A process for the preparation of ethanol by halogen-mediated oxidation of ethane

Abstract

The application relates to a method for preparing ethanol by halogen-mediated oxidation of ethane, wherein ethane is mixed with Cl2 generated by electrolysis of NaCl solution, under light conditions, the Cl-Cl bond in the Cl2 molecule is cracked to form active chlorine, the photo-catalytic reaction of ethane is promoted to generate CH3CH2Cl product, and ethanol is obtained after hydrolysis of the CH3CH2Cl product. 2 Compared with the prior art, the application can reach 78% of Faraday efficiency under the highest 1000 mA / cm 8 The ethanol yield reaches 1.56*10 cat / mu mol / g cat / h, which is the most advanced and efficient system for preparing ethanol by selective oxidation of ethane.

Description

Technical Field

[0001] This invention belongs to the field of alkane conversion to alcohol, and in particular relates to a halogen-mediated method for the oxidation of ethane to ethanol. Background Technology

[0002] Ethanol is a crucial basic chemical widely used in transportation fuels, chemical raw materials, and pharmaceutical disinfection, with a global annual production of approximately 100 million tons and an estimated market value exceeding US$40 billion. Industrially, ethanol is primarily produced through fermentation, using starch- or sugar-rich crops such as corn and sugarcane as raw materials. The fermentation process for ethanol production generates approximately 2.5 tons of carbon dioxide emissions per ton of ethanol produced, and using food crops as raw materials raises concerns about food security.

[0003] US53431090A discloses a high-pressure controlled oxidation method for the direct conversion of ethane to alcohol. Ethane is tightly mixed with air or oxygen before being introduced into a heated pre-reactor, allowing for a pre-reaction or induction period. The pre-reaction gas then enters the reactor, where the reaction occurs at elevated temperatures of 200°C to 350°C and elevated pressures of 10 to 150 atmospheres. This technology for the non-catalytic oxidation of ethane to ethanol under high pressure is costly, has low yields, and exhibits low ethanol selectivity.

[0004] The direct synthesis of ethanol from ethane using renewable electricity and water is a potential strategy for reducing carbon emissions in the chemical industry. Patent CN201710149289.7 discloses a method for preparing ethanol by photoelectrocatalytic reduction of carbon dioxide. This method utilizes graphene, which has strong adsorption properties, to adsorb atmospheric carbon dioxide as a source; a 360nm ultraviolet lamp within the photoelectrocatalytic response range of titanium dioxide nanotubes provides the light source required for photoelectrocatalytic reduction, thereby improving the efficiency of the photoelectrocatalytic reduction reaction; a constant-voltage DC power supply provides the external voltage required for photoelectrocatalysis, thereby improving the carbon dioxide reduction efficiency; and the selectivity for ethanol among the products of photoelectrocatalytic carbon dioxide reduction is enhanced by controlling the pH of the electrolyte. However, the current density of currently reported highly selective electrocatalytic ethane oxidation is generally below 10 mA / cm². 2 This is far from the industrial current density (typically 300 mA / cm²) required for large-scale industrial applications. 2 This is because, with increased current density, the increase in positive potential leads to excessive oxidation of ethane, generating more carbon dioxide as a byproduct, which in turn reduces the selectivity of the target product, ethanol. Summary of the Invention

[0005] The purpose of this invention is to overcome the defects of the prior art by providing a halogen-mediated ethane oxidation method for preparing ethanol. By introducing light irradiation to excite the associative cleavage of the Cl-Cl bond in the Cl2 molecule, active chlorine is formed, thereby accelerating the activation of ethane and achieving an order-of-magnitude increase in yield.

[0006] The objective of this invention can be achieved through the following technical solution: a halogen-mediated ethane oxidation method for preparing ethanol, wherein ethane is mixed with Cl2 generated by electrolysis of NaCl solution, and under light irradiation, the Cl-Cl bond in the Cl2 molecule is broken to form active chlorine, which promotes the photocatalytic reaction of ethane to generate CH3CH2Cl product, and the CH3CH2Cl product is hydrolyzed to obtain ethanol.

