Aromatic pitch

Aromatic Pitches from the Asphaltene-Free Distillate Fraction of Catalytic Cracker Bottoms... 

Catalytic cracking bottoms (CCB) is a widely used aromatic feedstock for carbon production, such as aromatic pitch, carbon black and carbon fibers. 

We fractionated CCB by a high vacuum distillation into several distillate fractions and undistlllable residue. The distillate fractions were subjected to a two-stage high temperature thermal process to convert them to aromatic pitches. The composition of the pitches produced was determined by a solvent analysis to define their suitability for synthetic carbon production. 

CCB distillate was transformed into an aromatic pitch by a two-stage process. Initially, the CCB-distillate was thermally-treated at high temperatures, 400-450°C, under atmospheric (nitrogen) pressure and finally the unreacted fractions were vacuum stripped at 0.5-1-0 mm/760 mm Hg, leaving the aromatic pitch in 30-40% yield in which there is up to 74% of a highly anisotropic toluene insolubles fraction. 

Aromatic pitches were produced by treating CCB-distillate at 400°C, 410°C, 420°C, 430°C, and 440°C. We found that process temperature is a very important parameter in determining the rate of toluene and pyridine insoluble formation. It was also found that a relatively high temperature (around 430°C) is required to produce a pitch with a high liquid crystal content. Table II gives the composition of pitches produced at 400-440°C. Figure 1 illustrates graphically, the effect of process temperature on the rate of toluene, pyridine, and quinoline insolubles formation. 

The aromatic pitches produced from CCB-distillate are being developed for pitch carbon fiber production. 

Heavy aromatic feedstock such as the by-products from the petroleum and coal industries are used for the production of aromatic pitches. The characteristics of the pitches produced depend on the chemistry of the feedstock and the process type and conditions. 

Both CCB fractions (distillate and residue) were transformed into aromatic pitches by a high temperature thermal process at atmospheric pressure followed by vacuum stripping. A number of reaction parameters effecting pitch yield and characteristics were investigated. 

DICKAKIAN Aromatic Pitches from Residue Fractions... 

Table V. Aromatic Pitch Production from CCB-Fractions...

Aromatic Pitch Production Using Steam-Cracker Tar... 

SCT can be converted into highly aromatic pitches by physical, thermal and chemical processes such as vacuum or steam stripping, thermal or catalytic oxidative-polymerization at 229-260°C, or by a thermal process at 370-450°C at atmospheric nitrogen or hydrogen pressure. The physical or chemical characteristics of the pitches produced from SCT depend on the type of process and conditions used. Table II gives the characteristics of SCT pitches produced by distillation, catalytic air-oxidation and thermal process. 

The formation of the mesophase by this route has the disadvantage of requiring rather long processing times. An alternative route is the solvent route [18]. Isotropic aromatic pitches contain a separable fraction which, when heated at 230-400°C, develops an optically anisotropic liquid crystal phase in <10 minutes. This mesophase has been called a neomesophase since it is highly soluble in solvents such as pyridine or quinoline, while the mesophase derived by the thermal route is insoluble. The separable fraction of isotropic pitch is insoluble in solvents like benzene, toluene, or mixtures of toluene and heptane. Thus, it can be separated by solvent extraction from isotropic or heat soaked pitches (Figure 5, b and b ). 

Carbon fibers from anisotropic mesophase pitch High molecular weight aromatic pitches that are mainly anisotropic in nature are referred to as mesophase pitches. 

Liquid-phase carbonizations, of aromatic, pitch-like materials, lead to the formation of graphitizable carbons which, essentially, are non-potous carbons. Hence, to make a... 

In liquid-phase carbonizations, the mechanisms are completely different from those in the solid phase. It is via liquid-phase carbonizations (but not all liquid phases) that graphitizable forms of carbon result. How does this come about The explanation takes us to a quite different subject area, that of anisotropic aromatic, discotic, nematic liquid crystals (called mesophase) formed as a result of growth and self-assembly of the constituent polycyclic aromatic molecules of the parent material. These usually are the highly aromatic coal-tar pitches, a liquid product from the making of metallurgical coke, from aromatic pitches synthesized by the petroleum industry as well as polycyclic aromatic model compounds. 

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