Method for the destruction of halogenated organic compounds in a contaminated medium

A method for the destruction of halogenated organic compounds contained in a contaminated medium comprises adding an aqueous solution of polyethylene glycol to the contaminated medium in an amount to provide from about 0.1 to about 20 weight percent of polyethylene glycol, based on the weight of the contaminated medium. An alkali metal hydroxide is then added in an amount of from about 2 to about 20 weight percent, based on the weight of the contaminated medium. The medium is then heated to substantially dehydrate the medium and then further heated at a temperature between about 100.degree. and 350.degree. C. to effect destruction of the halogenated organic compounds. An acid is then added to the medium in an amount sufficient to neutralize the same.

FIELD OF THE INVENTION 
The present invention relates to a method for the destruction of 
halogenated organic compounds contained in a contaminated medium. More 
particularly, the invention relates to a method for the destruction of 
halogenated organic compounds contained in a contaminated medium by use of 
an aqueous solution of polyethylene glycol, an alkali metal hydroxide, and 
an acid. 
BACKGROUND OF THE INVENTION 
The hazards to public health and the environment which are posed by a 
variety of synthetic halogenated organic compounds is well known. 
Compounds such as polychlorinated biphenyls (PCB's), dichlorodiphenyl 
trichloroethane (DDT), dieldrin, lindane and chlordane have been found to 
be persistent, environmentally toxic materials which require safe and 
efficient means of disposal PCB's pose a particularly serious disposal 
problem. Once widely used as dielectric fluid additives in electrical 
equipment such as transformers and capacitors because of their excellent 
insulating properties, the use of PCB's in many applications has been 
banned by the U.S. Environmental Protection Agency owing to their 
cumulative storage in the human body and extremely high toxicity. Thus, 
methods for the removal and/or destruction of halogenated organic 
compounds such as PCB's are required. 
Various methods for the removal and/or the destruction or decomposion of 
halogenated organic compounds are known in the art. For example, the 
Peterson U.S. Pat. Nos. 4,447,541 and 4,574,013 disclose methods for 
decontaminating soil which is contaminated with halogenated organic 
compounds. The Peterson U.S. Pat. No. 4,447,541 discloses process in which 
a reagent mixture of an alkaline constituent and a sulfoxide catalyst 
(DMSO) are intimately mixed with soil contaminated with PCB's. The reagent 
mixture affects a desorption of the halogenated contaminants from the soil 
and subsequently dehalogenates the contaminants. However, this process is 
disadvantageous in that the kinetics are relatively slow and therefore 
reduction of the PCB concentration to an acceptable level requires 
extended time periods ranging from weeks to months, the soil must be 
completely dry for the destruction to take place, large quantities of the 
reagent are required, and the sulfoxide catalyst may potentially transport 
contaminants prior to their destruction. The Peterson U.S. Pat. No. 
4,574,013 discloses a process wherein a heated slurry of contaminated soil 
is treated with a mixture of an alkaline constituent and a sulfoxide 
catalyst. However, this process is similarly disadvantageous in that the 
sulfoxide catalyst may transport contaminants into living systems, and the 
sulfoxide catalyst produces odorous compounds when heated to high 
temperatures and decomposes into combustible byproducts under elevated 
temperature conditions. This process is also disadvantageous in that it 
requires large amounts of reagents. 
The Rogers et al U.S. Pat. No. 4,675,464 discloses a method for the 
chemical destruction of halogenated aliphatic hydrocarbons, and more 
particularly a method for the chemical destruction of ethylene dibromide. 
An alkali metal hydroxide is dissolved in an ethylene glycol and the 
resulting product is reacted with the halogenated hydrocarbon. Rogers et 
al further disclose that the reaction temperature should be maintained at 
30.degree. C. or less to maintain the reaction products in solution. 
