Improved method for photocatalytic hydrocarboxylation of methanol with CO2 to produce acetic acid

Abstract

This invention discloses a photocatalytic method and methodology for the preparation of acetic acid by the hydrocarboxylation of methanol with carbon dioxide under visible light irradiation. Importantly, the reaction occurred under room temperature and ambient pressure conditions using readily available household LED lamps in the presence of a homogeneous, semiconducting, transition metal-based molecular photocatalyst and a CO2-philic solvent, without the addition of external electron and proton donors.

Description

[Technical field]

[0001] The present invention discloses a photocatalytic method and methodology for the preparation of acetic acid by hydrocarboxylation of methanol with carbon dioxide under visible light irradiation. Importantly, the reaction occurred under room temperature and ambient pressure conditions using a homogeneous, semiconducting supported transition metal-based molecular photocatalyst and a readily available household LED lamp in the presence of a CO2-affinitive solvent without the addition of external electron and proton donors. [Background technology]

[0002] Acetic acid is an important basic chemical that is widely used in various fields such as petrochemicals, polymers, organic synthetic chemistry, pharmaceuticals and agrochemicals. The conventional method for the synthesis of acetic acid involves the carbonylation of methanol with carbon monoxide.

[0003] There are three important processes known for the carbonylation of methanol; i) the Monsanto process, developed in the 1960s, which requires commercially available rhodium (Rh) complexes; ii) the Cativa process, developed in the 1990s, which requires the use of commercially available iridium (Ir) complexes; and iii) the Acetica process, which relies on the use of heterogeneous catalysts consisting of Rh complexes immobilized on polymers.

[0004] However, the above processes are highly energy intensive and involve laborious separation of products and difficult isolation and disposal or reuse of by-products. In particular, the Monsanto and Cativa processes require the use of homogeneous catalysts, which are difficult to isolate and reuse. Moreover, the use of noble and expensive metals, such as rhodium and iridium, exacerbates the shortcomings of the aforementioned processes.

[0005] The synthesis of acetic acid from renewable, abundant and inexpensive carbon dioxide (CO2) is of great importance, but known and reported routes encounter difficulties, particularly in terms of energy requirements, reaction selectivity, extent of CO2 conversion and activity.

[0006] CN107008502B discloses a method for synthesizing acetic acid from ethanol, carbon dioxide and hydrogen gas in the presence of ruthenium complex and rhodium complex catalysts, organic ligands, iodide cocatalysts and solvents. In this invention, a homogeneous catalytic system was used to achieve high yield and high selectivity of acetic acid under relatively mild conditions. The method disclosed by the invention has important implications for the reuse of carbon dioxide and the alleviation of environmental problems caused by carbon dioxide.

[0007] WO2016108389 discloses a catalyst for use in the reaction for preparing acetic acid by carbonylation of methanol with carbon dioxide, more specifically a heterogeneous catalyst represented by Rh / C3N4 in which a complex of a rhodium compound and 3-benzoylpyridine is fixed on a carbon nitride support.

[0008] KR19970025711 discloses a gas phase process for the carbonylation of methanol with CO2 in which an oxygen-containing oxidant is used to oxidize and regenerate the catalyst. The oxidant includes air, oxygen, nitrogen dioxide, nitric oxide, carbon dioxide, or peroxide, and the regenerated catalyst is used to convert the reaction rate and significantly improve the selectivity to acetic acid.

[0009] The paper Nature Communications, 7 (2016) 11481 reported the synthesis of acetic acid from CO2, methanol and H2 in the presence of Ru-Rh bimetallic catalyst using imidazole as a ligand and LiI as a promoter in 1,3-dimethyl-2-imidazolidinone (DMI) solvent. The reaction mechanism was proposed based on control experiments. The mechanism suggested that methanol was hydrocarboxylated to acetic acid by CO2 and H2 instead of carbonylation by conversion of CO2 to CO. The strategy opened new methods for acetic acid production and CO2 transformation, representing a significant advance in synthetic chemistry.

[0010] The paper Green Chem., 2017, 19, 3558-3565 reported the synthesis of acetic acid by hydrocarboxylation of methanol with CO2 and H2 using a rhodium-based catalyst. Among the various reaction parameters studied, Rh2(CO)4Cl2 and 4-methylimidazole (4-MI) as ligand in the presence of LiCl and LiI was found to be efficient at 150 °C. The TOF was 26.2 h -1 and the yield of acetic acid could reach 81.8% at 180° C. The catalytic system had obvious advantages, such as simplicity, high activity and selectivity, milder reaction conditions, and less corrosiveness.

