Method and system for increasing yield of low-carbon olefins through direct-current electric field coupling lanthanum ferrite synergistic reinforcement light alkane cracking

Abstract

The invention provides a method and a system for increasing the yield of low-carbon olefins through direct-current electric field coupling lanthanum ferrite synergistic reinforcement light alkane cracking, lanthanum ferrite is activated by a direct-current electric field, the microstructure of lanthanum ferrite is changed, and light alkane cracking is facilitated. Compared with a condition without an electric field, the conversion rate of light alkane at 400 DEG C can be increased by-36.5%, and the selectivity of low-carbon olefin can reach 64.1%-74.9%. The light alkane cracking process based on the electric field effect coupled lanthanum ferrite has the advantages of mild reaction conditions, high target product selectivity and the like, and solves the problems of high temperature and high energy consumption in the traditional metal oxide catalytic light hydrocarbon cracking process.

Description

Technical Field

[0001] This invention relates to the field of petrochemicals, specifically to a method and system for enhancing the cracking of light alkanes to produce more low-carbon olefins by coupling a DC electric field with lanthanum ferrite. Background Technology

[0002] Low-carbon olefins are key raw materials for synthetic fibers, plastics, and rubber. The cracking of light alkane to produce low-carbon olefins (mainly ethylene and propylene) is an important process with high economic value and wide applications. However, traditional steam cracking processes are energy-intensive, costly, and impose a significant environmental burden. With increasing environmental protection requirements and focus on energy efficiency, developing more efficient and environmentally friendly light alkane cracking technologies has become a research hotspot.

[0003] Green and low-carbon chemical technologies refer to environmentally friendly, energy-efficient, and low-carbon emission technologies and methods used in chemical production processes. Key technologies include process intensification, the development of more efficient / selective catalysts, and reactors matched to the catalytic process to improve reaction rates and product yields while reducing the generation of byproducts and waste. With the increasing prevalence of green electricity, using this green energy to drive chemical processes can reduce the use of traditional fossil fuel-based thermal energy, thereby lowering carbon emissions and achieving sustainable development. Furthermore, introducing an electric field during the reaction process can modulate the microstructure of the catalyst, thus influencing the reaction's progress.

[0004] Electro-driven chemical reactions have shown excellent performance in processes such as methane reforming and propane dehydrogenation. Yabe et al. utilized a conductive 1 wt% Ni / 10 mol% La-Zr... The catalyst, under an applied electric field and at 300°C, enabled the dry reforming of methane, C and C The conversion rates reached ~5% and ~7%, respectively, while thermally driven catalytic reactions are almost impossible to carry out at this temperature (Yabe T., et al., ACS Sustainable Chemistry & Engineering Zhang et al. prepared a Pt-In / TiO2 catalyst and drove the propane dehydrogenation reaction under an electric field. The propylene yield was 10.2% at 250℃, which far exceeded the thermodynamic equilibrium yield of 0.15% at the same temperature (Zhang J., et al., 2019, 7(6), 5690-5697). JACS Au , 2021, 1(10), 1688-1693).

[0005] The core of field-enhanced catalytic reaction processes lies in developing catalytic materials with suitable conductivity and catalytic activity. Metal oxides are a typical class of catalysts for the cracking of light alkanes, enabling the high-selectivity conversion of alkanes into target olefin products. Perovskite metal oxides are compounds with the molecular formula ABX3, where A is an alkali metal or alkaline earth metal, B is a transition metal, and X is O or a halogen. Due to their structural stability, high ionic and electronic conductivity, and multi-site substitutability, they have become a research hotspot in electrocatalysis applications. Currently, reported perovskite field-responsive catalysts include LaCoO3, SrCoO3, and B... S C F -δ These technologies can enhance electrocatalytic reactions occurring at the anode and cathode, exhibiting excellent performance in processes such as oxygen evolution reaction, hydrogen evolution reaction, and carbon dioxide electroreduction. Using a strontium-doped lanthanum cuprate gas diffusion electrode for CO2 electroreduction, the selectivity for methane and ethylene (29.4%) is significantly higher than that for alcohols, demonstrating significant advantages in selectivity, stability, and efficiency, making it a powerful alternative to traditional copper electrodes.

