Palladium carboxylate/boron trifluoride etherate catalyst system for the selective dimerization of styrene

The selective dimerization of styrene to 1,3-diphenyl-1-butene with Pd(carboxylate)₂ + BF₃OEt₂ catalyst system in both “phosphine-free” and “phosphine-modified” fashions has been investigated. For the Pd(OAc)₂ + 2PR₃ + 7BF₃OEt₂ catalyst system, a TON of 145 000 and 90% selectivity to dimers have been achieved at 80 °C for 5 h. This TON is twice as large as compared to that achieved with the Pd(β-diketonate)₂-based systems. Styrene dimers up to 95% consist of trans-1,3-diphenyl-1-butene. The simplicity of this catalyst system composition might be of industrial importance.     

Numerical study of flow uniformity and pressure characteristics within a microchannel array with triangular manifolds

Flow uniformity among individual channels within a microchannel array can be a significant factor affecting the performance of laminated structured micro-devices. In this study, numerical modeling is used to quantitatively investigate the impact of the geometry of the right triangular manifold and the dimensions of microchannels on desired uniformity and pressure drop. The CFD tool COMSOL is used to perform the simulations within the low-Reynolds number system (5 ≤ Re ≤ 25). In our biomedical application, it is important to have low dead volume and residence time in the manifolds. A methodical approach is introduced to identify a design that balances low manifold volume and maintenance of flow uniformity. It has also been shown that including a short vertical spacing at the corner of manifolds is critical to achieving a high level of flow uniformity. Careful analysis and physical interpretation of trends herein enables a more intuitive approach to array design.     

Modification of electrolyte surface with “windows” and “dimples array” structure for SOFC based on YSZ electrolyte

A strategy based on tape-casting and laser micro-processing was proposed to enhance the electrochemical performance of solid oxide fuel cells by modifying the electrolytes with a “windows” structure and a “dimples array” structure. Scanning electron microscopy images of the “windows” structure indicated that the thickness of electrolyte in the thin areas was reduced from 220 µm to 75 µm, resulting in a significant decrease in ohmic resistance by a factor of 1.69 at 800 °C. In addition, three-dimensional profile images of the “dimples array” structure showed a remarkable increase in the electrode/electrolyte interface area that is directly related to the triple-phase boundaries. Furthermore, following the modifications in this work, the optimal cell in this study achieved an encouraging performance relative to that of the reference cell, with the peak power density increasing by a factor of 1.63 at 800 °C. These results implied that effective structural modification may be a promising approach for improving cell performance.     

ϵ-OA for the solution of bi-objective generalized disjunctive programming problems in the synthesis of nonlinear process networks

There has been an increasing interest in multicriteria optimization (MCO) of nonlinear process network problems in recent years. Several mathematical models have been developed and solved using MCO methodologies including ϵ-constraint, weighted sum, and minimum distance. In this paper, we investigate the bi-objective nonlinear network synthesis problem and propose an effective algorithm, ϵ-OA, based on augmented ϵ-constraint and logic-based outer approximation (OA). We provide theoretical characterization of the proposed algorithm and show that the solutions generated are efficient. We illustrate the effectiveness of our novel algorithm on two benchmark problems. The ϵ-OA is compared to the straightforward use of OA with augmented ϵ-constraint algorithm (ϵ-con + OA), the augmented ϵ-constraint without OA (ϵ-MINLP), and the traditional ϵ-constraint (T-ϵ-con). Based on the results, our novel algorithm is very effective in solving the bi-objective generalized disjunctive programming problems in the synthesis of process networks.     

Prediction of chloride binding isotherms of cementitious materials by analytical model or numerical inverse analysis

In this paper, various methods of prediction of chloride-binding isotherms (CBIs) of cementitious materials at equilibrium and in saturated conditions are proposed. The first group of methods consists in numerical inverse analysis of an experimental total-chloride-concentration profile. In this group, a first method requires as input data the effective-chloride-diffusion coefficient (D_Cl ?), while a second method predicts D_Cl ?. Once D_Cl ? and the CBI are assessed, profiles after other exposure times can be predicted. The second group of methods is an analytical model based on the composition of the material, which includes physical and chemical components. The “numerical” and “analytical” CBIs respectively obtained, as well as D_Cl ? and the profiles predicted, have been compared to experimental data for various mixtures (with and without SCM) and ages. The excellent agreement observed between predicted and experimental results, as well as between “analytical” and “numerical” CBIs, demonstrates the reliability and accuracy of the proposed methods.     

