JP5965605B2 - Carbon dioxide conversion method and carbon dioxide conversion catalyst - Google Patents
Carbon dioxide conversion method and carbon dioxide conversion catalyst Download PDFInfo
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- JP5965605B2 JP5965605B2 JP2011227481A JP2011227481A JP5965605B2 JP 5965605 B2 JP5965605 B2 JP 5965605B2 JP 2011227481 A JP2011227481 A JP 2011227481A JP 2011227481 A JP2011227481 A JP 2011227481A JP 5965605 B2 JP5965605 B2 JP 5965605B2
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- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 title claims description 178
- 239000001569 carbon dioxide Substances 0.000 title claims description 89
- 229910002092 carbon dioxide Inorganic materials 0.000 title claims description 89
- 239000003054 catalyst Substances 0.000 title claims description 54
- 238000006243 chemical reaction Methods 0.000 title claims description 41
- 238000000034 method Methods 0.000 title claims description 25
- NUJOXMJBOLGQSY-UHFFFAOYSA-N manganese dioxide Chemical compound O=[Mn]=O NUJOXMJBOLGQSY-UHFFFAOYSA-N 0.000 claims description 127
- 239000007864 aqueous solution Substances 0.000 claims description 103
- JVTAAEKCZFNVCJ-UHFFFAOYSA-N lactic acid Chemical compound CC(O)C(O)=O JVTAAEKCZFNVCJ-UHFFFAOYSA-N 0.000 claims description 42
- BDAGIHXWWSANSR-UHFFFAOYSA-N methanoic acid Natural products OC=O BDAGIHXWWSANSR-UHFFFAOYSA-N 0.000 claims description 37
- QTBSBXVTEAMEQO-UHFFFAOYSA-N Acetic acid Chemical compound CC(O)=O QTBSBXVTEAMEQO-UHFFFAOYSA-N 0.000 claims description 36
- KDYFGRWQOYBRFD-UHFFFAOYSA-N succinic acid Chemical compound OC(=O)CCC(O)=O KDYFGRWQOYBRFD-UHFFFAOYSA-N 0.000 claims description 23
- 239000004310 lactic acid Substances 0.000 claims description 21
- 235000014655 lactic acid Nutrition 0.000 claims description 21
- 235000019253 formic acid Nutrition 0.000 claims description 19
- OSWFIVFLDKOXQC-UHFFFAOYSA-N 4-(3-methoxyphenyl)aniline Chemical compound COC1=CC=CC(C=2C=CC(N)=CC=2)=C1 OSWFIVFLDKOXQC-UHFFFAOYSA-N 0.000 claims description 18
- 239000000872 buffer Substances 0.000 claims description 15
- 230000002378 acidificating effect Effects 0.000 claims description 14
- LENZDBCJOHFCAS-UHFFFAOYSA-N tris Chemical compound OCC(N)(CO)CO LENZDBCJOHFCAS-UHFFFAOYSA-N 0.000 claims description 12
- 239000013078 crystal Substances 0.000 claims description 10
- 239000001384 succinic acid Substances 0.000 claims description 10
- BTBUEUYNUDRHOZ-UHFFFAOYSA-N Borate Chemical compound [O-]B([O-])[O-] BTBUEUYNUDRHOZ-UHFFFAOYSA-N 0.000 claims description 7
- 239000007853 buffer solution Substances 0.000 claims description 7
- 239000000243 solution Substances 0.000 claims description 7
- 150000004696 coordination complex Chemical class 0.000 claims description 5
- 235000011054 acetic acid Nutrition 0.000 claims description 3
- -1 hydrogencarbonate ions Chemical class 0.000 claims description 3
- 230000007935 neutral effect Effects 0.000 claims description 3
- QCBXSTAHRWEYAH-UHFFFAOYSA-N 1-[4-(2-hydroxyethyl)piperidin-1-yl]ethanesulfonic acid Chemical compound OS(=O)(=O)C(C)N1CCC(CCO)CC1 QCBXSTAHRWEYAH-UHFFFAOYSA-N 0.000 claims description 2
- 235000011044 succinic acid Nutrition 0.000 claims description 2
- 239000010970 precious metal Substances 0.000 claims 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 24
- 150000001732 carboxylic acid derivatives Chemical class 0.000 description 22
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 18
- KDLHZDBZIXYQEI-UHFFFAOYSA-N Palladium Chemical compound [Pd] KDLHZDBZIXYQEI-UHFFFAOYSA-N 0.000 description 16
- BVKZGUZCCUSVTD-UHFFFAOYSA-M Bicarbonate Chemical compound OC([O-])=O BVKZGUZCCUSVTD-UHFFFAOYSA-M 0.000 description 11
- 238000003756 stirring Methods 0.000 description 10
- 238000002441 X-ray diffraction Methods 0.000 description 9
- 150000002894 organic compounds Chemical class 0.000 description 9
- 239000000126 substance Substances 0.000 description 9
- 239000007983 Tris buffer Substances 0.000 description 8
- 239000011521 glass Substances 0.000 description 8
- 229910021642 ultra pure water Inorganic materials 0.000 description 8
- 239000012498 ultrapure water Substances 0.000 description 8
- JKMHFZQWWAIEOD-UHFFFAOYSA-N 2-[4-(2-hydroxyethyl)piperazin-1-yl]ethanesulfonic acid Chemical compound OCC[NH+]1CCN(CCS([O-])(=O)=O)CC1 JKMHFZQWWAIEOD-UHFFFAOYSA-N 0.000 description 6
- 239000003153 chemical reaction reagent Substances 0.000 description 6
- 238000002474 experimental method Methods 0.000 description 6
- PCHJSUWPFVWCPO-UHFFFAOYSA-N gold Chemical compound [Au] PCHJSUWPFVWCPO-UHFFFAOYSA-N 0.000 description 6
- 229910052737 gold Inorganic materials 0.000 description 6
- 239000010931 gold Substances 0.000 description 6
- 125000000896 monocarboxylic acid group Chemical group 0.000 description 6
- 150000007524 organic acids Chemical class 0.000 description 6
- 229910052763 palladium Inorganic materials 0.000 description 6
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 5
- 229910052799 carbon Inorganic materials 0.000 description 5
- 239000011572 manganese Substances 0.000 description 5
- 229910000510 noble metal Inorganic materials 0.000 description 5
- 239000012085 test solution Substances 0.000 description 5
- JVTAAEKCZFNVCJ-REOHCLBHSA-N L-lactic acid Chemical compound C[C@H](O)C(O)=O JVTAAEKCZFNVCJ-REOHCLBHSA-N 0.000 description 4
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 4
- 239000004809 Teflon Substances 0.000 description 4
- 229920006362 Teflon® Polymers 0.000 description 4
- AMWRITDGCCNYAT-UHFFFAOYSA-L hydroxy(oxo)manganese;manganese Chemical compound [Mn].O[Mn]=O.O[Mn]=O AMWRITDGCCNYAT-UHFFFAOYSA-L 0.000 description 4
- 150000002697 manganese compounds Chemical class 0.000 description 4
- 239000000463 material Substances 0.000 description 4
- 239000012528 membrane Substances 0.000 description 4
- 238000005374 membrane filtration Methods 0.000 description 4
- 229910001220 stainless steel Inorganic materials 0.000 description 4
- 239000010935 stainless steel Substances 0.000 description 4
- CSCPPACGZOOCGX-UHFFFAOYSA-N Acetone Chemical compound CC(C)=O CSCPPACGZOOCGX-UHFFFAOYSA-N 0.000 description 3
- UHOVQNZJYSORNB-UHFFFAOYSA-N Benzene Chemical compound C1=CC=CC=C1 UHOVQNZJYSORNB-UHFFFAOYSA-N 0.000 description 3
- MHAJPDPJQMAIIY-UHFFFAOYSA-N Hydrogen peroxide Chemical compound OO MHAJPDPJQMAIIY-UHFFFAOYSA-N 0.000 description 3
- KJTLSVCANCCWHF-UHFFFAOYSA-N Ruthenium Chemical compound [Ru] KJTLSVCANCCWHF-UHFFFAOYSA-N 0.000 description 3
- 239000002253 acid Substances 0.000 description 3
- 238000010306 acid treatment Methods 0.000 description 3
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 3
- KGBXLFKZBHKPEV-UHFFFAOYSA-N boric acid Chemical compound OB(O)O KGBXLFKZBHKPEV-UHFFFAOYSA-N 0.000 description 3
- 239000004327 boric acid Substances 0.000 description 3
- KDYFGRWQOYBRFD-NUQCWPJISA-N butanedioic acid Chemical compound O[14C](=O)CC[14C](O)=O KDYFGRWQOYBRFD-NUQCWPJISA-N 0.000 description 3
- 150000001735 carboxylic acids Chemical class 0.000 description 3
