Porous Cellulose Acetate Membranes Research Articles

Reverse osmosis separation of single and mixed alcohols in aqueous solutions using porous cellulose acetate membranes

Reverse osmosis transport for alcohol-water systems in the Taft number (σ*) region of 0 to −0.3 is explored in detail. The numerical value of the polar functional constant for alcohols is 15.5 for the above σ* region in the operating pressure range of 50 to 500 psig for the cellulose acetate membrane material used. An analysis of the combined effect of operating pressure and mass transfer coefficient on the high-pressure side of the membrane shows that, under certain conditions, solute separation could pass through a maximum with increase in operating pressure. A general experession for solute separation is derived as a function of pore structure on membrane surface, polarity of solute, and operating conditions of the experiment. Alcohols behave independently in mixed solute systems. A method is described and illustrated for predicting alcohol separation in alcohol–sucrose–water feed solutions from data on single solute systems.

Reverse osmosis separation of organic acids in aqueous solutions using porous cellulose acetate membranes

AbstractReverse osmosis data obtained using porous cellulose acetate membranes and aqueous feed solutions involving one of 22 monocarboxylic acids, seven dicarboxylic acids, and four hydroxycarboxylic acids have been analyzed. The operating pressure used was 250 psig in all cases, and the solute concentration used was ∼100 ppm in most cases. The results yield the following physicochemical criteria for preferential sorption at the membrane–solution interface with respect to the un‐ionized acid. At pKa = 4.2 (for monocarboxylic acids), or Taft number (σ*) = 0.6 or Hammett number (σ) = 0, neither the un‐ionized acid nor water is preferentially sorbed at the membrane–solution interface; at pKa < 4.2 (for monocarboxylic acids) or σ* > 0.6 or σ > 0, the un‐ionized acid is preferentially sorbed at the membrane–solution interface. For practical purposes, preferential sorption of water at the membrane–solution interface may be considered negligible in the σ* region of 0 to 0.6. The results also show that the criterion of acidity of the molecule governing the extent of its repulsion or attraction at the membrane–solution interface is valid for both ionized and un‐ionized acid. Further, when the acid molecule contains three or more straight‐chain carbon atoms not associated with a COOH group, the nonpolar character of the molecule also affects its separation in reverse osmosis.

Physicochemical criteria for reverse osmosis separation of monohydric and polyhydric alcohols in aqueous solutions using porous cellulose acetate membranes

Reverse osmosis data using different samples of Loeb-Sourirajan-type porous cellulose acetate membranes and single-solute aqueous solution systems involving 16 monohydric alcohols, 4 phenols, 18 polyhydric alcohols, pyrogallol, ethylene glycol monoethyl ether, 6 aldehydes, and 8 carbohydrates (sugars) have been studied. The solute concentrations used were in the range of 0.0005 to 0.003 g mole/l. (∼100 ppm), and operating pressure used was 250 psig in all cases. The results show that correlations of acidity and basicity parameters (obtained from IR spectra) with solute separation data are equivalent, and they have predictive capability. A method is given for estimating Taft numbers (Σσ*) for monohydric and polyhydric alcohols from available data based on the additive nature of σ*. Data on solute transport parameters (DAM/Kδ) for the different solutes were calculated from membrane performance data. For all the alcohols studied, the Σσ*-versus-log (DAM/K)δ correlation was found to be a straight line with a slope different for different ranges of Σσ*, but independent of the porous structure of the membrane. Based on this result, it is shown that the parameters of the Taft equation can serve as a basis for expressing solute transport parameter, and this basis offers a means for predicting membrane performance for all alcohol–water systems from a single set of experimental data for a reference solute system. This prediction technique is illustrated using experimental data for 1,3-butanediol taken as the reference solute. The general applicability of the technique has been tested for predicting the separation of some aldehydes and carbohydrates.

