- Email: [email protected]
Permeability of ionic solutes in polyamphoteric membrane
i i! l g l IP'-'Ii(el -"• i :t :1 d I~ I Pore structure of silica membranes Porous silica membranes were formed by a sol-gel technique on a y-alumina-coated s-alumina tube using sols which were prepared from tetraethoxysilane (TEOS) and octyl-, dodecyl- or octadecyltriethoxysilane. The° alkyltriethoxysilanes were used as the template to control the pore size. The effect of the length of alkyl groups on pore structure, as well as the permeation prolierties of the silica membranes were then investigated. The molar ratio of water to total alkoxides in the sols, x, strongly influenced the pore structure. A silica membrane which was prepared with octadecyltriethoxysilane contained meso-pores and cracks, but silica membranes prepared with octyland dodecyl-triethoxysilanes were defect-free. Permeation by gases with a variety of molecular sizes showed that the majority of micropores were in the 0.3-0.4 nm range for the silica membranes which had been calcined at 600°C. These micro-pores were basically formed by the decomposition of alkyl chains in the templates, while the mesopore structure was achieved during the gelation step. K. Kusakabe, S. Sakamoto, T. Saie, S. Morooka: Separation , & Purification ~chnology 16(2~ 139-146 (12 July 1999).
loading of 1.36 g KCoFC/g SiO 2. All the composites prepared had a non-stoichiometric composition of KCoFC. The type of coating mechanism was established to be dominantly inhomogeneous or plug coating. The cesium uptake capacity of the silica base and some selected SiO2.KCoFC composites was determined. The capacity of the composite B8/p4 was found to be 0.38 meq Cs/g composite. The removal efficiency of Cs by the composite B8/p4 was judged by measuring its distribution coefficient, Kd (ml/g composite) from varying concentrations of HCI, H N O 3, NaCI and KCI solutions. The Ka of Cs for HC1 in the concentration range of 0.001-3 M lies between 7.5 x 104 and 5.8 x 104. However, in the case Of H N O 3, the Kd of Cs decreases when the concentration exceeds 0.1 M. For NaCl in the concentration range of 0.001-1 M, the Ka of Cs remains almost constant (3 x 104). However, it decreases in the 1-2 M range, and again attains a constant value of about 1.99 × 103 in the 2-3 M NaC1 concentration interval. While the Kd of Cs for 0.001-0.01 M KCI lies in the range 2-3 x 105, it decreases when the concentration exceeds 0.03 M and reaches a value of 2 x 103 in 3 M KCI solution. A. Mardan, R. Ajaz, A. Mehmood, S.M. Raza, A. Ghaffar: Separation & Purification Technology 16(2) 147-158 (12 July 1999).
Preparing composite ion excnangers The preparation of SiO 2 potassium cobalt hexacyanofer~ate (SiO2.KCoFC) composites with a high loading of KCoFC on porous silica is described. This method involves the soaking of silica to a wet state with a concentrated solution of K4Fe(CN) 6, drying and then reacting the dried material with a Co(NO312 solution prepared in acetone. The composites, B4 and B6 were prepared by single and multi-step deposition of K4Fe(CN) 6 respectively, followed by precipitation with the Co(NO3) 2 solution. The composites (B8/pl to B8/p4) were prepared by alternate deposition and precipitation steps. After fot~r such steps, the composite B8/p4 was obtained with the highest KCoFC
Separation of 1-hexene! n-hexane mixtures Previously reported techniques for the separation of gaseous olefins from paraffins by means of membrane contactors, and fluid olofins from paraffins by means of liquid extraction, have been extended to the separation of liquid olefin/paraffin mixtures b~ means of a hybrid membrane/extraction system. In this research paper, emphasis is placed on the development of a hybrid membrane contacting system for the separation of liquid olefin/paraffln mixtures in the range up to C 6. The membrane contacting system described comprises nonporous polymeric membranes and a high boiling-point selective liquid
extractant flowing along polymeric membranes between the extractor and the membrane stripper at various temperatures and flow rates. The olefin components permeated through the polymeric films at elevated temperatures in a membrane stripper, making it possible to effect pervaporation transport. Selectivities of 1hexene/n-hexane separations ranged from 40 to 70. The 1-hexene permeation rate achieved at 62°C was up to 14 × 10-6 g/scm 2. D.G. Bessarabov, J.P. Theron, R.D. Sanderson, H.-H. Schwarz, M. Schossig-Tiedemann, D. Paul:
Separation & Purification Technology 16(2) 167-174 (12 July 1999).
