mechanisms, ionic bond and hydrophobic inter-action, act during sugar liquor decolourization. Different techniques have been used to study sugar colourants. One of these .... formed between the negative polar part of the colourant and the resin fixed .... The results obtained in the previous tests can be useful to understand ...
SIT
Paper
632
Organic and Inorganic compounds influence on the sugar c o l o u r a n t ion-exchange resin inter-action. -
Luis San Miguel Bento R A R - R e f i n a r i a s de Agdcar R e u n i d a s , S A P o r t o - Portugal
i. Introduction Sugar colourants consist in a wide group of organic compounds that can have origin in sugar cane or during extraction and refining processes. T h e use of m a c r o r e t i c u l a r strong base ion-exchange resins with ammonium q u a t e r n a r y ionic group, usually bound to chloride ion, for decolourization, is a general practice in modern sugar refining. Decolourizing process m e c h a n i s m s have been studied by different authors (i, 2, 3, 4, 5). It is accepted that two types of mechanisms, ionic bond a n d h y d r o p h o b i c inter-action, act during sugar liquor decolourization. Different techniques have been used to study sugar colourants. One of these techniques consists of fixing colourants to different adsorbents, causing afterwards their removal by selective elution (Chou and Rizutto used XAD2 resin, Bugaenko used AV-16 GS anionic resin, Tsuchida and Komoto, Parker et al. used DEAE cellulose, Parker et al. used IR 200 cationic resin)
(6). In the study here presented, interfering compounds were mixed with sugar solutions before contact with resins. The competitivity of these interfering compounds and sugar colourants for the resin adsorption sites was evaluated. It was observed that colourants removal capacity varied with nature and quantity of the interfering compounds in sugar liquor, with pH and resin types. IRA
900C
a
styrenic
strong
base
201
anionic
resin,
IRA 458 an
a c r y l i c s t r o n g b a s e a n i o n i c r e s i n and XAD2 an s t y r e n i c a d s o r b e n t resin were used in this study. C a r b o n a t e d l i q u o r from P o r t o R e f i n e r y was u s e d as s u g a r c o l o u r a n t s source. D u r i n g the study b e e t raw s u g a r was m i x e d w i t h cane s u g a r in the mingler. Interfering i n o r g a n i c c o m p o u n d s u s e d w e r e s o d i u m iodide, s o d i u m n i t r a t e and s o d i u m c h l o r i d e . As organic compounds, acetone, ethyl a l c o h o l and m e t h y l a l c o h o l w e r e used. The s o r p t i o n c a p a c i t y of r e s i n s for o r g a n i c acids in p r e s e n c e of i n o r g a n i c c o m p o u n d s was t e s t e d u s i n g s o r b i c acid. This acid was f i x e d t o a s t y r e n i c r e s i n in p r e s e n c e of s o d i u m c h l o r i d e and its r e m o v a l was p e r f o r m e d at d i f f e r e n t pH c o n d i t i o n s . Tests results can elucidate regeneration mechanisms.
2. E x p e r i m e n t a l
decolourization
and
salt
Procedures
a) D e c o l o u r i z a t i o n
of
sugar solutions containing inorganic and
organic compounds. In a i00 ml closed flask 25 ml of s u g a r s o l u t i o n (15 ml of c a r b o n a t e d l i q u o r and i 0 ml of ....d i s t i l l e d water) containing d i f f e r e n t q u a n t i t i e s of i n o r g a n i c salt, w e r e m i x e d w i t h 2.5 g of d r i e d i o n - e x c h a n g e resin, and m a i n t a i n e d at 40~C d u r i n g 4 hours. W h e n o r g a n i c c o m p o u n d s w e r e used, 15 ml of c a r b o n a t e d l i q u o r was m i x e d w i t h the c o m p o u n d and water, till a total v o l u m e of 25 ml. In a separate flask the same m i x t u r e of s u g a r s o l u t i o n and i n t e r f e r i n g c o m p o u n d , w i t h o u t resin, was m a i n t a i n e d in the same conditions and u s e d as the r e f e r e n c e solution. The s o l u t i o n pH was m a i n t a i n e d by a d d i n g HCI or N a O H d u r i n g the tests. The same quantity of t h e s e c h e m i c a l s was a d d e d to the r e f e r e n c e s o l u t i o n to avoid dilution errors. The s o l u t i o n s w e r e s e p a r a t e d from r e s i n by v a c u u m f i l t r a t i o n t h r o u g h a 0.8 microns filter. A filtrate volume of i0 ml of e a c h s o l u t i o n was c o r r e c t e d to pH 9.0 and the volume adjusted to 12 ml w i t h d i s t i l l e d water. A t t e n u a t i o n s ( A b s o r b a n c e / C e l l l e n g t h in cm * i000) w e r e m e a s u r e d at 420 nm in a 1 cm cell in a S p e c t r o p h o t o m e t e r P e r k i n - E l m e r LC 55B and GBC U V / V I S 9 1 6 . D e c o l o u r i s a t i o n was c a l c u l a t e d from the A t t e n u a n c e s r e a d i n g s , in r e l a t i o n to the r e f e r e n c e solution. Preliminary tests s h o w e d that 4 h o u r s w e r e e n o u g h to g u a r a n t e e t h a t e q u i l i b r i u m c o n d i t i o n s w e r e reached. A l s o the quantity of r e s i n u s e d was tested. H i g h e r q u a n t i t i e s imply h i g h e r c h e m i c a l s concentration and precipitation can occur interfering with results.
