REDOX PREPARATION PROCESS OF AN OXYGEN CARRIER FOR A CHEMICAL LOOPING PROCESS

Abstract

A process prepares an oxygen carrier for a chemical looping process including providing a material A having a first transition metal and/or an oxide of the first transition metal. The first transition metal is selected from chemical element groups 6-11 of the Periodic System. Material A is subjected to a reaction with H2 to reduce the first transition metal and/or oxide to form a reduced material B. Material B is treated with a salt solution of a second transition metal selected to have a standard reduction potential larger than the first transition metal. A portion of the first transition metal in the reduced material B is replaced by the second transition metal. A molar ratio of the first transition metal with respect to the second transition metal in material B ranges between 2:1 and 100:1. An oxygen carrier is obtained with the method and is regenerated using steam.

Claims

1. A process for preparation of an oxygen carrier for a chemical looping process, the process comprising the following steps: a. providing a material A comprising one or more of: at least one first transition metal and/or an oxide of the at least one first transition metal, wherein the at least one first transition metal is selected from one or more of chemical element groups 6-11 of the Periodic System, b. subjecting material A to a reaction with H2 to cause at least partial reduction of the one or more of the at least one first transition metal and the at least one first transition metal oxide to form a reduced material B, c. treating reduced material B with a solution of a salt of at least one second transition metal to obtain the oxygen carrier, wherein the at least one second transition metal is selected such that the at one second transition metal has a standard reduction potential that is larger than a standard reduction potential of the first transition metal, wherein a portion of the at least one first transition metal in the reduced material B is replaced by the at least one second transition metal, wherein a molar ratio of the at least one first transition metal with respect to the at least one second transition metal in the reduced material B ranges between 2:1 and 100:1, and d. washing the oxygen carrier.

2. The process according to claim 1, wherein the at least one first transition metal is chosen from one or more of chemical element groups 7-11.

3. The process according to claim 1, wherein the salt of the at least one second transition metal is selected from salts of one or more transition metals of the group comprising Cu, Co, Ni, Ru, Rh and a mixture of two or more hereof.

4. The process according to claim 1, wherein the salt of the at least one second transition metal is a halide salt.

5. The process according to claim 1, wherein the solution of the at least one second transition metal salt is an aqueous solution of the at least one second transition metal salt.

6. The process according to claim 1, wherein the oxygen carrier comprises between 10.0 and 70.0 wt. % of the at least one first transition metal, based on a total weight of the oxygen carrier.

7. The process according to claim 1, wherein the molar ratio between the at least one first transition metal and the at least one second transition metal is between 3:1 and 95:1.

8. The process according to claim 1, wherein the reaction with H2 is performed at a temperature of at least 200° C.

9. The process according to claim 1, wherein the oxygen carrier is dried at a temperature of 300° C. or lower.

10. An oxygen carrier obtained by the process according to claim 1.

11. The oxygen carrier according to claim 10, comprising between 10.0 and 70.0 wt. % of Fe, Mn or a mixture thereof and between 0.05 and 7.5 wt. % of Cu, based on a total weight of the oxygen carrier.

12. The process according to claim 1, comprising utilizing the oxygen carrier in a chemical looping process.

13. The process according to claim 12, wherein the oxygen carrier is regenerated by contacting the oxygen carrier with steam.

14. A process for the regeneration of an oxygen carrier according to claim 10, wherein the oxygen carrier is regenerated by contacting the oxygen carrier with steam.

15. The process according to claim 1, wherein the one or more of the at least one first transition metal and the oxide of the at least one first transition metal is supported on one or more support materials.

16. The process according to claim 1, further comprising drying the oxygen carrier.

17. The process according to claim 1, wherein the at least one first transition metal is chosen from one or more of: Fe, Co, Mn, Cu, Ni, Ru, Rh and a mixture of two or more thereof.

18. The process according to claim 3, wherein the salt of the second transition metal is a Cu(II) salt.

19. The process according to claim 4, wherein the salt of the at least one second transition metal is a chloride salt.

20. The oxygen carrier according to claim 11, comprising between 20.0 wt. % and 70.0 wt. % Fe, Mn or a mixture thereof.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0081] The invention will now be explained by way of the following examples without however being limited thereto.

[0082] FIG. 1 shows a view to a small scale reactor, wherein the following reference numerals are used:

[0083] 1. Reactor

[0084] 2. Furnace

[0085] 3. Computer

[0086] 4. Mass spectrometer

[0087] 5. Mass flow controller

[0088] 6. HPLC pump

[0089] 7. Vaporizer

[0090] 8. Vent.

