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International audience; General interest in solvent-free catalytic processes is driven by the development of environmentally and economically acceptable procedures. Such processes require the use of highly active and stable catalysts. This study reports on the synthesis, characterization, and kinetic evaluation of two highly active Pd catalysts supported on different carbons support, i.e., multi-walled carbon nanotubes (CNT) and few-layer graphene (FLG). These catalysts, with similar Pd loading (∼2 wt%) and containing both Pd single atoms (PdSA) and nanoparticles (PdNP), were systematically tested for solvent-free total hydrogenation of squalene (SQE) to obtain high-purity squalane (SQA). Thanks to the unique cooperative catalysis between PdSA and PdNP involving H-spillover, the activities of both catalysts were high compared to catalysts described in the literature. Solvent-free total hydrogenation of SQE could be performed under mild conditions (120 °C, 20 bar H2, 4 h) using ultralow Pd loading (60 ppm). However, since this reduction reaction is highly exothermic (ΔHR= − 765 kJ.mol−1), heat management during the reactor operation with these highly active catalysts is crucial to avoid deactivation and thermal runaway. Under these conditions, Pd/FLG was highly active but deactivated, unlike Pd/CNT, which still has high activity, but does not deactivate. Characterizations (ICP, XPS, Raman, TPD-MS, HAADF-STEM) of the Pd/FLG catalyst before and after reaction, supported by calculations based on density functional theory, allowed us to propose a new mechanism of catalyst deactivation involving the chemical reduction of specific surface oxygen groups of the carbon support induced by H-spillover.

During the aerobic oxidation of aldehydes, peracids accumulate in the reaction mixture and may be decomposed in a non-selective way during workup. Using carboxylate salts, the peracids are selectively transformed into the carboxylic acids in situ.

International audience; Pd/C catalysts are widely used for hydrogenation reactions in the chemical industry. One of the reasons for their high activity is the ability of Pd nanoparticles (PdNP) to dissociate H2 and promote H-spillover. Nevertheless, for selective hydrogenation unpromoted Pd/C catalysts show disappointing results. The use of supported Pd single atom (PdSA) catalysts permits to achieve high selectivity. However, PdSA show low activity because they have difficulty in activating H2. A cooperative catalysis between PdNP and PdSA operates for the hydrogenation of alkenes thanks to the H-spillover, which makes it possible to obtain active isolated PdSA−H species. Here, we present experimental and computational results obtained for phenylacetylene hydrogenation on Pd/CNT catalysts showing different PdSA/PdNP ratios. Tuning this ratio allows doubling the activity while reaching high selectivity to styrene at high conversion. DFT calculations suggest that the first coordination sphere of PdSA has a pronounced effect on their reactivity.

The transition from batch catalytic processes to continuous flow processes requires highly active and stable catalysts that still need to be developed. The preparation and characterization of catalysts where palladium single atoms and nanoparticles are simultaneously present on carbon nanotubes were recently reported by us. These catalysts are considerably more active than commercial or previously described catalysts for the liquid phase hydrogenation of terpenes. Herein is shown that under solvent-free conditions, squalene (SQE) could be converted into squalane (SQA,98 %) using only 300 ppm of Pd in less than 1.4 h at 20 bar H

International audience; We recently reported (R. Castro Contreras, B. Guicheret, B. F. Machado, C. Rivera-Cárcamo, M. A. Curiel Alvarez, B. Valdez Salas, M. Ruttert, T. Placke, A. Favre Réguillon, L. Vanoye, C. de Bellefon, R. Philippe and P. Serp, J. Catal., 2019, 372, 226–244) that a structure/activity correlation exists in Pd/C catalysts for myrcene hydrogenation, which integrates the Pd dispersion, and the surface concentration of oxygen groups and defects of the support. Here, through a combined experimental–theoretical study, we provide an explanation of the influence of these three structural characteristics of Pd/C catalysts for alkene hydrogenation. Highly dispersed Pd nanoparticles (PdNP) are necessary to activate dihydrogen. A high concentration of surface defects on the support is necessary to stabilize Pd single atoms (PdSA), which coexist with PdNP on Pd/C catalysts. A high concentration of oxygenated surface groups is also necessary on the support to allow hydrogen spillover. We demonstrate that such a combination allows cooperative catalysis to operate between PdNP and PdSA that involves the formation of PdSA–H species, which are much more active than PdNP–H for alkene hydrogenation but also isomerization. Importantly, we also report an efficient method to control the ratio between PdSA and PdNP in Pd/C catalysts of similar loadings and show that the control of this ratio allows the development of a new generation of stable and highly active catalysts integrating the ultra-rational use of precious metals in short supply. Indeed, for myrcene hydrogenation, activity variations of several orders of magnitude were measured as a function of the value of this ratio.

