A method for directional preparation of low-carbon olefins by biomass catalytic pyrolysis based on shape-selective deoxygenation-mild dehydrogenation cascade reaction

Abstract

The application discloses a method for preparing low-carbon olefins by biomass catalytic pyrolysis based on shape-selective deoxidization-mild dehydrogenation cascade reaction, and belongs to the technical field of biomass resource conversion and utilization. The application adopts a double-catalyst system of HZSM-5 and ion-exchange type Co / HZSM-5 arranged in stages, and steam generated by biomass pyrolysis is firstly subjected to shape-selective deoxidization through a front HZSM-5 catalyst bed, and then the generated product enters a downstream Co / HZSM-5 catalyst bed to perform mild dehydrogenation on C2-C4 alkane components, so that the yield of C2-C4 low-carbon olefin products is remarkably improved, and high-selectivity directional conversion of biomass to prepare low-carbon olefins is realized.

Description

Technical Field

[0001] This invention belongs to the field of biomass resource conversion and utilization technology, and in particular relates to a method for the directional production of low-carbon olefins from biomass catalytic pyrolysis based on a shape-selective deoxygenation-mild dehydrogenation cascade reaction. Background Technology

[0002] Given the continuously rising global demand for energy and the increasing prominence of environmental problems, the research and development of efficient conversion technologies for renewable resources has become a current research focus. Biomass, as the only carbon-containing renewable resource, is of paramount importance for environmental protection through its efficient conversion and utilization. Among numerous biomass energy conversion methods, pyrolysis is one of the most promising approaches for industrial application. As a key means of biomass conversion, pyrolysis technology can transform biomass into liquid fuels and high-value-added chemicals. However, traditional pyrolysis processes face a series of key challenges, including low product selectivity and high oxygen content.

[0003] Olefins, represented by ethylene, propylene, and butene, are important basic raw materials and platform compounds in organic synthesis. With my country's increasing dependence on imported crude oil and the intensifying supply-demand imbalance of olefins domestically, the tight supply of olefin raw materials has constrained the sustainable development of the olefin industry. Currently, olefins are mainly produced industrially through traditional processes such as petroleum cracking, natural gas cracking, and heavy oil hydrocracking, but these methods have significant environmental problems. Among existing technologies for the targeted production of low-carbon olefins through biomass catalytic pyrolysis, the yield of low-carbon olefins produced by HZSM-5 molecular sieve catalyst catalytic pyrolysis is low and difficult to further improve. Therefore, how to further optimize the reaction pathway to further convert the generated alkanes into olefins and significantly increase the yield of low-carbon olefins is an urgent problem to be solved in achieving highly selective targeted conversion of low-carbon olefins through biomass catalytic pyrolysis. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention proposes a method for the directional production of low-carbon olefins from biomass catalytic pyrolysis based on a shape-selective deoxygenation-mild dehydrogenation cascade reaction.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] This invention provides a method for the directional production of low-carbon olefins from biomass catalytic pyrolysis based on a shape-selective deoxygenation-mild dehydrogenation cascade reaction, comprising the following steps:

[0007] Step 1: Add biomass raw materials to the pyrolysis reactor to cause the biomass raw materials to undergo a pyrolysis reaction to generate pyrolysis vapor;

[0008] Step 2: The pyrolysis vapor undergoes a shape-selective deoxygenation reaction under the action of a carrier gas and the catalysis of HZSM-5 catalyst;

[0009] Step 3: The gaseous product after the shape-selective deoxygenation reaction undergoes a mild dehydrogenation reaction under the action of a carrier gas and a Co / HZSM-5 catalyst. The product is then condensed to obtain low-carbon olefins.

[0010] The low-carbon olefins are a mixed gas rich in C2-C4 low-carbon olefins.

[0011] The principle of this invention is as follows: This invention adopts a dual catalyst system of HZSM-5 and ion-exchange Co / HZSM-5 arranged in a stepped manner. Biomass pyrolysis steam first passes through the pre-HZSM-5 catalyst bed to complete shape-selective deoxygenation. The generated products then enter the downstream Co / HZSM-5 catalyst bed for mild dehydrogenation of C2-C4 alkane components, which significantly improves the yield of C2-C4 low-carbon olefin products and realizes the highly selective directional conversion of biomass to prepare low-carbon olefins.

[0012] Furthermore, in step one, before adding the biomass raw material into the pyrolysis reactor, the pyrolysis reactor is preheated and continuously supplied with carrier gas.

[0013] Furthermore, in step one, the biomass raw material is selected from lignin, cellulose, hemicellulose, or glucose.

[0014] Furthermore, in step one, the preheating temperature is the same as the pyrolysis reaction temperature, which is 500-700℃;

[0015] And / or, the carrier gas is a non-oxidizing gas.

[0016] Furthermore, in step two, the temperature of the shape-selective deoxidation reaction is 500-700℃;

[0017] And / or, the carrier gas is a non-oxidizing gas.

[0018] Furthermore, the non-oxidizing gas in steps one and two is selected from nitrogen, argon, helium, carbon monoxide, and carbon dioxide.

[0019] Furthermore, in step three, the temperature of the mild dehydrogenation reaction is 450-700°C.

[0020] Furthermore, in step three, the condensation temperature is 5-10℃.

[0021] Furthermore, in step three, the Co / HZSM-5 catalyst is prepared by ion exchange.

[0022] Furthermore, in step three, the preparation method of the Co / HZSM-5 catalyst is as follows: HZSM-5 and cobalt salt are mixed, and after ion exchange, the product is centrifuged, washed, dried, calcined, ground and reduced to obtain the Co / HZSM-5 catalyst.

