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Патент USA US2404253

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July 1s, 1946.
VFiled Dec. 21, 1944
439ans I
2 dlLS
ATroRNl-:Ysê ì . '7
vPatented July 16, 1946
2,404,253 v
Virgil Scarth, Bartlesville, Okla., .Vassîgnor t to
Phillipsrl’etroleum Company, a _corporation Vof
Application December 21, 1944, Serial No. 569,243
s claims. (o1. 19e-13)y
This invention relates to extractive distillation,
more particularly to extractive distillation of hy
drocarbon streams containing unsaturated hy
drocarbons using furfural as the solvent, and still
It is not desired to be limited to any theory as
' to the cause of the furfural becoming corrosive.
It is conventional practice to purify the fur- _
fural continuously by “re-running” a side stream
of the furfural leaving the stripper and recycled
to the absorber. This is carried out in ’accord
more particularly to extractive distillation for
the recovery of aliphatic monooleñns and/or ali
phatic conjugated dioleñns especially normal bu
tene and/or butadiene from hydrocarbon streams
containing same with furfural as the solvent.
It has become customary to recover unsat
urated aliphatic hydrocarbons especially butene
and/or butadiene from hydrocarbon streams con
taining them by extractively distilling the stream
ance Vwith U.v S. Patents to K. H. Hachmuth
2,372,668 and 2,350,609, and Buell et al. 2,350,584.
large portion of this loss is due to polymerization
of the furfural in the re-run unit. At present
the furfural is re-run for the purpose of remov
ing otherfcorrosive material as Well as the poly
in a fractional distillation column or absorber
into the top of which there is introduced con
15 mer.; If a feasible method of preventing the
tinuously a stream of furfural, usually contain
>ing a few per cent of dissolved Water, in amount
l suiïicient to dissolve the unsaturated hydrocar
However, there is considerable additional loss of
furfural during the re-running operation. A
The top of the column is refluxed with a
accumulation of corrosive material in the furfural
in the main system (i. e., in the absorbing and
stripping operations) were available, the amount
of furfural passed to the re-run unit could be ma
portion of condensed overhead vapors , in the 20, terially
usual Way and the bottom of the column is pro
vided with the conventional reboiler for the pur
pose of boiling the rich furfural as it attains the
bottomso as to free it from undesired paraffin
.and/or olefin. The rich furfural is withdrawn 25
decreased with many advantages princi
pal of which is the reduction of polymerization of
furfural in the re-running operation. Many
other advantageszof such a method will appear
The principal object of the present invention
`is to provide` an improved method of conducting
extractive distillation of unsaturated hydrocar
per is provided with reboiler and is refluxed with
bons with furfural. Another object is to pro
a portion of the condensed overhead. The pur
.vide a feasible method of preventing the accu
pose of ref‘luxing the absorber and stripper is to 30 mulation'of corrosive material in the furfural in
prevent carryover of furfural into the overhead Y an extractive. distillation system wherein unsat
urated hydrocarbons especially aliphatic mono
vapors. The stripped furfural is then returned
from the bottom of the stripper to the absorber.
oleflns and dioleñns are separated from hydro
. During extractive distillation of unsaturated
carbon streams containing same. Another object
lwdrocarbons with furfural the furiural becomes 35 is' to provide such an extractive distillation sys
contaminated with acids, polymer and other im
tem applied to the recovery of normal butene
purities which are very deleterious because they
and/or butadiene by means of furfural. Another
are highly corrosive to the metal equipment. The
object is to provide a method which greatly re
resulting corrosion'of expensive equipment in
duces the amount of furfural which has to bel
cluding fractional distillation columns and ac 40 passed to the re-run unit. Another object is to
prevent corrosion of the main system (i. e., the
cessories such as piping,` reboilers, condensers,
accumulators, pumps and so forth presents a
extractive distillation system proper as distin
serious problem for which various remedies have
guished frornthe re-run unit). Another object
been proposed none of which is entirely satisfac
is to reduce the loss of furfural in the extractive
tory, so far as I am aware. The cause of the 45 distillation system and in the re-running opera
formation of corrosive impurities in the furfural
tion. Another object is to prevent the formation
is not known even though the problem has been
of‘corrosive impurities in the furfural at the
extensively investigated. Factors which may con
point where those impurities are most deleterious.