Reverse osmosis separation of phenols in aqueous solutions using porous cellulose acetate membranes

AbstractReverse osmosis separations of phenol (9.4 to 108 ppm), p‐cresol (108 ppm), and p‐chlorophenol (129 ppm) were studied using Loeb‐Sourirajan‐type porous cellulose acetate membranes, and single‐solute aqueous feed solutions at 500 psig and the indicated solute concentrations. It was found that, by dissociating the solute by changing the pH of the feed solution, all the above phenols could be separated by reverse osmosis. Solute separation increased with increase in the degree of dissociation of the solute in the feed solution; and, by the appropriate choice of pore size on the membrane surface, separations of phenol approaching the degree of dissociation of phenol in the feed solution could be obtained under the operating conditions used. Similar experiments using aniline (93 ppm) as the solute showed that dissociation of solute molecules in the feed solution could be a technique generally applicable for the reverse osmosis separation of nonionic solutes in aqueous solution. The effects of operating pressure in the range 250 to 1500 psig and pore size on the membrane surface on the separation of un‐ionized phenol and p‐chlorophenol showed that, with respect to single‐solute aqueous feed solutions of phenols, the component whose relative acidity was greater was preferentially sorbed at the cellulose acetate membrane—aqueous solution interface, and the solute concentration in the membrane‐permeated product solution was a function of the extent and mobility of each of the sorbed species.

Studies on reverse osmosis for water pollution control

Reverse osmosis separations of sodium ortho- and polyphosphates, lecithin, ethyl phosphate, sodium nitrite, nitrate, chloride, fluoride and sulfate, ammonium chloride, glutamic acid, and phenyl mercuric acetate and benzoate in aqueous solutions at solute concentrations less than 2000 ppm were studied using improved porous cellulose acetate membranes at 250 psig. Solute separations were essentially independent of feed concentration under the test conditions used. With a film preshrunk at 82°C, the solute separations for sodium phosphates, NaNO3, NaNO2, NH4Cl, glutamic acid, NaCl, NaF, and Na2SO4 were 99.6, 91.2, 91.6, 95.3, 99.1, 96.2, 96.6 and 99.2 percent respectively, and the average membrane flux was 14.4gpd ft−2; with a film shrunk at 75°C, the separations for the above solutes were 99.4, 81.5, 83.0, 87.3, 98.6, 89.7, 94.4, and 98.9 per cent respectively, and the average membrane flux was 30.6 gpd ft−2. The separations obtained for lecithin were > 99 per cent, and those for the others were lower.

Physicochemical criteria for reverse osmosis separation of aldehydes, ketones, ethers, esters, and amines in aqueous solutions using porous cellulose acetate membranes

Reverse osmosis separation of 62 different proton acceptor compounds (bases) including 7 aldehydes, 8 ketones, 12 ethers, 11 esters, and 24 amines in aqueous solutions in the concentration range 0.00075 to 0.003 g mole/l. (∼100 ppm in most cases) have been studied using porous cellulose acetate membranes at 250 psig. All reverse osmosis data are for single solute systems. Solute separation data for aldehydes, ketones, ethers, and esters are correlated with Δvs (basicity) (shift in the OD band maximum in the IR spectra of CH3OD in benzene and other solvents used as solutes in reverse osmosis experiments), and those for the amines are correlated with dissociation constant (given as pKa) and the degree of dissociation of the molecule. Solute separation increases with increase in Δvs (basicity) for aldehydes, ketones, ethers, and esters and with increase in degree of dissociation for amines. The separation data and the basicity parameters for the above classes of compounds are also correlated with Taft numbers. The results are consistent with those reported earlier for alcohols, phenols, and monocarboxylic acids in aqueous solutions and show that data on Δvs (basicity), pKa, and Taft numbers are valid physicochemical criteria governing reverse osmosis separation of aldehydes, ketones, ethers, esters, and amines.

