Thermodynamic and kinetic studies of the MgCl2‐NH4Cl‐NH3‐H2O system for the production of high purity MgO from calcined low‐grade magnesite

To improve the overall sustainability of MgO‐based refractory production, a novel process to produce high purity MgO from calcined low‐grade magnesite in ammonium chloride solution was developed. The process was designed on the basis of the phase equilibria of the NH₄Cl‐MgCl₂‐NH₃‐H₂O system obtained using the Mixed Solvent Electrolyte model embedded in OLI software. The optimum calcination temperature of low‐grade magnesite was determined to be 650°C in terms of the conversion ratio of magnesium and calcium in the leaching experiments. An apparent activation energy of Mg extraction was 30.98 kJ/mol, which is slightly lower than that of Ca leaching. An empirical kinetic model of magnesium extraction was also developed to describe the effects of NH₄Cl concentration, particle size of calcined magnesite, and solid‐to‐liquid ratio on the extent of extraction of magnesium. At leaching time of 10 min, the leachate with high Mg/Ca molar ratio was obtained. Then, MgO with a purity of 99.09% was produced through the decomposition of intermediate 4MgCO₃·Mg(OH)₂·4H₂O. © 2015 American Institute of Chemical Engineers AIChE J, 61: 1933–1946, 2015     

Modeling solid–liquid equilibrium of NH4Cl‐MgCl2‐H2O system and its application to recovery of NH4Cl in MgO production

A new method to recover NH₄Cl from NH₄Cl‐rich aqueous solutions generated in the magnesia (MgO) production is developed on the basis of modeling the solid–liquid equilibrium (SLE) for the NH₄Cl‐MgCl₂‐H₂O system with the Pitzer model embedded in Aspen Plus? platform. The SLE values for the ternary system were determined from 278.15 to 348.15 K. The new standard‐state chemical potentials of NH₄Cl and MgCl₂·6H₂O were judicially obtained. The resulting equilibrium constants were used to determine new interaction parameters for the NH₄Cl‐H₂O and MgCl₂‐H₂O systems. These new parameters, together with the mixing parameters determined from correlating the experimental values, were used to correlate the equilibrium constant for NH₄MgCl₃·6H₂O, which plays a key role in NH₄Cl recovery. The results could extend SLE calculation for the NH₄Cl‐MgCl₂‐H₂O system from 278.15 to 388.15 K, satisfying the process identification and simulation requirement involved in the recovery process. The phase‐equilibrium diagram generated by modeling was illustrated to identify the process alternatives for recovering NH₄Cl. The resulting course to recover NH₄Cl by three fractional crystallization operations was finally proved feasible. © 2010 American Institute of Chemical Engineers AIChE J, 2011.     

High performance ZSM‐5 membranes on coarse macroporous α‐Al2O3 supports for dehydration of alcohols

High‐performance ZSM‐5 membranes with a low Si/Al ratio of 10.3 were prepared on cheap coarse macroporous α‐Al₂O₃ tubes by fluoride route without organic template. The effects of crystallization time and aluminum source on the growth, morphology and pervaporation (PV) performances of the as‐synthesized membranes were investigated. The feasibility of preparing ZSM‐5 membranes with different Si/Al ratio which was implemented by using different Al₂(SO₄)₃·18H₂O content in synthesis gel were discussed. It was found that the aluminum source had significant effect on the synthesis of membranes. The ZSM‐5 membranes prepared by using Al₂(SO₄)₃·18H₂O as an aluminum source from synthetic gel with composition of 1SiO₂/0.05Al₂O₃/0.17Na₂O/0.9NaF/45H₂O showed high reproducibility and high PV performance with flux of 3.85 kg/(m²·h) and separation factor of higher than 10,000 in dehydration of 90 wt % i‐PrOH/H₂O at 348 K. Moreover, the ZSM‐5 membranes exhibited high water perm‐selectivity performance for dehydration of 90 wt % n‐PrOH/H₂O, n‐BtOH/H₂O, and i‐BtOH/H₂O mixtures, respectively. © 2016 American Institute of Chemical Engineers AIChE J, 62: 2813–2824, 2016     

