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A composite sorbent based on bead cellulose and mercurated novolac
Reactive Polymers, 5 (1987) 133-140 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands
133
A C O M P O S I T E S O R B E N T B A S E D O N BEAD CELLULOSE AND MERCURATED NOVOLAC aIhi LENFELD and JIRi STAMBERG Institute of Macromolecular Chemistry, C:echoslouak ,4 cader~O' of Sciences. 162 06 Prague 6 ( Czechoslot,akiaj (Received March 21, 1986: accepted in revised form August 1, 1986)
,4 composite material, bead cellulose-novolac, was prepared and transformed by mercuration with mercurv(II) acetate into a sorbent containing - H g + ion-exchange groups. The course of mercuration was followed by measuring the time and concentration dependence. Materials with various rnercury contents" were obtained, with the highest attained mercury content 35.4%. Even at the highest novolac content and degree of mercuration the sorbents showed high swelling in water. The sorption properties were investigated using the sorption of chloride anions from aqueous solutions b v measuring the time dependence of sorption and the sorption isotherm. The sorbent possesses a high rate of sorption in addition to the well-known high selectiuitv of mercurated polymer structures.
INTRODUCTION
Mercurated polymeric sorbents, and especially mercurated styrene-divinylbenzene copolymers and phenolformaldehyde polycondensates, are known sorption materials which are used as selective anion exchangers [1-4], but also as sorbents of urea [5] and organic compounds containing thiol groups [6], or as carriers of biologically active compounds. They can be prepared with comparative ease by polymer-analogous mercuration
[1,5,71. Mercurated phenolformaldehyde resins were prepared by Miles et al. [6], who used them in the separation of glutathione and cysteine. The separation efficiency was very good, but their application was limited because of the imperfect external shape and the unsatisfactory porous structure of these 0167-6989/87/$03.50
mercurated polymers. The sorbent consisted of small, irregular particles so that it could be introduced only into small laboratory columns. The mercurated resin was almost nonporous and did not swell in an aqueous medium, as is usual with mercurated polymers, so that the sorption efficiency was limited only to the external surface of the individual particles. In order to keep a sufficiently extensive active surface, the powder form could not be replaced with the granular form, as is common for other types of sorbents. Some types of polymeric sorbents containing covalently bound mercury are also commercially available. As affinity chromatographic material for the selective purification of proteins containing thiol groups, the firm Bio-Rad Laboratories offers the sorbent AffiGel 501 [8], which contains phenylmercury
¢~ 1987 Elsevier Science Publishers B.V.
134 groups bound to a spherical agarose carrier through a spacer. A sorbent supplied by Sigma (p-hydroxymercuribenzoate agarose) has a similar composition and purpose [9]. In this study we describe the preparation and properties of a new type of sorbent containing an organomercury polymer and based on the composite principle. High-porosity bead cellulose [10] and a phenolformaldehyde novolac-type condensate were the starting materials. Pores of bead cellulose are partly filled in with novolac, which is mercurated in a further stage. In the composite sorbent thus obtained the phenolic component is the carrier of sorption activity, and the cellulose matrix guarantees the required physical macro- and microstructure, i.e., the external shape of the individual particles and their porosity.
(those used for analytical purposes analytical purity grade only); all were used without further purification.
Preparation of bead cellulose-novolac composites An amount of 50 g of bead cellulose swollen in water and filtered under suction on a glass filter was washed in a column with 50 ml of ethanol for 5 h. An amount of 2 g of washed cellulose was filtered under suction on a glass filter and mixed with 20 ml of ethanolic solution of novolac at a given concentration. The mixture was shaken at room temperature for 24 h, the sample was filtered under suction, quickly washed with 20 ml of ethanol during suction and used in characterization measurements or mercuration.
Mercuration of composites EXPERIMENTAL
Starting materials Bead cellulose (BC) (United Chemical and Metallurgical Works, 0 s t i nad Labem, Czechoslovakia) is a spherical cellulose sorbent, prepared from technical viscose according to a method reported earlier [10] by a suspension procedure using the thermal sol-gel transition and regeneration with boiling water. Its properties were characterized by the following data: water regain, 5.32 g H 2 0 / g dry matter (i.e., dry matter content 15.8%); particle size, 0.125-0.5 mm. Novolak 70 (Moravian Chemical Works, Ostrava, Czechoslovakia) is a soluble phenolformaldehyde condensate (in the following referred to as "novolac"), the properties of which are characterized by the following data: the softening point according to Nagel, 70 _+ 5°C; free phenol content, 6-9%; viscosity of a 50% ethanolic solution, 50-100 cP. The other chemicals and solvents were chemically pure or analytical purity grade
The cellulose sample with novolac (2 g) was placed in a 50 ml reaction flask, and 20 ml of mercuration solution (composition: 25 g mercury(II) acetate, 10 ml 70% perchloric acid, 25 ml acetic acid, completed with water to a total volume of 250 ml) was added. The reaction was conducted with shaking at 25 ° C for 24 h. On completion of the reaction, the sample was washed with water, methanol and water again (until the washing water no longer showed the colour reaction of Hg 2+ ions with diphenylcarbazide); the water regain or the dry matter content in the centrifuged sample and the mercury content in the dry matter were then determined.
