Wall slip and melt-fracture of polystyrene melts in capillary flow

We investigated slip and unstable flow phenomena of polystyrene melts in capillaries from the view of the effects of temperature and molecular weight by using three polystyrene samples with different molecular weights (M_w = 192,000, M_w = 258,000, and M_w = 321,000). The slip velocities are estimated by the Mooney method and the modified Mooney method. We found that the slip velocity increases and the critical slip stress above which a slip starts to occur decreases with the temperature. We also observed the melt-fracture at above a critical melt-fracture stress higher than . We found that the onset of melt fracture is affected by the extensional stress near the entry region to the capillary in the barrel and the melt-fracture tends to easily occur with increase of the molecular weight, but is not sensitive to the temperature.     

Anion exchanged polymerized ionic liquids: High free volume single ion conductors

In this study, we investigate the isolated effect of anion type on the chemical, thermal, and conductive properties of imidazolium-based polymerized ionic liquids (PILs). PILs with various anions at constant average chain length were prepared by ion exchange with a water-soluble PIL precursor, (poly(1-[(2-methacryloyloxy)ethyl]-3-butylimidazolium bromide) (poly(MEBIm-Br)). NMR, IR, and elemental analysis confirm that anion exchange of ploy(MEBIm-Br) with bis(trifluoromethanesulfonyl) imide (TFSI), tetrafluoroborate (BF₄), trifluoromethanesulfonate (Tf), and hexafluorophosphate (PF₆) in water resulted in nearly fully exchanged PILs. As a function of anion type, the glass transition temperature plays a dominant role, but not the sole role in determining ion conductivity. Other factors affecting ionic conductivity include the size and symmetry of the anion and dissociation energy of the ion pair. Both the Vogel-Fulcher-Tammann (VFT) and Williams-Landel-Ferry (WLF) equations were employed to investigate the temperature dependent ionic conductivities. The (9.03) and (168 K) values obtained from the WLF regression of these PILs greatly deviate from the classical WLF values originally obtained from the mechanical relaxation of uncharged polymers ( = 17.44,  = 51.6 K) and the WLF values obtained from the conductive properties of other polymer electrolytes. This suggests that the fractional free volume (f (T_g) = B/(2.303)) and Vogel temperature (T₀ = T_g − ) are strong functions of ion concentration, where high free volume allows for ion mobility at temperatures farther below the glass transition temperature of the polymer.     

Quantifying desorption and rearrangement rates of carbon monoxide on a PEM fuel cell electrode

A simple procedure to quantify the rates of carbon monoxide (CO) desorption from, and simultaneous rearrangement on, supported platinum fuel cell electrode (Pt on Vulcan XC-72R) is reported. The surface coverage of CO on Pt electrode in equilibrium with bulk CO was measured from the anodic peaks in the CO stripping voltammogram. The decline in these surface coverages due to desorption and rearrangement, once CO was replaced by N₂ in the gas phase was recorded and used in conjunction with a kinetic model to quantify the respective rates. Two distinct CO oxidation peaks observed in the voltammogram due to the oxidation of two distinct ad-species, namely weakly and strongly adsorbed CO ( and ), were baseline corrected and deconvoluted using a bimodal Gaussian distribution. Saturation surface coverage of decreased with increasing temperature, while the opposite was true for . Rearrangement from to was faster than the desorption rate of either CO species. The desorption rate of was at least an order of magnitude lower than that of molecules at all temperatures studied. The activation energies for desorption of and were estimated to be 24.08 and 27.99 kJ/mol, respectively. The activation energy for rearrangement from to was 35.23 kJ/mol and that from to was 27.55 kJ/mol.     

Effect of oxidizing agents on selenate formation in a wet FGD

In a coal combustion process, a considerable amount of selenium is captured in the wet FGD, where it is oxidized from selenite to selenate , which is difficult to remove. Diethyl-p-phenylene-diammonium (DPD) absorptiometric analysis and ion chromatography identified peroxodisulfate ion as the dominant oxidizing agent in the FGD liquor. Selenite was easily oxidized to selenate in the presence of and the oxidation was accelerated as the temperature increased. Addition of Mn²⁺ ion was found to be effective in controlling selenate formation. When Mn²⁺ ion was added, oxidized not selenite to selenate but rather Mn²⁺ to MnO₂, which captured some dissolved selenite.     

