A method for preparing fuel gas based on ultraviolet ultrasonic cooperation

Abstract

The application discloses a preparation method of fuel gas based on ultrasonic ultraviolet light cooperation, which comprises the following steps: using acetonitrile as a solvent, and under an inert atmosphere, using ultrasonic and ultraviolet light irradiation cooperation to convert hydroxyl carboxylic acid compounds into fuel gas; the main components of the fuel gas are CO, C2H4 and C2H6. The application uses the cooperation of ultrasonic and ultraviolet light to efficiently convert hydroxyl carboxylic acid compounds into multi-component carbon-containing fuel gas under catalyst-free, low-temperature and mild conditions, and realizes the directional conversion of hydroxyl carboxylic acid compounds.

Description

Technical Field

[0001] This invention relates to the fields of biomass energy utilization and low-carbon energy technology, and in particular to a method for preparing fuel gas based on ultrasound-ultraviolet light synergy. Background Technology

[0002] Hydroxycarboxylic acids are a class of organic compounds containing both hydroxyl (-OH) and carboxyl (-COOH) groups in their molecules. They are widely found in biomass hydrolysates, organic wastewater, fermentation wastewater, and degradation intermediates of biodegradable plastics such as polylactic acid (PLA). Typical hydroxycarboxylic acids include glycolic acid, hydroxypropionic acid (lactic acid), and hydroxybutyric acid (HPA). These substances often have high concentrations and long biodegradation cycles. Traditional treatment methods (such as aerobic / anaerobic biological treatment and high-temperature incineration) suffer from low treatment efficiency, high energy consumption, or secondary pollution. Therefore, developing novel technologies to convert hydroxycarboxylic acids into high-value gaseous fuels (such as CO, CH4, C2H4, and C2H6) under mild conditions is of dual significance for environmental protection and energy recovery.

[0003] The main pathways of existing hydroxycarboxylic acid conversion technologies are as follows: (1) Aqueous-phase photocatalytic / photochemical conversion technology. Existing photocatalytic reforming technologies using water as a solvent rely on water as a proton source. During photocatalysis, hydrogen evolution (H2 evolution) inevitably occurs, with hydrogen often becoming the main or even dominant product. Even for the conversion of carboxylic acid substrates, the selectivity for carbon-containing gases (CO, CH4) is generally low, and C2 and higher hydrocarbon products require complex proton-coupled electron transfer processes, making them difficult to obtain in large quantities. Furthermore, aqueous systems rely on solid catalysts, leading to problems such as high cost, difficulty in separation, and metal leaching.

[0004] (2) Photochemical / sonic chemical conversion technologies in organic solvents. Reports on photochemical or sonochemical reactions in organic solvents mainly focus on the following areas: (i) specific functional group transformations in organic synthesis; (ii) CO2 reduction (often requiring catalysts); and (iii) the conversion of biomass-derived platform compounds (such as furfural and lignin). However, the vast majority of these studies are oriented towards the synthesis or degradation and mineralization of target products, with very few targeting the production of fuel gases. More importantly, existing organic solvent systems also heavily rely on transition metal catalysts or photosensitizers, and catalyst-free systems have not been reported.

[0005] Acetonitrile, as an aprotic polar solvent, possesses excellent solubility, a wide electrochemical window, and a relatively low vapor pressure. In the field of photochemistry, acetonitrile is often used as a medium for CO2 reduction or photocatalytic organic reactions. However, existing acetonitrile systems all rely on: (i) homogeneous or heterogeneous catalysts (such as Ru, Re, Ir complexes, MOFs, COFs, etc.); (ii) sacrificial agents (such as methanol, triethanolamine); and (iii) added water or a proton source to regulate the reaction pathway.

