Deactivation of ferrierite during the skeletal isomerization of linear butenes

Deactivation of ferrierite during the skeletal isomerization of 1-butene at atmospheric pressure and 0.15 atm 1-butene partial pressure was studied. At 300°C, the carbon content shows a sharp increase during the first 30 min-on-stream, with a slower growth thereafter. Temperature-programmed oxidation profiles corresponding to different times-on-stream are similar, showing two well-defined combustion peaks centered at about 325 and 640°C, respectively. When starting the 1-butene feed with the catalytic bed at 100 or 200°C and then increasing the temperature up to 300°C, no significant difference is observed, neither in carbon content nor in oxidation profiles. Important differences in the profiles are observed by comparing at the same time at each temperature. The lower the temperature, the higher the reactivity toward oxidation at low temperature. The carbonaceous deposit formed at 100°C shows the main combustion peak at the lowest temperature (135°C) and a more olefinic character; it could be related to a strong adsorption of reactant molecules. At 200°C, the proportion of saturated species associated to oligomers increases; while at 300°C, coke shows both aromatic and olefinic species.     

Thermal properties of blends of poly(ethylene terephthalate) and a liquid crystalline copolyester

Summary A thermotropic liquid crystal copolyester (CHQ/BP/TA/IA; 40/10/40/10) (LCP), and melt blends of poly (ethylene terephthalate) (PET) with LCP have been studied for thermal transition and crystallization behaviour. The LCP has a mesophase transition (KM) in the temperature range of 295–315°C. The endothermic peak showing mesophase to Isotropic (MI) transition is observed around 420°C. These transitions are supported by hot stage polarizing microscopy. In blends of PET/LCP, the mesomorphic transition is observed at temperature around 314°C, along with the melting transition of PET around 274°C. The dynamic calorimetric measurements reveal that the two polymers are at least partially miscible.     

Studies on mechanism of phase transformation of carboxylated poly(phenylene oxide) and polystyrene blend by Fourier transform infrared spectrometry

Summary The thermally-induced phase transformation behaviors of carboxylated poly(phenylene oxide)(CPPO)/polystyrene(PS), and PPO/PS blends were studied by using a difference-spectrum method of Fourier Transform Infrared Spectrometry (FTIR). The difference intensities() and vibration frequency shifts() of the characteristic infrared absorption bands in both CPPO/PS and PPO/PS increased with raising temperature. A linear temperature dependence in the band frequency vs. temperature plots was observed for PPO/PS system, while three slopes corresponding to the three temperature ranges: below 190°C, 190°–215°C, and above 220°C, appeared in frequency-temperature curves for the CPPO/PS blend. These temperature ranges are consistent with the UCST area, the miscible area and the LCST area obtained by our previous works. The mechanism of phase transformation of CPPO/PS was discussed.     

Electrical characteristics of 18650 Li-ion cells at low temperatures

Low temperature electrical performance characteristics of A&T, Moli, and Panasonic 18650 Li-ion cells are described. Ragone plots of energy and power data of the cells for different temperatures from 25 °C to –40 °C are compared. Although the electrical performance of these cells at and around room temperature is respectable, at temperatures below 0 °C the performance is poor. For example, the delivered power and energy densities of the Panasonic cells at 25 °C are 800 W l^–1 and 100 Wh l^–1, respectively, and those at –40 °C are <10 W l^–1 and 5 Wh l^–1. To identify the source for this poor performance at subambient temperatures, both two- and three-electrode impedance studies were made on these cells. The two-electrode impedance data suggests that the cell ohmic resistance remains nearly constant from 25 to –20 °C but increases modestly at –40 °C while the overall cell impedance increases by an order of magnitude over the same temperature range. The three-electrode impedance data of the A&T cells show that the increase in cell resistance comes mostly from the cathode electrolyte interface and very little either from the anode electrolyte interface or from the ohmic resistance of the cell. This suggests that the poor performance of the cells comes mainly from the high cathode–electrolyte interfacial impedance.     

Dehydration of Alcohols by Microporous Niobium Silicate AM-11

The dehydration of ethanol, 1-propanol and 1-butanol has been studied at atmospheric pressure using the novel microporous niobium silicate AM-11 (Aveiro–Manchester structure number 11) in the temperature range 150–300 °C. The selectivity for alkenes increases with temperature for all three alcohols and reaches 100% for 100% conversion at 250–300 °C. At lower reaction temperatures (200 °C), ethers are also formed and their selectivity decreases markedly with the alcohol size.     