[0006] This invention develops a method and system for synergistically enhancing the cracking of light alkanes to produce more low-carbon olefins by coupling a DC electric field with the perovskite metal oxide lanthanum ferrite (LaFeO3). Compared with traditional thermocatalytic processes, the method of this invention has milder reaction conditions, lower energy consumption, and the electric field can modulate the microstructure of lanthanum ferrite, thereby improving catalytic activity. Summary of the Invention

[0007] Specifically, the purpose of this invention is to provide a method and system for enhancing the cracking of light alkanes to produce more low-carbon olefins by coupling a DC electric field with lanthanum ferrite, which has the advantage of significantly improving the performance of cracking light alkanes to produce low-carbon olefins under mild conditions.

[0008] This invention provides a method and system for enhancing alkane cracking to produce more low-carbon olefins using DC electric field coupling with lanthanum ferrite, the technical solution of which is as follows: The developed catalyst for enhancing the cracking of light alkanes to produce more low-carbon olefins is a perovskite-type metal oxide, lanthanum ferrite, prepared using a sol-gel method. The preparation method includes the following steps: ferric nitrate nonahydrate and lanthanum nitrate hexahydrate are weighed and prepared into a solution according to a specific ratio; a complexing agent is added to induce a complexation reaction and form a sol; the complexing agent includes citric acid monohydrate and / or ethylene glycol; the mixture is heated and stirred to form a gel. Subsequently, the gel is dried to form a dry gel, and then calcined to produce lanthanum ferrite.

[0009] A system for synergistic enhancement of light alkane cracking to produce more low-carbon olefins by DC electric field coupling of lanthanum ferrite includes a gas supply system, a DC electric field coupling lanthanum ferrite catalytic reaction system, a heating system, and an online detection system.

[0010] The gas supply system includes gas cylinders and corresponding gas lines to provide carrier gas for the catalytic cracking reaction. The DC electric field coupled lanthanum ferrite catalytic reaction system includes a raw material injection pump, a DC power supply, and a reactor equipped with conductive sieves. Light alkanes are pumped into the reactor via a stainless steel injection pump. The reactor is made of quartz. The lanthanum ferrite catalyst is placed between two conductive sieves and supported and fixed by stainless steel rods that act as positive and negative electrodes. The reaction raw materials and carrier gas enter through the gas inlet at the top of the reactor, and the products are discharged through the exhaust port at the bottom and enter the online detection system. A thermocouple is inserted at the bottom of the reactor to monitor the reaction temperature in real time. The thermocouple is sheathed with a quartz tube to ensure insulation. The heating system includes an open-type insulated tubular reactor and a gas-tracing heating tape. The online detection system includes a gas chromatograph, an air generator, and a hydrogen generator.

[0011] The electric field-coupled lanthanum ferrite catalyst synergistic enhancement process for light alkane cracking includes: pressing the catalyst into tablets, sieving, and loading an appropriate amount of the catalyst into a fixed-bed reactor equipped with a conductive sieve plate and electrode rods; introducing carrier gas into the reactor at a certain flow rate, raising the reactor to the target temperature, and applying direct current; introducing light alkane feedstock for reaction, and using gas chromatography for online analysis of product composition.

[0012] Preferably, the particle size of the catalyst is 20-40 mesh.

[0013] Preferably, the required catalyst mass is 0.3~1g.

[0014] Preferably, the stainless steel syringe pump has a capacity of 50 μL to 50 mL and an injection rate of 5 to 20 μL / min.

[0015] Preferably, the carrier gas includes any one or a combination of at least two of nitrogen, argon, and helium.

[0016] Preferably, the carrier gas flow rate is 3~20 mL / min.

[0017] Preferably, the temperature required for the pyrolysis reaction is 350~600 ℃.

[0018] Preferably, the applied DC voltage is 50~1500 V, the current is 10mA~1000 mA, and the power is 0.5~10 W.

[0019] Preferably, the light alkane is a C5-C10 alkane.

[0020] Compared with the prior art, the present invention has the following beneficial effects: The lanthanum ferrite catalyst provided by this invention is used to catalyze the cracking of light alkanes to produce low-carbon olefins under the action of an electric field. The electric field changes the microstructure of the catalyst, improves the catalytic activity, reduces the cracking reaction temperature, and improves the selectivity of low-carbon olefins. Attached Figure Description

[0021] To more clearly illustrate the technical solution of the present invention, the reaction system and some characterization results in the embodiments of the present invention are described with accompanying drawings.

[0022] Figure 1 This is a schematic diagram of a DC electric field coupled with lanthanum ferrite to synergistically enhance the cracking of light alkane and produce more low-carbon olefins.

