CN-122012132-A - Method for preparing mesophase pitch by plasma-assisted directional bromination and catalytic debromination regulation

Abstract

The invention discloses a method for preparing mesophase pitch by plasma-assisted directional bromination and catalytic debromination regulation, and belongs to the technical fields of high-value utilization of heavy oil and advanced carbon material preparation. The method comprises the steps of (1) taking aromatic hydrocarbon-rich heavy oil as a raw material, directionally introducing bromine atoms on aromatic rings as activation and orientation sites through low-temperature plasma-assisted liquid-phase bromination reaction to construct brominated modified linear precursor asphalt, (2) synchronously realizing total removal of the bromine atoms, linear coupling between aromatic rings and improvement of molecular planarity through supported metal hydride catalysis and debromination-oriented polycondensation reaction to prepare pre-mesophase asphalt, (3) carrying out heat treatment in a strong uniform magnetic field, and enabling liquid crystal molecules to be orderly arranged along the magnetic field direction by virtue of the orientation action of a magnetic field on pi electron cloud, thereby finally forming the spinnable mesophase asphalt with a wide-area streamline structure. The method realizes the precise regulation and control of a full chain from molecular structure design to macroscopic orientation, and the prepared mesophase pitch has the characteristics of high anisotropic content (> 98%), moderate softening point (260-300 ℃), highly ordered molecular arrangement and low quinoline insoluble content (< 0.1%). The invention has novel process and provides a brand new path for preparing high-performance mesophase pitch.

Inventors

• LI WENBO
• LIU DONG
• LOU BIN
• YANG XIUJIE
• SHI NAN
• WEN FUSHAN
• WANG ZIXIANG
• GUO ZHENWEI
• Shan Mingxiu

Assignees

• 中国石油大学(华东)

Dates

Publication Date

20260512

Application Date

20260402

Claims (5)

1. 1. The preparation method of the mesophase pitch regulated and controlled by plasma assisted directional bromination and catalytic debromination takes aromatic hydrocarbon-rich heavy oil as a raw material and is characterized by comprising the following steps: (1) Under inert atmosphere, adding bromine source into raw material, placing into low-temperature plasma reaction system to make plasma-assisted liquid-phase bromination reaction, directionally introducing bromine atom as activation and orientation site so as to obtain brominated modified linear precursor asphalt; (2) Mixing linear precursor asphalt with a supported metal hydride catalyst, and carrying out catalytic complete debromination and directional polycondensation reaction in an inert atmosphere to synchronously realize complete removal of bromine atoms, linear coupling of aromatic rings and planarization promotion to obtain pre-mesophase asphalt; (3) And (3) magnetic field assisted liquid phase carbonization, namely placing the pre-mesophase pitch in a strong uniform magnetic field environment for heat treatment to obtain the spinnable mesophase pitch.
2. 2. The method of claim 1, wherein in the step (1), the bromine source is one of liquid bromine, N-bromosuccinimide or copper bromide, the addition amount is 10% -50% of the molar equivalent of raw material aromatic hydrocarbon, the plasma assisted bromination reaction is carried out in an inert atmosphere, the low-temperature plasma power is 50-500W, the frequency is 10-40 kHz, the plasma treatment and bromination reaction are carried out synchronously, and the reaction time is 2-10 hours.
3. 3. The method of claim 1, wherein the supported metal hydride catalyst in the step (2) is NaH/Al 2 O 3 or CaH 2 /SiO 2 , the addition amount is 0.5% -5% of the mass of the linear precursor asphalt, the reaction temperature is 280-360 ℃, the reaction time is 5-20 hours, and the full removal of bromine atoms and the directional linear polycondensation of aromatic hydrocarbon molecules are realized.
4. 4. The method according to claim 1, wherein in the step (3), the uniform magnetic field strength is not lower than 1T, the heat treatment temperature is 380-420 ℃, the heat treatment time is 2-10 h, and the magnetic field direction is consistent with the flow direction of asphalt during the subsequent melt spinning.
5. 5. The method of claim 1, wherein the spinnable mesophase pitch obtained in step (3) has a softening point of 260 to 300 ℃, an optical anisotropy content of greater than 98%, and an H/C atomic ratio of 0.35 to 0.50.