Permeability of ionic solutes in polyamphoteric membrane A polyamphoteric gel membrane with both amino and carboxyl groups was prepared from Nsuccinyl chitosan and poly(vinyl alcohol). The permeabilities of three kinds of solute with similar sizes and different charged conditions anionic benzenesulfonic acid, neutral styrene glycol and cationic theophylline through the polyamphoteric membrane were investigated under various pH conditions. The permeability of benzenesulfonic acid decreased with increasing pH. This behaviour can be explained by the change of the electrostatic interaction between the solute and the polyamphoteric membrane, brought about by the change of the membrane's charged condition. At pH 3.0 the benzenesulfonic acid showed a large permeability because of the attractive interaction with the cationic membrane, whereas theophylline showed a low value because of the repulsive interaction. Thus, an effective separation among the three solutes was achieved in spite of the similar sizes, which was in contrast to the result that almost the same permeabilities were obtained with a poly(vinyl alcohol) membrane based on only the size exclusion effect. At pH 11.0 the polyamphoteric membrane became anionic which led to the benzenesuifonic acid having the
lowest permeability among the three solutes. The partition coefficients were measured for the three solutes in various pH conditions. The tendency obtained was similar to that of the permeability. H. Matsuyama, T. Tamura, Y. Kitamura: Separation & Purification Technology 16(2) 181-187 (12 July 1999).
Modified concentration polarisation models An improvement of a previous study for estimating the permeate flux of hollow-fibre membrane dltrafiltration has been made. This was achieved by removing an unrealistic condition on the decline of permeate flux near the fibre outlet, and the requirement of estimating the solute diffusivity at a condition corresponding to that existing at the membrane surface. H.M. Yeh, T.W. Cheng, J.W. Tsai:
Separation & Purification Technology 16(2) 189-192 (12 July 1999).
lrechnol Next
month News
Industry trends Commercial news New product releases • Contracts
Features Developments and applications around the world
Research Trends Latest membrane research
Patents World, US and European membrane patents
NetScope The best membrane sites reviewed
MembraneTechnologyNo. 113
loading of 1.36 g KCoFC/g SiO 2. All the composites prepared had a non-stoichiometric composition of KCoFC. The type of coating mechanism was established to be dominantly inhomogeneous or plug coating. The cesium uptake capacity of the silica base and some selected SiO2.KCoFC composites was determined. The capacity of the composite B8/p4 was found to be 0.38 meq Cs/g composite. The removal efficiency of Cs by the composite B8/p4 was judged by measuring its distribution coefficient, Kd (ml/g composite) from varying concentrations of HCI, H N O 3, NaCI and KCI solutions. The Ka of Cs for HC1 in the concentration range of 0.001-3 M lies between 7.5 x 104 and 5.8 x 104. However, in the case Of H N O 3, the Kd of Cs decreases when the concentration exceeds 0.1 M. For NaCl in the concentration range of 0.001-1 M, the Ka of Cs remains almost constant (3 x 104). However, it decreases in the 1-2 M range, and again attains a constant value of about 1.99 × 103 in the 2-3 M NaC1 concentration interval. While the Kd of Cs for 0.001-0.01 M KCI lies in the range 2-3 x 105, it decreases when the concentration exceeds 0.03 M and reaches a value of 2 x 103 in 3 M KCI solution. A. Mardan, R. Ajaz, A. Mehmood, S.M. Raza, A. Ghaffar: Separation & Purification Technology 16(2) 147-158 (12 July 1999).
