying the first feed stream to the fractionation column 2 and line 3 carrying the second feed stream comprising xylenes converter 45 effluent to the same fractionation column.
  • Light ends produced in the converter 45 may be withdrawn in part through line 46.
  • the converter 4S efiluent is fractionated much in the way the first feed stream is fractionated, and importantly with the same heat flow. That is, the p-xylene and o-xylene components are commingled with fresh quantities of these materials and are eventually passed out of the fractionation column 2 with corresponding components from the fresh feed.
  • conversion-produced o-xylene is fed along line 3 to the fractionation column 2 and is separated in that zone with fresh feed originated o-xylene for withdrawal from the column 2 along with heavy ends in line 15.
  • o-xylene needs to be made and both of the high utilities demanding steps, i.e. ethylbenzene separation and o-xylene separation, each from m-xylene and p-xylene, are accomplished with the same heat flow.
  • FIG. 2 A particularly advantageous aspect of the FIG. 2
  • oxylene product separated in column 35 can be returned along line 47 (dotted) to the xylene converter 4S, to be incorporated in the converter feed in line 44 or fed separately to converter 45 if desired, along line 34.
  • Appropriate control of the converter 45 operating conditions, in a known manner, converts the o-xylene at least partially to p-xylene for an increase in p-xylene yield at the expense of o-Xylene.
  • the m-xylene content of the sidestream in line 24 by appropriate control of the converter operating conditions, in a -known manner, may be converted to o-Xylene at least partially, for an increase in o-xylene production.
  • o-xylene greatly more or greatly less o-xylene can be produced than is provided in the feed stock.
  • FIG. 4 Another embodiment of the present process, depicted in FIG. 4 may be employed.
  • a feed mixture having typically the composition given above in connection with FIG. l, is introduced into the system along line 48 to the middle of prefractionation column 49 in which column bottoms are heated by continual circulation through reboiler loop 50 having reboiler ⁇ 51 to temperatures between 250 and 600 F. at pressures in the range of 10 and p.s.i.a., effectively preliminarily fractionating oxylene and some m-xylene and p-xylene in the process feed in line 48.
  • the prefractionator column 49 overhead which is relatively rich in ethylbenzene is passed to line 1 as the first feed to the column 2 at feed tray 4.
  • the prefractionator column 49 bottoms which is relatively rich in o-xylene is passed along line 3 as the second feed stream to the multilevel column 2 to enter the column at feed tray 5 below the first feed tray 4.
  • the first and second feed streams in lines 1 and 3 are subjected to fractionation in column 2, with the ethylbenzene and light ends being separated from m-Xylene and p-xylene in the upper portion of the column and o-xylene and heavy ends being separated from mxylene and p-xylene in the lower portion of the column.
  • the two different separations are effected with a single or common heat flow in the column 2 with heat input by reboiler loop ⁇ 6 serving to enable first separation of oxylene from m-xylene and p-xylene and then separation of ethylbenzene from m-Xylene and p-xylene higher up in the column as the heat travels upward.
  • the overhead and bottoms of the column 2 are taken off as described above in connection with FIG. 1.
  • Heat may be transferred from prefractionator column 49 to the complex fractionation column 2 by cycling prefractionator overhead through the fractionator column.
  • column 49 vapor overhead in line 1 enters column 2 just above the first feed tray 4 and liquid reflux smaller in quantity than the vapor overhead feed exits from column 2 in line 55 from the feed entry level to give a net transfer of overhead product from column 49 to column 2, comprising Feed No. 1 to column 2, and therewith a transfer of heat to column 2 from column 49.
  • Loop 52 is a reflux loop for column 49 and includes combination condenser/reboiler unit 53 and accumulator 54.
  • Loop 56 is an intermediate reboiler loop for column 2 and includes a side draw line 57 passing through the reboiler side of unit 53 back to column 2 above line 57 and below upper feed tray 4.
  • the side draw line 57 is at or near the level of the m-xylene/p-xylene sidestream line 24 so that the heat from preliminary fractionation column 49 overhead is utilizable in both stripping and rectification operations in the upper part of fractionation column 2.
  • the xylene isomer sidestream comprising predominantly m-xylene and p- Xylene is taken off in line 24 and processed to isolate p-xylene therefrom.
  • the sidestream is passed along line 24 to a p-Xylene separation zone 42 which may be a crystallizer as described above in connection with FIG. 2, or other type of separator operating e.g. by selective absorption, complexing, or other technique to isolate pxylene.
