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Document Type

Thesis - University Access Only

Award Date

2011

Degree Name

Master of Science (MS)

Department / School

Agricultural and Biosystems Engineering

Abstract

This study was done with a broad intention of enhancing sugar recovery of various biomass like corn stover, prairie cord grass, switchgrass, and big bluestream using microwave, ozone, and ultrasound pretreatment technologies. The parameters in the various experimental studies included: microwave power levels (20-100%), ultrasound amplitudes (20-100%), and ozones flow rates (47,4, and 1ug/ml). Exposure times for all the pretreatments were 5,10,15, and 20 min and chemical pretreatments with alkali (sodium hydroxide –NalH) and acid (sulphuric acid –H2SO4) were 0.1, 0.4, and 0.7% w/w. As a control for microwave, ultrasound and ozone treatments, feedstocks are also tested after soaking in deionized water (DI water). The compositional analysis was performed following standard NREL procedures. In the first study, the effect of power levels, processing time, alkali and acid concentrations on the resulting sugar recoveries using microwave as the physical pretreatment were determined for various biomass types. Increasing the power levels from 20 to 100% resulted in increased glucose and xylose recoveries with all biomass types when the substrate was soaked in DI water. Comparatively, irrespective of the biomass, chemical pretreatment prior to treating with microwave (soaking in alkali and acid concentrations of 0.1, 0.4 and 0.7% w/w) yielded greater sugar recoveries than the biomass samples which were not treated with alkali and acid concentrations prior to microwave pretreatment. A comparative study was done with chemical pretreatments versus the biomass treated with DI water where the biomass chemically treated gave a higher recovery than biomass treated with DI water. The optimum microwave power levels varied for all the biomass types. The higher glucose recovery of 76% at 0.7% alkali concentration was obtained for switchgrass. Overall, big bluestem treated with acid showed a higher glucose recovery for 72% at 0.7% concentration followed by acid pretreatments of prairie cord grass (70%), switchgrass (68.2%), and corn stover (35.4%) at 0.7% acid concentration level; whereas the order of xylose recovery for acid pretreatment was prarie cord grass (61%), switchgrass (56%), big bluestem (31.2%), and corn stover (29%) at 0.7% concentration level. Compared to acid treatment, alkali treatment showed a higher glucose recovery in case of switchgrass (76%) followed by alkali treatments of prairie cord grass (72%), big bluestem (70%) and corn stover (35%) at 0.7% concentration. The higher xylose recovery was observed in case prairie cord grass (59% at 0.4% concentration) followed by alkali pretreatments with switchgrass (42%), big bluestem (14%) at 0.7% concentration, and corn stover (36% at 0.4% concentration). The second study was conducted to test the effects of ultrasound pretreatment on sugar recovery. The amplitude levels, processing times, alkali and acid concentrations were the treatment variables evolved in this study. The optimum amplitude levels for treating the biomass was initially established using biomass that had only been soaked in DI water. Prairie cord grass gave a higher xylose recovery of 80% at 0.7% alkali concentration and 47% with acid pretreatment at 0.4% acid concentration followed by xylose recoveries of corn stover (17.9% and 0.7% alkali concentration and 15.4% at 0.4% acid concentration), big bluestem (5.2 and 4.2% at 0.7% alkali and acid concentrations) and switchgrass (14.6 at 0.4% and 16.6% at 0.7% alkali and acid concentrations). The order of glucose recovery from alkali soaking-ultrasound combination were big bluestem (48% at 0.7% concentration), prairie cord grass (41% at 0.7% concentration), switchgrass (35.3% at 0.4% concentration), cornstover (30% at 0.7% concentration). Glucose recovery was low for acid pretreatment compared to alkali pretreatment in combination was ultrasound and the higher recovery with acid treatment was obtained in case of big bluestem (40% at 0.7% concentration) followed by cornstover and prairie cord grass where both the grasses have the recovery of 27% at 0.7% and 25% at 0.4% acid concentration and switchgrass (20% at 0.7%). In the third study, the effect of ozone flow rate, processing times, alkali and acid concentrations on the resulting biomass were analyzed. As the flow rates increased different biomass showed increased sugar recoveries. These ozone concentration levels were chosen as the optimum levels for all the biomass with treatment in DI water which were done as the preliminary studies. Corn stover and switchgrass had their maximum sugar recoveries at1 ug/ml of ozone concentration. In the overall analysis, it was noticed that acid and alkali pretreatment along with ozone pretreatment yielded better results than with water soaking alone. Switchgrass showed a higher glucose recovery of 90% and 45% xylose recovery in case of alkali at 0.7% concentration followed by alkali pretreatments of corn stover (73.7% glucose and 17.7% xylose recoveries at 0.7% alkali concentration), prairie cord grass )65% glucose recovery at 0.1% alkali concentration and 23% xylose recovery at 0.7% alkali concentration) and big bluestem (64% glucose recovery at 0.1% alkali concentration and 5.17% xylose recovery at 0.7% alkali concentration). While in case of acid pretreatment, also switchgrass had a higher glucose recovery of 50% and xylose recovery of 19.5% followed by, prairie cord grass (41.6% glucose recovery at 0.4% acid concentration and 27% xylose recovery at 0.1% concentration), big bluestem (41.5% glucose recovery at 0.4% concentration and 3.5% xylose recovery at 0.7% concentration) and corn stover (38.4% glucose recovery and 14.7% xylose recovery at 0.1% xylose recovery at 0.1% acid concentration) respectively. Our experimental results have shown that the physico-chemical pretreatment i.e. combination of alkali or acid with ozone and alkali or acid with ultrasound gave a higher glucose and xylose recoveries than the individual pretreatments i.e., microwave, ozone and ultrasound treatment alone. The highest glucose recoveries for all the substrates: 90% for switchgrass, 48% for big bluestem, 76% for switchgrass. The highest glucose recoveries for switchgrass were obtained via the following conditions: 90% recovery using 0.7% alkali and 47ug/ml ozone pretreatment, 76% recovery using 0.7% alkali and 60% power level of microwave pretreatment. In case of big bluestem 48% was obtained via 0.7% alkali concentration with 20% amplitude level. The highest xylose recoveries for all substrates: 80% for prairie cord grass at 0.7% alkali concentration at 20% amplitude level, 61% for prairie cord grass at 0.7% acid concentration at 20% power level and 45% for switchgrass at 0.7% alkali concentration at 47 um/ml ozone concentration.

Library of Congress Subject Headings

Biomass conversion

Renewable energy sources

Lignocellulose

Corn stover -- Biotechnology

Spartina -- Biotechnology

Switchgrass -- Biotechnology

Andropogon furcatus -- Biotechnology

Format

application/pdf

Number of Pages

141

Publisher

South Dakota State University

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