IT201700006271A1 - Process for obtaining a porous material starting from powdered materials, porous material and its use for the capture of atmospheric particulate and organic contaminants - Google Patents

Description

DESCRIPTION

Field of application

In its more general aspect, the present invention refers to a process for the production of a porous, ceramic or glassy material, starting from powdered materials, comprising inorganic oxides, preferably waste powder material such as for example ashes or their derivatives. .

More specifically, the present invention relates to a process of the aforementioned type carried out by heating.

The present invention also relates to a porous, ceramic or glassy material, obtainable by means of the above-mentioned process according to the present invention, and its uses.

Known art

The improvement of air quality is an objective of increasing importance at a global, European and national level. Parallel to policies that promote a lifestyle with a decreased carbon footprint, there is a continuous search for new processes for the production of materials with a low environmental impact.

In particular, especially in the urban environment and with reference to those polluting emissions attributable to car traffic and obsolete civil heating systems, the problem of pollution caused by atmospheric particulate matter and high molecular weight organic substances, such as polycyclic aromatic hydrocarbons (PAHs). The overrun of the daily limit of fine particles imposed by law (50, ug / m <3> for PMio) is now a rather common circumstance that occurs even dozens of times a year in the main European urbanized areas, especially in those located in flat areas and inland, such as the Po Valley, the Parisian region and Polish Silesia, to name a few, as well as in mountainous areas, or located in the valley, characterized by intense anthropic activity.

The production of materials for use in construction as adsorbents of polluting substances such as for example cements capable of oxidizing the organic and inorganic polluting substances adsorbed, thanks to photo-catalysts duly introduced into the mixture at the time of formulation or deposited, is known in the art. on the surface of the material after its formation. See, for example, patent application WO 2004074202.

However, these materials have a rather limited application, as they are often excessively expensive materials. Therefore, these materials cannot represent a solution to the problem of air pollution in urban centers, especially in historic city centers or near major communication arteries such as ring roads and access roads to cities, as well as in mountainous or located localities. in the valley floor, characterized by intense anthropic activity.

The need is therefore felt to make available a material capable of adsorbing pollutants, particularly suitable for use in construction, having low cost and which can be applied not only to new structures, but also to buildings and infrastructures already existing.

Among the possible alternatives, there is activated carbon which can be used as a filter for aqueous solutions, as well as a filter inside air filtering equipment.

However, this type of material, in addition to not being particularly suitable for large-scale use for building applications, especially for cost issues, also presents significant desorption problems.

Therefore, it is necessary to develop not only inexpensive materials, but also with high adsorbing capacity and faster desorption kinetics with the possibility of being easily regenerated.

In this sense, a possible alternative to activated carbon can be provided by porous ceramic materials, which are quite known and widespread for various types of applications, for example as filters for aqueous solutions, but also as filters for the exhaust gases of chimneys and drain lines.

For both of the aforementioned applications, materials such as porous ceramic foams are known, for example ceramic foams of alumina, titanium oxide or zirconia.

In this sense, processes are known for obtaining porous ceramic materials obtained with the aid of an inorganic starting material, first of all alumina, and alginates, for example sodium alginate.

Commonly, these materials are also obtained by means of processes that involve a high temperature sintering step, typically higher than 1000 ° C.

A production process of these materials is exemplified in the publication "Formation of porous articles with ordcred capillary structure by alginate sol-gel tecnique" by B. Liebig and others, in which it is planned to start from ceramic powder (alumina and titanium oxide) and an alginate, carrying out a gelation step induced by reusing a source of copper ions, followed by leaching of the ions themselves. This process then ends with a sintering step at a temperature of 1200 ° C or 1500 ° C to obtain a ceramic foam.

Ultimately, the known processes for the production of porous ceramic materials which use as starting material inorganic powders and a polysaccharide as a gelling agent during the formulation procedure necessarily require a sintering step with heating at temperatures above 1000 ° C.

Therefore, these processes require suitable equipment to withstand high temperatures and, above all, they determine a large consumption of energy, making the finished product not only unsustainable ecologically, but also significantly expensive.

The need is therefore particularly felt to develop a process for the production of a porous adsorbent material at low cost and ecologically sustainable, as well as the provision of a material that boasts similar advantages; in particular, a porous material suitable for use in the construction field is required.

The main purpose of the present invention is therefore to develop a process for the production of a porous material, which does not require passages at high temperatures and at the same time is simple and economical to implement for an industrial application, so as to overcome the limitations of the known technologies mentioned above for obtaining porous ceramic materials.

Another object of the present invention is to provide a product, such as a material with high porosity, suitable for use as an adsorbent substrate for pollutants, specifically polluting species included in the air such as atmospheric particulate or organic substances such as high molecular weight.

Summary of the invention

In one embodiment, this technical problem is solved by a process for obtaining a porous, ceramic or glassy material, starting from powdered materials comprising inorganic oxides, in which this process can include the following steps:

a) mixing a solvent, preferably water, a gelling agent and a cross-linking agent under stirring, until a gelling solution is obtained;

b) adding, under stirring, to said gelling solution a powder material, comprising inorganic oxides, and a leavening agent, until a homogeneous mixture is obtained;

c) heating the homogeneous mixture to a predetermined temperature and time so as to obtain a porous solid material, where the temperature is between 35 ° C and 110 ° C and the time is greater than 45 minutes;

d) allowing this solid porous material to cool to room temperature.

