WO2018007484A1

WO2018007484A1 - Production of gasoline reformate blendstock

Info

Publication number: WO2018007484A1
Application number: PCT/EP2017/066863
Authority: WO
Inventors: Uffe Vie MENTZEL; Ian MENJON; Finn Joensen; Kim Aasberg-Petersen
Original assignee: Haldor Topsøe A/S
Priority date: 2016-07-08
Filing date: 2017-07-06
Publication date: 2018-01-11

Abstract

Process for producing a gasoline type reformate from a main feed comprising alcohols and/or ethers such as methanol and/or dimethyl ether, said process comprising the steps of - reacting a reaction feed over a zeolite or zeolite-containing catalyst thereby obtaining a reaction effluent comprising C1 -C10 hydrocarbons, - In a first separation, separating the reaction effluent into an aqueous phase, a first gas phase and a first liquid hydrocarbon phase, - separating the first liquid hydrocarbon phase into at least an incondensable gas phase, one or more intermediate liquid phases and a gasoline product phase, - recycling at least part of the one or more intermediate phases, where the reaction feed comprises the main feed and the at least part of the one or more intermediate phase recycle.

Description

Title: Production of gasoline reformate blendstock

The conversion of methanol (MeOH) and/or dimethyl ether (DME), into hydrocarbon fuels and chemicals is of significant industrial importance. Prominent examples comprise methanol-to-gasoline (MTG) and methanol-to-olefins (MTO) processes.

In general, any alcohol and ether may be converted into hydrocarbons by these processes, but methanol is the preferred feedstock, because it may be produced in large scale and with high efficiency from any carbon-containing resource, such as coal, bio- mass, waste and natural gas. Prior to the conversion into hydrocarbons the methanol or alcohol feed may be converted, at least partially, into its ether analogue e.g. methanol to DME.

In the MTG process oxygenates, e.g., methanol and/or DME is transformed into a mixture of hydrocarbons with carbon numbers C1 -C10 and minor amounts of heavier com- ponents Typically, synthetic gasoline consists of n-paraffins (1 -5 wt%), i-paraffins (30- 50 wt%), olefins (5-15 wt%), naphthenes (5-10 wt%) and aromatics (30-40 wt%). Typical yields of higher hydrocarbons, i.e., hydrocarbons with more than four carbon atoms (C5+) is around 80 wt% of the total hydrocarbon slate. One of the critical parameters of the gasoline product is the octane number. In particular olefins and aromatics have high blend octane numbers. However, a high content of olefins in the gasoline is less desirable, because olefins are less stable towards oxidation and polymerization (gum formation). Synthetic gasoline as produced in the MTG process typically has a research octane number (RON) of between 90 and 95 and a motor octane number (MON) of 80-85.

According to the present invention is provided a process by which the methanol-to-gasoline (MTG) process can be optimized to increase the content of aromatics, thereby increasing the octane number.

This and other advantages are achieved by a process for producing a gasoline type reformate from a main feed comprising alcohols and/or ethers such as methanol and/or dimethyl ether, said process comprising the steps of - reacting a reaction feed over a zeolite or zeolite-containing catalyst thereby obtaining a reaction effluent comprising C1 -C10 hydrocarbons,

- In a first separation, separating the reaction effluent into an aqueous phase, a first gas phase and a first liquid hydrocarbon phase,

- separating the first liquid hydrocarbon phase into at least an incondensable gas phase, one or more intermediate liquid phases and a gasoline product phase,

- recycling at least part of the one or more intermediate phases, where

the reaction feed comprises the main feed and the one or more intermediate phase recycle.

In other words, by the present invention is provided a process for producing gasoline from a feed comprising oxygenates such as alcohols (e.g., methanol) and/or ethers (e.g., dimethyl ether). The process comprises an oxygenate conversion step followed by more than one separation step from where is obtained one or more recycles of the one or more intermediate phases from the liquid hydrocarbon phase.

