Effect of Aerosol-Assisted Chemical Vapor Deposition Parameters on Characteristics of the Resulting Carbon-containing Particles

Specific features of the chemical vapor deposition of carbon-containing nanoparticles from aerosols of CH₅COOH–C₃H₇NO solutions, including the effect of the main technological parameters on the size characteristics, structure, and composition of the products being formed, are described. It is shown that the shape, size, and structure of the particles being formed are determined by processes occurring both in the downstream-first evaporation zone and in the main pyrolysis zone, and the temperatures of these zones are the most important technological parameters. It was found that the concentration of benzoic acid in solution can be used as a technological parameter making it possible to gradually vary the size characteristics of the carbon particles obtained. The results of the study form a basis for development of a technology and equipment for obtaining carbon-containing nanoparticles.     

Investigations on poly(vinyl chloride). II. Pyrolysis of chlorinated polybutadienes as model compounds for poly(vinyl chloride)

The pyrolysis of chlorinated polybutadienes (CPB) was investigated by using a pyrolysis gas chromatograph. CPB corresponds to poly(vinyl chloride) (PVC) constructed with head–head and tail–tail linkages of the vinyl chloride unit. Benzene, toluene, ethyl-benzene, o-xylene, styrene, vinyltoluene, chlorobenzenes, naphthalene, and methylnaphthalenes were detected in the pyrolysis products from CPB above 300°C, and no hydrocarbons could be detected at 200°C. The pyrolysis products from CPB were similar to those from PVC and new products could not be detected. Lower aliphatics, toluene, ethylbenzene, o-xylene, chlorobenzenes, and methylnaphthalenes were released more easily from pyrolysis of CPB than from PVC; amounts of benzene, styrene, and naphthalene formed were small. These results support the conclusion that recombination of chlorine atoms with the double bonds in the polyene chain takes place and that scission of the main chain may depend on the location of methylene groups isolated along the polyene chain during the thermal decomposition of PVC.     

Effect of aerosol chemical vapor deposition on characteristics of MoS<Subscript>2</Subscript> particles

Influence exerted by the main technological parameters in the process in which nano- and microparticles of molybdenum disulfide are formed by the aerosol chemical vapor deposition method from a gas phase containing aerosol particles of (NH₄)₂MoS₄?C₃H₇NO solutions on the dimension characteristics, structure, and composition of the products being formed was studied. It was shown that the shape, size, and structure of the particles being formed are determined by the processes occurring in the first, streamwise, reactor zone. The temperature of this zone is the most important technological parameter. The concentration of ammonium thiomolybdate in solution makes it possible to gradually vary the size of disulfide particles in a wide range (from tens of nanometers to micrometers). In the conditions under study, the technological conditions have no effect on the chemical composition of the products being synthesized, which is always described by the formula MoS₂. The results obtained can be used in development of industrial apparatus and technology for synthesis of molybdenum disulfide nano- and microparticles to be used as the antifriction component of lubricating materials.     

P-V-T Dependence for Methanol Solutions with Aromatic Hydrocarbons

The density of binary solutions methanol-para-xylene, methanol-ortho-xylene, and methanol-meta-xylene was measured on an installation for hydrostatic weighing in relation to pressure, temperature, and concentration. The experimental results are generalized using the equation of state.     

Renewable \begin{document}$p$\end{document}-Xylene Production by Co-catalytic Pyrolysis of Cellulose and Methanol

This work developed a one-step process for renewable p-xylene production by co-catalytic fast pyrolysis (co-CFP) of cellulose and methanol over the different metal oxides modified ZSM5 catalysts. It has been proven that \begin{document}${\rm{L}}{{\rm{a}}_{\rm{2}}}{{\rm{O}}_{\rm{3}}}$\end{document}-modified ZSM5(80) catalyst was an effective one for the production of bio-based p-xylene. The selectivity and yield of p-xylene strongly depended on the acidity of the catalysts, reaction temperature, and methanol content. The highest p-xylene yield of 14.5 C-mol% with a p-xylene/xylenes ratio of 86.8% was obtained by the co-CFP of cellulose with 33wt% methanol over 20%\begin{document}${\rm{L}}{{\rm{a}}_{\rm{2}}}{{\rm{O}}_{\rm{3}}}$\end{document}-ZSM5(80) catalyst. The deactivation of the catalysts during the catalytic pyrolysis process was investigated in detail. The reaction pathway for the formation of p-xylene from cellulose was proposed based on the analysis of products and the characterization of catalysts.     

