Biomass tar-based mesocarbon microbeads as well as microfluidics preparation method and application thereof

Abstract

The invention discloses biomass tar-based mesocarbon microbeads as well as a microflow control preparation method and application thereof, and belongs to the technical field of environment-friendly carbon materials. In order to realize high-value resource utilization of biomass tar, the invention provides a microfluidics preparation method of biomass tar-based mesocarbon microbeads, which comprises the following steps: mixing biomass tar and an emulsifying solvent to obtain a tar internal phase solution, respectively injecting the tar internal phase solution and an external phase solution into a single-stage capillary micro-fluidic chip, shearing to obtain tar-based monodisperse micro-droplets; the tar-based carbonaceous liquid crystal micro-droplets are dropped into a receiving phase through a collecting pipe to form tar-based carbonaceous liquid crystal micro-droplets; and carrying out hydrothermal carbonization to generate a layered carbonaceous intermediate phase, and then separating, cleaning and drying to obtain the product. According to the method, the advantage that biomass tar is rich in aromatic compounds, oxygen-containing functional groups, nitrogen-containing functional groups and the like is utilized, the micro-fluidic technology is adopted, the process conditions are regulated and controlled, pre-forming of the layered carbonaceous liquid crystals under the mild condition is promoted, and the method has the advantages of being high in yield, mild in liquid crystallization condition and the like.

Description

Technical Field

[0001] This invention belongs to the field of environmentally friendly carbon materials technology, specifically relating to a biomass tar-based mesophase carbon microsphere, its microfluidic preparation method, and its application. Background Technology

[0002] Biomass tar is a black, high-viscosity, semi-solid, complex mixed byproduct produced during the pyrolysis and gasification of biomass. Rich in aromatic compounds and with an extremely high carbon content, biomass tar, due to its high viscosity and flowability, can be thoroughly mixed with activators to create pores. After carbonization, it forms porous carbon materials with a large specific surface area, rich pore structure, high aromaticity, and high stability, finding wide applications in many fields.

[0003] CN117165315A discloses a continuous tar carbonization device and method, which drives tar flow and continuous carbonization through a cylinder containing a continuous stirring mechanism, and prepares porous carbon materials based on the activation of carbonizing gases such as CH4, CO, and CO2. CN115215338A discloses a process system and method for preparing porous carbon by carbonization and activation of biomass tar, in which biomass tar is premixed and dried with a pitting agent, and then carbonized and activated. The resulting solid product is then treated with neutralization and washing water to obtain porous carbon. However, the above processes do not fully consider the properties of biomass tar under high temperature conditions, such as fluidity, self-condensation, strong anisotropy, and easy graphitization. They simply carbonize the tar directly at high temperature or mix it with a pitting agent and then carbonize it directly. Because the high-temperature solid-phase carbonization and melting state of biomass tar is relatively short, the aromatic ring molecules in the tar undergo cracking and condensation, resulting in a disordered arrangement and orientation. The final carbon network layer exhibits irregular stacking, and the resulting tar-derived carbons are all amorphous carbon structures. Their activity, stability, and pore-forming potential are lower than those of highly graphitized carbon materials, leading to a significant reduction in the efficiency of tar resource utilization. Furthermore, since the porous carbon materials prepared by the above process have irregular morphologies, additional shaping processes are required for subsequent applications.

[0004] Mesophase carbon microspheres possess a structure of parallel stacked lamellar molecules, exhibiting significantly higher activity, stability, and pore-forming potential than the aforementioned amorphous carbon materials. They also possess spherical characteristics and uniform particle size distribution, making them a fundamental material for many novel carbon materials. Biomass tar, similar in composition to coal tar pitch, is rich in aromatic compounds, demonstrating its potential for preparing mesophase carbon microspheres. Furthermore, biomass tar uniquely contains a large number of oxygen-containing, nitrogen-containing, and heteroatoms. The oxygen-containing functional groups can promote the condensation of planar aromatic macromolecules at low temperatures, accelerating the nucleation of carbonaceous mesophases and resulting in higher yields of mesophase carbon microspheres. However, the anisotropy of heteroatoms and nitrogen-containing functional groups may hinder the ordered stacking of polycyclic aromatic hydrocarbons, forming a bridging disordered structure, thus preventing the formation of carbonaceous liquid crystals. CN108840331A discloses a high-spacing artificial graphite material and its preparation method, and CN108821275A discloses a high-capacity, high-rate graphite anode material for lithium-ion batteries and its preparation method. Both methods utilize the numerous functional groups on the aromatic rings of pitch, such as aldehydes, carbonyls, and hydroxyl groups, which can undergo cross-linking reactions with aliphatic units and oxygen-containing groups in biomass tar under suitable conditions. This promotes the polymerization degree of pitch molecules, leading to condensation and cross-linking to obtain cross-linked mesophase carbon. However, these methods suffer from low biomass tar utilization (pitch to biomass tar ratio: 100:3~30), stringent cross-linking conditions, high temperatures (350~550℃), and long processing times (10~24 h).

