PRODUCTION OF ACETIC ACID AND HYDROGEN IN AN AQUEOUS MEDIUM FROM ETHANOL AND ACETALDEHYDE VIA AN ORGANIC/INORGANIC CATALYST

Abstract

Disclosed are methods and systems of producing acetic acid and hydrogen from a two carbon (C.sub.2) alcohol source, the method comprising (a) obtaining a homogeneous aqueous solution comprising a C.sub.2 alcohol source and an organoruthenium (II) halide catalyst; and (b) subjecting the homogeneous aqueous solution to conditions suitable to produce a product stream comprising acetic acid and hydrogen.

Claims

1. A method of producing acetic acid and hydrogen from a two carbon (C.sub.2) alcohol source, the method comprising: (a) obtaining a homogeneous aqueous solution comprising water, a solvent having a boiling point great than 70 C., a C.sub.2 alcohol source and a organoruthenium (II) halide dimer catalyst; and (b) reacting the homogeneous aqueous solution at a temperature of 30 C. to 100 C. to produce a product stream comprising acetic acid and hydrogen.

2. The method of claim 1, wherein the C.sub.2 alcohol source is ethanol, hydrated acetaldehyde, or a mixture thereof.

3. The method of claim 2, wherein the C.sub.2 alcohol source is ethanol.

4. The method of claim 2, wherein the C.sub.2 alcohol source is hydrated acetaldehyde.

5. The method of claim 2, wherein the hydrated acetaldehyde source is acetaldehyde.

6. The method of claim 1, wherein the organoruthenium (II) halide catalyst comprises an aromatic compound, a phenyl group or a substituted phenyl group.

7. The method of claim 6, wherein the organoruthenium (II) halide catalyst is benzeneruthenium(II) chloride dimer, or dichloro(p-cymene)ruthenium dimer, or a mixture thereof.

8. The method of claim 7, wherein the organoruthenium (II) halide dimer catalyst is benzeneruthenium(II) chloride dimer.

9. The method of claim 7, wherein the organoruthenium (II) halide dimer catalyst is dichloro(p-cymene)ruthenium dimer.

10. The method claim 1, wherein the reaction temperature is 50 C. to 80 C., or 65 to 75 C.

11. (canceled)

12. The method of claim 1, wherein the solvent is acetonitrile, dimethylformamide, dimethoxyethane, pyridine or mixtures thereof.

13. The method of claim 1, wherein the solvent is acetonitrile.

14. The method of claim 1, further comprising incrementally adding additional amounts of the C.sub.2 alcohol source to the aqueous homogeneous solution.

15. The method of claim 1, wherein the catalyst has a turnover rate of 20 to 50, 25 to 40, or 28.

16. The method of claim 1, wherein the molar ratio of C.sub.2 alcohol source to organoruthenium (II) halide catalyst is 40 to 1500.

17. The method of claim 1, wherein the aqueous solution comprises potable water, purified water, tap water, or mixtures thereof.

18. A composition comprising a homogeneous aqueous solution comprising a C.sub.2 alcohol source, an organoruthenium (II) halide catalyst, acetic acid, and hydrogen.

19-20. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Advantages of the present invention may become apparent to those skilled in the art with the benefit of the following detailed description and upon reference to the accompanying drawings.

[0029] FIG. 1 shows a schematic of a system of the present invention that includes the homogenous organoruthenium (II) halide catalyst capable producing acetic acid and hydrogen.

[0030] FIG. 2 shows a GC-MS chromatograph and mass spectrum of the reaction mixture showing acetaldehyde.

[0031] FIG. 3A shows a GC-MS chromatograph and mass spectrum of the reaction mixture showing ethanol.

[0032] FIG. 3B shows a GC-MS chromatograph and mass spectrum of the reaction mixture showing acetic acid.

[0033] FIG. 4 shows a graphical representation of the reaction output of single injection versus cumulative injection in one embodiment of the current invention.

DETAILED DESCRIPTION OF THE INVENTION

[0034] A discovery has been made that provides a solution to the aforementioned problems and inefficiencies associated with the generation of acetic acid and hydrogen from a two carbon (C.sub.2) alcohol source. The discovery is based, in part, on the reaction of organoruthenium (II) halide catalyst with ethanol, acetaldehyde, or hydrated acetaldehyde under homogeneous aqueous conditions.

[0035] These and other non-limiting aspects of the present invention are discussed in further detail in the following sections.

