Bar Oxygen Pressure Research Articles

Facile synthesis of ammonium trivanadate(V)/nitrogen doped carbon composites with high catalytic activity for the selective oxidation of 5-hydroxymethylfurfural

2,5-Diformylfuran (DFF), arising as an oxidation product of 5-hydroxymethylfurfural (HMF), has garnered significant interest owing to its versatile range of applications. In this study, the desired catalyst of NH4V3O8/N-C was successfully prepared and investigated by various characterization methods. A systematic effect of reaction conditions was conducted, revealing that under 5 bar of oxygen pressure, DFF was synthesized from HMF selective oxidation using the NH4V3O8/N-C catalyst. This transformation was achieved within 2 h at 120 °C, exhibiting an impressive DFF selectivity of 97.8%. During the recycling experiment, the catalytic efficiency remained consistently high even after being employed for eight cycles.

Selective and Robust Ru Catalyst for the Aqueous Phase Aerobic Oxidation of Furfural to 2-Furoic Acid.

Synthesis of 2-furoic acid (FURA) via oxidation of furfural (FAL) is vital in evolving the biorefinery concept as FURA has numerous important applications in the pharmaceuticals and optic areas. Though few works on this reaction are done, those are marred with shortcomings such as the nonrecyclability of catalyst, dilute solutions, lower yields, or use of H2O2 as an oxidizing agent. Herein, we report catalytic aqueous phase oxidation of FAL to FURA using molecular oxygen as an oxidizing agent. For the synthesis of FURA, various catalysts with a combination of metal (Pt, Pd, Ru) and supports (carbon, Al2O3) were prepared and characterized by multiple techniques (X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer-Emmett-Teller (BET), X-ray photoelectron spectroscopy (XPS)). Oxidation of FAL carried out over 5 wt % Ru/C catalyst in the presence of Na2CO3 yielded 83% of FURA at 120 °C and 15 bar oxygen pressure. The catalyst could show potential for reusability as similar activity was achieved after subjecting the spent catalyst to mild reduction treatment (150 °C). Studies on the effects of temperature, pressure, and time could help accomplish enhanced yields of FURA. Additionally, learning about the effect of base (weak/strong/solid) revealed that due to the weak basicity of Na2CO3, higher yields could be achieved by maintaining approximately a pH of 11, which is optimal for suppressing side reactions. Under the given conditions, FURA is stable (>90%) and also adsorption studies divulge that it is immediately removed from the catalyst surface, and hence higher yields could be achieved in our catalytic system. Using the initial rates methodology, an activation energy of 21.91 kJ mol-1 was derived and also a high turn over frequency (TOF) (85.9 h-1) was observed under optimized conditions.

Kinetics study of catalytic wet oxidation of phenol over novel ceria promoted mesoporous silica supported Ru-Fe3O4 catalyst

A novel catalyst was synthesized via excess solution impregnation (ESI) of Ru and Fe3O4 nanoparticles (NPs) on ceria-loaded mesoporous SiO2 and mesoporous SiO2 was synthesized using sol-gel method. Degradation of phenol and effluent containing phenol from resin industry was performed over Ru-Fe3O4/CeOx-SiO2 (Ce3+/Ce4+, x = 1.64) catalyst in an autoclave reactor at 423 K and 14 bar oxygen pressure. Effective phenol degradation of 95% for the model aqueous solution of phenol and 92% for industrial effluent containing phenol were achieved when the both ruthenium and iron loadings were 0.25 wt% under optimized reaction conditions. The close contact between ruthenium and Fe3O4 nanoparticles facilitated the oxidation of phenol at very low temperature, whereas ceria NPs act as a promoter for oxidation reaction. The kinetics insights of oxidation reaction were studied and the catalysts were characterized thoroughly using BET, TPD, XRD, SEM, HR- TEM, ICP-AES, XPS and CO chemisorptions techniques. High surface area and large mesopores of silica facilitated the fine dispersion of the active catalytic sites and oxygen vacancy as supported by the DFT study for catalytic activity. Optimal process conditions could render much higher phenol degradation efficacy in comparison with previous scientific investigations.

