BehZilter (Inhalt ca. 0,3[Harzbett-Volumina) als Turm platzsparend iibereinanderstapeln. Eine IFP-Aufberei- tungsanlage l6Bt sich dadurch auch zu Kosten in derselben GroDenordnung wie bei den iiblichen Entsalzungsanlagen erstellen (Einzelheiten iiber dieses Verfahren s. die Ar- beiten von Honigschmid-Crossich, S. 605, und Erbschwen- der, S. 607, in diesem Heft).

lonenaustausch und Umwelt

Im Rahmen dieses kurzen uberblickes konnten die viel- fiiltigen Einsatzgebiete fur Ionenaustauscher und ihre Verfahrenstechnik nur in grol3en Ziigen umrissen werden. Sie sind heute bereits eine etablierte Verfahrenseinheit in der Chemischen Technik. Ionenaustauscher leisten aber auch einen wesentlichen Beitrag zum Umweltschutz durch Entgiftung von Abwasser und Abgasen, bei der Riickgewinnung von Konzentraten und durch die Ver- meidung von Abfallprodukten, wie z. B. bei der Katalyse. Die Moglichkeiten der ProzeDverbesserung und die Um- stellung auf umweltfreundliche Arbeitstechniken mittels

Ionenaustausch in der chemischen Industrie sind bisher noch langst nicht ausgeschopft.

Eingegangen am 9. Mai 1975 [B 39051

Literatur

[ 13 F. Helgerich, Ionenaustauscher, Verlag Chemie GmbH,

[2] Bayer AG, DBP 1045102 (1957) u. DBP 1113570 (1957). [3] F . Martinola, G. Naumann, Angew. makromol. Chem. 4/5,

[4] Bayer AG, Lewatit-Ringbuch 504-1 (1. 11. 1965). [5] S. Vajna, Dechems-Monographien Bd. 64, Verlag Chemie

GmbH , Weinheim/Bergstr . 19 70. [6] R. Schumann, Oberfl&che 11 [1969]. [7] Bayer AG, Information OC/I 20333 (1. 1. 1974). [8] W . K r h i g , G. Scharje, Erdol u. Kohle 19, 497 [1966]. [9] C. Oehme, Oberflilche - Surface 12, 105 [1971].

Weinheim/Bergstr. 1959.

185 [1968].

[lo] H.-W. Kauczor, Erzmetall 22, B 19 [1969]. [ l l ] Boehringer, Mannheim, DOS 1567325 (16. 4. 1970). [ 121 a. Kiihne, Bohrtechnik, Brunnenbau, Rohrleitungen 10,

[13] E. Merck, Darmstadt, Information 23/663/2/472 L. [14] G. Siegera, F. Martinola, Vom Wasser, Bd. 39, S. 377. Verlag

[15] H.-W. Kauczor, Chem. Ind. 11 [1970].

[ 19681.

Chemie GmbH, Weinheim/Bergatr. 1972.

A Comparison of Continuous Counter-Current Ion Exchange Equipment for Regeneration of Resins

Michael J. Slater, Paul F. Cooper and Godfrey B. ltari *

Three distinct types of continuous counter-current equipment for regeneration of ion exchange resin have been investigated. A pulsed, multi-stage column, a horizontal multi-stage stirred tank apparatus (the Morris contactor) and a periodically moving packed bed of resin were used. The resin residence time characteristics and axial mixing patterns were assessed. The moving packed bed system is most satisfactory and it has been shown that it can be superior to fixed bed apparatus.

A continuous counter-current flow ion exchange system must comprise units for extraction, resin regeneration, resin rinsing and possibly backwashing. Concurrent with the individual design of these items must be consideration of the mode of transfer of resin between the items and the control of resin flow to maintain suitable operating conditions. These requirements have great impact on the contacting equipment design and its successful opera- tion [l].

The design of equipment for continuous counter-current ion exchange under conditions of liquid film diffusion controlled mass transfer rates, and the very favourable equilibrium relationship often appropriate for treatment of dilute solutions, is well understood [2, 31. However, the regeneration of resins is a relatively slow process taking

* M . J . SZater, Ph. D., University of Bradford, Bradford, West Yorkshire, UK; P . 3’. Cooper, M. Sc., formerly of University of Bradford, West Yorkshire. UK; a. B. Itari, M. Sc., Govern- ment of Nigeria, Accra, Nigeria.

place under rather unfavourable equilibrium conditions compared to extraction [4]. The mass transfer process is generally controlled by the unsteady state diffusion rate of exchanging ions within the resin beads. The fundamen- tal aspects of the process are moderately well understood but diffusion coefficient data are lacking and application of present knowledge to the practical design of equipment is sparse.

