Isomerization Of 1-butene Research Articles

NCI Study of the Influence of Steric Hindrance on the Conformational Isomers of Propane, Butane, and Ethane Derivatives

AbstractThe role of the steric clash in the rotational energy barrier in CX3CX3 (X=H, CH3, F), propane, and butane compounds was studied using the NCI method and QTAIM approach. We found that the values of the repulsive density integral of NCI agrees with the traditional chemical steric model, as it increases with the size of the substituent. However, not in every case studied here, was the steric clash identified as the origin of the energy barrier. In the ethane case we note the absence of repulsive and attractive NCI across the full spectrum of the dihedral angles studied, whereas only in the propane and butane cases are the results consistent with the classical picture of the steric clash being the origin of the energy barrier. The energy profile for 2,2,3,3‐tetramethylbutane shows two energy barriers of 8.7 kcal/mol and 0.96 kcal/mol, their origin was analysed in terms of the alkyl‐alkyl interactions.

Gas-Phase Selective Oxidation of Butenes in the C4 Fraction by Nitrous Oxide

Direct oxidation of n-butenes is the preferred but yet unrealized route to methyl ethyl ketone (MEK). At the same time, N2O is a promising selective oxidant for conversion of olefins mainly to ketones. In this work, we studied the possibility of producing MEK via the gas-phase noncatalytic oxidation with N2O of butene isomers in the C4 refinery stream from catalytic cracking. The oxidation was performed at 573–823 K and a pressure of up to 2 MPa. NMR and gas chromatography methods were used to identify the reaction products. It was shown that N2O selectively oxidizes only butenes in the C4 fraction to form nitrogen and carbonyl products, among which MEK is predominant. The reaction proceeds through the 1,3-dipolar cycloaddition of N2O to the C═C bond of butenes. The proposed method allows obtaining valuable oxygenates without the separation of the C4 fraction and opens a potential way for the rational utilization of waste N2O, a powerful greenhouse gas.

Transfer printing platelike MFI crystals as seeds for the preparation of silicalite-1 membranes

High aspect ratio zeolite crystals and their seeding on support are of high desire for the fabrication of oriented zeolite membranes. Here, platelike MFI crystals, as zeolite seeds, are successfully seeded on a α-Al2O3 disk support through a transfer printing method. Firstly, platelike MFI crystals are spread on a flat substrate pre-coated with films of polyvinyl alcohol (PVA) and a fluoropolymer (4200UR) followed by coating a polymethyl methacrylate (PMMA) film. After dissolving the PVA film, the free-standing sandwich-like 4200UR-MFI-PMMA film is transferred onto the support. Then, platelike MFI crystals are successfully seeded after removing the organic species by calcination. Finally, highly (h0h)-oriented, dense and continuous silicalite-1 membranes are fabricated after a secondary growth in a zeolitic synthesis system, confirmed by XRD and SEM techniques. Binary separation of butane isomer has been performed on the silicalite-1 membranes prepared with different synthesis time, achieving a n-butane permeance and a separation factor of 2.27 × 10−7 mol m−2 s−1∙Pa−1) and 28.8 for an equimolar n-butane/i-butane mixture at 343 K, respectively.

One-Step Scalable Fabrication of Highly Selective Monolithic Zeolite MFI Membranes for Efficient Butane Isomer Separation.

The reproducible fabrication of large-area zeolite membranes for gas separation is still a great challenge. We report the scalable fabrication of high-performance zeolite MFI membranes by single-step secondary growth on the 19-channel alumina monoliths for the first time. The packing density and mechanical strength of the monolithic membranes are much higher for these than for tubular ones. Separation performance of the monolithic membranes toward the butane isomer mixture was comparably evaluated using the vacuum and Wicke-Kallenbach modes. The n-butane permeances and n-butane/i-butane separation factors for the three membranes with an effective area of ∼84 cm2 were >1.0 × 10-7 mol (m2 s Pa)-1 and >50 at 343 K for an equimolar n-butane/i-butane mixture, respectively. We succeeded in scaling up the membrane synthesis with the largest area of 270 cm2 to date which has 1.3 times the area of an industrial 1 m long tubular membrane. Monolith supported zeolite MFI membranes show great potential for industrial n-butane/i-butane separation.

