Thermal stability of chloroform in the steam-condensate cycle of CANDU-PHW nuclear power plant

Analysis of samples taken at the Gentilly 2 (Québec) CANDU-PHW (CANadian Deuterium Uranium - Pressurized Heavy Water) plant after chlorination and demineralization revealed the presence of all four trihalomethanes (THMs) (CHCl₃, CHBrCl₂, CHBr₂Cl and CHBr₃) and other unidentified halogenated volatile compounds. Among the THMs, chloroform was the major contaminant. A study of its thermal stability in water at different temperatures confirmed the degradation of the CHCl₃ molecule according to the equation CHCl₃ + H₂O → CO + 3 HCl. The reaction follow a first order kinetics and has an activation energy of 100 kJ/mol. The estimated half-life is six seconds at 260°C, the maximum temperature of the steam-condensate cycle.     

Thermal stability of morpholine additive in the steam-water cycle of CANDU-PHW nuclear power plants

The thermal decomposition of morpholine, an additive used in the steam-water cycles of nuclear power plants, was studied using a laboratory high-pressure reactor. The measured decomposition rate constants are 2.67, 8.73 and 21.25 × 10^?7 s^?1 at 260, 280 and 300°C respectively. The kinetics were found to be first-order and the activation energy was 131.9 kJ/mol. Ammonia, ethanolamine, 2-(2-aminoethoxy) ethanol, methylamine, ethylamine, ethylene glycol, and acetic and glycolic acids were identified as the major breakdown products. The decomposition route proposed was validated in the field by tracking these breakdown products in water samples taken at Gentilly 2 power plant.     

Dynamics of catalytic reactions and reactors

Heterogeneous catalytic reactions and catalytic reactors are known to exhibit complex dynamic behavior and significant progress has been made, in the past two decades, in understanding this complexity using the tools of nonlinear dynamics and advanced experimental methods. This article presents an overview of complex dynamic behavior in heterogeneous catalysis and points out their intriguing nature along with practical implications. The issues discussed are the source of oscillatory behavior, classification of complex motions, transitions to chaotic solutions and spatiotemporal patterns in reactors of various geometries.     

Polyacrylate anion exchangers in sorption of heavy metal ions with the biodegradable complexing agent

The removal of Co(II) and Ni(II) from aqueous solutions in the presence of complexing agent on the polyacrylate anion exchangers with different basicity of functional groups Amberlite IRA 458, Amberlite IRA 958 and Amberlite IRA 67 was described. The complexing agent Baypure CX 100 is a new generation of chelators, undergoing biodegradation. It constitutes an alternative for the reagents of EDTA or NTA type. The studies were carried out by the static (batch) and the dynamic (column) methods. The influence of several parameters such as ratio of M(II)–L, pH, temperature were studied with respect to sorption equilibrium. Sorption isotherms were obtained and fitted using the Langmuir and Freundlich models. Kinetic curves were fitted using the pseudo first-order, the pseudo second-order as well as the intraparticle diffusion model equations to evaluate most effective one. Physicochemical properties of anion exchangers such as their structure, basicity of functional groups were also taken into account. Additionally, the obtained results were compared with those for the weakly acidic cation exchanger Purolite C-104.     

Sorption of nickel and cadmium ions from aqueous solutions by a complexing resin based on modified polyamide fiber

The sorption of nickel and cadmium ions by a fibrous complexing resin containing functionally active amines was studied. The principal kinetic and concentration characteristics of the processes and the coordination properties of the resulting complexes were determined.     

Concentration forcing of isothermal plug-flow reactors for autocatalytic reactions

The performance of isothermal plug-flow reactors under feed concentration forcing is analysed for improvement in average yield of product B for a homogeneous autocatalytic reaction, A →k1 A₁ →k2 A_, →k3 B, where A₁ or A₂ has an activity influence on the reaction rate constant k₁. The performance of the periodically forced reactor with the autocatalytic reaction is compared with that of the corresponding uncatalysed reaction.     

Multiple oxidation reactions and diffusion in the catalytic layer of monolith reactors

Oxidation reactions of mobile exhaust gas in a catalytic monolith are considered in this paper. The exhaust gas is described by four concentrations, namely those of the carbon monoxide, fast- and slow-oxidizing hydrocarbons and hydrogen. The problem of multiple reactions and diffusion in the catalytic layer of the monolith walls is studied first. The diffusional resistance of the catalytic layer is often significant in spite of its thinness and it seems important to allow for both the hydrogen and hydrocarbon oxidation reactions in analyzing the system for steady-state. The influence of hydrogen on the multiplicity of steady-state wall temperatures is also studied and it is found to be important, because hydrogen reacts rapidly at lower temperatures.     

