Note: Descriptions are shown in the official language in which they were submitted.
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Conversion of oxygenates in purge from raw methanol evapo-
rator
The invention relates to an improved preparation process of
hydrocarbons useful as gasoline compounds from a feed com-
prising methanol.
Gasoline can be produced by conversion of raw methanol,
pure methanol and/or dimethyl ether. In known setups the
raw methanol is evaporated before being mixed with a recy-
cle gas from the conversion process and send to the gaso-
line reactor. The raw methanol contains impurities in form
of water and various oxygenates such as ketones, aldehydes
and higher alcohols. It has surprisingly been shown that
these oxygenates are concentrated in the evaporator/boiler
to a degree where it effects methanol evaporation due to an
increased boiling temperature. This lowers the vaporization
effectivity in the evaporator/boiler/reboiler and thus de-
creases the methanol flow from the evapora-
tor/boiler/reboiler.
Thus there is a need for a process and a plant enabling a
steady gas flow from the evaporator/boiler/reboiler.
In a first aspect of the present invention is provided a
process for running on raw methanol by avoiding building up
of too high concentrations of oxygenates with higher boil-
ing point than methanol.
In a second aspect of the present invention is provided a
process which increases the utilization of the oxygenates
in the gasoline synthesis loop.
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These and other advantages are achieved by a process com-
prising the steps of:
an evaporator, boiler, reboiler or similar forming a gas
phase methanol rich stream from a feed stream,
withdrawing a liquid purge from the evaporator, boiler, re-
boiler or similar said liquid purge comprising oxygenates
and water,
providing the gas phase methanol rich stream to a conver-
sion step, and
adding at least part of said liquid purge upstream the con-
version step.
Thus the oxygenates and other compounds are removed from
the evaporator or similar by the purge thereby ensuring
that the boiling point in the evaporator is kept within ac-
ceptable levels in order to ensure a desired flow of the
gas phase methanol rich stream. The purge is then added to
the conversion step thereby maximizing the product genera-
tion in the conversion loop as at least some of the purge
oxygenates are converted. I.e. by the present process a
purge is removed from the evaporator/boiler/reboiler with-
out wasting the oxygenates in the purge, as this purge is
sent to the conversion step. Moreover, this process config-
uration also has the benefit of enabling the use of raw
methanol as feed, thereby avoiding costly purification.
The purge may be removed continuously or on/off for example
in periodic or otherwise predetermined intervals. The
amount and/or frequency of the purge may in some embodi-
ments be controlled based on the need in order to maintain
the flow of the gas phase methanol rich stream at a desired
level.
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For example the conversion step can be a gasoline conver-
sion step in which case the methanol rich stream is con-
verted in presence of a catalyst into hydrocarbons stream
which in several embodiments is within the gasoline range,
such as predominantly C3-C10 hydrocarbons and water. The
conversion of oxygenates in the methanol rich stream is
carried out in a reactor in the presence of a catalyst be-
ing active in the reaction of oxygenates to hydrocarbons,
preferably C5+ hydrocarbons.
A preferred catalyst for the conversion reaction may be a
zeolite based catalyst such as ZSM-5 or similar
In various setups more than one conversion reactor is used.
In these setups the multiple reactors are preferably ar-
ranged in parallel.
The raw product from the converter in form of a gasoline
reactor may comprise hydrocarbons in the range from Cl to
C13 water and carbon dioxide.
By cooling and condensation of the effluent from the con-
verter a liquid phase of water and a liquid phase compris-
ing a mix of gasoline and light petroleum gas (LPG) is ob-
tamed, referred to as raw gasoline. The raw gasoline and
water may be separated from a tail gas comprising Methane,
Ethane, LPG, 002, CO, H2 and/or C5+, part of which is recy-
cled to the converter. The tail gas further may comprise
inerts, light hydrocarbons such as methane, ethane, etc.
and carbon dioxide which e.g. may be used as fuel gas. The
raw gasoline may be further processed by conventional means
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to obtain a lower-boiling gasoline fraction and a fraction
of LPG. LPG may often be regarded as mainly C3 and C4.
The recycle gas may be recycled and re-introduced into the
converter. The recycle stream may be compressed and/or at
one or more points during the flow from the separator to
the converter be heated, preferably by heat exchange uti-
lizing the heat from the effluent from the converter.
The gas phase methanol rich stream is preferably mixed into
the recycle stream thereby creating a mixed stream which is
introduced to the converter.
The oxygenates in the liquid purge may comprise ketones,
aldehydes and/or alcohols including higher alcohols. The
liquid purge may e.g. comprise water, 002, Dimethyl
ether(DME), Acetone, Propanol, Ethanol, Butanol, one or
more higher alcohols, Formaldehyde, Acetaldehyde, methyl
ethyl ketone and methanol.
