Environ. Sci. Technol. 1093, 27, 332-343
Isolation of Macromolecular Chlorolignosulfonic Acids and Lignosulfonic Acids from Pulp Mill Effluents and the River Rhine Using XAD-8 Macroporous Resin and Ultrafiltration Willem M. van Loon* and Jaap J. Boon Unit for Mass Spectrometry of Macromolecular Systems, FOM-Institute for Atomic and Molecular Physics, Kruislaan 407, 1098 SJ Amsterdam, The Netherlands Rob J. de Jong and Bob de Groot
Laboratory for Special Research, Water Transport Company Rijn-Kennemerland (WRK), Groenendael 6, 3439 LV Nleuwegeln, The Netherlands Dissolved chlorolignosulfonic acids and lignosulfonic acids in pulp mill effluents and the river Rhine can be isolated effectively by XAD-8 adsorption chromatography combined with ultrafiltration. Satisfying XAD-8 recoveries (55-78% of UVZ8,, absorbance) of pulp mill effluent, chlorolignosulfonic acid, and lignosulfonic acid are obtained using a sample pH of 1. A 0.1 M NaOH methanol (50/50 v/v) mixture is recommended as a stan ard eluent for XAD-8 chromatography because of its quantitative, reproducible, and rapid desorption properties. Ultrafiltration (MW cutoff 1000) gives a significantly higher retention of chlorolignosulfonic acids compared to aquatic humic substances. Pyrolysis-mass spectrometric (Py-MS) structural characterization of isolated chlorolignosulfonic acids reveals the presence of many mono- and dimethoxyphenol substructures and of sulfonic acid groups. In addition, pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) of the chlorolignosulfonic acids shows the presence of several chlorinated guaiacyl substructures. This isolation procedure probably can also be applied to kraft lignins dissolved in surface waters.
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Introduction There is considerable environmental interest in the large amounts of chlorolignins and lignosulfonic acids discharged by pulp mills worldwide (1). Pulp mills produce bleached or unbleached cellulose pulp by the extraction of the brown-colored lignins from wood using many kinds of pulping (2) and bleaching (3) processes. Lignosulfonic acids are macromolecular (MW >1000) lignins which are sulfonated and subsequently dissolved during sulfite pulping processes (2). Chlorolignosulfonic acids are lignosulfonic acids which remain in the cellulose pulp after sulfonation and which are chlorinated and extracted during subsequent chlorine bleaching steps (3). Chlorothiolignins are here defined as chlorinated lignins which are produced during kraft pulping and bleaching processes. Seven major sulfite pulp mills in Germany, France, and Switzerland discharge large amounts of chlorolignosulfonicacids and, to a lesser extent, lignosulfonic acids into the river Rhine (4). It has been calculated that their organic halogen discharge may account for 90% of the adsorbable organic halogen (AOX) concentration of this river system (4). The isolation of dissolved chlorothiolignins is not investigated in this paper since these compounds are not discharged into the Rhine. For brevity, chlorolignosulfonic acids and lignosulfonic acids are referred to as chlorolignosulfonic acids in this paper. The environmental interest in chlorolignosulfonic acids and chlorothiolignins is primarily fueled by their potential toxicity. It has been demonstrated that partial degradation of chlorothiolignins (5) and chlorolignosulfonic acids (6) by microorganisms into toxic chlorophenols and chloro332 Environ. Scl. Technol., Vol. 27, No. 2, 1993
guaiacols occurs. Furthermore, chlorolignosulfonic acids are very hydrophilic macromolecules due to their high sulfonic acid content. Consequently, it can be expected that only a minor fraction of the dissolved chlorolignosulfonic acids is removed from the water phase by adsorption onto particulate organic carbon or sediment or by water treatment processes. Therefore, it is expected that chlorolignosulfonic acids are present in drinking water if the river water source contains these macromolecules. For these reasons, many waterworks situated on the Rhine pursue the reduction of the chlorolignosulfonic acid concentrations in their water source. Due to the lack of analytical procedures for chlorolignosulfonicacids in river and drinking water, the waterworks Watertransport Co. Rijn-Kennemerland (WRK) initiated a research program on the isolation and the quantitative analysis of macromolecular chlorolignosulfonic acids in sulfite pulp mill effluents, in the Rhine and in drinking water. In the framework of this program, this paper describes an optimized isolation procedure for dissolved chlorolignosulfonic acids. Many analytical procedures have been developed for the isolation and characterization of chlorolignosulfonic acids and lignosulfonic acids in pulp mill effluents (4). In contrast, only a few isolation procedures for lignosulfonic acids in river water have been reported. Eberle and Schweer reported an ion-pair extraction procedure for lignosulfonic acids in river water (7).Their procedure was adopted by Wagner and Hoyer (8)and by Sontheimer and Wagner (9). Although these ion-pair extracts