claimed is:, 1. In a solvent extraction zone for the extraction of water of reduced@salt concentration from an aqueous salt solution of greater salt concentration by contacting said salt solution @ with' a water selective amine solvent @characterized by the formula Rl--N(R.@)-R3 wherein RI is a member of the group consisting of hy-. drogen and alkyl, R2 and R3@ are members of the group consisting of alkyl and alkenyl radicals having 1 to 4 carbon atoms, the total number of carbon atoms in,each amine being 4 to 7, to form in the zone an extract phase consisting essentially of said amine and dissolved water,@: and a raffinate phase consisting essentially of water with salt, the improved method comprising providing a temperature. gradient within the solvent extraction zone, separating the said raf-inate phase of increased salt concentration ftom the extract phase, heating the extract phase to cause separation of water from the amine solvent, -and then recovering water of substantially reduced salt concentration. 2. @The method @ of claim @ I wherein the extract hase p is heated to a temperature at which the solvent is substantially immi-sc-ib-le- wi-th the waier dissolved therein, and then separating the water from the amine solvent. 3. The process of claiin 2 wherein the minimum extraction temperatiire is 0 to 40' C. and the imposed temperature gredient is 5 to 30' C. 4 ' The process of claim 2 wherein the maximum extracti6n @temperature is 20 to 70' C. and the separation @temperature is 5 to 40' -C.,, above the extracti,on temperature. 5. The process of claim 2 wherein the ratio of solvent to salt solution is 0.511 to 10/ 1. 6. La -a @solvent extraction zone for the: extraction of water of reduced salt concentration from an aqueous salt soluiion of greater salt concentration by countercurrently contacting said salt solution with a water selective amine -solvent characterized by the: formula RI-N(R2)-R 3 wherein RI is a member of the group consisting of hy_@ drogen and alkyl, R2 and iR3 are members of the group consisting of alkyl and alkenyl radicals having @l to 4 carbbn atoms the total, number of@ carbon atoms in each amine being 4 @ to 7, to form in the zone an extract phase@ consisting essentially of said amine and dissolved water, and@ a raffinite phase consisting essentially of water: with salt, the improved method comprising providing a temperature gradient within the@,solvent:extraction zone ranging from about 5' C. to about 30' C., said tempera@ ture@gradient being one wherein the solvent input is at the low temperatiire and the extract withdrawal @phase at the higber ;teniperature, separating the said raffinate phase of increased salt concentration from the extract phase of reduced salt concentrati6ii, h6ating I th@- extract phase to su,fficiently higher teqlperature so that a solvent, extract 1)hase sel)arates from. an aqueous phase and be-, @omes substantially. @ immisc e thdrewith, separating. the, @later from the solvent extract phase and: re@covering water of substantiallv redu.ced. salt concentration, and 12 recovering also, a raffinate phase of increased salt colicentration. 7. The process of claiin i6 whe.rein reflux water of substantially reduced salt@concentrati n ' add6d to the ex0 is traction zone. 8. The process of claini 7 @wherein the separation of the water from the extract phase is performed at a temperature ranging from about'5' C. to about 40' C. a ove the maximum extraction temperature and. the I reflux con10 sists of about 10 to 50% of the volume of the extracted water. 9. The@ process of claim@ 7 Wherein the maximum 1 separation temperature is 20 to 80' C. IO. @ A method f or obtaining water of reduced sodium 1 5 chloride,concentration from a saline solution which comprises countercurrently . contacting said saline Solution with a solvent selective @for water selected from the group , consisting of triethylamine, methyll diethylaminel, dimethyl isopropylaniine dime , thyl tertiary butyl jamine, 20 and mixtures thereof, @hereby a temperature gradient is imposed on the extraction, said@ imposed dient the solvent input at the @low temperature a@d-:the: extract phase withdrawal@ at the@ high teniprrature, providing reflux water of substantially@ reduced@@salt concentration, 25 ;thereafter separating a rafrinate@ phase of increased salt@ concentration and-an extract @4ase@containing dissolved water bf@substantially reduced-salt concentration, heating the, separated @ extract phase to @ a @ temperature@ whereby the water dissolved in th6 solvent extract phase becomes 30 substantiauy @ inimiscible with the solvent, @ separating the water from the @solvent phase, recovering a water phase of @ substantially@ reduced@ salt : concentration, a solvent phase, and a raffinate phase of substantiall@ increased salt concentration. 35@ 1 1. The process of claim@ 10 wherein the inip@osed temperatii re @ gradient is 5 to 3 O' C., the@ separ ati6ntemperatuie 5 @ to 40' C. abov6 the maximum I @e@traction temp erature and the reflux @consists @ of: about 10:to 50% by volume of the volume of extracted water. 40 12@ The process of %claim 10 wherein @ the I minimum, extraction teniperature -is: 5 to 3 O' C.@ the maximiim . extraction temperature 20: to 50' C@@ the imposed tempprature gradient 10 to: 25 ';- C@, the@ separati6n temperature 5 to 30'@ C.@ above the maximum extraction - tem-by vol45 perature, and the @pereentage. of reflux @25 to 35 % ume of the volliine of the extra@ted water. -13 ' The Process of claim@@10 wherein the@:.solvent to salt solution ratio is@1/1 to 511. , 14. The process, of claim 10 wherein the separation 50 temperature is 20 to 60' C. . 