WO2011115889A2 - Bromine-sensitized solar photolysis of carbon dioxide - Google Patents
Bromine-sensitized solar photolysis of carbon dioxide Download PDFInfo
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- WO2011115889A2 WO2011115889A2 PCT/US2011/028316 US2011028316W WO2011115889A2 WO 2011115889 A2 WO2011115889 A2 WO 2011115889A2 US 2011028316 W US2011028316 W US 2011028316W WO 2011115889 A2 WO2011115889 A2 WO 2011115889A2
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- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J19/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
- B01J19/08—Processes employing the direct application of electric or wave energy, or particle radiation; Apparatus therefor
- B01J19/12—Processes employing the direct application of electric or wave energy, or particle radiation; Apparatus therefor employing electromagnetic waves
- B01J19/122—Incoherent waves
- B01J19/123—Ultra-violet light
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J19/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
- B01J19/08—Processes employing the direct application of electric or wave energy, or particle radiation; Apparatus therefor
- B01J19/12—Processes employing the direct application of electric or wave energy, or particle radiation; Apparatus therefor employing electromagnetic waves
- B01J19/122—Incoherent waves
- B01J19/127—Sunlight; Visible light
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- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B32/00—Carbon; Compounds thereof
- C01B32/05—Preparation or purification of carbon not covered by groups C01B32/15, C01B32/20, C01B32/25, C01B32/30
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- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
- C23C16/22—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the deposition of inorganic material, other than metallic material
- C23C16/26—Deposition of carbon only
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- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
- C23C16/44—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the method of coating
- C23C16/48—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the method of coating by irradiation, e.g. photolysis, radiolysis, particle radiation
- C23C16/482—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the method of coating by irradiation, e.g. photolysis, radiolysis, particle radiation using incoherent light, UV to IR, e.g. lamps
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
- C23C18/02—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by thermal decomposition
- C23C18/12—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by thermal decomposition characterised by the deposition of inorganic material other than metallic material
- C23C18/1204—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by thermal decomposition characterised by the deposition of inorganic material other than metallic material inorganic material, e.g. non-oxide and non-metallic such as sulfides, nitrides based compounds
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
- C23C18/14—Decomposition by irradiation, e.g. photolysis, particle radiation or by mixed irradiation sources
- C23C18/143—Radiation by light, e.g. photolysis or pyrolysis
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P20/00—Technologies relating to chemical industry
- Y02P20/10—Process efficiency
- Y02P20/133—Renewable energy sources, e.g. sunlight
Definitions
- Carbon dioxide itself is capable of absorbing only a tiny fraction of the wavelengths of the solar spectrum that reach the Earth's surface, and essentially none of the visible or UV wavelengths that are most likely to be able to initiate photochemical reactions.
- a major thrust of the research in solar energy conversion has been to develop sensitizing chemicals that are capable of absorbing solar photons, thereby creating a high-energy photochemical product, which then can carry out chemical reactions with C0 2 leading, ultimately, to the formation of molecules containing chemically-reduced carbon.
- Cobalt itself is relatively common (crustal abundance of 25 ppm), with a bulk cost of the element about $44 per kg.
- the CoPc sensitizer used in this particular process requires considerable additional synthesis steps, and currently has a bulk cost of over $5000 per kg.
- both a ruthenium-bis- pyridyl compound and the enzyme carbon monoxide dehydrogenase were attached to titania nanoparticles in order to achieve photoreduction of carbon dioxide to carbon monoxide
- This cell is solar-powered only in the sense that both the heat needed to maintain the high temperature, and the electricity used to drive the cell, can be derived from sunlight. That is, there is no intrinsic requirement for light in this process, which is fundamentally electrochemical and thermochemical, rather than photochemical.
- the use of solar energy in this process has the same challenging economic considerations as in the use of solar energy for other heating and electrical uses. Using other sources of energy (e.g. wind energy) might make more sense, not only from the point of view of economics but also in terms of maximizing the net carbon storage.
- a process for depositing carbon on a surface comprising, while contacting a mixture of C0 2 and Br 2 with a polar substrate presenting apposed surfaces, exposing a sufficient area of said mixture in the region of said apposed surfaces to light of sufficient intensity and frequency to result in deposition of carbon on at least some of said apposed surfaces.
- the polar substrate is a non-carbonaceous polar substrate.
