ES3064238T3 - Process to obtain synthetic pitches with high softening point from medium and heavy aromatic oils - Google Patents

Abstract

The present invention relates to a process for producing carbon precursors, particularly from medium and heavy aromatic oils, through thermal oxidative polymerization reactions. Therefore, the invention belongs to the field of obtaining carbon precursors from different sources, improving the overall carbon yield. (Automatic translation using Google Translate, no legal value)

Description

[0001] PROCEDURE FOR OBTAINING SYNTHETIC TARS WITH A HIGH FIRE POINT

[0002] SOFTENING FROM MEDIUM AND HEAVY AROMATIC OILS

[0004] Field of invention

[0006] The present invention relates to a process for obtaining synthetic pitches from medium and heavy aromatic oils by means of oxidative thermal polymerization reactions. The process of the invention allows obtaining a synthetic pitch with a high softening point and improving the total carbon yield in the process.

[0008] Background of the invention

[0010] Coal tar pitches, produced as a distillation residue of coal tar, are commonly used as a binder in the production of carbon anodes for alumina electrolysis and graphite electrodes for use in electric arc furnaces. The production and consumption of these pitches are therefore highly dependent on the demand for these products, and they are produced with characteristics that allow them to meet the requirements of these applications. The upcoming decarbonization of the steel industry will lead to the closure of coke oven batteries where the coal tar byproduct is produced. Therefore, there would be an increased demand for coal tar pitch to produce graphite electrodes and support the growth of electric arc furnaces (EAFs). Furthermore, the decline in coal tar supply and the introduction of stringent environmental regulations have compelled pitch producers to seek new strategies for synthesizing and preparing less toxic pitches. Thus, in recent years, new strategies have been developed to produce more environmentally friendly pitches while simultaneously addressing the coal tar shortage.

[0011] Furthermore, the decarbonization trend in the carbon black industry is also underway, and the strategies involved focus on the use of recovered carbon black and the substitution of fossil-based oils (anthracene oil, settling oil, or similar) with pyrolysis oils derived from waste such as municipal solid waste and used tires. This decarbonization trend will lead to a decrease in demand for these oils. Therefore, the heavy oil industry, like the coal chemical sector, is seeking diversification opportunities that do not involve combustion or any other thermal valorization.

[0012] In addition, in Asia, coal tar pitch coke is used to manufacture synthetic graphite for lithium-ion battery applications. In recent years, the demand for synthetic graphite has increased significantly and is expected to continue growing, particularly for applications such as electric vehicles. Synthetic graphite is projected to become the predominant anode material, replacing natural graphite. The production of synthetic graphite relies on high-quality coal tar pitches, from which the primary quinoline insoluble (QI) has been removed. The value proposition of increasing the availability of suitable raw materials to meet the growing demand for synthetic graphite aligns with electrification and the increasing use of energy storage solutions.

[0013] Patent EP1739153 describes a process for producing pitches, particularly those suitable for use as carbon precursors, from coal tars and distillates thereof, through a sequential, combined three-stage operation of oxidative heat treatment, inert atmosphere heat treatment, and fractional distillation. This document prioritizes other properties, such as the intermediate rheology of the product up to its conversion into carbon materials and the carbon yield for a given softening point. The applications to which this invention is directed require the most developed graphitic microstructure possible.

[0014] The document Environ. Sci. Technol. 2009, 43, 8126-8132 describes a process for producing novel, low-toxicity pitches from anthracene oil. The process involves oxidative treatment to polymerize and condense the components of the anthracene oil, followed by heat treatment and distillation. This publication is intended for the production of aluminum and silicon Söderberg anodes, applications that are currently obsolete.

[0015] The document Carbon 38 (2000) 1315-1322 reports the results obtained by air-blowing an industrial anthracene oil under different experimental conditions of temperature, time and air flow and the studies on the influence of these parameters on the final product.

[0016] In the document Coke and Chemistry, 2020, Vol.63, No.12, pp.569-575, the influence of batch composition on the microstructure of the coke produced and the oxidation conditions of moderate temperature coal tar pitch mixtures and the anthracene fraction of coal tar were investigated.

