Peculiarities of establishment of steady-state frontal polymerization of vinyl monomers

Frontal radical polymerization of vinyl monomers in non-stationary mode is investigated theoretically. It is shown that the formation and the time of establishment of steady-state polymerization heat autowaves considerably depend on the initial temperature, T_i. When T_i is less than the adiabatic heating temperature (T_a), the excess heat and relatively high conversion foster front formation before the non-stationary one. Whereas, for T_i > T_a, steady-state frontal polymerization regime is established, when the heat flow from the outer source is considerably less than the heat evolving due to the chemical reaction.     

Mechanism of pyrolysis of p-xylene

• 1.1. The pyrolysis of p-xylene at temperatures of 830°–1000°C with different hydrocarbon partial pressures (argon/p-xylene=10 : 1, 20 : 1, 30 : 1) has been investigated.
• 2.2. The suggested radical-chain mechanism of p-xylene pyrolysis at high temperatures has an initiation stage leading to the formation of a p-methylbenzyl radical.
• 3.3. It is concluded that toluene is formed mainly by the hydrodealkylation of p-xylene under the given conditions.

     

Intensification of the biocatalytic oxidation of phenol with the use of activators of interface oxygen transfer

The transport of oxygen from the gas to the aqueous phase determines the rate of the biocatalytic oxidation of phenol. In this work, activators of the interphase transfer of O₂ are used to intensify the process, thus raising considerably the rate of gas entering the reaction space without additional power consumption, in contrast to the widely used methods of mixing and bubbling. We present the results from studies of the effect a number of substances on the value of K _L a at various mixing speeds of 100 to 1200 rpm. The solid-liquid phase and its activators are compared in terms of effectiveness. The maximum K _L a increase under different hydrodynamic conditions was achieved for activated carbon (3.7 times), aerosol (1.5 times), n-dodecane (3.1 times). These results are explained by a shuttle mechanism of O₂ phase transfer. It is shown that when K _L a is increased from 2.8 to 18.5 h^T-1, the biocatalytic oxidation of phenol is accelerated by a factor of 2.4. Using activated carbon as an activator of O₂ phase transfer allows us to increase the rate of the biocatalytic oxidation of phenol by ∼20%.     

Effects of quenching mechanisms of carotenoids on the photosensitized oxidation of soybean oil

The effects of 0, 1.0 × 10”⁻⁵, 2.5 × 10⁻⁵, and 5.0 × 10⁻⁵ M β-apo-8'-carotenal, β-carotene, and canthaxanthin on the photooxidation of soybean oil in methylene chloride containing 3.3 × 10⁻⁹ M chlorophyll b were studied by measuring peroxide values and conjugated diene content. β-Apo-8'-carotenal, β-carotene, and canthaxanthin contain 10,11, and 13 conjugated double bonds, respectively. The peroxide values and conjugated diene contents of oils containing the carotenoids were significantly lower (P<0.05) than those of control oil containing no carotenoid. As the number of conjugated double bonds of the carotenoids increased, the peroxide values of soybean oils decreased significantly (P<0.05). The quenching mechanisms and kinetics of the carotenoids in the photosensitized oxidation of soybean oil were studied by measuring peroxide values. The steady-state kinetics study showed that carotenoids quenched singlet oxygen to reduce chlorophyll-sensitized photooxidation of soybean oil. The singlet-oxygen quenching rate constants ofβ- apo-8'-carotenal, β-carotene, and canthaxanthin were 3.06 × 10⁹, 4.60 × 10⁹, and 1.12 × 10¹⁰ M⁻¹sec⁻¹, respectively.     

Effects of preparation methods of support on the properties of nickel catalyst for hydrogenation of m-dinitrobenzene

