75 research outputs found
N‑Heterocyclic Carbene Promoted Decarboxylation of Lignin-Derived Aromatic Acids
Decarboxylation
is an important reaction in organic synthesis and
drug discovery, which is typically catalyzed by strong bases or metal-based
catalysts bearing low yield and selectivity. For the first time, we
demonstrated a new strategy of decarboxylation of hydroxyl cinnamic
acids such as <i>p</i>-coumaric acid, ferulic acid, sinapinic
acid, and caffeic acid in the presence of N-heterocyclic carbene (NHC)
precursors (i.e., 1-ethyl-3-methyl imidazolium acetate [C<sub>2</sub>C<sub>1</sub>Im]Â[OAc]), achieving high yields and selectivities up
to 100% under relatively mild conditions. [C<sub>2</sub>C<sub>1</sub>Im]Â[OAc] showed excellent recyclability as organocatalysis during
three times of recycling using biphasic reaction system. A mechanistic
study revealed that the decarboxylation was catalyzed by NHCs that
were in-situ generated by self-deprotonation of [C<sub>2</sub>C<sub>1</sub>Im]Â[OAc]. Our demonstrated route is especially appealing for
the production of lignin-derived renewable aromatics
Life-Cycle Greenhouse Gas and Water Intensity of Cellulosic Biofuel Production Using Cholinium Lysinate Ionic Liquid Pretreatment
Cellulosic
biofuels present an opportunity to meet a significant
fraction of liquid transportation fuel demand with renewable, low-carbon
alternatives. Certain ionic liquids (ILs) have proven effective at
facilitating hydrolysis of lignocellulose to produce fermentable sugars
with high yields. Although their negligible vapor pressure and low
flammability make ILs attractive solvents at the point of use, their
life-cycle environmental impacts have not been investigated in the
context of cellulosic biorefineries. This study provides the first
life-cycle greenhouse gas (GHG) and water use inventory for biofuels
produced using IL pretreatment. We explore two corn stover-to-ethanol
process configurations: the conventional water-wash (WW) route and
the more recently developed integrated high gravity (iHG) route, which
eliminates washing steps after pretreatment. Our results are based
on the use of a representative IL, cholinium lysinate ([Ch]Â[Lys]).
We find that the WW process results in unacceptably high GHG emissions.
The iHG process has the potential to reduce GHG emissions per megajoule
of fuel by ∼45% relative to gasoline if [Ch]Â[Lys] is used.
Use of a protic IL with comparable performance to [Ch]Â[Lys] could
achieve GHG reductions up to 70–85%. The water intensities
of the WW and iHG processes are both comparable to those of other
cellulosic biofuel technologies
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Chemoselective Methylation of Phenolic Hydroxyl Group Prevents Quinone Methide Formation and Repolymerization During Lignin Depolymerization
Chemoselective blocking
of the phenolic hydroxyl (Ar–OH)
group by methylation was found to suppress secondary repolymerization
and charring during lignin depolymerization. Methylation of Ar–OH
prevents formation of reactive quinone methide intermediates, which
are partly responsible for undesirable secondary repolymerization
reactions. Instead, this structurally modified lignin produces more
relatively low molecular weight products from lignin depolymerization
compared to unmodified lignin. This result demonstrates that structural
modification of lignin is desirable for production of low molecular
weight phenolic products. This approach could be directed toward alteration
of natural lignification processes to produce biomass that is more
amenable to chemical depolymerization
Dimethyl Sulfoxide Assisted Ionic Liquid Pretreatment of Switchgrass for Isoprenol Production
The production cost and viscosity
of certain ionic liquids (ILs)
are among the major factors preventing the establishment of economically
viable IL-based biomass pretreatment technologies. Recently, mixtures
of an IL with an organic solvent have been proposed for cellulose
processing and biomass pretreatment. Dimethyl sulfoxide (DMSO) is
an inexpensive organic solvent that is industrially produced from
lignin, a byproduct of the pulping process. We carry out a mechanistic
study of DMSO-assisted IL pretreatment of switchgrass. The physical
structures of biomass samples are studied by X-ray diffraction (XRD),
N<sub>2</sub> adsorption analysis, and small angle neutron scattering
(SANS). Both dry and aqueous suspensions of biomass samples are measured
by SANS which provides unique information on biomass pretreatment.