On the rheological behaviour of batch crystallisations

During batch processing the formation of a solid phase is often accompanied by a significant reduction in the mobility of a reaction mass as a “soft” solid is formed. Often the fluid becomes stagnant with a mobile zone or “cavern” around the agitator. This phenomenon was investigated using two in situ probes: (i) a particle size probe which detected the onset of crystallisation and (ii) a viscosity probe which detected the onset and extent of rheological problems. The viscosity probe measurement appears to correlate with the yield-stress of the slurry. A mechanistic analysis of the phenomenon suggests a new dimensionless number: the Nienow number (Ni), the ratio of turbulent stresses to the yield stress of a fluid. Complete mobility is generally achieved for Ni > 30. These systems scale with tip speed if super-saturation is controlled.     

Fabrication and microwave absorption properties of magnetite nanoparticle–carbon nanotube–hollow carbon fiber composites

Absorbents with “tree-like” structures, which were composed of hollow porous carbon fibers (HPCFs) acting as “trunk” structures, carbon nanotubes (CNTs) as “branch” structures and magnetite (Fe₃O₄) nanoparticles playing the role of “fruit” structures were prepared by chemical vapor deposition technique and chemical reaction. Microwave reflection loss, permittivity and permeability of Fe₃O₄–CNTs–HPCFs composites were investigated in the frequency range of 2–18 GHz. It was proven that prepared absorbents possessed the excellent electromagnetic wave absorbing performances. The bandwidth with a reflection loss less than −15 dB covers a wide frequency range from 10.2 to 18 GHz with the thickness of 1.5–3.0 mm, and the minimum reflection loss is −50.9 dB at 14.03 GHz with a 2.5 mm thick sample layer. Microwave absorbing mechanism of the Fe₃O₄–CNTs–HPCFs composites is concluded as dielectric polarization and the synergetic interactions exist between Fe₃O₄ and CNTs–HPCFs.     

Data-driven coordination of subproblems in enterprise-wide optimization under organizational considerations

While decomposition techniques in mathematical programming are usually designed for numerical efficiency, coordination problems within enterprise-wide optimization are often limited by organizational rather than numerical considerations. We propose a “data-driven” coordination framework which manages to recover the same optimum as the equivalent centralized formulation while allowing coordinating agents to retain autonomy, privacy, and flexibility over their own objectives, constraints, and variables. This approach updates the coordinated, or shared, variables based on derivative-free optimization (DFO) using only coordinated variables to agent-level optimal subproblem evaluation “data.” We compare the performance of our framework using different DFO solvers (CUATRO, Py-BOBYQA, DIRECT-L, GPyOpt) against conventional distributed optimization (ADMM) on three case studies: collaborative learning, facility location, and multiobjective blending. We show that in low-dimensional and nonconvex subproblems, the exploration-exploitation trade-offs of DFO solvers can be leveraged to converge faster and to a better solution than in distributed optimization.     

Application of water pinch technology in minimization of water consumption at a refinery

Water is the most significant entity that controls local and global development. The present research involves property integration technique, graphical and mathematical; to first establish accurate targets for maximum direct recycle of process sources, as well as minimum waste discharge and fresh water consumption at an oil refinery. Property-based water allocation network is designed for the process based on previously identified targets. Chemical oxygen demand (COD) and hardness properties are taken as pollutants (contaminants) and treated as single and double contaminant approach to dig out fresh water demand in the process. Both graphical and mathematical programming techniques exhibit the same water reduction of 149.0 m³/h (43.8%) and 208.0 m³/h (61.18%) for COD and hardness case, respectively, in single contaminant approach. While, a new double contaminant mathematical programming has shown a significant reduction of 39%, based on mixing rules of properties. Among the multiple water networks, one possible water allocation network is developed based on mass exchange.     

Design of high productivity sequential multi-column chromatography for antibody capture

An integrated experimental and modeling approach for the design of sequential multi-column chromatography (SMCC) is presented to maximize productivity in bioprocessing. The approach consists of three steps: (1) single-column model development and validation, (2) multi-column model development and validation, and (3) productivity optimization. The integrated use of process experimentation and modeling enables sufficient process understanding to be gained during process development such that the optimal SMCC design is found even with limited time and materials. The application of the approach is demonstrated by determining the optimal SMCC design that maximizes the capture of human IgG by a silica-based protein A adsorbent named AbSolute. For this example, the optimum productivity was found to increase from 2.9 kg L⁻¹ day⁻¹ for batch operation to 4.0 kg L⁻¹ day⁻¹ for SMCC operation with three columns. A second case study considering a hypothetical adsorbent of larger particle size and slower mass transfer is also presented, to further demonstrate the applicability of the integrated approach. The case studies clearly illustrate the capabilities of the integrated approach in quickly determining the optimal design and operation for an SMCC arrangement and with minimal, carefully targeted, experimentation.     

