Method for preparing olefin from flare gas

Abstract

The invention relates to the technical field of petrochemical engineering, and discloses a method for preparing olefin from flare gas.The method comprises the steps that a silicon source, boric acid, a template agent and active components are dissolved in a solvent to be prepared into gel, the active components comprise gallium salt, cerium salt and lanthanum oxide according to the mass ratio of 0.15-0.45: 0.13-0.35: 0-0.7, then the gel is crystallized, separated, dried and calcined to be prepared into a borosilicate molecular sieve, and the borosilicate molecular sieve is used for preparing olefin. Activating the borosilicate molecular sieve, and introducing flare gas and oxygen for oxidative dehydrogenation reaction after activation; according to the method, the total alkane conversion rate of the flare gas oxidative dehydrogenation reaction can reach 73%, the total olefin selectivity can reach 75%, the peroxidation degree can be reduced to 4% or below, and compared with a conventional borosilicate molecular sieve, the borosilicate molecular sieve provided by the method has the advantages that the total alkane conversion rate and the olefin selectivity of the catalytic flare gas oxidative dehydrogenation reaction are remarkably improved, and the peroxidation effect is remarkably reduced.

Description

Technical Field

[0001] This invention relates to the field of petrochemical technology, and in particular to a method for preparing olefins from flare gas. Background Technology

[0002] Flare gas is a mixed gas emitted during the production process in the petroleum refining industry. Its main components include low- and medium-carbon alkanes, olefins, nitrogen, carbon dioxide, and hydrogen sulfide. Its primary sources are operating losses from the equipment, start-up and shutdown emissions, and fuel combustion from flare lamps. The traditional method for treating flare gas is combustion. However, because flare gas is rich in olefins and low- and medium-carbon alkanes, direct combustion wastes resources and increases carbon dioxide emissions. Furthermore, the sulfur-containing substances in flare gas cause serious environmental problems upon combustion. Therefore, providing low-carbon, environmentally friendly, and efficient flare gas treatment methods is of great significance.

[0003] Currently, the main treatment of flare gas is recovery technology, which involves recycling high-value components. If the low- and medium-carbon alkanes in flare gas are used to prepare olefins through oxidative dehydrogenation, the resource recovery value of flare gas can be greatly increased, and the efficiency of high-value-added flare gas treatment can be further improved.

[0004] Currently, the dehydrogenation of alkanes to olefins mainly includes traditional thermal processing and catalytic methods. Catalytic methods, with their low energy consumption and high olefin selectivity, are the mainstream research direction. Catalyst preparation is the core step in alkane oxidative dehydrogenation and has become a hot research topic. For example, CN120079400A discloses a method for preparing a platinum-based catalyst for ethane oxidative dehydrogenation. Compared with existing catalysts supported by HZSM-5 molecular sieves, this catalyst exhibits higher ethane conversion, significantly reduced Pt metal sintering, and optimal ethylene selectivity of 52.05%, effectively solving the problems of low conversion, easy sintering of active metals, and poor stability of existing similar catalysts. CN 119702013A discloses a method for preparing a supported catalyst for ethane oxidative dehydrogenation. This catalyst, by improving the pore structure and specific surface area of ​​the M1 catalyst, regulating its surface active oxygen species, and enhancing its redox capacity, exhibits higher ethane conversion and ethylene selectivity in the ethane oxidative dehydrogenation to ethylene reaction. Furthermore, boron-based catalysts have solved the problem of high selectivity for peroxidation products on transition metal catalysts, exhibiting excellent olefin selectivity and yield, and have become the mainstream catalyst for researchers studying low-carbon alkanes. For example, CN115430460B discloses a borosilicate molecular sieve catalyst for the oxidative dehydrogenation of low-carbon alkanes and its preparation method. This catalyst, applied in a fixed-bed reactor, achieves excellent propane oxidative dehydrogenation performance under certain conditions. It inherits the high selectivity advantage of traditional boron-based catalysts while completely solving their key defect of insufficient hydrothermal stability. It also possesses excellent mechanical strength and is easy to mold, exhibiting superior performance compared to supported vanadium oxide, traditional supported boron, and boron nitride catalysts, demonstrating significant industrial application potential. This technical solution provides a borosilicate molecular sieve catalyst with excellent catalytic activity for the oxidative dehydrogenation of propane to propylene. Further research in this invention revealed the presence of multiple alkanes in petroleum refining flare gas. Under these conditions, the total alkane conversion and total olefin selectivity of these catalysts are low, and they exhibit a high degree of peroxidation. Therefore, it is of great significance to provide a catalyst with high alkane conversion, high olefin selectivity and low peroxidation for flare gas olefin production. Summary of the Invention

