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Ion pair extraction of water soluble dyes
C%#~~&ol~nrirg Science Vol. 37, No. 10, pp. lOWS37, printed in Gnat Britain.
1982
cal9-2sosmlols.mm Pemamcn Press Ltd.
ION PAIR EXTRACTION
OF WATER
SOLUBLE
DYES
M. RESCHKE, W. HALWACHS and K. SCHijGERL* Institut fiir Tectmlsche Chemie der Universitit Hannover, D-3000 Hannover, Callin& 3, West Germany (Rec.&cd 9 October
1981; uccepted 15 March 1982)
AbstracGThe removal of am dyes from water by ion pair extraction is investigated. Mathematical relationships are derived from batch data and applied to the continuous extraction in a reciprocating plate extraction column. lNTRODUCTlON,TREORY
Aliphatic amines are widely used as liquid anion exchangers in the extraction of metals and acids. The aim of most studies dealing with the extraction of acids is to obtain information about mechanism and kinetics of the extraction[l-91. Generally, experiments are carried out in stirring cells or with dzerent equipment for single drop investigation. Little work has been done on the use of amines in commonly used extraction columns. This paper is an investigation of the ion pair extra&en of water-soluble dyes. The practical aim is to develop an alternative method to the industrial puri6cation of dye containing waste water by adsorption. Theoretical attention is paid to the problem of data transfer obtained by batch experiments to continuous extraction. Most extractions were carried out with the same system. Orange II (a-Naphtholorange, C.I. lSSlO), the sodium satt of an aromatic sulfonic acid, is used as azo dye; Amberlite LA-2. a secondary amine, is used as carrier in a xylene solution. Orange II (0) is completely dissociated in water and insoluble in non-polar organic solvents, whereas the amine is insoluble in water. Extraction has been achieved by formation of an ion pair with the amine (L) under proton participation:
The addition of an acid is necessary to obtain a sufficient proton concentration and, by that, adequate degrees of extraction. Discontinuous extractions were carried out in aeparatory funnels and in a stirred transfer cell to determine the reaction equilibrium constant, extraction equilibria and kinetics. The continuous extractions were performed in a reciprocating plate extraction column. With thermodynamic and kinetic data from batch experiments a theoretical model was developed and applied to the continuous extraction. EWBIUMENTAL: MATEBULS,
METHODS
The extractions are carried out with the commercial azo dye Orange II (Z-hydroxy-naphthyl-azo(l)-benzenep-sulfonic acid-sodium salt, ClaH,,N2Na0.,S. molecular weight 350.33 g). *Author to whom correspondence should be addressed. tSupptied by Robm & Haas Camp., Philadelphia, U.S.A.
Orange II is insoluble in nonpolar organic solvents, the solubility in water is some 0.1 mol/l at room temperature. A secondary amine, Amber&e LA-2 (N-laurylN-trktlkylmethylamine, C12H25-NH-CRIR2Rsr RI + Rf + R, = 1 l-13 C-atoms),+ is used as carrier. The commercial product is purified by high vacuum rectification. The density at 2(PC is 0.8275 g/cm3. the molecular weight is determined to be 375 g/cm’[lO], The solubility in water is less than lOppm[ll]. The main use of LA-2 is the extraction of metals, especially actinides. Technical grade xylene is used as organic solvent.
EXPlWMENl’AL
PROCEDURES
Analysis is restricted to the determination of the dye concentration in the aqueous phase. This is carried out by measuring the extinction at 485 nm using a Beckman spektrophotometer Model 25, equipped with a Beckman recorder. A stirred transfer cell is used for determining the equilibrium constant Z& of tbe ion pair formation. The transfer cell is thermostated at 25°C. 150 ml of the aqueous and organic phase are moderately stirred under the pH- and azo dye-concentration control of the aqueous phase. It takes 6-8hr to reach the equilibrium state (change of extinction less than 0.001 in 30min). Final pH- and dye-concentration permits, by known start& conditions the calculatidn of &. Extractiane& were i%estiaated in the same tiansfer cell as above. Both phases we&stirred with a constant impeller speed of 185 min-‘, which keeps the interface nearly undisturbed. Continuous extractions are performed in a reciprocating plate extraction column. Figure 1 shows the apparatus used for the extraction experiments, the abbreviations are listed in Table 1. The column operates in countercurrent flow. An aqueous solution of Orange II, acidified with hydrochloric acid, is used as continuous phase and xylene/LA-2 as dispersed phase. To avoid handling large quantities of organic solvent, this phase partially circulates. Moreover, this arrangement allows the holdup variation at a constant overall Row rate. The characteristics of the column are listed in Table 2. All experiments w&e carried out at a stroke frequency of timin-‘, operating in the mixer-settler region. The frequency is controlled by a digital display. The amplitude (half+roke) was 5 mm. The flow rate range investigated 1529
1530
I
-
i-'
-
I-)
r
t
-
1
E2
Pl R3
.f Fii 1. Schematic diagram of extraction apparatus.
