Effect of ZnCl2‐ and SiCl4‐doped TiCl4/MgCl2/THF catalysts for ethylene polymerization

In this research, ethylene polymerization was carried out in the presence of different additives (ZnCl₂, SiCl₄, and the combined ZnCl₂‐SiCl₄) on TiCl₄/MgCl₂/THF catalytic system. The presence of ZnCl₂‐SiCl₄ mixtures showed higher activity in ethylene polymerization when compared with the catalytic activity in the presence of single Lewis acids, ZnCl₂, or SiCl₄. The modified catalyst with ZnCl₂‐SiCl₄ demonstrated the highest activity, which was more than three times the activity of the system without Lewis acid modification. The enhanced activity can be attributed to the reduction in the peak intensity of MgCl₂/THF complexes with Lewis acid compounds as proven by XRD. This was reasonable because of some THF removal from the structure of MgCl₂/THF by Lewis acid compounds. In addition to the effect of modification with additives on the partial elimination of THF, the catalytic activities could be increased due to the titanium atoms that have been locally concentrated on the surface as seen by energy dispersive X‐ray spectroscopy measurement. On the basis of the in situ electron spin resonance measurement, the mixed metal chlorides (ZnCl₂‐SiCl₄) addition could promote the amount of Ti³⁺after reduction with triethylaluminum. It revealed that the modification of TiCl₄/MgCl₂/THF catalytic system with mixed metal chlorides (ZnCl₂‐SiCl₄) is very useful for ethylene polymerization. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1588–1594, 2013     

Studies in the Crystallization of Ferrierite (FER) Type Zeolites in Presence of Promoting Medium

The zeolite Ferrierite (FER) was synthesized from the hydrogel containing template and promoting medium. The kinetic features of the ferrierite crystallization with varying SiO₂/Al₂O₃ ratio are reported. The apparent activation energies for nucleation (E_n) and crystallization (E_c) were evaluated applying the Arrhenius equation. The rates of both nucleation and crystallization have been found to increase significantly in the presence of promoters like ClO₄ ^-, PO₄ ^-3 and SO₄ ^-2 oxyanions during hydrothermal synthesis. The significant enhancement of the FER crystal growth rate due to promoting medium has been attributed to its greater polarizing and rapid condensation ability of tetrasiloxy silane species [Si-(O-Si)₄]. The crystalline FER products obtained from promoting medium were characterized by XRD, SEM, TG/DTA, IR, NMR and sorption techniques.     

Kinetics of the reduction of silicon tetrachloride and trichlorosilane by hydrogen

Reaction products from SiCl₄/H₂ and SiHCl₃/H₂ mixtures have been examined over the temperature range 800–1200°K, and the conditions under which equilibrium is reached have been established. The results point to a ΔH° for SiCl₄ of between ?162 and ?163 kcal/mole. The reaction rates expressed in mole/1/sec were: d[SiHCl₃]/dt = 7.8 × 10¹⁰ [SiCl₄] [H₂]^1/2 exp ?55,000/RT and d[SiH₂Cl₃]/dt = 2.0 × 10¹⁰ [SiHCl₃] exp ?51,000/RT and kinetic mechanisms have been suggested.     

Synthesis and preliminary gas permeation studies of a tubular NaA zeolite membrane (NZM)

Different from traditional seeded method, NaA zeolite membranes (NZMs) were prepared by in situ synthesis onto the inner side of porous α-alumina tubular supports in a hydrothermal synthesis reactor. The influences of pretreatment of porous tubular support, temperature, time, and synthetic cycle for the synthesis of the zeolite membranes were investigated. The operating conditions were optimized. Characterization of the membranes by scanning electron microscopy and X-ray diffraction showed that the crystalline materials on the inner surface of the porous α-alumina tubes were NaA-type zeolite. Single- and binary-gas permeation tests were conducted. Single-component permeabilities of hydrogen and nitrogen through the NZM changed slightly when the transmembrane pressure difference varied from 80 to 420?kPa. Its selectivity for H₂ relative to N₂ was about 5.3, which was greater than that of the Knudsen diffusion. The separation factors of binary gases H₂/N₂ and H₂/CO₂ at 473?K were 3.9 and 5.7, respectively, again exceeding the Knudsen diffusion level. The separation of binary gases suggests that the NaA-type zeolite membranes on α-alumina substrate were defect free and able to provide molecular sieving. The results demonstrate that the unseeded synthetic method presented in this work is successful and reliable.     

