Method for preparing ethylene by decarboxylation of succinic acid through polar-alternating square-wave electric oxidation

Abstract

The application discloses a method for preparing ethylene by decarboxylation of succinic acid through square-wave electro-oxidation with polarity alternation, and belongs to the technical field of new energy chemical industry. In order to eliminate the problems of catalyst deactivation and rapid poisoning, a graphite sheet is used as a working electrode in an electrolytic system, and a succinate aqueous solution is used as a substrate in an electrolyte. Square-wave alternating current with polarity alternation is applied between the working electrode and a counter electrode, so that ethylene and hydrogen are prepared through electro-catalysis. The application can effectively maintain the activity of the catalyst, accurately control the reaction path, complete the conversion from the Kolbe dimerization to the non-Kolbe path with high selectivity for generating ethylene, realize the efficient and continuous conversion of the succinic acid electro-oxidation decarboxylation for preparing ethylene, and is expected to be applied to actual production.

Description

Technical Field

[0001] This invention belongs to the field of new energy chemical technology, specifically relating to a method for producing ethylene by square wave electro-oxidation of succinic acid with alternating polarity to produce ethylene. Background Technology

[0002] Ethylene (C2H4), as the core monomer raw material of modern chemical industry, has a global annual production exceeding 100 million tons, with downstream derivatives covering all key sectors of the national economy, including plastics, fibers, rubber, and solvents. However, almost all ethylene production currently relies heavily on steam cracking processes using fossil fuels such as oil and natural gas. This traditional route is not only extremely energy-intensive but also accompanied by huge carbon dioxide emissions, running counter to the global trend of green chemical development. Therefore, developing a new technological route that can produce ethylene under mild conditions using renewable resources and clean energy is of crucial strategic significance for breaking fossil fuel dependence and promoting the green transformation of industry.

[0003] Electrocatalytic synthesis technology, due to its ability to directly utilize electricity generated from renewable energy sources (such as wind and solar power) to drive chemical reactions at ambient temperature and pressure, is considered one of the key disruptive pathways to achieving future zero-carbon chemistry. Against this backdrop, converting abundant and inexpensive biomass or waste resources (such as food waste and crop residues) into high-value platform chemicals, and then further upgrading them to ethylene through electrocatalysis, constitutes a highly attractive sustainable closed-loop pathway from waste to chemicals. Among these pathways, the electrochemical decarboxylation of carboxylic acids (salts), particularly the long-established Kolbe electrolysis reaction and its derived non-Kolbe pathways, provides a direct theoretical and reaction basis for this route.

[0004] The direct electrocatalytic pathway using succinate as a raw material offers significant advantages. This pathway aligns with the natural product form of upstream sustainable processes, avoiding the energy-intensive acidification step. In recent years, green production technologies such as carbon dioxide electroreduction, biomass fermentation, and catalytic degradation of waste plastics have made significant progress. These processes typically operate under alkaline or near-neutral conditions, directly yielding carboxylate salts, not free carboxylic acids. Converting these salts into the corresponding carboxylic acids for subsequent use requires the introduction of a stronger acid for neutralization. This step not only consumes large amounts of chemical reagents but also generates byproduct salt wastewater. Subsequent separation and purification processes are complex and energy-intensive, severely undermining the economic and environmental benefits of the entire process. Specifically, this technology focuses on a pathway where organic waste such as kitchen waste can be efficiently and cost-effectively converted into succinate (succinate) aqueous solutions through mature microbial fermentation technology. This fermentation broth is the most direct and economical raw material form. The core advantage of this technical route lies in directly using this succinate solution as the electrocatalytic feed, completely eliminating the expensive and environmentally unfriendly acidification and purification unit operations necessary for converting to free succinic acid. This not only significantly simplifies the process flow and reduces equipment investment and operating costs, but also achieves seamless integration of upstream bioconversion and downstream electrochemical synthesis in terms of material form, which is a key design to drive the integrated technology toward practical application.