Using tetraethyl orthosilicate (TEOS) as the precursor of silica, the silica aerogel and xerogel, which were used as supports of nickel-based catalysts for liquid hydrogenation of m-dinitrobenzene to m-phenylenediamine, were prepared by the sol-gel method combined with supercritical drying (SCD) and conventional drying, respectively. Then, a series of nickel-based catalyst samples supported on these supports were prepared by the incipient wetness impregnation method with an aqueous solution of nickel nitrate as well as lanthanum nitrate as impregnation liquids. Based on the characterization results of nitrogen adsorption-desorption (BET), X-ray diffraction (XRD), temperature programmed reduction (TPR), temperature-programmed desorption of hydrogen (H₂-TPD), and catalytic activity evaluation, the physico-chemical properties and catalytic performances of the catalysts were investigated. The results show that the nickel crystallites on the binary nickel catalyst using silica aerogel as support are of smaller particle size. However, compared with the sample supported on silica xerogel, the nickel catalyst supported on the silica aerogel exhibits lower activity and selectivity for the hydrogenation of m-dinitrobenzene because it has a lesser amount of active sites and weaker absorption ability to reactants caused by sintering of the nickel crystallites. The addition of promoter La₂O₃ could increase the activity and selectivity of the catalysts. Among all the nickel-based catalyst samples prepared, the La₂O₃ promoted ternary nickel-based catalyst supported on silica xerogel exhibits the highest activity and selectivity for the hydrogenation of m-dinitrobenzene to m-phenylenediamine, which could be attributed to its highest active surface area and appropriate absorption strength to reactants. Over this promising catalyst, the conversion of m-dinitrobenzene and the yield of m-phenylenediamine could reach 97.0% and 93.1%, respectively, under proper reaction conditions of hydrogen pressure 2.6 MPa, temperature 373 K, and reaction time 1 h. Translated from Journal of Chemical Engineering of Chinese Universities, 2006, 20(5): 723–727 [译自: 高校化学工程学报]     

Scientific foundations of preparation and technologies of production of the catalysts of reforming of gasoline fractions: Development of the process technology

The article summarizes the results of development of the scientific foundations of preparation of the catalysts, and of the experimental development works on creation of the new technologies of their production with the use of physical models, which were previously created on the basis of fundamental research. The results of the adoption of the new production technologies of the reforming catalysts of the PR series at the domestic plants are presented. The adoption consisted in creation and approbation of the fundamentally new technologies of production of the aluminum hydroxide (AHO) by means of the continuous method, modification of AHO by the elements of IV group, plasticization and forming of AHO in the production of the support, application of H₂PtCl₆ using the reactions of the ligand substitution of C⁻ by the functional groups of the support, and reduction and activation of the catalyst, which provide the optimal chemical com- position. Their operation during the 15-year period is analyzed. The reasons of high selectivity (up to 90%) of the new catalysts are found; the new technologies of the combined processing of mixture of C₃-C₄ alkanes with C₅₊ are developed and tested for the production of the high-octane catalysts with selectivity approaching 100%. The main effect of the C₅₊ yield increase of the end products is achieved by the transformation of the C₃-C₄ alkanes into the more high-molecular aromatic hydrocarbons. New processes of the combined processing of the mixtures of C₃-C₄ and gasoline fractions can be considered to be an alternative technology, which solves the important task of broadening the source of raw materials of the motor fuels by the inclusion of the C₃-C₄ alkanes of little value into the processing.     

Chemical assessment of the zinc status of some soils of the semi-arid region of India

To find critical tissue levels of Zn for wheat, and to evaluate various chemical extractants, a screen-house experiment was conducted on 21 diverse soils representing semi-arid regions in Haryana State, India. The extractants differed in the amounts of Zn extracted and the order was: 0.1 N HC1 > EDTA-NH₄OAc > EDTA-(NH₄)₂CO₃ > DTPA + CaCl₂. The amounts (mg kg^–1) of extractable Zn associated with a yield reduction of 20% were: DTPA + CaCl₂, 0.60; EDTA — (NH₄)₂CO₃, 0.80; EDTA-NH₄OAc, 0.92 and 0.1 N HCl, 1.20. The corresponding critical Zn concentration in ten weeks old plants was found to be 17 mg gm^–1. The DTPA + CaCl₂ method gave the best correlation (r = 0.85) between extracted Zn and Bray's per cent yield. It is recommended for assessing Zn status of soils of semi-arid region.     

Thermodynamic study of synthesis of titanium boride by the method of condensation combustion of gases

We have performed a thermodynamic calculation of the adiabatic combustion temperatures and equilibrium composition of products in theBCl ₃−TiCl₄−Na system at atmospheric pressure and temperatures of300–3000 K. The maximum combustion temperature is equal to1872 K. The conditions under which the final high-melting productsTi, TiB, TiB ₂, andB are produced have been found. The results obtained enable one to choose the conditions for synthesis of highly disperse powders of high-melting compounds and coatings based on them using combustion processes. Institute of Chemical Physics, Russian Academy of Sciences, Chernogolovka 142432. Translated from Fizika Goreniya i Vzryva, Vol. 33, No. 5, pp. 43–47, September–October, 1997.     