15' A process 6f obtaining potable . wbter having less than 500 pp'm' 'of sodium, chloride from salt @,ater having 3.5 to 4% sodiuin @ chloride which comprises @c I 6unt@rcurrently contacting aid salt soluti6n @ -with @a solvent in 55 ratio of solvent to solution @ of . I / 1 @ to 5 / I 1: said solvent being selective for water,. selected. from the group @ con @sisting of triethylamine, @ methyl diethyl amine dimethyl isopr I lamine,: dimethyl tertiary butylam'me, and opy mixtures thereof, whereby a tem@erature@ gradient is:@impbsed 60 on the - extraction, @ said, temperature gradidnt being between 5 @and 30': C., said- imposed gradient havili,- the solvent input at the low:temperature and the extract phase withdrawal at the high tempprature,@providing-5 to 35% by @ volume of reflux :water,, of ':substantially @ reduced salt: 65 c6ncentration,l thereafter separating a raffinato phase@,oi in I creased salt concentration and @an extract phase containing 4issolved- w t @ of sub8tantially,. reduced @ alt c6ncena er s tration, heating the sepa-ated extract phase@@to d temperature 5 to 40'@ C. above the maximum extracti6n tempera70 ture whereby@ the *ater dissolved iii the solveilt extract phase becomes' substantially. immiscible in' the extract phase:and@ the water:c6ncentr@tion is ieduced to 5 to: 1001d by voltime of the solvent,, @epar@ting @th. watet@ from the solvent, phase, reeovering 4 water phase containing less 75 than 500, p.p.m@ of s6dium,chloride,@@@ solvdnt;phase and

13 a raffinate phase of substantially increased salt c oncentration. 16. The process of claim 15 wherein the recovered raffinate phase contains at least 10% dissolved sodium chloride. 17. The process of claim 15 wherein the solvent to triethylamine, the minimum extraction temperature is about 10' C., the maximum extraction temperature about 22o C., the separation temperature about 30' C. and the ratio of solvent to salt solution is about 2/1 to 3/1. References Cited by I the Exaniiner UNITED STATES PATENTS 3,088,909 5163 Davison et al - ---------- 210-22 3,177,139 14 OTHER REFERENCFS "Report No. 22," Research on Liquid-Liquid Extraction for Saline Water Conversion, by The Agricultural and Mechanical College of Texas for Oi-iice of Saline Water, December 1958 (pages 1-14). Copy in 210S.W.D. "Report No. 27," Saline Water Conversion, Advances in Chemistry Series, by American Chemical Soc ety, 10 Washington, D.C. Copyright 1960 (pages 40-49). (Copy in Scientific Library.) MORRIS 0. WOLK, Primai-y Examiner.

United States Patent Office 321772139 P a t e n t e d A p r . 6 , 1 9 6 5 A@iother characte rist,'.c Of thd solvent is that though th6 3,177,'139 solvent is miscible with water at 16wer teniperatures, at DESALINATION BY SOLVENT EXTRACTION relatively slight increases iii tofnperature thd 8olvevit Is Charles Newton Kimberlin, Jr., Baton Rduoe, La., and almost t6tally immiscib le with wdter Therefo rd,. the Roger W. Richardson, Westfield, N.J., assignors to Esso Research and El ngineering Company, a corpolration of 5 water can be extracted froni the saline solution by golvent Delaware extraction and then the ,vater can be separated froiii the, F-Ued Dec. 2, 1963, Ser. No. 327,254 solvent by 0-@ily a slight incroase iii ten-iperattire. These 17 Claims. (Cl. 210-21) characteristics greatly decrease the Onergy requiremerts This invention relates to a process for the solvent ex- of th-. systera for tecoveting, fok exarxiple, @otable Water 10 from a saline solutio n. traction of water from an aqleous solution. Particularly, In accordance with the present invention desalination this i nvention relates to a proce@s of solvent extraction is carried out by countercurrent contactin.- of 4 saline of water from salt solutions. More particularly, this ins olution and a solvent stream, Th I e vvater in the salir@e vention relates to the solvent extraction of water from s olutioi is partially immiscible in the solvent at tble temsaline solutions to obtain potable water. Saline solu1- p@-i-atures at vihich the contacting is carried out. Th@ tions include brackish waters, sea water, and in general, 0 solvent is selective for water over salt. More water salt solutions of any kind in which the solvents system is will be extracted at the lo@ver tenipeatures until the t6mconipatible. The invention relates to a method of selec- perattire is reached at which th6 salt ,zolutioA and thp@ tively extracting water from a saline solution to obtain solvent are completely misc@ble. This temperature is a substantially salt-free water and a saline solution of in20 c alled the LCST teinp-@rature and fbr a particular @olcreased co-@icentration of salt. v ent will bo effected by the cOncOntration of salt in the The invention relates to a process of selectively extracts aliiie soltition being contacted. The highdr the salt coning water from an aqueous saline soltition by counterc entration, the gre,,iter the reduction in thd LCST temcurrent contact of the saline solution with an amine solp erattire. In carrying out the extr@iction it is - necessary vent selective for water at a temperature at wbich the 25 t o maintaiii the extraction temperature h:@gh enbugh so solvent is partially niiscible witli the water in the saline t hat there are two separate phases present, the saline soltition and selectively extracts water over salt. The s olution phase and the golvent phase contaillirig the exe crilical feature of th extracton step is that a temperatr acted water. Further, it is desirable to maintain a temture gradient is imposed on,the countercurrent extracp erature I high enough so that the niaximuin amount bf tion step and the extraction is carried out over a specified 3 0 water in the solvent during the extractiol does not extemperatur-. -ange. Subsequent to the countercurrent exc eed about 45% of the extract phase because at concentraction step, the extract phase is separated from the tr aiions'higher than this, the solvent b@-conles less si@lecraffinate phase, is hee-.ted to a temperature at which the ti ve to water and a relatively large amount of salt is exextracted water and the solvent are substahtially immiscitr acted with the v@aier. ble, a]Jowed to settle by gravity and a substantially salt35 I n accordance with this invention the solvent exttacfree aq,-leous phase is recovered and a substantia'lly waterti oii stei) is carried out in either a batch Or eb-@lti'nuous free solvent phase is recovered. 