UV Destruction of Phenolic Compounds under Alkaline Conditions

Chapter 6

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U V D e s t r u c t i o n of P h e n o l i c C o m p o u n d s under Alkaline Conditions Harry M. Castrantas and Robert D. Gibilisco FMC Corporation, Peroxygen Chemical Division, P.O. Box 8, Princeton, NJ 08543

This study provides data showing the range of conditions under which phenols and substituted phenols can be oxidatively destroyed using UV-H O . UV-H O was found to be considerably more e f f e c t i v e i n destroying phenol and substituted phenols than UV. Significant reaction rates were seen at lamp outputs of 60,000 and 240,000 uW-sec/cm over a phenol concentration range of 10-1000 mg/L, a pH range 4-10 and mole ratios of H O /Phenol of 2.8/1 to 8.3/1. By being effective under alkaline as well as acid conditions, UV-H O avoids the acid limitations of Fenton's reagent (Fe + H O ) which i s a well know chemistry used for destroying phenolic compounds. 2

2

2

2

2

2

2

2

2

2

2

Uncatalyzed hydrogen peroxide i s used commercially to destroy pollutants such as inorganic sulfides, thiosul fate, hypochlorite and formaldehyde. Without activation however, hydrogen peroxide w i l l not destroy the more d i f f i c u l t to oxidize pollutants such as phenols, chlori nated hydrocarbons and alcohols. Hydrogen peroxide can be activated to form hydroxyl radicals (ΟΗ·) which can destroy these organics and others. This increased a b i l i t y to destroy organics i s related to the substantially higher oxidation potential of the hydroxyl radical (2.80V) compared to hydrogen peroxide(1.78V). One method of generating hydroxyl radicals is by adding a soluble iron salt to an acid solution of hydro gen peroxide (Fenton's reagent) (1). The process is used commercially to destroy organics such as phenols, but is 0097-6156/90/0422-0077$06.75/0 © 1990 American Chemical Society In Emerging Technologies in Hazardous Waste Management; Tedder, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1990.

78

EMERGING TECHNOLOGIES IN HAZARDOUS WASTE MANAGEMENT


limited (2-4).

to reactions

Fe

2 +

Fe

3 +

carried

out under

acid

conditions

+ H 0

—> F e

3 +

2

+ OH" + OH-

(1)

+ H 0

—> F e

2 +

2

+Η00· + H+

(2)

2

2

Hydrogen peroxide can a l s o be a c t i v a t e d by UV, O3 and UV-O3 t o generate a c t i v e s p e c i e s such as hydroxyl r a d i c a l s (5-7). Each system has i t ' s u t i l i t y depending upon the o r g a n i c s being destroyed. UV-H 0 , t h e s u b j e c t o f t h i s s t u d y , has t h e f o l l o w i n g advantages over the i r o n - H 0 - a c i d system: (1) the r e a c t i o n i s not l i m i t e d t o an a c i d pH range and (2) an i r o n c a t a l y s t i s not r e q u i r e d . The UV l i g h t a c t i v a t e s t h e hydrogen p e r o x i d e c o n v e r t i n g i t t o hydroxyl r a d i c a l s ( 8 ) . 2

2

2

2

UV H

2°2

>

Η0· + H 0 2

H00-

H

e

°

1

ί)

> Η00· + H 0

2

Η00· + H 0 2

2

(2)

2

> Η0· + H 0 + 0

2

2

+ H00-

> H 0 2

2

+ 0

2

2

(3) (4)

The l i t e r a t u r e has s e v e r a l r e f e r e n c e s on the use of UV-H 0 t o destroy otherwise d i f f i c u l t t o o x i d i z e com pounds, e.g., a l c o h o l s , organic a c i d s , c h l o r i n a t e d hydro carbons, aromatics and phenol (9,10). UV l i g h t alone w i l l a t t a c k some molecules by bond cleavage and f r e e r a d i c a l generation, but u s u a l l y a t a much slower r a t e than with UV-H 0 systems. T h i s study was undertaken t o determine the e f f e c t of v a r i a b l e s such a s : UV l i g h t i n t e n s i t y , phenol concen t r a t i o n , r a t i o of H 0 /phenol, pH and e f f e c t of s u b s t i t u t e d phenols on r e a c t i o n r a t e s . Phenols were chosen f o r the UV-H 0 study s i n c e (1) phenols are commonly found as p o l l u t a n t s i n wastewater and groundwater; (2) many waters c o n t a i n i n g p h e n o l i c s are a l k a l i n e . 2

