US department of energy (DOE) has got a patent to produce methanol from carbon dioxide. The process developed by DOE is for the production of methanol from natural gas containing methane.
The inventors [patents] are Meyer Steinberg, USDOE scientist at the Brookhaven, NY, National Laboratory and Yuanji Dong, EPA scientist at National Risk Management and Environmental Protection Research Laboratory in North Carolina.
The objective of this project is to provide an efficient method for the production of methanol from natural and carbon dioxide.
“A process for the production of methanol from natural gas containing methane comprising the thermal decomposition of methane and the subsequent reaction of the resulting hydrogen gas with carbon dioxide in a catalyst containing methanol synthesis reactor to produce methanol”
Alternative methods include the gasification with carbon dioxide of at least a portion of the carbon produced by the decomposing step, to produce carbon monoxide, which is then reacted with hydrogen gas to produce methanol; or the reforming of a portion of the natural gas feedstock used in the decomposing step with carbon dioxide to produce carbon monoxide and hydrogen gas, which carbon monoxide and hydrogen are then combined with additional hydrogen from the natural gas decomposing step in a methanol synthesis reactor to produce methanol. The methods taught reduce the overall amount of carbon dioxide resulting from the methanol production process.
What is claimed?
A. Process for the production of methanol from methane containing natural gas comprised of:
a. Thermally decomposing said methane to produce hydrogen gas and elemental carbon; wherein this decomposing step is comprised of:
i. Bubbling the methane through a bath comprised of a molten material operating at a temperature of at least 800° C. and a pressure of 1 to 10 atm.;
ii. Cracking said methane through the use of said molten material such that elemental carbon and hydrogen gas are formed;
iii. Removing the hydrogen gas from the top of the bath; and
iv. Collecting the elemental carbon off the top of the liquid surface of the bath; and
B. Reacting said hydrogen gas with carbon dioxide in a methanol synthesis reactor in the presence of a catalyst to form a product containing methanol.
C. The process of claim A wherein the molten material is selected from the group comprising molten metal tin and molten metal iron.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is related to a method for the production of methanol, and more specifically, to a method for production of methanol by conversion of natural gas and carbon dioxide which method has reduced carbon dioxide emissions.
2. Description of the Prior Art
Methanol, which was first discovered in the late 1600′s, has found use as a chemical feedstock and as an efficient fuel. Its earliest and largest use to date is as a feedstock in the production of formaldehyde. While in recent years such use has decreased, methanol has found increasing use in the production of such materials as acetic acid and methyl tert-butyl ether (MTBE–a gasoline additive). In addition, methanol is being used directly (with increasing demand) as a fuel in race cars, in farm equipment and, in some areas, as a general purpose automotive fuel. Methanol is fast becoming an environmentally preferred alternative transportation fuel and can also serve as a clean stationary power plant fuel.
There are several commercially viable methods of producing methanol. These methods include:
1. The steam reforming of natural gas in accordance with the following reaction:
2. The gasification of natural gas with carbon dioxide in accordance with the following reaction:
CO2 +CH4 ➝2CO+2H2
Or a combination of these methods
As is clear to those skilled in the art the goal of each of these conventional methods is to produce or otherwise provide carbon monoxide and hydrogen in a molar ratio of 1 mole of CO to 2 moles of H2 .These reactants are then reacted in methanol synthesis reactor in the presence of a catalyst to produce methanol in accordance with the following exothermic reaction:
The processes known in the art often produce carbon dioxide which, if fed to the methanol synthesis reactor, results in a lower methanol yielding reaction which competes with the above reaction for the valuable hydrogen as follows:
Therefore, carbon dioxide must be removed prior to entry into the methanol synthesis reactor. This obviously adds additional complexity, and, therefore expense to the process. In addition, the creation and/or emission of carbon dioxide by the methanol forming process creates other problems since carbon dioxide is a green house gas, the negative effects of which are only beginning to be understood. What is well understood, however, is the desire to reduce or eliminate carbon dioxide production and processes which reduce such emissions or in fact consume carbon dioxide as part of the process are desirable.