[0005] Given the urgent need for high-value resource utilization of large quantities of biomass tar, developing novel, stable, and high-yield biomass tar-based mesophase carbon materials with mild liquid crystallization conditions can support the green and low-carbon transformation of energy-consuming terminals while realizing the high-value resource utilization of biomass tar by-products, which has significant economic and environmental benefits. Summary of the Invention

[0006] To address the problems of low efficiency in the utilization of biomass tar resources, unfavorable application due to amorphous carbon structure, and harsh crosslinking conditions in existing technologies, this invention utilizes microfluidic technology to achieve stable and high-yield preparation of biomass tar-based mesophase carbon materials from biomass tar feedstock under mild conditions.

[0007] This invention first provides a microfluidic preparation method for biomass tar-based mesophase carbon microspheres, which includes the following steps:

[0008] A. Biomass tar and emulsifying solvent are mixed to obtain an internal phase solution of tar. The internal phase solution of tar and the external phase solution are injected into a single-stage capillary microfluidic chip respectively. Through the shearing action of the external phase solution, the internal phase solution of tar is sheared into tar-based monodisperse microdroplets.

[0009] B. The tar monodisperse microdroplets obtained in step A are dropped into the receiving phase through a collection tube, and further carbon deposition is carried out to form tar-based carbonaceous liquid crystal microdroplets.

[0010] C. The tar-based carbonaceous liquid crystal microdroplets obtained in step B are heated to 200~450℃ and hydrothermally carbonized for 4~12 h to carry out planar aromatic macromolecular condensation and ordered orientation, generating a layered carbonaceous mesophase. After separation, washing and drying, biomass tar-based mesophase carbon microspheres with a layered structure are obtained.

[0011] In the microfluidic preparation method described above, in step A, the emulsifying solvent is at least one of ethanol, toluene, benzene, carbon disulfide, DMF, or chloroform.

[0012] In the microfluidic preparation method described above, in step A, the mass concentration of biomass tar in the tar inner phase solution is 4-17%.

[0013] In the microfluidic preparation method described above, in step A, the external phase solution is water.

[0014] In the microfluidic preparation method described above, in step A, the external phase solution is a 1-5 wt% aqueous solution of F127.

[0015] In the microfluidic preparation method described above, in step A, when injecting the single-stage capillary microfluidic chip, the flow rate of the tar inner phase solution is controlled to be 0.5~3.0 mL / h, and the flow rate of the outer phase solution is controlled to be 20~50 mL / h.

[0016] In the microfluidic preparation method described above, in step A, the flow rate of the external phase solution is controlled to be 5~50 mL / h.

[0017] In the microfluidic preparation method described above, in step A, the biomass tar is a semi-solid byproduct produced by pyrolysis or gasification of at least one of the following: straw, distiller's grains, rice husks, wheat bran, bamboo, wood, coconut shells, peanut shells, or walnut shells.

[0018] In the aforementioned microfluidic preparation method, step A, the single-stage capillary microfluidic chip is constructed by assembling a glass capillary and a quartz square tube on a glass slide, and using AB-type epoxy adhesive to bond the conical end of the glass capillary to the quartz square tube to form a droplet cutting channel. In the microfluidic chip, the tar inner phase solution channel is a glass capillary with an inlet inner diameter of 400-800 μm, an inlet outer diameter of 800-1200 μm, and an outlet conical end inner diameter of 100-600 μm, with the outlet conical end inner diameter being smaller than the inlet inner diameter. The outer phase solution channel is a quartz square tube with an inner diameter of 810-1210 μm, matching the inlet outer diameter of the tar inner phase solution channel. The inner and outer phase solution mixing channel is a glass capillary with an inner diameter of 400-800 μm and an outer diameter of 800-1200 μm, with both inner and outer diameters matching the inlet inner and outer diameters of the tar inner phase solution channel.

[0019] In the aforementioned microfluidic preparation method, step A involves injecting the tar inner-phase solution and the outer-phase solution into a single-stage capillary microfluidic chip using an injection tube. The inner diameter of the injection tube is 810~1210 μm, which matches the inlet outer diameter of the tar inner-phase solution channel. In this invention, a syringe pump can be used to advance the injection tube and pump the solution into the microfluidic chip to control the flow rate.

