Thermostabilizing agent for endothermic processes in a fixed bed

Abstract

A thermostabilizing agent is used in the production of olefinic hydrocarbons. A carrier for a thermostabilizing agent is obtained by mixing a product of rapid partial dehydration of gibbsite having the formula Al2O3·nH2O, where 0.43≤n≤1.5, and calcium compounds, and forming, drying and sintering granules at a temperature of 900-1400°С. The carrier contains, in terms of oxides: 10-36 wt% calcium oxide, and the remainder aluminium oxide. The percentage of pores having an effective radius of 60-70 nm is 70-78%. The thermostabilizing agent has a specific surface area of 8.0-35.0 m2 / g and a crush strength of 15-33 MPa. The technical result is the creation of a thermostabilizing agent that has a high specific surface area, high thermal stability, a constant phase composition, and high strength.

Description

[0001] THERMOSTABILIZING AGENT FOR ENDOTHERMIC PROCESSES IN A STATIONARY LAYER

[0002] Field of technology

[0003] The invention relates to the field of obtaining olefin hydrocarbons by dehydrogenation of C3-C5 paraffins and can find application in the chemical and petrochemical industries.

[0004] Prior art

[0005] At present, the main industrial catalytic processes of non-oxidative dehydrogenation of paraffin hydrocarbons in the world are the Russian Yarsintez process and the foreign STAR, Oleflex, Catadiene and Catofin processes. Of these, dehydrogenation on aluminochromium catalysts in stationary systems is carried out only in the Catadiene and Catofin processes, in the STAR and Oleflex processes, reactors with a moving bed are used, and in the Yarsintez process - with a fluidized bed.

[0006] The advantages of dehydrogenation processes in a fixed bed are the continuity of the dehydrogenation process and the high yield of the target product. The catalyst work increases due to constant regeneration, the heat from which goes to the subsequent dehydrogenation reaction, which helps to reduce production costs.

[0007] At the same time, the use of dehydrogenation catalysts in a fixed bed leads to a number of technological difficulties: the endothermic nature of the dehydrogenation process leads to a decrease in the temperature in the bed to 50-100°C, which requires the introduction of a large amount of heat from outside into the system. The lack of uniform heat distribution throughout the entire volume of the catalyst leads to the formation of local overheating and cooling zones. This in turn leads to rapid coking of the catalyst and subsequent deactivation.

[0008] To compensate for the endothermic effect, catalytically inert thermostabilizing agents (TSA, also known as “heat-generating materials”, “heat-releasing materials”, “heat generators”, etc.) are used in dehydrogenation reactions and side reactions accompanying the process. These agents serve as a source of additional heat and thereby maintain a stable temperature of the catalyst layer and the entire dehydrogenation process.

[0009] The prior art discloses the use of copper oxide stabilized on an inert alumina carrier as a heat-stabilizing agent, which is due to the ability of reversible reduction-oxidation of copper oxide under the conditions of a dehydrogenation process carried out in a periodic mode: dehydrogenation, oxidative regeneration, reductive activation.

[0010] Thus, an improved endothermic process for hydrocarbon conversion is known (patent EA 018474, IPC C10G11 / 18, B01J21 / 00, B01J23 / 00, published on 30.08.2013) and a catalytic layer system for implementing it. The method includes reacting an incoming hydrocarbon stream with a multicomponent catalytic layer in such a way that the temperature inside the catalytic layer is maintained within controlled temperature limits at all stages of the method. The multicomponent layer includes a catalyst specific to the reaction, physically mixed with a heat-generating material. The heat-generating material may contain copper, chromium, molybdenum, vanadium, cerium, yttrium, scandium, tungsten, manganese, iron, cobalt, nickel, silver, bismuth or combinations thereof.Various aluminum oxides or hydroxides are used as the carrier, such as aluminum trihydroxide, boehmite, pseudoboehmite, gibbsite, bayerite, transition aluminum oxides or alpha-alumina, silicon oxide / alumina, silicon oxide, silicates, aluminates such as calcium aluminate or barium hexaaluminate, calcined hydrotalcites, zeolites, zinc oxide, chromium oxides, magnesium oxides and combinations thereof. Possibly, the heat-generating second component may additionally contain an activator, such as an alkali or alkaline earth metal, lithium, sodium, potassium, rubidium, cesium, beryllium, magnesium, calcium, strontium, zirconium, barium and combinations thereof.

