EP3655135A1

EP3655135A1 - An apparatus for the abatement and conversion of atmospheric gaseous pollutants comprising a plasma/catalyst or a plasma/adsorbent coupled system

Info

Publication number: EP3655135A1
Application number: EP17794090.5A
Authority: EP
Inventors: Francesco Parisi; Katiuscia COSTABELLO
Original assignee: Grinp Srl
Current assignee: Grinp Srl
Priority date: 2017-07-21
Filing date: 2017-07-21
Publication date: 2020-05-27
Also published as: WO2019016837A1

Abstract

The invention relates to apparatus for the abatement at low temperature of gaseous atmospheric pollutants, such as nitrogen oxides (NO_x), volatile organic compounds (VOCs), NH₃, la CO₂, CH₄ and odours, comprising a coupled plasma/ catalyst, integrated, system, i.e. that forms a single working stage, wherein the plasma is a plasma at atmospheric pressure and the catalyst is heterogeneous. More particularly the apparatus according to the present invention provides for the use of a reducing plasma and of an adsorbent for the abatement of NO_x and the use of an oxidizing plasma and a catalyst for the abatement for VOCs. The invention also relates to a method for the abatement of volatile organic compounds (VOCs) by means of a coupled plasma/ catalyst, integrated, system. The invention also relates to a method for the abatement and the conversion of CO₂ into different types of chemical substances with high economic interest, such as for example dimethyl ether (DME), by means of a coupled plasma/ catalyst, integrated, system.

Description

An apparatus for the abatement and conversion of atmospheric gaseous pollutants comprising a plasma/ catalyst or a plasma/ adsorbent coupled system"

DESCRIPTION

TECHNICAL FIELD

The present invention relates to the environment sector and, in particular, to the abatement of gaseous atmospheric pollutants such as nitrogen oxides (nitrogen monoxide NO and nitrogen dioxide NO₂, denoted overall as nitrogen oxides NO_x), volatile organic compounds (VOCs), CO2, NH3, CH₄ and odours.

More precisely, the present invention relates to an apparatus for the abatement at low temperature of gaseous atmospheric pollutants comprising a coupled plasma/ catalyst or plasma/ adsorbent system, integrated.

Even more precisely, the present invention relates to an apparatus for the abatement and the conversion at low temperature of gaseous atmospheric pollutants comprising a coupled plasma/ catalyst or plasma/ adsorbent system with plasma at atmospheric pressure and heterogeneous adsorbent or catalyst.

In this new type of reactor it is the plasma which acts as catalyst for the system in that it supplies on the one hand

The present invention also relates to a method for the abatement of volatile organic compounds (VOCs) by means of a coupled plasma/ catalyst system, integrated.

The present invention also relates to a method for the abatement and the conversion of CO₂ into different types of chemical substances with high economic interest, such as for example dimethyl ether (DME), by means of a coupled plasma/ catalyst system, integrated.

The preferred and advantageous application of the present invention is for the abatement of NO_x produced by mobile systems (for example in the combustion chamber of internal combustion engines) and by fixed systems (such as, for example, thermoelectric power plants and industrial plants). In particular the method according to the present invention does not entail the production of carbon dioxide (CO2) and, therefore, considerably reduces the environmental impact of gaseous effluent from mobile and fixed sources.

A further preferred and advantageous application of the present invention is the total conversion of VOCs into CO2 thanks to the action of the catalytic plasma and also thanks to the oxidizing action of the ozone produced by the lighting of the plasma in air and in the presence of oxygen.

A further preferred and advantageous application of the present invention is for the abatement of odours and the conversion into CO2 thanks to the action of the catalytic plasma and also thanks to the oxidizing action of the ozone produced by the lighting of the plasma in air and in the presence of oxygen.

A further preferred and advantageous application of the present invention is the abatement and the conversion of CO2 into useful and economically interesting substances such as dimethyl ether (DME) and others.

A further preferred and advantageous application of the present invention is the abatement and the conversion of CH₄ into useful and economically interesting substances such as dimethyl ether (DME) and others.

A further preferred and advantageous application of the present invention is the abatement and the conversion of NH3.

STATE OF THE ART

As is known, there are five nitrogen oxides: nitrogen protoxide N2O, nitrogen monoxide NO, nitrogen dioxide NO2, dinotrogen trioxide N2O3 and dinitrogen pentoxide N2O5. N2O, NO and NO2 are naturally present in the atmosphere yet, while the nitrogen protoxide N2O is relatively inert, nitrogen monoxide NO and nitrogen dioxide NO2 are highly toxic and make an important contribution to many environmental problems such as the formation of smog and acid rain, the destruction of the ozone layer and the greenhouse effect.

Nitrogen monoxide NO and nitrogen dioxide NO2, denoted overall as nitrogen oxides NO_X/ are emitted into the atmosphere mainly from anthropogenic sources, in particular the production of NO_x by humans takes place from fixed systems (for example thermoelectric power plants and industrial systems) and mobile systems (for example in the combustion chamber of internal combustion engines). In general nitrogen oxides NO_x are generated by processes of combustion, whatever the fuel used, through direct reaction between the nitrogen and the oxygen present in the air at high temperature (higher than 1,200°C). The processes of combustion emit as main component nitrogen monoxide NO which subsequently, in the presence of ozone, is transformed into nitrogen dioxide NO2. The direct formation of nitrogen dioxide NO2 by the combustion processes, instead, is closely linked to the high values of pressure and temperature which occur inside the combustion chambers of engines. Volatile organic compounds (VOCs) comprise a series of chemical compounds of organic nature in the form of vapour or in liquid form but able to evaporate easily at ambient pressure and temperature, which are therefore found in the atmosphere mainly in gaseous phase. They include hydrocarbons (compounds containing only carbon and oxygen such as aliphatic hydrocarbons, such as methane, aromatic hydrocarbons, such as benzene and halogenated hydrocarbons, such as chloroform) and also oxygenated species such as acids, alcohols, aldehydes (such as formaldehyde), ketones and esters.

The natural emissions of the VOCs comprise the direct emission from vegetation and the degradation of organic material while anthropogenic emissions are mainly due to the incomplete combustion of hydrocarbons, to the evaporation of solvents and fuels and to processing industries.

Among the VOCs aromatic organic compounds are found to be particularly damaging and which have direct effects on human health. The most polluting species is benzene, relatively stable (average life span approximately four days) and with ascertained carcinogenic properties.

The VOCs are also responsible for the formation of secondary pollutants. In particular the class of alkenes is that of greatest interest in the atmospheric field due to their important role in the formation of oxidizing species.

In order to overcome the aforesaid problems, the systems of abatement of nitrogen oxides NOx and of the volatile organic compounds VOCs have been the subject of study for some time.

