Semi-fluorinated trialkyltin fluorides and fluorinated telechelic ionomers as viscosity-enhancing agents for carbon dioxide

Direct thickeners for dense carbon dioxide were designed and synthesized. Each thickener contained "CO2-philic" fluorinated groups to impart solubility in carbon dioxide and "CO2-phobic" functionalities to promote intermolecular associations for viscosity enhancement. Semifluorinated trialkyltin fluorides and fluorinated telechelic ionomers were soluble to at least several weight percent in dense liquid carbon dioxide without the use of a cosolvent. Increases in solution viscosity at 297 K were measured using falling cylinder viscometry. The viscosity of liquid carbon dioxide was increased by a factor of 2-3 at thickener concentrations of 2-4 wt %. These results demonstrate that carbon dioxide viscosity enhancement is possible without the need for a cosolvent through the design of compounds with the appropriate balance of CO2-philic groups for solubility and CO2-phobic associating groups for macromolecular, viscosity-enhancing interactions. Neither compound, however, was as effective as the (29% styrene-71% fluoroacrylate) copolymer we recently developed. More substantial increases in solution viscosity were not attained with the semi-fluorinated trialkyltin fluoride because the fluorinated alkyl chains disrupted the associations that formed viscosity-enhancing, weakly associating, linear polymers. The viscosity increases obtained with the telechelic ionomer were also less than expected because of the relatively low molecular weight of the carbon-dioxide-soluble ionomers. Higher-molecularweight ionomers would not be CO2-soluble, however

Proposed mechanism for the formation of dust horizons on bauxite residue disposal areas

Without some form of mitigation control bauxite residue disposal areas in Mediterranean climates can be subject to large-scale dust lift-off events during summer, with significant environmental impact. Intuitively dust formation relates simply to the process of drying. However, whilst wet solids will not produce dust, the converse is not always true. Both the rate of drying and the composition of the bauxite residue are critical factors in determining whether a potential dust event will occur. In this work a dust formation mechanism is proposed in which caustic salts transport and effloresce along with a changing phase composition in the brine solids from sodium bicarbonate through to trona and then to carbonate monohydrate. The efflorescence leads to a white dust event, but the carbonate phase change and the associated reduction in sodium molar volume critically breaks inter-particulate bonding between the residue particles leading to a more severe underlying red dust event

Poly(vinyl acetate), poly((1-O-(vinyloxy) ethyl-2,3,4,6-tetra-O-acetyl-beta-D-glucopyranoside) and amorphous poly (lactic acid) are the most CO2-soluble oxygenated hydrocarbon-based polymers

Poly(vinyl acetate), PVAc, remains the most CO2-soluble non-fluorous polymer identified to date. Small sugar acetates are known to be extraordinarily CO2-philic, but cellulose triacetate, a crystalline high molecule weight polymer is CO2 insoluble. Therefore, an amorphous high molecular weight polymer with pendant sugar acetates was synthesized. This polymer, poly(1-O-(vinyloxy) ethyl-2,3,4,6-tetra-O-acetyl-β-d-glucopyranoside, P(AcGIcVE), was indeed CO2-soluble, however cloud point pressures of P(AcGIcVE) at 5 wt% polymer and 298 K were greater than that required for the dissolution of PVAc. Finally, the solubility of amorphous poly(lactic acid), PLA, was determined over a wide range of molecular weight. The corresponding cloud point pressures were much greater than either PVAc or P(AcGIcVE). Ab initio calculations for the CO2/PVAc dimer and CO2/PLA dimer mixtures were conducted in an attempt to elucidate the dramatic differences in the cloud point values of PVAc and PLA. Our calculations indicate that there is little difference in the average interaction energies for the CO2/PLA and the CO2/IPA systems. The only indication that PVAc would be expected to be more CO2-soluble that PLA was that the vinyl acetate dimer has binding modes that will readily accept multiple CO2 molecules, whereas the binding modes for the lactic acid dimer can apparently only accommodate a single CO2 molecule at a time. © 2008 Elsevier B.V. All rights reserved

Design and evaluation of nonfluorous CO2-soluble oligomers and polymers.

Ab initio molecular modeling is used to design nonfluorous polymers that are potentially soluble in liquid CO2. We have used calculations to design three nonfluorous compounds meant to model the monomeric repeat units of polymers that exhibit multiple favorable binding sites for CO2. These compounds are methoxy isopropyl acetate, 2-methoxy ethoxy-propane, and 2-methoxy methoxy-propane. We have synthesized oligomers or polymers based on these small compounds and have tested their solubility in CO2. All three of these exhibit appreciable solubility in CO2. At 25 degrees C, oligo(3-acetoxy oxetane)6 is 5 wt % soluble at 25 MPa, the random copolymer (vinyl methoxymethyl ether30-co-vinyl acetate9) is 5 wt % soluble at 70 MPa and random copolymer (vinyl 1-methoxyethyl ether30-co-vinyl acetate9) is 3 wt % soluble at 120 MPa. These oligomers and polymers represent new additions to the very short list of nonfluorous CO2-soluble polymers. However, none of these are more soluble than poly(vinyl acetate), which exhibits the highest CO2 solubility of any known polymer containing only the elements C, H, and O