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Abstract: It is well known that sonochemistry is less efficient at high acoustic intensities. Many authors have attributed this effect to decoupling losses and shielding of the acoustic wave. In this study we investigate both phenomena for a 20kHz ultrasound field with an intensity ranging from 40 to 150W/cm2. Visualization of the bubble cloud has demonstrated that the void fraction below the ultrasound horn increases more than proportional with increasing power input. Nevertheless, the energy coupling between the horn and the liquid remains constant; this implies that decoupling losses are not reinforced for larger bubble clouds. On the contrary, microphone measurements have shown that due to the larger bubble cloud a substantial part of the supplied energy is lost at high power inputs. In striving towards more efficient sonochemistry, reduction of shielding appears as one of the major challenges. [Copyright &y& Elsevier]

Abstract: The long-term performance and thermal stability of ceramic-supported cross-linked poly(vinyl)alcohol membranes has been examined over a period of six months up to a temperature of 100°C. The membrane performance gradually changes at a temperature of 80°C. After six months the water flux has increased from 1 to 1.4kgm2 h−1, while the selectivity has decreased from 450 to 300. SEM analysis gives no indication that the decrease in performance is caused by defects in the membrane layers or a decreased adherence of the PVA layer to the γ-Al2O3 support. It is more likely that observed higher water flux and lower selectivity are caused by a decrease in cross-linking of the PVA-chains due to removal of maleic acid. At a temperature of 100°C the decline in performance is accelerated. At this temperature the selectivity drops from 300 to 25, over a period of two weeks. At 100°C, the thermal stability of the membranes is inadequate for most practical applications. [Copyright &y& Elsevier]

Abstract: Catalytic Amberlyst 15 layers have been deposited on composite ceramic/poly(vinyl)alcohol membranes by the dip-coat technique using Aculyn® as a rheology modifier. Tuning of the catalytic layer thickness is possible by varying the number of dip-coat steps. The obtained “dried-mud like” Amberlyst 15 layers are stable during pervaporation and reaction experiments. The catalytic activity of the Amberlyst-coated pervaporation membrane equals the activity of the unsupported catalyst. In the pervaporation-assisted esterification reaction between acetic acid and 1-butanol the catalytic membrane is able to couple catalytic activity and water removal. Due to the high activity of the Amberlyst catalyst the conversion of the esterification reaction is limited by the removal rate of water through the membrane. This is in contrast to zeolite-coated pervaporation membranes, for which the conversion of the esterification reaction between acetic acid and 1-butanol is limited by the catalytic activity. [Copyright &y& Elsevier]

Soft rubber foams like poly(ethylene-co-vinyl acetate) (EVA) are industrially applied in a broad range of products, including sports gear, insulation materials and drug delivery systems. In contrast to glassy polymers, few studies in literature concern the foaming of soft rubbers using supercritical carbon dioxide. In this study, open microporous matrices of EVA have been formed with CO2. Prior to the foam expansion, sorption and swelling isotherms of CO2 in EVA have been measured and the obtained isotherms have been correlated using the Sanchez–Lacombe equation of state. Additionally, a pressure-independent diffusion coefficient of CO2 in EVA has been obtained from these experiments. The microporous foams have been formed by a pressure quench of the CO2-swollen polymer matrix. Sorption pressure as well as temperature and decompression times appear to determine the pore size and bulk density of the foam. These parameters allow for a control of the foam structure of EVA rubbers. [Copyright &y& Elsevier]

Temperature polarization effects can considerably limit the overall performance of pervaporation modules. This study shows the measurement of temperatures in a pervaporation membrane module using ultrasonic computer tomography (U-CT). With this technique complete 2D-temperature distributions that occur in the module can be measured within seconds. Temperature distributions were also determined using computational fluid dynamics (CFD). Both temperature distributions are comparable and show that in the tubular pervaporation system studied, temperature segregation occurs. This segregation is a result of the occurring hydrodynamics in the system that is determined by mixed convection. Also, the measured water fluxes through the membrane show to be dependent of forced and natural convection. [Copyright &y& Elsevier]

