Formation Of Unsaturated Hydrocarbons Research Articles

A new insight into the CaO-induced inhibition pathways on PCDD/F formation: Metal passivation, dechlorination and hydroxide substitution

Ca-based inhibitors (especially CaO) for PCDD/F (polychlorinated dibenzo-p-dioxin and dibenzofuran) formation are considered as economic inhibitors with low toxicity and strong adsorption of acidic gases (e.g., HCl, Cl2, and SOx), whereas the insight understanding of its inhibition mechanisms is scarcely explored. Herein, CaO was used to inhibit the de novo reaction for PCDD/F formation (250–450 °C). The evolution of key elements (C, Cl, Cu, and Ca) combined with theoretical calculations was systematically investigated. The concentrations and distribution of PCDD/Fs demonstrated the significant inhibition effect of CaO on I-TEQ (international toxic equivalency) concentrations of PCDD/Fs (inhibition efficiencies: > 90 %) and hepta~octa chlorinated congeners (inhibition efficiencies: 51.5–99.8 %). And the conditions (5–10 % CaO, 350 °C) were supposed to be the preferred conditions applied in real MSWIs (municipal solid waste incinerators). CaO significantly suppressed the chlorination of carbon matrix (superficial organic Cl (CCl) reduced from 16.5 % to 6.5–11.3 %) and the formation of unsaturated hydrocarbons or aromatic carbon (superficial CC decreased from 6.7 % to 1.3–2.1 %). Also, CaO promoted the dechlorination of Cu-based catalysts and Cl solidification (e.g., conversion of CuCl2 to CuO, and formation of CaCl2). The dechlorination phenomenon was validated by the dechlorination of highly chlorinated PCDD/F-congeners (via DD/DF chlorination pathways). Density functional theory calculations revealed that CaO facilitated the substitution of Cl by -OH on the benzene ring to inhibit the polycondensation of the chlorobenzene and chlorophenol (Gibbs free energy reduced from +74.83 to −36.62 and − 148.88 kJ/mol), which also indicates the dechlorination effect of CaO on de novo synthesis.

Formation of Unsaturated Hydrocarbons and Hydrogen: Surface Chemistry of Methyltrioxorhenium(VII) in ALD of Mixed-Metal Oxide Structures Comprising Re(III) Units

We present the full investigation of the atomic layer deposition (ALD) of a mixed rhenium–aluminum oxide, namely ReAl2O3CH3, a material with tunable resistance, comprising the building unit of cond...

The Influence of the Cobalt-Containing Component of the Composite Catalyst on the One-Stage Process for Synthesis of Liquid Hydrocarbons from CO and H2

The influence of the cobalt-containing component (Co-Al2O3/SiO2, Co-Re/Al2O3 and Co-Re/TiO2) of a composite catalyst was studied in the Fischer – Tropsch combined process for synthesis and hydrotransformation of hydrocarbons. A flow fixed-bed reactor was used for characterization of the catalytic properties at 2 MPa, flow rate 1000 h–1, 240–280 °C for 40–90 hours of continuous operation. The highest productivity and selectivity to C5+ hydrocarbons equal to 106 kg/(m3 cat·ч) and 67.1 %, respectively, was characteristic of the composite catalyst Co-Al2O3/SiO2(35%)/ZSM-5(30%)/Al2O3(30%) at 240 °C. The comparable activities were observed with the catalysts Co-Re/Al2O3 and Co-Al2O3/SiO2 but the former provided the formation of unsaturated hydrocarbons in a lower proportion in the products. The use of the Co-Re/TiO2 catalyst at elevated temperature (up to 280 °C) allowed the molecular mass distribution of the products to be shifted towards the formation of the gasoline fraction. The rate of the catalyst deactivation was established to increase in the series Co-Al2O3/SiO2 > Co-Re/Al2O3 > Co-Re/TiO2.