[0023] Furthermore, the Co content in the Co / HZSM-5 catalyst is not less than 0.01 wt%.

[0024] Compared with the prior art, the present invention has the following advantages and technical effects:

[0025] This invention optimizes the distribution of biomass pyrolysis products through a cascade reaction pathway of shape-selective deoxygenation and mild dehydrogenation, efficiently converting biomass feedstock into low-carbon olefins such as ethylene, propylene, and butene. The invention employs a tiered dual-catalyst synergistic mechanism: a pre-bed HZSM-5 catalyst performs shape-selective deoxygenation on the pyrolysis products, reducing interference from oxygen-containing compounds; a downstream Co / HZSM-5 catalyst bed performs mild dehydrogenation of C2-C4 alkane components, significantly improving the yield of C2-C4 low-carbon olefin products. The Co / HZSM-5 molecular sieve catalyst exhibits high catalytic activity and olefin selectivity for the directional production of low-carbon olefins from biomass catalytic pyrolysis. The introduction of metallic Co effectively modulates the acidity and pore structure of the molecular sieve support, further influencing the distribution of low-carbon olefin products and addressing catalyst deactivation and coking issues. This metal-support synergistic mechanism achieves highly selective directional conversion of biomass into low-carbon olefins. Attached Figure Description

[0026] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0027] Figure 1 This is a schematic diagram of the apparatus for the directional production of low-carbon olefins from biomass catalytic pyrolysis based on a shape-selective deoxygenation-mild dehydrogenation cascade reaction, according to the present invention.

[0028] Figure 2 The image shows the XRD patterns of the Co / HZSM-5 catalysts prepared in Examples 1-3.

[0029] Figure 3 The images show SEM images of the HZSM-5 catalyst and the Co / HZSM-5 catalyst in Example 1, where (a) is the SEM image of the HZSM-5 catalyst at 1 μm, (b) is the SEM image of the HZSM-5 catalyst at 500 nm, (c) is the SEM image of the Co / HZSM-5 catalyst at 1 μm, and (d) is the SEM image of the Co / HZSM-5 catalyst at 500 nm.

[0030] Figure 4 The BET adsorption-desorption curves of the HZSM-5 catalyst and the Co / HZSM-5 catalyst (0.79wt% Co / HZSM-5) in Example 1 are shown.

[0031] Figure 5 The image shows the pore size distribution of the HZSM-5 catalyst and the Co / HZSM-5 catalyst (0.79wt% Co / HZSM-5) in Example 1. Detailed Implementation

[0032] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0033] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0034] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0035] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0036] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0037] Embodiments of the present invention provide a method for the directional production of low-carbon olefins from biomass catalytic pyrolysis based on a shape-selective deoxygenation-mild dehydrogenation cascade reaction, comprising the following steps:

[0038] Step 1: Add biomass feedstock into the pyrolysis reactor to cause the biomass feedstock to undergo a pyrolysis reaction and generate pyrolysis vapor;

[0039] Step 2: Under the action of the carrier gas and the catalysis of the HZSM-5 catalyst, the pyrolysis vapor undergoes a shape-selective deoxygenation reaction.

[0040] Step 3: The gaseous products after the shape-selective deoxygenation reaction undergo a mild dehydrogenation reaction under the action of a carrier gas and a Co / HZSM-5 catalyst. The products are then condensed to obtain low-carbon olefins.

[0041] Low-carbon olefins are a mixture of gases rich in C2-C4 low-carbon olefins.

[0042] The principle of this invention is as follows: A schematic diagram of the apparatus for the directional production of low-carbon olefins from biomass catalytic pyrolysis based on a shape-selective deoxygenation-mild dehydrogenation cascade reaction is shown below. Figure 1 As shown, this invention employs a cascaded HZSM-5 and ion-exchange Co / HZSM-5 dual-catalyst system. Biomass pyrolysis steam first undergoes shape-selective deoxygenation in the pre-HZSM-5 catalyst bed, and the resulting products then enter the downstream Co / HZSM-5 catalyst bed for mild dehydrogenation of C2-C4 alkane components. This significantly improves the yield of C2-C4 low-carbon olefin products, achieving highly selective directional conversion of biomass to produce low-carbon olefins.

[0043] In an embodiment of the present invention, in step one, before adding the biomass feedstock to the pyrolysis reactor, the pyrolysis reactor is preheated and continuously supplied with a carrier gas. The biomass feedstock includes biomass components and biomass-simulated compounds. The biomass components are selected from lignin, cellulose, or hemicellulose, and the biomass-simulated compounds are selected from glucose. The preheating temperature is the same as the pyrolysis reaction temperature, both being 500-700°C. The carrier gas is a non-oxidizing gas. Using a non-oxidizing gas as a carrier gas can prevent oxidation reactions of biomass or pyrolysis intermediates, ensuring that biomass is efficiently converted into low-carbon olefins through the catalytic pyrolysis pathway, and improving the selectivity of low-carbon olefins. At the same time, the non-oxidizing gas can extend the catalyst lifetime and maintain its acidity and pore structure stability. An oxidizing atmosphere may lead to catalyst deactivation and a reduction in active sites on the catalyst surface.

[0044] In an embodiment of the present invention, in step two, the temperature of the shape-selective deoxygenation reaction is 500-700°C; the carrier gas is a non-oxidizing gas.

[0045] In embodiments of the present invention, the non-oxidizing gas in steps one and two is selected from nitrogen, argon, helium, carbon monoxide, and carbon dioxide.