SiCl3CCl3 as a novel precursor for chemical vapor deposition of amorphous carbon films

Amorphous carbon films, characterized by XRD, AFM, SEM and Raman, were deposited from SiCl₃CCl₃ on quartz substrates at 773-1273 K by low pressure chemical vapor deposition using a hot-wall reactor. XPS studies showed that the films grown at 773 K contained 90% C and 10% Cl, while the films grown at 1273 K contained 100% C. SiCl₄, CCl₄ and Cl₂CCCl₂ were detected by on-line FT-IR studies. The extrusion of dichlorocarbene, :CCl₂, from SiCl₃CCl₃ should provide the source of carbon in the reaction. On Si substrates, an etching process at the film-substrate interface assisted the lift-off of the films from the substrates. The C films curled and formed rolls.     

New telechelic polymers and sequential copolymers by polyfunctional initiator-transfer agents (Inifers)

Summary This paper concerns the synthesis and characterization of new Si-Cl and Si-H end-groups containing polyisobutylenes. The syntheses involved 1) The preparation of polyisobutylenes carrying one or two -CH₂C-(CH₃)=CH₂ termini, ii) Hydrosilylation with H(CH₃)₂-SiCl, H(CH₃)SiCl₂, and HSiCl₃, and iii) Reduction of the Si-Cl groups to yield the corresponding -Si-H termini. A series of model compounds mimicking the end-groups have been synthesized and employed for end-group characterization. These Si-Cl and Si-H containing mono- and difunctional polyisobutylenes may be useful intermediates for the preparation of block and graft copolymers or for the synthesis of various terminal functional groups.     

New crystalline complex chlorides containing transition metal chlorides or oxychlorides as components of coordination catalysts

Novel complex chlorides have been obtained by reacting TiCl₄, VOCl₃, MoOCl₄, WOCl₄, or AlCl₃, with Be, Mg, Ca, or Sr chlorides in the presence of electron donors such as POCl₃ (L) or C₆H₅POCl₂, (L′). The resulting products, obtained with good yield, show defined stoichimetry, ionic character, and crystalline structure, and may be considered reference systems for high-yield catalysts in the low-pressure polymerization of ethylene (HDPE). Complexes (TiCl₆)MgL₆, (TiCl₅L′)₂ MgL′₆, and (Ti₂Cl₁₀)MgL₆ associated with (i-C₄H₉)₃Al were found very active in HDPE synthesis, but completely unable to polymerize propylene. This result and other evidence suggest that part of the catalytic activity of these systems is displayed by soluble species. The role played by the Mg ion in high-yield catalysts is displayed by soluble species. The role played by the Mg ion in high-yield catalysts is discussed in the light of the peculiar behavior shown by the complex chlorides containing this earth-alkali metal.     

Preparation of organosiloxane/silicate hybrid structures — Part II

‘QMD’ polymers have been prepared by the interaction of‘QM’ polymers (derived from a phlogopite) with (a) Me₂SiCl₂, (b)ClSiMe₂(OSiMe₂)₇OSiMe₃, and (c) CISiMe₂ (OSiMe₂)₇OSiMe₂Cl. Reaction of the products with sodium hydroxide in ethanol gives materials the structures of which are hybrids of polyorganosiloxanes composed of Si(O_1/2)₄, Me₃SiO_1/2 and Me₂Si(O)_1/2)₂ building units with sodium silicate units e.g. (O1/2)₂Si(O^?Na⁺)₂. These materials have melting points below 150°C, some products have been shown to form films from aqueous solution and from the melt.     

BaO−B2O3 system and its mysterious member Ba3B2O6

The first systematic study of the BaO–B₂O₃ system and barium orthoborate Ba₃B₂O₆ (3BaO·B₂O₃) was reported in 1949. Thereafter, the system was repeatedly refined but the structure of Ba₃B₂O₆ compound has not been adequately studied yet. In our study we have, for the first time, obtained the crystalline samples of Ba₃B₂O₆. The solved structure (Pbam, a = 13.5923(4) Å, b = 13.6702(4) Å, c = 14.8894(3) Å) belongs to the class of ‘anti‐zeolite’ borates with a pseudotetragonal [Ba₁₂(BO₃)₆]⁶⁺ cation pattern which contains channels along the c axis filled with anionic clusters. The Ba₃B₂O₆ compound may be regarded as a fluorine‐free end‐member of the Ba₃(BO₃)_2–xF_3x solid solution. The BaO–B₂O₃ phase diagram presented in our study is based on our research and literature data.     