The liquid hydrocarbon phase may comprise various aromatics such as benzene, toluene, xylenes, ethylbenzene, and heavier aromatic compounds with 9 or more carbon atoms, as well as paraffins, olefins, and naphthenes. Most of the hydrocarbons present in the liquid hydrocarbon stream may be components with 4 or more carbon atoms, but this stream may also comprise lighter hydrocarbons in low concentrations. The liquid hydrocarbon stream may also comprise small amounts of dissolved gases such as CO2, CO, light hydrocarbons, and H2. The aqueous condensate from the first separation comprises mainly water, but may also comprise small amounts of various oxygenates including methanol, other alcohols, aldehydes, and ketones as well as dissolved gases.

In the present process, a main feed stream comprising methanol and/or DME is pre- heated, mixed with one or more recycle streams and fed to the gasoline reactor.

The conversion of oxygenates to gasoline and light hydrocarbons may be carried out at a pressure of 5-60 bar, preferably 10-40 bar, at a temperature of 300-500°C, preferably 300-460°C, and a weight hourly space velocity (kg methanol and/or DME feed per kg of catalyst per hour) between 0.1 and 10, preferably 0.5-3.

Preferably the inlet temperature to the reactor is between 300°C and 380°C and the exit temperature is between 380°C and 460°C.

The conversion of oxygenates to hydrocarbons is strongly exothermic. Therefore, if a process layout involving adiabatic fixed bed reactors is applied, the oxygenate feed is preferably strongly diluted to avoid excesive temperature increase. Common practice is to use light gases formed in the conversion reactor and separated in the first separation as diluent for the oxygenate feed. The light gases comprises H2, CO, C02, CH4, C2H6 and other light hydrocarbons with methane, the least condensable of the hydrocarbons as the dominating component. Due to their limited solubility in the liquid hydrocarbon and aqueous phases these light gases tend to build up in the synthesis loop and, there- fore, constitute a convenient means of controlling the temperature in an adiabatic conversion reactor and at the same time to sustain the loop pressure. Excessive amounts of light gases are vented.

During operation the formation of carbonaceous residues ("coke") may gradually deac- tivate the catalyst. This may require that the catalyst be operated in a cyclical manner and regenerated at intervals by burning off the coke after which the catalyst is returned into service again.

In case the MTG reactor is adiabatic, the difference between the outlet temperature and the inlet temperature is preferably between 30 and 150°C, more preferably between 50 and 130°C.

In case the gasoline reactor is an adiabatic fixed bed reactor, the difference between the inlet temperature and the outlet temperature is preferably between 30 and 150°C, more preferably between 50 and 130°C. Preferably the inlet temperature to the reactor is between 300°C and 380°C and the outlet temperature is between 380°C and 460°C.

In order to achieve a desired selectivity to gasoline the oxygenate conversion catalyst preferably comprises a zeolite or zeotype. The zeolite/zeotype may be on the hydrogen form or it may be partly or even wholly exchanged or impregnated with a metal or metal oxide which catalyzes the dehydrogenation of naphthenes to aromatics and/or dehy- drogenation of paraffins to olefins. Different zeolite/zeotypes may be employed, including ZSM-5, ZSM-1 1 , ZSM-23, ZSM- 48, SAPO-34, however ZSM-5 may be preferred, since it has a suitable size selectivity to the desired methylated monocyclic aromatic species as well as a relatively low coking rate. The metal component of the catalyst may in advantageous embodiments be chosen from Zn, Ga, In, Ge, Ni, Mo, P, Ag, Sn, Pd and Pt or combinations thereof. Zn may be preferred over the other metals. Thus, a catalyst comprising H-ZSM-5 or partially Zn-exchanged or Zn-impregnated H-ZSM-5 may be a particularly preferred catalyst system for the gasoline synthesis process, because Zn tends to reduce the rate of formation of carbonaceous deposits on the catalyst. Furthermore, the MTG catalyst may comprise phosphorus, which leads to better hydrothermal stability of the catalyst and thus longer ultimate catalyst lifetime.

It may be preferred to use a binder material in order to shape the catalyst. This binder material may be a normally employed binder material such as AI203, MgAI204, Si02, Zr02, Ti02, MgO or mixtures thereof. AI203 may be preferred. If AI203 is used as binder, Zn may be present in the catalyst as ZnAI204. Similarly, if AI203 is used as binder P may be present in the catalyst as AIP04.