- 238000010304 firing Methods 0.000 description 3
- 239000007789 gas Substances 0.000 description 3
- 238000010438 heat treatment Methods 0.000 description 3
- IPJKJLXEVHOKSE-UHFFFAOYSA-L manganese dihydroxide Chemical compound [OH-].[OH-].[Mn+2] IPJKJLXEVHOKSE-UHFFFAOYSA-L 0.000 description 3
- 238000004519 manufacturing process Methods 0.000 description 3
- 239000001301 oxygen Substances 0.000 description 3
- 229910052760 oxygen Inorganic materials 0.000 description 3
- 229910052707 ruthenium Inorganic materials 0.000 description 3
- UIIMBOGNXHQVGW-UHFFFAOYSA-N sodium;hydron;carbonate Chemical compound [Na+].OC(O)=O UIIMBOGNXHQVGW-UHFFFAOYSA-N 0.000 description 3
- IKHGUXGNUITLKF-UHFFFAOYSA-N Acetaldehyde Chemical compound CC=O IKHGUXGNUITLKF-UHFFFAOYSA-N 0.000 description 2
- 229910003771 Gold(I) chloride Inorganic materials 0.000 description 2
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 description 2
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 description 2
- 229910021380 Manganese Chloride Inorganic materials 0.000 description 2
- GLFNIEUTAYBVOC-UHFFFAOYSA-L Manganese chloride Chemical compound Cl[Mn]Cl GLFNIEUTAYBVOC-UHFFFAOYSA-L 0.000 description 2
- UIIMBOGNXHQVGW-UHFFFAOYSA-M Sodium bicarbonate Chemical compound [Na+].OC([O-])=O UIIMBOGNXHQVGW-UHFFFAOYSA-M 0.000 description 2
- UIIMBOGNXHQVGW-DEQYMQKBSA-M Sodium bicarbonate-14C Chemical compound [Na+].O[14C]([O-])=O UIIMBOGNXHQVGW-DEQYMQKBSA-M 0.000 description 2
- 238000003917 TEM image Methods 0.000 description 2
- 239000003513 alkali Substances 0.000 description 2
- 238000004458 analytical method Methods 0.000 description 2
- 229910017052 cobalt Inorganic materials 0.000 description 2
- 239000010941 cobalt Substances 0.000 description 2
- GUTLYIVDDKVIGB-UHFFFAOYSA-N cobalt atom Chemical compound [Co] GUTLYIVDDKVIGB-UHFFFAOYSA-N 0.000 description 2
- FDWREHZXQUYJFJ-UHFFFAOYSA-M gold monochloride Chemical compound [Cl-].[Au+] FDWREHZXQUYJFJ-UHFFFAOYSA-M 0.000 description 2
- 229910052748 manganese Inorganic materials 0.000 description 2
- 235000002867 manganese chloride Nutrition 0.000 description 2
- 239000011565 manganese chloride Substances 0.000 description 2
- 229940099607 manganese chloride Drugs 0.000 description 2
- 229910001437 manganese ion Inorganic materials 0.000 description 2
- 229940099596 manganese sulfate Drugs 0.000 description 2
- 235000007079 manganese sulphate Nutrition 0.000 description 2
- 239000011702 manganese sulphate Substances 0.000 description 2
- SQQMAOCOWKFBNP-UHFFFAOYSA-L manganese(II) sulfate Chemical compound [Mn+2].[O-]S([O-])(=O)=O SQQMAOCOWKFBNP-UHFFFAOYSA-L 0.000 description 2
- 239000004417 polycarbonate Substances 0.000 description 2
- 229920000515 polycarbonate Polymers 0.000 description 2
- 238000005070 sampling Methods 0.000 description 2
- 239000007995 HEPES buffer Substances 0.000 description 1
- 229910015643 LiMn 2 O 4 Inorganic materials 0.000 description 1
- WAEMQWOKJMHJLA-UHFFFAOYSA-N Manganese(2+) Chemical compound [Mn+2] WAEMQWOKJMHJLA-UHFFFAOYSA-N 0.000 description 1
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 description 1
- JAWMENYCRQKKJY-UHFFFAOYSA-N [3-(2,4,6,7-tetrahydrotriazolo[4,5-c]pyridin-5-ylmethyl)-1-oxa-2,8-diazaspiro[4.5]dec-2-en-8-yl]-[2-[[3-(trifluoromethoxy)phenyl]methylamino]pyrimidin-5-yl]methanone Chemical compound N1N=NC=2CN(CCC=21)CC1=NOC2(C1)CCN(CC2)C(=O)C=1C=NC(=NC=1)NCC1=CC(=CC=C1)OC(F)(F)F JAWMENYCRQKKJY-UHFFFAOYSA-N 0.000 description 1
- LBBLDJJXDUQFQU-UHFFFAOYSA-N [C].[C].[C] Chemical compound [C].[C].[C] LBBLDJJXDUQFQU-UHFFFAOYSA-N 0.000 description 1
- GOPYZMJAIPBUGX-UHFFFAOYSA-N [O-2].[O-2].[Mn+4] Chemical class [O-2].[O-2].[Mn+4] GOPYZMJAIPBUGX-UHFFFAOYSA-N 0.000 description 1
- 239000011203 carbon fibre reinforced carbon Substances 0.000 description 1
- 230000003197 catalytic effect Effects 0.000 description 1
- 239000000919 ceramic Substances 0.000 description 1
- 238000011109 contamination Methods 0.000 description 1
- 238000001816 cooling Methods 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 239000000446 fuel Substances 0.000 description 1
- 238000005984 hydrogenation reaction Methods 0.000 description 1
- 235000006748 manganese carbonate Nutrition 0.000 description 1
- 239000011656 manganese carbonate Substances 0.000 description 1
- 229940093474 manganese carbonate Drugs 0.000 description 1
- MIVBAHRSNUNMPP-UHFFFAOYSA-N manganese(2+);dinitrate Chemical compound [Mn+2].[O-][N+]([O-])=O.[O-][N+]([O-])=O MIVBAHRSNUNMPP-UHFFFAOYSA-N 0.000 description 1
- WPBNNNQJVZRUHP-UHFFFAOYSA-L manganese(2+);methyl n-[[2-(methoxycarbonylcarbamothioylamino)phenyl]carbamothioyl]carbamate;n-[2-(sulfidocarbothioylamino)ethyl]carbamodithioate Chemical compound [Mn+2].[S-]C(=S)NCCNC([S-])=S.COC(=O)NC(=S)NC1=CC=CC=C1NC(=S)NC(=O)OC WPBNNNQJVZRUHP-UHFFFAOYSA-L 0.000 description 1
- RGVLTEMOWXGQOS-UHFFFAOYSA-L manganese(2+);oxalate Chemical compound [Mn+2].[O-]C(=O)C([O-])=O RGVLTEMOWXGQOS-UHFFFAOYSA-L 0.000 description 1
- 229910000016 manganese(II) carbonate Inorganic materials 0.000 description 1
- XMWCXZJXESXBBY-UHFFFAOYSA-L manganese(ii) carbonate Chemical compound [Mn+2].[O-]C([O-])=O XMWCXZJXESXBBY-UHFFFAOYSA-L 0.000 description 1
- 238000002844 melting Methods 0.000 description 1
- 230000008018 melting Effects 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 238000001683 neutron diffraction Methods 0.000 description 1
- 229910017604 nitric acid Inorganic materials 0.000 description 1
- 239000002245 particle Substances 0.000 description 1
- 239000008055 phosphate buffer solution Substances 0.000 description 1
- 239000004033 plastic Substances 0.000 description 1
- 239000000843 powder Substances 0.000 description 1
- 239000002994 raw material Substances 0.000 description 1
- 235000017557 sodium bicarbonate Nutrition 0.000 description 1
- 229910000030 sodium bicarbonate Inorganic materials 0.000 description 1
- KDYFGRWQOYBRFD-UHFFFAOYSA-L succinate(2-) Chemical compound [O-]C(=O)CCC([O-])=O KDYFGRWQOYBRFD-UHFFFAOYSA-L 0.000 description 1
- 238000001308 synthesis method Methods 0.000 description 1
- 230000002194 synthesizing effect Effects 0.000 description 1
- 238000010792 warming Methods 0.000 description 1
Classifications
-
- 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
- Y02P20/50—Improvements relating to the production of bulk chemicals
- Y02P20/52—Improvements relating to the production of bulk chemicals using catalysts, e.g. selective catalysts
Landscapes
- Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
- Low-Molecular Organic Synthesis Reactions Using Catalysts (AREA)
- Catalysts (AREA)
Description
本発明は、二酸化炭素を蟻酸（ＨＣＯＯＨ）、酢酸（ＣＨ３ＣＯＯＨ）、コハク酸（ＨＯＯＨ２Ｃ−ＣＨ２ＣＯＯＨ）または乳酸（ＣＨ３ＣＨ（ＯＨ）ＣＯＯＨ）等のカルボン酸（カルボシル基ＣＯＯＨを含む酸）等の有機化合物に変換する方法および二酸化炭素変換用触媒に関するものである。 In the present invention, carbon dioxide is converted into carboxylic acid (carbosyl group COOH) such as formic acid (HCOOH), acetic acid (CH 3 COOH), succinic acid (HOOH 2 C—CH 2 COOH) or lactic acid (CH 3 CH (OH) COOH). And a catalyst for carbon dioxide conversion.
