SEPAR"-TION OF BETAINE FROM MOLASSES

Teshome Worku

Department of Chemical EngineeringAddis Ababa University

ABSTRACT

This paper presents the result of an experimentalstudy dea.ling with the separation of betaine frommolasses. It is a part of an ongoing research workdesired to design'and develop a simulating movingbed (SMB) for the separation of main sugar andnon-sugar components from molasses withchromatography intended to optimize sugarindustries. In view of this, a series of pluseexperiments at different betaine concentrationswerecarried out in a fixed bed column packed with astrongly anionic exchange resin. The adsorptionequilibria for both lower (very dilute) and higherbetaine concentrations were identified from theeluted pulse peaks. The first moment, equilibriumconstants, solid phase concentrations andequilibrium isotherm are reported.

INTRODUCTION

Nowadays, there is a growing need for optimizationof sugar industries by employing effective methodsfor separating sugar and non-sugar components inmolasses mainly due to economic and environmentalreasons. In this context, several research works have

been carried out and appreciable results have beenachieved especially in the recovery of sugar molassescomponents.

Most sugar factories precipitate quite considerablevolume of molasses, frequently used as animal feedand as a raw material for the production of ethanol,

while still a large part of it is disposed of.,This posesserious environmental problems. affecting

particularly aquatic life owing to its high organicload and nutrient contents. Molasses is the final

sugar solution obtained after repeated crystallizationsteps. To increase productivity of sugar industriesand reduce the adverse envitonmental impact, thedesugarization of molasses through recovery of thedissolved sugar. and other valuable non-sugarfractions is gaining increasing importance [3,4,5].Amino acids are the most interesting non-sugarcomponents of molasses constituents. Betaine is oneof the most important amino acids [3,6,7] present in

Journal of EAEA, VoL 17,2000

a higher concentration usually between 4 and 7%

(w/w) compared to the rest of the amino acids [3]. Ithas found wide application in pharmaceutical andcosmetic industries among others.

Most of the industrial applications arid laboratoryscale studies performed so far concerning molassestreatment mainly focused on the separation of sugarand non-sugar components of molasses or on thesubsequent separation of sugar components from oneanother [3,8,10]. Liquid chromatography has beena suitable technique employed for the separation ofthe (fomponents of molasses from one another. Thisprocess not only gives a better separation of sucrosefrom the non-sugar components but also ensures theeffective separations of non-sugar from one another[2]. The process provides the possibility to collectthe sucrose in one fraction with high purity andrecovery as well as the non-sugar fractions according

to their properties and importance.

The results of a series of experimental works carriedout on beet molasses showed that more than 95%

sugar can be recovered. Similar results were alsoobtained in treating cane molasses. However theseparation of cane molasses yields; in addition to the

sugar and non-sugar fractions, a third fraCtio~ richin invert sugar [2]. In both cases the quality of theend product depends very much on the quality of themolasses used. For an industrial scale separation ofmolasses components, a simulated moving bed(5MB) is the commrlnly employed processtechnology [3,5,11]. For the design of the separation

unit on industrial scale, adsorption equilibrium andmass transfer efficiency are the essential parametersto be considered [12].

In this paper experimental results obtained for theseparation of betaine from the reference aqueoussolutions carned out in a laboratory unit with fixed­bed column are presented. The data was utilized toevaluate the key parameters that are essential for theindustrial scale design of a simulating moving bedunit to be uSed for the separation of betaine frommolasses.

Separation of Betaine from Molasses 21

EXPERIMENT

Apparatus and Procedure

The experimental apparatus for the elutionchromatography using a single column isschematically shown in Figure 1. Feed pump (3) isused to maintain the eluent (reservoir 1) and theinjected pulse streams flow through the column (6).Two three-way valves (5) are used to ensure therequired bypass flow. A pulse of desired betaineconcentration was injected into the pulse loop bymeans of a syringe, which flows to the detector (7)via a six-wayvalve (4). The loop volume is 6.15cm3. Tne column is connected to the thermostat (2)in order to maintain constant column temperature bycirculating water from tlie thermostat bath throughthe column jacket. The column is packed with aDOWEX 50 WX8-400, strongly acidic cationexchanger resins, in the form of K+, having averageparticle dia'meter of about 56 Jilll.