[0005] The electrochemical oxidative decarboxylation of carboxylic acids (salts), i.e., the classic Kolbe electrolysis, involves the loss of electrons by the carboxylate ion at the anode, generating an alkyl radical. Traditionally, two identical alkyl radicals undergo coupling dimerization to form symmetrical long-chain alkanes (such as decane), which are typical Kolbe products. Non-Kolbe reaction pathways involve the further oxidation of the resulting alkyl radicals to carbocations, which then undergo rearrangement, elimination, or capture steps to generate more reactive, high-value-added chemicals such as alkenes, alcohols, and esters. Ethylene, as one of the simplest olefins and non-Kolbe products, is a highly attractive target product due to its huge market demand and abundant downstream conversion routes. However, in aqueous Kolbe electrolysis systems, problems such as low current density and low olefin selectivity often exist, significantly limiting olefin production efficiency. Therefore, developing an electrocatalytic system that can efficiently and selectively guide specific carboxylate salts (such as succinate) to non-Kolbe pathways and stably produce ethylene is a core objective for achieving technological breakthroughs and value enhancement in this field.

[0006] Carbon-based anode materials such as graphite offer advantages such as high non-Kolbe product selectivity, low cost, and ease of scale-up production. However, applying a high operating potential (typically exceeding 2 volts (relative to a reversible hydrogen electrode) to achieve effective decarboxylation and suppress the competing oxygen evolution reaction (OER) can lead to irreversible electrochemical oxidation of the graphite electrode surface, forming oxygen-containing functional groups or causing corrosion. This results in a sharp decline in catalytic activity, significantly impacting production efficiency. Simultaneously, the deactivated electrode surface is more prone to side reactions such as water oxidation and over-oxidation, drastically reducing the Faradaic efficiency (current efficiency) of ethylene production, decreasing the utilization rate of raw materials and electrical energy, and causing uncontrolled production costs. Furthermore, frequent catalyst replacements due to catalyst stability issues threaten process continuity and economic viability, significantly increasing overall costs.

[0007] Research has shown (Zhang, X., Luo, L., Liu, C. et al. Anion intercalation enables efficient and stable carboxylate upgrading via aqueous non-Kolbeelectrolysis. Nature Communications, 2025, 16, 3719.) that passivation (poisoning) of graphite electrodes is not simply a matter of activity decay; it is often accompanied by damage to the surface microstructure, permanent coverage of active sites (such as blockage by polymer intermediates or carbonaceous deposits), or a decrease in mechanical strength. In actual scale-up processes, this directly manifests as a short catalyst lifetime. Frequent electrode downtime for regeneration, replacement, or reactor maintenance not only incurs high material and labor costs but also leads to production interruptions, fluctuations in product yield and quality, and makes the continuous operation reliability and overall manufacturing cost uncompetitive. For processes aimed at treating large quantities of waste biomass and producing bulk chemicals, the long-term operational stability of the catalyst (electrode) is a prerequisite for industrialization.

[0008] In conclusion, developing an integrated process for the highly selective synthesis of ethylene from succinate solution produced by waste biomass fermentation via aqueous-phase electrocatalytic decarboxylation is a significant potential pathway to achieve a green revolution in ethylene production. This pathway perfectly integrates with upstream sustainable resource conversion technologies, eliminates energy-intensive processes, and precisely targets high-value non-Kolby products, aligning with the trend of circular economy development.

[0009] However, the core obstacle to the industrial application of this technology lies in the fact that graphite anode materials, despite their low cost, inevitably suffer from severe passivation and deactivation under harsh aqueous oxidative decarboxylation reaction conditions. This leads to high reaction overpotentials, low Faraday efficiency, and short catalyst lifetime, severely restricting the economic benefits and operational reliability of the process. Therefore, effectively solving or significantly mitigating the stability problem of graphite electrodes in this specific application scenario, and developing anode catalyst materials or modification technologies that combine high activity, high ethylene selectivity, and long-term operational capability, is key to breaking through current R&D bottlenecks and propelling this green synthesis technology from the laboratory to industrial practice. This invention addresses this pressing industrial technical challenge by providing an innovative solution. Summary of the Invention

[0010] To address the severe passivation (poisoning) and deactivation problem of graphite electrodes under aqueous phase and high-potential oxidation conditions, this invention provides a method for the decarboxylation of succinic acid to ethylene via square wave electro-oxidation with alternating polarities. This method eliminates catalyst deactivation and rapid poisoning through square wave electrolysis, effectively maintaining catalyst activity and precisely controlling the reaction pathway. It completes the conversion from Kolbe dimerization to a non-Kolbe pathway with high selectivity for ethylene production, achieving efficient and continuous conversion of succinic acid to ethylene via electro-oxidation. This method is expected to be applied in actual production.