tribute to the formation include high tempera
Another object is to accomplish the foregoing ob
ture, presence of Water and presence of unsat 50 jects in‘a manner which does not cause foaming ’
urated hydrocarbons. It is believed by some in
of the furfural. Numerous other objects will
vestigators that the furfural selectively absorbs
hereinafter appear.
traces of corrosive material from the hydrocar
The accompanying drawing portrays diagram
bon feed or of material from the feed which be
matically one arrangement of equipment for‘car
;comes corrosive upon reacting with the furfural. 55 rying out the present invention.
and fed to a stripping column where the dissolved
unsaturated hydrocarbon is removed. The strip
? '3 V casta of the debutanizer overhead with' furfural where- y
I have discovered that
the extractive distil- Y
_, -
by the butadiene andbutene-Z content are dis
lation of hydrocarbon streams with furfural as
' the solvent to recover unsaturated hydrocarbons
therefrom the furfural may be prevented from
solved in the furfural and subsequently recovered
therefrom by the stripping operation, and finally
fractionally distilling the butadiene-butene-Z
becoming corrosive and from corroding the equip
mixture to separate pure butadiene from butene
2. This process y»is fully described in the copend
ing application ,of K. I-I. Hachmuth, Ser. No. 481,
Vment by,` intimately contacting the >furfural in
the extractive distillation system with lime. . The
term “lime” as used herein denotes calcium hy
droxide. I have determined that limestone will'.` -`i 305, filed March 31, 1943, which has now matured
10 into Patent No. 2,386,310, dated Oct. 9, 1945. The
' present invention is applicable to the furfural ex
the inné' I tractivedistillation system in step II or in step IV
not operate in the process of the present .in
The contacting of the furfural with
is commonly accomplished `by~introducing the
lime in finelyfdivided form into -the'furfural‘in
>or in both» Or it may be applied in those `bu
tadiene plants where normal butylene feed is
any suitable manner. The lime may be added 15 catalyticall'y-dehydrogenated-to butadiene and bu
tadiene-is> recovered from the eiiluent by extrac
n the dry form, as a dispersion or slurry> in Vfur-V
fural,> as a dispersion or slurry in water orbyv tive distillation with furfural.
other methods.
Insu'ch an extractiveV distillation process the i
l iurfural enriched in unsaturated hydrocarbon is
Probably the most convenient
method is to add it in the form of a suspension
withdrawn from the bottom >of the absorber and
or dispersion in a'portion‘or all of the makeup
water whichv is lcommonly added continuously to
passed to the stripper where the unsaturated hy
drocarbon is stripped therefrom. The stripped
. the fur‘fural fed to the absorber or absorbersiin
iurfural is then cooled and after addition of makee
up water is recycled to the absorber.V Usually a
v addition of"make-up water is for the purpose of 25 surge tank is provided inthe recycle line. A side
stream of the stripped furfural is continuously
replacing water volatilize'd from the furfural in
order to impart the desired content of dissolved
water to the furfural. It will be understood that
fed to a furfural re-run unit wherein it is steam
the absorbers and strippers. vThe use of furfural
containing dissolved Water as a solvent in the ex
distilled, e. g. in the manner of Buell et al. 2,350,
ing application of K. H. Ha'chmuth, Ser. No. 438,
„ i’rornk polymer and other material relatively non
, 584, to give a puriñed material consisting essen
tractive distillation of normal butene and/erbu
tadiene is disclosed and claimed in the _copend 30 tially of furfural and dissolved water and free
844, filed April 13, 1942.
volatile Awith steam. The re-run furfural is then
merge'd with the main recycle stream for passage
to furfural storage and ultimatelyto the absorber.
iuríural >Wherever the furfural becomes corrosive> 35 'I'he volume of furfural passed to the re-run unit
is preferably such as to maintain the concentra
due to conditions prevailing in the extractive dis
tion of polymer in the furfural in the system at
tillation system. The factors which cause the fur
below 1% by weight.