温暖化の進行に対処するため、種々の科学技術が模索されている。中でも、二酸化炭素を有用な物質に変換して固定する機能を有した触媒材料の開発に対する期待は極めて高い。二酸化マンガンの結晶構造にはアルファ型、ベータ型、ガンマ型、ラムダ型、イプシロン型、デルタ型、アール型（以下、ラムズデライト型、またはＲ型とも表記する）など種々の結晶構造が存在することが知られている。本発明者は、これまでに特許文献１においてＲ型の結晶構造を高純度に結晶内に含んだ二酸化マンガン触媒が二酸化炭素ガスＣＯ２をアセトン（ＣＨ３ＣＯＣＨ３）、アセトアルデヒト（ＣＨ３ＣＨＯ）、および酢酸（ＣＨ３ＣＯＯＨ）、等に変換する機能性を示すことを報告している。 In order to cope with the progress of global warming, various science and technology are being sought. In particular, the expectation for the development of a catalyst material having a function of converting and fixing carbon dioxide to a useful substance is extremely high. There are various crystal structures of manganese dioxide such as alpha, beta, gamma, lambda, epsilon, delta, and arele (hereinafter also referred to as ramsdelite or R). It has been known. The inventor of the present invention has heretofore proposed that a manganese dioxide catalyst containing an R-type crystal structure with high purity in Patent Document 1 contains carbon dioxide gas CO 2 as acetone (CH 3 COCH 3 ) and acetaldehyde (CH 3 CHO). ), And acetic acid (CH 3 COOH), etc.
二酸化炭素を他の物質に変換する機能性を有した触媒材料としては、二酸化炭素をポリカーボナートに変換するコバルト触媒（非特許文献１）や、超臨界二酸化炭素中における二酸化炭素の高速水素化反応を利用した蟻酸に変換するルテニウム触媒（特許文献２）等が存在する。 Examples of a catalyst material having a function of converting carbon dioxide into another substance include a cobalt catalyst (non-patent document 1) that converts carbon dioxide into polycarbonate, and a high-speed hydrogenation reaction of carbon dioxide in supercritical carbon dioxide. There is a ruthenium catalyst (Patent Document 2) that converts to formic acid using benzene.
特許文献１では、二酸化マンガン触媒の存在下で二酸化炭素ガスを他の物質に変換しているが、その変換効率が低いことが実用上問題であった。また、非特許文献１で使用されるコバルト触媒は高価であり、プラスチックの原料となるポリカーボナートへの変換に機能性が限られる。特許文献２で使用されるルテニウム触媒も高価であり、また二酸化炭素を超臨界にする必要があるなどコスト的な問題を有している。 In Patent Document 1, carbon dioxide gas is converted into another substance in the presence of a manganese dioxide catalyst. However, the low conversion efficiency has been a practical problem. Further, the cobalt catalyst used in Non-Patent Document 1 is expensive, and its functionality is limited to the conversion to polycarbonate which is a raw material for plastic. The ruthenium catalyst used in Patent Document 2 is also expensive and has a cost problem such as the necessity of making carbon dioxide supercritical.
そこで本発明は以上の通りの背景から、二酸化炭素を有機化合物に変換することができる方法および二酸化炭素変換用触媒を提供することを課題としている。 Then, this invention makes it a subject to provide the method and the catalyst for a carbon dioxide conversion which can convert a carbon dioxide into an organic compound from the background as mentioned above.
本発明の二酸化炭素の変換方法は、二酸化炭素を溶解した弱酸性、中性またはアルカリ性の水溶液中に、ラムズデライト型の結晶構造を含む二酸化マンガンを共存させ、前記水溶液中に溶存する炭酸水素イオンを、蟻酸、酢酸、コハク酸および乳酸からなる群から選ばれる少なくとも１種に変換することを特徴とする。 The method for converting carbon dioxide according to the present invention comprises a weakly acidic, neutral or alkaline aqueous solution in which carbon dioxide is dissolved in the presence of manganese dioxide containing a ramsdelite type crystal structure, and hydrogen carbonate ions dissolved in the aqueous solution. Is converted into at least one selected from the group consisting of formic acid, acetic acid, succinic acid and lactic acid .
この二酸化炭素の変換方法においては、前記水溶液が、その液性が弱酸性からアルカリ性に保たれた水溶液、または、アルカリ性緩衝液であることが好ましい。 In this carbon dioxide conversion method, the aqueous solution is preferably an aqueous solution whose liquidity is maintained from weakly acidic to alkaline, or an alkaline buffer.
また、この二酸化炭素の変換方法においては、前記アルカリ性緩衝溶液が、アルカリ性の、トリス（ヒドロキシメチル）アミノメタン、４−（２−ヒドロキシエチル）−１−ピペリジニルエタンスルホン酸（Trishydroxymethyl amino methane、4-(2-hydroxyethl)-1-piperazineethanesulfonic acid）、ホウ酸緩衝溶液、および重炭酸塩緩衝液からなる群から選ばれる少なくとも１種であることが好ましい。 Moreover, in this carbon dioxide conversion method, the alkaline buffer solution contains alkaline tris (hydroxymethyl) aminomethane, 4- (2-hydroxyethyl) -1-piperidinylethanesulfonic acid ( Trishydroxymethyl amino methane), 4- (2-hydroxyethl) -1-piperazineethanesulfonic acid ) , borate buffer solution, and bicarbonate buffer solution are preferred.
さらにまた、この二酸化炭素の変換方法においては、前記水溶液中に、さらに貴金属錯体を共存させることが好ましい。 Furthermore, in this carbon dioxide conversion method, it is preferable that a noble metal complex coexist in the aqueous solution.
そして、この二酸化炭素の変換方法においては、前記水溶液の温度が、１００℃以下であることが好ましい。 In this carbon dioxide conversion method, the temperature of the aqueous solution is preferably 100 ° C. or lower.
また、この二酸化炭素の変換方法においては、前記水溶液と、前記二酸化マンガンとを密閉容器内に封入し、この密閉容器内に前記二酸化炭素を圧入して前記水溶液中に前記二酸化炭素を溶解させることが好ましい。 Further, in this carbon dioxide conversion method, the aqueous solution and the manganese dioxide are sealed in a sealed container, and the carbon dioxide is injected into the sealed container to dissolve the carbon dioxide in the aqueous solution. Is preferred.
また、本発明の二酸化炭素変換用触媒は、上記の二酸化炭素の変換方法に用いられる触媒であって、ラムズデライト型の結晶構造を含む二酸化マンガンで構成されることを特徴とする。 The carbon dioxide conversion catalyst of the present invention is a catalyst used in the carbon dioxide conversion method described above, and is characterized by being composed of manganese dioxide containing a ramsdelite type crystal structure.
本発明によれば、ラムズデライト型の結晶構造を含む二酸化マンガンを用いて、二酸化炭素を有機化合物に変換することができる。 According to the present invention, carbon dioxide can be converted into an organic compound using manganese dioxide containing a ramsdelite type crystal structure.
以下、本発明を詳細に説明する。 Hereinafter, the present invention will be described in detail.
本発明は、上記のとおり、二酸化炭素を溶解した弱酸性、中性またはアルカリ性の水溶液中に、ラムズデライト型の結晶構造を含む二酸化マンガン（以下、Ｒ型二酸化マンガンともいう）を共存させ、二酸化炭素が水溶液中に溶解した際に発生する炭酸水素イオン（ＨＣＯ３ −）を有機化合物に変換する。 In the present invention, as described above, manganese dioxide containing a ramsdelite type crystal structure (hereinafter also referred to as R-type manganese dioxide) is allowed to coexist in a weakly acidic, neutral or alkaline aqueous solution in which carbon dioxide is dissolved. Hydrogen carbonate ions (HCO 3 − ) generated when carbon is dissolved in an aqueous solution are converted into an organic compound.
ここで、Ｒ型二酸化マンガンは、例えば、本発明者が上記特許文献１において報告している方法によって合成される。具体的には、炭酸マンガン、水酸化マンガン、塩化マンガン、硫酸マンガン、硝酸マンガン、シュウ酸マンガン等の２価のマンガン化合物を焼成し、これを酸処理することで得られる。 Here, the R-type manganese dioxide is synthesized, for example, by the method reported by the inventor in Patent Document 1 above. Specifically, it can be obtained by firing a divalent manganese compound such as manganese carbonate, manganese hydroxide, manganese chloride, manganese sulfate, manganese nitrate, manganese oxalate, and subjecting it to an acid treatment.
焼成温度は、例えば１８０℃〜３００℃であり、焼成時間は、１時間〜２０時間程度である。酸処理は、希塩酸、希硫酸、希硝酸等の希酸中に被処理物を添加し、これを１０分〜３時間程度撹拌することによってなされる。この酸処理は、１回または２回以上繰り返して行うことができる。 The firing temperature is, for example, 180 ° C. to 300 ° C., and the firing time is about 1 hour to 20 hours. The acid treatment is performed by adding an object to be treated in a dilute acid such as dilute hydrochloric acid, dilute sulfuric acid, dilute nitric acid and the like and stirring it for about 10 minutes to 3 hours. This acid treatment can be repeated once or twice or more.
上記した合成方法以外に、次のステップ１〜３を経てＲ型二酸化マンガンを合成することもできる。 In addition to the synthesis method described above, R-type manganese dioxide can be synthesized through the following steps 1 to 3.
