JPS6346800B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to premium coke suitable for use in the production of graphite electrodes. More particularly, it relates to a method for producing high grade coke from a mixture of pyrolysis tar and hydrotreated decant oil. High grade coke is well known in the art and is commercial quality coke with an acicular anisotropic microstructure. High-grade coke is used to produce graphite for electrodes. The use of this high grade coke creates various requirements for production from coke. Some of these requirements are pointed out here. Graphite electrodes used for arc melting of steel etc.
Since severe thermal shock occurs in such processes, it is necessary to have a low coefficient of thermal expansion (CTE) value.
The high-grade coke used to produce graphite electrodes must be capable of imparting a low CTE to the electrodes. The method for producing graphite electrodes from high-grade coke involves heating the electrodes at temperatures within the range of about 2000°C to about 3000°C to provide energy to convert the carbon in the coke to the crystalline graphite form and to volatilize impurities. It is necessary to heat it to When a carbon mass made from high-grade coke is heated to a temperature within the range of about 1000°C to about 2000°C, various sulfur-containing compounds present in the coke decompose, resulting in rapid decomposition of the carbon mass. Reversible expansion occurs. This phenomenon is called "puffing". It is desirable to use low sulfur containing precursors to produce high grade coke in order to minimize or preferably eliminate problems due to "puffing". Typically, commercially produced high-grade coke consists of decant oil from catalytic cracking, as well as low sulfur-containing, aromatic, and low-reactivity tars obtained by pyrolysis of decant oil and gas oil. Manufactured from raw materials. The use of pyrolysis tar as a feedstock for producing high grade coke is desirable because pyrolysis tar is a relatively inexpensive mixture of aromatic compounds and has a low sulfur content. Generally, pyrolysis tar is a heavy byproduct of the cracking process that produces ethylene. It is known that pyrolysis tar is not suitable for commercial production of high grade coke. The reason for this is that the production is carried out by a delayed coking process and highly reactive pyrolysis tars are coked into the coils of the delayed coking furnace. Another disadvantage of pyrolysis tars is that the high grade coke produced from these tars has an undesirable increase in the coefficient of thermal expansion (CTE) of the graphite electrodes. Traditional methods of producing high grade coke from pyrolysis tar suffer from poor economics and/or relatively high values of the coefficient of thermal expansion (CTE). In U.S. Pat. No. 3,817,853, pyrolysis tar is hydrotreated in the presence of an inert diluent to produce approximately
We have obtained raw materials for producing graphite electrodes with a coefficient of thermal expansion of 1.6×10 ^-6 and above. Although this is an improvement, high quality graphite electrodes have approximately
Coefficient of thermal expansion (CTE) of 0.5× ^10-6 or less
is necessary. The examples in the above patent also indicate the use of about 12.2 to about 18.7 standard cubic meters of hydrogen per barrel of pyrolysis tar. This is a relatively expensive method. U.S. Pat. No. 4,213,846 cokes pyrolysis tar, petroleum residue, and pyrolysis tar with a hydrogen donor diluent produced by catalytic hydrotreatment of a coked gas oil fraction produced by delayed coking of a mixture. Hydrogen treatment is carried out by oxidation. Hydrotreated feedstock is a mixture equivalent to fresh feedstock. This process has several drawbacks. The hydrotreated coked gas oil does not contribute to the yield of the process and the examples show up to 15% by weight of pyrolysis tar. The present invention overcomes the shortcomings of the prior art and provides a commercial method for producing high grade coke suitable for producing high quality graphite electrodes. In its broadest embodiment, the invention provides a
A method of producing high grade coke for producing graphite electrodes having a coefficient of thermal expansion (CTE) of less than about 0.5 x 10 ^-6 per cent. The method forms a mixture of hydrotreated decant oil and pyrolysis tar comprising about 50 to about 75% by weight pyrolysis tar and about 50 to about 25% by weight hydrotreated decant oil; The process consists of coking the mixture by tail coking to form high grade coke. In a preferred embodiment, the decant oil contains about 2 to about 4 molecules per average molecule of decant oil.
