JPH0222787B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for modifying coal tar. More particularly, the present invention relates to a method for reducing and/or modifying the content of quinoline insolubles in coal tar. Coal tar is usually obtained as a by-product during the distillation of coal in coke ovens, for example during the production of metallurgical coke. It consists of a mixture of a number of hydrocarbon compounds that can be separated by distillation of tar. The residue in the kettle after such distillation, pitch, is a viscous substance that softens and flows when heated. Pitch is conventionally classified according to its softening point and solubility in various solvents such as quinoline, benzene and dimethylformamide. The latter property is usually expressed as the percentage of pitch that is insoluble in the solvent; for example, the percentage of pitch that is quinoline insoluble Ql is a widely used property of pitch. Much of the Ql production occurs at the high temperatures that tar is exposed to during coke production and remains in the pitch residue after distillation. The presence of Ql in tar or pitch can be tolerated for a limited number of applications. However, in many applications the presence of significant amounts of Ql is considered an unfavorable property of the material. The granularity of Ql makes almost any process that requires the pitch to pass through a small orifice difficult. For example, it will be difficult for Pituchi to penetrate. Furthermore, if Ql
If it has a high ash-forming impurity content, it will significantly increase the combustion rate of the carbon body resulting from pitch coking (or carbonization). Accordingly, one object of the present invention is to provide a method for reducing and modifying the quinoline insoluble content in coal tar materials. It is also an object of the present invention to provide a method for obtaining pitch material with reduced quinoline insolubles content. In one aspect, the present invention relates to a method for reducing and modifying the quinoline insoluble content Ql of a coal tar material, the method comprising: converting a coal tar material into a coal tar material by adding n-methyl-2-pyrrolidone and a coal tar distillation boiling at 100-350°C. a solvent containing at least one fraction of the coal tar material, thereby forming a solvent soluble fraction and a solvent insoluble fraction of the coal tar material, and separating the two fractions, with Ql of the coal tar material being equal to the fraction of the latter fraction. The solvent-dissolved fraction becomes comprised of coal tar material with reduced and modified Ql. Preferably the method includes an additional step of recovering the solvent. In another aspect, the present invention provides reduced and modified Ql by distillation of the solvent-soluble fractions described above.
Concerning the production of pitch material with. FIG. 1 is a schematic flow diagram illustrating steps required by one embodiment of the present invention. Figures 2 (Figures 2a and 2b) are scanning electron micrographs of insoluble particulate matter in tar and pitch, respectively. The present invention deals with quinoline insoluble matter in coal tar materials.
The present invention relates to a method capable of reducing the content of Ql. The coal tar material thus processed was reduced
It can be distilled to obtain pitch with Ql. Moreover, the Ql contained in the pitch thus obtained usually has a different particle size distribution than a conventionally obtained pitch with the same Ql. This latter property according to the present invention is referred to as a "modification" of Ql. The present invention further relates to new coal tar pitch materials having significantly reduced viscosity and lower average particle size. Broadly speaking, the method of the present invention comprises solvent extraction of coal tar material to separate quinoline soluble from quinoline insoluble components. The solvent chosen for this operation then contains at least one of n-methyl-2-pyrrolidone and a coal tar distillate fraction boiling between 100 and 350°C, preferably between 200 and 350°C. In the following, the latter solvent will be referred to as cleaning oil. This term is widely used in the industry. As a result of the mixing of the coal tar material and the solvent, two fractions are formed which can subsequently be separated: a solvent-soluble fraction and a solvent-insoluble fraction containing the majority of Ql, the former fraction consisting of the coal tar material. has a significantly decreased Ql. These fractions may be separated by conventional methods such as filtration, centrifugation, decantation, etc. The solvent-dissolved fraction of the coal tar material thus treated can be distilled to separate different fractions with different boiling points to obtain pitch material with significantly reduced Ql. The pitch materials thus produced have a number of properties and uses associated with low Ql, significantly reduced viscosity and relatively low average particle size. The same distillation that serves to separate the high-boiling components from the pituitary residue also serves to separate the n-methyl-2-pyrrolidone, which is distilled off together with the high-boiling components, from the high-boiling components. n-Methyl-2-pyrrolidone has a lower boiling point than the light boiling components contained in the distillate and can therefore be separated from them. The washed oil fraction of the distillate is n-methyl-2-
