US2990437A

US2990437A - Process control system

Info

Publication number: US2990437A
Application number: US816407A
Authority: US
Inventors: Donald E Berger
Original assignee: Phillips Petroleum Co
Current assignee: Phillips Petroleum Co
Priority date: 1959-05-28
Filing date: 1959-05-28
Publication date: 1961-06-27
Anticipated expiration: 1978-06-27

Description

'June 27, 1961 D. E. BERGER PRocEss CONTROL SYSTEM Filed May 28, 1959 United States Patent 2,990,437 PROCESS CONTROL SYSTEM Donald E. Berger, Bartlesville, Okla., assignor to Phillips Petroleum Company, a corporation of Delaware Filed May 28, 1959, Ser. No. 816,407 4 Claims. (Cl. m50-683.43)

This invention relates to an improved method of and apparatus for controlling the separation of fluid mixtures by fractional distillation. In accordance with one aspect, this invention relates to an improved method for separating a feed mixture of organic compounds in a fractionation zone into overhead, bottoms, and intermediate product streams, which comprises regulating the temperature of the feed mixture passed to said zone responsive to the concentration of at least one of overhead and bottoms components in said intermediate stream. In accordance With another aspect, this invention relates to an improved method for fractionating a feed mixture of hydrocarbons into overhead, bottoms, and intermediate product streams, which comprises controlling the temperature of the feed passed to said zone responsive to the total concentration of overhead and bottoms materials in said intermediate stream. In accordance with another aspect, this invention relates to an improved method for separating the euent from a reaction process in a fractionation zone into overhead, bottoms, and intermediate product streams, and wherein said intermediate product is directly recycled to said process, said improvement comprising said zone responsive to the concentration ofl at least one of overhead and bottoms components in said intermediate recycle stream. In accordance with still another aspect, this invention relates to an improved alkylation process wherein said alkylation process hydrocarbon eff y PaentedJane 2319er 2 I ular constituent or constituents. The present invention relates to an improved control system of this` general type.

The demand for large volumes of high quality gasolines has brought about the development and commercialization of a number of processes for the conversion of non-gasoline range hydrocarbons into highI octane blending stocks. One of these processes, the alkylation lof light olelins, such as propylene and butylenes, with isobutane using liquid hydrofluoric acid as the catalyst, has proved to be particularly effective in producing alkylates for aviation and motor fuel blending. As a result of considerable operational experience, this process has'novrr been developed to such an extent that a commercial plant can be controlled by two men per shift to obtain desired product quality with safety. However, a substantial expenditure of laboratory and process engineering time still is required to coordinate the operations and to manipulate the process variables toward the economic optimum. In accordance with the present invention, an improved control system for such an alkylation process and for a fractionation column is provided. This control is based upon analyses of vsample streams removed from the upper, lower and intermediate regions ofv column. The heat and material balances ofthe column are adjusted in response to these analyses so asto proliuent is separated in a conned unitary fractionation zone fraction being directly recycled to said alkylation process,

said improvement comprising regulating the temperature of said eiluent passed to said fractionation zone responsive to the total concentration of overhead and bottoms components in said isobutane stream.

It'is common practice in the petroleum and chemical industries to separate fluid mixtures by means of fractionation columns. These columns are provided with .a plurality of liquid-vapor contacting surfaces, such as bubble trays or packing material. Heat is supplied to the lower region of the column to generate a vapor ow and to vaporize the feed mixture which is introduced into the column. A kettle product stream which is rich in the higher boiling constituents of the feed mixture is removed from the lower region of the column. A vapor stream which is rich in the lighter constituents is removed from the upper region of the column. Ihis vapor stream is partially or completely condensed and a portion of the condensed material normally is returned to the column as reflux. Also, in many operations, an intermediate'fraction or stream is removed at an intermediate portion of of the streamto determine theconcentration of a partic- 'i controlling the temperature of the feed mixture passedto 30 i vide at least three output product streams of desired composition. ,A I

Accordinglyfit is an object of this'invention to'provide an improved method for analyzing and for controlling the separation of uid mixtures'. Another object of this invention is to provide a method of and apparatus for controlling the operations of fractionation columns in response to an analysis of a sample stream removed from the column. A further object of this invention is to pro.- vide an improved control system for an alkylation process. A still further object of this invention is to provide a'control system for a fractionation column which operates to provide three product streams of desired composition. Y