[0011] The technical solution adopted in this invention is as follows:

[0012] A method for producing ethylene by alternating polarity square wave electro-oxidation of succinic acid to decarboxylate involves using a graphite sheet as the working electrode in an electrolytic system, and an aqueous solution of succinate as the substrate in the electrolyte. Alternating polarity square wave alternating current (e.g., ...) is applied between the working electrode and the counter electrode. Figure 1 As shown, ethylene and hydrogen are produced by electrocatalysis.

[0013] Furthermore, the electrocatalytic performance of graphite sheets can be modulated by changing the square wave period, square wave current, or square wave potential.

[0014] Furthermore, the pH value of the electrolyte is adjusted by adding acidic or alkaline substances that do not participate in the reaction.

[0015] Furthermore, the concentration of succinate in the electrolyte is 0.1 mol / L to 1 mol / L, preferably 0.5 mol / L.

[0016] Furthermore, the cation of the succinate is one or more of sodium ion, potassium ion, ammonium ion, and lithium ion.

[0017] Furthermore, the electrolysis system is a two-electrode system or a three-electrode system, and its reaction device is an H-type electrolytic cell, a flow-type electrolytic cell, or a membrane-free electrolytic cell, preferably a flow-type electrolytic cell.

[0018] Furthermore, the reference electrode in the electrolysis system is a mercurous sulfate electrode, a silver / silver chloride electrode, a saturated calomel electrode, or a mercury / mercury oxide electrode.

[0019] Furthermore, the membrane in the electrolysis system is a proton exchange membrane, an anion exchange membrane, or a bipolar membrane.

[0020] Furthermore, the duty cycle of the square wave alternating current is 20% to 80%, preferably 50%.

[0021] Furthermore, the period of the square wave alternating current is 1 second to 600 seconds, preferably 10 seconds to 240 seconds.

[0022] Furthermore, the current density of the square wave alternating current is 0.01 amperes per square centimeter to 0.5 amperes per square centimeter, preferably 0.05 amperes per square centimeter to 0.35 amperes per square centimeter.

[0023] Furthermore, the potential of the square wave alternating current is 2 volts to 15 volts, preferably 2 volts to 13 volts.

[0024] Furthermore, the thickness of the graphite sheet is 0.1 cm to 0.5 cm, preferably 0.1 cm.

[0025] Furthermore, the graphite sheet is cut to a size of 1 cm × 1 cm to 3 cm × 3 cm, preferably 1 cm × 2 cm.

[0026] Furthermore, the graphite sheet also includes a pretreatment process before use, specifically a cleaning and drying process.

[0027] This invention proposes a method for the decarboxylation of succinic acid to ethylene using square wave electro-oxidation with alternating polarities. Compared with the prior art, the advantages of this invention are as follows:

[0028] 1. Under aqueous phase and high-potential oxidation conditions, commonly used low-cost graphite electrodes suffer from severe passivation (poisoning) and deactivation, leading to continuously increasing overpotential, decreased Faraday efficiency (selectivity), and extremely short catalyst lifetime. This is the main obstacle restricting the industrialization of this technology. This invention effectively solves the aforementioned graphite electrode poisoning problem by applying alternating polarity square wave alternating current to the graphite electrode. While ensuring high catalytic activity and high ethylene selectivity, it significantly improves the long-term operational stability of the graphite electrode under harsh reaction conditions, and reduces energy consumption and electrode replacement frequency, making continuous, efficient, and economical industrial operation possible.

[0029] 2. Traditional carboxylic acid electrochemical conversion (Kolbe electrolysis) primarily aims to generate symmetrical long-chain alkanes (such as decane) as fuel, with limited added value and not ideal chemical feedstocks (such as ethylene). This invention, through square-wave electro-oxidation of succinate aqueous solution, precisely controls the reaction pathway to achieve a conversion from Kolbe dimerization to a non-Kolbe pathway with high selectivity for ethylene production. This elevates the target product from a low-value-added fuel component to ethylene, a basic chemical feedstock with the largest global demand and the most diverse downstream industrial chain, achieving a fundamental leap in the value chain of electrochemically upgraded products.