[0006] In the existing technologies, whether it is photocatalysis, acoustic catalysis or acoustic-photocatalysis combined system, there are common shortcomings: (1) they rely on catalysts, which have problems such as high cost, difficult separation and metal dissolution; (2) the hydrogen evolution reaction is serious, and a large number of protons in the water make hydrogen the dominant product, and the selectivity of carbon-containing products is low; (3) the yield of C2 hydrocarbons is extremely low and there is a lack of effective carbon chain growth methods. Summary of the Invention

[0007] This invention provides a method for preparing fuel gas based on ultrasound-ultraviolet light synergy, which directly converts hydroxycarboxylic acids into carbon-containing gases mainly composed of CO, C2H4, and C2H6 in acetonitrile, and can effectively suppress hydrogen production.

[0008] The technical solution of the present invention is as follows: A method for preparing fuel gas based on ultrasound-ultraviolet synergy includes the following steps: using acetonitrile as a solvent, under an inert atmosphere, hydroxycarboxylic acid compounds are converted into fuel gas by the synergistic effect of ultrasound and ultraviolet irradiation; the main components of the fuel gas are CO, C2H4 and C2H6.

[0009] Preferably, the conversion reaction of hydroxycarboxylic acid compounds is carried out under catalyst-free conditions.

[0010] In aqueous or proton-containing solvent systems, the hydrogen evolution reaction (2H+) + +2e - → H2) is a thermodynamically and kinetically highly competitive process, which makes any conversion strategy targeting carbon-containing products face the dilemma of hydrogen dominance. In contrast, acetonitrile is an aprotic solvent and does not provide free protons. When acetonitrile is used as the sole solvent and the system is strictly dehydrated (and protected by an inert atmosphere), the proton reduction pathway is effectively blocked, providing an ideal medium for suppressing hydrogen evolution and forcing electrons and free radicals to preferentially participate in carbon-carbon bond formation.

[0011] This invention uses acetonitrile as a solvent to block the supply of free protons at the source, effectively suppressing the hydrogen evolution side reaction and solving the problem of low selectivity for carbon-containing products. Ultrasonic light drives the efficient bond breaking of hydroxycarboxylic acid substrate molecules to generate free radical fragments, while ultrasound provides cavitation effects to enhance mass transfer and provides localized high-temperature hotspots to promote synergistic coupling and carbon chain growth among free radical fragments, solving the problem of low yield of C2 hydrocarbons. An inert atmosphere protects against oxygen quenching, stabilizing free radical intermediates and providing reaction assurance for synergistic coupling and carbon chain growth among free radical fragments. The synergistic effect of these techniques enables the efficient and highly selective conversion of hydroxycarboxylic acid compounds into multi-component carbon-containing fuel gases under catalyst-free conditions.

[0012] Preferably, the conversion reaction of hydroxycarboxylic acid compounds is carried out under isothermal conditions, with the conversion reaction temperature being 2-25℃.

[0013] Low-temperature isothermal conditions are used to suppress side reactions, ensuring the selectivity of reaction products and the stability of the system.

[0014] Preferably, the ultrasonic frequency is 30-50 kHz.

[0015] Preferably, the spectral range of ultraviolet irradiation is 200-780 nm.

[0016] Ultraviolet irradiation is provided by ultraviolet-enhanced xenon lamps, which have a power of 200-500 W and a spectral range from the ultraviolet to the visible light region.

[0017] Preferably, the inert atmosphere is an argon atmosphere; the initial pressure of the reaction system is 50-100 kPa.

[0018] Preferably, the hydroxycarboxylic acid compound is at least one of glycolic acid, lactic acid, (R)-2-hydroxybutyric acid, L-hydroxysuccinic acid, and 3-hydroxybutyric acid.

[0019] More preferably, the hydroxycarboxylic acid compound is at least one of DL-lactic acid, (R)-2-hydroxybutyric acid, hydroxysuccinic acid, and (R)-3-hydroxybutyric acid.

[0020] More preferably, the dosage of the hydroxycarboxylic acid compound in the 5 mL acetonitrile solvent system is 0.2-1 mmol.

