Individual Olefins Research Articles

Reaction pathway and kinetic modeling for transformation of light olefins over SAPO-34 in the absence of methanol

The current studies on SAPO-34 catalyzed MTO process are generally based on the hydrocarbon-pool mechanism, in which the individual olefin is generated in parallel by the competing reactions without interconversion of the resulted olefins. This situation is surely oversimplified and makes the reaction mechanism confusing. In this work, we investigated C3–C6 olefins transformation over SAPO-34 without methanol co-feeding to examine whether the oligomerization-cracking mechanism is applicable. Conversion pathways for individual olefin were discriminated with dimer-, trimer-, even tetramerization, by using Delplot analysis. The final reaction network was constructed with 11 reactions and a satisfactory correlation was achieved. Further validation tests were carried out by feeding C4 and C5 olefins mixture with excellent prediction performance obtained for the main product distribution, and comparison between SAPO-34 and ZSM-5 was done for a C4+ olefin feeding case, showing that SAPO-34 was much superior to ZSM-5 for higher olefin cracking.

Kinetic and Mechanisms of the Aqueous-Biphasic Hydroformylation of Olefins Contained in Naphtha Cuts Catalyzed by RhH(CO)(TPPTS)3 [TPPTS: Tri(sodium m-sulfonated-phenyl)phosphine

A kinetic study of the individual olefins present in naphtha, their mixture (synthetic naphtha) and the olefins present in a real naphtha was carried out using RhH(CO)(TPPTS)3 [TPPTS: tri(sodium m-sulfonated-phenyl)phosphine] as the catalyst precursor in aqueous-biphasic medium (toluene/water or naphtha/water), under mild reaction conditions: 80 °C, 800 psi (55.4 atm) and 600 rpm. The study consisted in the characterization of real naphtha, the selection of the model olefins, the preparation of synthetic naphtha, followed by hydroformylation of the individual olefins, of the olefin mixture and of a real naphtha cut. For 1-hexene aqueous-biphasic reaction, a kinetic study based on initial rate method showed a first order dependence on catalyst, substrate and dissolved hydrogen concentrations, whereas a fractional order was observed for carbon monoxide concentration. This kinetic results are in accord with the traditional hydroformylation mechanism, the hydrogenolysis of rhodium-acyl species being the rate-determining step of the cycle. From all the reaction profiles, it was corroborated by using the integral method that the dependence with respect to the olefin concentration was of first order for the aqueous-biphasic hydroformylation of individual olefins and their mixture, as well as for the olefins present in real naphtha cut. These results are important because of knowing the kinetics and mechanisms of the hydroformylation of the olefins present in naphtha, it is possible to improve the activity of the precatalyst and/or to design new ones for this type of application, i.e. the improving of the fuel quality through the green technology of aqueous-biphasic catalysis. A kinetic study of the individual olefins present in naphthas, their mixture (synthetic naphtha) and the olefins present in a real naphtha was carried out in aqueous-biphasic medium using RhH(CO)(TPPTS)3 [TPPTS = tri(sodium m-sulfonated-phenyl)phosphine] as the catalyst precursor in a aqueous-biphasic media, under mild reaction conditions: 80 °C, 800 psi (55.4 atm) and 600 rpm. The kinetic results are in accord with the traditional hydroformylation mechanism.

Olefin Isomers of a Triazole Bisphosphonate Synergistically Inhibit Geranylgeranyl Diphosphate Synthase.

The isoprenoid donor for protein geranylgeranylation reactions, geranylgeranyl diphosphate (GGDP), is the product of the enzyme GGDP synthase (GGDPS) that condenses farnesyl diphosphate (FDP) and isopentenyl pyrophosphate. GGDPS inhibition is of interest from a therapeutic perspective for multiple myeloma because we have shown that targeting Rab GTPase geranylgeranylation impairs monoclonal protein trafficking, leading to endoplasmic reticulum stress and apoptosis. We reported a series of triazole bisphosphonate GGDPS inhibitors, of which the most potent was a 3:1 mixture of homogeranyl (HG) and homoneryl (HN) isomers. Here we determined the activity of the individual olefin isomers. Enzymatic and cellular assays revealed that although HN is approximately threefold more potent than HG, HN is not more potent than the original mixture. Studies in which cells were treated with varying concentrations of each isomer alone and in different combinations revealed that the two isomers potentiate the induced-inhibition of protein geranylgeranylation when used in a 3:1 HG:HN combination. A synergistic interaction was observed between the two isomers in the GGDPS enzyme assay. These results suggested that the two isomers bind simultaneously to the enzyme but within different domains. Computational modeling studies revealed that HN is preferred at the FDP site, that HG is preferred at the GGDP site, and that both isomers may bind to the enzyme simultaneously. These studies are the first to report a set of olefin isomers that synergistically inhibit GGDPS, thus establishing a new paradigm for the future development of GGDPS inhibitors.