The Pytlewski et al U.S. Pat. No. 4,400,552 discloses a method for the 
decomposition of halogenated organic compounds which employs a reagent 
comprising the product of the reaction of an alkali metal hydroxide with a 
polyglycol or a polyglycol monoalkyl ether, and oxygen. The Pytlewski et 
al U.S. Pat. Nos. 4,337,368 and 4,602,994 disclose similar methods of 
decomposing halogenated organic compounds. However, these methods are 
disadvantageous in that excess amounts of the alkali metal hydroxide and 
polyglycol reagents are required in order to obtain a homogeneous 
distribution throughout the contaminated material, for example soil, 
sediment, sludge or the like, which is treated. Similarly, the Brunelle 
U.S. Pat. Nos. 4,351,718 and 4,353,793 disclose methods for removing 
polyhalogenated hydrocarbons from nonpolar organic solvent solutions by 
treating the contaminated solutions with a mixture of polyethylene glycol 
and an alkali metal hydroxide. These methods are similarly disadvantageous 
in that excess amounts of reagent are required. Additional methods for 
removing and/or destructing halogenated organic compounds contained in 
contaminated materials are disclosed in the Howard et al U.S. Pat. No. 
4,327,027, the Mendiratta et al U.S. Pat. No. 4,663,027, the Meenan et al 
U.S. Pat. Nos. 4,685,220 and 4,793,937, the Rossi et al U.S. Pat. No. 
4,761,221, the Zeff et al U.S. Pat. No. 4,792,407, European Patent 
Application No. 118,858, Chemical Abstracts, Vol. 82, No. 139620P (1975) 
and Kornel et al, Journal of Hazardous Materials, 12 (1985), pages 
161-176. However, these and additional processes known in the art for the 
removal and/or destruction of halogenated organic compounds in 
contaminated materials are inadequate in view of the time required for 
acceptable levels of removal and/or destruction, the use of excessive 
amounts of various reagents, the production of toxic and/or combustible 
byproducts, and/or the failure to obtain desired removal and/or 
destruction levels. Thus, a need exists for additional methods for the 
removal and/or destruction of halogenated organic compounds in 
contaminated materials, which methods overcome the disadvantages of the 
prior art. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of the present invention to provide a new 
method for the destruction of halogenated organic compounds contained in a 
contaminated medium. It is a further object of the invention to provide a 
method for the destruction of halogenated organic compounds contained in a 
contaminated medium which employs significantly less amounts of reagent as 
compared with prior art methods. It is a further object of the invention 
to provide such a method wherein environmentally acceptable levels of 
halogenated organic compounds are achieved in the treated materials. It is 
a related object of the invention to provide such a method wherein the 
environmentally acceptable levels of contaminants in the materials are 
obtainable within a short period of time. 
These and additional objects are achieved by the present invention which 
relates to methods for the destruction of halogenated organic compounds 
contained in a contaminated medium. The methods of the invention comprise 
the steps of adding an aqueous solution of polyethylene glycol to a 
contaminated medium containing the halogenated organic compounds. An 
alkali metal hydroxide is then added to the contaminated medium. Because 
the polyethylene glycol is added in an aqueous solution, water distributes 
the reagents throughout the medium and acts as a wetting agent. The 
contaminated medium is then heated at a temperature and for a time 
sufficient to substantially dehydrate the medium. Although the water is 
removed, the reagents are well distributed throughout the medium and are 
concentrated to a very reactive state. The medium is then further heated 
at a temperature between about 100.degree. and 350.degree. C. for a time 
sufficient to effect destruction of the halogenated organic compounds. 
Destruction of the halogenated compounds in the contaminated medium is 
more dependent on the presence of the alkali metal compound as the 
temperature increases within this range. Finally, an acid is added to the 
medium in an amount sufficient to neutralize the medium so that it may be 
returned to its original environment. Because the aqueous solution of 
polyethylene glycol is employed, the amounts of reagents which are 
required for the present methods are significantly reduced. Additionally, 
because the reagents are well distributed throughout the medium by the 
aqueous solution, a homogeneous destruction of the halogenated organic 
compounds is achieved. Moreover, because lower amounts of reagent are 
employed, recycling of excess reagents is not required. 
