DE2144251A1 - Process for removing salts from an aqueous solution - Google Patents

Description

DIPL.-ING. HANS W. GROENING

DIPL.-CHEM. DR. ALFRED SCHÖN 21 4425 I.

PATENT LAWYERS

S / R 14-66 e.g.

Rohm and Haas Company, Independence Mall West, Philadelphia,

Pa. 19105 / USA

Process for removing salts from an aqueous solution

The invention relates to the removal of salts and others Electrolytes from solutions using ion exchange resins. The invention is particularly applicable to the removal of salts applicable from aqueous solutions, from which 1) the salts should be removed as completely as possible, with 2) the ion exchange resins are to be regenerated as effectively as possible and it is undesirable that the pH of the Solution noticeably deviates from the neutral point during the procedure. The invention is also suitable for removing Impurities, for example for a third waste water treatment, as well as for the treatment of waste water from certain Deionization units.

It is known that salts can be removed from aqueous solutions in such a way that the solution is passed through a bed

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certain cation exchange resins in their hydrogen form and then passed through a bed of anion exchange resin will. It has also been found that by using certain anion exchange resins in which the polar groups are quaternary ammonium groups, this order can be reversed. If you follow any order however, the pH of the solution leaving the first bed differs markedly from that of the original Solution. In many cases, this is an undesirable condition affecting the applicability of ion exchange methods for removal constricts from salts. It is known that salts can be extracted from solutions using mixed beds of anion exchange resins in the base-regenerated form and cation exchange resins in the acid form can be removed. Even if many of those Mixed bed systems have been studied, however, only those have proven to be effective and technically interesting proven which contain quaternary ammonium anion exchange resins as the anion exchange resin component. The mixed bed system, which is the strongly basic quaternary ammonium anion exchange resin and the strong acid sulfonic acid cation exchange resin has been used extensively as it enables the utmost degree of salt removal achievable, and because the ion exchange resin components are easily removed separately and the individual ion exchange resins in the usual manner in the original ion exchange resin column can be regenerated (see, for example, U.S. Patent 2,578,937).

There are many cases in which it would be useful to use the strongly basic to replace quaternary ammonium anion exchange resin with a weakly basic anion exchange resin. this would result in significant economic benefits,

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since the weakly basic resin regenerates in a more economical manner can be called the former resin. It would also be possible to desalinate solutions that contain substances which can react with the strongly alkaline environment, which in the case of quaternary ammonium anion exchange resins are to be accepted in hydroxide form. Such systems have been investigated. However, their use could not be realized, since extremely poor results were obtained in a reproducible manner. Since weakly basic anion exchange resins in First and foremost, as acid adsorbents, the poor mode of operation of the mixed bed system was made up of a strongly acidic cation exchange resin and a weakly basic anion exchange resin, the unfavorable one Ascribed to the equilibrium that exists in such beds.

It has now surprisingly been found that it is possible is to produce mixed beds from strongly acidic cation exchange resins and certain weakly basic anion exchange resins, their mode of action by far exceeds the mode of action of such known mixed beds. In surprising The mode of action of such mixed beds can be determined by the kinetic mode of action of the weakly basic anion exchange resin component and not steer through the equilibrium of the mixed bed system. It was also found that it is possible, the suitability of the anion exchange resin component of this mixed bed system with reference to a kinetic To define the half-life of the anion exchange resin.

The poor results previously obtained using such mixed beds compared to multiple beds or in Series-connected beds made of strongly acidic cation exchange resins and weakly basic anion exchange resins

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obtained are demonstrated by Example 1 (the mesh numbers given in the examples relate to the US standard sieve series).