Hybrid Monte Carlo method with potential scaling for sampling from the canonical multimodal distribution and imitating the relaxation process.

Hybrid methods that combine molecular dynamics methods capable of analyzing dynamics with Monte Carlo (MC) methods that can efficiently treat thermodynamically stable states are valuable for understanding complex chemical processes in which an equilibrium state is reached through many elementary processes. The hybrid MC (HMC) method is one such promising method; however, it often fails to sample configurations properly from the canonical multimodal distribution due to the rugged potential energy surfaces. In this paper, we extend the HMC method to overcome this difficulty. The new method, which is termed potential scaling HMC (PS-HMC), makes use of an artificially modulated trajectory to propose a new configuration. The trajectory is generated from Hamilton's equations, but the potential energy surface is scaled to be gradually flattened and then recovered to the original surface, which facilitates barrier-crossing processes. We apply the PS-HMC method to three kinds of molecular processes: the thermal motion of argon particles, butane isomerization, and an atom transfer chemical reaction. These applications demonstrate that the PS-HMC method is capable of correctly constructing the canonical ensemble with a multimodal distribution. The sampling efficiency and accepted trajectories are examined to clarify the features of the PS-HMC method. Despite the potential scaling, many reactive atom transfer trajectories (elementary processes) pass through the vicinity of the minimum energy path. Furthermore, we demonstrate that the method can properly imitate the relaxation process owing to the inherent configurational continuity. By comparing the PS-HMC method with other relevant methods, we can conclude that the new method is a unique approach for studying both the dynamic and thermodynamic aspects of chemical processes.

Butane isomers mobility and framework dynamics in UiO-66 (Zr) MOF: Impact of the hydroxyl groups in zirconia cluster

UiO-66 (Zr) is a metal-organic framework (MOF) known for its thermal and chemical stability and wide range of adsorption-based applications. This MOF exhibits high separation selectivity for butane isomers. It has been earlier inferred that the separation performance of the material depends on the hydroxylation state of the zirconia cluster. In this contribution, we apply 2H solid-state NMR to characterize the dynamics of both the MOF organic framework itself and butane isomers in hydroxylated and dehydroxylated forms of UiO-66. It is established that the rate of π-flipping and the amplitude of the phenylene ring plane librations in the framework are higher for the dehydroxylated form. Self-diffusion coefficients of butane isomers have been estimated for both forms of UiO-66. The diffusivity is higher for n-butane in the dehydroxylated form, whereas the diffusion of isobutane is not affected by the presence of OH groups in the zirconia cluster of the MOF. Higher diffusivity of n-butane in dehydroxylated form is accounted for by the larger effective diameter of the window between the adjacent cages in this form, which arises from faster rotation and larger amplitude of framework linker libration. This rationalizes the higher efficiency of the dehydroxylated form of UiO-66(Zr) material for butane isomers separation.

INVESTIGATION OF THE ISOMERIZATION REACTION OF BUTENE-1 TO BUTENES-2 ON BINARY TUNGSTEN-CONTAINING CATALYSTS

The activity of tungsten-containing catalysts in the reaction of isomerization of butene-1 to butenes-2 was studied in the work. The results obtained showed that the ^ introduction of the second element into the composition of the tungsten oxide catalyst had a different effect on its activity in the butene-1 isomerization reaction. It was established that an increase in the amount of molybdenum in the composition of a binary tungsten-containing catalyst at low temperatures leads to a decrease in the degree of butene-1 isomerization while at high temperatures it leads to an increase in the rate of butene-1 isomerization. It found that the addition of titanium to the composition of the tungsten oxide catalyst leads to an increase in the butene-1 isomerization rate. When copper is added to the composition of the tungsten oxide catalyst, the total yield of butene-2 passes through a maximum, and on samples rich in copper, the isomerization of butene-1 practically does not occur. It revealed that the activity of binary tungsten oxide catalysts in the isomerization reaction of butene-1 to butenes-2 changes in the following order: Ti-W-O > Mo-W-O > Cu-WO.

