Michael D. Montross

Effect of anatomical fractionation on the enzymatic hydrolysis of acid and alkaline pretreated corn stover

Due to concerns with biomass collection systems and soil sustainability there are opportunities to investigate the optimal plant fractions to collect for conversion. An ideal feedstock would require a low severity pretreatment to release a maximum amount of sugar during enzymatic hydrolysis. Corn stover fractions were separated manually and analyzed for glucan, xylan, acid soluble lignin, acid insoluble lignin, and ash composition. The stover fractions were also pretreated with either 0%, 0.4%, or 0.8% NaOH for 2 h at room temperature, washed, autoclaved and saccharified. In addition, dilute sulfuric acid pretreated samples underwent simultaneous saccharification and fermentation (SSF) to ethanol. In general, the two pretreatments produced similar trends with cobs, husks, and leaves responding best to the pretreatments, the tops of stalks responding slightly less, and the bottom of the stalks responding the least. For example, corn husks pretreated with 0.8% NaOH released over 90% (standard error of 3.8%) of the available glucan, while only 45% (standard error of 1.1%) of the glucan was produced from identically treated stalk bottoms. Estimates of the theoretical ethanol yield using acid pretreatment followed by SSF were 65% (standard error of 15.9%) for husks and 29% (standard error of 1.8%) for stalk bottoms. This suggests that integration of biomass collection systems to remove sustainable feedstocks could be integrated with the processes within a biorefinery to minimize overall ethanol production costs.

EFFECT OF STOVER FRACTION ON GLUCOSE PRODUCTION USING ENZYMATIC HYDROLYSIS

Corn stover was fractionated into three fractions: cobs, stalks, and leaves and husks. The fractions were dried and ground through a 2 mm screen. Samples of the three fractions and whole corn stover with and without NaOH pretreatment were subjected to enzymatic hydrolysis in order to determine the effect of fractionation on glucose production. The average amounts of glucose released after 60 h of hydrolysis from pretreated cobs, leaves and husks, stalks, and whole stover were 0.50, 0.36, 0.28, and 0.36 g/g dry biomass, respectively. The average amounts of glucose released after 60 h of hydrolysis from nonpretreated cobs, leaves and husks, stalks, and whole stover were 0.32, 0.23, 0.17, and 0.20 g/g dry biomass, respectively. Pretreatment resulted in an average increase of 60% in glucose production for all fractions and whole stover. The effect of stover fraction type on glucose production was significant with and without pretreatment. By collecting the fractions of the corn stover with the highest glucose potential (all the cobs and 74% of the leaves and husks) and leaving the remaining fraction (26% of the leaves and husks, and all the stalks) in the field for erosion control, the glucose potential of the collected biomass would increase by 21%. This could represent a decrease of up to 17% in the cost of ethanol production. This indicates that fractionation and collection of the biomass with the highest glucose potential may produce a higher quality feedstock for glucose production.

Life cycle assessment of native plants and marginal lands for bioenergy agriculture in Kentucky as a model for south-eastern USA

The Brookings Institute analysis rate both Lexington and Louisville, Kentucky (USA) as two of the nations largest carbon emitters. This high carbon footprint is largely due to the fact that 95% of electricity is produced from coal. Kentucky has limited options for electric power production from low carbon sources such as solar, wind, geothermal, and hydroelectric. Other states (TN, IN, OH, WV, and IL) in this region are similarly limited in renewable energy capacity. Bioenergy agriculture could account for a proportion of renewable energy needs, but to what extent is unclear. Herein, we found that abandoned agricultural land, not including land that is in fallow or crop rotation, aquatic ecosystems, nor plant‐life that had passed through secondary ecological succession totaled 1.9 Mha and abandoned mine‐land totaled 0.3 Mha, which combined accounted for 21% of Kentuckys land mass. A life cycle assessment was performed based on local yield and agronomic data for native grass bioenergy agriculture. These data showed that utilizing Kentuckys marginal land to grow native C4 grasses for cellulosic ethanol and bioelectricity may account for up to 13.3% and 17.2% of the states 2 trillion MJ energy consumption and reduce green house gas emissions by 68% relative to gasoline.