[0011] An improved method of dehydrogenation using a heat-generating material is known (patent EA 032486, IPC C07C5 / 333, published on 28.06.2019). The invention describes a method for the endothermic conversion of hydrocarbons, including the interaction of hydrocarbons with a layer of a multicomponent catalyst and regeneration of the catalyst layer using air. When the catalyst layer is restored, the heat-generating component of the second catalytic composition generates heat, which passes into the first (and third) catalytic composition (for example, into its inert component). The heat-generating component is a material that generates heat when exposed to reducing and / or oxidative reaction conditions, but which is relatively inert with respect to the hydrocarbon feedstock during the dehydrogenation process.

[0012] An exothermic additive for dehydrogenation of alkanes and a method for producing and using it are known (patent CN 108300430, IPC C07C11 / 04, C07C11 / 06, C07C11 / 08, C07C11 / 10, C07C5 / 333, C09K5 / 14, C09K5 / 16, published 02.02.2021). The exothermic auxiliary agent contains 10-35 wt.% CaO, 50-85 wt.% AlO3, 5-30 wt.% CuO and 0-3 wt.% metal oxides selected from group VIII, group PV, group IIIB and group VIIB.

[0013] The closest in technical essence (prototype) is a catalytically inactive heat generator described in patent RU 2428250, IPC B01J23 / 26, B01J23 / 00, B01J21 / 04, C07C5 / 333, published 10.09.2011. The heat generator, also called the "secondary component" or "second heat-generating component", is a heat-generating inert material and a carrier suitable for applying the heat-generating inert material to it. The heat generator is catalytically inert with respect to dehydrogenation reactions and side reactions that occur during the dehydrogenation process and lead to increased coke formation. The heat generator (catalytically inert) is capable of generating heat in intermediate reduction and / or oxidation processes.

[0014] Supports for the secondary component include, but are not limited to, alumina, aluminas, alumina monohydrate, boehmite, pseudoboehmite, alumina trihydrate, gibbsite, bayerite, alumina-silicon oxide, transition aluminas, alpha-alumina, silica, silicates, aluminates, calcined hydrotalcites, zinc oxide, chromium oxides, magnesium oxides, and combinations thereof.

[0015] The heat-generating inert material may be selected from copper, chromium, molybdenum, vanadium, cerium, yttrium, scandium, tungsten, manganese, iron, cobalt, nickel, silver, bismuth and a combination thereof. The heat-generating inert material constitutes 1-40 wt.% of the total weight of the secondary component. In a more preferred embodiment, the heat-generating inert material constitutes 4-20 wt.% of the total weight of the secondary component, and in the most preferred embodiment, the amount of the heat-generating inert material constitutes 6-10 wt.% of the total weight of the secondary component. The secondary component may further comprise (optionally) a promoter such as an alkali or alkaline earth metal, lithium, sodium, potassium, rubidium, cesium, beryllium, magnesium, calcium, strontium, barium and a combination thereof.

[0016] The disadvantage of the listed analogs is that the heat-generating materials do not have optimal textural characteristics and are not strong enough. Disclosure of the invention

[0017] The objective of the invention is to develop an exothermic thermal stabilizing agent (hereinafter referred to as TSA) for carrying out endothermic processes in a stationary layer, which has optimal textural characteristics and has high strength.

[0018] The problem is solved using a carrier for obtaining a heat-stabilizing agent for endothermic processes in a stationary bed, including calcium aluminates and aluminum oxide. The product of rapid partial dehydration of gibbsite of the formula AlO3 nH2O, where 0.43 < n < 1.5, is used as a precursor of aluminum oxide. The porous structure of the carrier is such that the proportion of pores with an effective radius of 60-70 nm is 70-78%. The carrier has the following composition in terms of oxides, wt.%: calcium oxide - 10-36, aluminum oxide - the rest. Preferably, the phase composition of the carrier includes calcium aluminates CaALiO?, CaAl2Oi9, Ca3Al2Ob. The carrier preferably has a strength of 11-31 MPa, a specific surface area of ​​4.0-18.0 m 2 / g, total pore volume 0.16-0.34 cm 3 / g. The carrier additionally includes at least one compound from the group K2O, Na2O, BaO, SiCh, TiO2, Z1O2, ZnO, MgO in an amount of up to 10 wt.%.