fural to vbecome corrosive are but little under
In accordance with the present invention lim
stood but it is believed that they include the -high
temperatures especially in the reboiling- sections 40 is admixed with the furfural in the extractive
distillation system, for example, by suspending. it
of' the absorber and stripper, the presence ofwater
therein inA any suitable way.> It ispreferredgto
andunsaturatèd hydrocarbons especially oleñns
limit: the amount of lime to that'required to keep`
„ and dioleiins, the presence of air or oxygen. The
the acidity at the desired level. 'I'he amount of
development of corrosivity in the furfural is ac- `
lco'n'ipani'ed bythe «formation of polymer which 45 lime required is so small that in practice no dif
ficulty due to sedimentation of the .lime or its re
represents a?lo’ssV ciï furfuralland- causes poor heat
The present invention is applied t0 the extrac
tive distillation of unsaturated' hydrocarbons `with ' '
action products is encountered.Y The lime >or a
transfer ‘and other troubles. The presentv inven
portion thereof may dissolve in the furfural; the
tion-is especially applicable to the eXtractive-dis
presence of dissolved water in the furfural may
tillation of butadiene and/or normal Abutene with
fur-tural, this 'being the -principal if notrthe `only 50 enhance any such tendency.
commercial application of eXtractive distillation
with furfural as a‘means of lrecovering unsat
urated. hydrocarbons.
However,l vit may also be
applied where furi‘ural is used in the recovery by
extractive distillation of otherl aliphatic olefins
or aliphatic conjugated diole?lns from hydrocar
A very convenient method of contacting the
furfural with the lime is to employ an excess of
a dispersion of lim'efin water,-admix it very in
timately with the furfural Yin’any suitable way,
55 for example, by means of >a ycentrifugal mixing`
pump, run the resulting churned-up mixture'or
emulsion into a settling tank where it is allowed
to separate into two layers, an upper layer of>
The conversion of normalk butane to butadiene
the Water and lime which have. not dissolved in
is now commonly effected by a series of stepsin
cluding (I) catalytic dehydrogenation of normal 60 the furfural and a, lower layer of furfural which
butane to normal butene, (II) recovery of normal , is saturated with water and which may contain
dissolved lime. 'I‘hese layers are separately with
butene and recycle normal butane by ñrst frac
drawn, the water layer being recycled to the mix
tional-ly distilling the C4 content ofthe .effluent
ing lzone to save its water, lime and dissolved fur
>from-step I in a butene-l column> wherein butene
1 is recovered overhead followed by extractive dis 65 fural content and the furfural layerbeing fed'to
the absorber. Under conditions where corrosive
tillation of the resulting bottoms fraction of~nvness of thefurfural in the system can beikept
butane and butene-2 withfurfural to separate
down to a satisfactory level Such a treatment as
Vthe butene-Z from the normal butane which is re
just outlined may be appliedto asidestrearn of
cycled to step I, (III) passing the combined bu- ‘
`the recycle furfural, the resulting non-corrosive
tene-1 and butene-Z recovered in step II to a sec
furfural being intimately admixed with theÍ bal-ond catalytic stage and therein dehydrogenating
ance of the recycle furfural and the furfuralfrom
Ysame to butadiene, and iinally (IV) recovering
bon streams containing the same.
butadiene from the C4V content of the efliuent of
the re-run unit and allowed to stand as in a surge
.or storage tank for a. period of'time beforeV being
Step III bv a ,Sequence 'Ofsisps .includínsdde
propanizing, debutanizing, extractive distillation 75 re-introduced to the absorber.
_- " aap/i353
’ 5
Alternatively 1an excess :of .powdered lime may
be intimately'admixed with the'furfural and after
a suitable period of time separated therefrom by
and suitable means such as'îñltration, centrifug
the furfural to. reduce the acid content of the v
indicated above,> the ,acidcontent ofthe fur
fural is not necessarily an absolute index of its
corrosiveness. It is',` believed that the concentra-V
tion >of corrosive materialin the furfural in
creases somewhat in proportion to the acidity. At
levels of acidity greater than 0,04 percent itis
evident thatl some factor other than acidity
furfural in theextractive distillation system be
comes into play asa cause of corrosion since be
ing or sedimentation.
