A disentangled state using TiCl<Subscript>4</Subscript>/MgCl<Subscript>2</Subscript> catalyst: a case study of polyethylene

Fully entangled morphology which is usually expected for polyethylene produced using Ziegler–Natta (ZN) catalyst is due to the presence of active sites crowded on catalyst’s support surface as well as within its volume. In this research, the feasibility of producing disentangled, more precisely less entangled, polyethylene using a heterogeneous ZN catalyst supported on magnesium chloride, TiCl₄/MgCl₂, is introduced. Polymerization was carried out at rather low temperature and pressure, and the nascent polymer was characterized to investigate its entanglement state. The rheological measurements, at small amplitude oscillating in the time sweep mode, exhibited a rather good modulus build-up, demonstrating the nascent polymer in its dis(less)-entangled state. Tape and film samples were prepared from the synthesized polyethylene below its melting point to keep the morphology untapped. The solid-state drawability test was performed on the samples at 100 °C showing its improved drawability. Thus, it could be concluded that the polyethylene synthesized at rather low temperature of 0 °C and longer polymerization time was in disentangled state. Furthermore, a rheometrical analysis in frequency mode was used to estimate the molecular weight and molecular weight distribution of the synthesized polyethylene qualitatively. From X-ray diffraction patterns the existence of a small amount of hexagonal phase in the nascent polymer could be detected, which may be due to the formation of extended chains during polymerization.     

Nanofibrous ultrahigh molecular weight polyethylene synthesized using TiCl<Subscript>4</Subscript> as catalyst supported on MCM-41 and SBA-15

Nanofibrous ultrahigh molecular weight polyethylene (UHMWPE) was synthesized via Ziegler–Natta catalyst anchoring on MCM-41 and SBA-15 as supported catalysts, respectively. These supported catalysts exhibited high activity at different temperatures and Al/Ti ratios, and showed different polymerization kinetics behaviors which were well explained by their different pore structures. The ultrahigh molecular weight of polyethylene might be due to the restrained spaces of the supported catalysts mesopores prohibiting the polymer chains transfer reaction. The obtained nanofibrous morphology might be for the high enough stress generated in the mesopores extruding the polymer out to form.     

Ni-Co bimetallic catalyst for CH<Subscript>4</Subscript> reforming with CO<Subscript>2</Subscript>

A co-precipitation method was employed to prepare Ni/Al₂O₃-ZrO₂, Co/Al₂ O₃-ZrO₂ and Ni-Co/Al₂O₃-ZrO₂ catalysts. Their properties were characterized by N₂ adsorption (BET), thermogravimetric analysis (TGA), temperature-programmed reduction (TPR), temperature-programmed desorption (CO₂-TPD), and temperature-programmed surface reaction (CH₄-TPSR and CO₂-TPSR). Ni-Co/Al₂O₃-ZrO₂ bimetallic catalyst has good performance in the reduction of active components Ni, Co and CO₂ adsorption. Compared with mono-metallic catalyst, bimetallic catalyst could provide more active sites and CO₂ adsorption sites (C + CO₂ = 2CO) for the methane-reforming reaction, and a more appropriate force formed between active components and composite support (SMSI) for the catalytic reaction. According to the CH₄-CO₂-TPSR, there were 80.9% and 81.5% higher CH₄ and CO₂ conversion over Ni-Co/Al₂O₃-ZrO₂ catalyst, and its better resistance to carbon deposition, less than 0.5% of coke after 4 h reaction, was found by TGA. The high activity and excellent anti-coking of the Ni-Co/Al₂O₃-ZrO₂ catalyst were closely related to the synergy between Ni and Co active metal, the strong metal-support interaction and the use of composite support.     

Preparation and properties of thermoplastic polyurethane/ultra high molecular weight polyethylene blends

The blends of thermoplastic polyurethane and ultra high molecular weight polyethylene (UHMWPE) were prepared by a co‐twin screw extruder. Phase separation morphology of the blends was confirmed by the SEM observations. The incorporation of UHMWPE is detrimental to the mechanical properties of the blends prepared from stiffer TPU, whereas is beneficial to that of TPU with low hardness. The tribological behaviors of neat TPU and its blends were studied by the means of a block‐on‐ring apparatus. It was found that UHMWPE could greatly improve the tribological properties of TPU matrix both under dry sliding and water lubricating conditions due to the excellent self‐lubricating property of the UHMWPE materials and furthermore improve the wear failure limit of TPU. POLYM. COMPOS., 36:897–906, 2015. © 2014 Society of Plastics Engineers     

