A family of high activity catalysts for the vinyl addition polymerization of norbornene-type monomers based on cationic η-allylpalladium complexes coordinated by phosphine ligands has been discovered. The palladium complex [(η3-allyl)Pd(tricyclohexylphosphine)(ether)][B(3,5-(CF3)2C6H3)4] (2) was found to copolymerize 5-butylnorbornene and 5-triethoxysilylnorbornene (95:5 molar ratio) with truly high activity and is capable of producing more than a metric ton of copolymer per mole Pd per hour. Multicomponent catalyst systems based on the addition of salts of weakly coordinating anions (e.g., Na[B(3,5-(CF3)2C6H3)4] or Li[B(C6F5)4]·2.5Et2O) to (η3-allyl)Pd(X)(PR3) (X = chloride, acetate, nitrate, trifluoroacetate, and triflate) in the presence of norbornene-type monomers were developed. NMR tube experiments confirm that Na[B(3,5-(CF3)2C6H3)4] abstracts the Cl ligand from the palladium complex forming the cationic complex in situ. Control experiments confirmed that a high activity polymerization system requires a palladium cation containing an allyl ligand, a neutral, two-electron-donor phosphine ligand, and a weakly coordinating counterion. Those complexes where X contained electron-withdrawing groups such as trifluoroacetate or triflate were found to be the most active catalyst precursors. η3-Allylpalladium catalyst precursors with larger cone angle phosphine ligands yield lower molecular weight polymers. The poly(norbornene) molecular weights can be further tuned by addition of α-olefin chain transfer agents to the reaction mixture. The catalyst systems were also found to polymerize norbornene-type monomers in aqueous media to high conversion at very low catalyst loadings. The effect of molecular weight on thermomechanical properties was explored.
Low dielectric constant, porous silica was made from commercially available methyl silsesquioxane (MSQ) by the addition of a sacrificial polymer, substituted norbornene polymer containing triethoxysilyl groups (NB), to the MSQ. The silsesquioxane-NB polymer film mixture was thermally cured followed by decomposition of the NB at temperatures above 400°C. The dielectric constant of the MSQ was lowered from 2.7 to 2.3 by creating 70 nm pores in the MSQ. The voids created in the MSQ exhibited a closed-pore structure. The concentration of NB in the MSQ affected the number of pores but not their size. Porous films were also created in a methyl siloxane spin-on-glass and its dielectric constant was lowered from 3.1 to 2.7. Infrared spectroscopy was used to follow the curing of the MSQ and decomposition of the NB.
Per-and polyfluoroalkyl substances (PFAS) are contaminants of emerging concern. Granular activated carbon (GAC) is an adsorbent currently in use in removing long-chain PFAS from water.However, there are few studies that examine short-chain PFAS removal with GAC. The present Rapid Small-Scale Column Test study compares the removal of a suite of both long-and shortchain PFAS from groundwater. The results show that re-agglomerated, bituminous coal-based GACs, whether virgin or reactivated, are capable of effectively removing long-and short-chain PFAS with four or more perfluorinated carbons. It was also observed that perfluorobutanoic acid, a perfluorinated carboxylic acid with just three perfluorinated carbons, reached breakthrough far more quickly than all other PFAS in this study. Coconut-based and pool reactivated carbons, respectively, lasted 9 to 18% as long, and 43 to 57% as long, as the coal-based carbons studied prior to breakthrough of the PFAS. The results indicate that properly selected GACs (reagglomerated bituminous coal-based, virgin or reactivated), are a viable treatment option for PFAS contamination in water for all but the shortest perfluorinated carboxylic acids. AUTHORS' BIOGRAPHIES P. Westreich, PhD, is a Research and Development Manager at Calgon Carbon Corporation (a Kuraray Company) in Pittsburgh, Pennsylvania. His work is focused on carbon product development and applications, including water and air purification. Westreich received his BS (Hons.) in physics from McGill University and his MS and PhD in physics from Simon Fraser University. R. Mimna, PhD, is the Director of Business Innovation at Calgon Carbon Corporation (a Kuraray Company) in Pittsburgh, Pennsylvania. His work is focused on customer-driven product development and testing for a wide variety of applications in water and air purification. Mimna earned his BS in chemistry from Case Western Reserve University in Cleveland, Ohio, and his PhD in chemistry from the EPFL in Lausanne, Switzerland. J. Brewer is the Executive Director of New Market Development at Calgon Carbon Corporation (a Kuraray Company) in Pittsburgh, Pennsylvania. Her work is focused on new applications for activated carbon materials, including emerging contaminants in water and air. Brewer received her BS in chemical and biomolecular engineering from the University of Notre Dame and her Executive MBA from the University of Pittsburgh. F. Forrester is an Applications Engineer for the Municipal Business Unit at Calgon Carbon Corporation (a Kuraray Company) in Pittsburgh, Pennsylvania. His work is focused on treatment system design, product selection, and application design and he is the primary technical pointof-contact for PFAS applications at Calgon Carbon. Forrester earned his BS in chemical engineering and BA in mathematics from the State University of New York at Buffalo. How to cite this article: Westreich P, Mimna R, Brewer J, Forrester F. The removal of short-chain and long-chain perfluoroalkyl acids and sulfonates via granular activated carbons: A compar...
This article describes the challenge of treating drinking waters contaminated by perfluorinated compounds, especially perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS). A goal of the study was to establish the relative effectiveness for perfluorinated compound removal by the two primary types of granular activated carbons (GACs) commonly used in the treatment of municipal drinking water: bituminous coal‐based re‐agglomerated GAC and coconut‐based direct activated GAC. The effectiveness of GACs in removing PFOA and PFOS to nondetectable levels is demonstrated through the use of rapid small‐scale column testing. Results demonstrate that bituminous coal‐based re‐agglomerated carbons provide considerably greater removal capacity of the targeted compounds compared with the coconut‐based direct activated carbon. In support of these findings, summaries of additional third‐party test work and field installations are cited. In addition, the authors provide an overview of reactivation of activated carbon to improve the economics of the technology.
Granular activated carbon (GAC) is the most widely used and well-established treatment technology for the removal of per and polyfluoroalkyl substances (PFAS) contaminants from drinking water and wastewater. After the GAC has reached the end of its useful service life and become "spent carbon," it is common practice in industry to thermally treat it in a process known as reactivation. The reactivation process volatilizes and destroys adsorbed contaminants at high temperatures and restores the GAC to a near-virgin state so that it can be reused. Since the advent of PFAS regulatory actions, questions have arisen about the effectiveness of the reactivation process for the destruction of PFAS given their high thermal stability and the lack of documented study on this new topic. In light of this, a thorough program of testing was carried out at a full-scale GAC reactivation facility during the reactivation of a load of GAC known to contain adsorbed PFAS. The facility employs a multihearth Herreschoff furnace and a downstream abatement train that includes a thermal oxidizer, spray quench cooler, dry injection scrubber, and baghouse. All inputs and outputs of the system were tested for targeted PFAS compounds and fluoride (total and as hydrogen fluoride). Under typical operating conditions, the system demonstrated both full removal of PFAS compounds from GAC and >99.99% destruction of PFAS compounds through the furnace and abatement system.Additional key findings include: (1) a large portion of the PFAS destruction occurs in the furnace, before the thermal oxidizer; (2) the fluoride mass balance was close to 61.4%; and (3) emission levels were significantly lower than available public data for PFAS manufacturing emissions.
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