CA2966087A1

CA2966087A1 - Conversion of oxygenates in purge from raw methanol evaporator

Info

Publication number: CA2966087A1
Application number: CA2966087A
Authority: CA
Inventors: Arne Knudsen; Ian MENJON; Jan Due NIELSEN
Original assignee: Haldor Topsoe AS
Current assignee: Topsoe AS
Priority date: 2014-10-31
Filing date: 2015-10-30
Publication date: 2016-05-06
Also published as: MX2017005429A; EA201790927A1; AU2015340496B2; WO2016066813A1; US20170233661A1; BR112017008677A2; AU2015340496A1; CN107075386A

Abstract

The invention relates to a processes comprising the steps of: in an evaporator forming a gas phase methanol rich stream from a feed stream; withdrawing a liquid purge stream from the evaporator, said liquid purge stream comprising oxygenates and water; providing the gas phase methanol rich stream to a conversion step; and adding at least part of said liquid purge stream upstream the conversion step.

Description

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.

2 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.

3 PCT/EP2015/075276 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

4 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-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

6 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.

7 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

8 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

9 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 Temperature/pressure in the converter:
Temperature = 290 - 450 C, preferably 340 - 410 C C
Pressure = 18 - 30 barg, preferably 21.3 barg 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

11 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-

12 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.

13 PCT/EP2015/075276 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.

Claims

14

1.A processes comprising the steps of:
in an evaporator forming a gas phase methanol rich stream from a feed stream, withdrawing a liquid purge stream from the evaporator, said liquid purge stream comprising oxygenates and wa-ter, providing the gas phase methanol rich stream to a con-version step, and adding at least part of said liquid purge stream up-stream the conversion step.

2.A process according to claim 1, wherein the conversion step is a gasoline conversion step.

3.A process according to any of the preceding claims wherein the feed stream comprises raw methanol.

4.A process according to any of the preceding claims wherein the oxygenates comprises ketones, aldehydes and/or higher alcohols.

5.A process according to any of the preceding claims wherein the liquid purge stream is added to a recycle stream from the conversion step.

6.A process according to any of the preceding claims wherein the liquid purge stream is added to the recy-cle stream from the conversion step up- and/or down-stream a point where the gas phase methanol rich stream is added to the recycle stream from the conver-sion step.

7. A process according to any of the preceding claims wherein the liquid purge stream is added to the recy-cle stream from the conversion step by quenching.

8.A plant comprising an evaporator or boiler, a conver-sion loop, at least one methanol mixing point and at least one purge mixing point.

9.A plant according to claim 8 wherein the conversion loop comprises a conversion step, a separator and means for returning a recycle stream to the conversion step.

10. Plant according to claim 8 or 9 wherein the con-version loop further comprises one or more heaters for heating the recycle stream, one or more coolers and condensers for condensing the converter effluent.

11. Plant according to any of claims 8 - 10 wherein one or more purge mixing points are arranged up-steam and/or downstream the methanol mixing point.

12. Plant according to any of claim 8 - 11 arranged to carry out the process according to claim 1 - 7.

13. Gasoline product produced according to the pro-cess and plant according to any of the preceding claims.