Articles Anal. Chem. 1996, 68, 2459-2463
Characterization of Nonmicrobiological Paper Mill Deposits by Simultaneous TG-IR-MS Jeffrey M. McGuire* and Craig C. Lynch
Hercules Incorporated, Research Center, 500 Hercules Road, Wilmington, Delaware 19808-1599
The problem of deposits and their identification is one of the most persistent ones facing paper mills. Materials other than fibers accumulate in closed water circulation systems and may appear as impurities in pulp and paper or can contaminate wires and felts or build up deposits at various points in the mills. Traditionally, chromatographic and spectroscopic methods have been employed in the analysis of deposits and other pulp and paper process impurities. Simultaneous thermogravimetryinfrared-mass spectrometric (TG-IR-MS) analysis is a relatively new technique which, when applied to the analysis of mill deposits, provides a rapid means of identifying the source of these contaminants. The accumulation and deposition of materials other than fibers in the paper-making process can be extremely detrimental. To preserve machine runnability and paper quality, many mills maintain rigorous deposit control programs. These programs often include the use of microbiocides to eliminate microbiological deposits and other additives to inhibit the formation of inorganic (scale) and organic deposits.1,2 However, as changes are made in the process, such as revisions in the sizing system or modifications in the retention system, deposits may occur. Rapid characterization of these impurities is essential in order to reduce lost production of off-specification products. Current technologies used to characterize deposits found in paper products and on equipment in pulp and paper mills include solvent extraction followed by fractionation,3 pyrolysis gas chromatography4,5 (Py-GC), size-exclusion chromatography6 (SEC), and various spectroscopic techniques.7 Simultaneous thermogravimetry-mass spectrometry (TGMS)8,9 and thermogravimetry-Fourier transform infrared spectroscopy (TG-IR)10,11 are powerful techniques that combine the direct measurement of weight loss as a function of temperature (1) Glazer, J. A. Tappi J. 1991, 74, 72-74. (2) Nigrelli, A. S. Pulp Pap. 1990, 64, 68-72. (3) Dorris, G. M.; Douek, M.; Allen, L. H. J. Pulp Pap. Sci. 1985, 11, 149-154. (4) Sithole´, B. B.; Allen, L. H. J. Pulp Pap. Sci. 1994, 20, 168-172. (5) Hardell, H.-L. J. Anal. Appl. Pyrolysis 1993, 27, 73-85. (6) Sjo¨stro¨m, J.; Holmbom, B. J. Chromatogr. 1987, 411, 363-370. (7) Dwars, W. T. A. Print. Reprogr./Test. Conf., (Pap.) 1977, 151-153. (8) Leskela¨, M.; Lippmaa, M.; Niinisto ¨, L.; Soininen, P. Thermochim. Acta 1993, 214, 9. (9) Chung, H. L.; Aldridge, J. C. Anal. Instrum. 1992, 20, 123-135. (10) Solomon, P. R.; Serio, M. A.; Carangelo, R. M.; Bassilakis, R.; Yu, Z. Z.; Charpenay, S.; Whelan, J. J. J. Anal. Appl. Pyrolysis 1991, 19, 1-14. S0003-2700(96)00224-7 CCC: $12.00
© 1996 American Chemical Society
with the use of sensitive spectroscopic detectors. Such combined systems permit both qualitative and quantitative determinations of evolved volatile products. Recently, a simultaneous TG-IR-MS system has been developed and utilized for the examination of lignite coal.12 A specially constructed heated transfer line assembly allowed direct coupling of a Perkin-Elmer Model 7 thermogravimetric analyzer (TGA) to the injection port of a commercial GC-IR-MS system. We have designed and assembled a similar system in our laboratory using a TA Instruments Model 951 TGA, and we wish to report four separate applications of simultaneous TG-IR-MS to the characterization of deposits from paper mills and paper products. EXPERIMENTAL SECTION The TG-IR-MS configuration employed for this study consists of a standard Hewlett-Packard GC-IR-MS system (including the Models 5890A GC, 5965B IRD, and the 5970B MSD), coupled to a TA Instruments Model 951 TGA. Figure 1 illustrates the configuration of the various components of this