Note: Descriptions are shown in the official language in which they were submitted.
~s~
This invention relates to a process for preparing gasoline
containing tertiaryamyl methyl ether to improve the octane rating
thereof, and more particularly to the exclusion from the gasoline of
methanol residues which generally accompany such ether when it is
prepared for blending into gasoline.
It is well known in the art of preparing gasolines for
internal combustion engines that tert1aryamy1 methyl ether, among a few
other dialkyl ethers, can be used to improve the octane ratings of the
gasolines. Several authors have described various processes for
preparing gasolines containing this ether, most recently John D Chase
et al in USP 49l93,770. The processes generally involve etherification
of 2-methyl butenes with methanol and blending the resulting mixture
containing tertiaryamyl methyl ether product into a gasoline pool. The
reaction of 2 methyl butenes with methanol is a typical organic
reac~ion9 achieving an equilibrium which leaves a significant
proportion Qf the reactant methanol in admixture with the product
etherO Because methanol also has an octane improving effect in most
; gasoline pools, its presence is not objectionable with regard to octane
qualityg but there are objections on the grounds of the increased
~20 water miscibility which methanol imparts to the gasoline. The present
invention is intended to reduce the proportion of methanol which
generally accompanies tertiaryamyl methyl ether prepared from 2-methyl
bùtenes by etherification for blending into gasoline.
The invention thus consists in a process for the preparation
of gasoline containing tertiaryamyl methyl ether comprising:
(1) etherifying a hydrocarbon fraction of essentially five
carbon atom hydrocarbons containing 2-methyl butenes with methanol
under etherifying conditions to form a mixture containing tertiaryamyl
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964
methyl ether admixed with unreacted me-thanol and unreacted
hydrocarbons 3
(2) contacting at least part of said mixture containing
tertiaryamyl methyl ether admixed with unreaeted methanol and
hydrocarbons in liquid phase with a proportion of a hydrocarbon
1mmiscible liquid glycol phase to extract methanol therefrom and form a
raffinate phase of tertiaryamyl methyl ether and hydrocarbons, and
(3) blending said ether containing raffinate into a gasoline
product.
In a modified embodiment of the invention, in which part of
said mixture containing tertiaryamyl methyl ether admixed with
unreacted methanol and hydrocarbons is distilled to separate a
distillate of the more volatile hydrocarbons and at least some of the
~ methanol for recycling to the ether1fying step, from a residue of
tertiaryamyl methyl ether9 the less volatile hydrocarbons, and residual
methanolS the said residue also is contacted in liquid phase with a
proportion of an immis~ible liquid glycol phase to extract methanol
therefrom and form a raffinate phase of tertiaryamyl methyl ether and
~: ~ : hydrocarbons, uhich raffinate phase is blended into a gasoline product.
~20 In a preferred form of this modified embodiment of the invention, the
residue from thc distillation is combined with the part o~ the mixture
~: from the etherifying step which is directly contacted with the glycol
phase, whereby the distillat10n residue and etherification mixture part
: in combination contact the glycol phase for extraction of methanol.
25 : Throughout this specification and accompanying claims, all
: proportions and percentages are expressed on a weight basis unless otherwise specifically indicatedO
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The invention may be more readily understood From the
following description of particular embodiments which can be
illustrated by reference to the accompanying drawing. The drawing is a
flow sheet showing the preparation of product streams containing
tertiaryamyl methyl ether from methanol and the 2-methyl butenes
content of a light olefinic hydrocarbon stream with removal of methanol
from any tertiaryamyl methyl ether containing stream that is to be
blended into gasoline.
It is known in the art of preparing tertiaryamyl methyl
ether for blending into gasoline, particularly the aforementioned USP
4,193,770, that the light catalytically cracked gasoline (LCCG)
fraction from gas oil cracking operations and the partially
hydrogenated pyrolysis gasoline fraction (HPGB or "dripolene") from
steam cracking of naphtha or heavier distillate fractions are the major
sources of 2 methyl bu~enes for preparation of tertiaryamyl methyl
ether. The 2-methyl butenes are separated from either of thes~ sources
in a distillate stream of mixed hydrocarbons predominantly of
essentially five carbon atoms each, and this hydrocarbon fraction of
essentially five carbon atom hydrocarbons is mixed with methanol under
etherifying conditions to form the desired tertiaryamyl methyl ether.