Y -4
It is preferred to introduce enough lime Vinto
low 0.06 per cent by weight, measured as acetic
tween levels of 0.04 and 0.06 per cent acidity Vse
acid, and still more'upreferably below 0.04 per v10 rious corrosion may or` may not -occur and at
cent by weight. I have found that below 0.04- per
levels` of acidity above-0.06 percent .the corrosion
cent of acidity no appreciable corrosion occurs;
wliich'occurs is not always serious although it
between 0.04 and 0.06 perv cent Íacidity the con
>usually is. In any event, whatever the causes of
corrosion and’regardless of theory it has been
centration of the corrosive substance whatever
it isvmay or may not -be suchïthat >serious-corro 15 proven absolutely that by addition of lime to the
_sion occurs, apparently depending uponiactors
not understood at present; while, at an acidity»
above 0.06 per cent corrosion. always occurs >and, is
.usually so high that the equipment, especially
furiural in the system in an amount such as to
reduce the acidity to, or maintain the acidity at,
levels below 0.04 per cent serious corrosion is pre
vented and polymerization is inhibited; while re,
the fractionating columns (i. e. the absorbers) 20 duction of acidity to, or maintenance atylevels
and the strippers, would soon be eaten away be
between 0.04 and 0.06 per centiby the addition
low the point of safe operation if the plant con
tinued to'operate at such levels ofv acidity. Fur
thermore, the loss of furfural by polymerization
of lime in most cases prevents seriouscorrosion
and reduced polymerization of furiural to satis
at levels of acidity above 0.06 per cent becomes 25 In accordance with the present invention the
excessive so that furfuralY consumption exceeeds
acid content may be _reduced nearly to or to the
the available supply vwhich is exceedingly dan
Aneutral point or the furfural may be made valka
gerous to the synthetic rubber program.- The re
line although the latter practice is not ordinarily
lationship between level of acidity and poly
followed because the tendency of -furiural to pol
merization of furfural is at. present not under 30 ymerize is enhanced under y alkaline conditions.
stood and I do not wish to be limited to any the- ' It is preferred to add only enough lime to reduce
ory with regard thereto.
the acid content below 0.06 per cent and prefer
ably below 0.04 per cent which practically elim
fural at a point in the system such that the fur,
inates corrosion of carbon steel by the lfurfural,
iural is at a temperature of not over 130° F. at _the 35 however, the nearer the neutral point or the point
point where the admixture takes place. Usually
of zero acidity the’less polymers of furfural will
the coldest point- in the furfural system is just
be formed. When the acid content of furfural in
after the cooler or coolers which are employed
the main system is below 0.04 per cent the cor
' to cool the furfural leaving the stripper or strip
rosion of carbon steel equipment is negligible and
persand so it is preferred to add the lime at 40 the rate of formation oi polymer is substantially
this point. The reason for adding the lime at a
lower than when the acid content is above 0.06
. It is preferred to introduce the lime to the fur
point of `low temperature` is that the possibility
of , additional polymerization of furfural upon
the introduction of lime to hot furfural is there
by eliminated.
The purpose of lime addition is to reduce the
acid content of the furfural, reduce the» forma
tion of polymer and the corrosiveness of the fur
fural. The manner in which vthese several fac
tors are inter-related is not understood but it has
been deñnitely established that the Vaddition of
lime’does prevent the furfural from being cor-v
rosive and does` reduce the polymer formation,
`whether one causes the other or not. The pres
‘ entv invention may be employed kfrom th'e‘start-
of operations tokeep the furfural in the system
from ever becoming corrosive or may be applied
.per cent.
The products formed from the reaction of lime
are removed >from the system in there-run unit
with the polymers, so no problem due to accu
mulation of lime or its reaction products is en
countered. In ordinary operation the re-running
is carried out at such a rate that the furfural in
the entire system is re-run in a short time- -say
every two to` three days. If enough lime is added
to cause a sediment to form in the main system
it may be necessary to provide a trap or filter to
remove the sediment from the furfural. My in-
vention may be applied by adding lime to aïsmall
side stream of furiural andv any sedimentthat
„might beformed may be removed by iiltering or
some other method before the furfural is re
to systems in which the furfural hasbecome Vcor
turned to the main stream. However, it is voften
.rosive to eliminate lthe corrosivity and keep »the
-system thenceforth non-corrosive. Thus the ~ 60 desirable to add only enough lime to reduce’the
acid content of the furfural to the extentuindi
,process of the present invention prevents non
cated but not enough to result in difficulties due
ycorrosive furfural from becoming corrosive and
to lime or the reaction products of lime settling
also prevents corrosive furfural from exerting its
in the system,
deleterious action. The addition of lime inac
cordance with the present invention involves 65
fural which is added as makeup to the system
`more than simple neutralization of corrosive
may be treated with lime prior to its introduc
acidity since it inhibits polymer yformation as
tion into the extractive distillation system.
