US3929924A

US3929924A - Fractionation of effluent from HF catalyzed alkylation

Info

Publication number: US3929924A
Application number: US478226A
Authority: US
Inventors: Charles C Chapman
Original assignee: Phillips Petroleum Co
Current assignee: Phillips Petroleum Co
Priority date: 1974-06-11
Filing date: 1974-06-11
Publication date: 1975-12-30
Anticipated expiration: 1992-12-30

Abstract

A depropanizer overhead from fractionation of an HF catalyzed isoparaffin-olefin alkylation is partially condensed to form a stream relatively poor in ethane and vapors relatively rich in ethane. The stream relatively poor in ethane is used as reflux and is pumped by a pump to a depropanizer-fractionator. Vapors rich in ethane are condensed, contacted with liquid HF and are used as feed to an HF stripping zone. Bottoms from the stripping zone consisting essentially of ethane and propane to be yielded from the operation are flashed to form overhead ethane and propane yield and a bottoms propane stream poor in ethane and lean in HF and said stream poor in ethane and lean in HF is used as flush for said pump. HF stripper overhead is at least in part condensed, two liquid phases are formed, the acid phase is removed and the hydrocarbon phase is returned as reflux to the stripper and/or the overhead is at least in part condensed and the condensate thus obtained intermingled with the condensate obtained when condensing the vapors rich in ethane; phases are formed, and acid phase formed is separated and hydrocarbon phase is used as feed to the stripping zone. A pump is provided to draw from an extractor-settler HF acid settled therein and to admix therewith either or both the condensates obtained upon condensing the ethane rich vapor and that obtained upon condensing HF stripper overhead, thus intermingled liquids are passed to said extractor-settler from which an acid phase formed is separated and hydrocarbon phase formed is passed to the stripping operation. Flush for the pump is provided by the propane lean in ethane and lean in HF.

Description

[ 1 Dec. 30, 1975 FRACTIONATION OF EFFLUENT FROM HF CATALYZED ALKYLATION [75] Inventor: Charles C. Chapman, Bartlesville,

Okla.

[73] Assignee: Phillips Petroleum Company,

Bartlesville, Okla.

[22] Filed: June 11, 1974 [21] Appl. No.: 478,226

[52] US. Cl 260/683.42; 260/683.48 [51] Int. Cl. C07C 3/54 [58] Field of Search 260/683.48, 683.42

[56] References Cited UNITED STATES PATENTS 2,894,999 7/1959 Lawson Zoo/683.48 3,190,935 6/1965 Hutson, Jr. 260/683.42 3,763,265 10/1973 Hutson, Jr., et al. 260/683.48 3,767,726 10/1973 Hutson, Jr., et al. 260/683.48 3,804,918 4/1974 Henderson 260/683.48

Primary Examiner-Delbert E. Gantz Assistant ExaminerG. J. Crasanakis [57] ABSTRACT A depropanizer overhead from fractionation of an HF catalyzed isoparaffin-olefin alkylation is partially condensed to form a stream relatively poor in ethane and vapors relatively rich in ethane. The stream relatively poor in ethane is used as reflux and is pumped by a pump to a depropanizer-fractionator. Vapors rich in ethane are condensed, contacted with liquid HF and are used as feed to an HF stripping zone. Bottoms from the stripping zone consisting essentially of ethane and propane to be yielded from the operation are flashed to form overhead ethane and propane yield and a bottoms propane stream poor in ethane and lean in HF and said stream poor in ethane and lean in HF is used as flush for said pump. HF stripper overhead is at least in part condensed, two liquid phases are formed, the acid phase is removed and the hydrocarbon phase is returned as reflux to the stripper and/or the overhead is at least in part condensed and the condensate thus obtained intermingled with the condensate obtained when condensing the vapors rich in ethane; phases are formed, and acid phase formed is separated and hydrocarbon phase is used as feed to the stripping zone. A pump is provided to draw from an extractor-settler HF acid settled therein and to admix therewith either or both the condensates obtained upon condensing the ethane rich vapor and that obtained upon condensing HF stripper overhead, thus intermingled liquids are passed to said extractorsettler from which an acid phase formed is separated and hydrocarbon phase formed is passed to the stripping operation. Flush for the pump is provided by the propane lean in ethane and lean in HF.

