A METHOD FOR PRODUCING SYNGAS USING CATALYTIC REVERSE WATER GAS SHIFT

Abstract

The present invention relates to a method for producing syngas using a catalytic reverse water gas shift (RWGS) reaction, the method at least comprising the steps of: a) providing a feed stream (10) comprising at least hydrogen (H2) and carbon dioxide (CO2); b) heating the feed stream (10) provided in step a) in a first heat exchanger (3) thereby obtaining a first heated feed stream (20); c) introducing the first heated feed stream (20) into a RWGS reactor (2) and subjecting it to a catalytic RWGS reaction, thereby obtaining a syngas containing stream (30); d) cooling the syngas containing stream (30) obtained in step c) in the first heat exchanger (3) against the feed stream (10) provided in step a), thereby obtaining a first cooled syngas stream (40); c) cooling the first cooled syngas stream (40) obtained in step d) in a second heat exchanger (5) thereby obtaining a second cooled syngas stream (50); f) separating the second cooled syngas stream (50) obtained in step e) in a gas/liquid separator (6) thereby obtaining a water-enriched stream (110) and a water-depleted syngas stream (100); g) separating the water-depleted syngas stream (100) obtained in step f) in a CO.sub.2 removal unit (8) thereby obtaining a CO.sub.2-enriched stream (120) and a CO.sub.2-depleted syngas stream (130): and31?h) combining the CO.sub.2-enriched stream (120) obtained in step g) with the feed stream (10) provided in step a).

Claims

1.-9. (canceled)

10. A method for producing syngas using a catalytic reverse water gas shift (RWGS) reaction, the method at least comprising the steps of: a) providing a feed stream comprising at least hydrogen (H.sub.2) and carbon dioxide (CO.sub.2); b) heating the feed stream provided in step a) in a first heat exchanger thereby obtaining a first heated feed stream; c) introducing the first heated feed stream into a RWGS reactor and subjecting it to a catalytic RWGS reaction in the presence of a non-methanation promoting catalyst wherein the pressure as used in the RWGS reactor in step c) is above 20 bara and wherein the temperature as used in the RWGS reactor in step c) is in the range of from 450 to 700? C., thereby obtaining a syngas containing stream, wherein the syngas containing stream comprises at most 1.0 vol. % methane (CH.sub.4); d) cooling the syngas containing stream obtained in step c) in the first heat exchanger against the feed stream provided in step a), thereby obtaining a first cooled syngas stream; e) cooling the first cooled syngas stream obtained in step d) in a second heat exchanger thereby obtaining a second cooled syngas stream; f) separating the second cooled syngas stream obtained in step e) in a gas/liquid separator thereby obtaining a water-enriched stream and a water-depleted syngas stream; g) separating the water-depleted syngas stream obtained in step f) in a CO.sub.2 removal unit thereby obtaining a CO.sub.2-enriched stream and a CO.sub.2-depleted syngas stream, wherein the CO.sub.2-depleted syngas stream has a hydrogen to carbon monoxide (H.sub.2/CO) volume ratio in the range of 1.5 to 2.5; and h) combining the CO.sub.2-enriched stream obtained in step g) with the feed stream provided in step a).

11. The method according to claim 10, wherein the first heated stream obtained in step b) has a hydrogen to carbon dioxide (H.sub.2/CO.sub.2) volume ratio of below 2.0.

12. The method according to claim 10, wherein the first heated stream obtained in step b) has a hydrogen to carbon dioxide (H.sub.2/CO.sub.2) volume ratio of below 1.5.

13. The method according to claim 10, wherein the first heated stream obtained in step b) has a hydrogen to carbon dioxide (H.sub.2/CO.sub.2) volume ratio of below 1.2.

14. The method according to claim 10, wherein the RWGS reactor comprises a multi-tubular reactor heated by molten salt circulating around the tubes of the multi-tubular reactor.

15. The method according to claim 14 wherein the circulating being in counter-current operation.

16. The method according to claim 10, wherein the catalyst as used in the catalytic RWGS reaction in step c) comprises cerium oxide, zirconium oxide or a combination thereof.

17. The method according to claim 10, wherein the syngas containing stream obtained in step c) comprises at most 0.1 vol. % methane.

