WO2011066632A1 - Cylindrical electrochemical cell with doped coaxial diamond anode produced by deposition of diamond-bearing films on mechanically resistant cylindrical substrates, for use in aqueous solution purification processes - Google Patents

Abstract

The present invention relates to a cylindrical electrochemical cell for use in the purification of aqueous solutions, utilising a doped coaxial diamond anode produced by chemical vapour deposition, by a process during which the diamond-bearing films are deposited onto previously blasted, mechanically resistant cylindrical substrates, and makes it possible to obtain uniform, homogeneous and adherent films. More specifically, the electrochemical cell containing this anode can efficiently electrolyse undesirable substances contained in aqueous waste or drinking water, rendering these compounds innocuous and/or significantly reducing toxic compound concentration. It is an efficient process for direct and indirect oxidation, and does not cause any significant physical or chemical structural alterations of the anode surface even after long periods of operation.

Description

 "CYLINDRICAL ELECTROCHEMICAL CELL WITH COAXIAL DYNAMANT DIAMOND ANODE OBTAINED BY THE DEPOSITION PROCESS OF DIAMANTANT FILMS ON MECHANICALLY RESISTANT CYLINDRIC SUBSTRATES FOR APPLICATION IN PURIFICATION SOLUTION PROCESSES"

 FIELD OF INVENTION

 The present invention is a cylindrical electrochemical cell for use in the purification of aqueous solutions using coaxial doped diamond anode obtained by chemical vapor deposition process where diamond films are deposited on mechanically resistant cylindrical substrates. , previously blasted, and such process allows to obtain uniform, homogeneous and adherent films.

 More specifically, the electrochemical cell containing said anode is capable of efficiently electrolyzing undesirable substances contained in aqueous waste or drinking water, rendering such compounds harmless and / or significantly lowering the concentration of toxic compounds; It is effective in direct and indirect oxidation. besides the anode does not undergo significant physical or chemical structural changes in its surface during long periods of operation.

 BACKGROUND OF THE INVENTION

 Recently, it has been recognized that air pollution and deterioration of water quality in rivers, lakes and springs due to industrial waste and the livelihood of modern humanity have caused adverse effects on the environment and the human body. Thus, there is an urgent need for the development of preventive techniques against these problems.

Biological treatments, activated carbon adsorption and flocculation processes are extensively used to enable the disposal, in rivers or similar locations, or reuse of industrial and domestic waste containing undesirable compounds. However, these processes _r are not sufficient to eliminate many of the chemical compounds active and thus require secondary treatment, ie chemical oxidation. Among the secondary processes, many can create even more serious problems for human health and the environment, and some produce mud in large quantities.

 For the treatment of drinking water, domestic sewage and industrial aqueous waste, chlorine has been used to discolor, lower Chemical Oxygen Demand (COD) and / or sterilize water. However, the use of chlorine causes the production of admittedly more toxic chlorinated substances. Thus, procedures based on the oxidizing power of chlorine tend to be prohibited. In waste incineration, carcinogenic compounds (dioxins) can be produced in waste gas and therefore the safety of incineration has been questioned. In order to solve these problems, new processes have been studied. The Fenton reaction, which is used to treat hard to oxidize wastes, has the problem of generating a large amount of sludge due to the presence of the iron ion used as a catalyst.

 The selection of an optimal treatment will depend on control, reliability, cost-effectiveness and efficiency (chemical and economic). Of these technologies, electrochemical oxidation is considered one of the most promising (Canizares, et al. Detoxification of synthetic industrial waste-waters using electrochemical oxidation with boron-doped diamond anodes. J. Chem. Technol. Bíotechnol. 81, pp. 352-358 Canizares et al Electrochemical treatment of the effluent of a fine chemical manufacturing plant J. Hazard Mater 138, 173-181 2006 Alfaro et al Boron doped diamond electrode for the wastewater treatment J. Braz Chem Chem 17, 227-236, 2006).

Many electrode search investigations have been performed on various types of materials, such as RuO ₂ , PbO ₂ and SnO ₂ , which are used as anodes for the degradation of organic and inorganic pollutants (Poleara et al., Three-dimensional electrodes for the electrochemical combustion of organic pollutants Electrochim Acta 46, 389- 394, 2000). However, these anodes erode easily and tend to deactivate, decreasing their efficiency and useful life (Bonfatti et al, Electrochemical incineration of glucose as a model organic substrate I. Role of the electrode material. J. Electrochem. Soc. 146, Pp. 2175-2179, 1999).

 Recently, boron-doped diamond electrodes manufactured by the chemical vapor deposition process -

Chemical Vapor Deposition (CVD) are being applied with

successfully treating aqueous wastes containing persistent compounds in the environment. However, although diamond synthesis through the chemical vapor deposition process has been known since 1960, the major drawback of this technique is the difficulty of obtaining uniform and homogeneous films, and mainly because of its low deposition rate. .

 The CVD technique is based on the transformation of gaseous molecules into solid materials in the form of thin films on substrate. These films cover different geometries and can be of excellent quality. While the High Pressure High Temperature (HPHT) technique produces diamond crystals that can be attached to, for example, abrasive tools, the CVD technique makes it possible to coat diamond films on surfaces. materials not having a melting or softening point at a temperature below at least 700 ° C.

Diamond is a material with wide bandgap. (E _gap = 5.5 eV), normally being an electrical insulator. However, when material is doped with impurities such as boron, electrical conductivity is introduced in a controlled manner. At a doping level below 10 ¹⁹ B / cm ³ , the material behaves more like a semiconductor and when doped to higher levels it behaves like a semi-metal. 100-1000 S cm ^"1 electrical conductivity can be introduced into the material without compromising its other unique properties, making it sufficiently conductive for many electrochemical applications. The use of electrochemically conductive diamond as an electrode material is well established (Baranauskas et al. BRPI0600897-6; Teófilo et al. J. Solid State Electrochem., 11, pp. 1449-1457, 2007; Swain et al., Journal of Electrochemical Society, 141, pp. 3382-3393, 1994). The wide applicability of the diamond anode in electrolysis is due to its unique technologically important properties for electrochemical purposes such as: (1) chemical inertia and therefore high resistance to electrochemical blockage by polar molecules or possible surface contaminants; (2) corrosion resistance; (3) extreme hardness; (4) wide window of potential and optical transparency; (5) excellent thermal conductivity; (6) low and stable background current; (7) low capacitance; (8) magnificent microstructural and morphological stability even under aggressive electrochemical conditions; (9) mechanical strength (hardness 10 Mohs); (10) long term stability; (11) broad overpotential for oxygen evolution; (12) high thermal conductivity (20 Wcm ^" K ^{" 1} ); (13) high dimensional stability and (14) a constant sensitivity.

 In boron-doped diamond electrolysis, electrical energy, which is a clean energy for many countries, is used to control the chemical reaction on the electrode surface and thus produce extremely strong oxidizers such as oxygen, ozone, hydroxyl radical and hydrogen peroxide. Recently, the electrolysis process is being used to treat contaminated water as it is possible to indirectly decompose organic and inorganic pollutants, or adsorb pollutants on the electrode surface and, as a result, oxidize them directly.

Therefore, it is expected that the use of diamond as an electrode will be more efficient over electrochemical systems with the same purpose. From a practical point of view, improvements have been desired to promote increased cell efficiency. Thus, the configuration of the electrochemical cell and the arrangement of the diamond anode are fundamental for obtaining electrochemically and economically efficient processes.

 The various patent documents disclosed in the state of the art involving electrochemical cells and diamond electrodes are related to electrochemical cells in which said electrodes are made in the form of plates, arranged in parallel within the cells. In general, the main problems of cells using parallel plates are: leaks during cell assembly, difficulty in making electrical contact with the diamond, and difficulty in electrode handling during cell assembly.

