Haruhiko Ohya

Research of Polyimide Asymmetric Membrane For Gas Separation. II. The effect of evaporation period.

The effect of the N-dimethylacetamide (DMA) evaporation period during the casting process on the selectivity and permeability of asymmetric polyimide (PMDA-4, 4-ODA) membrane was investigated. The separation factor for a gaseous mixture of H2 and N2 with a concentration ratio of 50 : 50 at a operating temperature of 373 °K and a trans membrane pressure difference of 1.2 MPa, was 1.5 at 1-2 minutes and increased to 15 at 3 minutes. It assumed a maximum value of 21 at 4 minutes and decreased again to 1.5 after 5 minutes. With an increase of evaporation periods, the permeability decreased from 1.5×10-9 mol/ (m2·s·Pa) and assumed a minimum value of 7×10-11 mol/ (m2·s·Pa) at 3 minutesand then increased again to 5 × 10-10 mol/ (m22·s·Pa) at 4 minutes and 1.5 × 10-9 mol/ (m2·s·Pa) after 5 minutes.The permeabilities of H2, N2, CH4, Ar, CO2, CH3OH, C2H5OH, H2O, toluene and n-nonane were measured and with the exception of H2, found to be proportional to the boiling point temperatures at atmospheric pressure.

Reverse osmotic concentration of aqueous solution of low molecular weight organic solutes. Part II: Low pressure RO membranes.

Using four types of low pressure reverse osmosis membranes (NS-300, NS-301, NTR-7450, NTR-729 HF), reverse osmosis concentration of eight kinds of aliphatic acids in aqueous solution were carried out. The effect of ratio of trimesoyl chloride and isophthaloyl chloride on membrane performance have been investigated in the fabrication of NS-301 membrane.

The effect of the operating temperature on the reverse osmotic permeation flux and solute rejection.

Using three composite membranes (NS-300, NTR-7450, NTR-729 HF), reverse osmotic permeation flux and solute rejection have been measured at 1.5 MPa, 10-60° C for pure water, 0.5% NaCl and 0.5% MgSO4 aqueous solution. The results showed that the permeation remarkably increases, but rejection Ra slowly decreases, with the increase of operating temperature.The relationship between hydraulic permeability Lp and operating temperature in reverse osmotic separation have been theoretically derived using the solution-diffusion model. Introducing the temperature coefficient M defined by authors, the dependency of permeation on operating temperature can be expressed as following theoretical equation, lnLp (T) =lnLp (T) +Mln T/T0-Ps [Vs (T) /T-Vs (T0) /T0] (16) The dependence of rejection on temperature can be expressed as following experimental equation. Ra (T) =Ra (T0) (1+M/100) (T0/T-1) (19)

Materials for porous hollow fiber to support liquid membrane and its lifetime.

The permeation experiments of Cu2+ were carried out through liquid membranes supported on four kinds of porous hollow fibers, which contained LIX-65N of concentration ; 0.047-0.094, 1.6, 15-16 [mol/m3] as mobile carrier and kerosine and O-xylene of volumeric composition ratio ; 100/0, 75/25, 25/75, 0/100 [vol%/vol%] as diluent. The hydrophobic membranes were better for supporter than the hydrophilic. The richer the O-xylene was contained as diluent, the more remarkably the destruction of membranes occurred. By means of saturating both feed and recovery solutions with liquid membrane solution, the flux of Cu2+ through membrane was stabilized more than 50 days. It was found that the interfacial reaction between Cu2+ and LIX-65N on the membrane facing feed solution was rate determining step. The flux of Cu2+ through membrane was proportional to the first power of [HR] f, (concentration of mobile carrier in membrane on feed solution side), in region of [HR] f, greater than 0.1 [mol/m3] and the second power of [HR] f, less than 0.1 [mol/m3].

Asymmetric polyethersulforne membranes for gas saparations.

The asymmetic polyethersulfone (PES) membranes for gas separation were made by ordinary phase inversion method from casting solutions of PES (Supplied from Sumitomo Chemical, 200P) in dimethyle formamide (DMF). The membranes were vacuum dried at 0°C after being soaked in a mixture of 50 vol% ethylalcohol and 50 vol% isopropylalcohol. The dried membranes were characterized by permeabilities of pure gas (He, N2, CH4, CO2) and mixed gas (CO2 : CH4=1 : 1), and separation factor of mixed gas. Permeability decreases with the increase of casting temperature, evaporation time and PES concentration. Separation factor of gaseous mixture of CO2 and CH4 increases with the increase of PES concentration, with the increase of casting temperature, passing through maximum at 90°C, and with the increase of evaporation time, passing through maximum at 5 min.Membrane surface treatment by DMF using spin coater at 4000 r.p.m. did not increase separation factor and decrease permeability by 1/20-1/6000. Membrane surface treament by silicone using spin coater at 4000 r.p.m. decreased permeability by 1/3-1/200, but increased separation factor from 1.0 to 3-6, and in one case from 4 to 12.

Mass transfer of CO2 and O2 gas in chlorella suspension through hydrophobic microporous hollow fiber membrane.

The absorption of CO2 and O2 gas into the chlorella suspension and the stripping of O2 gas generated by photosynthesis of chlorella through the hydrophobic microporous hollow fiber membrane of polypropylene took place. The chlorella suspension flowed inside the hollow fibers and the gas mixture of CO2 and air flowed outside them. The following results were obtained :(1) Overall mass transfer coefficient of CO2 and O2 gas for absorption did not depend on the flow rate of gas mixture, the total pressure of gas mixture, the CO2 concentration of gas mixture and the chlorella concentration, but only on the flow rate of suspension, (2) Overall mass transfer coefficient was correlated by the dimensionless equation given below, Sh=A (Pe) 1/3The value of A in equation was smaller than that obtained in the previous papers using the similar type of membrane module. This difference in A was explained by the apparant decrease in interfacial area of membrane per unit volume of suspension due to the dence packing of hollow fibers per unit cross-sectional area of shell in our module as compared with the others, and(3) The supply of CO2 gas and the stripping of O2 gas generated by photosynthesis could be taken place at the same time through the one membrane module.

Gas permeability of the low temperature heat treated dried reverse osmosis cellulose acetate membrane.

Dried membranes heat treated at lower temperature less than 80°C did not virtually permeate gases when vacuum dried at room temperature but membranes dried at -25°C shows good permeability and did not shows good separation of CO2-CH4 gaseous mixture.90°C heat treated membrane dried at -25°C shows ca. 5 times larger permeability than that dried at room temperature and both membranes show almost the same separation factor for CO2CH4 gaseous mixture.70°C heat treated membrane dried at -25°C shows hysteresis phenomenon on the relation between permeation flux and pressure difference.