REFRIGERANT FLUIDS

Technical field

The present invention relates to reduction of Freon emission into the environment during the process of mechanical recycling of refrigerating devices. Freons, which are released during this process, are used as refrigerant fluids as well as for expanding of polyurethane thermal insulation foams contained in refrigerating devices. These compounds are halogenated hydrocarbons with at least one hydrogen atom is replaced by a halogen (Cl, F, Br, I), so they belong to a group of organohalogen compounds. Therefore, in the present invention, a common name Freons is used for organohalogen refrigerant fluids which include the following compounds: CFC 11 (CC1 ₃ F), CFC 12 (CCI2F2), CFC 22 (CHCIF2), CFC 113 (C2CI3F3) i CFC 134a (C2H2F4). Specifically, the present invention relates to a catalyst that has a key role in a technological process of catalytic decomposition (dehalogenation) of organohalogen refrigerant fluids.

Technical problem

During mechanical recycling of refrigerating devices, a mixture of organohalogen refrigerant fluids is obtained, where the most dominant in the mixture is CFC 22 (more than 80 % of the mixture). In order to lower the emission of organohalogen refrigerant fluids into the environment, until complete elimination, generally are used catalysts based on noble metals, supported on ceramic carriers or metallic meshes [F. J.Urbano J. M.Marinas, Hydrogenolysis of organohalogen compounds over palladium supported catalysts, Journal of Molecular Catalysis A: Chemical, 173 (2001) 329-345, Z. Dang, N. Singh, M. Morrill, G. Cullen, Oxidation catalyst and method for destruction of CO, VOC and halogenated VOC US-B2-8,475,755, K. Irie, T. Mori, H. Yokoyama, T. Tomiyama, T. Takano, S. Tamata, S. Kanno, Apparatus for processing perfluorocarbon US-B2-7,641,867]. These catalysts are produced by conventional thermochemical methods that include the following steps: impregnation, precipitation, coprecipitation, sol-gel etc. These methods are extremely complex from technical-technological aspect, and they usually last for 30 to 50 hours, even up to a few days. In addition, these known methods include a large number of steps such as: (1) preparation of solutions from which catalytically active material and/or carriers for catalytically active materials are synthetized, (2) formation of precursors for catalytically active materials and/or carriers, by adjusting the pH values of the solutions or by enabling other chemical reactions in those solutions, (3) separation of obtained precursor precipitates by filtration, (4) single drying of the precursor precipitates or, altemativly, multiple rinsing, filtration and drying, (5) calcination in a suitable atmosphere, (6) additional treatment of the catalyst obtained in the form of a powder in order to obtain a required shape by means of: pressing, pelletizing, washcoating of monolithic honeycombs and the like [A. J. Akande, R. O. Idem, A. K. Dalai: Synthesis, characterization and performance evaluation of N1/AI2O3 catalysts for reforming of crude ethanol for hydrogen production, Applied Catalysis A: General 287 (2005) 159-175, S. Y. Lai, W. Pan, C. Fai Ng: Catalytic hydrolysis of dichlorodifluoromethane (CFC-12) on unpromoted and sulfate promoted TiC -ZrCL mixed oxide catalysts, Applied Catalysis B: Environmental 24 (2000) 207-217, W. Hua, F. Zhang, Z. Ma, Y. Tang, Z. Gao, Catalytic hydrolysis of chlorofluorocarbon (CFC-12) over W03/Zr02, Catalysis Letters 65 (2000) 85-89, Z. Ma, W. Hua, Y. Tang, Z. Gao, Catalytic decomposition of CFC-12 over solid acids W03/M _x O _y (M = Ti, Sn, Fe), Journal of Molecular Catalysis A: Chemical 159 (2000) 335-345, G. R. Lester, Catalytic destruction of organohalogen compounds, US-A-5,176,897] As diosclosed in EP 0473396, monolithic catalyst based on Ti02-Si02 mixture is produced by a method that involves steps of precipitation, monolithic honeycomb mechanical extruding, sol-gel method and monolithic honeycomb washcoating, which lasts at least 49 to 50 h. In addition, thermochemical methods require using of solutions with complex chemical composition that contain chemicals from which catalysts are synthesized, e.g. various salts, organometallic compounds, as well as auxiliary synthesis agents such as hydroxides, hydrogen peroxide, etc. which is unfavorable from the aspect of environmental protection. Selection of raw materials used for catalysts production depends on applied thermochemical method. Those raw materials mostly include salts and other inorganic metal compounds, as well as organometallic compounds. In addition, various auxiliary chemicals are used (US 5759504A, US 5877391A).

