Propylene Pressure Research Articles

Epoxidation of propylene with H2O2 catalyzed by supported TS-1 catalyst in a fixed-bed reactor: Experiments and kinetics

The epoxidation of propylene with H2O2 catalyzed by a supported TS-1 catalyst in a fixed-bed reactor has been studied. The effects of methanol concentration (40–70wt.%), hydrogen peroxide concentration (5–20wt.%), propylene pressure (0.2–0.6MPa) and temperature (35–50°C) on the reaction are investigated. The experimental results show that the reaction rate increases with the increase in methanol concentrations, hydrogen peroxide concentrations, propylene pressure and temperature; the activation energy of the reaction is 46.8kJmol−1 and the reaction orders with respect to hydrogen peroxide and propylene are 0.32 and 0.68, respectively. The reaction was modeled with Eley–Rideal (E–R) and Langmuir–Hinshelwood (L–H) models, and the results show that the kinetic model of Eley–Rideal with H2O2 being adsorbed can give the best fit among the models compared for the epoxidation of propylene with H2O2.

Performance Enhancement of Vapex by Varying the Propane Injection Pressure with Time

Vapex or vapor extraction is an emerging green technology for heavy oil recovery. However, the oil production rates with Vapex are lower than those with the conventional recovery processes. This work aims at enhancing the oil production rates by investigating the effect of varying the injection pressure of solvent propane with time. For this purpose, experiments were designed and performed by injecting pure propane at injection pressures of 482.6, 551.6, 620.5, and 689.5 kPa and 21 °C into lab-scale physical models of heavy oil reservoirs. The physical models were packed with a porous medium and saturated with heavy oil. Three different permeabilities of the porous medium were used with heavy oils of two different viscosities and bed heights. The experiments were performed using different policies of solvent injection pressure versus time. Pressure variations were introduced by sudden release and re-injection of the solvent gas. In comparison to constant injection pressure, the pressure pulsing enhanced the oil production rate by 20–30%.

Phase Equilibria of Propane and Ethane Simple Hydrates in the Presence of Methanol or Ethylene Glycol Aqueous Solutions

We report dissociation pressures of propane and ethane simple hydrates in the presence of methanol or ethylene glycol aqueous solutions at different temperatures and various concentrations of inhibitor in aqueous solutions. The equilibrium data were generated using an isochoric pressure-search method. These data are compared with some selected experimental data from the literature on the dissociation conditions of propane and ethane simple hydrates in the presence of pure water to show the inhibition effects of the above-mentioned aqueous solutions. Comparisons are finally made between our experimental data and the corresponding literature data.

Epoxidation of propylene to propylene oxide catalyzed by large-grain TS-1 in supercritical CO 2

Large-grain titanium silicalite (TS-1, 3.0 μm long), which is a low-cost catalyst that can easily be separated from the product and exhibits an efficient catalyst recovery, was synthesized using tetrapropylammonium bromide (TPABr) as the template. However, it exhibited very poor catalytic activity in the traditional organic solvent compared with small-grain TS-1. The epoxidation of propylene to propylene oxide (PO) using the large-grain TS-1 as the catalyst and H 2O 2 as the oxidant in a supercritical CO 2 (scCO 2) medium was then investigated. The effects of the CO 2 pressure, reaction temperature, propylene pressure, cosolvent (methanol) concentration, and reaction time on the epoxidation reaction in scCO 2 were investigated and compared with those of the reaction in methanol. The use of scCO 2 as the reaction medium significantly improved the catalytic activity of the large-grain TS-1 and increased the PO yield from 50.1 to 83.5%. The effect of alkaline components [NaOH, NaHCO 3, urea, and (NH 4) 2CO 3] on the epoxidation reaction in scCO 2 was also investigated. The addition of alkaline components had a positive effect on the selectivity to PO as well as to H 2O 2 utilization. The addition of (NH 4) 2CO 3 yielded the best results, with the H 2O 2 conversion, PO selectivity, H 2O 2 utilization, and PO yield reaching 98.7%, 95.2%, 94.3%, and 88.6%, respectively. Therefore, a novel approach to PO production is introduced, which provides a basis as well as technical parameters for its further industrialization.

