. Photosynthesis of Biomass and Its C onversion-Related Properties

I. INTRODUCTION

Although many questions remain to be answered regarding the complex chem­istry of biomass growth, the reactions that occur when carbon dioxide (C02) is fixed in live green biomass are photochemical and biochemical conversions that involve the uptake of C02, water, and the solar energy absorbed by plant pigments. Carbon dioxide is reduced in the process and water is oxidized. The overall process is called photosynthesis and is expressed by a simple equation that affords monosaccharides as the initial organic products. Light energy is converted by photosynthesis into the chemical energy contained in the biomass components:

6C02 + 6H20 + light -> C6H1206 + 602.

Hexose

The inorganic materials, C02 and water, are converted to organic chemicals, and oxygen is released. The initial products of a large group of biochemical reactions that occur in the photosynthetic assimilation of ambient C02 are
sugars. Secondary products derived from key intermediates include polysaccha­rides, lipids, proteins and a wide range of organic compounds, which may or may not be produced in a given biomass species, such as simple low-molecular — weight organic chemicals (e. g., acids, alcohols, aldehydes, ethers, and esters), and complex alkaloids, nucleic acids, pyrroles, steroids, terpenes, waxes, and high-molecular-weight polymers such as the polyisoprenes. When biomass is burned, the process is reversed and the energy absorbed in photosynthesis is liberated along with the initial reactants.

The fundamentals of photosynthesis are examined in this chapter, with emphasis on how they relate to biomass production and its limitations. The compositions of different biomass species and the chemical structures of the major components are also examined in the context of biomass as an energy resource and feedstock.