Deep oxidation of halogenated organics with porous carbonaceous materials

Abstract: A method is provided for oxidising and/or hydrolysing halogenated organic compounds comprising contacting a mixture of the halogenated organic compound, excess oxygen, and-, optionally, water, with a carbonaceous catalyst under mild reaction conditions. The temperature of the reaction is typically below 400°C and the catalyst may be doped with acidic redox-active metal compounds.

Description: The present invention is concerned with the oxidation of halogenated organic compounds. In particular, the present invention is concerned with a method for oxidizing halogenated organic compounds in the presence of a carbonaceous catalyst. Halogenated organic compounds are useful for a number of purposes. In most applications of these materials, particularly in their use as solvents, the spent materials are discarded. Furthermore, the production and use of these halogenated organic compounds often result in the production of unwanted halogenated organic compound by-products. Unwanted by-products also are produced in processes employing halogenated organic compounds as intermediates. These unwanted by-products represent a waste of both the halogen and organic compounds thereof. It has been suggested that spent and unwanted organic compounds be further processed to provide useful materials, but often the capital investment required for such an operation far exceeds the economic justification for the further processing. Therefore, these unwanted halogenated organic compound by-products must be discarded. Disposal of halogenated organic compounds is complicated by the fact that these compounds cannot merely be released to the atmosphere or flushed away with water without causing serious pollution problems. The pollution problems arise because of the carcinogenic properties, the toxicity of some of the halogenated organic compounds, their immiscibility with water, and in many cases, their chemical stability which prevents them from breaking down readily into harmless waste products. Typical disposal methods for the undesirable halogenated organic compound by-products consist primarily of terrestrial burial methods. These disposal methods include ocean discharge, open pit burning, drum burial, and deep-well disposal. However, these methods have engendered serious criticism as being hazardous to the environment and are known to have contaminated ground water. In addition, these methods are economically unattractive because the cost of the disposal of the unwanted halogenated organic compound by-product is not diminished by recovery of some material of significant economic worth. Incineration of the undesirable halogenated organic compounds also has been proposed. US-A-3,453,073 discloses a process for recovering halogen from halogenated hydrocarbons comprising passing a chlorinated hydrocarbon, water and oxygen over catalysts, for example phosphoric acid or phosphomolybdate catalysts on activated carbon as carrier material, at elevated temperatures to form oxides of carbon, water, and hydrogen chloride. This process, however, requires the utilization of elevated temperatures which requires special equipment that is stable at such high temperatures and will resist corrosion by the hydrogen chloride and water produced. The production of carcinogenic materials such as dioxin also is a serious impediment to this mode of disposal. US-A-3,989,806 and US-A-3,989,807 propose a process for the recovery of chlorine from chlorinated organic compounds which comprises catalytically oxidizing a chlorinated organic compound feed by reacting the chlorinated organic feed with oxygen or an oxygen-containing gas at a reaction temperature of below 500°C and in the presence of a transition metal-containing supported catalyst. The catalytic supports employed in this method include zeolite materials and activated alumina. US-A-4,059,677 and US-A-4,065,543 also disclose a method for recovering halogen from halogenated organic compounds which comprises reacting the halogenated hydrocarbon with oxygen at relatively mild temperatures in the presence of a metal oxide catalyst system. The metal oxide catalyst system utilized in this method includes manganese oxide and cobalt oxide. US-A-4,423,024 also proposes a method for oxidizing a halogenated organic compound comprising reheating a mixture of the halogenated hydrocarbon, oxygen, and, where necessary, water and contacting this mixture with a molecular sieve catalyst at relatively mild temperatures. There also are known methods for regenerating saturated catalysts used to remove harmful organic compounds from water, soil or air. Typical regeneration methods include steam regeneration, superloading the catalyst and solvent regeneration. These methods have the drawback that although the catalyst may be regenerated, the steam or solvent effluent stream remains contaminated by the harmful organic compound and must be treated before disposal. The present invention is useful in the disposal of harmful halogenated organic compounds and in the regeneration of saturated carbonaceous adsorbents that have been used to remove halogenated organic compounds from soils, water and other solutions, and air. According to the present invention there is provided a method of oxidising halogenated organic compounds, which comprises: contacting the halogenated organic compound, excess oxygen and, optionally, water, with a carbonaceous catalyst, wherein: (a). the halogenated organic compound, excess oxygen and, optionally, water are contacted with the carbonaceous catalyst at a temperature of less than 400°C; and (b). the carbonaceous catalyst is a partially pyrolyzed resin having a surface area of at least 10 m²/g and containing macropores, mesopores and micropores, in which: (i). the macropores have a pore size of at least 500 Angstroms