James S. Johnson

Hyperfiltration. XXI. Dynamically formed hydrous Zr(IV) oxide-polyacrylate membranes

Summary Membranes consisting of a layer of polyacrylic acid on hydrous Zr(IV) oxide appear promising for hyperfiltration (reverse osmosis) of low-salinity waters. These membranes are formed dynamically by exposing a hydrous oxide membrane, also dynamically formed, to an acidic solution containing polyacrylic acid, and then raising the pH. The effects of variables during membrane formation and during subsequent operation on membrane properties are discussed.

Hyperfiltration studies XIV Porous tubes precoated with filteraids as supports for dynamically formed membranes

Abstract A surface favorable for dynamic formation of hyperfiltration membranes can be attained by thinly coating a coarsely porous material with particulate or fibrous substances. The coating is deposited by circulating a suspension of filteraids under pressure. The technique is illustrated with salt-filtering membranes formed dynamically of hydrous oxide and polymeric vinyl pyridine additives and with membranes formed from feed constituents of waste liquors generated in the sulfite pulping process. With this configuration, permeability may be restored by backwashing, after which the coating and membrane may be formed. We have earlier reported that salt-filtering films can be formed dynamically on porous bodies by circulating past them feeds containing certain additives(2/2-4). Membranes formed of polyelectrolytes, which might be expected to give ion-exchange layers, frequently have permeabilities which are extremely high in comparison with conventional detachable membranes — for example, cellulose acetate. Their salt rejection is lower than that of cellulose acetate, particularly at high feed concentrations. However, with brackish waters for which rejection requirements may not be high, they might have practical usefulness in the hyperfiltration, or reverse osmosis, desalination process. Membranes formed of non-electrolyte additives may have higher rejection, but usually seem to require supports of smaller and more homogeneous pores than those of polyelectrolytes; the layers probably need to be thinner for acceptable permeability (5). We have found that many solutions requiring treatment, for example, pulp-mill wastes (6) and sewage effluents (7), already contain membrane-forming materials which make it possible to eliminate much objectionable matter by hyperfiltration without the necessity of putting in additives. Realization of the practical possibilities of this class of membranes obviously requires the availability of suitable porous supports. The supports must be strong enough to contain the pressures necessary, must have pore sizes suitable for the membrane-forming material in question, and should be cheap, i.e., of low cost per unit production rate and of long lifetime. Pore sizes necessary for different additives or feeds vary, but usually fall in the tenth to a few microns range, and the pore sizes should be reasonably homogeneous. Even a small fraction of pores much larger than the median may be deleterious, if they present a gap too wide to be bridged by the additive, since a disproportionate fraction of the product stream will be feed which passed through the large pores unaffected. A favorable configuration would have a thin layer of the preferred pore size on which to lay the membrane, on top of a support having much larger pores to pass the product with minimum pressure drop. A procedure which one might predict would attain this configuration would be to circulate a slurry of fine particles under pressure past a body containing large pores. We have found that membranes can be formed on a surface layer deposited by this procedure. Combinations of many different porous materials with many different suspensions (commercially available as filteraids) have been effective. This procedure extends the usable pore sizes into those of commercial filters, of which there appear to be many more available from five micron pores up than in the range of sizes particularly suitable for membrane formation. Perhaps most important, membranes, along with the filteraid precoat, should be removable by backwashing, if permeability becomes undesirably low because of fouling or other reasons. The results obtained to date represent only a survey of the many possible porous bodies, filteraids, additives, and experimental conditions. It is improbable that the combinations so far tried are near the optimum for the membranes in question. We are encouraged enough by our results, however, to feel a reliminary report is warranted.

Modification of cation-exchange properties of activated carbon by treatment with nitric acid

Abstract The uptake of inorganic cations by high-surface-area activated carbon can be increased by an order of magnitude by controlled exposure to high concentrations of nitric acid at elevated temperatures. Distribution coefficients of cations are also increased. Acid strength of the functional groups from the nitric acid treatment is greater than those of the starting material. Surface area measurements and small- angel neutron scattering indicate that the increase in effective ion-exchange capacity is not accompanied by gross changes in the structure of the material. 13 C NMR on solid samples suggests that the concentration of carboxyl and phenolic functional groups in the carbon is increased by the treatment.

Hyperfiltration of laundry wastes

Abstract Hyperfiltration (reverse osmosis) with dynamically formed hydrous Zr(IV) oxide-polyacrylate membranes removed ∼98 per cent of the organic carbon from effluents from two commercial laundries. The filtrate was clear and essentially colorless to over 85 per cent water recovery. Fluxes were mostly between 50 and 100 (U.S.) gal day −1 ft −2 at temperatures typical of the laundry operations and at 950 psig pressure.

Ion-exchange properties of activated carbon filled with hydrous Zr(IV) and Zr(IV)—P(V) oxides

Abstract Filling the pores of activated carbon with hydrous oxides allows one to take advantage of the attractive ion-exchange properties of the oxides and to avoid difficulties of column operation with the hydrous oxides alone arising from particle size, particle uniformity, and dispersibility. Procedures are outlined for incorporation of useful amounts of hydrous Zr(IV) oxide and mixed oxides of Zr(IV) and P(V) in high surface area charcoals. A dilute solution of Zr(IV) salt in solutions of moderate acid concentration is first contacted with the carbon and the Zr(IV) taken up precipitated with ammonia. More than one cycle may be desirable. Higher Zr(IV) oxide contents may be attained by pretreating the charcoal with nitric acid at elevated temperature. The rates of exchange between filled carbons and solution are adequate for column separations.