  • p-Xylene product is passed out of the separation zone 42 along line 43.
  • Light ends may be removed at least in part from the converter eluent along line 46.
  • Separated o-Xylene can be passed along line 61 to the converter 45 for isomerization into p-xylene as desired.
  • the effluent from converter 45 is recycled to the fractionation column 2 along line 58 to column 2 at a point below the ⁇ sidestream take out line 24.
  • the fractionation column 2 thus has a supplementary feed or Feed #3 relatively rich in p-xylene and/ or o-xylene which is simultaneously fractionated with the #1 and ⁇ #-2 feeds into component fractions with a common heat ow in the column 2 provided by reboiler loop
  • a portion or all of the converter 45 eiuent may be returned along line 59 to the prefractionator column 49 for processing there with fresh feed prior to fractionation in the column 2 or the converter 4S effluent may be passed along line 60 to be combined with Feed #2 (prefractionator bottoms) in line 3 downstream of the prefractionator column.
  • the process feed in line 48 having typically the composition given above in the FIG. 1 embodiment description is prefractionated in column 49 to separate the process feed into an o-xylene rich bottoms stream in line 3 and ethylbenzene rich overhead stream in line 1.
  • Heat input to the column 49 is by reboiler loop 50.
  • the column 49 overhead vapor is condensed on the condenser side of combined condenser-reboiler unit 53 in reflux loop 52 against liquid intermediate level hydrocarbons in intermediate reboiler loop 56 vaporizing the liquid hydrocarbons on the reboiler side of the unit 53 for ret-urn t0 the multilevel fractionation column 2.
  • FIG. 6 an embodiment of the present process, particularly useful Where fuel costs are low, is depicted. In this embodiment specific provision for double utilization of prefractionator heat input is not made which may be acceptable with low fuel costs.
  • the process feed in line 48 is prefractonated in column 49 as in the FIG. 5 embodiment, just described.
  • Reflux loop 64 including condenser 65 and accumulator 66 returns a portion of the condensed overhead to column 49 and a portion is passed along line 1 to column 2 as the first feed stream.
  • the bottoms in column 49 are circulated through reboiler loop 50 and a portion thereof is passed along line 3 to the multilevel fractionation column 2 as the second feed l0 stream. Operation of the multilevel fractionation column 2 and product recovery therefrom is as described in connection with FIG. l above.
  • the process in the further em-bodiments shown in FIGS. 7 and 8 includes a preliminary treatment of the process feed to separate m-xylene and/or isomerize m-xylene to o-Xylene and/or p-xylene for the fractionation operations; in reference to FIGS. 7 and 8, a feed of mixed xylenes and ethylbenzene appropriate for fractionation (and conversion) to produce p-xylene as well as ethylbenzene and o-xylene, as above described, is introduced into the system through line l67.
  • the feed passes to a m-xylene separator and isomerizer 68 in which m-xylene is complexed with a complexing agent.
  • the m-xylene complex may be separated from the balance of the feed, then decomposed and the m-xylene all or in part isomerized to oand/ or p-xylene.
  • the separator and isomerizer 68 is a known unit which contains HF ⁇ -BF3 with which the feed from line 67 is intimately contacted at about 32 to 45 F. which results in essentially all the m-xylene in the feed forming complexes with HFBFB in an HF solution.
  • the m-xylene complex is passed as an HF solution to the isomerizer portion of separator 68 where the complex is heated to a temperature at which it is unstable and decomposes, freeing the m-xylene for recovery as such along line 70, and restoring the HF-BFS complex to its original condition for reuse.
  • the m-Xylene-HF-BF ⁇ 3 complex may be passed as such to the isomerizer portion of separator and isomerizer 68 and at least a portion of the m-xylene component isomerized to oand/or p-xylenes using the HF-BF3 present as a catalyst.
  • the isomerization products are then combined with the m-xylene depleted feed in line 1 to increase the o-xylene and p-xylene content thereof for processing in the fractionation column 2.
  • light ends may be separated at least in part in separator 68 and passed out of the system in line 69.
  • the m-xylene depleted feed is passed to the multilevel fractionation column 2 as a first feed stream to be heated within the column to simultaneously separate ethylbenzene from oand p-xylenes at an upper level of the Zone and p-xylene from o-xylene on a lower level of the column.
  • the use of a single heat ow in accordance with the teaching of this invention to effect these two separations in a m-xylene depleted feed is a departure from previous practice in processing m-Xylene depleted CB feeds.
