PROCESS TO SYNTHESIZE A CATALYST PERFORMING WATER-GAS SHIFT REACTION AT A HIGH TEMPERATURE

Abstract

A process to synthesize a catalyst performing Water-Gas shift reaction at a temperature more than 300° C. using a precursor having general formula [(Cu, Zn).sub.1−x (Al, M).sub.x (OH).sub.2].sup.x+ (A.sup.n−.sub.x/n).kH.sub.2O with M=Al, La, Ga or In, A=CO.sub.3, 0.33<x<0.5, 1<n<3.

Claims

1. A process to synthesize a catalyst for performing a water-gas shift reaction at a temperature more than 300° C. using a precursor having general formula:
[(Cu, Zn).sub.1−x(Al, M).sub.x(OH).sub.2].sup.x+(A.sup.n−.sub.x/n).kH.sub.2O with: M=Al, La, Ga or In, A=CO.sub.3 0.33<x<0.5 1<n<3.

2. The process of claim 1, wherein the process comprises the following steps: a) synthesis of precursor by coprecipitation method; b) washing of precursor, c) drying of precursor at a temperature between than 60° C. and 80° C. d) calcination at a temperature more than 500° C.

3. The process of claim 2, wherein the step d) lasts between 2 h and 6 h with a speed in temperature rise between 5° C./min and 10° C./min.

4. The process of claim 2, wherein at the step b) the precursor is washed with deionized water at a temperature between 25° C. and 60° C.

5. The process of claim 2, wherein the synthesis of precursor comprises the following steps: i) preparation of a copper, zinc, and aluminium salts aqueous solution, ii) droping of aqueous solution into a solution containing of sodium bicarbonate by maintaining the pH to 9.0±0.1 to obtain a precipitate, iii) ageing of this precipitate.

6. The process of claim 1, wherein the precursor has 0.5 to 5 wt % of copper and the catalyst has 0.5 to 5 wt % of copper.

7. The process of claim 1, wherein after the step d) the catalyst is doped with between 0.5 wt. % and 2 wt. % K.

8. The process of claim 1, wherein the precursor comprises Ga with Al/Ga ratio comprised between 0/1 and 100/1.

9. The process of claim 1, wherein the precursor is selected from: [Cu.sub.0.042Zn.sub.0.458Al.sub.0.500(OH).sub.2].sup.0.50+(CO.sub.3.sup.2−).sub.0.25kH.sub.2O, [Cu.sub.0.042Zn.sub.0.458Al.sub.0.490La.sub.0.010(OH).sub.2].sup.0.50+(CO.sub.3.sup.2−).sub.0.25kH.sub.2O, [Cu.sub.0.042Zn.sub.0.458Al.sub.0.490Ga.sub.0.010(OH).sub.2].sup.0.50+(CO.sub.3.sup.2−).sub.0.25kH.sub.2O, [Cu.sub.0.042Zn.sub.0.458Al.sub.0.490In.sub.0.010(OH).sub.2].sup.0.50+(CO.sub.3.sup.2−).sub.0.25kH.sub.2O, [Cu.sub.0.023Zn.sub.0.643Al.sub.0.334(OH).sub.2].sup.0.34+(CO.sub.3.sup.2−).sub.0.17kH.sub.2O, [Cu.sub.0.023Zn.sub.0.643Al.sub.0.327La.sub.0.007(OH).sub.2].sup.0.34+(CO.sub.3.sup.2−).sub.0.17kH.sub.2O, et [Cu.sub.0.022Zn.sub.0.645Al.sub.0.327Ga.sub.0.007(OH).sub.2].sup.0.34+(CO.sub.3.sup.2−).sub.0.17kH.sub.2O.

10. The process of claim 1, wherein the catalyst has the general formula:
(Cu, Zn).sub.1−x(Al, M).sub.xO.sub.x

11. The use of the catalyst obtained by the process of claim 1 for the conversion of CO from a synthesis gas mixture with a Steam/Dry Gas ratio of 0.1 to 0.9.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0071] For a further understanding of the nature and objects for the present invention, reference should be made to the following detailed description, taken in conjunction with the accompanying drawings, in which like elements are given the same or analogous reference numbers and wherein:

[0072] FIG. 1 illustrates the XRD (X-ray diffraction) powder patterns of some precursors (ZAC041cGa50, ZAC041cIn50 and ZAC022cGa50).

