Kinetics of hydrogasification of coke catalysed by Fe,Co and Ni

The catalysis of hydrogasification of carbon by Fe, Co and Ni was studied using a special petroleum coke with extremely low reactivity. The kinetics were studied with impregnated coke in a fixed-bed flow reactor between 1133 and 1235 K and up to 2 MPa, yielding the following rate equation: Apparent activation energies and heats of adsorption are: Fe, 152 and ?92 kJ mol^?1; Co, 201 and ?82 kJ mol^?1 Ni, 165 and ?50 kJ mol^?1. These studies with impregnated coke as well as further gasification experiments with cokes heat-treated after impregnation with metal salts up to 2273 K confirmed a spillover mechanism and excluded any influence of electronic interactions between carbon and the catalyst metals.     

Viscometric behaviour of polystyrene in tetralin/cyclohexane mixtures

For solutions of polystyrene (M=10⁵–10⁶ g mol^?1), intrinsic viscosities [η] have been measured at 34.5°C, which is the θ temperature for the polymer in cyclohexane. The solvents comprised cyclohexane in admixture with a thermodynamically good solvent, 1,2,3,4-tetrahydronaphthalene (tetralin, TET) over the whole range of solvent composition. From an assessment of several extrapolation procedures, a value of 85 × 10^?3$\text{(±1 × 10}{}^{\mathrm{?3}}\text{)}\text{cm}{}^3\text{g}{}^{\mathrm{<mtext>?3</mtext><mtext>2</mtext>}}\text{mol}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ was obtained for K_θ (in the relationship $\text{[η] = K}{}_{\mathrm{\theta }}\text{M}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{α}{}^3$, where α is the expansion factor), thus yielding $\text{0.681}\text{A}\text{?}\text{g}{}^{\mathrm{<mtext>?1</mtext><mtext>2</mtext>}}\text{mol}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$, 2.25 and 10.2 for the unperturbed dimensions, steric factor σ and characteristic ratio C_∞ respectively. The value of K_θ was independent of solvent composition despite the finite excess free energy of mixing for the solvent components alone, which has been asserted elsewhere to affect K_θ. The present results, in conjunction with previous ones relating to 98.4°C, indicate a value of ?0.89 × 10^?3 deg^?1 for the temperature coefficient of the unperturbed dimensions.     

Synthesis and solution properties of comb polystyrenes

A new method for the synthesis of comb shaped polystyrenes of predetermined structure is described. Silicon-chlorine bonds are introduced into the backbone polystyrene by reaction of SiMe₂Cl₂ with hydrolysed styrene/vinyl acetate copolymers and coupled with polystyryl-lithium in benzene. From a common backbone polymer a series of comb polymers are prepared that have a constant number of branches but vary in branch length. The $\text{M}{}_{\mathrm{w}}\text{M}{}_{\mathrm{n}}$ of the whole comb polymers is about 1.3. The comb polymers with high branch density show θ (A₂) temperatures lower than that for linear polystyrene. The radius of gyration at θ (A₂) [〈S²〉_{θ (A2)}] is always larger than calculated from random flight statistics. For comb polymers with 20–30 branches increases with λ^?0.46 where λ is the fraction of polymer in the backbone. The intrinsic viscosities of the comb polystyrenes at θ (A₂) are equal to that of the parent backbone polymer when λ > 0.25 and increase only little when λ becomes equal to 0.1. Similar behaviour is found in toluene. Intrinsic viscosities in cyclohexane at 35°C show a complex pattern because of the θ-temperature variation.     

Flow microcalorimetry on dilute polymer solutions

A flow microcalorimeter designed to measure the heat of mixing of dilute polymer solutions is described. The instrument is sensitive to steady state heating rates of ～10 μJ/sec. Measurements of heats of mixing of solutions of differing concentrations of n-hexane and cyclohexane are reported and are compared with recommended data of McGlashan and Stoeckli. Values of:

$\text{K}{}_1\text{=}\text{lim}\text{V}{}_2\text{→ 0}$

$\text{(}\text{H}\text{?}{}_1\text{?}\text{H}\text{?}{}^0{}_1\text{RTv}{}^2{}_2$ are obtained for four polymer—solvent systems: polyisobutylene—benzene, 0.22; polystyrene (PS)—cyclohexane, 0.33; PS—n-butyl acetate, ?0.06 all at 25°C; and PS—toluene, ?0.05 at 40°C. Various theoretical calculations of second virial coefficients A₂ made with use of the calorimetric data are compared with previously measured A₂ for the first two mixtures.     