Other aspects, objects, as well as the several advan tages, of this invention are apparent from a study of the disclosure, the drawing and the appended claims. In accordance with a basic concept of the present invention, I provide an improved method for separating a feed mixture of organic compounds which comprises passing said feed mixture to be separated to a fractionation zone, recovering overhead, bottoms, and intermediate product streams from said fractionation zone, ,said improvement comprising regulating the temperature of said feed mixture passed to said zone responsive to the concentration of at least one of overhead and kettle product components in said intermediate stream, said regulated temperature being an optimum feed temperature at which the concentration of impurities in said stream is at a minimum. I .use the term temperature as a measure of the enthalpy or heat content of the feed stream. It is actually the enthalpy of the feed stream that is regulated in accordance with this invention.. Because temperature is easier to measure than enthalpy and is proportional to enthalpy, the temperature of the feed stream is measured and controlled. As I referto the temperature of the feed stream hereafter, I mean the enthalpy of the feed stream as determined by the temperature of said stream. g l

More specifically, in accordance with the presentinvention, an. improved method is provided for separat-1 ing a feed mixture of hydrocarbonsv comprising :norm-al butane, isobutane, alkylate', propane, and .lighter mate`- rials-,into afr'st stream .comprising vpropane andfilighte materials, la .second-'stream comprising normal butan and alkylate and a third stream comprising isobutane,

said improvement comprising directing a stream of such a feed mixture to be separated to a fractionation zone, removing such :a first stream, :second Ystream and third stream from said. zone, Awithdrawing la .sample stream from said third stream, measuring the total concentration ,ofipropa'nefand normal butane insai'dsample stream and .adjusting the temperature Yof -said fractionation zone feed mixture in response'to the measurement `so as to maintainan optimum feed vtemperature Aat which the total concentrationof propane and normal butane in said isobutanestream is at a accordance withl a more specific concept of the present invention, I lprovide an improved method of measuring and controlling the operation of a chemical process, fr'example, the alkylation of oleins and isoparans in the presence of a catalyst which comprises passing the efluet from such a-pro`cessto a single conned unitary Afractionation zone', removing from ysaid fractionation Zone overhead, kettle and intermediate `product streams, fdirectly'recycling said intermediate product stream to said reaction process, analyzing said "intermediate 'prod- 'uct stream to determine the concentration of overhead kettle product components present in said intermediate Istream, and regulatingthe temperature of the feed *passedto said fractionation '.zone responsive to the concentration of voverhead and kettle product vcomponents in said `-rccycle "stream, `said "temperature being an optimum feed temperature at which the concentration of impurities in rthe intermediate product stream is at a In accordance with another concept of the present in- -`vfeiitiorl, I lprovide 'an improved arrangeme'rtof apparatus oan 'alkylation unit comprising a reactor, means to 'supply olet'ns 'and sopar'ains to said reactor, a 'fractionation' column adapted to separate said alkylation unit eiliuent vintotlzueeproduct streams, 'means to pass the reaction-product from` said 'reactor to .said fractionation column, a condenser, areux accumulator, means Vto removeuid'fromrthe top of said column and pass same through-said condens'erto said accumulator, means to .returna portion of theliq'uid in said accumulator to said column a'sreux, meansto remove a`kettle product from the bottom of said column, means to withdraw an intermediate product from an intermediate portionof ,said column torberecycled to said alkylation unit reactor, meansto'measure the overhead product and kettle product -components concentration in said intermediate product stream, and means responsive tof said measuring means adapted to control vthe'temperature of the feed passed Vto Vsaid-column responsive to the concentration of impurities in said intermediate stream. In accordance wit-h the present invention, the relative loading of the Atop and -bottom sections of a combined depropanizer-deisobutanizer column'ina streamlined alkyl-ation plant is controlled b'y manipulating the feed v2,990,437 Y j f Y I;

Y 4 fraction from a refinery. The conditions of temperature,

.pressureand time, as well .as the ratios .of isobutaneto oleln and of hydrocarbon to acid, are Well known in the art. However, the conditions in the alkylator can be as follows: temperature 50 to 15051:., pressure suicient to maintain liquid phase, average 'reaction time of the order of about 1 secondto 11'5 minutes and'rapid agitation to maintainf intimate contact between acid and'hydroca'bon phases. "I'he ratio-of isobutane to alkylating agent or olefin will befabout=6:l to 20:1 by weight, acid to hydrocarbon ratio will be about 2:1 by weight. Any suitable liquid alkylation catalyst which iscapableof .effecting alkylation of the isobutane with the olefin underteonditions -herein described may be employed. Generally speaking, I employ a liquid inorganic acid, such as anhydrous hydroiiuoric acid or concentrated sulfuric acid;

Inorder to further describe the apparatus and method of this invention, reference is made to the attached drawing. The drawing diagramamtically represents an arrangement of apparatus suitable for the practice of this invention. In order that vthis invention may be more clearly understood, -a brief description of an alkylation process will be made. It is to be understood that the flow diagram is diagrammatical and may be altered in many respects by those skilled in the art and, yet, remain Within the scope of my invention.

