RU2571152C2 - Radiation-thermal production of binder-pitch for fabrication of electrodes - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention may be used in production of electrodes. Proposed process comprises heating of coal-tar pitch to over 150°C. Produced flow of liquid coal-tar pitch is subjected to irradiation with electron beam with radiation dose of 10-150 kGy.

EFFECT: increased content of α-fraction in pitch by 6-12%, higher amount of coke residue by 6-10%, higher density and longer life of graphite electrodes.

2 cl, 1 tbl, 1 ex

Description

The invention relates to the field in the coke industry, in particular to methods for producing pitch used as a binder in the preparation of graphite products and anode mass.

Coal-medium or high-temperature pitch is used in the coke industry, mainly as a binder in the manufacture of electrodes. It is also possible to use pitch from heavy fractions of oil distillation (oil pitch).

In the manufacture of carbon or graphite products, the feedstock is a highly porous material (coking coal powder), therefore, the manufacturing process of graphite electrodes requires impregnation of the feedstock with pitch-binder, which reduces porosity and increases the strength of the final product (electrode for metallurgy). Pitch is often obtained from derivatives of coal, for example, from coal tar. Peck is a mixture of various substances, mainly hydrocarbons with a molecular weight in the range from 300 to 5000 au

Coal tar pitch can be conditionally divided into fractions according to the solubility of hydrocarbons in various organic solvents: a fraction soluble in heptane, a fraction insoluble in heptane / soluble in toluene (asphaltenes), and a fraction insoluble in toluene (asphaltenes) [1]. In addition, in the analysis of pitch, a fraction of hydrocarbons insoluble in quinoline is isolated.

The industry requirements for pitch-binder are reflected in the current Russian standard for pitch for electrode mixture, presented in Table 1 [2]. The currently existing industry method for producing medium-temperature coal tar pitch by a single evaporation of coal tar preheated in an oven to 380-420 ° C practically does not allow to control the content of α- and α1-fractions in the pitch, therefore these parameters of the pitch are almost completely determined by the properties feed pitch for pitch.

According to GOST 10200-83, “Coal tar pitch. Technical conditions ”[2], important parameters of the pitch composition are the fraction of the α fraction (pitch residue insoluble in toluene) and the fraction of the α1 fraction (pitch residue insoluble in quinoline). Depending on the fraction fraction α, GOST determines the class of finished pitch and its value for industrial applications.

Data on the characteristics of pitch of various grades according to GOST 10200-83 are shown in Table 1. From the GOST table it can be seen that a high proportion of alpha fraction in the pitch is a mandatory characteristic of raw materials for the production of standard graphite electrodes. It is also desirable to have a moderate yield of volatile substances, below 60% (vol.%).

In addition, the characteristic of the pitch binder for the electrodes is the coke number (or coconut residue). The procedure for determining the yield of volatile substances (V%) for pitch is determined by the standard GOST 9951-73 [3]. The procedure is described as pitch sublimation at a temperature of 850 ° C and actually sets the amount of coke residue in the pitch.

As can be seen from the standard data, it remains important for the electrode industry to develop a method for additional processing of coal tar pitch, which allows to increase the content of α-fraction and increase the coke residue to improve the properties of the pitch-binder. In the context of this invention, the fraction of the α-fraction in the starting and modified pitch is determined according to GOST 28357-89 [10], and the proportion of the α1-fraction is determined according to GOST 28572-89.

Further in this text, the term pitch-binder (also “modified pitch” or “binder picth”) means a pitch with a higher coke number than the original pitch. As a result of this modification of the pitch, upon annealing the mixture of graphite mass with the pitch binder with a high coconut number, the porosity of the final graphite electrode decreases (porosity is associated with the presence of the gas phase in the graphitized material). In other words, improving the quality of the pitch binder leads to an increase in the density and strength of the final electrode product.

Typically, known methods for preparing pitch with binder properties include multi-stage heat treatment at high temperatures or adding additional components in the form of hydrocarbon resins.

