Organic Pollutants in Water - American Chemical Society

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Downloaded by FUDAN UNIV on January 24, 2017 | http://pubs.acs.org Publication Date: December 15, 1986 | doi: 10.1021/ba-1987-0214.ch025

Evaluation of a Quaternary Resin for the Isolation or Concentration of Organic Substances from Water Shaaban Ben-Poorat, David C. Kennedy, and Carol H. Byington Envirodyne Engineers, Inc., St. Louis, MO 63146 A synthetic resin (Amberlite XAD-4 quaternary) was evaluated as an adsorbent for the concentration-isolation of 22 specific organic solutes at micrograms-per-liter levels. Adsorption and desorption processes were first developed and tested on a laboratory scale and then adapted for a pilot-scale model. Studies determining the effect of humic substances and inorganic salts on the adsorption-desorption of model compounds were also performed. The effect of 2 ppm of chlorine residual on the generation of chlorinated organic compounds was also studied. XAD-4 quaternary resin in hydroxide form was efficient in recovering the majority of model compounds. Mass balances indicated accountability was generally higher in bench-scale experiments. Statistical evaluation of pilot-scale studies suggested that the presence of humic substances affected the concentration of model compounds.

THE FIELD OF SEPARATION SCIENCE

has made great strides i n recent years i n developing techniques for isolating, separating, and concentrating organic species. One impetus for these advances has been the search for sensitive and accurate analytical methods for trace organics. A second impetus has been the need for effective concentration and isolation techniques for preparing biologically active substances for biomedical investigations; the objective of this project was directed toward this application. Within the realm of analytical separation systems, b y far the most fruitful approach has been the use of solid sorbent techniques. Although other approaches have been studied (reverse osmosis, solvent extraction, 0065-2393/87/0214/0535$06.25/0 ® 1987 American Chemical Society

Suffet and Malaiyandi; Organic Pollutants in Water Advances in Chemistry; American Chemical Society: Washington, DC, 1986.


536

O R G A N I C P O L L U T A N T S IN W A T E R

foam separation, etc.), none are so versatile and offer so much potential for selectivity, concentration, and field use as adsorption techniques. This project dealt only with the investigation of adsorbents for the isolation of organic substances for toxicological testing. Furthermore, it was limited to the investigation of newly developed synthetic sorbents such as the polymeric X A D - 4 quaternary anion-exchange resin adsor bent rather than traditional activated carbons. Our goal for this project was to develop a system for sampling 500 L (or more) of drinking water that might contain 1-50 p p b of organic compounds. Mass balances for each compound were determined to reveal the unrecovered amount of each compound. T h e mass balance determinations were required to determine whether recovery losses were the result of volatilization, adsorption, and/or chemical trans formation. Synthetic sorbents are known to contain artifacts in the resin that could be eluted during desorption of the organic compounds con centrated on the resin. Therefore, separate experiments using X A D - 4 quaternary resin ( O H " form) were also performed to evaluate the presence of artifacts, either those arising f r o m the interaction of chlorine with the resin or those f r o m the resin itself.

Experimental Preparation of Model Compound Test Solutions. Test solutions of the model compounds selected by the U.S. Environmental Protection Agency (USEPA) are shown in the box on page 537. These compounds, which were used in bench-scale and pilot-scale studies, were prepared by diluting the required volume(s) of stock solution with organic-free water containing an inorganic salt matrix. The salt matrix consisted of 77 ppm of NaHC0 , 120 ppm of Ca2S0 , and 47 ppm of CaCl2*2H20. During the experiments, some precipitation of salt occurred in the reservoir prior to passing the water through the column. The pH was, therefore, adjusted from approximately 8.5 to 7.0 with 1 Ν HCI to correct the problem. 3

4

Bench-Scale Column and Resin Preparation. The apparatus used during bench-scale studies was modeled after work done by Junk et al. (J). The adsorption-desorprion column was 37 cm long X 1 cm i.d. In most bench-scale studies, this column was filled with 13 cm of XAD-4 quaternary resin (OH~ form) of 40-80 mesh. This amount was equivalent to approximately 10 cm of wet resin. A diagram of the apparatus used for the isolation-concentration of organics from water is shown in Figure 1. Figure 2 shows the eluant concentra tion apparatus designed by Junk and notes the changes. Glassware shown in Figures 1 and 2 was manufactured by Southwestern Glass. The resin cleanup procedure employed during this project used Soxhlet extraction with the same solvents used for elution. This method assured that any impurities were eluted prior to the actual adsorbent studies. Combining the best recommendations from previous studies, the following purification procedure was used in our laboratory: 3


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BEN-POORAT E T AL.