[0020] In the microfluidic preparation method described above, in step B, the collection tube is connected to the outlet end of the inner and outer phase solution mixing channel, and the inner diameter of the collection tube is 810~1210 μm, which matches the outer diameter of the inner and outer phase solution mixing channel.

[0021] In the microfluidic preparation method described above, in step B, the length of the collection tube is 2~20 cm.

[0022] In the microfluidic preparation method described above, in step B, the temperature of the collection tube is 0~150℃.

[0023] Preferably, in the above microfluidic preparation method, in step B, the temperature of the collection tube is 0~80℃.

[0024] More preferably, in the above microfluidic preparation method, in step B, the temperature of the collection tube is 0~60℃.

[0025] In the microfluidic control preparation method described above, in step B, the receiving phase is water.

[0026] In the microfluidic preparation method described above, in step B, the receiving phase is a 1-5 wt% aqueous solution of F127.

[0027] In the microfluidic preparation method described above, in step B, the receiving phase is stirred at 200~1000 rpm during the droplet process.

[0028] In the microfluidic preparation method described above, in step B, the temperature of the receiving phase is 0~80℃ during the droplet process.

[0029] Preferably, in the above microfluidic preparation method, in step B, the temperature of the receiving phase is 0~60℃ during the droplet process.

[0030] More preferably, in the above microfluidic preparation method, in step B, the temperature of the receiving phase is 0~15℃ during the droplet process.

[0031] In the microfluidic preparation method described above, the heating rate in step C is 3~7℃ / min.

[0032] Preferably, in the above microfluidic preparation method, step C involves hydrothermal carbonization at 180~330℃ for 4~8 h.

[0033] In the microfluidic control preparation method described above, step C involves separation via centrifugation or filtration.

[0034] In the microfluidic preparation method described above, step C involves cleaning with ethanol and water until the washing solution becomes colorless.

[0035] In the microfluidic preparation method described above, step C involves drying via freeze drying at -50 to -90°C and 0.01 to 0.1 MPa, vacuum drying at 60 to 80°C and 0.08 to 0.1 MPa, or heating drying at 50 to 105°C.

[0036] The present invention also provides biomass tar-based mesophase carbon microspheres, which are prepared by the above-described microfluidic preparation method.

[0037] Among them, the particle size of the above-mentioned biomass tar-based mesophase carbon microspheres is 100~600 μm, and they exhibit scintillation anisotropy under polarized light.

[0038] The present invention also provides the application of the microfluidic preparation method described above or the biomass tar-based mesophase carbon microspheres described above in the preparation of lithium-ion battery anodes, carbon dioxide adsorption, hydrogen storage, hydrogen separation or low-carbon hydrocarbon separation.

[0039] The beneficial effects of this invention are:

[0040] This invention leverages the unique properties of biomass tar, which is rich in aromatic compounds and contains oxygen- and nitrogen-containing functional groups. Firstly, microfluidic technology is used to pre-emulsify and deposit biomass tar droplets under microfluidic liquid-phase shear. By controlling the composition of the pre-emulsifying solvent, the microfluidic shear rate, the length of the microfluidic collection tube, and the heating temperature, the anisotropy of monodisperse biomass tar microdroplets is controlled, promoting emulsification and deposition of biomass tar and the ordered stacking of planar macromolecules. This results in the preparation of ordered stacked particles with uniform and controllable particle size. The process involves two main steps: first, using tar-based carbonaceous liquid crystal microdroplets as carbon precursors to prepare mesophase carbon microspheres via hydrothermal carbonization. This effectively reduces the temperature at which carbonaceous liquid crystals form and aggregate during the hydrothermal process, shortening the formation time. Simultaneously, the oxygen- and nitrogen-containing functional groups of biomass tar promote the condensation of more planar aromatic macromolecules at low temperatures. The planar layered liquid crystal molecules in the droplets further orient themselves in an orderly manner to generate layered carbonaceous mesophases, accelerating the nucleation of carbonaceous mesophases and thus forming nitrogen-doped mesophase carbon.

[0041] This invention enables the high-value utilization of biomass tar. Taking advantage of the rich oxygen- and nitrogen-containing functional groups in biomass tar, microfluidic technology is used to promote the formation of layered carbon liquid crystals. Subsequently, mesophase carbon microspheres can be prepared based on the intercalation and pore-forming of the layered structure. It has the advantages of high yield and mild liquid crystallization conditions, and can be applied to the fields of carbon dioxide adsorption, hydrogen storage, hydrogen separation, and low-carbon hydrocarbon separation. Attached Figure Description

[0042] Figure 1 This is a schematic diagram of the actual microfluidic chip and its installation in an embodiment of the present invention.