1 co,,inter@,-,rrent contacting system but with a temperature Recently a method for the recovery of fresh water from g ra@.lient impos6d on the extraction. sq,line waters employiig various amine solvents, and mixApl-ilicarits recogn-'@ze that as teniperatui-es iiicrease the ttires thereof, has been proposed, see U.S. Patent 3,088,- z,( a motint of water that will remain d;ssolved in the extract 909 to Richard R. Davidson and Donald W. @Vood, dated p hase decreases. Applicants, however, undxpectedly May 7, 1963. The referenced process describes a techf <)und- that if the temperature is increased while the exnique of extracting water frorh a saline solution com. tr act phase is in contact with the raffinate phasd (for prising cotintercurrently contacting the saline so'lutio-n with e xaiiidle, while riia;ntaining the concentration of the, salt amine solvent or mixtures of amine solvents, wheroby th-@ j, @5 in the raffinate phas.- about the samo) that the am6unt extraction step is carried out isothermally. Subsequently, of sqlt in the water in th,,@ extract phase decreases ra@idly' the extract and raffinate phases are sevarated and the Tile aipou@it of water in the extract phase, howevdr, under extract phase is heated to a hi.-her t-,mperatiir-I at wluct'i t hese conditions, also d,-creases (this woutld difect yield of temperature the solvenf and water in the extract phase are water relative to solvent recycle rate) but at a n-iuch separaced. The reference process is limited in applica5( sl ower rate than the decrep@se -in @-alt co@lc@entratiori@ For tion to brackish waters containing only ab<)ut 3000 to 5000 parts per million of salt. The brine di@tharge cortains only about one percent of salt. That process is , limited in the salt content of the feed wluch it ca-@l handle becwase at the constart temperature conditioris emploved for the extraction, the solubility of the i@ater in the solvent is decreased markedly as the amotin" of salt present in the system increases; Thus, at the e constant temperature conditions an impractical large circulation rate o-.' solvent is reeuired to extract the water from mor-, concentral@ed salt solutions. In order to have an efficient economic solver@t exlraction process, it is necessary that the sol@vent recycle rate be kept low and that th-. solvent loss be n-iiiimized. Also, it is necessary that the salt concentration of the effluent rafflpate stream; i.e., the treated saline solutiori be as high as possible in order that the lowest volume of this stream need be treated to r--cover any dissolved solvent. Energy requirement in this particular system are greatly miniriiized by iitilizing the solvent extra@t:ion cha,acter@istics of thpsolvent..and its selectivity for water over salts as tLe basic means to separate the water from the saline solut;on. examp'.e, wtth reference to Table 11 I the 9,Yo bri-ie so'iutio-n raf-nnate in contact witli triethyl amine at 19.6' C. will give a so'.vent phase which dissolves above 10% water, which water has a salt conce ntration of about 0.22%. 55 The same 9% brine solution ratnftate phasi@, if contacted witb sol-,,ent at abbut 5' C., results in a solven' , phase cohtainin.@ 44% water, which water has a salt 6oricentration of abo,,it 5.6%. Therefore, by carryin g oat the extraction step where the raffinate phase had a constant 9% Go sal'L and ir@iposing a temp@-rattire gradient of 5 to 19.7' C. a subs@lantial reduction in salt coiicentration of the water dissolved in the solvent resi-ilts. The salt c6heentration of the water ir, the ex'@ract pha.-e is reduced from 5@6% at 5' to 0.22%. at 19.7' C. There is a@reduction by a 65 faletor of 25, while at the snnie time the aniount of water recovered is reduced only by a factor 6f about 41/2; But as a re-.ult of the colintercurrent c)@tract;on in additi o-Ti to the imposed t-Imperature gradient there exists a c6ncentratioti gradient of salt in the raffinate phase. 70 i Generally, the higher the concentration of the salt at @a specified temi)erature in the raffinate phase the smaller the amount of water the solvent will dissolve.

3,177 139 3 Again referring to Table @l at about 19.7' C. a brine raffinate ;phase containing 1% salt corresponds to a solvent extract phase which-will dissolve 36% 3 salt is' related to 22.5% water an d 6% salt to, 16.1% water., And finally a 9% salt in;the raffi--late phase to 10@19'o wal,er inthe extract phase. By initiating the extraction step at a lower temperature, for example, 10' C. and terminating it at a higher temperature of about 20' C. and by utilizitig a countercurrent contacting SYS7 tem, applicants @are thereb I y able to obtain a very con10 centrated raffinate, phase and an extract phase @with a relatively large. amount@ of water which is substantially no salt. Therefore, as the extract phase containing dissolved water and salt proceeds up the @column the, amount of salt dissolved in the water will be decreased due. to 15 the tempprature gradient effect of the extraction step and also due to.the washing pffert of the descending raffinlte, while the amount of water in the extract phase will tend to increase due to the decrease in the amount of salt in the. rafunate phase that the extract phase "sees" as @it 20 @proceeds up the column. The tenipprature gradient can be selected so that @the decreasing salt concentration of@ the raffinate phase is such that it will just balance the desolubilizing effect of the increase in temperature as the dxtract phase proceeds up the column. In. this manner 25 substantially the same amount of water will stay dissolved in the extract phase, which water wiU gradually. decrease in salt concentration due @to the lower concentration of salt in the raffinate phase that the extract sees. The salt in the ra-ffinate@ phase, undergoes a,gradual build30 up in salt concentration as it proceeds,@down the column and a reduction in temperature@ While the: solvent extract, phase, undergoes a gradual rise in temperlture and redi4etion in salt concentration of w@ater dissolved inthe extract phase, though @ the total amount of water dis3.5 solve@d in:the extra@ct phase can be made to remain about the same until the. end, of the eitraction step. The top of the column is at a temperature significantly above the temperature of the input saline solution feed and the @extract phase above @ the saline water input feed 40 pbint is countercurrently contacted with substantially saltfree reflux water. This effectively washes out, substantial amounts of the salt remaining in the water dissolved in the extract' phase, and dilutes the @salt concentration iti the raffinate phase.