Electrochemical membrane incinerator

Electrochemical incineration of p-benzoquinone was evaluated as a model for the mineralization of carbon in toxic aromatic compounds. A Ti or Pt anode was coated with a film of the oxides of Ti, Ru, Sn and Sb. This quaternary metal oxide film was stable; elemental analysis of the electrolyzed solution indicated the concentration of these metal ions to be 3 .mu.g/L or less. The anode showed good reactivity for the electrochemical incineration of benzoquinone. The use of a dissolved salt matrix as the so-called "supporting electrolyte" was eliminated in favor of a solid-state electrolyte sandwiched between the anode and cathode.

BACKGROUND OF THE INVENTION
 Public awareness of the discharge of industrial wastes has resulted in
 governmental and private development of efficient, economical and safe
 procedures for the destruction of toxic organic waste. Alternatives to the
 traditional use of thermal incineration include supercritical water
 oxidation, photochemical degradation, sonochemical oxidation and
 electrochemical incineration.
 Supercritical water oxidation is performed above the critical point of
 water (374.degree. C., 218 atm) in the presence of O.sub.2 or H.sub.2
 O.sub.2. Organic species only slightly soluble in water are miscible with
 supercritical water. The literature contains descriptions of reaction
 mechanisms, kinetics and engineering aspects of supercritical water
 oxidation applied to numerous organic pollutants including: phenol,
 1,3-dichlorobenzene and benzene, pyridine, acetic acid,
 1,4-dichlorobenzene, chlorophenols, pulp and paper mill sludge, and
 explosives. Major reaction products are water, carbon dioxide and
 inorganic salts. Supercritical water oxidation is well suited for
 destruction of large volumes of toxic organic waste; however, for disposal
 of small quantities of toxic organic waste, supercritical water oxidation
 is not considered feasible economically. Therefore, evaluation of less
 costly methods is appropriate.
 Recently, interest in photochemical degradation of toxic organic waste in
 aqueous media has expanded rapidly. The primary oxidant is the
 photogenerated hydroxyl radical formed on semiconductor metal oxide
 surfaces. Typically, TiO.sub.2 powder is the semiconductor used because it
 is inexpensive, insoluble under conditions used in photochemical
 degradation, stable and non-toxic. The literature of photochemical
 degradation describes applications to chlorophenols, dichloroacetate and
 oxalate, 4-chlorophenol, humic acids, dichlorophenols, benzene, phenol,
 dimethoxybenzene and toluene. Applications of photochemical degradation
 appear most suitable for solutions having low turbidity.
 Sonochemical oxidation has been used for degradation of phenol and humic
 acids; and of 4-chlorophenol, 3,4-dichloroaniline and
 2,4,6trinitrotoluene. The primary reaction in sonochemical oxidation is
 the pyrolysis of solute present in bubbles generated by acoustical
 cavitation. Secondary reactions also occur as a result of interactions of
 solute with hydroxyl radicals and hydrogen atoms produced by the
 sonication of water.
 Electrochemical incineration is an alternative to the degradation methods
 above described. This is a waste remediation process whereby oxygen atoms
 are transferred from H.sub.2 O in the solvent phase to the oxidation
 product(s) by direct or indirect reactions on the anode surface. This
 procedure is attractive for low-volume applications such as confined
 living spaces, e.g., spacecraft, and research laboratories. The prior art
 has described successful electrochemical incineration of waste biomass
 using Pt and PbO.sub.2 electrodes. The major advantages of electrochemical
 incineration over thermal incineration include: absence of CO and NO.sub.x
 generation, and low operating temperatures. Because of the high cost of Pt
 and the toxicity of lead salts, two Swiss groups compared PbO.sub.2 and Pt
 electrodes to SnO.sub.2 -film electrodes doped with Sb(V) ("Sb-SnO.sub.2
 "). Both Swiss groups demonstrated that phenol is removed from aqueous
 solution more efficiently with Sb-SnO.sub.2 anodes than with Pt and
 PbO.sub.2 anodes. Their work also indicated that for Pt anodes, oxidation
 stops with the formation of small carboxylic acids, e.g., maleic, fumaric
 and oxalic. More recently, Pt, IrO.sub.2 /Ti, and Sb-SnO.sub.2 /Ti anodes
 were compared and a mechanism for the electrolysis of organic compounds
 was proposed. These and other descriptions of electrochemical incineration
 have been reviewed in the literature; advantages of electrochemical
 incineration include: versatility, energy efficiency, amenability to
 automation, environmental compatibility and low cost.
