Plasma-assisted Pyrolysis Research Articles

Numerical Analysis for Predicting the Rate of Graphitization on Wood Biomass During the Plasma-Assisted Pyrolysis

Abstract The plasma-assisted pyrolysis process is a powerful treatment for converting wood biomass to graphitic carbon. In order to make this process more precise and effective in time, the rate of graphitization data is needed, especially for predicting the effective time of treatment. In this study, numerical analysis is conducted to predict the rate of graphitization. An explicit finite difference method is applied for the numerical analysis. Some initial parameters used are the wood thickness (5 mm), coefficient of diffusivity (0.082 mm2/s), input plasma temperature (4,000 C), initial wood temperature (35 C), and room temperature (27 C). The analysis was conducted with a variation of time differences of 1 s, 2 s, 3 s, 4 s, and 5 s. The assumption used in this analysis is that the minimum temperature for graphitic carbon conversion is 2,000 C. The result of this study is the values of graphitization rates and exposure times summarized in TABLE 1. Therefore, this numerical analysis can successfully be used to predict the rate of graphitization and plasma exposure time for different wood biomass thicknesses.

Plasma-assisted pyrolysis for converting oil palm fronds into reduced graphite oxide

One of the oil palm tree’s solid waste is oil palm fronds. Due to its lignocellulosic composition, it has the potency to convert it into carbon. The common heat treatment method to convert oil palm fronds into carbon-based material is pyrolysis. However, this process has some disadvantages, such as being time-consuming and just producing amorphous carbon. Different from common pyrolysis temperatures, in this study we use a higher temperature (4000 °C) generated by DC current arc plasma. This process is faster than the common pyrolysis process (less than 10 minutes) and produces crystalline material. This product is then characterized by Raman spectroscopy, SAED-TEM, XRD, FT-IR, and SEM/EDX. Based on Raman spectroscopy, this crystalline material shows the characteristics of semiconductor carbon. Based on the SAED-TEM, there is a (002) plane of hexagonal crystal structure detected (graphite phase characteristics). An XRD analysis shows the characteristics of the trigonal crystal structure (P3) constructed by O and H atoms. An FT-IR characterization shows that there are C=C, C-H, and O-H bonds, while the EDX analysis result shows a carbon-to-oxygen ratio of about 4.23. Therefore, based on the whole interpretation, the plasma-assisted pyrolysis treatment is successfully used to convert oil palm fronds into reduced graphite oxide (rGO).

Plasma-assisted pyrolysis and ignition of pre-vaporized n-heptane, iso-octane and n-decane

We intensively investigated the kinetic enhancement of dielectric-barrier-discharge (DBD) plasma on the pyrolysis and ignition of n-heptane, iso-octane, and n-decane fuels in a counterflow diffusion burner. The DBD plasma generated upstream from the fuel nozzle can contribute to low-temperature pyrolysis and high-temperature oxidation of pre-vaporized liquid fuels. Stable and short-lived intermediate species generated by plasma were measured by ex situ gas chromatography (GC) and in situ planar laser induced fluorescence (PLIF), respectively. GC results indicate that with plasma assistance approximately 2–3% of large hydrocarbons decompose at temperatures as low as 370 K and within 1 s. High-temperature oxidation experiments demonstrate that DBD can lower the ignition temperature of all three fuels with various global flow stretch rates. Experiments were compared with numerical analysis performed using the OPPDIF code that is formulated for the counterflow geometry. Finally, the discrete chemical explosive mode analysis (CEMA) elucidates the promotion of plasma-induced species, such as H2, C2H4, and OH radicals.

Plasma assisted pyrolysis for processing of composite ceramic coatings based on silazane precursor and TiB2 filler applied onto a sintered steel

In this work, silazane-based polymer coating loaded with reactive TiB2 filler was applied onto a sintered steel substrate. Two thermal processing routes were investigated for the conversion of the precursor and filler into a composite ceramic coating: conventional pyrolysis (CP) and plasma-assisted pyrolysis (PAP), both performed at nitrogen atmosphere. The sample substrate and coatings were characterized by optical and scanning electron microscopy, energy-dispersive spectrum, X-ray diffraction, and glow discharge optical emission spectroscopy. Microstructural analysis revealed a denser ceramic composite coating with an improved conversion of TiB2 filler when the pyrolysis process was assisted by plasma. Interdiffusion between the steel substrate and filled PDC coating leads to the formation of new phases in the coating, which in contrast, were not observed when the process was performed by conventional pyrolysis.

