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A novel induction heating apparatus is designed to mimic the exothermic process in an olefin polymerization gas-solid fluidized bed. Wax/graphite composites with core-shell structure are used as tracer particles to capture the agglomerates formed in the cold mode experiments. Pressure fluctuation sensors and image analysis methodology are used to characterize the detailed information on agglomerates such as mass, size, and compositions. Experimental results reveal that when the mass fraction of tracer particles is above 10%, agglomerates are formed in the fluidized bed. Compared with coarse particles, small particles lead to agglomeration much easier, and coalescence of small-small particles or small-coarse particles is the main mechanism by which agglomeration occurs. Analyzing the collision process of small particles and coarse particles, we conclude that collisions among small particles or collisions between small and coarse particles are more frequent and efficient than that of coarse particles. [ABSTRACT FROM AUTHOR]

Soluble poly[styrene- co-(acrylic acid)] (PSA) modified by magnesium compounds was used to support TiCl4. For ethylene polymerization, four catalysts were synthesized, namely PSA/TiCl4, PSA/MgCl2/TiCl4, PSA/( n-Bu)MgCl/TiCl4, and PSA/( n-Bu)2Mg/TiCl4. The catalysts were characterized by a set of complementary techniques including X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, scanning electron microscopy, and element analysis. Synthesis mechanisms of polymer-supported TiCl4 catalysts were proposed according to their chemical environments and physical structures. The binding energy of Ti 2p in PSA/TiCl4 was extremely low as TiCl4 attracted excessive electrons from COOH groups. Furthermore, the chain structure of PSA was destroyed because of intensive reactions taking place in PSA/TiCl4. With addition of ( n-Bu)MgCl or ( n-Bu)2Mg, COOH became COOMg- which then reacted with TiCl4 in synthesis of PSA/( n-Bu)MgCl/TiCl4 and PSA/( n-Bu)2Mg/TiCl4. Although MgCl2 coordinated with COOH first, TiCl4 would substitute MgCl2 to coordinate with COOH in PSA/MgCl2/TiCl4. Due to the different synthesis mechanisms, the four polymer-supported catalysts correspondingly showed various particle morphologies. Furthermore, the polymer-supported catalyst activity was enhanced by magnesium compounds in the following order: MgCl2 > ( n-Bu)MgCl > ( n-Bu)2Mg > no modifier. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012 [ABSTRACT FROM AUTHOR]

Reactor blends of ultrahigh-molecular-weight polyethylene (UHMWPE) and low-molecular-weight polyethylene (LMWPE) were synthesized by two-step polymerization using a hybrid catalyst. To prepare the hybrid catalyst, styrene acrylic copolymer (PSA) was first coated onto SiO/MgCl-supported TiCl; then, ( n-BuCp)ZrCl was immobilized onto the exterior PSA. UHMWPE was produced in the first polymerization stage with the presence of 1-hexene and modified methylaluminoxane (MMAO), and the LMWPE was prepared with the presence of hydrogen and triethylaluminium in the second polymerization stage. The activity of the hybrid catalyst was considerable (6.5 × 10 g PE (mol Zr) h), and was maintained for longer than 8 h during the two-step polymerization. The barrier property of PSA to the co-catalyst was verified using ethylene polymerization experiments. The appearance of a lag phase in the kinetic curve during the first-stage polymerization implied that the exterior catalyst (( n-BuCp)ZrCl) could be activated prior to the interior catalyst (M-1). Furthermore, the melting temperature, crystallinity, degree of branching, molecular weight and molecular-weight distribution of polyethylene obtained at various polymerization times showed that the M-1 catalyst began to be activated by MMAO after 40 min of the reaction. The activation of M-1 catalyst led to a decrease in the molecular weight of UHMWPE. Finally, the thermal behaviors of polyethylene blends were investigated using differential scanning calorimetry. Copyright © 2011 Society of Chemical Industry A hybrid catalyst was supported on an inorganic/organic support for use in the preparation of polymer blends with ultrahigh-molecular-weight polyethylene in the first reaction stage and low-molecular-weight polyethylene in the second reaction stage. Fragmentation of the styrene acrylic copolymer (PSA) support was studied. [ABSTRACT FROM AUTHOR]