 The major challenge for future development of electrochemical incineration
 is the discovery of nontoxic anode materials and electrolysis conditions
 that can achieve conversion of toxic organic waste to innocuous products
 with high current efficiencies. Other desirable electrode properties
 include low cost, lack of toxicity, high stability and high activity. The
 matter of current efficiency is especially pertinent because the desired
 O-transfer reactions require the anodic discharge of H.sub.2 O to produce
 adsorbed hydroxyl radicals (OH.sub.ads). However, a high surface excess of
 the OH.sub.ads species leads to evolution of O.sub.2, an undesired
 product. Previous work has demonstrated that electrodes comprised of
 Fe(III)-doped .beta.-PbO.sub.2 films on Ti substrates ("Fe-PbO.sub.2 /Ti")
 are quite stable in acetate buffered media (pH 5) and offer significantly
 improved catalytic activity over pure .beta.-PbO.sub.2 film electrodes for
 conversion of CN.sup.- to CNO.sup.- under potentiostatic conditions as
 well as the anodic degradation of p-benzoquinone under galvanostatic
 conditions.
 SUMMARY OF THE INVENTION
 The present invention in its preferred embodiment relates to
 electrochemical incineration using a quaternary metal oxide consisting of
 a SnO.sub.2 film doped with varying amounts of the oxides of antimony,
 titanium and ruthenium. The cathode is a porous stainless steel cylinder,
 and a Nafion membrane is used as a solid-state electrolyte sandwiched
 between the anode and cathode. Use of Nafion, a perfluorinated acid
 membrane, precludes the need for addition of soluble inorganic salts to
 function as supporting electrolytes. A dramatic increase in lifetime of
 the anodes has been observed to result from omission of added
 electrolytes. Furthermore, the low ionic strength of the electrolysis
 solution facilitates the use of ES-MS for determination of ionic products
 and there is little or no electrolyte to remove from the remediated
 solution.
 The invention consists of certain novel features and a combination of parts
 hereinafter fully described, illustrated in the accompanying drawings, and
 particularly pointed out in the appended claims, it being understood that
 various changes in the details may be made without departing from the
 spirit, or sacrificing any of the advantages of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT
 All chemicals were reagent grade (Fisher Scientific) and water was purified
 in a Nanopure-II system (Barnstead, Newton, Mass.). Quaternary metal oxide
 films were prepared from a solution comprised of 0.4M SnCl.sub.2 @2H.sub.2
 O, 0.03M SbCl.sub.3, 0.08M RuCl.sub.3 and 0.02M TiCl.sub.4 in a 1:1
 mixture of 12M HCl and i-propanol. This composition was chosen on the
 basis of patents claiming high stability for TiO.sub.2 -RuO.sub.2
 -SnO.sub.2 and RuO.sub.2 -Sb.sub.2 O.sub.3 -SnO.sub.2 films on Ti
 substrates in saline solutions. p-Benzoquinone (Fisher Scientific) was
 purified by sublimation and used for preparation of 100 mg/L stock
 solutions in water. Carboxylic acids (Aldrich) were dissolved in water to
 prepare 1000 mg/L standard stock solutions, which were then frozen until
 needed to prevent microbial degradation.
 Quaternary metal oxide films were prepared by a thermal procedure in which
 Ti or Pt substrates were alternately painted with the solution of the four
 metal salts followed by heating above the flame of a Bunsen burner for ca.
 15 s. After ten wetting-heating cycles, the electrode was annealed in a
 muffle furnace for 1 h at 600.degree. C. The resulting quaternary metal
 oxide films on Ti and Pt substrates are designated here as
 "Ru-Ti-Sb-SnO.sub.2 /Ti" and "Ru-Ti-Sb-SnO.sub.2 /Pt", respectively.
 Preliminary work made use of a Ti substrate (10 cm.sup.2 working area), in
 the form of a rectangular plate, and a Pt cathode. Subsequently, a Pt wire
 (0.62-mm o.d., 24-cm length, 4.7-cm.sup.2 working area) was used as the
 substrate for quaternary metal oxide films. In the latter case, a
 rectangular piece of Nafion 117 membrane (2 cm.times.4 cm) was placed
 around the tubular cathode and wrapped tightly with the quaternary metal
 oxide-coated wire anode, as shown in FIG. 1 wherein there is shown a
 schematic illustration of an electrolytic cell 10 in which there is
 provided an anode indicated by the (=a) in the form of a wire which may be
 any one of a variety of composite materials or of a metal, as will be
 hereinafter described, which surrounds a polymer electrolyte. Preferably,
 the polymer electrolyte is NAFION.RTM. which is a fluorinated organic
 polymer having multiple pendant sulfonic acid groups. NAFION.RTM. is a
 trademark of the DuPont Company for a commercially available
 polysulfonated membrane which has the following structure as set forth in
 U.S. Pat. No. 4,973,391 issued Nov. 27, 1990 to Madou et al. the
 disclosure of which is herein incorporated by reference.