  • a preliminary fractionation of the m-xyleue depleted feed in line 48 is accomplished as described in connection with FIG. 5 above.
  • the m-xylene depleted feed in line 48 is passed into column 49 and separated into an ethylbenzene rich portion overhead to line 1 and to the fractionation column 2 as the first feed stream and an o-xylene rich portion as bottoms along line 3 to the fractionation column 2 as the second feed stream.
  • the heat flow utilized in the preliminary fractionation of the feed in column 49 derived from heat exchanger 51 is transferred to multilevel fractionation column 2 through the combining condenserreboiler unit 53 in reux loop 52 and intermediate reboiler loop 56 described above, to be combined with the heat flow in multilevel column 2 from reboiler 7 so that the two heat flows are available to facilitate the relatively difficult separation of p-xylene and ethylbenzene, where heat demand is greatest.
  • Pressures within the columns 49 and 2 in the FIGS. 7 and 8 embodiments as in other embodiments herein are not narrowly critical and typically range between 10 and 150 p.s.i.a., but are not limited to this range where economic considerations suggest other pressure levels.
  • C9-H Apparatus may be arranged according to any of the ow sheets FIGS. l through 8, the choice of flow sheet being dependent upon the desired products of the process, the
  • the chosen apparatus may include, in just above tray 20 in column 2 and passed to p-Xylene addition to the complex fractionator, one or more of the separator 42.
  • the p-xylene product is passed along line following: a prefractionator; a p-xylene separation unit; 43 out of the system, and the o-xylene rich remainder of 20 a XylefleS SOmeTiZation Unit With o1" Without mXYene the sidestream 19 is passed from separator 42 back io Separati0r1; an ethylbenzene purication unit; and an 0- multilevel fractionation column 2 along line 58 as supxylene Puflealon unltplementary Feed #3 to the column.
  • a por- EXAMPLE 1 tion or all of the p-xylene separator eluent in line 58 r may be returned along line 72 (dotted) to the isomerizer 2')
  • a process for fractionation and conversion of the above 68 for conversion of excess xylene isomers from one to fnentioned typical feedstock may be eondueed accord' another, or along line 72 and thence along line 73 (dotted) mg t0 the FIG' 2 OW Sheet to obtaln three Pnmafy Prod' to the prefractionation column 49 to enhance overall ucts as follows: recovery of ethylbenzene product, or along lines 72 and 30 h (f1) Ethyllbenze equYalent to lbout 95 of that 1.n 73 and thence along line 74 (dotted) to be combined in t e ee fstgcj M19 0 mlnlmlm plglty o
  • I'f p-xylene product is desired at the expense (2) O Xy'lene equivalent to about 85% of that in .Ehe of o-xylene product, separated o-xylene product 1n lllle feedstock, at 95% minimum purity, containing a maxi- 18 may be returned alongline 75 (dotted) to isomeri'zer 35 mum of 4.0 m01 percent other CSHM material and 1.0 68 for conversion to additional p-xylene product. Simmolpercent heavy ends.
  • the apparatus includes (l) a Separator 42 following Separation of p xylene product multisection complex fractionating column lh avingabout along line 43 is returned to multilevel fractionation col- 1252 theormcal Stags.
  • a portion 45 ower section comprising a column of 70 trays, an intermediate section comprising a column of 150 trays, and an but not au of the P'Xyiene Separator emuent m lm e 3 upper section also comprising a column of 150 trays, havmay be remmef along 1m@ 72 (dott'd) to the lsomenzer ing a reux ratio of 14.0 (fresh feed basis), operable at 68 for Converslon Ofhexss xylene lsomers from .one t0 15.7 p.s.i.a.
  • additional p-xylene product may be and Capable of a heat input of 2-5 MM B-11-/ hour; (3) obtained by returning separated o-xylene product in line an o'xylene Purcation Column having about 35 theo' 18 along line 7S (dotted) to isomerizer 68 for conversion 55 retlcal Stages 55, actual trays a reflux rat10-0f 32 oper' to P Xylene or additional O Xylene p 1 0 duct may be ob able at 15.7 p.s.i.a., and capable of a heat input of 19.4 tained by separation of less than all of the p-xylene in MM B't'l-l/hour; (4) a p-Xylene Separauon umt m Whlch p-xylene is separated by crystallization; and (5) a xylenes Separator Hond retu'fn of .a Pomon of the effluent m isomerization
  • EXAMPLE 2 15 EXAMPLE 3 A process for fractionation of the above mentioned typical feedstock may be conducted according to the FIG. 5 flow sheet to obtain three primary products as follows:
  • the apparatus includes (l) a prefractionation column having about 74 theoretical stages, 100 actual trays, a reux ratio of 5.8 (feed basis), operable at ⁇ 61.1 p.s.i.a.
