BRPI0405915B1 - CATALYTIC PROCESS FOR DESTRUCTION OF CONTAMINANTS IN WATER USING HYDROGEN PEROXIDE AND HYPEROGENIC CATALYST - Google Patents

Description

"CATALYTIC PROCESS FOR THE DESTRUCTION OF

WATER CONTAMINANTS USING HYDROGEN PEROXIDE AND HYPEROGENIC CATALYST "This invention relates to a water treatment process containing organic contaminants using a heterogeneous iron oxide and hydroxide catalyst based on bituminous coal, which catalyzes decomposition. hydrogen peroxide, generating free radicals that do not selectively oxidize dissolved organic contaminants.The catalyst is a process that utilizes a solid that catalyzes the decomposition of hydrogen peroxide, producing highly oxidizing hydroxyl and hydroperoxyl radicals that are responsible for by the destruction of organic compounds present in waters.

There are numerous processes for treating liquid, biological or physicochemical effluents. However, some effluents contain compounds that are difficult to degrade and thus it is not always possible to achieve the level of purification required by environmental legislation through conventional processes. Alternative solutions to conventional activated sludge treatment and coagulation / decantation have been researched, including activated carbon adsorption, electrochemical treatment, ozonation and advanced oxidative processes. Advanced oxidative processes (POA's) are currently used for the destruction of organic pollutants and are based on the generation of hydroxyl radicals that are highly oxidizing and can rapidly and non-selectively destroy numerous compounds.

Among the many advanced oxidation processes is the classic Fenton process, which is based on the generation of hydroxyl radicals from ferrous ion catalyzed decomposition of hydrogen peroxide (Fe + 2) under acidic conditions according to equation 1 to follow. This process has been successfully employed in the treatment of many types of industrial wastewater.

(The classic Fenton process has been shown to be a technically and economically viable alternative for the treatment of industrial effluents. However, it has the drawbacks of being limited by the pH range (2-4) and of generating large sludge volume in the coagulation step after the oxidation.

Through the development of a heterogeneous catalyst to decompose hydrogen peroxide and produce hydroxyl radicals, ie a heterogeneous Fenton process, the above mentioned drawbacks can be overcome and the process can be performed in fixed bed reactor and eliminate the coagulation step, thus reducing the amount of chemical sludge generated. The present invention relates to a process consisting of contacting the water to be treated with the heterogeneous catalyst and the addition of hydrogen peroxide. The heterogeneous catalyst is a composite based on bituminous coal oxides and hydroxides of iron, which is active to decompose hydrogen peroxide and generate oxidizing free radicals, which then decompose organic compounds dissolved in water.

This process has some advantages when compared to others created for the treatment of waters containing organic contaminants. Among the main advantages: the high chemical and physical stability of the catalyst, presenting great resistance to dissolution when exposed to acid or alkaline conditions; high chemical activity to catalytically decompose hydrogen peroxide and generate oxidizing free radicals, which are capable of non-selectively oxidizing numerous organic compounds; the low operating cost of treatment; the production of high quality treated water. The catalyst is prepared by contacting an aqueous solution containing 10 to 150 g / l of iron ions and 1 to 50 g / l of aluminum ions with a bituminous coal for a period of 1 to 24 hours, followed by the addition of an agent. alkalinizing up to pH 2 to 10. The surface of bituminous coal must be neutral, to present high affinity for adsorption of iron and aluminum ions, with subsequent precipitation of iron and aluminum hydroxides, which are retained in the pores and on the rough surface of the holder. After neutralization, the mixture must be dried at a temperature in the range 150 to 250 ° C. The composite can be used as a granular filter medium. Bituminous coal used as support is used in the form of particles with a size between 0.1 and 2.0 mm and a specific surface area of at least 2.0 m2 / g. The zero load point of the supporting coal shall be close to neutral within the range 5.5 to 8.5. Under these conditions, the bituminous coal used as support has a high chemical affinity for iron ions in aqueous solution. The surface chemical characteristics of the mineral coal used as support give this material an approximately neutral surface, resulting in catalytic activity for iron oxidation and high adsorption capacity of iron ions. The composite is produced as a material consisting of insoluble iron and aluminum oxides and hydroxides supported on bituminous coal. The process for its production takes place through successive steps: (A) Immersion of coal with aqueous solution containing iron and aluminum ions (B) Adsorption; (C) Neutralization; (D) Drying.