[0011] The above-mentioned conventionally known methods are associated with certain drawbacks, such as expensive metal catalysts, hydrogen gas, high temperature and high pressure. Therefore, the drawbacks of the above-mentioned conventionally known methods reveal the need for the development of an improved method for producing acetic acid from methanol and CO2. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] CN107008502B [Patent Document 2] WO2016108389 [Patent Document 3] KR19970025711 [Non-patent literature]

[0013] [Non-Patent Document 1] Nature Communications, 7(2016)11481 [Non-Patent Document 2] Green Chem., 2017, 19, 3558~3565 Summary of the Invention [Problem to be solved by the invention]

[0014] The main objective of the present invention is to provide a photocatalytic method for producing acetic acid by hydrocarboxylation of methanol with CO2 under visible light irradiation, which eliminates the drawbacks of the previously known methods as detailed above. Moreover, the present invention is the first reported method for the hydrocarboxylation of methanol with CO2 via a photocatalytic route.

[0015] Another object of the present invention is to use visible light sources having wavelengths (λ) longer than 420 nm or broad spectrum solar energy containing such wavelengths for the activation and conversion of carbon dioxide under mild conditions.

[0016] It is yet another object of the present invention to provide a process for the hydrocarboxylation of methanol with CO using a low cost, non-noble transition metal catalyst, such as nickel, cobalt or copper, more specifically cobalt and nickel.

[0017] It is yet another object of the present invention to provide a process for the hydrocarboxylation of methanol with CO2 using highly stable chelating nitrogen containing macrocyclic ligands based on phthalocyanine, porphyrin, bipyridine, and like moieties.

[0018] Yet another object of the present invention is to provide a reusable photocatalyst by anchoring molecular photosensitizers to a photoactive support matrix, preferably heteroatoms such as nitrogen-containing carbon, octasulfur (S8), transition metal oxides and mixed metal oxides.

[0019] Yet another object of the present invention is to provide a process for the hydrocarboxylation of methanol with CO2 using CO2-compatible solvents such as N,N-dimethylformamide, N,N-dimethylacetamide, dimethylsulfoxide, dimethylimidazoline, etc., especially N-alkylamides.

[0020] Yet another object of the present invention is to provide a process for the hydrocarboxylation of methanol with CO2 without the use of a sacrificial electron donor.

[0021] It is yet another object of the present invention to provide a method for the photocatalytic hydrocarboxylation of methanol and carbon dioxide, in which the required hydrogen atoms are derived from the methanol itself without an external hydrogen source.

[0022] Yet another object of the present invention is to provide a process for selectively producing acetic acid from methanol and carbon dioxide at room temperature range usually between 15-40°C, preferably at 25°C and atmospheric pressure of CO2.

[0023] Yet another object of the present invention is to provide a process for photocatalytic hydrocarboxylation of methanol and carbon dioxide to produce acetic acid at 40-90% methanol conversion with a selectivity of more than 95% for acetic acid.

[0024] Yet another object of the present invention is to provide a plausible mechanism for the photocatalytic hydrocarboxylation of methanol and carbon dioxide to acetic acid under visible light irradiation. [Means for solving the problem]

[0025] In one aspect of the present disclosure: 1. An improved hydrocarboxylation process for the synthesis of acetic acid, comprising: a. reacting methanol with CO2 in the presence of a CO2-compatible solvent and a photocatalyst to obtain a reaction mixture; b. irradiating the reaction mixture obtained in step (a) under visible light to obtain acetic acid; A method is provided that includes:

[0026] These and other features, aspects, and advantages of the present subject matter will become better understood with reference to the following description and appended claims. This Summary is provided to introduce a selection of concepts in a simplified form. It is not intended to identify key features or essential features of the scope of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] The present invention will now be described in detail in connection with certain preferred and optional embodiments so that various aspects may be more fully understood and appreciated.

[0028] Definition: For convenience, before further describing the present disclosure, certain terms used in the specification and examples are described here. These definitions should be read in light of the remainder of the disclosure and should be understood by those skilled in the art. Terms used herein have meanings that are recognized and known to those skilled in the art, but for convenience and completeness, certain terms and their meanings are described below.

[0029] The articles "a", "an" and "the" are used to refer to one or to more than one (ie, to at least one) of the grammatical object of the article.

[0030] The terms "comprise" and "comprising" are used in an inclusive and open sense to indicate the possibility that additional elements may be included. The terms are not intended to be interpreted as "consists of only."

[0031] Throughout this specification, unless otherwise required by context, the word "comprise", and variations such as "comprises" and "comprising", are understood to imply the inclusion of a stated element or step, or group of elements or steps, but not the exclusion of any other element or step, or group of elements or steps.

[0032] As used herein, the term "hydrocarboxylation" refers to the reaction of a CO radical anion with methanol and atomic hydrogen (H + ) to the methyl cation radical produced from the acetic acid under visible light illumination.

[0033] As used herein, the term "electron and proton sacrificial donor" refers to methanol, which provides the electrons and hydrogen required for the hydrocarboxylation reaction.

[0034] The term "CO2-affinitive solvent" refers to a solvent that dissolves carbon dioxide. In this disclosure, the term "CO2-affinitive solvent" includes, but is not limited to, N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMA), N-methylpyrrolidone (NMP), dimethylimidazoline (DMI), water, tetrahydrofuran (THF), and hexane.

