An analysis of chemical reactor stability and control—VI : Two-phase chemical reacting systems with heat and mass transfer resistances

Pertinent to the design of any chemical reactor is a knowledge of its transient characteristics, in particular the stability of a steady state both to small and large disturbances. The dynamic behaviour of the well agitated continuous reactor both with and without control devices has been extensively studied for homogeneous reacting media. It is the purpose of this work to consider the natural behaviour of reacting systems involving two fluid phases in the well agitated continuous reactor operating under constant conditions.To this end models of the physical rate processes of interfacial heat and mass transfer are constructed for perfectly mixed systems and analysed for multiplicity and stability of steady state solutions. Some methods of non-linear mechanics are applied, and phase plots resulting from digital computer solutions of the non-linear transient equations are constructed for some chosen numerical examples. The study includes systems in which phases are in physical equilibrium, in which there are resistances to interfacial heat and mass transfer and in which components of a phase are in chemical equilibrium, the reaction rate being controlled by the transfer of mass.It is found that the number of possible steady state solutions to the non-isothermal equations depends on the rates of exchange of heat and material between the phases.Phase plots are shown for systems which have no stable state, but exhibit continued oscillations in temperature and concentration. Other examples are shown of systems which possess more than one steady state. In some cases a majority of these states are unstable.In this paper, which is continuation of Va and Vb, the cases in which there are resistances to heat and mass transfer are investigated.     

Modeling of chemical reactors — XVI Steady state axial heat and mass transfer in tubular reactors An analysis of the uniqueness of solutions

Numerical methods for the solution of steady state equations are reviewed and critically discussed. A new technique is presented which, for the parameter study of a problem, enables one to transform the boundary value problem to the initial value problem. Different criteria for testing of uniqueness and multiplicity respectively are discussed. The necessary and sufficient conditions of multiplicity and also analytical procedures providing an estimate of bounds of the Damköhler numbers where multiple solutions can occur, are presented. The mentioned criteria are presented for both an adiabatic and nonisothermal-nonadiabatic case.     

An analysis of farmers?? use of phosphorus fertiliser in industrial agriculture: a case study in the Bordeaux region (south-western France)

Global phosphorus (P) reserves are rapidly being depleted and agriculture is a major contributor to P consumption worldwide. Moreover, agricultural P use may lead to local excess of P in soils, resulting in water eutrophication. To remedy this situation, it is necessary to understand the key factors underlying P use by farmers within such a context. The objective of this article is to understand how farmers use P fertilisers under agricultural conditions. Particular attention was paid to the use of conventional decision-making tools such as soil analysis by farmers. Industrial agriculture, characterised by high levels of specialisation, input use and production yields, was considered as a case study. Forty farmers involved in industrial agriculture in south-western France were interviewed in 2008 about their P use. Soil analyses were collected when available. Input/output P balances were computed at the plot scale. Moreover, records of farmers?? fertilisation practices were analysed from a database developed by a technical advisory group. Results showed that 90% of farmers had a crop-specific and yearly P fertilisation strategy. This yielded very positive P balances for vegetable crops. Few farmers used recommendations based on soil analyses: in most cases, the amounts of P used by the farmers were lower than those recommended. When asked for their opinion about the role of P in agriculture, most farmers explained that P fertilisation helped boost the growth of spring crops in the event of adverse weather conditions. This revealed the emphasis placed on ??plant-based?? strategies for P management, as opposed to ??soil-based?? strategies, thus reinforcing annual fertilisation strategy. This study provides a foundation for understanding key factors underlying P consumption in agriculture.     

A combined canonical variate analysis and Fisher discriminant analysis (CVA–FDA) approach for fault diagnosis

This paper proposes a combined canonical variate analysis (CVA) and Fisher discriminant analysis (FDA) scheme (denoted as CVA–FDA) for fault diagnosis, which employs CVA for pretreating the data and subsequently utilizes FDA for fault classification. In addition to the improved handling of serial correlations in the data, the utilization of CVA in the first step provides similar or reduced dimensionality of the pretreated datasets compared with the original datasets, as well as decreased degree of overlap. The effectiveness of the proposed approach is demonstrated on the Tennessee Eastman process. The simulation results demonstrate that (i) CVA–FDA provides better and more consistent fault diagnosis than FDA, especially for data rich in dynamic behavior; and (ii) CVA–FDA outperforms dynamic FDA in both discriminatory power and computational time.     

