Advanced Oxidation

Catalytic Advanced Oxidation is a leading-edge approach to ecological methods of waste water remediation and other challenges that currently represent major unsolved pollution problems.  The method is based on the decomposition of hydrogen peroxide - the “cleanest” chemical, which produces only water and oxygen in its decomposition. 

Hydrogen Link developed a critical enabler for Catalytic Advanced Oxidation  - a unique heterogeneous catalyst that re-routs the decomposition reaction of H2O2 into formation of hydroxyl radicals as an intermediate stage of the H2O2 decomposition – one of the most powerful oxidative species.


Please contact us with inquiries about our catalysts for Catalytic Advanced Oxidation at contact@hydrogenlink.com


Oxidative reactions are the most effective way of degrading and eliminating all kinds of pollutants and waste chemicals - both in air and water. It is also one of the basic tools in a variety of chemical reactions and processes.

In general, oxidation can be achieved by using compounds which have higher oxidation potentials (Eo) than that of oxygen (1.23 V).  The difference of the oxidation potential over the potential of oxygen is a measure of the oxidative capability of oxidizing agents - the higher the oxidation potential, the stronger oxidative capability.

Amongst the typical anti-pollutants, the following have the best oxidative efficiency:

-          hydroxyl radical          -   Eo =   2.28 V

-          ozone                            -   Eo =   2.07 V

-          hydrogen peroxide     -   Eo =   1.78 V

This comparison shows that hydroxyl radicals have unmatched capability of oxidative treatment.  The only oxidant with even higher potential is fluorine, with its oxidation potential of Eo =   2.85 V, while chlorine (the common but toxic oxidant and disinfectant) has the oxidation potential of only   1.49 V.

Advanced oxidation process (AOP) is based on techniques of generation of highly reactive species (especially the hydroxyl radical OH.) that are able to react with a range of compound, even with chemicals that are otherwise very difficult to degrade.  These species are so reactive because one of their electrons is unpaired.  They are however extremely short-lived and need to be formed in situ in the close proximity of the contaminant molecules. The degradation reaction initiated by the radicals proceeds until thermodynamically stable oxidation products are formed, which results in mineralization, i.e. full degradation of the pollutants. The end products of complete oxidation (mineralization) of organic compounds are carbon dioxide (CO2) and water (H2O).

In general, the effectiveness of an Advanced Oxidation Processes is proportional to its ability to generate hydroxyl radicals. AOP methods such ozonation (O3), hydrogen peroxide (H2O2) and/or UV light may have mechanisms for destroying organic contaminants which involve formation of hydroxyl radicals (these methods are briefly described further below). 

Advanced Oxidation technologies are an environmentally friendly approach to target pollutants and contaminants, such as in air and waste water,  to remove toxic or non-degradable materials. AOP deals with the removal of aromatics, pesticides, petroleum constituents,  volatile organic compounds (VOC), petroleum hydrocarbons and chlorinated hydrocarbons, dyes and organic matter. 

Catalytic decomposition of hydrogen peroxide H2O- Catalytic Advanced Oxidation

Hydrogen Link has developed a method of Catalyzed Advanced Oxidation that is capable of generation of incomparable quantity of hydroxyl radicals through catalytic decomposition of hydrogen peroxide H2O2. While many catalyst are known to decompose hydrogen peroxide (such as manganese dioxide, silver, platinum etc,), the decomposition mechanism involves only a limited number of hydroxyl radicals. Our unique catalyst is based on nano-technology involving selective formation of varied oxidation states in the catalyst components. As a result, it is capable of abundant generation of hydroxyl radicals while decomposing hydrogen peroxide, thus giving this method an exceptional oxidative capability. The additional advantage is that the catalyst is heterogeneous (it is in the form soli-state powder or granules) and  it does not remain in the solution, but forms a heterogeneous sediment that is easily removed from the effluent.

 Our AOP method is able to decompose and mineralize organic and inorganic contaminants. Bleaching applications are also noteworthy, as catalyzed hydrogen peroxide is able to replace chlorine-based bleaches.

Hydrogen Link's catalyst  provides very high efficiency combined with low cost - it contains no noble or exotic elements. Our catalyst is stable and controllable, with unlimited shelf life. It can be stored and handled in air without deterioration and exhibits extraordinary capability in hydrogen peroxide decomposition in both alkaline and acidic condition. In these characteristics it is superior to Fenton reactions, which require pH adjustments. The catalyst can be used either for the Advanced Oxidation purposes, or as a very easy and convenient source of oxygen with H2O2.


 

Examples of applications:

(please click on the image to watch video demonstration)

Biomass degradation- purification and disinfection of water at pH=7

Dairy waste water purification and COD reduction

Water decontamination and disinfection by catalyzed advanced oxidation

 

Dye discoloration and degradation by advanced oxidation

Cellulose fibre upgrading and cottonization by advanced oxidation


 

Catalyzed Advanced Oxidation can be performed with the use of solid sources of hydrogen peroxide, such as sodium percarbonate (SPC) or percarbamide (urea H2Oadduct).

