RU2117650C1 - Method of catalytic dehydrogenation of hydrocarbons - Google Patents

Abstract

FIELD: catalytic dehydrogenation of hydrocarbons, in particular, dehydrogenation of butane with formation of butadiene under the effect of electromagnetic radiation of superhigh frequency range. SUBSTANCE: method includes employment of energy carrier in the form of powerful radiation of electromagnetic radiation of superhigh frequency range which is converted in mass of catalyst into heat energy to ensure conduction of endothermal process of dehydrogenation of hydrocarbon raw material in contact of raw material with catalyst without preliminary heating of hydrocarbon raw material. EFFECT: higher energy efficiency of reactor. 2 dwg, 2 tbl

Description

 The invention allows for the catalytic dehydrogenation of hydrocarbons, in particular, butene dehydrogenation with the formation of butadiene under the influence of microwave radiation. The proposed method of dehydrogenation is fundamentally different from the existing processes for producing butadiene by the method of supplying energy to the reaction zone, which significantly reduces energy consumption and simplifies the dehydrogenation process.

 Reducing energy costs during the industrial implementation of dehydrogenation reactions is the main problem, since it is necessary to deal with large thermal loads, since dehydrogenation is one of the least selective chemical reactions, and catalytic reactions, like thermal dehydrogenation reactions, are highly endothermic [5].

 In [1], a detailed description is given of the process for producing butadiene from butenes.

В результате дегидрирования все три изомерных бутена дают бутадиен-1,3

Тепловой эффект реакции - 113,7 кДж/моль.The butene dehydrogenation reaction is an equilibrium reaction and proceeds in the presence of catalysts according to the equation

As a result of dehydrogenation, all three isomeric butenes give butadiene-1,3

The thermal effect of the reaction is 113.7 kJ / mol.

Поэтому необходимо соблюдать условия, наиболее благоприятные для протекания основной реакции. К ним относятся применение избирательного катализатора и снижение парциального давления углеводородов, находящихся в зоне реакции.The main adverse reactions are the polymerization and pyrolysis of butadiene with the formation of lighter hydrocarbons and coke

Therefore, it is necessary to observe the conditions most favorable for the course of the main reaction. These include the use of a selective catalyst and a decrease in the partial pressure of hydrocarbons in the reaction zone.

 Many compounds are used as catalysts, in particular, oxides of magnesium, aluminum and chromium.

 Quite selective is the K-16u chromium-iron-zinc catalyst (TU 38.103155-85).

The optimum temperature for the dehydrogenation of butenes varies between 600 - 650 ^o C. At a lower temperature, the yields of butadiene and conversion are small. At a higher temperature, yields, despite a large conversion, are also unsatisfactory, which is associated with the occurrence of secondary pyrolysis processes.

 Reducing the partial pressure of butenes can significantly improve the equilibrium conditions and suppress side processes. To do this, dilute or dilute the reaction gas with inert diluents (nitrogen, carbon dioxide, water vapor).

In a widespread dehydrogenation technology in adiabatic reactors on a stationary layer of dehydrogenation catalysts, water vapor is used to introduce heat into the reaction zone, which is heated in furnaces to 700 - 750 ^o C. The butadiene fraction is also heated (up to 450 - 500 ^o C). Further, when the vapor-gas mixture enters the reactor, the catalyst is heated, mainly due to convective heat exchange with the vapor-gas mixture. The temperature in the reaction zone is set in the range of 600 - 650 ^o C.

 In contrast to the catalytic dehydrogenation technology described above, in the submitted application for the invention, instead of water vapor, the energy source uses a powerful microwave electromagnetic field (electromagnetic wavelength 1 <λ <10 cm) irradiating the reactor or generated in it. The electromagnetic radiation absorbed by the catalyst causes it to heat up, and in contact with unheated raw materials, a dehydrogenation process occurs. In a first approximation, without going into a description of the stages of the process and their flow rates, we can say that the process is inverse to the traditional technology, i.e., the catalyst is first heated, not raw materials and not a diluent.