and a pore volume of at least 0.05 ml/g; (ii). the mesopores have a pore size of from 20 to 500 Angstroms and a pore volume of at least 0.05 ml/g; and (iii). the micropores have a pore size of less than 20 Angstroms and a pore volume of at least 0.05 ml/g. One embodiment of the method of the present invention comprises passing a mixture of the halogenated organic compound and excess oxygen over the carbonaceous catalyst. The catalyst may be doped with an acidic redox-active transition metal compound. The present invention is based on the finding that carbonaceous adsorbents are useful in the catalytic oxidation of halogenated organic compounds. Oxidation of the halogenated organic compound can be realized at relatively mild temperatures in the presence of such catalyst. Also, carbonaceous adsorbents which have been used to remove halogenated organic compounds from soil, water and other solutions, or air can be regenerated by oxidation at relatively mild reaction temperatures. The catalytic oxidation of halogenated organic compounds may be effected by passing a mixture of oxygen and the organic compound over the catalyst or by passing a stream of oxygen through a carbonaceous adsorbent saturated with the halogenated organic material. If required, water can be added as one of the reactants as a source of hydrogen (if the particular halogenated organic compound is deficient in hydrogen) to complete the conversion to carbon dioxide and acid. Throughout the specification and claims, the phrase "halogenated organic compound", when used to describe a reactant to be oxidized in accordance with the method of the present invention, means any compound susceptible of oxidation which consists essentially of carbon, hydrogen and halide. Any halogenated organic compound can be oxidized according to the present invention including aliphatic halides as well as aromatic halides. Other halogenated organic compounds which can be oxidized include those compounds containing a component functional moiety where one of the hydrogens of the organic compound is substituted by an atom or functional moiety other than the halide. This functional moiety includes any functional group to which a halogenated organic compound can be attached. More specifically, the halogenated organic compound can be selected from CH₂Cl₂, CH₂Br₂, CH₂BrCl, CHCl₃, CHBrCl₂, CHBr₂Cl, C₂H₃Cl₃ (all isomers), C₂Cl₄, 1,2-dichloroethylene, 1,1-dichloroethylene, 1,2-dichloroethane, 1,1-dichloroethane, 1,1,2-trichlorethane, methylchloroform, 1,1,2,2-tetrachloroethane (and other isomers), trichloroethylene, CCl₄, CHBr₃, chlorinated benzenes such as PCB, chlorinated pesticides such as dieldrin (C₁₂H₈Cl₆O), endrin (C₁₂H₈Cl₆O), aldrin (C₁₂H₈Cl₆), and DDT(C₁₄H₉Cl₅), CH₂ClOC₂H₅, ClCH₂SC₂H₅, (ClC₂H₄)₂S, chlorophenols, and dioxin. Halogenated organic compounds such as CH₂Cl₂, C₂H₂Cl₄, C₂H₄Cl₂, CH₂Br₂, and trichlorobenzene are particularly preferred. Examples of specific aliphatic halogenated hydrocarbons suitable for use in the present invention correspond to the formula C n H m X p ; wherein n is a whole number, preferably from 1 to 10 inclusive, more preferably no more than 5, and most preferably no more than 3; p is a whole number from 1 to (2n + 2) inclusive; m is represented by ( 2n - p + 2 ), and is a whole number from 0 to ( 2n - p + 2 ) inclusive; and X represents any halide, preferably chlorine, bromine or iodine, more preferably chlorine and bromine, and most preferably chlorine. The stoichiometric quantities of oxygen, carbon dioxide and acid can then be calculated from the following formula for the reaction; C n H m X p +(p-n-1)H₂O+¹/₂(3n-p+1)O₂=nCO₂+pHX When the molar ratio of halide to hydrogen is less than 1, (i.e. p is less than m), it can be seen that water will be produced by the above equation due to the negative sign before the H₂O. Alternatively, when the molar ratio of halide to hydrogen is greater than 1 (i.e. p is greater than m and the organic compound is deficient in hydrogen), additional hydrogen must be supplied through the addition of water as would be shown by a positive integer before H₂O in above equation. The following examples will illustrate the above relationship in more detail. If the halogenated organic compound C₂H₄Cl₂ were oxidized, p would be less than m and water would be produced. In the above compound, n = 2, p =2, and m = (2n - p + 2) = 4 . The stoichiometric amount of H₂O would then be p-n-1 or -1. This would indicate that one mole of H₂O would be produced. On the other hand, if the halogenated organic compound CHCl₃ were oxidized, p would be greater than m and water would be a reactant. In the compound CHCl₃, n=1, p=3, and m=(2n - p + 2) = 1 . The stoichiometric amount of H₂O would then be p-n-1 or +1. Thus, water would be a reactant. The amount of water required to complete the conversion of a hydrogen-deficient halogenated organic compound must be at least stoichiometrically sufficient to oxidize all of the available carbon content to carbon dioxide and to convert all of the halogen and hydrogen content of the halogenated organic compound to acid. Generally, the amount of water actually utilized will be far in excess of the stoichiometric amount required to ensure complete oxidation of the hydrogen deficient halogenated organic compound. In accordance with the guidelines provided herein, the skilled practitioner in the art will be able to vary the amounts and sources of the water. Preferably, the halogenated organic compound used in the present invention is completely oxidized to carbon dioxide, water, and HX. The expression "complete oxidation" means at least 69%, preferably at least 70%, more preferably at least 80%, still more preferably at least 90%, and most preferably all, of the halogenated organic compound has been oxidized. To ensure complete oxidation, excess oxygen is required. The amount of oxygen used in the oxidation