Method for performing tar steam reforming by coupling low-temperature plasma with nickel-loaded hydrogen type molecular sieve composite catalyst

Abstract

The invention discloses a method for performing tar steam reforming by coupling low-temperature plasma with a nickel-loaded hydrogen type molecular sieve composite catalyst. The method comprises the following steps: preparing the nickel-loaded hydrogen type molecular sieve composite catalyst; the mass of Ni in the nickel-loaded hydrogen type molecular sieve composite catalyst accounts for 5-30% of the mass of the catalyst; introducing tar and water vapor into a dielectric barrier discharge plasma reactor filled with the nickel-loaded hydrogen type molecular sieve composite catalyst; starting the dielectric barrier discharge plasma reactor, and carrying out a tar steam reforming reaction; wherein the temperature of the tar steam reforming reaction is 150-525 DEG C, and the power of the tar steam reforming reaction is 30-90 W. The catalyst disclosed by the invention is coupled with a low-temperature plasma technology, so that good tar reforming performance, target product selectivity and system stability are realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of waste resource utilization, and relates to a method for tar steam reforming by using a composite catalyst of low-temperature plasma coupled with nickel-loaded hydrogen-type molecular sieve. Background Art

[0002] Tar is an inevitable by-product in the process of biomass gasification. Its components are complex and difficult to degrade, and it is easy to block pipelines and corrode equipment, which seriously restricts the efficient utilization of biomass energy. Tar reforming technology aims to convert macromolecular tar into utilizable syngas (such as H2, CO), which is a key link to improve the efficiency of the gasification system. The current mainstream methods include thermal cracking and catalytic reforming. Thermal cracking requires a relatively high temperature (>1000 °C), resulting in a high energy consumption problem. Catalytic reforming relies on high temperature (>600 °C) and catalysts. Although it can achieve a high tar conversion rate, there are problems such as high energy consumption and easy carbon deposition and deactivation of the catalyst. In recent years, low-temperature plasma technology has attracted attention due to its ability to generate active particles (such as high-energy electrons, free radicals) under mild conditions. However, the reforming of tar by plasma alone will inevitably form harmful by-products and it is difficult to achieve the directional conversion of syngas, resulting in a low selectivity. Existing research attempts to combine plasma with catalysts to break through the limitations of single technologies. Catalysts generally consist of active metals / metal oxides and supports. Among them, nickel-based catalysts are widely used because compared with noble metals, the transition metal nickel has rich reserves and low production costs, and at the same time has a high ability to break C-C and C-H bonds. Selecting a suitable support is the basis for improving the performance of the catalyst. Currently, commonly used catalyst supports include natural ores, activated carbon, and metal oxides, etc., but they all have the problem of low dispersion of active sites. During the reaction process, the active metal is prone to agglomeration and carbon deposition, causing catalyst deactivation, and the system stability is poor, affecting the reforming process and resulting in a low syngas selectivity for the coupling reforming of tar by plasma and catalyst. Summary of the Invention

[0003] Aiming at the problems existing in the prior art, the present invention provides a method for tar steam reforming by using a composite catalyst of low-temperature plasma coupled with nickel-loaded hydrogen-type molecular sieve, so as to solve the technical problems of low syngas selectivity for the coupling of plasma and catalyst to achieve tar reforming and poor system stability in the prior art.

[0004] The present invention is realized by the following technical solutions:

[0005] A method for tar steam reforming by using a composite catalyst of low-temperature plasma coupled with nickel-loaded hydrogen-type molecular sieve, comprising:

[0006] Prepare a nickel-loaded hydrogen-type molecular sieve composite catalyst; the mass of Ni in the nickel-loaded hydrogen-type molecular sieve composite catalyst accounts for 5% to 30% of the mass of the catalyst;

[0007] Pass the tar and steam into a dielectric barrier discharge plasma reactor equipped with the nickel-loaded hydrogen-type molecular sieve composite catalyst;

[0008] Turn on the dielectric barrier discharge plasma reactor to carry out the tar steam reforming reaction; among them, the temperature of the tar steam reforming reaction is 150 to 525 °C, and the power is 30 to 90 W.

[0009] Preferably, during the tar steam reforming reaction, the carrier gas is nitrogen, and the flow rate of the carrier gas is 0.1 to 4 L / min.

[0010] Preferably, the molar ratio of steam to carbon in the tar is 0.5 to 5.

[0011] Preferably, after mixing the nickel-loaded hydrogen-type molecular sieve composite catalyst with quartz sand, it is loaded into a dielectric barrier discharge plasma reactor; the mass ratio of the nickel-loaded hydrogen-type molecular sieve composite catalyst to quartz sand is (0.1 to 0.5):(0.7 to 0.9).

[0012] Preferably, the preparation process of the nickel-loaded hydrogen-type molecular sieve composite catalyst is as follows:

[0013] S1: Drop the NaAlO2 solution into NaOH, then add a soluble nickel salt, stir and mix evenly to obtain a mixed solution A;

[0014] S2: Add the solution A to the tetrapropylammonium hydroxide solution to obtain a mixed solution B;

[0015] S3: Drop the mixed solution B into the tetraethyl orthosilicate aqueous solution, and after ultrasonic treatment, obtain a mixed solution C;

[0016] S4: Carry out hydrothermal treatment on the mixed solution C, and after calcining the obtained product, prepare a Na-type ZSM-5 molecular sieve;

[0017] S5: Disperse the Na-type ZSM-5 molecular sieve in the NH4Cl solution, and after calcining the reaction product, prepare the nickel-loaded hydrogen-type molecular sieve composite catalyst;

[0018] Preferably, the mass ratio of NaAlO2, NaOH, soluble nickel salt and tetraethyl orthosilicate is 1:8:(2.5 to 11):125.

