ABSTRACT
Biological conversion of biomass to renewable energy products involves biochemical reactions that convert organic substrates into products that can be utilized for energy production. For example, sugars, starch, and cellulose can be converted to bioethanol or biobutanol through a series of biochemical reactions and organic wastes can be converted to methane or hydrogen through anaerobic digestion. The biomass that can be utilized for biological conversion include sugar crops (sugarcane, sweet sorghum, and sugar beet), grains (corn, wheat, rice, barley, etc.), trees, agricultural residues (corn stover,
wheat straw, etc.), grasses, and organic waste materials from municipalities, agriculture, and industries. A biological process usually consists of a series of elementary biochemical reactions catalyzed by enzymes, or enzymatic reactions. The overall process can be expressed as follows:
⎯⎯⎯⎯→ EnzymesSubstrate Product (5.1)
Elementary reactions are the very basic chemical reactions and examples are as follows:
⎯⎯→A B (5.2)
+ ⎯⎯→A A B (5.3)
+ ⎯⎯→A B C (5.4)
If the rate of an elementary reaction is de ned as the accumulation of the reactant(s) (mole) per unit reactor volume per unit time, then
= =
1 d d d d N C
r V t t
(5.5)
where rA is the rate of an elementary reaction (mol/L s) V is the reactor volume (L) NA are the moles of reactant A (mol) T is the reaction time (s) CA is the concentration of reactant A (mol/L)
The rates of the elementary reactions (Reactions 5.2 through 5.4) can be expressed respectively as follows:
= −A A Ar k C (5.6)
= − 2
A A Ar k C (5.7)
= −A A A Br k C C (5.8)
where kA is a kinetic constant. Based on these elementary reaction rate expressions, Reaction 5.2 is a rst-
order reaction, and Reactions 5.3 and 5.4 are second-order reactions.