202
b) T e s t s
with
sorbic
acid
in resin
column
In a 250 ml closed flask, 40 g of d r i e d s t r o n g base a n i o n i c resin, I R A 9 0 0 C in the c h l o r i d e form, was c o n t a c t e d w i t h 200 ml of NaCl 4M containing 0.002M Sorbic Acid. This m i x t u r e was c o n t a c t e d at 40~C w i t h m a g n e t i c stirrer, d u r i n g 4 hours. Resin was separated by vacuum f i l t r a t i o n t h r o u g h 0.8 nm f i l t e r and c o n t a c t e d w i t h p o r t i o n s of 200 ml of NaCl 4M solutions till A b s o r b a n c e s v a l u e s w e r e lower t h a n 0.500 at 2 6 0 n m and 1 cm cell. Salt s o l u t i o n s w e r e c o r r e c t e d to pH w i t h N a O H or HCl. A q u a n t i t y of I0 ml of resin was t h e n f i l l e d to a P h a r m a c i e Column. A solution of NaCl 4M, w i t h pH c o r r e c t e d , was t h e n p u m p e d d o w n flow t h r o u g h the c o l u m n at a f l o w rate of 1 ml per minute and directly to a continuous flow cell of a GBC UV/VIS 916 Spectrophotometer. R e a d i n g s w e r e m a d e at i n t e r v a l s of 1 s e c o n d at 260 nm. The salt s o l u t i o n f l o w e d t h r o u g h the r e s i n d u r i n g 30 minutes. A f t e r that time a w a s h i n g s o l u t i o n was fed at the same flow rate t h r o u g h the resin. A f t e r this w a s h i n g Ethyl Alcohol 30% v/v and/or a s o l u t i o n of NaCl 2M c o n t a i n i n g Ethyl A l c o h o l 30% v / v was fed to the resin.
3. R e s u l t s
a) R e m o v a l presence
and Discussion
of sugar colourants of d i f f e r e n t i n o r g a n i c
with salts
ion-exchange resin in and organic solvents.
S u g a r c o l o u r a n t s c o m p r i s e a h i g h d i v e r s i t y of o r g a n i c C o m p o u n d s . A g r e a t m a j o r i t y of t h e s e c o m p o u n d s p o s s e s s a n e g a t i v e form at alkaline medium and have an amphiphilic nature, with both h y d r o p h i l i c and h y d r o p h o b i c parts. Due to these c h a r a c t e r i s t i c s s u g a r c o l o u r a n t s can be f i x e d to s t r o n g base a n i o n i c s t y r e n i c r e s i n s by ionic bond and/or by hydrophobic inter-actions. In the first case the ionic b o n d is f o r m e d b e t w e e n the n e g a t i v e p o l a r p a r t of the c o l o u r a n t and the resin f i x e d ion. In the s e c o n d case the h y d r o p h o b i c p a r t of the c o l o u r a n t is f o r c e d a g a i n s t the resin matrix by hydrophobic inter-action. Weak Van-der-Waal forces will then b o n d the c o l o u r a n t to the r e s i n matrix. In this s t u d y we u s e d s t r o n g base a n i o n i c r e s i n s of two types. IRA900C with a polystirene / divinil-benzenic structure as matrix, and I R A 4 5 8 w i t h an a c r y l i c matrix. Both of t h e s e r e s i n s
203
have q u a t e r n a r y a m m o n i u m active groups. Styrenic resin has a matrix with a high h y d r o p h o b i c i t y character. Acrylic resins possess a low h y d r o p h o b i c i t y character and, therefore, these types of resins decolourize mainly through ionic bounding mechanisms. As a d s o r b e n t resin was used a XAD2 resin. These resins possess a m a t r i x identical to IRA900C but do not have any active charged group. Decolourization with this resin is only due to a d s o r p t i o n mechanisms. All the resins were prepared according to manufacture instructions. IRA900C was washed with acetone before being converted to the c h l o r i d e form. A n i o n i c resins were c o n v e r t e d to the c h l o r i d e form using sodium c h l o r i d e solution at I00 g/l.
i_~. S t y r e n i c
Resins
When carbonated liquor was c o n t a c t e d with styrenic resin (IRA 900C) in the c h l o r i d e form, anionic c o l o u r a n t s were e x c h a n g e d by the c h l o r i d e anion of the resin. Other c o l o u r a n t s were fixed to the m a t r i x resin by h y d r o p h o b i c i n t e r - a c t i o n with the colourants h y d r o p h o b i c ~ parts . . . . . At pH 9.0 a high d e c o l o u r i z a t i o n was o b t a i n e d and only a small p e r c e n t a g e of c o l o u r a n t s were not a d s o r b e d by the resin (Fig.l). Colourants not fixed to the styrenic resin at p H 9 . 0 will c o m p r i s e neutral c o m p o u n d s with low h y d r o p h o b i c i t y or ~ positive charged c o m p o u n d s at this pH. N e g a t i v e c h a r g e d c o l o u r a n t s will be bound i o n i c a l l y to the resin and h y d r o p h o b i c neutral or low charged colourants will be fixed to the resin matrix. For a better u n d e r s t a n d i n g of sugar c o l o u r a n t s b e h a v i o u r in presence of interfering compounds, a simplified distribution of c o l o u r a n t s ionic forms is p r e s e n t e d at Tables i, 2 and 3 (for symbols m e a n i n g see A b b r e v i a t i o n s ) . When liquor pH was lowered from pH 9 t o pH 2, part of the anionic c o m p o u n d s became neutral or p o s i t i v e and d e c o l o u r i z a t i o n decreased. A decolourization decrease from 93% to 65% was observed. Colourants that maintain a negative charge c o l o u r a n t s h i g h l y hydrophobic, neutral or with will be m a i n t a i n e d fixed to the resin (Table I).
