WO2019202615A1

WO2019202615A1 - Process for production of h2o2, metal peroxides and radicals from water and modular unit for the production of the same

Info

Publication number: WO2019202615A1
Application number: PCT/IN2019/050323
Authority: WO
Inventors: Krushnamurty KILLI; Chandana LAKKASANDRUM; Rahul Raju KANUMURU; Anil Kumar Kruthiventi
Original assignee: Fertis India Pvt. Ltd.
Priority date: 2018-04-21
Filing date: 2019-04-22
Publication date: 2019-10-24

Abstract

The present invention provides a modular unit for cost effective production process for the hydrogen peroxide and other related radicals / species from water as a starting material. According to the process of the present invention, water is subjected to oxidative degradation, by using the combination of electrical discharges and a catalyst. Electrical discharges is generated in water to induce different physical and chemical effects like high electric fields, UV radiation, overpressure shock waves, which results in the formation of chemically active species. The interaction of the high energy electrons created by the discharge with the water molecules produces highly oxidative species such as hydroxyl radicals (OH), ozone radical ions (O3-), ozone (O3), atomic oxygen (O), hydrogen peroxide (H2O2) and hydroperoxyl radicals (HO2). In the process of the reaction, suitable metal salts are employed to capture the radicals as metal peroxides (Mn+OOH).

Description

“Process for production of H₂O₂, Metal Peroxides and Radicals from Water and Modular Unit for the production of the same”

Technical Field:

This invention relates to an improved process for production of hydrogen peroxide and other metal peroxides using Non-thermal Plasma technology. More particularly, the invention relates to green process for production of hydrogen peroxide, metal peroxides and other radicals (OH, O, OOH) using a Non-thermal plasma reactor to achieve good yields.

Background and Prior Art:

Hydrogen peroxide (H2O2) is a weak acidic, colorless liquid, miscible with water. It is the simplest peroxide and is commercially available in aqueous solution over a wide concentration range. The main uses of hydrogen peroxide are in the preparation of other peroxides and as an oxidizing agent. Hydrogen peroxide is a bleaching compound that can be soluble in water. Hydrogen peroxide is the simplest peroxide and it is used as an oxidizer, largely used in mining and in the manufacturing of organic peroxides and also an additive in cosmetics and disinfectants. Hydrogen peroxide can oxidize chemical groups such as lignins, cyanides, sulphides and phenols. Hydrogen peroxide can also react to form HO or HOO or other species depending of the conditions chosen, which possess better antioxidant activity than H2O2.

Anthrahydroquinone autoxidation (AO) is known for the last 70 years. Hydrogen peroxide is manufactured using the anthraquinone process. The AO process involves indirect oxidation of hydrogen and thus avoids potentially explosive H2/Q2 mixture. According to this process, anthraquinone reacts with hydrogen in a reaction chamber to produce hydrogenated anthra-quinone, which further reacts with oxygen in the air to produce hydrogen peroxide. Hydrogen peroxide thus obtained is separated by distillation to obtain either a chemical or technical grade. Anthraquinone by products are reactivated and returned back to active anthraquinone and put back in the system Anthraquinone is the carrier molecule for the controlled reaction between hydrogen and oxygen to form hydrogen peroxide. Hydrogen peroxide is unstable and slowly decomposes in the presence of base or a catalyst. Because of its instability, hydrogen peroxide is typically stored with a stabilizer in a weakly acidic solution. The anthraquinone process is shown in scheme 1.

Scheme 1

The commercial process of manufacturing involves the catalysis of the reaction of

H₂ with atmospheric O2 to give H2O2. Anthraquinone (Q) is used as a H2 carrier.

Step 1

Hydrogenation: Palladium catalyzes the reaction between H2 and anthraquinone to create anthrahydroquinone (H2Q):

Q + H2 H2Q

Step 2

Filtration: The palladium catalyst is filtered out of the solution.

Step 3

Oxidation: The solution is oxidized by blowing air through the solution, forming the H2O2:

H2Q + O2 H2O2

Step 4

H₂O₂ Extraction: The hydrogen peroxide is removed in a liquid-liquid extraction column and concentrated by vacuum distillation. However, AO process presently can hardly be considered an environmentally friendly method. Therefore, more economical and environmentally cleaner routes have been explored for the production of H2O2 by the researchers, for example, catalytic synthesis.