[0030] 3. Traditionally, carboxylates obtained from biomass, waste, or CO2 conversion require a high-energy- and high-material-consumption acidification step to convert them into free carboxylic acids for further electrochemical conversion. This process is lengthy, costly, and generates a large amount of waste salt. This invention directly uses succinate aqueous solution produced by fermentation or other sustainable processes as the electrocatalytic feedstock, completely eliminating the expensive intermediate acidification and purification steps. It achieves seamless integration of upstream bioconversion and downstream electrosynthesis in terms of material form, greatly shortening the process chain, significantly reducing equipment investment, operating costs, and environmental burden, and enabling distributed, modular production. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the alternating polarity square wave AC proposed in this invention;

[0032] Figure 2 The Faraday efficiency of ethylene and acrylic acid under a 10-second square wave period in Example 1;

[0033] Figure 3 The Faraday efficiency of ethylene and acrylic acid under a 20-second square wave period in Example 1;

[0034] Figure 4 The Faraday efficiency of ethylene and acrylic acid under a 60-second square wave period in Example 1;

[0035] Figure 5 The current density-voltage curves under different square wave periods in Example 1 are shown.

[0036] Figure 6 The electrochemical in-situ impedance spectrum obtained from simulated DC electrolysis in Example 2;

[0037] Figure 7 The electrochemical in-situ impedance spectrum obtained from the simulated square wave electrolysis in Example 2;

[0038] Figure 8 The X-ray diffraction patterns of the initial graphite catalyst that did not participate in electrolysis, the graphite catalyst after DC electrolysis, and the graphite catalyst after square wave electrolysis in Example 3 are shown.

[0039] Figure 9 The images show scanning electron microscope (SEM) images and scanning electron microscope (SEM) component distribution surface scans of the initial graphite catalyst that did not participate in electrolysis in Example 3.

[0040] Figure 10 The images show scanning electron microscope (SEM) images and scanning electron microscope (SEM) images of the graphite catalyst after DC electrolysis in Example 3.

[0041] Figure 11 The images shown are scanning electron microscope (SEM) images and scanning electron microscope (SEM) component distribution surface scans of the graphite catalyst after square wave electrolysis in Example 3.

[0042] Figure 12 The Faraday efficiency of ethylene and acrylic acid under a 60-second square wave period in Example 4;

[0043] Figure 13 The Faraday efficiency of ethylene and acrylic acid under a 120-second square wave period in Example 4;

[0044] Figure 14 The Faraday efficiency of ethylene and acrylic acid under a 240-second square wave period in Example 4;

[0045] Figure 15 The current density-voltage curves under different square wave periods are shown in Example 4.

[0046] Figure 16 This is a stability performance diagram of DC electrolysis in Example 5;

[0047] Figure 17 The stability performance diagram of square wave electrolysis in Example 5 is shown.

[0048] Figure 18 The current-voltage curves of the membraneless flow electrolyzer in Example 6 are shown.

[0049] Figure 19 The ethylene Faraday efficiency of the membraneless flow electrolyzer in Example 6 at different potentials;

[0050] Figure 20 The current-time curve of the membraneless flow electrolyzer in Example 6;

[0051] Figure 21 The image shows the Faraday efficiency-time curve of the membraneless flow electrolyzer in Example 6. Detailed Implementation

[0052] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings. The illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0053] Example 1

[0054] This embodiment proposes a method for the decarboxylation of succinic acid to ethylene via square wave electro-oxidation with alternating polarity, comprising the following steps:

[0055] Step 1: Pretreatment of graphite catalyst:

[0056] Commercial graphite sheets with a thickness of 0.1 cm are cut into 1 cm × 2 cm graphite sheets. They are first sonicated in anhydrous ethanol for 10 minutes, then washed with ultrapure water, and finally dried overnight in a vacuum oven at 40 degrees Celsius to complete the pretreatment and obtain the graphite catalyst.

[0057] Step 2: The decarboxylation of succinic acid to ethylene is carried out in a flow electrolytic cell using alternating polarity square wave electrooxidation, specifically as follows:

[0058] The graphite catalyst obtained in step 1 was used as the working electrode, the platinum-plated titanium felt as the counter electrode, and silver / silver chloride as the reference electrode. A 0.5 M sodium succinate aqueous solution was used as the working electrode electrolyte, pumped into the working electrode side at a rate of 1 mL per minute, with an actual working area of ​​1.5 cm × 0.5 cm. A 0.5 mol / L sulfuric acid solution was used as the counter electrode electrolyte, pumped into the counter electrode side at a rate of 5 mL per minute, with an actual working area of ​​1.5 cm × 0.5 cm. The diaphragm was a proton exchange membrane.