Referring to the drawing, in detail, there is shown an alkylation reactor or contactor 10 which has an inlet conduit 11 communicating therewith to supply 'liquid hydrofluoric acidfrom acid purication unit 12. ,Ahydrocarbon feed stream is introduced into reactor lthrough 'a conduit 13. A'fresh isobutane `feed stream issupplied to inlet conduit 13 through 'a conduit V14. The :ow

. through conduit '1'4 is regulated byarateof flow contemperature to the column so as to insure a maximum combination column are also controlled lby analyzing-recording controllers.

T-hepresent inventionwill ibeipracticed primarily in connection withian alkylation ofdsobutane with. low boilingrolennfsucheas butyleuesfand/orrpropylene or amyl# The-'olen feedtmay comprise a"butane.butylene l:or fa 'butylenefamyene `lor sbutylene-propylene troller 15 which adjusts a control valve 16.V An'oleiin feedstream, which can be 'a `mixture ot' propylene and butylenes, for example, is supplied to conduit lf3 through a conduit 17. The "flow through conduit 17 is regulated by la rate of flow controller v18 which adjusts a control valve I9. :A recycle isobutane stream, to be moreffully described hereinbelow, is introduced into inlet conduit 13 by way of conduit 20. Recycle isobutane stream 20 is 'regulated by a rate of ow controller 21 which adjusts 'a control valve 22.

The alkylation reaction is completed in reactor I0 by intimately contacting the hydrocarbons with the hydro- -uoric acidcatalyst. The hydroluoric acidhydrocarbon mixture is removed fromreactor 10 through a conduit 23 which communicates with a settler 24. The acid phase insettler 24 is withdrawn through a conduit 73 which Vcommunicates with Van acid purification unit A12. All or a part of this acid is Apurified in puriiication .unit -12 by distilling the acid from water and acid soluble oils. The ratio of acid to hydrocarbon supplied to reactor`-10isv generally controlled at a selected Vlevel between approximately 0.2:1 to 3:1 parts by weight.

'I'fhe hydrocarbon phase,-Which may containsome sol- :uble hydrouoric acid, is removed lfrom settler 24 by -means of conduit 25 whichcommunicates With thevinlet ofgairactionation-column 32 that is operatedfasa combined depropanizer-deisobutanizer column ina streamlined alkylationvplant. The flow through conduitlS is regulated -by liquid level controller 26 on settler 24 which adjusts valve 27. The hydrocarbon phase passed through conduit 25 to column 32 is passed through heat exchanger 428. Afheating medium is circulated through heatfexlchanger 28 by Vmeans lof a conduit 29. The flow of heating material throughconduit 29 Yis regulated by fa temiper-rature recording controller 31 which adjusts a'rvalve 30 -in response to Ya measurement-oat the-temperature ott-he uid entering .column 32. The Set point of temperature recording controller 31 ismanipulated by an optimizing controller to be descri-bed more fullyv hereinafter. The :control system :of thegpresent invention .insures f that;` vthe teedastream supplied fto.co1u.mn. 32 is. maintained,l atswb.-

the optimum alkylate product. The normal butane and alkylate product are withdrawn as kettle product from column 32v through -a conduit 33 by pump 68. A pontion of the kettle product is withdrawn from the system for use elsewhere, not shown, through conduit 34. The rate of.V

`low through conduit 34 is regulated by a flow recording controller 35 which adjusts flow control valve 36. The

set point of ow recording controller 35 is manipulated by liquid level controller 37 on the bottom of column 32. Liquid level controller 37 maintains a constant liquid level in the bottom of column 32.

