ES2376938T3 - PROCEDURE TO PRODUCE BREA FROM ALQUITRANES AND ITS DISTILLATES FROM HULLA RENTAL THROUGH OXIDATIVE THERMAL TREATMENT. - Google Patents

Abstract

Obtaining breasts suitable for multiple applications from distillates from high temperature coal tar with a distillation range greater than 260 ° C, by sequential and combined three-stage application under mild conditions of pressure and temperature (<400 ° C, <10 bar g): oxidative heat treatment using as reactive air to oxygen, its mixtures, or oxygen depleted air; heat treatment in inert atmosphere, and fractional distillation. As a result, breases are obtained that present environmental and occupational health advantages, usable as carbonaceous precursors.

Description

Procedure for producing pitch from tars and their distillates from coal tar by oxidative heat treatment.

The invention relates to a method for produce breas, in particular those suitable for application as carbon precursors, from tars and their distillates, through the sequential and combined three-stage application:

one.-

Reaction: Heat Treatment oxidative, under mild pressure and temperature conditions (<400ºC, <10 bar g, residence time between 2-10 seconds, and preferably 350-400 ° C, 5-10 bar g, 6-10 seconds), using air as reagents, oxygen, oxygen depleted air, or mixtures thereof.

2.-

Atmospheric heat treatment inert (340-400 ° C, <10 bar g, time of residence between 3-10 hours, and preferably 370-400 ° C, atmospheric pressure, 4-6 hours) for the stabilization of the reaction product.

3.-

Fractional distillation (preferably in vacuum or by dragging with steam or gas inert) for setting the pitch softening point or carbonaceous precursor, according to the desired application.

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Background of the invention

Breas are mostly produced by distillation of coal tar. The tar, a once dehydrated and after removing a first light fraction of BTX (<5%), gives rise to the following fractions, attending to different distillation cuts:

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Naphthalene oil fraction. Within a distillation range <260ºC and with a content of naphthalene> 50%, represents approximately 20% of the primitive tar and is used for the recovery of naphthalene from high commercial value, and for the manufacture of oils technicians

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Fraction of anthracene oil. Complex mixture of polycyclic aromatic hydrocarbons with range Distillation 260-400ºC, mainly composed by anthracene, phenanthrene, fluorantene, pyrene and carbazole. It represents approximately 30% of the primitive tar, and is a directly marketable product for the production of black from smoke, in strong competition with different oil residues. It would also be commercially interesting to convert the largest Part of this fraction.

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Pitch. Most abundant product of the distillation of tar. It is a black solid with a point of approximate softening of 30-250 ° C, characterized in a basic way by the substance content insoluble in certain solvents, such as toluene and Quinolein It is a complex mixture of aromatic hydrocarbons polycyclic of three or more condensed aromatic rings. It represents approximately 50% of the tar, and is the matter premium used in the manufacture of electrodes for industries of aluminum and graphite.

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Since the procedure for obtaining pitch only consists of the separation of oils until adjusted the softening point of the pre-existing pitch in the tar, its production can therefore be considered a purely physical operation. Thus, the quality of the obtained breas in the state of the art it is, therefore, governed by the quality of the tars used in the process of production.

The characteristic of coal tar being A byproduct of coke batteries makes this raw material a highly inconsistent product, and this inconvenience is only compensable by formulating suitable mixtures of tars In any case, all types of tar and, for consequently, the breas obtained from them, possess solid particles in suspension (primary, secondary and carry-over) in addition to different types of impurities metallic, identifiable by its ash content. Both of them pollutants impair the quality of the pitch and / or decrease its potential application in advanced carbonaceous materials.

Anthracene oil is obtained during coal tar distillation and is characterized by its range of distillation, this being the one from about 260 ° C until corresponding temperature for setting the point of pitch softening obtained as final product (generally 400-410 ° C). Anthracene oil It consists mainly of aromatic hydrocarbons of 2-4 benzene rings and their corresponding heterocyclics of O, N and S, being its main components phenanthrene, anthracene, fluorantene, carbazole and pyrene. High aromaticity of anthracene oil and its characteristic of being a Distilled and fully distilled product throughout its range, make of this product a raw material highly consistent in quality, which suggests the possibility of more noble uses.