Three types of apparatus have been studied to establish most appropriate conditions for resin regeneration and to assess the relative importance of flow patterns and resin residence time relationships. The first of these was a pulsed multi-stage agitated bed column which was deve- loped to overcome problems of stability and restricted flow ratios in unpulsed multi-stage fluidized bed sys- tems [5 ] .

In multistage fluidized bed apparatus the liquid velocity must exceed the minimum fluidization velocity (in the present case about 0.2cm/s) if the resin bed is to be

588 Chemie-lng.-Techn. 47. lahrg. 19751 Nr. 14

sufficiently mobile to flow between stages. If the liquid/ resin flow ratio is to be near unity as in the case of regen- eration of resin the residence time in each stage must necessarily be very short. Agitation of resin beds by pulsing overcomes this difficulty to a certain extent because lower velocities may be used and longer residence times obtained, perhaps adequate for resin regeneration.

The second system considered was the Morris contac- tor [5]. This comprises a horizontal system of stirred boxes with transfer sections between stages. It has been used industrially for solvent extraction with liquid droplets solidifying at a particular qtage in the process. As originally conceived, ion exchange resin could circulate through stages of extraction, regeneration and rinsing and the problem of handling of resin between sections did not arise as in other systems. The handling and flow control of resin in a manner which avoids resin attrition has been a major design problem hampering the develop- ment of continuous ion exchange apparatus. The stirring of the stages of the Morris contactor does not damage the gel resin used. The mechanical simplicity of construction is a final attractive factor.

The third apparatus investigated was a periodically- moving packed bed of resin. Most of the industrial scale continuous ion exchange plants now in operation utilize such a system for regeneration yet no detailed studies of such apparatus have been published nor comparisons with other systems made. Periodic resin movement is adopted to solvtt problems of resin flow control [l, 6, 71.

The liquid and resin flow patterns in each type of appara- tus obviously were very different and the effect of these flow patterns on mass transfer performance must be accounted for in the chemical engineering design of continuous ion exchange equipment, just as in solvent extraction column design for example. The serious effects of non-plug flow patterns were first recognized in solvent extraction columns. Flow tracing tests were therefore carried out in the ion exchange apparatus considered as part of equipment assessment.

The second major factor affecting performance was the resin residence time since diffusion within the resin is known to be slow and rate controlling in regeneration. Studies of the relationships of resin flow rate and resin hold-up were therefore also required.

The system sodium chloride - calcium chloride - I R 120 cation exchange resin was used. The Amberlite IR 120 resin manufactured by Rohm and Haas was used in the condition in which it was received. The properties mea- sured are shown in Table l .

Table 1. Resin properties: IR 120. ~

kg'm3 water saturated Density NaR 1270 CaR 1290 kdm3 f

Sauter mean diameter (NaR) Particle size range

0.07'1 cm 0.02 to 0.12 cm

Pulsed multi-stage contactor

The pulsed contactor comprises a vertical Perspex (Plexi- glas) column divided into zones by imperforate horizontal plates, each of which have a weir with a baffle over it

(Fig. 1). On a large scale the use of a type of bubble cap plate can be envisaged. To avoid the instability associated with stage systems having separate transfer passages for liquids and solids a single orifice is used for both flows. The column is divided into a number of stages to avoid excessive resin and liquid mixing in an axial direction. Resin flow is achieved by internal pulsing to a degree sufficient to give flow reversal in the column. During flow reversal a dense slurry of resin can flow from each stage into the one beneath and on the return stroke of the pulse liquid alone can be returned to the stage above.

Calcium analyser

Liquid product

Resin feed

---. ._ - L A

183909.11 Fig. 1 Pulsed stage contactor.

For stable operation the average flow of resin has to be inherently equal from each stage at steady state. This requires a resin flow increase with resin bed height increase and vice versa. This was achieved in practice. Pulse frequencies up to 144 per minute are used, giving pulsed flows of up to 29.6 x 10-2 m3/s (equivalent to an average superficial velocity of 1.6 x 10-2 m/s alternately upwards and downwards).