- the polar substrate is selected from the group consisting of silica, silica-based glasses, alumina and titania, and mixtures thereof.
- the polar substrate is in particulate form.
- the polar substrate is selected from sand, silica gel, powdered alumina, titania, quartz sand, glass spheres, and glass wool.
- the light is a mixture of UV and visible light.
- the mixture of UV and visible light includes light in the wavelength range of 300 to 500 nm.
- the light is provided as sunlight.
- the sunlight is focused onto said mixture in said region of said apposed surfaces.
- the sunlight is focused using a parabolic or paraboloid mirror.
- the parabolic or paraboloid mirror is equipped to track the motion of the sun.
- the polar substrate, C0 2 and Br 2 and are contained in a UV- and visible-light transparent region of a reaction vessel.
- the range of transparency includes wavelengths of light from 300 to 500 nm.
- the reaction vessel is made from quartz or borosilicate glass.
- the pressure in the reaction vessel is between 1 and 71 bar.
- the C0 2 is predominantly in the form of a gaseous phase.
- the C0 2 is predominantly in the form of a liquid phase.
- the ratio of Br 2 to C0 2 is between 1 : 1 and 1 : 1000 by weight.
- a composition of matter comprising a polar substrate presenting apposed surfaces and a mixture of C0 2 and Br 2 in contact with at least some of said apposed surfaces.
- the polar substrate is a non-carbonaceous polar substrate.
- the polar substrate is selected from the group consisting of silica, silica-based glasses, alumina and titania, and mixtures thereof.
- the polar substrate is in particulate form.
- the polar substrate is selected from sand, silica gel, powdered alumina, titania, quartz sand, glass spheres, and glass wool (fiberglass).
- the polar substrate, C0 2 and Br 2 are contained in a UV- and visible-light transparent region of a reaction vessel.
- the UV- and visible-light transparent region is transparent to light having a wavelength of 300 to 500 nm.
- the reaction vessel is made from quartz or borosilicate glass.
- the pressure in the reaction vessel is between 1 and 71 bar.
- the C0 2 is predominantly in the form of a gaseous phase.
- the C0 2 is predominantly in the form of a liquid phase.
- the ratio of Br 2 to C0 2 is between 1 : 1000 and 1 : 1 by weight.
- composition of matter comprising a polar substrate presenting apposed surfaces and a material which is predominantly elemental carbon deposited on a portion of said apposed surfaces.
- the molar ratio of bromine to carbon in said material is less than 1: 12.
- the molar ratio of bromine to carbon in said material is from 0: 12 to 1: 12.
- the composition of matter has been formed by a process in accordance with an embodiment of the invention.
- a reactor for utilizing sunlight and bromine to reduce C0 2 comprising a reaction vessel and a sunlight focuser, at least a region of the reaction vessel being transparent to UV and visible light and said focuser focusing at least some of said sunlight on said region.
- said region of the reaction vessel is transparent to light in at least the range of 300-500 nm wavelength.
- the reaction vessel is capable of withstanding an internal pressure of at least from 0 to 71 bar.
- the reaction vessel is constructed at least in part from quartz or borosilicate glass.
- the reactor further comprises a cooling mechanism for cooling a portion of the reaction vessel.
- the reaction vessel is configured to hold a mixture of Br 2 and C0 2 in contact with a polar substrate having apposed surfaces in said region. In some embodiments, the reaction vessel contains a mixture of Br 2 and C0 2 in contact with a polar substrate having apposed surfaces. In some embodiments, the focuser is a parabolic or paraboloid mirror. In some embodiments the reactor is equipped to track the motion of the sun so as to keep the sunlight focused on said region of the reaction vessel as the Earth rotates.
- the invention described herein solves some of the problems with existing solar- powered reactions for chemical reduction of carbon dioxide.
- the claimed process works well at temperatures near room temperature.
- the process also utilizes an inexpensive material as a photosensitizer, viz. liquid Br 2 .
- this material has never previously been identified as being chemically reactive with C0 2, but it has been sold for nearly 100 years as a commodity on worldwide markets.
- Its current production level about a half-million metric tons annually, is more than 10,000 times that of ruthenium.
- Its 2009 bulk price was only a bit over $1000 per metric ton (corresponding to $1 per kg, or about 1/6000 the cost of elemental ruthenium, or of CoPc photosensitizer).