Effect of the Operating Conditions in the Transformation of DME to olefins over a HZSM-5 Zeolite Catalyst

The effect of the operating conditions (cofeeding methanol and water, temperature, space time, and feed concentration) on the reaction indices of the transformation of dimethyl ether (DME) to light olefins has been studied, using a HZSM-5 zeolite catalyst (SiO2/Al2O3 molar ratio of 280) agglomerated with boehmite and alumina. The experiments have been carried out in an isothermal fixed bed reactor under the following conditions: 300–400 °C, space time, 0.2–6 gcat h molC–1; feed, pure DME, and diluted in He (25–90% of DME); time on stream, 18 h. The studied reaction indices are DME conversion, yields, and selectivities of the individual olefins and byproduct fractions (C2—C4 paraffins, C5+ aliphatic, and BTX aromatics) and the catalyst stability. The reaction scheme is similar to that of the methanol transformation, although the reaction advance and deactivation by coke are higher in the transformation of DME, due to mainly the lower water concentration in the reaction medium. The suitable conditions to re...

Kinetic modeling of C2–C7 olefins interconversion over ZSM-5 catalyst

The kinetics of C2–C7 olefins interconversion were studied by feeding individual olefin into industrial ZSM-5 catalyst at temperatures of 400–490°C, space time of 0.0046–0.34h and partial pressure of 13.1kPa. A kinetic model involving oligomerization, cracking and aromatization of olefins was established. The results showed that the calculated apparent activation energy was negative for oligomerization reactions and positive for cracking reactions. The proposed kinetic model was able to predict the product concentrations in the C2–C7 olefins interconversion over ZSM-5 catalyst, with R2 values ranged from 0.969 to 0.996 for the major species.

Reaction pathway and kinetics of C3–C7 olefin transformation over high-silicon HZSM-5 zeolite at 400–490 °C

The pathway and kinetics of C3–C7 olefin transformation reactions were investigated in a fixed-bed reactor over a high-silicon HZSM-5 catalyst at 400–490°C in this work. The main reaction pathway was identified on the observations of the product distribution when the individual olefin was fed alone. The results show that C7= proceeds dominantly through a monomolecular cracking, whereas C4= and C3= through a bi- and trimolecular cracking, respectively, and both mono- and bimolecular cracking for C5= and C6=. On the basis of the proposed reaction pathway, the kinetic model was developed for each olefin, with the corresponding parameters correlated using the experimental data. Despite the fact that olefin cracking proceeds by a rather complex pathway, a fairly satisfactory agreement between the calculated and experimental data was achieved over the test temperature range of 400–490°C, and a phenomenon of the minus observed activation energy for both bi- and trimolecular cracking can be well interpreted by the combination of the reaction and adsorption steps on the catalyst surface.

Colloidal catalysts based on iron(III) oxides. 2. Peculiarities of catalyzed oxidation of palm oil

The catalytic activity of an iron(III)-oxide-based colloidal catalyst with respect to oxidation of palm oil with atmospheric oxygen at 60°C is investigated. In a microheterogeneous system of palm oil containing phospholipids and large amounts of α-tocopherol and β-carotene, oxidation in the presence of the catalyst proceeds by a latent radical mechanism. This mechanism manifests itself as oxygen uptake against a background of almost constant concentrations of natural antioxidants, i.e., α-tocopherol and β-carotene. Using a model reaction of oxidation of an individual natural olefin, limonene, it is shown that, in the presence of the catalyst and trace amounts of hydroperoxide, oxidation of the hydrocarbon occurs through the chain free-radical mechanism. The presence of a phospholipid (egg lecithin) dramatically decelerates the catalytic oxidation of limonene and makes the process proceed through the latent radical mechanism, the rate of which is unaffected by oil-soluble inhibitors.

Synthesis and study of antistatic diesel additives based on petroleum acids

Various alkyl nitronitrates based on individual olefins and mixtures of propylene trimer and tetramer isomers have been derived. Hydroxyesters have been synthesized via the reaction of natural naphthenic acid with propylene oxide in different molar ratios, as have complexes of chromium, nickel, and cobalt salts of natural naphthenic acids with alkyl nitronitrates. The electric conductivity of 0.001% solutions of nitro compounds in diesel fuels has been examined. It has been found that the antistatic properties of the chromium and nickel salts prevail, with the greatest antistatic effect being displayed by the complexes of the chromium salt. Hydroxyesters in a 1: 1 molar ratio also exhibit a strong antistatic effect.

