Formation Of Carbonaceous Residues Research Articles

Dynamics and Mechanism of Carbon Filament Formation during Methane Reforming on Supported Nickel Clusters

CH4–CO2 and CH4–H2O reforming on Ni-based catalysts can lead to the undesired formation of carbonaceous residues. The dynamics of the formation of carbon filaments and encapsulating layers on dispe...

Effects of two different agents, H3PO4 and NaCl, to increase the flame-retardant properties of cellulose fibers

After flame-retardant treatment by the two different agents, the thermal behaviors of Lyocell fibers are discussed. In this research, H3PO4 and NaCl reduced the degradation rate and increased the char yield of the Lyocell fibers, and also increased the limiting oxygen index with the char yield increased. After treatment, the integral procedure decomposition temperature and the activation energy of Lyocell fibers are significantly increased by various concentration factors. These phenomena were indicated by the dehydration, rearrangement, formation of carbonyl groups, the evolution of carbon monoxide and dioxide, and carbonaceous residue formation. These effects were indicating the slow pathway of flame retardancy for the Lyocell fibers and are attributed to the two different flame-retardant agent treatments.

Biopolymer blends from hardwood lignin and bio-polyamides: Compatibility and miscibility.

The compatibility of hardwood lignin (TcA)/bio-polyamide (PA) blends, prepared by melt compounding TcA with three different biobased polyamides, PA 1012, PA 1010 and PA 11 in a twin screw extruder has been studied. FTIR studies indicated the existence of physicochemical interactions between the TcA and polyamide. The melting temperatures of the blends were significantly reduced compared to the respective neat polyamides, which was attributed to the enhanced compatibility between the two components. The compatibility was also attributed to the increased glass transition (Tg) of the polyamide. Thermogravimetric studies, while not indicating any interaction during the processing stage, suggested that there was some during the thermal degradation stage, which assisted formation of carbonaceous residue. The addition of each polyamide to TcA considerably reduced its viscosity and enhanced its processability even at high lignin contents. Morphological analysis showed that heterogeneity for all the blends was quite uniform, although TcA domain sizes were considerably smaller (~0.5 μm) in the PA11 matrix compared to those in PA1010 and PA1012, suggesting better compatibility in the TcA/PA11 blends. This observation was consistent with the thermodynamic Gibbs' free energy values of the respective blends. Overall, the order of blend compatibility was TcA/PA11 > TcA/PA1010 > TcA/PA1012.

Three-way catalysis with supported gold catalysts: Poisoning effects of hydrocarbons

Poisoning phenomena recently observed during the conversion of three-way catalysis model feed (CO, NO propene, O2, without or with water) over supported Au catalysts [V. Ulrich et al., Applied Catalysis B 203 (2017) 572] were investigated by reaction studies (replacing propene by propane in model feed, study of CO oxidation without and with relevant additional components), by temperature-programmed oxidation of deposits (TG, TPO), by studying self-regeneration phenomena and by DRIFTS of CO adsorption and co-adsorption of CO and propene under different conditions. During CO oxidation in the presence of other components, two different poisoning phenomena were observed. In the presence of propane, propene, and/or NO, CO oxidation was significantly inhibited below 370 K over Au on Al2O3 or on La-stabilized Al2O3, but not on Au/CeZrOx where activity was relatively low anywhere. DRIFTS data on (co-)adsorption of CO and propene suggest that this poisoning is not merely a result of site blocking by the coadsorbate, but that electron transfer from the co-adsorbates towards the active sites, which are assumed to be at the perimeter of positively charged Au clusters with the support, might have additionally quenched the reaction. At higher temperatures, a different poisoning mechanism operates in propene-containing mixtures. From studies by TPO, TG, and DRIFTS, we conclude the formation of carbonaceous residues, which do not block, however, CO adsorption sites but the support surface around Au clusters instead. While this inhibits CO oxidation involving active support oxygen, the same oxygen species might combust the deposits at higher temperatures. This results in self-regeneration phenomena depending on the redox activity of the support, the temperature and the propene content in the feed. In transient experiments, it was observed that NO is most favorably reduced by intermediates of coke formation from propene. Under stationary conditions, however, NO reduction, mostly by CO, remains insufficient.