A typical catalyst may comprise 0 - 15 wt% Zn, or more preferably 0-10 wt% Zn. Furthermore a catalyst may comprise 0 - 10 wt% P, or more preferably 0-5 wt% P.

The incondensable gas phase typically comprises H2, CO, C02, CH4 and C2H6. It may be desirable to recycle at least part of this stream to the conversion reactor in order to sustain the loop pressure. The liquid product phase that remains after having separated the incondensable gas phase, e.g., by depressurization and/or distillation, consists of C3-C10 hydrocarbons. Higher hydrocarbons (C1 1 +) may also be present in minor amounts. The C3-C4 fraction of the liquid hydrocarbon product represents low value compared with gasoline and can only be tolerated in the gasoline in limited amounts due to their high vapor pressure. Therefore, the C3 fraction and major part of the C4 fraction is typically recovered and sold as LPG. Also the C5 fraction represents low value, in particular in regions with mandated blending of ethanol into the gasoline. Therefore, the lower-boiling part of the hydrocarbon product fraction may advantageously be recycled to the conversion reactor whereby at least part of the light fraction is converted into higher-boiling components.

In particular, olefins and naphthenes are reactive intermediates in the MTG reaction as both are intermediates in the transformation of oxygenates to aromatics. In addition, ar- omatics are characterized by high octane numbers. In other words, by recycling light hydrocarbons of low value to the gasoline reactor the overall aromatic yield is increased, the average carbon number and the content of aromatics in the gasoline product is increased making the gasoline product particularly suitable as a high-octane blendstock.

It may even be desirable to recycle the C6+ fraction in this way to further increase the amount of aromatics in the gasoline. Thus, according to the invention, the gasoline product may comprise C6+ or even C7+.

In one embodiment the gasoline product may arise from a split (distillation) of the first liquid hydrocarbon stream, done at conditions resulting in a distribution where benzene is preferentially found in the gasoline product phase rather than in the intermediate stream. Preferably, more than 70 wt% such as more than 80 wt% or more preferably more than 90 wt% of the benzene present in the first liquid hydrocarbon stream is retained in the gasoline product phase. A gasoline product stream obtained in such a way is referred to as "C6+". A C6+ gasoline product will typically be rich in aromatics and have research and motor octane numbers of 90-100 and 80-90, respectively.

In another embodiment, the split (distillation) of the first liquid hydrocarbon stream is done at conditions resulting in a distribution where toluene is preferentially found in the gasoline product phase rather than in the intermediate stream. Preferably, more than 70 wt% such as more than 80 wt% or more preferably more than 90 wt% of the toluene present in the first liquid hydrocarbon stream is retained in the gasoline product phase. A gasoline product stream obtained in such a way is referred to as "C7+". A C7+ gasoline product will typically be rich in aromatics and have research and motor octane numbers of 95-105 and 85-95, respectively.

In yet another embodiment, the split (distillation) of the first liquid hydrocarbon stream is done at conditions resulting in a distribution where xylenes are preferentially retained in the gasoline product phase rather than in the intermediate stream. Preferably, more than 70 wt% such as more than 80 wt% or more preferably more than 90 wt% of the m-xylene present in the first liquid hydrocarbon stream is retained in the gasoline product phase. A gasoline product stream obtained in such a way is referred to as "C8+". A C8+ gasoline product will typically be rich in aromatics and have research and motor octane numbers of 100-1 10 and 90-100, respectively.

The intermediate phases comprise C3-C5, C3-C6 or C3-C7 depending on the desired composition of the gasoline product phase being C6+ or C7+ or C8+.

At least part of the intermediate phase is recycled. The intermediate phase may be split into two or more phases a fractions such as a fraction comprising C3-C4 and a fraction comprising reactants comprising C5, C5-C6 or C5-C7. The C5 fraction is defined in a way that C6+ hydrocarbons may be included (e.g. paraffins and/or olefins). The C5-C6 fraction is defined in a way that C7+ hydrocarbons may be included (e.g. paraffins and/or olefins). It is possible that some C8+ hydrocarbons are present in the C5-C7 fraction (e.g. paraffins and/or olefins).

