The potential use of mass timber in mid-to high-rise construction and the associated carbon benefits in the United States.

Nonresidential and mid- to high-rise multifamily residential structures in the United States currently use little wood per unit floor area installed, because earlier building codes lacked provisions for structural wood use in those types of buildings. However, revisions to the International Building Code allow for increased wood use in the form of mass timber, as structural and fire safety concerns have been addressed through new science-based design standards and through newly specified construction materials and measures. This study used multiple models to describe alternative futures for new construction, mass timber adoption rates, and the associated carbon benefits in higher than three-story buildings in the United States. The use of mass timber, in place of traditional constructions (i.e., structures dominated by concrete and steel), in projected new higher than three-story buildings was shown to provide combined carbon benefits (i.e., global warming mitigation benefits), including avoided embodied carbon emissions due to the substitution of non-wood alternatives and additional biogenic carbon storage in mass timber materials, of between 9.9 and 16.5 million t CO2e/yr spanning 50 years, 2020 to 2070. These carbon benefits equate to 12% to 20% of the total U.S. harvested wood products carbon storage for 2020. Future research is needed to understand how greater mass timber adoption leads to changes in forest product markets, land use, and total forest sector carbon.

Air quality impact of slash pile burns: Simulated geo-spatial impact assessment for Washington State.

In the Western U.S., the prescribed burning of woody biomass in forests, mainly harvest slash, is the prevailing practice for in-woods fuel reduction and wildfire mitigation. Though these prescribed burns play an essential role in mitigating the wildfire risks, the resultant emission is a major air pollutants source that adversely affects air quality, negatively impacting human health. With an increased need for fire hazard reduction thinning, coupled with shrinking regional demand for lower quality biomass (pulpwood, hog-fuel, etc.), the volumes of unused biomass left on the forest floor as 'waste' will continue to grow. Reducing prescribed burns by utilizing this 'waste' biomass for alternate bio-based solutions (like bio-energy or bio-char) will enhance the economic feasibility of much-needed thinning operations and reduce uncontrolled emissions and related environmental and local health impacts. In this study, we simulate the increase in air pollutants due to additional prescribed fires in the Southwestern part of Washington State. Using the 'BlueSky smoke modeling system,' the study estimated the emissions associated with burning additional 726,000 dry t of residual biomass, which corresponds to a 30% increment from 2011. The burn was simulated over 29 days of the fall quarter and subsequently incorporated into the AIRPACT pollution transportation modeling system using the 2011 air quality and meteorological data as the baseline. The results showed that the ambient PM2.5 concentrations, due to the simulated pile burns, exceeded EPA's air quality standards on multiple days and in various locations across the Western part of the state, with two days reaching "very unhealthy" levels and one day reaching "hazardous" levels. By layering the census data on top of the pollution concentration data, the model estimated that, over the 29-day burn period, approximately 440,000 additional human days would be affected by higher than the EPA air-quality standards for ambient PM2.5 levels.

High temperature and fire behavior of hydrothermally modified wood impregnated with carbon nanomaterials.

Wood is one of the most widely used construction materials but it is thermally degradable and combustible, which poses serious safety concerns. In this research, the high temperature and fire behavior of hydrothermally modified western hemlock, impregnated with carbon nanomaterials pre-adsorbed with alkali lignin, was examined by cone calorimetry, scanning electron microscopy, thermal gravimetric analysis, and Fourier transform infrared spectroscopy. The hydrothermal treatment made the wood less hydrophilic, allowing the formation of a dense protective layer of carbon-rich additives on the external wood surface at low loading (5 wt%) after aqueous-phase vacuum impregnation. Results revealed that the unique combination of these two processes reduced the total heat release by up to 32%, diminished flame spread by 31%, decreased the average carbon dioxide yield by 12%, lowered the total mass loss by 10%, and significantly slowed the pyrolytic reactions of wood. This research has important implications for the development of valued-added wood products with superior fire safety from relatively low cost timbers, such as western hemlock.

Life cycle assessment of residual lignocellulosic biomass-based jet fuel with activated carbon and lignosulfonate as co-products.