[0046] In the embodiments of the present invention, the HZSM-5 catalyst is a hydrogen-form ZSM-5 zeolite molecular sieve.

[0047] In an embodiment of the present invention, in step three, the temperature of the mild dehydrogenation reaction is 450-700°C; the condensation temperature is 5°C-10°C, preferably 5°C.

[0048] In an embodiment of the present invention, in step three, the Co / HZSM-5 catalyst is prepared by ion exchange. The specific preparation method is as follows: HZSM-5 and cobalt salt are mixed and subjected to ion exchange. The product is then centrifuged, washed, dried, calcined, ground, and reduced to obtain the Co / HZSM-5 catalyst. The content of Co element in the Co / HZSM-5 catalyst is not less than 0.01 wt%.

[0049] In embodiments of the present invention, the cobalt salt is selected from cobalt nitrate, cobalt chloride, and cobalt sulfate, preferably cobalt nitrate.

[0050] In embodiments of the present invention, the carbon selectivity of ethylene, propylene, and butene is calculated as follows: carbon selectivity of ethylene = number of carbon atoms in ethylene / number of carbon atoms in total olefins × 100%; carbon selectivity of propylene = number of carbon atoms in propylene / number of carbon atoms in total olefins × 100%; carbon selectivity of butene = number of carbon atoms in butene / number of carbon atoms in total olefins × 100%.

[0051] The catalyst bed is the core structure in a fixed-bed reactor, referring to the specific region filled with solid catalyst particles. In this invention, the catalyst bed thickness is 5-50 mm. An excessively thick catalyst bed may increase the diffusion resistance of biomass pyrolysis volatiles within the catalyst channels, causing them to escape before fully contacting the active sites, thus reducing the conversion rate. An excessively thin catalyst bed may result in insufficient contact time, leading to incomplete conversion of intermediate oxygen-containing compounds into low-carbon olefins.

[0052] Unless otherwise specified, the room temperature in this invention is 25±2℃.

[0053] All raw materials used in the embodiments of this invention were obtained through commercial purchase. As an example, HZSM-5 was purchased from the Catalytic Reagent Factory of Nankai University.

[0054] It should be noted that all aspects not described in detail in this invention are conventional practices in the field and are not the focus of this invention. For example, the specific process of using a gas chromatograph to perform quantitative analysis of the target product is a conventional method in the field.

[0055] The technical solution of the present invention will be further illustrated by the following embodiments.

[0056] Example 1

[0057] Preparation of Co / HZSM-5 catalyst: 20g HZSM-5 and 2.0168g cobalt nitrate hexahydrate solution (mass concentration of 99%) (mass ratio of 10:1) were ion-exchanged three times at 80℃ for a total of 24h. The ion-exchanged sample was centrifuged at 10000r / 3min, washed with deionized water, and dried in an oven. Subsequently, the dried product was calcined at 550℃ for 4h in an air atmosphere in a tube furnace. The calcined product was ground into powder in a mortar and reduced in a hydrogen atmosphere in a reduction furnace for 2h to obtain the Co / HZSM-5 catalyst. The actual Co content was measured by ICP-OES to be 0.79wt%, which was recorded as 0.79wt% Co / HZSM-5.

[0058] The method for the directional production of low-carbon olefins from biomass catalytic pyrolysis based on a shape-selective deoxygenation-mild dehydrogenation cascade reaction comprises the following steps:

[0059] Step 1: Add the biomass analogue glucose raw material to a pyrolysis reactor that is maintained at a pyrolysis temperature of 600℃ and continuously supplied with nitrogen atmosphere, so that the biomass undergoes a rapid pyrolysis reaction to generate pyrolysis vapor;

[0060] Step 2: Pyrolysis vapors undergo a shape-selective deoxygenation reaction in the presence of nitrogen gas through the HZSM-5 catalytic bed, which is maintained at a shape-selective deoxygenation reaction temperature of 600℃.

[0061] Step 3: The gaseous products after shape-selective deoxygenation undergo a mild catalytic dehydrogenation reaction in the presence of nitrogen through a 0.79wt% Co / HZSM-5 catalytic bed maintained at a mild dehydrogenation reaction temperature of 600℃. After condensation at 5℃, the products yield a mixed gas rich in C2-C4 low-carbon olefins.

[0062] After the reaction, the target products were quantitatively analyzed using gas chromatography. The results showed that the carbon yield of low-carbon olefins relative to the biomass feedstock was 12.15%. Among them, the carbon selectivity of ethylene, propylene, and butene were 88.11%, 11.45%, and 0.44%, respectively.

[0063] Example 2

[0064] Preparation of Co / HZSM-5 catalyst: 20g HZSM-5 and 6.3077g cobalt nitrate hexahydrate solution (mass concentration of 99%) (mass ratio of 3:1) were subjected to ion exchange three times at 80℃ for a total of 24h. The ion-exchanged sample was centrifuged at 10000r / 3min, washed with deionized water, and dried in an oven. Subsequently, the dried product was calcined at 550℃ for 4h in an air atmosphere in a tube furnace. The calcined product was ground into powder in a mortar and reduced in a hydrogen atmosphere in a reduction furnace for 2h to obtain the Co / HZSM-5 catalyst. The actual Co content measured by ICP-OES was 0.88wt%, which was recorded as 0.88wt% Co / HZSM-5.

