Showing papers by "Shigeharu Morooka published in 1998"

Hydrogen recovery from a H2-H2O-HBr mixture utilizing silica-based membranes at elevated temperatures. 1. Preparation of H2O- and H2-selective membranes

Abstract: Amorphous silica-based membranes were prepared for use in recovering hydrogen at elevated temperatures from a H2−H2O−HBr mixture produced by a thermochemical water decomposition process (the UT-3 process). The silica-based membranes, which were formed on porous tubes by chemical vapor deposition of tetraethoxysilane at 650 °C with a forced cross-flow through the porous wall, exhibited a H2 or H2O selectivity, which was related to the preparation and posttreatment conditions. The microporous silica membrane formed on a macroporous α-alumina tube and heat-treated at 900 °C in an inert atmosphere showed a H2 permeance of (3−4) × 10-7 mol m-2 s-1 Pa-1 and a H2/H2O selectivity of 7−15 at permeation temperatures of 200−400 °C. The microporous silica membrane which was formed on a mesoporous γ-alumina layer coated on the α-alumina tube and then calcined in air showed a H2O permeance of the order of 10-6 mol m-2 s-1 Pa-1 and a H2O/H2 selectivity of 12−25 at 200−400 °C. This membrane rejected HBr at a H2O/HBr sele...

Carbon Molecular Sieving Membranes Derived from Condensed Polynuclear Aromatic (COPNA) Resins for Gas Separations

Abstract: Condensed polynuclear aromatic (COPNA) compounds were synthesized from pyrene, phenanthrene, and 1,4-benzenedimethanol. Each COPNA compound was dissolved in tetrahydrofuran, and the solution was used as a coating on the outer surface of a porous α-alumina support tube. The resulting green films were carbonized at 400−1000 °C. The permeances of the COPNA-based carbon membranes were largest for a carbonization temperature of 600 °C, where the mesopore structure was most developed. This optimum carbonization temperature was 50−100 °C lower than that found for polyimide films synthesized from 3,3‘4,4‘-biphenyltetracarboxylic dianhydride and 4,4‘-oxydianiline. The mesopores of the COPNA-based carbon membranes did not penetrate through the total thickness of each membrane and served as channels which increased permeances by linking the micropores. The permselectivities of the COPNA-based carbon membranes were similar to those of the polyimide-based carbon membranes, which contained only micropores.

Reactivity and Selectivity for the Hydrocracking of Vacuum Gas Oil over Metal-Loaded and Dealuminated Y-Zeolites

Abstract: Hydrocracking, hydrodenitrogenation (HDN), and hydrodesulfurization (HDS) of vacuum gas oil (VGO) were examined using Ni-, Co-, and Fe-loaded and dealuminated Y-zeolites at 300−380 °C under an initial hydrogen pressure of 5 MPa. The major fraction of the VGO was n-paraffins (45 wt %), and the second major fraction was alkyl-substituted 3- and 4-ring aromatics. Polar aromatics and 1- and 2-ring aromatics were minor components. Paraffins of 15−32 carbon chains and aromatic compounds of 3−4 rings were efficiently hydrocracked into a gasoline fraction over Ni−HY-A (Si/2Al = 16.0) zeolite, which gave the least yield of gaseous byproducts among the catalysts examined. Extensively dealuminated Ni−HY-B zeolite (Si/2Al = 50.0) produced a large amount of middle distillate fraction, while the yields of gas and coke that was deposited on the catalyst were markedly suppressed. Both zeolites exhibited excellent HDN and HDS activities. The Co−HY and Fe−HY zeolites showed a similar hydrocracking activity as did the Ni−HY...

Catalytic Cracking of Polyethylene-Liquefied Oil over Amorphous Aluminosilicate Catalysts

Abstract: Polyethylene was thermally cracked at 425, 450, and 475 °C in nitrogen at atmospheric pressure for 10-120 min. The major components of the oil were straight-chain olefins which contained 4-25 carbons. Pyrolysis at lower temperatures for shorter reaction times produced straight-chain olefins with a broad distribution of carbon atoms, and pyrolysis at 450 °C for 60 min or under more severe conditions produced mainly straight-chain olefins containing 4-12 carbons. The reaction at 475 °C produced C 1 -C 4 hydrocarbon gases and coke by the secondary cracking and polymerization. The oil was then cracked over catalysts at 500 °C for 2 s at a heating rate of 3000 °C/s using a Curie-point pyrolyzer in a flow of helium at atmospheric pressure. Metal-loaded and dealuminated Y-zeolites as well as aluminosilicate MCM-41 were prepared and examined as cracking catalysts, and their catalytic activities and selectivities were compared to those of conventional zeolite catalysts. Aluminosilicate MCM-41 of Si/2Al = 25 and Ni-HY zeolite of Si/2Al = 50 exhibited a mild cracking activity, giving products of the middle distillate range with no coke deposition. The metal-loaded and metal-free HY zeolites of Si/2Al = 16 exhibited an excessive cracking activity, producing C 5 -C 7 olefins with coke deposition, n-Octadecane was used as the model compound and was cracked over the catalysts under the same conditions as those used for the polyethylene oil. The reactivity of the catalysts was well-correlated with the amount of NH 3 adsorption per unit catalyst area. The metal-supported dealuminated Y-zeolites and aluminosilicate MCM-41 possessed less aluminum atoms and, as a result, a smaller number of acidic sites. The removal of aluminum atoms from the zeolite framework and the control of the acidity are thus key factors in achieving mild cracking of the paraffinic oil.

