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The technique of molecular-beam, mass spectrometric (MBMS) sampling is applied to the elucidation of the molecular pathways in the fast pyrolysis of wood and its principal isolated constituents. The goal is the optimization of high-value fuel products by thermal and catalytic means. The positive-ion mass spectra shown are obtained from real-time, direct sampling of light gases, reactive intermediates, and condensible vapors simultaneously. The cellulose, lignin, and hemicellulose (e.g., xylan) components of wood pyrolyze largely to monomer and monomer-related fragments and give characteristic mass spectral signatures. Whole wood appears to behave as the sum of its constituents, with few if any vapor species derived from interaction of the main polymer constituents. An important interaction, however, is the influence of mineral matter in the wood on the carbohydrate pyrolysis pathways. Vapor phase cracking of the primary products proceeds through a stage of light hydrocarbons and oxygenates to the ultimate formation of aromatic tars and H2, CO, C02, and H20. These steps are illustrated and discussed. Consistent with these observations, a relatively simple pyrolysis reaction scheme is proposed.

SUMMARYThe U.S. Department of Energy and the National Renewable Energy Laboratory are developing technologies to produce hydrogen from renewable, sustainable sources. A cost goal of $2.00-$3:00 kg À1 of hydrogen has been identified as the range at which delivered hydrogen becomes cost competitive with gasoline for passenger vehicles. Electrolysis of water is a standard commercial technology for producing hydrogen. Using wind and solar resources to produce the electricity for the process creates a renewable system. Biomass-to-hydrogen processes, including gasification, pyrolysis, and fermentation, are less well-developed technologies. These processes offer the possibility of producing hydrogen from energy crops and from biomass materials such as forest residue and municipal sewage. Solar energy can be used to produce hydrogen from water and biomass by several conversion pathways. Concentrated solar energy can generate high temperatures at which thermochemical reactions can be used to split water. Photoelectrochemical water splitting and photobiology are long-term options for producing hydrogen from water using solar energy. All these technologies are in the development stage.

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The conversion of pine pyrolysis vapors over fixed beds of HZSM-5 catalyst was studied as a function of deactivation of the catalyst, presumably by coking.

Summary 1.We separated the effects of plant species controls on decomposition rates from environmental controls in northern peatlands using a full factorial, reciprocal transplant experiment of eight dominant bryophytes in four distinct peatland types in boreal Alberta, Canada. Standard fractionation techniques as well as compound-specific pyrolysis molecular beam mass spectrometry were used to identify a biochemical mechanism underlying any interspecific differences in decomposition rates. 2. We found that over a 3-year field incubation, individual moss species and not micro-environmental conditions controlled early stages of decomposition. Across species, Sphagnum mosses exhibited a trade-off in resource partitioning into metabolic and structural carbohydrates, a pattern that served as a strong predictor of litter decomposition. 3. Decomposition rates showed a negative co-variation between species and their microtopographic position, as species that live in hummocks decomposed slowly but hummock microhabitats themselves corresponded to rapid decomposition rates. By forming litter that degrades slowly, hummock mosses appear to promote the maintenance of macropore structure in surface peat hummocks that aid in water retention. 4. Synthesis . Many northern regions are experiencing rapid climate warming that is expected to accelerate the decomposition of large soil carbon pools stored within peatlands. However, our results suggest that some common peatland moss species form tissue that resists decomposition across a range of peatland environments, suggesting that moss resource allocation could stabilize peatland carbon losses under a changing climate.