The single extraction of rhenium(VII) and uranium(VI) from nitric acid solution by dicyclohexano-18-crown-6 (DCH) solutions was investigated. The extraction of Re(VII), in the form of perrhenate (ReO4−) anion, was optimum for a nitric acid concentration of 3 M and was explained by the ion-pair extraction of perrhenate anions by the hydroxonium DCH complex. The stoichiometry of the Re(VII) complex was obtained from the distribution data by slope analysis and the extracted specie was identified as {ReO4−(DCH-H3O)+}. The uranyl extraction by DCH solutions was evaluated under the same conditions and the extracted specie was identified as {(NO3−)2(DCH-UO22+)} for a nitric acid concentration above 5 M. The extraction of rhenium(VII) from nitric acid solution by DCH solutions in the presence of large excess of uranium(VI) was then investigated. For a nitric acid concentration of 3 mol/L, the extraction efficiency of perrhenate was found to be almost independent of uranium concentration. Based on the chemical similarities between Re(VII) and Tc(VII), this suggests that DCH could be considered for the separation of technetium (VII)/uranium(VI) from nitric acid solution.

International audience; A process intensification study for the full hydrogenation of bio-derived platform molecule squalene (SQE) into squalane (SQA), using commercial heterogeneous Pd catalysts and Pd supported on carbon nanotubes (CNT) is reported. Pd/CNT shows a substantial improvement of the catalytic activity for the total hydrogenation of SQE into SQA thanks to cooperativities between Pd nanoparticles and single atoms simultaneously present on the CNT. However, the stirred reactor's productivity, scalability, and operability are limited by the exothermicity of the reaction (ΔrH = − 765 kJ.mol−1). The implementation of the Pd/CNT catalyst in flow was then studied after coating this catalyst on metallic open cell foams. Using the foam-based milli-reactor's characteristics, including high mass and heat transfer rates and safety, fully reduced SQA (>99 %) was obtained at 180 °C and 30 bar of H2 for a contact time of 1.45 min with a space–time yield of 68 molSQA.molPd−1.min−1. Finally, a scale-up strategy (7 fold) was successfully attempted in a commercially available pilot-scale reactor that meets further seamless scale-up requirements. A production capacity of 2 kg per day using a commercial intensified reactor with a reacting volume of 43.2 mL was obtained under mild conditions (120 °C and 30 bar of H2).

The organocatalyzed aerobic oxidation of aldehydes to acids was reproduced from the original report. In- and ex-situ analysis of the reaction mixture as the function of time reveals that, unlike the claim in the publication, the aerobic oxidation of aromatic and aliphatic aldehydes leads predominantly to the formation of peracids. The latter are transformed into the corresponding carboxylic acids during the workup procedure. The buildup of peracids in solution poses safety problems that should not be overlooked. This finding has also an influence on the way new catalysts are investigated to improve this reaction as well as on aerobic aldehyde-mediated co-oxidation.

An extractive-reaction process for the synthesis of HMF from fructose was implemented in microreactor. Experimental conditions were 10 wt.% fructose in water, MIBK as extracting solvent and HCl as catalyst in a temperature window of 120–160 °C, a MIBK/H2O ratio 1 to 9 and an HCl concentration of 0.25–2 M. The dehydration of fructose to HMF is achieved in less than 40s with a total HMF yield higher than 90% at 150 °C. Aqueous and organic phase spontaneously separate at the outlet of the reactor and HMF is obtained in MIBK with a yield of 80% and a purity of 92%.

An improved method for the oxidation of benzylic and aliphatic alcohols using concentrated bleach (1.6 M NaOCl) using 2-step continuous flow microreactors is reported herein. Enhancement of the reaction rate was obtained by on-line pH adjustment. In the first step, the pH of the bleach was precisely decreased to pH 8.5 using CO2. Such pH is a compromise between oxidative properties, chemical stability and unwanted precipitation. The aqueous bleach solution was subsequently used for the oxidation of benzyl alcohols in EtOAc using catalytic amounts of TBAB (n-Bu4N+Br−) in a segmented flow microreactor. The total conversion of benzyl alcohols was obtained in less than 1 min using 2 eq. of NaOCl at r.t. without any metal catalysts. Selective benzyl alcohol oxidation (>98%) was demonstrated on primary and secondary alcohols. For aliphatic alcohols, 0.1 mol% TEMPO was used as a co-catalyst in synergy with TBAB and a total conversion with high selectivity (>98%) was achieved in less than 2 min.

International audience; The monitoring of chemical reactions can be arduous especially when sampling is required with highly reactive compounds. Online spectroscopic methods provide efficient and non-invasive ways to record the composition of reactive mixtures, yet their use is often limited by the interpretation of spectroscopic data. Herein, we report an easy access and reproducible method for the online analysis of organic transformations through FTIR spectroscopy. Spectra are treated with a multivariate approach to lead to the accurate quantification of the chemicals involved. Further, the technique was applied to the acceptorless dehydrogenation coupling (ADC) of alcohol and allows the first in situ quantitative assessment of the aldehyde intermediate.