Initially, the coal (A) is immersed in an aqueous solution of ferric aluminous sulfate, or in the acid mine drainage, containing from 10 to 150 g / l of iron ions and from 1 to 50 g / l of Aluminum ions. As the surface of the coal is approximately neutral, it has high affinity for adsorption of both iron and aluminum ions, which are retained on the surface and finally precipitate forming a thin coating of hydrated ions.

Following an adsorption step (B), which may last from 1 to 24 hours, depending on the concentration of iron ions in the aqueous solution, the neutralization step (C) is followed by the addition of an alkali such as NaOH, KOH, Na2CO3. or NaHCO3. The amount of OH 'ions added should be sufficient for the pH of the medium to be in the range 2 to 11, preferably with the molar ratio between the concentrations of OH' and iron ions equal to 2.5 to 2.8. During neutralization of the solution, hydrated oxides and iron and aluminum hydroxides precipitate on the surface of the coal, forming a composite of iron oxides, aluminum oxides and bituminous coal. The formation of solid iron oxides requires the hydrolysis of hexa-aqueous cation (Fe (H20) 63+) according to reactions 2 and 3. (2) (3) Following is the drying step (D), after which the composite can again be immersed in solutions containing iron ions and the suspension again neutralized with alkali to perform successive layer coatings.

Trivalent aluminum cations, also present in the aqueous solution, are adsorbed on the iron oxides that are precipitating on the coal and on the acidic active sites present on the coal. The reaction with iron hydroxide oxides is described in reaction 4. (4) In this reaction, Al3 + ions have a strong affinity with the surface of goethite and lepidocrocyte (γ FeOOH), respectively, and the complex = FeOAIOH + has greater stability. than the complex = FeOAI (OH) 2. The drying step (D) should occur at temperatures in the range of 150 to 250 ° C until complete drying to allow strong adherence of the iron and aluminum oxide coating and to prevent coal oxidation. Fe203 concentration in composites is in the range 0.1 to 3.0% (w / w), and Al203 concentration in the range 0.1 to 0.5% (w / w), ie depends mainly on the amounts of iron and aluminum ions present in the aqueous solution, and on the precipitation pH.

The average characteristics of the composite are shown in Table 1.

Table 1 - Physicochemical characterization of composites Analysis Unit Value Standard Humidity% in mass 1.45 ± 0.50 NBR 14234 Effective size mm 0.80 ± 0.10 NBR 14234 Coefficient of - 1.65 ± 0.20 NBR 14234 uniformity Specific mass g / cm3 1.03 ± 0.05 MB 3413 Apparent Actual specific mass g / cm3 1.86 ± 0.10 NBR 14234 Surface area BET m2 / g 4.1 ± 0.50 N2 adsorption at 77K

Solubility in HCl Mass% 2.81 ± 0.25 NBR 14234 Solubility in NaOH Mass% 0.57 ± 0.10 NBR 14234 Total Acidity mEq.g / m2 3.37 ± 0.50 Salami &

