Isomerization Of 1-butene Research Articles

Carbohydrate pyrolysis mechanisms from isotopic labeling. Part 5. The pyrolysis of D-glucose: The origin of the light gases from the D-glucose molecule

Flash pyrolysis in air of the complete set of 13C1 isotopologs of D-glucose, monitored by GC/MS using an efficient column for separating the light gases, allowed us to determine the sources within D-glucose for a range of light hydrocarbons and carbon oxides. These include carbon monoxide (CO), carbon dioxide (CO2), ethyne, ethene, ethane, propadiene, propene, propane, various isomers of butene, 1,3-butadiene, 1,3-cyclopentadiene and benzene. Inasmuch as the pyrolysis product was swept into the chromatographic column as formed, changes in isotopic incorporation with temperature rise could be qualitatively observed as changes of isotopic content across the chromatographic peak. There was significant divergence in labeled origin of CO and CO2, suggesting substantial mutual independence of formation. For both, however, composition was dominated by the first four carbons of D-glucose. The high-temperature range of formation of these may reflect the composition of the underlying char undergoing combustion. Similarities in isotopic content of ethene and ethane, or of allene, propylene and propane or of the various C4 species suggest that the least saturated versions are formed initially, and then undergo free-radical chain induced hydrogenation. Concerted electrocyclic fragmentations were invoked to explain the dominant formation of ethene, ethyne, propadiene and 1,3-butadiene. CO formation was postulated to arise in part from the fragmentation of glyoxal. CO and CO2 showed strong evidence of preferential ionization of the 13C isotopologs relative to the 12C ipsologs under our conditions, due to the magnetic isotope effect. Overlaid on this was a partial chromatographic enrichment of 13CO2 in the leading edge of the chromatographic peak. The data were normalized to adjust for both effects.

Dimerization of Linear Butenes on Zeolite-Supported Ni2+

Nickel- and alkali-earth-modified LTA based zeolites catalyze the dimerization of 1-butene in the absence of Bronsted acid sites. The catalyst reaches over 95% selectivity to n-octenes and methylheptenes. The ratio of these two dimers is markedly influenced by the parallel isomerization of 1-butene to 2-butene, shifting the methylheptene/octene ratio from 0.7 to 1.4 as the conversion increases to 35%. At this conversion, the thermodynamic equilibrium of 90% cis- and trans-2-butenes is reached. Conversion of 2-butene results in methylheptene and dimethylhexene with rates that are 1 order of magnitude lower than those with 1-butene. The catalyst is deactivated rapidly by strongly adsorbed products in the presence of 2-butene. The presence of π-allyl-bound butene and Ni-alkyl intermediates was observed by IR spectroscopy, suggesting both to be reaction intermediates in isomerization and dimerization. Product distribution and apparent activation barriers suggest 1-butene dimerization to occur via a 1′-adsorpt...

Combined light naphtha isomerization and naphthenic ring opening reaction on modified platinum on chlorinated alumina catalyst

The effect of alumina phases on the catalytic performance of platinum (Pt) on chlorinated alumina catalysts studied in the combined light naphtha isomerization and naphthenic ring opening reaction. The results showed that the type of alumina had a great impact on the catalytic performance of the Pt on chlorinated alumina catalysts. The support prepared by a mixture of eta and gamma alumina with the ratio of 70:30 shows better surface area, acidity and catalytic performance. Extra pre-chlorination of catalysts had a positive effect on the catalytic performance in the butane isomerization reaction. Activities of prepared catalysts tested in a pilot plant with two consecutive fixed bed reactors under different operating conditions. Under the experimental conditions of this study, temperatures greater than 135 °C had a reverse effect on the octane number of the products. It was found that the high LHSV has a negative effect on the strong acidic sites and with returning the LHSV to the initial value, 22DMB/ΣC6 ratio and ring opening reaction rate could not be restored completely.

Enhanced Separation of Butane Isomers via Defect Control in a Fumarate/Zirconium-Based Metal Organic Framework.