18. The method according to claim 10, wherein the temperature of the syngas containing stream obtained in step c) is kept below 700? C.

19. The method according to claim 10, wherein the temperature of the syngas containing stream obtained in step c) is kept below 650? C.

20. The method according to claim 10, wherein the temperature of the syngas containing stream obtained in step c) is kept below 600? C.

21. The method according to claim 10, wherein the CO.sub.2-depleted syngas stream obtained in step g) comprises at most 10 vol. % CO.sub.2.

22. The method according to claim 10, wherein the CO.sub.2-depleted syngas stream obtained in step g) comprises at most 5 vol. % CO.sub.2.

23. The method according to claim 10, wherein the CO.sub.2-depleted syngas stream obtained in step g) comprises at most 2 vol. % CO.sub.2.

Description

[0074] Hereinafter the present invention will be further illustrated by the following non-limiting drawings. Herein shows:

[0075] FIG. 1 schematically a first embodiment of an apparatus suitable for performing the method for producing syngas using a catalytic RWGS reaction according to the present invention; and

[0076] FIG. 2 schematically examples of different reactor types that can be used for the RWGS reactor as used according to the present invention.

[0077] For the purpose of this description, same reference numbers refer to same or similar components.

[0078] The apparatus of FIG. 1, generally referred to with reference number 1, comprises a RWGS reactor 2, a first heat exchanger 3, a second heat exchanger 5, a further heat exchanger 4 and a first gas/liquid separator 6 (in the form of a H.sub.2O knock-out drum) and a CO.sub.2 removal unit 8.

[0079] In the embodiment of FIG. 1, the RWGS reactor 2 comprises a catalyst bed and is provided with external heating 7 (e.g. in the form of electrical heating or molten salt heater).

[0080] The heat exchangers 3, 4 and 5 may be integrated with the external heating 7.

[0081] During use, a feed stream 10 is provided, which comprises at least hydrogen (H.sub.2) and carbon dioxide (CO.sub.2).

[0082] The feed stream is heated in the first heat exchanger 3 thereby obtaining a first heated feed stream 20. As shown in the embodiment of FIG. 1, the heated feed stream 20 may be further heated in a further heat exchanger 4. This further heat exchanger 4 may form part of the (overhead of the) RWGS reactor 2.

[0083] The first heated feed stream 20 is introduced into the RWGS reactor 2 and subjected to a catalytic RWGS reaction, thereby obtaining a syngas containing stream, which is removed as stream 30 from the RWGS reactor 2.

[0084] Then, the syngas containing stream 30 is cooled in the first heat exchanger 3 by indirect heat exchange against the feed stream 10, thereby obtaining a first cooled syngas stream 40. The first cooled syngas stream 40 is further cooled in the second heat exchanger 5, thereby obtaining a second cooled syngas stream 50.

[0085] Subsequently, the second cooled syngas stream 50 is separated in the gas/liquid separator 6 thereby obtaining a water-enriched stream 110 and a water-depleted syngas stream 100.

[0086] The water-depleted syngas stream 100 is then separated in the CO.sub.2 removal unit, thereby obtaining a CO.sub.2-enriched stream 120 and a CO.sub.2-depleted syngas stream 130. Stream 130 can be further processed or used as a product stream.

[0087] The CO.sub.2-enriched stream 120 is combined with the feed stream 10.

[0088] FIG. 2 shows schematically non-limiting examples of different reactor types that can be used for the RWGS reactor in the apparatus 1 according to the present invention.

[0089] The reactor of FIG. 2a) comprises a multi-tubular reactor heated by a molten salt circulating around the tubes of the multi-tubular reactor. Preferably, the molten salt flow inside the shell of the multi-tubular reactor is counter-currently when compared to the flow of the gas inside the tubes. As shown, the molten salt may be heated by separate external heating, preferably an e-heater. If molten salt is used for two or more reactors, then there may be a common circuit for the molten salt.

[0090] The reactor of FIG. 2b) comprises a single catalyst bed, whilst the reactor of FIG. 2c) comprises a single catalyst bed provided with external heating. In FIG. 1 the reactor of the type shown in FIG. 2c) is used.

[0091] Further, the reactor of FIG. 2d comprises 3 catalyst beds with intermediate external heating between the beds.