For the abatement of the NO_x the use of catalysts is known. An example of catalyst for accumulating and reducing the NO_x (NSR-NO_x storage reduction) is described in the European patent application no. EP 0573 672 Al and is used for the abatement of NO_x from mobile sources. This catalyst is able to abate the nitrogen oxides in oxidizing conditions and can therefore be used coupled with high-efficiency engines which work in so-called "lean" conditions, that is to say with excess of oxygen and air/ fuel ratio higher than the stoichiometric one equal to 14.7. This catalyst is constituted by platinum Pt and barium Ba (in oxide form) supported on gamma alumina γ- AI2O3 with high surface area and is already active starting from 150°C, with maximum efficiency between 300 and 400°C. During normal functioning of the engine the catalyst accumulates the NO_x on the surface as barium nitrates Ba ( θ3)2· Subsequently, in order to restore the accumulation capacity of the catalyst, a pulse of fuel is fed which acts as reducent and, thanks to the catalytic intervention of the platinum Pt, the NO_x accumulated as nitrates are reduced to nitrogen N₂. The main disadvantage of this type of catalysts lies in the fact of entailing the waste of fuel for the recovery of the capacity of accumulation of the catalyst. Another disadvantage is represented by the use of very costly noble metals. A further disadvantage is due to the oxidizing working conditions, in that the presence of oxygen in the mixture leads to a smaller yield of the reaction of reduction and to a lower selectivity. A further disadvantage is represented by the production of carbon dioxide CO2.

In brief, the catalysts according to the prior art described above are mainly limited by the fact of having to operate at temperatures higher than ambient temperature, of requiring the use of noble metals, of producing CO2 and of having in any case low efficiencies of conversion of the NO_x into N₂.

For the abatement of NO_x solutions have also been developed which provide for the use of plasma in combination with a catalyst. An example of plasma/ catalyst combination for the abatement of NO_x is described in the US patent no. US 5,711,147, wherein a plasma assists a classic reduction catalyst in a two-stage system: first stage of oxidization and second stage of reduction. The role of the plasma is that of oxidizing completely the mixture in output from an engine, typically a mixture of NO and N0₂. Since a gas rich in N0₂ has to arrive at the catalyst to increase the selectivity of the reduction reaction, it is important that the oxidization of NO into NO₂ is complete and, therefore, is conducted into a plasma reactor, specifically a traditional DBD - dielectric barrier discharge - apparatus, which operates in oxidizing conditions, specifically with an incoming flow rich in O₂. The solution described in this document provides for a successive reduction in NO2 which is performed with traditional techniques in which the catalyst works in the presence of hydrocarbons HC deriving from the fuel. In particular the catalyst is a fixed bed reactor constituted by gamma alumina on which a zeolite named Cu ZSM-5 is deposited. The solution described in this document allows the achieving of a conversion of the NOx of approximately 70%.

The main disadvantages of the solution described in this document lie in a low percentage of conversion of the NOx into N₂ and in the need to work with hot fumes. At low temperature, ambient temperature, the catalyst used is not active.

In the US patent application no. US 2015/0298060 Al a plasma reactor is described which works at 250°C. The flow entering the reactor is a mixture of C¾ and N₂. The plasma serves to act as catalyst to the reaction of reduction of the bimolecular nitrogen to NH3, which is the reducent used to complete the reaction of abatement/ conversion of the nitrogen oxides into N₂. The remaining part of the system is a normal catalytic converter of the SCR (selective catalytic reduction) type. The plasma in this case is used to produce a reaction of oxide-reduction and is a secondary system with respect to that which is the main catalytic system of reduction of NO_x, which contains a fairly important quantity of precious metal.

The main disadvantages of the solution described in this document lie in the impossibility of working discontinuously with flows having a variable concentration of pollutant.

A mixed system of the solutions described in the two previous documents is that illustrated in the international application published under no. WO 2006/036311 A2. This system is composed of a normal catalytic converter which works with an SCR catalyst, therefore with feeding of ammonia into the chamber of reduction of the nitrogen oxides with bimolecular nitrogen. The plasma reactor is a quartz tube and the plasma is used as producer of ozone since, lit in air, the plasma acts as catalyst for the following reaction:

O2 + plasma in air→ O3

The ozone produced is a strongly reactive and oxidizing species and, fed into a reaction pre-chamber, serves to convert quantitatively the NO species into NO2 species, making the reduction reaction more efficient in terms of percentage conversion into bimolecular nitrogen. In this case too the plasma is not used as reducent of the NO_x but only as oxidizer and producer of ozone.

The main disadvantages of the solution described in this document lie in the fact of working at high temperature, higher than 450°C, and of being a system of the oxidizing type for NO_x.

In the US patent application no. US 2004/ 0131513 Al a plasma reactor is shown which works in atmospheric conditions and which is constituted by a cylindrical chamber wrapped in a complex system of various electrodes. The configuration of the cathodes according to this document is made so that, placed outside the chamber, they light the plasma inside the quartz tube. The plasma which is created in this case is of the DBD type.

The conversion of the gases treated, as VOCs, is however very low, around 65%. Another disadvantage of the solution described in this document lies in the fact that the plasma is of the thermal type.

Moreover, for the abatement of the VOCs, solutions are known which provide for burning them in thermal convertors at high temperature. These systems use large quantities of methane for the heating of the gas and their combustion and, consequently, have very high costs.

Regenerative converters are classic heat converters characterised by the recovery of the heat of the gas in output which, having an effective system of heat recovery, allow a more limited use of methane gas with lower running costs. The problem in this case is however bound by the dimensioning of the system, which allows good conversions and low running costs only if the system is used at full load while, in the opposite case, the running costs of the plant, in terms of use of methane, are very high and serve to heat the gas to be treated. The systems mentioned above provide however for a high production of carbon dioxide, gas obtained from the complete combustion of the various volatile organic molecules VOCs. At the present state of the art systems are not provided for capture and conversion of the CO2 downstream of the combusters.

In brief, the solutions according to the prior art described above are mainly limited by the fact of working well continuously but badly discontinuously. These solutions, moreover, have the disadvantages of providing very large structures and high running and maintenance costs.

The need is therefore also not fulfilled of having an apparatus for the abatement and conversion of nitrogen monoxide NO and nitrogen dioxide NO2, denoted overall as nitrogen oxides NO_x, and also of VOCs, odours, NH3, CO2 and CH , able to achieve very high efficiency of abatement also in conditions of low temperature.

The need is therefore also not fulfilled of having an apparatus for the very selective and economically advantageous abatement and conversion of nitrogen oxides Ox, and of VOCs, odours, NH3, CO2 and CH₄, which operates both discontinuously and continuously.

Finally, the need is therefore also not fulfilled of having an apparatus for the abatement of nitrogen oxides NO_x, and also of VOCs, odours, NH3, CO2 and CH₄, which is simple, not bulky, reliable, economical and flexible.

In brief, up to the current time, to the Applicant's knowledge, solutions are not known which, combining catalytic plasma with catalyst integrated in the reactor, and post- reactor catalyst, allow the abatement and conversion, with a very high efficiency also in conditions of low temperature, of the content of nitrogen oxides NO_x, VOCs, odours, NH3, CO2 and CH of gaseous mixtures from activities of the industrial type (producers of VOCs, painting processes, use of solvents), from energy production plants (incinerators, production of biogas), from agriculture (livestock farms) and from the transport sector (ships, heavy vehicles).

Therefore the Applicant, with the apparatus according to the present invention, intends to remedy this shortcoming.

OBJECTS AND SUMMARY OF THE INVENTION It is the object of the present invention to overcome the disadvantages of the prior art linked to the abatement of NO_X/ and also of VOCs, odours, NH3, CO2 and CH .

More specifically, it is the object of the present invention to improve the efficiency of abatement of NO_x, and also of VOCs, odours, NH3, CO2 and C¾ also in conditions of low temperature.

Moreover, it is the object of the present invention to increase the selectivity of abatement of NOx, and also of VOCs, odours, NH3, CO2 and C¾.

