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Ind. Eng. Chem. Res. 2001, 40, 60-66
KINETICS, CATALYSIS, AND REACTION ENGINEERING Wet Oxidation of Aqueous Polyvinyl Alcohol Solution Yang-Soo Won,† Sung-Ok Baek,† and Javad Tavakoli*,‡ Department of Environmental Engineering, Yeungnam University, Kyungsan City 712-749, Korea, and Department of Chemical Engineering, Lafayette College, Easton, Pennsylvania 18042
Wet air oxidation of aqueous solutions of poly(vinyl alcohol) (PVA) has been studied in a batch autoclave reactor at temperatures ranging from 175 to 250 °C in an excess of oxygen of 0-300% and at oxygen partial pressures (PO2) of 0.53-2.11 MPa. No destruction of PVA was observed below 175 °C. The decomposition of PVA and the removal of total organic carbon (TOC) and chemical oxygen demand (COD) rapidly increased at reactor temperatures above 200 °C. PVA decomposition was more sensitive to the reaction temperature than to PO2 or the excess oxygen ratio. About 90% destruction of PVA occurred in 90 min at 200 °C, 0% excess oxygen, and 0.7 MPa oxygen partial pressure. Whereas the amount of excess oxygen had little effect on PVA destruction, it accelerated COD and TOC removal. The main intermediates analyzed were carboxylic acids, in particular formic and acetic acids. Further oxidation of these acids resulted in carbon dioxide (CO2) and carbon monoxide (CO). The conversions of PVA to CO2 and CO were 78% and 5%, respectively, after 4 h of reaction at 200 °C and 100% excess oxygen. Our experimental results indicate that, of the two main intermediates, formic acid was short-lived, whereas acetic acid limited the wet oxidation process. Biodegradability of the solution substantially increased upon wet oxidation. Introduction Common biological processes of wastewater treatment adversely react to shock loads of pollutants and/or to toxic pollutants.1 Industrial waste streams with such characteristics, therefore, require alternative treatment methods or pretreatment of problematic wastes upstream that makes the final effluent suitable for biodegradation. One example is the discharge from the desizing and/or polyester reduction processes in the textile industry. These streams are known to contain biorefractory organics that impede application of commercially available technologies.2 The effluent from the desizing process contains high concentrations of sizing agents. Sizing agents are generally classified as natural (cornstarch) or synthetic (PVA and acryl). Poly(vinyl alcohol) (PVA) is mainly used as a sizing agent for filament synthetics, mixed spinning synthetics, and cotton yarns because of its strong adhesivity and flexibility.3 The amount of sizing agent used is 5-10%, by weight of textile, close to 85% of which is removed during the desizing process. Natural agents, such as cornstarch, are partially hydrolyzed by enzymes. PVA, on the other hand, has a low biochemical oxygen demand (BOD) and a high chemical oxygen demand (COD), indicating a low propensity to biotreatment. High temperature (ca. 95 °C) and high organic concentration (30-40% of total organic load of waste* Author to whom correspondence should be addressed. Phone: (610) 330-5433. Fax: (610) 330-5059. E-mail:
[email protected]. † Yeungnam University. ‡ Lafayette College.