Physicochemical criteria for reverse osmosis separation of alcohols, phenols, and monocarboxylic acid in aqueous solutions using porous cellulose acetate membranes

AbstractReverse osmosis data of 32 different alcohols and phenols and 22 different monocarboxylic acids in aqueous solutions in the concentration range 0.0001 to 0.007M (∼100 ppm in most cases) have been studied using porous cellulose acetate membranes at 250 psig. Solute separation data for alcohols and phenols are correlated with Δνs (shift in the OH band maximum in the IR spectra), and those for the monocarboxylic acids are correlated with Ka (dissociation constant) and the degree of dissociation of the molecule. Solute separation decreases with increase in Δνs for alcohols and phenols. The solute separation‐versus‐Ka correlation for acids passes through a minimum, and solute separation always increases with increase in the degree of dissociation. The separation data are also correlated with Taft and Hammett numbers which represent the effect of the substituent group on the polar effect of the molecule. The product rate data show a general tendency to decrease with decrease in solute separation in all cases. These results show that, with respect to the systems considered, solute separation in reverse osmosis is governed by the hydrogen bonding ability of the organic molecule when it is essentially undissociated and by electrostatic repulsion of ions when the molecule is partially or completely dissociated. Thus, data on Δνs for alcohols and phenols, and those on Ka and degree of dissociation for monocarboxylic acids, constitute precise physicochemical criteria for reverse osmosis separation of the above solutes in aqueous solutions using porous cellulose acetate membranes.

Reverse Osmosis Separation of Some Organic Solutes in Aqueous Solution Using Porous Cellulose Acetate Membranes

Reverse Osmosis Separation of Some Organic Solutes in Aqueous Solution Using Porous Cellulose Acetate Membranes

Development and performance of some porous cellulose acetate membranes for reverse osmosis desalination

AbstractThe effects of casting solution composition and evaporation period on the performance of resulting porous cellulose acetate membranes have been studied, and the results are discussed in terms of casting solution structure, solvent evaporation rate during film formation, and the film shrinkage temperature profile. The development of Batch 316‐type porous cellulose acetate membranes is reported. At 90% level of solute separation and feed flow conditions corresponding to a mass transfer coefficient of 45 × 10−4 cm/sec, the productivities of the above membranes are 21.5 gallons/day/ft2 at 250 psig using 3500 ppm of NaCl in the feed, and 53.9 gallons/day/ft2 at 600 psig using 5000 ppm of NaCl in the feed.

Performance of some improved porous cellulose acetate membranes for low pressure reverse osmosis desalination

The performance and correlations of experimental data with respect to a new and improved class of porous cellulose acetate membranes for low pressure reverse osmosis desalination are reported. These membranes were obtained from a casting solution of the following composition (weight %): acetone 68.0, cellulose acetate (acetyl content = 39.8% ) 17.0, water 13.5, and magnesium perchlorate 1.5; the temperature of the casting solution was 0°C, and the films were cast at the laboratory temperature (23–25°C) in an ambient atmosphere in equilibrium with 30 wt.% aqueous acetone solution; the solvent evaporation time on casting was 2 minutes, and the gelation medium was ice cold water. The productivity of the films made under the above conditions for brackish water desalination was 100 to 150% higher than that of other porous cellulose acetate membranes reported earlier at operating pressures of 250 psig or less. Some comparative data at higher operating pressures are also given.

High flux freeze‐dried cellulose acetate reverse osmosis membranes as microporous barriers in gas permeation and separation

AbstractThe permeations of helium, hydrogen, methane, ethylene, nitrogen, and argon, and helium–methane, nitrogen–ethylene, oxygen–nitrogen, and sulfur dioxide–nitrogen mixtures have been studied using freeze‐dried porous cellulose acetate reverse osmosis membranes. The results illustrate the existence of mobile and immobile sorbed layers and the governing influence of surface flow in gas‐phase reverse osmosis separations. Preshrunk freeze‐dried porous cellulose acetate membranes seem to offer a practical means of utilizing the reverse osmosis process for recovering helium from natural gas and separating sulfur dioxide from flue gases.

