Anisotropy and mesophase formation towards carbon fibre production from coal tar and petroleum pitches: a review

Abstract

A mesofase é o fator determinante para se produzir as propriedades e microestruturas desejadas dos materiais de carbono. A remoção das moléculas mais leves é necessária para sua produção, mas o rendimento pode ser melhorado com a utilização de pressão ou oxidação, antes da remoção das mesmas. Piches anisotrópicos podem ser produzidos através das tradicionais esferas de mesofase de Brooks e Taylor, ricas em resinas α, ou evitando-se as mesmas, através de outras técnicas, como a extração com solventes ou agitação intensa, para gerar, quase que exclusivamente, as resinas β. Piches anisotrópicos, contendo valores próximos a 100% de resinas β, têm sido fiados a temperaturas mais baixas, produzindo fibras de carbono de piche de maior qualidade. Estudos recentes mostraram, experimentalmente, porque os piches exibem comportamentos tão diferentes, no que diz respeito à produção da fibra de carbono, quando suas composições variam em termos de resinas α e β.Mesophase is a key issue to design carbon materials towards its properties and microstructures. The understanding of this intermediate phase has changed since it was first discovered. The removal of light molecules is necessary to produce mesophase, but the yield can be improved if other techniques, such as pressure and oxidation, can be used before they are carried out of the system, with nitrogen or vacuum. Anisotropic pitches can be produced throughout the traditional Brooks and Taylor mesophase spheres, rich in α-resins, or, avoiding them, with other techniques, such as solvent extraction or strong agitation, to generate, almost exclusively, β-resins. Anisotropic pitches exhibiting almost 100% β-resins have been meltspun at lower temperatures, producing pitch carbon fibres of higher quality. Recent studies were able to explain why the behaviour of the pitches is so different, towards the pitch carbon fibre production, when their compositions, in terms of α-resins and β-resins, change.

Mesophase formation behavior in petroleum residues

“…Such chemical reactions lead to the formation of large planar molecules. As the thermal soaking progresses, the size of the mesophase spheres grows and then they coalesce to form large mesophase spheres which separate from the lower density isotropic pitch phase and slowly settle [28]. Mesophase spheres observed in these cases, in size Figs.…”

“…When petroleum residues are thermally soaked, first, smaller aromatic molecules are formed by thermal polymerization, condensation and de-alkylation reactions [28]. These smaller aromatic molecules are then polymerized and condensed and form planar aromatic molecules.…”

Preparation, Characterization, and Applications of Carbonaceous Mesophase: A Review

“…It needs to be emphasized that carbonaceous precursors for the preparation of high-performance mesophase pitch are very crucial. Although commercial coal-tar pitch or petroleum pitch or heavy oil is very cheap and easy to obtain, these feedstocks are normally a complex mixture including with some heteroatoms and inorganic ash (~0.2 wt.%), which makes a spinnable mesophase pitch difficult to prepare [6][7][8]. So far, it is still very hard to massively produce cheap mesophase pitch with high quality, especially for continuously melt spinning high-performance carbon fibers.…”

Preparation of needle coke from petroleum by-products

“…It provides thermal energy to form a mesophase of the precursor during carbonization [6]. In carbonization, thermal cracking, thermal polymerization, condensation and dealkylation occur [7]. When starting materials are thermalized, cross-linkages are broken and polymerized aromatic molecules form liquid crystal and then adjacent liquid crystals coalesce [8].…”