Fritz Simeon

Bromine-catalyzed conversion of CO2 and epoxides to cyclic carbonates under continuous flow conditions.

A continuous method for the formation of cyclic carbonates from epoxides and carbon dioxide (CO2) is described. The catalysts used are inexpensive and effective in converting the reagents to the products in a residence time (t(R)) of 30 min. The cyclic carbonate products are obtained in good to excellent yield (51-92%). On the basis of a series of kinetics experiments, we propose a reaction mechanism involving epoxide activation by electrophilic bromine and CO2 activation by an amide.

Electrospun carbon nanofiber webs with controlled density of states for sensor applications.

1 DOI: 10.1002/adma.((please add manuscript number)) Electrospun Carbon Nanofiber Webs with Controlled Density of States for Sensor Applications By Xianwen Mao, Fritz Simeon, Gregory C. Rutledge* and T. Alan Hatton* [*] Prof. T. Alan Hatton, Prof. Gregory C. Rutledge, Xianwen Mao, Dr. Fritz Simeon. Department of Chemical Engineering, Massachusetts Institute of Technology 77 Massachusetts Avenue, Cambridge Massachusetts, 02139, USA E-mail: tahatton@mit.edu, rutledge@mit.edu

Analysis of polyhydroxybutyrate flux limitations by systematic genetic and metabolic perturbations

Poly-3-hydroxybutyrate (PHB) titers in Escherichia coli have benefited from 10+ years of metabolic engineering. In the majority of studies, PHB content, expressed as percent PHB (dry cell weight), is increased, although this increase can be explained by decreases in growth rate or increases in PHB flux. In this study, growth rate and PHB flux were quantified directly in response to systematic manipulation of (1) gene expression in the product-forming pathway and (2) growth rates in a nitrogen-limited chemostat. Gene expression manipulation revealed acetoacetyl-CoA reductase (phaB) limits flux to PHB, although overexpression of the entire pathway pushed the flux even higher. These increases in PHB flux are accompanied by decreases in growth rate, which can be explained by carbon diversion, rather than toxic effects of the PHB pathway. In chemostats, PHB flux was insensitive to growth rate. These results imply that PHB flux is primarily controlled by the expression levels of the product forming pathway and not by the availability of precursors. These results confirm prior in vitro measurements and metabolic models and show expression level is a major affecter of PHB flux.

Polyethylenimine-impregnated siliceous mesocellular foam particles as high capacity CO2 adsorbents

Siliceous mesostructured cellular foams (MCF) impregnated with polyethylenimine (PEI) of various molecular weights and structures were evaluated as CO2 adsorbents. The MCF solid support consisted of a well-defined interconnected three-dimensional mesoporous structure with large cell diameter of 30.3 nm and large window diameter of 11.3 nm, filled with polyethylenimine up to 70 weight percent or about 22.3% nitrogen atom by weight of the adsorbents. While other mesoporous solid supports lost their porosity after PEI impregnation, our MCF solid support maintained its pore volume over the range of 1.12 to 1.64 cm3 g−1. The importance of the porosity of PEI-impregnated MCF adsorbents for high capacity CO2 adsorbents was demonstrated. The highest CO2 sorption capacity (180.6 mg-CO2/g-adsorbent or 393.6 mg-CO2/g-PEI at 75 °C) was obtained for silica supports loaded with 50 weight percent branched PEI with average molecular weight of 600 g mol−1. Under dry atmospheric CO2 gas, this adsorbent reached the theoretical CO2 capacity of 0.50 mole-CO2 per mole-nitrogen within less than about 8 min, making this adsorbent one of the most effective CO2 adsorbents reported. Repeated multiple sorption cycles demonstrated good stability of this adsorbent for CO2 capture. The initial sorption kinetics determined the overall CO2 sorption capacity, which was limited by the formation of a carbamate layer as a result of the CO2–PEI complexation that due to inhibition of CO2 diffusion; the kinetics of “ionic” gelation of the impregnated PEI by CO2 controlled the overall performance of the CO2 adsorbents. At 75 °C, the operating temperature favored the molecular mobility of PEI and unrestricted diffusion of CO2 to allow the theoretical CO2 capacity of the PEI to be attained. Lower temperatures limited the mobilities of PEI and CO2 and the kinetics of “ionic” gel formation dominated, causing a lowered overall performance of the CO2 adsorbents. Overall, this study points to the importance of interconnected porous channel networks to optimize the performance of PEI-impregnated mesoporous silica particles.