Prediction of multi component equilibrium isotherms for light hydrocarbons adsorption on 5A zeolite

Multi component equilibrium isotherms for the adsorption of propane, n-butane, and i-butane mixture on 5A zeolite at 303 K were obtained experimentally and theoretically. The constant-volume method was used for measuring the experimental equilibria data. Both the extended Freundlich and modified extended Langmuir equations correlated the multi component experimental data fairly well. The selectivity of 5A zeolite to adsorb gases was also studied. The results of this study showed that n-butane was more selectively adsorbed than propane on 5A zeolite, while i-butane was not adsorbed on this zeolite at the studied temperature. Also, it was found that an increase in partial pressure of n-butane decreases the adsorbed amount of propane, while the increase of partial pressure of propane has no effect on adsorbed amount of n-butane.

Weed control and crop tolerance to propane flaming as influenced by the time of day

Time of day has been observed to affect flaming efficacy. The basis for the differential plant response is not well understood; however, daily variation in leaf relative water content (RWC) is thought to contribute to the response. Leaf RWC is the ratio of the amount of water in the leaf tissue compared to when fully turgid. To determine the influence of leaf RWC in plant response to propane flaming, greenhouse experiments were conducted during April and repeated in September of 2009. Two crops [4-leaf maize ( Zea mays) and second trifoliate soybean ( Glycine max)] and two weed species [5-leaf velvetleaf ( Abutilon theophrasti) and 6-leaf green foxtail ( Setaria viridis)] were flamed with four propane doses of 0, 29, 43 and 87 kg ha −1 at 0, 4, 8 and 12 h after sunrise-HAS. Leaf RWC was measured before treatment application. Flaming treatment was conducted utilizing a hand flamer with one VT 2–23 C vapor phase burner positioned 20 cm above soil surface and angled horizontally at 30°. The propane pressure was 120 kPa and the application speeds were 1.6, 3.2 and 4.8 km h −1. The plant responses evaluated were plant injury and fresh weight at 7 days after treatment (DAT). All plant species were more susceptible to flaming during the afternoon when they had lower leaf RWC at 8 HAS; however, the response of these plants did not differ with the plants flamed at 12 HAS. Green foxtail flamed at 87 kg ha −1 at 0, 8 and 12 HAS had injury of 62, 76 and 82%, respectively. The same response was observed in velvetleaf which had 80% injury when flamed with 87 kg ha −1 at 0 HAS and 93% injury when flamed at 12 HAS with the same propane dose at 7 DAT. Similar trends occurred for maize and soybean suggesting that leaf RWC could be one of the factors affecting plant response to flaming. Practical implication is that flaming operation should be conducted in the afternoon in order to improve efficacy of weed control and reduce propane consumption rate.

Coke Formation on Pt–Sn/Al2O3 Catalyst in Propane Dehydrogenation: Coke Characterization and Kinetic Study

The influences of gas compositions on the rates of coke formation over a Pt–Sn/Al2O3 catalyst are studied. The coke formed on the catalyst is characterized by thermal gravimetric analysis, IR spectroscopy, Raman spectroscopy and elemental analysis. Two kinds of coke are identified from the TPO profiles and assigned to the coke on the metal and the coke on the support, respectively. The coke formed on the metal is softer (containing more hydrogen) than that formed on the support. The rate of coke formation on the metal is weakly dependent on the propylene and hydrogen pressures but increasing with the propane pressure, while the rate of coke formation on the support is increasing with the propane and propylene pressures and decreasing with the hydrogen pressure. Based on the kinetic analysis, a mechanism for the coke formation on the Pt–Sn/Al2O3 catalyst is proposed, and the dimerization of adsorbed C3H6 is identified to be the kinetic relevant step for coke formation on the metal.