[0019] Preferably, in step S4, the temperature of the hydrothermal treatment is 150 - 300 °C, and the time is 20 - 30 h.

[0020] Preferably, in step S4, the temperature of the calcination treatment is 400 - 650 °C, and the time is 10 - 15 h.

[0021] Preferably, in step S5, when the Na-type ZSM-5 molecular sieve is dispersed in the NH4Cl solution for reaction, the reaction temperature is 50 - 110 °C, and the time is 2.5 - 5 h.

[0022] Preferably, in step S5, the temperature of the calcination treatment is 300 - 600 °C, and the time is 3 - 6 h.

[0023] Compared with the prior art, the present invention has the following beneficial technical effects:

[0024] The present invention discloses a method for tar steam reforming using a composite catalyst of low-temperature plasma coupled with nickel-loaded hydrogen-type molecular sieve. First, this method combines a nickel-loaded hydrogen-type molecular sieve composite catalyst (Ni / HZSM-5) with low-temperature plasma, effectively improving the tar conversion rate and syngas selectivity in the tar reforming reaction. In this catalyst, the mass of Ni in the nickel-loaded hydrogen-type molecular sieve composite catalyst accounts for 5% - 30% of the mass of the catalyst. As the active component of the catalyst, its loading amount directly affects the catalytic performance of the catalyst. If the loading amount is too low (<5%), insufficient active sites can be provided, resulting in limited catalytic effects. If the loading amount is too high (>30%), Ni particles will agglomerate, reducing the specific surface area and activity of the catalyst. At the same time, the specific surface area of the Ni / HZSM-5 catalyst is higher than that of commercial molecular sieves, and the crystallinity of the catalyst remains intact after Ni loading, enhancing the catalyst activity. Under the optimal Ni loading (15wt%), the particle size of metal oxides is smaller and the dispersion degree is higher, which can provide more reaction active sites and increase the utilization rate of active sites. In addition, the microporous structure of Ni / HZSM-5 will generate microdischarges, increasing the plasma discharge area under the condition of constant volume and average discharge energy, generating more excited species and active free radicals, making it easier for tar molecules to decompose. During the process of low-temperature plasma coupling with Ni / HZSM-5 for tar reforming, the reaction temperature is 150 - 525°C, and the reaction power is 30 - 90W. Excessive temperature (>600°C) will lead to catalyst deactivation and increased energy consumption. The reaction power directly affects the generation and intensity of low-temperature plasma. If the power is too low (<30W), insufficient high-energy electrons can be generated to excite and activate tar molecules. If the power is too high (>90W), it may lead to increased energy consumption and unnecessary side reactions. Since toluene and other monocyclic aromatic hydrocarbons in tar account for the largest proportion (about 46%) in the typical components of tar, the present invention uses toluene as a tar model compound, coupling a dielectric barrier discharge plasma reactor with a nickel-loaded hydrogen-type molecular sieve composite catalyst to achieve the steam reforming reaction of toluene. Among them, the toluene conversion rate is 94% - 100%, the H2 selectivity is 30% - 42%, and the CO selectivity is 22% - 32%. Therefore, based on the optimization of the catalyst, reforming reaction temperature, and power, the present invention effectively realizes the high-selectivity reforming process of tar.

[0025] Further, during the tar reforming reaction process, the carrier gas is one of argon, nitrogen, and air. The flow rate of the carrier gas is 0.1 - 4 L / min. The carrier gas carries tar and water vapor into the dielectric barrier discharge plasma reactor to ensure that the reactants can be evenly distributed on the catalyst surface, thereby improving the uniformity and efficiency of the reaction. Through the dilution of the carrier gas, the concentration of the reactants can be reduced, thereby slowing down the reaction rate, which is conducive to the precise control of the reaction and the optimization of the selectivity of the products. Setting the flow rate of the carrier gas to 0.1 - 4 L / min ensures an appropriate residence time of the reactants in the reactor, avoiding unnecessary side reactions and increasing energy consumption. The adjustment of the carrier gas flow rate can affect the contact time and reaction depth between the reactants and the catalyst, and thus affect the selectivity of the products. A flow rate of 0.1 - 4 L / min can optimize the product distribution to a certain extent and improve the selectivity of the target syngas (such as H2, CO).

[0026] Further, the molar ratio of water vapor to carbon in the tar is 0.5 - 5. In the tar reforming reaction, water vapor can provide ·OH, ·H, and ·O free radicals. These active free radicals can react with hydrocarbons in the tar to generate carbon monoxide and hydrogen, which are the main target products of tar reforming. In addition, water vapor absorbs heat during the reaction process, which helps to regulate the temperature of the reactor, prevent the catalyst from deactivating or increasing side reactions due to excessive temperature. At the same time, as a reaction medium, water vapor can promote the contact and reaction between tar molecules and the active sites of the catalyst, improving the efficiency and selectivity of the reaction.

[0027] Further, after mixing the nickel-loaded hydrogen-type zeolite composite catalyst with quartz sand, it is loaded into the dielectric barrier discharge plasma reactor; the mass ratio of the nickel-loaded hydrogen-type zeolite composite catalyst to quartz sand is (0.1 - 0.5):(0.7 - 0.9). Quartz sand, as an inert carrier, can effectively disperse the nickel-loaded hydrogen-type zeolite composite catalyst, prevent the agglomeration of catalyst particles, thereby increasing the contact area between the catalyst and the reactants and improving the catalytic efficiency. An appropriate amount of catalyst can provide sufficient active sites to promote the reforming reaction of tar. Excessive catalyst leads to increased costs and unnecessary side reactions; too little catalyst cannot provide sufficient catalytic activity, resulting in low reaction efficiency. An appropriate ratio can ensure sufficient contact between the reactants and the catalyst, thereby increasing the reaction rate. In addition, by optimizing this ratio, the product distribution can be optimized and the selectivity of the target product can be improved.