[0007] Furthermore, the Cl2 is obtained by electrolyzing NaCl solution in an electrocatalytic reaction cell, and the electrolyte containing Cl2 obtained at the anode after electrolysis is used as a reactant to react with ethane.

[0008] Furthermore, the current density applied during the electrolysis of NaCl solution is 300-1000 mA / cm². 2 The concentration of the NaCl solution is 0.5-5.4M.

[0009] Furthermore, the photocatalytic reaction is carried out in a continuous flow photocatalytic reaction cell, which is a transparent microchannel with an inner diameter of 3.5-10 mm;

[0010] The light source used is a xenon lamp with an output power of 200-400W and a wavelength of 300-1000nm.

[0011] Furthermore, the reaction pressure in the continuous flow photocatalytic reaction tank during the photocatalytic reaction process is 0.5-5 bar.

[0012] Furthermore, the flow rate of ethane introduced into the continuous flow photocatalytic reaction cell is 2-100 mL / min, and the flow rate of the electrolyte containing Cl2 is 1-15 mL / min.

[0013] Furthermore, the continuous flow photocatalytic reaction cell is made of PFA, glass, or quartz.

[0014] Furthermore, the CH3CH2Cl product hydrolysis involves mixing the CH3CH2Cl product with the cathode electrolyte obtained from the electrolysis of NaCl solution, and then heating the mixture to produce ethanol.

[0015] Furthermore, the temperature of the heating reaction is 60-100℃.

[0016] Furthermore, the heating reaction is carried out in a microreactor, which is a pipe with an inner diameter of 3.5-10 mm and equipped with a heating element made of PFA, glass or quartz.

[0017] This invention employs a cascaded photocatalytic system to efficiently convert ethane into ethanol. The system consists of an electrocatalytic reaction cell and a photocatalytic reaction cell, with the electrocatalytic reaction cell sequentially connected to a peristaltic pump, a three-way valve, and the photocatalytic reaction cell via pipelines. Applying voltage to the electrocatalytic reaction cell generates an electrolyte containing elemental chlorine. This chlorine-containing electrolyte is pumped to the three-way valve via the peristaltic pump, while ethane gas is also introduced into the three-way valve. The volume ratio of the chlorine-containing electrolyte to ethane is adjusted by regulating the three-way valve. The mixed gas then enters the photocatalytic reaction cell, where catalytic conversion occurs under light source excitation. The resulting mixture undergoes gas-liquid separation, and the resulting gas is mixed with the cathode electrolyte from the electrocatalytic reaction cell and then introduced into a microreactor. Under heating conditions, ethanol is obtained.

[0018] Compared with the prior art, the present invention has the following superior effects:

[0019] (1) This invention utilizes a chlorine-mediated strategy, introducing solar radiation to promote the cleavage of Cl-Cl bonds in Cl2 molecules, forming active chlorine, thereby promoting the conversion of ethane to ethanol. The current density reaches 1 A / cm². 2 The Faraday efficiency of ethanol can reach approximately 60%. (At 300 mA / cm²) 2 Operating for 110 hours under these conditions, the system consistently maintained approximately 78% Faraday efficiency and approximately 60% energy conversion efficiency. At a maximum of 1 A / cm²... 2 At the given current density, with a Faraday efficiency approaching 78%, the ethanol yield reached 1.56 × 10⁻⁶. 8 μmol / g cat / h is currently the most advanced and efficient system reported for the selective oxidation of ethane to produce ethanol.

[0020] (2) This invention utilizes anodic electrolysis of NaCl solution to obtain an anolyte containing Cl2. This anolyte is then reacted with ethane in a microreactor to form a gas-liquid plug flow, thereby improving mass transfer. A continuous-flow photocatalytic reaction tank with an inner diameter of 3.5-10 mm achieves gas-liquid closure. Photoexcitation decomposes Cl2 into active Cl, which reacts with ethane to selectively generate chloroethane. The continuous-flow photocatalytic reactor is a transparent spiral tube. The oscillation of surface waves formed at the gas-liquid interface within the tube accelerates interface renewal, thereby increasing the ethane mass transfer coefficient and ultimately achieving photoelectric reaction rate matching. After generating chloroethane, it is coupled with OH- generated at the cathode for hydrolysis, achieving efficient and selective ethanol production. The chloride ions generated from the hydrolysis of chloroethane can be reused for anodic electrolysis to produce elemental Cl2, realizing a Cl cycle.