Preparation of polypropylene/clay nanocomposites by in situ polymerization with TiCl4/MgCl2/clay compound catalyst

TiCl4/MgCl2/clay compound catalyst was prepared by chemical reaction. Exfoliated polypropylene (PP)/clay nanocomposites were synthesized by in situ polymerization with this compound catalyst. Effects of polymerization temperature, polymerization time, propylene pressure, solvent consumption and pre-treat time of catalyst on catalyst activity and catalytic stereospecificity were studied. Under optimal conditions, activity of the nano-compound catalyst is about 88.3 kg/(mol Ti·h). Isotacticity of PP obtained in the nanocomposites is in the range of 89%–99%, and its melting temperature is about 159°C. The weight-average molecular weight of PP can reach 6.7 × 105 − 7.8 × 105, and the molecular weight distribution is between 7.7 and 7.9.

FTIR Matrix-Isolation Study of the Reaction Products of Vanadium Atoms with Propene: Observation of Allylvanadium Hydride As a Precursor to Sacrificial Hydrogenation of Propene

Vanadium atoms have been reacted with different partial pressures of propene in Ar under matrix-isolation conditions, and the products have been observed using Fourier transform infrared (FTIR) spectroscopy. Under dilute propene in Ar conditions, new features are observed in the IR spectra corresponding to a C-H insertion product, identified here as H-V-(η(3)-allyl). Use of d(3)-propene (CD(3)-CH═CH(2)) demonstrates that the initial V-atom insertion occurs at the methyl group of the propene molecule, and DFT calculations have been used to support the identity of the initial product. Upon increasing the partial pressure of propene, additional features corresponding to propane (C(3)H(8)) are observed, with the hydrogen-atom source for the observed hydrogenation demonstrated to be additional propene units. Analysis of a systematic increase in the partial pressure of propene in the system demonstrates that the yield of propane correlates with the decrease of the allyl product, demonstrating the H-V(allyl) species as a reactive intermediate in the overall hydrogenation process. An overall mechanism is proposed to rationalize the formation of the insertion product and ultimately the products of hydrogenation, which agrees with previous gas-phase and matrix-isolation work involving propene and the related system, ethene.

Gas-Phase Hydroformylation of Propene over Silica-Supported PPh3-Modified Rhodium Catalysts

Heterogeneous rhodium catalysts supported on SiO2 were modified with PPh3 for the gas-phase hydroformylation of propene to produce n- and isobutanal. High selectivity to aldehydes was achieved, with no propane or alcohols formed. Investigation of the effects of reaction temperature, reactant partial pressures, total pressure, and PPh3/Rh ratio suggested that the supported catalyst behaved similarly to the homogeneous catalyst. In particular, the supported catalyst showed similar activation energies and partial and total pressure dependences of the reaction rates to those observed in homogeneous, liquid-phase reactions. The first order dependence of the hydroformylation rate on the partial pressures of propene, CO, and H2 individually led to a cubic dependence of butanal formation on total pressure for equimolar reactant mixtures. High regioselectivity with a typical n/i ratio of 14 was achieved.

Kinetics of propane dehydrogenation over Pt–Sn/Al 2O 3 catalyst

Langmuir–Hinshelwood kinetic models for catalytic propane dehydrogenation on Pt -Sn/Al 2O 3 are proposed based on the reaction mechanisms that take into account the one step or two-step dehydrogenation and are evaluated by fitting the experiments. When taking into consideration the fitting accuracy, the number of fitting parameters and the rigorousness of the reaction mechanism, the kinetics of propane dehydrogenation based on the assumptions of step-wise dehydrogenation, the first step dehydrogenation as the rate-determining step, and low surface coverage of C 3H 7 outperforms other kinetic models. The change of catalyst activity with time-on-stream is related to the rate of coke formation that depends on the partial pressures of propene and hydrogen. Finally a complete kinetic model, which includes propane dehydrogenation and cracking and catalyst deactivation because of coking, is developed, which is found to agree well with the changes of propane conversions with time-on-stream under different operating conditions. Direct measurement of coke formation is avoided by the approach employed in this study for the prediction of catalyst deactivation by coke deposition.