at this pH and a low charge,
When an inorganic i n t e r f e r i n g c o m p o u n d was mixed to the sugar s o l u t i o n its anion c o m p e t e d with colourants, for the resin ionic
204
adsorbing sites and decolourization decreased. This was o b s e r v e d when s o d i u m iodide was mixed with carbonated liquor (Fig.1)o It was observed that as iodide c o n c e n t r a t i o n in solution i n c r e a s e d d e c o l o u r i z a t i o n d e c r e a s e d d r a s t i c a l l y . This indicates that iodide ion has a great c o m p e t i t i v i t y for resin active groups , as compared with anionic sugar colourants. After a certain quantity of iodide anions a d d e d to the r e s i n d e c o l o u r i z a t i o n do not d e c r e a s e even with an i n c r e a s e of salt in solution. Colourants that were fixed to the resin even at high iodide c o n c e n t r a t i o n will p o s s e s s a high h y d r o p h o b i c i t y c h a r a c t e r and a low ionic charge, that will m a i n t a i n the c o l o u r a n t fixed by h y d r o p h o b i c i n t e r - a c t i o n to the resin m a t r i x (Table 2). The test with NaI m i x e d w i t h c a r b o n a t e d liquor was p e r f o r m e d d i f f e r e n t pH. It was o b s e r v e d that the i n t e r f e r e n c e of NaI d e c o l o u r i z a t i o n was h i g h e r at pH 9 than at pH 2 (Fig.l).
at on
AS the pH decreases, negative polar parts of amphiphilic compounds can change to a low charge or neutral form. Therefore, these compounds, that were fixed i o n i c a l l y to the resin at pH 9.0, w h e n pH drops, will be fixed hydrophobically and will be maintained in the resin phase, even at high NaI c o n c e n t r a t i o n s (Table 2). This e x p l a i n s the lower interference of NaI at a low pH. Other i n o r g a n i c c o m p o u n d s were m i x e d with c a r b o n a t e d liquor and d e c o l o u r i z a t i o n w i t h s t y r e n i c resins was t e s t e d in the d e s c r i b e d conditions. The effect of increasing quantities of s o d i u m nitrate and sodium chloride on sugar decolourization with styrenic resins are shown at Figure 2 and 3. These c o m p o u n d s show a lower i n t e r f e r e n c e in the d e c o l o u r i z a t i o n of carbonated liquor w i t h resins, s p e c i a l l y s o d i u m chloride. The i n f l u e n c e of s o d i u m c h l o r i d e on d e c o l o u r i z a t i o n is i m p o r t a n t as this salt is used to r e g e n e r a t e the r e s i n s . As it is o b s e r v e d the interference increases with pH w h i c h e x p l a i n s the b e t t e r r e g e n e r a t i o n r e s u l t s w h e n a l k a l i n e salt is used. The d e c o l o u r i z a t i o n o b t a i n e d w i t h s t y r e n i c resins in p r e s e n c e of s o d i u m iodide, s o d i u m n i t r a t e and s o d i u m c h l o r i d e at pH 9°0 is presented at Fig.4. H i g h e r i n t e r f e r e n c e was o b s e r v e d with NaI f o l l o w e d by NaNO3 and NaCI. This is in agreement with the relation between relative c o l o u r d e s o r p t i o n s t r e n g t h s and the ions h y d r a t i o n (2). H y d r a t i o n n u m b e r s of these ions are 0, 1 and 3 for I-, NO3- and Cl-, r e s p e c t i v e l y (I0). It w o u l d be i m p o r t a n t to u n d e r s t a n d the r e a s o n s why c h l o r i d e ion has a lower i n t e r f e r e n c e on the decolourization with styrenic
205
resins,
when c o m p a r e d with nitrate
and iodide
ion.
The influence of organic compounds in the d e c o l o u r i z a t i o n of c a r b o n a t e d liquor w i t h styrenic resins was also studied. In this case organic solvents interfere with hydrophobic fixed c o l o u r a n t s and do not interfere with ionically bound colourants. When acetone was m i x e d with c a r b o n a t e d liquor d e c o l o u r i z a t i o n d e c r e a s e s (Fig.5). At pH 9, the decolourization decreases slowly with i n c r e a s i n g amounts of acetone in solution. Acetone will remove c o l o u r a n t s fixed h y d r o p h o b i c a l l y to the resin and do not interfere w i t h the ionic bound c o l o u r a n t s (Table 3). When the pH of solutions is lowered to pH 2, d e c o l o u r i z a t i o n d e c r e a s e s as the acetone c o n c e n t r a t i o n in solution increases. In this case c o l o u r a n t s that switch from ionic to h y d r o p h o b i c fixation m e c h a n i s m to the resin would be r e m o v e d in presence of acetone (Table 3). At high a c e t o n e c o n c e n t r a t i o n s the only c o l o u r a n t s fixed to the resin w i l l be the c o l o u r a n t s that maintain a negative charge even at low pH (Table 3). This point was not a t t a i n e d in p r a c t i c e as h i g h e r acetone c o n c e n t r a t i o n s cause t u r b i d i t y in the liquor solution. Other o r g a n i c c o m p o u n d s were used mixed with c a r b o n a t e d liquor. Ethyl alcohol and methyl alcohol show a lower interference in the c o l o u r a n t s a d s o r p t i o n by s t y r e n i c resins (Fig. 5).
ii. A c r y l i c
resins.