Design and synthesis of a novel pH sensitive core and peripherally 1,8-naphthalimide-labeled PAMAM dendron as light harvesting antenna

The system surface was labeled with blue emitting 1,8-naphthalimide “donor” dyes capable of absorbing light and efficiently transferring the energy to a single yellow-green emitting 1,8-naphthalimide “acceptor” dye. The overlap between the blue emission of the donor and the absorbance of the acceptor (focal dye) was >70%. Due to the energy transfer from the periphery to the focal 1,8-naphthalimide chromophore (67%) the core fluorescence (λ_ex = 360 nm) was enhanced >36 times. It was also found that the novel light harvesting system displayed sensitive fluorescence signaling over a wide pH scale, which was ascribed to photoinduced electron transfer from the dendron bone to the blue emitting periphery. In acidic media the electron transfer was “switched off” and, in turn, the periphery emission was “switched on”, resulting in energy transfer enhancement to the focal chromophore up to 92%. This indicates the high potential of the novel light harvesting system as an efficient pH hemosensing material.     

Effects of additive LiF on the synthesis of cBN in the system of Li3N–hBN at HPHT

High-quality cBN single crystals were successfully synthesized in the system of Li₃N–hBN with additive LiF at high pressure and high temperature (HPHT). The lowest synthetic conditions of cBN decreased to 4.6 GPa, 1320 °C by employing 3 wt.% LiF, and it didn't change anymore though more than 3 wt.% LiF had been added. The quality of cBN crystals improved markedly. The cBN crystals and other products were examined by X-Ray diffraction and scanning electron microscopy. The X-Ray analysis reveals that the “graphitization index” (GI) of hBN increased by adding 3 wt.% LiF into the system of Li₃N–hBN at HPHT. The SEM photographs show that different growth steps were formed on the cBN crystal surface in systems of Li₃N–hBN and Li₃N–LiF–hBN, respectively.     

Mechanical strength and damage tolerance of highly porous alumina ceramics produced from sintered particle stabilized foams

Highly porous alumina particle stabilized foams were prepared by combining the concepts of particle stabilized foams and gelcasting, using sulfonate surfactants and poly vinyl alcohol (PVA) as the gelcasting polymer. The ceramic samples sintered at 1500 °C for 2 h had porosities from 65% to 93%, with pore sizes in two categories: “big pore” around 300 μm and “small pore”, around 100–150 μm, depending on the type and amount of surfactant added. The mechanical behaviour of the foams (axial and diametral compression) depended on the overall porosity and pore size. On average, tensile and compressive strengths around 5 and 16 MPa respectively were measured for samples with bigger pore sizes and larger porosities. Samples with smaller pore sizes and lower porosities produced average values of 12 and 57 MPa for tensile and compressive strengths, respectively. The elastic modulus reached a maximum around 3GPa for “small pore” size samples. The effect of increasing amount of PVA in the samples had a strong effect on the green mechanical strength, but it did not significantly affect the mechanical response of the sintered alumina foams. Large and complex shape sintered components produced using this route showed a remarkable damage tolerance, due to crack tip blunting.     

Supercritical fluid extraction from Syzygium aromaticum buds: Phase equilibrium,mathematical modeling and antimicrobial activity

Clove essential oil is an important product to food industry because it presents a powerful antioxidant and antimicrobial potential enabling its use for the substitution of synthetic commercial products for food preservation. The objective of this paper is to study the extraction kinetics for predicting operational condition to obtain Syzygium aromaticum essential oil using CO₂ as solvent by means of the introduction of thermodynamic approach into the mathematical modeling of the process. Extractions were performed at 9000 kPa/313.15 K, 10,000 kPa/313.15 K, 9000 kPa/323.15 K, and 10,000 kPa/323.15 K and the essential oil yields obtained were 14.17%, 12.32%, 13.11%, and 14.02%, respectively. To calculate the extract solubility in CO₂ supercritical, the Peng–Robinson EoS coupled with three mixing rules (van der Waals 1, van der Waals 2 and Mathias–Klotz–Prausnitz) was used and a mass transfer model was employed to represent the relationship yield versus extraction time. The mathematical modeling of the process using the calculated solubility presented high concordance with experimental data. The volatile extracts were analyzed by GC/MS and the major compounds were eugenol and β-caryophyllene. Also, minimum inhibitory concentration (MIC) of supercritical extracts was determined with respect to Escherichia coli, Staphylococcus aureus and Enterococcus faecalis by microdilution method. All samples inhibited the bacterial growth, being the extract obtained at 313.15 K/9000 kPa the most effective.     

Hyperbranched triazine-containing polyfluorenes: Efficient blue emitters for polymer light-emitting diodes (PLEDs)

A series of hyperbranched triazine-containing polyfluorenes were synthesized by an “A₂ + A′₂ + B₃” approach based on Suzuki polycodensation. The polymers showed pure blue emission and the maximum emissions red-shifted in polar solvents and in solid film. By introducing triazine into polyfluorene, the electron injection and transport properties were improved and green emission was suppressed. PLED devices fabricated with the polymers showed reasonably high external quantum efficiencies.     

