Experimental study of the effect of inclination angle on the minimum conveying velocity and the underlying mechanisms

This work investigated the effect of inclination angle on the minimum conveying velocity and the underlying mechanisms. Results showed that the pressure drop increased first and then decreased with the increasing inclination angle at the same mass flux and superficial gas velocity. The changing trend of minimum conveying velocity (u_min) and the pressure drop near it can be divided into two types by taking 45° as the boundary, which was consistent with the difference in flow regimes near u_min at different inclination angles based on results of high-speed photography and acoustic emission detection. Furthermore, the pressure drop was decomposed to investigate the underlying mechanism of the changing trend of u_min. Results showed that the changing trend of u_min was closely related to the particle velocity and the particle velocity obtained by high-speed photography was in good agreement with the theoretical analysis.     

Influence of substrate dideuteration on the reaction of the bifunctional heme enzyme psi factor producing oxygenase A (PpoA)

PpoA is a bifunctional enzyme that catalyzes the dioxygenation of unsaturated C18 fatty acids. The products of this reaction are termed psi factors and have been shown to play a crucial role in conferring a balance between sexual and asexual spore development as well as production of secondary metabolites in the fungus Aspergillus nidulans. Studies on the reaction mechanism revealed that PpoA uses two different heme domains to catalyze two subsequent reactions. Initially, the fatty acid substrate is dioxygenated at C8, yielding an 8‐hydroperoxy fatty acid at the N‐terminal domain. This reaction is catalyzed by a peroxidase/dioxygenase‐type domain that exhibits many similarities to prostaglandin H2 synthases and involves a stereospecific homolytic hydrogen abstraction from C8 of the substrate. The C terminus harbors a heme thiolate P450 domain in which rearrangement of the 8‐hydroperoxide to the final product, a 5,8‐dihydroxy fatty acid, takes place. To obtain further information about the intrinsic kinetics and reaction mechanism of PpoA, we synthesized C5‐dideutero‐ and C8‐dideutero‐oleic acid by a novel protocol that offers a straightforward synthesis without employing the toxic additive hexamethylphosphoramide (HMPA) during C? C coupling reactions or mercury salts upon thioketal deprotection. These deuterated fatty acids were then employed for kinetic analysis under multiple‐turnover conditions. The results indicate that the hydrogen abstraction at C8 is the rate‐determining step of the overall reaction because we observed a KIE (V_H/V_D) of ～33 at substrate saturation that suggests extensive nuclear tunneling contributions for hydrogen transfer. Deuteration of the substrate at C5, however, had little effect on V_H/V_D but resulted in a different product pattern presumably due to an altered lifetime and partitioning of a reaction intermediate.     

Molecular Dynamics Simulations of Antibiotic Ceftaroline at the Allosteric Site of Penicillin-Binding Protein 2a (PBP2a)

Methicillin-resistant Staphylococcus aureus (MRSA) tolerates β-lactam antibiotics by carrying out cell wall synthesis with the transpeptidase Penicillin-binding protein 2a (PBP2a), which cannot be inhibited by β-lactams. It has been proposed that PBP2a's active site is protected by two loops to reduce the probability of it binding with β-lactams. Previous crystallographic studies suggested that this protected active site opens for reaction once a native substrate binds at an allosteric domain of PBP2a. This opening was proposed for the new β-lactam ceftaroline's mechanism in successfully treating MRSA infections, i. e. by it binding to the allosteric site, thereby opening the active site to inhibition. In this work, we investigate the binding of ceftaroline at this proposed allosteric site using molecular dynamics simulations. Unstable binding was observed using the major force fields CHARMM36 and Amber ff14SB, and free energy calculations were unable to confirm a strong allosteric effect. Our study suggests that the allosteric effect induced by ceftaroline is weak at best.     

A Reaction Zone Hypothesis for the Effects of Particle Size and Water‐to‐Cement Ratio on the Early Hydration Kinetics of C3S

The hydration kinetics of tricalcium silicate (C₃S) has been the subject of much study, yet the experimentally observed effects of the water‐to‐cement (w/c) ratio and particle size distribution have been difficult to explain with models. Here, we propose a simple hypothesis that provides an explanation of the lack of any significant effect of w/c on the kinetics and for the strong effect of the particle size distribution on the amount of early hydration associated with the main hydration peak. The hypothesis is that during the early hydration period the calcium–silicate–hydrate product forms only in a reaction zone close to the surface of the C₃S particles. To test the hypothesis, a new microstructure‐based kinetics (MBK) model has been developed. The MBK model treats the C₃S particle size distribution in a statistical way to save computation time and treats the early hydration as essentially a boundary nucleation and growth process. The MBK model is used to fit kinetic data from two published studies for C₃S with different size distributions, one for alite (impure C₃S) pastes and one for stirred C₃S suspensions. The model is able to fit all the data sets with parameters that show no significant trend with particle size, providing support for the reaction zone hypothesis.     

