Analytical Techniques - Biomass Gasification, Pyrolysis and Torrefaction - page 446

i. Dried sample is removed and cooled down in a desiccator for an hour.
j. Take weight of the sample; the sample is called extractive-free sample.

13.1.3.3 Holocellulose
Holocellulose is a water-insoluble carbohydrate fraction of wood materials.
It can be extracted by the chlorination method by getting rid of the lignin.
A 2.5 g of extractive-free dry sample is placed in a 250 ml Erlenmeyer
flask. Then 80 ml hot distilled water, 0.5 ml acetone, and 1 g of sodium chlo-
rite (NaClO 2 ) are added to it. The mixture is heated in a water bath at 70 C
for 1 h. After this, another dose of 0.5 ml acetone, 1 g NaClO 2 are added and
heated further for 1 h. This process is repeated for 6 8 h until the lignin is

completely removed. The mixture is left for 24 h and then it is filtered through
a tarred and fritted disk glass thimble (Rowell, 2005, p. 63). The residue is
washed with acetone and left in a vacuum oven to dry at 105 C for 24 h.
ASTM E 1721 uses 72% sulfuric acid instead to hydrolyze the sample
instead of sodium chlorite used in the above process.
The solid whitish residue left on the filter gives the weight of the lignin-
free holocellulose.

13.1.3.4 Hemicellulose
The extractive- and lignin-free holocellulose as obtained from above is used
for the determination of hemicellulose. The sample is treated with sodium
hydroxide (NaOH) and acetic acid to get cellulose as a solid residue and
hemicellulose as the filtrate. This filtrate could be run on high performance
liquid chromatograph (HPLC) to determine the concentration of each differ-
ent monomer, for example, glucose, galactose, mannose (hexose), xylose,
and arabinose (pentose).
A dry sample of holocellulose (2 g) is taken in a 250 ml flask. Then
10 ml of 17.5% NaOH is added to the flask and a lid put on it. The flask is
kept in a water bath at 20 C and the mixture is stirred. After 5 min another
5 ml of the same 17.5% sodium hydroxide is added to it. The process is
repeated and continued for 15 min. After that it is left for 30 min and 33 ml
of water is added and kept at 20 C. The solid residue containing cellulose is
filtered through a tarred alkali resistance fritted glass filter. It is washed
again in 100 ml of 8.3% NaOH solution. The cellulose is subjected to acid
treatment in 15 ml of 10% acetic acid. Thereafter wash it in distilled water
and dry the residue containing cellulose before weighing it.

13.1.3.5 Lignin
ASTM D-1166-84 gives a method for determination of acid insoluble lignin
also called Klason lignin by dissolving a dry extractive-free sample in 72%
sulfuric acid followed by secondary hydrolysis in fucose. ASTM E 1721-1 is
based on hydrolysis in 72% sulfuric acid and water alone.