塩化マンガンや硫酸マンガンなどの水溶性の高い２価のマンガンを含むマンガン化合物の水溶液を調製し、この水溶液に水酸化ナトリウムなどのアルカリ試薬を加えてマンガンイオンを水酸化マンガンＭｎ（ＯＨ）２に変換する。これをステップ１とする。 An aqueous solution of a manganese compound containing divalent manganese having high water solubility such as manganese chloride and manganese sulfate is prepared, and an alkali reagent such as sodium hydroxide is added to this aqueous solution to convert manganese ions to manganese hydroxide Mn (OH) 2 . Convert. This is step 1.
２価のマンガンを含むマンガン化合物の水溶液は、例えば、マンガンイオン濃度が０．０５〜１．０ｗｔ％、好ましくは０．０８〜０．２ｗｔ％の水溶液が用いられる。 As the aqueous solution of the manganese compound containing divalent manganese, for example, an aqueous solution having a manganese ion concentration of 0.05 to 1.0 wt%, preferably 0.08 to 0.2 wt% is used.
ステップ２として、アルカリ試薬を添加した２価のマンガン化合物の水溶液に過酸化水素水を加えて、水酸化マンガンを、マンガンの価数が２．６７の酸化マンガンＭｎ３Ｏ４に変換する。このステップ２において、水溶液の水温を２５℃以下に保つことが好ましい。 In Step 2, hydrogen peroxide is added to an aqueous solution of a divalent manganese compound to which an alkali reagent is added to convert manganese hydroxide into manganese oxide Mn 3 O 4 having a manganese valence of 2.67. In Step 2, it is preferable to keep the water temperature of the aqueous solution at 25 ° C. or lower.
ステップ３として、酸化マンガンＭｎ３Ｏ４に希酸を加えて攪拌処理することによってＲ型二酸化マンガンを得る。 As Step 3, R-type manganese dioxide is obtained by adding a dilute acid to manganese oxide Mn 3 O 4 and stirring.
以上の方法によって合成された二酸化マンガンがラムズデライト型の結晶構造を有する二酸化マンガンであることは、非特許文献２（Ｆｏｎｇ, Ｃ., Ｋｅｎｎｅｄｙ, Ｂ. Ｊ. ａｎｄ Ｅｌｃｏｍｂｅ, Ｍ. Ｍ. Ａ ｐｏｗｄｅｒ ｎｅｕｔｒｏｎ ｄｉｆｆｒａｃｔｉｏｎ ｓｔｕｄｙ ｏｆ ｌａｍｂｄａ ａｎｄ ｇａｍｍａ ｍａｎｇａｎｅｓｅ ｄｉｏｘｉｄｅ ａｎｄ ｏｆ ＬｉＭｎ２Ｏ４. Ｚｅｉｔｓｃｈｒｉｆｔ Ｆｕｅｒ Ｋｒｉｓｔａｌｌｏｇｒａｐｈｉｅ ２０９, ９４１−９４５ （１９９４）.）のＸ線回折パターンデータを参照し、一般的な実験室用Ｘ線回折分析装置でＸ線回折パターンを分析することで確認できる。 Non-Patent Document 2 (Fong, C., Kennedy, B. J. and Elcombe, M. M. A powder) indicates that manganese dioxide synthesized by the above method is a manganese dioxide having a ramsdellite type crystal structure. neutron diffraction study of lambda and gamma manganese dioxide and of LiMn 2 O 4. Zeitschifft Fuel Kristalographie 209, 194 This can be confirmed by analyzing the X-ray diffraction pattern.
以上のＲ型二酸化マンガンは、二酸化炭素を溶解した水溶液中、二酸化炭素変換用触媒として使用される。この二酸化炭素変換用触媒は、水中の水酸化物イオン（ＯＨ−）から酸素を発生させながらプロトン（Ｈ＋）と電子を生成し、同触媒表面に帯電する性質を有しており、同触媒を懸濁させる水のｐＨを弱酸性〜アルカリ性に保つことにより触媒活性が高められる。 The above R-type manganese dioxide is used as a carbon dioxide conversion catalyst in an aqueous solution in which carbon dioxide is dissolved. This catalyst for carbon dioxide conversion has the property of generating protons (H + ) and electrons while generating oxygen from hydroxide ions (OH − ) in water, and charging the catalyst surface. The catalytic activity is enhanced by keeping the pH of the water in which water is suspended from weakly acidic to alkaline.
本発明においては、水溶液の液性を弱酸性〜アルカリ性に調整し、この水溶液に二酸化炭素を溶解している。水溶液の液性が弱酸性〜アルカリ性であれば、二酸化炭素（ＣＯ２）は水溶液中で炭酸水素イオン（ＨＣＯ３ −）として溶存する。ここで、弱酸性の水溶液とはｐＨ５以上の酸性水溶液のことをいう。そして、水溶液に二酸化炭素を溶解した後も水溶液の液性を弱酸性〜アルカリ性に保ち、炭酸水素イオンが溶存する水溶液に、二酸化炭素変換用触媒を共存させることで、炭酸水素イオンを有機化合物に変換することができる。 In the present invention, the liquidity of the aqueous solution is adjusted to be weakly acidic to alkaline, and carbon dioxide is dissolved in this aqueous solution. If the aqueous solution is weakly acidic to alkaline, carbon dioxide (CO 2 ) is dissolved in the aqueous solution as hydrogen carbonate ions (HCO 3 − ). Here, the weakly acidic aqueous solution means an acidic aqueous solution having a pH of 5 or more. And even after dissolving carbon dioxide in the aqueous solution, the liquidity of the aqueous solution is kept weakly acidic to alkaline, and by coexisting the carbon dioxide conversion catalyst in the aqueous solution in which the bicarbonate ions are dissolved, the bicarbonate ions are converted into organic compounds. Can be converted.
本発明においては、二酸化炭素を溶解させる水溶液として、アルカリ性緩衝液を用いることが好ましい。これによって炭酸水素イオンから有機化合物への変換効率を高めることができる。アルカリ性緩衝液の具体例としては、アルカリ性の、Trishydroxymethyl amino methane: NH2(OH)3 （以下トリスと記載)、4-(2-hydroxyethl)-1-piperazinee thanesulfonic acid: C8H18N2O4S（以下ヘペスと記載)や、ホウ酸緩衝液等を挙げることができる。また、重炭酸ナトリウム等のアルカリ性の重炭酸塩緩衝液や、リン酸緩衝溶液等を挙げることもできる。 In the present invention, an alkaline buffer is preferably used as the aqueous solution for dissolving carbon dioxide. Thereby, the conversion efficiency from hydrogen carbonate ions to organic compounds can be increased. Specific examples of the alkaline buffer include alkaline Trishydroxymethyl amino methane: NH 2 (OH) 3 (hereinafter referred to as “Tris”), 4- (2-hydroxyethl) -1-piperazinee thanesulfonic acid: C 8 H 18 N 2 O 4 S (hereinafter referred to as Hepes), borate buffer, and the like. Moreover, alkaline bicarbonate buffer solutions, such as sodium bicarbonate, a phosphate buffer solution, etc. can also be mentioned.
また、本発明においては、二酸化炭素を溶解した水溶液中に、二酸化炭素変換用触媒とともに貴金属錯体を共存させることが好ましい。これによって炭酸水素イオンから有機化合物への変換効率を高めることができる。貴金属錯体の具体例としては、金錯体（例えばＡｕＣｌ４ −）やパラジウム錯体（例えばＰｄ（Ｃｌ）２またはＰｄ（ＯＨ）２）等を挙げることができる。このような貴金属錯体は、例えば、水溶液中の金やパラジウム等の貴金属の濃度が１０〜１０００ｍｇ／Ｌとなるように添加される。 Moreover, in this invention, it is preferable to coexist a noble metal complex with the carbon dioxide conversion catalyst in the aqueous solution which melt | dissolved the carbon dioxide. Thereby, the conversion efficiency from hydrogen carbonate ions to organic compounds can be increased. Specific examples of the noble metal complex include a gold complex (eg, AuCl 4 − ) and a palladium complex (eg, Pd (Cl) 2 or Pd (OH) 2 ). Such a noble metal complex is added so that the density | concentration of noble metals, such as gold | metal | money and palladium, in aqueous solution will be 10-1000 mg / L, for example.
本発明の二酸化炭素の変換方法では、二酸化炭素を溶解した水溶液の温度を１００℃以下にして炭酸水素イオンを有機化合物に変換することができる。後述するように、水溶液の界面を大気中に開放するなどして二酸化炭素を大気圧下で水溶液中に溶解させる場合には、水溶液の温度を、水溶液の加熱によって、例えば４０℃〜９０℃、好ましくは５０℃〜７０℃に保持することで二酸化炭素の変換効率をより高めることができる。 In the carbon dioxide conversion method of the present invention, the temperature of an aqueous solution in which carbon dioxide is dissolved can be set to 100 ° C. or less to convert hydrogen carbonate ions into an organic compound. As will be described later, when carbon dioxide is dissolved in the aqueous solution under atmospheric pressure by opening the interface of the aqueous solution to the atmosphere, the temperature of the aqueous solution is set to 40 ° C. to 90 ° C., for example, by heating the aqueous solution. Preferably, the conversion efficiency of carbon dioxide can be further increased by maintaining the temperature at 50 ° C to 70 ° C.