[0017] Document RU2750991 C1 describes methods for producing petroleum pitch, used as a binder in the manufacture of various carbon products. However, the process of the invention is a more direct method, since the raw material is used directly without any prior distillation step. Furthermore, the stirrer used in the reaction is specifically designed to ensure complete consumption of the reagent and improve reaction efficiency. Additionally, the process of the invention achieves higher reaction yields compared to those demonstrated in the examples in this document, since the yield stated in this document is at most 39%, substantially lower than the yields obtained in the present invention.

[0018] US Patent Document 2014/0099691 A1 describes a continuous process for converting carbonaceous materials into a liquid hydrocarbon product and, accordingly, does not intend to obtain synthetic pitches as in the present invention.

[0019] US Patent Document 4013540 A describes the preparation of petroleum pitch for carbon electrodes made from full-range decanted oil by oxidative condensation.

[0020] Therefore, the present invention aims to obtain non-standard industrial synthetic pitches for applications in advanced carbon materials (carbon fibers, carbon foams, pitches for graphite pitch coating procedures for anode material in lithium-ion batteries for electric vehicles, needle coke as a precursor, electrical storage in renewable energy generation plants, etc.). For these types of applications, the secondary IQ is optimally minimized, the beta resin is maximized, and the fixed carbon yield is maximized. In addition, the softening point must be high.

[0021] In addition, for the manufacture of materials where a synthetic pitch with a high softening point is required, there are currently two alternatives: obtaining it from coal tar or from petrochemical bottoms (petroleum pitch).

[0023] • Starting from coal tar, the current problem is the elimination of the so-called primary quinoline insoluble (IQ), which generates heterogeneity in the precursors and whose elimination is tedious and costly.

[0024] • Starting from both raw materials, coal tar or petrochemical waste, requires a distillation temperature above 400ºC, which causes the generation of mesophase and solid deposits of semi-coke residue in the equipment, which causes serious mechanical maintenance problems.

[0026] The main applications of the present invention are centered on the manufacture of advanced carbon material precursors such as synthetic carbons for anodic active materials in Li-ion batteries (graphite, pitch coating), Na-ion batteries (hard carbon, soft/hard carbons…) where the final process performance and microstructure become crucially important.

[0029] DESCRIPTION OF THE INVENTION

[0031] Therefore, there is still a need to obtain improved procedures for obtaining synthetic pitches or advanced carbon material precursors for the applications mentioned above in order to overcome current limitations, namely, absence of primary IQ, improve the net yield of the procedure and control of the carbon microstructure.

[0032] The inventors of the present invention found that this objective can be achieved by the following procedure:

[0033] A process for obtaining synthetic pitches from at least one medium or heavy aromatic oil selected from the group consisting of anthracene oil, decalin, light anthracene oil, heavy anthracene oil, settling oil, and the heavy hydrothermal liquefaction fraction of tire pyrolysis oils, or mixtures thereof in any combination, the process comprising the steps of:

[0034] - provide at least one oil in a reactor;

[0035] - establish an initial reactor temperature lower than the starting boiling point of at least one oil, and

[0036] - react the at least one cited oil with an O<2> stream or an O<2> enriched air stream containing at least 21% O<2>v/v in the reactor at a temperature between 350 and 400ºC and a pressure of at least 11 bar for a residence time of between 5 minutes and 5 hours,

[0037] characterized in that the supply of the O<2> stream or the O<2> enriched air stream is between 0.075 and 0.2 kg of O<2> or O<2> enriched air per kg of at least one oil.

[0039] As described herein, an O₂ stream or an O₂-enriched air or gas stream is any gas containing at least the concentration of O₂ that is naturally present in air, i.e., at least 21% v/v, preferably at least 50% v/v, and more preferably approximately 95% v/v. The choice of the O₂ concentration in the gas depends primarily on economic and safety considerations. Due to the combined effects of increased oxygen supply, increased pressure, and increased reaction times, synthetic pitches with the desired properties can be obtained.

[0040] Figure 1 shows a possible layout of the installation.