[0092] Generally, if any of the reactors of 2b)-d) is used, then preheating (as in heat exchangers 4) is preferred.

EXAMPLES

Example 1

[0093] The apparatus of FIG. 1 was used for illustrating an exemplary method according to the present invention. The compositions and conditions of the streams in the various flow lines are provided in Table 1 below.

[0094] The values in Table 1 were calculated using a model generated with commercially available UniSim software, whilst using an equilibrium reactor with settings such that only the (R) WGS reactions are allowed to occur and whilst arranging the settings such that no methanation occurred (hence 0 vol % CH.sub.4 in all streams) . Thus, the standard Gibbs model was not used, which model would predict excess methanation (which does not occur or is at least minimized according to the present invention). Further, for the CO.sub.2 removal unit 8 a CO.sub.2 removal efficiency of 98% was assumed (this value of 98% is realistic; there are CO.sub.2 removal units that come close to an efficiency of 100%).

[0095] As can be seen from Table 1 below, an overall CO.sub.2 conversion of 97% was achieved, whilst aiming for a H.sub.2/CO ratio of 1.9, which ratio is e.g. suitable for subsequent Fischer-Tropsch reaction or production of methanol.

TABLE-US-00001 TABLE 1 stream 10 20 30 40 50 100 110 120 130 T [? C.] 25 480 550 153 40 40 40 40 40 CO.sub.2 26.3 49.1 31.6 31.6 31.6 38.2 100 1.2 [vol. %] H.sub.2 73.7 50.9 33.4 33.4 33.4 40.4 64.5 [vol. %] CO 0 0 17.5 17.5 17.5 21.1 33.7 [vol. %] H.sub.2O 0 0 17.5 17.5 17.5 0 100 [vol. %] H.sub.2/CO.sub.2 2.8 1 1.1 1.1 1.1 1.1 H.sub.2/CO 1.9 1.9 1.9 1.9 1.9 XCO.sub.2.sup.1 [%] 36 36 36 36 97 .sup.1XCO.sub.2 = % conversion of CO.sub.2, based on feed stream 10.

Example 2 (Comparative)

[0096] For comparison with FIG. 1, a set of calculations was performed for the line-up of FIG. 1 and with the same composition for feed stream 10 (with a H.sub.2/CO.sub.2 ratio of 2.8), but without combining the CO.sub.2-enriched stream 120 (as obtained in CO.sub.2 removal unit 8) with the feed stream 10. The same UniSim software as used in Example 1 was used.

[0097] Table 2 shows the compositions and conditions of the streams in the various flow lines.

[0098] As can be seen from Table 2, the line-up of FIG. 1 without combining the CO.sub.2-enriched stream 120 (as obtained in CO.sub.2 removal unit 8) with the feed stream 10 resulted in a relatively low CO.sub.2 conversion (54%) when compared to the line-up of FIG. 1 according to the present invention (97% for stream 130) where stream 120 was combined with the feed stream 10.

[0099] Further, due to the much lower conversion, the H.sub.2/CO ratio of the syngas product stream 130 is much higher than for Example 1 (viz. 4.1 vs 1.9). This higher H.sub.2/CO ratio is also much higher than the preferred range for subsequent use in Fischer-Tropsch or typical methanol or DME synthesis.

TABLE-US-00002 TABLE 2 Comparative - with CO.sub.2 removal unit 8, but no recycle. stream 10 20 30 40 50 100 110 120 130 T [? C.] 25 480 550 149 40 40 40 CO.sub.2 26.3 26.3 12.0 12.0 12.0 13.9 100 0.3 [vol. %] H.sub.2 73.7 73.7 59.4 59.4 59.4 69.1 80.3 [vol. %] CO 0 0 14.3 14.3 14.3 16.7 19.4 [vol. %] H.sub.2O 0 0 14.3 14.3 14.3 0 100 0 [vol. %] H.sub.2/CO.sub.2 2.8 2.8 5.0 5.0 5.0 5.0 H.sub.2/CO 4.1 4.1 4.1 4.1 4.1 XCO.sub.2.sup.1 [%] 54 54 54 54 54 .sup.1XCO.sub.2 = % conversion of CO.sub.2, based on feed stream 10.