Bandosz, 2003a Total Basicity mEq.g / m2 9.85 + 0.50 Salami &

Bandosz, 2003a a) Salami II and Bandosz TJ, Role of surface chemistry in adsorption of phenol on activated carbons, Journal of Colloid and Interface Science, 264 (2), 307-312 (2003)) The oxide-catalyzed heterogeneous Fenton process Minerals is an oxidative process in which the destruction of contaminants is achieved by the use of hydrogen peroxide in the presence of insoluble iron oxide. This process has the advantage of not requiring strict pH control and is effective in the pH range from 3 to 8. The formation of highly oxidizing free radicals through catalytic decomposition of hydrogen peroxide using Fe203 / coal composite can be represented by the reactions. 5 to 7. (5) (6) (7) The destruction of dissolved organic compounds in water occurs by reaction with the OH * or OOH * radicals (Equations 8 to 10). (8) (9) (10) Catalytic decomposition of hydrogen peroxide with metals or metal oxides can be described by the Langmuir-Hinshelwood (LH) mechanism and can be represented by equation 11. (11) Where Sr is the concentration total sites, [H2O2] is the hydrogen peroxide concentration; k and K are the velocity and equilibrium constants, respectively. The values of the constants k and K at different pH's are shown in Table 2. The decomposition rate of hydrogen peroxide is approximately pH independent, indicating the flexibility of the proposed treatment process.

Table 2- Parameters keK of model L-H. Treatment of waters containing organic contaminants may occur either in a fixed bed reactor containing the catalyst or by contact in a continuous or batch stirred reactor.

In operation in agitated reactors, contaminated water and hydrogen peroxide are added to a tank, and the hydrogen peroxide concentration should be adjusted depending on the concentration of organic contaminants at the ratio [H202]: Chemical oxygen demand in the range 0.1 to 10, preferably 1.0. The dosage of catalyst to be used is in the range of 10 to 300 g / l, depending on the concentration of dissolved organic contaminants in the water to be treated. The contact time should be at least 10 minutes, preferably 1 hour. The decomposition rate of a textile industrial effluent by the CATALYTIC PROCESS FOR WATER CONTAMINANT DESTRUCTION USING HYDROGEN PEROXIDE AND HETEROGENE CATALYZER, using the catalyst dosage of 300 g / l at pH 3.0 is shown in FIGURE 1. A Iron concentration in the aqueous phase was measured during the reaction and the results showed no iron leaching, indicating no homogeneous Fenton oxidation. The reaction can be divided into two steps: a fast first step followed by a slow one that is attributed to the rapid decomposition reaction of hydrogen peroxide to produce a large amount of hydroxy radicals. The hydroxyl radicals produced can react quickly with organic matter. Oxidized iron on the catalyst surface produced in the first stage reacts with hydrogen peroxide to produce hydroperoxyl radicals and regenerate the catalyst on the solid surface. Since hydroperoxyl radicals are less oxidative than hydroxyl radical, a second slow follows. GRAPH 1 represents the rate of degradation of the textile effluent by the CATALYTIC PROCESS FOR DESTRUCTION OF CONTAMINANTS IN WATER USING HYDROGEN PEROXIDE AND HYPEROGENIC CATALYZER, referring to catalyst dosage = 300 g / L; [H2 O] = 500 mg / L; pH = 3.0. Hydrogen peroxide disappearance kinetics were also evaluated during effluent degradation and the results are shown in GRAPH 2 where the hydrogen peroxide decomposition kinetics by the CATALYTIC PROCESS FOR DESTRUCTION OF WATER CONTAMINANTS USING HYDROGEN PEROXIDE AND Heterogeneous catalyst is represented by the dosage = 300 g / l; [H2 O] = 500 mg / L and pH = 3.0. The rate of hydroxyl radical formation (OH *) depends on the hydrogen peroxide concentration and the controlling step would be the surface reaction between the hydrogen peroxide adsorbed on the catalyst surface and the iron oxides / hydroxides. By increasing catalyst dosing, the efficiency of the process increases due to the higher number of catalytically active sites for hydrogen peroxide decomposition, as shown in GRAPH 3, which points out the effect of catalyst dosing on COD removal by PROCESS

CATALYTIC FOR DESTRUCTION OF CONTAMINANTS IN WATER USING HYDROGEN PEROXIDE AND HETEROGEN CATALYST (initial [H202] = 500 mg / L and pH = 3.0).