[0043] Figure 2 This is a microscopic observation of the formation of monodisperse droplets from the tar-based precursor in an embodiment of the present invention.

[0044] Figure 3 The images shown are SEM images of tar-based mesophase carbon and tar in embodiments of the present invention.

[0045] Figure 4 This is a polarized light microscope image of tar-based mesophase carbon and tar in an embodiment of the present invention.

[0046] Figure 5 The images show the XRD patterns of microfluidic mesophase carbon, conventional mesophase carbon, and tar in this embodiment of the invention.

[0047] Figure 6 These are Raman spectral characterization diagrams of microfluidic mesophase carbon and conventional mesophase carbon in embodiments of the present invention.

[0048] Figure 7 Breakthrough curves for hydrogen separation and purification of microfluidic mesophase carbon.

[0049] Figure 8This is the breakthrough curve for hydrogen separation and purification of conventional mesophase carbon. Detailed Implementation

[0050] Specifically, a microfluidic preparation method for biomass tar-based mesophase carbon microspheres includes the following steps:

[0051] A. Biomass tar and emulsifying solvent are mixed to obtain an internal phase solution of tar. The internal phase solution of tar and the external phase solution are injected into a single-stage capillary microfluidic chip respectively. Through the shearing action of the external phase solution, the internal phase solution of tar is sheared into tar-based monodisperse microdroplets.

[0052] B. The tar monodisperse microdroplets obtained in step A are dropped into the receiving phase through a collection tube, and further carbon deposition is carried out to form tar-based carbonaceous liquid crystal microdroplets.

[0053] C. The tar-based carbonaceous liquid crystal microdroplets obtained in step B are heated to 200~450℃ and hydrothermally carbonized for 4~12 h (the heating and holding of hydrothermal carbonization are generally carried out in a reactor) to perform planar aromatic macromolecular condensation and ordered orientation, generating a layered carbonaceous mesophase. After separation, washing and drying, biomass tar-based mesophase carbon microspheres with a layered structure are obtained.

[0054] In step A of this invention, biomass tar is prepared into an internal phase solution of suitable concentration using an emulsifying solvent. This solution is then subjected to shearing by an external phase solution using microfluidic technology to form tar-based monodisperse microdroplets. During the shearing and flow process within the mixing channel of the internal and external phase solutions, the tar-based monodisperse microdroplets gradually achieve initial carbon deposition. In step A, the emulsifying solvent is at least one of ethanol, toluene, benzene, carbon disulfide, DMF, or chloroform; the mass concentration of biomass tar in the internal phase solution is 4-17%; and the external phase solution is water or a 1-5 wt% aqueous solution of F127.

[0055] In step A of this invention, to promote the emulsification and deposition of biomass tar and the ordered stacking and condensation of planar aromatic macromolecules, the flow rates of the inner and outer phase solutions of the tar need to be controlled when injecting it into the single-stage capillary microfluidic chip. Experiments have shown that this invention controls the flow rate of the inner phase solution of the tar to be 0.5–3.0 mL / h, and the flow rate of the outer phase solution to be 20–50 mL / h or 5–50 mL / h. The flow rates of the inner and outer phase solutions of the tar also indirectly control the rate at which monodisperse microdroplets of tar are introduced into the receiving phase in step B.

[0056] In step A of this invention, the biomass tar is a common biomass tar in the art, such as a black, high-viscosity, pungent-odor semi-solid complex mixed byproduct produced by pyrolysis or gasification of at least one of straw, distiller's grains, rice husks, wheat bran, bamboo, wood bamboo, coconut shells, peanut shells, or walnut shells. It is rich in aromatic compounds and oxygen-containing and nitrogen-containing functional groups, has an extremely high carbon content, and has high viscosity and flowability.