Sixty-One-Channel Monolithic Silicalite-1 Membranes Fabricated by Single-Step Secondary Growth for Butane Isomer Separation

Sixty-One-Channel Monolithic Silicalite-1 Membranes Fabricated by Single-Step Secondary Growth for Butane Isomer Separation

Enhanced Selectivity and Stability of Finned Ferrierite Catalysts in Butene Isomerization.

Designing zeolite catalysts with improved mass transport properties is crucial for restrictive networks of either one- or two-dimensional pore topologies. Here, we demonstrate the synthesis of finned ferrierite (FER), a commercial zeolite with two-dimensional pores, where protrusions on crystal surfaces behave as pseudo nanoparticles. Catalytic tests of 1-butene isomerization reveal a 3-fold enhancement of catalyst lifetime and an increase of 12 % selectivity to isobutene for finned samples compared to corresponding seeds. Electron tomography was used to confirm the identical crystallographic registry of fins and seeds. Time-resolved titration of Brønsted acid sites confirmed the improved mass transport properties of finned ferrierite compared to conventional analogues. These findings highlight the advantages of introducing fins through facile and tunable post-synthesis modification to impart material properties that are otherwise unattainable by conventional synthesis methods.

Enhanced Selectivity and Stability of Finned Ferrierite Catalysts in Butene Isomerization

AbstractDesigning zeolite catalysts with improved mass transport properties is crucial for restrictive networks of either one‐ or two‐dimensional pore topologies. Here, we demonstrate the synthesis of finned ferrierite (FER), a commercial zeolite with two‐dimensional pores, where protrusions on crystal surfaces behave as pseudo nanoparticles. Catalytic tests of 1‐butene isomerization reveal a 3‐fold enhancement of catalyst lifetime and an increase of 12 % selectivity to isobutene for finned samples compared to corresponding seeds. Electron tomography was used to confirm the identical crystallographic registry of fins and seeds. Time‐resolved titration of Brønsted acid sites confirmed the improved mass transport properties of finned ferrierite compared to conventional analogues. These findings highlight the advantages of introducing fins through facile and tunable post‐synthesis modification to impart material properties that are otherwise unattainable by conventional synthesis methods.

Direct H abstraction by molecular oxygen from unsaturated C3–C5 hydrocarbons: A theoretical study

AbstractPotential energy surfaces for the H abstraction reactions by molecular oxygen from unsaturated closed‐shell C3–C5 hydrocarbons, including allene and propyne (C3H4), propene (C3H6), diacetylene (C4H2), vinylacetylene (C4H4), 1,3‐butadiene (C4H6), butene isomers (C4H8), cyclopentadiene (C5H6), and cyclopentene (C5H8), which were earlier identified among the main pyrolysis products of jet fuel components, have been explored at the CCSD(T)‐F12/cc‐pVTZ‐f12//ωB97XD/6‐311G** + ZPE(ωB97XD/6‐311G**) level of electronic structure theory. The results of the ab initio calculations were then utilized in transition state theory calculations of the reaction rate constants. The H abstraction reactions by O2 appeared to be most favorable from the allylic sites and from allene and propyne forming the propargyl radical, with the reactions involving the cyclic allylic sites in cyclopentadiene and cyclopentene exhibiting the lowest reaction endothermicities and barriers. They are followed by the reaction of O2 with cyclopentene producing cyclopent‐1‐en‐4‐yl and the reactions with vinylacetylene and 1,3‐butadiene forming the resonantly stabilized i‐C4H3 and i‐C4H5 radical products. The H abstractions from primary and secondary vinylic sites as well as from acetylenic sites are significantly less favorable and unlikely to compete. The calculated rate constants have been validated against the previous experimental and theoretical results for propene and butene isomers. All considered reactions of H abstraction by O2 are predicted to be rather slow, with their rate constants at 1500 K being on the order of 10–17‐10–16 cm3 molecule–1 s–1 and exhibiting a well‐defined Arrhenius behavior. Modified Arrhenius expressions for the reaction rate constants both in forward and reverse directions and Evans–Polanyi relationship between the activation and reaction energies have been generated and proposed for kinetic combustion models. The H abstractions by O2 forming the resonantly stabilized radicals were concluded to likely contribute to the initiation of oxidation of the unsaturated C3–C5 species produced in the pyrolysis of the important components of jet fuels.