Time and concentration dependence of the mercuration of composites During the concentration dependence measurements, the concentrations of mercury(II) acetate and perchloric acid in the mercuration solution were varied while maintaining their molar ratio (HC104/(CH3COO)2Hg= 1.5).
135 In the time dependence studies, only the time between addition of the mercuration solution and its fast washing-out on the glass filter with 50 ml of water completing the mercuration was measured. The other conditions were the same as described in the preceding 'paragraph.
Preparati~,,e mercuration of the composite An amount of 40 g of bead cellulose saturated with a 50% novolac solution in ethanol was mercurated as described above. The product contained 34.5% of dry matter: the mercury content in the dry matter was 27.1%, i.e., 1.35 mmol H g / g dry matter. The product was kept in water. The sample used in the determination of the n o v o l a c - H g bond stability in a sorbent eluted with water was prepared by employing a procedure as described above, using a mercuration solution containing 1 g mercuric acetate per 250 ml of solution. The sample contained 2.44% Hg and its water regain value was 4.96 g H e O / g dry matter.
with distilled water in a column at a rate 20 ml w a t e r / h . The eluate thus obtained was analyzed for the mercury content.
Sorption of chlorides by a mercurated composite To measure the time dependence of sorption, the preparative sample was centrifuged: 1 g was placed in a 50 ml flask, and 20 ml of an aqueous sodium chloride at a concentration of 0.01 or 0.05 m o l / l was added. The mixture was shaken in a closed flask at 25 °C for a certain time, after which the concentration of chloride ions in the aqueous phase was determined by potentiometric titration with an A g N O 3 solution. The amount of CI that was sorbed was determined from the decrease in concentration. The procedure employed for the measurement of the sorption isotherm was similar. The contact time was 24 h, and the NaCI concentration in the aqueous phase was varied from 0.0001 to 0.5 mol/1.
Analytical methods Determination of the sorbent stability during washing The stabilities in an alkaline and an acid aqueous or ethanolic solvent were determined by washing of 0.5 g of the sample centrifuged from water with 50 ml of the respective solution or solvent in a column for one hour. After thorough washing with water (ca. 200 ml) the sample was dried and the mercury content was determined. In the case of benzene, there was a successive exchange of the solvents w a t e r - e t h a n o l - b e n z e n e - e t h a n o l water. The bond stability between novolac and mercury in an aqueous medium was determined by washing with water. Of the sorbent sample (2.44% Hg), 1 ml was washed
To determine the water regain or the dry matter content, 2 ml of the swollen sample in a weighed column [11] was centrifuged (10 min, 900 g), weighed, dried (25°C, 13.3 Pa, 24 h), and weighed again. From the data thus obtained, the dry matter content (in percent) or the water regain (in g H x O / g dry matter) were calculated. The mercury content was determined gravimetrically. The sample was burned on a platinum gauze in a stream of oxygen, and the released mercury vapours were trapped on a gold foil. The mercury content was calculated from the increase in weight of the foil. During the investigation of the novolac Hg b o n d stability, the mercury content in the eluate was determined by atomic absorption spectroscopy.
136
RESULTS AND DISCUSSION
Preparation of the composite sorbent Preparation of the composite sorbent consisting of bead cellulose and mercurated phenolformaldehyde condensate of the novolac type may be divided into two steps. In the first step, introduction of an alcoholic solution of novolac into pores of bead cellulose leads to the formation of a basic composite material, which in the second step undergoes a polymer-analogous mercuration. The first step is preceded by an exchange of water for ethanol in the swollen and never-dried cellulose. The amount of novolac introduced into bead cellulose depends in particular on the volume and concentration of the novolac solution and on the contact time. Novolac was introduced into cellulose by a one-stage equilibration with a ten-fold excess volume of solution over that of cellulose. Quantitatively, the process was followed gravimetrically, by determining the dry matter in the composite material formed; it is of importance that even with a 50% novolac solution used, the resulting material still had a high degree of swelling (Table 1). TABLE 1 Effect of concentration of novolac solution on properties of composite sorbent Properties of original bead cellulose: water regain, 5.32 g HzO/g: dry matter content after exchange of water for ethanol, 20.3% Dry matter Water regainb Hg content Novolac g H 20/g in dry concentra- content (EtOH) a matter b % tion, %
%
10 20 50
21.4 25.2 30.2
3.54 2.69 1.44
12.2 19.8 33.5
Determined after saturation of bead cellulose with ethanolic solution of novolac. b Determined after mercuration.
The composite samples thus obtained were subjected to polymeranalogous mercuration. Mercuration with mercury(II) acetate proceeds on aromatic nuclei of novolac and may be described by Scheme 1. This reaction pro-
CH2
+ (CH3COO)2Ng CH3COOH--HCIO4
CH2 Hg+-OCOCH3
Scheme 1.
