Can leaves be used to power humanity? Let's check the science!
To begin with, there are 340 billion trees that discard leaves every year in the fall. Each one sheds about 50,000 leaves. That amounts to a total of 17 quadrillion leaves.
Each leaf weighs one gram. That means 17 trillion kilograms of matter.
Each leaf also contains about 10% cellulose by mass, which can be extracted and converted into fuel. That comes out to 1.7 trillion kilograms of cellulose.
The chemical equation to convert cellulose to ethanol is as follows:
C6H10O5 + H2O → C6H12O6 → 2(C2H5OH) + 2(CO2)
Now we must use this equation to first convert cellulose's mass to moles, then convert it to moles of ethanol, then to the mass of ethanol.
1.7 trillion kilograms of cellulose is 1.7 quadrillion grams. The periodic table tells us that the molar mass of cellulose is 162.139 grams/mole, which works out to 10,484,830,916,682.6 moles of cellulose.
Because each mole of cellulose in the equation corresponds to 2 moles of ethanol, we multiply the above figure by 2, which gives us 20,969,661,833,365.2 moles of ethanol, which using ethanol's molar mass of 46.0678 grams/mole becomes 966,026,187,407,101.3 grams, or 966,026,187,407.1 kilograms, or 966,026,187.4 metric tons of ethanol.
So in all we are looking at about a billion metric tons of extractable ethanol from all the leaves of planet earth each year. By comparison, humanity currently uses about 131 million metric tons of ethanol annually, or about one eighth of this figure.
Of course, it's entirely unfeasible given current technology to collect and process that many leaves. This is only a mental exercise. But it does give some idea of just what the upper ceiling of nature's bounty is in this case.
I hope you learned something from this in-depth exploration of biomass harvesting. Take care, and see you next time.
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