Oxidative degradation of poly (vinyl acetate) and poly (ε-caprolactone) and their mixtures in solution

The oxidative degradation of the poly (ε-caprolactone) (PCL), poly (vinyl acetate) (PVAC) and their mixtures in dichlorobenzene has been investigated at various temperatures (70-130°C) in the presence of benzoyl peroxide. The interaction between the polymers is quantified by monitoring the molecular weights of individual polymers using gel-permeation chromatography. The various physical mixtures employed in the present investigation are , and wt%/wt% PCL/PVAC. Experimental data indicated that the degradation is random without cross-linking and repolymerization. An optimum in degradation temperature (corresponding to maximum degradation rate) of 105°C was observed for the entire range of polymer compositions (0-100% PCL) investigated. This optimum temperature of degradation is characteristic mostly of the initiator and only to a small extent of the degrading polymer system. The experimental results of the mixtures indicated that the degradation rates of PVAC are significantly enhanced, while the degradation rates of PCL are decreased in the physical mixture. This can be attributed to the proton-accepting and proton-donating nature of PCL and PVAC, respectively. A radical mechanism for the oxidative degradation of pure polymers and their mixtures has been proposed and a model based on continuous distribution kinetics was developed considering the interaction of the polymers through hydrogen abstraction and the parameters were evaluated numerically. The activation energies for the peroxide attack for the PCL and PVAC are 10.5 and , respectively. The activation energies for the random chain scission of PCL and PVAC are 10.6 and , respectively.     

Dynamic quenching of 5-(2′-ethyl-hexyloxy)-p-phenylene vinylene (MEH-PPV) by charge transfer to a C60 derivative in solution

The fluorescence of 5-(2′-ethyl-hexyloxy)-p-phenylene vinylene (MEH-PPV) quenched in solution in 1,2-dichlorobenzene by a soluble derivative of C₆₀ [1-(3-methoxycarbonyl)propyl-1-phenyl[6,6]C₆₁; [6,6]PCBM] is studied by changing the concentration of the quencher and by varying the temperature. For MEH-PPV and PCBM dissolved in 1,2-dichlorobenzene, the Stern–Volmer constant (K_SV) is 2 × 10³M⁻¹. At high temperature, K_SV is enhanced because thermal energy facilitates the diffusion of PCBM. The results show that dynamic quenching (rather than static quenching) is the basic mechanism. Comparison with data obtained from quenching studies of trans-stilbene indicates that a single acceptor in contact with an MEH-PPV macromolecule quenches the luminescence from hundreds of repeat units. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2553–2557, 2001     

Electrode reactions of tris(2,2′-bipyridine)-iron(II) and tris(2,2′-bipyridine)iron(III) complexes in acetonitrile solution

The electrode processes of tris(2,2′-bipyridine)iron(II) and tris(2,2′-bipyridine)iron(III) complexes at the rotated platinum electrode and the dropping mercury electrode (dme) in acetonitrile solutions have been investigated by the measurement of current/potential curves, dc and ac polarograms and Kalousek polarograms. The system of the iron(II) and the iron(III) complex was reversible at the rotated platinum electrode. The iron(II) complex gave a five-step reduction wave at the dme when tetraethylammonium perchlorate was used as supporting electrolyte. The limiting currents of the first three steps named from positive to negative potentials were all diffusion-controlled and of a one-electron reduction processes. From the effect of free 2,2′-bipyridine and water on the reduction wave of the iron(II) complex and from the shape of Kalousek polarograms, the electrode processes for the first three steps are concluded to be the reductions from [Fe(bipy)₃]²⁺, [Fe(bipy)₃]⁺ and [Fe(bipy) ₃], respectively. It has been proposed that at the third step univalent tris(2,2′-bipyridine)-ferrate anions, [Fe(bipy)₃]⁻, are formed at the electrode surface in acetonitrile.     

ω-Iodinated poly(dimethylsiloxane) as a chain transfer agent in iodine transfer radical polymerization of vinyl acetate and dibutyl maleate: synthesis and structural characterization

Iodine transfer radical homo- (ITP) and copolymerization (ITCP) of vinyl acetate (VAc) with dibutyl maleate (DBM) initiated by 2,2?-azobis(isobutyronitrile) (AIBN) were performed in bulk at 80 °C in the presence of ω-iodo- terminated poly(dimethylsiloxane) (PDMS-I) as a macro-chain transfer agent (macro-CTA). ¹H-NMR and gel permeation chromatography (GPC) results confirmed formation of the PDMS-b-PVAc diblock copolymer. Moreover, the results of ¹H-NMR showed that the iodo-terminated chain ends are unstable and decompose to the aldehyde moieties. On the other hand, different behaviour was observed in the ITCP of the VAc and DBM. ¹H-NMR and GPC results showed that presence of DBM in the reaction medium leads to degradation of the C-I bond of the PDMS-I, resulting in the generation of HI. In fact, PDMS-I acts as in situ generator of the CTA in the presence of DBM via reaction between the generated HI and VAc. In other words, it was found that P(VAc-co-DBM) copolymer chains are synthesised by ITP mechanism in the presence of in situ generated 1-iodoethyl acetate as a CTA. Therefore, a mixture of PDMS and P(VAc-co-DBM) chains was obtained.     