The continuous selective aerobic oxidation of benzyl alcohol in flow was developed using an immobilized Ru0 catalyst. After optimization of the reaction conditions, the stability and productivity of the equipment were examined over time using tert-amyl alcohol as solvent, and no deactivation occurred. A cumulative TON close to 15 000 was obtained with a constant activity (TOF = 4 min−1). A semi-empirical kinetic rate expression was proposed.

The Mukaiyama epoxidation was studied using a segmented flow reactor. Full conversion of cis-cyclooctene (0.67 M) with high selectivity (>99%) towards cyclooctene oxide was reached in 5 minutes using 2-ethylhexanal (2 M) as a sacrificial co-reductant, 100 ppm of Mn(II) as catalyst and 5 bar of oxygen. To gain further insights into the Mukaiyama reaction we have investigated the influence of the cis-cyclooctene/2-ethylhexanal ratio and cis-cyclooctene concentration. It was shown that after an induction period during which time aldehyde was oxidised faster than the alkene, the theoretical stoichiometry of the Mukaiyama reaction (1 mole of epoxide per mole of oxidised aldehyde) was observed. Then, different metal catalysts and catalyst loading were evaluated. The best results were obtained with Mn(II). We can suspect that the differences in productivity described in the literature for Mukaiyama epoxidation reaction could be explained by oxygen mass transfer resistance rather than catalytic efficiency. Surprisingly the selectivity of 2-ethylhexanal oxidation toward 2-ethylhexanoic acid was not improved by the co-oxidation of cis-cyclooctene. These results raised questions regarding the activated oxygen specie(s) responsible for the epoxidation and the exact mechanism of this reaction.

International audience; A selective acylation protocol using cerium chloride (CeCl3) as catalyst was applied to functionalize silybinin (1), a natural antioxidant flavonolignan from milk thistle fruit, in order to increase its solubility in lipophilic media while retaining its strong antioxidant activity. The selective esterification of 1 at the position 3-OH with a palmitate acyl chain leading to the formation of the 3-O-palmitoyl-silybin (2) was confirmed by both mass spectroscopy (MS) and nuclear magnetic resonance (NMR) analyses. The antioxidant activity of 1 was at least retained and even increased with the CUPRAC assay designed to estimate the antioxidant activity of both hydrophilic and lipophilic compounds. Finally, the 3-O-palmitoylation of 1, resulting in the formation of 2, also increased its anti-lipoperoxidant activity (i.e., inhibition of conjugated diene production) in two different lipophilic media (bulk oil and o/w emulsion) subjected to accelerated storage test.

International audience; The mechanism of acceptorless dehydrogenative coupling reaction (ADC) of alcohols to esters catalyzed by aliphatic pincer PHNP ruthenium complexes was experimentally studied. Relevant intermediate species involved in the catalytic cycle were isolated and structurally characterized by single-crystal X-ray diffraction studies, and their reactivity (including toward substrates related to the catalytic process) was probed. VT NMR studies unveiled several chemical exchanges connecting the Ru amido hydride, the Ru alkoxide, and the alcohol substrate. Under catalytic conditions, in situ IR spectroscopy monitoring demonstrated the production of ester via aldehyde as intermediate. A Tishchenko-like pathway is proposed as the main path for the production of ester from aldehyde, involving alkoxide and hemiacetaloxide Ru species (the latter being identified in the reaction mixture by NMR). Catalytic system deactivation under base-free conditions was found to be related to water traces in the reaction medium (either as impurity or derived from aldol reactions) that lead to the formation of catalytically inactive acetato Ru complexes. These react with alkali metal alkoxides to afford catalytically active Ru species. In line with this observation, running the ADC reaction in the presence of water scavengers or alkoxides allows maintaining sustained catalytic activity.

Continuous-flow technology with channel dimension in the millimeter region found widespread applications in numerous applications. The epoxidation of methyl oleate with molecular oxygen using an aldehyde as sacrificial reductant (Mukaiyama reaction) was implemented in a segmented flow microreactor. The effect of aldehyde structure and aldehyde/methyl oleate molar ratio on the conversion to epoxides was studied. Total conversion of methyl oleate (0.67 M in heptane) with a selectivity higher than 99% and a cis/trans ratio ∼75/25 was reach in less than 4 min, at room temperature, using three equivalents of 2-ethylhexanal, 100 ppm of Mn(II) as catalyst and five bar of oxygen. Practical applications: As the result of the small reactor volumes, very high surface-to-volume ratio and high heat exchange efficiency compared to classical batch reactors, the overall safety of oxidation processes is significantly improved using continuous-flow technology. Microreactors also provide better mass transfer, and thus, improve the productivity of the aerobic epoxidation of methyl oleate using aldehyde as sacrificial reductant while maintaining the high selectivity of the process. (i) Epoxidation of methyl oleate with molecular oxygen is performed safely using continuous-flow technology. (ii) Total conversion is obtained in 4 min at r.t. using 100 ppm of Mn(II) and a sacrificial reductant. (iii) The selectivity and cis/trans ratio are comparable to batch.

