Higher Degree Of Conversion Research Articles

Conversion kinetics of rapid photo-polymerized resin composites

ObjectiveTo measure the degrees of conversion (DC), conversion kinetics, and the effect of post-irradiation time on rapid photo-polymerized bulk-fill resin composites under conditions equivalent to clinical depths of 1 and 4mm. Methods36 specimens (n=3), based on two resin composites incorporating PowerCure rapid-polymerization technology in two consistencies (PFill; PFlow) and two comparators with matching consistencies (Eceram; EFlow), were investigated from the same manufacturer (Ivoclar AG, Liechtenstein). Specimens were prepared within 4mm diameter cylindrical molds, of either 1mm or 4mm depths respectively, to simulate near-surface and deep locations in a bulk-fill restoration. The independent variables in this study were: materials, thickness and time. Two high irradiance polymerization protocols were utilized for PowerCure materials: 2000 and 3050mW/cm2 for 5 and 3s, respectively. A standard (1200mW/cm2) polymerization protocol was used with control materials. FTIR was utilized to measure DC in real-time for 24h post-irradiation. The data were analyzed using Welch’s-ANOVA, Games-Howell post-hoc test, kinetic dual-exponential sum function and independent sample t-tests (p=0.05). ResultsThe DC of the materials ranged between 44.7–59.0 % after 5min, which increased after 24h reaching 55.7–71.0 % (p<0.05). Specimen thickness did not influence the overall DC. At 5min, the highest DC was shown in EFlow. But PFlow, irradiated for 3s and 5s exhibited comparable results (p>0.05). PFill composite irradiated with the 3s and 5s protocols did not differ from ECeram (p>0.05). Specimen thickness and material viscosity affected polymerization kinetics and rate of polymerization (RPmax). Faster polymerization occurred in 1mm specimens (except PFill-5s and ECeram). PFill and PFlow exhibited faster conversion than the controls. RPmax varied across the specimen groups between 4.3–8.8 %/s with corresponding DC RPmax between 22.2–45.3 %. SignificancePolymerization kinetics and RPmax were influenced by specimen thickness and material viscosity. PFill and PFlow materials produced an overall comparable conversion at 5min and 24h post-irradiation, despite the ultra-short irradiation times, throughout the 4mm specimen thickness.

Dehydration of rhyolite: activation energy, water speciation and morphological investigation

Rhyolite is an extrusive, igneous rock of aluminosilicate composition that upon rapid cooling forms obsidian. Obsidian is amorphous and contains limited water portions ( 5 mass%). In the current study, kinetics of hydrous rhyolite dehydration were investigated by thermogravimetry up to 1000 °C, at heating rates of 2.5, 5, 10 and 20 °C min−1 and under inert atmosphere. The mass loss is approx. 7.6 mass%, occurs along wide temperature range (100–800 °C) and is solely attributed to the release of molecular water ((H2O)m) and hydroxyl groups (OH). Rhyolite dehydration was considered as a solid-state reaction, and the apparent activation energy (Ea) of dehydration was calculated throughout the whole conversion range (a) by applying the isoconversional Friedman and advanced Vyazovkin methods. Both methods revealed inverse sigmoid trend in Ea values versus conversion degree, possessing almost stable value of 61 ± 5 kJ mol−1 for Friedman method and 59.44 kJ mol−1 for Vyazovkin method on conversion range between 0.25 and 0.75, and sharp increase at higher conversion degree. The intensive change in Ea during dehydration progression is attributed to the change in releasing species (from (H2O)m to OH). Raman and FT-IR spectroscopy analyses of raw and partially dehydrated samples at different stages revealed that up to 300 °C mainly (H2O)m is diffused out of the material causing sample enrichment in OH groups. OH release, which occurs at relatively higher temperature, is accompanied by increase in apparent Ea value of dehydration. Concerning microstructure of raw rhyolite, it exhibits a network of micro-fractures which serve as water release routes. Upon heating, more and wider fractures are created. At 600 °C, fractures merging occurs creating voids, which constitute forerunners of the expansion phenomenon. Further temperature increase causes material softening allowing local plastic deformation, which under the high pressure that is exerted by the releasing water species incites the formation of large cavities and fractures, initiating expansion.

Polymerization shrinkage, shrinkage stress, and mechanical evaluation of novel prototype dental composite resin.