Straining mechanisms of hard elastic fibers obtained by broad line nuclear magnetic resonance measurements

Summary Broad line NMR measurements give information on energy-elastic processes during straining of hard elastic fibers, as there are the shearing of the crystalline regions and transformation of parts of the crystalline into amorphous. The amount of these parts is proportional to straining and recrystallizes again, dependent on temperature and time. Sheared crystalline regions relax within few days, even at very low temperature (–175°C, –120°C). In the case of isotactic polypropylene the mobility of various groups depends not directly on the temperature but on the nearest neighbour distances. Thus methyl groups in the sheared crystalline regions even at –175°C undergo hindered rotation.Presented at the 22nd Microsymposium, Characterization of Structure and Dynamics of Macromolecular Systems by NMR Methods, Prague, July 20–23, 1981     

Thermal cross-link behavior of an amorphous poly (para-arylene sulfide sulfone amide)

Cross-link behavior of an amorphous poly (para-arylene sulfide sulfone amide) synthesized via low temperature solution polycondensation was observed for the first time, when the polymer was subject to a series of thermal curing at 260 °C in air condition. The formation of cross-link network was demonstrated by the DSC and TGA results that T_g of the polymer enhanced from 259.17 °C to 268.89 °C, and the 1% weight loss temperature increased remarkably from 243.75 °C to 345.87 °C. EPR analysis further suggested that two kinds of free radicals, CO and C, induced by thermal curing were responsible for this cross-link behavior. According to FT-IR spectrum, the origin of these free radicals was confirmed as amide CO group in the polymer backbone. The cross-linking type was attributed to conventional radical cross-link reaction and the cross-link mechanism was discussed in detail subsequently.     

Study of the thermal stability of a poremit emulsion

Results are presented from a study of the thermal stability of a poremit emulsion. Safe storage and processing times and temperatures are indicated along with the effect of the emulsion on the thermal stability of other materials. Satisfactory thermal stability is attained with an emulsion of poremit in lubricating oils and fuel oils containing up to 3.5% sulfur and from 10 to 17% water. No heat is released for several days at temperatures of 90–110°C. The emulsion begins to break down at 205–210°C, this process intensifying at 240–250°C. The self-ignition temperature of the emulsion is within the range 310–370°C.State Scientific Research Institute Kristall, 606007, Dzerzhinsk. Translated from Fizika Goreniya i Vzryva, Vol. 30, No. 6, pp. 89–96, November–December, 1994.     

Dynamics of Phase Transitions in the SHS of a 3Cu–Al Powder Mixture in the Regime of Thermal Explosion

The paper reports results of dynamic xray photography of selfpropagating hightemperature synthesis of a 3Cu–Al powder mixture in the regime of thermal explosion. The stages of formation of the final product are considered, beginning with the heating of the starting mixture and interaction of its components and ending with phase transitions during cooling of the product — intermetallides Cu₉Al₄ and Cu₃Al, which are the main components of Cu based tribotechnical materials. It is shown that upon heating in the temperature range of 550 – 590°C, the intensity of diffraction lines of Al drops to the background level. The exothermicreaction of synthesis of the intermetallide is initiated at a temperature of 610 – 630°C. In the period of sharp increase in temperature to 1040°C, the presence of the starting copper and the newly formed hightemperature phase with the Cu₉Al₄ tructure are detected simultaneously in the combustion wave. When cooled to 300$°C, the material contains two cubic phases — Cu₉Al₄ and an solid solution of Al in Cu. Further cooling is accompanied by formation and increase of peaks of the Cu₃Al phase with an orthorhombic lattice. The phase composition of aluminum bronze produced by SHS with combustion in the regime of thermal explosion is not in equilibrium.     

Thermal conductivity of graphite refractories

Summary The method developed for measuring the thermal conductivity of graphitic refractories up to 1150° C makes it possible to obtain results with a reproducibility of about 3% with a maximum theoretical error of up to 8%.The relationship obtained for temperature and in the 600–1100° C range shows a strictly linear reduction in thermal conductivity with rise in temperature, which enables extrapolation to be made up to 1400° C.Owing to the development of texture during pressing, the coefficients of thermal conductivity of the goods in the directions perpendicular and parallel to the forces of pressing are different by a factor of 1.4.The proposed method can be used for studying the thermal properties of electric conducting ceramics possessing a high thermal conductivity.     

Thermal transitions of liquid crystal polyesters: Poly(decamethylene-4,4′-diphenoxy terephthalate)

Summary The thermal transitions of liquid crystalline poly (decamethylene-4,4-diphenoxy terephthalate) have been studied by differential scanning calorimetry, X ray diffraction and thermoptical microscopy. At room temperature a three dimensional order and a smectic mesophase coexist. The crystal-smectic mesophase transition occurs at 240°C and at higher temperature, 250–260°C, a transition from smectic C to nematic has been observed, before the isotropic transition at 290°C. The no previously known smectic C-nematic transition has been detected by microscopy, observing bars and striated textures, and by X ray diffraction patterns obtained in the whole range of temperatures.     