Many of the aromatic hydrocarbons present in anthracene oil and some heteroaromatics are transformed by slow heat treatment, up to 1000ºC in closed container properly pressurized to prevent evaporation, in materials carbonaceous anisotropic and graffiti. A heat treatment to lower temperature would leave the transformation in an intermediate state, the pitch, although with low yields. The process consists of a dehydrogenative aromatic condensation that is generated via Radicalaria Said intermediate step for obtaining pitch continues still under excessively high and low temperatures Conversion rates to be applied on an industrial scale. This suggests the possibility of inducing aromatic condensation by catalytic reactions that promote the generation of radicals, their condensation and dehydrogenation at lower temperatures and higher performance. Among the possible inductors already known for this type of reactions are the catalysts of the type Friedel-Craft (BF 3 / HF, AlCl 3) and sulfur. Both for the quality of the final products and for the costs operational and waste / by-products originated, these catalysts they are not advisable, proposing in this case, and constituting a Object of the present invention, the use of oxygen, air, oxygen depleted air, and mixtures thereof.

Air treatment of tars and breasts, as well as composite materials, self-interposing mesophase and fibers It has already been used for different purposes, such as increase the molecular weight and softening point of breasts and tars, avoid swelling during carbonization in carbon / carbon and mesophase composites, and thermostabilize the fibers before carbonization.

US 4892642 describes the production of Breas from coal tar in three stages: a treatment thermal oxidative at 350-400ºC and 1-3 atm, a heat treatment under an inert atmosphere and a distillation fractional

The patent EP-A-0167046 describes the production of a pitch with low solids content, by oxidation with air or oxygen of a distillation fraction selected from coal tar or heavy oil derived from it, while heats at temperatures of 315-385 ° C preferably, although the possibility of working from a lower temperature (149ºC), until a product is obtained Desired intermediate. This intermediate product is subjected subsequently to distillation by stripping with steam or a inert gas, although such distillation could be removed using higher temperatures in the oxidation phase. The result is an impregnation pitch especially usable for manufacturing electrodes

This patent does not contemplate the possibility of introducing an intermediate heat treatment to improve the pitch quality (in rheological terms and fixed carbon) and the final performance, nor are the pressure conditions or the time required for the processing stages.

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Description of the invention

The process of the invention, compared to the state of the art, part of a wider range of subjects premiums, including aromatic petrochemical fractions. The breas obtained according to the invention, in comparison with those of the state of the art, have a higher intrinsic quality and better properties in relation to health (carcinogenesis) and medium ambient.

The reaction of air oxygen with oil of anthracene at temperatures <400ºC and preferably> 350ºC, produces a molecular condensation through mechanisms that, to judge by the reactivity of the main oil components anthracene, seem to be similar to those observed when It uses sulfur as a catalyst.

It has been observed that parameters such as temperature, residence time, gas flow (air / oxygen), reactor load and pressure, alter the course of the reaction, favoring or inhibiting aromatic condensation reactions, which are critical for the formation of molecular structures compatible to promote aromatic condensation reactions in place of polymerization and crosslinking reactions. A additional heat treatment in an inert atmosphere, allows to increase the flatness of the molecules and stabilize the reaction product in terms of debugging possible side reactions, which favors its wettability, increases its graffiti and improves reaction yields in general.

Breas produced by this invention show a substantial reduction of components carcinogens due to its limited presence in the oil of anthracene and its reaction through the operating conditions proposals. At the same time, performing a distillation fractionated in vacuum, together with the molecular weight distribution which is achieved through the selected operating conditions, generate a pitch with reduced volatility which implies a substantial environmental benefit.

