ES2221574B1 - PROCEDURE AND EQUIPMENT FOR THE CONTINUOUS DEVELOPMENT OF BREA DE MESOFASE. - Google Patents

Abstract

Procedure and equipment for the continuous elaboration of mesophase pitch. A method is presented for the continuous production of mesophase pitch from various petroleum or coal derivatives, which may have varying mesophase contents of 60 to 100%. The production system is simple and economical, consisting of a single-body reactor with two differentiated temperature zones. A high temperature zone where the pyrolysis of the organic precursor takes place forming the mesophase, and a second low temperature zone where the mesophase sediments and coalesces formed the mesophase pitch. The transfer of the mesophase from zone 1 to zone 2 occurs spontaneously. Zone 2 has a device for the removal of the mesophase pitch, while zone 1 has a device for the contribution of raw material necessary to maintain the balance of matter inside the reactor.

Description

Procedure and equipment for processing in brea of mesophase pitch.

Technical sector

The invention is framed within the area of chemistry, more specifically within chemical engineering, since It is about the design of a continuous production reactor. In addition, the invention may have repercussions in other sectors. related to the numerous applications of the areas of mesophase, as a manufacturing of high modulus carbon fibers, high density graphites or electrode precursors for systems of energy storage.

State of the art

The need for new materials is a constant in our technological society, where materials with very specific properties are demanded by many sectors Industrial or productive. Carbon materials have found an important gap in the field of new materials because they meet a series of properties (high mechanical resistance and modulus, low density, high conductivity thermal and electrical, etc.) that makes them irreplaceable in some Applications. However, they have always found a brake important for the generalization of its use at its high price, since that both the cost of precursors and the processes of Production is high. This method presents a method for the production of mesophase pitch that uses economic precursors and a very simple procedure to obtain. This mesophase pitch it can be a suitable precursor for the manufacture of fibers of high modulus carbon, high density isotropic graphites, thermoconducting foams, and also as active material for electrodes in energy storage systems, such as batteries and supercapacitors.

To date, numerous methods have been described. for the production of mesophase breas, although very few of them They have been taken on an industrial scale. In addition, many of them are complex and use discontinuous processes, which can hardly Be profitable industrially.

There are several methods of mesophase production that combine heat treatments at moderate temperatures (around 400ºC) with gas bubbling to drag the light molecules concentrating mesogens, such as patents assigned to E. I. Du Pont de Nemours and Company (US patent 4,551,225 of 1985), where the main drawbacks of method are long treatment times and high flow rates of inert gas used. A similar method is presented in the US patent 4,931,162 assigned to Conoco Inc. in 1990, where times Heat treatment ranges from 3 to 4 days at temperatures close to 380ºC, with the consequent consumption of gas and energy. In order to reduce the treatment time it company presents in the US patent 4,904,371 of 1990 and also in the 5,198,101 of 1993, a variant in which an oxidizing gas is used (depleted air) in a first phase of treatment, to accelerate the polymerization of mesogens, thus reducing the Treatment time to just over 2 days. They also change strategy (US patent 4,892,642 also from 1990 and assigned to Conoco Inc.) replacing gas bubbling with an extraction with solvents, which achieves the same objective of concentrating mesogens significantly cutting treatment time. But the use of organic solvents involves a series of significant disadvantages regarding the difficulties and risks of handling, environmental problems and energy expenditure high in solvent recovery processes. Also they overall yields for obtaining mesophase pitch are very low, concentrating only a narrow fraction of mesogens.

Other patents in which the solvent extraction were presented previously, as US patent 4,575,412 assigned to Kawasaki Steel Corporation in 1986. This is a first heat treatment in which Mesophase is generated and subsequently extracted with a solvent. The soluble fraction, after removing the solvent is subjected to a second heat treatment to now generate a mesophase suitable as a precursor of carbon fibers.