Hybrid titanium catalysts supported on silicapolystyrenecoacrylic acid SiO2PSA coreshell carrier were prepared and studied. The resulting catalysts were characterized by Fourier transform infrared FTIR spectroscopy, laser scattering particle analyzer and scanning electronic microscope SEM. The hybrid catalyst TiCl3MgCl2THFSiO2·TiCl4MgCl2PSA showed coreshell structure and the thickness of the PSA layer in the two different hybrid catalysts was 2.0 μm and 5.0 μm, respectively. The activities of the hybrid catalysts were comparable to the conventional titaniumbased ZieglerNatta catalyst TiCl3MgCl2THFSiO2. The hybrid catalysts showed lower initial polymerization rate and longer polymerization life time compared with TiCl3MgCl2THFSiO2. The activities of the hybrid catalysts were enhanced firstly and then decreased with increasing PH2PC2H4. Higher molecular weight and broader molecular weight distribution MWD of polyethylene produced by the coreshell hybrid catalysts were obtained. Particularly, the hybrid catalyst with a PSA layer of 5.0 μm obtained the longest polymerization life time with the highest activity 2071 kg PE mol−1Ti h−1 and the resulting polyethylene had the broadest MWD polydispersity index 11.5 under our experimental conditions. The morphology of the polyethylene particles produced by the hybrid catalysts was spherical, but with irregular subparticles due to the influence of PSA layer. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [ABSTRACT FROM AUTHOR]

The article discusses a study on a novel non-invasive technique based on acoustic emission for the early detection of horizontal stirred bed reactors (HSBR) agglomeration. The study explained the types of experiments conducted for optimizing the attractor comparison experiments and tested the influences of agitator speed. This method is reportedly sensitive to small changes in the particle size distribution. The study suggested further experimental research before using the method in an industrial HSBR for detecting agglomeration.

Diffusion coefficients of four organic solvents: dichloromethane, trichloromethane, tetrachloromethane and n-hexane in polyethylene particles at infinite dilution were determined by use of inverse gas chromatography (IGC). The polymer particles were used as supplied by the producer to pack the chromatographic columns. This allowed a direct measurement of the interested properties in a particle with the same morphology obtained at the reactor outlet. The particle morphology was investigated and classical mathematical model for chromatographic process was adopted based upon the analysis of particle microstructure. It was found that the limitation step for mass transfer was in the polymer matrix rather than in macropores, and when interpreted in terms of diffusion coefficients for spherical particles, the measured diffusion coefficients compared favourably with predicted values from literature relationships and free volume theory. [ABSTRACT FROM AUTHOR]

The quantitative structure-property relationship (QSPR) of constrained geometry catalysts (CGCs) has been analyzed by combining density functional theory (DFT) and multivariate linear regression (MLR). QSPR models for determining the reaction energy barriers of ethylene and 1-octene and molecular descriptors were established and validated with a testing set. At the initiation stage, the quaternary QSPR models for ethylene and 1-octene feature R² values of 0.90 and 0.82, respectively, while the corresponding leave-one-out Q² values for ethylene and 1-octene are determined to be 0.82 and 0.69. Using the generated QSPR models, the electronic effect was proven to be more critical for determining the energy barriers of ethylene and 1-octene insertion processes. At the propagation stage, the quaternary QSPR models for ethylene and 1-octene feature R² values of 0.97 and 0.96, respectively, while the corresponding leave-one-out Q² values for ethylene and 1-octene are determined to be 0.93. Particularly, the impact of the steric effect on the energy barriers of ethylene and 1-octene insertion is more pronounced. Furthermore, the correlation between the corresponding energy barriers and experimental activities with three series of CGCs was discussed, which revealed that theoretical calculations are consistent with the experimental results. [ABSTRACT FROM AUTHOR]

