Propane Molecules Research Articles

Enhanced propylene/propane separation by carbonaceous membrane derived from poly (aryl ether ketone)/2,6-bis(4-azidobenzylidene)-4-methyl-cyclohexanone interpenetrating network

An innovative combination of a photosensitive crosslinker, 2,6-bis(4-azidobenzylidene)-4-methyl-cyclohexanone (Azide) with poly (aryl ether ketone) (PAEK) is utilized to form a semi-interpenetrating network (IPN) as the precursor for carbon membranes. Low temperature pyrolysis (450–650 °C) of this precursor produces carbon membranes with excellent olefin/paraffin separation performance that surpasses the conventional trade-off line. The carbon membranes have reasonably good flexibility since excessive closure of the micropores is avoided. This is evident from the mechanical properties of the carbon membranes obtained from nanoindention to the pore size distribution derived from CO 2 adsorption. By varying the composition of Azide/PAEK and optimizing the low-temperature pyrolysis protocol, it was found that PAEK/Azide (80:20) pyrolysed at 550 °C exhibits the best propane/propylene separation performance with C 3H 6 permeability of 48 barrer and ideal C 3H 6/C 3H 8 selectivity of 44. Due to strong competitive sorption of propane and propylene molecules, the C 3H 6 permeability is lowered to 3.6 barrer and the C 3H 6/C 3H 8 selectivity to 32 in mixed gas experiments. However, this separation performance is still above the trade-off line. Even though both Azide and PAEK cannot form useful carbon membranes, their IPN is a unique precursor that can produce carbon membranes with comparable performance.

DFT analysis of propane cyclization over binuclear Ga-clusters in mordenite

Molecular and dissociative adsorption of propane on binuclear (Ga 2O 2) 2+ cluster located at the cation positions of Ga-exchanged mordenite zeolite are modeled using DFT calculations via the isolated cluster approach. Relative energies of the dissociative intermediates show the most stable bidentate complexes, i.e., via both primary C atoms of propane to both Ga atoms. This structure really is the suitable precursor of cyclo-propane formation. The hypothesis of cyclo-propane intermediate was proposed by Derouane et al. to explain the 13C/ 12C exchange migration within propane molecules in Ga-exchanged zeolites.

Polypropylene Nanocomposites Based on Designed Synthetic Nanoplatelets

Synthetic nanoplatelets derived from α-zirconium phosphate (α-ZrP) were prepared for in situ propylene polymerization, yielding polypropylene (PP) nanocomposites. The designed α-ZrP-derivatives contain methyl groups on the surface to increase hydrophobicity, which gives rise to a better compatibility with toluene and propylene molecules. The incorporation of methyl groups on the layers of α-ZrP-derivatives also produces a “porous pathway” structure in the nanoplatelet gallery, which facilitates the diffusion of propylene monomers. PP/α-ZrP nanocomposites were successfully prepared with a high level of exfoliation. The implications of the present findings are discussed.

A molecular dynamic study of water/methane/propane

We present a molecular dynamic simulation for water/methane/propane. The simulation is performed in a constant NPT ensemble at a temperature of 240 K and a pressure of 300 bar. The simulation is analysed to calculate the propensity for hydrogen bond formation, potential energy, number density profile and radial distribution function. Compared with the binary system (water/methane), relatively slight changes in hydrogen bond number and potential energy for the ternary system (water/methane/propane) indicate that the presence of propane retards the rate of hydrate growth. It is interesting to observe that propane, which is also of hydrophobic nature as methane, does not promote the formation of hydrate, but is rather driven out of the middle aqueous region. No hydrate formation was observed even after all of the propane had been driven out of the water film. We suggest that the size of water clusters and hydrogen bond network is likely to be disrupted by propane molecules, hindering the growth of the nuclei to the critical size required for sustained growth. The presence of the propane might also affect the net flux of methane into the aqueous phase, which is critical for hydrate formation.