'Ihe remaining portion of the kettle product removed from column 32 by way of conduit 33 is returned to column 32 by conduit 38, furnace 39 and conduit 40. The ilow .through conduit 38 is regulated by a rate of ow controller 41 which adjusts a control valve 42. Fuel is fed to direct fired reboiler furnace 39 by means of a conduit 43 which is provided with a ow controller 44 that adjusts a valve 45. Flow controller 44 is reset by.`

temperature recording controller 46. Pressure recorder controller `69 maintains an elevated pressure in line 40 by manipulating throttle valve 70. An elevated pressure is desired in line 40 so as to maintain the contents of line 40 largely in the liquid phase. 'Ihis makes it possible to heat the contents of line 40 to a temperature of about 450 F. -in direct red reboiler furnace 39. Thermal deiluorination of the contents of line 40 is thus eifected in furnace 39. That is, organic uoride compounds present in the bottoms product are decomposed to hydrouoric acid and light hydrocarbons. The hydrotluoric acid is later removed as a separated liquid phase from accumu' lator 51 through line 72 and recycled to contactor 10.`

A sample stream is removed from a lower portion of column 32 through a conduit 47 which communicatesA with an isobutane analyzer 4S. Isobutane analyzer-re-- eerder-controller 48 provides an output signalwhich'is In actual operation, it is desired that the kettle productA Analyzercontain a amount of isobutane. recorder-controller 48 provides an output signal which is representative of the isobutane concentration of the lower region of column 32. If the measured isobutane concentration should increase above a preselected value, for example, yanalyzer 48 manipulates the set point of rate of ow controller 41 so as to open Valve 42 further. This increases the ow of kettle product recycled through reboiler furnace 39 thereby adding more heat to the bottom of column 32. This increased addition of heat produces `an'increased flow of vapor upward through column 32 which results in an improved separation of isobutane from "the bottoms product. The isobutane passes up` ward in the vcolumn and is removed at an intermediate point in the column as described hereinafter.

.-. Propane and lighter hydrocarbon components, the hydrofluoric acid liberated by thermal defluorination in reboiler furnace- 39, and the hydrolluoric acid contained in .the feed are removed from the top of column 32 through a conduit 49 which communicates with an accumulator 51 through a condenser 50. The ow through conduit 49 .is controlled by means of a pressure controller 52 which adjustsa control v-alve 53'. 'Ihe etlluent from condenser Sseparates into'a. 'gaseous phase, a liquid hydrocarbon'phase, and -a liquid lhydroiluoric acid .phase in accumulator 51. The small volume of gaseous phase, principally "girl hydrocarbons with some HF, isl removed The densaiitndfilydonidc vacid phrase 'se-mes' Q -the bottom of the accumulator, is withdrawn through conancona? duit 72l and recycled to acid purification unir-:12. fhe.l liquid hydrocarbon phase, principallyv propane with dissolved hydroiluoric acid, -is withdrawn vfrom accumu-l lator 51 through conduit 54 which extendsa few inches'v above` the bottom ofthe accumulator so as to avoid with-Q drawing any liquid hydroluoric acid. A portion. of "the, liquid hydrocarbonsris returned-to lcolumn 322s rellux through conduit 55. The ow through conduit 55 is regut lated by a rate of flow controller 56 which adjusts a vallvefl 57. 'Ilhe remainder of `lthe liquid hydrocarbons. with-1 drawn as product through conduit 58. The owthrough conduit 58 -is regulated by a rate of llow controller 59? which adjusts a control valve 60. Ihe set point of ow recording controller 59 is manipulated by liquid level -conrtroller 61 on accumulator 51.

Asdiscussed above, the operation of column 32 tion of the column.

butane in the sample stream removed through conduit 62 normally is quite small lbecause column 32 is operated j to remove substantially all yof the isobutane at an inter- 'y mediate point in vcolumn 32.v Analyzer recorder'con- .troller 63 provides an output .signal which is representa-1., tive of this concentration. If the isobutane concentra-1" tion should exceed a predetermined value, for example;v the set point of rate of flow .controller 56 is manipulatedf" so asto open valve 57 further to increase the reux rate". 1 This serves to decrease the amount of isobutanein the.. In 'view of the 'above dis-ff cussion, it--should be evident that the two analyzer re--l corder controllers' 48 and 63 cooperate with one anotherfr ina manner so as to accomplish an efficient separation between the various fractions in column 32. Loss ofv iso- -butane in bothtop and bottom products is held 'to a mini'-"' mum by analyzers which control reflux ratio and boil-up` rate. As the feed temperature `is decreased, the loadinfvv the lower portion of the columnis increased at the expenseof the load in the upper portion' of the columniy' This results lfromthe lfact that cool feed condenses somef of the -rising vapors 'at'the feed tray thereby' decreasing" the vapor ow in the upper portion 'of the colurrnn and creasingthe liquid llow in the lower portion..v As Yfeed temperature is increased, the load in the u pperporj tion 'increases relative to the load -in the lower portion., At lowyfeed temperatures the low upper .column .loading, insufficient propane will be `forced out the top .of the column and, hence, will dilute the isobutane recycle.l l stream to an undesirable extent. -At high feed temperatures and low lower column loading, insuflicient normal@ butane will be forced out the bottom-of the column and will` dilute atheisobutane recycle stream. Thus, there:

upperregion of column 32.

