Asumaru Nakamura

Dimethyl carbonate synthesis and other oxidative reactions using alkyl nitrites

The oxidative reactions using the alkyl nitrites (RONO) as an oxidant have been developed by Ube Industries, Ltd. In the alkyl nitrite reactions, substrates such as CO andyor unsaturated- andyor carbonyl-compounds are oxidized over the palladium catalysts in no direct contact with molecular oxygen. The dimethyl carbonate (DMC), dialkyl oxalates and other useful chemicals are synthesized efficiently under moderate conditions by the alkyl nitrite reactions.

Vapor permeation and pervaporation separation of water-ethanol mixtures through polyimide membranes

Abstract Vapor permeation (VP) and pervaporation (PV) separation of water-ethanol mixtures were investigated for a series of polyimide membranes. Membrane performance for PV was described by both the permeability coefficient of water, P W , which was caluclated using the equilibrium partial pressure as the driving force, and the separation factor at the membrane separation step, α mem . For PV, the dependence of P W and α mem on feed composition (wt.% of ethanol, x E ) was rather small. For VP, with a decrease in x E , P W increased and α VP decreased. P W was larger for PV than for VP, while α mem was smaller for PV. The differences between PV and VP were larger for BPDA-DDBT and BPDA-ODA/DABA (4/6) polyimides having a higher total sorption in the liquid phase, but were small for Kapton-H and BPDA-ODA/DABA (8/2) polyimide having a lower sorption. In the case of the former polymers, the swelling effect was no large for PV that it spoiled membrane performance seriously, whereas it was not so large for VP.

Gas permeability and permselectivity in polyimides based on 3,3',4,4'-biphenyltetracarboxylic dianhydride

Abstract Permeation rates of hydrogen, carbon monoxide, carbon dioxide and methane were measured for amorphous films of a series of polyimides prepared from 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA) and each of the following diamines: 4,4′-oxydianiline (ODA), 4,4′-methylenedianiline (MDA), 4,4′-diaminodiphenyl sulfone (DDS), and dimethyl-3,7-diaminodibenzothiophene 5,5′-dioxide (DDBT). The permeability coefficients ( P ) at 10 atm and 50°C were in the order BPDA-DDBT > BPDA-DDS ≥ BPDA-MDA > BPDA-ODA. On going from BPDA-ODA to BPDA-DDBT, P increased by 6.0- and 9.4-fold for hydrogen and carbon dioxide, respectively. This was due to 1.4- and 3.2-fold increases in the diffusion coefficients accompanied by appreciable decreases in activation energies, and also to a 3.7-fold increase in the solubility coefficients. These results suggest that both high rigidity and bulkiness of a polymer backbone may prevent efficient chain packing and result in a more open structure for gas transport. BPDA-DDBT displayed high permselectivities for hydrogen/methane and carbon dioxide/methane in addition to high permeability coefficients, and has a high potential for use as a membrane material for gas separation.

Gas permeability and permselectivity in homo- and copolyimides from 3,3',4,4'-biphenyltetracarboxylic dianhydride and 3,3'- and 4,4'-diaminodiphenylsulfones.

The gas transport properties of homo- and copolyimides prepared from 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA) and 3,3′- and 4,4′-diaminodiphenylsulfones (m-DDS and p-DDS, respectively) are investigated. With increasing fraction of m-DDS, the density of the polyimide films increased by 1.1% and the glass transition temperature decreased by 70 K. With increasing fraction of m-DDS, permeability coefficients P of H2 and CO2 in the film decreased to 1/3 and 1/15, while P ratios of H2 to CO and CO2 to CH4 increased by 4.1 and 1.8 times, respectively, as a result of decrease in the diffusion coefficient and increase in diffusivity selectivity. These observations are interpreted in terms of changes in free volume fraction, distribution of size of free volume, and segmental mobility.

Catalysis and characterization of Pd/NaY for dimethyl carbonate synthesis from methyl nitrite and CO

A vapor phase synthesis of dimethyl carbonate (DMC) from carbon monoxide and methyl nitrite (MN) has been carried out over Pd/NaY catalysts at 383 K, DMC was produced in a good yield. The selectivity to DMC was >85% on the basis of consumed CO or MN. The by-products were dimethyl oxalate, CO2, N2O, methyl formate and dimethoxymethane. The catalytic properties of Pd/NaY were investigated as a function of Pd content and calcination temperature. It was found that 1 wt.% Pd/NaY calcined at 473 K in air was the optimum catalyst for the present DMC synthesis. The oxidation state and dispersion of Pd in the Pd/NaY catalysts were characterized by EXAFS and XPS. It was revealed that Pd(NH3)42+ in 1 wt.% Pd/NaY changed into Pd metal clusters during the catalytic reaction. Pd metal clusters/NaY showed a stable activity for the DMC synthesis even after 700 h. These results suggest that the cage structure of NaY and anchoring effects of protons suppress Pd metal sintering and stabilize very small Pd metal clusters (Pd13) in the zeolite cages during the reaction.

Sorption and transport of carbon dioxide in a polyimide from 3,3′,4,4′-biphenyltetracarboxylic dianhydride and dimethyl-3,7-diaminodibenzothiophene-5,5′-dioxide

Abstract Polyimide prepared from 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA) and dimethyl-3,7-diaminodibenzothiophene-5,5′-dioxide (DDBT) displayed CO2 plasticization effects on sorption and transport of CO2, in spite of its very rigid polymer backbone. Slow components of solubility and permeability coefficients (S and P) were observed which were attributed to the relaxation of the polymer chain caused by dissolved CO2 at a higher pressure. Increasing P with increasing feed pressure was represented by the extended dual-mode transport model taking into account the concentration dependence of the diffusion coefficient.

A new oxidation system using nitrite oxidants

The oxidative reactions using alkyl nitrites (RONO) as oxidant have been developed by Ube Industries, Ltd. The substrates such as CO and/or unsaturated-and/or carbonyl-compounds are oxidized by RONO over the palladium catalyst with no contact of molecular oxygen. Dialkyl carbonates, dialkyl oxalates and other useful chemicals are synthesized efficiently under moderate conditions by this alkyl nitrite technology.