[0035] The term "visible light" means light having a wavelength λ longer than 420 nm.

[0036] As used herein, the term "visible illumination" refers to irradiating a reaction mixture with visible light. In this disclosure, visible illumination is performed using a 15-30 W LED light having a wavelength longer than 420 nm.

[0037] The term "photocatalyst" refers to a material capable of absorbing light and donating the absorbed energy to reactants in a chemical reaction. In this disclosure, the term "photocatalyst" includes, but is not limited to, macrocyclic complexes of transition metals, such as ruthenium, cobalt, nickel, and copper, with ligands, such as porphyrins, polypyridines, and phthalocyanines.

[0038] The term "photoactive semiconductor support" as used herein means a support based on photoactive and semiconductor materials for immobilizing photocatalysts. In the present disclosure, the term "photoactive semiconductor support" includes, but is not limited to, N-doped carbon, graphitic carbon nitride, naturally occurring allotropes of sulfur (S8) and metal oxides of titanium, nickel, cobalt, iron, zinc and bismuth, preferably NiO and TiO2.

[0039] Ratios, concentrations, amounts, and other numerical data may be expressed in a range format herein. It is to be understood that such range formats are used merely for convenience and brevity, and should be interpreted flexibly to include not only the numerical values ​​specified as the limits of the range, but also to include all the individual numerical values ​​or subranges contained within the range as if each numerical value and subrange were specified. For example, a temperature range of 15°C to 35°C should be interpreted to include not only the specified limits of 18°C ​​to 29°C, but also subranges such as 17°C to 22°C, etc., and individual amounts within the specified range, such as 19.6°C and 27.3°C.

[0040] The present disclosure is not to be limited in scope by the specific embodiments described herein, which are for illustrative purposes only, and functionally equivalent products, compositions, and methods are clearly within the scope of the present disclosure described herein.

[0041] The present disclosure provides a method for producing acetic acid by photocatalytic hydrocarboxylation of methanol with CO2 using a molecular photocatalyst and a CO2-affinitive solvent to enhance the miscibility of CO2 in the reaction mixture under visible light irradiation without the use of an external electron or proton sacrificial donor. The molecular photocatalyst is a low-cost macrocyclic complex of a transition metal that can be used homogeneously or after immobilization on a photoactive semiconductor support for easy recovery and reuse.

[0042] In one embodiment of the present disclosure, a hydrocarboxylation process for the synthesis of acetic acid is provided, comprising: a. reacting methanol with CO in the presence of a CO-compatible solvent and a photocatalyst to obtain a reaction mixture; and b. irradiating the reaction mixture obtained in step (a) under visible illumination to obtain acetic acid.

[0043] In one embodiment of the present disclosure, there is provided a hydrocarboxylation method for the synthesis of acetic acid, wherein the CO2-affinitive solvent is selected from N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMA), N-methylpyrrolidone (NMP), dimethylimidazoline (DMI), water, tetrahydrofuran (THF) and hexane. Selected from the group consisting of In another embodiment of the present disclosure, a hydrocarboxylation method for the synthesis of acetic acid is provided, wherein the CO2-affinitive solvent is N,N-dimethylacetamide (DMA).

[0044] In one embodiment of the present disclosure, a hydrocarboxylation process for the synthesis of acetic acid is provided, comprising the steps of: a) reacting N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMA), N-methylpyrrolidone (NMP), dimethylimidazoline (DMI), water, tetrahydrofuran (THF) and hexane; Selected from the group consisting of a. reacting methanol with CO in the presence of a CO-compatible solvent and a photocatalyst to obtain a reaction mixture; and b. irradiating the reaction mixture obtained in step (a) under visible illumination to obtain acetic acid.

[0045] In one embodiment of the present disclosure, there is provided a hydrocarboxylation method for the synthesis of acetic acid, wherein the photocatalyst is selected from the group consisting of ruthenium, cobalt, nickel, copper and iron. Selected from the group consisting of Transition metals and porphyrins, polypyridines and phthalocyanines Selected from the group consisting of In another embodiment of the present disclosure, there is provided a hydrocarboxylation process for the synthesis of acetic acid, wherein the photocatalyst is preferably a macrocyclic chelate complex with a ligand that is capable of reacting with the carboxyl group of the cations ... Selected from the group consisting of The method further comprises the step of: providing a macrocyclic chelate complex of a transition metal with a phthalocyanine;

[0046] In one embodiment of the present disclosure, there is provided a hydrocarboxylation method for the synthesis of acetic acid, comprising the steps of: a. reacting methanol with CO in the presence of a CO2-compatible solvent and a photocatalyst to obtain a reaction mixture, wherein the photocatalyst is selected from the group consisting of ruthenium, cobalt, nickel, copper and iron. Selected from the group consisting of Transition metals and porphyrins, polypyridines and phthalocyanines Selected from the group consisting of and b. irradiating the reaction mixture obtained in step (a) under visible light to obtain acetic acid.