The pulsating action is obtained by introducing compres- sed air into a section of the column near the base and venting it periodically using a rotary valve. Liquid in the column is necessarily back-mixed because of the mixing action of the pulse on the upward stroke and the co- current transfer with resin downwards.

The Morris contactor

The Morris contactor comprises a horizontal arrangement of well mixed stages and transfer zones alternately (Figs. 2 and 3). The device therefore has features of discrete stage and differential contactors since both zones contribute to mass transfer. The mixed zones are agitated by a gate paddle type of impeller with no axial thrust, a t speeds in the range 300 to 600 rev/min (400 revlmin in the present case).

Chemie-lng.-Techn. 47. Jahrg. 19751 Nr. .14 589

The agitation creates an almost uniform distribution of resin and raises resin from the lower orifices to the top of the mixed zone where it is swept over into the top of the transfer zone. The resin can then escape the zone of influence of the paddle. Both at the lower and upper orifices a circulatory. motion in a horizontal plane is set up with resin slurry moving in one direction and leaner mixture in the other direction. The distribution of resin and liquid in transfer zones is uneven and considerable channelling is evident, with some recirculation. Con- siderable liquid back-mixing has already been demonstra- ted in a liquid-liquid system in a Morris contactor [8].

pmq Fig. 2. Multistage Morris contactor.

Fig. 3. Morris regenerating stage.

A 21 stage Morris contactor was used for continuous operation at first. This was provided on loan from the Royal Ordnance Factory, Bridgewater. Early attempts to operate the 21-stage apparatus with the mass transfer operations and washing taking place simultaneously failed. The difficulty was that the regenerant (sodium chloride) had a density sufficiently greater than the dilute liquid feed and wash water to allow flow of regene- rant into all parts of the apparatus. Various modifications were made at each end of the seven stage regeneration section to allow resin input and output without transfer of regenerant in excessive quantities but without success.

Level control of the regenerant in the section to equalize pressures at critical points was also unsuccessful on the small scale but might be satisfactory on a large scale. A separate replica regeneration section of seven stages was therefore built for study of the regeneration process independently of extraction and washing processes,

590

Moving packed bed

A perspex circular cross-section column 1 m high, 7.5 cm diameter was used to contain a packed bed of resin about 87 cm deep (Fig. 4). Regenerant solution enters at the

Liquid Resin product drain to

TjLrr

Fig. 4. Moving packed bed apparatus.

a, de-ionized water reservoir; b, metering pumps; c, resin feed tank; d, rotary valve motor; e, gear box; f, main column; g, rotary valve; h, resin product reservoir; i, regenerant feed tank; k, photo-electric cell; 1, lamp.

column base through a simple perforated pipe distributor and overflows at the top of the column. Resin is fed' intermittently into the top of the column by metering water into a closed tank full of resin and water which displaces a dense slurry of resin. Resin is removed at the base of the column using a rotary valve controlled by a timer. Various quantities of resin up to 400 ml can be removed at intervals of up to 12 min. When a plug of resin is removed the bed slides down the column and a photocell at the top of the bed then allows more resin to enter at the top until the photocell light path is blocked.

Hydrodynamic characteristics of the contactors

The flow of resin through the pulsed column and the hold-up of resin in the stages was controlled by the pulsing action in a complex manner. An empirical correlation of hold-up was developed which showed that resin residence times were typically very short (Table 3). The short residence times were unfavourable yet could not be greatly increased because of the flooding limits.

Flooding of the column due to excessive resin feed rate was a complex empirical function, very dependent on column geometry. The form [5] was

( V , - Vsr)aU;;' . (1)

The Morris contactor depends for its operation on the fact that resin is lifted over a barrier between the mixing zone and the transfer zone. The flow and hold-up of resin in the mixer therefore depend on the degree of turbulence provided by the mechanical impeller and not on gravita- tional forces. Hartland [8] gives results for liquid-liquid extraction in a Morris contactor and shows the hold-up of disperse phase as a power function of resin superficial velocity and stirrer speed. The geometry of the mixer, the design of impeller and the properties of the two phases would affect this type of correlation. MzLmford [g] in work on liquid-liquid extraction in a Morris contactor of similar dimensions, shows flooding results in the form,

Chemie-lng.-Techn. 47. Jahrg. 1975 IN^. 14

which is derived from the slip velocity equation

(3)

which has frequently been used in cases of low dispersed phase hold-up with no interdroplet coalescence for many types of solvent extraction column [lo]. However, for a series of stirred tanks the hold-up is not determined by the relative velocity but by the flow ratio. In this case the slip velocity is constant and the flow ratio is a simple function of hold-up, i.e.