Hence, there is a need for a catalyst that may be used for the decomposition of organohalogen refrigerant fluids which would have the same efficiency as catalysts known in the art, but that could be produced by a simplified production process involving a reduced number of process steps but at the same time which would be considerably more favorable from the aspect of environmental protection, and thereby would not require additional, specific, production equipment.

Background

EP 0473396 describes a monolithic catalyst used for removal of nitrogen oxides (NO _x ) from gases emitted from boilers, furnaces, gas turbines, diesel engines and various industrial processes, where these gases may also contain halogenated hydrocarbons. Treatment of gases, as disclosed herein, is carried out at temperatures between 200° and 700°C. Described monolithic catalyst contains a mixture of metal oxides i.e. TiCfr-SiCh system with a coating containing ZrC or ZrSi0 ₄ . Catalytically active layer of the catalysts described in this disclosure contains 90.0wt% ZrSiC>4 and 10.0wt% WO3. Production methods of those catalysts are based on conventional thermochemical methods, that are complex and consist of combination of successive mechanical and thermochemical methods. Although EP 0473396 discloses that this catalyst can be used for treatment of gases that contain halogenated hydrocarbons, it does not consider catalytic decomposition of organohalogen refrigerant fluids.

Further, US 5759504A describes a method for efficient catalytic decomposition of halogenated hydrocarbons: chlorofluorocarbons (CFC), trichlorethylene, methyl bromide, halon, and similar compounds at temperatures between 200°C i 500°C. Catalyst used in this method contains T1O2 and WO3. This catalyst is obtained by thermochemical method of impregnation, including: granulation and pelletization of commercially available T1O2 or synthesis of starting T1O2 powder by precipitation method following by immersion of pellets into aqueous solution containing W source and calcination in the air atmosphere in order to obtain WO3 on the catalyst surface.

US 5176897A describes a catalyst based on metal oxides and a catalytic process for organic compounds treatment involving catalytic decomposition of halogenated hydrocarbons at temperatures between 200° and 50Q°C. The main catalyst component is T1O2, but the catalyst preferably also contains V2O5, WO3, SnCh and at least one of the oxides of Pt, Pd and Rh. Catalyst is synthesized by combination of complex thermochemical methods that include T1O2 powder or spheres impregnation, as well as impregnation of monolithic ceramic carriers with previously deposited T1O2 by solutions of suitable additional active components. The process is continued by drying and calcination in the air atmosphere, or by wahcoating of the monolithic ceramic carriers with a suspension of suitable density. The suspension contains catalyst powder synthesized by precipitation or impregnation. The washcoated carriers are blowed through and calcined in the air atmosphere. However, US 5176897A does not consider a problem of catalytic decomposition of organohalogen refrigerant fluids.

US 5877391A describes a method for catalytic decomposition of gas mixture that contains halogenated hydrocarbons, at temperatures between 250° and 500°C. Catalyst based on metal oxides described in this publication possesses high catalytic performans and consists of T1O2, WO3 and S1O2. Synthesis of this catalyst requires both thermochemical and mechanical methods. T1O2 particles are impregnated by aqueous solutions of hydrogen peroxide and by compounds that are a source of other catalyst components. Finally, the particles are dried and calcined in the air atmosphere.

Hence, there is a need for synthesis of a catalyst for the decomposition of organohalogen refrigerant fluids, by a method which would be considerably simplified in comparison with methods known in the art, specifically in terms of efficient management of material flows in the production process (from the beginning to the end of the process). Moreover, there is a need for a process that would require a reduced number of required steps, in comparison with conventional thermochemical methods that are known in the art, but at the same time, would be considerably more favorable from the aspect of environmental protection. Thus, the objective of the present invention is to provide a process for synthesis of the catalyst, where the catalyst may be used in the process of the decomposition of organohalogen refrigerant fluids, which would meet all the above mentioned requirements, but would, at the same time retain the same efficiency as catalysts known in the art.