Propylene-induced plasticization in silver polymer electrolyte membranes

Silver polymer electrolyte membranes consisting of AgBF 4 or AgCF 3SO 3 dissolved in poly(2-ethyl-2-oxazoline) (POZ) or poly(N-vinyl pyrrolidone) (PVP) have previously shown outstanding separation performance for propylene/propane mixtures. The ideal separation factor (i.e. pure gas selectivity) of propylene over propane reached 15,000, but the actual selectivity (i.e. mixed gas selectivity) was approximately 50. In this study, the origin of large difference between pure and mixed gas selectivities has been elucidated in terms of membrane plasticization by propylene molecules. The membrane plasticization was confirmed by the decrease of selectivity with increasing propylene concentration in the feed, resulting from the increase of both propylene and propane permeances. The decrease of glass transition temperature ( T g) in silver polymer electrolytes upon the sorption of propylene also supported the membrane plasticization, determined by in situ high-pressure differential scanning calorimetry (HPDSC). Further analysis of configuration entropy model revealed that the interaction of propylene/silver ion in POZ/AgBF 4 was approximately 2-fold stronger than that in POZ/AgCF 3SO 3, which is in good agreement with the results of propylene solubility and FT-IR spectra.

1,3-Di-4-pyridylpropane–2-hydroxybenzene-1,4-dicarboxylic acid (1/2)

In the title compound, C13H14N2·2C8H6O5, which crystallized in the monoclinic C2/c space group, the 1,3-bis­(4-pyrid­yl)propane mol­ecules and 2-hydr­oxy-1,4-benzene­dicarboxylic acid mol­ecules are alternately linked by O—H⋯N and O—H⋯O hydrogen bonds into herringbone/zigzag chains.

Rotational dynamics of propylene inside Na-Y zeolite cages

We report here the quasielastic neutron scattering (QENS) studies on the dynamics of propylene inside Na-Y zeolite using triple axis spectrometer (TAS) at Dhruva reactor, Trombay. Molecular dynamics (MD) simulations performed on the system had shown that the rotational motion involves energy larger than that involved in the translational motion. Therefore, rotational motion was not observed in our earlier QENS studies on propylene adsorbed Na-Y zeolite using a higher resolution spectrometer at Dhruva. Analysis of the TAS spectra revealed that the quasielastic broadening observed in propylene-loaded zeolite spectra is due to the rotational motion of the propylene molecules. This is consistent with our simulation result. Further, the rotational motion is found to be isotropic. The rotational diffusion coefficient has been obtained.

Enhancing effect of S and F moieties on the performance of Fenton system in the selective oxidation of propane

The selective oxidation of propane to oxygenated products (isopropanol, n-propanol, propionic aldehyde and acetone) mediated by the Fe(II)/H 2O 2 Fenton system at 80 °C in the presence of solid acid and superacid promoters containing S and F moieties has been studied. The occurrence of a radical reaction pathway accounting for the activation of the C H bonds of the propane molecule by OH radicals has been proved by assessing the inhibiting effect of both Cl − and NO 3 − radical scavengers and organic (CH 3COOH, CH 3CN, DMSO) reaction media on the reaction pattern. S and F functionalities of several solid agents promote the electron transfer processes controlling the H 2O 2 activation. Any effect of the Brönsted acid features of the solid promoters on the reaction kinetics and pathway has been disregarded.

On the Importance of the Aqueous Interface in the Multiphasic Rhodium Catalyzed Hydroformylation of Propene: a Molecular Dynamics Study

We report a molecular dynamics study of propene/water biphasic systems involved in the hydroformylation of propene catalyzed by water soluble rhodium complexes with TPPTS 3- ligands (where TPPTS 3- is the tris(m-sulfonatophenyl)phosphine ligand), neutralized by Na + counterions). The neat biphasic system is found to display a quite thin and irregular involving some propene partitioning to the bulk aqueous phase. Interestingly, when propene is diluted (at low presssures), propene molecules tend to somewhat condense at the interface. The most important finding concerns the interfacial activity of key reaction partners (the free TPPTS 3- ligands, the active catalyst [RhH(CO)(TPPTS) 2 ] 6- , and the reaction intermediate [RhH(CO)-(TPPTS) 2 (prnpene)] 6- ). This is found first by following the outcome of the phase separation of randomly mixed water/propene solutions with these different solutes, and further supported by potential of mean force (PMF) calculations on the migration of the [RhH(CO)(TPPTS)2(propene)]6 - complex across the interface. Added butyraldehyde molecules (the product of the reaction) are shown to increase the surface activity the [RhH(CO)(TPPTS)2(propene)] 6- complex, due to increased attractions of the complex with the organic phase. These results point to the importance of the aqueous interface in the multiphasic catalyzed reaction, and suggest that a significant amount of propene reacts right at the interface, i.e., in a region of less than 1 nm width of the solution.