[0021] Preferably, the total yield of CO, C2H4, and C2H6 in the product fuel gas is 10-100 μmol / 0.5mmol of hydroxycarboxylic acid compounds, and the yields of CO, C2H4, and C2H6 are 4-35 μmol / 0.5mmol of hydroxycarboxylic acid compounds, 2-30 μmol / 0.5mmol of hydroxycarboxylic acid compounds, and 4-35 μmol / 0.5mmol of hydroxycarboxylic acid compounds, respectively. In the product fuel gas, the total volume percentage of CO, C2H4, and C2H6 is over 98%.

[0022] The method of the present invention has the following applications: (1) Multi-component carbon-containing fuel gas generator; (2) Used for laboratory or industrial-grade on-site preparation of fuel gases mainly composed of CO, C2H4, and C2H6, replacing traditional high-temperature or catalytic cracking processes; (3) Biomass waste liquid resource utilization equipment: used to treat industrial organic waste liquid containing hydroxycarboxylic acid, convert it into combustible gas, and realize the resource utilization of waste liquid; (4) Green chemical intermediate preparation platform: As a green synthesis route for low-carbon olefins (C2H4) and ethane (C2H6), it can replace the petroleum cracking route for small-scale feed gas supply in chemical industrial parks.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The method of this invention achieves the resource-based conversion of hydroxycarboxylic acid compounds under mild conditions. Traditional treatment methods (biodegradation, high-temperature incineration) have problems such as long cycles, high energy consumption, or secondary pollution. This invention provides a simple conversion method at room temperature and pressure to directly convert hydroxycarboxylic acid compounds into gaseous fuels with energy value; (2) The method of this invention eliminates the dependence on catalysts. Existing photocatalytic and acoustic catalytic conversion systems all require the addition of homogeneous or heterogeneous catalysts, resulting in problems such as high cost, difficult separation, and metal dissolution. This invention provides a completely new conversion pathway that does not require the addition of any catalyst; (3) The method of the present invention effectively suppresses hydrogen evolution side reactions and improves the selectivity of carbon-containing gases. In existing aqueous systems, due to the abundance of protons, hydrogen evolution reactions dominate, resulting in low selectivity of carbon-containing gases (CO, CH4), with C2 hydrocarbons being almost invisible. The present invention utilizes the aprotic solvent acetonitrile to block the source of protons, suppressing hydrogen generation from the source and forcing the reaction to proceed in the direction of carbon-carbon bond formation; (4) The method of the present invention achieves efficient generation of C2 hydrocarbons (ethylene, ethane). In the prior art, the conversion products of hydroxycarboxylic acid compounds are mainly H2 and CO2, and the yield of C2 and above hydrocarbons is extremely low, lacking effective carbon chain growth methods. The present invention promotes free radical coupling through the synergistic effect of ultrasonic cavitation and ultraviolet photolysis, realizing the directional generation of energy fuels such as C2H4 and C2H6. Attached Figure Description

[0024] Figure 1 Performance evaluation diagrams for preparing fuel gas using ultrasound-UV synergistic photoacoustic conversion (UUS-PAC) with different hydroxycarboxylic acid substrates; Figure 2 Comparison of fuel gas preparation performance for different dosages of (R)-2-hydroxybutyric acid UUS-PAC; Figure 3 Preparation of fuel gas dynamics evaluation diagram for (R)-2-hydroxybutyric acid UUS-PAC; Figure 4 Comparison of experimental performance of (R)-2-hydroxybutyric acid UUS-PAC in fuel gas control preparation; Figure 5 Comparison of fuel gas preparation performance for different chiral hydroxycarboxylic acid substrates UUS-PAC. Detailed Implementation

[0025] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be noted that the embodiments described below are intended to facilitate the understanding of the present invention and do not limit it in any way.

[0026] The complete technical solution of this invention is implemented according to the following steps: Step 1: Preparation of the reaction solution In a Pyrex glass reactor, 5 mL of acetonitrile (ACN) was added as the reaction solvent, followed by a predetermined amount of hydroxycarboxylic acid substrate. The mixture was thoroughly dissolved and mixed to form a reaction solution. The hydroxycarboxylic acid substrate contains both hydroxyl and carboxyl functional groups.