The discovery of appropriate synthetic reaction conditions for fabricating a stable zirconium-based molecular sieve (Zr-fum-fcu-MOF) with minimal defects and its utilization in the challenging separation of linear paraffins from branched paraffins is reported. The crystallinity and structural defects were modulated and adjusted at the molecular level by controlling the synthetic reaction conditions (i.e., amounts of modulators and ligands). The impact of molecular defects on the separation of n-butane from iso-butane was studied through the preparation, fine characterization, and performance evaluation of Zr-fum-fcu-MOFs with varying degrees of defects. Defect-rich Zr-fum-fcu-MOFs were found to have poor n-butane/iso-butane separation, mainly driven by thermodynamics, while Zr-fum-fcu-MOFs with fewer or minimal defects showed efficient separation, driven mainly by kinetics and full molecular exclusion mechanisms. The impact of intrinsic defects (i.e., missing organic or inorganic blocks) on the associated mechanisms involved in the separation of n-butane/iso-butane was evidenced through single-gas adsorption, mixed-gas column breakthrough experiments, and calorimetric studies. This investigation demonstrates, for the first time, the importance of controlling intrinsic defects to maintain the selective exclusion behavior of hydrocarbon isomers when using molecular sieves.

Raman high-pressure study of butane isomers up to 40 GPa

Raman spectroscopy studies on n and i-butane were performed at pressures of up to 40 GPa at ambient temperatures using the DAC technique. Normal butane undergoes two phase transitions at 1.9(5) GPa and 2.9(5) GPa and isobutane at 2.7(5) GPa and 3.5(5) GPa. These phase transitions were identified based on observations of the splitting Raman modes and the appearance or disappearance of particular Raman peaks. Our results demonstrate the complex, high-pressure behavior of butane isomers.

Selective Crystallization of Aluminophosphate Molecular Sieve with AEL Structure

The influence of temperature and ageing of initial aluminophosphate gels on their chemical and phase composition was studied. The hydrated oxide (boehmite) was used as the source of aluminum to prepare gels containing ammonium phosphate, undissolved pseudoboehmite and amorphous aluminophosphate in different proportions. The gel with predominant amorphous aluminophosphate was shown to provide selective crystallization of high phase purity AlPO4-11 with the crystallinity degree close to 100 %. The developed method for preparation of these disperse molecular aluminophosphate sieves AlPO4-11 is a step to crystallization of silicoaluminophosphates SAPO-11 that are promising Russian catalysts for industrial processes of hydroisomerization of n-paraffins used for manufacturing of Arctic diesel fuel, III group oils and isomerization of butenes.

H–D Exchange Mechanism of Butene on a D-Absorbed Pd–Au Alloy Surface

Complete H–D exchange of butene was reported on a D-absorbed Pd–Au alloy surface. However, its reaction mechanism has not been clarified yet. Here we investigate the reaction of cis-2- and 1-butene on Pd70Au30(110) by means of high-resolution electron energy loss spectroscopy. We demonstrate that both butene isomers are in the π-bonded state and that 1-butene irreversibly converts to cis-2-butene around 250 K. This isomerization accounts for previously observed similar product distributions in the H–D exchange reaction of cis-2- and 1-butene on the D-absorbed Pd70Au30(110) surface. Since the reverse change from cis-2- to 1-butene is not observed at any temperature, we conclude that the H–D exchange proceeds by the dissociative mechanism via vinylic and π-allylic intermediates rather than the Horiuti–Polanyi mechanism.

Computational Kinetics of Hydroperoxybutylperoxy Isomerizations and Decompositions: A Study of the Effect of Hydrogen Bonding