Moreover, it is the object of the present invention to simplify and make economically advantageous the abatement of NOx, and also of VOCs, odours, NH3, CO₂ and CH₄. These objectives are achieved with the apparatus according to the present invention which, advantageously integrating a catalytic plasma reactor at atmospheric pressure with catalyst integrated in the reactor and post-reactor catalyst of the heterogeneous type, allows the achieving of a very high efficiency of abatement of NO_x, and also of VOCs, odours, NH3, CO2 and CH₄, also in conditions of low temperature (for example 20°C).

The apparatus, thanks to the innovative system which it implements, means that it is the plasma that acts as "super" catalyst of the reaction, in other words the plasma in this case implements both the principles of traditional catalysis and those of photocatalysis. On the one hand therefore it lowers the energy of activation of the reaction in such a way as to make it take place with good yields in the chosen conditions of temperature and pressure, on the other hand it supplies energy in the form of light, therefore providing the energy necessary for the reaction to take place. Specifically, the abovementioned and other objects and advantages of the invention, as will be seen from the rest of the description, are achieved with an apparatus of abatement of nitrogen oxides NO_x, and also of VOCs, odours, NH3, CO2 and CH₄ according to claim 1.

Preferred embodiments and variants of the apparatus of abatement of nitrogen oxides NO_x and/ or of volatile organic compounds VOCs, odours, NH3, CO₂ and CH according to the present invention constitute the object of the dependent claims. More particularly, in a first preferred and advantageous embodiment for the abatement of ΝΟχ and of CO^the apparatus according to the present invention provides for the use of a reducing plasma and of an adsorbent. More particularly, in a second preferred and advantageous embodiment for the abatement of VOCs and NH3 and odours and CH₄, the apparatus according to the present invention provides for the use of an oxidizing plasma and of a catalyst.

Another aspect of the present invention relates to a method for the abatement of volatile organic compounds VOCs, odours, NH3, CO₂ and CH₄ by means of an integrated plasma at atmospheric pressure/ heterogeneous catalyst or atmospheric pressure plasma/ heterogeneous adsorbent system.

Another aspect of the present invention relates to a method for the abatement and the conversion of CO2 into different types of chemical substances with high economic interest, such as for example dimethyl ether (DME), by means of a coupled plasma/ catalyst, integrated system.

It is understood that all the appended claims form an integral part of the present description and that each of the technical features claimed therein is optionally independent and usable autonomously with respect to the other aspects of the invention.

It will be immediately clear that innumerable changes may be made to what is described (for example relating to shape, sizes, arrangements and parts with equivalent functions) without departing from the sphere of protection of the invention as claimed in the appended claims.

Advantageously, the apparatus according to the present invention, thanks to its versatility and adaptability to the different types of pollutants and to odours, is suitable for being used in activities of the industrial type (producers of VOCs, painting processes, use of solvents), in energy production plants (incinerators, production of biogas), in agriculture (livestock farms) and in the transport sector (ships, heavy vehicles). With the apparatus according to the present invention, in fact, it is possible to abate both the pollutants termed as climate change (O3, CO2, CH₄, N₂O) and those directly responsible for atmospheric pollution (VOCs, NO_x, SO_x, PM, NH3).

Moreover, advantageously, the technical solution according to the present invention allows:

- achieving of a high conversion efficiency also with low working temperatures;

- abating, in a very selective and economically advantageous manner, of pollutants such as ΝΟχ and also VOCs, odours, NH3, CO2 and CH independently of the composition of the incoming gas, therefore also of the percentage of oxygen (in the case of the NO_x) or nitrogen (in the case of the VOCs) present;

- using the plasma to cause reactions which normally take place only at high temperature and pressure, such as for example the conversion of CO2 with methane;

- in the specific case of abatement of VOCs, using the plasma as producer of ozone, secondary product of the lighting of the plasma in air and in the presence of oxygen and promoter of the total conversion of the residual VOCs into CO2;

- making maintenance of the system less burdensome and costly as a result of its constructional and operational simplicity;

- allow the self-cleaning of the apparatus thanks to the providing of support media for the catalyst, or cathodes, covered with self -cleaning material with a base of photocatalytic titanium oxide modified so as to be able to work with the wavelength produced in the plasma (specifically, titanium oxide modified with N and F in case of reactions of the oxidizing type and modified with Fe and Cu in the case of reactions of the reducing type);

- reducing the dimensions of the plants and the corresponding running costs;

- ensuring working flexibility and ease;

- having availability of a system which with the same structure has the possibility of abating and converting atmospheric pollutants of different types. The system, so- called multi-pollutant, is in fact able to work with different pollutants also present simultaneously in the incoming flow;

- use of a so-called plug-and-play system, easy to install and use;

- having the possibility of adapting the treatment conditions on the basis of the pollutant gases in output, thanks to the fact that the apparatus works in real-time adapting conditions with smart online probe integrated in the system;

- having availability of a versatile system, that is to say having the possibility of working in different conditions of power and method according to needs (for example with a plasma of continuous type or pulsed and with variable frequencies) and, consequently, of obtaining high conversions also in conditions of high concentrations of pollutants and also in the presence of several pollutants simultaneously.

Further advantageous features will be made clearer by the following description of preferred but not exclusive embodiments, given purely by way of a non-limiting example.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be described here below by means of some preferred embodiments, given by way of a non-limiting example, with reference to the accompanying drawings. These drawings illustrate different aspects and examples of the present invention and, where appropriate, structures, components, materials and/ or elements that are similar in different drawings are denoted by similar reference numerals.

Fig. 1 is a schematic representation of the first embodiment, for the abatement of NO_x, of the apparatus according to the invention;

Fig. 2 is a schematic representation of the first embodiment, for the abatement of NO_x, of the apparatus according to the invention, in a first variant which provides an active carbons filter upstream of the same apparatus;

Fig. 3 is a schematic representation of the adsorbent used, for the abatement of NO_x, of the apparatus according to the invention;

Fig. 4A is a schematic representation of the first working phase of a second variant of the first embodiment, for the abatement of NO_x, of the apparatus according to the invention;

Fig.4B is a schematic representation of the second working phase of the second variant of the first embodiment, for the abatement of NO_x, of the apparatus according to the invention;

Fig. 4C is a graphic representation of the reducing gas in the two working phases of the apparatus of Figs. 4A and 4B;

Fig. 4D is a graphic representation of the plasma in the two working phases of the apparatus of Figs. 4A and 4B;

Fig. 5 is a schematic representation of the second embodiment, for the abatement of VOCS, of the apparatus according to the invention;

Fig. 6 is a schematic representation of the catalyst used, for the abatement of VOCS, of the apparatus according to the invention;

Fig. 7 is a schematic representation of the support media whereon the catalyst of the apparatus according to the invention is deposited;

Fig. 8A is a schematic representation of a first configuration of the plasma reactor of the apparatus according to the invention;

Fig. 8B is a schematic representation of a second configuration of the plasma reactor of the apparatus according to the invention;

Fig. 9 A is a schematic representation of a first type of plasma reactor of the apparatus according to the invention;

Fig. 9B is a schematic representation of a second type of plasma reactor of the apparatus according to the invention; and

Fig. 10 is a schematic representation of the apparatus according to the invention fitted with cooling plate which allows efficient control of the temperature of the system. DETAILED DESCRIPTION OF THE INVENTION

While the invention is subject to various changes and alternative constructions, some preferred embodiments are shown in the drawings and will be described here below in detail.