  • a process for fractionation and conversion of the above mentioned typical feedstock may be conducted according to the FIG. 3 flow sheet to obtain three primary products as follows:
  • the apparatus includes (l) a prefractionation column having about 73 theoretical stages, 105 actual trays, a reflux ratio of 5.7 (feed basis), operable at 50.5 p.s.i.a.
  • the process for fractionating predominantly C8 aromatic hydrocarbon mixtures containing ethylbenzene and xylenes into component fractions that includes feeding a first C8 aromatics stream relatively rich in ethylbenzene into a multilevel fractionation zone at a first feed tray located intermediate the top and bottom of said zone, feeding a second C8 aromatics feed stream relatively rich in o-xylene into said zone at a second feed tray located intermediate the top and bottom of said zone and below said rst feed tray, and heating both feed streams with a common heat ow in the multilevel fractionation zone, and separating a predominantly ethylbenzene overhead stream, a predominantly o-Xylene bottom stream and a xylene isomer sidestream at a level of said zone between said first and second feed trays.
  • the process for fractionating predominantly C8 aromatic hydrocarbon mixtures containing ethylbenzene and xylenes into component fractions that includes feeding a first C8 aromatics stream relatively rich in ethylbenzene into a multilevel fractionation zone at a first feed tray located intermediate the top and bottom of said zone, feeding a second C8 aromatics feed stream relatively rich in o-Xylene into said zone at a second feed tray located intermediate the top and bottom of said zone and below said first feed tray, heating both feed streams with a common heat flow in the multilevel fractionation zone, and separating a predominantly ethylbenzene overhead stream, a predominantly o-xylene bottom stream and a xylene isomer sidestream at a level of said zone between said first and second feed trays, processing said xylene isomer sidestream to isolate p-xylene therefrom, processing the resulting p-xylene depleted sidestream in a conversion zone to convert m-xylene isomer present therein
  • Process according to claim 5 including converting m-xylene to o-xylene in said conversion zone.
  • Process according to claim 5 including converting m-xylene to p-xylene in said conversion zone.
  • Process according to claim S including converting o-xylene to p-xylene in said conversion zone.
  • Process according to claim 5 including converting p-Xylene to o-xylene in said conversion zone.
  • Process according to claim 13 including returning separated o-xylene to the conversion zone for conversion into p-xylene.
  • the process lfor fractionating a predominantly C8 aromatic hydrocarbon mixture containing ethylbenzene and xylenes into component fractions that includes heating said mixture in a preliminary fractionation zone, and separating said mixture into an overhead portion relatively rich in ethylbenzene and a bottom portion relatively rich in o-xylene, feeding said overhead portion into a multilevel fractionation zone at a first feed tray located intermediate the top and bottom of said zone, feeding said bottom portion into said multilevel zone at a second feed tray located intermediate the top and bottom of said zone and below said first feed tray, and heating both feed streams with a common heat ow in the multilevel fractionation zone, and separating a predominantly ethylbenzene overhead stream, a predominantly o-xylene bottom stream and a xylene isomer sidestream at a level of said multilevel zone between said first and second feed trays.
  • Process according to claim 16 including transferring heat from said preliminary fractionation zone to said fractionation zone.
  • Process according to claim 22 including also incrementally heating the first stream in the fractionation zone to separate ethylbenzene and light ends from the pxylene and m-xylene in said first stream.
  • Process according to claim 16 including also reboiling hydrocarbons in the multilevel fractionation zone between the feed streams against condensation of preliminary fractionation zone overhead vapors outside said fractionation zone.
  • Process according to claim 24 including drawing hydrocarbons for reboiling from the fractionation zone at the level of said sidestream, whereby said preliminary fractionation zone heat is utilized in both stripping and rectification operations in the multilevel fractionating zone.
  • Process according to claim 26 including transferring heat from said preliminary fractionation zone to said fractionation zone.
  • Process according to claim 26 including also reboiling hydrocarbons in the multilevel fractionation zone between the feed streams against condensation of preliminary fractionation zone overhead vapors outside said fractionation zone.