[0019] The task is also solved using the method for obtaining the above-mentioned carrier, including mixing aluminum hydroxides and calcium compounds, molding, drying and calcination. The product of rapid partial dehydration of gibbsite of the formula AIO3-nH2O, where 0.43<n<1.5, is used as aluminum hydroxide. The carrier granules are calcined at a temperature of 900-1400°C.

[0020] The task is also solved using a heat-stabilizing agent for endothermic processes in a stationary layer, including calcium compounds, copper and aluminum oxides. This heat-stabilizing agent includes the above-mentioned carrier obtained by the above-mentioned method. The heat-stabilizing agent has a specific surface area of ​​8.0-35.0 m 2 / g and a crushing strength of 15-33 MPa. The heat-stabilizing agent preferably contains calcium compounds in an amount of 8-25 wt.% based on the oxide, copper oxide in an amount of 5-25 wt.%, and aluminum oxide - the rest. The heat-stabilizing agent additionally includes at least one compound from the group K2O, MagO, BaO, SiC>2, TiO2, ZrO2, ZnO, MgO in an amount of up to 10 wt.%. The heat-stabilizing agent preferably has pores with an effective radius of 40-55 nm, the proportion of which is 52-56%. The claimed heat-stabilizing agent has a highly durable structure, and its mechanical crushing strength after testing under cyclic oxidation-reduction conditions does not decrease for at least 100 cycles. Also, after testing under cyclic oxidation-reduction conditions for at least 100 cycles, the thermal stabilizing agent has a stable phase composition - copper oxide and carrier phases, while copper-aluminum spinel phases are absent.

[0021] The technical result is the creation of a heat-stabilizing agent for endothermic processes in a stationary layer, which has optimal textural characteristics and has high strength.

[0022] As a result of interaction of calcium oxide with the product of rapid partial dehydration of gibbsite of formula AlO3-nH2O, where 0.43<n<1.5, calcium aluminates of various phase composition are formed, which have high operational characteristics as carriers for TCA, such as high thermal stability, mechanical strength, constant phase composition. At temperatures of 900-1400°C, predominantly calcium-enriched phases are formed - calcium aluminates of various phase composition. The proposed method allows obtaining phases CaAl2O3, CaAl2O3, Ca3Al2O3, which have maximum strength.

[0023] To prepare the carrier samples for TCA, calcium hydroxide or its mixture with calcium carbonate were used as calcium compounds.

[0024] The product of rapid partial dehydration of gibbsite (hereinafter referred to as the TCA product) obtained by dehydration under conditions of pulsed heating of technical alumina hydrate - gibbsite Al(OH)3 was used as aluminum hydroxide. The TCA product is in an X-ray amorphous state, possibly with a content of crystalline phases in an amount of no more than 10 wt.%, and has the composition Al2O3 nH2O, where 0.43<n<1.5. The TCA product has high reactivity and is easily hydrated in an aqueous or vapor-phase medium to form aluminum hydroxide of a pseudoboehmite, bayerite structure mixed with an amorphous phase. The use of the TCA product ensures high crushing strength and a high specific surface area of ​​the granules.

[0025] The samples of the heat-stabilizing agent were obtained from the samples of the prepared carriers by impregnation by moisture capacity with an aqueous solution of Cu(NO3)2'3H2O heated to 50-60°C. After impregnation, the samples were withered, dried at a temperature of 80-200°C for 0.5-8.0 h and calcined at a temperature of 550-750°C for 2-8 h in an air flow. The composition and properties of the obtained carriers and the heat-stabilizing agent TSA are given in Table 2 and Table 3, respectively. The samples of TS A were tested under cyclic oxidation-reduction conditions (CRC) in order to track changes in the characteristics of TS A and changes in any process characteristics: heating of the layer / temperature of the TSA layer at each of the stages (reduction of CuO and oxidation of Cu), the volume of absorbed hydrogen and oxygen, the stability of the TSA operation under conditions close to real ones. The physicochemical properties of the samples before and after the CRC tests were also determined.

[0026] In particular, the TSA sample according to Example 4 was tested in 118 reduction-oxidation cycles. The test results are shown in Figs. 1-3, where:

[0027] Fig. 1 - dependences of the temperature in the layer and the concentration of gases on the time of the reduction stage (left) and oxidation (right);

[0028] Fig. 2 - the volume of gases absorbed during the reduction of V(Hi) and oxidation of Y(O2);

[0029] Fig. 3 - temperature difference of the TSA layer during reduction and oxidation.

