Sugar Technology Reviews, 14 (1988) 207-274 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands

RECENT TRENDS IN THE USE OF ION EXCHANGE IN THE SUGAR INDUSTRY

Xavier Lancrenon" and Daniel Herve""

CONTENTS

11. Progress Made in Recent Years,209 A. Resin Characteristics,209 B. Ion Exchange Process, Engineering and Equipment,211 C. Ion Exchange Plant Control,218 D. Ion Exchange and Waste Waters,220 E . Integration of Ion Exchange in the Process, 223

111. Principal Industrial Applications for Ion Exchange in the Sugar Industry, 232 A. Deliming (Beet Sugar Factory),232 B. Nonsugar Removal from Different Streams of a Beet Sugar Factory,243 C. Production of Liquid Sugar without Preliminary Crystallization, 256 D. Other Well-Established Ion Exchange Processes Used in the Sugar

Industry, 258

Summary, 271 (in Spanish, 274 )

References, 272

I. INTRODUCTION

The purpose of this article is not to explain the principle of ion ex-

change and recount the history of its application in the sugar industry. An

excellent and very comprehensive review of Landi and ~antovani,' published in

1975, provides a good basis for understanding the ion exchange principle, as

well as a chronology of its use in the beet sugar industry from 1941 to the

mid-seventies.

We will discuss here the trends observed in the industry over the last

ten years or so.

Our discussion will be limited to the so-called "conventional" sugar in-

dustry. We would be remiss, however, if we failed to mention that during this

same '75-'85 period a new sugar industry emerged,L one with an impressive growth

rate in the United States: the manufacture of high fructose corn syrup by the

*Applexion S.A., 15700 Lathrop Avenue, Harvey, Illinois 60426, USA. **Applexion S.A., 3 avenue de la Mauldre, 78680 Epone, France.

corn refiners. This industry presently produces more than 40% of all the

sweeteners consumed in the United States, and at the heart of their manufactur-

ing process we find the latest enzymatic and ion exchange technologies. In

reading this review one should keep in mind that this young industry of high

fructose corn syrups has created a market for ion exchange resins which is now

far greater (in terms of resin volume consumption) than the volume of resin

presently consumed by the conventional sugar industry.

The sugar industry (and we will henceforth be speaking of the conven-

tional sugar industry) now faces a great challenge--one which will determine

its future existence: how to decrease production costs and increase sugar re-

covery in order to remain competitive with the new high fructose corn syrup

industry.

One answer, and to a large degree the most significant, is ion exchange.

Ion exchange is now used by most of the world's important sugar producers

To present ion exchange in the sugar industry as a new technology--pio-

neered by small, specially-funded groups which experiment with new, unproven

technologies--is a gross misrepresentation. The fact is, ion exchange is now

the Intelligent choice of most progressive companies, who use this unit opera-

tion for separation very profitably in their sugar process, when dictated by

their particular market and the current economic situation.

When used wisely, ion exchange can significantly improve the profit margin

of the sugar manufacturer. Most successful sugar manufacturers in the Western

world use it extensively. Increased profits through the use of ion exchange

are, however, seldom publicized. This is probably mainly because ion exchange

is not used by every sugar manufacturer, and, in a market where competition is

keener than ever, the deciding factor between two competing companies could di-

rectly relate to the use of ion exchange.

The increased profits enjoyed by those in the sugar industry employing

ion exchange processes confirm the progress made in this area in the last decade.

This progress is reflected in

- better resin characteristics, I

- better ion exchange engineering, I - better plant control, I - inclusion of waste water treatment in the ion exchange process (when

required), and

- optimum integration of the ion exchange system in the general factory process--which generates indirect, supplementary savings to further enhance global factory economics.

The principal industrial applications for ion exchange in the sugar in-

dustry today are:

- thin juice deliming (beet sugar industry)

- nonsugar removal from b e e t t h i n j u i c e l t h i c k ju i ce / low g reen syrup/ molasses (bee t suga r i n d u s t r y )

- l i q u i d suga r p roduc t ion from t h i c k j u i c e (bee t suga r i n d u s t r y ) - Quentin p roces s (bee t sugar i n d u s t r y )

- d e c o l o r i z a t i o n of f i n e l i q u o r s (cane and b e e t sugar r e f i n e r i e s )

11. PROGRESS MADE I N RECENT YEARS

A . Res in C h a r a c t e r i s t i c s

1. Macro re t i cu l a r* Resins

Developed i n e a r l y 1960 by Rohm and H a a ~ , ~ t h e m a c r o r e t i c u l a r r e s i n s

have, wi thout a doubt , had a profound e f f e c t on t h e p rog res s of i o n exchange

i n t h e suga r i n d u s t r y . P roces ses which p rev ious ly used g e l type r e s i n s were

upgraded by us ing t h i s new range of p roduc t s a v a i l a b l e on t h e market .

One of t h e main r ea sons f o r t h e succes s of t h e s e r e s i n s i s t h e i r excel -

l e n t p h y s i c a l s t a b i l i t y , which a l lows f o r a t t r i t i o n r e s i s t a n c e under cond i t i ons

of h igh f low r a t e and s e v e r e osmot ic shock. This i s p a r t i c u l a r l y impor tant

i n p roces ses where, du r ing t h e same c y c l e , suga r sy rups a t h igh Br ix and ve ry

d i l u t e water s o l u t i o n s a r e passed s u c c e s s i v e l y through a r e s i n bed: Gry l lu s

p roces s , d e c o l o r i z a t i o n of f i n e l i q u o r , Quentin p roces s , e t c .

Another r ea son f o r t h e i r u s e i s t h a t they a r e p a r t i c u l a r l y e f f i c i e n t i n

t h e removal of c o l l o i d a l and h igh molecular weight subs t ances ( e . g . , product ion

of l i q u i d suga r s from cane molasses)

More r e c e n t l y , t h e development of a complete range of m a c r o r e t i c u l a r ad-

so rben t r e s i n s opened a new avenue i n t h e d e c o l o r i z a t i o n of sugar s o l u t i o n s .

These adsorbent r e s i n s have been used by t h e b e e t suga r i n d u s t r y f o r s e v e r a l

y e a r s now i n t h e p roduc t ion of l i q u i d suga r from t h i c k j u i c e .

2. A c r y l i c Res ins

Po lys ty rene type r e s i n s have been used i n t h e suga r i n d u s t r y f o r y e a r s ,

f o r a l l a p p l i c a t i o n s .

S p e c i a l a p p l i c a t i o n s have now been developed f o r t h e a c r y l i c type r e s i n s ,

s i g n i f i c a n t l y improving t h e economics of t he p roces ses i nvo lved . For example,

we have

(1) t h e use of a c r y l i c anion exchange r e s i n s f o r t he demine ra l i za t ion of

t h i n j u i c e i n t h e b e e t suga r i n d u s t r y , 1

(2) t h e use of a c r y l i c , s t r o n g an ion exchange r e s i n s i n t he c h l o r i d e form

f o r t h e d e c o l o r i z a t i o n of f i n e l i q u o r s i n t he suga r refiner^,^ and

* The term "macro re t i cu l a r " , i n t roduced by Rohm and Haas Company, c h a r a c t e r i z e s t h e p h y s i c a l pore s t r u c t u r e of t h i s new type of i o n exchange r e s i n and poly- mer ic adso rben t . I n a d s o r p t i o n terminology, m a c r o r e t i c u l a r r e f e r s t o pores of a d iameter l a r g e r t han 400 angst roms.

( 3 ) the use of acrylic, weak cation exchange resins5 for the final af-

fination of liquid sucrose in mixed-bed ion exchangers.

For each of these cases acrylic resin offers a different advantage:

For (1) - High capacity nonsugar removal.

For (2) - High capacity decolorization, and excellent yield in regenera-

t ion.

For (3) - Low acidity, avoiding the production of invert sugar.

3. Improvement in Capacity of Polystyrenic Macroreticular Anion

Exchangers

For the demineralization of beet sugar products, acrylic weak-base resins,

due to their higher nonsugar removal capacity, are often preferred to the poly-

styrenic weak-base resins.

The resin manufacturers have endeavored to provide new, high-capacity,

macroreticular, polystyrenic weak-base resins for the demineralization of sugar

products.6 This has been mainly in response to the demands of the corn refining

industry, which has always preferred polystyrenic resins over the acrylic resins.

Presently, high-capacity, weak-base acrylic, and high-capacity, weak-base poly-

choice of acrylic or polystyrenic resin is based more on factors such as regen-

eration efficiency, physical stability, resin life, the product treated, etc.

styrenic resins give very similar results in terms of nonsugar removal. The

1 Ion exchange resins come in granular and spherical forms. The spherical

form is presently the most popular due to its superior hydraulic characteristics.

Most ion exchange resins are supplied as spherical beads having a diameter be-

tween 0.2 and 1.2 mm, with 90% of the beads within t 20% of the mean bead size. Dow Chemical company7 recently introduced what they term "monosphere"

resins, the resin beads being within + 10% of the mean bead size. This bead size, they claim, is "tailored" to the customer's requirements. This latest

improvement will mainly affect the hydraulic characteristics of the resin.

I

5. Reproducibility of Resin

In industrial use, different batches of the same brand-name resin some-

times display differences in resin behavior which cannot always be attributed

to operating differences in the ion exchange plant.8 Small differences in the

resin manufacturing process itself can in fact affect the properties of the

resin. This is extremely difficult to detect early in resin life, since the

rinsing properties or physical characteristics (bead moisture, bead breakage,

etc.) can only be judged after many cycles. Part of the progress achieved in

resin characteristics is, therefore, in the standardization and better control

of resin manufacture in order to ensure perfect reproduction from one batch

of resin to another.

