why is sulphur removed from crude oil?

There are several reasons why it is good to remove sulfur
from crude oil.

First of all, the sulfur present in the
crude oil can harm the catalysts that are used in the refining of crude oil into the
many useful products obtained from crude oil.  Catalysts are materials used to promote
chemical reactions without taking part in the reactions themselves.  Catalysts are
generally very expensive materials and anything that inhibits their activity or shortens
their life increases the cost of the refining
process.

Second, if sulfur remains in diesel fuel and/or
gasoline when it is introduced into a car or truck engine, it will again interfere with
the catalytic convertor installed in the exhaust system of the vehicle. The catalytic
convertor helps to reduce emissions from the car thus improving air
quality.

Third, if sulfur is present in fuel, when the fuel
is burned it will be converted to SO2 which is a known precursor to acid
rain.