In accordance with an alternative embodiment, this technical problem is solved by a process for applying a coating of a porous, ceramic or glassy material, obtained from powdered materials comprising inorganic oxides, to a pre-existing solid surface, in which this procedure can include the following steps:

a) mixing a solvent, preferably water, a gelling agent and a cross-linking agent under stirring, until a gelling solution is obtained;

b) adding, under stirring, to this gelling solution a powder material, comprising inorganic oxides, and a leavening agent, until a homogeneous mixture is obtained;

c) adding a further portion of said solvent to said homogeneous mixture under stirring until a diluted homogeneous mixture is obtained;

d) applying such diluted homogeneous mixture to a hard surface so as to form a diluted homogeneous mixture coating on such pre-existing solid surface, where such coating may preferably have a thickness between 0, Imm and 5 mm;

e) heating the diluted homogeneous mixture coating to a predetermined temperature and time so as to obtain a coating of porous solid material, in which the temperature is between 35 ° C and 110 ° C and the time is greater than 45 minutes;

f) allowing this coating of porous solid material to cool to room temperature.

Preferably, in accordance with this alternative embodiment, the step of applying the diluted homogeneous mixture to a hard surface according to the last described embodiment of the process of the invention can be carried out by spraying.

More generally, in accordance with a generic process of the present invention, the aforementioned powder material, comprising inorganic oxides, can be a waste material deriving from industrial, civil or agricultural processes.

Preferably, this waste material in powder form, deriving from industrial, civil or agricultural processes, comprising inorganic oxides, can be any element selected from the group consisting of smoked silica, wood ash, coal ash, desulfurization ash, ash deriving from combustion of sewage sludge and any combination of the above.

Equally preferably, the aforementioned gelling agent can be a polysaccharide, more preferably an alginate.

According to a particular embodiment, the process according to the present invention provides for the further step of placing the aforementioned homogeneous mixture in a mold, before carrying out this heating step c).

The aforementioned technical problem can also be solved thanks to the provision of a porous, ceramic or glassy material, obtainable by any process according to the present invention, comprising an amorphous phase and obtained from a powdered material, comprising inorganic oxides, preferably material waste and deriving from industrial, civil or agricultural processes, in which this material has a density between 500 kg / m <3> and 900 kg / m <3> and has pores with an average size of less than or equal to 50 gm.

The amorphous phase comprised in the aforementioned material in turn comprises inorganic oxides in an amount by weight greater than or equal to 10% with respect to the weight of this amorphous phase, preferably it can comprise organic oxides in an amount by weight greater than or equal to 30% with respect to weight of this amorphous phase.

Specifically, the amorphous phase can comprise any of the elements selected from the group consisting of silica, aluminum oxide, ferric oxide, ferrous oxide and any combination of these. Preferably, the amorphous phase comprises silica.

Equally preferred, this amorphous phase comprises an organic ligand, which can be a polysaccharide, more preferably an alginate.

In order to solve the aforementioned technical problem, the present invention also provides that the aforementioned porous material, ceramic or glass, can be used as a filter for the adsorption of fine atmospheric particulate and / or organic contaminants, preferably in the covering of buildings, roofs or in the covering of road architectural elements.

Detailed description

. After extensive research, the inventors have perfected a new process for the production of a porous, ceramic or vitreous material, starting from powdered materials, including inorganic oxides, which allows the above purposes to be achieved brilliantly.

Preferably, the process in question has made it possible to develop a porous material, ceramic or vitreous, starting from waste materials in powder form, deriving from industrial, civil or agricultural processes including inorganic oxides.

For the purposes of the present invention, the term "waste materials in powder form, deriving from industrial, civil or agricultural processes, including inorganic oxides" means a solid mixture comprising mostly inorganic substances obtained as by-products during industrial processes, including oxides, hydroxides or salts of metals and / or metalloids with an average particle size between 0.2 gm and 50 gm.

Pursuant to the present invention, the term "silica fumé" means a by-product obtained in smelting plants in the production industry of elemental silicon and ferro-silicon alloys. Specifically, the reduction reaction of silica to elemental silicon, which occurs at temperatures above 2000 ° C, causes the formation of S1O2 vapors, which in turn condense in the cooler areas of the reactor as fine particulate comprising mainly noncrystalline silica. Generally, smoked silica can contain an amount of silica ranging from 85% to 95% by weight.

Pursuant to the present invention, the term "wood ash" means a by-product obtained by combustion and / or fractionation of plant material from forest plant sources (wood, wood by-products, twigs) or from waste from the agro-food industry such as walnut shells, hazelnut shells, rice husks, fruit kernels, olive pomace, corn cobs, wheat straw, discarded parts of cereal kernels, sugar cane stalks, pomace and grape seeds. Wood ash may comprise inorganic oxides in amorphous form, such as silica, for example, and may comprise inorganic oxides in crystalline form such as calcium oxides and fairchildite.

For the purposes of the present invention, the term "coal ash" means a by-product obtained during the combustion of coal. Coal ash can be coarser grained, being identified as "bottom ash", i.e. fine particles that precipitate directly into the combustion chamber, or it can be made up of even finer particles that remain suspended in the gas stream and are transported by the flow of combustion gases out of the furnace, being identified with the expression “fly ash”. The coal ash may comprise inorganic oxides in amorphous form, such as silica, for example, and may comprise inorganic oxides in crystalline form such as quartz, hematite and mullite.

According to the present invention, the term "desulphurization ash" means a by-product obtained from the thermoelectric combustion cycle of coal, more specifically desulfurization gypsum obtained by desulphurization of the combustion gases generated by the combustion of. coal by reaction. between sulfur dioxide, calcium carbonate and water.

As briefly anticipated in the summary, a process according to the invention may include different steps which will be reported below.

According to a first step of this process, it is envisaged to mix a solvent, preferably water, a gelling agent, and a cross-linking agent under stirring, until a gelling solution is obtained.

According to a second step, it is envisaged to add to this gelling solution, under stirring, a powder material comprising inorganic oxides, and a leavening agent, until a homogeneous mixture is obtained.