ceeds readily also at room temperature, due to the catalytic effect of perchloric acid, which together with mercury(II) acetate forms a reactive complex CH3COOHgC104 [12]. An insoluble mercurated polymer is formed in cellulose pores when the mercuration solution comes into contact with novolac. The chemical transformation is thus accompanied by the immobilization of a fine precipitate of mercurated novolac in cellulose macropores. We used reaction conditions leading to the highest degree of mercuration in order to be able to characterize the effect of concentration of the novolac solution on the attainable mercury content in the final product. The results summarized in Table 1 suggest that the mercury content increases with the novolac content, while the comparatively high degree of swelling in water remains preserved. In order to obtain a sorbent with a sufficiently high sorption capacity, further experiments were carried out, this time using only bead cellulose saturated with a 50% novolac solution in ethanol. The mercuration process itself was investigated in greater detail by measurements of the dependence on time and concentration of the reaction. Figure 1 shows that the reaction was completed after approximately six hours. In the same figure one can also see the dependence of water regain of the mercurated composite on time. The results confirm once again that even with a high degree of
137 ]
T
.~ o -r-
.~
_ 30 -~o
~
t)
2 -2 10
©
l 0
(~--0
I(ii
5
I
10 15 25 reachon time ~ h
Fig. 1. Time dependence of mercuration of composite.
mercuration the sorbent may sufficiently swell in water. The dependence of the transformation on the concentration of the mercurating agent (Fig. 2) indicates the possibility of preparation of mercurated sorbents with various mercury cont,mts from the same starting composite. Another possibility is the use of cellulose samples containing different amounts
I
I
_ 30
c o u
c~ I
of novolac, which are suitable in those cases where organomercury ion exchangers possessing higher or optional degrees of swelling or a low mercury content are to be obtained. The curve in Fig. 2 also suggests that even the highest concentration of mercury(II) acetate in the mercuration solution used (9%) did not result in the highest possible degree of mercuration. However, the rise in the mercury content attainable by employing a higher concentration of mercury(II) acetate is small. A comparison of the results described above provides information on the reproducibility of the whole process of preparation of the composite mercurated sorbent. Under virtually the same conditions, samples containing 33.5% Hg (cf. Table 1), 32.2% Hg (Fig. 1) and 35.4% Hg (Fig. 2) were obtained. A preparative sample for sorption measurements containing 27.1% Hg was prepared under somewhat different conditions (twenty times larger charge). Scatter of these values is comparatively large. The main cause of these differences is the procedure employed in the preparation of the starting composite material, where--after saturation of bead cellulose with an ethanolic solution of novolac--the sample is washed with pure ethanol to prevent the conglomeration of particles. The washing, even if performed in a standard manner, is accompanied by an uncontrollable partial removal of novolac from the beads, which is the cause of the observed differences. Sorption measurements
20
~0
,O
I
I
5
~0 Hg(OAc)2 ~ %
Fig. 2. Concentration dependence of mercuration of composite.
Mercurated polymers can be used as selective anion exchangers [2-6]. Their effectiveness is derived from the ability of organomercuric salts to form undissociated compounds with halides, thiocyanates, cyanides, sulfides, and mercaptides. The sorption properties of the sorbent were characterized by the sorption of chloride anions from aqueous solutions of sodium chloride, which can be described by Scheme 2.
138
CH
+
+ CH3COONa
CH
NaCI
Hg÷ -CI
Hg + -OCOCH3
Scheme 2.
The sorption process was investigated by analyzing the aqueous phase, i.e., by determining the loss of chloride anions in the sorption solution. Only dilute solutions were used, for which the loss of chloride anions could be determined with sufficient reliability. The rate of sorption was measured using a preparative sample of the mercurated sorbent in sodium chloride solutions of concentrations 0.01 and 0.05 mol/1. The dependen,.es in ~ ,g. 3 clearly show the high rate of sorption. The half-time of sorption is approximately 30 s, while, for example, the half-time of sorption determined for the mercurated macroreticular styrene-divinylbenzene copolymer Amberlite XAD-2 (23.5% Hg, 0.035 mol NaC1/1, 25°C) was 5 min [1]. Such a pronounced difference in the sorption kinetics is a consequence of the hydrophilicity
I
I
of the composite sorbent caused by the presence of the cellulose skeleton. The sorption properties of the composite ion exchanger are also made evident by the sorption isotherm (Fig. 4). The highest possible capacity of the ion exchanger (100%) has been derived from the mercury content in the measured sample (1.35 mmol H g / g dry matter). If these results are compared with the already mentioned mercurated Amberlite XAD-2, it can be seen that in the case of the mercurated composite sorbent based on cellulose the utilization of the mercury is better (with mercurated Amberlite XAD-2, only ca. 65% of the mercury was utilized). On the other hand, however, the affinity of the mercurated cellulose composite with respect to chloride anions is somewhat poorer than that of the mercurated Amberlite XAD-2; with a 0.1 mol/1 NaC1 solution, only 50% of the maximal capacity was reached for the cellulose composite, while for Amberlite XAD-2 the value was over 90%. The high affinity of the mercurated composite sorbent for chloride anions becomes evident especially at low concentrations. This is illustrated by the differences between experimental and calculated values of the sorption isotherm in Fig. 4.
JJ I
Stability ~,
T0. E
A
0.05 mol NaCL/[
L)
0.01 moL NaCI/I
jj •
Z.
i C..;,
O--4~3-
43
0.2
I 30 sorption
I j~ I 60 1440 tirne~ min
Fig. 3. Time dependence of sorption of chloride ions by mercurated composite.