Porous carbon-coated LiFePO4 nanocrystals prepared by in situ plasma-assisted pyrolysis as superior cathode materials for lithium ion batteries

The porous carbon-coated LiFePO4 (LFP) nanocrystals synthesized by in situ plasma-assisted pyrolysis are reported. The particle size of LFP nanoparticles is well controlled through the coating of polyaniline (PANI) on FePO4. The effect of PANI content in FePO4/PANI on the morphology and electrochemical performance of LiFePO4 particles is extensively investigated. Results show that the optimized amount of PANI in FePO4/PANI is 10.16% and the corresponding carbon content in activated porous carbon-coated LiFePO4 (LFP/AC-P4) is 9.27%. The primary particle size of LFP/AC-P4 is 20~50 nm which are wrapped and connected homogeneously and loosely by activated porous carbon. The LFP/AC-P4 composite delivers a capacity of 166.9 mAh g−1 at 0.2 C, which is much higher than carbon-encapsulated LiFePO4 nanocomposite (LFP/C) synthesized without the assistance of plasma pyrolysis (163.5 mAh g−1). Even at high rate of 5 C, a specific capacity of 128.4 mAh g−1 is achievable with no obvious capacity fading after 250 cycles.

Two-Stage Processing of a Material with Predominant Combustible Matter

The authors have presented an improved technology for processing of organic substances, which is based on an analysis of various methods described in the literature and results of experimental investigations of thermal conversion and plasma-assisted pyrolysis, conducted at the A. V. Luikov Heat and Mass Transfer Institute of the National Academy of Sciences of Belarus. The proposed technology includes two stages the first of which is pyrolysis with a temperature of 400 to 550oC. The combustible matter of the material decomposes with the resulting formation of volatile hydrocarbons and solid coke-ash residue with a high content of carbon and a developed surface. Thus, after the pyrolytic stage step, the hydrocarbon part of the substance goes into a gas phase, and the coke-ash residue is dispersed. The second stage is high-temperature (1100–1400oC) processing of the products of the first stage by the mechanism of partial oxidation. Additional oxygen is fed to convert carbon into CO. As a result, all the hydrocarbons are converted into a syngas which consists of CO and H2. This gas has a high calorific value and can be utilized as a fuel in an electric generator. The inorganic matter can be vitrified and is suitable for safe burial.

Pyrolysis and Oxidation of Methane in a RF Plasma Reactor

The chemical kinetic effects of RF plasma on the pyrolysis and oxidation of methane were studied experimentally and computationally in a laminar flow reactor at 100 Torr and 373 K with and without oxygen addition into He/CH4 mixtures. The formation of excited species as well as intermediate species and products in the RF plasma reactor was measured with optical emission spectrometer and Gas Chromatography and the data were used to validate the kinetic model. The kinetic analysis was performed to understand the key reaction pathways. The experimental results showed that H2, C2 and C3 hydrocarbon formation was the major pathways for plasma assisted pyrolysis of methane. In contrast, with oxygen addition, C2 and C3 formation dramatically decreased, and syngas (H2 and CO) became the major products. The above results revealed oxygen addition significantly modified the chemistry of plasma assisted fuel pyrolysis in a RF discharge. Moreover, an increase of E/n was found to be more beneficial for the formation of higher hydrocarbons while a small amount of oxygen was presented in a He/CH4 mixture. A reaction path flux analysis showed that in a RF plasma, the formation of active species such as CH3, CH2, CH, H, O and O (1D) via the electron impact dissociation reactions played a critical role in the subsequent processes of radical chain propagating and products formation. The results showed that the electronically excitation, ionization, and dissociation processes as well as the products formation were selective and strongly dependent on the reduced electric field.

Kinetics of plasma assisted pyrolysis and oxidation of ethylene. Part 1: Plasma flow reactor experiments

Pyrolysis and oxidation kinetics of ethylene were studied with and without a high-voltage plasma discharge at atmospheric pressure from 420K to 1250K. Experiments were performed in a nearly isothermal flow reactor using mixtures diluted in either argon, helium, or nitrogen to minimize the temperature changes from chemical reactions. At the end of the isothermal reaction zone, the gas temperature was rapidly lowered to quench the reaction. Gas composition was then determined using inline non-dispersive infrared analysis and sample extraction, where samples are stored in a multi-position valve for subsequent analysis with gas chromatography. Experiments were performed by fixing the flow rate or residence time in the reactor, and varying the temperature to achieve a reactivity map. The discharge region occupied approximately 11% of the total length of the isothermal reaction zone and could be placed anywhere along the length of the reactor. The discharge was found to enhance both the pyrolysis and oxidation reactions from 420K to the self-ignition temperature of the fuel. Ethylene pyrolysis was enhanced nearly as much as oxidation below 750K. For plasma-assisted pyrolysis, the results suggest that ethylene dissociation by electron-impact and collisional quenching with electronically excited states of argon, resulted in the direct formation of acetylene and the growth of larger hydrocarbons. During plasma-assisted oxidation, dissociation, and excitation of oxygen led to further fuel consumption, and enhanced the low temperature oxidative chemistry. Above 750K, thermal reactions began to couple to the plasma driven reactions providing further oxidation. At the highest temperatures, the radical production by thermal reactions became competitive and the effectiveness of the plasma discharge decreased.

