Olefins In Gas Phase Research Articles

Active Site Descriptors from 95Mo NMR Signatures of Silica-Supported Mo-Based Olefin Metathesis Catalysts.

The olefin metathesis activity of silica-supported molybdenum oxides depends strongly on metal loading and preparation conditions, indicating that the nature and/or amounts of the active sites vary across compositionally similar catalysts. This is illustrated by comparing Mo-based (pre)catalysts prepared by impregnation (2.5-15.6 wt % Mo) and a model material (2.3 wt % Mo) synthesized via surface organometallic chemistry (SOMC). Analyses of FTIR, UV-vis, and Mo K-edge X-ray absorption spectra show that these (pre)catalysts are composed predominantly of similar isolated Mo dioxo sites. However, they exhibit different reaction properties in both liquid and gas-phase olefin metathesis with the SOMC-derived catalyst outperforming a classical catalyst of a similar Mo loading by ×1.5-2.0. Notably, solid-state 95Mo NMR analyses leveraging state-of-the-art high-field (28.2 T) measurement conditions resolve four distinct surface Mo dioxo sites with distributions that depend on the (pre)catalyst preparation methods. The intensity of a specific deshielded 95Mo NMR signal, which is most prominent in the SOMC-derived catalyst, is linked to reducibility and catalytic activity. First-principles calculations show that 95Mo NMR parameters directly manifest the local strain and coordination environment: acute (SiO-Mo(O)2-OSi) angles and low coordination numbers at Mo lead to highly deshielded 95Mo chemical shifts and small quadrupolar coupling constants, respectively. Natural chemical shift analyses relate the 95Mo NMR signature of strained species to low LUMO energies, which is consistent with their high reducibility and corresponding reactivity. The 95Mo chemical shifts of supported Mo dioxo sites are thus linked to their specific electronic structures, providing a powerful descriptor for their propensity toward reduction and formation of active sites.

Multiscale modelling of multizone gas phase propylene (co)polymerization reactors—A comprehensive review

AbstractCatalysts and polymerization processes have evolved over the years. Such significant developments have allowed producers to broaden the range of polymer microstructure and process productivity, thereby making it possible to offer a wide range of end‐use properties at a reasonably low cost. However, these advantages in catalyst performance and reactor operation require that we understand as much as possible about reactor operation in the broadest sense. In addition to the fundamental experimental study of polymer chemistry, this means that one needs to develop complete, robust process models. The present paper provides a rapid overview of recent developments in various gas phase propylene (co)polymerization reactors in use today, concentrating on multizone gas phase polypropylene reactors: that is, multizone circulating reactor, fluidized bed reactor with internal circulation, fluidized bed reactor with external circulation, and horizontal stirred bed reactor. We then concentrate on the advances in multiscale modelling of gas phase propylene (co)polymerization reactors, from microscale kinetics at the active sites, to the mesoscale, including physical transport and thermodynamic modelling at the single‐particle level and its boundary layer, up to the macroscale reactor modelling. A systematic guideline used for the selection of appropriate thermodynamic models is proposed for gas phase olefin polymerization processes. Finally, current challenges and remaining issues related with the development of mathematical multiscale modelling are addressed.

Applied Thermodynamics for Process Modeling in Catalytic Gas Phase Olefin Polymerization Reactors

AbstractThe Sanchez–Lacombe Equation of State (SL EoS) is used to model the solubility of different industrial alkane penetrants in polyethylene to explain the importance of considering different diluents for different processes, and the impact that this choice can have on operating conditions, especially for the production of linear low density polyethylene (LLDPE). Extension of this approach to ternary (ethylene/penetrant/LLDPE) systems shows the effect of composition of penetrant/ethylene mixtures on the solubility of such mixtures in LLDPE and swelling of the polymer phase at conditions of industrial relevance. This analysis reveals that using a constant polymer density instead of that predicted by the SL EoS can result in erroneous calculations of the particle size distribution developments in an olefin polymerization reactor.

Advances in Mathematical Modeling of Gas-Phase Olefin Polymerization

Mathematical modeling of olefin polymerization processes has advanced significantly, driven by factors such as the need for higher-quality end products and more environmentally-friendly processes. The modeling studies have had a wide scope, from reactant and catalyst characterization and polymer synthesis to model validation with plant data. This article reviews mathematical models developed for olefin polymerization processes. Coordination and free-radical mechanisms occurring in different types of reactors, such as fluidized bed reactor (FBR), horizontal-stirred-bed reactor (HSBR), vertical-stirred-bed reactor (VSBR), and tubular reactor are reviewed. A guideline for the development of mathematical models of gas-phase olefin polymerization processes is presented.