Study of chemical stability of titanium in model hydrochloric acid solutions of refining production

The report includes the results of the studies of titanium corrosion rate in hydrochloric solutions in open and closed systems as a function of various factors, including concentration of hydrochloric acid, temperature, concentration of oxidizer (sodium chlorate) and salts of precious metals, and excess oxygen pressure. The studies provided the stability limits of titanium VT1-0 in hydrochloric media at temperatures above 100 оС. It was found that the rate of titanium corrosion in the temperature range of up to 110 оС, concentration of hydrochloric acid up to 110 g/dm3, and under excess (more than 7 bar) oxygen pressure does not exceed 0.1 mm/year. Similar corrosion rate is observed in the temperature range of up to 160 оС with hydrochloric acid concentration less than 40 g/dm3. The rate of titanium corrosion in closed systems in refinery hydrochloric solutions, with the concentration of at least one of platinum, palladium, gold, or rhodium of over 5 g/dm3, decreases even in the absence of excess oxygen pressure. The presence of salts of precious metals in a closed system with excess oxygen pressure of more than 7 bar does not result in any significant change in titanium corrosion rate. It was found that gold and palladium may potentially deposit on titanium surface, primarily at defect sites, at temperatures above 110 оС upon contact with solutions of precious metal salts. No deposition of other precious metals was observed. In all cases, a continuous uniform corrosion is typical for titanium. The corrosion rate at 120–160 оC in hydrochloric solutions with added sodium chlorate is in the range of 0.3–0.5 mm/year, while it is already 10–12 mm/year at 180–200 оС. Thermodynamic calculations demonstrated potential modification of sodium chlorate decomposition at temperatures above 160 оC, which results in more than 30-fold acceleration of corrosion.

Activated Carbon-Supported Ruthenium as a Catalyst for the Solvent- and Initiator-Free Aerobic Epoxidation of Limonene

The activity and selectivity of ruthenium catalysts supported on various activated carbons have been investigated in the epoxidation of limonene using molecular oxygen, the greenest oxidizing agent, under solvent/reductant- and initiator-free reaction conditions. The catalysts were prepared via different methods including impregnation, sol immobilization, and cation exchange. Supported Ru catalysts with a metal particle size ranging from 1.8 to 21 nm were obtained. The catalyst prepared by cation exchange using Darco G60, with the highest mesopore surface area and pore volume and the lowest Ru particle size (1.8 nm), was found to give the best combination of limonene conversion of 35% and higher selectivity for epoxidation products (Sepox) of 57% at 80 °C and 3 bar oxygen pressure, compared to the total selectivity of 25.5% for allylic oxidation products (Sallyl). Other activated carbon supports, e.g., Darco MRX, Norit RB4C, and Norit RX3, were found to yield less effective catalysts. In addition, the sol immobilization method led to the highest conversion of limonene (40.4%) but with a lower total selectivity toward epoxidation products (Sepox) of 36.8% and that toward allylic oxidation products (Sallyl) of 33.6%. The textural parameters of carbon-supported Ru catalysts were determined by BET, TEM, SEM, TPR, and CO chemisorption. Highly dispersed Ru particles were found to promote the formation of limonene epoxides via the reaction of limonene hydroperoxide with limonene instead of hydroperoxide decomposition to allylic radicals. Finally, the appropriate reaction conditions to maximize the selectivity of the epoxides and the reusability of the catalyst were established.

Thermal stability and decomposition kinetics of NdNiO3−δ at 1 bar of O2

Despite the interest in rare-earth nickelates for applications, their processing under 1 bar of oxygen pressure is still challenging. In this work, we report the co-precipitation synthesis, thermal stability and thermally driven decomposition of NdNiO3 phase, in order to determine the synthesis parameters towards a pure perovskite phase. We concluded that using a 1% molar excess of Nd during preparation and posterior annealing at around 900 °C at 1 bar of O2 yields an almost pure NdNiO3−δ phase (with a hexagonal Nd2O3 phase below 0.6% molar), with an oxygen deficiency of δ = 0.082 ± 0.001. The decomposition of the NdNiO3−δ phase into Nd4Ni3O10 and NiO was found to start above 900 °C. On further heating, above 1050 °C, the Nd4Ni3O10 decomposes into Nd2NiO4 and NiO phases. Structural parameters and Raman spectra are provided for the NdNiO3, Nd4Ni3O10 and Nd2NiO4 compounds.

