Patent Application
20170233661
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, H2 and/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.
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.
Temperature=140-180° C., preferably 160° C.
Pressure=18-30 barg, preferably 24.1 barg
Temperature=160-205° C., preferably 182° C.
Pressure=18-30 barg, preferably 23.8 barg
Temperature=160-205° C., preferably 182° C.
Pressure=18-30 barg, preferably 23.8 barg
Temperature=160-205° C., preferably 182° C.
Pressure=18-30 barg, preferably 23.8 barg
Temperature=290-450° C., preferably [340-410° C.] ° C.
Pressure=18-30 barg, preferably 21.3 barg
Temperature=290-450° C., preferably 340-410° C. ° C.
Pressure=18-30 barg, preferably 21.3 barg
Temperature=320-480° C., preferably 340-410° C. ° C.
Pressure=18-30 barg, preferably 20.0 barg
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.
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 disadvantageous 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 ratio 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 mixing point and/or more than purge mixing point are also possible setups where e.g. temperature or flow conditions renders it advantageous.
In
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.
| Number | Date | Country | Kind |
|---|---|---|---|
| PA 2014 00634 | Oct 2014 | DK | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2015/075276 | 10/30/2015 | WO | 00 |