Effect of Li-LSX-zeolite on the in-situ catalytic deoxygenation and denitrogenation of Isochrysis sp. microalgae pyrolysis vapours

In this work, we report for the first time the use of Li-LSX-zeolite as catalyst for the catalytic pyrolysis of biomass (Isochrysis sp. Microalgae). Li-LSX-zeolite showed a good catalytic performance, principally for bio-oil denitrogenation (mainly in form of NH3), and good activity for olefins and aromatics production. At 500 °C, 11.8% aromatics and 23.1% aliphatics were produced. The increase of temperature led to transfer of C to the gas phase, coke formation on the catalyst surface and decrease in N-compounds in the bio-oil. The increase of the catalyst to biomass ratio from 0 to 3:1 resulted in the aromatics being five-fold those non-catalytically obtained and in a higher cracking power that reduced the bio-oil to 23% at expenses of olefins rich gas. However, a linear correlation between coke formation and aromatic yield was observed as the catalyst to microalgae ratio was increased. Therefore, the experimental results indicate that Li-LSX-zeolite could be used as catalyst for in-situ denitrogenation of microalgae bio-oil and for enhancing aliphatics and aromatics formation to be blend in gasoline and diesel and olefins in gas phase.

Enhancing Thermal Stability and Living Fashion in α-Diimine–Nickel-Catalyzed (Co)polymerization of Ethylene and Polar Monomer by Increasing the Steric Bulk of Ligand Backbone

Development of thermally stable nickel-based catalysts is highly desirable for industrial gas-phase olefin polymerizations. On the basis of the strategy of promoting the thermostability of nickel catalyst by the ligand backbone, we herein reported novel dibenzobarrelene-derived α-diimine nickel precatalysts for ethylene polymerization. Increasing the steric bulk on the ligand backbone was expected to inhibit the N-aryl rotation of the α-diimine ligands by the repulsive interactions, thus enhancing thermal stability (100 °C) and living fashion a temperatures up to 80 °C. Bulk ligand backbone also improved tolerance of nickel catalyst toward polar groups, and the α-diimine nickel catalyst containing a 2,6-tBu-dibenzobarrelene backbone catalyzed living copolymerization of ethylene and methyl 10-undecenoate.

Experimental and simulation study of heat transfer in fluidized beds with heat production

As a result of highly exothermic reactions during gas-phase olefin polymerization in fluidized bed reactors, difficulties with respect to the heat management play an important role in the optimization of these reactors. To obtain a better understanding of the particle temperature distribution in fluidized beds, a high speed infrared (IR) camera and a visual camera have been coupled to capture the hydrodynamic and thermal behavior of a pseudo-2D fluidized bed. The experimental data were subsequently used to validate an in-house developed computational fluid dynamics and discrete element model (CFD-DEM). In order to mimic the heat effect due to the exothermic polymerization reaction, a model system was used. In this model system, heat is released in zeolite 13X particles (1.8–2.0mm, Geldart D type) due to the adsorption of CO2. All key aspects of the adsorption process (kinetics, equilibrium and heat effect) were studied separately using Thermogravimetric Analysis (TGA) and Simultaneous Thermal Analysis (STA), and subsequently fluidized bed experiments were conducted, by feeding gas mixtures of CO2 and N2 with different CO2 concentrations to the bed, where the total heat of liberation could be controlled. The combined infrared/visual camera technique generated detailed information on the thermal behavior of the bed. Furthermore, the comparison of the spatial and temporal distributions of the particle temperature measured in the fluidized bed with the simulation results of CFD-DEM provides qualitative and quantitative validation of the CFD-DEM, in particular concerning the thermal aspects.

CFD Analysis of Gas-Particle Heat Transfer in Gas-Phase Olefin Polymerizations

CFD Analysis of Gas-Particle Heat Transfer in Gas-Phase Olefin Polymerizations

CFD Analysis of Gas-Particle Heat Transfer in Gas-Phase Olefin Polymerizations

CFD Analysis of Gas-Particle Heat Transfer in Gas-Phase Olefin Polymerizations

Hydrodynamics and particle mixing/segregation measurements in an industrial gas phase olefin polymerization reactor using image processing technique and CFD-PBM model

Particle size distribution (PSD) has a significant impact on the performance of fluidized bed reactors due to uneven distribution in the segregation and mixing phenomena. This paper develops a new method of digital image processing that investigates the hydrodynamics of an industrial gas phase olefin polymerization reactor and studies the fluidization structure of a wide range of particle size distribution in an industrial gas phase polymerization reactor by means of a CFD-PBM coupled model, where the direct quadrature method of moments (DQMOM) was implemented to solve the population balance model. It was shown that the applied parameter assumptions and closure laws were appropriately chosen to satisfactorily predict the available operational data in terms of pressure drop and bed height. The transient CFD-PBM/DQMOM coupled model and image analysis technique are then implemented extensively to analyze bubble fluidization structure and segregation phenomena at different velocities. The particle segregation indicates that the small bubbles present in the bed are unable to induce vigorous mixing at low superficial gas velocity while particle mixing improves at a velocity above the minimum fluidization velocity. Further, the predicted results show higher axial segregation phenomena when compared to the radial direction.

