Study of the activities of new catalytic systems in the oxidative dehydrogenation reaction of methanol

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Study of the activities of new catalytic systems in the oxidative dehydrogenation reaction of methanol

Suleymanova G.N., Efendi A.C., Novruzov N.N., Azerbaijan State University of Oil and Industry

Keywords: methanol, formaldehyde, zirconium, vanadium, molybdenum, alloy, catalysts.

Introduction

The fact that our country has large hydrocarbon reserves makes it important to purchase important organic compounds that are widely used based on them. In recent times, especially the discovery and commissioning of new oil and gas fields, many production areas have been created based on this raw material base. In this regard, the commissioning of the "Methanol" plant with a large production capacity in our republic is commendable.

In addition to the sale of methanol as a raw material, which is a product of the methanol plant, it is considered appropriate to convert it into very valuable substances, including very valuable dimethoxymethane, widely used formaldehyde, acetic acid, dimethyl ether, dimethyl carbonate, methyl tributyl ether, and methyl formate as an additive to fuels.

Synthesis, selection and determination of activity of new catalytic systems for catalytic oxidation of methanol to formaldehyde, dimethyl ether and other valuable compounds are considered to be urgent problems. Synthesis of new catalytic systems based on vanadium, molybdenum, zirconium, cobalt, iron for the conversion of methanol to formaldehyde, determination of their activity and kinetic regularities of the process.

Methanol (CH₃OH), which can be obtained from the conversion of natural gas, has a large reserve in our country, so there is a methanol plant with a production capacity of about 600,000 tons. Recently, metal oxides (Ni, Co, Sb, V) deposited on various carriers (Al₂O₃, SiO₂, MgO), which are widely used for the thermocatalytic decomposition of methane, have shown high activity.

Currently, the production of formaldehyde from methanol is carried out with the presence of Ag and iron-molybdate catalysts. Various catalytic systems and alloys containing metallic Ag and silver allow the oxidative dehydrogenation of formaldehyde at high temperature (950-1000 K) and pressure. The main disadvantages of these processes are that they are carried out at high temperature and pressure, although the conversion of methanol is very low. In order to perform the dehydrogenation of methanol to formaldehyde, many catalytic systems containing copper were obtained and their activities were tested. Although it was possible to increase the stability of the catalyst by adding Zn, Se to the catalyst, the conversion of methanol at 900 K did not exceed 10-15%, although the yield of formalin reached 6068%.

catalytic formaldehyde activity molybdenum

Experimental part

Based on the known information, a number of catalysts were synthesized and brief information about their initial activities was given. Initially, in order to obtain alloys of V, Mo, Fe with Zr with different composition, their samples were taken at different atomic weights and melted together in the furnace. For example: Az(Zr)=91.224, Az(Mo)=95.94, M(_ZrMo2)=91.224+2.95.94=283.104 for obtaining ZrMo2 intermetallics. In this composition, Mo=67.8%, Zr=32.2%. After synthesizing catalyst alloys, modern physico-chemical analysis methods were used to determine the composition of their samples. Initially, all samples were studied by irradiation of their composition using the RFA method of X-ray phase analysis.

In order to determine the activities of the obtained alloy and other catalyst samples, we place their amounts of 0.2 g and 0.3 g in pulse and open flow reactors, respectively. The experiment in the device operating in the open flow mode is carried out in the following sequence. By means of a stream of purified nitrogen (1), methanol vapors are supplied to the mixer (5), which enters the purified oxygen (1) by passing through the saturator (4). The temperature of the mixer is maintained at a constant temperature by a thermostat (10). Then, this mixture enters the reactor placed in the heating furnace (11) and is heated to the reaction temperature, and a stationary mode is obtained for 20-30 minutes. After that, the reaction products from the reactor are directed to the analysis by taking a sample for the chromatograph by means of a six- pass faucet. The other part of the reaction products is released and collected. The reaction temperature in the reactor is regulated by means of a thermocouple placed there. At the same time, the flow rate is regulated by controlling the O₂:N₂ ratio, the methanol flow rate, and the PCH:PO₂ ratio.

Catalyst samples were analyzed by X-ray diffraction (XRD) using Rigoku Mini Flex 600 (K 1.5 4060 A) CuK a-irradiating Ni-filter and diffractometer Bruker "D2 Phaser" as well as CuK a-irradiating DRON-2 device.

Based on the results of the X-ray diffractometric analysis, it can be said that zirconium is mainly present in the oxidized phase on the surface of the catalysts (Figure 1).

