Dynamical regimes of a pH-oscillator operated in two mass-coupled flow-through reactors

We present results of experiments focused on emergent and cooperative dynamics in a system of two coupled flow-through stirred reaction cells with diffusion-like mass exchange and a strongly nonlinear chemical reaction between hydrogen peroxide and thiosulphate catalysed by cupric ions in diluted solution of sulphuric acid. Due to complex mechanism, in which a crucial role is played by hydrogen and/or hydroxide ions, dynamics in a single cell entail multiple stationary states, excitability and oscillations conveniently indicated by measuring pH. When coupled, the system shows a plethora of dynamical regimes depending on the coupling strength and flow rate. Under certain conditions both cells display dynamics close to that in the absence of coupling, but majority of the regimes are emergent and cannot be deduced from dynamics of decoupled reactors. The most prominent is a stationary state maintaining highly acidic values of pH in one of the reactors and weakly acidic in the other. When each cell is set to display excitability and the coupled system is externally perturbed, the cells may cooperate and transmit excitations elicited by pulsed perturbations in one cell to the other. Periodic pulses induce firing patterns marked by a various degree of propagated excitations and by being periodic or irregular.     

Biodegradation of chlorinated aliphatics and aromatic compounds in total-recycle expanded-bed biofilm reactors

Applied Biochemistry and Biotechnology - Ground-water contamination by chlorinated aliphatic compounds is a major cause for concern because of their toxicity. This study examined the biodegradation...     

Activity reduction of radioactive mixed wastes for subsequent carboxylate determinations

Instrumental neutron activation analysis (INAA) based on a nuclear reactor and proton induced X-ray emission (PIXE) based on a 2 Me V Van de Graaff accelerator were used to analyse different environmental samples including coal, sawdust, fly ash and landfill materials. These samples represent a large component of the solid waste being buried in the ground, and may be a potential source of toxicity which can have not only adverse effects on the soil and ground water, if diffused during leaching processes, but may also be transferred to humans through the food chain. Both techniques were employed to determine trace element concentrations in these matrices. The concentration of 30 elements were detemined, namely Na, Mg. Cl, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Br, Rb, Cd, Ba, La, Sm, Eu, Tb, Ho, Yb, Hf, Ta and Th. The detection limits in the various sample matrices were calculated and a comparison was made for those elements commonly detected by both techniques.     

Determination of monobutyl phosphate and dibutyl phosphate in mixed hazardous wastes by ion-pair chromatography

Ion-pair chromatography was tested for its applicability in determining monobutyl phosphate (MBP) and dibutyl phosphate (DBP), which are degradation products of tributyl phosphate, in Hanford tank wastes. In tests with simulant waste mixtures, tetrahexylammonium bromide, an ion-pairing agent, was used to complex with all three phosphate species. Recovery studies indicated that ion-pairing chromatography is quantitative for determining the analytes in spiked samples. Initial results demonstrated that DBP could be detected easily and was fairly well separated from other peaks, but MBP was frequently lost due to large negative peaks. Then a preconcentration column procedure was used to clean up the waste-sample matrix, and the negative peaks disappeared. Results indicated that 80% of MBP and 90% of DBP could be recovered. Most of the radioactivity was removed from actual waste tank samples so that additional sample preparation could be performed safely in a fume hood rather than a hot cell. Dibutyl phosphate was identified in an actual tank waste, but MBP was not found; this result was confimed by ion chromatography with conductivity detection.     

Multi-scan cyclic voltammetry of a solution containing mixed valence states

Journal of Solid State Electrochemistry - When both members of a redox pair are present in a voltammetric cell, the applied signal must start at the null potential if pure cyclic voltammetry is to...     

