US2389604A

US2389604A - Temperature control for hydrocarbon oil processing

Info

Publication number: US2389604A
Application number: US529075A
Authority: US
Inventors: Leonard F Dowding
Original assignee: Texaco Inc
Current assignee: Texaco Inc
Priority date: 1944-04-01
Filing date: 1944-04-01
Publication date: 1945-11-27
Anticipated expiration: 1962-11-27

Description

Nov. 27, 1945. L F. DOWDING TEMPERATURE CONTROL FOR HYDROCARBON OIL PROCESSING Filed April' l, 1944 3 Sheets-Sheet 1 Nov' 27, L.. F. DOWING TEMPERATURE CONTROL FOR HYDROCARBON OIL PROCESSING Filed April l, 1944 3 Sheets-Sheet 2 @TLV Nov. 2.7, 1945 L F. DowDlNG TEMPERATURE CONTROL B OR HYDROCARBON OI'L PROCESSING 3 Sheets-Sheet 3 Filed April l, 1944 a liqueiled normally gaseous Patented Nov. 27, 1945 TEMPERATURE CONTROL FOR HYDRO- CARBON OIL PROCESSING l 4Leonard F. Dowding, Eastchesgter, N.

Y., assigner to The TexasCompany, New York, N. Y., a corporation of Delaware Application April l, 1944, Serial No. 529,075

18 Claims.

This invention relates to hydrocarbon oil processing, and more particularly to temperature control for such processing by indirect heat exchange with a liquefied normally gaseous hydrocarbon refrigerant obtained from the hydrocarbon oil stabilizing and fractionating system. The invention is particularly applicable to alkylation units and combination alkylation-isomerization units for the manufacture of motor fuel or aviation gasoline, and wherein propane or other liquefied normally gaseous hydrocarbon obtained from the alkylate fractionating system is utilized as the refrigerant for temperature 'control in the alkylation or combination alkylation-isomerization units;

In the modern reilnery, one or more alkylation units are generally provided for the purpose of converting refinery gases or other hydrocarbon products into high octane motor fuel or aviation gasoline by isoparailin-olen alkylation. Also, such an alkylation unit may be combined with an isomerization unit, the latter furnishing the low-boiling isoparailin, such as isobutane, to the alkylation unit. Temperature control for the alkylation unit, and also for certain operations in the isomerization unit, is generally accomplished by indirect heat exchange with a suitable refrigerant. The latter is recirculated from a refrigerating unit to the heat exchange chiller and back again through repeated stages of compression and cooling for liquefaction and indirect heat exchange for vaporization. A very satisfactory and economical sourceof refrigerant is hydrocarbon, such as propane, obtained directly from the refinery, such as from the alkylate stabilizing and fractionating system. For example, refrigerant propane makeup to the refrigeration unit may be obtained from the overhead condensate of the depropanizer tower, which latter is a part of the stabilizing and fractionating system of the alkylation unit or combination alkylation-isomerization unit.

During continued recirculation in the refrigeration unit and chillers, the refrigerant propane frequently becomes contaminated with heavier normally liquid impurities which accumulate and remain in the einher side of the refrigeration unit. The liqueed propane refrigerant is partially vaporized in the chilling coils by indirect heat exchange with the hydrocarbon oil being processed, and the resulting propane vapors are passed to the refrigerating unit where they are compressed in propanel compressors and then cooled by indirect heat exchange with cooling water. The compressors are conventionally supplied with lubricating oil on the interior of the compressor cylinder for lubrication of the piston movement therein. A small proportion of this lubricating oil may become entrained in the compressed propane and carried out of the compressor cylinder therewith to the propane condenser and thence to a liquefied propane receiver. 'I'he refrigerant so contaminated is then returned to the cooling coils by way of a propane accumulator. Since this lubricating oil is higher boiling than the propane, it is not evaporated and returned with the propane vapors to the refrigerating unit, but remains in the propane accumulator and chiller.

In addition to this lubricating oil contaminav tion, the propane refrigerant may also become contaminated with other liquid impurities, such as water, and also acid and liquid hydrocarbons resulting from leakage of the hydrocarbon-acid emulsion into the propane chiller at the alkylationvunit, or similar leakage in the chiller at the isomerization unit. The resulting build-up of such liquid impurities in the liquefied propane on the chiller side of the refrigerating unit during long periods of continuous operation eventually may seriously impair or entirely stop the proper flow of propane through the chilling coils and refrigerant ow passages. The resulting decrease in refrigerating effect disturbs the temperature control and deleteriously affects the alkylation or other operations.

One of the principal objects of the present invention is to 'overcome the above-noted defects and provide an improved temperature control for hydrocarbon oil processing, wherein the liquefied normally gaseous hydrocarbon refrigerant is maintained throughout long periods of continu-v ous operation substantially free from such normally liquid contamination, and high refrigerating elciency and effective temperature control are thereby secured.

Another object of the present invention is to provide. in combination with an isoparamolefin alkylation unit for the manufacture of motor fuel or aviation gasoline, an improved propane or other liquefied normally gaseous hydrocarbon refrigerating system, wherein the makeup propane or other liquefied normally gaseous hydrocarbon for the refrigerating system is obtained from the stabilizing and fractionating system of the alkylation unit, and wherein the liquefied propane in the refrigeratin system is maintained in a puriiied condition by recirculation and purification of a portion thereof in the Y fied normally gaseous ma alkylatembmzlng and fmuonaung 'm- Still another object of the present invention is to provide. in combination unit employing an acid catalyst and unit. A further object of the present invention is to provide, in a combined l unit, improved propane refrigeration for either or Vboth of the alkylation and i'somerization treatments, and wherein the liqueed propane refrigerant is maintained in a; purified condition by treatment o f a portion thereof in the neutralizing and fractionating system of the combined alkylation-isomerization' unit.