[0065] The method for the directional production of low-carbon olefins from biomass catalytic pyrolysis based on a shape-selective deoxygenation-mild dehydrogenation cascade reaction comprises the following steps:

[0066] Step 1: Add the biomass analogue glucose raw material to a pyrolysis reactor that is maintained at a pyrolysis temperature of 600℃ and continuously supplied with nitrogen atmosphere, so that the biomass undergoes a rapid pyrolysis reaction to generate pyrolysis vapor;

[0067] Step 2: Pyrolysis vapors undergo a shape-selective deoxygenation reaction in the presence of nitrogen gas through the HZSM-5 catalytic bed, which is maintained at a shape-selective deoxygenation reaction temperature of 600℃.

[0068] Step 3: The gaseous products after shape-selective deoxygenation undergo a mild catalytic dehydrogenation reaction in the presence of nitrogen through a 0.88wt% Co / HZSM-5 catalyst bed maintained at a mild dehydrogenation reaction temperature of 600℃. The products are then condensed at 5℃ to obtain a mixed gas rich in C2-C4 low-carbon olefins.

[0069] After the reaction, the target products were quantitatively analyzed using gas chromatography. The results showed that the carbon yield of low-carbon olefins relative to the biomass feedstock was 12.89%. The carbon selectivity for ethylene, propylene, and butene was 86.79%, 12.60%, and 0.61%, respectively.

[0070] Example 3

[0071] Preparation of Co / HZSM-5 catalyst: 20g HZSM-5 and 10.9802g cobalt nitrate hexahydrate solution (mass concentration of 99%) (mass ratio of 2:1) were subjected to ion exchange three times at 80℃ for a total of 24h. The ion-exchanged sample was centrifuged at 10000r / 3min, washed with deionized water, and dried in an oven. Subsequently, the dried product was calcined at 550℃ for 4h in an air atmosphere in a tube furnace. The calcined product was ground into powder in a mortar and reduced in a hydrogen atmosphere in a reduction furnace for 2h to obtain the Co / HZSM-5 catalyst. The actual Co content measured by ICP-OES was 0.90wt%, which was recorded as 0.90wt% Co / HZSM-5.

[0072] The method for the directional production of low-carbon olefins from biomass catalytic pyrolysis based on a shape-selective deoxygenation-mild dehydrogenation cascade reaction comprises the following steps:

[0073] Step 1: Add the biomass analogue glucose raw material to a pyrolysis reactor that is maintained at a pyrolysis temperature of 600℃ and continuously supplied with nitrogen atmosphere, so that the biomass undergoes a rapid pyrolysis reaction to generate pyrolysis vapor;

[0074] Step 2: Pyrolysis vapors undergo a shape-selective deoxygenation reaction in the presence of nitrogen gas through the HZSM-5 catalytic bed, which is maintained at a shape-selective deoxygenation reaction temperature of 600℃.

[0075] Step 3: The gaseous products after shape-selective deoxygenation undergo a mild catalytic dehydrogenation reaction in the presence of nitrogen through a 0.90wt% Co / HZSM-5 catalyst bed maintained at a mild dehydrogenation reaction temperature of 700℃. The products are then condensed at 5℃ to obtain a mixed gas rich in C2-C4 low-carbon olefins.

[0076] After the reaction, the target products were quantitatively analyzed using gas chromatography. The results showed that the carbon yield of low-carbon olefins relative to the biomass feedstock was 14.20%. Among them, the carbon selectivity of ethylene, propylene, and butene were 84.02%, 15.32%, and 0.66%, respectively.

[0077] Example 4

[0078] Preparation of Co / HZSM-5 catalyst: 20g of HZSM-5 and 2.0168g of cobalt nitrate hexahydrate solution (mass concentration of 99%) (mass ratio of 10:1) were subjected to ion exchange three times at 80℃ for a total of 24h. The ion-exchanged sample was centrifuged at 10000r / 3min, washed with deionized water, and dried in an oven. Subsequently, the dried product was calcined at 550℃ for 4h in an air atmosphere in a tube furnace. The calcined product was ground into powder in a mortar and reduced in a hydrogen atmosphere in a reduction furnace for 2h to obtain the Co / HZSM-5 catalyst. The actual Co content measured by ICP-OES was 0.79wt%.

[0079] The method for the directional production of low-carbon olefins from biomass catalytic pyrolysis based on a shape-selective deoxygenation-mild dehydrogenation cascade reaction comprises the following steps:

[0080] Step 1: Add biomass raw material wood chips into a pyrolysis reactor that is maintained at a pyrolysis temperature of 600℃ and continuously supplied with nitrogen atmosphere, so that the biomass undergoes a rapid pyrolysis reaction to generate pyrolysis vapor;

[0081] Step 2: Pyrolysis vapors undergo a shape-selective deoxygenation reaction in the presence of nitrogen gas through the HZSM-5 catalytic bed, which is maintained at a shape-selective deoxygenation reaction temperature of 600℃.

[0082] Step 3: The gaseous products after shape-selective deoxygenation undergo a mild catalytic dehydrogenation reaction in the presence of nitrogen through a 0.79wt% Co / HZSM-5 catalytic bed maintained at a mild dehydrogenation reaction temperature of 700℃. After condensation at 5℃, the products yield a mixed gas rich in C2-C4 low-carbon olefins.

[0083] After the reaction, the target products were quantitatively analyzed using gas chromatography. The results showed that the carbon yield of low-carbon olefins relative to the biomass feedstock was 3.74%. Among them, the carbon selectivity of ethylene, propylene, and butene were 76.77%, 18.34%, and 4.89%, respectively.

[0084] Comparative Example 1

[0085] The method for producing low-carbon olefins based on catalytic pyrolysis using HZSM-5 catalyst comprises the following steps:

[0086] Step 1: Add glucose, a biomass analog compound, to a pyrolysis reactor that is maintained at a pyrolysis temperature of 500°C and continuously supplied with an argon atmosphere, so that the biomass undergoes a rapid pyrolysis reaction to generate pyrolysis vapor.