well. Moreover, it has been found by experimen
In accordance with the present invention lime
tal work that neither the acid content nor the pH
Aof furfuralis necessarily an index of its corro 70 is added in the main system, i. e. in the extractive
distillation system proper, as distinguished from
siveness. . It will be obvious that acid content and
the re-run unit. 'I’he addition of lime to the y
VpH are not the same since it is common to have
1a high acid content associated with' a pH rang
re-run unit is disclosed and claimed in my copend
»ing from 0 to '7 or a lowïacid content anda pI-I
ing application Ser. No. 607,212, filed July` 26,
l»ranging from‘llto .7.;
_ -75
amount of lime ademend-.the .rate fat :which rur-l
7 ¿it iis-often -desirabie-to-appiy the presentimen
tionf-‘to extractive distillation` ?system-s ~ wherein
~furîural »has'rbeoome «excessively corrosive.
> tion.
suchcaseit may be desirable toadd-enough fur-’-y
furalin' the mainsystem to `reducethe acidity V0.02
In themanufacture ofibuta'diene by 'twoestage
. per-cent each day until it is «below 0.04 perV cent
'dehydrogenation of normal butano. afrecoverv
and -to then reduce the amount of <liifneaddeol
system, as lshown in the drawing, was employed.
Furfural was fed continuously into the ‘absorbers
2 and 4 at the rate of '260,000 gai/hr. entering
toa lñgure which will‘hold-theacidityat `thisleveL`
Referring to the >accompanying drawing, I have
illustrated diagrammatically., .the Y `'application >of
, my invention toßarplant in .whichbut‘adiene is
io both absorbers. The furfural v'corit‘a'ined-öfïàfo‘iî
made .by the twoesta'ge .catalytic dehydregenation
Water Áby Wei'ghtrbased on 'the Weight Aof furfn‘ural
and water. The stripped ‘furfural >from Yboth
of normalbutane. The mixture of normal «butane
>and butene-Z >recovered .from .step I'oiîV the .process
enters absorber 2 via line I., while the C4 hydro'
strippers was cooled to 1Z0-130° F. and the major
part' of the cooled product waspassed tothe
surge tank 2l. A side'stream of 3500 gah/hr. 'was
carbons uderivedirom step III . and >containing
butene-Z and. butadiene enter ‘absorber .4 via line Y
» withdrawn via line '23 and 'fed >to refrun unit 24. '
3. Absorbersz and 4 carry out the extractive dis
tillation of thefeed with furfural injected into
V?l‘he total volume of'fu‘rfural in the entiresystem was 225,000 gallons. ‘Theacidity-ofthe fur*v
f'ural in the main system was 0.510 weight per centV
>the top via lines 5 and 6, respectively. Absorbers v20 measured as acetic acid.y This vwasexceedingly
2 and 4 areprovided with conventional reboiling
corrosive to the equipment and polymer formation
means and means for condensing and returning a
was excessive. The acidity had> been 'approxi
mately 0.10% lfor ten days, during which time
portion ofthe overhead as reflux, the latter being
indicated diagrammatically by a cooling coil in
the polymer content increased> from 0.4 t'o_~1.5
the top of each absorber. . The undissolvednormal 25 per cent by weight. Under these conditions, .
namely at 0.10% acidity, [1,5% polymer( concene Y
butane leaves absorber 2 via line 1„ while >the
»furfural rich in butene~2 is> withdrawn‘asjbottom
tration and 3500 gal/hr.y of 'iurfural 're-run,
product via line ß` and fed <to ,stripper 9 where j equilibrium 'had been established. ' However.,
operations were unsatisfactory and it was con
the dissolved butene-2 is driven 01T. ¿ Stripper 9
Vis likewise provided‘withy conventional reboiler V."II) sidered imperative to vreduce corrosionV andi poly
yandmeans for condensing and returning a portion
merization because otherwise the plant would be
corroded away in a short time and it would be
yof the overhead as reñux. .