6. Outlook: New Products for Decolorization or Demineralization of

Sugar

(a) Powdered Resins

Although the subject under discussion here is the use of resin beads

i which can be saturated and regenerated in ion exchange reactors, we must not

overlook the recent use in the sugar industry of powdered resins--mainly for

7 decolorization of concentrated syrups9--which act in the same way as powdered

activated carbon and can be used in conjunction with the filtration process for i

I these syrups. I 1

(b) Mineral Resins

I The term "ion exchange resins" is very often considered as calling

i for organic polymeric compounds, in exactly the same way as the membranes were ~ assimilated in organic compounds. Today, research is being carried on using I I mineral porous beads1' as raw material for the production of ion exchange resins.

This follows the same trend observed in membrane technology with the recent de-

velopment of mineral membranes.

Concluding this chapter on the progress made in resin manufacture, it can be

stated unequivocally that the commercial resins now available have improved

characteristics, compared with those produced ten to fifteen years ago. This

means that the processes using resins are now more economical because of im-

proved resin performance and extended resin life. In certain cases, the use

in the sugar industry of new types of resin (such as the strong-base acrylic

resins) has been a real technological breakthrough.

B. Ion Exchange Process, Engineering and Equipment

As is the case with most technologies, ion exchange is in perpetual

evolution as a result of the work being continually carried on for the purpose

of improving the process, the engineering, and the equipment.

We will not go into detail here with regard to the different technologies

being applied, but rather summarize briefly the recent trends, as well as the

guidelines being followed.

L P r o c e s s Considerations

(a) Continuous System Versus Fixed-Bed

Between 1960 and 1975 intensive efforts were made by innovative

process designers 11'12 to promote the "universal" continuous system, where

resins are moved continuously, countercurrent to the different fluids they en-

counter. While the theory is very attractive, most of these systems have ulti-

mately proven unsuccessful.

Experience shows that for ion exchange technology, as is true for

other technologies, there is no universal system. Furthermore, here, the

simple solution is the ultimate answer: It is easier to move the different

fluid streams through the resin beads.

More than 95% of the industrial-scale ion exchange plants using

resin in today's sugar industry are of the so-called fixed-bed type, where

the resin is placed in a fixed reactor, where all the operations of a cycle

take place (sweetening-on/off, regeneration, rinsing, etc.). The only sequence

where resin can sometimes be moved out of the reactor is the backwashing se-

quence.

It is important to consider the progress made in the design of these

fixed-bed systems--which can be any of a variety of designs, depending on the

resin used and the type of application involved.

A word about the use of fixed beds as a "discontinuous" process

technology: Ion exchange is discontinuous in principle due to its sequential

characteristic, the resin being submitted to different operations in a method-

ical, sequential order. The fixed-bed technology is particularly well adapted

to this sequential characteristic. This does not mean, however, that a proper

arrangement of fixed-bed reactors cannot fit perfectly into a continuous process.

This is especially true today, in light of the progress made in automatic con-

trol.

(b) Use of Reagents for Resin Regeneration

In most cases, the use of ion exchange systems in the sugar industry

requires reagents for the regeneration of the resins. The cost of these re-

agents is always an important consideration in the decision to install an ion

exchange system. Therefore, the process designer takes into account the reagent

consumption in the conception of his ion exchange system design. Based on this

consideration, the evolution of the process has tended to concentrate on:

- Minimization of reagent consumption.

- Recovery of reagents for marketing in another form (such as fertilizer).

- Recycling of reagents. - Complete elimination of reagents.

(i) Minimization of Reagent Consumption

Considerable progress has been made in recent years in minimiz-

ing the consumption of reagents. A decisive step in this progress has been the

systematic use of countercurrent regeneration in the design of ion exchangers--

particularly those using strong cation or strong anion resins. When applied,

this allows savings of up to 40% of the normal amount of reagent required in

the cocurrent regeneration of these types of resin. 13

(ii) Recovery of Reagents for Marketing in Another Form

Another way to minimize the cost of reagent consumption is to

recover the reagents after regeneration to sell in another form.

For example: In the thin juice demineralization using the H-OH

form of the resins, sulfuric acid and ammonia used for the regeneration of the

resins can be sold as fertilizer, when combined with potassium extracted from

the thin juice. 14

(iii)

Efforts have been made to design systems which recover reagents

through the use of other unit operations, such as distillation. The systems use

reagents which are sufficiently volatile to be recovered in this manner, such as

ammonium carbonate. 15

It does not appear that a real industrial breakthrough has been

achieved in this area, although an industrial plant has run for several cam-

paigns at the Enns factory (Austria) using this principle.

Recently, laboratory tests and pilot studies, with ammonium bicar-

bonate as the regenerant, have been conducted using the same principle 1 6 3 1 7 to

seek better regeneration techniques.

(iv) Eliminating the Use of External Reagent

Some processes have been developed which eliminate totally the

use of external reagents for resin regeneration. The most well-known of these

processes is the Gryllus. 18' l9 In this process, thick juice or low green syrup

is used for the regeneration of the resins after their exhaustion. The conven-

tional deliming system uses brine, an external reagent, for the same purpose.

The Gryllus process is a clever technique for totally eliminat-

ing the use of external regenerant by employing in the process one of the beet

sugar factory's internal syrup streams for the purpose of regeneration.

Another example of a process which does not consume reagents is

the ion exclusion process, based on the chromatographic separation of sugar and

nonsugar. This has been developed on an industrial scale for the purification

of beet molasses.20 It should be noted, however, that before this process is

initiated, a complete softening of the molasses must be accomplished. This

softening consumes reagents (NaC1 or HC1, or NaOH).

Needless to say, in the process design, reagent cost is not the

only factor to be considered in the economic evaluation.

In comparing a process using reagents with a process assumed to

not use reagents, it is important to consider the entire process, including

both pre-treatment and post-treatment. The cost for these auxiliary treatments

can be very high, not only in reagents and energy, but also in sugar losses.

It w i l l be i n t e r e s t i n g t o f o l l o w t h e f u t u r e of two nonsugar r e -

moval t echno log ie s i n t h e bee t suga r i n d u s t r y : i o n e x c l u s i o n f o r t h e t r ea tmen t

of bee t molasses v e r s u s i o n exchange f o r t h e t r ea tmen t of t h i n j u i c e s and t h i c k

j u i c e s

( c ) Problems of Product I n t e r m i x t u r e

E f f o r t s have a l s o been made i n r e c e n t y e a r s t o dec rease product

intermixture--which c r e a t e s r e c y c l e problems--through improved p roces s des ign .

When us ing s o l u t i o n s of d i f f e r e n t d e n s i t i e s i n t h e i o n exchange r e a c t o r s , t h e

i d e a i s t o r e s p e c t t h e n a t u r a l o r d e r of i n t r o d u c t i o n of p roduc t s i n t h e r e -

ac to r . ' l For example: A lower d e n s i t y s o l u t i o n would be in t roduced i n downflow,

i f i t i s i n t roduced i n t h e system a f t e r a heavy d e n s i t y s o l u t i o n .

Using downflow o r upflow sys tems, depending on t h e d e n s i t y of t h e

product , i s no longe r a d i f f i c u l t eng inee r ing problem. Designs a r e now much

more f l e x i b l e i n t h i s r ega rd . As a r e s u l t , t h e d i l u t i o n e f f e c t , o r sweetwater

p roduc t ion , i s b e t t e r c o n t r o l l e d , t hus r ende r ing t h e i o n exchange process more

a t t r a c t i v e t han i n t h e p a s t .

2. Engineer ing Cons ide ra t ions

( a ) S i z ing of Reactors

One of t h e r u l e s i n des ign ing fixed-bed columns i s t o end up wi th a

r e s i n bed which a l lows enough c o n t a c t t ime f o r t h e i o n exchange r e a c t i o n , a s

w e l l a s smooth hand l ing of t h e r e s i n du r ing t h e run (no exces s ive p r e s s u r e drop,

space f o r t h e r e s i n t o s w e l l , e t c . ) , and a smooth r e g e n e r a t i o n (backwashing pos-

s i b i l i t i e s f o r a r e s i n expansion of up t o 50% o r more of i t s compacted volume).

There have been no major breakthroughs h e r e .

Usua l ly , t h e i o n exchangers a r e made of c y l i n d r i c a l r e a c t o r s conta in-

i n g beds of r e s i n having a bed dep th of 0 . 7 t o 2 m. I n c e r t a i n c a s e s , i n o rde r

t o a l l ow t h e r e s i n t o s w e l l , t h e r e a c t o r s have a c o n i c a l shape .

Due t o t h e more e x t e n s i v e use of i o n exchange r e s i n s , t h e r e i s now a

demand f o r l a r g e r i o n exchange r e a c t o r s t han i n t h e p a s t . With a l a r g e volume

r e a c t o r , s p e c i a l eng inee r ing f e a t u r e s must be i nco rpo ra t ed . The c o n s t r u c t i o n

of p re s su r i zed v e s s e l s i n a workshop i s l i m i t e d by t h e maximum a l lowab le diam-

e t e r f o r t r a n s p o r t i n g t h e v e s s e l from t h e workshop t o t h e f a c t o r y . As the bed

depth r equ i r ed f o r smooth o p e r a t i o n i n a s i n g l e bed of r e s i n i s a l s o l i m i t e d ,

one can see t h a t t h e r e a r e r e s t r i c t i o n s t o cons ide r i n t h e c o n s t r u c t i o n of

s i n g l e c e l l systems. It i s t h e r e s p o n s i b i l i t y of t h e i o n exchange s p e c i a l i s t

t o dec ide i f , f o r t h e volume of r e s i n cons ide red , a s i n g l e c e l l o r m u l t i p l e

c e l l system i s r e q u i r e d .

