Note: Descriptions are shown in the official language in which they were submitted.
5~
This inver,t.lon xelates to improvements in the
processing of light olefinic hy~rocarbon streams containing
tertiary olefins and more particularly to processincJ in which
the tertiary olefins in such streams are subjected to
etherification and the remaini.ng hydrocarbons in the streams
are subsequently to be subjected to additional processing to
produce high octane components suitable for blending into
gasoline.
It is known in the art that olefinic mixtures of
light hydrocarbons of predomi.nantly four carbon atoms each
can be processed to provide high octane gasoline ingredients
by etherifying the isobutylene cornponent thereof with methanol
to convert the isobutylene to methyl tertiarybutyl ether (MTBE),
a high octane ingredient for gasoline blending, and optionally
further processing the remaining hydrocarbons of the mixtures
to convert other components thereof to compounds of higher
octane value, for example by pol~nerization or alkylation
processes for making polygas and alkylate respectively. It
is also known in the art that olefinic mixtures of hydroca.rbons
containing predominantly five carhon atoms each can be processed
to convert most of the isoamylene content thereof to tertiary~
amyl methyl ether (TP~IE) which is another high octane ingredi.ent
suitable for blendin~ into gasoline. It has further been
suggested in the art that olefinic mixtures containing hydro~
carbons of both four and f.ive carbon atoms each can be
processed in an etherification reactor to convert simultaneously
both four and ~ive carbon atom tertiary olefins therein to the
tertiary ethers MTBE and TP~IE. USP 3,482,g52 suggests
R,~
etherlfication of an even more ~omplex olefinic mixture of
hydrocarbons with ~rom four to six carbon atoms inclusive,
to form tertiary ethers of higher octane rating than the
original hydrocarbon fraction, distillatlon to separate a
hi.gher boiling ether containing portion from the remaining
hydrocarbons, and alkylation of the portion of remaining
hydrocarbons to form a higher octane alkylated ingredient
. suitable for gasoline.
Because the etherification reaction between
tertiary olefins and methanol .is an equilibrium reaction,
it is not possible to reduce the concentration of methanol
in the effluent from the etherification process below the
equilibrium concentration of methanol and ether products~
Thus such effluent always contains some methanol. It is
now known that such methanol, on distillation of the
effluent, forms minimum boillng binary aæeotropes, not only
Wit}l the ethers MTBE and TAM~ and a number of the higher
boiling hydrocarbons in the C5~C6 range, but also even with
n-butane. Thus any attempt to fractionate, simply by
distillation, tlle effluent of a process etherifying a mixture
of C4-C6 hydrocarbons with methanol, is bound to produce a
distillate containing some methanol; even a distillate free
of binary ether-methanol azeotropes from such ef1uent
contains some methanol~n-butane azeotrope (and some methanol
pentane azeotrope if C5 hydrocarbons are taken into the
distillate). Becallse methanol is so deleterious to the
catalysts usually used in alkylatioll processes or in the
pol~merization process for p;oduction of polygas, lt is not
~ 2
5~7
practi.cable to u6e, in such processes, the effluellt from the
etherification proces-i in which an olefinic C~-C6 hydrocarbon
raction is etherified with methanol, even if the effluent. is
distilled to separate higher boiling material, notably the
ethers, from the hydrocarbon material to be fuxther processed
by alkylation or polymerizationO
The art of preparing the e-thers MTBE and TA~IE
from olefinic mixtures of hydrocarbons also has indicated a
preference for separately etherifying olefinic mixtures of
hydrocarbons of predom:irlantly four carbon atoms each and
olefinic mixtures of hydrocarbons of predominantly five carbon
atoms.each rather than etherifyin~ them in admixture, in
significant part because of the difficulty of separating, from
the effluent of a process for their combined etherification,
hydrocarbon streams of suffic.iently low methanol content to be
. suitable for subsequent processing by al~ylation or polymerization.