BACKGROUND: Bio-jet fuels are emerging as a valuable alternative to petroleum-based fuels for their potential for reducing greenhouse gas emissions and fossil fuel dependence. In this study, residual woody biomass from slash piles in the U.S. Pacific Northwest is used as a feedstock to produce iso-paraffinic kerosene, through the production of sugar and subsequent patented proprietary fermentation and upgrading. To enhance the economic viability and reduce the environmental impacts of iso-paraffinic kerosene, two co-products, activated carbon and lignosulfonate, are simultaneously produced within the same bio-refinery. A cradle-to-grave life cycle assessment (LCA) is performed for the residual woody biomass-based bio-jet fuel and compared against the cradle-to-grave LCA of petroleum-based jet fuel. This paper also discusses the differences in the environmental impacts of the residual biomass-based bio-jet fuel using two different approaches, mass allocation and system expansion, to partition the impacts between the bio-fuel and the co-products, which are produced in the bio-refinery. RESULTS: The environmental assessment of biomass-based bio-jet fuel reveals an improvement along most critical environmental criteria, as compared to its petroleum-based counterpart. However, the results present significant differences in the environmental impact of biomass-based bio-jet fuel, based on the partitioning method adopted. The mass allocation approach shows a greater improvement along most of the environmental criteria, as compared to the system expansion approach. However, independent of the partitioning approach, the results of this study reveal that more than the EISA mandated 60% reduction in the global warming potential could be achieved by substituting petroleum-based jet fuel with residual woody biomass-based jet fuel. Converting residual woody biomass from slash piles into bio-jet fuel presents the additional benefit of avoiding the impacts of slash pile burning in the forest, which results in a net negative impact on 'Carcinogenics' and 'Respiratory effects', and substantial reduction in the 'Smog' and 'Ecotoxicity' impacts. The production of woody biomass-based bio-jet fuel, however, did not show any significant improvement in the 'Acidification' and 'Eutrophication' impact categories. CONCLUSIONS: The study reveals that residual woody biomass recovered from slash piles represents a more sustainable alternative to petroleum for the production of jet fuel with a lower impact on global warming and local pollution. Future research should focus on the optimization of chemical processes of the bio-refinery to reduce the impacts on the 'Acidification' and 'Eutrophication' impact categories.

Lignin-Modified Carbon Nanotube/Graphene Hybrid Coating as Efficient Flame Retardant.

To reduce fire hazards and expand high-value applications of lignocellulosic materials, thin films comprising graphene nanoplatelets (GnPs) and multi-wall carbon nanotubes (CNTs) pre-adsorbed with alkali lignin were deposited by a Meyer rod process. Lightweight and highly flexible papers with increased gas impermeability were obtained by coating a protective layer of carbon nanomaterials in a randomly oriented and overlapped network structure. Assessment of the thermal and flammability properties of papers containing as low as 4 wt % carbon nanomaterials exhibited self-extinguishing behavior and yielded up to 83.5% and 87.7% reduction in weight loss and burning area, respectively, compared to the blank papers. The maximum burning temperature as measured by infrared pyrometry also decreased from 834 °C to 705 °C with the presence of flame retardants. Furthermore, papers coated with composites of GnPs and CNTs pre-adsorbed with lignin showed enhanced thermal stability and superior fire resistance than samples treated with either component alone. These outstanding flame-retardant properties can be attributed to the synergistic effects between GnPs, CNTs and lignin, enhancing physical barrier characteristics, formation of char and thermal management of the material. These results provide great opportunities for the development of efficient, cost-effective and environmentally sustainable flame retardants.

Environmental assessment of mild bisulfite pretreatment of forest residues into fermentable sugars for biofuel production.

BACKGROUND: Sugar production via pretreatment and enzymatic hydrolysis of cellulosic feedstock, in this case softwood harvest residues, is a critical step in the biochemical conversion pathway towards drop-in biofuels. Mild bisulfite (MBS) pretreatment is an emerging option for the breakdown and subsequent processing of biomass towards fermentable sugars. An environmental assessment of this process is critical to discern its future sustainability in the ever-changing biofuels landscape. RESULTS: The subsequent cradle-to-gate assessment of a proposed sugar production facility analyzes sugar made from woody biomass using MBS pretreatment across all seven impact categories (functional unit 1 kg dry mass sugar), with a specific focus on potential global warming and eutrophication impacts. The study found that the eutrophication impact (0.000201 kg N equivalent) is less than the impacts from conventional beet and cane sugars, while the global warming impact (0.353 kg CO2 equivalent) falls within the range of conventional processes. CONCLUSIONS: This work discusses some of the environmental impacts of designing and operating a sugar production facility that uses MBS as a method of treating cellulosic forest residuals. The impacts of each unit process in the proposed facility are highlighted. A comparison to other sugar-making process is detailed and will inform the growing biofuels literature.