Environmental concerns about urban air quality, global climate change, energy
security and economic considerations motivate a growing interest in alternative fuels for
the transportation sector. Ethanol, a fermentation-derived fuel, can be produced by
bioconversion of renewable materials, such as wood, grass, and waste. Combustion of
ethanol fuel, in both neat and blended form, can improve the engine efficiency, and lower
the emission of CO, NO[subscript x], and volatile organic compounds (VOC), hence reducing the
urban ozone level. Moreover, enhanced agricultural activities for production and
collection of lignocellulosic feedstocks and industrial developments for production of
ethanol will help the economic growth by creating new jobs and new income sources.
Bioconversion of lignocellulosic feedstocks into ethanol requires a pretreatment process to
increase the digestibility of cellulose by cellulolytic enzymes. The dilute-sulfuric acid
pretreatment can hydrolyze hemicelluloses (xylan), disrupt lignin structure, and increase
the yield of ethanol production from fermentation of monomeric units of cellulose
(glucose). In this study, herbaceous (corn stover and switchgrass) and woody (poplar
chips) feedstocks were pretreated with dilute sulfuric acid (0.6, 0.9, and 1.2% w/w) in a
batch reactor at relatively high temperatures (140, 160 and 180��C). A unifying kinetic
model including reaction time, temperature and acid concentration was developed, and
pertinent kinetic parameters were determined. This model can predict the percentages of
xylan remaining in the pretreated solids, net xylose yield in the liquid prehydrolysate, and
xylose loss after pretreatment of a feedstock at a certain set of reaction conditions. Using
this model, four optimum reaction conditions for obtaining maximum net xylose yield in
the liquid prehydrolysate were identified. The yield and rate of ethanol production from
the optimum prehydrolysates by the pentose fermenting yeast, Pichia stipitis, were
determined. It was found that pretreating the selected feedstocks at 170-180��C with 1.0-1.2% sulfuric acid for 1-3 min resulted in the recovery of 80-85% of the original xylan in
the liquid prehyrolysate. It was also found that feedstocks with higher neutralizing
capacity (e.g., corn stover) produced lower sugar yields as a result of acid neutralization.
Pretreatment of feedstocks at conditions beyond the optimum reaction conditions would
increase the extent of xylose degradation, and lower the yield and rate of ethanol
production due to loss of fermentable sugars and formation of toxic byproducts. The
optimum prehydrolysates of corn stover produced the highest yields of ethanol (0.39-0.47
g ethanol/g xylose) followed by switchgrass (0.36-0.45) and poplar (0.26-0.44). The
inhibitory effects of byproducts (e.g., acetate) was more pronounced in poplar
prehydrolysates. / Graduation date: 1997
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/34308 |
| Date | 25 September 1996 |
| Creators | Esteghlalian, Alireza |
| Contributors | Hashimoto, Andrew G. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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