It can be distilled off together with pyrrolidone and can equally be used (individually or in combination with n-methyl-2-pyrrolidone) as a solvent in this solvent extraction process. This allows some flexibility in the distillation operation. The n-methyl-2-pyrrolidone and/or wash oil fraction contained in the distillate can then be recycled for extraction of further coal tar material. The amount of solvent used in this extraction depends on the viscosity of the resulting coal tar solvent mixture required by the separation technique (and this also depends on the temperature of the process).
It is also determined in part by the amount required to dissolve substantially all of the quinoline soluble material. Typically the proportion of solvent in the mixture is usually about 20% of the mixture.
It would be in the range of ~80%. That is, the solvent:tar ratio is within the range of 1:4 to 4:1. Referring now to FIG. 1, the n-methyl-2-pyrrolidone introduced via line 1 can be mixed with recycled solvent, which may additionally contain some light boiling components, and line 2 It is then introduced into a mixing tank 10, where it is mixed with the untreated tar that has already been introduced into this tank via line 4 at a high temperature that is sufficiently easy to handle and further process. The mixture then passes via line 6 to a separation step 20 where the solvent-soluble fraction and the solvent-insoluble fraction are separated, preferably by difference in specific gravity or by filtration, so that the former fraction passes via line 8. Leaving this step, the latter fraction leaves the step via line 7. The former fraction containing tar with reduced Ql is distilled in a distillation step 30, from which n-methyl-2-pyrrolidone and light boilers appear as an initial fraction of the distillate, optionally in a separation step 40. can be separated from each other at
Alternatively, it can be recycled via lines 13 and 15 for use as a solvent in the extraction of the next batch of coal tar material. The pitch residue obtained from this distillation via line 9 has, in addition to a reduced Ql content, a significantly reduced viscosity and a low average particle size of insolubles. The advantages to the user of this method are many and not only the extent of Ql removal from coal tar that results from the use of this method. Some of the other advantageous embodiments of the process are based on the solvent system used in the process, namely n-methyl-2-
It originates from the light-boiling fraction of pyrrolidone and/or tar distillate; in particular the ease of use of the solvent, the ease of recovery, the ease of reuse and the convenience of incorporating these operations into conventional pitch production processes. The surprising result of this method is that the viscosity of pitch and Ql
This is how it is affected by the grain size distribution. The particle size distribution of pitches derived from unextracted tar, or pitches extracted with solvents different from those of the present invention, is often characterized by a greater degree of particle agglomeration. The pitch material thus obtained is characterized by a lower viscosity than that of pitch obtained by distillation of untreated coal tar. This is particularly important in applications such as impregnation of prebaked electrodes where pitch particle size is important. The following examples will serve to illustrate the invention. Example 1 This example illustrates how the Ql of a conventional coal tar material can be reduced according to the present invention using the light boiling fraction of coal tar distillate (washing oil) as the solvent. A sample of coal tar with a Ql of 6.5% and properties typical of products obtained from steel mills was mixed with wash oil at a tar to wash oil ratio of 3:2. The mixture was run on a Buchner funnel No. 1 using a medium vacuum to facilitate the process. The Ql of the treated tar was measured. Therefore, the liquid was distilled under atmospheric pressure, and the Ql content of the pitch residue was determined according to ASTM D2318. The experimental results are summarized in Table 1 below. The above procedure was repeated for two other commercial coal tar samples with Ql values of 7.0 and 23.7%, respectively. In both cases the Ql in the treated tar was only a small fraction of the Ql in the original sample. Perhaps a more significant outcome, indicative of the extent of Ql removal occurring in the above process, was the lower Ql content in the pitch residue compared to the original tar. Ql
is typically due in part to a large reduction in capacity.
This is surprising since it also concentrates in the pitch, in part due to some cracking that occurs during distillation. Despite that,
In all cases the Ql in the pitch was only a small fraction of the Ql in the previous tar. The above procedure was repeated on the same three tar samples using a tar:solvent ratio of 1:4. Experimental results, which are qualitatively substantially the same as the previous set, are also summarized in Table 1 below.