Abstract: The physics and chemistry of nonlinearly oscillating acoustic cavitation bubbles are strongly influenced by the dissolved gas in the surrounding liquid. Changing the gas alters among others the luminescence spectrum, and the radical production of the collapsing bubbles. An overview of experiments with various gas types and concentration described in literature is given and is compared to mechanisms that lead to the observed changes in luminescence spectra and radical production. The dissolved gas type changes the bubble adiabatic ratio, thermal conductivity, and the liquid surface tension, and consequently the hot spot temperature. The gas can also participate in chemical reactions, which can enhance radical production or luminescence of a cavitation bubble. With this knowledge, the gas content in cavitation can be tailored to obtain the desired output. [Copyright &y& Elsevier]

Abstract: The kinetics of 1-octene hydroformylation catalyzed by triphenylphosphine modified rhodium in carbon dioxide have been explored at 90°C and pressures up to 48MPa. The apparent catalyst solubility was determined by evaluating the reaction rate for different rhodium amounts. The kinetics follow a first order in 1-octene, a negative order of −1.2 in carbon monoxide, an order of 0.25 in hydrogen, and a negative order of −0.2 in triphenylphosphine, which is to a great extent in agreement with studies on the hydroformylation of linear 1-alkenes in organic solvents. The observed apparent turnover frequencies range from 1900 to 7000molaldehyde molRh −1 h−1. These turnover frequencies are of the same order of magnitude as observed for hydroformylations in organic solvents, indicating that rhodium modified with triphenylphosphine can be used with high efficiency in supercritical carbon dioxide rich mixtures. [Copyright &y& Elsevier]

Abstract: The kinetics of the hydroformylation of 1-octene in a supercritical carbon dioxide medium, catalyzed by a tris(3,5-bis[trifluoromethyl]phenyl)phosphine-modified rhodium catalyst, have been investigated. The influence of the concentration of carbon dioxide, reactants, catalyst precursors, and the reaction temperature has been determined. A kinetic model was developed, which describes the concentration-time profiles of the reactants, the linear and branched aldehydes, and the internal alkenes. Using the kinetic model activation energies for hydroformylation of 1-octene to nonanal and 2-methyloctanal were determined. Throughout the concentration ranges studied an approximate first order dependence of the hydroformylation rate on the hydrogen and catalyst concentration was found which indicated that oxidative addition of hydrogen was the rate limiting step. The increase in reaction rate and regioselectivity with an increase in ligand concentration is a striking feature of the catalyst investigated here. At higher concentrations the reaction rate was found to have a strong negative order dependence on the carbon monoxide concentration. The reaction rate had a positive order in 1-octene at a concentration lower than 0.5molL−1 while saturation kinetics were observed at a higher concentration. The results were explained by invoking the contribution of both monophosphine and diphosphine rhodium species to the hydroformylation catalysis. [Copyright &y& Elsevier]

Abstract: The sonochemical oxidation efficiency of a commercial titanium alloy ultrasound horn has been measured using potassium iodide as a dosimeter at its main resonance frequency (20kHz) and two higher resonance frequencies (41 and 62kHz). Narrow power and frequency ranges have been chosen to minimise secondary effects such as changing bubble stability, and time available for radical diffusion from the bubble to the liquid. The oxidation efficiency, , is proportional to the frequency and to the power transmitted to the liquid (275mL) in the applied power range (1–6W) under argon. Luminol radical visualisation measurements show that the radical generation rate increases and a redistribution of radical producing zones is achieved at increasing frequency. Argon, helium, air, nitrogen, oxygen, and carbon dioxide have been used as saturation gases in potassium iodide oxidation experiments. The highest has been observed at 5W under air at 62kHz. The presence of carbon dioxide in air gives enhanced nucleation at 41 and 62kHz and has a strong influence on . This is supported by the luminol images, the measured dependence of on input power, and bubble images recorded under carbon dioxide. The results give insight into the interplay between saturation gas and frequency, nucleation, and their effect on . [Copyright &y& Elsevier]