It is therefore an object of the present invention to provide an efficient method for the production of methanol from natural gas and carbon dioxide.
It is another object of the present invention to provide a method which produces a high yield of methanol per unit feedstock.
It is yet another object to the present invention to provide a method for the production of methanol having reduced carbon dioxide emissions. It is another object of the present invention to utilize waste CO2 from coal burning power plants and other sources to produce methanol to reduce overall net CO2 emissions.
It is another object of the present invention to produce carbon as a co-product to the production of methanol.
SUMMARY OF THE INVENTION
This invention relates to the production of methanol by conversion of natural gas (which is comprised mainly of methane) and carbon dioxide. The process of the present invention is comprised of two (2) basic steps, the thermal decomposition of methane (natural gas) to produce elemental carbon and hydrogen gas followed by the catalyzed reaction of the hydrogen gas produced in step one of the process with carbon dioxide in a methanol synthesis reactor to produce a gas stream containing methanol. The methanol may then be separated from the gas stream by known techniques. The carbon is separated as a co-product of the process.
As discussed above described in more detail below, the process of the invention consumes a substantial amount of carbon dioxide.
The source of the carbon dioxide used in the present invention may be any sources. However, since as indicated above the net creation and/or emission of carbon dioxide is something to be reduced or avoided, the process of the present invention may be most advantageously operated in conjunction with a carbon dioxide producing process such as a fossil fuel fired energy producing plant (i.e., e.g., a coal fired electrical generation plant or waste incinerators).
As is well known in the art such fossil fuel fired plants produce carbon dioxide as well as other gases which, if they are not otherwise dealt with, are discharged to the air, having many negative impacts on the environment such as global warming. However, such a plant operated in conjunction with the present invention could result in reduced carbon dioxide emissions since a substantial portion of the carbon dioxide generated could be consumed in the process of the present invention.
In addition, as indicated above, the present invention has the added feature of producing elemental carbon.
The carbon which is removed from the thermal decomposition step may be stored, sold or employed in other processes where elemental carbon is of value such as the production of carbon black.
An alternate embodiment of the present invention involves the additional step of gasification of a portion of the elemental carbon produced in step one with carbon dioxide to produce carbon monoxide and thereafter reacting the hydrogen produced in the natural gas thermal decomposition step with the carbon monoxide in a catalyzed reaction in a methanol synthesis reactor to form methanol.
A third embodiment of the present invention involves the step of reforming a portion of the natural gas feedstock with carbon dioxide to produce carbon monoxide and hydrogen which constituents are then provided to a methanol synthesis reactor along with the hydrogen gas produced in the methane decomposition step, where the carbon monoxide and hydrogen are combined in a catalyzed reaction to produce methanol.
It will be clear to those skilled in the art that the thermal energy necessary to cause the thermal decomposition of the natural gas in step one in the above described process may be provided in any of the known manners, but it is most commonly provided by the combustion of natural gas in accordance with the following reaction:
2CH4 +4O2 ➝CO2+4H2O
As can be seen this reaction produces carbon dioxide. However, since the process of the present invention also consumes carbon dioxide and in fact does so in an amount greater than that produced by the above reaction 5, the use of the present process results in the reduction of carbon dioxide produced by the methanol producing process.
In addition, if hydrogen gas produced by methane decomposition is substituted as the fuel in the process or if an alternative non-fossil fuel method of supplying thermal energy (e.g. solar energy or nuclear energy to the methane decomposition reactor is employed, for the decomposition step, the production of carbon dioxide in the process of the present invention is further reduced.
The carbon produced in the process is either sequestered or used as a materials commodity and is not burned as fuel.
When methanol is used as an alternative transportation fuel in automotive engines or as a clean stationary power plant fuel, the methanol combustion reaction is as follows:
CH3OH+3/2O2 ➝CO2 +2H2O
As indicated, carbon dioxide is produced. However, since carbon dioxide recovered from a fossil fuel burning power plant is used in the synthesis of methanol, the net carbon dioxide produced in the system becomes near zero when methane is used as a fuel to heat the methane decomposition reaction of step one of the process or is zero when hydrogen is used as a fuel.