Methanol to olefin (MTO) process

Abstract

A process for producing an olefin stream, said process comprising passing a feedstock stream comprising oxygenates over catalyst comprises a zeolite with a framework having a 10-ring pore structure, in which said 10-ring pore structure comprises a unidimensional (1-D) pore structure, such as *MRE, at a pressure of 1-25 bar and a temperature of 240-360° C. The olefin stream may be converted to jet fuel, particularly sustainable aviation fuel (SAF) by further oligomerization and hydrogenation.

Claims

1. A process for producing an olefin stream, said process comprising passing a feedstock stream comprising oxygenates over a catalyst active in the conversion of oxygenates, in which the catalyst comprises a zeolite with a framework having a 10-ring pore structure, in which said 10-ring pore structure is a unidimensional (1-D) pore structure, at a pressure of 1-25 bar, and a temperature of 240-360° C.; and wherein said 1-D pore structure is any of *MRE (ZSM-48), MTT (ZSM-23), TON (ZSM-22), or combinations thereof, wherein the feedstock stream is combined with a diluent, the feedstock stream is methanol and it is diluted to a methanol concentration in the feedstock of 2-20 vol. %.

2. The process according to claim 1, wherein the catalyst comprises a binder selected from the group of alumina, aluminum phosphate, silica, silica-alumina, zirconia, titania and combinations of these metal oxides, and other refractory oxides, and clays, kaolin, palygorskite, smectite and attapulgite.

3. The process according to claim 2, wherein the catalyst contains up to 30-90 wt % zeolite with the binder, suitably 50-80 wt %, the binder suitably comprising an alumina component.

4. The process according to claim 1, wherein the zeolite has a silica-to-alumina ratio (SAR) of up to 240.

5. (canceled)

6. The process according to claim 1, wherein the process further comprises recycling a portion of an olefin containing stream to the feedstock stream, said portion of the olefin containing stream suitably being a stream comprising C2-C3 olefins or a C3 olefin stream (propylene stream) which is withdrawn from said olefin stream.

7. The process according to claim 1, wherein the feedstock stream comprising oxygenates is derived from one or more oxygenates taken from the group consisting of triglycerides, fatty acids, resin acids, ketones, aldehydes or alcohols or ethers, where said oxygenates originate from one or more of a biological source, a gasification process, a pyrolysis process, Fischer-Tropsch synthesis, or methanol-based synthesis.

8. The process according to claim 1, wherein the oxygenates are selected from methanol (MeOH), dimethyl ether (DME), or combinations thereof.

9. The process according to claim 1, comprising: using a first reactor set including a single reactor or several reactors, for the partial or full conversion of the oxygenates.

10. The process according to claim 9, further comprising using a second reactor set including a single reactor or several reactors, for the further conversion of the oxygenates, and a phase separation stage in between the first reactor set and the second reactor set, for thereby forming the olefin stream.

11. The process according to claim 10, comprising: passing the feedstock stream comprising oxygenates through the first reactor set under conditions for partly converting the oxygenates, thereby forming a raw olefin stream comprising unconverted oxygenates and C2-C8 olefins; passing the raw olefin stream through said phase separation stage, for producing: a first olefin stream, which is rich in lower olefins; a separated oxygenate stream comprising the unconverted oxygenates; a second olefin stream, which is rich in higher olefins; combining the first olefin stream with the separated oxygenate stream comprising the unconverted oxygenates, thereby forming a combined stream comprising lower olefins and the unconverted oxygenates; passing the resulting combined stream comprising lower olefins and the unconverted oxygenates through the second reactor set under conditions for fully converting the unconverted oxygenates and the lower olefins, into a third olefin stream which is rich in higher olefins; combining the second olefin stream with the third olefin stream, thereby forming said olefin stream.

12. The process according to claim 1, further comprising: separating from the olefin stream an isoparaffin stream.

13. The process according to claim 1, further comprising: passing at least a portion of the olefin stream, e.g. after separating said isoparaffin stream, through an oligomerization step over an oligomerization catalyst, and optionally subsequently conducting a separation step, for thereby producing an oligomerized stream.

14. The process according to claim 1, wherein the olefin stream, e.g. the entire olefin stream after separating said isoparaffin stream, is passed directly to the oligomerization step.

15. The process according to claim 13, further comprising: passing at least a portion of the oligomerized stream through a hydrogenation step over a hydrogenation catalyst, and optionally subsequently conducting a separation step, for thereby producing a hydrocarbon stream comprising hydrocarbons boiling in the jet fuel range.