@ Additionally, h6ating th&: extract 45 phase tends to.desolubflize some of the water in the extract phase and provides some or all of the reflux water. The teniperature gradient irhpbsed on the extraction step is such that the maximum amount of water will be dissolved in @ the @ solvent in the extractor at the low tem50 perature inlet of the extraction colunin consistent with selectivity of water over@ salt. Aftet the extraction step ,is completed, the extract and raffinate phases are separated and t-he extrac@t phase is heated and increased in tei,nperature till @ a temperature is reached at @which @the water and water dissolvina s6lvent are I substantially im- 55 miscible. The extract phase is@then allowed to settle by gravity and@ a substantially pure water phase, withdrawn@ and treated to recover any solvent in the watbr and a salt-free @solv@ent phase containing 5 to 10,Yo chssolved@ water is recovered and recycled to the system, By imposing a temperatlire gradient on the extraction step substantially @ highly concentrated saline solutions can be treated in accordance with, th6 @present invention while st-ill obtaining the benefits of low e ments to carry out, the separation. :Raffinate saline solutions of concentrations up @to 12%, salt or more can 1 be discharged while feed @olutioiis c6ntaining up to 3112. @to 4% salt or , more can be treated t6 obtain a substantially salt@free water having less than 500 p.pm. of salt. This 70 technique allov6,s for treating of a m@inimum volume of saline solutibn feed:which substantially reduces th-..solvent recycle rate.arid the energy reqtiirements for distilling or, ot,herwise recovering solvent: fiom th6 -raffin te -phase. FIGURE I of the drawitigs is a schem@tic flow sheet 75 nergy require- 65 :N-methyl-see-butylamine 4 of a simpl-ified solvent extraction process for saline waters. FIGURE 2 is a graph showing the sblubility curve of water in typical amine so nt as re ate - to tempe ature. Curves are also,presented showing the depression of the curve due to aldditibn of salt to the. system. The @preferred,s6lvent that, can be used in acclordance with this invention: are @secbndary and tertiary amines with 5 to 7 carbon atoms per molecule which- have almost ideal physical - properties. for use in the desalination of water by solvent extraction. The low isolvent extraction temperatures make it 'possible to use low@@level heat and by selecting a part-icular solvent or solvent,s and/or;varying the particular solvent: mixture. the ot)erating tempdrature fbr the extraction and separation steps inay be varied to. suit ambient@ conditions. Salt is alniost completely insoluble in these sol@ents. With water they- have lower critical slolution temperatures (LCST). At temperatures below the LCST they are completely nuscible with water; at temperatures only moderately above the LCST, they are almost completely immiscible. Thus, the @,bulk 6f the solvent can be recovered for recycle by merely heating t@he extract and raffinate phases to a teinperature modera.tely above@ the LCST. The proper selection of solvent will@ allow the extraction to be conducted in a @convenient temperature range and decrease the h6atin,@ and cooling reqw'rements. The secondary and tertiary amines which are used in conjunction with this process may be used by themselves or in adniixture with each other. @ Selection of solvents can produce, a tailor-made solvent to.@fit the preferred operating conditions @ for @ a particular separa@tion. The solvents and solvents ratio@ if mixtures are used wiH vary with the: separation to be carried out, the ainbicnt temperatures where the separation is to be carried out, and the salt concentration in the feed. water. as well as. the minimum @alt concentration;desired iii the water:@p@od-Uct. Especially useful amine solv,ents for this process are those having. @the general, formula@ Ri-N(R,.)- R@ wherein Ri can be hydrogen or alky,l, and R2 and R 3 can be alkyl @ or @ C3 6r C4; alkeni@l ra@icals such @as @allyl, methyl @allyl@ and.butenyl, and the total number 6f carbon atoms in@ the molecule is 4 to 7. Examples of thecompounds that can be u@ed are listed below.@ Ttiethylan-iino@,,. MethylethyHsopropylamine Methylet-hyl-n-propylan-iine Dimethyl-secondary@butylamine Dimethyl-tertiary-biitylaniine, Dimethylisobutylan-iine. Dimethylethylamine,@ Methyld@iethylamine Dimethylallylanu'ne Dimethyl-n-propylamine Dimethylisopropylamine Diisopropylamine Di-n-propylamine Di-allylamine N-methyl-n-amyl@@e N-ethyl-n-butylamine N-ethyl-see-buty.1ainine N-ethyl-tertiary-butylamine@ N-ethyl-n-propylamine N-etllyl-iso@ropyl@niine N7Methyl-n-butylam'me N-methyl-iso-butvlanune N-methyl-tertiary b@tylamine Dimethyl, 111-dimeth pr6pylaniine@ -Yi Dimethyl, 1-methyl butylamine Particularly preferred @compounds for carryin 6ut applicants', process @ aric@ @triethylan-tin!Dl mefhyldiethylamine dimethylisoprop@lamine,@ diri@ethyl tertiary but3,lamin.e,, and mixtures thereof. The aqueous solutions that can be contacted @with the@