Synthesis of 2-Ethylhexanal from Propylene in a Single Pot Using an Ecofriendly Multifunctional Catalyst Synthesized by Intercalation of HRhCO(TPPTS)3 Complex in the Interlayer Space of Hydrotalcite

Catalytic activity of HRhCO(TPPTS)3 intercalated hydrotalcite (Mg/Al molar ratio =3.5) as a multifunctional catalyst [HT(3.5)-INT] was studied for synthesis of C8 aldehydes (2-ethylhex-2-enal and 2-ethylhexanal) from propylene in a single pot. The effect of catalyst amount, partial pressure of propylene, and aldol temperature (T2) on the selectivity of 2-ethylhexanal and 2-ethylhex-2-enal was studied in detail to optimize the reaction parameters. The highest selectivity for C8 aldehydes (49%) was obtained at 1200 mg of catalyst and 10 atm partial pressure of propylene. Reusability experiments revealed that the HRhCO(TPPTS)3 intercalated hydrotalcite shows activity even after fourth cycle for hydroformylation reaction; however, selectivity of C8 aldehydes decreased after the second cycle. Rates of the product formation were determined individually for hydroformylation of propylene, aldol condensation of n-butanal, and hydrogenation of 2-ethylhex-2-enal catalyzed by [HT(3.5)-INT] using propylene, n-butanal, and 2-ethylhex-2-enal as reactants. Reaction conditions were maintained identical to those used for the single-pot synthesis of C8 aldehydes from propylene. The calculated rates of reaction for the single-pot synthesis of C8 aldehydes were compared with the rates of reaction determined individually.

架橋型モノシクロペンタジエニルアミドジメチルチタン錯体を用いたプロピレン重合におけるシクロペンタジエニル配位子の効果

Propylene polymerization was conducted with ansa-monocyclopentadienylamidodimethyltitanium complexes ([(η1-t-BuN)SiMe2(Cp)]TiMe2, Cp = C5Me4, 1; C9H6, 2) in heptane as solvent at 0°C in the presence of dried modified methylaluminoxane (dMMAO), from which free Me3Al and iBu3Al were reduced to ca. 0.1 mol%. The effects of cyclopentadienyl ligands on propylene polymerization were investigated under atmospheric pressure of propylene in a semi-batch system where the polymerization rate was followed by the amount of propylene consumed. System 2 showed almost the same consumption rate as that of system 1 in the initial stage, but the rate gradually decreased with increasing polymerization time. In contrast, the rate of system 1 gradually increased during the polymerization. The produced polymer in system 1 had high molecular weight (Mn = 143,600) and relatively narrow molecular weight distribution (Mw/Mn = 1.31). Furthermore, the number-average molecular weight of the polymer linearly increased in proportion to the polymer yield with keeping the number of polymer chains constant. Thus, it was found that quasi-living polymerization of propylene proceeded in the 1-dMMAO/heptane system. The 13C NMR measurement of polypropylenes obtained indicated that systems 1 and 2 produced syndiotactic-enriched and isotactic-enriched polymers, respectively.

ChemInform Abstract: The Kinetics of Propylene Metathesis Catalyzed by a Molybdenum (100) Single Crystal

Abstract It is shown, using a high-pressure reactor incorporated into an ultrahigh-vacuum chamber, that an initially clean molybdenum (100) single crystal can catalyze propylene metathesis. The reaction is found to be first-order in propylene pressure which proceeds with a high activation energy (∼65 kcal/mol). Auger spectroscopy reveals the presence of a thick (∼10 monolayers) carbonaceous layer on the surface of the catalyst following reaction. It is further demonstrated, using restart reactions, that metathesis proceeds in presence of this layer. However, the reaction prefactor is ∼ 8 × 1012 site−1 s−1 so that the reaction appears not to be drastically inhibited by the presence of the carbonaceous layer, rather, the high reaction activation energy is primarily responsible for the low rate. Methylcyclopropane and hydrogenolysis products are also formed in the reaction, an observation that is consistent with the reaction proceeding at the surface via the carbene mechanism.