A new photocurable composite resin for dental restorations was synthesized using a monovinyl acrylate diluent. Its polymerization shrinkage, shrinkage stress, degree of conversion, and mechanical properties were investigated and compared to those of a conventional composite resin synthesized using a triethyleneglycol dimethacrylate diluent as well as three commercial resins: Tetric N-Ceram, Neofil, and Gradia Direct. The polymerization shrinkage and shrinkage stress of the new composite resin were statistically lower than those of the conventional resin (p<0.05), but not those of the commercial resins (p>0.05). The degree of conversion of the new resin was statistically better than all other tested resins (p<0.05) except the Neofil resin (p>0.05). The mechanical properties of the resins were not statistically different (p>0.05). Overall, the new composite resin exhibited less polymerization shrinkage, lower shrinkage stress, a higher degree of conversion, and similar mechanical properties to the other resins, demonstrating its potential for clinical application.

Preparation of Petrochemical Feedstock from Rubber Wastes by Thermal Solvolysis

The thermal decomposition of crumb rubber based on isoprene pure rubber in an autoclave in various media such as toluene, isopropyl alcohol, and water has been studied. The highest degree of conversion of pure rubber is achieved in a toluene medium, while the lowest is in water. The formation of a gas is minimum in the aqueous medium and maximum in a medium of isopropyl alcohol; however, the yield of the gaseous products is much lower than in the processes of high-temperature pyrolysis of rubber. The fractional composition of the liquid products varies within a wide range, namely, more gasoline fractions are formed in the medium of toluene; oil fractions, in water; and middle distillates predominate in the products obtained in the isopropyl alcohol medium. The concentration of dipentene and p-cymene, which may be of interest as the feedstock for industrial organic synthesis, in the distillate fractions reaches 10–16 wt %. Unsaturated aliphatic structures predominate in the oil fractions obtained in the medium of water or isopropyl alcohol, while alkylbenzenes predominate in the “toluene” oils. The oil fractions can be of interest as a feedstock for the production of both lubricating and process oils. The solid carbonaceous residue from the thermal solvolysis of rubber contains not only untransformed carbon black, but also zinc oxide and sulfide, so that it can be sent to the production of zinc or be reused as a rubber filler.

The Synthesis of 3-Aryl-2-oxazolidinones from CO2, Ethylene Oxide, and Anilines Under Mild Conditions Using PVA-DFNT/Ni

A novel nanocatalyst design using nanomaterials through active-zone crystallisation was proposed. The hydrothermal crystallisation of amorphous dendritic fibrous nano-titanium dioxide with Ni (DFNT/Ni) sites was determined to be the main step in producing extremely active dendritic DFNT/Ni zones, which in turn dramatically enhanced their catalytic activities. DFNT/Ni was then combined with polyvinyl alcohol (PVA) by using a traditional individual-nozzle electrospinning method, and the resulting material was named PVA-DFNT/Ni. This method was utilised to produce 3-aryl-2-oxazolidinones from ethylene oxide, CO2, and anilines. The prepared catalytic apparatus was eco-friendly and had the advantages of high catalytic activity, ability to improve the reaction mixture, and reusability without a considerable decrease in efficiency. It is extracted in the straight and adoptive chemical fixation of flue-gas CO2 obtained from industrial emissions, thereby achieving high degrees of CO2 absorption and conversion.

The Process of Producing Bioethanol from Delignified Cellulose Isolated from Plants of the Miscanthus Genus.

Plants of the Miscanthus genus (Miscanthus Anderss.) have a unique index of biomass production in relation to the occupied area. Miscanthus plants can be attributed to promising second-generation raw materials for the production of bioethanol and biofuel. Miscanthus plants are characterized by a high cellulose content. Herein, we report the results of a study on the obtained delignified cellulose with subsequent processing into bioethanol using microbial communities. In the course of the study, the optimal conditions for the delignification of the initial plant material for cellulose were selected. Ethanol with a high degree of conversion was successfully obtained from the isolated delignified cellulose. The article describes the pilot technological scheme for the conversion of Miscanthus plant biomass to bioethanol involving the delignification stages, followed by the conversion of the resulting cellulose into bioethanol by a consortium of microorganisms. As a result of the study, it was found that delignification using trifluoroacetic acid leads to the production of cellulose of high purity. Bioethanol with a yield of 3.1% to 3.4% in terms of the initial amount of biomass was successfully obtained by a microorganism consortium of Saccharomyces cerevisiae M Y-4242/Pachysolen tannophilus Y-3269, and Scheffersomyces stipitis Y-3264.