[0023] In the attached image: 1-Raw material injection pump, 2-Liquid pipeline, 3-Heat tracing tape, 4-Gas cylinder, 5-Gas path, 6-DC power supply, 7-Quartz reactor, 8-Positive electrode rod, 9-Conductive sieve plate, 10-Lanium ferrite, 11-Negative electrode rod, 12-Thermocouple, 13-Gas chromatograph, 14-Hydrogen generator, 15-Air generator, 16-Tube furnace, 17-Mass flow meter Figure 2 The images show enlarged XRD patterns of fresh lanthanum ferrite and lanthanum ferrite after electric field treatment in Examples 12 and 13. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. The reagents, materials, instruments, etc., used in the following embodiments are all commercially available.

[0025] Example 1: (1) Weigh ferric nitrate nonahydrate, lanthanum nitrate hexahydrate and citric acid monohydrate in a molar ratio of 1:1:1, add them to a round-bottom flask, heat and stir at 80°C for 4 hours to obtain a gel, then dry at 120°C for 24 hours to obtain a dry gel, and calcine at 700°C for 2 hours to obtain lanthanum ferrite.

[0026] (2) The prepared lanthanum ferrite was compressed into tablets, sieved to obtain catalyst particles of 20-40 mesh, and 0.5 g of catalyst was weighed and loaded into a fixed-bed reactor equipped with a conductive sieve plate and electrode rod. Nitrogen gas was introduced into the reactor at a flow rate of 15 mL / min, the reactor was heated to 400 °C, no electric field was applied, and n-hexane was introduced at a rate of 12.6 μL / min for 30 min. The composition of the product was analyzed by gas chromatography online. The conversion rate of n-hexane was 0.7%, and no triene or triphenylene was detected in the product.

[0027] Example 2: (1) Lanthanum ferrite was prepared according to the same method and steps as in Example 1.

[0028] (2) The prepared lanthanum ferrite was compressed into tablets, sieved to obtain catalyst particles of 20-40 mesh, and 0.5 g of catalyst was weighed and loaded into a fixed-bed reactor equipped with a conductive sieve plate and electrode rod. Nitrogen gas was introduced into the reactor at a flow rate of 15 mL / min, the reactor was heated to 400 °C, an electric field of 3 W was applied, and n-hexane was introduced at a rate of 12.6 μL / min. The reaction was carried out for 30 min. The composition of the product was analyzed by gas chromatography online. The conversion rate of n-hexane was 8.2%, the selectivity of trienes was 66.8%, and the selectivity of BTX was 0.1%.

[0029] Example 3: (1) Lanthanum ferrite was prepared according to the same method and steps as in Example 1.

[0030] (2) The prepared lanthanum ferrite was compressed into tablets, sieved to obtain catalyst particles of 20-40 mesh, and 0.5 g of catalyst was weighed and loaded into a fixed-bed reactor equipped with a conductive sieve plate and electrode rod. Nitrogen gas was introduced into the reactor at a flow rate of 15 mL / min, the reactor was heated to 400 °C, an electric field of 5 W was applied, and n-hexane was introduced at a rate of 12.6 μL / min. The reaction was carried out for 30 min. The composition of the product was analyzed by gas chromatography online. The conversion rate of n-hexane was 26.2%, the selectivity of trienes was 75.6%, and the selectivity of BTX was 0.3%.

[0031] Example 4: (1) Lanthanum ferrite was prepared according to the same method and steps as in Example 1.

[0032] (2) The prepared lanthanum ferrite was compressed into tablets, sieved to obtain catalyst particles of 20-40 mesh, and 0.5 g of catalyst was weighed and loaded into a fixed-bed reactor equipped with a conductive sieve plate and electrode rod. Nitrogen gas was introduced into the reactor at a flow rate of 15 mL / min, the reactor was heated to 450 °C, no electric field was applied, and n-hexane was introduced at a rate of 12.6 μL / min for 30 min. The composition of the product was analyzed by gas chromatography online. The conversion rate of n-hexane was 1.7%, and no triene or triphenylene was detected in the product.

[0033] Example 5: (1) Lanthanum ferrite was prepared according to the same method and steps as in Example 1.

[0034] (2) The prepared lanthanum ferrite was compressed into tablets, sieved to obtain catalyst particles of 20-40 mesh, and 0.5 g of catalyst was weighed and loaded into a fixed-bed reactor equipped with a conductive sieve plate and electrode rod. Nitrogen gas was introduced into the reactor at a flow rate of 15 mL / min, the reactor was heated to 450 °C, an electric field of 5 W was applied, and n-hexane was introduced at a rate of 10 μL / min. The reaction was carried out for 30 min. The composition of the product was analyzed by gas chromatography online. The conversion rate of n-hexane was 37.7%, the selectivity of trienes was 75.9%, and the selectivity of BTX was 0.1%.

