US3169997A - Simplified debutanizer for use in isobutylene extraction - Google Patents

Description

16, 1965 s. P. BAUMANN ETAL 3,

smmnan DEBUTANIZER FOR USE IN ISOBUTYLENE EXTRACTION Filed June 15. 1960 STEAM DEBUTANIZER SETTLER George--R1Bnumunn Earls: A. Nirmuier By I 7 ;M Puteni Attorney invemors acid when needed;

i amass? f snarmarnnnnnnraruana non use as rsoabrrrnrsa nxrnaorrom United States Patent low temperature stage. In the preferred f ormYof the invention the C hydrocarbon fraction, either the.

George P. Eauni'ann, gpa rta, and Earle A.'Nirmaier,

Mapiewood, Nah,- assignors tt'i EssoRese'arch and Engineer'ing Company, a corporation or Delaware. v

Filed lane 15, rate, Ser.'No. 3%,23-6

Claims. (til. Edd -539) The present invention relates to processes for extracting :isobutylenefro m refinery C streams to thus obtain concentrated n-butene feed strearnstor dehydrogenation.

More particularly, this invention relates to improved processes of the type wherein isobutylene is absorbed in sulfuric'acid, and the extract stream is either (1) diluted and stripped under. conditions 3 to obtain predominantly isobutylene monomer, or (2,) heated to 250-380 F. to

dimerize the isobutylene, followed by settling to separate the dimer from the sulfuric acid. In the "former case the raffinate stream is distilled ina. debutanizer tower to gaseous; orliquid state, is contacted withthe partially spent acid from the low temperature stage. at a ternpera- I tore between 90 :and 110 15., preferably 100"R, in'any suitable mannen For example, resort may be had to agitation inaconnnon vessel or to 'couhtercur-renfflOw. It is desirable when employing the C fraction-in a V gaseous state to conduct the process in counter-current fashion; through a packedtower as this system lendsitself most readilyto intimate distribution of the tertiary olefin" in the-absorbent- By. using an acid extract as theabsorbent which contains from 0.6 to 1.5 molsof isobutylene per mol of. 100% sulfuric acid and operating at a tem-' H perature between 90 and 110"B, '65to 8.5% of the iso- =butylene in the C fraction is absorbed without any sub} stantial absorption of the secondary-olefins; The unseparate the n-butenes overhead from smallaniountsof alcohol and polymer and in the latter case the dimer and vention relates to an improved debutani zer tower wherein caustic treating is obtained within the tower itself by feeding causticto the top of the tower andpr ovi'ding a large caustic'h'oldup zone in the area of the feed plate of the towerJ i.

. The present invention provides lar ge savings over the 2' prior art processes. Thus, it is known that raflinate (and traction and settling operations. To provide for these upabsorbed '15 to 35% isobut yleneis then absorbedin fresh sulfuric acid having a concentration between 55, and 65 wtpereent, preferably 63 wt. percent if steel construction isto be used, atatemperature between 55 and 75 F.,

preferably 60 F. Thewcontact between the acidand the jolefin may be, carried out in any manner as described above butis'likewi'se preferably carried out'in a packed column. The acid extract thus formed contains between 0.2 and 0.6 mol of isobutylene permol of acid (basedon 100 sulfuric acid) and is particularly suitable for use as the absorbent in the high temperaturefstageg' The C ratlinate stream (along with the extract dimer hydrocarbonstream-if dimer 'is produced) is then debutanized in order to provide a C free normal butene stream for dehydrogenation. 1

dimer) streams from: the extraction process vary fwidely in acid leveldue to periodic minor upsets in the exsuppliedto the tower.

sets large. amounts of caustic have been required in the) conventional caustic treat facilities to neutralize "this Additionally. it has usually been thought necessary to utilize Monellining in the dc butariiz'er tower to provide against acids carried over to 1 the towerand against acids formed in the tower from acid esters. Thus these acid 'estersare only partiallyremoved bycaustic treating andthey break down at'the elevated fltemper'ature prevailing in the lower section of ther tower. It has now.be en discovered that towrsof "the type de-' scribed in this invention may. be constructed of ordinary carbon steel, the large caustic holdup zoneand the caustic providing sufficient protection against corrosion.

