BACKGROUND OF THE INVENTION

There are a number of toxic organic substances that are so resistant to both thermal degra¬ dation and biological degradation that their improper disposal results in severe environmental pollution problems. These toxic organic substances usually un¬ dergo only partial destruction in conventional inciner- ators vith the result that unreacted or partially oxi¬ dized toxic compounds are discharged vith the stack gases into the atmosphere and may subsequently cause pollution of the air, soil, and vatervays.

The U.S. Environmental Protection Agency has listed hundreds of toxic and hazardous organic sub¬ stances that must be disposed of in an environmentally acceptable manner to safeguard the public health. These include such highly toxic chlorinated cyclic hydrocarbons as the dioxins and the polychlorinated biphenyls (PCB's). They comprise a host of pesticides and pesticide residues, including the carbamates and the organophosphates. In addition, large quantities of chemical vaste products are produced in the course of the manufacture of organic chemicals and in the refin- ing of crude oil. Thus, the refinery bottoms frequent¬ ly contain carcinogenic poly-cyclics that must be safe¬ ly destroyed.

Incineration has been a traditional mode of disposal- Hovever, there is an increasing avareness that conventional incineration frequently results in the emission of partial combustion or recombination products that constitute a serious air pollution haz¬ ard. The present invention affords an environmentally superior disposal means in that it assures quantitative destruction and produces no stack emissions vhatever. In addition it converts the toxic or hazardous organic substances or vaste materials into a clean, medium-BTU fuel or synthesis gas, that can readily be converted to methanol, high-octane gasoline, or natural gas (meth¬ ane) .

DESCRIPTION OF THE INVENTION This invention relates to a process for the decomposition of toxic organic substances that are unusually resistant to thermal degradation. The pro¬ cess for the destruction of toxic refractory organic substances may be superimposed on an efficient, energy- producing gasification process that operates at temper¬ atures substantially higher than those of air-supported incinerators. In this vay the quantitative thermal destruction of toxic refractory organic substances is accomplished at a negligible increase in the cost of producing a clean, medium BTU fuel or synthesis gas. ^τ -" ile the process of this invention can be used to descroy any organic substance that is resistant to thermal and biological degradation, it is of partic¬ ular value in the destruction of those refractory or- ganic substances that are toxic to living organisms and that vhen subjected to heating in conventional inciner¬ ators yield toxic degradation products that vhen re¬ leased into the atmosphere cause serious pollution

problems. Such toxic materials include dioxins; poly¬ halogenated biphenyls; organophosphates, such as Parathion; halogenated biocides, such as hexachloro- benzene, Chlordane, DDT, and 2,4,5-trichlorophenoxy- acetic acid; and vaste streams from the production of these toxic substances.

In the process of this invention, the toxic refractory organic substance is reacted vith an oxidiz¬ ing medium under conditions so controlled as to main- tain a flame or combustion temperature in the range of 2500°F to 3200°F, preferably in the range of 2800°F to 3100°F, for a period of from 5 to 500 milliseconds in a reaction chamber that may have a refractory lining and that contains incandescent carbon or incandescent re- fractory oxides, such as alumina or zirconia. The high temperature environment is created and maintained by the partial oxidation of the refractory organic sub¬ stance.

The refractory organic substance that is introduced into the combustion chamber may be a liquid, a gas, or a solution or suspension of a solid in a combustible organic liquid.

The oxidizing medium used in this process may be a gas, such as oxygen, oxygen-enriched air, or air that has been sufficiently preheated to sustain the desired flame temperature; or a liquid, such as nitro¬ gen tetroxide. It is preferably oxygen or oxygen-en¬ riched air.

Steam is fed to the gasification chamber to maintain the reaction temperature in the desired range, that is, betveen 2500°F and 3200°F, and to provide a reducing atmosphere beyond the partial combustion zone or flame.

The amount of oxygen or other oxidizing medium that is fed into the reaction chamber is depen¬ dent upon such factors as the properties of the toxic refractory organic substance and the apparatus in vhich the degradation of the refractory substance is to be effected. Excellent results have been obtained using the amount of oxidizing medium that is required stoichiometrically for complete combustion of the re¬ fractory material as veil as more or less than this amount. When the refractory substance is destroyed in a gasifier or in a combination of a torch and a gasifi- er, the amount of oxidizing medium used is that re¬ quired for the partial oxidation of the refractory substance and the gasification of the carbonaceous fuel so as to generate a temperature of at least 2500 ^β F.

The relative amounts of steam and oxidizing medium that are used are so regulated as to maintain the desired reaction temperature.

