Process and equipment for preparing carbon nanotubes from biomass methane and co-producing methanol and biochar

Abstract

The present invention belongs to the technical field of biomass treatment, and specifically relates to a process for preparing carbon nanotubes and co-producing methanol and biochar from biomass methane, comprising: (1) crushing and pre-treating biomass; (2) filtering the pre-treated biomass particles and performing anaerobic fermentation; (3) concentrating, drying and carbonizing the residue after anaerobic fermentation to obtain biochar; (4) drying, purifying and separating methane and carbon dioxide, and firstly performing a thermal cracking reaction on methane to obtain carbon nanotubes and hydrogen; (5) performing a methanol synthesis reaction on the hydrogen produced in step (4) and the separated carbon dioxide to obtain methanol. The above process couples the processes of anaerobic fermentation of biomass, high temperature cracking of methane, carbonization of biomass residues and co-production of methanol, so as to maximize the utilization of biomass, effectively solve the problem of biomass resource utilization, and co-produce methanol to prepare various chemicals, thereby achieving the fixation of carbon and high value utilization of biomass.

Description

Technical Field

[0001] The invention belongs to the technical field of biomass treatment, and specifically relates to a process and equipment for preparing carbon nanotubes and co-producing methanol and biochar by catalytic cracking of biomass methane. Background Art

[0002] The resource utilization and high value-added utilization of biomass such as garden waste and crop straw are attracting more and more attention. Since the above biomass can be used to obtain methane and carbon dioxide through thermochemical methods or biological fermentation, although methane and carbon dioxide can be used to obtain synthesis gas through dry reforming, and then methanol, and methanol can be used to obtain different high-value-added chemicals through a series of reactions, the above synthesis route is long, and water is often produced during the synthesis process, which has a certain impact on the stability of the catalyst, and methanol and water need to be separated later, which requires a large investment. Summary of the invention

[0003] One of the purposes of the present invention is to provide a biomass conversion process to solve the problem of low economic value of methane produced in existing biomass anaerobic fermentation.

[0004] To solve the above problems, the present invention provides a process for preparing carbon nanotubes from biomass methane and co-producing methanol and biochar, comprising the following steps:

[0005] (1) crushing and pre-treating the biomass;

[0006] (2) filtering the pretreated biomass particles and performing anaerobic fermentation to produce methane and carbon dioxide;

[0007] (3) concentrating, drying and carbonizing the residue after anaerobic fermentation to obtain biochar;

[0008] (4) drying, purifying and separating methane and carbon dioxide, wherein methane is first subjected to thermal cracking reaction to obtain carbon nanotubes and hydrogen;

[0009] (5) The hydrogen produced in step (4) and the separated carbon dioxide are reacted with methanol to obtain methanol.

[0010] Preferably, in order to facilitate the subsequent anaerobic fermentation of the biomass particles, the pretreatment in step (1) includes soaking the crushed biomass particles in a NaOH solution for 24 hours to better remove lignin.

[0011] As a preferred solution, in order to improve the efficiency and effectiveness of anaerobic fermentation, the reaction system temperature is maintained at 35°C and the pH is maintained at 6.8-7.2 in step (2) until the amount of gas generated is significantly reduced, and then the residue is removed and the pretreated biomass particles are added again.

[0012] As a preferred solution, in order to better purify the generated hydrogen, the generated hydrogen is purified by pressure swing adsorption after step (4).

[0013] As a preferred solution, in order to ensure the efficient performance of the retainer synthesis reaction, the methanol synthesis reaction in step (5) uses a Zn-Zr-based catalyst, the reaction temperature is 210° C., and the pressure is 8 MPa.

[0014] Another object of the present invention is to provide a device for preparing carbon nanotubes from biomass methane and co-producing methanol and biochar, comprising a pretreatment device, a methane synthesis device, a pyrolysis carbonization device, a catalytic thermal cracking device and a methanol synthesis reaction device; wherein,

[0015] A pretreatment device for soaking biomass particles in alkaline solution to remove lignin;

[0016] A methane synthesis device for anaerobic fermentation of biomass particles to produce methane and carbon dioxide;

[0017] A pyrolysis carbonization device, used to carbonize the fermentation residue into biochar;

[0018] A catalytic thermal cracking device for thermally cracking methane to obtain carbon nanotubes and hydrogen;

[0019] The methanol synthesis reaction device is used to produce methanol through the methanol synthesis reaction of hydrogen and carbon dioxide.

[0020] As a preferred solution, in order to obtain purer methanol, a crude methanol storage tank and a methanol separation tower are sequentially arranged after the methanol synthesis reaction device.