Preparing composite ion excnangers The preparation of SiO 2 potassium cobalt hexacyanofer~ate (SiO2.KCoFC) composites with a high loading of KCoFC on porous silica is described. This method involves the soaking of silica to a wet state with a concentrated solution of K4Fe(CN) 6, drying and then reacting the dried material with a Co(NO312 solution prepared in acetone. The composites, B4 and B6 were prepared by single and multi-step deposition of K4Fe(CN) 6 respectively, followed by precipitation with the Co(NO3) 2 solution. The composites (B8/pl to B8/p4) were prepared by alternate deposition and precipitation steps. After fot~r such steps, the composite B8/p4 was obtained with the highest KCoFC
Separation of 1-hexene! n-hexane mixtures Previously reported techniques for the separation of gaseous olefins from paraffins by means of membrane contactors, and fluid olofins from paraffins by means of liquid extraction, have been extended to the separation of liquid olefin/paraffin mixtures b~ means of a hybrid membrane/extraction system. In this research paper, emphasis is placed on the development of a hybrid membrane contacting system for the separation of liquid olefin/paraffln mixtures in the range up to C 6. The membrane contacting system described comprises nonporous polymeric membranes and a high boiling-point selective liquid
extractant flowing along polymeric membranes between the extractor and the membrane stripper at various temperatures and flow rates. The olefin components permeated through the polymeric films at elevated temperatures in a membrane stripper, making it possible to effect pervaporation transport. Selectivities of 1hexene/n-hexane separations ranged from 40 to 70. The 1-hexene permeation rate achieved at 62°C was up to 14 × 10-6 g/scm 2. D.G. Bessarabov, J.P. Theron, R.D. Sanderson, H.-H. Schwarz, M. Schossig-Tiedemann, D. Paul:
Separation & Purification Technology 16(2) 167-174 (12 July 1999).
Permeability of ionic solutes in polyamphoteric membrane A polyamphoteric gel membrane with both amino and carboxyl groups was prepared from Nsuccinyl chitosan and poly(vinyl alcohol). The permeabilities of three kinds of solute with similar sizes and different charged conditions anionic benzenesulfonic acid, neutral styrene glycol and cationic theophylline through the polyamphoteric membrane were investigated under various pH conditions. The permeability of benzenesulfonic acid decreased with increasing pH. This behaviour can be explained by the change of the electrostatic interaction between the solute and the polyamphoteric membrane, brought about by the change of the membrane's charged condition. At pH 3.0 the benzenesulfonic acid showed a large permeability because of the attractive interaction with the cationic membrane, whereas theophylline showed a low value because of the repulsive interaction. Thus, an effective separation among the three solutes was achieved in spite of the similar sizes, which was in contrast to the result that almost the same permeabilities were obtained with a poly(vinyl alcohol) membrane based on only the size exclusion effect. At pH 11.0 the polyamphoteric membrane became anionic which led to the benzenesuifonic acid having the
lowest permeability among the three solutes. The partition coefficients were measured for the three solutes in various pH conditions. The tendency obtained was similar to that of the permeability. H. Matsuyama, T. Tamura, Y. Kitamura: Separation & Purification Technology 16(2) 181-187 (12 July 1999).
Modified concentration polarisation models An improvement of a previous study for estimating the permeate flux of hollow-fibre membrane dltrafiltration has been made. This was achieved by removing an unrealistic condition on the decline of permeate flux near the fibre outlet, and the requirement of estimating the solute diffusivity at a condition corresponding to that existing at the membrane surface. H.M. Yeh, T.W. Cheng, J.W. Tsai:
Separation & Purification Technology 16(2) 189-192 (12 July 1999).
lrechnol Next
month News
Industry trends Commercial news New product releases • Contracts
Features Developments and applications around the world
Research Trends Latest membrane research
Patents World, US and European membrane patents
NetScope The best membrane sites reviewed
MembraneTechnologyNo. 113