6 Claims, 1 Drawing Figure PUMP FLUSH FRACTIONATION OF EFFLUENT FROM HF CATALYZED ALKYLATION This invention relates to the alkylation of an isoparaffin with an olefin in the presence of HF acid. It also relates to the fractionation of an. alkylation effluent obtained from the HF catalyzed alkylation of an isoparaffin with an olefin.

In one of its concepts the invention provides for the fractionation of an HF-catalyzed alkylation effluent to obtain a depropanizer overhead vapor containing ethane, propane, HF and organic fluorides. The overhead is partially condensed forming a liquid rich in propane and and lean in ethane. Said liquid is pumped with a pump as reflux to the depropanizer. The ethane rich vapor containing HF thus remaining is condensed, liquid acid is separated therefrom, and a liquid hydrocarbon phase thus obtained is passed to an HF stripping operation wherefrom a bottoms consisting essentially of ethane and propane are obtained. The bottoms are flashed to obtain a vaporous ethanepropane yield, and a bottoms essentially consisting of propane poor in ethane and lean in HF, and said bottoms are used as flush for said pump. In another of its concepts there is provided in an operation as just described a recontacting of the stream obtained when the ethane rich vapors are condensed with an HF acid phase separated upon the partial condensation of the depropanizer overhead thus to remove organic fluorides from said ethane rich stream into the acid. Still further, in another concept there is provided a condensing of overhead from the HF stripping, containing HF, ethane, and propane, and the condensate thus obtained is admixed with the liquid obtained upon condensing said ethane rich vapor obtained upon said partial condensing. In a further concept still the thus admixed liquids are pumped and further admixed as in an eductor with liquid HF taken from an extractor-settler and the thus admixed liquids are passed to said extractor-settler from which a liquid acid phase is removed and from which hydrocarbon phase is passed to said HF stripping operation. Further still according to a concept of the invention the HF stripper overhead is cooled condensed forming an acid phase which is recovered and a hydrocarbon phase which is returned to the stripper as reflux therefore.

Considering the energy shortfall, which is now extant and which has been building for some years and which is becoming increasingly critical and which will be in existence for a number of years, it is imperative to seek to improve operations wherewith to save energy. Further, wherever there is a process requiring venting of nonconde'nsables as when ethane in the feed to an alkylation is significantly above one percent of the propane volume in the feed there results a problem in that there is loss of HF acid in the venting, and the concomitant energy which has been required to produce the same. Further this loss causes a degree of pollution and/or requires costly treatment of the gases or vapors to sequester the acid. Still further it is desirable to reduce the pressure at which fractionation is accomplished because of the cost of fractionating equipment the thickness of which and the energy to produce which considerably increases in proportion to the pressure at which operation is needed to be conducted.

l have now conceived of a combination of steps in which itis possible to lower considerably the pressure at which a depropanizer is operated. Thus 1 have conceived that if the depropanizer overhead is only partially condensed I can obtain therefrom a liquid hydrocarbon phase or propane-rich stream quite lean in ethane and that this stream can be pumped as reflux to the depropanizer operation which now can be operated at a lower pressure than conventionally. Further, according to my concept, I provide for the condensing of the thus obtained ethane-rich vapors, separtion of liquid HF acid therefrom upon settling to form a liquid acid phase, and then stripping in an HF stripping operation the hydrocarbon phase remaining to obtain a stripped bottoms which contain the ethane-propane yield, which then are flashed to obtain ethane-propane yield from the operation, and a flashed liquid bottoms consisting essentially of propane and lean in ethane and lean in HF which is used for pumped flush. Further, I have conceived related operations as described herein.