ChemInform Abstract: Supported Single‐Site Organometallic Catalysts for the Synthesis of High‐Performance Polyolefins

AbstractReview: 127 refs.

Supported Single-Site Organometallic Catalysts for the Synthesis of High-Performance Polyolefins

Single-site organometallic catalysts supported on solid inorganic or organic substrates are making an important contribution to heterogeneous catalysis. Early and late transition metal single-site catalysts have changed the polyolefin manufacturing industry and research with their ability to produce polymers with unique properties. Moreover, several of these catalysts have been commercialized on a large scale. Their heterogenization for slurry or gas phase olefin polymerization is important to produce polyolefin as beads and to avoid reactor fouling. The large majority of supports currently used in industry are inorganic materials (SiO2, Al2O3, MgCl2), with silica being the most important. Single-site supported catalysts are most commonly prepared by molecular-level anchoring/chemisorption, in which a molecular precursor undergoes reaction with the surface while maintaining most of the ligand sphere of the parent molecule. Chemisorption of discrete organometallic complexes on solid supports yields catalysts with well-defined active sites, greater thermal stability than the homogeneous analogues, and decreased reactor fouling versus the homogeneous analogues. This review presents a detailed account of the synthesis, characterization and polymerization properties of single-site catalysts supported on metal oxides and metal sulfated oxides, primarily carried out at Northwestern University. Early and late transition metal single-site catalysts supported on inorganic surfaces have changed the polyolefin research and production with their unique ability to produce polymeric materials with unique architectures. This review presents a detailed account of the synthesis, characterization, and polymerization properties of single-site catalysts supported on metal oxide surfaces.

A 2‐D observer to estimate the reaction rate in a stopped flow fixed bed reactor for gas phase olefin polymerization

A two‐dimensional high gain observer has been constructed to estimate the reaction rate parameters in a laboratory scale stopped flow fixed bed reactor for gas phase ethylene polymerization. The observer is based on the heat balances of a validated model of the reactor and the measured variable is the outlet temperature of the fixed bed. To create an observable system of equations, the polymerization rate is considered in two parts, an activation energy term and a lumped parameter. The effective radial conductivity in the fixed bed and the heat‐transfer coefficient at the wall are considered separately. The polymerization rate is calculated from the observer results and is in good agreement with the measured data and calculated values. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3511–3523, 2014

OH Radical-Initiated Chemistry of Isoprene in Aqueous Media. Atmospheric Implications

The fate of isoprene (2-methyl-1,3-butadiene, ISO) emissions into the atmosphere is not fully understood. Increasing awareness that ISO is only partially processed in the gas-phase has turned attention to its reactive uptake by fog, cloud, and aerosol droplets. A hydrophobic gas, ISO would preferentially partition to the surface rather than the bulk of aqueous media. Such media normally contain dissolved O2 and water-soluble unsaturated organics and support •OH generation rates (from the solar photolysis of dissolved H2O2) that are several orders of magnitude larger than in the gas-phase. Thus, ISO should be converted therein to heavier products rather than into the C4-C5 volatile compounds produced in the gas-phase. Here we substantiate such a scenario by reporting that the λ > 305 nm photolysis of H2O2 in dilute aqueous ISO solutions yields C10H15OH species as primary products, whose formation both requires and is inhibited by O2. A minimum of seven C10H15OH isomers are resolved by reverse-phase high-performance liquid chromatography and detected as MH(+) (m/z = 153) and MH(+)-18 (m/z = 135) signals by electrospray ionization mass spectrometry. Our findings are consistent with the addition of •OH to ISO, followed by HO-ISO• reactions with ISO in competition with O2, leading to second generation HO(ISO)2• radicals that terminate as C10H15OH via β-H abstraction by O2. We show that a significant fraction of gas-phase olefins should be converted into less volatile species via this process on wet airborne particles.

How hydrogen‐bonded MnO4‐can influence oxidation of olefins in both gas phase and solution?