Enthalpies of vaporization of oligomers of poly(hexamethylene sebacate) and esters of alkylcarboxylic acids

Enthalpies of vaporization for esters covering a molecular weight range of about 74–939 g/mol · [monocarboxylics; linear esters of sebacic series; branched esters of triglyceride series; and, oligomer esters of poly(hexamethylene sebacate)] and a temperature range of about 273.15–523.15 K have been empirically fitted to within about 5% to an equation of the following form: ΔHv(T,M) = S(T)f(M) + I₀(T), where S(T) = C Ln(T) + K₀, I₀(T) = aT + b₀, and f(M) = M/(1 + a₀M), M is the molecular weight (molar mass); T is in degrees Kelvin; and, C, K₀, a, b₀, and a₀ are constants. These results were used to determine the heat capacity difference, ΔC_p = C_p(l) − C_p(g), and compared to calculated values from functional relationships of C_p(l) and C_p(g), l is liquid g is gas. The heat capacity difference results in conjunction with C_p(l) were used to empirically calculate the heat capacity of the gas, C_p(g), over the molecular weight and temperature ranges investigated and compared to a group contribution method. The functional forms for ΔHv(T,M), ΔC_p(T,M), C_p(l), and C_p(g) were also found to be applicable for n-alkanes. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 731–746, 1998     

Effect of parameters of state on phase transitions of carbonized periclase refractories

Thermodynamic physicochemical modelling and calculation methods are used to study the effect of temperature on phase and chemical transitions in the system MgO-C-Al-Al₂OC-Al₈B₄C₇-Al₄O₄C-Al₂O₃-Al₄C₃-H₂O-air at 298–2400 K applied to the behavior of carbonized periclase refractories under production and operating conditions. Partial and total pressure, developed by gaseous reaction products of material with an average pore space (CO₂, CO, CH₄, H₂O, H₂, etc.) are determined in relation to pressure. The effect of gasification for the carbon component, porosity, original and atmospheric moisture, that is not currently subject to experimental observation, are considered. __________ Translated from Novye Ogneupory, No. 10, pp. 44–50, October 2007.     

Kinetics of Adhesion Interaction of Polyolefins with Metals Under Conditions of Contact Thermooxidation

The development of peel strength of adhesive joints between a PE containing organic peroxide (dicumy1 peroxide) and steel has been studied. It has been found that the kinetics of this process are controlled by the contact oxidation processes in a thin boundary layer. The peel strength, A, as a function of the contact time, t, is determined by the content of dicumy1 peroxide, c _per, in the adhesive, contact temperature, T, and the content of oxygen in the contacting environment. The value of A reaches its maximum, A _max, at a certain contact time, t _Amax..

The kinetic characteristics A _max and t _Amax as well as the initial growth rate of A,A ^{= t}=0 = lim da/dt _t=0, are determined by c _per and T. There is a growth of A _max and A ⁼ _t=0 with c _per and a decrease of t _Amax with T.

The shape of A(t) curves for a peroxide-containing PE, similar to a pure PE, is defined by the competitive influence of two principal tendencies in contact oxidation: oxidative cross-linking inducing the growth of A and oxidative destruction causing the reduction of A. There is a growth of the output of contact oxidation reactions with the increase of c _per. The empirical constants of an equation describing the A(t)-functions are calculated and the efficiency of the use of peroxides for promoting the PE-adhesion is estimated.

It has been proved that the peel strength at a fixed contact time is determined by the ratio of the gel-fraction in the polymer layer, c _gel, which is a measure of the outcome of the oxidative cross-linking, and the content of extractable low-molecular products, C _Im, characterizing the effect of oxidative destruction.     