Pure Hydrogen Production for Low Temperature Fuel Cells

The electric car industry is rapidly growing worldwide. There are two ways of providing the electricity needed in these vehicles, i.e. by means of either batteries or fuel cells. A reliable source of pure hydrogen is necessary for the latter alternative. Having in mind that the steam reforming of natural gas is at present the main source of this gas, different options for its production are discussed. This hydrogen needs further purification to get rid of the carbon monoxide (< 10 ppm) that irreversibly poisons the electrodes of the fuel cells. This work examines membrane reactors and hollow fiber membrane reactors. The latter are very attractive due to the severe mass (concentration polarization) and heat transport limitations that should be minimized at industrial scale. The work also presents examples of catalysts especially tailored for use in these applications. The main features of these formulations are high selectivity and stability. Their durability is directly connected with the sintering resistance and a very low activity to promote the formation of carbonaceous residues. The ultimate goal of this prospective contribution is to provide tools for the reader to evaluate present trends in research and the opportunities open in the field of H2 fuel production suitable for fuel cell cars.

Durable flame retardant cellulosic fibers modified with novel, facile and efficient phytic acid-based finishing agent

As a renewable, abundant, and eco-friendly bio-based compound, phytic acid (PA) possesses high phosphorus content, which is a potential flame retardant for cellulosic fibers. Generally, PA is not efficient for cellulosic fibers due to strong acidity that results in greatly reduced strength and lack of soft hand. As proved elsewhere, the compounds with phosphorous and nitrogen was reported to be an efficient flame retardant and exhibited synergistic effect for cellulosic fibers. Therefore, PA was firstly reacted with urea to synthesize a novel green flame retardant containing a high level of phosphorus and nitrogen elements, i.e., phytic acid ammonium, then it was employed for lyocell fibers through pad-dry-cure finishing process. As expected, flame retardancy and durability of finished lyocell fabrics were considerably improved, as evidenced by an increase of limiting oxygen index value up to 39.2% and still 29.7% after 30 laundering cycles. TG–MS and TG–FTIR coupled techniques demonstrate that the formation of carbonaceous residue and non-combustion gases preferably generated during thermal pyrolysis process of finished lyocell fibers.

Direct determination of chromium in infant formulas employing high-resolution continuum source electrothermal atomic absorption spectrometry and solid sample analysis

The present work proposed an analytical method for the direct determination of chromium in infant formulas employing the high-resolution continuum source electrothermal atomic absorption spectrometry combined with the solid sample analysis (SS–HR-CS ET AAS). Sample masses up to 2.0mg were directly weighted on a solid sampling platform and introduced into the graphite tube. In order to minimize the formation of carbonaceous residues and to improve the contact of the modifier solution with the solid sample, a volume of 10µL of a solution containing 6% (v/v) H2O2, 20% (v/v) ethanol and 1% (v/v) HNO3 was added. The pyrolysis and atomization temperatures established were 1600 and 2400°C, respectively, using magnesium as chemical modifier. The calibration technique was evaluated by comparing the slopes of calibration curves established using aqueous and solid standards. This test revealed that chromium can be determined employing the external calibration technique using aqueous standards. Under these conditions, the method developed allows the direct determination of chromium with limit of quantification of 11.5ngg−1, precision expressed as relative standard deviation (RSD) in the range of 4.0–17.9% (n=3) and a characteristic mass of 1.2pg of chromium. The accuracy was confirmed by analysis of a certified reference material of tomato leaves furnished by National Institute of Standards and Technology.The method proposed was applied for the determination of chromium in five different infant formula samples. The chromium content found varied in the range of 33.9–58.1ngg−1 (n=3). These samples were also analyzed employing ICP-MS. A statistical test demonstrated that there is no significant difference between the results found by two methods. The chromium concentrations achieved are lower than the maximum limit permissible for chromium in foods by Brazilian Legislation.

Fast pyrolysis of muconic acid and formic acid salt mixtures

Lignocellulosic feedstocks are a potential renewable resource for the production of liquid fuels and chemicals. As a major by-product of the pulping industry, lignin is an underutilized source of organic carbon in lignocellulosic biomass. Residual lignin remaining in pulp after cooking of lignocellulosic biomass is typically removed during the bleaching stage of a pulping operation. This stage is composed of a sequence of steps including oxidation and alkaline extraction. Given that muconic acid and formic acid are formed during oxygen treatment of alkaline solutions of lignin, fast pyrolysis coupled with gas chromatography–mass spectrometry (Py–GC/MS) of alkali/alkaline earth salt mixtures of muconic acid and formic acid was employed to produce significantly deoxygenated products, such as cyclic ketones, hydrocarbons, aromatics, and phenolics. The cations investigated in this study were sodium, calcium, and magnesium to observe the difference in product distribution, volatile formation, and the formation of carbonaceous residue. The compounds observed after pyrolysis of the various salts suggest that along with the expected intramolecular condensation reactions, free radical reactions are likely occurring at the temperatures investigated explaining the observed alkylation and hydrogenation of the vapor products beyond deoxygenation which can be expected from reactive hydrogen formed by formate decomposition. Hydrogenation may also be occurring as a result of catalytic effects of the metal cations on the pyrolysis vapors. Pyrolysis of calcium muconate favors cyclic ketone formation almost exclusively, and when formate is added a 61wt% reduction in carbonaceous residue formation is observed at 550°C in a thermogravimetric analyzer (TGA) equipped with an evolved gas analyzer furnace (EGA). The highest yields of gaseous species were observed for the magnesium muconate–formate mixture, approximately 47wt%, while the least amount of carbonaceous residue was formed upon pyrolysis of the sodium muconate–formate mixture, both at 550°C in a TGA. The data suggests that pyrolysis at 550°C of sodium formate and oxidized lignin mixtures may be of interest for the production of aromatic compounds.