The presentprocess and apparatus willbe more clearly understood from,a consideration of the total process. for; preparing feed streams for dehydrogenation of. normal {butenes to butadiene. Thus, in the production of butadiene it is preferably thatjisobutylene be removed so -that the butenefeedstreamrnay be 'dehydrogenated'to extinction. ,A refinery C4 stream 'obtained for. example 1 from steam cracking is absorbed in dilute sulfuric acid fiowingdownwardly'in the lower section of the column The stream or streams from the extraction process sup plied to thedebutanizer will contain acid esters and free acid (nonnally about 0.2 percent-meld), Since the esters break down during heating bothqcompounds re v sultin corrosive conditions in the towen According to i the prior :art corrosive conditions in the debutanizer tower were alleviated by caustic washing the feed stream l in an orifice mixer andisettler system prior to its being A considerable investment; is m involved'in'this prior. art systernsinceas previouslydis, cussed large capacity mustbeprovided-to take care: of the highly acid conditions encountered during minor upsets. Further, it hasbeen found'in'commercial operaQ tions using such a caustic prev/ash system that isevere corrosion and operating} difiiculties 'areAstill/obtained. Thus, for example, the following notes were recordedin connection with a commercial ,isobutyleiie extraction and dimerizatienoperation. -.y i

(a) luneQ, UnitUpset. ffi 'cid circulationjwajs op and the caustic increased to; maximum 'available ji Even after four durnps'of caustic inventoryfithe system was 7 still acid. This meant we could not neutralizetheester' content'of the rallinate from the extraction settlers a (b) June 9. Rerun tower feed preheater'tubes corrodedthrough and the unit was shut down. Inspection "showed that somejet tabson the feed tray marten 1 thinned down.

- -"(c-) December 19.- The 'systerrrwas fairly well lined p out when a leak'was-discovered at a weld in the 3. inch spent butenes line'to the caustic mixer downstream of,

The .line wa'srfoundto be and the isobutylene acid extract is removed by settling.

A preferred method for carrrying out this process is described for example in US. 2,424,186 whieh patent is hereby includedby reference. Tnge'neraI {a C4 traction, containing parafiins, secondary, and tertiary ole'fins is absorbed in sulfuric acid preferablyin two stages using i i higher temperature in the first stage than in the second,

a partially spent acidbeing used as the absorbentiin the '1 .the caustic addition. point.

seriouslyeorroded-and very thiu-onlthe upperiside whler e' 2" "the butenes entered for about linchesffrorri the edge' ofrf the .butene' entrytpointi Minor. corrosion 'on'the' upper part of the line continued for 'ab out 30 ftfi These illustrative problems 'j and others reported' in erating isobutylene extractionfunitsllwill' be av'oided utilizing;'the simple combinedjdebutanizer and caustic:

treattower of this invention.

"high temperature stage and fresh acidbeingused in the Illustrative of the investment-savings obtained by the p 7 masses, Patented Feb. 16, 1965 I present invention it is estimated that for a typical isobutylene extraction and dimerization operation the conventional caustic treat system (which is eliminated in the present operation) costs about $40,000 or 6% of the total investment of $650,000 for an entire isobutylene extraction plant. Additionally in the preferred embodiment the need for Monel lining of the dimer tower is eliminated providing large additional savings.