Assessment of micro-structured fixed-bed reactors for highly exothermic gas-phase reactions

The application of micro-structured fixed-bed reactors for highly exothermic partial oxidation reactions and their comparison to established multi-tubular fixed-bed reactors was investigated by numerical simulation. As examples, the partial oxidations of butane to maleic anhydride and of o-xylene to phthalic anhydride were chosen. The simulation results revealed that the reactor productivity, i.e. the amount of product per unit of reactor volume, achievable in micro-structured fixed-bed reactors is between 2.5 and 7 times higher than in conventional multi-tubular fixed-bed reactors without the danger of excessive pressure drop. For the partial oxidation of butane to maleic anhydride this can be explained by the increased reactor efficiency caused by lower efficiency losses through heat and mass transfer limitations. In addition, maleic anhydride selectivities and yields are higher in micro-structured fixed-bed reactors. In the case of o-xylene oxidation to phthalic anhydride the main advantage is that egg-shell catalysts in the conventional fixed-bed reactor can be replaced by bulk catalysts in the micro-structured fixed-bed reactor. For this reaction, product selectivities are very similar for all reactor configurations. Thus the catalyst inventory and reactor productivity are strongly increased. This study underlines, that micro-structured fixed-bed reactors exhibit the potential to intensify large scale industrial processes significantly.     

焙烧-水化络合法脱除镁废渣中钙杂质的研究

以含钙镁废渣为原料,采用高温焙烧-EDTA络合法脱除其中的钙杂质制备高纯氧化镁,探究了焙烧温度与时间、EDTA溶液浓度、络合温度、液固质量比与水化时间对钙杂质脱除效果的影响。利用X射线衍射(XRD)、X射线光电子能谱(XPS)等方法对样品结构进行表征。结果表明,镁废渣中钙、镁分别以碳酸钙(CaCO₃)和碱式碳酸镁[4MgCO₃·Mg(OH)₂·4H₂O]形式存在,经过高温焙烧过程分别分解为氧化钙(CaO)和氧化镁(MgO)。热力学计算表明,体系中钙、镁离子与EDTA的络合能力存在较大差异,EDTA与钙离子络合能力强,与镁离子络合能力极弱,络合作用促进CaO溶解,使钙离子进入液相,MgO停留在固相,实现钙、镁分离。在800℃、0.5 h、c(EDTA)=0.01 mol/L、液固质量比为80∶1、常温水化时间为2.0 h时,钙脱除率达到98.78%,产物经105℃烘干8.0 h,MgO纯度大于99.00%。     

Poly(ethyleneimine) as complexing agent for separation of metal ions using membrane filtration

Summary The complexation properties of poly(ethyleneimine) were investigated for cobalt, nickel, zinc, cadmium, and copper using membrane filtration. The elution curves of each metal were determined at different pH values in homogeneous phase. Poly(ethyleneimine) was found to be an effective complexing agent and suitable for retention and separation of metals in aqueous diluted solutions.On leave from the Vernadsky Institute of Geochemistry and Analytical Chemistry, Academy of Sciences, Moscow, USSR     

Markov chain models of complex chemical reactions in continuous flow reactors

A stochastic approach, namely, a Markov chain, has been adopted to simulate the dynamics of complex reactions in a flow chemical reactor without either solving directly differential equations governing the performance of the reactor or obtaining a closed form solution to such equations. All calculations have been carried out iteratively with the aid of a computer. The results are in good agreement with the known results obtained from the deterministic approach. The present technique can be applied to a variety of flow reactors with complex chemical reactions, which cannot be handled easily by deterministic approaches.     

高岭土的还原、络合漂白工艺研究

用还原和络合的方法对高岭土进行漂白，有效降低高岭土中铁的含量，并通过综合分析，采用正交实验设计方法优化选择出最佳的漂白工艺条件，为生产白度达85％的高岭土提供一种最简便有效的方法。     

Effect of channeling on the performance of adiabatic flow tank reactors for exothermic reactions

The performance of CSTR's can be affected significantly by the presence of channeling, for irreversible exothermic first and second order reactions, under adiabatic conditions. Theoretical curves exhibit the variation of the conversion with residence time, for different channeling intensities and various values of the kinetic parameters. A certain degree of channeling can be greatly beneficial to the reactor performance, especially when the activation energy and heat of reaction are high, where multiple steady states can exist. For second order reactions, the ratio of the initial concentrations of A and B, considered as a parameter, plays a role similar to that of the kinetic parameters.     

