A Study on Carbonization of Pitches

Abstract

The present investigation was undertaken to know the effect of chemical structure of pitches and quinoline insoluble on the formation and the growth of spherical bodies observed in the early stage of carbonization of pitches. Naphtha pitch and coal tar pitch were used as samples, and were fractionated by n-hexane, acetone, benzene and quinoline into four fractions No.1, No.2, No.3 and No.4, respectively. And then, each fraction was carbonized to examine by polarized-light microscope.
Then, the structural parameters for each fraction of naphtha pitch and coal tar pitch were estimated from hydrogen distribution determined by NMR spectra, elemental analyses and molecular weight. It has been found that the aromaticity of naphtha pitch was lower than coal tar pitch, and the number of side-chains in naphtha pitch was high value compared with coal tar pitch. Furthermore, the average number of condesed aromatic rings of each fraction had a tendency to increase in the order No.1 to No.3 in both naphtha pitch and coal tar pitch.
Although the formation and the growth of spherical bodies in fractions of both naphtha pitch and coal tar pitch were easy in the order No.3 to No.1, the formation and the growth of spherical bodies in naphtha pitch were easy compared with coal tar pitch. For example, the formation of spherical bodies in the fraction No.3 of naphtha pitch was observed at the condition of 400°C and 2 hr, but that of coal tar pitch at 420°C and 2 hr.
It is interesting that the fraction No.4, that is, quinoline soluble-benzene insoluble fraction, did not fused even at 600°C and 2hr. From above result, one might have concluded that it was necessary, in the formation and the growth of spherical bodies, that pitch had a suitable size of condensed aromatic rings and some side-chains with the rings.
Further investigation was carried out for the purpose to clarify the effect of the quinoline insoluble on the formation and the growth of spherical bodies. When a small amount (less than 1%) of the quinoline insoluble was mixed into the fraction No.3 of coal tar pitch, no effect was observed in the formation and the growth. But, when in excess (more than 5%), it interfered them.