Selective dimerisation of α-olefins using tungsten-based initiators

The selective dimerisation of the alpha-olefins 1-pentene through to 1-nonene is reported using an in situ-generated catalyst derived from tungsten hexachloride, aniline, triethylamine and alkylaluminium halide. The influence of reagent identity and reaction stoichiometry, along with activator, solvent and alpha-olefin substrate choice are probed. The catalyst is found to be highly selective towards dimerisation, minimising the formation of undesired heavier oligomers. Notably, the selectivity within the dimer fraction is found to favour the formation of products with methyl branches. The selectivity towards individual olefin isomers has been determined and the system is found to also produce trace levels of dienes and alkanes. A kinetic study of the system reveals a second order dependence on substrate. Comparison of the products observed, with those expected for metallacyclic and Cossee-type mechanisms, suggests that the latter is in operation, something confirmed by the results of a C(2)H(4)/C(2)D(4) co-dimerisation experiment which showed full isotopic scrambling in the products. Thus a mechanistic proposal is made to account for the observed behaviour of the system, including the diene and alkane formation.

Carbonylation of Naphtha by a Rhodium Complex Immobilized on Poly(4-vinylpyridine)

This work describes the carbonylation of hex-1-ene, cyclohexene, 2,3-dimethyl-but-1-ene and 2-methyl-pent-2-ene, their quaternary mixture and a real Venezuelan naphtha, catalyzed by a rhodium(I) [Rh(cod)(4-picoline)2](PF6) (cod = 1,5-cyclooctadiene) complex immobilized on poly(4-vinylpiridine) (P(4-VP)) in contact with methanol under carbon monoxide atmosphere. The conversion (%) of olefins to carbonylated products for the individual olefins decreases in the order: hex-1-ene (63) > cyclohexene (58) > 2,3-dimethyl-but-1-ene (50) > 2-methyl-pent-2-ene (31), under the following conditions: 0.5 g of P(4-VP) for [Rh] = 2 wt.% (1 × 10−4 mol), 10 mL of CH3OH, [olefin] = 1 × 10−2 mol, S/C = 100, P(CO) = 33 atm at 110 °C for 24 h. Other products such as H2 and CO2 coming from the catalysis of the water–gas shift reaction are observed. In this work, the carbonylation of hex-1-ene, cyclohexene, 2,3-dimethyl-but-1-ene and 2-methyl-pent-2-ene, their quaternary mixture and a real Venezuelan naphtha, catalyzed by a rhodium(I) [Rh(cod)(4-picoline)2](PF6) (cod = 1,5-cyclooctadiene) complex immobilized on poly(4-vinylpiridine) (P(4-VP)) in contact with methanol under carbon monoxide atmosphere is described.

Aqueous biphasic catalytic hydrogenation of olefins and olefin mixtures by the [Rh(μ-Pz)(CO)(TPPMS)] 2 complex, Pz = pyrazolate, TPPMS = (C 6H 5) 2P(C 6H 4SO 3Na)

The hydrosoluble complex [Rh(μ-Pz)(CO)(TPPMS)] 2, Pz = pyrazolate ligand, and TPPMS = (C 6H 5) 2P(C 6H 4SO 3Na) was used as catalytic precursor in the two phase hydrogenation reaction of the individual olefins (1-hexene, styrene, cyclohexene and 2,3-dimethyl-1-butene) to give the main expected saturated products. Under the best operational conditions (80 °C, 200 psi H 2, S/C 535/1, and 600 rpm), the substrates showed the following hydrogenation reactivity order: 1-hexene > styrene > cyclohexene > 2,3-dimethyl-1-butene. The quaternary equimolar mixture of olefin and an olefin mixture that simulates a real composition of olefin present in a naphtha showed a different hydrogenation order; styrene > 1-hexene > cyclohexene > 2,3-dimethyl-1-butene. The catalyst can be recycled without significant loss of activity and showed sulfur tolerance, demonstrated by using benzothiophene in the olefin mixtures.

Kinetic Modeling of the Methanol-to-Olefins Process on a Silicoaluminophosphate (SAPO-18) Catalyst by Considering Deactivation and the Formation of Individual Olefins

A kinetic model for the formation of individual olefins (ethylene, propylene, and C4+ olefins) from methanol over a SAPO-18 catalyst in a wide range of operating conditions has been proposed. The kinetic model takes into account three steps that evolve with time on stream: initiation period (where active intermediate compounds are formed), olefin production, and deactivation (by degradation of intermediate compounds to coke). This kinetic model predicts the experimental evolution of olefin production with time on stream, which initially increases, subsequently passes through a maximum (corresponding to the time on stream at which the maximum concentration of active intermediates is reached), and finally decreases (when deactivation by degeneration of intermediates to coke is faster than their formation). Different kinetic schemes for the formation of each individual olefin have been tested. Models that consider interconversion between olefins do not provide significant improvement over the model that qua...

