Higher Degree Of Conversion Research Articles

SELECTIVE HYDROGENATION OF ISOPRENE, PIPERYLENE AND THEIR MIXTURES ON SKELETAL NICKEL CATALYSTS

Results of the hydrogenation process of isoprene and piperylene mixtures, as well as their mixtures on multicomponent skeletal nickel catalysts are reported in this article. Hydrogenation of piperylene and isoprene proceeds at a higher rate (W=215-220 cm3/min·g Ni) on Ni-Mo-Cu alloy catalyst than on skeletal nickel (W=112-115 cm3/min·g Ni). The results of chromatographic analysis indicate that the hydrogenation of piperylene proceeds with high selectivity. The selectivity coefficient Кs is 0.95 and 0.98 on skeletal nickel and Ni-Mo-Cu catalyst, respectively. At hydrogenation of the piperylene-isoprene mixture the piperylene conversion rate (P > J) is prevailed. At piperylene conversion degree P=50 % the isoprene J conversion is 35-37 % on Renea Nickel. 34 % on Ni-Mo-Cu catalyst. The selectivity degree of hydrogenation of this mixture is Sp-i = 0.34-0.36 on Renea Nickel, Sp-i = 0.40 on Ni-Mo-Cu. It was found that during hydrogenation of piperylene and isoprene mixtures on Ni-Al-Mo-Cu (42-50-3-5 %) catalysts the mono- and disubstituted acetylenes are saturated with a high degree of conversion compared with isoprene.

Biosynthetic fuels: A marriage of renewable resources and chemical thermodynamics

Terpenes represent a highly diverse group of natural products with wide applications. Terpenoid structures can be derived from different renewable sources and utilized as fuels. Application as fuels requires hydrogenation of the double bonds in the respective molecules to ensure clean combustion. This hydrogenation can be performed either directly with elemental hydrogen or indirectly via transfer hydrogenation with a Liquid Organic Hydrogen Carrier. In this study, the thermochemical fundamentals of these reaction has been evaluated. For this task, for a first time a combination of experimental thermochemistry and quantum-chemical molecular modelling has been applied. The results show the hydrogenation of the respective structures is thermodynamically highly favourable. Correspondingly, dehydrogenation would be comparatively unfavorable. Yet, for a fuel no dehydrogenation is required. As an alternative to conventional hydrogenation, transfer hydrogenation, which is often subject to partial conversions due to limitations by the reaction equilibrium, can be realized with a high degree of conversion. While the entropy of reaction for hydrogen transfer from cyclohexyl-structures to terpene structures is close to zero, the enthalpy of reaction is highly negative. This leads to a Gibbs energy of reaction which is clearly negative and ensures a large thermodynamic driving force for the reaction. As a consequence, downstream processing, which is usually very demanding for transfer hydrogenations, is comparatively easy. These finding underline the great potential of these bio-derived substances for conversion into sustainable fuels.

Kinetic investigation of aschalcha heavy oil oxidation in the presence of cobalt biocatalysts during in-situ combustion

The catalytic effect of cobalt tall oil and cobalt sunflower oil catalysts on the oxidation kinetics of heavy crude oil was investigated in this study. Comprehensive kinetic analyses, employing differential scanning calorimetry, thermogravimetric analysis, and kinetic modeling techniques, revealed that the presence of these catalysts significantly influenced the oxidation behavior of heavy oil. The catalysts exhibited pronounced shifts in the DSC and TG curves towards lower temperatures, indicating facilitated initiation of oxidation reactions at lower onset temperatures. Quantitative kinetic parameters, including activation energies and frequency factors, were determined using the Friedman and Kissinger-Akahira-Sunose analyses. The cobalt tall oil catalyst demonstrated superior performance, effectively lowering the activation energy barrier and increasing oxidation rates, particularly at higher conversion degrees. Catalyst characterization techniques, including X-ray diffraction, scanning electron microscopy, and Fourier-transform infrared spectroscopy, revealed the formation of highly crystalline cobalt oxide nanoparticles with optimal dispersion and size distribution, as well as the presence of favorable functional groups for surface interactions. The results elucidated the role of these catalysts in facilitating the oxidation process through the provision of active sites, altered reaction pathways, favorable steric environments, and efficient oxygen activation capabilities. These findings contribute to the development of efficient catalytic systems for heavy oil upgrading processes and offer insights for further optimization of catalyst properties to achieve desired oxidation kinetics behavior.