A. Organoruthenium Catalyst

[0036] In one embodiment, the transition metal catalyst of the present invention is a ruthenium halide compound. Non-limiting examples of ruthenium halide compounds include RuCl(p-cymene)[(R,R)-TsDPEN], RuCl(p-cymene)[(S,S)-TsDPEN], RuCl(p-cymene)[(R,R)-FsDPEN], RuCl(p-cymene)[(S,S)-FsDPEN], RuCl(mesitylene) [(R,R) -TsDP EN], RuCl(mesitylene)[(S,S)-TsDPEN], RuCl(mesitylene)[(R,R)-FsDPEN], RuCl(mesitylene)[(S,S)-FsDPEN], [(R,R)-Teth-TsDPEN RuCl], and [(S,S)-Teth-TsDPEN RuCl], dichloro(p-cymene)triphenylphosphineruthenium(II) [RuCl.sub.2(p-cymene)(PPh.sub.3)], dichloro(p-cymene)tricyclohexylphosphineruthenium(II) [RuCl.sub.2(p-cymene)(PCy.sub.3)], cyclopentadienyl(.sup.6-napthalene)ruthenium(II) hexafluorophosphate [CpRu(.sup.6-napthalene)].sup.+ PF.sub.6.sup., cyclopentadienyl(p-cymene)ruthenium(II) hexafluorophosphate [CpRu(p-cymene)].sup.+ PF.sub.6.sup., benzeneruthenium(II) chloride dimer, [RuCl.sub.2(benzene)] .sub.2, benzeneruthenium(II) bromidedimer [RuBr.sub.2(benzene)].sub.2, benzeneruthenium (II) iodide dimer [RuI.sub.2(benzene)].sub.2, dichloro(toluene)ruthenium(II) dimer [RuCl.sub.2(toluene)].sub.2, dibromo(toluene)ruthenium(II) dimer [RuBr.sub.2(toluene)].sub.2, diido(toluene)ruthenium(II) dimer [RuI.sub.2(toluene)].sub.2, dichloro(xylene)ruthenium(II) dimer [RuCl.sub.2(xylene)].sub.2, dibromo(xylene)ruthenium(II) dimer [RuB r.sub.2 xylene)].sub.2, diido(xylene)ruthenium (II) dimer [RuI.sub.2(xylene)].sub.2, dichloro(p-cymene)ruthenium(II) dimer [RuCl.sub.2(p-cymene)].sub.2, dibromo(p-cymene)ruthenium(II) dimer [RuBr.sub.2(p-cymene)].sub.2, diido(p-cymene)ruthenium(II) dimer [RuI.sub.2(p-cymene)].sub.2, dichloro(mesitylene)ruthenium(II) dimer [Ru(mesitylene)Cl.sub.2].sub.2, dibromo(mesitylene)ruthenium(II) dimer [Ru(mesitylene)Br.sub.2].sub.2, diiodo(mesitylene)ruthenium(II) dimer [Ru(mesitylene)I.sub.2].sub.2, dichloro(hexamethylbenzene)ruthenium(II) dimer [(C.sub.6Me.sub.6)RuCl.sub.2].sub.2, dibromo(hexamethylbenzene)ruthenium (II) dimer [(C.sub.6Me.sub.6)RuI.sub.2].sub.2, diiodo(hexamethylbenzene)ruthenium(II) dimer [(C.sub.6Me.sub.6)RuCl.sub.2].sub.2, pentamethylcyclopentadienylbis(triphenylphosphine)ruthenium(II) chloride [(C.sub.5Me.sub.5)Ru(PPh.sub.3).sub.2Cl], chloro(pentamethylcyclopentadienyl)(cyclooctadiene)ruthenium(II) [(C.sub.5Me.sub.5)Ru(COD)Cl], dichloro(pentamethylcyclopentadienyl)ruthenium(III) polymer [(C.sub.5Me.sub.5)RuCl.sub.2], and chloro(-methanethioato)(pentamethylcyclopentadienyl)ruthenium(III) dimer [(C.sub.5Me.sub.5)Ru(SMe)Cl].sub.2. Preferably the ruthenium compound of the present invention is an organoruthenium halide catalyst containing ruthenium metal with an oxidation state of 2.sup.+ (II) and aromatic compound, such as a phenyl group or a substituted phenyl group having the general structure (I) shown below:

##STR00001##

where X can be a halogen (Cl, Br, or I), preferably Cl, and R.sub.1-R.sub.6 can be substituents that are the same or different. R.sub.1-R.sub.6 can be H, C.sub.1 to C.sub.4 alkyl, alkoxy, or haloalkyl moieties, or a combination thereof. In a preferred embodiment, R.sub.1-R.sub.6 are H, R.sub.1-R.sub.5 are H and R.sub.6 is methyl, R.sub.2, R.sub.4, R.sub.5, and R.sub.6 are H and R.sub.1 and R.sub.3 are methyl, R.sub.2, R.sub.4, R.sub.6 are H and R.sub.1, R.sub.3, R.sub.5 are methyl, R.sub.2, R.sub.3, R.sub.5, and R.sub.6 are H and R.sub.1 is methyl and R.sub.4 is isopropyl, or R.sub.1-R.sub.6 are methyl. In a particular embodiment, the organoruthenium (II) halide catalyst is [RuCl.sub.2(benzene)].sub.2, [RuCl.sub.2(toluene)].sub.2, [RuCl.sub.2(xylene)].sub.2, [RuCl.sub.2(p-cymene)].sub.2, or [RuCl.sub.2(mesitylene)].sub.2. Non-limiting commercial sources of [RuCl.sub.2(benzene)].sub.2 and [RuCl.sub.2(p-cymene)].sub.2 include Sigma-Aldrich, USA.

B. Reactants and Medium for Production of Acetic Acid and Hydrogen

[0037] 1. Reactants

[0038] The reactants for producing acetic acid and hydrogen can include a two carbon (C.sub.2) alcohol source, such as ethanol or acetaldehyde. Ethanol can be absolute ethanol, azeotropic distilled ethanol (95%), or aqueous ethanol (for example 50% in water). Acetaldehyde can be anhydrous acetaldehyde, aqueous acetaldehyde solutions (for example 40% in water), paraldehyde (2,4,6-trimethyl-1,3,5-trioxane), metaladehyde (2,4,6,8-tetramethyl-1,3,5,7-tetraoxocanemetacetaldehyde), or combinations thereof. Paraldehyde is the cyclic trimer of acetaldehyde and metaladehyde is the cyclic tetramer of acetaldehyde. Hydrated acetaldehyde can be in acetal form where water and acetaldehyde combine to form equilibrium concentrations of ethane-1,1-diol. Acetaldehyde can also be acetaldehyde in alcoholic solution (for example 50% in ethanol). Acetaldehyde and ethanol can combine to form equilibrium concentrations of hemiacetal 1-ethoxyethanol. Without being limited by theory, ethane-1,1-diol and/or 1-ethoxyethanol can be present in the reactions of the present invention. Ethanol and acetaldehyde are available from many commercial manufacturers, for example, Sigma Aldrich, U.S.A. In certain embodiments, the molar ratio of C.sub.2 alcohol source to organoruthenium (II) halide catalyst in the reaction medium is 40 to 1500 and all ratios there between including 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 210, 220, 230, 240, 250, 260, 270, 280, 290, 300, 310, 320, 330, 340, 350, 360, 370, 380, 390, 400, 410, 420, 430, 440, 450, 460, 470, 480, 490, 500, 510, 520, 530, 540, 550, 560, 570, 580, 590, 600, 610, 620, 630, 640, 650, 660, 670, 680, 690, 700, 810, 820, 830, 840, 850, 860, 870, 880, 990, 1000, 1010, 1020, 1030, 1040, 1050, 1060, 1070, 1080, 1090, 1110, 1120, 1130, 1140, 1150, 1160, 1170, 1180, 1190, 1200, 1210, 1220, 1230, 1240, 1250, 1260, 1270, 1280, 1290, 1300, 1310, 1320, 1330, 1340, 1350, 1360, 1370, 1380, 1390, 1400, 1410, 1420, 1430, 1440, 1450, 1460, 1470, 1480, and 1490, preferably from 200 to 800, or 300 to 700, or 400 to 500.

[0039] 2. Medium

[0040] The production of acetic acid and hydrogen from ethanol or acetaldehyde can be performed in any type of medium that can solubilize the catalyst and reagents. In a preferred embodiment, the medium is aqueous containing water. Non-limiting examples of water include de-ionized water, distilled water, softened water, salt water, ocean water, river water, tap water, potable water, purified water, rain water, canal water, city canal water or the like. In a particular embodiment, the water includes potable water, purified water, tap water, or mixtures thereof. Additional solvent(s) that are miscible with water and have a boiling point above 50 C., preferably 70 C., can be added to the aqueous medium. A suitable solvent that may be added to the aqueous medium of the present invention include acetonitrile (ACN), dimethylformamide (DMF), dimethylacetamide (DMA), dimethylsulfoxide (DMSO), 1,4-dioxane, dimethoxyethane (DME), tetrahydrofuran (THF), pyridine, acetone, or mixtures thereof. Preferably, the suitable solvent can be acetonitrile, dimethylformamide, dimethoxyethane, pyridine, or mixtures thereof. The amount of solvent or mixtures of solvents that can be added to the aqueous medium can range from 0 to 50 vol. % and any percentage there between including 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, or 49%.

