Isobutane Molecules Research Articles

Secondary scintillation yield from GEM electron avalanches in - and --isobutane for CYGNO — Directional Dark Matter search with an optical TPC

CYGNO is an international collaboration with the aim of operating a ▪ optical time projection chamber (TPC) for directional Dark Matter (DM) searches and solar neutrino spectroscopy, to be deployed at the Laboratori Nazionali del Gran Sasso (LNGS). A ▪/▪ (60/40) mixture is used, along with a triple Gas Electron Multiplier (GEM) cascade to amplify the ionisation signal. The scintillation produced in the electron avalanches is read out using a scientific complementary metal–oxide–semiconductor (sCMOS) camera. This solution has proven to provide very high sensitivity to interactions in the few ▪ energy range. The inclusion of a hydrogen-based gas will offer an even lighter target, resulting in a more efficient energy transfer in a DM particle collision, and consequently, a lower detection threshold. Additionally, longer track lengths of light nuclear recoils are easier to detect with a clearer direction. However, the addition of such gas will contribute to quenching the scintillation, jeopardizing the TPC performance. In this work, we demonstrate the feasibility of adding 1% to 5% isobutane to the ▪/▪ (60/40) mixture by measuring the respective absolute scintillation yield output. The overall scintillation produced in the charge avalanches is not drastically suppressed by quenching due to the isobutane addition. The presence of Penning transfer from excited He atoms to isobutane molecules increases the number of electrons in the avalanches, partially compensating for the loss of scintillation due to quenching. For the highest applied GEM voltage, the total number of photons produced in the avalanche per ▪ deposited in the absorption region presents a decrease of only a factor of about three, from 2.30(20)×104 to 8.2(4)×103▪, as the isobutane content increases from 0 to 5%. The quantification of the visible component of the scintillation shows that isobutane quenches both visible and ultraviolet (UV) photons emitted by ▪/▪.

Phosphoborane nanosheets as a sensing element for liquefied petroleum gas – A first-principles study

Nowadays, elemental monolayer materials are focused by the research communities due to their excellent selectivity, sensitivity, and stability toward air pollutants. In the present work, we deployed stable phosphoborane as a sensor to detect Liquefied Petroleum Gas (LPG) gases, namely isobutane and n-propane. Initially, the structural stability of pure phosphoborane is verified by cohesive energy. Further, the electronic characteristics of phosphoborane are studied with the support of band structure and projected density of states (PDOS) spectrum. The band gap of phosphoborane is calculated to be 2.734 eV (hybrid-GGA/B3LYP) which shows a semiconducting nature. Significantly, the adsorption properties of isobutane and n-propane molecules on phosphoborane are studied by ascertaining adsorption energy, relative band gap variation, and Mulliken charge transfer. In particular, the computed adsorption energy is noticed in the physisorption regime (−0.225 eV to −0.774 eV) and the Mulliken charge transfer is found in the range of 0.027 e to 0.223 e that infers the proposed phosphoborane is a promising sensor to detect the LPG molecules.

Insight into the selective oxidation of isobutene to methacrolein over Ce-accelerated Mo-Bi-Fe-Co-K-O catalyst

Understanding the mechanism of multi-component metal oxide catalyst for the selective oxidation of isobutene to methacrolein has long been challenging for its complexity. Herein, the key role of Ce on the Mo-Bi-Fe-Co-K-O catalysts for accelerating the selectivity of methacrolein was revealed. It was suggested that the Ce addition could replace the Bi3+ and then generate defects which changed the transformation of electron and the migration mobility of ions: Ⅰ. the production of Ce3+/Ce4+ and Co2+/Co3+ redox couples regulated the catalytic redox ability; and Ⅱ. the interaction effect between Ce and Co enhanced the storage capacity and mobility of oxygen which could benefit the adsorption and activation ability for isobutene molecules. Interestingly, it was found that adding appropriate amount of Ce adjusted the molar ratio of the catalytically active lattice oxygen and defect oxygen species. Therefore, proper amount of Ce addition to the catalyst significantly accelerated the methacrolein selectivity from 47.9% to 70.6%.