Lignans and neolignans are principal bioactive components of Linum usitatissimum L. (Flax), having multiple pharmacological activities. In present study, we are reporting an authoritative abiotic elicitation strategy of photoperiod regimes along with UV-C radiations. Cell cultures were grown in different photoperiod regimes (24 h-dark, 24 h-light and 16L/8D h photoperiod) either alone or in combination with various doses (1.8-10.8 kJ/m(2)) of ultraviolet-C (UV-C) radiations. Secoisolariciresinol diglucoside (SDG), lariciresinol diglucoside (LDG), dehydrodiconiferyl alcohol glucoside (DCG), and guaiacylglycerol-p-coniferyl alcohol ether glucoside (GGCG) were quantified by using reverse phase-high performance liquid chromatography (RP-HPLC). Results showed that the cultures exposed to UV-C radiations, accumulated higher levels of lignans, neolignans and other biochemical markers than cultures grown under different photoperiod regimes. 3.6 kJ/m(2) dose of UV-C radiations resulted in 1.86-fold (7.1 mg/g DW) increase in accumulation of SDG, 2.25-fold (21.6 mg/g DW) in LDG, and 1.33-fold (9.2 mg/g DW) in GGCG in cell cultures grown under UV + photoperiod than their respective controls. Furthermore, cell cultures grown under UV + dark showed 1.36-fold (60.0 mg/g DW) increase in accumulation of DCG in response to 1.8 kJ/m(2) dose of UV-C radiations. Smilar trends were observed in productivity of SDG, LDG and GGCG. Additionally, 3.6 kJ/m(2) dose of UV-C radiations also resulted in 2.82-fold (195.65 mg/I) increase in total phenolic production, 2.94-fold (98.9 mg/I) in total flavonoid production and 1.04-fold (95%) in antioxidant activity of cell cultures grown under UV + photoperiod. These findings open new dimensions for feasible production of biologically active lignans and neolignans by Flax cell cultures.

1,1,3,3-Tetramethyldisiloxane (TMDS) and polymethylhydrosiloxane (PMHS), when associated with titanium(IV) isopropoxide, provide two convenient systems for the reduction of nitriles into the corresponding primary amines. Kinetics of the two systems have been studied by 1 H NMR and demonstrated that reduction with PMHS occurs faster than with TMDS. These two titanium-based systems reduce both aromatic and aliphatic nitriles in the presence of Br, C C, NO 2 , OH, and cyclopropyl-ring. In the case of cyclopropyl-nitriles, the formation of secondary amines, which come from an intermolecular reductive alkylation reaction was observed. This result was exploited for the reduction of dinitriles, which led, in one-step, to azepane, piperidine, pyrrolidine, and azetidine derivatives through an intramolecular reductive alkylation reaction.

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International audience; Commercially available H-Y (Faujasite) and H-ZSM5 zeolites with various SiO2/Al2O3 ratio (from 5 to 280) were used as acid catalyst for vapour phase methanol dehydration in mild condition (T\textless250 degrees C; P\textless5 bar). All tested catalysts were giving very high selectivity while conversion was highly dependent on both acid content and surface hydrophobicity expressed as Weitkamp hydrophobicity index (HI index). For H-Y and H-ZSM5 zeolites, a correlation was found between catalysts productivity expressed in kg of DME per hour per concentration of acid sites and HI index. Such results could rise to the design of more efficient catalyst for gas-phase DME synthesis from methanol.

An efficient and metal-free method for the oxidation of aldehydes to the corresponding carboxylic acids has been developed. In a simple continuous-flow photochemical reactor, the use of camphorquinone (CQ) irradiated with a white light-emitting diode (LED) source enhanced the autoxidation of aldehydes. Under 5 bar of oxygen, visible light, and 0.3 mol% of CQ, the rate of oxidation was increased from 6 times with 2-ethylhexanal to 30 times for n-nonanal. The large interfacial area generated by a segmented flow apparatus associated with radicals formed by photooxidation of CQ ensures metal-free high throughput of carboxylic acids under safe conditions.