Preparation of CuO-CeO<Subscript>2</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst with mesopore structure for water gas shift reaction

The water gas shift (WGS) reaction has been investigated widely in fuel cell technologies due to the potential for high fuel efficiency and lower emissions during the production of pure hydrogen. Industrially, the WGS reaction occurs in one of the following two ways: (a) high-temperature in the range of 310–450°C with Fe-Cr catalyst, (b) low-temperature in the range of 210–250°C with Cu-ZnO-Al₂O₃. In this study, a mesoporous catalyst was prepared, with a large surface area and uniformity in both pore size and distribution, by using a one-pot synthesis method. The prepared CuO-CeO₂-Al₂O₃ brought high CO conversion (82%), and was suitable for WGS reaction at low temperature (250 °C). This article is dedicated to Professor Chang Kyun Choi for celebrating his retirement from the School of Chemical and Biological Engineering, Seoul National University.     

Preparation and characteristics of nano-B4C/PVA particles and ultra high molecular weight polyethylene composites

In-situ mechanical process for preparation of the polyvinyl alcohol (PVA) coated nano-B₄C powder was investigated by using a high-energy ball mill. The produced PVA coat on the surface of nano-B₄C particles was observed by x-ray diffraction (XRD) and confirmed by TEM images. The average particle size of the produced nano-B₄C/PVA particles was in the range of several tens to hundreds of nanometers depending on the milling conditions. The polymer composites were fabricated by hot pressing ultra high molecular weight polyethylene (UHMWPE) powder mixed with nano-B₄C/PAV and micro-B₄C powders, respectively. Nano-B₄C/PVA dispersed UHMWPE shows slightly lower crystallinity and stiffness than micro-B₄C dispersed UHMWPE based on differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) evaluations.     

Preparation of sulfide ceramic materials based on BaSm<Subscript>2</Subscript>S<Subscript>4</Subscript>and CaGd<Subscript>2</Subscript>S<Subscript>4</Subscript> with the use of sol-gel and cryochemical technologies

Solid solutions in the MeLn₂S₄?x (mol %) MeS (Ln₂S₃) (Me = Ca, Ba; Ln = Sm, Gd) systems are prepared. The regions of solid solution formation are determined, the unit cell parameters of the crystal lattice are calculated, the total conductivity is investigated, and the activation energies for electrical conduction are calculated for samples with different prehistories. The electrolytic properties of phases based on calcium and barium thiolanthanates are studied, and the mechanism of defect formation is proposed.     

Highly ordered mesoporous CoFe<Subscript>2</Subscript>O<Subscript>4</Subscript> and CuFe<Subscript>2</Subscript>O<Subscript>4</Subscript> with crystalline walls

The highly ordered mesoporous CoFe₂O₄ and CuFe₂O₄ with crystalline walls can be synthesized by hard template with using mesoporous silica SBA-15 as hard template and using ferric nitrate, cobalt nitrate, and copper nitrate as metal precursors. These new mesoporous materials above have high surface areas, narrow pore size distribution, and large pore volumes, which are believed to be valuable for the potential application in the field of sensors, catalysis, message recording, magnetics, and biology. This work provides a method to fabricate the highly ordered mesoporous materials composed of multi-metal oxides with crystalline walls. The development of such versatile approach is of great significance in practical application. It can be envisaged that this established method is significantly expandable to the controlled synthesis of the mesoporous functional materials with diverse compositions.     

The catalytic effect of both oxygen-bearing functional group and ash in carbonaceous catalyst on CH<Subscript>4</Subscript>-CO<Subscript>2</Subscript> reforming

A kind of new catalyst—carbonaceous catalyst—for CH₄-CO₂ reformation has been developed in our laboratory. The effect of both oxygen-bearing functional group such as phenolic hydroxyl, carbonyl, carboxyl, and lactonic, and ash such as Fe₂O₃, Na₂CO₃, and K₂CO₃ in the carbonaceous catalyst on the CH₄-CO₂ reforming has been investigated with a fixed-bed reactor. It has been found that the carbonaceous catalyst is an efficient catalyst on CO₂-CH₄ reforming. With the decrease of oxygen-bearing functional group, the catalytic activity of carbonaceous catalyst decreases quickly. The oxygen-bearing functional groups play a significant role in the carbonaceous-catalyzed CO₂-CH₄ reforming; the ash components in carbonaceous catalyst also have an important influence on the CO₂-CH₄ reforming. Fe₂O₃, Na₂CO₃, and K₂CO₃ in the ash can catalyze the CO₂-CH₄ reforming reaction; CaO has little effect on CO₂-CH₄ reforming reaction. CaO can catalyze the gasification between carbonaceous catalyst and CO₂; Al₂O₃ and MgO inhibit the CO₂-CH₄ reforming.     