It has llOW ~een found that, by means o a combination of either
an absorption or an extraction step and one or more simple
frdctional distillation steps, it is possible to separate the
2~ effluent from an etherification process, in which an ole~inic
: mixture of hydrocarbons contalning predominantly both four and
f ive carbon atom compounds is etherified with me-thanol, to
provide a fraction containing substantially all of the ethers
and at least one other fraction containing hydrocarbons
substantially ~ree o~ methanol and suitable for urther
processing, for example, by alkylation, polymerization to
polygas, or other process in which methanol i.s deleterious to
operation. Such alkylation, polymerixation and other processes
7~
recJularly r-quire feeds containing less than 200 mole ppm of
methanol, pxeferrabl.y less than 50 mole ppm and most pr~ferrably
less than 10 mole ppm of methanol.
The present invent.ion thus consists in a methocl
for processing an olefinie hydroearbon stream, consisting
essential].y of a mixture including both four and five earbon
atom etherifiable olefins, for the formation of high octane
components for ~lending into gasoline, said method eomprising
1. passing said stream into an etherification
reactor with a proporti.on of methanol under etherifying
conditions, to contact an etherifieation eatalyst therein
and etherify tertiary olefins in said stream,
2. passing the entire effluent stream from said
etherifieation reaetor into a glycol eontaeting unit and
eontaeting it therein with a stream of liquid glyeol to
remove methanol from said effluent and reduee the methanol
eoneentxation in the effluen.t stream to no greater than 200
mole ppm in said effluent,
3. separating said effluent stream irom said
glycol and fraetionally dis~illing the reduced ef1uent to
separate a distillate eontaining hydrocarbons of predominantly
four~earbon atorns each and no greater than 200 mole ppm
methanol from a higher boiling high octane fraction containing
ethers and hydrocarbons of predominantly more than four carhon
25 atoms each. The invention further consists in a proeess as
aforesaid and ineluding the additional step of ractionally
distilllng a proportion of said higher boiling fraction to
separate a distil.late of hydrocarbons of predominantly fi~e
carbon atoms each from a hi.gher boiling ether containing
- 4 -
portlon, arld recycling said d.isti.llate of hydrocarbons of
predominantly fi.ve carbon atoms each as additional feed to
said etherification react.or. The inventioll still further
consists in a process as aforesald and including the additional
steps of fractionally distilling the glycol separated from the
effluent stream to obtain a distillate of methanol and a
residue of glycol, recycling said distillate of methanol as
part of the methanol ~eed to said etherification reactor and
recycling said residue of glycol to said g].ycol contacting
unit as the stream of lic~uid gl~col~
The invention may be more readi:Ly understood from
the follow.ing description of the accompanying drawing which
shows in diagrammatical. form a f].ow sheet illustrating
optional em~odiments of the process of the invention~ In
lS accordance with the invention an olefinic stream of mixed
hydrocarbons contai.ni.ng substanti,~lly only hydrocarbons of
four and five carbon atoms each :is suppl.ied by a :Eeed line 1
into an etherification reactor 3; a second feed line 2 feeds
a stream of methanol to the reactor. In the reactor the
methanoL and hydrocarbons contact an etherification catalyst
undex etherifying conditions, thereby converting a lar~e
proportion o the tertiary olefins of the mixed hydrocarbon
stream to tertiary ethers. ~he mixed stream of ethers and
unreacted methanol and hydrocarbons flows from the reactor
through line 4 into a counter-current ext.ractor 5 where it
contacts a stream of ethylene glycol fxom rec,vcle line 36 or
added to the extractor via line 6. In the extractor,
unreacted methanol i5 extracted from the ether hydrocarbon
~trealll into the et:hylelle glycol s~rear.l. The ethylene glycol
stream containi.ng methanol is withdrawn from the extractor
by l.ine 7 and passes to a fractional distillation column 8,
conveniently equipped with a condenser 9 and reboiler 10.