[0005] This invention provides a method for preparing olefins from flare gas. The method employs alkane oxidative dehydrogenation, with oxygen as the oxidant and borosilicate molecular sieve as the catalyst. The borosilicate molecular sieve exhibits excellent oxidative dehydrogenation activity for low-carbon alkanes such as ethane and propane in the flare gas. This invention modifies the borosilicate molecular sieve with an active additive, significantly reducing the over-oxidation effect during the catalytic oxidative dehydrogenation reaction and significantly improving the total alkane conversion and total olefin selectivity of the borosilicate molecular sieve in the flare gas oxidative dehydrogenation reaction. Mechanism of action of the active component: Gallium ions (Ga... 3+GaO-Si coordination sites are formed with oxygen in the borosilicate molecular sieve framework. These sites possess moderate Lewis acidity and can form weak coordination interactions with the CH bonds of various low-carbon alkanes, weakening the CH bond energy rather than directly breaking it, thus lowering the activation energy of the dehydrogenation reaction. Considering the coexistence of polyalkanes in flare gas, GaO-Si... 3+ The charge density and coordination environment can be adapted to the differences in CH bonds between C1-C4 alkanes, avoiding the problem of activation of a single alkane and inefficient conversion of other alkanes. Cerium ions (Ce) 4+ / Ce 3+ It possesses reversible redox properties, forming CeOx species on the surface of borosilicate molecular sieves, acting as an "oxygen buffer": Ce... 4+ The release of lattice oxygen participates in the dehydrogenation of alkanes, reducing itself to Ce. 3+ Ce 3+ It is then oxidized to Ce by gaseous oxygen. 4+ The cycle is completed. This process avoids the reaction of excess gaseous oxygen with olefins, significantly reducing the degree of peroxidation. Lanthanum oxide, as a basic auxiliary agent, can neutralize the strongly bronsted acidic sites on the surface of borosilicate molecular sieves (these sites easily lead to alkane cracking and olefin polymerization to form carbon deposits), retaining only Ga. 3+ The provided moderate Lewis acid sites significantly reduce carbon buildup and enhance catalyst stability.

[0006] The specific technical solution of this invention is as follows: A method for preparing olefins from flare gas includes the following steps: (1) A gel is prepared by dissolving silicon source, boric acid, template agent and active components in a solvent. The gel is then crystallized, separated, dried and calcined to prepare borosilicate molecular sieve. The active components include gallium salt, cerium salt and lanthanum oxide in a mass ratio of 0.15~0.45:0.13~0.35:0~0.7. (2) The borosilicate molecular sieve is activated and then flare gas and oxygen are introduced to carry out an oxidative dehydrogenation reaction.

[0007] Preferably, the silicon source includes tetraethyl orthosilicate, the template agent includes tetrapropylammonium hydroxide, and the mass ratio of the silicon source to the template agent is 0.05:1 to 0.3:1.

[0008] Preferably, the mass ratio of silicon source to solvent is 1:10 to 1:100.

[0009] Preferably, the solvent includes one of water, ethylene glycol, a water-ethanol mixture, and a water-propylene glycol mixture.