2

2

2

2

2

2

2

Experimental Equipment and Operation. A continuous flow ultraviolet u n i t ( U l t r a v i o l e t Technology Inc., Model 40 L) i n which the lamps were suspended i n a t u b u l a r arrangement o u t s i d e and p a r a l l e l t o a t e f l o n r e a c t o r tube was used f o r t h i s study (Figure 1). The u n i t normally holds four 1.5 cm by 84 cm low pressure UV lamps (# 10002) but the u n i t was modified t o h o l d e i g h t o f these lamps. The lamps emit approximately 90% of the u l t r a v i o l e t energy a t 253.7 nm. The lamps were spaced 5.3 cm from each other and were 2.7 cm from the s u r f a c e of the t e f l o n r e a c t o r tube ( 5 cm.

In Emerging Technologies in Hazardous Waste Management; Tedder, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1990.


6. CASTRANTAS & GIBILISCO

UV Destruction ofPhenolic Compounds

79

SOLUTION FLOW UV UNIT TEFLON SLEEVE

SAMPLE PORT

FLJOW METER

Ο h-PUMP UV LAMPS 254 NM~

ο

sL

f WATER

TRANSPARENT TEFLON SLEEVE HOUSING-

\°

SOLUTION TO BE TREATED

)° ο

END VIEW OF UV UNIT F i g u r e 1.

Schematic diagram o f UV apparatus p h e n o l i c compound o x i d a t i o n .

used f o r


80

EMERGING TECHNOLOGIES IN HAZARDOUS WASTE MANAGEMENT

diameter by 91 cm long). Every other lamp was equipped with an aluminum r e f l e c t o r . Four switches permitted the use of 2, 4, 6 or 8 lamps. Each lamp drew 51.7 watts based on c u r r e n t measurements of 0.45 amperes per lamp at 115 v o l t s . These numbers t r a n s l a t e d t o a c a l c u l a t e d energy output a t the lamp's s u r f a c e of 34,592 uW-sec/cm which d i f f e r e d somewhat from the manufacturer's r a t e d output f o r a new lamp of 30,000 uW-sec/cm . Since the phenol study was conducted with new lamps, the l a t t e r output was a r b i t r a r i l y s e l e c t e d f o r r e f e r e n c i n g i n t h i s study. The a c t u a l energy r e a c h i n g the t e f l o n tube w i l l be s i g n i f i c a n t l y l e s s than 30,000 uW-sec/cm e x i s t i n g a t the s u r f a c e of each lamp. The energy reaching the t e f l o n tube was not c a l c u l a t e d due t o v a r i o u s assumptions t h a t would add t o the u n c e r t a i n t y e.g., the e f f e c t of r e f l e c t i o n s from the s t a i n l e s s s t e e l w a l l s , quartz sleeve and the aluminum r e f l e c t o r s . PVC f i t t i n g s and 0.95 cm diameter p o l y e t h y l e n e t u b i n g were attached t o the ends of the UV u n i t t o make a r e c i r c u l a t i n g l o o p . A g l a s s v a l v e f o r sampling was p o s i t i o n e d i n the p o l y e t h y l e n e l i n e where the s o l u t i o n e x i t s from the t e f l o n r e a c t o r tube but p r i o r t o r e i n j e c t i o n of the t r e a t e d s o l u t i o n i n t o an 18 l i t e r g l a s s r e s e r v o i r . A c e n t r i f u g a l pump (Eastern model D-8 type 304) was used t o c i r c u l a t e the s o l u t i o n . The flow r a t e was measured with a rotameter. S o l u t i o n flows were maint a i n e d between 0.9 L/min and 1.8 L/min. Sources and grades of the r e a c t a n t s used i n the experiments were as f o l l o w s : 2


2

2

Phenol (Fisher P u r i f i e d ) , m-Cresol (MCB P r a c t i c a l ) , 2-Chlorophenol ( A l d r i c h 99+%), 2,5-Dichlorophenol ( A l d r i c h 98%) 2,5-Dimethylphenol ( A l d r i c h 99+%), Hydrogen Peroxide (FMC Standard Grade) Experimental Plan. The two p a r t program i n v o l v e d (1) a f a c t o r i a l study on the e f f e c t of the f o l l o w i n g v a r i a b l e s on the d e s t r u c t i o n of phenol: l i g h t i n t e n s i t y , pH, mole r a t i o of H 0 / p h e n o l , and phenol c o n c e n t r a t i o n . (2) a study of the r e l a t i v e r e a c t i v i t y of s u b s t i t u t e d phenols with UV and UV-H 0 . 2

