A METHOD FOR PRODUCING SYNGAS USING CATALYTIC REVERSE WATER GAS SHIFT

Abstract

A method for producing syngas that comprises providing a feed stream comprising H.sub.2 and CO.sub.2; heating the feed stream in a first heat exchanger to obtain a first heated feed stream; introducing the first heated feed stream into a first RWGS reactor to obtain a first syngas containing stream; cooling the first syngas containing stream in the first heat exchanger against the feed stream to obtain a first cooled syngas stream; separating the first cooled syngas stream in a first gas/liquid separator to obtain a water-enriched stream and a water-depleted syngas stream; heating the water-depleted syngas stream in a second heat exchanger to obtain a heated water-depleted syngas stream; introducing the heated water-depleted syngas stream into a second RWGS reactor to obtain a second syngas containing stream; and cooling the second syngas containing stream in the second heat exchanger against the water-depleted syngas to obtain a cooled syngas product stream.

Claims

1. 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 first RWGS reactor and subjecting it to a first catalytic RWGS reaction, thereby obtaining a first syngas containing stream; d) removing the first syngas containing stream obtained in step c) from the first RWGS reactor; e) cooling the first syngas containing stream removed from the first RWGS reactor in step d) in the first heat exchanger against the feed stream provided in step a), thereby obtaining a first cooled syngas stream; f) separating the first cooled syngas stream obtained in step e) in a first gas/liquid separator thereby obtaining a water-enriched stream and a water-depleted syngas stream; g) heating the water-depleted syngas stream obtained in step f) in a second heat exchanger thereby obtaining a heated water-depleted syngas stream; h) introducing the heated water-depleted syngas stream obtained in step g) into a second RWGS reactor and subjecting it to a second catalytic RWGS reaction, thereby obtaining a second syngas containing stream; i) removing the second syngas containing stream obtained in step h) from the second RWGS reactor; and j) cooling the second syngas containing stream removed from the second RWGS reactor in step i) in the second heat exchanger against the water-depleted syngas stream obtained in step f), thereby obtaining a cooled syngas product stream.

2. The method according to claim 1, wherein the temperature of the first catalytic RWGS reaction in step c) is kept below 700 C.

3. The method according to claim 1, wherein at least one of the first and the second RWGS reactors contains two or more catalyst beds with additional intermediate heating between the two or more catalyst beds.

4. The method according to claim 1, wherein at least one of the first and the second RWGS reactors comprises a multi-tubular reactor heated by molten salt circulating around the tubes of the multi-tubular reactor.

5. The method according to claim 1, wherein the first syngas containing stream comprises at most 1.0 vol. % methane (CH.sub.4).

6. The method according to claim 1, wherein the temperature of the second catalytic RWGS reaction in step h) is kept below 700 C.

7. The method according to claim 1, wherein the method further comprises the step of separating the cooled syngas product stream obtained in step j) in a second gas/liquid separator, thereby obtaining a water-enriched stream and a water-depleted syngas product stream.

8. An apparatus (1) suitable for performing the method for producing syngas according to claim 1, the apparatus at least comprising: a first heat exchanger for heat exchanging the feed stream against the first syngas containing stream removed from the first RWGS reactor, to obtain a first heated feed stream and a first cooled syngas stream; a first RWGS reactor to obtain a first syngas containing stream; a first gas/liquid separator for separating the first cooled syngas stream to obtain a water-enriched stream and a water-depleted syngas stream; a second heat exchanger for heat exchanging the water-depleted syngas and the second syngas containing stream removed from the second RWGS reactor, to obtain a heated water-depleted syngas stream and a cooled syngas product stream; a second RWGS reactor to obtain a second syngas containing stream.

9. The apparatus according to claim 8, wherein at least one of the first and the second RWGS reactors contains two or more catalyst beds with additional intermediate heating between the two or more catalyst beds.

10. The apparatus according to claim 8, further comprising a second gas/liquid separator for separating the cooled syngas product stream to obtain a water-enriched stream and a water-depleted syngas product stream.

11. The method according to claim 1, wherein the temperature of the first catalytic RWGS reaction in step c) is kept below 600 C.

12. The method according to claim 1, wherein the first syngas containing stream comprises at most 0.1 vol. % methane.

13. The method according to claim 1, wherein the temperature of the second catalytic RWGS reaction in step h) is kept below 700 C.

Description

[0081] Hereinafter the present invention will be further illustrated by the following non-limiting drawings. Herein shows:

[0082] 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

[0083] FIG. 2 schematically examples of different reactor types that can be used for the RWGS reactors as used according to the present invention; and

[0084] FIG. 3 schematically an example of an apparatus with a single RWGS reactor (included for comparative purposes).

[0085] For the purpose of this description, same reference numbers refer to same or similar components.

[0086] The apparatus of FIG. 1, generally referred to with reference number 1, comprises a first RWGS reactor 2, a second RWGS reactor 12 and a third RWGS reactor 22; a first heat exchanger 3, a second heat exchanger 13 and a third heat exchanger 23; further heat exchangers 4, 5, 14, 15 and 24; and a first gas/liquid separator 6 and a second gas/liquid separator 16.