Kinetics of absorption of carbon dioxide into aqueous blends of 2-(1-piperazinyl)-ethylamine and N-methyldiethanolamine

The kinetics absorption of CO₂ into aqueous blends of 2-(1-piperazinyl)-ethylamine (PZEA) and N-methyldiethanolamine (MDEA) were studied at 303, 313, and 323 K using a wetted wall column absorber. The PZEA concentrations in the blends with MDEA varied from 0 to to see the effect of PZEA as an activator in the blends with two different total amine concentrations (1.0 and ). Based on the pseudo-first-order condition for the CO₂ absorption, the overall second-order reaction rate constants were determined from the kinetic measurements. The kinetic rate parameters were calculated and presented at each experimental condition.     

Proteolytic cleaning of a surface-bound rubisco protein stain

We present a combined experimental and mathematical study of the proteolysis of a surface-bound rubisco protein stain. The adsorption and desorption of subtilisin A (SA) onto and from surface-bound rubisco films were found to be a strong function of the surface chemistry underlying the protein stain; the stain acted as a biosensor able to convey information about the underlying surface to the attacking protease. The apparent protease adsorption rate constants (k_a) were 0.016±0.007, 0.014±0.004 and while the apparent desorption rate constants (k_d) were 1.60±0.15, 1.05±0.02 and for hydrophobic, neutral-hydrophilic and negatively charged hydrophilic surfaces, respectively. The apparent proteolysis rate constant of surface-bound rubisco and the enzyme deactivation rate constant were estimated to be and , respectively, independent of underlying surface chemistry. The results demonstrated higher protein removal from the charged hydrophilic surface relative to the other two surfaces. Rubisco cleanability from the charged and hydrophobic surfaces increased with increasing bulk enzyme concentration (and hence surface enzyme concentration) and was better for the charged surface, perhaps reflecting the higher k_a value. Conversely, rubisco cleanability from the neutral hydrophilic surface was surprisingly insensitive to variation in bulk enzyme concentration. Overall cleaning efficiency was also substantially lower for the neutral hydrophilic surface when compared with the hydrophobic surface, even though k_a values for each surface were similar. These findings indicate that surface proteolysis is significantly impaired at low values of k_d, suggesting that enzyme mobility at the interface may be closely linked to cleaning performance. The model presented here is expected to be a useful tool in the detergent industries to screen and gauge the cleaning performance of detergent-enzyme formulations, and may also be able to facilitate the design of surface treatments that convey cleaning signals to attacking proteases.     

Use of angle resolved PIV to estimate local specific energy dissipation rates for up- and down-pumping pitched blade agitators in a stirred tank

Up-pumping pitched blade turbines (and similar impellers) have recently been shown to be particularly effective for achieving a variety of mixing duties. Here, their turbulent flow characteristics are analysed by angle-resolved particle image velocimetry (PIV) for the first time and compared with their down-pumping equivalent, the usual time-averaged parameters also being determined for each. The work was conducted in 0.15 m diameter vessel (T) with a 45° impeller of diameter D (=0.45T) in water. The angle-resolved PIV enables a number of novel features to be identified. Firstly, the two pumping directions are shown to give very different vortex structures, even though the flow numbers, Fl, are the same (=0.79). In addition, the ‘spottiness’ of the normalized kinetic energy along a radius as the trailing vortex moved away from each impeller can be identified, which is not shown from time-averaged data. Often, the most important parameter for processing is the local normalized specific energy dissipation rate, and this is estimated using three methodologies: by measurement of the components of the stress tensor directly, ; by dimensional analysis, , with measured integral length scales (ILS); and by the Smagorinsky closure method, , to model unresolved scales (with a Smagorinsky constant used in the literature on stirred vessels). Again, only the angle-resolved results show the spottiness of and also higher values than the time-averaged. Differences in the values obtained by the three methods are discussed and compared with the existing literature. Most importantly, for the first time, the power input in the PIV-interrogated region is calculated from the three methods and compared to the input based on the impeller torque. Both DA and SGS methods are shown to overestimate the true power by a factor of 5 and 2, respectively, whilst the DE method provided a significant underestimate (1/5th) due to the limitation of the resolved length scales. The SGS method shows the greatest promise and by changing the value of the Smagorinsky constant in accordance with recent recommendations, good agreement is obtained. Nevertheless, it is concluded that there is still a need for improved methods for determining the important mixing parameter, .     