Acrylic resins were tested c a r b o n a t e d liquors in p r e s e n c e 458 was used as ,an acrylic with this resin were c o n d u c t e d o b s e r v e d at low pH.
to study the d e c o l o u r i z a t i o n of of interfering compounds. IRA strong base anionic resin. Tests only at pH 9.0 due to instability
It was observed that acrylic resins have a lower c a p a c i t y to decolourize carbonated liquor when compared with styrenic resins. It was observed a decolourization of 78.5% when c a r b o n a t e d liquor was mixed w i t h this resin, at pH 9, compared with 92.9% w i t h s t y r e n i c resins (Fig.6). As these resins have a m a t r i x with low h y d r o p h o b i c i t y , they do not remove amphiphilic neutral or low charged colourants as styrenic resins do by h y d r o p h o b i c i n t e r - a c t i o n mechanisms, w h i c h explains the decrease of d e c o l o u r i z a t i o n observed. With these resins, at high NaI c o n c e n t r a t i o n in the liquor, there will be no c o l o u r a n t s fixed ionically to the resin and
206
decolourization would be minimal. In fact this was o b s e r v e d when NaI c o n c e n t r a t i o n increases in solution decolourization decreased practically to zero at 1.4 M NaI (Fig.7). D e c o l o u r i z a t i o n d i f f e r e n c e when a c r y l i c resins are c o m p a r e d w i t h styrenic resins is p r a c t i c a l l y c o n s t a n t as the NaI c o n c e n t r a t i o n increases. When sodium n i t r a t e and s o d i u m c h l o r i d e were used as i n t e r f e r i n g compounds, decolourization also decreased to zero, as it happened with sodium iodide (Fig.6). These r e s u l t s show that c h l o r i d e and n i t r a t e ion are as effective as iodide ion to interfere w i t h ionic b o n d i n g colourants. T h e r e f o r e the lower i n t e r f e r e n c e of NaCl on d e c o l o u r i z a t i o n with styrenic resins m u s t be due to c o l o u r a n t s fixed hydrophobically to the resin matrix at high salt concentration. Decolourizations difference between IRA900C and IRA458 in presence of NaCl is shown at Fig.8. This d i f f e r e n c e i n c r e a s e s with the salt c o n c e n t r a t i o n in the liquor, up to a maximum, and a f t e r w a r d s is m a i n t a i n e d c o n s t a n t . The influence of organic compounds on decolourization with acrylic r e s i n s was also s t u d i e d . R e s u l t s of tests w i t h acetone, ethyl alcohol and methyl alcohol are presented at F i g . 9 . P r a c t i c a l l y there is no i n t e r f e r e n c e of these compounds with d e c o l o u r i z a t i o n of a c r y l i c resins.
iii. A d s o r b e n t
resins
Adsorbent resins have a hydrophobic styrenic/divinil benzene m a t r i x and have no ionic active groups. These resins remove sugar colourants from solutions by h y d r o p h o b i c i n t e r - a c t i o n s b e t w e e n a p o l a r parts o f c o l o u r a n t s and s t y r e n i c / d i v i n i l - b e n z e n i c m a t r i x of XAD2 resin. Decolourization of carbonated liquor w i t h XAD2 in p r e s e n c e of NaI and NaCl at pH 2 and 9 was studied (Fig.10). As the colourants are mostly in their neutral form at pH 2, d e c o l o u r i z a t i o n w i t h XAD2 resin is h i g h e r at this pH than at pH 9. S o d i u m iodide p r a c t i c a l l y does not i n t e r f e r e w i t h a d s o r p t i o n of c o l o u r a n t s w i t h this kind of resins. On the contrary the adsorption of c o l o u r a n t s i n c r e a s e s w i t h the i n c r e a s e of NaCl in solution. As NaCl concentration increases a d s o r p t i o n w i t h XAD2 d e c r e a s e s at low increase constantly with the salt
207
in solution colourants salt concentrations but content at higher salt
c o n c e n t r a t i o n s . This b e h a v i o u r is identical to the v a r i a t i o n of osmotic coefficient of salt s o l u t i o n s with NaCl c o n c e n t r a t i o n s (7). This can e x p l a i n the low s o l u b i l i t y of h y d r o p h o b i c anionic colourants in presence of adsorbent resins as the salt c o n c e n t r a t i o n i n c r e a s e s in solution. This s a l t i n g - o u t effect, r e f e r r e d to in the l i t e r a t u r e (2, 8, 9), can e x p l a i n the lower i n t e r f e r e n c e o b s e r v e d w h e n NaCl is m i x e d with liquor decolourized by s t y r e n i c resin w h e n c o m p a r e d with acrylic resin decolourization.
b. R e g e n e r a t i o n
of s t y r e n i c resins.