Disclosure of Invention

When considering the processing of organohalogen refrigerant fluids, gas-phase catalytic decomposing technologies are the most convenient from the aspect of energy efficiency. Those technologies include catalytic processes of hydrogenation, oxidation and hydrolysis. Among the above mentioned processes, catalytic hydrolysis is the most favorable from the thermodynamic aspect [Montreal Protocol On Substances that Deplete the Ozone Layer, Volume 3 B, Report of the Task Force on Destruction Technologies, Dawn Lindon, TUE Eindhoven, Netherlands, 2002., S. Y. Lai, W. Pan, C. Fai Ng, Catalytic hydrolysis of dichlorodifluoromethane (CFC-12) on unpromoted and sulfate promoted Ti0 ₂ -Zr0 ₂ mixed oxide catalysts, Applied Catalysis B: Environmental 24 (2000) 207-217, B. Huang, C. Lei, C. Wei, G. Zeng, Chlorinated volatile organic compounds (Cl-VOCs) in environment - sources, potential human health impacts, and current remediation technologies, Environment International, 71 (2014) 118-138].

The present disclosure relates to a catalyst for gas-phase catalytic hydrolysis of organohalogen refrigerant fluids. The aim of the present invention is to prevent release of such matters into the environment because they have considerably harmful effects on the ozone layer. Generally, by using hydrolysis process in the presence of catalyst based on metal oxides, organohalogen refrigerant fluids are decomposed to the following reaction products: carbon(IV) oxide, hydrohalic acid and water. Chemical reaction of the hydrolysis process of organohalogen refrigerant fluids mixture is shown in equation 1. The organohalogen refrigerant fluids mixture includes: CFC 11, CFC 12, CFC 22, CFC 113 i CFC 134a.

CCl ₃ F(g) + CCl ₂ F ₂ (g) + CHClF ₂ (g) + C ₂ Cl ₃ F ₃ (g) + C ₂ H ₂ F ₄ (g) + 2,5 0 ₂ (g) + 10 H ₂ 0(g) =

= 9 HCl(g) + 12 HF(g) + 7 C0 ₂ (g) + H ₂ 0(g) (1)

The present invention provides a process for synthesis of the catalyst for the decomposition of organohalogen refrigerant fluids. Materials required to obtain a catalytically active layer include a solid phase containing powders of tungsten(III) oxide, zirconium(IV) silicate and clay of kaolinite group, where the content of alkaline metal oxides, such as sodium and potassium oxide, is not lower than 1.5 wt%, and a liquid phase containing water or, optionally, aqueous solution of H ₂ SC>4.

The process for synthesis of the catalyst for the decomposition of organohalogen refrigerant fluids involves washcoating of ceramic Raschig rings by a layer of catalytically active composition according to the present invention, and specifically immersion into a suspension that contains powder of catalytically active material, which is followed by drying and finally, sintering, in order to obtain the final product.

Specifically, the process for synthesis of the catalyst, according to the present invention, is simplified compared to the known thermochemical processes in terms of reducing the number of technological operations and type of operations used in the process. The following steps are eliminated from the process commonly used in the prior art: (1) preparing of complex solutions, (2) obtaining of intermediates for catalysts synthesis from these solutions, (3) separation of obtained intermediates and (4) further treatment of intermediates, which includes rinsing, filtration and drying. In addition, the excess of the suspension remaining after Raschig rings immersing, is reused to obtain the catalytically active layer. By adding a liquid phase, in order to again achieve optimal ratio of solid and liquid phase, the catalytically active layer is reformed without deteriorating its composition and quality. Thus, the recycled material is very simply returned into catalytically active layer production process. Recycling of materials in this process is one of the examples of efficient material flow management, which is considerably favorable from the aspect of environmental protection.

Considering known thermochemical methods for catalyst synthesis, recycling of materials in the production process, in order to obtain catalytically active material was not possible. The reason is, for example, very low concentration of chemicals in starting solutions used for the catalysts synthesis, where after the separation of solid catalyst precursors and liquid phase, the chemicals remain in the liquid phase only in traces, i.e., their concentration is insignificant. Furthermore, in the case of precipitation and coprecipitation methods, after separation of solid precurors and liquid phase, the liquid phase represents a solution in which an agent for precipitation/neutralization dominates. In addition, due to significantly low concentrations of chemicals in starting solutions required for the catalysts synthesis, thermochemical synthesis methods require considerable amounts of these solutions. Therefore, in these processes, large quantities of waste solutions are generated. These solutions represent a mixture of various chemicals that can not be returned to the catalysts production process, which is particularly unfavorable from the aspect of the environmental impact of these processes.