[0028] Furthermore, the present invention also discloses a preparation method of the above-mentioned nickel-loaded hydrogen-type molecular sieve composite catalyst. During the preparation of this catalyst, the NaAlO₂ solution is dropped into NaOH, and then a soluble nickel salt is added. After stirring and mixing evenly, a mixed solution A is obtained. NaAlO₂ mainly serves as an aluminum source and, together with the nickel salt added subsequently, forms the active component of the catalyst. NaOH provides an alkaline environment, enabling better dissolution of sodium aluminate and uniform mixing with other reagents. At the same time, NaOH may also react with the aluminum source to generate corresponding aluminates, which helps the formation of the subsequent molecular sieve. Then, the solution A is added to the tetrapropylammonium hydroxide solution to obtain a mixed solution B. Tetrapropylammonium hydroxide serves as a template agent and is crucial for the formation of the molecular sieve structure. The mixed solution B is dropped into the aqueous solution of tetraethyl orthosilicate. After ultrasonic treatment, a mixed solution C is obtained. Tetraethyl orthosilicate is a silicon source used to form the framework of ZSM-5 molecular sieve. During the dropping process, ultrasonic treatment is carried out. Ultrasonic treatment can accelerate the reaction rate, uniformly mix the reagents, and disperse the particles, thereby improving the stability and uniformity of the sample. The mixed solution C is subjected to hydrothermal treatment, and the obtained product is calcined to prepare the Na-type ZSM-5 molecular sieve. Hydrothermal treatment forms the structure of ZSM-5 molecular sieve from the silicate in the solution through the crystallization process. The treated product is calcined to remove the template agent and other impurities, and at the same time make the molecular sieve structure more stable. The Na-type ZSM-5 molecular sieve is dispersed in the NH₄Cl solution for ammonium ion exchange. This process is to replace the sodium ions in the molecular sieve with ammonium ions. The reaction product is calcined to remove the ammonium ions and convert it into the hydrogen-type molecular sieve (HZSM-5), thus preparing the nickel-loaded hydrogen-type molecular sieve composite catalyst.

[0029] Furthermore, the mass ratio of NaAlO₂, NaOH, soluble nickel salt, and tetraethyl orthosilicate is 1:8:(2.5 - 11):125, which can balance the reaction particles and the template agent structure, and can better regulate the crystal structure subsequently.

[0030] Furthermore, in step S4, the temperature of the hydrothermal treatment is 150 - 300 °C, and the time is 20 - 30 h, which can make the crystal grains grow completely and obtain the required crystal form.

[0031] Furthermore, in step S4, the temperature of the calcination treatment is 400 - 650 °C, and the time is 10 - 15 h, which can decompose the metal salt and promote the metal ion exchange in the catalyst.

[0032] Furthermore, in step S5, when the Na-type ZSM-5 molecular sieve is dispersed in the NH₄Cl solution for reaction, the reaction temperature is 50 - 110 °C, and the time is 2.5 - 5 h, which is beneficial to the formation of the NH₄ + type ZSM-5 molecular sieve.

[0033] Further, in step S5, the temperature of the calcination treatment is 300-600 °C and the time is 3-6 h, which can decompose the metal salt and promote the metal ion exchange in the catalyst. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as limiting the scope. For those of ordinary skill in the art, other related drawings can be obtained based on these drawings without creative efforts.

[0035] Figure 1 It is a schematic flow chart of a preparation method of a nickel-loaded hydrogen-type molecular sieve composite catalyst in the present invention;

[0036] Figure 2 It is an XRD pattern of a nickel-loaded hydrogen-type molecular sieve composite catalyst prepared in Example 2 and Comparative Example 1 of the present invention. Among them, a: commercial molecular sieve, b: HZSM-5 (i.e., the product of Comparative Example 1), c: 15% Ni / HZSM-5 (i.e., the product of Example 2);

[0037] Figure 3 It is an NH3-TPD pattern of a nickel-loaded hydrogen-type molecular sieve composite catalyst prepared in Example 2 and Comparative Example 1 of the present invention. Among them, a: commercial molecular sieve, b: HZSM-5 (i.e., the product of Comparative Example 1), c: 15% Ni / HZSM-5 (i.e., the product of Example 2);

[0038] Figure 4 It is the stability test result of a 48-hour toluene reforming reaction using the catalyst prepared in Example 2 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0039] To enable those skilled in the art to understand the features and effects of the present invention, the following provides a general description and definition of the terms and phrases mentioned in the specification and claims. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art for the present invention. When there are conflicts, the definition in this specification shall prevail.

[0040] The theories or mechanisms described and disclosed herein, whether correct or incorrect, shall not limit the scope of the present invention in any way, that is, the content of the present invention can be implemented without being limited by any specific theory or mechanism.

[0041] In this text, all features defined in the form of numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are only for the sake of brevity and convenience. Accordingly, the description of numerical ranges or percentage ranges should be regarded as having covered and specifically disclosed all possible sub-ranges and individual numerical values within the ranges (including integers and fractions).

[0042] In this text, unless otherwise specified, the terms "comprising", "including", "containing", "having", or similar terms cover the meanings of "consisting of" and "consisting essentially of". For example, "A comprises a" covers the meanings of "A comprises a and others" and "A consists only of a".

[0043] In this text, for the sake of concise description, all possible combinations of all technical features in each embodiment or example are not described. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each embodiment or example can be combined arbitrarily, and all possible combinations should be considered as within the scope described in this specification.