The l a r g e r t h e i on exchange r e a c t o r , t h e l a r g e r t h e s u r f a c e a r e a

f o r t he d i s t r i b u t i o n and c o l l e c t i o n of t h e f l u i d s passed through t h e r e a c t o r .

i n g c h a r a c t e r i s t i c s of t h e r e s i n i n t h e p roces s , and t h e r e q u i r e d volume of

The re fo re , s p e c i a l c a r e must be t aken t o a s s u r e t h a t t h e r e i s a homogeneous

d i s t r i b u t i o n of f l u i d s through t h e r e a c t o r .

(b) Decompression and Backwashing of t h e Resins

S p e c i a l mention should be made of t h e backwashing p o s s i b i l i t i e s of

a r e s i n bed i n a r e a c t o r , s i n c e t h i s i s one of t h e key f a c t o r s i n good regenera-

t i o n .

Convent ional ly , backwashing i s made a t t h e conclus ion of every c y c l e

t o v e r i f y

(1 ) t h e e l i m i n a t i o n of suspended s o l i d s s t i l l p r e sen t i n t h e product and

which have been f i l t e r e d by t h e r e s i n bed du r ing t h e running pe r iod ;

( 2 ) t h e e l i m i n a t i o n of r e s i n f i n e s c r e a t e d by r e s i n a t t r i t i o n and which

should n o t be allowed t o accumulate i n t h e r e s i n bed; and

(3) t h e t o t a l s w e l l i n g of t h e r e s i n , making c e r t a i n t h a t no p a r t of t h e

bed remains compacted--which could c r e a t e premature r e s i n a t t r i t i o n

and p o s s i b l e channel ing , w i t h p r e f e r e n t i a l passages f o r t h e f l u i d s .

Depending on t h e "c leanness" of t h e product t o be t r e a t e d , t h e swel l -

r e s i n f o r t h e a p p l i c a t i o n , t h e above t h r e e r e q u i s i t e s can be accomplished--

e i t h e r t o g e t h e r o r separa te ly--dur ing t h e backwashing of t h e r e s i n . For ex-

ample: For an upflow p roces s des ign t h e r e s i n w i l l r i s e t o t h e t o p of t h e r e -

a c t o r du r ing t h e run and mig ra t e t o t h e bottom of t h e r e a c t o r du r ing t h e down-

f low r e g e n e r a t i o n . Res in decompaction w i l l a u t o m a t i c a l l y occur when advancing

from t h e run t o t h e r e g e n e r a t i o n , making backwashing a t every c y c l e unnecessary ,

i f t h e product t r e a t e d i s c l e a n and t h e r e s i n i s i n good c o n d i t i o n . The back-

washing dev ice is des igned acco rd ing ly .

Th i s p a r t i c u l a r example shows t h e type of p rog res s ach ievab le w i th

a good unders tanding of t h e t r u e f u n c t i o n of t h e backwashing o p e r a t i o n .

Fewer backwashings can mean cons ide rab le s av ings i n wa te r .

( c ) Countercurrent Regenera t ion

Even wi thou t a " r evo lu t ion" i n i o n exchange technology, t h e p re sen t

e x t e n s i v e use of coun te rcu r r en t r e g e n e r a t i o n i s c e r t a i n l y one of t h e most pro-

g r e s s i v e s t e p s made i n i o n exchange technology. Cocurrent r e g e n e r a t i o n is no

longe r j u s t i f i ed - - a long wi th t h e b u i l d i n g of i o n exchange p l a n t s u s ing s t r o n g

an ion r e s i n s r egene ra t ed wi th NaOH o r s t r o n g c a t i o n r e s i n s r egene ra t ed wi th

hydroch lo r i c o r s u l f u r i c a c i d .

Even i f t h e coun te rcu r r en t r e g e n e r a t i o n r e q u i r e s a s l i g h t l y h ighe r

c a p i t a l c o s t inves tment , t h i s i s ve ry qu ick ly recovered through sav ings i n r e -

agen t consumption.

When u s i n g t h i s technology i t i s impor tant t o make s u r e t h a t t h e

bed of r e s i n is p rope r ly packed. I f t h e r e g e n e r a t i o n i s made i n upflow, t h e

r e s i n should never be f l u i d i z e d . Each eng inee r ing group has i t s method f o r ac-

complishing t h i s . Regardless of how t h i s i s achieved, proper bed packing w i l l

ensure t h e e f f i c i e n c y of t h e r e g e n e r a t i o n .

(d) Upflow Design

I n speaking of t h e p rog res s made i n eng inee r ing des ign , a word should

be s a i d r ega rd ing t h e cho ice of upflow des ign where t h e r e a r e i n t e r m i x t u r e prob-

lems o r where t h e d e n s i t y of t h e r e s i n is lower t han t h a t of t h e product t o be

t r e a t e d . For example: I n t h e t r ea tmen t of sy rups a t 60% t o t a l s o l i d s o r more,

t h e r e s i n may f l o a t i n t h e sy rup . I n such c a s e s , t h e downflow system does n o t

guarantee good packing of t h e r e s i n bed.

S ince t h e concept ion of upflow des ign no longe r p r e s e n t s a problem,

t h e engineer now has t h e choice of upflow o r downflow, depending on t h e process

requirement . This l ends much more f l e x i b i l i t y t o i o n exchange technology.

The upflow des ign i s now much more v i s i b l e i n i n d u s t r y . The Bayer

Company has c o n t r i b u t e d g r e a t l y t o t h i s phenomenon. 22,23

3.Equipment Cons ide ra t ions

( a ) P re s su r i zed Vesse l s

Ion exchange r e a c t o r s a r e u s u a l l y p r e s s u r i z e d v e s s e l s , e s p e c i a l l y

t hose f o r l a r g e i n d u s t r i a l p l a n t s . The c u r r e n t range of p r e s s u r e v a r i e s between

3 and 10 b a r s , depending on t h e a p p l i c a t i o n . Pas s ing sy rups o r o t h e r v i scous

p roduc t s through i o n exchange r e a c t o r s ( a s i s t h e ca se w i th t h e suga r i n d u s t r y )

makes i t neces sa ry t o apply p r e s s u r e t o t h e s e f l u i d s . Care must be taken t o

c o n t r o l t h e p r e s s u r e drop through t h e r e s i n beds. I t i s impor t an t t o avoid a

b i g p re s su re d rop through t h e r e s i n bed. Depending on t h e r e s i n s , a p r e s s u r e

drop of 0 .2 t o 2 b a r s i s w i t h i n t h e a c c e p t a b l e l i m i t .

(b) Rubber Lining

While d i scuss ing the p rog res s made i n i o n exchange technology, i t i s I impor tant t o p o i n t out a t t h e same time c e r t a i n s t a t e - o f - t h e - a r t f e a t u r e s which

have been improved on, but n o t r a d i c a l l y changed. Rubber l i n i n g i s one such

f e a t u r e , A t t h i s s t a g e of t h e technology, no b e t t e r p r o t e c t i o n a g a i n s t corro-

s i v e products and r eagen t s has been found than rubbe r - l i n ing t h e r e a c t o r s .

Rubber l i n i n g i s w e l l adapted t o t h e s t a t i c shape of t h e i o n exchange p l a n t and

t h e u s u a l range of tempera ture and p roduc t s t r e a t e d . I t p r e s e n t l y has no eco-

nomical e q u i v a l e n t , i n s o f a r a s r e s i s t a n c e t o c o r r o s i o n from d i l u t e d a c i d s , such

a s hydroch lo r i c o r s u l f u r i c a c i d , o r t h e o rgan ic a c i d s o f t e n p re sen t i n t h e

p roduc t s be ing t r e a t e d . Improvements i n rubber l i n i n g s have been made s p e c i f -

i c a l l y f o r t h e food and sweeteners i n d u s t r i e s , t o meet FDA and USDA r e q u i r e -

ments.

( c ) D i s t r i b u t i o n System

An impor tant p a r t of t h e i o n exchange r e a c t o r i s t h e dev ice f o r

d i s t r i b u t i n g and c o l l e c t i n g t h e d i f f e r e n t f l u i d s passed through t h e r e s i n .

There a r e two main types of equipment p r e s e n t l y i n u se :

(1 ) D i s t r i b u t i o n P la t fo rms

These a r e p l a t fo rms wi th numerous p e r f o r a t i o n s . Each ho le i s

equipped wi th a s p e c i a l nozz l e which a l lows on ly t h e f l u i d t o pass

through, n o t t h e r e s i n . P l a t fo rms a r e used when t h e r e s i n bed must

be suppor ted by them o r compacted a g a i n s t them. When us ing t h e

p l a t fo rm a t e i t h e r ex t r emi ty of t h e r e a c t o r , t h e d i s t r i b u t i o n of

t he f l u i d s i s made on t h e s i d e of t h e p l a t fo rm where t h e r e s i n is

n o t p r e s e n t . The un i fo rmi ty of d i s t r i b u t i o n a c r o s s t h e r e a c t o r i s

ensured by t h e i n d i v i d u a l nozz l e s be ing p laced a t measured i n t e r -

v a l s .

Network of Tubular Screens

Another method f o r d i s t r i b u t i n g and c o l l e c t i n g f l u i d s i s by t h e u se

of a network of s p e c i a l t u b u l a r s c r e e n s p l aced a c r o s s t h e r e a c t o r

and connected t o a c e n t r a l c o l l e c t o r . The s c r e e n s a r e s l o t t e d , a l -

lowing t h e f l u i d t o pas s through and l e a v e t h e r e s i n behind. This

system is now widely used i n t h e i n d u s t r y and i s p a r t i c u l a r l y w e l l

s u i t e d t o mixed-bed technology, o r coun te rcu r r en t technology, where

i t i s neces sa ry t o have t h e d i s t r i b u t i o n system p laced i n s i d e t h e

l o a d of r e s i n .