A mixture of 42 wt % [C<sub>2</sub>C<sub>1</sub>Im]Â[OAc] and 58 wt
% DMSO is proposed as the optimal pretreatment solution, and the recycling
and reuse of the mixture of solvents are also studied. The fermentability
of the hydrolysates generated after pretreatment is evaluated using
an E. coli strain engineered to produce
isoprenol. This study suggests an avenue for developing more efficient
and cost-effective IL-based processes for the production of lignocellulosic
biofuels and bioproducts
Survey of Lignin-Structure Changes and Depolymerization during Ionic Liquid Pretreatment
A detailed
study of chemical changes in lignin structure during the ionic liquid
(IL) pretreatment process is not only pivotal for understanding and
overcoming biomass recalcitrance during IL pretreatment but is also
necessary for designing new routes for lignin valorization. Chemical
changes in lignin were systematically studied as a function of pretreatment
temperature, time, and type of IL used. Kraft lignin was used as the
lignin source, and common pretreatment conditions were employed using
three different ILs of varying chemical structure in terms of acidic
or basic character. The chemical changes in the lignin structure due
to IL pretreatment processes were monitored using <sup>1</sup>H–<sup>13</sup>C heteronuclear single quantum coherence (HSQC) nuclear magnetic
resonance (NMR), <sup>31</sup>P NMR, elemental analysis, gel permeation
chromatography (GPC), and Fourier transform infrared (FT-IR), and
the depolymerized products were analyzed using gas chromatography
mass spectrometry (GC-MS). Although, with pretreatment in acidic IL,
triethylÂammonium hydrogensulfate ([TEA]Â[HSO<sub>4</sub>]) results
in the maximum decrease in the β-aryl ether bond, maximum dehydration
and recondensation pathways were also evident, with the net process
showing a minimum decrease in the molecular weight of regenerated
lignin. However, 1-ethyl-3-methylÂimidazolium acetate ([C<sub>2</sub>C<sub>1</sub>Im]Â[OAc]) pretreatment yields a smaller decrease
in the β-aryl ether content along with minimum evidence of recondensation,
resulting in the maximum decrease in the molecular weight. Cholinium
lysinate ([Ch]Â[Lys]) pretreatment shows an intermediate result, with
moderate depolymerization, dehydration, and recondensation observed.
The depolymerization products after IL pretreatment are found to be
a function of the pretreatment temperature and the specific chemical
nature of the IL used. At higher pretreatment temperature, [Ch]Â[Lys]
pretreatment yields guaiacol, [TEA]Â[HSO<sub>4</sub>] yields guaiacylacetone,
and [C<sub>2</sub>C<sub>1</sub>Im]Â[OAc] yields both guaiacol and guaiacylacetone
as major products. These results clearly indicate that the changes
in lignin structure as well as the depolymerized product profile depend
on the pretreatment conditions and the nature of the ILs. The insight
gained on lignin structure changes and possible depolymerized products
during IL pretreatment process would help future lignin valorization
efforts in a potential IL-based lignocellulosic biorefinery
Pylum composition of microbial communities from mesophilic and thermophilic enrichments on rice straw.
<p>Pylum composition of microbial communities from mesophilic and thermophilic enrichments on rice straw.</p
Image_1_Microbial Community Structure and Functional Potential Along a Hypersaline Gradient.TIF
<p>Salinity is one of the strongest environmental drivers of microbial evolution and community composition. Here we aimed to determine the impact of salt concentrations (2.5, 7.5, and 33.2%) on the microbial community structure of reclaimed saltern ponds near San Francisco, California, and to discover prospective enzymes with potential biotechnological applications. Community compositions were determined by 16S rRNA amplicon sequencing revealing both higher richness and evenness in the pond sediments compared to the water columns. Co-occurrence network analysis additionally uncovered the presence of microbial seed bank communities, potentially primed to respond to rapid changes in salinity. In addition, functional annotation of shotgun metagenomic DNA showed different capabilities if the microbial communities at different salinities for methanogenesis, amino acid metabolism, and carbohydrate-active enzymes. There was an overall shift with increasing salinity in the functional potential for starch degradation, and a decrease in degradation of cellulose and other oligosaccharides. Further, many carbohydrate-active enzymes identified have acidic isoelectric points that have potential biotechnological applications, including deconstruction of biofuel feedstocks under high ionic conditions. Metagenome-assembled genomes (MAGs) of individual halotolerant and halophilic microbes were binned revealing a variety of carbohydrate-degrading potential of individual pond inhabitants.</p
Rarefaction curves from pyrotag data for enriched mesophilic and thermophilic microbial communities.
<p>Dashed lines indicate ±1 standard error.</p
Contig cluster properties for selected clusters (Figure 3) with high abundance or large contigs in thermophilic and mesophilic communities.
*<p>T, thermophilic community; M, mesophilic community.</p
Ecological measures for microbial communities from mesophilic and thermophilic enrichments on rice straw.
<p>Ecological measures for microbial communities from mesophilic and thermophilic enrichments on rice straw.</p
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