Spatial distribution of atmospheric oil and natural gas volatile organic compounds in the Northern Colorado Front Range

Methane and nonmethane volatile organic compounds (VOCs) were monitored near Boulder in the Northern Colorado Front Range to investigate their spatial distribution and sources as a part of the Front Range Air Pollution and Photochemistry Experiment (FRAPPE) and the Deriving Information on Surface conditions from Column and Vertically Resolved Observations Relevant to Air Quality (DISCOVER-AQ) campaign, in summer 2014. A particular emphasis was the study of the contribution of emissions from oil and natural gas (O&NG) operations on the regional air quality. One network extended along an elevation gradient from the City of Boulder (elevation ≈1,600 m) to the University of Colorado Mountain Research Station (≈2900 m) on the eastern slopes of the Rocky Mountains. Light alkane petroleum hydrocarbons had the highest mole fraction of the VOCs that could be analyzed with the applied techniques. The longer lived VOCs ethane and propane decreased with increasing elevation, suggesting that Boulder and the surrounding plains were a source of these anthropogenic compounds. VOC diurnal time series showed a few events with elevated mole fractions at the mountain sites, which were likely the result of the upslope transport of plumes with elevated VOCs from the plains. Within the other site network, which extended into suburban East Boulder County (EBC), VOCs were monitored at 5 sites increasingly close to O&NG development in the Denver Julesburg Basin. Mean mole fractions and variability of primarily O&NG-associated VOCs (ethane, propane, butane isomers) increased by a factor of 2.4–5.2 with closer proximity to the O&NG producing region. Median mole fractions of C2–C5 n-alkanes and of imuch-butane at the EBC sites were higher than those previously reported from 28 larger urban areas in the United States. Among the VOCs that could be quantified with the gas chromatography methods, VOCs most clearly associated to O&NG-related emissions (C2–C5 alkanes) accounted for 52%–79% of the VOC hydroxyl radical reactivity (OHR). The horizontal gradient in OHR of the considered VOCs, with ≈3 times higher values at the furthest eastern sites, points toward higher chemical reactivity and ozone production potential from these ozone precursors in the eastern area of the county than within the City of Boulder.

Selective dehydration of 1-butanol to butenes over silica supported heteropolyacid catalysts: Mechanistic aspect

Butenes are considered as important olefinic building block to produce fuels/fuel additives and commodity chemicals. In the present investigation, selective dehydration of 1-butanol to butenes was studied in a continuous-flow fixed-bed reactor using various silica-supported heteropolyacid (HPA) catalysts such as phosphotungstic acid (PTA), silicotungstic acid (STA), phosphomolybdic acid (PMA), and silicomolybdic acid (SMA) as the solid acid catalysts. The physicochemical properties of these HPA were determined by BET, powder XRD, FTIR, NH3-TPD, and Py-FTIR. The acid strength and Brønsted/Lewis (B/L) acid ratio were increased with higher loading of HPA on silica. The nature of HPA (addenda and hetero atom) and loading of HPA are important factors for the dehydration of 1-butanol and selectivity towards butenes. PTA and STA showed superior catalytic activity than PMA and SMA. The reaction temperature and WHSV also strongly affected the butanol conversion and selectivity of butenes. The selectivity of di-n‑butyl ether decreases with the rising temperature from 523 K to 623 K. The isomerization of 1-butene leading to the formation of other butene isomers depends on the HPA loading, temperature, and WHSV. The presence of molybdenum addendum atom in PMA and SMA promotes dehydrogenation and hydrogenation, leading to the formation of various light hydrocarbons. The 20PTA/SiO2 catalyst afforded 99.8% selectivity towards butenes at quantitative conversion of 1-butanol, whereas the 20STA/SiO2 catalyst gave nearly 97.0% conversion of 1-butanol and 99.9% butenes selectivity at 673 K, 37.4 h−1 of WHSV.