[0021] As a preferred solution, a drying tank, a carbon dioxide separation tower and a methane separation tower are sequentially arranged after the anaerobic fermentation device, and the carbon dioxide separation tower and the methane separation tower are respectively connected to a carbon dioxide storage tank and a methane storage tank.

[0022] As a preferred solution, the gas outlet of the catalytic thermal cracking device is connected to a pressure swing adsorption device and a hydrogen storage tank.

[0023] The present invention couples the processes of anaerobic fermentation of biomass, high-temperature cracking of methane, carbonization of biomass residues, and co-production of methanol to maximize the utilization of biomass. It can not only effectively solve the problem of biomass resource utilization, but also co-produce methanol to prepare various chemicals, thereby achieving carbon fixation and high-value utilization of biomass. Its main advantages are as follows:

[0024] (1) In the present invention, the biomass is pretreated and anaerobic fermented, and the reaction conditions are relatively mild, without high temperature and high pressure, and the biomass residue is concentrated and dried, which can be used for the preparation of biochar to fix carbon. The generated methane and carbon dioxide are stored for subsequent reactions, reducing greenhouse gas emissions.

[0025] (2) The present invention uses high-temperature cracking to highly selectively convert methane into carbon nanotubes and hydrogen. The carbon nanotubes can be used as an additive phase for composite materials, and can also be used for high-performance electrochemical devices and high-specific surface area catalyst carriers, etc., and have a wide range of uses and high value.

[0026] (3) The core of the catalytic hydrogenation methanol synthesis process involved in the present invention is the catalyst. The Zn-Zr-based catalyst involved has high reaction activity and is easy to scale up and industrialize.

[0027] (4) The present invention also utilizes the carbon dioxide and hydrogen generated during the reaction to co-produce methanol under the action of a catalyst, thereby producing chemicals with higher value, which is conducive to the high-value utilization of biomass. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings in the following description are some embodiments of the present invention.

[0029] Figure 1 This is the process of preparing carbon nanotubes and co-producing methanol and biochar by catalytic cracking of biomass methane in this embodiment.

[0030] Figure 2 This is a process for preparing carbon nanotubes and co-producing methanol and biochar by catalytic cracking of biomass methane in this embodiment.

[0031] The figure includes: L-1: screw feeder; J-1: alkali liquid tank 1; J-2: alkali liquid recovery tank 1; Y-1: pretreatment tank; S-1: residue storage tank; R-1: pyrolysis carbonization reactor; R-2: anaerobic fermentation tank; G-1: drying tank; M-1: methane separation tower; M-2: carbon dioxide separation tower; C-1: methane storage tank; C-2: carbon dioxide storage tank; C-3: hydrogen storage tank; R-3: catalytic thermal cracking reactor; R-4: methanol synthesis reactor; A-1: ​​pressure swing adsorption device; S-2: carbon nanotube storage tank; S-3: crude methanol storage tank; F-1: methanol separation tower. DETAILED DESCRIPTION

[0032] The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention. If no specific techniques or conditions are specified in the examples, the techniques or conditions described in the literature in the art or the product instructions are used.

[0033] In the description of the present invention, unless otherwise specified, the terms "upper", "lower", etc. indicating the orientation or state relationship are based on the orientation or state relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0034] In the following examples, the instruments and equipment used without indicating the manufacturer are all conventional products that can be purchased through regular channels. The methods described are conventional methods unless otherwise specified, and the raw materials described can be obtained from public commercial channels unless otherwise specified.

[0035] Example 1

[0036] like Figure 1 and Figure 2 As shown, this embodiment provides a process and equipment for preparing carbon nanotubes and co-producing methanol and biochar by catalytic cracking of biomass methane, the equipment includes a pretreatment device, a methane synthesis device, a pyrolysis carbonization device, a catalytic pyrolysis device and a methanol synthesis reaction device; wherein,

[0037] A pretreatment device for soaking biomass particles in alkali to remove lignin;

[0038] A methane synthesis device for anaerobic fermentation of biomass particles to produce methane and carbon dioxide;

[0039] A pyrolysis carbonization device, used to carbonize the fermentation residue into biochar;

[0040] A catalytic thermal cracking device for thermally cracking methane to obtain carbon nanotubes and hydrogen;

[0041] The methanol synthesis reaction device is used to produce methanol through the methanol synthesis reaction of hydrogen and carbon dioxide.