BACKGROUND: Cloud point extraction (CPE) is an attractive alternative to solvent extraction. However, comparisons between both techniques are lacking. In this paper, the extraction of uranium(VI) using 8-hydroxyquinoline (HQ) as chelating agent was studied by CPE using Triton X-114 as non-ionic surfactant and by solvent extraction using CHCl3 as diluent. RESULTS: Using CPE, a quantitative extraction was observed for pH higher than 4.5 with a HQ/U ratio of 10. Using solvent extraction an increase in the HQ/U ratio up to 50 is necessary to obtain a near quantitative extraction. Both extraction systems were then compared with respect to the nature of extracted species, and the extraction constants determined using log-log analysis of the extraction data. In the solvent extraction system, the extracted species were identified as UO2Q2 and the corresponding extraction constant was found to be log kex = − 3.6 ± 0.2 on the molar scale. Considering that UO2Q2 is also the extracted species in CPE, a slightly higher extraction constant, i.e. log kex = − 2.5 ± 0.3, was found. CONCLUSION: Such a small difference in favour of the CPE system may arise from the combination of various phenomena, including effects of temperature and effects of ‘extractant environment’. However, a change in the nature of the extracted species, namely from UO2Q2 in the solvent extraction system to the formation of adducts, i.e. UO2Q2(HQ) and UO2Q2(HQ)2 in the CPE system, due to higher HQ concentration in the surfactant-rich phase compared with chloroform, cannot be precluded, but requires confirmation. Copyright © 2012 Society of Chemical Industry

The oil extraction industry generates two by-products, an aqueous effluent, olive mill wastewater (OMWW) and a solid residue, olive mill solid waste (OMSW). OMWW is considered as the major pollutant in the Mediterranean area causing severe environmental threats. The main problem regarding the disposal of OMWW is to find an environmental and economical viable solution. A new valorisation strategy has been carried out which includes the following steps: (a) absorption of OMWW on low-cost renewable absorbents, (b) natural evaporation of the water and (c) energy recovery by combustion of the impregnated absorbents. Sawdust and OMSW were selected as low-cost renewable absorbents. Thermal behaviour of the impregnated samples was studied under inert and oxidative atmosphere from 20 °C to 900 °C using thermogravimetric analysis (TGA). Kinetic parameters were obtained and compared for the different samples. Gaseous emissions such as CO2, CO and volatile organic compounds (VOC) were measured under oxidative conditions at 500 °C, 600 °C and at 700 °C in a fixed bed reactor. The results indicate that for samples containing the same amount of OMWW, the reaction time of impregnated sawdust is lower compared to impregnated OMSW. Combined treatment of OMMW proposed in this study may be a promising method for the reduction of their environmental impact and for the energetic valorisation of the organic content of OMWW.

The disposal of olive mill wastewater (OMWW) by-product is one of the principal environmental problems of the olive oil industry. Therefore, several treatments have been proposed to reduce their environmental impacts; however, the high cost and the antibacterial effect of polyphenols are limiting factors for the different processes. A new valorisation strategy of OMWW based on absorption on sawdust followed by combustion has been studied. Two OMWW/sawdust blends, named impregnated samples (IS) with different mass ratios of OMWW in the mixture were prepared. In order to study the thermal behaviour of IS samples, combustion experiments were performed in a fixed bed reactor under isothermal conditions in a temperature range of 500–700 °C. In order to estimate the efficiency of the thermal process, emission factors of carbon oxides and oxygen consumption were measured. The thermal behaviours of IS were compared with that of the original sawdust under the same experimental conditions.

International audience; Acetic acid, a common biomass transformation residue, can be converted into acetone by direct ketonization in the gas phase over gamma-Fe2O3 (maghemite) pre-activated at 450 degrees C under air. This reaction was performed in a continuous flow reactor with varying temperature from 250 to 300 degrees C and different carrier gases. Using N-2 as carrier gas, the activity of the iron based catalyst normally increased with increasing temperature and contact time and remained constant under stationary operating conditions. A slight decrease of activity was observed using a N-2/CO2 mixture as carrier gas. A strong enhancement of the activity was observed when H-2 was introduced in the carrier gas, as a N-2/H-2 or CO2/H-2 mixture. This improvement could be attributed to the modification of the oxidation state of the iron catalyst used for which in situ characterisation is still to be performed.

A continuous-flow microreactor is applied for the selective aerobic neat oxidation of 2-ethylhexanal. Under 7.5 bar of O2 and 10 ppm of Mn(II) as catalyst, a production of up to 130 g/h of 2-ethylhexanoic acid can be obtained with a PFA tubing of 7 m (O 1.65 mm, reactor volume ca. 15 mL). The synergistic use of alkali metal salts and Mn(II) as catalyst improve the selectivity up to 94% under those conditions. We show that the productivity of this simple tube microreactor is limited by the thermal management.

International audience; A simple and useful method for the reduction of primary amides into the corresponding amines using a polymethylhydrosiloxane (PMHS)–Ti(OiPr)4 reducing system is described. Aromatic as well as aliphatic primary amides are reduced in high selectivity and excellent yields. The reduction could proceed via dehydration of the primary amide group into the corresponding nitrile which is then reduced into the corresponding primary amine.

