H. Kumazawa

Reaction kinetics of carbon dioxide with amines in non-aqueous solvents

Abstract The rates of absorption of carbon dioxide into aqueous and non-aqueous solutions of monoisopropanolamine and cyclohexylamine were measured using a semibatch stirred tank with a plane gas-liquid interface at 303 K. The absorption rates under the fast reaction regime were analysed using chemical absorption theory. It was found that the order of reaction with respect to carbon dioxide was unity in every solution system, whereas the order of reaction with respect to mono-isopropanolamine was unity for an aqueous solution and had a value between 1.46 and 1.93 for the other alcoholic solution systems, as in the monoethanolamine case. The dependence of the logarithms of the reaction rate parameters included in the reaction scheme via a zwitterion on the solubility parameter of the solvent was found to be approximately linear, as in the ethanolamine case. The order of reaction with respect to cyclohexylamine was almost unity for aqueous and alcoholic solutions and 2 for toluene solution. The dependence of the logarithms of the second-order reaction rate constants in aqueous and alcoholic solutions on the reciprocal of the dielectric constant of the solvent was found to be approximately linear.

Chemical absorption in a bubble column loading concentrated slurry

Abstract Carbon dioxide was absorbed into aqueous slurries of magnesium hydroxide or calcium hydroxide particles in a bubble column at 308 K and 0.1013 MPa. The volumetric mass transfer coefficient and the effective gas-liquid interfacial area were obtained separately by these absorption experiments. It was found that the liquid-side physical mass transfer coefficient as well as the effective gas-liquid interfacial area decrease with increasing the slurry concentration and that there is an optimal point of fine reactant particle concentration where the chemical absorption rate has its maximum value. The process of gas absorption into slurry in a bubble column was formulated by a film-theory model incorporating a finite dissolution rate of solid particles. The observed absorption rates of carbon dioxide into calcium hydroxide slurries in the bubble column were successfully predicted by the proposed model.

Hydrothermal synthesis of barium ferrite fine particles from goethite

Barium ferrite fine particles were prepared from aqueous suspensions containing goethite (α-FeOOH) and barium hydroxide by a hydrothermal method. Barium ferrite particles of thin hexagonal plate shape could be produced from commercially available goethite with an Fe: Ba molar ratio of 7.2, whereas barium ferrite particles could be produced from synthesized goethite with a molar ratio of unity. The effects on the size of hexagonal platelike particles of such reaction conditions as temperature, stirring speed and alkali concentration were investigated. Particles of 0.6 to 0.8 μm mean size were prepared under the reaction conditions covered here.

Chemical absorption into concentrated slurry: Absorptions of carbon dioxide and sulfur dioxide into aqueous concentrated slurries of calcium hydroxide

Abstract The absorption of sulfur dioxide and carbon dioxide into aqueous calcium hydroxide slurries were performed using a stirred tank with a plane gas-liquid interface at 308 K. The absorption rates were found to be lower than those predicted by assuming that the solid particles are uniformly suspending in the liquid-film as well as the bulk liquid phase.It might be due to the possibility that there is no particle suspending in the vicinity of the interface. The process of gas absorption with reaction in the slurry was formulated by film-theory model incorporating the presence of an inert region in which there is no particle. The observed absorption rates of sulfur dioxide and carbon dioxide were successfully predicted by the proposed model.

Mechanism of gas permeation through glassy polymer films

Abstract The observed pressure dependence of the mean permeability coefficients of carbon dioxide and methane in glassy polymer films such as polycarbonate, Kapton® polyimide and polysulfone, taken from existing papers, was compared with the predictions in terms of a dual-mode mobility model and a modified mobility model in which both the Henrys Law and Langmuir populations execute four kinds of diffusive movement. The pressure dependence is simulated better by the modified model than by the original model. The mean permeability coefficients and sorption isotherms for carbon dioxide and methane in commercially available polysulfone films were measured at four temperature levels between 30 and 45°C and at gas pressures up to 33 atm and 61 atm, respectively. The pressure dependence of the mean permeability coefficients for the above systems is also described well by the modified mobility model, whereas the sorption isotherms are described well by the dual-mode sorption model.