The present invention will be more clearly Understood from a consideration of the accompanying drawing depicting a preferred debutanizer tower and associated equipment. Although the tower may be either of the tray or of the packed type a bubble cap tray tower is described in the drawing. Turning to the drawing the normal butene raffinate stream from the isobutylene extraction settler is supplied to the tower 3 through line 1. If the process is of the type where isobutylene dimer is produced this dimer is also passed to the column (from the dimer settler where sulfuric acid is removed) through lines 2 and 1. Both of these streams are of course acidic. The single or the combined feed stream is supplied through a sparger (not shown) into the liquid on feed tray 4 located in the central section of the tower. This feed should preferably be supplied as a liquid although vapor or mixed vapor-liquid feeds can be used. The feed tray is of special design so as to be able to neutralize the equivalent of 20 minutes flow of 5 wt. percent entrainment of 65 wt. percent sulfuric acid. This large caustic holdup assures complete neutralization during the ordinary minor upsets in the isobutylene processes above described so that no pH change of the stream leaving this feed tray occurs. Dilute aqueous caustic solution is supplied to the upper part of the tower through line 3a. In a preferred embodiment open steam is supplied through line 4a and an additional sparger (not shown) into the liquid on the feed tray to provide feed preheat and additional steam is supplied through line 4b to the bottom of the tower to provide heat for the distillation.

III. RELATIVE AMOUNTS OF TOWER STREAMS General Preferred Specific Ralfinate to Dimer Stream (where dimer is produced), percent by weight. 300-800 500-700 600 Lb. oi Caustic Solution/lb. t Feed. 0. -0. 5 0.1-0.2 0.15 Composition of Caustic, wt. percent NaOH 1-10 2-5 3 Dimer Operation, Bottoms on Feed, percent by weight"; -50 -40 Monomer Operation, Bottoms on Feed, percent by weight 1-15 2-10 5 IV. OPERATING CONDITIONS Tower Pressure, p.s.i.g -100 -70 65 Temperature Bottom 0 F 230-300 240-290 265 Temeprature, p of 70-100 80-150 124 Reflux Ratio 0 5:12:1 0.8:11.5:1 1:1 Open Steam Supplied, lb. Steam/lb.

of Feed 0.2-0.7 0.3-0. 5 0.35

V. DESCRIPTION OF COLUMN Plates (Feed to Middle Section of Column) 10-40 15-30 20 Caustic Holdup on Feed Plate,

Gallons Holdup/grill. of Feed 00-. 30 1-. 2 15 VI. 0 STREAM OVERHEAD COMPOSITION, PERCENT BY WEIGHT VII. DIMER BOTTOMS COMPOSITION (CAUSTIC FREE),

PERCENT BY WEIGHT o4 Turner 5-35 10-30 18 C4 Dimer 60-90 65-88 78 C 0-10 2-8 4 It should be noted that this steam should not be added I directly to the feed stream due to the acid nature of said feed stream. Alternatively conventional reboilers and feed preheaters can be used. From the top of the tower the overhead C stream is passed through line 5 to condenser 6 through line 7 to drum 3 and from said drum a part of the liquid stream is passed through line 9 back to-the tower and the remainder of the stream is passed through line 10 to further processing. From the bottom of the tower the caustic and the heavier organic materials,

VIIL- NON DIMER OPERATION BOTTOMS COMPOSITION V PERCENT BY WEIGHT I. COMPOSITION OF BUTENE RAFFINATE FEED STREAM FROM SULFURIC ACID EXTRACTION. PERCENT BY WEIGHT I II. COMPOSITION OF DIMER FEED STREAMS FROM ACID EXTRACT SEPARATOI{,PERCENT BY WEIGHT Isobutylene Dimer .Q-

30-00 00-80 Isobutylene Butene Codimer- 5-30 5-20 15 5-30 5-20 15 Isobutylene Trimer.

The present invention will also be advantageously utilized in extraction'processes for separating isopentenes from normal pentenes. In these processes a refinery C stream obtained from steam cracking, catalytic cracking etc. is absorbed in 55 to 65 wt. percent sulfuricacid, e.g.

63 wt. percent sulfuric acid and the extract stream is either stripped with steam under conditions to obtain high yields of the monomer or is ree'xtracted with a hydrocarbon solvent to separate the isopentenes fromthe sulfuric acid fat solvent. In either event the raffinate stream from the acid extraction process is advantageously processed in the distillation system of the present invention. The normal pentenes ratfinate feed stream to the tower will in general have compositions similar to those described for C hydrocarbons. Thus, the ranges will be: for isopentenes, those shown for isobutylene; for normal pentenes, those shown for normal butyl enes; and for pentanes those shown for butanes. Similarly the tower will be operated under the same conditions as those described above for the processing of butene rafiinate feed streams.