Investigations on poly(vinyl chloride). I. Evolution of aromatics on pyrolysis of poly(vinyl chloride) and its mechanism

Poly(vinyl chloride) (PVC) alone or mixed with 10 wt-% and 50 wt-% TiO₂, SnO₂, ZnO, and Al₂O₃ were pyrolyzed by using a pyrolysis gas chromatograph. Benzene, toluene, ethylbenzene, o-xylene, styrene, naphthalene, and various chlorobenzenes were identified. No hydrocarbons could be detected in pyrolysis products of any samples at 200°C. More aromatic hydrocarbons than aliphatic hydrocarbons are released from the PVC–TiO₂ system and in preheated PVC. The contrary result is observed in the PVC–ZnO and PVC–SnO₂ systems. Aromatics having methyl endgroups are easily released from the PVC–ZnO and PVC–SnO₂ systems and at elevated pyrolysis temperature, because methylene groups are easily isolated along the chain by ZnO, SnO₂ and the heating. The release of ethylbenzene o-xylene, and chlorobenzenes suggests a repeated dehydrochlorination and recombination of HCl and Cl₂ to double bonds along the chain. Possible decomposition mechanisms of PVC are discussed.     

Regio- and stereo-selectivities of the ortho and meta photocycloaddition reactions of ethylenes to benzene and its simple derivatives

The photoreactions of benzene, toluene, anisole, and benzonitrile with acrylonitrile, methacrylonitrile, and vinyl acetate, and of toluene and o- and p-xylene with maleic anhydride are described. The acrylonitriles do not react with benzonitrile but yield mixtures of ortho photocycloadducts with the other arenes. Contrary to previous findings both exo and endo stereoisomers of the ortho cycloadducts of benzene and acryloitrile are formed: the reaction is selective towards the exo isomer but the stereoisomers from methacrylonitrite and benzene are formed with approximately equal efficiencies. Complex mixtures of regio- and stereoisomers of the ortho cycloadducts are formed between toluene and the acrylonitriles but their addition to anisole is more selective and in acetonitrile essentially only 1,2-attack of the ethylene on the arene is observed. The 2:1 photoadducts of maleic anhydride with toluene and o- and p-xylene reflect formation of two regio ortho photocycloadducts in each case. The variation in the ratios of these isomers with temperature and light intensity is interpreted in terms of the differing photolabilities of the 1:1 adducts and their reactivities towards the thermal addition of the second molecule of maleic anhydride. Vinyl acetate undergoes 1,2-cycloaddition to benzonitrile but with the other arenes, meta cycloadducts are favoured. These latter additions are specifically 2,6- with respect to toluene and anisole but there is little regioselectivity with respect to the ethylene although the 7-endo acetate of the meta cycloadduct with benzene does constitute 60% of the reaction mixture.     

Reversal of order of chemical shifts. Differential solvent effects in the hydrogen shifts of toluene,m-xylene and o-xylene as determined by 320 MHz tritium NMR spectroscopy

Chemical shifts for the aromatic tritons of toluene decrease in the order meta>para>ortho for pure toluene, but in the order meta>ortho>para for dilute solutions of toluene in carbon tetrachloride, chloroform, cyclohexane and dimethyl sulphoxide; m-xylene shifts are 5>4,6>2 in the pure state and 5>2>4,6 in carbon tetrachloride and dimethyl sulphoxide; o-xylene shifts are 4,5>3,6 in the pure state and reversed in carbon tetrachloride.     