[0044] In a first aspect, the present invention discloses a method for tar steam reforming using a low-temperature plasma-coupled nickel-loaded hydrogen-type molecular sieve composite catalyst, comprising:

[0045] Preparing a nickel-loaded hydrogen-type molecular sieve composite catalyst; the mass of Ni in the nickel-loaded hydrogen-type molecular sieve composite catalyst accounts for 5% to 30% of the mass of the catalyst;

[0046] Feeding tar and steam together into a dielectric barrier discharge plasma reactor filled with the nickel-loaded hydrogen-type molecular sieve composite catalyst;

[0047] Starting the dielectric barrier discharge plasma reactor to carry out tar reforming reaction; wherein, the temperature of the tar reforming reaction is 150 to 525 °C, and the power is 30 to 90 W.

[0048] Preferably, during the tar reforming reaction, the carrier gas is one of argon, nitrogen, and air, and the flow rate of the carrier gas is 0.5 to 4 L / min.

[0049] More preferably, the molar ratio of steam to carbon in the tar is 0.5 to 5.

[0050] In addition, after mixing the nickel-loaded hydrogen-type molecular sieve composite catalyst with quartz sand, it is loaded into the dielectric barrier discharge plasma reactor; wherein the mass ratio of the nickel-loaded hydrogen-type molecular sieve composite catalyst to quartz sand is (0.1 to 0.5):(0.7 to 0.9).

[0051] In the present invention, toluene is used as a tar model compound. A nickel-loaded hydrogen-type molecular sieve composite catalyst is placed in a dielectric barrier discharge plasma reactor. Argon, nitrogen, or air is used as a carrier gas to introduce toluene raw gas and water vapor. The steam reforming reaction with toluene as the tar model compound is realized through plasma discharge. In the steam reforming reaction, the toluene conversion rate is 94% - 100%, the H2 selectivity is 30% - 42%, and the CO selectivity is 22% - 32%.

[0052] In a second aspect, as Figure 1 shown, the present invention also provides a preparation method of the above-mentioned nickel-loaded hydrogen-type molecular sieve composite catalyst, including the following steps:

[0053] S1: Drop the NaAlO2 solution into NaOH, then add a soluble nickel salt, and stir and mix evenly to obtain a mixed solution A;

[0054] S2: Add the solution A into the tetrapropylammonium hydroxide solution to obtain a mixed solution B;

[0055] S3: Drop the mixed solution B into the tetraethyl orthosilicate aqueous solution, and after ultrasonic treatment for 10 - 30 min, obtain a mixed solution C;

[0056] S4: Perform hydrothermal treatment on the mixed solution C, and after calcining the obtained product, prepare the Na-type ZSM-5 molecular sieve; wherein, the temperature of the hydrothermal treatment is 150 - 300 °C, and the time is 20 - 30 h. The temperature of the calcining treatment is 400 - 650 °C, and the time is 10 - 15 h.

[0057] S5: Disperse the Na-type ZSM-5 molecular sieve in the NH4Cl solution, and after calcining the reaction product, prepare the nickel-loaded hydrogen-type molecular sieve composite catalyst. When dispersing the Na-type ZSM-5 molecular sieve in the NH4Cl solution for reaction, the reaction temperature is 50 - 110 °C, and the time is 2.5 - 5 h. The temperature of the calcining treatment is 300 - 600 °C, and the time is 3 - 6 h.

[0058] In the above method, the mass ratio of NaAlO2, NaOH, the soluble nickel salt, and tetraethyl orthosilicate is 1:8:(2.5 - 11):125.

[0059] The plasma-coupled catalytic process is specifically as follows: Place the catalyst inside the dielectric barrier discharge (DBD) region, and adopt the coupling method of low-temperature plasma discharge and the catalyst; The low-temperature plasma discharge can generate high-energy electrons, which undergo inelastic collisions with water molecules and carrier gas molecules, and then form active particles such as free radicals (such as ·H, ·O, and ·OH), excited atoms, ions, and molecules after excitation, ionization, and dissociation. The reactants are bombarded and dissociated by high-energy electrons and active particles, resulting in the breaking of chemical bonds. A series of benzene derivatives are produced after cracking, and are further decomposed into small-molecule organic compounds after ring opening. These small molecules are reduced by the action of active free radicals (active oxygen, hydroxyl, etc.) to generate more syngas. The flue gas after the reaction in the plasma-assisted catalytic device is monitored online. First, when the toluene concentration is stable at a certain level through online monitoring, the low-temperature plasma discharge device is turned on to carry out the plasma-catalytic steam reforming reaction of toluene. The active substances generated by the catalyst and the discharge react with toluene molecules to convert more toluene into syngas. When the product concentration remains stable for a period of time, the low-temperature plasma discharge device is turned off, and this operation is repeated at different reaction temperatures and discharge powers.

[0060] The following further elaborates the present invention in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

[0061] Conventional instrument equipment in the art is used in the following embodiments. For the experimental methods without specific conditions noted in the following embodiments, they are usually carried out under conventional conditions or according to the conditions recommended by the manufacturer. Various raw materials are used in the following embodiments. Unless otherwise stated, commercially available products are used, and their specifications are the conventional specifications in the art. In the specification of the present invention and the following embodiments, unless otherwise specified, "%" represents weight percentage, "parts" represents weight parts, and the ratio represents weight ratio.

[0062] Example 1

[0063] The reforming catalyst in this example is prepared according to the following steps:

[0064] Step 1: Dissolve NaAlO2 and NaOH with a mass ratio of 1:8 in deionized water. Slowly drop the NaAlO2 solution into the NaOH solution, and at the same time add 2.9081 g of Ni(NO3)2·6H2O, and mix well to obtain a mixed solution A2.

[0065] Step 2: Weigh 6.1008 g of 2M TPAOH and dissolve it in deionized water while stirring, and at the same time add the above-mentioned mixed solution A2. Slowly add the obtained solution dropwise to a certain amount of TEOS aqueous solution, and perform ultrasonic oscillation treatment for 30 min.