Still another object of the present invention is to provide an improvedpropane or other liquesystem especially adapted for use in a refinery or other source of supply of the hydrocarbon refrigerant, and wherein the liquefied refrigerant is maintained free from liquid contamination over long periods of operation by cyclic recirculation and purication treatment.

Other objects and advantages of the invention will be apparent from the following description when taken in commotion with the appended claims and the several -figures of the attached drawings.

The present invention is more particularly illustrated by way of preferred embodiments thereof in the drawings, in which Figure 1 is a diagrammatic elevational view, with certain parts in section, of an isoparafiinoleiin alkylation unit with associated refrigerating system constructed in accordance with the present invention;l 4 Figure 2 is a diagrammatic elevational view similar to Figure 1 of a modification, showing a different order of alkylate stabilization and fractionation; and

Figure 3 is a diagrammatic elevational view of a combined alkylation-isomerization unit, `showing -a plurality of propane accumulators and chillers connected to a single refrigeration unit, and having provisions for continuous purification of the liquefied propane from any or all of the accumulators in accordance with the method of the present invention.

While the invention is speciiicaily described as applied to an alkylation unit or a combination alkylation-isomerization unit, it is to be understood that this is merely by way of example and not by way of limitation. Thek improved refrigerating system of the present invention can be utilized for indirect heat exchange with or chilling of any treating or processing operation where temperature control, particularly the maintenance of relatively low temperatures. is found desirable. Thus, the invention may be applied to low-temperature short-contact-time hydrocarbon oil acid-treating, or to other cat- 'alytic hydrocarbon conversion processes, such as aromatic-olefin alkylation, naphthene-olen alkylation, normal paraihn-olen hydrogen exchange reactions, and other hydrocarbon synthesis reactions. It is to be understood that' in these various applications, the

alkylation-isomerization hydrocarbon refrigerating assacoc alkylation, naphthafor other normal paraffin isomerization,

acid, is introduced vizer 21 by line 32 Aby line 32e.'

propaneorotherliqueednormally gaseoushydrocarbon refrigerant withdrawn from the refrigerating unit will be purified by mixing with a broad boiling range oil. and the mixture then passed to the stabilizing and fractionating system supplying makeup propane orl other liquefied hydrocarbon .to the refrileratinl unit, v Also, treatment foi-,the prevention of corrosion and fouling in the system, vsuoli as caustic or other alkaline neutralization and water washing, can be given the withdrawn refrigerant in advance' of the stabilizing and fracticnating treatment Referring-to Figure 1, an alkylation contactar of theimpeller internal-recirculation type. such as' a Stratcc reactor, is diagrammatically indicated at il. This is equipped with a motor Il driving an impeller of the reactor to circulate upwardly through the annular chamber between the outer casing and an inner shell i3, and thence return downwardly through the central passage to the impeller. Fresh feed isobutane is introduced by line Il and is mixed with an olefin feed stock from line II, the resulting mixture having a molar excess of isobutane to oleiin passing by line l0 into the contactor'. IMakeup acid, such as strong sulfuric v by line It to supply the required alkylation catalyst which forms an emulsion with the hydrocarbons in the contactor that -is internally recirculated in conventional manner.

A stream of the emulsion is continuously withdrawn by line I9 to a settler 2li where an upper hydrocarbon phase settles from a lower acid phase. Acid is continuously removed from the lower acid layer by line 2i; and all or any portion thereof may be recycled line 22 containing pump 23 and line I8, the balance being discharged to recovery by line 2l.

The hydrocarbon phase of settler 20 is continuously withdrawn by line 25 and introduced together with. caustic soda from line 28 into a neutralizer 21. The neutralized hydrocarbons separate as an upper layer from a lower aqueous caustic layer which is withdrawn by line 2l. Any portion of the withdrawn caustic soda stream may be recirculated by line 29 containing pump 30 and line 26 for the treatment of furtherquantities of hydrocarbons, the balance being discharged by line 3l. A stream of the neutralized hydrocarbon layer lis withdrawn from neutraland passed to a water wash and surge drum 33. Any remaining caustic and water soluble reaction products are removed from the hydrocarbon oil at this point by introducing water from line 32a into line 32 through a suitable mixer. The mixture then passes into the surge drum 33, where the hydrocarbon oil stratiiles as an upper layer from a lower water layer which is removed by bottom line 32h. A portion of the water may be recircuiated by pump 32e and line 32a, the balance being discharged byy line 32d. Fresh makeup water is introduced v From the surge drum 33, a stream of the hydrocarbons is withdrawn by line Il which extends -upwardly'from the bottoni of the drum into the hydrocarbon layer. Line 34 serves to introduce the hydrocarbons into a stabilizing tower I5 customarily termed a product debutanizer. This tower 35 is operated under conditions to stabilize the resulting alkylate, removing overhead by line lnormal-butane and lighter. The stabilized alkylate is passed by bottom line 31 to a nal i2 which forces the contents to the reactor byk fractionator 38, where the desired aviation or motor fuel fraction isremoved overhead by line 39,

and any heavier material, termed alkylate bottoms, is removed by line 40. The overhead gases from the product debutanizer, which in the case of C4 alkylate consist largely of normal butane,

the excess isobutane and some propane, are introduced by line 36 into ay deisobutanizer v4|,

i pane stream is removed overhead by line 44. The bottoms from this tower consisting essentially of isobutane are withdrawn by line 45 and recycled to the alkylation contactor by way of lines I4 Aand I6. The overhead propane vapors are condensed in a water-cooled condenser 46 and passed to an accumulator 41. Any uncondensed -vapors may be removed from accumulator 41 by vapor relief line 48. A minor proportion of the liquefled propane from accumulator 41 is passed by line 49 to the refrigerating unit indicated generally Aat and to be hereinafter more specifically described. The major proportion of the condensate propane is returned by line 50 and pump 56a to the upper portion of tower 43 to serve as reflux therein. Any excess propane not required for refrigeration or reux may be passed by line 52 to tankage or other suitable disposal.

