The effect of particle size distribution on the olefin polymer reactor dynamics

Mass and energy balances in a reactor have been derived to study the effect of particle size distribution (PSD) for each reaction mechanism on the reactor dynamics. It was observed that the PSD affects both bed height and particle volume. A feasible region for reactor operation has been calculated by using physical constraints. In a nonisothermal polymerization system, the reactor temperature does not change appreciably as catalyst injection rate increases. A unique steady state solution is found in a gas-phase continuous stirred-bed propylene polymerization reactor. The eigenvalues of the system of equations indicate that the steady state is unstable. A comparison with published data allows the observation that the actual reactor dynamics may be readily explained by using only the PSD derived from a simple reaction mechanism.     

Particle size distribution in olefin continuous stirred-bed polymerization reactors

The control of polymer particle size and PSD is of industrial importance. Very fine particles pack poorly, thereby limiting reactor capacity, and present a dust explosion hazard. In olefin polymerization, a particle size distribution (PSD) in the polymerization reactor has been derived using population balances. Three reasonable reaction mechanisms for Ziegler-Natta catalysts, i.e., a simple reaction model, an active site reduction model, and a two sites model, have been used to derive the average number of active sites. It was observed that the PSD depends not only on residence time, but also on the reaction mechanism. It was also found that multiple active sites change the PSD slightly. The PSD, however, does not depend on initial catalyst volume.     

Effect of active site distribution on liquid-phase olefin hydrogenation over polymer-supported palladium complex

Chloromethylated polystyrene beads with different distributions have been prepared and phosphinated. PdCl₂ was supported on the phosphinated supports to give polymer-supported Pd complex catalysts with different active site distributions. The effect of active site distribution on catalytic activity was investigated in the hydrogenation of olefins.     

Surface science studies of Ziegler-Natta olefin polymerization system: Correlations between polymerization kinetics, polymer structures, and active site structures on model catalysts

The surface composition and structure of model Ziegler-Natta catalysts, polymerizing α-olefins to produce polyolefins, have been studied using modern surface science techniques and compared with their polymerization behaviors. Two types of thin films — TiCl_x/MgCl₂ and TiCl_y/Au — were fabricated on an inert gold substrate, using chemical vapor deposition methods, to model the high-yield catalysts of MgCl₂-supported TiCl₄ and TiCl₃-based catalysts, respectively. The model catalysts could be activated by exposure to triethylaluminum (AlFt₃) vapor. Once activated, both catalysts were active for polymerization of ethylene and propylene in the absence of excess AlEt₃ during polymerization. The model catalysts had polymerization activities comparable to the high-surface-area industrial catalysts. Though both catalysts were terminated with chlorine at the surface, each catalyst assumed different surface structures. The TiCl_x/MgCl₂ film surface was composed of two structures: the (001) basal plane of these halide crystallites and a non-basal plane structure. The TiCl_y/Au film surface assumed only the non-basal plane structure. These structural differences resulted in different tacticity of the polypropylene produced with these catalysts. The TiCl_x/MgCl₂ catalyst produced both atactic and isotactic polypropylene, while the TiCl_y/Au catalyst without the MgCl₂ support produced exclusively isotactic polypropylene. The titanium oxidation state distribution did not have a critical role in determining the tacticity of the polypropylene.     

Nonlinear model order reduction and control of particle size distribution in a semibatch vinyl acetate/butyl acrylate emulsion copolymerization reactor

This paper addresses the control of the full particle size distribution (PSD) in a semibatch emulsion copolymerization reactor. The numerical approximation of a fundamental population balance model results in a high order system to accurately describe the distribution of particle size; therefore, model order reduction is required. Pseudo random input signals are input to the mechanistic model to generate a data set which covers the reachable region of the system, on the basis of which the transformation matrices are calculated by principal component analysis (PCA). A linear time varying model with reduced order obtained from the transformation matrices is augmented in the prediction equation of linear model predictive control. The performance of the controller is evaluated to drive the particle size distribution at the final time of the batch to the desired distribution in the presence of disturbances. This paper is dedicated to Professor Hyun-Ku Rhee on the occasion of his retirement from the Seoul National University.     