[0042] Specifically, the pretreatment device adopts a pretreatment tank Y-1, which is fed by a screw feeder L-1; about 5% sodium hydroxide solution is supplied through an alkali liquid tank J-1, and the alkali liquid after use is recovered through an alkali liquid recovery tank J-2. The discharge port of the pretreatment tank Y-1 is connected to a methane synthesis device. The methane synthesis device of this embodiment adopts an anaerobic fermentation tank R-2. The residue produced by the fermentation enters a residue storage tank S-1 and is further carbonized into biochar through a pyrolysis carbonization device. The pyrolysis carbonization device of this embodiment adopts a pyrolysis carbonization reactor R-1, which is a rotary kiln reactor. The rotary kiln reactor is driven to rotate by the rotation of a motor. The inner wall of the reactor is equipped with staggered spiral blades to ensure uniform material transmission. The temperature in the reactor is controlled by a thermocouple; the gas outlet of the anaerobic fermentation tank R-2 is connected to a drying tank G-1 to remove moisture, and then the gas first passes through a carbon dioxide separation tower M-2 to collect carbon dioxide and send it to a carbon dioxide separation tower M-2. Carbon storage tank C-2, then the gas passes through the methane separation tower M-1, methane is collected and sent to the methane storage tank C-1, the methane storage tank C-1 is connected to the catalytic thermal cracking device to thermally crack the methane to obtain carbon nanotubes and hydrogen. This embodiment adopts the catalytic thermal cracking reactor R-3, which is a traditional fixed bed reactor or a fluidized bed reactor. The gas produced by the reaction first passes through the pressure swing adsorption device A-1 to obtain pure hydrogen, and then the hydrogen is sent to the hydrogen storage tank C-3, and the produced carbon nanotubes are sent to the carbon nanotube storage tank S-2; finally, the carbon dioxide storage tank C-2 and the hydrogen storage tank C-3 are connected to the methanol synthesis reaction device. The methanol synthesis reaction device of this embodiment selects the common methanol synthesis reactor R-4 on the market. Hydrogen and carbon dioxide undergo a methanol synthesis reaction to generate methanol. The methanol first enters the crude methanol storage tank S-3, and then enters the methanol separation tower F-1, so as to obtain pure methanol.

[0043] This method mainly includes the following steps:

[0044] (1) crushing the biomass and pretreating it, wherein the pretreatment includes soaking the crushed biomass particles in a NaOH solution for 24 hours, wherein the mass fraction of the NaOH solution is preferably about 5%;

[0045] (2) filtering the pretreated biomass particles and performing anaerobic fermentation to produce methane and carbon dioxide, maintaining the reaction system temperature at 35° C. and the pH at 6.8 to 7.2 until the amount of gas produced is significantly reduced, discharging the residue and re-adding the pretreated biomass particles;

[0046] (3) concentrating, drying and carbonizing the residue after anaerobic fermentation to obtain biochar;

[0047] (4) drying, purifying and separating methane and carbon dioxide, wherein methane is first subjected to thermal cracking reaction to obtain carbon nanotubes and hydrogen, and the generated hydrogen is purified by pressure swing adsorption;

[0048] (5) The hydrogen produced in step (4) and the separated carbon dioxide are reacted with methanol to obtain methanol. The methanol synthesis reaction uses a Zn-Zr-based catalyst, the reaction temperature is 210° C., and the pressure is 8 MPa.

[0049] Specifically, the biomass (including garden waste, crop straw, etc.) is first crushed into 1 cm square particles, transported to the pretreatment tank through a screw feeder, and separated after soaking in a 5% NaOH solution for 24 hours. The liquid is transferred to the alkali recovery tank, and the solid is transferred to the anaerobic fermentation tank. The reaction system temperature is maintained at 35°C and the pH is between 6.8 and 7.2. The preferred pH in this embodiment is 7.0 until the amount of gas generated is significantly reduced. The solid is separated, and then after concentration and drying, it is transported to a pyrolysis carbonization reactor at 550°C to obtain biochar. The methane and carbon dioxide generated during the fermentation process are respectively sent to the corresponding storage tanks through the methane and carbon dioxide separation towers. If an abnormality occurs in the methane storage tank, it is directly discharged into the incineration system. The methane in the methane storage tank is introduced into the methane cracking reactor at a certain flow rate (30mL / min of methane gas). Under the condition of Ni-based catalyst, at a reaction temperature of 650°C, the conversion rate of methane can reach more than 55%, and the products are carbon nanotubes and hydrogen. The carbon nanotubes can be purified by conventional acid washing, and the hydrogen can be purified by pressure swing adsorption (PSA). The carbon dioxide in the carbon dioxide storage tank and the hydrogen in the generated hydrogen storage tank are introduced into the large methanol synthesis reactor after a certain ratio through a compressor. Under the condition of the presence of Zn-Zr-based catalyst, crude methanol can be generated at 210°C and 8Mpa. The crude methanol in the crude methanol storage tank is pumped into a methanol separation tower (i.e., a methanol distillation tower) to obtain pure methanol. The incompletely reacted carbon dioxide and hydrogen can be further reacted by recycling to maximize the utilization of raw materials. If abnormal phenomena occur, they can also be discharged into the incineration system for power generation to reduce risks as much as possible.