- the overall content of bromine in the Earth's crust is 0.3 ppm, or 100 times that of ruthenium. Elemental bromine can easily be produced in most countries on Earth from sea water, which is 70 ppm bromine. However, its richest source on Earth is the contents of the Dead Sea, which is 5% bromine by weight. Indeed, Israel and the US each produce about 40% of the world's elemental bromine, with China accounting for most of the rest. Furthermore, unlike complex photosensitizers based on transition metals such as ruthenium or cobalt, elemental bromine itself strongly absorbs visible light, and therefore it can work directly as a photosensitizer for solar-powered photoreduction of C0 2 , as described herein.
- the process requires only a polar substrate presenting apposed surfaces, such as particulate or fibrous silica, titania or alumina; a reaction vessel capable of holding these materials at an elevated pressure; and light of sufficient energy and intensity, such as can be obtained in focused sunlight.
- a reaction vessel or the like that is transparent to UV and/or visible light, such transparency will generally be across the entire UV and visible range, but need not necessarily be so, provided that the transparency is through a range of wavelengths sufficient to enable the reaction to proceed.
- FIGs. 1A and IB are photographs of a reaction vessel after reaction of molecular bromine and C0 2 in accordance with an embodiment of the invention
- Fig. 2 shows possible intermediates and products from the reaction of molecular bromine with C0 2 , and their calculated energies, in accordance with an embodiment of the invention
- Fig. 3 is a photograph of a reaction vessel after reaction of molecular bromine and C0 2 in accordance with an embodiment of the invention
- FIG. 4 is a photograph of a reactor in accordance with an embodiment of the invention.
- Fig. 5 is a photograph of a reaction vessel after reaction of molecular bromine and C0 2 in accordance with an embodiment of the invention
- Figs. 6A and 6B are electron micrographs
- Fig. 6C is a scanning electron micrograph, of products of the reaction of molecular bromine and C0 2 in accordance with embodiments of the invention.
- Figs. 7A and 7B are perspective and cross-sectional views of a reactor constructed and operative in accordance with embodiments of the invention
- Fig. 7C is a cross-sectional view of a reaction vessel constructed and operative in accordance with embodiments of the invention and containing silicon dioxide, Br 2 and C0 2 .
- the presently claimed invention in various embodiments thereof, facilitates the utilization of solar energy to split C0 2 into a solid species containing chemically-reduced carbon, and 0 2 .
- the elemental analysis results obtained to date provide a direct demonstration only of the deposition of a solid material containing carbon, as a black film, on surfaces of crystalline alumina, titania, silica, or silica-based glasses, the concomitant formation of elemental oxygen is an inescapable conclusion based on well-established chemical principles (see below, under Identity of the Oxidized Photoproduct).
- ChemGlass all with internal diameters under 1 cm, were found to be suitable for these experiments.
- the C0 2 sample is most easily obtained, stored, and handled as a solid, i.e. as a block or chunk of dry ice, which is commercially available in this form to the general public from numerous sources. A chunk of dry ice is broken up into particles small enough to fit through the ⁇ 5-mm-diameter neck of the reaction vessel, immediately prior to transfer so as to minimize formation of water frost on its surfaces.
- solid C0 2 is the most convenient form to use for implementation on a small ( ⁇ 5 g) scale, in principle the C0 2 may be supplied as a gas.
- Br 2 is easily generated as needed in small quantities by mixing similar masses of solid NaBr and Mn0 2 in a glass vessel, adding concentrated sulfuric acid, and then distilling, with collection of the red Br 2 distillate into a dry-ice-chilled vessel.
- solid C0 2 these are readily available materials, even to the general public.
- the NaBr was obtained in a standard commercial packet sold at a swimming pool supply company; the concentrated sulfuric acid was a commercial drain cleaner; and the Mn0 2 was obtained from a sliced-open, unused standard AA-size 1.5V alkaline battery.
- a preferred embodiment of a small-scale photoreaction vessel is a ⁇ 1- cm outer diameter, ⁇ 10-cm-long fused-silica (quartz) test tube with a standard GL14 thread (ISO designation of a standard glass thread), combined with a GL14 cap closure with a poly- tetrafluoroethylene (PTFE) seal.