[0035] Example 6: (1) Lanthanum ferrite was prepared according to the same method and steps as in Example 1.

[0036] (2) The prepared lanthanum ferrite was compressed into tablets, sieved to obtain catalyst particles of 20-40 mesh, and 0.5 g of catalyst was weighed and loaded into a fixed-bed reactor equipped with a conductive sieve plate and electrode rod. Nitrogen gas was introduced into the reactor at a flow rate of 20 mL / min, the reactor was heated to 350 °C, no electric field was applied, and n-hexane was introduced at a rate of 12.6 μL / min for 30 min. The product composition was analyzed by gas chromatography online. The conversion rate of n-hexane was 0.7%, and no triene or triphenylene was detected in the product.

[0037] Example 7: (1) Lanthanum ferrite was prepared according to the same method and steps as in Example 1.

[0038] (2) The prepared lanthanum ferrite was compressed into tablets, sieved to obtain catalyst particles of 20-40 mesh, and 0.5 g of catalyst was weighed and loaded into a fixed-bed reactor equipped with a conductive sieve plate and electrode rod. Argon carrier gas was introduced into the reactor at a flow rate of 10 mL / min, the reactor was heated to 350 °C, an electric field of 5 W was applied, and n-hexane was introduced at a rate of 12.6 μL / min. The reaction was carried out for 30 min. The composition of the product was analyzed by gas chromatography online. The conversion rate of n-hexane was 20.7%, the selectivity of trienes was 70.5%, and the selectivity of BTX was 0.2%.

[0039] Example 8: (1) Lanthanum ferrite was prepared according to the same method and steps as in Example 1.

[0040] (2) The prepared lanthanum ferrite was compressed into tablets, sieved to obtain catalyst particles of 20-40 mesh, and 0.5 g of catalyst was weighed and loaded into a fixed-bed reactor equipped with a conductive sieve plate and electrode rod. Nitrogen gas was introduced into the reactor at a flow rate of 15 mL / min, the reactor was heated to 600 °C, no electric field was applied, and n-hexane was introduced at a rate of 12.6 μL / min for 30 min. The product composition was analyzed by gas chromatography online. The n-hexane conversion rate was 12.9%, the triene selectivity was 65.4%, and the BTX selectivity was 0.2%.

[0041] Example 9: (1) Lanthanum ferrite was prepared according to the same method and steps as in Example 1.

[0042] (2) The prepared lanthanum ferrite was compressed into tablets, sieved to obtain catalyst particles of 20-40 mesh, and 0.5 g of catalyst was weighed and loaded into a fixed-bed reactor equipped with a conductive sieve plate and electrode rod. Nitrogen gas was introduced into the reactor at a flow rate of 15 mL / min, the reactor was heated to 600 °C, an electric field of 5 W was applied, and n-hexane was introduced at a rate of 12.6 μL / min. The reaction was carried out for 30 min. The composition of the product was analyzed by gas chromatography online. The conversion rate of n-hexane was 53.1%, the selectivity of trienes was 73.2%, and the selectivity of BTX was 0.7%.

[0043] Example 10: (1) Lanthanum ferrite was prepared according to the same method and steps as in Example 1.

[0044] (2) The prepared lanthanum ferrite was compressed into tablets, sieved to obtain catalyst particles of 20-40 mesh, and 0.5 g of catalyst was weighed and loaded into a fixed-bed reactor equipped with a conductive sieve plate and electrode rod. Nitrogen gas was introduced into the reactor at a flow rate of 15 mL / min, the reactor was heated to 400 °C, an electric field of 5 W was applied, and n-pentane was introduced at a rate of 18 μL / min. The reaction was carried out for 30 min. The composition of the product was analyzed by gas chromatography online. The conversion rate of n-pentane was 20.6%, the selectivity of trienes was 68.1%, and the selectivity of BTX was 0.1%.

[0045] Example 11: (1) Lanthanum ferrite was prepared according to the same method and steps as in Example 1.