水溶液中に二酸化炭素を溶解させる方法としては、水溶液の界面を大気中に開放し、水溶液の界面と大気とを接触させるなどして大気中の二酸化炭素を水溶液中に溶解させる方法であってもよい。この手法ではギ酸や酢酸が乳酸およびコハク酸らと共に検出される。また、密閉容器に水溶液と二酸化炭素変換用触媒とを封入し、この密閉容器内に二酸化炭素を圧入して水溶液中に二酸化炭素を溶解させる方法であってもよい。後者の方法は、前者の方法と比べて、低酸素分圧下で二酸化炭素を高濃度に溶解させることができ、変換後に主として乳酸が得られる。 As a method of dissolving carbon dioxide in an aqueous solution, even if the interface of the aqueous solution is opened to the atmosphere and the interface of the aqueous solution is brought into contact with the atmosphere, the carbon dioxide in the atmosphere is dissolved in the aqueous solution. Good. In this method, formic acid and acetic acid are detected together with lactic acid and succinic acid. Alternatively, a method may be used in which an aqueous solution and a carbon dioxide conversion catalyst are sealed in a sealed container, and carbon dioxide is injected into the sealed container to dissolve the carbon dioxide in the aqueous solution. Compared with the former method, the latter method can dissolve carbon dioxide at a high concentration under a low oxygen partial pressure, and lactic acid is mainly obtained after the conversion.
本発明においては、上記のとおり、炭酸水素イオンを有機化合物に変換することができる。例えば、炭酸水素イオンを蟻酸、酢酸、コハク酸、乳酸等のカルボン酸に変換することができる。 In the present invention, as described above, hydrogen carbonate ions can be converted into an organic compound. For example, bicarbonate ions can be converted into carboxylic acids such as formic acid, acetic acid, succinic acid, and lactic acid.
酢酸およびコハク酸は、その分子構造に炭素−炭素結合（Ｃ−Ｃ結合）を有するカルボン酸であり、乳酸は、炭素−炭素−炭素（Ｃ−Ｃ−Ｃ結合）を有するカルボン酸である。二酸化炭素変換用触媒によってＣ−Ｃ結合やＣ−Ｃ−Ｃ結合を作り出せることは、本発明の大きな特徴である。また、従来の二酸化炭素変換触媒材料には確認されていなかった乳酸、コハク酸への変換を可能としたことも本発明の大きな特徴である。さらにまた本発明の大きな特徴として、二酸化炭素を効率よく変換できることも挙げられる。例えば、特許文献２に記載の蟻酸の合成方法では、高価なルテニウム触媒を用いるとともに二酸化炭素を超臨界にする必要があったが、本発明では、二酸化炭素変換用触媒を低コストで製造でき、また従来の二酸化炭素変換触媒材料と比べて安価に入手でき、しかも反応系を超臨界（７．３８２ＭＰａ）にする必要がなく、より穏和な条件（例えば、０．５ＭＰａ）で二酸化炭素を蟻酸などの有機化合物に変換することができる。 Acetic acid and succinic acid are carboxylic acids having a carbon-carbon bond (C—C bond) in their molecular structure, and lactic acid is a carboxylic acid having a carbon-carbon-carbon (C—C—C bond). The ability to create a C—C bond or a C—C—C bond with a catalyst for carbon dioxide conversion is a major feature of the present invention. Another major feature of the present invention is that conversion to lactic acid or succinic acid, which has not been confirmed in conventional carbon dioxide conversion catalyst materials, is possible. Furthermore, a major feature of the present invention is that carbon dioxide can be converted efficiently. For example, in the method for synthesizing formic acid described in Patent Document 2, it was necessary to use an expensive ruthenium catalyst and to make carbon dioxide supercritical, but in the present invention, a carbon dioxide conversion catalyst can be produced at low cost, In addition, it can be obtained at a lower cost than conventional carbon dioxide conversion catalyst materials, and it is not necessary to make the reaction system supercritical (7.382 MPa), so that carbon dioxide is formic acid under milder conditions (for example, 0.5 MPa). Can be converted to the organic compound.
以下に実施例を示し、さらに詳しく説明する。もちろん以下の例によって本発明の実施態様が限定されることはない。 Hereinafter, examples will be shown and described in more detail. Of course, the following examples do not limit the embodiments of the present invention.
＜実施例１＞大気中に置かれたアルカリ性水溶液中で大気中から自然に溶解してくる二酸化炭素がＲ型二酸化マンガン触媒との反応によってカルボン酸に変換された例 <Example 1> An example in which carbon dioxide naturally dissolved from the atmosphere in an alkaline aqueous solution placed in the atmosphere is converted into a carboxylic acid by reaction with an R-type manganese dioxide catalyst.
ガラス製ビーカーに超純水（ミリポア社製の超純水製造装置で製造）１００ｍＬに、予め大気圧下１３０℃で２週間以上乾燥した二酸化マンガン触媒０．５ｇを懸濁させ、ガラス製のマグネチック・スターラーで攪拌しながら５日間、水温約５０℃を保った。水量の減少は適時、超純水を追加して１００ｍＬを保った。水溶液のｐＨは水溶液にＲ型二酸化マンガン触媒を懸濁させた後、適時、水酸化ナトリウム水溶液を添加してｐＨ７．２６から７．８３を保った。 In a glass beaker, 0.5 g of manganese dioxide catalyst previously dried at 130 ° C. under atmospheric pressure for 2 weeks or more in 100 mL of ultrapure water (produced by an ultrapure water production apparatus manufactured by Millipore) was suspended, and glass magnet The water temperature was kept at about 50 ° C. for 5 days while stirring with a tic stirrer. When the amount of water decreased, ultrapure water was added to keep 100 mL. The pH of the aqueous solution was maintained at pH 7.26 to 7.83 by suspending the R-type manganese dioxide catalyst in the aqueous solution and then adding an aqueous sodium hydroxide solution at an appropriate time.
図１に、使用したＲ型二酸化マンガンの透過型電子検鏡写真、および図２に、そのＸ線回折パターンを示す。図２のＸ線回折パターンでは、図の横軸上に記載したＲ型に特有なピーク位置を示す目盛りとほぼ同じ回折角度にピークが現れていることがわかる。具体的には、回折角２１．５°近辺にＲ型に特有な回折ピークが見られる。 FIG. 1 shows a transmission electron micrograph of the used R-type manganese dioxide, and FIG. 2 shows its X-ray diffraction pattern. In the X-ray diffraction pattern of FIG. 2, it can be seen that a peak appears at substantially the same diffraction angle as the scale indicating the peak position peculiar to the R type described on the horizontal axis of the figure. Specifically, a diffraction peak peculiar to the R type can be seen around a diffraction angle of 21.5 °.
５日間の攪拌後に、テフロン（登録商標）製のメンブラン膜ろ過ユニット（アドバンテック製ＤＩＳＭＩＣ）を用いて実験水溶液中から水をサンプリングし、島津製作所製の有機酸分析装置でサンプル水中に含まれるカルボン酸濃度を計測した。 After stirring for 5 days, water was sampled from the experimental aqueous solution using a membrane membrane filtration unit made by Teflon (registered trademark) (DISMIC made by Advantech), and the carboxylic acid contained in the sample water with an organic acid analyzer made by Shimadzu Corporation. Concentration was measured.
その結果、乳酸濃度が６．０９３ｍｇ／Ｌ、蟻酸濃度が０．１９０ｍｇ／Ｌ、および酢酸濃度は０．６８４ｍｇ／Ｌと定量された。使用したガラス器具類や特級薬品類、およびＲ型二酸化マンガン触媒にはこれらのカルボン酸による汚染は存在しないため、大気中から二酸化炭素が実験水溶液に炭酸水素イオンとして溶解し、Ｒ型二酸化マンガン触媒と反応することでカルボン酸に変換されたものと考えられた。 As a result, the lactic acid concentration was determined to be 6.093 mg / L, the formic acid concentration was 0.190 mg / L, and the acetic acid concentration was 0.684 mg / L. Since the glasswares and special chemicals used and the R-type manganese dioxide catalyst are free from contamination by these carboxylic acids, carbon dioxide dissolves in the experimental aqueous solution as hydrogen carbonate ions from the atmosphere, and the R-type manganese dioxide catalyst It was thought that it was converted to carboxylic acid by reacting with.
また、５０℃から室温に冷ました上記実験水溶液の水面には油膜の発生が見られた。そこで、冷蔵庫内で３℃に同実験水溶液を１時間冷やして再度サンプリングし、同様にカルボン酸濃度を調べたところ、乳酸濃度が１．３８９ｍｇ／Ｌと、５０℃の場合に比べて低下し、蟻酸濃度は０．２１３ｍｇ／Ｌとほぼ変わらず、酢酸濃度は検出されなかった。この理由は、乳酸は融点が１６．８℃であるため、３℃への冷却によって水面に固化浮遊したために実験水溶液のサンプルからは検出されなかったものと考えられる。 In addition, generation of an oil film was observed on the water surface of the experimental aqueous solution cooled from 50 ° C. to room temperature. Therefore, the aqueous test solution was cooled to 3 ° C. for 1 hour in the refrigerator and sampled again. Similarly, when the carboxylic acid concentration was examined, the lactic acid concentration was 1.389 mg / L, which was lower than that at 50 ° C., The formic acid concentration was almost unchanged at 0.213 mg / L, and no acetic acid concentration was detected. This is probably because lactic acid has a melting point of 16.8 ° C., and was solidified and suspended on the surface of the water by cooling to 3 ° C., so that it was not detected from the sample of the experimental aqueous solution.