 Regarding the electrolyte leaks that occur during the assembly of an electrochemical cell, it can be stated that, in general, the larger the area of the plate diamond electrode that is intended to be installed in a cell, the greater the difficulty. There are usually problems with electrolyte leaks due to a number of factors, notably the fragility of diamond films when they are pressed against gaskets and gaskets. Otherwise, chemical adhesives, which are responsible for waterproofing the edges and contours of the electrodes, are usually not effective due to detachment caused by gas evolution or oxidation caused by generated oxidants. Additionally, the use of conductive adhesives to attach a silicon plate to a metal plate, in addition to significantly increasing the final cost of building a cell, has the risk that the glue will degrade during the process and thus decrease the efficiency. .

Electrical contact is another problematic factor. Making electrical contact with a semiconductor, such as a doped diamond, requires the use of metallic conductive adhesives or welds. Ideally, these adhesive materials should not come into contact with the electrolyte and often these are isolated with epoxy resins. During the degradation process these resins are attacked by the oxidants generated on the electrode surface and are degraded. After a short time the electrical contact is exposed to the electrolyte and the process should be interrupted.

 Cell mounts also require special attention. Silicon plates, for example, are fragile to manipulate. To assemble an electrolytic cell with these plates containing deposited diamond films, they need to be packed in polymeric supports such as Teflon®. During the assembly process, these plates often break together with the diamond film deposited on them and the anode is lost.

 Some documents involving electrochemical cells and diamond electrodes are detailed below:

 U.S. 5,900,127; U.S. 5,399,247; EP 0659 691; U.S. 6,375,827 and BRPI0502246-0 describe the possibility of using doped diamond as an electrode for treating contaminants in water. In all these documents the electrochemical cells are made up of two plates in which the diamond can be used as anode or as anode and cathode.

US 5,900,127 describes an electrochemical cell using parallel plates, where neither the anode nor the cathode is cylindrical. In addition to the difference in cell configuration, the invention differs from this document for other reasons, which are listed below. The cathode used in US 5,900,127 was constructed using materials such as platinum, palladium, iridium, ruthenium, osmium, rhodium, etc., and oxides of these metals, such as iridium oxide, etc. The diamond in this patent was preferably grown on titanium or a metal or semi metal that allows carbide generation. Three electrochemical cell configurations were presented: two with double compartments and one with triple compartment. In dual compartment cells, the cell is divided by an ion exchange membrane intimately disposed between the anode and cathode or disposed at the connector portion having a small diameter and spaced from the cathode and anode. In the triple compartment, the division consists of the following sequence: a cathode attached to an ion exchange membrane, a separation and an ion exchange membrane attached to the anode.

US 5,399,247; EP0659691 and BRPI0502246-0 show configurations of electrochemical cells mounted with parallel plates. In US 5,399,247 and EP 0659 691, the boron-doped diamond anode was grown in silicon and purchased from the US company Advanced Technology Materials, Inc. The anode, having an area of 3 cm ² , was fixed to a plate and disposed in parallel. to a 12 cm ² 304 stainless steel plate used as a cathode. A nylon mesh was used between the plates to promote aqueous flow turbulence. Although the present invention has in common with US 5,399,247 and EP0659691 the use of conductive diamond as anode for treating solutes in liquid solution, it differs in that the cell is mounted with parallel plates. This type of configuration presents the same drawbacks already reported for parallel plates, especially regarding leaks and difficulty in making electrical contacts.

 BRPI0502246-0 describes an electrochemical oxidation process of organic compounds using a reactor equivalent to that described in US 5,399,247 and EP 0659 691. Although the present invention has in common with BRPI0502246-0 the use of diamond conductor as anode for mounting the electrochemical cell differs in that the cell is assembled with parallel plates, where a silicon plate is glued onto a stainless steel plate using a conductive adhesive in an attempt to increase the mechanical resistance of the electrode. .

US 6,375,827 is characterized by the use of diamond as both anode and cathode material, in which the electrochemical cell is assembled with two parallel plates, and an ion exchange membrane can be added between the plates, thus obtaining a cell in two compartments. . Although the present invention has in common with US 6,375,827 the use of conductive diamond as anode for The electrochemical cell assembly differs in that the cell is assembled with parallel plates, where the cathode is also a conductive diamond.

 U.S. 6,267,866 and U.S. 7,217,347 describe the use of doped diamond electrodes for electrolysis.

 U.S. 6,267,866 describes electrode construction using diamond deposition on a metal mesh. It is indicated for use as cathode or anode. The term mesh is defined as a grid of interwoven metallic filaments. The goal would be to make the electrode hollow and with large surface area for electrochemical applications. Although the present invention has in common with U.S. 6,267,866 the fact that it uses conductive diamond in the electrode assembly, it differs in that it is a plate-shaped assembly. It does not claim an electrochemical cell, but an electrode (anode and cathode). The disadvantage of using this plate is the realization and isolation of the electrical contact and the assembly of the anode - cathode configuration of the cell, as both must be completely immersed in the electrolyte solution without the use of polymeric support.

US 7,217,347 describes the construction of the electrode on a Magneli titanium phase. The goal is to extend the life of the diamond when grown on this material. Although the present invention has in common with US 7,217,347 the fact that it uses conductive diamond in the electrochemical cell assembly, it differs in that it is a wire mesh assembly using a different substrate, most of which of the figures shows the diamond powder mixed with titanium oxide powder. It does not claim an electrochemical cell, but an electrode (anode and cathode). The disadvantage of this technology lies in the electrode manufacturing process, which requires the use of Magneli phase titanium oxide substrate, diamond powder, titanium powder and a catalyst layer. This makes the cost of manufacturing the process relatively high and complex. US 6,306,270 and EP1031645, which refer to the same invention, relate to an electrochemical cell including an anode, a cathode and at least one bipolar electrode arranged between the anode and the cathode. This cell is characterized by a bipolar electrode that includes a substrate and a doped diamond film. Two cell configurations are presented, one with plate electrodes and one with spherical electrodes immersed in an electrolyte solution. Although the present invention has in common with US 6,306,270 and EP1031645 the use of conductive diamond as a bipolar electrode for the treatment of solutes in liquid solution and one of the assemblies involves a cylindrical cell, it differs in that the cylindrical cell is assembled. in a different embodiment from the present invention, wherein the solution passes through small polarizing spheres. In addition, the cylinder is placed inside a container, unlike the proposed electrochemical cell, where the cylinder containing the diamond film (anode) is coaxially disposed within another stainless steel or other metal (cathode) cylinder. Diamond-coated anode and cathode polarize diamond-coated spheres. Assembly requires a membrane through which the solution to be degraded crosses and the spheres do not. This is a complex and expensive assembly, unlike the present invention.

 Other electrochemical cell configurations are disclosed in U.S. 7,232,507; CA 2439744; U.S. 6,315,886; CA2355346; 6,554,977 and EP1369384. However, these patents claim the use of the doped diamond anode and the proposed cell configurations are based on parallel plates, different from the cell configuration claimed in the present invention.

US 7,232,507 and CA2439744, which refer to the same invention, describe the use of a complex electrochemical reactor for treating low concentration contaminants in low electrical conductivity aqueous solutions and claim the use as a coating material. of cell, a semiconductor diamond. Although the present invention has in common with US 7,232,507 and CA2439744 the fact that using semiconductor diamond for electrodegradation of organic compounds in water, it differs in that the configuration of the cell and the electrodes are completely different. The complexity of the cell configuration would certainly increase the difficulties of its industrial fabrication, which would result in higher costs compared to the proposed technology. Certainly there would still be the difficulty of perfectly cutting the plates, which are usually imported in the form of silicon wafers.

 By analyzing U.S. 6,554,977, it was possible to find the possibility of using a conductive diamond anode and cathode, but that document does not point to this possibility. Although the present invention has in common with U.S. 6,554,977 the fact that it claims a durable electrochemical cell for electrochemical oxidation of contaminants in aqueous solutions, the similarities cease here. The excellence of the most successful stainless steel electrodes is countless times lower than that of diamond electrodes. Metal electrodes generally do not produce hydroxyl radicals on their surface. Strong oxidizers, such as hydroxyl radicals, attack organic and / or inorganic compounds and degrade them. In addition, it is noteworthy that stainless steel electrodes used as anode have a short service life. The service life of stainless steel used as anode is a few hours, depending on the pH of the electrolyte used and the current density applied. By applying a positive potential to the stainless steel electrode, the metallic iron present in its steel composition undergoes oxidation and dissolves in solution and thus the anode self-oxidizes.

