United States Environmental Protection Agency Municipal Environmental Research ~ Laboratory Cincinnati OH 45268 Research and Development EPA-600/S2-83-091 Dec. 1983 Project Summary Bromination Process for Disposal of Spilled Hazardous Materials A.J. Darnell A novel process was tested for oxi- dizing organic materials, including so- called "refractory organics" and pesti- cides. Bromine and water were allowed to react with such materials at 250° to 300°C to form carbon dioxide and aqueous hydrobromic acid. The HBr solution can be electrolyzed at ambient conditions, using a membraneless electrolysis cell, to produce hydrogen and regenerate bromine for recycling. The byproduct hydrogen can be sold or used as fuel for the process. The bromination process has now been evaluated for the destruction of hazardous waste spills on both a laboratory and a pilot-plant scale. Mala- thion,* the selected model compound, was successfully treated in an 8-liter, tantalum-lined autoclave at 300*C as part of a simulated spill mixture consisting of the malathion, soil, sand, humus, and moisture. Essentially complete destruction of the malathion (>99.9999%) was achieved. The aqueous HBr solution resulting from the oxidation was electrolyzed in an inclined membraneless cell with graphite electrodes to yield a solution containing about 20 wt % HBr and 18 wt % dissolved bromine. Coulombic efficiency for the electrolysis was about 96%. A conceptual design for a larger-scale system was developed on the basis of the laboratory and pilot-plant results. This design consisted of batch oxidation coupled with continuous electrolysis. It could process hazardous wastes at an •Mention of trade names or commercial products does not constitute endorsement or recommendation for use. average rate of 7.5 kg/hr. The total capital cost for such a system installed at an available site was estimated at $625.000 in January 1979. Of this total, $350,000 represented actual costs for equipment. Laboratory-scale oxidations using bromine were also carried out using two chlorinated hydrocarbons, gamma- lindane, and heptachlor. Under the conditions employed, which were not optimized, decomposition of both of these compounds was less efficient than when trichloroethane was the substrate. The HBr yields for lindane and heptachlor were 56% and 71%, respectively. This Project Summary was developed by EPA's Municipal Environmental Research Laboratory, Cincinnati, OH, to announce key findings of the research project that is fully documented in a separate report of the same title (see Project Report ordering information at back). Introduction and Background The health and safety factors related to hazardous materials mandate that a high level technology be used in their disposal or destruction. Methods used to dispose of hazardous wastes must also be able to cope with the nonhazardous materials that are often present, such as dirt, vegetation, and water. The variability in hazardous wastes encountered and the conditions under which cleanup must be conducted create unique problems for response and cleanup personnel. Rockwell International has developed a novel process that uses oxidation with bromine and water to destroy organic ------- materials. When allowed to react with bromine and water at 250° to 300°C in a closed system, organics (represented by CH) are oxidized to carbon dioxide and aqueous hydrobromic acid according to the general Equation 1: COi (To Atmosphere) H2 for Use or Flare CH + 2.5 Br2 + 2 H20 - 5HBr(aq. sol.) + CO2 (1) The carbon dioxide can be released to the atmosphere after the bromine and hydrogen bromine vapors have been stripped. The hydrobromic acid solution can be electrolyzed, as in Equation 2, to produce hydrogen and bromine: SHBr (aq.) electrolytic cell • > 2.5H2 + 2.5Br2(indil.HBr) (2) The hydrogen can be sold or used as fuel for the process, and the bromine can be recycled to the oxidation process. The process sequence is shown schematically in Figure 1. During the first portion of this program (designated as Task 1), laboratory investi- gations were conducted on the bromine plus water oxidation of three typical hazardous chemicals—copper acetate, trichloroethane, and malathion. At the preferred reaction temperature of 300°C, destruction of all three compounds was essentially complete in 1, 3, and 5 hr, respectively. The chlorine, phosphorus, and sulfur in the compounds were converted to hydrochloric, phosphoric, and sulfuric acid, respectively. The project demonstrated that the metallic bromides formed from the copper (and from other inorganic components that might be in an actual spilled waste) could be treated with sulfuric acid to recover the bromine and reduce the bromide content of the residue (inorganic sulfates) to 0.6 ppm. Task 1 was alsodevoted to developing a suitable process for the electrolysis of aqueous HBr solutions. With the constant boiling, 47% HBr/water azeotrope, a minimum no-load decomposition poten- tial of 0.69 volts was measured at 25°C. Though lower decomposition voltages can be obtained at higher