Soot Oxidation Reaction Research Articles

Evolution of structure and oxidation reactivity from early-stage soot to mature soot sampled from a laminar coflow diffusion flame of ethylene

This work investigated the structure and oxidation reactivity of soot sampled from a laminar coflow diffusion flame of ethylene. A capillary-nozzle-hybrid sampling method was developed to extract soot from five sampling positions along flame axis, covering both early-stage and mature soot samples. The results reveal that residence time plays an important role in modifying surface functional groups. Oxygenated and aliphatic groups gradually disappear, soot structure becomes more organized. As a consequence, the rate of mass losses is impaired during thermo-chemical conversion. The derivative thermogravimetry (DTG) results show that oxidation of early-stage soot can be separated into low-temperature (low-T) conversion and carbonaceous substances oxidation processes. The former process including both volatile organic fraction (VOF) releasing and early oxidation reactions generates the first maximum mass loss rate at about 510 °C, while the latter forms the second maximum mass loss rate at about 600 °C. Recognizing that the two processes are partially merged, the distributed activation energy model (DAEM) was introduced to decouple the bimodal behavior of DTG curves. The DAEM results reveal that with increased degree of soot maturity, relative contribution from low-T conversion process decreases abruptly, and DTG curve eventually becomes unimodal and can be well simulated by considering only carbonaceous substances oxidation process.

Synthesis of superficially modified Ce1−x(Zr + Y)xO2−δ solid solutions and thermogravimetric analysis of their performance in the catalytic soot combustion

In this work, solid solutions of general formula Ce1−x(Zr + Y)xO2−δ were chemically synthesized through the so-called citrate-EDTA complexing method, wherein the doping cations Zr and Y were substituted in the ceria lattice with an equimolar amount of 0.05 ≤ x ≤ = 0.25. The ternary oxides were heat-treated, and those that showed the best textural properties were superficially impregnated with Fe2O3 particles by the thermal decomposition method using a metalorganic precursor. The X-ray diffraction results suggest that co-doping with Zr4+ and Y3+ promotes a slight distortion of the CeO2 cubic cell. Nevertheless, the fluorite cubic structure of the oxides remains stable after being exposed to heat treatments. Furthermore, using scanning electron microscopy and Raman techniques, the presence of deposited Fe2O3 and the formation of extrinsic vacancies in the materials could be corroborated. Finally, the oxides’ catalytic evaluation in the soot oxidation reaction was carried out using the thermogravimetry technique. The ternary oxide with cerium molar content equal to 0.9 and impregnated with Fe2O3 presented excellent catalytic behavior for soot oxidation. T10, T50, and T90 temperatures were 310, 383, and 416 °C, respectively.

Properties and oxidation of exhaust particulates from dual fuel combustion: A comparative study of premixed gasoline, n-butanol and their blends.

The focus of this comparative study was to evaluate the oxidation behavior and related properties of exhaust particulates from dual fuel combustion with various low reactivity fuels. Samples from premixed gasoline, n-butanol and gasoline/n-butanol blends with a fixed substitution of 40% (noted as G40, B40 and G20B20, respectively) were characterized by high-resolution transmission electron microscope (HR-TEM), Raman spectroscopy (RS) and X-ray photoelectron spectroscopy (XPS) and thermogravimetric (TG). TG results showed that the oxidation reactivity of particulates from dual fuel combustion followed the order of G40>G20B20>B40, and above particles were more reactive to oxidation than diesel soot. It can be inferred that applying gasoline/diesel dual fuel combustion has beneficial implications for the diesel particulate filter regeneration and even lifetime, in comparison to n-butanol/diesel dual fuel combustion. In comparison to G40 soot, B40 soot exhibited a more ordered nanostructure with longer fringe length but shorter tortuosity from HR-TEM as well as lower ID1/IG and ID3/IG values from RS. Note that the differences in the soot nanostructure between B40 and G20B20 samples were low, and actually the effects of premixed fuels on both soot reactivity and nanostructure were slight. Hence, soot reactivity is only partially structure-controlled. In addition, TEM images showed that soot from premixed butanol had smaller primary particle than premixed gasoline. Particulates from dual fuel combustion exhibited higher C-OH concentrations than diesel soot, but no significant trend can be observed for CO concentrations among various samples. Both primary particle size and oxygenated surface functional groups were not correlated with soot oxidation reactivity.