A hydrotreated decant oil is produced by hydrotreating the oil until about 2 to about 3 hydrogen atoms have been added, more preferably from about 2 to about 3 hydrogen atoms. Another preferred embodiment of the invention is a graphite electrode made from the high grade coke of the invention. Further embodiments and advantages of the invention are described in, and will be apparent from, the following specification. Pyrolysis tars used herein and according to the prior art generally range from about 760°C to about 760°C in the presence of water vapor.
temperature of 930℃, and about 100KPa to about 200KPa (15
It is the heaviest byproduct of the production of olefins by gas phase cracking of liquid hydrocarbons at pressures of ~30 psi). This tar is a distillate that boils at temperatures above about 200°C. The decant oils used here and according to the prior art are generally the highest boiling by-products of gasoline production by catalytic cracking after removal of catalyst particles by settling. This oil is generally about
Boils at temperatures above 300°C. Preferably, the pyrolysis tar used in this invention should have a sulfur content of less than about 1% by weight, and the decant oil used in this invention should have a sulfur content of less than about 2% by weight. It is necessary. Hydrotreating the decant oil has the concomitant advantage that the decant oil is hydrodesulphurized. Therefore, the potential problem of puffing is reduced or eliminated even without hydrogen treatment for this purpose. Generally, hydrotreating of decant oil can be carried out by conventional techniques of contacting the decant oil with hydrogen at high temperature and pressure in the presence of a suitable catalyst. For a fuller understanding of the features and objects of the invention, reference should be made to the following detailed description in conjunction with the accompanying drawings. Non-limiting examples of the invention are detailed below. Many other examples will readily occur in light of the guiding principles and teachings contained in this invention. The examples presented herein are illustrative of the invention and are not in any way limiting to the manner in which the invention may be practiced. Parts and percentages mentioned herein and throughout this specification are by weight, unless otherwise specified. Example 1 Gas oil based pyrolysis tar A having the properties shown in Table 1 was mixed with hydrotreated decant oil A having the properties shown in Table 2. Three mixtures were prepared in which the amount of pyrolysis tar A was 25%, 50%, and 75% (wt%). Table 1 Pyrolysis tar A specific gravity, 15.6℃ (60〓) ......1.1238 Distillation Initial boiling point 230℃ 5% 280℃ 10% 290℃ 20% 320% 30% 336% 40% 364% 50% 390% 60% 450% 70% 80% 90% 95% Final Point % Recovery 67.5 Molecular Weight 319 Carbon, wt% 91.7 Hydrogen, wt% 6.78 Nitrogen, wt% 0.21 Ash, wt% 0.0018 Metals, ppm Sulfur, wt% 1.20 Modified Conradson Carbon, Weight% 23.1 Aromaticity, weight% Proton NMR 40.09 13C NMR 80.6 Pour point 19℃ Flash point 127℃ Bromine number 15.44 Viscosity, centistokes 38℃ (100〓) 4079 99℃ (210〓) 206 TGA Pitzchi fraction (550 ℃±) 29.6% by weight Toluene insolubles, % by weight 4.6 Insolubles in heptane, % by weight 21.1 Table 2 Hydrogen-treated decant oil A specific gravity ……1.0187 Distillation Initial boiling point 229℃ 5% 290 10% 318 20% 346 30% 363 40% 377 50% 389 60% 404 70% 424 80% 449 90% 502 95% − Final point recovery % 90% Molecular weight Carbon, wt% 90.59 Hydrogen, wt% 9.29 Nitrogen, wt% 0.13 Sulfur, wt % 0.37 Modified Conradson carbon, weight % 2.63 Aromaticity, proton NMR 20.5 13 _{C NMR} 57.6 Pour point -13°C Flash point (open cup) 138°C Bromine number 6.47 Viscosity, centistokes 38°C (100〓) 69.42 99°C ( 210〓) 5.65 TGA Pitch fraction (550℃+) 48.7 Toluene insolubles, weight% 0.20 Heptane insolubles, weight% 0.01 Average number of hydrogen atoms per molecule 3 The bench-scale delayed coking unit shown in Figure 1 Each of the mixtures, as well as pyrolysis tar A and hydrotreated decant oil A, were coked separately using The caulking unit of FIG. 1 is operated as follows. Approximately 1 minute per minute of raw material liquid 1 in tank 2
It is fed through line 3 by pump 4 at a rate of 17 to about 24 g. The raw material liquid 1 in the pipe 3 is transferred to the heating and pressurizing coil 6 which is maintained at a high pressure by the pressure unit 7. The material in the coil 6 communicates through a pipe 8 to the top of a heated and pressurized tank 9. The temperature of coil 6 and tank 9 is approximately 475℃,
and the pressure was about 689 KPa. The feeding time was about 140 to about 170 minutes. After the feed was completed, the coke was further devolatilized by heating to about 500°C at a rate of about 50°C per hour and holding at this temperature for about 75 to about 90 minutes. A pressure control valve 11 is provided to remove distillate and coking gas. Further heating was performed for each mixture at approximately 1000°C. The yields of these examples are shown in Table 3. The values shown in Table 3 are based on measurements and deviate slightly from the sum of the components equal to 100%.