[0073] FIG. 2 illustrates the HT-structure containing carbonates topotactically evolving by calcinations.

[0074] FIG. 3 illustrates that after catalytic tests the presence of more crystalline Cu.sup.0.

[0075] FIG. 4 illustrates the comparison of the activity for the ZAC041cM50 catalysts [(M(II)/M(III)=1 atomic ratio; Al/M=50 atomic ratio; M=Al, In or Ga], in accordance with one embodiment of the present invention.

[0076] FIG. 5 illustrates the comparison of the activity for a commercial-like catalyst and ZAC041cGa50 one [M(II)/M(III)=1 as atomic ratio; Al/Ga=50 as atomic ratio], in accordance with one embodiment of the present invention.

[0077] FIG. 6 illustrates the comparison of the activity of ZAC022cM50 undoped and K-doped catalysts [(M(II)/M(III)=2 as atomic ratio; Al/M=50 as atomic ratio; M=Al or Ga], in accordance with one embodiment of the present invention.

[0078] FIG. 7 illustrates the comparison of the activity at different temperature for the ZAC041c catalyst [(M(II)/M(III)=1 as atomic ratio], in accordance with one embodiment of the present invention.

[0079] FIG. 8 illustrates the comparison of the activity at different temperatures for the K-doped ZAC041cGa50_1K catalyst [(M(II)/M(III)=1 as atomic ratio; Al/GA=50 as atomic ratio], in accordance with one embodiment of the present invention.

[0080] FIG. 9 illustrates the comparison of the activity at different temperature and S/DG volumetric ratio for the ZAC041cGa50_1K catalyst [(M(II)/M(III)=1 as atomic ratio; Al/Ga=50], in accordance with one embodiment of the present invention.

[0081] FIG. 10 illustrates the stability of the catalyst vs ToS, in accordance with one embodiment of the present invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0082] FIG. 1 shows the XRD (X-ray diffraction) powder patterns of some precursors (ZAC041cGa50, ZAC041cIn50 and ZAC022cGa50) The presence of carbonate ions during precipitation results in the HT-structure formation, as identified by XRD analysis, together with very small amounts of Zn(OH).sub.2.

[0083] As shown in FIG. 2, the HT-structure containing carbonates topotactically evolves by calcination and XRD patterns showed ZnO-like and (Zn,Cu)Al.sub.2O.sub.4 phases with a higher intensity of ZnO peaks in the sample with higher M(II)/M(III) or 1-x/x atomic ratio. M(II)/M(III) is the atomic ratio between the bivalent and trivalent cations inside the hydrotalcite-type precursors (obviously the GA replace partially the Al) This ratio has been claimed in the literature to obtain hydrotalcite.type phases ranging from 5 to 0.1, but the values at the extremity very probably forms also side amorphous phases. More realistically this ratio ranges from 3 to 2.

[0084] After the catalytic tests (FIG. 3) the XRD patterns reveal the presence of the same phases as before the tests, although more crystalline. Cu.sup.0 is detected in traces only in very few samples, in agreement with the low Cu content and its well dispersion in the oxide matrix.

[0085] A summary of the chemical-physical properties is reported in Table 1. A significant increase of the BET surface area and Cu.sup.0 surface area (MSA) as well as Cu dispersion (D %) is observed by addition of very small amount of promoters (La, Ga or In), evidencing the positive effect of these elements on the chemical-physical properties of the obtained catalysts. On the contrary, the K-doping decrease generally all these parameters.

TABLE-US-00001 TABLE 1 S.sub.BET SAMPLE Phases [m.sup.2/g] MSA [m.sup.2/g.sub.CAT] D [%] ZAC041c ZnO, spinel 73 1 4 ZAC041cLa50 ZnO, spinel 87 4 13 ZAC041cln50 ZnO, spinel 103 6 22 ZAC041cGa50 ZnO, spinel 97 5 20 ZAC041cLa50_1K ZnO, spinel 85 4 13 ZAC041cGa50_1K ZnO, spinel 87 5 20 ZAC022c_1K ZnO, spinel 40 1 9 ZAC022cLa50 ZnO, spinel 97 2 20 ZAC022cGa50 ZnO, spinel 106 2 17 ZAC022cGa50_1K ZnO, spinel 95 1 9