Table1. Apparatus, abbreviations rsciprocating variable
frequency
spaed
plate
extraction
motor
control display for aqueous tan*’ for aqueous’ tank for organic
ltorege tank
phase
ovut law storage
phase
overflow
tank
for
orgado
phase phase
punpS overflow photometer: recorder flcu meter mmpling QT injection intarf ace
points
column
Ion pair extractionof
extends from 5 to 301/h for both phases. The azo dye concentration is varied from 1 x 10S5 to 1 x low3 mol/l, the amine concentration in the organic phase varies from 0 to 5 X IO-* mol/l (O-2 vol.%). The dye concentration in the aqueous phase is measured continuously to control the steady-state of the extraction. Samples of the aqueous phase are taken and determined additionally. Thereby, falsilkation of results by adsorption of dye in tubes or vessels is prevented. RENL’rsANliDISCU!WON Extraction equilibrium data Equation (1) leads to the following expression for the equilibrium constant of the complex forming reaction:
(1)
KG=
co.0 - co crf ’co *(CL&- co,0+ COY
(2)
In several experiments the equilibrium constant is determined in the following concentration range of the participating compounds: Orange II : 2.540
X lO+ mol/l
LA-2: 5 X lo-’ - 1 x lop3 mol/l. We obtain a mean value of Kc = 1.86 x lo9 l’lmol’ (standard deviation 0.18 x 10!‘12/molz). An increase of the amine concentration uu to 10-l mol/l yields a higher (2.5-3 _ x .10?*/mo12). I._I. KG _.. -.._-... .. . -... _ In snite of this high value, an extraction of Orange II in neutral solution only leads to small degrees of extracted dye. An efficient extraction is obtained by addition of a strong acid. Comparison with equilibrium constants for the reaction of LA-2 with other anions shows a rather high value for the dye extraction. Considering a distinct proportionality between KG and the size of the -extracted anions, the measured values agree with other results.
water solubledyes
The following constants are found for the extraction of haloic acids (7): HCl: KG = 5.62 x 105I’/moP HBr: K. = 1.58 X 106lz/mol* HJ: & = 8.32 x ld lz/mol’. The extraction equilibria were determined in acidic solution. Hydrochloric acid is chosen by reason of the bad extractability of chloride compared with the anions of other commonly used acids[7,8]. In several series of tests aqueous solutions with the same concentration of Orange II are adjusted to a tked pH and extracted with organic solutions of dzerent LA-2-concentration. Experiments were made with various dye and proton concentrations. Figure 2 shows the results for a dye concentration of 2.85 X lOA mol/l as the degree of extraction (l- G,/c~.~) vs amine concentration. As expected, the degree of extraction E increases to a stoichiometric amount of LA-2. At an i&al pH of 4.0 the reaction is limited by the proton concentration, which decreases during extraction to pH 5-7 (depending on the amine concentration). Table 3 shows the concentration dependent extraction degree using stoichiometric amounts of dye and carrier. The. increase of E with the concentration is due to the mass action law. Calculation of the extraction equilibria with the measured equilibrium constant & leads to good agreement with the experimental results. (2) Extraction kinetics The extraction rate of Orange II was measured at a constant pH of 2.0. In several experiments the concentrations of axe dye and carrier were varied. Furthermore, the influence of changing the volume ratlo of both phases on the rate of extraction was investigated. Theoretical kinetic mod& Based on Whitman’s twofilm-theory a model for the extraction kinetics was
kg cL,o (mol/l) Pi
1531
2. Degree of dye extractionvs amineconcentration.
1532
M. ltl?%XiKeet al.
developed. The model is restricted to the following conditions: -The reaction takes place at the interface. -The transport of the reactants to Qesp. from) the interface is the rate determining step. -The concentration of protons at the phase bonndary corresponds to the concentration in the bulk phase according to the excess of hydrochloric acid: cr., = cr,,.
Fiie 3 shows the concentration profiles of the reactams during their transport through the phase boundary: The mass transfer of Orange II, LA-2 and the complex formed is given by: io = MC0 jr =
IHOL = kr0&~0U
Table 2. Column data lO!DOKUM 54 nun 2240 cm3 15 18 uom
column height: column diameter: column volume: number Of plates: plate spacing: mean distance between the upper plate and the top bf the column:
165 rmn
mean distance between the lowest plate and the bottom of the column:
160 IUII 10 mm 53.1 mm 150 2.0'mm 1.05mm 0.239 5mm
shaft diameter: plate diameter:
holes/plate: hole diameter: plate thickness: fractional free area of plate: amplitude (half sttoke):
Table 3. Extraction degree at Merent COP
CL.0
PH,
concentrations
E
D
%
molt1
m0Ul
2.85.10-s
2.85.1OW
2.0
98.09
51.4
2.85* 10-4
2.85.IO-'
2.0
99.80
496.5
2.85.lo->
2.85.10-a
2.0
99.92
1250
2.85.lo-*
2.85.lo-*
2.0
99.985
6670
aqueous
phase
- co.*)
~L(c.-
phase boundary
organic phase
Fig. 3. Concentration protiles in the aqueous and orqauic phase.