Finally, this porous solid material is allowed to cool to room temperature.

As anticipated in the summary, in accordance with a particular embodiment, the process according to the present invention described above provides for the further step of placing the aforementioned homogeneous mixture in a mold, before carrying out this heating step.

In this way, therefore, in an absolutely advantageous way, the process according to the present invention described above allows to obtain products in porous, ceramic or glassy material, with a predetermined shape and thickness, in which these shapes and thicknesses can be completely improved according to the end use.

In accordance with an alternative embodiment, the present invention provides a process for applying a coating of a porous, ceramic or glassy material, obtained from powdered materials, including inorganic oxides, to a pre-existing solid surface, where such procedure includes the following steps:

- mixing a solvent, preferably water, a gelling agent and a cross-linking agent under stirring, until a gelling solution is obtained;

- adding, under stirring, to this gelling solution a powder material, comprising inorganic oxides, and a leavening agent, until a homogeneous mixture is obtained;

- adding a further portion of said solvent to said homogeneous mixture under stirring until a diluted homogeneous mixture is obtained;

- applying such a diluted homogeneous mixture to a hard surface so as to form a coating of this diluted homogeneous mixture on such a pre-existing solid surface, in which this coating can preferably have a thickness of between 0, Imm and 5 mm;

- heating the diluted homogeneous mixture coating to a predetermined temperature and time so as to obtain a coating of porous solid material, where the temperature is between 35 ° C and 110 ° C and the time is greater than 45 minutes; in the end,

- allow this coating of porous solid material to cool to room temperature.

Preferably, in the step of adding under stirring to the. homogeneous mixture a further portion of solvent until a diluted homogeneous mixture is obtained, the additional portion of solvent is equal to 1-5 parts by weight with respect to the weight of the other components of the diluted homogeneous mixture.

More preferably, the step of applying this diluted homogeneous mixture to a hard surface according to the process of the invention just described can be carried out by spraying.

The process of applying a coating of a porous material, ceramic or glass, to a pre-existing solid surface actually involves an in situ application of a homogeneous mixture comprising a solvent, a gelling agent, a cross-linking agent, a leavening agent and a material. powder, comprising inorganic oxides. More precisely, rather than providing for the realization of an artifact of predetermined dimensions, this alternative procedure contemplates the covering of pre-existing solid surfaces with a thin coating of fluid and viscous material to be subsequently heated to obtain a solid surface covered with a thin coating. of porous, ceramic or glassy material.

In detail, once the thin coating layer has been deposited, the heating (and drying) phase of the previously deposited homogeneous mixture follows, which can easily occur by means of a flow of hot air.

For example, this heating and drying phase can be carried out by simple exposure to the atmosphere of the surface thus covered.

In fact, the in situ application of the process according to the present invention is particularly suitable for the covering of architectural elements, of new construction or in the maintenance phase, such as internal surfaces of walls, for example inside or outside industrial buildings. and warehouses, roofs, building facades, or elements of road infrastructure, such as roadway edge elements: concrete bridges and overpasses, safety barriers and sound-absorbing barriers, for example.

More specifically and referring in general terms to a generic process according to the present invention, the gelling agent can be any polysaccharide suitable for the purpose, i.e. any completely soluble polysaccharide, compatible with the other elements of the mixture and capable of guaranteeing an increase viscosity in the solvent medium. More preferably, the polysaccharide can be an alginate, even more preferably sodium alginate.

As anticipated in the summary, in an entirely advantageous way, this powdered material can be a waste material in powder form deriving from industrial, civil or agricultural processes. In accordance with this preferred embodiment, it is therefore possible to further enhance the entire production process, using materials otherwise intended for potentially unprofitable uses and / or to be discarded.

Then, it should be specified that this waste material in powder form, deriving from industrial, civil or agricultural processes, including inorganic oxides, is preferably smoked silica and / or wood ash and / or coal ash and / or desulfurization ash and / or ash from the combustion of sewage sludge, for example sludge obtained during a waste water purification process.

The waste materials mentioned above have the best cost / benefit ratio among similar ones available on the market. In fact, these are waste materials which have a low cost, mainly due to their easy availability and to the simple preliminary treatments they undergo before being put on the market. At the same time they are particularly suitable for use during the process according to the invention and for obtaining a product according to the invention with optimal characteristics, which will be described later.

Preferably, the solvent is present in the gelling solution in an amount equal to 35-60 parts by weight and the gelling agent is present in the gelling solution in an amount equal to 1-10 parts by weight.

Preferably, the crosslinking agent is a calcium or barium salt soluble in an aqueous environment, more preferably it is selected from one of the elements of the group consisting of calcium iodate, calcium chloride, barium chloride and any combination of these elements.

Even more preferably, the crosslinking agent is calcium iodate. Specifically, when the crosslinking agent is calcium iodate, it is mixed in this first phase with the other elements of the mixture so as to be present in said gelling solution in an amount equal to 1-10 parts by weight.

More preferably, in said homogeneous mixture said powder material is present in quantities equal to 25-55 parts by weight with respect to the parts by weight of the other components of said homogeneous mixture.

Furthermore, the leavening agent is preferably an inorganic leavening agent; more preferably, the leavening agent is an element of the group consisting of sodium hydrogen carbonate, ammonium hydrogen carbonate, potassium hydrogen carbonate, sodium carbonate, an alkali metal salt of tartaric acid and any combination of these elements .

Specifically, when the levitating agent is sodium hydrogen carbonate, it is mixed in this second phase with the other elements of the homogeneous mixture so as to be present in said homogeneous mixture in an amount equal to 1-15 parts by weight.