system. Basically, the transfer line uses a 0.32-mm deactivated fused silica capillary enclosed in an 1/8-in. stainless steel sleeve to carry TG effluent to the GC oven. The sleeve is enclosed in a 1/4-in. copper tube which permits a connection to the TGA quartz furnace tube and the inlet block of the GC. The entire transfer line is surrounded by a thermal jacket and maintained at 300 °C. Helium flow rate through this transfer line is controlled by a needle valve on a vent line from the outlet of the TGA furnace tube. This vent line contains a particulate filter and serves as a controlled condensation zone, preventing contamination and potential plugging of the needle valve. A three-way valve is mounted on the gas inlet of the TGA. This provides a means to backflush the quartz furnace tube and prevent air from entering the system when the TGA is opened. The total helium flow through the TGA is typically 60-100 mL/min, with 7-10 mL/ min traversing the transfer line and entering the IRD. Once inside the GC oven, the 0.32-mm capillary is connected to the IRD flow cell in a conventional manner. The IRD flow cell outlet is connected in series with the MSD via a 0.1-mm deactivated fused silica capillary. All heated zones are maintained at 300 °C. (11) DeGroot, W. F.; Pan, W. P.; Rahman, M. D.; Richards, G. N. J. Anal. Appl. Pyrolysis 1988, 13, 221-231. (12) Buchanan, R. M.; Holbrook, K. M.; Meuzelaar, H. L. C.; Leibrand, R. Hewlett Packard Application Brief, 1991; IRD 91-4.
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Figure 1. Schematic diagram of TG-IR-MS instrument configuration.
Figure 2. Thermogravimetric curve of roller deposit (sample 1).
The TGA uses 5-10-mg samples with a heating rate of 20 °C/ min. IR spectra are acquired every second while scanning from 4000 to 550 cm-1 with a resolution of 8 cm-1. Mass spectra are acquired in the electron impact mode (70 eV) every second while scanning from 10 to 800 Da.
Figure 3. Averaged infrared spectrum (a) and mass spectrum (b) of evolved volatiles from 600 °C to 1000 °C from roller deposit (sample 1).
and writing qualities of the paper.13 As shown below, the AKD is hydrolyzed by water to give a mixture of ketones.14
RESULTS AND DISCUSSION The first deposit was taken from a roller in the wet end of a Fourdrinier paper machine. Figure 2 shows the thermogravimetric curve obtained from the TG-IR-MS analysis. The TG data show the weight loss plotted as a function of temperature. It is immediately obvious that a substantial portion of the deposit is inorganic. Over 40% of the sample weight remains even after heating to 1000 °C. Furthermore, the infrared and mass spectra of the species evolved between 600 and 1000 °C indicate primarily CO2, as shown in Figure 3. This CO2 loss is most likely due to the decomposition of calcium carbonate, a typical filler used in alkaline paper-making. A subsequent analysis of a chloroforminsoluble fraction of this deposit by IR alone confirmed a mixture of calcium carbonate and talc. The organic portion of this deposit has been identified as the hydrolyzate of alkylketene dimer (AKD). AKD is a reactive sizing agent added to the pulp slurry in order to improve the printing 2460
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Figure 4 shows the infrared and mass spectra taken at a temperature of 300 °C. These spectra are typical of the AKD hydrolysis products.15 The mass spectrum in particular is very characteristic of the long-chain aliphatic ketones. Intense fragment ions due to R-cleavage and formation of acylium ions RCtO+ are observed at m/z 239 and 267, while a “McLafferty + 1” rearrangement gives rise to ions at m/z 255 and 283. The low molecular weight ions (m/z 41, 43, 55, 57, etc.) are due to alkyl chain fragments. (13) Davis, J. W.; Roberson, W. H.; Weisgerber, C. A. Tappi J. 1956, 39, 2123. (14) Sithole´, B. B.; Nyarku, S.; Allen, L. H. Analyst 1995, 120, 1163-1169. (15) Dart, P. J.; McCalley, D. V. Analyst 1990, 115, 13-16.