In the drawing, 1 is a hydrocarbon feed stream containing
2-methyl butenes, for example the aforementioned LCC~ or HPGB fraction.
A fractional distillation column 2 separates, as distillate, a smaller
fraction of essentially five carbon atom hydrocarbons containing the
2-methyl butenes, the smaller fraction passes via line 3 to an
etherifying reactor 4 containing conventional etherifying catalysty
where it mixes and reacts with methanol introduced via lines 5 and 6.
The effluent discharging from the reactor via line 7 is a mixture of
3 _
~lSq~
tertiaramyl methyl ether, unreacted methanol, and hydrocarbons,
including some unreacted 2 methyl butenes whose concentration is
unlikely to have been reduced to the equilibrium concentration in the
etherification reaction. For that reason, and more particularly
because even the equilibrium concentration does not require high
conversion of 2-methyl butenes, as is pointed out in the aforementloned
USP 4,1939770, it is usually desirable to fractionally distill part,
but not all, of the reactor effluent in order to separate from a
residue containing the tertiaryamyl methyl ether, a distillate
containing the unreacted 2-methyl butenes for recycle to reactor 4.
Although it is not necessary to the performance of the present
invention, in preferred embodiments of the present invention such
recycle operation is included~ Hence the e~ffluent flowing through
line 7 is directed entirely into line 8 if it is not desired to
increase conversion of 2-methyl butenes by recycling as described in
USP 4,193,7709 or the effluent through line 7 is divided and part is
diverted through line 9~ for recycling as described in USP 4,193,770,
: with the remalnder of the effluent being directed into line 8. Effluent
in line 8 flows into the bottom of a liquid liquid extraction column
lO, wherein it is contacted9 preferrably in counter-current flow, with
a stream of a hydrocarbon immiscible glycol extractant phase which
: : enters the column9 for example through line 11. In the column, the
stream of glycol extracts from the effluent substantially all of the
methanol and effluent discharges from the column as a raffinate phase
via line 12 with substantially no residual methanol content. The
effluent thus contains the tertiaryamyl methyl ether product of the
etherification reaction in a mixed hydrocarbon stream which is suitable
for blending into a gasoline product. When part of the reactor
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9~i4
effluent is diverted through line 9 for recycle of the unreacted
2-methyl butenes9 this part of the effluent is fractionally distilled,
as is disclosed in USP 4,193,770, to separate the 2-methyl butenes with
other volatile hydrocarbons in the distillate from the tertiaryamyl
methyl ether and less volatile hydrocarbons in the residue. Some of
the methanol in this part of the effluent distills into the distillate
with the 2-methyl butenes, and the rest remains in the residue. As
shown in the drawing, the residue withdrawn from the bottom of this
fractional distillation is removed via line 13. When the fractional
distillation is highly efficient, only a small and perhaps
insignificant proportion of the methanol in the effluent is retained in
the residue, by far the largest proportion of it distilling into the
distillate, with one or more hydrocarbon components of which It forms
mlnimum boiling azeotropes. When ~here is only an insignificant amount
~15 of methanol in the distillation residue of tertiaryamyl methyl ether
and hydrocarbon removed in line 13, this residue can be blended
directly in~o a gasoline product. When there is an undesirable
proportion of methanol in the distillation residue removed in line 13,
the residue i5 diverted through lîne 14 to join the flow in line 8 to
exkraction column 10~ Because the Feature of directing this
distillation residue to the extraction column is optional, depending on
~here being both reactor effluent recycled via line 9 and significant
methanol being retained in the distillation residue rather than
distilling~with recycled distillate, the line I4 is shown as a broken
~25~ line. The extractant glycol liquid phase with extracted methanolleaves the extraction column 10 via line 15 and ls passed to
fractionating column 16 in which methanol 1S distilled from the glycol;
the glycol then recycles via line 11 to extraction column 10~ Methanol
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dist;lled from the glycol in column 16 is removed via line 17 and
returned to etherification reactor 4 via line 6.