Abstract: CAE surfactants (carboxylic acid end-standing triblock copolymers of poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide)) are amphiphiles that are able to bind multivalent cations thermoreversibly; a property that can be used to develop new environmentally friendly separation and ion exchange applications. The analysis of the binding of multivalent ions to CAE micelles is more difficult as compared to conventional surfactants because of its thermo-responsive micellization behavior and its low CMC at room temperature. Conventional analysis techniques like conductometry and surface tensiometry are highly sensitive to temperature and are therefore very difficult to apply in surfactant solutions with strong temperature dependent micellization behavior. For this reason, binding of multivalent ions to CAE micelles has been investigated using isothermal titration calorimetry (ITC) and an alternative conductometric analysis method. Conductometry was used to construct ‘Eisenberg’ plots, which show the binding and release behavior of monovalent ions in the presence of multivalent ions. Regarding the CAE-85 (modified Pluronic P85) micellar system, both methods provide information about the exchange of multivalent cations for monovalent ions above the critical micellization temperature (CMT) of CAE-85. ITC results confirm that dehydration of multivalent ions plays a dominant role in the observed heat effect during the titration of multivalent chloride salts to CAE-85 solutions. The multivalent ions investigated in this study are Ca2+, Cu2+, Zn2+, Co2+, Mg2+, Ba2+, Mn2+ and La3+. Additionally, using the alternative conductivity approach a change in micellar shape was observed upon the addition of multivalent ions when the molar amount of cationic charges balances the molar amount of anionic carboxylate end groups of the surfactant. [Copyright &y& Elsevier]

Abstract: Reversible on/off-switching of bovine serum albumin (BSA) permeation through a thermoresponsive composite membrane with negligible permeation in the off-state is demonstrated. UV-photografting of poly(N-isopropylacrylamide) onto a poly(ethylene terephthalate) microfiltration membrane results in a hydrogel graft layer on the irradiated side of the membrane only. The amount of hydrogel grafted onto the membrane can be controlled by the amount of crosslinker. Above the lower critical solution temperature (LCST) of the hydrogel (on-state), the shrunken state of the graft layer appears to only partially cover the membrane, allowing BSA permeation through the uncovered pores. Provided the grafting degree is high enough, the swollen hydrogel covers the membrane completely below the LCST (off-state), thus preventing BSA permeation. The on-demand release mechanism proposed here is based on switching the membrane surface coverage rather than previously reported switches based on effective pore size or hydrogel mesh size. The main advantage of our mechanism is that higher fluxes can be achieved in the on-state, since permeation is not limited by pore-narrowing. [Copyright &y& Elsevier]

Abstract: For the hydroformylation of 1-octene in supercritical carbon dioxide the relationship between the change in pressure and the change in reaction mixture composition as a function of time has been investigated. The activity and selectivity has been studied for the catalyst based on tris(3,5-bis(trifluoromethyl)phenyl)phosphine and rhodium(I) dicarbonyl acetylacetonate. The influence of the ligand to rhodium ratio on the hydroformylation has been used to demonstrate how the pressure can be correlated to the conversion and yield. The initial rate of reaction is in good agreement with the initial pressure change in the batch reactor. Up to an aldehyde yield of 80%, the pressure drop appears to be independent of the reaction rate and selectivity. The highest average reaction rate, , has been obtained for a ligand to rhodium ratio of 50 and an initial concentration of 1-octene of 0.5molL−1. Both the reaction rate and the selectivity increase when the ligand to rhodium ratio is increased. The Peng–Robinson equation of state has been used to describe the pressure as a function of the concentration of the reactants and products. The calculated pressure corresponds reasonably well with the observed reactor pressure. Following the progress of the reaction by monitoring the pressure is a good alternative to reaction mixture sampling, especially for fast reactions. [Copyright &y& Elsevier]