[0057] In step A of this invention, the single-stage capillary microfluidic chip is constructed by assembling a glass capillary and a quartz square tube on a glass slide, and using AB-type epoxy adhesive to bond the conical end of the glass capillary to the quartz square tube to form a droplet cutting channel. In the microfluidic chip, the tar inner phase solution channel is a glass capillary with an inlet inner diameter of 400-800 μm, an inlet outer diameter of 800-1200 μm, and an outlet conical end inner diameter of 100-600 μm, with the outlet conical end inner diameter being smaller than the inlet inner diameter. The outer phase solution channel is a quartz square tube with an inner diameter of 810-1210 μm, matching the inlet outer diameter of the tar inner phase solution channel. The inner and outer phase solution mixing channel is a glass capillary with an inner diameter of 400-800 μm and an outer diameter of 800-1200 μm, with both inner and outer diameters matching the inlet inner and outer diameters of the tar inner phase solution channel. The tar internal phase solution and external phase solution can be injected using the following method: the tar internal phase solution and external phase solution are injected separately into the tar internal phase solution channel and external phase solution channel through injection tubes, respectively, and the injection flow rates of the tar internal phase solution and external phase solution are controlled separately. Then, the solutions flow, mix, and shear within the internal and external phase solution mixing channel. According to the specifications of the single-stage capillary microfluidic chip, the inner diameter of the injection tube is 810~1210μm, which is consistent with the inlet outer diameter of the tar internal phase solution channel.

[0058] In step B of this invention, the collecting tube is connected to the outlet end of the mixing channel for the inner and outer phase solutions. The inner diameter of the collecting tube is 810~1210 μm, which matches the outer diameter of the mixing channel. The anisotropy of the monodisperse tar microdroplets is controlled by extending the length of the collecting tube or by heating it, promoting the formation of layered carbonaceous liquid crystals. The length of the collecting tube is 2~20 cm; the temperature of the collecting tube is 0~150℃. By controlling the temperature of the collecting tube, the temperature of the system after the inner and outer phases are mixed is controlled for better solidification and formation of microspheres. Preferably, the temperature of the collecting tube is 0~80℃; more preferably, it is 0~60℃.

[0059] Meanwhile, in step B, the receiving phase is water or a 1-5 wt% F127 aqueous solution; during the dripping process, the receiving phase is stirred at 200-1000 rpm; during the dripping process, the temperature of the receiving phase is 0-80℃. To better solidify the monodisperse tar microdroplets and form microspheres, preferably, the temperature of the receiving phase is 0-60℃; more preferably, it is 0-15℃.

[0060] In step C of this invention, the heating rate is 3~7℃ / min; mesophase carbon microspheres are prepared by hydrothermal carbonization using tar-based carbonaceous liquid crystal microdroplets as carbon precursors, effectively reducing the temperature (180~330℃) for the formation and aggregation of carbonaceous liquid crystals during the hydrothermal process and shortening the formation time (4~8h); after the formation of layered carbonaceous mesophase, the system is a turbid liquid. The turbid liquid is centrifuged or filtered, the solid is collected, and then washed and dried. The washing method is to wash with ethanol and water until the washing liquid is colorless; the drying method is freeze-drying at -50~-90℃ and 0.01~0.1MPa, vacuum drying at 60~80℃ and 0.08~0.1MPa, or heating drying at 50~105℃.

[0061] Based on the microfluidic preparation method of the above-mentioned biomass tar-based mesophase carbon microspheres, the present invention also provides biomass tar-based mesophase carbon microspheres with a particle size of 100~600 μm, which exhibit scintillation anisotropy under polarized light.

[0062] This invention also provides the application of the above-mentioned biomass tar-based mesophase carbon microspheres in the preparation of lithium-ion battery anodes, carbon dioxide adsorption, hydrogen storage, hydrogen separation, or low-carbon hydrocarbon separation.

[0063] The present invention will be further described in detail below through embodiments, but the scope of protection of the present invention is not limited to the embodiments described herein.

[0064] Example 1

[0065] 1. Construction of microfluidic devices

[0066] This embodiment uses a single-emulsion glass capillary microfluidic chip, the structure of which is as follows:

[0067] 1.1 Chip Components

[0068] External channel: Quartz square tube (inner diameter 1 mm);

[0069] Internal phase channel: Circular glass capillary (inner diameter 550 μm, outer diameter 960 μm, inner diameter of tapered end is 180 μm).

[0070] Substrate: Glass slide;

[0071] Two steel tubes that hold the capillary in place (obtained by burning off the plastic part of the injection head).

[0072] 1.2 Connection Method

[0073] Cut the glass capillary into two sections, each 3-5 cm in length: one section serves as the tar internal phase solution channel, and the other as the internal and external phase solution mixing channel. Machine one end of the tar internal phase solution channel into a conical shape using a needle-drawing and needle-forging machine. Then, arrange the tar internal phase solution channel, the external phase solution channel, and the internal and external phase solution mixing channel according to the following... Figure 1 The chip is assembled onto a glass slide using a specific method, and then bonded to the slide using AB epoxy resin. Finally, ethanol is introduced into the chip for surface inspection, and the chip fabrication is completed after cleaning.

