NOVEL COKING RESISTANT NiFeAl CATALYST FOR PARTIAL OXIDATION OF METHANE TO SYNTHESIS GAS

Abstract

A novel NiFeAl-based catalytic material was developed for the conversion of methane, the main constituent of natural gas, to synthesis gas, which is a mixture of H.sub.2 and CO in a H.sub.2/CO molar ratio of 2, through partial oxidation by air at reasonable temperatures.

Claims

1. A catalyst for use in the conversion of methane into synthesis gas, wherein: (1) the catalyst comprises a support of Ni supported over Fe-doped γ-Al.sub.2O.sub.3; (2) the catalyst is a NiFeAl catalyst and the Ni concentration in the catalyst is 8 to 12% of the catalyst by weight; and (3) the Fe: Al molar ratio in the support is in the range of 0.030:0.970-0.050:0.950.

2. The catalyst of claim 1, wherein the Ni concentration is 9 to 11% of the catalyst by weight.

3. The catalyst of claim 1, wherein the Ni concentration is 10% of the catalyst by weight.

4. The catalyst of claim 1, wherein the molar concentration of elements of the catalyst is 16.4% Ni, 1% Fe, 32.5% Al, and 50.1% O.

5. The catalyst of claim 1, wherein: (1) efficiency of the conversion of methane into synthesis gas is 85 to 99%; (2) selectivity of the process of conversion of methane into synthesis gas ranges from 95 to 99%; (3) the synthesis gas produced has a H.sub.2 to CO molar ratio of 2; and (4) an amount of carbon deposit produced in the process of conversion of methane into synthesis gas is zero.

6. The catalyst of claim 5, wherein the conversion of methane has an efficiency of 95 to 99%;

7. The catalyst of claim 1, wherein the process of conversion of methane into synthesis gas has a selectivity ranging from 97 to 99%.

8. The catalyst of claim 5, wherein the process of conversion of methane into synthesis gas has an efficiency of at least 91%.

9. The catalyst of claim 5, wherein the process of conversion of methane into synthesis gas has a selectivity of at least 98%.

10. The catalyst of claim 5, wherein the synthesis gas is further processed to produce liquid fuels and other chemicals.

11. A method for the conversion of methane (CH.sub.4) into synthesis gas, comprising bringing the methane gas into contact with the catalyst of claim 1, wherein: (1) methane is converted into synthesis gas; (2) efficiency of the process of conversion of methane into synthesis gas ranges from 85 to 100%; (3) selectivity of the process of conversion of methane into synthesis gas ranges from 95 to 100%; (4) an amount of carbon deposit produced in the process of conversion of methane into synthesis is substantially zero; and (5) the synthesis gas produced has a H.sub.2 to CO molar ratio of 2.

12. The method of claim 11, wherein the process of conversion of methane into synthesis gas has an efficiency ranging from 90 to 95%.

13. The method of claim 11, wherein the process of conversion of methane into synthesis gas has a selectivity ranging from 97 to 99%.

14. The method of claim 11, wherein the process of conversion of methane into synthesis gas has an efficiency of at least 91%.

15. The method of claim 11, wherein the process of conversion of methane into synthesis gas has a selectivity of at least 98-%.

16. The method of claim 11, wherein the synthesis gas is further processed to produce liquid fuels and other chemicals.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0013] FIG. 1. TEM images of selected catalyst samples.

[0014] FIG. 2 Results of catalytic activity tests at 700° C. and 1 atm. The results in the plots are averages of CH.sub.4 conversion, products' selectivity, and H.sub.2/CO ratio from 100-hr reactions.

[0015] FIGS. 3A-3D Characteristics of spent catalysts after 100 hrs on-stream at 700° C., and 1 atm. FIG. 3A XRD patterns, FIG. 3B TGA profiles, FIG. 3C Raman spectra, and FIG. 3D images of the catalysts before and after reaction.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

[0016] The current invention involves a new composite material that provides a solution to the coking problem where tests in long term reactions have shown that coking can be completely prevented.