[0087] Each of the RWGS reactors 2, 12 and 22 comprise a catalyst bed and is provided with external heating 7, 17, 27 (e.g. in the form of electrical heating or molten salt heater).

[0088] During use, a feed stream 10 is provided, which feed stream comprises at least hydrogen (H.sub.2) and carbon dioxide (CO.sub.2).

[0089] 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 first RWGS reactor 2.

[0090] The first heated feed stream 20 is introduced into the first RWGS reactor 2 and subjected to a first catalytic RWGS reaction, thereby obtaining a first syngas containing stream, which is removed as stream 30 from the first RWGS reactor 2.

[0091] Then, the first 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. As shown in the embodiment of FIG. 1, the cooled syngas stream 40 may be further cooled in the further heat exchanger 5.

[0092] Subsequently, the first cooled syngas stream 40 is separated in the first gas/liquid separator 6 thereby obtaining a water-enriched stream 60 and a water-depleted syngas stream 50.

[0093] The water-depleted syngas stream 50 is then heated in the second heat exchanger 13 thereby obtaining a heated water-depleted syngas stream 70. This heated water-depleted syngas stream 70 is then introduced into the second RWGS reactor 12 and subjected to a second catalytic RWGS reaction, thereby obtaining a second syngas containing stream which is removed from the second RWGS reactor 12 as stream 80.

[0094] This second syngas containing stream 80 is cooled in the second heat exchanger 13 by indirect heat exchange against the water-depleted syngas stream 50, thereby obtaining a cooled syngas product stream 90.

[0095] In the embodiment of FIG. 1, this cooled syngas product stream 90 is subjected to another round of separating (in gas/liquid separator 16), heating (in third heat exchanger 23), RWGS reaction (in third RWGS reactor 22) and cooling (in third heat exchanger 23), to obtain the final product stream 140.

[0096] The heat exchangers 4, 14 and 24 may be integrated with the external heating 7, 17 and 27.

[0097] FIG. 2 shows schematically non-limiting examples of different reactor types that can be used for the RWGS reactors in the apparatus 1 according to the present invention. The apparatus may comprise different types of reactors.

[0098] 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.

[0099] 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 reactors of the type shown in FIG. 2c) are used.

[0100] Further, the reactor of FIG. 2d comprises 3 catalyst beds with intermediate external heating between the beds.

[0101] Generally, if any of the reactors of 2b)-d) is used, then preheating (as in heat exchangers 4, 14, 24) is required.

[0102] FIG. 3 shows an example of an apparatus with a single RWGS reactor. FIG. 3 is not according to the present invention, but included for comparative purposes.

EXAMPLES

Example 1

[0103] 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.

[0104] 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).

TABLE-US-00001 TABLE 1 stream 10 20 30 40 50 60 70 80 90 100 110 120 130 140 T [ C.] 65 450 550 160 40 40 450 550 140 40 40 450 550 140 CO.sub.2 30 30 15 15 18 0 18 11 11 12 0 11 8 8 [vol. %] H.sub.2 70 70 54 54 64 0 64 57 57 61 0 62 58 58 [vol. %] CO 0 0 15 15 18 0 18 25 25 27 0 27 31 31 [vol. %] H.sub.2O 0-10 0-10 15 15 0 100 0 7 7 0 100 0 4 4 [vol. %] H.sub.2O/CO.sub.2 2.3 H.sub.2O/CO 3.6 3.6 3.6 3.6 2.3 2.3 2.3 2.3 1.9 1.9 XCO.sub.2.sup.1 50.6 50.6 70.0 70.0 80.2 .sup.1XCO.sub.2 = conversion of CO.sub.2, based on feed stream 10.

Example 2 (Comparative)

[0105] For comparison with FIG. 1, two sets of calculations were performed for the line-up of FIG. 3 whilst using the same UniSim software as used in Example 1.

[0106] Table 2A shows the compositions and conditions of the streams in the various flow lines whilst performing the RWGS reaction in the reactor 2 at lower temperature (550 C.; comparable with Example 1) and Table 2B the same at higher temperatures (1100 C.).

TABLE-US-00002 TABLE 2A stream 10 20 30 40 T [ C.] 65 450 550 160 CO.sub.2 30 30 15 15 [vol. %] H.sub.2 70 70 55 55 [vol. %] CO 0 0 15 15 [vol. %] H.sub.2O 0-10 10 15 15 [vol. %] H.sub.2O/CO.sub.2 2.3 H.sub.2O/CO 3.6 3.6 XCO.sub.2 50.6

TABLE-US-00003 TABLE 2B stream 10 20 30 40 T [ C.] 65 950 1100 190 CO.sub.2 30 30 6 6 [vol. %] H.sub.2 70 70 45 45 [vol. %] CO 0 0 24 24 [vol. %] H.sub.2O 0-10 10 24 24 [vol. %] H.sub.2O/CO.sub.2 2.3 H.sub.2O/CO 1.9 XCO.sub.2 80.0
As can be seen from Table 2A, the line-up of FIG. 3 with only one RWGS reactor resulted in a relatively low CO.sub.2 conversion (50.6%) when operated at about 550 C.