Structural changes of alcohol-solubilized yallourn coal in the hydrogenation over a Ru/Al2O3 catalyst

Abstract: Yallourn coal was oxidized in aqueous H 2 O 2 in the presence of 1-propanol at 70 °C for 6 h under atmospheric pressure. The coal was partially decomposed by the OH radicals formed from H 2 O 2 , and carboxy and methylene groups originating from H 2 O 2 and 1-propanol were added to the coal structure. As a result, the solubility of the coal in ethanol was increased to 80 kg per 100 kg of the raw coal. The H/C ratio, which was 0.95 for the raw coal, was increased to 1.07 by the oxidization in the presence of 1-propanol. The ethanol-soluble fraction of the oxidized coal was then hydrogenated using a Ru/Al 2 O 3 catalyst in a mixed solvent of ethanol and acetic acid at 120 °C for 12-72 h at a hydrogen pressure of 10 MPa. After the hydrogenation, a yellowish white solid (hereafter referred to as hydrogenated white coal) was obtained. Major gaseous products were CO and CO 2 , and the yield of these gases produced by the hydrogenation in the presence of acetic acid was less than 3 kg per 100 kg of raw coal. The H/C ratio of the hydrogenated coal increased with increasing hydrogenation time and amount of acetic acid and was 1.23 after a 72 h reaction. The hydrogenation also decreased the total nitrogen content in the raw coal. The denitrogenation increased with increasing hydrogenation time and reached 60% after 72 h. It is noteworthy that this conversion was attained by a reaction at 120 °C. The IR peaks at 3000 and 2900 cm -1 , assigned to methylene group, were increased by the hydrogenation. Further structural analyses of the hydrogenated white coal indicated that aromatic rings were changed to saturated rings, i.e., that the sp 2 bonding structure of the coal was transformed to the sp 3 bonding structure. In order to better understand the hydrogenation mechanism, benzyl alcohol, benzoic acid, phenol, and toluene were hydrogenated as model compounds, representing the structure of the alcohol-soluble fraction of the oxidized coal. The addition of carboxylic acids greatly enhanced the hydrogenation of aromatic rings in the model compounds over the Ru/Al 2 O 3 catalyst. The molecular orbital calculation, based on the WinMOPAC program, suggested that dipole moments and charges on the oxygen atoms of carboxylic acids played important roles in the above transformation of the coal structure.

Synthesis and Electrical Properties of Phosphorus-Doped Homoepitaxial Diamond (111) by Microwave Plasma-Assisted Chemical Vapor Deposition Using Triethylphosphine as a Dopant Source

Abstract: A phosphorus-doped (111) diamond film was formed homoepitaxially on a nondoped diamond film, which was also formed homoepitaxially on a type Ib (111) diamond substrate, by microwave plasma-assisted chemical vapor deposition using CH4 as the carbon source and triethylphosphine (TEP, P(C2H5)3) as the dopant source. The P-doped film, which was approximately 800 nm in thickness, exhibited an n-type conduction in the temperature range of 100–500 K. This represents the first such observation, for a film prepared using TEP as the dopant. The activation energy for carrier concentration was 0.09 eV in the range of 145–500 K. The Hall mobility reached a maximum of approximately 3.5 cm2/(Vs) at 145 K and decreased to 0.15 cm2/(Vs) at 500 K. Phosphorus was uniformly incorporated into the diamond film, as evidenced by secondary ion mass spectrometry.

Incorporation of butyl groups into chlorinated diamond surface carbons by organic reactions at ambient temperature

Abstract: Hydrogenated diamond powder has been chlorinated by a radical reaction using sulfuryl chloride in chloroform at 50°C. The chlorinated diamond was then treated with n-, sec- and tert-butyllithium in tetrahydrofuran at 30°C for 4 h, and butyl groups were incorporated onto the surface. The modified diamond powder was characterized by diffuse reflectance IR Fourier-transformed (DRIFT) spectroscopy. The surface substituents were decomposed by flash pyrolysis in a nitrogen flow at temperatures between 255 and 1040°C and essentially all organic fragments were recovered. When the pyrolysis temperature was increased, the total amount of recovered carbons gradually approached a constant value. The fraction of butylated surface carbons to the total surface carbons was calculated based on pyrolysis products obtained at 1040°C and was 0.055 for n-butylation, 0.040 for sec-butylation and 0.047 for tert-butylation.