water stream) further complicate biological treatment of desizing discharges.2 Hence, it is desirable to treat these streams separately using an alternative technology. This would simplify the process and enhance the efficiency of the overall treatment of wastewater generated in textile plants. Several technologies have been reported for the treatment of desizing effluents containing PVA. One method is PVA removal by coagulation.4-5 Although this is an effective process, its dependency on the level of dissolved oxygen and temperature of the discharge, both critical in biodegradation, are limiting. Another potential technology is wet air oxidation (WAO), which has been successfully applied to the treatment of hazardous waste streams discharged from different chemical industries.1,6-9 WAO is superior to other alternatives because of its energy recovery when applied to highly contaminated waste streams. Another positive attribute of the WAO process is its ability to stoichiometrically oxidize most organic compounds, with carbon converting to carbon dioxide, hydrogen to water, halogens to halides, sulfur to sulfate, phosphorus to phosphate, and nitrogen to ammonia or elemental nitrogen. Air pollutants such as SOx and NOx are not produced, and heavy metals are oxidized to their highest oxidation states.1,6-8 When partial oxidation occurrs, nonbiodegradable materials are converted to biodegradable ones such as lowmolecular-weight caboxylic acids. Wet air oxidation, however, is carried out under severe reaction conditions that necessitate high operating and installation costs. Investigators have attempted to mitigate these conditions in specific applications.10-15 Wet air oxidation involves the liquid-phase oxidation
10.1021/ie000658l CCC: $20.00 © 2001 American Chemical Society Published on Web 12/08/2000
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Figure 2. Schematic diagram of experimental system. Table 1. Experimental Parameter Figure 1. Physical properties of water and oxygen at elevated temperatures.17-20
of organic or oxidizable inorganic components at elevated temperatures (125-320 °C) and pressures (0.510 MPa) using a gaseous source of oxygen (usually air). The enhanced solubility and diffusion coefficient of oxygen in aqueous solutions at elevated temperatures provides a strong driving force for the oxidation of organics. The elevated pressures are required to keep water in the liquid state. Water also acts as a moderating agent by providing a medium for heat transfer and removing excess heat by evaporation.1,6-9 The degree of oxidation in this process is mainly a function of the temperature, oxygen partial pressure, excess oxygen ratio, reaction time, and oxidizability of the pollutants under considerations. Generally, the degree of oxidation increases with increasing temperature, time, and oxygen partial pressure. The effluent consists of lowmolecular-weight oxygenated compounds, predominantly carboxylic acids.6,11,16 Figure 1 illustrates the solubility and diffusion coefficient of oxygen in aqueous solution as functions of temperature (at 0.48 MPa oxygen pressure at 25 °C). The solubility of oxygen decreases to a minimum near 100 °C and then rises exponentially. The diffusion coefficient of oxygen increases linearly with temperature. Furthermore, the viscosity and dielectric constant of the solution decrease with temperature rise. These changes in the physical properties of the solution at high temperatures enhance the oxidative characteristics of the reacting system. The main objective of this work is to examine the applicability of wet air oxidation to the treatment of waste streams containing PVA. Particular attention is given to the impact of operating conditions on the overall treatment efficiency and thus optimization of the WAO treatment process for this type of effluents. Moreover, the improvement in biodegradability is studied, and effluent gas species are characterized. Experimental Section Materials and Procedure. A schematic of the experimental apparatus is shown in Figure 2. Five grams of granular poly(vinyl alcohol) (1500 degrees of polymerization and 99% of saponification; Yakuri Pure Chemical Co, Japan) was dissolved in 1000 mL of distilled water to produce 5000 ppm controlled sample
target solution parameters
reactor type agitation speed
5000 ppm of PVA solution reaction temp (°C) 175, 200, 225, 250 excess O2 (%) 0, 100, 200, 300 reaction time (min) 0-240 PO2 (MPa) 0.7, 1.4, 2.1, 2.8 PVA solution vol (ppm) 200, 250, 333, 500 hollow shaft turbine type impeller batch reactor (stainless steel 316L) 400 rpm