In a preferred embodiment, catalysts production process involves washcoating of ceramic Raschig rings with catalytically active layer based on WC /ZrSiC system. In another embodiment, desirable catalyst shape is obtained by a method of pressing of catalytically active material based on WCb/ZrSiiTi system. These methods provide catalysts in a solid state. Therefore, unlike catalysts obtained by conventional thermochemical methods, there is no need for an additional treatment in order to transform a catalyst from the powder form into a preferred solid shape. Presence of clay enables obtaining a preferred solid catalyst shape, as well as preferred mechanical properties. In the composition according to the present invention, clay of kaolinite group is preferably used because it has an advantage of being low temperature sintering clay and it has total content of alkaline metal oxides, such as sodium and potassium oxide, not lower than 1.5 wt% with respect to the weight of clay. This clay possesses good binding properties and, as an additive to the catalytically active layer, enables the sintering process. In the case of ceramic Raschig rings washcoating, by catalytically active composition in accordance with the present invention, adhesion of catalytically active layer to ceramic Raschig rings is improved. Preferably, the clay contains S1O2 from 56.0 wt% to 70.0 wt%, AI2O3 from 18.0 wt% to 30.0 wt%, Fe2Cb from 1.0 wt% to 2.6 wt%, T1O2 from 0.8 wt% to 1.2 wt%, CaO from 0.4 wt% to 1.6 wt%, MgO from 0.4 wt% to 1.0 wt%, alkaline metal oxides, such as sodium and potassium oxide, at least 1.5 wt% with respect to the weight of clay (up to approximately 2.0 wt% with respect to the weight of clay).

Alternatively, in the catalysts production process, different types of clay can be used as a binding agent, such as clays that in general consist of kaolinite, illite and montmorillonite.

Furthermore, the present patent application describes catalyst functionality testing in the process of catalytic decomposition of organohalogen refrigerant fluids both in laboratory and in industrial conditions.

Catalyst functionality in laboratory conditions is tested, as an example, in the process of CFC 22 catalytic decomposition. Ratio of catalyst specific surface area and unit CFC 22 flow rate in inlet gas stream mixture was in the following range: 110-140 [m ² ] catalyst / 1 [m ³ /h] CFC 22. At temperatures of 400°C and 500°C, efficiency of CFC 22 decomposing process was 95.9 % and 99.5 %, respectively. It is important to note that catalyst described in the present patent application is not limited for the use in CFC 22 decomposition, but it is intended for the decomposition of the mixture of various types of organohalogen refrigerant fluids, which are released during mechanical recycling of refrigerating devices.

For the purpose of catalyst functionality testing in industrial conditions, the same ratio of catalyst specific surface area and unit flow rate of organohalogen refrigerant fluids as for the laboratory conditions was used: 110-140 [m ² ] catalyst / 1 [m ³ /h] refrigerant fluids. In the process, a mixture of several types of these fluids was used, where the fluids originated from waste household refrigerators, with the efficiency of the process being over 94%.

Brief Description of Drawings

Figure 1: Diagram of fracture force test in the lateral position of the sample 5

Figure 2: Diagram of fracture force test in the upright position of the sample 5 Figure 3: Diagram of fracture force test in the lateral position of the sample 6

Figure 4: Diagram of fracture force test in the upright position of the sample 6

Figure 5: Photograph of cross-section of sample 6 sintered at 1240°C

Figure 6: Photograph of cross-section of sample 2 sintered at 1240°C

Figure 7: Photograph of cross-section of sample 3 sintered at 1240°C

Figure 8: Diffractogram of starting WO3 powder

Figure 9: Diffractogram of catalytically active layer of sample 6 sintered at 800°C

Figure 10: Photograph of cross-section of optimal sample sintered at 1050°C

Figure 11: Photograph of polished surface of optimal sample sintered at 1050°C

Figure 12: Diagram of catalytic decomposition process of organohalogen refrigerant fluids.