Regardless of t h e system used, p l a t fo rm o r t u b u l a r s c r e e n , i t i s

ve ry impor tant t h a t t h e system be suppor ted by t h e proper mechanica l dev ice t o

w i ths t and t h e f o r c e s exe r t ed w i t h i n t h e r e a c t o r . These f o r c e s a r e due t o

- -pressure drop through t h e r e s i n bed, and

- -swel l ing of t h e r e s i n , which can r e s u l t i n i n t e n s e p r e s s u r e

a g a i n s t t h e d i s t r i b u t i o n system, e s p e c i a l l y i f t h i s system i s

l o c a t e d i n s i d e t h e r e s i n bed.

Typ ica l m a t e r i a l s of c o n s t r u c t i o n f o r t h e nozz l e s and sc reens a r e

polypropylene o r s t a i n l e s s s t e e l . The s t a i n l e s s s t e e l i s more s u i t a b l e f o r t h e

s c reens due t o i t s mechanical c h a r a c t e r i s t i c s , but s p e c i a l c a r e must be taken

due t o p o s s i b l e c o r r o s i o n problems.

(d) Valves

Valves a r e an i n t r i n s i c p a r t of i o n exchange technology, s i n c e t h i s

technology uses so many d i f f e r e n t t ypes of f l u i d s which must be i n t roduced i n t o

t h e system and c o l l e c t e d from i t , one a f t e r t h e o t h e r .

Each fluid is controlled by one or several valves at the inlet and

outlet of the reactor--particularly when using automatic systems, which is now

generally the case. Depending on its complexity and the process in use, an ion

exchange plant in the sugar industry may include anywhere from thirty to three

hundred automatic valves.

The reliability of these valves is essential to the successful oper-

ation of the ion exchange plant. Needless to say, their proper maintenance is

an important factor.

Until recently, the most popular valve in use in an ion exchange

plant was the diaphragm type valve, rubber lined or not, depending on the flu-

ids. Recent improvements in the "tightness" of the butterfly valve make it an

interesting alternative to the diaphragm valve, particularly for diameters over

150 mm.

C. Ion Exchange Plant Control

In the development of ion exchange in the sugar industry, one very ob-

vious advancement is in plant control.

Most plants installed before the seventies were manual plants. These

had limited instrumentation and were controlled only by the skill of the oper-

ator. These operators could not be employed in other jobs in the factory and,

too, each operator had his own individual method of operation. This limited

the ion exchange possibilities to relatively simple processes, such as deliming

of thin juice, for example, where the number of valves and fluids to be con-

trolled was not excessive.

The limits for the manually controlled ion exchange plant in the sugar

industry were probably reached with the demineralization of thin juice, where

the short cycle means that at least three sets of cation and anion exchangers

must be used for continuous operation--two in regeneration while the third is

in operation. The success of such a plant was entirely dependent upon the oper-

ator's skill. The possibilities for human error were such that the manually-

operated plant could not be considered absolutely reliable.

One recent industrial application of ion exchange technology in the sugar

industry is the production of high quality liquid sucrose from thick juice,

without using crystalli~ation.~~ This most essential progress for the sucrose

industry would not have been possible without automatic plant control and reli-

able instrumentation.

1. Control Instruments

In the past, the ion exchange plant was often controlled by the factory's

laboratory, whose duty it was to determine the end of the cycles, or give the

operators the main parameters for the regeneration.

)

This control still exists today, but only as a check for the automatic

controls. For example: The cycle of a demineralization train is fixed to a

certain volume of product being treated. This is controlled by measurement

of the feed flow of the incoming product, by means of an electromagnetic flow-

meter, and calculating therefrom the exact volume passed through the system,

until a certain preselected amount is reached. When this preselected volume

is reached, the plant automatically starts the next sequence.

In order not to rely solely on a volume controller, there are additional

controls to check the quality of the product emerging. In the case of a de-

mineralization train, the continual measurement of pH and conductivity of the

f outgoing product will trigger an alarm if there is a quality problem, calling

I this to the operator's attention--and, if necessary, stop the plant.

Progress such as this in instrument control has made the ion exchange pro-

cess much more reliable and easier to operate.

I One principle applied in today's ion exchange unit is that of relying on

1 the actual volume passed through the system during each sequence, rather than

the time elapsed, as was done in the past. The control panels of these plants,

therefore, include a number of volume counters, whereas before there were timer

controls.

Summarizing the different levels of control in the modern ion exchange

unit, the general rule would be:

Level 1 Control through preselected volume.

Level 2 On-line quality control by specific sensors

(pH, conductivity, color, etc.).

i Level 3 Laboratory control. (Level 1 is the routine control, Level 2 the alarm control, and

Level 3 the optimization control.)

In certain cases, there are no existing, or at least no reliable, on-line

controls. For example: For the control of calcium removal in a deliming plant

there is at present no on-line sensor. In this case, only Level 1 and Level 3

apply. The setting for Level 1 is determined by the analysis made at Level 3.

2. Automatic Sequence Control

The instrumentation allows the operator to control the flow, volume and

characteristics of the product passed through the ion exchange system in one

sequence and to stop that sequence when desired. Passing from one sequence to

the next (opening/closing of specific valves, and starting/stopping of specific

pumps, etc.) is controlled by an automated device. In early ion exchange tech-

nology this was done manually.

There were several stages of improvement in sequence control between

the sixties and eighties. The beginning of automation was in the use of pneu-

matic systems for opening and closing the pneumatic valves individually from a

control panel. This relieved the operator of the responsibility of doing this

manually. Further improvement came about in the form of a "combined" valve

control for a simultaneous opening and closing of the appropriate valves for

a sequence. This was accomplished by means of pre-engineered mechanical de-

vices which allowed air distribution to the valves in a predefined order. It,

however, had the disadvantage of being a very rigid arrangement which did not

make allowance for changes in the established sequence. Then, in the seventies,

came the use of electrically activated solenoid valves for the control of the

pneumatic valves. Sequence programming could be arranged by means of a diode

matrix, assigning to each sequence the necessary valves and pumps. This had

the advantage of flexibility, since the sequence programming could be easily

changed by simply removing and resetting the removable diodes.

Next to arrive on the scene, at the end of the seventies, were the pro-

grammable controllers, using microprocessors. This is the latest stage in the

development of this technology, and it represents total control of the sequen-

tial operations of an ion exchange plant. The programmable controller system

offers the required flexibility, with absolute reliability, and it can be con-

nected to computers which monitor the overall operation of the factory.

This relatively recent progress in control of ion exchange through auto-

mation has, without a doubt, been a decisive factor in the extended use of this

unit operation in the sugar industry. Also, automation of the control system

has made the industry less inclined to opt for the continuous process over the

fixed-bed, since the problems previously associated with fixed beds for con-

tinuous processes have been resolved.

D. Ion Exchange and Waste Waters

Waste water was not a sensitive issue, either in the sugar industry or

in ion exchange, until the seventies. Since then, governmental pressure and

the energy crisis have caused this to become a major problem, not only for en-

vironmental reasons, but also for economic reasons, as it was discovered that

reducing wastes has a tremendous impact on the utilities consumption of a fac-

tory.

As is the case with other unit operations, ion exchange can no longer

be considered on the basis of only its own input and output of utilities and

wastes, but rather viewed as part of an integrated system which includes the

necessary pretreatment of utilities and post-treatment of wastes. Imaginative

engineering has brought about considerable improvement in this area. In most

cases, this has meant savings in dollars for the factory. (See Figure No. 1.)

EVOLUTION OF THE UNIT OPERATION CONCEPT I N RECENT YEARS

OUTPUT OUTPUT

I AFTER I INPUT (NATURAL ENVIRONMENT)

POST-TREATMENT w 4 PRETREATMENT

t OUTPUT (NATURAL ENV IRONMENT)

NOW, MUCH MORE THAN I N THE PAST, EACH UNIT OPERATION OF A PROCESS I S CONSIDERED FOR ALL PRE- AND POST-TREATMENTS I T GENERATES, RATHER THAN FOR ITSELF ALONE.

PRETREATMENT

UNIT OPERATI ON

-

FIGURE NO. I

PR0CES5w

1. Water Consumption in Regeneration

Due to the cost of water, one of the first priorities was to decrease

water consumption in resin regeneration. For example: In a conventional de-

liming plant regenerated with lime, it was possible by recovering the water

used for the final rinse of resins after regeneration and reusing it at the

following regeneration--for purposes such as backwashing, brine dilution, or

first rinse--to decrease water consumption by five bed volumes (from 11 to 6

bed volumes). This decreased water consumption, and thereby effluent volume,

by 45%. 2 5

In another case, the systematic recovery or recycling of water used for

the regeneration of the resins in a thin juice demineralization plant resulted

in an increase in effluent concentration from 3%-4% total solids to 7.5%-8.5%

total solids. The evaporation of these effluents represented a considerable

saving in energy.

2. Treatment of Effluents from the Ion Exchange System - Most of the ion exchange systems used in the sugar industry have now

been studied for possible treatment of their effluents. An outstanding example

is in the concentration of effluents from demineralization or ion exclusion.

The existing demineralization plants for removal of nonsugar from thin

juice by H-OH demineralization, or the removal of nonsugar from molasses by

ion exclusion, are equipped with specific effluent treatment systems which use

concentration and crystallization. In the case of H-OH demineralization, the

effluents are concentrated and crystallized for the production of two co-prod-

ucts: a fertilizer, which combines the potassium of the nonsugar with the sul-

fates and ammonium ions coming from the regenerants; and an organic compound,

rich in proteinic substances, which can be used as livestock feed or used to

enrich the pulp in amino acids. 14

The effluents of an ion exclusion plant are usually concentrated to give

a residual molasses with a purity of 20%, which can, for example, still be sold

as molasses for livestock feed.