[0087] Step 2: Pyrolysis vapors undergo a shape-selective deoxygenation reaction in the presence of argon gas through the HZSM-5 catalytic bed, which is maintained at a shape-selective deoxygenation reaction temperature of 500℃.

[0088] Step 3: The gaseous products after shape-selective deoxygenation undergo a mild catalytic dehydrogenation reaction in the presence of argon through an HZSM-5 catalytic bed maintained at a mild dehydrogenation reaction temperature of 450℃. The products are then condensed at 5℃ to obtain a mixed gas rich in C2-C4 low-carbon olefins.

[0089] After the reaction, the target products were quantitatively analyzed using gas chromatography. The results showed that the carbon yield of low-carbon olefins relative to the biomass feedstock was 8.43%. Among them, the carbon selectivity of ethylene, propylene, and butene were 91.81%, 7.90%, and 0.29%, respectively.

[0090] Comparative Example 2

[0091] Preparation of Co / HZSM-5 catalyst: 20 g of HZSM-5 and 2.0168 g of cobalt chloride hexahydrate solution (99% mass concentration) (mass ratio 10:1) were subjected to ion exchange three times at 80 °C for a total of 24 h. The ion-exchanged sample was centrifuged at 10000 r / 3 min, washed with deionized water, and dried in an oven. Subsequently, the dried product was calcined at 550 °C for 4 h in an air atmosphere in a tube furnace. The calcined product was ground into powder in a mortar and reduced in a hydrogen atmosphere in a reduction furnace for 2 h to obtain the Co / HZSM-5 catalyst. The actual Co content measured by ICP-OES was 0.79 wt%.

[0092] Step 1: Add glucose, a biomass-simulated compound, to a pyrolysis reactor that is maintained at a pyrolysis temperature of 600℃ and continuously supplied with a helium atmosphere, so that the biomass undergoes a rapid pyrolysis reaction to generate pyrolysis vapor.

[0093] Step 2: Under the action of helium, the pyrolysis vapor undergoes a shape-selective deoxygenation reaction through a mixed catalytic bed of HZSM-5 and 0.79wt% Co / HZSM-5 maintained at a shape-selective deoxygenation reaction temperature of 700℃.

[0094] Step 3: The gaseous products after shape-selective deoxygenation undergo a mild catalytic dehydrogenation reaction under the action of helium through a mixed catalytic bed of HZSM-5 and 0.79wt% Co / HZSM-5 maintained at a mild dehydrogenation reaction temperature of 700℃. After condensation at 5℃, the products are obtained as a mixed gas rich in C2-C4 low-carbon olefins.

[0095] After the reaction, the target products were quantitatively analyzed using gas chromatography. The results showed that the carbon yield of low-carbon olefins relative to the biomass feedstock was 9.59%. The carbon selectivities for ethylene, propylene, and butene were 90.38%, 8.95%, and 0.67%, respectively.

[0096] Comparative Example 3

[0097] Preparation of Co / HZSM-5 catalyst: 20 g of HZSM-5 and 2.0168 g of cobalt chloride hexahydrate solution (99% mass concentration) (mass ratio 10:1) were subjected to ion exchange three times at 80 °C for a total of 24 h. The ion-exchanged sample was centrifuged at 10000 r / 3 min, washed with deionized water, and dried in an oven. Subsequently, the dried product was calcined at 550 °C for 4 h in an air atmosphere in a tube furnace. The calcined product was ground into powder in a mortar and reduced in a hydrogen atmosphere in a reduction furnace for 2 h to obtain the Co / HZSM-5 catalyst. The actual Co content measured by ICP-OES was 0.79 wt%.

[0098] Step 1: Add glucose, a biomass-simulated compound, to a pyrolysis reactor that is maintained at 700°C and continuously supplied with a carbon monoxide atmosphere, so that the biomass undergoes a rapid pyrolysis reaction to generate pyrolysis vapor.

[0099] Step 2: Under the action of carbon monoxide, the pyrolysis vapor undergoes a shape-selective deoxygenation reaction through a 0.79wt% Co / HZSM-5 catalytic bed maintained at a shape-selective deoxygenation reaction temperature of 700℃;

[0100] Step 3: The gaseous products after shape-selective deoxygenation undergo a mild catalytic dehydrogenation reaction in the presence of carbon monoxide through a 0.79wt% Co / HZSM-5 catalyst bed maintained at a mild dehydrogenation reaction temperature of 700℃. After condensation at 5℃, the products yield a mixed gas rich in C2-C4 low-carbon olefins.

[0101] After the reaction, the target products were quantitatively analyzed using gas chromatography. The results showed that the carbon yield of low-carbon olefins relative to the biomass feedstock was 9.78%. Among them, the carbon selectivity of ethylene, propylene, and butene were 90.82%, 8.05%, and 1.13%, respectively.

[0102] Comparative Example 4

[0103] Step 1: Add glucose, a biomass analog compound, to a pyrolysis reactor that is maintained at a pyrolysis temperature of 500°C and continuously supplied with nitrogen gas, so that the biomass undergoes a rapid pyrolysis reaction to generate pyrolysis vapor.

[0104] Step 2: Under the action of nitrogen, the pyrolysis vapor undergoes a shape-selective deoxygenation reaction in the HZSM-5 catalytic bed maintained at a shape-selective deoxygenation reaction temperature of 600℃. The product is condensed at 5℃ to obtain a mixed gas rich in C2-C4 low-carbon olefins.

