Pyrolysis behaviour study of a tar- and sulphur-rich brown coal and GC–FID/MS analysis of its tar

• A maximum tar yield of about 16 wt.% (dry and ash free basis) was found at 610 °C.
• Phenol and m-cresol were the most abundant components in the pyrolysis tar.
• The main sulphur component detected in the tar was dimethyl trisulphide.

A non-energetic utilisation of brown coal is enabled by the thermo-chemical treatment method of pyrolysis. During this process, the tar/oil fraction of the coal is released and can serve as raw material for the petrochemical industry. Thus, a tar- and sulphur-rich Central German brown coal was tested for its pyrolysis behaviour in a laboratory-scale fixed bed reactor in order to assess its applicability as a chemical feedstock. Pyrolysis temperature as well as heating rate, holding time and particle size were varied. The investigation aimed at maximising the tar/oil fraction of the studied coal, whereby pyrolysis yields and product compositions were thoroughly examined. Particular attention was given to the analysis of the liquid pyrolysis product, conducted by gas chromatography with flame-ionisation and mass spectroscopic detection (GC–FID/MS). For the examined coal, a temperature of about 600 °C was found to be most adequate in terms of tar release with a tar/oil yield of about 16 wt.% (dry and ash free basis). Phenol was identified as tar component that forms in largest quantities (2 wt.% of tar for a pyrolysis up to 610 °C). Heating rate changes between 5 and 90 K/min and holding time variations below 30 min showed only marginal influences on product yields and compositions. No clear effect on product yields was observed for different particle sizes below 6.3 mm. In total, 131 chemical compounds or about 22 wt.% (d) of coal tar could be quantified by GC–FID/MS.