Table 3 shows that the yield of distillate and cracking gas decreased as the amount of pyrolysis tar increased. The coke from each of the trials was used to manufacture graphite electrodes by conventional testing processes. The manufacturing process is generally as follows. 55% ± 10% of coke baked at 1000℃
A powder was obtained by crushing and grinding until it passed through a 200 mesh sieve. Approximately 130 mm in length and 19 in diameter from this powder
I made a mm rod. This rod was then converted into a graphite electrode. Typically, the graphitization temperature is within the range of about 2800<0>C to about 3000<0>C. The coefficient of thermal expansion (CTE) in the longitudinal direction of each rod is
Measurements were made in the temperature range of 30°C to 100°C. here,
Only the longitudinal coefficient of thermal expansion (CTE) should be looked at. Table 4 shows the coefficient of thermal expansion (CTE) values for bars made from various mixtures. FIG. 2 illustrates how the CTE of a bar is affected by the pyrolysis tar percentage in the feed mixture.

[Table] Surprisingly, a graphite electrode having an excellent coefficient of thermal expansion can be obtained with about 50% of pyrolysis tar A in the mixture. Pyrolysis tar A and hydrogen treated decant oil A
The CTE of a bar made from a 50:50 mixture of
As is clear from Figure 2, the temperature is 0.24×10 ^-6 /°C lower than the law of mixing dictates. The hydrotreated decant oil modifies the pyrolysis tar, allowing good continuous tailed coking and giving excellent values of the coefficient of thermal expansion for a high proportion of pyrolysis tar. The amount of hydrogen treatment imparted to the decanted oil will have an effect on the process. If the decant oil is saturated, it will not act as a donor. The lower limit for hydrotreating the decanted oil for various mixtures can be determined experimentally. Example 1 shows that high coke yields can be obtained for relatively low amounts of hydrogen. It is also economically advantageous to hydrotreat decant oil rather than pyrolysis tar. Example 2 The tests carried out in Example 1 were carried out using the hydrotreated decant oil A of Example 1 and the pyrolysis tar B, which was primarily kerosene based and had the properties shown in Table 5. Table 5 Pyrolysis tar B specific gravity 1.0835 ASTM distillation Initial boiling point 171℃ 5% 238 10% 249 20% 268 30% 288 40% 321 50% 371 60% 410 70% 441 80% - 90% - 95% 0 Recovery rate % 70% Molecular Weight 398 Carbon, wt% 90.97 Hydrogen, wt% 7.62 Nitrogen, wt% 0.66 Ash, wt% 0.01 Metals, ppm 0.1 Sulfur, wt% 0.50 Modified Conradson Carbon, wt% 16 Aromaticity, Proton NMR 42.9 13 _{C NMR} - Pour point 3℃ Flash point (open cup) 77℃ Bromine number 17.98 Viscosity, centitalk 38℃ (100〓) 1154 99℃ (210〓) 27 TGA Pitzchi fraction (550℃±) 30.1 Toluene insoluble matter, weight % 0.1 Heptane insolubles, wt% 19.2 Table 6 shows the yields for various mixtures and Table 7 shows the values of the longitudinal coefficient of thermal expansion (CTE) measured for graphite electrodes made from the mixtures. There is. The measured coefficients of thermal expansion (CTE) of graphite electrodes prepared from mixtures with 50% and 75% pyrolysis tar are lower than those calculated for binary mixtures and higher than 0.1 × 10 ^-6 / °C. , this is clear from Figure 3.

【table】

[Table] Example 3 When hydrotreated decant oil A of Example 1 and pyrolysis tar B of Example 2 are mixed and the pyrolysis tar content is 0%, 50%, 75%, and 100% We conducted tests on A pilot plant delayed coking unit as shown in FIG. 4 was used. The operation of this pilot plant delayed coking unit is as follows. A raw material mixture to be coked is supplied from a raw material tank 12. A pump 13 sends the mixture from the raw material tank 12 through a pipe 14 to a preheater 16 and then to a delayed coking machine 17.
Distillate and cracking gas from coking unit 17 reach fractionator 19 through line 18 .
Heavy products suitable for recirculation are sent to pump 16.
Light products from the fractionator 19 pass through a pipe 23 to a quench cooler 24 where they are cooled. The light products in the quencher 24, which are suitable for recirculation, are sent by pump 22 via line 26 to the preheater 16. Light products in the quench cooler 24 that are not suitable for recirculation are removed from line 27. The gas in the fractionator 19 is removed from the pipe 28. Table 8 shows some of the delayed coking unit pilot plant operating parameters. Maintain a pressure of about 275K Pa, keep the production ratio as close to 2.0 as possible, and keep the furnace temperature between about 470℃ and approx.
It was within the range of 500℃. Higher temperatures were used for less reactive feedstocks and lower temperatures were used for more reactive feedstocks.