Data on the stability of the sorbent in an alkaline and an acid medium and in some organic solvents are summarized in Table 2. These data are important particularly with respect to the contingent regenerability of the ion exchanger after sorption. By treatment with aqueous NaOH (0.1 m o l / l ) the novolac phase is completely washed out off the composite; at lower NaOH concentration less novolac is eluted. This was to be expected because of the known solubility of novolac and of hydroxyphenyl-mercuric hydroxides in dilute sodium hydroxide. Replacement of water with ethanol at the same NaOH con-
13 ~) T
1
r
100
~o
vo Q)
s0k
L
0.0001
I
0.001
0.01
0.1 C [ - moUl
1.0
Fig. 4. Sorption isotherm of sorption of chloride ions by mercurated composite at 25 ° C. e: experimental values: - - : calculated Langmuir-type isotherm.
centration considerably reduces the effect of the alkali. In other media the sorbent is comparatively stable, and a decrease in the mercury content is not pronounced, compared with the starting material. These results are only preliminary, of course: to a great extent, they only bear evidence as to the stability of the composite sorbent as a whole and not to the stability of the covalent bond
between novolac and mercury. In this respect the situation can be adequately' described by measurement of the water extract of one sample of mercurated sorbents with a lower mercury content (2.44%, Hg). It was found that the yield is 28.7/xg Hg/1 eluate from 1 ml of the sample, The instability of the sorbent in an alkaline medium also presents an important problem in its applications. A consequence of this instability is that the sorbent which has been used in, for example, the sorption of halides cannot be regenerated in the usual way, i.e., by the reaction - H g ~ C I + N a O H - - - * -Hg ~ O H + N a C 1 Therefore, the procedures to be considered are, in particular, single applications with no regeneration assumed or such applications in which a multistage regeneration procedure rec o m m e n d e d for commercial organomercuric sorbents is no drawback [8,9]. There is not doubt that the sorbent would prove useful, e.g., in the separation of mercaptans as described by Miles et al. [6], for analytical purposes, in laboratory-scale chromatographic processes, or as a cleansing sorption-active medium for single use. CONCLUSION
TABLE 2 Stability of sorbent in washing Washing medium
Hg content
Type
Concentration,
NaOH/H20 N a O H / H 20 NaOH/ethanol NaOH/ethanol HC 1 / H 20 Acetone 1,4-Dioxane Benzene h
0.1 0.01 1.0 0.1 1.0
tool/1
in sorbent after washing ~, 0 24.0 21.0 21.8 26.5 26.0 25.5 26.5
" Hg content in sorbent before washing 27.1%. ~' Successive exchange of solvents water ethanol-benzene -ethanol-water.
The mercurated composite sorbent based on bead cellulose and phenolformaldehyde novolac-type condensate is a new sorption material, combining functional properties of mercurated novolac with the hydrophilicity, porosity and spherical shape of bead cellulose. Its particular advantages are the high rate of sorption and good selectivity, which predetermine its use in the sorption from dilute aqueous solutions. A certain shortcoming is seen in its lower stability in alkaline medium, which impairs the possibilities of regeneration and reduces the range of its applicability, restricting it mainly to single-sorption or sorption-desorption processes.
140
ACKNOWLEDGEMENT
The authors thank Mrs. E. Kni~flkovfl, M.Sc, for analyses of mercury contents, and their colleagues in the Water Research Institute, Prague, and Research Institute for Veterinary Medicine, Brno, for determinations of the mercury extract from the sorbent.
REFERENCES
5
6
7 8
1 J. Lenfeld, J. Pe~ka and J. Stamberg, Surface oriented mercuration of poly(vinylaromatics), Reactive Polymers, 1 (1982) 47. 2 A.G. Pashkov, V.F. Alexandrova, M.I. Itkina and I.G. Stebeneva, Synthesis and investigation of mercurated copolymers, Plast. Massy, No. 3 (1967) 19. 3 W. Szczepaniak, Organomercuric polymers as ion exchangers. I. Anion exchange properties of mercurated styrene-divinylbenzene copolymers, Chem. Anal. (Warsaw), 13 (1968) 479; Chem. Abstr., 69 (1968) 107321 g. 4 W. Szczepaniak, Organomercuric polymers as ion
9 10 11
12
exchangers. II. Ion exchange properties of a mercury containing divinylbenzene-styrene copolymer of macroporous structure, Poznan. Tow. Przyj. Nauk Pr. Kom. Mat.-Przyr., Pr.Chem., 12 (1971) 303; Chem. Abstr., 76 (1972) 73094n. J. Stamberg and H.P. Gregor, Synthesis and properties of mercury polyelectrolytes, Faserforsch. Texfiltech., 24 (1973) 101. H.T. Miles, E.R. Stadtman and W.W. Kielley, A resin for the selective retention of sulfhydryl compounds, J. Amer. Chem. Soc., 76 (1954) 4041. T.G. Traylor, Mercuration of aromatic polymers, J. Polym Sci., 37 (1959) 541. Catalog Bio-Rad Laboratories, 1983, catalog numbers 153-5101, 153-5199. Sigma Price List, Feb. 1986, product number H 3133. J. Stamberg and J. Pe~ka, Preparation of porous spherical cellulose, Reactive Polymers, 1 (1983) 145. J. Stamberg and S. SevEik, Chemical transformations of polymers. III. Selective hydrolysis of a copolymer of diethylene glycol methacrylate and diethylene glycol dimethacrylate, Collect. Czech. Chem. Commun, 31 (1966) 1009. J. Stamberg, V. Petrus and H.P. Gregor, Chemical transformations of polymers. XI. Mercuration of polystyrene, J. Appl. Polym. Sci., 23 (1979) 503.