Effect of substrate curvature on microstructure and gas permeability of hollow fiber MFI zeolite membranes

Literature data show that gas permeability of MFI zeolite membrane varies depending on the geometry of supports. The present work investigates the effects of the surface curvature of substrates on the microstructure and the gas permeation property of supported zeolite membranes. MFI zeolite membranes were grown on porous alumina hollow fibers with different diameters (surface curvature) by the secondary growth method. Single gas permeation and H₂/CO₂ binary gas separation from 25 to 300 were conducted to study the membrane quality. The zeolite membranes on supports of larger surface curvature have higher permeability and lower selectivity due to the presence of more inter‐crystalline gaps in the zeolite layer formed during the template removal step. The effects of the support surface curvature (and geometry) on zeolite membrane microstructure and gas permeation characteristics are semi‐quantitatively analyzed by a transport model considering both structural change and gas diffusion in micropores. © 2018 American Institute of Chemical Engineers AIChE J, 64: 3419–3428, 2018     

One-Step Synthesis of Thermoplastic Phenylsilsesquioxane Polymer and Its Copolymers with Diphenylsiloxanes

The preparation of reversibly softening polymers and copolymers of phenylsilsesquioxane in a one-step synthesis has been studied. The synthetic methods are based on hydrolytic polycondensation of PhSiCl₃ or copolycondensation of PhSiCl₃ with Ph₂SiCl₂ using moistened or hydrated salts: (1) moistened Na₂CO₃, K₂CO₃, (2) Na₂B₄O₇·10H₂O, (3) Na₃PO₄·12H₂O. Syntheses (1) and (2) gave products as reversibly softening and soluble materials, whereas synthesis (3) produced partially cross-linked resins from which a soluble material might be extracted. Polycondensation using borax gave polymers and copolymers with incorporated boron atoms. The polysilsesquioxanes were characterized by size exclusion chromatography (SEC), ¹H and ²⁹Si NMR, IR spectroscopy, and elemental analysis. Thermal properties were studied by DSC and thermogravimetry.     

Solution combustion synthesis of nanostructured iron oxides with controllable morphology,composition and electrochemical performance

Nanostructured iron oxides have emerged as promising materials for electrochemical energy storage and conversion devices due to their high theoretical capacity, eco-friendliness and earth abundance. Particularly, the morphology- and composition-controllable synthesis of nanostructured iron oxides is extremely important to optimize their electrochemical performance. However, the development of facile and effective synthetic method is still a great challenge. In this paper, we demonstrated a one-pot solution combustion synthesis (SCS) approach for the time- and energy-effective preparation of nanostructured iron oxides with controllable morphology and composition just by tuning the molar ratio (φ) of fuel (glycine) to oxidizer (ferric nitrate). Innovatively, the effects of φ value on the control of combustion reaction mechanism, morphology and composition of SCS products, and the electrochemical properties in relation to the morphology and composition have been systematically investigated. The results revealed that with the increase of φ value, the reaction mechanism varied from pyrolysis to combustion and the combustion phenomenon changed from volumetric mode to self-propagating mode. Correspondingly, the morphology of products evolved from uniform nanoneedles to porous nanosheets, and finally into aggregated nanoparticles. Meanwhile, the phase composition of these products changed from amorphous α-Fe₂O₃ to crystalline α-Fe₂O₃, and eventually into α-Fe₂O₃/Fe₃O₄ composites. When evaluated as lithium ion battery anode, the as-prepared α-Fe₂O₃/Fe₃O₄ porous nanosheets (φ = 1.0 product) exhibited the best electrochemical properties (a high reversible capacity of ~ 1200 mA h g^?1 and an excellent rate capability) among all the SCS products, which may be attributed to its mesoporous structure (supply favorable accessibility for electrons), nanosheet morphology (shorten the transport length of Li⁺) and appropriate proportion of Fe₃O₄ phase (enhance the electronic conductivity). Consequently, the facile SCS method demonstrated here might provide a new methodology for the morphology and composition-controllable synthesis of nanomaterials, for which a number of prospective applications in electrochemical fields can be envisioned.     