Alcohol‐Activated Vanadium‐Containing Polyoxometalate Complexes in Homogeneous Glucose Oxidation Identified with 51V‐NMR and EPR Spectroscopy

AbstractAlcoholic solvents, especially methanol, show an activating affect for heteropolyacids in homogenously catalysed glucose transformation reactions. In detail, they manipulate the polyoxometalate‐based catalyst in a way that thermodynamically favoured total oxidation to CO2 can be completely supressed. This allows a nearly 100 % carbon efficiency in the transformation reaction of glucose to methyl formate in methanolic solution at mild reaction conditions of 90 °C and 20 bar oxygen pressure. By using powerful spectroscopic tools like 51V‐NMR and continuous wave EPR we could unambiguously prove that the vanadate‐methanol‐complex[VO(OMe)3]n is responsible for the selectivity shift in methanolic solution compared to the aqueous reference system.

Effect of sea buckthorn biomass on oxidation stability and sensory attractiveness of cereal biscuits

The purpose of this work was to investigate the effect of 5%, 10%, 15%, and 20% additions of sea buckthorn biomass to cereal biscuits and analyze the oxidation stability and sensory attractiveness. The oxidation stability of the biscuits was evaluated with an Oxitest reactor under 6.0 bar oxygen pressure at 110 °C, and the increase in the induction period with increasing addition of sea buckthorn biomass up to 15% level was found. An increase in the induction period was observed with increasing addition of sea buckthorn biomass up to 15% level. In contrast, 20% addition of biomass caused a decrease in the induction period by 30 h compared to the induction period with 15% biomass addition. Sensory analysis revealed that brittleness and hardness of the biscuits decreased with increasing addition of sea buckthorn biomass. Overall, the most sensory acceptable from the point of view of assessors were biscuits with 15% addition. It was concluded that 15% addition of sea buckthorn biomass to cereal biscuits was the most optimal content in terms of oxidation stability and sensory attractiveness. The results of this study pointed out the excellent possibilities of fortification of cereal products with sea buckthorn biomass.

Recovery of Gallium from Smartphones—Part II: Oxidative Alkaline Pressure Leaching of Gallium from Pyrolysis Residue

In this article, we examine the selective hydrometallurgical extraction of gallium from pyrolyzed smartphones. Gallium-enriched pyrolysis residue originating from pyrolyzed smartphones was leached using NaOH and gaseous oxygen at elevated temperatures and pressures. The high content of organic carbon in the material strongly influenced the leaching performance. Oxygen, which is indispensable for the dissolution of gallium, also oxidized the organic carbon in the feed so that CO2 was released, which had a neutralizing effect on the alkaline solution. As a result, the CO2 formation complicated the accurate process control as the leaching temperature increased. The highest gallium yield of 82% was obtained at 180 °C, 5 g/L NaOH and 5 bar oxygen pressure. Decreased temperatures, NaOH concentrations and oxygen pressures resulted in lower leaching yields but with a higher selectivity for Ga. Temperatures higher than 180 °C resulted in extensive carbon oxidation, NaOH consumption and the coextraction of Cu and Ag. We propose that those conditions also facilitated the formation of water-soluble organic compounds, which would also influence the metal dissolution.

A Carbon Catalyst Co-Doped with P and N for Efficient and Selective Oxidation of 5-Hydroxymethylfurfural into 2,5-Diformylfuran.

A newly designed N and P co-doped carbon material has been developed to catalyze the conversion of 5-hydroxymethylfurfural (HMF) to 2,5-furandialdehyde (DFF) with unprecedented yield and selectivity and demonstrating a synergistic effect between the heteroatoms. The desired catalyst was first synthesized via a pyrolysis method using urea as the nitrogen and carbon source followed by calcination with phytic acid solution as the phosphorus source. The mass ratio of phytic acid to C3 N4 and calcination temperature were varied to investigate their effects on catalyst synthesis and microstructure as well as subsequent catalytic activity in simple reaction systems under oxygen. The effect of reaction conditions on the final HMF conversion and DFF selectivity were also investigated systematically. The P-C-N-5-800 catalyst obtained with the optimized annealing temperature of 800 °C and mass ratio of phytic acid/C3 N4 of 5 enabled a 99.5 % DFF yield at 120 °C for 9 h under 10 bar oxygen pressure, being the highest among any reported metal-free heterogeneous catalyst to date. The excellent performance of P-C-N-5-800 could be ascribed to the synergy between N and P heteroatoms as well as the high content of graphitic-N and the P-C species within the carbon structure. Reusability studies show that the P-C-N-5-800 catalyst was stable and reusable without deactivation. These results strongly suggest that P-C-N-5-800 is a promising catalyst for large-scale production of DFF in a green manner.