New system for complexation of uranyl ions from liquid wastes of low‐level activity: Polypyrrole doped with complexing polyanions

Polymer composites consisting of polypyrrole doped by uranyl complexing polyanions [i.e., poly(2‐acrylamidoglycolic acid) and poly(2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid)] were electrochemically synthesized. Bulk material and thin layers strongly adhering to inert supporting electrodes were prepared. These composites were used to precipitate uranyl ions from simulated radioactive wastes. Among different experimental techniques used for the analysis of uranium immobilized in the composites, the Rutherford backscattering of α particles proved efficient in thin layers. Leaching tests confirmed the persistence of the uranium complexation in the solid composites. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1230–1239, 2000     

Formation and reactions of cluster ions from aromatic carboxylic acids together with amino acids

The cluster formation of several aromatic carboxylic acids, ferulic acid, vanillic acid, sinapinic acid, and 3,4-dihydroxybenzoic acid was investigated by means of laser desorption into a supersonic beam followed by multiphoton ionization-time-of-flight mass spectrometry. The formation of not only homogeneous clusters, but also of heterogeneous clusters with some small amino acids was studied. The different neutral clusters formed in the supersonic expansion were ionized by a multiphoton process employing either nano- or femtosecond laser pulses. Strong differences in the detection of cluster ions due to the laser pulse length employed for multiphoton ionization were observed. Only femtosecond activation led to mass spectra with intense signals of the cluster ions. In addition, in the case of femtosecond ionization, protonated amino acids were detected in the mass spectra. As direct ionization of the free amino acids is not possible under the chosen ionization conditions because they lack an adequate chromophore, these protonated amino acids are assumed to be formed via an intracluster proton transfer in the heterogeneous dimer and subsequent decay of the ionized cluster (dissociative proton transfer). Such well-known processes for heterogeneous clusters consisting of a substituted aromatic molecule and small polar solvent molecules may be involved in the matrixassisted laser desorption ionization (MALDI) process.     

N－亚硝基苯胲铵络合去除硫酸铝中铁的研究

利用络合剂N－亚硝基苯胲铵去除含铁硫酸铝溶液中的铁,考察了N－亚硝基苯胲铵用量、溶液酸度、反应时间、反应温度等因素对除铁效果的影响。实验结果表明,络合剂N－亚硝基苯胲铵用乙醇-水复合溶剂（体积比为1∶3）配制、用量（以100 mL含铁硫酸铝溶液计）为1.4 g、酸度（溶液中氢离子浓度）为0.5 mol/L、60 ℃条件下反应1 h,铁的去除率达到97.8 %,硫酸铝中铁质量分数为0.01%,优于HG/T 2225-2010《工业硫酸铝》Ⅱ类一等品质量指标（铁质量分数≤0.30%）。     

Imaging of hydrocarbon reactions in zeolite packed-bed reactors using positron emission profiling

The ability of positron emission profiling (PEP) to measure concentration profiles of molecules labelled with positron-emitting nuclei, such as ¹¹C, ¹³N, and ¹⁵O, inside chemical reactors has been demonstrated for the system n-hexane–Pt/H-zeolites under conditions typical of the hydroisomerization reaction. Data obtained in the absence of reaction were first measured and used to model mass transport processes in these biporous, packed-bed reactors. Images obtained under conditions where injected, labelled pulses underwent reaction revealed that the products did not exit the reactor and thus demonstrated the need for in situ measurement. Such experiments should provide a valuable new tool in the study of transient, initial phenomena so often of importance in heterogeneous catalysis, such as “preconditioning” and deactivation. This revised version was published online in July 2006 with corrections to the Cover Date.     

Optimal operation of simulated-moving-bed reactors for nonlinear adsorption isotherms and equilibrium reactions

An explicit design procedure for simulated-moving-bed reactors (SMBRs) is presented, incorporating a nonlinear, competitive isotherm, and an equilibrium reaction involving three species, e.g., A⇔B+C. This design procedure is based on an equilibrium theory model of a true-moving-bed (TMB) reactor and it is in close analogy to the well-known design procedure for purely separative SMB-units, the so-called ‘triangle theory’ (Journal of Chromatography A, 769, 3 (1997)). It allows an easy determination of the optimal point of operation and can also evaluate the robustness of an operation point. The operating region of full conversion and complete separation for the TMBR is compared to the one of a purely separative TMB unit, to which only the products are fed. The underlying explicit relations for the new design procedure are presented and their reliability is validated by comparison with experimental data of a SMBR for the synthesis of methyl acetate.