[0086] MSA and D % values are evaluated by N.sub.2O titration method. The sample (100 mg) is loaded in a small reactor and pre-reduced by a 80 mL/min flow of 5 vol. % H.sub.2/N.sub.2 mixture from 40 to 350° C. (10° C./min) and held at this temperature for 60 min. After the catalyst bed is flushed under He stream for 20 min to remove all the H.sub.2, the reactor is cooled to 40° C. and, successively, pulses of N.sub.2O (250 μL) are introduced into a He carrier stream by a 6-port valve to selectively oxidize the Cu.sup.0 surface:

2Cu+N.sub.2O.fwdarw.N.sub.2+Cu.sub.2O

[0087] After each pulse, N.sub.2 and N.sub.2O are separated by using a GS-Carbon Plot column and the titration occurs until no further N.sub.2O conversion is observed. A Thermal Conductivity Detector (TCD) is used to measure the effluent gas evolved via N.sub.2O decomposition. The specific surface area of Cu.sup.0 was calculated from the total amount of N.sub.2O consumption, assuming a copper density of 1.46×10.sup.19 Cu.sup.0 atoms/m.sup.2 and a molar stoichiometry of Cu/N.sub.2O=2.

[0088] The HT precursors after calcination have been reduced before the catalytic tests under HTS conditions, to obtain the main active phase. A typical procedure comprises: [0089] 1) remove oxygen (O.sub.2) by purging nitrogen (N.sub.2) in the reactor and, after that, to heat the catalyst to 275° C. (50° C./h) and pressurize the reactor at 1.0 MPa (10 bar). [0090] 2) Introduce of the process gas (Steam+Dry Gas) at 1.0 MPa (10 bar), then ramp of 30° C./h up to 350° C., taking into account of the flow rate in the high temperature reaction conditions of the further tests. [0091] 3) At 350° C., increase of the pressure up to the value of the test. The H.sub.2-TPR (TPR=Temperature Programmed Reduction with Hydrogen) profiles of the calcined catalysts before the tests show two reduction peaks, a most intense one at about 340° C., typical of the reduction of Cu.sup.2+ species stabilized by strong interaction with the support, and a small peak at about 550° C., attributable to Cu-containing spinel-type phase. The addition of small amounts of promoters (La, Ga or In) lowers maximum of the first reduction peak of about 20° C., while that at higher temperature remains unchanged. After the catalytic tests, the first most intense peak decrease at about 200° C. with a complex shape, evidencing the formation of free CuO with different crystal size. ZnO-likes phase does not reduce under the experimental conditions.

[0092] The catalysts of the present invention together with the reference catalyst are shaped as pellets with size between 30 and 40 mesh and tested in a plug-flow reactor. The tubular reactor is heated by an oven in order to have a temperature between 350 and 450° C. (±1° C.), measured immediately at the exit of the catalytic bed, and pressurized to 15 bar. Dry Gas (DG) and Steam (S) are pre-heated (215° C.) and mixed (mass flow controller) before passing over the catalyst. In order to determine the activity in the HTS processes of the catalysts prepared by the various examples, a typical DG composition containing 18.8 vol % CO, 4.6 vol % CO2, 4.6 vol % CH4 with the balance H2 is used and passed over the pre-reduced catalysts with a steam to dry gas (S/DG) ratio of 0.55 and 0.25 v/v. Concentration of all components is regularly measured both inlet and exit dry gas by means of Agilent gas chromatograph calibrated towards a gas mixture of known composition. The Gas Hourly Space Velocity (GHSV) is between 3,600 and 14,400 h-1.

[0093] Table 2 and Table 3 summarize the catalytic results obtained for some of the catalysts claimed in the present invention, as merely illustrative, but not exhaustive examples: More specific comparisons as a function of the different parameters are illustrated in the FIGS. 4-9.

