Coal Tar Pitch Volatiles Analysis Essay
COAL TAR PITCH VOLATILES
Benzene soluble particulate matter should not be attributed to coal tar pitch volatiles unless polynuclear aromatic hydrocarbons (PNAHs) are present. OSHA Method 58 specifies the collection of particulates using a glass fibre filter (GFF) and the gravimetric determination of the benzene-soluble fraction (BSF). If the BSF exceeds 0.2 mg/m3, then the sample should be analyzed by high performance liquid chromatography (HPLC) to determine the presence of selected PNAHs. The detection limit of the gravimetric procedure is listed as 6 ug per sample; the detection limit of the HPLC procedure is significantly lower. In many cases, NIOSH Method 5506 is preferred, as this method specifies collection using a filter as well as an XAD tube and collects both particulate and vapor phase PNAHs; analyses of both is performed by HPLC. The NIOSH method eliminates possible interferences and inaccuracies produced by the tedious extraction specified in the OSHA method. You can request two different PNAH HPLC scans: 5 compounds or 17 compounds.
This paper discusses the influence of pitch composition on its thermal behaviour. The value of the approach consisting in the characterization of these materials by analysis of their volatile fraction is demonstrated. The pyrolysis of nine coal tar pitches was studied by thermogravimetric analysis (t.g.a.) and derivative thermogravimetry (d.t.g.). The coke yield was closely related to both the rate of weight loss and the temperatures at which the d.t.g. curve reached maxima. To obtain information about the influence of the structures present in pitches on their thermal behaviour, the composition of the volatile fraction (evaluated by gas chromatography) was considered. The degree of condensation and the relative proportions of the different kinds of polycyclic aromatic hydrocarbons in this fraction were related to important thermal parameters deduced through t.g.a. and d.t.g. High coke yields are associated with a highly condensed volatile fraction in which alternant peri-condensed polycyclic aromatic hydrocarbons predominate over non-alternant systems.