Nickel nanoparticles supported on nitrogen–doped carbon nanotubes are a highly active, selective and stable CO2 methanation catalyst

CO2 methanation using nickel-based catalysts has attracted large interest as a promising power-to-gas route. Ni nanoparticles supported on nitrogen-doped CNTs with Ni loadings in the range from 10 wt% to 50 wt% were synthesized by impregnation, calcination and reduction and characterized by elemental analysis, X-ray powder diffraction, H2 temperature-programmed reduction, CO pulse chemisorption and transmission electron microscopy. The Ni/NCNT catalysts were highly active in CO2 methanation at atmospheric pressure, reaching over 50% CO2 conversion and over 95% CH4 selectivity at 340 °C and a GHSV of 50,000 mL g−1 h−1 under kinetically controlled conditions. The small Ni particle sizes below 10 nm despite the high Ni loading is ascribed to the efficient anchoring on the N-doped CNTs. The optimum loading of 30 wt%–40 wt% Ni was found to result in the highest Ni surface area, the highest degree of conversion and the highest selectivity to methane. A constant TOF of 0.3 s−1 was obtained indicating similar catalytic properties of the Ni nanoparticles in the range from 10 wt% to 50 wt% Ni loading. Long-term experiments showed that the Ni/NCNT catalyst with 30 wt% Ni was highly stable for 100 h time on stream.

Polymerization Stress and Gap Formation of Self-adhesive, Bulk-fill and Flowable Composite Resins.

Bulk-fill materials show a similar or better performance than control flowable materials regarding interfacial integrity. However, some self-adhesive composites need improvements to achieve competitive performance. Objective: This laboratory study compared the polymerization stress and gap formation of self-adhesive, bulk-fill and control flowable composites. The degree of conversion (DC) and post-gel shrinkage were also assessed.Methods: Two self-adhesive (Vertise Flow and Fusio Liquid Dentin), two bulk-fill (Tetric N-Flow Bulk-Fill and Filtek Bulk-Fill Flowable Restorative), and two control flowable (Z350 XT Flowable Restorative and Tetric N-Flow) composites were evaluated. Polymerization stress (PS) was determined in a universal testing machine (n=5). Gap formation was evaluated by scanning electron microscopy in class I restorations (n=6). DC was measured by Fourier transform infrared spectroscopy (n=3). Post-gel volumetric shrinkage (VS) was measured using the strain gauge method (n=5). Data were submitted to one-way analysis of variance or a Kruskal-Wallis test (α=0.05).Results: Vertise Flow and Fusio Liquid Dentin presented the highest interfacial gap (27%±5% and 21%±6%, respectively), which was associated with their highest PS (4.1±0.8 MPa and 3.5±0.6 MPa, respectively) and DC (63%±2% and 60%±2%, respectively) in spite of the lowest VS (1.0%±0.2% and 1.0%±0.3%, respectively). Tetric N-Flow Bulk-Fill and Filtek Bulk-Fill Flowable Restorative presented similar PS (2.9± 0.3 MPa and 2.4±0.2 MPa, respectively) to both control materials. However, the Tetric N-Flow Bulk-Fill showed the lowest gap (7%±2%) and the highest DC (64.3%±0.4%), and the Filtek Bulk-fill presented a marginal gap (17.8%±3.4%) and a DC (54.5%±2.7%) similar to the control materials. The VS values of both bulk-fill materials were similar to those of Tetric N-Flow and lower than that of Z350 XT Flowable Restorative.Conclusions: Bulk-fill composites showed either similar or significantly lower interfacial gaps and PS than the control flowable composites. The self-adhesive composites showed a significantly higher gap percentage and PS than the control and bulk-fill materials.