Another option that has been considered to produce Mesophase breas is the addition of different types of substances to organic precursors (breases or pure compounds) for mesophase breas generation. Thus, US Patent 4,631,181 assigned to Nippon Steel Corporation in 1986 adds important amounts of alcohols or phenols to coal tar breasts, working with very high autogenous pressure, besides not getting totally anisotropic breas. The addition of catalysts, essentially Lewis acids, it has been the preferred strategy for the production of mesophase breas. US patent 4,443,324, from Exxon Research and Engineering Co of 1984, shows the possibility of producing mesophasic breasts from compounds cigars such as chromene or triphenylene through a reaction Catalyzed by AlCl 3 followed by solvent extraction. US Patent 4,704,333 (Phillips Petroleum Company, 1987) collects the results with a large number of catalysts. The main disadvantage of this type of process is that the catalyst metallic remains in the carbonaceous material, which for the purpose Practical seriously limits its viability.

An important milestone in scale production industrial mesophase pitch was produced with a variant of this method, in which naphthalene was used as a precursor or methyl naphthalene, and as a catalyst a mixture of HF and BF3, which, being gaseous, was easily and totally eliminated from the resulting pitch, and can be reused. Despite the difficulty of catalyst manipulation due to its toxicity and nature corrosive, and the need to work at high pressures, it got an industrial production of the product, although the cost end of the mesophase pitch is high. Japanese patents 1-309482 and 2-27200, from 1989 and 1990, respectively, as well as US Patent 5,182,010 of 1993, all they assigned to Mitshubishi Gas Chemical Inc., collect the Details of this invention.

Another mesophase that has reached the level of industrial production is known as "solvated mesophase" Produced by Conoco Inc., and used for the production of high modulus carbon fibers (US patents 5,437,780 of 1985; 5,540,903; 5,538,621 and 5,489,374; the latter of 1996). For it, a high molecular weight isotropic pitch, obtained from a residue of modified oil, mixed with a solvent such as xylene and undergoes extraction at high temperature and pressure. The insoluble in xylene are subsequently dried and treated at high temperature and pressure in the presence of a compound such as Phenanthrene, which is incorporated into the carbon structure, generating a mesophase with a high phenanthrene content (hence the denomination of solvatada) and with a low softening point. The process is complex, expensive and offers very low performance in Mesophase pitch.

There is also a group of patents that produce mesophase pitch based on the same physical principles as used in this invention. Thus, US patent 4,529,498 assigned to Kashima Oil Company Limited in 1985 and the US patent assigned to Toa Nenryo Kogyo Kabushiki Kaisha in 1988 describe similar methods, in which after treating a thermal oil residue for produce mesophase, a period of time is left at a temperature below 400 ° C, producing coalescence of the mesophase and its sedimentation at the bottom of the reactor, which allows its subsequent separation. This is done in a discontinuous way. The US patent 4,512,874 assigned to Kashima Oil Company Limited in 1985 da one step further and transform the process into continuous. The process It consists of two containers, one in which the reaction of mesophase formation, and another in which sedimentation occurs and coalescence of it. It is therefore necessary to transfer the pyrolized material to the sedimentation reactor, and the return of the non-anisotropic material to the first reactor after separation. This transport of very viscous material from one container to another presents  serious difficulties In addition, the cited patent only uses as starting material petroleum products.

The invention presented herein It has obvious advantages over the previous ones as it is a continuous process that is carried out in a single reactor, avoiding material transfers from one site to another.

Description of the invention

Mesophase breasts are precursors of Carbon materials with numerous industrial applications, such as the manufacture of high modulus carbon fibers, thermoconductive carbon foams or electrode materials in energy storage systems Breas production of Mesophase is a technically complex problem, which requires the adequacy of precursors, as well as numerous stages of production. In addition, most of the methods developed are from discontinuous production, which makes the product even more expensive. In This invention presents a method for producing breasts of mesophase in continuous using a single reactor where it is generated and separates the mesophase, which is a simplification with respect to All processes presented to date.