[0059] Electrolysis tests were conducted using square wave alternating current with the following parameters: anode current densities of 50, 75, 100, 125, 150, and 175 mA per square centimeter, and corresponding cathode current densities of -50, -75, -100, -125, -150, and -175 mA per square centimeter. The anode and cathode currents had the same value but opposite signs, and the application times were 5, 10, and 30 seconds, with total periods of 10, 20, and 60 seconds, respectively.

[0060] Electrolysis was performed continuously for 30 minutes in a three-electrode system of a flow electrolyzer. Afterward, gaseous and liquid products were collected for analysis, and the potentials corresponding to different current densities were recorded.

[0061] The gaseous product of the reaction (ethylene) was passed through an argon carrier gas at a flow rate of 40 standard cubic centimeters per minute. An eight-minute mixture of ethylene and argon was collected using a gas collecting bag and then sent online to a gas chromatograph equipped with a thermal conductivity detector for analysis. After electrolysis, 5 mL of electrolyte from the anode chamber was collected, and the liquid product of the reaction (acrylic acid) was detected using high-performance liquid chromatography (HPLC). The Faraday efficiencies of ethylene and acrylic acid at the working electrode were calculated. The Faraday efficiencies of ethylene and acrylic acid at total periods of 10, 20, and 60 seconds are as follows: Figures 2-4 As shown, the Faraday efficiency of ethylene varies with the square wave current density, reaching a maximum of 27%.

[0062] Figure 5The current density-voltage curves for different cycles show that, compared to existing technologies, the potentials are higher across all cycles. At low current densities, the voltages are essentially consistent across cycles. At high current densities, the voltage is lower at a 10-second cycle compared to cycles of 20 and 60 seconds, indicating a stronger depollution effect on the catalyst at a 10-second cycle. It should be noted that... Figures 2-4 It can be observed that the Faraday efficiency is generally low when the period is 10 seconds. This is because, under the same current, more charge is used for charging and discharging, while less charge is used for the actual reaction. In practical applications, the period should be selected appropriately based on the above considerations.

[0063] Example 2

[0064] This embodiment simulates both direct current electrolysis and square wave electrolysis processes in an H-type electrolytic cell, and performs in-situ electrochemical impedance spectroscopy on the pretreated graphite catalyst obtained in Example 1. Specifically:

[0065] The pretreated graphite catalyst obtained in Example 1 was used as the working electrode, platinum-plated titanium felt as the counter electrode, silver / silver chloride as the reference electrode, and a 0.5 mol sodium succinate aqueous solution as the anolyte. A diaphragm was used as the proton exchange membrane.

[0066] For the DC electrolysis process, the constant current potential was 1.5 volts relative to the silver / silver chloride electrode, the frequency range was 1 MHz to 0.1 Hz, and the impedance spectroscopy was performed 20 times. The resulting electrochemical in-situ impedance spectrum is shown below. Figure 6 As shown, with increasing scan count, the semicircle representing charge transfer resistance gradually increases, indicating an increase in charge transfer resistance and a slowdown in electrocatalytic reaction kinetics. This phenomenon is attributed to the dielectric oxide graphite layer, whose formation trend is similar to that of the solid electrolyte interface in a battery, leading to inhibition of electron transfer. The deactivation of the graphite catalyst is attributed to the formation of a fully oxidized surface layer, which blocks active sites in the form of oxidized functional groups and hinders electron transfer, resulting in increased reaction potential and decreased catalytic performance.

[0067] For the square wave electrolysis process, the square wave AC potential was ±1.5 volts relative to the silver / silver chloride electrode, alternating between cycles, with a frequency range of 1 MHz to 0.1 Hz. The impedance spectroscopy was performed 20 times, and the resulting in-situ electrochemical impedance spectroscopy is shown below. Figure 7 As shown, with the increase of the number of scans, the semicircle representing the charge transfer resistance remains in a small range, indicating that the square wave electrolysis with alternating polarities can solve the poisoning problem of graphite catalysts.