Light scattering in an electric field: variations of the HH(θ) component around θ = 90°

The studies of the changes ΔH_H of the H_H component of the light scattered by dilute suspensions of particles oriented by an electric field E₀ are shown to be convenient and reliable methods for obtaining simultaneous information on the electrical (μ), geometrical (ω) and optical (δ) anisotropies of the particles. Indeed, when E₀ is applied in three particular directions, which are related to the exterior and interior bisectrices of the observation angle θ, ΔH_H(θ = 90°) generally has the same sign as (?μω), (+μω) or (?μ), according to the direction of E₀. Moreover, under the same conditions, the slopes of ΔH_H(θ) versus θ are shown to be much more informative than those of $\text{ΔH}{}_{\mathrm{H}}\text{(θ)}\text{H}{}_{\mathrm{H}}\text{(θ)}$, having the sign of (?μδ), (+μδ) or (?μδω). Experiments on TMV particles illustrate in a very satisfactory manner these theoretical conclusions.     

Pseudo diffusion of nonvolatile metals in electro graphite

The apparent diffusion coefficients for Ti, V, Cr, Nb, Mo and Hf as carbides and for elementary Fe, Ni and Cu in electro graphite have been determined by means of an electron-microprobe analyzer. These pseudo diffusion coefficients were found to vary with the heat treatment time. However, after one hour these remain constant and follow the Arrhenius type of relation D = D₀exp(?Q/RT). The activation energy Q was nearly constant for the metals investigated. An attempt was made to correlate the frequency factor D₀ with the heat of formation $\text{ΔH}{}_{\mathrm{?}}{}^{298}$ of the corresponding carbides. A plot of log D₀vsΔH_f yielded two straight lines, one for the negative $\text{ΔH}{}_{\mathrm{?}}$, the other for positive $\text{ΔH}{}_{\mathrm{?}}$. This method was satisfactorily applied to predict the diffusion coefficients of Zr, Sb and Bi.     

The θ-behaviour of heterogeneous macromolecules

A polymer chain consisting of N_r segments with a repulsive interaction (binary cluster integral β_r) and N_a ? N_r segments with a stronger, attractive and pairwise saturable interaction (β_a), which is at the averaged θ-point N²_rβ_r + N²_aβ_a = 0 deviations from the predictions of the two parameter theory: $\text{α}{}^2{}_{\mathrm{<mtext>R</mtext>}}\text{? 1 ～ δz}{}_{\mathrm{<mtext>r</mtext>}}\text{< 0}$ and A₂ ～ δz_r > 0 with $\text{δz}{}_{\mathrm{<mtext>r</mtext>}}\text{～ β}{}_{\mathrm{<mtext>r</mtext>}}\text{(}\text{N}{}_{\mathrm{<mtext>a</mtext>}}\text{N}{}_{\mathrm{<mtext>r</mtext>}}\text{)}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$. It is shown that the deviations from the universal behaviour are due to the existence of an intermediate length scale $\text{～}\text{N}{}_{\mathrm{<mtext>a</mtext>}}\text{N}{}_{\mathrm{<mtext>r</mtext>}}$.     

Interpretation of hydrogenation kinetics of spent oil distillate from u.v. spectroscopy

Hydrotreatment of spent oil distillate was carried out on a commercial Ni-Mo-alumina catalyst in the temperature range 260–340 °C, with a liquid hourly space velocity (LHSV) of 0.7–2.0 h^?1, pressure of 4.5 MPa and $\text{H}{}_2\text{oil}$ ratio of 300 NL L^?1 (normal litre of H₂ per litre of feedstock). U.v. spectra of hydrogenated and original spent oil distillates (measured in normal hexane) gave a band with a maximum at 230 nm. The change in absorbance at three selected wavelengths for original oil distillate and hydrotreated oil at different operating conditions was taken as a guide for the determination of hydrogenation reaction rates (including partial saturation of aromatics and sulphur compound hydrogenolysis). The rate constants of hydrogenation reactions (k) using a second-order equation and a model of two parallel first-order reactions (k₁ and k₂) were calculated. Finally, the apparent activation energy (E_a), enthalpy of activation ($\text{ΔH}{}^1$) and entropy ($\text{ΔS}{}^1$) were calculated based on the values of k, k₁, and k₂. The calculated values of E_a based on k, k₁ and k₂ were 81.479, 71.188 and 62.882 kJ mol^?1, respectively. The values of $\text{ΔH}{}^1$ based on the same rate constants were 76.670, 66.564 and 58.433 kJ mol^?1, while the values of $\text{ΔS}{}^1$ were ?117.150, ?133.779 and ?150.823 J mol^?1 K^?1, respectively.     

