Hydrotreating is a chemical process used to reduce the amount of sulfur in natural gas and refined petroleum. This is done to reduce the environmental impact, improve fuel quality, and prevent poisoning of catalytic reforming units. The process involves introducing hydrogen to split the carbon and sulfur bond, and the remaining sulfur is reduced to sulfuric acid or by-product sulfur. Other unwanted elements such as unsaturated hydrocarbons and nitrogen are also removed to further purify the fuel.
Hydrotreating, formally known as hydrodesulfurization (HDS), is a chemical process used on natural gas and refined petroleum. The purpose of this process is to decrease the amount of sulfur in the oil by increasing the amount of hydrogen in the product. This is done for a variety of reasons, such as reducing the environmental impact when these petroleum products are used and to prevent the reformers that process the petroleum from being poisoned. Most of the sulfur produced annually comes from this process.
When oil or natural gas is first extracted from the Earth, it contains a high amount of sulfur. This sulphur, which was not removed until the end of World War II, is harmful to the environment when the petroleum product is used. While the environment is the primary reason to reduce sulfur, another reason is because less sulfur provides a higher quality fuel. Fuel odor and color are also better when sulfur is reduced.
Another reason is to aid the longevity of the parts involved in processing the fuel. When the fuel is processed, it passes through a catalytic reforming unit which can improve the octane number of the fuel. Catalytic reforming units are made of noble metals, mainly platinum and rhenium. While both metals are resistant to corrosion, slight amounts of sulfur poison these metals and render them useless in octane boosting.
In hydrotreating, hydrogen is introduced into a mixture to increase the overall hydrogen number. Petroleum undergoes what is specifically called hydrogenolysis. This is when the carbon and sulfur bond contained in oil is split and a hydrogen atom is attached to both the carbon and sulfur atom. Through this process, sulfur can be removed from the oil to an acceptable level.
After hydrotreating, the remaining sulfur is reduced to sulfuric acid or by-product sulfur, which is similar to its natural elemental state. Most of the sulfur produced and purchased comes from this process, because there is a large supply of residual sulfur from oil refineries after hydrotreating is complete. In addition to making the oil refinery more money, this means that less sulfur needs to be extracted to adequately supply the market. Sulfur is the major element removed from fuel by hydrotreating, but there are also other elements removed that are considered unwanted in petroleum. Both unsaturated hydrocarbons and nitrogen are taken from the oil supply. This further purifies the fuel and improves its value.
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