Table: For higher proportions of pyrolysis tar B in the mixture, the coke yield increased and the distillate yield decreased. The coke yield for 100% pyrolysis tar B was higher than expected from other results. The reason for this is that the production rate for this test was significantly higher than the production rate used for the other tests. Graphite electrodes were manufactured from coke baked at 1000° C. in the same manner as in Example 1, and the coefficient of thermal expansion (CTE) of each electrode was measured. The measured values are shown in Table 9 and FIG. 5. The CTE of coke made from mixtures containing 50-75% pyrolysis tar is 0.3-0.4 x 10 ^-6 /°C lower than expected from the law of mixtures.
These results indicate that good high grade coke is made from a mixture containing 75% pyrolysis tar, a result that would not be expected based on the proportional contributions by the two feedstock components. The coking tests in this example demonstrate other benefits of coking a pyrolysis tar/hydrotreated decant oil mixture. Coking is carried out at 40 Psig in pure pyrolysis tar where the reactivity of the feedstock causes the coking coils and furnace inlet tubes to become clogged. Mixing the hydrotreated decant oil with pyrolysis tar eliminated this tendency to block the coil and inlet tube.

EXAMPLE 4 A mixture was prepared from a hydrotreated decant oil B having the properties shown in Table 10 and a naphtha-based pyrolysis tar C having the materials shown in Table 11. Coking was carried out as described in Example 1.
The coking yields, distillates, and cracking gases from various mixtures are shown in Table 12. Graphite electrodes for testing were prepared from 1000℃ calcined coke. Table 13
The results shown in Figure 6 indicate that the CTE of coke made from the mixture is 0.2 to 0.5 × 10 ^-6 /℃ lower than that indicated by the law of mixtures, and this is a considerable synergistic effect due to the mixture. It represents. Table 10 Hydrogenated Decant Oil B Specific Gravity 1.04 Molecular Weight 309 Carbon, wt% 89.0 Hydrogen, wt% 8.7 Sulfur, wt% 0.79 Modified Conradson Carbon, wt% 1.8 Aromaticity, Proton NMR% 25 Oxygen, wt% 0.5 Average Added hydrogen per molecule 2.5 Table 11 Pyrolysis tar C specific gravity 1.08 Carbon, wt% 91.0 Hydrogen, wt% 7.5 Ash, wt% 0.002 Sulfur, wt% 0.1 Modified Conradson carbon, wt% 12 Aromaticity, proton NMR% 52.4 Toluene insolubles% 0.1 Heptane insolubles% 0.1

【table】

[Table] Example 5 Pyrolysis tar D having the properties shown in Table 14 and hydrotreated decant oil A were mixed together and coked in a pilot plant of a delayed coking unit. 0% pyrolysis tar, 50
%, 75% and 100% were used. Table 14 Pyrolysis tar D specific gravity 1.1313 Distillation Initial boiling point - 5% 160℃ 20% 172 30% 191 40% 207 50% 232 60% 268 70% - 80% - 90% - 95% - Final point - Recovery rate ,% 55.0 Carbon, wt% 93.1 Hydrogen, wt% 6.8 Nitrogen, wt% 0.0 Ash, wt% 0.02 Metals, ppm 0.1 Sulfur, wt% 0.22 Modified Conradson Carbon, wt% 25.1 Aromaticity, proton NMR 48.3 13 _{C NMR} 84.3 Pour point 14℃ Flash point (open cup) 146℃ Bromine number 12.88 Viscosity, centistokes 38℃ 14456 99℃ 80 TGA Pitch fraction (550℃+) 40.6 Toluene insolubles, wt% 4.1 Heptane insolubles, wt% 22.8 days Some of the pilot operating parameters for the laid coking unit are shown in Table 15. The coking yield increased as the proportion of pyrolysis tar increased.

[Table] Graphite electrodes for testing were manufactured. The measured values of the coefficient of thermal expansion are shown in Table 16 and FIG. The CTE of coke made from a mixture containing 50 to 75% by weight of pyrolysis tar is 0.1 to 0.1 lower than that indicated by the law of mixtures.
0.2×10 ^-7 /℃ lower, and it represents the quality of high grade coke.

