Catalytic Oxidation of Phenol in Dilute Concentrcrtion in Air Michael A. Walsh and James R. Katzer* Department of Chemical Engineering, rniversity of Delaware, S e w a r k , Delaware 1912 2
The vapor-phase oxidation of phenol at concentrations from 875 to 26 ppm (vol) over copper oxide on alumina was studied in a fixed-bed tubular reactor between 150 and 270" in the presence of 8.4 to 13.4 water vapor. Catechol, hydroquinone, and organic acids, which are reported to form in appreciable mol quantities in the homogeneous oxidation of phenol, are not observed in the vapor-phase catalytic oxidation. Organic intermediates, probably 0- and p-benzoquinone, occur in appreciable quantities in the catalytic oxidation at intermediate phenol conversions. At moderate temperatures (-250") and low conversions
%
(-30%) approximately one-half of the phenol oxidized i s converted completely to COz and H20. This indicates that ring opening i s a relatively difficult step in the reaction network. The vapor-phase oxidation i s first order with respect to phenol over the range of conditions studied and exhibits an Arrhenius activation energy of 10 kcal/mol.
Emissions of organics in t h e u.S., about 70 billion pounds in 1970, are about equally divided between stationary and mobile sources. With the projected control of mobile sources, stationary sources if not controlled will contribute 96% of the total organic emissions by the year 2000 (Phillips aiid Rolke, 1972). Organic emissions from stationary sources have already come under control in California and will soon be controlled more broadly. Where such emissions are odorous, local governments have forced control, and specific laws are being enacted defining and controlling malodors (Chena. Eng., 1972). Catalytic Oxidation is an effective means of controlling organic emissions aiid achieving odor control. The use of catalytic osidation for solvent vapors (Hardison, 1968; Miller and Sowards, 1968; Miller and Kilhoyte, 1967) and for fume and odor control (Luiiche, 1968; Turk, 1969) has been discussed. Lunche (1968) notes t h a t in a number of instances t h e odor and eye irritation index have actually increased across a catalytic conibust'or due t o the formation of partial oxidation Iiroducts. This is due to inadequate design with respect to both reaction kinetics .and mass transfer (Miller, et al., 1967, 1968 ; Hawthorn, 1972). Litt,le information is available on t,he catalytic oxidation of organic compounds in gas streams other than engine exhaust and almost none on reaction kinetics. Vapor-phase catalytic oxidation is effective for oxidizing organic compound,s in vaporized liquid effluents in spacecraft eiiabliiig recycle of writer for drinking (Intorre and A l l p x , 19693, 1969b; Netzger, et al., 1968) and for oxidizing organic compounds i n blow-down gases from the Zimmermari \vet, oxidation process (Intorre and ;ilper, 1969b). Borkowski (1967) demonstrated almost complete oxidation of phenols and other impurities in evaporated effluents a t temperatures between 300 and 450" over several catalysts. d copper oxide catalyst was most' effective. So iiiforniation on kinetics or reaction network !vas given. Ahmad, et al. (1970), st'udied t h e vaporphase oxidat'ioii of phenol in air over lIo03-V205 aiid Cr203V?Oj on Si02 in a fluidized bed. 11aleic anhydride arid p benzoquinone were major intermediates, but t h e main oxidat'ioii route was directly to C 0 2and H20. Phenol appears in a number of waste streams in the petroleum, chemical, coke, paper, and plastics indust'ries. It is
generally associated with water pollution but also appears in a number of vapor streams in these industries. This study determined the kinetics of phenol oxidation over supported copper oxide under conditions which might be found in bleed, purge, blow-dowi, or steam-stripping streams. Experimental Section
The experimental apparat'us (Figure 1) consisted of a feed reservoir containing water-phenol solution, a vaporizer into which the solution was dripped and mixed with air, aiid a fixed-bed tubular reactor housed in a 76-em tube furnace. The reactor was 2.5-em 0.d. Pyrex tubing and contained a 25 cm leugth filled with 6-mm Pyrex Raschig rings beloiv the catalyst for preheating the reactants. A thermocouple in the catalyst bed was used to measure and control bed temperature. Alirflow was measured by a wet test meter before entering the vaporizer; all lines following the vaporizer were heated. Temperature of the vaporizer and transfer lines was monitored. Samples could be taken before and after t h e reactor for analysis. The 6-mm Pyres Raschig rings in the vaporizer and preheat section of the reactor showed no catalytic activity. The air was filtered and theii passed through indicating Drierite after t h e wet test meter. Phenol was reagent grade and contained a trace (