exists` an optimumfeed temperature at which the concentration of impurities, fthatis, propane and normal butane, in the isobutane recyclestream is ata In accordance with the present invention, a. sample stream is removed `from recycle isobutane conduit 20 through conduit 64 and passed to analyzer 6 5. Recycle isobutane is withdrawn -from column 32 at an intermediate point of column 32. 'I'he concentration of normal but-aneand propane removed through conduit 20 normal;

.kettle'pr'oduct and'substantially all of the propane in is controlled in accordance with this invention in order to sep- .arate propane and lighter components from isobutane in"JV vthe upper sectionof the column and to separate n-butanel and heavier components fromisobutane in the lower sec- A second sample stream is removed', from the overhead conduit 49 through a conduit 62 which Y," communicates with the inlet .of a second isobutane,` ana-" lyzer recorder controller 63. The concentration of isothe overhead product. Analyzer provides output signals which are representative of the concentration of .p1-'01.A paneand n-butane' in 'recycle isobutane stream in conduit'c.' 20. 'Si-gnals obtained in analyzer 65, representativeof ,the concentration f. both propane. and normal-buien@ in sample stream`v 64, are'passed to an analog adder 66 theteneetn @QnsqlitretlOl-isignalsr@@deteste einen.. e al whiclrd;representsnotal'concentration oli-f1 AV andmorrnal nt n,

d 655311;Y benny coni; h

oissdf) tape essi, aecmlingln.'

mthell.

measures.J thessepanate concentrations .,ofcpropaneand u. butaneinwrecycleisobutane As 'tneanif :2Q ffrenank an` .j intermediate pointin .column 3Q fangpasses vsignalisapro- @heeft forinlbutanqrto analog adder 66. Theanglog addensqrnsH the two signals andsencls a'result/ing-singlesnal, propgr; tional to the total eoncentration'of brnanej an@ n butane, to the ont-roll'er y67.3'I11e optir'nizing oon'trollyer corngares signal *froml 'the analog adder WithNthe preyif ousAsign'aband then adjusts the heat supplied to the vfeed passzecllto column A,32.*- These stepsare repeateduntljtheg: sirgnalfroni analog adder` 66 isa minimum vit Which eondiition the frotionatr ffeedftemperature is optirnuinlV Anal log adder 66 may bea Philbriel' KZX ampliner, ianufa6' tuned by`V George A; Philbrick Researches Inc., ('23O'VCOA1'1'- gress St.' `Boston 10,l Mass. l

TherQuarie Optimal 'Controller is discussed in an arti-j, cle apgearing in Instruments and Automation, November 1956jpagesV 2212-2216: Sinee the details andthe internal OperetQe. of the Quer@ Cottrellef. .de Het forme Part f" tbirlxentientxpt as. Seid cqtlollerfcan ble as Previously derhed. adetailed.. desriptiql. theef'f s". Olmiftiffpm. this. Spqifcatee. However.; as' @destined if! the.. art will. understand 'readme -this dissere. th Quede .controller is. deserbed heringby frieren?? teilie.. Sad .aU-isle, whidar i1; fum., refers t9 Otherattilef nwoteclabve, therQuarie Optimal Controller is acontroller wheheyses ,a .Change in .the .temperature 0f. the-feed we fractionatjng column and, then, compares this ehangezir'i`r the reyl/isobutane impurity conentration with the pre-i viouis .epnentrartvionvand, then, hunts-fj if netjessary,` by. adjnting`the-heatlsupplied to therfeed streamby vway of* flgygrcontrloller 30 until therisobutane impurity concentrafiqnisamigmum 'The .cllange in any one. 0f the process valablest ae- Serilved hereinabove, causes-.communi Qhages in Other.-

.s .variables '111e .instrumfntatOA 0f this.. iQYeD- y ftofrnatiallymaiies the necessary adjustments son thaganoverheadvproduct and a 'bottoms kettleprodut substantially free of isobutene are. continuously recovered fromE the co,1nrn n. Further, an intermediate fraction4 con; ingsslentially isobutaneV is withdrawnfrom an intehediate'portiongof. the column which issubstantialll free,ofoyerhead and bottorns product and recycled. to'y anK ,allqflationv By ntiliningV lthree Aanalyzers,A 3 5.Y di?? sorib d boye, theheat and `rriaterial balances in the `frantipuatingsolumnare controlled within` quite. close The following is a speei example of operation acorcl;`

to. the. present invention, as describedA abovefin eqnnction; `with the .attahed drawing.