Interpreting the effect of hydrogen addition on the auto-ignition of branched alkane: A case study of iso-butane/hydrogen/O2/Ar mixtures

Auto-ignition of iso-butane/hydrogen mixtures were measured in a shock tube at pressures of 2 and 10 atm, equivalence ratio of 0.5, and temperatures from 1050 to 1590 K. New ignition delay time data of the binary mixtures were given to guide practical application and model development. Ignition delay time correlations of the iso-butane/hydrogen mixtures were provided. Four available kinetic models, namely the Aramco3.0 Mech, JetSurf2.0 Mech, USC2.0 Mech, and Li Mech, were validated against the experimental data. Li Mech can reproduce the ignition delay behavior of hydrogen, iso-butane, and their blends, therefore was adopted in this study to interpret the ignition chemistry of the iso-butane/hydrogen mixture. Hydrogen addition can promote the iso-butane ignition non-linearly at high temperatures. iso-butane molecule and the derived radicals break their chemical bonds mainly by colliding with free radicals under the current conditions, hydrogen addition can increase the radical pool concentration thus promote the reactivity. The hydrogen oxidation channel become dominated when the hydrogen ratio is as large as 98% thus lead to the significantly reduced ignition delay time.

Polyethylene with radiation-grafted sulfonated polystyrene membranes for butane and butenes separation

The possibility of paraffins and C4 olefins mixture separation on membranes made of polyethylene with radiation-grafted sulfonated polystyrene is shown. The selective separation is achieved due to the butenes and isobutene facilitated transfer in the form of a π-complex with a proton. Moreover, despite the significantly larger cross-sectional size, obstructing the transfer, isobutene molecules are also transferred much faster than butane, and the separation coefficient reaches 3.8. An unusual fact was discovered of separation selectivity and permeability increase with the separated gases flow humidity rise.

Promoting the sulfuric acid catalyzed isobutane alkylation by quaternary ammonium ionic liquids

AbstractSeven typical quaternary ammonium ionic liquids, amino acid ionic liquids, and imidazolium ionic liquids were synthesized, characterized, and investigated as co‐catalyst for the sulfuric acid catalyzed isobutane alkylation. The results show that the introduction of [OPSIm][HSO4] or [Pr3NPS][HSO4] both leads to a better catalytic performance and higher quality of alkylate products. The molecular dynamic simulation indicates that the [OPSIm][HSO4] can promote the dissolution of isobutane molecules at interface, further improving the ratio of isobutane to olefin from 1.02 to 1.18. Differently, the [Pr3NPS][HSO4] can significantly increase the interface width from 0.66 to 0.97 nm and reduce the interface tension from 28.49 to 14.62 mN/m, thereby enhancing the reaction area and improving the ion transfer. The [Pro][HSO4] and [Gly][HSO4] result in a worse quality of alkylate products due to no positive effect on the interfacial properties such as interfacial solubility of isobutane.

Characterization of additives in plastics: From MS to MS10 multistep mass analysis and theoretical calculations of tris(2,4-di-tert-butylphenyl)phosphate.

In the analysis by electrospray (+) of an extract of hemp sprouts put in a polypropylene vial, we found a large contamination of a plastic additive. It was characterized by multiple-stage MSn experiments (MS ÷ MS10 ) and identified as tris(2,4-di-tert-butylphenyl)phosphate, also known with the synonyms F32IRS6B46, oxidized Naugard 524, and others. The MS2 ÷ MS7 spectra are characterized by consecutive eliminations of six isobutene molecules from the tert-butyl moieties, some of them also occurring in the ion source. The first three are calculated to occur preferentially from the ortho positions, whereas eliminations from the para positions are estimated to be less favored at about 5-6 kcal/mol in each step. Once the first three isobutene molecules are eliminated, the remaining three are lost from the tert-butyl moieties in para positions (MS5 ÷ MS7 ), yielding protonated triphenylphosphate, whose structure has been confirmed by the MS2 spectrum of triphenylphosphate standard: the latter spectrum is almost superimposable with the MS8 spectrum of the analyte under investigation. MS8 and MS9 spectra show main losses of water and C6 H4 molecules. The MS10 spectrum of precursor ions at m/z 215 shows the gas-phase addition of water and methanol and ions at m/z 168, attributable to the loss of a phosphorus oxide radical. Density functional theory (DFT) calculations (Becke 3LYP [B3LYP] 6-311+G(2d,2p)) have been used to evaluate structure and stability of different ionic and neutral species involved in the decomposition pathways and to calculate thermochemical data of the decomposition reactions. This multistep mass analysis combined with theoretical calculations resulted to be particularly useful and effective, yielding chemical, thermochemical, and mechanistic data of significant utility in the structural characterization and identification of the unknown analyte as well as to define its gas-phase reactivity under a multistep low-energy collision-induced dissociation regime.