V S = Vk

us h 4- 1 - h

and

(4)

(5)

The flooding relationship obtained by differentiating each velocity in turn with respect to hold-up and equating t o zero is

USf/VSf == - h f ) 1 2 (6)

Usp = Vkh' . (7 1

from which i t is found that

This relationship is valid for hold-up less than 15% and is a better description of results for resin-liquid and liquid- liquid systems than is equation (2) (Table 2) [ill. For larger hold-up flooding occurs by blockage of transfer ports with resin. When U,/h is much larger than V,/(l - h) as for regeneration with low values of h,

Us N Vkh (8)

hence the resin residence time (proportional to h/U,) is approximately constant for a given design. I n the 21- stage apparatus the amount of resin in circulation predominantly determines the resin flow rate. The contact time in a stage is much greater than that in the pulsed column.

Table 2. 400 revlmin.

Morris contactor flooding data. Regeneration Section,

R I, U s r hr [ml/min] [ml/min] [ W s I

108 1492 0.0567 0.109 178 1320 0.0935 0.141 220 1420 0.1155 0.151 315 1207 0.1660 0.164 390 1085 0.2050 0.176

In the moving packed bed the hold-up of resin is constant a t about 60% and the total resin residence time is deter- mined by the resin flow rate and equipment height.

Flow patterns and axial mixing

Flow patterns were analysed using radioactive tracers. Sodium phosphate (P-32) (Radiochemical Catalogue No. PBS ZP), a 1.71 MeV fl emitter with a half-life of 14.3 d

was used for the liquid and sodium chloride (Na-24), with 1.39 MeV 8, 1.37 and 2.75 MeV y activity, half-life 15 h, was used for the resin. To avoid loss of tracer on to resin during experiments the phosphate anion was used in dilute solution; to avoid loss of sodium-24 into solu- tion during resin tracing de-ionized water was used as the liquid phase. A y active tracer is required for resin; j3 activity is seriously reduced by self absorption in resin samples. All counting of radioactivity was carried out in a gamma well-counter.

Two types of experiment were carried out for the pulsed column [12] and the Morris contactor. Steady-state back- mixing experiments were undertaken using well-documen- ted techniques to determine the degree of true flow in the direction counter to the main flow [13]. The second type of experiment determined the net effect of axial mixing phenomena. The experiments were in some cases carried out simultaneously by injecting a steady flow of tracer a t a point distant from both ends of the contactor being studied, measuring the axial mixing response down- stream immediately and sampling upstream after a long time to obtain data on back-mixing.

In both cases a flow model comprising a series of well- mixed cells with backflow between them was adopted. For the Morris contactor expected axial mixing responses were obtained by analogue computer simulation of seven well-mixed cells with backflow, taking closed end boun- dary conditions into account (Figs. 5,6). Early attempts

v+r c,

liquid in v, q,r ,v u Liquid f l o w rates v resinslurry C tracer concenirations ', G u*v, c , ,- $190951

Fig. 5. Liquid flows and concentrations for the stagewise back- mixing model with step-input of tracer into stage 5.

ill,

me response toslep 19+flI, t i l l input 10 $!age 5

.~ -~ 83909 s_ .me base

Fig. 6. Analogue computer simulation of 7-stage mixing model with backmixing.

f = q / w ; g = r / v ; p = u / v ; TL - retention time of liquid in stage; yx = fractional approach to equilibrium in stage x; T = time base.

failed to match predicted and observed axial mixing responses assuming backflow between seven mixed cells with plug flow zones between each cell to represent the transfer zones. The best fit was obtained assuming seven mixed cells with backflow, the volume of each cell being the volume of a mixer plus the volume of two halves of a transfer zone. The impeller mixing action was clearly observed to extend well into each transfer zone. This

Chemie-lng.-Techn. 47. fahrg. 1975/ Nr. 14 591

effect explains why the slip velocity concept does not apply. The backflow coefficient measured directly gave excellent agreement of observed and computed axial mixing results based on the measured value (Fig. 7). No backmixing of resin between cells was observable (Fig. 8).

0 20 LO 60 80 100 rnin 120 L O

Fig. 7. Experimental results for liquid axial mixing test.

