|P A T E N T C L A I M S
1 . Method for recovery of carbon dioxide to methane, characterized by reacting carbon dioxide with hydrogen to form methane and water by performing a free radical reaction, in that hydrogen gas is dissolved in a supercritical state carbon dioxide gas, and said free radical reaction is initiated with hydrogen peroxide or oxygen gas or a mixture thereof, and energy is added to initiate the free racial initiation. 2. Method according to claim 1 , characterized in that said hydrogen gas is dissolved in supercritical state carbon dioxide gas at a stoichiometric ratio of 4:1 .
3. Method according to claim 1 , characterized in that the reaction is initiated with hydrogen peroxide and optionally oxygen gas at a ratio of 1 :0 to 1 :1 .
4. Method according to claim 1 , characterized in that the ratio of hydrogen peroxide to oxygen gas is at a ratio 2: 1 .
5. Method according to any of the preceding claims, characterized by energy is added in form of electro magnetic energy, such as microwave energy and/or other forms of energy including laser or electricity, including static electricity to provide for the free racial initiation.
6. Method according to any of the preceding claims, characterized in that the method is carried out as a batch process type or as a continuous flow reaction.
7. Method according to any of the preceding claims, characterized in that the temperature of the method is maintained at between 300 and 500 °C. 8. Method according to any of the preceding claims, characterized in that precursors for free radical formation are used to further increase the initiation of free radical formation.
7. Method according to claim 8, characterized in that said optional precursors are selected from compounds comprising N2O, NO, NO3, HNO2, HCIO, and perchlorate.
8. Method according to any of the preceding claims, characterized in that said reactant hydrogen gas for the main process, and said oxygen gas for said free radical initiation in the process, are prepared by electrolysis of water. 9. Method according to claim 8, characterized in that the electrical energy is provided from a hydro electric power plant or a from geothermal power plant facility.
10. Method according to any of the preceding claims, characterized by converting the methane produced to higher order hydrocarbons.
The present invention relates to a method for the recovery of carbon dioxide to methane, as disclosed in the preamble of claim 1 .
Field of the invention
A lot of focus has been aimed at C0 2 recovery due to its undesirable environmental impact, and many methods have been developed to address this problem, for example by capturing and storing CO2. In some of these sequestering methods C0 2 is separated from other flue gases either pre- or post-combustion, compressed to the supercritical state, and injected into geological storage or oil fields. In other methods the carbon is recycled into a solid phase, by use of the Bosh reaction, where CO2 gas is reacted with hydrogen gas to carbon monoxide gas CO and water H 2 O, and a second step where the CO gas is then reacted with more hydrogen gas to form solid carbon and more water. The solid carbon may then be combusted or refined to methanol for example. Alternatively, the Bosh reaction can be stopped after the first step, and the CO gas can be reacted with hydrogen gas in a Fisher Tropsch reaction to form more complex hydrocarbons.
Regarding the state of art, reference is made to the following publications: JP-2006 169095, WO2009/043081 , US-5.362.373, US-5.140.049, GB-2.448.685 and DE-19 644 681.
The present invention addresses the abovementioned problem in a novel manner, by reacting CO 2 in a supercritical phase with hydrogen gas (the H2 is dissolved in the supercritical CO2) in a free-radical reaction with hydrogen peroxide H2O2 and optionally oxygen, as radical-initiator.
Thus, the method according to present invention is characterized by reacting carbon dioxide with hydrogen to form methane and water by performing a free radical reaction, in that hydrogen gas is dissolved in a supercritical state carbon dioxide gas, and said free radical reaction is initiated with hydrogen peroxide or oxygen gas or a mixture thereof, and energy is added to initiate the free racial initiation. Preferably is said hydrogen gas dissolved in supercritical state carbon dioxide gas at a stoichiometric ratio of 4: 1 .
According to a preferred embodiment the reaction is initiated with hydrogen peroxide and optionally oxygen gas at a ratio of 1 :0 to 1 :1 , and preferably the ratio of hydrogen peroxide to oxygen gas is ratio 2:1 , based on a stoichiometric balance of the reactants.
According to a preferred embodiment the necessary energy is added in form of microwave energy and/or other forms of energy including laser or electricity, including static electricity to provide for the free racial initiation.
According to a preferred embodiment, the method is carried out as a batch process type or as a continuous flow reaction. Further the temperature of the method is maintained at between 300 and 500 °C.
According to a another preferred embodiment precursors for free radical formation are used to further increase the initiation of free radical formation. The optional precursors are selected from compounds comprising N 2 0, NO, NO3, HNO 2 , HCIO, and perchlorate.