Development of a finite-element stored grain ecosystem model

An axisymmetric finite–element model was developed that predicts the heat, mass, and momentum transfer that occurred in upright corrugated steel storage structures due to conduction, diffusion, and natural convection using realistic boundary conditions. Weather data that included hourly total solar radiation, wind speed, ambient temperature, and relative humidity were used to model the temperature, moisture content, dry matter loss, and maize weevil development during storage with no aeration, and with ambient and chilled aeration. Periods of aeration were simulated assuming a uniform airflow rate through the grain mass. Heat and mass balances were used to calculate the temperature and absolute humidity in the headspace and plenum based on solar radiation, wind speed, ambient conditions, air infiltration, convective heat and mass transfer from the grain surface, and permeable boundaries that allowed natural convection currents to cross grain surfaces. A heat balance was used to estimate the wall temperature. The type of weather data in terms of solar radiation and frequency of data appear to be important when predicting the grain temperature, moisture content, dry matter loss, and maize weevil development.

Regional examination shows potential for native feedstock options for cellulosic biofuel production

Kentucky, as with many regions around the globe, has a relatively long growing season with significant rainfall that could produce sizeable quantities of perennial herbaceous and woody biomass on land that does not compete with food crops. Additionally, there are limited options for renewable power production from low carbon sources such as solar‐photovoltaic, wind and hydroelectric. Recent studies have shown that producing renewable energy from perennial cellulosic crops, as opposed to starch‐based biofuel crops, will have a carbon‐mitigating outcome. Currently, there is a lack of data regarding regionally suitable genotypes. Herein, we establish baseline values for multiple entry selections of three native C4 grass species, switchgrass (SW) (Panicum virgatum L.), eastern gamagrass (EG) (Trispicum dactyloides L.) and big bluestem (BB) (Andropogon gerardii Vitman). Yield potential examined over 7 years showed that environment, species and entries had a significant impact on yield, but EG had higher total yield over the duration of the study. Cellulosic biofuel potential was examined by measurement of saccharification efficiency, relative lignocellulosic energy density, cellulose content and lignin content during three growing seasons. EG had significantly higher digestibility rate than SW and BB. Underlying this was a negative correlation between lignification and saccharification efficiency. However, higher lignin content and higher cellulose content among SW entries resulted in higher energy density relative to EG and BB. These data reveal that locally bred EG varieties were most suited to cellulosic ethanol production under the growing conditions of central Kentucky, USA, compared with SW and BB and suggest the importance of regional examination.

Mechanical properties of corn and soybean meal

Ground corn and soybean meal are common ingredients in feed mixes. The knowledge of their mechanical properties is important to the feed manufacturer and consumer. Changes in these properties can lead to abnormally high or low levels of active ingredients in finished feed, thus decreasing its quality. Mechanical properties of wheat, corn meal, and soybean meal were investigated using a modified direct shear apparatus. The moisture content (wet basis), uncompacted bulk density, and particle density were: 10.4%, 733 kg/m 3 , and 1410 kg/m 3 for soft red winter wheat; 11.4%, 583 kg/m 3 , and 1350 kg/m 3 for soybean meal; and 11.7%, 595 kg/m 3 , and 1410 kg/m 3 for corn meal, respectively. A relatively long sliding path of 60 mm was utilized in shear testing to account for the high compressibility of the materials and minimize boundary effects. The compressibility of the materials was determined at a maximum vertical pressure of 34.4 kPa, which caused a density increase of 21% for corn meal while the density of wheat and soybean meal increased by approximately 5%. Frictional properties were tested for seven levels of vertical consolidation pressures ranging from 4.1 to 20.7 kPa. The high compressibility of corn meal resulted in severe stick-slip behavior of the frictional force-displacement relationships. The angles of internal friction of wheat, soybean meal, and corn meal were found to be 26.3° ±0.3°, 33.9° ±0.9°, and 30.7° ±1.4°, respectively. Cohesion of soybean meal and corn meal was approximately 0.7 kPa without a clear relation to consolidation stress and approximately 0.3 kPa for wheat. With cohesion values lower than 4 kPa, all three materials should be treated as free-flowing in terms of Eurocode 1. Corn and soybean meals are known to cause flow problems in practice that were not confirmed during testing. In practical storage conditions, materials undergo a longer consolidation period. Our tests have shown that with processes that have a short duration and low consolidation pressures, these materials should be treated as free-flowing.