Best Mode for Carrying Out of the Invention

Catalysts according to the present invention are based on W03/ZrSiC>4 system and are used for decomposition of organohalogen refrigerant fluids. These catalysts are mainly intended for operators for mechanical recycling of refrigerating devices.

Besides catalytically active layer based on W0 ₃ /ZrSi0 ₄ system, the catalyst preferably contains ceramic Raschig rings, that serve as supports i.e. carriers for catalytically active layer. The composition forming the catalytically active layer, contains ZrSiC>4 and WO _3, but also clay, preferably clay of kaolinite group, which is sintered at low temperatures and has a total content of alkaline metal oxides not lower than 1.5 wt% with respect to weight of the clay. Presence of the clay in the catalyst enables preferred catalyst shape formation. Moreover, the clay serves as a binding agent and enables achieving satisfactory mechanical properties (US5176897A, US3090094A, US4360598A). In the present invention, clay enables sintering process and obtaining of compact catalytically active layer.

In order to produce the catalyst according to the present invention, it is desirable to apply a method of ceramic carrier washcoating using catalytically active composition.

To produce the catalyst in accordance with the present invention, the following commercially available starting materials were used: tungsten(III) oxide (WO ₃ ), preferably with particle size below 100 pm, zircon flour i.e. zirconium(IV) silicate (ZrSiC ), preferably with particle size below 75 pm (preferably more than 95 % of particles), clay of kaolinite group, preferably with particle size below 43 pm (preferably 99 % of particles) and liquid phase: water or, optionally, aqueous solution of sulfuric acid, preferably with concentration of 16 %vol. In general, aqueous solution of sulfuric acid is used as a source of SO4 ions in order to increase acidity of reaction centers in the catalytically active layer. This is desirable from the aspect of reducing the harmful effect of reaction products, formed in the process of catalytic hydrolysis of organohalogen refrigerant fluids, that may impair the activity of the catalysts. Namely, it is known that reaction products, such as HC1 and HF, are aggressive and can lead to the catalyst deactivation by corroding the particular oxide components of the catalyst or by forming compounds inactive in the catalytic process.

It is important to note that the use of the same clay type as a raw material for Raschig rings production and as a component of catalytically active composition contributes to the improvement of adhesion of active layer to the rings in final, sintered catalysts. Additionally, in order to improve adhesion, the rings have an extremely rough surface, obtained in the step of extrusion by continuous creasing using a brush at the outlet of the matrix for clay paste molding.

Method for Raschig rings production in accordance with the present invention involves extrusion and sintering. This method is well known in the art and it comprises:

- preparation of starting raw materials - adding of water into dry clay powder and mixing to obtain a paste suitable for the extrusion process; extrusion includes obtaining the preferred shape by pushing out the paste through the extruder matrix. This paste may also contain various additives that contribute to the extrusion process, e.g. lubricants, etc.),

- molding i.e. clay tube forming by using an extruder and cutting the clay tube along a cross- section to obtaing pieces of the preferred length i.e. Raschig rings,

- drying of Raschig rings for the gradual removal of humidity (water added in the paste preparation, as well as chemically bound water in clay), thus preventing the appearance of cracks during the sintering process,

- sintering of dried Raschig rings in order to obtain ceramic pieces with satisfactory mechanical properties.

However, commercially available ceramic Raschig rings can also be used as active layer carriers. Catalyst production and optimization of the production process

To coat the sintered ceramic Raschig rings with catalytically active layer, initially, an aqueous suspension is prepared and it contains, as a solid phase, a powder mixture of WO3, ZrSiC and clay of kaolinite group and as a liquid phase water or, optionally, aqueous solution of sulfuric acid. Content of a solid phase in the suspension is between 30.0 and 75.0 wt%, and the liquid phase is present in the range of 25.0 wt% to 70.0 wt%. Then the Raschig rings are immersed into the suspension and during removal from the suspension, the excess material is removed by decanting. The coated rings are dried and then sintered to obtain the final product - catalyst. The catalyst production process according to the present invention includes the following steps:

- Dry homogenization of zirconium(IV) silicate, tungsten(III) oxide, and clay, that make the solid phase and they are preferably in the form of dry powder, preferably 15-30 min,

- Addition of the liquid phase to obtain the suspension,

- Mixing, preferably 15-30 min,

- Immersing of carriers, for example Raschig rings into the suspension,

- Removing of carriers from the suspension,

- Drying of carriers obtained in the previous step, preferably in ambient conditions,

Sintering, preferably at a temperature of 1050 °C to 1250°C to obtain the catalyst according to the present invention.

