HYDROGEN PROCESS

Abstract

A process for the production of hydrogen is described, the process comprises the steps of: (a) generating a synthesis gas comprising hydrogen, carbon monoxide, carbon dioxide and steam in a synthesis gas generation unit; (b) increasing the hydrogen content of the synthesis gas and decreasing the carbon monoxide content by subjecting it to one or more water-gas shift stages in a water-gas shift unit to provide a hydrogen-enriched gas, (c) cooling the hydrogen-enriched gas and separating condensed water therefrom, (d) passing the resulting de-watered hydrogen-enriched gas to a carbon dioxide separation unit to provide a carbon dioxide gas stream and a hydrogen gas stream, wherein the synthesis gas from step (a) is fed without adjustment of the carbon monoxide content to a water gas shift reactor.

Claims

1. A process for the production of hydrogen comprising the steps of: (a) generating a synthesis gas comprising hydrogen, carbon monoxide, carbon dioxide and steam in a synthesis gas generation unit; (b) increasing the hydrogen content of the synthesis gas and decreasing the carbon monoxide content by subjecting it to one or more water-gas shift stages in a water-gas shift unit to provide a hydrogen-enriched gas, (c) cooling the hydrogen-enriched gas and separating condensed water therefrom, (d) passing the resulting de-watered hydrogen-enriched gas to a carbon dioxide separation unit to provide a carbon dioxide gas stream and a hydrogen gas stream, wherein the synthesis gas from step (a) is fed without adjustment of the carbon monoxide content to a water gas shift reactor, operated adiabatically or with cooling, at an inlet temperature in the range 200 to 280° C. and an exit temperature below 360° C., and containing a catalyst comprising 30 to 70% by weight of copper, expressed as CuO, combined with zinc oxide, alumina and silica, said catalyst having a silica content, expressed as SiO.sub.2, in the range of 0.1 to 5.0 wt%.

2. The process according to claim 1, wherein the synthesis gas generation comprises one or more steps selected from adiabatic pre-reforming, catalytic steam reforming in a fired- or gas-heated reformer, autothermal reforming, and catalytic partial oxidation, applied to a gaseous or vapourised hydrocarbon such as natural gas, naphtha or a refinery off-gas.

3. The process according to claim 1, wherein the synthesis gas generation comprises non-catalytic partial oxidation or gasification of a carbonaceous feedstock such as coal, biomass or municipal waste, optionally followed by one or more stages of catalytic steam reforming or autothermal reforming.

4. The process according to claim 1, wherein the synthesis gas generation unit comprises an autothermal reformer, fed with a reformed synthesis gas obtained from an upstream adiabatic pre-reformer, a fired steam reformer or a gas-heated reformer.

5. The process according to claim 1, wherein the hydrogen content of the synthesis gas fed to the water gas shift reactor, on a wet gas basis, is in the range 30-50% vol and the carbon monoxide content of the synthesis gas fed to the water gas shift reactor, on a wet gas basis, is in the range 6-20% vol.

6. The process according to claim 1, wherein the water gas shift unit comprises a stage of medium temperature shift, or isothermal shift and optionally a downstream low-temperature shift stage.

7. The process according to claim 1, wherein the catalyst has a copper content, expressed as CuO, in the range of 45 to 65% wt.

8. The process according to claim 1, wherein the catalyst has a zinc content, expressed as ZnO, in the range 20-50% wt.

9. The process according to claim 1, wherein the catalyst has an aluminium content, expressed as Al.sub.2O.sub.3, in the range 5-40% wt.

10. The process according to claim 1, wherein the catalyst has a one or more promoter metal oxides, selected from oxides of Mg, Co, Mn, V, Ti, Zr or rare earths, present in an mount in the range 0.1-5% wt.

11. The process according to claim 1, wherein the catalyst has a silica content, expressed as SiO.sub.2, in the range of 0.1 to 2.0% by weight.

12. TheA process according to claim 1, wherein the carbon dioxide removal stage is performed using a physical wash system or a reactive wash system.

13. The process according to claim 1, wherein one or more of the carbon dioxide removal unit streams are heated in heat exchange with the hydrogen-enriched gas stream.

14. The process according to claim 1, wherein the process further comprises passing the hydrogen gas stream to a purification unit to provide a purified hydrogen gas.

15. The process according to claim 14, wherein the purification unit is a pressure-swing adsorption unit or a temperature swing adsorption unit.

Description

[0051] The invention is illustrated by reference to the accompanying drawing in which:

[0052] FIG. 1 is a diagrammatic flowsheet of one embodiment of the invention.

[0053] It will be understood by those skilled in the art that the drawings are diagrammatic and that further items of equipment such as reflux drums, pumps, vacuum pumps, temperature sensors, pressure sensors, pressure relief valves, control valves, flow controllers, level controllers, holding tanks, storage tanks, and the like may be required in a commercial plant. The provision of such ancillary items of equipment forms no part of the present invention and is in accordance with conventional chemical engineering practice.