S The distillation column separates the methanol, which is
withdrawn at the top of the column and is returned by line 11
as part of the methanol feed to reactor 3, from ethylene
glycol which is withdrawn at the bottom of the column by line
36 for recycle to the extractor 5. Thè mixed ether-hydrocarbon
stream, substantially completely freed of methanol, is with-
drawn from the extractor 5 by line 12 and passed to a
fractional distillation column 13 equipped with a condensex
14 and reboiler 15. In the distillation column 13 the lower
boiling hydrocarbons containing predominantly four carbon
atoms each are separated and withdrawn as a distillate stream
from the top of the column via line l6. This stream of mixed
hydrocarbons containing predominantly four carbon atoms each,
being substantially completely free of methanol, is suitable
for feeding directly to an alkylation ~nit or to a polygas
unit for production of alkylate or poly~as fractions to blend
into gasoline. From the bottom of column 13 a residue stream
17, containing ethers produced in reactor 3 and hydrocarbons
of predominantly more than four carbon atoms eachr can be
withdrawn via line.l7B and passed directly to gasoline blending,
for which it is.a high octane component and eminently suitedO
This residue stream 17 from the bo~tom of column 13 contains
substantially all the ethers formed from the tertialy h~dro~
carbons ~both.isobutylene and isoamylene) in the olefinic
35~
mixtu.re of hydr~)Garbons origina1.ly fed to the etheriication
reactor; it additi~nally contains hydrocarbons of predominantly
five carbon atoms each, includin~ some isoamylene which passed
unreacted through the etherlfication reactor, and usually some
5 SiX carbon hydrocarbons. As an optional feature of this
invention, part of this initially unreacted isoamylene is
recycled to the etherification reactor by separating a
proportion of the residue stream 17 and passing it via line
17A for additional processing illustrated in the part of the
drawing enclosed by the dotted rectanyleO The proportion of
residue stream to be additionally processed is fed by line 17A
to a fractional distillation column 18 equipped with a
condenser 19 and a reboiler 20. This column is operated to
separate the ethers and the higher boiling part of the hydro-
carbons through the bottom of the column via line 21 and themore volatile predominantly five carbon atom hydrocarbons,
includiny the isoamylenes, which dist:ill thxough the top of
the column, via line 22. Line 22 condllcts this more volati.le
fraction back to reactor 3 where t.he isoamylenes in the
fraction are again subject to etherification alon~ with the
hydrocarbon feed stream from line 1, The proportion of the
residue stream 17 from column 13 which is passed through
line 17A for recycle processing can vary between zero and 100
percent of the stream. When none of the stream is taken, the
process of the invention acllieves only single pass conversion
to TAME of the isoamylenes in the feed which~ with the
excellent single pass conversion of isobutylene to MT~E that
can be achieved r may be suficient to provide the desired
~8SgL7
octane improvement of the feed stream, particularly in
combination with the aclditional octane improvement that can
be obtained by the alkylation or other treatment of the stream
of hydrocarbons of preclominantly four carbon a~oms recovered
from line 16. When 100~ of the residue stream 17 from column
13 is directed through line 17A, the ether containing residue
from the bottom of column 13 is all subjected to a fractional
distillation which requires significant quantities of heat,
the cost of which may not be warranted for the incremental
increase in octane which is achieved by such a high degree of
recycling. It is more expedient therefore to recycle
considerably less than the total amount of the residue stream
17 from column 13, and a preferred proportion for recycle
through line 17A is between 10% and 85~ of the residue stream
17 and more preferrably between 15% and 40~ of said stream.
When a recycle portion is withdrawn through line 17~ and
fractionall~v distilled in column 18, the higher boiling,
ether containing bottom fraction wi~hdrawn through line 21
is a superior octane component for gasoline blending.