133
A C O M P O S I T E S O R B E N T B A S E D O N BEAD CELLULOSE AND MERCURATED NOVOLAC aIhi LENFELD and JIRi STAMBERG Institute of Macromolecular Chemistry, C:echoslouak ,4 cader~O' of Sciences. 162 06 Prague 6 ( Czechoslot,akiaj (Received March 21, 1986: accepted in revised form August 1, 1986)
,4 composite material, bead cellulose-novolac, was prepared and transformed by mercuration with mercurv(II) acetate into a sorbent containing - H g + ion-exchange groups. The course of mercuration was followed by measuring the time and concentration dependence. Materials with various rnercury contents" were obtained, with the highest attained mercury content 35.4%. Even at the highest novolac content and degree of mercuration the sorbents showed high swelling in water. The sorption properties were investigated using the sorption of chloride anions from aqueous solutions b v measuring the time dependence of sorption and the sorption isotherm. The sorbent possesses a high rate of sorption in addition to the well-known high selectiuitv of mercurated polymer structures.
INTRODUCTION
Mercurated polymeric sorbents, and especially mercurated styrene-divinylbenzene copolymers and phenolformaldehyde polycondensates, are known sorption materials which are used as selective anion exchangers [1-4], but also as sorbents of urea [5] and organic compounds containing thiol groups [6], or as carriers of biologically active compounds. They can be prepared with comparative ease by polymer-analogous mercuration
[1,5,71. Mercurated phenolformaldehyde resins were prepared by Miles et al. [6], who used them in the separation of glutathione and cysteine. The separation efficiency was very good, but their application was limited because of the imperfect external shape and the unsatisfactory porous structure of these 0167-6989/87/$03.50
mercurated polymers. The sorbent consisted of small, irregular particles so that it could be introduced only into small laboratory columns. The mercurated resin was almost nonporous and did not swell in an aqueous medium, as is usual with mercurated polymers, so that the sorption efficiency was limited only to the external surface of the individual particles. In order to keep a sufficiently extensive active surface, the powder form could not be replaced with the granular form, as is common for other types of sorbents. Some types of polymeric sorbents containing covalently bound mercury are also commercially available. As affinity chromatographic material for the selective purification of proteins containing thiol groups, the firm Bio-Rad Laboratories offers the sorbent AffiGel 501 [8], which contains phenylmercury
¢~ 1987 Elsevier Science Publishers B.V.
134 groups bound to a spherical agarose carrier through a spacer. A sorbent supplied by Sigma (p-hydroxymercuribenzoate agarose) has a similar composition and purpose [9]. In this study we describe the preparation and properties of a new type of sorbent containing an organomercury polymer and based on the composite principle. High-porosity bead cellulose [10] and a phenolformaldehyde novolac-type condensate were the starting materials. Pores of bead cellulose are partly filled in with novolac, which is mercurated in a further stage. In the composite sorbent thus obtained the phenolic component is the carrier of sorption activity, and the cellulose matrix guarantees the required physical macro- and microstructure, i.e., the external shape of the individual particles and their porosity.
(those used for analytical purposes analytical purity grade only); all were used without further purification.
Preparation of bead cellulose-novolac composites An amount of 50 g of bead cellulose swollen in water and filtered under suction on a glass filter was washed in a column with 50 ml of ethanol for 5 h. An amount of 2 g of washed cellulose was filtered under suction on a glass filter and mixed with 20 ml of ethanolic solution of novolac at a given concentration. The mixture was shaken at room temperature for 24 h, the sample was filtered under suction, quickly washed with 20 ml of ethanol during suction and used in characterization measurements or mercuration.
Mercuration of composites EXPERIMENTAL
Starting materials Bead cellulose (BC) (United Chemical and Metallurgical Works, 0 s t i nad Labem, Czechoslovakia) is a spherical cellulose sorbent, prepared from technical viscose according to a method reported earlier [10] by a suspension procedure using the thermal sol-gel transition and regeneration with boiling water. Its properties were characterized by the following data: water regain, 5.32 g H 2 0 / g dry matter (i.e., dry matter content 15.8%); particle size, 0.125-0.5 mm. Novolak 70 (Moravian Chemical Works, Ostrava, Czechoslovakia) is a soluble phenolformaldehyde condensate (in the following referred to as "novolac"), the properties of which are characterized by the following data: the softening point according to Nagel, 70 _+ 5°C; free phenol content, 6-9%; viscosity of a 50% ethanolic solution, 50-100 cP. The other chemicals and solvents were chemically pure or analytical purity grade
The cellulose sample with novolac (2 g) was placed in a 50 ml reaction flask, and 20 ml of mercuration solution (composition: 25 g mercury(II) acetate, 10 ml 70% perchloric acid, 25 ml acetic acid, completed with water to a total volume of 250 ml) was added. The reaction was conducted with shaking at 25 ° C for 24 h. On completion of the reaction, the sample was washed with water, methanol and water again (until the washing water no longer showed the colour reaction of Hg 2+ ions with diphenylcarbazide); the water regain or the dry matter content in the centrifuged sample and the mercury content in the dry matter were then determined.
Time and concentration dependence of the mercuration of composites During the concentration dependence measurements, the concentrations of mercury(II) acetate and perchloric acid in the mercuration solution were varied while maintaining their molar ratio (HC104/(CH3COO)2Hg= 1.5).