[0017] The novelty of the new catalytic material stems from its significantly higher resistance to coke formation during reactions leading to longer life-time and higher efficiency. Coking during natural gas conversions has been one of the major causes of catalysts' deactivation. In addition, carbon deposits usually block reactors resulting in unsafe pressure buildup. These drawbacks of the currently employed catalysts increase the operation costs. Therefore, the coking resistance that the new catalytic material exhibits provides a solution to the most severe problem associated with the currently employed and widely studied catalysts for natural gas conversion processes, and leads to more robust, durable, safe, efficient, and cost-effective naturel gas conversion processes.

[0018] Disclosed herein is a NiFeAl-based catalyst for use in the conversion of natural gas to synthesis gas, which is a mixture of H.sub.2 and CO in a H.sub.2/CO.

[0019] The Ni/Al.sub.2O.sub.3 catalyst of the present invention was modified with a low-cost metal, Fe, using cost-effective preparation process. A novel NiFeAl-based catalyst was prepared and was tested in POM reaction at 700° C., where around 91% methane conversion was obtained with selectivity to H.sub.2 and CO close to 99%, and almost zero coke formation after 100 hrs on-stream.

[0020] Furthermore, the H.sub.2:CO ratio was 2.02 (±0.01) as desired for Fischer-Tropsch synthesis. The prepared catalyst was compared with other related reference catalysts and its novel performance and durability was confirmed. The unique behavior of the new catalyst was supported by, and was explained based on, results from different experimental techniques. No other materials have shown similar suppression of coke formation and stable methane conversion in POM.

[0021] In a first embodiment, disclosed herein is a catalyst composed of Ni supported over Fe-doped γ-Al.sub.2O.sub.3, where the Ni concentration is approximately 8 to 12% of the catalyst by weight and the Fe:Al molar ratio in the support is in the range of 0.030:0.970-0.050:0.950.

[0022] In another embodiment, the Ni concentration is approximately 9 to 11% of the catalyst by weight and the Fe:Al molar ratio in the support is in the range of 0.030:0.970-0.050:0.950.

[0023] In another embodiment, the Ni concentration is approximately 10% of the catalyst by weight and the Fe:Al molar ratio in the support is in the range of 0.030:0.970-0.050:0.950.

[0024] In another embodiment, the molar concentration of the elements of the catalyst of the present invention is approximately 16.4% Ni, 1% Fe, 32.5% Al, and 50.1% O.

[0025] In a second embodiment, disclosed herein is a NiFeAl-based catalyst for converting methane into synthesis gas, where the efficiency of the process of conversion of methane into synthesis gas ranges approximately from 85 to 100%.

[0026] In a preferred embodiment, the efficiency of the process of conversion of methane into synthesis gas ranges approximately from 95 to 99%.

[0027] In a most preferred embodiment, the efficiency of the process of conversion of methane into synthesis gas is approximately from 91%.

[0028] In another embodiments, the selectivity of the process of conversion of methane into synthesis gas is approximately 95 to 100%.

[0029] In a preferred embodiments, the selectivity of the process of conversion of methane into synthesis gas is approximately 97 to 99%.

[0030] In a most preferred embodiments, the selectivity of the process of conversion of methane into synthesis gas is approximately 98%.

[0031] In another most preferred embodiment, the catalyst of the present invention produces high methane conversion (around 91%) and selectivity to syngas around 99%, with H.sub.2:CO molar ratio of 2.02 (±0.01) as desired for Fischer-Tropsch synthesis.

[0032] Disclosed herein is a method for the conversion of methane (CH.sub.4) into synthesis gas, utilizing a NiFeAl based catalyst, where the synthetic gas produced has a H.sub.2 to CO ratio of approximately 2.

[0033] In an another embodiment, disclosed herein is a method for the conversion of methane (CH.sub.4) into synthesis gas method for the conversion of methane (CH.sub.4) into synthesis gas, where the efficiency of the process of conversion of methane into synthesis gas ranges approximately from 85 to 100%.