Atomic Scale Mechanisms of the Reduction of Nickel–Magnesium Aluminate Spinels

The dynamics of the reduction reaction of Ni_xMg_1?xAl₂O₄ to form nickel metal and a remnant oxide was quantified to understand spinel behavior in catalysis applications. X‐ray diffraction, thermogravimetry, and pycnometry were employed to track the evolution of high‐Ni spinels to metastable nonstiochiometric spinels during reduction, but before the phase transformation to theta alumina. Rietveld refinements of X‐ray diffraction data were used to quantify structural changes in the spinel and the phase fraction, crystallite size, and microstrain of all phases during H₂ reduction. During reduction, one O^2? is lost for each Ni²⁺ reduced to Ni metal. Ni_0.25Mg_0.75Al₂O₄ and Ni_0.5Mg_0.5Al₂O₄ were shown to form Ni metal and a non‐stoichiometric spinel of the same Mg‐Al ratio as the starting composition. NiAl₂O₄ and Ni_0.75Mg_0.25Al₂O₄ were found to become unstable as full reduction was approached, and metastable spinel, Θ‐Al₂O₃, and α‐Al₂O₃ formed sequentially given sufficient time at temperature.     

Effect of the Mg/Al Atomic Ratio of Ni‐Mg‐Al Catalysts for the Hydrodealkylation of 1,2,4‐Trimethylbenzene

The hydrodealkylation of 1,2,4‐trimethylbenzene (1,2,4‐TMB) to benzene, toluene and xylenes (BTX) was investigated on Ni‐Mg‐Al catalysts prepared by the coprecipitation method. The catalytic performances of these catalysts were considerably influenced by the Mg content of the catalyst. The catalysts were characterized via X‐ray diffraction, H₂‐temperature‐programmed reduction, NH₃‐temperature‐programmed desorption (TPD), CO₂‐TPD, and Fourier transform infrared spectroscopy. The results demonstrated that the appropriate amount of Mg species significantly affected the structural properties and caused the Ni nanoparticles to become highly dispersed. The higher activity of the catalysts might be ascribed to the homogenous distribution of the Ni nanoparticles, and the synergetic effects between Ni⁰, NiAl₂O₄ and MgAl₂O₄ were the key factor for obtaining the BTX.     

Kinetic analysis for crystal growth rate of NH4Cl in the NaCl‐MgCl2‐H2O system with a thermodynamic approach

A growth kinetic model has been developed from a rigorous thermodynamic perspective to describe the crystal growth rates of NH₄Cl on the basis of the difference of chemical potentials of NH₄Cl at solid–liquid interface in aqueous NH₄Cl, NH₄Cl‐NaCl, and NH₄Cl‐MgCl₂ solutions. The solid–liquid equilibrium and activity coefficient of NH₄Cl are calculated by the newly developed accurate Pitzer model with aid of Aspen Plus? platform. The predictions of the resulting model are in good agreement with the experimental data published in literature and determined in this work at 283.15–333.15 K within the supersaturation up to 0.1. The kinetic model was subsequently used to analyze the effect of several operation variables, including temperature (283.15–333.15 K), supersaturation (up to 0.1), and NaCl or MgCl₂ concentration (0～2.5 mol kg^?1), on the crystal growth rate of NH₄Cl. The crystal growth rate of NH₄Cl, with activation energy of 39 kJ mol^?1, is strongly temperature‐dependent and increases with increasing temperature in the three systems investigated. The advantage of MgCl₂ over NaCl on the recovery of NH₄Cl is theoretically and experimentally illustrated from the thermodynamic and kinetic perspectives with the aid of the established model. © 2011 American Institute of Chemical Engineers AIChE J, 2012     

Phase equilibrium of the ternary system of NH<Subscript>4</Subscript>Cl-CaCl<Subscript>2</Subscript>-H<Subscript>2</Subscript>O at 50°C

The equilibrium data on the ternary system of NH₄Cl—CaCl₂—H₂O at 50°C were investigated using the wet-residue method. The experimental results show that there are three pure phase crystal areas of NH₄Cl, 2NH₄Cl·CaCl₂·3H₂O and CaCl·2H₂O, two mixture phase crystal areas of NH₄Cl and 2NH₄Cl·CaCl·3H₂O, and 2NH₄Cl ·CaCl₂·3H₂O and CaCl·2H₂O in the system. A new hydration double salt (2NH₄Cl·CaCl·3H₂O) was found in the ternary equilibrium system for the first time.     