[0027] Step 2: Reactor connection and gas pipeline assembly The Pyrex reactor from step one is sealed and connected to a fully automated online gas analyzer (Popile μGas1000, hereinafter referred to as the gas analysis system) via a gas pipeline. The gas analysis system has automatic vacuuming, automatic gas inlet, carrier gas rinsing, and online sampling and analysis functions. The gas inlet and outlet of the reactor are connected to the inlet valve and sampling valve of the gas analysis system, respectively, forming a closed-loop or flow-through gas circuit.

[0028] Step 3: Vacuuming and Argon Replacement The gas analysis system is activated, and the reactor is first evacuated to remove residual air from the reactor and pipelines. After evacuation, high-purity argon (Ar, purity ≥ 99.999%) is automatically introduced as a carrier gas to rinse the reaction system and further replace residual gases. This rinsing operation can be repeated to ensure that oxygen is fully removed from the reaction system.

[0029] Step 4: Pressurize with argon gas to the initial reaction pressure. After rinsing, argon gas is continuously introduced to fill the reaction system to an initial pressure of 80 kPa. 80 kPa represents a slightly negative pressure, slightly below atmospheric pressure, which is beneficial for online sampling and analysis of gaseous products and subsequent detection. Argon gas acts as a protective atmosphere throughout the reaction, eliminating the quenching effect of oxygen on free radicals and providing a stable microenvironment for free radical coupling and carbon chain growth.

[0030] Step 5: Low-temperature constant temperature control The Pyrex reactor containing the reaction solution was placed in a constant-temperature circulating water bath, and the reaction temperature was controlled at 2°C. The low temperature of 2°C was used to suppress non-target side reactions and to avoid overheating of the solution during ultrasonic cavitation, which could lead to solvent evaporation or thermal decomposition of the substrate.

[0031] Step Six: Coordinated Irradiation with Ultrasonic and Ultraviolet-Enhanced Xenon Lamp Under constant temperature of 2℃, the ultrasonic device and ultraviolet-enhanced xenon lamp light source were turned on simultaneously to synergistically irradiate the reaction solution for 2 hours.

[0032] The ultrasonic device operates at a frequency of 40 kHz and generates cavitation effect by acting ultrasonic waves on the reaction liquid. The mechanism of ultrasonic cavitation effect includes: (1) forming local high temperature and high pressure hot spots in the solution (the hot spot temperature can reach thousands of Kelvin), providing energy conditions for the synergistic coupling between free radical fragments and the growth of carbon chains; (2) strengthening the mass transfer process and promoting the collision frequency between substrate molecules and free radical intermediates; (3) continuously cleaning the reactor wall and preventing product deposition from affecting the light transmission efficiency.

[0033] The ultraviolet-enhanced xenon lamp is a 300 W xenon lamp source with a wavelength in the range of 200-780 nm. The mechanism of action of the ultraviolet radiation component is as follows: it provides high-energy photons that directly act on hydroxycarboxylic acid substrates, driving the efficient breaking of C-C and CO bonds, generating reactive intermediate fragments such as alkyl and acyl radicals. This efficient bond-breaking process is a prerequisite step for carbon chain reconstruction and the generation of carbon-containing gaseous products in this technical solution.

[0034] The synergistic effect of ultrasound and ultraviolet radiation manifests as follows: ultraviolet radiation is responsible for the primary bond breaking of substrate molecules, generating small molecule free radical fragments; the ultrasonic cavitation effect provides local high-temperature hotspots, promoting secondary coupling reactions between free radical fragments, achieving carbon chain growth and the directional generation of C2 hydrocarbon products. Both are synergistic and indispensable.

