Patent Application
20180353942
This invention relates generally to the methane reforming and, more particularly, to catalysts and processing useful in the dry reforming of methane (DRM).
Syngas or synthesis gas is a mixture of primarily hydrogen and carbon monoxide commonly used as a feedstock in Fischer-Tropsch synthesis. Syngas is a primary building block used to create many products and chemicals currently generated by the petrochemical industry. In 2014, the global syngas production was 116,600 Mth, which translates to 11.6 trillion cubic feet (or 3.3×1011 m3). Syngas has maintained market price stability of $0.10-$0.11/m3. This translate to a value of the market in the range of μ$33-36 billion. The market is estimated to reach 213,100 MWth (6.0×1011 m3) by 2020, at a compound annual growth rate (CAGR) of 9.5% or even higher between 2015 and 2020. The projected syngas market for 2025 is shown in
As shown in Table 1, the H2/CO ratios for the common state-of-the-art syngas production technologies of methane steam reforming reaction, partial oxidation of biomass, and underground coal gasification, are >3, 1.0, and 2, respectively.
Currently, the methane steam reforming reaction (CH4+H2OCO+3H2) is the most conventional method of producing syngas with partial oxidation of biomass as an alternative method for producing syngas. The H2/CO ratio for typical biomass-derived syngas is about 1.0, with many side products being produced, such as tar, ammonia, and sulfur compounds. While the gaseous products can be used to produce liquid fuels and chemicals, tar is produced as a side product. Such tar is or can be difficult to remove and is also or may be to the catalyst and processing units.
Syngas can also be produced from coal. Underground coal gasification is a promising technology for reducing the cost of producing syngas from coal. In underground coal gasification, a gas mixture (containing H2, CO, CO2, CH4, and possibly small quantities of various contaminants including SOx, NOx and H2S, for example) is produced and extracted through wells drilled into an unmined coal seam. Injection wells are used to supply oxidants (e.g., air or oxygen) and steam to ignite and fuel underground combustion, which is conducted at temperatures from 700 to 900° C.
Among the common state-of-the-art syngas production technologies, methane steam reforming is the most mature technology for large scale syngas production. Methane steam reforming is typically carried out in a packed bed reactor at high pressure (i.e., 2.0-2.6 MPa). The H2/CO ratio is greater than 3 due to the water-gas shift reaction (H2O+COCO2+H2), making it more valuable to produce high-purity Hz or low-carbon-content chemicals such as methanol.
Current methane dry reforming technologies for producing syngas commonly employ packed bed reactors, where metal catalysts (e.g., Rh, Pt, Ir, Pd, Ru, and Ni) are utilized to catalyze the reaction. Among these metal catalysts, noble metal catalysts have shown better resistance to coking, as compared to Ni catalysts. However, due to the limited availability and high cost of noble metals, there is a need and a demand for the development of a suitable non-noble metal catalyst for use in methane dry reforming.
One aspect of the current development relates to a new nickel (Ni) nanoparticle catalyst, supported on a hollow fiber substrate, such as an α-Al2O3 hollow fiber substrate support. In one embodiment, extremely small Ni nanoparticles were successfully deposited on hollow fibers to form desired catalyst material. In one embodiment, a new nickel (Ni) nanoparticle catalyst, supported on a hollow fiber substrate, is synthesized by atomic layer deposition (ALD).
In another aspect of the current development, such a catalyst can desirably be employed to catalyze DRM reaction. In one embodiment, such a catalyzed DRM reaction produced or showed a methane reforming rate of 2040 Lh−1 gNi−1 at 800° C.
In another aspect of the current development, a method for producing a catalyst for dry reforming methane is provided. In one embodiment, such a method involves depositing nickel (Ni) nanoparticles onto a hollow fiber substrate support, such as of α-Al2O3, by atomic layer deposition. If desired, one or more layers of a promoter coating, such as of Al2O3, can be applied over the nickel (Ni) nanoparticles on the hollow fiber substrate support, such as by atomic layer deposition.
As used herein, references to “Ni nanoparticles” are in accordance with one preferred embodiment to be understood to encompass nanoparticles of nickel including nanoparticles of only nickel as well as nanoparticles of nickel-containing combinations such as nickel containing bimetallic nanoparticles such as Ni+Co bimetallic nanoparticles and/or Ni+Pt bimetallic nanoparticles, for example. In accordance with one preferred embodiment, Ni nanoparticles used in the practice of the invention are desirably composed of nanoparticles of neat nickel, e.g., only nickel.
Objects and features of this invention will be better understood from the following description taken in conjunction with the drawings, wherein:
As identified above, in accordance with one aspect of the subject development, a new nickel (Ni) nanoparticle catalyst, supported on a hollow fiber substrate is provided.