Mg(OH)<Subscript>2</Subscript> Films Prepared by Ink-Jet Printing and Their Photocatalytic Activity in CO<Subscript>2</Subscript> Reduction and H<Subscript>2</Subscript>O Conversion

Mg(OH)₂ films on Al substrates were fabricated by ink-jet printing, and they were applied as photocatalysts in solar fuels production (H₂ and CH₃OH) from CO₂ and H₂O conversion. The films were fabricated by means of a deposition of a solution composed of magnesium complex nanoparticles over aluminum foils, which were submitted to a heat treatment to promote the crystallization of Mg(OH)₂. The films were characterized by razing incidence X-ray diffraction (GZXD), Fourier-transform infrared spectroscopy (FTIR), Scanning electronic microscopy, X-ray photoelectron spectroscopy (XPS), and N₂ physisorption by BET method. The Mg(OH)₂ was detected in all the samples synthesized with 1 to 40 layers. According to XPS and FTIR analysis, it was detected the presence of carbonates related to Mg₃O(CO₃)₂ and Al⁰ and Al³⁺ due to the substrate. The highest photocatalytic activity was reached using 30 layers of Mg(OH)₂ for H₂ and CH₃OH generation, which it was 268 and 15 µmol g^??1h^??1, respectively. These results were associated to the presence of adequate amounts of MgO and Al₂O₃ that promote an efficient transfer of the photogenerated electrons between them. Furthermore, the formation of porous structures with high surface area and relative high roughness promoted an increase in the mass transport between the gas and liquid phase, which increase the effectiveness of the photocatalysts.     

Phase equilibrium of the ternary system of NH4Cl-CaCl2-H2O at 50°C

The equilibrium data on the ternary system of NH₄Cl—CaCl₂—H₂O at 50°C were investigated using the wet-residue method. The experimental results show that there are three pure phase crystal areas of NH₄Cl, 2NH₄Cl·CaCl₂·3H₂O and CaCl·2H₂O, two mixture phase crystal areas of NH₄Cl and 2NH₄Cl·CaCl·3H₂O, and 2NH₄Cl ·CaCl₂·3H₂O and CaCl·2H₂O in the system. A new hydration double salt (2NH₄Cl·CaCl·3H₂O) was found in the ternary equilibrium system for the first time.     

Preparation of γ‐Fe2O3 Catalysts and their deNOx Performance: Effects of Precipitation Conditions

Magnetic γ‐Fe₂O₃ catalysts were prepared by microwave‐assisted coprecipitation utilizing the direct‐titrate and back‐titrate precipitation technique with different precipitants, namely, (NH₄)₂CO₃, NaOH, Na₂CO₃, and NH₄OH, which were evaluated in the selective catalytic reduction of NO_x with NH₃. The optimum γ‐Fe₂O₃ catalyst preparation method was direct titration with NH₄OH as the precipitant, which exhibits high deNO_x efficiency. This direct titration was effective to maintain the proper crystallization degree of γ‐Fe₂O₃, improve the pore structure, and suppress the formation of α‐Fe₂O₃ phase, being advantageous to get tiny and uniform discrete γ‐Fe₂O₃ particles with high activity in selective catalytic reduction. NH₄⁺‐based precipitants in direct titration leads to an increase of the surface O/Fe atom ratio, and more lattice oxygen sites are exposed to the crystal surface.     

Electrokinetic Properties of Vermiculite and Expanded Vermiculite: Effects of pH,Clay Concentration and Mono- and Multivalent Electrolytes

Abstract

In this study, the zeta potential values of vermiculite and expanded vermiculite were measured to determine the effect of pH, clay concentration, and various mono- and multivalent electrolytes including NaCl, KCl, NH₄Cl, NaNO₃, NaClO₄, Na₂SO₄, Na₂CO₃, Na₃PO₄·12H₂O, MgCl₂·6H₂O, CaCl₂·2H₂O, BaCl₂, SrCl₂·6H₂O, CuCl₂·2H₂O, CoCl₂·6H₂O, NiCl₂, AlCl₃, and CrCl₃·6H₂O on the electrokinetic properties of vermiculite samples. It was found that generally the measured zeta potential values of expanded vermiculite for the studied systems were slightly more negative than that of vermiculite. The pH profiles of vermiculite and expanded vermiculite at acidic, natural, and basic pH values were obtained to determine the effect of time on the pH values of clay suspensions. The zeta potential measurements showed that the surface charge of clay particles was negative in water. The isoelectric point of vermiculite and expanded vermiculite were determined as pH 2.30 and 2.57, respectively. Divalent cations (Mg²⁺, Ca²⁺, Sr²⁺, and Ba²⁺), heavy metal ions (Cu²⁺, Ni²⁺, and Co²⁺) and trivalent cations (Al³⁺ and Cr³⁺) were potential determining ions for vermiculite and expanded vermiculite particles. Moreover, divalent and trivalent cations caused the change of surface charge from negative to positive. On the other hand, monovalent cations (Na⁺, K⁺ and NH₄ ⁺), monovalent anions (Cl^?, NO₃ ^?, and ClO₄ ^?) and multivalent anions (SO₄ ^2?, CO₃ ^2?, and PO₄ ^3?) acted as indifferent ions for these clay particles.     