Particle size distribution of PM-10 and heavy metal emission with different temperature and HCl concentrations from incinerators

Emission characteristics of particulate matter and heavy metals from 12 small waste incinerators, whose capacity ranged from 25 to 200 kg/h of waste, were investigated to determine the factors affecting the particulate matter generation and growth mechanisms. The ratio of fine particles to coarse particles increased with the flue gas temperature. Particulate matter showed bimodal forms in particle size distributions. The finer particle mode in particle size distribution shifted toward the coarser particle mode with a decrease in flue gas temperature. Experimental results were in agreement with coagulation theory: It is thought that the coarser particles were mechanically generated and the finer particles were generated by gas-to-particle conversion mechanisms such as nucleation, condensation, and coagulation. Heavy metal enrichment in finer particulate matter was also observed and related to particle formation and growth from vaporized metals. Emission of all heavy metals except zinc was affected by hydrogen chloride concentrations, while some metal emissions such as manganese, chromium, and copper were not varied with flue gas temperature. This paper is dedicated to Professor Dong Sup Doh on the occasion of his retirement from Korea University.     

Ammoxidation of methylaromatics over vanadium phosphate catalysts II. Catalyst formation, active sites and reaction mechanism

The interactions of VOHPO₄· 0.5H₂O and (VO)₂P₂O₇ with the ammoxidation feed and the single components such as ammonia, oxygen, water and component mixtures were studied in detail using XRD and temperature-programmed reaction spectroscopy. The aim of this work was to improve the knowledge of the formation of the active phases or active sites of the catalysts from their precursors under the condition of the ammoxidation reaction. Similar catalytic properties of various applied VPO materials were discussed in terms of the presence of similar structure elements (domains of adjacent edge-sharing VO₆ octahedra-units and P-O-NH₄ groups).     

Particle size effect on the filtration drag of fly ash from a coal power plant

In order to investigate the filtration properties of fly ash from a conventional coal power plant, the filtration drag across the dust cake over an absolute fiberglass filter element was measured. A fluidized bed column was utilized to obtain a well characterized particle stream. The cake resistance coefficient was analyzed by the equation proposed by Endo et al. [1998] in order to observe the effect of particle size and polydispersity. The filtration drag was measured for three kinds of particle stream having the geometric mean particle size of 3.15, 6.07, and 7.83 μm and the geometric standard deviation less than 1.44 in the practical operation conditions for the field applications of face velocity of 0.03–0.06 m/s and area dust load up to 0.2 kg/m². A dust cake of smaller particle size showed larger pressure drop even though the porosity was higher and presented high compressibility according to the face velocity. The particle polydispersity was also a dominant factor affecting the compressibility of the dust cake.     

The effect of particle size distribution on the properties of blended cements incorporating GGBFS and natural pozzolan (NP)

This paper investigates the effect of particle size distribution on the properties of blended cements incorporating ground granulated blast-furnace slag (GGBFS) and natural pozzolan (NP). Pure Portland cement (PPC), NP and GGBFS were used to obtain blended cements that contain 10, 20, 30% additives. The cements were produced by intergrinding and separate grinding and then blending. Each group had two different Blaine fineness of 280 m²/g and 480 m²/g. According to the particle size distribution (PSD) curves, 46% of the coarser specimens and 69% of the finer specimens passed through the 20 μm sieve. It was observed that the separately ground specimens were relatively finer than the interground ones and had higher compressive strength and sulfate resistance. The separately ground coarser specimens had the lowest heat of hydration. The separately ground finer specimens, which had the highest compressive strength and sulfate resistance, had the highest percent passing for each sieve size. For these specimens 34, 69, 81 and 99% passed through 5, 20, 30 and 55 μm sieves, respectively. For the interground specimens, which had the same fineness, the respective values for the same sieves were 32, 68, 75 and 94%.     