[0041] The types of medium or heavy aromatic oils that can be used as raw materials in the process of the invention should ideally have the following desirable properties:

[0042] • Oils of petrochemical, carbochemical or pyrolysis origin, or any mixed fraction, that present the following physicochemical properties:

[0043] • The vapor pressure at the reaction temperature should be at least 5 bar lower than the selected reaction pressure to minimize the loss of volatiles and enhance the liquid-phase reaction, • An aromatic index (C/H atomic ratio) of 0.55 to 1.20,

[0044] • A preferred inorganic ash content of less than 5%, but more preferably, for advanced carbon materials, not exceeding 0.3% and even more preferably not exceeding 0.1%, to minimize impurities.

[0045] • Illustrative examples of this type of compounds are: Decalin, Tetraline, Light anthracene oil, Heavy anthracene oil, Settling oil, heavy aromatic oil fractions from more sustainable sources such as pyrolysis of used tires or hydrothermal liquefaction (HTL) or biomass and municipal waste residues among others, alone or in any combination between them.

[0047] In the process of the invention, a stream of O₂ or gas containing O₂ is bubbled into the liquid heavy aromatic oil. The unreacted oxygen accumulates at the top of the reactor and, thanks to the agitator, is reintroduced into the liquid. This is because the agitator has an orifice at the top which, at the agitation speed (1000 rpm), by means of the Venturi effect, draws in the unreacted gas and reintroduces it into the liquid through the bottom (see Figure 2).

[0048] In preferred embodiments, the supply of O<2>o O<2>enriched air is between 0.075 – 0.1 kg of O<2>o O<2>enriched air/kg of at least one oil, more preferably between 0.08 – 0.095 kg of O<2>o O<2>enriched air/kg of at least one oil, or even more preferably around 0.091 kg of O<2>o O<2>enriched air/kg of at least one oil, for the entire residence time of the reactants in the reactor.

[0049] In preferred embodiments, the reaction temperature is between 300 – 400ºC, more preferably around 375ºC.

[0050] In preferred embodiments, the reaction pressure is between 11 and 100 bar, more preferably between 12 and 50 bar, even more preferably between 15 and 20 bar, and most preferably around 16 bar.

[0051] In preferred embodiments, the residence time is between 5 minutes and 5 hours, more preferably between 10 minutes and 2 hours, even more preferably between 0.5 and 1 hour, and most preferably around 0.5 hours.

[0052] In preferred embodiments, the at least one oil is selected from the group consisting of anthracene oil, decalin, light anthracene oil, heavy anthracene oil, decanting oil, heavy fraction of tire pyrolysis oils, and heavy fraction of HTL.

[0053] After the reaction step described above, the process of the invention may preferably comprise an additional post-heat treatment at a temperature between 350°C and 450°C for a residence time of between 30 minutes and 6 hours, in an inert atmosphere. More preferably, the residence time in the indicated post-heat treatment is between 2 hours and 5 hours, and even more preferably between 2 and 4 hours.

[0054] In a preferred embodiment, the process is carried out in a reactor that includes an air diffusion system.

[0056] Products obtained

[0057] Following the procedure explained above, the products obtained show the following total mass balance:

[0058] • Condensable oils (40ºC): < 15%

[0059] • Non-condensable gases (40ºC) < 5%

[0060] • Reaction product yield: > 80% (softening point 60ºC)

[0061] o Distilled oils (< 25%)

[0062] o Exhaust gases: < 2%

[0063] or Precursor yield with softening point 110 – 120ºC (Mettler) (>70%)

[0064]  Distilled oils: < 40%

[0065]  Exhaust gases: < 2%

[0066]  Carbon yield: 40 – 60%

[0067]  Net carbon yield: 40 – 50% (from the initial precursor)

[0069] The TGA analysis of the resulting product is performed as follows: under a nitrogen flow of 60 mL/min, a first heating ramp is carried out from 25 to 270°C at a rate of 10 K/min, followed by an isothermal stage at 270°C for 50 minutes. After this time, it is heated from 270 to 650°C at 10 K/min. The TGA profile and the explanation of the data obtained can be seen in Figure 3.