16. The process according to claim 13, wherein the oligomerization step and hydrogenation step are combined in a single hydro-oligomerization step, wherein the oligomerization step is dimerization, optionally also trimerization, by the hydro-oligomerization step being conducted by reacting, under the presence of hydrogen, the olefin stream, over a catalyst comprising a hydrogenation metal.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0153] FIG. 1 is a simplified figure showing the conversion of oxygenates to olefins and optional further conversion to jet fuel in accordance with an embodiment of the invention.

[0154] FIG. 2 is a simplified figure showing a particular embodiment of the invention for the conversion a feedstock comprising oxygenates to olefins and optional further conversion to jet fuel.

[0155] FIG. 3 shows a plot of methanol conversion and C3-C8 selectivity as a function of the temperature in accordance with Example 1

[0156] FIG. 4 shows a plot of the methanol conversion and yields as a function of cycle time of the catalyst (hours-on-stream, HOS) at the specific temperature of 360° C., in accordance with Example 1.

[0157] FIG. 5 shows a plot of the content of aromatics in the olefin stream at different temperatures as well as a function of methanol partial pressures (P.sub.MeoH), in accordance with Example 3

[0158] FIG. 6 shows a plot of methanol conversion as a function of temperature with a neat feed of methanol compared to a feed comprising propylene as co-feed, in accordance with Example 4

DETAILED DESCRIPTION

[0159] With reference to FIG. 1, a feedstock comprising oxygenates 100, such as methanol and/or DME, is directed together with an optional hydrogen stream 102 and an olefin stream 104 comprising C2-C3 olefins which is withdrawn from the olefin stream 106 formed in oxygenate conversion section 200. The oxygenate conversion section 200, for instance a MTO section, converts the oxygenates over a zeolite catalyst such as ZSM-48 having SAR of for instance up to 110 at e.g. 1-15 bar and 260-360° C., e.g. 300-360° C., or 300-350° C. The resulting olefin stream 106 at these conditions is rich in higher olefins (C3=-C8=) and low in aromatics and is optionally further converted (as shown by stippled lines) to a hydrocarbon stream 112 comprising hydrocarbons boiling in the jet fuel range (C8-C16).

[0160] This further conversion is conducted in downstream oligomerization and hydrogenation section 300, which preferably is combined as a single hydro-oligomerization step, for instance in a single reactor. The olefin stream 106, suitably after removing its water content, is mixed with optional oligomerization olefin stream 110 comprising C8-hydrocarbons and resulting from cracked C9-C16 hydrocarbons withdrawn from said hydrocarbon stream 112 comprising hydrocarbons boiling in the jet fuel range. The resulting mixed stream is then directed to section 300 and converted, under the presence of hydrogen being fed as stream 108, over a catalyst such as Ni supported on a zeolite having a FAU or MTT structure, for instance Y-zeolite, or ZSM-23, at e.g. 20-40 bar and 50-350° C., to the hydrocarbon stream 112 comprising hydrocarbons boiling in the jet fuel range. At these conditions, particularly the lower pressures, the single reactor in section 300 operates such that the oligomerization is dimerization and optionally also trimerization, and at the same time there is hydrogenation activity. Due to the higher olefins, isoparaffins, low aromatics (e.g. below 1 wt %), low ethylene (e.g. below 1 wt %) of the olefin stream 106, the hydrocarbons in stream 112 boiling in the jet fuel range i.e. jet fuel, can be used as SAF.

[0161] With reference to FIG. 2, a feedstock stream 100 comprising oxygenates such as methanol and/or DME passes through a first reactor set 200′, for instance three reactors arranged in parallel, for thereby achieving 50-70% conversion of the methanol and producing a raw olefin stream 105 comprising water, methanol and olefins e.g. C2-C8 olefins. The raw olefin stream 105 is subjected to separation in 3-phase separator 200″ thereby producing a first olefin stream 105a, which is rich in lower olefins, particularly C2-C3 olefins or mainly C2 olefins (ethylene), a separated oxygenate stream 105b comprising the unconverted oxygenates, e.g. unconverted methanol, and a second olefin stream 105c which is rich in higher olefins, particularly C3-C8 olefins incl. C4-C8 olefins. The first olefin stream 105a is combined with the separated oxygenate stream 105b comprising the unconverted oxygenates, thereby forming a combined stream 105d comprising lower olefins, particularly C2-C3 olefins or mainly ethylene, and the unconverted oxygenates. This combined stream is pressurized and fed to a second reactor set 200′″ arranged downstream, and which may for instance include two reactors arranged in parallel, for thereby achieving full conversion e.g. 85% or 90% or higher. The first reactor set 200′ and second reactor set 200′″ are thereby arranged in series. A third olefin stream 105e is produced which is rich in higher olefins, particularly C3-C8 olefins. Finally, the second olefin stream 105c (bypass stream) is combined with the third olefin stream 105e, thereby forming said olefin stream 106 which may have been pressurized. By the above arrangement of the MTO section 200, the rectors of the first and second set can be operated at low temperature, e.g. 250-350° C. or 260-360° C., suitably at a lower temperature than when using the embodiment of FIG. 1, which helps improving the life-time conversion capacity of the catalysts used and improve the selectivity to higher olefins due to less cracking. The resulting olefin stream 106, suitably after removing its water content, is optionally further converted (as shown by the stippled lines) in a downstream oligomerization and hydrogenation section 300, which is combined as a single hydro-oligomerization step, for instance in a single reactor, thereby producing hydrocarbon stream 112 comprising hydrocarbons boiling in the jet fuel range (C8-C16), particularly SAF, as explained in connection with FIG. 1.