 ##STR1##
 In addition, to the polymeric electrolyte denoted by letter b in FIG. 1,
 there is also disclosed a cathode denoted by (-c) which may be any
 conventional material such as stainless steel. Preferably, but not
 necessarily, the cell 10 is tubular in shape and more preferably
 cylindrical in shape, is inserted into an electrolytic solution which
 contains toxic organic compounds to be remediated. The anode a and the
 cathode c are connected to a source of energy and is applied between the
 cathode and the anode, the toxic organic compounds in the electrolytic
 solution will be remediated, as hereinafter described.
 The cathode was prepared from a rod of type-360 stainless steel (6.4-mm
 o.d. and 3.5-cm length) drilled with 20 holes (3-mm dia.) positioned
 normal to the axis of the rod. Other anodes include those described by
 Feng et al. , J. Electrochemical soc., 138 (1991) 3328 and Electrochemical
 Soc. 142 (1995) 626, the disclosures of which are herein incorporated by
 reference.
 Referring to FIG. 1, the electrolysis cell was assembled from a 50-mL
 three-necked pyrex flask. Teflon stoppers were machined to fit the outer
 two ports of the cell. One stopper allowed entry of the electrode
 assembly. The other stopper allowed passage of a hypodermic needle to add
 water or introduce a solid phase microextraction fiber for headspace
 analysis. A tapwater-cooled condenser was inserted in the center neck of
 the cell to decrease evaporative water loss during long electrolysis
 periods. All glassware was washed in 1M KOH in a 1:1 mixture of ethanol
 and water, then in 2M H.sub.2 SO.sub.4, then rinsed with water and then
 dried overnight at 100.degree. C.
 The power supply was a potentiostat/galvanostat (model 363, EG&G Princeton
 Applied Research, Princeton, N.J.) operated in the galvanostatic mode.
 Electrolyses were performed under galvanostatic control at 1.0 A (ca. 0.2
 A/cm.sup.2) on 50-mL aliquots of benzoquinone stock solution. At the
 conclusion of each lectrolysis, deionized water was added to bring the
 volume in the cell back to 50 mL, i.e., the starting volume.
 The elemental content of the initial benzoquinone solution and one that had
 been electrolyzed for 64 h was determined by inductively coupled
 plasma-mass spectrometry (ICP-MS). The apparatus and typical operating
 conditions have been described in the prior art. A semiquantitative
 analysis mode was used for calibration. Spectral scans were measured in
 separate m/z windows typically 50 daltons wide. Analyte signals were
 adjusted for blank signal, isotopic abundance and approximate degree of
 ionization and then compared to those for known concentrations of Co, La
 or TI, whichever was in the particular m/z window of interest. Scans of
 the full m/z range showed that matrix effects were negligible.
 In addition to the starting solution, samples representing eight
 electrolysis periods in the range 0.5-64 h were analyzed for TOC, COD, pH,
 and inorganic and organic anions. TOC was determined at the University of
 lowa's Hygienic Laboratory, which is EPA approved. Samples were analyzed
 by a DC190 TOC Analyzer (Dohrmann, Santa Clara, Calif.) using a combustion
 infrared method. COD was determined by titration with KMnO.sub.4 as known
 in the art or by a Hach DR2000 analyzer (Loveland, CO).
 Quinone and phenolic compounds were separated with a reverse phase Zorbax
 SBC18 column (25-cm length, 4.6-mm dia.) developed by Rockland
 Technologies (Chadds Ford, Pa.) and detected by absorption at 240-nm using
 a Kratos Analytical Spectroflow photometer (Ramsey, N.J.) or with a
 Perkin-Elmer SCIEX API/1 ES-MS (Thornhill ON, Canada) based on a single
 quadrupole mass spectrometer. The ES-MS was equipped with a Perkin-Elmer
 SCIEX Turbolon Spray heating probe (Thornhill ON, Canada). The
 TurbolonSpray employs a heated gas flow near the electrospray needle which
 increases evaporation of solvent and allows liquid flow rates up to 1
 mL/min. TurbolonSpray eliminates the need to split the eluent stream from
 the HPLC, eliminates some background peaks, improves detection limits
 where background peaks are eliminated, and allows use of low organic
 solvent levels. Methanol and water at a 1:1 ratio was the eluent used at a
 flow rate of 0.3 m/min. In addition, inorganic and organic anions in the
 electrolysis solutions were monitored by direct infusion into the ES-MS.