[0047] In one embodiment of the present disclosure, a hydrocarboxylation process for the synthesis of acetic acid is provided, comprising the steps of: a) reacting N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMA), N-methylpyrrolidone (NMP), dimethylimidazoline (DMI), water, tetrahydrofuran (THF) and hexane; Selected from the group consisting of Reacting methanol with CO2 in the presence of a CO2-compatible solvent and a photocatalyst to obtain a reaction mixture, the photocatalyst being selected from the group consisting of ruthenium, cobalt, nickel, copper and iron. Selected from the group consisting of Transition metals and porphyrins, polypyridines and phthalocyanines Selected from the group consisting of and b. irradiating the reaction mixture obtained in step (a) under visible light to obtain acetic acid.

[0048] In one embodiment of the present disclosure, a hydrocarboxylation process for the synthesis of acetic acid is provided, in which a photocatalyst is immobilized on a photoactive semiconductor support.

[0049] In one embodiment of the present disclosure, a hydrocarboxylation process for the synthesis of acetic acid is provided, comprising: a. reacting methanol with CO in the presence of a CO-affinitive solvent and a photocatalyst immobilized on a photoactive semiconductor support to obtain a reaction mixture; and b. irradiating the reaction mixture obtained in step (a) under visible illumination to obtain acetic acid.

[0050] In one embodiment of the present disclosure, there is provided a hydrocarboxylation process for the synthesis of acetic acid, wherein the photoactive semiconductor support is selected from the group consisting of N-doped carbon, graphitic carbon nitride, naturally occurring allotropes of sulfur (S8), and metal oxides of titanium, nickel, cobalt, iron, zinc, and bismuth, preferably NiO and TiO2. Selected from the group consisting of In another embodiment of the present disclosure, a hydrocarboxylation method for the synthesis of acetic acid is provided, wherein the photoactive semiconductor support is selected from naturally occurring allotropes of sulfur (S8). In yet another embodiment of the present disclosure, a hydrocarboxylation method for the synthesis of acetic acid is provided, wherein the photocatalyst is immobilized on a photoactive semiconductor support, and the photoactive semiconductor support is selected from heteroatom-doped carbon, naturally occurring allotropes of sulfur (S8), transition metal oxides or mixed metal oxides. Selected from the group consisting of A method is provided whereby

[0051] In one embodiment of the present disclosure, a hydrocarboxylation process for the synthesis of acetic acid comprises the steps of: a. reacting methanol with CO in the presence of a CO-compatible solvent and a photocatalyst to obtain a reaction mixture; and b. irradiating the reaction mixture obtained in step (a) under visible illumination to obtain acetic acid, wherein the photocatalyst is selected from the group consisting of N-doped carbon, graphitic carbon nitride, naturally occurring allotropes of sulfur (S8), and metal oxides of titanium, nickel, cobalt, iron, zinc, and bismuth, preferably NiO and TiO2. Selected from the group consisting of A method is provided in which the photoactive semiconductor is fixed to a substrate.

[0052] In one embodiment of the present disclosure, a hydrocarboxylation process for the synthesis of acetic acid is provided, in which the photocatalyst is reused.

[0053] In one embodiment of the present disclosure, a hydrocarboxylation process for the synthesis of acetic acid is provided, wherein the ratio of methanol to CO2-compatible solvent is in the range of 5:1 to 1:1, and the ratio of methanol to CO2 is 2:1.

[0054] In one embodiment of the present disclosure, a hydrocarboxylation method for the synthesis of acetic acid is provided, in which the mass ratio of methanol to CO2-affinity solvent is in the range of 5:2 to 2:0.5. In another embodiment of the present disclosure, a hydrocarboxylation method for the synthesis of acetic acid is provided, in which the mass ratio of methanol to CO2-affinity solvent is in the range of 2:1 to 1:1. In yet another embodiment of the present disclosure, a hydrocarboxylation method for the synthesis of acetic acid is provided, in which the mass ratio of methanol to CO2-affinity solvent is 1:1.

[0055] In one embodiment of the present disclosure, a hydrocarboxylation method for the synthesis of acetic acid is provided, comprising: a. reacting methanol with CO2 in the presence of a CO2-compatible solvent and a photocatalyst to obtain a reaction mixture; and b. irradiating the reaction mixture obtained in step (a) under visible illumination to obtain acetic acid, wherein the ratio of methanol to CO2-compatible solvent is in the range of 5:1 to 1:1, and the ratio of methanol to CO2 is 2:1.

[0056] In one embodiment of the present disclosure, there is provided a hydrocarboxylation process for the synthesis of acetic acid, wherein the reaction is carried out at a temperature in the range of 15-35° C. and a pressure in the range of 1-2 bar. In another embodiment of the present disclosure, there is provided a hydrocarboxylation process for the synthesis of acetic acid, wherein the reaction is carried out under room temperature and ambient pressure conditions.

