Youichi Negishi

Separation of hydrogen from thermochemical processes using zirconia-silica composite membrane

Abstract For the purpose of purifying H 2 from gaseous mixtures from thermochemical water decomposition processes, the characteristics of zirconia-silica composite membranes coated on porous ceramic tubing were investigated up to 773 K. The maximum content of the Zr(OC 3 H 7 ) 4 in the metal-alkoxide solution used successfully in the coating process was 60 mol%. The separation experiments for the gaseous mixtures of H 2 H 2 OHBr (for the UT-3 process) and of HIH 2 O (for the IS process) were carried out at 423–773 K, and it was found that hydrogen can be purified as reject stream and that HBr and HI can be recoverved from the permeation side of the membranes.

Methanation of carbon dioxide by using membrane reactor integrated with water vapor permselective membrane and its analysis

Using membrane reactor integrated with water vapor permselective membrane, the Sabatier reaction for the methanation of carbon dioxide with hydrogen, CO2+4H2 ⇔ CH4+2H2O, was investigated. The reaction experiments were carried out under the conditions of superficial space velocity 0.030−0.123 s−1, molar ratio of H2 to CO2 in the feed gas, 1–5, operating pressure 0.2 MPa absolute, and temperature 480–719 K. The conversion was increased about 18% in maximum with the membrane. Theoretical equations for Sabatier reaction with and without membrane were derived and applied to analyze the experimental data of CO2 conversion.

Study on molecular weight cut-off performance of asymmetric aromatic polyimide membrane

Abstract Asymmetric aromatic polyimide membranes for a petroleum refinery were made by casting solution of 18 wt.% polyamic acid blending of the trade name Pyle-ML5057 (Du Pont Co.) and PMDA-DABP in the ratio of 1:1 and 20 wt.% phenanthrene in dimethylacetamide at 303–363 K, with 1 and 3-min evaporation times, followed by a cycle process of thermal treatment in a bath of dioctyl sebacate under N2 in three steps: 1 h at 373 K, 1 h at 473 K and 1 h at 573 K. The asymmetric aromatic polyimide membranes fabricated with combinations of preparation conditions had a molecular weight (MW) cut-off ranging from 170 to 400 Da. The membrane which has a MW cut-off of 170 Da succeeded in separating the gasoline-kerosine mixtures. A separation factor (for gasoline/kerosene) of 19.5 was obtained.

Separation of gaseous mixtures of CO2 and CH4 using a composite microporous glass membrane on ceramic tubing

Abstract Separation of a gaseous mixture of CO 2 and CH 4 was carried out using a microporous, thin glass membrane coated on the surface of a porous ceramic tubing. The glass membrane was prepared by repeating the following procedure: dipping the ceramic tubing into a metal alkoxide solution containing B 2 O 3 , followed by drying, heating and leaching in HCl solution. The thickness of the membrane was in the range of 5-23 μm, depending upon the number of dips. The structure of the membrane was investigated by means of a scanning electron microscope. The mean pore diameter estimated was in the range of 4–64 nm. The maximum separation factor of 1.48 was obtained with the composite membranes which were coated over 15 times with a casting solution in which the ratio of B 2 O 3 : SiO 2 was 0.25:1. Composite membranes with less than 5 coatings showed no ability to separate. When decreasing the content of B 2 O 3 , carbon dioxide seemed to permeate through the composite membrane by the surface diffusion mechanism in the pores.

Properties of new inorganic membranes prepared by metal alkoxide methods. Part III: New inorganic lithium permselective ion exchange membrane

Inorganic lithium permselective ion exchange membranes were prepared on a microporous alumina substrate by dip-coating solution containing Si(OC2H5)4, LiOC2H5, Mn(OC2H5)2 and C2H5OH. The membranes showed ion-selectivity for cation over anion and permselectivity for Li+ over Na+. The static transport number for cation [K+] is 0.75 and the permselectivity for Na+ over Li+ is 0.29, comparing 2.57 for ordinary organic ion exchange membrane.