Synthesis, characterization, and thermal analysis of alginate and monoethanolamine product

Characterization, thermal stability, and thermal decomposition of a reaction product between alginic acid (Halg) and monoethanolamine (Mea) and of these complexes with drugs were investigated employing elemental analysis, thermogravimetry (TG), infrared spectroscopy (FTIR), TG-FTIR, differential scanning calorimetry and nuclear magnetic resonance (NMR) spectroscopy to carbon (13C NMR). The drugs used were acetaminophen (Apap), thioconazole (Thio), and ramipril (Ram). All the compounds were obtained in the hydrated state, and the thermal decomposition occurs in two steps for complexes after dehydration. Elemental analysis and TG results suggested that the Mea-alg have 11 % hydration water with general formula C8H13O6N·5.4H2O. The TG curve profile showed that sample decomposed in two steps after dehydration with formation of carbonaceous residue. FTIR revealed some evidences that the Mea-alg is a mixture of salt and ester. TG-FTIR showed that the gaseous products evolved during the thermal decomposition were ammonia, water and CO2. From NMR13C, it was possible to find substitution degree (77 %) of Mea-alg. In the characterization of complexes, it was possible to conclude that the interaction mechanism between drugs and Mea-alg is dependent on the characteristics of the molecules such as size and functional groups.

Effect of Cellulose Crystallinity on Solid/Liquid Phase Reactions Responsible for the Formation of Carbonaceous Residues during Pyrolysis

This study reports changes in solid phase composition when samples of Avicel cellulose (crystallinity: 60.5%) and ball-milled microcrystalline cellulose (crystallinity: 6.5%) were subjected to pyrolysis in a spoon reactor. Solid state chemistry evolution was examined by hydrolysis-ion exchange chromatography, scanning electron miscroscopy (SEM), Fourier transform infrared (FTIR), and 13C nuclear magnetic resonance (NMR). The liquid reaction intermediate was found to cause particle agglomeration at temperatures below 300 °C. At higher temperatures, the ball-milled cellulose melted completely but the more crystalline cellulose conserved its fibrous structure. The formation of C═O and C═C groups was accelerated by the presence of liquid intermediates derived from the amorphous cellulose. The content of cross-linked cellulose was quantified by the combined use of acid hydrolysis and 13C NMR. A new reaction mechanism to describe the changes in the solid residue composition at different reaction conditions is proposed.

Improvement of the Benzene Yield During Pyrolysis of Terephthalic Acid Using a CaO Fixed-Bed Reactor

Effects of pyrolysis temperature and terephthalic acid (TPA) gas concentration on TPA degradation as a model substance for poly(ethylene terephthalate) (PET) degradation products were investigated with emphasis on benzene yield and decrease of carbonaceous residue. TPA was decarboxylated using a spiral tube reactor filled with CaO. The best results were achieved at 600 °C and TPA gas load of 28 mg L–1, yielding 84% benzene. Of the initial carbon, 29% remained in the reactor, consisting of carbonate and carbonaceous residue. Benzene purity was more than 97 wt % under all reaction conditions. Low TPA gas loads and high gas velocities resulted in good benzene yields and purities because TPA gas deeply penetrated the CaO fixed bed before adsorption. This resulted in lower TPA concentration at the CaO surface, reducing the interference between neighboring TPA molecules and limiting carbonaceous residue formation.