Another effort has been in the treatment of effluents from ion exchange

decolorization plants which use brine as a reagent. In this area there have as

yet been no industrial plants equipped with such treatment facilities--probably

due to the fact that most of such sugar refineries are located near the sea and

do not face great pressure from the populace or authorities for discharging

salty effluents to this environment. There are, however, processes which oxi-

dize the brine,26 or separate the coloring material from brine by membranes, 27

which will certainly be applied to such treatment in the future.

3. Waste-free P roces ses

There a l s o e x i s t s i n t h e suga r i n d u s t r y t h e p o s s i b i l i t y of t o t a l l y

e l i m i n a t i n g t h e e f f l u e n t s t r eam from an i o n exchange p roces s , t h u s obv ia t ing

t h e problem of e f f l u e n t t r ea tmen t . The b e s t example of t h i s i s u se of t h e

Gry l lu s p roces s28 i n sugar j u i c e del iming, where t h e r egene ran t and r i n s i n g

f l u i d s a r e t h i c k j u i c e o r low green sy rups and t h i n j u i c e . I n t h i s ca se ,

t h e r e i s no water i n p u t and, t h e r e f o r e , no e f f l u e n t i s c r e a t e d . The Gry l lu s

p roces s w i l l be d i scussed i n d e t a i l i n t h e chap te r cover ing s p e c i f i c p roces ses .

Another i n t e r e s t i n g endeavor i n t h i s f i e l d i s proposed by A s s a l i n i 2 9

f o r t h e r e g e n e r a t i o n of t h e Quentin c a t i o n exchange r e s i n s u s ing Quentin mo-

l a s s e s ( r i c h i n magnesium), which would avoid t h e p roduc t ion of waste water

i n a manner s i m i l a r t o t h e G r y l l u s p roces s

E. INTEGRATION OF I O N EXCHANGE I N THE PROCESS

More than any o t h e r u n i t o p e r a t i o n of s e p a r a t i o n , i o n exchange i n t h e

suga r i n d u s t r y should be cons ide red n o t only f o r i t s d i r e c t e f f e c t , but a l s o

t h e i n d i r e c t e f f e c t s of i t s presence i n t h e p roces s . These i n d i r e c t e f f e c t s

have, i n f a c t , proven i n many c a s e s t o be t h e r ea son f o r t h e succes s o r f a i l u r e

of a p l a n t .

1. Example 1: I n t e g r a t i o n of Deliming i n a Beet Sugar Fac to ry

The d i r e c t e f f e c t of a de l iming p l a n t i s t h e e l i m i n a t i o n of ca lc ium from

t h e t h i n j u i c e i n o r d e r t o dec rease f o u l i n g of t he evapora to r s .

Deliming p l a n t s have f o r y e a r s been running w i t h a b r i n e r e g e n e r a t i o n

system copied from t h e conven t iona l wa te r sof teners- -wi th t h e fo l lowing d i r e c t

e f f e c t s :

-- Sugar l o s s e s i n molasses (due t o t h e replacement of ca lc ium by sodium).

-- Sugar l o s s e s du r ing t h e sweetening-on and sweetening-off of t h e p l a n t .

-- Consumption of water f o r t h e r e g e n e r a t i o n . -- Consumption of b r i n e . -- Product ion of ho t waste wa te r s c o n t a i n i n g c h l o r i d e s .

A l l t h e above can be avoided by i n t e g r a t i n g t h e del iming p l a n t i n t h e

suga r f a c t o r y p roces s and us ing t h e i n t e r n a l l y genera ted p roduc t s of t h e fac-

t o r y ( t h i c k j u i c e o r low green syrup) f o r t h e regenera t ion--a c l o s e d loop. 28

It i s i n t e r e s t i n g t o n o t e t h a t a l t hough t h e Gry l lu s p roces s p r i n c i p l e

was de f ined i n t h e l a t e f i f t i e s , i t was not recognized by t h e suga r i n d u s t r y

u n t i l twenty y e a r s l a t e r , and i s now widely used.

2. Example 2 : I n t e g r a t i o n of Demine ra l i za t ion i n a Beet Sugar Factory

The d i r e c t e f f e c t of a d e m i n e r a l i z a t i o n p l a n t i n a bee t suga r f a c t o r y

i s t h e removal of nonsugar, which i n c r e a s e s suga r y i e l d . There a r e , however,

indirect effects. The location chosen, within the process, for the installa-

tion of the demineralization plant can have a great impact on the successful

operation of the plant. If the plant is demineralizing molasses, it will pro-

duce an extra sugar stream which will be sent to crystallization and overload

the crystallization process with sugar and recycled nonsugar. This will result

in a higher energy demand for crystallization. Conversely, if the plant is de-

mineralizing thin juice, it will remove nonsugar from the main process stream.

As a result, the volume of massecuite necessary for the crystallization will

be lower and the energy consumption lower. 3 0

The diagrams shown represent:

In Figure No. 2 -- Crystallization in a beet sugar factory, with the conven- tional method, using the remelt of sugar I1 and sugar 111. In this case a

massecuite volume of 35.8 11% beet is necessary for a sugar extraction yield

of 84%.

In Figure No. 3 -- Crystallization of the same beet sugar factory, with the

demineralization of thin juice. In this case, due to considerable improvement

in the color of the standard liquor, it is possible to have a sugar extraction

yield of 87.9% with a massecuite volume of 26.7 11% beet.

3. Example 3: Integration of a Liquid Sugar Plant in a Cane Sugar

Refinery

The use of ion exchange for the production of liquid sugar may change

drastically the production diagram of a refinery.

The five diagrams shown here (Figure Nos. 4, 5, 6, 7 and 8) represent

the interaction between liquid sugar production and the diagram of the factory--

depending on different production capacities tor liquid sugar, different raw

materials used for the liquid sugar production, and different capacities for

the factory itself.

It is interesting to note the interaction between the production of

liquid sugar and

-- massecuite volume,

-- production of final molasses, and

-- the possibility of increasing the refinery capacity without increas-

ing the massecuite volume.

From the three examples given, it is obvious that the use of ion exchange

technology in the sugar industry has a profound effect on the process itself.

When implementing the ion exchange plant, one should at the same time modify

the areas of the factory which will be affected by its operation (evaporators,

crystallizers, etc.), in order to maintain a good heat and material balance

in the modified factory, and thereby benefit from all the good side effects

(color removal, massecuite volume reduction, etc.) of the ion exchange plant.

CRYSTALLIZATION WITH REMELT OF SUCROSE I 1 AND SUCROSE Ill DIAGRAM NO. 1

.DRY SUBSTANCE. . 17.39

.COLORATIOH..... 1650 24.60 .......

.DRY SUBSTANCE.. 26.03

.COLOAATIW..... 1650 28.24 ......

.DRY SUBSTANCE.. 29.88

FIRST STRIKE I

...... I .SUCROSE.. 14.08 I - o A .CEE POINTS.. ... 8 . 2 - I..... L T - 7

;;;;A ?T;:$:R 1 :;%2;:kb$k: : : : IT: 3 1 .DRY SUBSTAW.. 11.95

:rz:::::: :,.: 1;;: 1 I:bW.$kb ;::: 1 . . "ASSECUITE 11 .NW-SUCROSE.. .MYSUBSTANCE.. 12.67 . WY SV89TANCE.. SECOND STRIKE I

THIRD STRIKE ...... I .PURITY... 98.5 1

LITERS OF MSSECUlTEs - 21.7 + 9.1 + 5.0 = 35.8 FIGURE NO. 2

C R Y S T A L L I Z A T I O N WITH D E M I N E R A L I Z A T I O N OF T H I N J U I C E DlAGRAM NO. 2

..... X DEUINERALIZU) JUICE.. 35.5 S OMINERALIZATI(W I N THE

~ ~ $ [ ~ l : f # ~ U ~ f i E ~ . .... 75 %ilE?~J~&!~h%kt: : : : :. 7. 37

... ...... . M Y SUBSTANCE.. 17.02

I

i - REMELT SUCROSE Ill - 2000 ICUMSA 18.1 l

.DRY SUBSTANC~: : IS. 16

MASSECUITE I

FIRST STRIKE r

........ I ... . .SUCROSE CEE POINTS.. I .......

.DRY SUBSTANCE.. 8.76

... a MILCUATION.. 3970 ...... MASSECUlTE I J .SUCROSE.. ........ NON-SUCROSE. .SUCROSE . ... .. SUBSTANCE.. 9.95 NWSVCROSE.. SECOND STRIKE

.DRY SUESTANCE. .

...... .SVMK15E.. 4.19 ..... .CEE POINTS 17.5 4 7

.PURITY.. ....... .. HOTHER LIQUOR . W - S ~ E . .