The reaction of anthracene oil with air generates only by-products / effluents only water (slightly contaminated with ammonia and water composition equivalent ammonials obtained during the distillation process of tar) and a gaseous stream containing depleted air, CO and CO 2. Being free of solid particles and impurities metallic, the pitch or the resulting carbonaceous material will not have such components.

Depending on the reaction conditions selected, the resulting pitch can generate cokes that observed under polarized light microscope may present 100% anisotropic or 100% isotropic, depending on the properties of the pitch of which be concerned.

In view of the advantageous features of the breasts obtained by the process of the invention, those Breas are suitable for applications belonging to the field of carbonaceous precursors, and in particular for the manufacture of electrodes for the aluminum industry, graphite electrodes and synthetic graphite in general, binders for the industry refractories, water repellent materials and electrometallurgical paste.

Because of the low selectivity of the reaction, anthracene oil that does not react can be directly marketable, according to the usual applications of said matter premium obtained by tar distillation. Additionally, the increase in anthracene / phenanthrene concentration, because poorly reactive components, would cause that fraction promote current interest in pasta making anthracene.

During the process three situations are generated phenomenological derived from collateral reactions to avoid:

one.

Formation of gums / structures crisscrossed

2.

Particle generation solid.

3.

Generation of high structures molecular weight.

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The processing conditions were determined in order to avoid collateral reactions previously mentioned, while maximizing performance, economy and process safety For this reason the following operation parameters:

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Temperature: 250-400 ° C, preferably 350-400 ° C.

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Pressure: 5-10 bar g.

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Specific air flow (21% O2): 0.1-0.25 kg / kg of oil anthracene.

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Residence time in reaction: 2-10 seconds, preferably 6-10 seconds

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Conversion in a single stage: ≤40%. Successive stages of transformation are achieved net returns greater than 60%.

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Atmospheric heat treatment inert: 340-400 ° C, 3-10 hours, 0-10 bar g, preferably 370-400ºC, atmospheric pressure and 4-6 hours.

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Distillation to the point of softening: According to the application. For applications conventional between 85-250ºC, Mettler.

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According to the invention the procedure is performed by sequential application combined in three stages:

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Oxidative heat treatment (reaction).

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Atmospheric heat treatment inert (stabilization).

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Vacuum fractional distillation (softening point setting and component depletion volatile)

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The pitch thus obtained, compared to the produced according to standard procedures, for example EP-A-0167046, provides yields around 50%. It is a pitch usable in multiple applications and presents better properties in relation to health (content in carcinogenic components) and environment (content in volatile components).

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Description of the drawings

To perform the process of the invention the pilot plant was used, without binding or limiting nature whose scheme is illustrated in the attached Figure 1, in which the respective numerical references designate:

one.

Reactor.

2.

Recirculation pumps

3.

Reagent Dosing System (air / oxygen).

Four.

Static mixer.

5.

Oxygen analyzer

6.

Heat treatment tank.

7.

Distillation column for setting the point of softening.

8.

Pressure regulator.

9.

Temperature regulators

10.

Heating systems.

eleven.

Collection of vents.

12.

Anthracene oil inlet.

13.

Purge.

14.

Anthracene oil recirculation that does not reaction to.

fifteen.

Pitch output

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Examples

The following examples correspond to ways of embodiment of the invention, which are given by way of non-limitation.

Oil is used as a preferable raw material of anthracene from coal coal distillation, with the following average characteristics (aspect no limitative):

one

In accordance with the advantageous characteristics of The invention can be used without any inconvenience in how much quality of the product generated, different fractions carbochemicals, by expanding or narrowing the range of proposed distillation. The only substantial modification that is obtained will be that derived from a greater or lesser yield of process.

If non-carbochemical oils are used or components with a high content of heteroatoms and / or components with high content in naphthenic structures and side chains, the reaction must be controlled with caution to avoid formation of gums and cross-linked structures. The temperature maximization and reduce conversion to one stage.