The influence of thermal pretreatment of Re/γ-alumina catalysts in hydrogen on their activity for hydrogenation and hydrogenolysis of benzene

The specific activity of Re/-alumina catalysts (10.4 and 1.04 wt% Re) preheated in hydrogen at 550–800°C for benzene hydrogenation and hydrogenolysis at 80–300°C has been found to not change or to increase with increasing pretreatment temperature, respectively. The results are discussed in relation to the metal dispersion.     

Synthesis of poly(α-thiophenediyl)benzylidene with high molecular weight and its thermal stability

Summary The synthesis of poly(-thiophenediyl)benzylidene (PTB) with high molecular weight is described. Number-average degrees of polymerization reached about 74. The characterizations of the polymer was investigated by ¹H-NMR, ¹³C-NMR, IR, and UV-VIS spectra. The polymer with well-defined structure and high molecular weight was obtained by polymerization at low temperature and in polar solvent. This polymer was thermally stable and a thermal decomposition took place at 391°C under nitrogen and at 370°C under air. The glass transformation temperature was 117°C and this PTB was nonfusible.     

Partial oxidation of methane to syngas over Co/MgO catalysts. Is it low temperature?

Co/MgO catalysts with high Co-loading (>28 wt%) are able to initiate the reaction of methane with oxygen at temperatures around 500 °C. High conversions of methane ( 70%) and very high selectivities for hydrogen and carbon monoxide ( 90%) are obtained at very high reactant gas space velocities (10⁵–10⁶ h^–1). The temperature of the catalyst at the conditions of partial oxidation of methane to form syngas was found to be extremely high (1200–1300 °C); it is about 600–850 °C higher than that previously reported by others. At these temperatures, high temperature homogeneous reactions may prevail. It is suggested that combustion of methane to carbon dioxide occurs on the catalyst with major heat release and that methane and water, respectively methane and carbon dioxide are reformed thermally in an endothermic reaction leading to syngas.     

Preliminary study of cationic copolymerization of α-methylstyrene and isobutyl vinyl ether

Summary -Methyl styrène polymerization was carried out using t-BuCl/Et₂AlCl/CH₂Cl₂ system in the temperature range of 0° to –63.5°C. The effect of temperature on yield and molecular weights of Poly -Methyl styrene was determined. Based on Arrhenius plots, average activation energies of molecular weights were determined to be –9.2 ± 1.0 K cal/mole. (0° to 40°C) and 0 ± 0.5 K cal/mole (–40° to –63.5°C). These were postulated to reflect the molecular weight governing mechanisms such as transfer to monomer and termination respectively.     

High-temperature chlorine corrosion of technical carbons Part II. Anodic corrosion in chloride melt

Medium (200 to 400°C) to high (600 to 800°C) temperature corrosion of technical carbons (Acheson graphites) have been investigated in alkali chloride melts at chlorine evolving anodes. At low temperature in chloride melts containing free Lewis acid (AlCl₃) no chlorine is evolved — even at high current densities — because chlorine, together with aluminium chloride, instantaneously form intercalation compounds with graphite and, as a consequence, the carbon desintegrates very rapidly. At 200°C carbon is consumed anodically in a C/Cl of molar ratio 70/1. With increasing temperature Scheson graphites become more stable so that at 700°C short term destruction cannot be observed in melts which contain free Lewis acid. Chlorine corrosion of carbon electrodes in purified basic alkali chloride melts, which are free of oxygen carriers and, in particular, free of water at temperatures between 600 and 800°C in basic chloride melts, is an electrochemical reaction proceeding at low current densities slower than anticipated from thermodynamic data for carbon chlorination equilibria. The anodic carbon corrosion reaction has an activation energy of only 50 kJ mol^–1 and its rate increases with increasing anode potential, or anodic current densities (rate: exp (i)). At a technical current density of 0.4 A cm^–2 at 700°C the corrosion rate is estimated to be of the order of centimeters per year, rendering carbon anodes dimensionally unstable. Most important is to note that apart from CCl₄, chlorinated carbon compounds (olefins and arenes) are generated as side-products which are noxious and ecologically dangerous and must not be released from processes which use carbon anodes for chlorine evolution from salt melts.This paper is dedicated to Professor Dr Fritz Beck on the occasion of his 60th birthday.     