The results obtained in the p r e v i o u s tests can be useful to u n d e r s t a n d the m e c h a n i s m s involved during ion exchange resin regeneration. A compound that competes strongly with sugar c o l o u r a n t s f o r d e c o l o u r i z a t i o n r e s i n sites will be a good resin regenerant. Therefore, the b e h a v i o u r of s o d i u m c h l o r i d e is very i m p o r t a n t as this salt is u s e d for resin r e g e n e r a t i o n . We can consider that s t y r e n i c resins b e h a v e as a m i x t u r e of a resin with only ionic influence on colourants, as a c r y l i c resins, and a resin with only hydrophobic adsorption of c o l o u r a n t s , as XAD2 adsorbent resin (Fig. ii). During resin regeneration salt s o l u t i o n d i s l o c a t e s the w a t e r m i x e d with r e s i n and the s a l t c o n c e n t r a t i o n in t h e solution in contact with resin increases. At low salt c o n c e n t r a t i o n s low c h a r g e d c o l o u r a n t s are r e l e a s e d (II). At high salt concentrations ionic bound c o l o u r a n t s will be removed. On the contrary, colourants that possess a high hydrophobicity will r e m a i n fixed to the resin m a t r i x due to the s a l t i n g - o u t effect. At this high salt c o n c e n t r a t i o n an increase of solution pH would be benefit as the the hydrophobic a d s o r p t i o n d e c r e a s e s as c o l o u r a n t s change to a n e g a t i v e form. A possibility to r e m o v e c o l o u r a n t s fixed h y d r o p h o b i c a l y to the resin m a t r i x at this salt c o n c e n t r a t i o n w o u l d be by mixing a solvent with the salt. Ethyl alcohol was m i x e d with NaCl and i n f l u e n c e of this m i x t u r e on liquor d e c o l o u r i z a t i o n was studied (Fig.12). It was o b s e r v e d that d e c o l o u r i z a t i o n d e c r e a s e d almost to the level of NaI i n t e r f e r e n c e when 2.5 M ethyl alcohol was mixed with NaCl 2M. This m i x t u r e was t e s t e d after a normal
208
regeneration. The test was p e r f o r m e d in a 1 liter r e s i n column after a liquor cycle of 50 BV of c a r b o n a t e d liquor. A f t e r a normal r e g e n e r a t i o n w i t h 3 BV of NaCl at i00 g/1, 1 BV of a mixture of NaCl at 100g/l w i t h ethyl a l c o h o l at 20% v/v was p a s s e d t h r o u g h the r e s i n bed. R e s u l t s are p r e s e n t e d at Fig. 13. As expected a g r e a t a m o u n t of c o l o u r a n t s was r e l e a s e d from the resin when the m i x t u r e of salt and ethyl a l c o h o l was used. A test with ethyl alcohol without NaCl mixed with, was m a d e w i t h o u t any extra r e m o v a l of sugar c o l o u r a n t s (Fig. 13). After regeneration salt is r e m o v e d from the r e s i n c o l u m n s w i t h water. D u r i n g this w a s h i n g the c o n c e n t r a t i o n of s o d i u m c h l o r i d e d e c r e a s e s and c o l o u r a n t s fixed h y d r o p h o b i c a l l y will be p a r t i a l l y removed, as the h y d r o p h o b i c i n t e r - a c t i o n is lower at low salt concentrations. As at t h e s e low c o n c e n t r a t i o n s the i n f l u e n c e of c h l o r i d e ion in ionic b o n d is lower, a n i o n i c c o l o u r a n t s can be re-fixed to the r e s i n by ionic bond. This switch e f f e c t d e c r e a s e s the r e g e n e r a t i o n e f f i c i e n c y (less c o l o u r a n t s are r e l e a s e d d u r i n g r e g e n e r a t i o n ) and decreases the resin capacity (active groups remain occupied with colourants even a f t e r salt r e g e n e r a t i o n ) . This can e x p l a i n the d e c r e a s e of decolourization capacity o b s e r v e d w i t h s t y r e n i c r e s i n s after a few w o r k i n g cycles. To m i n i m i s e this e f f e c t it w o u l d be b e n e f i c to lower the pH w h e n salt c o n c e n t r a t i o n d e c r e a s e s during wash. At low pH these colourants remain n e u t r a l or w i t h a low c h a r g e and will not be r e - f i x e d to the s t y r e n i c resin. This acid wash, after resin regeneration, was tested in a 1 liter r e s i n c o l u m n a f t e r a c a r b o n a t e d l i q u o r c y c l e of 50BY. R e s i n was r e g e n e r a t e d with 3 BV of NaCl at i00 g/l f o l l o w e d by an a c i d r e g e n e r a t i o n at low salt c o n c e n t r a t i o n w i t h 1 BV of NaCl at 30 g/l m i x e d with 0.5% of HCl. R e s u l t s are p r e s e n t e d at Fig. 14. An e x t r a c o l o u r a n t s removal was observed. When in refinery conditions, a neutralization would be necessary to avoid sugar inversions d u r i n g l i q u o r cycle. This effect was observed IRA900C styrenic resin being conditions.
c. S o r p t i o n styrenic
By the liquors,
and desorption resins.
previous it was
in tests with sorbic acid fixed a f t e r w a r d s r e m o v e d at d i f f e r e n t
of
sorbic
tests results, concluded that
209
acid with
performed amphiphilic
to pH
ion e x c h a n g e
with carbonated anionic sugar
colourants have a great s u g a r l i q u o r s and on r e s i n s An
organic
influence on the d e c o l o u r i z a t i o n regeneration.
of
acid
with amphiphilic character, sorbic acid, was choosen to s u b s t i t u t e the sugar colourants in the same t e s t s p r e v i o u s l y d e s c r i b e d . This acid possesses a hydrophobic part and a polar carboxylic group, negative at high pH. To analyse the s o r b i c a c i d A O A C t e s t 11.070 (12) was u s e d at A b s o r b a n c e s r e a d i n g s w i t h a GBC UV\VIS 916 S p e c t r o p h o t o m e t e r at 260 nm in a 1 cm cell.