EP 1369384 describes the use of conductive plate diamonds as electrodes, but such document refers to the use of oxyacids or oxyacid salts, which should be used in the solution to be treated to improve treatment efficiency. Although the present invention has in common with EP 1369384 the fact that it makes use of conductive diamond electrodes, it does not consider the effects of oxyacids or oxyacid salts in the solutions to be treated. Furthermore, the focus of this invention is on mounting the electrochemical system and not on chemical additives to be added in the process.

 BRPI0502245-2 describes a process for preparing an electrochemical cell using diamond electrodes grown on silicon plates. The opposite side of the diamond film is glued to a metal plate, such as stainless steel. Although the present invention has in common with BRPI0502245-2 the use of doped diamonds deposited on substrates, it differs in that it avoids the inconvenience of performing a prior step to increase substrate strength and produce efficient electrical contact. In the present invention the substrate is mechanically strong enough to be easily manipulated. In addition, the substrate where the diamond is deposited is protected by a stainless steel cylinder, which ensures greater protection against unwanted breakage. The main problems of the electrochemical cell proposed in document BRPI0502245-2 present the same drawbacks already reported for parallel plates, mainly regarding leakage and difficulty in making electrical contacts.

Document BRPI0600897-6 describes a manufacturing process of electrochemically doped diamond electrodes comprising two main steps: i) diamond deposition and ii) the actual construction of the electrodes. In relation to the process of deposition of boron-doped diamond and carbon, it decreases or eliminates the formation of unaddressed carbons on the electrode surface. The electrodes obtained by this process can be used in electrochemistry, electroanalysis and electrosynthesis with the advantage of being resistant to surface passivation by organic compounds. The electrodes now treated have electrical contacts with wires embedded or welded in the doped diamond, and with insulated metal parts, which improves the practicality and ohmic contact of these electrodes in electroanalysis or electrosynthesis as working electrode. Although the present invention has in common with document BRPI0600897-6 the fact that boron-doped diamond films are deposited using HFCVD reactor, it differs in that in area BRPI0600897-6 the area and size of the substrate are reduced ( wires with a diameter of approximately 238 pm and a length of approximately 30 mm). This is because the application proposed in this document is to obtain electrodes with small areas (approximately 0.030 cm ^"2 ) in order to be polarizable in electrochemical analysis and studies. In addition, there is no claim of electrochemical cell but of electrode production. In the present invention, the dimensions (diameter from 4.0 mm and length from 30.0 mm) and electrode area are larger (from 4.0 cm ² ) as it is desired to avoid polarization during The cylindrical configuration of the entire cell including the stainless steel cathode and the production of a doped diamond film on mechanically resistant cylindrical substrates is further claimed, and the cell proposed here has another purpose, ie , electrochemical degradation of persistent chemical compounds.

Considering the above descriptions, it may be appreciated that a more suitable electrochemical cell configuration is required, especially for the purification of aqueous waste or potable water containing persistent chemical compounds. In this sense, the present invention is interesting since the electrochemical cell proposed for the purification of aqueous solutions simultaneously meets the advantages offered by i) electrochemical cells designed in cylindrical shape; ii) by electrochemical cells using doped diamond anode; and iii) the fact that the diamond anode used is obtained by a chemical deposition process from the vapor phase, where said diamond films are deposited on mechanically resistant cylindrical substrates of larger diameters (from 4.0 mm), previously blasted with iron or steel grit as detailed below. Electrochemical cells designed in cylindrical shape have the following advantages: space minimization; ease in making electrical contacts; easy assembly of large-scale cells - serial or parallel connection - and prevents leaks during cell use. The use of doped diamond anode in the assembly of electrochemical cells, regardless of their shape, has the following advantages: mechanical strength; chemical inertia; operating potential in harsh environments; broad overpotential for oxygen evolution; efficiency to withstand anodic oxygen transfer reactions; high thermal conductivity; High dimensional stability and constant sensitivity.

 However, when doped diamond anodes to be used in the assembly of electrochemical cells are obtained by chemical deposition process from the vapor phase, where said diamond films are deposited on mechanically resistant cylindrical substrates of larger diameters (in this case, the 4.0mm), previously blasted with iron or steel grit, the following advantages are offered: long service life of the electrochemical cell due to the mechanical rigidity of the parts involved, durability due to the chemical inertness of the diamond compared to other materials , reproducibility of results due to maintenance of diamond film integrity. In order to obtain good degradation results of organic compounds through diamond films it is necessary that they are homogeneous, uniform and well adherent to their respective substrates, so that there is no peeling of the film, thus exposing the substrate to the solution to be degraded. If metal substrates were used, the entire solution would be contaminated with iron ions. In this invention, grit blasting increases the contact surface between the substrate and the film to coat it as well as considerably increases the surface roughness of the substrate.

Additionally, since diamond films are grown on mechanically resistant cylindrical substrates protected by a metallic cylindrical shell, it is possible to avoid breakage problems and cracking during handling and / or assembly of cells. As a resistant substrate, we chose to use quartz due to the ease of adhesion of the diamond on it. In addition, quartz can be easily manipulated to flat and cylindrical shapes.

 Diamond adhesion processes in quartz plates, for example, have already been reported in the literature. The technique used in the work of STOTTER et al (Stotter, J .; Show, Y .; Wang, S .; Swain, G .; Comparison of the Electrical, Optical, and Electrochemical Properties of Diamond and Indium Tin Oxide Thin-Film Electrodes Chem. Mater., 2005, 17, 4880-4888) describes the realization of one type of polishing using diamond dust and sandpaper. The work of Joseph et al (Joseph, A.; Tanger, C.; Wei, J.; Tzeng, Y. Diamond-Coated Quartz and Sapphire Optical Windows. Diamond Films and Technology, 1995, No 2, Vol. 5, No 2.) portrays a common example of publications in the literature that involve diamond coating on quartz, as they do not disclose the technique used to obtain these diamond films. Likewise, they do not mention any adhesion tests that have been done to prove that the diamond films were actually adherent. However, no documents were found in the literature reporting the deposition of diamond films on quartz tubes, except for thin wires.

US 5,387,447 describes a diamond coating process on thin strands (diameters ranging from 0.025 to 2.5 mm) of general materials that support the conditions under which the diamond is deposited. The present invention differs from this document in that it proposes a process of depositing uniform, homogeneous and adherent diamond films on cylindrical substrates of larger diameters (from 4.0 mm). Moreover, by reproducing the diamond deposition process as proposed in US 5,387,447, the obtained films were uniform and of good quality, but they were peeled, which makes them unfeasible for the application contemplated in the present invention, once that the turbulent flow needed to perform the renovation of the solution on the anode surface would remove all diamond film from the substrate. Additionally, as both works refer to substrates of different dimensions, their applications become distinct. For example, for electroanalysis applications (determination of pesticides, drugs, neurotransmitters, metals, nitrogenous compounds, among other classes of organic and inorganic compounds), small area electrodes of less than 3 mm ^{2 are required} . For electrodegradation applications such as the present invention, it is necessary to use diamond electrodes having a larger area, ie larger than 1 cm ^2, and for large scale applications areas of 100 to 1000 cm ² would be ideals.

 WO 2004009498-A1, U.S. 20060124453-A1 and U.S. 7422668-B2 describe a cylindrical electrochemical cell that resembles the shape of the object cell of the present invention, however, some differences may be observed. The main difference is in the composition of the materials used. The documents describe the use of ruthenium-coated titanium and iridium oxide and the use of a ceramic material composed of aluminum, zirconium and yttrium oxide. However, the documents do not mention the use of doped diamond. Furthermore, sealing technical details of the invention of the cited documents are different from the present invention.

