DE2151207A1 - Desalination of aq solns - using a polyethylene oxide /polypropylene oxide copolymer as aid - Google Patents

Abstract

The copolymer of mol. wt. 500-1500 is added to the aq. soln. e.g. sea water which, opt. on raising the temp. separates into a copolymer rich, low salt content phase (1) and a copolymer poor, high salt content phase (2). These are separated and an aq. low salt content phase recovered from (1) by raising the temp. e.g. to 50-85 degrees C. The copolymers are not saponified during the process and do not appreciably increase the soln. viscosity so that the process can be operated continuously. Phase separation is rapid.

Description

Process for lowering the salt content of aqueous, saline Solutions The present application relates to a method for lowering the salt content of aqueous salt solutions. Copolymers of the polyethylene oxide / polypropylene oxide type are used used to by any number of separation operations aqueous phases with compared to the Starting solution to obtain reduced salt content.

US Pat. No. 3,386,913 already discloses a method for reducing it the salt content of aqueous solutions, especially for the desalination of seawater, known. Copolymers with molecular weights of at least 5,000 are used here, which are added as aqueous solutions or directly to the water to be desalinated, to obtain aqueous, low-salt solutions through multiple demixing processes and phase separations to obtain. Examples of organic auxiliaries are copolymers, which Have ester groups or other functional groups such as nitrile groups, for example copolymers of various diesters of maleic acid. Such Copolymers have the disadvantage that, when higher temperatures are used, saponifications respectively.

undesirable reactions on the functional groups of the copolymer enter. It also makes use of copolymers with molecular weights from 5,000 to 10,000 even the increase in viscosity of the solution or phases is disadvantageous noticeable, which leads to an increased susceptibility of the pumps during continuous operation of the desalination process.

It has now been found that low molecular weight copolymers with molecular weights in the range from 500 to 1,500 from the monomers ethylene oxide and propylene oxide for Reduction of the salt content of aqueous solutions, e.g. seawater desalination, particularly suitable.

These copolymers have the advantage that they are under the reaction conditions the process does not saponify and also the viscosity of the The salt solutions to be processed are not unnecessarily increased, which is advantageous the continuous implementation of the procedure. From the specialist could not low molecular weight copolymers of this type are expected to be advantageous with aqueous salt solutions as a function of the temperature in the mixing range in which a rapid phase separation takes place.

The invention therefore relates to a method for lowering the salt content aqueous, saline solutions in the presence of low molecular weight copolymers, if necessary, heating the solution until two phases with different copolymer content are found form, namely one that is rich in copolymers, low in salt and one is low in copolymers, rich in salt Phase, separation of the water-containing, copolymer-rich, low-salt phase, separation this phase by heating to a higher temperature and obtaining an aqueous, low-salt phase from these separated phases, which is characterized by that copolymers of the type rolyäthylenoxid / polypropylene oxide are used, the Have molecular weights in the range from 500 to 1,500.

Possible copolymers for the process according to the invention are those having molecular weights in the range from 500 to 1,500, preferably copolymers with molecular weights in the range from 600 to 1,100 are used.

The miscibility gaps in the systems Easser, Salt, Copolymer depending on the temperature are given on the one hand by the molecular weight on the other hand by the composition of the copolymer, as well as the composition of the Kompoccntn.

The temperatures used for phase separation are for the lower Temperature range between +15 and + 45MG, for the upper temperature range between +60 and +9000.

The copolaser generally has a larger proportion of polypropylene oxide proportions of 84 to 95 percent by weight of polypropylene oxide are preferred and correspondingly 5 to 16 percent by weight of polyethylene oxide, based on the monomer, used.

The process can be either discontinuous or continuous be performed; temperatures in the range from 20 to 8500 are generally used adhered to, with temperatures of preferably for the lower segregation range 20 to 4500 and for the upper segregation range temperatures between 50 and 8500 applied we? @en. The copol; 'mers can be used in the form of aqueous solutions be or in the liquid or solid state directly to the saline aqueous Solution, the salt content of which is to be reduced, can be added. Under certain Conditions, it is also possible that when adding the copolymer to the aqueous Saline solution form two phases.

In this case it is not necessary to cool it down accordingly produce a homogeneous solution and then phase separate again by heating bring about. In such a case the first operative act takes place as an extraction stage and after separation of the copolymer-rich, low-salt phase this is followed by heating to temperatures in the range from 50 to 8500, with again two phases are obtained, which are further processed in the usual way.

The copolymers of the invention are preferred, in particular if they are in the liquid state of aggregation, directly to the aqueous salt solution given. In general, concentrations of 20% are used in the aqueous salt solution up to 80 percent by volume, based on the copolymer, are preferably prepared however, concentrations of 45 to 70 percent by volume, based on the copolymer applied. It is also possible to first dissolve the copolymers in water and then add to the aqueous salt solution, however, this route is economical Associated disadvantages. This is done according to the procedure (II is based on the following From exemplary embodiment e explained in more detail.