Time. f

1 , I , I , ~ , ( . I I 0 20 LO 60 min

Tlme,t

Fig. 8. Experimental results of resin axial mixing test. Step input of Na-24 radioactive resin applied to stage 5.

sample from stage 2 outlet; - response curve for outlet of 4 perfectly mixed stages to a step input of resin tracer; R =

102.4 ml/min wsr.; L = 614.0 ml/min; t~ = 2.34 min.

In the pulsed column a different approach was taken [12]. The extent of liquid back-flow between real stages was determined by flow rates and pulsing conditions. The amount of liquid transferred backwards relative to the steady liquid flow upwards is

( VP - V , - 2 Us)/ Vs (9)

for a pulse taking the same time on the upstroke as on the downstroke, and the relative forward flow is

hence the backflow coefficient is

On measuring the back-mixing coefficient by sampling at every stage a different value as was observed. The values were reconciled by assuming a model of N cells within n real stages with a back-flow coefficient of a between cells. For this case

It was found that Nln varied with resin hold-up. However, alternatively a recycle system within each stage was physically plausible and other relationships between a and as can be obtained and satisfied and uncertainty can arise in deciding the nature of flow. Further experiments on axial mixing were carried out to provide more evidence for a decision on model type.

Since many liquid mixing cells were postulated to exist, axial mixing experiments were designed to meet condi- tions of a system of mixed cells with backflow infinite in both directions. A steady injection of tracer near the middle of the column was made and samples were taken a short distance downstream (one stage distant) at a point still remote from the end of the contactor (in terms of the large number of mixed cells). Under these conditions the axial mixing response can be calculated numerically. The transfer function or impulsive response has been shown by Buflham [14] to be

h~ (0) = a-(N-1)/21N-1 (2 all@) exp [ - (1 + a)@] (13) where

0 = t / [ ( l - a)tc] . For a step input function as used here the output response is

f ( @ ) = (1 - a) a-(N-1)/2 f IN-,(2a1/2t)

exp [ - (1 + a ) t ] d r .

8

0

(14)

The values of a calculated from flow conditions and N obtained from back-mixing data were used in computing axial mixing responses with success. Other models of flow were proved inadequate by examining the first and second moments of these responses for different models.

No backmixing of resin was observable and a model of one mixed cell of resin per real stage was used. However, it was found that the average residence time of resin parti- cles in a stage depended on particle size.

The calculation of responses is preferred to methods based on moments but the analytical solution has serious limitations. Only a small number of cells can be considered and the backmixing coefficient must not be large, other- wise the product of the large Bessel function and the small exponential terms becomes difficult to evaluate accurately.

In the moving packed bed liquid velocities were kept well below the minimum fluidization velocity to avoid ex- cessive bed expansion and consequent axial mixing of resin. Very little axial mixing of solution was expected during periods of no resin flow. Turner [15] has shown thkt a near plug flow of solution exists in a packed resin bed. However, on moving a plug of resin downwards in the column an approximately equal volume of solution is backmixed, representing a large fractional back-flow similar in degree to that suffered in the other apparatus.

Mass transfer performance

Equilibrium data were obtained by the column technique and the results were fitted for calculation purposes by the theoretical equation :

(15) KQ CICO - q'/Q -____-__. _____

(1 - $I&)' CO (1 - C/Co)'

with KQ having a value of 4.5 keq/m3 and C , 1.5 keq/m3. Calcium loaded resin was regenerated with 1.5 keq/ms (1.5N) sodium chloride. Under these conditions the rate of ion exchange is controlled by the diffusion of ions in the resin beads. This was confirmed for conditions in the Morris contactor by varying stirring speed and finding no

592 Chernie-hg.-Techn. 47. lahrg. 19751 Nr. 14

Table 3. l’wforinance data.