EXAMPLE 6 A mixture of pyrolysis tar D and decant oil C having the properties shown in Table 17 was prepared to show the results of the mixture not according to the invention. Pyrolysis tar 0%, 50%, 75% and 100%
The bench scale delayed coking unit of Example 1 was used for a mixture where: Table 18 shows some of the operating parameters. Relatively high sulfur levels for graphite electrodes made from mixtures containing more than 75% decant oil would be expected to cause puffing problems and would be considered unacceptable. This high sulfur content is due to the omission of hydrotreatment which reduces the sulfur content of the decanted oil. Table 17 Decant oil C specific gravity, 15.6℃ (60〓) 1.0029 Distillation Initial boiling point 230℃ 5% 310 10% 354 20% 372 30% 380 40% 390 50% 395 60% 410 70% 420 80% 447 90% 465 95% 493 Recovery % 95% Molecular Weight 275 Carbon, wt% 89.6 Hydrogen, wt% 9.48 Nitrogen, wt% 0.30 Ash, wt% 0.003 Metals, ppm N/A Sulfur, wt% 1.46 Modified Conradson Carbon, wt% 2.0 Aroma Family, proton NMR 17.4 13 _{C NMR} 57.0 Pour point 18℃ Flash point (open cup) 149℃ Bromine number 15.4 Viscosity, centistoke 38℃ (100〓) 51 99℃ (210〓) 5 TGA Pitschi fraction (550℃ +) 4.8 Toluene insolubles, wt% 0.0 Heptane insolubles, wt% 0.4

[Table] Graphite electrodes were manufactured from mixtures other than those containing 25% pyrolysis tar. Table 19 and Figure 8 show the CTE of graphite electrodes made from coke derived from the mixture. The results shown in Figure 8 are:
The coke CTE is not meaningfully different from that predicted by the law of mixing.

[Table] Example 7 Pyrolysis tar D 0%, 50%, 75% and 100
The tests carried out in Example 6 were repeated in the pilot plant of a delayed coking unit for mixtures containing %. Additionally, Decant Oil C was hydrogen treated until approximately 2.5 hydrogen atoms were added per average molecule of Decant Oil. This mixture of 50% hydrotreated decant oil and 50% pyrolysis tar D was also coked in the pilot plant of the coking unit. Table 20 shows the operating parameters and coke yield. Results for mixtures containing 50% hydrotreated decant oil
It is indicated by 50 ^* .

【table】

[Table] Table 21 and Figure 9 show that coke produced from a mixture containing untreated decant oil has a coefficient of thermal expansion according to that calculated by the mixture standard, while containing 50% hydrotreated decant oil. The results show that the coke from the mixture has a significantly lower coefficient of thermal expansion than that calculated from the mixture standard. It will be understood that there is no limitation to the precise details shown and described herein or to other variations that will occur to those skilled in the art.

[Brief explanation of drawings]

FIG. 1 is a simplified block system diagram of a bench-scale delayed coking unit used in a laboratory; FIGS. 2 and 3 illustrate the results shown in Tables 4 and 7, respectively. Diagram, Figure 4 is a simplified block system diagram of the pilot plant of the delayed coking unit, Figures 5 to 9.
The figures are diagrams illustrating the results shown in Tables 9, 13, 16, 19, and 21, respectively. 1... Raw material liquid, 2... Tank, 4... Pump, 7... Pressure unit, 6... Heating coil, 9... Tank, 12
...Raw material tank, 13...Pump, 16...Preheater, 1
7... Coke generator, 19... Fractionator, 24... Quencher, 22... Pump.

Claims (1)

[Claims] 1. A high-grade coke for producing graphite electrodes having a coefficient of thermal expansion of less than about 0.5×10 ^-6 per 1°C, characterized by comprising the following steps (a) and (b). Manufacturing method. (b) About 50 to 75% by weight of pyrolysis tar and about 50 to about 25% by weight
% by weight of hydrotreated decant oil. (b) A step of coking the mixture by delayed coking to form the high-grade coke. 2 About 2 to about 4 per average molecule of decant oil
2. The method for producing high-grade coke according to claim 1, wherein the hydrotreated decant oil is produced by hydrotreating the decant oil until 50 hydrogen atoms are added. 3 About 2 to about 3 per average molecule of decant oil
2. The method for producing high-grade coke according to claim 1, wherein the hydrotreated decant oil is produced by hydrotreating the decant oil until 50 hydrogen atoms are added.