solutions. High purity (99.99%) bottled oxygen supplied by International BOC Gas Co. was used as the oxygen source. The reactor used was a 316-L stainless steel chamber (Autoclave Engineers Inc.) with a hollow shaft supporting a six-bladed impeller. It had an effective volume of 1000 mL. A thermal sensor, cooling coil, external heating element, and stirring-speed-adjusting device were provided to monitor and control the temperature of the reactor to within (1 °C. Operating pressures were taken as the sum of the water vapor pressure at the corresponding reaction temperature and the oxygen pressure. The reactor was charged with the 5000 ppm PVA solution for all runs. It was sealed and flushed with argon to prevent PVA oxidation in the preheating process. Once the desired reactor temperature was achieved, the calculated amount of oxygen, based on a stoichiometric excess ratio of oxygen to the volume of the reactor headspace, was fed into the reactor from a compressed oxygen bottle. The injection time of oxygen was taken as the reaction initiation time. The stirrer operated at 400 rpm to minimize the gas/liquid interfacial resistance for oxygen dissolution in liquid and to keep the reactor contents well mixed. Liquid samples of approximately 3 mL in volume were drawn from the bottom of the reactor. These samples were kept to a minimum so that the volume of the reacting solution was not substantially affected. The experimental conditions under which the effects of reaction temperature, oxygen partial pressure, excess ratio of oxygen, and reaction time on the decomposition of PVA, total organic carbon (TOC), and chemical oxygen demand (COD) were studied are listed in Table 1. Analysis. The quantity of residual PVA in solution was determined by spectrophotometry (690 nm) using the colorimetric method.21 The CODCr was determined by the standard method,22 and BOD was assessed by standard BOD5 tests using sludge from a local sewage
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Figure 3. Photograph of samples at different reaction times.
treatment plant. The TOC content was measured using a Shimatzu TOC-5000A analyzer. The reaction intermediate products, mainly carboxylic acids, were analyzed by gas chromatography with FID detection (HP 5890II). The column used was a 6.5-ft × 0.125-in. stainless steel column packed with Hayesep-R (80/100 mesh, Alltech Co.). The GC oven was operated isothermally at 220 °C. Evacuated 25-mL Pyrex sample cylinders were used for periodic collection of gas samples. Gases (CH4, CO, and CO2) were separated using a 6.5-ft × 0.125-in. stainless steel column packed with carbosphere (80/100 mesh; Alltech Co.). The effluent of the packed column was directed to a catalytic converter column (methanizer) packed with 5% ruthenium on alumina (30/40 mesh). The methanizer was operated at 315 °C and charged with a continuous hydrogen stream at a flow rate of 10 mL/min. Carbon monoxide and carbon dioxide leaving this column in the form of methane were analyzed using GC/FID. Results and Discussion Color Change of the PVA Solution with Reaction Time. Figure 3 demonstrates the color change of withdrawn samples with reaction time at 225 °C. The first clear sample from the left is a fresh 5000 ppm PVA solution. The sample next to it was taken after the reactor was preheated to the reaction temperature in the presence of argon. The similarity in color of these two samples indicates, qualitatively, the absence of any substantive chemical change in the preheating process. This was confirmed by analyzing the PVA concentration of the second sample. The third and subsequent samples from the left in Figure 3 were collected at 30 min time intervals after the injection of oxygen. The samples gradually changed color from dark to light brown with increasing reaction time and eventually became almost colorless after 4 h. Higher reaction temperatures accelerated the color change. The dark brown color of samples three and four from the left is said to be due to catechol compounds resulting from the formation of intermediate products generated during PVA oxidation.
Figure 4. Normalized PVA concentration vs reaction time at different temperatures.
With further oxidation of PVA, the dark brown catechols are converted to low-molecular-weight organic acids or are mineralized, resulting in a relatively colorless solution, the sample to the far right. Similar observations have been reported for the wet air oxidation of phenol.7-8,10 Concentration Changes of PVA, COD, and TOC with Reaction Temperature. The thermal stability of granular poly(vinyl alcohol) was confirmed up to 500 °C using a themogravimetric analyzer (TGA). In a controlled nitrogen atmosphere, the degradation of PVA started at 200 °C and increased exponentially above 300 °C.22 Figure 4 shows the variation of normalized PVA concentration (defined as the ratio of the actual to the initial concentration, CPVA/CPVAo) versus reaction time for four different reaction temperatures. The stoichiometric amount of oxygen (excess oxygen ratio ) 0%) needed for complete oxidation of 5000 ppm of PVA was 0.7 MPa, based on the pressure of the reactor headspace. Figure 4 illustrates that insignificant PVA decomposition occurred at temperatures below 175 °C. At tem-
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Figure 5. Normalized COD concentration vs reaction time at different temperatures.