The present inventionwill additionally be advantageously utilized in the production of secondary butanol. In this process a refinery C normal butene stream obtained as above described (i.e. the overhead from the debutanizer) is absorbed in to wt. percent sulfuric acid in 2 or more stages. This feed stream will contain 25 to wt. pecent, e.g. 80 Wt. percent, normal butenes, O-S wt. percent, cg. 0.5 wt. percent, isobutenes, and the remainder parafiins. The sulfuric acid absorption will be similar to the 2-stage process described above in connection with the production of isobutylene or isobutyli the range of 0.06

' ene dimer. In the production of butyl alcohol the extract stream is diluted with Water to about 40-50 wt. percent sulfuric acid concentration and the dilutedsolution is then stripped with steam to obtain the alcohol. The rafiinate stream is processed in the combined caustic treat debutanizer tower'of this invention, under the conditions previously described for processing C raffinate streams from isobutylene extraction.

The present invention can also be used in other processes plate. to obtain countercurrent flow of liquid caustic to the ascending hydrocarbon vapors in said distillation column, holding liquid caustic solution in said distillation column on said intermediate hydrocarbon feed plate in an amount and for a time suflicient to substantially neutralize said dimer-containing raftinate stream and separating C hydrocarbons overhead from dimer and other heavier boiling materials.

with other olefins in the presence'of a phosphoric acid on j Kieselguhr catalyst.

The foregoing description contains a limited number of embodiments of the present invention. It will be understood that this invention is not limited thereto since numerous variations are possible without departing from the scope of the following claims. t What is claimed is:

l. A process for preparing normal butene which comprises contacting a C hydrocarbon feed stream containi ing isobutylene and normal buteneswith sulfuric acid to obtain absorption of a major portion of theiisobutylene in said sulfuric acid, separating an extract stream from an acidic 'raifinate stream, feeding said ralfinate stream directly to an intermediate hydrocarbon feed plate to a multiplate distillation column, feeding liquid caustic solution to .a plate above said hydrocarbon feed plate to obtain a, countercurrent flowof liquid caustic to the ascending hydrocarbonvapors in said distillation column, holding 4. The process of claim 3 wherein the feedstream to the tower is supplied as a vapor and the volume of caustic solution holdup on the feed plate is in the range of 0.06

to 0.30 gallons of caustic solution per gallon per'hour of feed.

5. A process for the production of secondary butanol and separation of C hydrocarbons which comprises contacting a substantially isobutylene-free C hydrocarbon stream containing 25 to 95 wt. percent of normal butylenes with 75 to 85 wt. percent sulfuric acid to obtain an acid extract containing normal butylenes, separating said acid liquid caustic solution in said distillation column on said t v intermediate hydrocarbon feed plate in an, amount and for a time sufficient to substantially neutralize the acids contained in' said raflinatc stream and recovering overheadv substantially neutralized (lghydrocarbons 2. The process of claim 1- wherein the raifinate stream is supplied to. the column as a liquid and the holdup of caustic solutionon "said feed plate of the column is in to 0.30 gallons holdup/ gallon per hour of feed.

-3. A process for preparing a normal butene=containing stream suitable for conversion to'butadiene by dehydrogenation which comprises contacting a C hydrocarbon normal butenes; and other hydrocarbons, separating said" extract fromthe resulting acidic raflinate stream'containplate ofa multiplate distillation column, feeding liquid.