[0034] In a preferred embodiment, where the efficiency of the process of conversion of methane into synthesis gas ranges approximately from 95 to 99%.

[0035] In a most preferred embodiment, where the efficiency of the process of conversion of methane into synthesis gas is approximately from 91%.

[0036] In a further embodiment, the selectivity of the process of conversion of methane into synthesis gas is approximately 95 to 100%.

[0037] In a preferred embodiment, the selectivity of the process of conversion of methane into synthesis gas is approximately 97 to 99%.

[0038] In a most preferred embodiment, the selectivity of the process of conversion of methane into synthesis gas is approximately 98%.

[0039] In another most preferred embodiment, the method of the present invention produces high methane conversion (around 91%) and selectivity to syngas around 99%, with H.sub.2:CO ratio of 2.02 (±0.01) as desired for Fischer-Tropsch synthesis.

[0040] In one embodiment, high syngas selectivity doesn't require the addition of any other material in the reactants feed other than air and methane.

[0041] In another embodiment, the amount of carbon deposit produced in the process of conversion of methane into synthesis is approximately zero, whether measured in grams or moles.

[0042] In another embodiment, the present invention unique benefits include longer life-time, durability, compared with existing catalysts since the deactivation problem that usually results from carbon deposits is completely solved. Further, the process of conversion is safe as a result of avoiding pressure buildup due to reactor blocking that usually results from carbon deposits, and is highly efficient as a result of protecting the Ni active sites from being blocked by carbon. Also, the catalyst′ preparation requires a minimum number of steps, without the need for high temperatures or pressures, and the process is of low cost as it depends on abundant cost-effective elements.

[0043] In yet another embodiment, the synthesis gas produced by the conversion can be further processed to produce liquid fuels and other chemicals.

[0044] The present invention has a significant impact in developing more efficient and commercially feasible technology for better utilization of natural gas through methane conversion to liquid fuels and other value-added products to the benefit of the gas industry sector and related industries. No disadvantages are associated with the invented material and no limitations to its implementation are anticipated.

[0045] Materials and Preparation

[0046] The Catalyst Composition

[0047] The invented catalyst is composed of Ni supported over Fe-doped γ-Al.sub.2O.sub.3, where the Ni concentration is 10% of the catalyst by weight and the Fe:Al molar ratio in the support is in the range of 0.03:0.97-0.05:0.95. The composition of Fe:Al ratio of 0.03:0.97 gives a molar concentration of all elements as follow: 16.4% Ni, 1% Fe, 32.5% Al, and 50.1% O.

[0048] The precursor materials: Aluminum sec-butoxide ((Al(OCH(CH.sub.3)C.sub.2H.sub.5).sub.3, 98% pure), Ni(II) nitrate (Ni(NO.sub.3).sub.2.6H.sub.2O, 99.8%), and Fe(III) nitrate (Fe(NO.sub.3).sub.3.9H.sub.2O, 98%), and 2-propyl alcohol as a solvent.

[0049] The Preparation of the Invented Catalyst:

[0050] The Fe-doped γ-Al.sub.2O.sub.3 support was prepared via a sol-gel method. In a typical preparation 10 ml (0.039 mol) Al(OCH(CH.sub.3)C.sub.2H.sub.5).sub.3 was dissolved in 150 mL solution of 0.48 g (0.0011 mol) of Fe(NO.sub.3).sub.3.9H.sub.2O in 2-propyl alcohol. After mixing for 10 minutes, 2.8 ml of distilled water was added dropwise to the solution under continuous stirring. The mixture was stirred for 4 hours where a colloidal gel was obtained, which was aged for 24 hrs at room temperature in a covered beaker. The solvent was then removed by evaporation in a water bath at 80° C. The solid product was then dried in a furnace at 120° C. before calcination at 800° C. for 4 hrs.

[0051] The Ni was added to the support by wetness impregnation where 1.0 g of the calcined support was impregnated with 1.5 mL aqueous solution of the required amount of Ni(NO.sub.3).sub.2.6H.sub.2O. The impregnated paste-like composite was aged for 24 hrs before drying at 120° C. for 2 hrs followed by calcination at 700° C. for 4 hrs.