＜実施例２＞大気中に置かれたアルカリ性水溶液中に金錯体を添加し、大気中から自然に溶解してくる二酸化炭素が、同アルカリ水溶液中でＲ型二酸化マンガン触媒との反応によってカルボン酸に変換された例 <Example 2> A gold complex is added to an alkaline aqueous solution placed in the atmosphere, and carbon dioxide which is naturally dissolved from the atmosphere is reacted with an R-type manganese dioxide catalyst in the alkaline aqueous solution to react with a carboxylic acid. Example converted to
実施例１に示した実験を、同様なＲ型二酸化マンガン触媒の添加量（０．５ｇ）、および容量２００ｍＬの水溶液中に金錯体（ＡｕＣｌ４ −）（金濃度１０００ｍｇ／Ｌ）を共存させて実施し、５０℃に保温しながらｐＨ８．０から９．０を４日間保持した。 In the experiment shown in Example 1, the same amount of R-type manganese dioxide catalyst was added (0.5 g), and a gold complex (AuCl 4 − ) (gold concentration 1000 mg / L) was allowed to coexist in an aqueous solution having a capacity of 200 mL. This was carried out and maintained at pH 8.0 to 9.0 for 4 days while maintaining the temperature at 50 ° C.
その結果、実施例１と同様な実験水溶液のサンプリングと分析によって、コハク酸濃度１２．３４５ｍｇ／Ｌ、蟻酸濃度２．８１７ｍｇ／Ｌ、および酢酸濃度５．８８５ｍｇ／Ｌを確認した。 As a result, the succinic acid concentration of 12.345 mg / L, the formic acid concentration of 2.817 mg / L, and the acetic acid concentration of 5.885 mg / L were confirmed by sampling and analysis of the experimental aqueous solution similar to Example 1.
実施例１の結果と異なって乳酸の発生を確認できなかった。実施例１に記載した、Ｒ型二酸化マンガン触媒だけをアルカリ性の水溶液に懸濁させて５０℃に加温した場合に比較して、金錯体を共存させた本実施例２では乳酸の代わりにコハク酸が検出されたことが特徴である。 Unlike the results of Example 1, generation of lactic acid could not be confirmed. Compared with the case where only the R-type manganese dioxide catalyst described in Example 1 is suspended in an alkaline aqueous solution and heated to 50 ° C., in this Example 2 in which a gold complex coexists, succinate is used instead of lactic acid. It is characteristic that acid is detected.
＜実施例３＞大気中に置かれたアルカリ性水溶液中にパラジウム錯体を添加し、大気中から自然に溶解してくる二酸化炭素がＲ型二酸化マンガン触媒との反応によってカルボン酸に変換された例 <Example 3> An example in which a palladium complex is added to an alkaline aqueous solution placed in the atmosphere, and carbon dioxide that is naturally dissolved from the atmosphere is converted into a carboxylic acid by reaction with an R-type manganese dioxide catalyst.
実施例１に示した実験を、同様なＲ型二酸化マンガン触媒の添加量（０．５ｇ）、および容量１００ｍＬの水溶液中にパラジウム錯体（Ｐｄ（Ｃｌ）２またはＰｄ（ＯＨ）２）（パラジウム濃度１０００ｍｇ／Ｌ）を共存させて実施し、室温２４℃下で、ｐＨ６．０から７．０を４日間保持した。 The experiment shown in Example 1 was carried out by adding a palladium complex (Pd (Cl) 2 or Pd (OH) 2 ) (palladium concentration) in an aqueous solution having a similar amount of R-type manganese dioxide catalyst (0.5 g) and a volume of 100 mL. 1000 mg / L) was co-existing, and the pH of 6.0 to 7.0 was maintained for 4 days at room temperature of 24 ° C.
その結果、実験水溶液の水面に油膜の発生が観察された。実施例１と同様な実験水溶液のサンプリングと分析によって、コハク酸濃度０．６２９ｍｇ／Ｌ、蟻酸濃度２．７７９ｍｇ／Ｌ、および酢酸濃度４．９０６ｍｇ／Ｌを確認した。 As a result, generation of an oil film was observed on the water surface of the experimental aqueous solution. The succinic acid concentration of 0.629 mg / L, formic acid concentration of 2.779 mg / L, and acetic acid concentration of 4.906 mg / L were confirmed by sampling and analysis of the experimental aqueous solution similar to Example 1.
その後、同実験水溶液を５０℃に加温した状態で２日間攪拌した実験水溶液からは、乳酸濃度０．７２３ｍｇ／Ｌ、コハク酸濃度０．５９２ｍｇ／Ｌ、蟻酸濃度０．２８５ｍｇ／Ｌ、酢酸濃度７．７３７ｍｇ／Ｌが検出された。 Thereafter, from the experimental aqueous solution stirred for 2 days in the state where the experimental aqueous solution was heated to 50 ° C., the lactic acid concentration was 0.723 mg / L, the succinic acid concentration was 0.592 mg / L, the formic acid concentration was 0.285 mg / L, and the acetic acid concentration. 7.737 mg / L was detected.
実施例１に記載した、Ｒ型二酸化マンガン触媒だけをアルカリ性の水溶液に懸濁させて５０℃に加温した場合に比較して、パラジウム錯体を共存させた実施例３ではコハク酸が検出されることが特徴である。 Compared with the case where only the R-type manganese dioxide catalyst described in Example 1 is suspended in an alkaline aqueous solution and heated to 50 ° C., succinic acid is detected in Example 3 in which a palladium complex coexists. It is a feature.
＜実施例４＞大気中に置かれたアルカリ性緩衝水溶液（トリス水溶液）中で大気中から自然に溶解してくる二酸化炭素がＲ型二酸化マンガン触媒との反応によってカルボン酸に変換された例 <Example 4> An example in which carbon dioxide spontaneously dissolved from the atmosphere in an alkaline buffer aqueous solution (Tris aqueous solution) placed in the atmosphere is converted into a carboxylic acid by reaction with an R-type manganese dioxide catalyst.
実験に使用したトリス水溶液は和光純薬製試薬トリス０．１２gを１００mＬの超純水（ミリポア社製の超純水製造装置で製造）に溶解させて作成した。これに水酸化ナトリウム水溶液を適量滴下してｐＨ１０とした。水温は１９℃であった。このトリス水溶液をガラスビーカー内でＲ型二酸化マンガン０．２５gを懸濁させて、ガラス製のマグネチック・スターラーで室温下攪拌しながら１日間保持した。攪拌終了時のｐＨは９．１４、水温は２１．４℃であった。次に、テフロン（登録商標）製のメンブラン膜ろ過ユニット（アドバンテック製ＤＩＳＭＩＣ）を用いて実験水溶液中から水をサンプリングし、島津製作所製の有機酸分析装置でサンプル水中に含まれるカルボン酸濃度を計測した。その結果、乳酸濃度４．７９４mg／Ｌ、ギ酸濃度２６．５４９mg／Ｌを確認した。トリスはその化学式 NH2(OH)3に炭素やカルボシル基ＣＯＯＨを含まないため、大気中から実験水溶液への二酸化炭素の溶解が炭素の起源であると考えられた。 The Tris aqueous solution used in the experiment was prepared by dissolving 0.12 g of the reagent Tris manufactured by Wako Pure Chemical Industries, Ltd. in 100 mL of ultrapure water (produced by an ultrapure water production apparatus manufactured by Millipore). An appropriate amount of aqueous sodium hydroxide solution was added dropwise thereto to adjust the pH to 10. The water temperature was 19 ° C. 0.25 g of R-type manganese dioxide was suspended in this tris aqueous solution in a glass beaker and held for 1 day while stirring at room temperature with a glass magnetic stirrer. The pH at the end of stirring was 9.14, and the water temperature was 21.4 ° C. Next, water was sampled from the aqueous test solution using a membrane membrane filtration unit made by Teflon (registered trademark) (DISMIC made by Advantech), and the concentration of carboxylic acid contained in the sample water was measured using an organic acid analyzer manufactured by Shimadzu Corporation. did. As a result, a lactic acid concentration of 4.794 mg / L and a formic acid concentration of 26.549 mg / L were confirmed. Since Tris does not contain carbon or carbosyl group COOH in its chemical formula NH 2 (OH) 3 , it was considered that carbon dioxide was dissolved in the experimental aqueous solution from the atmosphere.