Microscopic Insights into Methane Activation and Related Processes on Pt/Ceria Model Catalysts

Ceria-based supported noble-metal catalysts release oxygen, which may help to reduce the formation of carbonaceous residues, for example during hydrocarbon reforming. To gain insight into the microscopic origins of these effects, a model study is performed under ultrahigh-vacuum conditions using single-crystal-based supported model catalysts. The model systems are based on ordered CeO(2)(111) films on Cu(111), on which Pt nanoparticles are grown by physical vapor deposition. The growth and structure of the surfaces are characterized by means of scanning tunneling microscopy, and the electronic structure and reactivity are probed by X-ray photoelectron spectroscopy. Specifically, it is shown that the fully oxidized CeO(2) thin films undergo slight reduction upon Pt deposition (CeO(1.99)). This effect is enhanced upon annealing (CeO(1.96)), thus indicating facile oxygen release and reverse spillover. The model system is structurally stable up to temperatures exceeding 700 K. The activation of methane is investigated using high-kinetic-energy CH(4) (0.83 eV), generated by a supersonic molecular beam. It is shown that dehydrogenation occurs under rapid formation of CH or C species without detectable amounts of CH(3) being formed, even at low temperatures (100 K). The released hydrogen spills over to the CeO(2) support, which leads to the formation of OH groups. At 200 K and above, the OH groups start to decompose leaving additional Ce(3+) centers behind (CeO(1.97-1.94)). At up to 700 K, carbon deposits are quantitatively removed by reaction with oxygen, which is supplied by reverse spillover from the CeO(2) film, thus leading to substantial reduction of the support (approximately CeO(1.90-1.85)).

Thermal behaviour and interactions of cassava starch filled with glycerol plasticized polyvinyl alcohol blends

Thermal behaviour and interactions of glycerol plasticized polyvinyl alcohol (PVOH)– cassava starch (CSS) blended films were analysed using thermogravimetry and differential scanning calorimetry methods. The outcomes showed that addition of glycerol has reduced the onset and end-point melting temperatures of the blended films. Samples with 30 and 40 wt.% of PVOH–glycerol blended with CSS exhibited experimental enthalpy of melting (Δ H m ) lower than theoretical enthalpy of melting (Δ H mi ). Meanwhile, the thermogravimetry degradation of the PVOH–glycerol– cassava starch can be divided into three phases, whereby phase 1 is the vaporization of volatiles, phase 2 is the rapid decomposition/dehydration and elimination of degradants and phase 3 is the formation of carbonaceous residues. These samples have thermogravimetry degradation activation energy ( E a ) higher than their original components. For instance, 20 wt.% of PVOH–glycerol blended with CSS has a E a which is 6.36 and 4.07 times higher than glycerol plasticized PVOH and CSS, respectively. Blending of PVOH–glycerol and CSS are favorable to produce biodegradable compounds resist to thermal attacks.

A Numerical Comparison of Spray Combustion between Raw and Water-in-Oil Emulsified Fuel

Heavy fuel-oils, used engine oils and animal fat can be used as dense, viscous combustibles within industrial boilers. Burning these combustibles in the form of an emulsion with water enables to decrease the flame length and the formation of carbonaceous residue, in comparison with raw combustibles. These effects are due to the secondary atomization among the spray, which is a consequence of the micro-explosion phenomenon. This phenomenon acts in a single emulsion droplet by the fast (&lt; 0.1 ms) vaporization of the inside water droplets, leading to complete disintegration of the whole emulsion droplet. First, the present work demonstrates a model of spray combustion of raw fuel. Secondly, the spray combustion of water-in-oil emulsified fuel is exposed to the same burning conditions, taking into account the micro-explosion phenomenon. Finally, the comparison between the results with and without second atomization shows some similar qualitative tendencies with experimental measurements from the literature.

Decomposition of catechol and carbonaceous residues on TiO2(110): A model system for cleaning of extreme ultraviolet lithography optics

High energy photons used to expose photoresists in extreme ultraviolet lithography (92eV, 13.5nm) photoexcite electrons from Mo∕Si multilayer mirror surfaces. Photoemitted electrons participate in the formation of carbonaceous residues on the mirror surface significantly affecting the mirror reflectivity. We explore mitigation strategies utilizing TiO2(110) as a model for the capping layer. Two carbon containing surfaces are examined; an ordered catechol monolayer and a carbonaceous layer. Excimer laser sources (XeF and KrF) coupled with oxidizing gas backgrounds (NO and O2) are shown to be effective for the photocatalytic removal of carbon. Utilizing x-ray photoemission spectroscopy and scanning tunneling microscopy carbon removal is shown to proceed through oxidation of the overlayer.