are suitable for UV analysis, they contain large amounts of inorganic anions. For this reason, these extracts are unsuitable for, for example, analytical pyrolysis (IO). In conclusion, no isolation procedure for macromolecular chlorolignosulfonic acids from river or drinking water that is compatible with analytical pyrolysis is available. In contrast with chlorolignosulfonicacids, many isolation procedures for oligomeric and high molecular weight aquatic humic substances have been reported and reviewed ( I I , I 2 ) . Adsorption procedures using XAD-8 macroporous acrylic ester polymer resins are generally recommended for the isolation of aquatic humic substances (11, 12). XAD-8 adsorption chromatography has been applied to kraft lignins in pulp mill effluents (13). The application of XAD-8 Chromatography to dissolved chlorolignosulfonic acids has been suggested (4) but has never been reported. Weak anion exchangers have been recommended for the isolation of humic and fulvic acids (14). However, the desorption step introduces large amounts of inorganic salts into the sample and additional desalting using XAD-8 adsorption chromatography is required (14). Ultrafiltration and reversed osmosis are used for the isolation of DOC and give high yields (12,15).However, a low concentration of dissolved inorganic salts is essential for the successful
0013-936X/93/0927-0332$04.00/0
0 1993 American Chemical Society
application of these procedures (15). Ultrafiltration is very suitable as a molecular size fractionation technique (16) and is preferred over size-exclusion chromatography by many authors. Advantages of ultrafiltration are its reproducibility, simplicity, and preparative scale and the occurrence of much less solute-ultrafilter interactions compared to solute-stationary-phase interactions in sizeexclusion chromatography (16). The combination of XAD-8 adsorption chromatography and ultrafiltration has been proposed to obtain high molecular weight hydrophobic acid fractions from river water (12). In-source platinum filament pyrolysis-mass spectrometry (Py-MS) is a mass spectrometric technique in which polymeric materials are thermally degraded into monomeric and oligomeric structural units inside the ion source. Py-MS has been used frequently for the structural characterization of synthetic polymers and bio- and geopolymers (17). Advantages of this technique are the acquisition of general structural information (functional groups, major monomeric and oligomeric units), low compound losses due to in-source pyrolysis, temperature-resolved pyrolysis information (25-900 "C), small sample sizes (1-5 Hg), and speed (analysis time 1-2 min). Due to the low electron impact (EI) ionization energy (14-16 eV), fragmentation of aromatic compounds is low and the interpretation of the Py-MS spectra is improved. Disadvantages of this technique are that unambigious structural assignments to m / z values is often not possible due to overlap of isobaric compounds and their fragment ions, and consequently, quantification of pyrolysis products often is a complicated task. Furthermore, ion source contamination occurs more rapidly compared to pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS). Py-GC-MS is a MS technique in which pyrolysis products are separated prior to MS detection. The pyrolysis process may be based on Curie-point pyrolysis, using reproducible and rapid heating of a ferromagnetic wire by radiofrequency energy to a fixed Curie-point temperature, or on filament pyrolysis in which a platinum filament is resistively heated by a programmable current. Py-GC-MS is a well-known technique for the structural characterization of synthetic polymers and bio- and geopolymers (18,19). More specifically,several reports on the Py-GC-MS characterization of chlorolignosulfonic acids (4,20,21) have appeared. Advantages of Py-GC-MS are that detailed structural information on macromolecules, on at least the monomeric level, can be obtained reproducibly. The GC separation of pyrolysis products enables their unambiguous identification. This paper presents the use of XAD-8 adsorption chromatography and ultrafiltration for the isolation of macromolecular chlorolignosulfonicacids from sulfite pulp mill effluents and from river water. The performance of the isolation procedure is evaluated with respect to the yield of chlorolignosulfonicacids and the reproducibility, the desalting, and the selective removal of coisolated aquatic humic substances. Py-MS and Py-GC-MS are used to structurally investigate the chlorolignosulfonic acids isolated from pulp mill effluents and the DOC isolated from the Rhine. Experimental Procedures Materials. Lignosulfonic acid was obtained from Roth (Karlsruhe, FRG). Chlorolignosulfonic acid was synthesized by addition of 8.1 mL of NaOCl solution (Janssen Chimica, Beerse, Belgium; 1.3% chlorine w/w) to a sodium lignosulfonate solution (220 mg/ 100 mL). Under stirring and pH control, the pH was titrated from 11to 6 using 0.03 M HC1 and an addition flow rate of 1mL/min. [At pH
4-8,OCl- is converted into the reactive HOC1 species (22); at pH