[0021] Compared to previous reports, the maximum bias current density of this system exceeds 800 mA / cm². 2 (Currently reported technologies are all below 20mA / cm) 2 It maintains excellent ethanol selectivity and production efficiency even after running continuously for more than 100 hours, making it a more efficient and stable reaction system compared to currently reported electrocatalytic or photocatalytic technologies.

[0022] (3) The present invention adopts a biomass green ethanol preparation technology with low energy consumption, high carbon utilization rate and high efficiency, which has obvious advantages over the current biomass ethanol in terms of economic feasibility and technical superiority. Attached Figure Description

[0023] Figure 1 Schematic diagram of a reaction system for the continuous electro-photocatalytic production of ethanol from ethane;

[0024] Figure 2 This invention is compared with previously reported selective electro-oxidation techniques for the preparation of alcohols from alkanes.

[0025] Figure 3 The Faraday efficiency of selective oxidation of ethane at different current densities;

[0026] Figure 4 The conversion rate of ethane chloride to ethanol at different current densities;

[0027] Figure 5 The results are from the 1H NMR spectrum of ethanol. Detailed Implementation

[0028] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0029] This invention provides a halogen-mediated photoelectrocatalytic conversion of ethane to ethanol, employing methods such as... Figure 1 The continuous electro-photocatalytic reaction system shown includes, in sequence, an electrocatalytic reaction cell 1, a peristaltic pump 2, a three-way valve 3, a continuous flow photocatalytic reaction cell 4, a gas-liquid separator 6, a microreactor 8, and a gas-liquid separation device 9. A light source 5 is installed on the continuous flow photocatalytic reaction cell 4. The gas separated by the gas-liquid separator 6 enters the microreactor 8, while the liquid returns to the electrolyte storage container 7 of the electrocatalytic reaction cell 1. The specific method is as follows:

[0030] (1) Preparation of the anode catalyst: Titanium felt was used as the supporting electrode and impregnated in an aqueous solution of iridium chloride, with the pH controlled at 7-8, for 20-40 minutes, preferably 30 minutes. Subsequently, it was calcined in air at 300-400℃ for 2-4 hours. The iridium loading was 0.05-0.2 mg / cm³.2 0.1 mg / cm³ is preferred. 2 The resulting titanium felt-supported iridium oxide catalyst served as the anode catalyst.

[0031] (2) Preparation of cathode catalyst: A commercially available 50% Pt / C catalyst was dispersed in ethanol, and Nafion solution was added. The dispersion was then uniformly prepared under ultrasonic conditions. The catalyst was then sprayed layer by layer onto H-060 carbon paper from Toray Industries, Ltd. of Japan, and vacuum dried at room temperature. The loading of the Pt / C catalyst was controlled at 0.5-2 mg / cm³. 2 1 mg / cm 2 A cathode catalyst was obtained.

[0032] (3) Construction of electrocatalytic reaction cell 1: The anode catalyst obtained in step (1) and the cathode catalyst obtained in step (2) are respectively placed on both sides of the proton exchange membrane to form a three-in-one membrane electrode. Multiple membrane electrodes are stacked between the anode and cathode plates and an electrolyte is introduced to form a zero-gap membrane electrode cell. A 0.5-5.4M, preferably 5.4M NaCl solution is used as the electrolyte for electrolytic Cl- oxidation to prepare Cl2.

[0033] (4) Apply 300-1000 mA / cm to electrocatalytic reaction tank 1 2 The current is used to electrolyze a NaCl solution. At the anode, an electrolyte containing Cl2 is obtained, and at the cathode, a solution containing NaOH is obtained.