 There is also known a method for the catalytic dehydrogenation of hydrocarbons, in particular, butene to butadiene using a low-frequency electromagnetic field [4].

 Unlike the latter, the proposed method uses high-frequency electromagnetic radiation, which, not dissipating in the walls of the reactor, acts on the catalyst, heating it. Upon contact of the feed with the heated catalyst, a dehydrogenation reaction occurs. Raw materials are used unheated.

The use of electromagnetic radiation as an energy carrier has a number of undeniable advantages:
1) the inertia of the impact. When the generator is turned on, there is an instant effect of microwave radiation on the substance, providing a high heating rate. When the generator is turned off, the effect of radiation on the substance instantly ceases;
2) transformation by a substance, in particular, a catalyst K-16u of electromagnetic energy into heat;
3) high coefficient of performance (COP), significantly exceeding the efficiency of traditional heating methods.

 As indicated above, the catalyst, absorbing the energy of the microwave field, is a source of thermal energy for the catalytic conversion of hydrocarbons. It is significant that this process of energy storage in the catalyst in the absence of heat removal and its dehydrogenation costs can lead to a gradual loss of some necessary properties of the catalyst (Table 1).

With prolonged exposure to the K-16u catalyst in the absence of hydrocarbons and diluent, for example, a certain decrease in its specific surface occurs, while the content of CrO ₃ in the catalyst slightly increases.

 Thus, in the process of catalytic dehydrogenation in a microwave field, it is necessary to balance the energy introduced by microwave radiation with the energy transferred through the catalyst to the endothermic dehydrogenation reaction, which was achieved using a number of well-known techniques.

 The nature of the heating of the K-16u catalyst in the microwave field can be judged by FIG. 1. A diagram of a laboratory setup for the catalytic dehydrogenation of butene in the microwave electromagnetic field is shown in FIG. 2.

The experiments are carried out as follows. Diluted with nitrogen, butene I through a dosing system at a temperature of 20 ^o C is fed into a vertical reactor 1, filled with catalyst K-16u. The reactor was made from a transparent quartz tube with a diameter of 20 mm and a wall thickness of 1.5 mm. The volume occupied by the catalyst in the reactor is 30 cm ³ . The reactor was installed in the resonator 2 of a microwave generator 3 (electromagnetic frequency 2450 MHz) with a power of 750 watts. A mixture of butene and nitrogen with a volumetric feed rate W (the ratio of gas volume to catalyst volume per unit time) is supplied to the reactor at atmospheric pressure when the mass-average temperature of the catalyst in the electromagnetic field is set in the range 500 - 540 ^o C. The products of reaction II are analyzed by chromatographic method, the temperature in the reaction zone is determined using an optical pyrometer 4 and a thermocouple 5. The power consumed by the microwave radiation generator is determined by the readings of ammeter 6 and voltmeter 7.

The experimental data are given in table. 2. As can be seen from the data table. 2, during catalytic dehydrogenation in a microwave field, a noticeable yield of butadiene is observed even at a temperature of 480 ^o C. At a temperature in the reaction zone of 520 ^o C, the yield of butadiene is more than 13 wt.%. A characteristic feature of this method of carrying out the dehydrogenation process is that the raw material does not require preheating, and this leads to an increase in the energy efficiency of the reactor.

 This installation of catalytic dehydrogenation of hydrocarbons under the influence of high-frequency electromagnetic radiation has an efficiency of 4.6%, which is 4 times higher than the efficiency of existing laboratory plants for catalytic dehydrogenation of hydrocarbons in adiabatic reactors with electric heating spirals, and also 2 times higher than the efficiency of industrial plants.

Claims (1)

 A method for the catalytic dehydrogenation of hydrocarbons, in particular butene to butadiene, using an energy carrier and exposure to electromagnetic radiation, characterized in that ultrahigh-frequency electromagnetic radiation is used as an energy carrier, which acts on the catalyst, followed by contacting the heated catalyst with the feedstock.

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