Isothermal Phase Equilibrium Studies on the Binary Mixtures of some Alkylbenzenes

Abstract

The gas chromatographic method proposed by us for simple and accurate measurement of isothermal phase equilibria has been applied to the binary mixtures formed by alkylbenzenes amongst themselves. Results on the binary mixtures of: benzene - toluene, toluene + o-xylene, toluene + p-xylene, toluene + ethylbenzene, ethylbenzene + o-xylene and ethylbenzene + p-xylene are presented in this paper. The present measurements on benzene + toluene system at 40°C are in good agreement with the isothermal phase equilibrium data available in the literature.     

Pyrolysis and mass spectra of some aromatic-imides

The electron-impact induced loss of CO₂ from phthalanil and 4-phthalimidobiphenyl is paralleled by the formation of large amounts of CO₂ on pyrolysis. CO is also a major pyrolysis product, but the loss of CO from these compounds under electron-impact is not an important fragmentation process. The mass spectra of meta and para-chlorophthalanils show prominent [M ? CO₂] peaks but the corresponding peak for the ortho isomer is of relatively low intensity. CO and CO₂ are the principal gaseous products of the thermal decomposition of o-chlorophthalanil.     

Thermal decomposition of methylene bridges and methyl groups at aromatic rings in phenol-formaldehyde polycondensates

Phenol-formaldehyde polycondensates which contain methyl (or ethyl) substituents at different positions on the phenolic rings and methylene bridges at ortho or ortho and para positions were investigated. The products of pyrolysis at 600° C were analysed and the amounts of the alkylbenzenes and alkylphenols were related to the structure of the polycondensate pyrolysed. Most of the monoaromatic pyrolysis products are alkylphenols. The same alkyl substituents occur in the alkylphenolic pyrolysis products at the same positions that were present in the macromolecule. Methyl substituents were also found at the positions of the methylene bridges of the polycondensate, but their amounts in the pyrolysis products proved to be considerably lower than those of the methylene bridges related to the aromatic rings in the macromolecule.The amount of alkylbenzenes is only a few percent of that of alkylphenols in the 600°C pyrolysate, but the occurrence of the substituents in the alkylbenzene pyrolysis products reflects well the presence of the substituents and methylene bridges in the macromolecule.     

Formation of ring-retaining products from the OH radical-initated reactions of o-, m-, and p-xylene

The ring-retaining products formed from the OH radical-initiated reactions of o-, m-, and p-xylene in the presence of NO_x have been identified and their formation yields determined. Experiments were carried out at 298 ± 2 K and in the presence of 740 torr total pressure of air. The products observed, and their yields, were: from o-xylene, o-tolualdehyde, 0.0453; 2-methylbenzyl nitrate, (0.0135 + 5.5 × 10^?17 [NO₂]); 2,3-dimethylphenol, 0.097; 3,4-dimethyl-phenol, 0.064; 3-nitro-o-xylene, 0.0059; 4-nitro-o-xylene, (0.0111 + 9.9 × 10^?17 [NO₂]); from m-xylene, m-tolualdehyde, 0.0331; 3-methylbenzyl nitrate, 0.0061; 2,4-dimethylphenol, 0.099; 2,6-dimethylphenol, 0.111; 4-nitro-m-xylene, 0.0018; 5-nitro-m-xylene, (0.0032 + 1.6 × 10^?17 [NO₂]); from p-xylene, p-tolualdehyde, 0.0701; 4-methylbenzyl nitrate, 0.0082; 2,5-dimethylphenol, 0.188, 2-nitro-p-xylene, (0.0120 + 2.8 × 10^?17 [NO₂]), where the NO₂ concentration is in molecule cm^?3 units. The nitro-xylene data are consistent with our recent product study of the corresponding reactions of benzene and toluene and indicate that under the experimental conditions employed the dimethylhydroxycyclohexadienyl radicals reacted with NO₂ and not with O₂. When combined with literature ring-cleavage product yields, these data show that ca. 55–80% of the reaction pathways are accounted for.     