Carbon dioxide separation from nitrogen using Y-type zeolite membranes

Abstract: A polycrystalline Y-type zeolite membrane was formed by hydrothermal synthesis on the outer surface of a porous a-alumina support tube, which was polished with a finely powdered X-type zeolite for use as seeds. When an equimolar mixture of CO 2 and N 2 was fed into the feed side, the CO 2 permeance was nearly equal to that for the single-component system, and the N 2 permeance for the mixture was greatly decreased, especially at lower permeation temperatures. At 30°C, the permeance of CO 2 was higher than 10-7 mol.m 2 .s 1 .Pa 1 , and the permselectivity of CO 2 to N 2 was 20-100.

Hydrogen recovery from a H2-H2O-HBr mixture utilizing silica-based membranes at elevated temperatures. 2. Calculation of exergy losses in H2 separation using inorganic membranes

Abstract: The separation of hydrogen in a thermochemical water decomposition process (UT-3 process) is discussed from the point of view of exergy analysis. In this process, hydrogen is produced by hydrolysis of CaBr and FeBr 2 , which are contained in reactors connected in series, and is separated from H 2 O and HBr at the outlet of the FeBr 2 hydrolysis reactor at 220-560 °C. Hydrogen concentration is anticipated to be of the order of 5 mol %. On the basis of the permeation properties of H 2 O- and H 2 -selective membranes developed in the preceding study, exergy losses for the hydrogen separation are calculated for plausible cases. The total exergy loss is smallest for a two-stage separation system: Steam is separated from a H 2 -H 2 O-HBr mixture using a H 2 O-selective membrane with a minimum loss of pressure and is recycled to the CaBr 2 hydrolysis reactor. The permeate is recompressed to the feed side of the second stage, and hydrogen is then recovered using a H 2 -selective membrane.

Deep desulfurization of refractory sulfur species in gas oil using skeletal isomerization reaction over zeolite catalyst (part1) quantum chemical analysis of desulfurization reactivity of alkyldibenzothiophenes

Abstract: 軽油中に含有される難脱硫性硫黄化合物4,6-ジメチルジベンゾチオフェン (4,6-DMDBT) をn-デカン中, 270°C, 水素圧2.5MPaでNi担持Y-ゼオライト (Ni-HYゼオライト) を用いてメチル基の異性化反応を行い, 引き続き中間体であるアルキルジベンゾチオフェン類 (Cx-DBT) を同反応条件でCoMo/Al2O3で脱硫し, それらの脱硫反応速度を算出した。また, 反応中間体の構造を決定するため, 数種類のアルキルジベンゾチオフェン類を合成した。このようにして構造決定できたアルキルジベンゾチオフェン類の脱硫反応速度の実測値と, 分子軌道計算で得られた硫黄原子上の電子密度との関係を考察し, ゼオライトによるメチル基転位反応が難脱硫性硫黄化合物の脱硫反応性に及ぼす影響を調べた。Ni-HYゼオライトによる異性化反応で生成した側鎖炭素数1～4のアルキルジベンゾチオフェン類は, 脱硫反応速度の違いにより以下の4グループに分類できた: 4,6-DMDBT (グループI)<4-MDBT, 3,6-DMDBTおよび未同定のC3-DBT類 (グループII)<2,3,4-トリメチルジベンゾチオフェン, および未同定のC3-DBT類 (グループIII)<2,8-DMDBT, および未同定のC1-DBT (グループIV)。これらの化合物の硫黄原子の非結合電子軌道 (Sσn軌道; 分子平面方向) は脱硫反応速度と良い相関を示した。また, このSσn軌道の電子密度は, 4,6-ジメチルジベンゾチオフェンのメチル基が4-位あるいは4,6-位から移動するに伴って増加した。分子軌道の解析から, アルキルジベンゾチオフェンの硫黄原子が触媒活性点に最接近する場合, 硫黄原子のSσn軌道の断面積は4,6-DMDBTの11A2から, 4-MDBTで20A2, DBTで42A2まで増加した。これらの知見から, 4,6-ジメチルジベンゾチオフェンの脱硫反応におけるゼオライトの役割は, メチル基を転位させて硫黄原子近傍の立体障害を解消し, 硫黄原子と触媒活性サイトとの接近を容易にするとともに, 硫黄原子の脱硫活性サイトへの配位を促進することであると結論した。

Epitaxial Growth of Diamond on an Iridium (100) Substrate by Microwave Plasma-Assisted Chemical Vapor Deposition

Abstract: Diamond films were grown heteroepitaxially on iridium (100) substrates by microwave plasma-assisted chemical vapor deposition (MPCVD) using methane gas as the carbon source. The iridium substrate, which was formed on a MgO (100) substrate by means of sputtering at 850 °C, was treated by imposing a negative bias between -150 and -200 V for 15 min. Methane concentration and substrate temperature were maintained at 3° and 650–740 °c, respectively. At a substrate temperature of 740 °C, diamond particles were formed at a population density of (0.15- 1.5)x108 cm-2, and most of them were oriented to MgO (100). After a further reaction for 1 h under conditions which were optimized for diamond growth, the oriented diamond particles were coalesced, and islands of (100) diamond were formed.