The mechanism for formation of “skinned” membranes : II. Equilibrium properties and osmotic flows determining membrane structure

The critical water concentrations required for initiating precipitation of cellulose acetate from 20% solutions in acetone, dioxane, acetic acid, triethyl phosphate (TEP), dimethyl formamide (DMF) and dimethyl sulfoxide (DMSO) have been determined. The direction and magnitude of volume flow as well as the contribution of solvent and water to this osmotic flow through a porous cellulose acetate membrane separating pure water from a 2:3 water-solvent mixture have been measured. A mechanism based on the assumption that the density of each layer of the membrane is determined by the concentration of the corresponding layer of the cast polymer solution at the precipitation point has been suggested. The volume concentration of the polymer at the precipitation point has been correlated to: 1. the concentration of non solvent required for precipitating cellulose acetate 2. the direction and magnitude of osmotic flows of liquids into or out of the cast solution during leaching

Effect of casting conditions on the performance of porous cellulose acetate membranes in reverse osmosis

AbstractSeveral sets of porous cellulose acetate membranes were made using the same casting solution composition and gelation conditions but varying the casting solution temperature and solvent evaporation conditions. The films were tested in reverse osmosis experiments at 250 psig using aqueous feed solutions containing 3500 ppm NaCl. The results show that the product rate obtained at a given level of solute separation is independent of evaporation time in the range tested and, for a given casting solution composition, the temperature of the casting solution and conditions of solvent evaporation during film formation together constitute an important interconnected variable governing the porous structure of the resulting membranes. These results offer a new approach to the problem of developing more productive reverse osmosis membranes and have led to a new class of porous cellulose acetate membranes capable of giving product rates 100% to 150% higher than those of the best membranes reported, at any given level of solute separation under the experimental conditions used. These results are of practical importance in low‐pressure reverse osmosis applications.

Reverse Osmosis Separation of Some Inorganic Salts in Aqueous Solution Containing Mixed Solutes with a Common Ion

Abstract : A simple method for predicting the performance of Loeb-Sourirajan type porous cellulose acetate membranes for low concentrations of mixed solutes in aqueous feed solution systems involves two or more inorganic salts with a common ion. The method requires only data on membrane specifications and the applicable mass transfer coefficient correlation for the corresponding single solute systems. (Author)

Performance of Porous Cellulose Acetate Membranes for the Reverse Osmosis Separation of Mixtures of Organic Liquids

Abstract : The reverse osmosis technique is applicable for the separation of binary mixtures of alcohols and/or hydrocarbons, including azeotropic and isomeric mixtures. The porous structures of the cellulose acetate membranes used were affected by the composition of the feed solution in contact with them; hydrocarbon liquids tended to collapse their porous structures on continued contact. Hydrogen bonding and solubility parameter may offer valid criteria of preferential sorption for nonelectrolyte binary feed mixtures containing components whose solubilities are governed primarily by either polar or dispersion forces. (Author)

Performance of porous cellulose acetate membranes for the reverse osmosis treatment of hard and waste waters

Abstract : The performance of a few typical Loeb-Sourirajan type porous cellulose acetate membranes is reported for the treatment of hard, polluted, and sewage waters. The membranes used are specified in terms of pure water permeability constant and solute transport parameter for sodium chloride. Using feed waters containing 300- to 800-p.p.m. hardness (expressed as CaCO3), product waters containing 2 p.p.m. or less could be obtained with 90% product recovery and an average initial flux of 38 gallons per day per sq. foot at 1000 p.s.i.g. The possibility of producing 'ultrapure' waters by repeated reverse osmosis processing is indicated. The separation of common pollutants such as nitrates, borates, fluoride, alkyl benzene sulfonate (ABS), ammonia, and phosphates, and a few others usually present in plating wastes, and the applicability of the reverse osmosis process for the treatment of sewage waters and water renovation are illustrated. (Author)

Specification, Selectivity, and Performance of Porous Cellulose Acetate Membranes in Reverse Osmossis