[0035] Step 7: Online Sampling and Quantitative Analysis During the 2-hour reaction, the gas analysis system automatically samples from the top space of the reactor at preset time intervals. Online qualitative and quantitative analysis of the gaseous products is performed using a gas chromatograph (FULI F60) equipped with a thermal conductivity detector (TCD) and a flame ionization detector (FID). Argon is used as the carrier gas. The detected gaseous components include, but are not limited to: carbon monoxide (CO), methane (CH4), ethylene (C2H4), ethane (C2H6), and potentially generated hydrogen (H2).

[0036] Examples 1-5 Under the same optimized reaction conditions (substrate amount 0.2 mmol, acetonitrile solvent 5 mL, argon atmosphere 80 kPa, ultrasonic-UV synergistic photoacoustic conversion reaction system), Examples 1-5 selected glycolic acid, L-lactic acid, (R)-2-hydroxybutyric acid, L-hydroxysuccinic acid, and (R)-3-hydroxybutyric acid as substrates to investigate their effects on the production yield of gaseous products (CO, C2H4, C2H6, H2).

[0037] The results are as follows Figure 1 As shown, the carbon chain length and α-substituent structure of the substrate significantly affect the radical coupling efficiency and the distribution of gaseous products. Among them, (R)-2-hydroxybutyric acid exhibited the best conversion performance: the yields of CO, C2H4, and C2H6 reached 4.3 μmol, 2.3 μmol, and 4.5 μmol, respectively, after 2 hours of reaction, and their total yields were significantly higher than those of other hydroxycarboxylic acid substrates. In the gaseous products, the overall integrals of CO, C2H4, and C2H6 were all above 98%.

[0038] Examples 6-10 The dosage of (R)-2-hydroxybutyric acid was systematically optimized. See [link to relevant documentation]. Figure 2 In a 5 mL acetonitrile solvent system, the yield of gaseous products was investigated under different substrate dosages (0.1, 0.3, 0.5, 0.8, and 1.0 mmol in Examples 6-11, and 0.2 mmol in Example 1).

[0039] Experimental results showed that 0.5 mmol was the optimal substrate dosage. Under these conditions, after 2 hours of reaction, the yields of CO, C2H4, and C2H6 reached 6.7 μmol, 3.9 μmol, and 6.1 μmol, respectively. Calculations showed that the selectivity for carbon-containing products was close to 100%, indicating that the hydrogen evolution side reaction was effectively suppressed, and the reaction pathway was almost entirely directed towards the formation of carbon-containing gaseous products. Among the gaseous products, the overall integrals of CO, C2H4, and C2H6 were all above 98%.

[0040] Comparative Example 1 Compared to Example 1, the substrate dosage was 0, and the results are shown in [the table below]. Figure 2 .

[0041] Example 11 This embodiment verifies the long-term operational stability of the technical solution. See also Figure 3 Under optimal reaction conditions, using (R)-2-hydroxybutyric acid (0.5 mmol) as the substrate, 5 mL of acetonitrile, argon gas at 80 kPa, 2℃, and UV-ultrasound synergistic treatment were continuously applied for 15 hours, with gaseous product analysis performed every 2 hours. The results showed that the gaseous product yield exhibited a good linear cumulative trend over time. After 15 hours, the cumulative yields of CO, C2H4, and C2H6 were approximately 30.8 μmol, 23.4 μmol, and 30.3 μmol, respectively. These results indicate that the technical solution of this invention has good reaction stability and is suitable for long-term continuous operation.

[0042] Comparative Examples 2-4 The synergistic mechanism of ultrasound and ultraviolet radiation was confirmed through controlled experiments. (See also...) Figure 4 The following four control experiments were designed: Comparative Example 2: Ultraviolet irradiation group (only 300 W UV xenon lamp is turned on, ultrasound is not turned on); Comparative Example 3: Ultrasonic treatment group only (40 kHz ultrasound only, UV light source not turned on). Comparative Example 4: Untreated control group (no energy source applied); Example 8: Ultraviolet + Ultrasound Synergistic Treatment Group (two energy sources are turned on simultaneously); All experimental groups were prepared using 0.5 mmol (R)-2-hydroxybutyric acid, 5 mL acetonitrile, argon atmosphere at 80 kPa, constant temperature at 2℃, and reaction conditions for 2 hours.