IJS8956508 discloses the process of H2O2 production in cold plasma reactor (equipped with a system of 2 dielectric barriers). The plasma region is filled with nonwoven quartz fibers formed of quartz covered with T1O2 having a specific surface of 40 m²/g. The gas mixture is introduced continuously at the top of the reactor. The gas mixture has an excess of hydrogen and has the composition 97.75 vol % of hydrogen and 2.25 vol % of oxygen and reported that at 5°C the yield is 7 .57% with selectivity 61.52%.

The catalytic synthesis of H2O2 meant for small-scale/on-site production from H 2 and O2, although a good technology however, suffers from drawbacks such as poor selectivity of the catalyst and potential hazards associated with H2/O2 mixtures. Various catalysts are reported for this catalytic synthesis. Photocatalytic hydrogen peroxide synthesis from water and oxygen is also well reported in the prior art.

In the past two decades, several studies have been carried out to understand the prospects of low temperature and atmospheric pressure plasma in various fields such as waste water treatment, air purification, surface treatment, sterilization, nanotechnology and biological applications. Various kinds of plasmas such as, dielectric barrier discharges (DBD), corona discharge, arc discharge, atmospheric pressure plasma jet (APPJ) and needle plasma are in practice. The production of reactive oxygen species (ROS) and reactive nitrogen species (RNS) strongly depends on the chemical composition of the gas and liquid phases, applied parameters like electric field (voltage and frequency), and of course the reactor configuration. Many efforts have been taken to understand the generation mechanism of the reactive species in aqueous medium; however the complete knowledge on this subject is still limited. An article titled "Review of the methods to form hydrogen peroxide in electrical discharge plasma with liquid water" by Bruce R Locke et.al reports that the energy yields for hydrogen peroxide generation by plasma from water span approximately three orders of magnitude from 4 x 10 ² to 80g/kWh. The highest efficiency plasma process utilizes liquid water droplets that may enhance efficiency by sequestering hydrogen peroxide in the liquid and by suppressing decomposition reactions by radicals from the gas and at the interface. Kinetic simulations of water vapor reported in the literature suggest that plasma generation of hydrogen peroxide should approach 45% of the thermodynamics limit, and this fact coupled with experimental studies demonstrating improvements with the presence of the condensed liquid phase suggest that further improvements in energy yield may be possible. Plasma generation of hydrogen peroxide directly from water compares favorably with a number of other methods including electron beam, ultrasound, electrochemical and photochemical methods, and other chemical processes.

Another article titled "Hydrogen Peroxide Production in an Atmospheric Pressure RF Glow Discharge: Comparison of Models and Experiments" by C. A. Vasko investigated the production of H2O2 in an atmospheric pressure RF glow discharge in helium - water vapor mixtures as a function of plasma dissipated power, water concentration, gas flow (residence time) and power modulation of the plasma. H2O2 concentrations up to 8 ppm in the gas phase and a maximum energy efficiency of 0.12 g/kWh are found The H2O2 increases linearly with the H2O concentration up to 1 % water, and increasing the power and flow rate increases the IT2O2 density.

Simon J. Freakley et.al., reported the direct synthesis of hydrogen peroxide (H2O2) from H2 and O2 that represents a potentially atom-efficient alternative to the current industrial indirect process. The addition of tin to palladium catalysts coupled with an appropriate heat treatment cycle switches off the sequential hydrogenation and decomposition reactions, enabling selectivity of >95% towards H2O2. This effect arises from a tin oxide surface layer that encapsulates small Pd- rich particles while leaving larger Pd-Sn alloy particles exposed. This article explains that this effect is a general feature for oxide-supported Pd catalysts containing an appropriate second metal oxide component, and thus set out the design principles for producing high-selectivity Pd based catalysts for direct H2O2 production that do not contain gold.