[0030] The obtained high and constant values ​​of the strength of the TSA samples (Table 1), as well as the data on the phase composition, demonstrate the high stability of TSA to high-temperature processes in an oxidation-reduction atmosphere.

[0031] Table 1. Change in crushing strength of TSA during CV tests.

[0032] After 96 cycles, steam treatment was carried out and the performance of the TSA was again checked in the COV tests.

[0033] The results of the COV tests showed:

[0034] - the presence of strong heating of the TCA layer (Fig. 1) both at the reduction stage and at the oxidation stage, and in the case of oxidation, the heating is stronger due to the greater exo-effect of the copper oxidation reaction;

[0035] - the mechanical strength and phase composition remain stable throughout the entire TSA operation. X-ray phase analysis showed the presence of a CuO phase and carrier phases. The presence of phases of individual aluminum and calcium oxides, as well as copper-aluminum spinel, was not detected either on the fresh sample or after the COV tests, which indicates a low interaction of CuO with the surface of the spinel carrier and demonstrates high stability of TSA to high-temperature processes in an oxidation-reduction atmosphere; - the TS A sample (CuO / calcium aluminate) is not prone to strong deactivation and is stable during operation under reducing-oxidizing conditions, both in terms of hydrogen / oxygen absorption and temperature conditions (Figs. 2, 3);

[0036] - steam treatment did not affect the stability of TS A;

[0037] - TS A has a long development period associated with the redistribution of copper oxide on the granule.

[0038] The best embodiment of the invention

[0039] The essence of the invention is illustrated by the following examples.

[0040] Example 1.

[0041] 150 g of aluminum hydroxide, a TCA product of the formula AlO3 nH2O, where n=0.9, are loaded into a Z-shaped mixer. The plastic mass is obtained by peptizing aluminum hydroxide with nitric acid. Then, calcium hydroxide is introduced in an amount of 15.42 g. The resulting mass is formed into granules. The carrier granules are dried at a temperature of 80-200°C for 0.5-8 hours. Then the carrier is calcined at a temperature of 900-1400°C for 2-8 hours in an air flow.

[0042] The composition of the carrier in terms of calcium and aluminum oxides (wt.%): AlO3 - 90.0; CaO - 10.0. The properties of the carrier are given in Table 2.

[0043] TSA is prepared by impregnating the carrier granules with a solution prepared by dissolving copper (II) nitrate trihydrate in water at a temperature of 50-60°C. The amount of copper (II) nitrate trihydrate is determined based on the copper (II) oxide content of 8 wt.% in the calcined TSA. The TSA granules are dried at a temperature of 80-200°C for 8 hours in a stepwise mode. Then the TSA is calcined at a temperature of 550-750°C for 2-8 hours in an air flow. The properties of TSA are given in Table 3.

[0044] Example 2.

[0045] The carrier is prepared similarly to example 1, differing only in the composition of the carrier.

[0046] The composition of the carrier in terms of calcium and aluminum oxides (wt.%): AGO3 - 85.2; CaO - 14.8. The properties of the carrier are given in Table 2.

[0047] TSA is prepared similarly to example 1, differing only in composition. The composition and properties of TSA are given in Table 3.

[0048] Example 3.

[0049] The carrier is prepared similarly to example 1, differing only in the composition of the carrier. A mixture of calcium hydroxide and calcium carbonate is used as a calcium precursor. The composition of the carrier in terms of calcium and aluminum oxides (wt.%): Al2O3 - 77.8; CaO - 22.2. The properties of the carrier are given in Table 2.

[0050] TS A is prepared similarly to example 1, differing only in composition. The composition and properties of TS A are given in Table 3.

[0051] Example 4.

[0052] The carrier is prepared similarly to example 1, differing only in the composition of the carrier; aluminum hydroxide of the formula AlO3 nH2O is used, where n=1.4. To form a stable structure, promoters are introduced - zinc oxide and magnesium oxide.

[0053] The composition of the carrier in terms of oxides (wt.%): AI2O3 - 82.1; CaO - 16.3, ZnO - 0.8; MgO - 0.8. The properties of the carrier are given in Table 2.