Deposition and Analysis of Al‐Rich c‐AlxTi1−xN Coating with Preferred Orientation

Metastable c‐Al_xT_1?xN is an important and well‐established hard coating in the tool industry. To improve the mechanical and thermal properties, Al‐rich c‐Al_xTi_1?xN coatings with controllable preferred crystal orientations were fabricated via low‐pressure chemical vapor deposition (LP‐CVD) in an industrial plant, using an AlCl₃–TiCl₄–NH₃–Ar–H₂ precursor system. The c‐Al_xTi_1?xN coatings with (100)‐ and (111)‐preferred orientations and average x values of 0.82 and 0.73, respectively, comprised c‐Al(Ti)N/c‐Ti(Al)N nanolamellae with average compositions of c‐Al_0.9Ti_0.1N/c‐Al_0.6Ti_0.4N and c‐Al_0.80Ti_0.20N/c‐Al_0.50Ti_0.50N; the average lamellar periods were 7.7 and 4.5 nm, respectively. High‐resolution transmission electron microscopy indicated that the c‐Al(Ti)N/c‐Ti(Al)N nanolamellae were modulated along the <100> direction, implying coherent spinodal decomposition of c‐Al_xTi_1?xN in the as‐deposited state. The hardness of the c‐Al_xTi_1?xN coatings varied from 33 to 36 GPa, depending on the (100)‐ or (111)‐preferred orientation. Residual stress measurements in the as‐deposited state showed tensile stress values of 1.8 and 4.6 GPa for the (100)‐ and (111)‐oriented c‐Al_xT_1?xN coatings, respectively. This stress may be generated by the difference in the thermal expansion coefficient of the c‐Al_xT_1?xN coating and the carbide substrate and by coherency stress in the c‐Al(Ti)N/c‐Ti(Al)N nanolamellae. In situ high‐temperature X‐Ray diffraction results revealed high thermal stability up to 1000°C.     

Self‐Assembled 3D Hierarchically Structured Gamma Alumina by Hydrothermal Method

Self‐assembled γ‐Al₂O₃ with hierarchical structure was successfully obtained via thermolysis of γ‐boehmite (γ‐AlOOH) particles, which was hydrothermally derived from aluminum ammonium sulfate hydrate (NH₄Al(SO₄)₂·12H₂O), urea, poly‐glycol (PEG)‐2000, and deionized water. SEM observations indicate that the as‐synthesized γ‐AlOOH has hierarchical flower‐like structure, composing of needle‐like building blocks. After calcinations at 800°C, it converts to cubic γ‐Al₂O₃ with hierarchical structure retained by a topotactical process. N₂ adsorption and desorption reveal that the obtained γ‐Al₂O₃ has a BET surface area of 101 m²/g with a narrow mesoporous size of about 13 nm and a broad macroporous‐size distributions of 200–500 nm, respectively. The as‐generated γ‐Al₂O₃ with hierarchical structure shows good capacities for removing Congo red from wastewater, indicating that 3D hierarchical structure has excellent adsorption ability.     

Layered double hydroxide/NaSb(OH)6–poly(vinyl chloride) nanocomposites: Preparation,characterization, and thermal stability

A novel layered double hydroxide/NaSb(OH)₆‐based nanocomposite (Sb‐LDH) has been prepared via intercalation of thio‐antimonite (SbS₃^3?) and reconstruction of LDH using Mg‐Al LDH as precursors. It is composed of LDH nanolayers with thickness of 25 nm and NaSb(OH)₆ nanoparticles with diameter of 3–25 nm. The presence of NaSb(OH)₆ will decrease the decomposition intensity and hinder the decomposition of Mg‐Al LDH because of the potential synergetic effect. When applied to poly(vinyl chloride) (PVC) composites, both Mg‐Al LDH and Sb‐LDH can enhance the thermal stability and increase the decomposition temperature of PVC. Compared with Mg‐Al LDH, Sb‐LDH results in higher decomposition temperatures and whiteness and higher initial and long‐term stabilities due to the presence of NaSb(OH)₆, which can react with HCl and coordinate with Cl in the PVC chains. Because Mg‐Al LDH will accelerate the dehydrochlorination of PVC driving by the Lewis acid such as AlCl₃, the thermal stability of PVC decreases with increasing nanofiller loading. When 1 wt % Sb‐LDH was added, the color change time and Congo red time of PVC composites are 140 min and 154 min, respectively. With enhanced thermal stabilization, this novel LDH nanocomposite could gain promising application in thermal stabilizer for PVC resins. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Control of Oxidation State of Eu Ions in Na2O–Al2O3–SiO2 Glasses

