Ozone provides an economical means for oxidizing phenolic compounds in coke oven wastes
FIGURE
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PHENOLS DESTRUCi ION WITH OZONE
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OZONE APPUED.9PM
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years ago a resourceful engineer with the Ohio River Valley Water Sanitation Commission asked whether ozone would destroy phenols in industrial wastes. The Welsbach Corp. engineer to whom the question had been asked, replied in the affirmative but added that ozone might be too expensive since the treatment of coke plant wastes would yield no salable by-product to offset the treatment cost. The Welsbach engineer knew that ozone had been used successfully to destroy phenol in drinking water, but such waters carried less than 2 p.p.m. of phenols. He also knew that his company’s research laboratories had studied extensively the ozone-phenols reactions. He suggested that the Welsbach research strtff supply the economic answer. It was recommended that a joint program be established to study the destruction of phenol by oxidation with both ozone and chlorine. Twenty-three coke plants in the Ohio River Basin accounted for the major portion of the phenol pollution problem in the Ohio River drinking water; operations at the Armco Steel Corp., Hamilton, Ohio, are typical of these coke oven plants. Based on the technical data presented by the Welsbach organization, Armco along with others joined the commission in sponsoring the research project. FEW
November 1951
engineerirg data for the design of a full scale treatment plant was also obtained from these pilot scale studies. The oxidation of phenols and relationship to ozone dosage is shown in Figure 1 for two typical samples. In sample A, the initial phenol content of the waste was 170 p.p.m., whereas sample B had a lower value of 80 p.p.m. Phenol appears not t o be the determining factor in evaluating the ozone demand of the waste for, with pure phenol as shown by the dotted curve, much less ozone is required to complete the oxidation. The explanation for this situation is probably that other oxidizable materials than phenols are present. For instance, cyanides, thiosulfates, thiocyanates, sulfides, and other complex organics are present in CHLORlNL I P P L I I D . PPY coke oven wastes. Chlozine under typical conditions required about 6000 p.p.m. to reduce point which the U. S. Public Health the phenols to a remaining 3 p.p.m. Service consider8 to be the taste producing limit for drinking water ~iupply. The reason (Continued on page 196 A ) New York State has already adopted the standard of 5 parts per billion maximum phenol concentration in streams used as a source of drinking water supply. California is considering the adoption of similar limits, and Pennsylvania limits the concentration in the waste effluent to zero with no allowance for dilution by the stream. Laboratory studies made under various conditions of pretreatment, temperature, and p H indicated that ozone, chlorine, and chlorine dioxide would destroy coke oven phenols. Pilot plant operations were then made to determine the relation between the degree of phenol oxidation and m oxidant dosage. Necessary OZOHE O O S A G I . P P Y
It was decided to use in the experiments the effluent from an ammonia still following a Koppers’ vapor recirculation type dephenolizer. The phenols content of the still effluent varied from 28 to 332 p.p.m. The term phenols includeB phenol, cresols, xylenes, and other monohydroxy derivatives of benzene. The objective was to reduce the phenols concentration to 5 parts per billion (not million), the
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industrial Wastes for this tremendous chlorine demand is that the chlorine oxidizes many other constituents of the waste, particularly the ammonia, before oxidizing the phenols present (Figure 2). Because of the high degree of selectivity of ozone to oxidize phenols and not the other organic components in coke oven effluents the cost of processing with ozone is less than the cost of chlorine used for the same purpose. It is reported that the relatively high first cost of ozone-producing equip ment is offset in a few years by the low operating cost for ozone. Only recently has “tonnage ozone” been available. In the manufacture of ozone, only air or oxygen is required as the raw material along with cheap electric power. The air is cleaned bj7 electrostatic precipitation followed by a paper filtration. After being compressed to 10 pounds per square inch, the air is cooled to condense most of the water vapor and is then dried thoroughly by passage over activated alumina. This purified air then enters the ozonator tubes where it is subjected to a silent electrical discharge which converts a portion of the oxygen in the air to ozone. In large installations commercial oxygen is substituted for air with the result that twice the amount of ozone is produced per kilowatt-hour of input. Commercial ozone made from air in Welsbach ozonators has a concentration of 1% by weight; the concentration when using oxygen is 2y0, With a substantial sacrifice of output and power efficiency, it is possible to obtain concentrations of 5 to 6% of ozone. When using oxygen it is economically essential to recycle the residual oxygen after stripping the ozone from the reaction gas. The instability of ozone as well &s its dilution make it necessary to manufacture the ozone at the point of use. The ozonators are fully automatic and do not require full time operating labor or even close supervision. A large type ozonator has a capxity of 120 pounds of ozone per 24 hours and requires 60 cubic feet per minute of dry oxygen using 480-volt, 94-amp., single-phase, 60-cycle alternating current. In a 100-oven coke plant the waste treatment cost including all fixed and operating charges would, according to reports, be approximately 3 cents per ton of coal carbonized. A corresponding (Continued on page I d 8 A ) 126 A
Industrial Wastes cost for a 300-oven plant is said to be 2 cents a coal ton. If low cost oxygen were available this cost would approach 1.25 cents per coal ton. Although the Welsbach Corp. considers the life of their generating equipment to be around 24 years, these cost estimates are made with an assumed write-off of 12 yeais. Where quick write-offs are allowable in new facilities, a large plant could expect a cost of 1 cent per coal ton after a 5year amortization. According to the Welsbach Corp., who prepared Figures 1 and 2, the corresponding cost for chlorine would be a t least two to three times as high as ozone costs, Kith chlorine in short supply, the use of ozone as a chemical oxidant of selective nature seems logical and practical. Ozone treatment of coke oven waste waters is the first application of ozone to industrial waste problems, but more uses are imminent. For instance, Figure 3 shows laboratoiy results of ozone-oxidation on catalytic refining waste. The curve on the right represents the ozone demand when the phenolic waste was oxidized with ozone without removal of the sulfides present in the waste. The curve on the left shows the reduced ozone demand of the waste after removing the sulfides by simple aeration. Oil refinery waste, when given a pretreatment by aeration, will show worth-while economics in ozone usage. Ozone also oxidizes cyanides; this fact should be given serious attention by metal processing industries which use plating operations. The simplicity in ozone production and usage is particularly applicable to those smaller companies not staffed with technical personnel adequate to service waste treatment operations which use chlorine or other chemicals. There are at least two favorable conditions inherent in ozone over other oxidation chemicals: First, the selective ability to oxidize single substances, and secondly, ozone leaves no residual chemical to contaminate the product or the stream. An increasing application of ozone by industry is certain. Resourcefulness and ingenuity are necessary in finding its practical uses. Coirespondence concerning this column will be forwarded promptly if addressed t o the author, % Editor, INDUSTRIAL A N D ENQINEERINQ CHEMIBTAY, 1155--16th St., h’.W., Washington 6, D. C .
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