The use of doped diamond films for electrochemical degradation of persistent compounds in aqueous solutions is well described in the literature, as well as the use of titanium electrodes. However, the working potential window of electrodes mounted with doped diamond anodes is much larger than those of titanium. In addition, diamond is an inert material, robust in aggressive solutions and has high passivation resistance, unlike titanium electrodes. Titanium electrodes are not as efficient as diamond electrodes in the total mineralization of persistent organic compounds in aqueous solutions due to anode deactivation (S. Yoshihara and M. Murugananthan, Decomposition of various endocrine-disrupting chemicals at boron-doped diamond electrode. Electrochimic Acts Vol. 54, pp. 2031-2038, 2009). Diamond film coatings are generally performed at temperatures no lower than 500 ° C. Since the coefficient of thermal expansion of the diamond is quite low, when shutting down the CVD reactor, which produces the diamond film, there is a temperature variation large enough to cause cracking in the film. Although the diamond is generally mechanically stronger, it is significantly smaller in thickness than the substrate tube. In the work of RK Singh, DR Gilbert, J Fitz-Gerald, S Harkness, Engineered Interfaces for Adherent Diamond Coatings on Large Thermal-Expansion Coefficient Mismatched Substrates. Science Vol. 272, No. 5260, Page 396-398, 1996, discusses the difficulty of obtaining integrally adherent diamond film on some materials due to differences in the coefficient of thermal expansion. Diamond has one of the lowest coefficients of thermal expansion that exists in nature, which provides, even with large temperature variations, very little contraction or expansion of the material.

 In this sense, the present invention differs from the state of the art by proposing to obtain a diamond film and doped diamond materials which have adequate adhesion to mechanically resistant cylindrical substrates (which support the substrate pretreatment conditions, in this case blasting with iron or steel grit; and the conditions of the chemical vapor deposition process) such as quartz, titanium, tungsten and stainless steel.

 Still on the difficulties of depositing adherent diamond films on cylindrical substrates, especially with larger diameters (in this case, from 4.0 mm), no document describing growth, or at least mentioning the difficulties of depositing diamonds, was found. grow films into tubes of similar dimensions to those of the present invention.

Sticking diamond films over large areas is not a trivial task, and the difficulty becomes even greater if the surface is curved. The difference in coefficients of thermal expansion between substrates and movies is the main critical point. As diamond is one of the least swelling materials of all known materials, generally this type of film swells less than the substrates on which it is deposited. Therefore, in the case of substrates with relatively large area (between 10 and 50 cm ² ) or curved, during the process of finishing the chemical deposition the diamond film ends up cracking or peeling. In the case of coating of relatively large diameter cylindrical substrates, the diamond film may crack.

In this respect, the use of quartz as a substrate is an interesting alternative because it supports the deposition conditions of diamond films very well, and still has a coefficient of thermal expansion similar to that of diamond. Thus, the present invention was only possible when diamond films could be efficiently, evenly and evenly adhered to the surfaces of quartz tubes, which had to go through a blasting step (substrate pre-grinding). The purpose of the blasting was to increase the roughness and surface area that would receive the CVD film, thus allowing to obtain well adherent films, even in relatively large dimensions (between 10 and 50 cm ² ). ; BRIEF DESCRIPTION OF THE INVENTION

In a first aspect, the present invention provides a cylindrical electrochemical cell capable of efficiently electrolyzing undesirable substances contained in aqueous waste or drinking water, rendering such compounds harmless and / or significantly lowering the concentration of toxic compounds. The proposed electrochemical cell, which uses a coaxial doped diamond anode obtained by chemical vapor deposition process, where said diamond films are deposited uniformly, homogeneously and adherently on mechanically resistant cylindrical substrates of larger diameters (from previously blasted, provides favorable conditions and ease of handling for industrial applications involving electrochemical treatments related to the decomposition of substances in contaminated waters. The cylindrical shape Cell (closed) allows space minimization, facilitates electrical contacts, facilitates large-scale cell assembly (serial or parallel connection), and prevents leakage during cell assembly. Additionally, the use of the proposed cell in the purification of aqueous solutions presents substantial improvements compared to the prior art similar geometries.

Specifically, the proposed cylindrical electrochemical cell offers the advantage for treatment of low conductivity aqueous solutions, ie, with conductivities between 0.005 S / m and 0.010 S / m and for the treatment of aqueous solutions containing low concentrations of contaminants, ie compounds in concentration at pg range L ^"1. in addition to these advantages, the anode used in the assembly of said cell can work in extremely acidic or basic solutions ie between pH 1 to 14, which is a characteristic of the diamond anode and stainless steel cathode AISI 304, which are resistant to these conditions.

 The proposed electrochemical cell allows an external electrical contact to the region where the solution treatment occurs and thus the electrical contact remains protected and immune to any aggressive liquid.

 The proposed electrochemical cell allows the coupling of electrode series connections. The cylindrical shape has the advantage that it can be arranged in a small cell array and thus gain time in treating large volumes of aqueous solution in an optimized physical space.

 The configuration of the proposed electrochemical cell allows for ease of handling, ease of assembly and disassembly due to threaded connections and an extremely efficient seal that prevents the leakage of liquids and gases without the use of resins or adhesives.

In a second aspect, the present invention provides a process of depositing uniform, homogeneous and adherent diamond films on larger diameter tough cylindrical substrates (at from 4.0 mm), preferably between 4 and 20 mm, previously blasted with iron or steel grit, performed by the CVD (Chemical Vapor Deposition) technique to obtain coaxial doped diamond anodes. The process treated here consists basically of two steps. The first stage comprises the preparation of the mechanically resistant cylindrical substrate, and the second stage comprises the deposition of doped diamond films on said substrates.

 Specifically in relation to the step comprising the preparation of the resistant cylindrical substrates, it was necessary to perform a surface treatment of quartz tubes. Quartz has a number of advantages when used to receive CVD diamonds, as it can withstand the deposition conditions of diamond films and has a coefficient of thermal expansion similar to that of diamonds. However, under certain experimental conditions, diamond quartz films may crack or peel. However, the increase of quartz surface roughness is a possible solution to this problem. For the present invention, a sandpaper polish was first performed to increase substrate roughness, but did not give satisfactory results. In this sense, it was decided to blast iron and steel shot, which significantly increased the roughness and surface area of the quartz surface. The results of diamond deposition on the blasted quartz substrate were satisfactory.

Regarding the stage that comprises the deposition of doped diamond films on said previously blasted substrates, the growth parameters used for the growth of boron-doped diamond films is well described in the literature (Teófilo et al. Improvement of the electrochemical properties of "as-grown" boron-doped polycrystalline diamond electrodes deposited on tungsten wires using ethanol (J. Solid State Electrochem., 11, pp. 1449-1457, 2007); except for pre-treatment with shot. The deposition was performed in a reactor developed for the growth of carbonic structures (including diamond) on tubes. Conventional HFCVD reactors are generally designed for the growth of diamond films on flat structures. The differential of this reactor is the viability of growing diamond structures in cylindrical or conical geometry, ie, on tubular or conical substrates, due to: (i) implantation of a magnetic coupling system between the substrate and a small electric motor, and (ii) implementation of a thermomechanical filament expansion balance system developed to provide this capability to conventional reactors.

 In a third aspect, the present invention provides the coaxial doped diamond anodes obtained by the chemical deposition process from the thermally decomposed hot phase vapor (CVD) phase of organic compounds from mechanically resistant cylindrical substrates of larger diameter. (from 4.0 mm), preferably between 4 and 20 mm, previously blasted with iron or steel shot. The anodes thus produced have excellent durability. However, to achieve adequate degradation with generation of strong oxidizers such as the hydroxyl radical (OH) on the doped diamond surface, the aqueous tailings should preferably be at pH 2 to 7.