＜実施例５＞二酸化炭素を圧入した密閉容器内で、アルカリ性緩衝水溶液（トリス水溶液）中においてＲ型二酸化マンガン触媒が二酸化炭素をカルボン酸に変換した例
上記の実施例１−４では、大気開放した実験水溶液中に大気から自然に溶解してくる二酸化炭素がカルボン酸へ変換された例について述べた。
<Example 5> An example in which an R-type manganese dioxide catalyst converted carbon dioxide into carboxylic acid in an alkaline buffer aqueous solution (Tris aqueous solution) in an airtight container into which carbon dioxide was injected. An example in which carbon dioxide that naturally dissolves from the atmosphere in the experimental aqueous solution was converted to carboxylic acid was described.
本実施例５では、予め大気圧下１３０℃で２週間以上乾燥したＲ型二酸化マンガン触媒を準備し、この触媒０．２５ｇを実施例４と同様のトリス水溶液１００ｍＬ（ｐＨ１０）に懸濁させて実験水溶液とし、この実験水溶液を密閉容器（日本炭酸瓦斯社製のステンレス製サイホン・エスプーマスパークリングＭ）内に密栓し、付属のソーダカートリッジに封入された二酸化炭素８ｇを取り扱い説明書にしたがって同密閉容器内に圧入した。密閉容器内部の０．５〜０．７ＭＰａ圧力下にある実験水溶液をガラス製のマグネチック・スターラーで攪拌しながら室温２１℃下で１日間保った。次に同密閉容器を開封し、テフロン（登録商標）製のメンブラン膜ろ過ユニット（アドバンテック製ＤＩＳＭＩＣ）を用いて実験水溶液中から水をサンプリングし、島津製作所製の有機酸分析装置でサンプル水中に含まれるカルボン酸濃度を計測した。その結果、コハク酸１．６３８ｍg／Ｌ、乳酸１．１３８ｍg／Ｌ、ギ酸１１．５６３ｍg／Ｌが確認された。また、開封直後の実験水溶液がｐＨ５．４、および水温２０．８℃であることを測定確認した。実施例４の結果と比較して乳酸濃度およびギ酸濃度は本実施例の方が低い値であったが、密閉容器内で加圧することによってコハク酸の発生が見られた。ギ酸濃度が低い値であった理由は密閉容器内の酸素分圧が大気中に比べて低いことが原因のひとつとして考えられた。 In this Example 5, an R-type manganese dioxide catalyst previously dried at 130 ° C. under atmospheric pressure for 2 weeks or more was prepared, and 0.25 g of this catalyst was suspended in 100 mL of Tris aqueous solution (pH 10) as in Example 4. This experimental aqueous solution was sealed in a sealed container (stainless steel siphon Espuma Sparkling M manufactured by Nippon Carbon Gas Co., Ltd.), and 8 g of carbon dioxide enclosed in the attached soda cartridge was sealed in accordance with the instruction manual. Press-fitted inside. The experimental aqueous solution under a pressure of 0.5 to 0.7 MPa inside the sealed container was kept at a room temperature of 21 ° C. for 1 day while stirring with a glass magnetic stirrer. Next, the sealed container is opened, water is sampled from the aqueous test solution using a membrane membrane filtration unit made by Teflon (registered trademark) (DISMIC made by Advantech), and contained in the sample water with an organic acid analyzer made by Shimadzu Corporation. The carboxylic acid concentration was measured. As a result, 1.638 mg / L succinic acid, 1.138 mg / L lactic acid, and 11.563 mg / L formic acid were confirmed. Moreover, it was measured and confirmed that the experimental aqueous solution immediately after opening was pH 5.4 and the water temperature was 20.8 ° C. Compared with the results of Example 4, the lactic acid concentration and formic acid concentration were lower in this example, but generation of succinic acid was observed by pressurization in a closed container. The reason why the formic acid concentration was low was thought to be one of the reasons that the oxygen partial pressure in the sealed container was lower than that in the atmosphere.
＜実施例６＞二酸化炭素を圧入した密閉容器内で、アルカリ性緩衝水溶液（ヘペス水溶液）中においてＲ型二酸化マンガン触媒が二酸化炭素をカルボン酸に変換した例 <Example 6> An example in which an R-type manganese dioxide catalyst converted carbon dioxide into carboxylic acid in an alkaline buffer aqueous solution (Hepes aqueous solution) in a sealed container into which carbon dioxide was injected.
本実施例６では、実施例５と同様の実験を、ヘペス水溶液をアルカリ性緩衝水溶液として用いた。ヘペス水溶液の調整にあたっては、和光純薬製試薬HEPES：4-(2-hydroxyethl)-1-piperazinee thanesulfonic acid（C8H18N2O4S）２３．８gを２００mＬの超純水に溶解させた後、水酸化ナトリウム水溶液を適量滴下してｐＨ８．２とした。予め大気圧下１３０℃で２週間以上乾燥したＲ型二酸化マンガン触媒を準備し、この触媒０．２５ｇをヘペス水溶液１００mＬ（ｐＨ８．２）に懸濁させて実験水溶液とし、この実験水溶液を容量５Ｌのステンレス製密閉容器内に密栓し、二酸化炭素ボンベから二酸化炭素ガスを０．０５ＭＰａの圧力で同密閉容器内に圧入・保持した。密閉容器内部の０．０５ＭＰａ圧力下にある実験水溶液をガラス製のマグネチック・スターラーで攪拌しながら室温２１℃下で１日間保った。次に同密閉容器を開封し、テフロン（登録商標）製のメンブラン膜ろ過ユニット（アドバンテック製ＤＩＳＭＩＣ）を用いて実験水溶液中から水をサンプリングし、島津製作所製の有機酸分析装置でサンプル水中に含まれるカルボン酸濃度を計測した。その結果、乳酸１．１４２ｍg／Ｌ、ギ酸９．６９５ｍg／Ｌが確認された。また、開封直後の実験水溶液がｐＨ７．１２、および水温２１．２℃であることを測定確認した。 In Example 6, the same experiment as in Example 5 was performed using a Hepes aqueous solution as an alkaline buffer aqueous solution. In preparing the Hepes aqueous solution, 23.8 g of WEP Pure Chemical reagent HEPES: 4- (2-hydroxyethl) -1-piperazinee thanesulfonic acid (C 8 H 18 N 2 O 4 S) was dissolved in 200 mL of ultrapure water. After that, an appropriate amount of an aqueous sodium hydroxide solution was dropped to adjust the pH to 8.2. An R-type manganese dioxide catalyst that had been dried at 130 ° C. for 2 weeks or more in advance under atmospheric pressure was prepared, and 0.25 g of this catalyst was suspended in 100 mL of a Hepes aqueous solution (pH 8.2) to obtain an experimental aqueous solution. Were sealed in a stainless steel sealed container, and carbon dioxide gas was press-fitted and held in the sealed container at a pressure of 0.05 MPa from a carbon dioxide cylinder. The experimental aqueous solution under a pressure of 0.05 MPa inside the sealed container was kept at a room temperature of 21 ° C. for 1 day while stirring with a glass magnetic stirrer. Next, the sealed container is opened, water is sampled from the aqueous test solution using a membrane membrane filtration unit made by Teflon (registered trademark) (DISMIC made by Advantech), and contained in the sample water with an organic acid analyzer made by Shimadzu Corporation. The carboxylic acid concentration was measured. As a result, 1.142 mg / L lactic acid and 9.695 mg / L formic acid were confirmed. Moreover, it was measured and confirmed that the experimental aqueous solution immediately after opening was pH 7.12 and the water temperature was 21.2 ° C.
＜実施例７＞二酸化炭素を圧入した密閉容器内で、重炭酸ナトリウムを添加したアルカリ性の水溶液中においてＲ型二酸化マンガン触媒が二酸化炭素をカルボン酸に変換した例 <Example 7> An example in which an R-type manganese dioxide catalyst converted carbon dioxide into carboxylic acid in an alkaline aqueous solution to which sodium bicarbonate was added in a sealed container into which carbon dioxide was injected.
本実施例７では、密閉容器（日本炭酸瓦斯社製のステンレス製サイホン・エスプーマスパークリングＭ）中に２００ｍＬの超純水（ミリポア社製の超純水製造装置で製造）をとり、予め大気圧下１３０℃で２週間以上乾燥したＲ型二酸化マンガン触媒０．５ｇ、および重炭酸ナトリウム１０ｇを懸濁させた後、密栓し、付属のソーダカートリッジに封入された二酸化炭素８ｇを取り扱い説明書にしたがって同密閉容器内に圧入した。密閉容器内部の０．５〜０．７ＭＰａ圧力下にある実験水溶液をガラス製のマグネチック・スターラーで攪拌しながら室温２４℃下で２日間保った。 In Example 7, 200 mL of ultrapure water (manufactured by an ultrapure water production apparatus manufactured by Millipore) was placed in a closed container (stainless steel siphon / espuma sparkling M manufactured by Nippon Carbon Gas Co., Ltd.), and previously stored under atmospheric pressure After suspending 0.5 g of R-type manganese dioxide catalyst dried at 130 ° C. for 2 weeks or more and 10 g of sodium bicarbonate, tightly plug it, and seal 8 g of carbon dioxide enclosed in the attached soda cartridge according to the instruction manual. Press-fitted into a sealed container. The experimental aqueous solution under a pressure of 0.5 to 0.7 MPa inside the sealed container was kept at a room temperature of 24 ° C. for 2 days while stirring with a glass magnetic stirrer.