Isothermal Phase Equilibria Through Gas Chromatography for Petrochemical Processing

Abstract

A gas chromatographic technique has been used to measure the isothermal phase equilibria likely to be of importance in petrochemical processing. The measurements on the binary mixtures formed by chlorobenzene with some aromatic hydrocarbons (toluene, o-xylene, p-xylene) and aliphatic alcohols (ethanol, 1-propanol, 1-butanol) are given in this paper. Our measurements on chlorobenzene + 1-propanol mixtures are in good agreement with the literature data.     

Thermal and pyrolysis studies of copolyesters

Random copolyesters of dimethyl terephthalate (DMT), ethylene glycol (EG), and butane-1,4-diol (BD) and the homopolyesters poly(ethylene terephthalate) (PET) and poly(butylene terephthalate) (PBT) have been subjected to degradation and pyrolysis studies. Differential thermal analysis (DTA) showed that the decomposition temperature is dependent on the percentage of EG and BD present in the copolyesters. Thermal volatilization analysis (TVA) also showed that the decomposition temperature is dependent on the percentage of EG and BD present in the copolyesters. The trend for the decomposition temperatures obtained from TVA studies for these copolyesters is similar to such other thermal properties as melting temperature T_m, ΔH_f, ΔH_c, etc. The subambient thermal volatilization analysis (SATVA) curves obtained for these polymers are also presented. The SATVA curve is the fingerprint of the total volatile products formed during the degradation in high vacuum. The isothermal pyrolysis of these materials was carried out in high vacuum at 450°C. The products formed were separated in a gas chromatograph and were subsequently identified in a mass spectrometer. The major pyrolysis products from PBT were butadiene and tetrahydrofuran, whereas those from PET were ethylene and acetaldehyde. The ratio of acetaldehyde to ethylene increases with the EG content in the copolyester, suggesting a different decomposition mechanism compared to the decomposition mechanism of PBT and PET.     

The feasibility of inert colloidal processing of silicon nanoparticles

Silicon nanoparticles have important applications, including nonvolatile floating-gate memory devices. To prevent device performance variations, particle size and oxide thicknesses need to be controlled with a high degree of precision. Additionally, producing well-ordered, two-dimensional arrays of nanoparticles may require the exploitation of self-assembly techniques and colloidal forces, which in turn requires that silicon nanoparticles first come into contact with liquids. Until recently, aerosol silicon nanoparticle collection into liquid was assumed to be an inert process. Once formed, the silicon nanoparticle colloid was assumed to be inert. In fact, silicon nanoparticles produced in the aerosol phase by dilute silane pyrolysis and size classified with a differential mobility analyzer undergo a size reduction upon collection in ethylene glycol, water, and ethanol. Unclassified polydisperse silicon aerosol nanoparticles with an average diameter of 11 nm become monodisperse when collected in a colloid and have a final particle diameter of 2-5 nm. Further evidence suggests that silicon nanoparticles collected in ethanol react with the ethanol to produce tetraalkylorthosilicate-like species. Collections of aerosol silicon nanoparticles in degassed water do not show measurable differences between the aerosol and colloidal size distributions. This reduced reactivity to the solvent indicates that the presence of dissolved oxygen in the solvent may be responsible for the reactivity between the silicon nanoparticles and the solvent.     

Structure and properties of p-phenylenevinylene-p-xylylene copolymers prepared by vapor-deposition polymerization

Films based on the p-phenylenevinylene-p-xylylene precursor are prepared via vapor-deposition polymerization during the pyrolysis of ??, ????-dichloro-p-xylene on a copper grid in vacuum at substrate temperatures ?196, 25, and 50°C. Subsequent annealing of the precursor at 250°C yields the final material: the copolymer of p-phenylenevinylene and p-xylylene. The structure, surface morphology, and optical properties of the copolymer are studied at different substrate temperatures and copper amounts in the pyrolysis zone. It is found that p-phenylenevinylene units mostly occur in trans configurations. The thermal treatment of the precursor is accompanied by an increase in the mean-square surface roughness and a decrease in roughness coefficient ?? from 0.84 ± 0.05 to 0.79 ± 0.05. As the content of copper in the pyrolysis zone increases, the concentration of p-xylylene fragments in the copolymer tends to increase; the band gap increases from ?2.5 to 3.1 eV. Depending on synthesis conditions, the copolymer is characterized by a shift of the fluorescence spectrum maximum that achieves 150 nm in the visible spectral region.     