Whereas the cylindrical electrochemical cell conceived in the present invention proposes to provide an electrochemical treatment for oxidizing substances contained in aqueous solution, which can be accomplished by introducing the solution containing substances to be treated into the electrochemical cell with a cylindrical anode and cathode and passing An electric current through them is therefore an additional object of the present invention the use of said cylindrical electrochemical cell in the purification of aqueous solutions, which utilizes coaxial diamond anode obtained by depositing uniform, homogeneous and adherent diamond films on mechanically resistant cylindrical substrates of larger diameters (from 4.0 mm), preferably between 4 and 20 mm, previously blasted with iron or steel grit, performed by the CVD technique.

The compounds to be degraded by the present invention should preferably be in an aqueous solution having some electrical conductivity, preferably between 0.005 S / m and 0.010 S / m with a pH preferably between 2 and 7. The electrolytes providing the conductance may be any inorganic salt. high solubility in water (> 15% w / v), preferably Na ₂ SO ₄ .

 These and other objects of the present invention will be better understood and appreciated from the detailed description of the invention and the appended claims.

 BRIEF DESCRIPTION OF THE FIGURES

 The following description is not intended to limit the scope of the present invention but to exemplify some possible embodiments thereof.

 Figure 1. Diagrammatic view illustrating an example of an electrolysis cell for use in the method of the invention for decomposing organic compounds contained in an aqueous solution. In this figure, the solution to be treated placed in the compartment (1) is transferred by the pump (2) to the cell (3) where the electrolysis occurs following a defined flow (F). The cell is connected to a current source (5) by conductor cables (4) external to the reaction region. The solution recirculates following the defined flow (F), until complete cleaning and is directed to the disposal (6).

 Figure 2. Diagrammatic view illustrating an example of a set of electrolysis cells connected in parallel. In this figure, the solution to be treated passes through a plurality of cells (3) connected in series by conductor cables (4) to a current source (5) and arranged in a compartment (7). Item 8 represents an immediate disposal, without recirculation: the solution goes through the arrangement only once.

Figure 3. Cross-sectional schematic view showing a detailed example of the electrochemical cell (3) with the flow (FE) through the interior of an inner cylindrical electrode (9). In this figure, the cell is composed of a hollow cylindrical anode, composed of a semiconductor material, in which the doped diamond (10) is deposited on its surface. This anode is placed internally and in the center of a hollow cylinder (11) of conductive material, the cathode. An internal screw cap (12), of inert and non-conductive material, with a conical central opening of a diameter slightly larger than the anode diameter; and an internal screw cap (13) for flow outlet, composes one of the cell sealing items. A high density tapered rubber (14) with a central opening of anode diameter and laterally opening is used to make the seal. Another internal screw cap (15) and a high density inner rubber (16), both with a central opening, are responsible for the complete sealing of the system by pressing the conical rubber (14) over the diamond tube that passes through it. the central openings described. On the opposite side of the cell, an internal screw cap (17) of inert, nonconductive material is used for sealing on this side. This cap is composed of a hollow, hollow, centered inner tapered pin (18) for supporting the anode and escaping the solution to be treated into the cell. The solution to be treated enters the cylinder (19) that makes up the anode and leaks through holes (18) into the reaction region (20), where the compounds present in the solution to be treated are oxidized between the anode and the cathode. The anode is connected by a positive pole (21) and the cathode by a negative pole (22). Liquid flow follows the indicative arrows (F).

Figure 4. Cross-sectional schematic view showing a detailed example of the electrochemical cell with the flow entering through the interior of the inner cylindrical electrode and the presence of a helical turbulence promoter. In this figure, a helical turbulence promoting device (23) of non-conductive inert material is placed between the anode and the cathode to assist in the contact time of the solution in the reaction medium (20). Figure 5. Cross-sectional schematic view showing a detailed example of the electrochemical cell to be used in which the substrate (9) where the diamond is grown may or may not be hollow, with flow (FE) entering laterally into the cell. In this scheme, the cylindrical substrate is pierced axially by the stainless steel tube (11) and on both open sides of the stainless steel tube, the sealing systems are identical. In this figure, the solution flow inlet and outlet occur at (24) and (25), respectively. The arrows (FE, FS) indicate the direction of flow.

 Figure 6. Cross-sectional schematic view showing a detailed example of the electrochemical cell with the flow entering laterally to the cell and the presence of a helical turbulence-promoting cylindrical device. In this figure, the helical turbulence promoting device of non-conductive and inert material (23) is placed between the anode and cathode to assist in the contact time of the solution in the reaction medium (20).

 Figure 7. Cross-sectional schematic view showing a detailed example of the electrochemical cell with the flow entering laterally to the cell and the presence of an ion exchange membrane intimately bonded to the electrode walls. The membrane is closely adhered to the diamond surface (26) and also to the inner surface of the cathode (27).

 Figure 8. Removal of TOC and fluorescence intensity of aqueous waste from domestic sewage in the presence of electrolyte.

 Figure 9. Removal of TOC and fluorescence intensity of drinking water provided by sanitation company in the absence of electrolyte.

Figure 10. Cross-sectional schematic view showing a detailed example of the electrochemical cell sealing system emphasizing the upper cover assembly and the lower cover. The upper cover assembly comprises an internal screw cap (12) made of inert and non-conductive material with a tapered central opening (28) in diameter slightly larger than the anode; a high density conical rubber (14) with a central aperture of a diameter equal to said anode; and an inner screw cap (15) containing a high density inner rubber (16), both with a central opening. The lower cap (17) comprises an internal screw cap, made of inert and non-conductive material, containing a hollow, hollow centralized inner tapered pin (18) when said anode is hollow; or containing a recess for centering said anode when it is not hollow.

 Figure 11. Cross-sectional schematic view showing a detailed example of the helical turbulence-promoting cylindrical device (23). Such a device comprises a hollow cylinder of inert and non-conductive material configured to provide the formation of a turbulent flow in a helical path within said cylinder.

 DETAILED DESCRIPTION OF THE INVENTION

 The examples shown below only illustrate one of many embodiments of the invention. Therefore they should not be viewed restrictively, but illustratively.

 For the purposes of this invention, a "cylindrical electrochemical cell" means an electrochemical cell composed of a conductive diamond electrode connected to the positive terminus of a direct current source and defined as anode, as well as a metal electrode connected to the negative terminus of a direct current source and defined as a cathode.

 For the purpose of this invention, "undivided cylindrical electrochemical cell" is understood to mean a cell where the anode and cathode are not separated by plates or membranes but only by an aqueous solution.

For the purposes of this invention, "mechanically resistant cylindrical substrate" means quartz substrates, or those selected from metal conductors in general, such as stainless steel, and having a cylindrical or tubular cylindrical shape. For the purpose of this invention, "blasting" means mechanically resistant cylindrical substrates subjected to a homogeneous blasting process with iron or steel grit. This process is performed to increase the contact surface between the deposited diamond film and the resistant cylindrical substrate and thereby increase the friction between the parts.

 For the purpose of this invention, "coaxial doped diamond anode" means an anode obtained by a chemical vapor deposition process, wherein said diamond films are uniformly, homogeneously and adherently deposited on mechanically resistant cylindrical substrates of diameter upper (from 4.0 mm), preferably between 4 and 20 mm, previously blasted, and said obtained anode is inserted into another hollow cylindrical: the cathode. In this case, both have a common axis.

 For the purpose of this invention, "chemical vapor deposition process" is a technique based on the transformation of gaseous molecules into solid materials in the form of thin films on a given substrate. All CVD deposition systems share basically the same principle of operation. They require continuous flow feeding of carbon-containing molecules in their structure. These molecules are usually in the gaseous state and usually flow with molecular hydrogen. An energy activation source is used by the system for two purposes: dissociating the precursor molecules into radicals so that they react on the substrate surface; and dissociate hydrogen molecules into atoms.