The mechanism of propene oxidation to acrolein on iron antimony oxide

Density functional theory is used to investigate the microscopic mechanisms of oxidation of propene (CH 3 CH CH 2) to acrolein (CH 2 CH CHO) over iron antimony oxide (FeSbO 4). Two routes for acrolein formation are investigated. The first starts from a chemisorbed state, in which propene binds with the surface via the π orbitals; acrolein formation can be triggered first by the abstraction of an allylic H atom towards the active bridging O atom, followed by the abstraction of a second H atom toward either an O or an Sb atom and the subsequent desorption of the acrolein thereby formed. The second route starts from a direct dissociation of the propene molecule without the need to proceed through a chemisorbed precursor, which, however, is kinetically hindered. The first route is compared with the mechanisms proposed from experiment. We also discuss the mechanisms of propane oxidation to acrolein, in which propene oxidation is an important step.

Reaction Dynamics on the Formation of 1- and 3-Cyanopropylene in the Crossed Beams Reaction of Ground-State Cyano Radicals (CN) with Propylene (C3H6) and Its Deuterated Isotopologues

Crossed molecular beams experiments were utilized to explore the chemical reaction dynamics of ground-state cyano radicals, CN(X(2)Sigma(+)), with propylene (CH3CHCH2) together with two d3-isotopologues (CD3CHCH2, CH3CDCD2) as potential pathways to form organic nitriles under single collision conditions in the atmosphere of Saturn's moon Titan and in the interstellar medium. On the basis of the center-of-mass translational and angular distributions, the reaction dynamics were deduced to be indirect and commenced via an addition of the electrophilic cyano radical with its radical center to the alpha-carbon atom of the propylene molecule yielding a doublet radical intermediate: CH3CHCH2CN. Crossed beam experiments with propylene-1,1,2-d3 (CH3CDCD2) and propylene-3,3,3-d3 (CD3CHCH2) indicated that the reaction intermediates CH3CDCD2CN (from propylene-1,1,2-d3) and CD3CHCH2CN (from propylene-3,3,3-d3) eject both atomic hydrogen through tight exit transition states located about 40-50 kJ mol(-1) above the separated products: 3-butenenitrile [H2CCDCD2CN] (25%), and cis/trans-2-butenenitrile [CD3CHCHCN] (75%), respectively, plus atomic hydrogen. Applications of our results to the chemical processing of cold molecular clouds like TMC-1 and OMC-1 are also presented.

Polymerization in the Gas Phase, in Clusters, and on Nanoparticle Surfaces

Gas phase and cluster experiments provide unique opportunities to quantitatively study the effects of initiators, solvents, chain transfer agents, and inhibitors on the mechanisms of polymerization. Furthermore, a number of important phenomena, unique structures, and novel properties may exist during gas-phase and cluster polymerization. In this regime, the structure of the growing polymer may change dramatically and the rate coefficient may vary significantly upon the addition of a single molecule of the monomer. These changes would be reflected in the properties of the oligomers deposited from the gas phase. At low pressures, cationic and radical cationic polymerizations may proceed in the gas phase through elimination reactions. In the same systems at high pressure, however, the ionic intermediates may be stabilized, and addition without elimination may occur. In isolated van der Waals clusters of monomer molecules, sequential polymerization with several condensation steps can occur on a time scale of a few microseconds following the ionization of the gas-phase cluster. The cluster reactions, which bridge gas-phase and condensed-phase chemistry, allow examination of the effects of controlled states of aggregation. This Account describes several examples of gas-phase and cluster polymerization studies where the most significant results can be summarized as follows: (1) The carbocation polymerization of isobutene shows slower rates with increasing polymerization steps resulting from entropy barriers, which could explain the need for low temperatures for the efficient propagation of high molecular weight polymers. (2) Radical cation polymerization of propene can be initiated by partial charge transfer from an ionized aromatic molecule such as benzene coupled with covalent condensation of the associated propene molecules. This novel mechanism leads exclusively to the formation of propene oligomer ions and avoids other competitive products. (3) Structural information on the oligomers formed by gas-phase polymerization can be obtained using the mass-selected ion mobility technique where the measured collision cross-sections of the selected oligomer ions and collision-induced dissociation can provide fairly accurate structural identifications. The identification of the structures of the dimers and trimers formed in the gas-phase thermal polymerization of styrene confirms that the polymerization proceeds according to the Mayo mechanism. Similarly, the ion mobility technique has been utilized to confirm the formation of benzene cations by intracluster polymerization following the ionization of acetylene clusters. Finally, it has been shown that polymerization of styrene vapor on the surface of activated nanoparticles can lead to the incorporation of a variety of metal and metal oxide nanoparticles within polystyrene films. The ability to probe the reactivity and structure of the small growing oligomers in the gas phase can provide fundamental insight into mechanisms of polymerization that are difficult to obtain from condensed-phase studies. These experiments are also important for understanding the growth mechanisms of complex organics in flames, combustion processes, interstellar clouds, and solar nebula where gas-phase reactions, cluster polymerization, and surface catalysis on dust nanoparticles represent the major synthetic pathways. This research can lead to the discovery of novel initiation mechanisms and reaction pathways with applications in the synthesis of oligomers and nanocomposites with unique and improved properties.

