New catalyst for efficient bi-reforming of methane from any source for methanol and hydrocarbon synthesis; “metgas”
Researchers at the Loker Hydrocarbon Research Institute and Department of Chemistry, University of Southern California, have developed a new catalyst based on nickel oxide on magnesium oxide (NiO/MgO) that is effective for the bi-reforming with steam and CO2 (combined steam and dry reforming) of methane as well as natural gas in a tubular flow reactor at elevated pressures (5−30 atm) and temperatures (800−950 °C).
In a paper published in the Journal of the American Chemical Society, they report that the bi-reforming effectively converts methane and its natural sources (natural or shale gas, coal-bed methane, methane hydrates) to what they call “metgas”, a 2/1 H2/CO mixture directly applicable for subsequent well-studied methanol synthesis with high selectivity. A typical single pass conversion at 7 atm is about 70−75%, which can be increased to 80−85% by adjusting the feed gas composition. Unreacted feed gases can be recycled.
This efficient conversion of methane to methanol via metgas can also be used for subsequent synthesis of various hydrocarbons and their products through zeolite-based chemistry or over various bi-functional acidic−basic catalytic routes giving alkenes (mainly ethylene and propylene) and their derived products, thereby replacing petroleum oil as the source material, the team concluded.
Methanol and its derivatives are becoming increasingly significant fuels and starting materials for varied chemical products. We have discussed methanol’s potential role and relevant chemistry that was developed in the framework of the “Methanol Economy” in a series of publications, patents, and a monograph. [Earlier post.] The current production of methanol is based on syn-gas following a process first developed by Mittasch et al. in 1923 and further improved over the years by companies including BASF and ICI. What is needed, however, for a wider use of methanol are more efficient and economic ways of preparation.
The synthesis of methanol from syn-gas requires a H2/CO ratio of about 2. The most commonly used reforming technology for methane, steam reforming, produces a syn-gas mixture with a H2/CO ratio close to 3...This means that additional steps are needed to adjust the H2/CO ratio. Carbon dioxide reforming of methane, called dry reforming, produces a syn-gas with a H2/CO ratio close to 1...which is too low and has also to be adjusted. Partial oxidation of methane with oxygen can produce a H2/CO ratio of 2, but is difficult to control and can lead to local hot spots and associated dangers of explosions...The combination of steam reforming and partial oxidation (autothermal reforming) as practiced industrially produces the H2/CO ratio of 2 by further separation and adjustment steps, which makes the overall process complex and more expensive.
...We now report the exclusive preparation of a syn-gas mixture of a 2/1 H2/CO ratio suitable for methanol synthesis in which dry and steam reforming are combined in a single step, called bi-reforming. In bi-reforming, a specific ratio of methane, steam, and CO2 of 3/2/1 produces a gas mixture with essentially a 2/1 ratio of hydrogen to carbon monoxide, which was suggested to be called “metgas” to underline its difference from the widely used syn-gas mixtures of varying H/CO ratio. This specific 2/1 H2/CO gas mixture is for the preparation of methanol and subsequently derived hydrocarbon products, with complete utilization of all the hydrogen.—Olah et al.
They reported studying bi-reforming of methane as well as of natural gas at pressures up to 30 atm in a tubular flow reactor system. All the surfaces in contact with the catalyst and reacting gases at the high temperatures were made of alumina to avoid any side reactions or possible deterioration of the reactor materials. The preferred catalyst was based on NiO deposited on magnesium oxide, i.e., NiO/MgO, with NiO content in NiO/MgO can be between 5 and 35%.
As an example, they activated a catalyst composed of 15% NiO on MgO (15-NiO-MgO) at 850 °C under hydrogen, then applied it in a bi-reforming reaction at 830 °C and 7 atm for 320 h. The H2/CO ratio remained essentially 2 and also remained stable over the reaction time.
The selectivity for CO and H2 were 100% and 98%, respectively. When the temperature was increased from 830 to 910 °C, the conversion of both methane and CO2 increased. Methane conversion increased about 15% to reach 86% at 910 °C. The H2/CO ratio decreased only very slightly from 1.99 to 1.97.
George A. Olah, Alain Goeppert, Miklos Czaun, and G. K. Surya Prakash (2012) Bi-reforming of Methane from Any Source with Steam and Carbon Dioxide Exclusively to Metgas (CO–2H2) for Methanol and Hydrocarbon Synthesis. Journal of the American Chemical Society doi: 10.1021/ja311796n