135 In the time dependence studies, only the time between addition of the mercuration solution and its fast washing-out on the glass filter with 50 ml of water completing the mercuration was measured. The other conditions were the same as described in the preceding 'paragraph.
Preparati~,,e mercuration of the composite An amount of 40 g of bead cellulose saturated with a 50% novolac solution in ethanol was mercurated as described above. The product contained 34.5% of dry matter: the mercury content in the dry matter was 27.1%, i.e., 1.35 mmol H g / g dry matter. The product was kept in water. The sample used in the determination of the n o v o l a c - H g bond stability in a sorbent eluted with water was prepared by employing a procedure as described above, using a mercuration solution containing 1 g mercuric acetate per 250 ml of solution. The sample contained 2.44% Hg and its water regain value was 4.96 g H e O / g dry matter.
with distilled water in a column at a rate 20 ml w a t e r / h . The eluate thus obtained was analyzed for the mercury content.
Sorption of chlorides by a mercurated composite To measure the time dependence of sorption, the preparative sample was centrifuged: 1 g was placed in a 50 ml flask, and 20 ml of an aqueous sodium chloride at a concentration of 0.01 or 0.05 m o l / l was added. The mixture was shaken in a closed flask at 25 °C for a certain time, after which the concentration of chloride ions in the aqueous phase was determined by potentiometric titration with an A g N O 3 solution. The amount of CI that was sorbed was determined from the decrease in concentration. The procedure employed for the measurement of the sorption isotherm was similar. The contact time was 24 h, and the NaCI concentration in the aqueous phase was varied from 0.0001 to 0.5 mol/1.
Analytical methods Determination of the sorbent stability during washing The stabilities in an alkaline and an acid aqueous or ethanolic solvent were determined by washing of 0.5 g of the sample centrifuged from water with 50 ml of the respective solution or solvent in a column for one hour. After thorough washing with water (ca. 200 ml) the sample was dried and the mercury content was determined. In the case of benzene, there was a successive exchange of the solvents w a t e r - e t h a n o l - b e n z e n e - e t h a n o l water. The bond stability between novolac and mercury in an aqueous medium was determined by washing with water. Of the sorbent sample (2.44% Hg), 1 ml was washed
To determine the water regain or the dry matter content, 2 ml of the swollen sample in a weighed column [11] was centrifuged (10 min, 900 g), weighed, dried (25°C, 13.3 Pa, 24 h), and weighed again. From the data thus obtained, the dry matter content (in percent) or the water regain (in g H x O / g dry matter) were calculated. The mercury content was determined gravimetrically. The sample was burned on a platinum gauze in a stream of oxygen, and the released mercury vapours were trapped on a gold foil. The mercury content was calculated from the increase in weight of the foil. During the investigation of the novolac Hg b o n d stability, the mercury content in the eluate was determined by atomic absorption spectroscopy.
136
RESULTS AND DISCUSSION
Preparation of the composite sorbent Preparation of the composite sorbent consisting of bead cellulose and mercurated phenolformaldehyde condensate of the novolac type may be divided into two steps. In the first step, introduction of an alcoholic solution of novolac into pores of bead cellulose leads to the formation of a basic composite material, which in the second step undergoes a polymer-analogous mercuration. The first step is preceded by an exchange of water for ethanol in the swollen and never-dried cellulose. The amount of novolac introduced into bead cellulose depends in particular on the volume and concentration of the novolac solution and on the contact time. Novolac was introduced into cellulose by a one-stage equilibration with a ten-fold excess volume of solution over that of cellulose. Quantitatively, the process was followed gravimetrically, by determining the dry matter in the composite material formed; it is of importance that even with a 50% novolac solution used, the resulting material still had a high degree of swelling (Table 1). TABLE 1 Effect of concentration of novolac solution on properties of composite sorbent Properties of original bead cellulose: water regain, 5.32 g HzO/g: dry matter content after exchange of water for ethanol, 20.3% Dry matter Water regainb Hg content Novolac g H 20/g in dry concentra- content (EtOH) a matter b % tion, %
%
10 20 50
21.4 25.2 30.2
3.54 2.69 1.44
12.2 19.8 33.5
Determined after saturation of bead cellulose with ethanolic solution of novolac. b Determined after mercuration.
The composite samples thus obtained were subjected to polymeranalogous mercuration. Mercuration with mercury(II) acetate proceeds on aromatic nuclei of novolac and may be described by Scheme 1. This reaction pro-
CH2
+ (CH3COO)2Ng CH3COOH--HCIO4
CH2 Hg+-OCOCH3
Scheme 1.
