Conversion of methane, carbon dioxide and water using microwave radiation - Patent 5266175
This is a lengthy dispatch.
Keep in mind, through all of it, our earlier suggestions that the mandated geologic sequestration of Carbon Dioxide, in nearly-depleted petroleum reservoirs, just might be a scam being perpetrated on the coal industry, and on coal people, by Big Oil; him being intent on having us finance the scavenging of the last petroleum dregs from his nearly-depleted oil reservoirs, and having us pay him to take and store, all the transport at our expense, Carbon Dioxide in those reservoirs, until he wants it back for his own purposes.
When we suggested in earlier reports that Big Oil, through his support of Carbon Dioxide sequestration in old oil wells, all to be paid for by the coal-use industry and US taxpayers, wasn't just conniving to get other people to pay for the scrounging of a last bit of petroleum out of nearly-depleted oil reservoirs, but actually stealing, through deception, a potentially-valuable resource for later exploitation and commercial use, we weren't joking.
Herein, we document, with a US Patent, that ExxonMobil intends to recycle Carbon Dioxide, by converting it into synthesis gas from which liquid fuels can be produced via Fischer-Tropsch, and other, catalytic processes.
The excerpt, with comment interspersed and appended:
"Conversion of methane, carbon dioxide and water using microwave radiation
United States Patent 5266175
A mixture of methane, water and carbon dioxide can be effectively converted to carbon monoxide and hydrogen by subjecting the mixture to microwave radiation in the presence of at least one plasma initiator that is capable of initiating an electric discharge in an electromagnetic field.
Inventors: Murphy, William J. (Brights Grove, CA)
Publication Date: 11/30/1993; Filing Date: 12/04/1992
Assignee: Exxon Research & Engineering Company (Florham Park, NJ)
Claims:
1. A method for converting methane and carbon dioxide to carbon monoxide and hydrogen which comprises:
(a) introducing a feed stream containing methane, carbon dioxide and from about 0.02 to about 20 wt% water, based on the feed stream, into a reaction zone that contains at least one plasma initiator which initiates an electric discharge in an electromagnetic field,
(b) subjecting the reaction zone to microwave radiation thereby initiating an electric discharge in said reaction zone, and
(c) ionizing the methane, carbon dioxide and water reactants whereby at least a portion of the methane and carbon dioxide are converted to carbon monoxide and hydrogen.
(A mixture of "carbon monoxide and hydrogen" would be your basic synthesis gas, from which liquid fuels can be made.)
8. The method of claim 1 wherein the methane, carbon dioxide and water are introduced into the reaction zone at pressures of from about 10 Torr to about 15 atm.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method for converting methane and carbon dioxide in the presence of water to carbon monoxide and hydrogen using microwave radiation.
2. Description of Related Art
Microwave energy has been used to convert methane to other hydrocarbons. For example, U.S. Pat. No. 4,574,038 discloses that methane can be converted to ethylene and hydrogen in a batch process at pressures of from 0.3 to 1 atmosphere by subjecting the methane to microwave radiation in the presence of a metal powder catalyst. Another example of methane conversion using microwave energy is disclosed in U.S. Pat. No. 3,663,394.
In addition, the conversion of methane and carbon dioxide into carbon monoxide and hydrogen using a microwave discharge at -5 torr pressure has been disclosed by Tanaka et al, J. Chem. Soc., Chem. Comm., pp. 921-922, (1982). U.S. Pat. No. 4,975,164 discloses the conversion of C2 + hydrocarbons to primarily unsaturated hydrocarbons and hydrogen using microwave radiation.
SUMMARY OF THE INVENTION
This invention concerns a method for converting methane and carbon dioxide to carbon monoxide and hydrogen which comprises:
(a) introducing a feed stream containing methane, carbon dioxide (and) from about 0.02 to about 20 wt% water, based on the feed stream, into a reaction zone that contains at least one plasma initiator capable of initiating an electric discharge in an electromagnetic field,
(b) subjecting the reaction zone to microwave radiation thereby initiating an electric discharge in said reaction zone, and
(c) ionizing the methane, carbon dioxide and water reactants whereby at least a portion of the methane and carbon dioxide are converted to carbon monoxide and hydrogen.
DETAILED DESCRIPTION OF THE INVENTION
This invention requires the presence of methane, carbon dioxide, water, at least one elongated plasma initiator capable of initiating an electric discharge in an electromagnetic field, and a source of microwave energy.
The methane and carbon dioxide may be pure or mixed with other hydrocarbons (e.g., methane may be a component of natural gas), or both may be components of refinery gas or gas streams from a gas producing well.
By initiating the conversion of methane and carbon dioxide in the presence of water, it has been discovered that the energy efficiency or rate of dissociation of methane and carbon dioxide is substantially increased thereby increasing the overall conversion of methane and carbon dioxide into carbon monoxide and hydrogen.
The plasma initiator may be essentially any material capable of accumulating an electric charge when placed in an electromagnetic field and then dissipating the charge (or initiating an electric discharge), for example, by ionizing a gas environment. ... silica composited with a metal initiator or another non-metal initiator would be a suitable plasma initiator.