example 1

50 ml (16-50 mesh) of a strong sulfonic acid cation exchange resin made from a sulfonated gel-like crosslinked polystyrene resin (available for example under the trademark Amberlite IR-120) and an equal volume of one
Polystyrene / polyamine weakly basic gel-type anion exchange resin (20-50 mesh) (available for example under the trademark Amberlite IR-45), manufactured in accordance with US Pat Plastic hoses are connected in series (system B), the burette containing the cation exchange resin being connected in front of the burette containing the weakly basic anion exchange resin. The strongly acidic cation exchange resin is in the hydrogen form, while the weakly basic anion exchange resin is in the form of
free base is present. Another 100 ml glass burette is packed with 100 ml of a mixture, the 50 ml of each
the above-mentioned ion exchange resin (system A). A solution containing 500 ppm NaCl is then passed through systems A and B in parallel with a contact time of approximately 2 minutes. The outflows from both systems A and B are monitored by conductivity measurements. The following results are obtained:

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Drain

electrical resistance of the drain

Bed volume

1)

System A Ohm-cm 600,000 System B (! Mixed bed) 500,000 (Line) 500,000 20,000 1,000,000 10,000 1,000,000 1,000 1,000,000 1,000,000 800,000 600,000

Bed volume = combined volume of anion and cation exchange resin

The resistivity in ohm-cm of a 500 ppm NaCl solution is about 1,000.

Since the electrical resistance of the draining water changes directly with its purity, so is the resistance higher, the purer the water is. The mode of action of the usual two-bed system ^ - (B) is compared to the mode of action of the Superior to mixed bed system (A) when the above ion exchange resins are used.

Example 2

The anion exchange resin of Example 1 is replaced by a macroreticular weakly basic tertiary amine anion exchange resin (with such a particle size,

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particles pass through a 25 mesh screen and 95% remain on a 50 mesh screen) and repeated The procedure of Example 1 is then obtained results given below.

The macroreticular weakly basic anion exchange resin contains a tertiary amine functionality on a styrene / divinylbenzene matrix and has a strong fixed porosity in the resin bed structure. This weakly basic macroreticular Resin has a density of about 0.6408 g / ccm (40 lbs./cu. Ft.) And has about 40% voids and has a minimum exchange capacity of approximately 124 g (21 kilograins) (as calcium carbonate) per 0.028 m (cubic foot). These macroreticular resins are known materials and can be produced by known methods, for example according to the methods described in British Patents 932 125 and 9 32 126. The macroreticular mentioned above weakly basic resin is available, for example, under the trademark Amberlite XE-270.

Drain

lot t.vo'Lumen

electrical resistance of the drain

System A (mixed bed)

5,000,000

6,000,000 6,000,000 4,000,000 1,000,000

800,000

0hm-cm

System B
(Line)

2,000,000 2,000,000 2,000,000 2,000,000 1,000,000 800,000

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From the above values it can be seen that the replacement of the weakly basic gel resin in the mixed bed with the macroreticular weakly basic anion exchange resin achieved a remarkable effect.

Examples 1 and 2 are based on cation exchange resins that have been fully regenerated to the hydrogen form. Under normal operating conditions the cation exchange resin will usually regenerated to levels of 25 to 50% of the total that can be regenerated to the hydrogen form. Example 3 describes experiments which, when carried out, regenerate the cation exchange resin to such an extent has been.

Example 3

The procedure described in Example 2 is repeated with the exception that the cation exchange resin is reduced to one content is regenerated by 50% into the hydrogen form. The following values are achieved:

Drain Drainage loss (%)
(500 ppm NaCl inflow) System B Bed volume System A (Line) (Mixed bed) 60 2 <0, l 50 5 <0.1 HO 10 <0.1 35 15th <0.1 HO 20th 0.5 50 25th 1.0 60 30th 5.0

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The effectiveness of the mixed bed system is based on the above values in comparison to the two-bed system under practical regeneration conditions and operating conditions before.