Example 3 (Comparative)

[0100] For further comparison with the present invention (again using the same UniSim software), a set of calculations was performed for the line-up of FIG. 1 with the same composition for the feed stream 10 (with a H.sub.2/CO.sub.2 ratio of 2.8), but without the presence of the CO.sub.2 removal unit 8 (and hence also without combining the CO.sub.2-enriched stream 120 as obtained in a CO.sub.2 removal unit 8 with the feed stream 10).

[0101] Table 3 shows the compositions and conditions of the streams in the various flow lines. The results are similar as for Example 2, except that most of the CO.sub.2 has now not been removed for the final syngas product stream (in this case stream 100) thereby diluting the syngas without changing the overall conversion of CO.sub.2 (54%) or the H.sub.2/CO ratio (4.1) in the product stream 100. Hence, also for Example 3, both CO.sub.2 conversion and H.sub.2/CO ratio of the syngas product stream compare very unfavourable to Example 1.

[0102] As in Table 2, the overall CO.sub.2 conversion for stream 100 in Table 3 is again relatively low. As can be seen from Table 3, the H.sub.2/CO ratio (viz. 4.1) for the water-depleted syngas stream 100 was a lot higher than for Table 1 (viz. 1.9). Such a high H.sub.2/CO ratio would make the stream virtually unsuitable for use in the main target applications (such as in Fischer-Tropsch reactions or reactions to obtain methanol or DME).

TABLE-US-00003 TABLE 3 Comparative - no CO.sub.2 removal unit 8. Same H.sub.2/CO.sub.2 ratio for feed stream 10 stream 10 20 30 40 50 100 110 120 130 T [? C.] 25 480 550 149 40 40 40 N.A. N.A. CO.sub.2 26.3 26.3 12.0 12.0 12.0 13.9 N.A. N.A. [vol. %] H.sub.2 73.7 73.7 59.4 59.4 59.4 69.1 N.A. N.A. [vol. %] CO 14.3 14.3 14.3 16.7 N.A. N.A. [vol. %] H.sub.2O 14.3 14.3 14.3 0 100 N.A. N.A. [vol. %] H.sub.2/CO.sub.2 2.8 2.8 5.0 5.0 5.0 5.0 N.A. N.A. H.sub.2/CO 4.1 4.1 4.1 4.1 N.A. N.A. XCO.sub.2.sup.1 [%] 54 54 54 54 N.A. N.A. .sup.1XCO.sub.2 = % conversion of CO.sub.2, based on feed stream 10.

Example 4 (Comparative)

[0103] In comparative Examples 2 and 3 the composition of the feed stream 10 was kept the same as in Example 1. Due to lower conversion in examples 2 and 3, the H.sub.2/CO ratio in the product stream 100 appeared unfavourable. In this comparative Example 4, the H.sub.2/CO.sub.2 of the feed stream was adjusted to obtain the same H.sub.2/CO ratio for the stream 100 as in Example 1. Therefore, in this comparative example, a set of calculations was performed (again using the same UniSim software) , whilstlike in Example 3again using the line-up of FIG. 1 and also without the presence of the CO.sub.2 removal unit 8 (and hence also without combining the CO.sub.2-enriched stream 120 as obtained in a CO.sub.2 removal unit 8 with the feed stream 10), and the composition for the feed stream 10 was adapted to arrive at the same H.sub.2/CO ratio (viz. 1.9) for the water-depleted syngas stream 100. The same temperature was used for the syngas containing stream 30 (viz. 550? C.) as in FIG. 1/Table 1 according to the present invention.

[0104] Table 4 below shows the compositions and conditions of the streams in the various flow lines.

[0105] As can be seen from Table 4, to arrive at the same H.sub.2/CO ratio (viz. 1.9) for the water-depleted syngas stream 100 as in FIG. 1/Table 1 according to the present invention, the H.sub.2/CO.sub.2 ratio for the feed stream 10 needed to be significantly lowered (from 2.8 in Table 1 to 1.0 in Table 4).

[0106] A drawback of such a low H.sub.2/CO.sub.2 ratio for the feed stream 10 is that the equilibrium conversion is lowered even further (viz. 36%).