 Carboxylic acids were identified using an ICE-AS6 ion-exclusion column
 from Dionex (Sunnyvale, Calif.) coupled to ES-MS as known in the art.
 The inorganic and organic anions were quantified using an AS11
 anion-exchange column with an ED40 conductivity detector from Dionex. A
 sodium hydroxide and methanol gradient elution program as described in the
 literature accompanying the column provided the needed separation of the
 analytes of interest.
 Polyacrylate and carbowaxdivinylbenzene coated SPME fibers from Supelco
 (Bellefonte, Pa.) were used to extract constituents in the benzoquinone
 solution and in the headspace. Solid phase microextraction fibers
 underwent thermal desorption in a Varian 3400 gas chromatograph (Palo
 Alto, Calif.) equipped with a DB-1 or DB-5 column from J&W Scientific
 (Folsom, Calif.), and coupled to a Finnigan TSQ-700 triple quadrupole mass
 spectrometer (San Jose, Calif.).
 Aldehydes and ketones were collected with Sep-Pak (DNPH-Silica) cartridges
 manufactured by Waters Chromatography (Marlborough, Mass.). The HPLC
 analysis of the eluent in the Sep-Pak cartridges was performed as
 described in the manufacturer's instructions accompanying the cartridges.
 Table 1 presents a comparison of the performance of seven electrode
 materials applied for anodic degradation of benzoquinone in acetate
 buffer. Included are values of COD following electrolysis for specified
 time periods and brief comments pertaining to the electrolysis solution or
 the electrode surfaces. The COD in these solutions was determined by
 titration with standard KMnO.sub.4, a procedure that ignores contribution
 from the acetate/acetic acid components. The Au anode was least effective,
 requiring 48 h to decrease the COD to 582 mg/mL, i.e., a 46% decrease from
 the original value. The Ru/Ti anode was slightly more effective than Au
 with a COD of 28 mg/L after 48 h. The PbO.sub.2 /Ti anode decreased the
 COD to 12 mg/L after 24 h; however, the Fe-PbO.sub.2 /Ti anode decreased
 the COD to 8 mg/L after only 10 h. The Ru-Ti-Sb-SnO.sub.2 /Ti anode was
 somewhat less efficient than the Fe-PbO.sub.2 /Ti anode, producing a COD
 of 6 mg/L after 24 h. The glassy carbon anode exhibited significant
 degradation within 10 h and corrosion of the Ti surface in the
 Sb-SnO.sub.2 /Ti anode was observed after only 0.5 h.
 Comments are frequently offered by environmentalists that use of toxic
 lead-based anodes is not acceptable for electrochemical incineration
 applied to potable waters. Therefore, even though Ru-Ti-Sb-SnO.sub.2 /Ti
 anodes were slower to oxidize benzoquinone than Fe-PbO.sub.2 anodes, the
 former are preferred.
 TABLE 1
 Comparison of values for chemical oxygen demand (COD) and
 current efficiency achieved with seven electrode materials for the
 electrochemical incineration of 50 mL of 10 mM benzoquinone in acetate
 buffer.
 Cur-
 rent
 Electrode (mA/ Time COD.sup.a
 (10 cm.sup.2) cm.sup.2) (h) (mg/L) Observations
 None n.a. 0 1071 Brown-black
 solution.
 Au 10 48 582 Deep yellow
 solution.
 Ru/Ti 10 48 28 Yellow solution.
 Glassy carbon 10 10 -- Carbon particles
 suspended in solution.
 PbO.sub.2 /Ti 10 24 12 Colorless solution.
 Fe--PbO.sub.2 /Ti 10 10 8 Colorless solution.
 Sb--SnO.sub.2 /Ti 10 0.5 -- Apparent corrosion
 of Ti substrate.
 Ru--Ti--Sb--SnO.sub.2 /Ti 10 24 6 Colorless solution.
 .sup.a COD determined by titration with KMnO.sub.4.
 Quaternary metal oxide films corroded slowly when operated at large current
 densities (100 mA/cm.sup.2) and ambient temperatures (25-35.degree. C.).
 The U-tube shape of the Ru-Ti-Sb-SnO.sub.2 /Ti anode permitted circulation
 of thermostated water. With this electrode, the quaternary metal oxide
 films exhibited less corrosion when operated at higher temperature.
 Typically, corrosive losses were not visible nor detectable by gravimetry
 following 70-h electrolysis periods when the Ru-Ti-Sb-SnO.sub.2 /Ti
 tubular anode were operated at 200 mA/cm.sup.2 and 60.degree. C. The
 observed benefit from a higher operating temperature is not understood;
 however, it is known in the art that increased temperature increases the
 rate of water discharge and, therefore, causes the anode potential to be
 decreased.