Formation of unsaturated hydrocarbons, carbonyl compounds and PAHs in a non-premixed methane/air flame doped with methyl butanoate: CFD modeling and comparison with experimental data

The study proposes a base kinetic model of biodiesel fuels to distinguish mass-spectrometrically measured hydrocarbons, carbonyl compounds and light-weight polycyclic aromatic hydrocarbons (PAHs) in a methane/air non-premixed flame doped with methyl butanoate (MB). The computational procedure starts with reducing a detailed MB mechanism to generate a minimized but reasonably accurate skeletal mechanism which is then used to combine with previously published submodels that describe PAHs and related compounds. The newly derived MB-PAH mechanism with 83 species and 520 reactions is systematically validated against results of existing detailed and skeletal MB mechanisms. Without empirical adjustment of rate constants in elementary reactions, the MB-PAH mechanism incorporated into a 2-D axisymmetric laminar finite-rate model, for the first time, is able to predict experimentally measured centerline mole fractions of 14 intermediates. The computationally identified intermediates are in accordance with the mass-spectrometric determinations, where the species include propyne/propadiene (C3H4), propene (C3H6), vinylacetylene (C4H4), but-1-ene/but-2-ene (C4H8), ketenes (CH3CHCO and C2H5CHCO), prop-2-enal (C2H3CHO), 1,3,5-Hexatriyne (C6H2), benzene (C6H6), naphthalene (C10H8), phenanthrene (C14H10) and pyrene (C16H10). Moreover, the reaction pathway analysis reveals the correlation between the decomposition of MB and formation of the investigated intermediates.

Formation of unsaturated hydrocarbons in interstellar ice analogues by cosmic rays

The formation of double and triple C-C bonds from the processing of pure c-C6H12 (cyclohexane) and mixed H2O:NH3:c-C6H12 (1:0.3:0.7) ices by highly-charged, and energetic ions (219 MeV O^{7+} and 632 MeV Ni^{24+}) is studied. The experiments simulate the physical chemistry induced by medium-mass and heavy-ion cosmic rays in interstellar ices analogs. The measurements were performed inside a high vacuum chamber at the heavy-ion accelerator GANIL (Grand Accel\'erat\'eur National d'Ions Lourds) in Caen, France. The gas samples were deposited onto a polished CsI substrate previously cooled to 13 K. In-situ analysis was performed by a Fourier transform infrared (FTIR) spectrometry at different ion fluences. Dissociation cross section of cyclohexane and its half-life in astrophysical environments were determined. A comparison between spectra of bombarded ices and young stellar sources indicates that the initial composition of grains in theses environments should contain a mixture of H2O, NH3, CO (or CO2), simple alkanes, and CH3OH. Several species containing double or triple bounds were identified in the radiochemical products, such as hexene, cyclohexene, benzene, OCN-, CO, CO2, as well as several aliphatic and aromatic alkenes and alkynes. The results suggest an alternative scenario for the production of unsaturated hydrocarbons and possibly aromatic rings (via dehydrogenation processes) in interstellar ices induced by cosmic ray bombardment.

Transient Stages in the Chemical Vapor Deposition of Silicon Carbide

Transient CVD experiments were simulated by varying continuously the deposition temperature or the initial gas flow rates (Q(MTS) or Q(H2)). Their consequences on the physicochemical properties of the coatings have been first examined. The adhesion of SiC/SiC bilayers containing these "transient interphases" (phi(Tr)) was investigated by scratch testing. For transient stages resulting from a decrease of Q(MTS) or T, free silicon can be co-deposited in proportions depending on alpha = Q(H2)/Q(MTS), T and P. This phenomenon is related to the high reactivity of the Si bearing species and is activated by high T and P and low a values. In this case, the continuous covalent bonding through the Si-rich interphases preserves the adhesion between the two SiC layers. Transient stages resulting from a decrease of Q(H2) lead first to larger and columnar SiC grains and finally to the deposition of anisotropic carbon, due to the formation of unsaturated hydrocarbons in the gas phase. The interphases with the highest carbon concentrations and thicknesses lead to delamination and local chipping of the outer SiC layer. The poor shear strength of these continuous and anisotropic layers is detrimental to the adherence of the bilayers.