Hydrophobicity of an isobutane dimer in water, methanol and acetonitrile as solvents — A classical molecular dynamics study

The potential of mean forces (PMFs) has been determined for an isobutane dimer in various solvent environments such as water, methanol and acetonitrile at a temperature of 298 K and pressure of 1 bar using GROMACS software. All the molecular dynamics (MD) simulations are carried out using a TIP3P water model under a CHARMM36 forcefield. Following Umbrella Sampling technique, PMFs are calculated and analyzed using Weighted Histogram Analysis Method (WHAM) and coordination number of first solvation shell is extracted for all solvents using radial distribution function. The shape of PMFs contains contact minima, solvent-separated minima and desolvation maxima. The values of contact minima are not affected much by solvent environment and found to be at 0.5377, 0.5480 and 0.5495 nm for water, methanol and acetonitrile respectively. The corresponding energy depths are found −0.9134, −0.7080 and −0.5295 kcalmol[Formula: see text]. The variation observed at solvent-separated minima is noticeable and found at 0.9012, 0.9721 and 0.9151 nm for water, methanol and acetonitrile, respectively. The coordination number of the first solvation shell by taking an isobutane molecule as a reference from their center of mass is found to be 28.1, 16.9 and 14.8 for water, methanol and acetonitrile, respectively. There is a soft hydrophobic interaction between isobutane dimer and solvents like methanol and acetonitrile relative to water, might be due to the presence of competitive methyl group of methanol and acetonitrile in the solvent medium.

Gas phase lubrication on diamond-like carbon film: Tribochemical reactions under isobutane condition

Abstract Diamond-like carbon (DLC) film, with a host of intriguing properties, has emerged as a unique tribological material to be used in many fields. However, incomplete knowledge about the crucial parts, which control the frictional behavior under different gases, limits the further use of them. Here, we show that the tribological performance of hydrogen-free DLC film changed over a wide range by introducing hydrocarbon molecules into the frictional system. And the friction coefficient increased while the wear decreased with the increasing of isobutane amount. It was that the adsorbates which dissociate from isobutane molecules during tribochemical process on sliding interfaces caused the increasing trend of friction coefficient and provided a layer to prevent the sliding surface from wear.

Experimental and model studies about the lubrication of physisorbed isobutane molecules on hydrogenated diamond-like carbon films

As one amorphous carbon consisting of sp2 and sp3 bonding, diamond-like carbon (DLC) films present excellent tribological characteristics. Meanwhile, frictional properties could present great complexity with the varied interaction. In this work, research on the tribological performances of hydrogenated DLC films under the various isobutane conditions, which was similar to some polar fluids, was carried out. The results showed that friction coefficient increased with the isobutane amount. And the wear was constant after a certain amount of isobutane was adsorbed. Combining these experimental results with models, the mechanism has been proposed. It was the isobutane molecules physisorbed on the interface that prevented the hydrogenated DLC films from wear, resulting in the increasing of friction coefficient with gas pressure.

Systematic kinetic modeling of the propyl tert-butyl ether synthesis reaction

The kinetics of the liquid-phase addition of 1-propanol to isobutene to produce propyl tert-butyl ether (PTBE) has been studied using the ion-exchange resin Amberlyst™ 35 as the catalyst. Reaction rates free from mass transfer limitations have been experimentally determined in the temperature range 303–352 K, for different initial proportions of alcohol and isobutene, and using two different reactor types (i.e., a batch stirred tank reactor, to obtain most of the experimental data, and a tubular reactor, to validate those results). To find out the best kinetic model, a systematic approach has been adopted. The overall etherification reaction has been decomposed as the result of elementary steps based on Langmuir–Hinshelwood–Hougen–Watson or Eley–Rideal mechanisms. Candidate kinetic equations have been originated from all possible combinations of adsorbed and non-adsorbed compounds, and rate-determining step. The possible effect of the interaction between the reaction medium and the resin on reaction rates has been also examined. Since all experimental data have been used at once in the fit of the kinetic equations, all combinations of significant or non-significant temperature dependence of model parameters have been also considered. As a result, 1404 candidate kinetic equations have been fitted separately to experimental data. Discrimination among models is based on mathematical and physico-chemical criteria. The final choice of the best kinetic model involves multimodel inference. It corresponds to an Eley–Rideal mechanism where one 1-propanol molecule adsorbed on the catalyst reacts with one isobutene molecule from the liquid phase to form one adsorbed PTBE molecule, the surface reaction being the rate-determining step.