.DRY 9UIISTANE. . 4.57

THIRD STRIKE I .PURITY ......... s3.5 I

LITERS OF MASSECUITEt - 1 .59 + 7.1 r 3.7 = 26.7 F I G U R E NO. 3

LIQUID SUGAR PROJECT 0 REFINERY DIAGRAM

400 T/D WITHOUT LIQUID SUGAR PRODUCTION

REMELT 5 = 420.3 5 = 420.3

P = 99 B R I X = 90

* I SYRUP 2 MASSECUITE 3

5 - 90 S = 90 .," .. -

P = 95.8 P = 95.8

i I

SUGAR 3 SYRUP 3 5 = 46.2 S = 43.0

NS = 0 . 2 NS = 3 . 8 P = 99.5 P = 92

FIGURE NO. 4

LIQUID SUGAR PROJECT 1 REFINERY DIAGRAM

400 T/D 20 T/DAY PRODUCTION OF LlQUID SUGAR

MOLASSES

NS= 7.0 P = 40.0

NS = 0 NS = 4 P = 100 P = 97.9 P = 97.9 BRIX = 91

FIGURE NO. 5

LIQUID SUGAR PROJECT 2 REFINERY DIAGRAM

400 T/D 35 T/DAY PRODUCTION OF LIQUID SUGAR

400 T/DAY AFFIN. MOLASSES

NS = 11.9 NS = 3.3 NS = 23.6

P = 97 P = 92.5 BRIX = 75

MASSECUITE 2 5 = 210.4 5 - 174.5 S = 174.5

NS = 3.8 NS = 3.8 P = 100 P = 97.9 P = 97.9 * - SUGAR 2 SYRUP 2

5 = 94.2 S = 80.3 - 5 = 80.3 NS = 0.2 ~ NS= 3.6 NS = 3.6

P = 95.-7

SYRUP 3 S - 41.4 S = 38.9

NS= 0 .3 NS = 3.3 P = 99.3 P = 92.5

FIGURE NO. 6

L I Q U I D SUGAR PROJECT 3 REFINERY DIAGRAM

400 T / D 35 T/DAY PRODUCTION OF L I Q U I D SUGAR, EL IM INAT ING MOLASSES

SUGAR 3 S = 42.1 S = 38.9

NS= 3.3 P = 99.5 P = 92.5

FIGURE NO. 7

LIQUID SUGAR PROJECT 4 REFINERY DIAGRAM

600 T/D 35 T/DAY PRODUCTION OF LIQUID SUGAR

MASSECUITE 2

NS = 5.9 P = 100 P = 97.9 P = 97.9

SUGAR 2 SYRUP 2 MASSECUITE 3 5 = 143.2 5 = 126.7 5 = 126.7 NS = 0.4 NS = 5.5 P = 99.7 P = 95.8 P = 95.8

8 I

SUGAR 3 S = 65.1 9 = 61.3 NS = 0.3 NS = 5.2 P = 99.5 P = 92.2

FIGURE NO. 8

111. PRINCIPAL INDUSTRIAL APPLICATIONS FOR ION EXCHANGE IN THE SUGAR

INDUSTRY

Following are brief descriptions of typical full-scale ion exchange pro-

cesses in the sugar industry:

A. Deliming (Beet Sugar Factory)

1. Benefits of Thin Juice Deliming to the Beet Sugar Industry

After two carbonation and two filtrations the purified thin juice con-

tains between 40 mg/l and 200 mg/l soluble calcium, expressed as CaO, depending

on the site of the beet sugar factory and the season. This can be even higher

if the beets have been altered by too lengthy storage, or due to frost. (Values

as high as 600 mg/l can be reached.)

The calcium left in the thin juice has an adverse effect on results at

the beet sugar factory, mainly for two reasons:

(1) An important part of this calcium is precipitated on the evaporator

tubes in the form of calcium carbonate, which adversely affects the

investment, energy and manpower costs of the factory, as explained

below.

(2) The calcium left in the thick juice after concentration may, in

certain cases, be responsible for the turbidity sometimes observed

when white sugar is dissolved to produce liquid sugar.

Although this second possibility can be very costly, especially if you

lose a market due to a quality problem, we will at this time consider in more

detail the effect of the calcium precipitation on the tube evaporators.

The main effect of this precipitation is to create scaling of the evap-

orator tubes. As a result, there is a reduction in the overall heat transfer

coefficient.

Using a U of 600 Btu/hr/sq.ft./"F for a clean surface, the necessary

thickness of calcium carbonate to reduce this value by 50% is only 0.026 in. 32

The heat transfer coefficient is proportional to the inverse of the sur-

face area considered. Therefore, due to scaling of the tubes in a factory hav-

ing no deliming system, provision for surface area must be made in advance,

taking into account the calcium carbonate scaling. For example: For a beet

sugar factory processing 5,500 metric tons of beet per day, if there is no

deliming plant, a surface area of 120,000 square feet should be calculated.

With a deliming plant, this surface area would be reduced to 90,000 square

feet, and the difference in investment would be at least US$300,000. Moreover,

for a given surface area, due to the progressive scaling of the tubes, the

delta T between steam and juice must be increased in order to maintain the same

evaporation--and this results in higher energy consumption.

It is estimated that for a sugar factory having no deliming device, an

increase in steam consumption of 20 kg per ton of treated beet must be calcu-

lated. This means--for 5,500 metric tons per day, a 150-day season and steam

cost of US$b.OO/ton--an additional cost of ~~$100,000 per season. (This fig-

ure is based on a coal-operated factory. It should be doubled if the factory

is using fuel oil.)

To help maintain a clean evaporator, the sugar factory is usually

thermically equilibrated in order to recover all the condensation heat of the

vapors on recovery systems.

When efficiency decreases due to scaling, in order to retain the con-

centration effect, the delta T is increased through control of the vacuum on

the last effect, progressively introducing more vapor to the final condenser.

At this stage, when the maximum delta T has been reached, it is necessary to

proceed with manual cleaning of the evaporator. This means an additional cost

in manpower, and this figure must be determined by each sugar factory.

Summarizing the benefits of deliming:

-- No turbidity in remelt from whiLe sugar. -- Lower investment in evaporation, or no investment necessary to in-

crease factory capacity.

-- Lower steam consumption.

-- Elimination of boilout during the season, representing savings in

sugar losses and manpower costs.

2. Normal Configuration of a Deliming Plant

Figure No. 9 shows the usual arrangement of a deliming plant, using

the three-vessel configuration. In this case, two reactors are simultaneously

delimiiig thin juice when the third is in regeneration. The main advantage

here is that of obtaining a soft thin juice, which is a mixture of the treated

juice of one reactor at the beginning of its run and the juice of the other at

the end of its run. The resulting mixture, therefore, has a CaO content which

represents an average quality soft thin juice.

In some cases, especially where the hardness of thin juice is very high,

it is more economical to have a two-reactor configuration (one in deliming and

the other in regeneration).

3. Gryllus Process

The material balance shown in Figure 10 outlines the principle of the

Gryllus process, using low green syrup for the regeneration of the resin.

It is clear that at the inlet of the system no water is used, only thin

juice and low green syrup. Therefore, no dilution occurs in the system.

The low green syrup is used as a reagent for regeneration. Its high

potassium and sodium content and high sugar concentration make it very

ARRANGEMENT OF THREE VESSELS FOR THIN JUICE DELIMING

DELIMED THIN JUICE m-

I I I I I TIME 0 T 2T 3 T 4T

COLUMN I I PRODUCTION 'REENFR~ ITN' PRODUCT I ON I

COLUMN 2 I PRODUCTION 'REENFRTT r i i ~ '

COLUMN 3 I PRODUCTION I

8 = In-IIT 8 = MINIMUM PERIOD ALLOWED FOR A RUN n = NUMBER OF VESSELS T = NECESSARY TIME FOR A REGENERATION

FIGURE NO. 9

FIGURE NO. 10

GRYLLUS REGENERATI ON SYSTEM

MATERIAL BALANCE FOR ONE COLUMN

I . PRODUCTION 1.5 + 2.0 = 2. PARTIAL DRAINING A EVAPORATION

3. AIR SCOURING

4. REGENERATION A

5. REGENERATION B

7. SWEETENING-OFF A

8. SWEETENING-OFF B

9. SWEETENING-OFF C

10. PARTIAL DRAINING C

11. AIR SCOURING

12. BACKWASHING A

13. WAITING

B. V. = BED VOLUME OF RESIN LGS = LOW GREEN SYRUP

NO DILUTION, NO WASTE, NO CHEMICAL

efficient to regenerate the resin after exhaustion with calcium. Therefore,

no extra reagent is required for the regeneration.

At the outlet of the system, the juices and intermediate products from

sweetening-on and sweetening-off are either recirculated prior to the second

filtration or sent to the third crystallization. Therefore, no waste is pro-

duced by this .system.

One important advantage of the Gryllus system is that no sodium is in-

troduced in the system for the resin regeneration. Since the sodium ion has

a melassigenic effect, the sugar factory using the Gryllus system has a better

sugar extraction yield, compared with a sugar factory using the conventional

process.

This is called "the Gryllus effect".

For an 85-day season, a sugar savings of 550 tons is estimated for a

5,000 tons/day beet sugar factory using the Gryllus process, compared with the

same factory using the conventional process. 3 3

Figure Nos. 11 and 12 show the integration of the Gryllus system in a

beet sugar factory, and a typical regeneration curve for this system.

4. N.R.S. Process 25, 63

The material balance shown in Figure 13 outlines the principle of the

N.R. S. process.

As in the Gryllus process, no water is used, only thin juice. Therefore,

no dilution occurs in the system.

For the regeneration, caustic soda is added to cold (40°C) delimed juice

at the rate of 40 grams NaOH per liter of juice. One volume of reagent is used

to regenerate one volume of resin.

The calcium from the resin is exchanged for the sodium in the juice and

forms a soluble calcium-saccharate vith the sugar present in the juice.

It is important to maintain a low temperature during the regeneration

in order to avoid saccharate precipitation.

At the outlet of the system, the juice is returned either to filtration

2 or to carbonation 2.

The juice containing the calcium removed from the resin is sent to car-

bonation, where the calcium is separated from the sucrose and calcium precipi-

tated as calcium carbonate.

The calcium carbonate will be removed at the second filtration. The

calcium is completely removed from the process with the sludge of carbonation.

Again, it can be seen that with this process no waste is discharged to

the environment. Sodium, however, is added to the molasses, having the same

melassigenic effect as with a conventional deliming process which uses brine

for the regeneration.