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Example 1

In the pilot plant described above, processed a sample of anthracene oil under the following terms:

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Temperature: 300ºC.

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Residence time: 6 seconds.

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Specific air flow: 60 Nl / h air per kg of oil.

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Pressure: 5 bar g.

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Heat treatment: 400ºC, 5 hours, 10 bar g.

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Distillation: Adjustment to the point of softening 90 ° C, Mettler.

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A pitch was obtained with the following characteristics, compared to an impregnation pitch standard, and the net yield in brea was 55%:

2

The substantial increase in Theological properties of the pitch obtained, measured through the filtration rate and increases in beta resin and fixed carbon.

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Example 2

In the pilot plant described above, processed a sample of anthracene oil under the following terms:

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Temperature: 350ºC.

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Residence time: 4 seconds.

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Specific air flow: 60 Nl / h air per kg of anthracene oil.

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Pressure: 5 bar g.

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Heat treatment: 400ºC, 5 hours, 10 bar g.

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Distillation: Adjustment to the point of softening 90 ° C, Mettler.

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A pitch was obtained with the following characteristics, compared to an impregnation pitch standard, and the net yield in brea was 38%:

3

4

It is noted that conversion control and a higher reaction temperature (with respect to Example 1) provide a product with improved filtration rate and lower generation of insoluble quinolein, as a result of a lower generation of crosslinked structures, which are composed of high molecular weight and, when the process is performed in a lower time, less generation of solids.

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Example 3

In the pilot plant described above, processed a sample of anthracene oil under the following terms:

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Temperature: 350ºC.

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Residence time: 4 seconds.

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Specific air flow: 60 Nl / h air per kg of anthracene oil.

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Pressure: 5 bar g.

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Heat treatment: 400ºC, 5 hours, 10 bar g.

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Distillation: Adjustment to the point of softening 110 ° C, Mettler.

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A pitch was obtained with the following characteristics, compared to an impregnation pitch standard, and the net yield in pitch was 35%:

5

In this example the resulting pitch would be suitable for application as a binding pitch for electrodes of the aluminum industry When a higher proportion of insoluble in quinolein, it is possible to prepare mixtures with a pitch carbochemical with high insoluble content, in which case it would obtain a pitch with beta resin and fixed carbon (normalized to insoluble level) with improved parameters.

From the previous properties, it deduce the potential advantages of the process to generate carbon precursors with lower compound content carcinogens (B [a] P equiv.) and less impact environmental (absence of volatile components at 360 ° C).

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Example 4

In the pilot unit described above, processed a sample of anthracene oil under the following terms:

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Temperature: 350ºC.

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Residence time: 4 seconds.

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Specific air flow: 60 Nl / h air per kg of anthracene oil.

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Pressure: 5 bar g.

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Heat treatment: None.

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Distillation: Adjustment to the point of softening 90 ° C, Mettler.

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A pitch was obtained with the following characteristics, compared to an impregnation pitch standard, and the net yield in pitch was 35%. I also know set forth in the following table, by way of additional comparison, the results of the sample obtained in Example 2 as reference of the efficiency of the intermediate heat treatment recommended by the invention.

6

In this case it is observed how the application of a stabilization heat treatment improves filtration rate (rheological properties). At the same time the influence is verified on beta resin, fixed carbon and overall performance of heat treatment.

Claims (2)

1. Procedure to produce breasts from tars and their distillates, carried out in three stages: oxidative heat treatment, inert atmosphere heat treatment, and fractional distillation, characterized in that the oxidative heat treatment stage is carried out at a temperature less than 400 ° C, a pressure less than 10 bar g and a residence time in the range between 2-10 seconds, and preferably 350-400 ° C, 5-10 bar g and 6-10 seconds, using as reactive air, oxygen, oxygen depleted air, or their mixtures 2. Method according to claim 1, characterized in that as a by-product anthracene oil is obtained which has an increased anthracene / phenanthrene concentration.