In some embodiments at least part of fraction C3-C4 may be recycled to the main feed thereby forming part of the reaction feed. Recycling the C3-C4 stream may be beneficial since the molar fraction of H2 in the reactor feed stream may be lower as a conse- quence of recycling C3-C4, which facilitate dehydrogenation reactions, in particular when a Zn-containing catalyst is applied, and thus a higher yield of aromatics. Furthermore, the C3-C4 stream contains olefins which may oligomerize, cyclize and aromatize when recycled to the gasoline reactor. Propane and butanes are not very reactive, but may to a lesser extent be converted to aromatics via dehydrogenation to olefins. At least part of the fraction comprising reactants comprising C5, C5-C6 or C5-C7 may be recycled in order to utilize any reactants such as olefins and naphthenes thereby increasing the aromatics yield. C5-C6 or C5-C7 paraffins may also be converted to aro- matics (via dehydrogenation to olefins). Generally paraffins are not very reactive under the reaction conditions in the MTG reactor, but longer (C5+) chained paraffins are more reactive than propane and butane, and some conversion of the C5+ paraffins through cracking and recombination reactions is possible. The C3-C4 fraction may be sold as LPG product, and it may be a possibility to recycle to the MTG reactor only the C5, C5- C6 or C5-C7 fractions.

The C3-C4 fraction as well as the fraction comprising reactants comprising C5, C5-C6 or C5-C7 is essentially free of H2 which makes the fraction comprising C3-C4 and the fraction comprising C5, C5-C6 or C5-C7 ideal as recycles. Low H2 levels in the recycles is advantageous as high H2 levels in the reactor inlet may inhibit the dehydrogena- tion reactions and thus reducing the aromatic yield. In some embodiments the hydrogen molar fraction at the gasoline reactor inlet is less than 15 mol%, more preferably less than 10 mol% and even more preferably less than 5 mol%, such as less than 1 mol%. At least part of the first gas phase from the first separator may also be used as recycle to the reactor. Alternatively, or in combination, at least part of the first gas phase may be purged.

Depending on the degree of recycle of the first gas phase the first separator may be run to achieve specific compositions of the first gas phase.

Typically, if the first gas phase is recycled the first gas phase may preferably comprise H2, CO, C02, C1 -C4 hydrocarbons. This may be achieved by running the first separator at temperatures between 25 and 60°C, most preferably between 40 and 50°C and pressures between 10 and 30 bar, most preferably between 15 and 25 bar.

In case no or only a limited part of the first gas phase is recycled the separation may preferably be conducted at higher pressure and/or lower temperature to increase the solubility of light hydrocarbons such as propane, propene, butanes and butenes in the first liquid phase.

In other advantageous embodiment of the invention, the flow of recycle gas form the first separator in the MTG loop to the inlet of the MTG reactor is very low, preferably 0, resulting in a low content of H2 at the inlet to the MTG reactor. The low molar fraction of H2 at the inlet of the MTG reactor may lead to high dehydrogenation activity of the MTG catalyst, and thus higher yield of aromatics. If there is no gas recycle from the first separator in the MTG loop, the temperature increase in the MTG reactor may be high, if too little recycle of one or more intermediate liquid phases is added to the feed stream.

As the reaction feed is a combination of the main feed and one or more recycles, the reaction feed may comprise the feed stream as well as recycles of the C3-C4 fraction, the fraction comprising reactants comprising C5, C5-C6 or C5-C7 and first gas phase.

Thus according to the present invention a variety of streams downstream the gasoline reactor may be returned back to the gasoline reactor whereby it is possible to increase the yield of aromatics, thereby producing a high-octane reformate blendstock.

For example it is possible to cut the liquid product phase in a C7+ fraction which constitutes the product and recirculate at least part of the C7- fraction back to the reactor. This has several potential benefits:

The C3-C4 fraction comprise paraffins (e.g. propane, butane) that help to re- duce the hydrogen molar fraction in the MTG reactor. In addition, this fraction also contains olefins (propene and butenes) which are building blocks for making higher hydrocarbons such as aromatics.