An object of this invention is to provide an improved process for the alkylation of an isoparaffin-olefin. A further object of the invention is to provide a process for the fractionation of the effluent from an HF catalyzed alkylation of an isoparaffin and an olefin. Further still an object of the invention is to provide a lower pressure fractionation for depropanizing an alkylation effluent as herein described. Still further an object of the invention is to provide a reflux for a depropanizing operation the reflux being lean in ethane. Further still an object of the invention is to provide a pump flush consisting essentially of propane lean in ethane and lean in HF. A further object still is to provide a combination operation in which organic fluorides are recovered in an acid phase. A still further object of the invention is to provide an improved HF stripper feed processing. Another object still is to provide an improved HF stripper operation. lmportantly, another object is to provide for the reduction in cost of equipment and cost of operation. Also, importantly, an object of the invention is to reduce energy requirements to produce and to operate equipment required for the alkylation of an isoparaffin with an olefin in the presence of HF acid. Another important object of the invention is to reduce losses of expensively obtained HF acid catalysts.

Aspects, concepts, objects and the several advantages of the invention are apparent from a study of this disclosure, the drawing and the appended claims.

According to the present invention, there is provided an alkylation operation for alkylating an isoparaffin with an olefin, e.g., isobutane and/or isopentane with at least one of ethylene, propylene, a butylene, an amylene and a hexylene, wherein in the alkylation hydrocarbon effluent there are present ethane, propane, normal butane, isobutane, organic fluorides and heavier hydro-' carbons including alkylate boiling range hydrocarbons, and HF catalyst, and wherein the effluent is fractionated in a fractionation zone to remove therefrom a vapor stream rich in ethane, propane and HF, and organic fluorides, the steps in combination which comprise partially condensing said stream to form a first liquid hydrocarbon phase rich in propane and relatively lean in ethane and a first acid phase and using at least a portion of said first liquid hydrocarbon phase by pumping the same with a pump as reflux for said fractionation zone, thereby being able to operate said fractionation zone at a pressure significantly lower than when the overhead therefrom is not treated to reduce the ethane contents thereof as herein described.

Further according to the invention, there is provided an operation as is described wherein upon said partial condensing results a vapor stream relatively rich in ethane and containing propane, HF and organic fluorides, said vapor stream is condensed to form a second liquid phase containing propane, HF and organic fluorides and relatively rich in ethane, said second liquid phase is settled to form and separate therefrom a second liquid acid phase leaving a second liquid hydrocarbon phase, said second liquid hydrocarbon phase is passed to an HF stripping Zone, in said stripping zone there is removed a stripped bottoms consisting substantially of only ethane and propane, said bottoms are flashed obtaining ethane and propane vapors yielding a flashed liquid bottoms stream lean in ethane and lean in HF, and consisting essentially of propane and using said stream as flush for the reflux pump, and for the charge pump for the HF stripper.

Other features of the invention are apparent from this disclosure and are claimed as in the appended claims.

Generally, there are known in the art the conditions for the alkylation of an isoparaffln with an olefin, the alkylation resulting in an alkylation effluent which is fractionated. The description of the drawing will be made in connection with an effluent containing hydrocarbons boiling in the alkylate gasoline boiling point range, normal butane, isobutane, ethane, propane, HF and organic fluorides together with some noncondensables which if not vented will accumulate in the equipment.

Referring now to the drawing, an alkylate containing effluent feed is passed to fractionator 11 from which there are removed an alkylate product bottoms 13, a side stream of vaporous normal butane 12, a side stream of isobutane vapor l4, and from above the feed, an isobutane liquid stream 15 as well as an overhead vapor stream 16 containing principally ethane, propane, HF and organic fluorides. Stream 16 is partially condensed at 17 and passed into accumulator 18 in which liquid hydrocarbon and liquid acid phases are formed, and from which a vapor rich in ethane 21 is taken off and passed to condenser 22 and therein con densed. Liquid propane lean in ethane is pumped by the pump and from accumulator 18 to the top portion of the fractionator 11 as reflux therefor. According to the invention, by supplying an ethane-lean propane reflux the pressure in the fractionator or depropanizer can be considerably lower than conventional, as earlier noted.

