Siloxane

Decamethylcyclopentasiloxane, a cyclic siloxane

A siloxane is any chemical compound composed of units of the form R₂SiO, where R is a hydrogen atom or a hydrocarbon group. A siloxane has a branched or unbranched backbone of alternating silicon and oxygen atoms -Si-O-Si-O-, with side chains R attached to the silicon atoms.Siloxanes, IUPAC Gold Book

The word siloxane is derived from the words silicon, oxygen, and alkane.

Siloxanes can be found in products such as cosmetics, deodorant, water repelling windshield coating, food additives and some soaps. They occur in landfill gas and are being evaluated as alternatives to perchloroethylene for drycleaning. Perchloroethylene is widely considered environmentally undesirable.

Polymerized siloxanes with organic side chains (R ≠ H) are commonly known as silicones or as polysiloxanes. Representative examples are [SiO(CH₃)₂]_n (dimethylsiloxane) and [SiO(C₆H₅)₂]_n (diphenylsiloxane). These compounds can be viewed as a hybrid of both organic and inorganic compounds. The organic side chains confer hydrophobic properties while the -Si-O-Si-O- backbone is purely inorganic. Dimethylpolysiloxane is added to vegetable oil as an antifoaming agent. McDonalds uses this type of vegetable oil to cook certain productsMcDonald\'s USA Ingredients Listing for Popular Menu Items.

Siloxanes in biogas

In internal combustion engines deposits on pistons and cylinder heads are extremely abrasive and causes damage to the internal components of the engine. Engines can require a complete overhaul at 5,000 h or less of operation. Deposits on the turbine of the turbocharger will eventually reduce the components efficiency.

Stirling engines are more resistant against siloxanes, though deposits on the tubes of the heat exchanger will reduce the efficiency.Presentation - Siloxanes in landfill gasPaper - Siloxanes in landfill and digester gas

References

External links

• EPA report: Siloxane D5 in Dry-cleaning

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