[0107] As can be seen from Table 2B, when the same line-up of FIG. 3 was operated at higher temperature (at about 1100 C.) a desirable CO.sub.2 conversion (80%) was obtained.

Example 3

[0108] A microflow reactor was used to experimentally test the high overall conversion of CO.sub.2 by operating catalytic RWGS in two (or more) stages with intermediate removal of H.sub.2O, at relatively low temperatures, mimicking the line-up of FIG. 1.

[0109] In the microflow reactor 1.05 gram of a 30-80 mesh sieve fraction CeO.sub.2/ZrO.sub.2 catalyst (Actalys; obtainable from Solvay) was loaded in a 48 cm long Aluminide-coated Alloy 800 reactor tube with an internal diameter of 3.0 mm, obtainable from Diffusion Alloys Limited (UK).

[0110] The catalyst bed had a height of 5 cm and was located in the isothermal zone of the reactor by means of an internal inert Al.sub.2O.sub.3 rod with a length of 15 cm and an outer diameter of 2.2 mm. The rod itself was kept in place by a plug of quartz wool located at the cold bottom part of the reactor. The reactor was placed in an electrically heated oven.

[0111] With the use of thermal mass flow controllers (obtainable from Brooks (Veenendaal, the Netherlands)) calibrated gas flows, were passed in down-flow over the catalyst bed at a pressure of 10.6 bara. The nitrogen flow rate was 0.5 Nl/h and was used as an internal standard. After water condensation, the dry product composition was measured with an online micro-GC (Interscience (Breda, NL)). By using nitrogen as internal standard, the CO.sub.2 conversion was calculated.

[0112] The catalyst showed very stable performance at the applied conditions and hardly any methane formation was observed. In all experiments the gas composition was essentially equal to the calculated RWGS thermodynamic equilibrium composition, provided for the latter the methanation reaction is excluded from that calculation.

[0113] In Example 3A the conditions were selected to represent the first stage RWGS reactor of FIG. 1.

[0114] Table 3 below shows the results of this Example 3A. From Table 3, it can be seen that the measured CO.sub.2 conversion matches exactly the conversion predicted by thermodynamics, provided the formation of methane is assumed not to take place at all. Note that thermodynamically methane will be formed in high amounts at the conditions of the experiments, at >90% selectivity.

[0115] In Example 3B, the CO/H.sub.2 outlet ratio of Example 3A was used as inlet composition, albeit not exactly, i.e. at a bit too high CO/H.sub.2. This simulates the second stage RWGS reactor of FIG. 1. The GHSV was adapted accordingly, i.e. lowered to represent the reduction in total flow to this second stage RWGS reactor of FIG. 1 due to removal of H.sub.2O.

[0116] In Example 3C, Example 3B was repeated but with an inlet CO/H.sub.2 ratio closer to the outlet of Example 3A.

[0117] Table 3 below shows the results of the three experiments Example 3A, 3B, and 3C as well as the calculated total CO.sub.2 conversions, i.e. calculated form the CO.sub.2 outlet concentration of Example 3B and the inlet CO.sub.2 concentration of Example 3A, and similarly for Example 3C and Example 3A, simulating the expected CO.sub.2 conversion in a two-stage reactor with intermediate H.sub.2O removal as per FIG. 1 with multi-tubular reactor 2a) of FIG. 2.

[0118] The row 3A+3B in Table 3 demonstrates a high CO.sub.2 conversion of 72% obtainable at a relatively low temperature of 570 C., with the line-up of FIG. 1, whereas a conventional single stage reactor would only achieve 54% CO.sub.2 conversion. Similarly, the row 3B+3C in Table 3 demonstrates a high CO.sub.2 conversion of 70% obtainable at a relatively low temperature of 570 C., with the line-up of FIG. 1, whereas a conventional single stage reactor would only achieve 54% CO.sub.2 conversion.

TABLE-US-00004 TABLE 3 CO.sub.2 thermodynamic CO.sub.2 equilibrium Methane T GHSV H.sub.2/CO.sub.2 CO/H.sub.2 CO/H.sub.2 conversion conversion [%] selectivity Example [ C.] [Nl/l .Math. h] inlet inlet outlet [%] (excl. methane) [%] Ex. 3A 570 11323 2.5 0 0.28 54 54 <0.1 Ex. 3B 570 9766 3.6 0.36 0.53 38 39 <0.2 Ex. 3C 570 9200 3.6 0.25 0.42 44 44 <0.3 3A + 3B 570 N/A 2.5 0 0.53 72 73 <0.2 3A + 3C 570 N/A 2.5 0 0.42 70 70 <0.3

DISCUSSION

[0119] 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 catalytic RWGS reaction, whilst maintaining the temperature in the RWGS reactors below 700 C. and whilst still achieving desirable CO.sub.2 conversions (of above 65%), with just 2 RGWS stages. When more RWGS stages are used, CO.sub.2 conversions of 75% or more (even above 80%) can be achieved.

[0120] The person skilled in the art will readily understand that many modifications may be made without departing from the scope of the invention.