Modified Hybrid Hydroxyapatite-Silver Nanoparticles Activated via a Blue Light Source in Various Concentrations in Two-Step Self-Etch Adhesive to Caries-Affected Primary Dentin.

Aims: To evaluate hydroxyapatite-silver (HA-Ag) hybrid nanoparticles (NPs), as an antibacterial agent when integrated in self-etch (SE) adhesive. Blue light activated HA-Ag hybrid NP incorporation on mechanical properties, degree of conversion (DC), and microtensile bond strength (μTBS). Method: Eighty primary molar teeth have carious lesions reaching the dentin but not involving the pulp. The infected dentin was removed and carious-affected dentin (CAD) was preserved. Forty samples were inoculated with Streptococcus mutans. All primary teeth (n = 80) were allocated into four groups based on the incorporation of HA-Ag hybrid NPs in different concentrations (0%, 1%, 5%, and 10%). Group 1: 0% HA-Ag hybrid NPs + Clearfil SE bond primer, group 2: 1% HA-Ag hybrid NPs + Clearfil SE bond primer, group 3: 5 wt% HA-Ag NPs + Clearfil SE bond primer, and group 4: 10 wt% HA-Ag NPs + Clearfil SE bond primer. The survival rate assessment of S. mutans was conducted on 40 inoculated samples. On the remaining primary teeth (n = 40), Clearfil SE bonding agent was applied uniformly via a blue light source. The composite buildup was performed on the samples and μTBS and failure analysis assessed. Fourier transform infrared spectroscopy was performed to assess DC. Survival rates of S. mutans and μTBS among the tested groups were compared using ANOVA and Tukey post hoc analysis. Results: 10 wt % HA-Ag NPs + Clearfil SE bond primer exhibited the highest level of antibacterial efficacy (0.14 ± 0.02 CFU/mL) against S. mutans. The highest μTBS (18.38 ± 0.78 MPa) at the composite/CAD interface was in group 2 (1 wt % HA-Ag NPs + Clearfil SE bond primer + Clearfil SE bonding agent + activation with a blue light source). The highest DC was observed in the control group with Clearfil SE bond primer + Clearfil SE bonding agent + activation with a blue light source. Conclusion: 1 wt% HA-Ag hybrid NPs showed enhanced antibacterial effectiveness, DC, and bond strength of the SE adhesive to the primary CAD.

Light-curable urushiol enhanced bisphenol A glycidyl dimethacrylate dentin bonding agent

ObjectivesThe low durability of composite resin restorations can be attributed to the degradation of the resin dentin bonding interface. Owing to the presence of hydrophilic components in the adhesive, the integrity of the resin dentin bonding interface is easily compromised, which, in turn, leads to a reduction in bond strength. The hydrophilic nature of the adhesive leads to water sorption, phase separation, and leaching of the resin component. Therefore, hydrophobic adhesives could effectively be used to stabilize the integrity and durability of the resin dentin bonding interface. MethodsWe synthesized a novel hydrophobic dentin adhesive by partially replacing bisphenol A glycidyl dimethacrylate (Bis-GMA) with a light-curable urushiol monomer. The properties of the produced adhesive, including the degree of conversion, viscosity, contact angle, water sorption/solubility, and mechanical strength, were comprehensively examined and compared to those of the commercially adhesive Adper Single Bond2 as a positive control. The adhesive properties were determined using microtensile bond strength measurements, laser confocal microscopy, scanning electron microscopy observations, and nanoleakage tests. Finally, the novel adhesive was subjected to biocompatibility testing to determine its potential cytotoxicity. ResultsAt a light-curable urushiol content of 20 %, the synthesized adhesive exhibited high degrees of conversion and hydrophobicity, low cytotoxicity, good mechanical properties, and outstanding adhesive strength. ConclusionsThe introduction of the light-curable urushiol into dentin adhesives can significantly enhance their hydrophobic, mechanical, and bonding properties, demonstrating potential to significantly improve restoration longevity. Clinical significanceThe integration of light-curable urushiol has endowed the experimental adhesives with several enhanced functionalities. These notable benefits underscore the suitability of this monomer for expanded applications in clinical practice.

