Analytical Techniques - Biomass Gasification, Pyrolysis and Torrefaction - page 444

covered by specific ASTM standards ( Table 13.2 ). The following is a brief
description of methods that extracts the constituents of the cell walls of
wood for their determination. The methods described follow those
described by Rowell et al. (2005).

13.1.3.1 Sample Preparation
The biomass sample should be taken such that it truly represents the stock it
is taken from. The sample is to be prepared such that it is free from foreign
elements. ASTM standard, E 1757 describes a standard method for the prep-
aration of a sample for the analysis. The sample is dried at 105 C for several
hours to free it from moisture and is then ground to below 40 mesh size.

13.1.3.2 Extractive Components of Biomass
Extractives are the natural chemical products of biomass that are capable of
being extracted by some solvents. Based on the solvent used in extraction
process, extractives can be classified as water soluble, toluene ethanol, and

ether soluble extractives (Rowell, 2005). Major chemicals in an extractive of
biomass are fats, fatty acids, fatty alcohols, phenols, terpenes, steroids, resin
acids, rosin, waxes, and other organic compounds. Extractives are nonstruc-
tured nonpolymer composition of biomass that could affect the analysis of
polymer compositions. Therefore, it needs to be removed prior to down-
stream analysis of the biomass sample (NREL, 2008).
ASTM standard D 1105-96 is available to determine the extractive compo-
nents of wood in which ethanol benzene and hot water are used as the solvents.

Ethanol benzene is used to extract waxes, fats, resins, and a portion of wood

gums whereas hot water is used to remove tannins, gums, sugars, starches, and
color producing chemicals (TAPPI, 2007). On the other hand, ASTM standard
test methods E 1690-08/95 are also used for extractive measurement in biomass.
These standards are applicable for wider biomass materials such as for both
hard and soft barkless woods, herbaceous materials (switchgrass and sericea),
agriculture residues (corn stover, wheat straw, and bagasse), and waste papers
(office waste, boxboard, and newsprint). Extractives can be removed from
wood by using neutral solvents, water, toluene or ethanol, or combinations of
solvents. The nature of solvents may change according to the type of chemicals
present as an extractive in different biomass.
The following methods as per Rowell (2005) may be used for determination
of the extractives. A fresh sample is recommended to avoid the errors due to
fungal attack. It is also desirable to peel off the bark from the stem. To prepare,
the sample is dried at 105 C in an oven for 24 h prior to milling. It is then
ground to an average size of 0.40 mm using a Wiley mill. Major apparatus
required for this method include Buchner funnel, extraction thimbles, extraction
apparatus, extraction flask (500 ml), Soxhlet extraction tube, heating mantle,
boiling chips for taming boiling action, chemical fume hood, and vacuum oven