peratures above 200 °C, however, the decay of PVA is enhanced. The reaction times for 90% decomposition of PVA at 200, 225 and 250 °C, for example, were observed to be 100, 50, and 10 min, respectively. At 200 °C, Figure 4 demonstrates a lag time in PVA decomposition, referred to as the induction period. The induction period, which was over 30 min at 200 °C, decreased with increasing temperature. In this experiment, the PVA decay curve at 200 °C resembles a typical rate curve of a polymer autoxidation. Figure 5 presents the variation of the normalized COD concentration (COD/CODo) versus reaction time for the three temperatures 200, 225, and 250 °C and for 0% excess O2. As expected, the COD removal rate increases with the reaction temperature, showing a trend similar to that for PVA decay. The COD removal rates, however, are relatively slower than those of PVA at the above-mentioned three reaction temperatures (Figure 5). This is due to the formation of intermediate products such as acetic acid that are refractory to wet air oxidation. TOC analysis is a good tool for characterizing intermediate residues in the liquid phase. In addition, we have used TOC analysis to identify the degree of organic carbon mineralization (conversion to CO2 and CO). The latter is obtained from the difference of the initial TOC and the TOC for specific reaction conditions. Figure 6 shows the variation of the normalized TOC concentration for the three different reaction temperatures 200, 225, and 250 °C and for 0% excess O2. A comparison of Figures 5 and 6 indicates that the TOC and COD removals have similar patterns. The higher the reaction temperature, the closer are the removed quantities of TOC and COD (Figures 5 and 6). It should be noted here that, whereas the difference between the initial and final carbon content of a solution accounts for the concentration of inorganic gases produced, the difference between the carbon found in PVA and that in the solution accounts for the intermediate products formed during the oxidation process. Effects of Excess Oxygen/PO2 on PVA Decomposition and COD/TOC Removal. The normalized PVA concentrations are illustrated in Figure 7 as a function of reaction time for four different excess oxygen ratios.
Figure 6. Normalized TOC concentration vs reaction time at different temperatures.
Figure 7. Normalized PVA concentration vs reaction time at different excess oxygen ratios.
At a reaction temperature of 200 °C, a change in the amount of excess oxygen from 0% (0.7 MPa oxygen partial pressure) to 300% (2.8 MPa oxygen partial pressure) has a minimal impact on the PVA decomposition rate. Slightly faster decay is observed (Figure 7) at higher excess oxygen ratios. Moreover, a change in excess oxygen ratio has little effect on the PVA decomposition trends, indicating that PVA decomposition at this temperature is due to thermal destruction with no or little contribution from the oxidation process. However, we have observed that the type of intermediates formed from the thermal decomposition of PVA were influenced by the excess oxygen ratio. Figure 8 illustrates the effect that the excess oxygen ratio has on the decay of COD at 225 °C. Whereas the excess O2 ratio has a minimal effect on the decomposition of PVA (Figure 7), it affects the COD removal significantly. This indicates the important role of the excess oxygen ratio and oxygen partial pressure in the formation of intermediates and final products in the WAO process. The impact of the excess oxygen ratio is diminished beyond 200% (2.11 Mpa oxygen, Figure 8) because of the formation of species refractory to wet air oxidation. The rates of COD removal at 200 and 300%
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Figure 8. Normalized COD concentration vs reaction time at different excess O2 ratios.
Figure 10. Normalized COD concentration vs excess oxygen at PO2 ) 2.1 MPa.
Figure 11. Normalized COD concentration vs initial oxygen partial pressure at 200% excess oxygen ratio.