(3)
cL.d
- c&70&
1533
Ion pair extraction of water soluble dyes At quasi-steady-state
the following equation holds:
.
.
.
(4)
30 = h = 3zfor Combining equilibrium
these relations constant:
with the expression
for the
CH0L.i KG= C&Z. CL,i ’ CO,i
(5)
and the rate equation applied to the disappearing from the aqueous phase: -dcddt
= koao(co
of dye
- c,,i),
(6)
we obtain:
k,_ . CL +T-co - \1[0.25.( +
(
This
k,o,
kL
* KG
* CH
k, kr..co kHoL.KD++ko.Ka.cw
+++J
- CHOL
values of & kL and kHoL were determined by adapting the measured and the calculated concentrafibn-timecurve for the case of equal concentrations of dye and amine (see appendix). This leads to the following coefficients (in stirred cells): b = 6.5 X 10e4 cm/s kL = 6.0 x 10m4cm/s k HoL = 4.0 X lOed cm/s. Using these parameters it is possible to calculate the rate of extraction for other concentrations and, after modifying the above equation, also for other phase ratios. Some typical results are shown in Figs. 4 and 5; the solid lines are the calculated values, experimental results are represented as single points. The phase ratio in picture 5 is chosen to simulate the volumetric flow rate ratio of the aqueous and organic phase in the continuous extraction (see Section 3). Theory and experiment agree well with one another.
> (7)
)I1-
equation allows the calculation of the time-depeadent decrease of dye-concentration in the aqueous phase. The equilibrium constant & has been determined to be 1.86 x 109 lZ/molz, the value of 00 is 0.293 cm-‘. The
(3) Contimous extraction The residence time distriiution of the continuous phase in the column is best described by the tanks-inseries model. The identified number of tanks depends on the flow rates of both phases. This number varies between 3 and 8. The holdup of the dispersed phase is proportional to the organic flow rate and almost independent of the flow rate of the aqueous phase in the investigated range
---T---
0
co,o - 2,05 -10-S mol/l
Vaq/Vorg - 1
50 oxtraction time Fii.
(min)
4. Extraction rate of Orange II by Ambcrlite LA-2-xylenc solution.
-4
M. REscmc6el af.
1534
(5-301/h). Tbe degree of the azo dye extraction
is determined in several tests, dependent on diRerent parameters: (i) amine concentration; (ii) dye, concentration; (iii) flow rate of aqueous phase; (iv) flow rate of organic phase. It takes 1%3Omin to obtain steady-state conditions (2-4 mean residence times). The pulsation frequency of the column plates is held at 60 mm-’ for all experiments, the pH of the aqueous dye sohrtions is adjusted to 2.0 with hydrochloric acid. ULCULATION RESt%TS
For calculating the degree of extraction the reciprocating plate column is treated as a CSTR series with countercurrent flow; the muuher of reactors is determined by measurements of tbe residence time distribution. Equation (7) and the mass balance yields the conversion in one reactor:
(8)
Cole-
With the help of the following expressions tbe unknown concentrauons cL, c noL and cn can be eliminated: CL= cr_o+ Paq/c&o CH CHOL
=
cFf.0
+
=
CHOL.0
(co +
-
-co.,)
kq/
ibdco,,
veq/vorg-15
0, CL o =,1,13 -10’‘molll l
t 0: CL3o =1,13*lo-3
-4 molll rnol/l I
do
ixrrectim Fig. 5.
(10) -
co).
tfu
A half-internal search method is applicable to calculate the working point of the reactor. The total interval includiug the solution (in that case O-co.J is transported to a Section O-l. Calculation starts with a solution corresponding to dimensionless 0.5. By inserting the parameters into the CSTR-mass balance it is ascertained whether the working point is too low or too high. The next calculation is executed at point 0.75 (resp. 0.25) of the total interval. The ith step varies the working point about +/-2-‘. That means a precision of the solution of 1% at 10 steps. At 20 steps the deviation of the numerically achieved solution from the true solution of the mass balance is less than 1 ppm. A flow sheet in Table 4 shows the method for calculatiug the conversion in the whole extraction column with regard to the circulation of tbe organic phase. The final amine concentration is estimated and the calculation is executed until computed and real inlet amine concentration agree well with one another. The calculations are performed with the measured extraction equilibrium constant (Kcr = 1.86 X 10’l*/mol*)
2,85 ~10-5mol/l
rtCL0=2,25~10
(9)
co.0)
time
Extraction rate of Orange II by Amberlite LA-P-xylencsolution.