The hydrocarbon immiscible liquid glycol which is required
for the process of this invention must have the ability, as a separate
liquid phasey to extract substantially all of the methanol from an
etherification reactor effluent containing some tertiaryamyl methyl
ether but comprising principally hydrocarbons~ without at the same t1me
extracting any significant proportion of the said ether from the
hydrocarbon phase. Some of the ether will, of course, initially be
extracted by the glycol, but this will not be a continuous drain on ~he
yield of ether going to gasoline product providing that the glycol is
recycled to further extraction of methanol after previously extracted
methanol is stripped therefrom without stripping out initially
extracted ether~ Recycling of the glycol soon saturates it with the
ether and no further extraction of ether from the raffinate
occurs. Suitable glycols include, -For example, (mono) ethylene glycol9
; diethylene glycol9 triethylene 91yCol9 propylene glycol~ and mixtures
of any of these.
The range of relative proportions of glycol extractant and
.
: 20 extractor feed (on a methanol free basis) is wide, with a minimum ratio
set by the need to limit the number of extracting stages or limit the
height of an extracting column to a practicable figure, and a maximum
rctio set by the need to limit the amount of glycol being used to a
reasonable, economic quantity. Preferred ratios lie in the range from
0.074 to 6.5 on a weight basis and most preferred ratios lie in the
range from 0.11 to 0.33.
The operating conditions in the critical step of the present
invention, namely the contacting of glycol phase with a hydrocarbon
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phase containing methanol and tertiaryamyl methyl ether, are not severe
and do not require any unconventional equlpment. The pressure
condition prevailing during the contacting must be sufficiently high to
maintain all the ~aterials in the liquid phase at the temperature
prevailing during the extraction, but need not be significantly higher;
because of the volatility of some of the components, pressure usually
will be at least slightly above atmospheric. Suitable temperature
during extraction does not require that there be any heating of the
components; ambient room temperatures are eminently suitable, and
temperatures above these, for example the ambient temperature of the
effluent from the etherification reactor9 are likewise suitab1e
providing they do not create vapor pressures of the components to
exceed the pressure limits of the equipment being used.
It will be apparent to those skilled in the art that t~lo
; 15 functions are performed by fractional distillation column 2, in the
invention embodiments shown in the accompanying drawing~ viz: (1)
separation of a hydrocarbon fraction ~for example LCCG or HPGB) into a
distillate of five carbon atom hydrocarbons and a residue of higher
~: boiling hydrocarbons of more than five carbon atoms, and (2) separation
of an etherification reactor effluent into a residue of tertiaryamyl
methyl ether in admixture with less volatile hydrocarbons and a
: distillate o~ more volatile hydrocarbons of essentially five carbon
atoms. It should also be apparent to such persons, from the disclosure
of USP 4,193,770, that two separate fractional distillation columns
could be~utîlized to perform the two functions9 rather than the one
column, and performance of the process of the invention with either
arrangement of apparatus is fully contemplated within the scope of the
; appended claimsO
:
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It will also be apparent to those skilled in the art that if
all of an etherification reactor effluent as contemplated in this
invention is distilled to separate a fraction o~ the most volatile
hydrocarbons as distillate for recycle to the etherification reactor,
the most volatile component would accumulate in such cycle, to preclude
such accumulation, it would be necessary to bleed off part of such
distillate (which contains methanol) for blending into gasoline
product, and before such blending to extract this portion of the
distillate as well as extracting methanol from the distillation
residue. Because this method of operation involves recomb1ning
fractions that have just been separated by distillation, it is most
inefficient from an energy consumption standpoint and is not
recommended. For all practicable operations it is recommended that at
. least part of the effluent From an etherification reaction as
contemplated for this invention should be diverted directly to the
llquid liquid extraction step disclosed herein, thereby providing a
bleed-off for the most volatile component of the reaction system even
., .
: when a high proportion of the eFfluent is recycled to achieve higher
conversion of 2-methyl butenes to tertiaryamyl methyl ether.
The following examples are is given to illustrate, but not
to limit the scope of the invention.