The reaction pathway (including the transition state) of ethylene addition to permanganate (MnO4‐) in the presence of ethylene glycol (EG) has been qualitatively and quantitatively studied by means of B3LYP/6‐311++G** theoretical analysis. Interestingly, by cluster formation of the EG with permanganate, oxidation reaction becomes thermodynamically and kinetically more favorable. The influences of electron‐withdrawing as well as electron‐donating substituents were also explored.Results of the quantum theory of atoms in molecules and natural bond orbital analyses revealed that [3 + 2] addition reaction of alkenes in the presence of EG as hydrogen bonding donor to MnO4‐becomes more exothermic. Natural resonance theory (NRT) is used to calculate natural bond order and bond polarity. The NRT result indicates that the polarity of Mn–O bond is affected by EG coordinated to MnO4‐. Moreover, the conceptual DFT descriptors such as chemical potential (μ), hardness (η) and electrophilicity index (ω) show that hydrogen bonding to permanganate can affect the addition of MnO4‐to double bond in a satisfactory way. We also carried out geometrical optimizations with the polarizable continuum model to account for the solvent effect, and the results were compared with those in the gas phase. Copyright © 2012 John Wiley & Sons, Ltd.

Decentralized Advanced Model Predictive Controller of Fluidized-Bed for Polymerization Process

The control of fluidized-bed operations processes is still one of the major areas of research due to the complexity of the process and the inherent nonlinearity and varying dynamics involved in its operation. There are varieties of problems in chemical engineering that can be formulated as NonLinear Programming (NLPs). The quality of the developed solution significantly affects the performance of such system. Controller design involves tuning the process controllers and implementing them to achieve certain performance of controlled variables by using Sequential Quadratic Programming (SQP) method to tackle the constrained high NLPs problem for modified mathematical model for gas phase olefin polymerization in fluidized-bed catalytic reactor. The objective of this work is to present a comparative study; PID control is compared to an advanced neural network based MPC decentralized controller and also, see the effect of SQP on the performance of controlled variables. The two control approached were evaluated for set point tracking and load rejection properties giving acceptable results.

Dynamic modelling of a stopped flow fixed bed reactor for gas phase olefin polymerisation

A heterogeneous 2D dynamic model of a stopped flow fixed bed reactor for gas phase ethylene polymerisation has been constructed and validated. The reactor contains two solid phases with accumulation of mass within the reactor bed and the experiments modelled are of very short duration (0.1–75s). There is a good fit between measured data and calculated values, and the model results allow us to interpret the experimentally observed temperature rises. Higher than expected catalyst temperatures are found towards the reactor centre and exit which are due to the initial intensity of the polymerisation reaction.

Packed‐bed reactor for short time gas phase olefin polymerization: Heat transfer study and reactor optimization

AbstractA specially conceived packed‐bed stopped flow minireactor (3 mL) suitable for short gas phase catalytic reactions has been used to study the start‐up of ethylene homopolymerization with a supported metallocene catalyst. Focus has been put on the heat transfer characteristics of the supported catalysts and on understanding the relationship between the initial rate and the relative gas/particle velocities and the influence of particle parameters in the packed bed. We performed a comprehensive study on the influence of various physical parameters on the heat transfer regime at start up conditions. The catalyst activity as well as the polymer morphology is shown to be dependent on heat transfer regime. The knowledge thus obtained is applicable to industrial problems like catalyst injection in fluidized beds and helps preventing experimental artifacts due to overheating in following studies. © 2011 American Institute of Chemical Engineers AIChE J, 2012

An experimental study on the early stages of gas‐phase olefin polymerizations using supported Ziegler–Natta and metallocene catalysts

AbstractThe initial stages of gas‐phase polymerizations of propylene and ethylene are analyzed using a fixed bed stopped flow reactor. The very early development of particle morphology and polymer properties is analyzed for three different commercial catalyst systems: MgCl2‐ and SiO2‐supported Ziegler–Natta and SiO2‐supported metallocene. It is shown that, depending on the operating conditions, distinct nonuniform catalyst fragmentation patterns can develop, confirming different scenarios described by published fragmentation models. In addition, it is shown that the molecular weight distributions and polymer yields obtained during the very early stages of the polymerization suggest the existence of significant temperature gradients inside the growing polymer particles. Finally, it is shown that the ratio of catalyst to glass beads in the bed can have a pronounced effect on the evolution of the polymerization reaction. This can be interpreted in terms of the significant temperature difference between the polymer particles and the gaseous monomer stream. POLYM. ENG. SCI., 2011. © 2010 Society of Plastics Engineers

CFD simulation of hydrodynamics and heat transfer in gas phase ethylene polymerization reactors

The hydrodynamics and temperature of a two-dimensional gas–solid fluidized bed of gas phase olefin polymerization reactor had been studied. A two-fluid Eularian Computational Fluid Dynamics (CFD) model with closure relationships according to the kinetic theory of granular flow has been applied in order to simulate the gas–solid flow. Fluidization regime and gas–solid flow pattern were investigated using three different drag models. Model predictions of bed pressure drop were compared with corresponding experimental data reported in the literature to validate the model. The predicted values were in reasonable agreement with the experimental data. The temperature behavior of fluidized bed with various drag models was investigated. The temperature gradient in the primary section of the bed was much larger than the gradient in other sections and the effect of all drag models on temperature gradient along the bed was approximately similar.