No abstract

The stability against gamma radiation of MeTODGA (methyl tetraoctyldiglycolamide) and Me2TODGA (dimethyl tetraoctyldiglycolamide), derivatives from the well-known extractant TODGA (N,N,N',N'-tetraoctyldiglycolamide), were studied and compared. Solutions of MeTODGA and Me2TODGA in alkane diluents were subjected to (60)Co γ-irradiation in the presence and absence of nitric acid and analyzed using LC-MS to determine their rates of radiolytic concentration decrease, as well as to identify radiolysis products. The results of product identification from three different laboratories are compared and found to be in good agreement. The diglycolamide (DGA) concentrations decreased exponentially with increasing absorbed dose. The MeTODGA degradation rate constants (dose constants) were uninfluenced by the presence of nitric acid, but the acid increased the rate of degradation for Me2TODGA. The degradation products formed by irradiation are also initially produced in greater amounts in acid-contacted solution, but products may also be degraded by continued radiolysis. The identified radiolysis products suggest that the weakest bonds are those in the diglycolamide center of these molecules.

Biomass storage conditions are a major source of feedstock quality variability that impact downstream preprocessing, feeding, handling, and conversion into biofuels, chemicals and products. Microbial activity in the stored biomass can result in heating that can modify or degrade the cell walls of the biomass, changing its characteristics. Analytical pyrolysis has been used to characterize biomass, but at temperatures typically used (∼600 °C), the differentiation of samples having different storage histories is subtle or nonexistent. In this study, lower-temperature (400 °C) pyrolysis was used to show large differences in corn stover samples that had experienced different biological heating histories, indicated by pyrolysis products that were identified and, in several cases, quantified using two-dimensional gas chromatography/mass spectrometry. Pyrolysis of the samples originating from biomass that had experienced biological heating during storage generated small oxygenates such as furfural, 5-methyl furfural, and 2-(5H)-furanone with efficiencies that were as much as ten times greater than those measured for samples that were not significantly heated. Most of the pyrolysis products with enhanced efficiencies were C5 oxygenates, suggesting formation from hemicellulosic precursor polymers in the corn stover. The findings suggest that biological heating disrupts the cell wall structure, fragmenting the hemicellulose or cellulose chains and generating more polymer termini that have a higher efficiency in the generation of oxygenates at lower temperatures. Further, analytical pyrolysis conducted at lower temperatures may be a beneficial strategy for improved biomass cell wall characterization and the provision of insights to understand and manage the feedstock variability and inform harvest and storage best management practices.