Polymerization of butadiene using neodymium versatate‐based catalyst systems: preformed catalysts with SiCl4 as halide source

The ternary neodymium versatate (NdV₃)‐based catalyst system, NdV₃/SiCl₄/Al(iso‐Bu)₂H, for the stereospecific polymerization of 1,3‐butadiene (Bd) has been studied at a catalyst concentration of 0.11 mmol Nd per 100 g Bd. The effects of the concentration of SiCl₄ following in situ activation, preformed at 20 °C in the presence and absence of isoprene and the substitution of Al(iso‐Bu)₂H with AlEt₃ as alkylating agent, were established and compared to the performance of NdV₃‐based catalyst systems incorporating ethylaluminium sesquichloride (EASC), diethylaluminium chloride (DEAC) and t‐butyl chloride (t‐BuCl) as chloride sources. Comparable catalytic activity between the control catalysts based on EASC, DEAC and t‐BuCl and the studied NdV₃/SiCl₄/Al(iso‐Bu)₂H system was achieved once the optimum concentration ratios of NdV₃/SiCl₄/Al(iso‐Bu)₂H = 1:1:25 were applied in conjunction with preforming the catalyst components in the presence of isoprene for 72 h at 20 °C. Polybutadiene cis‐1,4 contents were consistently high (about 97 %) for all polymerizations. © 2000 Society of Chemical Industry     

Preparation of ionic polyphosphonasiloxanes

Mixtures of polyphosphonasiloxane oligomers have been prepared by the interaction of Ph₂SiCl₂ with PhPO(OH)₂ and of Me₂SiCl₂ with MePO(OH)₂. Substitution of LiH₂PO₄ for PhPO(OH)₂ and MePO(OH)₂ leads to the formation of polyphosphonasiloxanes containing - O^?Li₊ groups. The Tg's of these products increase as greater amounts of lithium phosphate are incorporated. Use of NaH₂PO₄ does not produce polymers containing - O^?Na⁺, instead reaction of the -O^?Na⁺ groups with Si-Cl leads to the elimination of NaCl and the formation of cross-linked polymers.     

CH3 and Cl2 coadsorbed on Si/Cu(100)

X-ray photoelectron spectroscopy (XPS) and temperature-programmed desorption (TPD) studies were used to investigate the reactions of coadsorbed CH₃ and Cl₂ on Si/Cu(100). TPD results showed that the individual exposure of Si/Cu(100) to CH₃ and Cl₂ resulted primarily in the desorption of (CH₃)₃SiH and SiCl₄, respectively. Coadsorption of CH₃ and Cl₂ at specific surface concentrations on Si/Cu(100) resulted in the desorption of (CH₃)_4-xSiCl_x (x ranges from 1 to 3) species. The relative surface concentration of CH₃ and Cl (resulting from Cl₂ dissociation), however, controlled the stoichiometry of the methylchlorosilane product. XPS results suggested that more Si was removed from the Si/Cu(100) surface as gaseous product when CH₃ and Cl₂ were coadsorbed on the surface than when CH₃ and Cl₂ were adsorbed alone.     

Chemical synthesis of cross-linked polyaniline by a novel solvothermal metathesis reaction of p-dichlorobenzene with sodium amide

We reported the chemical synthesis of cross-linked polyaniline (PANI) by a novel solvothermal metathesis reaction of p-dichlorobenzene (C₆H₄Cl₂) with sodium amide (NaNH₂) in benzene at 220 °C. In this method, the aniline monomer and complicated treatment were needless and the yield of final products was over 50%. The as-synthesized brown samples were NMP-soluble but water-insoluble; and they were characterized by XRD, FT-IR, UV-vis absorption, XPS, elemental analysis, TGA, and TEM. It was found that solvents have significant influence on the final product. The predominant mechanism of chain growth in PANI polymerizations was proposed as the ionic S_NAr process; however, further theoretical and experimental investigations are needed to obtain the undoubted evidences. We believe that this novel solvothermal metathesis reaction will give us a new guideline for the synthesis of some polymers.     

Intercluster porous nanocomposites from combination of [AlO4Al12(OH)24(H2O)12]7+ cation and Anderson-type [Al1? x Cr x Mo6O24H6]3? anion: XRD, TG-DTA, SEM-EDAX and EPR studies

The synthesis of intercluster porous nanocomposites obtained from polyoxometallate compounds such as the [AlO₄Al₁₂(OH)₂₄(H₂O)₁₂]⁷⁺ cation (named Al₁₃) and the Anderson-type [Al_1−x Cr _x Mo₆O₂₄H₆]³⁻ anion (named Al_1−x Cr _x Mo₆) has been performed in order to study the interaction between the two cluster ions, the stability of the XMo₆ planar configuration, the products obtained after thermal treatment, the structure and the local symmetry of the Cr³⁺ species. Chemical, thermal, structural and spectroscopic characterizations of the original and thermally treated phases have been followed by different techniques such as TG-DTA, XRD, SEM-EDAX, and mainly by EPR. All the results have shown that the structure of the intercluster nanocomposites (Al₁₃)(Al_1−x Cr _x Mo₆)₂ precursors is similar to that reported by Son et al. for the chromium-free (Al₁₃)(AlMo₆)₂ intercluster nanocomposite [Son et al., J. Am. Chem. Soc. 122 (2000) 7432]. After thermal treatment in air at several temperatures of the (Al₁₃)(Al_1−x Cr _x Mo₆)₂ nanocomposites the following phases have been observed and characterised: (i) at 400 °C an amorphous phase containing dispersed Cr³⁺ ions; (ii) at 700 °C a crystalline phase corresponding to Cr₂(MoO₄)₃/Al₂(MoO₄)₃ solid solutions; (iii) at 950 °C α-Al₂O₃/Cr₂O₃ solid solutions with a random dispersion of the Cr³⁺ ions.     