Thermogravimetric analysis of a cotton fabric incorporated by ‘Graham’s salt’ applied as a flame-retardant

Abstract We have investigated the effect of ‘Graham’s salt’ as a phosphorous containing flame-retardant applied onto cotton fabric. The optimum loading of this salt to impart flameretardancy has been determined to be about 36.78-41-31 g salt per 100 g cotton woven fabric (plain 144 g m−2). Thermogravimetry of pure cotton, treated cotton fabric and the pure salt were accomplished. The curves were then compared and commented. They reveal that this salt thermosensibilized combustion of the treated substrate as a dehydrating agent. The results obtained fortified the ‘Chemical Theory’ and ‘Coating Theory’ evidenced the formation of carbonaceous residue upon the cellulosic substrate during the combustion.

Hydrogen production in membrane reactors using Rh catalysts on binary supports

The binary supports employed in this work were prepared by different methods. The Ti(7%)–MgO and the Ti(13%)–SiO 2 were obtained using the grafting technique. The La(27%)–SiO 2 was obtained through the incipient wetness impregnation with La(NO 3) 3 of Aerosil 300, previously calcined at 1173 K. The Rh was incorporated to these supports by wet impregnation. The catalysts were first evaluated for the CH 4 + CO 2 reaction in a fixed-bed reactor. They were found to be active and stable as to justify their use in the membrane reactor, which was operated at 823 K achieving methane conversions up to twice as much as the equilibrium values. In all cases, the activity of the Rh solids remained constant after 120 h on stream with very little formation of carbonaceous residues only detected through LRS. The catalysts were characterized through either hydrogen or carbon monoxide chemisorption, TPR, XRD, LRS and XPS. The Rh(0.6)/La–SiO 2 catalyst showed a high metal dispersion that remained constant after use and the highest capacity to restore the CH 4 + CO 2 equilibrium when H 2 was permeated out of the reaction section. The Rh(0.8)/Ti–MgO showed the highest Rh/oxide interaction associated with the lowest capacity to restore the reaction equilibrium. The Rh(0.8)/Ti–SiO 2 exhibited an intermediate activity due in part to the partial segregation of the TiO 2 upon calcinations and the subsequent appearance of small Rh° crystallites in the used catalysts.

BETA zeolite supported on silicon carbide for Friedel-Crafts fixed-bed reactions

Beta zeolite coated on a preshaped medium surface area silicon carbide (SiC) carrier was prepared via a hydrothermal synthesis. The SiC support allows the precise control of the macroscopic shape of the final catalyst, which significantly decreases the diffusion pathway of the reactants to the active site. 27Al MAS-NMR analysis revealed that all the aluminum was in a tetrahedral coordination and no trace of extraframework aluminium was observed. The full width at half maximum of the NMR peak was about 10 ppm, which indicates the presence of small zeolite crystals inside the sample. SEM observation has shown that the zeolite homogeneously coated the outer surface of the silicon carbide extrudate support with different size and shape and random orientation. The existence of a layer of silica and silicon oxycarbide on the surface of the support allows a strong anchoring of the coated zeolite which prevents the loss of the deposited zeolite during handling and operation. The as-prepared catalyst exhibits a high catalytic activity in the benzoylation of anisole in a fixed-bed configuration. In addition, the catalyst was extremely stable, as no deactivation was observed after several hours of test, whereas bulk zeolite exhibits a strong deactivation with the time mainly due to the formation of carbonaceous residues inside the channel network.

Oxidative degradation of EVA copolymers in the presence of MCM-41

In this work, a study of the degradation of PE and an EVA copolymer under air atmosphere, in the presence and absence of mesoporous MCM-41, was carried out using thermogravimetric analysis (TGA), focusing on the analysis of the EVA behaviour during this the process. The results obtained show that the air atmosphere causes an increase of the complexity of the process, with respect to the thermal and catalytic pyrolysis in N 2 atmosphere, exhibiting more decomposition steps. The results obtained for both polymers show that the presence of MCM-41 does not practically affect the temperature of the oxidative decomposition processes, but a clear effect has been found on the main step of degradation, that supports the existence of cracking or incomplete oxidation reactions, and clearly it enhances the carbonaceous residue formation.

Physico-chemical processes occurring inside a pyrolyzing two-dimensional tobacco particle

A two-dimensional, variable property, mathematical model of the transient pyrolysis of tobacco particle, in response to the smoldering (low heating rate) and puffing (fast heating rate) conditions in a burning cigarette, is presented. The model considers pyrolysis of tobacco obeying four-step Arrhenius kinetics, evaporation of water from tobacco following a mass-transfer and rate-determined process, and the formation of carbonaceous residue. From the physical point of view, the model describes convective, conductive and radiative heat transfer, and velocity and pressure variations interior to the porous tobacco particle (Darcy’s law). Furthermore, porosity, permeability and thermal conductivity vary with the composition of the reacting medium. Time and space evolution of the main variables, and reaction product distribution, are simulated by varying the tobacco heating rates.