CN1100093C - Prepn. method of mesophase asphalt carbon microsphere - Google Patents

Abstract

The preparation method of the mesophase pitch carbon microspheres of the present invention is to carry out thermal polycondensation reaction of polycyclic aromatic hydrocarbon raw materials and additives (0.1-10wt% of the aromatic hydrocarbon raw materials) to generate mesophase pitch containing microspheres, and then combine them with a boiling range of 200-360°C The industrial heavy oil within the range is mixed and heated, filtered, and then the microspheres are separated from the remaining isotropic pitch components with an organic solvent to obtain mesophase pitch carbon microspheres. The additive used in the method is graphitizable carbon powder such as coke powder, graphite powder or mesophase microspheres with a particle size of <100 μm, and the addition thereof does not affect the easy graphitization performance of the carbon microspheres. The mesophase pitch carbon microspheres prepared by the method have uniform particle size, high yield and high extraction efficiency.

Description

Preparation method of mesophase pitch carbon microspheres

technical field

The invention relates to a method for preparing a carbon material precursor-mesophase pitch carbon microspheres.

The method includes two processes of synthesis and extraction of intermediate pitch carbon microspheres with polycyclic aromatic hydrocarbons as raw materials.

Background technique

Mesocarbon Microbeads (MCMB) is a new type of high-performance carbon material precursor. In addition to being used as a high-density and high-strength isotropic carbon material raw material, it can also be used as a high-performance liquid chromatography column packing and catalyst carrier. , ultra-high specific surface area activated carbon, etc. What is particularly interesting is that the mesophase pitch carbon microspheres are used as electrode materials for lithium-ion secondary batteries to show extremely excellent performance, which has caused worldwide competition in research and development.

At present, there are two main methods for the preparation of mesophase pitch carbon microspheres: emulsification method and polymerization method. The emulsification method takes the melted mesophase pitch as the raw material and emulsifies it into balls through a high-temperature dispersion medium. The polymerization method uses direct heat treatment to first condense the polycyclic aromatic hydrocarbon raw materials to form mesophase pellets, and then use appropriate means to extract the pellets from the mother liquid pitch come out. Compared with the emulsification method, the polymerization method has the characteristics of simple process (no need for cumbersome non-melting and high-temperature dispersion processes), the size and distribution of microspheres can be controlled in the thermal reaction stage, and the investment in equipment is less. Therefore, the polymerization method is the current intermediate The main method for the synthesis of phase microspheres. As we all know, both coal tar pitch and petroleum residue have a wide molecular weight distribution of aromatic hydrocarbons and a certain content of heteroatoms. When they undergo thermal condensation polymerization, they will cause step-by-step polymerization due to the difference in molecular size and activity, making microspheres The particle distribution is not uniform, and the spheres are prone to fusion, so it is difficult to obtain a large number of small spheres with uniform diameter distribution. Therefore, the selection of suitable aromatic hydrocarbon raw materials, additives and thermal polycondensation reaction conditions has a great influence on the formation and morphology of microspheres. Some studies believe that the use of additives, such as primary quinoline insolubles (including carbon black and other impurities, referred to as QI) or carbon black, can promote the formation of mesophase globules and prevent them from growing and merging. Japanese patent (JP07-126659) and literature (Carbon 35 (7), 875 (1997)) introduced adding carbon black to coal tar and pitch or naphthalene catalytic synthesis pitch, not only can improve the yield of mesophase microsphere, and The size of the microspheres can be controlled to make them more evenly distributed; the literature (Journal of Materials Science 29, 4757 (1994)) reports that the formation and growth of mesophase microspheres can be controlled by controlling the primary QI content in the asphalt. In addition, literature (Carbon 32, 1073 (1994); Carbon 34, 1473 (1996)) reports that adding organometallic compounds such as ferrocene and carbonyl iron to coal tar pitch can effectively promote the uniform generation of mesophase microspheres and prevent their formation. Merge. Whether the above additives are carbon black or primary QI are non-graphitizable substances, they are mixed in the middle of the extracted microspheres, reducing the graphitization performance and other physical properties (such as electrical conductivity) of mesophase microspheres, and increasing the impurity content. , will eventually affect the performance of mesophase carbon microspheres (such as when it is used as the negative electrode material of lithium ion secondary battery, it will reduce the reversible capacity and cycle life of the battery). At present, there are mainly two methods for extracting microspheres from mesophase pitch containing microspheres: high-temperature centrifugation (Extended Abstracts of 17 ^th Biennial Conference on Carbon, p.409, 1985; J.Electrochem.Soc.142, 1041 (1995) and one-step solvent extraction (JP07-126659; USP 3956436). The high-temperature centrifugation requires high equipment costs, and it is difficult to control the fusion phenomenon between microspheres during centrifugal sedimentation; one-step solvent extraction generally requires Strong polar solvents, such as pyridine, quinoline, etc., require repeated direct extraction of mesophase pitch, which not only consumes a large amount of organic solvents, but also due to the solvent gradient effect, solvents such as pyridine will severely etch the microspheres, It makes the sphericity worse, thus affecting the quality of mesophase pitch microspheres.