Hydroperoxyalkylperoxy (OOQOOH) radicals are important intermediates in combustion chemistry. The conventional isomerization of OOQOOH radicals to form ketohydroperoxides has been long believed to be the most important chain branching reaction under the low-temperature combustion conditions. In this work, the kinetics of competing pathways (alternative isomerization, concerted elimination, and H-exchange pathways) to the conventional isomerization of different β-, γ- and Δ-OOQOOH butane isomers are investigated. Six- and seven-membered ring conventional isomerizations are found to be the dominant pathways, whereas alternative isomerizations are more important than conventional isomerization, when the latter proceeded via a more strained transition state ring. The oxygen atoms in OOQOOH radicals introduce intramolecular hydrogen bonding (HB) that significantly affects the energies of reacting species and transition states, ultimately influencing chemical kinetics. Conceptually, HB has a dual effect on the stability of chemical species, the first being the stabilizing effect of the actual intramolecular HB force, and the second being the destabilizing effect of ring strain imposed by the HB conformer. The overall effect can be quantified by determining the difference between the minimum energy conformers of a chemical species or transition state that have HB and that do not have HB (non-hydrogen bonding (NHB)). The stabilization effect of HB on the species and transition sates is assessed, and its effect on the calculated rate constants is also considered. Our results show that, for most species and transition states, HB stabilizes their energies by as much as 2.5 kcal/mol. However, NHB conformers are found to be more stable by up to 2.7 kcal/mol for a few of the considered species. To study the effect of HB on rate constants, reactions are categorized into two groups ( groups one and two) based on the structural similarity of the minimum energy conformers of the reactant and transition state, for a particular reaction. For cases where the reactant and transition state conformers are similar (i.e., both HB or NHB structures), group one, the effect of HB on reaction kinetics is major only if the magnitudes of the stabilization energy of the reactant and transition state are quite different. Meanwhile, for group two, where the reactant and transition state prefer different conformers (one HB and the other NHB), HB affects the kinetics when the stabilization energy of the reactant or transition state is significant or the entropy effect is important. This information is useful in determining corrections accounting for HB effects when assigning rate parameters for chemical reactions using estimation and/or analogy, where analogies usually result in inaccuracies when modeling atmospheric and combustion processes.

Controlling Structure and Reactivity in Cationic Solid-State Molecular Organometallic Systems Using Anion Templating

The role that the supporting anion has on the stability, structure, and catalytic performance, in solid-state molecular organometallic systems (SMOM) based upon [Rh(Cy2PCH2CH2PCy2)(η2η2-NBD)][BArX4], [1-NBD][BArX4], is reported (X = Cl, F, H; NBD = norbornadiene). The tetra-aryl borate anion is systematically varied at the 3,5-position, ArX= 3,5-X2C6H3, and the stability and structure in the solid-state compared with the previously reported [1-NBD][BArCF34] complex. Single-crystal X-ray crystallography shows that the three complexes have different packing motifs, in which the cation sits on the shared face of two parallelepipeds for [1-NBD][BArCl4], is surrounded by eight anions in a gyrobifastigium arrangement for [1-NBD][BArF4], or the six anions show an octahedral cage arrangement in [1-NBD][BArH4], similar to that of [1-NBD][BArCF34]. C–X···X–C contacts, commonly encountered in crystal-engineering, are suggested to be important in determining structure. Addition of H2 in a solid/gas reaction affords the resulting σ-alkane complexes, [Rh(Cy2PCH2CH2PCy2)(η2η2-NBA)][BArX4] [1-NBA][BArX4] (NBA = norbornane), which can then proceed to lose the alkane and form the zwitterionic, anion-coordinated, complexes. The relative rates at which hydrogenation and then decomposition of σ-alkane complexes proceed are shown to be anion dependent. [BArCF34]– promotes fast hydrogenation and an indefinitely stable σ-alkane complex. With [BArH4]– hydrogenation is slow and the σ-alkane complex so unstable it is not observed. [BArCl4]– and [BArF4]– promote intermediate reactivity profiles, and for [BArCl4]–, a single-crystal to single-crystal hydrogenation results in [1-NBA][BArCl4]. The molecular structure derived from X-ray diffraction reveals a σ-alkane complex in which the NBA fragment is bound through two exo Rh···H–C interactions-different from the endo selective binding observed with [1-NBA][BArCF34]. Periodic DFT calculations demonstrate that this selectivity is driven by the microenvironment dictated by the surrounding anions. [1-NBA][BArX4] are catalysts for gas/solid 1-butene isomerization (298 K, 1 atm), and their activity can be directly correlated to the stability of the σ-alkane complex compared to the anion-coordinated decomposition products.