!ianli Zhao et. a!., reported novel in-site H2.O2 strategy for the liquid-phase epoxidation of propene catalyzed by titanium silicalite (TS-1). Said in-site H2O2 strategy is based on the direct synthesis of H2O2. from Tb and O2 under atmospheric pressure via nonequilibrium plasma reactions. Methanol is used to absorb H2O2 from the dielectric barrier discharge (DBD) reactor. Methanol also serves as the desired solvent for the liquid phase epoxidation reactor. The efficiency of the integrated process for in-site synthesis of H2O2 reached 69% selectivity, and 62% yield with a non-explosive H2/O2 mixture when the DBD reactor worked at an input power of 3.5 W (energy con sumption- 12.4 kWh/kg H2O2). The liquid phase epoxidation of propene using the in-site H2.O2 successfully proceeded over an 18 h time course under the conditions of 50°C and 3.0 MPa, more than 92% H2O2 conversion and more than 93% PO selectivity were obtained The two-reactor integrated process worked smoothly during continuous operation, no performance decay was observed for both the DBD reactor and the epoxidation reactor. Juncheng Zhou showed that under ambient conditions, H2O2 can be synthesized with 32.51 % yield and 56.25% selectivity via the gas-phase reaction of H2./O2 nonequilibrium plasma.

Gaseous H2/Ό2 plasma reactions have been demonstrated to be controllable for the direct synthesis of H2O2 when using a double aqueous electrode DDBD reactor by Yanhui Yi et.al. In this method, low electron density favors the generation of H2O2 by a chain termination path. This plasma method is promising for the direct synthesis of neutral, high concentration (ca. 60 wt%) and high purity (electronic grade) H2O2. A plasma reactor consisting of multiple parallel DBD tubes was designed to scale up the H2O2 synthesis by Zhao Jian!i etaL The number of tubes had no significant effect on the discharge mode, and no decay occurred in H2O2 selectivity during the scale-up process. These advantages made this technology more stable and efficient. The reactor's energy efficiency increased with the number of tubes and reached 136 g ThCb/kWh in the four-tube reaction.

Energy yield for hydrogen peroxide formation increases as the mean discharge power decreases, and the trend was independent of the variables that affected the power when a pulsed power supply was utilized to generate the discharge.

Ryo Saeki et, ak presents suitable conditions for pulsed plasma generation in oxygen bubbles for effective and rapid formation of H2O2. The experimental results show that low-voltage-driven and long pulse width plasma is best for H2O2 generation. The highest H2O2 generation rate of 61.8 mg/h and energy yield of 2.1 g/kWh were obtained at 2.5 kV voltage, 4 kHz pulse frequency, and Ips pulse width.

H2.G2 formation in plasma reactors was reported with a variety of feed gases (Ar, O2, air and N2) and interesting observation is that its formation takes place even in the absence of oxygen bubbling. H2O2 formation in water for three model gases is reported to be observed in the following order N.i < Ar <air < O2.

Table 1 summarizes the selected reports that deal with quantitative information on II2O2 formation and the corresponding reactions responsible for its formation. It may be concluded that the feed gas may affect the formation of oxygen based reactive species such as OH, O3, O and positive & negative charged ions like *02+, H30+, *02-, _*03 -H202 formed by the following reactions.

Table 1.: Summary of hydrogen peroxide generation in plasma reactor.

The most challenging task is the quantification of radical species during plasma treatment, because of their short lifetime. The formed *GH are often measured indirectly using chemical probe molecules such as terephthalic acid (TA), disodium salt of terephthalic acid (NaTA) and dimethyl sulfoxide (DMSG).

Therefore, there remains a need in the art for a low cost raw materials and new process to achieve the production of H2Q2 in a simple and cost effective manner. Therefore, it becomes an objective of the present invention to develop a cost effective technology for the production of hydrogen peroxide by oxidative degradation of water.

Another objective of the invention is to develop a modular unit that can be used to generate the hydrogen peroxide in good yield and purity.

Description of drawings

Figure 1: The process for production of hydrogen peroxide by electron impact disassociation of water molecules in air- water interface by NTP-DBD treatment Figure 2: (a) Quantification of H2O2 with air, O2, Ar and He atmosphere (b) the effect i e ^: salt on H2O2 concentration during oxygen plasma treatment (At 20 kV voltage and 300 seem of gas flow)

Figure 3: Quantification of H2O2 with O2 (a) the effect of applied voltage (16-20 kV) and (b) the effect of flow rate (100-300 seem)

Figure 4: H2O2 quantification with various gases (at 20 kV voltage, zero air, nitrogen, argon as bubbling gases, and 300 seem of gas flow rate).

Figure 5: hydrogen peroxide concentration measurements during plasma treatment

Figure 6: Schematic of the experimental reactor setup.

Summary of the Invention:

In line with the above objective, the present invention provides a cost effective process for production of hydrogen peroxide and other related radicals/species from water as a starting material.

