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ref: -0 tags: co2 capture entropy carbon dioxide date: 09-22-2019 00:46 gmt revision:1 [0] [head]

How much energy is thermodynamically required to concentrate CO 2CO_2 from one liter of air?

CO 2CO_2 concentration is 400ppm, or 0.4%. 1l of air is 1/22.4 or 44mMol. From wikipedia, the entropy of mixing is:

Δ mixS=nR(x 1ln(x 1)+x 2ln(x 2)) \Delta_{mix} S = n R (x_1 ln(x_1) + x_2 ln(x_2)) where x 1x_1 and x 2x_2 are the fraction of air and CO 2CO_2 (0.996 and 0.004)

This works out to 9.5e3J/K9.5e-3 J/K . At STP, 300K, this means you need only about 2.9J2.9 J to extract the carbon dioxide.

A car driving 1 km emits about 150g carbon dioxide. This is 3.4 moles, which will diffuse into 852 moles of air, or 19e3 liters of air (19 cubic meters). To pull this back out of the air then you'd need at minimum 55.3 kJ.

This is not much at all -- a car produces 100kW mechanical power, or 100kJ every second, and presumably it takes a minute to drive that 1km. But such perfectly efficient purification is not possible.

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ref: notes-0 tags: CO2 global warming carbon dioxide indonesia brazil date: 03-14-2008 21:34 gmt revision:0 [head]

From the New Yorker, Feb 25:

  • "Just two countries - Indonesia and Brazil - account for ten percent of the greenhouse gasses released into the atmosphere. "
  • "During the next twenty-four hours the effect of losing forests in Brazil and Indonesia will be the same as if eight million people boarded airplanes at Heathrow airport and flew en mass to New York. "