Ni—MgO—ZnO solid catalysts for syngas preparation and process for the preparation thereof

Abstract

The present invention provides a process and catalyst for the production of synthesis gas (a mixture of CO and H.sub.2) by reforming of methane with carbon dioxide. The process provides a direct single step selective vapor phase dry reforming of methane with carbon dioxide to produce synthesis gas over NiMgOZnO catalyst between temperature range of 600? C. to 800? C. at 1 atmospheric pressure. The process provides a methane conversion of 5-95% with H.sub.2 to CO mole ratio of 0.83-1.2.

Claims

1. A process for the preparation of a NiMgOZnO solid catalyst, the catalyst comprising: a) Ni in the range of 2-10%, b) MgO in the range of 2-10% and c) ZnO in the range of 90-95%, wherein the said process comprises the steps of: i. dissolving Zinc nitrate hexahydrate and Magnesium nitrate hexahydrate in water, ii. adding Nickel nitrate hexahydrate in water to the mixture as obtained in step (i) followed by stirring to obtain a homogenous mixture; iii. adding a solution of CTAB (cetyltrimethylammonium bromide) in ethanol to the mixture as obtained in step (ii) with stirring for period in the range of 1 to 2 hours followed by adding hydrazine hydrate with adjusting the pH of the solution in the range of 8-12 to obtain a solution, iv. stirring the solution as obtained in step (iii) for a period in the range of 1-3 hours followed by autoclaving for period in the range of 12 to 48 hours at a temperature in the range of 160 to 180? C. to obtain a precipitate; v. filtering the precipitate as obtained in step (iv) with water and drying at a temperature ranging between 60 to 110? C. for a time period ranging between 12-20 hours followed by calcining at a temperature in the range of 400-750? C. for a time period of 4-8 hours to obtain the NiMgOZnO catalyst.

2. The process as claimed in claim 1, wherein the Ni to NiMgOZnO of the catalyst varied in the range of 2 to 10%.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1 represents X-ray Diffraction (XRD) of 5% Ni-5% MgOZnO.

(2) FIG. 2 represents Scanning Electron Microscope (SEM) image of 5% Ni-5% MgOZnO.

(3) FIG. 3 represents Low magnification Transmission Electron Microscope (TEM) image of 5% Ni-5% MgOZnO.

(4) FIG. 4 represents High magnification TEM image of 5% Ni-5% MgOZnO.

(5) FIG. 5 represents Mapping of Zn in 5% Ni-5% MgOZnO.

(6) FIG. 6 represents Mapping of Mg in 5% Ni-5% MgOZnO.

(7) FIG. 7 represents Mapping of Ni in 5% Ni-5% MgOZnO.

(8) FIG. 8 represents X-ray Diffraction (XRD) of 2.5% Ni-5% MgOZnO.

(9) FIG. 9 represents SEM image of 2.5% Ni-5% MgOZnO.

(10) FIG. 10 represents Low magnification TEM image of 2.5% Ni-5% MgOZnO.

(11) FIG. 11 represents High magnification TEM image of 2.5% Ni-5% MgOZnO.

(12) FIG. 12 represents Mapping of Zn in 2.5% Ni-5% MgOZnO.

(13) FIG. 13 represents Mapping of Mg in 2.5% Ni-5% MgOZnO.

(14) FIG. 14 represents Mapping of Ni in 2.5% Ni-5% MgOZnO.

DETAILED DESCRIPTION OF THE INVENTION

(15) The present invention provides a NiMgOZnO solid catalyst useful for reforming of methane to obtain the desired syngas, said catalyst comprising of Ni in the range of 2-10%, MgO in the range of 2-10% and ZnO in the range of 90-95%.

