Oxygen compounds Diethyl ether/ethyl ether ("ether") (CH3CH2OCH2CH3) [R-610] (from dehydrogenation of ethanol; extremely flammable) Methyl formate (HCOOCH3) [R-611] (from carbonylation of methanol, which usually both come from syngas; or by condensation of methanol; highly flammable) Dimethyl ether (CH3OCH3) [R-E170] (From dehydration of methanol which comes from syngas, natural gas or from some biofuels; highly flammable, medium toxicity) Nitrogen compounds Methylamine (CH3NH2) [R-630] (from reaction of ammonia and methanol; medium toxicity; controlled substance) Ethylamine (CH3CH2NH2) [R-631] (from reaction of ammonia and ethanol; very toxic) Lubricant In refrigeration systems, oil is used to lubricate parts in the compressor to ensure proper function. In typical operations, some of this lubricant may inadvertently pass into another part of the system. This negatively impacts the heat transfer and frictional characteristics of the refrigerant. In order to avoid this, the lubricant oil needs to be sufficiently compatible and miscible with the refrigerant. CFC systems utilize mineral oils, however HFC systems are not compatible and need to rely on ester and polyalkylene-glycol based oils, which are significantly more expensive. Hydrocarbons have a sign solubility with standard mineral oils, so very low solubility lubricants are needed. Polyalkylene Glycol and Polyalphaolefin are typically used in these systems for their low pour point and vapor pressures. Traditional oils cannot be used for lubricants in carbon dioxide systems since it is more solvent than most HFCs. Polyester oil is specifically designed to be used in carbon dioxide based systems and also helps to guard against increased bearing wear and maintenance costs that may come from a result of the higher stresses and pressures on a carbon dioxide system. Ammonia requires lubricants with low operating temperatures and high oxidation resistances, fluidity, and viscosity. Polyalphaolefin or Polyalphaolefin and Alkylbenzene blends are typically used. References External links Greenpeace, Natural Refrigerants: The Solutions See also List of refrigerants Sustainable automotive air conditioning, also covering the Alliance for CO2 Solutions eurammon, a European non-profit initiative for natural refrigerants Refrigerants Heating, ventilation, and air conditioning Environmental controversies