Process for the preparation of isotropic pitch for coating and spinning

Abstract

The present application relates to a preparation method of isotropic pitch for coating and spinning, which uses ethylene tar, catalytic cracking slurry, medium-low temperature coal tar, bio-tar and other aromatic-rich heavy oil as raw material, carries out hydrogenation stabilization and isomerization modification on the raw material by adopting ebullated bed reaction form, obtains pre-polymerized pitch under the induced polymerization of oxygen-containing linear polymer in the ebullated bed hydrogenation tail oil, carries out oxidation cross-linking reaction under the action of plasma radiation, further improves the softening point and carbon residue value of the obtained isotropic pitch product, and inhibits the generation of mesophase optical structure, and the molecular weight distribution of the isotropic pitch product is relatively concentrated, which exhibits excellent coating performance and homogeneous melting and spinning performance.

Description

Technical Field

[0001] This invention relates to a method for preparing isotropic pitch for coating and spinning, belonging to the field of advanced novel carbon material preparation technology. Background Technology

[0002] Carbon fiber is an excellent lightweight material; however, its high cost and complex manufacturing process greatly limit its application in automobiles. Therefore, reducing the cost of carbon fiber is a top priority. Pitch-based carbon fiber, with its light weight, low density, strong corrosion and wear resistance, and high electrical and thermal conductivity, is widely used in ultra-high thermal conductivity materials, aerospace manufacturing, new building reinforcement materials, automotive component materials, sporting goods, and wind power generation. Considering the production cost and mechanical properties of carbon fiber, isotropic pitch-based carbon fiber is considered one of the most ideal candidate materials. However, obtaining cost-effective isotropic pitch-based carbon fiber with excellent mechanical properties remains a significant challenge.

[0003] The main commercially available lithium-ion battery anode materials are graphite-based (including natural graphite, artificial graphite, and MCMB). Other materials, such as soft carbon, hard carbon, silicon / carbon composites, and lithium titanate, are still in the experimental development stage and in small-scale pilot production. The raw materials for graphite-based anode materials mainly include natural graphite, petroleum coke, pitch coke, needle coke, and coated pitch. To overcome some structural defects inherent in graphite, it needs to be coated depending on the application, reducing its initial irreversible capacity and improving cycle performance. Generally, natural graphite-based anode materials require coating, and coated pitch has a considerable market.

[0004] Numerous attempts have been made in the prior art to prepare isotropic pitch with excellent properties. CN116288816A discloses a method for preparing isotropic pitch-based carbon fibers, including the following steps: treating ethylene tar under a nitrogen atmosphere, mixing it with steel coal tar pitch and dissolving it in benzene to obtain mixed pitch; adding nitrogen-bromosuccinimide and mechanically stirring under xenon lamp irradiation to obtain brominated mixed pitch; distilling to remove benzene from the mixed pitch, followed by treatment to obtain debrominated polymerized pitch; preparing pitch fibers using a melt spinning machine; and heating in a tube furnace first with oxygen and then nitrogen to obtain isotropic pitch-based carbon fibers. CN115466626A discloses a method for preparing high-quality isotropic pitch, which involves mixing brominated methylnaphthalene with coal tar pitch and performing a co-carbonization reaction. The co-carbonization method improves the reactivity of coal tar pitch, overcomes its inherent disadvantage in polymerization, improves the rheological properties of polymerized pitch, and further increases the degree of polymerization of the synthesized pitch. CN115558306A provides a method for preparing isotropic asphalt material, wherein a base material and a modified material are mixed and then subjected to high-temperature stirring treatment. The polymer chain structure in the modified material is grafted onto the aromatic molecular structure of the base material, thereby preventing the formation of large planar sheet structures and inhibiting the formation of anisotropic structural materials, thus obtaining an isotropic asphalt material. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for preparing isotropic pitch for coating and spinning. The method involves sequentially employing fluidized bed hydrogenation stabilization and isomerization modification, induced polymerization of oxygen-containing linear polymers, and plasma radiation oxidation crosslinking reaction. This further improves the softening point and carbon residue of the obtained isotropic pitch product and suppresses the formation of mesophase optical structures. The molecular weight distribution of the obtained isotropic pitch product is relatively concentrated, exhibiting excellent coating performance and homogeneous melt spinning performance.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] A method for preparing isotropic pitch for coating and spinning, using one or more of the following aromatic oils such as ethylene tar, catalytic cracking slurry oil, medium-low temperature coal tar, and bio-tar as raw materials, includes the following specific steps:

[0008] (1) The feedstock oil is hydrotreated and isomerized through a fluidized bed reaction mode to obtain hydrotreated tail oil;

[0009] The fluidized bed reaction uses a transition metal / silica-alumina zeolite-based catalyst, with a reaction temperature of 250-350℃, an initial hydrogen pressure of 1-8 MPa, and a reaction time of 0.5-4 h; the transition metal is selected from platinum, nickel, or molybdenum.