According to the method disclosed in GB 1249569, resin fractions boiling at 210-230 ° C or 230-290 ° C in a 2: 1 ratio are added to the medium-temperature coal tar pitch to obtain a pitch binder, and then the pitch-resin mixture is heated to 350- 450 ° C for 6-8 hours (Treatment of coal tar pitch, GB1249569, class C10C 01/19, publ. 1971-10-13). At the same time, from medium-temperature pitch with a softening temperature of 60 ° C and with an initial content of the α-fraction of 21% and the content of the α1-fraction of 6%, improved peaks with a softening temperature of 93-104 ° C are obtained; in the pitch-binder, the content of the α-fraction is 30-36% and the content of the α1-fraction is 15%. That is, the proportion of both insoluble fractions increases, and an increase in the softening temperature of the modified pitch is observed. The disadvantage of this method is the need to add a fraction of coal tar and the duration of the sublimation process.

In addition to the use of coal tar pitch (medium or high temperature pitch) as a feedstock, recently the issues of using petrochemical production residues to obtain a pitch-binder that meets the requirements of electrode production have been studied. In the dissertation [3], the mechanism of obtaining pitch-binder from tar was studied. The aim of [3] was to investigate the process of obtaining an analogue of pitch-binder in the form of an oil sintering additive (NDS) by the method of thermal polycondensation of tar. As a result, a variant of the technological scheme of the process of obtaining oil sintering additive was proposed. Data were obtained on the composition of the α-fraction of the pitch, satisfying the standard GOST 10200-83 [2]. Thus, the heavy residues of the petrochemical industry can be converted to a pitch binder. This creates certain price advantages: prices on the coal tar pitch market strongly depend on the industry's demand for coke, and price fluctuations for heavy oil products (tar, pitch) can differ in a favorable direction.

The standard GOST 10200-83 sets the limit on the alpha1 fraction. Also, the procedure for determining this fraction (quinoline insoluble component - QI) in the pitch is described in foreign standards ASTM Standard D4746 or ASTM Standard D2318. And the fraction of a substance insoluble in toluene (TI - Toluene Insolubles) is determined by the method of ASTM Standard D4072 (or D4312).

Upon receipt of coal tar pitch from coal tar, solid particles consisting of pyrolytic carbon, coal and ash get into the final product (pitch). These particles form an alpha1 fraction (a fraction insoluble in quinoline) and enter the pitch upon distillation of the resins. These particles reduce the quality of the pitch binder. Some technologies for producing graphite electrodes with high conductivity and strength require a very low alpha1 fraction in the pitch binder. (These impurities should not be confused with mesophase pitch, which is also insoluble in quinoline). A moderate amount of the α1 fraction (up to 10%) is acceptable for most technologies for producing graphite electrodes.

For most samples of coal tar pitch, the coke number (carbon yield after annealing the pitch without air) is 40-50%. It is also desirable to increase the coke number of the pitch binder. Thus, US Pat. No. 6,827,841 describes petroleum pitch with a softening point of 118 to 124 ° C. and a coke number of about 50%.

In patent application US 20090288983 A1 describes a method for producing a pitch binder with a low alpha1 fraction and a high coke number, which involves heating creosote oil (high boiling coal tar distillate) with a boiling point of at least 270 ° C to produce pitch impregnation (pitch binder) with the following parameters: coke number is more than 55%, the softening temperature of the pitch is in the range of 90-140 ° C, and the fraction of the α1 fraction is less than 0.5%. The disadvantage of this method is the complexity of the process, the use of toxic creosote oil and high heat consumption.

A known method for producing high-quality pitch-binder from a conventional coal tar (a pitch-binder with an extremely low content of quinoline insoluble fraction is obtained.) The publication [5] describes a method for mixing coal tar with heavy creosote oil (in a 1: 1 ratio) with further precipitation particles insoluble in quinoline. Precipitation is carried out for a liquid resin-oil mixture at 90-100 ° C and decantation of the feed is carried out (particles of the α1 fraction remain in the sediment). Next, the decanted fraction is heated at a temperature of about 360 ° C without oxygen, and the polymerization of the hydrocarbon mixture results in a pitch binder with a very low admixture of quinoline insoluble substances (<0.1%). The disadvantage of this method is the duration of the procedure (2 days) and the need to use creosote oil.

A significant part of the processing of hydrocarbon raw materials to obtain pitch-binder (raw materials in the form of coal tar pitch or heavy fractions of oil distillation) is reduced to a prolonged temperature exposure without oxygen or distillation under reduced pressure.