[0066] Step 3: Pour the above solution into a hydrothermal reaction kettle lined with polytetrafluoroethylene, and carry out hydrothermal reaction at 180 °C for 24 h. After centrifugation and methanol washing at least three times, dry it overnight at 80 °C to obtain a white solid product. Place it in a muffle furnace and calcine it at 550 °C for 12 h to obtain Na-type ZSM-5 molecular sieve.

[0067] Step 4: Disperse the obtained Na-type HZSM-5 in an appropriate amount of 1M NH4Cl solution, and place it in an oil bath at 80 °C for reaction for 4 h. Then, perform suction filtration and water washing twice repeatedly, and dry to obtain NH4 + type ZSM-5 molecular sieve. Subsequently, calcine it in a muffle furnace at 550 °C for 4 h to obtain the reforming catalyst 10 wt% Ni / HZSM-5 of the present invention.

[0068] Control the mass ratio of the composite catalyst obtained in this example to quartz sand to be 0.3:0.9. After mixing, load it into a dielectric barrier discharge plasma reactor. Use nitrogen with a flow rate of 1 L / min as the carrier gas to carry toluene and water vapor into the dielectric barrier discharge plasma reactor equipped with the nickel-loaded hydrogen-type molecular sieve composite catalyst, and turn on the dielectric barrier discharge plasma reactor to carry out toluene reforming reaction.

[0069] The conversion rate of low-temperature reforming toluene prepared by the method of this example can reach 85.89% when the reaction temperature is 150 °C and the power is 75 W. The H2 selectivity is 21.83%, and the CO selectivity is 19.69%.

[0070] Example 2

[0071] The difference between this example and Example 1 is only that the nickel loading amount of the catalyst Ni / HZSM-5 is 15 wt%, that is, the amount of Ni(NO3)2·6H2O added in Step 1 becomes 4.3622 g.

[0072] Control the mass ratio of the composite catalyst obtained in this example to quartz sand to be 0.3:0.9. After mixing, load it into a dielectric barrier discharge plasma reactor. Use nitrogen with a flow rate of 1 L / min as the carrier gas to carry toluene and water vapor into the dielectric barrier discharge plasma reactor equipped with the nickel-loaded hydrogen-type molecular sieve composite catalyst, and turn on the dielectric barrier discharge plasma reactor to carry out toluene reforming reaction.

[0073] The conversion rate of toluene in low-temperature reforming prepared by the method of this embodiment can reach 93.74% when the reaction temperature is 150 °C and the power is 75 W. The selectivity of H2 is 24.56%, and the selectivity of CO is 25.84%.

[0074] Example 3

[0075] The difference between this embodiment and Example 1 is only that the nickel loading of the catalyst Ni / HZSM-5 is 20 wt%, that is, the amount of Ni(NO3)2·6H2O added in Step 1 becomes 5.8162 g.

[0076] Control the mass ratio of the composite catalyst obtained in this embodiment to quartz sand to be 0.3:0.9. After mixing, it is loaded into a dielectric barrier discharge plasma reactor. Nitrogen with a flow rate of 1 L / min is used as the carrier gas to carry toluene and water vapor into the dielectric barrier discharge plasma reactor equipped with the nickel-loaded hydrogen-type molecular sieve composite catalyst. Turn on the dielectric barrier discharge plasma reactor to carry out toluene reforming reaction.

[0077] The conversion rate of toluene in low-temperature reforming prepared by the method of this embodiment can reach 88.74% when the reaction temperature is 150 °C and the power is 75 W. The selectivity of H2 is 19.62%, and the selectivity of CO is 18.05%.

[0078] Comparative Example 1

[0079] The reforming catalyst in this embodiment is prepared according to the following steps:

[0080] Step 1: Dissolve NaAlO2 and NaOH with a mass ratio of 1:8 in deionized water. Slowly drop the NaAlO2 solution into the NaOH solution and mix well to obtain a mixed solution A1.

[0081] Step 2: Weigh 6.1008 g of 2M TPAOH and dissolve it in deionized water and stir. At the same time, add the above mixed solution A1. Slowly drop the obtained solution into a certain amount of TEOS aqueous solution and perform ultrasonic oscillation treatment for 30 min.

[0082] Step 3: Pour the above solution into a hydrothermal reaction kettle lined with polytetrafluoroethylene and carry out hydrothermal reaction at 180 °C for 24 h. After centrifugation and washing with methanol at least three times, dry overnight at 80 °C to obtain a white solid product. Place it in a muffle furnace and calcine at 550 °C for 12 h to obtain Na-type ZSM-5 molecular sieve.

[0083] Step 4: Disperse the obtained Na-type HZSM-5 in an appropriate amount of 1M NH4Cl solution and place it in an 80 °C oil bath for reaction for 4 h. Then, perform suction filtration and washing with water twice repeatedly and dry to obtain NH4 +ZSM-5 zeolite of the type. Subsequently, it was calcined in a muffle furnace at 550 °C for 4 h to obtain HZSM-5 zeolite.

[0084] The conversion rate of toluene prepared by the method of this comparative example can reach 84.7% when the reaction temperature is 150 °C and the power is 75 W. The selectivity of H2 is 17.05%, and the selectivity of CO is 16.07%.

[0085] Comparative Example 2

[0086] In the process of testing the conversion rate of toluene in this comparative example, compared with Example 2, only plasma operation was carried out without adding other catalysts. The conversion rate of toluene in low-temperature reforming in this comparative example can reach 78.82% when the reaction temperature is 150 °C and the power is 75 W. The selectivity of H2 is 6.77%, and the selectivity of CO is 14.08%.

[0087] The activity data of different Ni loadings are shown in Table 1 (temperature: 150 °C; power: 75 W; S / C: 1). It can be seen from Table 1 that after loading Ni, the conversion rate of toluene is significantly improved, and at the same time, the selectivities of H2 and CO are also significantly improved. At the same time, compared with the simple low-temperature plasma reforming of toluene, after adding the catalyst, the synergistic effect of the catalyst and the plasma effectively improves the conversion rate of toluene and the selectivity of the target product.