Description

Method for preparing mesophase pitch by plasma-assisted directional bromination and catalytic debromination regulation Technical Field The invention relates to a preparation method of mesophase pitch, in particular to a method for directionally preparing a precursor with a high linearity molecular structure by utilizing low-temperature plasma field assisted selective directional activation of bromine on aromatic hydrocarbon and combining catalytic debromination directional polycondensation, and further converting the precursor into high-performance spinnable mesophase pitch, belonging to the technical fields of high value-added utilization of heavy oil and advanced carbon material preparation. Background The mesophase pitch is a nematic liquid crystal substance formed by polycyclic aromatic hydrocarbon molecules in the liquid phase carbonization process, and is used as a precursor for preparing key materials such as high-performance carbon fibers, foam carbon and the like, and the molecular structural characteristics of the mesophase pitch directly determine the mechanical and heat-conducting properties of the final carbon material. Ideally, it should be composed of highly planar, linearly linked aromatic macromolecules and exhibit a highly ordered "wide-area streamline" optically anisotropic structure in the molten state. The structure endows the mesophase pitch with the characteristics of proper softening point, excellent melt fluidity, high carbon residue value and easy graphitization, so that the mesophase pitch becomes a functional carbon material with high added value, and can be directly or after subsequent treatment used in the fields of high-end heat conduction materials, composite material matrixes, electrochemical electrodes and the like. At present, the industrialized preparation of mesophase pitch mainly depends on a thermal polycondensation method. The method is usually carried out at a high temperature above 400 ℃ in an inert atmosphere, and the condensation is realized by means of free radical thermal reaction of aromatic hydrocarbon molecules. The method has the advantages of simple process, obvious inherent defects, namely (1) strong reaction caused by high temperature, complete random condensation sites and directions of various aromatic hydrocarbon molecules, extremely easy formation of branched, distorted or crosslinked molecular structures, but non-ideal linear aromatic hydrocarbon oligomers, (2) poor product uniformity, difficult controlled reaction process, wide molecular weight distribution and high softening point of the product, and difficult structure regulation, wherein a large amount of insoluble quinoline insoluble substances (QI) are generated, and the obtained mesophase is mainly in a fine mosaic structure and a small watershed structure, is difficult to spontaneously form a large-size wide area streamline structure, so that the upper performance limit of subsequent application is limited. In order to overcome the shortcomings of the thermal polycondensation process, researchers have developed catalytic polycondensation processes, for example, using lewis acid catalysts such as AlCl 3、HF/BF3. The catalyst can activate aromatic rings at a lower temperature (300-380 ℃) to improve the reaction efficiency and partial selectivity. However, the method has new bottlenecks of (1) catalyst separation and pollution, namely that the catalyst is difficult to thoroughly remove from high-viscosity asphalt products, residues corrode equipment, pollute products and influence subsequent processes, and (2) molecular configuration control force is insufficient, namely that the method still lacks accurate guiding capability on the connection mode (such as ortho position, para position and condensation ring number) among aromatic hydrocarbon molecules although the reaction condition is milder, and has limited effect on constructing a highly linear molecular skeleton. In recent years, there have been attempts to introduce hydrogen-donating solvents (such as tetrahydronaphthalene) or specific extraction and separation steps to regulate the raw material composition or reaction environment (such as CN110629326B, CN119552674 a), but these methods mainly adjust the reactant ratio or remove part of the components from the physical level, and do not substantially interfere with the reaction path and bonding direction of aromatic hydrocarbon condensation. Therefore, the common dilemma of the prior art is that an effective means capable of actively guiding aromatic hydrocarbon molecules to conduct 'directional condensation' from the molecular reaction mechanism level is lacking, so that a linear and planar molecular framework is accurately constructed. This results in the prepared mesophase pitch being difficult to achieve a breakthrough improvement in molecular linearity, structural order and overall properties. The development of a novel preparation process capable of realizing molecular-level structura