CH3-CH=CH-CH=CH-COOH,
The influence of NaCl on the a c i d r e m o v a l w i t h s t y r e n i c r e s i n I R A 9 0 0 C and adsorbent resin XAD2 was studied in the same conditions as d e s c r i b e d for s u g a r c o l o u r a n t s . A 250mi s o l u t i o n of s o r b i c a c i d was u s e d at 0.002 M in c o n t a c t w i t h 7 g of resin. Tests results are presented at Fig.15 a n d 16. The removal v a l u e s w e r e c a l c u l a t e d by the p e r c e n t a g e of the difference of sorbic acid c o n c e n t r a t i o n in the r e f e r e n c e and in the s o l u t i o n in c o n t a c t w i t h the resin. These results are similar as the one o b s e r v e d as w i t h sugar colourants. The salting out effect when salt concentration increases was also observed. It was o b s e r v e d a h i g h e r i n f l u e n c e of salt c o n c e n t r a t i o n on i n c r e a s e of s o r b i c acid removal from s t y r e n i c resins, at pH 2, w h e n c o m p a r e d w i t h a d s o r b e n t resins. As sorbic a c i d b e h a v e s in a s i m i l a r w a y as a n i o n i c a m p h i p h i l i c sugar colourants when contacted with styrenic and adsorbent resins, we have used this compound to s t u d y the m e c h a n i s m s involved during salt regeneration, specially during salt wash f r o m the resin. This study was performed by f i x i n g s o r b i c a c i d to I R A 9 0 0 C in p r e s e n c e of NaCl 4M at pH 2 and Ii. At this high salt concentration sorbic acid will be fixed only to the r e s i n matrix. R e s i n was c h a r g e d to a i0 ml column and afterwards washed at the s a m e pH c o n d i t i o n s as the r e s i n p r e p a r a t i o n . A f u r t h e r w a s h w i t h ethyl alcohol, or/and a mixture of ethyl alcohol and s a l t w a s u s e d to r e m o v e the r e m i n i s c e n t s o r b i c acid f i x e d to the resin. It was o b s e r v e d t h a t at a c i d i c c o n d i t i o n s , w i t h s o r b i c acid in a n o n - i o n i s e d form, a g r e a t r e m o v a l of this acid occurred when salt concentration decreased due to the a c i d i c w a t e r wash. A further sorbic acid removal was o b s e r v e d w i t h the m i x t u r e of salt and e t h y l a l c o h o l (Fig.17). Ethyl alcohol alone do not r e m o v e any s o r b i c a c i d f r o m the resin. At a l k a l i n e
conditions,
with
the a c i d
210
ionised
negatively,
it was
observed that there was no sorbic acid removal from IRA900C resin during alkaline water wash. Sorbic acid was removed only with a mixture of salt and ethyl alcohol (Fig.18). These results indicate that at low pH, sorbic acid is removed from resin during washing. This fact was not observed when alkaline wash was used.
4. C o n c l u s i o n
The study of the influence of inorganic and o r g a n i c compounds in the sugar liquor d e c o l o u r i z a t i o n with ion exchange resins can elucidate the mechanisms involved during d e c o l o u r i z a t i o n of different c o l o u r a n t s type. This study showed the influence of both mechanisms, ionic bond and hydrophobic inter-action, on sugar decolourization. Amphiphilic anionic colourants can switch from ionic bond to h y d r o p h o b i c i n t e r - a c t i o n fixation mechanism, d e p e n d i n g on their ionic form and consequently are differently influenced by inorganic and organic interfering compounds. It was also observed that sodium chloride and sodium n i t r a t e have a lower interference when compared with sodium iodide, on decolourization with s t y r e n i c resins. Differently, with acrylic resins, all the three inorganic salts have the same influence on sugar liquor d e c o l o u r i z a t i o n . As this type of resin d e c o l o u r i z e sugar liquors m a i n l y t h r o u g h i o n - e x c h a n g e mechanisms, one can conclude that the low i n t e r f e r e n c e o b s e r v e d with styrenic resins refer to the colourants fixed by hydrophobic inter-action mechanism. Observing the behaviour of adsorbent resin in presence of inorganic interfering compounds, a salting-out effect observed with anionic compounds when sodium c h l o r i d e c o n c e n t r a t i o n increases in solution. This effect can explain the lower interference sodium chloride on decolourization when styrenic resins are used. To d e c r e a s e this salting-out effect, that is detrimental during resin regeneration with sodium chloride, ethyl alcohol can be mixed with the salt, during regeneration. Also it was o b s e r v e d that a b e t t e r removal of colourants is a t t a i n e d if an acid wash is p e r f o r m e d in the final of the resin regeneration.
211
AcknowledgementThis work is part of the Project "Regenera9~o de Resinas com T r a t a m e n t o de Efluentes" financed by the SINPEDIP Program. A u t h o r wishes to thank to his assistants D.Maria Emilia Pereira and E n g . C r i s t i n a Costa Correia for their colaboration and L a u r a Correia for the analysis work. He also wishes to thank to Rohm + Haas Portugal in supplying resins samples.