[0088] Table 1 Performance data of low-temperature reforming of toluene by the materials obtained from Examples 1 to 3 and Comparative Example 1

[0089]

[0090] *: Without adding catalyst

[0091] Preferably, Example 2 has the highest toluene conversion rate and syngas selectivity, that is, when the loading is 15 wt%, the reaction temperature is 150 °C, and the power is 75 W, the toluene conversion rate can reach 93.74%. The selectivity of H2 is 24.56%, and the selectivity of CO is 25.84%.

[0092] In order to compare the performance of the catalyst prepared by the present invention at different reaction temperatures in the low-temperature plasma reforming of toluene, the following experiments were carried out:

[0093] Experiment 1:

[0094] The composite catalyst obtained in Example 2 of the present invention was used for low-temperature plasma reforming of toluene at 275 °C. When carrying out low-temperature plasma reforming of toluene at 275 °C, the toluene conversion rate can reach 94.62% when the power is 75 W. The selectivity of H2 is 33.78%, and the selectivity of CO is 27.73%.

[0095] Experiment 2:

[0096] The composite catalyst obtained in Example 2 of the present invention was used for low-temperature plasma reforming of toluene at 525 °C. When performing low-temperature plasma reforming of toluene at 525 °C and a power of 75 W, the toluene conversion rate can reach 97.58%. The H2 selectivity is 42.0%, and the CO selectivity is 31.72%.

[0097] The data of each group for toluene reforming reaction at different reaction temperatures are shown in Table 2 (Ni loading: 15 wt%; power: 75 W; S / C: 1):

[0098] Table 2 Test results of toluene reforming of the composite catalytic material prepared in Example 2 at different test temperatures

[0099]

[0100]

[0101] Preferably, in Experiment 2, toluene has the highest toluene conversion rate and syngas selectivity. That is, when the loading is 15 wt%, the reaction temperature is 525 °C, and the power is 75 W, the toluene conversion rate can reach 97.58%. The H2 selectivity is 42.0%, and the CO selectivity is 31.72%.

[0102] In order to compare the performance of the catalyst prepared by the present invention at different powers in low-temperature plasma reforming of toluene, the following experiments were carried out:

[0103] Experiment 3:

[0104] The composite catalyst obtained in Example 2 of the present invention was used for low-temperature plasma reforming of toluene at 275 °C. When performing low-temperature plasma reforming of toluene at 275 °C and a power of 30 W, it can reach 76.56%. The H2 selectivity is 15.91%, and the CO selectivity is 13.43%.

[0105] Experiment 4:

[0106] The composite catalyst obtained in Example 2 of the present invention was used for low-temperature plasma reforming of toluene at 275 °C. When performing low-temperature plasma reforming of toluene at 275 °C and a power of 90 W, it can reach 96.83%. The H2 selectivity is 37.73%, and the CO selectivity is 32.01%.

[0107] The data of each group for toluene reforming reaction at different powers are shown in Table 3 (Ni loading: 15 wt%; temperature: 275 °C; S / C: 1):

[0108] Table 3 Test results of toluene reforming of the composite catalytic material prepared in Example 2 at different powers

[0109]

[0110] Preferably, in Experiment 4 of the above specific examples, the toluene conversion rate and the syngas selectivity are the highest. That is, when the loading is 15 wt%, the reaction temperature is 275 °C, and the power is 90 W, the toluene conversion rate can reach 96.83%. The H2 selectivity is 37.73%, and the CO selectivity is 32.01%.

[0111] By the method of combining low-temperature plasma with Ni / HZSM-5 catalyst, the present invention can significantly improve the toluene conversion rate and the syngas selectivity under low-temperature conditions.

[0112] In order to characterize the performance of the catalyst prepared in the present invention, the following tests are carried out:

[0113] Figure 2 XRD patterns of several nickel-loaded hydrogen-type zeolite composite catalysts prepared in Example 2 of the present invention and Comparative Example 1 are shown. Among them, a: commercial zeolite, b: HZSM-5 (i.e., the product of Comparative Example 1), c: 15% Ni / HZSM-5 (i.e., the product of Example 2). It can be seen from the figure that all catalysts show typical characteristic diffraction peaks of MFI-type zeolite (JCPDS 44-0003) at about 2θ of 23.0°, 23.9° and 24.4°, and there are no other impurity peaks, and the crystallinity is intact. This shows that the self-synthesized zeolite in this experiment conforms to the characteristic structure of traditional zeolite, proving the successful preparation of the zeolite and its good stability.

[0114] Figure 3 NH3-TPD diagrams of several nickel-loaded hydrogen-type zeolite composite catalysts prepared in Example 2 of the present invention and Comparative Example 1 are shown. Among them, a: commercial zeolite, b: HZSM-5 (i.e., the product of Comparative Example 1), c: 15% Ni / HZSM-5 (i.e., the product of Example 2). It can be seen from the figure that the intensity of medium acid sites and strong acid sites of the Ni-loaded catalyst weakens, which is beneficial to slowing down the catalyst deactivation rate and improving its anti-coking ability.

[0115] Figure 4 The stability test results of the toluene reforming reaction using the catalyst prepared in Example 2 of the present invention are shown. It can be seen from the figure that after 48 h of testing, the toluene conversion rate only decreased by 6.05%, and the H2 and CO selectivities decreased by 8.27% and 11.52% respectively, proving that the Ni / HZSM-5 catalyst synthesized in the present invention has good stability.