As shown, alkylation contacter I0 is equipped with a chilling tube bundle 54 mounted on the upper head of the contactor with the chilling tubes depending into the circulating emulsion stream within the reactor. Liquefled propane is supplied from a propane accumulator 55 through line 56 to a header 51, from which the propane passes into a Yplurality of the tubes of the bank in parallel. The propane flows downwardly ample, about one-fth of the propane owing by line 56 to the chilling bundle may be vaporized in each pass by heat exchange in -the chilling tubes, the remaining four-fths of the liquefied propane returning in liquid state together with the resulting dispersed vapors by line 59 to the accumulator. The baiiies 60 provide for separation between the liquefied and vaporized propane,

the vapor accumulating in the vapor. space and' being withdrawn by compressor suction through Y line 62 to the refrigerating unit.

Anyconventional type of rerfigerating unit of the compressor-condenser type can be employed. As shown, line 62 discharges into a suction trap 1|) designed to eiect a separation of any entrained liquid propane from the vapors, so that liquid does not enter the compressor cylinders. The vapors are withdrawn from the suction trap 10 by line 1| to the compressor 12, which forces the compressed vapors through line 13 to watercooled condensers indicated at 14. The resulting liquid propane then flows by line 15 into a -propane receiver 16. Any liquid propane separated in suction trap 10 may be passed by line 11 and transfer .pump 18 to the receiver 16. From the latter, liquefied propane is withdrawn by depending line 19, which communicates with line 63 for return of liquid propane to accumulator 55 in accordance with the liquid level control.

As previously described, propane refrigerant for the refrigerating unit is obtained from the overhead condensate of depropanizer tower 43 of the alkylate stabilizing and fractionating system. In order to remove any SO2 which is sometimes found in this overhead, the propane makeupY from line 49 may be treated with caustic soda ina small vessel 80, the caustic soda being recirculated by means of a suitable eductor. The caustic soda is settled Afrom the liquid propane and the latter may then be passed through a drier containing flake calcium chloride or unslaked lime to remove water. The makeup propane, free from SO2 and water, passes by line 82 to a f storage drum 83, from which it is withdrawn as through these tubes which open at their lower ends into surrounding return tubes providing a double tube type of chiller, the outer tubes serving to return the propane to header 58. During its passage through the chilling tube's, the liquefied propane is heated by indirect heat exchange with the recirculating emulsion, with the result that a portion of the propane is vaporized during its flow through the outerreturn tubes. The mixed propane liquid and vapor returns from header 58 by line 59 to accumulator 55,'being discharged against suitable rliquid entrainment baffles 60 designed to effect a separation between liquid and vapor. The resulting propane vapors are released from accumulator 55 by vapor line 62 and passed to the refrigerating unit 5|. Liqueedpropane is returned'from the refrigerating unit through linev 63 under the control of valve 64 to accumulator 55. kA liquid level controller 6,5 of conventional type and equipped with fluid line 66 serves to actuate valve 64 to maintain a constant'` level' of liquid propane within accumulator '55, asindicated 'at l61,

It is thus seen that a thermo-siphonic circula- "tion of liqueed propane is*v set up betweenthe* propane and accumulator 55 Iand the chilling tube bundle 54",v and." in which a. substantial part oi vlthe propane` `"remains,` virlliquid state. For exneeded by line 84 and transfer pump 18 and passed to the propane receiver 16.

In accordance with the present invention, a

stream of liquid propane is withdrawn from ac- I cumulator by bleed line 86. This stream may be passed by line 81 controlled by valve 88 to -line 25, where the propane is mixed with the hydrocarbon oil steam passing from settler 2|] to neutralizer 21. Or the propane can be passed by line 89 controlled by valve 90 to line 32, where it is mixed with the hydrocarbon oil stream flowing from neutralizar 21 to surge drum 33 in advance ofthe Water wash line 32a. The rate of withdrawal of propane is conveniently controlled by a, throttle valve 9| which is regulated in accordance with an indicating flow meter V92. Generally, the bleeding ou of only a small proportion of the liquefied propane in the refrigerating system is sufficient to maintain the liquid propane in the system effectively free from the contaminating impurities. The withdrawal of propane from the refrigeration systemV is preferably continuous and at auniform rate as controllen by the throme vaiveal: although `the will be closed and valve 88opened`, so thatthe propane bleed stream passes by line 31 to be mixed with the unstabilized alkylate in advance of the neutralizer. 4The mixing of the propane stream with the hydrocarbon oil in either line 25 or line 32 results in the absorption of the propane 5 in the heavier hydrocarbon oil, thereby facilitating the purification treatment and enabling the use of lower pressures, and higher temperatures, thereby avoiding difiiculties which would be involved in the treatment of the volatile propane at the high pressures or low temperatures other-f wise required. Both the neutralizer 21 and the surge drum 33 of the-alkylation unitare operated at lower pressures than the propane accumulator 55, the pressure differential being used to transfer the propane bleed under the control of the throttle valve 9|. The mixed propane and unstabilized alkylate from line 25 are then subjected to the neutralizing action of the caustic solution from line 26 in neutralizer 21, whereby 20 retained acid is removed from both the alkylate and the propane bleed stream. The mixed alkylate and absorbed propane then passes to the water wash and surge drum 33 and thence to the alkylate fractionating system. 25

Where acid contamination is not involved, and the only liquid impurities are heavier hydrocarbons and water, valve 88 will be closed and valve 90 opened so that the propane bleed stream iiows by line 89 and is mixed with the hydro- 30 carbon oil stream in line 32 following the neutralization of the latter. Here again the propane bleed stream is preferably introduced into the flowing hydrocarbon oil stream to obtain the desired turbulent mixing and absorption effects.