These and additional objects and advantages will become more fully 
understood in view of the following detailed description. 
DETAILED DESCRIPTION 
The present invention comprises methods for the destuction of halogenated 
organic compounds contained in a contaminated medium. The contaminated 
medium may comprise soil, sludge, sediment or a liquid. The present 
methods are particularly adapted for use with soils, sludges and 
sediments. The methods are suitable for use with mediums which contain up 
to 100,000 ppm of halogenated organic compounds, aliphatic or aromatic, 
for example PCB's, or even higher levels of the halogenated organic 
compounds. The contaminated mediums which are suitable for use in the 
invention may also include an absorbent or adsorbent, for example spent 
activated carbon or the like. 
Generally, the methods of the invention comprise adding an aqueous solution 
of polyethylene glycol to the contaminated medium, adding an alkali metal 
hydroxide to the contaminated medium, heating the contaminated medium to 
obtain substantial dehydration, and further heating the medium to destruct 
the halogenated organic compounds. The water included in the polyethylene 
glycol solution distributes the reagents throughout the contaminated 
medium. In the final step, the medium is treated with an acid to provide a 
neutral pH so that the medium may be safely returned to its original 
environmental if desired. 
The aqueous solution of polyethylene glycol is added to the contaminated 
medium in an amount to provide from about 0.1 to about 20 weight percent 
polyethylene glycol, based on the weight of the contaminated medium. 
Additionally, the aqueous solution contains sufficient water to effect 
homogeneous distribution of the polyethylene glycol and the subsequently 
added alkali metal hydroxide throughout the contaminated medium. While the 
particular amount of the aqueous solution of polyethylene glycol which is 
added to the contaminated medium generally depends on the level of 
halogenated organic compounds contained in the medium, in a preferred 
embodiment, the aqueous solution of polyethylene glycol is added in an 
amount sufficient to provide from about 1 to about 5 weight percent 
polyethylene glycol, based on the weight of the contaminated medium. 
Various polyethylene glycol materials are known in the art and are suitable 
for use in the invention. Preferred polyethylene glycols suitable for use 
in the invention have an average molecular weight, Mw, from about 120 to 
1,000 Daltons. It is noted that throughout the present specification and 
claims the term "polyethylene glycol" includes such compounds and/or the 
monomethyl ethers. 
The alkali metal hydroxide is added to the contaminated medium in an amount 
of from about 2 to about 20 weight percent, again based on the weight of 
the contaminated medium. As with the aqueous solution of polethylene 
glycol, the specific amount of alkali metal hydroxide which is required is 
dependent on the level of halogenated organic compounds contained in the 
contaminated medium. In a preferred embodiment, the alkali metal hydroxide 
is added in an amount of from about 2 to about 12 weight percent based on 
the weight of the contaminated medium. The metal which forms the hydroxide 
reagent may be any of the alkali metals, or mixtures thereof. Preferred 
alkali metals include lithium, sodium and potassium with sodium and 
potassium being particularly preferred. 
After addition of the aqueous solution of polyethylene glycol and the 
alkali metal hydroxide, the contaminated medium is heated at a temperature 
and for a time sufficient to substantially dehydrate the medium, i.e., to 
remove 75 weight percent or more of the water contained therein. As will 
be demonstrated in the Examples, this heating step may be performed at 
atmospheric pressure or at reduced or elevated pressures if so desired. As 
noted above, the water which is included in the aqueous solution of 
polyethylene glycol allows homogeneous distribution of both the 
polyethylene glycol and the alkali metal hydroxide throughout the medium 
and acts as a wetting agent and a penetrant. When the water is removed 
from the medium during the dehydration step, the reagents are then 
concentrated to a very reactive state yet are well distributed throughout 
the contaminated medium. 
After dehydration, the medium is further heated at a temperature between 
about 100.degree. and 350.degree. C. for a time sufficient to effect 
destruction of the halogenated organic compounds. More preferably, the 
medium is heated at a temperature between about 125.degree. C. and 
350.degree. C. to effect destruction of the halogenated organic compounds. 
