Efficiency of adsorbents for removal of organosulphur compounds in water

e>

War. ScL T,ch. Vol. 38. No.6. pp.

Pergamon

13~146.

1998.

lAWQ C 1998 Published by Elsevier Sdence LId.

PIT: S0273-1223(98)OO575-7

Printed In Oreat Britain. AIl rlgbU reserved 0273-1223198 $19-00 + 0-00

EFFICIENCY OF ADSORBENTS FOR REMOVAL OF ORGANOSULPHUR COMPOUNDS IN WATER W. Y. Leong. E. H. Teo, C. H. Lim and Y. L. Tan DSO National Laboratories. 20 Science Park Drive. Singapore 118230

ABSTRACf Four carbonaceous adsorbcnts - Ambersorb XEN-S63, Carbochem LQ830, Carbochem LQIOOO and Morganite FYS - were evaluated in tenns of adsorptive capacity for organosulphur compounds (thiodiglycol, ethyl 2-hydroxyethylsulphidc. J,4-thioxane. ethyl vinylsulphide) in water. The adsorption isothenns in single-solute and multi-component systems were fitted to Freundlich isotherins which give a first-cut estimation of the adsorptive capacities and breakthrough times. All four adsorbents demonstrated decreasing adsorptive capacity with increasing polarity of the adsorbates. Morganite FYS and Amhenorb XEN-S63 exhibited the highest adsorptive capacity for the selected adsorbates. The study was also extended to six non• carbonaceous adsorbents - Amberlite XAD-4 and XAD-7; Biobeads SM2, SM4 and SM7; and molecular sieve 13X. The overall efficiency of adsorption of the four vessicants was SM4 > XAD-4 > SM2 > SM7 > XAD- 7 > J3X. C J998 Published by Elsevier Science Ltd. All rights reserved

KEYWORDS Activated carbon: adsorption; breakthrough: Freundlich isotherm; sulphur vessicant. INTRODUCTION Numerous hazardous compounds are introduced into environmental waters as a result of man-made activities, and modem purification processes must be capable of coping with these challenges. Distillation does not entirely remove organics like dimethyl methylphosphonate. diethyl malonate. ethyl benzoate and tributyl phosphate from contaminated feed water (Leong. 1996). Adsorption has been considered to be the 'best available technology' for removing organics from water in the US Safe Drinking Water Act (Ram. et al., 1990). The efficiency of the process is dependent on the type of pollutant and adsorbent. In this study, we challenged a number of adsorbents with compounds which are related to sulphur mustard vessicant. The objective was to select the most cost-efficient phase for an adsorption polishing unit, to be retro-fitted to a reverse osmosis system, to produce water for normal consumption. The carbonaceous adsorbents studied are LQ830, LQ1OOO, FYS and Ambersorb XEN-563, and the synthetic XAD-7, SM2, SM4, SM7 and molecular sieve 13X. Their physical polymeric adsorbents are characteristics are summarized In Tables I and 2. The compounds studied (Table 3) are thiodiglycol (TOG). ethyl 2_hydroxyethylsulphide (EHS), l,4-thioxane (TX) and ethyl vinylsulphide (EVS), the polarities of which vary in the order: TOG > EHS > TX > EVS. The blistering agent, sulphur mustard, hydrolyses to thiodiglycol in water with a half-life of 8.S min at 25°C (Lundin, 1991) and its analogue, 2-chloroethyl 139

XAI?-4.

140

W. Y. LEONG el al

ethylsulphide. hydrolyses to ethyl 2-hydroxyethylsulphide. 1,4-Thioxane and ethyl vinylsulphide can be found as by-products in mustard arsenals. Table I. hysical properties of carbonaceous adsorbents* Adsorbent

LQ830

Coal 950 850 0.80 8-30

Origin

Surface area (m2/g) Iodine number (mglg) Pore volume (cm3/g) Mesh size Microporosity (mUg) Mesoporosity (mUg) Macroporosity (mUg) Cost- (SSlkg)

FYS

LQl000 Coal 1100

1000 0.90 12-40

N.A. N.A. N.A

N.A. N.A. N.A.

4.75

Ambenorb XEN S63 Synthetic 550

Coconut shell Il50 llOO 0.68 12 - 30 0.37 0.12 0.19 2.80

5.68

N.A. N.A.