(mid
Ion Pair extmctim of water soluble dyes ‘f&e
4. Calcalabion of the ion-f&
Stertfnq :
1535
exfracth in a csT%scriss with ~~~~taewent~w acar& prwiaion: 2-j X lOl%
conqentration of transition cdmponent end initgal pa are defined
Calculation of the cawonent in the 1. final ooncentration in the
(dye)
(n cells) w haif*
+
(n-l).call
I
The workpoint of the n. cell im oeloulrted by solving th13 CSTn-mws balanoe for the reactive extracticn. The operating conditions in tha n. call deiine the etarting condition6 in the (n+l). cell
[The working
inlet
component amine
+
E
r)
I
I
f
ci
+_ point
of the
lest cell is just Calwlatad?r 1
reaction
+
(LA-2) oonoentration. adequately
tion ia varied .of the initial
ie carpered
with
the real
The final emine concentraabout
a fraction
of
+/-2-l
concentration
-.-
Va,+org-16
1
0 : kinetic data
excmne dye
Pig. 6. Degree of dye cxtrwtion VI mike wnccnhGon.
no
'
1536
M. RESCHIE
and an estimated value for the specific interfacial’area (co = 2.5cml’). An adaption of results is possible by varying the mass transfer coefllcients. Optimal agreement of calculated and experimental results is obtained with the following coefficients (reciprocating plate column): &o = 1.95 x W3 cm/s 4 = 1.80 X lo-” cm/s kHoL = 1.20 X 10m3cm/s. The ratio of mass transfer coefficients corresponds to the coefficient ratio calculated from the extractions in the transfer cell. Due to the Merent hydrodynamic conditions, the resultiug coefficients for the continuous extraction are three times higher.
et d.
Calculations are carried out with these values. Figures 6-9 show experimental (single points) and calculated results (solid lines) for variation of the four described parameters. The dotted lines show the equilibrium disbibution. coNcLugIoN The ion-pair extraction of an azo dye (Orange II) from water is investigated. A secondary amine (Amberlite _LA-2) in a xylene solution is used as carrier. In batch ‘experiments the extraction equilibrium constant is determined to be 1.86 x 10’t2/mo12.That means, an azo dye extraction into the organic phase of 98-100% using stoichiometric amounts of dye and amine. Continuous extractions are performed in a reciprocating plate extraction column. L&95% of the dye can be removed from the aqueous phase.
,I
0
0 *
cL,o -437~10-3 &+Jorg=
16
OS kinetic
date
o:equilibriumdietrfbution
I I
I exceee amino
svxeedye
-40 log co,* [mot 11) Fig. 7,
Degmeof dye extraction vs dye concentration.
o: kinetic d&e
I
P: equilibrium I 2.0
distribution
’tieq
(I/h)
Fig. 8. Degree of dye extraction vs Bow rate of the aqueous phase.
1537
Ion pair extraction of water soluble dyes
-
J
xi--
a Y
0
50.-
0
-2
cO o= 2,85 -lt+
mol/ I
CL.0 -4.37.10-4
molll
o: kinetic 10
data
I
0
20 %rg
(Ilh)
Fig. 9. Degree of dye extraction vs flow rate of the organic phase.
A simple theoretical model was developed from the results of batch experiments, which allows a satisfactory description of the continuous extraction. NOTATION II
k E
H HOL d k L I: t Indices aq HOL i L 0 0 org
specific interfacial area. cm-’ concentration, mol/l distribution coefficient extraction degree, % proton dye-amine-complex molar Bow rate, (mol/cm* - s) extraction equilibrium constant, 121mo12 mass transfer coefficient, cm/s LA-2, amine molar flow rate, mol/s Orange II, dye mean residence time, 6
aqueous dye-amine-complex phase boundary LA-2, amine Orange II, dye start organic
ItEFXRltNCES [II Nakashio F., Sakai W., Inoue K. and Kawano Y. Kagaku Koguku 1974Xi(l) 41.
121Nakashio F., Tsuneyuki T., fnoue K. and Sakai W. Pmt. Inr. Solonr Exrr. conf. 19712 831. 131Kataoka T., Niibiki T. and Ueyama K. Muss tmnsfu wick liqvid anion exchangeChem. Bngng 3. 197510 189. [4] Kataoka T., Nishiki T. and Ueyama K. Chem. EmgtigI. 1976 I2 133. [S] Tsuneyuki T., Konda K.. Kawano Y. and Nakashio F. J them. l!?ngngJupun 1978 ll(3) 198. [4] lnoue K. and Ogawa V. L Chem. Engng Japan 1980 13I3) 237. u] Scibona G., Orlandini F. and Danesi P. R. X Znorg.MC/. ckm. 196628 1701. [E] Russo U.. Zanin S. and Cescon P. Annali di chimica 197565 [9] zset II Hamelin R., Matutano L. C. R. Acad SC. Pmis 19652.61679. [lo] Hiinsel R. Ex&akrion gekoppelt mit chemischer Reakiion, Untersuchnngen im Zweiphasensystem Wasser-Xylol am Beispicl der Salicylsdnn utd anderer ammatischcr SOuren. Diploma&it, Inst. f. Teclm. Cbemie, Uni Hannover 1981. [l 11 Rohm & Haas Comp.. Philadelphia; Amberlite LA-2, Technical Notes. APPENutx Determinationof mass transfer ccetllcicnts Using high excess of amine, eqn (7) reduces to
The evaluation of corresponding experiments leads to the coefscient lk, = 7 X lo4 cm/s. The caiculation of the diBusion coetlicicn~s of the amine and the dye-amine*mplex leads to a ratio &JkHoL= 1.5. Wii these preconditions the adaption of measured and calculated concentration-time-curves is carried out.