The origin of the particle-size-dependent selectivity in 1-butene isomerization and hydrogenation on Pd/Al2O3 catalysts

The selectivity of 1-butene hydrogenation/isomerization on Pd catalysts is known to be particle size dependent. Here we show that combining well-defined model catalysts, atmospheric pressure reaction kinetics, DFT calculations and microkinetic modeling enables to rationalize the particle size effect based on the abundance and the specific properties of the contributing surface facets.

Doping rich ethylene premixed flames: Influence of C[formula omitted][sbnd]C[formula omitted] alcohols on the structure of the steady one-dimensional laminar flame

The addition of alcohols to fueled mixture has been extensively documented as a practical way to significantly mitigate soot emissions by internal combustion engines. While being crucial to the initiation of some soot precursors formation, some chemical pathways attributed to the presence of alcohol-derived species remain unclear. Consequently, atmospheric steady flat laminar rich (equivalence ratio ϕ=1.7) ethylene/air premixed flames were established over a McKenna burner. The unburnt stream was seeded by prevaporized alcohols ranging from C3 to C5. Every flame was probed and sampled gases were investigated using a gas chromatography (GC) device equipped with a flame ionization detector (FID). Thus, quantitative mole fraction profiles are reported as a function of the distance to the burner tip. In total, 17 chemical compounds, including isomeric species (butene and pentene) have been detected quantitatively. Significant discrepancies among the intermediate species pool were observed, especially the amount of propene, butene, and pentene isomers (produced mostly due to the addition of propanol, butanol, and pentanol, respectively). Several kinetic mechanisms support the experimental results, none of them do reproduce properly the alkene production measured. Further numerical investigations were conducted focusing on the pathways that lead to the production of the alkenes identified. To the authors’ knowledge, the results reported are the first that (i) provide experimental results for the addition of 2,2-dimethyl-propanol, (ii) document unambiguously the mole fraction profiles of the three butene and five pentene isomers, and (iii) unveil similar trends on alkene production due to the addition of C3 to C5 alcohols, i.e. a clear hierarchy among primary, secondary, and tertiary alcohols for the rich atmospheric premixed flames studied.

Isomerization and hydroformylation of butenes under the catalysis of Rh-BIPHEPHOS

The isomerization and hydroformylation of butene under the catalysis of Rh-BIPHEPHOS were investigated by varying the butene feed and reaction temperature. The results indicate that in the presence of syngas, with 1-butene as feed, more isomerization product (i.e. 2-butene) is detected in comparison with the hydroformylation products, whereas with 2-butene as the feed, the hydroformylation is superior to isomerization. Due to the equilibrium limit between 1-butene and 2-butene, the increase of temperature shows a great positive effect on the isomerization reaction. Furthermore, under the catalysis of Rh-BIPHEPHOS, more n-pentanal is always formed than i-pentanal, as the larger bite angle of BIPHEPHOS restricts the intermediate rearrangement in the formation of i-pentanal.