Microemulsion polymerization of styrene using developed redox initiation system and study of rheological properties of obtained latices

Microemulsion polymerization of styrene was kinetically studied using a potassium persulfate (KPS)/P‐methyl benzaldehyde sodium bisulfite (MeBSBS) adduct as the developed redox pair initiation system. The rate of microemulsion polymerization of styrene was found to be dependent on the initiator, emulsifier, and monomer to the powers of 1.4, −0.77, and 0.83, respectively. The apparent Arrhenius activation energy (E_a) estimated for the microemulsion polymerization system was 6.5 × 10⁴ J/mol. Also, the morphological parameters were studied at different initiator concentrations. The rheological measurements for the prepared microemulsions were carried out to investigate the effect of the preparation parameters on the rheological behavior of the polystyrene microemulsions. The rheological flow curves of the polystyrene microemulsion latices prepared at different temperatures were carried out, and we found that the plastic viscosity and Bingham yield values of the flow curves increased with an increasing reaction temperature. That may be due to the cage effect of the prepared polymer particles, which trapped the medium molecules. The plastic viscosity increased with increasing emulsifier concentration while the Bingham yield value decreased. For the polystyrene microemulsion prepared in the presence of different initiator concentrations, the plastic viscosity and Bingham yield increased with increasing initiator concentration. This trend was found to be the same for the microemulsion latices prepared in the presence of different monomer concentrations. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1240–1249, 2000     

New catalyst of SO 4 2− /Al2O3–ZrO2 for n-butane isomerization

The catalytic behavior of Al-promoted sulfated zirconia for n-butane isomerization at low temperature in the absence of H₂ and at high temperature in the presence of H₂ was studied. The addition of Al enhances the activity and stability of the catalysts for reaction at 250°C and in the presence of H₂ significantly. After on stream for 120 h, the n-butane conversion of the catalyst containing 3 mol% Al₂O₃ keeps steadily at 88% of its equilibrium conversion and no observable trend of further deactivation has been observed. The difference in behavior of the promoted and unpromoted catalysts at low and high temperature is associated with a change of reaction mechanism from bimolecular to monomolecular. Experimental evidence is presented to show that the promoting effect of Al is different from that of the transition metals. Microcalorimetric measurements of NH₃ adsorption on catalysts reveal that the remarkable activity and stability of the Al-promoted catalysts are caused by an enhancement in the number of acid sites effective for the isomerization reaction. This revised version was published online in June 2006 with corrections to the Cover Date.     

The effect of non‐ideal mixing on the number of steady states and dynamic behaviour for autocatalytical reactions in a CSTR

In this paper, we analyze the concentration multiplicity and dynamic behavior for an autocatalytical reaction, A + R → (n + 1)R + products with an overall rate expression given by – γ_a= kc_a^pc_r^r(p > 0 and r > 0) in a imperfectly mixed (Cholette's model) CSTR. We proved that non‐ideal mixing had an effect on the number of steady states and dynamic behavior for the reaction orders r > 1 and r = 1. However, the above‐mentioned effect does not happen for the reaction order r < 1. Furthermore, a simulated example was used to demonstrate our results.     

Rheological,thermal, and curing properties of natural rubber‐g‐poly(methyl methacrylate)

Graft copolymers of NR and PMMA (i.e., NR‐g‐PMMA) were prepared with the bipolar redox initiation system, using various percentages of molar ratios of NR/MMA at 95/5, 90/10, 80/20, 70/30, and 60/40. It was found that the Mooney viscosity, shear stress, and shear viscosity of the NR‐g‐PMMA increased with an increase in the molar ratio of MMA used in the graft copolymerization. This may be attributed to an increasing trend of the chemical interaction between polar functional groups within the grafted PMMA molecules. Furthermore, a decreasing trend of storage moduli was observed with increasing molar ratios of MMA. The glass transition temperature was obtained from the tan δ curves. We found a slightly increasing trend of the T_g's with an increase in molar ratios of MMA used in the grafting reaction. The NR‐g‐PMMA was later compounded using TBBS as an accelerator. With an increase in molar ratios of MMA in the grafting reaction, we observed an increasing trend of minimum torque, maximum torque, cure time, and scorch time, but quite similar levels of torque difference and crosslink density. Furthermore, the tensile strength of the NR‐g‐PMMA gum vulcanizate increased with an increase in molar ratios of MMA, whereas the elongation at break decreased. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1600–1614, 2006     