[0054] In FIG. 1, a stream containing methane 10, steam 12 and an oxygen stream 14 are fed to a syngas generation unit 16 comprising a gas-heated reformer and an autothermal reformer. The natural gas is steam reformed with steam in externally-heated catalyst filled tubes and the reformed gas subjected to autothermal reforming in the autothermal reformer with oxygen to generate a synthesis gas mixture comprising hydrogen, carbon dioxide, carbon monoxide and steam. The synthesis gas mixture is cooled to the desired inlet temperature in heat exchange with water to generate steam (not shown) and fed via line 18 to a water gas shift unit 20 consisting of an isothermal shift reactor containing a bed of water gas shift catalyst as described herein to generate a hydrogen-enriched gas mixture in which the hydrogen and carbon dioxide contents are increased and the steam and carbon monoxide contents decreased. Optionally, the hydrogen enriched gas may be fed to a low-temperature shift reactor included in the water gas shift unit downstream of the isothermal shift reactor. The hydrogen-enriched gas mixture is fed from the water-gas shift unit 20 via line 22 to a heat recovery unit 24 that cools the hydrogen-enriched gas to condense steam. The condensate is separated in one or more gas-liquid separators and recovered from the unit 24 via line 26. The condensate is recycled via line 26 to the synthesis gas generation unit 16 to generate steam for the gas heated reformer and/or autothermal reformer. A de-watered hydrogen enriched gas is fed from the heat recovery unit 24 via line 28 to a carbon dioxide removal unit 30 operating by means of reactive absorption. A carbon dioxide stream is recovered from the separation unit 30 by line 32. A hydrogen stream is recovered from the carbon dioxide removal unit 30 via line 34 and passed to an optional hydrogen purification unit 36 containing a membrane system, a temperature swing adsorption system, or a pressure swing adsorption system, in which impurities in the hydrogen are removed to provide a high purity hydrogen stream 38 comprising more than 99.5% vol H.sub.2.

[0055] The invention is further illustrated by reference to the following Example.

Example 1

[0056] A CuO/ZnO/Al.sub.2O.sub.3/MgO/SiO.sub.2 formulation was produced by precipitating a mixed metal nitrate solution containing Cu, Zn and Mg nitrates against a potassium carbonate solution at a pH of 6.3-6.8 and a temperature between 65-70° C., whilst simultaneously adding a mixed colloidal dispersion containing both boehmite and silica (Snowtex ST-O) at flowrates and concentrations necessary to achieve the final composition as shown in Table 1 below. Following precipitation, the resultant slurry was aged for up to 2 hours at 65-70° C., filtered, washed, dried and calcined at 350° C. Finally, the calcined powder was pelleted to a final pellet density of 2.32 g/ml.

[0057] An X-ray diffraction (XRD) pattern was obtained on the powdered catalyst using a Bruker D8 diffractometer equipped with a Göbel mirror, Lynxeye detector and a copper x-ray tube. Phase identification was completed using the Bruker EVA v5.1.0.5 software. The diffraction pattern obtained is shown in FIG. 2. The intensity ratio of the ZnO peak at about 32.5° to that of the CuO peak at 35° is 0.47:1.

Comparative Example 1

[0058] The method of Example 1 was repeated with the exception that the colloidal dispersion did not contain Snowtex ST-O.

TABLE-US-00001 Catalysts CuO Wt% ZnO Wt% Al.sub.2O.sub.3 Wt% MgO Wt% SiO.sub.2 Wt% Cu surface area m.sup.2/g catalyst Example 1 62.8 24.8 10.5 1.1 0.39 58 Comparative Example 1 63.7 23.4 11.2 0.86 0.00 54

[0059] The catalysts testing was conducted using a Micro-Berty reactor, operated adiabatically. A flow of synthesis gas was fed to the reactor via a mass flow controller. The dry gas was mixed with the water feed in a packed vaporiser vessel and the wet gas transferred to the heated and stirred reactor via a heated line. A condenser system downstream of the reactor removed excess water from the gas stream. A bleed of the dry gas was fed to a calibrated IR analyser measuring CO, CO.sub.2 and H.sub.2 concentration.

[0060] Catalyst Reduction. In each test, 0.8 g of catalyst were charged to the reactor basket. The test was carried out at 31 barg. For catalyst reduction, 2% hydrogen in nitrogen was introduced at 100 I/h and 120 degC and then the reactor was ramped to 280 degC over 14 hours and then held for 6 hours.

[0061] Testing. Following reduction, the dry gas composition was set to 71% H.sub.2, 17% CO, 12% CO.sub.2, maintaining a flow of 100 I/h. Simultaneously, water addition was started to give molar steam: dry gas ratio of 0.8:1 and the catalyst tested for 120 h at 280° C. whilst monitoring CO conversion. The results obtained are shown in FIG. 3, were the ratio of X/X.sub.i is plotted for each catalyst, where X.sub.i is defined as the initial CO conversion measured in each case, and X is the corresponding conversion after the specified period of time on-line. E1 is Example 1, CE1 is Comparative Example 1. This plot clearly shows the improved stability of the catalyst containing a small amount of silica.

[0062] In a further test, the method described above was repeated with an initial aging period of 5 days at 280° C., followed by a further aging period of 5 days at 300° C. to accelerate the ageing. In this case, at the end of both the first and the second aging periods, flow scans were carried out at 220° C. over both catalysts in order to generate conversion versus flowrate curves. These curves were then used to estimate relative activities by taking a ratio of the flowrate required on each catalyst to achieve a certain conversion. The results obtained are summarised in Table 2.

TABLE-US-00002 Catalyst Relative activity to CE1 after 5 days aging at 280° C. Relative activity to CE1 after further 5 days aging at 300° C. Example 1 1.21 1.35

This test again clearly demonstrates the improved performance of the catalyst containing silica.