 A freshly prepared quaternary metal oxide film on Ti that had not been used
 for electrolysis was examined by scanning electron microscopy. The
 micrograph indicated a moderately uniform film corresponding to an
 aggregation of small crystallites with individual diameters &lt;2 .mu.m. The
 results of energy dispersive spectroscopy for this surface confirmed the
 presence of Sb, Ru, Ti and Sn. An elemental analysis of two different
 regions of the electrode surface yielded the following percent
 compositions: Sb=7 and 8%, Ru=9 and 9%, Ti=10 and 21%, and Sn=34 and 39%.
 In comparison, the relative concentrations of metallic components of the
 solution used for thermal preparation of quaternary metal oxide films
 were: Sb=6%, Ru=14%, Ti=3% and Sn=77%.
 The Nafion membrane eliminated the need for added soluble salts to serve as
 supporting electrolytes, which facilitated direct analysis of product
 solutions using ES-MS. These analyses can only be performed on solutions
 of low ionic strength to prevent build-up of salt deposits that plug the
 orifice cone in the ES-MS. The Nafion 117 membrane also prevented film
 formation on the anode surfaces during electrochemical incineration of 10
 mM benzoquinone solutions over periods of several weeks. The prior art has
 reported formation of organic films on Pt electrodes applied for anodic
 degradation of phenol and stated that film formation was exacerbated by
 high pH, low current density, high temperature and high phenol
 concentrations. Similar problems of film formation with loss of electrode
 activity have been encountered in this laboratory during amperometric
 detection of phenol at Pt electrodes and electrolysis of benzoquinone at
 Pt, but the latter has yet to be published.
 Construction of electrolysis cells using a solid-state electrolyte requires
 that the membrane be sandwiched tightly between porous anode and cathode
 materials. Undoubtedly, for applications to solutions having zero ionic
 strength, i.e., very low conductivity, electrolysis occurred only on those
 small portions of the electrode surfaces that were in simultaneous contact
 with solution and membrane. The result was a severely attenuated working
 area of the electrodes with a corresponding increase in the effective
 current density. We observed cell voltages &gt;10 V as compared to &lt;5 V for
 the presence of acetate buffer (pH 5).
 Whereas this loss of effective electrode area, with a resulting increase in
 cell voltage, is seen as a disadvantage of this cell design, it is
 probably the explanation for the absence of organic film build-up on our
 anode surfaces. The higher effective current density resulted in an
 elevated rate of H.sub.2 O discharge at the working portions of the anode
 with a corresponding large flux density for OH radicals that are believed
 to be the source of O-atoms transferred to the product(s) of the
 electrochemical incineration reaction(s). Therefore, the lifetime of
 organic radicals was greatly diminished with the beneficial decrease (or
 elimination) of radical polymerization to form surface films. The smell of
 O.sub.3 (g) also was detected above the electrode assemblies constructed
 with the Nafion membranes. This has been reported and can be expected when
 high current densities are applied at noble electrodes. It is not known to
 what extent the evolution of some O.sub.3 assists in promoting the desired
 electrochemical incineration.
 A disadvantage of using the solid-state electrolyte in place of added
 soluble electrolyte was a significant increase in the electrolysis time
 needed to decrease COD values to specified levels. For example, addition
 of 0.1M acetate buffer (pH 5) to our cell resulted in a ca. 50% decrease
 in time required to achieve &gt;90% decrease in COD.
 FIG. 2 contains plots showing the change in COD and pH as a function of
 electrolysis time during the electrochemical incineration of a solution
 containing 100 mg/L benzoquinone. Values for COD, obtained with the Hach
 DR2000, steadily decreased from an initial value of 190 mg/L to 2 mg/L
 during a 64-h electrolysis period. Values of TOC (not shown) decreased to
 1.2 mg/L during this same period. The pH of the electrolysis solution
 decreased sharply to a minimum of ca. 3 at 2 h followed by a gradual
 increase to a final value of ca. 4. Whereas the rate of CO.sub.2 evolution
 is maximum immediately following the onset of electrolysis, ionization of
 the resulting H.sub.2 CO.sub.3 (pK.sub.a,1 =6.3) is not sufficiently
 strong to explain the sharp drop in pH. The most probable explanation is
 the formation of carboxylic acids by the first steps in benzoquinone
 degradation. The prior art reports the presence of maleic, fumaric and
 oxalic acids following electrolysis of phenol solutions.