of the halogenated organic compounds in accordance with the present process should be an amount that is sufficient to incinerate (oxidize) the specific quantity of halogenated organic compound contained in the supply stream. The amount of oxygen should be at least stoichiometrically sufficient to oxidize substantially all of the carbon content of the halogenated organic compound to carbon dioxide and, when the molar ratio of halogen to hydrogen in the halogenated organic compound is less than 1, preferably is sufficient to oxidize both the carbon content and available hydrogen content of the halogenated organic compound to carbon dioxide and water, respectively. The available hydrogen content is the hydrogen remaining after the hydrogen and halide have reacted to form the acid. Generally, the amount of oxygen used will be far in excess of the stoichiometric amounts required to ensure substantially complete oxidative decomposition of the halogenated organic compound. The amount of excess oxygen used can vary provided that sufficient quantities are made available to enable the aforesaid described degree of oxidation to be accomplished. The oxygen can be provided by utilizing air, oxygen, or oxygen-enriched air. The oxygen-containing stream also can be mixed with steam. For example, the oxygen can be provided by utilising oxygen, air, oxygen-enriched air, or mixtures of steam with oxygen, air or oxygen-enriched air. Preferably, the oxygen is provided by utilising oxygen, air or mixtures of steam with oxygen or air. One advantage of using steam is to recover the acid in an aqueous solution. In one embodiment of the process of the present invention, the oxygen is bubbled through the halogenated organic compound liquid mixture and the resultant saturated gas stream, which is saturated with respect to the halogenated organic compounds, then is passed over the catalyst. Lower feed rates of the halogenated organic compounds can be attained by passing the oxygen over a reservoir of liquid (heated or cooled if necessary) comprising the halogenated organic compound, to obtain a gaseous feed stream which is unsaturated with respect to the halogenated organic compounds. In another embodiment, the halogenated organic compound is delivered as a liquid and volatilized in a precatalyst reactor zone. The vapour is carried to the catalyst rather than bubbling the oxygen through the liquid. This method allows for feed rates greater than those achieved by bubbling oxygen-containing gas through the reactant because the concentration of the reactant in the vapour is not limited by equilibrium (saturation) considerations. In another embodiment, the catalyst is saturated with a halogenated organic compound (for example, by using the catalyst to remove halogenated organic compounds from soil, water and other solutions, or air), and then heated to the reaction temperature while passing oxygen, air, or mixtures of steam with oxygen or air, over it to oxidize the halogenated organic compound and regenerate the catalyst. Carbons prepared by the pyrolysis of resinous polymers are an example of hard carbons. "Hard carbons" are known to possess good structural integrity and do not slough dust particles. Hard carbon catalysts, which are prepared by the pyrolysis of resinous polymers, are known in the art. The catalysts and their method of preparation are, for example, described in US-A-4,040,990, which is incorporated herein by reference. As described therein, these carbons are partially pyrolyzed particles, preferably in the form of hard beads or spheres. They are produced by the controlled decomposition of a synthetic polymer. The pyrolysis, as described in US-A-4,040,990, is generally conducted in an inert atmosphere comprised of, for example, helium, argon, or nitrogen. Preferably, the polymer is heated rapidly to a maximum temperature in the range from about 300°C. to about 900°C.; heated at the maximum temperature for a period of up to about 20 minutes; and cooled to room temperature before exposing to air. For the purposes of this invention, maximum temperatures of up to about 1200°C. are also suitable, and longer heating times are not deleterious. Any of the many synthetic polymers, disclosed in US-A-4,040,990 and incorporated herein by reference, can be employed in preparing the carbonaceous catalyst for the process of this invention. Preferred are polymers derived from aliphatic and aromatic materials which are ethylenically unsaturated. Preferably, the polymer is cross-linked, because cross-linking stabilizes the polymer thermally and leads to greater carbon yields. Preferably also, the polymer contains a carbon-fixing moiety, such as a cation, anion, strong base, weak base, sulfonic acid, carboxylic acid, halogen, or alkylamine moiety. The more preferred polymers include polylvinylidene chloride, and macroreticular ion-exchange resins derived from aliphatic and aromatic materials which are ethylenically unsaturated. Most preferably, the polymer is a polystyrene divinylbenzene sulfonic acid ion-exchange resin. In addition to the polymers disclosed in US-A-4,040,990, any of the polysulfonated polymers disclosed in US-A-4,839,331, and incorporated herein by reference, can be employed in preparing the carbonaceous catalyst for the process of the invention. The carbonaceous catalyst, which is prepared by the pyrolysis of a resinous polymer, contains at least three distinct sets of pores of differing average size. One set comprises large pores, macropores, which originate from the resinous starting material, and range in size of at least 500 Angstroms in average diameter. The second set comprises intermediate pores, mesopores, which range in size from 20 Angstroms to 500 Angstroms. The third set and smallest pores, micropores, originate on pyrolysis of the resinous polymer. These small pores are less than 20 Angstroms in average