Mechanism-guided design of flow systems for multicomponent reactions: conversion of CO2 and olefins to cyclic carbonates

A mechanism-guided design of a multi-step flow system enabled an efficient general process for the synthesis of cyclic carbonates from alkenes and CO2. The flow system proved to be an ideal platform for multicomponent reactions because it was straightforward to introduce reagents at specific stages without their interacting with each other or with reaction intermediates prone to destruction by them. This system exhibited superior reactivity, increased yield, and broader substrate scope relative to conventional batch conditions and suppressed the formation of undesired byproducts, such as, epoxides and 1,2-dibromoalkanes.

Post- combustion carbon dioxide capture using electrochemically mediated amine regeneration

Electrochemically mediated amine regeneration is a new post-combustion capture technology with the potential to exploit the excellent removal efficiencies of thermal amine scrubbers while reducing parasitic energy losses and capital costs. The improvements result from the use of an electrochemical stripping cycle, in lieu of the traditional thermal swing, to facilitate CO2 desorption and amine regeneration; metal cations generated at an anode react with the amines, displacing the CO2, which is then flashed off, and the amines are regenerated by subsequent reduction of the metal cations in a cathode cell. The advantages of such a process include higher CO2 desorption pressures, smaller absorbers, and lower energy demands. Several example chemistries using different polyamines and copper are presented. Experimental results indicate an open-circuit efficiency of 54% (15 kJ per mole CO2) is achievable at the tested conditions and models predict that 69% efficiency is possible at higher temperatures and pressures. A bench scale system produced 1.6 mL min−1 CO2 while operating at 0.4 volts and 42% Faradaic efficiency; this corresponds to a work of less than 100 kJ per mole.

Postsynthetic Functionalization of Mg-MOF-74 with Tetraethylenepentamine: Structural Characterization and Enhanced CO2 Adsorption

Postsynthetic functionalization of magnesium 2,5-dihydroxyterephthalate (Mg-MOF-74) with tetraethylenepentamine (TEPA) resulted in improved CO2 adsorption performance under dry and humid conditions. XPS, elemental analysis, and neutron powder diffraction studies indicated that TEPA was incorporated throughout the MOF particle, although it coordinated preferentially with the unsaturated metal sites located in the immediate proximity to the surface. Neutron and X-ray powder diffraction analyses showed that the MOF structure was preserved after amine incorporation, with slight changes in the lattice parameters. The adsorption capacity of the functionalized amino-Mg-MOF-74 (TEPA-MOF) for CO2 was as high as 26.9 wt % versus 23.4 wt % for the original MOF due to the extra binding sites provided by the multiunit amines. The degree of functionalization with the amines was found to be important in enhancing CO2 adsorption, as the optimal surface coverage improved performance and stability under both pure CO2 and CO2/H2O coadsorption, and with partially saturated surface coverage, optimal CO2 capacity could be achieved under both wet and dry conditions by a synergistic binding of CO2 to the amines as well as metal centers.

Formation of magnetic nanotubes by the cooperative self-assembly of chiral amphiphilic molecules and Fe3O4 nanoparticles

Single- and double-walled magnetic nanotubes are obtained in a one-step liquid phase reaction by the cooperative self-assembly of chiral amphiphiles and nanoparticles on cooling of heated mixtures of N-dodecanoyl-L-serine and Fe(3)O(4) nanoparticles in toluene. The nanotubes are composed of well-ordered, close-packed nanoparticle assemblies, and can be transformed into chiral magnetic nanostructures, such as helical coils, by subsequent calcination. The nanoparticle assemblies and their variations on calcination are attributed to the collective organization of the surfactant molecules adsorbed on the nanoparticles and the freely dispersed chiral molecules, and the dewetting effects guided by the primitive constitution of the chiral amphiphilic molecular assemblies.