Pulsed Morris Moving Packed Bed Contactor Contactor

Run 1 Run 1 Run 2 Run 4 Run 6 Run 16 Run 9 R [ml/mm] (xw) 350 95 53 26.5 53 53 26.5 L [mlimin] 38 1 152 368 32 75 200 75

1.09 1.60 6.95 1.21 1.42 3.77 2.80 0.067 0.0051 0.0029 0.0098 0.0196 0.0196 0.0098 0.139 0.0130 0.0316 0.012 0.028 0.074 0.028 0.920 1.566 0.840 4.240 4.240 4.240 4.240

LIE U s [cmisl V s [cmlsl

OR[SI

tL [s]

4 [keq/m31

VR [I] 158 1155 1092 9600 4800 4800 9600 - - - 480 240 240 480 - - - 5 5 5 5 t R [Sl

0.135 0.840 1.50 1.54 1.56 1.71 1.76 0.77 0.500 0.125 o! - - - -

change in kinet,ics. The mathematical description of ion exchange kinetics controlled by resin phase diffusion, under batch stirred ta,nk conditions, has been given by Helferrich [4]. The extension of the principles to flow systems has not yet been successfully carried out and applied t,o red systems.

The performance of the pulsed contactor is very poor due to t>he short resin residence times and substantial liquid axial mixing (Table 3), Fig. 9. For complete resin regen- eration a very tall column would be required. The Morris contactor is very much better and could reasonably be used for regeneration purposes (Table 3). However, satisfactory regenerant utilization can only be achieved under condit,ions of a high degree of liquid back-mixing, making the use of a large number of stages necessary.

10 60 cm 80 ”.

rims 9 Contactor leng‘h

Fig. 9. Resin conipos:’ti(m profiles.

The moving packed bed is most satisfactory for resin regeneration (Table 3) because of the greater volume of resin used arid longer resin residence times. However, the improvement over the Morris contactor is not remarkable and it. would appear from runs 4 and 6 that higher flow rates of bot’h phases could be tolerated. To obtain higher degrees of regeneration and a high degree of regenerant utilizat,ion the column must be taller; similarly the Morris contactor would need more stages and the pulsed column would have to be very much higher.

The moving packed bed was much easier to operate and was more stable t,han the other devices. In the apparatus used the resin flow rate was limited to about 53 ml/min by the rotary valve syst,em and timer but flows up to 200 ml/ min (equivalent to 0.074 cm/s) should be possible.

A series of experiments were carried out using the packed column as a fixed bed. The elution curves were obtained at three liquid flow rates for the same height of bed as

used in the moving bed tests. After any given time of elution the average composition of the bed and the amount of calcium removed can be calculated. The “production rate” of partially regenerated resin is then the bed volume divided by the time of elution. By comparing fixed bed data expressed in this manner with moving bed data (Fig. 10) it appears that the periodically moving packed bed can be much more effective. The superiority would be even more marked with a taller column giving near complete regeneration at high resin flow rates.

0 2C LG 60 Irnimin Resin f l o w ra te , R EGO9 1@

Flg. 10. Comparlson of performance of moving packed bed and a fixed bed.

Fixed bed performance: A L = 63 ml/min; 0 L = 85 ml/min; L = 100ml/mm; Movlng packed bed performance: A L =

63 ml/min; o L = 75 ml/min; L = 100 ml/min.

Conclusions

The use of periodically moving packed beds for ion exchange resin regeneration is to be preferred over the pulsed column described and the Morris contactor. The performance of a moving packed bed can be superior tc that of a packed bed of the same volume.

Received: May 7, 1975 [B 39091

References

[ l ] M. J. Slater, Brit. Chew,. Eng. 14, 41, Jan. [1969]. [a] M. J. Slater, Can. J. Chem. Eng. 52, 43, Feb. [1974]. [3] M. J. Slater, M . Zumer, Inst. Chem. Eng. Symp. on Hydro-

[4] F. Helferrich, “Ion Exchange”, McGraw-Hill, New York metallurgy, Symp. Ser. 42 (1975).

1962.

Chernie-lng.-Jechn. 47. Jahrg. 1975 I Nr. 14 593

[5] M . J . Slater, SOC. Chem. Ind. Symp., “Ion Exchange in the

[6] I . R. Higgins, R. C. Chopra, SOC. Chem. Ind. Symp. “Ion

[7] J . Bouchard, SOC. Chem. Ind. Symp. “Ion Exchange in the

[S] S. Hartland, G . D. Wise, Tr. Inst. Chem. Eng. 45, 353 [1967]. [9] C . J . Mumford, SOC. Chem. Ind. Int. Solvent Extraction

Process Industries”, London 1969.

Exchange in the Process Industries”, London 1969.

Process Industries”, London 1969.