The mixture of partial and complete combustion products leaving the gasifier is passed through a heat exchanger for the recovery of heat and into a conventional scrubber for the removal of noxious inorganic decomposition products, such as hydrogen chloride, hydrogen sulfide, ammonia, or phosphine. The scrubbed product gas may be used as a synthesis gas or fuel. Any solid inorganic impurities introduced vith the carbonaceous feed material may be vithdravn from the hearth of the gasifier in the form of a molten slag.

The process of this invention may be carried out in any suitable and convenient apparatus in vhich the refractory organic material can be exposed to an oxidizing medium and steam at a temperature in the range of 2500 ^β F to 3200°F for a period of 5 to 500

milliseconds. It is preferably carried out in a torch, a slagging gasifier, or a combination thereof. For example, it may be carried out in an alumina-lined reaction chamber having inlets for steam and oxidizing medium; an oxypropane torch may be provided as a pilot light. The chamber may be fitted vith zirconia cylin¬ ders, bricks, rods, saddles, or bars. The thermal decomposition may also be carried out in a slagging, moving-burden gasifier, such as the gasifiers described in detail in U.S. Patent No. 4,340,397 and U.S. Patent No. 4,052,173; or in a combination of a refractory- lined torch feeding into a gasifier.

In one of the preferred embodiments of the invention, the refractory organic substance is intro- duced into a reaction chamber that is designed to pro¬ vide a residence time of 5 to 500 milliseconds vherein it is reacted vith an oxidizing medium and steam at a temperature of 2500°F to 3200°F. The partial combus¬ tion products are then contacted vith refractory inor- ganic surfaces that comprise the vails and internal packing of the reaction chamber vhich have been heated to incandescence by the reaction products. Steam is fed to the partial combustion zone of the reaction chamber to maintain the temperature in the desired range and to provide a reducing atmosphere beyond this zone. The complete and partial combustion products leaving the reaction chamber are passed through a heat exchanger and into a scrubber. The scrubbed product vhich contains substantially no toxic compounds may be employed as a synthesis gas or fuel.

In another preferred embodiment of the invention, the process is carried out in an apparatus that comprises a slagging, moving-burden gasifier. The gasifier vhich is preferably of the type disclosed in

U.S. Patent No. 4,052,173 or U.S. Patent No. 4,340,397, vhich are incorporated herein by reference and consist of a vertical shaft furnace surmounted by a convention¬ al lock hopper. It may be operated at pressures of 1 to 100 atmospheres but is preferably operated at atmo¬ spheric pressure. The carbonaceous fuel.that is intro¬ duced through the lock hopper may be, for example, anthracite coal, petroleum coke, metallurgical coke or vood char. An oxygen-rich gas and steam are fed to the hearth zone of the shaft furnace in a ratio so regulated as to maintain the hearth temperature in the range of 2500°F to 3200 ^β F vhile at the same time a toxic refractory organic substance is introduced into the hearth zone. When employing a gasifier of the type described in U.S. Patent No. 4,340,397, the rav gaseous products reaching the ^' top of the gasifier are recycled to the partial combustion zone through an internal or external conduit by means of a steam jet. At the same time, at least a portion of the resultant tar-free gas leaving the partial combustion zone is vithdravn as product at a point belov the pyrolysis and coking zone of the shaft furnace.

The toxic organic substance may be introduced to the partial combustion zone in the form of a liquid, a solution, a slurry or a vapor by means of a torch or tuyere vhich simultaneously admits the regulated flovs of oxygen-rich gas and steam to form a flame. The resultant reaction products issuing from the flame are then brought in contact vith a bed of incandescent coke or char and/or refractory oxide vhere they are further pyrolyzed and reduced so that all higher-boiling organic molecules are cracked to non- condensible gases, predominantly carbon monoxide, car-

bon dioxide, hydrogen and methane. The flov of oxygen and steam may be so regulated that the consumption of the gravitating bed of metallurgical coke, petroleum coke, or char may be slov or rapid. In either case, the solid carbonaceous substrate vill be maintained at incandescent heat by the upvard flov of the partial combustion products.

The process of this invention is preferably carried out in a vertical shaft furnace, surmounted by a lock hopper through vhich the coke is admitted to the furnace. The torches or tuyeres through vhich the reactants are fed to the partial combustion zone are mounted just above the hearth floor of the furnace. The hearth floor contains a taphole through vhich the molten slag resulting from inorganic components in the coke is continuously vithdravn into a connecting quench chamber in vhich the molten slag is quenched vith wa¬ ter, and from vhich the' fritted slag is vithdravn through a lock hopp3r. The flovs of reactants, and the flame temperature are so regulated as to secure destruction efficiencies of the toxic organic substances being processed of 99.9999% or better. Depending on the heat stability of the toxic organic substances being pro- cessed, a residence time in the range of 50 to 500 milliseconds is required.

