Pitch coking value

The specification requirements for electrode binder pitch, eg, high C/H ratio, high coking value, and high P-resin content, effectively ruled out pitches from gasworks or low temperature tars. The cmde tar is distilled to a medium-soft pitch residue and then hardened by heating for several hours at 385—400°C. This treatment increases the toluene-insoluble content and produces only a slight increase in the quinoline-insoluble (Ql) material, the latter by the formation of mesophase. 

Coke materials are generally made by heat-treatment of petroleum pitch or coal-tar pitch in an N2 atmosphere. Coke made from petroleum is called "petroleum coke" and that from coal is called "pitch coke". These materials have the closest-packed hexagonal structures. The crystallinity of coke materials is not so high as that of graphite. The crystallite size of coke along the c-axis (Lc) is small (about 10-20 A) and the interlayer distance (d value about 3.38-3.80 A) is large. 

ASTM D-2416. Standard Test Method for Coking Value of Tar and Pitch (Modified Conradson). 

Other test methods that are used for determining the coking value of tar and pitch (ASTM D-2416, ASTM D-4715), which indicates the relative coke-forming properties of tars and pitches, might also be applied to asphalt. Both test methods are applicable to tar and pitch with an ash content <0.5% (ASTM D-2415). The former test method (ASTM D-2416) gives results close to those obtained by the Conradson carbon residue test (ASTM D-189, IP 13). However, in the latter test method (ASTM D-4715), a sample is heated for a specified time at 550 10°C (1022 18°F) in an electric furnace. The percentage of residue is reported as the coking value. 

ASTM. 201 Id. Test Methodfor Coking Value of Tar and Pitch (Modified Conradson) (ASTM D2416). Annual Book of ASTM Standards, Section 04.04. American Society for Testing and Materials, West Conshohocken, PA. 

The coke yield is particularly dependent on the coking value of the raw material for atmospheric residues, it is around 20%, for pyrolysis residues around 35% and for coal tar pitch over 50%. Table 13.1 compares the yields from delayed coking of residues of different origins. 

The origins and development of the concept of carbonaceous mesophase, as derived from discotic aromatic nematic liquid crystals, enable applications to be made to industrial processes. The world availability of pitch materials is such that there is an abundance of pitch which produces cokes of little commercial value. A major incentive for research into the Chemistry of mesophase formation is the commercial up-grading of such pitches and the development of specialized pitches. Structure in cokes is described in terms of optical texture. 

The world availability of pitch materials is such that there is an abundance of pitch which produces cokes of little industrial value. The economic pressures within the industry are to upgrade the commercial value of these pitches. Three ways of doing this appear as possibilities - (i) from fractionation separation of pitch systems to select molecular species (a process of "molecular cropping") most amenable to formation of mesophase. (ii) to add, by blending, materials which have been proven to up-grade the quality of resultant cokes. 

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