Accordingly, the invention provides a process for production of hydrogen peroxide under non-thermal plasma conditions with high purity and yield which comprises electron impact disassociation of water molecules in air-water interface by Non-Thermal Process by Dielectric Barrier Discharges (NTP-DBD) treatment to produce hydrogen peroxide and other related species.

According to the process of the present invention, water is subjected to oxidative degradation, by using the combination of electrical discharges and ferrous ion as a catalyst. Electrical discharges are generated in water to induce different physical and chemical effects like high electric fields, UV radiation, overpressure shock waves, which results in the formation of chemically active species. The interaction of the high energy electrons created by the discharge with the water molecules produces highly oxidative species such as hydroxyl radicals (OH), ozone radical ions (O3^"), ozone (O3), atomic oxygen (O), hydrogen peroxide (H2O2) and hydroperoxyl radicals (HO?.). In the process of the reaction, suitable metal salts are employed to capture the radicals as metal peroxides (Mⁿ⁺OOH).

The discharge power source for generating NTP is selected from DC or pulsed DC, AC or DC + AC, radiofrequency (RF), and microwave, to obtain different types of plasma such as DC corona discharge, pulsed corona discharge, dielectric barrier discharge, ferroelectric packed-bed barrier discharge, microwave discharge, RF discharge, plasma jet, gliding arc, and etc.

In one aspect, the electrical discharges are generated in water to induce high electric fields, UV radiation, overpressure shock waves for formation of chemically active species.

The process of the present invention involves Corona discharges and Dielectric Barrier Discharges (DBDs) in water and at the water-air interface, wherein the interaction of the high energy electrons created by the discharge with the water molecules produces highly oxidative species such as hydroxyl radicals (OH), ozone radical ions (03-), ozone (03), atomic oxygen (O), hydrogen peroxide (H202) and hydroperoxyl radicals (H02).

In an aspect, the quantification of H202 has been carried out with various gases atmosphere selected from Air, Ar, 02 and He.

In another aspect, it is observed that the formation of H202 is higher in oxygen/ argon plasma than in air/helium plasma, due to the fact that part consumption of the input energy to excite / dissociate nitrogen molecules in air (Eq. 14), whereas, in the case of argon / oxygen flow, the discharge energy is used for the production of reactive oxygen species like ·0H, H202 and 03. It is further observed that the formation of H202 is higher in oxygen/ argon plasma than in air/helium plasma, due to the competing reaction between 0H and NO & N02 in aqueous medium (Eq. 15). The breakdown voltage of helium is observed to be less when compared to that of argon even though the amount of reactive species formation is more in argon plasma, due to the high electron density and the long lifetime of the excited Ar (3p) metastable species which can transfer the energy between the excited plasma species and water molecules.

The production of H202 under various gas atmospheres is observed to follow the order: oxygen > argon > air > He, as at the end of 100 min of plasma treatment, 108 ppm of H202 was observed in oxygen plasma and that decreased to 99, 46 and 23 ppm for argon, air and helium, respectively.

In another aspect, the high flow rate provides more number of oxygen molecules in the plasma discharge zone and this can increase the H202 concentration. Accordingly, in an aspect, the flow rate was fixed at 300 seem the amount of H202 formed was around 108 ppm and it was slightly decreased to 102 and 94 ppm for 200 seem and 100 seem, respectively.

In an additional aspect, the invention provides a modular design as shown in figure 6, which can be used for waste water treatment and can be tested based on quantification of H202 and other reactive species such as degradation of methylene blue in an aqueous medium, degradation and Mineralization of Dyes and Mineralization of Sulfamethoxazole.

In additional aspect, the designed reactor and the output water containing peroxides can be further used for the purpose of seed treatment such as to enhance the seed viability, shelf life extension, increasing the germination potential, etc., and also for field applications, to enhance the soil fertility by having a positive impact on soil mierobiome, to mobilize bound minerals and break down the organic waste to release organic carbon. Detailed Description of the Invention:

The invention will now be described in detail in connection with certain preferred and optional embodiments, so that various aspects thereof may be fully understood and appreciated. The present invention provides a cost effective process for production of hydrogen peroxide and other related radicals/species from water as a starting material.