The bypass and eluted streams were directlyconveyed to a refractive index (RT) detector .(model1047 A. HP rmbH). Data acquisition was performedwith a personal computer (9) coupled with the unit

by means of a Chrom Card software.

6

Objective of the Experiment

The purpose of this experimental research work isaimed at determining and establishing the adsorptionequilibria of the main sugar and non-sug:ucomponents. with emphasis on one of the mostimportant amino acids, betaine, found in both caneand beat molasses. Since the adsorption equilibriumis one of the key parameters considered for thedesign of a separation process, its determination is ofimmense importance. To this end, series ofexperimental runs were carried out in column and

bypass. In the first case, a pulse of a referenceaqueous solutions of specific betaine concentrationswas injected into the plus loop [11], which was thenintroduced into the column via a six-way valve withthe three-way valves kept open. In the second case,the solution was injected and directly introduced tothe detector via the six-way valve bypassing thecolumn with one of the three-way valves beingmaintained in a closed position. The chromatogramsfor all pulse experimental runs were observed andevaluated.

The equilibration of the column with eluent orbackground concentration was performed prior torunning each pulse experiment. This was done by

1. Feed tank with eluent2. Thermostat

3. Feedpump4. Six,way valve

Figure 1 Equipment set-up

5. Three-way-valve6. Packed column

7. IR.detector (HP 1047A)8. Storage tank for eluent flow

9. PC with Chrom-Card Soft ware10. Printer

11. Pulse loop

Journal of EAEA, Vol. 17, 2000

22 Separation of Betaine from Molasses

pumping the. eluent or solution of backgroundconcentration until a constant baseline was

maintained by the detector. The flow rate used forequilibration and experimental runs were the same.All experimental runs were conducted at a constant

column temperature of 40°C.

very dilute betaine concentration. These values aredifferent for higher betaine concentrations thusindicatiRg the non linearity of the process. Withregard to transport phenomena, Eq. (4) can also beexpressed in terms of the height of equivalenttheoretical plate, HETP given by Eq. (6).

Evaluation

The variance of the' pulse peak cT is evaluated byusing the following equation:

(8)

(6)

(7)

HETP = 2DL + 2VE (~) 2V 1- E ] + K' tmlI

where rp indicates the particle radius and DSj thediffusion coefficient of component j inside thepolymer matrix.

Eq. (6) is the well-known Van Deemter equation[15]. The efficiency of the column is governed bythe factor related to fluid dynamics non-ideality andthe interparticle transport phenomena lumped in thetime parameter. Its actual expression is determined

by the assumed particle morphology [3]. In gel-typeion exchange resins, two diffusion steps are usuallyidentified: transport through the external fluid filmand diffusion tluough the polymeric matrix in theadsorbed phase [3]. Hence the characteristicdiffusion time is given by the equation.

The local slope of the isotherm is readily determinedif one knows the structural properties of the of theabsorbent £ and 1; R the retention time . Theproc::edure is then repeated for different backgroundconcentrations yielding peaks with different

retention time and the isotherm is constructed bynumerical integration from the concentration Cj to

any other concentration Cj+] using the followingEq. [21].

where dq/dc is the derivative of the adsorptionisotherm. The adsorbed phase concentration q isexpressed in units coherent with the units of the

liquid phase concentration c, that is, gramesadsorbed per unit volume of solid adsorbent.

(2)

(3)

(1)

(4)

(5)K'=K1-££

'2

2 2LDL ( '2)2 LcK(J' = --]+K +2--t. v3 ] _ C m

L( 1-£)'R = -;; 1t-£-K

Lwhere To = ~uFrom Eqs.(l) and (2), it follows,that,

Retention time or equivalently the first moment of

the peak TR for different pulse concentration was

determined. The equilibrium constant or the ,localslope of the isotherm was also evaluated. It isknown [21] that the retention time is given byEq. (1).