Application of a Scaled‐up Dielectric Barrier Discharge Reactor in the Trace Oxygen Removal in Hydrogen‐Rich Gas Mixtures at Ambient and Elevated Pressure

AbstractDielectric barrier discharges (DBDs) are frequently utilized in various gas conversion processes. For industrial applications a low flow resistance and scalability are crucial. In this study a tenfold scaled‐up reactor based on a surface dielectric barrier discharge (SDBD) was employed for the removal of oxygen traces from H2/N2/O2 gas mixtures. The conversion efficiency of the reactor with ten electrode configurations was investigated for different admixtures of O2, and high degrees of conversion were observed that decreased with increasing flow rate, but remained constant when raising the pressure to 2 bar(g). A new generator based on silicon carbide field‐effect transistors (SiC‐FETs) was used and compared to a generator based on classical metal oxide semiconductor field‐effect transistors (MOS‐FETs).

Hydrogen-donating capacity of hydrothermal system in catalytic and non-catalytic desulfurization of sulfur compound of unconventional crudes and residues: Deuterium tracing study

This research tries to figure out the role of water as a green and environmental hydrogen-donor solvent for catalytic and non-catalytic hydrothermal desulfurization (HT-DS) of dibenzyl sulfide (DBS) as a sulfur model compound of unconventional crudes and petroleum residues using deuterium tracing techniques. In addition, the ordinary water (H2O) was replaced by heavy water (D2O) to ease the evaluation of the donating capacity of water as a hydrogen donor during HT-DS process of selected sulfur model compound. The hydrothermal conversion (HTC) of dibenzyl sulfide and donating performance of heavy water were deeply investigated through comprehensive analysis of the initial and converted obtained products encompassing gas, liquid, and solid phase (if obtained), using different techniques GC, GC–MS, FTIR, high resolution deuterium (2H) NMR, and isotope analysis. The results of the non-catalytic and catalytic HTC of DBS show high conversion degree of 75.79 and 97.34 %, respectively, resulting in the formation of desulfurized compounds consisting of bibenzyl and stilbene. Additionally, the results of the deuterium tracing study proved the role of water as a green and environmental hydrogen-donor solvent during HT-DS of DBS, verified by considerable deuterium substitution (H/D exchanges) in both liquid (converted) and gases products. The results of the GC–MS as a tracing technique showed by molecular weight data the formation of the individual deuterium containing products in liquid and gas phases for both catalytic and non-catalytic HT-DS. Simultaneously, both experimental and DFT results showed that the application of nickel (II) stearate as an oil-soluble catalyst promoted both HTC of DBS. The important finding about the role of water in catalytic and non-catalytic HT-DS of DBS not only enriches the theoretical basis in this area, but also provides a strong support for the combined use of water and catalysts for improving conversion and desulfurization performance, thereby offering insights into the optimization of hydrothermal processes for unconventional sources of energy.

Effects of different LED light curing units on the degree of conversion and microhardness of different composites: FT-IR and SEM-EDX analysis

The aim of this study was to evaluate the degree of conversion (DC), Vickers microhardness (VHN), main components and surface properties of a microhybrid and two bulk-fill composite resins polymerized with second and third generation light emitting diodes (LED). Sixty cylindrical specimens of Filtek™ Bulk-Fill, everX Posterior (bulk technique) and Filtek Z250 (incremental technique) were prepared in plexiglass molds (5 mm in diameter and 4 mm in thickness) and cured with second-generation LED (Woodpecker LED.B) and third-generation LED (Valo) resulting in six groups (n = 10). DC was determined using Fourier transform infrared spectroscopy (FT-IR), and VHN with Vickers microhardness tester. The main components were identified by means of energy-dispersive X-ray spectroscopy (EDX) microanalysis; whereas filler particles and surface properties were analyzed by scanning electron microscopy (SEM). VHN and DC data were analyzed using two-way ANOVA, followed by t-test with Bonferroni correction for pairwise comparison (p < 0.05). When DC and VHN values were evaluated, after polymerization with second and third generation LED, there was a statistical difference in bulk-fill composites, while there was no statistical difference in microhybrid composite. While, the highest DC and VHN values were obtained after polymerization of Filtek Z250 with Valo, the lowest DC and VHN values were obtained with Filtek Bulk-Fill with Woodpecker LED.B. The degree of conversion and microhardness are affected by the structure of the composite resin and LEDs.

Formulation and Characterization of New Experimental Dental Composites with Zirconium Filling in Different Forms.