[0046] (2) The prepared lanthanum ferrite was compressed into tablets, sieved to obtain catalyst particles of 20-40 mesh, and 0.5 g of catalyst was weighed and loaded into a fixed-bed reactor equipped with a conductive sieve plate and electrode rod. Argon carrier gas was introduced into the reactor at a flow rate of 10 mL / min, the reactor was heated to 400 °C, an electric field of 5 W was applied, and n-decane was introduced at a rate of 10 μL / min. The reaction was carried out for 30 min. The composition of the product was analyzed by gas chromatography online. The conversion rate of n-decane was 21.5%, the triene selectivity was 67.3%, and the BTX selectivity was 0.9%.

[0047] Example 12: (1) Lanthanum ferrite was prepared according to the same method and steps as in Example 1.

[0048] (2) The prepared lanthanum ferrite was pressed into tablets, sieved to obtain catalyst particles of 20-40 mesh, and 0.5 g of catalyst was weighed and loaded into a fixed-bed reactor equipped with a conductive sieve plate and electrode rod. Nitrogen gas was introduced into the reactor at a flow rate of 15 mL / min, and the reactor was heated to 400 °C. The catalyst was treated for 30 min without an electric field. The catalyst was taken out in a glove box and its structure was analyzed by X-ray diffraction. The analysis of the spectrum showed no peak shift compared with the spectrum of the untreated fresh catalyst.

[0049] Example 13: (1) Lanthanum ferrite was prepared according to the same method and steps as in Example 1.

[0050] (2) The prepared lanthanum ferrite tablets were pressed and sieved to obtain catalyst particles of 20-40 mesh. 0.5 g of the catalyst was weighed and loaded into a fixed-bed reactor equipped with a conductive sieve plate and electrode rod. Nitrogen gas was introduced into the reactor at a flow rate of 15 mL / min. The reactor was heated to 400 °C and a 5 W electric field was applied to treat the catalyst for 30 min. The catalyst was taken out in a glove box and its structure was analyzed by X-ray diffraction. The analysis of the spectrum showed that, compared with the untreated fresh catalyst, the diffraction peaks of the catalyst treated with the 5 W electric field shifted to the left. X-ray photoelectron spectroscopy was used to analyze the valence states of each element and oxygen species in the catalyst. The analysis of the spectrum showed that, compared with the untreated fresh catalyst, the lattice oxygen content of the catalyst treated with the 5 W electric field decreased and the active adsorbed oxygen content increased, indicating that the oxygen vacancies increased and the Fe ions with larger ionic radii increased. 2+ Replaced Fe 3+ This causes the XRD characteristic peaks to shift.

[0051] The above description is merely a specific implementation step of this invention, but the scope of protection of this invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this invention should be included within the scope of protection of this invention.

Claims

1. A method and system for enhancing the cracking of light alkanes to produce more low-carbon olefins by coupling a DC electric field with lanthanum ferrite, characterized in that, The system includes a gas supply system, a DC electric field coupled lanthanum ferrite catalytic reaction system, a heating system, and an online monitoring system; the gas supply system includes gas cylinders and corresponding gas lines to provide carrier gas for the catalytic cracking reaction. The DC electric field coupled lanthanum ferrite catalytic reaction system includes a raw material injection pump, a DC power supply, and a reactor equipped with conductive sieves. Light alkanes are pumped into the reactor via a stainless steel injection pump. The reactor is made of quartz. The lanthanum ferrite catalyst is placed between two conductive sieves and supported and fixed by stainless steel rods that act as positive and negative electrodes. The reaction raw materials and carrier gas enter through the gas inlet at the top of the reactor, and the products are discharged through the exhaust port at the bottom and enter the online detection system. A thermocouple is inserted at the bottom of the reactor to monitor the reaction temperature in real time. The thermocouple is sheathed with a quartz tube to ensure insulation. The heating system includes an open-type insulated tubular reactor and a gas-tracing heating tape. The online detection system includes a gas chromatograph, an air generator, and a hydrogen generator.

2. The method according to claim 1, wherein the lanthanum ferrite catalyst is synthesized by a gelation method.

3. The system according to claim 1, wherein the catalyst used for catalytic cracking of light alkane has a particle size of 20-40 mesh, the required catalyst mass is 0.3-1g, the carrier gas includes any one or a combination of at least two of nitrogen, argon, and helium, and the carrier gas flow rate is 3-20 mL / min.

4. According to the system of claim 1, the temperature required for cracking light alkane is 350~600℃, the applied DC voltage is 50~1500V, the current is 10mA~1000mA, the power is 0.5~10W, and the light alkane is C5~C10 alkane.

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