Effect of temperature and frequency in fatigue of polymers

The effects of frequency and temperature on fatigue crack propagation rate in poly(methyl methacrylate) and polycarbonate have been studied using centrally notched plate specimens cycled in tension between constant stress intensity limits. Crack growth was monitored at frequencies between 0.1 Hz and 100 Hz and at temperatures between ?60°C and 40°C. A linear relationship between the cyclic crack growth rate $\text{d}\text{(2a)}\text{d}\text{N}$ and appropriate levels of toughness, K, has been proposed: $\text{d}\text{(2a)}\text{d}\text{N}\text{= A?}{}^{\mathrm{\alpha }}$, where $\text{? =}\text{(λ ? λ}{}_{\mathrm{<mtext>th</mtext>}}\text{)}\text{(K}{}^2{}_{\mathrm{<mtext>1</mtext><mtext>C</mtext>}}\text{? K}{}^2{}_{\mathrm{<mtext>max</mtext>}}\text{)}$, λ = K²_max ? K²_min, λ_th is the threshold limit and A and α are constants. Also, the influence of mean stress intensity was briefly discussed.     

PdSiO2: I. In situ X-ray diffraction studies during treatment and hydrogenolysis

Simple techniques for studies of X-ray diffraction from $\text{Pd}\text{SiO}{}_2$ catalysts during catalytic reactions are reported here. The catalytic activity of $\text{Pd}\text{SiO}{}_2$ of low percentage metal exposed for methylcyclopropane hydrogenolysis at 0 °C is less for catalyst cooled from 450 °C in H₂ than for that cooled in He. This effect appears to result from differing amounts of hydride formation. Ease of formation of hydride decreases with decreasing Pd particle size. Exposing the catalysts with D_h = 13.8 and 29.3% to hydrogen at ~25 °C results in nearly complete conversion of particles of Pd to hydride. Purging with helium (even at 0 °C) reconverts the hydride to palladium, but this reconversion exhibits an induction period; hydride formation is more rapid. Passing hydrogen plus methylcyclopropane results in the conversion into hydride of a substantial fraction of catalyst particles originally present as palladium. The palladium hydride particles of catalyst produced by cooling from 450 °C in H₂ remain as PdH_0.7 during the hydrogenolysis reaction. The lattice parameter of palladium particles is indistinguishable from that of bulk palladium, at least for particle diameters ≥45 Å.     

Rigid backbone polymers, XVII: Solution viscosity of polydisperse systems

When plotted against concentration V⁰₂, the viscosity η⁰ curve of isotropic solutions of lyotropic nematic mesomorphic polymers increases according to:

$\text{η}{}^0\text{=η}{}_0\text{[[η]V}{}^0{}_2\text{+(}\text{π}\text{4}\text{)[η]}{}^2\text{(V}{}^0{}_2\text{)}{}^2\text{+K}{}_2\text{(}\text{ln}\text{x}\text{)}{}^2\text{[η]}{}^3\text{(V}{}^0{}_2\text{)}{}^3\text{+…]}$

in which η₀ is the solvent viscosity, K₂ a numerical constant, x? is the average molecular axial ratio and [η] the intrinsic viscosity as defined by:

$\text{[η]=}\text{2}\text{x}{}^2\text{45}\text{1}\text{ln}\text{2}\text{x}\text{?1.84}\text{+}\text{3}\text{ln}\text{2}\text{x}\text{?0.61}\text{(+}\text{14}\text{15}\text{)}$

At the concentration $\text{v1}{}_2$ an anisotropic phase appears and the viscosity curve shows a decrease in slope followed by a change in direction at a peak viscosity η^p at v^p₂. Upon further increase in v⁰₂ the system undergoes a phase inversion and finally turns fully anisotropic at v^A₂. In the biphasic interval the viscosity is described by:

$\text{η}{}^0\text{=η}{}_{\mathrm{<mtext>mat</mtext>}}\text{1+}\text{(5λ+2)}\text{2(λ+1)}\text{V}{}_{\mathrm{<mtext>inc</mtext>}}$

where $\text{λ =}\text{η}{}_{\mathrm{<mtext>inc</mtext>}}\text{η}{}_{\mathrm{<mtext>mat</mtext>}}$, the ratio of the inclusions viscosity to the matrix viscosity, and v_inc the volume fraction of the inclusions in the system. It must be emphasized that the molecular weight of the polymer in both phases changes continuously with concentration, resulting in commensurate changes in η_ince, η_mat and their ratio λ. In the anisotropic region the viscosity first decreases moderately and then increases precipitously with v⁰₂, according to:

$\text{η}{}^0\text{=η}{}_0\text{[}\text{2}\text{x}{}^2\text{90S}\text{(}\text{5}\text{ln}\text{2}\text{x}\text{?1.8}\text{+}\text{6}\text{ln}\text{2}\text{x}\text{?0.61}\text{)+2]}\text{V}{}^0{}_2\text{1-}\text{V}{}_{\mathrm{25°}}\text{V}{}_{\mathrm{E}}$

in which S is an order parameter and V₂₅, V_E are volumes swept by the orbits of the flowing rodlike macromolecules. The equations give results in good qualitative and fair quantitative agreement with experimental data in the literature.     

Characterization of poly(1,4-phenyleneterephthalamide) in concentrated sulphuric acid: 1. Static and dynamic properties

Laser light scattering including angular dependence of total integrated scattered intensity and of the spectral distribution has been used to characterize five samples of poly(1,4-phenylene terephthalamide), PPTA (commercially known as Kevlar), of different molecular weights in 96% sulphuric acid and 0.1 NK₂SO₄. The data are supplemented by intrinsic viscosity measurements used to detect the possible effects of association, by differential refractometry providing a measure of the refractive index increments in mixed solvents (H₂O, H₂SO₄ and K₂SO₄) and by spectrophotometry for the extinction coefficient needed in the correction of attenuation in light scattering studies. The results show 〈D〉Z = 2.11 × 10^?5$\text{M}\text{?}{}_{\mathrm{<mtext>W</mtext>}}{}^{\mathrm{?0.75}}\text{cm}{}^{\mathrm{?2}}\text{s}{}^{\mathrm{?1}}$ in reasonable agreement with an average of many of the published intrinsic viscosity data obeying [η] = 1.09 × 10?3 M_w^1.25 ml g^?1 and _w expressed in g mol^?1.     

New techniques for measuring maximum reflectance of vitrinite and dispersed vitrinite in sediments

Maximum reflectance, R_max, can be calculated by the following equation: $\text{R}{}_{\max }\text{= (}\text{R}{}_1\text{+ R}{}_3\text{2}\text{) + (}\text{(R}{}_1\text{? R}{}_2\text{)}{}^2\text{+ (R}{}_2\text{? R}{}_3\text{)}{}^2\text{2}\text{)}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ in which R₁, R₂, and R₃ are three separate reflectance readings on the same vitrinite grain at 45° angular intervals. The equation is derived from the reflectance distribution function for a central section of a reflectance indicatrix: R_α = R_maxcos²α + R′_minsin²α where R_α is the reflectance measured in the direction α degrees from R_max, R′_min is an apparent minimum which has the minimum value on this central section, and R_max ? R′_min ? R_min. This new technique can be further simplified by rotating the polarizer in 45-degree intervals to obtain three photometer readings and then converting them to R₁, R₂, and R₃, by the use of empirically-established conversion factors. The new techniques do not require the full revolution of the microscope stage and, therefore, are particularly suitable for measuring small grains of vitrinite.     

Conversion of bituminous coal in COH2O systems: 2. pH Dependence

Under $\text{CO}\text{H}{}_2\text{O}$ systems at initial pH values s> 12.6, an Illinois No. 6 coal, PSOC-26, was converted to a fully pyridine-soluble product, with benzene and hexane solubilities of 50% and 18%, respectively. The product gases were H₂ and CO₂. However, the expected $\text{H}{}_2\text{CO}{}_2$ ratio of 1.0 based on the water gas shift reaction was not observed, but the deficit in hydrogen was found in the increased hydrogen content of the coal product. 95% coal carbon recovery and good hydrogen balances were obtained, and the coal products were found to be very similar to those from conventional tetralin systems. The results suggest an efficient base-catalysed process, and that $\text{CO}\text{H}{}_2\text{O}$ systems are useful for coal studies.     