氧化铝陶瓷热压铸压成型与颗粒尺寸分布关系的研究

研究了石蜡加入量及烧成收缩率与颗粒尺寸分布的关系 ,发现蜡浆含蜡量及烧成收缩率与理论计算的准积气孔率密切相关。     

Ethylene polymerization with homogeneous nickel-diimine catalysts: effects of catalyst structure and polymerization conditions on catalyst activity and polymer properties

Ethylene polymerization was carried out using three nickel α-diimine catalysts ((ArNC(An)-C(An)NAr)NiBr₂ (1), (ArNC(CH₃)-C(CH₃)NAr)NiBr₂ (2) and (ArNC(H)-C(H)NAr)NiBr₂ (3); where An=acenaphthene and Ar=2,6-(i-Pr)₂C₆H₃) activated with modified methylaluminoxane (MMAO) in a slurry semi-batch reactor. We investigated the effects of ethylene pressure, reaction temperature, and α-diimine backbone structure variation on the catalyst activity and polymer properties. Changes in the α-diimine backbone structure had remarkable effect on the polymer microstructure as well as the catalyst activity. Catalyst 2 produced polymer with the highest molecular weight, while Catalyst 3 produced polymer with the lowest molecular weight. In addition, Catalyst 2 produced polymer with the lowest melting point, while Catalyst 3 produced the highest melting level exhibiting a melting behavior typical of high-density polyethylene (HDPE). With all the three catalysts, polymer molecular weight tended to decrease with increasing polymerization temperature due to the increase in chain transfer rates. In general, there was no clear and consistent trend observed for the effects of ethylene pressure on the polymer molecular weight. However, in polyethylene produced with Catalyst 2, the molecular weight was independent of ethylene pressure suggesting that chain transfer to ethylene may be a dominant mechanism for this catalyst.     

Propylene polymerization over supported Ziegler–Natta catalysts: Effect of internal and external donors on distribution of active sites according to stereospecificity

Data on the content of fractions with different microtacticities for polypropylene (PP) samples produced over three catalysts [the “donor‐free” titanium–magnesium catalyst and catalysts with dibutyl phthalate and 1,3‐diether(fluorene) used as internal donors] upon polymerization in the absence/presence of an external donor (ED) have been obtained by preparative temperature rising elution fractionation method. The effect of internal and EDs on the distribution of PP fractions with different microtacticity is discussed. Data on molecular weight and thermophysical characteristics were obtained for individual fractions with different microtacticities. Correlations were found between microtacticity, molecular weight, and the melting points of these fractions. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46291.     

On the role of an unconventional rigid rodlike cationic surfactant on the styrene emulsion polymerization. Kinetics, particle size and particle size distribution

An unconventional amphiphile (1-[ω-(4′-methoxy-4-biphenylyloxy)octyl]pyridinium bromide, PC8) was used as surfactant in the emulsion polymerization of styrene. At low surfactant concentration (6, 12 or 36 mmol l⁻¹), curves of polymerization rate versus conversion obeyed the typical behavior characterized by intervals I, II and III. However, at high concentration (48 or 72 mmol l⁻¹) the interval II was not observed. The particle size distribution curves showed two families of polymer particles, indicating the participation of at least two mechanisms of particle formation, one being the simple micellar nucleation and the other probably the coagulative nucleation of precursor particles. The latter was considered to occur during the nucleation interval.     