Short glass fibers are generally used in posterior dental restorations to enhance the mechanical properties and improve the material microstructure. Two resin-based composites (S0 and SF) were formulated and characterized to investigate the influence of zirconium in their characteristics and properties. The organic part of the investigated materials was the same (BisGMA, TEGDMA, and a photochemical polymerization system), and in the inorganic part, besides quart, glassA, and hydroxylapatite with Zn, sample S0 contained strontium glass with zirconium and sample SF contained fiber powder of chopped zirconium. The samples were characterized by the degree of conversion (DC), mechanical properties, water sorption (WS), scanning electron microscopy (SEM), atomic force microscopy (AFM) before and after the WS test, and antimicrobial properties. The results obtained were subjected to one-way ANOVA and Tukey's statistical tests. Both samples had a high DC. Regarding the mechanical properties, both samples were very similar, except DTS, which was higher for the composite without fibers. After 14 days, the WS value of the SF sample was lower than that of the S0 sample. Water caused significant changes in the topography of the SF sample, but thanks to its antimicrobial properties and the diffusion phenomenon, SF had a more pronounced antimicrobial effect. This study shows that the addition of appropriate amounts of Sr-Zr-glass powder gives the material in which it is added similar properties to material containing chopped zirconium glass fiber powder. According to the antimicrobial test results, resin composites containing experimental zirconia fillings can be considered in future in vitro clinical studies for posterior reconstructions with significantly improved mechanical properties.

Tuning conditions for the amine-functionalization of carbonyls formed in biobased polyfurfuryl alcohol

Biobased furan resins (furfuryl alcohol based) are functionalized by taking advantage of a side-reaction occurring during its polymerization. The furan ring-opening reactions yields carbonyls which can be functionalized by reaction with primary amines. Light is shed on unexplored parameters impacting the properties of PFA/Amine systems. First, PFA/Amines were prepared using PFA resins at conversion degree between 0.3 and 0.95. Overall, high conversion degrees (0.9 and above) are best suited to produce rigid materials. In addition, a precipitation process may be used to reach high Tg biobased materials (145 °C). Finally, the impact of the amines’ basicity on the properties of PFA/Amines was investigated. The results highlighted that PFAs at conversion degrees above 0.9 are little affected by the basicity. However, the properties of PFA functionalized at lower conversion degrees are strongly affected by the bases, i.e. high brittleness. This can be circumvented by limiting the functionalization degree to 0.25 and below.

Synthesis and Morphology Characteristics of New Highly Branched Polycaprolactone PCL.

A simple and efficient method for the synthesis of biodegradable, highly branched polycaprolactone (PCL) is presented. The solvent-free (bulk) reaction was carried out via ring opening polymerization (ROP), catalyzed by tin octanoate Sn(Oct)2, and it employed hyperbranched polyamide (HPPA) as a macro-initiator. The core-shell structure of the obtained products (PCL-HPPA), with the hyperbranched HPPA core and linear PCL chains as shell, was in the focus of the product characterization. 1H nuclear magnetic resonance (1H NMR) and elemental analysis confirmed the covalent incorporation of the HPPA in the products, as well as a high degree of grafting conversion of its amino functional groups. Confocal Raman Micro spectroscopy, and especially Time-of-Flight Secondary Ion Mass Spectrometry, further supported the existence of a core-shell structure in the products. Direct observation of macromolecules by means of cryogenic transmission electron microscopy, as well as gel permeation chromatography (GPC), suggested the existence of a minor 'aggregated' product fraction with multiple HPPA cores, which was attributed to transesterification reactions. Differential scanning calorimetry, as well as X-ray diffraction, demonstrated that the PCL-HPPA polymers displayed a similar degree of crystallinity to linear neat PCL, but that the branched products possessed smaller and less regular crystallites.