 Benzoquinone is very reactive in water and undergoes condensation
 reactions. The identity of these condensation products is highly dependent
 upon starting concentration and pH. Products include dibenzofuran,
 biphenols, a trimer of molecular weight (MW) 290, plus a higher MW
 polymer. Condensation occurs rapidly in alkaline media but only slowly in
 neutral and acidic media. Following addition of benzoquinone to pure
 water, the color of the solution changes from light yellow to a tea color
 within 72 hrs and to coffee brown within one week. Because a similar color
 transition is observed during the initial phase of the electrochemical
 incineration of benzoquinone, an attempt was made to look for the
 compounds named above. None of these compounds was detected using a solid
 phase microextraction fiber in combination with GC-MS for a 10 mM
 benzoquinone solution.
 In the electrolysis solutions (100 mg/L benzoquinone), only hydroquinone
 and resorcinol were detected on the solid phase microextraction fibers
 even though the sensitivity for phenols was increased by derivatization
 with acetic anhydride. Derivatization was not performed on the 10 mM
 benzoquinone solution. Results obtained using the polyacrylate fiber
 during electrolysis were consistent with the presence of hydroquinone and
 resorcinol following 0.5, 1 and 2 h. At 4 h, hydroquinone was not detected
 and at 8 h, resorcinol was not detected.
 ES-MS was also used to look for dibenzofuran, biphenols and other phenolic
 compounds. Although ES-MS could detect these compounds in standard
 solutions, dibenzofuran and biphenols were not observed before or during
 the electrolysis of solutions containing 100 mg/L or 10 mM benzoquinone.
 However, phenol was detected in a stock solution of week-old 10 mM
 benzoquinone that had not undergone electrolysis.
 ES-MS identified p-benzoquinone and hydroquinone in electrolysis solutions
 at #4 h. Chromatograms are compared in FIG. 3 for a benzoquinone solution
 after 1 h of electrolysis (A) and a standard solution (B). In addition to
 the standards shown in the chromatogram, selected ion monitoring was used
 to look for 2-hydroxybenzoquinone. The prior art has shown that
 benzoquinone in dilute aqueous solution was converted to hydroquinone and
 2-hydroxybenzoquinone via a benzene-1,2,4-triol intermediate product. A
 peak was not seen in the chromatogram for 2-hydroxybenzoquinone but a
 signal was obtained at m/z=123 whenever benzoquinone or hydroquinone were
 eluted from the column. 2-Hydroxybenzoquinone was not commercially
 available and was too unstable to be synthesized and stored. However,
 2,5-dihydroxybenzoquinone was detected by ES-MS.
 Because resorcinol was detected in the electrolysis sample by the solid
 phase microextraction method but not when using ES-MS, resorcinol might
 have formed in the sample preparation step of the microextraction method.
 A high pH was required for the derivatization with acetic anhydride and
 benzoquinone is very reactive under these conditions. Another possible
 explanation is that the solid phase microextraction method was more
 sensitive to resorcinol than LC-ES-MS.
 The Zorbax SBC18 HPLC column works well for the separation of phenols in
 conjunction with ES-MS. One method of separating phenols is ion
 suppression chromatography which uses a phosphate buffer (pH 4) to
 suppress ionization. Phosphate buffers are known to suppress the ES-MS
 signal. Methanol and water are commonly used as a solvent for ES-MS
 analyses; fortunately the SBC18 column retained the phenols with only this
 eluent. Because detection limits improve as column diameter decreases, the
 use of a SBC18 column (3-mm i.d.) was tested to improve the sensitivity of
 the analytical technique. However, resolution between hydroquinone and its
 isomers was lost unless trifluoroacetic acid was added to the eluent at
 such a high concentration that signal suppression occurred in the ES-MS.
 Detection limits for HPLC-ES-MS of phenols were as follows: hydroquinone
 and benzoquinone=100 .mu.g/L, phenol and 2,5-dihydroxybenzoquinone=300
 .mu.g/L, and resorcinol and pyrocatechol=50 .mu.g/L. When the same
 chromatographic conditions were coupled to an absorbance detector, the
 limits of detection for all six compounds were ca. 20 .mu.g/L.
 Table 2 shows the acidic intermediate products detected during the
 electrochemical incineration of 100 mg/L benzoquinone. The major
 identified intermediate products were formic, acetic, maleic, succinic and
 malonic acids. Maleic acid concentrations peaked at 2 h and, by 8 h, had
 decreased to &lt;500 .mu.g/L. The presence of succinic, malonic, acetic and
 formic acids persisted after 32 h of electrolysis. Fumaric acid was
 detected in the first 4 h of electrolysis; however, concentrations were
 always less than 500 .mu.g/L. The inorganic anions chloride and sulfate
 were present as impurities in the starting solution (#1 mg/L). As a result
 of the anodic oxidation of chloride, chlorate was found in most
 electrolysis solutions at low levels (ca. 500 .mu.g/L). Because the
 detection limit for perchlorate was ca. 5 mg/L with the anion-exchange
 column, it could not be detected with the conductivity detector. However,
 perchlorate was detectable by ES-MS in all samples after ca. 4 h at
 concentrations estimated to be &lt;5 mg/L.
