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Issues
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Sulphur is present in all oil and gas
deposits, usually as hydrogen sulphide or as alkyl sulphides.
Combustion of fossil fuels will therefore produce sulphur dioxide,
which will dissolve in atmospheric water vapour to produce acidic
precipitation. The presence of sulphur compounds in oil and gas
can also cause problems when these are used as chemical feedstock,
as catalysts are often "poisoned" by sulphur.
The change of feedstock
for sulphuric acid from mined elemental sulphur to recovered sulphur
from fuels reflects concern about the impact of sulphur dioxide
on health and the environment. Industry now accounts for less
than 10% of all sulphur dioxide emissions, natural and human,
and the largest contribution is now from transport.
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Some problems associated with sulphur dioxide
include:
- Sulphur dioxide is a choking irritant at
high levels, but even at low levels can result in respiratory
problems
- Sulphur dioxide reacts with water and oxygen
in the air, making dilute sulphuric acid which may fall as precipitation
("acid rain"), with effects on the pH (acidity) of
water and soil
- Acid soil and water conditions may
have a detrimental effect on plant and animal habitat, and may
attack buildings made from limestone.
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Sulphuric Acid Recycling
Sulphuric acid is used as a reagent in many
processes, often as a catalyst. Disposal of spent sulphuric acid
as waste is increasingly being seen as economically and environmentally
undesirable, and much effort has gone into developing efficient
methods for recovery and recycling of the acid. In some cases the
used acid is "cleaned", but where this is not feasible,
it may be broken down to provide feedstock for the manufacture of
fresh acid. For more details on these developments
see the acid recycling section. |
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