20 - SO 0.23 0.14 0.23 640.0

-UnitOOll.atl997

Table 2. hysical properties of non-<:arbonaceous adsorbents* AdsorbeDt

XAD-4

XAD-7

SM2 SM4 SM7 Mol.sieve

13X

Material Polyaromatic acrylate Polyaromatic acrylate Polystyrenedivinylbenzene Polystyrenedivinylbenzene Polyacrylate

MeaD .urface area (m2/g) 725

MeaD pore diameter 40

Mesb .ize (USA) 20-60

450

90

20-60

300

90

725 450

(A)

crystalline sodium aluminosilicate

Wet

Polarity Non-polar

density (glml) 1.02 1.05

20-50

Intermediate polarity Non-polar

1.02

40

20-50

Non-polar

1.02

90

20-50

Intermediate polarity

1.05

10

• 8ourllO: Tecbniool buUetinl a cilia opeoi6<:IIioa .... from ROJ{}.{ .. HAAS, SUPELCO, CJlEMTIlADE INC. MORGANlIl! CAllBON """BDH

Table 3. Chemical properties of adsorbates Compound

TDG

Chemical Structure

O~S"~OH

Polarity Molecular weight Water affinity

ERS OH

S.

EVS

TX

(s)

~s~

0

Most Polar

~

Largest

~

Hvdrophilic

~

Least Polar

Smallest Hvdronhobic

EXPERIMENTAL Ambersorb XEN-563 (Rohm and Haas). Carbochem LQ-830 GAC (Chemtrade). Carbochem LQ-lOoo GAC (Chemtrade). Microcarb FYS GAC (Morgan), Amberlite XAD-4 and XAD-7 (Supelco), Biobeads SM2. SM4 and SM7 (Bio-Rad), and molecular sieve 13X (liS" pellet, BDH) were obtained commercially. Bis(2-

Efficiency of adsorbents

141

hydroxyethyl)sUlphide or thiodiglycol, IDG (Merck); ethyl 2-hydroxyethylsulphide, EHS (Merck); 1,4• thioxane, TX (Aldrich); ethyl vinylsulphide, EVS (fCl), and HPLC-grade acetonitrile (Labscan) were used without further purification. Distilled water was obtained from an Aquatron A4D double distiller. Analysis was performed by HPI050 LC with HP Gl306A DAD (Hewlett-Packard). Agitation of samples was carried out on a Stuart Scientific SFI 8-flask shaker. A solution containing 100 mgll each of TOG, ERS, TX and EVS in distilled water was prepared. (fo achieve a fair comparison of the adsorbents under reproducible conditions, we did not use environmental water, to avoid competitive adsorption from unforeseen pollutants.) For determination of isotherms, ~o ml of this solution were dispensed into lOO-ml bottles containing different quantities of adsorbent. The bottles were capped and agitated (350 osc/min) at 25°C for 48 hours, after which a sample from each bottle was filtered through 0.45 11m nylon filter (Phenomenex) and analysed by HPLC with pre-column derivatization (Leong, 1995). Derivatization was performed by adding 10 III of ~,OOO mgll chloroamine-B (in MeOH) to I ml of water sample and heating at 80°C for 1/2 hour. Calibration standards at 10, 20, 50 and 100 mgll in water were injected, linearity was observed up to 100 mgll and the limit of quantitation (SIN ratio of 5) was 0.5 mgll. The samples and standards, injected in volumes of 50 Ill, were eluted with acetonitrile-water (3:7) at I mVmin, through a Spherisorb ODS I column (250 x 4.6 mm; 5 11m) at 40°C, with UV detection at 225 nm. From this work, FY5 was identified to be the best adsorbent. The above procedure was repeated on FY5, but each time with only one sulphur compound in the water. For evaluation of the non-carbonaceous adsorbents, 0.1 g of each adsorbent was shaken with water samples containing 100 mgll each ofTDG, ERS, TX and EVS for 48 hours, and the water samples were then filtered and analysed similarly. RESULTS AND DISCUSSIONS From the graphs of equilibrium concentration of adsorbates vs weight of adsorbent (fig. I), the smallest and most hydrophobic EVS was preferentially adsorbed whereas the most polar TOG was least efficiently adsorbed. EHS was better adsorbed than TX, although it was more polar. Equilibrium data were transformed to isotherms (Fig. 2) which give a first-cut evaluation of the adsorption efficiency. IDG, ERS and TX exhibited type I isotherms with the carbonaceous adsorbents. With increasing equilibrium concentration, the adsorptive capacity rose to a plateau, characteristic of solids containing micropores. In a multi-component study by Jiang (1991), there was little competitive adsorption between phenol I humic acid and heavy metals, presumably because of different adsorption mechanisms. In our system, competition between the sulphur compounds set in at higher equilibrium concentrations, corresponding to the lower amounts of adsorbent. TOG tended to be displaced by the other adsorbates. In a multi-component study involving halogenated hydrocarbons, the Freundlich equation was found to suffice as a straightforward expression to fit the data adequately (Crittenden, 1985). Our isotherms on FY5 in multi-component and in single-component systems (Fig. 3) also fitted into the Freundlich equation, X = KC lin where K and n are constants (Fig. 4). All four adsorbates show higher equilibrium constant K and low'er n in single component system (fable 4). Table 4. Freundlich constants from the isotherms of single and multi-component systems __._ Compoun~_ ..__ TDO (single) TDO (mixture) EHS (single) EHS (mixture) TX (single) TX (mixture)