Nylon 6 polymerization in the solid state

The postcondensation of nylon 6 in the solid state was studied. The reactions were carried out on fine powder in a fluidized bed reactor in a stream of dry nitrogen in the temperature range 110–205°C and during 1–24 h. The solid-state polymerization (SSP) did not follow melt kinetics, but was found to be limited by the diffusion of the autocatalyzing acid chain end group. Factors thought to influence SSP were studied, e.g., heat treatment, starting molecular weight, and remelting. Surprisningly, heat treatment had little effect, but the starting molecular weight had a strong effect on the reaction rate. The higher the starting molecular weight, the faster the reaction. This could be explained as a changing concentration distribution of the reactive groups in the solid state on SSP. The kinetics of the SSP had more than one region, and the rate of reaction for conversions of over 30% could be expressed as ? dc/dt = k(c/t), where k is a dimensionless constant independent of temperature with a value of 0.28. The integrated form has the form ? In(c/c_o) = k In(t/τ), where c_o is the acid end-group concentration at the start, t is the reaction time, and τ is the induction time. The value of τ is both dependent on the starting concentration c_o and the reaction temperature and has an activation energy of 105 kJ/mol.     

Effect of Hydrogen Peroxide on the Photocatalytic Degradation of Methyl tert-butyl Ether

The photocatalytic degradation of methyl tert-butyl ether (MTBE) was investigated in the aqueous slurry of titanium dioxide (TiO₂) particles irradiated with xenon lamp in a batch reactor, in the presence and absence of hydrogen peroxide. The reaction was found to follow a pseudo-first-order kinetics and the initial reaction rate constant increased by raising the TiO₂ loading and reached an apparent optimum value at 0.5 g TiO₂/L. The addition of small amounts of hydrogen peroxide to the TiO₂ slurry, which is generally known to enhance the oxidation process in treating organic pollutants, decreased the initial MTBE degradation rate by as much as nearly 50%. However, this trend was reversed and reaction rate approached a plateau at higher concentration levels of hydrogen peroxide.     

Graft copolymerization of methacrylic acid onto xanthan gum by Fe2+/H2O2 redox initiator

The graft copolymer of xanthan gum with methacrylic acid was synthesized in inert atmosphere by using Fentos reagent as a redox initiator. The effect of reaction conditions on grafting parameters [G(%), E(%), C(%), A(%), H(%), and R_g] was investigated. Similar trend was observed on increasing the concentration of ferrous ion and hydrogen peroxide from 4.0 to 20.0 × 10^?3 mol dm^?3 and 2.5 to 10 × 10^?3 mol dm^?3 respectively, i.e., initially grafting parameters increased and after a certain range of concentration grafting parameters showed decreasing trend. Hydrogen ion shows influenced result i.e., small increment of concentration in hydrogen ion presents much increment in percent of grafting. It was observed that the [G(%), E(%), C(%), A(%), and R_g] increased upto 6.67 × 10^?2 mol dm^?3 concentration of methacylic acid after that it decreased. Maximum G(%) was obtained at minimum concentration of xanthan gum i.e., at 40 × 10^?2 g dm^?3. The optimum temperature and time duration of reaction for maximum percentage of grafting were found to be 45°C and 150 min respectively. Thermogravimetric analysis showed that the xanthan gum‐g‐methacrylic acid is thermally more stable than pure gum. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Solvent Effects on the Selectivity of Palladium-Catalyzed Suzuki-Miyaura Couplings

The use of polar solvents MeCN or dimethylformamide (DMF) was previously shown to induce a selectivity switch in the Pd/P^tBu₃-catalyzed Suzuki-Miyaura coupling of chloroaryl triflates. This phenomenon was attributed to the ability of polar solvents to stabilize anionic transition states for oxidative addition. However, we demonstrate that selectivity in this reaction does not trend with solvent dielectic constant. Unlike MeCN and DMF, water, alcohols, and several polar aprotic solvents such as MeNO₂, acetone, and propylene carbonate provide the same selectivity as nonpolar solvents. These results indicate that the role of solvent on the selectivity of Suzuki-Miyaura couplings may be more complex than previously envisioned. Furthermore, this observation has the potential for synthetic value as it greatly broadens the scope of solvents that can be used for chloride-selective cross coupling of chloroaryl triflates.     

