Soot-free synthesis of C60

A new synthetic medium for the production of C₆₀ has been found that does not produce soot. C₆₀ was produced in the liquid phase of an aerosol of precursor soot at 700 °C. The precursor soot aerosol, a high temperature stable form of hydrocarbon, was produced by pyrolysis of acetylene at atmospheric pressure in a flow tube reactor. At 700 °C, the effluent particles were found to contain PAHs, small hydrocarbons and fullerenes but no observable black material. However, when the reactor temperature was changed to 800 °C, soot was also produced in the effluent particles along with PAHs and other small hydrocarbons, and the fullerene product disappeared. These results show a clear competition between the production of fullerenes and other forms of carbon. The filter-collected effluent was shown to be completely soluble in conventional solvents suggesting the possibility of an efficient cyclic synthetic process. Fullerenes were only found in the particle phase implying the first observed liquid phase synthesis of C₆₀.     

Soot-free synthesis of C60

A new synthetic medium for the production of C₆₀ has been found that does not produce soot. C₆₀ was produced in the liquid phase of an aerosol of precursor soot at 700 °C. The precursor soot aerosol, a high temperature stable form of hydrocarbon, was produced by pyrolysis of acetylene at atmospheric pressure in a flow tube reactor. At 700 °C, the effluent particles were found to contain PAHs, small hydrocarbons and fullerenes but no observable black material. However, when the reactor temperature was changed to 800 °C, soot was also produced in the effluent particles along with PAHs and other small hydrocarbons, and the fullerene product disappeared. These results show a clear competition between the production of fullerenes and other forms of carbon. The filter-collected effluent was shown to be completely soluble in conventional solvents suggesting the possibility of an efficient cyclic synthetic process. Fullerenes were only found in the particle phase implying the first observed liquid phase synthesis of C₆₀.     

Reaction of silica-supported fullerene C60 with nonylamine vapor

The reaction of silica-supported [60]fullerene with vaporous nonylamine at 150 °C produces a mixture of addition products. Quantum chemical calculations, at the B3LYP/STO-3G level of theory, support that the addition reaction most likely takes place across the 6,6 bonds of C₆₀ pyracyclene units (and not across the 5,6 bonds). Numerous peaks were found in high-performance liquid chromatograms, apparently due to a large number of possible isomers. According to elemental analysis data (C:N ratio), the number of nonylamine molecules attached to C₆₀ is 3 on average. Thermogravimetric analysis of the nonylamine adduct showed two weight losses, one between 360 and 590 °C due to thermal decomposition of nonylamine moieties, and one between 725 and 840 °C due to decomposition of the remaining fullerene-derived carbonized material. Field-desorption mass spectrometric study revealed a number of molecular and fragment ions corresponding to the adducts with up to six nonylamine moieties attached to [60]fullerene; some of them were observed as multiply-charged ions. The temperature behavior of these peaks is similar to that for TGA, with maxima shifted to lower temperatures due to the cooperative effect of the strong electric field. C₆₀ can be partially regenerated by pyrolysis of the nonylamine adduct, although at very low yields (below 1%, after heating at 350 °C under air for 2 h).     

Hydrogen adsorption on partially truncated and open cage C60 fullerene

C₆₀ buckyball molecules were partially truncated by a controlled oxidation at 400 °C and 2 bar oxygen pressure to create unique pore textures suitable for hydrogen adsorption. Pore textural analysis and density measurement confirmed the success of cage-opening and the creation of pore structures accessible to gas molecules. The specific surface area of the C₆₀ sample were increased from below detection to a measurable value (BET: 85 m²/g). Raman spectral study showed that the three main bands of C₆₀, H_g(1), A_g(1) and A_g(2) remained and significant defects were created after the C₆₀ fullerenes were partially oxidized. XRD and SEM measurements suggested that the C₆₀ fullerenes lost their crystallinity and the crystal surfaces were etched after the oxidation step. Hydrogen adsorption on the C₆₀ fullerenes were measured at three temperatures (77, 143 and 228 K) and hydrogen pressures up to 150 bar. Hydrogen adsorption capacity on C₆₀ fullerenes at 77 K at 120 bar was more than tripled (from 3.9 to 13 wt.%) after the C₆₀ fullerenes were partially oxidized. The average heat of adsorption of hydrogen on the partially oxidized C₆₀ fullerene molecules (2.38 kJ/mol) is within the range of the reported values of heat of adsorption on other porous adsorbents.     