In neither case, the resultant mixture from surge drum 33 passes to the product debutanizer 35 where the propane is removed overhead along with isobutane and normal, butane, and thereby separated from heavier liquid impurities, such as lubricating oil and water. The latter remain in the stabilized alkylate which passes by line 31 to the final fractionator 3B. The lubricating oil will of course remain in the alkylate bottoms withdrawn by line 40; and these bottoms can be 45 subsequently fractionated if desired to separate a heavier motor fuel fraction from the lubricating oil and any other heavier material'contained therein. Any water will pass overhead from fractionator 38 along with the aviation alkylate, 50

which is led by line 39 to a suitable condenser and accumulator. The water will then separate out as a lower layer in the accumulator and may be Withdrawn from the system.

The overhead propane and other gases from product debutanizer 35 pass by line 35 to the deisobutanizer 4|, from where isobutaneand propane pass overhead by line 42 to depropanizer 43. In the latter tower, the propane, including that introduced by propane bleed line 86 and that 60 present in the alkylation feed stock from lines |4 and I5, will be separated by overhead line 44 from the isobutane which is recycled to the alkylation unit by line 45. A purified propane condensate, free from heavier liquid impurities, is thereby returned from accumulator 41 by line 49 to the refrigerating unit 5|. This return may be by pressure differential between accumulator 41 and stocks required to keep the propane tanks Il and 16properly supplied with the refrigerant.

The alkylate fractionating system described above is that customarily employed when alkylating isobutane with an oletinic charge stock, such as a .'renery C4 cracking gas fraction. It is to be understood that the present invention is applicable to the alkylation of other low-boiling isoparafnn, such as isopentane, with any olefin, either normally gaseous or normally liquid, or other alkylating agent, such as an alkyl ester, alcohol or ether. Suitable provisions are made in the alkylate fractionating system to separate the propane or other normally gaseous hydrocarbon refrigerant from the alkylate and from the isoparaftin recycle to the alkylation unit. While sulfuric acid has been specifically described above as the alkylation catalyst, it is to be understood that any other suitable alkylation catalyst may be employed, such as hydrofluoric acid, boron trifiuoride-water complex, aluminum chloride-hydrocarbon complex preferably with a small proportion of HC1, and the like. Moreover, any suitable contacter can be employed for the alkylation in place of the Stratco reactor, such as a pump and time tank reactorVjet reactor, tower reactor, and the like. Moreover, the .alkylate fractionating system can be modified from that shown in Figure l.

This 'is illustrated more particularly in Figure 2 which discloses an alkylation reactor of the pump and time tank type and a fractlonating system of the so-called reverse iiow type. As shown in this figure, a mixed stream of isoparaflln and olen is introduced by line into the suction side of a centrifugal pump 96 where it is mixed with a recirculating emulsion stream from line 91, the mixture being passed by line 98 through cooling coils 99'in a chiller |00'. The resulting cooled emulsion then passes by line |0| to a battled time tank |02 from which a stream of the emulsion is withdrawn by line |03. The latter stream is divided, the major portion being recirculated by line 91 and a minor portion being passed by line |04 to'settler 20'.

Refrigerant propane is supplied from accumulator 55 by line 56 to the jacket of chiller |00 surrounding the coils 99, the mixed propane liquid and vapors being 'returned by line 59 to accumulator 55'. Except as described herein, the construction ofthe other elements in Figure 2 is the same'as that heretofore described in connection with Figure 1, and similar primed reference numerals are used to designate these corresponding parts. Propane bleed from accumulator 55 is passed byline 86' arid either lines 81 or, 89' to mix with the unstabilized alkylate, either in advance of the neutralizer 21' or following the neutralizer and immediately in advance of the Water wash and surge drum 33'.

In this case, `the hydrocarbon stream from surge drum 33 passes by line |06 to a product deisobutanizer |01 which is operated to remove overhead by line |08 isobutane and lighter. The bottoms from tower |01 pass by line |09 to a product debutanizer ||0, where .the desired stabilization of the alkylatev is accomplished by removing normal butane overhead by line 'Ihe stabilized alkylate then passes by line ||2 to a final fractionator I3, where the aviation alkylate is removed overhead by ||4 and the alkylate bottoms are discharged by H5. The overhead stream from deisobutanizer |01 passes by line |08 to a depropanizer III, from vwhich a bottom recycle stream of isobutane is removed by line m.- 'rna u preferably mired lwith recycle acid from bottom line ||8 of settler 2l' in advance of the additionof any makeup acid .by line ||9. and the Vmixture or emulsion then by pumpl2l and line |2| into the main emulsion recycle line 81 in advance 'of pump 96. The overhead propane vapors from depropanixer ||6 are passed by line |23 to water-cooled ycondenser' |24. and thence by run-down line |25 lto accumulator |26. 'Propane condensate is supplied asA recycle and malteup propane from acstimulatorv |26 by lineY |21 to the refrigerating vunit inthe manner heretofore described.

Figure 3 discloses lthe invention as` l applied` to a combination alkylation-isomerization unit.' wherein a plurality-of propane accumulators and associated chillers are connected to a common refrigeration As shown, isobutane from line |38 and-olefln` from line 3| are introduced intolan alkylation contactor and settling system '2 indicated atically at |32, to which acid alkylation catalyst is supplied by line |33. Temperature .control of the Aalkylation contacter is accomplished by a chilling coil supplied withpropane from accumulator |34 by line |35. The

Liquid propane is bled 'on from accumulator |34by line |42 containing its individual throttle valvef|43rand flow meter indicator |44. vThis around 200 211'.. dissolves aluminum chloride'to substantial titration: and this solution then passes by line |68 to a mixer |69 where itumeets the main stream of n-butane from line |65a and a stream of normal butane containing HC1 from line |19 and prepared as hereinafter described.