[0068] Example 3

[0069] This embodiment characterizes the initial graphite catalyst before electrolysis, the graphite catalyst after DC electrolysis, and the graphite catalyst after square wave electrolysis, respectively; wherein, the initial graphite catalyst before electrolysis is the pretreated graphite catalyst obtained in Example 1; the graphite catalyst after DC electrolysis and the graphite catalyst after square wave electrolysis are obtained by electrocatalysis in a flow electrolytic cell, specifically:

[0070] The pretreated graphite catalyst obtained in Example 1 was used as the working electrode, the platinum-plated titanium felt as the counter electrode, and silver / silver chloride as the reference electrode. A 0.5 mol sodium succinate aqueous solution was used as the working electrode electrolyte and was pumped into the working electrode side at a rate of 1 mL per minute, with an actual working area of ​​1.5 cm × 0.5 cm. A 0.5 mol / L sulfuric acid solution was used as the counter electrode electrolyte and was pumped into the counter electrode side at a rate of 5 mL per minute, with an actual working area of ​​1.5 cm × 0.5 cm. The membrane was a proton exchange membrane.

[0071] A constant current electrolysis method was used, with a current density of 100 mA per square centimeter and an electrolysis time of 1 hour, to obtain a graphite catalyst after DC electrolysis.

[0072] Square wave AC electrolysis was adopted, with the following parameters: the anode current density was 100 mA per square centimeter, and correspondingly, the cathode current density was -100 mA per square centimeter. The anode and cathode currents had the same value but opposite signs. The application time was 5 seconds, the total cycle was 10 seconds, and the electrolysis time was 1 hour, resulting in a graphite catalyst after square wave electrolysis.

[0073] The initial graphite catalyst that did not participate in electrolysis, the graphite catalyst after DC electrolysis, and the graphite catalyst after square wave electrolysis were vacuum dried for 12 hours and then characterized as follows:

[0074] The X-ray diffraction patterns of the three are as follows: Figure 8 As shown, neither the constant current electrolysis reaction nor the square wave AC electrolysis reaction changed the basic structure of the graphite catalyst.

[0075] The scanning electron microscope images and component distribution plane scans of the three are as follows: Figures 9-11 As shown, where, Figure 9 of (a) Figure 10 (a) and Figure 11 (a) are all corresponding scanning electron microscope images. Figure 9 (bd) Figure 10 (bd) and Figure 11The (bd) images are the corresponding component distribution surface scans. It can be seen that the surface of the initial graphite catalyst that did not participate in the electrolysis contained only a small amount of oxygen. The graphite catalyst after DC electrolysis contained more oxygen, while the graphite catalyst after square wave electrolysis did not show a significant increase in oxygen. This indicates that the square wave electrolysis method can reduce the surface oxidation and poisoning of graphite electrodes during the reaction process, thereby extending the stability of the electrodes.

[0076] Example 4

[0077] This embodiment proposes a method for the decarboxylation of succinic acid to ethylene via square wave electro-oxidation with alternating polarity, comprising the following steps:

[0078] Step 1: Pretreatment of the graphite catalyst is carried out according to Step 1 of Example 1.

[0079] Step 2: The decarboxylation of succinic acid to ethylene is carried out in a flow electrolytic cell using alternating polarity square wave electrooxidation, specifically as follows:

[0080] The graphite catalyst obtained in step 1 was used as the working electrode, the platinum-plated titanium felt as the counter electrode, and silver / silver chloride as the reference electrode. An aqueous solution of 0.5 mol disodium succinate and 0.1 mol potassium hydroxide was used as the working electrode electrolyte, which was pumped into the working electrode side at a rate of 1 mL per minute, with an actual working area of ​​1.5 cm × 0.5 cm. A potassium hydroxide solution with a concentration of 0.5 mol per liter was used as the counter electrode electrolyte, which was pumped into the counter electrode side at a rate of 5 mL per minute, with an actual working area of ​​1.5 cm × 0.5 cm. The membrane was a proton exchange membrane.

[0081] Electrolysis tests were conducted using square wave alternating current with the following parameters: anode current densities of 50, 100, 150, 200, 250, and 300 mA per square centimeter, and corresponding cathode current densities of -50, -100, -150, -200, -250, and -300 mA per square centimeter. The anode and cathode currents had the same value but opposite signs, and the application times were 30, 60, and 120 seconds, with total periods of 60, 120, and 240 seconds, respectively.

[0082] Electrolysis was performed continuously for 30 minutes in a three-electrode system of a flow electrolyzer. Afterward, gaseous and liquid products were collected for analysis, and the potentials corresponding to different current densities were recorded.

