3 ms·

To force hydrogen to bond with CO2 must expense a large amount of energy. The energy has to come from somewhere and delivering the proper amount cannot be a tri

To force hydrogen to bond with CO2 must expense a large amount of energy. The energy has to come from somewhere and delivering the proper amount cannot be a trivial thing. The reaction between CO2 and H2 to form hydrocarbons is actually energetically favorable (thermodynamically spontaneous). It doesn't require outside energy inputs to force the reaction forward. See e.g. "CO2 valorisation via Reverse Water-Gas Shift reaction" https://www.sciencedirect.com/science/article/pii/S221298201730433X https://www.sciencedirect.com/science/article/pii/S221298201... and "Turning carbon dioxide into fuel" http://rsta.royalsocietypublishing.org/content/roypta/368/1923/3343.full.pdf http://rsta.royalsocietypublishing.org/content/roypta/368/19... The key issue is, as you note later, producing large quantities of hydrogen without relying on fossil sources.

technicalbard 8y ago
Except the reactions happen at 300C, and the FT reaction is exothermic between H2 and CO, not CO2. taking CO2 apart is endothermic. And then you need to refine the hydrocarbons (because they will look like diesel or wax, not gasoline).
- philipkglass 8y ago
  Using the standard gas-phase enthalpies of formation, the production of 1 mole of n-octane and 16 moles of water from 8 moles of CO2 and 25 moles of hydrogen is exothermic by 923 kilojoules. 8 CO2 + 25 H2 -> C8H18 + 16 H2O Energy of products minus energy of reactants: (-208.7 + 16 * -241.83) - (8 * -393.52 + 25 * 0) = -923 Experimental values are from NIST WebBook. The hydrogenation of CO2 to CO and water is endothermic and kinetically hindered. The hydrogenation of CO2 to saturated hydrocarbons and water is exothermic (though still kinetically hindered). There are also hydrocarbon synthesis paths that involve less reforming and purification of high-boiling products than F-T, e.g. methanol synthesis starting from CO2 and H2 followed by Mobil methanol-to-gasoline.

technicalbard 8y ago

Except the reactions happen at 300C, and the FT reaction is exothermic between H2 and CO, not CO2. taking CO2 apart is endothermic. And then you need to refine the hydrocarbons (because they will look like diesel or wax, not gasoline).

philipkglass 8y ago
Using the standard gas-phase enthalpies of formation, the production of 1 mole of n-octane and 16 moles of water from 8 moles of CO2 and 25 moles of hydrogen is exothermic by 923 kilojoules. 8 CO2 + 25 H2 -> C8H18 + 16 H2O Energy of products minus energy of reactants: (-208.7 + 16 * -241.83) - (8 * -393.52 + 25 * 0) = -923 Experimental values are from NIST WebBook. The hydrogenation of CO2 to CO and water is endothermic and kinetically hindered. The hydrogenation of CO2 to saturated hydrocarbons and water is exothermic (though still kinetically hindered). There are also hydrocarbon synthesis paths that involve less reforming and purification of high-boiling products than F-T, e.g. methanol synthesis starting from CO2 and H2 followed by Mobil methanol-to-gasoline.