According to the process of the present invention, water is subjected to oxidative degradation, by using the combination of electrical discharges and catalyst. Electrical discharges are generated in water to induce different physical and chemical effects like high electric fields, UV radiation, overpressure shock waves, which results in the formation of chemically active species. The interaction of the high energy electrons created by the discharge with the water molecules produces highly oxidative species such as hydroxyl radicals (OH), ozone radical ions (O3^"), ozone (O3), atomic oxygen (O), hydrogen peroxide (H2O2) and hydroperoxyl radicals {1 IO2). Oxygen is used as inlet gas (instead of air) in the Corona NTP device with spray of water jet, yielded 15 - 20% H2O2 production. The diagrammatic description of the device is given in Figure-6, the inlet oxygen flow was 900 LHR and the water flow rate was 15 ml/ min.

According to the invention, the process for production of hydrogen peroxide comprises electron impact disassociation of water molecules in air-water interface by NTP-DBD treatment (figure 1). The process of the present invention involves Corona discharges and Dielectric Barrier Discharges (DBDs) in water and at the water-gas interface. Further, NTP is generated by means of combustion, flames, electrically heated furnaces, electrically or magnetically or chemically driven shocks, and electric discharge. NTP reactors generated by electric discharge can be subdivided into few different types depending upon the type of the discharge power source, the presence of dielectric barrier and catalyst, reactor design and geometry, and the discharge mode. The discharge power source for g6enerating NTP can be obtained from DC or pulsed DC, AC or DC + AC, radiofrequency (RF), and microwave. These variations of NTP origin give different types of reactor or plasma such as DC corona discharge, pulsed corona discharge, dielectric barrier discharge, ferroelectric packed-bed barrier discharge, microwave discharge, RF discharge, plasma jet, gliding arc, and etc.

According to the process of the present invention, the strong oxidizer like hydrogen peroxide (FlzCb) is formed during in NTP-DBD treatment in air water interface by the electron impact dissociation of water molecules. NTP process was used to develop for water in-situ conversion into H2O2. When compared to the industrial process, wherein anthraquinione is used as the starting material, the present invention utilizes water (H2O) as a low cost alternative starting material.

General Reactions involved in the H2O2 and *OH Formation:

In a liquid solution, highly energetic electrons are capable of penetrating only to a short distance. The interaction between these species (He*, Ar*, N*, O* and NO*) with the liquid lead to the formation of Reactive oxygen species (ROS) and Reactive Nitrogen species (RNS). It is possible that the electrons from the discharge gas can dissociate the water molecule, forming ·OH and ·H in the liquid phase (Eq. 6). Ionization of water molecules by the excited electrons, followed by the reaction of H₂0⁺ with another water molecule to form ·OH (Eq. 7,8). However, this ionization process requires higher energy (12.6 eV) than the dissociation energy of the H2O molecule (6.4 eV). In the case of Ar/N2/He, ·OH can also be formed by the dissociation of the water molecule collided by the excited Ar*/N2*/He* (Eq. 9-11). The recombination of two ·OH led to the formation of H2O2 (Eq. 12). H2O2 under UV light dissociates into ·OH (Eq. 13). During the plasma discharge, molecular oxygen dissociates into atomic oxygen (Eq. 1), which lost its energy to either molecular oxygen or water molecule, forming ozone or ·OH (Eq. 2,3). Ozone further reacts with H2OLHO2 to form •OH (Eq. 4,5). *e + O2 *0 + *0 + e (1)

*0 + 0₂ 0₃ (2)

*0 + H₂0 ·OH + ·OH (3)

3Cb + H2O 2·OH + 40₂ (4)

O3 + ·H02 ·OH + 02 + 02- (5)

*e + H₂0 ·OH + ·H + e (6)

*e + H2O H₂0⁺ + 2e (7)

H₂0⁺ + H₂0 H₃0⁺ + ·OH (8)

M* + H₂0 M + ·OH + ·H (9)

M* + H₂0 M + H₂0* (10)

(M = Ar/N₂/He)

H₂0* •OH + H⁺ + e (11)

•OH + ·OH H2O2 (12)

H2O2 + UV •OH + ·OH (13)

The quantification of H2O2 has to be carried out with various gases atmosphere (Air, Ar, O2 and He). The formation of H2O2 is higher in oxygen/argon plasma than in air/helium plasma. This may be due to the fact that part of the input energy may be used to excite/dissociate nitrogen molecules in air (Eq. 14), whereas, in the case of argon/oxygen flow, the discharge energy is mainly used for the production of reactive oxygen species like ·OH, H2O2 and O3. One more possibility is the competing reaction between ·OH and NO & NO2 in aqueous medium (Eq. 15). The breakdown voltage of helium is less when compared to that of argon even though the amount of reactive species formation is more in argon plasma. This is because of the high electron density and the long lifetime of the excited Ar (3p) metastable species which can transfer the energy between the excited plasma species and water molecules

