Overview

The crude oil being produced around the world is showing a higher content of organic sulfur [world figures: 1990 output: 70,800 thousand barrels a day (tbd) with 1.13 wt% sulfur; 2010 projected output: 83,450 tbd with 1.27 wt% sulfur], so refineries now have to deal with severely impure feedstocks. Sulfur levels in crude oil range from 1,000 to 30,000 ppm. Diesel sulfur levels are much higher and are on the order of 5,000 ppm. Currently acceptable sulfur levels are on the order of 500 ppm and are soon to be reduced to 10 to 15 ppm. Sulfur oxides obtained from the combustion of gasoline poison the catalytic converters in automobile exhaust systems.

It is estimated that around 80 million barrels of oil are pumped from the earth every day. Most of these hydrocarbons are burned for energy. Most liquid and solid reserves are contaminated with sulfur, so direct combustion will release large amounts of sulfur oxides into the atmosphere, the natural consequence of which is acid rain. To avoid such adverse environmental effects, the following measures have been adopted.

• Limit sulfur emissions from power plants by using low sulfur fuels and postcombustion wet gas scrubbing

• Impose increasingly stringent restrictions on sulfur levels in transportation fuels and home heating oil (targets: European Union, heating oil 1,000 ppm by 1999 and diesel fuel less than 100 ppm by 2005; United States, gasoline 50 to 100 ppm).

Recently, it has been found that for any refiner, the major source of sulfur is cat-cracked naphtha.