Formation of fullerenes by pyrolysis of 1,2′-binaphthyl and 1,3-oligonaphthylene

High-temperature pyrolysis of two fullerene precursors - 1,2′-binaphthyl and 1,3-oligonaphthyl - has been investigated. An oligomer of naphthalene with the appropriate orientation of fragments, which contains all 60 carbon atoms, 12 of 20 six-membered rings and 71 of 90 carbon-carbon bonds required to form the C₆₀ fullerene cage was synthesized in a three-step synthesis from naphthalene. The formation of fullerene during pyrolysis was confirmed by MALDI-TOF and HPLC analysis of the toluene extract obtained from the raw soot. It was found that the toluene extract contains free C₆₀ fullerene but the main share of fullerenes exists in the form of their derivatives. The yield of free C₆₀ was estimated as 0.1% by HPLC but the overall yield of C₆₀ seems to be higher and was estimated as ≈1%.     

Gas evolution kinetics of two coal samples during rapid pyrolysis

Quantitative gas evolution kinetics of coal primary pyrolysis at high heating rates is critical for developing predictive coal pyrolysis models. This study aims to investigate the gaseous species evolution kinetics of a low rank coal and a subbituminous coal during pyrolysis at a heating rate of 1000 °C s^− 1 and pressures up to 50 bar using a wire mesh reactor. The main gaseous species, including H₂, CO, CO₂, and light hydrocarbons CH₄, C₂H₂, C₂H₄, C₂H₆, C₃H₆, C₃H₈, were quantified using high sensitivity gas chromatography. It was found that the yields of gaseous species increased with increasing pyrolysis temperature up to 1100 °C. The low rank coal generated more CO and CO₂ than the subbituminous coal under similar pyrolysis conditions. Pyrolysis of the low rank coal at 50 bar produced more gas than at atmospheric pressure, especially CO₂, indicating that the tar precursor had undergone thermal cracking during pyrolysis at the elevated pressure.     

Preparation of microporous carbon films from fluorinated aromatic polyimides

Pyrolysis and carbonization behaviors of fluorinated aromatic polyimide films synthesized from fluorinated dianhydrides and diamines were investigated by thermogravimetric and mass spectrometric measurements. Evolution of fluorine compound gases and related species was observed during the pyrolysis in the temperature range from 450 to 700 °C, in addition to the evolution of CO and CO₂ due to the imide ring degradation. By the carbonization of these fluorinated polyimides at 600-1000 °C, highly microporous carbons were obtained without any activation process, of which adsorption/desorption isotherm of N₂ gas was typical type I and pore size distribution was sharp at around 0.55 nm in width. Surface area increased with increasing fluorine content in the repeating unit of fluorinated polyimide: the polyimide with the highest fluorine content of 31.3 mass% gave a high microporous surface area of 1342 m² g⁻¹ and micropore volume of 0.44 mL g⁻¹.     

Reaction rate coefficient of fullerene (C60) consumption by soot

The reaction of fullerene molecules with soot was studied by contacting sublimed C₆₀ fullerenes with commercially available carbon black particles at different temperatures in the range 1023-1273 K. Fullerene mass data collected both pre- and post-reaction were fit to a simple first-order kinetic model and yielded a temperature-dependent reaction rate expression. The calculated collision efficiency of the reaction is of the order 10⁻⁸ and the activation energy is ∼9.8 kcal mol⁻¹, which would be consistent with a surface diffusion reaction or a heterogeneous reaction. Simple extrapolation of the observed rate to the conditions of a fullerene forming flame would give a consumption rate six orders of magnitude too small to account for the rate of fullerene consumption observed in the post-flame zone of a fullerene-forming benzene/oxygen/argon flame. Extrapolation of the reaction rate to flame conditions also shows that the rate of consumption calculated here is too small to account for observed oscillations in the fullerene concentration profile which can be related to changes in the relative rates of consumption and formation. Calculation of activation energies required for the extrapolation of rates observed here to match those observed in flames yields significantly larger values than those obtained in the present study and are so large as to suggest that mechanisms other than those studied here control fullerenes consumption in flames. Other mechanistic possibilities for the consumption of fullerenes in flames include reactions of fullerenes with other flame species and fullerene-soot reactions in which soot reactivity depends on soot reactions with other flame species.     