diameter; however, the exact size depends on the temperature of pyrolysis. In addition to pore size, the pyrolysis temperature also controls total pore volumes. Generally, as the pyrolysis temperature increases, the micropore volume increases. However, at pyrolysis temperatures about 900°C, the micropore volume is low. It is believed that the micropores control the product selectivities in the deep oxidation reaction; however, such a theory should not be construed to be binding or limiting of the scope of the invention. The macropore, mesopore and micropore volumes of the carbonaceous catalyst used in this invention are each at least 0.05 ml/g. The macropore volume of the carbonaceous catalyst used in this invention should preferably be at least 0.10 ml/g; more preferably in the range from about 0.10 ml/g to about 0.35 ml/g; still more preferably in the range from about 0.15 ml/g to about 0.30 ml/g; and most preferably in the range from about 0.20 ml/g to about 0.25 ml/g. The mesopore volume of the carbonaceous catalyst used in the present invention is typically in the range from 0.05 ml/g to 0.30 ml/g; preferably in the range from about 0.10 ml/g to about 0.20 ml/g; and most preferably in the range from about 0.12 ml/g to about 0.18 ml/g. The micropore volume of the pyrolyzed carbon catalyst used in this invention is preferably at least 0.10 ml/g. More preferably, the micropore volume of the pyrolyzed carbon catalyst used in this invention is in the range from about 0.20 ml/g to about 0.35 ml/g; and most preferably in the range from about 0.22 ml/g to about 0.32 ml/g. Preferably, the carbonaceous catalyst is a pyrolyzed polymer with redox activity and acidic properties. Preferably, such a pyrolyzed polymer has a macropore size of at least 500 Angstroms in average diameter, a mesopore size in the range from 20 Angstroms to 500 Angstroms in average diameter, and a micropore size of less than 20 Angstroms in average diameter, and wherein the macropores have a volume of at least 0.10 ml/g, the mesopores have a volume in the range from 0.05 ml/g to 0.30 ml/g, and the micropores have a volume of at least 0.10 ml/g, preferably in the range from 0.10 ml/g to 0.40 ml/g. The measurement of porosity is derived from surface area and pore volume measurements obtained on any suitable instrument, such as a Micrometitics DIGISORB 2500 unit, using nitrogen as the adsorbate at the boiling point of nitrogen, 77K. The porosity of the carbonaceous catalysts used in the present invention is a function of the pyrolysis conditions, the activation of the catalyst and the porosity of the initial co-polymer used to make the catalyst. The methods used to obtain surface area and pore volumes are described by S. Lowell in Introduction to Powder Surface Area (John Wiley & Sons, 1979), or in the manuals provided with the DIGISORB 2500 instrument made by the Micromeritics Instrument Corporation. The carbonaceous catalyst used in this invention possesses a surface area of at least 10 m²/g. Preferably, the carbonaceous catalyst possesses a surface area in the range of from 100 m²/g to 2000 m²/g; more preferably, in the range of from 400 m²/g to 1500 m²/g; and most preferably in the range from 600 m²/g to 900 m²/g. The surface area is measured by the Brunauer-Emmett-Teller (BET) method. The BET method is described by R.B. Anderson, in Experimental Methods in Catalytic Research, Academic Press, 1968, pp. 48-66. The pore volume, pore size and surface area of the catalyst used in the present invention can be altered by modifying the catalyst formation conditions. For example, the temperature of pyrolysis as well as the pore volume of the initial co-polymer can be adjusted to bring the pyrolyzed catalyst to within the desired range. The skilled practitioner in the art will appreciate other known methods of modifying the parameters of the carbon catalyst in order to achieve the oxidation, e.g. the complete oxidation of the selected halogenated organic compound. Although we do not wish to be bound by any theory, it is believed that the activity of the catalyst may be related to not only the pore size, pore volume and surface area, but also the redox activity and acidity of active sites within the pores of the catalyst. For example, washing the catalyst with dilute base substantially decreases the activity of the catalyst without changing the pore volume. The skilled practitioner will appreciate other known methods of modifying the redox activity and acidity of the catalyst. Accordingly, all parameters of the catalyst must be accounted for by the skilled practitioner in the art when selecting the appropriate catalyst useful for the oxidation, e.g. the complete oxidation, of the selected halogenated organic compound. The carbonaceous catalyst used in the present invention may be doped with an acidic, redox-active metal compound. A wide variety of acidic, redox-active metal compounds can be employed as dopants. Typically, the compounds are volatile, or soluble in solvents that disperse the compound over the carbonaceous material. Such compounds may be active in the form added, or may be active as the oxide, hydroxide or oxychloride formed upon hydrolysis. Particularly preferred dopants include CrO₃, TiO₂, Ce(NO₃)₃ and KMnO₄. The carbonaceous catalysts used in the present invention also have the ability to absorb halogenated organic compounds at ordinary temperatures normally near room temperature. Thus, these catalysts are known to be useful in removing halogenated organic compounds from the soil, water and other solutions, or air. The carbonaceous catalyst can then be regenerated by contacting the catalyst with oxygen at the reaction temperature to oxidize the halogenated organic compounds absorbed on the catalyst. The halogenated organic compound is completely removed from the catalyst, and the reactor effluent is free from harmful halogenated organic