IL46510A - Process for the removal of urea from aqueous solutions thereof - Google Patents

Description

PROCESS FOR THE REMOVAL OF UREA FROM AQUEOUS SOLUTIONS THEREOF m»a»an n«mo*ana ηκ»ηκ monV y>nn The present invention relates to a novel process for the separation of urea from aqueous solutions of same. The 7^ invention further releates to a process for the separation of urea and of other solutes from aqueous solutions and from body fluids. The invention further relates to novel devices for the separation of urea, possibly together with other solutes, from aqueous solutions and especially from body fluids. Other and further features of the present invention will become apparent hereinafter.

The present invention is based on the unexpected discovery that certain types of membranes, some of which are known from the field of desalinatio and the sweetening of water, can be used for th effective and selective separation of urea, possibly together with other solutes* from aqueous solutions. The results obtained are other surprising* asAdesalinatlon membranes have been tried, and hitherto no^sa isfactory results were obtained, PRIOR ART: Considerable developments have been made during recent years in the desalination of seawater and of brackish water by reverse osmosis.

Little has been done in the application of similar techniques for the removal of urea from aqueous solutions* and especially from body fluids. Interest has been shown in a process for the removal of urea from urine in space flight (J.App.Pol.Sci. 1£ (1973)* 2277), A process of this type is of value in the development of light-weight artificial kidneys (fl.S, Pat, 3#579#44l, uVS, Pat. 3#799*873s P S Pat* App. aerial Ho. Z92,W*> German Pat. App. P 2321168.95 P 2321188.3). In such devices the purification from accumulated metabolites is effected by hyperfiltration (reverse osmosis) of water used for dialpais, and the thus purified water may be used for ther dialysis. The polymerused generally for desalination is cellulose acetate.

Hembranes of this type are characterized by a high salt rejection, but . acetate membranes, cellulose triacetate films gave a 66$ rejection (OSW R&D Progress Report 447 ) . Still better results were obtairSS^ with heat treated cellulose acetate butyrate membranes which gave a 81.8$ urea rejection from 1$ feed solution at a filtration rate of 1.75 gfd at 600 psi (j.Appl . Pol . Sci. 1£ (1973) 2277 ) . Recently certain aromatic polymers with nitrogen containing linking groups were suggested for desalination, and these are reported to have better mechanical properties (US Pat.3*567*632 ) . A single report deals with the re jection of urea by a membrane of this type having polyamide gicups and aromatic moieties, and this was stated to be about 92$ from 1.8$ feed solution at a filtration rate of 2 gfd at 600 psi: McKinney, Separation and Purification Methods, 1 (1972 ) 31. Porous glass was reported to reject 91.6 urea from a 1$ solution but this was at a flow rate of only 0.26 gfd, at 1200 psi and depends to a large extent on the specific batch of glass. The results obtained according to the present invention are better than those of the known processes , a higher rejection is obtained and furthermore the membranes according to the present invention can be produced in a simple manner* as will be set out hereinafter. e process accor ng o e presen nven on compr ses effecting a selective removal of urea - possibly together with other solutes - from an aqueous solution of same, inclusive of body fluids, by reverse OBmosis effected by means of a polymeric membrane of the type wherein A designates an aromatic group and X designates a bivalent linking group, the aromatic group being a group such as phenyl, biphenyl, naphthyl, or a mixture of such groups, or such groups connected by means of linkages such as -0-, -S0- -NH-, -CH2-, -P0(R) (wherein R is alkyl); or a mixture of aromatic and aliphatic groups such as aliphatic chains of not more than 6 carbon atoms which do not constitute above 40 mole-# of the A-groups; or a mixture of aromatic and alicyclic groups wherein the alicyclic moieties do not constitute more than 50 mole«$ of the A-groupsj or a mixture of aromatic and heterocyclic groupsj wherein said groups A may be substituted by one or more substituents selected from alkyl of up to 4 carbon atoms, alkoxy of up to 4 carbon atoms, alkoxy of up to 4 carbon atoms, amino, dialkylamlno, hydroxy, carboxy, carboxamido and sulfonic acid groups; the group X being selected from amidqjaf (-NH-C0-), substituted amidoyf (-NR-C0-) wherein R is lower alkyl, provided that the substituted amido groups do not constitute more than 50 mole-$ of the X groupsi hydrazido (-C0-NH-NH-C0-), ureido (-NH-C0-NH-), semicarbazido (-NH-C0-NH-NH-C0-) , or sulfonamide (-SOg- H-), and wherein 11 is about 80 to 300.