'Ihe normal butane, containing dissolved aluminum chloride and HCl, is dispersed into the i bottoni oi' 4tower |12 from line |1I, and passes upwardly in the form of a multitude of tine liquid drops through. the maintained liquid catalyst body as the continuous phase. During this passage through the liquid catalyst, the hydrocarbon gives up its aluminum chloride to the catalyst body, thereby maintainingthe activity of the latter. The hydrocarbon drops, upon reaching the y upper surface of the liquid catalyst body, form a propane -bl'eed is passed by line |45 and either of branch llines |46 or|41 to mix the propane with me unstabmzed aikyiatestream m the man ner heretofore ydescribed. VLine |46 thus empties into line |,48Vcarrying a hydrocarbon stream from the settler of' the alkylation -unit to theneutralizer |49 in advance of the caustic soda inlet |50.` Line |41 discharges into line 5| carrying y the neutralized hydrocarbon stream from neutralizer |49 to surge drum |52 in advance of the water wash inlet |52a.

TheJ bottoms consisting largely of normal butane from butane fractionator are passed by line |65 and pump |66 to branch lines |65a and |65b, the latter containing an aluminum chloride absorber |61. The latter contains lump aluminum chloride which is utilized as makeup catalyst for the isomerization -unit to maintain the activity of the aluminum 'chloride-hydrocarbon complex catalyst employed in the isomerization reactor at the desired'level. The normal butane, which is preferably at a temperature of superposed hydrocarbon layer oi' mixed isobutane and normal butane, from which a stream is with-v drawn by line |15. This stream of crude isomate is introduced into a complex trap |16 containing a Raschig ring nest |11 o r other suitable packing, which removes any complex liquid carried along with the hydrocarbon stream. Any separated -complex may be withdrawn by line |18.

The hydrocarbons along with the HCl removed overhead in stream |15 then passby line |88 through water-cooled condenser |8| and propane chillerv |82, which cool the stream to a temperature of about 50 F. The cooled stream then passes by line |83 toa complex knock-out drum |84, where any remaining complex separates and is removed by line |85. 'Ihe hydrocarbons containing-HC1 then pass by line |86 into a HCl stripper |81, which is operated to distill all the HC1 overhead together with a small proportion oi' the butanes. This requires reboiling in the base of tower |81. The heated isomate from the bottom of the stripper passes by line |88 to a watercooler |89, where the temperature is lowered suillciently for caustic neutralization, water washing, and introduction into the ,alkylatev fractionating system.

As shown, the cooled Vbutane stream then is pass/ed by line |90 to a caustic-and water wash unit |9| where the Vbutanes are neutralized and then washed with water. 'I'he puriiied butanes are then passed by line |92 which communicates with valve controlled branch: lines |92a and |92b opening respectively into the butane fractionator |55 and the product debutanizer |53. Where the crude isomate contains some pentanes and heavier, the latter will remain in the butane stream discharged by line |88 from the base of HC1 stripper |81. In such case, all or a portion of the stream may be passed by lines 92 and |92b to the product debutanizer, so that the pentanes and heavier will remain in the stabilized total alkylate which is passed by line |56 to the ilnal fractionator, and thus separated from the butanes and lighter passed overhead by line |54. This prevents undesirable build-up of pentanes and heavier in the isomerization system. Or the stream from line |92 may be passed for a period of time p cumulator 204 by line 205.

by line |92a to the butane fractionator |99 until the pentanes build up to a certain maximum proportion, and then diverted by line |92b to product debutanizer 09 for another period of time to reduce the pentane content to a certain minimum proportion, with repetition of this alternate shifting to maintainythe pentane content within the isomerization unit within a predetermined range which tends to' minimize the formation of pentanes andfheavier in the isomerization reactor |12 and render the isomerization. reaction more selective for the production of isobutane.

In either case, the isobutane produced in the isomerization unit is separated from n-butane in the. butane fractionato'r |09 and is eventually supplied by line |09 to serve as make-up isobutane for thealkylation unit. The n-butane charge to the isomerization unit may come entirely from the fresh feed to thealkylation unit, such as from the cracking gas fraction introduced by line |9|, and which n-butane passes unreacted through the alkylation system and is eventually removed asbottoms from butane fractionator by line |95. If additional makeup butanes are required, these may be supplied by line |93 from any suitable source, such as a C4 fraction from the stabilizationfof natural gasoline, and introduced into ythe butane fractionator lill.v

The overhead from the HC1 stripper |91, consisting of HC1 and mixed butanes, passes by line The resulting normal butane stream with absorbed HC1 is returned from absorber |99 by line 202 to the surge drum |91. From the latter, a stream of the butanes with absorbed HCl is passed by line to mixer |89 for introduction into the isomerization reactor |12. In this manner, the desired HC1 concentration is maintained within the isomerization reactor, while loss of HC1 from the system is minimized.

The propane chiller |82 for the crude isomate stream is supplied with liquid propane from ac- Mixed propane liquid and vapors return from chiller |92 to accumulator 204 by line 209. Propane vapors from accumulator 204 are withdrawn by line 201 to the refrigeration unit |39; and propane liquid is supplied from the unit by line 209 to accumulator 204 in accordance with a liquid level control as previously described. While lines |38|40 and lines 201-208 are shown for convenience as connected to the refrigeration unit at diiIerent locations, it will be understood that these lines lead to a common compressor and cooling unit of the l character shown in Figure 1. Liquid propane is bled from accumulator 204 by line 2|0 under the control of throttle valve 2|| and indicating flow meter 2|2. Line 2| 0 joins line |45 for return of this propane to the allq'late neutralizing and fractionating system along with the propane bleed from accumulator |94.