２日後に密閉容器を開栓し、実施例１と同様に実験水溶液をサンプリングし、開封直後のｐＨとカルボン酸濃度をｐＨメーターと有機酸分析装置で調べたところ、ｐＨ７．０、乳酸濃度１．９３２ｍｇ／Ｌを検出した。 Two days later, the sealed container was opened, the aqueous test solution was sampled in the same manner as in Example 1, and the pH and carboxylic acid concentration immediately after opening were examined with a pH meter and an organic acid analyzer. The pH was 7.0 and the lactic acid concentration was 1. 932 mg / L was detected.
＜実施例８＞二酸化炭素を圧入した密閉容器内で、アルカリ性のホウ酸緩衝水溶液中においてＲ型二酸化マンガン触媒が二酸化炭素をカルボン酸に変換した例 <Example 8> An example in which an R-type manganese dioxide catalyst converted carbon dioxide into carboxylic acid in an alkaline borate buffer aqueous solution in a sealed container into which carbon dioxide was injected.
密閉容器（日本炭酸瓦斯社製のステンレス製サイホン・エスプーマスパークリングＭ）中に１００ｍＬのアルカリ性ホウ酸緩衝水溶液（ｐＨ９.５３）をとり、予め大気圧下１３０℃で２週間以上乾燥したＲ型二酸化マンガン触媒０．２５ｇを懸濁させた後、密栓し、付属のソーダカートリッジに封入された二酸化炭素８ｇを同密閉容器内に圧入した。密閉容器内部の０．５〜０．７ＭＰａ圧力下にある実験水溶液をガラス製のマグネチック・スターラーで攪拌しながら室温２２℃下で１日間保った。そして、１日後に密閉容器を開栓した。ホウ酸緩衝水溶液の調整にあたっては、和光純薬製特級試薬ホウ酸、および濃度１Ｍの水酸化ナトリウム水溶液を用いて、ホウ酸濃度０.１Ｍのホウ酸緩衝水溶液９０mＬに水酸化ナトリウム水溶液と超純水を滴下して、容量１００mＬ、ｐＨ９.５３のホウ酸緩衝水溶液とした。 R-type manganese dioxide in which 100 mL of alkaline borate buffer aqueous solution (pH 9.53) is placed in a closed container (stainless steel siphon Espuma sparkling M manufactured by Nippon Carbon Gas Co., Ltd.) and dried in advance at 130 ° C. for 2 weeks or more under atmospheric pressure. After 0.25 g of the catalyst was suspended, it was sealed and 8 g of carbon dioxide enclosed in an attached soda cartridge was pressed into the sealed container. The experimental aqueous solution under a pressure of 0.5 to 0.7 MPa inside the sealed container was kept at a room temperature of 22 ° C. for 1 day while stirring with a glass magnetic stirrer. The sealed container was opened after 1 day. In preparing the borate buffer aqueous solution, using Wako Pure Chemical's special grade reagent boric acid and a 1M sodium hydroxide aqueous solution, 90 ml of boric acid buffer aqueous solution having a boric acid concentration of 0.1M was added to an aqueous solution of sodium hydroxide and ultrapure. Water was added dropwise to prepare a borate buffer aqueous solution having a volume of 100 mL and a pH of 9.53.
開栓後に他の実施例と同様に実験水溶液をサンプリングし、開封直後のｐＨおよび水温とカルボン酸濃度をｐＨメーターと有機酸分析装置で調べたところ、ｐＨ６．０７、２２.０℃、乳酸濃度７．６７６ｍｇ／Ｌを検出した。 After opening, the experimental aqueous solution was sampled in the same manner as in the other examples, and the pH immediately after opening and the water temperature and carboxylic acid concentration were examined with a pH meter and an organic acid analyzer. The pH was 6.07, 22.0 ° C., the lactic acid concentration. 7.676 mg / L was detected.
また、Ｒ型二酸化マンガン触媒の代わりに下記の市販の２種のガンマ型二酸化マンガンの各々について本実施例と同条件で実験したところ、それぞれ乳酸濃度約２ｍｇ／Ｌを検出した。この結果から、本実施形態に係るＲ型二酸化マンガン触媒の方が、二酸化炭素変換用触媒としての性能が優れていることが確認できた。 Moreover, when it experimented on each of the following two commercially available gamma-type manganese dioxide instead of R type manganese dioxide catalyst on the same conditions as this Example, the lactic acid density | concentration of about 2 mg / L was detected, respectively. From this result, it was confirmed that the R-type manganese dioxide catalyst according to the present embodiment was superior in performance as a carbon dioxide conversion catalyst.
使用した２種のガンマ型二酸化マンガンは、添川理化学株式会社製のガンマ型二酸化マンガン（０２３２０Ｂ）、中央電気工業株式会社製の化成二酸化マンガン（ＣＭＤ−１００）である。これら市販のガンマ型二酸化マンガンのＸ線回折パターンを図３に示す。図３（ａ）が添川理化学株式会社製のガンマ型二酸化マンガン（０２３２０Ｂ）のＸ線回折パターンであり、図３（ｂ）が中央電気工業株式会社製の化成二酸化マンガン（ＣＭＤ−１００）のＸ線回折パターンである。 The two types of gamma-type manganese dioxide used are gamma-type manganese dioxide (02320B) manufactured by Soegawa Richemical Co., Ltd. and chemical manganese dioxide (CMD-100) manufactured by Chuo Electric Industry Co., Ltd. The X-ray diffraction patterns of these commercially available gamma-type manganese dioxides are shown in FIG. FIG. 3 (a) is an X-ray diffraction pattern of gamma-type manganese dioxide (02320B) manufactured by Soekawa RI Chemical Co., Ltd., and FIG. 3 (b) is an X of chemical manganese dioxide (CMD-100) manufactured by Chuo Electric Industry Co., Ltd. It is a line diffraction pattern.
さらにまた、Ｒ型二酸化マンガン触媒の代わりにベータ型二酸化マンガンについて本実施例と同条件で実験したところ、乳酸濃度約２ｍｇ／Ｌを検出した。この結果から、本実施形態に係るＲ型二酸化マンガン触媒の方が、二酸化炭素変換用触媒としての性能が優れていることが確認できた。 Furthermore, when an experiment was conducted on beta-type manganese dioxide instead of the R-type manganese dioxide catalyst under the same conditions as in this example, a lactic acid concentration of about 2 mg / L was detected. From this result, it was confirmed that the R-type manganese dioxide catalyst according to the present embodiment was superior in performance as a carbon dioxide conversion catalyst.
上記のベータ型二酸化マンガンは、ベータ型の結晶構造を有する二酸化マンガンである。ここで使用したベータ型二酸化マンガンは、平均粒子径１〜５０ｎｍのサイズを有している。このようなベータ型二酸化マンガンは、上記した添川理化学株式会社製のガンマ型二酸化マンガン（０２３２０Ｂ）をセラミックるつぼにとり、電気炉内で、大気中４００℃で３日間加熱する操作によって合成することができる。このベータ型二酸化マンガンのＸ線回折パターンを図４に示す。 The beta-type manganese dioxide is manganese dioxide having a beta-type crystal structure. The beta-type manganese dioxide used here has an average particle size of 1 to 50 nm. Such beta-type manganese dioxide can be synthesized by taking the above-mentioned gamma-type manganese dioxide (02320B) manufactured by Soekawa Rikagaku Co., Ltd. in a ceramic crucible and heating in an electric furnace at 400 ° C. for 3 days. . The X-ray diffraction pattern of this beta-type manganese dioxide is shown in FIG.
以上に記載の全実施例において、アルカリ緩衝水溶液の使用やアルカリ試薬の添加によって実験溶液を弱酸性からアルカリ性（ｐＨ５〜９）に保った際に、カルボン酸が検出された。これに対して、０．１Ｍの希硫酸または希塩酸などを添加したｐＨ１〜４の酸性水溶液中でも実験を実施したが、乳酸の発生も他のカルボン酸の発生も検出できなかった。したがって、二酸化炭素を溶解した水溶液のｐＨを二酸化炭素変換用触媒の活性が高まる弱酸性からアルカリ性に保つことが、実験水溶液を加熱するなど外部エネルギーを加える手法と共に、二酸化炭素からカルボン酸への変換を促す重要な要素であることがわかった。 In all the examples described above, carboxylic acid was detected when the experimental solution was kept from weakly acidic to alkaline (pH 5 to 9) by using an alkaline buffer aqueous solution or adding an alkaline reagent. On the other hand, the experiment was carried out even in an acidic aqueous solution having a pH of 1 to 4 to which 0.1 M dilute sulfuric acid or dilute hydrochloric acid was added. However, neither lactic acid nor other carboxylic acid was detected. Therefore, maintaining the pH of an aqueous solution in which carbon dioxide is dissolved from weakly acidic to alkaline, where the activity of the catalyst for carbon dioxide conversion is increased, it is possible to convert carbon dioxide to carboxylic acid, along with techniques for applying external energy, such as heating the experimental aqueous solution. It was found to be an important factor that encourages
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