[0034] The reaction equation is: 2NaCl + H₂O = Cl₂ + 2NaOH

[0035] (5) Ethane and the electrolyte containing Cl2 obtained in step (4) are mixed through a three-way valve 3 and then introduced into a continuous flow photocatalytic reaction cell 4. The flow rate of ethane gas is controlled at 2-100 mL / min and the flow rate of electrolyte containing Cl2 is controlled at 1-15 mL / min. The photocatalytic reaction is carried out under light conditions using a 1 bar pressure gauge.

[0036] The reaction equation is: CH3CH3 + Cl2 = CH3CH2Cl + HCl

[0037] Among them, the continuous flow photocatalytic reaction cell 4 is a transparent microchannel with an inner diameter of 3.5-10mm; the light source used is a xenon lamp with an output power of 200-400W and a wavelength of 300-1000nm;

[0038] (6) The gas and solution obtained from the photocatalytic reaction in step (5) are separated by a gas-liquid separator 6. The separated gas is a mixture of ethane and chloroethane, and the resulting solution is returned to the storage container 7 for storing NaCl solution.

[0039] (7) The ethane / chloroethane mixed gas obtained in step (6) is mixed with the NaOH-containing solution prepared in step (4), and then fed into microreactor 8 and heated to react at 60-100℃.

[0040] The reaction equation is: CH3CH2Cl + NaOH = CH3CH2OH + NaCl

[0041] Among them, the microreactor 8 is a reactor with an inner diameter of 3.5-10mm, and the material is PFA, glass or quartz.

[0042] (8) The gas and liquid after the reaction in the microreactor 8 are separated by a gas-liquid separator 9. The gas is unreacted ethane, and the final ethanol product is collected in the liquid.

[0043] like Figure 2 The figure shows a comparison between the present invention and existing technologies for the selective oxidation of ethane to ethanol. It can be seen that the present invention achieves [efforts] at 1000 mA / cm². 2 At current densities, the invention achieves a Faraday efficiency exceeding 78%, and a maximum bias current density exceeding 800 mA / cm² compared to previously reported methods. 2 (Currently reported technologies are all below 20mA / cm) 2 This invention maintains excellent ethanol selectivity and production efficiency even after continuous operation for over 100 hours, making it a more efficient and stable reaction system compared to currently reported electrocatalytic or photocatalytic technologies. This invention achieves a breakthrough in current density by two orders of magnitude while ensuring high ethanol selectivity and Faraday efficiency.

[0044] Unless otherwise specified, the raw materials and equipment used in this invention are all commercially available or commonly used equipment.

[0045] Example 1

[0046] The selective oxidation of ethane to ethanol via photocoupled low current density is described in the following steps:

[0047] (1) Titanium felt was used as the supporting electrode and immersed in an aqueous solution of iridium chloride at a pH of 7-8 for 30 minutes. It was then calcined in air at 350°C for 3 hours. The iridium loading was 0.1 mg / cm³. 2 The titanium felt-supported iridium oxide prepared was used as the anode catalyst.

[0048] (2) 20 mg of commercially available 50% Pt / C catalyst (i.e., 10 mg Pt, 10 mg C) was dispersed in 1.5 mL of ethanol, and 100 μL of Nafion solution was added. The dispersion was then uniformly dispersed under ultrasonic conditions. The catalyst was then sprayed layer by layer onto H-060 carbon paper from Toray Industries, Inc. of Japan, and vacuum dried at room temperature. The loading of the Pt / C catalyst was controlled at 1 mg / cm³. 2 A cathode catalyst was obtained.

[0049] (3) The anode catalyst obtained in step (1) and the cathode catalyst obtained in step (2) are placed on both sides of the proton exchange membrane to form a "three-in-one" membrane electrode. Multiple membrane electrodes are stacked to form an electrocatalytic reaction cell 1. Both the cathode and anode electrolytes are 5.4M NaCl. The current density applied to the electrocatalytic reaction cell 1 is controlled to be 300 mA / cm². 2 Electrolysis of NaCl solution yields an electrolyte containing Cl2 at the anode and a catholyte containing NaOH at the cathode.