Heat and mass transfer coefficients of liquid desiccant dehumidification/regeneration processes with non-thermal equilibrium(Ⅰ) Model and Le-hD evaluation method

溶液除湿装置是溶液除湿空调系统中一个重要单元,其内部传热传质规律对系统性能起到决定性影响。在溶液绝热除湿模型基础上,提出考虑热不平衡的除湿模型用以计算溶液除湿过程的传热传质系数。模拟计算发现考虑热不平衡模型计算的溶液和空气出口参数与实验值能更好吻合,从而说明该模型能更准确计算除湿过程传热传质系数。当热容率比C^*≥1.0时,考虑热不平衡除湿模型计算的传质单元数和Lewis数要远优于绝热模型计算结果;而当C^*≤0.05时,考虑热不平衡除湿模型和绝热模型计算结果相差较小。     

A novel green inhibitor for C-steel corrosion in 2.0 mol·L~(-1) hydrochloric acid solution

The corrosion inhibition characteristics of aqueous extract of seeds of Melia azedarach L.(MA) have been studied as eco-friendly green inhibitor for corrosion control of C-steel in 2 mol·L~(-1) HCl solution by gravimetric and electrochemical methods. The results depict that, the extract inhibits efficiently the corrosion of carbon steel in hydrochloric acid. The efficiency of extract is increased with increasing the extract concentration but independent on the studied temperature. The adsorption of the extract components onto the steel surface was found to be spontaneous, and follows Langmuir adsorption isotherm. The surface morphology of C-steel, in the absence and presence of MA extract in 2.0 mol·L~(-1) hydrochloric acid solution, was studied using scanning electron microscopy(SEM).     

Highly efficient near-infrared (NIR) luminescent tris-β-diketonate Yb3 + complex in solution and in PMMA

In the series of binary tris-β-diketonate complexes [Ln(L)₃(Phen)] (HL = (Z)-3-methyl-1-phenyl-4-(2,2,2-trifluoro-1-hydroxyethylidene)-1H-pyrazol-5(4H)-one; Phen = 1,10-phenanthroline; Ln = La, 1; Ln = Nd, 2; Ln = Yb, 3; Ln = Er, 4 or Ln = Gd, 5), the relatively lower ligands-based ³ππ^⁎ energy level (18,727 cm^− 1) results in the highly efficient NIR luminescence (Ф_Yb^Yb = 1.37% and Ф_Yb^L = 1.06%) of Yb^3 +-based 3 in solution and the higher NIR quantum yield (Ф_Yb^Yb = 1.77% and Ф_Yb^L = 1.31%) in PMMA (Poly(methyl methacrylate) besides the improved physical properties.     

Electro-catalytic characterization and dye degradation of Ti1−x(Bi)xO2 in acidic solution

The authors in this study used the sol–gel process to prepare Bi-doped TiO₂ as a novel electrocatalyst. Results show that Bi can be doped successfully into TiO₂ from 1% to 90%. The electrical conductivity of a 1% Bi-doped TiO₂ particle-suspended solution is increased nearly twice that of pure TiO₂. The electro-catalyzing property of the synthesized Bi-doped TiO₂ catalyst was performed under acidic conditions toward a methyl blue dye solution. The observed removal percentage of methyl blue dye was from 5% to 75%. The optimized electro-catalyzing condition was observed at 5% Bi-doped TiO₂ with a working voltage of 5 V.     

Experimental electrohydrodynamics of poly(γ-Benzyl-L-Glutamate) in M-Cresol solution subjected to shear flow and electric fields

Electrohydrodynamics of a dilute solution of rigid macromolecules was experimentally studied in a continuation of previous theoretical work. We used poly(γ-benzyl-L-glutamate), having 4 different molecular weights ranging from 15,000 to 236,000, dissolved in m-cresol. Poly(γ-benzyl-L-glutamate) solutions were subjected to combinations of simple shear flow field and uniform electric field perpendicular to the shear direction. Transient birefringence and extinction angle were simultaneously measured using the phase-modulated birefringence method. Steady state results were compared with the theoretical prediction from previous works and rotational difiusivity and permanent dipole strength of PBLG were obtained from multiple parameter fitting. Consequently, the optical state of PBLG solution could be explained to a certain extent by the dimensionless field parameters established in the previous theory.     