In various embodiments the liquid purge is added to the re-
cycle from the conversion step. As the recycle is heated
the liquid purge will evaporate when e.g. sprayed into the
recycle stream at points after heating of the recycle.
The liquid purge can be added to the recycle from the con-
version step up- and/or downstream the point where the
methanol rich stream is mixed with the recycle from the
conversion step. Depending on where the liquid purge is
added the heat from the recycle stream can be optimally
used to ensure evaporation of the liquid purge when enter-
ing the recycle stream and/or mixed stream (recycle + meth-
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anal rich stream). I.e. it may be advantageous to add the
purge to the recycle stream and/or mixed stream where the
temperature is high, such as above 180 C. Alternatively or
in combination the liquid purge can be added to the gas
5 phase methanol rich stream upstream and preferably close to
the methanol mixing point in order to utilize the heat from
the hot recycle stream.
The liquid purge may be added to the recycle from the con-
version step by quenching such as via a spray nozzle to
evaporate the liquid in the recycle stream.
The improved process described in this invention allows to
run on raw methanol as opposed to pure (grade AA) methanol.
Typically, in order to produce pure methanol, a set of dis-
tillation steps are required after the methanol synthesis.
This separation is highly energy intensive due to the in-
herent difficulty in separating water and methanol and/or
other oxygenates like ketones, aldehydes, higher alcohols,
etc. Therefore, a process modification which allows produc-
ing gasoline from a raw methanol feedstock is of great ad-
vantage because it makes possible to remove the distilla-
tion steps and thus significantly reduce the investment
cost. Moreover, the energy demand is greatly reduced. By
way of example, the energy required for the methanol puri-
fication is equivalent to half the energy demand in the
gasoline synthesis loop.
It is known that in the grade AA methanol specification,
there are maximum values for acetone and ethanol. Nonethe-
less if no purification step is included, the raw methanol
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may also comprise aldehydes, methyl-ethyl-ketone and/or C3+
alcohols, which are not included in the specifications.
The present process is preferably carried out in a plant
comprising an evaporator, reboiler or boiler, a conversion
loop, at least one methanol mixing point for adding the gas
phase methanol rich stream upstream the converter and at
least one purge mixing point for adding the liquid purge to
the recycle or mixed stream of recycle/methanol rich
stream. One or more of the purge mixing point may e.g. be
arranged up-stream and/or downstream the methanol mixing
point. The position of the methanol and purge mixing points
may be chosen based on various parameters temperature, flow
and/or pressure considerations as discussed above.
For example, the methanol rich mixing point(s) may advanta-
geously be arranged to mix the gas phase methanol rich
stream into the hot recycle stream upstream a final heating
of the stream to the conversion step in order to maintain
optimal temperature control of the conversion feed. The
purge mixing point(s) may preferably be arranged to ensure
full evaporation of the purge to avoid purge droplets in
the system. For example the purge mixing point(s) is ar-
ranged where the recycle stream and/or mixed stream is hot.
Alternatively one or more purge mixing points can be ar-
ranged to mix liquid purge into the methanol rich stream a
stage close to the methanol mixing point. I.e. the purge
can be added to the methanol rich stream just before the
methanol rich stream is heated as it is mixed with hot re-
cycle.
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The conversion loop may comprise a conversion step, a sepa-
rator and means for returning a recycle stream to the con-
version step.
The conversion loop may further comprise one or more heat-
ers for heating the recycle stream, one or more coolers
and/or one or more condensers for condensing the converter
effluent.
Example:
Below are exemplary parameters for conditions and composi-
tions in the present plant and process. The values are ex-
emplary and serve to illustrate the present invention and
are not to be construed as limiting to the invention.