Effects of fullerene addition on the carbonization of synthetic naphthalene isotropic pitch

The toluene soluble fraction of fullerene soot, consisting of C₆₀ and C₇₀ and other fullerenes, was co-carbonized with synthesized isotropic pitch derived from naphthalene. Mixtures of fullerene and pitch gave carbons in higher yield than expected from their single carbonizations at fullerene contents <30 wt%. The fullerenes suppressed the expansion of the pitch during carbonizations, and changed the optical textures of resultant carbons. At levels of addition of fullerenes <30 wt%, no fullerenes could be detected in resultant carbons by spectroscopy, but were detected as spheres of ca. 10–20 nm diameter in the carbons by TEM. It is considered that fullerenes remove hydrogen from the naphthenic structures of the pitch and so alter carbonization characteristics. Hydrogenation breaks the spheroidal fullerene framework.     

The effects of oxygen on the yields of the thermal decomposition products of catechol under pyrolysis and fuel-rich oxidation conditions

In order to investigate the effects of oxygen on the distribution of thermal decomposition products from complex solid fuels, pyrolysis and fuel-rich oxidation experiments have been performed in an isothermal laminar-flow reactor, using the model fuel catechol (ortho-dihydroxybenzene), a phenol-type compound representative of structural entities in coal, wood, and biomass. The gas-phase catechol pyrolysis experiments are conducted at a residence time of 0.3 s, over a temperature range of 500-1000 °C, and at oxygen ratios ranging from 0 (pure pyrolysis) to 0.92 (near stoichiometric oxidation). The pyrolysis products are analyzed by nondispersive infrared analysis and by gas chromatography with flame-ionization and mass spectrometric detection. In addition to an abundance of polycyclic aromatic hydrocarbons, catechol pyrolysis and fuel-rich oxidation produce a range of C₁-C₅ light hydrocarbons as well as single-ring aromatics. Quantification of the products reveals that the major products are CO, acetylene, 1,3-butadiene, phenol, benzene, vinylacetylene, ethylene, methane, cyclopentadiene, styrene, and phenylacetylene; minor products are ethane, propyne, propadiene, propylene and toluene. Under oxidative conditions, CO₂ is also produced. At temperatures <850 °C, increases in oxygen concentration bring about increases in catechol conversion and yields of C₁-C₅ and single-ring aromatic products—in accordance with increased rates of pyrolytic reactions, due to the enhanced free-radical pool. At temperatures >850 °C, catechol conversion is complete, and increases in oxygen bring about drastic decreases in the yields of virtually all hydrocarbon products, as oxidative destruction reactions dominate. Reactions responsible for the formation of the C₁-C₅ and single-ring aromatic products from catechol, under pyrolytic and oxidative conditions, are discussed.     

Pyrolysis of wood at high temperature: The influence of experimental parameters on gaseous products

The pyrolysis of wood was carried out in an Entrained Flow Reactor at high temperature (650 to 950 °C) and under rapid heating conditions (> 10³ K s^− 1). The influence of the diameter and initial moisture of the particle, reactor temperature, residence time and the nature of the gaseous atmosphere on the composition of the gaseous products has been characterised. Particle size, between 80-125 and 160-200 μm, did not show any impact. Pyrolysis and tar cracking essentially happen in very short time period: less than 0.6 s; the products yields are only slightly modified after 0.6 s in the short residence times (several seconds) of our experiments. Higher temperatures improve hydrogen yield in the gaseous product while CO yield decreases. Under nitrogen atmosphere, after 2 s at 950 °C, 76% (daf) of the mass of wood is recovered as gases: CO, CO₂, H₂, CH₄, C₂H₂, C₂H₄ and H₂O. Tests performed under steam partial pressure showed that hydrogen production is slightly enhanced.     