[0091] FIGS. 2A-B represent SEM-EDS images of the oxygen carrier material of example 1, 0.013 g Cu deposited on SPRV9_4 pre-reduced at 850° C., as a result of which a final ratio Fe:Cu of 36.1:1 was obtained.

[0092] FIGS. 3A-B represent enlarged views of FIGS. 2A-B, with SEM-EDS of the oxygen carrier material of example 1, 0.013 g Cu deposited on SPRV9_4 pre-reduced at 850° C., as a result of which a final ratio Fe:Cu of 36.1:1 was obtained).

[0093] FIGS. 4A and C represent reactor test results on 0.25 g of the oxygen carrier material obtained in example 3, FIGS. 4B and D represent reactor test results on 0.25 g of the oxygen carrier material obtained in example 2.

[0094] FIG. 5A-B represent reactor test results on 0.25 g of SPRV9_4 oxygen carrier material after it had been subjected to pre-reduction, and before being contacted with the Cu.sup.2+ solution.

DESCRIPTION OF EMBODIMENTS

Materials Preparation

[0095] The Cu-modified oxygen carrier was synthesized by a spray drying method combined with a post treatment. Briefly, 60-70 wt. % α-Fe.sub.2O.sub.3 (Alfa Aesar, 98% (metals basis), −325 mesh powder), 8.5-11.3 wt. % MgO (MAF Magnesite, MagChem 30) and 21.5-28.7 wt. % α-Al.sub.2O.sub.3 (Almatis, CT3000SG) particles (molar ratio MgO/Al.sub.2O.sub.3 of 1/1) were dispersed in de-ionized water with the necessary dispersants (Darvan C (T Vanderbilt, USA), or Dolapix, types A88, PC75 and PC80 (Zschimmer & Schwarz, Germany)). These suspensions were homogenized by milling in a planetary ball mill (Retsch, Pulverisette 5, Germany). After adding a suitable polymeric binder(polyethyleneoxide PEO, type PEO-1Z (Sumitomo Seika, Japan), and/or polyvinyl-alcohol, PVA 15000 (Fluka, Switzerland), and/or polyethyleneglycol, PEG 6000 (Merck-Schuchardt, Germany)), the suspension was spray-dried. The chamber fraction collected underneath the cone was then sieved to obtain particles of suitable dimensions for an industrial chemical looping process inside an interconnected fluidized bed process.

[0096] These particles were then calcined at 500° C. for 1 hour in air and afterwards a sintering procedure was performed in air at 1175° C. using a high temperature furnace (Bouvier, Belgium) to obtain oxygen carrier particles with sufficient mechanical properties. The Fe.sub.2O.sub.3-phase was then reduced completely to Fe by a mixture of 20% H.sub.2/He at 650-900° C.

[0097] The Cu phase was then deposited on the oxygen carriers by a modified incipient wetness impregnation method wherein CuCl.sub.2-solution with concentrations varying from 0.28 mol/l to 5.4 mol/l were made and used to fill the pores of the oxygen carrier material. As a result, part of the available metallic Fe is replaced by Cu by a spontaneous and quantitative redox reaction: Fe+Cu.sup.2+.fwdarw.Fe.sup.2++Cu. After having been contacted with the Cu solution for two minutes, the oxygen carriers were washed several times by an excess of deionized water in order to remove remaining free ions and then dried at moderate temperatures (50-120° C.). After sufficient drying, the Cu-modified oxygen carriers were characterized and used during reactor tests.

Specific Preparation Concentrations and Weights:

Example 1

[0098] A pre-reduced oxygen carrier material was obtained by reducing an oxygen carrier material overnight in a 20 vol. % H.sub.2 in He gas flow, 100 sccm, at a temperature of 850° C.

[0099] 0.76 g CuCl.sub.2.2H.sub.2O was dissolved in 1.1 ml H.sub.2O, so that a 4.05 M Cu.sup.2+-solution was obtained. 0.050 g of this solution was contacted with 0.5072 g of pre-reduced oxygen carrier (OC) material. In case of a quantitative reaction, 0.013 g Cu (s) can be deposited. The final molar ratio Fe:Cu observed was 36.1:1.

Example 2

[0100] 0.0241 g CuCl.sub.2.2H.sub.2O were dissolved in 0.4993 g H.sub.2O, so that a 0.283 M Cu.sup.2+-solution was obtained.

[0101] 0.30 g of this solution was contacted with 1 g of pre-reduced oxygen carrier material, obtained by overnight reduction in 20 vol. % H.sub.2 in He, 100 sccm, at a temperature of 900° C. In case of a quantitative reaction 0.0054 g Cu (s) can be deposited. It was observed that the molar ratio Fe:Cu in the obtained end product was 87:1.