[0083] The gaseous product of the reaction (ethylene) was passed through an argon carrier gas at a flow rate of 40 standard cubic centimeters per minute. An eight-minute mixture of ethylene and argon was collected using a gas collecting bag and then sent online to a gas chromatograph equipped with a thermal conductivity detector for analysis. After electrolysis, 5 mL of electrolyte from the anode chamber was collected, and the liquid product of the reaction (acrylic acid) was detected using high-performance liquid chromatography (HPLC). The Faraday efficiencies of ethylene and acrylic acid at the working electrode were calculated. The Faraday efficiencies of ethylene and acrylic acid at total periods of 60, 120, and 240 seconds are as follows: Figures 12-14 As shown, it can be seen that the ethylene Faraday efficiency and square wave current density are further improved in the alkaline electrolyte environment compared with the acidic electrolyte environment of Example 1.

[0084] Figure 15 The current density-voltage curves under different cycles are consistent with those in Example 1. Under low current density, the voltage under different cycles is basically the same. Under high current density, the voltage is lower at a cycle of 60 seconds compared to cycles of 120 and 240 seconds, indicating that the depollution ability of the catalyst is stronger at a cycle of 60 seconds.

[0085] Example 5

[0086] In this embodiment, constant current electrolysis and square wave AC electrolysis were performed in a flow electrolytic cell to test the stability of the graphite catalyst. Specifically:

[0087] The pretreated graphite catalyst obtained in Example 1 was used as the working electrode, platinum-plated titanium felt as the counter electrode, and silver / silver chloride as the reference electrode. A working electrode electrolyte consisted of 0.5 mol / L disodium succinate and 0.1 mol / L potassium hydroxide aqueous solution, pumped into the working electrode side at a rate of 1 mL / min, with an actual working area of ​​1.5 cm × 0.5 cm. A counter electrode electrolyte consisted of 0.5 mol / L potassium hydroxide solution, pumped into the counter electrode side at a rate of 5 mL / min, with an actual working area of ​​1.5 cm × 0.5 cm. The membrane was a proton exchange membrane.

[0088] Constant current electrolysis and square wave AC electrolysis were performed in a flow electrolytic cell. The current density of constant current electrolysis was 200 mA per square centimeter. The square wave parameters of square wave AC electrolysis were as follows: anode current density 200 mA per square centimeter, correspondingly, cathode current density -200 mA per square centimeter. The anode current and cathode current had the same value but opposite signs. The application time was 120 seconds, and the total cycle was 240 seconds.

[0089] In a flow electrolyzer, gaseous and liquid phase products are continuously collected and analyzed using a three-electrode system, and the potentials corresponding to different current densities are recorded.

[0090] The gaseous product of the reaction (ethylene) was passed through an argon carrier gas at a flow rate of 40 standard cubic centimeters per minute. The mixture of ethylene and argon was collected for eight minutes using a gas collecting bag and then sent online to a gas chromatograph equipped with a thermal conductivity detector for analysis. After electrolysis, 5 mL of electrolyte from the anolyte chamber was collected, and the liquid product of the reaction (acrylic acid) was detected using high-performance liquid chromatography (HPLC). The Faraday efficiency and potential changes of ethylene and acrylic acid over time were calculated for both DC electrolysis and square wave electrolysis. Figure 16 The graph shows the stability performance of DC electrolysis. It can be seen that after two hours of DC electrolysis, the potential begins to rise sharply, and the Faraday efficiency of the target product ethylene drops sharply. Figure 17 The stability performance diagram of square wave electrolysis shows that the ethylene Faraday efficiency is significantly higher than that of DC electrolysis, the catalyst performance stability is much higher than that of DC electrolysis, and the potential can be maintained at a lower level for a longer period of time compared with DC electrolysis, which demonstrates the superiority of the square wave electrolysis method.

[0091] Example 6

[0092] This embodiment proposes a method for the decarboxylation of succinic acid to ethylene via square wave electro-oxidation with alternating polarity, comprising the following steps:

[0093] Step 1: Cut commercial graphite sheets with a thickness of 0.1 cm into 2.5 cm × 2.5 cm graphite sheets and perform pretreatment of graphite catalyst according to Step 1 of Example 1.

[0094] Step 2: The decarboxylation of succinic acid to ethylene is carried out using a square-wave electro-oxidation process with alternating polarities in a membrane-free flowing electrolytic cell. Specifically:

[0095] The graphite catalyst obtained in step 1 was used as the working electrode, with an actual working area of ​​2 cm × 2 cm; an aqueous solution of 0.5 mol disodium succinate and 0.1 mol potassium hydroxide was used as the electrolyte for the full cell and was pumped into the working electrode side at a rate of 10 ml per minute.