In another embodiment, the destruction of the toxic organic substance by reaction vith oxygen and steam may be carried out in a refractory-lined combus¬ tion chamber so designed that the partial combustion products issuing from the torch or tuyere are caused to traverse a checkervork of inorganic refractory oxides

such as alumina, silica, zirconia, or combinations of these. Again the residence time is controlled to as¬ sure destruction efficiencies of the toxic organic substances being processed of 99.9999% or better. In this embodiment, the need for consumable carbonaceous substrate is obviated. Upon issuing from the shaft furnace or the refractory-packed reaction chamber, the product gas is cooled by heat exchange in conventional equipment and then scrubbed in a venturi scrubber for the removal of liberated hydrogen chloride and other acidic impurities. The pH of the scrubber vater is maintained on the alkaline side through the addition of a base such as milk of lime to insure the efficient removal of these liberated inorganic components. The scrubbed gas is then further treated for the removal of hydrogen sulfide, if sulfur is introduced vith the toxic organic substance or vith the carbonaceous sub¬ strate. The sulfur removal and recovery are accom¬ plished by vell-knovn commercial processes. The process of this invention employs a combination of high temperature chemical reactions that occur in parallel or in rapid sequence to produce fi¬ nally a product gas comprised of simple molecules such as hydrogen, carbon monoxide, methane, carbon dioxide, nitrogen, hydrogen chloride, and hydrogen sulfide. The noxious acidic gases are quantitatively removed from the product gas by veil-established commercial process¬ es. The principal reactions occurring in the shaft furnace or the refractory packed reaction chamber in¬ clude the folloving:

1. C + l/20 ₂ = CO

2. C + 0 ₂ = C0 ₂

3. C0 ₂ * ^■ C = 2CO

4. C + H-0 = CO + H,

5. CO + H ₂ 0 = C0 ₂ + H ₂

6. C + 2H ₂ = CH ₄

7. CO + 3H ₂ = CH ₄ + H ₂ 0

8. 2CO + 2H ₂ = CH ₄ + 0 ₂

9. S + H ₂ = H ₂ S , 10. RCl _χ + n0 ₂ + mH ₂ 0 = xHCl + yCO + zH ₂

In a preferred embodiment, the reactions are carried out by injecting the toxic organic substances or vaste products into the partial combustion zone of a refractory-lined shaft furnace through one or more tuyeres or torches that enter the shaft furnace just above the hearth floor of said shaft furnace. Each tuyere or torch is fed simultaneously vith oxygen and steam so that a veil-mixed stream of these three reac- tants is injected into the hearth section of the shaft furnace to form a flame having a temperature in the range of 2500°F to 3200°F. The flame impinges upon a gravitating bed of incandescent coke or char vhich provides a strongly reducing atmosphere as veil as active reaction sites vhich promote the further pyrolysis of partial combustion and decomposition prod¬ ucts. To the extent that there is any unreacted oxygen or steam present in the partial combustion products issuing from the flame, these vill react vith the in- candescent carbon according to reactions 1 and 4. By increasing the flov of oxygen and steam above that required to react vith the toxic organic chemicals being processed, the consumption of coke may be arbi¬ trarily increased to augment the production of synthe¬ sis gas comprised principally of carbon monoxide and hydrogen. In operating the process, the ratio of oxy¬ gen to steam is so controlled that the desired flame or reaction temperature is maintained. The temperature may be observed through a viev port built into each

tuyere. A recording pyrometer may be focused on the flame or the incandescent coke particles upon vhich it impinges. This reading may in turn be used to control the flov of oxygen, given a fixed flov rate of steam and toxic feed stream.

The shaft furnace may consist of a vater- cooled steel shell lined vith an acid-resistant refrac¬ tory. The furnace is surmounted by a lock hopper through vhich the coke or petroleum coke is fed to the furnace. The product gas is vithdravn through a heat exchanger to an alkaline scrubber to a convention gas clean-up train. There are no stacks associated vith the operation of the shaft furnace, and the resultant product gas is scrubbed free of all air-polluting con- taminants, so that it may be used as fuel in a gas turbine or in a public utility boiler, where it burns as cleanly as natural gas.