Example 3

[0102] 0.4614 g CuCl.sub.2.2H.sub.2O were dissolved in 0.5058 g H.sub.2O, so that a 5.35 M solution in H.sub.2O was obtained. 0.30 g of this solution was contacted with 1 g of pre-reduced oxygen carrier material overnight, obtained by reduction of the oxygen carrier material in the presence of a 20 vol. % H.sub.2 flow in He, 100 sccm, at a temperature of 900° C.

[0103] In case of a quantitative reaction, 0.102 g Cu (s) can be deposited on the oxygen carrier material. The final molar ratio Fe:Cu obtained was 3.7:1

SEM & Optical Microscopy

[0104] The microstructure of the oxygen carriers was investigated by optical microscopy (SteREO Imager, ZEISS) and by scanning electron microscopy using a FEI NOVA Nanosem 450 with an energy dispersive spectroscopy (EDS) system on polished cross-sections of embedded particles inside an epoxy resin.

Reactor Tests

[0105] FIG. 1 shows a small lab-scale reactor used for investigating the reduction and oxidation reactions of the oxygen carriers. Calibrated mass flow controllers introduced a total flow of 100 sccm of inert and reacting gases in the reactor where a packed bed of 0.25 g of the OC material was inserted in the quartz reactor tube of 6 mm internal diameter. During the methane step, the oxygen carriers were reduced by 20 sccm methane and during the oxidation phase steam was generated in a heated vaporizer from where inert gases such as nitrogen and helium transport 0.020 ml/min vaporized water which was introduced in the vaporizer by a high performance liquid chromatography (HPLC) pump. The experiments were conducted at a temperature of 900° C., which was measured by a thermocouple outside but in close contact with the reactor tube. The composition of the gases exiting the reactor was measured using mass spectrometry.

Results

[0106] The results shown in FIGS. 4A-D and 5A-B were obtained by using the following formulas:

[00001]${\mathrm{Selectivity}}_{\mathrm{CO}}=S_{\mathrm{CO}}=\frac{n_{\mathrm{CO},\mathrm{produced}}}{n_{{\mathrm{CH}}_4,\mathrm{converted}}}=\frac{n_{\mathrm{CO},\left(1\right)}}{\frac{1}{2}\left(n_{H_2,\mathrm{tot}}+n_{H_{2}O,\left(3\right)}\right)}$${\mathrm{Selectivity}}_{H_2}=S_{H_2}=\frac{\frac{1}{2}\left(n_{H_2,\mathrm{produced}}\right)}{n_{{\mathrm{CH}}_4,\mathrm{converted}}}=\frac{n_{H_2,\mathrm{tot}}}{n_{H_2,\mathrm{tot}}+n_{H_{2}O,\left(3\right)}}$$C_{{\mathrm{CH}}_4}=\frac{\frac{1}{2}\left(n_{H_2,\mathrm{tot}}+n_{H_{2}O,\left(3\right)}\right)}{n_{{\mathrm{CH}}_4,\mathrm{out}}+\frac{1}{2}\left(n_{H_2,\mathrm{tot}}+n_{H_{2}O,\left(3\right)}\right)}$$C_{H2O}=n_{H2}\text{/}\left(n_{H2O}+n_{H2}\right)$$S_{H2}=n_{H2}\text{/}\left(n_{H2}+n_{\mathrm{CO}}\right)$

TABLE-US-00001 TABLE 1 Molar ratio Fe:Cu 1:0 87:1 3.7:1 10:1 Crushing strength 1.46N 1.10N Attrition resistance, 0.2%/h 4.2%/h modified method Highest oxidation state Fe.sub.3O.sub.4 Fe.sub.3O.sub.4 Fe.sub.3O.sub.4 Fe.sub.3O.sub.4 by steam Lowest oxidation state Fe/Fe.sub.3C Fe/Fe.sub.3C Fe/Fe.sub.3C Fe/Fe.sub.3C by CH.sub.4 Time needed for   9 min 4.5 min 3.5 min converting Fe.sub.3O.sub.4.fwdarw.Fe.sup.[a] Time before conversion 7.75 min   3 min 1.5 min during reduction >50%.sup.[a] Reactivity with CH.sub.4.sup.[a] improved improved improved Average selectivity 64.2% 65.1% 65.1% towards H.sub.2 production when conversion CH.sub.4 >50%.sup.[a] Time needed for  5-6 min 5-6 min 5-6 min converting Fe.fwdarw.Fe.sub.3O.sub.4.sup.[a] Reactivity with H.sub.2O.sup.[a] No No No No differences differences differences differences observed observed observed observed H.sub.2-selectivity during 76.5% 84.6% 77.1% oxidation.sup.[a] .sup.[a]during packed-bed testing