Self-assembled network structures in Al/C60 composites

A method is explored for the development of nano-network structures in aluminum-based composites containing C₆₀-fullerenes by annealing at 500 °C. During annealing, although carbon atoms are decomposed from fullerenes attempting to form carbides, they cannot readily form carbides because C₆₀-fullerenes are individually dispersed and the driving force for long-range diffusion of carbon atoms is not sufficient at 500 °C. Carbon atoms rather occupy the interstices of aluminum, providing a meta-stable supersaturated aluminum phase with distorted crystal structures. The supersaturated aluminum phases grow with a strong anisotropy derived from lattice mismatch, meet neighboring phases, and then self-assemble into network structures. These nano-scale network structures are extremely stable at 500 °C, and offer significant potential for the development of structural aluminum matrix composites with a GPa-level strength.     

Fabrication and characterization of fullerene-Nafion composite membranes

Fullerene-Nafion composite membranes have been fabricated through a new solution casting for the first time. The fullerenes used for the composites included C₆₀ and polyhydroxy fullerene (PHF), C₆₀(OH)_n (n ∼ 12). The dispersion of the fullerene in the composite membrane was much more refined with smaller agglomeration particles, relative to the previously prepared fullerene-Nafion composites in which the fullerene was introduced through doping. The miscibility of the hydrophobic fullerene, C₆₀, in the Nafion matrix was further improved by a new fullerene dispersant, poly[tri(ethylene oxide)benzyl]fullerene, C₆₀[CH₂C₆H₄(OCH₂CH₂O)₃OCH₃]_n (n ∼ 5), synthesized in this work. The solution-cast fullerene composites also demonstrated a significant improvement in the physical stability relative to the fullerene-doped Nafion composites through a better integration of the fullerene into the Nafion matrix. Furthermore, increased loadings of the fullerene in Nafion were made possible through the new solution-casting method, compared to the previous doping method. The water characteristics in the fullerene composites have been examined by TGA and ¹H pulse NMR measurements. The interactions between the fullerene and the Nafion have been studied through ATR FT-IR and molecular dynamics simulations which suggested PHF resides primarily in the hydrophobic domain of Nafion when the loading was low. The voltammetric measurements also have shown that the fullerene composites have the reduced limiting current density, compared to Nafion membranes without fullerenes.     

Pyrolysis of poly-l-leucine under combustion-like conditions

The protein poly-l-leucine has been used as a model compound for the nitrogen in biomass fuels. It was pyrolysed in a fluidised bed at 700 and 800 °C and the pyrolysis gases were analysed with a FT-IR spectrometer. HCN, NH₃ and HNCO were identified as the main nitrogen-containing species, while neither NO nor N₂O were found among the pyrolysis gases. At 700 °C, as much as 58% of the nitrogen content was converted into HCN and 31% into NH₃. The HCN/NH₃ ratio increased from about 1.9 at 700 °C to above 2.2 at 800 °C. Pyrolysis of another protein, poly-l-proline, at 800 °C gave a HCN/NH₃ ratio close to 10. This revealed that the protein's amino acid composition has a marked impact on the composition of the pyrolysate.     

Evaluation of utilization of corn stalks for energy and carbon material production by using rapid pyrolysis at high temperature

Pyrolysis of agricultural residues (corn stalks) took place batch wise in a laboratory captive sample reactor (wire mesh) at atmospheric pressure. The process was studied by varying the temperature (470-710 °C) with an average heating rate of 60 °C s⁻¹ and a reaction time of 0.2 s. The carrier gas used for both pyrolysis and GC analysis was He. The nature and quantity of gases produced and the main characteristics of the charcoals formed have been determined. From the GC analysis, CO showed the higher yield, followed by H₂, CH₄ and CO₂. The increase in temperature is especially important to increase the production of gas, mainly hydrogen. From gas composition and proximate analysis, the heating value of gas and solid phases has been determined. A kinetic model of pyrolysis based on first order kinetics and on total devolatilization has been developed. According to this model, kinetic constants, pre-exponential factors and activation energies have also been determined for low and high temperatures.     

Evaluation of structural features of chars from pyrolysis of biomass of different particle sizes

The structural features of chars derived from pyrolysis of mallee wood of different particle sizes in a novel fluidized-bed/fixed-bed reactor have been investigated. Raman spectroscopy was used for structural evaluation of chars. Spectra were curve-fitted with 10 Gaussian bands representing typical structural features of the chars. The temperature had a significant influence on the evolution of char structure and thus the total Raman peak area between 800 and 1800 cm^− 1 is seen to decrease significantly with increasing pyrolysis temperature for all chars. On the other hand, the ratio I_D/I_{(Gr + Vl + Vr)} between the band intensities of condensed aromatic ring systems (> 6 rings) and amorphous char structures with small aromatic ring (3-5 rings) systems is seen to increase with increasing temperature. The particle size of biomass has a great role in char structure at fast heating rate (> 1000 °C/s) pyrolysis although it has no effect on char structure at slow heating rate pyrolysis (0.17 °C/s). However, in the bigger biomass particle, the structure of char prepared under fast heating rate pyrolysis is similar to that of the structure of char prepared under slow heating rate pyrolysis.     