INTEGRATION OF THE GRYLLUS SYSTEM I N THE SUGAR FACTORY

THIN JUICE FROn SECOND CARBONATION

STRIKE 3

HMASSES SUGAR 3

FIGURE NO. I I

REGENERATION BY GRYLLUS PROCESS I I I I I '

1 PARTIAL 1 5W I 5W 5W 1 I REGEN. B I REGEN. A I D I o ~ ~ ~ ~ O F F B ~ O F F C

I 1

FIGURE NO. 12

OF RESIN

N. R. 5. REGENERATI ON SYSTEM

MATERIAL BALANCE FOR ONE COLUMN

2. PARTIAL DRAINING

3. AIR SCOURING

4. BACKWASHING

6. REGENERATI ON

7. SLOW RINSING

8. FAST RINSING

9. WAITING

B. V. = BED VOLUME OF RE5 IN

NO DILUTION NO WASTE NO ADDITIONAL CHEMICAL (IF CAUSTIC SODA IS BEING USED FOR THIN JUICE ALKALINIZATIONI

FIGURE NO. 13

Figure Nos. 14 and 15 show the integration of the N.R.S. process in the

sugar factory, and a typical regeneration curve for this system.

5. Softening, Using a Weak Cation Resin in the Hydrogen Form

This fairly recent process has been described by ~choenrock~~

and uses the high affinity of weak acidic cation exchangers for the calcium

ions.

The advantages of this system are as follows:

(1) High capacity of the ion exchanger, as compared with other deliming

systems (0.8 eq/l for a Gryllus or N.R.S. system versus 2.5 eq/l

for this system).

This would reduce the investment cost considerably.

(2) Regeneration of the cation exchanger with a stoichiometric quan-

tity of acid, due to the high affinity of the resin for the hydro-

gen ion.

(3) Possibility of neutralizing the treated thin juice with active mag-

nesium oxide, contributing to less molasses formation.

(4) Using sulfuric acid for the regeneration, it is possible to use the

gypsum formed after the regeneration as a pulp-pressing aid for the

pulp dewatering.

These advantages are great, if we compare this system with the conven-

tional system using brine for regeneration.

There are, however, certain things which must be taken into consideration

in using this system: +

(1) Risk of sucrose inversion in the cation resins in the H form:

Flow and temperature parameters must be very carefully controlled.

(2) Sensitivity to suspended solids in the feed: Due to the very high

flow rates used to avoid sucrose inversion, the reactors are more

susceptible to plugging by suspended materials. The thin juice

feed must be perfectly clear.

(3) Resin stability: The weak acidic exchangers are carboxylic resins

which have less stability than the conventional polystyrenic strong

cation resins. Resin consumption is, therefore, higher.

Comparing this with the Gryllus and N.R.S., where no water is sent to

the reactors, this system also has the three disadvantages of the conventional

brine regeneration system:

INTEGRATION OF THE N.R.S. SYSTEM I N THE SUGAR FACTORY

FIGURE NO. 14

REGENERA TI ON BY N. R . 5. PROCESS

I I I I 1 FAST I I VOW RINSING I RINSING I I I I

I B.V.= 7 BED VOLUME OF RESIN

F I G U R E NO. 15

. k s . F y

-- Consumption of water.

-- Dilution effect on the juice during sweetening-on and -off. -- Losses in sugar at the end of each cycle.

Figure No. 16 represents the integration of the H+ softening system in

the sugar factory.

B. Nonsugar Removal from Different Streams of the Beet Sugar Factory

After carbonation and filtration, the thin juice of the beet sugar fac-

tory has a purity varying between 88% and 92%, depending on the factory setup.

i For the conventional factory, the amount of nonsucrose present in the

thin juice after carbonation and filtration will directly determine the amount

of sucrose lost in molasses. This can be calculated as follows: For each ton

of nonsucrose sent to crystallization, one and one-half tons of sucrose will be

lost in molasses. This is estimated to represent an extraction loss of 12%-16%

of the sucrose contained in the unprocessed beet. 3 5

1. Brief Review of the Methods Being Used to Increase Sugar Extraction

Needless to say, sugar technologists have been trying since the birth of

the industry to minimize the amount of sugar carried out of the beet sugar fac-

tory in molasses

Various methods have been applied to improve extraction.

(a) Methods for Decreasing Molasses Production of the Factory

(i) Improve crystallization by boiling to high density, cool-

ing to low temperature, and allowing a longer period of time for crystalliza-

t ion.

(ii) Decrease the melassigenic effect of the nonsucrose by

partially replacing the sodium and potassium in the nonsucrose with magnesium.

(iii) Remove nonsugar from thinlthick juice or low green

syrup by demineralization. This reduces the molasses produced in proportion

to the amount of nonsugar removed.

(b) Methods for Molasses Re-treatment

(i) Precipitate a calcium saccharate from the molasses for

recycling to factory carbonation (Steffen process).

(ii) Separate sucrose and nonsucrose in molasses by using ion

exclusion. The sucrose fraction recovered after separation is then recycled

through the factory process.

All of these methods are presently used in the beet sugar industry.

The factory's improvement in sucrose yield varies, depending on the method

chosen:

-- Methods (a)(i) and (a)(ii) increase sucrose recovery by up to 4% of the su-

crose present in the beet.

-- Methods (a) (iii), (b) (i) and (b) (ii) make possible an increase in sucrose

recovery which can exceed 10% oE the available sucrose in the beet.

2. Removal of Nonsugar from ThinIThick Juice or Low Green Syrup by

Demineralization

(a) Brief History

The first industrial trials on demineralization of these products

were in the United States. 36' 37 Between 1945 and 1949 four units were oper-

ating in the U.S.A., but by the early fifties all had been closed dorm due to

the poor economics of the operation

These plants employed the simple demineralization system, using t

cation exchangers in the H form and anion exchangers in the OH- form.

Improvements in this technology brought renewed interest, and in

1957 a French company, Generale Sucriere, started up several new demineraliza-

tion plants for thin juice demineralization. (It should be noted that some of

these plants have been running ever since their start-up, which now represents

some thirty years of experience in this technology for each of these plants.)

This so-called H-OH demineralization has benefited over the years from the

evolution of ion exchange technology in general. The system has been applied

in 1taly,12 and, more recently, again in the U.S.A. 39

For nonsugar removal by ion exchange, H-OH demineralization using

thinlthick juice or low green syrup is the only technology which has been con-

firmed over the years as being commercially feasible. During its development,

several other demineralization processes were proposed and tried, but ulti-

mately failed, e.g.,

-- using ion exchange for nonsugar removal and eliminating the carbonation of diffusion juice in the beet sugar factory:

Assalini "A" process ; 40 and

-- recycling the regenerating chemicals necessary for the de- mineralization process: Moebes process41 and Vajna process.

42

Schoenrock 16' l7 recently proposed a new version of the Moebes process, using

ammonium bicarbonate as a regenerant. This has not, however, been applied on

a commercial scale.

(b) Location of the H-OH Demineralization Plant within the%Beet

Sugar Process

The best location for the H-OH demineralization plant within the

beet sugar process is at the point of thin or thick juice treatment, as al-

ready emphasized in Chapter 11, paragraph E (2). The reasons for this are:

( i ) These products a r e c l e a r l i q u i d s which do n o t c o n t a i n

suspended m a t e r i a l s t h a t could p lug the r e s i n bed. They have been c l a r i f i e d

by ca rbona t ion and f i l t r a t i o n . Th i s i s always p a r t of t he b e e t suga r p roces s .

On t h e o t h e r hand, i n t h e cane suga r i n d u s t r y , t h e l a c k of c l a r i f i c a t i o n of

equ iva l en t p roduc t s has u n t i l now been a b a r r i e r f o r t h e i o n exchange p roces ses .

( i i ) These a r e r e l a t i v e l y h igh p u r i t y p roduc t s which do no t

exhaust t oo qu ick ly the i o n exchange r e s i n s used f o r t h e i r p u r i f i c a t i o n .

( i i i ) Removing nonsugars from t h e product b e f o r e c r y s t a l l i z a -

t i o n has an i n d i r e c t and d e s i r a b l e e f f e c t on the c r y s t a l l i z a t i o n diagram. 3 0

The energy saved i n c r y s t a l l i z a t i o n w i l l coun te rb l ance t h e energy neces sa ry

f o r t he c o n c e n t r a t i o n and c r y s t a l l i z a t i o n of t h e d e m i n e r a l i z a t i o n e f f l u e n t s .

F igure 17 i l l u s t r a t e s a t y p i c a l i n t e g r a t i o n of an H-OH d e m i n e r a l i z a t i o n p l a n t

i n t h e b e e t suga r f a c t o r y .

I n a n ion exchange process sugar l o s s e s a r e a lmost n e g l i g i b l e , s i n c e

on ly t h e i m p u r i t i e s a r e r e t a i n e d by t h e r e s i n . The re fo re , a t t h e end of a pro-

duc t ion run , t h e sugar i n t h e i on exchange r e a c t o r can be complete ly washed ou t

of t h e r e s i n , f o r an almost t o t a l sugar recovery . The suga r y i e l d obta ined i s ,

i n f a c t , i n exces s of 9 9 . 5 % .

( c ) P r a c t i c a l Arrangement of an H-OH Demine ra l i za t ion P l a n t

The average demine ra l i za t ion p l a n t i s des igned t o r e c e i v e cont in-

uously t h e f low of j u i c e t o be t r e a t e d .

It c o n s i s t s of t h r e e i d e n t i c a l l i n e s , each having a s t r o n g c a t i o n

exchanger i n t h e H+ form and a weak base an ion exchanger i n t h e OH- form.

The j u i c e , a t a concen t r a t ion which can va ry from 16 t o 35 Br ix ,

i s passed through two exchangers i n succes s ion a t a tempera ture of lZ°C. I n

t h e c a t i o n exchanger t h e mine ra l c a t i o n s (potass ium, sodium, ca lc ium, magnesium,

e t c . ) and t h e o rgan ic c a t i o n s ( b e t a i n e , amino a c i d s , e t c . ) a r e r e t a i n e d . I n

t h e anion exchanger t h e mine ra l an ions ( c h l o r i d e s , s u l f a t e s , n i t r a t e s , e t c . )

and o rgan ic a c i d s (g lu tamic a c i d , weak a c i d s produced by suga r deg rada t ion , e t c . )

a r e r e t a i n e d . Low tempera ture of t h e j u i c e i s neces sa ry i n o r d e r t o avoid in-

v e r s i o n i n t he c a t i o n i c r e s i n , which would be d e t r i m e n t a l t o t h e product ion of

g ranu la t ed suga r .