Adsorption Isotherm and Pore Characteristics of Nano Alumina Derived from Sol-Gel Boehmite

This paper deals with a systematic investigation on the synthesis of aluminium oxide starting from mono hydroxy aluminium oxide (boehmite, (AlOOH)) which in turn is synthesized from aluminium nitrate. Boehmite on heating forms , transitional alumina and -alumina phases in the temperature range 400–600, 800–1050 and 1050–1100°C respectively. Calculation from XRD, using Scherer equation shows that -alumina has crystallite size in the range 5–10 nm, while and -alumina are in the range 10–20 nm and -alumina is about 33 nm. The textural features of aqueous sol-gel boehmite samples calcined at various temperatures were analyzed by specific surface area measurements and adsorption isotherm features. Maximum specific surface area of 266 m²/g is observed for the precursor calcined at 400°C and a minimum of 5 m²/g at 1100°C. Total pore volume is maximum for the precursor calcined at 600°C (0.2653 cm³/g). Average pore size ranges from 3 nm (400°C) to 11 nm (1100°C). The adsorption isotherms also show a change from Type IV to Type II with increase in temperature showing difference in surface properties. The information from t-plots, pore size distribution and cumulative pore volume data also indicates differences in porosity features of boehmite on calcination. The adsorption isotherm and pore size distribution analysis show maximum microporosity at 400°C, while maximum mesoporosity is observed at 600°C. At higher temperatures, porosity decreases, even though small fraction of pores in the mesopore range is still retained. At 1100°C, there is structural transformation from transitional to -alumina, with very low specific surface area 5 m²/g and pores in the size range of 11 nm. The various data presented in this study will be useful in the synthesis of alumina with tailor made properties.     

Mechanism of Microwave Heating of Zeolite A

The mechanism of microwave heating of A zeolite was studied by comparing the heating properties, cation distributions and dielectric properties of 3A, 4A and 5A zeolites. It was easy to heat hydrated 4A zeolite to a glowing (melting) temperature by microwave (2.45 GHz) radiation from room temperature but was difficult to heat the same zeolite with little hydration. When 4A zeolite was preheated to 120°C, it could be easily heated by microwave radiation. However, 3A zeolite was not heated by microwaves under the above condition used for 4A zeolite. 3A zeolite with little hydration at room temperature could not be heated by microwaves but could be heated after hydrating it to 5 H₂O per unit cell (puc) or preheating 3A to 254°C. 5A zeolite could not be heated at all. The easiness of microwave heating was in the order of 4A < 3A 5A. There are differences in the cation distribution among these zeolites, i.e., 5A zeolite has no cations on the 4- and 8-membered oxygen ring sites but the other two have. It was expected from dielectric properties reported so far that the cation on 4-ring site can absorb microwave at <450°C with a higher efficiency but cations in other locations are ineffective for absorption. The following mechanism for the microwave heating was proposed: In the initial period, the hydratedzeolite absorbs the microwaves through its adsorbed water and its temperature rises. The adsorbed water completes desorption by ca. 400–470°C. In this temperature range the zeolite begins to absorb microwaves and the absorption efficiency becomes high with increasing temperature. When zeolite reaches 450–500°C thermal runaway starts. 5A zeolite cannot reach thermal runaway conditions because of absence of cation on 4-ring site. The adsorbed water plays the role of preheating agent in the initial period of microwave heating. Its role, however, can be substituted by other ways, e.g., preheating by conventional heating.     

Characterization of random glass fiber-reinforced polypropylene for processing

DSC thermal analysis and multi-channel recording have been used to investigate the processing conditions for fiber-reinforced thermoplastic composites. The process combined the film stacking and intermingled fiber techniques using needle-punching to improve the fiber-matrix distribution. The preheating temperature and mold temperature for fiber-reinforced polypropylene composites were in the ranges of 180 200 °C and 60 100 °C, respectively. DSC analysis and X-ray methods showed the presence of an a crystalline form for PP and PP/GF with the cooling rate at 10 °C/min. Increasing the cooling rate to 20 °C/min, they revealed the presence of a mixture of the monoclinic a crystalline form and the hexagonal crystalline form. A multi channel recorder was used to determine the completion of impregnation on multi-layer glass fiber reinforced polypropylene, which could significantly reduce the manufacturing cycle time. The main steps in the processing cycle on the surface of composite or inside the composite were determined. The concept of a processing window with respect to solidification rate and molding pressure is introduced and briefly discussed. The mechanical properties of fiber-reinforced polypropylene composite inside the processing window were better than those outside the processing window and were comparable to GE AZDEL®.