[0052] The Preparation of the Refence Catalyst Ref. 1:

[0053] The Ref. 1 catalyst was prepared by the same procedure described above except that no Fe precursor was added during the preparation of the support, which was a pure γ-Al.sub.2O.sub.3.

[0054] The Preparation of the Refence Catalyst Ref. 2:

[0055] In the second reference catalyst, Ref. 2, the support was also pure γ-Al.sub.2O.sub.3 prepared according to the method described above. Fe was co-impregnated with Ni on the surface of the calcined pure γ-Al.sub.2O.sub.3, where 1.0 g of the support was impregnated with 1.5 ml of an aqueous solution of the required amounts of the precursors of both metals. In all studied catalysts, the support was calcined at 800° C. and after the addition of Ni by impregnation, the catalyst was calcined at 700° C.

EXPERIMENTAL EXAMPLES

[0056] The invented material (NiFeAl) was tested several times in the process of partial oxidation of methane to syngas at 700° C. The material was characterized by various techniques before and after reactions. Structural characteristics were investigated by powder X-ray diffraction, Uv-Vis-NIR and Raman spectroscopy, which assisted in identifying all phases that existed under different conditions. The textural and morphological characteristics were studied by N.sub.2 sorption and transmission electron microscopy, which confirmed the formation of highly porous powders with relatively high surface areas and nano-scale particles of Ni on the surface of the support as shown in FIG. 1.

[0057] The surface acid-base characteristics of the catalyst were studied by temperature programmed desorption of NH.sub.3 and CO.sub.2. The reducibility of the catalyst was investigated by H.sub.2-temperature programmed reduction.

[0058] The catalytic performance of the catalyst was tested in 100-hr reactions using a continuous flow fixed bed reactor. The catalytic activity of the invented material was also compared with two reference catalysts. The first reference catalyst (Ref. 1) was composed of Ni supported over pure γ-Al.sub.2O.sub.3, which represents the most widely employed and investigated catalysts. The second reference catalyst (Ref. 2) was composed of Ni and Fe supported on the surface of the alumina support by co-impregnation of the precursors of both metals. It is noteworthy to mention that most reported studies that involved attempts to modify the Ni catalysts by doping with another metal have been prepared by the same method used here for the preparation of Ref. 2. While the three catalysts showed comparable CH.sub.4 conversion during 100-hr reactions, the invented catalyst showed noticeable enhanced selectivity to syngas as shown in FIG. 2. Conversion of methane around 91% and syngas selectivity around 98% was continuously obtained. Interestingly, the invented catalytic materials showed the complete absence of carbon deposit on the catalyst during the reaction allowing very stable conversion and selectivity to syngas. However, considerable amounts of carbon accumulated on the reference catalysts that blocked the reactor, due to which the reaction was stopped after 100 hrs. The coke formation on the reference catalysts and its absence from the invented catalyst was confirmed by different experimental techniques as well as from the color of the samples before and after reactions as shown in FIGS. 3A-3D. The powder X-ray diffraction (XRD) pattern of the invented material shows the absence of the carbon characteristic peak at 2θ-angle around 26°, while such peak is strongly evident in the patterns of the two reference catalysts, especially in Ref. 2. Thermal gravimetric analysis (TGA) shows the weight loss due to carbon combustion and removal from the spent catalysts. The weight loss at temperatures in the ranges of 250-400° C. and 400-800° C. is usually referred to soft and hard carbon, respectively. While the profiles of the two reference catalysts showed considerable weight loss, especially at high temperatures indicating considerable crystalline carbon deposits, the profile of the invented material shows almost zero weight loss indicating the absence of carbon, FIG. 3B. Raman spectra further confirms the absence of carbon in the spent invented material as indicated by the absence of the two typical peaks of carbon, which are shown by the spectra of the two reference catalysts. Furthermore, the picture of the new material after reaction confirms the absence of deposited carbon, while the two reference catalyst turned black due to the presence of coke.

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