Hygrothermal aging of Nafion Collette, Floraine M.; Lorentz, Chantal; Gebel, Gérard ...
Journal of membrane science,
2009, Letnik:
330, Številka:
1
Journal Article
Recenzirano
The membrane durability is a critical issue for the development of Proton Exchange Membrane Fuel Cells (PEMFC). Since PEMFC in situ tests were not conclusive to determine Nafion
® membrane ...degradation mechanism, ex situ aging tests were performed on Nafion
® 112 in practical fuel cell usage conditions. The polymer chemical structure evolution was investigated by infrared spectroscopy (IR) and Nuclear Magnetic Resonance (NMR) while its hydrophilicity, directly linked to its protonic conductivity, is established through sorption isotherms by Dynamical Vapour Sorption (DVS). Durability studies over a period of 400 days revealed membrane degradation through a modification of sulfonic acid end-groups. Formation of sulfonic anhydride (from the condensation of sulfonic acids) was strongly demonstrated by IR spectroscopy and, indirectly, by NMR. The substitution of ionic end-groups by less hydrophilic anhydrides leads to a significant decrease of water uptake and thus of its hydrophilicity. Surprisingly, kinetic study reveals that the hygrometric level accelerates this condensation reaction.
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•Continuous HTL of carbohydrate-rich and lipid-rich microalgae followed by HDT.•Advanced characterization of HTL and HDT oils.•The HTL bio-oil from rich-lipid microalgae was easier to ...upgrade.•The HDT oils fell mainly in the diesel range.•Biofuel yield was directly related to the biomass lipid content.
Direct C–H functionalization catalyzed by a robust and recyclable heterogeneous catalyst is highly desirable for sustainable fine chemical synthesis. Bipyridine units covalently incorporated into the ...backbone of a porous organic polymer were used as a porous macroligand for the heterogenization of a molecular nickel catalyst. A controlled nickel loading within the porous macroligand is achieved, and the nickel coordination to the bipyridine (bpy) sites is assessed at the molecular level using IR and solid-state NMR spectroscopy. The heterogenized Ni-bpy catalyst was successfully applied to the direct and fully selective C2 arylation of benzothiophenes, thiophene, and selenophene, as well as for the arylation of free NH-indole. Recyclability of the catalyst was achieved by employing hydride activators to reach a cumulative turnover number of more than 300 after seven cycles of catalysis, which corresponds to a total productivity of 12 g of 2-phenylbenzothiophene, chosen as model target biaryl, per gram of catalyst.
The hydrothermal liquefaction of
Spirulina
sp. microalgae (
i.e.
cyanobacteria) byproducts was investigated for the production of road binders from renewable sources. In the 220–300 °C temperature ...range, a water-insoluble viscous material was obtained in a
ca.
50% yield, which consisted of an oily fatty acid-based fraction mixed with organic and inorganic solid residues (
ca.
20%). More interestingly, this material exhibited viscoelastic properties similar to elastomer-containing bitumen, when operating the hydrothermal liquefaction between 240 and 260 °C. This is the first example of a bio-sourced product showing such properties. At higher temperature, fragmentation of species of high molecular weight occurred, resulting in less viscous materials that were no more thermorheologically simple. The reactor filling ratio was also allowed to vary (
i.e.
30%
versus
60%), showing very little influence in terms of yield and viscoelastic properties of the resulting bio-binders.
Selective ring opening is an important hydrotreating process for gas oil upgrading. In this work, we have used an Ir/NaY bifunctional catalyst -highly efficient in sulfur-free conditions- as a ...reference system to assess the effect of H2S impurity concentration (0-1 %) on the kinetics and mechanisms of naphthene conversion under high hydrogen pressure (5 MPa). Three model naphthenic molecules (decalin, perhydroindan and butylcyclohexane) were compared to evaluate the influence of the ring size (C5 vs C6) and number (1 vs 2). The numerous reaction products were identified, quantified and classified by using two-dimensional gas chromatography (GC x GC). In the absence of sulfur, it is confirmed that C5 rings are opened faster than C6 rings, and that single-ring naphthenes are converted faster than double-ring naphthenes. The presence of H2S, even at concentrations as low as 30ppm, drastically and irreversibly changes the dominant catalytic function (from metallic to acidic), mechanism (from dicarbene-mediated to carbocation rearrangement) and family of products (from ring-opening products to skeletal-isomerization products). Together with experiments at variable reactant conversion, these results allow us to propose mechanistic reaction schemes for the three naphthenes under similar conditions, both for sulfur-free and sulfur-rich atmospheres.