The chemical composition of mixed wastes: Analysis of the photolysis products of organic ligands

A survey of the literature regarding the composition of mixed wastes originating from the clean ups of spills of radioactive solutions shows that (1) the mixtures obtained in studies of the X-ray and -ray radiolysis, and of the UV-photolysis of organics in aqueous solutions have very similar composition provided the photolysis is carried out with UV beams with wavelengths below 242 nm; (2) the composition of the organic fraction of mixed wastes containing initially EDTA, NTA, and/or citric acid is complex. The mass recoveries are between 20 and 60%; and (3) the UV-photolysis of complexing agents gives much more complex mixtures at high pH than at low pH, because carbonyl compounds are formed, and these compounds undergo complex series of reactions in strongly alkaline solutions. The mixed wastes considered have a high pH due to the necessity of complexing strongly the heavy metals involved in spills. These results are confirmed by an investigation of the properties of the products of the UV-irradiation of EDTA, citric acid and some of their binary mixtures. The products of the esterification by BF₃/BuOH are only partly soluble in methylene chloride. Much better yields are obtained by using BF₃/BuOH as the reagent.¹³C NMR illustrates the composition of the mixture, without requiring a separation and is useful to follow the fate of compounds during their methylene chloride extraction after esterification.     

Distribution of 14C and 3H in low level radioactive wastes generated by wet waste streams from pressurized water reactors

Summary It is impossible to detect ¹⁴C and ³H by direct methods such as γ-spectroscopy because they are pure b-emitters and thus they are classified as hard to measure nuclides (HTM). In this paper the analysis results of ¹⁴C and ³H in the low level radioactive wastes (LLWs), including spent ion exchange resin, evaporated bottom and sludge are presented. The LLWs were generated by three nuclear power plants (NPPs), in Korea all with pressurized water type reactors (PWRs). A simultaneous separation procedure for ¹⁴C and ³H in LLWs was established by wet oxidation-acid stripping. A liquid scintillation analyzer was used for the measurement of ¹⁴C and ³H. It was found that the recovery of ¹⁴C and ³H was 82-99 and 78-103%, respectively, by wet oxidation-acid stripping with diluted standard solutions. At the lowest injection of ¹⁴C and ³H, i.e., at 1.44 Bq for ¹⁴C and 1.22 Bq for ³H, the minimum detectable activity (MDA) of ¹⁴C and ³H was calculated as 0.88 and 0.78 Bq/g, respectively, for the minimum allowable sample weight, using wet oxidation and 16 wt% H₂SO₄ acid. By the wet oxidation-16 wt% H₂SO₄ stripping method no interfering nuclides were detected in the trapping solution of ¹⁴CO₂ and the distillate of ³H. The activity concentration range of ¹⁴C in the analyzed samples, i.e., spent ion exchange resin, evaporated bottom and sludge, was 0.17-110,000, 8.4-1380 and 0.1-10,006 Bq/g, respectively, and that of ³H in the same was from no detectable to 769, 134-14,383 and 0.7-4820 Bq/g, respectively.     

Qualitative determination of low-molecular-weight organic acids in mixed hazardous wastes using thermospray liquid chromatography/mass spectrometry

A technique has been developed for the qualitative determination of low-molecular-weight organic acids in radioactive, mixed hazardous wastes using thermospray liquid chromatography/mass spectrometry. A tank waste was analyzed, and the results indicated the presence of citric, glycolic, acetic, and nitrosoiminodiacetic acid (NIDA). Further investigation revealed NIDA was formed under acidic conditions with the reaction of iminodiacetic acid and the high nitrate/nitrite concentration present in the waste.     

Separation of63Ni traces from low and medium level radioactive wastes produced during the operation of nuclear power reactors

The classification of low and medium level radioactive wastes produced regularly by nuclear power plants is becoming ever more important in Mexico, after a few years of running the first of two units, 600 MeV each, in Laguna Verde nuclear power plant. This paper describes a method to separate and detect traces of the weak -emitter⁶³Ni, which is one of the activation products used to classify low and medium level radioactive wastes originating from the operation of nuclear power plants.     

Chemistry in microstructured reactors

The application of microstructured reactors in the chemical process industry has gained significant importance in recent years. Companies that offer not only microstructured reactors, but also entire chemical process plants and services relating to them, are already in existence. In addition, many institutes and universities are active within this field, and process-engineering-oriented reviews and a specialized book are available. Microstructured systems can be applied with particular success in the investigation of highly exothermic and fast reactions. Often the presence of temperature-induced side reactions can be significantly reduced through isothermal operations. Although microstructured reaction techniques have been shown to optimize many synthetic procedures, they have not yet received the attention they deserve in organic chemistry. For this reason, this Review aims to address this by providing an overview of the chemistry in microstructured reactors, grouped into liquid-phase, gas-phase, and gas-liquid reactions.     