Chemistry of novolac resins. X. Polymerization studies of HMTA and strategically synthesized model compounds

The reactions between hexamethylenetetramine (HMTA) and compounds which model novolac resins have been studied by ¹³C‐ and ¹⁵N‐NMR techniques. The dimer and tetramer compounds vary in molecular size and structure and react with HMTA to yield benzylamines and benzoxazine as the major initial‐formed intermediates and convert to methylene linked compounds at increased temperatures. The reaction of the compounds with only ortho reactive sites paralleled the 2,4‐xylenol–HMTA case reported by us previously; however, increasing molecular weight favored the formation of benzylamines and not benzoxazines. Those compounds with only para reactive sites paralleled the 2,6‐xylenol–HMTA case. The reactivity of the systems containing both ortho and para reactive sites depends on the ratio of ortho/para sites and various aspects such as the chemical structure and molecular weight of the compound, the HMTA level, and the melting point and pH of the system. These results parallel those obtained from novolac/HMTA systems. The xylenol/HMTA reactions formed similar products but showed quite different relative reaction rates by varying the HMTA ratio and structures of the materials. The importance of careful selection of model systems is also discussed. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1347–1355, 1999     

m-Xylene Isomerization in SAPO-11/HZSM-5 Mixed Catalyst

The catalytic isomerization of m-xylene was studied over a solid acid silicoaluminophosphate type SAPO-11, mixed to HZSM-5 zeolite. The reaction was processed varying the temperature and weight hourly space velocity, using a fixed bed continuous flow reactor. The m-xylene suffers isomerization to p-xylene and o-xylene by molecular displacement of methyl groups. The mixed catalyst was selective to p-xylene at 623 K and 2.5 h⁻¹ with a maximum p/o ratio of 2.05. The ethylbenzene formation was not observed in the products. In this process an apparent activation energy of the order of 13.9 kJ mol⁻¹ was obtained. This revised version was published online in June 2006 with corrections to the Cover Date.     

Vapour–liquid equilibria of butyl acetate with aromatic hydrocarbons at 298.15 K

Vapour pressures of butyl acetate?+?benzene or toluene or o- or m- or p-xylene were measured by static method at 298.15?±?0.01?K over the entire composition range. The activity coefficients and excess molar Gibb's free energies of mixing (G ^E) for these binary mixtures were calculated by fitting vapour pressure data to the Redlich–Kister equation using Barker's method of minimizing the residual pressure. The G ^E values for the binary mixtures containing benzene are positive; while these are negative for toluene, ortho, meta and para xylene system over the whole composition range. The G ^E values of an equimolar mixture for these systems vary in the order: benzene?>?m-xylene?>?o-xylene?>?p-xylene?>?toluene     

Structure of carbon nanoparticles synthesized by adiabatic compression of acetylene and their application in supercapacitors

The work reports the study of the structure of carbon nanoparticles prepared by the pyrolysis of heliumdiluted acetylene under adiabatic compression in a piston reactor. At a pushing gas pressure of 0.5 MPa, 0.7 MPa, and 0.9 MPa the reaction gas was heated to temperatures of 400 °C, 600 °C, and 750 °C. By transmission electron microscopy it is found that carbon nanoparticles have a spherical shape and their size varies from 20 nm to 60 nm. The structural features of carbon nanoparticles are determined from the X-ray photoelectron spectroscopy data and the analysis of the near-edge X-ray absorption fine structure spectroscopy. Carbon nanoparticles prepared at a pushing gas pressure of 0.5 MPa have an amorphous structure and consist of hydrogenated carbon with impurities of polycyclic aromatic fragments. At a stronger compression ratio, carbon nanoparticles with a layered structure consisting mainly of sp² hybridized carbon atoms are formed. The capacitance behavior and electrochemical impedance of carbon nanoparticle-based supercapacitors are compared.