Figure 9. Normalized TOC concentration vs reaction time at different excess O2 ratios.
excess oxygen ratios after 150 min of reaction time are practically equal (Figure 8). Hence, it can be concluded that a 200% excess oxygen ratio is the optimum ratio for the wet air oxidation of PVA under our experimental conditions. The distribution of TOC for four different excess oxygen ratios at 225 °C is presented in Figure 9. A comparison of Figures 8 and 9 show that both COD and TOC have similar decay trends at the same excess oxygen ratios. Whereas the rate of elimination of TOC was greatly enhanced when the excess O2 ratio was raised from 0 to 200%, its decay rate above 200% excess O2 did not improve substantially. The normalized TOC concentration under oxygen-rich conditions reached an apparent steady state after about 160 min, implying that intermediates refractory to wet oxidation dominate the composition of the reacting solution. We have found that the concentrations of these intermediates (mainly carboxylic acids) remain relatively constant at longer reaction times. Effects of Excess Oxygen on COD at Constant Oxygen Partial Pressure (PO2). At a constant partial pressure of oxygen in the reactor, we changed the loaded
volume of PVA solution to investigate the significance of excess oxygen on COD decay. Figure 10 illustrates the effect of excess oxygen on the normalized COD concentration at a constant oxygen partial pressure of 2.11 MPa. At a constant oxygen partial pressure of 2.11 MPa, a temperature of 200 °C, and a reaction time of 60 min, 7%, 57%, 73% and 77% COD removal were obtained for 0, 100, 200, and 300% excess oxygen ratios, respectively. It is apparent from Figure 10 that the COD removal rapidly increases with the excess oxygen ratio from 0 to 100%, and then it slows beyond 200% and reaches a somewhat steady state at a normalized COD value of about 75%. Effects of Oxygen Partial Pressure on COD Concentration at a Constant Excess Oxygen Ratio. Figure 11 demonstrates the change in the normalized COD with oxygen partial pressure at a 200% excess oxygen ratio. Experiments were conducted at 200 °C for a 3-h reaction time. The COD concentration linearly decreased with increasing oxygen partial pressure under our experimental conditions. This is due to the higher solubility of oxygen at elevated oxygen partial pressures in the system, which, in turn, enhances the oxidation of intermediate species formed in the system. Our studies indicate that the impact of the oxygen partial pressure on COD removal is greater than that of the excess oxygen ratio. This is consistent with Henry’s law. Intermediate Products. The distributions of carboxylic acids at 200 and 250 °C are shown in Figure 12. The concentration of acetic acid formed is larger
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Figure 13. BOD5 and BOD5/COD of PVA treated solutions vs reaction time.
Figure 12. Formic acid and acetic acid concentrations vs reaction time.
than that of formic acid by a factor of 5 or more for both reaction temperatures. At 250 °C, the rate of formation of acetic acid is high within the first 60 min of the reaction but later plateaus (Figure 12). This is due to the resistance of some intermediate products, including acetic acid, to wet air oxidation. Other intermediates, such as formic acid, are short-lived. They rise to a maximum and further react or decompose. No formic acid, for example, was detected after 200 min at 250 °C. The distributions for acetic and formic acids at 200 and 250 °C were similar (Figure 12), with slower formation rates at 200 °C. These acids can be further oxidized to carbon dioxide and water if sufficient oxidative conditions are provided. The low-molecular-weight carboxylic acids, acetic acid in particular, are known to be refractory to wet air oxidation.1,9,11 This is a major limitation of the WAO technology. We have found that acetic and formic acids were the main intermediates in our reaction system, whereas propionic and butyric acids were present in traces. BOD. A gross biodegradability index of a sample is identified by the BOD5/COD ratio. The biodegradability of liquid samples taken at different reaction times and assessed by BOD5 and the BOD5/COD ratio are shown in Figure 13. The initial BOD5 and COD values of the original 5000 ppm PVA solution were 43 and 3500 ppm, respectively. This value increases with time (Figure 13), showing a distribution very similar to that of acetic acid (Figure 12). One can conclude from this comparison that intermediates formed in the wet oxidation process are biodegradable although they might resist WAO. After 3 h of oxidation, the BOD5 values of samples increase by a factor of 3. Furthermore, during the 3-h reaction period, the BOD5/COD ratio rises by a factor of ca. 30 (Figure 13), indicating that PVA, a nonbiodegradable material, is broken into biodegradable compounds. A reasonable level of biodegradability (ca. BOD5/COD > 0.5) of the liquid sample was reached in 3 h. Considering our results, it is conceivable that wet oxidation is a viable pretreatment method for PVA-containing wastewater streams.