Abstract : The general specifications of the Loeb-Sourirajan type porous cellulose acetate membranes are given in terms of the pure water permeability constant, A, and the solute transport parameter for sodium chloride at different operating pressures. A scale of membrane selectivity is presented for 12 inorganic and two organic solutes in terms of their relative values of the solute transport parameter for several membrane specification and selectivity, and the applicable mass transfer coefficient, k, obtained from a generalized correlation, the performance data for different membranes solution systems, and operating conditions have been calculated. These data related membrane specification to membrane performance expressed in simple terms of solute separation and product rate. The effects of variation of the solute transport parameter, feed concentration, feed flow rate, operating temperature, A-factor (membrane compaction), and chemical nature of solute on membrane performance are illustrated and discussed. The order of solute separation with respect to any two solutes does not always correspond to that of their relative values of the solute transport parameter, and the former is a function of the latter and the operating conditions of pressure, feed concentration, and the mass transfer coefficient, k. (Author)

Performance of Porous Cellulose Acetate Membranes in Some Reverse Osmosis Experiments

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTPerformance of Porous Cellulose Acetate Membranes in Some Reverse Osmosis ExperimentsJ. Kopeček and S. SourirajanCite this: Ind. Eng. Chem. Prod. Res. Dev. 1969, 8, 3, 274–279Publication Date (Print):September 1, 1969Publication History Published online1 May 2002Published inissue 1 September 1969https://doi.org/10.1021/i360031a012RIGHTS & PERMISSIONSArticle Views57Altmetric-Citations2LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (512 KB) Get e-Alerts

Some parametric studies in water desalination by reverse osmosis using porous cellulose acetate membranes

A Loeb-Sourirajan type porous cellulose acetate membrane can be specified for reverse osmosis desalination in terms of the pure water permeability constant A, and the solute transport parameter ( D AM / kδ) at a given operating pressure. A reverse osmosis system for water desalination can be specified in terms of three dimensionless quantities γ, θ, and λ defined in terms of the properties of the solution, specifications of the membrane and the operating conditions of the experiment. For a system so specified, the general equations for reverse osmosis process design are summarized. The application of the above equations for parametric studies in water desalination is illustrated with a set of numerical calculations. The results indicate that operating pressures of about 150 atm. or more, and high mass transfer coefficients on the high pressure side of the membrane (corresponding to λ θ values of about 5), and least membrane compaction during continuous operation are the most favorable conditions for the economic desalination of sea water with the presently available Loeb-Sourirajan type porous cellulose acetate membranes.

Structure of porous cellulose acetate membranes and a method for improving their performance in reverse osmosis

AbstractExperimental data support the hypothesis that the surface layer of the asymmetric Loeb‐Sourirajan type porous cellulose acetate membranes has a heterogeneous microporous structure. A general method is proposed for improving the performance of the above membranes in reverse osmosis, by which product rates are increased without decreasing solute separation. The method consists in pumping pure water past the back side of the membrane under just enough pressure for a sufficiently prolonged period of time; after such pretreatment, the membrane is used in the reverse osmosis experiments in the normal manner with the surface layer facing the feed solution. Back‐pressure treatment at 400 psig for 85 hr on preshrunk and normally pressure‐treated membranes increases the product rate by over 20% without decreasing solute separation in reverse osmosis experiments at 600 psig with the use of 0.5 wt‐% NaCl–H2O feed solutions; with a different sequence of back‐pressure treatment, similar results have been obtained in reverse osmosis experiments at 1500 psig also. The compaction effect of a normal membrane and that of a back pressure treated membrane are the same during continuous reverse osmosis operation under 600 psig; the effects of back‐pressure treatment on a normal membrane and a compacted membrane are also the same. The pure water permeability data obtained in cyclic experiments show that the smaller pores on the surface layer are opened more than the bigger ones during the back side operation. The probable structural changes taking place in the film during back‐pressure treatment are discussed.