The absorptivity of each component, Kj is readilyestimated using Eq. (1) or (3). Moreover,' thelinearity and non-linearity of the adsorptionequilibria were checked by the pulse experiments at

d,ifferent.. concentrations. In this regard,approximately constant K values' are obtained for

where To is the through flow time of the bed, v is theintergranular or interstitial velocity of the fluidphase, L the column length, K the adsorptionequilibrium constant, DL the axial mixingcoefficient, t,;, a characteristic diffusion time ofcomponent in the resin particle and K' capacityfactor, defined as

Journal of EAEA, VoL 17, 2000

Separation of Betaine from Molasses 23

Time (min)

The peak moments which are referred to in Eqs. (1)and (3) have to account for the effect ofchromatographic column only. However, theexperimental data are affected by extra column partsof the unit, such as injector, tubing, valves, anddetectors [3]. In linear chromatographic theory[3,13] the sulting moments are expressed taking intoaccount the superposition of these effects and thecorrected values of the moments to be used in Eqs.(1) and (3) which are evaluated by means of thefollowing equations.

'l10;;-8

j.0~ 6~~ 420

0

10

20

... o· ·colurm plak

-- b,'IESS plak

'30 40 '50

(9)

(10)

Figure 3: By-pass and eluted peaks for 7.3 gmJlbetaine with background concentraion

Parameter Estimation

25

INTERPRETATION OF RESULTS

lllustrative Examples

3

..

2.51.5 2

Concentration, (gI1)

0.5

....••• .J.. ••

o

~ 4 T' -----------­

~3 I1ilc:o02E:>

g 1'S .

S' 0 I:-~---,.--,-----r--'--.-,~I

To identify a possible concentration dependence ofthe equilibrium constant of betaine, values ofequilibrium constant were estimated for the whole

series of pulse experiments. The reported values ofequilibrium constant are approximately the same forvery dilute concentrations thus representing alinearity of the process. It has also become obvious

from the results that for higher concentrations theprocess is non-linear. Figures 4 and 5 represent aplot of equilibrium constant versus concentration forlower and higher concentrations respectively.Isotherms

The. data obtained in chromatographic experimentscan be used for the design of a simulating movingbed unit. desired for the separation of betaine fromsucrose and othet non-sugar components usually

present in molasses. The data was utilized toevaluate the key parameters such as retention time,

equilibrium constant, solid phase c~)llcentration, andHEPT r~quired for the design of a desired unit forthe separation of betaine from molasses. The resultsare reported graphically.

120100

O· . ·0· .column peak

-- bypass peak

40 60 80

Tlrre (mn)

20

:;-E

15bE-m

10c: 0>

JLi:i5

o~ ,

0

20

Figure 2 shows the experimental eluted peaks'obtained in pulse bypass (without column) and pulsecolumn runs for 0:7 g/l betaine concentration witheluent pure water. Figure 3 depicts the experimentaleluted peaks in the pulse column and bypass runsrespectively for 7.3 g/l betaine concentration withbackground (saturation) solution i.e.,when column issaturated with eluent solution.

The values of the extra column moments estimated

by the bypass pulse experiments were completelyequivalent to those described above.

Figure 2: Bypass and eluted peaks for 0.7 g/lbetaine concentration with backgroundpure water

Figure 4 Equilibrium constant vs concentration

with background pure water

Journal of EAEA, Vol. 17,2000

24 Separation of Betaine from Molasses

~ 3c::

~ 2.5§ 2

~ 1.5°e 1@ 0.5'g. 0w

o 5 ro ffi ~ ~ ~ ~ ~ ~ ~ ~

Q:ncertratim (gQ

0.8E -3- 0.60-~ 0.4w r 0.2

00

0.2 0.4 0.6 0.8' 1

velocity (cm'/min)

1.2

Figure 5 Equilibrium constmlt vs with background

Figure 7 HETP vs fluid velocity for La g/lbetaine concentration

Figure 8 HETP vs fluid velocity for 2.0 g/lbetaine concentration

1.2'- 0.2 0.4 0.6 0.8

velocity (mt/rrin)