Conf. ISEC 71, The Hague, Holland. [lo] J . D. Thornton, Chem. Eng. Sci. 5, 201 [1956]. [ i l l P. F . Cooper, M. Sc. Thesis, University of Bradford, UK,

[12] M . J . Slater, Ph. D. Thesis, University of Bradford, UK,

[ 131 K. Bischoff, 0. Levenspiel, “Advances in Chemical Engineer-

[I41 B. Buffham, Ind. Eng. Chem. (Funds) 8,428 [1969]. [15] J . C . R. Turner, SOC. Chem. Ind. Symp. “Ion Exchange in

1968.

1971.

ing’’, Academic Press 4, 95 [1963].

the Process Industries”, London 1969.

Nomenclature

constant

total ionic concentration in solution concentration/time output signal transfer function flooding hold-up of dispersed phase (resin) Bessel function, order N - 1 selectivity coefficient

[keq/m3] concentration in solution [keq/m3]

L rml/min] liquid flow rate n number of real stages N number of cells Q [keq/m3] resin capacity (wet settled resin) Q* [keq/m3] equilibrium concentration of calcium on

4 [keq/m3] change in resin concentration achieved resin (wet settled resin)

(wet settled resin)

resin flow rate (wet settled resin) time residence time liquid flow time resin flow time time base superficial resin velocity superficial resin flooding velocity characteristic velocities pulsing velocity superficial liquid velocity superficial liquid flooding velocity volume of wet settled resin

G r e e k Symbols

as stage backmixing coefficient 0 time variable z time variable t L [min] liquid residence time zR [min] resin residence time

U backmixing coefficient

Abhangig keit der lonenaustauscher-Eigenschaften von der chemischen Struktur

Ewald Blasius und Klaus-Peter Janzen

Es wird eine Ubersicht iiber die Eigenschaften von Ionenaustauschern auf Kunst- harz-Basis, ihre Wirkungsgruppen und Strukturen sowie den dadurch bedingten praktischen Einsatz snhand von Beispielen aus der Literatur und aus eigenen Ar- beiten gegeben. Behandelt werden nach einer kurzen geschichtlichen Einfiihrung stark saure Kationen- Austauscher und stark basische Anionen-Austauscher, schwach saure Kationen-Austauscher und schwach basische Anionen-Austauscher, chelat- bildende Austauscher, Austauscher mit makrocyclischen Polyathern als Anker- gruppe, fliissige Austauscher, optisch aktive Austauscher und Adsorberharze. Eine SchluBbetrachtung weist auf die Herstellung im industriellen und 1abormaBigen MaSstab und einige Anwendungsmoglichkeiten der Austauscher mit makrocyclischen Polyiithern als Ankergruppen hin.

Ionenaustauscher sind hochmolekulare unlosliche Poly- elektrolyte, die in irgendeiner Form ionogene Gruppen fest mit dem Grundgeriist verbunden enthalten und die an dieser Gruppe gebundenen Gegenionen auszutauschen vermogen. Die wissenschaftliche Entdeckung der Ionen- austausch-Vorgange beginnt mit den in den Jahren 1850 bis 1852 veroffentlichten Untersuchungen an Ackerboden durch Thompson und Spence [l] sowie von Way [2] in England. Sie stellten fest, dnB in den Boden Ca2f und Mg2+ in aquivalenten Mengen gegen K+ und NH: ausge-

* Prof. Dr.-Ing. E. BZasius und Dr. K.-P. Janzen, Fachrichtung Anorganisohe Analytik und Radiochemie der Universitiit des Ssarlandes, 66 Saarbriicken-11, Universitiit.

594

tauscht werden kbnnen. Way schrieb diesen Effekt den in dem Boden enthaltenen silicatischen Tonmineralien zu und bemerkte auch eine gewisse Selektivitat, die in einer Reihe zum Ausdruck kommt, nach der sich die Kationen gegenseitig verdrangen: Na+ < K+ < Caz+ < MgZf < NH:. 1905 stellte Gans [3] erstmals synthetische Alumo- siilcate durch Fiillungsreaktionen, spater durch Schmelzen von Quarz, Ton und Soda her.

Die Grundlage fur die heutigen hochkapazitiven, sehr be- standigen und in ihren Wirkungsgruppen definierten synthetischen Austauscher auf Kunstharz-Basis bilden die von Adams und Holmes [4] 1935 veroffentlichten Arbeiten. Im Jahr 1944 stellte dann D’AZelio [5] durch

Chemie-hg.-Techn. 47. Jahrg. 1975 I Nr. 14