For the purposes of this invention, "persistent inorganic and organic compounds" are understood to be highly stable chemical compounds due to the strength of their covalent bonds and structural configuration. They are poorly reactive compounds and do not donate electrons easily and are therefore complicated to oxidize to less toxic or inert products. For the purposes of this invention, "treatment and purification of aqueous solutions or treatment of aqueous waste" means the degradation of undesirable organic and inorganic compounds present in said solutions or waste.

 In a first aspect, the present invention provides a cylindrical electrochemical cell for treatment and purification of aqueous solutions or treatment of aqueous waste using coaxial doped diamond anode obtained by chemical deposition process from the vapor phase, where the Said diamond films are uniformly, homogeneously and adherently deposited on mechanically resistant cylindrical substrates of larger diameters (from 4.0 mm), preferably between 4 and 20 mm, previously blasted with iron or steel grit.

 It is therefore an object of the present invention a cylindrical electrochemical cell assembled with cylindrical electrodes, wherein said cell comprises:

 The. a hollow cylindrical cathode (11);

 B. a cylindrical anode (9) arranged coaxially within said cathode, consisting of a mechanically resistant cylindrical substrate, previously blasted, uniformly coated, homogeneously and adhered by an electrically semiconductor doped diamond material (10);

 ç. means for sealing the cell;

 d. at least one connection for solution entry into the cell (19; 24); and. at least one solution outlet connection from the cell (3; 25); f. optionally a helical turbulence promoting device

(23);

 g. optionally an ion exchange resin or membrane; and

 H. optionally means for connecting a plurality of cells to one another (4).

Where: - the cathode comprises a metallic material, whether or not coated with a doped diamond material.

 The metal material constituting the cathode should be selected from a stainless material, preferably from the group comprising stainless steel.

 - the doped diamond material optionally lining the cathode metal material comprises a diamond material subjected to electrical conduction by doping with preferably boron.

- the doped diamond material optionally lining the metal material constituting the cathode may be a p-type, n-type or co-doped semiconductor (donor, electron receptor or both, respectively).

 - the cathode must be less than said anode in length.

- the cathode must have a diameter larger than said anode.

 - the cathode must be stable at negative potential.

 - the anode may be hollow or not.

 - the mechanically resistant cylindrical substrate constituting the anode comprises an outside diameter from 4 mm, preferably from 4 to 20 mm.

 - the mechanically resistant cylindrical substrate constituting the anode is selected from the group comprising a conductive or insulating material capable of withstanding the conditions of the blasting processes; able to withstand the conditions of chemical deposition processes from the vapor phase; and which may be made of cylindrical or spherical or cylindrical tubular shape.

- the mechanically resistant cylindrical substrate constituting the anode may be quartz, titanium, tungsten or stainless steel. - doped diamond material lining the anode comprises diamond material subjected to electrical conduction by doping with some selected impurity from the chemical elements boron, phosphorus, bismuth, nitrogen or sulfur.

 - the doped diamond material lining the anode may be a p-type, n-type or co-doped semiconductor (donor, electron receptor or both, respectively).

 - the blasting process is carried out with iron or steel shot.

 - the doped diamond material lining the anode comprises a film of thickness preferably ranging from 0.5 to 50 μιτι.

 The cylindrical electrochemical cell can be mounted with a doped diamond cylindrical anode obtained by chemical vapor deposition process, wherein said diamond films are uniformly, homogeneously and adherently deposited on a mechanically resistant quartz cylindrical substrate of 6 mm outside diameter, arranged coaxially inside a 9 mm inside diameter stainless steel cathode. The seals are made with rubber threaded snap rings. In the cathode body there are two connections for inlet and outlet of the solution to be treated. Hoses connect these connections in series with a mechanical pump (to establish solution flow through the system) and a storage container (for solution collection or exchange). Electrical contacts are made on the anode body. Conductive glue is used to establish contact between the conductive wires and the diamond film when the substrate used is insulating. Power is supplied by a direct current stabilized voltage source.

Additionally, in the space of separation between anode and cathode some mesh, plastic screen or some other porous insulator, both inert, can be placed to promote turbulence. This arrangement minimizes the anode-cathode distance, thereby reducing cell voltage. Besides that, In this way it is possible to treat low conductivity solutions (0.005 S m ^"1 ), ie drinking water.

 Additionally, the cylindrical electrochemical cell may be divided by one or more ion exchange membranes or resin. The configuration comprising the ion exchange membrane (s) or resin may be used in situations where the solution to be treated has low electrical conductivity. If used, the ion exchange membrane may be fluororesin or hydrocarbon based. In practice, however, a corrosion resistant resin is desired. Commercially available membranes for use in the present invention are: Nafion (DuPont), Aciplex (Asahi Chemical Industry Co., Ltd.), Flemion (Asahi Glass Co., Ltd.), etc.

The membrane or resin is preferably used in close contact with the anode and / or cathode. For this purpose, the membrane must be mechanically bonded to each electrode. Preferably, the ion exchange membrane, if used, should be pressed from 0.1 to 30 kg cm- ² during electrolysis.

Specifically with respect to the solution containing one substance or many substances to be treated, it is used as an electrolyte solution. The solution is placed in contact with the anode made of doped diamond and the cathode made of a conductive material, whether or not doped diamond. Substances may be directly or indirectly oxidized to low molecular weight substances or mineralized to CO ₂ .

Electrolysis conditions vary depending on the solution to be used, etc., but the temperature is preferably from 5 to 40 ° C and the current density is preferably from 1 to 100 mA cm ² .

The materials that can be used in the construction of the electrochemical cell are glass, titanium, stainless steel, PTFE (Teflon ^® ) resin, quartz, tungsten and high density rubber. The goal is to use materials with excellent corrosion resistance, durable and stable when in the presence of strong oxidizers that are produced during the process. In a second aspect, the present invention provides for a process of depositing uniform, homogeneous and adherent diamond films on larger diameter tough cylindrical substrates (from 4.0 mm), preferably between 4 and 20 mm, previously shot blasted with grit. iron or steel, made by the CVD (Chemical Vapor Deposition) technique to obtain coaxial doped diamond anodes.

 It is therefore a further object of the present invention a diamond film deposition process to obtain diamond anodes comprising the steps of:

 (i) Preparation of the resistant cylindrical substrate for further deposition of the diamond film, wherein said preparation comprises the steps of:

 (a) homogeneously blast resistant cylindrical substrates with iron or steel grit to increase the contact surface between the deposited diamond and the substrate and thereby increase friction between the parts;

 b) clean the resistant cylindrical substrates blasted with ultrasonic bath in alcoholic solution for 30 minutes;

 c) perform the "sowing" process, which includes the insertion of small diamond grains in the substrate to enable the growth of diamond structures. This process can be performed via ultrasonic bathing on tough (clean and sandblasted) cylindrical substrates in hexane solution with diamond dust;

 (ii) deposition of the diamond film on the substrate, where said deposition process involves the steps of:

a) After the "seeding" process, the substrates are inserted into the hot-filament chemical vapor deposition (HFCVD) assisted chemical deposition reactor chamber. Diamond films can be grown from a carbon source in the presence of hydrogen. using the CVD technique. The carbon sources may be organic gases such as methane (CH ₄ ), the most commonly used, or liquid gases such as ethanol (C ₂ H ₅ OH), which was used in the present invention.

 (b) A solution of up to 5% organic molecules (eg ethanol) in hydrogen is inserted into the chamber of a reactor at subatmospheric pressure (between 20 and 200 Torr). c) The molecules are transported into the HFCVD reactor chamber where they interact with an active region which in the present case is held by the hot filament (energized to ~ 2400 ° C), but could be any other, eg microwave, arc discharge, plasma activated. The high temperature of the filaments enables the fragmentation of these molecules into radicals and atoms that may impact on the substrate surface. On the surface, mechanisms of adsorption, diffusion, chemical recombination and desorption occur. Radicals such as methyl can collide with pre-existing diamond cores and react by favoring the growth of diamond cores. About 20 hours later, the diamond film completely coated the entire substrate that was inserted with polycrystalline diamond of similar quality to natural, yet semiconductor diamonds.