Glasses doped with well‐controlled Eu³⁺ and Eu²⁺ ions have attracted considerable interest due to the possibility of tuning the wavelength range of the emitted light from violet to red by using their ⁵D₀→⁷F_j and 5d–4f electron transitions. Glasses were prepared to dope Eu³⁺ ions in a Na₂O–Al₂O₃–SiO₂ system, and the changes in the valence state of Eu³⁺ ions and the glass structure surrounding the Eu atoms during heating under H₂ atmosphere were investigated using fluorescence spectroscopy, X‐ray absorption fine‐structure spectroscopy, and ²⁷Al magic‐angle spinning solid‐state nuclear magnetic resonance spectroscopy. The reduction behavior of Eu³⁺ ions was dependent on the Al/Na molar ratio of the glass. For Al/Na < 1, the Al³⁺ ions formed the AlO₄ network structure accompanied by the Na⁺ ions as charge compensators; the Eu³⁺ ions occupied the interstitial positions in the SiO₄ network structure and were not reduced even under heating in H₂ gas. On the other hand, in the glasses containing Al₂O₃ with the Al/Na ratio exceeding unity, the Eu³⁺ ions commenced to be coordinated by the AlO₄ units in addition to the SiO₄ network structure. When heated in H₂ gas, H₂ gas molecules reacted with the AlO₄ units surrounding Eu³⁺ ions to form AlO₆ units terminated with OH bonds, and reduced Eu³⁺ ions to Eu²⁺ via the extracted electrons.     

Interfacial Reactions Between Anorthite (CaAl2Si2O8) and Al 7075 Alloy at 850°C and 1150°C

The present work reports an investigation of the interactions of Al 7075 alloy and anorthite at 850°C (150 h) and 1150°C (24 h). Transmission electron microscopy, electron probe microanalysis, X‐ray diffraction, and scanning electron microscopy coupled with energy‐dispersive spectroscopy were used to identify the mineralogical and microstructural changes at the metal–ceramic interface. At 850°C, the phase formation mechanisms were (a) Si⁴⁺–Al³⁺ interdiffusion between the Al alloy and anorthite to form calcium dialuminate (CA₂) and Ca²⁺–Mg²⁺ interdiffusion between the Al alloy and calcium dialuminate to form spinel. At 1150°C, spinel + Al₂O₃ and calcium hexaluminate (CA₆) + CA₂ were the major and minor phase mixtures, respectively in the corroded area. A thin layer of calcium monoaluminate (CA), gehlenite, and Si was present in the immediate vicinity of anorthite. The early stages of corrosion at 1150°C and 850°C were identical. However, due to thickening of the corroded region (viz., spinel formation) and enhanced evaporation of Mg at the higher temperature, the interdiffusion path evolves from Si⁴⁺–Al³⁺ + Ca²⁺–Mg²⁺ to Si⁴⁺–Al³⁺ + Ca²⁺–Al³⁺, thus establishing the following phase evolution path at the interface:      

Microstructured Al‐fiber@meso‐Al2O3@Fe‐Mn‐K Fischer–Tropsch catalyst for lower olefins

A thin‐sheet Al‐fiber@meso‐Al₂O₃@Fe‐Mn‐K catalyst is developed for the mass/heat‐transfer limited Fischer–Tropsch synthesis to lower olefins (FTO), delivering a high iron time yield of 206.9 µmol_CO s^?1 at 90% CO conversion with 40% selectivity to C₂‐C₄ olefins under optimal reaction conditions (350°C, 4.0 MPa, 10,000 mL/(g·h)). A microfibrous structure consisting of 10 vol % 60‐µm Al‐fiber and 90 vol % voidage undergoes a steam‐only‐oxidation and calcination to create 0.6 µm mesoporous γ‐Al₂O₃ shell along with the Al‐fiber core. Active components of Fe and Mn as well as additives (K, Mg, or Zr) are then placed into the pore surface of γ‐Al₂O₃ shell of the Al‐fiber@meso‐Al₂O₃ composite by incipient wetness impregnation method. Neither Mg‐modified nor Zr‐modified structured catalyst yields better FTO results than K‐modified one, because of their lower reducibility, poorer carbonization property, and fewer basicity. The favorable heat/mass‐transfer characteristics of this new approach are also discussed. © 2015 American Institute of Chemical Engineers AIChE J, 62: 742–752, 2016     