Broccoli byproducts for protection and co-delivery of EGCG and tuna oil

Neat epigallocatechin gallate (EGCG) has low bioavailability and tuna oil (TO) is prone to oxidation. Broccoli byproducts (BBP) were used for preparing TO-BBP (25% oil, dry basis) and TO-EGCG-BBP (20% oil and 20% EGCG, dry basis) powders. The gross composition and surface fat of powders and morphology of reconstituted emulsions were characterized. Oxipres® data (80 °C, 5 bar oxygen pressure) showed that the TO-EGCG-BBP formulation was more oxidatively stable [Induction period (IP) > 100 h] than TO-BBP (IP ~ 20 h). During in vitro digestion, 90% of EGCG was recovered in the whole intestinal digesta of the TO-EGCG-BBP formulation compared to 76% for the EGCG-BBP formulation and 66% for the neat EGCG. The use of BBP for co-delivering EGCG and TO increases oxidative stability of TO and improves EGCG stability during in vitro digestion. This study highlights the potential for formulating functional ingredient with BBP and contribute to food waste reduction.

Slurry loop tubular membrane reactor for the catalysed aerobic oxidation of benzyl alcohol

A novel reactor that combines a catalyst slurry flowing inside a loop configuration, incorporating a tubular membrane (Teflon AF-2400) for controlled oxygen delivery was designed and employed for the aerobic oxidation of benzyl alcohol using a 1 wt% Au-Pd/TiO2 powdered catalyst. This reactor keeps the liquid phase saturated with oxygen, while avoiding the creation of bubbles in it, thus enhancing operation safety. Experimental results in batch mode compared with those of a conventional autoclave demonstrated that the slurry loop membrane reactor reached a similar oxidation turnover frequency (20,000–25,000 h−1) with comparable values of benzaldehyde selectivity (∼70%). Continuous operation was achieved by using a crossflow filter connected to the loop to keep the catalyst from exiting the reactor. Using a 60 cm long tubular membrane, with the slurry flow circulating at 10 mL/min, continuous reaction was performed at 100–120 °C, 0–5 bar oxygen pressure and 1.2–5.0 g/L catalyst loading. Selectivity to benzaldehyde increased by either decreasing the reaction temperature or increasing the external oxygen pressure. The oxygen consumption rate decreased linearly with the catalyst loading, suggesting negligible gas-liquid mass transfer resistance. This was further evidenced by doubling the length of the tubular membrane, which had no effect on the oxidation turnover frequency. The slurry loop membrane reactor showed significantly better performance than packed-bed membrane microchannel reactors, and similar performance as that of a trickle-bed capillary reactor. This reactor can be implemented for a wide range of applications, which rely on the use of powder catalyst, are limited by gaseous reactant availability and require safe operation.

Co‐Al Hydrotalcites: Highly Active Catalysts for the One‐Pot Conversion of Fructose to 2,5‐Diformylfuran

AbstractIn this work, a series of Co−Al hydrotalcites were synthesized in the molar ratio of 1:1(cat‐3), 2:1(cat‐4), 3:1(cat‐5). These synthesized Co−Al hydrotalcites were characterized by different characterization techniques such as XRD, XPS, FT‐IR, SEM, EDX, TGA, and N2 physical adsorption. The catalytic properties of the prepared Co−Al hydrotalcites in different molar ratio were investigated for the dehydration of fructose to 5‐hydroxymethylfurfural (HMF), and selective oxidation of the HMF into 2,5‐diformylfuran (DFF). The complete conversion of HMF led to 95% yield of DFF at 120 °C under 3 bar oxygen pressure in dimethyl sulfoxide (DMSO) for 6 h. DFF in the yield of 87% with 100% conversion of fructose could be achieved in a one pot and two‐step reaction using Co−Al calacite in ratio of 2:1(cat‐4). A 77% yield of DFF was obtained in one‐pot and one‐step reaction using the same hydrotalcite catalyst. A DFF yield of 59% was achieved in a one pot and one‐step reaction using air as oxidant. After completion of the reaction, the catalyst can be separate very easily and can be reused up to four times without any significant loss in its catalytic activity.