[0050] (4) The obtained anolyte (a solution containing elemental Cl2) is mixed with ethane through a three-way valve 2 and then introduced into a continuous flow photocatalytic reaction cell 4. The ethane gas flow rate is controlled at 10 mL / min and the anolyte flow rate is controlled at 5 mL / min, using a 1 bar pressure gauge.

[0051] (5) The continuous flow photocatalytic reaction cell 4 is a transparent microchannel. In this embodiment, a transparent quartz tube with an inner diameter of 3.5 mm is selected. The illumination conditions include: xenon lamp output power of 300 W and wavelength of 300-1000 nm; reaction pressure of 1 bar; and the material of the transparent microchannel is PFA.

[0052] (6) The gas and solution obtained from the reaction in the continuous flow photocatalytic reactor 4 are separated by a gas-liquid separator. The resulting solution is returned to the electrolyte storage container 7, and the resulting gas is an ethane / chloroethane mixture.

[0053] (7) The ethane / monochloroethane mixed gas is mixed with the cathode electrolyte after the reaction in the electrocatalytic reaction cell 1, and then passed into the microreactor 8 for heating at a temperature of 80°C. The gas and liquid after the reaction in the microreactor 8 are separated by a gas-liquid separator 9. The gas is unreacted ethane, and the final ethanol product is collected in the liquid. In this embodiment, the microreactor 8 is a quartz tube with an inner diameter of 3.5 mm.

[0054] The collected liquid products were analyzed by proton nuclear magnetic resonance (NMR) spectroscopy. 1 H NMR) confirmed, such as Figure 5 As shown, through the product 1Analysis of the H-NMR spectrum revealed a triplet at approximately δ 1.2 ppm, originating from the methyl group (-CH3-) in the ethanol molecule. Another triplet was observed at approximately δ 3.5 ppm, also originating from the methylene group (-CH2-) in the ethanol molecule. A dimethyl sulfoxide (DMSO) signal was detected at δ 2.3 ppm. No other significant impurity signals were detected. Therefore, the main component of the product can be identified as ethanol.

[0055] The Faraday efficiency of selective oxidation of ethane at different current densities is as follows: Figure 3 As shown. For example, at 300mA / cm 2 At the given current density, the Faraday efficiency is 78%, and the partial current density of ethanol can reach 234 mA / cm². 2 .

[0056] The conversion rate of chloroethane to ethanol at different current densities, such as Figure 4 As shown, at a current density of 300 mA / cm² 2 At that time, the selectivity of ethanol was 98%, which indicates that the method used has a significant effect on improving the selectivity of ethanol.

[0057] Example 2

[0058] The selective oxidation of ethane to ethanol via high-current-density photocoupled oxidation was performed, with a current density of 500 mA / cm² applied to the electrocatalytic reaction cell in step (1). 2 The rest is the same as in Example 1.

[0059] Example 3

[0060] The selective oxidation of ethane to ethanol via high-current-density photocoupled oxidation was performed, with a current density of 750 mA / cm² applied to the electrocatalytic reaction cell in step (1). 2 The rest is the same as in Example 1.

[0061] Example 4

[0062] The selective oxidation of ethane to ethanol via high-current-density photocoupled oxidation was performed, with a current density of 1000 mA / cm² applied to the electrocatalytic reaction cell in step (1). 2 The rest is the same as in Example 1.

[0063] The products obtained in each embodiment and comparative example were subjected to performance testing, as follows:

[0064] Detection method: Collect the liquid phase containing the product and analyze it by nuclear magnetic resonance (NMR) 1H spectroscopy (NMR). 1 Confirmed by H NMR.

[0065] Yield calculation formula:

[0066]

[0067] Where, m a It is the amount of ethanol produced in the reaction, m cat t is the amount of catalyst used in the reaction, and t is the reaction time.

[0068] Faraday efficiency calculation formula:

[0069]

[0070] Where F is the Faraday constant, n a c is the number of electrons transferred during the formation of 1 mole of ethanol from ethane. a Through nuclear magnetic resonance hydrogen spectrum ( 1 The ethanol or ethanol concentration detected by H NMR, where V is the volume of the absorption solution and Q is the total current.