Example 4

a) A mixed bed system is prepared according to Example 2, with the exception that the strongly acidic sulfonic acid cation exchange resin is used a macroreticular sulfonated crosslinked polystyrene resin and in place of the weakly basic resin Macroreticular weak base tertiary amine oxide resin (-25 + 50 mesh) containing approximately 20% amine oxide functionality (kinetic half-life of less than 7 minutes) is used. The quality of the draining water (where a 500 ppm NaCl solution is used) after 10 bed volumes

7th
is approximately 10 ohm-cm.

b) A mixed bed system is prepared according to the method described in Example 2, with the exception that instead of the weakly basic resin, a weakly basic crosslinked gel resin (-25 + 50 mesh) is used which is formed by condensation of polyethyleneimine and ethylene dichloride (the resin has an anionic exchange capacity of approximately 16.5 meq / g dry matter and a kinetic half-life of less than 7 minutes) '. The quality of this Mixed bed of runoff water (again being a 500 ppm NaCl solution used as eluant) is approximately 3 to 4 million ohm-cm after 10 to 15 bed volumes.

Are the results of the above examples interpreted in summary, one arrives at the conclusion that a mixed bed of a sulfonic acid cation exchanger har

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and a weakly basic anion exchange resin is either orders of magnitude better or worse than a conventional one Two-bed deionization system based on the same type of ion exchange resins. However, it was found that the effect depends primarily on the nature of the weakly basic ion exchanger, especially the kinetic ones Properties, in contrast to the prevailing opinion that the equilibrium behavior depends on the exercises a controlling function. It has also been found that the kinetic properties of the weakly basic anion exchange resin are critical. Is the exchange rate (kinetics) of the weakly basic anion exchange resin below a certain value, the effect of the material in the mixed bed is considerably worse than this is the case when the material is used in the double deionization system. If the speed is above this value, the effect is so noticeably improved, that it exceeds that of the two-bed system + ^ ms. if Even the importance of kinetics in ion exchange technology is known, but has never been so before the extreme sensitivity of the mixed bed system on one sulfonic acid cation exchange resin and one weak basic anion exchange resin, realized with respect to the kinetics of the last-mentioned ion exchanger.

The kinetic behavior of weakly basic anion exchange resins can by measuring the half-life of the reaction between the regenerated weakly basic anion exchange resins and a measured amount of a standard hydrochloric acid can be compared. The kinetic half-life measurement is carried out as follows:

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10 milliequivalents of the anion exchange resin whose kinetic half-life is to be determined with 2000 ml of 0.01 η-hydrochloric acid at room temperature (20-25 ° C) contacted, whereupon the mixture is stirred. Samples of the acid are then taken periodically and examined for their acidity until 5 mÄ have been consumed. Until this level of acid neutralization is reached The time required is plotted as the kinetic half-life of the time required for this is that half the capacity of the anion exchange resin is neutralized.

If this procedure is followed, the kinetic half-life becomes (or half-neutralization time) of the gel-like weakly basic anion exchange resin used according to Example 1 is determined to be about 30 minutes while the corresponding value of the macroreticular weak base anion exchange resin of Example 2 has a kinetic half-life of approximately 3 minutes. Even if the above examples and studies show that a kinetic half-life of 30 minutes is too long kinetic half-life reaction time should not be just 3 minutes. A reasonable upper limit is around 7 minutes. For effective practice of the present invention therefore requires that the weakly basic anion exchange resin has a kinetic half-life reaction time (or neutralization time) of about 7 minutes or less. the kinetic half-life reaction time of the weakly basic anion exchange resin must be about 7 minutes or less for this resin to be in a mixed bed in which the cation exchange resin component a sulfonic acid cation exchanger

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is, acts in a corresponding manner.

If the process is carried out on a technical scale the mixed bed operated in a column, to which the solution to be treated is fed in the usual manner in the downward direction will. It should be noted, however, that in practice there are cases in which the solution through the mixed bed in is sent in an upward direction. There are also installations in which the resin mixture is continuously countercurrent is guided to the direction of liquid flow. The invention is applicable to all of these installations and modes of operation applicable.