Cytochrome P4507B1 7alpha-hydroxylates dehydroepiandrosterone (DHEA), epiandrosterone (EpiA) and 5alpha-androstane-3beta,17beta-diol (Adiol). 11beta-Hydroxysteroid dehydrogenase type 1 (11beta-HSD1) interconverts 7alpha- and 7beta-forms. Whether the interconversion proceeds through oxido-reductive steps or epimerase activity was investigated. Experiments using [(3)H]-labelled 7beta-hydroxy-DHEA, 7beta-hydroxy-EpiA and 7beta-hydroxy-Adiol showed the (3)H-label to accumulate in the 7-oxo-DHEA trap but not in 7-oxo-EpiA or 7-oxo-Adiol traps. Computed models of 7-oxygenated steroids docked in the active site of 11beta-HSD1 either in a flipped or turned form relative to cortisone and cortisol. 7-Oxo-steroid reduction in 7alpha- or 7beta-hydroxylated derivatives resulted from either turned or flipped forms. 11beta-HSD1 incubation in H(2)(18)O medium with each 7-hydroxysteroid did not incorporate (18)O in 7-hydroxylated derivatives of EpiA and Adiol independently of the cofactor used. Thus oxido-reductive steps apply for the interconversion of 7alpha- and 7beta-hydroxy-DHEA through 7-oxo-DHEA. Epimerization may proceed on the 7-hydroxylated derivatives of EpiA and Adiol through a mechanism involving the cofactor and Ser(170). The physiopathological importance of this epimerization process is related to 7beta-hydroxy-EpiA production and its effects in triggering the resolution of inflammation.

Synthesis of sulfocatecholamide (CAMS) and hydroxypyridinone (HOPO) calixarene ligands and determination of their binding abilities for the uranyl cation were described. Chelating properties were determined by UV spectrophotometry in aqueous media under various pH conditions and further studied by 1 H NMR analysis of the resonance signals of both aromatics' protons of the chelating groups. Each ligand shows a more or less pronounced affinity for uranium. HOPO calixarenes exhibit significant affinity towards uranyl ion at acidic and neutral pH while CAMS calixarene is more efficient at basic pH.

Adsorptive desulfurization was studied using straight-run gas oil (SRGO) with various sulfur contents (390 and 60 ppm S). Immobilization of electron-poor molecules (π-acceptors) on macroporous resins was achieved in three steps starting from commercially available poly(styrene-co-divinylbenzene) beads. Influence of the temperature on adsorption was studied, and the process was examined on the basis of breakthrough curves. The regeneration of the support was studied using fixed-bed technology and was efficiently performed with toluene as the solvent. The extracted compounds were easily recovered after evaporation of the toluene and the affinity of the resins toward alkyldibenzothiophenes was confirmed by GC-FPD analysis. On the basis of these preliminary experimental results, a new concept is proposed for ultradeep desulfurization of SRGO.

The cis-syn-cis isomer of dicyclohexano-18-crown-6 (DCH18C6) has been shown to be an efficient extractant able to perform the separation of Pu(IV) and U(VI) from fission products and then the separation of Pu(IV) from U(VI) without valence exchange as required in the PUREX process. This macrocycle was irradiated in nitric acid with a 137Cs γ source to study its radiation chemical stability. Radiation chemical yields (G) were determined by gas chromatography. The results show that the presence of uranyl nitrate has a strong influence on DCH18C6 radiation chemical stability. Indeed, the presence of this template ion increases the macrocycle stability by promoting fragments recombination.

Calixarenes 5–8 capped with DTPA bridges were synthesized by condensation of the corresponding 1,3-(distal)-diaminocalixarenes and DTPA dianhydride in DMF. The chelating properties of the DTPA-calixarenes were evaluated towards europium and the resulting complexes were characterized by mass spectroscopy.

A procedure for the selective removal of uranium traces dissolved in drinking water has been studied. Plate module membrane filtration equipment was operated to evaluate the performance and selectivity of three different nanofiltration flat-sheet membranes. Experiments were carried out using various commercial mineral waters with distinct physicochemical compositions. The membranes were first discriminating by their ability to reject uranium in the presence of the main cations found in mineral waters, using a 2 mg L(-1) (2000 ppb) concentration of uranium. The rejection of U(VI) was dependent on the uranyl speciation and the ionic strength. Second, removal of uranium traces (0.02 mg L(-1), 20 ppb) was performed using the nanofiltration membrane showing the highest selectivity for uranium toward alkaline and alkaline-earth ions. The results showed a high performance of the nanofiltration membrane, Osmonics DL, for selective uranium rejection at low pressure (1 bar), illustrating the advantage of nanofiltration for the selective removal of uranium from drinking water.

For the Am/Eu separation, the chelating agent diethylenetriaminepentaacetic acid (DTPA) was used to selectively decrease the permeability of Am across the nanofiltration membrane Desal GH. Using an Am/Eu/DTPA mixture, we have showed that the difference of permeability can be explained by the chemical speciation in solution. The membrane selectivity is thus determined by the difference of the stability constants of the 1:1 complexes of Am and Eu with DTPA. The influence of DTPA concentration on the separation factor (SF) was then investigated. The SF determined with an Eu/Am initial ratio of 3700 varied within the range of 1.2–3.5.