- a standard GL14 thread ISO designation of a standard glass thread
- PTFE poly- tetrafluoroethylene
- C0 2 will be most easily transported as a liquid, gas, or supercritical fluid, either in pipes or in pressurized vessels at ambient temperatures, and that it will remain in one of these fluid forms during its transfer into a larger photoreaction vessel.
- larger reaction vessels will be mostly metallic, e.g. stainless steel, with high-pressure couplings to permit feeding of fluid C0 2 and Br 2 , and containing tightly-sealed UV-transparent windows through which sunlight can be suitably focused.
- reaction vessel 16 7C and containing Br 2 , C0 2 and silicon dioxide, is held in place by the hub 18 of bicycle wheel 20; hub 18 is itself held in place by a plurality of spokes 22.
- the bottom of reaction vessel 16 protrudes through the bottom of the hub so that sunlight 12 can be focused thereupon by paraboloid reflector 14.
- the upper part of reaction vessel 16 remains inside hub 18.
- Inserted through the rim of the wheel is copper tubing 24, which wraps several times around hub 18 and then exits the wheel.
- Tubing 24, which is soldered to hub 18 using silver to maximize thermal contact therewith, may carry circulating coolant (e.g. ice water) therethrough, thereby cooling the upper part reaction vessel 16.
- coolant e.g. ice water
- the apparent motion of the sun across the sky is as high as -15 degrees per hour, or approximately 0.5 degrees (the angular extent of the sun) every 2 minutes.
- the device used to for rotating the sample and focusing optic simultaneously, thereby maintaining a fixed location of the focused solar image upon the sample was a hobbyists' telescope equatorial mount and tripod, obtained from Tasco.
- the telescope itself was removed from the equatorial mount by removing its mounting screws.
- the equatorial mount's elevation angle clamp was adjusted to correspond to the latitude of usage (43 degrees N). The correct elevation angle was reproducibly obtained to within about 1 degree, simply by leveling the tripod mount with reference to the built-in bubble level.
- the direction of true north was determined, relative to an exterior wall of a nearby building which was within ⁇ 5 degrees of north-south. This exterior wall was then used during all subsequent experiments as an azimuthal reference for positioning the tripod of the equatorial mount.
- the bubble-level and azimuthal references permitted the rapid and consistent visual alignment of the equatorial mount's rotation axis, to within ⁇ 2 degrees of parallel to the Earth's rotation axis. This in turn permitted tracking of the sun across the sky for periods of up to 20-30 min by adjustment of a single manual screw-knob on the equatorial mount; and for periods up to several hours with additional minor adjustments to a second screw-knob adjustment on the equatorial mount.
- the paraboloid reflectors were too large to be mounted on the same equatorial telescope mount used in experiments 1-3. However, their larger size and cylindrical symmetry facilitated pointing them accurately toward the sun while being hand-held. These reflectors all had circular holes at their rear, centered on the paraboloid axis. Furthermore, these reflectors were equipped with symmetrical sample- mounts that held the reactor vial along the same axis (see Fig. 4 for an example of the mounting device used, which was based on a simple bicycle wheel clamped to the outside of the paraboloid reflector). Thus, these reflectors could easily be aligned to point their axis directly towards the sun, simply by insuring that the shadow of the sample holder was centered on the rear hole in the reflector.
- ruby-red viscous liquid accumulates in the region of intense solar illumination, sometimes taking on the shape of a flattened droplet on the inside of the quartz or borosilicate tube containing the sample.
- the ruby-red color of this material is similar to that reported for known alkyl hypobromites [Bushong, (1896-96) Transactions of the Annual Meetings of the Kansas Academy of Science 15, 81-82; Walling and Padwa, J. Org. Chem. 27, 2976-2978 (1962); Roscher and Nguyen, J. Org. Chem. 50, 716-717 (1985)].
- Acyl hypobromites on the other hand, have been reported to have a distinct green color [Kogure et al., J. Mol.
- the ruby-red intermediate is less likely to represent bromoformyl hypobromite than the double adduct of Br 2 to C0 2 , namely Br 2 C(OBr) 2 , dibromo methyl dihypobromite.
- Br 2 C(OBr) 2 bromoformylhypobromite
- all other hypothetical adducts of one or more bromine atoms to C0 2 lack 8-electron valence shells for at least one atom, or else contain a highly-strained 3-member ring (specifically dibromodioxirane; see below), and are thus expected to be even less stable.