The process also involves addition of the liquid phase to the suspension residue that remains after the removal of Raschig rings, in order to be used again for washcoating of the carriers, i.e. new Raschig rings.

Therefore, in order to achieve the efficient material flow management and to reduce harmful environmental impact, the excess of the suspension used to obtain the catalytically active layer, which remains after removal of washcoated Raschig rings from the suspension, represents recycling material that is reused in the catalyst production process. Reuse of this material in order to obtain the active layer is simple and in no way impairs the composition and quality of the obtained catalytic layer. Liquid phase is added to the recycling material, until achieving optimal solid / liquid ratio, and then new Raschig rings are washcoated by immersion into the obtained suspension.

To optimize catalyst production process from the aspect of mechanical properties and adhesion of a catalytically active layer to Raschig rings, a comparative analysis of a series of samples was carried out, and the samples were prepared by using different contents of WO ₃ , from 14.0 to 22.0 wt%, ZrSiC _, from 75.0 wt% to 83.0 wt% and clay, from 0.0 wt% to 8.0 wt%, while liquid phase content was constant. In total, seven different compositions were tested, from which the catalysts were prepared by coating method and catalysts were sintered at two different temperatures (1150 °C and 1250°C), as shown in Tables 1 and 2.

Catalyst fracture force was tested in the lateral position, since in this position catalysts suffer the largest load in industrial conditions. A fracture force test in the upright position was repeated on the sample that showed the best mechanical properties. Also, on each sample, an adhesion of the catalytically active layer on the surface of the Raschig rings was examined by optical microscopy.

Table 1.

As shown in the Table 1, for samples sintered at 1150°C, the presence of clay of kaolinite group that is sintered at low temperatures, in the active layer, has a very favorable effect on the fracture force values, i.e. on the catalyst mechanical properties (samples 3, 5, 6, 7). The sample 5 has demonstrated the highest fracture force value. Diagrams of fracture force testing in the lateral and upright position for this catalyst are shown in Figures 1 and 2. For samples that do not contain any clay in a catalytically active layer (samples 1, 2, and 4), it was observed that the layer is too thin and that the adhesion to the surface of the Raschig rings is not satisfactory.

In spite of the best mechanical properties compared to other samples sintered at 1150°C, the adhesion of a catalytically active layer was still unsatisfactory for sample 5, and it was concluded that the catalysts needed to be sintered at a higher temperature. Therefore, the same series of samples was examined, this time sintered at 1240°C, as shown in Table 2.

Table 2.

Testings of mechanical properties indicated that among all samples, at both sintering temperatures, the highest fracture force was demonstrated using the sample 6 and by sintering at 1240°C (Table 2). Diagrams of fracture force testing in the lateral and upright position for this sample are shown in Figures 3 and 4.

Comparative analysis of catalyst samples containing clay in a catalytically active layer, compared to the samples without the clay, showed that clay improves the adhesion of a catalytically active layer to the Raschig rings. It is preferred that clay content in the catalytically active layer is at least 3.0 wt%.

By increasing the sintering temperature to 1240°C, all the samples exhibited improved adhesion compared to that achieved by sintering at 1150°C. Regardless of the adhesion improvement, all samples without clay in the active layer (samples 1, 2 and 4) had too thin catalytically active layer that does not completely cover the Raschig rings surface. By examining the intersection of the optimal sample 6, shown in Figure 5, it can be clearly noted that a thin layer of active matter, with a thickness between 0.14 and 0.18 mm, was formed on the surface of the Raschig rings, and whose adhesion for the ceramic support (Raschig ring) is particularly good compared to other samples.

By examining the intersection of one of the samples without clay content in the active layer, e.g. sample 2 that was also sintered at 1240°C, and that is shown in Figure 6, is noted that the layer on the Raschig rings is unevenly applied and is prone to cracking.