5 above-mentioned solvents to carry out selective water extr@ction from the solutions can contain any conipound which is water soluble and which compound is not soluble in the solvent used and will not react with the solvent. In a more speciiic aspect of the present invention saline water solutions are contacted v;ith the solvents to selectively remove substantially salt-free water. Saline waters include brackish water, sea water and in gen@-ral salt solutions of a-@iy kind in which the solvent system is compatible. Thiswouldincludesodium,cliloridesaitsolLitions of from between 0.5 w,,t. percent chloride to ;about 10% sodium chloride. The critical fedttire of the present invention is to carry out the extraction step over an imposed temperature gradient rather than isothermally. When an isotherriial extrac,tion is carried out the amoiint of salt present in the water dissolved in the extract phase is set by equilibrium conditions at that temperati-ire and these are related to the amount of salt in the saline solation raffinate phase. - Therefore, isothermal condition at best can only reduce the salt concentradon a relatively minor arnoliilt. To obtain potable water, therefore, it is necessary that the saline sol.tition fed to the process where the extraction is carried out isothermally be relatively dilute; namely, less than abolit 1% salt concentration. The raffinate phase discharge will contain arotind 1% or sligh'tly more salt concentration. Therefore, it is a novel feature of this invention to carry out the extraction step over an imposed itemperatlire gradient. -Ihe temperature gradient is selected s6 that during the countercurrent extraction, the temperatlire which the eytract phase sees is gradually increase, while the salt concentration of the raffinate that the extract phase sees is gradually decreased@ Tbe.increase in teqiperattire of the extract phase and the decrease in salt concentration of tl-ie raffinate phase are adjusted so that one compe@isates for the other and the total amount of water dissolved in the extract phase remains about the same throiighout the extraction; e.g' , 30 to 40%, while the salt concentration of the water in the extract phase is substantially decreased during the counterctirrent contacting -.and extracting step. The temperattire gradient imposed on the extraction step is selected so that, at the minimtim temperattire of tile extraction step, the solvent will dissolve about 35 to 45% water, whereas at the maximum temperattue of the extraction step, the solvent will still contain about 25 to 35% water. The maximum temperature of the extraction step is s.-lected so th,,lt the solvent will still contain at least 20% water. Minimum solvent extraction temperature can be O' C. to 40' C., ge@ierdly 5' C@ to 30' C., ard preferably about 10 to 20' C. This minimum temperature will depend Lipon the elivironmental conditions at which the ex-traction is to be c,,)xiied out, the conceiitration of the saline water being treat6d, lan'd the selection of solvent. The extraction temperature gradient iriposed upon the extraction step will be between about 5 to 30' C., more generally 10 to 25' C., preferably about 15 to 20' C. The maximum extraction temperature will be 20 to 70' C., generally 20 to 50' C. As the water dissolved in the extract phase approaches pu.,e water and the water in the raffinate phase; that is, the water in contact with the extract phase, due to reflux becomes more dilute, the solubility curve of water dissolved in ti-le solvent phase approaches that of the pure water curve. The solubility clirve for pure water for a typical amine solvent is shown in FIGURE 2 of the drawings. Addition of salt to the w-,tter being tre,,ited will lower this curve on the temperature scale but it will still maintain abolit its same shape. Therefore, if the water being treated has 0% salt (curve 1), it will have the pure water curve. If it has 5% salt, it will be lower (cu,rve 2), and if it has 10% salt it will b,e still lower (ctirve 3); As the extraction is being carried oil-t the salt in.,the water in the extract phase is reduced and the salt concentrationof tlae feed being tre ated; i.e., ra.Tihate,phase, is gradually 3,177,139 6 increased. The salt concentration in the raffinate layer decreases in 'Lhe irea in the tower above the water feed inlet dLTe to reflux and the salt concentration in the Nvater layer becomes very diluted and the solubility curve approaciies -that of the pure water curve. Th-- separation temperature is that temperattire at which the ext.-act phase, after being separated from the raffinate pha-Se, is heated at which the water becomes substantially immiscible with the solvent. The solvent is selected so 1( that it requires a minimum incraase in temperatlire from the ,Op of the extraction tower temperature to the separation temperature. The temperature is selected so that the amount of water that remains dissolved in the separated solvent to be recycled is less thanabout 5 to 10% 15 water. Depending on the system used, this temp@-rature will be 20 to 80' C. or generally 20 to 6O.' C., and specifically n@bout 30 to 50' C. The temperature difference between the reflux temperature and the separation temperature is desirable to be kept at a minimum with the 20 requirement that less than about 5 to 10% water be present in the @separated solvent, but can be 5 to 40' C., generally 5 to 30' C., and specifically 10 to 20' C. The factor which concerns the economics most, other than solvent loss from the system, is the amount of solvent 25 recycle that is required to obtain a specific quantity of desired salt concentration water. Solvent to saline water feed ratios will generally be in the range of 0.5, to 10, more generary I to 5, and preferably 2 to 3. The solvent ratio is selected so that maximum water is extraeled 30 from the saline feed solution per recycle rate of solvent to system. As @the extract phase continues up the coliimn after the countercurrent contact with the feed, it passes the feed point of the soine feed solution and goes iiito the reflux section of the tower. In this section the sep35 @arate water phase, in the two pl-iase extraction step, can be provided by reilILix of fresh weler. This reflux section can be heated above the temperature existing at the point of water feed entry and at this temperature some water dissolved in the solvent is thrown out of soliition. This 40 may serve as a refliix or additional reflux can be added. Tle total percentage refflix wiU be 10 to 50%, and preferably about 25 to 35% by volume