Thermal decomposed behavior and kinetic study for untreated and flame retardant treated regenerated cellulose fibers using thermogravimetric analysis

In the present work, pyrolysis kinetic mechanism was studied for regenerated cellulosic fiber (RCF) and composite RCF containing silicon/nitrogen flame retardants. Limited oxygen index and microscale combustion calorimeter tests show that the loading of nitrogen/silicon into the RCF enhanced flame retardancy. The kinetic triplets of the two kinds of samples were determined by applying iso-conversional methods and integral master plots approach. Compared to the untreated RCF, flame retardant (FR) treated RCF shows enhanced activation energy due to the physical barrier layer due to dehydration of silicate and charring effect resulting from organic–inorganic interaction. Exponential nucleation model can be successful in describing experimental results for RCF in higher conversion degree (0.4–0.9). Simultaneously, the degradation process of FR treated RCF in the main pyrolysis stage (0.2–0.7) is consistent with kinetics of nuclei growth and could be described by one-step reaction whose rate presented an Avrami–Erofeev-type model (n = 2.38).

Evaluation of dimensional accuracy and degree of polymerization of stereolithography photopolymer resin under different postpolymerization conditions: An in vitro study

Statement of problemThe appropriate postpolymerization of stereolithography (SLA) resins with the least effect on dimensional accuracy and with optimal polymerization is unclear. PurposeThe purpose of this in vitro study was to investigate the dimensional accuracy and degree of polymerization of a photopolymer resin for SLA with different postpolymerizing times and temperatures. Material and methodsSixty 1.5-mm-thick specimens were made from clear photopolymer resin with a 3D printer to simulate a maxillary complete denture. They were postpolymerized for different periods (15 and 30 minutes) at 3 different temperatures (40 °C, 60 °C, and 80 °C). Both prepolymerization and postpolymerization gap sizes for each specimen were measured at 5 different locations under a stereomicroscope. The tissue surface was scanned before and after polymerization, and the images were superimposed. The deviation was analyzed by using computer-aided design (CAD) software; root mean square estimates (RMSE) and color map data were obtained. Fourier transform infrared spectrometry was used to determine the degree of conversion (DC) of all specimens. The Kruskal-Wallis and Mann-Whitney tests were used to calculate the difference value of the gap sizes (α=.05). One-way ANOVA and the Tukey test were used for RMSE and DC (α=.05). ResultsThe smallest average change in gap sizes was found at 15 minutes and 40 °C, and the largest change at 30 minutes and 80 °C. The lowest RMSE was obtained at 30 minutes and 40 °C (P<.05). On the color map, a uniform deposited layer was created at 15 minutes and 40 °C and 30 minutes and 40 °C. The highest DC was found at 30 minutes and 60 °C, which differed significantly from 15 minutes and 40 °C (P<.05). The lowest degree of polymerization was found at 30 minutes and 40 °C. ConclusionsThe polymerizing temperature exerted a greater effect than polymerizing time, with lower temperatures leading to improved fit and tissue surface accuracy. The recommended parameters for SLA polymerization are 15 minutes and 40 °C. These conditions offered high dimensional accuracy, favorable surface tissue adaptation, and satisfactory DC.

Polycondensation Kinetics: 2. Time-Dependent29Si NMR Spectra of Poly-Dimethyldimethoxysilane

The polycondensation of dimethyldimethoxysilane has been studied by 29Si NMR to high degrees of conversion at pH 2.8. The relative concentrations of nonbonded Si atoms (D0) and bound by one (D1) and two (D2) Si–O–Si bonds have been determined from the integrated intensities of the multiplets assigned to them. The measurement results have been considered in terms of the kinetic scheme proposed in the first paper. It has been found that the D0(t), D1(t), and D2(t) curves coincide with those measured for the ratio of the constants of competing processes of aggregation and addition of monomers k ≈ 0.15. The time-dependent molecular mass distributions have been determined with allowance for chain termination during the formation of cyclic and entangled oligomers.

Novel Urethane-Dimethacrylate Monomers and Compositions for Use as Matrices in Dental Restorative Materials.

In this study, novel urethane-dimethacrylate monomers were synthesized from 1,3-bis(1-isocyanato-1-methylethyl)benzene (MEBDI) and oligoethylene glycols monomethacrylates, containing one to three oxyethylene groups. They can potentially be utilized as matrices in dental restorative materials. The obtained monomers were used to prepare four new formulations. Two of them were solely composed of the MEBDI-based monomers. In a second pair, a monomer based on triethylene glycol monomethacrylate, used in 20 wt.%, was replaced with triethylene glycol dimethacrylate (TEGDMA), a reactive diluent typically used in dental materials. For comparison purposes, two formulations, using typical dental dimethacrylates (bisphenol A glycerolate dimethacrylate (Bis-GMA), urethane-dimethacrylate (UDMA) and TEGDMA) were prepared. The monomers and mixtures were tested for the viscosity and density. The homopolymers and copolymers, obtained via photopolymerization, were tested for the degree of conversion, polymerization shrinkage, water sorption and solubility, hardness, flexural strength and modulus. The newly developed formulations achieved promising physico-chemical and mechanical characteristics so as to be suitable for applications as dental composite matrices. A combination of the MEBDI-based urethane-dimethacrylates with TEGDMA resulted in copolymers with a high degree of conversion, low polymerization shrinkage, low water sorption and water solubility, and good mechanical properties. These parameters showed an improvement in relation to currently used dental formulations.