[0071] Formula for calculating electricity conversion efficiency:

[0072]

[0073] in, It is the thermodynamic potential of the product, E cell It is the battery voltage (non-iR compensation), ΔG o It is the change in Gibbs free energy of the reaction.

[0074] The test results are as follows:

[0075] Example 1 Example 2 Example 3 Example 4 Ethanol Faraday efficiency (%) 78 72 81 78 Ethanol selectivity (%) 98％ 98％ 97.9％ 98％ Ethanol yield (pmol / g cat / h) 4.36*10 7 ]]> 6.72*10 7 ]]> 1.13*10 8 ]]> 1.56*10 8 <!-- 5 -->]]> Ethanol partial current density 234 360 607 780

[0076]

[0077] As can be seen from the table above, the ethanol Faraday efficiency consistently remains above 70%, and the selectivity consistently remains above 97%, indicating that this invention exhibits good single-selectivity for ethanol. The ethanol partial current density can reach a maximum of 780 mA / cm². 2 The energy utilization efficiency can reach 55%, indicating that the present invention has feasible application prospects. In summary, these data fully demonstrate that our technical solution has superior performance advantages and can meet practical application needs.

Claims

1. A method for preparing ethanol by halogen-mediated ethane oxidation, characterized in that, Ethane is mixed with Cl2 generated from the electrolysis of NaCl solution. Under light irradiation, the Cl-Cl bonds in the Cl2 molecules break, forming active chlorine, which promotes the photocatalytic reaction of ethane to produce CH3CH2Cl product. The CH3CH2Cl product is then hydrolyzed to give ethanol.

2. The method for preparing ethanol by halogen-mediated ethane oxidation according to claim 1, characterized in that, The Cl2 is obtained by electrolyzing NaCl solution in an electrocatalytic reaction cell, and the electrolyte containing Cl2 obtained at the anode after electrolysis is used as a reactant to react with ethane.

3. The method for preparing ethanol by halogen-mediated ethane oxidation according to claim 2, characterized in that, The applied current density for electrolyzing NaCl solution is 300-1000 mA / cm². 2 The concentration of the NaCl solution is 0.5-5.4M.

4. The method for preparing ethanol by halogen-mediated ethane oxidation according to claim 1, characterized in that, The photocatalytic reaction is carried out in a continuous flow photocatalytic reaction cell, which is a transparent microchannel with an inner diameter of 3.5-10 mm. The light source used is a xenon lamp with an output power of 200-400W and a wavelength of 300-1000nm.

5. The method for preparing ethanol by halogen-mediated ethane oxidation according to claim 4, characterized in that, The reaction pressure in the continuous flow photocatalytic reaction tank during the photocatalytic reaction process is 0.5-5 bar.

6. The method for preparing ethanol by halogen-mediated ethane oxidation according to claim 4, characterized in that, The flow rate of ethane introduced into the continuous flow photocatalytic reaction cell is 2-100 mL / min, and the flow rate of the electrolyte containing Cl2 is 1-15 mL / min.

7. The method for preparing ethanol by halogen-mediated ethane oxidation according to claim 4, characterized in that, The continuous flow photocatalytic reaction cell is made of PFA, glass, or quartz.

8. The method for preparing ethanol by halogen-mediated ethane oxidation according to claim 1, characterized in that, The aforementioned CH3CH2Cl product hydrolysis involves mixing the CH3CH2Cl product with the cathode electrolyte obtained from the electrolysis of NaCl solution, and then heating the mixture to produce ethanol.

9. The method for preparing ethanol by halogen-mediated ethane oxidation according to claim 8, characterized in that, The heating reaction is carried out at a temperature of 60-100℃.

10. The method for preparing ethanol by halogen-mediated ethane oxidation according to claim 8, characterized in that, The heating reaction is carried out in a microreactor, which is a pipe with an inner diameter of 3.5-10 mm and equipped with a heating element made of PFA, glass or quartz.

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