_.-!!.!!__._ _._._.. _!!!(!9. _.._ _ 0.48 0.33 0.38 0.31 0.43 0.36

2.07 1.70 2.96 2.53 2.61 2.20

~ __ 2.09 3.04 2.64 3.24 2.31 2.75

__.__._._.._ ~_ 7.91 5.46 19.22 12.61 13.59 9.00

_._

...:!t

0

.~

0-

.

o~

"'" >-

~l

[a

~~

e!t

""0 ,...

...

~E

O\a

VI-

~~ . ...

[t

~[

Ef

.§'O'

...

-~

.5'9

ag

ir a.

il

~n

'C?9

•~[ c

.bE

a.s

irS.

it

~; ,...-

S)

!j

i!

e1 ,,-

u

=) 0.4

0.6

0.1

(a)

Wolght of Adaorbent edded lal

(l2

1

20

40

llll

llll

tOO

(C)

0.2 0.4 0.1 0.11 Wolght of Adaorbent .tded lal 1

Equilibrium concentration (mg/l) vs Weight of Amber!lOrb added (g)

20

~! ~

~i

is)

100

wI

Equilibrium concen1ratlon (mgIL) va Weight of LCIa30 added

__ EVS

-G-EHS __ lX

_ _ 100

_ _ EVS

_ _ 1)(

_ _ EHS

_ _ 'TOO

0

eo

20 10 0

0

(b)

wI

0.8 0.8 0.4 0.2 Wolght of Adaorbent .tded lal

w)

Equilibrium concentration (mg/l) va Weight of FY5 added 100 " -

eo

0

20

:~~

(d)

08 08 0.2 0.4 Weight of "dlGrbent added (al

:j E~~

Ii

~j

~i

=1

is

100

__ EVS

_ _ TX

_ _ EHS

_ _100

__ EVS

__lX

_ _'TOO _ _ EHS

Equlllblfum concentration (mg/ll va Weight of LQ1000 added

~

e..

~

§

~

:<

E

Efficiency of adsorbcnts

143

~ f

~

i

E

i_ ~

~.

".s e is 1 !.

R

~

~

1 E

0

~

,

/

I

i

i i ..... "0

\

,~

~

\

~ ~~

~

II

il

!. ~ ~.s

"

R

~

0

.s

0

§ i

~

~ ~ ......

"""

Fl

iii

iii

~

!.

.s

"0'

"""

R

~

0

Figure 2. Adsorption isotherms of TOO, EHS and TX in multi-<:omponent system with cubonaccous lldsorbcnts at 25°C for (8) Carboc:hem LQ830, (b) Carbochem LQ1000. (c) Arnbersorb XEN-563 and (d) Microcarb FY5 GAC.

144

W. Y. LEONG et (II

Adsorption Isotherm for FYI

70 10 50

j )(

I-""

40 30 20 10 0

,/

..--

0

-----

V

--

~

20

40

--

C.CmlllLl

eo

-eo

_ _ TDOln Mixture

_ _ TDO

100

(a) Adsorption lsotharm for FYI

70

eo

./

50 ,

40

;C 30 20 10

J

rI'"

1/,-' V

./'

-----

.--.