Oxidation behaviors and nanostructure of particulate matter produced from a diesel engine fueled with n-pentanol and 2-ethylhexyl nitrate additives

Experiments were performed on a high pressure common-rail diesel engine fueled with D100 (diesel fuel), DP15 (15% n-pentanol and 85% diesel, v/v), DP30 (30% n-pentanol and 70% diesel, v/v), DP30E1 (DP30 and 1000 ppm EHN) and DP30E2 (DP30 and 2000 ppm EHN), respectively. Particulates were sampled from the engine exhaust tailpipe and further analyzed with transmission electron microscope (TEM), Raman spectroscopy (RS) and thermogravimetric analysis (TGA). Results showed that an increase in soot oxidation reactivity was observed with increasing n-pentanol concentration in diesel/n-pentanol mixtures. This trend was in line with the poorer structural ordering of soot particles generated from blended fuels by both TEM and RS analyses. Regarding the impact of EHN addition to DP30 fuel, the soot oxidation reactivity decreased as the fuel was changed from DP30 to DP30E1, and then increased as the fuel was changed from DP30E1 to DP30E2. Notably, the soot from DP30 + EHN additive was easier to be oxidized than that from DP30. Similarly, the trends in soot oxidation reactivity with EHN additive can qualitatively capture the variations in soot nanostructure. The correlation between soot reactivity and nanostructure in this study was nonlinear, which infers that soot oxidation reactivity would be also influenced by other features like active surface area and surface functional group. It can be suggested that the application of DP30 would significantly affect the regeneration performance of diesel particulate filter (DPF); when the baseline fuel is DP30, the impacts of EHN additives on regeneration performance of DPF are relatively slight.

Soot properties in ethylene inverse diffusion flames blended with different carbon chain length alcohols

This study was devoted to the characterization of soot properties in ethylene inverse diffusion flames with different carbon length alcohols, which mainly contained the soot morphology, soot nanostructure, and oxidation reactivity. Ethanol, n-butanol, n-hexanol, and n-octanol were selected as the fuel additives. For all blended flames, a 30% volume fraction of ethylene was substituted by different alcohol additives, and the flow rates of the alcohols were adjusted to achieve the same number of carbon atoms. A combination of the thermophoretic sampling technique and the quartz plate sampling method was applied to gain soot features. The transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), Raman spectroscopy, and thermogravimetric analysis (TGA) were used. The results showed that soot production was reduced with the addition of all alcohols, and the minimum soot yield was observed with ethanol addition. The soot-reducing ability gradually decreased as the alcohols move higher. The sizes of the primary particles and soot aggregates increased slightly faster with the increasing carbon chain length. Furthermore, the soot generated from higher alcohol-doped flame has a higher degree of graphitization with longer fringe length and smaller fringe tortuosity. The four different alcohol additives all could improve soot oxidation reactivity. There was a correlation between soot oxidation reactivity and the carbon chain length of the alcohols that the longer carbon chain of these alcohol additives led to lower soot reactivity.

Formation and characteristics of soot from pyrolysis of ethylene blended with furan fuels