The polymers for the membranes of the present Invention are prepared by a number of processes. Amongst these there may be mentioned the polycondensation at low temperatures. According to one of the embodiments of the invention the polyamide polymers are prepared by dissolving a suitable aromatic diamine, or mixture of aromatic diamines in a suitable solvent, such as N, N-diraethylacetamide, cooling the o solution to a temperature of about -10 to -30 G, adding an aromatic diacid chloride (or a mixture of such chlorides) either in solid form or as solution,mixing at the low temperature fi>r a predetermined period of time and allowing the reaction mixture to warm up to ambient temperature or above. After completion of the reaction to a degree of at least about 95$ the liberated hydrogen chloride is neutralized by the addition of a base such as pyridine and the polymer is precipitated by pouring the reaction mixture into an ice water mixture in which it is insoluble. The precipitate is washed and dried under reduced pressure.

Membranes are cast from the polymer dissolved in a suitable solvent, or they may be cast directly from t he reaction mixture defined above. Amongst suitable solvents there may be mentioned N,N-diraethylacetamide dimethyl sulfoxide or hexamethyl phosphoramide containing about 5$ by weight of a suitab-te salt, such as lithium chloride or p¾rridine hydrochloride, The cast membranes may be precipitated in a non- partially solvent, such as water, or the solvent may be first/evaporated at a suitable temperature and pressure.

The membranes are suitable for the selective rejection of urea, possibly together with other solutes, and at a urea concentration of about 5000 ppm, at 600 psi operating pressure the urea rejection is at least 60$. In many cases a rejection better than 5$ can be attained, and this is considerably better than the rejection possible hitherto by similar processes.

Hyperfiltra lon of Solutions Containing Urea: Membranes prepared as described above can be used in stirred, high pressure reserve osmosis cells, flow-through cells, plate and frame such membranes at pressuas exceeding the osmotic pressure of such solutions (generally over 10 atm. ) The concentration of urea in the permeate does not exceed 4C$ of that of tine feed solution and generally is very much lower. As the membranes of this invention are also effective desalination membranes, salts, sugars and other solutes contained in the feed solution are also rejected to a large extent. The permeate thus contains a low concentration of solutes and - if used for example in conjunction with an artificial kidney device - may be reused for further dialysis.

Examples Example -ji Polymerization of a Mixture of meta- and para-Phenylenediamine with iso-fhthaloyl Chloride. (Polymer MP-M) A mixture of 5.4 gr (50 mmol) of m-phenylenediamine and 5.4 gr (50 mmol) of p-phenylenediamine is dissolved in 112 ml of dry N,N-dimethylacet-amide under dry nitrogen. The solution is cooled to -20°C and 20.3gr (100 mmol) of solid isophthaloyl chloride are added in portions of about 5 gr. The viscous mixture obtained is stirred at -20°C for 15 minutes, warmed gradually to room temperature and 17.7 ml (200 mmol) of dry pyridine are added. Part of the polymer is precipitated by pouring into ice-water in a blender. The precipitate is washed thoroughly with water and alcohol, air-dried and finally dried in a vacuum oven at 80°C.

Example II: Membrane Preparation and Characterization Membranes are cast either directly from the reaction mixture of Example I or from redissolved polymer. When prepared from the reaction mixture the solution is stored (usually for at least 24 hours) before casting,so as to let gas bubbles escape. When preparing filtered through sintered stainless steel and stored for at least 24 hours. ^ Membranes are cast at a thickness of 0.2 - 0.5 ram on a clean, dry glass plate. The plate with the cast solution is placed in an oven at the desired temperature for a predetermined period. The membrane is then coagulated by immersing the plate into distilled water at room temperature. The membrane performance is tested after at least 24 hr storage in water. In Table I are summarized performance data of membranes prepared from the polymer of Example I under various condition TABLE I Urea Rejection of Membranes Prepared from Polymer MP-M under Various Conditions (a) 80 1 58 1.65 80 2 1.20 90 1 75 1.05 110 1 84 0.75 (a) Membranes were prepared from MP-M polymer precipitated and rediss-olved to give a 20$ solutions casting thickness was 0.4 ms final; about 0„ lmm. Feed solution concentration was 0. $ Pressure: 50 atm.