Different effects of active minor admixtures on hydrogen and methane ignitions

The methane combustion inhibitor CCl4 exerts no effect on the first ignition limit of hydrogen; therefore, the role of hydrogen atoms in hydrocarbon oxidation consists at least of participating in longer reaction chains than are observed in hydrogen oxidation. The upper limits of the rate constants of the reactions of hydrogen atoms with propylene and isobutylene molecules were estimated by the self-ignition limit method to be (1.0 ± 0.3) × 10−11 exp(−1450 ± 400/T) and (0.8 ± 0.3) × 10−11 exp(−550 ± 200/T) cm3 molecule−1 s−1, respectively, in the temperature range of 840–950 K. These data are evidence that the stronger inductive effect of the two methyl groups in isobutylene lowers the energy barrier to the H + iso-C4H8 reaction. It has been demonstrated experimentally that chemiluminescence in the hydrocarbon flame front at atmospheric pressure precedes heat evolution. Throughout the pressure and temperature ranges examined (5–750 Torr, 298–950 K), the chain mechanism determines the basic laws of combustion.

Electron and positron scattering cross sections for propene and cyclopropane

In this paper we investigate electron and positron total and electron vibrational excitation scattering cross sections for propene and cyclopropane molecules. The electron and positron total cross sections were measured over the energy range 0.2--1000 eV using a retarding-potential time-of-flight method while the electron impact vibrational excitation cross sections were measured using a crossed-beam method. For both molecules, bending and stretching vibrational modes are studied at loss energies 0.12 and 0.37 eV, respectively, for propene, and 0.13 and 0.37 eV, respectively, for cyclopropane, at the scattering angle of 90\ifmmode^\circ\else\textdegree\fi{} and impact energy range 1--16 eV.

Reaction Dynamics of Phenyl Radicals (C6H5) with Propylene (CH3CHCH2) and Its Deuterated Isotopologues

The reactions between phenyl radicals (C6H5) and propylene (CH3CHCH2) together with its D6- and two D3-isotopologues were studied under single collision conditions using the crossed molecular beams technique. The chemical dynamics inferred from the center-of-mass translational and angular distributions suggests that the reactions are indirect and initiated by an addition of the phenyl radical to the alpha-carbon atom (C1 carbon atom) of the propylene molecule at the =CH2 unit to form a radical intermediate (CH3CHCH2C6H5) on the doublet surface. Investigations with D6-propylene specified that only a deuterium atom was emitted; the phenyl group was found to stay intact. Studies with 1,1,2-D3- and 3,3,3-D3-propylene indicated that the initial collision complexes CH3CDCD2C6H5 (from 1,1,2-D3-propylene) and CD3CHCH2C6H5 (from 3,3,3-D3-propylene) eject both a hydrogen atom via rather loose exit transition states to form the D3-isotopomers of cis/trans-1-phenylpropene (CH3CHCHC6H5) (80-90%) and 3-phenylpropene (H2CCHCH2C6H5) (10-20%), respectively. Implications of these findings for the formation of polycyclic aromatic hydrocarbons (PAHs) and their precursors in combustion flames are discussed.