Acid phase is separated at 19 from the leg of accumulator 18 and can be returned to the alkylation unit for reuse as a catalyst in the alkylation reaction. This is shown at 34 and 35. However, in the embodiment now described the separated acid is recombined with the condensate from condenser 22 passed by 23, 25, 26 and pump 27 to eductor 28 whence it is passed by 30 into extractor-settler 31. Phases are formed in extractor-settler 31, a lower liquid acid phase being drawn into eductor 28 by 29 and an upper liquid hydrocarbon phase being passed by 36 and 38 to HF stripper 39 having bottoms reboiler 40. A portion of the hydrocarbon phase taken through 36 can be passed by 24 into pipe 25 for further contacting with acid as just described. Bottoms 41 from HF stripper 39 consist essentially of the ethane-propane which is passed through heater 42 and flashed in tank 43 yielding overhead vapor at 47 which is condensed at 48 to produce the liquid yield 49 of ethane and propane from the process. This yield is passed to an operation (not shown) to remove residual fluoride therefrom. Bottoms liquid 44 from flash tank 43 are passed by cooler 37 and used as pump flush by way of 46 and 45. The use of pump flush, generally, is known in the art. According to a feature of this invention the pump flush is lean in corrosive HF and lean in ethane and therefore, significantly, the reflux at 20 does not add any real significant quantity of ethane to thefractionation operation, nor corrosive HP in the pump flush. Similarly the operation of HF stripper 39 is considerably improved because the flush to pump 27 does not recycle any really significant portion of ethane to the stripper.

'The overhead from stripper 39 is at least in part treated by at least one of the following alternates.

Overhead 50 is passed by conduit 55 to condenser 56 and to phase separator 57 from the bottom of which a liquid acid phase 58 is removed and returned to alkylation as earlier discussed for stream 35. Noncondensables, if any, are vented from the top of 57, and liquid hydrocarbon phase taken through 59 as reflux for stripper 39.

Alternately, at least a portion 51 of the HF stripper is condensed at 52 liquid accumulating in accumulator 53. Accumulator 53 is provided with a refrigerated vent gas release. Liquid from accumulator 53 is passed by 54 into 26 and thence to pump 27 for admixture with the hydrocarbons and acid which are contacted by vigorous intermixing at 28, pass via conduit 30 into 31, and separate into two liquid phases in extractor-settler 31, as already described.

The addition of stripper feed pump 27, in the apparatus described, will allow the propane yield to contain from about 2 up to about 10 percent ethane. The pump suction flow is the net volume of propane-ethane from the depropanizer overhead to be yielded out the bot tom of the stripper plus the stripper overhead. The HF stripper bottoms are made up of the net propaneethane yield plus two pump flushes. The flash on the stripper bottoms will further increase the ethane content of the yield and reduce the amount of ethane that otherwise would be recycled in the pump flush and be recovered in the bottoms.

It is within the broad scope of the invention to pass the vapor stream 21, even as a vapor in part or all of it directly to the HF stripper.

Depending upon the feedstock, catalyst and other characteristics of a particular operation, as one skilled in the art in possession of this disclosure will understand, the specific conditions of operation given below can vary within the approximate ranges which are also given.

continued,

. CALCULATED OPERATION- Approximate b. condensing said first vapor stream to form a second liquid phase containing propane, HF- and .organic'fluorides-and relatively rich in ethane,

,T i l Ranges 0. settling said second. liquid phase to form and to Bomm temperature): 1 l 41 150 separate therefrom a second acid phase from a Pressure, psia 330 280 430 second llquld hydrocarbon phase, 57 and Accumulator 01. passing said second liquid hydrocarbon phase to an emperature, "F 100 60 l25 pressure psia 325 275 425 HF stripping zone, in said stripping zone removmg Flash Unit 43: a stripped bottoms consisting substantially of only Temperature, "F 142 I20 150 Pressure, psia 325 275 425 etharie P e. flashing sa1d stripped bottoms to remove therefrom a second vapor stream containing ethane and pro- In the table below there are given the compositions of Pane thus g f g aggshechbottoms stream lean m the principal streams in the process for the typical h fg i an I th operating conditions above Set out f. using sai as e ottoms stream can 1n e ane,