*e-+ N₂ *N + *N + e· (14)

NO2 / NO3 + *OH HN02/ HN03 (15)

H2Q2 and ^®OH quantification methods: The long-lived species H2O2 formed during the discharge process were quantified by using titanium sulfate, which forms a yellow colored pertitanic acid shows a maximum absorbance at 420 nm (T9G+ IJV-vis spectrometer, PG 94 Instalments Ltd., India). For this purpose, 0.5 g of anhydrous titanium dioxide in 50 ml of sulfuric acid was heated up to 150°C on a sand bath for 15 h to get the titanium sulfate reagent and the solution obtained was diluted, filtered through 0.45 pm filter paper. The reaction of H2O2 with titanium sulfate is given in following equation (Eq. 16).

Ti⁴⁺ + H2O2 + 2H₂0 H2T1O4 ÷ 4H⁺ (16)

The quantification of active species, such as ^»OH and N2OT were difficult because of their less survival time. Therefore, chemical dosimetry method has been employed for this purpose, where terephthalic acid (TA) reacts with OH to form 2-hydroxy terephthalic acid (HTA), which is a fluorescent compound. 2 mM of TA and 5 mM of the NaOH containing solution w^?as treated with different plasma gas atmosphere (air, O2, He and Ar). During fluorescence spectroscopy, TA and HTA molecules in the solution were irradiated by UV light with an excitation wavelength of 310 nm, only HTA shows the emission spectrum at 425 nm (Eq. 17).

TA+ _*OH HTA (17)

Other features and embodiments of the invention will become apparent by the following examples which are given only for the purpose of illustration of the invention rather than limiting its intended scope. Various changes and modifications to the disclosed embodiments will be apparent to those skilled in the art.

Experimental Setup

A schematic of the non-thermal plasma jet setup is shown in Fig. 6. As seen from the figure, the plasma was produced by passing the desired gas over a stainless steel rod (Outer dia-15 mm, with a central hole of 2 mm), placed in a three neck round bottom (RB) flask. The ground electrode was a stainless steel mesh, placed at the bottom of the outer surface. The desired gas was passed through the inner electrode and plasma jet was created by applying a potential difference between the electrodes (16-20 kV at 50 Hz). The other two necks of the RB flask were used for 1) Sample collection and 2). Connected to the gas analyzers. The power dissipated in the discharge was calculated based on the widely accepted voltage- charge Lissajous (V-Q) method. The applied voltage was plotted against the charge to get a closed loop, whose area was multiplied by the frequency gives the power dissipated in the discharge using Tektronix TDS 2014B, ! OOMHz, l .OGS/s oscilloscope. The maximum power dissipated in the discharge, while operating with air, oxygen, argon and helium was 2.1 W, 1.8 W 1.4 W and 0.8 W, respectively.

EXAMPLES:

Example 1

A Comparative Study of Plasma promoted water chemistry with Non- Thermai Plasma and Plasma Fenton;

Example la. II₂O₂ Quantification with various gas atmospheres

Air, Ar, O2 and He gases were sent through an inner electrode at a flow rate of 300 seem and the H2O2 obtained from these gases were compared. As shown in Fig. 2 (a) the concentration of H2O2 was increased gradually with increasing the plasma treatment time. At the end of 100 min of plasma treatment, 108 ppm of H2O2 was observed in oxygen plasma and that decreased to 99, 46 and 23 ppm for argon, air and helium, respectively. The formation of H2O2 is higher in oxygen/argon plasma than in air/helium plasma. This may be due to the fact that part of the input energy may be used to excite/dissociate nitrogen molecules in air (Eq. 14), whereas, in the case of argon/oxygen flow, the discharge energy is mainly used for the production of reactive oxygen species like *OH, H2G2 and O3. One more possibility is the competing reaction between ·OH and NO & NO2 in aqueous medium (Eq. 15). The breakdown voltage of helium is less when compared to that of argon even though the amount of reactive species formation is more in argon plasma. This is because of the high electron density and the long lifetime of the excited Ar (3p) metastable species which can transfer the energy between the excited plasma species and water molecules. During plasma discharge, molecular oxygen dissociates into atomic oxygen (Eq. 1), which lost its energy to either molecular oxygen or water molecule, forming ozone or ·OH (Eq. 2,3). Ozone further reacts with EbO HO2 to form ·OH (Eq. 4,5). It is possible that the electrons from the discharge gas can dissociate the water molecule, forming ·OH and ·H in the liquid phase (Eq. 6). Ionization of water molecules by the excited electrons, followed by the reaction of EbO⁺ with another water molecule to form ·OH (Eq. 7,8). However, this ionization process requires higher energy (12.6 eV) than the dissociation energy of the H2O molecule (6.4 eV). In the case of Ar/N2/He, ·OH can also be formed by the dissociation of the water molecule collided by the excited Ar*/N2*/He* (Eq. 9-11). The recombination of two ·OH led to the formation of H2O2 (Eq. 12). The production of H2O2 under various gas atmospheres followed the order: oxygen > argon > air > He.