Quantification and redox property of the oxygen-bridged Cu<Superscript>2+</Superscript> dimers as the active sites for the NO decomposition over Cu-ZSM-5 catalysts

For a range of Cu-ZSM-5 catalysts with different Cu-exchange levels on the two kinds of ZSM-5 with different Si/A1 ratios, temperature programmed reduction using CO (CO-TPR) followed by H₂ (H₂-TPR), and temperature programmed desorption of oxygen (O₂-TPD) were conducted using an online mass spectrometer to characterize and quantify the copper species on the catalysts in the calcined state. Copper species on the ZSM-5 were quantitatively characterized as Cu²⁺, (Cu-O-Cu)²⁺ and CuO after calcination in oxygen environment. The N₂ formation activities of the catalysts in the decomposition of NO were well correlated with the quantified catalytic amounts of the Cu²⁺ ions involved in the Cu-dimers, (Cu-O-Cu)²⁺. The mol fraction of the Cu ions present as the Cu-dimers increased at the sacrifice of the isolated Cu²⁺ with increasing Cu ion exchange level, suggesting that the species could be formed between the two Cu²⁺ in close proximity. Oxygen that could be thermally desorbed from the oxidized catalysts in the O₂-TPD was responsible for the reduction of the Cu-dimers. It was concluded that the decomposition of NO over Cu-ZSM-5 catalyst proceeded by the redox of (Cu-O-Cu)²⁺, as active centers. With the temperature programmed surface reaction using N₂O or NO over an oxidized catalyst sample as well as the O₂-TPD, it was possible to estimate the change of the oxidation state of the Cu ions engaged in the Cu-dimers.     

Characteristics of critical solid-liquid separation and its effect on the performance of an anaerobic sequencing batch reactor treating municipal sludge

Solid-liquid separation and its type greatly affected the stability and performance of an anaerobic sequencing batch reactor (ASBR) for municipal sludge digestion. Flotation thickening occurred in the mesophilic ASBR, while solid-liquid separation in the thermophilic ASBR followed gravity thickening. Hydraulic retention times (HRT) and cycle period as well as type of thickening were key parameters governing sludge thickenability and critical solids accumulation. Thickened sludge bed volume was a critical operating variable in the ASBR with gravity thickening, which had poor performance because of the loss of thickened solids, and sludge interface disruption or instability of sludge bed due to internal gas evolution. A cyclic mutual effect between thickened volume and gas production was serious in gravity thickening, whereas it was insignificant in flotation thickening.     

Plausible guard effect on the active sites of heterogeneous Ziegler–Natta catalyst by coordinating monomers and growing polymer chains in the initial stage of propene polymerization

Investigation of propene polymerization by a modified stopped‐flow technique using TiCl₄/ethylbenzoate(EB)/MgCl₂ Ziegler–Natta catalyst with or without pretreating the catalyst with triethylaluminium (TEA) within an ultra‐short period (ca 1 s) was conducted to gain new understanding of the nature of active sites related to TEA in the early stage of polymerization. When the catalyst was pretreated by a cocatalyst, deactivation behaviour was clearly observed, even within an extremely short pretreatment period. In contrast, without pretreatment, the deactivation of active sites can be neglected within the polymerization period indicating that the activated Ti species might be protected from deactivation by TEA when monomer is present in the system. A plausible guard effect on the active sites by coordinating monomer and growing polymer chains in the initial stage of polymerization is proposed to account for this phenomenon. Copyright © 2004 Society of Chemical Industry     

The effect of particle size distribution on the microstructure and properties of Al2O3 ceramics formed by stereolithography