Influence of calcination temperature on catalytic, acid and textural properties of SO42−/La2O3/HZSM-5 type catalysts for biodiesel production by esterification

In this study, the efficiency of catalysts based on La2O3/SO42− supported on HZSM-5 zeolites was evaluated for the biodiesel production by esterification. The effect of a prior dealumination of the zeolite on the prepared catalysts properties was analyzed, as well as the influence of the calcination temperature. These materials were characterized by TGA, XRD, N2 adsorption/desorption, FTIR, and FTIR with adsorption of probe molecules (pyridine and collidine) for the identification and quantification of acid sites. Model reaction of double bond position isomerization of 1-butene was also performed, in order to evaluate the acidity of the new catalysts produced. These solids were tested in the esterification reaction of oleic acid in presence of methanol and the influence of the molar ratio between the reactants was evaluated. The results indicate that HZSM-5 modified with La2O3/SO42− can be an efficient catalyst for the esterification reaction. Whatever the reactants molar ratio used, the sulfated catalysts were more efficient than the starting zeolite in the esterification of oleic acid. The dealumination of the zeolite prior to the impregnation with SO42−/La2O3 leads to materials with improved properties. Moreover, low temperature calcination (350 °C) was revealed to also produce catalysts with more interesting properties. The enhancement of the external surface properties (acidity and area) was the main parameter influencing the activity of the catalysts for the considered reaction.

On the role of oxocarbenium ions formed in Brønsted acidic condition on γ-Al2O3 surface in the ring-opening of γ-valerolactone

The ring-opening and decarboxylation reaction of γ-valerolactone (GVL), yielding a mixture of butene isomers, constitutes an important transformative step for the upgradation of biomass-derived precursors into high value fuels and chemicals. In this study, density functional theory (DFT) simulations were utilized to gain insights into the ring-opening of GVL in presence of Brønsted acid promoted γ-Al2O3 catalyst. DFT simulations suggested towards the formation of stable oxocarbenium ion of GVL on the γ- Al2O3 surface via a proton transfer to the carbonyl oxygen in presence of the Brønsted acid. The surface oxygen atoms of γ-Al2O3 were observed to show high affinity for H-abstraction from the oxocarbenium ion to yield the carbenium ion intermediate, which subsequently gave the product butene via a combination of hydride transfer and decarboxylation steps. Higher reactivity of the Brønsted acid promoted γ-Al2O3 surface, was attributed to the direct ring-opening (Ea = 13 kJ/mol) of the surface adsorbed oxocarbenium ion of GVL, leading to the formation of the γ-carbenium ion, which was unlikely to form with the adsorbed GVL structure. In addition, H-abstraction by the surface oxygen from the C5 of adsorbed oxocarbenium ion (Ea = 13 kJ/mol) was calculated to be of lower activation barrier as compared to the H-abstraction from C5 of the adsorbed GVL (Ea = 40 kJ/mol), which may also lead to facile ring-opening in presence of a Brønsted acid on γ-Al2O3.

Thiol Treatment Creates Selective Palladium Catalysts for Semihydrogenation of Internal Alkynes

Summary Surface and interfacial engineering of heterogeneous metal catalysts is effective and critical for optimizing selective hydrogenation for fine chemicals. By using thiol-treated ultrathin Pd nanosheets as a model catalyst, we demonstrate the development of stable, efficient, and selective Pd catalysts for semihydrogenation of internal alkynes. In the hydrogenation of 1-phenyl-1-propyne, the thiol-treated Pd nanosheets exhibited excellent catalytic selectivity (>97%) toward the semihydrogenation product (1-phenyl-1-propene). The catalyst was highly stable and showed no obvious decay in either activity or selectivity for over ten cycles. Systematic studies demonstrated that a unique Pd-sulfide/thiolate interface created by the thiol treatment was crucial to the semihydrogenation. The high catalytic selectivity and activity benefited from the combined steric and electronic effects that inhibited the deeper hydrogenation of C=C bonds. More importantly, this thiol treatment strategy is applicable to creating highly active and selective practical catalysts from commercial Pd/C catalysts for semihydrogenation of internal alkynes.

Improvement of Activity and Stability of CuGa Promoted Sulfated Zirconia Catalyst for n-Butane Isomerization

The use of CuGa promoted sulfated zirconia (CuGa/SZ) catalyst for the isomerization of n-butane to isobutane has potential value as a replacement for the current catalyst for this important reaction (chlorinated alumina). Ga promoted SZ work well but deactivate rapidly. Several related catalysts (SZ, Ga/SZ, Cu/SZ, and CuGa/SZ) were compared. Only CuGa/SZ shows the most interesting properties: The stable conversion is 55%, and the selectivity to isobutane is 82% for 200 h. This is mainly attributed to Cu promoting a better incorporation of GaOx into the support, higher Bronsted/Lewis ratio, smaller ZrO2 crystallite, retard in the transformation from tetragonal (active for isomerization) to monoclinic (inactive) ZrO2 and higher sulfate stability. This effect is finally compared to the effect of Pd and Pt, demonstrating potential benefits of CuGa/SZ for commercial application due to their similar yields of isobutane (40–45%).