As can be seen from the X-ray image (Fig. 1), peaks 20=30.00 in the X-ray image of the initially synthesized ZrV0.3 sample (Fig. 1 a), 35.70, 51,590, 62.30, 67.50, which can be in both monoclinic and tetragonal structure of ZrO2. ZrO2 (JCPDS:37- 1434, 17-923) 20=32.00, 35,680, 40.09, 54,750 peaks indicate the presence of metallic zirconium (JCPDS%5-665). Thus, in this initial sample, mainly metallic Zr and m- ZrO2, t-ZrO₂ are observed, and vanadium oxides are generally absent. Only after treatment with O₂ in air for 1 h at 873 K, phase changes occur in the sample (Figure 1 b, Tables 1-2), which leads to a decrease in catalytic activity.

Figure 1. X-ray image of ZrV0.3 catalyst samples before and after processing. a) ZrV0.3 b) Air, 873 K, 3 hours.

After oxidation of the catalyst surface with air (873 K, 1 hour), it is observed that the ortho-rhombic and tetragonal phase analysis of V₂O₅ is formed on the surface (2q=20.60, 24.60, 27.00, 32.50, 50.20 ). Also, the presence of VO₂ phase (2q=26.30, 37.10, 42.00, 56.50, JCPDS 43-1051) and other oxides of VOx, even mixed oxides, is not excluded, as vanadium can form a number of oxides with oxygen . But at this time, the activity of the VFe0.2 catalyst remains at a low level. Only after treatment with H2 for 1 h at 873 K, the activity of the catalyst begins to increase, which is related not only to the change in the surface phase composition, but also to the valence of the components.

Table 1. X-ray diffraction analysis results of the initial ZrV0.3 catalyst sample.

Table 2. X-ray diffraction analysis results of ZrV0.3 catalyst sample after treatment with О2- and Н2.

Figure 2. X-ray image of ZrMo2 catalyst after treatment with 02 and H2. a) with air at 773 K, 3 hours, b) with H2 at 873 K, 1 hour.

Conclusion

When we consider the change in the activity of some of these catalytic systems in a wide temperature regime (423-543 K), we see again the high activity of catalysts based on vanadium zirconium (curve 3, 6) and zirconium molybdenum (curve 4) alloys compared to other catalysts (Figure 3.) that the V-Mo-O/Al2O3 catalyst showed the highest activity (Figure 3, curve 7). However, despite the high activity of these catalysts in the conversion of methanol, the yield of formaldehyde was very low. As shown, the newly synthesized alloy catalysts based on vanadium and molybdenum also initially showed high activity (Figure 4.).

The obtained results show that the activities of newly synthesized catalyst samples at 563-723 K even at higher temperatures did not exceed 12-15%.

These alloy catalytic systems are activated only after undergoing an oxidation- reduction process.

Figure 5(a). Time-dependent sequential change in the oxidation reactivity of methanol in DME and FA after the 773 K oxidation-reduction process of the catalyst. 1 - ZrV0.30, 2- ZrV, 3 - ZrV2.

As can be seen from the obtained results, the influence of the reaction temperature in the range of 403-583 K on the oxidation reaction of methanol in the presence of ZrV2.0 was studied. In the temperature range of 403-413 K, the methanol conversion of the redox catalyst increases to 38-56% and reaches 60% at 423 K, when the DMM yield reaches its maximum value of 36-37%. . At further temperature increase (up to 583 K), methanol conversion increases to 64%, but DMM yield decreases to 21-22%. At the same time, the yield of FA also goes towards the maximum decrease at 433-453 K.

Figure 3. Temperature-dependent change of activity of catalytic systems in the oxidation-dehydrogenation reaction of methanol. 1 - ZSM +Cu, 2 - VOx/ZrO2, 3 - VFe0.4, 4 - ZrMo2, 5 - ZrV0.3, 6 - ZrV2, 7 - V-Mo-O/Al2O3.

Figure 4. Temperature-dependent change of the activities of the newly synthesized catalysts in the oxidation-dehydrogenation reaction of methanol before the oxidation 1 - ZrV0.3, 2 - ZrMo0.5, 3 - ZrFe, 4 - ZrVFe 2, 5 - ZrV2.

Figure 5(b). Effect of temperature on activity of methanol in oxidation-reduction process. 1 - ZrV0.30, 2- ZrV, 3 - ZrV2.

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