Molecular structure and vibrational spectra of 1,3-bis(4-piperidyl)propane by quantum chemical calculations

The infrared and Raman spectra of 1,3-bis(4-piperidyl)propane molecule have been recorded between 4000–400 cm −1 region and 3500–150 cm −1 region, respectively. The vibrational frequencies of the molecule are investigated. The molecular geometry and vibrational frequencies of 1,3-bis(4-piperidyl)propane (also named 4,4′-trimethylenedipiperidine (TMDP)) in the ground state have been calculated by using density functional methods (B3LYP and BLYP) with 6-311 G(d,p) and 6-31 G(d) as basis sets. The comparison of the observed fundamental vibrational frequencies of 1,3-bis(4-piperidyl) propane and calculated results by density functional B3LYP and BLYP methods indicates that B3LYP is superior to the scaled BLYP approach for molecular vibrational problems.

Molecule fragmentation at the Dresden EBIS-A

We report on molecule fragmentation measurements of propane in high dense electron beams of a room-temperature electron beam ion source, the so-called Dresden EBIS-A. After fragmentation of propane molecules in the electron beam the fragments were continuously extracted and q/A separated by a bifocal dipole magnet. Fragmentation spectra were measured at working gas pressures of 10(-9) mbar up to 10(-8) mbar, electron currents of 29 mA up to 75 mA, and electron energies of 11 keV up to 15 keV. Thereby all possible stoichiometric ratios of propane fragments were detected. At low electron beam currents the ion current output of the CH(x)(+) (x=0-3) and the C(2)H(x)(+) (x=0-5) fragments is nearly identically. At higher electron currents the CH(x)(+) (x=0-3) peaks dominate the spectra and the ratio between the C(+) peak and CH(x)(+) (x=0-3) peaks increases from 2:1 to 3:1. It was shown that the working gas pressure has no significant influence on the fragment distribution but on the total ion current.

Use of the IR spectra of adsorbed ethane and propane molecules to characterize the strength of active sites in zeolites and to analyze the activation of C-H bonds in these paraffins

The adsorption and activation of ethane and propane on the hydrogen and cationic forms of mordenite, zeolite ZSM-5, and zeolite Y were studied by diffuse-reflectance IR spectroscopy. The effect of the polarization of these molecules by adsorption sites on the intensities and shifts of absorption bands due to C-H stretching vibrations were studied. It was found that weak adsorption species were formed on the hydrogen forms of the above zeolites. In this case, both the intensity distributions and the positions of absorption bands due to C-H stretching vibrations were almost independent of the nature of zeolites. However, both absorption band maximum positions and relative intensity distributions changed upon paraffin adsorption on the cationic forms. It was also found that relative intensity distributions and shifts of absorption bands due to C-H stretching vibrations strongly depended on the nature of cations and zeolites. In this case, the initially totally symmetrical C-H vibrations were found most strongly disturbed. The low-frequency shifts and relative intensities of absorption bands due to these vibrations for various cations and zeolites were found to increase in the following orders: H < Na < Ca < Mg < Zn and zeolite Y < Mord ≈ ZSM-5. The experimental results suggest that ethane and propane molecules can be used as molecular probes for acquiring information on the nature and properties of acidbase sites in zeolites. In this case, both the low-frequency shifts and the relative intensities of absorption bands due to C-H stretching vibrations can be used as measures to characterize the nature of cations and zeolites. However, the latter was found to be much more sensitive to the nature of active sites.

Hydrogen transfer from guest molecule to radical in adjacent hydrate-cages

Electron spin resonance measurement of gamma-ray-irradiated propane hydrates shows that the normal propyl radical withdraws hydrogen from the adjacent propane molecule through the hexagonal planes of the hydrate cage without water molecule bridging.

Propane activation by MC 5H +5 (M = Ni and Co): An experimental and theoretical work

The reactions of MC 5H + 5 (M = Ni and Co) with propane in gaseous phase have been studied with an ion trap mass spectrometer; the MC 5H + 5 ions are able to activate the propane molecule which undergoes a dehydrogenation reaction. At variance with the reactions of the bare metal ions no loss of methane is observed; the reaction mechanism has been explored by means of DFT calculations and a possible explanation is offered for the different reactivity of these ligated ions.