Visible Light Transparency for Polycrystalline Ceramics of MgO·2Al2O3 and MgO·2.5Al2O3 Spinel Solid Solutions

Magnesium aluminate spinel solid solutions with the alumina‐rich compositions MgO·2Al₂O₃ and MgO·2.5Al₂O₃ have been prepared as polycrystalline ceramics with average in‐line transmissions at 550 nm of 85.5 ± 0.3% and 80.9 ± 0.4%, respectively. Starting powders are prepared from combinations of high purity Mg(OH)₂ and γ‐Al₂O₃ thoroughly mixed in an aqueous slurry, and the solids are collected, dried, calcined, mixed with LiF sintering aid, and sieved. The optimum amount of LiF added varies with the alumina composition of the spinel solid solution. The powders are sintered into dense ceramics by hot pressing at 1600°C under vacuum and 20 MPa uniaxial load followed by hot isostatic pressing at 1850°C under 200 MPa in Ar. Both compositions exhibit exaggerated grain growth with average sizes well over 500 μm. Knoop hardness measurements are 11.2 ± 0.3 GPa for MgO·2Al₂O₃ and 11.0 ± 0.4 GPa for MgO·2.5Al₂O₃.     

Rapid Synthesis of Mesoporous,Nano‐Sized MgCr2O4 and Its Catalytic Properties

Monophasic MgCr₂O₄ has been synthesized by calcining the gel formed by the addition of epoxide to an ethanolic solution containing MgCl₂·6H₂O and CrCl₃·6H₂O. The sample has been characterized by a variety of analytical techniques including powder X‐ray diffraction (PXRD), FT‐IR, Raman, UV–Visible spectroscopy, transmission electron microscopy, and magnetic measurements at room temperature. Calcining the xerogel at 500°C and 700°C for 2 h yielded MgCr₂O₄ (yield of almost 61% by weight). BET surface area of 33.95 m²/g with an average pore diameter of 28.45 nm was obtained for the sample after calcination at 700°C. Square facets of the cubic spinel structure were observed in TEM images with an average crystallite diameter of 18 nm. HR‐TEM experiments and SAED measurements confirmed the spinel structure and negated the presence of other phases. The presence of MO₄ tetrahedral and MO₆ octahedral units in MgCr₂O₄ has also been evidenced from FTIR and Raman spectra. The sample showed paramagnetic behavior at room temperature with μ_eff of 3.54 B.M suggesting the presence of Cr in III oxidation state. Its use as an efficient catalyst for the oxidative degradation of Xylenol Orange (XO) and the photo degradation of Rhodamine‐6G (Rh‐6G) dyes have been demonstrated as these dye molecules are environmental pollutants.     

Ethylene/1‐octadecene copolymerization using [η5:η1‐C5Me4‐4‐R1‐6‐R‐C6H2O]TiCl2 catalysts

Copolymerization of ethylene with 1‐octadecene was studied using [η⁵:η¹‐C₅Me₄‐4‐R₁‐6‐R‐C₆H₂O]TiCl₂ [R₁ = ^tBu (1), H (2, 3, 4); R = ^tBu (1, 2), Me (3), Ph (4)] as catalysts in the presence of Al(i‐Bu)₃ and [Ph₃C][B(C₆F₅)₄]. The effect of the concentration of comonomer in the feed and Al/Ti molar ratio on the catalytic activity and molecular weight of the resultant copolymer were investigated. The substituents on the phenyl ring of the ligand affect considerably both the catalytic activity and comonomer incorporation. The 1 /Al(i‐Bu)₃/[Ph₃C][B(C₆F₅)₄] catalyst system exhibits the highest catalytic activity and produces copolymers with the highest molecular weight, while the 2 /Al(i‐Bu)₃/[Ph₃C][B(C₆F₅)₄] catalyst system gives copolymers with the highest comonomer incorporation under similar conditions. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011