 TABLE 2
 Acidic intermediates identified in the product solution during
 electrochemical incineration of benzoquinone.
 Peak Concentration Electrolysis Time
 Compound (mg/L) (h)
 p-Hydroquinone 1 1
 Formic acid 5 0.5
 Fumaric acid &lt;1 0.5
 Maleic acid 9 2
 Malonic acid 1 8, 16
 Succinic acid 10 8
 Acetic acid 8 64
 It was not possible to identify all of the ions detected by direct infusion
 of the sample into the ES-MS. Because of the numerous reactions occurring
 in the electrolysis solution and fragmentation and clustering occurring in
 the electrospray ionization process, the interpretation of these data was
 difficult and necessitated the coupling of the ES-MS with LC.
 A Dionex AS11 anion-exchange column with a conductivity detector was used
 to quantify the anions listed in Table 2. Fifteen peaks were detected and
 a typical chromatogram is shown in FIG. 4. Because more peaks could be
 detected with the anion exchange column than with the ion exclusion column
 using ES-MS detection, the identities of all peaks shown in FIG. 4 have
 not been established. The anion-exchange column could not be coupled with
 ES-MS because the sodium hydroxide eluent was not compatible with ES-MS.
 Using LC-ES-MS, acetic acid, formic acid, chloride, succinic acid, malonic
 acid, maleic acid, fumaric acid and sulfate were identified. Fumaric acid
 was quantified using LC with absorbance detection.
 FIG. 5 compares remediation rates for four compounds generated during
 electrochemical incineration of benzoquinone. Whereas benzoquinone and
 maleic acid quickly undergo a redox reaction in the electrolysis solution,
 succinic and acetic acids were only slowly oxidized by electrochemical
 incineration. At 64 h, acetic acid was the only significant organic
 compound remaining in solution. Malonic acid levels were never higher than
 1 mg/L and, therefore, it is apparent that malonate is oxidized more
 rapidly than either succinate or acetate. Formic acid levels gradually
 dropped throughout the course of the electrolysis from 5 mg/L in the
 solution electrolyzed for 0.5 h.
 The first attempt to analyze the gas phase above the benzoquinone solution
 during anodic oxidation was to measure the yield of CO.sub.2 using Pt mesh
 electrodes and compare the CO.sub.2 yields with that from the
 thermostatically controlled Ru-Ti-Sb-SnO.sub.2 /Ti tubular anode. The
 tubular electrodes were previously known. Concentrations of CO.sub.2 were
 determined gravimetrically and yields with Pt mesh electrodes were 63%
 without use of an antifoam and 72% with an antifoam. Carbon dioxide yields
 using the quaternary metal oxide tubular electrodes were 74% for
 electrolysis periods in the range 48-72 h. As stated earlier, there was
 evidence that some of the organic intermediate products were swept out of
 the solution by co-evolution of CO.sub.2 and O.sub.2 with the result of
 CO.sub.2 yields &lt;100%.
 Results from analysis of the headspace above the coiled electrode assembly
 using the solid phase microextraction fiber indicated the presence of
 acetaldehyde and benzoquinone. Therefore, Sep-Pak cartridges were used to
 quantify aldehydes and ketones emitted from the electrolysis solution. The
 Sep-Pak cartridges concentrated aldehydes and ketones from the gas stream.
 After a 48-h electrolysis period, &lt;1% of the carbon in benzoquinone
 appeared to have been oxidized to acetaldehyde and acetone. No
 formaldehyde was detected in the gas stream.
 Because some of the small carboxylic acids generated by electrolysis are
 volatile, the condenser above the electrolysis cell was rinsed to see if
 any acids might adhere to it. Indeed, small peaks for acetic and formic
 acids were obtained using absorbance detection; however, no attempt was
 made to quantify these acids.
 Conceivably, metals from the quaternary metal oxide film, the Pt substrate,
 or the stainless steel cathode could be dissolved into the product
 solution. This is an issue of concern in consideration of metal oxide
 films for remediating organic waste solutions. Therefore, the elemental
 content of a benzoquinone solution after a 64-h incineration period at a
 well-used electrode was determined by ICP-MS. The estimated concentrations
 (.mu.g/L) are: Ti=0.5, Cr=0.5, Mn=1, Ni=3, Zn=32, Ru=2.4, Sn =1, Sb=1 and
 Pt=0.6. The concentrations determined following electrolysis using a
 newly-prepared electrode ranged from ten to one hundred times larger than
 those values reported here for a well-used electrode.