Membranes prepared directly from the reaction mixture of polymer MP-M and heated at 90°C for 1 hour exhibited a rejection of 9 $ with a filtration rate of 1.74 gfd.

Example III; Polymerization of m-Phenylenediamlne with a Mixture of tere - and iso-Phthaloyl Chloride and Membrane Preparation. (Polymer M-MP) The polymer is prepared by the procedure described in Example I.

Membrane performance data are summarized in Table II.

TABLE II Urea Rejection of Membranes Prepared from Polymer M-MP under Various Conditions (a) Polymer Oven Temp. Oven Time Urea Filtration Solution (°C) (hr) Rejection Rate Concentration^) { ) (gfd) 20 90 0.5 75 1.35 20 90 1 96 1.20 10 90 1 42 2.55 10 90 2 73 2.25 (a) Membranes were prepared directly from the reaction mixture. Casting thickness 0.4mm, final thickness: 0.1mm. Peed solution concentration was 0.5#* Pressure - 0 s&m.

Example IV; Polymerization of m-Phenylenediamine with iso Phthaloyl Chloride and Membrane Preparation. (Polymer MM) The polymer and membranes are prepared as described In Examples I and II. Membrane performance data are summarized in Table III.

TABLE III Urea Rejection of Membranes Prepared from Polymer MM under Various Conditions (a) Casting Thiclcness Oven Temp. Oven Time Urea Filtration (mm) (°C) (hr) Rejection Rate 0.2 80 2 78 1.20 0.4 90 1 86 1.70 (a) Pressure 50 atm. solution concentration 20$ Example V ; Hyperflltration of Various Urea Containing Solutions Through Aromatic Polyamlde Membranes In Table IV are summarized data on the hyperflltration of various solutions through membranes prepared from Polymer M-MP. These data show that the presence of other solutes does not affect appreciably the rejection of urea.

TABLE IV Hyperfiltration of Complex Solutions Composition of Filtered Solution Filtration Rate Solute Rejectio *^ 5000 ppm urea 1.12 Urea NaCl Creatini ~95 = = 5000 ppm urea 1.12 95 97 99 5OOO ppm NaCl 1000 ppm Creatinine 5OOO ppm urea 0.9 9 97 3OOOO ppm NaCl Example VI: Hyperfiltration of Peritoneal Dialysis Solutions The membranes of this invention may be used for purification of spent peritoneal dialysis solutions by hyperfiltration. In these filtrations rejection for urea and other nitrogen-containing metabolites is at least as high as with simple binary solutions, as shown in Table V.

TABLE V Hyperfiltration of Spent Peritoneal Dialysate with a M-MP Membrane Solution Urea Rejection ($) Filtration Rate (gfd) Peritoneal dialysate 9 1.7^ 5000 ppm urea 89 1·65 Example VII: Polymerization of Para Aminobenzhydrazide "with iso Phthaloyl Chloride Membrane Preparation and Characterize atlor Para-aminobenzhydrazide and isophthaloyl chloride were polymerized as described in Example I. Membranes were prepared essentially as described in Example II but were then heat treated. Thus a merabpsne heated at 100° for 1 hr exhibited a urea rejection of 65$ (0.5$ feed solution, 50 atm) while an untreated membrane rejected only 12$ urea.

Example VIII Polymerization of p.p. '-diaminodiphenylsulfone with Isophthaloyl chloride and Membrane Preparation p.p. *-Dlamlnodlphenylsulfone and Isophthaloyl chloride were polymerited at low temperature as described in Example I. Membranes were prepared as described in Example II. In hyperfiltration of 0.5$ urea solution through such a membrane of 50 atm, urea rejection was 88$ and filtration rate 0.15 gfd.

Example IX Polymerization of plperaaine with isophthaloyl Chloride and Membrane Preparation Piperazine may be polymerized with isophthaloyl chloride by interfacral pol condensation following L.Credali etal, Desalination, 14, 137 (1974), Membranes are cast from formic acid solutions.

