Grantee Research Project Results
2007 Progress Report: Evaluating the Impacts of Nanomanufacturing via Thermodynamic and Life Cycle Analysis
EPA Grant Number: R832532Title: Evaluating the Impacts of Nanomanufacturing via Thermodynamic and Life Cycle Analysis
Investigators: Bakshi, Bhavik R. , Lee, L. James
Institution: The Ohio State University
EPA Project Officer: Hahn, Intaek
Project Period: January 1, 2006 through December 31, 2010
Project Period Covered by this Report: January 1, 2007 through December 31,2007
Project Amount: $375,000
RFA: Exploratory Research: Nanotechnology Research Grants Investigating Environmental and Human Health Effects of Manufactured Nanomaterials: A Joint Research Solicitation - EPA, NSF, NIOSH (2005) RFA Text | Recipients Lists
Research Category: Safer Chemicals , Nanotechnology
Objective:
This work presents the first most comprehensive life cycle energy analysis of carbon nanofiber (CNF) based polymer nanocomposites (PNCs). Previous work on the life cycle assessment of CNFs is expanded to study the use of CNF for polymer composite products. The use of CNF reinforced polymer composites in automotive body panels as a substitute for traditional materials is evaluated. Another objective of the current work is the energetic and environmental evaluation of titanium dioxide nanoparticles. Nanoscaled titanium dioxide has attracted interest because of its use in sunscreens and catalytic applications.
Approach:
Through collaboration with leading academic groups, industry, and a national laboratory, life cycle inventory data and modules will be developed for the synthesis and use of nanoclays and carbon nanofibres. These modules will be combined with life cycle information at different spatial scales, ranging from equipment to ecosystems, and used to perform multiscale or hybrid LCA of several potential products. Different scenarios for the manufacture, use, end of life, emissions and exposure of typical consumable and durable products, such as automotive body panels and food wrapping film, will be analyzed along with estimates of uncertainty. Thermodynamic LCA will treat industrial and ecological systems as networks of energy flow and combine the features of systems ecology, LCA and systems engineering. The proposed hypotheses will be tested in a statistical sound manner via several case studies.
Progress Summary:
Progress Summary/Accomplishments:
Life cycle energetic evaluation of carbon nanofiber polymer composites. PNCs have enhanced mechanical properties, high strength-to-weight ratios, and are capable of offering specific functionalities such as desired level of electrical conductivity. These combinations of properties are making PNCs as one of the fastest growing plastic segment and an attractive alternative to conventional materials like steel and aluminum. In the current work, a cradle-to-gate life cycle study of CNF based PNCs is carried out. Previous work on CNF life cycle by the authors served as a basis for this analysis. The boundaries of the CNF life cycle are expanded to include the production of PNC and the end product manufacture. A typical life cycle for nanocomposites consists of alternatives at each processing stage based on the choice of feedstock and the final product manufacture. Polypropylene based CNF nanocomposites are considered as the example. Once the CNFs are dispersed in the polymer, these reinforced materials can be either extruded or injection-molded to obtain a variety of end products.
A cradle-to-gate energetic life cycle assessment of CNF reinforced polypropylene is performed and compared with steel. The functional unit for comparison is the equal stiffness of different components. Five different cases are investigated with varying loading ratios of the CNF in the polypropylene matrix. Two cases with both CNFs and glass fibers are also studied. As depicted in figure 2, it is observed that for equal stiffness of the components, on a cradle-to-gate basis, CNF reinforced polypropylene composites are 2-10 times more energy intensive as compared to steel. It is further concluded that the product use phase might govern whether the high upstream energy can be offset during the use phase to realize any life cycle energy savings.
Finally the use of CNF reinforced nanocomposites in body panels of light-duty vehicles is evaluated. The life cycle of a midsize automobile with CNF reinforced nanocomposite body panels is evaluated and compared relative to conventional steel panels. The results are shown in figure 1 (b). It is concluded that the use of polymer nanocomposites in automotive body panels results in marginal life cycle energy savings. Besides, polymer nanocomposites based body panels with higher CNF loading ratios appear to be almost at par with steel on a total life cycle basis and do not offer any additional life cycle energy savings. Further, use of CNFs with other additives like glass fibers might be more promising for automotive applications in the near term with net energy savings of around 8 percent relative to steel.
Figure 1 (a) Life cycle comparison of carbon nanofiber (CNF) reinforced polymer composites (a) material comparison for equal component stiffness design (b) comparison of CNF polymer composites for automotive body panels
The results obtained have high degree of uncertainty owing to several reasons. Some of these are: huge life cycle energy requirements for the production of CNFs, possible achievable weight reductions of polymer nanocomposite based components, and the end-of-life issues specific to polymer nanocomposites that can be significant. Besides, PNCs might be difficult to recycle, reuse, and or dispose compared to conventional materials like steel and aluminum. Current work is in progress to address these uncertainty issues and evaluate other thermoset based nanocomposite materials.