Combined FTIR and Temperature Programmed Fischer-Tropsch Synthesis over Ru/SiO2and Ru-Ag/SiO2Supported Catalysts

Combined temperature programmed reaction (TPR) and infrared (IR) spectroscopic studies for Fischer- Tropsch reaction have been performed over Ru/SiO2 and Ru-Ag/SiO2 supported catalysts. Reaction of linearly absorbed CO with hydrogen starts at 375 K over Ru/SiO2 catalyst and reaches maximum at 420 K accompanied with an intensity decrease of linear CO absorption. The reaction with bridged absorbed CO peaks around 510-535 K. Addition of Ag yields mixed Ru-Ag bimetallic sites while it suppresses the formation of bridged bonded CO. Formation of methane on this modified surface occurs at 390 K and reaches maximum at 444 K. Suppression of hydrogen on the Ag-doped surface also occurs resulting in the formation of unsaturated hydrocarbons and of CHx intermediates not observed with Ru/SiO2 catalyst. Such intermediates are believed to be the building blocks of higher hydrocarbons during the Fischer-Tropsch synthesis. Linearly absorbed CO is found to be more reactive as compared to bridged CO. The Ag-modified surface also produces CO2 and carbon. On this surface, hydrogenation of CO begins at 390 K and reaches maximum at 494 K. The high temperature for hydrogenation of absorbed CO and C over Ru-Ag/SiO2 catalyst as compared to Ru/SiO2 catalyst is due to the formation of Ru-Ag bimetallic surfaces impeding hydrogen adsorption.

Temperature dependence of radiation effects in polyethylene: Cross-linking and gas evolution

High-density polyethylene (HDPE) and low-density polyethylene (LDPE) were irradiated in vacuo at 30–220 and 30–360°C, respectively, with γ-rays at doses of 10–400 kGy. Temperature dependence of cross-linking and gas evolution was investigated. It was found that cross-linking was the predominant process up to 300°C and the gel point decreased smoothly with temperature. The increase of G(x) with temperature was likely attributed to the temperature effect on addition of radicals to the double bonds present in the polymer. Above 300°C, the gel fraction at a given dose decreased remarkably with temperature and turned to zero at 360°C. The molecular weight variation determined with gel permeation chromatography (GPC) indicated the enhanced degradation at 360°C by radiation. G-values of H2 increased with temperature and varied with dose. The compositions of the C1–C4 hydrocarbons evolved depended on the structures of side branches. Raising the temperature favored the formation of unsaturated hydrocarbons, and the yield of unsaturated relative to saturated hydrocarbons decreased with dose. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1541–1548, 1999

Lipoxygenase-mediated formation of hydrocarbons and unsaturated aldehydes in freshwater diatoms

Upon initiation of lipoxygenase reactions one group of freshwater diatoms synthesized unsaturated acyclic and alicyclic hydrocarbons (ectocarpene, dictyopterenes and fucoserratene); another group synthesized polyunsaturated aldehydes. Among others (2 E),(4 Z),(7 Z)-decatrienal is described as a new lipoxygenase cleavage product in Melosira. The patterns of the volatile organic compounds were typical for particular species of diatoms, indicating different specificities of the enzymes involved. The formation of unsaturated hydrocarbons and aldehydes was fully inhibited by strict exclusion of dioxygen, but could be regained by subsequent addition of dioxygen. The application of radical scavengers or chelating agents resulted in a high percentage inhibition of hydrocarbon and aldehyde formation.

Pressurized laser pyrolysis of coal

A set-up for the laser-induced pyrolysis of coal using the visible blue-green emission from an argon ion laser is described. The design of the pyrolysis cell allows buffer gas pressures up to about 10 bar enabling pyrolysis studies under pressurized conditions. The gaseous products formed in helium and the reactive atmosphere of hydrogen and deuterium have been identified by on-line gas chromatography/mass spectrometry. Deuterium has been utilized as a buffer gas at various pressures and the in situ deuteration of the products during the pyrolysis has been studied. In this way, mechanisms for the formation of unsaturated hydrocarbons have been disclosed and the results for ethylene formation are reported.