Physico-chemical properties of MoO3/ZrO2 catalysts prepared by dry mixing for isobutane alkylation and butene transformations

MoO3/ZrO2 catalysts were prepared either by wet impregnation or tableting dry mechanical mixtures of corresponding zirconium hydroxide and molybdenum containing precursors. It was shown that synthesis parameters influence the phase composition, structure, nature and strength of the acid sites. The structural and textural properties of MoO3/ZrO2 catalysts were characterized by a range of techniques including DTA, XRD, N2-physisorption, pH-measurements, selective adsorption of a series of acid-base indicators and FTIR spectroscopy of adsorbed pyridine. It is shown that an increase in the concentration of MoO3 gave a rise to Brønsted acidity concomitant with an increase of 1-butene conversion in isobutane alkylation and butene dimerization. Introduction of up to 6.6% of MoO3 resulted in sharp changes in physico-chemical properties as well as in catalytic behaviour allowing generation of products with an increased content of C8 compounds because of alkylation and dimerization. A further increase of MoO3 content to 13.2% predominantly led to isomerization of 1-butene to 2-butene which can be related to elevated Brønsted acidity.

Synthesis optimization of (h 0 h)-oriented silicalite-1 membranes for butane isomer separation

Tubular oriented silicalite-1 membranes were prepared on the inner surface of α-alumina tubes by secondary (seeded) growth. Membrane microstructures including orientation, thickness and defect densities which affected membrane performance could be regulated by synthesis optimization for butane isomer separation. Synthesis parameters such as synthesis temperature, synthesis time and solution composition were modified. Membrane orientation was greatly affected by synthesis temperature. Two typical membranes of highly (h0h)-oriented and mixed (h0h)&c-oriented membranes were obtained after synthesis optimization. Four highly (h0h)-oriented silicalite-1 membranes prepared under optimized synthesis conditions showed ideal H2/SF6 selectivities of 1325 ± 35, which was much higher than that of mixed (h0h)&c-oriented membrane M3 (300), indicating that the former membranes had fewer boundary defects. These highly (h0h)-oriented membranes displayed n-butane permeances and separation factors were (2.26 ± 0.23) × 10−7 mol (m2 s Pa)−1 and 32.7 ± 2.5 for an equimolar n-butane/i-butane mixture at 333 K, respectively. The low deviations in permeance and selectivity indicate that membrane synthesis had a good reproducibility. This average n-butane permeance for these highly (h0h)-oriented membranes was 4 times higher than that of mixed (h0h)&c-oriented membrane M3. Both kinds of highly (h0h)- and (h0h)&c- silicalite-1 membranes displayed the similar trend with test temperature and pressure.

Mixed matrix formulations with MOF molecular sieving for key energy-intensive separations.

Membrane-based separations can improve energy efficiency and reduce the environmental impacts associated with traditional approaches. Nevertheless, many challenges must be overcome to design membranes that can replace conventional gas separation processes. Here, we report on the incorporation of engineered submicrometre-sized metal-organic framework (MOF) crystals into polymers to form hybrid materials that successfully translate the excellent molecular sieving properties of face-centred cubic (fcu)-MOFs into the resultant membranes. We demonstrate, simultaneously, exceptionally enhanced separation performance in hybrid membranes for two challenging and economically important applications: the removal of CO2 and H2S from natural gas and the separation of butane isomers. Notably, the membrane molecular sieving properties demonstrate that the deliberately regulated and contracted MOF pore-aperture size can discriminate between molecular pairs. The improved performance results from precise control of the linkers delimiting the triangular window, which is the sole entrance to the fcu-MOF pore. This rational-design hybrid approach provides a general toolbox for enhancing the transport properties of advanced membranes bearing molecular sieve fillers with sub-nanometre-sized pore-apertures.

A perfect match.

A metal–organic framework with tailored porosity provides a mixed matrix membrane with excellent performance for natural gas purification and butane isomer separation.