Energetic and Environmental Evaluation of Titanium Dioxide Nanoparticles. Typical rutile phase pigment grade TiO2 particles are on the order of 250 nm to 1 mm in diameter. However, recent demand for smaller particles for use in sunscreens and for catalytic applications has opened up a market for 20-50 nm anatase phase particles. The Altair hydrochloride process uses a spray hydrolysis step, which allows for further flexibility in the phase and size distribution of the produced particles. Also, almost complete recycle of the hydrochloric acid used in the process affords energetic and monetary advantages over the older processes. The Altair hydrochloride process is shown in Figure 2. The current project uses the best available information to investigate energy and exergy use in the Altair TiO2 hydrochloride process at both the process and life cycle scales. The goal of this part of the project is to identify key steps that consume the most exergy and identify opportunities for improvement at both the process and life cycle scales.
The Altair TiO2 hydrochloride process was broken up into nine main process units and about 25 major flows. Energy input to each unit was calculated from process information available in the literature from Altair. Any missing energy inputs were estimated from these publications or from other sources considering similar units. The compositions and physicochemical properties of the major flows were also taken from these publications or estimated when necessary.
The major energy inputs to the process were in the form of electricity to several units, methane to the two hydrolysis units, and high pressure steam for the distillation unit. Overall it was found that approximately 61 MJ were required for the production of 1 kg of the final product at the process scale. This number is comparable with the findings of Reck and Richards using the older sulphate process to produce TiO2 from ilmenite. They reported values ranging from 70-80 MJ per kg of TiO2 produced. Because the Altair hydrochloride process is a materials process, exergy analysis is especially informative because it is able to quantify the usable energy of both material and energy flows in a common unit (kJ/mol). Exergy of the major flows was calculated as the sum of the chemical and physical exergy. Potential, kinetic, and nuclear exergy were assumed to be negligible for this process. Exergetic efficiency has been calculated for each major unit in the process. Preliminary results of this analysis show that exergy destruction is greatest in the two hydrolysis units and the distillation unit, while the exergetic efficiency is the lowest for those same units.
In order to calculate the minimum exergy required to produce one mole of TiO2 particles using this process, the inputs were scaled according to the stoichiometrically required amount of ilmenite ore to produce a single mole of product. That is to say that theoretically none of the titanium was lost in the process and all avoidable exergy losses were avoided. This value was calculated to be approximately 4 MJ/mol of product.
Expected Results:
LCA of nanotechnology is essential for guiding and managing risk in research, development and commercialization while preventing irrational optimism or unfounded fear of this emerging field. However, it presents formidable obstacles since data and knowledge about resource consumption, emissions and their impact are either unknown or not readily available. This work will lay the foundation for LCA of polymer nanocomposites and other emerging technologies. Validation of the first hypothesis will provide useful insight about nano versus traditional technologies while the second hypothesis will provide a proxy for the ecotoxicological impact of the emissions. These hypotheses will be useful for nano and other emerging technologies before detailed emissions data and ecotoxicological studies are available. As more information about manufacturing, emissions and their impact becomes available it will be incorporated in the proposed studies and tool.
Future Activities:
Future work is expected to use the life cycle inventory of carbon nanofiber for evaluating catalytic applications. In addition, life cycle assessment results of carbon nanofiber reinforced polymer composites will be used for evaluating other end product applications. Energetic evaluation of titanium dioxide nanoparticles will be further expanded to perform traditional process and exergetic LCA to develop a general methodology for identifying and quantifying opportunities for improvement both at the process and life cycle scales. It is expected that the current and future case studies will reveal a general model for choosing an evaluation method for improvement analysis. Based on these and other studies, enough data seems to be available for a statistical analysis of the relationship between impact and resource use. Any correlation between these outputs and inputs could be useful for life cycle evaluation of emerging technologies where impacts are not yet known.
Journal Articles:
No journal articles submitted with this report: View all 19 publications for this projectSupplemental Keywords:
Life cycle assessment, carbon nanofibers, polymer nanocomposites, titanium dioxide, energy analysis, exergy analysis, life cycle inventory.
, Health, Scientific Discipline, ENVIRONMENTAL MANAGEMENT, Environmental Chemistry, Risk Assessments, Environmental Microbiology, Risk Assessment, ecological risk assessment, environmental risks, carbon fullerene, nanotechnology, human exposure, nanomaterials, nanoparticulate aerosol, polymer nanocomposites, nanoparticle toxicity, exposure assessment
Relevant Websites:
www.chbmeng.ohio-state.edu/~bakshi/research
Progress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.