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In this study, we evaluated the pelleting characteristics of southern yellow pine (SYP), switchgrass (SG), and their blends for thermochemical conversion processes, such as pyrolysis and gasification. Using a pilot-scale ring-die pellet mill, we specifically assessed the impact of blend moisture, length-to-diameter (L/D) ratio in the pellet die, and ratio of pine to SG on the physico-chemical properties of the resulting pellets. We found that an increase in pine content by 25–50% marginally affected the bulk density; however, it also led to an increase in calorific value by 7% and a decrease in ash content by 72%. A moisture content of 25% (wet basis) and an L/D ratio of 5 resulted in poor pellet durability at 3, but increasing the L/D ratio to 9 and lowering the moisture content to 20% (w.b.) improved the pellet durability to >90% and the bulk density to >500 kg/m3. Blends with ≥50% pine content resulted in lower energy consumption, while a lower L/D ratio resulted in higher pelleting energy. Based on these findings, we successfully demonstrated the high-moisture pelleting of 2.5 ton of pine top residues blended with SG at 60:40 and 50:50 ratios. The quality of the pellets was monitored off-line and at-line by near infrared (NIR) spectroscopy. Multivariate models constructed by combining the NIR data and the pelleting process variables could successfully predict the pine content (R2 = 0.99), higher heating value (R2 = 0.98), ash (R2 = 0.95), durability (R2 = 0.94), and bulk density (R2 = 0.86) of the pellets. Thus, we established how blending and densification of SYP and SG biomass could improve feedstock specifications and that NIR spectroscopy can effectively monitor the pellet properties during the high-moisture pelleting process.

Lignocellulosic biomass is an alternative source of energy that can reduce our dependency on fossil fuels and limit greenhouse gas emissions. Several techno-economic analyses have consistently shown that all the steps in biomass-to-bioproduct processes needs improvement. Simultaneous assessment of genotypes for multiple productivity characteristics and integrating information across production stages has seldom been the focus of research efforts. To address this gap, we first determined the agronomic performance of 10 poplar genotypes. Differences between genotypes in height, diameter at breast height (DBH), tree mass and yield were consistently observed. Correlation analyses revealed that height and DBH are positively correlated with tree mass and yield, whereas bark content is negatively correlated with tree mass, yield and disease incidence. Four highest-yielding genotypes were subjected to proximate, ultimate, targeted chemical analyses, along with assessment of sugar production by acid hydrolysis and enzymatic saccharification. Despite having only marginal changes in overall chemistry, the genotypes showed differential conversion efficiencies of enzymatic saccharification. Interestingly, the genotype that showed highest cellulose conversion efficiency had the lowest estimated sugar yields due to its low biomass yield, whereas the genotype with lowest conversion efficiency had the highest estimated sugar yields. These results show the importance of integrating information across the stages of biomass production and bioconversion. These results also demonstrate the complexity of biomass feedstock production and the need for future studies to assess whether these tradeoffs can be genetically separated to guide the selection of genotypes that can maximize the overall biomass feedstock production efficiency.

Samples were prepared using stem xylem from cottonwood (Populus deltoides) and two cottonwood hybrids (P. deltoides × Populus maximowiczii and P. deltoides × Populus trichocarpa), which grew in Tennessee, United States. The anatomical characteristics, microfibril angle, and mechanical properties of the cell wall in juvenile wood (two-year-old) were investigated by means of microscopy image analysis system, X-ray diffraction, and nanoindentation (NI). The results showed that the double-wall thickness of the fiber cells in the hybrid poplars was thicker than that of the pure poplar, and the ratio of wall to lumen of fiber cell (0.40) of the P. deltoides × P. trichocarpa, which had the slowest growth rate, reached the greatest value among the three poplar clones. Their microfibril angles (MFA) of the cell wall in the investigated samples ranged between 11.5° and 16.7°, and they correlated positively with growth rates of the three poplar clones. The average hardness and reduced elastic modulus were 0.25 GPa and 8.58 GPa for P. deltoides, 0.28 GPa and 8.34 GPa for P. deltoides × P. maximowiczii, and 0.31 GPa and 12.2 GPa for P. deltoides × P. trichocarpa, respectively. P. deltoides × P. trichocarpa with the slowest growth rate had the greatest micromechanical values among the three poplar clones. In combination with growth characteristics of the three poplar clones, the findings of the analyses on their wood properties provided information-rich data that not only could describe juvenile wood properties but also could be used in selective breeding for the three poplar clones in Tennessee, USA.

The 2012 Sun Grant National Conference on Science for Biomass Feedstock Production and Utilization was held on 2–5 October 2012, in New Orleans, LA, USA. The Sun Grant Initiative set out to highlight recent advances in science and technology contributing to the deployment of conventional and advanced biofuels and bioproducts from agricultural and forest systems. The Initiative, with sponsorship from the Department of Energy’s Bioenergy Technologies Office (BETO), assembled an agenda focusing on promoting collaboration between academic, industry, non-profit, and government partners. This special issue is comprised of a small sample of conference presentations selected to reflect important research progress and to highlight the range of issues that must be considered as the transition to biomass energy takes hold.