[0043] Experimental results show that the high yield and high selectivity achieved by the invention stem from the positive synergistic effect between ultraviolet light and ultrasound, rather than the individual effect of either energy source.

[0044] Example 12, Comparative Examples 5-7 The differences in conversion performance of hydroxycarboxylic acids with different chiral configurations under the technical solution of this invention were further investigated. See also Figure 5Different chiral hydroxycarboxylic acids were selected as substrates ((R)-2-hydroxybutyric acid in Example 8, (S)-2-hydroxybutyric acid in Comparative Example 5, DL-lactic acid in Example 12, D-lactic acid in Comparative Example 6, and L-lactic acid in Comparative Example 7). Conversion experiments were conducted under the same reaction conditions (0.5 mmol substrate, 5 mL acetonitrile, argon gas at 80 kPa, 2℃, and UV + ultrasound synergistic treatment), and the formation kinetics of CO, C2H4, and C2H6 gaseous products were continuously monitored. The experimental results showed that the gas conversion kinetics of CO, C2H4, and C2H6 were significantly dependent on the chirality of the substrate. Significant differences existed in the formation rate and final yield of gaseous products between the two chiral substrate configurations, indicating that the free radical bond breaking and coupling processes in the present invention are regulated by the spatial configuration of the substrate molecule.

[0045] The embodiments described above provide a detailed explanation of the technical solutions and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, additions, and equivalent substitutions made within the scope of the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing fuel gas based on ultrasound-ultraviolet light synergy, characterized in that, Includes the following steps: Using acetonitrile as a solvent, under an inert atmosphere, hydroxycarboxylic acid compounds are converted into fuel gas by the synergistic effect of ultrasound and ultraviolet irradiation; the main components of the fuel gas are CO, C2H4 and C2H6.

2. The method for preparing fuel gas based on ultrasound-ultraviolet light synergy according to claim 1, characterized in that, The conversion reaction of hydroxycarboxylic acid compounds is carried out under catalyst-free conditions.

3. The method for preparing fuel gas based on ultrasound-ultraviolet light synergy according to claim 1, characterized in that, The conversion reaction of hydroxycarboxylic acid compounds is carried out under isothermal conditions, with a conversion temperature of 2-25℃.

4. The method for preparing fuel gas based on ultrasound-ultraviolet light synergy according to claim 1, characterized in that, The ultrasonic frequency is 30-50 kHz; the spectral range of ultraviolet irradiation is 200-780 nm.

5. The method for preparing fuel gas based on ultrasound-ultraviolet light synergy according to claim 1, characterized in that, The inert atmosphere is argon; the initial pressure of the reaction system is 50-100 kPa.

6. The method for preparing fuel gas based on ultrasound-ultraviolet light synergy according to claim 1, characterized in that, The hydroxycarboxylic acid compound is at least one of glycolic acid, lactic acid, (R)-2-hydroxybutyric acid, hydroxysuccinic acid, and 3-hydroxybutyric acid.

7. The method for preparing fuel gas based on ultrasound-ultraviolet light synergy according to claim 1, characterized in that, The hydroxycarboxylic acid compound is at least one of DL-lactic acid, (R)-2-hydroxybutyric acid, L-hydroxysuccinic acid, and (R)-3-hydroxybutyric acid.

8. The method for preparing fuel gas based on ultrasound-ultraviolet light synergy according to claim 1, characterized in that, The dosage of hydroxycarboxylic acid compounds in a 5 mL acetonitrile solvent system is 0.2-1 mmol.

9. The method for preparing fuel gas based on ultrasound-ultraviolet light synergy according to claim 1, characterized in that, In the product fuel gas, the total volume percentage of CO, C2H4, and C2H6 is over 98%.

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