Daniel Vincent Laciak

Polyelectrolyte membranes for acid gas separations

Abstract New facilitated transport membranes have been synthesized and shown to selectively permeate carbon dioxide and hydrogen sulfide from methane and hydrogen. The membranes are based on the polyelectrolyte poly(vinylbenzyltrimethyl-ammonium fluoride), PVBTAF, and exhibit exceptional permselective properties. For example, at 23°C and 32 cmHg CO 2 , a PVBTAF composite membrane displayed a CO 2 permeance of 6×10 −6 cm 3 /cm 2 s cmHg and CO 2 /H 2 and CO 2 /CH 4 selectivities of 87 and 1000, respectively. The CO 2 /H 2 selectivity is the highest reported for any membrane. The permeance of both CO 2 and H 2 S increased with decreasing feed partial pressure of the respective gases, a characteristic of facilitated transport membranes. The permselectivity is also dependent on the hydration state of the membrane and is optimal at a gas stream relative humidity in the range 0.25−0.50. The membranes show no deterioration after 30 days of continuous operation but react with trace level sulfur-containing contaminants common to cylinder H 2 S.

Polyelectrolyte-salt blend membranes for acid gas separations

Abstract The CO 2 CH 4 and CO 2 H 2 permselectivity of poly(vinylbenzyltrimethylammonium fluoride), PVBTAF, polyelectrolyte membranes can be significantly improved by blending in certain fluoride-containing organic and inorganic salts. For example, the CO 2 permeance of a PVBTAF-4CsF (4 mol CsF/mol repeat unit) composite membrane was more than four times that of a simple PVBTAF composite membrane while CO 2 CH 4 and CO 2 H 2 selectivities were comparable. Surprisingly, the blends are at least macroscopically homogeneous even with as much a 6 mol salt/mol PVBTAF repeat unit. The optimal salt loading appears to be approximately 4 mol CsF/mol polyelectrolyte repeat unit. Membrane performance is strongly dependent on the relative humidity of the gas streams and is maximized in the range of 30–50% relative humidity. Membranes containing choline fluoride exhibited improved membrane performance at relative humidities below 30%. Permselective data suggests that CO 2 transport is kinetically limited in 10 μm thick films. The blends are stable in CO 2 /CH 4 /H 2 streams for more than 30 days of continuous operation, however, the membranes suffer an irreversible degradation due to reaction with trace level sulfur-containing contaminants common to cylinder H 2 S.

Selective Permeation of Ammonia and Carbon Dioxide by Novel Membranes

Abstract Experimental results are presented on membranes of novel composition which selectively permeate ammonia and carbon dioxide from mixtures containing hydrogen. The CO2-selective membrane, which consists of a thin liquid film of the salt hydrate tetramethylammonium fluoride tetrahydrate, exhibits a CO2 permeance of 4-1 × 10−5 cm3/cm2·s·cmHg with selectivity, α(CO2/H2), ranging from 360-30. The NH3-selective membrane, poly(vinylammonium thiocyanate), displays a high NH3 permeance, 5−20 × 10−5 cm3/cm2·s·cmHg, with α(NH3/N2) as high as 3600 and α(NH3/H2) as high as 6000. Such membranes, which retain H2 at pressure in the feed stream, may offer new opportunities in the design of separation processes.

Molten salt facilitated transport membranes. Part 2. Separation of ammonia from nitrogen and hydrogen at high temperatures

Abstract Immobilized molten salt (IMS) membranes have been prepared and shown to be effective for the separation of NH3 from mixtures with N2 and H2 at the high temperature encountered in the recycle loop of ammonia synthesis plants. The membranes were prepared by immobilizing molten LiNO3 and ZnCl2, salts which react reversibly with NH3 but not with N2 or H2, in thin porous supports. Ammonia permeabilities of 103 to 105 barrer and NH3/N2 and NH3/H2 selectivities of at least 1000 were observed at 250–300°C. The extraordinary NH3 permeability through the ZnCl2 IMS membrane is explained by a carrier-mediated facilitated transport model wherein zinc ammoniate complexes function as mobile carriers.

Synthesis and gas transport properties of random amide imide copolymers

Fully imidized random amide imide copolymers (rPAI) can be prepared in an aprotic solvent from trimellitic anhydride chloride (TMAc) and mixtures of various aromatic diamines via condensation polymerization. The polymers are soluble in a number of aprotic organic solvents including 1-methyl-2-pyrrolidinone (NMP), N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), and dimethylsulfoxide (DMSO). The gas transport properties of the rPAI materials are governed by the local structure around both the amide and imide linkages and can be tuned by the choice and ratio of diamines used. Significant improvement in selectivity relative to polyimides can be achieved. When inorganic carbonate salts are used to scavenge byproduct hydrogen chloride, the amount of residual salt in the dense films has a substantial effect on their gas transport properties. A fugitive salt process was identified, which eliminated this problem of residual inorganic salts. The activation energy for O2, N2, He, CO2, and CH4 permeability was determined for one of the copolymers.