It has to be understood, however, that there is no intention to limit the invention to the specific embodiments illustrated but, on the contrary, the invention intends covering all the changes, alternative constructions and equivalents which fall within the sphere of the invention as defined in the claims.

In the following description, therefore, the use of "for example", "etc.", "or" indicates non-exclusive alternatives without any limitation, barring indication otherwise. The use of "also" means "including, but not limited to" unless indicated otherwise. The use of "includes / comprises" means "includes / comprises, but not limited to" unless indicated otherwise. The apparatus for the abatement of gaseous pollutants, such as nitrogen oxides (NO_x) and volatile organic compounds (VOCs), odours, NH3, CO2 and CH₄ of the present invention is based on the innovative concept of abating pollutant compounds by means of the synergic action of plasma and catalyst, whether it is with oxidizing or reducing action according to the types of molecules to be treated. This innovative system allows very high efficiency of abatement and conversion to be achieved, comprised between 97 and 99 %, of the NO_x, of the VOCs and of other pollutants such as odours, NH3, CO2 and CH₄.

The inventors have in fact surprisingly and unexpectedly discovered that the use of a plasma coupled with an appropriate catalyst is particularly effective in the abatement and in the conversion of many classes of atmospheric pollutants, such as nitrogen oxides (NOx), volatile organic compounds (VOCs), odours, NH3, CO₂ and CH₄.

An important feature of this apparatus lies in the fact of being able to perform the abatement with efficacy, with high conversion, with reduced dimensions and with reduced running costs.

Moreover the apparatus can be provided with an innovative real-time adapting device which allows operation in optimal conditions both with continuous and discontinuous flow.

In the present description the term "nitrogen oxides NO_x" is intended to indicate any mixture of nitrogen monoxide NO and nitrogen dioxide NO₂ in any ratio. The terms "nitrogen oxides NO_x" and "mixture of nitrogen monoxide NO and nitrogen dioxide NO₂", in the present description, are used indifferently, as synonyms.

In the present description the term "volatile organic compounds VOCs" is intended to indicate any mixture of volatile organic compounds which, at the temperature of 293.15 K (20°C), have a vapour pressure of 0.01 kPa or higher.

In the present description the term "odours" refers to one or more volatilised chemical compounds also at a very low concentration, which human beings or other animals perceive through the sense of smell.

In the present description the term "adsorbent" is intended to indicate an oxidic material formed by a metal or by a non-metal and by oxygen. An adsorbent as defined here is used in a first embodiment of the invention, as will be described here below, for the abatement of NO_x.

In the present description the term "catalyst" is intended to indicate an adsorbent on which a precious metal has been inserted. A "catalyst" as defined here is used in a second embodiment of the invention, as will be described here below, for the abatement of VOCs.

In the present description the term "heterogeneous adsorbent" refers to an adsorbent in solid phase.

In the present description the term "heterogeneous catalyst" refers to a catalyst in solid phase.

The general configuration of the apparatus for the abatement of gaseous pollutants, such as nitrogen oxides NO _/ volatile organic compounds VOCs, odours, NH₃, CO2 and CH₄, of the present invention is that of a plasma reactor at atmospheric pressure integrated with a catalyst/ adsorbent. More specifically these are oxidizing systems in the case of the abatement of gaseous substances such as VOCs, CH₄, particulate, dioxins, perfluorocarbons (PFC) and NH3 and reducing systems for the abatement of

The oxidizing systems are able to catalyse the oxidation reaction of the pollutant substance by promoting the loss of atoms of hydrogen H and increasing the quantity of atoms of oxygen O and the presence of oxygen O₂ is necessary in the reaction mixture. The reducing systems, instead, are able to catalyse the reaction of oxidation of the pollutant substance by promoting the loss of atoms of oxygen O and increasing the quantity of atoms of hydrogen H.

The main part of the apparatus is represented by the plasma reactor, which is made up of two parts:

- the actual plasma reactor, which in turn is composed of different parts and is the zone in which the plasma is generated by means of an electrical discharge passing between two electrodes (cathode and anode), and

- the plasma generator P.

In the plasma reactor the materials used for the electrodes can be of different type, such as for example steel and/ or cordierite. Plastic materials resistant to high temperatures can also be used such as transparent or orange Kapton.

Essential requisites of all the materials which constitute the plasma reactor are thermal stability and resistance to mechanical stresses. On the one hand, in fact, the system, when it works continuously, tends to raise the temperature of the electrodes and it is therefore indispensable that they resist the high , while, on the other hand, it is important instead that the electrodes be resistant to flows of air, high at times, which contain the pollutants to be abated.

The plasma reactor is managed by a generator which is an integral part of the system. The plasma generated by the generator can be of the continuous or pulsed type, SDBD (superficial dielectric barrier discharge) or VDBD (volume dielectric barrier discharge) on the basis of the geometry of the plates and of the reactor, which causes a different type of plasma. The DBD plasma can in fact be generated in a volume (VDBD) or on a flat surface (SDBD). In the VDBD the plasma is generated between two electrodes, for example between two parallel plates with dielectric in the middle; in the SDBD the micro-discharges are generated on the surface of a dielectric, which translates into a very homogeneous plasma. In the SDBD the micro-discharges are limited to the surface, therefore their density is higher with respect to the VDBD. Both configurations have proved to be effective in the treatment/ abatement of pollutant species. The modulation of the type of plasma generated is closely correlated to the geometry of the reactor and the type of plates used to construct it and the type of reaction to cause. It is very important to modulate in a precise and constant manner the type of energy supplied with the plasma system and the right quantity of energy is to be evaluated according to the type of reaction to be produced. By modulating the plasma characteristics, continuous or pulsed, and modifying the power thereof, it is possible to provide in a very precise way the quantity of energy required, avoiding producing secondary reactions which inevitably lower the yield of the reaction and originating at times undesired and possibly damaging secondary products (for example, in the case wherein the reaction of reduction of the nitrogen oxides and nitrogen is caused, it is possible to have the production of NP¾ in the outgoing mixture). It is possible to avoid the production of damaging substances by modulating precisely the energy supplied by the plasma and providing the reducing reagents in a stoichiometric manner with respect to the reaction and the quantities of incoming nitrogen oxides.

It is considered useful to specify that all the reactions listed in the present description are illustrative but not exhaustive of those which are the real mechanisms of reaction which take place in the single cases and the inventors do not intend to be constrained by these reactions for a real and complete comprehension of the mechanisms which intervene in the single processes.

Referring to Fig. 1 wherein a first embodiment is represented schematically, for the abatement of NO_x, the apparatus 1 according to the invention comprises:

- at least one plasma reactor at atmospheric pressure 3,

- at least one heterogeneous catalyst 5 deposited on a plurality of support media 7, and

- means 9) for maintaining the operating temperature at a value greater than 20°C, preferably between a minimum value of 20°C and a maximum value of 350°C

The support media 7 for the heterogeneous catalyst 5, to which reference will also be made as to cathodes, are placed inside the plasma reactor at atmospheric pressure 3 so as to form an integrated system 3,5,7.

It is pointed out that the type of apparatus illustrated in Fig. 1 is also suitable for the abatement of C0₂ and that therefore, in the present description, when reference is made to the apparatus for the abatement of NO_x if necessary the abatement of C0₂ will also be understood to be included.

According to the specific application for the abatement of nitrogen oxides (NO_x) and/ or CO2, the apparatus 1 comprises a reactor 3 which uses a reducing plasma GR and an adsorbent 5.