Pyrolysis of scrap printed circuit board plastic particles in a fluidized bed

Pyrolysis behavior and corresponding pyrolysis products of printed circuit board plastic particles (PCBP particles) were investigated in a fluidized bed using TG-FTIR analysis system. PCBP particles were separated from crashed printed circuit boards using fluidized beds, 354 μm crashed plastic particles were pyrolyzed at the temperature ranging from 20 to 900 °C by a thermogravimetric analyzer. Two stages of decomposition were identified for PCBP particles under nitrogen conditions. The activation energy was 90.49 kJ/mol for the first-stage reaction and 137.80 kJ/mol for the second-stage reaction. Further, gas products, liquid products, and solid residues yielded in the fluidized bed were analyzed using an elemental analyzer and FTIR. It has been found that the liquid yields increased with an increase in pyrolysis temperature, and with an increase in superficial gas velocity. The main compositions of liquid products were aromatic compounds including substituted benzenes. Whereas, the solid products mainly contained char and fiberglass.     

The role of Fe species in the pyrolysis of Fe phthalocyanine and phenolic resin for preparation of carbon-based cathode catalysts

Pyrolysis of a mixture of Fe phthalocyanine and phenolic resin (FePc/PhRs) was studied to clarify the details of the preparation protocol of nitrogen-doped carbon-based materials for cathode catalysts in polymer electrolyte membrane fuel cells. TEM images show that nanoshell carbon is formed by the pyrolysis of FePc/PhRs in the temperature range of 600-800 °C. The optimum pyrolysis temperature for the FePc/PhRs mixture was 600 °C, where moderate conductivity and high nitrogen content of the prepared carbon were both satisfied. This catalyst showed a promising fuel cell performance with 1.01 V open-circuit voltage and 0.33 W cm⁻² maximum output, at 0.2 MPa absolute pressure and 80 °C. A detailed study of the carbonization process suggests that the presence of Fe species during carbonization process contributes to higher nitrogen content and growth of nanoshell structure of the resulting carbon.     

An experimental study of oil recovery from sewage sludge by low-temperature pyrolysis in a fluidised-bed

Pyrolysis of activated sewage sludge was investigated under inert conditions in a fluidised-bed to study the effects of temperature and gas residence time on the product distribution and composition with an aim to maximise the oil yield. The temperature was varied from 300 to 600 °C and the gas residence time from 1.5 to 3.5 s. Three groups of products were produced, namely, a non-condensable gas (NCG) phase, a solid phase (char) and a liquid phase (oil). A maximum of 30% oil yield (wt% daf of sludge fed) was achieved at a pyrolysis temperature of 525 °C and a gas residence time of 1.5 s. Higher temperatures and longer gas residence times favoured the formation of NCG, suggesting that secondary cracking reactions had occurred. The oil obtained was analysed using GC-MS and H NMR to determine the oil's composition and structure, a unit structure of the oil was proposed which consisted of aromatic rings connected by hydrocarbons with -OH functional groups attached.     

On an improved pyrolytic synthesis of [60]- and [70]-fullerene

The nickel-catalyzed pyrolysis of two fullerene precursors — (1) naphthalene and (2) 1-bromonaphthalene — at 1200°C in an argon atmosphere has been investigated. Fullerenes, polycyclic aromatic hydrocarbons (PAHs), and polycyclic aromatic brominated species (the latter obtained in pyrolysis of 1-bromonaphthalene only) were extracted from the pyrolysates by reflux in toluene. The toluene extracts were subjected to mass spectrometric analysis using the chemical ionization technique in the negative mode. Mass spectra are included with discussions on fullerene yields and on the mechanism by which fullerenes are formed in pyrolysis. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to characterize the toluene-insoluble material.