In Figure 7, a photograph of the cross-section of the sample 3, which is sintered at 1240°C, is shown. Compared to sample 6, the catalytically active layer of the sample 3 has a higher clay content. The active layer is crumbling, however, the adhesion of the layer on the ceramic support (Raschig ring) is good, which again indicates that the presence of a kaolin group clay in a catalytically active layer provides good adhesion of layer on the Raschig rings.

X-ray diffraction analysis of the catalyst active layer (XRD)

After determining the optimal system for the catalyst production from the aspect of mechanical properties and adhesion of the catalytically active layer on Raschig rings, X-ray diffraction (XRD) analysis of the active layer of sample 6 (Table 2) was also performed, after sintering at different temperatures. The aim of this analysis was to determine and monitor the phase composition of the layer.

In addition, the phase composition of the starting WO3 powder, used as one of the active layer components, was also examined. The reason for this analysis is to eliminate the possibility of active layer contamination by undesirable phases that originate from this starting material in case that the layer composition deviates from the predicted.

XRD analysis was carried out on the X-ray diffractometer“PHILIPS”, model PW- 1710, with a curved graphite monochromator and a scintillation counter. Intensities of the diffracted CuKa X-ray radiation (l=1, 54178 A) were measured at room temperature at intervals of 0,02 °2<9 and for 1 s, in the range from 4 to 90, and from 4 to 70 °2Q. X-ray tube was exposed to a voltage of 40 kV and a current of 30 mA, while the slots for directing the primary and diffracted beam were 1° i 0.1 mm.

Diffractogram of the starting WO3 powder is shown in Figure 8. In the analyzed sample, only the presence of monoclinic WO3 was detected, i.e. no other phase was detected, indicating that active layer is not contaminated by any undesirable phase originating from this starting material (or undesirable phases are below the detection limit).

Additional testing included catalyst samples with the catalytically active layer composition identical to that of sample 6 (Table 2), that were sintered at 800°C, in order to determine whether the active layer is contaminated by an undesirable phase in the production process for any reason. Diffractogram of catalytically active layer of such samples is presented in Figure 9 and indicates that none of the starting materials contaminates the active layer with undesirable phases, and there is no contamination in the catalyst production process (or undesirable phases are below the detection limit). In addition, at this temperature there was no formation of a phase having low melting temperature (or these phases are below the detection limit). This is very important because the presence of a phase having low melting temperature could reduce the catalyst activity in several ways (e.g, when a compound inactive in catalytic decomposition of organohalogen refrigerant fluids is formed, or when the phase exhibiting low melting temperature coats catalytically active particles and thus prevents contact between gas mixtures and these particles).

In another embodiment of the present invention, sample 6 (Table 2) additionally contains from approximately 6.0 wt% to approximately 8.0 wt% B2O3, which enables lowering the catalyst sintering temperature. B2O3 may be obtained by thermal treatment of H3BO3 at temperatures above 300 °C in suitable atmosphere, and is used in order to avoid diffusion of this additive into the body of the Raschig rings from the catalytically active layer, which is disadvantageous as B2O3 content in the layer can be reduced in that way. In this embodiment, to obtain the catalytically active layer, the following commercially available materials were used: tungsten(III) oxide (WO3), preferably having particle size below 100 pm, zircon flour i.e. zirconium(IV) silicate (ZrSi0 ₄ ), preferably having particle size below 75 pm (preferably more than 95 % particles), clay of kaolinite group, preferably having particle size belowe 43 pm (preferably at least 99 % particles), liquid phase, and preferably, B2O3 _, preferably having particle size below 100 pm, preferably in an amount from 6.2 wt% to 8.2 wt%, which is also commercially available.

By using the composition containing B2O3 _, as shown in Table 3, at a sintering temperature 1050°C, completely equal adhesion of a catalytically active layer to the Raschig rings is achieved, as when optimal system for the catalyst synthesis is used, wherein the optimal system is represented by the sample 6 (Table 2) and a sintering temperature 1240°C. Therefore, Table 3 shows the optimal composition of the catalyst from the aspect of achieved mechanical properties, the adhesion of the catalytically active layer to the Raschig rings as well as the sintering temperature.