[0054] TSA is prepared similarly to example 1, differing only in composition. The composition and properties of TS A are given in Table 3.

[0055] Example 5.

[0056] The carrier is prepared similarly to example 1, differing only in the composition of the carrier. To form a stable structure, a promoter is introduced - sodium hydroxide.

[0057] The composition of the carrier in terms of oxides (wt.%): AI2O3 - 82.1; CaO - 15.8, Na2O - 2.1. The properties of the carrier are given in Table 2.

[0058] TSA is prepared similarly to example 1, differing only in composition, the amount of CuO in TSA is 5.0 wt.%. The properties of TSA are given in Table 3.

[0059] Example 6.

[0060] The carrier is prepared similarly to example 1, differing only in the composition of the carrier.

[0061] The composition of the carrier in terms of calcium and aluminum oxides (wt.%): AlO3 - 83.7; CaO - 16.3. The properties of the carrier are given in Table 2.

[0062] TSA is prepared similarly to example 1, differing only in composition, the amount of CuO in TSA is 25.0 wt.%. The properties of TSA are given in Table 3.

[0063] Example 7.

[0064] The carrier is prepared similarly to example 1, differing only in the composition of the carrier.

[0065] The composition of the carrier in terms of calcium and aluminum oxides (wt.%): AI2O3 - 80.0; CaO - 20.0. The properties of the carrier are given in Table 2.

[0066] TSA is prepared similarly to example 1, differing only in composition, the amount of CuO in TSA is 15.0 wt.%. The properties of TSA are given in Table 3.

[0067] Example 8.

[0068] The carrier is prepared similarly to example 1, differing only in the composition of the carrier; to form a stable structure, promoters are introduced - potassium oxide and titanium oxide. The composition of the carrier in terms of oxides (wt.%): AI2O3 - 72.8; CaO - 22.2; K2O - 1.9; TiCh - 3.1. The properties of the carrier are given in Table 2.

[0069] TSA is prepared similarly to example 1, differing only in composition, the amount of CuO in TSA is 25.0 wt.%. The properties of TSA are given in Table 3.

[0070] Example 9.

[0071] The carrier is prepared similarly to example 1, differing only in the composition of the carrier; aluminum hydroxide of the formula AlO3 nH2O is used, where n=0.6. To form a stable structure, promoters are introduced - barium oxide and zirconium oxide.

[0072] The composition of the carrier in terms of oxides (wt.%): AI O3 - 58.0; CaO - 36.0; BaO - 3.2; ZrO2 - 2.8. The properties of the carrier are given in Table 2.

[0073] TSA is prepared similarly to example 1, differing only in composition, the amount of CuO in TSA is 10.0 wt.%. The properties of TSA are given in Table 3.

[0074] Example 10.

[0075] The carrier is prepared similarly to example 1, differing only in the composition of the carrier; a promoter is introduced - magnesium oxide.

[0076] The composition of the carrier in terms of calcium and aluminum oxides (wt.%): AI2O3 - 79.0; CaO - 18.0; MgO - 3.0. The properties of the carrier are given in Table 2.

[0077] TSA is prepared similarly to example 1, differing only in composition, the amount of CuO in TSA is 13.0 wt.%. The properties of TSA are given in Table 3.

[0078] Example 11.

[0079] The carrier is prepared similarly to example 1, differing only in the composition of the carrier; to form a stable structure, promoters are introduced - sodium oxide and silicon oxide.

[0080] The composition of the carrier in terms of oxides (wt.%): AI2O3 - 77.1; CaO - 15.0; Na2O - 2.2; SiO2 - 5.7. The properties of the carrier are given in Table 2.

[0081] TSA is prepared similarly to example 1, differing only in composition, the amount of CuO in TSA is 12.0 wt.%. The properties of TSA are given in Table 3.

[0082] Example 12.

[0083] The carrier is prepared similarly to example 1, differing only in the composition of the carrier, a promoter is introduced - TiO2. The properties of the carrier are given in table 2.

[0084] Carrier composition (wt.%): AI2O3 - 80.0; CaO - 16.0; TiO2 - 4.0.

[0085] TSA is prepared similarly to example 1, differing only in composition, the amount of CuO in TSA is 9.0 wt.%. The properties of TSA are given in Table 3.