- the underlying silica gel did not immediately return to its starting color (which was orange-tinged due to the Br 2 ). Instead, it passed through a period of brownish coloration. This brown color was assumed to occur due to a temporary local accumulation of some other adsorbed polar material, which was nevertheless soluble in liquid-C0 2 -and therefore subsequently (over the course of several h) dissipated through diffusion.
- bromine appears to carry out at least two roles.
- Photoreactions of Br 2 are well known in chemistry, and include in particular the splitting of this molecule into two neutral Br atoms, upon visible light absorption. This photochemical splitting of Br 2 is the only plausible primary photochemical reaction that may be occurring at a significant rate at the onset of solar irradiation.
- a pair of Br atoms still does not carry enough energy, relative to the recombined diatomic molecule, to accomplish the splitting of a C0 2 molecule.
- This molecule has no resonance structures that satisfy the octet rule, and also none that lack a formal zwitterionic structure.
- Fig. 2 also includes triplet dibromocarbene, as well as its stable dimer tetrabromoethylene. These appear to be the most likely initial products if triplet 0 2 (i.e.
- ground-state molecular dioxygen is cleaved from any of the 3 indicated potential (singlet) precursors with the formula Br 2 C0 2 .
- the chart in Fig. 2 shows that it is at least in theory possible to carry out a bromine- sensitized solar photolysis reaction of C0 2 by using only a series of energetic jumps that are smaller than the quanta contained in visible photons.
- the chart furthermore suggests that initial stable end products might be bromocarbons.
- all known bromocarbons are thermodynamically unstable with respect to splitting into their constituent elements (i.e. with respect to liquid Br 2 , and graphite), and therefore the formation of solid bromocarbons (e.g. hexabromobenzene) would represent a storage of energy at least as great as that represented by formation of pure elemental carbon.
- Each of the two Br 2 additions might proceed by sequential addition of isolated solvated Br atoms, which accumulate under intense illumination of the Br 2 -containing solution, with the intermediate formation of a monobrominated radical species.
- subsequent endothermic steps in the overall process might then include: photolytic expulsion of Br 2 to form dibromodioxirane; and then an additional photolytic expulsion of triplet 0 2 to form a triplet dibromocarbene.
- the latter species is known to be just a bit higher in energy than singlet dibromocarbene, which is a reactive intermediate that is routinely made from bromoform and used by organic chemists in a variety of synthetic steps.
- Direct photolytic splitting of a dioxirane into a carbene plus molecular 0 2 has not apparently been reported.
- dioxiranes are well known to undergo other types of photochemical reaction upon light absorption into their UV absorption band near 350 nm.
- This UV absorption band has been detected not only in a variety of metastable dialkyldioxiranes, but also in the known molecule difluorodioxirane. This is a direct halogenated analog of dibromodioxirane that is stable enough to have had a number of its spectroscopic properties measured.
- dioxiranes can thermally rearrange to form the isomeric carbonyl oxides, which might also have a UV-induced photolysis process that would lead to photolytic release of molecular dioxygen plus dibromocarbene.
- the data in Fig. 2 support, at least weakly, the possibility of such a thermal rearrangement in the overall observed process, since the strained dibromodioxirane is only -70 kJ/mol lower in energy than the dibromocarbonyl oxide.
- dibromodioxirane has a photoreactive UV absorption band that is similar to the ⁇ 350-nm absorption band of difluorodioxirane.
- the overall photochemical splitting in this scheme would then be storing a bit less than 50% of the combined energy of the 4 photons.
- the formation of reduced C from C0 2 requires at least one other product with an increase in its oxidation state, relative to the starting materials.
- Other than 0 2 there are no molecules with 0:C ratios greater than 2, or that represent chemically oxidized species, that are kinetically stable near room temperature, and that could be made from the elements present in the reaction container.
- the most obvious other possible oxidized product molecules with 0:C > 2 are, like 0 2 , carbon-less and gaseous near room temperature. These include 0 3 (ozone) and the metastable oxides of bromine.
- the polar substrate e.g. silica or alumina
- the reaction vial might undergo an oxidation reaction when the elemental carbon is produced.
- the polar substrate e.g. silica or alumina
- the 0:C ratio in carbon monoxide (CO) is less than in the starting C0 2 , and it contains no atoms with increased oxidation numbers, so a hypothetical CO product could not contribute to the requisite elemental and redox balancing.