of the water in the extract phase solvent. The amount of reflux required to obt@tin water product 45 6f the desired purity obviously affects the economics of the system. The more reflux that is used ' the purer the recovered water will be. However, the less water recovered per volume of solvent recycle. The process will be explained in more detail with ref50 erence t6 FIGURE 1 of the drawings. FIGURE I is a diagrqinm-,tic diagram illustrating the method of the preserit invention. Valves, pumps, heaters and similar apparattis have been omitted for the sake of simplicity. It is to be understood that those ar-- to be provided as 55 reqti,.red as will be appaxent to those skilled in the art. Referring to the drawing, saline water having a 2 to 4% concentrgti6n in sodium chloride is fed through line I into heat exchanger 2 whereby the ten-iperature of the water feed is adjasted to a temperature interpiediate the maxiGo mum extraction temperatur6 and solvent input tempera. tl,,re; for example, about 16' C. The thus heated water is passed into extractor 4 through line 3 and passes downwardly therethrough colintercurrently to solvent entering through 'line 31 at the bottom of' the extract6r. The 65 solvent, prior to entering the extractor, is cooled by heat excbanger 29 to a temperature a little below the minimum extraction t ei-nperature,arid is rnaintained; for exam-ple, at about 7' C. The temperature gradie@it in extractor 4 between the top ald boftom of the extractor is i-nain70 tained at about 12' C. by controlling the rate of solvent feed and water feed and ihe de,-ree of cooling of this I solvent and the aniount of heatina, in, the heater section 14 of the extrac,Lor (which heating pro-@ides part or all of the reflux). By controlling the temperature of th,-se tv,,o 75, streams and th-. voltime of throughput of each stream, the

7 .temperature -radient in the extractor can be -carefully controlled. Additional control can be obtained by separately heatin.- or cooling sections of the tower externally. .The raffinate is removed through line 13 and will contain 8 to 12% or more salt concentration. The cool raffinate 5 is removed from extractor 1 4 through.line 18 and is i-@i,directly contacted with recycle solvent in exchanger 19. -This contact,serves to @precool the solvent prior to the @adding of refrigeration to the solvent. The raffinate is then @sent@ to isolvent recovery stage 20 as will be ex10 plained hereinafter. The extract phase as it continues to rise, in extractor 4 countercuriently to @the deseeiiding @raffinate phase, is gradi,ially heated from about 9 to 10' C. to about 22' C. in the column' Part of the heat is@ added throu,-h pre15 heatin.@ th-. saline water solution to be treated' and the remainder , is a I dded by he@ting the extract phase jlst .before @it leaves the extractor column by h--atin-, means 14, and the descending warm reflux water which is , separated out of the extract phase due to the heating pro20 vided by hedter 14. The extract is rcinoved overhead. from the extractor 41 @through line 5. Additiora@l refluk water, which @has bee-n preheated to the desired teniperature, may be admitted in the top of the tower as neces.Sary, throtigh line @5A. The thus warmed extract phase, is then heated to the separation teinperature and sent to separator 11, where .it is allowed by gravity settling to. separate, into two phases, a substantially w@ter-free solvent phase 9 and: a substantially solvent-free water phase;10. Heat to raise 3o the@ temperature of the extract phase to the separation tempe,rattire can be -provided by any siitabl-- h@ating means., For exaniple, a suitable heat exchang-@ means whereby heat is recovered from the hot solvent iin layer 10 by suitable @heat exchange in exch I anger 6 can b 35 ,e provided@ Additional heat can be provided from a low value heat source; for example, from; low temperatut@steam, introduced through line 5 and removed through line 16 in a suitable heat exchanger 8. The ratio of solvent to saline water feed is controlled 'iO so that-the solvent ratio of about 3 to I is used. At the initiation temperature of the extraction of about 101, f-I and the outlet temperature@ of the extract -phase of about 22' C. the temperature gradient is established inL the extractor column 4 of abo ut 12' C. The extract phase 45 bei.ug remov&d fro @ the, m extractor at a temperature 6f about 22' C. needs only to be @inereased by about 10' C@ to a temperature of about 32' C. to provide substantig inimiscibility between th@- solvent I and water I dissolved in the A sufficient: amount I of a sub tantially 60 salt-ftee water can be refluxed in the tower, which refiux can be provided by heating up the extract phase by heati@n.@ means 14 and provide reflux of about 25 to 35%@ of the extiact water. In the scli6me illust 55 raied in FIGURE 1, which is merely one @ proposed scheme, several heat exchange econoniies are: provided. For example, the heit from the rec,ycle solvent from the separator is absorbed in -the top of th-, tower t6 provide reflux, and is also usecl to provide preheat for the saline water feed. The solvent is further 60 dooled by indirect contact - with I the cold co@icentrated briia6 solution removed from extractor 4, in- heat exL. changer @19, and refrigeralion' is added in heat exchanger 29.@ @ The heat from @ t I he @ water ;Phase, before or after 3,177,139 8 vent separited in phase 9 -will contain about 5 to 10% water at the separation temperature used.and is recycled to the process. Make-up solvent is added through line 13 together w-ith solvent recovered from @the two solvent z,recovery systems. The solvent can be suitably recovered from the wattr product by heating @.to@ distill the sblvent overhead or by suitable solvent extraction with a solvent wh:ch is immiscib.