In accordance with a preferred embodiment, during the step of adding under stirring to the gelling solution a powder material can be added titanium oxide and / or zinc oxide and / or any suitable catalyst with photocatalytic properties and / or any mixture of them. Specifically, when titanium oxide and / or zinc oxide and / or a mixture of these is added, titanium oxide and / or zinc oxide and / or a mixture of these is present in the aforementioned homogeneous mixture in an amount comprised between 1 and 10 parts by weight.

Most preferably, this predetermined temperature in a generic step of heating the homogeneous mixture or the diluted homogeneous mixture is comprised between 70 ° C and 90 ° C, even more preferably it is equal to about 80 ° C.

The heat in fact allows the hydrogen carbonate ion or the carbonate ion present in the leavening agent to release gaseous carbon dioxide: the progressive accumulation of this gas gives rise to the formation of bubbles in the highly viscous mixture in the process of solidification, which remain trapped there.

In this way, the highly viscous material, drying up, necessarily becomes porous.

The choice of the type of leavening agent is conditioned by the dispersibility of the same in the mixture, by the temperature at which it decomposes to give CO2, as well as by the cost of the same.

Equally preferably, this predetermined time in a generic step of heating the homogeneous mixture or the diluted homogeneous mixture is equal to about 60 minutes.

Preferably, the porous solid material obtained by means of a generic process according to the invention can be subjected to a further phase of curing. During this further phase the material is stored for a predetermined time at room temperature. More preferably, this predetermined time is greater than two weeks, even more preferably it is greater than three weeks.

The present invention also refers to a porous, ceramic or glassy material, obtainable through any process according to the present invention, generally comprising an amorphous phase, obtained from powdered materials, comprising inorganic oxides, preferably waste materials and deriving from industrial processes , civil or agricultural, in which this porous material has a density between 500 kg / m <3> and 900 kg / m <3> and has pores with an average size less than or equal to 50 pm,

According to the present invention, the expression "porous, ceramic or glassy material, generally comprising an amorphous phase", means that the material according to the present invention, when of the ceramic type, can often also include a crystalline phase, in addition to the amorphous phase.

The amorphous phase generally included in the material according to the invention can comprise inorganic oxides in an amount by weight greater than or equal to 10% with respect to the weight of this amorphous phase, more preferably greater than or equal to 30% with respect to the weight of this amorphous phase.

The amount by weight of inorganic oxides included in the amorphous phase of the material in question depends on the type of material used in the process according to the invention.

For example, in the case of using a material with a high silica content, such as smoked silica, the inorganic oxides included in the amorphous phase can be present in an amount by weight equal to greater than 40%, preferably equal to or greater than 50%. , more preferably equal to or greater than 60%, still more preferably equal to or greater than 70%.

Furthermore, the specific weight of the porous material according to the invention can preferably be comprised between 5000-10000 kg-nr <2> -s <~ 2>.

In particular, the amorphous phase of the material in question is substantially constituted by microscopic granules of inorganic material, deriving from powdered materials, and comprising inorganic oxides, used in the production process, and a polymeric network of organic binder, deriving from a gelling agent used in the production process.

Equally preferred, the organic binder comprised in the aforementioned amorphous phase can be a polysaccharide polymer, more preferably an alginate.

Specifically, the individual chains of the polysaccharide network, especially when the gelling agent used is an alginate, are linked together by "metal bridges" made up of positive metal ions. More in detail, the metal bridges are made up of calcium ions or barium ions deriving from a cross-linking agent used during the process of obtaining the porous material in question.

Advantageously, the porous material, ceramic or glass, according to the present invention can have pores with an average size less than or equal to 10 gm, more preferably it can have an average pore size less than or equal to 1 gm.

The mean pore size was calculated by mercury intrusion poresimetry.

Furthermore, the porous material, ceramic or glass, according to the invention can comprise from 70% to 100% by weight of the amorphous phase on the total weight of the material.

In fact, according to a particular embodiment of the present invention, the material according to the present invention can also comprise a crystalline phase from 0 to 30% by weight of the total weight of the material.

The crystalline phase possibly included in the material according to the invention may in turn include calcium carbonate (CaCOs), nahcolite (NaHCO.3) and calcium iodate monohydrate (Ca {I03) 2-H20).

Specifically, this crystalline phase can be present on the surface of the porous, ceramic or glassy material, according to the invention as isolated and physically distinct crystalline formations.

Within the amorphous phase, the material according to the present invention can further comprise a colored pigment. Thanks to the presence of a possible colored pigment, the material according to the present invention is more pleasing to the eye. In fact, in the absence of pigments, the material according to the invention can have a color ranging from white to dark gray.

More generally, the material according to the invention, thanks to its high porosity, is able to adsorb polluting solid particles and organic macromolecules present in the atmosphere with which it comes into contact.

In particular, the material according to the invention is able to adsorb heavy metals, removing them from the fluids with which the surface of the same is put in contact.

The material according to the invention is particularly suitable for adsorbing atmospheric particulate resulting from the combustion of fossil fuels or waste fuels and for adsorbing polycyclic aromatic hydrocarbons.

In particular, the surface crystalline formations mentioned above do not in any way affect the properties associated with the material according to the invention.

Another aspect of the material according to the present invention is the fact that it can be "regenerated" by simple washing with water.

Specifically, after exposure to polluted air and full of atmospheric particulate matter and / or polluting organic macromolecules, the material according to the invention can be effectively washed by simply applying a jet of water on the surface of the same.

Due to the force exerted on the surface of the material by the applied water flow, the particulate and organic substances adsorbed on the surface of the material according to the invention are removed and transported by the flow itself, significantly cleaning the surface of the material so that it can adsorb further particulate matter and polluting molecules.

In accordance with an embodiment, the alternative porous material according to the present invention can comprise titanium oxide and / or zinc oxide and / or any catalyst with photo-catalytic properties and / or any combination thereof.