  • Process according to claim 33 including drawing hydrocarbons for reboiling from the fractionation zone at the level of said sidestream, whereby said preliminary fractionation zone heat is utilized in both stripping and rectification operations in the multilevel fractionating zone.
  • Process according to claim 26 including converting m-Xylene to o-xylene in said conversion zone.
  • Process according to claim 26 including converting m-xylene to p-xylene in said conversion zone.
  • Process according to claim 26 including converting p-xylene to o-xylene in said conversion zone.
  • Process according to claim 26 including converting o-xylene to p-xylene in the conversion zone.
  • Process according to claim 40 including also returning separated o-Xylene to the conversion zone for conversion into p-xylene.
  • Process according to claim 42 including also chemg ically modifying the m-xylene to a form separable from 20 the first feed stream to facilitate m-xylene depletion therefrom.
  • Process according to claim 42 including also processing said sidestream to isolate p-xylene therefrom and returning the p-xylene depleted stream to said multilevel fractionation zone at a point below said sidestream level, said p-xylene depleted stream comprising all or part of said second feed stream to said fractionation zone.
  • Process according to claim 42 including also processing said sidestream to isolate p-xylene therefrom and returning at least a portion of said p-Xylene depleted stream to the feed ahead of the m-Xylene depleting zone.
  • Process according to claim 42 including also processing said sidestream to isolate p-xylene therefrom and returning a portion of said p-Xylene depleted stream to said multilevel fractionation zone at a point abovel said sidestream level.
  • Process according to claim 42 including also converting m-xylene separated from said mixture in said depleting step to o-xylene and feeding the o-xylene obtained to said multilevel fractionation zone.
  • Process according to claim 42 including also converting m-xylene separated from said mixture in said depleting step to p-xylene and feeding the p-Xylene obtained to said multilevel fractionation zone.
  • Process according to claim 42 including also converting m-xylene separated from said mixture in said depleting step into o-Xylene and p-xylene and in which said common heat fiow in the multilevel fractionation zone is utilized to separate from each other o-Xylene and p-Xylene so produced.
  • Process according to claim 42 including also converting separated o-Xylene to p-xylene and feeding the p-xylene so produced to the multilevel fractionation zone.
  • Process according to claim 49 including also converting isolated p-xylene to o-xylene and feeding the o-xylene so produced to the multilevel fractionation zone.
  • the process for fractionating a predominantly C8 aromatic hydrocarbon mixture containing ethylbenzene and xylene into component fractions that includes chemically separating m-Xylene from the mixture to deplete the feed of m-xylene, heating the m-Xylene depleted mixture in a preliminary fractionation zone, and separating said mixture into an overhead portion relatively rich in ethylbenzene and a bottom portion relatively rich in o-Xylene, feeding said overhead portion into a multilevel fractionation zone as a first feed stream at a first feed tray located intermediate the top and bottom of said zone, feeding said bottom portion into said zone as a second feed stream at a second feed tray located intermediate the top and bottom of said zone and below said first feed tray, heating both feed streams with a common heat flow in the multilevel fractionation zone, and separating a predominantly ethylbenzene overhead stream, a predominantly o-xylene bottom stream and a predominantly pxylene sidestream at a level of said zone between said
  • Process according to claim S8 including also processing said sidestream to isolate p-xylene therefrom and returning at least a portion of the p-xylene depleted stream to said fractionation zone.
  • Process according to claim 58 including also processing said sidestream to isolate p-xylene therefrom and returning at least a portion of the p-xylene depleted stream to said preliminary fractionation zone.
  • Process according to claim 58 including also processing said sidestream to isolate p-xylene therefrom and returning at least a portion of the p-xylene depleted stream to the feed ahead of the m-Xylene depleting zone.
  • Process according to claim 58 including transferring heat from said preliminary fractionation zone to said fractionation zone.
  • Process according to claim 58 including also reboiling the hydrocarbon in the fractionation zone between the feed streams against condensation of preliminary fractionation zone overhead vapors outside said fractionation zone.
  • Process according to claim 70 including drawing hydrocarbons for reboiling from the fractionation zone at the level of said sidestreaim, whereby said preliminary 22 fractionation zone heat is utilized in both stripping and rectification operations in the fractionating zone.
  • Process according to claim 58 including also converting m-xylene separated from said mixture to o-xylene and feeding the o-xylene obtained to said multilevel fractionation zone.
  • Process according to claim 58 including also converting m-xylene separated from said mixture to p-xylene and feeding the p-xylene obtained to said multilevel fractionation zone.