[0074] The outer phase channel is connected to the injection tube of syringe pump A, the inner phase channel is connected to the injection tube of syringe pump B, and the outlet end is connected to the external receiving container.

[0075] 2. Preparation of the liquid phase system

[0076] 2.1 External phase solution (2 wt% F127 solution)

[0077] Dissolve 2 g of Pluronic® F-127 reagent in 98 g of deionized water, stir and sonicate until completely dissolved, to prepare an aqueous solution of F127 with a mass concentration of 2 wt%, as the external phase solution.

[0078] 2.2 Internal phase solution (4 wt% tar solution):

[0079] Take about 2 g of corn stalk gasification tar (from a biomass gasification plant in Henan) and add it to toluene (48 mL) until it is completely dissolved to prepare a tar solution.

[0080] 3. Preparation process of mesophase carbon spheres

[0081] 3.1 Fluid Transport

[0082] Start syringe pump A and push the syringe tube to introduce the external phase F127 aqueous solution into the external phase channel of the chip at a flow rate of 10 mL / h.

[0083] Start the syringe pump B and push the syringe tube to introduce the inner phase tar solution into the inner phase channel of the chip at a flow rate of 1 mL / h;

[0084] Under the combined use of a high-speed camera and microscope, it was observed that, in the shearing action of the external phase fluid, the internal phase solution of the tar-based precursor forms monodisperse microdroplets of tar-based microparticles at the capillary end. This process facilitates the formation of subsequent mesophase carbon spheres. The shearing process is as follows: Figure 2 As shown.

[0085] 3.2 Droplet Collection and Hydrothermal Treatment

[0086] Tar-based monodisperse microdroplets were collected in a collection tube with an inner diameter of 1 mm and a length of 5 cm. The collection tube was kept at 60 °C. The droplets were added to a 2 wt% F127 aqueous solution as the receiving phase. The collection tube was rotated at 400 rpm and kept at 60 °C. After carbon deposition, tar-based carbonaceous liquid crystal microdroplets were formed. The microdroplets were then placed in a hydrothermal reactor and heated from room temperature to 250 °C at a rate of 5 °C / min. The temperature was maintained for 4 h and then allowed to cool naturally. The microdroplets were then washed by centrifugation with anhydrous ethanol and water, and dried at 80 °C for 12 h to obtain tar-based mesophase carbon microspheres.

[0087] The preparation of the conventional mesophase involved no microfluidic shearing or deposition process. Approximately 2 g of corn stalk gasification byproduct (from a biomass gasification plant in Henan) was directly added to toluene (48 mL) until completely dissolved, preparing a tar solution. This solution was then placed in a hydrothermal reactor and heated from room temperature to 250°C at a rate of 5°C / min, held for 4 h, and allowed to cool naturally. After centrifugation and washing with anhydrous ethanol and water, the solution was dried at 80°C for 12 h to obtain conventional tar-based mesophase carbon microspheres.

[0088] 4. Product Characterization

[0089] 4.1 Morphological Characterization (SEM)

[0090] The microfluidically treated tar-based mesophase carbon and the original tar were characterized by scanning electron microscopy (SEM), and the results are as follows: Figure 3 As shown. Figure 3 (1) Clear nanoscale spherical particles can be observed. These are mesophase microspheres formed by the "nucleation-growth-aggregation" process of the mesophase liquid crystal microregion during thermal conversion. The spherical units further aggregate into micron-scale aggregates. Figure 3 (2) The original tar has no clear structural unit and is an amorphous block / sheet accumulation. It is a condensate formed by the disordered aggregation of asphaltenes molecules through van der Waals forces. It only contains micron-sized broken blocks and no nano-sized dispersed units.

[0091] 4.2 Polarizing Microscope

[0092] The microfluidic-treated tar-based mesophase carbon and the original tar were characterized by polarized light microscopy, and the results are as follows: Figure 4 As shown. Tar-based mesophase carbon microspheres Figure 4 (1) The anisotropy of the mesophase is evident, with bright spots / particles appearing in the field of view: This is due to the "anisotropic structure (birefringence)" of the mesophase carbon. The mesophase carbon is transformed from the liquid crystal state mesophase, and the molecules (aromatic lamellae) are preferentially oriented, satisfying the birefringence condition, thus "shining" under crossed polarized light; the presence of the bright spots verifies its "mesophase structure". These bright areas correspond to the "quasi-spherical mesophase microspheres" observed in SEM, which is the core feature that distinguishes mesophase carbon from ordinary carbon. Original tar Figure 4 (2) It reflects the isotropic nature of organic mixtures, and the field of view is almost completely black, with only very weak stray light (no obvious bright area). This is due to the isotropic characteristics of the original tar. The original tar is an amorphous organic mixture with no preferred orientation of molecules and no birefringence. Therefore, it cannot transmit light under crossed polarized light and appears almost black.