Degree of Conversion Contributes to Dentin Bonding Durability of Contemporary Universal Adhesives.

The degree of conversion of contemporary universal adhesives positively correlates with the bond strength to dentin. The correlation is more marked after thermocycling, suggesting that a high degree of conversion is required for long-term dentin bonding durability. Purpose: The objectives of this study were to evaluate the micro-tensile bond strength (μTBS) of five contemporary universal adhesives to dentin after 24 hours and thermocycling (TC), to measure their degrees of conversion (DC) and to test the correlation between μTBS and DC.Methods and Materials: Four commercially available universal adhesives, Prime&Bond universal (PBU), Ecosite Bond (EB), G-Premio Bond (GPB), and Clearfil Universal Bond Quick (UBQ), and one experimental adhesive, UBQ without an amide monomer (UBQ-A), were used in this study. For the μTBS test, midcoronal dentin of 50 human molars was exposed, ground using 600-grit SiC paper, and the adhesives were applied according to the manufacturers' instructions. After resin-composite buildup and 24-hour water storage, one-half of the specimens were subjected to 15,000 thermal cycles. The specimens were sectioned into beams and stressed in tension at a crosshead speed of 1 mm/min until failure. The DC of adhesives applied to dentin was evaluated using attenuated total reflectance Fourier-transform infrared spectroscopy immediately after light-curing. All data were statistically analyzed at a significance level of 0.05.Results: The highest μTBSs were obtained with UBQ, UBQ-A, and PBU, which were not significantly different from each other both after 24 hours and TC. The μTBS of GPB was lower compared with the aforementioned adhesives, but significantly only after TC, and the lowest μTBSs were obtained with EB. TC did not affect the μTBSs of UBQ, UBQ-A, and PBU significantly, but a significant decrease was observed with GPB and EB. The highest DC was obtained with PBU and UBQ, followed by 2-hydroxyethyl methacrylate-rich adhesives UBQ-A and EB, which exhibited significantly lower DCs. The DC of GPB could not be determined because the reference peak at 1608 cm-1 was not detected in its spectra. A significant positive correlation was shown between μTBS and DC after 24 hours (r=0.716) and TC (r=0.856).Conclusion: μTBS and DC were positively correlated, more markedly after TC, which suggests that DC may be an important factor for bond durability.

Comparative Study on The Structure, Physical Properties and Hardness Indentation of a Bulk Fill &amp; An Incremental Composite Resin Restorative Materials

Totally 80 disk-shaped specimens of Filtek™ Bulk-Fill, 3M ESPE, and Filtek™ Z250 XT, 3M ESPE, were prepared by using split-Teflon mold (4mm×10mm). Specimen characterization XRD, Surface roughness, degree of conversion, Surface microhardness, and depth of cure of the specimens were evaluated after the specimens were stored in distilled water in darkness at 37°C for 24 h. Statistical analysis was done using t-test with a significance level at p&lt;0.05. FiltekTM Z350 XT showed the highest mean value of Vickers microhardness either on top surface 94.94% or bottom surface 69.92% and recorded 76.51% while FiltekTM Bulk-Fill was 66.85% for depth of cure. Filtek bulk-fill recorded a lower mean value of 0.73 for Surface roughness than FiltekTM Z350 XT and the highest degree of conversion of 84.34%. Statistical analysis showed that there was a significant difference between the mean values for all tested results. Increasing the filler content proved to have ability to enhance some properties, specially the surface roughness. Incorporation of some structurally rigid monomers like Bis-DMA, UDMA, TEGDMA within the resin matrix have a great influence on the measured properties, including degree of conversion reached to 84.34%, depth of cure to a level of 76.51% and Vickers microhardness to 94.94%.