[0086] Example 13 (based on the prototype). The fuel component is manufactured in accordance with invention RU 2428250 (example D), as follows: calcium aluminate (Ca-aluminate) is granulated to approximately 3.5 mm in size, then the Ca-aluminate is calcined at a temperature of about 1300°C for about 10 hours. Then the calcined material is impregnated with an enriched solution of copper (II) nitrate hexahydrate and manganese nitrate, the impregnated material is dried for about 4 hours at a temperature of about 250°C after calcination at a temperature of about 500°C for 5 hours. The concentration of CuO in the second fuel component is about 11 wt.%; the concentration of MnO2 is 0.5 wt.% based on the total weight of the secondary component.

[0087] Table 2. Composition and properties of carriers. Table 3. Composition and properties of samples of heat-stabilizing agents (TSA).

[0088] It follows from the given examples that in order to obtain a highly effective TSA with high strength, a support based on aluminum oxide is proposed, including calcium oxide and, possibly, promoters, having specified textural characteristics, wherein the proportion of pores with an effective radius of 60-70 nm is 70-78%. Using the proposed support and the method for its preparation based on the product of rapid partial dehydration of gibbsite, a TSA is obtained that has a high-strength structure and high stability to high-temperature processes in an oxidation-reduction atmosphere.

[0089] Industrial applicability

[0090] The heat-stabilizing agent can find application in the chemical and petrochemical industries in the processes of obtaining olefin hydrocarbons by dehydrogenation of C3-C5 paraffins.

Claims

CLAUSES OF THE INVENTION 1. A carrier for producing a heat-stabilizing agent for endothermic processes in a fixed bed, comprising calcium aluminates and aluminum oxide, characterized in that the product of rapid partial dehydration of gibbsite of the formula AEO3 nH2O, where 0.43<n<1.5, is used as the precursor of aluminum oxide, and the porous structure of the carrier is such that the proportion of pores with an effective radius of 60-70 nm is 70-78%, and the carrier has the following composition in terms of oxides, wt.%: calcium oxide - 10-36; aluminum oxide - the rest.

2. The carrier according to claim 1, characterized in that the phase composition includes calcium aluminates CaAEO?, CaAli2Oi9, Ca3AEOb.

3. The carrier according to item 1, characterized in that it has a strength of 11-31 MPa, a specific surface area of ​​4.0-18.0 m 2 / g, total pore volume 0.16-0.34 cm 3 / G.

4. The carrier according to claim 1, characterized in that it additionally includes at least one compound from the group K2O, IagO, BaO, SiCh, TiO2, ZrCh, ZnO, MgO in an amount of up to 10 wt.%.

5. A method for producing a carrier according to any one of paragraphs 1-4, comprising mixing aluminum hydroxides and calcium compounds, molding, drying and calcining, characterized in that the aluminum hydroxide used is a product of rapid partial dehydration of gibbsite of the formula AEO3 nH2O, where 0.43<n<1.5, and the carrier granules are calcined at a temperature of 900-1400°C.

6. A heat-stabilizing agent for endothermic processes in a fixed bed, including calcium compounds, copper and aluminum oxides, characterized in that it includes a carrier according to any of paragraphs 1-4, obtained by the method according to paragraph 5, has a specific surface area of ​​8.0-35.0 m 2 / g and crushing strength of 15-33 MPa.

7. A heat-stabilizing agent according to claim 6, characterized in that it contains calcium compounds in an amount of 8-25% by weight based on oxide, copper oxide in an amount of 5-25% by weight, and aluminum oxide - the rest.

8. A heat-stabilizing agent according to any one of paragraphs 6, 7, characterized in that it additionally includes at least one compound from the group K2O, IagO, BaO, SiO2, TiO2, ZrO2, ZnO, MgO in an amount of up to 10 wt.%.

9. A heat-stabilizing agent according to claim 6, characterized in that the proportion of pores with an effective radius of 40-55 nm is 52-56%.

10. A heat-stabilizing agent according to any one of paragraphs 6-9, characterized in that it has a high-strength structure, and its mechanical crushing strength after testing under cyclic oxidation-reduction conditions does not decrease for at least 100 cycles.

11. A heat-stabilizing agent according to any one of paragraphs 6-9, characterized in that after testing under cyclic oxidation-reduction conditions for at least 100 cycles it has a stable phase composition - copper oxide and carrier phases, while copper-aluminum spinel phases are absent.

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