To produce high-quality pulp more effectively, it is necessary to
remove organic compounds (mostly galactan) from the algae
effectively during the extraction process so that excessive use of bleaching chemicals for treating solid remnants can be avoided.
The dry weight of the soluble carbohydrates in the extracts can
be increased at elevated extraction temperatures, but temperatures
over 140 C usually cause darkening of the solid remnants
and bleaching of the darkened remnants is very difficult, if not
impossible by our experimental procedure. To produce ethanol
effectively from the extracts, the soluble carbohydrates in the extracts
should have a low degree of polymerization (DP) with minimum
amounts of impurities such as furfurals and hydroxymethyl
furfurals (HMFs). In the present study, Gelidium corneum, harvested
off the Atlantic coast of south Morocco, was extracted with water
in the presence of sulfuric acid or sodium thiosulfate, and the
extraction efficiency was compared with that of water alone. Sulfuric
acid was selected as an additive in the extraction process to enhance
de-polymerization of galactan. Sodium thiosulfate was
selected as it was superior to other sulfur-containing chemicals
such as sodium bisulfate, sodium hydrosulfite, and sodium metabisulfite
in respect of making easy in bleaching, protecting red algae
pulp fibers from weakening, and producing large amount of agar
extract. Sulfur-containing chemicals usually increase carbohydrate
retention and protect cellulosic fiber strength in wood kraft pulping
(Casey, 1980). Another important consideration for additive
selection was the amount of fermentation inhibitors (e.g., furfurals
and HMFs) generated in the extraction process.