3.2. Optimization of pretreatment conditions for cassava pulp
To determine optimal pretreatment methods for ethanol
production from cassava pulp, hydrothermal reaction with and
without dilute sulfuric acid was examined. The experimental
procedure is summarized in Fig. 1. First, to test the effects of
a combination of hydrothermal reaction (120–180 C for 60 min)
and addition of H2SO4 (0.1% and 2%), glucose yield in the pulp
hydrolysates was measured after enzyme treatments of the cassava
pulp (Fig. 1).
The greatest glucose yield (0.75 g/g pulp) was obtained under
hydrothermal conditions (140 C for 1 h) without addition of H2SO4
(Fig. 2). Yields were equivalent to approximately 90% of the theoretical
value according to the composition shown in Table 1. No
major differences in glucose yields between 120 C and 160 Cwere
found with or without addition of 0.1% H2SO4 (Fig 2). Glucose yields
from hydrothermal reaction with 2% H2SO4 were lower than those
with or without 0.1% H2SO4 (Fig. 2), suggesting formation of byproducts
with increased H2SO4 concentration. Reports have indicated
that by-products, such as hydroxylmethyl-furfural (HMF),
furfural, furoic acid, and phenol, are produced from irreversible
conversion of pentoses, hexoses, and lignin during pretreatment
with acid [8]. Based on these results, hydrothermal reaction at
140 C without H2SO4 was used to pretreat cassava pulp.