Evaluation of Microleakage and Degree of Conversion of Three Composite Res-ins Polymerized at Different Power Densities

Objectives: This study aims to evaluate the degree of conversion (DC) and microlekage scores of three different composite resins polymerized with a LED curing device in standard and extra-power mode. Material and Methods: One bulk-fill (Tetric EvoCeram Bulk-Fill – TECBF) and two conventional composite materials (Clearfil Majesty Posterior – CMP and Tetric EvoCeram – TEC) were evaluated. A total of 30 specimens were prepared for six groups (N = 5). These groups were polymerized with a LED curing device as follows: TECBF-6: 3200mW/cm2 for six seconds, TECBF-20: 1000mW/cm2 for 20 seconds, CMP-6: 3200mW/cm2 for six seconds, CMP-20: 1000mW/cm2 for 20 seconds, TEC-6: 3200mW/cm2 for six seconds, TEC - 20: 1000 mW/cm2 for 20 seconds. After 24 hours of water storage, DC was measured by Raman spectroscopy. Microleakage scores of the six groups were bonded to various adhesive systems (Clearfil SE Bond or Adhese Bond Universal) were also evaluated at Class II box cavities (N = 10). Results: While the highest DC was found at the top (TECBF-20= 79.92% and TECBF-6= 79.02%) and bottom surfaces (TECBF-20 = 68.94% and TECBF-6= 71.04%) for TECBF groups, TEC groups (TEC-20top = 59.06%, TEC-6top=49.66%, TEC-20bottom = 43.72% and TEC-6bottom= 40.68%) showed the lowest DC for the both surfaces (p &lt; 0.05). Polymerization of materials in standard or extra-power mode was similar to DC (p &gt; 0.05). Microleakage scores were found to be similar (p &gt; 0.05). Conclusion: According to the results of the study, different power densities of LED curing light did not affect the DC of composite resins and microleakage values of restorations at small Class II cavities.KEYWORDSBulk-fill composite; degree of conversion; LED curing device; microleakage; Raman spectroscopy.

Master-eğriler kinetik yönteminin izotermal olmayan selüloz pirolizine uygulanması ve piroliz işleminin termodinamik analizi

Kinetic modeling of thermochemical conversion methods such as pyrolysis is one of the most challenging issues for bio-refineries. It is known that cellulose together with hemicellulose and lignin mainly affect the characteristics of biomass pyrolysis. However, there is still limited knowledge about the thermal behaviors of biopolymers that go into complex multi-phase pyrolysis reactions in the literature. Therefore, cellulose pyrolysis kinetics and thermodynamics were investigated in this study. Kinetic parameters of the pyrolysis process were calculated by a combined method of master-plots and Friedman method. Active pyrolysis of cellulose is found to occur between 263 and 455 °C. Applied Friedman method was perfectly fitted with the experimental data and activation energy of the thermochemical conversion process was found between 150.8 and 190.2 kJ/mol while the mean activation energy was calculated as 164.3 kJ/mol. The comparison of kinetic models used of solid-state thermal decomposition processes indicated that the cellulose pyrolysis mechanism is a diffusion-controlled (D3) degradation process at lower conversions (0&amp;lt;α&amp;lt;0.5) and the process can be explained by reaction-based mechanisms at higher conversion degrees.

Cascade Synthesis from Cyclohexane to ϵ-Caprolactone by Visible-Light-Driven Photocatalysis Combined with Whole-Cell Biological Oxidation.

Cyclohexane was directly oxy-functionalised to ϵ-caprolactone through a cascade reaction sequence combining visible-light-driven photocatalysis with cyclohexanone monooxygenase (CHMO) whole-cell biocatalysis. Two available photocatalysts, Au-doped TiO2 (Au-TiO2 ) and graphitic carbonitride (g-C3 N4 ), were evaluated in the experiment and some optimisations to the cascade reaction were applied. In stepwise mode, the highest degree of conversion from cyclohexanol to ϵ-caprolactone can be up to 41 %, with use of g-C3 N4 . The cascade reaction from cyclohexane to ϵ-caprolactone is achievable under a light intensity of 149 μW cm-2 .