[0010] Preferably, the crystallization treatment conditions include: temperature 100~150 ℃, time 12~72 h.

[0011] Preferably, the drying conditions include 80~120 ℃ for 12~24 h.

[0012] Preferably, the calcination conditions include: temperature 450~700 ℃, time 3~8 h, and air atmosphere.

[0013] Preferably, the temperature of the oxidative dehydrogenation reaction is 500~700 ℃.

[0014] Preferably, the feed ratio of flare gas to oxygen is 1:2 to 3:2.

[0015] Preferably, the oxidation reaction space velocity is 2~10 m / s. 3 / kg•h.

[0016] This invention provides a method for preparing olefins from flare gas. This method uses borosilicate molecular sieves to oxidize and dehydrogenate a mixture of alkanes in the flare gas. The borosilicate molecular sieve prepared by this method exhibits excellent oxidative dehydrogenation activity for the mixed alkanes in the flare gas. In the application of conventional borosilicate molecular sieves to the oxidative dehydrogenation reaction of a mixture of alkanes in flare gas, it was found that while conventional borosilicate molecular sieves exhibit high propane conversion and propylene selectivity when oxidizing and dehydrogenating pure propane gas, they suffer from low total alkane conversion, low total olefin selectivity, and high degree of peroxidation when oxidizing and dehydrogenating flare gas. Therefore, further improvement of the borosilicate molecular sieve is needed to enable it to possess high catalytic activity for oxidative dehydrogenation of flare gas. This invention adds an active agent composed of gallium salt, cerium salt, and lanthanum oxide during the preparation of the borosilicate molecular sieve, significantly reducing the peroxidation effect during the catalytic oxidation of flare gas by the borosilicate molecular sieve and significantly improving the total alkane conversion and total olefin selectivity of the flare gas.

[0017] Compared with the prior art, this application has the following technical effects: This invention uses gallium salt, cerium salt, and lanthanum oxide as active additives to modify borosilicate molecular sieves. The resulting borosilicate molecular sieves, when used for the oxidative dehydrogenation of flare gas alkane to olefins, can significantly inhibit the reaction over-oxidation, significantly improve the total alkane conversion rate of flare gas, and significantly improve the total olefin selectivity of flare gas. The peroxidation degree can be reduced to below 6%, the total alkane conversion rate can reach more than 65%, and the total olefin selectivity can reach more than 65%. Detailed Implementation

[0018] The present invention will be further described below with reference to embodiments.

[0019] To better understand the content of this invention, further explanation is provided below with reference to specific embodiments. It should be understood that the following embodiments are for illustrative purposes only and are not intended to limit the scope of this invention.

[0020] Example 1: A method for preparing olefins from flare gas includes the following steps: (1) Take 40 mL of tetraethyl orthosilicate and place it in a container. Then place the container in a 25 ℃ constant temperature water bath. Then slowly add 10 mL of deionized water to the container and stir evenly. Then adjust the pH to 2.0 to 2.5 to prepare a silicon source hydrolysate. (2) Take 0.37 g of boric acid and add it to 20 mL of deionized water to fully dissolve it to prepare a boric acid solution. Slowly inject the silicon source hydrolysate into the boric acid solution and stir for 30 min to prepare a gel solution. (3) Weigh 32.54 g of template agent (40 wt% tetrapropylammonium hydroxide aqueous solution), gallium nitrate solution (0.41 g gallium nitrate dissolved in 10 mL deionized water), cerium nitrate solution (0.346 g cerium nitrate dissolved in 10 mL deionized water) and lanthanum oxide aqueous dispersion (0.5 g lanthanum oxide dispersed in 10 mL water) and slowly add them to the gel solution, and add deionized water to make the total volume control between 90 mL and 100 mL. Stir thoroughly for 30 min to make a milky white gel. Adjust the pH of the milky white gel to 8 to 9 to make a gel ready for use. (4) The gel was transferred to a polytetrafluoroethylene reactor, the reactor was sealed and placed in a constant temperature oil bath at 120 ℃, and statically crystallized for 48 h to prepare a crystallized product. The crystallized product was filtered and separated into a precipitate. The precipitate was placed in a 100 ℃ forced air drying oven and dried for 12 h to obtain a precursor. The precursor was transferred to a muffle furnace and heated to 600 ℃ at a heating rate of 5 ℃ / min for 5 h to prepare a borosilicate molecular sieve. (5) Activate the borosilicate molecular sieve at 650 °C for 1 h, then use 4.5 m 3 Flare gas and oxygen (feed ratio of flare gas to oxygen is 1:1) are introduced at a space velocity of / kg•h to carry out oxidative dehydrogenation reaction. Methane accounts for 9% of the total alkanes, ethane accounts for 41% of the total alkanes, and propane accounts for 50% of the total alkanes in the flare gas.

