Note: Descriptions are shown in the official language in which they were submitted.
-- ~ACKGROUND OF T~E INVENTION
The present invention relates to a process for the
production of an ether-rich additive for gasoline and, more
particularly, the production of ter amyl methyl ether (TAME)
from FCC light hydrocarbon streams containing nitriles.
MTBE, TAME or mixtures thereof are used extensively as
fuel extenders and octane value improving agents in the
production of unleaded gasoline. Generally, but for the
inclusion of such fuel extenders and octane value improving
agents, acceptable octane values can only be obtained by
varying the compounding additives in the gasoline, that is,
increasing the lead content of the gasoline. The
desirability of lead free gasolines is clearly recognized.
Lead additives in gasolines result in the emission of
pollutants in exhaust gases from internal combustion
engines thereby contributing to overall environmental
pollution. The employment of substitutes for lead in
gasoline compounds which improve the octane value of the
gasoline will lead to a cleaner burning gasoline thereby
improving air quality and the overall environmental
condition.
Currently, MTBE is frequently selected as the octane
value improving additive over TAME due to processing
considerations; however, TAME is a highly desirable octane
value improving additive.
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There are many processes developed in the prior art
for producing MTBE (methyl t-butyl ether) and TAME (methyl
t-amyl ether). Typical etherification processes are
disclosed in U.S. Patents 5,001,292; 4,925,455; 4,827,045;
and 4,830,635 to Harandi et al. Other known processes
include that disclosed in U.S. Patent 4,025,989 to Hagan et
al. For the most part, these known processes for preparing
ethers as additives for gasoline comprise reacting a
primary alcohol, such as methanol, with an olefin having a
double bond on a tertiary carbon atom, such as, isobutylene
and isoamylenes. It is known in the prior art to react the
alcohol and the olefin in the presence of a catalyst.
Suitable known catalysts include Lewis acids (sulfuric
acid) and organic acids (alkyl and aryl sulfonic acids). A
particularly suitable catalyst for these reactions are ion
exchange resins in their acid form of the type marketed
under the trademark "AMBERLIST 15" which is a trademark of
Rohm and ~aas or Bayer product K2631. While many
hydrocarbon feedstocks may be used for the manufacture of
MTBE and TAME it is particularly useful in the petroleum
refining operation to process TAME from light hydrocarbon
streams resulting from fluid catalytic cracking (FCC)
refinery operations. When processing FCC hydrocarbon
streams under etherification conditions to form TAME it has
been found that the catalysts used in the process are
rapidly poisoned, that
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is, the catalysts are deactivated. As the catalyst
materials used in known processes are relatively
expensive, the foregoing problem of catalyst deacti-
vation leads to not only process inefficiency but also
substantial increases in processing costs. None of
the prior art processes, and particularly none of the
U.S. Patents discussed above, deal with the aforesaid
problem or suggest solutions thereto.
Naturally, it would be highly desirable to pro-
vide a process for the conversion of hydrocarbonstreams, particularly light naphtha hydrocarbon
streams from FCC refinery processes, to TAME which
overcome the problems of catalyst poisoning as dis-
cussed above.
Accordingly, the present invention seeks to pro-
vide a process for the conversion of liquid light
hydrocarbon streams to TAME in an efficient and
economic manner.
In particular, the present invention seeks to
provide a process as aforesaid wherein the poisoning
of the catalysts used in the etherification process is
inhibited.
Still further the present invention seeks to pro-
vide a process as aforesaid wherein the liquid light
hydrocarbon feedstock fed to the etherification zone
is pretreated for processing under etherification con-
ditions in the presence of the catalyst.
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In accordance with the invention there is
provided a process for the production of tertiaryamyl
methyl ether (TAME) comprising:
(a) providing a liquid hydrocarbon C4-C12
feedstock containing nitriles and isoamylenes;
(b) admixing said liquid hydrocarbon C4-C12
feedstock with an alcohol selected from the group
consisting of methanol, ethanol, propanol or mixtures
10 thereof to form a mixture of hydrocarbon feedstock and
alcohol;
(c) distilling said mixture of hydrocarbon feed-
stock and alcohol under controlled conditions so as to
obtain a product comprising a C5 hydrocarbon-alcohol
15 azeotrope feedstock rich in C5 hydrocarbons
substantially free of nitriles; and
(d) contacting said C5 hydrocarbon alcohol
azeotrope with a catalyst under etherification process
conditions to produce tertiaryamyl methyl ether
(TAME).
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More especially the present invention relates to
a process for the production of an ether-rich additive
from light hydrocarbon feedstocks and, more parti-
cularly, from FCC light hydrocarbon feedstocks havingsignificant concentrations of nitriles, particularly
propionitrile. The liquid hydrocarbon feedstocks from
FCC process facilities are admixed with an alcohol for
removing nitriles during distillation so as to form a
Cs-alcohol azeotrope feedstock prior to subjecting the
feedstock to the etherification process conditions in
the presence of the catalyst. The purified Cs-alcohol
azeotrope feedstock to the etherification zone is sub-
stantially free of nitriles. It has been found in
accordance with the present invention that by
pretreating the light hydrocarbon feedstock as afore-
said, the rate of poisoning of the catalyst employed
in the etherification process is greatly reduced
thereby increasing process efficiency while at the
same time decreasing processing costs.