Study of kinematics and dynamics of film blowing of different polyethylenes

An extensive experimental study of the effects of material characteristics and processing parameters on the kinematics and dynamics of film blowing is presented. Three polyethylene resins, a high-density polyethylene (HDPE), a low-density polyethylene (LDPE), and a linear low-density polyethylene (LLDPE) were investigated. The convergent flow analysis of Cogswell was used to characterize the elongational flow behavior of the polymers. Strain rates and pressure inside the bubble (P_i) have been determined over a wide range of film blowing conditions. Moreover, on-line bubble temperature and birefringence measurements have been carried out along the length of the bubble. The experimental results reveal that the three polymers display different behaviors. The LLDPE requires the highest P_i value and the LDPE, the lowest. Consistent with this, the LLDPE shows the lowest in-plane birefringence and the LDPE, the highest. Interactions between various process parameters affecting the P_i value are characterized. Bubble instability is correlated to the apparent uniaxial elongational viscosity and P_i. The most stable polymer (LDPE) has the highest elongational viscosity and requires the lowest P_i. Stresses have been calculated with the help of the birefringence and P_i data. The stress and strain rate data were used to calculate an apparent nonuniform biaxial elongational viscosity of the melts, but could not be correlated through any simple constitutive equation.     

Preparation of regioisomers of structured TAG consisting of one mole of CLA and two moles of caprylic acid

TAG (MLM) with medium-chain FA (MCFA) at the 1,3-positions and long-chain FA (LCFA) at the 2-position, and TAG (LMM) with LCFA at the 1(3)-position and MCFA at 2,3(1)-positions are a pair of TAG regioisomers. Large-scale preparation of the two TAG regioisomers was attempted. A commercially available FFA mixture (FFA-CLA) containing 9-cis, 11-trans (9c, 11t)- and 10t,12c-CLA was selected as LCFA, and caprylic acid (C₈FA) was selected as MCFA. The MLM isomer was synthesized by acidolysis of acyglycerols (AG) containing two CLA isomers with C₈FA: A mixture of AG-CLA/C₈ FA (1∶10, mol/mol) and 4 wt% immobilized Rhizomucor miehei lipase was agitated at 30°C for 72 h. The ratio of MLM to total AG was 51.1 wt%. Meanwhile, LMM isomer was synthesized by acidolysis of tricaprylin with FFA-CLA: A mixture of tricaprylin/FFA-CLA (1∶2, mol/mol) and 4 wt% immobilized R. miehei lipase was agitated at 30°C for 24 h. The ratio of LMM to total AG was 51.8 wt%. MLM and LMM were purified from 1,968 and 813 g reaction mixtures by stepwise short-path distillation, respectively. Consequently, MLM was purified to 92.3% with 49.1% recovery, and LMM was purified to 93.2% with 52.3% recovery. Regiospecific analyses of MLM and LMM indicated that the 2-positions of MLM and LMM were 95.1 mol% LCFA and 98.3 mol% C₈ FA, respectively. The results showed that a process comprising lipase reaction and short-path distillation is effective for large-scale preparation of high-purity regiospecific TAG isomers.     

Theoretical analysis of constants of elasticity of lead calcium alumino-borosilicate glass system

This paper reports on the constants of elasticity of xPbO-RNa₂B₄O₇-(100 ? R ? x) CAS with 0 ?? x ?? 50, and 50 ?? R ?? 75 mol % glass system (CAS is calcium alumino silicate glasses). The constants of elasticity were calculated in terms of the bond compression model and Makishima-Mackenzie model. The average cross-link density, the number of network bonds per unit volume, the average stretching-force constant, and the ratio of the estimated bulk modulus (K _bc ) to the experimentally determined (K _e ), have been calculated and discussed in terms of the bond compression model to analyze the role of PbO. Young??s modulus, the packing density and dissociation energy have been calculated and analyzed according to the Makishima-Mackenzie model. The dimensionality of the glassy network has been calculated in terms of the d ratio (4C ₄₄/C ₁₂) and discussed in terms of the cross-link density of these glasses. C ₁₂ = C ₁₁?2C ₄₄, C ₁₁ and C ₄₄ are the longitudinal and shear elastic constant. The results show good agreement between the experimental and theoretical data for the representation of the constants of elasticity of borosilicate glasses.     