[0021] Example 2: A method for preparing olefins from flare gas includes the following steps: (1) Take 40 mL of tetraethyl orthosilicate and place it in a container. Then place the container in a 25 ℃ constant temperature water bath. Then slowly add 10 mL of deionized water to the container and stir evenly. Then adjust the pH to 2.0 to 2.5 to prepare a silicon source hydrolysate. (2) Take 0.37 g of boric acid and add it to 20 mL of deionized water to fully dissolve it to prepare a boric acid solution. Slowly inject the silicon source hydrolysate into the boric acid solution and stir for 30 min to prepare a gel solution. (3) Weigh 32.54 g of template agent (40 wt% tetrapropylammonium hydroxide aqueous solution), gallium nitrate solution (0.21 g gallium nitrate dissolved in 10 mL deionized water), cerium nitrate solution (0.208 g cerium nitrate dissolved in 10 mL deionized water) and lanthanum oxide aqueous dispersion (0.5 g lanthanum oxide dispersed in 10 mL water) and slowly add them to the gel solution, and add deionized water to make the total volume control between 90 mL and 100 mL. Stir thoroughly for 30 min to make a milky white gel. Adjust the pH of the milky white gel to 8 to 9 to make a gel ready for use. (4) The gel was transferred to a polytetrafluoroethylene reactor, the reactor was sealed and placed in a constant temperature oil bath at 120 ℃, and statically crystallized for 48 h to prepare a crystallized product. The crystallized product was filtered and separated into a precipitate. The precipitate was placed in a 100 ℃ forced air drying oven and dried for 12 h to obtain a precursor. The precursor was transferred to a muffle furnace and heated to 600 ℃ at a heating rate of 5 ℃ / min for 5 h to prepare a borosilicate molecular sieve. (5) Activate the borosilicate molecular sieve at 600 °C for 1 h, then use 4.5 m 3 Flare gas and oxygen (feed ratio of flare gas to oxygen is 1:1) are introduced at a space velocity of / kg•h to carry out oxidative dehydrogenation reaction. Methane accounts for 9% of the total alkanes, ethane accounts for 41% of the total alkanes, and propane accounts for 50% of the total alkanes in the flare gas.