[0116] In addition, through the N2 adsorption-desorption test of the several nickel-loaded hydrogen-type zeolite composite catalysts prepared in Examples 1-3 of the present invention, the zeolite without Ni loading, and the commercial zeolite, the test results are shown in Table 4. It can be seen from Table 4 that the specific surface area of the self-synthesized HZSM-5 catalyst is 286.22 m2 / g) is significantly higher than that of commercial molecular sieves (152.55 m 2 / g). With the addition of nickel, the average pore diameter of the catalyst increases (2.69 nm), which helps to improve the catalytic reforming performance.

[0117] Table 4 N2-adsorption and desorption test data of the supported nickel hydrogen-type molecular sieve composite catalyst, the molecular sieve without Ni loading, and the commercial molecular sieve prepared in Example 2 of the present invention

[0118]

[0119] Example 4

[0120] A preparation method of a supported nickel hydrogen-type molecular sieve composite catalyst, comprising the following steps:

[0121] S1: Drop the NaAlO2 solution into NaOH, then add a soluble nickel salt, stir and mix evenly to obtain a mixed solution A;

[0122] S2: Add the solution A into the tetrapropylammonium hydroxide solution to obtain a mixed solution B;

[0123] S3: Drop the mixed solution B into the tetraethyl orthosilicate aqueous solution, and after ultrasonic treatment for 10 min, obtain a mixed solution C;

[0124] S4: Perform hydrothermal treatment on the mixed solution C, and after calcining the obtained product, prepare a Na-type ZSM-5 molecular sieve; wherein, the temperature of the hydrothermal treatment is 150 °C and the time is 30 h. The temperature of the calcination treatment is 400 °C and the time is 15 h.

[0125] S5: Disperse the Na-type ZSM-5 molecular sieve in the NH4Cl solution, and after calcining the reaction product, prepare the supported nickel hydrogen-type molecular sieve composite catalyst, wherein when dispersing the Na-type ZSM-5 molecular sieve in the NH4Cl solution for reaction, the reaction temperature is 50 °C and the time is 5 h. The temperature of the calcination treatment is 300 °C and the time is 6 h.

[0126] In the above method, the mass ratio of NaAlO2, NaOH, the soluble nickel salt, and tetraethyl orthosilicate is 1:8:2.5:125.

[0127] In this example, the mass ratio of the obtained composite catalyst to quartz sand is 0.1:0.7. After mixing, it is loaded into a dielectric barrier discharge plasma reactor. Argon with a flow rate of 0.5 L / min is used as the carrier gas to carry tar and water vapor into the dielectric barrier discharge plasma reactor filled with the nickel-loaded hydrogen-type molecular sieve composite catalyst. Among them, the molar ratio of water vapor to carbon in tar is 0.5. Then, the dielectric barrier discharge plasma reactor is started to carry out the tar reforming reaction.

[0128] When the reaction temperature is 275 °C and the power is 75 W, the conversion rate of toluene in low-temperature reforming prepared by the method of this example can reach 95.51%. The H2 selectivity is 29%, and the CO selectivity is 23.5%.

[0129] Example 5

[0130] A preparation method of a nickel-loaded hydrogen-type molecular sieve composite catalyst includes the following steps:

[0131] S1: Drop the NaAlO2 solution into NaOH, then add a soluble nickel salt, and stir and mix evenly to obtain a mixed solution A;

[0132] S2: Add the solution A into the tetrapropylammonium hydroxide solution to obtain a mixed solution B;

[0133] S3: Drop the mixed solution B into the tetraethyl orthosilicate aqueous solution, and after ultrasonic treatment for 30 min, obtain a mixed solution C;

[0134] S4: Carry out hydrothermal treatment on the mixed solution C, and after the obtained product is calcined, prepare the Na-type ZSM-5 molecular sieve; among them, the temperature of the hydrothermal treatment is 300 °C and the time is 20 h. The temperature of the calcination treatment is 650 °C and the time is 10 h.

[0135] S5: Disperse the Na-type ZSM-5 molecular sieve in the NH4Cl solution, and the obtained product after the reaction is calcined to prepare the nickel-loaded hydrogen-type molecular sieve composite catalyst. When dispersing the Na-type ZSM-5 molecular sieve in the NH4Cl solution for reaction, the reaction temperature is 110 °C and the time is 2.5 h. The temperature of the calcination treatment is 600 °C and the time is 3 h.

[0136] In the above method, the mass ratio of NaAlO2, NaOH, soluble nickel salt, and tetraethyl orthosilicate is 1:8:11:125.

[0137] The mass ratio of the composite catalyst obtained in this example to quartz sand is 0.4:0.9. After mixing, it is loaded into a dielectric barrier discharge plasma reactor. Air with a flow rate of 0.8 L / min is used as the carrier gas to carry tar and water vapor into the dielectric barrier discharge plasma reactor filled with the nickel-loaded hydrogen-type molecular sieve composite catalyst. Among them, the molar ratio of water vapor to carbon in tar is 0.8. Then, the dielectric barrier discharge plasma reactor is started to carry out the tar reforming reaction.

[0138] When the reaction temperature is 275 °C and the power is 75 W, the conversion rate of toluene for low-temperature reforming prepared by the method of this example can reach 96%. The H2 selectivity is 30%, and the CO selectivity is 21.61%.

[0139] Example 6

[0140] A preparation method of a nickel-loaded hydrogen-type molecular sieve composite catalyst includes the following steps:

[0141] S1: Drop the NaAlO2 solution into NaOH, and then add a soluble nickel salt, stir and mix evenly to obtain a mixed solution A;

[0142] S2: Add the solution A into the tetrapropylammonium hydroxide solution to obtain a mixed solution B;

[0143] S3: Drop the mixed solution B into the tetraethyl orthosilicate aqueous solution, and after ultrasonic treatment for 20 min, obtain a mixed solution C;

[0144] S4: Perform hydrothermal treatment on the mixed solution C, and after calcining the obtained product, prepare the Na-type ZSM-5 molecular sieve; among them, the temperature of the hydrothermal treatment is 200 °C and the time is 25 h. The temperature of the calcination treatment is 500 °C and the time is 12 h.