Kinetics of plasma assisted pyrolysis and oxidation of ethylene. Part 2: Kinetic modeling studies

The kinetics of plasma-assisted pyrolysis and oxidation of ethylene have been numerically investigated. Combining plasma chemistry processes including electron-impact reactions, and reactions of electronically excited species with a comprehensive combustion mechanism, a plasma-assisted kinetic mechanism of ethylene pyrolysis and oxidation has been constructed. To test the accuracy of the constructed mechanism, numerical results were compared to experimental data obtained in a plasma flow reactor, performed under highly diluted conditions in argon at a pressure of 1atm for temperatures ranging from 520K to 1250K. Comparison of plasma-assisted pyrolysis results indicates little discrepancy between the model and experiments. Direct collisional quenching of electronically excited argon by ethylene is responsible for the low temperature enhancement of fuel consumption seen in the plasma-assisted pyrolysis experiments. Hydrocarbon radicals generally undergo addition and recombination reactions to yield several C3 and C4 hydrocarbon intermediates. As temperature increases, the plasma effects diminish and the reaction is overtaken by thermal pyrolysis. Comparison of experimental and modeling results for plasma-assisted oxidation of ethylene demonstrated relatively good agreement for most major and minor species. However, poor agreement was found for ethylene and acetaldehyde for T < 750K. In the oxidation system, collisional quenching of excited argon by O2 to generate the O-atom radical pool complemented the plasma-specific fuel dissociation reactions. The plasma was found to have different effects on the oxidation kinetics at different temperatures. At low temperatures, R+O2 type chemistry (R being a hydrocarbon radical) facilitates the formation of oxygenated species to enhance oxidation by way of formaldehyde. At intermediate temperatures, the formation of hydrocarbon and alcohol intermediates slows the oxidation process relative to the low temperatures. Finally, at high temperatures, plasma chemical reactions are unable to compete against the high temperature chain-branching reactions of the neutral chemistry that dominate and control the overall oxidation process.

3D carbon nanofiber microelectrode arrays fabricated by plasma-assisted pyrolysis to enhance sensitivity and stability of real-time dopamine detection.

In this paper, we have fabricated 3D carbon nanofiber microelectrode arrays (MEAs) with highly reproducible and rich chemical surface areas for fast scan cyclic voltammetry (FSCV). Carbon nanofibers are created from negative photoresist by a new process called dual O2 plasma-assisted pyrolysis. The proposed approach significantly improves film adhesion and increases surface reactivity. We showcase our sensor's compatibility with FSCV analysis by demonstrating highly sensitive and stable FSCV dopamine measurements on a prototype 4-channel array. We envision with proper surface fuctionalization the 3D carbon nanofiber MEA enable sensitive and reliable detection of multiple neurotransmitters simultaneously.

A novel approach to develop composite ceramics based on active filler loaded precursor employing plasma assisted pyrolysis

Aim of the work was to employ for the first time the novel process of plasma assisted pyrolysis (PAP) for developing dense ceramic composites based on a polyorganosilazane as a ceramic forming binder and TiSi2 as active filler.Initially it was necessary to investigate the influence of PAP on the pyrolysis behavior of the precursor in comparison to conventional pyrolysis. We could demonstrate that the ceramic yield as well as the elemental composition of the polyorganosilazane are not adversely influenced by PAP process. This is an indication that no depolymerization of the precursor occurred under plasma atmosphere, which is a precondition for the use as ceramic binder to manufacture ceramic composites.TiSi2 exhibits a high mass gain during thermal treatment in air, but the conversion under N2 atmosphere into nitrides is insufficient. In contrast the use of PAP led not only to an enhanced filler conversion but also to a densification of the composite. The resulting microstructure is dominated by Ti(C,N) as well as a mixture of α- and β-Si3N4 phases embedded in an amorphous SiCN matrix.It could be demonstrated that plasma assisted pyrolysis is a very suitable technology to process dense Ti–Si–C–N composite materials with a tailored microstructure.

High deposition rate coating with nanodisperse SiC powder by plasma-assisted pulse pyrolysis

With regard to the development of a high deposition rate coating process at low substrate temperatures, we investigated whether this can be realized by the formation of nanodisperse SiC particles and their deposition in a one-step process. The SiC powders were obtained by plasma-assisted pyrolysis of tetramethylsilane (TMS) as particle precursor. Owing to a reduction in the amount of particles and the prevention of substrate heating, the particles were formed by pulse pyrolysis at temperatures of 1200–2000 K and at pulse times of 0.1–4 ms. The investigations were performed by means of a shock tube. The powders obtained are nanodisperse with particle sizes in the range below 40 nm consisting of variable contents of both amorphous SiC and crystalline β-SiC. The powders form very thin layers; a single pulse generates a layer with a thickness in the range 40–80 nm, determined by ellipsometric measurements. The layers adhere on the substrate but because of a lack of deposition energy their solidity and adherence on the substrate are not sufficient. Investigations were performed to increase the solidity of the layers by subsequent energy transfer to the layer.