[0057] In one embodiment of the present disclosure, there is provided a hydrocarboxylation process for the synthesis of acetic acid comprising: a. reacting methanol with CO in the presence of a CO-compatible solvent and a photocatalyst at a temperature in the range of 15-35° C. and a pressure in the range of 1-2 bar to obtain a reaction mixture; and b. irradiating the reaction mixture obtained in step (a) under visible illumination to obtain acetic acid.

[0058] In one embodiment of the present disclosure, there is provided a hydrocarboxylation method for the synthesis of acetic acid, comprising: a. reacting methanol with CO2 in the presence of a CO2-affinitive solvent and a photocatalyst to obtain a reaction mixture, wherein the ratio of methanol to CO2-affinitive solvent is in the range of 5:1 to 1:1, and the ratio of methanol to CO2 is 2:1; and b. irradiating the reaction mixture obtained in step (a) under visible illumination to obtain acetic acid, wherein the reaction is carried out at a temperature in the range of 15-35°C and a pressure in the range of 1-2 bar.

[0059] In one embodiment of the present disclosure, a hydrocarboxylation process for the synthesis of acetic acid is provided, wherein visible illumination is performed using a 15-30 W LED light having a wavelength in the range of 400 nm to 800 nm for a period in the range of 10 to 30 hours.

[0060] In one embodiment of the present disclosure, there is provided a hydrocarboxylation method for the synthesis of acetic acid, wherein visible illumination is performed with an 18-26 W LED light having a wavelength longer than 420 nm for a period ranging from 15 to 27 hours. In another embodiment of the present disclosure, there is provided a hydrocarboxylation method for the synthesis of acetic acid, wherein visible illumination is performed with a 20 W LED light having a wavelength longer than 420 nm for a period ranging from 24 hours.

[0061] In one embodiment of the present disclosure, there is provided a hydrocarboxylation method for the synthesis of acetic acid, comprising the steps of: a. reacting methanol with CO in the presence of a CO-compatible solvent and a photocatalyst to obtain a reaction mixture; and b. irradiating the reaction mixture obtained in step (a) under visible illumination to obtain acetic acid, wherein the visible illumination is performed using a 15-30 W LED light having a wavelength longer than 420 nm for a period ranging from 10 to 30 hours.

[0062] In one embodiment of the present disclosure, a hydrocarboxylation process for the synthesis of acetic acid is provided, in which the yield of acetic acid is in the range of 30-80% and the selectivity is in the range of 95-99%. In one embodiment of the present disclosure, a hydrocarboxylation process for the synthesis of acetic acid is provided, in which the yield of acetic acid is in the range of 35-70% and the selectivity is greater than 96%.

[0063] In one embodiment of the present disclosure, a hydrocarboxylation process for the synthesis of acetic acid is provided, comprising: a. reacting methanol with CO in the presence of a CO-compatible solvent and a photocatalyst to obtain a reaction mixture; and b. irradiating the reaction mixture obtained in step (a) under visible illumination to obtain acetic acid, wherein the yield of acetic acid is in the range of 30-80% and the selectivity is greater than 96%.

[0064] In one embodiment of the present disclosure, there is provided a hydrocarboxylation method for the synthesis of acetic acid, comprising: a. reacting methanol with CO2 in the presence of a CO2-compatible solvent and a photocatalyst to obtain a reaction mixture, wherein the ratio of methanol to CO2-compatible solvent is in the range of 5:1 to 1:1, and the ratio of methanol to CO2 is 2:1; and b. irradiating the reaction mixture obtained in step (a) under visible illumination to obtain acetic acid, wherein the visible illumination is performed using a 15-30 W LED light having a wavelength longer than 420 nm for a period in the range of 10 to 30 hours, wherein the reaction is carried out at a temperature in the range of 15-35°C and a pressure in the range of 1-2 bar, and the yield of acetic acid is in the range of 30-80% and the selectivity is greater than 96%.

[0065] In one embodiment of the present disclosure, an improved method is provided for producing acetic acid from methanol and CO2 in the presence of a catalytic amount of a macrocyclic complex of a transition metal such as cobalt, nickel or copper, both supported on a homogeneous or photoactive semiconductor support, in the presence of a CO2-compatible solvent without the use of an external sacrificial electron or proton donor, for a period of 24 hours in a batch photoreactor using household visible light at a temperature range of 20-40°C to obtain the desired acetic acid with a selectivity of 85-99% in the range of 20-80%. After consumption of CO2, the solvent can be recovered from the reaction mixture under reduced pressure.

[0066] In one embodiment of the present disclosure, a hydrocarboxylation process for the synthesis of acetic acid is provided, where the same process can be used to produce other carboxylic acids from the hydrocarboxylation of other alcohols such as ethanol, propanol, etc.

[0067] In one embodiment of the present disclosure, a hydrocarboxylation method for the synthesis of acetic acid is provided, in which the amount of photocatalyst used is in the range of 0.1-10 mol %. In another embodiment of the present disclosure, a hydrocarboxylation method for the synthesis of acetic acid is provided, in which the amount of photocatalyst used is preferably in the range of 1-10 mol %. In another embodiment of the present disclosure, a hydrocarboxylation method for the synthesis of acetic acid is provided, in which the amount of photocatalyst used is preferably in the range of 2-5 mol %.