B. Production of Acetic Acid and Hydrogen

[0041] The organoruthenium (II) halide catalyst can catalyze the oxidation of a two carbon (C.sub.2) alcohol source to generate acetic acid and hydrogen under oxygen-resilient, chemically robust, and energy efficient reaction conditions. A method to produce acetic acid and hydrogen from a C.sub.2 alcohol source, such as ethanol or acetaldehyde can include obtaining a homogeneous aqueous solution that includes the C.sub.2 alcohol source and the organoruthenium (II) halide catalyst. The homogeneous aqueous solution can then be subjected to conditions suitable to produce a product stream that includes acetic acid and hydrogen. In some embodiments, the reaction medium includes a temperature of 20 C. to 100 C. and any temperature there between, including 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, or 99 C. Specifically, the reaction medium can include a temperature range of 50 C. to 80 C. or 65 to 75 C. In a preferred embodiment, the organoruthenium (II) halide catalyst is soluble in the reaction medium, thus allowing homogenous catalysis to occur. In some embodiments, the hydrogen gas produced from the reaction can be collected in a cylinder and analyzed by GC-TCD and the resulting reaction mixture containing acetic acid can be analyzed by NMR and GC-MS.

[0042] It was surprisingly found that the activity of the catalyst can be increased when incrementally adding additional amounts of the C.sub.2 alcohol source to the aqueous homogeneous medium during the progress of the reaction. Without being limited by theory, it is believed that the catalytic activity can be limited by the concentration of hydrolyzed C.sub.2 alcohol source, which is controlled by C.sub.2 alcohol source/hydrolyzed C.sub.2 alcohol source equilibrium. Lower concentration of C.sub.2 alcohol source can give a lower concentration of hydrolyzed C.sub.2 alcohol source, which can lower activity. In one aspect, the concentration of hydrolyzed C.sub.2 alcohol source can be increased by increasing the concentration of C.sub.2 alcohol source, which can increase catalyst activity. In certain aspects, the C.sub.2 alcohol source is acetaldehyde and the equilibrium is acetaldehyde/ethane-1,1-diol. Additional amounts of the C.sub.2 alcohol source that can be added by cumulative addition to the medium include 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.9, or 1.0 or more equivalents of the C.sub.2 alcohol source added every 10 to 240 minutes or 30 to 120 minutes or more. The addition of additional C.sub.2 alcohol source can be performed using generally known addition techniques (e.g., by injection, dripping, pouring, purging, etc.). In a specific embodiment, the amount of additional C.sub.2 alcohol source added by cumulative injection ranges from 0.4 to 0.5 equivalents added once about every 60 minutes. A non-limiting example of cumulative addition is shown in FIG. 2 of the Examples.

[0043] In other embodiments of the method, the catalyst of the present invention can have a turnover rate number (TON) of 20 to 120 or any rate or range there between including 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112, 113, 114, 115, 116, 117, 118, or 119 TON. Specifically, in the presence of 0.054 equivalents of C.sub.2 alcohol source the catalyst can have a turnover rate number of 102 after 300 minutes.