Synthesis, characterization and thermodynamic properties of poly(3-mesityl-2-hydroxypropyl methacrylate-co-N-vinyl-2-pyrrolidone)

Poly(3-mesityl-2-hydroxypropyl methacrylate-co-N-vinyl-2-pyrrolidone) P(MHPMA-co-VP) was synthesized in 1, 4-dioxane solution using benzoyl peroxide (BPO) as initiator at 60 °C. The copolymer was characterized by ¹H ¹³C NMR, FT-IR, DSC, TGA, size exclusion chromatography analysis (SEC) and elemental analysis techniques. According to SEC, the number-average molecular weight (M_n), weight-average molecular weight (M_w) and polydispersity index (PDI) values of PMHPMA-co-VP were found to be 58,000, 481,000 g/mol and 8.26, respectively. According to TGA, carbonaceous residue value of PMHPMA-co-VP was found to be 6% at 500 °C. Also, some thermodynamic properties of PMHPMA-co-VP such as the adsorption enthalpy, ΔH_a, molar evaporation enthalpy, ΔH_v, the sorption enthalpy, , sorption free energy, , sorption entropy, , the partial molar free energy, , the partial molar heat of mixing, , at infinite dilution was determined for the interactions of PMHPMA-co-VP with selected alcohols and alkanes by inverse gas chromatography (IGC) method in the temperature range of 323-463 K. According to the specific retention volumes, , the weight fraction activity coefficients of solute probes at infinite dilution, , and Flory-Huggins interaction parameters, between PMHPMA-co-VP-solvents were determined in 413-453 K. According to and , selected alcohols and alkanes were found to be non-solvent for PMHPMA-co-VP at 413-453 K. The glass transition temperature, T_g, of the PMHPMA-co-VP found to be 370 and 363 K, respectively, by IGC and DSC techniques, respectively.     

Dispersion mechanism of nano-particulate aggregates using a high pressure wet-type jet mill

A high pressure wet-type jet mill was employed to disperse nano-particle suspensions. Commercially available nano-particles, fumed silica (SiO₂) of primary particle diameter (d₀) ranging from 7 to 40 nm, alumina (Al₂O₃) of and titanium oxide (TiO₂) of were dispersed in the continuous phase up to viscosity . Ion exchanged water, aqueous ethylene glycol and aqueous polyethylene glycol solutions with molecular weight up to 2 000 000, were used as the continuous phase. Particle size distribution, zeta potential and suspension viscosity were measured under a wide range of process conditions. The smaller the d₀ was, the harder it was to disperse the aggregates. Zeta potential was largely dependent on d₀ at any process conditions and became dependent on η_c for . The energy barrier was evaluated by taking van der Waals attractive forces, electrostatic repulsive forces and dispersive forces into consideration. Cavitation measurements showed a negligible cavitation during the passage through the jet mill; therefore aggregate disruption was modeled for fully turbulent flow. Aggregate disruption occurred in inertia sub-range for and in viscous sub-range for . By balancing mechanical energy with turbulent disruptive energy, a mechanistic model was developed for each sub-range. The analysis of fractal dimensionality showed that nano-aggregates were made up by particle-particle collision in inertia sub-range and orthokinetic cluster-cluster collision in viscous sub-range. The rheological data obtained were expressed according to a modified Casson model.     

Flashback propensity of syngas fuels

This paper presents experimental measurements of the critical velocity gradient and flashback behavior of H₂-CO and H₂-CH₄ mixtures. Effects of H₂ concentration, external excitation, and swirl on the flashback behavior for flames of these fuel mixtures are discussed. For H₂ concentration burner and scaling studies the critical velocity gradient (g_F), defined as the ratio of the square of the laminar burning velocity to the thermal diffusivity of the mixture , was used to quantify the flashback propensity of the flames. The critical velocity gradient of both H₂-CH₄ and H₂-CO flames changed nonlinearly with the increase in H₂ contents in the mixture. The critical velocity gradient (g_F) of 5-95% and 15-85% H₂-CO mixtures somewhat agreed with the scaling relation and yielded an average c value of 0.04. Similarly, values of a 25%H₂-75%CH₄ for different burner diameters were also fitted using the scaling relation yielding an average c value of 0.044. The g_F values of 25-75% H₂-CO mixture showed non-linear variation with the ratio (especially for ), and at a lower ratios burner diameter had small effect on critical velocity gradient measurements. The opposite trend was observed for a 25-75% H₂-CH₄ mixture showing non-linear variation at a lower ratios (for ) and having less effect at higher ratios. It was also determined that the effect of external excitation on the flashback propensity of H₂-CO flames with more than 5% H₂ was not significant. Flashback through two mechanisms and their dependence on combustor parameters were also identified for swirl stabilized H₂-CO flames.     

Labyrinthine pattern of polymer crystals from supercooled ultrathin films

We report the observation of a labyrinthine crystal pattern with a periodic structure in the crystal width direction in ultrathin films of poly(ethylene oxide) fractions with molecular weight ranging from 25,000 to 932,000 g/mol. The polymer thin films are crystallized at temperatures well below the bulk melting temperature, thus the system is characterized by limited diffusion of the polymer chains and rapid growth of the crystal fronts. The competition of these two competing factors leads to the formation of the labyrinthine pattern. This mechanism is supported by a scaling relation between the long period and molecular weight, , indicating the importance of chain diffusion. Furthermore, a linear relationship between and is observed, implying that the crystal growth is dominated by a secondary nucleation.     