ceeds readily also at room temperature, due to the catalytic effect of perchloric acid, which together with mercury(II) acetate forms a reactive complex CH3COOHgC104 [12]. An insoluble mercurated polymer is formed in cellulose pores when the mercuration solution comes into contact with novolac. The chemical transformation is thus accompanied by the immobilization of a fine precipitate of mercurated novolac in cellulose macropores. We used reaction conditions leading to the highest degree of mercuration in order to be able to characterize the effect of concentration of the novolac solution on the attainable mercury content in the final product. The results summarized in Table 1 suggest that the mercury content increases with the novolac content, while the comparatively high degree of swelling in water remains preserved. In order to obtain a sorbent with a sufficiently high sorption capacity, further experiments were carried out, this time using only bead cellulose saturated with a 50% novolac solution in ethanol. The mercuration process itself was investigated in greater detail by measurements of the dependence on time and concentration of the reaction. Figure 1 shows that the reaction was completed after approximately six hours. In the same figure one can also see the dependence of water regain of the mercurated composite on time. The results confirm once again that even with a high degree of
137 ]
T
.~ o -r-
.~
_ 30 -~o
~
t)
2 -2 10
©
l 0
(~--0
I(ii
5
I
10 15 25 reachon time ~ h
Fig. 1. Time dependence of mercuration of composite.
mercuration the sorbent may sufficiently swell in water. The dependence of the transformation on the concentration of the mercurating agent (Fig. 2) indicates the possibility of preparation of mercurated sorbents with various mercury cont,mts from the same starting composite. Another possibility is the use of cellulose samples containing different amounts
I
I
_ 30
c o u
c~ I
of novolac, which are suitable in those cases where organomercury ion exchangers possessing higher or optional degrees of swelling or a low mercury content are to be obtained. The curve in Fig. 2 also suggests that even the highest concentration of mercury(II) acetate in the mercuration solution used (9%) did not result in the highest possible degree of mercuration. However, the rise in the mercury content attainable by employing a higher concentration of mercury(II) acetate is small. A comparison of the results described above provides information on the reproducibility of the whole process of preparation of the composite mercurated sorbent. Under virtually the same conditions, samples containing 33.5% Hg (cf. Table 1), 32.2% Hg (Fig. 1) and 35.4% Hg (Fig. 2) were obtained. A preparative sample for sorption measurements containing 27.1% Hg was prepared under somewhat different conditions (twenty times larger charge). Scatter of these values is comparatively large. The main cause of these differences is the procedure employed in the preparation of the starting composite material, where--after saturation of bead cellulose with an ethanolic solution of novolac--the sample is washed with pure ethanol to prevent the conglomeration of particles. The washing, even if performed in a standard manner, is accompanied by an uncontrollable partial removal of novolac from the beads, which is the cause of the observed differences. Sorption measurements
20
~0
,O
I
I
5
~0 Hg(OAc)2 ~ %
Fig. 2. Concentration dependence of mercuration of composite.
Mercurated polymers can be used as selective anion exchangers [2-6]. Their effectiveness is derived from the ability of organomercuric salts to form undissociated compounds with halides, thiocyanates, cyanides, sulfides, and mercaptides. The sorption properties of the sorbent were characterized by the sorption of chloride anions from aqueous solutions of sodium chloride, which can be described by Scheme 2.
138
CH
+
+ CH3COONa
CH
NaCI
Hg÷ -CI
Hg + -OCOCH3
Scheme 2.
The sorption process was investigated by analyzing the aqueous phase, i.e., by determining the loss of chloride anions in the sorption solution. Only dilute solutions were used, for which the loss of chloride anions could be determined with sufficient reliability. The rate of sorption was measured using a preparative sample of the mercurated sorbent in sodium chloride solutions of concentrations 0.01 and 0.05 mol/1. The dependen,.es in ~ ,g. 3 clearly show the high rate of sorption. The half-time of sorption is approximately 30 s, while, for example, the half-time of sorption determined for the mercurated macroreticular styrene-divinylbenzene copolymer Amberlite XAD-2 (23.5% Hg, 0.035 mol NaC1/1, 25°C) was 5 min [1]. Such a pronounced difference in the sorption kinetics is a consequence of the hydrophilicity
I
I
of the composite sorbent caused by the presence of the cellulose skeleton. The sorption properties of the composite ion exchanger are also made evident by the sorption isotherm (Fig. 4). The highest possible capacity of the ion exchanger (100%) has been derived from the mercury content in the measured sample (1.35 mmol H g / g dry matter). If these results are compared with the already mentioned mercurated Amberlite XAD-2, it can be seen that in the case of the mercurated composite sorbent based on cellulose the utilization of the mercury is better (with mercurated Amberlite XAD-2, only ca. 65% of the mercury was utilized). On the other hand, however, the affinity of the mercurated cellulose composite with respect to chloride anions is somewhat poorer than that of the mercurated Amberlite XAD-2; with a 0.1 mol/1 NaC1 solution, only 50% of the maximal capacity was reached for the cellulose composite, while for Amberlite XAD-2 the value was over 90%. The high affinity of the mercurated composite sorbent for chloride anions becomes evident especially at low concentrations. This is illustrated by the differences between experimental and calculated values of the sorption isotherm in Fig. 4.
JJ I
Stability ~,
T0. E
A
0.05 mol NaCL/[
L)
0.01 moL NaCI/I
jj •
Z.
i C..;,
O--4~3-
43
0.2
I 30 sorption
I j~ I 60 1440 tirne~ min
Fig. 3. Time dependence of sorption of chloride ions by mercurated composite.
