Page 23 - Biofuels Refining and Performance

6 Chapter One

TABLE 1.1 Energy Content of Some Common Substances
Food value or fuel value
Food value Fuel value, kcal/g
Carbohydrates 4
Proteins 5
Fats (lipids) 9
Plant biomass (wet) 2
Plant biomass (ash free, dry) 4.5
Animal biomass (wet) 2.5
Animal biomass (ash free, dry) 5.5
Coal 7.0 [3200 kcal/lb]
Gasoline 11.5 [42,000 kcal/gal]
Average need for an adult human as consumer
Total social and
Personal or establishment Ratio
survival need need (total:personal)
Air 300 cuft/d 5000 cft/d 17:1
Water 0.66 gal/d 2000 gal/d 3030:1
Water (nonreturn) 0.3 gal/d 750 gal/d 2500:1
6
6
Energy (food) 1 10 kcal/yr 87 10 kcal/yr 87:1
Land (vegetarian food) 0.3 acre/yr 0.6 acre/yr
Land (nonvegetarian food) 0.3 acre/yr 4 acre/yr
Plant body other than food
1 ton dry weight per year 1-acre forest (and/or 3 tall trees of 12-in. diameter or 15 small
trees of 6-in. diameter)

place only if the energy status changes, i.e., A will be converted to B only
if B has a free energy content less than that of a change in free energy
F that is easy and spontaneous; reactions may be written as

A B ( F ) or A B F

or
F F F B
A
The reaction is called exergonic, or energy is evolved or given out. If
F has a positive expression, the reaction is driven by the input of energy
and called endergonic; such reactions are difficult to complete. At equi-
librium, F 0 (±), a point which may be arrived at by the end of the
reaction, or a reaction may be typically of that type (practically sluggish,
the progress of the reaction will depend on the change in concentration
of reactants, the change of temperature or pressure, etc.).
F F RT ln B/A, where B/A is the ratio at equilibrium or equilib-
0
. Then, 0 F RT ln B/A or F RT ln B/A
rium constant, i.e., K eq 0 0