EXAMPLE p Ina speeifri; example employing a control arrangement` d'esribedjn .conneetion withj the drawing, alkylationregie-V tQr. liwperatedet7851?: and, at a Sudent Presse@ tomantainaliquid state. The ratio of isobutaneto olefin supplied" to Yreactor 10 based on parts by weight 4.10.120- Hrdwur acid. is emnleyed as fh Catalyst.-

aeid :issuppliedto reactor 1(). at a ratioof 1 to 1 AonY.catalyst'.to hydrocarbon parts by Weight. In 091.1... Stor, lgah barrel 0f Qlnreacte with iLZbHIrFlS" 0f.,i.SP.a1e-.t0.pr9duee 1-7 barrels. of total. alkyletealkylate isy nenioyel from settler 24 and npassedl through cndnit 25.8.1.1@ heater 28 .Where tsheetdff. a temperate@ @t100 t0.. 35.0? Ff and inirduedw lumfn' 52.-` Cqlilmn. 32 iS. Prated at. 300`PfSfi-gl5J30 toptengperature, 350 P. bottomytemperatnrefand, a, reugtoieedratw 1 t0 1i The Comrpsitqnnst #10W- fetes. @mush the SeveralY conduits are fellow:

Table 5,000Y barrels/day.

Clelia @54.0.7

Progylene V- l 1,635 barrelsday Propane 635 barrels/day.l

Table-Continued Fresh isobutane (14) 3,249 barrels/day.

Propane 67 barrels/day. Isobutane 3,1115 barrels/day.

` 'n-Butane 67 barrels/day'.`

Temperature 90 F. Recycle isobutane (20) 29,600"barrels/day;.

l 'Propane 300 barrels/day.

Isobutane 29,000barrels/day. "-n-Butane 300 barrels/day. Temperature 90 'R i Hydrocarbon from settler (25) 37,000 barrels/day. Isobutane 29,000 barrels/day. Propane 1,000 barrels/day. n-Butane 600 barrels/day. Alkylate 5,600 barrels/day. Dissolved HF 800 barrels/day.

Catalyst (11) 37,850 barrels/day.

Wt. percent HF 90%. Temperature 78 F.

Contacter l' Pressure, p.s.i.a. 115. Temperature, F. 95. Isobutane/olefin mol ratio 8.4:1. 'Catalyst/hydrocarbon vol ratio 1:1.

Alkylate (butane free) 5,600 barrels/day.

From the foregoing, it should be evident that there is provided in accordance with this invention an improved control-system for a streamlined alkylation unit whereinthe alkylation unit eluent is-passed directly toa combined depropanizer-deisobutanizer-column.. While the invention has been described-in conjunction with a particular reaction of isobutane with lightv olens, it should be evident that it is not limited to this specific reaction. Also, the fractionation column control system is adaptable to `any system wherein it is desired to separate a uid mixture into three or more product streams of desired composition.

The terms overhead product streams and bottoms product streams referred to herein in the specification and the claims refer to one or more of such streams removed from the fractionation column above and below the feed point and withdrawal point of the intermediate product stream. In connection with the specific embodiment described in the accompanying drawing, butane may be withdrawn at some point between the feed point and the very base of the column, `as well as an alkylate stream Withdrawn from the bottom of the column. Similarly, in the upper region of the column, propane could be withdrawn at some point between the iSobutane withdrawal point and the very top of the column, and lighter materials withdrawn from the top.

Also, as discussed hereinbefore, the feed temperature to a fractionation column is controlled or regulated responsive to the concentration of impurities in an intermediate stream withdrawn from the `fractionation zone. Impurities measured in the intermediate fraction may be either lighter, i.e., lower boiling, overhead materials or higher boiling bottom product materials or the total concentration of both bottom and overhead product materials can be advantageously measured in the intermediate product stream.