Stereolithography (SL) shows advantages for preparing alumina-based ceramics with complex structures. The effects of the particle size distribution, which strongly influence the sintering properties in ceramic SL, have not been systematically explored until now. Herein, the influence of the particle size distribution on SL-manufactured alumina ceramics was investigated, including bending strength at room temperature, post-sintering shrinkage, porosity, and microstructural morphology. Seven particle size distributions of alumina ceramics were studied (in μm/μm: 30/5, 20/3, 10/2, 5/2, 5/0.8, 3/0.5, and 2/0.3); a coarse:fine particle ratio of 6:4 was maintained. At the same sintering temperature, the degree of sintering was greater for finer particle sizes. The particle size distribution had a larger influence on flexural strength, porosity and shrinkage than sintering temperature when the particle size distribution difference reached 10-fold but was weaker for 10 μm/2 μm, 5 μm/2 μm and 5 μm/0.8 μm. The sintering shrinkage characteristics of cuboid samples with different particle sizes were studied. The use of coarse particles influenced the accuracy of small-scale samples. When the particle size was comparable to the sample width, such as 30 μm/5 μm and 5 mm, the width shrinkage was consistent with the height shrinkage. When the particle size was much smaller than the sample width, such as 2 μm/0.3 μm and 5 mm, the width shrinkage was consistent with the length shrinkage. The results of this study provide meaningful guidance for future research on applications of SL and precise control of alumina ceramics through particle gradation.     

Transition metal oxides supported on active carbons as low temperature catalysts for the selective catalytic reduction (SCR) of NO with NH3

The selective catalytic reduction of nitric oxide with ammonia was studied using Fe₂O₃, Cr₂O₃ and CuO loaded active carbons as catalysts in the presence and absence of oxygen at reaction temperatures between 100 and 500°C. Active carbons pretreated with concentrated nitric acid showed a higher catalytic activity in SCR than catalysts which were oxidized in air. The ash content (from 0.2 to 7.1 wt.%) of different unloaded active carbons had no effect on the catalytic activity below 300°C in the absence of oxygen. However, in the presence of oxygen an increasing ash content resulted in an increase in activity. Transition-metal oxide loading led to an increase in SCR activity, especially in the absence of oxygen. An increasing transition-metal content from 1 to 10 wt.% improved the activity as well. The presence of oxygen in the reaction mixture enhanced the conversion of nitric oxide especially in the low-temperature range between 100 and 200°C. Activity and selectivity of the respective catalysts were influenced by the type of metal oxide: in the presence of oxygen, catalysts with 10 wt.% Fe were the most active and selective.     

The effect of copper valence on catalytic combustion of styrene over the copper based catalysts in the absence and presence of water vapor☆

Catalysts Cu Ox/γ-Al_2O_3-IH and Cu Ox/γ-Al_2O_3-IM were prepared, characterized, and tested for styrene combustion in the absence and presence of water vapor. The effect of copper valence of the catalysts on the catalytic activity for styrene combustion was discussed using the theory of hard soft acids and bases(HSAB).The results showed that the existence of water vapor in feed stream inhibited the catalytic activity for styrene combustion due to the competition adsorption of water molecule. HSAB theory confirmed that the local soft acidity of the catalyst Cu Ox/γ-Al_2O_3-IH was much stronger than that of the catalyst Cu Ox/γ-Al_2O_3-IM because of the higher content of soft acid Cu+on its surface, which increased the adsorption ability toward soft base of styrene and reduced the adsorption toward hard base of water vapor, and thus increased the catalytic activity for styrene combustion and weakened the negative influence of water vapor.     

The positive effect of hydrogen on the reaction of nitric oxide with carbon monoxide over platinum and rhodium catalysts

The effect of adding 330–4930 ppm hydrogen to a reaction mixture of NO and CO (2000 ppm each) over platinum and rhodium catalysts has been investigated at temperatures around 200–250°C. Hydrogen causes large increases in the conversion of NO and, surprisingly, also of CO. Oxygen atoms from the additional NO converted are eventually combined with CO to give CO₂ rather than react with hydrogen to form water. This reaction is described by CO + NO +3/2H₂ CO₂ + NH₃ and accounts for 50–100% of the CO₂ formed with Pt/Al₂O₃ and 20–50% with Rh/Al₂O₃. With the latter catalyst a substantial amount of NO converted produces nitrous oxide. Comparison with a known study of unsupported noble metals suggests that isocyanic acid (HNCO) might be an important intermediate in a reaction system with NO, CO and H₂ present.