Tetraethylenepentamine-functionalized magnetic mesoporous composites as a novel adsorbent for the removal Cr(Ⅲ)-ethylenediaminetetraacetic acid in complex solution

A novel tetraethylenepentamine（TEPA） functionalized magnetic mesoporous silica adsorbent（FNMs/TEPA） was prepared for the adsorption of Cr（Ⅲ）-ethylenediaminetetraacetic acid（EDTA）from wastewater. The characterization of the prepared adsorbent certified that TEPA was modified onto the magnetic mesoporous silicon（FNMs）, while FNMs/TEPA maintained the ordered mesoporous and pristine magnetic properties. The batch adsorption experiments demonstrated that TEPA significantly enhanced the removal capacity of the adsorbent for Cr（Ⅲ）-EDTA. FNMs/TEPA exhibited an excellent adsorption property(13.84 mg·g^-1) at p H 4.0. Even in the presence of high concentrations of coexisting ions and organic acids, the adsorption performance of FNMs/TEPA was stable. Experimental characterization and DFT demonstrated that the adsorption of Cr（Ⅲ）-EDTA was ascribed to the electrostatic interaction, hydrogen bonding, and complexation between Cr（Ⅲ）-EDTA and amino groups on the adsorbent surface. The analysis of the independent gradient model（IGM） shows that electrostatic interaction is the main mode of action in the adsorption process. Moreover, FNMs/TEPA demonstrated remarkable reusability in three regeneration cycles. These findings indicated that FNMs/TEPA possessed excellent application prospects in the disposal of wastewater containing Cr（Ⅲ）-EDTA.     

An ecofriendly approach for corrosion control of 6061 Al-15％(v) SiC(p) composite and its base alloy

Corrosion inhibition characteristics of bio polymer dextran was studied for the corrosion control of 6061 Al-15%_((v)) SiC_((P)) composite and its base alloy in 1 mol·L~(-1) HCl. Standard electrochemical techniques such as potentiodynamic polarization(PDP) measurements and electrochemical impedance spectroscopy(EIS) method were adopted for corrosion rate measurement. Surface morphology was studied by scanning electron microscopy(SEM) and elemental mapping was done by energy dispersive X-ray(EDX) analysis. Suitable mechanism was proposed for corrosion and inhibition process. Results indicated that dextran acts as an excellent anticorrosive agent for the corrosion control of 6061 Al-15%_((v)) SiC_((P)) composite, with maximum inhibition efficiency of 91% for the concentration of 0.4 g·L~(-1) at 303 K. Dextran acted as a mixed type of inhibitor, and got physically adsorbed both on composite and base alloy by obeying Langmuir adsorption isotherm. Dextran is proved to be a green inhibitor with environmental and economic benefits.     

GC–MS analysis of oxysterols and their formation in cultivated liver cells (HepG2)

Oxysterols play a key role in many (patho)physiological processes and they are potential biomarkers for oxidative stress in several diseases. Here we developed a rapid gas chromatographic-mass spectrometry-based method for the separation and quantification of 11 biologically relevant oxysterols bearing hydroxy, epoxy, and dihydroxy groups. Efficient chromatographic separation (resolution ≥ 1.9) was achieved using a medium polarity 35%-diphenyl/65%-dimethyl polysiloxane stationary phase material (30 m × 0.25 mm inner diameter and 0.25 μm film thickness). Based on thorough analysis of the fragmentation during electron ionization we developed a strategy to deduce structural information of the oxysterols. Optimized sample preparation includes (i) extraction with a mixture of n-hexane/iso-propanol, (ii) removal of cholesterol by solid phase extraction with unmodified silica, and (iii) trimethylsilylation. The method was successfully applied on the analysis of brain samples, showing consistent results with previous studies and a good intra- and interday precision of ≤20%. Finally, we used the method for the investigation of oxysterol formation during oxidative stress in HepG2 cells. Incubation with tert-butyl hydroperoxide led to a massive increase in free radical formed oxysterols (7-keto-chol > 7β-OH-chol >> 7α-OH-chol), while 24 h incubation with the glutathione peroxidase 4 inhibitor RSL3 showed no increase in oxidative stress based on the oxysterol pattern. Overall, the new method described here enables the robust analysis of a biologically meaningful pattern of oxysterols with high sensitivity and precision allowing us to gain new insights in the biological formation and role of oxysterols.