[0022] Example 3: A method for preparing olefins from flare gas includes the following steps: (1) Take 40 mL of tetraethyl orthosilicate and place it in a container. Then place the container in a 25 ℃ constant temperature water bath. Then slowly add 10 mL of deionized water to the container and stir evenly. Then adjust the pH to 2.0 to 2.5 to prepare a silicon source hydrolysate. (2) Take 0.37 g of boric acid and add it to 20 mL of deionized water to fully dissolve it to prepare a boric acid solution. Slowly inject the silicon source hydrolysate into the boric acid solution and stir for 30 min to prepare a gel solution. (3) Weigh 32.54 g of template agent (40 wt% tetrapropylammonium hydroxide aqueous solution), gallium nitrate solution (0.45 g gallium nitrate dissolved in 10 mL deionized water), cerium nitrate solution (0.138 g cerium nitrate dissolved in 10 mL deionized water) and lanthanum oxide aqueous dispersion (0.7 g lanthanum oxide dispersed in 10 mL water) and slowly add them to the gel solution, and add deionized water to make the total volume control between 90 mL and 100 mL. Stir thoroughly for 30 min to make a milky white gel. Adjust the pH of the milky white gel to 8 to 9 to make a gel ready for use. (4) The gel was transferred to a polytetrafluoroethylene reactor, the reactor was sealed and placed in a constant temperature oil bath at 120 ℃, and statically crystallized for 48 h to prepare a crystallized product. The crystallized product was filtered and separated into a precipitate. The precipitate was placed in a 100 ℃ forced air drying oven and dried for 12 h to obtain a precursor. The precursor was transferred to a muffle furnace and heated to 600 ℃ at a heating rate of 5 ℃ / min for 5 h to prepare a borosilicate molecular sieve. (5) Activate the borosilicate molecular sieve at 600 °C for 1 h, then use 4.5 m 3 Flare gas and oxygen (feed ratio of flare gas to oxygen is 1:1) are introduced at a space velocity of / kg•h to carry out oxidative dehydrogenation reaction. Methane accounts for 9% of the total alkanes, ethane accounts for 41% of the total alkanes, and propane accounts for 50% of the total alkanes in the flare gas.

[0023] Example 4: A method for preparing olefins from flare gas includes the following steps: (1) Take 40 mL of tetraethyl orthosilicate and place it in a container. Then place the container in a 25 ℃ constant temperature water bath. Then slowly add 10 mL of deionized water to the container and stir evenly. Then adjust the pH to 2.0 to 2.5 to prepare a silicon source hydrolysate. (2) Take 0.37 g of boric acid and add it to 20 mL of deionized water to fully dissolve it to prepare a boric acid solution. Slowly inject the silicon source hydrolysate into the boric acid solution and stir for 30 min to prepare a gel solution. (3) Weigh 32.54 g of template agent (40 wt% tetrapropylammonium hydroxide aqueous solution), gallium nitrate solution (0.41 g gallium nitrate dissolved in 10 mL deionized water), cerium nitrate solution (0.346 g cerium nitrate dissolved in 10 mL deionized water) and lanthanum oxide aqueous dispersion (0.5 g lanthanum oxide dispersed in 10 mL water) and slowly add them to the gel solution, and add deionized water to make the total volume control between 90 mL and 100 mL. Stir thoroughly for 30 min to make a milky white gel. Adjust the pH of the milky white gel to 8 to 9 to make a gel ready for use. (4) The gel was transferred to a polytetrafluoroethylene reactor, the reactor was sealed and placed in a constant temperature oil bath at 120 ℃, and statically crystallized for 48 h to prepare a crystallized product. The crystallized product was filtered and separated into a precipitate. The precipitate was placed in a 100 ℃ forced air drying oven and dried for 12 h to obtain a precursor. The precursor was transferred to a muffle furnace and heated to 600 ℃ at a heating rate of 5 ℃ / min for 5 h to prepare a borosilicate molecular sieve. (5) Activate the borosilicate molecular sieve at 600 °C for 1 h, then use 4.5 m 3Flare gas and oxygen (feed ratio of flare gas to oxygen is 1:1) are introduced at a space velocity of / kg•h to carry out oxidative dehydrogenation reaction. Methane accounts for 9% of the total alkanes, ethane accounts for 41% of the total alkanes, and propane accounts for 50% of the total alkanes in the flare gas.