Syndiospecific Polymerization of Styrene Using Half-Titanocene Catalyst Covalently Supported on MgCl<Subscript>2</Subscript>/AlEt<Subscript>n</Subscript>(OEt)<Subscript>3-n</Subscript>

The novel half-titanocene catalyst bearing reactive functional amino group, η⁵-pentamethylcyclopentadienyltri(p-amino-phenoxyl) titanium [Cp^∗Ti(p-OC₆H₄NH₂)₃], was easily synthesized by the reaction of η⁵-pentamethylcyclopentadienyltrichloride titanium (Cp^∗TiCl₃) with p-amino phenol in the presence of triethyl amine (NEt₃). Cp^∗Ti(p-OC₆H₄NH₂)₃ covalently anchored on MgCl₂/AlEt_n(OEt)_3-n support obtained from the reaction of triethylaluminium (AlEt₃) with the adduct of magnesium chloride (MgCl₂) and ethanol (EtOH), has been investigated and used to catalyze syndiospecific polymerization of styrene. Influences of the support structure, cocatalyst, and the molar ratio of Al in methylaluminoxane (MAO) and Ti (Al_MAO/Ti) on catalytic activity, syndiotacticity and molecular weight of the resultant polystyrene were investigated. Compared with the corresponding Cp^∗Ti(p-OC₆H₄NH₂)₃ homogeneous catalyst, a considerable increase in activity and molecular weight of syndiotactic polystyrene (sPS) was observed for the Cp^∗Ti(p-OC₆H₄NH₂)₃-MgCl₂/AlEt_n(OEt)_3-n supported catalyst even at a relatively low Al_MAO/Ti ratio of 50, and the kinetics of polymerization was stable during the reaction process.     

Photoelectrocatalytic activity of bi-layer TiO<Subscript>2</Subscript>/WO<Subscript>3</Subscript> coatings for the degradation of 4-chlorophenol: effect of morphology and catalyst loading

WO₃ and bi-layer WO₃/TiO₂ coatings of different catalyst loadings were electrosynthesized on stainless steel 304 (SS) substrates from acidic aqueous solutions by single-step and consecutive steps potentiostatic cathodic deposition. The resulting WO₃/SS and TiO₂/WO₃/SS photoelectrodes were screened for their photoresponse under ultraviolet (UV) and visible light illumination by photovoltammetry and photoamperometry in sulphate solutions, in the absence and presence of 4-chlorophenol (4-CP). They were also evaluated for bulk photo-oxidation of 4-CP under constant potential, in the voltage range determined on the basis of the photovoltammetric tests. The optimal weight ratio between TiO₂ and WO₃ was also established, ensuring the best performance of these photoelectrodes for the photooxidation of 4-CP under UV and visible light irradiation.     

Performance of Ni catalyst supported on La-hexaaluminate in CO<Subscript>2</Subscript> reforming of CH<Subscript>4</Subscript>

CO₂ reforming of CH₄ was performed using Ni catalyst supported on La-hexaaluminate which has been an well-known material for high-temperature combustion. La-hexaaluminate was synthesized by sol-gel method at various conditions where different amount of Ni (5–20 wt%) was loaded. Ni/La-hexaaluminate experienced 72 h reaction and its catalytic activity was compared with that of Ni/Al₂O₃, Ni/La-hexaaluminate shows higher reforming activity and resistance to coke deposition compared to the Ni/Al₂O₃ model catalyst. Coke deposition increases proportionally to Ni content. Consequently, Ni(5)/La-hexaaluminate(700) is the most efficient catalyst among various Ni/La-hexaaluminate catalysts regarding the cost of Ni in Ni(X)/La-hexaaluminate catalysts. BET surface area, XRD, EA, TGA and TPO were performed for surface characterization. This work was presented at the 6 ^th Korea-China Workshop on Clean Energy Technology held at Busan, Korea, July 4–7, 2006.     