Propane chiller |99 for the overhead from HCl 'Y stripper |81 is supplied with refrigerant propane from accumulator 2|2 by line 2|3; and the propane liquid and vapor are returned from chiller aseacoc |99 by line 2|4 to accumulator 2|2. vapors from 2|2 are removed through line 2 |"l, which-Joins line 291 leading to'the refrigeration unit |99. liquid propane is returned from the refrigeration unit by '5 lines 209and 2|.9 to accumulator2l2 in accordance with its individualliquid level regulator. Liquid propane is also bled from accumulator 2|2 by line 2|1 under the control of its individual throttle valve 2|9 and indicating flow meter 2|9. Line 211 joins line 2| 9 for the return of this bleed propane through the said lines and line |40 to the alkylate neutralizing and fractionating system as heretofore described.

It is thus seen that .the depropanizer |59 of the combined alkylate and isomate fractionating system supplies the propane refrigerant to a v common refrigeration unit |99, which in turn supplies the accumulators |94, 204, and 2|2 for the various thermo-siphonio chilling circuits.

The bleed of liquid propane from each individual I accumulator and associated chilling circuit can be independently controlled and regulated; and makeup liquid propane from the common refrigeration unit 'is likewise under independent control. The cyclic process of bleeding propane from the various chilling units to the combined alkylation-isomerization fractionationl system, with return oi.' purified recycle and makeup propane to the common refrigeration unit, maintains the 3o propane refrigerant in all of the chilling circuits in a proper and highly eilicient condition over long periods of continuous operation and in very economical manner.

While liquid phase isomerization has been speciilcally disclosed, it isdto be understood that vapor phase operation may b e used. While an aluminum Achloride-hydrocarbon complex has been specically mentioned above as the isomerization catalyst, it is to be understood that the invention is 40 applicable to other lsomerization catalysts, such as aluminum bromide, zirconium chloride, complexes thereof, etc. Moreover, while isomerization of normal butane to produce isobutane for the alkylation unit has been specifically described, it is to be understood that the invention is appli cable to the isomerlzation of other normal par' aflins, such as the isomerization of normal pentane to produce isopentane for alkylation with oleflns or for blending directly with fthe motor fuel.

The following specic example'is given as illustratory of the presen-t invention. Ina commercial alkylation plant having a rated capacity of 1180 BPOD, utilizing three type Stratco contactors in parallel. and a refrigeration unit having a rated capacity of 607 A. S. R. E. tons (each ton equivalent to 12,000 B. t. u. per hour), diiiiculty had been experienced due to the accumulation of lubricating oil in the refrigerant propane in the chillers for the three contactors. The plant was modified in accordance with the present invention to install propane bleed lines from the several accumulators to the alkylateA fractionating system. A bleed of about lf2 barrel (21 gallons) per hour of liquid propane was then taken from each accumulator. The plant was designed for total olefln feed of 96.8 'barrels per hour, and total isobutane feed of 158.5 barrels per hour, making a total combined feed of 255.3 barrels per hour, which is split between the three contactors. Consequently, 'each contactar has a designed fresh feed rate of about 85.1 barrels per hour. Each contactor was designed to operate with an internal recirculation rate 'of about 4 5,000-50,000 gallons per minute. The volume of propane in the chilling coils and lines for each contactor is approximately 800 gallons, and the volume of the propane in the associated accumulator is opproxigaseous'v hydrocarbon from sani stabilizing and mately 250 gallons, giving a total volume of pro- Y pane imder thermo-siphonic circulation of about 1,050 gallons. The refrigeration unit was designed ,fractionsting operation to the chilling zone.

2. Themethod according to claim 1,'wherein the withdrawn portionof -contaminated liquid to vmaintain a reactor temperature of about 50 F. 1

accumulator is maintained at about54 pounds per For this condition, the pressure on the propane f square inch, resulting in the evaporation of propane in the chilling coils at about 35 F.; and the compressors of the refrigeration unit are designed for a suction pressure of about 57 pounds per square inch and a discharge pressure of 175 pounds per square inch with condensation. of the com-V alkylate fractionating system, with the return of suicient` purified propane from the alkylate de"- propanizer to supply recycle and makeup propane for the refrigeration unit, has served tomaintain the refrigerant eifectively free from liquid contamination, and satisfactory operation has now been secured over several months of continuous service since installation of the said propane 'refrigerant is subiected'to a.V neutralizing and water washing'treatment before being subjected vto the stabilizing and fractiouating operation.

3. In a continuous process forcatalytically re acting hydrocarbons in the presence oi'v a catalyst, wherein the hydrocarbons undergoing re- 'action' are maintained at a controlled temperature by indirect heat exchange in a chilling'zone witha liquefied normally gaseous hydrocarbon refrigerant maintained in a closed expansioncompression refrigeration circuit, the resulting hydrocarbon reaction products are separated from the catalyst and then'stabilized and fractionated tol recover a nished hydrocarbon product, and wherein the recirculating normally gaseous hydrocarbon refrigerant tends to become contaminated with vheavier normally liquid impurities which build up inthe liqueed refrigerant on the chilling zone side of the refrigeration circuit, the improvement whichcomprises bleeding olf a minor proportion of the liquefied refriger-` ant from the chilling zone side of the refrigeration circuit, mixing said bled-olf refrigerant with said `resulting hydrocarbon reaction products, stabilizing said mixture toremove overhead a Avapor fraction including the normally gaseous f hydrocarbon refrigerant and thereby separate bleeds. The propane from the .alkylate depropanizer tower has been found to meet all oi thespeciilcations for commercial propane; and the maintenance of this propane in a pure condition is signicant, since less power is required-when using a relatively pure propane than when impure propane is employed.