[0024] Example 5: A method for preparing olefins from flare gas includes the following steps: (1) Take 40 mL of tetraethyl orthosilicate and place it in a container. Then place the container in a 25 ℃ constant temperature water bath. Then slowly add 10 mL of deionized water to the container and stir evenly. Then adjust the pH to 2.0 to 2.5 to prepare a silicon source hydrolysate. (2) Take 0.37 g of boric acid and add it to 20 mL of deionized water to fully dissolve it to prepare a boric acid solution. Slowly inject the silicon source hydrolysate into the boric acid solution and stir for 30 min to prepare a gel solution. (3) Weigh 32.54 g of template agent (40 wt% tetrapropylammonium hydroxide aqueous solution), gallium nitrate solution (0.41 g gallium nitrate dissolved in 10 mL deionized water), cerium nitrate solution (0.346 g cerium nitrate dissolved in 10 mL deionized water) and lanthanum oxide aqueous dispersion (0.5 g lanthanum oxide dispersed in 10 mL water) and slowly add them to the gel solution, and add deionized water to make the total volume control between 90 mL and 100 mL. Stir thoroughly for 30 min to make a milky white gel. Adjust the pH of the milky white gel to 8 to 9 to make a gel ready for use. (4) The gel was transferred to a polytetrafluoroethylene reactor, the reactor was sealed and placed in a constant temperature oil bath at 120 ℃, and statically crystallized for 48 h to prepare a crystallized product. The crystallized product was filtered and separated into a precipitate. The precipitate was placed in a 100 ℃ forced air drying oven and dried for 12 h to obtain a precursor. The precursor was transferred to a muffle furnace and heated to 600 ℃ at a heating rate of 5 ℃ / min for 5 h to prepare a borosilicate molecular sieve. (5) Activate the borosilicate molecular sieve at 600 °C for 1 h, then use 4.5 m 3 Flare gas and oxygen (feed ratio of flare gas to oxygen is 1:2) are introduced at a space velocity of / kg•h to carry out oxidative dehydrogenation reaction. Methane accounts for 9% of the total alkanes, ethane accounts for 41% of the total alkanes, and propane accounts for 50% of the total alkanes in the flare gas.

[0025] Comparative Example 1: The difference between Comparative Example 1 and Example 1 is that gallium nitrate, cerium nitrate, and lanthanum oxide were not added, while all other conditions were the same as in Example 1.

[0026] Comparative Example 2: The difference between Comparative Example 2 and Example 1 is that cerium nitrate was not added, while all other conditions were the same as in Example 1.

[0027] Comparative Example 3: The difference between Comparative Example 3 and Example 1 is that Comparative Example 3 involves alkaline leaching treatment, including the following steps: (1) Take 40 mL of tetraethyl orthosilicate and place it in a container. Then place the container in a 25 ℃ constant temperature water bath. Then slowly add 10 mL of deionized water to the container and stir evenly. Then adjust the pH to 2.0 to 2.5 to prepare a silicon source hydrolysate. (2) Take 0.37 g of boric acid and add it to 20 mL of deionized water to fully dissolve it to prepare a boric acid solution. Slowly inject the silicon source hydrolysate into the boric acid solution and stir for 30 min to prepare a gel solution. (3) Weigh 32.54 g of template agent (40 wt% tetrapropylammonium hydroxide aqueous solution), gallium nitrate solution (0.41 g gallium nitrate dissolved in 10 mL deionized water), cerium nitrate solution (0.346 g cerium nitrate dissolved in 10 mL deionized water) and lanthanum oxide aqueous dispersion (0.5 g lanthanum oxide dispersed in 10 mL water) and slowly add them to the gel solution, and add deionized water to make the total volume control between 90 mL and 100 mL. Stir thoroughly for 30 min to make a milky white gel. Adjust the pH of the milky white gel to 8 to 9 to make a gel ready for use. (4) The gel was transferred to a polytetrafluoroethylene reactor, the reactor was sealed and placed in a constant temperature oil bath at 120 ℃, and statically crystallized for 48 h to prepare a crystallized product. The crystallized product was filtered and separated into a precipitate. The precipitate was placed in a 100 ℃ forced air drying oven and dried for 12 h to obtain a precursor. The precursor was transferred to a muffle furnace and heated to 600 ℃ at a heating rate of 5 ℃ / min for 5 h to prepare a borosilicate molecular sieve. (5) Immerse the borosilicate molecular sieve in a sodium hydroxide solution (concentration of 4 mol / L) at 50 °C for 24 h, and then wash and dry it with ammonia water; the other conditions are the same as in Example 1.