EXAMPLES

Example 1. Product Selectivity in MTO

[0162] MTO tests were run in a fixed catalyst bed (fixed bed) reactor with a zeolite catalyst ZSM-48 (EU-2) having a 1-D pore structure and a silica to alumina ration (SAR) of 110, and at the following operating conditions: zeolite catalyst load: 250 mg cat/750 mg SiC, pressure=1 barg (2 bar), space velocity (WHSV)=2 h.sup.−1, total flow=3.5 NL/h (59 mL/min); methanol concentration in the feed (C.sub.MeOH)=10% (volume basis) with nitrogen as the diluent. Thus, P.sub.MeoH is 0.2 bar. The temperature used is in the range 320-360° C.

[0163] FIG. 3 shows the methanol conversion as a function of the temperature. It is observed, that already at 320° C., there is almost 100% conversion, and at 360° C. there is 100% conversion. Aromatics are formed but are kept at a low level, namely below 1 wt %, more specifically at about 0.5 wt % at 360° C. and near 1 wt % at 320° C. Hence, there is low selectivity towards formation of aromatics. At the same time, the content of isoparaffins in the olefin stream increases with decreasing temperatures to a range of 10-15 wt % in the temperature window 320-360° C., while the content of the C2-olefin (ethylene, in the figure denoted as O2) decreases with temperature and becomes 1 wt % or less in the same temperature window, thus providing an olefin stream free of ethylene. For instance, at 320° C., the ethylene content is as low as 0.2 wt %. The content of higher olefins (C3-C8, in the figure denoted as O3-O8) is kept at a high level, namely in the range 70-80 wt % of the olefin stream. Olefins having more than nine (9) carbons (in the figure denoted as O9+) are also maintained at a low level.

[0164] The table below shows the olefin distribution in wt % in the olefin stream.

TABLE-US-00001 C8= and T (° C.) C2= C3= C4= C5= C6= C7= C9= 320 <1 21 27 28 15 7 1 360 1 31 28 26 9 4 1 400 2 37 28 25 5 3 n.d.* 440 6 47 24 18 3 2 n.d.* 480 11 50 22 13 2 2 n.d.* *not detectable

[0165] FIG. 4 shows the methanol conversion and yields (mass,% in Y-axis) in terms of time on stream (time in hours in X-axis) at the specific temperature of 360° C. It is observed that the catalyst cycle time is maintained over prolonged periods, thus making it suitably for commercial application i.e. industrial application.

[0166] Compared to the prior art according to U.S. Pat. No. 4,476,338, where MTO is conducted over a ZSM-48 having SAR of 113 or 180 and at 370° C. (Example 1 and 2 therein), the olefin stream according to the present invention enables a higher production of total olefins (e.g. C2-C8 olefins); lower production of ethylene, for instance the content of ethylene now being less than 1 wt %; lower production of aromatics, for instance the content of aromatic compounds now being below 1 wt %; and higher production of isoparaffins, for instance now 10-15 wt %. Furthermore, the catalyst lifetime is increased.

Example 2. Effect of Binder in the Catalyst in MTO

[0167] The same tests with ZSM-48 (EU-2) where conducted at WSHV=2 h.sup.−1, methanol concentration in the feed (C.sub.MeOH)=8% (volume basis) with nitrogen as diluent and pressure of 5 bar, using a catalyst with a binder: 60 wt % zeolite and 40 wt % alumina. The table below shows the effect of adding the binder.