temperatures, the nature of hazardous waste disposal is such that it seemed advisable to carry out the HBr electrolysis at ambient tempera- ture and pressure in spite of this penalty. Decomposition voltage was also found to depend on HBr concentration, with higher voltages required for 20% and 65% HBr than for 47% HBr. Carbonaceous -^ Waste Water — Concentrated Hydrogen Bromide (Aqueous) Electric 'Power Ash or Inorganic Residue Bromine + Dilute Hydrogen Bromide (Aqueous) Figure 1. Schematic flow diagram for disposal of carbonaceous wastes by the bromination process. The results of Task 1 of this program were reported in the Proceedings of the 1978 National Conference on Control of Hazardous Material Spills, Miami Beach, Florida, 1978. p. 221. Hazardous Materials Control Research Institute, Rockville, MD (now in Silver Spring, MD). Experimental Procedures and Results Laboratory Oxidations Using Bromine Parameters affecting the oxidation reaction were evaluated by carrying out a series of experiments, first with pure malathion in water and then with a simulated spill mixture containing 70 wt % malathion, 10 wt % sand, 10 wt % sand, 5 wt % humus, and 5 wt % moisture. The bromine was supplied first as a solution of bromine and water and later as a solution in aqueous hydrobromic acid, as might be produced from the electrolysis. The test apparatus consisted of a 600-ml glass ampule that was sealed and placed inside a 2000-ml steel autoclave. The autoclave was heated to 300°Cand maintained at that temperature for up to 5 hr. After the required time, the autoclave was chilled in liquid nitrogen to condense the carbon dioxide in the reaction ampule, and the ampule seal was broken. Analyses for malathion residues were carried out on the gas phase, the liquid phase, and (if present) the solid residue from the reaction using gas chromatogra- phy with a flame photometric analyzer sensitive to phosphorus. An electron capture detector was later substituted to achieve increased sensitivity. Liquid samples were extracted with petroleum ether before analysis. Solid residues obtained when the simulated spill mixture was used were filtered to separate the solids, which were then extracted by refluxing in aqueous hydrobromic acid at 127°C for 30 min. The liquid was then extracted with petroleum ether to obtain a sample for analysis. The first three experiments were intended to demonstrate that changes from Task 1 conditions would not affect the results of subsequent experiments. These experiments were as follows: 1) A control experiment was conducted under the same conditions as in Task 1, except that reactant quantities were increased about tenfold. The same size of ampule was used (600-ml), which meant that the pressure developed from carbon dioxide would be about 10 atm instead of 1 atm. 2) An experiment was done in which bromine dissolved in 22 wt % hydrobromic acid was substituted for the bromine/wa- ter reagent. This test was necessary, since the plan was to reuse the recovered solutions from the electrolysis as the source of bromine in the bromination reaction. ------- 3) An experiment was conducted using the simulated spill mixture of malathion with soil, sand, humus, and moisture and bromine dissolved in 22 wt % hydrobromic acid. The change did not adversely affect the results in any of the three experiments. After reaction at 300°C for 5 hr, no organo-phosphorus residue was detected in the gaseous, liquid, or solid phases of the reaction mixture. Based on the sensitivity of the analytical procedures, the bromination reaction effectively destroyed more than 99.9998% of the malathion. An experiment was then carried out to assess the effect of agitation on reaction time. Agitation, which was accomplished by rocking the autoclave and furnace assembly at 3 cycles/min, had a clearly beneficial effect on the destruction rate (Table 1). Reaction of the simulated spill mixture with bromine and water for 5 hr required more bromine than malathion alone required, since each of the added materials (particularly the humus) also consumed some bromine. Table 2 summa- rizes some of the data on bromine consumption by the other constituents in the mixture. Table 1. Effect of Agitation on Reaction of Malathion with Bromine and Water!*) Amount of Malathion Used Reaction Time Ihr) 1 2 2 5 Without Agitation 1%) 85ft) 89ft) >99 999ft) With Agitation ss (*IReaction with an initial Br2/H£)/malathion mole ratio of 40/600/1 ftlFrom analyses of HBr. HiSOt. and Hz POt formed ft)From analysis of malathion residuals by gas chromatography Table 2. Amount of Bromine that Reacted with Debris in 5 hr at 300°C Component Sand So/I Humus Bromine Reacted* Ig Bromine/ g of Debris Component) 004 0 11 4.74 "For comparison, the reaction used IS.Sg of bromine for each gram of malathion consumed Tests were also carried out in the laboratory apparatus at 300°C for 1 hr using lindane (gamma-CeHeCU) and heptachlor (CioHsCI?). With the production of HBr as a measure of oxidation, it was clear that both of these cyclic chlorinated compounds were considerably