[0105] After the reaction, the target products were quantitatively analyzed using gas chromatography. The results showed that the carbon yield of low-carbon olefins relative to the biomass feedstock was 7.80%. The carbon selectivity for ethylene, propylene, and butene was 92.33%, 7.42%, and 0.25%, respectively.

[0106] Comparative Example 5

[0107] Preparation of Co / HZSM-5 catalyst: 20 g of HZSM-5 and 2.0168 g of cobalt sulfate heptahydrate solution (mass concentration 99.99%) (mass ratio 10:1) were subjected to ion exchange three times at 80 °C for a total of 24 h. The ion-exchanged sample was centrifuged at 10000 r / 3 min, washed with deionized water, and dried in an oven. Subsequently, the dried product was calcined at 550 °C for 4 h in an air atmosphere in a tube furnace. The calcined product was ground into powder in a mortar and reduced in a hydrogen atmosphere in a reduction furnace for 2 h to obtain the Co / HZSM-5 catalyst. The actual Co content measured by ICP-OES was 0.79 wt%.

[0108] The method for producing low-carbon olefins based on the above-mentioned catalyst-catalyzed pyrolysis comprises the following steps:

[0109] Step 1: Add glucose, a biomass analog compound, to a pyrolysis reactor that is maintained at 700°C and continuously supplied with nitrogen gas, so that the biomass undergoes a rapid pyrolysis reaction to generate pyrolysis vapor.

[0110] Step 2: The pyrolysis vapor undergoes a mild catalytic dehydrogenation reaction under the action of nitrogen through a 0.79wt% Co / HZSM-5 catalytic bed maintained at a mild dehydrogenation reaction temperature of 600℃. The product is condensed at 5℃ to obtain a mixed gas rich in C2-C4 low-carbon olefins.

[0111] After the reaction, the target products were quantitatively analyzed using gas chromatography. The results showed that the carbon yield of low-carbon olefins relative to the biomass feedstock was 8.85%. Among them, the carbon selectivity of ethylene, propylene, and butene were 91.57%, 7.56%, and 0.87%, respectively.

[0112] Comparative Example 6

[0113] Step 1: Add glucose, a biomass analog compound, to a pyrolysis reactor that is maintained at 600°C and continuously supplied with nitrogen gas, so that the biomass undergoes a rapid pyrolysis reaction to generate pyrolysis vapor.

[0114] Step 2: The pyrolysis vapor undergoes a catalytic reaction without passing through the catalytic bed under the action of nitrogen. After condensation at 5°C, a gaseous product rich in low-carbon olefins (C2-C4) is obtained.

[0115] After the reaction, the target products were quantitatively analyzed using gas chromatography. The results showed that the carbon yield of low-carbon olefins relative to the biomass feedstock was 0.57%. The carbon selectivity for ethylene, propylene, and butene was 79.31%, 18.52%, and 2.17%, respectively.

[0116] Comparative Example 7

[0117] The method for producing low-carbon olefins based on catalytic pyrolysis using HZSM-5 catalyst comprises the following steps:

[0118] Step 1: Add biomass raw material wood chips into a pyrolysis reactor that is maintained at a pyrolysis temperature of 500℃ and continuously supplied with nitrogen atmosphere, so that the biomass undergoes a rapid pyrolysis reaction to generate pyrolysis vapor;

[0119] Step 2: Pyrolysis vapors undergo a shape-selective deoxygenation reaction in the presence of nitrogen gas through the HZSM-5 catalytic bed, which is maintained at a shape-selective deoxygenation reaction temperature of 500℃.

[0120] Step 3: The gaseous products after shape-selective deoxygenation undergo a mild catalytic dehydrogenation reaction in the presence of nitrogen through an HZSM-5 catalytic bed maintained at a mild dehydrogenation reaction temperature of 450℃. After condensation at 5℃, the products yield a mixed gas rich in C2-C4 low-carbon olefins.

[0121] After the reaction, the target products were quantitatively analyzed using gas chromatography. The results showed that the carbon yield of low-carbon olefins relative to the biomass feedstock was 1.12%. Among them, the carbon selectivity of ethylene, propylene, and butene were 70.51%, 22.80%, and 6.69%, respectively.

[0122] Comparative Example 8

[0123] Preparation of Ga / HZSM-5 catalyst: 20g of HZSM-5 and 2.4463g of gallium nitrate nonahydrate solution (mass concentration of 99.9%) (mass ratio of 10:1) were subjected to ion exchange three times at 80℃ for a total of 24h. The ion-exchanged sample was centrifuged at 10000r / 3min, washed with deionized water, and dried in an oven. Subsequently, the dried product was calcined at 550℃ for 4h in an air atmosphere in a tube furnace. The calcined product was ground into powder in a mortar and reduced in a hydrogen atmosphere in a reduction furnace for 2h to obtain Ga / HZSM-5 catalyst. The actual Ga content was measured by ICP-OES to be 1.86wt%, which was recorded as 1.86wt% Ga / HZSM-5.

[0124] The method for producing low-carbon olefins based on the above-mentioned catalyst-catalyzed pyrolysis comprises the following steps:

[0125] Step 1: Add the biomass analogue glucose raw material to a pyrolysis reactor that is maintained at a pyrolysis temperature of 600℃ and continuously supplied with nitrogen atmosphere, so that the biomass undergoes a rapid pyrolysis reaction to generate pyrolysis vapor;

[0126] Step 2: Pyrolysis vapors undergo a shape-selective deoxygenation reaction in the presence of nitrogen gas through the HZSM-5 catalytic bed, which is maintained at a shape-selective deoxygenation reaction temperature of 600℃.