As two renewable oxygenated biofuels, 2,5-dimethylfuran and 2-methylfuran (DMF and MF) have been considered to be two of the most potential fuels in the future due to the development of the second-generation biosynthetic technologies. The atmosphere pyrolysis experiments with 0%, 25%, 50%, 75% and 100% replacement of ethylene by DMF/MF at 1173 and 1273 K were conducted. Collected soot samples were characterized by high resolution transmission electron microscopy (HRTEM) and thermogravimetric analysis (TGA) to acquire their internal structure and oxidation reactivity. Results showed that soot mass was positively related with DMF addition ratios and the reaction temperature. Soot production was also enhanced when the MF addition ratio gradually increased from 0% to 75%. The influences of DMF addition can promote soot formation more obviously than MF. Temperatures showed a more significant influence on soot morphology than fuel types and DMF/MF addition ratios. For a fixed addition ratio of DMF/MF, soot showed liquid-like substances at 1173 K. At 1273 K, approximately round particles formed and linked together in chains. Moreover, at 1273 K, the aggregates obtained by adding MF contained more single particles, longer carbon chains, and larger projection area compared with the aggregates by adding same MF. For nanostructures, as the addition ratios of DMF/MF increased, as well as the reaction temperature improved, the fringe length of the carbon layer increased, the average fringe tortuosity decreased, and the stacking arrangement of soot became more orderly, the soot oxidation reactivity was lower. Under a same addition ratio and reaction temperature, soot obtained by adding DMF possessed slightly longer fringe length, smaller fringe tortuosity and lower oxidation reactivity than those of the soot obtained by adding MF. High correlation between fringe parameters and soot oxidation reactivity was discovered. The more ordered soot nanostructure, the longer fringe length, and the smaller fringe tortuosity could make the oxidation reactivity of soot get lower.

Experimental study of impact of lubricant-derived ash on oxidation reactivity of soot generated in diesel engines

The objective of the present study was to understand how the lubricant-derived ash-loaded diesel particulate filter (DPF) impacted the soot oxidation reactivity during the regeneration process. Four major commercial lubricant additives (i.e. Ca, Zn-P, Ca-Zn-P, and Mo-P) were heated up in a muffle furnace to generate ash particles, which were mixed with diesel soot in a loose-contact pattern for further analysis. Thermogravimetric analysis (TGA) was employed for both non-isothermal and isothermal conditions to examine the oxidation reaction parameters, including ignition temperature, peak temperature and burnout temperature. In the meantime, the sizes and nanostructures of the primary soot particles during the oxidation process were characterized by high-resolution transmission electron microscopy (HRTEM). Results showed that lubricant-derived ashes accelerated the oxidation of soot particles as indicated by the reduced oxidation characteristic temperatures and increased oxidation rate. Based on the analysis of HRTEM images, both surface and internal burning phenomena existed in the oxidation processes of pure soot conditions and soot-ash mixtures conditions. The structures of shell-core, onion- and capsule-like, hollow and carbonization fragments appeared sequentially through the entire oxidation processes. Comparing to the pure soot conditions, the tendency of surface burning of the soot particles was notably increased by the lubricant-derived ashes. It was thus concluded that, the lubricant-derived ash components played the role as catalyst to promote soot oxidation and favor the whole regeneration process, even though the ashes may deteriorate performance of DPF by increased backpressures.

On the effects of opposed flow conditions on non-buoyant flames spreading over polyethylene-coated wires – Part II: Soot oxidation quenching and smoke release

Smoke release in the limited volume of a spaceship poses a major threat to the life of astronauts in long range exploration missions. If the absence of buoyant flows fundamentally affects combustion mechanisms, the possibility of atmospheric design in spacecraft environment provides a new leverage, not usually available on Earth. Investigating a non-buoyant flame spreading over the polyethylene coating of an electrical wire in an opposed laminar flow, the previous paper highlighted how flow conditions, namely oxygen content, flow velocity, and ambient pressure, affected spread rate and soot formation rate. The implementation of the Broadband Modulated Absorption/Emission (B-MAE) technique provided mappings of soot temperature and volume fraction in the spreading flames during parabolic flights. In this second paper, the link between these microscopic observations and new macroscopic findings regarding the influence of flow conditions on the smoke production of a flame in the same configuration is presented. Taking into account other requirements of space exploration, atmospheric conditions below normoxic values present a clear interest from a fire safety perspective. In the process, a threshold temperature at which soot oxidation reactions are frozen is identified. The value of 1400 K brought forward conforms with past measurements performed at normal gravity, while discrepancies with previous microgravity measurements are addressed. Given the broad capability of human lungs to adapt to various conditions, the overall mapping of smoke production as a function of flow conditions is a valuable tool for atmospheric design considerations.