Reasonable Variation and modification are possible within the scope of the foregoing disclosure, the drawing and the appended claims to the invention, the essence of which is that there have been provided a method and an apparatus for automatically optimizing a fractionator feed temperature, the method according to the invention comprising passing an effluent stream from a reaction system, such as an alkylation unit, to a fractionation zone, fractionating said eiuent stream into an overhead, bottoms, and an intermediate product stream, recycling said intermediate stream to said reaction system, analyzing said intermediate fraction for concentration of Overv. analyze said intermediate fraction for overhead and bot-` `1o'- head and bottoms impurities present in said intermediate stream, regulating the temperature of the |feed passed to said'fractionation zone responsive to the concentration of contaminants or impurities in said intermediate recycle stream. .and seeking or holding an optimum feed tem-` peratur'e'atk which the concentration of impurities in said recycle stream is at a minimum; the apparatus comprising,in` combination, a reactor, `a fractionation column, means to conduct reactor effluent to said column, overhead vaporwithdrawal meanscondensing means and accumulator means, bottom Withdrawal means, reboiler means and means at an intermediate portion of saidl co1- umn for withdrawing an intermediate fraction, means to 1. In an alkylation process 'wherein an isoparain is reacted with an olein under alkylating conditions to produce an alkylation reaction mixture efduent, the improvement which comprises directly passing said euent as a feed mixture into a unitary confined fractionation zone, withdrawing an overhead product yfrom an upper portion o f said fractionation zone, introducing a portion of said withdrawn overhead product into an upper portion of said fractionation zone, withdrawing a kettle product from a lower portion. of said fractionation zone, introducing heat into `said -lower portion of said fractionation zone, withdrawin'g l.an intermediate product as an .intermediate frac- 35" tionfrom an intermediate portion of said fractionation zone, 'analyzing said overhead product to determine the concentration of said intermediate product in said overhead product, adjusting the rate of ow of reflux into said zone so as to maintain the concentration of said intermediate product yin said overhead product at a minimum, analyzing said kettle product to determine the concentration of said intermediate product in said kettle product, adjusting the rate of ow of kettle product from said zone so Ias to maintain the concentration of said intermediate product therein at la minimum, analyzing said intermediate fraction to determine the concentration of overhead and kettle products in said intermediate fraction, and adjusting the temperature of the fractionation zone feed in response to the analysis of said intermediate fraction so as to tend to maintain the analyzed concentration at a value and hold the fractionation zone feed temperature -at an optimum temperature.

2. A process for separating the euent from an alkylation process consisting essentially of propane, normal butane, isobutane and lalkylate which comprises passing said effluent as a feed mixture intoja unitary confined fractionation zone, withdrawing an overhead product stream comprising propane from an upper portion of said zone, introducing a portion of said withdrawn overhead product stream into an upper portion of said zone, withdrawing a kettle product stream comprising normal butane and alkylate from a lower portion of said zone, withdrawing an intermediate product stream comprising isobutane from an intermediate portion of said zone, adding heat to the lower portion of said zone, analyzing the overhead product stream to determine the concentration of isobutane, adjusting the reflux passed to said zone responsive to said isobutane concentration, `analyzing the kettle product stream to determine the concentration of isobutane, adjusting the ilow of kettle product through a heating zone in the lower portion of said zone, analyzing said intermediate product to determine the concentration of propane and normal butane inmpurities in said intermediate product, comparing said analyzed impurity concentration with an earlier determined impurity concentration, and

1G11- adiusfig Said ffactionatis med-eed @imperante asma; Si lfd smprn S0 as its maintain an', 1 fi11a111ffv` tionat'ion one ed temperature Vat which theconcentn tion of lsaid impurities Kin saidintermediate product islat ahm'm t A. y

3.5i A process forseparating a stream comprising i 1jst,1A second and third components which comprises passing,KVA saidfstr'eam as a feed mixtureinto a unitaryv -fractionation` zone', withdrawing an overhead product stream` comprisingvr second and third componentswhich comprises passing said stream as a feed Irnixtiire into a unitary fractionation zone, withdtawingtan overhead product stream,` comprising .said tirst comporientfrom anupper portionto. said zone, intro- 5 Vducing .a portion of. sadwithdrawn. oilerheadproduct I' st-ream'into-.annp'per portion, of vsaidzone as rreiux,V withdrawing a kettle productY stream ,comprisingsaidsecond componentfrioma llovverportionof said zone, withdraw. ing anintennediate product strearntcompxising saidtthird said' first component` from an upper portion of said zone: z1Q component. frorna'nr intermediate.portion oft, saidczone,

intrrdflcing a portion offsaidwithdrawn'overhead product stream into an vupper portion of said zone as reux, withf drawing `a kettlevproducnstream comprising said'secondY component from a lower lportion rof said Yzone, withdrawaddingheat to, the lowerportion oftsaid zone, analyzing the overhead product stream to determine the concentrationof said third-component therein, adjusting said rreiugr'.v responsive lto, said .third component concentration inv said ingan intermediate product stream comprising said j15 vvoverhead:stream,analyzingthe. kettle product stream to component from an intermediate portion of saidzone,HA adding heat to the lower portion of 'said zonl?, analyzing; they overhead productnstreamlto determine therconjntpa fion offsaid third ,comrsasntfhreia adjusting ,saiarefias detemninemhe concentration of said third component therein, adjustingtheow ofvkettle product through atgheating zone,responsireltov said third component concentration in said tkettleproduct stream, Aanalyzing said intermediate.'