Redox features in the catalytic mechanism of the “standard” and “fast” NH3-SCR of NOx over a V-based catalyst investigated by dynamic methods

The redox mechanism governing the selective catalytic reduction (SCR) of NO/NO₂ by ammonia at low temperature was investigated by transient reactive experiments over a commercial V₂O₅/WO₃/TiO₂ catalyst for diesel exhaust aftertreatment. NO + NH₃ temperature-programmed reaction runs over reduced catalyst samples pretreated with various oxidizing species showed that both NO₂ and HNO₃ were able to reoxidize the V catalyst at much lower temperature than gaseous O₂: furthermore, they significantly enhanced the NO + NH₃ reactivity below 250 °C via the buildup of adsorbed nitrates, which act as a surface pool of oxidizing agents but are decomposed above that temperature. Both such features, which were not observed in comparative experiments over a V-free WO₃/TiO₂ catalyst, point out a key catalytic role of the vanadium redox properties and can explain the greater deNO_x efficiency of the “fast” SCR (NO + NH₃ + NO₂) compared with the “standard” SCR (NO + NH₃ + O₂) reaction. A unifying redox approach is proposed to interpret the overall NO/NO₂–NH₃ SCR chemistry over V-based catalysts, in which vanadium sites are reduced by the reaction between NO and NH₃ and are reoxidized either by oxygen (standard SCR) or by nitrates (fast SCR), with the latter formed via NO₂ disproportion over other nonreducible oxide catalyst components.     

Fabrication of self-binding noble metal/flexible graphene composite paper

Self-binding noble metal (Pt, Au, and Ag)/graphene composite papers as large as 13 cm in diameter were fabricated using a flow-directed method where in situ reduced graphene served as a “binder”. The papers were characterized by X-ray diffraction, scanning and transmission electron microscopy, Raman spectroscopy and X-ray photoelectron spectroscopy. This approach yielded well dispersed metals with various nanostructures both on and between the graphene layers to form papers with good conductivity and flexiblility. The 300 °C-annealed Ag/graphene papers were evaluated as binder-free anodes for lithium ion batteries, delivering a reversible charge capacity of 689 mAh/g at a current density of 20 mA/g.     

Chemical composition and microstructure of Al3BC3 prepared by different densification methods

“Al₈B₄C₇” and Al₃BC₃ powders were synthesized, and the formation of secondary phases was suppressed during the densification of the ternary aluminum borocarbides. The so-called “Al₈B₄C₇” was Al₃BC₃ containing excess Al and B. The excess components in “Al₈B₄C₇” promoted the densification of Al₃BC₃. The formation of secondary phases could not be controlled when using the reactive hot pressing method during the densification of Al₃BC₃. In contrast, monolithic Al₃BC₃ was obtained by separating calcination and hot pressing stage. The hardness, Young's modulus and fracture toughness of the sintered Al₃BC₃ were 13.9 GPa, 136 GPa and 2.2 MPa m^1/2, respectively.     

Mechanically activated alite: New insights into alite hydration

For superior understanding of alite hydration an investigation of mechanically activated alite (M3 modification) was performed by XRD and heat flow calorimetry. Activation resulted in reduced particle size, a decreased mean crystallite size and partial amorphization. For the samples of activated alite a significantly accelerated and intensified hydration was observed and complete conversion of alite was found after 24 h. The enthalpy of reaction for crystalline alite was determined to be − 548 J/g from measured heat of hydration after 24 h. The enthalpy of reaction of amorphous “alite” was found to be less exothermic (− 386 J/g). The main hydration period is controlled by nucleation of C–S–H, while the transition from acceleration to deceleration period takes place after consumption of the small alite particles. XRD amorphous C–S–H phase is indicated to precipitate in considerable amount even in the highest activated alite before “long-range ordered”, XRD detectable C–S–H was observed.     

Pure vs ultra-pure γ-alumina: A spectroscopic study and catalysis of ethanol conversion

Spectroscopic and catalytic properties of “pure” and “ultrapure” γ-Al₂O₃ samples, both from Sasol, are compared. The “pure” sample has additional absorption in the UV region, much stronger luminescence in the Raman scattering experiments, slightly different skeletal surface OH groups IR spectra, and more evident features of weakly adsorbed pyridine. These effects are attributed to small amounts of Fe^3 +, Ti^4 +, surface silanol groups and Na⁺ ions. The “ultrapure” sample is more selective for the production of ethylene from ethanol at total conversion, while in the presence of oxygen is less active in oxidizing ethanol to other oxygenates and to CO_x.