Solubilities of mesophases into pitch distillates

Solubilities distillates

Yang Faculty

of mesophases into pitch

Duk Park, Asao &a

and Sugio

Otani

of Technology,

(Received

Gunma University, Kiryu, Gunma 376, Japan 20 September 1982)

This study investigated the solubilities of mesophases in pitch distillates. The mesophases and distillates prepared from five pitches were mixed and then heated at 673 K for 2 h. The resulting samples were observed under polarized light. Distillates with high hydrogen donor abilities and not very high aromaticity or aliphaticity were good mesophase solvents. Whereas, the mesophases with quinoline-insiluble (al) components having larger crystallite size did not readily dissolve in the distillates. The mesophases dissolved into the distillates via formation of the network mesophase. (Keywords:

mesophase,

pitch distillate,

solubility)

Mesophase appears at the initial stage in the carbonization of coal’*’ and is known to strongly influence the structure and properties of the resulting coke3. New applications of the mesophase pitch itself, e.g. preparation of high performance carbon fibre, have become of interest in recent years 4v5. These factors have prompted current research. It is well known that the mesophase is an anisotropic substance, being similar to a liquid crystal, which appears in an isotropic carbonaceous liquid matrix’v2. It could, therefore, be regarded as a kind of emulsion, which suggests that mesophase formation must be intimately influenced by the isotropic matrix. If such interaction were clearly revealed, the mesophase formation could be controlled more carefully and would lead to the preparation of high quality coke and of mesophase pitch suitable for new practical applications. In the present work the solubilities of the mesophases into pitch distillates were examined. EXPERIMENTAL Materials used

Analytical and other data of the five pitches used are shown in Table 1. Pitch I, and pitches A and N were commercially available coal tar pitch and petroleum pitches, respectively. Pitch S was a coal tar pitch prepared Table 1

Analytical

experimentally. Pitch M was prepared by heating naphthalene in a molten salt bath (AlCl,-NaCl-KCl) at 573K for 1 h, of which details are reported elsewhere6. Preparation of mesophase samples and distillates Distillates. To prepare pitch distillates, the pitches I, S

and A were heated in a test tube to 723K under a stream of argon. The resulting samples used were the distillates from pitch I at 573-673K (reference ID-40) and 673-723K (ID-45), from pitch S at 573-723K (SD-45) and from pitch .4 at 573-723 (AD-45). Mesophases. After heating pitches I, S and A to obtain the distillates, the residue in the test tube was slowly cooled to sedimentate the mesophase with higher density. Only pitch N was heated up to 703K. The resulting residues were separated into fractions with particular optical textures. The fractions consisting of mesophase with a small amount of isotropic matrix were used as the mesophase sample. Pitch M was used without separation because almost no isotropic region was observed under polarized light. The abbreviations used for the mesophase samples are shown in Table 2. Examination of solubility

The prepared mesophase samples were added to the distillates at the rate of 10 to 50 wt% ratios

data of raw pitches

Abbreviation

Pitch

Source

C (wt%)

H (wt%)

Atomic ratio (H/C)

H,IHr+Hlb

M N A S

Naphthalene pitch Ligare-N (Kureha) A-240 (Ashland) a IP-70 (Nittetsu)

naphthalene petroleum petroleum coal coal

89.2 95.6 95.9 92.7 92.6

4.51 4.82 6.05 5.04 5.04

0.61 0.61 0.76 0.65 0.65

0.91 0.84 0.46 0.82 0.79

I

a Prepared experimentally b H,; aromatic H (6-9 ppm in ‘H n.m.r.); 001~2361/83/06070&06(s3.00 @ 1983 Butterworth & Co. (Publishers)

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1983, Vol 62, June

HI,

aliphatic

H (0.5-4

ppm in 1’H

n.m.r.1

Solubilities Table 2

Analytical

data of mesophase samples ala

Meso-

Atomic ratio

component

phase

(H/C)

(wt%)

0.61 0.54 0.59 0.51 0.51

32.4 65.7 47.8 78.1 58.5

M-M N-M A-M S-M I-M

M N A S

24 24 37 24

I

a Quinoline-insoluble

Figure

1

Optical

3.46 3.48 3.44 3.46

fraction

anisotropic

textures

of the mesophase

of mesophases

into pitch

distillates:

Y. 0. Park et al.

(mesophase:distillate = 1:9 to 1 :l) and heated at 673K for 2 h under argon, with argon bubbled through the mixture. The resulting samples were investigated using polarized light optical microscopy and for some structural analyses as described below. Three degrees of solubility were identified based on the extent of anisortopic region observed, i.e., soluble, partially soluble and insoluble. Analytical

methods

analysis and solvent extraction. Elemental analysis was carried out according to Japanese Industrial Elemental

samples

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Solubilities of mesophases into pitch distillates: Y. D. Park et al Tab/e 3