Multitechnique determination of metals and non-metals in sports supplements after microwave-assisted digestion using diluted acid

Microwave-assisted digestion using diluted acid under oxygen pressure is proposed for sample preparation of sports supplements and subsequent determination of Ca, Cu, Fe, K, Mg, Mn, Na, Zn, P and S by inductively coupled plasma-optical emission spectrometry (ICP-OES). In this sense, 1350 mg of sport supplement were digested in a microwave oven using only 6 mL of 5 mol L−1 HNO3 under 5 bar of oxygen pressure during 15 min. Accuracy of proposed method was evaluated by recovery tests using a standard solution and using a certified reference material. Suitable recoveries (ranging from 86% to 108%) were obtained in both evaluations for all analytes. Results were compared with those obtained by conventional microwave-assisted digestion (without oxygen pressure) for further analytes determination by ICP-OES, and no statistical differences were observed (Student's t-test, confidence level of 95%, p > 0.05). The precision of proposed method was evaluated in terms of repeatability (RSDs ≤3%) and intermediate precision (RSDs ≤7%), and suitable results were obtained for all analytes. In addition, the limits of detection for all analytes using proposed method were lower than those obtained using conventional digestion in view of use a high sample mass and a diluted acid solution for sample digestion. The use of diluted acid reduces risks to analyst – since it eliminates the concentrated acid handling; reduces the consumption of reagents and, consequently, the waste generation, in accordance with the principles of green chemistry. Using the proposed method was possible to perform the determination of ten elements in a single analysis with suitable precision and accuracy. Six sport supplements were analyzed and the results are alarming because in most cases they were in disagreement with those informed on the label. Thus, a suitable quality control of sports supplements should be performed and the proposed method is a green, safe, accurate, precise and sensitive alternative for this purpose.

New and feasible method for total phosphorus and sulfur determination in dietary supplements by ion chromatography

The microwave-assisted digestion of dietary supplements using diluted nitric acid under oxygen pressure for subsequent indirect determination of phosphorus and sulfur by ion chromatography (IC) was proposed. Different concentrations of nitric acid (from 1 to 14.4 mol L−1) and oxygen pressures (from 5 to 20 bar) were evaluated. Dissolved organic carbon and residual acidity were used to choose the most suitable digestion condition. Using the proposed method, it was possible to digest up to 1350 mg of dietary supplements using only 5 mol L−1 HNO3 under 5 bar of oxygen pressure. Comparing to conventional digestion procedure it was possible to digest up to 60% higher sample mass using HNO3 around 30% more diluted. Recoveries ranging from 96 to 102% were obtained when recovery tests using a standard solution or a mixture with certificate reference material were carried out. The concentration of P and S indirectly determined by IC agreed with the results obtained by conventional microwave-assisted digestion using concentrated HNO3 and subsequent determination by inductively coupled plasma optical emission spectrometry.

Synthesis and Characterization of Oligomeric Ionic Liquid/Heteropoly Acid Composite as a New Heterogeneous Catalyst through Anion-Exchange Method for Selective Cyclohexane Oxidation with Molecular Oxygen under Solvent-Free Conditions

In this work, we investigated solvent-free oxidation of cyclohexane using oligomeric ionic liquid (OIL)/heteropoly acid (HPA) composite with molecular oxygen under solvent-free conditions. OIL has six imidazolium cores which synthesized in three successive stages and was anion-exchanged by phosphomolybdic acid (H3PMo12O40, PMo) to synthesize OIL/HPA composite. OIL and OIL/HPA composite were characterized by different techniques such as, FT-IR, UV, BET, TGA, XRD, FESEM, EDX, and TEM. Optimal reaction conditions were obtained by evaluating the effective parameters on the reaction including temperature, time, oxygen pressure, and amount of the catalyst. The main product of the reaction in the presence of 20 mg of catalyst and 5 mL of cyclohexane was cyclohexanone by 21% conversion and 75% selectivity at 110 °C and 20 bar oxygen pressure after 5 h. The OIL/HPA showed good stability under reaction conditions and maintained its catalytic activity up to five cycles with little decrease in reaction conversion.

Extraction Coupled Oxidative Desulfurization of Fuels to Sulfate and Water-Soluble Sulfur Compounds Using Polyoxometalate Catalysts and Molecular Oxygen

Our contribution demonstrates a new way of fuel desulfurization, namely selective oxidation of organic S-compounds present in fuels to water-soluble sulfur compounds followed by in situ extraction of the latter into an aqueous phase. Different from common oxidative desulfurization (ODS) processes, we demonstrate a technique that converts sulfur compounds in fuel to a large extent to sulfate (60–70%) using oxygen as the oxidant and an aqueous H8PV5Mo7O40 (HPA-5) solution as the catalyst phase. Other water-soluble desulfurization products are sulfoacetic acid (SAA) with a share of 10–20%, 2-sulfobenzoic acid (2-SBA), and 2-(sulfooxy)benzoic acid (2-SOBA), the latter two with a share of <10%. The new desulfurization method has been optimized for removing benzothiophene from isooctane, giving the best results with a degree of desulfurization of 99% applying 120 °C, 20 bar oxygen pressure, and 1000 rpm of 6 h reaction time using a volume water/oil ration of 10/1. Furthermore, we also successfully demonstrated ...