Figure 4. (a) Infrared spectrum of AKD hydrolysate taken at 300 °C. (b) Mass spectrum of AKD hydrolyzate taken at 300 °C.
Figure 5. Thermogravimetric curve of ASA filter deposit (sample 2).
The second sample analyzed was a deposit taken from a filter in a mill using ASA sizing agent. Alkenylsuccinic anhydride (ASA) is also used as a reactive sizing agent in paper-making. ASA-type sizes are obtained by heating maleic anhydride with R-olefins or internal olefins:
Figure 5 shows the TG curve obtained from the TG-IR-MS analysis. Unlike the AKD deposit, the thermogravimetric data indicate that the majority of this deposit sample is organic in nature, with only a 7.5% residue after heating to 1000 °C. The residue is most likely due to an inorganic filler. In addition to several minor weight losses, a major weight loss (∼70%) occurs between 200 and 350 °C. Figure 6 shows typical infrared and mass spectra of the volatiles evolved between these temperatures. The mass spectrum is similar to that obtained by Brinen16 from pilot paper machine paper containing ASA as internal size. Of particular importance is the m/z 322 ion, which has been ascribed by Brinen to the loss of CO from a parent (16) Brinen, J. S. Nord. Pulp Pap. Res. J. 1993, 1, 123-129.
Figure 6. Averaged infrared spectrum (a) and mass spectrum (b) of evolved volatiles from 200 to 350 °C from ASA filter deposit (sample 2).
Figure 7. Thermogravimetric curve of methylene chloride-extracted spot on liquid packaging board (sample 3).
molecule. This ion may also arise from loss of CH2O2 from a dicarboxylic acid,17 since ASA reacts rapidly with water to form a diacid hydrolysis product.18 Furthermore, the presence of the
dicarboxylic acid may explain the observance of CO2 in the infrared spectrum (Figure 6a), which would result from partial thermal decarboxylation. The hydrolysis product of ASA is a poor sizing agent, and depending on the alkalinity during the paper-making process, organic salts could be formed preferentially over the carboxylic acid,16 leading to deposit formation. In another example demonstrating the utility of simultaneous TG-IR-MS, the methylene chloride extract of a spot from a liquid packaging board was characterized. Figure 7 shows the TG curve obtained and indicates that the sample is organic in nature, since complete vaporization occurs by 600 °C. Typical infrared and (17) McLafferty, F. W. Interpretation of Mass Spectra, 3rd ed.; University Science Books: Mill Valley, CA, 1980; p 207. (18) McCarthy, W. R.; Stratton, R. A. Tappi J. 1987, 70, 117-121.
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Figure 8. Averaged infrared spectrum (a) and mass spectrum (b) of evolved volatiles from 150 to 400 °C from sample 3.
Figure 9. Thermogravimetric curve of methylene chloride extract from paper used in cartons (sample 4).