Abstract: The permeation of supercritical CO2 and SF6 across two different types of microporous membranes has been studied as a function of temperature and feed pressure. A general picture appears where for both species the permeance as a function of the feed pressure has a maximum. For both the polymeric and the silica membranes close to the temperature where the different species become supercritical the maximum in the permeance is observed at the critical pressure. In the supercritical regime the main mechanism for the mass transport is viscous flow, and there is almost no contribution from surface diffusion through the micropores. The permeance of the fluids obtained for different condition can be described by a single mobility constant, which is independent of temperature and pressure. [Copyright &y& Elsevier]

Abstract: Esterification of acetic acid with butanol has been studied in a heterogeneous reaction system, using a variety of solid acid catalysts. Comparative esterification experiments have been carried out using the homogeneous catalysts sulphuric acid, p-toluenesulphuric acid and a heteropolyacid. The catalysts have been characterised using gas adsorption analysis (BET), X-ray diffraction (XRD), scanning electron microscopy (SEM) and temperature-programmed decomposition (TPD) techniques. The weight-based activity of the heterogeneous catalysts decreases in the following order: Smopex-101>Amberlyst 15>sulphated ZrO2 >H-USY-20>H-BETA-12.5>H-MOR-45>Nb2O5 >H-ZSM-5-12.5. The low activity of ZSM-5 is a result of internal diffusion limitations in the medium sized pores of this zeolite type material. For H-MOR the low activity can be explained by pore blocking in the one-dimensional H-MOR channels. For the H-USY-type zeolites, the influence of the Si/Al ratio on catalytic activity has been examined. Although the amount of acid sites decreases with an increase in the Si/Al ratio, an optimum Si/Al ratio of 20 has been found. The activity of sulphated zirconia shows an optimum calcination temperature, even though both the amount and acidity of the acid sites increase monotonically with calcination temperature. Most likely, at higher calcination temperatures Lewis acid sites are formed and Brønsted acid sites are removed. As Brønsted acid sites are essential for catalysis of esterification reactions this explains the decrease in activity. [Copyright &y& Elsevier]

Abstract: In this paper we describe qualitatively and quantitatively the non-random scission of polymers by ultrasound. Scission experiments have been performed using monodisperse polymethyl methacrylate dissolved in methyl methacrylate, showing that fracture occurs close to the center of the polymer chain. A mechanism is proposed for this non-random fracture, from which it can be concluded that complete stretching of the polymer chains is required before breakage can occur. The developed model, which is a combination of strain rate and drag force calculations, predicts a limiting molecular weight, which has experimentally been confirmed. The scission rate depends almost quadratically on the molecular weight, which is derived by modeling the experimental time-dependent molecular weight distributions. This dependence supports the requirement of complete stretching of the polymer chain before breakage. The developed degradation model is also capable to describe the effects of various process variables on cavitation-induced polymer scission. [Copyright &y& Elsevier]

A membrane reactor is presented for homogeneous catalysis in supercritical carbon dioxide with in situ catalyst separation. This concept offers the advantages of benign high-density gases, i.e., the possibility of achieving a high concentration of gaseous reactants in the same phase as the substrates and catalyst as well as easy catalyst localization by means of a membrane. For the separation of the homogeneous catalyst from the products an inorganic microporous membrane is used. The concept is demonstrated for the hydrogenation of 1-butene using a fluorous derivative of Wilkinson''s catalyst [RhCl{P–(C6H4-p-SiMe2CH2CH2C8F17)3}3]. The size of Wilkinson''s catalyst, 2–4 nm, is clearly larger than the pore diameter, 0.5–0.8 nm, of the silica membrane. The membrane will, therefore, retain the catalyst, while the substrates and products diffuse through the membrane. Stable operation and continuous production of n-butane has been achieved at a temperature of 353 K and a pressure of 20 MPa. A turnover number of 1.2×105 has been obtained during 32 h of reaction. The retention of the catalyst was checked using UV–vis spectroscopy and ICP-AAS; no rhodium or phosphorous species were detected at the permeate side of the membrane. [Copyright &y& Elsevier]

Abstract: A new route for the chlorination of methane is described using ultrasound irradiation, which allows for an intrinsically safe process at ambient pressure and temperature. By tuning the gas feed composition methyl chloride yields of up to 19% have been obtained. [Copyright &y& Elsevier]