Heat and Mass Transport in Processing of Lignocellulosic Biomass for Fuels and Chemicals - Sustainable Biotechnology: Sources of Renewable Energy - page 6

Heat and Mass Transport in Processing
of Lignocellulosic Biomass for Fuels
and Chemicals

Sridhar Viamajala, Bryon S. Donohoe, Stephen R. Decker, Todd B. Vinzant,
Michael J. Selig, Michael E. Himmel, and Melvin P. Tucker

Abstract Lignocellulosic biomass, a major feedstock for renewable biofuels and
chemicals, is processed by various thermochemical and/or biochemical means. This
multi-step processing often involves reactive transformations limited by heat and
mass transport. These limitations are dictated by restrictions including (1) plant
anatomy, (2) complex ultra-structure and chemical composition of plant cell walls,
(3) process engineering requirements or, (4) a combination of these factors. The
plant macro- and micro-structural features impose limitations on chemical and
enzyme accessibility to carbohydrate containing polymers (cellulose and hemicel-
lulose) which can limit conversion rates and extents. Multiphase systems containing
insoluble substrates, soluble catalysts and, in some cases, gaseous steam can pose
additional heat and mass transfer restrictions leading to non-uniform reactions. In
this chapter, some of these transport challenges relevant to biochemical conversion
are discussed in order to underscore the importance of a fundamental understanding
of these processes for development of robust and cost-effective routes to fuels and
products from lignocellulosic biomass.

Keywords Lignocellulose · Biomass · Biofuels · Heat transport · Mass transport

1 Introduction

The biochemical conversion of lignocellulosic biomass requires several processing
steps designed to convert structural carbohydrates, such as cellulose and hemicellu-
lose, to monomeric sugars, which include glucose, xylose, arabinose, and mannose.
These sugars can be fermented to ethanol and other products, to varying degrees
of effectiveness, by wild type and modified microbial strains. The front end of the
process includes feedstock size reduction followed by a thermal chemical treatment,
called pretreatment. In practice, this unit operation usually involves the exposure of