Civil Engineering Reference
In-Depth Information
Tar, solvents and other oil-based chemicals and products that contain them
have a strong risk factor as waste products - these substances are highly poiso-
nous and have to be placed at special disposal depots. The dumping of waste
plastic can lead to the release of poisonous substances such as heavy metals into
the environment. Plastic materials in themselves are not usually poisonous, but
pose a problem mainly because of their volume, as they break down very slow-
ly in the natural environment.
Old asphalt can be recycled quite effectively by mixing it with new asphalt.
Recycling is also possible for a few plastics. All plastics, however, contain addi-
tives and impurities which lead to a lower quality plastic after recycling (down-
cycling). Even if the primary energy consumption through down-cycling is only
10 per cent of the cost of manufacture of new plastic, the high energy costs of
transport still have to be taken into account, as the plastics industry is highly
centralized. Plastic materials can be recycled at least four or five times before
they finally have to be abandoned as waste.
Most of the waste products from solvents, oil-based chemicals and plastics can
be transformed into energy. With few exceptions, the materials must be burned
in furnaces with special facilities for cleaning the emissions. Even so, there is a
Table 9.2:
Primary energy consumption for
different oil products
Product
MJ/kg
Bitumen
10-11
Asphalt
3
Solvents
14-36
Other chemicals:
Urea
14
Formaldehyde
14
Phenol
18
Ethylene (gas)
27
Acetone
13
Ethanol
15
Plastics:
Polyvinyl chloride
56-84
Polypropylene
71
Polystyrene
75
Polyethylene
67
Polyester
22
Phenolic plastic
22
Acrylic plastic
56
Polyurethane
98-110
Note:
All the products except for gas and asphalt weigh
about 1 kg/l.