The reducing plasma GR is chosen in the group comprising H₂, He and Ar, and mixtures thereof.

The means 9 are preferably liquid heat exchangers.

Using the apparatus 1, the efficiency of abatement of the content of NO_x and/ or CO2 is equal to or higher than 80%.

The general reaction which takes place inside the apparatus 1 with abatable pollutants in reducing conditions is the following:

NOx + GR (in the presence of H ) -> N₂ + H₂O

Referring to Fig. 2 wherein a first variant of the first embodiment is represented schematically, the apparatus 1' comprises:

- at least one plasma reactor at atmospheric pressure 3',

- at least one heterogeneous catalyst 5' deposited on a plurality of support media 7',

- means 9' for maintaining the operating temperature at a value greater than 20°C, preferably between a minimum value of 20°C and a maximum value of 350°Q and

- a selective active carbons filter for the oxygen 11 placed upstream of the integrated system 3',5',Τ.

The support media 7' are similar to the support media 7 described in reference to Fig. 1.

The means 9' are preferably liquid heat exchangers.

The active carbons filter 11 is preferably a substance with high absorbing capacity, thanks to its porosity, most of the organic substances and on the consequent possibility of extracting them using a "vehicle" which is generally vapour.

In the apparatus 1', the selective active carbons filter for the oxygen 11 operates so as to eliminate most thereof and have a reaction chamber in which the plasma can work in conditions of excess reducent. In this way collateral reactions, able to originate undesired and potentially damaging chemical species, are avoided.

Using the apparatus 1', provided with filter 11, the efficiency of abatement of the content of NO_x and/ or CO₂ is equal to or higher than 90%.

Referring to Fig. 3, the structure is noted of the biphasic adsorbent 5;5' used in the first embodiment for the abatement of NO_x and/ or CO₂, which is formed by an inert support medium X, X', chosen in the group comprising oxides and metals, and by an adsorbent Y;Y', chosen in the group of the oxides of alkaline and alkaline earth metals. The inert support medium, in turn, comprises a porous oxide X;X' and an oxide in nanometric form Υ,Υ'; preferably the porous oxide X;X' is alumina, aluminium oxide and/ or silicon oxide and the oxide in nanometric form Υ,Υ' is barium oxide, an oxide with particular affinity to the nitrogen oxides. This oxide forms with the nitrogen oxide an ionic bond giving rise to nitrate ions with negative charge. The greater the surface area of the adsorbent, the greater the number of nitrate ions formed and the greater the efficiency of the system will be and there will be therefore a greater conversion of the reactor in percentage points (%) per unit of time.

As can be seen clearly in Fig. 3, the biphasic adsorbent 5;5' is deposited on the support media 7;7'.

Preferably, in the apparatus according to the invention, a so-called heterogeneous catalyst/ adsorbent is used, in that it is not in the same phase (solid, liquid or gaseous) in which the reagents are present. The heterogeneous catalyst/ adsorbent is in general formed by different elements.

- a support medium, generally inert, having high surface area and good thermal and mechanical stability;

- on this basis the actual catalyst is deposited, whether mono or biphasic, and optionally compounds for preventing the sintering thereof, as well as optional promoters (substances which act in a particular way, improving or modulating the catalytic performance).

The particles of heterogeneous catalyst/ adsorbent selected have in general a porous structure, therefore catalysis takes place both on the outer surface of the catalyst and on the inner one. This means that the surface available for the exchange of material is of different orders of greater magnitude with respect to that which would be obtained if the structure of the heterogeneous catalyst were compact (high surface area). Since the inner surface of a heterogeneous catalyst is much more extended than its outer surface, at the stage of design of the apparatus account has to be taken of the transport of material inside the pores of the catalyst.

In detail the adsorbent 5;5' used in the first embodiment, for the abatement of NO_x, and/ or of C02 is constituted by three different phases:

- a ceramic substrate (aluminium oxide, cerium oxide, silicon oxide, zinc, nickel oxide, magnesium oxide or mixed oxide of these) having high area. The smaller the dimension of the particle, the greater the surface area of the oxide. On occasions structured oxides are also used with porosity of different diameter (from micro to nano) so as to have a further increase in the surface area; these materials are called micro or mesoporous according to the dimension of the pores.

- An adsorbent oxide with specific properties of absorbing the pollutant species and forming with them ionic bonds; and

- a precious metal (Au, Pt, Pa, Rh, Fe, Ar, Ru) in nanoparticle form so as to have a high surface area and consequently a good contact with the pollutants. The metal is not however necessary in all the embodiments of the present invention (mention is made in fact of catalyst if this is constituted also by nanoparticles of metal, precious and appropriately dispersed, and supported on mixed oxides. The nanoparticles used are different according to the type of application required and of the type of reaction which is to be produced. The use of nanoparticles of precious metal greatly increases, obviously, the cost of the catalyst).

Referring to Figs.4A and 4B, a second variant of the first embodiment of the apparatus according to the invention is illustrated, which comprises:

- a first integrated system 3a,5a,7a;3' 'a,5' 'a,7' a

- a second integrated system 3b,5b,7b;3'b,5'b,7'b

- means 9,9' are preferably liquid heat exchangers.

- a switch 13.

The two integrated systems 3a,5a,7a;3'a,5'a,7'a and 3b,5b,7b;3'b,5'b,7'b operate in an alternate manner one in relation to the other thanks to the action of the switch 13, for example the first integrated system 3a,5a,7a;3'a,5'a,7'a operates with plasma unlit and the second integrated system b,5b,7b;?)'b,5'b,7'b operates with plasma lit (as can be seen in Fig. 4A), or the first integrated system 3a,5a,7a;3' 'a,5' 'a,7 'a operates with plasma lit and the second integrated system 3b,5b,7b;3'b,5'b,7'b operates with plasma unlit (as can be seen in Fig. 4B).

In particular Fig. 4A), represents the first operative phase in which, as mentioned previously, the first integrated system 3a,5a,7a;3'a,5'a,7'a operates with plasma unlit and the second integrated system 3b,5b,7b^3'b,5'b_r7'b operates with plasma lit, while Fig.4B), represents the second operative phase in which, as mentioned previously, the first integrated system 3a,5a,7a;3'a,5'a,7'a operates with plasma lit and the second integrated system 3b,5b,7b;3'b,5'b,7'b operates with plasma unlit.

More particularly two stages of the process are observed:

In the first stage (Fig. 4A), the flow of gas is conveyed into the first integrated system 3a,5a,7a}3' a,5' a,7' a wherein the plasma P is unlit and the flow of reducing gas GR is absent. The molecules of NO_x are adsorbed on the surface of the barium oxide, creating NO^3- species.

The reaction of adsorption of the nitrogen oxide on the barium oxide (storage) which takes place in the first integrated system 3a,5a,7a;3' 'a,5' 'a,7' ^'a is the following:

In the second integrated system 3b,5b,7b;3'b,5'b,7'b, instead, the plasma P is lit and the reducing gas GR is present. The energy supplied by the plasma is used to reduce the NO^3~species adsorbed previously according to the conversion reaction (reduction):

N0³-_ads + GR (in the presence of Kb) -> N_ + H₂0

The second integrated system 3b,5b,7b 3'b,5'b,7'b is open and the reduced gas can exit the reactor.

In the second stage (Fig. 4B), the flow of gas is conveyed now into the second integrated system 3b,5b,7b;3'b,5'b,7'b, which is now closed, and the pollutant gas is adsorbed by the adsorbent material. In this second stage the reaction of reduction takes place in the first integrated system 3a,5a,7a;3'a,5'a,7'a by the plasma P and the reducing gas GR.