In this stage, a hydrogen free radical source is formed by reaction of the 
polyethylene glycol and the alkali metal hydroxide, particularly at 
temperatures of 250.degree.-350.degree. C., preferably of 330.degree. to 
350.degree. C. as shown in Examples 3 and 4. The hydrogen free radical 
source reacts with the halogenated organic compounds. Again, this step may 
be conducted at atmospheric pressure or at reduced or elevated pressures. 
The time required for destruction of the halogenated organic compounds 
similarly depends upon the level of such compounds in the contaminated 
material. Generally however, a time period of from about 0.5 to about 4 
hours is sufficient. 
Finally, the medium is treated with an acid for neutralization. Preferably, 
the acid is added in amount sufficient to provide the medium with a pH 
value of from about 7 to about 9. Suitable acids for use in the invention 
comprise sulfuric acid, phosphoric acid, hydrochloric acid and nitric 
acid. With the exception of hydrochloric acid, these acids not only 
neutralize the medium but also provide valuable soil fertilizers, for 
example Na.sub.2 SO.sub.4 or sodium sulfate from use of sulfuric acid, 
NaH.sub.2 PO.sub.4, Na.sub.2 HPO.sub.4, Na.sub.3 PO.sub.4 or sodium 
phosphates from the use of phosphoric acid, and NaNO.sub.3 or sodium 
nitrate from the use of nitric acid, given that NaOH is employed as the 
alkali metal hydroxide. If KOH is used, then the potassium salts are 
produced. 
Generally, oxygen is not a detriment to the methods of the present 
invention and therefore air need not be excluded. When applied to the 
decontamination of hydrocarbon fluids, either aliphatic or aromatic, it 
may be desirable to exclude air in order to prevent ignition of the 
hydrocarbon. Thus, the present methods may be performed either in the 
presence or the absence of an oxygen-containing atmosphere. 
Because the present methods employ relatively small amounts of both the 
polyethylene glycol and alkali metal hydroxide reagents, there is no need 
to recover excess reagents for reuse. Moreover, because the present 
invention employs water to wet the contaminated medium and to distribute 
the polyethylene glycol and alkali metal hydroxide reagents therein, the 
present methods are significantly less costly than prior art methods which 
employ polyethylene glycol alone to wet the contaminated medium. The 
present methods may be performed in either a continuous or a batch system, 
and, if desired, all steps may be performed in a single reactor. As will 
be demonstrated in the Examples, the methods of the invention reduce the 
halogenated organic compounds, particularly haloaromatic compounds, to 
nondetectable levels. Additionally, the products of the present methods 
are non-mutagenic, non-teratogenic and non-toxic to life forms.

The methods of the present invention are demonstrated in the following 
Examples: 
EXAMPLE 1 
This example demonstrates the application of the method according to the 
present invention to a contaminated material comprising PCB contaminated 
soil from Guam U.S.A. The soil contained approximately 2,000 to 2,500 ppm 
of a PCB having the commercial designation Aroclor 1260. One hundred grams 
of the contaminated soil was placed in a round bottom flask provided with 
a stirrer and a distillation head condenser and receiver. To the 
contamined soil was added 25 ml of water containing 5 grams of PEG-400 (a 
polyethylene glycol having an average molecular weight of 400 Daltons). 
The resulting slurry was thoroughly mixed for about five minutes after 
which 12.5 grams of 98 percent sodium hydroxide was added. Mixing was 
resumed and heating of the reaction was commenced. Water was distilled off 
over a 1-1/2 to 2-1/2 hour period, after which the contents of the reactor 
were further heated to a temperature between 135.degree. and 155.degree. 
C. for four hours. After heating, the reactor was cooled and the contents 
were neutralized by acid addition to have a pH of between 7 and 9. The 
resulting product was subjected to PCB analysis which revealed that the 
residual PCB's remaining in the soil were less than 2 ppm. 