Aerobic oxidation using a combination of copper salts and 2,2,6,6-tetramethylpiperidine N-oxyl (TEMPO) represent useful tools for organic synthesis and several closely related catalyst systems have been reported. To gain further insights, these catalytic systems were evaluated in a gas–liquid segmented flow device. The improvement of oxygen mass transfer has a significant influence on the turnover-limiting step. Hence, an improved catalytic system using copper(II) as copper source was implemented in a microreactor for the safe and efficient oxidation of primary alcohol.

The synthesis and solvent extraction behavior of dipicolinic acid (pyridine-2,6-dicarboxylic acid, PDCA) and their derivatives have been studied for possible use in selective back-extraction of actinides, especially americium. The extraction was performed from an organic phase containing a mixture of trivalent actinides and lanthanides pre-extracted with N,N,N’,N’-tetraoctyl diglycolamide (TODGA). The efficiency of the back-extraction was enhanced when the picolinate platform was used in a heterocyclic decadentate ligand called h4tpaen. Beyond selective An/Ln extraction, the aqueous soluble h4tpaen ligand seemed a potential reagent for an intra-group Am(III)/Cm(III) separation with a separation factor SFCm/Am of about 3.5.

Membrane filtration equipment was used to evaluate zirconium and hafnium separation efficiency by a membrane separation process. High rejection of Zr and Hf species in aqueous solution were obtained with nanofiltration and ultrafiltration membranes. This high rejection could be explained by the formation of high molecular weight polynuclear species. Enhanced transportation across the nanofiltration and ultrafiltration membranes was observed when aminocarboxylic ligands, like EDTA, were introduced in the solution. This enhancement could be explained by a depolymerization process of the polynuclear complexes induced by the ligands. The rejection of Zr and Hf was markedly influenced by the counter anions and the EDTA/metal ratio. By using Zr and Hf oxynitrates instead of oxychlorides a difference of rejection of up to 20% was observed for Zr and Hf indicating that the membrane separation process could be an alternative process for Zr and Hf separation.

Sorption behavior of zirconium and hafnium on different commercial anion exchange resins with different amine functions; ammonium (Amberjet 4200Cl), pyridine (PVP) and pyridinium (HPQ) was investigated in hydrochloric acid by both batch and column methods. Experiments were studied as a function of the concentration of hydrochloric acid. For all resins, zirconium was preferably extracted. The highest separation factors at equilibrium conditions were obtained by poly(vinyl‐pyridine) (PVP) with a hydrochloric acid concentration of 9.5 M. It was observed that a single contact of the loaded resins with pure water completely back extracted the metal ions from the resins. On the basis of the significant difference between distribution coefficients of Zr and Hf, the separation was performed on a glass column (25×160 mm), packed with the resin. The breakthrough curves showed a competitive sorption and desorption process between Zr and Hf for the three resins studied.

The aim of this work was to investigate the mechanisms behind the rejection of polyaminocarboxylic acids, especially the influence of membrane and solute properties. The rejections of five polyaminocarboxylic acids by commercially available charged nanofiltration membrane (Desal GH, Osmonics) were studied at constant ionic strength, pressure and temperature as a function of the pH. The rejections of polyaminocarboxylic acids with Desal GH spiral-wound membrane varied from 10 to 99% at pH ranging from 1 to 7. Findings of this study indicated that the rejection of polyaminocarboxylic acids was primarily driven by Donnan exclusion and correlated with the net charge of the solute which could be calculated using protonation constants. The effects of molecular weight and molecular parameters on rejection were studied when polyaminocarboxylic acids had a net charge close to zero.

The extraction of zirconium and hafnium from aqueous HCl solutions by means of Aliquat 336 in organic diluents was systematically studied. The following three aspects were discussed: the extraction dependence on HCl, the Aliquat 336 concentrations, and the nature of diluents. Both of the metals were stripped with deionized water and the influence of phase ratio on the efficiency of the stripping has been investigated. The stoichiometry of the extracted Zr and Hf species from single metal ion were studied and a possible extraction mechanism for the Zr‐Hf mixture is discussed in the light of the results obtained.