As previous studies confirmed that the oxygen showed highest production of 1 FO . further experiments were carried out with the same discharge gas. The effect of Fe²~ salt on H2O2 concentration was studied under oxygen atmosphere. The concentration of 120 mg/L of Fe^ salt was added to the solution before plasma treatment. The concentration of H2O2 present in the solution decreased gradually and becomes zero after 60 min of the treatment time (Fig. 2 (b)). This is due to the in- situ decomposition of H2O2 into ^®OH via Fenton reaction (Eq. 16).

Fe^2÷ ÷ H2O2 OH + OH- + Fe^3÷ (18)

Example lb. H₂O₂ Quantification with various voltages and flow rate: In order to understand the influence of applied voltage and flow rate of the desired gas on the production of FI2Q2, plasma treatment was carried out under oxygen plasma (Fig. 3 (a) & 2 (b)). When the voltage was at 20 kV, the amount of H2O2 formed was around 108 ppm and it was decreased to 97 and 89 ppm for 18 and 16 kV, respectively. With increasing the applied voltage, electric field gets enhanced to form more number of active species. When the flow rate was fixed at 300 seem the amount of H2O2 formed was around 108 ppm and it was slightly decreased to 102 and 94 ppm for 200 seem and 100 seem, respectively. High flow rate provides more number of oxygen molecules in the plasma discharge zone and this may increase the II2O2 concentration.

Example 2

Atmospheric pressure non-thermal plasma jet for the degradation of methylene blue in an aqueous medium; Quantification of H2O2

Figure 4 represents the amount of H2Q2 formed during the plasma discharge. Interesting observation is that at the end of 40 min of plasma treatment, argon jet produced 50 ppm of H2G2, whereas it was 16 ppm and 7 ppm for nitrogen and zero air. This may be due to the high electron density and long life time of the excited Ar (3p) species that facilitate the energy transfer between the excited plasma species and water molecules leading to the formation of H2O2

Example 3

Degradation and Mineralization of Dyes by dielectric barrier discharge nonthermal plasma reactor; Formation of H2O2: As stated earlier hydrogen peroxide was formed during in NTP-DBD treatment in air water interface by the electron impact dissociation of water molecules. Fig 5 shows the concentration of H2O2 as a function of time at different applied voltages for 200 ml/min flow rate of air As seen in Fig 5, significant amount of H2O2 was generated in DBD and its concentration increases with increasing applied voltage. Also, H2O2 concentration increases with time for any applied voltage and nearly 60 ppm of H2Q2 was observed at 18 kV after 25 min of plasma treatment.

Example 4

Catalytic Plasma Reactor for Mineralization of Sulfamethoxazole; Effect of feed gas: Feed gas may also influence the degradation of the pollutants in plasma reactors, as it may affect the formation of oxidants, positive and negative charged ions. On formation, these primary species react with each other or react with pollutant to produce secondary oxidant. During the present study oxygen, zero air and argon are bubbled through the Sulfamethoxazole (SMX) solution. Oxygen bubbling is better than zero air and argon bubbling. The first-order rate constant SMX degradation also decreased in the order· oxygen> zero air > Argon > (0.017, 0.023, and 0.007 rain·' respectively). It is worth meaning that H2O2 formation is also effected by changing the gas. H2O2 obtained during the present study was 68, 60 and 29 ppm respectively with oxygen, zero air and argon gases.

