Physical treatment - deasphalting

Feedstocks for cracking processes are now usually the vacuum residue or heavy distillates from vacuum distillation. 

Heavy oils and residues contain substantial amounts of asphaltenes, which preclude the use of these residues as fuel oils or lubricating stocks. Subjecting these residues directly to thermal cracking is economically advantageous, since, on the one hand, the final result is the production of lower-boiling fractions on the other hand, asphaltenes in the residue are regarded as coke-forming constituents and may even promote coke formation from the compounds of the residue. 

Marcel Dekker, Inc. 270 Madison Avenue, New York, New York 10016 

Furthermore, to avoid catalyst poisoning or reduction in catalyst activity, it is essential that as much nitrogen and heavy metals as possible are removed from the feedstock. It has been shown [9] that a greater part of the heteroatoms (nitrogen, oxygen and sulfur) and the heavy metals are contained in or associated with asphaltenes. It is necessary for the cracking processes that asphaltenes are removed from the cracking feedstock. 

There are a number of thermal processes, such a visbreaking and coking, that are directed at upgrading feedstock by the removal of asphaltenes. There is also the method of deasphalting with liquid hydrocarbons or gases such as propane, butane or iso-butane. This is very effective in the preparation of vacuum residues as cracking feedstock. 

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Treatment for crude oil residues is intended to minimize the adverse effects of the presence of asphaltenes during thermal processing. Generally, two types of treatment possibilities are available. There are physical and chemical treatments. The physical treatment essentially involves deasphalting whereas the chemical treatment includes thermal processes such as visbreaking and coking. 

In this section the stability and compatibility of petroleum will be discussed in terms of physical treatment such as distillation, deasphalting and diluent addition for pipeline transportation, and in terms of chemical treatment such as upgrading. 

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