Pyrolysis gasoline

Pyrolysis gasoline is a by-product of the production of ethylene or propene in the steam cracker . It has a characteristically unpleasant odor and is yellow in color. Pyrolysis gasoline is strongly aromatic (30% benzene , 15% toluene , 20% C ₈ - aromatics ) and contains many olefins and conjugated diolefins. ( Bromine number about 50, diene number 5-50). The boiling range is approx. 25–210 ° C.

The processing takes place in several steps.

• Distillative separation of the heaviest gas oil-like components of the pyrolysis gasoline, so-called pygas tail (boiling range: ~ 230– ~ 300 ° C, is recycled as so-called quench oil back to the steam cracker)
• Selective hydrogenation of the diolefins.
  • The diolefins are selectively hydrogenated to olefins on special catalysts with hydrogen. (Pressure 50 bar, 70 ° C, catalyst palladium or nickel )
• Desulfurization and hydrogenation of olefins
  • Removal of sulfur , nitrogen and oxygen from the hydrocarbon mixture .
  • For this purpose, the product is treated with hydrogen on the catalyst . (50 bar, 300 ° C, cobalt / nickel / molybdenum sulfide catalyst). The result is H ₂ S and saturated hydrocarbons. The aromatics are not hydrogenated under the process condition.
• Distillative separation in
  • Pytops, a boiling section similar to petroleum ether (boiling range: 25–70 ° C, C ₅ / C ₆ , blend component for gasoline , or recycle to the steam cracker)
  • Benzene cut (boiling range: 70– ~ 90 ° C, only benzene and non-aromatic compounds)
  • Toluene cut (boiling range: ~ 90– ~ 115 ° C, only toluene and non-aromatic compounds)
  • C _{8 cut} (boiling range: ~ 115– ~ 145 ° C, xylenes , ethylbenzene , low proportion of non-aromatics, blending component for gasoline, or sale as a semi-finished product)
  • C _{9+ cut} (boiling range: ~ 145– ~ 230/240 ° C, C ₉₊ aromatics, very low proportion of non-aromatics, blending component for gasoline, or as a thinner for heavy oil )

• Pure preparation of benzene and toluene by extraction or extractive distillation. The so-called raffinate streams (C ₆ - and C ₇ -non-aromatics) produced in this way are used as blended gasoline components or returned to the steam cracker.

See also

• Pyrolysis

literature

• Entry on pyrolysis gasoline. In: Römpp Online . Georg Thieme Verlag, accessed on August 10, 2015.
• Klaus Weissermel , Hans-Jürgen Arpe : Industrial organic chemistry . 5th edition. Wiley-VHC, Weinheim 1999, ISBN 978-3-527-28856-4 ( limited preview in Google book search).