Specifically, it has been observed that, in a material according to the present invention comprising a catalyst with photocatalytic properties, when first polluting organic substances, such as polycyclic aromatic hydrocarbons, are adsorbed on the surface, and then it is hit by a beam of light comprising ultraviolet radiation , these adsorbed organic polluting substances undergo progressive degradation.

Therefore, the material according to the invention is not only able to adsorb any polluting organic substances, removing them from the environment and purifying the air that comes into contact with the surface of the same, but it can also catalyze the decomposition of these compounds to chemical species. less polluting and, above all, less harmful to human health.

With reference to what is described in the immediately preceding paragraphs, the present invention also provides that the aforementioned porous, ceramic or glassy material can be used as a filter for the adsorption of fine atmospheric particulate and / or organic contaminants, possibly present in the atmosphere.

Specifically, as previously mentioned in relation to the process according to the invention, the material in question can be used as a covering coating for new or existing buildings, for example in the renovation phase, for example for covering roofs. o walls / facades, or in the covering of new or existing road architectural elements, for example during maintenance.

Particularly indicated is the use of the material according to the present invention as a covering coating for buildings or in the covering of architectural road elements in urban centers, especially in historic city centers or near major communication arteries such as ring roads and access roads to cities. , as well as in mountain areas, or located in the valley, characterized by intense anthropic activity.

The use of the material according to the present invention just mentioned is particularly effective since it allows to purify the polluted air directly in the vicinity of the pollution source, such as for example particulate matter and organic polluting substances formed by combustion of fossil fuels in diesel engines. explosion or in boilers for homes / offices, particulate matter formed due to wear of the components that make up the braking systems of vehicles (cars and motor vehicles, rail transport), particulate formed by rubbing tires on the roadway or particulate from industrial sources , such as incinerators, often located not far from inhabited centers.

In particular, when the material according to the present invention is used for covering through an external surface coating of buildings or architectural elements exposed to bad weather, the material according to the present invention can be advantageously regenerated by the action of rainwater; rainwater removes atmospheric particulate matter and organic molecules adsorbed on the surface and in the surface micro cavities of the material according to the invention by leaching. The flow of water formed, in which particulate matter and polluting organic molecules are dispersed, is naturally conveyed to the sewer by gravity.

Furthermore, the porous material according to the present invention can be made as a manufactured article. This product can be used as a filter for a polluted fluid, more precisely as a filter intended as a replaceable element, in which this replaceable element is part of a more complex equipment or system, designed to remove impurities from a flow of polluted fluid.

Furthermore, again thanks to the high porosity, the material according to the present invention is able to effectively adsorb sound waves. Consequently, when applied to the walls of buildings or on the external surface of sound-absorbing barriers, for example, it can be not only useful in the abatement of pollutants present in the air, but it can also prove very effective in reducing the noise pollution that it is often a non-secondary problem for the inhabitants of buildings located near major roads or busy roads in urban centers.

Ultimately, the process for obtaining a porous, ceramic or glassy material, starting from powdered materials, including inorganic oxides, the process for applying a thin coating of a porous, ceramic or glassy material, obtained from a powdered materials, comprising inorganic oxides, to a pre-existing solid surface and the porous material, ceramic or glass, described above according to the present invention, allow to achieve numerous advantages: the main one is to provide a porous solid material of the ceramic type or glassy type at low cost with high capacity to adsorb on its surface atmospheric particulate and polluting organic macromolecules, such as polycyclic aromatic hydrocarbons.

A further advantage is certainly that of providing a material with high added value thanks to the simple production process through which it is obtained and the optional reuse of a waste material such as coal and wood ashes, smoked silica, ashes of desulphurization and ashes deriving from sewage sludge.

In fact, some solid by-products deriving from combustion, such as those exemplified in the present description, are commonly disposed of in large quantities in conventional landfills, representing an economic and environmental cost.

There are also further advantages among which are listed:

- the provision of an economic and ecological production process, with particular reference to the low temperatures required during the heating phase;

- the possibility of obtaining and applying the material according to the present invention directly in the place of use, for example by means of a spray application technique with subsequent heating and cooling in situ;

- the provision of an easily washable material, whose adsorbent properties can be periodically regenerated by simply washing the surface of the same with water;

- the provision of a material with photocatalytic properties that allows the gradual destruction of the polluting organic substances adsorbed on the surface of the same;

- the possibility of incorporating in the material according to the present invention a colored pigment so as to make it more pleasing to the eye.

Further features and advantages of the invention will be evident from the following examples, given as an indication and not a limitation with reference to the attached figures in which:

- Figure 1 shows an article obtained in accordance with a process according to the invention (right), and an article obtained with a process according to the invention followed by a sintering step (left);

- Figure 2 shows the cross section of a detail of the product obtained in accordance with a process according to the invention, shown in Figure 1;

- Figure 3 shows an image made with a scanning electron microscope representing the surface of a sample of the material according to the invention, obtained with the process according to the invention;

- figure 4 shows an enlargement of a detail of the image shown in figure 3;

- figure 5 shows an enlargement of a different detail of the image shown in figure 3;

- Figure 6 represents an X-ray diffractogram of a sample of material according to the invention, obtained in accordance with a process according to the invention;

- Figure 7 shows two different images taken with an optical microscope, on the left a sample of material according to the invention and, on the right, a sample of material according to the invention subjected to an adsorption test;

- Figure 8 shows an image taken with a conventional camera, representing on the right a sample of material according to the invention after having been subjected to an adsorption test and, on the left, a sample of material according to the invention subjected to an adsorption test first and then a washout test.

Example 1: production of porous ceramic material obtained from smoked silica

A sample of porous ceramic material was prepared from gray smoky silica.

