US20170233661A1

US20170233661A1 - Conversion of oxgenates in purge from raw methanol evaporator

Info

Publication number: US20170233661A1
Application number: US15/519,049
Authority: US
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: 2017-08-17
Also published as: CA2966087A1; AU2015340496B2; CN107075386A; AU2015340496A1; WO2016066813A1; EA201790927A1; BR112017008677A2; MX2017005429A

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

The invention relates to an improved preparation process of hydrocarbons useful as gasoline compounds from a feed comprising 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 recycle gas from the conversion process and send to the gasoline 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 decreases the methanol flow from the evaporator/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 boiling 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.
These and other advantages are achieved by a process comprising 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, reboiler or similar said liquid purge comprising oxygenates and water,
providing the gas phase methanol rich stream to a conversion step, and
adding at least part of said liquid purge upstream the conversion 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 acceptable 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 generation 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 without wasting the oxygenates in the purge, as this purge is sent to the conversion step. Moreover, this process configuration 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 embodiments be controlled based on the need in order to maintain the flow of the gas phase methanol rich stream at a desired level.
For example the conversion step can be a gasoline conversion step in which case the methanol rich stream is converted 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 being 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 arranged in parallel.
The raw product from the converter in form of a gasoline reactor may comprise hydrocarbons in the range from C1 to C13 water and carbon dioxide.
By cooling and condensation of the effluent from the converter a liquid phase of water and a liquid phase comprising a mix of gasoline and light petroleum gas (LPG) is obtained, referred to as raw gasoline. The raw gasoline and water may be separated from a tail gas comprising Methane, Ethane, LPG, CO₂, CO, H₂and/or C5+, part of which is recycled 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 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 utilizing 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, CO₂, 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 recycle 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 conversion 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 entering the recycle stream and/or mixed stream (recycle+methanol 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 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 conversion 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 distillation steps are required after the methanol synthesis. This separation is highly energy intensive due to the inherent difficulty in separating water and methanol and/or other oxygenates like ketones, aldehydes, higher alcohols, etc. Therefore, a process modification which allows producing gasoline from a raw methanol feedstock is of great advantage because it makes possible to remove the distillation 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 purification 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. Nonetheless if no purification step is included, the raw methanol 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 advantageously 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 arranged where the recycle stream and/or mixed stream is hot. Alternatively one or more purge mixing points can be arranged 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 recycle.
The conversion loop may comprise a conversion step, a separator and means for returning a recycle stream to the conversion step.
The conversion loop may further comprise one or more heaters 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 compositions in the present plant and process. The values are exemplary 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

Evaporator:

Temperature=160-205° C., preferably 182° C.
Pressure=18-30 barg, preferably 23.8 barg

Liquid Purge:


	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:


	Compound	wt %

	Water	11.4
	Carbon Dioxide	0.3
	Dimethyl Ether	576 wtppm
	Acetone	57 wtppm
	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

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

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 into 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 described 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 converters 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 10 a, 10 b 10 c for the purge mixing point are indicated by dotted lines. If point 10 a is used, insufficient vaporization may under disadvantageous parameters lead to a second phase. If point 10 b is used, a similar result to that in alternative 10 is obtained, being the difference that a higher gas/liquid ratio goes through the nozzle. If point 10 c 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 mixing point and/or more than purge mixing point are also possible setups where e.g. temperature or flow conditions renders it advantageous.
In FIG. 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.
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 whereby the (mixed) feed to the converter is heated while the effluent from the converter is cooled before condensing and separation.

Claims

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 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.

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

3. A process according to claim 1, wherein the feed stream comprises raw methanol.

4. A process according to claim 1, wherein the oxygenates comprises ketones, aldehydes and/or higher alcohols.

5. A process according to claim 1, wherein the liquid purge stream is added to a recycle stream from the conversion step.

6. A process according to claim 1, wherein the liquid purge stream is added to the recycle stream from the conversion step up- and/or downstream a point where the gas phase methanol rich stream is added to the recycle stream from the conversion step.

7. A process according to claim 1, wherein the liquid purge stream is added to the recycle stream from the conversion step by quenching.

8. A plant comprising an evaporator or boiler, a conversion 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 wherein the conversion 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 claim 8, wherein one or more purge mixing points are arranged up-steam and/or downstream the methanol mixing point.

12. A plant comprising an evaporator or boiler, a conversion loop, at least one methanol mixing point and at least one purge mixing point, arranged to carry out the process according to claim 1.

13. Gasoline product produced according to the process of claim 1.

14. Gasoline product produced by the plant of claim 8.