2~ ~he glycol contacting unit for removal of methanol
from the effluent stream of the etherification reactor, as
referred to above, may be either a liquid-liquid type or a
vapor absorber type, but preferrably is of the liquid-liquid
type, most preferrably the counter-current liquid-liquid
type. The vapor absorber type of contacting unit requires
that the etherification reactor effluent all he vaporized
before passing to the contacting unit, which incrèases the
~emoval costs, therefore liquid--liquid extraction UIlitS are
5~
pre.erre~d, a~ th~ are genera.lly at least as efficient as
the vapor absorber type of corltacting unit. The liquid glycol
stream which i.s used to contact the reactor effluent stream
for extraction of methanol therefrom can be a single li~uid
glycol or a mixture of liquid glycols, for example ethylene
glycol, diethylene glycol, trieth~lene glycoll propylene
glycol, and mixtures of any of these. The essential property
of the liquid glycol i.n the extracti.on unit is its ability,
as a separate phase, to absorb or extract substantially all
of the methanol from the effluent and leave substantiall.y all
the dialkyl ethers in admixture with the hydrocarbons of the
effluent for blending into gasoline~ The simple (mono)ethylene
glycol is the best and most preferred, as it combines
optimum properties of extractant for methanol and low miscibil.ity
with MTBE and TAME. Di- and triethylene glycols are operable
but less preferred because of lower solubility for methanol
and increased miscibility with MTBE and TAME.
The temperature at which the methanol removal
; unit is operated generally is lower when using liquid-liquid
extraction ~han when using a gas absorber type of unit. In
either case it generall.y is in the range from lO~F (-12C) to
450F (232C) and with the pre~erred liquid-liquid extraction
units it~is preferrably in the r.ange from 50F to 150F (10C
to 650Cj. The mole flow rate of glycol~ in proportion to the
mole flow rate o eff].uent in the contactlng unit, may be in
the range from 0.10 to 4.0; preferrabl~ it is in the range
from 0.20 to 0.70.
r~ 9 ~-
35~7
C'onventional con~ercial eclui.pment for conventional
gas absorpti.on or li.quid~liquid extraction operations is
suitable for the mei:hanol removal unit required in the present
invention. In particular, both packed and pla-te type vapor-
li~uid contacting columns are suitable for gas absorption if
desired, and likewise either type of column can be used for
liquid-liquid extraction. Additionally, other types of
mechanical liquid-liquid contactors e.g. rotating disk
contactors, can be used. Both counter-current and co-current
liquid-liquid extractors are suitable, wi-th the more efficient
counter-current type being preferred.
The invention may be more readily unders-tood from
the followi.ng specific examples thereof which are given for
illustration only and not to limit the following claims~ The
proportions given therein and throughout the specification
and claims are proportions by weight unless otherwise
specifically indi.cated.
EX~MPLE 1
An olefi.nic mixed hydrocarbon stream of hydro-
carbons of predominantly four and five carbon atoms was
separated from the products of a catalyti.c cracklng operation,
principally by fractional distillation; chromatographic
analysis of the stream established that its composition was
made up of 53.5~ of four carbon atom hydrocarbons including
7.5% C4 reactable with methanol to form ether (i.e. isobutylene)
and 46.0~ unreactable C4'sr 39.5% of five carbon atom hydro
carbons i~cluding 16.7% C5's reactable with methanol to form
-- 10 ~
ether (i.e. isoamylenes) and 22.8~ unreacta~le C5ls, and 7
of six carbon atom hydrocarbons (considered unreactable),
This stream was fed continuously, together with a stream of
methanol, into a tubular reactor packed with "Ionac C-252"
(Trademark) commercial ion e~change resin in the acid form,
used as an etherification catalyst; the molar ratio of
methanol to total reactable C4 and C5 hydrocarbons in the
reactor feed was maintained at 1.30. The total flow of feed
to the reactor provided a liquid hourly space velocity in
the reactor of 2.5. Pressure in the reactor was maintained
around 13.6 atmospheres and temperature of the feed to the
reactor at 160F (71~C). Average temperature across the
reactor during the exothermic reaction therein was 184F
(84C). The etherification reactor effluent contained 6.5%
methanol, which could not be adequately separated from the
other components of the effluent by fractional distillation.