TABLE Barrels Per Day Stream l0 l2 l3 l4 l5 16 21 25 38 41 44 47 5O 59 58 Composition Ethane & Lighter 34 2 5 200 27 27 76 29 43 24.7 47 47 Propane 2147 583 873 12642 834 834 1247 977 287 69] 270 270 lsobutane 20557 18 4 9888 10646 339 5 5 9 8 l l l l Normal Butane 4142 299 184 1925 1734 3 Pentanes Plus 3685 25 3370 l90 I00 HF 195 266 34 160 9 Nil (.004) 8.9 2.48 6.42 160 and lean in HF, a flush for said pump in step (a), Reasonable variation and modification are possible whereby the intermingling of the flush from the within the scope of the foregoing disclosure, drawing, pump with said reflux will not significantly add and the appended claims of the invention the essence 3O ethane to said reflux and therefore to said fractionof which is that there have been provided an improved, considerably less energy-consuming over all alkylation of an isoparaffin with an olefin in the presence of HF acid included in the concept of which are partial condensing to obtain an ethane-lean propane reflux thus to permit operation of the depropanizer zone at a lower pressure than usual, steps in combination to produce an ethane lean and HF lean propane flush for the reflux pump and other pumps in the operation thus avoiding corrosion and also the return of ethane to the system, the combination of steps in connection with the HF stripper as described in treating the overhead as well as the bottoms thus to reduce ethane venting and HF loss, to increase the ability of the operation to produce ethane in the propane yield thus reducing it in the operation having set forth substantially as described.

I claim:

1. In an alkylation operation of which an isoparaffin is alkylated with an olefin and wherein in the alkylation effluent there are present ethane, propane, butane, isobutane, organic fluorides and heavier hydrocarbons including alkylate boiling range hydrocarbons, and HF catalyst, and wherein the effluent is fractionated in a fractionation zone to remove therefrom a stream rich in ethane, propane, and HF, and organic fluorides, the steps in combination which comprise a. partially condensing said stream to form a first liquid hydrocarbon phase rich in propane and relatively lean in ethane, a first vapor stream relatively rich in ethane and containing propane, HF and organic fluorides, and a first acid phase and using at least a portion of said first liquid hydrocarbon phase by pumping the same with a pump as reflux for said fractionation zone, thereby operating said fractionation zone at a pressure significantly lower than when the overhead therefrom is not treated to remove the ethane content thereof as herein described,

ation zone.

2. An operation according to claim 1 wherein said second liquid phase containing propane, HF and organic fluorides and relatively rich in ethane is intermingled with said first acid phase, thus to reduce said organic fluorides in said second liquid phase, the intermingled phases are settled to form a third acid phase which is separated from the operation and a third hydrocarbon phase and said third hydrocarbon phase is passed to said stripping zone.

3. An operation according to claim 2 wherein said third hydrocarbon phase is passed to said stripping zone with a pump and a portion of said flashed bottoms stream lean in ethane and lean in HF, is used as a flush for said pump whereby the intermingling of the flush from said pump with said third hydrocarbon phase will not significantly add ethane to said third hydrocarbon phase thereby increasing significantly the efficiency of the stripping and of the removal of ethane from the operation.

4. An operation according to claim 2 wherein the stripping zone overhead containing HF, ethane and propane is at least in part condensed, there are formed an acid phase which is separated and a hydrocarbon phase which is returned to the stripping zone as reflux therefor.

5. An operation according to claim 2 wherein the stripping zone overhead containing HF, ethane and propane is at least in part condensed and the condensate is combined with said second liquid phase containing propane, HF, organic fluorides and which is relatively rich in ethane.

