PRODUCTION OF SULPHUR BY HYDROTREATING CRUDE OIL.

A number of contaminants are found in crude oil..As the fractions travel through the refinery processing units,these impurities can damage the equipment,the catalysts and the quality of the products..There are also legal limits on the contents of some impurities,like sulphur in products..

Hydrotreating is one way of removing many of the contaminants from many of the intermediate or final products..in the hydrotreating process,the entering feedstock is mixed with hydrogen and heated to 300-380degree celsius..the oil combined with the hydrogen then enters a reactor loaded with a catalyst which
promotes several reactions

--->Hydrogen combines with sulphur to form hydrogen sulphide..

--->Nitrogen compounds are converted to ammonia

--->Any metals contained in the oil are deposited on the catalyst

---->Some of the oleffins,aromatics or naphtenes become saturated with hydrogen to become paraffins and some cracking takes place,causing the creation of some methane,ethane,propane, and butanes...


SULPHUR RECOVERY PLANTS

The hydrogen sulphide created from hydrotreating is a toxic gas that needs further treatment..The usual process involves two steps:

--->The removal of the hydrogen sulphide gas from the hydrocarbon stream
--->The conversion of hydrogen sulphide to elemental sulphur, a non-toxic and useful chemical

Solvent extraction,using a solution of diethanolamine[DEA] dissolved in water is applied to seperate the hydrogen sulphide gas from the process stream..The hydrocarbon gas stream containing the hydrogen sulphide is bibbled through a solution of diethanolamine solution[DEA] under high pressure,such that the hydrogen sulphide gas dissolves in the DEA..The DEA and hydrogen mixture is heated at a low pressure and the dissolved hydrogen sulphide is released as a concentrated gas stream which is sent to another plant for conversion into sulphur...


conversion of the concentrated hydrogen sulphide gas into sulphur occurs in two stages

-->Combustion of part of the hydrogen sulphide stream in a furnace,producing sulphur dioxide,water and sulphur..

--->Reaction of the remainder of the hydrogen sulphide with the combustion products in the presence of a catalyst..The hydrogen sulphide reacts with the sulphur dioxide to form SULPHUR..

As the reaction products are cooled,the sulphur drops out of the reaction vessel in a molten state..Sulphur can be stored and shipped in either a molten or solid state...