Corn Stover Availability and Collection Efficiency Using Typical Hay Equipment

Corn stover has been identified as a potential feedstock for the production of fermentable sugars and thermochemical processes. The availability and efficiency of typical hay equipment for collecting corn stover has not been well quantified. Corn stover was collected for two years on a central Kentucky farm near Louisville. Six different harvesting treatments, using traditional hay equipment, were used to harvest corn stover. A rotary mower, rotary scythe (flail-type mower with windrow-forming shields), parallel bar rake, and a round baler were utilized. The average stover moisture content prior to grain harvest was above 40%, and field drying was required before baling. All treatments were analyzed for collection efficiency and corn stover yield. The stover collection yields varied from 1.93 to 5.34 dry t/ha, with collection efficiencies (ratio of stover collected to the total above-ground stover excluding grain) between 32.1% and 94.5%. The most promising collection strategy was disengaging the straw chopper and spreader to produce a windrow behind the combine. This windrow could then be baled in a separate operation that resulted in a collection efficiency of 74.1%.

VALIDATION OF A FINITE–ELEMENT STORED GRAIN ECOSYSTEM MODEL

An axisymmetric finite–element model was validated with respect to predicting the heat, mass, and momentum transfer that occurred in upright corrugated–steel storage bins due to conduction, diffusion, and natural convection using realistic boundary conditions. Hourly weather data that included hourly total solar radiation, wind speed, ambient temperature, and relative humidity were used to model the corn temperature and moisture content during storage with no aeration, and with ambient and chilled aeration. Periods of aeration were simulated assuming a uniform airflow rate through the grain mass. Sixteen bins with a capacity of 11.7 t each and instrumented with temperature cables were available to validate the model using two years of measured corn temperatures and moisture contents during summer storage. The average standard error between the experimental and predicted temperatures was 2.4³C (1.1³C to 5.7³C range), and the standard error between experimental and predicted moisture contents was 0.7 percentage points. The average standard error was 1.5³C in three non–aerated bins with sealed plenums when corn temperature was predicted as a function of the natural convection equation. The predicted natural convection effect was not applicable unless the plenum was assumed sealed.

Moisture Content Prediction in the Switchgrass (Panicum virgatum) Drying Process Using Artificial Neural Networks

This article proposes two artificial neural network (ANN)-based models to characterize the switchgrass drying process: The first one models processes with constant air temperature and relative humidity and the second one models processes with variable air conditions and rainfall. The two ANN-based models proposed estimated the moisture content (MC) as a function of temperature, relative humidity, previous MC, time, and precipitation information. The first ANN-based model describes MC evolution data more accurately than six mathematical empirical equations typically proposed in the literature. The second ANN-based model estimated the MC with a correlation coefficient greater than 98.8%.

Chapter 2:Energy Crops for the Production of Biofuels

Numerous options are available to supply biomass to biorefineries. Potential feedstocks include short rotation woody crops, herbaceous energy crops, and residues (forestry and agricultural). Each feedstock has unique chemical and physical properties that will influence the products and profitability from a biorefinery. For example, herbaceous feedstocks will have higher ash contents on average than woody products. Herbaceous feedstocks typically will have a lower lignin content and as a result a lower heating value than woody crops. Feedstock selection should consider the availability of equipment to establish, maintain, and harvest energy crops. In most cases, the equipment required is available to produce energy crops within the forestry and agricultural industries but is not optimized for energy crop production. Deciding which feedstock to produce will depend on site-specific considerations (soil type, temperature, and rainfall) that will influence the cost, yield, and composition of energy crops. Collection, storage, and transportation of energy crops is expensive relative to current fossil fuels, although biomass energy crops have lower greenhouse gas emissions than fossil fuels.