Shigeyuki Uemiya

Hydrogen permeable palladium-silver alloy membrane supported on porous ceramics

Abstract The hydrogen permeability and selectivity of a composite membrane consisting of miscible palladium-silver alloy film supported on the outer surface of a porous alumina cylinder were investigated. The membrane showed much greater flux than commercially obtainable palladium-based membranes for hydrogen separation. The high hydrogen flux was due to both the thinness of the film and its high hydrogen solubility. In addition, hydrogen embrittlement was suppressed by alloying the thin palladium film with silver, and 100% hydrogen selectivity was retained even at relatively low temperatures.

Separation of hydrogen through palladium thin film supported on a porous glass tube

Abstract Studies have been conducted on the characterization of hydrogen separation by a composite membrane consisting of a thin palladium film supported on the outer surface of a porous glass cylinder. The composite membrane was highly permeable to hydrogen, having an extremely high selectivity for hydrogen separation. The high flux was related to the thinness of the palladium film. The addition of copper or silver to the palladium film improved the membrane, making it suitable to be utilized below 573 K, at the same time maintaining the extremely high selectivity. The rate of hydrogen permeation, however, was reduced by the addition of these elements causing the film to become inhomogeneous.

Steam reforming of methane in a hydrogen-permeable membrane reactor

Abstract Steam reforming of methane was carried out in a reactor incorporating a hydrogen-permeable membrane, which consisted of a thin palladium film supported on a porous glass cylinder. It was shown that the supported palladium membrane promoted the hydrogen production reaction more effectively than a porous Vycor glass membrane. The level of methane conversion exceeded the equilibrium attainable in a closed system in the temperature range of 623–773 K as a result of selective removal of hydrogen from the reaction system. Under the same conditions the porous Vycor glass membrane exhibited little effect on the shift of equilibrium. The difference between these two types of membranes is attributed to their hydrogen permeabilities. Although high reaction pressures are thermodynamically unfavorable for steam reforming, the level of methane conversion in the palladium membrane reactor increased with increasing pressure on the reaction side, as a result of accelerated hydrogen flow to the permeation side.

Hydrogen Production from Methane Steam Reforming Assisted by Use of Membrane Reactor

Abstract It was found that hydrogen could effectively be produced via methane steam reforming at 773 K by use of palladium membrane reactor. The used catalyst was for low-temperature steam reforming to produce methane from naphtha. The level of methane conversion depended on the efficiency of membrane for hydrogen permeation in the case where the rate of hydrogen production was large enough as in the present case. An excellent performance of hydrogen permeation was attained by a thin palladium-silver alloy membrane supported on porous alumina ceramics. Such membranes were prepared by successive deposition of palladium and silver films on the support, followed by thermal treatment above 1073 K.

Promotion of the conversion of propane to aromatics by use of a palladium membrane

Abstract The conversion of propane to aromatics on a gallium loaded H-ZSM-5 catalyst was studied using a hydrogen-permeable membrane reactor. The membrane used was composed of a thin palladium film (8.6μm) supported on the outer surface of a porous alumina cylinder. For the aromatization of propane, the yield of aromatics in this membrane reactor was higher than yields reported in conventional packed bed reactors. The high yield of aromatics was credited to the suppression of the formation of by-products, methane or ethane, probably due to the selective removal of hydrogen from the reaction system. It was found from a comparative study on the conversion of propene that dehydrogenation of propane to propene was efficiently promoted using the membrane reactor.

Gasification Kinetics of Coal Chars Carbonized Under Rapid and Slow Heating Conditions at Elevated Temperatures

Measurements of CO 2 gasification kinetics of coal chars at temperatures of 1273-1873 K were conducted by using a bench-scale fluidized bed reactor (FBR) made of alumina. The gasification rates of chars carbonized under both rapid heating and slow heating conditions were measured using a high-volatile bituminous coal and a medium-volatile bituminous coal. The significant difference in reactivity between rapid heating chars and slow heating chars, and the decrease of char reactivity at high temperature were discussed.

Computation Transport Phenomena in Chemical Engineering. Numerical Simulation of Monosilane Conversion and Fine Elutriation in Polycrystalline Silicon Particle Production via Fluidized Bed CVD.

モノシランを原料とした流動層CVD法による多結晶シリコン粒子製造のシミュレーションを行った.国井-Levenspielの二相モデルにモノシラン熱分解速度式を組み合わせたモデルにより, モノシランの転化率, 微粉への転化率 (微粉生成率) および気泡部の温度分布を計算した.さらに微粉の取り込み (スキャベンジング), 生成微粉への析出および層内温度分布の存在が, 両転化率 (モノシラン転化率と微粉への転化率) に対して与える影響を評価した.両転化率についてHsuらの実験結果と計算結果を比較した.微粉上への析出を考慮した場合には, 従来の計算結果よりも両転化率の値が大きくなった.一方, スキャベンジングや層内温度分布を考慮すると, 両転化率とも小さくなる.これらを考慮した上で実験結果を説明するためには, 微粉上への析出を考慮する必要がある.また, 温度の上昇と共に粒子付着性が増大し, スキャベンジングが起こりやすくなる, または二次粒子径が増大するとすれば, 温度に対する依存性も定性的に説明できることが指摘された.