[0068] In one embodiment of the present disclosure, a hydrocarboxylation method for the synthesis of acetic acid is provided, wherein the visible light source used is preferably a 10-30W household LED light.

[0069] In one embodiment of the present disclosure, a hydrocarboxylation process for the synthesis of acetic acid is provided, in which the conversion rate of methanol to acetic acid is analyzed by GC-TCD based on unreacted methanol in the reaction.

[0070] In one embodiment of the present disclosure, a hydrocarboxylation process for the synthesis of acetic acid is provided, in which a solvent used to increase CO solubility in the reaction mixture is recovered after photocatalysis.

[0071] In one embodiment of the present disclosure, a hydrocarboxylation process for the synthesis of acetic acid is provided, wherein the conversion rate of methanol to acetic acid remains between 20-70% based on the methanol used.

[0072] In one embodiment of the present disclosure, a hydrocarboxylation process for the synthesis of acetic acid is provided, in which no by-products are observed in the liquid phase and the selectivity of acetic acid remains greater than 80%. However, trace amounts (less than 3%) of hydrocarbons, such as ethane and propane, are observed in the gas phase as determined by GC-FID and RGA analytical techniques.

[0073] In one embodiment of the present disclosure, a hydrocarboxylation process for the synthesis of acetic acid is provided, in which the hydrocarboxylation of methanol with CO occurs without the addition of external sacrificial electron and proton donors.

[0074] In one embodiment of the present disclosure, a hydrocarboxylation method for the synthesis of acetic acid is provided, where the possible mechanism suggests the formation of methyl radical cation and CO2 anion radical from the oxidation of methanol and CO2 under photocatalytic conditions, respectively. The coupling of the radicals followed by the abstraction of hydrogen from another molecule of methanol gave acetic acid. EXAMPLES

[0075] The following are examples presented to further illustrate the present invention and should not be construed as limiting the scope of the invention.

[0076] According to the present invention, a solution of methanol and N,N-dimethylacetamide (DMA) (2:1 to 1:1 wt%) was placed in a 60 mL vessel. In addition, a transition metal photocatalyst (1 to 10 mol%) was added, and the resulting mixture was saturated with CO2 by purging. The reactor was sealed and irradiated with a LED, 20 W light (model HP-FL-20 WF, Hope LED Opto-Electric CO., Ltd.) for 24 hours. The intensity of the LED light in the reaction flask was 86 W / m2 as measured by a power meter. 2 The conversion and selectivity of acetic acid were checked by GC-TCD based on unreacted methanol. Furthermore, unreacted methanol and solvent were recovered by distillation under reduced pressure and the resulting mixture was analyzed by HPLC for confirmation of acetic acid product. The conversion of methanol remained between 40-80% and the selectivity of acetic acid remained above 95%, as well as traces (less than 3%) of hydrocarbons (ethylene, ethane, propane) in the gas phase were also confirmed by RGA.

[0077] Example 1 Preparation of metal phthalocyanine complexes Phthalic anhydride (4 g, 19.6 mmol), metal salts (5.45 mmol), urea (48 g, 0.8 mmol), ammonium chloride (4.048 g, 75.7 mmol) and ammonium molybdate (0.44 g, 2.23 mmol) were ground in a mortar, placed in a 50 mL quartz container and irradiated in a microwave oven at 440 W for 15 min. The reaction product was then rinsed with deionized water, suction filtered and dried at 120 °C under vacuum. The crude product was added to 2% HCl and the resulting mixture was heated to boiling for 30 min. After filtering and drying the product, it was added to 1% NaOH aqueous solution, boiled for 30 min, filtered and dried. The acid / base wash was repeated three times. Finally, the resulting bluish solid was oven-dried to give metal phthalocyanines in 81–85% yield. The oven-dried product was used as is for the photocatalytic hydrocarboxylation of methanol with CO2 to produce acetic acid. Similarly, phthalocyanine complexes of other transition metals such as copper, nickel, and iron were synthesized and used in the hydrocarboxylation reaction.

[0078] IR(KBr); 2962, 2896, 2855, 1616, 1528, 1484, 1365, 1338, 1256, 1195, 1145, 1082, 1056, 923, 828, 745, 688, 553 cm-1. MS: m / z 800 (M+). UV-Vis(n-Hexane) λmax: B band (328 nm); Q band (567 nm, 674 nm).

[0079] Example 2 Preparation of metalloporphyrin complexes In a typical synthesis, metal free base porphyrin (1.0 g) was treated with metal salt (3.0 g) in DMF (100 mL) at 60 °C for 5-6 h. After the reaction was completed, the mixture was diluted with water and extracted with dichloromethane (150 mL). The organic layer was dried over anhydrous sodium sulfate and concentrated under reduced pressure. The crude product was purified by silica gel chromatography using CHCl and methanol (10:1). Finally, the product was dried under vacuum to give a yield of 85-92%.

