Gas permeation performance of cellulose hollow fiber membranes made from the cellulose/N-methylmorpholine-N-oxide/H2O system

Cellulose hollow fiber membranes (CHFM) were prepared using a spinning solution containing N-methylmorpholine-N-oxide as solvent and water as a nonsolvent additive. Water was also used as both the internal and external coagulant. It was demonstrated that the phase separation mechanism of this system was delayed demixing. The CHFM was revealed to be homogeneously dense structure after desiccation. The gas permeation properties of CO2, N-2, CH4, and H-2 through CHFM were investigated as a function of membrane water content and operation pressure. The water content of CHFM had crucial influence on gas permeation performance, and the permeation rates of all gases increased sharply with the increase of membrane water content. The permeation rate of CO2 increased with the increase of operation pressure, which has no significant effect on N-2, H-2, and CH4. At the end of this article a detailed comparison of gas permeation performance and mechanism between the CHFM and cellulose acetate flat membrane was given. (C) 2003 Wiley Periodicals, Inc.

Synthesis, properties, and gas permeation performance of cardo poly(arylene ether sulfone)s containing phthalimide side groups

Novel bisphenol monomers (1a-d) containing phthalimide groups were synthesized by the reaction of phenolphthalein with ammonia, methylamine, aniline, and 4-tert-butylanilne, respectively. A series of cardo poly (arylene ether sulfone)s was synthesized via aromatic nucleophilic substitution of 1a-d with dichlorodiphenylsulfone, and characterized in terms of thermal, mechanical and gas transport properties to H-2, O-2, N-2, and CO2. The polymers showed high glass transition temperature in the range 230-296 degrees C, good solubility in polar solvents as well as excellent thermal stability with 5% weight loss above 410 degrees C. The most permeable membrane studied showed permeability coefficients of 1.78 barrers to O-2 and 13.80 barrers to CO2, with ideal selectivity. factors of 4.24 for O-2/N-2 pair and 28.75 for CO2/CH4 pair. Furthermore, the structure-property relationship among these cardo poly(arylene ether sulfone)s had been discussed on solubility, thermal stability, mechanical, and gas permeation properties. The results indicated that introducing 4-tert-butylphenyl group improved the gas permeability of polymers evidently.

Relationship between structure and gas permeation properties of polyimides prepared from oxydiphthalic dianhydride

Gas permeability coefficients of a series of aromatic polyimides, which were prepared from oxydiphthalic dianhydride (ODPA) with various aromatic diamines, with respect to H-2, CO2, O-2, N-2, and CH4 were measured under 10 atm and in the temperature range from 30 to 150 degrees C. A significant change in gas permeability and permselectivity resulting from systematic variation of the chemical structure of the polyimides was found. Among the polyimides which were prepared from phenylenediamine and its derivatives as well as bridged diamines without side groups on the benzene rings of the diamine residues, the increase of the gas permeability is accompanied by a decrease of the permselectivity. However, both the gas permeability and the permselectivity of the polyimides which were prepared from bridged diamines with methyl or methoxy groups on the benzene rings of the diamine residues simultaneously increase.

Gas permeation properties of copolyimides from 1,4-bis(3,4-dicarboxyphenoxy)benzene dianhydride and 2,2-bis(3,4-dicarboxyphenyl)hexafluoroisopropane dianhydride

A series of aromatic copolyimides was prepared from 1,4-bis(3,4-dicarboxyphenoxy)benzene dianhydride (HQDPA) and 2,2-bis(3,4-dicarboxyphenyl)hexafluoroisopropane dianhydride (6FDA) with 3,3'-dimethyl-4,4'-methylene dianiline (DMMDA) by a chemical imidization. The gas permeability coefficients of the copolyimides to H-2, CO2, O-2, N-2 and CH4 were measured under 7 atm. pressure. The fractional free volume of 6FDA-DMMDA is larger than that of HQDPA-DMMDA, while the chain segmental mobility of 6FDA-DMMDA is lower than that of HQDPA-DMMDA. The gas permeability of 6FDA-DMMDA is much higher than that of HQDPA-DMMDA but the permselectivity of 6FDA-DMMDA for H-2, CO2, O-2, N-2 over CH4 is lower than that of HQDPA-DMMDA. The experimental values of the gas permeability coefficients of the copolyimides are in satisfactory agreement with the values estimated from the gas permeability coefficients of the constituent homopolyimides and their weight fractions.

Gas permeation properties of cardo polyaryletherketones containing different alkyl substituents

The gas permeation properties of a series of cardo polyaryletherketone materials are reported, In this series, the hydrogen atoms of benzene rings on the backbone are systematically replaced with different alkyl substituents. The effects of temperature and structure variation on gas permeability and selectivity are discussed in detail. The experimental results revealed that the polyetherketone obtained by the introduction of dimethyl and diisopropyl substituents to phenolphthalein unit is 3 similar to 6 times more permeable than the unmodified one for the gases studied.

An industrial scale dehydration process for natural gas involving membranes

An industrial scale dehydration process based on hollow fiber membranes for lowering the dew point of natural gas is described in this paper. A pilot test with the feed flux scale of 12x10(4) Nm(3)/d was carried out. Dew points of -8 degreesC-13 degreesC at a gas transport pressure in the pipeline of 4.6M Pa and methane recovery of more than 98% were attained. The water vapor content of the product gas could be maintained around 0.01 vol% during a continuous run of about 700 hours. The effects of feed flux and operation pressure on methane recovery and water vapor content were also investigated. Additionally, some auxiliary technologies, such as a full-time engine using natural gas as fuel and the utilization of vent gas in the process, are also discussed. A small amount of the vent gas from the system was used as a fuel for an engine to drive vacuum pumps, and the heat expelled from the engine was used to warm up the natural gas feed. The whole system can be operated in a self-sustainable manner from an energy point of view, and has a relatively high efficiency in the utilization of natural gas.

Synthesis and gas permeation properties of an NaA zeolite membrane

A high quality NaA zeolite membrane, which shows a H-2/n-C4H10 permselectivity of 106, has been synthesized on a seeded alpha-Al2O3 support by a multistage synthesis method.