The effluent was fed continuously, at a rate of 5.3 lb. moles
per hour, to the bottom o a continuous counter-current
packed ~ed extraction column, 2 inches (5 cm) in diameter
and 14 feet (4 3 m~ high, maintained at a pressure of 3.8
atmospheres. A counter~current stream of ethylene glycol at
a temperature of 72F (22C) was fed to the top of the
extraction column at a mole ratio of 0~45 in proportion to
the feed to the bottom of the column. Extracted effluent
(raffinate~, withdrawn from the top of the column, was found
to contain 10 mole ppm of methan~l and was passed to the
middle of a two-inch (5 cm~ diameter distillation sieve tray
colu~l having 30 ~ray~. A distillate fraction of hydrocarbons
o~ predomiIlcln-Lly our carbon atoms ;~as obtained rom the top
of this column and was su~stant~ally free (less than lO mole
ppm or 5 weight ppm) of methanol and eminently suitable as
feed for either an alkylation process or a polymeriæation
proces~ for production of high octane components for yasoline
blending. The residue fraction withdrawn continuously from
the bottom of the distillation column was a high octane
component for gasoline blending and upon analyses by gas
chromatography was found to have the following composition:
C~mp~nent Weight
Unreactable C4's 2,05
Reactable C4's n . 04
Unreactable C5's51.14
Reactable C5's 14,86
lS C6 ~Iydrocarbons 6.70
Methanol 0,0005
M.T.B.E. 12~90
T.A.M.E. 12.30
The proportions of reactable C4 and C5 hydrocarbons in the
original feed stream that were converted to ethers and
recovered in this blendiny component were 70~ and 32%
respectively in this sinyle pass reaction. The ethylene
glycol extract withdrawn from the bottom of the extraction
column was found to contain 7.8% methanol and was fed to a
packed stripping column in which the methanol was stripped
from the ylycol and recycled to the etherification reactor;
stripped ethylene glycol containiny 150 ppm methanol was
recycled from the bottom o the strippiny column to the top
of the extraction column for urther extraction of methanol.
- 12
3S~7
~Y~PLE 2
~ n olefinic rnixed hydrocarbon stream of origin
similar ~o that of ~he hydrocar~on mixture used as feed in
the previous example was used as raw material in this example
and had the following proximate composition: 45.8% C4 hydro-
carbons, including 7.9~ isobutylene and 37.9% C4 h~drocarbons
unreactable for MTB~ production, 48.8% C5 hydrocarbons
including 16.5~ isoamylenes and 32,2% C5 hydrocarbons
unreactable to form TAME, and 5~5~ C~ hydrocarbons ~considered
unreactable). Utilizing the apparatus used in Example 1 and
additionally a 25-plat:e sieve tray fractional distillation
column two inches in diameter, with its associated condenser
and reboiler, the apparatus was arran~ed as shown diagrammatically
in the accompanying drawing with the additional column used
for fractionation of a recycle stream. The olefin.ic hydro-
carbon stream was fed continuously to the reactor together with
a recycle portion obtai.ned as a dist.illate from the top of the
foregoing additional sieve tray column; the recycle stream is
fuxther identified later herein~ Simultaneously a stream of
methanol was fed to the xeactor in a molar ratio of 0.91 relative
to the reactable C4 and C5 hydrocarbons in the total reactor
feèd. The total reactor feed rate produced an LHSV of 2.0 in
the reactor r and the average temperature across the reactor
was 180F (82C). Pressure in the reactor was maintained
around 13.6 atmospheres. Effluent from the etherification
reactor was extracted by a counter~current stream of ethylene
glycol in the same manner as in Example 1, and the raffinate
dist.illed as in Example 1, to provide a di~s-tillate of mixed
~ 13 ~
a~
prcdominantly C'4 hydrocarbons suhst~ntially free of methanol
(less than 10 mole ppm) and suitahle as feed for high octane
alkylate or polygas production. A proportion of 30% of the
residue from this first distillation was passed to the
additional distillation column referred to above, whe.rein it
was fractionated to provide a hydrocarbon distillate of pre-
dominantly five carbon atom hydrocarbons and a high octane
residue containing MTBE and TA~lE formed in the reactor, along
with the less volatile of the C5 hydrocarbons and any hi.gher
boiliny hydrocarbons in the feed. The remaining 70% of the
residue from the irst distillation was a hish octane blending
- component suitable for blending directly into a gasoline pool.