(16) The present invention provides a process for the preparation of NiMgOZnO solid catalyst involves the following steps: a) The precursor salts of Zinc nitrate hexahydrate and Magnesium nitrate hexahydrate was dissolved in required volume of water. b) The solution of Nickel nitrate hexahydrate in water was added to the previous mixture of solution. c) The whole mixture was stirred well to mix the precursors homogeneously. d) The solution of CTAB (cetyltrimethylammonium bromide) in ethanol was added to the mixture solution. e) The whole mixture was stirred for 1-2 hour and then a few ml of hydrazine hydrate is added. f) The pH of the solution was adjusted to about 8-12 using 1(M) Na.sub.2CO.sub.3 solution. g) The mixture solution was continued stirring for 1-3 h. to form a thick gel like mixture. h) The mixture was then taken into an autoclave and kept for 12-48 hrs. at 180? C. i) The autoclave was taken out from oven and cooled to room temperature. j) The precipitate was then washed with water and dried at 100? C. overnight for 12-20 h. k) The obtained solid was calcined at 550? C. to obtained NiZnOMgO catalyst.

(17) production of syngas from dry reforming of methane under atmospheric pressure is carried out over the obtained NiZnOMgO catalysts in a fixed bed down-flow reactor using methane (99.999% of purity) and carbon dioxide (9.9% of purity balanced He) as feeds for 1 to 100 h to get syngas. The process pressure is kept at 1 atm and the reaction temperature is preferably in the range 600-800? C. is used. The methane conversion is obtained 5-99 mol % and H.sub.2/CO ratio of syngas obtained is in the range of 0.83-1.2.

(18) Accordingly the present invention provides an improved process for the reforming of methane with carbon dioxide to produce synthesis gas under atmospheric pressure at a temperature range 600-800? C. with a Gas Hourly Space Velocity (GHSV, for/g catalyst/hr.) in the range of 5000-550000 ml g-1 h-1 in the presence of Ni: MgOZnO with Ni in the range 2-10% and MgO in the range of 2-10% to obtain desired syngas for a period of 1 to 100 h.

(19) The wt % of Ni to ZnO of the catalyst varied in the range of 2-10%.

(20) The feed ratio in the reaction is CH.sub.4:CO.sub.2:He=1:1:12.

EXAMPLES

(21) Following examples are given by way of illustration and therefore should not be construed to limit the scope of the invention.

Example-1

(22) Preparation of 5% Ni-5% MgOZnO

(23) An aqueous (20 ml water) solution of Nickel nitrate hexahydrate (1.54 g) was added with another aqueous (40 ml) solution of Zinc nitrate hexahydrate (22.4 g) and Magnesium nitrate hexahydrate (0.96 g). Then an ethanolic (20 ml) solution of CTAB (cetyltrimethylammonium bromide) (1.7 g) was added to the mixture solution after mixing the all solution homogeneously. The solution was then continued stirring for 1 h. before adding 40 drops of hydrazine hydrate. The pH of the solution was maintained to about 9-10 using 1(M) Na.sub.2CO.sub.3 solution. The whole mixture solution was then continued stirring for 1 h. to form a gel like mixture. The whole mixture was then put into an autoclave and kept at 180? C. for 24 hrs. After taking out the autoclave from oven the autoclave was cooled to room temperature. The ppt was then washed with water and dried at 100? C. overnight. The obtained solid was calcined at 550? C.

(24) The material was characterized by XRD, SEM, Elemental mapping and TEM. The XRD image as in FIG. 1 reveals the presence of NiO, ZnO, and MgO in the prepared sample. SEM image as indicated in FIG. 2 and elemental mapping shows that the catalyst particles are in the nanoparticle range and Ni is uniformly distributed in the sample. The TEM images as indicated FIG. 3 reveal that the nanoparticles are in the range between 50-100 nm.

