Page 141 - Advances in bioenergy (2016)

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Transportation Fuels from Biomass via Fast Pyrolysis

and Hydroprocessing

Douglas C. Elliott *
Pacific Northwest National Laboratory, Richland, WA, USA

INTRODUCTION

Biomass is a renewable source of carbon, which could provide a means to reduce the
greenhouse gas impact from fossil fuel combustion in the transportation sector and provide for
an option in an increasingly petroleum-constrained world. Recycling of carbon dioxide from
the atmosphere, either by direct chemical conversion or via biomass growth based on solar
energy, provides the only renewable source of liquid fuels, which could displace petroleum-
derived products. Using appropriate methods, such as fast pyrolysis and catalytic
hydroprocessing, solid biomass can be converted to hydrocarbon liquids. 1,2

Extensive processing is required for conversion of solid biomass, which is a collection of
highly oxygenated biopolymer structural components, to liquid fuels, which are typically free
of oxygen content. Fast pyrolysis is a method of direct thermochemical conversion
(nonbioconversion) of biomass to a liquid product. Utilization of the thermal instability of the
biostructures in biomass is a key element in the process. Although the direct conversion
product, called bio-oil, is liquid, it is not compatible with the fuel handling systems currently
used for transportation. As a mixture of oxygenated components, it has neither the physical nor
chemical properties to compete with petroleum distillates as transportation fuel. However, its
liquid form does facilitate further processing.

Upgrading the product via catalytic processing with hydrogen gas, hydroprocessing, is a means
that has been demonstrated in the laboratory. A comparison of the oil products is presented in
Table 6.1. Current research focuses on bringing this technology out of the laboratory. By
hydroprocessing, the bio-oil can be deoxygenated to hydrocarbons, which can be renewable
replacements of the refined hydrocarbon distillates from petroleum. Although the hydrocarbons
from biomass tend to be more in cyclic structures, rather than the straight chains typically found
in petroleum, their use should not be limited by this difference.

Commercial entities are currently bringing the fast pyrolysis of biomass into the marketplace.
Although small-scale plants have been operated since the 1990s, they were and are for
production of chemical products for use in the food industry. Large-scale demonstration plants

of fast pyrolysis of biomass for whole bio-oil production have been built and operated, and
commercial facilities are now under construction in North America and Europe. The upgrading
of the liquid product by hydroprocessing remains in development, although it is moving out of