[0093] 4.3 Crystal structure characterization (XRD)

[0094] Tar-based mesophase carbon exhibits short-range order, with localized stacking of aromatic lamellae (corresponding to the liquid crystal structure of the mesophase, from which the anisotropy under polarized light originates). From Figure 5 It can be seen that both conventional mesophase carbon and microfluidic mesophase carbon are at approximately 26 o A sharp, high-intensity (002) peak indicates that the synthesized biomass tar-based mesophase carbon is highly graphitized and highly ordered. It is derived from a liquid crystal state (mesophase), with regular carbon layer arrangement, high parallelism, and interlayer spacing close to ideal graphite. Furthermore, the microfluidic-treated mesophase carbon phase exhibits an increase in the number of carbon layers located at 23°C compared to conventional mesophase carbon. o The presence of graphite-like carbon nitride on the left and right indicates that the microfluidic shearing and pre-deposition steps can promote the cross-linking of nitrogen-containing compounds in biomass tar, forming nitrogen-doped mesophase carbon rich in alkaline sites, which can promote the adsorption of acidic gases such as CO2 and H2S.

[0095] 4.4 Characterization of Aromaticization Degree

[0096] D peak (~1350 cm⁻¹) in the Raman spectrum of carbon materials -1 ): Represents defects, edges, or disordered structures in aromatic rings. Related to sp2 carbons, heteroatoms, bent carbon layers, etc. G peak (~1580 cm⁻¹) -1 ): Represents the in-plane stretching vibration of sp2 carbon atoms in the aromatic ring, and is a characteristic peak of graphitized or ordered structures. Among them, I D / I G A smaller intensity ratio indicates a larger average size of aromatic ring lamellae, fewer defects, and higher degree of order. Conversely, a larger ratio indicates a disordered structure and more defects. Figure 6 The results indicate that microfluidic mesophase carbon has lower graphitization and aromaticity, and higher defect rate, making it unsuitable for electrochemical applications, but more suitable for applications involving the adsorption and separation of pollutants.

[0097] 4.5 Application of mesophase carbon H2 separation and purification

[0098] Based on the above characterization, the two mesophase carbons were applied to the separation experiment of impure hydrogen gas. Figure 7As can be seen, the outlet concentration of H2 from the microfluidic mesophase carbon prepared in Example 1 rose almost immediately to near the inlet concentration and remained high until it was diluted and decreased later due to the large-scale breakthrough of CO2. This indicates that H2 is almost completely unadsorbed and can pass through the adsorption bed rapidly. The breakthrough time of CO2 was very long (significant breakthrough only began after approximately 2500 seconds), meaning that the material has a large adsorption capacity and extremely strong selectivity for CO2. The adsorption capacity for CO was moderate. The selectivity order was: CO2 >> CO > H2. This is ideal for purifying hydrogen from mixed gases such as syngas.

[0099] Depend on Figure 8 It is known that the CO2 breakthrough time of conventional mesophase carbon is significantly earlier than 2500 seconds, indicating that it has a certain degree of H2 adsorption, but a low adsorption capacity / selectivity for CO2. This directly leads to some H2 being adsorbed or retained in the bed during the adsorption stage of pressure swing adsorption, reducing the hydrogen recovery rate.

Claims

1. A microfluidic preparation method for biomass tar-based mesophase carbon microspheres, characterized in that: Includes the following steps: A. Biomass tar and emulsifying solvent are mixed to obtain an internal phase solution of tar. The internal phase solution of tar and the external phase solution are injected into a single-stage capillary microfluidic chip respectively. Through the shearing action of the external phase solution, the internal phase solution of tar is sheared into tar-based monodisperse microdroplets. B. The tar monodisperse microdroplets obtained in step A are dropped into the receiving phase through a collection tube, and further carbon deposition is carried out to form tar-based carbonaceous liquid crystal microdroplets. C. The tar-based carbonaceous liquid crystal microdroplets obtained in step B are heated to 200~450℃ and hydrothermally carbonized for 4~12 h to carry out planar aromatic macromolecular condensation and ordered orientation, generating a layered carbonaceous mesophase. After separation, washing and drying, biomass tar-based mesophase carbon microspheres with a layered structure are obtained.