Comparative Study on Soot Reduction, Soot Nanostructure and Oxidation Reactivity of n-heptane/DMC and Isooctane/DMC Inverse Diffusion Flames

Dimethyl carbonate (DMC) is an environmentally oxygenated compound which can be used efficiently for soot reduction. This paper compared the soot reduction, soot nanostructure and oxidation reactivity from inverse diffusion flames (IDFs) of the hydrocarbon fuels, namely n-heptane and isooctane doped with DMC. Effects of DMC additions on soot reduction were discussed. DMC addition is more effective for the soot reduction of n-heptane/DMC IDF than isooctane/DMC IDF. The morphology and nanostructures of soot particles were investigated by Transmission Electron Microscopy (TEM) and High Resolution TEM (HRTEM), and the soot graphitization and oxidation reactivity were analyzed by X-ray Diffraction (XRD) and Thermogravimetric Analyzer (TGA), respectively. The results of HRTEM images showed that many larger aggregates were observed for the structures of soot particles from IDFs with DMC additions. The soot particles exhibited more liquid-like material, more amorphous, higher disorganized layers, and less graphitic than that of IDFs without DMC additions. With increasing of DMC blending rate, soot particles changed younger to have shorter fringe length, higher tortuosity, and greater fringe separation. Based on the XRD and TGA results, the degree of the soot graphitization level decreased; the soot mass lost significantly faster, and the soot become more reactive.

Petroleum and Fischer–Tropsch diesel soot: A comparison of morphology, nanostructure and oxidation reactivity

This study investigated the physical properties of the exhaust soot particles from a light-duty diesel engine fueled with an ultra-low sulfur diesel fuel (ULSD) and Fischer–Tropsch diesel fuel synthesized from coal (CFT). The morphology and nanostructure of the obtained soot were characterized using a high-resolution transmission electron microscopy, while the oxidation reactivity of soot was evaluated by the thermogravimetric analysis (TGA). Despite the different fuel properties, both the ULSD and CFT soot exhibits similar changes in fractal dimension, primary particle size and nanostructure parameters (including fringe length, separation distance and tortuosity) when varying the engine speed or load. However, the CFT soot has smaller fractal dimensions and primary particle sizes and a more ordered nanostructure as compared to the ULSD soot. The TGA results demonstrate that the CFT soot has the higher apparent activation energy, indicating that it is less reactive than the ULSD soot. The length and tortuosity of the fringes within the soot structure are found to have definite correlations with soot reactivity.

Physical properties of exhaust soot from dimethyl carbonate-diesel blends: Characterizations and impact on soot oxidation behavior

This study presents the physical properties and oxidation reactivity of exhaust soot from a modern direct injection diesel engine fueled with dimethyl carbonate (DMC)-diesel blends and discusses the relationship between physical properties and oxidation reactivity of soot. The soot morphology, size, fractal dimension and nanostructure were analyzed by transmission electron microscopy and Raman scattering spectrometry. The thermogravimetric analysis was carried out to characterize soot oxidation reactivity in the form of apparent activation energy. The results showed that soot aggregates from DMC/diesel blended fuels exhibited fewer and smaller primary particles as well as small-sized clusters than the diesel soot aggregates. Soot primary particles presented shorter fringe length, wider separation distance and greater tortuosity with increasing DMC blending amount, while the degree of graphitization for soot presented an increasing trend. It was also found that soot from DMC/diesel blends, or low loading operation had higher oxidation reactivity than those from pure diesel or heavy loading operation. Among the physical properties, fractal dimension and primary particle size appeared to be insignificant than the nanostructure for governing the soot oxidation reactivity. Further analysis showed the separation distance was more correlated with soot oxidation characteristics than fringe length and tortuosity. These results illustrated that the use of DMC blended diesel fuel affects the physical properties of soot, enhances soot particle oxidation reactivity, which will be significant for improving the regeneration efficiency of after-treatment device.