Exploring the interaction kinetics of butene isomers and NOx at low temperatures and diluted conditions

The oxidation of 1-butene and i-butene with and without addition of 1000 ppm NO was experimentally and numerically studied primarily at fuel-rich (ϕ = 2.0) conditions under high dilution (96% Ar) in a flow reactor operated at atmospheric pressure in the low temperature range of approximately 600-1200 K. Numerous intermediate species were detected and quantified using synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS). An elementary-step reaction mechanism consisting of 3996 reactions among 682 species, based on literature and this work, was established to describe the reactions and interaction kinetics of the butene isomers with oxygen and nitrogenous components. Model predictions were compared with the experimental results to gain insight into the low- and high-temperature fuel consumption without and with NO addition and thus the respective interaction chemistry. This investigation firstly contributes a consistent set of temperature-dependent concentration profiles for these two butene isomers under conditions relevant for engine exhaust gases. Secondly, the observed oxidation kinetics is significantly altered with the addition of NO. Specifically, NO promotes fuel consumption and introduces for i-butene a low-temperature behavior featuring a negative temperature coefficient (NTC) region. The present model shows reasonable agreement with the experimental results for major products and intermediate species, and it is capable to explain the promoting effect of NO that is initiated by its contribution to the radical pool. Further, it can describe the observed NTC region for the i-butene/NO mixture as a result of the competition of chain propagation and chain terminating reactions that were identified by reaction flow and sensitivity analyses.

UiO-66 (Zr) MOF as a Promising Material for Butane Isomers Separation: Evidence Based on the Analysis of the Adsorbed Alkanes Mobility by 2H NMR and Molecular Dynamics Simulation

UiO-66 (Zr) MOF as a Promising Material for Butane Isomers Separation: Evidence Based on the Analysis of the Adsorbed Alkanes Mobility by ²H NMR and Molecular Dynamics Simulation

Development and application of a foundational fuel chemistry mechanism for pyrolysis and oxidation of propene and butenes

Propene and three butene isomers are mediate-sized foundational fuels during the conversion of large hydrocarbons, which play important roles in determining reactivities, combustion properties and emission behaviors of practical fuels. The objective of the present study was to develop a detailed foundational fuel chemistry mechanism to describe the decomposition of propene and three butenes, with emphasis on the molecular weight growth kinetics. In the first part of the paper, a new foundational fuel chemistry mechanism, TJU mechanism or TJU mech, containing 976 species and 11,505 reactions, was developed based on the CSM master pyrolysis mechanism along with the oxidation reactions stripped from the Aramco Mech 2.0. The thus-developed TJU mech was tested against a comprehensive speciation dataset from the oxidation and pyrolysis of propene and butenes over a wide range of operating conditions. Results showed that TJU mech provided good predictions for fuel conversions, formation of major and minor light products, and molecular weight growth species, including butadiene, cyclopentadiene, cyclohexadiene, benzene, toluene, etc. The second part of the paper involved the applications of TJU mech. Updated with improved understanding of the olefine reaction kinetics, TJU mech was firstly used to describe the formation of molecular weight growth species during pyrolysis of ethane and propane under high conversions, then it was utilized in Hybrid Chemistry model to predict formation of critical intermediates generated from i-octane and two jet fuels, Jet A and JP-10, respectively. Results highlighted importance of foundational fuel chemistry mechanism in describing the combustion kinetics of practical fuels.

Effects of the acidity and shape selectivity of dealuminated zeolite beta on butene transformations

The acidity and shape selectivity of zeolites are two important catalytic properties, and they have been extensively applied to the chemical and petrochemical industries. Here, we investigated the various effect mechanisms of Brønsted acid sites (BASs) from bridged hydroxyl groups in zeolite Beta and Lewis acid sites (LASs) from silanol nests in Si-Beta on butene transformation and their reaction pathways by diffuse-reflectance infrared Fourier-transform spectroscopy. BAS catalysis of butenes double bond activation and isomerization follows the classical carbenium ion mechanism, while catalysis by silanol nests as weak LASs due to hydrogen bond interaction is achieved by formation of allyl species and alkoxyl groups. Moreover, the oligomerization reactions of butene isomers are affected by the dynamic diameters and activation energies of the butene isomers and the synergy between acidity and shape selectivity of the zeolite. Oligomerization of n-butene and cis-2-butene is more likely to be affected by acids on the sample, while oligomerization of trans-2-butene and isobutene is influenced by the shape selectivity of the channel, in addition to the acidity on partly dealuminated zeolite Beta.