Olefin oligomerization by main group Ga3+ and Zn2+ single site catalysts on SiO2.

In heterogeneous catalysis, olefin oligomerization is typically performed on immobilized transition metal ions, such as Ni2+ and Cr3+. Here we report that silica-supported, single site catalysts containing immobilized, main group Zn2+ and Ga3+ ion sites catalyze ethylene and propylene oligomerization to an equilibrium distribution of linear olefins with rates similar to that of Ni2+. The molecular weight distribution of products formed on Zn2+ is similar to Ni2+, while Ga3+ forms higher molecular weight olefins. In situ spectroscopic and computational studies suggest that oligomerization unexpectedly occurs by the Cossee-Arlman mechanism via metal hydride and metal alkyl intermediates formed during olefin insertion and ß-hydride elimination elementary steps. Initiation of the catalytic cycle is proposed to occur by heterolytic C-H dissociation of ethylene, which occurs at about 250 °C where oligomerization is catalytically relevant. This work illuminates new chemistry for main group metal catalysts with potential for development of new oligomerization processes.

Bifunctionalized organic-inorganic charged nanocomposite membrane for pervaporation dehydration of ethanol.

Chitosan was modified into N-p-carboxy benzyl chitosan (NCBC) by introducing an aromatic ring grafted with acidic -COOH group and highly stable and cross-linked nanostructured NCBC-silica composite membranes were prepared for pervaporation dehydration of water-ethanol mixture. These membranes were tailored to comprise three regions namely: hydrophobic region, highly charged region and selective region, in which weak acidic group (-COOH) was grafted at organic segment while strong acidic group (-SO(3)H) was grafted at inorganic segment to achieve high stability and less swelling in water-ethanol mixture. Cross-linking density and NCBC-silica content in membrane matrix has been systematically optimized to control the nanostructure of the developed polymer matrix for studying the effects of molecular structure on the swelling, and PV performance. Among prepared membranes, nanocomposite membrane with 3h cross-linking time and 90% (w/w) of NCBC-silica content (PCS-3-3) exhibited 1.66×10(-4)cm(3)(STP) cm/cm(2) s cmHg water permeability (P(W)), while 1.35×10(-7) cm(3)(STP) cm/cm(2) s cmHg ethanol permeability (P(EtOH)) of developed membrane and 1231 PV selectivity factor at 30 °C for separating water from 90% (w/w) ethanol mixture.

Membrane-based techniques for the separation and purification of proteins: an overview.

Membrane processes are increasingly reported for various applications in both upstream and downstream technology, such as microfiltration, ultrafiltration, emerging processes as membrane chromatography, high performance tangential flow filtration and electrophoretic membrane contactor. Membrane-based processes are playing critical role in the field of separation/purification of biotechnological products. Membranes became an integral part of biotechnology and improvements in membrane technology are now focused on high resolution of bioproduct. In bioseparation, applications of membrane technologies include protein production/purification, protein-virus separation. This manuscript provides an overview of recent developments and published literature in membrane technology, focusing on special characteristics of the membranes and membrane-based processes that are now used for the production and purification of proteins.

An improved process for separation of proteins using modified chitosan-silica cross-linked charged ultrafilter membranes under coupled driving forces: isoelectric separation of proteins.

Functionalized chitosan namely as N-methylene phosphonic chitosan (PC) and quaternized chitosan (QC) silica composite charged ultrafilter membranes were prepared by acid catalyzed sol-gel method in the aqueous media and gelated in methanol for tailoring their pore structure. These membranes were employed for developing a simple membrane process for pH sensitive protein fractionation under coupled driving forces (pressure and electric gradient). Protein transmission (selectivity) and membrane throughput across both membranes were studied using binary mixture of protein under different gradients at pH points: 2.0, 4.8, 10.7, and 13.0. It was concluded that separation from the binary mixture of BSA-LYS, separation LYS at pH 4.8 (pI of BSA) using negatively charged PC-Si membrane or separation BSA at pH 10.7 (pI of LYS) using positively charged QC-Si membrane, was possible with high selectivity. Also in all cases, due to coupling of driving forces, filtrate flux and selectivity were enhanced by several folds. Furthermore, applied electric gradient progressively increased the separation factor values, which was close to 10 for PC-Si and 15 for QC-Si membranes. Relatively high separation value of individual protein from binary mixture and filtrate velocity suggests the practical usefulness of this novel process and biopolymer membranes.

Sulfonated poly(styrene-co-maleic anhydride)-poly(ethylene glycol)-silica nanocomposite polyelectrolyte membranes for fuel cell applications.

A method for the preparation of highly conductive and stable organic-inorganic nanocomposite polyelectrolyte membranes with controlled spacing between inorganic segment and covalently bound sulfonic acid functional groups has been established. These polyelectrolyte membranes were prepared by condensation polymerization of the silica precursor (tetraethylorthosilicate) in dimethylacetamide in the presence of poly(ethylene glycol) (PEG) of desired molecular weight, and sulfonated poly(styrene-co-maleic anhydride) was attached to the polymeric backbone by hydrogen bonding. Molecular weight of PEG has been systematically changed to control the nanostructure of the developed polymer matrix for studying the effects of molecular structure on the thermal as well as conductive properties. These polyelectrolyte membranes were extensively characterized by studying their thermo-gravimetric analysis (TGA), ion-exchange capacity (IEC), water content, conductivity, methanol permeability, and current-voltage polarization curves under direct methanol fuel cell (DMFC) operating conditions as a function of silica content and molecular weight of PEG used for membrane preparation. Moreover, from these studies and estimation of selectivity parameter among all synthesized membranes, 30% silica content and 400 Da molecular weight of PEG resulted in the best nanocomposite polyelectrolyte membranes, which exhibited performance comparable to that of the Nafion 117 membrane for DMFC applications.

Preparation and characterization of N-methylene phosphonic and quaternized chitosan composite membranes for electrolyte separations.

Chitosan was functionalized either by introducing a phosphonic acid group or by quaternization of existing primary ammonium groups in order to make it a water-soluble material. Functionalized chitosans and poly(vinyl alcohol) (PVA)-based nanoporous charged membranes were prepared in aqueous media and gelated in methanol at 10 degrees C to tailor their pore structure. These membranes were extensively characterized for their physicochemical, electrochemical, and permeation characteristics using FTIR, TGA, DSC, water content, ion-exchange capacity, ionic transport properties, and membrane permeability studies. N-Methylene phosphonic chitosan (NMPC)/PVA-based membranes exhibited mild cation selectivity and quaternized chitosan (QC)/PVA composite membranes had mild anion selectivity, while a blend of NMPC-QC/PVA membranes exhibited weak cation selectivity because of formation of zwitterionic structure. Viscosity measurements and interaction studies for individual and mixed solutions of NMPC and QC were carried out for the prediction of charge interactions between -PO3H2 and -N+(CH3)3 groups and effect on molecular weight due to functionalization. Elaborate electrochemical and permeation experiments were conducted in order to predict suitability of these membranes for the separation of mono- and bivalent electrolytes based on their hydrated ionic radius, and it was found that among all the synthesized membranes, PC/QC-30 had the highest relative permeability, which may extend its suitability for electrolyte separations. Observations were correlated with equivalent pore radius of the different membranes as estimated by membrane permeability measurements.