First, 7 g of sodium alginate and 2 g of calcium iodate were added to 50 ml of demineralized water (ultrapure milli-Q® water). The mixture was left to stir for a few minutes until a very viscous transparent solution was obtained. To the viscous solution thus obtained, 35 g of gray smoky silica, coming from companies that deal with iron-silicon alloys, were added under vigorous stirring, then 10 g of sodium bicarbonate. The mixture thus obtained was left to stir for a few minutes until a homogeneous mixture with a uniform anthracite gray color was obtained.

Subsequently, 30 ml of the homogeneous mixture thus obtained was adapted in an aluminum mold.

The mold thus filled was then placed on an Arex type heating plate by Velp Scientifica, placed at a temperature of 80 <D> C.

After a time equal to 60 min, the mold containing the mixture was withdrawn from the plate; the homogeneous mixture placed in the mold had the consistency of a very rough and visibly porous solid disc on the surface.

The mold containing the solid disc was then placed in a dry environment at a temperature of approximately 20 ° C for four weeks.

The solid disc thus obtained had a gray color, slightly less intense than the disc immediately after the withdrawal of the mold from the heating plate. By exerting a modest pressure, the solid disc thus obtained was broken into two parts. The internal surface in correspondence with the sectional fracture of the parts thus obtained showed a porous structure even within the solid disc.

Example 2: comparative test between a porous ceramic material obtained from low temperature smoky silica and a similar material obtained by sintering

In accordance with the process already described in example 1, a homogeneous mixture was obtained comprising smoky gray silica.

Subsequently, 60 ml of the homogeneous mixture thus obtained were extruded directly onto an Arex type heating plate by Velp Scientifica, by means of a completely conventional 20 ml polypropylene syringe, obtaining two different "waffle" -shaped mixtures.

The mixtures thus obtained were heated for 60 minutes at a temperature of 80 ° C.

Subsequently, the solidified doughs were withdrawn from the plate, obtaining two artifacts.

A first product thus obtained was then placed in a dry environment with a temperature of approximately 20 ° C for four weeks.

At the same time, a second product was subjected to a sintering treatment in a tubular oven at a temperature of 500 ° C, for a total time of 2 hours.

The first dough and the second dough thus obtained are shown in figure 1.

The consistency of the first mixture and the consistency of the second artifact were completely comparable.

Figure 2 shows a cross section of the first manufactured article obtained according to the present example: the internal macroporous structure of the thus obtained article is evident.

Example 3: characterization of porous ceramic material obtained from gray smoky silica

The mixture of example 1 obtained by a process according to the invention with final "curing" at room temperature for four weeks was characterized by means of a scanning electron microscope (SEM) and by X-ray diffraction spectroscopy (XRD ).

In figure 3, in figure 4 and in figure 5 are represented SEM images of the surface of the solid mixture of example 1, obtained with gray fumé silica and with a process according to the invention.

In figure 3 it can be clearly seen that on the surface of the material there are diffuse crystalline, needle-like formations, in stark contrast to a prevalent and darker amorphous phase.

Figure 4 shows an enlargement of these needle-like crystalline formations present on the surface of the sample represented in Figure 3.

Figure 5 shows an enlargement of the surface of the sample depicted in Figure 3 in an area devoid of such crystalline formations: the microporosity of the material in correspondence with the amorphous phase with pores having a diameter of less than 1 gm is evident.

Figure 6 shows a diffractogram of a sample of material taken from the surface of the mixture according to example 1, obtained with gray smoky silica and with a process according to the invention.

The presence of the characteristic peaks of calcium carbonate salts, nahcolite and calcium iodate monohydrate is noted; this analysis confirms the chemical nature of the crystals observed during analysis with a scanning microscope.

Example 4: porous ceramic material obtained from white smoky silica and adsorption test

By the same procedure already described in Example 1, a homogeneous mixture was obtained comprising smoky silica of white color.

Subsequently, 30 ml of the homogeneous mixture thus obtained was placed in an aluminum mold.

The mold thus filled was then placed on an Arex type heating plate by Velp Scientifica, placed at a temperature of 80 ° C.

After a time equal to 60 min, the mold containing the mixture was withdrawn from the plate; the homogeneous mixture placed in the mold had the consistency of a very rough white solid disc on the surface.

The mold containing the solid disc was then placed in a dry environment at a temperature of approximately 20 ° C for four weeks.

The artifact thus obtained was broken into several parts to preliminarily verify the internal structure with the naked eye: the material proved to be visibly porous both externally and internally.

Subsequently, a portion of the product was subjected to an adsorption test to verify the particulate capture properties of the material. The material was put in contact with a stream of exhaust gas coming from the exhaust pipe of a diesel car engine for 15 minutes.

Figure 7 shows two different images taken with an optical microscope; on the left an image taken on the sample before being subjected to the adsorption test, on the right an image of the sample after being subjected to the adsorption test.

From figure 7 it is evident how the tested material according to the invention is particularly suitable, in general, for the adsorption of pollutants (presumably mostly solid particles) on its porous surface.

Example 5: porous ceramic material obtained from white smoky silica and washout test

The sample of the artefact subjected to a particulate capture test according to the previous example and shown in figure 7 was then subjected to a washout test.

The sample in question was placed in a beaker and washed with 20 ml of demineralized water (ultrapure milli-Q® water) using a syringe.

Figure 8 shows the comparison between a sample of porous material according to the invention after exposure to an exhaust gas flow coming from an exhaust pipe of a diesel engine according to the method of the previous example (left) and a sample of the same type subsequently subjected to a washout operation.

From the comparison between the two different samples shown in figure 8, it is evident how the material according to the invention is easily washable with a modest flow of water, which is able to easily remove the polluting solid material of dark color adsorbed on the surface of the porous material.