When t h e r e s i n s of one l i n e a r e exhausted , t h i s l i n e i s prepared f o r

r egene ra t ion . S u l f u r i c a c i d i s u s u a l l y used f o r t h e r e g e n e r a t i o n of t h e c a t i o n

exchanger, and ammonia f o r t h e r e g e n e r a t i o n of t h e anion exchanger.

Time neces sa ry f o r r e g e n e r a t i o n i s approximate ly double t h a t r e -

qu i r ed f o r t h e product ion cyc l e .

SCHEMATIC DIAGRAM OF DEMINERALIZATION INTEGRATION IN THE SUGAR FACTORY PROCESS

I SEMH) FILmATION SECOH) I EFFECTS 1 AND 2 EVAPORATION

CAG80N1TION

A

I

WIIPWNO

r - - - - - - A CRYSTAL FERTILIZER

,STEAM

I

EVAPORATION STRIKE 1 STRIKE 2 STFtIKE 3 HMAS5E5 EFFECTS 3 TO 5 I I

FIGURE NO. 17

Therefore, a continuous system, with three lines of cation and anion

exchangers, runs as follows:

Line 1 P R P R P R - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Line 2 R P R P R P R - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Line 3 R P R P R P ---------- - ---------- - ---------- -

P = Production R = Regeneration

In the system indicated, one line is always in service while the

other two are in regeneration.

It is the responsibility of the ion exchange engineer to choose the

correct volume of resin and the proper ratio of cationic resin to anionic resin,

based on the type of resin selected and the type of product to be treated.

It should be noted14 that some variations of the system have been de-

signed to recover valuable nonsugars such as betaine, amino acids and pyrroli-

done carboxylic acid (PCA).

Bichsel 43' 44 developed a very interesting concept--which was applied

at the Holly Sugar Corporation's beet sugar factory in Hamilton City, California,

and later at American Crystal Sugar's beet sugar factory in Moorhead, Minnesota--

where the cation and anion exchangers run independently and are controlled by

conductivity and pH, respectively. In this system two weak anion exchangers

(primary and secondary) are run in succession. This allows full loading of the

primary anion exchanger with nonsugar at each production cycle.

At the Nassandres (France) beet sugar factory of the Generale Su-

criere (whose demineralization plant was built by Applexion) ,45 the deminerali-

zation system includes two strong anion exchangers in the OH- form, for the pur-

pose of pH adjustment prior to concentration of the demineralized juice.

All existing improvements to the H-OH demineralization plant have not

been published, partly to protect the confidential interests of the end-users.

Actually, this process, which is in full operation in many countries (France,

Italy, Holland, Japan, etc.), has been in a state of ongoing evolution since its

beginning--shortly after World War 11.

(d) Treatment of the Effluents of Ion Exchange Demineralization

The effluents of the modern demineralization plant are never rejected

to the environment, but are treated for the production of co-products from the

nonsugar which has been recovered from the juice plus reagents which were used

for regeneration of the resins.

Two principal co-products are normally manufactured: a solid ferti-

lizer containing mainly potassium and ammonium sulfate; and a liquid organic

concentrate, rich in proteinic nitrogen, which can be used as a dietary supple-

ment in animal feed. The methods normally used to separate the minerals from

the organics are fractionation directly at the elution of the resins, 46, 47

or by crystallization 45y 48 of the minerals after concentration of the total

effluents. Experiments have also been done using spray drying4' of the mineral

fraction for the production of special types of fertilizers.

To ensure the best economics for a demineralization plant, it is es-

sential that the energy required for the production of the co-products be offset

by the energy savings brought about by the use of the demineralization plant in

the sugar factory. Marketing of the co-products is also a very important con-

sideration. If these products are properly marketed, the profit derived from

their sale adds to the overall profitability of the demineralization process.

(e) Indications of the Economics of the H-OH Demineralization

Process

The figures given below represent the published commercial perform-

ance3' of a modern plant running at 80% of its maximum design capacity:

-- Nonsugar elimination: 155 g of nonsugar per liter of resin (cation

+ anion) per day. -- Water to be evaporated from effluents and sugar streams: 40.9 tons

per ton of nonsugar eliminated.

-- 100% H2S04 : 0.8 ton per ton of nonsugar eliminated.

-- 100% NH3 : 0.32 ton per ton of nonsugar eliminated.

-- Additional sugar produced by the factory: 1.32 tons of sugar per ton

of nonsugar eliminated (or 204 kg of sugar per cubic meter of resin

installed per day).

The above figures are not given as the general rule or as the final state of

the art (~uerinl~ indicates a performance by a commercial unit of 405 kg sugar

recovered per cubic meter of resin installed per day). They can, however, be

taken as solid, conservative figures for the study of this technology.

It is not possible to complete a cost estimate for the introduction

of H-OH demineralization in a beet sugar factory without an integration study

to evaluate all the side effects of demineralization on factory economics.

Demineralization cannot be placed in a beet sugar factory as a complement to

the conventional process. It must be introduced as a new, essential part of

the general process, modifying radically the crystallization diagram.

3. Removal of Nonsugar from Molasses by Ion Exclusion

(a) Brief History

Landi and ~antovani' relate the history of the laboratory and pilot

scale development of ion exclusion--from heato on's^^ research in the early fifties to the encouraging data compiled by ~ r o s s ~ l in the early seventies.

The real commercial development of ion exclusion on beet molasses

began at the plants of The Finnish Sugar and Pfeifer und Langen I Company.52 A few first generation commercial plants were built in Europe

during the seventies, using the discrete fraction recirculation system, i.e.,

discontinuous ion exclusion system. Since that time, however, development of

this technology has been very slow. Ion exclusion technology, as reported by

~ u n i n , ~ ~ by the mid-eighties had not yet shown any "commercial promise".

New hope for the development of ion exclusion has been raised more

recently, with the appearance on the market of the better performing resins, 54

and the use of the simulated moving-bed technology (continuous chromatographic

separation). This technology, invented by Broughton and ~erhold, 55 and applied

successfully since the early eighties for the separation of glucose and fruc-

tose, improves the actual performance of the ion exclusion process. Schoen-

rock56 indicates the existence of two commercial units in Japan, in operation

in 1987, using the simulated moving-bed technology, and considers "highly prob-

able that the universal application of ion exclusion may be unavoidable in the

sugar industry if this industry is to stay competitive against substitute sweet-

eners".

(b) Location of the Ion Exclusion Plant in the Beet Sugar Process

The principle of ion exclusion--the chromatographic separation of

sucrose and nonsucrose--makes impractical the total recovery of the sucrose

entered in the separation system. Yields of 70%-85% are currently observed

for commercial plants using the discontinuous system. 57y 58 With sugar yields

such as this, it is impossible to place an ion exclusion system for the puri-

fication of products such as thin or thick juice--or even machine syrup. In

fact, all the existing commercial plants have been using beet molasses as raw

material.

The sucrose fraction obtained after ion exclusion is a product hav-

ing a purity of 90%-95%, which is usually sent to the head of the sugar factory

process at the carbonation step.

The nonsucrose load of the purified molasses.must be added to the

normal nonsucrose of the main stream. This is very important to consider for

the avoidance of "surprises" in sugar quality and overload of the crystallization

equipment. ~driaensen~~ reports an increase in thin juice color--from the normal

value of 900 ICUMSA, up to a value of 1390 ICUMSA units--and a thick juice color

of 3500 instead of 1700 ICUMSA, due to the recycling of purified molasses.

Progress has been reported56 recently, and sugar yields as high as

97% have been claimed possible. This means that future plants could use ion

exclusion starting from products having a higher purity than molasses, such as

machine syrup, or even low green syrup.

( c ) P r a c t i c a l Arrangement of an Ion Exclus ion P l a n t

The molasses t o be t r e a t e d must be delimed and f i l t e r e d .

Deliming i s e s s e n t i a l , s i n c e t h e c a t i o n i c r e s i n used f o r t h e chro- +

matographic s e p a r a t i o n i s i n t h e Na form. I f ca lc ium and magnesium a r e pre-

s e n t i n t h e molasses , t hey w i l l be exchanged i n t h e r e s i n f o r sodium i o n s ,

and p r o g r e s s i v e l y exhaust t h e r e s i n . As a r e s u l t , t h e r e s i n w i l l l o s e i t s

s e p a r a t i o n e f f i c i e n c y .

To avoid r a p i d f o u l i n g of t h e r e s i n s by suspended m a t e r i a l s , which

w i l l n e c e s s i t a t e f r e q u e n t backwashing, good f i l t r a t i o n of t h e molasses p r i o r

t o e n t e r i n g t h e chromatographic s e p a r a t i o n u n i t i s a l s o e s s e n t i a l .

The p r e t r e a t e d molasses , d i l u t e d t o 40-70 Br ix , i s s e n t a t h igh

tempera ture t o s e p a r a t i o n . The water used f o r t h e chromatographic s e p a r a t i o n

must be e i t h e r s o f t e n e d o r condensed w a t e r .

I n o rde r t o avoid degass ing of f l u i d s w i th in t h e s e p a r a t i o n column,

which could c r e a t e c h a n n e l l i n g and d i s t u r b t h e chromatographic p roces s , i t i s

necesa ry t o d e g a s i f y f l u i d s p r i o r t o t h e i r e n t r y i n t he column.

The s e p a r a t i o n p r i n c i p l e i s p r i m a r i l y t h e a p p l i c a t i