The two integrated systems therefore work in an alternate manner with plasma unlit and plasma lit respectively in storage or reduction mode.

The apparatus 1;1' constituted by a system with two stages which work in an alternate manner, as illustrated in Figs. 4A and 4B, has the specific advantage of working with good conversions of NOx and in low temperature conditions.

Referring to Figs. 4C and 4D, the corresponding graphic representations of the reducing gas GR and of the plasma P in the two working phases of the apparatus of Figs. 4A and 4B show that, in the two-stage system, the reactor works in plasma conditions of pulsed type, with moments wherein the plasma P is lit - in ON phase - and moments in which the plasma P is unlit - in OFF phase. In the moment in which the plasma P is lit, the reducing gas GR is inserted in the reaction chamber while the flow of reducing gas GR is blocked when the plasma P is unlit.

Referring to Fig. 5 wherein a second embodiment is represented schematically, for the abatement of VOCs, the apparatus 1" according to the invention comprises:

- at least one plasma reactor at atmospheric pressure 3"

- at least one heterogeneous catalyst 5" deposited on a plurality of support media 7", and

- means 9" for maintaining the operating temperature at a value greater than 20°C, preferably between a minimum value of 20°C and a maximum value of 350°C.

The support media 7" are similar to the support media 7 described in reference to Fig. 1.

It is pointed out that the type of apparatus illustrated in Fig. 5 is also suitable for the abatement of CH₄ and of odours and that therefore, in the present description, when reference is made to the apparatus for the abatement of VOCs if necessary the abatement of CH₄ and/ or of odours will also be understood to be included.

According to the specific application for the abatement of VOCs and/ or CH4 and/ or odours and/ or N¾, the apparatus 1" comprises a reactor 3" which uses an oxidizing plasma GO and a catalyst 5".

The oxidizing plasma GO is chosen in the group comprising He or Ar with O2, and mixtures thereof.

The means 9" are preferably liquid heat exchangers.

Using the apparatus 1" the efficiency of abatement of the content of VOCs and/or odours is equal to or higher than 97%. In the case of CH₄the conversion is equal to or higher than 32%. In the case of NH3 the conversion is higher than 98%. In the case of odours the conversion is higher than 99%.

Fig. 5 illustrates, more specifically, a variant of the second embodiment which also comprises, downstream of the integrated system 3",5",7", an additional stage 15 in which the ozone O3 produced in the integrated system 3", 5", 7" acts as promoter for the total conversion of the residual volatile organic compounds (VOCs) into CO2, thus further incrementing the efficiency of the apparatus. Using the apparatus 1" provided with the additional stage 15, the efficiency of abatement of the content of VOCs and/ or C¾ and/ or odours and/ or NKb, is equal to or higher than 85%.

Some of the reactions which can take place inside the apparatus 1" wherein pollutants are treated which can be abated in oxidizing conditions are the following:

VOC + GO (in the presence of O₂) -> CO₂ +H₂O

C¾ + GO (in the presence of O₂) -> CO₂ +H₂O

NH₃ + GO (in the presence of O₂) -> N₂ +H₂O

Referring to Fig. 6, the structure is noted of the biphasic catalyst 5" used in the second embodiment for the abatement of VOCs and/ or of CH₄ and/ or of odours and/ or of NH_3/ which is formed by an inert support medium X", chosen in the group comprising oxides and metals, and by a catalyst Z", chosen in the group of precious metals.

The inert support medium X" is preferably aluminium oxide (gamma alumina) structured with porous base.

The catalyst Z" is preferably manganese oxide MnO in nanopowder form. A catalyst of metal type such as gold Au is also deposited in the form of nanopowder on the biphasic system which has been created.

As can be seen clearly in Fig. 6, the biphasic catalyst 5" is deposited on the support media 7".

Referring to Fig. 7 a schematic representation is seen of the support media 7;7';7" whereon the adsorbent/ the catalyst 5;5';5" of the apparatus according to the invention is deposited. In the enlargement of Fig. 7 it is noted that the adsorbent or catalytic material 5;5';5" in the form of nanometric powder is deposited directly on the support media creating a more or less uniform layer on their surface.

More particularly, in Fig. 7 it is seen that the plurality of support media 7;7';7" are flat plates. Alternatively the support media 7;7';7" can be undulated plates (which have a greater surface area with respect to the flat plates) or fibres, metal or glass, or again beds of ceramic material or glass.

Preferably the support media 7;7';7" are metal, since they have a greater stability to thermal, chemical and mechanical stresses. These support media are resistant, lightweight, not bulky and capable of large exchange surfaces.

In the case of ceramic support media 7;7';7" the chosen structure is the honeycomb one and covered in all its points by a porous substance, a mixture of refractory oxides appropriately mixed one with the other, impregnated with precious metals. The degree of dispersion of the noble metal defines the performance of the catalyst: the more it is dispersed, the higher the performance will be.

The catalyst 5;5';5" is deposited on the ceramic support media 7;7';7" by means of impregnation, that is to say by means of an operation apt to deposit on the porous ceramic support medium the metal active in the catalysis in the most dispersed form possible. The active metal is typically an element of the group of platinoids but can also be not noble, such as iron or cobalt.

As a function of the chemical reaction to be produced, each type of catalysis requires a special specific support medium-metal combination.

According to a particularly advantageous embodiment of the present invention, on the surface of the support media 7;7';7" a chemically modified photocatalytic material with oxidizing action is deposited with self-cleaning function of the apparatus 1;1';1".

More particularly, the photocatalytic material is titanium oxide modified with Fe and

Cu in the case of reactions of the reducing type, that is to say for the first embodiment of the present invention for the treatment of NO_x and/ or CO 2 while it is titanium oxide modified with N and F in the case of reactions of the oxidizing type, that is to say for the second embodiment of the present invention for the treatment of VOCs and/ or

CH₄ and/ or odours.

According to another particularly advantageous embodiment of the present invention, the apparatus 1;Γ;1" is able to treat different pollutants also present simultaneously in the incoming flow, thus resulting in a multi-pollutant apparatus. This feature is conferred to the apparatus 1;1';1" using appropriate catalysts according to the type of reaction to bring about, whether reducing or oxidizing.

According to another particularly advantageous embodiment of the present invention the apparatus (1;1';1") comprises also a plug-and-play device so that it is easy to install and to use. According to another particularly advantageous embodiment of the present invention the apparatus 1; ;1" also comprises a smart online probe integrated in the same apparatus so as to allow the latter to function in real-time adapting conditions, i.e. adapting the conditions of treatment on the basis of the values of output pollutant gases values.

Fig. 8A shows a first configuration of plasma reactor 3i;3i';3i" of the apparatus 1;1';1" according to the invention. In this first configuration plates of different material (metal or plastic) are used which are placed in a parallel way one in relation to the other. The electrical current is carried through the cathodes themselves and a passage of voltage is created as illustrated in the drawing. The plasma is lit in a volume and is called VDBD.

Fig. 8B shows a second configuration of plasma reactor Sifiifii' of the apparatus 1;1';1" according to the invention. In this second configuration plates of metal material are present constituted by small undulations in sheet meal with different structures. The sheet metal can have thickness varying between 0.02 and 0.2 mm according to the surface area required for the specific application. The drawing shows in detail the zone in which the passage of voltage is created. The plasma is lit only on the surface on the plate and is called SDBD.