After the resin mixture is exhausted, it can be separated into its components in such a way that a stream of water or a stream of other suitable liquid upwardly through the mixture at such a rate is sent that the less dense weakly basic anion exchange particles are discharged and the denser cation exchange particles remain. The most suitable The speed at which the water flows upwards depends on the particle size of the resins, their relative Density, the uniformity of the particle size, the temperature of the water and other factors. That by a Bed of an anion exchange resin, water flowing upwards has the consequence that the bed expands, the expansion with increasing speed of the upstream water increases until the resin has been completely carried out by the water. The flow velocity that leads to the Has the consequence that a certain ion exchange resin is carried out by the water, is hereinafter referred to as "fluidization rate" of the ion exchange resin. To the

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Separation of the mixture of ion exchange resins should be a Columns are used whose volume is greater than that of the amount of ion exchange resin to be treated. Preferably the volume should be 1 1/2 to 2 times the volume of the resin to be treated. That through the column in an upward direction pouring water expands the bed. Since the bed is kept in its expanded state, the Density difference between the two ion exchange resins causes the lighter resins to collect on top and enrich the heavier ones below. To effect a separation of the mixture of ion exchange resins, the flow rate of the upward flowing water can be increased gradually until the speed is between the fluidization speed the weakly basic anion exchange resin and the fluidization rate of the cation exchange resin lies. The speed can also first be increased to a point at which a predetermined Expansion of the ion exchange bed is present, for example a 100% expansion, whereupon the speed is kept at this value so that a partial or complete separation of the ion exchange resin components takes place, whereupon the flow rate is increased to such a point that the weakly basic anion exchange resin is fluidized. After the anionic and the cationic exchange resin are separated once in this way, they can be regenerated at the same time in the same unit, for example according to that in US Pat. No. 2,578,9 described technology.

The above examples explain the invention by reference to a simple aqueous saline solution. The Invention

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However, training is also applicable in the same way to other aqueous solutions of ionizable materials, for example on solutions of salts of alkalis, alkaline earths and heavy metals with mineral acids, such as halogen acids, Sulfuric acid or phosphoric acid, as well as with organic acids such as formic acid, acetic acid, oxalic acid, Succinic acid, malic acid and citric acid. Other materials can also be used.

Similarly, the invention is not limited to the deionization of water alone, but can also apply to the purification of solutions of organic materials containing polar impurities can be applied, for example on the removal of salts from sugar solutions, for example acidic conditions during sugar refining to avoid.

In general, the process is using weak base anion exchange resins of specific gravity in water of less than 1.15 and with cation exchange resins with a specific weight in water of more applicable as 1.2.

Although the above examples demonstrate the effective use of a gel-like strong acid cation exchange resin in Combination with a macroreticular weakly basic anxon exchange resin show, so the invention is nonetheless also with both gel-type resins and with a macroreticular weak base anxon exchange resin and both feasible with gel-like resins as well as macroreticular resins or any combination of these resins, as long as the kinetic half-life of the weakly basic

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Resin is maintained. However, the weakly basic resin is preferably a macroreticular one Resin. The cation exchange resins used in the mixed bed are, for example, the sulfated or sulfonated phenol / formaldehyde resins, for example the in U.S. Patent Nos. 2,191,853, 2,228,159 and 2,258,160 Resins, the sulfonated styrene / divinylbenzene resins, described in U.S. Patent 2,366,007, in particular those containing 5% or more of divinylbenzene as a crosslinking agent in the copolymer, as well as the crosslinked ones Polymers of polymerizable acids described in U.S. Patents 2,340,110 and 2,3UO,111.

As mentioned above, the weakly basic resins can be either gel-like or macroreticular. From a chemical point of view, the weakly basic / ^ ion exchange resins can consist of the reaction products of a primary amine or a secondary amine or a mixture of two such amine types and an insoluble crosslinked copolymer of an aromatic monovinyl hydrocarbon and an aromatic divinic hydrocarbon, the copolymer being haloalkyl groups of the formula "C _n H _2n X comprises wherein X stands for a chlorine or bromine atom, and - ^c _n ^H 2n" ~ ^ne ^ ^e alkylene group, in which η is an integer of 1 to 4 Resins of this type are described in U.S. Patent 2,591,574. Other weakly basic resins which can also be used are, for example, the condensate resins which are prepared by the condensation of, for example, epichlorohydrin with a polyalkylene polyamine (see, for example, US Pat. Nos. 2,898,309 and 3,005,786). Other weak base resins that can be used are the newer weak base anion exchange resins, the one