Fractionation in this additional distillation column was
controlled to remove, in the distillate, most of the
etherifiable C5 hydrocarbons (isoamylenes) fed into the column
from the preceding distillat:Lon. This distillate, which
contained 1.76~ C~ hydrocarbons, 97,23% C5 hydrocarbons
including 21.70% isoamylenes, 1.53% C~j hydrocarbonsr and trace
methanol, was recycled to the reactor as the recycle portion,
referred to above, from the additional distillation column.
The distillation residue, withdrawn from the bottom of the
column, contained 35.~5% MTBE, 36.48% TAME, trace methanol,
balance C5 and C6 hydrocarbons including only 2 54%
etherifiable C5 hydrocarbons ~isoamylenes), and was eminently
suitable as a high octane blending component for blending into
gasollne. The overall conversion to TAME of isoamylenes in
the fresh feed, with the additional processing of 30% of the
residue from the irst distillation as thus descîibed, was
substantially ~15!o~ A proport.i.orl of su~stclntially 71% of the
isobu-tylene in the fresh ~eed was converted to MTBE at the
same time, with no recycle of any siynificant proportlon
of C4 hydrocarbons from the raffirlate.
Numerous advantages over the prior art are
achieved by use of the present invention. The known method
of removing unreacted methanol ~rom etherification effluent
by water washing requires preliminary distlllation to
separate and recover the ethers, which have significant
solubility in water and could, to a considerable and
unacceptable extent, be lost in the wash water, In the
process of the present invention the volatility of the
ylycols, relative to the other components, and the
miscibility of the glycols with C4 and C5 hydrocarbons are
both sufficiently low that there is no significant risk of
glycol entrainment ox contamination i.n the predominantly
hydrocarbon streams. Thus there need be no concern about
glycol contamination of the C4 hydrocarbon stream from -the
process when it is to be used in an alkylation unit or a
polygas unit. Additionally, with respect to any miscibility
of ethers in the glycol layer which, subsequent to contacting
etherificati~n e~fluent, normally is recovered by
distillation of methanol therefrom, there is no tendency of
the glycol to distill azeotropically with any traces of
ethers therein because the glycol~ether pairs do not form
azeotropes as the water/ether pairs generally do. Hence
the more volatile ether can fractionallv distill from the
glycol along with methanol for recycle to an etherification
~ lS ~
unit and avoid causing any yield loss. Furthermore, the
presence of glycol in an etherification step i~ not
detri.menta]. to the operation of that process, whereas the
presence of any water which might be entrained in methanol
being recycled to an etheri:Eication step would be detrimental
to the etherification reactor operation. The .low tolerance
for water in hydrocarbon feed streams for HF alkylation
processes generally requixes that such feed streams be
dried, e.g~ with molecular sieves, and a preliminary water
washing of such a feed stream would obviously requ.ire a
subsequent drying step before HF alkylation~ The use of
glycol in the present invention precludes any need for drying
I-IF alkylation feed streams with molecular sieves~ Ris]c of
corrosion by wet HF in such alkylations also is reduced by
use of glycol ln accordance with the present invention.
It will be recognized that numerous modifications
may be incorpoxated within the process just described without
departing from the spirit or scope of the invention, which is
defined in the following claims.