[0127] Step 3: The gaseous products after shape-selective deoxygenation undergo a mild catalytic dehydrogenation reaction in the presence of nitrogen through a 1.86wt% Ga / HZSM-5 catalyst bed maintained at a mild dehydrogenation reaction temperature of 600℃. After condensation at 5℃, the products yield a mixed gas rich in C2-C4 low-carbon olefins.

[0128] After the reaction, the target products were quantitatively analyzed using gas chromatography. The results showed that the carbon yield of low-carbon olefins relative to the biomass feedstock was 8.81%. Among them, the carbon selectivity of ethylene, propylene, and butene were 90.66%, 8.90%, and 0.44%, respectively.

[0129] Comparative Example 9

[0130] Preparation of Zn / HZSM-5 catalyst: 20g HZSM-5 and 1.8675g zinc nitrate hexahydrate solution (mass concentration of 99%) (mass ratio of 10:1) were subjected to ion exchange three times at 80℃ for a total of 24h. The ion-exchanged sample was centrifuged at 10000r / 3min, washed with deionized water, and dried in an oven. Subsequently, the dried product was calcined at 550℃ for 4h in an air atmosphere in a tube furnace. The calcined product was ground into powder in a mortar and reduced in a hydrogen atmosphere in a reduction furnace for 2h to obtain Zn / HZSM-5 catalyst. The actual Zn content was measured by ICP-OES to be 1.81wt%, which was recorded as 1.81wt% Zn / HZSM-5.

[0131] The method for producing low-carbon olefins based on the above-mentioned catalyst-catalyzed pyrolysis comprises the following steps:

[0132] Step 1: Add the biomass analogue glucose raw material to a pyrolysis reactor that is maintained at a pyrolysis temperature of 600℃ and continuously supplied with nitrogen atmosphere, so that the biomass undergoes a rapid pyrolysis reaction to generate pyrolysis vapor;

[0133] Step 2: Pyrolysis vapors undergo a shape-selective deoxygenation reaction in the presence of nitrogen gas through the HZSM-5 catalytic bed, which is maintained at a shape-selective deoxygenation reaction temperature of 600℃.

[0134] Step 3: The gaseous products after shape-selective deoxygenation undergo a mild catalytic dehydrogenation reaction in the presence of nitrogen through a 1.81wt% Zn / HZSM-5 catalyst bed maintained at a mild dehydrogenation reaction temperature of 600℃. After condensation at 5℃, the products yield a mixed gas rich in C2-C4 low-carbon olefins.

[0135] After the reaction, the target products were quantitatively analyzed using gas chromatography. The results showed that the carbon yield of low-carbon olefins relative to the biomass feedstock was 9.89%. Among them, the carbon selectivity of ethylene, propylene, and butene were 93.32%, 6.46%, and 0.22%, respectively.

[0136] The carbon yield and olefin selectivity of the directional production of C2-C4 low-carbon olefins by biomass catalytic pyrolysis in Examples 1-4 and Comparative Examples 1-9 are shown in Table 1.

[0137] Table 1. Carbon yield and olefin selectivity of biomass catalytic pyrolysis for the directed production of C2-C4 low-carbon olefins in Examples 1-4 and Comparative Examples 1-9.

[0138]

[0139]

[0140] The XRD patterns of the Co / HZSM-5 catalysts prepared in Examples 1-3 are as follows: Figure 2 As shown in the XRD patterns, it is clear that the crystal structure of HZSM-5 in each catalyst did not change significantly, and all exhibited the same characteristic diffraction peaks. Metal modification did not alter the MFI-type zeolite structure of HZSM-5. The diffraction peak intensities of the metal-modified HZSM-5 were significantly reduced, and no special peaks related to the introduced metal were found, indicating that the introduced metal was highly dispersed on the HZSM-5 catalyst.

[0141] SEM images of the HZSM-5 catalyst and the Co / HZSM-5 catalyst in Example 1 are shown below. Figure 3 As shown, it can be clearly seen that HZSM-5 exhibits regular hexagonal prism-shaped crystals with smooth surfaces and clear edges; the Co / HZSM-5 prepared in Example 1 of this invention maintains the particle size and hexagonal prism-shaped morphology of HZSM-5.

[0142] The BET adsorption-desorption curves of the HZSM-5 catalyst and the Co / HZSM-5 catalyst in Example 1 are shown below. Figure 4 As shown, 5 represents the HZSM-5 catalyst and the Co / HZSM-5 catalyst (0.79 wt% Co / HZSM-5) from Example 1. Figure 5 As shown in Table 2, the BET data of the HZSM-5 catalyst and the Co / HZSM-5 catalyst in Example 1 are shown in Table 2.

[0143] Table 2. BET data for HZSM-5 catalyst and Co / HZSM-5 catalyst in Example 1.

[0144]

[0145] It is evident that the specific surface area of ​​the Co / HZSM-5 catalyst decreased slightly after Co modification. Co dispersed on the HZSM-5 catalyst blocked some of the micropores. Both the HZSM-5 and Co / HZSM-5 catalysts exhibited significant hysteresis loops in their nitrogen adsorption-desorption isotherms, indicating the formation of a mesoporous structure. The average pore size of the Co / HZSM-5 catalyst was 3.7235 nm.