Poly(ortho-vinylbenzophenone)

This article reports the synthesis and free radical polymerization of ortho-vinylbenzophenone. The glass transition temperature T_g of the homopolymer is 136°C. The products synthesized appeared to be atactic and amorphous. The Mark-Houwink constants for poly (o-vinylbenzophenone) in tetrahydrofuran are K = 4.2 × 10^?2 cm³ g^?1 and a = 0.765. The pre-exponential constant under theta conditions, K_θ, is estimated to be 5.93 × 10^?2 cm³ g^?1. The ratio of unperturbed dimensions of the actual polymer and free rotating analogue chain is 3.93, which is almost double that of polystyrene. The Flory-Huggins interaction parameter for poly $\text{(o-}\text{vinylbenzophenone}\text{)}\text{tetrahydrofuran}$ is 0.48 at room temperature. The $\text{k}{}_{\mathrm{<mtext>p</mtext>}}\text{k}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}{}_{\mathrm{<mtext>t</mtext>}}$ ratio at 60°C is $\text{1.1 × 10}{}^{\mathrm{?2}}\text{l}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{mol}{}^{\mathrm{<mtext>?1</mtext><mtext>2</mtext>}}\text{s}{}^{\mathrm{<mtext>?1</mtext><mtext>2</mtext>}}$. In free radical copolymerizations with styrene at 70°C, r₁ (o-vinylbenzophenone) = 1.216, r₂ = 0.751. This copolymerizations is virtually random.     

Unperturbed dimensions of poly(phenyl acrylate)

Thirteen fractions of poly(phenyl acrylate) have been prepared with weight-average molecular weight ranging from 0.158 × 10⁶ to 2.57 × 10⁶ g mol^?1. The temperature coefficient of the unperturbed dimensions and the glass transition temperature were found to be ?1.8 × 10^?3 deg^?1 and 55.6°C respectively. Good accord was obtained among different methods for establishing θ-conditions of 11.5°C in ethyl lactate. From viscometry, osmometry and light scattering under θ-conditions, as well as in a good solvent, the unperturbed dimensions were determined via several procedures yielding a value of $\text{[〈r}{}^2\text{〉}{}_{\mathrm{0w}}\text{M}\text{?}{}_{\mathrm{w}}\text{]}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 6.0 (±0.2) × 10}{}^{\mathrm{?9}}\text{cm g}{}^{\mathrm{<mtext>?1</mtext><mtext>2</mtext>}}\text{mol}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$. This corresponds to a steric factor υ = 2.37 (±0.08) and a characteristic ratio C_∞ = 11.3 (±0.8). The polymer chain is thus more rigid than poly(methyl acrylate), but less rigid than poly(phenyl methacrylate). With respect to its T_g and flexibility, poly(phenyl acrylate) bears a strong similarity to poly(benzyl methacrylate).     

Universal relation for polymer crystallization rates from the melt

Analysis of spherulitic growth rate data for a number of linear polymers has shown that the temperature at maximum growth rate, $\text{T}{}^1$, is related to the glass transition temperature, T_g, through the empirical equation, $\text{T}{}^1\text{= 1.26 T}{}_{\mathrm{g}}$. The universal master curve for the temperature dependence of the growth rate of crystals from the melt in reduced Gandica—Magill coordinates, $\text{ln}\text{(}\text{G}\text{G}{}^1\text{) =}\text{f(T ? T}{}_{\mathrm{\infty }}\text{)}\text{(T}{}_{\mathrm{m}}\text{? T}{}_{\mathrm{\infty }}\text{)}$, is possible only on the condition that the following empirical equation holds: $\text{0.26 =}\text{T}{}_{\mathrm{\infty }}\text{T}{}_{\mathrm{g}}\text{?}\text{T}{}_{\mathrm{\infty }}\text{T}{}_{\mathrm{m}}$. Finally, limits of variation of the ‘conformational’ contribution to the excess entropy, and of the free volume fraction at $\text{T}{}^1$ were evaluated for some polymers.