Example 6: porous ceramic material obtained from gray smoky silica and adsorption test for polycyclic aromatic hydrocarbons

A portion of the product of example 1 weighing 0.66 g and obtained through a process according to the invention, with final "seasoning" at room temperature for four weeks, was tested for the adsorption of polycyclic aromatic hydrocarbons.

The sample was placed in a beaker containing a standard solution of polycyclic aromatic hydrocarbons (PAHs) containing acenaphthylene with concentration 20 pg / L and acenaphthene with concentration 20 pg / L.

The sample was left to soak for 60 minutes.

Subsequently, the adsorption capacity with reference to the PAHs present in the standard solution was evaluated by mass spectroscopy, comparing the intensity of the characteristic peaks of the aforementioned PAHs in the standard solution with that of the same peaks in the solution after immersion of the sample for 60 minutes.

The test result was particularly successful as it was estimated that more than two fifths of the acenaphthylene and about one third of the acenaphthene present in the standard solution were adsorbed by the sample under examination.

Example 7: porous ceramic material obtained from gray smoky silica and decomposition test of polycyclic aromatic hydrocarbons A sample of porous ceramic material was prepared starting from gray smoky silica.

First, 7 g of sodium alginate and 2 g of calcium iodate were added to 50 ml of demineralized water (ultrapure milli-Q® water). The mixture was left under stirring for a few minutes until a very viscous transparent solution was obtained. To the viscous solution thus obtained, 35 g of gray smoky silica, coming from companies that deal with iron-silicon alloys, were added under vigorous stirring, then 2 g of titania, and finally 10 g of sodium bicarbonate. The mixture thus obtained was left under stirring for a few minutes until a homogeneous mixture with a uniform anthracite gray color was obtained.

Subsequently, 30 ml of the homogeneous mixture thus obtained was adapted in an aluminum mold.

The mold thus filled was then placed on an Arex type heating plate by Velp Scientifica, placed at a temperature of 80 ° C.

After a time equal to 60 min, the mold containing the mixture was withdrawn from the plate; the homogeneous mixture placed in the mold had the consistency of a very rough and visibly porous solid disc on the surface.

The mold containing the solid disc was then placed in a dry environment at a temperature of approximately 20 ° C for four weeks.

The solid disc thus obtained had a gray color, slightly less intense than the disc immediately after the withdrawal of the mold from the heating plate.

A portion weighing 0.66 g of the disc thus obtained was tested for the adsorption of polycyclic aromatic hydrocarbons, exactly following the procedure described in Example 6.

Following immersion in the solution containing IPA, the sample was stored overnight in a dry environment at a temperature of 20 ° C.

The following morning the sample was subjected to a decomposition test by subjecting it to a beam of UV light generated by a Philips UV lamp, emission in the range 340-410 nm with a maximum at 365 nm, for 12 hours.

Then, the quantity of PAHs adsorbed on the sample surface following the decomposition test was evaluated and subsequently the decomposition capacity with reference to the PAHs present in the standard solution by mass spectroscopy.

The amount of PAH adsorbed on the sample surface evaluated in example 6 was compared with the amount of PAH evaluated on the sample of the present example after being subjected to the decomposition test.

The outcome of this comparison showed that about 90% of the acenaphthene and 90% of the acenaphthylene adsorbed on the sample was decomposed following the decomposition test. The material according to the invention therefore showed an excellent ability to decompose the polycyclic aromatic hydrocarbons adsorbed on its surface when subjected to UV radiation.

Example 8: production of porous ceramic material obtained from coal ash

A sample of porous ceramic material was prepared from coal ash.

First, 8 g of sodium alginate and 2 g of calcium iodate were added to 50 ml of demineralized water (ultrapure milli-Q® water). The mixture was left to stir for a few minutes until a very viscous transparent solution was obtained.

To the viscous solution thus obtained, 37 g of coal ash, coming from coal-fired thermal power stations, were added under vigorous stirring, then 7 g of sodium bicarbonate. The mixture thus obtained was left to stir for a few minutes until a homogeneous mixture with a dark gray, almost black, uniform color was obtained.

Subsequently, 30 ml of the homogeneous mixture thus obtained was adapted in an aluminum mold.

The mold thus filled was then placed on an Arex type heating plate by Velp Scientifica, placed at a temperature of 80 ° C.

After a time equal to 60 min, the mold containing the mixture was withdrawn from the plate; the homogeneous mixture placed in the mold had the consistency of a very rough and visibly porous solid disc on the surface.

The mold containing the solid disc was then placed in a dry environment at a temperature of approximately 20 ° C for four weeks.

The solid disc thus obtained had a dark gray color, slightly less intense than the disc immediately after the withdrawal of the mold from the heating plate. By exerting a modest pressure, the solid disc thus obtained was broken into two parts. The internal surface in correspondence with the sectional fracture of the parts thus obtained showed a porous structure also inside the solid disc.

Example 9: obtaining of porous ceramic material obtained from wood ash

A sample of porous ceramic material was prepared from wood ash.

First, 8 g of sodium alginate and 2 g of calcium iodate were added to 45 ml of demineralized water (ultrapure milli-Q® water). The mixture was left under stirring for a few minutes until a very viscous transparent solution was obtained.

To the viscous solution thus obtained, first 45 g of wood ash (beech), then 12 g of sodium bicarbonate, were added under vigorous stirring. The mixture thus obtained was left under stirring for a few minutes until a homogeneous mixture with a uniform graphite gray color was obtained.

Subsequently, 25 ml of the homogeneous mixture thus obtained was adapted in an aluminum mold.

The mold thus filled was then placed on an Arex type heating plate by Velp Scientifica, placed at a temperature of 80 ° C.

After a time equal to 60 min, the mold containing the mixture was withdrawn from the plate; the homogeneous mixture placed in the mold had the consistency of a very rough and visibly porous solid disc on the surface.