C. System to Produce Acetic Acid and Hydrogen

[0044] FIG. 1 is a schematic of an embodiment of a system to produce acetic acid and hydrogen. Referring to FIG. 1, system 100 may include a reactor 102 and a reaction zone 104 containing a homogeneous aqueous solution having a C.sub.2 alcohol source and an organoruthenium (II) halide catalyst. In a preferred embodiment, the C.sub.2 alcohol source and the organoruthenium (II) halide catalyst in reaction zone 104 is ethanol, hydrated acetaldehyde, or a mixture thereof, and [RuCl.sub.2(benzene)].sub.2 or [RuCl.sub.2(p-cymene)].sub.2 respectively. In some aspects, reactor 102 can optionally be a continuous flow reactor having a reactant stream that includes a feed substrate 106 (C.sub.2 alcohol source) that can enter reactor 102 via an optional feed inlet 108 in one portion, in intermitted portions, or continuously. In preferred embodiments, the system includes a first outlet 110 in fluid communication with reaction zone 104 and the first outlet 104 is configured to receive a first portion of the product stream 112 that includes hydrogen gas. The reactor 102 includes a second outlet 114 in fluid communication with reaction zone 104, which is configured to receive a second portion of the product stream 116 that includes acetic acid. In further embodiments, system 100 may also optionally include a separation zone 118 in fluid communication with the second outlet 114 that is configured to separate acetic acid from the second portion of the product stream. The optional separation zone 118 can be configured with the purpose of preventing the loss of C.sub.2 alcohol source and/or organoruthenium (II) halide catalyst from the homogeneous aqueous solution of reaction zone 104. In some embodiments, the temperature of reaction zone 104 containing a homogeneous aqueous solution having a C.sub.2 alcohol source and an organoruthenium (II) halide catalyst can be operated at a temperature greater than, equal to, or between any two of 20 C., 30 C., 40 C., 50 C., 60 C., 70 C., 80 C., 90 C., 100 C. In a preferred embodiment, the temperature can range from 65 to 75 C. The temperature of reaction zone 104 can be maintained and/or adjusted using generally known heating or cooling techniques.

[0045] The resulting acetic acid and hydrogen produced from the systems of the invention can be highly pure. However, if necessary, the resulting acetic acid or hydrogen can be further purified and/or dried using common liquid or gas purification and/or drying techniques, such as vacuum distillation, cryogenic distillation, membrane separation and the like. The system can further include storing the directly produced or subsequently purified and/or dried acetic acid and/or hydrogen gas.

EXAMPLES

[0046] The present invention will be described in greater detail by way of specific examples. The following examples are offered for illustrative purposes only, and are not intended to limit the invention in any manner. Those of skill in the art will readily recognize a variety of noncritical parameters, which can be changed or modified to yield essentially the same results.

[0047] Catalyst were obtained from Strem Chemicals Inc. U.S.A. Water was deionized under standard conditions. Acetaldehyde (99.5% purity) was obtained from Acros Organics (ThermalFisher Scientific, U.S.A.). Gas chromatograph with athermal conductivity detector (GC-TCD) was performed using an Agilent 7820A GC (Agilent Technologies Inc., U.S.A.) equipped with a TCD and an Agilent HP-Molesieve column. The GC inlet temperature was 45 C. (splitless injection), pressure 3 psi (0.02 MPa) for 2 min, 9 psi/min (0.06 Mpa/min) until end, the TCD had a temperature of 100 C., reference (helium) and ramp rate of 50 mL/min, the GC column temperature was 45 C. for 2.5 min, 20 C. per min till 100 C. and 100 C. for 13 min. NMR was performed on a Bruker AVANCE II 400 (Bruker Corporation, U.S.A.) with Sample Changer. GC-mass spectrometry (GC-MS) was performed using an Agilent 7820A GC equipped with a Agilent 5975 MS detector, with an GC inlet temperature of 200 C. (splitless), a pressure 10 psi (0.068 MPa), a carrier gas (argon) rate of 1.3 mL/min, at 10 psi (0.068 MPa), a GC column temperature of about 40 C. for 1.5 min, 12 C./min till 300 C., 300 C. for 2 min.

Example 1

Catalyst Evaluation

[0048] Acetaldehyde (3 mL, 54 mmol) was charged into a reactor fitted with a condenser and diluted with water (50 mL). The catalyst (0.25 mmol) was added and the resultant solution was heated to 70 C. for 3 hours. The amount of acetaldehyde at the start of the reaction was quantified at 43 mmol due to evaporative loss at 70 C. Gas produced from the reaction was collected in a cylinder and analyzed by GC-TCD and the resulting reaction mixture was analyzed by NMR and GC-MS. Mass spectra analysis of the GC peaks at 1.09 min., 1.28 min., and 1.46 to 1.58 min. was performed. Table 1 lists the catalysts that were evaluated and resultant total volume of gas (H.sub.2) produced. As shown from the data in Table 1, only ruthenium catalysts that included an aromatic substituent catalyzed the formation of hydrogen gas and acetic acid from the acetaldehyde. FIGS. 2, 3A, and 3B are GC-MS spectra of the reaction mixture when [Ru(p-cymene)Cl.sub.2].sub.2 was evaluated. FIG. 2 shows the GC-MS peak at 1.09 min in the reaction mixture, which corresponds to acetaldehyde (m/z of 44). FIGS. 3A and 3B show the GC-MS the peaks 1.28 min and 1.4 to 1.58 min of the reaction mixture, which correspond ethanol (m/z of 45) and acetic acid (m/z of 60) respectively. From the GC-MS and the evolution of hydrogen it was determined that acetic acid was formed from acetaldehyde when [Ru(p-cymene)Cl.sub.2].sub.2 was used as the catalyst. The formation of ethanol was due to the reduction of acetaldehyde and/or acetic acid.