Cloud-point extraction (CPE) was used with lipophilic chelating agent to extract uranium(VI) from aqueous solutions. The methodology used is based on the formation of metal complexes soluble in a micellar phase of a non-ionic surfactant, Triton X-114. The metal ions complexes are then extracted into the surfactant-rich phase at a temperature above the cloud-point temperature. The influence of surfactant concentration on extraction efficiency was studied and the advantage of adding 8-hydroxyquinoline (8HQ) as lipophilic chelating agent was evidenced. High extraction efficiency was observed, indicating the feasibility of extracting U(VI) using CPE. This study describes a four-step process—(1) extraction, (2) thermo-induced phase splitting, (3) back-extraction and (4) second phase splitting—for the recovery of uranium from water. In our conditions, the extraction yield is quantitative and the concentration factor obtained is superior to 100. After stripping with a diluted nitric acid solution (pH < 1), the system can be recycled through a new four-step cycle. Copyright © 2006 Society of Chemical Industry

The aim of this work is to evaluate the gadolinium(III) rejection by nanofiltration assisted by complexation with diethylenetriaminepentaacetic acid (DTPA) as chelating agent. The experimental Gd(III) rejections as a function of the pH were compared to species distribution for the Gd(III)–DTPA system calculated using the protonation and thermodynamic stability constants. The Gd(III) rejection varies from 5 to 95% as a function of the pH and follows the Gd(III)/DTPA speciation. However for pH below 1.5 and for high Gd(III) rejection, some differences between the Gd(III)/DTPA speciation and the observed Gd(III) rejection could be noticed. For this reason, the surface charge of organic NF membrane Desal G10 was determined from tangential streaming potential measurements for different pH values (2.0–6.0) in the presence of 0.5 mM of Gd(III) nitrate and 0.5 mM of DTPA. The isoelectric point (p I ) of the Desal G10 membrane was found to be close to 3.4. Thus the rejection of Gd(III) at low pH could be explained by surface force interactions. The influence of the operating parameters on Gd(III) rejection above p I was then studied. For an operational pressure of 3 bar, a complex concentration of 0.4 mM, a tangential velocity of 145 mm s −1 and a temperature of 15 °C, the differences between the Gd(III)/DTPA speciation and the observed Gd(III) rejection are low and thus Gd(III) rejection with Desal G10 membranes can fit the speciation.

Cross‐flow membrane filtration equipment was operated to evaluate the selective uranium carbonate rejection from seawater of different flat sheet membranes. The membranes were discriminating by the rejection of uranium, calcium, and sodium under geochemical conditions that mimic uranium in seawater. Then, operating parameters were optimized, and the selective rejection of dissolved uranium was checked on prefiltrated seawater. Concentration factors of 1.1 and 8.5 for sodium and uranium(VI), respectively, were obtained for a nanofiltration volume ratio of 0.96.

A less‐common extraction procedure, cloud‐point extraction, is used with a lipophilic chelating agent (8‐hydroxyquinoline) to extract and separate lanthanum(III) and gadolinium(III) ions from an aqueous solution. Surfactant solutions are used in conjunction with 8‐hydroxyquinoline to form a lanthanide complex that is extracted into the micellar phase at a temperature above the cloud‐point temperature. The structure of the lipophilic part of the nonionic surfactant, the chelating agent–metal molar ratio, and the cloud‐point temperature are identified as factors determining the extraction efficiency and selectivity. With Triton X‐114, a selectivity higher than 30 and a decontamination factor of 50 for Gd(III) indicate that micelle‐mediated cloud‐point extraction is promising for the specific separation of actinide ions from nuclear waste. Finally, a microwave procedure is proposed to decrease the duration of the experiment to less than 6 min. The authors are grateful to Seppic S.A., Paris, France, ...

Four 14-membered azamacrocycles 2a−d, each containing a pyridine moiety and three acetic and/or propionic acid pendent arms, were prepared from regioselectively functionalised polyamines. The stability constants of the lanthanide complexes (La, Pr, Nd, Eu, Gd, Tb, Er, Yb, Lu) formed with the triacetic acid compound 2a were determined by spectroscopic methods (luminescence and/or UV/Vis spectroscopy). Other characteristics of the luminescent EuIII and TbIII complexes formed with the triacetic acid derivative 2a were also evaluated. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Cesium‐137 is considered as one of the most dangerous radioactive materials that can be very easy move into the environment and contaminate it. This study aims to determine the optimum conditions for cesium/sodium separation by nanofiltration (NF)–complexation on Nanomax 50 membrane with resorcinarene as the complexing agent. Protonation constants of resorcinarene were determined by potentiometric titration in 0.1 mol/L NaNO3 at 25°C (log K H1 = 9.24 ± 0.06; log K H2 = 10.21 ± 0.03; log K H3 = 8.59 ± 0.07; log K H4 = 7.85 ± 0.08). The apparent formation constants of the Cs+–resorcinarene (log K CsL) were determined by UV spectrophotometry to evaluate the selectivity of resorcinarene toward cesium complex formation as a function of the pH. Parameters such as the pH, [resorcinarene]/[Cs+] ratio were studied to reach 80% of cesium rejection in 3 mol/L of NaNO3. The stability of resorcinarene was studied as a function of the pH and the concentration of NaNO3 by 1H and 13C NMR studies in D2O. Resorcin...