Catalytic deamination on solid surfaces. Part 1.—Kinetic studies by stopped-flow gas chromatography

Stopped-flow gas chromatography was used to study the detailed kinetics of formation of unsaturated hydrocarbons by deamination on aluminium oxide and on porous glass of aminocyclohexane, 2-aminopropane, 1-aminobutane, 2-aminobutane, 1-amino-2-methylpropane and 2-amino-2-methylpropane. The results are consistent with a proposed mechanism in which the reacting amine is rapidly adsorbed on two or three kinds of active sites of aluminium oxide or porous glass, respectively, leading to unsaturated hydrocarbons through the formation of an intermediate adsorbed product on each site. Based on this mechanism, theoretical equations are derived which adequately describe the experimental reaction rate as a function of time. Analysis of the data by means of these equations permits the calculation of the various rate constants for the surface processes. True activation energies and frequency factors for the deamination of aminocyclohexane on aluminium oxide have also been determined.

Coupure cathodique de liaisons carbone-oxygene—I reduction electrochimique d'alcools insatures application a la reduction tetraelectronique de certaines cetones en carbures

Some unsaturated alcohols are reduced electrochemically on mercury at very negative potential values. For many of them, it has been shown that the carbon-oxygen bond is cleaved with formation of unsaturated hydrocarbons, in a two electron reaction. However, in some cases, there exists for the anion radical another possibility of reaction: protonation to form a saturated alcohol. When the protonation reaction is slow compared to the cleavage reaction, a direct method of electroreduction of ketones to hydrocarbons, through the intermediate alcohol, can be proposed.

Oxidative dehydrogenation of C5 hydrocarbons in the presence of hydrochloric acid

The oxidative dehydrogenation of C5 paraffin hydrocarbons on Fe catalysts in the presence of HCl leads mainly to the formation of unsaturated hydrocarbons, which have the same structure of the carbon skeleton as the starting hydrocarbon, in which connection the yield of olefinic hydrocarbons proved to be substantially higher (25% from isopentane and 32% from n-pentane) than the yield of dienes (respectively 15% of isoprene and 11% of piperylene).

Isomerization of saturated hydrocarbons Communication 3. Isomerizations of cycloalkanes

1. The isomerization of C6–C9 cycloalkanes was carried out in presence of a multifunctional catalyst and of hydrogen under pressure. 2. The compositions of the isomerization products from C7 and C8 cycloalkanes were in good agreement with the calculated thermodynamic values. 3. A mechanism was proposed for the isomerization of cycloalkanes. It is considered that, as in the case of the isomerization of paraffins, the first stage of the reaction is the formation of unsaturated hydrocarbons. 4. The effects of pressure and temperature on the course of the reactions of cycloalkanes in presence of multifunctional catalysts were demonstrated.

Attempt to set up a semiquantitative theory of mutual effects of atoms in organic compounds Communication 2. Electronic charges of bonds and physical properties of molecules

1. Simple semiempirical equations are proposed for the relation between force constants and characteristic frequencies of bonds on the one hand and total (σ- + π-) electronic charges of bonds on the other. These equations are checked by calculation of the total electronic charges of ethylene and acetylene. The electronegativity of acetylenic carbon is determined. 2. It is shown that it is possible to calculate π-electronic charges of bonds by two methods which give closely agreeing results-from bond lengths and from electronegativities. 3. An additive scheme is proposed for the calculation of heats of formation of unsaturated hydrocarbons from their elements; the scheme is analogous to that already proposed for saturated hydrocarbons. The separate π-electronic energies of C-C and C-H bonds are calculated. Electronegativities are calculated for carbon atoms in the α- and β -positions with respect to the acetylenic bond of normal 1-alkynes. 4. It is shown that dipole moments of polyatomic molec,,les are generally determined by the nonintegral character of the electronic charges of individual bonds. It is possible to estimate electronegativities of atoms from from dipole moments.