The mold containing the solid disc was then placed in a dry environment at a temperature of approximately 20 ° C for four weeks.

The solid disc thus obtained had a marked gray color, slightly less intense than the disc immediately after the withdrawal of the mold from the heating plate. By exerting a modest pressure, the solid disc thus obtained was broken into two parts. The internal surface in correspondence with the sectional fracture of the parts thus obtained showed a porous structure also inside the solid disc.

Claims (18)

CLAIMS 1. A process for the preparation of a porous, ceramic or glassy material, starting from powdered materials, comprising inorganic oxides, said process comprising the following steps: a) mixing a solvent, preferably water, a gelling agent and a cross-linking agent under stirring, until a gelling solution is obtained; b) adding, under stirring, to said gelling solution a powder material, comprising inorganic oxides, and a leavening agent, until a homogeneous mixture is obtained; c) heating said homogeneous mixture to a predetermined temperature and time until a porous solid material is obtained, in which said predetermined temperature is comprised between 35 <D> C and 110 ° C, and said time is greater than 45 minutes; d) allowing said solid porous material to cool to room temperature. 2. Process according to claim 1, said process comprising the further step of arranging said homogeneous mixture in a mold, before carrying out said heating step c). 3. A process for applying a coating of a porous, ceramic or glassy material, obtained from powdered materials, including inorganic oxides, to a pre-existing solid surface, said process comprising the following steps: a) mixing a solvent, preferably water, a gelling agent and a cross-linking agent under stirring, until a gelling solution is obtained; b) adding, under stirring, to said gelling solution a powder material, comprising inorganic oxides, and a leavening agent, until a homogeneous mixture is obtained; c) adding a further portion of said solvent to said homogeneous mixture under stirring until a diluted homogeneous mixture is obtained; d) applying said diluted homogeneous mixture to a pre-existing solid surface so as to form a covering coating of said diluted homogeneous mixture on said hard surface, in which said coating preferably has a thickness comprised between 0, Imm and 5 mm; e) heating said covering coating of said homogeneous diluted mixture to a predetermined temperature and time so as to obtain a coating of porous solid material, in which said temperature is between 35 ° C and 110 ° C and said time is greater than 45 minutes; f) allowing said coating of porous solid material to cool to room temperature. 4. Process according to claim 3, wherein said step of applying the diluted homogeneous mixture to a pre-existing solid surface can be carried out by spraying. 5. Process according to any one of the preceding claims, wherein said powder material is a waste material, deriving from industrial, civil or agricultural processes. 6. Process according to the preceding claim 5, wherein said powdered material is an element selected from the group consisting of smoky silica, wood ash, coal ash, desulfurization ash, ash resulting from the combustion of sewage sludge and any combination of the previous elements. 7. Process according to any one of the preceding claims, wherein said gelling agent is a polysaccharide, said gelling agent being preferably an alginate. 8. Process according to any one of the preceding claims, wherein said solvent is present in said gelling solution in an amount equal to 35-60 parts by weight and said gelling agent is present in said gelling solution in an amount equal to 1-10 parts in weight. weight. 9. Process according to any one of the preceding claims, wherein said crosslinking agent is a calcium or barium salt soluble in aqueous environment, said crosslinking agent being preferably selected from one of the elements of the group consisting of calcium iodate, calcium chloride, barium chloride and any combination of these elements, more preferably being said calcium iodate cross-linking agent and said cross-linking agent being present in said gelling solution in an amount equal to 1-10 parts by weight. 10. Process according to one of the preceding claims 8 or 9, wherein in said homogeneous mixture said powder material is present in an amount equal to 25-55 parts by weight. 11. Process according to any one of the preceding claims, wherein said leavening agent is an element of the group consisting of sodium hydrogen carbonate, ammonium hydrogen carbonate, potassium hydrogen carbonate, sodium carbonate, an alkali metal salt of tartaric acid and any combination of these elements, preferably said leavening agent hydrogen sodium carbonate and said leavening agent present in said homogeneous mixture in an amount equal to 1-15 parts by weight. 12. Process according to any one of the preceding claims, wherein said predetermined temperature is between 70 ° C and 90 ° C, preferably said predetermined temperature being equal to about 80 ° C. 13. Process according to any one of the preceding claims, said process comprising a further curing step, said porous solid material or said porous solid material coating being kept at room temperature for a predetermined time, preferably said predetermined time greater than two weeks, more preferably longer than three weeks. 14. A porous, ceramic or glassy material, obtainable through a process according to any one of the preceding claims, in which said material is derived from powdered materials, preferably waste and deriving from industrial, civil or agricultural processes, comprises an amorphous phase, has a density between 500 kg / m <3> and 900 kg / m <3> and has pores with an average size lower than or equal to 50 μιη, said amorphous phase comprising inorganic oxides in a quantity by weight greater than or equal to 10 % with respect to the weight of said amorphous phase, preferably said amorphous phase comprising inorganic oxides in an amount by weight greater than or equal to 30% with respect to the weight of said amorphous phase. 15. A porous material according to claim 14, wherein said amorphous phase comprises an organic binder, preferably said organic binder being a polysaccharide polymer, more preferably said organic binder being an alginate. 16. Porous material according to any one of the preceding claims 14 or 15, wherein said pores have an average size less than or equal to 10 gm, preferably having said pores an average size less than or equal to 1 gm. 17. Use of a material according to any of the preceding claims from 14 to 16 as a filter for the adsorption of fine atmospheric particulate and / or organic contaminants, preferably in the covering of buildings, roofs or in the covering of road architectural elements. 18. Product made with a porous material according to any of the previous claims 14-16, said product being suitable for use as a filter for a fluid comprising pollutants.