[0028] Comparative Example 4: The borosilicate molecular sieve prepared in Comparative Example 1 was subjected to acid leaching treatment. The treatment steps were as follows: the borosilicate molecular sieve was immersed in hydrogen chloride solution (concentration of 4 mol / L) for 12 h, then washed with deionized water until neutral, then washed with ethanol, and then dried in a forced-air drying oven at 100 ℃ for 12 h.

[0029] Comparative Example 5: The borosilicate molecular sieve prepared in Comparative Example 1 was subjected to acid leaching and alkali leaching treatments. The treatment steps were as follows: the borosilicate molecular sieve was immersed in hydrogen chloride solution (concentration of 4 mol / L) for 12 h, then washed with deionized water until neutral, then washed with ethanol, and then dried in a forced-air drying oven at 100 ℃ for 12 h; the acid-leached borosilicate molecular sieve was then immersed in sodium hydroxide solution (concentration of 4 mol / L) at 50 ℃ for 24 h, then washed and dried with ammonia water. All other conditions were the same as in Example 1.

[0030] Detection Example 1: The total alkane conversion, total olefin selectivity and degree of peroxidation of Examples 1 to 5 and Comparative Examples 1 to 5 were tested, and the test results are shown in Table 1. Table 1 Test Results As shown in Table 1, Examples 1-5 are technical solutions for oxidative dehydrogenation of flare gas to olefins using the method provided by the present invention. The results show that the total alkane conversion rate of Examples 1-5 can reach up to 84.67%, the total olefin selectivity can reach up to 75.11%, and the peroxidation degree can be reduced to down to 1.36%.

[0031] Comparative Example 1 illustrates a technique for oxidative dehydrogenation of flare gas using a conventional borosilicate catalyst. Its total alkane conversion rate was 30.25%, total olefin selectivity was 46.12%, and peroxidation degree was 20.58%. Comparing the results of Comparative Example 1 with Examples 1-5 reveals that using a conventional borosilicate catalyst for oxidative dehydrogenation of flare gas suffers from low total alkane conversion rate, low olefin selectivity, and high peroxidation degree. However, the borosilicate molecular sieve modified with gallium nitrate, cerium nitrate, and lanthanum oxide significantly improves the total alkane conversion rate and olefin selectivity, while also significantly suppressing peroxidation.

[0032] Comparative Example 2, which uses a technology without added cerium nitrate, shows a total alkane conversion rate of 61.71%, a total olefin selectivity of 60.33%, and a peroxidation degree of 10.11%. Comparing the results of Comparative Example 1, Comparative Example 2, and Example 1, it can be seen that modifying the borosilicate catalyst with gallium nitrate and lanthanum oxide significantly improves the total alkane conversion rate and total olefin selectivity in the oxidative dehydrogenation of flare gas, while also significantly reducing the peroxidation degree. Gallium nitrate and lanthanum oxide have a significant effect on improving the oxidative dehydrogenation reaction of flare gas catalyzed by the borosilicate catalyst. Furthermore, further modification of the borosilicate catalyst with cerium nitrate can further improve the total alkane conversion rate and total olefin selectivity, and further suppress peroxidation.