Experimental investigation of integrated CO2 capture and conversion to syngas via calcium looping coupled with dry reforming of CH4

Calcium looping integrated with dry reforming of CH4 is a promising strategy for CO2 capture and in situ conversion to syngas. This intensified process is usually conducted with bifunctional materials that combine CO2 capture (CaO) and catalytic (Ni) active sites. Herein, the integrated calcium looping/dry reforming process was examined by investigating various bifunctional materials and operating conditions. The Ni loading of materials affected the interaction between active and inert phases, while adding a CaZrO3 promoter enhanced the CO2 capture and catalytic activities and the resistance toward sintering. Conducting experiments with a fluidized bed reactor (700 °C, 3% CH4 in feed) led to nearly complete CH4 conversion and ∼52% utilization of captured CO2 toward syngas production with steady H2/CO ratio close to unity. Temperature comprised a decisive parameter, with low values enabling high degrees of CO2 conversion up to ∼80%. The increase of CH4 concentration in the gas feedstock enhanced the rate of calcination and the conversion of CO2 over its desorption in the gas phase. Co-feeding O2 with CH4 was proposed to mitigate the energy demand, which reduced the reforming selectivity for the partial oxidation reaction and increased the H2/CO ratio of syngas.

Obtaining fuel products by combined hydrogenation of coal and shale

Background: Coal and oil shale are one of the promising types of organic raw materials that can largely compensate and replace petroleum products and gas in the future. Unlike other types of solid fossil fuels oil shales contain significant amounts of hydrogen in organic matter. The possibility of obtaining liquid and gaseous hydrocarbons from a mixture of coal and oil shale similar in composition and properties to petroleum products and natural gas allows us to consider them as important strategic resources.&#x0D; Aim: This article is devoted to the study of the process of obtaining fuel products of co-hydrogenation of coal and shale.&#x0D; Materials and methods: Coal from the Taldykol deposit and slate from the Kiin deposit were taken as objects of research. The process of coal and shale liquefaction was carried out on a laboratory installation at a pressure of 5 MPa and a temperature of 425°C, a reaction time of 1 h. Gas chromatographic and elemental analyses were used.&#x0D; Results: The research results showed that the optimal amount of shale added to coal is 15.0%. The implementation of the co-hydrogenation process under these conditions has increased the yield of liquid products by 10%, namely fractions with a boiling point of up to 200°C from 14.9% to 15.3%, fractions with a boiling point of 200–370°C from 22.1% to 26.4%, fractions with a boiling point above 370°C from 34.6% to 38.8%. Solid residue with a boiling point above 370°C tested as an organic binder for road construction.&#x0D; Conclusion: The proposed process technology also makes it possible to obtain gasoline and diesel fractions, which after appropriate hydrotreating can be used as motor fuels. The addition of oil shale to coal allows the process to be carried out under optimal conditions with a high degree of conversion into liquid products without coke formation. The degree of transformation of the mixture of organic mass of shale and coal is much higher than just coal.

In vitro characterization of a novel resin-based restorative material containing alkaline fillers.

In this study, a comparative evaluation of the physicochemical properties of Cention N and other direct restorative materials was performed. Three restorative materials-a resin-modified glass ionomer (Fuji II LC), an alkasite-based resinous material (Cention N), and a resin composite (Tetric N Ceram)-were characterized in terms of degree of conversion, Knoop hardness number (KHN) ratio, flexural strength, elastic modulus, water sorption, water solubility, microshear bond strength to dentin, immediate microleakage, and radiopacity. The microshear bond strength to dentin and microleakage of Cention N were evaluated with and without the application of an adhesive system (Tetric N Bond Universal). A one-way ANOVA test was used to analyze the data in terms of degree of conversion, KHN ratio, water sorption, water solubility, microshear bond strength to dentin, and radiopacity. A two-way ANOVA test (carried out considering the material type and ethanol aging as factors) was used to analyze the data in terms of flexural strength and elastic modulus. The Kruskal-Wallis test was used to statistically analyze the data on microleakage. A significance level of α=0.05 was used for all tests. Fuji II LC was found to have the highest degree of conversion, water sorption, and microleakage, as well as the lowest flexural strength. Cention N had the highest solubility; when used with an adhesive system, it achieved bond strength and microleakage similar to those of the Tetric N Ceram composite. Tetric N Ceram had the highest degree of conversion, KHN ratio, and radiopacity. Conclusion: The properties of Cention N validate its efficacy as an alternative direct restorative material when used in conjunction with an adhesive system.

A novel low shrinkage dimethacrylate monomer as an alternative to BisGMA for adhesive and resin-based composite applications.