Table: Example 2 This example illustrates the use of n-methyl-2-pyrrolidone as a solvent in the extraction of Ql from tar. A tar sample identical to that of Example 1 was subjected to substantially the same procedures and tests as described in the previous example. The results of these experimental runs, summarized in Table 2, follow substantially the same pattern as in Example 1. The treated tar has a greatly reduced Ql, which is also indicated by the low Ql content of the pitch residue left after tar distillation.

[Table] Example 3 This example shows the particle size of the insoluble matter in the tar extracted using a conventional solvent (quinoline in this case) and the residue in the pitch after extraction of the precursor tar according to the present invention. A qualitative comparison with the particle size of insoluble matter is shown. FIG. 2a is a scanning electron microscopy (SEM) photograph of residual tar Ql resulting from extraction using quinoline.
Figure 2b shows the SE of insoluble matter in pitch made from the same tar after n-methyl-2-pyrrolidone extraction.
M. It's a photo. It can be easily seen in the former photograph that the typical particle size is about 1 micron or more, with the aggregated particle size ranging up to about 4 microns. The particle size in the latter photograph (Figure 2b) is approximately 0.1 microns or less to approx.
In the 0.5 micron range, larger aggregates are about 1 micron in size. The particles in the latter photo not only contain insoluble matter due to tar extraction, but also the original Ql is concentrated and Ql
The difference in particle size distribution is even more substantial when one realizes that it also includes "secondary" Ql produced during tar distillation for pitch production, which acts as a nucleus for particle growth. The operations described above are susceptible to a wide variety of modifications that will be obvious to those skilled in the art and that fall within the scope of the claims.

[Brief explanation of drawings]

FIG. 1 is a schematic flow diagram illustrating steps required by one embodiment of the present invention;
Figures a and b are scanning electron micrographs of insoluble particles in tar and pitch, respectively. In the figure, 10: mixing tank, 20: separation process, 3
0: Distillation process, 40: Separation process.

Claims (1)

[Claims] 1. A method for reducing the content of quinoline insoluble Ql in a coal tar material, comprising:
mixing with a solvent containing at least one fraction of a coal tar distillate boiling between separation from the fraction, in which Ql is concentrated in the solvent-insoluble fraction and the solvent-soluble fraction is
A method as described above, characterized in that it consists of a coal tar material with reduced Ql. 2 An additional step of distilling a solvent-soluble fraction of the coal tar material to obtain a pitch material, wherein the pitch material has a lower Ql than the pitch material obtained by distillation of the coal tar material.
2. A method according to claim 1, comprising an additional step of obtaining a . 3. The method of claim 2, wherein the distillation further serves to separate the solvent from the solvent-dissolved fraction. 4. The method of claim 3, wherein the separated solvent is used for the extraction of another coal tar material. 5. The method of claim 1, 2 or 3, wherein the ratio of solvent to coal tar material ranges from about 4:1 to about 1:4. 6. A method according to claim 1, 2 or 3, wherein the mixing and separating steps are carried out at a temperature range of 75 to 95°C. 7 the separation is carried out by sieving the mixture;
A method according to claim 1, 2 or 3. 8. A method according to claim 1, 2 or 3, wherein the separation is carried out by centrifugation of the mixture. 9. A method according to claim 1, 2 or 3, wherein the separation is gravity separation.