However, methods of radiation-chemical treatment of hydrocarbons are also known in petrochemistry. When irradiated with X-rays or a beam of fast electrons in liquid hydrocarbons, chain reactions with the participation of active radicals are triggered; these reactions not only reduce the molecular average of all hydrocarbons (a process is called radiation cracking), but irradiation leads to the cleavage of radiation-unstable bonds in large hydrocarbon molecules.

For example, the radiation thermal cracking (RTK) of heavy oil was described in [6].

In [7, 8], a method was described for producing lighter fractions by irradiating asphaltene oil products (atmospheric distillation residue) with a fast electron beam (energy 1.3 MeV) with a total radiation dose of 10 kilograms (1 Gray is a unit of absorbed radiation energy equal to 1 J / kg). During radiation-thermal treatment of asphaltene oil products (as compared to thermal cracking), a decrease in the viscosity of the final oil product and a broadening of the spectrum of hydrocarbons identified by high-temperature gas chromatography are observed. However, this work does not disclose the effects of radiation on large aromatic aggregates (which make up more than 20% of heavy asphaltene oil product). Thus, this work does not answer the question of how exactly the radiation dose will affect the yield of polyaromatic components in heavy petroleum products or how to increase the fraction of the α-fraction (insoluble hydrocarbons in toluene) to a level of more than 20%.

Although in general radiation-chemical processes in liquid PAHs are complex and multi-stage reactions, it is important within the framework of this invention that fast electrons from a beam upon ionization of a liquid medium initiate self-sustaining chemical reactions involving radicals and radical ions. These reactions include the separation of alkene groups from polyaromatic molecules and also the process of synthesizing polyaromatic hydrocarbons into higher molecular weight compounds. In this case, the volatile components obtained during such radiolysis gradually leave the irradiated hydrocarbon product.

As you know, coal tar pitch and coal tar have a high content of polyaromatic hydrocarbons. Therefore, the inventors expect changes in the properties of the pitch when this complex mixture of hydrocarbons is irradiated with a beam of fast electrons.

A known method of producing pitch for electrode materials described in patent RU 2119522 (published September 27, 1998, IPC C10C 3/04). This method involves treating medium-temperature coal tar pitch with a mixture of coal tar fractions with air at an elevated temperature, the proportion of coal tar added being less than 10%, and the initial mixture after mixing is treated with air at a temperature of 280-350 ° C. It is known that the rate of thermal reactions in the pitch can be significantly increased by heat treatment in the presence of atmospheric oxygen. According to this method, by oxygen-heat treatment it is possible to increase the rate of formation of the α-fraction in the pitch, but at the same time, the rate of formation of the α1-fraction almost does not increase. The disadvantage of this method is the need to add a resin with an uncontrolled composition and the removal into the atmosphere of the products of oxidation of aromatic hydrocarbons (carcinogens).

The closest prototype of the present invention can be considered the method described in patent RU 2288938 C1, according to which a pitch binder for electrode materials is obtained by treating a mixture of coal tar pitch and its mixture with coal tar fractions with an air stream, the liquid mixture being treated with air (temperature 200 ° C) in the field of shock-cavitation pulses (in shock-cavitation emulsifier). As a result, the coconut number of the modified pitch increases, and the softening temperature of the modified pitch also increases and the volatile content decreases. The disadvantage of this method is the necessity of using a cavitation emulsifier having rapid wear and the release of toxic volatile components into the air.

The technical problem of the invention is the conversion of coal tar pitch to a pitch binder having a mass fraction of the α fraction above 25%.

The technical problem is solved due to the fact that in the method for producing pitch, the initial coal pitch is treated with radiation at a temperature above the softening temperature of the pitch, preferably at a temperature above 180 ° C. At lower temperatures, the increased viscosity of liquid pitch creates technological difficulties in pumping.

The technical result of the invention is to simplify the procedure for obtaining a modified pitch and increase the coke residue in the pitch.

Another technical result is the improvement of the mechanical properties of graphitized electrodes (in particular, increased density) with the addition of a modified pitch that has undergone radiation-heat treatment and increased electrode life.

The feedstock for the production of modified pitch is medium or high temperature coal tar pitch.

As one of the characteristics, pitch has a softening point. The softening temperature is determined according to the procedure in the standard GOST 9950-83 [9].