6. An operation according to claim '1 wherein said second liquid phase containing propane, HF, organic fluorides and relatively rich in ethane is comingled with said first acid phase and wherein the thus comingled liquids are vigorously admixed with HF acid supplied from an extractor-settling zone, the final admixture 3,929,924 8 thus obtained [8 passed into said extractor-settling is removed and wherein a hydrocarbon phase f d zone thus extractin into said HF acid the or anic fluorides in Said Secognd liquid Phase Said final m said extractor-settling zone 18 passed to said stripping ture being settled in said extractor-settling zone, an HF Zone as the feed therefor acid phase containing said extracted organic fluorides

Claims

1. IN AN ALKYLATION OPERATION OF WHICH AN ISOPARAFFIN IS ALKYLATED WITH AN OLEFIN AND WHEREIN IN THE ALKYLATION EFFLUENT THERE ARE PRESENT ETHANE, PROPANE, BUTANE, ISOBUTANE, ORGANIC FLUORIDES AND HEAVIER HYDROCARBONS INCLUDING ALKYLATE BOILING RANGE HYDROCARBONS, AND HF CATALYST, AND WHEREIN THE EFFLUENT IS FRACTIONATED IN A FRACTIONATION ZONE TO REMOVE THEREFROM A STREAM RICH IN ETHANE, PROPANE, AND HF, AND ORGANIC FLUORIDES, THE STEPS IN COMBINATION WHICH COMPRISE A. PARTIALLY CONDENSING SAID STREAM TO FORM A FIRST LIQUID HYDROCARBON PHASE RICH IN PROPANE AND RELATIVELY LEAN IN ETHANE, A FIRST VAPOR STREAM RELATIVELY RICH IN ETHANE AND CONTAINING PROPANE, HF AND ORGANIC FLUORIDES, AND A FIRST ACID PHASE AND USING AT LEAST A PORTION OF SAID FIRST LIQUID HYDROCARBON PHASE BY PUMPING THE SAME WITH A PUMP AS REFLUX FOR SAID FRACTIONATION ZONE, THEREBY OPERATING SAID FRACTIONATION ZONE AT A PRESSURE SIGNIFICANTLY LOWER THAN WHEN THE OVERHEAD THEREFROM IS NOT TREATED TO REMOVE THE ETHANE CONTENT THEREOF AS HEREIN DESCRIBED, D. CONDENSING SAID FIRST VAPOR STREAM TO FORM A SECOND LIQUID PHASE CONTAINING PROPANE, HF AND ORGANIC FLUORIDES AND RELATIVELY RICH IN ETHANE, C. SETTLING SAID SECOND LIQUID PHASE TO FORM AND TO SEPARATE THEREFROM A SECOND ACID PHASE FROM A SECOND LIQUID HYDROCARBON PHASE, D. PASSING SAID SECOND LIQUID HYDROCARBON PHASE TO AN HF STRIPPING ZONE, IN SAID STRIPPING ZONE REMOVING A STRIPPED BOTTOMS CONSISTING SUBSTANTIALLY OF ONLY ETHANE AND PROPANE, E. FLASHING SAID STRIPPED BOTTOMS TO REMOVE THEREFROM A SECOND VAPOR STREAM CONTAINING ETHANE AND PROPANE, THUS YIELDING A FLASHED BOTTOMS STREAM LEAN IN ETHANE, AND LEAN IN HF, AND F. USING SAID FLASHED BOTTOMS STREAM LEAN IN ETHANE, AND LEAN IN HF, A FLUSH FOR SAID PUMP IN STEP (A), WHEREBY THE INTERMINGLING OF THE FLUSH FROM THE PUMP WITH SAID REFLUX WILL NOT SIGNIFICANTLY ADD ETHANE TO SAID REFLUX AND THEREFORE TO SAID FRACTIONATION ZONE.

6. An operation according to claim 1 wherein said second liquid phase containing propane, HF, organic fluorides and relatively rich in ethane is comingled with said first acid phase and wherein the thus comingled liquids are vigorously admixed with HF acid supplied from an extractor-settling zone, the final admixture thus obtained is passed into said extractor-settling zone, thus extracting into said HF acid the organic fluorides in said second liquid phase, said final admixture being settled in said extractor-settling zone, an HF acid phase containing said extracted organic fluorides is removed, and wherein a hydrocarbon phase formed in said extractor-settling zone is passed to said stripping zone as the feed therefor.