 Chromium, Sn and Pt are elements of major environmental concern and these
 were present at very low levels (0.5-1 .mu.g/L). The count rates for the
 Fe peaks at m/z=54 and 56 were approximately the same as for the
 unremediated blank and, therefore, virtually no Fe dissolved from the
 stainless steel counter electrode during electrolysis.
 FIG. 6 is a possible mechanism for the oxidation of benzoquinone to maleic
 acid. If benzoquinone is absorbed onto the electrode surface and gives up
 an electron, a neighboring adsorbed OH radical then attacks the
 benzoquinone. If this process repeats itself at the para position, the
 ring could open to form maleic acid and ethene. No ethene was detected in
 the headspace analysis; however, it has beeni reported that ethene is
 oxidized to CO.sub.2 at Pt but oxidized to acetaldehyde, acetone and
 propionaldehyde on Au or Pd electrodes.
 The mechanism in FIG. 6 suggests that maleic acid is reduced to succinic
 acid at the cathode followed by oxidation to malonic and acetic acid at
 the anode. The occurrence has been reported on the electroreduction of
 maleic and fumaric acids to succinic acid at a lead cathode. We found an
 electrolysis of succinic acid resulted in the appearance of malonic acid
 followed by acetic acid. The prior art reports that alcohols can be
 oxidized to the corresponding carboxylic acids if the reactants are not
 reduced at the cathode. It is possible that use of divided cells to
 prevent access of maleic acid to the cathode might decrease the time for
 total electrochemical incineration.
 Quaternary metal oxide films applied to Ti or Pt substrates exhibited high
 and persistent activity as anode materials for the electrochemical
 incineration of benzoquinone. Use of a Nafion membrane, sandwiched between
 the anode and cathode, eliminated the need for addition of soluble salts
 and, thereby, permitted product solutions to be analyzed by ES-MS.
 However, the low ionic strength of the solutions resulted in a substantial
 decrease in the working area of the electrodes with a corresponding
 increase in the electrolysis period needed to bring the COD effectively to
 a zero value.
 Numerous ionic intermediate products formed during the electrochemical
 incineration of benzoquinone were identified and quantified. The major
 intermediate products identified were p-hydroquinone, formic acid, fumaric
 acid, maleic acid, malonic acid, succinic acid and acetic acid.
 A distinct advantage of using the solid-state electrolyte in large-scale
 applications of electrochemical incineration is the production of a final
 product which is essentially pure water that can be disposed into sanitary
 sewage systems without the need for desalting or pH adjustment.
 In general, the anode may be formed of a relatively inert metal such as Pt,
 Ir, Au, Pd or Ti or the alloys thereof. Alternately, the anode may be a
 composite in which there is a metal substrate having thereon an oxide of a
 variety of materials to enhance the efficiency and operation of the anode
 substrate. For instance, the anode may be a composite which includes a
 substrate selected from Sn, W, Zr, Ta, Ir, Pd, Pt, Ti, Au, Cu alloys, Ru,
 C and Ag thereof. Most preferably, the anode substrate if it is to be
 combined with an oxide enhancing material is selected from Sn, Pt, Ti, Cu,
 Cu-Ag alloys, Ru and Ag. Various oxides are used to enhance electrical
 properties, chemical reactivity of properties, chemical reactivity of the
 anode material with respect to the toxic organic compounds in the
 electrolysis solution and to provide adhesiveness of the outside layer to
 the substrate. More particularly, antimony oxide is a good material to
 enhance the electrical conductivity in a composite anode and Ru oxides are
 good materials to enchance the chemical activity of a composite anode. In
 addition to the oxides of Ru, the oxides of the transition metals may be
 substituted for Ru to enhance the chemical activity of the oxide matrix on
 the metal substrate in a composite anode. Preferably, the oxide of the
 substrate metal is used to increase the adhesiveness of the oxide material
 to the substrate metal. For instance, if the substrate metal is Ti, then
 the preferred oxide to increase the adhesiveness of the oxide material in
 the composite anode is Ti oxide.
 In the preferred embodiment, the Sn oxide was used as a matrix for the Ti,
 Ru and Sb oxides. Moreover, a potential is normally applied across the
 anode and the cathode, but a well recognized alternative is to pass a
 controlled current through the electrolysis cell, and it is intended that
 both methods are to be included by reference to applying a potential
 across the anode and cathode.
 While there has been disclosed what is considered to be the preferred
 embodiment of the present invention, it is understood that various changes
 in the details may be made without departing from the spirit, or
 sacrificing any of the advantages of the present invention.