[0080] Similarly, polypyridyl complexes of transition metals such as ruthenium, cobalt, and nickel were synthesized by treating the metal salts with bipyridine in acetonitrile at reflux for 5–6 h, followed by the usual workup to give the final metal complexes in 80–85% yield.

[0081] Example 3 Immobilization of metal complexes on photoactive semiconductor supports In a typical synthesis procedure, 100 mg of metal complex (as synthesized in Example 1) was dispersed in 10 mL of ethanol in a beaker under vigorous stirring at room temperature for 2 h. In another beaker, 1 g of photoactive semiconductor support (N-doped carbon, graphitic carbon nitride, naturally occurring allotrope of sulfur (S8), transition metal oxide, mixed metal oxide) was added to 10 mL of deionized water and sonicated for 2 h. Then, both solutions were mixed and kept stirring overnight or until the solvent was completely evaporated. The residue so obtained was thoroughly washed with ethanol and dried at 60 °C under reduced pressure. The metal content in the complex was determined by ICP-AES.

[0082] Example 4 4.1 Preparation of acetic acid by methanol hydrocarboxylation using CO2 The photocatalytic hydrocarboxylation reaction was carried out in a 60 mL borosil vessel containing methanol (3 mL), DMA (3.5 mL) and photocatalyst (2 mol%). The reaction mixture was saturated by purging with CO2 for 30 min. The reactor was sealed and irradiated with a LED, 20 W light (model no. HP-FL-20 WF, Hope LED Opto-Electric CO., Ltd.) for 24 h. The intensity of the LED light at the reaction flask was measured to be 86 W / m 2 After the reaction was completed, the photocatalyst was removed by syringe filter or by filtration for reuse, and the resulting residue was subjected to analysis to determine the conversion and selectivity of acetic acid by GC-TCD based on unreacted methanol. Furthermore, after the reaction, unreacted methanol and solvent could be recovered by distillation under reduced pressure, and the residue was analyzed by HPLC for confirmation of acetic acid. The conversion of methanol remained at 20-80%, and the selectivity of acetic acid remained at >95-98%, as well as trace (2-3%) of hydrocarbon products in the gas phase were also confirmed by RGA.

[0083] 4.2 Preparation of acetic acid by the reaction of methanol hydrocarboxylation with CO2 using different photocatalysts The photocatalytic hydrocarboxylation reaction was carried out in a 60 mL borosil vessel containing methanol (3 mL), DMA (3.5 mL) and the photocatalyst mentioned in Example 1 (5 mol%). The reaction mixture was saturated by purging with CO2 for 30 min. The reactor was sealed and irradiated with a LED, 20 W light (model number HP-FL-20 WF, Hope LED Opto-Electric CO., Ltd.) for 24 h. The intensity of the LED light at the reaction flask was measured to be 86 W / m 2After the reaction was completed, the reaction mixture was subjected to the usual work-up and analysis mentioned in the previous examples. Under the same experimental conditions, the conversion of methanol and the selectivity of acetic acid obtained with different photocatalysts as described above in Example 3.1 are summarized in Table 1 (Examples 1-17). Among all the photocatalysts investigated, CoPc / S8 showed the highest conversion of methanol and the highest selectivity of acetic acid.

[0084] 4.3 Preparation of acetic acid by reaction of methanol hydrocarboxylation with CO2 (different solvents) The photocatalytic hydrocarboxylation reaction was carried out in a 60 mL borosil vessel containing methanol (3 mL), solvent (3.5 mL) and photocatalyst (5 mol%). The solvents tested were: water, N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMA), N-methylpyrrolidone (NMP), dimethylimidazoline (DMI), tetrahydrofuran (THF) and hexane. The reaction mixture was saturated by purging with CO2 for 30 min. The reactor was sealed and irradiated with a LED, 20 W light (model no. HP-FL-20 WF, Hope LED Opto-Electric CO., Ltd) for 24 h. The intensity of the LED light in the reaction flask was measured to be 86 W / m 2 After the reaction was completed, the photocatalyst and the resulting filtrate were analyzed by syringe filter, and the conversion and selectivity of acetic acid were determined by GC-TCD based on unreacted methanol. The results of these experiments are summarized in Table 1 (Examples 19-25).

[0085] 4.4 Preparation of acetic acid by reaction of methanol hydrocarboxylation with CO2 (different amounts of photocatalyst) The photocatalytic hydrocarboxylation reaction was carried out in a 60 mL borosil vessel containing methanol (3 mL), DMA (3.5 mL) and photocatalyst (1-10 mol%). The reaction mixture was saturated by purging with CO2 for 30 min. The reactor was sealed and irradiated with an LED, 20 W light (model no. HP-FL-20 WF, Hope LED Opto-Electric CO., Ltd.) for 24 h. The intensity of the LED light at the reaction flask was measured to be 86 W / m 2 After the reaction was completed, the photocatalyst removed by syringe filter and the resulting filtrate were analyzed to determine the conversion and selectivity of acetic acid by GC-TCD based on unreacted methanol. The results of these experiments are summarized in Table 1 (Examples 26-31). Among the various amounts tested, 2-5 mol% photocatalyst was found to be optimal, giving maximum conversion of methanol with selective production of acetic acid.