Co-hydroprocessing and hydrocracking of alternative feed mixture (vacuum gas oil/waste lubricating oil/waste cooking oil) with the aim of producing high quality fuels

Hydroprocessing of waste cooking oil (WCO), waste lubricating oil (WLO) and vacuum gas oil (VGO) and mixtures of them are studied for high quality fuels production. The results are compared to VGO hydroprocessing results to illustrate the value added by blending waste oils to VGO, which is one of the well-known conventional hydroprocessing feed. The effect of blending WCO and WLO with VGO has proven a better performance in a fixed bed hydroprocessing reactor, over commercial industrial catalysts manufactured especially to hydroprocess VGO. Blending of WCO and WLO with VGO will reduce environmental pollution resulting from spilling of these wastes in addition to provide an alternative lower-cost feed than pure VGO. A binary bed of hydrotreating catalyst (Ni-Mo oxides supported on Al2O3) and catalyst specified for hydrocracking (Ni–W oxides supported on SiO2/Al2O3) were used. Hydroprocessing experiments were executed at a temperature range 380–440 °C, pressure of 7.0 MPa, LHSV of 1.5 h−1, H2/(HC)feed ratio of 400 Nm3/m3, and different WLO and WCO percentage of (10, 20 wt%). At the specified operating conditions, a high degree of conversion was noticed especially for diesel yield that increases by increasing WLO percentage in the feed mixture. On the other hand, increasing WCO content in the feed mixtures led to higher kerosene and gasoline yields. Higher rates of hydrocracking reactions were achieved by increasing the reaction temperature that was confirmed by the lower percentages of total amount of n-paraffins in the product final mixture with a higher WCO and WLO percent in feed mixture. In conclusion, at all studied temperature ranges it was confirmed that, by increasing the reaction temperature, the gasoline and LPG yields will increase on the expense of kerosene and diesel yields. However, the highest diesel yield could be achieved at 400 °C.

Intensifying the PC conversion in the raceway by means of coke oven gas

Among numerous measures to accelerate the PC conversion within the blast furnace (BF) raceway, local increase of oxygen concentration is the most common one. On the other hand, the presence of cold media (oxygen) in the vicinity of the coal stream might affect its ignition and combustion negatively. A minor amount of coke oven gas (COG) may increase the temperature and consequently accelerate the coal conversion. To examine this effect, laboratory trials under blast furnace simulating conditions were performed using the Multifunctional Injection Rig for Ironmaking (MIRI). The results of the simulation testified a higher conversion degree of coal while adding the COG. The temperature increase is measurable in the reaction chamber and the off-gas stream. Optical microscopy of the original PC particles and residues after reaction confirm the findings of the off-gas analysis and the increase in temperature during the experiments with addition of COG. The thermogravimetric analysis was applied to determine and to compare the behaviour of coal in different atmospheres including an atmosphere with COG. A stand at one tuyère at a modern BF was erected and tests were performed targeting the observation of the ignition behaviour of coal at different COG rates, using a camera image analysis system. Laboratory trials under blast furnace raceway simulating conditions showed, that even a small amount of COG significantly improves the PC conversion degree. A new technology of PC injection, including addition of small amount of COG to the PC transporting gas, aimed at neutralization of the oxygen local cooling effect, elaborated, justified and tested.

The activation and conversion of carbon dioxide on the surface of zirconia-promoted ceria oxides

This study reports the conversion of carbon dioxide (CO2) by ceria (CeO2)-zirconia (ZrO2) composites with various ZrO2 contents (0, 20, 50, 80 and 100 %). The modification introduced by ZrO2 altered the structural properties of the ceria samples, affecting their reducibility and subsequent activity to convert CO2. The characterisation results showed a clear relationship between the structural properties of the materials and the activity for CO2 conversion. The addition of ZrO2 was effective to improve a close interaction between CeO2 and ZrO2 and induced the formation of structural defects that further promoted oxygen transport and facilitated the creation of oxygen vacancies that were critical for CO2 conversion. All samples investigated were found to be effective in converting CO2 into carbon monoxide (CO) at 450 °C, and the addition of ZrO2 was also found to be effective in improving the thermal resistance and stabilising the crystalline structure of the samples especially when the ZrO2 content was > 50 %. When the content of ZrO2 controlled between 50 % and 80 %, the onset temperature for CO2 conversion was found to be 285 °C, which was about 80 °C lower than that required for the sample without ZrO2 modification. Thus, modifying CeO2 by ZrO2 was effective to prevent both the textural and structural alteration of the samples under a high temperature environment as well as cyclic redox operations, resulting in a constant and high degree of CO2 conversion into CO.