Brief Description of the Invention

In this invention a process is presented simple, that uses economic precursors and available in the market, in which in a single reactor that has two zones of different temperature generates a mesophase pitch with a high Mesophase content. The upper zone (zone 1) of the reactor is is at a temperature that allows reactions pyrolytics that lead to the formation of mesophase, which in a way spontaneously deposited in the lower zone of the reactor (zone 2), which It is at a lower temperature, where it settles and coalesces before if removed from the reactor as the final product. They are not used or solvents, or catalysts, or any other additive, having as the only product of the reaction the mesophase pitch.

Brief description of the content of the figures

Figure 1 presents a diagram of the reactor in continuous for the production of mesophase pitch.

Figure 2 shows images taken at Mesophase optical microscope in different reactor zones when treating an oil pitch.

Figure 3 shows images taken at Mesophase optical microscope in different reactor zones when treating a coal tar pitch.

Detailed description of the invention

The present invention uses as raw materials petroleum or coal products, preferably Breas of both origins or other heavy waste with a high content in the carbon element. The type of precursor has profound incidence both in the type of mesophase obtained and in the experimental conditions required. The use of precursors High molecular weight allows working at atmospheric pressure, which which simplifies the demands of the equipment used, maintaining product yields obtained very high, higher than 60-70% by weight. To get these same yields with lower molecular weight precursors, such as it can be a decanted oil or a pyrolysis tar, it is the use of pressure in the reactor is necessary. All the Precursors used, breasts or waste, are available in the Market at a low price and are of an isotropic nature.

The process of transformation of these precursors in a mesophase pitch it is performed in a reactor like the one schematized in Figure 1, and whose development represents the main claim of this patent. The raw material is found in a warehouse from which you can feed the main reactor This raw material is in state liquid and at a temperature that allows it to be transferred with ease, which is normally less than 200 ° C. In these conditions used precursors allow transport with ease of being thermally stable and presenting a low viscosity. The main reactor is fed from this tank to keep the liquid level stable in it. A part of fed liquid evaporates and is collected together with others lightweight craking products in a condensate tank, of Where they can be eliminated. The reactor itself has a series of heating systems that allow to maintain two temperature differentiated zones. The upper zone (zone 1) operates at temperatures between 400 and 480 ° C, temperatures at which occurs the pyrolysis of the carbonaceous precursor and all reactions involved in the formation of an optically phase Anisotropic called mesophase. This mesophase appears in the form of spheres and the speed of formation depends so much on nature precursor chemistry as of the experimental conditions used, especially pressure and temperature.

The mesophase spheres are, by their own constitution of stacked flat molecules, denser than the phase isotropic from which they come, which causes these spheres, reached a certain size, they tend to spontaneously deposit at the bottom of the reactor. The gentle mechanical agitation that exists in This reactor zone allows heat transfer without avoid sedimentation of mesophase spheres. This mesophase newly formed presents some very interesting properties, since at  it is a liquid crystal conjugates a molecular orientation preferred (pregraphitic structure) with a plasticity that It conditions your subsequent applications. This plasticity is loses over time at high temperature, due to the  progressive transformation of the mesophase into coke. As mentioned previously, the newly formed mesophase starts a path descending into the reactor until it spontaneously reaches the zone 2, which is at a lower temperature (between 350 and 400ºC) and where pyrolytic reactions slow down greatly, which stops the hardening of the mesophase. The temperature must be high enough for the mesophase spheres to have the possibility of continuing to descend while coalescing between them, forming a single mass mesophase body, which finally It is deposited at the bottom of the reactor as a phase majority, where it can be extracted through a device such as a worm or a properly heated valve (depending on the use of one system or another of the conditions of operation, specifically the use or not of pressure).