[0086] [Table 1A]

[0087] [Table 1B]

[0088] As can be seen from Table 1 above, Examples 1-17 showed a comparison of different homogeneous and supported photocatalysts for the conversion of methanol and selectivity for acetic acid under the described photocatalytic hydrocarboxylation conditions. Among the various photocatalysts tested, octasulfur-supported cobalt phthalocyanine gave a maximum conversion of 64% and selectivity for acetic acid of 98% in the presence of DMA as a solvent under visible illumination for 24 hours, with the added advantage of easy recovery of the photocatalyst by filtration and reusability in three subsequent runs. Example 18 showed that in the absence of a photocatalyst, no hydrocarboxylation of methanol with CO2 occurred under the described conditions.

[0089] Examples 19-25 in Table 1 show a comparison of different solvents for methanol conversion and acetic acid selectivity under the described photocatalytic hydrocarboxylation conditions. Among the various solvents tested, DMA provided the highest conversion of methanol (47%) with selective production of acetic acid using NiPc as catalyst. As shown in Example 25, poor conversion of methanol to acetic acid was observed in the absence of a CO2-compatible solvent.

[0090] Examples 26-31 in Table 1 showed the effect of photocatalyst amount on the conversion of methanol and selectivity for acetic acid under the described photocatalytic hydrocarboxylation conditions. Among the various amounts used, 2-5 mol% of photocatalyst is optimal for maximum conversion of methanol with selective production of acetic acid. Example 31 clearly demonstrated the photocatalytic nature of the reaction since no conversion occurred under otherwise optimal conditions in the absence of visible light.

[0091] Advantages of the Invention The present invention describes, for the first time, the photocatalytic production of acetic acid from the hydrocarboxylation of methanol with CO2 under room temperature and ambient pressure conditions.

[0092] The present invention uses carbon dioxide, which is an abundant, available, safe and inexpensive carboxylating agent compared to carbon monoxide, which is used in the industrial production of acetic acid.

[0093] The present invention provides activation of CO2 using renewable energy under ambient conditions.

[0094] The present invention provides a cost-effective transition metal catalyst for the hydrocarboxylation of methanol with CO2 to produce acetic acid.

[0095] The present invention provides a very simple protocol for the production of acetic acid using CO2 as a feedstock.

[0096] The disclosed invention represents a very facile and cost-effective new approach for the hydrocarboxylation of methanol using CO2, and therefore has great potential for developing a commercial process for the production of acetic acid from methanol and CO2 under mild conditions.

Claims

1. 1. An improved hydrocarboxylation process for the synthesis of acetic acid, comprising: a.CO 2 CO synthesis using methanol in the presence of an affinity solvent and photocatalyst 2 to obtain a reaction mixture; b. irradiating the reaction mixture obtained in step (a) under visible light to obtain acetic acid; A method comprising: The method of claim 1, wherein the photocatalyst is a macrocyclic complex of a transition metal selected from the group consisting of ruthenium, cobalt, nickel, and copper, and a ligand selected from the group consisting of porphyrins, polypyridines, and phthalocyanines.

2. CO 2 2. The method of claim 1, wherein the affinity solvent is selected from the group consisting of N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMA), N-methylpyrrolidone (NMP), dimethylimidazoline (DMI), water, tetrahydrofuran (THF) and hexane.

3. a photocatalyst is immobilized on a photoactive semiconductor support; 2. The method of claim 1, wherein the photoactive semiconductor support is selected from the group consisting of N-doped carbon, graphitic carbon nitride, naturally occurring allotropes of sulfur (S8), and metal oxides of titanium, nickel, cobalt, iron, zinc, and bismuth.

4. The photoactive semiconductor support is made of NiO and TiO 2 4. The method of claim 3, wherein the compound is selected from the group consisting of:

5. The method of claim 1 , wherein the photocatalyst is reused.

6. Methanol and CO 2 The affinity solvents are in the range of 5:1 to 1:1 ratios, with methanol and CO 2 The method of claim 1, wherein the ratio is 2:

1.

7. 2. The process of claim 1, wherein the reaction is carried out at a temperature in the range of 15 to 35° C. and a pressure in the range of 1 to 2 bar.

8. 10. The method of claim 1, wherein the visible illumination is performed with a 15-30 W LED light having a wavelength in the range of 400 nm to 800 nm for a period in the range of 10 to 30 hours.

9. 2. The improved hydrocarboxylation process of claim 1, wherein the yield of acetic acid is in the range of 30-80% and the selectivity is in the range of 95-99%.

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