Reaction rate and MWD changes in crosslinking of PVC,with dithioltriazine

The reaction rate of crosslinking of PVC with dithioltriazine has been studied by following gel formation and changes in the molecular weight distribution (MWD). Compounding was performed on a roll mill at 145°C and crosslinking by heat treatment at 180 or 90°C. In this system crosslinking is executed by the thiolate anion, formed in situ by reaction with MgO. We have studied the catalyzing effect of several polyols in order to achieve a more efficient reaction. Most likely, these catalysts work by chelating the Mg²⁺ ions, thus increasing the nucleophilic character of the thiolate. With the most efficient ones, ditrimethylolpropane and HO(CH₂CH₂)_6-7H, complete crosslinking can be obtained in 3 min at 180°C, i.e., at processing temperatures. We also followed the changes in the MWD before gelation at a considerably lower temperature, 145°C, and found an extensive molecular enlargement even after 5-10 min. Most surprisingly, μM_n increased up to 100% without formation of insoluble material. By ¹H-NMR measurements on low molecular weight extracts, we have shown this to be due to a fast and selective reaction with allylic chlorine in the unsaturated end groups, ～ CH₂? CH?CH? CH₂Cl, formed in the mechanism of chain transfer to monomer. Due to this reaction, formulations with too high reactivity may crosslink during processing, which calls for a careful balancing of the reactivity for each processing case.     

Foliar spraying of potassium gluconate promotes the synthesis of the seed oil of Styrax tonkinensis

Styrax tonkinensis is a promising woody biodiesel species. In this experiment, we investigated how foliar spraying of potassium gluconate solution affected the production of seed oil in S. tonkinensis. Leaf spraying of potassium gluconate solution appreciably promoted the photosynthesis of S. tonkinensis leaves through both the light reaction and the dark reaction. By boosting the activity of enzymes involved in glucose metabolism and seed oil synthesis, foliar spraying of potassium gluconate solution also dramatically enhanced glucose metabolism and seed oil synthesis in the S. tonkinensis seeds. This indicates that foliar spraying with potassium gluconate solution discernibly improved the synthesis of seed oil in S. tonkinensis by encouraging the transit of photosynthetic products from the source to the reservoir and the flow of carbon into the seed oil synthesis in the seeds. Overall, the medium concentration of potassium gluconate solution (4 g/L) was found to be the most effective for increasing the oil content of S. tonkinensis seeds. While higher potassium gluconate solution concentrations (6 g/L) had a slight inhibitory effect on specific indicators (ACCase) during specific seed development periods. This study highlighted the importance of potassium for seed oil synthesis in woody plants and provided a useful foundation for future cultivation practices aimed at enhancing seed oil synthesis in woody plants.     

Influence of the synthesis conditions on the curing behavior of phenol–urea–formaldehyde resol resins

The curing behavior of synthesized phenol–urea–formaldehyde (PUF) resol resins with various formaldehyde/urea/phenol ratios was studied with differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). The results indicated that the synthesis parameters, including the urea content, formaldehyde/phenol ratio, and pH value, had a combined effect on the curing behavior. The pH value played an important role in affecting the shape of the DSC curing curves, the activation energy, and the reaction rate constant. Depending on the pH value, one or two peaks could appear in the DSC curve. The activation energy was lower when pH was below 11. The reaction rate constant increased with an increase in the pH value at both low and high temperatures. The urea content and formaldehyde/phenol ratio had no significant influence on the activation energy and rate constant. DMA showed that both the gel point and tan δ peak temperature (T_tanδ) had the lowest values in the mid‐pH range for the PUF resins. A different trend was observed for the phenol–formaldehyde resin without the urea component. Instead, the gel point and T_tanδ decreased monotonically with an increase in the pH value. For the PUF resins, a high urea content or a low formaldehyde/phenol ratio resulted in a high gel point. The effect of the urea content on T_tanδ was bigger than that on the gel point because of the reversible reaction associated with the urea component. Too much formaldehyde could lead to more reversible reactions and a higher T_tanδ value. The effects of the synthesis conditions on the rigidity of the cured network were complex for the PUF resins. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 95: 1368–1375, 2005     

Control of the product distribution in the hydrogenation of vegetable oils over nickel on silica catalysts

Several nickel on silica catalysts, prepared by impregnation or precipitation/deposition, and a commercial catalyst were tested for activity and selectivity in the sunflower seed oil hydrogenation. An average turn-over frequency of 2.57 s^?1 was found for the catalysts, assuming inaccessibility of nickel in pores smaller than 2 nm and a constant nickel surface concentration poisoned by the reaction mixture. After studying the mass-transfer steps, the effect of temperature (373-453 K) and pressure (101-608 kPa) on reaction rates in the kinetic regime was analyzed, and the corresponding apparent activation energies and reaction orders were obtained. Conclusions on the effect of temperature and pressure on the selectivity to the preferential hydrogenation of polyunsaturates (S_o) and to the formation of trans-isomers ((S_trans)₀) in the kinetic regime were derived from the results. Finally, a similar analysis was carried out when diffusion limitations were known to be present.     

