10 research outputs found
Theoretical Study of 1-Methoxy-2-sulfanylethan-1-yl Cation:Â Insight into Intermediates in Glycosidation Reactions
Fungal Biotransformation of Insoluble Kraft Lignin into a Water Soluble Polymer
Low
substrate solubility and slow decomposition/biotransformation
rate are among the main impediments for industrial scale lignin biotreatment.
The outcome and dynamics of kraft lignin biomodification by basidiomycetous
fungi, <i>Coriolus versicolor</i>, were investigated in
the presence of dimethyl sulfoxide (DMSO). The addition of 2 vol %
DMSO to aqueous media increased the lignin solubility up to 70%, while
the quasi-immobilized fungi (pregrown on agar containing kenaf biomass)
maintained their ability to produce lignolytic enzymes. Basidiomycetous
fungi were able to grow on solid media containing both 5â25
g/L lignin and up to 5 vol % DMSO, in contrast to no growth in liquid
media as a free suspended culture. When a fungal culture pregrown
on agar was used for lignin treatment in an aqueous medium containing
2â5% DMSO with up to 25 g/L lignin, significant lignin modification
was observed in 1â6 days. The product analysis suggests that
lignin was biotransformed, rather than biodegraded, into an oxygenated
and cross-linked phenolic polymer. The resulting product showed the
removal of phenolic monomers and/or their immediate precursors based
on gas chromatography and thermal desorptionâpyrolysisâgas
chromatographyâmass spectrometry analyses. Significant intramolecular
cross-linking among the reaction products was shown by thermal carbon
analysis and <sup>1</sup>H NMR spectroscopy. An increase in polarity,
presumably due to oxygenation, and a decrease in polydispersity of
the lignin treatment product compared to untreated lignin were observed
while using liquid chromatography
Triacylglyceride Thermal Cracking: Pathways to Cyclic Hydrocarbons
Thermal cracking of triacylglyceride (TG) oils results
in complex mixtures, containing nearly 20% cyclic hydrocarbons, which
can be further processed into middle-distillate transportation fuels
and byproduct chemicals. The occurrence patterns of cyclic products
obtained via the thermal cracking of several TG feedstocks, such as
canola and soybean oils, as well as triolein and tristearin (conducted
at 430â440 °C in the absence of catalysts under vacuum),
were investigated to probe possible formation mechanisms. Detailed
gas chromatographic characterization furnished full molar homology/molecular
size and partial isomeric profiles for cyclopentanes, cyclopentenes,
cyclohexanes, cyclohexenes, aromatics, and polycyclic aromatic hydrocarbons
(PAHs). It was found that the data were inconsistent with previously
proposed mechanisms involving the DielsâAlder reaction as a
single pathway. An alternate mechanism was proposed and supported
with experimental evidence based on the intramolecular cyclization
of alkenyl and alkadienyl radicals formed as a result of TG cracking.
The product homology profiles corroborate the proposed mechanism and
show the depletion of medium-size alkenes coupled with the accumulation
of corresponding monocyclic hydrocarbons (those with the matching
number of carbon atoms). Similarly, the product mixtures were depleted
of long-chain alkyl-substituted monocyclic hydrocarbons because of
the formation of the corresponding PAHs as long as sufficient time
is available. Entropy appears to determine the type and size of cyclic
hydrocarbons formed