0 0

20

40

C.CMlIlLl

_ _ EMS I"

ml.'ur. _ _ EHS

eo

ao

100

(b) Adsorption lsotharm for FYI

70

~

eo eo ,

40

,/'

;C 30 20 10

o

__ TXln

./ ]I'

V o

mI.'ur. _ _ TX

".

~

.....

~

ao

20

100

(c)

Figure 3. AdsOlJltion isothenn. of (a) TOO. (b) EllS. (c) 'IX, OD FY5 in lingle solute system and multi-solute system at 25°C.

Efficiency of adsorbcnts

14~

4.,--------------------::;:;:I!t-----, Adsorption Isotherm of TOG

3.5

3

..

g

2.5 2

1.5

1-1-----_--o

2

----_-----l

In (C,l

3

5

(a) Adsorption Isotherm of EHS

A simple mass balance derived from the Freundlich equation can be used to estimate the breakthrough time as (Kci/n I Co)WIQ where Co is the influent concentration, W is the weight of the carbon and Q is the volumetric flow rate (Ram, et al., 1990). The breakthrough estimates for I kg of carbon, treating 600 Vday of water contaminated at 100 mgll, are given in Table 5. Further work has been embarked on for a more accurate assessment under kinetic conditions and for environmental waters.

146

W. Y. LEONG et al

Extension of the study to non-carbonaceous adsorbents gave the overall adsorption as SM4 > XAD-4 > 5M2 > SM7 > XAD-7 > 13X (Fig. 5). However, XEN-563 and FY5 still have higher adsorptive capacity (0.7 g for adsorption of 100 mg/l of TDG, TEG, TX and EVS from 50 ml water; compared to 1.0 g of LQ830 and 1.2 g of LQ 1000 GAC). FY5 is the most cost-effective adsorbent (S$0.00196 for complete removal of 100 mg/l of TOG. EHS, TX and EVS).

,-------------------------------

I

C.m,lfl.on 0' ,"ol)#nt.,lc Ad.orbe"ts to FY5

to. a•

x (Mi'L)

•• ,. 40

•

TDO

•

TfG

a

e"VS

on FY~

lA04

)(A07

8M 2

Figure 5. Equilibrium concentration X of contaminants after treatment with adsorbents for 48 hours.

Table 5. Breakthrough time for I kg ofFY5 and 600 I/day of influent with 100 mg/l contaminant Compound

Estimated breakthrough time (day)

TDG

TDG

(>ingle)

(Mixture) 0.42

1.2

EHS

EHS

(.S'ingle)

(Mixture) 0.88

1.84

TX

TX

(.S'mgle)

(MIxture) 0.79

1.64

CONCLUSIONS The adsorption isotherms of the organosulphur vessicants on carbonaceous adsorbents were found to fit the Freundlich equation. Competition for adsorption was seen to arise when the compounds were present as a mixture. The adsorptive capacity was least for hydrophilic TOG and highest for hydrophobic EVS. XEN· 563 and FY5 have the highest adsorptive capacities but FY5 is more cost-effective.

REFERENCES Crittenden, J. C.• Luft. P.• Hand. D. W.• Oravitz, J. L., Loper, S. W. and Arl. M. (1985). Prediction of multicomponent adsorption equilibria using ideal adsorbed solution theory. Environ. Sci. Technol., 19(11). 1037-1043. . Jiang. Z. P., Yang, Z. H., Yang. 1. X. and Zhu. W. P. (1991). I ?mpetitive adsorption on activated carbon of some orgamc compounds and heavy metals. Water Treatment. 6. 13-24. Leong. W. Y. and Ng. W. F. (1995). Analysis of toxic sulfur contaminants in water. Proceedings of the 1995 ERDEC Scientific Conference on Chemical and Biological Defence Research (ERDEC-SP·043), Aberdeen Proving Ground, USA, 14·/7 Nov 1995. Leong. W. Y. (1996). Distillation of sea waler with volatile organic contamination. International Association of Water Quality (IA WQ) 18th Biennial Conference, Singapore, 23·28 June 1996. Lundin, S. J. (cd) (1991). Verification ofDual-use Chemicals under the Chemical Weapons Convention: The Case of Thiodiglycol. Oxford University Press. pp. 4-23. Ram. N. M.• Christman. R. F, and Cantor. K. P. (1990). Significance and Treatment of Volatile Organic Compounds in Water Supplies, Lewis Publishers. USA. pp. 229.