[0096] Electrolysis tests were conducted using square-wave alternating current, with a total cycle of 240 seconds. The currents corresponding to different potentials were recorded to obtain current-voltage curves, such as... Figure 18 As shown, the maximum current can reach 1.8 amperes.

[0097] The gaseous products were continuously collected and analyzed via electrolysis. The gaseous product (ethylene) was passed through an argon carrier gas at a flow rate of 40 standard cubic centimeters per minute. The mixture of ethylene and argon was collected for eight minutes using a gas collecting bag and then online to a gas chromatograph equipped with a thermal conductivity detector for analysis. The results were calculated as follows: Figure 19 The Faraday efficiency of ethylene at different potentials is shown. For a square wave voltage of ±8.48 volts, the calculated values ​​are as follows: Figure 20 The current-time curves shown and as follows Figure 21The Faraday efficiency-time curve shown indicates that the stability of the square wave AC electrolysis can be maintained for about 28 hours. The Faraday efficiency of ethylene is always higher than 25%, and the current is higher than 1 ampere without decay, which proves the feasibility of the square wave AC current method in the device.

[0098] The above describes a method for preparing ethylene from succinic acid by alternating polarity square wave electro-oxidation of succinic acid using alternating polarity. Specific examples have been used to illustrate the principles and implementation methods of this invention. These embodiments are merely illustrative to aid in understanding the method and its core ideas, including the best mode, and to enable any person skilled in the art to practice this invention, including manufacturing and using any apparatus or system, and implementing any combined method. It should be noted that those skilled in the art can make various improvements and modifications to this invention without departing from its principles, and these improvements and modifications also fall within the scope of protection of the claims. The scope of protection of this patent is defined by the claims and may include other embodiments conceived by those skilled in the art. If these other embodiments have structural elements that are not different from the wording of the claims, or if they include equivalent structural elements that are not substantially different from the wording of the claims, then these other embodiments should also be included within the scope of the claims.

Claims

1. A method for producing ethylene by square wave electro-oxidation of succinic acid with alternating polarities to produce ethylene, characterized in that, In the electrolysis system, graphite sheets are used as working electrodes, and succinate aqueous solution is used as substrate in the electrolyte. Ethylene and hydrogen are produced by electrocatalysis by applying alternating square wave current with alternating polarity between the working electrode and the counter electrode.

2. The method for producing ethylene by alternating polarity square wave electro-oxidation of succinic acid to decarboxylate according to claim 1, characterized in that, The electrocatalytic performance of graphite sheets can be controlled by changing the square wave period, square wave current, or square wave potential.

3. The method for producing ethylene by alternating polarity square wave electro-oxidation of succinic acid to decarboxylate according to claim 1, characterized in that, The electrolyte pH value is adjusted by adding acidic or alkaline substances that do not participate in the reaction.

4. The method for producing ethylene by alternating polarity square wave electro-oxidation of succinic acid to remove carboxylation according to claim 1, characterized in that, The concentration of succinate in the electrolyte is 0.1 mol / L to 1 mol / L.

5. The method for producing ethylene by alternating polarity square wave electro-oxidation of succinic acid to remove carboxylation according to claim 1, characterized in that, The cation of the succinate is one or more of sodium ion, potassium ion, ammonium ion, and lithium ion.

6. The method for producing ethylene by alternating polarity square wave electro-oxidation of succinic acid to remove carboxylation according to claim 1, characterized in that, The electrolysis system is a two-electrode system or a three-electrode system, and its reaction device is an H-type electrolytic cell, a flow electrolytic cell, or a membrane-free electrolytic cell.

7. The method for producing ethylene by alternating polarity square wave electro-oxidation of succinic acid to decarboxylate according to claim 1, characterized in that, The duty cycle of the square wave alternating current is 20% to 80%.

8. The method for producing ethylene by alternating polarity square wave electro-oxidation of succinic acid to remove carboxylation according to claim 1, characterized in that, The period of the square wave alternating current is 1 second to 600 seconds.

9. The method for producing ethylene by alternating polarity square wave electro-oxidation of succinic acid to remove carboxylation according to claim 1, characterized in that, The current density of the square wave alternating current is 0.01 amperes per square centimeter to 0.5 amperes per square centimeter.

10. The method for producing ethylene by alternating polarity square wave electro-oxidation of succinic acid to decarboxylate according to claim 1, characterized in that, The potential of the square wave alternating current is 2 volts to 15 volts.

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