more resistant to bromine oxidation than was trichloroethane. The yields of HBr were 56% for li ndane and 71 % for the heptachlor, but reaction conditions had not been optimized. Pilot-Plant Bromine Oxidation The pilot-plant apparatus consisted of an 8-liter, tantalum-lined autoclave plus all the auxiliary equipment for stirring, heating, and temperature and pressure monitoring. A simulated spill mixture composed of 35 g malathion, 5 g sand, 5 g soil, 2.5 g humus, and 2.5 g moisture was allowed to react with a 5 wt % excess of bromine at 300°C for 2 hr. When the reaction was complete and the autoclave was cool, the residual pressure from carbon dioxide was 1208 kPa. Since the calculated carbon dioxide pressure for complete reaction was 1159 kPa, the reaction of the malathion plus debris mixture was essentially complete. No malathion residue was detected in the gaseous, liquid, or solid products. Laboratory Electrolysis Since the electrolyzed solution was to be reused as the source of bromine, electrolysis was carried out with solutions that would be produced from copper acetate, chlorinated organics and mala- thion (copper (II), chloride, sulfate and phosphate). These tests were carried out in a cell containing graphite electrodes (surface area - 14 cm ) and an aluminum oxide, fibered-felt membrane separator. Electrolyzing the hydrobromic acid solution from a copper acetate reaction required a lower decomposition voltage than when copper-free hydrobromic acid was used, possibly because of the increased ion concentration in the solution. At a voltage of 3.2V, copper was also observed to plate out on the cathode. During electrolysis of the 47% hydro- bromic acid solution from the trichloroe- thane reaction (which also contained hydrochloric acid), the decomposition voltage was about 10% lower than with the control. Note that no chlorine evolution was detected, since the decom- position voltage for hydrochloric acid is about 0.5 V higher than that of hydrobro- mic acid. When malathion was the organic being oxidized, 2 moles of sulfuric acid and 1 mole of phosphoric acid were formed for each 64 moles of hydrobromic acid. Electrolysis of this reaction solution required a higher decomposition voltage than the control. Several explanations are offered for this observation. Pilot-Scale Electrolysis The electrolysis apparatus used in the laboratory experiments was first scaled up about tenfold in electrode surface area. With this equipment a noticeable decrease in coulombic efficiency was observed when the hydrobromic acid solution contained large amounts of dissolved bromine. The efficiency of electrolysis was also reduced, and diffusion of bromine through the membrane increased significantly. Since the plan was to use an HBr solution that would be rich in bromine, these observations were quite serious. A search of the literature indicated that a membraneless electrolysis cell such as the mercury cell used in salt electrolysis could overcome these difficulties. Based on this review, the design selectedf or the pilot-scale electrolysis cell consisted of graphite electrodes separated by Teflon spacers. The upper electrode was the cathode. When current is passed through a cell of this design, the hydrogen formed at the cathode rises and escapes from ports at the upper surface. The bromine formed at the anode combines with HBr to form HBra, which is more dense than HBr and flows out ports at the lower end of the cell. Tilting the assembly so that the gas exit at the cathode was only slightly above the horizontal (3°) improved the coulombic efficiency significantly (Table 3). These results may reflect reduced turbulence and mixing of the denser HBra The inclined, membraneless cell was then used as part of a regeneration system. Concentrated hydrobromic acid electrolyte was pumped at 2 ml/min from a reservoir to the upper end of the cell, and the product solution of bromine and dilute hydrobromic acid was removed at the lower end. The hydrogen byproduct gas was scrubbed with water and sodium bromide solution to remove bromine and HBr vapors. The scrubbed exit gas contained less than 2 ppm of combined bromine and HBr. The bromine/bromide content could be further reduced to 0.1 ppm by the addition of a 10% sodium hydroxide scrubber to the train. Decomposition voltages for electrolysis of the 38% HBr solution from a malathion bromination essentially paralleled those obtained in the 4-liter membrane cell, but the coulombic efficiency of the membrane- less, flow-through cell was much higher. The voltage (energy) requirements were also considered to be several-fold higher than expected by comparison with other electrolysis processes. In an effort to reduce the needed voltage, the graphite cathode was coated with 5.5 mg/cm2 of ------- Table 3. Coulombic Efficiency of Membraneless Cell Electrode Current Density Milliamps/crr? 50 100 50 100 Electrode Angle (Degrees from Horizontal) 16 16 3 3 Coulombic Efficiency (Percent) 66 64 96 92 platinum by electrochemical deposition. This modification resulted in a significant (more