-le viith water @ancl vzhich selectively dissolves, the arii-ine solvent. Th-- @so'@vent @ recovery from the brine solution cAn be by heating it to distill it off, b@,it pre,,@erably since @ this is @ dt low temperature,: a suitable selec@tive solvent extraction techniql@e can b,@ used. All the above means for recovery of solvetit are iknown in the art and need not:b@ further de@eribed. The product waller @an be passed bver charcoal or other adsorbent slich. as silica gel or adsorbent clay to remo-,,e any small am@ ouats of sol@ent. remaining;in:ffie water., The adso.-bent can be re.-e-@iera@ted when required alidthe amines can be recovered. FIGURE 2 of the drawings.shows a graph of a typical amine s,olvent of tels invention wherein the weight percent of water dissolved is plotted aga-@'nst temperature. Where thele is no sodium chloride in th-. system, solubility of the water in the solvent is showli by curve I. - TE@s culrve represents the amount of witer -that will.stay in solution in,a typica@l solvent at a particular temperature. Curve 2 shows.the amount t solu i curve will be depressed by adding about 5% sodium C e to @the s,,,stem. The amount of salt in the water dissolved in the solvent will be stibstantia-Uy less than the aniount of salt..in the water phase. Ctirve 3 -ho-,vs a sirnilar curve fbr a system containing about@12% water@ It can be seen from these typical @ curvos @-that the solu-, bility of Water in a typical@ solvent at a specific temperature is substantiallv reduced -a@ the salt conteiit of the water@phase increases., By carrying out a coiintereurrent solvent extraction step with an in, posed temperature gradient, and a suitable reflux @and@ by proper selection of the maximum and minimum temperatures;of the,imposed temperature gradient, a separation can@ be @cairied out: whereby the, -solvent will @ inaiutain dbout a 30 to 45 % water concentration while the salt concentration is:graduallydecreased,@ For example, @considei a countercurrent c6ntact tower where the extract phase at the top of the t6wer@ in the.reflux section sees water i n the raffinate phas-- PonWning ab6ut 0.25% sodium chlo ride and , the extiact phase at the l:bottom of the:tower sees raffinate @hase containin@, 12% sodium chloride., At the nupimui-n tenlperature iof the extract step , of about 5' C@, repre sented by@ point A; on the gtaph, the soiv ent extract phase wfll dissolve about 44% Nvater and the salt concentration 6f the@ water in the, extract phase will be about 51/2 % salt. As@ the extract @hase rises in the contact tower and is heated to al,)out 10 degrees while being, contdctod coun@tercurrentlv with d,scending raf-nnate pha se havmg about 5 9@o sodium, chloride &@e water @ concentrati6n in the eX7 tract phase will be about 40%, aiid@thel salt concentration of the water in this phase: about 41/2%. @ Ati,the top of the tower @where @the, extract conta@,ts reflux, having ab6ut 0.25% salt: and at a temperature, of -about 20' C., the extr@act phase, will @ coni@rise. about 30% water and will have a salt conci-ntration of about 500 P.P.m@ As t@he water in. the@ ex@ract phase becomes. substantially j'ree of g-al@, and the: -water in ;the@ @@ra,%nate ' phase @ ' @ ich with wh solvent recovery from the water phase, is recovered in, 65 it has @baen contacted becom es@more di@lute in salt, the curve of solubility of water in the solvetit@app roaches that heat exchan.- er.6 to provide additional heat for the sol@ vent extract phase removed in the e I xtractor. In' this proeof the pure water system represented by curve 1. - A suitabla separation. tem re tild @e @ about @ 40'@ peratti wo which ess,. a. ;concenttation @ of sodium chlo@-ide ' in the ia@Knate is@marke,,d by point C@L The temperatur@ gradicit i osed layer will-be- about 8 to 12% -or -more. MP 70 on extractio n slep is @ measure d by points Al and B on. the The economics of this process is severelv affected bv graph I @ going fiom the ina mun., extrar@ I , s n xi _Lion te@np-.rathe loss of olveiit. The sol@,ni riu t recdicred from ture 20 point B @@to the-sel)arati on ten,.perature @40 point the r@ffi@late @layer thr-oilgh a @uitable qolvept' recovery C, oil i 20' increase is required@ to' separate th6 extract stagd 20 and also recovefed from the water prbduct layer phase into by suitable solvent ree6ver - I ivater having@less than 500: p.p.ri. sodiun, chloy ayer system 26. The sol- -5 ride and aiuine solv e -ep t e n t T h a r a e d @ o l v e n t . P h a s e i w i l l

3,177@139 9 contain less than about 5% water, The solveit can then be recycled directly to the process. The@ invention is further illusttated by the following exaniples. EXAMPLE- 1 5 l,n order to% illustrate the solvent-waterl.-salt relatioilship, a I to I ratio of triethylamine solvent to a saline solution Nvere@ mixed at varying t-ziiip-.rattires gnd concentratio,iis of, sodium chloride. The water-feed to the extraction steps were varifd between I and 9 wt. percent slodiiin-i 10 .ciiloride and- extractions were carried otit in temp-@ratiires between 5 and 19 1 .7' 1 C. I-n each case the solven-t and water feed were mixed then allowed tb se@narate int 0 two layers and each layer anajyzed for water content, sol@ve,nt content, an'd salt coicetitration. The results ob- 15 tained are reported in the foilovvin.- Table 1. Table I 10 temperature of about 16' and descends in the column countercurrently to a, rising stream of solvent which is introduced at about 5' C. to give a minimum extraction temperature of 9.5' C. The ratio of triethylamine solvent to salt water is ab6ut 2.5 to 1. The temperature of the salt water and of t,he solvent and rate of introduction is controlled, so that the temperature gradient existi-.ig between th.- bottom of the tower where the solvent is introduced and at the 3 ft. mark where the salt water is introduced@is about 16' C. The last 15, feet of the, 18 foot-colun-in is us-,d for rectification and in the top of the column refl@ux is provided by heating the extract,phase to a ten-lperat-are of about 22' C. adding heat by indirect cont@act in the top of the tower. This increase in the temperature causes about 30% of the water in the solvent extract phaso to come out of solution and the water is used to wash DISTRIBUTION COEFFICIENTS H20-TRIETHYLAMINE-NaCl SYSTEM RATIO BRINE TO SOLVENT 1:1 Feed Extract Phase, Wt. Rafrinate Phase, Wt. H20 Percent Perc ent LCST, Toinp., 0. wt. C. Percent NaCl H20 NaCl Solv. HzO NaCl Solv. 0 ------ 19.6 ---- ------ ------ -------------- ----- --- 19.7 ----------------------- 1 36.0 .162 1( .42) 63.8 88.0 1.22 1( 1.39) 10.75. 