The inorganic impurities or ash present in the carbonaceous substrate forms a molten slag vhich collects on the hearth floor from vhich it is continu¬ ously vithdravn through a tap hole and quenched in vater. The resulting slag granules are vithdravn from the connecting quench vessel through a lock hopper. In another embodiment the reactants may be introduced through tuyeres or torches mounted in the top head of a cylindrical combustion chamber to flov dovnvardly over a refractory structure or packing. The structure may be in the form of a brick checkervork, vertically or horizontally mounted tubes or rods, a series of truncated cone-shaped baffles, or refractory saddles. The refractory lining and the packing materi¬ al are preferably of an acid resistant composition rich in alumina, silica, or zirconia. The free volume of the combustion chamber and the flov rates are so chosen

- li ¬

as to afford destruction efficiencies of the toxic organic substance being processed of 99.9999% or bet¬ ter. This normally requires a residence time of 50 to 500 milliseconds. After passing through the packed combustion chamber, the resultant product gas passes dovnvardly through a radiant cooling section into a convective heat exchanger and finally into an alkaline venturi scrubber. This invention is further illustrated by the following examples.

EXAMPLE 1 The folloving procedure vas carried out in a slagging, moving burden gasifier of the type that is disclosed in U.S. Patent No. 4,340,397. This gasifier is a vertical shaft furnace that comprises, successive¬ ly from top to bottom, a preheating and drying zone, a pyrolysis and coking zone, a high temperature reaction zone, and a partial combustion zone. Sized coke vas charged through a lock hopper- on top of the gasifier and gasified by partially oxi¬ dizing it vith oxygen in the presence of steam at a hearth temperature of 2900°F to 3100°F. This vas ac¬ complished by controlling the amounts of oxygen and steam introduced into the partial combustion zone so that the exothermic partial combustion reaction vas balanced by the endothermic vatergas reaction.

When steady-state operation of the gasifier had been established, a hot stream of hexachlorobenzene dissolved in toluene vas fed directly into the partial

2 combustion zone at the rate of 500 kg/m /hr.

The product gas issuing from the gasifier vas analyzed for unreacted hexachlorobenzene and hydro-

gen chloride. These analyses, vhich vere confirmed by gas chromatographic analysis of the off-gas, indicated that 99.99993% of the hexachlorobenzene had been de¬ stroyed.

⁵ EXAMPLE 2

The folloving procedure vas carried out in an alumina-lined reaction chamber fitted vith an inter¬ nal structure of zirconia rods, vhich vas provided vith a torch and a steam/oxygen tuyere. The chamber vas 10 sized to afford a residence time of the order of 100 milliseconds at the feed rates employed.

A 55% solution of Malathion (0,0-dimethyl dithiophosphate of diethyl mercaptosuccinate) in xylene vas fed as fuel to the torch vhich used oxygen and ¹⁵ steam as the reaction medium. The oxygen vas fed in an amount that vas less than the stoichiometric amount required for complete combustion of the Malathion solu¬ tion, and the steam flov vas regulated to maintain the combustion temperature in the range of 2900°F to 0. 3100°F.

The off-gas vas quenched vith aqueous milk of lime in a spray scrubber to remove acidic decomposi¬ tion products.

Gas chromatographic analysis of the scrubbed 5 gas indicated that 99.99992% of the Malathion had been destroyed.

EXAMPLE 3 The folloving procedure vas carried out in a reaction, chamber of the type described in Example 2 ³⁰ vhich fed into the high temperature reaction zone of a slagging, moving burden gasifier of the type disclosed in U.S. Patent No. 4,340,397 vhich is a vertical shaft

furnace comprising successively from top to bottom, a preheating and drying zone, a pyrolysis and coking zone, a high temperature reaction zone, and a partial combustion zone. Polychlorinated biphenyl (a mixture of tetrachlorobiphenyl isomers) vas burned in the torch, vhich used oxygen and steam as the reaction medium.

Less than the stoichiometric amount of oxygen required for complete combustion of the polychlorinated biphenyl vas fed to the torch. The steam flov vas regulated to maintain the flame tempera¬ ture of the torch at about 3000°F.

The combustion products issuing from the reaction chamber vere brought into contact vith the incandescent coke in the partial combustion and high temperature reaction zones of the gasifier. During this process, the partial combustion zone of the gas¬ ifier vas maintained at about 2800°F. The residence time of the polychlorinated biphenyls in the torch and partial combustion zone of the gasifier vas 50 to 100 milliseconds.

Analysis of the product gas issuing from the gasifier shoved that 99.99998% of the polychlorinated biphenyls had been destroyed.