 Where:

 - Diamond synthesis can be performed by the process of chemical deposition from the hot filament vapor phase (HFCVD) with thermal decomposition of organic compounds such as ethanol, methanol, methane, etc. as carbon source in a reducing atmosphere such as as hydrogen gas.

The doped diamond on the substrate constitutes the active part of the electrode, which thus produced has high potential to be used. j as anode or cathode is excellent durability. However, due to the acidity of the solution, said electrode should preferably be used as anode.

 On some substrates, pretreatment was performed using motor oil. Scanning electron microscope analyzes were performed and it was verified that the film did not present cracks, besides presenting excellent quality and homogeneity.

 In a third aspect, the present invention provides the coaxial doped diamond anodes obtained by the chemical deposition process from the hot filament vapor phase (HFCVD) with thermal decomposition of organic compounds from larger diameter resistant cylindrical substrates, preferably between 4 and 20 mm, previously blasted with iron or steel shot. The anodes thus produced have excellent durability. In addition to being obtained in a versatile format that can be placed inside pipes and with the potential for space saving series coupling.

 It is therefore a further object of the present invention a diamond cylindrical anode, wherein said anode comprises a mechanically resistant, hollow or unblasted, uniformly coated, homogeneous and adherent cylindrical substrate adhered by at least one layer of diamond thin film. doped, where:

 - the mechanically resistant cylindrical substrate constituting the anode comprises an outside diameter from 4 mm, preferably from 4 to 20 mm.

- the mechanically resistant cylindrical substrate constituting the anode is selected from the group comprising a conductive or insulating material capable of withstanding the conditions of the blasting processes; able to withstand the conditions of chemical deposition processes from the vapor phase; and which may be made of cylindrical or spherical or cylindrical tubular shape. - the mechanically resistant cylindrical substrate constituting the anode may be quartz, titanium, tungsten or stainless steel.

 - doped diamond material lining the anode comprises diamond material subjected to electrical conduction by doping with some selected impurity from the chemical elements boron, phosphorus, bismuth, nitrogen or sulfur.

 - the doped diamond material lining the anode may be a p-type, n-type or co-doped semiconductor (donor, electron receptor or both, respectively).

 - the blasting process is carried out with iron or steel shot.

 the doped diamond material lining the anode comprises a film of thickness preferably ranging from 0.5 to 50 pm.

 - the doped diamond material lining the anode is preferably deposited by the chemical deposition process from the vapor phase.

Whereas the cylindrical electrochemical cell conceived in the present invention proposes to provide an electrochemical treatment for oxidizing substances contained in aqueous solution, which can be accomplished by introducing the solution containing substances to be treated into the electrochemical cell with a cylindrical anode and cathode and passing An electric current through them is therefore an additional object of the present invention the use of said cylindrical electrochemical cell in the purification of aqueous solutions, which utilizes coaxial diamond anode obtained by depositing uniform, homogeneous and adherent diamond films on Cylindrical substrates of larger diameters, preferably between 4 and 20 mm, previously blasted with iron or steel grit, performed by the CVD technique. It is therefore an object of the present invention a cylindrical electrochemical cell assembled with cylindrical electrodes, wherein said cell comprises:

 Some examples of cell application proposed herein are described below, but should not be considered as restrictive but rather illustrative embodiments.

 EXAMPLE 1

Using an undivided electrochemical cell with the boron-doped diamond coated anode and the stainless steel cathode (AISI 304), an aqueous waste from domestic sewage, with electrolyte (Na ₂ SO ₄ ) added at pH 2 and compounds phenol, catechol, hydroquinone, p-cresol, m-cresol and guaiacol were oxidized. Concentrations of the compounds in the solution were 94 pg ml ^-1 for phenol, 10 pg ml ^-1 for hydroquinone, guaiacol and catechol and 53 pg ml ^-1 for p-cresol and m-cresol. Therefore, a total concentration of 530 pmol mL ^"1 . Measurement of total organic carbon (TOC) and molecular fluorescence intensity was performed during degradation. FIG. 8 shows the removal of both. With a current of 35 mA and an average voltage of 6 V the energy cost was 7.56 kW hm ^"3 for the removal of 64.40% of TOC and 94.95% of molecular fluorescence intensity, the latter being measures total aromaticity removal.

 EXAMPLE 2

Using an undivided electrochemical cell with the boron-doped diamond coated anode and the stainless steel cathode (AISI 304), a potable water solution distributed by the Campinas / SP sanitation company, without the addition of electrolyte at an initial pH of 7 The phenol, catechol, hydroquinone, p-cresol, m-cresol and guaiacol compounds were oxidized. Concentrations of the compounds in the solution were 94 pg mL ^"1 for phenol, 110 pg mL ^{" 1} for hydroquinone, guaiacol and catechol and 53 pg mL ^"1 for p-cresol and m-cresol. Therefore, a total concentration of 530 pmol mL ^"1 . Measurement of total organic carbon (TOC) and molecular fluorescence intensity was performed during degradation. FIG. 9 shows the removal of COT and fluorescence intensity. With a current of 35 mA and an average voltage of 31 V the energy cost was 54.50 kW hm ^"3 for the removal of 60.51% of TOC and 74.50% of total aromaticity. If only the first 0.6 A h L ^"1 past load, the energy cost decreases to 21, 09 kW hm ^{" 3} with 73.40% total aromaticity removed.

Claims

 1. A CYLINDRICAL ELECTROCHEMICAL CELL, characterized by comprising:

 The. a hollow cylindrical cathode (11);

 B. a cylindrical anode (9) arranged coaxially within said cathode, consisting of a mechanically resistant cylindrical substrate, previously blasted, uniformly coated, homogeneously and adhered by an electrically semiconductor doped diamond material (10);

 ç. means for sealing the cell;

 d. at least one connection for solution entry into the cell (19; 24); and. at least one solution output connection of the cell (13; 25); f. optionally a helical turbulence promoting device (23);

 g. optionally an ion exchange resin or membrane; and

 H. optionally means for connecting a plurality of cells to one another.

 Cell according to Claim 1, characterized in that the hollow cylindrical cathode comprises a metallic material, whether or not coated with a doped diamond material.

 Cell according to claim 2, characterized in that the metal material constituting the cathode is a stainless material.

 Cell according to claim 3, characterized in that the stainless material is selected from the group preferably comprising stainless steel.

 Cell according to any one of claims 2 to 4, characterized in that the doped diamond material optionally coated with the metallic material comprises a diamond material subjected to electrical conduction by doping with preferably boron.

Cell according to any one of claims 2 to 5, characterized in that the doped diamond material optionally coated the material Metallic is a semiconductor selected from the group comprising p-type, n-co-doped type.

 Cell according to any one of claims 1 to 6, characterized in that the cathode is stable at negative potential, has a larger diameter and a shorter length than said anode.

 Cell according to claim 1, characterized in that the anode is hollow.

Cell according to claim 1, characterized in that the anode is solid.

 Cell according to claim 1, characterized in that the mechanically resistant cylindrical substrate constituting the anode comprises an outside diameter from 4 mm.

 Cell according to claim 10, characterized in that the outer diameter is preferably from 4 to 20 mm.

 Cell according to any one of claims 1, 10 and 1, characterized in that the mechanically resistant cylindrical substrate constituting the anode is selected from the group comprising a conductive or insulating material capable of withstanding the conditions of the blasting processes; able to withstand the conditions of chemical deposition processes from the vapor phase; and which may be made in cylindrical, spherical, or cylindrical tubular shapes.

 Cell according to claim 12, characterized in that the conductive or insulating material is chosen from the group comprising quartz, titanium, tungsten and stainless steel.

 Cell according to claim 13, characterized in that the conductive or insulating material is preferably quartz.

 Cell according to Claim 12, characterized in that the blasting process is carried out with shot blasting material capable of increasing the roughness and surface area of said cylindrical substrate.

Cell according to claim 15, characterized in that the shot is of iron.

Cell according to claim 15, characterized in that the shot is of steel.

