Frank P. Lucien

Solubilities of solid mixtures in supercritical carbon dioxide: a review

Abstract A wealth of information on the solubility of materials in supercritical fluids (SCFs) has been published in the literature. For the most part, this information is concerned with the solubility of individual solutes in supercritical CO 2 (binary systems). It has become clear from the relatively few studies on the solubility of solid mixtures that binary solubility data represent a limited picture of the complex intermolecular interactions that may occur in the SCF phase. In particular, the solubility of a solid may be enhanced significantly, compared to its binary system, in the presence of a second solid. In this review, published data on the solubilities of solid mixtures in supercritical CO 2 are examined to highlight unique solubility phenomena associated with these systems. An extensive compilation of solubility enhancement data, the first of its kind, is presented for this purpose. The phase behaviour of solid mixtures under high pressure is considered as well as the effect of melting on solubility enhancement. The impact of solubility enhancement on selectivity is assessed and opportunities for improving the selectivity of extraction are highlighted. For most solid mixtures, solubility enhancement can be explained in terms of an entrainer effect similar to that observed in cosolvent systems. However, if the solid mixture partially melts, solubility enhancement becomes heavily dependent on which species is present as an excess solid phase. An examination of the phase behaviour of solid mixtures is therefore essential for the interpretation of solubility enhancement data.

Polymerization induced self-assembly: tuning of nano-object morphology by use of CO2

Polymeric nano-objects of non-spherical morphology (e.g. rods, vesicles) have a range of potential applications, and it is thus of great interest to develop synthetic approaches that enable large scale production as well as fine tuning of the morphology. To this end, we have developed reversible addition–fragmentation chain transfer (RAFT) dispersion polymerization in an alcoholic medium pressurized to low pressure (8.0 MPa) with CO2. It is demonstrated that the presence of CO2 has a profound effect on the morphology of the resulting polymer aggregates. In the presence of CO2, the formation of nano-objects with a high interfacial core/corona curvature is favoured relative to the corresponding system without CO2, e.g. rods are formed (with CO2) under conditions where vesicles (no CO2) would otherwise form. This is a convenient method for tuning the morphology without altering the recipe, and represents an attractive route to pure rod morphology, which is typically somewhat elusive.

Three-phase catalytic hydrogenation of α-methylstyrene in supercritical carbon dioxide

Abstract The three-phase catalytic hydrogenation (TPCH) of α-methylstyrene using supercritical carbon dioxide (scCO 2 ) in a slurry reactor is reported. Kinetic data are presented for the reaction at 323 K over the range of pressure from 7.0 to 13.0 MPa using a carbon-supported palladium catalyst. The experimental data are fitted to a first-order power-law model. A detailed explanation of the methodology used to isolate the effect of CO 2 on the rate of reaction is presented. Particular attention is given to the phase behaviour of the reaction system and the volumetric expansion of the liquid phase with CO 2 . It is shown that scCO 2 significantly enhances the rate of reaction. This effect is attributed to the enhancement of the solubility of hydrogen in the liquid phase.

Volumetric expansion and vapour–liquid equilibria of α-methylstyrene and cumene with carbon dioxide at elevated pressure

Abstract Volumetric expansion data and vapour-liquid equilibria (VLE) for α-methylstyrene (AMS) with CO2 are reported at temperatures of 308 and 323 K and pressures approaching the mixture critical point. Similar data are reported for the mixture of carbon dioxide and cumene at a temperature of 323 K. It is shown that the volumetric expansion data for the various systems coincide when plotted as a function of the solubility of CO2 in the liquid phase. A procedure is described for calculating the molar volume of the liquid phase from the phase compositions and volumetric expansion data. The experimental VLE data are correlated with the Peng-Robinson (PR) equation of state and the interaction parameter for each binary system is obtained by regression. The interaction parameter is subsequently used to predict the liquid molar volume for each binary system. The use of a single interaction parameter with the PR equation of state provides a satisfactory correlation of the liquid molar volume.

Evaluating the impact of recycled fiber content on effluent recycling in newsprint manufacture.