Analytical

data of QI components

LC

01

(lo-”

M-01 N-QI A-01 S-01 I-QI

26 35 31 31 25

m)

d (0021 (lo-” m) 3.45 3.45 3.48 3.44 3.45

Atomic ratio (H/C) 0.57 0.47 0.52 0.48 0.45

components extracted from the mesophase samples. The L, values of the QI components are not necessarily larger than those of their parent mesophases but the H/C ratios of QI components are smaller than those of the samples in all cases. By comparison, the H/C ratios of the distillates (Table 4) are considerably larger. AD-45 and SD-45, in particular, have large values, 0.82 and 0.74 respectively. A distillate with a lower atomic H/C ratio generally has a higher melting point. Mesophase solubilities

Table 4

Analytical

data of distillates

Distillate

Atomic ratio (H/C)

H/H,

I D-40 SD-45 AD-45 I D-45

0.69 0.74 0.82 0.63

0.85 0.82 0.48 0.88

+ H ,a

MP (K) 313 288 308 330

a See Table 1

Standards (JIS) M-8813-1978. Solvent extraction was undertaken according to JIS K-2325, in which pitch is extracted with quinoline at 343K. X-ray diffruction. An (002) X-ray diffraction profile of the powdered sample was obtained using a recording diffractometer with Ni-filtered CuKa-radiation. A crystallite size L, and an interlayer spacing dOo2were calculated from the (002) profile after correcting for the Lorents polarization and absorption factors. Melting point. A small piece of solid pitch distillate was sealed in a capillary and then heated in an optical microscope with a hot stage. The melting point was defined as the temperature at which an angular pitch particle becomes round. Hydrogen donor ability. The distillate was heated with anthracene (distillate:anthracene = 5:l) at 603K for 1 h under argon. The resulting sample was dissolved in C,D5N and examined using ‘H n.m.r. The H-donor ability of the distillate was evaluated from the intensity of peak around 3.8 ppm which is due to the resulting 9,10dihydroanthracene.

The solubilities of the mesophase samples in the pitch distillates are summarized in Figure 2. As can be seen, up to 14% of the mesophase dissolved completely in the distillate ID-40 (mesophase :distillate = 1:6), except for NM. SD-45 is also a good mesophase solvent, especially for S-M. The two distillates with high solubilities were extracted from coal tar pitches. The distillates ID-45 and AD-45, however, did not completely dissolve any mesophase sample, although there are insufficient data to show clear trends. Figure 2 also seems to indicate that the solubility of mesophase in distillates varies with the combinations. Using the QI data shown in Table 2, the mesophase solubilities were converted into the solubilities of QI components, e.g., the maximum amount of I-M dissolved completely by ID-40 is 14x, which corresponds to 8% of QI component. The results in Figure 3 show that 5 to 13% of QI components dissolve in the distillates. Figures 4 and 5 show the changes in optical textures of A-M/ID-40 and I-M/ID-40 mixtures in various ratios, after heating at 673K for 2 h. The original mesophase samples, in both cases, consisted of bulk anisotropic

100

50

100

ID-40

A-M

Insoluble

RESULTS

100

I-M

Figure 2

Solubilities

m

100 so-45

I-M

AD-45

Parbally Soluble

of the mesophases

50

I-M

0

Soluble

in the pitch distillates

Structures of mesophase samples, QI components and distillates

The optical texture of the mesophase samples are shown in Figure 1. All samples consist of the mesophase and a small amount of isotropic material, although the textures differ considerably from each other. Analytical data of the mesophase samples are shown in Table 2. Under the microscope all samples, as seen in Figure 1, seem to be largely mesophase but their quinoline-insoluble (QI) contents ranged from 78% of SM to 32.4% of M-M. Atomic ratios (H/C) of the mesophase samples, except for M-M, were lower than those of the parent pitches by O.O7(N-M) to O.l7(A-M). X-ray parameters of M-M could not be obtained because of its very broad (002) diffraction profile. Table 3 shows X-ray parameters and H/C ratios of QI

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1

ID-40

I-M

0

1

0

A-M

M-M

SD-45

I-M

AD-45

M-M

Insoluble Figure 3 Solubilities pitch distillates

m

Partially Soluble

of 01 components

0

Soluble

in the mesophases

in the

Solubilities of mesophases into pitch distillates: Y. D. Park et al.