Particle growth and fragmentation of solid self-supported Ziegler–Natta-type catalysts in propylene polymerization

Particle growth and fragmentation of solid Ziegler–Natta-type catalysts prepared via emulsion technique were studied in propylene polymerization. Before polymerizations the catalyst particles were activated with triethyl aluminum (TEA) and cyclohexyl methyl dimethoxy silane (CMMS). Polymerizations were carried out in gas-phase in a micro-reactor system that allows the particle growth to be observed with a microscope. Several polymerizations were done under a propylene pressure of 2 bar and with polymerization times from 20 s to 2 h. Fragmentation morphology of the catalyst particles and cross-sections of the particles after polymerization were studied by scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS). Fragmentation morphology of the catalysts prepared via emulsion technique was compared with the fragmentation morphology of a conventional MgCl 2-supported Ziegler–Natta-type catalyst, which could be described by the multigrain model. Polymer growth appeared to occur throughout the emulsion-based catalyst particle right from the start of the polymerization, even though the surface area and porosity of the catalyst were low. The surface of the catalyst particles broke up at the beginning of the polymerization, and catalyst fragments appeared on the surface as plates between which the polymer was growing.

Phase Behaviour and Physical Property Measurements for VAPEX Solvents: Part II. Propane, Carbon Dioxide and Athabasca Bitumen

Abstract The solubility of pure carbon dioxide in Athabasca bitumen was measured and compared with the literature data. Multiple liquid phases were observed at carbon dioxide contents above approximately 12 wt%. A correlation based on Henry's law was found to fit the saturation pressures at carbon dioxide contents below 12 wt%. The saturation pressure and solubility of carbon dioxide and propane in Athabasca bitumen, as well as the liquid phase densities and viscosities, were measured for three ternary mixtures at temperatures from 10 to 25 °C. Two liquid phases (carbon dioxide-rich and bitumen-rich) were observed at 13 wt% carbon dioxide and 19 wt% propane. Only liquid and vapour-liquid regions were observed for the other two mixtures (13.5 wt% propane and 11.0 wt% carbon dioxide; 24.0 wt% propane and 6.2 wt% carbon dioxide). The saturation pressures for the latter mixtures were predicted using the correlation for the carbon dioxide partial pressure and a previously developed correlation for the propane partial pressure. The mixture viscosities were predicted with the Lobe mixing rule. Introduction In Part I of this work(1), mixtures of carbon dioxide and propane were identified as a potential solvent for the VAPEX process. At typical heavy oil reservoir conditions (pressure of ~1.2 MPa and temperature of ~10 °C), propane and butane have sufficient solubility to reduce the oil viscosity to a level where gravity drainage can occur in an economic time scale. However, propane and butane are expensive solvents and the success of the process depends on how much solvent can be recovered. As well, the VAPEX process operates below the saturation pressure of the solvent and, therefore, propane and butane cannot be used at higher reservoir pressures where they exist only in the liquid phase. Methane can be added to achieve the desired pressures(2). However, carbon dioxide may also be a better VAPEX solvent than methane because it is more soluble in heavy oil and significantly reduces the viscosity(3). Mixtures of carbon dioxide and propane may achieve the desired reduction in viscosity while minimizing the required propane volumes. Hence, there is an incentive to evaluate mixtures of carbon dioxide and propane as a VAPEX solvent. VAPEX performance depends on the viscosity and density of the liquid phase that forms at the edge of the vapour chamber. In order to design and optimize VAPEX and other solvent-based processes, it is critical to be able to determine the diffusivity of the solvent in the heavy oil, identify the phases that form in the solvent and heavy oil mixtures at various temperatures and pressures, and determine the density and viscosity of the liquid phase. Other solvent-based processes (steam and solvent injection for heavy oil recovery and solvent extraction of oil sands) require similar data. In Part I of this work(1), saturation pressures and liquid phase densities and viscosities were measured for propane and Athabasca bitumen. There are also considerable data in the literature for mixtures of carbon dioxide and crude oils. Simon and Graue(4) measured the solubility, swelling and viscosity of mixtures of carbon dioxide and nine different oils.