Claims

We claim,

1. A process for production of hydrogen peroxide under non-thermal plasma conditions with high purity and yield comprising electron impact disassociation of water molecules in air-water interface by Non-Thermal Process by Dielectric Barrier Discharges (NTP-DBD) treatment to produce hydrogen peroxide and other related species.

2. The process as claimed in claim 1, wherein the process comprising:

a) subjecting water in a modular unit to electron impact oxidative degradation, by using the combination of electrical discharges and a catalyst to produce highly oxidative chemically active species, hydroxyl radicals (OH), ozone radical ions (03-), ozone (03), atomic oxygen (O), hydrogen peroxide (H202), hydroperoxyl radicals (H02); and

b) optionally employing suitable metal salts to capture the hydroperoxyl radicals as metal peroxides (Mn+OOH).

3. The process as claimed in claim 1, wherein, the discharge power source for generating NTP is selected from DC or pulsed DC, AC or DC + AC, radiofrequency (RF), and microwave, to obtain different types of plasma such as DC corona discharge, pulsed corona discharge, dielectric barrier discharge, ferroelectric packed-bed barrier discharge, microwave discharge, RF discharge, plasma jet, gliding arc, and etc.

4. The process as claimed in claim 1, wherein, the electrical discharges are generated in water to induce high electric fields, UV radiation, overpressure shock waves for formation of chemically active species.

5. The process as claimed in claim 1, wherein the process involves Corona discharges and Dielectric Barrier Discharges (DBDs) in water and at the water-air interface.

6. The process as claimed in claim 1, wherein the interaction of the high energy electrons created by the discharge with the water molecules produces highly oxidative species such as hydroxyl radicals (OH), ozone radical ions (O3^'), ozone (O3), atomic oxygen (O), hydrogen peroxide (H2O2) and hydroperoxyl radicals (HO2).

7. The process as claimed in claim 1, wherein the quantification of H2O2 is carried out with various gases atmosphere selected from Air, Ar, O2 and He.

8. The process as claimed in claim 7, wherein at the end of 100 min of plasma treatment, 108 ppm of H2O2 was observed in oxygen plasma and that decreased to 99, 46 and 23 ppm for argon, air and helium, respectively.

9. The process as claimed in claim 8, wherein the formation of H2O2 is higher in oxygen/ argon plasma than in air/helium plasma, due to the fact that part consumption of the input energy to excite / dissociate nitrogen molecules in air (Eq. 14), whereas, in the case of argon / oxygen flow, the discharge energy is used for the production of reactive oxygen species like •OH, H2O2 and O3.

10. The process as claimed in claim 9, wherein the formation of H2O2 is higher in oxygen/ argon plasma than in air/helium plasma, due to the competing reaction between ·OH and NO & NO2 in aqueous medium (Eq. 15).

11. The process as claimed in claim 9, wherein the breakdown voltage of helium is less when compared to that of argon even though the amount of reactive species formation is more in argon plasma, due to the high electron density and the long lifetime of the excited Ar (3p) metastable species which can transfer the energy between the excited plasma species and water molecules.

12. The process as claimed in any one of the preceding claims 7,8,9,10 andl l, wherein the production of H2O2 under various gas atmospheres followed the order: oxygen > argon > air > He.

13. The process as claimed in any one of the claim 7,8,9,10,11 andl2, wherein the flow rate was fixed at 300 seem the amount of H2O2 formed was around 108 ppm and it was slightly decreased to 102 and 94 ppm for 200 seem and 100 seem, respectively.

14. The process as claimed in claim 13, wherein high flow rate provides more number of oxygen molecules in the plasma discharge zone and this can increase the H2O2 concentration.

15. The process as claimed in claim 1 to 14, wherein water is subjected to oxidative degradation, by using the combination of electrical discharges and ferrous ion as a catalyst.

16. The process as claimed in claim 1, wherein the designed modular reactor can be used for waste water treatment and can be tested based on quantification of H2O2 and other reactive species such as degradation of methylene blue in an aqueous medium, degradation and Mineralization of Dyes and Mineralization of Sulfamethoxazole.

17. The process as claimed in claim 1 to 15, wherein the designed reactor and the output water containing peroxides can be used for the purpose of seed treatment such as to enhance the seed viability, shelf life extension, increasing the germination potential, etc., and also for field applications, to enhance the soil fertility by having a positive impact on soil microbiome, to mobilize bound minerals and break down the organic waste to release organic carbon.