Cool diffusion flames of butane isomers activated by ozone in the counterflow

Ignition in low temperature combustion engines is governed by a coupling between low-temperature oxidation kinetics and diffusive transport. Therefore, a detailed understanding of the coupled effects of heat release, low-temperature oxidation chemistry, and molecular transport in cool flames is imperative to the advancement of new combustion concepts. This study provides an understanding of the low temperature cool flame behavior of butane isomers in the counterflow configuration through the addition of ozone. The initiation and extinction limits of butane isomers’ cool flames have been investigated under a variety of strain rates. Results revealed that, with ozone addition, establishment of butane cool diffusion flames was successful at low and moderate strain rates. iso-Butane has lower reactivity than n-butane, as shown by higher fuel mole fractions needed for cool flame initiation and lower extinction strain rate limits. Ozone addition showed a significant influence on the initiation and sustenance of cool diffusion flames; as ozone-less cool diffusion flame of butane isomers could not be established even at high fuel mole fractions. The structure of a stable n-butane cool diffusion flame was qualitatively examined using a time of flight mass spectrometer. Numerical simulations were performed using a detailed chemical kinetic model and molecular transport to simulate the extinction limits of the cool diffusion flames of the tested fuels. The model qualitatively captured experimental trends for both fuels and ozone levels, but over-predicted extinction limits of the flames. Reactions involving low-temperature species predominantly govern extinction limits of cool flames. The simulations were used to understand the effects of methyl branching on the behavior of n-butane and iso-butane cool diffusion flames.

Experimental and kinetic modeling investigation on pyrolysis and combustion of n-butane and i-butane at various pressures

Butane is the smallest alkane with normal and branched isomers. To obtain insight into the effects of fuel structure and pressure on its intermediate-to-high temperature combustion chemistry, flow reactor pyrolysis and laminar burning velocities of the butane isomers were investigated at various pressures. In the pyrolysis experiments, species profiles were measured as function of the heating temperature at 0.04, 0.2 and 1 atm using synchrotron vacuum ultraviolet photoionization mass spectrometry. Laminar burning velocities of both n-butane/air and i-butane/air mixtures were measured at 298 K and 1–10 atm using spherically expanding flames. It was observed that both the pyrolysis and combustion behaviors of the butane isomers were influenced by the fuel structures. A detailed kinetic model of butane isomers was developed and validated against the new experimental data. Both rate of production analysis and sensitivity analysis were performed to give insight into the chemistry of butane pyrolysis and combustion. In the flow reactor pyrolysis, the weaker primary-tertiary CC bond than the primary-secondary and secondary-secondary CC bonds leads to lower initial decomposition temperatures of i-butane than n-butane. Under both pyrolysis and combustion conditions, the reaction pathways towards C2 and C3 species pool are emphasized for the decomposition of n-butane and i-butane, respectively. The more abundant production of C3 precursors explains the higher concentrations of benzene in the i-butane pyrolysis, while the higher laminar burning velocities of n-butane/air mixtures at all investigated pressures are mainly attributed to the easy production of H atom from n-butane decomposition and the dominance of the reactive C2 chemistry. Moreover, the i-butane/air flames exhibit stronger pressure dependence than the n-butane/air flames. The model was further validated against a wide range of experimental data in the literature, including ignition delay times and species profiles in flow reactor pyrolysis and oxidation, shock tube pyrolysis and oxidation, jet-stirred reactor oxidation and laminar premixed flames.

A Zeolite Family Nonjointly Built from the 1,3-Stellated Cubic Building Unit.

From a technological point of view, the synthesis of new high-silica zeolites is of prime importance owing to their high potential as industrial catalysts and catalyst supports. Two such materials have been synthesized which are made up of the 1,3-stellated cubic unit (hexahedral ([42 54 ]) bre unit) as a secondary building unit, with the aid of existing imidazolium-based structure-directing agents under "excess fluoride" conditions. One of them, denoted PST-21, is the first aluminosilicate zeolite consisting of 9-ring apertures solely; it displays exceptional activity towards steering the skeletal isomerization of 1-butene to isobutene and bridges the gap between small- and medium-pore structures. A series of hypothetical structures are also described that are nonjointly built from the bre unit; all of these structures are chemically feasible and will thus be helpful in designing the synthesis of novel zeolites containing 9-ring and/or 10-ring channels.