The process of the present invention wherein the
feedstock to the etherification reactor is pretreated
so as to remove nitriles allows for the efficient and
economical
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production of TAME by improving the life of the catalyst
used in the etherification process.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a schematic flow diagram illustrating a
prior art process.
Figure 2 is a schematic flow diagram illustrating the
process of the present invention.
Figure 3 is a graph demonstrating the degeneration
effect of nitriles on the acid catalyst activity used in
the etherification of light hydrocarbon feedstocks to TAME
and the advantages of the process of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
Figure 1 is a schematic illustration of a prior art
process for the production of TAME from a light hydrocarbon
feedstock resulting from a fluid catalytic cracking (FCC)
process. The facility 10 as illustrated in Figure 1
comprises a FCC production facility 12 and an
etherification zone 14 for converting a light hydrocarbon
feedstock to an ether-rich additive, particularly, TAME.
In accordance with the prior art, the light hydrocarbon
feedstock from the FCC production facility 12 is delivered
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via conduit 16 to a unit 18 wherein any mercaptans in the
hydrocarbon feedstock are oxidized in known manner. The
treated product from unit 18 is thereafter passed via
conduit 20 to a distillation unit 22 so as to produce a top
product rich in C5 for feed via line 24 to the
etherification zone 14. The bottoms from the distillation
unit 22 taken off line 26 are rich in C6+. The
ether-rich TAME product is thereafter removed from the
etherification zone 14 via line 28. A typical product from
the FCC refinery facility 12 which is drawn off via line 16
is characterized by the following composition: isobutene in
the range of 2-7 wt.%; isoamylenes in the range of 5-10
wt.~; diolefins in the range of 1-2 wt.%; and a nitrogen
concentration in the range of 22-27 ppm wherein nitriles
are present in the range of 6-10 ppm. The feedstock
leaving unit 18 via line 20 has a nitrile concentration in
the range of 6-10 ppm. This feedstock when treated under
appropriate conditions in distillation unit 22 yields an
overhead product rich in C5 and having a nitrile
concentration in the range of between 10-14 ppm. The
overhead feed from line 24 is admixed with alcohol from
unit 28 and thereafter introduced into etherification zone
14 wherein it is subject to processing under the following
operating conditions: pressure of between 150-300 psi,
temperature of between 130-140~F, a methanol to isoalkene
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ratio in the range of 1.00-1.50 moles/moles, and a ratio of
H2 to diolefins in the range of between 1.5 to 3.2
moles/mole. A typical catalyst used in the prior art in
the etherification reaction is an acidic ion exchange resin
such as the type sold under the trademark "AMBERLIST" by
Rohm and Haas or Bayer prodcut K2631.
It has been found that when carrying out the process
in accordance with the present invention as described above
with regard to Figure 1 that the catalyst in the
etherification zone deactivates substantially over time.
As a result, the efficiency of the process is reduced and
the overall cost for practicing the process is increased.
With reference to Figure 2, the process of the present
invention which is an improvement over the above described
prior art processes, is described in detail. With
reference to Figure 2, like reference numerals are employed
to reference like components employed in the prior art
process described in Figure 1. Accordingly, in the process
of the present invention an FCC refinery facility 12
produces a feedstock which is fed via line 16 to unit 18
wherein mercaptans within the feedstock are oxidized. The
product from unit 18 is ultimately fed to distillation unit
22 via line 20 wherein the feed is distilled so as to
produce an overhead feed for the etherification zone 14 via
line 24 which is rich in C5-alcohol azeotrope.
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In accordance with the present invention a unit 30 is
provided downstream of unit 18 and upstream of the
distillation unit 22 for delivering a primary alcohol,
particularly an alcohol selected from the group consisting
of methanol, ethanol, propanol and mixtures thereof to feed
line 20 for admixing the alcohol with the feedstock to the
distillation unit 22. It has been found in accordance with
the present invention that the C5-nitriles azeotropes in
the feedstock, particularly propionitriles, are broken by
the presence of the alcohol introduced into the feed
stream, since the C5 has a great affinity for the alcohol
so as to form a C5-alcohol azeotripe. The feed stream is
subject to distillation in the distillation unit 22. The
C5-alcohol azeotrope and some C6-alcohol azeotrope are
separated in unit 22 and fed to the etherification zone.
The nitrile concentration in the feed to the etherification
zone is less than or equal to 2 ppm. The remaining
nitriles from the feedstock are recovered in the bottom
stream 26 from the distillation unit 22.