TABLE-US-00001 TABLE 1 Catalyst Total gas volume (mL) Blank (no catalyst) 0 Ru.sub.3(CO).sub.12 0 [Ru(p-cymene)Cl.sub.2].sub.2 320 RuCl.sub.2(PPh.sub.3).sub.3 0 [Ru(benzene)Cl.sub.2].sub.2 140 RuCl.sub.3 0 Ru(OH).sub.3/Fe.sub.nanoparticles 0 Ru nitrosylnitrate 0 Ru(acac).sub.3 0 RuO.sub.2 0 IrCl.sub.3 0

Example 2

Double Concentration of Substrate

[0049] Acetaldehyde (6 mL, 108 mmol) was charged into a reactor fitted with a condenser and diluted with water (50 mL). [Ru(p-cymene)Cl.sub.2].sub.2 (150 mg, 0.25 mmol) was added and the resultant solution was heated to 70 C. The amount of acetaldehyde at the start of reaction was 86 mmol due to evaporative loss at 70 C. Gas produced from the reaction was collected in a cylinder and analyzed by GC-TCD and the resulting reaction mixture was analyzed by NMR and GC-MS. The amount of gas produced was 560 mL (H.sub.2, 25 mmol) after 3 h and 930 mL (H.sub.2, 42 mmol) after 22 h.

Example 3

Double Injection of Substrate

[0050] Acetaldehyde (3 mL, 54 mmol) was charged into a reactor fitted with a condenser and diluted with water (50 mL). [Ru(p-cymene)Cl.sub.2].sub.2 (150 mg, 0.25 mmol) was added and the resultant solution was heated to 70 C. The amount of acetaldehyde at the start of reaction was 43 mmol due to evaporative loss at 70 C. Gas produced from the reaction was collected in a cylinder and analyzed by GC-TCD, and the resulting reaction mixture was analyzed by NMR and GC-MS. The amount of gas produced was 650 mL (H.sub.2, 28 mmol) after 20 h. After 20 h, no further gas was produced. A second aliquot of acetaldehyde (3 mL, 54 mmol) was injected. The amount of total gas produced after 24 more hours was 1290 mL. Hence, 640 ml (H.sub.2, 28 mmol) of gas was produced for the second aliquot of acetaldehyde.

Example 4

Solvent Evaluation

[0051] Solvents boiling at greater than 70 C. and miscible with water were evaluated. Acetaldehyde (1 mL, 18 mmol) was charged into a reactor fitted with a condenser and diluted with water or a solvent/water mixture. [Ru(p-cymene)Cl.sub.2].sub.2 (50 mg, 0.08 mmol) was added and the resultant solution was heated to 70 C. for 1 h. Gas produced from the reaction was collected in a cylinder and analyzed by GC-TCD. Table 2 shows the resultant total volume of gas (H.sub.2) produced and the water: solvent vol. ratio.

TABLE-US-00002 TABLE 2 Solvent Total gas volume (mL) Water 70 Water:acetonitrile (1:1) 32 Water:dimethylformamide (1:1) 66 Water:dimethoxyethane (1:1) 52 Water:pyridine (1:1) 12

Example 5

Cumulative Addition

[0052] The following reaction was prepared in duplicate and run in parallel. Acetaldehyde (3 mL, 54 mmol) was charged into a reactor fitted with a condenser and diluted with water (50 mL). The amount of acetaldehyde at the start of reaction was 43 mmol due to evaporative loss at 70 C. [Ru(p-cymene)Cl.sub.2].sub.2 (150 mg, 0.025 mmol) was added to both reactions and the resultant solutions were heated to 70 C. FIG. 4 shows the reaction progress of the two parallel reactions. The first reaction 200 was allowed to progress unchanged but the second reaction 202 was injected with acetaldehyde (1.1 mL, 20 mmol) every hour in cumulative fashion. Gas produced from the reaction was collected in a cylinder and analyzed by GC-TCD and the resulting reaction mixture was analyzed by NMR and GC-MS.