Exame~e l
~ Principal parts o~ the equipment for carrying out this
:~25 example are arranged as shown in the accompanying drawing. From alight catalytically cracked gasoline fraction, a smaller fraction of
: : fiv~:carbon atom hydrocarbons is distilled in a fractional distillation
: column and fed to an etherification reactor containing acid form,
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sulfonated, cross~linked, polystyrene ion-exchange resin etherification
catalyst. Simult~neously a stream of methanol is fed to the reactor,
in a proportion of about one mol per mol of 2-methyl butenes in the
hydrocarbon feed, thereby forming a proportion of tertiaryamyl methyl
ether in the reactor. Effluent withdrawn from the reactor is divided
into two streams, with one of the streams (80% of the effluent) being
recycled to the distillation column and the other (20% of the effluent)
being fed to the bottom of a liquid-liquid extraction tower ~3.9 cm
internal diameter) packed (to a height of 183 cm) with 0~61 cm
"Pro Pak"(trademark) protruded sta;nless steel packing having a
sur~ace/volume factor (a) of 1223 m2/m3. The stream of reactor
effluent recycled to the distillation column is fractionated therein,
along with the light cracked gasoline fraction9 whereby five carbon
atom hydrocarbons are separated as d;st;llate and sent to the
etherification reactor while higher boiling hydrocarbons and
tertiar~yamyl methyl ether are withdrawn as residue from the bottom of
the distillation column. Methanol in the distillation column, coming
from the reactor effluent, largely distills with the five carbon atom
hydrocarbons and returns therewith to the etherification reactor
for additional etheriflcation reaction. Methanol in the distillation
column~which~does not distill overhead is withdrawn in the residue with
the tertiaryamyl methyl ether and residue hydrocarbons~ This entire
residue, comprising mostly hydrocarbons, is fed into the bottom of the
liquid-liquid extraction tower referred to above~ where it combines
~25 with the stream of effluent flowing directly from the etherification
reactor, giving a combined flow of 3.3 kg per hour, and together they
are contacted with a counter-current flow of (mono)ethylene glycol.
The concentrations of methanol and tertiaryamyl methyl ether in the
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~iS496~
hydrocarbon phase entering the bottom of the extraction tower are 4.5%
and 12% by weight respectively, and the weight ratio of the rate oF
glycol feed at the top of the tower to 1;he rate of feed of hydrocarbon
phase at the bottom of the tower, on a methanol free basis, is 0.038.
Temperature in the tower is maintained at substantially 23C average,
and the associated pressure is slightly above atmospheric. The
pressure drop in the Flow of the hydrocarbon phase across the
extraction tower is 7.47 kilopascals (kPa). The raffinate effluent of
! tertiaryamyl methyl ether and hydrocarbons flowing from the top of the
tower is found to contain only OolO weight percent methanol, and is
eminently suitable for blending into gasoline. Ethylene glycol
containing approximately 30 weight percent extracted methanol is
withdrawn from the bottom of the extraction tower and passed to a
stripping~column wherein methanol is distilled from the glycol; the
methanol is recycled to the etherification reactor and the glycol,
containing ~30 parts per million of methanol9 is recycled to the top of
the extraction towerG
':
This example utilizes the same general arrangement of
equipment as the previous example, but with a shorter liquid-liquid
extraction tower and a modified recycle flow. As in the previous
example, a stream of five carbon atom hydrocarbons from a light
catalytically cracked gasoline fraction is reacted with methanol in an
ZS etherification reactor, forming a reactor effluent stream containing
tertiaryamyl methyl ether. Again the eFfluent is divided into two
streams; this time only 30% of the efFluent is recycled for
~ distillation and 70% of the efFluent passes directly to the bottom of a
; ~ '
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liquid-liquid extraction tower 3O9 cm Int:ernal diameter packed to a
height of 152 cm~ again using 0.61 cm "Pro-Pak" packing as previously
used. Methanol concentration in the disl:illation residue is so low as
not to require removal, and only etheriflcation reactor effluent~ at a
rate of 3.3 kg/hour, is fed to the extraction tower for methanol
extraction Methanol concentration ih this effluent is 6.36% by
weight, with 12.2% tertiaryamy1 methyl etherl balance hydrocarbons~
and feed rates of glycol to the top of the extraction tower and
effluent to the bottom of the tower are in the ratio of 0.159 by
weight. Temperature in the tower is maintained at substantially 23C
and pressure is slightly above atmospheric. The pressure drop in the
flow of the hydrocarbon phase across the extraction tower is 6.22 kPa.
Raffinate from the top of the tower contains only 0.04% methanol by
weight, and is eminently suitable for blending into gasoline. Glycol
containing extracted methanol is readily stripped of methanol and
recycled to the extraction tower.
Numerous modifications may be made in the various expedients
and embodiments of the invention described herein without departing
from the scope of the invention which is defined in the following
claims.
.
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