For radiation-thermal effects on a fluid pitch (at a temperature above the softening temperature of the pitch), a distributed beam of fast electrons is used, which is obtained at the output of an electron accelerator. Moreover, the electron energy exceeds the energy of 1 MeV. There are several series of industrial electron accelerators that satisfy this requirement. For example, the desired level of beam power and energy is provided at the ILU-6 electron accelerator (manufactured by the Institute of Nuclear Physics SB RAS, Russia). The high energy of the electron beam ensures that radiation deceleration to thermal electrons is carried out at a thickness of the hydrocarbon layer with a scale of more than 10 mm (effective thickness of the irradiation channel). In addition, industrial accelerators have the ability to deliver a distributed electron beam (to uniformly irradiate the flow of matter).

A method of obtaining a pitch binder is as follows. The starting pitch is heated to a temperature above the softening point of the pitch, preferably to a temperature in the range of 180-250 ° C., at which the pitch has a low viscosity and sufficient fluidity. The pitch in a fluid state is fed into the irradiation channel connected to the output of the electron accelerator. In this case, the beam power and the feed rate of the liquid pitch are selected so that the total radiation dose for the liquid material passing through the irradiation channel is in the range from 10 to 50 kg.

The channel for irradiating a liquid material has a height of up to 30 mm and a width close to the width of the outgoing beam of fast electrons. Uniform irradiation of liquid pitch across the entire width of the irradiation channel initiates radiation-chemical reactions that change the initial composition of the pitch towards GOST according to the pitch-binder (this effect increases the fraction of the α-fraction and the coke residue in the irradiated pitch). Next, the radiation-irradiated liquid pitch enters the liquid pitch accumulation chamber, where the temperature of the pitch is maintained near the temperature recommended for the pitch-binder in existing technologies for the production of graphite electrodes.

It is important to note that the described method for producing pitch-binder is embedded in existing technologies for the production of graphite materials, which confirms the industrial applicability of this method.

Example

Coal tar pitch was transferred to a liquid state at temperatures of 150 ° C, 180 ° C, 220 ° C (temperatures above the softening point of coal tar pitch) and pumped through the irradiation channel in order to irradiate the electron stream from the ILU-6 electron accelerator. In this case, the dose dose of liquid pitch was in the range of 10-150 kg.

The fraction of the α fraction in the modified (irradiated) pitch was 6–12% higher than the fraction of the fraction in the initial pitch. Higher temperatures of radiation-thermal treatment of liquid-flowing pitch led to accelerated pitch modification. The coke residue of the pitch after radiation-thermal treatment is increased by 6-10%.

Information sources

1. F. Karasa et al., Molecular mass range of coal tar pitches fractions by mass spectrometry and size-exclusion chromatography, Rapid Communications in Mass Spectrometry, 2009, Vol.23, P.2087-2098.

2. GOST 10200-83. TU Peck coal-electrode. Technical conditions

3. GOST 9951-73. The pitch is coal. Method for determining the yield of volatile substances.

4. Morozov AN, Investigation of the process of thermal polycondensation of tar in order to obtain an oil sintering additive, the dissertation, Ph.D., Ufa, 2007.

5. K. Karthik, et al., Technology for the production of Zero Q. I pitch from coal tar, AIP Conference Proceedings, 1538, P.104-108 (2013);

6. R.F. Zaikina et al., Radiation-thermal processing of high-viscous oil from Karazazhanbas field, Rad. Phys. Chem, 60 (2001), p. 211-221.

7. R.F. Zaikina et al., Specific approach to radiation processing of Mgh-sulfuric oil, Rad. Phys. Chem 71 (2004), p. 467-470.

8. SPE 153528, Utilization of charged particles as an efficient way to improve rheological properties of heavy asphaltic petroleum fluids, 2012

9. GOST 9950-83. The pitch is coal. Methods for determining the softening temperature.

10. GOST 28357-89 Accelerated method for determining the mass fraction of substances insoluble in toluene.

Claims (2)

1. A method of obtaining a pitch-binder for electrode materials, comprising heating coal tar pitch to a temperature above 150 ° C, characterized in that the flow of liquid coal tar pitch is irradiated with an electron beam with an irradiation dose in the range from 10 to 150 kGy. 2. The method according to p. 1, characterized in that the flow of liquid coal tar pitch is irradiated with an electron beam at a temperature of coal tar pitch in the range from 150 ° C to 250 ° C.