According to a preferred embodiment said reactant hydrogen gas for the main reaction, and said oxygen gas for said free radical initiation/reaction in the process, are prepared by electrolysis of water.
According to a preferred embodiment the electrical energy needed is provided from a hydro electric power plant or a from geothermal power plant facility.
Preferably the methane produced is converted to higher order hydrocarbons. Reaction parameters of the method according to the present invention
At STP (standard conditions for temperature and pressure) CO 2 is a gas, and it can be frozen to a liquid (dry ice). If the temperature and pressure are both increased to at or above the critical point for CO2, it becomes a supercritical fluid. The critical temperature and pressure for CO2 is 31 .1 °C and 73 atmospheres, respectively.
When the CO2 is in a supercritical phase, it is neither gas nor liquid, but rather a fluid with properties of both. It can expand to fill a container much like a gas, but has the density of a liquid. It can diffuse through solids like a gas, but dissolve materials like a liquid. Thus the hydrogen gas is easily dissolved in the supercritical C0 2 according to the present invention. Thus, in a supercritical phase the CO2 will be present in a very dense phase, where there exists no phase separations that may slow the reaction between supercritical CO2 fluid and hydrogen gas. In the method steps according to the present invention, the following reaction then takes place, based on stoichiometric balanced equations: C0 2 (supercritical) + 2 H 2 (gas)→ CH4 (gas)+ 2H2O (liquid)
In order for this reaction to take place a catalyst is needed, and this catalyst is comprised of small amounts of H2O2 and optionally O2. Said catalyst is present as a radical-initiator, i.e. it initiates free radical formation. The catalyst is required only for the initiation, then a cascade reaction will start, and the reactions will continue even without the presence of the catalyst until there are no reactant or stabile forms of molecules left. Since they act only as initiators/catalyst, only very small amounts of H 2 0 2 and O2 are necessary for the method to work. Preferably the catalyst is comprised of both H 2 0 2 and 0 2 . The combination is optimal for radical formation. H2O2 contributes to the formation of the advantageous HO- radicals, which hydrogenate easily, while O2 also readily produces other free radicals. It is however possible to run the reaction without O 2> and as it is very explosive this might be preferable in some instances. If O2 is used, the most preferred ratio between H2O2 and O2 is 2:1 . One can however use up to equal amounts of H2O2 and O2 and still get usable if not optimal results. Thus, the catalyst comprises H2O2 and O2 at a ratio of 1 :0 to 1 : 1 , with an optimum of 2:1 .
In addition electromagnetic energy, such as microwaves are used continually during the method as an energy source. Eventually a water phase will usually build up in the bottom of the reactor. The method is then done, and CO2 or other gasses are then not in a supercritical phase anymore.
The reaction is capable of running at quite low temperatures due to free-radical mechanisms. Preferably the reaction temperature is maintained at between 300 and 500 °C. The optimal temperature will depend on other reaction parameters, such as the pressure. The reaction may be run at different temperatures and pressures, as long as the C0 2 remains in the supercritical phase.
In the following detailed reaction scheme, radicals (also often referred to as free radicals) are labeled with a dot ( ■ ), and are uncharged, hyper reactive molecules, atoms or ions with unpaired electrons on an open shell configuration. The labels (g) and (I) refers to gas and liquid phase, respectively. The presence of a catalyst comprising of H2O2 and preferably O2, as well as microwaves, is required for free radical initiation.
Reaction scheme of the method according to the present invention.
Reference is made to the enclosed figure, showing the steps of the invention.
1. Main/major reaction:
C02(g) + H2(g)→ Heat/Microwaves→
CO2 (Super Critical) + 2H 2 (dissolved in CO2)→ Heat/Microwaves →
CH 4 (g) + 2H 2 0(I)
The microwaves create free radicals by release of energy to the vibrating molecules. H2O2 and O2 form free radicals easily/rapidly.
2. Side reactions/free radical reactions:
H 2 0 2 (l)→ H 2 0- + O-
H 2 0 2 (l)→ 2HO-
Hydrogenation is most usual with the HO- radical (Li et al 1991) Examples CO2/O2: O 2 (g)→ 2O-
CO 2 + O-→ CO- + O 2 CO- + HO-→ CH- + H 2 O Possible radical formation of CH4:
CH- + 3HO-→ CH 4 + 3O-
The reaction will continue until there are no more reactants/stabile molecules present.