The aim of this study was to develop a mixture of dimethacrylate isomers (PG6EMA) as a potential monomer for dental adhesives and composites. PG6EMA was synthesized de novo and characterized in the presence of ethanol (3%, 6% or 9%). BisGMA/TEGDMA (BTEG, 50/50 wt.%) was used as the resin control. Composites were formulated with 60 wt.% of either PG6EMA or BisGMA (40 wt.% TEGDMA and 70 wt.% filler). DMPA (0.2 wt.%) and DPI-PF6 (0.4 wt.%) were added as photoinitiators, irradiated with a mercury arc lamp (320-500 nm, 500 mW/cm2; Acticure). All materials were tested for polymerization kinetics (near-infrared), viscosity (η) and storage modulus (G', oscillatory rheometry). The composites were further characterized for water sorption/solubility, wet/dry flexural strength/modulus and polymerization stress. Data were analyzed with one-way ANOVA/Tukey's test (α = 0.05). The PG6EMA resins showed lower rates of polymerization compared with BTEG (p = 0.001) but high degrees of conversion (p = 0.002). Solvent concentration did not affect RPMAX but the 6% and 9% mixtures showed higher final DC, likely due to reduced viscosity. PG6EMA had much higher viscosity than BTEG (p <0.001) and lower G' (p = 0.003). Composites modified with PG6EMA have slower polymerization rates (p = 0.001) but higher final DC (p = 0.04) than the control. PG6EMA/TEGDMA showed lower dry/wet flexural strength and comparable dry modulus. The PG6EMA/TEGDMA composite showed a 18.4% polymerization stress reduction compared to the BTEG composite. Both base monomers had similar WS/SL and G'. Within its limitations, this study demonstrated that the newly synthesized PG6EMA was a viable alternative to BisGMA in dental composites.

A mini-review on different polymerization protocols for resin-based dental composites

Biocompatibility is one of the major prerequisites for safe clinical application of materials. Dental resin composites may release their components into oral environment, which can lead to adverse reactions. Several studies have identified that many organic components of composites resin, such as bisphenol-A-glycidyl-methacrylate (Bis-GMA), triethylene glycol dimethacrylate (TEGDMA), urethane dimethacrylate (UDMA) and 2-hydroxyethyl methacrylate (HEMA) show a cytotoxic profile. Cytotoxicity is mainly sustained by free monomers released after polymerization process. Direct restorations are polymerized at body temperature by visible light emitting lamps, but the conversion from monomer to polymer after light-curing is never complete. To improve the degree of conversion of resin-based composites, additional curing protocols performed at increased temperatures, such as heat-curing, can be employed. Polymerization reaction plays a key role in the conversion of the free monomers into polymers and resin-based composites with high degree of conversion might show higher biocompatibility. The aim of this mini-review is to report current knowledge about the cytotoxicity of different composite resins, cured in two different ways. Further studies are necessary to better understand the relationship between the cytotoxicity and the degree of polymerization of resin-based composites.

NiFe2O4/biochar decorated porous polymer membranes for the flow-through photo-Fenton degradation of tetracycline

Herein, coffee grounds derived biochar was used as support for the fabrication of NiFe2O4/biochar composite particles. The composites achieved up to 10x higher turnover frequencies (TOF) in the photo-Fenton degradation of tetracycline (20 mg/L) in batch compared to the pure NiFe2O4 particles. This could be correlated to a decreased agglomeration, lower band gap energy and electronic interaction with the biochar. The hydrophobic support further enabled the incorporation of the NiFe2O4/biochar powders into porous polyethersulfone (PES) membranes via film casting cum phase separation. The resulting about 150 µm thick porous flow-through membrane reactors achieved high degrees of conversion (95–99 %) at a flux of 100 L/m2h in the continuous photo-Fenton degradation of tetracycline (20 mg/L) in water. We could further show that the TOF values are 5-20x times higher in flow-through the catalytic membranes compared to the NiFe2O4/biochar catalyst particles used in batch mode. We also demonstrated that our photocatalytic membranes can remove low concentrations of tetracycline (2 and 0.2 mg/L) toward values below the detection limit of the used mass spectrometry analysis. Monitoring the leaching of Ni and Fe from one membrane over 28 h of flow-through revealed that Ni predominantly leaches from the incorporated NiFe2O4/biochar, which, however, did not lead to any loss of the catalytic activity. Moreover, we found that the residence time in the membrane has a direct influence on the tetracycline degradation pathways and the resulting product profile, which represents a novel approach for tuning Fenton-like reactions towards specific products.