Preparation and thermal transformations of nanocrystals in the LaPO<Subscript>4</Subscript>-LuPO<Subscript>4</Subscript>-H<Subscript>2</Subscript>O system

Powders of nanosized particles of individual and mixed lanthanum and lutetium orthophosphates are synthesized. The grain growth process is studied in the temperature range of 200–1100°C. Temperature and concentration regions of existence of the solid solutions based on hexagonal and monoclinic forms of LaPO₄ as well as on tetragonal LuPO₄ are determined.     

Controllable synthesis of EU-1 molecular sieve with high SiO<Subscript>2</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> ratios in thermodynamic stable sol system

A new green chemical route was designed in this paper for the synthesis of high-silica EU-1 molecular sieve in TEAOH–SiO₂–Al₂O₃–HMBr₂–H₂O system in which tetraethylammonium hydroxide (TEAOH) substituted for sodium hydroxide (NaOH) as an alkali source. The physicochemical properties of the synthesized samples characterized by such means as X-ray powder diffraction (XRD), electrophoresis apparatus, precise pH meter, scanning electron microscope, Fourier infrared spectrometer (FT-IR), thermo gravimetric analyzer (TG) and temperature programmed desorption (NH₃-TPD). The research results showed that the SiO₂/Al₂O₃ ratio of EU-1 molecular sieve could reach 706 with TEAOH as an alkali source. The SiO₂/Al₂O₃ ratio of the product was improved greatly to 1046 with the template agent increasing. The new synthetic route has also significantly expanded the synthetic phase region. The absolute value of zeta potential of the TEAOH sol system was obviously higher than that of the NaOH sol system, indicating the thermodynamic stability of the former sol system was higher and better for the synthesis of pure high-silica EU-1 molecular sieve. The FT-IR spectra and TG/DTG diagrams of products indicated that TEA⁺ occluded in the final products could balance electronegative framework. The amount of strong, weak and the total acidity reduced with the increase of SiO₂/Al₂O₃ ratio. The catalytic results of methanol-to-hydrocarbon demonstrated that the molecular sieve prepared by the new method has better catalytic performance.     

Low-Temperature Preparation of Superparamagnetic CoFe<Subscript>2</Subscript>O<Subscript>4</Subscript> Microspheres with High Saturation Magnetization

Based on a low-temperature route, monodispersed CoFe₂O₄ microspheres (MSs) were fabricated through aggregation of primary nanoparticles. The microstructural and magnetic characteristics of the as-prepared MSs were characterized by X-ray diffraction/photoelectron spectroscopy, scanning/transmitting electron microscopy, and vibrating sample magnetometer. The results indicate that the diameters of CoFe₂O₄ MSs with narrow size distribution can be tuned from over 200 to ~330 nm. Magnetic measurements reveal these MSs exhibit superparamagnetic behavior at room temperature with high saturation magnetization. Furthermore, the mechanism of formation of the monodispersed CoFe₂O₄ MSs was discussed on the basis of time-dependent experiments, in which hydrophilic PVP plays a crucial role.     

Preparation and application of zeolite beta with super-low SiO<Subscript>2</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> ratio

This paper presents the direct synthesis of super-low SiO₂/Al₂O₃ ratio zeolite beta molecular sieve through a novel route, by which some of aluminium species are added during crystaling process. The IR results show that with the increase of aluminium content in the framework, the frequency of the band in the range of framework vibration (1060–1090 cm⁻¹) shifts to the lower wave-number; the BET surface-area decreases and the basicity of zeolite becomes stronger. In a second step, new adsorbents were obtained by solid-state ion exchanging zeolite beta with Cu(I), Ag(I) cations. The deep-desulfurization (sulfur levels of <1 ppmw) tests were performed using fixed-bed adsorption technique, the sulfur content of the treated and untreated gasoline was analyzed by microcoulometry. The experimental results show that the desulfurization performance of sorbents decreases in order: Cu(I)beta > Ag(I)beta > Na-beta. The best sorbent, Cu(I)beta, has breakthrough adsorption capacities of 0.236 mmolS/g of sorbent for model gasoline.     