than 50%) decrease in the decom- position voltages at comparable current densities. For example, at lOOmilliamps/ cm2, the decomposition voltage was reduced from 2.95 to 1.24 V. In addition, this value did not deteriorate over the 4 hr of the test, during which time coulombic efficiency was about 97%. Design Study A review of the magnitude of reported spills suggested that a unit capable of treating 22.7 kg of hazardous chemical would be suitable for field use. This figure was used as the basis for the design of a field-scale system. Batch bromination coupled with continuous electrolysis for bromine regeneration were selected as the least costly scenario. The design reflected the laboratory and pilot-plant results indicating that 2 hr at 300° and 8500 kPa were the maximum conditions needed. Also considered were the reactivity of other debris and the need to remove solids after reaction. The tantalum lining of the reactor was retained. The electrolysis unit (to be operated continuously once a reserve of hydrobro- mic acid liquor was generated) would operate at 25°C and atmospheric pressu re and convert the bromination reactor effluent to a final recyclestream containing 22% HBr and 16% bromine. The completed design is shown sche- matically in Figure 2. A total capital cost of $299,800 was estimated from vendor quotes and other sources. Piping, overhead, construction costs, etc., resulted in a total installed cost (1979) at an available site of $625,000 (Table 4). The system is capable of processing about 7.5 kg/hr of hazardous chemicals. Table 4. Cost Summary for 7.5-kg/hr Disposal System* Item Major equipment Minor equipment Installation Piping Total Cost $299,800 50,000 150,000 125,000 $624,800 *1979 dollars. CO2 Makeup Water Nz Purge Spill Charge Bromine Dissolved in Dilute HBr — — — — Dashed Lines Indicate Flow During Shutdown Figure 2. Block diagram of a conceptual disposal system. 4 ------- Conclusions Pilot-plant testing demonstrated that an organic hazardous chemical such as malathion can be completely destroyed (99.9999%) by an oxidation process usi ng bromine, even in a simulated spill mixture. Bromine and/or hydrobromic acid also react with other organic and inorganic components of such mixtures to a limited extent during the process. Some inorganic materials form metallic bromides that consume bromine, but the bromine can be recovered readily by treating these residues with sulfuric acid. The concentrated, aqueous hydrobromic acid effluent from the bromine oxidation process can be electrolyzed to make the bromine available for reuse. Based on pilot-plant studies, the electrolysis can be carried out in a single pass at ambient temperature and pressure using a mem- braneless electrolysis cell. The addition of small amounts of a platinum catalyst to the graphite cathode reduces the electrical power requirements by more than 50%. A full-scale system capable of treating 7.5 kg/hr of hazardous waste had an estimated installed capital cost of about $650,000 in January 1979. Recommendations The oxidation of hazardous wastes by bromine should be considered as an option for the destruction of hazardous chemcials, even when these are mixed with nonhazardous debris. Further studies should be done to include the use of catalysts and to accelerate the oxidation reaction or reduce the required temperature. Similar- ly, techniques should be explored to increase the reactivity with other chlorin- ated hydrocarbons such as lindane and heptachlor, which may be encountered in spill cleanup situations. The amount of platinum required on the graphite cathode to catalyze the electrolysis of aqueous hydrobromic acid should be better defined. Alternative methods of activating the electrodes and catalyzing the electrolysis (such as the reported use of nitric acid) should be investigated. A unit capable of destroying 8 to 10 kg/hr of hazardous wastes should be constructed for larger-scale confirmation of the pilot-plant results and for possible field testing. The full report was submitted in partial fulfillment of Contract No. 68-03-2493 by Rockwell International under the sponsor- ship of the U.S. Environmental Protection Agency. A. J. Darnell is with Rockwell International, Canoga Park, CA 91304. John E. Brugger is the EPA Project Officer (see below). The complete report, entitled "Bromination Process for Disposal of Spilled Hazardous Materials," (Order No. PB 83-263 806; Cost: $10.00. subject to change) will be available only from: National Technical Information Service 5285 Port Royal Road Springfield, VA 22161 Telephone: 703-487-4650 The EPA Project Officer can be contacted at: Oil and Hazardous Materials Spill Branch Municipal Environmental Research Laboratory-Cincinnati U.S. Environmental Protection Agency Edison, NJ 08837 ------- United States Environmental Protection Agency Center for Environmental Research Information Cincinnati OH 45268 BULK RATE U.S. POSTAGE PAID Cincinnati, Ohio Permit No. G35 Official Business Penalty for Private Use $300 r U S GOVERNMENT PRINTING OFFICE 1984-759-102/815 i ------- |