Raw methanol:
Temperature = 140 - 180 C, preferably 160 C
Pressure = 18 - 30 barg, preferably 24.1 barg
Compound wt%
Water 11.6
Carbon Dioxide 0.3
Dimethyl Ether 563 wtppm
Acetone 56 wtppm
Propanol 2046 wtppm
Butanol 824 wtppm
Ethanol 1249 wtppm
Higher alcohols 821 wtppm
Methyl Ethyl Ketone 44 wtppm
Methanol balance
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Evaporator:
Temperature = 160 - 205 C, preferably 182 C
Pressure = 18 - 30 barg, preferably 23.8 barg
Liquid Purge:
Temperature = 160 - 205 C, preferably 182 C
Pressure = 18 - 30 barg, preferably 23.8 barg
Compound wt%
Water 18.7
Carbon Dioxide 6.59E-03
Dimethyl Ether 142 wtppm
Acetone 38 wtppm
Propanol 2459 wtppm
Butanol 1230 wtppm
Ethanol 1266 wtppm
Higher alcohols 1483 wtppm
Methyl Ethyl Ketone 33 wtppm
Methanol balance
Methanol rich stream exiting evaporator:
Temperature = 160 - 205 C, preferably 182 C
Pressure = 18 - 30 barg, preferably 23.8 barg
Compound wt%
Water 11.4
Carbon Dioxide 0.3
Dimethyl Ether 576 wtppm
Acetone 57 wtppm
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Propanol 2033 wtppm
Butanol 812 wtppm
Ethanol 1249 wtppm
Higher alcohols 800 wtppm
Methyl Ethyl Ketone 44 wtppm
Methanol balance
Methanol rich stream + recycle before introduction in the
converter:
Temperature = 290 - 450 C, preferably [340 - 410 C] C
Pressure = 18 - 30 barg, preferably 21.3 barg
Compound wt%
Hydrogen 0.5
Water 1.7
Carbon Monoxide 9.2
Carbon Dioxide 15.7
Methane 27.6
Ethane 500 wtppm
LPG 24.140
Ethanol 100 wtppm
Methanol 10.480
Dimethyl Ether 100 wtppm
Acetone < 0 wtppm
Propanol 200 wtppm
Butanol 100 wtppm
Higher alcohols 100 wtppm
Methyl Ethyl Ketone < 0 wtppm
C5+ balance
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Temperature/pressure in the converter:
Temperature = 290 - 450 C, preferably 340 - 410 C C
Pressure = 18 - 30 barg, preferably 21.3 barg
5
Stream leaving the converter (converter effluent):
Temperature = 320 - 480 C, preferably 340 - 410 C C
Pressure = 18 - 30 barg, preferably 20.0 barg
10 Composition
Compound wt%
Hydrogen 0.5
Water 7.6
Carbon Monoxide 9.2
Carbon Dioxide 15.7
Methane 27.7
Ethane 473 wtppm
LPG 25.1
Ethanol 100 wtppm
Methanol < 0 wtppm
Dimethyl Ether 100 wtppm
Acetone < 0 wtppm
Propanol 200 wtppm
Butanol 100 wtppm
Higher alcohols < 0 wtppm
Methyl Ethyl Ketone < 0 wtppm
C5+ balance
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Drawings
In the following the process and plant is further describe
by reference to the figures. The embodiments in the figures
are exemplary and are not to be construed as limiting to
the invention.
Fig 1 shows a simplified diagram of the process and plant.
Fig. 2 shows a diagram of the process and plant indicating
some options for the process and plant.
Fig. 1 shows a principle diagram of the present process and
plant. The diagram shows an evaporator 1 receiving a feed 2
in form of raw methanol. From the evaporator a gas phase
methanol rich stream 3 and a liquid purge 4 are withdrawn.
The methanol rich stream and the liquid purge is mixed into
a gasoline conversion loop comprising a conversion step 5
in which at least the methanol rich stream is converted in-
to at converted mixture (converter effluent) comprising raw
gasoline. The converted mixture is separated into at least
a recycle stream 6 and a raw gasoline stream 7. At least
part of the recycle is returned to the conversion step and
the raw gasoline may be send to further treatment, use
and/or storage.
Fig. 2 shows options for various embodiments of the present
process and plant. The base process is the same as de-
scribed in fig. 1 and for like parts like numbers are used.
The mixing point 8 where the methanol rich stream is mixed
with the recycle is here arranged up-steam a heater 9 which
helps ensure a desired temperature of the stream to the
converter 5. As indicated by dotted lines several convert-
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ers may be arranged in parallel. The number of converters
may e.g. depend on the flow in the system. The parallel
converts may be worked one or more at a time while one or
more converters are being regenerated.
The purge mixing point 10 is here arranged downstream a
heat exchanger 11 heating the recycle stream and upstream
the methanol mixing point 8, thus vaporizing the totality
of the liquid purge. Alternative positions 10a, 10b 10c for
the purge mixing point are indicated by dotted lines. If
point 10a is used, insufficient vaporization may under dis-
advantageous parameters lead to a second phase. If point
10b is used, a similar result to that in alternative 10 is
obtained, being the difference that a higher gas/liquid ra-
tio goes through the nozzle. If point 10c is used, several
nozzles are required (one per converter) which may increase
the operation complexity due to parallel flow but may still
be a functional and relevant alternative.
Processes and plants comprising more than one methanol mix-
ing point and/or more than purge mixing point are also pos-
sible setups where e.g. temperature or flow conditions ren-
ders it advantageous.
In figure 2 is also indicated how the effluent 12 from the
converter 5 is preferably cooled by at least a cooler 13
before being separated in a separator 14 into the recycle
stream 6, the raw gasoline stream 7 and process water 15. A
purge 16 can be taken e.g. from the recycle stream in order
to reduce the amount of inerts etc. in the system.
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A pump 17 for the liquid purge from the evaporator 1 and a
compressor 18 for the recycle stream is also indicated in
the figure.
In several embodiments one or more of the heat exchangers 9
and 11 utilize the heat in the converter effluent 12 where-
by the (mixed) feed to the converter is heated while the
effluent from the converter is cooled before condensing and
separation.