compounds. Accordingly, in one embodiment of the present invention the carbonaceous catalyst is contacted with soil, water or air, containing the halogenated organic compound, at room temperature to remove the halogenated organic compound from the soil, water or air, and the resulting saturated carbonaceous catalyst is contacted with the excess oxygen, and optionally the water, at a temperature of less than 400°C to oxidise the halogenated organic compound and to regenerate the carbonaceous catalyst. In another embodiment of the present invention the carbonaceous catalyst, saturated with the halogenated organic compound, is contacted with the excess oxygen, and optionally the water, at a temperature of less than 400°C, whereby the halogenated organic compound is oxidised and the catalyst is regenerated. The process of the present invention is carried out at mild reaction conditions at temperatures sufficient to effect the oxidation reaction, preferably at temperatures sufficient to complete the oxidation reaction. The reaction temperature is less than 400°C; preferably less than 300°C; more preferably less than 275°C; and most preferably about 250°C. The particular flow rates of reactants, temperatures and pressures of the reaction, and retention time of reactants, all vary depending upon the particular halogenated compound. Those which decompose or oxidize less readily require slower feed rates and longer retention times in the reactor. It is also difficult to accurately predict the operating capacities of a particular catalyst for a multi-component system without results from an actual column study. Static adsorption isotherm data can be used to approximate the weight or volume of an adsorbent required at a given contaminant concentration level. Flow rate constraints can then be used to estimate how long the colum can remain in service. The particular type of reactor also varies with the halogenated organic compound oxidized. Generally, the reactor can be a standard fluid or fixed bed reactor designed to withstand the acidic products and reactants. The skilled practitioner in the art appreciates the manner in which these process condition and parameters can be modified. The following Examples are presented to illustrate the preferred embodiments of the present invention. EXAMPLES EXAMPLE 1 A catalyst was prepared for the deep oxidation of methylene chloride by placing 2.5 g of Anderson AX21 carbonaceous material (dried in vacuum at 100°C for 8 hours) in a round bottom flask with 50 ml of deionized water. The mixture was stirred and 0.5g (3.47 x 10⁻³ moles) of MoO₃ were added to the flask. The slurry was refluxed for a minimum of 6 hours. The excess water was removed by rotary evaporation and subsequent drying in vacuum at 100°C for 8 hours to produce a doped Anderson AX21 catalyst. The resulting catalyst was utilized in the oxidation of methylene chloride to HC1 and CO₂. The catalyst (0.5g) was placed in a glass reactor tube, and a 15.24 cm (six inches) length of glass beads was placed over the catalyst to aid in mixing and preheating the reactants. The glass reactor tube was heated to 250°C for a minimum of 2 hours. Methylene chloride (5.0 ml) was placed in a bubbler and kept at 0°C. An air stream of 1 ml/min was passed through the bubbler and the methylene chloride-saturated vapour was fed to the reactor and brought into contact with the catalyst. The post-catalyst stream was then passed through a water bubbler in order to trap the HCl formed in the reaction. The amount of methylene chloride destroyed was calculated by determining the amount of HCl in the post-catalyst stream. Hence, the conversion of methylene chloride to HCl and CO₂ was calculated. Conversion of methylene chloride to HCl and CO₂ in a single pass over the catalyst was 20% based on the titration of the exit bubbler. However, formation of the volatile compound MoO₂Cl₂ during the reaction (deposited along the walls of the reaction tube beneath the catalyst) led to loss of activity after 20 hours. EXAMPLE 2 Example 1 was repeated using essentially the same catalyst preparation method illustrated in Example 1 except WO₃ was used in place of MoO₃. Tungsten was used to avoid formation of volatile oxychloride compounds which deposit along the walls of the reactor and lead to a loss in activity. Utilization of this catalyst according to the method described in Example 1 gave 16% conversion of the CH₂Cl₂ with no observed loss in activity over time. EXAMPLE 3 Example 1 was repeated using essentially the same catalyst preparation method illustrated in Example 1 except (NH₄)₂WO₄ was used in place of MoO₃. Use of this catalyst according to the method described in Example 1 gave 15% conversion of methylene chloride. EXAMPLE 4 A deep oxidation experiment was performed according to the method of Example 1 with two exceptions; Ambersorb 563 carbonaceous absorbent was used as the catalyst, and the exit bubbler contained NaOH solution rather water (to better trap the HCl). Use of this catalyst and exit bubbler according to the method described in Example 1 gave 14% conversion. EXAMPLE 5 The method of Example 4 was repeated using Ambersorb 564 or Ambersorb 575 carbonaceous adsorbents in place of Ambersorb 563 as the catalyst. Using these catalysts according to the method of Example 4 gave 16% and 24% conversion respectively of methylene chloride. EXAMPLE 6 A metal doped catalyst was prepared by dissolving 7.0 x 10⁻³ moles (0.70 g) of CrO₃ in 5.0 ml deionized water. This solution was added to 5.0 g of evacuated Ambersorb 563 carbonaceous adsorbents to form a slightly clumpy solid and no excess water was observed. This material was dried in vacuum for 2 to 3 hours at 100°C in order to obtain the final doped catalyst. The resulting catalyst was utilized according to the method of Example 4, replacing Ambersorb 563 carbonaceous adsorbent as the catalyst, and 