1982
cal9-2sosmlols.mm Pemamcn Press Ltd.
ION PAIR EXTRACTION
OF WATER
SOLUBLE
DYES
M. RESCHKE, W. HALWACHS and K. SCHijGERL* Institut fiir Tectmlsche Chemie der Universitit Hannover, D-3000 Hannover, Callin& 3, West Germany (Rec.&cd 9 October
1981; uccepted 15 March 1982)
AbstracGThe removal of am dyes from water by ion pair extraction is investigated. Mathematical relationships are derived from batch data and applied to the continuous extraction in a reciprocating plate extraction column. lNTRODUCTlON,TREORY
Aliphatic amines are widely used as liquid anion exchangers in the extraction of metals and acids. The aim of most studies dealing with the extraction of acids is to obtain information about mechanism and kinetics of the extraction[l-91. Generally, experiments are carried out in stirring cells or with dzerent equipment for single drop investigation. Little work has been done on the use of amines in commonly used extraction columns. This paper is an investigation of the ion pair extra&en of water-soluble dyes. The practical aim is to develop an alternative method to the industrial puri6cation of dye containing waste water by adsorption. Theoretical attention is paid to the problem of data transfer obtained by batch experiments to continuous extraction. Most extractions were carried out with the same system. Orange II (a-Naphtholorange, C.I. lSSlO), the sodium satt of an aromatic sulfonic acid, is used as azo dye; Amberlite LA-2. a secondary amine, is used as carrier in a xylene solution. Orange II (0) is completely dissociated in water and insoluble in non-polar organic solvents, whereas the amine is insoluble in water. Extraction has been achieved by formation of an ion pair with the amine (L) under proton participation:
The addition of an acid is necessary to obtain a sufficient proton concentration and, by that, adequate degrees of extraction. Discontinuous extractions were carried out in aeparatory funnels and in a stirred transfer cell to determine the reaction equilibrium constant, extraction equilibria and kinetics. The continuous extractions were performed in a reciprocating plate extraction column. With thermodynamic and kinetic data from batch experiments a theoretical model was developed and applied to the continuous extraction. EWBIUMENTAL: MATEBULS,
METHODS
The extractions are carried out with the commercial azo dye Orange II (Z-hydroxy-naphthyl-azo(l)-benzenep-sulfonic acid-sodium salt, ClaH,,N2Na0.,S. molecular weight 350.33 g). *Author to whom correspondence should be addressed. tSupptied by Robm & Haas Camp., Philadelphia, U.S.A.
Orange II is insoluble in nonpolar organic solvents, the solubility in water is some 0.1 mol/l at room temperature. A secondary amine, Amber&e LA-2 (N-laurylN-trktlkylmethylamine, C12H25-NH-CRIR2Rsr RI + Rf + R, = 1 l-13 C-atoms),+ is used as carrier. The commercial product is purified by high vacuum rectification. The density at 2(PC is 0.8275 g/cm3. the molecular weight is determined to be 375 g/cm’[lO], The solubility in water is less than lOppm[ll]. The main use of LA-2 is the extraction of metals, especially actinides. Technical grade xylene is used as organic solvent.
EXPlWMENl’AL
PROCEDURES
Analysis is restricted to the determination of the dye concentration in the aqueous phase. This is carried out by measuring the extinction at 485 nm using a Beckman spektrophotometer Model 25, equipped with a Beckman recorder. A stirred transfer cell is used for determining the equilibrium constant Z& of tbe ion pair formation. The transfer cell is thermostated at 25°C. 150 ml of the aqueous and organic phase are moderately stirred under the pH- and azo dye-concentration control of the aqueous phase. It takes 6-8hr to reach the equilibrium state (change of extinction less than 0.001 in 30min). Final pH- and dye-concentration permits, by known start& conditions the calculatidn of &. Extractiane& were i%estiaated in the same tiansfer cell as above. Both phases we&stirred with a constant impeller speed of 185 min-‘, which keeps the interface nearly undisturbed. Continuous extractions are performed in a reciprocating plate extraction column. Figure 1 shows the apparatus used for the extraction experiments, the abbreviations are listed in Table 1. The column operates in countercurrent flow. An aqueous solution of Orange II, acidified with hydrochloric acid, is used as continuous phase and xylene/LA-2 as dispersed phase. To avoid handling large quantities of organic solvent, this phase partially circulates. Moreover, this arrangement allows the holdup variation at a constant overall Row rate. The characteristics of the column are listed in Table 2. All experiments w&e carried out at a stroke frequency of timin-‘, operating in the mixer-settler region. The frequency is controlled by a digital display. The amplitude (half+roke) was 5 mm. The flow rate range investigated 1529
1530
I
-
i-'
-
I-)
r
t
-
1
E2
Pl R3
.f Fii 1. Schematic diagram of extraction apparatus.