- the presence of any significant concentration of 0 2 in the gas phase means also that any CO formed would also be expected to be metastable, so CO also is unlikely to be a significant by-product of this photochemical reaction, although it also seems likely that it is produced in small quantities, i.e. far below a 1: 1 stoichiometry.
- Experiment #1 In late December, a sample consisting of -0.5 g washed quartz sand, -0.5 g Owens-Corning type-E fiberglass ("glass wool"), 75 ⁇ freshly distilled Br 2 , and 3 g solid C0 2 were subjected to ⁇ 2-min episodes of illumination with focused sunlight. These all occurred between 11:30 and 13:00 Eastern Standard Time, when the sun was at an elevation between 20 and 25 degrees above the horizon at latitude 42.9 degrees. The ambient outdoor temperature was between -5 and 0°C during this time period. Due to challenges in maintaining alignment of the focusing mirror, it is estimated that the actual total illumination time with well-focused sunlight was ⁇ 30 min.
- the glass wool was then removed from the quartz tube with tweezers, placed in 1.5-mL polyethylene Eppendorf centrifuge tube, tightly capped and sealed with Parafilm , and then subjected to 1 week of digestion, at 80°C, with 4 M NaCl containing additionally 1 M NaOH, with vigorous manual agitation for several minutes each day.
- the glass wool that was not covered by the black carbonaceous coating disintegrated into microscopically small pieces.
- the black colored material remained in patches as large as -1 mm, over the entire duration of this treatment, as well as after subsequent extensive washing with deionized water. When examined by eye and under an optical microscope, these patches clearly still contained some mats of glass fibers.
- the chemical coating of these mats of fibers with the black colored photoproduct served to protect them from chemical attack by aqueous salt solutions. Such solutions are otherwise clearly capable of causing the mechanical weakening, and eventual breakdown, of such glass fibers.
- microcentrifuge (000x g) after each of these washes. The final pellet was dried at 80°C for 48 h, and weighed. Its weight was 5 mg, and it formed a cohesive mass that simplified its transfer to and from a weighing boat within the Mettler analytic balance used for the mass determination.
- Experiment #2 In late February, a sample consisting of 0.5 g silica gel (Sorbent Technologies, 40-70 micron particle size), 1 g of 3-mm glass spheres (marketed as bacterial sample spreaders for culture plates, but never used for this purpose) 20 ⁇ freshly distilled Br 2 , and 3 g solid C0 2 were subjected to focused sunlight under cloudless, but slightly hazy skies on both days. On the first day, periods of illumination began at 11:30 EST, and production of black photoproduct continued intermittently until 2:30 p.m. On the second day, illumination began at 11 a.m. EST and continued intermittently until 1 p.m.
- the sun was at an elevation between 31 and 42 degrees above the horizon at latitude 42.9 degrees.
- the ambient outdoor temperature was between 0°C and 15°C during these time periods.
- the sample container was removed from its clamp, and subjected to -30 s of gentle shaking, to disrupt the spots where blackened photoproduct had formed, and release this photoproduct as tiny black fibrous specks within the silica gel, which was otherwise orange-colored due to adsorbed Br 2 .
- Experiment #4 In late April, a sample consisting of 0.25 g powdered titanium dioxide (titania; Degussa P25) at the bottom, 10 ⁇ Br 2 , and 3 g solid C0 2 were subjected to three separate episodes of illumination with focused sunlight, each 2-5 min in duration. These all occurred between 10:00 and 10: 15 Eastern Daylight Time, when the sun was at an elevation between 45 and 56 degrees above the horizon. The ambient outdoor temperature was between 10° and 20°C during this time period. A total of 3 spots of blackened material were produced, each similar in size and appearance to those that had previously been produced with alumina (see Experiment #3). Subsequently, the pressure was released and the sample was allowed to dry. An attempt was made to dissolve the alumina in the sample by treating with 10 M NaOH at 80°C for 1 week. However, the sample never significantly dissolved, and as a result, no elemental analysis was undertaken.
- the results of dual combustion analyses showed that the illuminated sample contained 4.5% C (4.69%, 4.36%), while the unilluminated control sample contained 0.6% C (0.44%, 0.72%).
- the bromine- sensitized solar photolysis therefore produced at least 1.6 mg (3.9% of 41 mg) of reduced carbon from C0 2 , by means of at most 40 s worth of solar illumination captured by the 12-inch-diameter reflector.