[0070] The residue value at a temperature of 650°C corresponds to the parameter “Net Carbon”, which is also called carbon residue. On the other hand, the oils obtained from the process of the invention are separated into two during the distillation stage:

[0071] • Light oils: oils distilled before the isothermal ramp at 270ºC, i.e., the TG value at that point

[0072] • Heavy oils: distilled oils from the end of the isothermal ramp at 270ºC and the end of the test at 650ºC.

[0073] In addition to these values, and given that the weight loss evolution profiles with temperature are different for each sample, the different carbon yields of the product obtained can be simulated if a pre-distillation is carried out at a specific temperature. In this way, the Fixed Carbon FC #XXX values are obtained, where the value “#XXX” refers to the temperature on the TGA graph (see Figure 3).

[0074] Table 1: Comparison of the weight percent composition of selected samples measured by thermogravimetric analysis (TGA) for standard coal tar (STD coal tar) and anthracene oil Oil A.

[0076]

[0078] Distillation was carried out at a temperature between 270°C and 400°C; distillation at temperatures above 400°C is not advisable due to the progressive thermal decomposition of the pitch, which turns into coke.

[0079] From the data in the table, we can conclude that, although the fixed carbon values of Oil A at 400ºC are very interesting, it is not profitable given that its overall performance is very low (Net Carbon = 0.4%).

[0080] To improve its performance, the reaction product obtained can be subjected to a further heat treatment stage to stabilize its structure and increase the fixed carbon and net carbon yield.

[0081] According to the descriptive memorandum of the final product and the total conversion rate, the reaction may require an additional distillation stage to reach the desired final softening point.

[0082] Brief description of the Figures

[0083] Figure 1: Reactor diagram.

[0084] Figure 2: Schematic of a typical jet agitator.

[0085] Figure 3: Thermogravimetric analysis (TGA) of an unreacted oil (grey line) and a standard coal tar (black).

[0086] Figure 4: Optical texture microscopy of the synthetic pitches obtained in Example 1A. The photograph shows the typical optical structure obtained in these synthetic pitches obtained by the process of the invention after a carbonization stage (temperature 650ºC). The photo shows the absence of primary IQ (various defects can also be observed during polishing).

[0087] Figure 5: Optical texture microscopy of the synthetic tars obtained in Example 1B. The photograph shows a mosaic structure that is significantly different from the structure shown in Example 1A. This demonstrates that the procedure of this invention is capable of modulating the crystalline structure. Experimental Examples

[0088] In the Experimental Examples, the following reaction conditions were used. A comparison with the reaction conditions used in the prior art is also provided in Patent Document EP1739153:

[0089] Table 2: Comparison between the properties of the synthetic pitches of the present invention and the pitches obtained in Patent Document EP1739153

[0091]

[0092]

[0093] )

[0095] Example 1

[0096] In the configuration described above, a sample of anthracene oil (Oil A) was processed under the following conditions:

[0098] Example #1A:

[0099] • Raw material: Anthracene oil

[0100] • Temperature: 375ºC

[0101] • Residence time: 30 minutes

[0102] • Oil Flow A: 1 kg/h

[0103] • Oxygen supply: 0.091 kg pure O<2>/kg of oil

[0104] • Pressure: 16 bar

[0106] Example #1B:

[0107] • Raw material: Anthracene oil

[0108] • Temperature: 375ºC

[0109] • Residence time: 45 minutes

[0110] • Oxygen supply: 0.091 kg pure O<2>/kg oil

[0111] • Pressure: 16 bar

[0113] Example #1C:

[0114] • Raw material: Decanted oil

[0115] • Temperature: 300ºC

[0116] • Residence time: 1.82 hours

[0117] • Oxygen supply: 0.083 kg pure O<2>/kg oil

[0118] • Pressure: 16 bar

[0120] The TGA results of Examples #1A, 1B, and 1C were compared to a standard coal tar and two heavy aromatic oils: anthracene oil (Oil A) and settling oil (Oil D).

[0122] Table 3: Comparison of the properties of Example 1

[0124]

[0127] The values provided for Oil A refer to the raw material used in Examples #1A and #1B, while Oil D refers to the raw material used in Example #1C. The values provided for standard coal tar are given for comparative purposes.