 Cell according to claim 1, characterized in that the doped diamond material lining the anode comprises a diamond material subjected to electrical conduction by doping with some impurity selected from the chemical elements boron, phosphorus, bismuth, nitrogen and sulfur.

 Cell according to claims 1 and 18, characterized in that the anode-doped diamond material is a semiconductor selected from the group comprising type p, type n and co-doped.

 Cell according to any one of claims 1, 18 and 19, characterized in that the anode-doped diamond material comprises a film of thickness preferably ranging from 0.5 to 50 µm.

Cell according to claim 1, characterized in that the means for sealing the cell comprises an upper lid assembly and a lower lid.

 Cell according to claims 1 and 21, characterized in that the upper cover assembly comprises an internal screw cap (12), consisting of inert and non-conductive material, with a conical central opening (28) slightly larger than the anode. ; a high density conical rubber (14) having a central opening of a diameter equal to said anode; and an inner screw cap (15) containing a high density inner rubber (16), both with a central opening.

Cell according to claims 1 and 21, characterized in that the lower cap comprises an internal screw cap (17), consisting of inert and non-conductive material, containing a hollow, hollow centralized inner tapered pin (18) when said anode is hollow.

Cell according to Claims 1 and 21, characterized in that the lower cap comprises an internal screw cap (17) made of material. inert and non-conductive, containing a recess for centering said anode when it is massive.

 Cell according to claims 1 and 21, characterized in that the lower cap comprises an internal screw cap (12) made of inert and non-conductive material; a high density conical rubber (14) having a central opening of a diameter equal to said anode; and an inner screw cap (15) containing a high density inner rubber (16), both with a central opening.

Cell according to claims 1 and 8, characterized in that the solution inlet connection in the cell is located at the anode (19).

Cell according to claims 1 and 8, characterized in that the solution inlet connection in the cell is located in the cathode (24).

 Cell according to claims 1 and 9, characterized in that the solution inlet connection in the cell is located in the cathode (24).

 Cell according to claim 1, characterized in that the solution outlet connection of the cell is located at the cathode (25).

 Cell according to claims 1 and 21, characterized in that the solution outlet connection of the cell is located in the internal screw cap (13).

31 Cell according to claim 1, characterized in that the helical turbulence-promoting device (23) comprises a hollow cylinder of inert and non-conductive material configured to provide the formation of a turbulent flow in a helical path within said cylinder. .

Cell according to claim 1, characterized in that the ion exchange resin or membrane comprises a corrosion resistant material.

 Cell according to claims 1 and 32, characterized in that the ion exchange resin or membrane is mechanically adhered to the outer surface of the anode (26) and the inner surface of the cathode (27), so that said membrane is in contact. with the electrolyte.

Cell according to claim 1, characterized in that the means for connecting at least two cells together, in series or in parallel, comprises at least one connector hose.

Cell according to Claim 1, characterized in that the cell is made of a corrosion-resistant material, durable and stable in the presence of strong oxidizers.

Cell according to claim 35, characterized in that the resistant material is preferably chosen from the group comprising titanium, stainless steel, PTFE (Teflon ^® ) resin, quartz, tungsten and high density rubber.

 Cell according to claim 1, characterized in that the electrical contacts do not come into contact with the liquid to be treated.

Cell as defined in claims 1 to 37, characterized in that it is used for the direct or indirect oxidation of contaminants present in aqueous solution or low conductivity aqueous tailings, preferably between 0.005 S / m and 0.010 S / m, which contains low concentrations of contaminants. preferably in the range of pg L ^"1 .

Cell according to claim 38, characterized in that the aqueous solution or aqueous waste preferably has pH 2 to 7.

 A process for purifying aqueous solutions or aqueous waste, comprising at least one cylindrical electrochemical cell as defined in all the preceding claims. <

 Process according to Claim 40, characterized in that the aqueous solution or aqueous waste to be purified is located in a space between the anode and the cathode and does not come into contact with the locations where the electrical contacts occur.

Process according to any one of claims 40 to 41, characterized in that the aqueous solution or aqueous waste to be purified comprises low conductivity; low concentration of contaminants; and acidic to neutral pH.

Process according to Claim 42, characterized in that the conductivity preferably comprises 0.005 to 0.010 S / m.

Process according to Claim 42, characterized in that the concentration of contaminants preferably comprises a range of the order of g L ^"1 .

 Process according to Claim 42, characterized in that it preferably comprises pH 2 to 7.

Process according to any one of claims 40 to 45, characterized in that the current density at the anode surface comprises a preferred range of 1 to 100 mA cm ² .

 Process according to any one of claims 40 to 46, characterized in that the temperature of said process comprises a preferred range of 5 to 40 ° C.

 Process according to Claims 1 to 47, characterized in that it comprises at least one cylindrical electrochemical cell (3).

 A method according to any one of claims 1 to 48, characterized in that it comprises a plurality of cells connected in series or in parallel.

 50. Deposition process of DIAMANTIFERO MATERIAL FOR OBTAINED DIAMOND ANODE, wherein the improvement comprises a step of treating the mechanically resistant cylindrical substrate prior to said deposition process.

Process according to Claim 50, characterized in that the mechanically resistant cylindrical substrate comprises an outside diameter from 4 mm.

 Process according to Claim 51, characterized in that the outer diameter is preferably from 4 to 20 mm.

Process according to Claims 50 to 52, characterized in that the mechanically resistant cylindrical substrate is selected from the group comprising a conductive or insulating material capable of withstanding the conditions of the blasting processes; able to withstand the conditions of chemical deposition processes from the vapor phase; and which may be made of cylindrical or spherical or cylindrical tubular shape.

Process according to Claim 53, characterized in that the conductive or insulating material is chosen from the group comprising quartz, titanium, tungsten and stainless steel.

 Process according to any one of claims 50 to 54, characterized in that the substrate treatment step comprises the steps of: a) homogeneously blasting the mechanically resistant cylindrical substrates with iron or steel shot;

 b) clean mechanically resistant cylindrical substrates, previously blasted, with an ultrasonic bath in alcoholic solution for about 30 minutes; and

 c) Immerse the clean, sandblasted, mechanically resistant cylindrical substrates in a hexane solution containing diamond dust in an ultrasonic bath.

 56. Cylindrical anode comprising a mechanically resistant hollow or unblasted cylindrical substrate, pre-blasted, uniformly coated, homogeneous and adhered to by an electrically semiconductor doped diamond material (10).

 Anode according to claim 56, characterized in that the mechanically resistant cylindrical substrate comprises an outside diameter from 4 mm.

 Anode according to Claim 57, characterized in that the outer diameter is preferably from 4 to 20 mm.

 Anode according to any one of claims 56 to 58, characterized in that the mechanically resistant cylindrical substrate is selected from the group comprising a conductive or insulating material capable of withstanding the conditions of blasting processes capable of withstanding the conditions of chemical deposition processes. from the vapor phase; and which may be made of cylindrical or spherical or cylindrical tubular shape.

Anode according to claim 59, characterized in that the conductive or insulating material is chosen from the group comprising quartz, titanium, tungsten and stainless steel.

Anode according to claim 59, characterized in that the blasting process is carried out with shot blasting material capable of increasing the roughness and surface area of said cylindrical substrate.

 A cell according to claim 61, characterized in that the shot is of iron.

 Cell according to claim 61, characterized in that the shot is of steel.

 Anode according to claim 56, characterized in that the doped diamond material lining the anode comprises a diamond material subjected to electric conduction by doping with some impurity selected from the chemical elements boron, phosphorus, bismuth, nitrogen and sulfur.

 Anode according to claims 56 and 64, characterized in that the anode-doped diamond material is a semiconductor selected from the group comprising type p, type n and co-doped.

 Anode according to any one of claims 56 to 65, characterized in that the anode-doped diamond material comprises a film of thickness preferably ranging from 0.5 to 50 mm.

Anode according to claim 66, characterized in that the film is preferably deposited by the chemical deposition process from the vapor phase.