17% conversion was obtained in this example. EXAMPLE 7 The catalyst preparation method of Example 6 was repeated except Ambersorb 575 carbonaceous adsorbent was used as the carbonaceous support. Use of this catalyst according to the method of Example 4 gave 30% conversion. EXAMPLE 8 The Ambersorb 563 catalyst as prepared in Example 7 was utilized in the method of Example 4 with the exception of using a methylene chloride reservoir in place of a methylene chloride bubbler. The reservoir allows for only the vapour over the liquid to be carried to the catalyst rather than actually bubbling air through the liquid and saturating the carrier with the reactant. The amount of methylene chloride used in the reservoir was 1.0 ml. Titration of the exit bubbler after reaction indicated 93% conversion of the methylene chloride to HCl. This result was corroborated by comparison of pre-catalyst and post-catalyst gas streams with GC(TCD) analysis which showed 95% of the methylene chloride converted to products. EXAMPLE 9 The method of Example 8 was repeated with the exception of using 2.0g of catalyst instead of 0.5 g. The conversion according to this method was 99.9%, which was verified by GC analysis. EXAMPLE 10 The method of Example 8 was repeated with the exception of using 1,2-dichloroethane as the chlorinated reactant. The reservoir was kept at 25°C in order to allow for a vapour pressure comparable to methylene chloride at 0°C. The conversion according to this method was 91% of the reactant in a single pass. EXAMPLE 11 The method of Example 9 was repeated with the exceptions of using untreated Ambersorb 563 carbonaceous adsorbents as the catalyst and 0.50 ml of methylene chloride in the reservoir. 69% conversion was observed. EXAMPLE 12 The following Example shows that a porous carbonaceous support is needed to obtain high conversions of methylene chloride. A solution was made up of 7.0 x 10⁻³ moles (0.70 g) of chromium trioxide in 5.0 ml deionized water. This solution was added to 5.0 g dry silica gel (Davison grade 62). An additional 10 ml aliquot of water was added to fully saturate the support and completely disperse the chromium solution throughout the entire mixture. The mixture was then rotary evaporated and vacuum dried overnight to produce a doped silica gel catalyst which was a dark orange solid. This catalyst was utilized according to the method of Example 8 and resulted in 49% conversion based on titration of the exit trap. However, volatilization of the metal was observed as soon as 1 hour after initiation, as was evidenced by a green coloured deposit in the cool region of the reactor zone. The colour of the catalyst after reaction was black. EXAMPLE 13 A titanium doped catalyst was prepared as follows: 6.0 ml of 1.0 m titanium tetrachloride in dichloromethane was added to 4.06 g of Ambersorb 572 carbonaceous adsorbent in the presence of nitrogen. The solvent was removed by evacuation at room temperature for 14 hours. Hydrolysis to titanium dioxide was easily accomplished by exposure to atmospheric water vapour. Fuming of the material indicated the evolution of gaseous hydrochloric acid upon hydrolysis. The resulting catalyst was utilized according to the method of Example 9 and a 93% conversion was observed by GC analysis. EXAMPLE 14 A mixed metal catalyst was prepared by the addition of a solution consisting of 0.04 g cerium nitrate and 0.04 g potassium permangate dissolved in 10 ml water to 2.0 g of Ambersorb 572 carbonaceous adsorbent. The clumpy solid was then dried at 100 °C in vacuum for three hours to obtain the final catalyst. The resulting catalyst was used according to the method of Example 9 and a 95% conversion was observed by GC analysis. EXAMPLE 15 The method of Example 9 was repeated with the exception of using a pyrolyzed, macroreticular polyacrylonitrile carbonaceous material as the catalyst. GC analysis showed 99.8% conversion which was repeatable to within 0.1%. This Example illustrates the high activity obtained for certain undoped carbonaceous materials for deep oxidation. The results of the foregoing Examples are summarised in Table 1. Example Reactant Addition Method Catalyst (Amnt. in g.) Dopant Conversion % 1 MeCl₂ Bubbling 0₂ AX21 (0.5) MoO₃ 20 2 MeCl₂ Bubbling 0₂ AX21 (0.5) WO₃ 16 3 MeCl₂ Bubbling 0₂ AX21 (0.5) (NH₄)₂WO₄ 15 4 MeCl₂ Bubbling 0₂ 563 (0.5) 14 5 MeCl₂ Bubbling 0₂ 564 (0.5) 16 MeCl₂ Bubbling 0₂ 575 (0.5) 24 6 MeCl₂ Bubbling 0₂ 563 (0.5) CrO₃ 17 7 MeCl₂ Bubbling 0₂ 575 (0.5) CrO₃ 30 8 MeCl₂ Reservoir 563 (0.5) CrO₃ 93 9 MeCl₂ Reservoir 563 (2.0) CrO₃ 99.9 10 1,2, dichloroethane Reservoir 563 (0.5) CrO₃ 91 11 MeCl₂ Reservoir 563(2.0) 69 12 MeCl₂ Reservoir Silica gel (0.5) CrO₃ 49 13 MeCl₂ Reservoir 572 (2.0) TiO₂ 93 14 MeCl₂ Reservoir 572 (2.0) Ce(NO₃)₃ and KMNO₄ 95 15 MeCl₂ Reservoir pyrolyzed-polyacrylonitrile (2.0) 99.8 As can be seen by the above Table, when the concentration of reactants is too high, and the amount of oxygen is deficient or the amount of catalyst is deficient, complete oxidation of the halogenated organic compound cannot be realized. For example, bubbling the oxygen through the halogenated organic compound can result in an oxygen stream saturated with the organic compound and stoichiometrically deficient in oxygen. Thus, these Examples emphasize the necessity of maintaining the stoichiometric amounts of oxygen and water as well as halogenated organic compound in order to effect the complete oxidation. The following Examples illustrate other embodiments of the present invention. EXAMPLE 16 The method of Example 9 was repeated with the exception of using CH₂Br₂ in the reservoir as the halogenated reactant, and a conversion was 93% as observed by GC analysis. EXAMPLE 17 The following Example demonstrates the utility of the catalyst for reactants with a molar ratio of Cl to H (Cl/H) greater than 1. The method of Example 9 was repeated with the exceptions of utilizing 1,1,1,2-tetrachloroethane as the reactant, heating the reservoir to 100°C and inserting a water bubbler in the stream preceding the halogenated organic reservoir. The intent is to utilize water as a hydrogen source for HCl formation where, as here, the reactant is hydrogen deficient relative to chlorine. Titration results show 63% conversion of available Cl to HCl, which corresponds to 127% conversion of the available organic H to HCl. These results show that water added to the reactants stream contributed hydrogen for the deep oxidation reaction. EXAMPLE 18 This Example demonstrates that halogenated aromatic compounds can be utilized in the deep oxidation system. 