Surface deacidification of ZSM5 by SiCl4 treatment: Assessment of surface specificity by methylene blue adsorption

A study has been made of ZSM5 zeolite deacidification (dealumination) by high temperature treatment in SiCl₄ vapour, monitoring total acidity by Na⁺-exchange, and external surface acidity by methylene blue adsorption (exchange), with comparative measurements of theN _Si/N_Al ratio (nominally external surface) by XPS.Using H-ZSM5, the highest specificity for external surface deacidification was found at the lowest usable values of treatment temperature, time andp _Sicl4. Using Na-ZSM5 in place of H-ZSM5 did not offer a useful improvement.A steaming/HCl-leaching method was shown not to be suitable for selective external surface deacidification.Values ofN _Si/N_Al by XPS were dependent on the method of sample preparation, with mechanical stress (pelleting, pressing) tending to give abnormally low values due to crystal or aggregate fracture: this effect became more serious with increasing severity of SiCl₄ treatment. Even after correcting for XPS emission from subsurface layers, agreement between surfaceN _Si/N_Al values from XPS and acidity measurements was poor for samples with a low degree of bulk deacidification (mild SiCl₄ treatments), and is ascribed to non-acidic surface Al.     

Synthesis of SUZ-4 zeolite by a dry gel conversion method

SUZ-4 zeolite was synthesized by the dry gel conversion (DGC) process with water vapor as gas phase, and characterized by XRD, SEM and N₂ adsorption. The dry gel was prepared with the assistance of a small amount of crystalline seed and organic template tetraethylammonium hydroxide (TEAOH). Molar ratios of SiO₂/Al₂O₃, KOH/SiO₂, TEAOH/SiO₂ and H₂O/SiO₂, amounts of seed and dry gel, types of silica sources, and crystallization temperature and time, were changed to optimize synthesis conditions. The results show that the DGC method leads to formation of SUZ-4 zeolite in a broad range of crystallization temperature 120–180 °C. Under the optimal conditions, i.e., SiO₂/Al₂O₃ = 22.5, KOH/SiO₂ = 0.44, TEAOH/SiO₂ = 0.044, H₂O/SiO₂ = 22.2, seed amount = 0.1 wt%, fumed silica as the silica source, 160 °C and 5 days, SUZ-4 zeolite is obtained with a high crystallinity. Compared to hydrothermal synthesis, the present DGC approach employs far less amount of organic template and allows using inert fumed silica as silica source, producing smaller rod-like SUZ-4 zeolite crystals.     

Synthesis of ZSM-5 zeolite and silicalite from rice husk ash

Local rice husk was precleaned and properly heat treated to produce high purity amorphous SiO₂ for use in the synthesis of ZSM-5 zeolite and silicalite by hydrothermal treatment (150 °C) of the precursor gels (pH 11) under autogenous pressure in a short reaction time (4–24 h). A wide range of SiO₂/Al₂O₃ molar ratios (30–2075) and a small template content were employed to fully exploit the potential of rice husk ash (RHA). The mineralogical phases, morphology, specific surface area and pore volume of the synthesized products were investigated by XRD, FT-IR, SEM and BET analyses, respectively. Under the employed conditions, it was found that the gels with a low range of SiO₂/Al₂O₃ molar ratios (<80) produced an amorphous phase to poorly crystalline ZSM-5 zeolite; those with a medium range (80–200) favored well crystalline ZSM-5 zeolite production with a large surface area; whilst those with a high range of SiO₂/Al₂O₃ molar ratios (>200) yielded silicalite. The increase in Na₂O content, which was derived from the addition of NaAlO₂ to attain the desired SiO₂/Al₂O₃ molar ratio of the gel, did not significantly enhance the crystallization rate, crystallinity, or yield of products. On the contrary, these properties were greatly affected by the increase in the SiO₂/Al₂O₃ molar ratio.