1 I I

E'0.8~0.6a..I- 0.4wI,O.2

.° I I

°

The solid phase concentrations q at different liquidconcentrations c.were calculated and the results are

reported. ,These results are represented by the plot ofsolid phase concentration vs liquid phase

concentration. Figure 6 represents the equilibriumisotherni of betaine at 40°C in accordance with the

computed values of q and c. As can be seen from theplot, the isotherm is non-linear. This prevails for allhigher concentrations· as observed in this work

Isotherms

CONCLUSIONS

The results of experimental study for the separationof betaine are presented. This study has shown thatthe adsorption of betaine follows linear

chromatography theory for lower (very diluted)betaine concentrations where as for higherconcentrations the process becomes non-linear.

Hence, the design of a separation unit may be carriedout following the existing methods of linearchromatography for lower concentrations and non­

linear chromatography for higher concentrations.

The experimental data generated and the parametersestimated can be conveniently employed in thedesign of the unit.

~4lGJ

E 18::s

g 16:E 14o~ 12

~ 100-C 8o'jij 6~ 4GJ

g 2o() 0

o 5 m·~ 4l ~ ~ ~ ~ E ~ ffi

CacertrctiCl1,C (gl)

Figure 6 Equilibrium isotherm for betaine withbackground concentration

In order. to evaluate the efficiency of the column,HETP values were estimated for two concentrationsat different liquid flow rates. A reasonable goodlinearity of HETP vs fluid velocity was'verified asshown in Figs. 7 and 8 .

ab

NOMENCLATURE

Constant (Eq.12)Constant (Eq.12)

Liquid p.h~se concen~ation (9m. 1'1)AXial nuxmg coeffiCIent (cm .s·t)

Diffusion coefficient inside the bed particle(cm2s'I)

Journal of EAEA, Vol. 17, 2000

Separation of Betaine from Molasses 25

de

HEr?K

K

LQ

q

p

.c

bp

Lm

ps

Column diameter (em)Height equivalent to a theoretical plate (em)Equiiibrium constant adsorptionCapacity factorColumn length (em)Volumetric flow rate (1.min·l)

. Solid phase concentration (gm. betaine/l ofadsorbent)Particle radius (em)Characteristic time of diffusion

Supe~.cial velocity (cm.min'l)Void fraction

First moment (min)Variance (min2)

densitY of fluid (gm. cm'3)

SUBSCRIPTS

column

bypassthe ith componentliquid phaseaverage ~ondit,on (mean)

parti~lesolid phase.

ACKNOWLEDGMENT

[4]

[5]

[6]

[7]

[8]

[9]

[10]

[11]

[12]

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H.A. Pavanan, Zuckerind 122 (1997) 28.

H.Heikkila, G,Hyoky, 1.Kuisma,US.Pat.no.5 (1992) 533.

P.E.Barker, K.Joshi, 1.Chern. Tech.

Biotechnology 52 (1991) 93.

S.Kishiara, S. Fujii, H. Tamaki, K.B. Kim,N. Wakiuchi,T.Yomamoto, Int. Sugar1.94(1994) 305.

M.Saska,S.J. Clarke; M.D. Wu,K.Igbal,Sep.Sci. Techno1.27 (1992) 1711.

D.M.Ruthven, C.B.Ching,Chem.Eng.Sci.44 (1989)1011.

M.D.Levain, G.Carta, C.M. yon, in: D.W.Green, 1.0. Maloney (Eds), Perry's.Chern. Engineerings' Bandbook, ~edition, Mc.Graw-Hill, New York, 1997.

H.W. Haynes, P.N. Sarma, AICHE1.19(1973) 1043.

This research has been supported by grants from theSardinia governIhent (Italy). The authcr thanks

Professor G. Tola of~e University ofCagliari, headof Chemical Engineering and Material Science

Department for. the provision of facilities andnumber of helpful comments. The author is alsograteful to .professor G. Sort of the University ofZurich, LTH Center, Switzerland. for his pertinentcomments.

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[15]

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Journal of EAEA, VoL 17, 2000