Energy and Electricity - Introduction to Carbon Capture and Sequestration - page 37

On average, the lifetime mileage of a car is about 185,000 miles,
and the average miles per gallon (mpg) for a car ranges from 14 to 29
mpg. We chose to compare a 2011 Prius to a 2010 H3 4WD Hummer.
We used the combined city/highway EPA miles per gallon listing for
both the Hummer (14 mpg) and the Prius (50 mpg). Assuming these
conditions, a Prius will consume about 3,700 gallons and a Hummer
13,214 gallons of gasoline over its lifetime. We can calculate the num-
ber of moles of CO 2 produced per gallon of gasoline starting with the
balanced equation for octane combustion (octane is a reasonable proxy
for pure gasoline):

2C 8 H 18 + 25O 2 → 16CO 2 + 18H 2 O

A gallon of 87-octane gas contains approximately 2.8 kg of C 8 H 18 per
gallon (density about 0.75g/cm 3 ). That gives us:

2800 g C H 1 mole C H 16 moles CO

818 818 2

× ×

1 gallon 114.2 g C H 2 moles C H

818 818

= 196 moles CO per gallon

2

We calculate that 1 gallon produces 196 moles of CO 2 , or about
8,628 grams of CO 2 . The EPA cites this number as slightly higher, around
8,800 grams (200 moles) of CO 2 per gallon of gasoline, though they may
be assuming a higher octane gasoline. So, if anything, we are calculating
a lower limit of this system.
Now on to our novel capture solution. We know from our calcination
equation that:

CaO + CO 2 → CaCO 3

This means 1 gallon of gas producing 196 moles of CO 2 would yield
196 moles (about 19.6 kg) of CaCO 3 via calcination. Next, we apply this
metric to the lifetime amount of gasoline used by our two varieties of
cars.
In all categories, we see that the Hummer uses more than 3.5 times
the resources compared to the Prius. To quantify this in terms of surface
area of limestone, we need to assume a few building parameters. Most
stone used for paving has a density between 3,000 and 3,300 kg/m 3 , but
limestone's density ranges from 1,741 to 2,800 kg/m 3 . For better paving