REFERENCES I
•
•
•
•
O
•
•
•
•
Vender M., (1977), The role of c o m p o s i t i o n of liquor ash and of ionic form of the resin in d e c o l o u r i z a t i o n of refinery syrups. Proc. T.S.C.R.R. Satoshii Fujii, Ichiri Shibutani, Masahik Komoto, (1980), Studies of c o l o u r i n g matter produced by c o n t a c t between quaternary a m m o n i u m ion-exchange resin and glucose. Part I. its sorption and d e s o r p t i o n from the resin. ISJ, 199-203. Williams John C., (1984), The performance of ion exchange resins in d e c o l o u r i s i n g c a r b o n a t e d liquor. An analysis of p e r f o r m a n c e data. Proc. S . P . R . I . Williams John C. , Bhardwaj C.L., (1988) , The use of H P L C colour analysis to investigate the mechanism of resin decolorization. Proc. S.P.R.I. Abram J.C. , Cookson D. , Parker K.J., (1971), The m e c h a n i s m of colour removal by ion-exchange resins. Adsorption from solution in model systems. La Sucrerie Belge, 90, 1971, 525 Chou C.C. colurants,
, R i z u t t o A.E., (1972), The acid nature of sugar Proc. T.S.C.S.R.R., 8-21
Robinson Solutions,
R.A. and Stokes R H., (1959 ), Ed. A c a d e m i c Press Inc, New York.
Amber!ite Department.
XAD-2. Technical Bulletin. Ion Rohm and Haas Company, Philadelphia.
Electrolyte
Exchange
Fritz J.S. , Tateda, (1968), Studies on the Anion Exchange Behaviour of Carboxylic Acids and Phenols. Analytical Chemistry, Voi.40, Dec.1968, 2115-2119.
i0. Padova J., ( i~6~4 ), Solva~ion approach to ion solvent interaction. T h e Journal of Chemical Physics, Vol. 40, 1, Feb.1964.
212
ii.
Bento resins
12.
AOAC
L.S.M., (1989), with regenerant
Methods
Sugar decolourization by ion-exchange r e c o v e r y , Proc. S . I . T . , 1 7 6 - 2 0 0
(1980)
Abbreviations
A
:
Amphoteric at h i g h pH
BV
•
Bed
HFB
•
Hydrophobic
HP
•
Amphiphilic colourant and polar parts.
- m
-
HP
colourants
negative
HP m +
-
HP
colourants
neutral
at
pH
9 and
positive
HP i m
"
HP
colourants
neutral
at
pH
9 and
2.
N
•
Negative
P
•
Colourants colourants
Res.
•
Resin
Sol.
"
Solution
HP
colourants and neutral
and Polar colourants at l o w pH.
negative
Volumes. inter-action
colourants
ionic
at
at
positively at p H 9 .
phase. phase.
213
mechanism
pH
pH
forms
9 and
9 and
with
neutral
hydrophobic
at
pH
2
at p H
2
2.
charged
or
polar
neutral
Figure 1. Interference of Nal on Carbonated Liquor Decoiourization w i t h I R A 9 0 0 C
Figure 2. Interference of NaNO3 on Carbonated Liquor Decolourization with IRA900C
9oi!
% Decolourization
% Decolourization 100~
1001
90.
I
8O
!
7O ! I
8O
!
50-
I
I
40 i-
I
30-
t t
2 0 I-
i
10 0 0
'°f
loiI
01
j
0
0.2
~
0.4
~
I
i
i
O.O
0.8
1
1.2
1.4
1.6
I
I
i
I
0,2
0.4
0.8
0.8
Nal Moles/liter -"-
pH2
-+-
pH3
pH 1'
~
pH 9
,
I
I
I
1.2
I
1.4
1.8
NaNO3 Moles/liter
~
-"--
pH5
pH 2
--t-- pH 3
-e-- pHil'
~
--w- pH 5
pH9
RARlY
RARIO
Figure 4. Interference on Carbonated Liquor Decolourization w i t h I R A g 0 0 c at pH 9
•Figure 3. Interference of NaCI on Carbonated Liquor Decolourization with IRA900C
% Decolourization
% Decolourization
100
100 r 1
90
70
60 50-
"
~
"
60
:
40-
.
i
302 0 ~100 0
l
I,
!
I
f
[
0.2
0.4
o~s
0.8
1
~2
,
I
~4
1.0
NaCI Moles/liter
0 |
~
0
0.2
,
l
0.4
0.8
i
~
L
z
0.8
1
1.2
1.4
MOles/liter pH 2 - e - - pH 7
~
p14 3
-~-
pile
--w- pH 6 r ~
Nil
~ .
RAWl8
RARZT
214
NsNO3 .
.
.
~ .
NICI
1.6
Figure 6. Interference of Inorganic Compounds on Decolourization w i t h IRA458 pH 9.0
Figure 5. Interference of organic compounds on Decoiourization with IRA900C
% Decolourization 1°° l
% Decoiourization 10OL_ 90~-
:"
....
~
~o~
~
70 60
~
o
o
eoi-
\\
'
,!o ,?, 1°i 0
0
~
I
!
0.5
1
1.5
,.