537

Evaluation of a Quaternary Resin

Adsorption System Model Organic Compounds Amount (*g/L)

Acids Quinaldic acid Trimesic acid Stearic acid Humic acid Glycine

50 50 50 2000 50


Carbohydrates Glucose

50

50

Hydrocarbons 1-Chlorododecane Biphenyl

5 50

Polyaromatic Hydrocarbons Phenanthrene

Amount (m/L)

Quinoline Caffeine 5-Chlorouracil

50 50 50

Esters Bis(2-ethylhexyl) phthalate

Aldehydes Furfural

Amines

so

Chlorobiphenyls 2,4'-Dichlorobiphenyl 2,2',5,5'-Tetrachlorobiphenyl

so 5

Ketones Isophorone Anthraquinone Methyl isobutyl ketone

50 50 50

Phenols 1

2,4-Dichlorophenol 2,6-Di-tert-butyl-4-methylphenol

50 so

Trihalomethanes Chloroform

50

1. 2. 3. 4. 5. 6.

A slurry of the resin was made with distilled water. The resin was stirred gently. The resin fines were removed by décantation. Steps 1-3 were repeated three times. The resin was rinsed with methanol three times. The resin was then purified by sequential solvent extractions with methanol, acetonitrile, and ethyl ether in a Soxhlet extractor for 8 h per solvent. 7. The purified resin was stored in glass-stoppered bottles under water to maintain its purity. 8. The resin was not allowed to dry because cracking results in the release of impurities from the interior of the resin.

One other solvent, methylene chloride, was also used for resin cleanup but only during the resin blank study. The XAD-4 quaternary resin was stored in the chloride form under water rather than under methanol because our consul-



538


Figure 1. Apparatus for extracting organic solutes from water. A, pure inert gas pressure source; B, cap; C, 2-L reservoir; D, polytetrafluoroethylene stopcock; E, 24/40; F, 1.0-cm i.d. X 37-cm long glass tube packed with 13 cm of resin; G, sUanized glass wool plug. tants (G. A. Junk and J. S. Fritz) noted that XAD-4 quaternary resin is not stable when stored under methanol. The XAD-4 quaternary resin used in these studies was prepared by the Ames Laboratory in Ames, Iowa. This resin had been used in studies by the Ames group for the adsorption and selective separation of acidic material in waste waters. For this study, the resin was chosen for its effectiveness in concentrating anionic material from solution. At the same time, it was thought that sufficient sites would be available to effectively adsorb neutral organic compounds from water. The resin was basically an XAD-4 macroreticular cross-linked polystyrene into which a trimethylamine group was introduced. The resin was stored in the chloride form but was converted to the hydroxide form before use in the resin sorption experiments.


25.

BEN-POORAT E T AL.


539

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BEN-POORAT E T AL.

551


At a linear velocity of 41 cm/s, the breakthrough occurred at approximately 800-1000 b e d volumes. A t 22 cm/s, the breakthrough was at about 1800 b e d volumes, and at 10.3 cm/s, the breakthrough was at about 2400 bed volumes. Figure 4 shows the predicted breakthrough curves for 500 L per 24-h volume using the same linear velocities as those employed in the three experiments for quinaldic acid. Figure 4 was based on calculations of experimental data, assuming constant linear velocities, residence time, and f l o w rate. These results are considered to be worst case predictions because of the higher concentrations used and the possibility of channeling having occurred in the small 1-cm experimental column setup. The results of the breakthrough studies indicated that the optimum flow rate would be approximately 50-100 b e d volumes/h. These results were used to scale-up the bench-scale columns for pilot plant studies. 3

Pilot Plant Design, Experiments, and Results. Design of the pilot plant scale-up was based upon the earlier study involving quinaldic acid breakthrough. Because this compound may represent a worst case, other factors must be considered. The inside diameter and length of the resin b e d were determined b y considering the following two factors: (1) residence time and (2) b e d volume per unit time or throughput. It was decided to keep these two factors as close as possible during scale-up f r o m bench-scale studies to the pilot plant studies. The first factor controls the rate of adsorption, and the throughput controls the capacity of the X A D - 4 quaternary resin. The breakthrough studies on quinaldic acid can be summarized as follows: Flow (mL/min)

Velocity (cm/min)

Residence Time M

Red Volume per Hour

6.75 3.66 1.72

40.6 22.0 10.3

9 16.4 35.0

405 220 103

Figure 3 shows that at 10% breakthrough at 10.3 cm/min, the b e d volume is approximately 3200 m L . The project requirement for sampling was 500 L of water to be concentrated during a 24-h period. Therefore, the following calculation w o u l d result in the amount of resin needed: f l o w = 1.72 m L / m i n ; 1.72 m L / m i n X 60 min/h = 103 b e d volumes/h; 103 b e d volumes/h X 24 h = 2472 bed volumes; 500 L/2472 b e d volumes = —2 L of resin. This calculation shows that the bed volume of about 2500 m L found


Suffet and Malaiyandi; Organic Pollutants in Water Advances in Chemistry; American Chemical Society: Washington, DC, 1986. z

3

Figure 4. Predicted quinaldic acid (salted H O) breakthrough curves for 500-L volumes (bed volume = 1 cm ).