Effect of cooling rate and alumina dissolution on the determination of temperature of critical viscosity of molten slag

In slagging gasifiers with crystalline slag, the fluctuation in temperature near the temperature of critical viscosity (T_cv) can rapidly increase the molten slag viscosity and cause an accumulation of slag inside the gasifier. In order to prevent operational problems caused by the slag, one therefore needs to obtain an accurate measurement of T_cv. The effects of cooling profile and the extent of alumina dissolution on the experimentally determined T_cv were investigated. A synthetic slag was prepared using a composition of Alaskan Usibelli ash, which exhibited crystalline slag behavior, and T_cv was determined under constant cooling and equilibrium conditions. The T_cv measured under 2°C/min of constant cooling was 33°C lower than the T_cv under equilibrium conditions. The effect of alumina dissolution was determined using a platinum (Pt) lined crucible. At a 2°C/min cooling rate, the T_cv measured using a bare alumina crucible was 23°C higher than that from the Pt-lined crucible, offsetting the difference caused by constant cooling. In order to determine a safe gasification temperature range, however, the measurement of T_cv under constant cooling conditions should be avoided.     

Effect of Temperature on the Shrinkage Rate of Compacts Composed of Nanoparticles

An expression describing the shrinkage rate of compacts composed of nanoparticles is obtained under the assumption that nanoparticles undergo fluctuation melting. The expression derived has the following form: dY/dt = Aexp(−(T _M + q)/T), where dY/dt is the shrinkage rate; T _M is the melting temperature of nanoparticles; T is the sintering temperature; and A and q are constants that depend on the material, the initial porosity, and the size of nanoparticles in the compact. The experimental data on the shrinkage rate of compacts composed of copper and nickel nanoparticles 70 nm in size are compared with the shrinkage rates calculated according to the derived expression. This comparison shows that the experimentally measured shrinkage rates are close to the calculated values.Original Russian Text Copyright © 2005 by Fizika i Khimiya Stekla, Stepanov, Alymov, Evstratov.     

Explosive synthesis of ultrafine Al2O3 and effect of temperature of explosion

Synthesis of ultrafine Al₂O₃ is considered. An X-ray phase analysis indicates that ultrafine γ-Al₂O₃, (θ + α)-Al₂O₃, and α-Al₂O₃ are synthesized by explosion of water-gel explosives with a zero oxygen balance, prepared by mixing aluminum nitrate, RDX, and carbamide. All granules of ultrafine Al₂O₃ are spherical and homogeneous, and the granule size varies from 10 to 30 nm. The average crystal sizes of ultrafine Al₂O₃ are calculated by the Scherrer equation. The temperatures of explosion of water-gel explosives are found by a simplified approach. A comparison indicates that the higher the temperature of explosion, the greater the average nanocrystal size. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 5, pp. 127–131, September–October, 2006.     

Effect of reactivity of different types of hydroxyl groups of HTPB on mechanical properties of the cured product

The amount of three types of hydroxyl functional groups (G_OH, H_OH, and V_OH) in hydroxyl terminated polybutadiene (HTPB), remaining in samples acetylated to the same extent under two different conditions, viz., fast acetylation using acetyl chloride in presence of N-methyl imidazole catalyst and slow acetylation by acetic anhydride, differed significantly. For the fast acetylation there is a uniform reduction in all the three types of hydroxyls, probably because the reaction becomes random at rapid rates and the reactivity of the different types of hydroxyls does not play a major role. However, in the slow reaction, the reduction of G-type hydroxyls was 30% more than the expected value and there was a corresponding increase in the amount of V-type hydroxyls remaining in the acetylated product, showing reactivity of OH in the order of G > H > V. When the reaction is slow, it becomes selective and the change in reactivity of the three types of OH groups is reflected in the extent of conversion. The mechanical properties and the crosslink density data show a reduction in the samples containing lesser amounts of G_OH, confirming the branching nature of G_OH, which is involved in the crosslinking reaction. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 1313–1320, 1997     

Characterization of the seed oils of some commercial cultivars of melon

Proximate analysis of the seeds from three commercial melon cultivars (Honey Dew, Hy‐mark and Orange Flesh) showed high percentage of lipids (25.7—27.6%) and proteins (15.2—19.2%). The physico‐chemical properties of the hexane‐extracted oil from the seeds of these cultivars were determined. Gas chromatographic analysis of the oils showed the presence of almost all fatty acids starting from C₆— C₂₄ except that of C₁₁ , C₂₁ C₂₃ , C_18:2 being the principal fatty acid followed by C_18:1 , C_16:0 , and C_18:0 fatty acids. The number of fatty acids, which were present in concentrations higher than 0.01% of total fatty acids, was 17, 14, and 13, respectively, in these cultivars