Engineering topics
Publications and source records attributed to Kent, Michael S..
Aqueous oxidative deconstruction of low-density polyethylene (LDPE) using homogeneous first-row transition metal catalysts under mild conditions (130–150 °C and 100 PSI oxygen pressure).
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Experimental studies and ab initio quantum chemistry calculations were combined to investigate the process by which a Fenton reaction breaks down polystyrene sulfonate. The experimental results show that both molecular weight reduction and loss of aromaticity occur nearly simultaneously, a finding that is supported by the calculations. The results show that more than half of the material is broken down to low molecular weight compounds (< 500 g/mol) with two molar equivalents of H 2 O 2 per styrene monomer. The calculations provide insights into the reaction pathways and indicate that at least two hydroxyl radicals are required to cleave backbone Csingle bondC bonds or to eliminate aromaticity. The calculations also show that, of the aromatic carbons, hydroxyl radical is most likely to add to the carbon bonded to sulfur. This finding explains the loss of hydrogen sulfite anion early in the process and also the efficient reduction of Fe(III) to Fe(II) through semiquinone formation. Taken together the experimental and computational results indicate that the reaction is very efficient and that very little H 2 O 2 is lost to unproductive reactions. In conclusion, this high efficiency is attributed to the close association of Fe atoms with the sulfonate group such that hydroxyl radicals are generated near the polymer chains.
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Biopolymers such as lignin are gaining renewed appeal due to the need for sustainable materials. Herein, we used chelator-mediated Fenton (CMF) chemistry to oxidize Kraft lignin to develop sustainable super absorbent materials. The CMF chemistry adds oxygen, opens aromatic rings and increases COOH content, producing hydrophilic lignin without depolymerization. UV absorption, molecular weight, elemental analysis, and titration were used to study the chemical compositions of CMF-processed lignin. Then the chemically modified hydrophilic lignin was used to produce lignin-based hydrogels utilizing an aqueous polymerization and cross-linking reaction that enabled tunable properties. The resulting lignin hydrogels absorbed water up to 96% and swelled up to 2400%, as well as being re-swellable in water. These lignin-based hydrogels may be applicable in water-absorbing products in consumer goods and agriculture.
The generating value from lignin through depolymerization and biological conversion to valuable fuels, chemicals, or intermediates has great promise but is limited by several factors including lack of cost-effective depolymerization methods, toxicity within the breakdown products, and low bioconversion of the breakdown products. High yield depolymerization of natural lignins requires cleaving carbon-carbon bonds in addition to ether bonds. To address that need, we report that a chelator-mediated Fenton reaction can efficiently cleave C-C bonds in sulfonated polymers at or near room temperature, and that unwanted repolymerization can be minimized through optimizing reaction conditions. This method was used to depolymerize lignosulfonate from M w = 28,000 g/mol to M w = 800 g/mol. The breakdown products were characterized by SEC, FTIR and NMR and evaluated for bioavailability. The breakdown products are rich in acid, aldehyde, and alcohol functionalities but are largely devoid of aromatics and aliphatic dienes. A panel of nine organisms were tested for the ability to grow on the breakdown products. Growth at a low level was observed for several monocultures on the depolymerized LS in absence of glucose. Much stronger growth was observed in the presence of 0.2% glucose and for one organism we demonstrate doubling of melanin production in the presence of depolymerized LS. The results suggest that this chelator-mediated Fenton method is a promising new approach for biological conversion of lignin into higher value chemicals or intermediates.
The present invention relates to methods for identifying candidate therapeutics for a disease caused by a viral envelope protein. In particular, the method can include contacting a test envelope protein with the candidate and determining its activity.
The present invention provides for a method to depolymerize a lignin comprising: (a) mixing a lignin, a chelator, and FeCl3 to produce a first solution, (b) optionally incubating the solution for a first suitable period of time, (c) introducing an oxidizing agent to the first solution to produce a second solution, and (d) optionally incubating the solution for a second suitable period of time; such that at least one aromatic ring of one lignin polymer is opened.