TABLE-US-00004 TABLE 4 Comparative. - no CO.sub.2 removal unit 8. Same H.sub.2/CO ratio for the water-depleted syngas stream 100 stream 10 20 30 40 50 100 110 120 130 T [? C.] 25 480 550 160 40 40 40 N.A. N.A. CO.sub.2 49 49 31.5 31.5 31.5 38.1 N.A. N.A. [vol. %] H.sub.2 51 51 33.5 33.5 33.5 40.5 N.A. N.A. [vol. %] CO 17.5 17.5 17.5 21.1 N.A. N.A. [vol. %] H.sub.2O 17.5 17.5 17.5 0 100 N.A. N.A. [vol. %] H.sub.2/CO.sub.2 1.0 1.0 1.1 1.1 1.1 1.1 N.A. N.A. H.sub.2/CO 1.9 1.9 1.9 1.9 N.A. N.A. XCO.sub.2.sup.1 [ %] 36 36 36 36 N.A. N.A. .sup.1XCO.sub.2 = % conversion of CO.sub.2, based on feed stream 10.

Example 5 (comparative)

[0107] In this comparative example, being a variant of Example 4, a further set of calculations was performed (again using the same UniSim software). As in Examples 3 and 4, the same line-up of FIG. 1 was used, again without the presence of the CO.sub.2 removal unit 8 (and hence also without combining the CO.sub.2-enriched stream 120 as obtained in a CO.sub.2 removal unit 8 with the feed stream 10).

[0108] In this Example 5, the same composition for the feed stream 10 (with a H.sub.2/CO.sub.2 ratio of 2.8) as used in Example 1 and Example 3 was used, but the temperature of the syngas containing stream 30 obtained at the outlet of the RWGS reactor composition was adapted (rather than adapting the composition for the feed stream 10 as done in Example 4). This, to try to arrive at the same overall CO.sub.2 conversion (viz. 97%) and hence also at the same H.sub.2/CO ratio (viz. 1.9) for the water-depleted syngas stream 100 as in FIG. 1/Table 1 according to the present invention.

[0109] Table 5 below shows the compositions and conditions of the streams in the various flow lines.

[0110] As can be seen from Table 5, the H.sub.2/CO.sub.2 ratio for the feed stream 10 needed was kept the same as in Tables 1 and 3 (viz. 2.8), but the temperature in the RWGS reactor was allowed to increase to try to arrive at the same H.sub.2/CO ratio (viz. 1.9) for the water-depleted syngas stream 100 as in FIG. 1/Table 1 according to the present invention. However, already with a relatively high temperature of 750? C. for the syngas containing stream 30, the H.sub.2/CO ratio for the water-depleted syngas stream 100 was still well above 1.9 (viz. 3.0), because the overall CO.sub.2 conversion is still well below the 97% of Example 1 (viz. 70%).

TABLE-US-00005 TABLE 5 Comparative - no CO.sub.2 removal unit 8. Higher temperature for syngas containing stream 30 stream 10 20 30 40 50 100 110 120 130 T [? C.] 25 650 750 163 40 40 40 N.A. N.A. CO.sub.2 26.3 26.3 7.8 7.8 7.8 9.5 N.A. N.A. [vol. %] H.sub.2 73.7 73.7 55.1 55.1 55.1 67.6 N.A. N.A. [vol. %] CO 18.5 18.5 18.5 22.7 N.A. N.A. [vol. %] H.sub.2O 18.5 18.5 18.5 0 100 N.A. N.A. [vol. %] H.sub.2/CO.sub.2 2.8 2.8 7.1 7.1 7.1 7.1 N.A. N.A. H.sub.2/CO 3.0 3.0 3.0 3.0 N.A. N.A. XCO.sub.2.sup.1 [%] 70 70 70 70 N.A. N.A. .sup.1XCO.sub.2 = % conversion of CO.sub.2, based on feed stream 10.

Discussion

[0111] As can be seen from the above Examples, the method according to the present invention allows for an effective way of producing syngas using a single stage, catalytic RWGS reaction, whilst maintaining the temperature in the RWGS reactors below 700? C. and whilst still achieving desirable CO.sub.2 conversion (of above 95%), with just 1 RWGS stage.

[0112] The person skilled in the art will readily understand that many modifications may be made without departing from the scope of the invention.