[0050] As for the selection of other reaction parameters, those skilled in the art can determine them based on common knowledge. For example, the temperatures at the top and bottom of the methanol separation tower are controlled at about 66°C and 105°C respectively, the pressures at the bottom and top are 140 kPa (absolute pressure) and normal pressure respectively, and the temperature of the pyrolysis carbonization reactor is controlled at about 550°C, which will not be elaborated here.

[0051] Anaerobic fermentation of biomass produces methane and carbon dioxide. After separation, the methane is thermally cracked to obtain carbon nanotubes and hydrogen. Carbon nanotubes can be used as an excellent composite material additive, as a high-performance electrochemical device, or as a high-specific surface area catalyst carrier, and have a wide range of uses. The hydrogen produced can react with the generated carbon dioxide in a certain proportion to obtain methanol, and methanol can be used to obtain high-value-added chemicals through various reactions. Even excess hydrogen can be used in various hydrogenation reactions to achieve high-value-added utilization of raw materials. This route can not only maximize the utilization of biomass, but also shorten the process and improve the application value of raw materials. The generated carbon nanotubes also have a good carbon fixation effect.

[0052] In addition, the residues produced by the fermentation process of biomass such as garden waste and crop straw can also be obtained through the pyrolysis and carbonization process to obtain biochar, which can then be used for soil improvement or adsorbent. Therefore, in summary, this method has high application value.

[0053] This patent is based on the above-mentioned related contents. After improvement and past research, various processes are coupled together to form a process in which biomass such as garden waste and crop straw is pretreated and fermented for methanation, cracking reaction and carbonization, and finally carbon nanotubes and biochar are obtained. The intermediate products of the reaction are separated, purified and recovered, and finally methanol is co-produced under the action of a catalyst.

[0054] Chemical equations for the reactions involved:

[0055] CH4=C+2H2

[0056] CO2+3H2=CH3OH+H2O

[0057] The above is only an embodiment of the present invention, and the common sense such as the known specific structure, characteristics and reactant ratio in the scheme is not described too much here. It should be pointed out that for those skilled in the art, without departing from the concept of the present invention, some deformations and improvements can also be made, such as simply adjusting the selection of parameters within or near the specified parameter range, which should also be regarded as the protection scope of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The protection scope required by this application shall be based on the content of its claims, and the specific implementation methods in the specification and other records can be used to explain the content of the claims.

Claims

1. A process for preparing carbon nanotubes and co-producing methanol and biochar by catalytic cracking of biomass methane, characterized in that The steps include: (1) crushing and pre-treating the biomass; (2) filtering the pretreated biomass particles and performing anaerobic fermentation to produce methane and carbon dioxide; (3) concentrating, drying and carbonizing the residue after anaerobic fermentation to obtain biochar; (4) drying, purifying and separating methane and carbon dioxide, wherein methane is first subjected to thermal cracking reaction to obtain carbon nanotubes and hydrogen; (5) subjecting the hydrogen produced in step (4) to a methanol synthesis reaction with the separated carbon dioxide to obtain methanol; In the step (4), methane is thermally cracked in the presence of a Ni-based catalyst at a reaction temperature of 650° C. to produce carbon nanotubes and hydrogen.

2. The process for preparing carbon nanotubes from biomass methane and co-producing methanol and biochar according to claim 1, characterized in that: The pretreatment in step (1) includes soaking the crushed biomass particles in a NaOH solution for 24 hours.

3. The process for preparing carbon nanotubes from biomass methane and co-producing methanol and biochar according to claim 1, characterized in that: In step (2), the reaction system temperature is maintained at 35° C. and the pH is maintained at 6.8 to 7.2 until the amount of gas generated is significantly reduced.

4. The process for preparing carbon nanotubes from biomass methane and co-producing methanol and biochar according to claim 1, characterized in that: After step (4), the generated hydrogen is purified by pressure swing adsorption.

5. The process for preparing carbon nanotubes from biomass methane and co-producing methanol and biochar according to claim 1, characterized in that: The methanol synthesis reaction in step (5) uses a Zn-Zr based catalyst, the reaction temperature is 210° C., and the pressure is 8 MPa.

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