Figure 14. CO2 and CO concentrations in effluent gas vs reaction time.
Effluent. The desired final products of PVA oxidative destruction are carbon dioxide and water. However, during a wet air oxidation process, some intermediates that are refractory to the process, are formed. The tendency for conversion from organic to inorganic compounds in this system was measured by the amount of CO and CO2 formed. Figure 14 shows the concentrations of carbon monoxide and carbon dioxide versus reaction time at 200 °C and 100% excess oxygen. The CO2 and CO concentrations are seen to increase with reaction time. Calculations indicated that, when a solution of 5000 ppm PVA is completely oxidized, the stoichiometric amount of CO2 should occupy 41%, by volume, of the reactor headspace, not considering the water vapor. Figure 14 indicates that, at 200 °C and 100% excess oxygen, 78% of the PVA is completely oxidized to CO2 and 5% to CO after 4 h. The remaining 17% of carbon counts for the unreacted PVA and other intermediates in the aqueous phase. Conclusion The wet oxidation of aqueous poly(vinyl alcohol) solution has been studied to characterize the intermedi-
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ates and final products. The experiments were conducted at temperatures ranging from 175 to 250 °C, reaction times of 0-4 h, oxygen partial pressures of 0.53-2.11 MPa, and excess oxygen ratios of 0-300%. TOC, COD, and BOD5 of the reacting systems were monitored, and samples were analyzed for carboxylic acids and effluent gases. The reaction temperature was found to have a significant effect on the decomposition of PVA. The removal of PVA paralleled the increases in TOC and COD at reactor temperatures above 200 °C. The excess oxygen ratio and oxygen partial pressure had little or no effect on the decomposition rate of PVA, whereas they improved the decay of COD and TOC. Acetic and formic acids were analyzed as the main intermediates. Higher reaction temperatures speeded the formation rate of these acids. Acetic acid was much more resistant to wet air oxidation than formic acid. Values of BOD5 were seen to increase with reaction time. Also, BOD5/COD ratios improved substantially. This is due to the conversion of PVA, a biorefractory material, into biodegradable compounds such as the short-chain acids acetic and formic acid examined in this study. Under our reaction conditions, formic acid was completely oxidized to carbon dioxide and water, whereas acetic acid was partially oxidized. Total oxidation of acetic acid to CO2 and H2O proved to be difficult because acetic acid resisted wet oxidation even under more severe conditions. Therefore, an integrated chemicalbiological process, using wet air oxidation as a pretreatment step, could provide an attractive alternative to conventional biological treatment of PVA. Acknowledgment This work was partially supported by Grant 2000-230700-001-3 from the Basic Research Program of the Korea Science & Engineering Foundation. Literature Cited (1) Mishra, V. S.; Mahajani, V. V.; Joshi, J. B. Reviews of Wet Air Oxidation. Ind. Eng. Chem. Res. 1995, 34 (1), 2. (2) Lin, S. H.; Ho, S. J. Catalytic Wet Air Oxidation of High Strength Industrial Wastewater. Appl. Catal. B: Environ. 1996, 9, 133. (3) Bergenthal, J.; Bergenthal, J. Wastewater Recycle and Reuse Potential for Indirect Discharge Textile Finishing Mills; Technical Report EPA-600/2-84-0; U.S. Environmental Protection Agency, Government Printing Office: Washington, D.C., 1984; Vol. 1. (4) Shin, J. S. Desizing Wastewater Treatment Discharged from Textile Mills by Coagulation and Ultrafiltration Methodology. Master’s Thesis, Yeungnam University, Kyungsan, Korea, 1994.
