Conversion of natural gas into clean liquid fuels

#The present invention is generally directed to processes and systems for upgrading natural gas to value-added oxycarbon products.

#The production of natural gas in the U.S. is projected to increase by 30% and 55% in 2025 and 2040, respectively, mainly thanks to the recent explosive growth of shale gas exploration. In fact, the supply of natural gas in U.S. will quickly exceed the domestic consumption. As a result, the (crude) oil-to-(natural) gas price ratio is expected to increase from 2.5 in 2015 to 3.1 and 4.9 in 2025 and 2040, respectively. Oxycarbon products are much more valuable than the crude oil. The prices of oxycarbon products are around 10-20 times as much as that of natural gas based on the same carbon molarity. For example, the prices of methanol (CH3OH), formic acid (HCOOH), and methyl formate (HCOOCH3) are 7.9, 15.7, and 17.5 times as much as that of natural gas, respectively, based on the same carbon molarity.

#High abundance and low cost of natural gas provide a clear motivation and unique opportunity for upgrading methane, the dominant component of natural gas, to value-added and handling-convenient oxycarbon products. Note that the natural gas can be liquefied, called liquefied natural gas (LNG), via a cooling process at a very low temperature (typically, −160° C.). And thus, the handling and transportation of LNG are rather costly, largely because LNG demands the expensive cryogenic conditions for all the time to maintain its liquid form. Compared with LNG, converting natural gas to oxycarbon products is a preferred route.

#FIG. 1 is a schematic diagram of the reaction mechanisms in accordance with one embodiment of the present invention;

#FIG. 2 is a schematic diagram of the reaction mechanisms in accordance with another embodiment of the present invention;

#FIG. 3 is a schematic diagram of a system for converting methane to oxycarbon products in accordance with one embodiment of the present invention;

#Embodiments of the present invention are directed to methods of converting methane to oxycarbon product and systems for implementing these methods. Methane activation (i.e., to methyl radical) and conversion to desirable products can be improved over prior art methods due to metal-surface facilitation using hydroxyl radicals as an activating agent in aqueous systems. Metal-surface facilitation enables a desired decoupling design, which provides freedom in controlling the methane activation and product distribution. In one or more embodiments, the method comprises converting methane to an oxycarbon product by dissolving the methane in an aqueous solution comprising hydroxyl radicals and reacting the methane and hydroxyl radicals in the presence of a metal catalyst to produce the oxycarbon product. In certain embodiment, the aqueous solution may further comprise hydrogen peroxide and a source of ferrous (Fe2+) ions, which react with each other to provide a reliable supply of hydroxyl radicals.

#Advantageously, the methods described herein, and particularly the dissolving and reacting steps noted above, can be effectively performed under ambient conditions and still achieve a high level of desirable oxycarbon products. As used herein, the term “ambient conditions” refers to the prevailing and uncontrolled pressure, temperature, humidity, and atmospheric (e.g., O2, CO2, N2, etc.) conditions in a room or environment where the reaction is taking place. This is particularly advantageous over prior art methane upgrade methods that require high temperatures and pressures, which increases the complexity and cost of such methods. In certain embodiments, the dissolving and/or reacting steps are performed at a temperature of less than about 50° C., preferably less than about 40° C., and more preferably less than about 35° C. In certain embodiments, the dissolving and/or reacting steps are performed at a temperature of about 0° C. to about 100° C., preferably about 10° C. to about 50° C., and more preferably about 20° C. to about 25° C. In certain embodiments, the dissolving and/or reacting steps are performed at a pressure of less than about 10 bar, preferably less than about 5 bar, and more preferably less than about 2 bar. In certain embodiments, the dissolving and/or reacting steps are performed at a pressure of about 0.1 bar to about 10 bar, preferably about 0.5 bar to about 5 bar, and more preferably about 0.7 bar to about 2 bar. In a particularly preferred embodiment, the dissolving and/or reacting steps are performed at a pressure of about 1 bar. Additionally, the dissolving and/or reacting steps can be performed without introduction of an external electrical charge to convert the methane to oxycarbon products, which is a particular advantage over prior art electrochemical methods.

#The metal catalyst may be any of a variety of metal catalysts, so long as the catalyst allows for the production of oxycarbon products over the less desirable carbon oxides. In certain embodiments, the metal catalyst comprises a metal selected from the group consisting of platinum, rhenium, palladium, copper, gold, iridium, ruthenium, silver, oxides thereof, combinations thereof, and alloys thereof. In certain embodiments, the metal catalyst is in elemental form and does not comprise metal oxides, although in certain other embodiments, metal oxides may be present in the metal catalyst. In particularly preferred embodiments, the metal catalyst does not include or contain, and preferably excludes, cobalt phthalocyanine. In certain embodiments, the metal catalyst has a CH3.−M (methane or methyl radical to metal) binding energy of less than about 0 eV, preferably less than about −0.8 eV, more preferably less than about −1.8 eV. In certain embodiments, the metal catalyst has a CH3.−M binding energy of from about −10 eV to about 0 eV, preferably from about −5 eV to about −1 eV, and more preferably from about −3 eV to about −1.5 eV. However, in certain other embodiments, the metal catalyst may have a CH3.−M binding energy even lower (i.e., less than about −10 eV). The metal catalyst may be provided as a solid structure comprising the metal catalyst material or as a support coated with the metal catalyst. The metal catalyst may be provided on any of a variety of known supports and be of a variety of shapes and sizes, depending on the particular application. In certain embodiments, the metal catalyst comprises a zeolite support. In certain embodiments, the metal catalyst is provided as a shaped body having a geometric shape selected from the group consisting of foils, spheres, pellets, cylinders, trilobes, quadralobes, and mixtures thereof. The metal catalyst may also be provided in the form of a mesh or gauze.