[0146] Comparative examples 1-3 and 1-6, 8-9 show that, compared to single-stage catalytic pyrolysis, two-stage catalytic pyrolysis can optimize the reaction pathway and effectively suppress side reactions. Changing the catalyst loading method resulted in a decrease in olefin catalytic efficiency, possibly due to the different active acid sites of the two catalysts. Two-stage Co / HZSM-5 catalysts caused severe coking and side reactions, leading to catalyst deactivation; two-stage HZSM-5 catalysts prevented further dehydrogenation of catalytically decomposed alkanes into olefins. The synergistic catalytic effect of the HZSM-5 + 0.79wt% Co / HZSM-5 dual catalyst was the best, with an olefin yield of 12.15%. With separate loading, the first-stage catalyst rapidly deoxygenated the pyrolyzed alkanes to produce aromatics, while the second-stage catalyst dehydrogenated the pyrolyzed alkanes to produce olefins. This indicates that the optimal effect is achieved by first deoxygenating and then dehydrogenating the pyrolysis products. With increasing Co loading, the carbon yields of C2-C4 olefins all significantly improved, with the yield of low-carbon olefins from the catalytic pyrolysis of HZSM-5 + 0.90 wt% Co / HZSM-5 reaching 14.20%. This is likely due to the increased activity of Co. 2+ An increase in the number of active sites directly enhances dehydrogenation capacity. Changing the type of metal supported on the catalyst resulted in a decrease in catalytic efficiency. This may be because alterations to the metal active sites affect the distribution of olefin products. Co 2+ It possesses a moderate redox potential, enabling efficient catalysis of alkane dehydrogenation to olefins while avoiding over-reaction. The addition of Co metal can modulate the acidic sites of strong acids, and also effectively optimizes the yield and selectivity distribution of low-carbon olefins.

[0147] Comparing Example 4 and Comparative Example 7, it can be seen that in the experiment of directional production of low-carbon olefins by catalytic pyrolysis of biomass wood chips, the synergistic effect of the HZSM-5 + 0.79wt% Co / HZSM-5 dual catalyst integrates catalytic pyrolysis and alkane dehydrogenation, exhibiting high carbon yield and high selectivity for olefins, with a C2-C4 olefin carbon yield of 3.56%. This is a 100% improvement compared to HZSM-5 + HZSM-5, demonstrating better catalytic performance.

[0148] In summary, this invention employs a cascaded HZSM-5 and ion-exchange Co / HZSM-5 dual catalyst system. Biomass pyrolysis steam first undergoes shape-selective deoxygenation in the pre-HZSM-5 catalyst bed, and the resulting products then enter the downstream Co / HZSM-5 catalyst bed for mild dehydrogenation of C2-C4 alkane components. This significantly improves the yield of C2-C4 low-carbon olefin products and achieves highly selective directional conversion of biomass to produce low-carbon olefins.

[0149] The above are merely preferred embodiments of the present invention, but the scope of protection of the present 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 the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for the directional production of low-carbon olefins from biomass catalytic pyrolysis based on a shape-selective deoxygenation-mild dehydrogenation cascade reaction, characterized in that, Includes the following steps: Step 1: Add biomass raw materials to a pyrolysis reactor to cause the biomass raw materials to undergo a pyrolysis reaction to generate pyrolysis vapor. The biomass raw materials are glucose or sawdust. Step 2: The pyrolysis vapor undergoes a shape-selective deoxygenation reaction under the action of a carrier gas and the catalysis of HZSM-5 catalyst; Step 3: The gaseous products after the shape-selective deoxygenation reaction undergo a dehydrogenation reaction under the action of a carrier gas and a Co / HZSM-5 catalyst. The products are then condensed to obtain low-carbon olefins. The low-carbon olefins are a mixed gas rich in C2-C4 low-carbon olefins; In step one, before adding the biomass raw material into the pyrolysis reactor, the pyrolysis reactor is preheated and continuously supplied with carrier gas; The carrier gas used in steps one and two is selected from nitrogen, argon, helium, carbon monoxide, and carbon dioxide.

2. The method for the directional production of low-carbon olefins from biomass catalytic pyrolysis based on a shape-selective deoxygenation-mild dehydrogenation cascade reaction according to claim 1, characterized in that, In step one, the preheating temperature is the same as the pyrolysis reaction temperature, which is 500-700℃.

3. The method for the directional production of low-carbon olefins from biomass catalytic pyrolysis based on a shape-selective deoxygenation-mild dehydrogenation cascade reaction according to claim 1, characterized in that, In step two, the temperature of the shape-selective deoxygenation reaction is 500-700℃.

4. The method for the directional production of low-carbon olefins from biomass catalytic pyrolysis based on a shape-selective deoxygenation-mild dehydrogenation cascade reaction according to claim 1, characterized in that, In step three, the temperature of the dehydrogenation reaction is 450-700℃.

5. The method for the directional production of low-carbon olefins from biomass catalytic pyrolysis based on a shape-selective deoxygenation-mild dehydrogenation cascade reaction according to claim 1, characterized in that, In step three, the Co / HZSM-5 catalyst is prepared by ion exchange.

6. The method for the directional production of low-carbon olefins from biomass catalytic pyrolysis based on a shape-selective deoxygenation-mild dehydrogenation cascade reaction according to claim 5, characterized in that, In step three, the preparation method of the Co / HZSM-5 catalyst is as follows: HZSM-5 and cobalt salt are mixed and subjected to ion exchange. The resulting product is centrifuged, washed, dried, calcined, ground, and reduced to obtain the Co / HZSM-5 catalyst.

7. The method for the directional production of low-carbon olefins from biomass catalytic pyrolysis based on a shape-selective deoxygenation-mild dehydrogenation cascade reaction according to claim 6, characterized in that, The Co / HZSM-5 catalyst contains no less than 0.01 wt% Co.

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