The C5 fraction contains pentenes and cyclopentanes which are both aromatics precursors. This fraction may additionally contain minor amounts of C6 hydrocarbons · The C6 and C7 fractions are relatively poor in aromatics. These fractions mainly comprise n-paraffins (e.g., hexane and heptane, both of which have very low octane numbers) and isoparaffins (e.g. 2-methylpentane and 2-methylhexane) as well as olefins (e.g., methylpentenes and methylhexenes) and naphthenes (e.g., methyl- and ethylcyclopentane and cyclohexane and methylcyclohexane). These fractions, when being recycled to the reactor, are given an extra chance to react and produce more ar- omatics.

Any recycle of the C5, C5-C6 or C5-C7 fractions will further contribute to reducing the hydrogen molar fraction in the synthesis loop. At reduced hydrogen molar fraction more naphthenes and possibly paraffins as well may become dehydrogenated and thereby further increase the selectivity to aromatics.

Figures 1 shows an exemplary embodiment where a methanol containing feed (1 ) is warmed up and mixed with the recycle stream (6) and optionally with the stream (1 1 b) comprising at least part of one or more one or more intermediate liquid phases into the reactor inlet stream (2). The reactor effluent (3) is cooled down and separated in a separator (14) into a water phase (7), a first liquid hydrocarbon phase (8) and a first gas phase (4). The first gas phase can be split into a purge (5) and the recycle stream (6). The first liquid hydrocarbon phase (8) is separated in a series of separation units (15), typically distillation columns, into an incondensable gas phase (9) comprising H2, CO, C02, C1 -C2 hydrocarbons, a C3-C4 fraction (stream 10a) comprising propane and/or butane, an phase comprising C5 or C5-C6 or C5-C7 hydrocarbon fractions (stream 1 1 a, comprising paraffins, olefins and naphthenes) and a product C6+ or C7+ or C8+ fraction, comprising aromatic compounds (stream 12). The intermediate phase comprising C5 or C5-C6 or C5-C7 (1 1 a) can be mixed with, for example, the feed (1 ) using stream 1 1 b or the recycle gas (6), etc. Optionally, the C3-C4 fraction can be combined to the C5 or C5-C6 or C5-C7 fraction, through stream (10b), constituting the intermediate phase.

Fig 2 shows another embodiment wherein the C3-C4 fraction (10c) and/or phase comprising C5 or C5-C6 or C5-C7 (1 1 c) can be added at any point in the reactor, either as a simple mix or as a quench in between catalyst beds. Fig. 3 A typical MTG product PIONA distribution (sorted according to carbon number) shows that there are two main groups of peaks: one around C3-C6 where paraffins are the main components and another around C8-C10 where aromatics are the main component. It is easy to see that a cut around C5, C6 or C7 would further increase the aromatic content at the expense of having an extra C5-C6 or C5-C7 stream. A process modification where the C5, C5-C6 and/or C5-C7 cut is recirculated to the synthesis reactor is described here. This entails that the paraffin rich stream (containing also olefins and naphthenes) has an extra chance to be converted over the MTG catalyst into aromatics (via dehydrogenation into olefins).

The result is an improvement in the gasoline aromaticity, making it a more valuable product than gasoline produced by current technology. Figure 4 shows how the aromaticity of the gasoline produced in the MTG process wears off with prolonged operation of the plant (15 consecutive operation/regeneration cycles). Operating the plant according to the present invention allows for maintaining a constant and high aromatic content in the gasoline by controlling the recirculation rate of the C3-C5, C3-C6 or C3-C7 fraction. I.e. the option to use and control the various recycles allows the optimization of the MTG process even after prolonged operation.

Claims

1 . Process for producing a gasoline type reformate from a main feed comprising alcohols and/or ethers such as methanol and/or dimethyl ether, said process comprising the steps of

- reacting a reaction feed over a zeolite or zeolite-containing catalyst thereby obtaining a reaction effluent comprising C1 -C10 hydrocarbons,

- recycling at least part of the one or more intermediate phases, where

the reaction feed comprises the main feed and the at least part of the one or more intermediate phase recycle.

2. Process according to claim 1 , wherein the incondensable gas phase comprises H2, CO, C02, C1 -C2 hydrocarbons.

3. Process according to any of the preceding claims, wherein the gasoline product phase comprises C6+, C7+ or C8+ aromatic compounds.