[0010] (2) Add oxygen-containing linear polymers to the hydrotreated tail oil to induce polymerization reaction and obtain prepolymerized asphalt;

[0011] The oxygen-containing linear polymer is phenolic resin or polyacrylic acid, and the addition amount is 1-10 wt% of the hydrogenated tail oil.

[0012] The induction polymerization reaction temperature is 150-350℃, and the reaction time is 1-2 hours;

[0013] (3) Prepolymerized asphalt undergoes homogeneous oxidative crosslinking reaction under the simultaneous action of oxidizing gas bubbling and plasma radiation to obtain isotropic asphalt for coating and spinning with a softening point of 220-280℃ and a carbon residue value of ≥70%.

[0014] The homogeneous oxidation crosslinking reaction temperature is 200-350℃, the plasma irradiation dose is 10-100kGy, and the reaction time is 1-10h;

[0015] Oxidizing gases include, but are not limited to, air, oxygen, and ozone / nitrogen mixtures, with a gas flow rate of 0.5-5.0 L / min. -1 ·kg -1 .

[0016] In this invention, step (1) uses a fluidized bed reaction to achieve hydrogenation stabilization and isomerization modification. During the reaction, the temperature inside the reactor is more uniform and the gas-liquid-solid three-phase mass transfer is more efficient, making it more suitable for heavy oil feedstock systems. Steps (2) and (3) are mutually matched and coupled reaction processes. The oxygen-containing linear polymer-induced polymerization reaction and the plasma radiation oxidation crosslinking reaction interact with each other to accelerate the reaction rate and reduce the reaction conditions.

[0017] At the induced polymerization temperature, oxygen-containing linear polymers undergo pyrolysis to generate a large number of small molecule free radicals. These free radicals induce the activation of aromatic molecules in the form of hydrogen abstraction. The activated aromatic molecules combine in the form of methylene "bridging" to obtain polycyclic aromatic macromolecules with high linearity, which significantly improves the flexibility of asphalt molecules and makes them exhibit high spinnability. At the same time, the free radicals generated by the cracking of oxygen-containing linear polymers also combine with asphalt product molecules, increasing the number of alkyl side chains around the aromatic core, which helps to improve the oxidation reactivity of isotropic asphalt and the wetting properties of coated asphalt.

[0018] In the plasma radiation oxidation crosslinking reaction, the bubbling oxidation of oxidizing gas transforms the linear methylene "bridged" structure of the activated aromatic molecule into a three-dimensional structure and increases the number of oxygen-containing functional groups on the alkyl side chains around the aromatic nucleus. In the plasma radiation reaction, the oxygen-containing functional groups on the alkyl side chains around the aromatic nucleus are removed, and a large number of free radicals are generated. The free radicals further combine with the asphalt product molecules to generate isotropic asphalt products of excellent quality.

[0019] The present invention also provides isotropic pitch obtained by the above preparation method, and the application of isotropic pitch in the preparation of coated pitch and spinning pitch. The pitch-based fiber precursor formed after spinning the isotropic pitch is pre-oxidized at 300°C, and the carbon fiber obtained by carbonizing at 1200°C for 2 hours after pre-oxidation has a tensile strength of 937-992 MPa.

[0020] Compared with the prior art, the beneficial effects of the present invention are:

[0021] (1) The raw materials involved in this invention are abundant and have a high degree of freedom; the design is reasonable, the production process is precise, the raw material processing depth is high, the equipment requirements are low, and it is easy to realize industrialization.