2

2

2

Phenol and S u b s t i t u t e d Phenols. The phenol compound was weighed (Mettler PE 360 balance) and d i s s o l v e d i n 80 ml of d e i o n i z e d water. T h i s concentrate was added t o an 18 l i t e r g l a s s carboy with s u f f i c i e n t d e i o n i z e d water t o make up 12 l i t e r s . Hydrogen p e r o x i d e (when used) was added t o t h e s o l u t i o n i n t h e r e s e r v o i r and t h e pH adjusted with aqueous sodium hydroxide or s u l f u r i c a c i d (Corning Model 255 pH meter). The c e n t r i f u g a l pump was turned on t o c i r c u l a t e the s o l u t i o n through the UV u n i t . During s t a r t u p , i t was o c c a s i o n a l l y necessary t o expel a i r pockets from the t e f l o n tube by s l i g h t l y t i l t i n g the UV u n i t upward. When the t e f l o n chamber was f r e e of a i r


6. CASTRANTAS & GIBILISCO

UV Destruction of Phenolic Compounds

81


pockets, the p r o t e c t i v e s t a i n l e s s s t e e l cover was p l a c e d on the u n i t and the UV lamps were switched on. P e r i o d i c a l l y , 80 ml a l i q u o t s were removed f o r immediate temperature readings followed as r a p i d l y as p o s s i b l e by pH, phenol and hydrogen peroxide determinations. A n a l y t i c a l Methods. Phenols were determined u s i n g a t e s t k i t (Chemetrics Model P-12) based on the formation of a red c o l o r by 4-aminoantipyrine when a p h e n o l i c compound was present (11). The c o l o r forming r e a c t i o n i s i n i t i a t e d by potassium f e r r i c y a n i d e . An ampoule i s s t i r r e d i n a 25 ml sample of the p h e n o l i c s o l u t i o n t o d i s s o l v e the f e r r i cyanide c r y s t a l s adhering t o i t . The ampoule t i p i s then snapped t o draw s o l u t i o n i n t o t h e vacuum chamber c o n t a i n i n g 4-aminoantipyrine. The ampoule contents are mixed by i n v e r t i n g s e v e r a l times. The ampoule i s then h e l d next t o one of two c o l o r comparators c o v e r i n g the range 0.1-1.0 mg/L ± 4 % and 1-12 mg/L ± 4 % u n t i l t h e c l o s e s t match i s found. For h i g h e r c o n c e n t r a t i o n s of phenols, s e r i a l d i l u t i o n s are performed. The l i m i t of phenol d e t e c t i o n i s 0.1 mg/L + 4%. H2O2 r e s i d u a l s were determined with a t e s t k i t (Chemetrics Model HP-10) based on the o x i d a t i o n of i r o n by hydrogen peroxide and the formation of the c o l o r e d f e r r i c thiocyanate complex (12). An ampoule c o n t a i n i n g ammonium t h i o c y a n a t e - f e r r o u s s o l u t i o n i s introduced i n t o a 2 5 ml sample of t h e s o l u t i o n c o n t a i n i n g H2O2. The ampoule t i p i s then broken a l l o w i n g the H2O2 s o l u t i o n t o e n t e r . A f t e r i n v e r t i n g s e v e r a l times t o i n s u r e the contents are mixed, the ampoule i s h e l d next t o one of two c o l o r comparators c o v e r i n g the range 0.1-1.0 mg/L ± 4 % and 1.0-10.0 mg/L ± 4 % u n t i l the c l o s e s t match i s found. The l i m i t of H2O2 d e t e c t i o n i s 0.1 mg/L ± 4 % . D i s c u s s i o n and R e s u l t s General. The summary of the experimental c o n d i t i o n s and complete r a t e data f o r the phenol and s u b s t i t u t e d phenol runs w i l l be found i n Tables I and I I . A l l r e a c t i o n s were c o n d u c t e d a t room t e m p e r a t u r e (21°C-24°C) . D u r i n g r e a c t i o n , a modest 1°C t o 7°C temperature r i s e was seen. T h i s was a t t r i b u t e d t o mechanical h e a t i n g by the c e n t r i f u g a l pump, the heat given o f f by the lamps and a c o n t r i b u t i o n from the heats of r e a c t i o n . Based on a flow r a t e of 0.9 L/min and 1.8 L/min t h e temperature o f t h e s o l u t i o n i n s i d e the t e f l o n tube (1.75 l i t e r s ) was c a l c u l a t e d t o be only 0.4°C and 0.2°C r e s p e c t i v e l y higher than at the p o i n t of a c t u a l measurement a t the o u t l e t of the t e f l o n tube. With the exception of run 7 t h a t used two UV lamps, a l l other UV runs u t i l i z e d e i g h t lamps. A r e g r e s s i o n equation was developed (Appendix A) u s i n g t h e d a t a from runs 4 and 6-16, T a b l e I . T h i s r e g r e s s i o n equation was used t o generate F i g u r e s 5-8. The


