For the production of bioethanol from the lignocellulosic biomass, it is important that the development of technologies considering cost and environmental impacts for the process as well as improving the efficiency. This study investigated the effect of delignification of Pinusrigida which is one of the conifers by organosolv pretreatment to improve the cellulose conversion to glucose in enzymatic process for bioethanol production.
All organosolv pretreatment was conducted in the mini bomb reactor. The wood chips were prepared from the lower part of a fresh-cut 34 year-old log. The size of the chops was set as 30mm long, 3mm wide and 3mm thick. The amount of wood chip charged into the reactor was 5g(dry base) for all experiment. The solvent used for all organosolv pretreatment was 65 and 75% (v/v) ethanol-water mixture, giving an liquor to wood ratio of 7 : 1(ml / g) with the sulfuric acid of 1.25 to 2.0% (w/w, based on the wood chips). The H-factor was used to create the uniform setting of process and express the severity of delignification by combining reaction time and temperature in a single value.
Lignocellulosic biomass of P. rigida used in this experiment was chipped for reduction of mechanical energy put into the process of powdering. After pretreatment, relatively high yield of pulp was obtained a range from 19.40% to 47.14%. The maximum pulp yield was obtained pretreated with 1.7% of sulfuric acid and 75% of ethanol at H-factor 1,600. Pulp yield was decreased and the reject showed a range from 0% to 41.54% was also decreased when the H-factor incresed.
The residual lignin content in the pretreated pulps was showed a range from 12.22% to 25.10%. Although the lowest lignin content was obtained for P. rigida pretreated with 2.0% sulfuric acid and 65% of ethanol at an H-factor 6,300, the pulp yield lower than other pretreated pulp in different condition. It was predicted that H-factor 6,300 was ineffective in obtain cellulose substrate used as a raw material in the process of enzymatic hydrolysis with high yield.
As a result of analysis of the total sugar contents in the pretreated pulp, the range of whole sugar content was found to be 40.30-54.10%. In this study, when the degree of delignification was increased, total sugar contents was also increased. However, the concentration of ethanol, related with the degree of delignification, used in pretreatment was increased, the sugar content was decreased even if at the same concentration of catalyst in high H-factor. It is considered that the
concentration of ethanol affected the loss of carbohydrate as well as lignin removal in the lignocellulosic biomass.
In order to investigate chemical changes occurring during organosolv pretreatment, pretreated fibers was chracterized by FT-IR spectroscopy. A comparison of the untreated sample and organosolv pretreated pulp shows that a similar feature in IR spectra was found in the wavenumber range from 4000-800 cm-1 and a difference occurred at the 1738 cm-1. The peak band at 1738 cm-1, which has been ascribed to ester group in lignin-carbohydrate complex, cannot be detected in all pretreated samples.
SEM images of P. rigida were conducted. It appears that the organosolv pretreatment had a significant impact on the change in the appearance of the pulp. And, although not certain, some droplet appears to be present on the surface of organosolv pretreated pulp.