Land Contamination: Technical Guidance on Special Sites: Acid Tar ...

• benzole refining;• refining petroleum fractions, particularly in white oil production; and• oil re-refining.A brief outline of each of these processes is provided below.Benzole Refining Process• Benzole is a mixture of predominantly aromatic hydrocarbons that result from thewashing of residues from coal carbonisation processes with concentrated sulphuricacid to remove impurities, followed by distillation;• use of relatively untreated benzole in motor vehicle fuel declined in the 1960s andattempts were made at producing a more saleable product, including the use of moresevere acid treatment that produced a more acidic, thicker, more complex acid tar thanpreviously;• attempts to find new markets for benzole failed, however, and there are now very fewbenzole refineries in existence.White Oil Production Process• White oil is a liquid paraffin, frequently used in medicinal preparation, that is producedby removing unsaturated and aromatic hydrocarbons together with sulphur compoundsfrom heavy lubricant fractions;• the process involved a repetitive series of acid and alkali treatments (the acid being‘oleum’ - the most concentrated form of sulphuric acid) and the resulting acid tars weregenerally thicker, more acrid and more hazardous than those from benzole refining.Typically, Fuller’s Earth was used to absorb residual acid and is generally found codisposedwith acid tars;• sulphuric acid was also used in other petroleum fraction refining operations,particularly before 1930 when it was the only available process.Oil Re-refining Process (including oil refining)• Oil re-refining involved the removal of impurities such as lead, zinc and manganesefrom spent lubricating oils using concentrated sulphuric acid;• the acid tar resulting from this process was much more variable in composition thanthat from benzole refining and white oil production; its composition being dependenton a number of variables including the nature of the oil, the contaminants it containedand the amount of acid used.R&D <strong>Technical</strong> Report P5-042/TR/04 8