responsive to said third component concentration :29. lproduct to determine theconcentcation of said rst and overhead stream, -analyzingthe kettleproduct strealrrrt p determine the concentration of said third component thsfenadissiing tha QW totY kade/.product throishfa hatilazonetresponsa@ te Said. .tlzlird` wmmnsnt Conesa;

second components .sin .saidintermediate product, and adjusting the temperature of said feed mixture responsvetov4 the analysis of saidlintermediatefraction so as to tend to maintain the analyzed concentration. of said rst and sectration insaid kettle product stream, analyzing saidpint'erf`2gn ond components .thereinat a minimum value.

mediate product to determine the concentrati()1 1v or said* first "and secondycomponents in] said intenmedifateproduoh comparing said analyzed-concentration of jsaiglY second components with an earlier concentration. ofsaidf iirst and ysecond` components and adjustingsaid fractiorrafV '3 0 2,34056995 tion Vzone *feed temperatureresponsive to said` comparison to maintainan optimum fractionation, zone lfeed tentpera-l turev at which the 'c'roncerrtration of said rst andsecond1 comppnents'in said intermediate product is a "4;, A- processvfor separating austrearn comprising qiryst,v3t

References Cited in the le of this patent t UNITEDSTATES PATENTS t lamb et "a1- A Feb. 1, 1944l l 2,342,365 Parker Feb. `22, 1944,; 2546];114. 1 Wilson, Apr. 12, 1943" 2,119,278 Y Gilmore i- June?, 19,55 2,909,335, Miller Aug. 18,- 1959!:

Claims

1. IN AN ALKYLATION PROCESS WHEREIN AN ISOPARAFFIN IS REACTED WITH AN OLEFIN UNDER ALKYLATING CONDITIONS TO PRODUCE AN ALKYLATION REACTION MIXTURE EFFLUENT, THE IMPROVEMENT WHICH COMPRISES DIRECTLY PASSING SAID EFFLUENT AS A FEED MIXTURE INTO A UNITARY CONFINED FRACTIONATION ZONE, WITHDRAWING AN OVERHEAD PRODUCT FROM AN UPPER PORTION OF SAID FRACTIONATION ZONE, INTRODUCING A PORTION OF SAID WITHDRAWN OVERHEAD PRODUCT INTO AN UPPER PORTION OF SAID FRACTIONATION ZONE, WITHDRAWING A KETTLE PRODUCT FROM A LOWER PORTION OF SAID FRACTIONATION ZONE, INTRODUCING HEAT INTO SAID LOWER PORTION OF SAID FRACTIONATION ZONE, WITHDRAWING AN INTERMEDIATE PRODUCT AS AN INTERMEDIATE FRACTION FROM AN INTERMEDIATE PORTION OF SAID FRACTIONATION ZONE, ANALYZING SAID OVERHEAD PRODUCT TO DETERMINE THE CONCENTRATION OF SAID INTERMEDIATE PRODUCT IN SAID OVERHEAD PRODUCT, ADJUSTING THE RATE OF FLOW OF REFLUX INTO SAID ZONE SO AS TO MAINTAIN THE CONCENTRATION OF SAID INTERMEDIATE PRODUCT IN SAID OVERHEAD PRODUCT AT A MINIMUM, ANALYZING SAID KETTLE PRODUCT TO DETERMINE THE CONCENTRATION OF SAID INTERMEDIATE PRODUCT IN SAID KETTLE PRODUCT, ADJUSTING THE RATE OF FLOW OF KETTLE PRODUCT FROM SAID ZONE SO AS TO MAINTAIN THE CONCENTRATION OF SAID INTERMEDIATE PRODUCT THEREIN AT A MINIMUM, ANALYZING SAID INTERMEDIATE FRACTION TO DETERMINE THE CONCENTRATION OF OVERHEAD AND KETTLE PRODUCTS IN SAID INTERMEDIATE FRACTION, AND ADJUSTING THE TEMPERATURE OF THE FRACTIONATION ZONE FEED IN RESPONSE TO THE ANALYSIS OF SAID INTERMEDIATE FRACTION SO AS TO TEND TO MAINTAIN THE ANALYZED CONCENTRATION AT A MINIMUM VALUE AND HOLD THE FRACTIONATION ZONE FEED TEMPERATURE AT AN OPTIMUM TEMPERATURE.