In this process, the catalyst powder or granules is added to the  solid powder of SPC. Addition of water to this mixture results in the dissolution of sodium percarbonate and the release of hydrogen peroxide into the solution, which is instantly decomposed by the catalyst into oxygen or hydroxyl radicals. Alternatively, instead of water - an effluent can be added to the solid mixture, resulting in the instant oxidative action of the decomposing hydrogen peroxide. As a result, all kinds of pollutants can be eliminated -  including organic matter, dyes and chemicals. Catalyzed oxidation is much more efficient than the action of the sodium percarbonate alone, as shown below. The pictures show a comparison of the decoloration of methylene blue by sodium percaronate only and with the Hydrogen Link catalyst.

   

 

  

Catalyzed sodium percarbonate used in discoloration of methylene blue solution


Please contact us with inquires related to our catalyst for Catalytic Advanced Oxidation at contact@hydrogenlink.com


 

General types of the Advanced Oxidation Processes (AOP):

Ozonation

In the ozonation technology, hydroxyl radicals are formed when ozone O3 is decomposed in water. Ozone is a strong oxidant, but it is much less powerful than hydroxyl radicals. Decomposition of ozone requires high pH (>10), therefore ozone treatment of organic chemicals proceeds faster in alkaline solutions than at neutral or acidic pH.  The ozone treatment is also relatively expensive.

Hydrogen Peroxide and Ozone (H2O2/O3)

When O3 and H2O2  are simultaneously added to water, they participate in a complex chain of reactions that result in the formation of radicals such as the hydroxyl radical (•OH) and the superoxide radical (O2•). H2O2 enhances the transformation of O3 to •OH in solution and as a result this treatment is more effective than either ozonation or hydrogen peroxide alone.

Photocatalytic oxidation processes

Advanced Oxidation Processes can be enhanced by using ultraviolet (UV) radiation, which induces formation of free radicals. Ultraviolet irradiation can be used together with ozone (O3/UV ) or  hydrogen peroxide (UV/H2O2). Degradation of organic compounds occurs by hydroxyl radicals reaction, in addition to direct photolysis  and oxidation by molecular ozone or hydrogen peroxide. Generally, UV treatment with ozone is more effective than UV in combination with H2O2

Advanced Oxidation treatment using a combination of ultraviolet irradiation catalyzed with TiO2 is based on the illumination of the titanium dioxide (which is a semiconductor) with ultraviolet light. This results the excitation of its valence band electrons to the conduction band and the formation of holes. Adsorbed water molecules take part in the reaction of producing hydroxyl radicals, while superoxide anion radical (O2•) is also generated. The problems with this method are related to fouling of theTiO2 catalyst in highly contaminated slurries, which on one hand reduce UV light penetration throughout the waste stream and on the other hand can block the access of the UV to the clean surface of TiO2 (a critical step for the excitation effect). In addition, the reaction efficiency is highly pH dependent.

The major problem with all photocatalytic methods is that they are energy and cost intensive. Also, turbidity and lack of transparency for UV light in highly colored or contaminated effluents significantly reduces the efficiency of these processes.

Fenton Reaction  Fe2+  / H2O2

Fenton's reagent is a solution of hydrogen peroxide and an iron catalyst.  Iron (II) sulfate is a typical iron compound in Fenton's reagent.

Hydrogen peroxide reacts with ferrous iron (II) to form ferric iron (II) complex) that subsequently reacts to form hydroxyl radicals.

 Fe2+ + H2O2 → Fe3+ + OH· + OH

 Fe3+ + H2O2 → Fe2+ + OOH· + H+

In the second reaction, iron (III) is reduced back to iron(II), along with the formation of a peroxide radical and a proton, as a result of the hydrogen peroxide disproportionation. 

The above reactions cycle iron between the ferrous and ferric oxidation states until the H2O2 is fully consumed, producing •OH in the process.

The Fenton process requires adjustment of the solution toward acidic, i.e. low pH (2 to 5).  If the pH is too high, the iron precipitates as Fe(OH)3.  This is a drawback, because the usually highly alkaline textile-processing wastewaters (with high pH) cause large volumes of waste sludge which are generated by the precipitation of ferric iron salts and the process loses effectiveness as H2O2 is catalytically decomposed to oxygen.

 In comparison to ozonation, the Fenton process is relatively cheap and results generally in a larger chemical oxygen demand (COD) reduction.  COD represents the amount of oxygen that is needed by the water in the decomposition and oxidation processes of organic matter, inorganic matter or chemicals.

Fenton’s process requires very little energy compared to other oxidation technologies that use O3 or UV.


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