PLS-based kinetics modeling and optimization of the oxidative coupling of methane over Na<Subscript>2</Subscript>WO<Subscript>4</Subscript>/Mn/SiO<Subscript>2</Subscript> catalyst

Reactor modeling for the oxidative coupling of methane over Na₂WO₄/Mn/SiO₂ catalyst was addressed in the present study. The catalyst loading part was designed to be thicker than the inlet and outlet parts to reduce the rates of side reactions in the gas phase, and the optimal aspect ratio (L to D ratio) for no pressure drop and minimum side reactions was determined in experimental studies. Experiments were also conducted under a variety of operating conditions such as gas hourly space velocity (GHSV), CH₄/O₂ ratio and reaction temperature, and partial least-squares model was applied to predict the performance of the reactor. The validity of the developed model was corroborated by the comparison with experimental data, and normalized parametric sensitivity analysis was carried out. Finally, the genetic algorithm (GA) was applied to determine the optimal conditions for maximum production of ethane and ethylene.     

Preparation of H<Subscript>5</Subscript>PMo<Subscript>10</Subscript>V<Subscript>2</Subscript>O<Subscript>40</Subscript> catalyst immobilized on spherical carbon and its application to the vapor-phase 2-propanol conversion reaction

Spherical carbon (SC) with a diameter of ca. 9 μm was synthesized by a hydrothermal method using sucrose as a carbon precursor. The spherical carbon was then modified to have a positive charge, and thus, to provide a site for the immobilization of H₅PMo₁₀V₂O₄₀ (PMo₁₀V₂) catalyst. The PMo₁₀V₂ catalyst was immobilized on the surface-modified spherical carbon by taking advantage of the overall negative charge of [PMo₁₀V₂O₄₀]⁵⁻. The PMo₁₀V₂ catalyst immobilized on the spherical carbon (PMo₁₀V₂/SC) was applied to the vapor-phase 2-propanol conversion reaction. In the catalytic reaction, the PMo₁₀V₂/SC catalyst showed a higher 2-propanol conversion than the unsupported PMo₁₀V₂ catalyst. Furthermore, the PMo₁₀V₂/SC catalyst showed enhanced oxidation catalytic activity (formation of acetone) and the suppressed acid catalytic activity (formation of propylene and isopropyl ether) compared to the unsupported PMo₁₀V₂ catalyst. The enhanced oxidation activity of PMo₁₀V₂/SC catalyst was due to the fine dispersion of [PMo₁₀V₂O₄₀]⁵⁻ on the spherical carbon formed via chemical immobilization.     

Separation characteristics of tetrapropylammoniumbromide templating silica/alumina composite membrane in CO<Subscript>2</Subscript>/N<Subscript>2</Subscript>, CO<Subscript>2</Subscript>/H<Subscript>2</Subscript> and CH<Subscript>4</Subscript>/H<Subscript>2</Subscript> systems

Nanoporous silica membrane without any pinholes and cracks was synthesized by organic templating method. The tetrapropylammoniumbromide (TPABr)-templating silica sols were coated on tubular alumina composite support ( γ-Al₂O₃/ α-Al₂O₃ composite) by dip coating and then heat-treated at 550 °C. By using the prepared TPABr templating silica/alumina composite membrane, adsorption and membrane transport experiments were performed on the CO₂/N₂, CO₂/H₂ and CH₄/H₂ systems. Adsorption and permeation by using single gas and binary mixtures were measured in order to examine the transport mechanism in the membrane. In the single gas systems, adsorption characteristics on the α-Al₂O₃ support and nanoporous unsupport (TPABr templating SiO₂/ γ-Al₂O₃ composite layer without α-Al₂O₃ support) were investigated at 20–40 °C conditions and 0.0–1.0 atm pressure range. The experimental adsorption equilibrium was well fitted with Langmuir or/and Langmuir-Freundlich isotherm models. The α-Al₂O₃ support had a little adsorption capacity compared to the unsupport which had relatively larger adsorption capacity for CO₂ and CH₄. While the adsorption rates in the unsupport showed in the order of H₂> CO₂> N₂> CH₄ at low pressure range, the permeate flux in the membrane was in the order of H₂≫N₂> CH₄> CO₂. Separation properties of the unsupport could be confirmed by the separation experiments of adsorbable/non-adsorbable mixed gases, such as CO₂/H₂ and CH₄/H₂ systems. Although light and non-adsorbable molecules, such as H₂, showed the highest permeation in the single gas permeate experiments, heavier and strongly adsorbable molecules, such as CO₂ and CH₄, showed a higher separation factor (CO₂/H₂=5-7, CH₄/H₂=4-9). These results might be caused by the surface diffusion or/and blocking effects of adsorbed molecules in the unsupport. And these results could be explained by surface diffusion. This paper is dedicated to Professor Hyun-Ku Rhee on the occasion of his retirement from Seoul National University.