A novel coupling-dephenolization scheme for full-strength coal-conversion wastewaters: results of wastewater study and a cost analysis

Abstract

Results of a feasibility study using an actual coal-gasification wastewater confirm the promising nature of a coupling-dephenolization scheme which we have proposed previously. Kinetic results indicate that the aerobic coupling of phenols, which is the heart of the proposed scheme, occurs at a sufficiently high rate in the actual wastewater to make the scheme practical. A cost anal sis of the scheme indicates that for a commercial-scale coal gasification plant with a daily output of 200 X 10' J of synthetic natural gas and 3 X lo6 gal of wastewater, the treatment cost for a 99% removal of phenols from a wastewater containing 4 g of phenol/L is $8.6/103 gal (1 980 dollar); this compares favorably with the estimated costs of $12.91 1 O3 gal for a biooxidation scheme and $12.81 lo3 gal for a solvent extraction scheme. Additional advantages of the coupling scheme are its simplicity and fast treatment under mild conditions, ability to withstand process interruptions, easy disposal of organic precipitates by incineration, and the ability to remove other pollutants such as sulfides and aromatic amines. I n t r o d u c t i o nA recent kinetic study from our laboratory (Lim et al., 1983) indicates that aqueous phenols, in the presence of oxygen and a catalytic amount of cuprous chloride, undergo a facile oxidative coupling reaction to form insoluble coupling products. The reaction involves primarily the oxidative oligomerization of phenols, although it is also accompanied by a limited amount of hydroxylation reaction. The coupling products share the characteristics of humic acids which are known to be formed in the permanganate oxidation of phenol (Ficek and Boll, 1980); they have been tentatively identified as low molecular weight humic acids.The results have led us to propose a novel dephenolization scheme for treating full-strength coal-conversion wastewaters which are not easily handled by such conventional wastewater treatment schemes as solvent extraction (Beychok, 1974;Cavanaugh et al., 1977;Greminger et al., 1982) and biooxidation (Benefield et al., 1977;Cavanaugh et al., 1977; Holladay et al., 1978; Luthy and Tallon, 1980). Phenol extractants are inherently polar in nature; they are sufficiently soluble in water to warrant an expensive solvent recovery step in an extraction scheme.Biooxidation, on the other hand, is limited to dilute phenolic wastewaters (typically less than 1000 mg/L of phenols); it is slow and highly sensitive to process interruptions and fluctuations in temperature, solution pH, nutrients, and loadings (Holladay et al., 1978; Luthy and Tallon, 1980; Vela and Ralston, 1978).We have tested the feasibility of our proposed coupling-dephenolization scheme using an actual full-strength wastewater that was generated in a fixed-bed coal gasifier (run no. 99) at the Morgantown Energy Technology Center (METC), Morgantown, WV (Fernald, 1983). In this paper we present the results of the feasibility study along with the results of a cost analysis of the proposed scheme. The results show that the coupling...

Segregation of metals at the oil-water interface: results and implications

“…Reactions that may be advantageously conducted in an O-W interfacial mode include reactions that are potentially useful for materials synthesis and waste treatment, such as oxidative coupling reactions (Hay, 1962;Bach, 1968; Giles et al, 1986;Chin et al, 1985) and photocatalytic degradation reactions (Hackman, 1978;Sittig, 1985). The latter are of particular interest in light of the fact that the two commonly used photocatalysts, titanium dioxide and cadmium sulfide (MacKay, 1981;Henglein, 1984), are surface-active; see Table I.…”

Irreversible adsorption of phenolic compounds by activated carbons

“…Consistently, Chin et al (1985) found that the rate of The degree of ionization of a sorbate does not seem to be the primary variable determing its reactivity on carbon, however. If it were, the lower the pKa value of a sorbate, the more reactive it should be in neutral aqueous solutions.…”

“…Basic aqueous solutions promote oxidation of phenolics (Penketh et al, 1957;Chin et al, 1985;and Previous studies have attempted to rationalize the differing abilities of solvents to regenerate phenol from activated carbon (Pahl et al, 1973;Knickmeyer et al, 1973;and Fuchs and Kuhn, 1976). In the first two studies, the solvents were held at 40oc, so surface reactions might have affected the results.…”

Cooperative research in coal liquefaction. Final report, May 1, 1992--April 30, 1993

“…The cost of this systemis $l.Wm3 of treated wastewater. This is much cheaper than alternate dephenolization schemes such as aerobic coupling (Chin et al, 1985), solvent extraction (Greminger et al, 19821, and bio-oxidation (Goldstein and Yung, 1977) whose costs are 4.31, 6.42 and 6.47 $/m3 of treated wastewater, respectively. These results suggest that the devised membrane-hybrid system can indeed be technically and economically effective in tackling dephenolization problems in coal liquefaction.…”