Preparation of Dimethyl Disulfide Adducts from the Mono‐Trans Octadecadienoic Acid Methyl Esters

The dimethyl disulfide (DMDS) adduct method is one of the more effective methods for determining double bond positions of dienoic acid. The DMDS method can be simply used to obtain the characteristic ions in which cleavage occurs between the methylthio group‐added double‐bond carbons as can be seen in the mass spectrum obtained using gas chromatography/electron ionization‐mass spectrometry. In the case of the methylene‐interrupted di‐cis type and di‐trans type dienoic acid, the DMDS addition reaction only occurs at one double‐bond position, and cannot occur at the remaining double‐bond position due to steric hindrance. As a result, two types of adducts are produced in the addition reaction. However, in the case of the methylene‐interrupted mono‐trans (mono‐cis) type dienoic acid, the DMDS addition reaction only occurs at the cis‐double bond. As a result, one type of adduct is produced in the addition reaction. In this report, we investigate the cause of the reaction selectivity by focusing on the addition reaction time.     

Predicting the effect of dissolved carbon dioxide on the glass transition temperature of poly(acrylic acid)

The morphology and size of poly(acrylic acid) (PAA) particles produced by precipitation polymerization in supercritical CO₂ (scCO₂) depends on the glass transition temperature (T_g) of the polymer at reaction conditions. In this study, the use of the Sanchez–Lacombe equation of state (SL‐EOS), in conjunction with Chow's equation, to predict the effect of CO₂ pressure on the T_g of PAA was evaluated. Characteristic parameters for PAA were determined by fitting density data. Characteristic parameters for CO₂ were determined by fitting density data in the supercritical region. When the SL‐EOS was used in a purely predictive mode, with a binary interaction parameter (ψ) of 1, the solubility of CO₂ in PAA was underestimated and T_g was overestimated, although the trend of T_g with CO₂ pressure was captured. When was determined by fitting the SL‐EOS to the measured sorption of scCO₂ in PAA, the calculated T_g's agreed very well with measured values. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Bridging the gap between homogeneous and heterogeneous gold catalysis: supported gold nanoparticles as heterogeneous catalysts for the benzannulation reaction

Gold nanoparticles supported on metal oxides and activated carbon are able to catalyze the benzannulation reaction of o-(phenylethynyl)benzaldehyde and phenylacetylene to 1-benzoyl-2-phenylnaphtalene with high selectivity at 99% conversion. Benzannulation of ortho-alkynyl benzaldehydes is a reaction typically catalyzed by soluble AuCl₃ and, now, we have found that it can also be catalyzed by heterogeneous gold supported catalysts. The heterogeneous catalytic system can be reused several times without loss of activity or selectivities.     

Roles of local reactivity on the solid-state addition reaction kinetics

A predominant factor of the diffusion-controlled kinetics of a solid-state addition reaction using powder is the particle size of the reactants, into which the other chemical species are migrating. However, diffusion-controlled kinetic equations are seldom satisfactorily applicable even when the effects of particle size are thoroughly accounted. One of the representative nongeometrical items affecting the solid-state reaction process is the reactivity of solids (ROS), which has not been accounted in any of the established kinetic equations. Change in ROS is the consequence of the imperfections of the crystalline solids. In this study, we try to discuss the effects of ROS on the solid-state reaction kinetics. A typical solid-state addition reaction, formation of BaTiO₃ from the equimolar mixture of TiO₂ and BaCO₃, was chosen as a model. For this reaction, the rate-determining step is established to be the diffusion of Ba²⁺ ions into TiO₂. Since the defect concentration is known to be higher at the near-surface region, the local distribution of ROS that is discussed here is based on a simple core-shell model of the host TiO₂ particles with higher reactivity at the shell part. The ratio of the rate of diffusion within the shell part relative to that of the core (factor n), and the ratio of shell thickness, R_s, relative to the particle radius, R_p, (factor g) were chosen as main parameters to be iterated. By systematically varying these two factors, n and g, we succeeded in minimizing the fluctuation of apparent diffusion rate constant by the particle size. Despite the oversimplified model and lacking experimental evidences of the hypothetical parameters, the present proposal may pave the way to introduce ROS and its local distribution into the reaction kinetics. We also discussed the effects of second phases by comparing the same reaction process observed from the decomposition of the reactant and formation of the products.