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contain tertiary amine oxide functionality and, for example

in the German patent specification (patent application

P 20 HO 618.2) . Other weakly basic resins can also be used. This weakly basic resins may be used as long as they can be used in a suitable form to a kinetic half-life of approximately 7 minutes to give or less. While the particle size of the resin can vary within the ranges commonly accepted in the art, it is still preferred that the particle size and particle size distribution be as narrow and uniform as possible. In particular, the particle size should be * 25 ' + 50, ie -25 or fall through a 25 mesh sieve, with the majority being retained on a 50 mesh sieve.

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Claims (7)

Claims 1. A method for removing salts from an aqueous solution, characterized in that the solution by a Bed is sent, which is a mixture of an anion exchange resin and a strongly acidic cation exchange resin contains, wherein the anion exchange resin is a weakly basic anion exchange resin with a kinetic half-life reaction time of about 7 minutes or less. 2. The method according to claim 1, characterized in that the cation exchange resin used as sulfonic acid groups contains polar groups. 3. The method according to claim 1, characterized in that as a solution to be treated containing an ionizable material Sugar solution is used. 4. Modification of the process according to claims 1 to 3 as a cyclic process for deionizing a liquid, characterized in that the liquid by a mixture of a weakly basic anion exchange resin and a Cation exchange resin is sent, the weakly basic anion exchange resin having a specific weight in water below 1.15 and a kinetic half-life reaction time of about 7 minutes or less, and the cation exchange resin The liquid contains sulfonic acid groups and has a specific weight in volume / water of more than 1.2 separating from the resin, water in an upward direction 209819/05 «/. BADORBBML 21U25i is passed through a column of the mixed ion exchange resins at a rate sufficient to that there is a 50 to 100% expansion of the ion exchange resin bed and a stratification of the two ion exchange resins, the speed of the upward flowing water for fluidizing the anion exchanger and for its separation is increased by the cation exchanger, the separate exchangers are regenerated and then the regenerated ones Resins are mixed again. 5. The method according to claim 4, characterized in that the liquid through a mixture of a weakly basic anion exchange resin and a cationic exchange resin is sent, the weakly basic anion exchange resin having a specific gravity in water below 1.15 and a kinetic half-life reaction time of about 7 minutes or less, and the cationic exchange resin Has sulfonic acid groups and has a specific gravity in water of about 1.2, the liquid is separated from the resin, water in an upward direction through a column in which the mixed resin is present, with a Speed from about 15.9 to 49, b 1 (4 to 12 1/2 gals) per 0.09 m (square foot) column cross-section per minute to cause an expansion of the resin bed and to layer the two "resins, the flow rate in the upward direction to 75.7 to 114.0 1 / 0.09 m ² / minute- (20 to 30 gals./sq.ft./min.) Is increased to fluidize the anion exchange resin and separate it from the cation exchange resin, regenerate the separated resins, and mix the regenerated resins again. _819/054 / * BÄD original 2H4251 6. The method according to claim U, characterized in that the liquid through a mixture of a weakly basic anion exchange resin and a cation exchange resin is sent, the weakly basic anion exchange resin having a specific weight in water below 1.15 and has a kinetic half-life reaction time of about 7 minutes or less, and the cationic exchange resin Contains sulfonic acid groups and has a specific gravity in water of above 1.2, the liquid from the resin separating water in an upward direction through a column of the mixed resins at an increasing flow rate from up to 75.7 to 114.0 1 (20 to 30 gallons) per 0.09 m (square foot) column cross-section per minute is sent to cause the resin bed to expand, to layer the two resins and finally to fluidize the anion exchange resin, whereby this resin is separated from the cation exchange resin , the separated resins are regenerated and the regenerated resins be mixed again. 7. The method according to claim 1, characterized in that the weakly basic anion exchanger used macroreticular resin is. BAD ORiQiNAL 209819/0544