Kinetic analysis of morphologies and crystal planes of nanostructured CeO2 catalysts on soot oxidation

Soot oxidation is a triple-phase reaction system involved in solid soot, solid catalyst and gaseous oxidant, which makes its kinetic behavior difficult to be determined. Herein, we report the kinetic behavior of crystal planes on the CeO2 catalysts with various morphologies for soot oxidation. We establish a kinetic model of crystal planes of CeO2 in soot oxidation by means of the distributed activation energy model (DAEM). Through analyzing the distribution function of apparent activation energies (f (Ea)) under loose contact condition, we discover that the Ea of the exposed (1 0 0), (1 1 1) planes and non-catalytic gaseous O2 on soot oxidation distributes in the range of 60–100, 100–150, and 150–250 kJ mol−1, respectively. Our findings show that compared with other catalysts, CeO2 nanocubes exhibit the higher intrinsic activity (turnover frequency, TOF) under loose contact condition, because of the higher f (Ea) value of abundant active exposed (1 0 0) planes located at the lower Ea range. Our work develops a methodology of kinetic analysis to investigate the soot oxidation reaction, which could be potentially extended to other complex oxidation systems.

Deposition of Potassium Salts on Soot Oxidation Activity of Cu-SSZ-13 as a SCRF Catalyst: Laboratory Study

Cu-SSZ-13 catalyst, as the most popular selective catalytic reduction on filter (SCRF) catalyst in diesel exhaust purification, may suffer from severe alkali deposition derived from engine oil, urea solution and biodiesel fuel. These accumulated deposits inevitably affect both of the NOx reduction and soot oxidation reactions. Unlike deactivation effect of alkali impurities on Cu-SSZ-13 catalyst for NH3-SCR process, which has been extensively studied and well documented, the impact of alkali deposition on soot oxidation over SCRF catalyst is still poorly understood. Herein, we reported the influence of potassium salts deposition on soot oxidation of Cu-SSZ-13 catalyst. Compared with the fresh Cu-SSZ-13, these K-impregnated catalysts show promoted activities toward soot oxidation with the promotion effect of K2SO4 > K2CO3 > K3PO4. The generated copper compounds instead of potassium salts are found to be responsible for the enhanced catalytic activity. The NO oxidation over the K2CO3-impregnated catalyst is accelerated by CuOx clusters, resulting in a low ignition temperature toward soot oxidation in the presence of NOx. Contrarily, K2SO4- and K3PO4-impregnated catalysts show higher ignition temperature values because the generated copper sulfates and phosphates present weakened NO oxidation activities especially in the low-temperature region. This work provides new insight into understanding the affecting mechanism of alkali impurities on SCRF catalysts. The generated Cu species induced by the deposition of different potassium salts, rather than alkali species themselves, are responsible for the promoted soot oxidation activity of the K-impregnated Cu-SSZ-13 as a SCRF catalyst.

Effects of Feed Gas Composition on Fresh and Aged TWC-Coated GPFs Loaded with Real Soot

Catalyzed gasoline particulate filters (cGPFs) are one of the most promising technologies to meet future stringent gaseous and particulate emission limits for gasoline-powered vehicles. The successful adoption of this technology relies on several important properties including high filtration efficiency, low back-pressure, high conversion efficiency, and great durability compliance. Particularly in this work, the conversion efficiency and durability of model cGPF catalysts were studied under different feed temperatures and multicomponent feed gas mixtures. The samples consisted of soot-free and real soot-loaded GPFs coated with noble metals supported on alumina and Ce-Zr mixed oxides. Prior to testing, the samples were subjected to diverse hydrothermal aging conditions. Some physicochemical characterization techniques, including scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDS), X-ray diffraction (XRD), transmission electron microscopy (TEM), and nitrogen physisorption, were employed to study the fundamental relations between the state of the samples and their catalytic properties. The results showed that the introduction of soot appeared to have both a positive and negative effect on the catalyst activity. The catalyst surface is masked by the introduction of soot, blocking active sites and inhibiting species conversion. At the same time, the exothermicity of the soot oxidation reaction increases the catalyst temperature, reducing the light-off temperature, for the severely aged samples. Besides the presence of soot, the catalyst aging considerably influences the reactions over cGPFs. In particular, the conversions of ethylene and toluene were more affected by the catalyst aging than CO, which became even worse in the presence of NO in the feed gas. The formation of side products (NH3 and N2O) over the cGPFs was also examined under diverse practical conditions.