Catalytic Conversion of Fructose and 5-Hydroxymethylfurfural into 2,5-Diformylfuran over SBA-15 Supported Ruthenium Catalysts

In this study, the mesporous SBA-15 was prepared and used to graft biimidazole groups, which were used to anchor Ru3+ to give rise to a new ruthenium catalyst (SBA-15-Biimidazole-Ru). The structure of the SBA-15-Biimidazole-Ru catalyst was well characterized and used for the aerobic oxidation of 5-hydroxymethylfurfural (HMF) into 2,5-diformylfuran (DFF). Several important parameters were studied and found that the reaction solvent and oxygen pressure showed a crucial role in the activity of the as-prepared SBA-15-Biimidazole-Ru catalyst. HMF conversion of 96.9% and DFF yield of 88.7% were achieved after 11 h at 110 °C under 15 bar oxygen pressure. One important characteristic of the SBA-15-Biimidazole-Ru catalyst is that it was very stable without loss of its catalytic activity during the recycling experiments, which was due to the strong interaction between the Ru3+ and the Biimidazole groups on the surface of SBA-15. Finally, the direct conversion of fructose into DFF was also performed by the use of Amberlyst 15 and SBA-15-Biimidazole-Ru as two binary catalysts. The dehydration of fructose over Amberlyst 15 catalyst and the subsequent oxidation of HMF over SBA-15-Biimidazole-Ru catalyst afforded DFF with an overall yield of 72.4%.

Synthesis of 2,5-furandicarboxylic acid by the aerobic oxidation of 5-hydroxymethyl furfural over supported metal catalysts

Supported Pt catalysts are synthesized, characterized and are used in the liquid phase air oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA). Under the optimum reaction conditions of a stepwise increase in the reaction temperature (75 and 140 °C for 12 h each), we achieved as high as 96 % FDCA yield in presence of 1 bar oxygen pressure over Pt/γ-Al2O3. It is shown that as the oxygen pressure increases (1–10 bar), the FDCA yields decrease, since at higher partial pressure of oxygen, overoxidation reactions of substrate and product(s) are possible. It is interesting to note that even with air as an oxidant, we obtained similar yields of FDCA as that with oxygen. Moreover, the effects of base (weak or strong), its concentration (equimolar or excess) were studied in detail. It is important to increase the reaction temperature in a stepwise manner to achieve higher yields of FDCA since at higher temperatures HMF undergoes self-degradation and thus the yields of FDCA decrease. The self-degradation of HMF is also proved by undertaking the reaction under nitrogen environment. The study on the effect of substrate-to-catalyst ratio is done to improve up on the economics of overall process. The effect of supports (reducible and non-reducible) and their oxygen storage capacity is discussed and is proposed to be one of the factors to change the course of reaction. Furthermore, we have shown that FDCA formed in the reaction can be successfully isolated (91 %, isolated yield) in the pure form and its purity is confirmed by NMR, melting point, and elemental analysis. The catalysts were characterized with X-ray powder diffraction, transmission electron microscopy and inductively coupled plasma-optical emission spectroscopy techniques.

The oxidative resistance of polymeric geosynthetic barriers (GBR-P) used for road and railway tunnels

The results of autoclave tests according to DIN EN ISO 13438 (method C) and conventional oven tests in line with DIN EN 14575 are presented for the evaluation of the resistance to oxidation of geosynthetic barriers GBR-P based on polyethylene. These GBR-P products are used as a barrier layer against water in road and railway tunnels. The residual mechanical stability of the exposed materials was determined by tensile testing. The remaining activity of the stabiliser was investigated using the OIT method. The results of both accelerating test methods are discussed and compared in detail. Based on autoclave tests at three temperatures (e.g. 60, 70 and 80 °C) and 50 bar oxygen pressure, and additionally two more measurements at 80 °C and 10 and 20 bar oxygen pressure, a modified Arrhenius extrapolation is used for an assessment of the expected service time of one of the GBR-P products.