Table 3

In Figures 10 and 11, cross-section of this sample and its surface, polished so that the part of the active layer is removed, are shown. The cross-section as shown indicates that a thin and compact layer of catalytically active material, having thickness between 0.14 mm and 0.18 mm, was formed on the surface of the Raschig ring, without gaps between the layer and the ceramic support i.e. Raschig ring. During the polishing, it appeared that it was very difficult to remove the active layer from the sample surface. In addition, slightly darkened boundary between the ceramic support and the remaining part of the active layer is observed on the polished surface. This darkened boundary represents a hybrid inter-layer. The boundary is vaguely defined, which is also a proof that an extremely strong bond proving exceptionally good adhesion between the active layer and the ceramic support has been achieved. Thus, the addition of B2O3, in order to reduce the temperature during the sintering step, also improved the mechanical properties of the catalyst and the adhesion of the catalytically active layer to the Raschig rings.

Industrial Applicability

The functionality of the catalyst according to the present invention was tested in the process of the decomposing of organohalogen refrigerant fluids in industrial conditions. During testing it was confirmed that the mechanical properties of the catalyst fully meet the criteria for the application in industrial conditions, since there was no damage of the catalyst package observed in the catalytic chamber.

The diagram of the catalytic decomposing process of organohalogen refrigerant fluids in industrial conditions is presented in Figure 12. The process for the catalytic decomposing of these fluids includes the following steps: 1) mechanical treatment of waste gases, 2) preheating of waste gases with simultaneous water vapor introduction, 3) catalytic decomposing of refrigerant fluids, 4) cooling the gases after catalytic treatment, 5) purification of gases after catalytic decomposing.

The technological tests of the catalyst functionality in accordance with the present invention, in industrial conditions, were carried out using a poured layer (packing) of the catalyst with a volume of 1.66 m ³ .

The tests were carried out at a temperature of 400°C. Ratio of catalyst specific surface area and unit flow rate of organohalogen refrigerant fluids was in the following range: 110- 140 [m ² J catalyst / 1 [m ³ /h] refrigerant fluids. The inlet gas stream mixture contained the following components:

- process air (carrier gas and oxygen source required in the reaction of catalytic decomposition of organohalogen refrigerant fluids),

- organohalogen refrigerant fluids (a mixture of several types of fluids, originating from a household refrigerators, the mixture was diluted in the process air),

- water vapor (the source of hydrogen required in the reaction of catalytic decomposition of organohalogen refrigerant fluids).

Since during the testing, the total concentration of the organohalogen refrigerant fluids mixture was unknown, whereby their quantity in the recycling plant corresponds to a capacity of 2 t/h of waste refrigerators and organic carbon (C-H bond) originates mostly from those fluids, the efficiency of the catalytic decomposing process was determined indirectly - by measuring the concentration of total organic carbon (TOC). For each measurement, it was determined the reference value i.e. zero TOC concentration, by direct introduction of the equal amount of organohalogen refrigerant fluids into the pipeline, at a position which is directly in front of the measuring point, i.e. right in front of the facility for the catalytic decomposing, thus preventing catalytic reaction.

Efficiency of the catalytic decomposing of organohalogen refrigerant fluids process was determined by calculation, using the following equation:

e ⁼ (1- Cout/Czer) X 100

wherein:

Cout -TOC concentration in outlet mixture of gases after catalytic reaction, C _Z er - reference TOC concentration prior to the catalysis reaction,

e— efficiency of the process of catalytic decomposing of organohalogen refrigerant fluids (%)·

Based on the obtained results of the measurements, it was concluded that the use of the catalyst according to the present invention in industrial conditions, the achieved efficiency of the process of the catalytic decomposing of organohalogen refrigerant fluids is e = 94.4 %, while the efficiency of the catalyst itself is even higher than this value. This is due to the fact that one part of the organic carbon detected in the outlet gas stream is generated by thermal decomposing of micron particles originating from polyurethane thermal insulation foams, which reach the catalytic system by passing a part of the filter plant. Since the products of polyurethane foams thermal decomposition reaction do not belong to the group of organohalogen refrigerant fluids, these compounds do not participate in catalytic reactions, thereby increasing the total output concentration of TOC. Table 4 shows the measurments of TOC concentration in the air generated during the recycling process of refrigerating devices (without the treatment of this air in the presence of catalyst as well as after the treatment) at the full capacity of the facility. The process during which the measurements were carried out included refrigerators recycling.

Table 4.