(5) Tipper, C. F. H. In Oxidation and Combustion Review; Elsevier Publishing Co.; New York, 1990; Vol. 1, p 187. (6) Randall, T. L.; Knopp, P. V. Detoxification of Specific Organic Substances by Wet oxidation. J. Water Pollut. Fed. 1980, 52 (8), 2117. (7) Dietrich, M. J.; Randall, T. L.; Canney, P. J. Wet Air Oxidation of Hazardous in Wastewater. Environ. Prog. 1985, 4, 171. (8) Heimbuch, J. A.; Wilhelmi, A. R. Wet Air OxidationsA Treatment Means for Aqueous Hazardous Waste Streams. J. Haz. Mater. 1985, 12, 187. (9) Mantzavinos, D.; Livingston, A. G.; Hellenbrand, R.; Metcalfe, I. S. Wet Oxidation of Polyethylene Glycols. Chem. Eng. Sci. 1996, 51 (18), 4219. (10) Sadana, A.; Kartzer, J. R. Catalytic Oxidation of Phenol in Aqueous Solution over Copper Oxides. Ind. Eng. Chem. Fundam. 1974, 13 (2), 127. (11) Imamura, S.; Sakai, T.; Ikuyama, T. Wet Air Oxidation Acetic Catalyzed by Salts. Chem. Abstr. 1982, 25, 74. (12) Imamura, S.; Hirano, A.; Kawabata, N. Wet Oxidation of Acetic Acid Catalyzed by Co-Bi Complex Oxides. Ind. Eng. Prod. Res. Dev. 1982, 21, 570. (13) Donlagic, J.; Levec, J. Oxidation of an Azo Dye in Subcritical Aqueous Solutions. Ind. Eng. Chem. Res. 1997, 36, 3480. (14) Lei, L.; Hu, X.; Chu, H. P.; Chen, G.; Yue, P. L. Catalytic Wet Air Oxidation of Dyeing and Printing Wastewater. Water Sci. Technol. 1997, 35 (4), 311. (15) Lei, H.; Hu, X.; Yue, P. Improved Wet Oxidation for The Treatment of Dyeing Wastewater Concentrate from Membrane Separation Process. Water Resour. 1998, 32 (9), 2753. (16) Bjerre, A. B.; Sorensen, E. Thermal Decomposition of Diluted Aqueous Formic Acid Solution. Ind. Eng. Chem. Res. 1992, 31, 1574. (17) Himmelbalu, D. M. J. Chem. Eng. Data 1960, 5, 10. (18) Quist, A. S.; Marshall, W. L. J. Phy. Chem. 1965, 69 (9), 3165. (19) St. Dennis, C. E.; Fell, C. D. Can. J. Chem. Eng. 1971, 49 (6), 885. (20) Daubertm, T. E.; Danner, R. P. Physical Properties of Pure Chemicals: Data Compilation; Hemisphere Publishing: New York, 1991. (21) Finley, J. H. Spectrophotometric Determination of PVA in Paper Coatings. Anal. Chem. 1961, 33, 1925. (22) Greenberg. A. E., Connors, J. J., Jenkin, D., Eds. Standard Methods, 16th ed.; American Public Health Association: Washington, D.C., 1985. (23) Kim, S. T. Decomposition of PVA Solution by Wet Air Oxidation. Master’s Thesis, Yeungnam University, Kyungsan, Korea, 1997.
Received for review July 14, 2000 Revised manuscript received October 16, 2000 Accepted October 20, 2000 IE000658L