[0022] (2) The fluidized bed hydrogenation stabilization and isomerization modification-induced polymerization of oxygen-containing linear polymers-plasma radiation oxidation crosslinking reaction can suppress the formation of intermediate phase optical structure during oxidation. The molecular weight distribution of isotropic pitch products is relatively concentrated, and the softening point and carbon residue are improved, showing excellent coating performance and homogeneous melt spinning performance. Detailed Implementation

[0023] Example 1

[0024] 70 wt% ethylene tar and 30 wt% low-temperature coal tar were mixed as feedstock. Hydrogenation isomerization was performed at 300℃ using a platinum / silica-alumina zeolite-based catalyst, with an initial hydrogen pressure of 2 MPa and a reaction time of 4 h, yielding hydrotreated tail oil. 8 wt% phenolic resin was added to the hydrotreated tail oil, and induced polymerization was carried out at 310℃ for 2 h to obtain prepolymerized asphalt. The prepolymerized asphalt underwent homogeneous oxidative crosslinking under the simultaneous action of oxidizing gas bubbling and plasma radiation. The oxidative crosslinking reaction temperature was 330℃, the plasma irradiation dose was 80 kGy, and the reaction time was 4 h. Air was used as the oxidizing gas at a flow rate of 4.0 L·min⁻¹. -1 ·kg -1 An isotropic pitch for coating and spinning with a softening point of 258℃ and a carbon residue of 73% was obtained. The pitch-based fiber precursor formed after spinning was pre-oxidized at 300℃. After pre-oxidation, the carbon fiber obtained by carbonization at 1200℃ for 2 hours achieved a tensile strength of 937MPa.

[0025] Example 2

[0026] A mixture of 60 wt% catalytic cracking slurry, 20 wt% ethylene tar, and 20 wt% bio-tar was used as feedstock. Hydrogenation and isomerization were performed at 330℃ using a (nickel-molybdenum) / silica-alumina zeolite-based catalyst, with an initial hydrogen pressure of 6 MPa and a reaction time of 1 h, in a fluidized bed reaction mode to obtain hydrotreated tail oil. 6 wt% of polyacrylic acid was added to the hydrotreated tail oil, and induced polymerization was carried out at 200℃ for 2 h to obtain prepolymerized asphalt. The prepolymerized asphalt underwent homogeneous oxidative crosslinking under the simultaneous action of oxidizing gas bubbling and plasma radiation. The oxidative crosslinking reaction temperature was 270℃, the plasma irradiation dose was 60 kGy, and the reaction time was 8 h. Oxygen was used as the oxidizing gas at a flow rate of 3.0 L·min⁻¹. -1 ·kg -1 An isotropic pitch for coating and spinning with a softening point of 271℃ and a carbon residue of 78% was obtained. The pitch-based fiber precursor formed after spinning was pre-oxidized at 300℃. After pre-oxidation, the carbon fiber obtained by carbonization at 1200℃ for 2 hours achieved a tensile strength of 992MPa.

Claims

1. A method for preparing isotropic pitch for coating and spinning, using aromatic oil as raw material, wherein the aromatic oil is selected from one or more of ethylene tar, catalytic cracking slurry oil, medium-low temperature coal tar, or bio-tar, characterized in that, Includes the following steps: (1) The feedstock oil is hydrogenated and isomerized through a fluidized bed reaction mode to obtain hydrogenated tail oil; the fluidized bed reaction uses a transition metal / silica-alumina zeolite-based catalyst, the reaction temperature is 250-350℃, the initial hydrogen pressure is 1-8MPa, the reaction time is 0.5-4h, and the transition metal is selected from platinum, nickel or molybdenum. (2) Add oxygen-containing linear polymer to hydrotreated tail oil to induce polymerization reaction to obtain prepolymerized asphalt; the oxygen-containing linear polymer is phenolic resin or polyacrylic acid, the amount of oxygen-containing linear polymer added is 1-10 wt% of the mass of hydrotreated tail oil, the induction polymerization reaction temperature is 150-350℃, and the reaction time is 1-2h. (3) The prepolymerized asphalt undergoes a homogeneous oxidative crosslinking reaction under the simultaneous action of oxidizing gas bubbling and plasma radiation to obtain isotropic asphalt for coating and spinning with a softening point of 220-280℃ and a carbon residue value ≥70%; the temperature of the homogeneous oxidative crosslinking reaction is 200-350℃, the reaction time is 1-10h, and the plasma irradiation dose is 10-100kGy; the oxidizing gas is selected from air, oxygen, and ozone / nitrogen mixture, and the gas flow rate is 0.5-5.0 L·min -1 ·kg -1 .

2. The isotropic pitch for coating and spinning obtained by the preparation method of claim 1.

3. The isotropic pitch for coating and spinning according to claim 2, characterized in that, The pitch-based fiber precursor formed by isotropic pitch spinning is pre-oxidized at 300℃, and carbonized at 1200℃ for 2 h after pre-oxidation to obtain carbon fibers with a tensile strength of 937-992 MPa.