3027 - The method of removing of wood preservatives containing polycyclic aromatic hydrocarbons (PAH) from wood waste materials (e.g. railway sleepers) by using supercritical extraction.

Robert Brzozowski, Stefan Szarlik, Zbigniew Kolodziej, Piotr Palucki

Industrial Chemistry Research Institute

Patent P. 415392

Wooden objects used outdoor such as railroad sleepers, poles, construction items, fences etc. which can underwent to atmospheric and biological influence have been usually preserved with creosote oil, i.e. a mixture of polycyclic aromatic hydrocarbons (PAH). However, PAH were found to be carcinogenic, bio-accumulative and toxic both for human and for the environment. The wood waste materials, collected during the renovation of railways are classified as a hazardous wastes (code 17 02 04*) and must be supervised and under inventory control. The wood waste materials are stored in large waste stock piles, and currently there is not known an efficient method to recycle them. The proposed methods of burning or gasification of the wastes is difficult and needs to fulfil severe requirements for PAH pollutant emission. Moreover, wood wastes must be grind down prior to burning or gasification, that can lead to the unwanted additional PAH emission. There was also proposed a method of creosote repellent removing from wood wastes (railroad slippers) by special bacterial strains. This method, however, has drawbacks such as time-consuming, wet wood is obtained that needs additional drying and large quantities of water wastes are obtained which are contaminated with bacteria and chemicals. According to our method, PAH containing repellent is removed from wood items (railroad sleepers) by supercritical extraction with re-circulating carbon dioxide stream. Depending on extraction conditions, almost total cleaning of wood is possible. The waste wood cleaned with our method can be reused more efficiently than for energetic purposes. Moreover, creosote oil can be reused for wood impregnation or utilized for other purposes.

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