4. Process according to any of the preceding claims, wherein the intermediate phases comprise C3-C4 hydrocarbons and at least a fraction comprising C5 hydrocarbons, or C5-C6 or C5-C7 hydrocarbons.

5. Process according to any of the preceding claims, wherein the one or more intermediate phases recycled is C5 hydrocarbons.

6. Process according to any of the preceding claims, wherein the one or more intermediate phases recycled is C5-C6 hydrocarbons.

7. Process according to any of the preceding claims, wherein the one or more intermediate phases recycled is C5-C7 hydrocarbons.

8. Process according to any of the preceding claims, wherein the one or more intermediate phases comprises propane, propene, butane and/or butenes.

9. Process according to any of the preceding claims, wherein the intermediate phases comprises reactants with a carbon number of 5 or higher, comprising olefins, paraffins and/or naphthenes.

10. Process according to any of the preceding claims, wherein the first gas phase comprises H2, CO, C02, C1 -C4 hydrocarbons.

1 1. Process according to any of the preceding claims, wherein at least part of the first gas phase is purged

12. Process according to any of the preceding claims, wherein at least part of the first gas phase is recycled as part of the reaction feed, such as 10-100%, such as 15 -

95%, such as above 20% of the first gas phase is recycled as part of the reaction feed.

13. Process according to any of the preceding claims, wherein 0 - 10% of the first gas phase is recycled as part of the reaction feed, such as below 8% or below 5%, such as 0,1 - 5%, such as 0,5 - 2% or below 2% or below 1 % of the first gas phase is recycled as part of the reaction feed.

14. Process according to any of the preceding claims, wherein at least part of one or more of the intermediate phase is used to control the temperature in the MTG reactors by means of recycle.

15. Process according to any of the preceding claims, wherein the first separation is done in one or several separation or distillation operations.

16. Process according to any of the preceding claims, wherein the feed stream comprising oxygenates is converted in the MTG reactor over a bifunctional catalyst comprising a zeolite and a dehydrogenation function (metal or oxide).

17. Process according to any of the preceding claims, wherein the feed stream comprising oxygenates is converted in the MTG reactor over a bifunctional catalyst comprising zeolite ZSM-5 and 0.2 - 15 wt% Zn, such as 3 - 15 wt% Zn or 5-15 wt% Zn.

18. Process according to any of the preceding claims, wherein the feed stream com- prising oxygenates is converted in the MTG reactor over a bifunctional catalyst comprising zeolite ZSM-5, Zn and 0 - 10 wt% P, such as 0.1 - 8 wt% P or 0.5 - 5 wt% P.

19. Process according to any of the preceding claims, wherein the feed stream comprising oxygenates is converted in the MTG reactor over a bifunctional catalyst comprising zeolite ZSM-5 and Zn, where AI203 is used as binder to shape the catalyst.

20. Process according to any of the preceding claims, wherein the feed stream comprising oxygenates is converted over one or more beds of catalyst in one or more catalytic reactors

21. Process according to any of the preceding claims, wherein the feed stream comprising oxygenates is converted in one or more fixed bed reactors.

22. Method for optimizing a MTG process, by regulating the recycle of one or more recycles,

- controlling the recycle of the C3-C4 fraction as reactant and/or to adjust the hydrogen molar fraction in the MTG synthesis section and/or

- controlling the recycle of the C5 or C5-C6 and/or C5-C7 fractions as reactant and/or for adjusting the hydrogen molar fraction in the MTG synthesis section and/or

- controlling the recycle of the first gas phase as reactant and/or for adjusting the hydrogen molar fraction in the MTG synthesis section.

23. A plant arranged to enable the optimization of an MTG process, said plant comprising

- means for providing a main feed

- a reactor

- a first separator

- a separation section

-means for - recycle and/or control of the C3-C4 fraction as a reactant and/or to adjusting the hydrogen molar fraction in the MTG synthesis loop.

- recycle and/or control the recycle of the intermediate fraction as reactant and/or for adjusting hydrogen molar fraction, in the MTG synthesis loop and/or - recycle and/or control the recycle of the first gas phase as reactant and/or for adjusting hydrogen molar fraction in the MTG synthesis loop.