[0128] The advantages of the process of the invention can be clearly seen in the table above. The prior patent EP1739153 B1 focused on optimizing the process to obtain an intermediate product, a pitch, with specific rheological characteristics (a softening point of around 110°C Mettler) for the specific requirements of the applications for which it was intended, namely, electrodes for the electrolysis of alumina and standard graphite electrodes. In this respect, patent EP1739153 B1 emphasized limiting the conversion of the process to around 30-35%. In the present invention, these rheological requirements do not exist, and a high-softening-point pitch can or even should be used. The process can be extended, thereby obtaining a higher carbon yield, as shown in the FC#350 and FC#400 values.

[0129] The values presented in the FCXXX data represent the fixed carbon of the product obtained after distillation at XXX °C using TGA simulation. Considering the amount of volatile matter when distilled at a given temperature, using the process of the invention, it is possible to obtain precursors with a higher softening point at a certain temperature and gain in fixed carbon. This is further enhanced by increasing the distillation temperature.

[0130] Furthermore, another advantage of the process can be achieved by obtaining a high-softening-point pitch. Since the oxidative heat treatment process generates heavy structures, the oils that need to be distilled to obtain them are primarily light oils. Obtaining a high-softening-point pitch (> 250°C Mettler) can be considered a technologically complex process if starting directly from a carbochemical tar, where distillation temperatures above 400°C are required (even under high vacuum). These process temperatures generate mesophase and high levels of solid deposits on the product and equipment through the generation of semi-coke solids. From Examples #1A and #1B, pitches with a softening point of 300°C can be obtained without the need to reach such high temperatures (< 400°C).

[0131] These results are further improved when a petrochemical oil is used as the settling oil.

[0133] Example 2

[0134] The pitch in Example 2 was produced using the following conditions:

[0135] • Raw material: Anthracene oil

[0136] • Temperature: 375ºC

[0137] • Residence time: 30 minutes

[0138] • Oxygen supply: 0.091 kg pure O<2>/kg oil

[0139] • Pressure: 16 bar

[0140] • Distillation: Adjustment to softening point 110ºC Mettler

[0142] The product distilled at 110°C is compared in the following table with the product obtained in Patent EP1739153B1 and with a standard pitch. The pitches obtained in this example show a clear advantage in the net carbon yield value.

[0144] T l 4. m r i n nr l E m l 2 r n r l m n P n EP17 1 B1.

[0146]

[0149] In the case of a standard pitch obtained from coal tar, the IQ value corresponds to the primary IQ, which is an infusible material obtained during the production of the coal tar raw material, whereas in the case of the synthetic pitches obtained in the invention and in Patent EP1739153 B1, it corresponds to the secondary IQ, which is a highly condensed fusible material. In other words, the table above shows that the standard pitches have a significant amount of IQ (corresponding to the primary IQ), while the synthetic pitches have a significantly lower amount of IQ (which is not the primary IQ, but the secondary IQ).

[0151] Example 3

[0152] The product obtained from Example 2 was subjected to further heat treatment in an inert atmosphere after the polymerization reaction to modify the final properties of the pitch and was carried out under the following conditions:

[0153] • Raw material: The product obtained in Example 2.

[0154] • Heat treatment: 2h, 375ºC, 16 bar, nitrogen atmosphere.

[0155] • Distillation: Adjustment to softening point 110ºC Mettler

[0157] Tl. m r i n l E m l r n r m n P n EP17 1

[0159]

[0162] In this experiment, the advantages obtained in the previous examples are improved, as fixed carbon, pitch yield and net carbon yield are improved.

[0163] Therefore, by performing a heat treatment after the oxidative reaction, the benefits of the product are improved.

[0164] In summary, with the process of the invention, it is possible to obtain, at a temperature similar to that of other prior art processes, a precursor with a higher softening point that also exhibits a higher fixed carbon value. Alternatively, it is also possible to obtain a precursor with a similar softening point at a lower temperature than in prior art processes, and this effect is enhanced by increasing the distillation temperature or the required softening point. This technical effect is highly advantageous and completely unexpected based on a review of the prior art. The products obtained with the process of the invention can be advantageously used in advanced applications such as carbon fibers, carbon foams, pitches for graphite pitch coating processes for anode material in lithium-ion batteries for electric vehicles, needle coke as a precursor, electrical storage in renewable energy generation plants, etc.