Membranes are cast thi-ckness of 0.4 mm and evaporated at 60° for 30 minutes show urea rejections of 80-89$ and iltration rates of 1.0-1.5 gfd. (0.5$ urea feed, 50 atm).

Example X Polymerization of 4.4t-Dlamlnodlc clohexyl methane with Isophthaloyl Chloride 4.4'-Diaminodicyclohexyl methane was polymerized with isophthaloyl chloride in dimethylacetamlde solution as described in Example I.

Membranes of 0.4 mm easting thickness and evaporated for 30 min. o at 90 , show urea rejections of 75-35$ and filtration rates of 0.7-1.1 gffd (0.5$ urea feed, 50 atm).

Example XI Polymerization of 4.4'-Diamino-3j3l-dlmethyldiphenyl methane with a Mixture of Iso-and Terephthaloyl chloride 4. ,4'-Diamino-3i3ldimethyldiphenyl methane is polymerized with a mixture of iso-and terephthaloyl chloride as described in Exanple I. Membranes prepared by casting at a thickness of 0.4-0.5 mm and evaporated for 30'-60' at 90° exhibit urea rejections of 75-85$

Claims (3)

1. A process for the removal of urea from an aqueous solution of same, which comprises effecting reverse osmosis by means of a polymeric membrane of the type: wherein A designates an aromatic group and X designates a bivalent linking group, the aromatic group being a group such as phenyl, biphenyl, naphthyl, or a mixture of such groups, or such groups connected by means of linkages such as -0-, -S02~, -SO-, -NH-, -CHg-i -P0(R) (wherein R Is alkyl); or a mixture of aromatic and aliphatic groups such as aliphatic chafas of not more than 6 carbon atoms which do not constitute above 40 mole-$ of the A-groupsj or a mixture of aromatic and alicyclic groups wherein the alicyclic moieties do not constitute more than 50 mole-$ of the A-groupsj or a mixture of aromatic and heterocyclic groupsj wherein said groups A may be substituted by one or more substituents selected from alkyl of up to 4 carbon atoms, alkoxy of up to 4 carbon atoms, alkoxy of up to carbon atoms, amino, dialkylamino, hydroxy, carboxy, carboxamido and sulfonic acid groups; the group X being selected from amido^ (-NH-C0-), substAtued amidoj/ (-NR-C0-) iherein R is lower alkyl, provided that the substituted amido groups do not constitute more than 50 mole- of the X groups; hydrazido (-C0-NH-NH-C0-) , ureido (-NH-C0-NH-), semicarbazido (-NH-C0-NH-NH-C0- ) , or sulfonamido (-S02-NH-), and wherein n is about 80 to 300.

2. A process according to claim 1, wherein the membrane material is a polymerization product of raeta-phenylenediamine and para-phenylenediamine with iso-phthaloy^ chloride. ^ 3. A process according to claim 1, wherein the membrane material is a polymerization product of meta-phenylene diamine and a mixture of tere- and iso-phthaloyl chloride. 4. A process according to claim 1, wherein the membrane material is a polymerization product of τη=·phenylenediamine and isophthaloyl chloride. 5. A process according to claim 1, wherein the ^membrane material is a polymerization product of p-arainobenzhydrazide and isophthaloyl-chloride. 6. A process according to claim 1, wherein the membrane material is a polymerization product of p, p»diaminodiphenylsulfone and isophthaloylchlo ide. 7. A process according to claim Ij, wherein the membrane material is a polymerization product of piperazine with isophthaloyl chloride.

3. A process according to claim ls wherein the membrane material is a polyme isation product of 4J)4,-diaminodicyclohexylmethane with isophthaloyl chloride. 9.' A process according to claim 1, wherein the membrane material is a polymerization product of 4i4l=diamino-3_.3 '-dimeth ldipheny isophthaloxyl methane with fephteleyl chloride and terephthaloyl chloride. 10.Process for the removal of urea from aqueous solutions and from body fluids, substantially as hereinbefore described and with reference to any of the examples. 11.An artificial kidney device., equipped with a membrane as defined in any of claims 1 to 10.