Influence of Nanoscale Surface Arrangements on the Oxygen Transfer Ability of Ceria–Zirconia Mixed Oxide

Ceria-based materials, and particularly CeO2–ZrO2 (CZ) solid solutions are key ingredient in catalyst formulations for several applications due to the ability of ceria to easily cycling its oxidation state between Ce4+ and Ce3+. Ceria-based catalysts have a great soot oxidation potential and the mechanism deeply relies on the degree of contact between CeO2 and carbon. In this study, carbon soot has been used as solid reductant to better understand the oxygen transfer ability of ceria–zirconia at low temperatures; the effect of different atmosphere and contact conditions has been investigated. The difference in the contact morphology between carbon soot and CZ particles is shown to strongly affect the oxygen transfer ability of ceria; in particular, increasing the carbon–ceria interfacial area, the reactivity of CZ lattice oxygen is significantly improved. In addition, with a higher degree of contact, the soot oxidation is less affected by the presence of NOx. The NO oxidation over CZ in the presence of soot has also been analyzed. The existence of a core/shell structure strongly enhances reactivity of interfacial oxygen species while affecting negatively NO oxidation characteristics. These findings are significant in the understanding of the redox chemistry of substituted ceria and help determining the role of active species in soot oxidation reaction as a function of the degree of contact between ceria and carbon.

Effects of Magnetic Fields on Morphology and Nanostructure Evolution of Incipient Soot Particles from n-heptane/2,5-dimethylfuran Inverse Diffusion Flames

Differences of the morphology and nanostructure evolution of incipient soot particles generated in n-heptane/2,5-dimethylfuran (DMF) inverse diffusion flames (IDFs) with/without magnetic fields were investigated. Utilizing a high resolution transmission electron spectroscopy, the morphology and nanostructures of soot sampled from spatial locations at different heights in IDFs were analyzed. The graphitization and the oxidation reactivity of soot were tested by an X-ray diffraction and a thermogravimetric analyzer, respectively. Results demonstrated that the magnetic force on paramagnetic species, such as oxygen molecules, can modify the soot formation and oxidation. More incipient soot particles with larger diameters appeared in chains or branches or tufted forms on the flame wing region and the higher position than that on the flame centerline region and the lower position. With magnetic fields, greater amounts of clustered soot particles displayed more crowded distribution and larger diameters. Soot particles with typical structures of the core-shell were promoted to own more orderly bordered lamellae with longer fringe length and smaller fringe tortuosity by the magnetic force acting on oxygen at the same sample position. These modifications resulted in relatively larger diffraction angle of the peak, higher graphitization degree and slightly lower oxidation reactivity of soot.

Impact of lubricating base oil on diesel soot oxidation reactivity

In this study, the surface functional groups types and concentrations, graphitization degree, and oxidation reactivity of exhaust soot samples generated by a heavy-duty engine when employing neat diesel and four base oil dosed mixtures as the fuel was compared. Fourier transform infrared (FTIR), Raman spectroscopy and Thermal gravimetric analyzer (TGA) were used to characterize particle physicochemical properties. Four lubricating base oils were blended in diesel at a mass ratio of 0.5% and 1.0% for combustion. It was found that although the chemical compositions of these four base oils were different, the aliphatic CH functional groups content, graphitization degree and oxidation reactivity of exhaust soot exhibited similar trends. The combustion of base oil was found to change the graphitization degree of emitted soot and lead to soot with a more disordered nanostructure. The soot particles derived from base oil blended fuels had higher aliphatic CH groups concentration than those from neat diesel. Soot oxidation reactivity analyses showed that soot generated from base oil blended fuels had lower characteristic temperatures and lower activation energy than that from neat diesel. Besides, there was a clear correlation between the soot graphitization degree, relative concentration of aliphatic CH groups and its oxidation reactivity.