Example 1 containing 26 parts by volume of a liquid copolymer 90% propylene oxide and 10% ethylene oxide (molecular weight MW = 1090) were with 14 parts an aqueous saline solution with a concentration of C 'NaCl = 30 g / l at 2000 (Point Ao in Fig. 1; the salt concentration in Figs. 1 to 3 is respectively converted to the amount of water contained in each mixture or phase.

i) such concentrations are uniform in all figures with C @.) When heated to 37 ° C, the homogeneous solution resulted two phases of the following composition: Upper phase: (point A 'in Fig. 1) 11 parts by volume with CNACL 1 = 28 g / l.

16 5E of these 11 parts by volume consisted of the copolymer propylene oxide - Ethylene oxide, hereinafter referred to as PÄO, and 84% from 1120. On water In relation to this, this would correspond to a salt concentration C 'NaCl = 33.3 g / l.

Sub-phase: (Point A '' in Fig. 1) 29 volume parts were used as the sub-phase obtained, for which CNACl ranges to 0.2 g / l.

These 29 parts by volume consisted of 80% PAE and 20% H20. In relation to water, a salt concentration of is obtained for the lower phase C 'NaCl = 1 g / l.

The lower phase was separated from the upper phase and heated to 8000, two phases B 'and B "with the following composition: were obtained: Upper phase: 2 parts by volume of an aqueous salt solution with a concentration of CNaCl = 18 g / l, or C ' = 18 g / l The upper phase practically no longer contained any PAO (point B ').

Lower phase: 26 parts by volume The lower phase consisted of 88% PAO and 12% from 1120 and was practically salt-free (C '= O g / l).

The upper phase divides the water depleted in salt, from 14 parts a saline solution with a concentration of C resp.

C '= 30 g / l were 2 parts of a lower-salt solution of the concentration C '= 18 g / l obtained. By repeating this separation process as often as you like or through continuous process management, for example, seawater can be completely desalinated will.

Example 2 25 parts by volume of a liquid copolymer Consists of 84% polypropylene oxide and 16% polyethylene oxide (MW = 900), at 20 ° C with 25 parts by volume of an aqueous salt solution, the concentration C'NaCl 30 g / l mixed (point A1, Fig. 2) Figure 2 shows the results of this experiment shown, with the salt concentrations converted to the water content C'NaCl are given as the ordinate. When heated to 3500 emerged from the homogeneous Solution of two phases A'1 and A "1 of the following composition: Upper phase A1 s 21 parts by volume consisting of 1% PÄO and 99% H20; C'NaCl = 37.4 g / l, sub-phase A @ ': 29 parts by volume consisting of 79% PÄO and 21% H2O; C'Nacl = 8.1 g / l.

The lower phase separated off at 35 ° C. was heated to 85 ° C., the Phases B @ and B @ 'were obtained: Oberphas'o t 1 3 parts by volume of aqueous salt solution; CNaCl = 15.5 g / i This upper phase contained practically no PAEO for 34 seconds 26 parts by volume (88% PAE and 12% H2O); = O g / l.

The sub-phase Bt 'obtained in this experiment at 85 ° C. can be advantageous instead of pure, liquid copolymer as a starting solution for further separations can be used.

Example 3 A liquid copolymer was used for this experiment 95% propylene oxide and 5% Äthty lenoxid with the molecular weight MW = 673 used. (Fig. 3) 18 parts by volume of the copolymer were mixed with 28 parts by volume of saline Water (CNaCl = 30 g / l) mixed at 2000 (point A2, Fig. 3) Ilierbei was none obtain homogeneous solution; 2 phases were already formed at this temperature AO and A '', of the following composition: Upper phase A2: 28 parts; CNaCl = 30.5 g / l. This upper phase consisted of 12% PAE and 88% water.

Based on water, C'NaCl = 34.7 g / l.

Sub-phase A2 ': 18 parts by volume; CNaCl = 2.6 g / l. This sub-phase consisted of 73% PAE and 27% water. In relation to water is calculated C? NaCl at 9.6 g / l.

The lower phase A21 was separated off at 20.degree. C. and heated to 85.degree.

Two phases B2 and 32 'formed with the following composition: Upper phase B'2: 1.5 parts by volume: CNaCl = 18 g / l. The upper phase consisted of 8% PÄO and 92% water, from this C'NaCl is calculated as 19.5 gXl.

Sub-phase B ″ 2: 14.5 parts by volume; CNaCl = 0.2 gjl, of which omitted 84% on PAE and 16% on water; from this information, C'NaCl is 1.2 g / l.

Claims (1)

Claim Process for lowering the salt content of aqueous, saline Solutions by adding low molecular weight copolymers, if necessary heating the solution until two phases of different copolymer content are formed, namely a copolymer-rich, low-salt phase and a copolymer-poor, salt-rich phase, Separating the copolymer-rich, low-salt phase, separating this phase through Heating to a higher temperature and obtaining an aqueous, low-salt phase, thereby gekennzetinet that copolymers of the polyethylene oxide / polypropylene oxide type used, which has molecular weights in the range 500 to 1,500. Sign. L e r s e i t e