mass spectra of the volatiles evolved between 150 and 400 °C are shown in Figure 8. The spectra are representative of a paraffinic oil. Aliphatic hydrocarbons are routinely used as carriers in defoamer formulations.19 Defoamers are common process additives in the pulp and paper industry. In a final example illustrating the usefulness of this technique, a paper mill experienced a loss in sizing efficiency of a laminated paper product used in liquid packaging cartons. Preliminary tests indicated that a residual surfactant might be present on the paper surface, and a methylene chloride extract of the delaminated paper was analyzed. Figure 9 shows the TG curve obtained from the TG-IR-MS analysis of the extract. Again, the sample appears to be predominantly organic in nature, although a small residue (∼4%) remains after heating to 1000 °C. Figure 10 shows the infrared and mass spectra of the volatiles evolved between 200 and 400 °C. The spectra are indicative of an N,N-dimethyl-substituted amine. Upon closer examination of the mass spectral data, tentative molecular ions were identified at m/z 373 and 297. By inspecting the extracted ion profiles (ion intensity plotted as a function of time) for these two ions, it was possible to determine at what temperatures maximum volatility was achieved for these species and thus obtain individual spectra. Figure 11a shows the mass spectrum for the m/z 373 species taken (19) Kroschwitz, J. I.; Howe-Grant, M. Kirk-Othmer Encyclopedia of Chemical Technology, 4th ed.; John Wiley & Sons: New York, 1993; Vol. 7, p 928.
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Figure 10. Averaged infrared spectrum (a) and mass spectrum (b) of evolved volatiles from 200 °C to 400 °C from sample 4.
Figure 11. (a) Mass spectrum of m/z 373 species taken at 325 °C. (b) Mass spectrum of m/z 297 species taken at 215 °C.
at 325 °C, while Figure 11b shows the mass spectrum for the m/z 297 species taken at 215 °C. The m/z 297 species has been unambiguously identified as N,N-dimethyloctadecanamine on the basis of a comparison of the spectrum with a known library spectrum. The m/z 373 species has been tentatively identified as N-methyl-N-benzyloctadecanamine,
The base peak, m/z 134, arises from R-cleavage (a dominant reaction of amines) and formation of an immonium ion,
Likewise, the m/z 91 ion arises from R-cleavage and formation of the C7H7+ ion. Based on the identification of these two amines and a third species, (chloromethyl)benzene (C6H5CH2Cl), the extracted contaminant was identified as an alkylbenzyldimethylammonium chloride, R(C6H5CH2)N+(CH3)2Cl-, where R ) C18H37. This quaternary ammonium salt is representative of a class of surfac-
tants known as benzalkonium chlorides, with wide-spectrum antimicrobial activity.20 The amines and (chloromethyl)benzene observed have been rationalized as thermal decomposition prod-
ucts of the quaternary salt. A similar mechanism has been previously postulated by Charlier et al. for the dequaternization of dodecyltrimethylammonium iodide.21 Identification of methyl chloride was not possible due to its coevolution with the (chloromethyl)benzene. CONCLUSIONS Simultaneous TG-IR-MS has proven to be an excellent analytical tool for the rapid characterization of contaminants in paper mills. The technique can provide both qualitative information regarding the composition of evolved volatiles, based on (20) Reference 19, Vol. 8, p 257. (21) Charlier, P.; Je´rome, R.; Teyssie´, P.; Prud’homme, R. E. J. Polym. Sci., Part A: Polym. Chem. 1993, 31, 129-134.
interpretation of the spectroscopic data, and quantitative data on the organic/inorganic nature of the deposit from the thermogravimetric curve. For most samples, minimal preparation is required prior to analysis, and in certain cases the samples may be analyzed “as received”. With the current configuration of our instrument, it is also possible to quickly return the system to a GC-IR-MS mode of operation. Two GC injection ports are available, and separate operation of the TGA and GC-IR-MS instruments is achieved by merely exchanging capillary columns. Furthermore, efforts are currently underway to interface the thermogravimetric analyzer to the GC-IR-MS system via a chromatographic column in order to achieve the triply hyphenated technique of TG-GCIR-MS. ACKNOWLEDGMENT The authors thank Phillip J. Powis, Charles A. Potter, and James R. Personti for their valuable suggestions in the construction of the system, and Joan B. Updyke for providing the samples for analysis. This article is Hercules Research Center Contribution No. 2271. Received for review March 7, 1996. Accepted April 30, 1996.X AC960224T X
Abstract published in Advance ACS Abstracts, June 1, 1996.
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