Hydrotreating and Hydrocracking

In addition, oily sludge from a wastewater treatment facility that results from treating sour wastewaters may be a hazardous waste (unless recycled in the refining process). These include API separator sludge, primary treatment sludge, sludge from various gravitational separation units, and float from dissolved air flotation units. 

Propylene, another source of toxic releases from refineries, is produced as a light end during cracking and coking processes. It is volatile as well as soluble in water, which increases its potential for release to both air and water during processing. 

Like catalytic cracking, hydrocracking processes generate toxic metal compounds, many of which are present in spent catalyst sludge and catalyst fines generated from catalytic cracking and hydrocracking. These include metals such as nickel, cobalt, and molybdenum. 

The off-gas stream from hydrotreating is usually very rich in hydrogen sulfide and light fuel gas. This gas is usually sent to a sour gas treatment and sulfur recovery unit along with other refinery sour gases. 

Fugitive air emissions of volatile components released during hydrotreating may also be toxic components. These include toluene, benzene, xylenes, and other volatiles that are reported as toxic chemical releases under the EPA Toxics Release Inventory. 

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Rabo J.A. (ed.) (1979) Zeolite Chemistry and Catalysis, American Chemical Society, Washington, DC Ward J.W. and Qader, S.A. (eds) (1975) Hydrocracking and Hydrotreating, ACS Symposium Series, 20, American Chemical Society, Washington, DC,... 

Use of hydrocracking and hydrotreating processes that produce lower wastewater loadings than existing processes. 

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