Hydrothermal synthesis of barium titanate fine particles from amorphous and crystalline titania

Barium titanate fine particles of cubic system were synthesized hydrothermally from aqueous barium hydroxide solutions with fine particles of either amorphous or crystalline (rutile) titania in suspension. The mean size of barium titanate particles prepared from amorphous titania ranged from 0.03 μm to 0.11 μm, depending on hydrothermal conditions. The particle size approximately agreed with the crystallite size (0.04–0.09 μm). On the other hand, the mean size of barium titanate particles prepared from rutile titania ranged from 0.2 to 0.7 μm, which was about six times as large as the crystallite size. The difference of sizes of barium titanate particles prepared might be ascribed to the difference in dissolution rates of amorphous or crystalline titania particles.

Preparation of barium titanate ultrafine particles from amorphous titania by a hydrothermal method and specific dielectric constants of sintered discs of the prepared particles

Barium titanate ultrafine particles were synthesized from amorphous titania by a hydrothermal method. The mean size of the barium titanate particles prepared at a hydrothermal treatment time of 4 h, was nearly equal to 0.04 5 μm in the range of barium-to-titanium molar ratio (BT) ⩾ 2, and approximately agreed well with the crystallite size. At a BT molar ratio of 1.0, the mean particle size increased to 0.2 μm, while the crystallite size remained constant at 0.045 μm. When the particle size ranged from 0.12–0.20 μm, prepared for the BT molar ratio of 1.0–1.4, the specific dielectric constant for a sintered disc composed of these particles attained a value of 5000 or more. As the BT molar ratio increased to exceed 1.5, when the mean particle size decreased from 0.13 μm to 0.045 μm, the specific dielectric constant for the sintered disc was decreased greatly. The specific dielectric constant for the sintered disc can be correlated well with the size of the composing particles.

HYDROTHERMAL SYNTHESIS OF ULTRAFINE FERRITE PARTICLES

Abstract Ultralfine Ni-, Co- and Zn-ferrite particles were synthesized by hydrothermal treatment of the same gel-like precipitates formed at room temperature. Round ultrafine particles were formed, whose size ranged from 6 to 16 nm, depending on hydrothermal conditions. The size distribution could be described by a log-normal function, and the geometric standard deviation defined as 84.1%-size/50%-side in the size distribution was determined to be about 1.2 regardless of hydrothermal temperature and time. The effect of the reaction conditions on the mean particle size was investigated. As the hydrothermal temperature rises, the particle size increases and crystallization is promoted. The effects of stirring speed in the autoclave and initial loadings of raw materials on the mean size of ferrites are negligibly small.

Chemical kinetics of the reaction of carbon dioxide with triethanolamine in non-aqueous solvents

Abstract The rates of absorption of carbon dioxide into aqueous and alcoholic (methanol, ethanol and 2-propanol) solutions of triethanolamine (TEA) were measure

Permeation of carbon dioxide in glassy poly(ether imide) and poly(ether ether ketone) membranes

Abstract Sorption equilibria and permeation rates for CO 2 , O 2 and N 2 in poly(ether imide) (PEI) membrane which has a glass-transition temeperature of 216°C and in poly(ether ether ketone) (PEEK) (a typical crystalline polymer, crystallinity=0.4) membrane, whose glass-transition temperature is 143°C, were measured at 25, 30 and 40°C and at pressures up to 3 MPa. The pressure dependence of the mean permeability coefficients of PEEK membrane to O 2 and CO 2 obeyed conventional dual-mode mobility model, whereas that of PEI membrane to CO 2 did not follow the conventional dual-mode mobility model. A modified dual-mode mobility model which takes into account four kinds of diffusive movements was satisfactorily used to simulate the pressure dependence.