Qbviously many modiilcations and variations of the invention, as hereinbefore set forth, may be made without departing from the spiri't and scope thereof, and therefore only such limitations should be imposed as are indicated in theA appended claims. i

I claim:

1. The cyclic method of controlling the temperature in a refinery hydrocarbon oil processing step, which comprises stabilizing and fractionating a hydrocarbon fraction to separate a normally gaseous hydrocarbonfrom heavier hydrocartoons, passing said normally'gaseous hydro-l carbon in liquefied form through a chilling zone in indirect heat exchange with the hydrocarbon oil `being processed, whereby a portion of the liquefied normally gaseous hydrocarbon is vaporized, removing the vapors to a zone of compression and cooling for liquefacticn and returning the liqueiied refrigerant to the chilling zone, recirculating the refrigerant through repeated stages of said'compression and cooling for liquefaction and indirect heat exchange for evaporation, whereby the refrigerant tends to become contaminated with heavier liquid impurities which accumulate in the chilling zone, withdrawing a minor portion of the contaminated liquefied refrigerant from the chilling zone, mixing the same with the said hydrocarbon fraction and then subjectingv the resulting mixture 'to the stabilizing and fractionating operation, whereby the hydrocarbon refrigerant is separated from the heavier liquid impurities, and returning the yseparated purified hydrocarbon refrigerant together with any additional make-up normally the same from a liquid bottom s containing the desired hydrocarbon zproductand heavier impurities, fractionating said 'bottoms to recover the desired hydrocarbon product, recovering normally gaseous hydrocarbon refrigerant from said overhead vapor fraction, and returning said recovered refrigerant to said refrigeration circuit.

4; Process in accordance with claim 3, wherein the overhead vapor fraction includes unreacted hydrocarbon as well as the normally gaseous hydrocarbon refrigerant, said vapor fraction is fractionated to separate the refrigerant as an overhead vapor from a liquid bottoms which is rich in the unreacted hydrocarbon, said liquid bottoms is recycled to the catalytic reaction, and

said overhead refrigerant is returned to the reneutralized, water washed, and then stabilized and fractionated to recover a gasoline alkylate, and wherein the recirculating normallygaseous hydrocarbon refrigerant tends to become con'- taminated with heavier normally liquid impurities which build up in the liqueed refrigerant on the chilling zone side of the refrigeration cir' cuit, the improvement which comprises bleeding oif a minor proportion of th'e liqueed refrigerant from the chilling zone side of the refrigeration circuit, mixing said bled-oit refrigerant with said resulting hydrocarbon reaction products, stabilizing said mixture to remove overhead a vapor fraction including the normally gaseous Vhyelrocarbon refrigerant and thereby separate the same from a liquid bottoms containing the gasoline alkylate and heavier impurities, fractionats ing said bottoms to recover the gasoline alkylate, recovering normally gaseous hydrocarbon refrig-` erant from said overhead vapor fraction, and

returning said recovered refrigerant to saidI refrigeration circuit.

6. 'I'he method according to claim 5, wherein the hydrocarbons supplied to the alkylation reaction include a proportion of the normally gaseous hydrocarbon employed as refrigerant, additional' make-up normally gaseous hydrocarbon is separated along with the purified refrigerant from the stabilizing and recovery operations, and the additional make-up hydrocarbon is returned along with the purified refrigerant to the refrigeratingcircuit to maintain the latter supplied with refrigerant over long periods of continuous operation. f

'1. The method according to claim 5, wherein the low-boiling isoparamn is isobutane, the olefin is a C4 oleiln present in a renery hydrocarbon fraction also containing some propane, the refrigerant is propane, the overhead vapor fraction separated in the stabilizing operation contains excess unreacted isobutane along with thepropane, isobutane is separated from said fraction for recycling to the alkylation step, and propane is separated from said fraction to supply both makeup and recycledpuriiled propane for the refrigeration circuit.

8. The method according to claim 5, wherein the liquefied refrigerant bleed stream is mixed with the said hydrocarbon reaction products following separation of the alkylation catalyst and prior to neutralization and water washing thereof.

9. In a continuous process involving catalytic 4alkylation of an isoparaln with an olefin of a normally gaseous hydrocarbon fraction to produce gasoline hydrocarbons, stabilization and fractionation of the resulting hydrocarbon alkylation reaction products to separate from the latter the gasoline hydrocarbons, excess unreacted isoparafn, and also corresponding normal paraiiin and a different normally gaseous hydrocarbon included in said alkylation feed, recycling said isoparailln to the alkylation step, subjecting said normal paramn to catalytic isomerization to produce additional quantities of said isoparamn, and returning hydrocarbon isomerization products to said stabilizing and fractionating operation, the improvement which comprises passing at least a portion of said different normally gaseous hydrocarbon to a refrigeration circuit of the compression-expansion type to serve as a liquefied refrigerant therein, bringing said liquefied refrigerant in the refrigeration circuit in indirect heat exchange in separate chilling zones with products of both said alkylation step and said isomerization step for temperature control of both steps, bleeding of! separate streams of said liquefied refrigerant from the said separate chilling zones, and mixing said refrigerantstreams with the hydrocarbon reaction products of the alkylation step, whereby the mixed refrigerant and hydrocarbon reaction products are subjected to the stabilizing and fractionating operation,

and purifiedrefrigerant along with fresh make-up normally gaseous hydrocarbon is returned from the lstabilizing and fractlonating operation to the refrigeration circuit.