• Agitation results in a constant bed voidage with periodically fluctuation. • Axial gas mixing can be described by the "open" vessel dispersion model. • Gas flow is divided into two regions by the inner diameter of the helical ribbon. • Flow regimes are classified with an empirical correlation of Re and Fr number. The gas–solid vertical single helical ribbon agitated reactor is widely used in the polypropylene industry. The gas flow and mass transfer determine the heat transfer capacity and product quality. In this work, the pressure drop was measured below and above minimum fluidization velocity (u mf). Then, the axial and radial dispersion coefficients (D L and D R) were estimated below u mf by measuring the step residence time distribution and the stationary radial tracer profiles, respectively. Pressure analysis show the agitation significantly reduces the bed pressure drop, changing the fixed bed below u mf and bubbling bed above u mf to an agitated bed with a periodic voidage. The D L was proportional to the gas velocity, with little influences of the stirring speed. The radial tracer profiles show the bed is divided by the inner diameter of the helical ribbon into the peripheral ascending region and the central descending region, without gas exchange between them. Furthermore. the tracer profiles in the descending region are classified into two types. For type I, the D R , calculated by the plug flow model with radial dispersion, is proportional to the gas velocity, with little effects of stirring speed. Type II shows uniform profiles due to the deflection of the gas flow toward the low pressure area at the inner diameter of helical ribbon. The causes of the two types are explained by the relative size of particle circulation and gas flux. These two flow regimes are quantitatively clarified with an empirical correlation of Re and Fr as flow regime transition boundary, namely dispersed plug flow and perfect mixing flow. With lower Re and higher Fr , it changes from dispersed plug flow to perfect mixing flow. [ABSTRACT FROM AUTHOR]

The conventional methods for recovering effluent gas in polyethylene processes include compression condensing, membrane separation, cryogenic separation systems and pressure swing adsorption. Since the effluent gas content varies with the process, there is no single recovery technic can meet all effluent gas content conditions. Therefore, a systematic strategy is needed to guide the selection of recovery technologies. This article introduces a method to select the best recovery system for certain compositions of effluent gas. After searching the feasible content region for the recovery systems according to the specified concentration of recycle stream and outlet streams, it shows PSA system has the largest feasible region while compression condensation system has the smallest one. In comparison of economic and exergetic performance, the cryogenic separation system shows its outstanding peculiarity to recover the effluent gas. The obtained result is effective in guiding the design of recovery system. [ABSTRACT FROM AUTHOR]

The performance of gas-solid fluidized bed reactors (FBRs) strongly depends on the behavior of gas bubbles. Mechanical agitation is widely used in industrial FBRs to enhance gas-solid mixing; however, its influence on bubble behaviors has been poorly studied, especially in experimental study. Pressure fluctuations in a 300 mm inner diameter plexiglas column fluidized bed of Geldart D particles with an arch agitator were measured under various gas velocities and agitation speeds. The bubble sizes were evaluated by incoherent analysis of pressure fluctuations. The effects of mechanical agitation on axial bubble growth, bubble sizes, regime transition velocity and fines elutriation were comprehensively investigated. Results show that mechanical agitation promotes bubble growth at 1.7 Umf but reduces the bubble sizes with increasing gas velocities. The axial maximum bubble size with increasing gas velocity occurs at 1.2 m/s without agitation and 1.0 m/s with agitation speeds of 14 and 21 rpm. Interestingly, mechanical agitation leads to a small increase in minimum fluidizing velocity and a slight decrease in critical turbulent velocity. Furthermore, the entrainment rate is reduced with mechanical agitation, due to the decreasing bed height and small fines ejection at the bed surface. The arch agitator helps to reduce the channel flow, enhance the gas-solid contact efficiency and improve the fluidization quality. [ABSTRACT FROM AUTHOR]