[0165] As shown in the previous example, the IQ value is significantly lower than the IQ values obtained with standard pitch. Therefore, due to the change in the process conditions, the process of this invention results in a reduction of the IQ value compared to Patent EP1739153B1. This represents an improvement in the quality of the final pitch, as the pitch exhibits a more fluid state and a lower probability of encountering carbonaceous structures generated during the unwanted partial combustion of anthracene oil with O<2>. This particular combustion generates a local increase in temperature (hot spots) and the formation of soot.

[0166] In conclusion, the following advantages are obtained with the procedure of the invention:

[0167] - It is easier to obtain high softening point pitches compared to those obtained in Patent Document EP1739153B1 of the prior art and the conventional tar route (110°C pitch distillation → high softening point pitch distillation).

[0168] - A higher overall yield of raw materials for carbon generation is obtained compared to Patent Document EP1739153B1 and tar.

[0169] - The procedure is of particular interest if the synergy of this procedure is used in conjunction with the procedure for obtaining carbonaceous materials to recycle and convert distillates into carbonaceous materials.

[0171] It is especially recommended to combine both procedures, i.e., the thermal oxidation of the raw material, with or without heat treatment, with or without distillation, to obtain a specific softening point, and the procedure for producing carbons. The oils generated to obtain the carbonaceous material can be reintroduced into the procedure, achieving the maximum conversion of the initial raw material into carbon.

[0172] In a net process, the oils that evolve during precursor formation and those released during carbonization can be recirculated into the process and therefore do not need to be burned for carbon black application or as fuel, thus increasing overall throughput and contributing to decarbonization.

Claims (14)

1. CLAIMS 1. A process for obtaining synthetic pitches from at least one medium or heavy liquid oil selected from the group consisting of anthracene oil, decalin, light anthracene oil, heavy anthracene oil, settling oil and the heavy fraction of the hydrothermal liquefaction (HTL) of tire pyrolysis oils, or mixtures thereof in any combination, the process comprising the steps of: - establish an initial reactor temperature lower than the initial boiling point of at least one oil, and - allowing the at least one mentioned oil to react with a stream of O2 or O2-enriched air containing at least 21% O2 v/v in the reactor at a temperature between 350 and 400°C and a pressure of at least 11 bar for a residence time of between 5 minutes and 5 h, characterized in that the supply of the O2 or O2-enriched air is between 0.075 and 0.2 kg of O2 or O2-enriched air per kg of the at least one oil. 2. The method of claim 1 wherein the supply of the O<2> stream or O<2> enriched air is between 0.08 – 0.095 kg of O<2> or O<2> enriched air/kg of at least one oil. 3. The process of claim 1 wherein the supply of the O<2> stream or O<2> enriched air is around 0.091 kg of O<2> or O<2> enriched air/kg of at least one oil. 4. The procedure of claim 1 wherein the temperature is 375ºC. 5. The procedure of any one of the preceding claims 1-4 wherein the pressure is between 11 and 100 bar. 6. The procedure of claim 5, wherein the pressure is between 12 and 50 bar. 7. The procedure of claim 5, wherein the pressure is approximately 16 bar. 8. The procedure of any one of the preceding claims 1-7, wherein the residence time is between 10 minutes and 2 hours. 9. The process of any one of the preceding claims 1 to 8, wherein the concentration of O<2> in the O<2>enriched air is at least 50% v/v. 10. The process of claim 9, wherein the concentration of O<2> in the O<2> enriched air is approximately 95% v/v. 11. The process of any one of the preceding claims 1 to 10, wherein the O<2> stream or O<2> enriched air is bubbled into a medium or heavy liquid aromatic oil. 12. The process of any one of the preceding claims 1 to 11, further comprising a post-heat treatment at a temperature of between 350°C and 450°C for a residence time of between 30 minutes and 6 hours in an inert atmosphere. 13. The procedure of claim 12, wherein the residence time is between 2 and 4 hours. 14. The process of claim 12 or 13, wherein the temperature in the subsequent heat treatment is the same as the temperature in the reaction stage of the oil with the O<2> stream or O<2> enriched air.