Molecular dynamics simulations on homogeneous condensation of R600a refrigerant

Molecular Dynamics (MD) simulations have been employed to study the homogeneous condensation phenomenon of R600a (isobutane) refrigerant in the vapor compression refrigeration system. The molecular system consists of superheated vapor isobutane in a cuboid simulation cell with periodic boundary conditions in all directions. A more physically reliable thermostat and a barostat are applied to control the temperature and pressure of the cell containing the molecules. Based on AHRI standard 460 rating conditions, the simulations started from the initial configuration of vapor phase isobutane system, and once the equilibration is established at 361K with 1atm, the system is suddenly cooled to the ambient temperature of 308K and is set under the condensing pressure of 7.1658bar corresponding to the saturation temperature at 325K of the compound at supersaturation ratio 1.548. The density, internal potential energy, and volume changing with time of superheated vapor molecules in the homogeneous condensation process of the system are investigated. The results show that vapor molecules have underwent a rapid phase transition to the subcooled liquid at a certain critical time period. Subcritical clusters of isobutane molecules are formed in the preliminary part of the simulations, which then aggregate to generate the critical condensate nucleus over time. An examination of the radial distribution functions (RDFs) shows that the bonding and non-bonding interactions are formed in the vapor and liquid phases of isobutane. It is truly consistent with the internal potential energy and phase change properties. The computed densities of both phases agree well with the NIST standard reference thermodynamic and transport property data of the compound. A comparative study is executed through several simulations for various values of supersaturation and undersaturation ratios with different numbers of molecules to investigate the critical time of phase transition in the homogeneous condensation process.

Zeolite Catalysis: Water Can Dramatically Increase or Suppress Alkane C–H Bond Activation

Zeolite-catalyzed alkane C–H bond activation reactions carried out at room temperature, low pressure, and low reagent loadings demonstrate that water can act either to increase or to suppress the observed reaction rates. Isobutane-d10 undergoes hydrogen/deuterium exchange with the acidic zeolite HZSM-5 at subambient temperatures, as first reported by us (Truitt et al. J. Am. Chem. Soc. 2004, 126, 11144 and Truitt et al. J. Am. Chem. Soc. 2006, 128, 1847). New experiments demonstrate that the C–H bond activation chemistry is very sensitive to the presence of water. Isobutane reaction rate constants increase by an order of magnitude at water loadings in the range of ≤1 water molecule per catalyst active site relative to the dry catalyst. Conversely, water loadings greater than about 1–3 water molecules per active site retard isobutane reaction. In situ solid-state NMR data show that water molecules and isobutane molecules are simultaneously proximate to the catalyst active site. These results indicate that water can be an active participant in reactions involving hydrophobic molecules in solid acid catalysts, possibly via transition state stabilization, as long as the water concentration is essentially stoichiometric. Such conditions exist in well-known catalytic reactions, e.g., methanol-to-hydrocarbon chemistries, since stoichiometric water is a first-formed byproduct.

Mechanisms of alkylation of isobutane by butenes and H/D exchange in isobutane molecules on acid zeolites

The mechanisms of alkylation of isobutane by butenes are discussed. As a result of critical analysis of the literature on the regioselectivity of protonation of isobutane a mechanism of H/D exchange in the isobutane molecule at the acid centers is proposed as possible first stage of alkylation.

Activation energy of hydride transfer between isobutane molecules on USY zeolite. First direct experimental measurement by in situ MAS NMR using mixtures of isotopomers

In situ13C and 1H MAS NMR study of hydride transfer between 13C and 2H isotopically labeled isobutanes on acidic zeolites enabled to estimate the activation energy of this process for the first time and allow full re-evaluation of C–H bond activation mechanism at moderate temperatures. The hydride transfer was shown to occur on the methine position of the molecule. The rates of the intermolecular H/D exchange were measured at different temperatures, and the activation energy was determined to be ca. 55kJ/mol. These new results definitively support the carbenium mechanism for alkane activation over zeolites through a bimolecular process.