Doped barium cerate perovskite catalysts for simultaneous NOx storage and soot oxidation

A series of doped barium cerate perovskite catalysts (BaCeO3-δ, BaCe0.8Zr0.2O3-δ and BaCe0.8Zr0.1Co0.1O3-δ) were prepared by a two-step process consisting of solid-state synthesis followed by high-energy ball milling. X-ray diffraction studies showed that the dopants (Zr and Co) were incorporated into the perovskite lattice. TPR studies revealed that the high-energy ball milling process significantly enhanced the reducibility of the catalysts. XPS data indicated a shift in electron density away from the metal centres and an increase in defect oxides, for the high-energy ball milled catalysts, which led to enhanced activity of the catalysts. The catalytic performance was evaluated in a fixed bed reactor system under simulated diesel exhaust conditions, including water. The high-energy ball milled barium cerate sample co-doped with Zr and Co exhibited NOx storage of ∼228 μmol/g at 380 °C and a Tmax, at which the rate of soot oxidation reaction was maximum, of 436 °C.

Formation and nanoscale-characteristics of soot from pyrolysis of ethylene blended with ethanol/dimethyl ether

Ethanol and dimethyl ether (DME) have been considered to be two of the most potential additives for conventional hydrocarbon fuels. This paper focused on the nanoscale characteristics of soot from ethylene pyrolysis with ethanol and DME additions. The pyrolysis experiments were conducted in a α-alumina tube flow reactor at 1273 K, 1373 K and 1473 K, with the replacement of 0%, 50% and 100% (mole fraction) ethylene by the two oxygenated fuels. The gas-phase kinetic modeling was also performed to explore and understand the soot formation process. The main pathways and some key soot precursors in the pyrolysis have been obtained. Soot samples were characterized by high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD) and thermogravimetric analysis (TGA) to acquire their internal structure and oxidation reactivity. Results showed that the mass of collected soot diminished with the increase of the replacement of ethylene by ethanol/DME. The effects of DME to inhibit the formation of soot were more obvious. The least amount of soot was collected in the pyrolysis of pure DME. Peak mole fraction of C2H2, C4H2, C4H4 and C5H5 also decreased with the increase of replacement of ethylene by ethanol/DME, displaying the same tendency with the variation trend of soot mass in the different pyrolysis conditions. According to TEM and HRTEM results, the additions of ethanol and DME could decrease the growth rate of soot contrasted with the pyrolysis of pure ethylene. Soot collected from the pyrolysis of pure DME at 1273 K and 1373 K showed a typical amorphous structure with short, highly-curved and turbulent fringe. With the reduction of the replacement of ethylene by DME, mature soot with longer and more ordered fringe formed at 1373 K and 1473 K. The sequence of the mean fringe tortuosity of soot samples was 100% ethylene<50% DME<100% ethanol<50% ethanol< 100% DME. The order was the same as the sequence of oxidation reactivity. Furthermore, with the increase of temperature, the mass of soot increased. More mature soot with higher degree of graphization, longer fringe length, smaller fringe tortuosity and lower oxidation reactivity was obtained. High correlation between soot nanostructure and soot oxidation reactivity was found.

Nanostructure and reactivity of soot from biofuel 2,5-dimethylfuran pyrolysis with CO2 additions

This paper investigated the nanostructure and oxidation reactivity of soot generated from biofuel 2,5-dimethylfuran pyrolysis with different CO2 additions and different temperatures in a quartz tube flow reactor. The morphology and nanostructure of soot samples were characterized by a low and a high resolution transmission electron spectroscopy (TEM and HRTEM) and an X-ray diffraction (XRD). The oxidation reactivity of these samples was explored by a thermogravimetric analyzer (TGA). Different soot samples were collected in the tail of the tube. With the increase of temperature, the soot showed a smaller mean particle diameter, a longer fringe length, and a lower fringe tortuosity, as well as a higher degree of graphization. However, the variation of soot nanostructures resulting from different CO2 additions was not linear. Compared with 0%, 50%, and 100% CO2 additions at one fixed temperature, the soot collected from the 10% CO2 addition has the highest degree of graphization and crystallization. At three temperatures of 1173 K, 1223 K, and 1273 K, the mean values of fringe length distribution displayed a ranking of 10% CO2 > 100% CO2 > 50% CO2 while the mean particle diameters showed the same order. Furthermore, the oxidation reactivity of different soot samples decreased in the ranking of 50% CO2 addition > 100% CO2 addition > 10% CO2 addition, which was equal to the ranking of mean values of fringe tortuosity distribution. The result further confirmed the close relationship between soot nanostructure and oxidation reactivity.