Table1. Apparatus, abbreviations rsciprocating variable
frequency
spaed
plate
extraction
motor
control display for aqueous tan*’ for aqueous’ tank for organic
ltorege tank
phase
ovut law storage
phase
overflow
tank
for
orgado
phase phase
punpS overflow photometer: recorder flcu meter mmpling QT injection intarf ace
points
column
Ion pair extractionof
extends from 5 to 301/h for both phases. The azo dye concentration is varied from 1 x 10S5 to 1 x low3 mol/l, the amine concentration in the organic phase varies from 0 to 5 X IO-* mol/l (O-2 vol.%). The dye concentration in the aqueous phase is measured continuously to control the steady-state of the extraction. Samples of the aqueous phase are taken and determined additionally. Thereby, falsilkation of results by adsorption of dye in tubes or vessels is prevented. RENL’rsANliDISCU!WON Extraction equilibrium data Equation (1) leads to the following expression for the equilibrium constant of the complex forming reaction:
(1)
KG=
co.0 - co crf ’co *(CL&- co,0+ COY
(2)
In several experiments the equilibrium constant is determined in the following concentration range of the participating compounds: Orange II : 2.540
X lO+ mol/l
LA-2: 5 X lo-’ - 1 x lop3 mol/l. We obtain a mean value of Kc = 1.86 x lo9 l’lmol’ (standard deviation 0.18 x 10!‘12/molz). An increase of the amine concentration uu to 10-l mol/l yields a higher (2.5-3 _ x .10?*/mo12). I._I. KG _.. -.._-... .. . -... _ In snite of this high value, an extraction of Orange II in neutral solution only leads to small degrees of extracted dye. An efficient extraction is obtained by addition of a strong acid. Comparison with equilibrium constants for the reaction of LA-2 with other anions shows a rather high value for the dye extraction. Considering a distinct proportionality between KG and the size of the -extracted anions, the measured values agree with other results.
water solubledyes
The following constants are found for the extraction of haloic acids (7): HCl: KG = 5.62 x 105I’/moP HBr: K. = 1.58 X 106lz/mol* HJ: & = 8.32 x ld lz/mol’. The extraction equilibria were determined in acidic solution. Hydrochloric acid is chosen by reason of the bad extractability of chloride compared with the anions of other commonly used acids[7,8]. In several series of tests aqueous solutions with the same concentration of Orange II are adjusted to a tked pH and extracted with organic solutions of dzerent LA-2-concentration. Experiments were made with various dye and proton concentrations. Figure 2 shows the results for a dye concentration of 2.85 X lOA mol/l as the degree of extraction (l- G,/c~.~) vs amine concentration. As expected, the degree of extraction E increases to a stoichiometric amount of LA-2. At an i&al pH of 4.0 the reaction is limited by the proton concentration, which decreases during extraction to pH 5-7 (depending on the amine concentration). Table 3 shows the concentration dependent extraction degree using stoichiometric amounts of dye and carrier. The. increase of E with the concentration is due to the mass action law. Calculation of the extraction equilibria with the measured equilibrium constant & leads to good agreement with the experimental results. (2) Extraction kinetics The extraction rate of Orange II was measured at a constant pH of 2.0. In several experiments the concentrations of axe dye and carrier were varied. Furthermore, the influence of changing the volume ratlo of both phases on the rate of extraction was investigated. Theoretical kinetic mod& Based on Whitman’s twofilm-theory a model for the extraction kinetics was
kg cL,o (mol/l) Pi
1531
2. Degree of dye extractionvs amineconcentration.
1532
M. ltl?%XiKeet al.
developed. The model is restricted to the following conditions: -The reaction takes place at the interface. -The transport of the reactants to Qesp. from) the interface is the rate determining step. -The concentration of protons at the phase bonndary corresponds to the concentration in the bulk phase according to the excess of hydrochloric acid: cr., = cr,,.
Fiie 3 shows the concentration profiles of the reactams during their transport through the phase boundary: The mass transfer of Orange II, LA-2 and the complex formed is given by: io = MC0 jr =
IHOL = kr0&~0U
Table 2. Column data lO!DOKUM 54 nun 2240 cm3 15 18 uom
column height: column diameter: column volume: number Of plates: plate spacing: mean distance between the upper plate and the top bf the column:
165 rmn
mean distance between the lowest plate and the bottom of the column:
160 IUII 10 mm 53.1 mm 150 2.0'mm 1.05mm 0.239 5mm
shaft diameter: plate diameter:
holes/plate: hole diameter: plate thickness: fractional free area of plate: amplitude (half sttoke):
Table 3. Extraction degree at Merent COP
CL.0
PH,
concentrations
E
D
%
molt1
m0Ul
2.85.10-s
2.85.1OW
2.0
98.09
51.4
2.85* 10-4
2.85.IO-'
2.0
99.80
496.5
2.85.lo->
2.85.10-a
2.0
99.92
1250
2.85.lo-*
2.85.lo-*
2.0
99.985
6670
aqueous
phase
- co.*)
~L(c.-
phase boundary
organic phase
Fig. 3. Concentration protiles in the aqueous and orqauic phase.
(3)
cL.d
- c&70&
1533
Ion pair extraction of water soluble dyes At quasi-steady-state
the following equation holds:
.