Influence of ceria and nickel addition to alumina-supported Rh catalyst for propane steam reforming at low temperatures

Kinetic studies reveal that loading ceria and Ni onto alumina-supported Rh dramatically increases the propane reforming rates; adding CeO 2 promotes steam and propane adsorption and activation, while adding Ni mainly enhances C 3 H 8 adsorption and activation. The influence of ceria and nickel addition to alumina-supported Rh catalyst for steam reforming of propane at low temperatures has been studied by preparing and examining 2 wt%Rh/Al 2 O 3 , 2 wt%Rh/20 wt%CeO 2 –Al 2 O 3 , and 2 wt%Rh–5 wt%Ni/20 wt%CeO 2 –Al 2 O 3 . TPR characterization showed that adding ceria makes rhodium oxide easier to reduce and the presence of rhodium also makes ceria easier to reduce through Rh–Ce interaction, whereas the addition of Ni makes Rh 2 O 3 and ceria more difficult to reduce, likely due to Rh–Ni and Ce–Ni interactions. Adding ceria and nickel significantly improved the catalytic activity of Rh catalyst for propane conversion at 475 °C. Kinetic study at different temperatures (450–650 °C) indicated that the addition of ceria and Ni can greatly increase the propane reforming rates by lowering the activation energies from 67.6–68.8 kJ/mol for 2Rh/Al to 50.1–50.4 kJ/mol for 2Rh/20CeAl and to 42.1–42.5 kJ/mol for 2Rh5Ni/20CeAl. The feed steam/carbon molar ratios corresponding to maximum reaction rates at 475 °C increased from 2.0 for 2Rh/Al to 3.0 for 2Rh/20CeAl and 4.5 for 2Rh5Ni/20CeAl catalyst. A kinetic equation based on Langmuir–Hinshelwood model best fitting the experimental data was applied for the propane steam reforming over the Rh-based catalysts. Kinetic results at different partial pressures of propane and steam revealed that the addition of ceria could enhance the steam and propane adsorption, while the addition of Ni could significantly promote the propane adsorption, probably through working with Rh as propane adsorption sites.

Phase Behaviour and Physical Property Measurements for VAPEX Solvents: Part I. Propane and Athabasca Bitumen

Abstract The saturation pressure and solubility of propane in Athabasca bitumen, as well as the liquid phase densities and viscosities, were measured for temperatures from 10 to 50 °C. Equilibration proved challenging for this fluid mixture and required some experimental modifications that are discussed. Only liquid and liquid-vapour phase regions were observed at propane contents below 20 wt%. A second liquid phase appeared to have formed at higher propane contents. The saturation pressures, where only a single dense phase formed, ranged from 600 to 1,600 kPa and these were fitted with a modification to Raoult's law. Viscosities less than 210 mPa.s were obtained at a propane content of 15.6 wt%. All of the viscosity data of the liquid phase were predicted from the propane and bitumen viscosities using the Lobe mixing rule. Introduction The worldwide original oil-in-place (OOIP) of heavy oil and bitumen is estimated to be approximately 6 trillion barrels. A major part of these resources are in Canada (~36%) and Venezuela (~27%)(1). In Canada, steam-based methods are often employed to improve heavy oil recovery. However, the industry is starting to seek alternatives to these methods because they are energy intensive and are drawing heavily on the available water supply. Solvent-based recovery methods are a potential alternative capable of providing high recovery factors without substantial water requirements(2, 3). One option is the vapour extraction method (VAPEX), which is a solvent-based analogue of the Steam-Assisted Gravity Drainage (SAGD) process(4–7). VAPEX is implemented with a pair of horizontal wells: a production well at the bottom of the reservoir and a solvent injection well located directly above the production well(5), as shown in Figure 1. The vapourized solvent is injected through the injection well and a chamber of solvent vapour forms around the well. At the walls of the chamber, the solvent diffuses into a surface layer of the heavy oil and dramatically reduces its viscosity. The diluted oil layer is then mobile enough to drain down, under the influence of gravity, into the production well. VAPEX performance depends on the viscosity and density of the liquid phase that forms at the edge of the solvent chamber. In order to design and optimize VAPEX and other solvent-based processes, it is critical to be able to determine the diffusivity of the solvent in the heavy oil, identify the phases that form in the solvent and heavy oil mixtures at various temperatures and pressures, and determine the density and viscosity of the liquid phase. Other solvent-based processes (steam and solvent injection for heavy oil recovery and solvent extraction of oil sands) require similar data. Most research on VAPEX has focused on physical model experiments with light alkane solvents; particularly mixtures of methane and propane(3). However, mixtures of carbon dioxide and propane may be a more viable option. Currently, carbon dioxide is expensive, but costs are expected to decrease if environmental incentives to sequester carbon dioxide are introduced. Carbon dioxide may also be a better VAPEX solvent than methane because it is more soluble in heavy oil and reduces the viscosity more(8).