[0168] At high temperatures i.e. above 360° C. such as 400, 440 or 480° C., as shown in the table, a high amount of paraffins is formed, almost exclusively as methane, which is highly likely a result of MeOH/DME cracking i.e. MeOH and/or DME cracking. At lower temperatures corresponding to the present invention (360° C.), the cracking becomes negligible, resulting in an effective conversion of the DME/MeOH into olefins.

TABLE-US-00002 MeOH Olefin Paraffin Methane Temperature, conversion, yield, yield, yield, C. % wt % wt % wt. % 480 100 45 48 48 440 100 68 23 23 400 100 80 6 6 360 96 80 2 1

Example 3. Effect of Methanol Partial Pressure in MTO

[0169] The same tests with ZSM-48 (EU-2) where conducted at WSHV=2 h.sup.−1 and methanol concentration in the feed (C.sub.MeOH)=10% (volume basis). FIG. 5 shows the content of aromatics (total aromatics, wt %) measured as benzene (B), toluene (T), xylene (X) and ethylbenzene (Total aromatics), at the different temperatures as well as a function of methanol partial pressures P.sub.MeoH at the different temperatures. At a given temperature, for instance at 320° C., each column designates a P.sub.MeoH: the column in the left is P.sub.MeOH=0.2 bar, the column in the center P.sub.MeoH=0.3 bar and the column in the right P.sub.MeOH=0.5 bar. At a methanol concentration in the feed of 10%, the pressure (total pressure) at each give partial pressure is respectively: 2 bar, 3 bar and 5 bar.

[0170] It is observed that is that at low temperature, from 360° C. and below, the MeOH partial pressure does not seem to have any significant influence on the content of aromatics in the resulting olefin stream. The (negative) effect of high MeOH partial pressure in terms of higher production of aromatics, thus appears to decrease drastically at 360° C. and more or less vanish at temperatures below about 350° C. This enables an increase in the pressure used for conducting MTO, which provides benefits in terms of i.a. higher throughout in the MTO and reduction of equipment size in the plant for producing SAF.

[0171] As shown in FIG. 5, at the lower temperatures, the content of aromatics is maintained below 2 wt % and at similar values regardless of the P.sub.MeoH. For instance, with MTO operating at 400° C., at P.sub.MeoH of 0.3 and 0.5 the content of aromatics is about 2 wt % and 6 wt %, respectively. When operating the MTO at 360° C., at P.sub.MeoH of 0.3 and 0.5 the content of aromatics is about 1 wt % and 2 wt %, respectively. When operating the MTO at 320° C., at P.sub.MeoH of 0.3 and 0.5 the content of aromatics is about 1 wt % at both P.sub.MeoH.

[0172] When co-feed of light olefins such as the C3-olefin (propylene) is provided, see Example 4, this enables a further reduction in temperature and, in turn, a further reduction in hydrogen transfer (less generation of e.g. aromatics), higher olefin chain length and, additionally, more freedom with respect to total (or methanol partial) pressure extend ultimate catalyst longevity.

Example 4. Effect of Lower Olefin Co-Feed in MTO

[0173] The effect of adding the lower olefin propylene (propene) into the methanol feed, is shown in FIG. 6.

[0174] The comparison is conducted with the same zeolite ZSM-48 (EU-2) at the same reaction conditions in the MTO with 1 mole % propylene (propene), and without (i.e. neat methanol feed). Operating conditions: zeolite catalyst load: 250 mg cat/750 mg SiC, pressure=2 barg (3 bar), space velocity (WHSV)=2 h.sup.−1, total flow=3.5 NL/h (59 mL/min); methanol concentration in the feed (C.sub.MeOH)=10% (volume basis) with nitrogen as the diluent.

[0175] FIG. 6 shows that adding propylene as co-feed (upper line in the figure) significantly promotes the kick-off or initiation of the oxygenate (methanol) conversion. In the operation of the MTO, there will be significant amounts of light olefins, namely C2-C3 olefins, in the recycle stream, suitably as a portion of the olefin stream, and which may be utilized anyway for temperature control in the MTO due to its exothermicity. The addition of the lower olefin, e.g. as recycle stream, to the methanol feed enables a significant reduction of the inlet temperature to the MTO, whereby the content of aromatics and paraffins (as used herein, also incl. methane) decreases, while the average olefin chain length increases—and hence the content of higher olefins. Furthermore, the co-feed with the lower olefin significantly increases catalyst longevity, for instance as measured by catalyst cycle time. Moreover, hydrogen transfer reactions are minimized, and not least the lower temperature of the MTO, e.g. 320° C., enables operation at the higher pressure range, which may be also advantageous, as described in connection with Example 3.