Though γ-Al2O3 has been widely used as support for Ni-based catalysts, it is not suitable for the industrial DRM process due to phase transformation when the temperature is higher than 770° C., which also accompanies with a decrease in surface area. Among different phases of Al2O3, α-Al2O3 is the most stable phase. The better thermal and mechanical stability of α-Al2O3, as compared to other phases of Al2O3, makes it more suitable for industrial application and α-Al2O3 has been employed to prepare industrial packed bed catalyst support.
In one embodiment, such a catalyst material in accordance with the subject development can desirably be synthesized by atomic layer deposition (ALD). For example, in the ALD process, a NiAl2O4 spinel is formed when Ni nanoparticles are deposited on alpha-alumina substrates, such as can act to inhibit sintering of the Ni nanoparticles.
A coat or coatings of one or more promoters, such as of Al2O3, CeO2, CaO and La2O3, for example, can be employed such as to increase catalyst performance such as by further improving the interaction between the Ni nanoparticles and the hollow fiber substrate supports. In one embodiment, such a promoter coating produced or synthesized by atomic layer deposition (ALD) is desirably employed. In one particular embodiment, Al2O3 ALD films, can be employed to further improve the interaction between the Ni nanoparticles and the hollow fiber support. Different cycles (e.g., 2, 5, and 10) of promoter, e.g., Al2O3 ALD, films have been applied on the hollow fiber supported Ni catalysts. For example, both catalyst activity and stability were improved with the deposition of the Al2O3 ALD overcoat films. Among the ALD coated catalysts, the catalysts with 5 cycles of Al2O3 ALD exhibited the best performance, e.g., catalyst activity and stability, in the reforming of methane. Those skilled in the art and guided by the teachings herein provided will understand and appreciate that the broader practice of the invention is not necessarily limited by the method or technique by which the metal oxide promoter, if present, is prepared as, for example, the metal oxide promoters can be prepared by alternative methods such as liquid phase impregnation, for example.
Table 1, below, identifies H2/CO ratios for the common state-of-the-art syngas production technologies of methane steam reforming reaction, partial oxidation of biomass, and underground coal gasification, as well as for dry reforming of methane in accordance with the invention.
In contrast with the H2/CO ratios for the common state-of-the-art syngas production technologies of methane steam reforming reaction, partial oxidation of biomass, and underground coal gasification, of >3, 1.0, and 2, respectively, the projected H2/CO ratio of dry reforming using the invention technology is 0.70-0.95, which H2/CO ratio is more favorable for C5+ hydrocarbon production.
It is envisioned that, at full scale, the subject technology can utilize CO2 captured from a coal-fired power plant (550 MWe), at approximately 11,000 tons of CO2/day, which can produce 790 million standard cubic feet of syngas/day using the dry reforming technology. Please note that this is simply estimated by the chemical reaction equation (CO2+CH4→2H2+2CO). The global syngas market is estimated to reach 6.0×1011 m3 by 2020. If this amount of syngas is produced by the subject technology, approximately 3.0×108 ton CO2 will be consumed per year. This is the equivalent to the total CO2 emission from 420 coal-fired power plants (each with 550 MWe (net) capacity). Moreover, technologies for syngas conversion to valuable fuels and chemicals, such as transportation fuels, are currently being developed. Thus, if the economics of syngas conversion processes improve, the market for syngas will increase substantially.
In accordance with one embodiment of the subject development, highly dispersed Ni nanoparticles are deposited on high specific surface α-alumina hollow fibers, along with a catalyst promoter film deposited on Ni/alumina catalysts by ALD. The subject development features at least the following advantages/improvements over current technologies:
Ni nanoparticles used in the practice of the subject development may, in accordance with one preferred embodiment, desirably and preferably be 2-6 nm in size. In another preferred embodiment, Ni nanoparticles used in the practice of the subject development are desirably and preferably 2-4 nm in size.
While in the foregoing detailed description this invention has been described in relation to certain preferred embodiments thereof, and many details have been set forth for purposes of illustration, it will be apparent to those skilled in the art that the invention is susceptible to additional embodiments and that certain of the details described herein can be varied considerably without departing from the basic principles of the invention.
This application claims the benefit of U.S. Provisional Patent Application, Ser. No. 62/518,904, filed on 13 Jun. 2017. The co-pending Provisional Application is hereby incorporated by reference herein in its entirety and is made a part hereof, including but not limited to those portions which specifically appear hereinafter.
| Number | Date | Country | |
|---|---|---|---|
| 62518904 | Jun 2017 | US |