3. Cascade reaction initiated by free radical reactions:
CO 2 + 2 H- → COH- + OH- HO- is the most stabile of these radicals, and will be formed and continue to hydrogenate (Li et al 1991 ), the reaction itself will "run amuck" until there is no possibility for any further free radicals, and because a water phase will be formed. The main reaction (point 1 above) will therefore produce the major/main product. Ideally the method is conducted by mixing the amounts of ingredients/reactants in stoichiometric composed mixtures, according to the abovementioned balanced equations. However it will be obvious for an expert that above reactions will occur at any reactant ratio of the specific ingredients in the mixture of gases, as also is indicated in claim 1.
4. Consequence of the main reaction (point 1 above):
When the reaction is completed/done in a batch process type, that is, when the reactants are consumed or no more stabile radicals can be formed, there is a water phase (liquid phase) left in the reactor, and a gas phase of methane (CH 4 ).
The method may of course be carried out as a continuous reaction, in a continuous flow reactor. Advantages and preferred embodiments of the method
according to the present invention
There are some distinct advantages to using CO2 in a supercritical phase according to the present invention. By using CO 2 in a supercritical phase much lower temperatures may be used when compared to the traditional Bosh reaction method. The reaction is quite safe since the reactants are in very close proximity to each other (in near liquid phase). Use of free radical initiation allows the reactions the reactions to run at said lower temperatures, and low pressure. As a consequence, the method according to the present invention is conducted at a lower temperature and pressure, in a less complicated reactor, and is cheaper to carry out than the previous known methods.
In a preferred embodiment of the present invention, the process of CO 2 recovery is used as part of a complete system, where the energy and other components needed as well as further processing of the resulting methane is all part of one integrated system.
The CO 2 can be of any origin, but in the above mentioned preferred embodiment of a system of the present invention it is obtained from industry or recycled from the atmosphere by aid of existing membrane technology. The CO 2 is used in the present invention as a carbon source via free-radical mechanisms as described herein.
Preferably the hydrogen and oxygen needed for the process of CO 2 recovery is produced by electrolysis of water. The necessary electrical energy is provided from a hydro electric power plant or a from geothermal power plant facility acquiring the energy of high pressure steam from a geothermal heat energy facility in the ground. Either directly by heat differentials, or by heat exchangers. This energy is used for electrolysis of water H 2 0 to oxygen O2 and hydrogen H 2 . The oxygen and hydrogen gasses can also be sold as bi-products, and the oxygen can be used as free-radical initiator according to the invention. The H2O2 used as free-radical initiator together with the oxygen can be purchased or made onsite. The methane produced by the CO 2 recovery may in turn be converted by water gas reactions/ Fisher Tropsch reactions to higher order hydrocarbons. The system according to said preferred embodiment does not cover large areas for production of bio-methanol, and will be very economical in areas with easily available geothermalal energy, such as Iceland. Please see drawing figure for a flow chart overview of the method steps conducted in a reactor tank according to the preferred embodiment of the present invention. The initial method step of producing hydrogen and oxygen, respectively, by electrolysis for the main method and the catalytic process, is shown in the upper part of the figure.
Although a preferred embodiment of the invention is described above as a complete system, it will be apparent to anybody skilled in the art that numerous substitutions to this system can be made. This system is a preferred embodiment because coupling the CO2 recovery with a geothermal facility has several advantages, not the least of which is cost efficiency and clean production.
According to the present invention, H2O2 and preferably O2 as well, is used as a catalyst/radical formation initiator, also denoted a precursor. In addition, according to a preferred embodiment of the present invention, other materials including all forms of gasses, liquids or solid materials that may be used as precursors for free radical formation may be used with the present invention in order to jump start the reaction between supercritical C0 2 and dissolved H 2 . For example di-nitrogen oxide, N 2 0 forms free radicals very readily and therefore is very environmentally damaging (it is 200 times more damaging than C0 2 ), which makes it an excellent choice for improving the free radical formation of the present invention, if that is desired. Although any free radical formation precursors may be used according to the present invention, preferred examples include NO, NO3, HNO 2 , HCIO, and perchlorate.
The main source of energy for the method according to the present invention is microwaves. Microwaves according to the present invention are electromagnetic energy waves of 300 MHz to 300 GHz. Preferably, the invention uses microwaves of a frequency of 2,5 to 6 GHz, and most preferably a frequency of 4 to 5 GHz. In addition to microwaves, other forms of energy sources can be employed in order to form free radicals according to the present invention. Such energy sources may be any kind of energy, including laser or electricity; static or not.
Next Patent: APPARATUS AND METHOD OF LAYING AN ELONGATE ARTICLE FROM A VESSEL