Synthetic and renewable fuels are likely to be able to answer both climate change and air pollution concerns, to a greater or lesser extent.
Which gases are best to use for which purpose ? Gases good for combustion release a lot of heat when oxidised. Gases good for trade by liquefaction have boiling points closer to 0° C than further away from it. Simple covalently-bound molecules are most appropriate for reactor chemistry – where transformational reactions are fostered.
Which liquids are best for which application ? Liquids for cleaner combustion are likely to be oxygenate – have oxygen in their formula; and when their thermochemical properties suit the engines they are to be burned in.
Here is a first pass at summarising some of the molecules being investigated – molecules that can be synthesised from basic input chemical feedstocks.
Table : A Selection of Compounds in Industrial Gas and Fuels Chemistry
Note : STP = Standard Temperature and Pressure (20° C to 25° C, at 1 atmosphere of pressure).
Note : DME is here used for Dimethyl ether, and not Dimethoxyethane.
Note : Oxymethylene Dimethyl Ethers are also known as PODE, Polyoxymethylene dimethyl ethers; POMDME or OMDME.
| Compound | Formula | Boiling Point (° C) | State (STP) | Use |
| Hydrogen | H2 | -252.87 | Gas | Fuel, Feedstock |
| Water | H2O | +100 | Liquid | Feedstock |
| Oxygen | O2 | -182.95 | Gas | Combustion |
| Carbon monoxide | CO | -191.5 | Gas | Fuel, Feedstock |
| Carbon dioxide | CO2 | -57 | Gas | Exhaust, Feedstock |
| Ammonia | NH3 | -33.34 | Gas | Product |
| Nitrogen | N2 | -195.8 | Gas | Feedstock |
| Nitrous oxide | N2O | -88.46 | Gas | Exhaust |
| Nitrogen dioxide | NO2 | +21.15 | Liquid/Gas | Exhaust |
| Nitric oxide, nitrogen monoxide | NO | -152 | Gas | Exhaust |
| Methane | CH4 | -161.50 | Gas | Fuel, Feedstock |
| Ethane | C2H6; H3C-CH3 | -88.5 | Gas | Fuel, Feedstock |
| Propane | C3H8; H3C-CH2-CH3 | -42 | Gas | Fuel, Feedstock |
| Butane, n-Butane | C4H10; H3C-CH2-CH2-CH3 | -0.5 | Gas | Fuel, Feedstock |
| isoButane, 2-Methylpropane | C4H10; H3C-CH(-CH3)-CH3 | -11.7 | Gas | Fuel, Feedstock |
| Ethene, Ethylene | C2H4; H2C=CH2 | -103.7 | Gas | Feedstock |
| Propene, Propylene, Methyl ethylene | C3H6; H2C=CH(-CH3) | -185.2 | Gas | Feedstock |
| Butene, Butylene, as alpha-Butylene | C4H8; H2C=CH(-CH2CH3) | -6.3 | Gas | Feedstock |
| Butene, Butylene, as cis-beta-Butylene | C4H8; H3C-CH=(CH(-CH3)) | +2.25, +3.72… | Gas | Feedstock |
| Butene, Butylene, as trans-beta-Butylene | C4H8; H3C-CH=(CH(-CH3)) | +2.25, +3.73… | Gas | Feedstock |
| Butene, Butylene, as isoButylene | C4H8; H2C=C(-CH3)CH3 | -6.9 | Gas | Feedstock |
| Methanol, MeOH | CH3OH; H3C-OH | +64.7 | Liquid | Fuel, Feedstock |
| Ethanol, EtOH | C2H6O; H3C-CH2-OH | +78.24 | Liquid | Fuel, Feedstock |
| Propanol, 1-Propanol | C3H8O; H3C-CH2-CH2-OH | +97 to +98 | Liquid | Fuel, Feedstock |
| isoPropanol, isoPropyl Alcohol, IPA, 2-Propanol | C3H8O; H3C-CH(-OH)-CH3 | 82.6 | Liquid | Fuel, Feedstock |
| Butanol, n-Butanol, 1-Butanol, butan-1-ol | C4H9OH; H3C-CH2-CH2-CH2-OH | +117.6 | Liquid | Fuel, Feedstock |
| sec-Butanol, 2-Butanol, butan-2-ol | C4H9OH; H3C-CH2-CH(-OH)-CH3 | +98 to +100 | Liquid | Fuel, Feedstock |
| isoButanol, 2-methylpropan-1-ol | C4H9OH; H3C-CH(-CH3)-CH2-OH | +107.89 | Liquid | Fuel, Feedstock |
| tert-Butanol, 2-methylpropan-2-ol | C4H10O; H3C-CH3(-CH3)-OH | +82.3 | Liquid | Fuel, Feedstock |
| Methanal, Formaldehyde | CH2O; H2C=O | +64.7 | Liquid | Feedstock |
| Dimethyl ether, Methoxymethane, DME, PODE-0, OMDME-0 | C2H6O; H3C-O-CH3 | -24 | Gas | Fuel, Feedstock |
| Oxymethylene Dimethyl Ether 1, OME-1, Methylal, Dimethoxymethane, PODE-1, OMDME-1, DMM | C3H8O2; H3C-O-CH2-O-CH3 | +42, +45.2 | Liquid | Fuel, Feedstock |
| Oxymethylene Dimethyl Ether 2, OME-2, PODE-2, OMDME-2 | C4H10O3; H3C-O-CH2-O-CH2-O-CH3 | +105 | Liquid | Fuel |
| Oxymethylene Dimethyl Ether 3, OME-3, PODE-3, OMDME-3 | C5H12O4; H3C-O-CH2-O-CH2-O-CH2-O-CH3 | +156 | Liquid | Fuel |
| Oxymethylene Dimethyl Ether 4, OME-4, PODE-4, OMDME-4 | C6H14O5; H3C-O-CH2-O-CH2-O-CH2-O-CH2-O-CH3 | +202 | Liquid | Fuel |
| Oxymethylene Dimethyl Ether 5, OME-5, PODE-5, OMDME-5 | C7H16O6; H3C-O-CH2-O-CH2-O-CH2-O-CH2-O-CH2-O-CH3 | +242 | Liquid | Fuel |
| Trioxane | C3H6O3; -CH2-O-CH2-O-CH2-O- | +114.5 | Liquid | Feedstock |
| Diethyl ether, Ether, Ethoxyethane, DEE, OMDEE-0 | C4H10O; H3C-H2C-O-CH2-CH3 | +35 | Liquid | Fuel |
| Oxymethylene Diethyl Ether 1, Diethoxymethane, Ethylal, DEM, OMDEE-1 | C5H12O2; H3C-H2C-O-CH2-O-CH2-CH3 | +88 | Liquid | Fuel, Feedstock |
| Oxymethylene Diethyl Ether 2, OMDEE-2 | C6H14O3; H3C-H2C-O-CH2-O-CH2-O-CH2-CH3 | +140 | Liquid | Fuel |
| Oxymethylene Diethyl Ether 3, OMDEE-3 | C7H16O4; H3C-H2C-O-CH2-O-CH2-O-CH2-O-CH2-CH3 | +185 | Liquid | Fuel |
| Oxymethylene Diethyl Ether 4, OMDEE-4 | C8H18O5; H3C-H2C-O-CH2-O-CH2-O-CH2-O-CH2-O-CH2-CH3 | +225 | Liquid | Fuel |
| Dibutyl ether, DBE | C8H18O; H3C-H2C-H2C-H2C-O-CH2-CH2-CH2-CH3 | +140.8 | Liquid | Fuel |