.
.
(4)
30 = h = 3zfor Combining equilibrium
these relations constant:
with the expression
for the
CH0L.i KG= C&Z. CL,i ’ CO,i
(5)
and the rate equation applied to the disappearing from the aqueous phase: -dcddt
= koao(co
of dye
- c,,i),
(6)
we obtain:
k,_ . CL +T-co - \1[0.25.( +
(
This
k,o,
kL
* KG
* CH
k, kr..co kHoL.KD++ko.Ka.cw
+++J
- CHOL
values of & kL and kHoL were determined by adapting the measured and the calculated concentrafibn-timecurve for the case of equal concentrations of dye and amine (see appendix). This leads to the following coefficients (in stirred cells): b = 6.5 X 10e4 cm/s kL = 6.0 x 10m4cm/s k HoL = 4.0 X lOed cm/s. Using these parameters it is possible to calculate the rate of extraction for other concentrations and, after modifying the above equation, also for other phase ratios. Some typical results are shown in Figs. 4 and 5; the solid lines are the calculated values, experimental results are represented as single points. The phase ratio in picture 5 is chosen to simulate the volumetric flow rate ratio of the aqueous and organic phase in the continuous extraction (see Section 3). Theory and experiment agree well with one another.
> (7)
)I1-
equation allows the calculation of the time-depeadent decrease of dye-concentration in the aqueous phase. The equilibrium constant & has been determined to be 1.86 x 109 lZ/molz, the value of 00 is 0.293 cm-‘. The
(3) Contimous extraction The residence time distriiution of the continuous phase in the column is best described by the tanks-inseries model. The identified number of tanks depends on the flow rates of both phases. This number varies between 3 and 8. The holdup of the dispersed phase is proportional to the organic flow rate and almost independent of the flow rate of the aqueous phase in the investigated range
---T---
0
co,o - 2,05 -10-S mol/l
Vaq/Vorg - 1
50 oxtraction time Fii.
(min)
4. Extraction rate of Orange II by Ambcrlite LA-2-xylenc solution.
-4
M. REscmc6el af.
1534
(5-301/h). Tbe degree of the azo dye extraction
is determined in several tests, dependent on diRerent parameters: (i) amine concentration; (ii) dye, concentration; (iii) flow rate of aqueous phase; (iv) flow rate of organic phase. It takes 1%3Omin to obtain steady-state conditions (2-4 mean residence times). The pulsation frequency of the column plates is held at 60 mm-’ for all experiments, the pH of the aqueous dye sohrtions is adjusted to 2.0 with hydrochloric acid. ULCULATION RESt%TS
For calculating the degree of extraction the reciprocating plate column is treated as a CSTR series with countercurrent flow; the muuher of reactors is determined by measurements of tbe residence time distribution. Equation (7) and the mass balance yields the conversion in one reactor:
(8)
Cole-
With the help of the following expressions tbe unknown concentrauons cL, c noL and cn can be eliminated: CL= cr_o+ Paq/c&o CH CHOL
=
cFf.0
+
=
CHOL.0
(co +
-
-co.,)
kq/
ibdco,,
veq/vorg-15
0, CL o =,1,13 -10’‘molll l
t 0: CL3o =1,13*lo-3
-4 molll rnol/l I
do
ixrrectim Fig. 5.
(10) -
co).
tfu
A half-internal search method is applicable to calculate the working point of the reactor. The total interval includiug the solution (in that case O-co.J is transported to a Section O-l. Calculation starts with a solution corresponding to dimensionless 0.5. By inserting the parameters into the CSTR-mass balance it is ascertained whether the working point is too low or too high. The next calculation is executed at point 0.75 (resp. 0.25) of the total interval. The ith step varies the working point about +/-2-‘. That means a precision of the solution of 1% at 10 steps. At 20 steps the deviation of the numerically achieved solution from the true solution of the mass balance is less than 1 ppm. A flow sheet in Table 4 shows the method for calculatiug the conversion in the whole extraction column with regard to the circulation of tbe organic phase. The final amine concentration is estimated and the calculation is executed until computed and real inlet amine concentration agree well with one another. The calculations are performed with the measured extraction equilibrium constant (Kcr = 1.86 X 10’l*/mol*)
2,85 ~10-5mol/l
rtCL0=2,25~10
(9)
co.0)
time
Extraction rate of Orange II by Amberlite LA-P-xylencsolution.