Contents of the invention

The purpose of the present invention is to provide a preparation method capable of obtaining mesophase pitch carbon microspheres with good quality and high yield. In the method, new additives are added to polycyclic aromatic hydrocarbon raw materials to prepare mesophase pitch microspheres by means of polymerization, and then the mesophase pitch carbon microspheres are extracted through two steps of heavy oil thermal melting and solvent extraction. The microspheres prepared by the method have uniform particle size, and the yield and extraction efficiency are both high.

The preparation method of the mesophase pitch carbon microspheres of the present invention is the same as that of the prior art in that aromatic hydrocarbon raw materials are uniformly mixed with additives, and the thermal polycondensation reaction is carried out in the range of 350-500°C under the protection of an inert gas to obtain microspheres containing The mesophase pitch is extracted and separated from the microspheres with an organic solvent to obtain the mesophase pitch carbon microspheres. The difference is that the aromatic raw materials used are: coal tar, coal tar pitch, petroleum residue, petroleum pitch, polyvinyl chloride pitch or solvent refined coal. The additive adopts graphitizable carbon powder, the dosage of the additive is 0.1-10 wt% of the aromatic hydrocarbon raw material, and the particle size of the additive is less than 100 μm. Before extracting and separating with an organic solvent, the industrial heavy oil is hot-melted and filtered to enrich the microspheres. The boiling range of the industrial heavy oil is in the range of 200-360°C. The graphitizable carbon powder used is: coke powder, graphite powder or mesophase carbon microspheres. The dosage of the additive is preferably 1-6 wt% of the aromatic hydrocarbon raw material. The particle size of the additive is preferably less than 30 µm.

The synthesis conditions of the mesophase pitch provided by the preparation method of the mesophase pitch carbon microspheres of the present invention are the same as those of the known technology, that is, the additive and the aromatic hydrocarbon raw material are uniformly mixed in proportion, and the thermal polycondensation reaction is carried out at 350-500 ° C under the protection of an inert gas. The residence time thereof is not more than 20 hours, and a mesophase pitch containing microspheres is obtained. The additives of the present invention are coke powder, graphite powder or mesocarbon microspheres, all of which are graphitizable substances, and their existence does not affect the performance of the final mesophase carbon microspheres. The particle size of the additive has a great influence on the formation of mesophase microspheres, and the particle size should be less than 100 μm. If the particles are too large, the effect of promoting the formation of small balls and inhibiting fusion will be weakened; if the particles are too small, the preparation cost of the additive will be increased, preferably with a particle size of <30 μm; the amount of the additive should be 0.1 to 10 wt% of the aromatic hydrocarbon raw material . If the amount of additive is too small, the expected effect will not be achieved, and the generated microspheres are easy to fuse; when it is greater than 10wt%, the viscosity of the system increases rapidly, and it is difficult to form mesophase spheres with large particle sizes, and only tiny crystal nuclei below 1 μm can be formed , and too many additives may have adverse effects on the use of MCMB in the future. The dosage of the additive is preferably in the range of 1-6wt%.

The separation of the mesophase microspheres provided by the preparation method of the mesophase pitch carbon microspheres of the present invention is to adopt a two-step extraction method. Firstly, the pitch containing the mesophase microspheres is mixed with industrial heavy oil and melted, and the mesophase is enriched by hot filtration. Microspheres, and then use an organic solvent to separate the microspheres from the remaining isotropic pitch components to obtain mesophase pitch carbon microspheres. The industrial heavy oil used in the first step of microsphere extraction should have a relatively high boiling range and low viscosity. It is better to use an industrial heavy oil with a boiling range in the range of 200-360°C. The amount used is 1% of the weight of the mesophase pitch. ~20 times is appropriate. If the amount of heavy oil added is too small, filtration will be difficult and the amount of bitumen dissolved will be less; if the amount added is too large, raw materials will be wasted and the preparation cost will be increased. The solvent used in the second step can be selected from common solvents: benzene, toluene, tetrahydrofuran, pyridine or quinoline, etc., and the color of the filtrate is colorless as the standard for pumping out. The mesophase pitch carbon microspheres prepared by the invention have the characteristics of uniform particle size, high yield and high extraction efficiency.