Biodegradation of polyorganosiloxanes

Biodegradation of various polyorganosiloxanes (about 30 substances) under the influence of several biotype bacteria strain (16 types) were studied. A special procedure of biodegradation and analytical methods of evaluation the degree of degradation were applied. It was found that nearly all polysiloxanes tested are biodegradable but the degree of degradation depends on their composition and structure, as well as on the type of bacteria strain chosen.     

Synthesis and ionic conductivity of mixed substituted polysiloxanes with oligoethyleneoxy and cyclic carbonate substituents

New comb polysiloxanes with mixed substituents were synthesized by hydrosilylation of PMHS with 4-allyloxymethyl-[1,3]dioxolan-2-one and tri(ethylene glycol) allyl methyl ether (AMPEO₃). The effect of the incorporation of carbonate groups on ionic transport, viscosity and thermal properties has been investigated. When doped with lithium bis(trifluorosulfonyl) imide, LiTFSI, the mixed substituted polysiloxane polymers with varying carbonate content all exhibited conductivity higher than those for the polysiloxanes with pure carbonate or pure oligoethyleneoxy substituents. The maximum ambient conductivity in this series was 1.62× 10⁻⁴ S/cm, occurring for the polymer containing 8.5% polar carbonate groups at a doping level of EO/LiTFSI = 15. The impedance measurement results showed that polymers containing larger amounts of carbonate groups exhibited lower conductivity, probably because of their increased viscosity and higher glass transition temperature. The conduction mechanism for these new comb polymers obeys free volume theory, as indicated by conductivity data fit to the VTF equation. We dedicate this paper to Professor Dick Jones, polysilane pioneer and valued friend.     

聚醚酯的生物降解性研究

根据修正后的CECL - 33-T - 82试验方法 ,对用于新型冷冻机润滑的聚醚酯的生物降解性进行评估 ,并作一些机理的探讨     

Biodegradation of arsenosugars in marine sediment

In the marine environment, arsenic accumulates in seaweed and occurs mostly in the form of arsenoribofuranosides (often called arsenosugars). This study investigated the degradation pathways of arsenosugars from decaying seaweed in a mesocosm experiment. Brown seaweed (Laminaria digitata) was placed on top of a marine sediment soaked with seawater. Seawater and porewater samples from different depths were collected and analysed for arsenic species in order to identify the degradation products using high‐performance liquid chomatography–inductively coupled plasma mass spectrometry. During the first 10 days most of the arsenic found in the seawater and the shallow sediment is in the form of the arsenosugars released from the seaweed. Dimethylarsenoylethanol (DMAE), dimethylarsinic acid (DMA(V)) and, later, monomethylarsonic acid (MMA(V)) and arsenite and arsenate were also formed. In the deeper anaerobic sediment, the arsenosugars disappear more quickly and DMAE is the main metabolite with 60–80% of the total arsenic for the first 60 days besides a constant DMA(V) contribution of 10–20% of total soluble arsenic. With the degradation of the soluble DMAE the solubility of arsenic decreases in the sediment. The final soluble degradation products (after 106 days) were arsenite, arsenate, MMA(V) and DMA(V). No arsenobetaine or arsenocholine were identified in the porewater. Copyright © 2005 John Wiley & Sons, Ltd.     

二氧化碳-环氧乙烷共聚物的微生物降解研究

通过生物降解试验证明 ,二氧化碳 -环氧乙烷共聚物PEC可被铜绿假单胞菌AS1 .50、构巢曲霉AS3.391 5、黑曲霉AS3.392 8、出芽短梗霉AS3.3984、球毛壳AS3.963和绳状青霉AS3.3875等分解。具体介绍了微生物降解测试方法     

Lipids of kenaf wastes

The total phospholipids of kenaf wastes have been characterized qualitatively and quantitatively. Kenaf wastes may serve as an additional source of raw material for obtaining the total phospholipids and a homogeneous PC.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR. Uzbek Experimental Station of Tannin Crops, Central Asian Division of the Lenin All-Union Academy of Agricultural Sciences, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 686–688, November–December, 1986.