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BEN-POORAT E T AL.


553

is close to the b e d volume of 3200 m L i n the breakthrough study of quinaldic acid. Because the volume of the resin required has been established (to handle 103 b e d volumes/h), the inside diameter (D) and the length (L) of the b e d can be determined i n order to be comparable to the residence time of the quinaldic breakthrough study. T w o approaches can be followed i n length and diameter determinations. One involves duplicating the breakthrough or the bench-scale studies. The second approach involves the practical aspects such as L/D and the pressure drop phenomenon. As a general rule, L/D should be more than or equal to 10. Therefore, a 16-in. X 1.0-in. i . d . column was constructed with the following characteristics: surface area = 4.9 c m ; residence time = 0.57 min; b e d volume/h = 103; flow rate = 347 m L / m i n ; linear velocity = 70.8 cm/min; L/D = 16. A total of four pilot plant studies was performed: 2

Sample

Resin Blank

Resin 1

Resin 2

Resin 3

Salts Model compounds Humic substances

Present Absent Absent

Present Present Absent

Absent Present Absent

Present Present Present

M a n y of the major peaks i n the acidic eluant samples were polymethyl polysiloxanes (PMPS), w h i c h are believed to be artifacts f r o m the column or septa. When a nonacidic solvent such as ether was analyzed, very few siloxane compounds were found. At least two of the samples contained a compound identified b y the library as methyl sulfate. This finding might suggest the presence of organic salts when the acidic eluants are concentrated rather than the presence of inorganic salts. In general, when a compound was found i n both the reagent and resin blanks, the concentration of the compound was higher in the resin blank. The source of the PMPS compounds is not k n o w n , but one possible explanation could be the stripping of the column liquid phase b y the acidic solvents. Pilot Plant Studies. The experimental work involved in pilot plant studies 1, 2, and 3 was basically the same as the resin blank pilot study. Twenty-one of the 22 model compounds were present in all three studies, but the inorganic salts were present i n two studies, and the humic substances were included only in the last experiment. This order was chosen on the basis of the possibility that the humic substances might not be desorbed 1008? and therefore alter the effectiveness of the resin in the adsorption of other model compounds. The desorption steps were performed in the columns three times


554


w i t h 150 m L of solvents as i n the resin blank pilot plant study. T h e resin was shaken each time and then allowed to stand for 20-30 m i n before it was drained. Volumes were adjusted when necessary to take aliquots for different analyses. Internal standards were added immediately prior to analysis to eliminate the need for exact measurement of the volumes and compensation in sample-size injection. Table I V provides results of the three runs and the concentration of each model compound i n the 500-L pilot plant study.


Conclusions The procedure used i n this study for the isolation-concentration of organic compounds in drinking water demonstrated that the X A D - 4 quaternary resin ( O H " ) is effective for most neutral, acidic, and semivolatile compounds. Because of the quaternary function of this resin, it was possible to concentrate several acidic compounds without any change i n the p H of the sampling water. This feature is an advantage over normal X A D resins for on-site compositing or grab sampling because the p r o b l e m of continuous acid addition and subsequent p H monitoring is avoided. Many classes of organic compounds adsorbed b y this resin can be desorbed b y solvents such as ether (or acidic methanol and ether). The acidic solvents can be concentrated to remove inorganic acid, but some residual inorganic acid always remained i n the concentrated eluants. Residual acid, or possible trace of water i n the concentrated eluants, caused analytical variances when methylation was attempted. Therefore, quinaldic a c i d , trimesic acid, and 5-chlorouracil were analyzed b y H P L C rather than b y G C - F I D . H u m i c substances were concentrated more than 50-fold on the X A D - 4 quaternary resin, but a saturated HCl/methanol solution was required for the desorption. This eluant was not concentrated further because the concentration of humic substances could be measured directly with a spectrophotometer. Total recovery of humic substances was higher i n the bench-scale experiments than i n the pilot plant studies. O n the basis of the pilot plant results (see summary of experiment 3), it appears that the adsorption of humic substances was affected b y the higher velocity or the loading capacity because 45% was recovered i n the effluent water. T h e higher velocity i n the pilot plant studies d i d not have a similar effect on other compounds such as quinaldic acid, for example, w h i c h was recovered at almost 100$. It is believed that caffeine, w h i c h was concentrated during bench-scale studies, was also affected b y the higher velocity in the pilot plant studies. The effect of inorganic salts on the concentration of the model compounds appeared to be inconsistent throughout the bench-scale



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Organic Pollutants in Water - American Chemical Society

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