Analysis of a two-stage membrane reactor integrated with porous membrane having Knudsen diffusion characteristics for the thermal decomposition of hydrogen sulfide

Abstract Using basic equation for material balance, the thermal decomposition of hydrogen sulfide to produce hydrogen was investigated in a two-stage membrane reactor integrated with porous membrane having Knudsen diffusion characteristics. It was evaluated the effect of membrane area ratio S m,P / S m,R and the pressure in the 1st permeate chamber p P 1 on H 2 concentration in the 2nd permeate chamber y H 2 ,P 2 and the flow rate of H 2 in the 2nd U H 2 . With the decrease of S m,P / S m,R , y H 2 ,P 2 increases and takes constant value which is larger than the H 2 concentration in the permeate chamber for the single-stage membrane reactor by about 1.7 times. There is ( S m,P / S m,R ) limit corresponding to the condition that no flow in the 1st permeate chamber. With the increase of S m,P / S m,R , U H 2 increases and takes maximum value U H 2 ,max at ( S m,P / S m,R ) limit . There is an optimum p P 1 for higher U H 2 ,max , but the difference between the highest value of U H 2 ,max and the lowest one is small. The maximum value of U H 2 ,max is larger than the amount of H 2 obtained in the single-stage by about 1.1 times.

Diffusional characteristics of sodium chloride in symmetrical cellulose acetate membranes measured by an unsteady-state dialysis method

Abstract Unsteady-state dialysis and steady-state reverse osmosis (RO) experiments for aqueous NaCl solutions were carried out with cellulose acetate (CA) symmetrical membranes. The distribution and overall diffusion coefficients of NaCl, K and D were obtained from the unsteady-state dialysis experimental data, taking the effect of osmosis into consideration. D was found to increase with the increase of the solute concentration. The concentration dependency of D can be explained by applying a two-part (perfect or dense and imperfect or porous) model of the membrane. The concentration independent diffusion coefficients of NaCl in the dense part Dd and in the porous Dp are obtained from the assumption of the two-part model for the membrane. Dd does not depend on the water content in the membrane Ww, but on dope composition. Contrary to Dd, Dp increases with the increase of Ww and can be correlated only with Ww and Dp(Ww=0) is found almost equal to the averaged D d for each type of membrane: D p,c = D d exp (γ × Ww). It seems from these facts that the structure of membrane becomes tight with the decrease of the ratio of formamide to CA and loose with the decrease the concentration of CA in dope solutions. D c (c = 0) at the zero concentration can be calculated as follows: D c (0) ≈ W w D p,c + (1−W w ) D d . Solute permeability ω obtained by RO experiments agrees well with ω c = [K · D c (0) ] (l · β) , those calculated from Dc(0) and distribution coefficient K.

Characteristics of a zirconia composite membrane fabricated by a laser firing method

Abstract By a method of laser firing, a high zirconia containing (70%) composite membrane on porous ceramic tubing was successfully fabricated. The laser sintered composite membrane was characterized by gas separation/permeation experiments. In the separation experiment of a CO 2 CH 4 gaseous mixture, it was found that the separation factor of CH 4 over CO 2 was 1.15. In the pure gases permeation experiment, it was found that Knudsen diffusion is considered to be predominant in the permeation mechanism for pure gases H 2 , He, CH 4 , N 2 , O 2 , and CO 2 , and the permeation mechanism of H 2 O at lower temperature depends mainly on surface diffusion and on Knudsen diffusion at higher temperature.

Hydrogen purification using zirconia-silica composite membranes for thermochemical process

Abstract For the purpose of purifying H 2 from a gaseous mixture of thermochemical water decomposition processes, the characteristics of zirconia-silica composite membranes coated on porous ceramic tubing were investigated up to 773 K. The maximum content of the Zr(OC 3 H 7 ) 4 in the metal-alkoxides solution used successfully in the coating process was 60 mol %. Separation experiments of gaseous mixtures of H 4 -H 2 O-HBr (UT-3 process) and of HI-H 2 O (IS process) were carried out at 423–773 K, and it was found that hydrogen can be purified as a reject stream and that HBr and HI can be recovered on the permeation side through the membranes.

Nonempirical Design of Rapid Thermal Processing System

In order to develop a nonempirical technology to design a rapid thermal processing (RTP) system, a direct approach model using the ray tracing simulation (DARTS) is applied for designing the small RTP system composed of tungsten/halogen filament lamps, specular reflectors and a silicon wafer. The temperature profiles on the silicon wafer surface are theoretically predicted and experimentally evaluated using the two RTP systems. The quantitative agreement of the theoretically predicted and experimentally evaluated temperature profiles on the silicon surface suggests that the nonempirical design of the RTP system is possible using the DARTS model. The reflection-resolved analysis based on this model is considered to provide information on the entire path of the rays from the lamps to the silicon wafer surface and on the heat loss caused by the reflectors in the RTP system.