Although methane/carbon dioxide conversion in the presence of water can be effected using only one plasma initiator, conversion is enhanced if more than one (e.g., 6 or more) plasma initiators are used.
If more than one plasma initiator is used, a minimum distance should be maintained between each initiator to facilitate dissipation of the electric charge. However, the minimum distance will vary depending upon the frequency of the microwave source.
The plasma initiators should be elongated, but may be formed, combined, or bent in any convenient shape (e.g., straight, helix, spiral, and the like). Preferably, the initiators should be formed such that there are points or sharp edges at the ends or on the surface of the initiators. Particulate powders are not suitable plasma initiators.
The plasma initiators may be stationary within the reaction zone or they may be in motion. The motion can result from the initiators being fluidized by a gas (e.g. the methane feedstock) or by other means (e.g. an external magnetic field gradient).
The frequency of the microwave source can vary broadly. Typically, the microwave energy will have a frequency of at least 0.3 GHz, with frequencies centered around 0.915, 2.45, 5.80, or 22.0 GHz being presently preferred in North America; particularly frequencies centered around 0.915, 2.45, or 5.80 GHz; especially frequencies centered around 0.915 or 2.45 GHz.
(Gosh, darn! they know a lot about all of this, don't they? How long might they have been at work on it, do you suppose?)
The microwave energy used in this invention may be continuous or pulsed. If pulsed, the duration of on-time pulses can vary broadly, but typically will range from about I nanosecond to about 20 seconds, preferably from about 1 millisecond to about 10 seconds, and most preferably from about 0.01 to about 0.2 seconds. The duration of off-time rests can vary broadly as well, but, typically, will range from about 1 nanosecond to about 100 seconds, preferably from about 0.003 to about 60 seconds, and most preferably from about 0.03 to about 5 seconds.
The conversion process of this invention can be practiced at any convenient temperature, including ambient conditions. The subject process has the advantage that pressures of one atmosphere or greater can be employed. Pressures of from about 10 torr to about 15 atm, preferably about 1 to about 2 atm are suitable.
This invention will be further understood by reference to the following Examples which are not intended to restrict the scope of the claims appended hereto.
EXAMPLE 1
Conversion of Methane and Carbon Dioxide
A methane/carbon dioxide mixture (1:1.15 mole ratio) flowing at 75 ml/min (milliliters/minute) at atmospheric pressure was contacted with 0.37 g of a straight tungsten wire (approximately 0.76 mm in diameter and cut into about 47 mm lengths) in a reactor fabricated from a straight piece of quartz tubing, 7 mm in internal diameter. The part of the tube containing the wire was inserted in a WR430 microwave waveguide and positioned approximately one-quarter wavelength from a short circuit plate. The reactor was then irradiated with microwave radiation centered at a 2.45 GHz frequency and pulsed in an on/off cycle (0.07 seconds on in a total of 0.73 seconds) with an average power of 9.8 watts.
EXAMPLE 2
Effect of Water on the Conversion of Methane and Carbon Dioxide
A methane/carbon dioxide mixture (1:1.15 mole ratio) containing 0.29 wt% water and having a flow rate of 75 ml/min (milliliters/minute) at atmospheric pressure was contacted with 0.37 g of a straight tungsten wire (approximately 0.76 mm in diameter and cut into about 47 mm lengths) in a reactor as described in Example 1 and using the procedure (except that the average power was 9.9 watts) as also described in Example 1. The methane conversion was calculated to be 90.1% and the conversion of carbon dioxide was calculated to be 87.2%.
The primary products formed were carbon monoxide (an average of 79.2 wt%), hydrogen (an average of 4.6 wt%) and water (an average of 3.5 wt%). The product stream also contained carbon dioxide (an average of 9.7 wt% versus 76.2 wt% in the mixture fed to the reactor), methane (an average of 2.4 wt% versus 24.1 wt% in the mixture fed to the reactor) and small amounts of higher hydrocarbons.
EXAMPLE 3
Effect of Water on Conversion of Methane and Carbon Dioxide
Using the apparatus and procedure of example 2 (except that the average power was 10.1 watts and the feed water content was 0.28 wt%), the methane/carbon dioxide/water mixture was converted to carbon monoxide (an average of 78.5 wt%), hydrogen (an average of 4.9 wt%) and water (an average of 3.7 wt%). The methane and carbon dioxide conversions were 89.7 and 87.0% respectively.
In comparing Examples 2 or 3 with Example 1, the addition of a small amount of water to the feed stream results in substantial increases in conversion rates. As can be seen from these data, conversion of methane increases from 48.9% to about 90% and conversion of carbon dioxide from 43.4% to about 87%."
---------
Note in the last "EXAMPLE" we include in our excerpt - there are more than a dozen described - fully 87% of Carbon Dioxide was, when combined with Methane and Water, converted into a synthesis gas presumably suitable for Fischer-Tropsch, or other, catalysis into liquid fuels.
Now, in this and other Carbon Dioxide conversion technologies, such as Penn State's "Tri-reforming" system, Methane is required as a co-reactant for Carbon Dioxide, and, as we have many times documented, the needed Methane can be also synthesized, via Sabatier, and related, technology from Carbon Dioxide. It can also be manufactured, as we have many times documented, through the gasification of coal.