caustic solution to a plate above said intermediate feed plate to obtain countercurrent-flow of liquid caustic to the ascending hydrocarbon' vapors' in said distillation column', holding liquid caustic solution in contact with said rafiinat e stream on said" intermediate feed plate for a time sufficient to substantially neutralizeysaid raffinate and dis,-

til1ing'C hydrocarbons overhead from said distillation" column. g

V References Cited in the file of this patent V V UNITED STATES PATENTS, 2,105,874 Aldridge et al.' Q. Ian; "18, 1938 2,394,678 Frankel et all -Q; Feb; 1 2, 1946 2,456,260 Draeger Decf14, 1948 2,474,569 Bannon June 28, 1949 2,476,010 Whittlesey July 12,1949 1 2,962,537 PctfilS 61'. al NOV. 29, 1900 FOREIGN. PATENTS g 715,483 "Qreat Britain- Sept.'15, 1954

Claims (2)

1. A PROCESS FOR PREPARING NORMAL BUTENE WHICH COMPRISES CONTACTNG A C4 HYDROCARBON FEED STREAM CONTAINING ISOBUTYLENE AND NORMAL BUTENES WITH SULFURIC ACID TO OBTAIN ABSORPTION OF A MAJOR PORTION OF THE ISOBUTYLENE IN SAID SULFURIC ACID, SEPARATING AN EXTRACT STREAM FROM AN ACIDIC RAFFINATE STREAM, FEEDING SAID RAFFINATE STREAM DIRECTLY TO AN INTERMEDIATE HYDROCARBON FEED PLATE TO A MULTIPLATE DISTILLATION COLUMN, FEEDING LIQUID CAUSTIC SOLUTION TO A PLATE ABOVE SAID HYDROCARBON FEED PLATE TO OBTAIN A COUNTERCURRENT FLOW OF LIQUID CAUSTIC TO THE ASCENDING HYDROCARBON VAPORS IN SAID DISTILLATION COLUMN, HOLDING LIQUID CAUSTIC SOLUTION IN SAID DISTILLATION COLUMN ON SAID INTERMEDIATE HYDROCARBON FEED PLATE IN AN AMOUNT AND FOR A TIME SUFFICIENT TO SUBSTANTIALLY NEUTRALIZE THE ACIDS CONTAINED IN SAID RAFFNATE STREAM AND RECOVERING OVERHEAD SUBSTANTIALLY NEUTRALIZED C4 HYDROCARBONS.

5. A PROCESS FOR THE PRODUCTION OF SECONDARY BUTANOL AND SEPARATION OF C4 HYDROCARBONS WHICH COMPRISES CONTACTING A SUBSTANTIALLY ISOBUTYLENE-FREE C4 HYDROCARBON STREAM CONTAINING 25 TO 95 WT. PERCENT OF NORMAL BUTYLENES WITH 75 TO 85 WT. PERCENT SULFURIC ACID TO OBTAIN AN ACID EXTRACT CONTAINING NORMAL BUTYLENES, SEPARATING SAID ACID EXTRACT FROM THE RESULTING ACIDIC RAFFINATE STREAM CONTAINING C4 HYDROCARBONS, DILUTING SAID ACID EXTRACT TO ABOUT 40 TO 50 WT. PERCENT SULFURIC ACID CONCENTRATION AND STRIPPING SAID EXTRACT TO OBTAIN SECONDARY BUTANL, PASSING SAID ACIDIC RAFFINATE STREAM DIRECTLY TO AN INTERMEDIATE FEED PLATE OF MULTIPLATE DISTILLATION COLUMN, FEEDING LIQUID CAUSTIC SOLUTION TO A PLATE ABOVE SAID IANTERMEDIATE FEED PLATE TO OBTAIN COUNTERCURRENT FLOW OF LIQUID CAUSTIC TO THE ASCENDING HYDROCARBON VAPORS IN SAID DISTILLATION COLUMN, HOLDING LIQUID CAUSTIC SOLUTION IN CONTACT WITH SAID RAFFINATE STREAM ON SAID INTERMEDIATE FEED PLATE FOR A TIME SUFFICIENT TO SUBSTANTIALLY NEUTRALIZE SAID RAFFINATE AND DISTILLING C4 HYDROCARBONS OVERHEAD FROM SAID DISTILLATION COLUMN.

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