2.0 g of the catalyst as prepared in Example 6 was placed in the fixed bed flow system described in Example 1. 0.1 ml of 1,2,4-trichlorobenzene was placed in a syringe and mechanically pumped at 0.06 cc/hr to the top of the catalyst zone. The reactant was vaporized and carried over the catalyst by the air stream. The air flow rate was adjusted to 6 ml./min in order to maintain the appropriate reaction stoichiometry. According to this method, 19% conversion of the reactant was obtained. The above feed rate is comparable to the feed rate of CH₂Cl₂ (0.05 cc/hr) utilized in Examples 1 through 7. EXAMPLE 19 The following Example shows the need for maintaining acidic sites on the catalyst for optimal activity in deep oxidation. A catalyst was prepared by treating 5.0 g of Ambersorb 563 with 5.0 ml of 28% NH₃ (aq). The resulting mixture was dried in vacuum at 100°C for 5 hours. 2.0 g of this catalyst was utilized according to the method of Example 11. According to this method, 52% conversion of the reactant was obtained. (A comparison of this result to that with untreated Ambersorb 563 carbonaceous adsorbent (Example 11) indicates that the presence of a base does have an adverse effect on deep oxidation activity). EXAMPLE 20 The method of Example 18 was repeated with the exception of using 5.0 ml of 1.764 M KOH(alc) to treat the Ambersorb 563 carbonaceous adsorbent. The resulting catalyst was utilized in the method of Example 11. According to this method, the conversion was 32% of the reactant. This Example demonstrates that very strong bases have a significantly more detrimental effect on deep oxidation activity than weaker bases. EXAMPLE 21 The following Example demonstrates the utility of the deep oxidation reaction in the presence of a high concentration of water vapour. A catalyst was prepared according to the method of Example 13 with the exceptions of using 6.26 ml of TiCl₄/CH₂Cl₂ solution and 10.0g of Ambersorb 572 to give a catalyst with 5.1% TiO₂ by weight. 2.0 g of the catalyst was utilized in the method of Example 10 (1,2-dichloroethane reactant) with the exception of adding a rapid water feed of 0.6 ml/hr (liquid). The initial segment of the experiment was performed with no water in order to determine the optimal conversion level using the catalyst. 99.7% conversion of the substrate was observed. Upon addition of the water feed, the conversion dropped and levelled off at 65.0%. This water feed corresponds to ca. 1000 bed volumes per hour of steam contacting the catalyst. The water feed was stopped and the system was allowed to equilibrate so that the reversibility of water inhibition could be determined. The conversion level returned to 99.7%, indicating no irreversible deactivation of the catalyst occurs upon contact with high concentration of water vapour. EXAMPLE 22 The method of Example 21 was repeated with the exception of using a water feed of 0.12 ml/hr (liquid). This corresponds to ca. 200 bed volumes of steam per hour passing over the catalyst. The conversion observed was 93.8% dichloroethane reacted. This Example illustrates the retention of high catalytic activity in the presence of a fairly high water concentration. EXAMPLE 23 The method of Example 22 was repeated with the exception of using 235°C as the reaction temperature. 91.5% conversion was observed in this Example. EXAMPLE 24 The method of Example 22 was repeated with the exception of using 225°C as the reaction temperature. 65.6 % conversion was obtained. The foregoing Examples illustrate the method of the present in completely converting certain halogenated hydrocarbons to the desired acid and carbon dioxide products. Other like halogenated hydrocarbons or mixtures can also be oxidized by the method of the present invention. EXAMPLE 25 The method of Example 24 was repeated with the exception of using no water feed. Conversion was 84.9%. This example, along with Example 24, illustrate that at temperatures less than 250 °C the catalyst is still active both in the absence and the presence of water vapour. EXAMPLE 26 This Example demonstrates that hydrogen can be provided solely from a non-organic source when utilizing a totally halogenated organic reactant. The method of Example 17 was repeated with the exceptions of using tetrachloroethylene as the organic reactant and a reservoir temperature of 60°C. Conversion of the reactant was 16%. This low conversion is a result of using water as a limiting reagent to contribute the hydrogen due to the fact that the reactant of this Example contributed no hydrogen at all. EXAMPLE 27 The initial segment of Example 21 (1,2-dichloroethane reactant, no water feed, TiO₂/Ambersorb 572 catalyst) was repeated using undoped Ambersorb 572 in place of the titanium doped analog. Conversion was 97.4%. A water feed of 0.12 ml/hr (liquid) was added to the reactant stream to determine the effect of water vapour on undoped carbonaceous materials. The conversion with water present was 96.8%. This observation, when compared to Example 22, indicates a much lower influence of water vapour on undoped vs. doped carbonaceous supports. "Digisorb" and "Ambersorb" are trademarks which may be registered in some of the designated countries.