3.3 16.9 19.6 ----------------------- 3 22@ 5 . l@5, .51) 77.4 89.2 3.26 3.53) 7. 6 6.95 10.9 19.6 ----------------------- 6 16.1 .069 .42) @3@3,8 86. @ 8.35 8.8 5@ 2 22.8 5.8 19.6 ----------------------- 9 10.1 .022 .22) 89.9 81.2 8.73 9 ' I 4.1 45 <1. 9 @17.0 -------- ------- 3 82.1 .34 (1@ 06) 67.6 88.0 3. @@4 3@- 76) 8.6 3.7 10.9 14.6 --------------- : ------- 3 43.4 .88 (1.98) 55.7 85.7 3. 72 4.16) ID..6 2.14 10. 9 14@6 ----------------------- 6 25.3 .385 (1@5 ) 74.3 87.0 6.73 7.2 ) 6.3 4.92 5.8 14@6 ------------------------ 9 16.2 .162 ( .98) 83.6 86.2 9.17 9.6@) 4.7 10@ 6 <1. 9 9.5 ------- -------- 6, 40.9 1.97 (4.6,) 57.2 83.6 7.8 8.5 8.6 1.92 5.8 9.5 ------------ ----------- - 9 28.6 .82 (2.8 ) 71.2 84.8 9 @10 -5 5.3 3.97 <1@9 5.0 ------------------------ 9 44.4 2.62 (5.6 ) @53.0 83.9 11.5 (12.1 4.6 2@3- <1.9 I Values iii parentheses are on a NaCI+H20 basis. The equilibrium data for the water-trie',liylaniire-sodiun, cl-iloride system at the @everaltemperatures presented in Table I show that by proper adjustment of th-. extraclio tion temperature aiid the maintaining of a ten-iperatu.-e gradient in the. extraction, zone, it is. possible to. apply the solvent extraction, prbcess to the desalination of salt solutions@ at least as concentrated as, sea water (3.5% ) and to discharge a brine containing at least 12% salt. The decreasf, in the ability of the solvent to extract water at constant temperature as the salt content of 'Lhe feed water was increased was clearly shown iii Table 1, thus, when triethylamine was contacted, with 1 % salt sol,,ition: at 19.7' C. the extract pha e contained 36.0% water, but when the solvent was contacted With 9@% salt solution at 50 19.6' C. 6n'y 10@1% viater was contained in the extract pha.@e. Hoviever, the data also show that the presence of salt lowers the LCST, thus permitting the extraction operation to be conducted@ at a temperature below the normal LCST with pure water; thus, for triethylamine the 55 LCST with pure water was 19.6' C., but with 9To salt solution it was below 1.9' C. Furthermore, as the temperature was lowe;,ed: the ability of the solvent to extract water from a solution of a given salt content was increased; thus, w@'ien triethylamine was@ contacted with 9 % salt solu- 60 t;on at 19.6' C. the extract phase contained only 10.1% water, but when the same exppriment was conducted at 5.0' C. the extract phase contained 44.4% water. The separation factors (a's) were not adversely affected by decreasing the- temperature as the salt @ontent of the feed 65 water was increased. All of the alpha values shown,were extre@-nely favorable with the lowes@L- being , 1.9. EXA@VIPL E II A count-rcurrent extraction is carried but in extraction 70 apparati.is coiisistling 6f an equivalent to 18 theoretical 'plates packed column, 18 feet in height. Feed water is introduced into the 18 foot @ column at: a point about 3 ft. from the bottom of the colunin. Salt water feed contaiiiing about 3.5% sodium eiiloride is introduced at a 75 salt out of the water remaining in the extmet phase, as it rises in the columr,. About 70% of the water remaining in the extract phase i removed and contains about 118 p.p@m. sodium chloridei Th,- extract phase is then sel3arately heated to a temperature of about 30@' C., at which temperature the water is substantially immiscible with the triethylamine solvent and allowed to separate i,-@ito two@ layers. The solvent will comprise about twice the volume of the water and will contain in solution 5% wa*er. As the. salt viater feed goes down the column, in@ admixture with the reflux from the top of the column, it cont creases in sodium chloride concentration ond@ s renioved from the botiom of the column. at a teinperature of about 9.5 ' C. andl coiitains a salt concentration of abotit 15% sodium chlorido,. Iii- addition% to,desalination of salt water th6 invention can be einployed to concentrate various brines for the recovery of valuable salts. Other advantages accrue from this technique ' The highly concentrated brine that is discliarged can- be an economic source of bromine and potassium and in ce:tain areas make the production of solar salt -@ttractive. The small volume of the discharge brine means a lower cost for the recovery of solvent from this stream. It also means that a smaller volume of feed wate,r need be handled to y,'@eld a given volume of desalinatedt water@ The process is versatile with respect to energy sources, sliice esse,ntiallv free heat can be obtained from such low . value sources as exhaust steam, gases of industrial engines, cooling the water from condensers, and from any other sourco with a relatively low temperature heat. Theprocess lends itself well to adaptation to existing,environme-@,ital conditions. Feed water ranging in temperature from 15@ to 55' C. can be handled by altering the nature of thi-, solvent co@nposition to give the inost economic advantages. In those processes requiring high temperatures, ttie prob-lens of scaling and corrosion present formidabl-. barriers to economic production of fresh water. In sol-

3)177 l@39 vent extraction the problem of@ scaling is eliminated by ,the low temperature of the operati6n and the solvents eliminate the growth of slimid- and encrusting organisms. Corrosion is reduced becaus@'of the inhibitory reaction of amines towards the corrosion of iron. Although tlle invention has been described primarily with r--gard to the production of water from the extract .phase, it also is useful for low temperature dewatering in the production of conceiitrates from the raffinate phase. It is apparent froni the reading of the foregoing specification that the invention is susceptible tb variotis changes and modiiications without departing from the spirit and scopq thereof. What is