Detailed ways

The following examples are provided to illustrate the present invention in detail.

Table 1 lists the preparation conditions of the mesophase microspheres provided by the present invention.

Embodiment: the middle temperature coal tar or asphalt (i.e. pyridine soluble component), purified petroleum residue oil or asphalt and the additives listed in Table 1 are mixed uniformly in a certain proportion and then loaded into the reaction In the still, under the protection of nitrogen, the thermal polycondensation reaction is carried out, and then rapidly cooled to room temperature to obtain pitch containing mesophase microspheres. Mix the mesophase pitch with a heavy component of catalytic cracking naphtha (boiling range 280-360°C) in a weight ratio of 1:10, stir and heat-dissolve below the boiling point of the heavy oil, and then use a No. 5 acid-resistant funnel to filter and enrich the mesophase microspheres, and finally use pyridine as a solvent for Soxhlet extraction to obtain MCMB. The time required for the two-step extraction of No. 1 to No. 6 in Table 1 does not exceed 6 hours.

The yield of No. 1 MCMB in Table 1 is 50% (based on raw pitch), and the results of scanning electron microscopy show that the particle size is uniform and the sphericity is good.

The yield of No. 5MCMB in Table 1 is 24% (based on raw material residue), and the scanning electron microscope results show that the particle size is uniform and the sphericity is good.

Comparative Example 1 Without using additives, the medium-temperature coal tar pitch from which PI was removed once was directly thermally condensed under the same reaction conditions as No. 1 in Table 1. The obtained mesophase pitch has been completely converted into a 100% fusion texture without intermediate Phase globules exist.

Comparative Example 2 The mesophase pitch containing microspheres in No. 1 of Table 1 was directly extracted with pyridine in a Soxhlet extractor without being treated with industrial heavy oil. It took 18 hours to extract cleanly, and the obtained pyridine insoluble matter The SEM results showed that there were more non-spherical particles and poor sphericity. However, the mesophase bitumen treated with heavy oil can be extracted in only 3 hours with the same weight.

Table 1 Preparation conditions of mesophase microspheres serial number Aromatic raw material additive Thermal polycondensation reaction conditions name Amount (wt%)* Particle size (μm) temperature-time 1 coal tar pitch graphite powder 2 <30 420℃-5min 2 coal tar pitch graphite powder 2 90<d<100 420℃-5min 3 coal tar pitch Scorched powder 10 <30 420℃-5min 4 coal tar pitch mesophase microspheres 6 <13 410℃-30min 5 petroleum residue graphite powder 1 <30 420℃-240min 6 petroleum residue graphite powder 0.1 <30 420℃-300min

^* Aromatic raw material weight percent

Claims (4)

1. A method for preparing mesophase pitch carbon microspheres, using aromatic hydrocarbon raw materials and additives to uniformly mix, and under the protection of an inert gas, carry out thermal polycondensation reaction in the range of 350-500°C to obtain mesophase pitch containing microspheres, and then use The organic solvent extracts and separates the microspheres from the residual isotropic pitch to obtain the mesophase pitch carbon microspheres, which are characterized in that: Aromatic raw materials are: coal tar, coal tar pitch, petroleum residue, petroleum pitch, polyvinyl chloride pitch or solvent refined coal; The additive is graphitizable carbon powder, the dosage of the additive is 0.1-10wt% of the aromatic hydrocarbon raw material, and the particle size of the additive is less than 100 μm; Before extracting and separating with an organic solvent, the industrial heavy oil is hot-melted and filtered to enrich the microspheres. The boiling range of the industrial heavy oil is in the range of 200-360°C. 2. The preparation method according to claim 1, wherein the graphitizable carbon powder is: coke powder, graphite powder or mesocarbon microspheres. 3. The preparation method according to claim 1, characterized in that: the dosage of the additive is 1-6wt% of the aromatic hydrocarbon raw material. 4. The preparation method according to claim 1, characterized in that the particle size of the additive is <30 μm.