EXAMPLE 2 
This example further demonstrates the methods according to the present 
invention. One hundred grams of the PCB-containing soil described in 
Example 1 were placed in the same type of reactor as described in Example 
1. To the mixture was added 25 ml of water containing 5 grams of PEG-400. 
The mixture was stirred for approximately five minutes and 12.5 grams of 
98 percent sodium hydroxide was added. Mixing was resumed and heating was 
initiated. A vacuum of about 29 inches of Hg was drawn on the reactor and 
water was distilled off at a temperature of from 35 to 85.degree. C. After 
the water had been removed, in about 0.5 to 1 hour, the reactor contents 
rose in temperature to about 145.degree. to 350.degree. C. within 10 to 30 
minutes. A temperature of 145.degree. to 350.degree. C. was maintained for 
1 to 1.5 hours, after which the reactor was cooled. The treated soil was 
analyzed for residual PCB's as in Example 1. Again, the analysis showed a 
residual PCB level of less than 2 ppm. 
EXAMPLE 3 
This example demonstrates the application of the method according to the 
present invention to a contaminated material comprising PCB-contaminated 
soil from Mechanicsburg, Pa. The soil had been spiked with 
pentachlorophenol to a level of 10.25 mg per 10 grams of soil. In a 100 ml 
round-bottom flask, 20.5 grams of the soil was placed, after which 5 ml of 
water containing 0.20 ml of PEG-400 and 0.20 ml of tetraethyleneglycol 
(TEG) were added. The contents of the flask were thoroughly mixed. After 
mixing, 2.0 grams of sodium hydroxide pellets were added. The flask was 
equipped with a distillation head, condensor and receiving flask, and a 
thermoprobe was inserted through the distillation head so that the probe 
tip rested in the soil slurry. The flask temperature was raised by means 
of a heating mantle to approximately 333.degree.-350.degree. C. and was 
maintained within this temperature range for 5 hours. After cooling, 11 
grams of residual soil were removed from the reactor and adjusted to a pH 
of 2, with dilute hydrochloric acid (HCl). This material was then 
extracted, and the concentrated extract was subjected to analysis by Gas 
chromatography-Mass spectrometry (GC-MS). No pentachlorophenol was 
detected, nor were any PCB congeners detected in this treated soil 
extract. Further, the glassware, including the distillation head and 
condensor, were rinsed with acetone into the receiving flask which 
contained the distilled and condensed water. This water acetone mixture 
was adjusted to a pH of 2 with HCl and extracted into hexane. The hexane 
was concentrated to 10 ml and analyzed by GC-MS as in the case of the soil 
extract. Again, no PCP was detected, nor any of the PCP break down 
products, which would be expected if no reaction had occurred. Only traces 
of PCB congeners were detected in this distilled condensed material. 
EXAMPLE 4 
This example further demonstrates the application of the present methods 
for destruction of halogenated organic compounds. To an additional sample 
of the Mechanicsburg, Pa. soil as described in Example 3, was added 
Aroclor 1242 at 1.5 mg per 10 grams of soil, and Dieldrin at 1.75 mg per 
10 grams of soil. Twenty grams of the resulting spiked-contaminated soil 
were placed into the same reaction equipment as described in Example 3, 
together with 5 ml of water containing 0.20 ml of TEG and 0.20 ml of 
PEG-400. After mixing, 2.4 grams of sodium hydroxide in pellet form were 
added and the reaction equipment was set up as in Example 3. The 
temperature was raised to and maintained between 330.degree.-345.degree. 
C. for 4 hours. After cooling, the soil, as well as any condensate, was 
extracted and analyzed via GC-MS. Analysis of the soil revealed that no 
Lindane, Dieldrin, or PCB's were remaining in the treated soil sample. 
Analysis of the distillate revealed no Lindane or Dieldrin and only traces 
of PCB congeners. 
The preceding examples are set forth to illustrate specific embodiments of 
the invention, and are not intended to limit the scope of the methods of 
the present invention. Additional embodiments and advantages within the 
scope of the claimed invention will be apparent to one of ordinary skill 
in the art.