The demand for energy worldwide and the environmental concerns are increasing over the years, and microalgae is a potential raw material for third-generation fuel. In this work, the Chlorella ...sorokiniana microalga was converted by hydrothermal liquefaction (HTL) into a bio-oil using a batch reactor at 300 °C, under 10 MPa, for 30 min. Then, the bio-oil was upgraded using a batch reactor at three temperatures (350 °C, 375 °C, and 400 °C) under 10 MPa (H2) over NiW/Al2O3 sulfided catalyst. The bio-oil and upgraded fractions were characterized by elemental analysis, GPC-RID/DAD, 13CNMR, Sim-Dis, and GC×GC–MS/FID to identify the bio-oil molecular composition and follow its evolution. The lipids in the initial biomass, composed mainly of C16 and C18 chains/triglycerides, were converted into C16 and C18 fatty acids during the HTL reaction, corresponding to 41 % of bio-oil. Then, during the upgrading stage, these carboxylic acids were converted into C15 to C18 n-alkanes through two routes: hydrogenation or decarboxylation/decarbonylation, which was favored by temperature increase. >60 % of upgraded bio-oil eluted on the diesel range, as observed by Sim-Dis. The higher heating value (HHV) increased from 36 MJ/kg in the HTL bio-oil to 47 MJ/kg in the oil upgraded at 400 °C, and the average molar mass decreased from 333 to 203 g/mol. Oxygen and nitrogen compounds such as phenols, phytosterols, pyrroles, indoles, carbazoles, and amides were identified and quantified. Some insights about sulfur compounds are also given. The degree of deoxygenation, denitrogenation and desulfurization was higher than 90 % after the upgrading stage at 400 °C. Nevertheless, heterocyclic nitrogen compounds remained in the upgraded biooil. Therefore, catalytic hydrotreatment is confirmed as a relevant technology for upgrading HTL micro-algal bio-oil. However, catalyst performances can be improved to reduce less reactive nitrogen components.
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•Catalytic upgrading of algal HTL oil over NiW/Al2O3 at different temperatures.•GCxGC-MS/FID, 13C NMR, GPC, and SIMDIS analysis of algal HTL and HDT oils.•Fatty acids, phenols, and phytosterols were almost totally converted.•Heavy sulfur compounds were more challenging to convert than light compounds.•Refractory nitrogen compounds were identified and quantified.
Hydrothermal liquefaction (HTL) of microalgae-derived feedstocks into a bio-binder was investigated in the absence or presence of a catalyst. The resulting products of HTL of Scenedesmus species ...(sp.) residues present rheological properties close to those of a petroleum-derived bitumen. The chemical composition of the biobinder was analysed by two-dimensional gas chromatography (GCxGC-MS), gel permeation chromatography (GPC), and negative and positive-ion laser desorption/ionization FT-ICR MS to provide a complementary analysis of the biobinder and understanding of the role of catalysts. A detailed description of the heavy nitrogen compounds contained in the biobitumen is given.
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•Valorization of microalgae residues by catalytic HTL.•GPC, GCxGC-MS, FT-ICR MS and elemental analysis were carried out on the biocrudes.•FT-ICR MS provides description of the heavy nitrogen compounds in biocrudes.•Bio-binder similar to petroleum one assessed by rheological characterization.
Comprehensive two-dimensional gas chromatography (GC × GC) is a powerful technique for analyzing mixtures of hundreds of hydrocarbons. In the context of fuel upgrading through selective ring opening, ...we propose a methodology for GC × GC analysis of complex mixtures resulting from the hydroprocessing of a single model gas oil compound, decalin, over two different types of bifunctional catalysts based on a transition-metal sulfide (NiWS on amorphous silica–alumina) or a noble metal (Ir on La,Na–Y zeolite). The reactions lead to several products families, the dominant ones being ring-opening products (ROPs) and skeletal-isomerization products (SkIPs). First, it is shown that the ROP distribution can be characterized in terms of isomerization degree by using the cumulative distribution function of the GC × GC (GC Image) software. Second, in a more quantitative approach, the products families have been subdivided into chemical groups, according to the isomerization degrees of the individual compounds, which were almost all tentatively identified by two-dimensional gas chromatography coupled with mass spectrometry (GC × GC-MS) through the use of literature data. This allows us to thoroughly analyze the influence of the catalyst nature and the presence of H2S in the reactant feed on the products distribution, and thereby gain insight into the mechanism of decalin hydroconversion over bifunctional catalysts. In particular, it is shown that metal sulfidation suppresses the metal-catalyzed C–C hydrogenolysis pathway at the benefit of undesirable acid-catalyzed isomerization steps. The methodologic work presented here for decalin is believed to be applicable to other bicyclic (naphthenic or aromatic) compounds.
•Hydrocracking of VGO studied in a batch reactor for different NiMoS and zeolite loadings.•Products distributions analyzed using two dimensional chromatography.•Overall activity in hydrocracking is ...determined by zeolite loading.•Selectivity to middle distillate improves with the increase of metal to zeolite ratio.
A new approach has been developed to characterize bifunctional catalysts in a complex matrix of hydrotreated vacuum gas oil using a batch reactor test. Triphasic reactions were carried out in a reactor equipped with a stationary basket, hydrogen injection and products sampling systems. Bifunctional catalysts containing different relative amounts of alumina-supported NiMo sulfide and zeolite were tested at 400°C under 120 bars over different reaction times. The repeatability of the test conditions was validated and the lack of mass transfer limitations at phase interfaces was confirmed. Gas and liquid samples were analyzed by one and two-dimensional gas chromatography (GC×GC) respectively to obtain quantitative distributions of linear and branched paraffins, naphthenes and aromatics. The details of the products distribution provided by chromatography were explained using mechanisms of bifunctional catalysis. It has been established that the limiting step defining the total conversion is the scission of the hydrocarbon chains on acid sites of the zeolite. The increase of the molybdenum to zeolite ratio provided an improvement of middle distillate selectivity.
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