Intermolecular Hydrogen Transfer in Isobutane Hydrate

Electron spin resonance (ESR) spectra of butyl radicals induced with γ-ray irradiation in the simple isobutane (2-methylpropane) hydrate (prepared with deuterated water) were investigated. Isothermal annealing results of the γ-ray-irradiated isobutane hydrate reveal that the isobutyl radical in a large cage withdraws a hydrogen atom from the isobutane molecule through shared hexagonal-faces of adjacent large cages. During this “hydrogen picking” process, the isobutyl radical is apparently transformed into a tert-butyl radical, while the sum of isobutyl and tert-butyl radicals remains constant. The apparent transformation from isobutyl to tert-butyl radicals is an irreversible first-order reaction and the activation energy was estimated to be 35 ± 3 kJ/mol, which was in agreement with the activation energy (39 ± 5 kJ/mol) of hydrogen picking in the γ-ray-irradiated propane hydrate with deuterated water.

Distribution of the products from the alkylation of isobutane with butenes at a zeolite catalyst and the reaction mechanism

The mechanisms of formation are proposed on the basis of the distribution of the intermediate and final products of zeolite alkylation of isobutane with butenes. The mechanisms are based on activation of the isobutane molecule at the methyl groups, simultaneous intermolecular and intramolecular hydride transfer, and β dissociation during skeletal isomerization of the carbonium ions.

ChemInform Abstract: Transformation of Butanes Over ZSM-5 Zeolites. Part 2. Formation of Aromatic Hydrocarbons Over Zn-ZSM-5 and Ga-ZSM-5.

Selectivities for aromatic hydrocarbons in the transformation of butanes are greatly enhanced by incorporating zinc or gallium cations into H-ZSM-5. This work is concerned with the activation of butanes over Zn-ZSM-5 and Ga-ZSM-5 at 773 K. The zinc and gallium cations serve as catalysts for dehydrogenation of the starting alkanes. In the case of the transformation of butane, 80–85% of butane molecules undergo dehydrogenation on the cationic centres, while the remainder (15–20%) undergo cracking on the acidic sites. In the case of isobutane, ca. 70% of isobutane molecules undergo dehydrogenation and ca. 30% undergo cracking. The mode of activation of alkanes depends on the ease of carbenium-ion formation and the acid strength of the zeolite. The metal cations act also as very efficient catalytic centres for dehydrogenating the intermediate alkenes into aromatic hydrocarbons.Because of the higher acidity of Ga-ZSM-5, the intermediate alkenes undergo hydrogen-transfer reactions to form alkanes as well as aromatics. This leads to a lower yield of aromatics over Ga-ZSM-5 in comparison with Zn-ZSM-5.

Solid acid alkylation of isobutane by butenes: the path from the ascertainment of the reasons for fast deactivation to the technological execution of the process

A short review of solid acid alkylation processes; the conception of the mechanism of goal and side conversion of isobutane and butenes, the deactivation nature of catalysts being used, and the possibility for their reactivation and industrial application is given. It was demonstrated that hydride transfer from isobutane molecules is the key process under which the catalytic cycles of alkylation retain and saturated hydrocarbons are formed as the process products. The main reason for the deactivation of alkylation catalysts is the formation of alkylcyclopentadienes and related compounds belonging to butenes. The problems of the fast deactivation of solid alkylation catalysts are substantially solved by the organization of catalyst performance in the connected reaction-regeneration system and in the application of hydrogenation and extraction procedures of activity regeneration, for which hydrogen and initial isobutane are used. Many companies incline to this kind of organizing of uninterrupted solid acid alkylation, which is an alternate to liquid acid alkylation.

Diffusion of n-butane/ iso-butane mixtures in silicalite-1 investigated using infrared (IR) microscopy

Adsorption and diffusion of n-butane/ iso-butane mixtures in individual silicalite-1 crystals has been investigated using infrared (IR) microscopy. The equilibrium sorption isotherm for an equimolar gas phase mixture is calculated using Configurational Bias Monte-Carlo simulations. The comparison between simulation results and the experimental data enabled the determination of absolute values of concentration in the IR experiments. n-Butane uptake under presence of iso-butane and, vice versa, iso-butane uptake under presence of n-butane have been studied experimentally. It is shown that the n-butane counter-uptake is not limited by the n-butane diffusivity, but by the availability of free sites, which is, in turn, determined by the mobility of iso-butane. A site-percolation threshold, given by the number of iso-butane molecules blocking the ‘traffic junctions’ of the channel network, has been employed for explaining the occurrence of network regions which are initially inaccessible for n-butane in the counter-uptake process.