[0033] Comparative Examples 3, 4, and 5 investigated the effects of acid and alkali leaching treatments on the catalytic performance of borosilicate molecular sieves. The results showed that conventional borosilicate molecular sieves, after acid and alkali leaching, exhibited significantly improved total alkane and total olefin conversion rates in the flare gas oxidative dehydrogenation reaction, and significantly suppressed peroxidation, but the effects were significantly lower than those provided by the method of this invention. However, after alkali leaching, the borosilicate molecular sieve prepared according to this invention showed a decrease in the total alkane and total olefin conversion rates in the flare gas oxidative dehydrogenation reaction, and a weakening of the peroxidation inhibition. The reason for this phenomenon is that acid and alkali treatment of conventional borosilicate molecular sieves can modify the active sites of the sieve, thereby improving the catalytic efficiency of conventional borosilicate molecular sieves in the flare gas oxidative dehydrogenation reaction. However, alkali modification of the borosilicate molecular sieve modified with gallium nitrate, cerium nitrate, and lanthanum oxide in this invention destroys the special structures of gallium oxide, cerium oxide, and lanthanum oxide within the borosilicate molecular sieve, reducing the catalytic efficiency of the borosilicate molecular sieve in the flare gas oxidative dehydrogenation reaction.

[0034] Furthermore, analysis of the results from Examples 1-5 revealed that the effect of borosilicate molecular sieves initially increased and then decreased with increasing amounts of gallium nitrate, cerium nitrate, and lanthanum oxide. This indicates that there is an optimal amount of gallium nitrate, cerium nitrate, and lanthanum oxide, at which the borosilicate molecular sieve exhibits the best performance. Additionally, Examples 1-5 investigated the flare gas / oxygen feed ratio and catalyst activation temperature during oxidative dehydrogenation. The results showed that increasing the oxygen content is beneficial for alkane conversion but also increases the degree of peroxidation, leading to a decrease in olefin selectivity. Conversely, excessively low or high catalytic temperatures significantly reduced the effectiveness of the oxidative dehydrogenation reaction. This indicates that the catalyst activation temperature has a significant impact on the oxidative dehydrogenation reaction, and only by reaching a suitable activation temperature can the optimal conversion effect of flare gas alkane oxidative dehydrogenation to olefins be obtained.

[0035] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, alterations, and equivalent transformations made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing olefins from flare gas, characterized in that, Includes the following steps: (1) A gel is prepared by dissolving silicon source, boric acid, template agent and active components in a solvent. The gel is then crystallized, separated, dried and calcined to prepare borosilicate molecular sieve. The active components include gallium salt, cerium salt and lanthanum oxide in a mass ratio of 0.15~0.45:0.13~0.35:0~0.

7. (2) The borosilicate molecular sieve is activated and then flare gas and oxygen are introduced to carry out an oxidative dehydrogenation reaction.

2. The method according to claim 1, characterized in that, The silicon source includes tetraethyl orthosilicate, and the template agent includes tetrapropylammonium hydroxide. The mass ratio of the silicon source to the template agent is 0.05:1 to 0.3:

1.

3. The method according to claim 1, characterized in that, The mass ratio of silicon source to solvent is 1:10 to 1:

100.

4. The method according to claim 1 or 3, characterized in that, The solvent includes one of water, ethylene glycol, a water-ethanol mixture, and a water-propylene glycol mixture.

5. The method according to claim 1, characterized in that, The conditions for crystallization treatment include: temperature 100~150 ℃, time 12~72 h.

6. The method according to claim 1, characterized in that, The drying conditions include 80~120 ℃ and a time of 12~24h.

7. The method according to claim 1, characterized in that, The calcination conditions include: temperature 450~700 ℃, time 3~8h, and air atmosphere.

8. The method according to claim 1, characterized in that, The temperature for the oxidative dehydrogenation reaction is 500~700 ℃.

9. The method according to claim 1, characterized in that, The feed ratio of flare gas to oxygen is 1:2 to 3:

2.

10. The method according to claim 1 or 9, characterized in that, The space velocity of the oxidation reaction is 2~10 m. 3 / kg•h.

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