Fig. 9 A shows a first type of plasma reactor 33;33';33" of the apparatus 1; ; ' according to the invention. This first type provides a quartz tube, connected to earth, in which an electrode is inserted which conducts the high voltage and generates the plasma and the reactor is filled with ceramic or glass spheres (beads) whereon the necessary catalyst is deposited.

Fig. 9B shows a second type of plasma reactor 34;34';3₄" of the apparatus 1;1';1" according to the invention. This second type also provides a quartz tube, connected to earth, in which an electrode is inserted which conducts the high voltage and generates the plasma and, in this case, the reactor is filled with metal fibres whereon the necessary catalyst is deposited.

Note that for both types both the transverse section and the side one are schematised. The adhesion of the catalyst nanoparticles on the different types of support medium is made optimal via different types of surface treatment. In particular, on the metal fibres and on the steel it is in fact necessary to perform treatments to give them affinity with the catalytic material, such as passivation or electrodeposition of ceramic material by means of which a layer of oxide is created on the metal with affinity through composition with the ceramic material to be deposited.

According to a further particularly advantageous embodiment of the present invention illustrated in Fig. 10, the apparatus 1;1';1" is provided with a cooling or heating plate 17, in whose interior a cooling or heating fluid 17 flows, which allows an efficient control of the temperature of the system.

According to an independent and autonomously usable aspect, the present invention provides a method for the abatement of volatile organic compounds VOCs and/ or CH₄ and/ or odours and/ or NHb, comprising the steps of:

a. providing an apparatus 1" comprising a reactor 3" which uses an oxidizing plasma GO and a heterogeneous catalyst 5" according to what is described previously in relation to the treatment of volatile organic compounds VOCs and/or CH₄ and/ or odours and/ or NH¾

b. maintaining the operating temperature of the apparatus 1" between a minimum value of 20°C and a maximum value of 350°C; and

c. making a stream of volatile organic compounds VOCs and/ or CH and/ or odours and/ or NHb flow through the apparatus 1".

The oxidizing plasma GO is chosen in the group comprising He or Ar with O₂, and mixtures thereof.

Using the abovementioned method, the efficiency of abatement of the content of volatile organic compounds VOCs and/ or CH₄ and/ or odours and/ or NH3, is equal to or higher than 97% .

According to an independent and autonomously usable aspect, the present invention provides a method for the abatement and the conversion of CO2, comprising the steps of:

a. providing an apparatus 1;1' comprising a reactor 3;3' which uses a reducing plasma GR and a heterogeneous catalyst 5;5' according to what is described previously in relation to the treatment of NO_x and/ or C02;

e. maintaining the operating temperature of the apparatus 1;1' between a minimum value of 20°C and a maximum value of 350°C; and

f. making a stream of CO2 flow through the apparatus 1; , thus obtaining different types of chemical substances with high economic interest, such as for example dimethyl ether DME.

Using the abovementioned method, the efficiency of abatement of CO2 is equal to or higher than 50%.

Finally, in particular, the apparatus according to the present invention can be used as plasma chamber in a method of abatement of nitrogen oxides NO_x studied by the same Applicant, which forms the object of a separate yet simultaneous Italian patent application entitled "Method of abatement of NO_x by means of a coupled plasma/ adsorbent system".

As is deduced from what is set out above, the innovative technical solution described here has the following advantageous features:

- high conversion efficiency also with low working temperatures;

- abating, in a very selective and economically advantageous manner, of polluting substances such as NO_x and VOCs, independently of the composition of the incoming gas, therefore also of the percentage of oxygen (in the case of NO_x) or nitrogen (in the case of the VOCs) present;

- possibility of using the plasma to cause reactions which normally take place only at high temperature and pressure, such as for example the conversion of CO2 to methane;

- possibility of use also in a discontinuous manner while maintaining high abatement efficiencies;

- in the specific case of abatement of VOCs, possibility of using the plasma as producer of ozone, secondary product of the lighting of the plasma in air and in the presence of oxygen and promoter of the total conversion of the residual VOCs into CO₂;

- maintenance of the system less burdensome and costly;

- decrease in the dimensions of the plants and in the corresponding running costs (for example limited consumptions of electrical current);

- working flexibility and ease;

- lack of production of damaging chemical substances, difficult and costly to dispose of.

From the description given above it is clear, therefore, how the technical solution according to the present invention, in its different aspects, allows the objects proposed to be reached.

It is equally evident, to a person skilled in the art, that it is possible to make changes and variants to the solution described with reference to the accompanying drawings, without thereby departing from the teaching of the present invention and the sphere of protection as defined by the appended claims.

- high conversion efficiency also with low working temperatures;

- abating, in a very selective and economically advantageous manner, of polluting substances such as NO_x independently of the composition of the incoming gas, therefore also of the percentage of oxygen (in the case of the NO_x) or nitrogen (in the case of the VOCs) present;

- possibility of using the plasma to cause reactions which normally take place only at high temperature and pressure;

- maintenance of the system less burdensome and costly;

- decrease in the dimensions of the plants and in the corresponding running costs;

- working flexibility and ease.

From the description given above it is clear, therefore, how the technical solution according to the present invention, in its different aspects, allows the objects proposed to be reached. The plasma system in oxidizing configuration is definitely advantageous with respect to traditional systems because:

- it works in conditions of ambient temperature, therefore the flow of incoming gas does not have to be preheated in order to be purified, and methane is not therefore used for running of the system;

- it has reduced dimensions with respect to thermal combustion systems, regenerative and otherwise;

- it has limited consumptions of electrical current;

- it does not produce chemical substances that are damaging to dispose of;

- it has low running costs;

- it can be used in systems in discontinuous mode, maintaining the efficiency of the system high,

- the abatement is very selective and economically advantageous of polluting substances such as VOCs independently of the composition of the incoming gas, therefore also of the percentage of nitrogen present.

The plasma system in reducing configuration is definitely advantageous with respect to traditional systems because:

- it has reduced dimensions with respect to traditional systems;

- it has limited consumptions of electrical current;

- it does not use ammonia or urea as reducing substances;

- it does not produce chemical substances that are damaging to dispose of;

- it has low running costs;

- it uses an adsorbent system at low cost in which precious metals are not inserted;

- the abatement is very selective and economically advantageous of polluting substances such as NOx independently of the composition of the incoming gas, therefore also of the percentage of nitrogen present.

Example 1: abatement of NO_x present in the gaseous effluent of a thermoelectric power plant or an industrial plant

An important aspect of the present invention, independent and usable autonomously with respect to the other aspects of the invention, relates to the application of the method with gaseous mixture containing nitrogen oxides NOx coming from a fixed system, for example a thermoelectric power plant or an industrial plant. Such a mixture comprises nitrogen monoxide NO and nitrogen dioxide NO₂.

The possibility of using the method according to the present invention for treating gaseous effluent of a thermoelectric power plant or of an industrial plant is particularly advantageous because, as is deduced from what is set out above, the innovative technical solution described here in reducing configuration has the following advantageous features:

- high conversion efficiency also with low working temperatures;

- maintenance of the system less burdensome and costly;

- working flexibility and ease.

Example 2: abatement of VOCs in a painting plant

In painting plants different types of VOC are emitted, the type of pollutant in the gas correlated to the composition of the painting used in the painting booth. Typical examples are painting booths for cars, for the body or for the bumpers.