(mid
Ion Pair extmctim of water soluble dyes ‘f&e
4. Calcalabion of the ion-f&
Stertfnq :
1535
exfracth in a csT%scriss with ~~~~taewent~w acar& prwiaion: 2-j X lOl%
conqentration of transition cdmponent end initgal pa are defined
Calculation of the cawonent in the 1. final ooncentration in the
(dye)
(n cells) w haif*
+
(n-l).call
I
The workpoint of the n. cell im oeloulrted by solving th13 CSTn-mws balanoe for the reactive extracticn. The operating conditions in tha n. call deiine the etarting condition6 in the (n+l). cell
[The working
inlet
component amine
+
E
r)
I
I
f
ci
+_ point
of the
lest cell is just Calwlatad?r 1
reaction
+
(LA-2) oonoentration. adequately
tion ia varied .of the initial
ie carpered
with
the real
The final emine concentraabout
a fraction
of
+/-2-l
concentration
-.-
Va,+org-16
1
0 : kinetic data
excmne dye
Pig. 6. Degree of dye cxtrwtion VI mike wnccnhGon.
no
'
1536
M. RESCHIE
and an estimated value for the specific interfacial’area (co = 2.5cml’). An adaption of results is possible by varying the mass transfer coefllcients. Optimal agreement of calculated and experimental results is obtained with the following coefficients (reciprocating plate column): &o = 1.95 x W3 cm/s 4 = 1.80 X lo-” cm/s kHoL = 1.20 X 10m3cm/s. The ratio of mass transfer coefficients corresponds to the coefficient ratio calculated from the extractions in the transfer cell. Due to the Merent hydrodynamic conditions, the resultiug coefficients for the continuous extraction are three times higher.
et d.
Calculations are carried out with these values. Figures 6-9 show experimental (single points) and calculated results (solid lines) for variation of the four described parameters. The dotted lines show the equilibrium disbibution. coNcLugIoN The ion-pair extraction of an azo dye (Orange II) from water is investigated. A secondary amine (Amberlite _LA-2) in a xylene solution is used as carrier. In batch ‘experiments the extraction equilibrium constant is determined to be 1.86 x 10’t2/mo12.That means, an azo dye extraction into the organic phase of 98-100% using stoichiometric amounts of dye and amine. Continuous extractions are performed in a reciprocating plate extraction column. L&95% of the dye can be removed from the aqueous phase.
,I
0
0 *
cL,o -437~10-3 &+Jorg=
16
OS kinetic
date
o:equilibriumdietrfbution
I I
I exceee amino
svxeedye
-40 log co,* [mot 11) Fig. 7,
Degmeof dye extraction vs dye concentration.
o: kinetic d&e
I
P: equilibrium I 2.0
distribution
’tieq
(I/h)
Fig. 8. Degree of dye extraction vs Bow rate of the aqueous phase.
1537
Ion pair extraction of water soluble dyes
-
J
xi--
a Y
0
50.-
0
-2
cO o= 2,85 -lt+
mol/ I
CL.0 -4.37.10-4
molll
o: kinetic 10
data
I
0
20 %rg
(Ilh)
Fig. 9. Degree of dye extraction vs flow rate of the organic phase.
A simple theoretical model was developed from the results of batch experiments, which allows a satisfactory description of the continuous extraction. NOTATION II
k E
H HOL d k L I: t Indices aq HOL i L 0 0 org
specific interfacial area. cm-’ concentration, mol/l distribution coefficient extraction degree, % proton dye-amine-complex molar Bow rate, (mol/cm* - s) extraction equilibrium constant, 121mo12 mass transfer coefficient, cm/s LA-2, amine molar flow rate, mol/s Orange II, dye mean residence time, 6
aqueous dye-amine-complex phase boundary LA-2, amine Orange II, dye start organic
ItEFXRltNCES [II Nakashio F., Sakai W., Inoue K. and Kawano Y. Kagaku Koguku 1974Xi(l) 41.
121Nakashio F., Tsuneyuki T., fnoue K. and Sakai W. Pmt. Inr. Solonr Exrr. conf. 19712 831. 131Kataoka T., Niibiki T. and Ueyama K. Muss tmnsfu wick liqvid anion exchangeChem. Bngng 3. 197510 189. [4] Kataoka T., Nishiki T. and Ueyama K. Chem. EmgtigI. 1976 I2 133. [S] Tsuneyuki T., Konda K.. Kawano Y. and Nakashio F. J them. l!?ngngJupun 1978 ll(3) 198. [4] lnoue K. and Ogawa V. L Chem. Engng Japan 1980 13I3) 237. u] Scibona G., Orlandini F. and Danesi P. R. X Znorg.MC/. ckm. 196628 1701. [E] Russo U.. Zanin S. and Cescon P. Annali di chimica 197565 [9] zset II Hamelin R., Matutano L. C. R. Acad SC. Pmis 19652.61679. [lo] Hiinsel R. Ex&akrion gekoppelt mit chemischer Reakiion, Untersuchnngen im Zweiphasensystem Wasser-Xylol am Beispicl der Salicylsdnn utd anderer ammatischcr SOuren. Diploma&it, Inst. f. Teclm. Cbemie, Uni Hannover 1981. [l 11 Rohm & Haas Comp.. Philadelphia; Amberlite LA-2, Technical Notes. APPENutx Determinationof mass transfer ccetllcicnts Using high excess of amine, eqn (7) reduces to
The evaluation of corresponding experiments leads to the coefscient lk, = 7 X lo4 cm/s. The caiculation of the diBusion coetlicicn~s of the amine and the dye-amine*mplex leads to a ratio &JkHoL= 1.5. Wii these preconditions the adaption of measured and calculated concentration-time-curves is carried out.