Example 2

(25) Preparation of 5% Ni-5% MgOZnO

(26) An aqueous (10 ml water) solution of Nickel nitrate hexahydrate (0.39 g) was added with another aqueous (20 ml) solution of Zinc nitrate hexahydrate (11.4 g) and Magnesium nitrate hexahydrate (0.48 g). Then an ethanolic (5 ml) solution of CTAB (cetyltrimethylammonium bromide) (0.43 g) was added to the mixture solution after mixing the all solution homogeneously. The solution was then continued stirring for 1 h. before adding 10 drops of hydrazine hydrate. The pH of the solution was maintained to about 9-10 using 1(M) Na.sub.2CO.sub.3 solution. The whole mixture solution was then continued stirring for 1 h. to form a gel like mixture. The whole mixture was then put into an autoclave and kept at 180? C. for 24 hrs. After taking out the autoclave from oven the autoclave was cooled to room temperature. The ppt was then washed with water and dried at 100? C. overnight. The obtained solid was calcined at 550? C. The material was characterized by XRD, SEM, Elemental mapping and TEM. The XRD reveals the presence of NiO, ZnO, and MgO in the prepared sample. SEM image and elemental mapping shows that the catalyst particles are in the nanoparticle range and Ni is uniformly distributed in the sample. The TEM images reveal that the nanoparticles are in the range between 50-100 nm.

Example 3

(27) General Procedure for the Dry Reforming of Methane

(28) The dry reforming of methane was carried out in a fixed-bed down flow reactor at atmospheric pressure. Typically 15-300 mg of catalyst was placed in between two quartz wool plugged in the center of the 6 mm quartz reactor. Dry reforming of methane was carried out at different temperature (600-800? C.). The gas hourly space velocity (GHSV) was varied between 5000 mlg.sup.?1 h.sup.?1 to 550000 mlg.sup.?1h.sup.?1 with a molar ratio of CH.sub.4:CO.sub.2:He of 1:1:12. The reaction products were analyzed using an online gas chromatography (Agilent 7890A) fitted with a TCD detector using two different columns Molecular sieves (for analysing H.sub.2) and PoraPack-Q (for analysing CH.sub.4, CO.sub.2 and CO).

Example 4

(29) The example describes the effect of temperature on conversion and H.sub.2/CO ratio of dry reforming of methane. The product analysis presented in Table-1.

(30) Process Conditions:

(31) Catalyst: 0.24 g

(32) Ni:MgO:ZnO weight ratio in the catalyst=5:5:95

(33) Reaction time: 7 h

(34) Process pressure=1 atm.

(35) Gas hourly space velocity (GHSV): 30000 ml g-1 h-1

(36) TABLE-US-00001 TABLE 1 Effect of temperature on conversion of methane and H.sub.2/CO ratio of dry reforming of methane Tem- Methane CO.sub.2 GHSV perature Conversion Conversion H.sub.2/CO Catalyst (mlg.sup.?1h.sup.?1) (? C.) (%) (%) ratio 5% Ni:5% 30000 600 1.0 1.1 MgOZnO 30000 700 70.7 72.7 0.97 30000 800 99.4 92.3 1.17

Example 5

(37) The example describes the effect of gas hourly space velocity on the conversion of methane and H.sub.2/CO ratio of dry reforming of methane. The product analysis presented in Table-2.

(38) Process Conditions:

(39) Catalyst: 0.015 g

(40) Ni:MgO:ZnO weight ratio in the catalyst=5:5:95.

(41) Process pressure: 1 atm

(42) Temperature: 800? C.

(43) Reaction time: 7 h

(44) TABLE-US-00002 TABLE 2 Effect of temperature on conversion of methane and H.sub.2/CO ratio of dry reforming of methane Tem- Methane CO.sub.2 GHSV perature Conversion Conversion H.sub.2/CO Catalyst (mlg.sup.?1h.sup.?1) (? C.) (%) (%) ratio 5% Ni:5% 550000 600 8.5 5.8 0.82 MgOZnO 550000 700 27.1 34.4 0.88 550000 800 47.6 58.8 0.83

Example 6

(45) The example describes the effect of gas hourly space velocity on the conversion of methane and H.sub.2/CO ratio of dry reforming of methane. The product analysis presented in Table-3.