Claims: A method of oxidising halogenated organic compounds, which comprises: contacting the halogenated organic compound, excess oxygen, and, optionally, water with a carbonaceous catalyst, wherein: (a). the halogenated organic compound, excess oxygen and, optionally, water are contacted with the carbonaceous catalyst at a temperature of less than 400°C; and (b). the carbonaceous catalyst is a partially pyrolyzed resin having a surface area of at least 10 m²/g and containing macropores, mesopores and micropores, in which: (i). the macropores have a pore size of at least 500 Angstroms and a pore volume of at least 0.05 ml/g; (ii). the mesopores have a pore size of from 20 to 500 Angstroms and a pore volume of at least 0.05 ml/g; and (iii). the micropores have a pore size of less than 20 Angstroms and a pore volume of at least 0.05 ml/g. A method as claimed in claim 1, wherein the carbonaceous catalyst, saturated with the halogenated organic compound, is contacted with the excess oxygen, and optionally the water, at a temperature of less than 400°C, whereby the halogenated organic compound is oxidised and the catalyst is regenerated. A method as claimed in claim 2, wherein the carbonaceous catalyst is contacted with soil, water or air, containing the halogenated organic compound, at room temperature to remove the halogenated organic compound from the soil, water or air, and the resulting saturated carbonaceous catalyst is contacted with the excess oxygen, and optionally the water, at a temperature of less than 400°C to oxidise the halogenated organic compound and to regenerate the carbonaceous catalyst. A method, as claimed in any preceding claim, wherein the excess oxygen is present in the form of oxygen, air, oxygen-enriched air, or mixtures of steam with oxygen, air, or oxygen-enriched air. A method, as claimed in any preceding claim wherein the halogenated organic compound is selected from aliphatic halides and aromatic halides. A method, as claimed in claim 5, wherein said aliphatic halide has the structural formula (I): C n H m X p wherein n is a whole number ranging from 1 to 10 inclusive, p is a whole number ranging from 1 to (2n +2) inclusive, m is represented by 2n-p+2 , and is a whole number ranging from 0 to ( 2n-p+2 ) inclusive, and X represents any halide. A method, as claimed in claim 6, wherein X is Cl, Br or I, preferably Cl. A method, as claimed in claim 5, wherein said aliphatic halide is selected from CH₂Cl₂, C₂H₂Cl₄, C₂H₄Cl₂, CH₂Br₂, and trichlorobenzene. A method, as claimed in any preceding claim, wherein the catalyst has a specific area in the range from 100 m²/g to 2000m²/g, preferably in the range from 600 m²/g to 900 m²/g. A method, as claimed in any preceding claim, wherein the reaction temperature is below 300°C, and preferably below 275°C. A method, as claimed in any preceding claim, wherein the carbonaceous catalyst has a redox activity and acidity sufficient to achieve oxidation of the halogenated organic compound. A method, as claimed in any preceding claim, wherein the carbonaceous catalyst is a pyrolyzed polymer with redox activity and acidic properties. A method, as claimed in claim 12, wherein, in said carbonaceous catalyst, the macropores have a volume of at least 0.10 ml/g, the mesopores have a volume in the range from 0.05 ml/g to 0.30 ml/g, and the micropores have a volume of at least 0.10 ml/g, preferably a volume in the range of from 0.10 ml/g to 0.40 ml/g. A method, as claimed in any preceding claim, wherein the carbonaceous catalyst is doped with an acidic, redox-active metal compound. A method, as claim in claim 14, wherein the carbonaceous catalyst is doped with CrO₃, TiO₂, Ce(NO₃)₃ or KM n O₄. A method, as claimed in any preceding claim, wherein at least 69%, preferably at least 70%, of halogenated organic compound is oxidised.

Inventors: BRENDLEY WILLIAM HARRY JR, DRAGO RUSSELL STEPHAN, GRUNEWALD GERALD, PETROSIUS STEVEN, BRENDLEY, WILLIAM HARRY, JR., DRAGO, RUSSELL, STEPHAN, GRUNEWALD, GERALD, PETROSIUS, STEVEN
Applicants: DRAGO RUSSELL, GRUNEWALD GERALD, PETROSIUS STEVEN, ROHM & HAAS, DRAGO, RUSSELL, GRUNEWALD, GERALD, PETROSIUS, STEVEN, ROHM AND HAAS COMPANY
Application year: 1992
Main classification: A62D3
IPC codes: A62D3, B01J21, A62D101, C09K3