Monoterpene cyclization mechanisms and the use of natural abundance deuterium NMR—short cut or primrose path?

Separate incubations of [2- 2H, 2- 13C]geranyl diphosphate (GPP) with (+)- and (−)-pinene cyclases isolated from common sage ( Salvia officinalis) gave a mixture of acyclic and cyclic monoterpene olefins. Mass spectrometric analysis of the derived labelled monoterpenes established that cyclization had taken place with complete retention of the deuterium label. In a complementary set of experiments, GC-mass spectrometric analysis of the individual olefins arising from incubations of a 1:1 mixture of [2- 2H, 2- 13C]GPP and unlabelled GPP confirmed the complete retention of deuterium and ruled out any intermolecular transfer of the C-2 deuterium of GPP from one substrate to another. These results, which are fully consistent with the currently accepted mechanism of monoterpene cyclization, are used to critically evaluate literature reports based on natural abundance deuterium NMR analysis of cyclic monoterpenes which had indicated substantial depletion of deuterium at the carbon atom corresponding to C-2 of GPP.

Novel Adsorption Distillation Hybrid Scheme for Propane/Propylene Separation

Abstract A novel adsorption–distillation hybrid scheme is proposed for propane/propylene separation. The suggested scheme has potential for saving up to ∼50% energy and ∼15–30% in capital costs as compared with current technology. The key concept of the proposed scheme is to separate olefins from alkanes by adsorption and then separate individual olefins and alkanes by simple distillation, thereby eliminating energy intensive and expensive olefin-alkane distillation. A conceptual flow schematic for the proposed hybrid scheme and potential savings are outlined.

Kinetics of the hydrogenation of C6-C9 olefins in the presence of aromatic hydrocarbons on a palladium sulfide catalyst

1. A kinetic model has been established for the hydrogenation of C6-C9 olefins on a palladium sulfide catalyst at atmospheric pressure in the presence of benzene, toluene, and xylenes, according to which the aromatic hydrocarbons inhibit the reaction due to adsorptive displacement. 2. When hydrogen is replaced by deuterium, kinetic isotope effects are observed in hydrogenation as well as in isomerization; this indicates the participation of hydrogen in the slow stages of both reactions. 3. The hydrogenation rates of the individual olefins in mixtures can be calculated on the basis of constants determined in the investigation of the individual olefins, i.e., simple interactions take place in the system.

Ring-opening polymerization of norbornene catalysed by W(CO) 3Cl 2(AsPh 3) 2 in the presence of other olefins

The steric course of ring-opening polymerization catalysed by W(CO) 3Cl 2(AsPh 3) 2 is strongly influenced by the presence of other cyclic or linear olefins, such as cyclooctene, cyclohexene, 1-hexene and 1,7-octadiene. The blockiness of the polymer increases linearly with the overall olefin concentration in the reaction mixture. This effect of the individual olefins is independent of whether or not they participate in the cross-metathesis reaction to a detectable extent. The results are in agreement with the existence of two major kinetically-distinct propagating metallacarbene species, one cis- and one trans-directing. Terminal olefins act as chain transfer agents. Based on polymer fractionation, 13C NMR and GC-MS studies, two more kinds of selectivity of the catalyst was found besides the increase of σ c and r c r t , of the polymer: 1. The formation, exclusively, of oligomers of a nonsymmetric structure; 2. The lack of detectable products of the homometathesis of linear chain olefins. The results are explained by the reluctance to form CH 2 carbenes and the relatively high reaction rate of propagation, chain transfer and degenerate metathesis, compared to the productive metathesis of the terminal olefins.

Isolation of individual olefins from the C4 fraction

1. The possibility of using the isomerization of 1-butene to 2-butenes to facilitate the isolation of highpurity isobutylene from the C4 fraction of pyrogas has been shown. 2. A modified scheme for separating the C4 fraction hydrocarbons is recommended. 3. Conditions have been worked out for the isomerization of 2-butenes to 1-butene for continuous preparation of the latter from a mixture of n-butenes.

Catalytic transformations of individual paraffins and olefins in the presence of benzene over synthetic aluminum silicates

1. An investigation was made of the catalytic transformations of heptane, 2,2,4-trimethylpentane, hexadecane, octene, and a mixture of amylenes in presence of benzene over synthetic aluminum silicates. 2. At 500–525° and 15 atm the catalytic transformations of these aliphatic hydrocarbons in presence of benzene are directed mainly toward the formation of toluene, xylenes, and other alkylbenzenes of low molecular weight. 3. The presence of benzene in the mixture favors the aromatization of the original hydrocarbons, Other reactions which occur to some extent are destructive alkylation of benzene, isomerization, hydrocracking, and autodestructive alkylation of aliphatic hydrocarbons and their decomposition products.