10.1The method according to claim 9, wherein the hydrocarbon alkylation reaction products are subjected to neutralization and water washing prior to the stabilization and fractionation, and the bleed refrigerant streams are mixed with the said hydrocarbon alhlation reaction products in advance of said neutralization and .water washing steps.

11. In a process of temperature control by indirect heat exchange with a liquefied normally gaseous hydrocarbon refrigerant, which is repeatedly recirculated in a closed refrigeration circuit including a chilling zone where a portion of the liquefied refrigerant is vaporlzed, and a compression and cooling zone where `the vapors are reliqueed and then returned to the chilling zone, and wherein the refrigerant tends to become contaminatedwlth higher boiling impurities which accumulate in the liquened refrigerant on the chilling zone side of the refrigeration circuitthe improvement for maintaining the refrigerant eifectively free from said impurities which comprises withdrawing a minor portion of the liquefied refrigerant from the chilling zone side of said refrigeration circuit, mixing said withdrawn refrigerant with a broad boiling range hydrocarbon fraction containingl higher boiling hydrocarbons as well as some hydrocarbon of the same character and boiling range as said normally gaseous hydrocarbon refrigerant, subjecting said mixture to stabilization and fractionation to thereby separate higher boiling hydrocarbons and impurities from a hydrocarbon cut consisting essentially of said purified normally gaseous hydrocarbon refrigerant along with additional hydrocarbon of the same character obtained from said broad boiling range fraction, and-supplying said hydrocarbon cut to the refrigerating circuit to provide make-up and puriiled recycle refrigerant therefor.

l2. The process according to claim 11, wherein the said mixture is treated with a caustic solution and then water washed before being sub- Jected to the said stabilization and fractionation.

13. The process according to claim 11, wherein the refrigerant is propane, and the broad boiling range hydrocarbon fraction is composed primarily of hydrocarbons of gasoline boiling range.

14. The process according to claim l1, wherein the refrigerant is propane, and the broad boiling range hydrocarbon fraction is the unstabilized hydrocarbon reaction products of isobutane-olefin alkylation.

15. In combination, a hydrocarbon oil stabilizing and fractinating system comprising a debutanizer and a depropanizer in series, means for supplying a broad boiling rangehydrocarbon oil mixture containing both normally liquid and normally gaseous hydrocarbons to said debu' tanizer, a refrigerationunit and chiller for indirect heat exchange wlth-said hydrocarbon oil mixture in advance of said stabilizing and fractionating system, means for supplying a liquein heavier normally liquid impurities tend to accumulate in the recirculating refrigerant, and means for bleeding a minor portion of the recirculating liquefled refrigerant into the debutanizer of said hydrocarbon oil mixture stabilizing and fractionatingv system, whereby the heavier impurities are separated from the nor' mally gaseous hydrocarbon refrigerant in the said stabilizing and fractionating system, and said supply means serves to return the purified refrigerant together with required make-up reflrxigerant from said system to the refrigeration 16'. In combination, a hydrocarbon gas conversion unit, an indirect heat exchange chiller ior controlling temperature of said unit, a neutralizer for causticneutralization oi hydrocarbon oil produced in said unit comprising va mixture of normally liquid and liqueiied normally gaseous hydrocarbons. a stabilizing and fractionating system comprising a debutanizer and a depropanizer connected to receive overhead from said debutanizer, means for passing neutralired hydrocarbon oil from said neutralizer vto said debutanizer, a refrigerating unit connected to said chiller for recirculation of refrigerant through repeated stages oi' compression and cooling for liqueiaction and indirect heat exchange for evaporation, means for supplying at least a portion of the overhead from said depropanizer to said refrigerating unit and chiller to serve as the refrigerant therein, and a bleed line for returning a portion ot the liqueed reirigerant from said chiller to said neutralizer to be processed in admixture with the hydrocarbon oil in said neutralizer and then in said stabilizing and fractionating system.

17. In combination, an alkylation contactor, means for supplying isoparain, oleiin and alkylation catalyst to said contacter, a stabilizing and iractionating system comprising a debutanizer and a depropanizer connected to receive overhead from said debutanizer, connections betweensaid contactor and said debutanizer for supplying hydrocarbon alkylation reaction products produced in said contactar to said stabilizing and fractionating system, a chilling coil associated with said contacter for indirect heat exchange with the hydrocarbons undergoing reaction therein, a refrigeration unit including a compressor and coolerconnected to said chilling coil to provide a refrigeration circuit of the compression-expansion Itype, means for supplying liquefied normally gaseous hydrocarbon overhead from said depropanizer to said refrigeration circuit to serve as the refrigerant therein. and a bleedcline extending from said refrigeration circuit to said connections between said contactor and said debutanizer for bleeding oil' a portion of the liqueiled refrigerant from the chiller side of said refrigeration circuit and mixing the said bleed stream with the hydrocarbon alkylation reaction products for processing in the stabilizing and fractionating system.

18. In combination, an alkylation reactor, a neutralizer for the hydrocarbon alkylation reactionproducts, a water wash and surge tank i'or the neutralized hydrocarbon alkylation products, a stabilizing and fractionating system for the neutralized and washed hydrocarbon products including a product debutanizer, a deisobutanizer and a depropanizer, an isomerization unit, means for supplying liquid bottoms from'the butane fractionator to the isomerization unit, means for returning isomate from the isomerization unit to said stabilizing and fractionating system, a refrigeration circuit including separate chilling coils associated respectively with the alkylation reactor and the isomerization unit and connected to a common refrigeration unit having a compressor and cooling means, means for passing overhead normally gaseous hydrocarbon from said depropanizer to said refrigeration unit to supply refrigerant ror said refrigeration cirtralizer, water wash and surge tank, and Stabilizing and fractionating system.

LEONARD F. DOWDING.