[0145] S5: Disperse the Na-type ZSM-5 molecular sieve in the NH4Cl solution, and after calcining the reaction product, prepare the nickel-loaded hydrogen-type molecular sieve composite catalyst. When dispersing the Na-type ZSM-5 molecular sieve in the NH4Cl solution for reaction, the reaction temperature is 80 °C and the time is 3 h. The temperature of the calcination treatment is 500 °C and the time is 4 h.

[0146] In the above method, the mass ratio of NaAlO2, NaOH, soluble nickel salt, and tetraethyl orthosilicate is 1:8:5:125.

[0147] The mass ratio of the composite catalyst obtained in this embodiment to quartz sand is 0.5:0.9. After mixing, it is loaded into a dielectric barrier discharge plasma reactor. Nitrogen with a flow rate of 1 L / min is used as the carrier gas to carry tar and water vapor into the dielectric barrier discharge plasma reactor equipped with the hydrogen-type molecular sieve composite catalyst loaded with nickel. Among them, the molar ratio of water vapor to carbon in tar is 1. The dielectric barrier discharge plasma reactor is turned on to carry out the tar reforming reaction.

[0148] The conversion rate of low-temperature reforming toluene prepared by the method of this embodiment can reach 98.21% when the reaction temperature is 275°C and the power is 75W, the H2 selectivity is 31.5%, and the CO selectivity is 26.71%.

[0149] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

[0150] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for tar steam reforming using a composite catalyst of low-temperature plasma coupled with nickel-loaded hydrogen-type molecular sieve, characterized in that, Including: Preparing a nickel-loaded hydrogen-type molecular sieve composite catalyst; the mass of Ni in the nickel-loaded hydrogen-type molecular sieve composite catalyst accounts for 5% - 30% of the mass of the catalyst; Feeding tar and steam into a dielectric barrier discharge plasma reactor filled with the nickel-loaded hydrogen-type molecular sieve composite catalyst; Starting the dielectric barrier discharge plasma reactor to carry out tar steam reforming reaction; wherein, the temperature of the tar steam reforming reaction is 150 - 525 °C and the power is 30 - 90 W.

2. A method for tar steam reforming using a composite catalyst of a low-temperature plasma-coupled nickel-loaded hydrogen-type molecular sieve according to claim 1, characterized in that During the tar steam reforming reaction, the carrier gas is one of argon, nitrogen, and air, and the flow rate of the carrier gas is 0.1 - 4 L / min.

3. A method for tar steam reforming using a composite catalyst of low-temperature plasma coupled with nickel-loaded hydrogen-type molecular sieve according to claim 1, characterized in that, The molar ratio of steam to carbon in the tar is 0.5 - 5.

4. A method for tar steam reforming using a composite catalyst of low-temperature plasma-coupled nickel-loaded hydrogen-type molecular sieve according to claim 1, characterized in that, Mixing the nickel-loaded hydrogen-type molecular sieve composite catalyst with quartz sand and then loading them into the dielectric barrier discharge plasma reactor; wherein the mass ratio of the nickel-loaded hydrogen-type molecular sieve composite catalyst to quartz sand is (0.1 - 0.5):(0.7 - 0.9).

5. A method for tar steam reforming using a composite catalyst of low-temperature plasma coupled with nickel-loaded hydrogen-type molecular sieve according to claim 1, characterized in that, The preparation process of the nickel-loaded hydrogen-type molecular sieve composite catalyst is as follows: S1: Drop the NaAlO₂ solution into NaOH, then add a soluble nickel salt, stir and mix evenly to obtain a mixed solution A; S2: Add the solution A into the tetrapropylammonium hydroxide solution to obtain a mixed solution B; S3: Drop the mixed solution B into the tetraethyl orthosilicate aqueous solution, and after ultrasonic treatment, obtain a mixed solution C; S4: Carry out hydrothermal treatment on the mixed solution C, and after calcining the obtained product, prepare a Na-type ZSM-5 molecular sieve; S5: Disperse the Na-type ZSM-5 molecular sieve in the NH₄Cl solution, and after calcining the reaction product, prepare the nickel-loaded hydrogen-type molecular sieve composite catalyst.

6. A method for tar steam reforming using a composite catalyst of low-temperature plasma coupled with nickel-loaded hydrogen-type molecular sieve according to claim 5, characterized in that, The mass ratio of NaAlO₂, NaOH, soluble nickel salt, and tetraethyl orthosilicate is 1:8:(2.5 - 11):

125.

7. A method for tar steam reforming using a composite catalyst of low-temperature plasma coupled with nickel-loaded hydrogen-type molecular sieve according to claim 5, characterized in that, In step S4, the temperature of the hydrothermal treatment is 150 - 300 °C and the time is 20 - 30 h.

8. A method for tar steam reforming using a composite catalyst of low-temperature plasma coupled with nickel-loaded hydrogen-type molecular sieve according to claim 5, characterized in that, In step S4, the temperature of the calcination treatment is 400 - 650 °C and the time is 10 - 15 h.

9. A method for tar steam reforming using a composite catalyst of low-temperature plasma-coupled nickel-loaded hydrogen-type molecular sieve according to claim 5, characterized in that, In step S5, when dispersing the Na-type ZSM-5 molecular sieve in the NH₄Cl solution for reaction, the reaction temperature is 50 - 110 °C and the time is 2.5 - 5 h.

10. A method for tar steam reforming using a composite catalyst of low-temperature plasma-coupled nickel-loaded hydrogen-type molecular sieve according to claim 5, characterized in that, In step S5, the temperature of the calcination treatment is 300 - 600 °C and the time is 3 - 6 h.

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