  • Process according to claim S8 including also converting m-xylene separated from said mixture into o-xylene and p-xylene and in which said common heat flow in the multilevel fractionation zone is utilized to separate from each other o-xylene and p xylene so produced.
  • Process according to claim 58 including also converting separated o-xylene to p-xylene and feeding the p-xylene so produced to the multilevel fractionation zone.
  • Process according to claim 65 including also converting isolated p-xylene to o-xylene and feeding the o-xylene so produced to the multilevel fractionation zone.

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Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3700744A (en) * 1970-09-18 1972-10-24 Universal Oil Prod Co Simultaneous recovery and production of pure xylenes from a c aromatic mixture
US20140224637A1 (en) * 2013-02-11 2014-08-14 Gtc Technology Us Llc Method for reducing energy consumption by thermal coupling
WO2015047644A1 (en) 2013-09-27 2015-04-02 Uop Llc Apparatuses and methods for isolating c8 aromatics
WO2015094857A1 (en) * 2013-12-17 2015-06-25 Bp Corporation North America Inc. Enhanced heat recovery in paraxylene plant
US10266462B2 (en) 2014-02-13 2019-04-23 Bp Corporation North America Inc. Energy efficient fractionation process for separating the reactor effluent from TOL/A9+ transalkylation processes
US10647641B2 (en) 2018-07-20 2020-05-12 Scg Chemicals Co., Ltd. Process for the separation of ethylbenzene from other C8 aromatic compounds
US10975006B2 (en) 2018-07-20 2021-04-13 Scg Chemicals Co., Ltd. Integrated processes for para-xylene production

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2121816B (en) * 1982-06-16 1986-08-20 Ici Plc Treatment of hydrocarbon feedstocks

Cited By (15)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3700744A (en) * 1970-09-18 1972-10-24 Universal Oil Prod Co Simultaneous recovery and production of pure xylenes from a c aromatic mixture
US20140224637A1 (en) * 2013-02-11 2014-08-14 Gtc Technology Us Llc Method for reducing energy consumption by thermal coupling
US10035079B2 (en) * 2013-02-11 2018-07-31 Gtc Technology Us Llc Distillation system for reducing energy consumption by thermal coupling
WO2015047644A1 (en) 2013-09-27 2015-04-02 Uop Llc Apparatuses and methods for isolating c8 aromatics
EP3049381A1 (de) * 2013-09-27 2016-08-03 Uop Llc Vorrichtung und verfahren zur isolierung von c8-aromaten
EP3049381A4 (de) * 2013-09-27 2017-05-03 Uop Llc Vorrichtung und verfahren zur isolierung von c8-aromaten
US20160318831A1 (en) * 2013-12-17 2016-11-03 Bp Corporation North America Inc. Enhanced Heat Recovery in Paraxylene Plant
CN105828899A (zh) * 2013-12-17 2016-08-03 Bp北美公司 对二甲苯厂中的加强热回收
WO2015094857A1 (en) * 2013-12-17 2015-06-25 Bp Corporation North America Inc. Enhanced heat recovery in paraxylene plant
US10266460B2 (en) * 2013-12-17 2019-04-23 Bp Corporation North America Inc. Enhanced heat recovery in paraxylene plant
RU2689619C1 (ru) * 2013-12-17 2019-05-28 Бипи Корпорейшен Норт Америка Инк. Улучшенная рекуперация тепла на установке получения параксилола
CN105828899B (zh) * 2013-12-17 2021-09-24 Bp北美公司 对二甲苯厂中的加强热回收
US10266462B2 (en) 2014-02-13 2019-04-23 Bp Corporation North America Inc. Energy efficient fractionation process for separating the reactor effluent from TOL/A9+ transalkylation processes
US10647641B2 (en) 2018-07-20 2020-05-12 Scg Chemicals Co., Ltd. Process for the separation of ethylbenzene from other C8 aromatic compounds
US10975006B2 (en) 2018-07-20 2021-04-13 Scg Chemicals Co., Ltd. Integrated processes for para-xylene production

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NL7103906A (de) 1971-09-27
ES389498A2 (es) 1977-08-01
FR2088254A2 (de) 1972-01-07
IT1008006B (it) 1976-11-10
GB1311606A (en) 1973-03-28
FR2088254B2 (de) 1973-06-08
CA941779A (en) 1974-02-12
BE764671R (fr) 1971-09-23
DE2112004A1 (de) 1971-10-07

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