„ v
The undissolved C4 hydrocarbons leave absorber
impossible to obtain ‘sumcient furfural to continue
4 via line I0 While the -furfurall rich in butene-2
and butadiene passes via line II lto stripper I2
Under the foregoing conditions, 'lime wasadded
Whichperformsthe same function asstripper 9,
v to the furfural-in the vmainïsystem at a rate vof
the butene-2 Vand butadiene mixture leaving via
line I3. The stripped furfural streamer-leaving
stripper 9 via line I4 and stripper I2 viafline I5,
are merged and fed via lline IB to cooler Il. YIt
will be understood that a >cooler may be provided
11 lbs/hr.V 'I‘he lime wasI added in the form of
a slurry in the makeup water Whichwas employed
>to keep the water concentration at approximately
6%. The slurry was admixed with the furfural
recycle stream immediately after the cooler.- as
for each stripped furfural stream if desired. The
cooled furfural ñowing vin line I8 is passed via
began to decrease at the rate »of approximately
lines I9 and 20 to furfural >surge or storage 2|
0.015% pel' day. When` the acidity reached 0.04%`
whence it is recycled via line V22> and lines?) and .G
_to thevabsorbers. A side stream ofrîurfuralï is
passedrvia line`23 to the re-run unit 2l whereit Yis
lbs/hr. Aand the acidity varied ‘from 0.03Y tol
0.030% from then lon 'for an irideñnite-fpe'riod.
vshovvn in the drawing. The acidityY immediately
the rate of addition of lime was decreased `to 6
continuously pur'iñed, inthe manner new well
-The polymer content had'decreased 'to’0.3% and
know-n in the art, to removerthe polymer there
remained at abouttiiis figure. Vsimultaneo'usly
Vfrom.V The re-run furfural -is `passed via line `2'5 15o with the attainment of 0.04% 'acidity,`the'rate 'of
into the main recycle stream inline I9.
reerunning 'o‘f lfurfu'ral was rreduced 'to 2000
` In accordance with thepresent invention'lime
gaL/hr. whichfsumced to keep 'the polymer con
_is continuously fed in the properamounts indi
cated above vinto the main recycle stream Vflowing
centration from increasing above 0.3%. '
As a result of 'the use of lime in the'manner
. in line I9. This is accomplished by means of line
described inr the foregoing example'the .loss of‘
26 which, it will be understocd'is `purely .dia
furfural'in the 'plant Was vreduced vfrom’ 4000 Yto
grammatic. Usually Íboth lime and water are
injected into the stream in line I9. As explained
Vabove it is'often convenient to inject the make
up water at this point. A 'point of injection off
lime `close to cooler Il is preferred because the
temperature is at substantially kthe 'lowest level
at this point and because this gives ajre'latively
long line between the point of injection of lime
Vand furfural surge 2|. Intimate'mixing of the
lime with fur'fural may take place in the long pipe
indicated by lines I9_ and ‘20.
It will be understood that _the showing in the
drawing is purely diagrammatic and that the
lime and water may be added "separately or in any
desired manner and that »provision> maybe made
'for the removal -of any excess lime'or sediment.
It mayor may not be‘necessary' ‘to-provide for' the
removal of the reaction ïproduötsïof lime an‘díth'e
I impurities in the furfural, depending' uporiltli'e
The amountV of lime necessary to 'be added'to
the rurfurai in accordance with the present 1in
vention 'in order to keep the furfural from be
coming >corrosive and .the polymer content thereof
from increasing is extremely small. ' Under’ordi
nary conditionsoi operation; 'it `ranges from
0.000005 to 'O-.OOOOGÄlbs/gal. of kf'urfural> ie‘d into
the y»absorber perhour. Thus,A the >total ypounds
etlime in the systemat'any onetime isvery small,
'usually less 'thani10'00 lb'sjîfor a system `containing
225,000 ygallons furfural as in thefexample.
‘From the foregoing, many advantages of the
present invention will ‘be’ apparent îto those
VVskilled in the
that corrosion of ’the lequipment'inthe main Y
y system> is prevented.' “This allows the ‘use of
equipment of ` carbon - steel'which -ismuch' flessrex‘
pensive than corrosion-res'i‘starít’metala‘ïrnn-- _
other major advantage of the present invention
no» problem due to sediment in the main system
is presented. 'I'he lime or its reaction products
is completely removed from the furfural in the
is that it inhibits polymer formation in the main
system which of itself gives rise to many advan
tages well known to those skilled in the art. The
invention accomplishes simultaneous reduction
in the level of acid concentration in furfural in
the extractive distillation system and reduction
in the rate of polymerization of furfural. The
invention is simple and can be carried out with
out requiring expensive additional equipment or
introducing complications into the existing ex
tractive distillation system and re-run unit. By
using lime, there is no danger of high concen
tration of alkaline material at any point which
re-running operation. Many other advantages
of the process of the present invention will be
apparent to those skilled in the art.
