First Principles of Pretreatment and Cracking Biomass to Fundamental Building Blocks 207
occurred in softwood at 40 kGy dosage of irradiation, while in hardwood it was at
90 kGy dosage. Several researches showed that irradiation pretreatment due to cellulose
hydrolysis and lignin disruption lead to decreased mechanical properties of wood.
Charlesby (1995) showed that the molecular weight of cellulose decreases with
increasing radiation dose. Many researchers have since studied the relationship
between irradiation dose and cellulose fiber degradation (Dubeyet al., 2004). Takacs
et al. (2000) reported that the DP of cotton cellulose was reduced from 1600 to 300
after 10 kGy ofγ-irradiation. Other studies also showed that radiation pretreatment
leads to a reduction of the cellulose crystallinity (Kasprzyket al., 2004; Albertiet al.,
2005). Kasprzyket al. (2004) showed thatγ-irradiation could reduce the amount of
crystallinity in cellulose fibers which, is observed at dosage higher than 100 kGy. The
crystallinity index of microcrystalline cellulose (MCC), flax, cotton, and viscose was
reduced up to 12% with a irradiation dose of 200 kGy (Albertiet al., 2005).
Market al. (2009) reported the reduction of crystallinity in biomass using electron
beam pretreatment, and Baket al. (2009) investigated the improvement of saccharifica-
tion conversion using electron beam irradiation pretreatment. However, electron beam
is a relatively low energy beam (usually 1–5 MeV). For pretreatment, it is necessary to
useitathighdosage(Market al., 2009; Baket al., 2009).
Proton beam irradiation (PBI) has been used in a variety of disciplines such as nan-
otechnology, medicine, information technology, and biotechnology due to its efficiency
and benefits. It can be used in low doses for effective degradation of biomass. In addi-
tion, if PBI is used with liquid ammonia pretreatment, the yield of fermentable sugars
increases due to the increasing accessibility of enzyme to cellulose (Kimet al., 2008).
6.7.4 Acid Pretreatment
Acid pretreatment involves the use of concentrated and diluted acids to break down
the rigid structure of the lignocellulosic material. The most commonly used acids are
sulfuric acid, hydrochloric acid, nitric acid, and phosphoric acid. Due to the ability
of the acid to remove hemicelluloses, acid pretreatments have been used as a part of
overall processes in fractionating the components of hemicellulosic from lignocellulosic
biomass. Acid pretreatment (removal of hemicelluloses) followed by alkali pretreatment
(removal of lignin) results in relatively pure cellulose (Brodeuret al., 2011). In acid
pretreatment process, dilute or concentrated acid is added to the biomass and then
allowed to stand for a given time and temperature.
Acid hydrolysis has been one of the traditional pretreatment methods to preterits
lignocellulosic materials before the fermentation process. Bracont (1819) found that
pretreatment of wood by concentrated sulfuric acid leads to production of glucose
(Goldstein, 1983). Franzidis and Porteous (1981) investigated the first commercial
acid hydrolysis process. The American process that is named as the sisman was used
between 1910 and 1922. Wood particles were hydrolyzed under a batch process by using
0.5% sulfuric acid and high pressure steam at 912 kPa. The total ethanol yield from this
process was a 22 Gal per ton that is uneconomical. A few years later, another process
was invented by Heinrich Scholler in Germany that produced improved production
yield of ethanol (55–58 Gal per ton of biomass) in 13–20 h. The Scholler method is a
percolation method. In this method, sulfuric acid with a concentration of 0.8% and at
temperature between 120 and 180∘C is passed through wood wastes. The maximum