Propene−Norbornene Copolymers byC2-Symmetric Metallocenerac-Et(Ind)2ZrCl2: Influence of Reaction Conditions on Reactivity and Copolymer Properties

The copolymerization of propene and norbornene by catalytic systems composed by C2 symmetric rac-Et(Ind)2ZrCl2 (1), methylaluminoxane, and triisobutylaluminum was investigated. Propene−norbornene (P−N) copolymers with about 50 mol % of norbornene are highly alternating at low temperature and pressure. The influence of propene pressure (1−8 bar) and temperature (30−70 °C) on activity, norbornene content, molar masses, and glass transition temperatures of (P−N) copolymers has been assessed. A deeper analysis of the complex 13C NMR spectra of these copolymers has allowed us to evaluate the diad composition, as well as the propene placement in the chain. A great number of 1,3-propene insertions were found, all occurring after an inserted norbornene unit, especially at high temperature and pressure. This indicates that the limiting step in P−N copolymerization is the difficulty to insert a P after N. For the first time, copolymerization parameters were estimated. It was found that P−N copolymers are alternating at temperature as low as 30−40 °C and tend to become random as temperature increases. Chain terminations are likely to occur when the last inserted unit is propene. This along with an increase in kP would explain the decrease of norbornene content, molar mass, and glass transition temperature, observed at high T and P.

Kinetic and Active Centre Studies on the Polymerization of Propylene using MgCl2 Supported Ziegler – Natta Catalysts and 1,3 Diether Donors

AbstractAll polymerization experiments were carried out in a Büchi glass reactor capable of operating at propylene pressures of 1‐7 atmospheres. Two types of MgCl2 supported catalysts with controlled morphology were studied, viz., catalyst systems containing either a 1,3 diether (Catalysts A and D), 9,9‐bis (methoxymethyl) fluorene, or a simple diester (Catalysts B, C and E) such as diisobutylphthalate, used as reference systems. The kinetic behaviours of these catalysts were investigated for propylene polymerization. The 1,3‐diether based systems proved to be excellent catalyst systems for propylene polymerization showing high polymerization activities and stable rate‐time profiles and produced spherical polymer particles. Catalyst pre‐treatment was found to play an important role in controlling the morphology of the final polymer. A tritiated alcohol radio‐quenching technique was used to determine the concentrations active centres: values of 7.5 and 5.1 mol/mol % respectively were obtained for catalysts A and D and 3.5, 2.9 and 2.2 mol/mol % respectively were obtained for catalysts B, C and E. Catalysts A and D showed very high polymerization activities and also higher C0* values. All polymers produced were characterized by SEM, DSC, extraction and molecular weight determinations.