The plasma system in oxidizing configuration is definitely advantageous with respect to traditional systems because:

it works in conditions of ambient temperature, therefore the flow of incoming gas does not have to be preheated in order to be purified, and methane is not therefore used for running of the system;

it has limited consumptions of electrical current;

- it does not produce chemical substances that are damaging to dispose of;

- it has low running costs;

it can be used in systems in discontinuous mode, maintaining the efficiency of the system high,

Example 3: abatement of NH3 on brake pads firing system

Inside the blend of the brake pads there is a resin with organic base containing amines. In the process of firing of the pads therefore a high quantity of NH3 is released. Ammonia is a difficult pollutant to eliminate since if oxidized in a normal combustion system it produces NOx.

- it works in conditions of ambient temperature, therefore the flow of incoming gas does not have to be preheated in order to be purified, and methane is not therefore used for running of the system; - it has reduced dimensions with respect to traditional systems;

- it has limited consumptions of electrical current;

it does not use ammonia or urea as reducing substances;

it does not produce chemical substances that are damaging to dispose of; it has low running costs;

it uses an adsorbent system at low cost in which precious metals are not inserted;

it can be used in systems in discontinuous mode, maintaining the efficiency of the system high;

Claims

1. Apparatus (1;1';1") for the abatement and the conversion of gaseous pollutants such as nitrogen oxides (NO_x), volatile organic compounds (VOCs), NH3, CO_¾ CH₄ and odours, comprising:

- at least one plasma reactor at atmospheric pressure (3;3';3"),

- at least one heterogeneous catalyst (5;5';5") deposited on a plurality of support media (7;7';7"), and

means (9;9';9") for maintaining the operating temperature between a minimum value of 20°C and a maximum value of 350°C

characterised in that said plurality of support media (7;7';7") for said heterogeneous catalyst (5;5';5") are placed inside said plasma reactor at atmospheric pressure (3;3';3") so as to form an integrated system (3,5,7; 3',5',7';3",5",7").

2. Apparatus (1;1') according to claim 1 for the abatement of nitrogen oxides (NO_x) and/ or CO2, wherein said reactor (3;3') uses a reducing plasma (GR) and said heterogeneous catalyst (5;5') is an adsorbent.

3. Apparatus (1') according to claim 2 for the abatement of nitrogen oxides (NO_x) and/ or CO2, moreover comprising, upstream of said integrated system (3',5',7')_r a selective active carbons for oxygen (11).

4. Apparatus (1;1 ') according to claim 2 or 3 for the abatement of nitrogen oxides (NOx) and/ or CO₂, wherein said catalyst (5;5') is biphasic formed by an inert support medium (X, Y, X', Y'), chosen in the group comprising oxides and metals, and by an adsorbent (Ζ;Ζ'), chosen in the group of the oxides of alkaline and alkaline earth metals.

5. Apparatus (1;1') according any one of the preceding claims for the abatement of nitrogen oxides (NO_x) and/ or CO₂, comprising a first (3a,5a,7a;3'a,5'a,7'a) and a second integrated system (3b,5b,7b;3'b,5'b,7'b), corresponding means (9;9') and a switch (13), the first of said two integrated systems (3a,5a,7a;3'a,5'a,7'a) operating in an alternate manner with respect to the second (3b,5b,7b;3'b,5'b,7'b), and vice versa, that is to say the first (3a,5a,7a;3'a,5'a,7'a) operating with unlit plasma and the second (3b,5b,7b;3'b,5'b,7'b) operating with lit plasma, and vice versa.

6. Apparatus (1") according to claim 1 for the abatement of volatile organic compounds (VOCs) and/ or CH and/ or odours and/ or NH₃, wherein said reactor (3") uses an oxidizing plasma (GO) and said heterogeneous catalyst (5") is a heterogeneous catalyst with base of Au.

7. Apparatus (1") according to claim 6 for the abatement of volatile organic compounds(VOCs) and/ or CH₄ and/ or odours and/ or NH₃, comprising moreover downstream of said integrated system (3", 5", 7"), an additional stage (15) in which the ozone (O₃) produced in said integrated system (3", 5", 7") acts as promoter for the total conversion of the residual volatile organic compounds (VOCs) into CO₂.

8. Apparatus (1;1') according to claim 6 or 7 for the abatement of volatile organic compounds (VOCs) and/ or CH , and/ or odours and/ or NH3, wherein said catalyst (5") is biphasic formed by an inert support medium (X"), chosen in the group comprising oxides and metals, and by a metal (Z") chosen in the group of precious metals.

9. Apparatus (1;1';1") according to any one of the preceding claims, wherein said plurality of support media (7;7';7") are plates, flat or undulated.

10. Apparatus (1;1';1") according to any one of the preceding claims from 1 to 8, wherein said plurality of support media (7;7';7") are fibres, metal or glass.

11. Apparatus (1;1';1") according to any one of the preceding claims from 1 to 8, wherein said plurality of support media, (7;7';7") are beds, in ceramic material or glass.

12. Apparatus (1;1';1") according to any one of the preceding claims 9 or 10 or 11, wherein on the surface of said plurality of support media (7;7';7") a chemically modified photocatalytic material with oxidizing action is deposited with self -cleaning function of the apparatus.

13. Apparatus (1;1';1") according to claim 12, wherein said photocatalytic material is titanium oxide modified with N and F in case of reactions of oxidizing type and modified with Fe and Cu in the case of reactions of the reducing type.

14. Apparatus (1;1';1") according to any one of the preceding claims, able to treat different pollutants also present simultaneously in the incoming flow, so that the apparatus is multi-pollutant.

15. Apparatus (1;1'; ') according to any one of the preceding clams, comprising a plug- and play device so that the apparatus is easy to install and to use.

16. Apparatus (1;1';1") according to any one of the preceding claims, comprising a smart online probe integrated in the apparatus so as to allow the latter to function in real-time adapting conditions, i.e. adapting the conditions of treatment on the basis of the values of the output pollutant gases.

17. Method for the abatement of volatile organic compounds (VOCs) and/or CH and/ or odours and/ or NH3, comprising the steps of:

a. setting up an apparatus (1") comprising a reactor (3") which uses an oxidizing plasma and a heterogeneous catalyst (5") according to any one of claims 6 to 16;

b. maintaining the operating temperature of said apparatus (1") between a minimum value of 20°C and a maximum value of 350°C; and c. making a stream of volatile organic compounds (VOCs) and/or CH₄ and/ or odours flow through said apparatus (1").

18. Method according to claim 17, wherein said oxidizing plasma is chosen in the group comprising He or Ar with O₂, and mixtures thereof.

19. Method according to claim 17 or 18, wherein said stream of volatile organic compounds (VOCs) has any percentage of nitrogen (N₂).

20. Method according to any one of the preceding claims from 17 to 19, wherein the efficiency of abatement of the content of volatile organic compounds (VOCs) and/ or CH₄ and/ or odours is equal to or higher than 97%.

21. Method for the abatement and the conversion of CO₂, comprising the steps of:

d. setting up an apparatus (1;1') comprising a reactor (3;3') which uses a reducing plasma and a heterogeneous catalyst (5;5') according to any one of claims 2 to 5;

e. maintaining the operating temperature of said apparatus (1; ) between a minimum value of 20°C and a maximum value of 350°C; and f. making a stream of CO2 flow through said apparatus (1;1'), thus obtaining different types of chemical substances with high economic interest, such as for example dimethyl ether (DME).