Effective Fractional Distillation of 'Coal Tars'

i-Fischer Engineering (Germany) have successfully developed and installed distillation systems for fractionating 'Coal Tar' by following the standards; ASTM D2892 (TBP) and ASTM D5236 (Potstill).

The critical Coal Tar products are components with aromatic multiple-ring systems including, for example, phenanthrene, pyrene and flourene. These components show melting points between 80…200°C and much worse, these components show “sublimation” effects.

Thus, the distillation of Coal Tar is performed similarily to the previosuly stated ASTM procedures, but the distillation units have to be modified significantly according to the product characteristics of typical coal tar components.

The sublimation of some components do cause a blocking of product or vacuum valves and lines, while solidified substances are difficult to dissolve by usual solvents, such as toluene and light naphtha. As a result of this sublimation, essential parts of the distillation system can become 'out of order' and cannot easily be cleaned anymore due to the solidified residues.

Distillation units following ASTM standard designs are not useful for handling Coal Tar samples, but will face serious operational disruptions, whilst some of the plant components could even be destroyed within a short time period.

Reflecting on these specific product requirements, distillation units suitable for Coal Tar sample fractionation have to pass a qualified re-engineering process in order to be modified for proper and reliable handling of the sublimation effect.

As an example, the photo shows a fully automated distillation system with modified design for operating Coal Tar samples following the standard, ASTM D2892. The result is a distillation report as well as a total material balance with complete print-out of TBP-data and TBP-curves in the range IBP…340°C AET.

Combining the above data with those collected from ASTM D5236 results a complete set of TBP data and curves.

In summary; distilling or fractionating Coal Tar products is possible, even in accordance to the a.m. ASTM-standards, but a well adapted apparatus design is the key point.