Data on the stability of the sorbent in an alkaline and an acid medium and in some organic solvents are summarized in Table 2. These data are important particularly with respect to the contingent regenerability of the ion exchanger after sorption. By treatment with aqueous NaOH (0.1 m o l / l ) the novolac phase is completely washed out off the composite; at lower NaOH concentration less novolac is eluted. This was to be expected because of the known solubility of novolac and of hydroxyphenyl-mercuric hydroxides in dilute sodium hydroxide. Replacement of water with ethanol at the same NaOH con-
13 ~) T
1
r
100
~o
vo Q)
s0k
L
0.0001
I
0.001
0.01
0.1 C [ - moUl
1.0
Fig. 4. Sorption isotherm of sorption of chloride ions by mercurated composite at 25 ° C. e: experimental values: - - : calculated Langmuir-type isotherm.
centration considerably reduces the effect of the alkali. In other media the sorbent is comparatively stable, and a decrease in the mercury content is not pronounced, compared with the starting material. These results are only preliminary, of course: to a great extent, they only bear evidence as to the stability of the composite sorbent as a whole and not to the stability of the covalent bond
between novolac and mercury. In this respect the situation can be adequately' described by measurement of the water extract of one sample of mercurated sorbents with a lower mercury content (2.44%, Hg). It was found that the yield is 28.7/xg Hg/1 eluate from 1 ml of the sample, The instability of the sorbent in an alkaline medium also presents an important problem in its applications. A consequence of this instability is that the sorbent which has been used in, for example, the sorption of halides cannot be regenerated in the usual way, i.e., by the reaction - H g ~ C I + N a O H - - - * -Hg ~ O H + N a C 1 Therefore, the procedures to be considered are, in particular, single applications with no regeneration assumed or such applications in which a multistage regeneration procedure rec o m m e n d e d for commercial organomercuric sorbents is no drawback [8,9]. There is not doubt that the sorbent would prove useful, e.g., in the separation of mercaptans as described by Miles et al. [6], for analytical purposes, in laboratory-scale chromatographic processes, or as a cleansing sorption-active medium for single use. CONCLUSION
TABLE 2 Stability of sorbent in washing Washing medium
Hg content
Type
Concentration,
NaOH/H20 N a O H / H 20 NaOH/ethanol NaOH/ethanol HC 1 / H 20 Acetone 1,4-Dioxane Benzene h
0.1 0.01 1.0 0.1 1.0
tool/1
in sorbent after washing ~, 0 24.0 21.0 21.8 26.5 26.0 25.5 26.5
" Hg content in sorbent before washing 27.1%. ~' Successive exchange of solvents water ethanol-benzene -ethanol-water.
The mercurated composite sorbent based on bead cellulose and phenolformaldehyde novolac-type condensate is a new sorption material, combining functional properties of mercurated novolac with the hydrophilicity, porosity and spherical shape of bead cellulose. Its particular advantages are the high rate of sorption and good selectivity, which predetermine its use in the sorption from dilute aqueous solutions. A certain shortcoming is seen in its lower stability in alkaline medium, which impairs the possibilities of regeneration and reduces the range of its applicability, restricting it mainly to single-sorption or sorption-desorption processes.
140
ACKNOWLEDGEMENT
The authors thank Mrs. E. Kni~flkovfl, M.Sc, for analyses of mercury contents, and their colleagues in the Water Research Institute, Prague, and Research Institute for Veterinary Medicine, Brno, for determinations of the mercury extract from the sorbent.
REFERENCES
5
6
7 8
1 J. Lenfeld, J. Pe~ka and J. Stamberg, Surface oriented mercuration of poly(vinylaromatics), Reactive Polymers, 1 (1982) 47. 2 A.G. Pashkov, V.F. Alexandrova, M.I. Itkina and I.G. Stebeneva, Synthesis and investigation of mercurated copolymers, Plast. Massy, No. 3 (1967) 19. 3 W. Szczepaniak, Organomercuric polymers as ion exchangers. I. Anion exchange properties of mercurated styrene-divinylbenzene copolymers, Chem. Anal. (Warsaw), 13 (1968) 479; Chem. Abstr., 69 (1968) 107321 g. 4 W. Szczepaniak, Organomercuric polymers as ion
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12
exchangers. II. Ion exchange properties of a mercury containing divinylbenzene-styrene copolymer of macroporous structure, Poznan. Tow. Przyj. Nauk Pr. Kom. Mat.-Przyr., Pr.Chem., 12 (1971) 303; Chem. Abstr., 76 (1972) 73094n. J. Stamberg and H.P. Gregor, Synthesis and properties of mercury polyelectrolytes, Faserforsch. Texfiltech., 24 (1973) 101. H.T. Miles, E.R. Stadtman and W.W. Kielley, A resin for the selective retention of sulfhydryl compounds, J. Amer. Chem. Soc., 76 (1954) 4041. T.G. Traylor, Mercuration of aromatic polymers, J. Polym Sci., 37 (1959) 541. Catalog Bio-Rad Laboratories, 1983, catalog numbers 153-5101, 153-5199. Sigma Price List, Feb. 1986, product number H 3133. J. Stamberg and J. Pe~ka, Preparation of porous spherical cellulose, Reactive Polymers, 1 (1983) 145. J. Stamberg and S. SevEik, Chemical transformations of polymers. III. Selective hydrolysis of a copolymer of diethylene glycol methacrylate and diethylene glycol dimethacrylate, Collect. Czech. Chem. Commun, 31 (1966) 1009. J. Stamberg, V. Petrus and H.P. Gregor, Chemical transformations of polymers. XI. Mercuration of polystyrene, J. Appl. Polym. Sci., 23 (1979) 503.