Gas-solid adsorption of selected volatile organic compounds on titanium dioxide Degussa P25

This paper focuses on the adsorption of gaseous trichloroethylene, toluene and chlorobenzene on the photocatalyst TiO₂ Degussa P25. An optimized EPICS (Equilibrium Partitioning In Closed Systems) methodology was used to study equilibrium partitioning. For the three compounds investigated, equilibrium adsorption was reached within of incubation. Adsorption isotherms, determined at a temperature (T) of and relative humidities (RH) of 0.0% and 57.8% were found to be linear (R²>0.993,n=5), indicating that no monolayer surface coverage was reached in the concentration interval studied ). Within the linear part of the isotherm, the influence of both relative humidity and temperature was investigated in a systematic way and discussed from a thermodynamic point of view. Data analysis resulted in a double linear regression for 22% ?RH?90% and . The equilibrium adsorption coefficient represents the equilibrium concentration ratio and ΔU_ads is the internal energy of adsorption . At RH=0.0%, experimental K values were a factor 5-10 higher than those expected from the regression equation, indicating that another adsorption mechanism becomes important below monolayer surface coverage of TiO₂ by water vapour molecules. Since surface interactions are of primary importance in photocatalytic reactions, this paper contributes to a better understanding of the basic mechanisms of TiO₂ mediated heterogeneous photocatalysis and is an interesting tool for developing optimized mathematical models.     

Role of hydrodynamic flow parameters in lipase deactivation in bubble column reactor

The dynamic environment within the bioreactor and in the purification equipment is known to affect the activity and yield of enzyme production. In the present work, the effect of hydrodynamic flow parameters and τ_N,max) and interfacial flow parameters ( and ) on the activity of lipase has been comprehensively investigated in bubble column reactors. Lipase solution was subjected to hydrodynamic flow parameters in 0.15 and 0.385 m i.d. bubble column reactors over a wide range of superficial gas velocity (0.01<V_G<0.4-). The flow parameters were estimated using an in-house CFD simulation code based on k-ε approach. The extent of lipase deactivation in both the columns was found to increase with an increase in hydrodynamic and interfacial flow parameters. However, at equal value of any of these parameters, the extent of deactivation was different in the two columns. The rate of deactivation was found to follow first order kinetics. An attempt has been made to develop rational correlations for the extent of deactivation as well as for the deactivation constant. The rate of deactivation was found to be depending on the average turbulent normal stress and interfacial flow parameters such as bubble diameter and bubble rise velocity.     

Exothermic oxidations in supercritical CO2: effects of pressure-tunable heat capacity on adiabatic temperature rise and parametric sensitivity

Many oxidation reactions, including H₂ combustion with O₂, have been shown to admit the phenomenon of parametric sensitivity. Given its inertness to oxidation and non-flammable nature, supercritical CO₂ (scCO₂) is a desirable solvent for performing oxidations. Further, for oxidations that employ H₂O₂ as an oxidant, the use of scCO₂ as a solvent has been suggested for producing H₂O₂ in situ by reacting H₂ and O₂. Another significant, and as yet not fully understood, advantage of using scCO₂ is the ability to exploit its liquid-like heat capacity, which exhibits a maximum in the near-critical region (1.01-1.2T_c and 0.9-2.0P_c). It is shown in this modeling study that by performing an oxidation reaction in scCO₂, the temperature rise accompanying the highly exothermic reaction can be effectively controlled. To demonstrate this concept, we simulated the maximum temperature rise (ΔT_ad) for H₂ combustion with O₂ in CO₂ in a constant-pressure adiabatic reactor, at feed temperatures ranging from 300 to and reactor pressures from 1 to . At a feed temperature of , a five-fold reduction in ΔT_ad value (from 209 to ) is predicted by tuning the operating pressure from 1 to . In contrast, the ΔT_ad in N₂ medium is relatively insensitive in the 1- pressure range and is six times greater (roughly ) compared to the value predicted with CO₂ medium at . Further, the values of β (the dimensionless temperature rise parameter) may also be sensitively tuned with pressure in the near-critical region such that parametric sensitivity is minimized. These results indicate that the liquid-like heat capacities of scCO₂ may be exploited to control the adiabatic temperature rise and to ameliorate parametric sensitivity during exothermic reactions, a problem of fundamental and practical significance.