TABLE-US-00002 TABLE 2 Summary of the catalytic results in terms of CO conversion and H.sub.2 yield T (° C.) 350 350 350 400 400 450 450 S/DG (v/v) 0.55 0.55 0.55 0.55 0.55 0.55 0.55 Contact time (s) Catalyst 0.25 0.50 1.00 0.50 1.00 0.50 1.00 ZAC041c CO conv. 35 51 68 74 78 72 74 (%) H.sub.2 yield 36 52 72 76 78 71 72 (%) ZAC041cLa50 CO conv. 70 84 87 74 81 73 73 (%) H.sub.2 yield 69 83 84 70 78 72 72 (%) ZAC041cIn50 CO conv. 24 40 56 58 68 64 71 (%) H.sub.2 yield 26 41 56 58 69 62 72 (%) ZAC041cGa50 CO conv. 78 85 86 82 81 74 73 (%) H.sub.2 yield 80 88 89 86 85 79 78 (%) ZAC041cLa501K CO conv. 72 86 88 78 81 73 73 (%) H.sub.2 yield 70 85 87 75 80 73 73 (%) ZAC041cGa501K CO conv. 83 86 86 81 80 74 74 (%) H.sub.2 yield 85 89 85 79 83 73 75 (%) ZAC022c1K CO conv. 60 68 85 76 80 74 74 (%) H.sub.2 yield 60 62 85 68 69 75 75 (%) ZAC022cGa50 CO conv. 14 25 39 30 40 28 38 (%) H.sub.2 yield 14 26 39 32 41 30 40 (%) ZAC022cGa501K CO conv. 39 59 73 / / / / (%) H.sub.2 yield 40 60 72 / / / / (%)

TABLE-US-00003 TABLE 3 Summary of the catalytic results in terms of CO.sub.2 selectivity and amount of by-product MeOH formed T (° C.) 350 350 350 400 400 450 450 S/DG (v/v) 0.55 0.55 0.55 0.55 0.55 0.55 0.55 Contact time (s) Catalyst 0.25 0.50 1.00 0.50 1.00 0.50 1.00 ZAC041c CO.sub.2 sel. (%) 98 100 96 97 97 100 98 MeOH (ppm) 14 69 93 50 57 26 19 ZAC041cLa50 CO.sub.2 sel. (%) 96 96 98 100 98 97 98 MeOH (ppm) 123 172 248 135 131 48 31 ZAC041cIn50 CO.sub.2 sel. (%) 98 100 98 99 98 100 99 MeOH (ppm) 45 167 209 183 173 193 84 ZAC041cGa50 CO.sub.2 sel. (%) 96 96 90 95 97 98 99 MeOH (ppm) 332 455 526 232 203 80 68 ZAC041cLa501K CO.sub.2 sel. (%) 96 96 98 100 98 97 98 MeOH (ppm) 106 263 372 235 171 118 40 ZAC041cGa501K CO.sub.2 sel. (%) 99 100 96 99 100 100 100 MeOH (ppm) 494 649 692 269 162 104 67 ZAC022c1K CO.sub.2 sel. (%) 100 99 100 99 99 90 86 MeOH (ppm) 43 57 21 52 68 32 21 ZAC022cGa50 CO.sub.2 sel. (%) 100 100 95 100 97 100 100 MeOH (ppm) 74 115 148 60 50 27 20 ZAC022cGa501K CO.sub.2 sel. (%) 100 97 97 / / / / MeOH (ppm) 80 164 263 / / / /

[0094] Table 2, shows that the catalysts present generally a good catalytic activity, with significantly better results observed for the samples with lower M(II)/M(II) or 1-x/x atomic ratio. At 400° and 450° c almost all the catalyst approach the thermodynamic equilibrium value regardless of the contact time value. The replacement of small amount of Al by In (Al/In=50 as atomic ratio) worsen the catalytic activity unlike that observed adding small amount of La and, surprisingly, Ga. This latter catalyst exhibits, as doped or K-doped, very good catalytic performances, reaching the thermodynamic equilibrium values also for the lowest temperature investigated, i.e. operating at medium temperature. All catalysts, regardless of the composition, show the further formation only of small amounts of methanol (Table 3) without any other side products, in agreement with the high values of selectivity in CO.sub.2 detected in all the reaction conditions. More detailed comparison are reported in the FIGS. 4-9.

[0095] FIG. 4 illustrates the comparison of the activity for the ZAC041cM50 catalysts [(M(II)/M(III)=1 atomic ratio; Al/M=50 atomic ratio; M=Al, In or Ga].