I claim:
1. In the process of >separating unsaturated
aliphatic hydrocarbons from a mixed hydrocar
bon stream containing such unsaturates by ex
tractive distillation wherein said mixed hydro
carbon stream is passed upward through an ab
sorber tower in countercurrent to a descending
stream of solvent composed of furfural contain
ing dissolved water; a bottoms product consist
ing of furfural rich in unsaturated hydrocarbonV
is withdrawn from said absorber tower; said bot
tom product is introduced into a stripper 'column
and there stripped of its unsaturated hydrocar
bon content; a bottoms product consisting of
stripped furfural is withdrawn from said strip
per column and split into tWo Streams; one of
such resulting streams is passed to a re-run unit
`and. there distilled to give a. purified material
would be harmful because it would cause an un
duly high rate of polymerization of furfural;
lime is unable to give a highly alkaline condition
by reason of its nature and limited solubility in
furfural. The invention is extremely economical
to apply because of the small amount of lime and
because lime is cheap. The invention greatly
reduces the amount of furfural which has to be
re-run in order to remove polymer. This reduc
tion in amount of furfural re-run gives rise to
many other advantages, the principal of which
is the markedly reduced loss of furfural and the
lowered cost of re-running the smaller amount
of furfural. It will be understood by those skilled
in the art that loss of furfural in the re-run
’ consisting essentially of furfural `and water dis
solved therein; the purified furfural is combined
with the other stream of stripped furfural and
the resulting combined furfural stream is re
cycled to said absorber tower as solvent for the
system is high because the re-running itself
extractive distillation step; that improvement
the re-run unit.
factors other than acidity by introducing lime
causes additional polymerization and because it 30 which consists of simultaneously inhibiting poly
merization of furfural corrosion of equipment
is necessary to leave aconsiderable amount of
due to `acids and corrosion of equipment due to
furfural in the polymer in order to get it out of
The invention is further advantageous in that
it accomplishes prevention of formation of im 35
purities at the very point where such impurities
are most deleterious, namely in the extractive dis
tillation system which embodies very expensive
absorber and stripper units. A very marked ad- '
vantage of the present invention is that it causes 40
no foaming of the furfural in the extractive dis
tillation system. Foaming of furfural in the ab
sorbers and strippers is most objectionable. The
behavior of lime introduced in accordance with
the present invention is to be compared with that
droxide. Undoubtedly such sodium compounds
tion of polymers; however, such alkaline-reacting
between the place where said stripped furfural
stream is split and Ithe place where the recycled
stripped furfural is fed into said absorber tower;
and controlling the amount of lime so introduced
so that the acidity of the furfural in the extrac
tive distillation system is maintained between
0.2% and 0.6% by weight, calculated as acetic
2. The process of claim 1 wherein the lime is
introduced into the furfural in the form of an
aqueous dispersion.
3. The process of claim 1 wherein the introduc
of soda ash, sodium bircarbonate or sodium hy
would, if added to the furfural in the main sys
tem, substantially decrease corrosion and forma
into that branch of the stripped furfural stream
which bypasses the said re-run unit, at a point
alkali metal compounds cause ythe furfural to
foam which cannot be tolerated in processes of
absorption and stripping. Even traces of sodium
hydroxide, carbonate or bicarbonate cause foam
ing of furfural so that it would be completely im
possible to use such materials in place of lime in
accordance with the present invention.
Another advantage of the present invention is
that the amount of lime required is so small that 60
tion of said lime is accomplished by admixing
same with said branch of the stripped furfural
stream which bypasses the re-run unit While said
furfural is at a temperature of not over 130° F.
4. The process of claim 1 wherein said hydro
carbon stream is an aliphatic C4. stream and
wherein said unsaturated hydrocarbon is an ali
phatic C4 hydrocarbon.
5. The process of claim 1 wherein said unsat
urated hydrocarbon comprises butene-Z,
6. The process of claim l wherein said unsat
urated hydrocarbon comprises butadiene.
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