During the destruction reaction of organic compounds, the reaction site (= Fe + 3) must be regenerated through equation (9) and the adsorption of hydrogen peroxide is much faster than the others.

The CATALYTIC PROCESS FOR WATER CONTAMINANT DESTRUCTION USING HYDROGEN PEROXIDE AND HYPEROGENIC CATALYST is practically insensitive to water pH, as shown in GRAPH 4 and 5. GRAPH 4 represents the effect of pH on CATALI color removal FOR DESTRUCTION OF CONTAMINANTS IN WATER USING HYDROGEN PEROXIDE AND HETEROGENE CATALYST (catalyst dosage = 300 g / L; [H202] = 500 mg / L; reaction time = 1 h). GRAPH 5 represents the effect of pH on the removal of aromatic compounds through the CATALYTIC PROCESS FOR DESTRUCTION OF

WATER CONTAMINANTS USING HYDROGEN PEROXIDE AND Heterogeneous Catalyst (catalyst dosage = 300 g / L; initial [H202] - 500 mg / L; reaction time = 1 h).

THE CATALYTIC PROCESS FOR DESTRUCTION OF CONTAMINANTS IN

WATER USING HYDROGEN PEROXIDE AND Heterogeneous Catalyst can also be performed in a fixed bed reactor containing the catalyst. In this case, the residence time in the liquid should be greater than 10 minutes. GRAPH 6 demonstrates the discoloration of a textile effluent through the CATALYTIC PROCESS FOR DESTRUCTION OF WATER CONTAMINANTS USING HYDROGEN PEROXIDE AND FIXED CATALYZER in a fixed bed reactor. Graph 6 shows the discoloration of the textile effluent through the CATALYTIC PROCESS FOR DESTRUCTION OF WATER CONTAMINANTS USING HYDROGEN PEROXIDE IN FIXED BED (pH = 3.0; residence time 10 minutes and [DQ0] / [H2 O] input = 4: 1).

CATALYTIC PROCESS FOR DESTRUCTION OF CONTAMINANTS IN

WATER USING HYDROGEN PEROXIDE AND CATALYST

HETEROGENEOUS

Claims (4)

1. “CATALYTIC PROCESS FOR WATER CONTAMINANT DESTRUCTION USING HYDROGEN PEROXIDE AND HYPEROGENIC CATALYST” is a water treatment process containing organic contaminants using a heterogeneous catalyst containing 0.5 to 3.0% of iron oxides and hydroxides (expressed as Fe203) supported on bituminous coal, which catalyzes the decomposition of hydrogen peroxide, under procedural conditions of contact of the agitated liquid medium with the catalytic system or through a fixed bed column filled with the heterogeneous catalyst for a residence time of more than 10 minutes, and wherein the pH of the water to be treated is in the range of 3 to 8. 2. "CATALYTIC PROCESS FOR DESTRUCTION OF WATER CONTAMINANTS USING HYDROGEN PEROXIDE AND HYPEROGENIC CATALYST" according to claim 1 characterized in that hydrogen peroxide is catalytically decomposed on the heterogeneous catalyst generating highly oxidizing free radicals selectively dissolved organic contaminants. 3. "CATALYTIC PROCESS FOR DESTRUCTION OF WATER CONTAMINANTS USING HYDROGEN PEROXIDE AND HETEROGENE CATALYST" according to Claim 3, characterized in that it is a heterogeneous catalyst based on a composite made up of immobilized coal oxides and hydroxides. adsorbent mineral. 4. "CATALYTIC PROCESS FOR DESTRUCTION OF WATER CONTAMINANTS USING HYDROGEN PEROXIDE AND HETEROGENE CATALYST" according to claim 3, characterized in that its catalyst has a bituminous coal containing 30 to 60% ash.