One of the great advantages of the procedure presented here consists of the homogeneity of the mesophase ready In any discontinuous procedure, where the precursor is pyrolyzed for a certain time until obtaining a defined amount of mesophase, which is then subjected to a process of separation, the mesophase formed in the first stages of the Pyrolysis is not equal to that formed at the end, so you have a material with some heterogeneity. However, with the procedure described here, the residence time of the spheres of mesophase in the pyrolysis zone is self-regulated by itself system (the spheres reach a size from which sediment), so that the product is more homogeneous, owned by special interest in applications such as fiber production carbon, one of the potential applications of these areas of mesophase

It is important to mention the different characteristics of the mesophase according to its origin be oil or Coal. It is well known that coal breasts are usually accompanied by a variable content of solid particles called primary quinoline insoluble (pQI), which have a special impact on the formation and development of the mesophase These particles are placed around the spheres of mesophase greatly hindering its coalescence, which clearly It affects the yields and properties of the obtained mesophase. PQI-free coal breasts (by prior filtration of the brea) behave similarly in this invention to breas of oil, which indicates that it is the presence of these particles, more than the chemical nature of the precursor, which determines its behavior in this invention. The examples cited to continuation allow to obtain greater understanding of the properties of the invention described herein.

Examples of the embodiment of the invention Example 1

This example illustrates the operation of the invention with an oil pitch. The Ashland Oil Pitch 240 is fed to the reactor until a predetermined level is reached. The working temperature of zone 1 was 430 ° C and the experiment It is done at atmospheric pressure. The temperature of zone 2 is set at 380 ° C. The mesophase that is removed from the reactor had a point of softening of 320ºC, a higher anisotropy content 97% and insoluble toluene less than 80%. Figure 2 illustrates the appearance of the pitch inside the reactor in different areas at the end of the experience. So, it looks like in the upper part of the mesophase content is very low, and presents Only small spheres. As you descend on the reactor, the mesophase is increasingly abundant, while the spheres are larger and mesophase appears coalesced Finally, at the bottom of the reactor you observes coalesced mesophase, which is what is extracted through the endless screw.

Example 2

This example illustrates the operation of the invention with a coal tar pitch with a content in pQI close to 3%. All experimental conditions are kept constant with respect to those shown in example 1, in order to compare both raw materials. In this case the pitch which is extracted from the reactor had a lower mesophase content at 80%, and a softening point greater than 350 ° C. The figure 3 illustrates the appearance of the pitch inside the reactor at the End of the experiment. Comparing the comments with the Figure 2 the difficulty of the mesophase spheres for coalescer, due to the presence of solid particles present in the pitch. Although this mesophase pitch is not a suitable precursor for obtaining carbon fibers, yes what It is for obtaining other types of materials, such as high density isotropic graphites or electrode materials in  energy storage systems It must be taken into account that Due to the simplicity of the procurement process, the price of these materials must be low compared to similar ones obtained by other means

Claims (7)

1. Device for the elaboration of mesophase pitch continuously characterized in that the reactor with agitation of a single body has two differentiated temperature zones, where the mesophase formed in the high temperature zone is spontaneously transferred to the low zone temperature where it is concentrated and extracted using an auger. 2. Device for the elaboration of mesophase pitch in accordance with claim 1, characterized in that the temperature in the upper zone is 400-480 ° C and that in the lower one is 350-400 ° C. 3. Device for the elaboration of mesophase pitch in accordance with claim 1, characterized in that the temperature in the upper area is preferably 430 ° C and that in the lower one of 380 ° C. 4. Process for the elaboration of mesophase pitch continuously characterized by the use of a commercial petroleum-derived precursor, in accordance with the conditions set forth in claims 2 and 3. 5. Process for the elaboration of mesophase pitch continuously characterized by the use of a commercial precursor derived from coal with pQI contents of less than 3%, in accordance with the conditions set forth in claims 2 and 3. 6. Process for the elaboration of mesophase pitch continuously characterized in that by slowly coalescing the mesophase spheres, according to claim 1 and deposited at the bottom, a homogeneity is achieved throughout the process. 7. Use of mesophase pitch with pQI lower than 3% obtained with the equipment and procedure of claims above for materials such as isotropic graphites, materials for electrodes, etc.