(46) Process Conditions

(47) Catalyst: 0.015 g

(48) Ni:MgO:ZnO weight ratio in the catalyst=5:5:95.

(49) Process pressure: 1 atm

(50) Temperature: 800? C.

(51) Reaction time: 7 h

(52) TABLE-US-00003 TABLE 3 Effect of GHSV on conversion and H.sub.2/CO ratio of dry reforming of methane Tem- Methane CO.sub.2 perature WHSV Conversion Conversion H.sub.2/CO Catalyst (? C.) (mlg.sup.?1h.sup.?1) (%) (%) ratio 5% Ni:5% 800 550000 47.6 58.8 0.83 MgOZnO 800 250000 52.3 72.6 0.81 800 150000 99.2 99.5 0.99 800 100000 99.5 90.3 1.20 800 30000 99.4 92.3 1.17

Example 7

(53) The example describes the effect of time on stream on conversion of methane and H.sub.2/CO ratio of dry reforming of methane. The product analysis presented in Table 4.

(54) Process Conditions:

(55) Catalyst: 0.24 g

(56) Ni:MgO:ZnO weight ratio in the catalyst=5:5:95

(57) Process pressure: 1 atm

(58) Gas hourly space velocity (GHSV): 30000 ml g-1 h-1

(59) Reaction temperature: 800? C.

(60) TABLE-US-00004 TABLE 4 Effect of Time on Stream on conversion and H.sub.2/CO ratio of dry reforming of methane Methane CO.sub.2 Tem- Con- Con- Time perature WHSV version version H.sub.2/CO Catalyst (h.sup.?1) (? C.) (mlg.sup.?1h.sup.?1) (%) (%) ratio 5%Ni:5% 0 800 30000 89.4 83.7 1.17 MgOZnO 1 800 30000 89.0 84.1 1.16 2 800 30000 89.2 84.8 1.15 3 800 30000 90.6 85.9 1.13 4 800 30000 95.7 90.5 1.13 5 800 30000 99.4 92.3 1.15 6 800 30000 99.5 92.2 1.15 7 800 30000 99.4 92.3 1.15 8 800 30000 99.4 92.4 1.15 9 800 30000 99.4 92.4 1.15 10 800 30000 99.4 92.5 1.15 12 800 30000 99.4 92.3 1.15 14 800 30000 99.4 92.3 1.15 16 800 30000 99.4 93.6 1.15 18 800 30000 99.4 92.3 1.15 20 800 30000 99.4 92.5 1.15 25 800 30000 99.4 92.4 1.15 30 800 30000 99.3 92.2 1.15 35 800 30000 99.4 92.5 1.15 40 800 30000 99.5 91.3 1.15 45 800 30000 99.3 92.9 1.15 50 800 30000 99.3 92.9 1.15 55 800 30000 99.2 92.2 1.15 60 800 30000 99.2 91.3 1.16 65 800 30000 99.3 91.2 1.16 70 800 30000 99.2 91.1 1.16 80 800 30000 99.2 91.4 1.16 90 800 30000 99.2 92.1 1.16 100 800 30000 99.2 92.1 1.16

ADVANTAGES OF THE INVENTION

(61) The main advantages of the present invention are: a) The process of the present invention is to utilize two major greenhouse gasses CH.sub.4 and CO.sub.2 to convert to syngas by dry reforming in a single step with a single catalyst. b) The process provides not only good conversion but also good H.sub.2/CO ratio of syngas. c) The process uses very dilute feed with ratio CH.sub.4:CO.sub.2:He=1:1:12. d) The process utilizes two major greenhouse gases at a time to produce syngas with H.sub.2/CO ratio almost equal to unity, which can be further used for the production of valuable chemicals. e) The process does not produce any major by-products which is also a major advantage of this process. f) The catalyst shows no deactivation up to 100 h time on stream at 800? C.; which supports the thermal stability of the catalyst. g) The catalyst is used in very low amounts.