[0096] FIG. 5 illustrates the comparison of the activity for a commercial-like catalyst and ZAC041cGa50 one [M(II)/M(III)=1 as atomic ratio; Al/Ga=50 as atomic ratio].

[0097] FIG. 6 illustrates the comparison of the activity of ZAC022cM50 undoped and K-doped catalysts [(M(II)/M(III)=2 as atomic ratio; Al/M=50 as atomic ratio; M=Al or Ga].

[0098] FIG. 7 illustrates the comparison of the activity at different temperature for the ZAC041c catalyst [(M(II)/M(III)=1 as atomic ratio].

[0099] FIG. 8 illustrates the comparison of the activity at different temperatures for the K-doped ZAC041cGa50_1K catalyst [(M(II)/M(III)=1 as atomic ratio; Al/GA=50 as atomic ratio].

[0100] FIG. 9 illustrates the comparison of the activity at different temperature and S/DG volumetric ratio for the ZAC041cGa50_1K catalyst [(M(II)/M(III)=1 as atomic ratio; Al/Ga=50].

[0101] In particular FIG. 9 show a very good activity and stability of Ga-promoted catalysts also under hard reaction conditions, such as operating with a S/DG ratio significantly higher than those used in the industrial plants. On the other hand, low S/DG values offer very interesting economic advantages, allowing to improve the productivity, decreasing costs and reactor size. However, to have data on the stability of most wide application, the activity of ZAC041cGa_1K was investigated also in a lab scale pilot plant for long time-on-stream.

[0102] Stability of the ZAC041cGa50_1K catalyst was evaluated by means of a long duration test performed during more than 300h for the same set of operating conditions. After loading in the reactor, the catalyst (9 g, 30/40 mesh) is activated at 320° C. by using a syngas mixture diluted in steam at a steam/carbon ratio=10 during 2 h, then temperature is increased following a ramp up to 400° C. for 3 hours.

[0103] After, the injection of steam is reduced in order to achieve a ratio Steam/DryGas (S/DG)=0.55, at a pressure of 15 bars. Inlet temperature is targeted at 390° C. and contact time value is close to 2 seconds. DG composition is H2/CO/CO2/CH4=0.75/0.168/0.041/0.041% mol.

[0104] During the long test, temperatures (in/out) are monitored and the resulting dry gas exiting the reactor is continuously analyzed by means of IR detectors (CO, CO2, CH4). At the outlet of the reactor, wet gas is quenched by a cooler, then after crossing a separator pot, dry gas is recovered at the top of the pot and condensates are collected at the bottom part.

[0105] During the 300 h of test, temperatures and composition of the gas remained stable. CO slip is in agreement with Equilibrium prediction with a CH4 content staying stable. No side product was detected in the gas phase and only some traces of MeOH present in the condensates were detected and again in agreement with Equilibrium.

[0106] The FIG. 10 presents the stability of the catalyst vs ToS (Time on stream).

[0107] Based on these results and uncertainties of measurements, we can consider that this new catalyst performs at Equilibrium without abnormal production of side-products.

[0108] Although most of catalysts described in the literature to operate in HTS conditions are made of Iron and Chromium, the catalysts of the present invention have a high activity operating in HTS conditions (form 350° C. to 450° C.) close to thermodynamic equilibrium with a very good stability upon time-on-stream, but without Iron and without Chromium.

[0109] Contrary to other patents claiming the use of ZnAl-based materials for HTS applications, the catalysts of the present invention also contain small amount of copper, which enable a fast start-up of the reaction and an activity also at temperatures lower than 350° C.

[0110] The addition of small amount of La or, mainly Ga, significantly increases the catalytic activity and stability. The behavior of Ga is very surprising considering the worsening observed with indium, since Al, Ga and In are all members of the III group of the Periodic Table of Elements.

[0111] The doping by a small percentage of potassium, improve further the performance of the Ga-promoted catalysts also at low temperature.

[0112] Furthermore, high activity and selectivity values were observed also operating at low contact time and S/DG values, i.e. in conditions of high industrial interest.

[0113] It will be understood that many additional changes in the details, materials, steps and arrangement of parts, which have been herein described in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims. Thus, the present invention is not intended to be limited to the specific embodiments in the examples given above.