,~,
I
I
2
2.5
3
3.5 o
Moles/liter
o.5
1
1.5
Moles/liter -"-
E t O H pH 9
-4--
E t O H pH 2
+
A c c t . pH 9
A c c t . pH 2
--v,- M t O H pH 9
~
M t O H pH 2
Nsl
NsCI I I
- - ~ NAN03
RAR94
RARI01
Figure 7. Difference on Decoiourization with IRA900C and IRA458 in presence of Nal
Figure 8. Difference on Decolourization with IRA900C and IRA458 in presence of NaCI
% Decolourization I00~
% Decolourization 100, -
I
1
8 0 ~
I
i i
I i Ii
i
40
I
!
i
20
0
1 0
0.2
--'--IRA
0.4
0.6 0.8 1 Nal M o l e s / l i t e r
900 C
+
IRA 4 6 8
1.2
-~
1.4
1.6
0
Difference
0.2
I ~
RARIOII
RAR106
215
0.4
0.6 0.8 1 1.2 NaCI M o l e s / l l t e r
IRA 9 0 0 C
--4-- IRA 4 6 8
" ~
1.4
Difference
1.6
i
F i g u r e 9. Decolourization with IRA458 in p r e s e n c e o f O r g a n i c C o m p o u n d s
F i g u r e 10. D e c o l o u r i z a t i o n w i t h X A D 2 resin in p r e s e n c e o f i n o r g a n i c c o m p o u n d s
% Decolourization 1oof
% Decolourization lOO /
9ot-
I
80 P 7O ~-
o
8 0 I-
I
|
6 0 ~-
1
t
f
,o
50~
I
,o!t
60
! 3O ~1!
i t
x
201-
'° I
J
40 01 0
I 0.5
L 1
I 1.5
I 2
J 2.5
0
j 3
' 0.5
J 1
3.5
I 1.5
l 2
I 2.5
: 3
i 3.5
Moles/liter
Moles/liter I
,
- ' - - Acetone
- + - EtOH
,
~
j
MtOH
RARIO0
NaCI pH 9
- + - - N s C I pH 2
Nal pH 9
~
'
J
Nal pH 2
I
RARI16
F i g u r e 11. I n f l u e n c e o f DH o n I o n i c B o n d a n d Hydrophobic Action during Regeneration
F i g u r e 12. I n t e r f e r e n c e o f a m i x t u r e o f NaCI and E t O H on D e c o l o u r i z a t i o n w i t h I R A 9 0 0 C
%
% Decolourization
lOO~
~o~ \
80
70 6O
IONIC
HFB,
" O
~~
121 "
Q
10
0 •
PH 'i" RAR134
~
i
NaC,
,,,..
o.5.
~
~.S
2
2.5
3
-&5
4
4.s"
Moles/liter . . . --I--. .NaNO3 . . . . ~. . NaCI . . . ~. . NaCI.EtOH l. . . Nai
PH -t RARSe
216
5
Figure 13. Regeneration w i t h 3 BV NaCI and 1 BV (I) NaCI,EtOH / (11) EtOH NaCI g/I
Attenuances
1120
20J
L
•
.
~
~
~
~
~
~
i'0
.,~. ~ . ~
100
''i \\
0
"
40
-t
t
0
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
BV (I) NaCI / NaCI+EtOH
NaCI (I)
(11) NaCi / EtOH
NaCI
(11)
Figure 14. Regeneration w i t h 3 BV NaCI and 1 BV NaCi + HCI pH
Attenuances .
.
.
.
.
120
.
+
6 5
t
+
100
80
4
-
60
3 40
2
20
1 O, 0
0 0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
5.5
BV .
.
.
.
.
.
.
.
.
I --+..
.
.
Atten.420nrn .
.
.
.
.
-+-NaCI
g/I
....... pH I I
.
217
6
Figure 16. Sorbic Acid Sorption with XAD 2 in presence of Sodium Chloride
Figure 15. Sorbic Acid Sorption with IRA900C in presence of Sodium Chloride % Removal
100
lOO~
% of Removal X
X
X
X
X
•
90 80 70 rn
60 50
50F
I
40~
4o~ o
f
30
!
I
1
I
1
I
I
:
0.5
1
1.5
2
2.5
3
3.5
4
4.5
1
:
I
I
I
0.8
1
1.5
2
2.5
Moles/liter
Moles/liter pH 2
~
--~'- pH 2
pH 11 RARS22
RAR?I
F i g u r e 17. Desorption of S o r b i c A c i d from IRA900C w i t h NaCl pH2/Water pH2/EtOH/EtOH+NaCl
'="~"~=" o.soo I
I---,
N,c,
I
0.400
1
I---*
Water at pH 2
.J
i 0.2O0
''''' '*0" Jl
"t
0.000 ,
NaCI * EtOH
II
S.O00 ~,
Z
10.00 ,;0"3
TIIm
218
15.00 1
#
I
-'e- PH 11 I
Figure 18. D e s o r p t i o n of So r b i c Acid from IRAgOOC with NaCI pill1 / Water pill1 / NaCI+EtOH
AomorOlnce
NaCl
I---)
Water
at DH 11
°
0 . 8 0 0 "~
] ]
I---~
NaCI * EtOH
_1
0.600
-
1 0.,400
..I
I" . . . . . . .
: :0"] I'
L
.
.
.
.
.
' %5. O 0
10. O0
5.000
I
Ttl~ I
,
I
I
Table 1
IRA900C
Carbonated Liquor
Sol. pH 9 Res.
HP
- •
Sol.
HPm÷
HP
mm mm.
HP.+
pH 2 Res.
HP
219
- •
HP'=
Table 2
Carbonated Liquor + Nal
IRA900C
Sol. pH 9
P
A
N
HP
- •
J Res.
HPI+
Sol.
HP-,,
HPI+
pH 2 Res.
HP
- •
HP
,, ,,
Table 3
IRA900C
Carbonated Liquor + Acetone
Sol.
HP=÷
HP==
HP=÷
HPm=
pH 9 Res.
HP
- 1
Sol.
HP
- •
pH 2 Res.
220