- the overall efficiency of solar energy storage can be computed from this result.
- the approximate area of solar collection was 0.07 m (taking into account some occlusion of the reflector by the hub and spokes); the time of collection was 40 s; and the solar constant is 1366 W/m .
- the total amount of solar energy collected was thus the product of these values, or 3.8 kJ.
- the amount of energy stored in the 1.6 mg of reduced carbon (0.13 mmol) was 0.00013 mol ⁇ 400 kJ moP, or 0.052 kJ.
- the overall efficiency of energy storage was thus 0.052/3.8, or about 1.3%. Although this is much lower than the values achieved for typical silicon solar cells, it is roughly comparable to plant-based photosynthesis.
- This experiment (#5) produced a quantity of product large enough for a reliable measurement of the relative amounts of bromine and carbon in the product.
- Bromine elemental analysis showed that this sample contained approximately 2.1% bromine (1.80% and 2.50% in repeat analyses), or a bit more than half of the 3.9% carbon content by weight.
- the observed C/Br weight ratio of 1.9 corresponds, however, to a molar ratio greater than 12. That is, the product molecules have, on average, only one bromine atom incorporated for evey 12 carbon atoms. This result suggests that the bromine acts photocatalytically, i.e. that each Br 2 molecule in the reaction volume can carry out reduction of multiple C0 2 molecules.
- Experiment #6 In mid-November, 0.1 g quartz wool was stuffed tightly into the bottom of a 6-mL-capacity custom-made borosilicate tube (of similar manufacture to that used in experiment #5), and dried at 80 Q C under a stream of dry air for 1 h. At 11:30, 10 ⁇ ⁇ of Br 2 was added, and then, within 1 min, 0.05 g solid C0 2 . (The solid C0 2 was a single compact roughly spherical chunk that fit through the 4-mm-diameter neck of the borosilicate reaction flask.
- the quartz wool was removed from the reaction vessel, and the blackened regions were cut away from a control sample, consisting of the remainder of the quartz wool that was mostly unreacted.
- the blackened and control samples were heated for 24 h at 75 Q C in order to allow volatile materials to evaporate, each with a small ( ⁇ 3 cm) piece of fresh Kimwipe ® stuffed into the top of the drying tube in order to collect any less-volatile materials that might easily re-condense.
- the tube with the blackened quartz wool did show the presence of a brownish material on the Kimwipe .
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IL221963A IL221963A (en) | 2010-03-14 | 2012-09-13 | Bromine-sensitized solar photolysis of carbon dioxide |
US15/011,677 US9885111B2 (en) | 2010-03-14 | 2016-02-01 | Bromine-sensitized solar photolysis of carbon dioxide |
IL255933A IL255933A (en) | 2010-03-14 | 2017-11-26 | Bromine-sensitized solar photolysis of carbon dioxide |
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US3977952A (en) * | 1973-08-16 | 1976-08-31 | C. F. Spiess & Sohn | Process for decomposing carbon-containing compounds |
US5045288A (en) * | 1989-09-15 | 1991-09-03 | Arizona Board Of Regents, A Body Corporate Acting On Behalf Of Arizona State University | Gas-solid photocatalytic oxidation of environmental pollutants |
US5854967A (en) * | 1989-10-30 | 1998-12-29 | Cerus Corporation | Device and method for photoactivation |
KR100944539B1 (en) * | 2009-12-30 | 2010-03-03 | (주) 오씨아드 | Method and apparatus for removing carbon dioxide from exhaust gas by combustion using alkalinized sea water |
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US3977952A (en) * | 1973-08-16 | 1976-08-31 | C. F. Spiess & Sohn | Process for decomposing carbon-containing compounds |
US5045288A (en) * | 1989-09-15 | 1991-09-03 | Arizona Board Of Regents, A Body Corporate Acting On Behalf Of Arizona State University | Gas-solid photocatalytic oxidation of environmental pollutants |
US5854967A (en) * | 1989-10-30 | 1998-12-29 | Cerus Corporation | Device and method for photoactivation |
KR100944539B1 (en) * | 2009-12-30 | 2010-03-03 | (주) 오씨아드 | Method and apparatus for removing carbon dioxide from exhaust gas by combustion using alkalinized sea water |
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