Figure 4

Changes in anisotropic

textures in A-M/ID-40

Figure 5

Changes in anisotropic

textures in I-M/ID-40

mixtures of various ratios, after heating to 673 K for 2 h

mixtures

of various ratios, after heating to 673 K for 2 h

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Solubilities of mesophases into pitch distillates: Y. D. Park et al

due to the resulting 9,10-dihydroanthracene, increased in intensities in the order SD-45 > ID-40> AD-45 > ID-45.

DISCUSSION

AND CONCLUSIONS

As can be seen from Figure 2, there are some differences in compatibilities between mesophases and distillates, although all the relevant controlling factors were not necessarily revealed. Some points to be emphasized are discussed below.

Distillates

The distillate into which the mesophase readily dissolves is characterized by two factors; the high hydrogen donor ability; and the intermediate structure with lower aromaticity or aliphaticity. Although the latter factor cannot easily be explained, the former can be explained by the fact that the additive with good hydrogen donor ability is very effective in developing the mesophase into flow or domain textures in the resulting coke via more fluidous state’. It should be emphasized, therefore, that the distillate fractions with good donor ability exist in commercial pitches. Another point to be noted is the reaction temperature of distillate with anthracene to evaluate the hydrogen donor ability of the distillate. Obara et al.’ used 673K which is 70K higher than the temperature used here. A more effective evaluation occurs at 603K, which gives milder reaction conditions, because the reaction proceeds more selectively at a lower temperature.

Mesophases

10

9

876543210 8,PPt-n

Figure 6 1l-i n.m.r. spectra of the mixtures of the distillates and anthracene (distiIIate:anthracene = 5:l). after heating to 603 K for lh

textures but the 1 :l mixtures after heating exhibit clearly the isotropic matrix region and the mesophase region consisting of the fine textures. Here it is difficult to conclude that whether or not the mesophase dissolved in the distillate. In A-M/ID-40 (1:4) and I-M/ID-40 (1:3) mixtures, the mesophase resulted in network structures, after heating. A-M/ID-40, less soluble than I-M/ID-40, exhibited stronger anisotropy under polarized light. Similar network structures were also formed in the mixture systems in which the complete dissolution was never accomplished. A-M and I-M dissolved completely into ID-40 at the ratios of A-M :ID-40 = 1:9 and I-M :ID-40 = 1:7, respectively. Hydrogen donor abilities of the distillates Figure 6 shows ‘H n.m.r. spectra of the C,D,N-soluble

components of the distillate and anthracene mixtures, after heating at 603K for 1 h. The peaks around 3.8 ppm,

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In general, the mesophase sample with lower QI content and larger atomic H/C ratio can be expected to dissolve more readily the distillate. However, the present results do not necessarily coincide with such predictions. Rather the crystallite size may be a factor determining solubility of mesophase in distillate; the QI components of N-M and A-M have considerably larger L, values than those of the mesophase samples; and these parent samples are generally difficult to dissolve. However, no details are known. The hydrogen acceptor ability may be an important factor, though this ability has not heen measured. According to Sanada’, the affinity between mesophase and isotropic matrix is characterized by similarity between their atomic H/C ratios and this is a useful factor in determining the solubility between them. As stated above, however, the present results were not reasonably explained using this factor.

Dissolution process of the mesophase in distillate

As suggested from Figures 4 and 5, though not proved, the mesophase dissolves in the distillate by the following processes : bulk mesophase+fine mesophase+network mesophase. The formation of network mesophase suggests that this was not formed at the cooling stage after complete dissolution but through gradual dissolution. Such a dissolution process is known to occur in the case of polymers.

Solubilities of mesophases into pitch distillates: Y. 0. Park et al. REFERENCES I

Brooks, J. D. and Taylor, G. H. ‘Chemistry and Physics of Carbon (Ed.P. L. Walker, Jr.), Vol. 4, Marcel Dekker, New York, 1968, p. 243 2 Marsh, H. and Walker Jr., P. L. ibid., Idol. 15, 2979, p. 229 3 Marsh, H. Fuel 1973,52,205 4 Otani, S., Watanabe, S. and Ogino, H. Bull. Chem. Sot. Japan 1972, 45,3715

5 6

Singer, L. S. Carbon 1978, 16,408

Uta. E.. Inoue. S.. Horieuchi. M. and Gtani. S. Bull. Chem. Sot. Jaoan 1979,52,3400 ” 7 Mochida, I., Amamoto, K., Maeda, K., Takeshita, K. and Marsh, H. Proc. 5th London Carbon Conf. 1978, p. 237 8 Obara, T., Yokono, T., Miyazawa, K. and Sanada, Y. Carbon 1981, 19,263 9 Sanada, Y. J. Fuel Sot. Japan 1978, 57, 3

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