2. The microfluidic preparation method of biomass tar-based mesophase carbon microspheres according to claim 1, characterized in that: In step A, at least one of the following must be satisfied: The emulsifying solvent is at least one of ethanol, toluene, benzene, carbon disulfide, DMF, or chloroform; The mass concentration of biomass tar in the tar internal phase solution is 4-17%; The external phase solution is water; or, the external phase solution is a 1-5 wt% aqueous solution of F127; When injecting into a single-stage capillary microfluidic chip, the flow rate of the tar inner phase solution is controlled at 0.5~3.0 mL / h, and the flow rate of the outer phase solution is controlled at 20~50 mL / h; or, the flow rate of the outer phase solution is controlled at 5~50 mL / h.

3. The microfluidic preparation method of biomass tar-based mesophase carbon microspheres according to claim 1, characterized in that: In step A, at least one of the following must be satisfied: The biomass tar is a semi-solid byproduct produced by pyrolysis or gasification of at least one of the following: straw, distiller's grains, rice husks, wheat bran, bamboo, wood, coconut shells, peanut shells, or walnut shells. The single-stage capillary microfluidic chip is constructed by assembling a glass capillary and a quartz square tube on a glass slide, using AB-type epoxy adhesive to bond the conical end of the glass capillary to the quartz square tube, forming a droplet cutting channel. In the microfluidic chip, the tar inner phase solution channel is a glass capillary with an inlet inner diameter of 400-800 μm, an inlet outer diameter of 800-1200 μm, and an outlet conical end inner diameter of 100-600 μm, with the outlet conical end inner diameter being smaller than the inlet inner diameter. The outer phase solution channel is a quartz square tube with an inner diameter of 810-1210 μm, matching the inlet outer diameter of the tar inner phase solution channel. The inner and outer phase solution mixing channel is a glass capillary with an inner diameter of 400-800 μm and an outer diameter of 800-1200 μm, with both inner and outer diameters matching the inlet inner and outer diameters of the tar inner phase solution channel. The tar inner phase solution and the outer phase solution are injected into the single-stage capillary microfluidic chip using an injection tube with an inner diameter of 810~1210μm, which is consistent with the outer diameter of the inlet of the tar inner phase solution channel.

4. The microfluidic preparation method of biomass tar-based mesophase carbon microspheres according to claim 1, characterized in that: In step B, at least one of the following must be satisfied: The collection tube is connected to the outlet end of the inner and outer phase solution mixing channel. The inner diameter of the collection tube is 810~1210μm, and its inner diameter matches the outer diameter of the inner and outer phase solution mixing channel. The length of the collection tube is 2~20 cm; The temperature of the collecting tube is 0~150℃; preferably 0~80℃; more preferably 0~60℃.

5. The microfluidic preparation method of biomass tar-based mesophase carbon microspheres according to claim 1, characterized in that: In step B, at least one of the following must be satisfied: The receiving phase is water; or, the receiving phase is a 1-5 wt% aqueous solution of F127. During the dripping process, the receiving phase is stirred at 200~1000 rpm; During the dripping process, the temperature of the receiving phase is 0~80℃; preferably 0~60℃; more preferably 0~15℃.

6. The microfluidic preparation method of biomass tar-based mesophase carbon microspheres according to claim 1, characterized in that, In step C, hydrothermal carbonization is carried out at 180~330℃ for 4~8 hours.

7. The microfluidic preparation method of biomass tar-based mesophase carbon microspheres according to claim 1, characterized in that, In step C, at least one of the following must be satisfied: The separation method is centrifugation or filtration; The cleaning method involves using ethanol and water to clean until the washing solution becomes colorless. The drying method is freeze drying at -50~-90℃ and 0.01~0.1MPa, vacuum drying at 60~80℃ and 0.08~0.1MPa, or heating drying at 50~105℃.

8. Biomass tar-based mesophase carbon microspheres prepared by the microfluidic preparation method of biomass tar-based mesophase carbon microspheres according to any one of claims 1 to 7.

9. The biomass tar-based mesophase carbon microspheres according to claim 8, characterized in that: The biomass tar-based mesophase carbon microspheres have a particle size of 100~600 μm and exhibit scintillation anisotropy under polarized light.

10. Biomass tar-based mesophase carbon microspheres prepared by the microfluidic preparation method of biomass tar-based mesophase carbon microspheres according to any one of claims 1 to 7, or the application of biomass tar-based mesophase carbon microspheres according to claims 8 to 9 in the preparation of lithium-ion battery anodes, carbon dioxide adsorption, hydrogen storage, hydrogen separation, or low-carbon hydrocarbon separation.

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