In order to remove substantially all of the
propionitriles from the feedstock in the distillation unit
22 it has been found that the amount of alcohol introduced
into the feed to the distillation unit 22 in line 20 is
proportional to the amount of C5 in the feedstock to the
distillation unit 22. It has been determined that the
alcohol should be present in the final feedstock
composition to the distillation unit 22 in an amount equal
to at least 10 wt.% with respect to the wt.% of C5 in the
feedstock. For typical light hydrocarbon streams from FCC
processing facilities, this amounts to an addition of
between 2-4% by wt. alcohol into the feedstock for the
distillation unit 22.
The C5 in the feed to the distillation unit 22 have
a greater affinity for the alcohol introduced into the feed
line than for the propionitriles in the feed gas stream and
accordingly, when the feedstock is distilled in unit 22 the
C5 overhead stream is substantially free of nitriles, that
is, a nitrile concentration of less than or equal to 2 ppm.
The distillation tower is operated under the following
conditions: pressure in the range of about 0-50 psig,
temperature in the range of about 167 to about 194~F, and
the ratio of isoamilenes to alcohol in the range of 0.4 to
0.6 by wt. The overhead stream substantially free of
nitriles is thereafter admixed with alcohol as described
above with reference to the prior art and subjected to
etherification under the following conditions to produce a
TAME product: pressure of between 150-300 psi, temperature
of between 130-140~F, a methanol to isoalkene ratio in the
range of 1.00-1.50 moles/moles, and a ratio of H2 to
diolefins in the range of between 1.5 to 3.2 moles/mole.
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92-141
As can be seen from the foregoing, the process of the
present invention allows for the pretreatment of the
feedstock to the etherification zone in an efficient
manner. The advantages and superior results obtained by
the process of the present invention will be made clear
hereinbelow from a consideration of the following
illustrative examples.
Example I
In order to demonstrate the poisoning effect of
nitriles such as propionitriles and acetonitriles on the
catalyst employed in the etherification process, an
untreated FCC feedstock rich in C5 and having the
composition set forth in Table I below was subject to
etherification in the presence of an AMBERLIST ion exchange
catalyst under the process and conditions set forth below
in Table II. Figure 2 shows the ,conversion of the
feedstock to the ether-enriched product TAME over time. In
order to demonstrate the benefits of pretreatment in
accordance with the present invention, the same feedstock
was pretreated with a methanol in an amount equal to 10
wt.% with respect to the C5 content of the feedstock to
obtain a purifièd feedstock having the concentration
described below in Table I. This purified feedstock was
thereafter subjected to etherification under the same
process conditions set forth in Table II. The results of
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the effect of this feedstock on the feedstock conversion to
TAME and thus the deterioration of the catalyst used in the
etherification process is illustrated in Figure 2. It can
be seen from Figure 2 that after 60 days the effectiveness
on conversion of the catalyst employed in the
etherification process when processing a purified feedstock
treated in accordance with the present invention is
substantially identical to that obtained from the virgin
catalyst while the conversion effectiveness of the catalyst
when processing a feedstock which was not treated in
accordance with the present invention decreases
substantially over time. This example clearly illustrates
the effectiveness of the pretreatment of the feedstock in
accordance with the present invention.
TABLE I
FEEDINGUNTREATED TREATED
Isobutene (% wt) 8.20 8.00
Isoamylenes (% wt) 10.10 10.10
Diolefins (% wt) 0.83 0.77
Mercaptan (ppm) 5.00 less than
Nitrogen Total (ppm)18.00 less than 2
Nitriles (ppm) 17.00 less than
Nitrogen Basic (ppm) less than 1 less than
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TABLE II
Temperature of feeding 132 degrees F
Process Pressure 175-200 psig
LHSV 2 V/V/hr
Ratio MeOH/ISOALKENES 1.05 ml/ml
Example II
In order to demonstrate the effect of the addition of
alcohol to the feedstock so as to separate nitriles from
the C5-C6 overhead feed from a distillation unit the
feedstock described in Table III below was treated in a
distillation unit under the conditions set forth in Table
IV. The resulting C5 overhead from the distillation
process were then compared for nitrile removal and the
feedstock treated with the methanol was shown to have a net
reduction in nitrile concentration of greater than 80~.
TABLE III
c4 4.0 wt.%
c5 25.0 wt.%
Isoamylenes 6.1 wt.%
C6 21.0 wt.
C6+ 50.0 wt.~
Total Nitrogen 25.6 ppm
Nitriles:
Acetonitrile 1.7 ppm
Propionitrile 5.4 ppm
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TABLE IV
Feeding Temperature45~C
Feeding Plate 30
Condenser Water Temp. 0~C
Reboiler Temp. 75~C
Feeding Flow 8 L/H
Methanol Quantity 3.00 wt.% to feeding
As can be seen from the foregoing, the process of the
present invention provides for an effective and economical
process for producing ether-rich additives such as TAME and
MTBE from light hydrocarbon feedstocks.
This invention may be embodied in other forms or
carried out in other ways without departing from the spirit
or essential characteristics thereof. The present
embodiment is therefore to be considered as in all respects
illustrative and not restrictive, the scope of the
invention being indicated by the appended claims, and all
changes which come within the meaning and range of
equivalency are intended to be embraced therein.