Degradation kinetics of epoxidized soybean oil composites filled with sisal fiber

AbstractEpoxidized soybean oil (ESO) composites were cured with methyl tetrahydrophthalic anhydride (MTHPA) and 2,4,6‐tris(dimethylaminomethyl)phenol (DEH 35) as a catalyst, sisal fibers were added at 10% and 30% of percent per weight. Composites curing was monitored using Fourier transform infrared spectroscopy, whereas the thermal stability and the degradation kinetics were investigated using thermogravimetry (TG). ESO/MTHPA/DEH35/S10 and ESO/MTHPA/DEH35/S30 composites displayed curing temperatures approximately 100°C lower related to ESO/MTHPA/DEH35, as well as higher degree of conversion. Sisal addition improved the thermal stability, shifting the weight loss shifting the weight loss onset to higher temperature (from 82 to 120°C). Thermal degradation energy was determined using Friedman, Kissinger‐Akahira‐Sunose and Ozawa‐Flynn‐Wall models. Sisal significantly increased , especially in the intermediate phase (α = 0.2 and 0.8). The degradation kinetics was investigated by TG, and the degradation mechanisms modeled using Kamal‐Sourour, Sestack‐Berggren, and 1st order (F1), showed excellent fit, with R2 &gt; 0.99. Acquired results demonstrate that sisal fiber addition benefited the curing process and increased the thermal stability of ESO composites.

Fundamentals of enhanced oxygen releasability of Mn-Na2WO4/SiO2 through cofed water for efficient oxidative coupling of methane in a chemical looping mode

The oxidative coupling of methane (OCM) to C2H6 and C2H4 (C2-hydrocarbons) is an industrially attractive reaction, which has not yet been commercialized. Apart from the low selectivity to C2-hydrocarbons at high degrees of CH4 conversion, another substantial drawback is the necessity to use pure O2 when this oxidant and methane are cofed. Original OCM studies used an approach called chemical looping OCM (CL-OCM) that consists of alternating feeding of methane and air for product formation and catalyst reoxidation, respectively. The developed catalysts, however, suffer from their low ability to provide lattice oxygen for the desired reaction. Herein, we demonstrate that this catalyst property can be significantly improved when performing CL-OCM over Mn-Na2WO4/SiO2 catalysts in the presence of water. In comparison to water-free CL-OCM, both methane conversion and C2-hydrocarbons selectivity increase resulting in at least doubling of the yield of these products. The selectivity to ethylene of about 53 % was obtained at about 24 % CH4 conversion. The total selectivity to C2-hydrocarbons was about 76 %. The analysis of selectivity-conversion relationships for C2H4, C2H6, CO and CO2 proved that water does not alter their general formation pathways but influences the kinetics of their formation.In situ X-ray diffraction, in situ UV–vis spectroscopic, and temperature-programmed tests (H2-TPR and O2-TPD with or without cofed H2O) showed that Mn2O3 acts as the oxygen carrier in CL-OCM. In-situ DRIFTS proved the presence of O2– and O22–. They can interact with water yielding OH radicals that accelerate CH4 conversion.

Unveiling the Role of Key Parameters during Molecular Growth for Optimal Poly(glycerol sebacate) Synthesis

AbstractPoly(glycerol sebacate) (PGS) belongs to the hyperbranched polyesters family (HBP), which possesses an extensive variety of applications due to its tunable chemical and mechanical properties, together with its biocompatibility and biodegradability. However, the understanding of PGS synthesis becomes a challenge due to the lack of consistency when determining its synthesis parameters. Understanding these parameters is fundamental to control PGS synthesis and obtain a scalable and reproducible final product for biomedical applications. To unveil their effect on diverging PGS properties, diols are used as glycerol analogs and the reaction is chemically and thermally monitored, suggesting a heterogeneous reactivity of the exposed hydroxyl groups. Also, confinement of the prepolymerization is proven to be fundamental In order to maintain the equimolar ratio of initial monomers during synthesis. Early stages of the polycondensation (first 4 h) tend to linear and less branched oligomers by consuming primary hydroxyls rather than secondary hydroxyls. However, physicochemical characterization determines that a high degree of conversion (40%) is reached during these early stages. Afterward, the oligomers tend to condense through the secondary hydroxyls into a more crosslinked elastomer. This study demonstrates how hydroxyl affinity, water presence, and glycerol loss are crucial for the scalability and reproducibility of its final product.