In Emerging Technologies in Hazardous Waste Management; Tedder, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1990. 30

1.2 10 30

Flow Rate-L/min

Phenol mg/L-Initial + 4%

H 0 0 0

Power Output uW-sec/cm^xlO*

24

Power Output uW-sec/cn£x10*

24

24

24

24

2.8/1 8 8

8

8.3/1

2.8/1

8

8

8.3/1

8.3/1

2

2

H 0 /Phenol Mole Ratio

1000

100

30

UV-Lamps-Number Used

mg/L-Initial + 4%

30

2

30

2

H 0

1000

100 10

10

10

Phenol mg/L-Initial + 4%

1.6

31 1.2

1.2

1.3

1.2

Flow Rate-L/min

27

24

23

24

24

8

8.3/1

3000

24

24

2.8/1 8

2.8/1 8

1000 3000

1000

1.0 1000

2.9 1.8

1.7 1000

23 29

4.3

9.6

29

24 22 22

Temp °C Final

3.2

7.4

16

24

8

5.5/1

200

100

1.2

23

23

7.5

7.8

8

22

6.2

6.0

9.2

4.3

15

6

2

5.5/1

200

100

1.2

30

21

6.1

7.8

7

8.0

14

0

0

2.8/1

30

10

1.2

25

23

5.2

10.0

6

13

24

8

0

0

10

1.1

24

22

6.1

10.0

5

Conditions

12

24

8

2.8/1

10

10

1.2

23

23

21

23

21

Temp °C I n i t i a l

7.8 3.2

6.8

pH-Final

7.4

6.2

pH-Initial

6.0

9

11

24

8

0

0

10

1.1

26

22

9.8 9.9

-

4

4.0

3

10

24

8

8.3/1

1.2

23

21

RUN

2

8.3/1

2

H 0 /Phenol Mole Ratio

UV-Lamps-Number Used

mg/L-Initial • 4%

24

Temp °C Final

2

23

Temp °C I n i t i a l

2

10

4.0 3.3

4.0

4.0

2

pH-Final

1

pH-Initial

RUN

Table I-A. Phenol Runs-Summary of Reaction


8


% H2O2 Remaining

Run 8 Time-Minutes % Phenol Remaining

% H2O2 Remaining


2

0 100 100

0 100 100

0 100 100

Run 6 Time-Minutes % Phenol Remaining % H 0 Remaining

2

0 100

0 100 100

0 100

0 100 100

0 100 100


% H2O2 Remaining



% H2O2 Remaining


% H2O2 Remaining


5 75 86

8 75 92

5 100 100

9 100

5 72 72

4 100

5 25 83

5 100 100

15 40 82

18 75 85

15 100 100

45 100

15 55 61

5 100

16 6 67

15 100 100

35 30 218

48 50 69

25 100 100

25 39 61

15 93

40 100 100

75 25 76

78 50 69

45 100 100

45 28 50

40 77

135 9 70

123 40 68

75 6 38

210 F=0.0001

2

% Dest = 67.88 + 44.71X2 + 7.82X2 - 3.83X3 - 5.04X3 + 11.72X4 - 42.92X6 + 19.07X1X5 - 17.95X1X6 + 4.50X2X3 = 17.92X2X4 + 8.54X2X6 Where:

XI X2 X3 X4 X5 X6

= = = = = =

2

(Ratio-2) (Ln(Time)-3.748)/2.139 (Orig pH - 8)/1.8 (Flow Mean - .39)/.09 (Temp Mean - 24)/3 (Ln(Phenol)-4.46)/2.45

Uncertainty limit for this equation at the 5% error level is 12% RECEIVED January

12,1990


99

UV Destruction of Phenolic Compounds under Alkaline Conditions

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