This paper investigates the effect of using recycled fiber (RCF) in newsprint production on the effluent quality and its treatability using membrane operations for internal and external recycling and reuse. Increased chemical usage in RCF for deinking had significant impact on the silica and sodium content of the effluent which in turn limits the membranes operation. Increasing the RCF content from 0% to 50% is estimated to increase the silica content from 4 to 119mgL(-1) and sodium content from 135 to 500mgL(-1). A process model was developed to calculate the impact of these excess chemicals on the greenhouse gas (GHG) emission and brine disposal for an integrated membrane plant design producing 4MLday(-1) of recycled water. As the ratio of RCF increased from 0% to 50% in the mill process, the operating pressure increased for nanofiltration (NF) and reverse osmosis (RO). Additionally, organics presence in the feed increased the NF operating pressure above the simulated value and reduced the silica removal efficiency by 15%. Incorporation of lime coagulation pretreatment was found to be essential to operate RO at high recoveries with relatively GHG emissions. Without pretreatment, as RCF content increased from 0% to 50%, RO recovery decreased from 80% to 22% and the expended GHG increased from 0.9 to 3.5kgCO2m(-3). Although the excess sodium concentration limits the brine disposal for irrigation purposes, a partial blending of the treated wastewater with other process streams resulted in the reduction of sodium absorption ratio by 20%.

Radical polymerization of miniemulsions induced by compressed gases

Generation of miniemulsions (nanoemulsions) comprising hydrophobic vinyl monomers and water by use of the compressed gases carbon dioxide and ethylene, respectively, has been investigated in the absence of high energy mixing. It is proposed that transparent/translucent miniemulsions are formed at the transparency pressure (PT) as a result of the refractive index of the dispersed phase being reduced due to expansion with carbon dioxide/ethylene, resulting in refractive index matched miniemulsions with enhanced stability. Radical polymerization of methyl acrylate at 40 °C in miniemulsions induced by carbon dioxide at PT proceeds as a hybrid miniemulsion/emulsion polymerization system generating particles with diameters less than 100 nm. The experimental data are consistent with particle formation occurring mainly via monomer droplet nucleation (miniemulsion polymerization) but also via secondary nucleation in the aqueous phase (emulsion polymerization). Polymerizations at a range of pressures above and below PT revealed limited pressure effects on the polymerization rate and particle size for both carbon dioxide and ethylene.

Water and Carbon Dioxide: A Unique Solvent for the Catalytic Polymerization of Ethylene in Miniemulsion

The catalytic polymerization of ethylene is performed in water pressurized with CO2 . The size of the initial monomer droplets and of the resulting polymer particles can be varied by simply changing the CO2 pressure. Furthermore, at identical ethylene partial pressure, the polymerizations performed in the presence of CO2 are significantly faster than in its absence. Thus, the combination of CO2 and water is a promising green solvent for catalytic emulsion polymerizations.

Design of CeyCoxTi (1-x) O3+δ Perovskite for Photocatalysis: A Statistical Study

Abstract The influence of metal composition and preparation pH on the properties and photoactivity of sol-gel synthesised CeyCoxTi1-xO3+δ perovskite (0.05 ≤ x, y ≤ 0.20) has been investigated. Composite oxide samples were obtained following an orthogonal design plan and characterised using N2 adsorption, XRD, NH3-TPD, UV-diffuse reflectance and FTIR spectroscopy. Photoactivity was evaluated based on the oxidative mineralization of phydroxybenzoic acid in an internally-radiated slurry reactor at 300 K. Statistical analysis revealed that increased Co content caused a significant reduction in band-gap energy although detrimental to BET surface area. The addition of Ce improved photoactivity and the trend appeared to be closely linked to the presence of stronger acid sites in these perovskite catalysts. Preparation pH, however, has only marginal effect on the physicochemical properties and a statistically negative effect on the photoactivity. Data were fitted to multi-linear regression models which were subsequently used to obtain optimum conditions for the preparation of the perovskite for each of the key performance indices with a Ce0.05Co0.2Ti 0.8O1.875 synthesised at pH=4 emerging as the optimum recipe for photoactivity.