CS243932B1 - A method of plasma activation of tungsten or molybdenum oxide catalysts - Google Patents

Abstract

The invention relates to a method for activating oxide catalysts on a silica gel support. The essence of the invention lies in the direct exposure of the activated catalyst to the effects of low-temperature nitrogen or argon N2, Ar plasma of a high-frequency discharge in a fluidized bed at a pressure of 40 to 100 Pa.

Description

The present invention relates to a process for activating oxide catalysts on a silica gel support. SUMMARY OF THE INVENTION The subject of the invention is the direct exposure of the activated catalytic converter to the low-temperature nitrogen or argon N2, Ar plasma of the high-frequency discharge in the fluidized bed at a pressure of 40 to 100 Pa. 243932 2439 3

The present invention relates to a method of plasma activation of tungsten or molybdenum oxide catalysts on a silica gel support for disproportionate reactions.

Activation of the catalyst for the disproportionation reaction consists in heating it to the working temperature in stream N2 for 30 minutes and as a result of the action of the alkene at working temperature until the activity stabilizes, i.e., about 100 minutes. The procedure serves to eliminate catalytic poisons and to form active centers by reducing the energy of metal d-orbital by their interaction with the non-filled ligands. Examples of activation and their variations can be found in available literature, such as F. Adámek: Study of Propene Disproportionation on Heterogeneous Catalysts, Candidate Dissertation, Bratislava 1977, J. Horák, J. Pasek: Laboratory Chemical Industrial Reactor Design, SNTL, Praha 1980.

The disadvantage of classical activation is the long preparation time, high energy consumption (working temperature of the disproportionation reactors with oxide catalysts is about 400 ° C) and considerable gas consumption.

The above-mentioned drawbacks are eliminated to a great extent by the process according to the invention, characterized in that the catalyst is subjected to a low-temperature nitrogen or argon plasma of a high-frequency discharge of 10 to 15 MHz, preferably 12 MHz in a fluidized bed at a pressure of 40 to 100 Pa, flow rate 2 to 3.5.10 -4 m. with a temperature of neutral plasma particles of 75 to 150 degrees Celsius for 30 to 120 seconds, preferably 40 seconds.

The process of activating oxide catalysts in low temperature plasma is based on the simultaneous effect of all plasma components (electrons, metastabils, ions, heat, photochemical action) on the catalyst deposited on the SiO 2 carrier. The result is a reduction of oxides, a change in the surface structure of the silica gel, in particular the removal of some OH groups, water and siloxane bonds, and a change in the oxide distribution on the surface and in the catalyst pores. Advantages of the process of activating the oxide catalysts are to shorten the activation period of the catalyst preparation by up to 2/3 of the equilibrium degree of conversion at less than 4 times the spatial time, allowing to increase the yield of dispropononating reactors, increase catalyst life and suppress the formation of active centers during dimerization and cracking . The composition of the disproportionation products is more shifted to ethylene formation.

SUMMARY OF THE INVENTION The following examples illustrate the invention. Přikladl

Prepare a catalyst such as 5% by weight in a fluidization reactor. WO3 / SiO2. Set the flow N2 to 3.10 “4 m3. s_1 and create a 10 MHz RF discharge over the fluidized layer. The column pressure reaches 60 Pa and the neutral gas temperature is 103 ° C at 460 W. After 30 seconds of exposure, the catalyst is placed in a reactor in which it is activated in the stream of alkene until constant activity is obtained. Steady-state conversion is achieved at 5 times lower spatial time values. Example 2

The procedure is as in Example 1, except that the exposure time is 120 seconds. Example 3

The procedure is as in Example 1, except that the power of the RF plasma generator is 800 W and the neutral gas temperature is 150 degrees Celsius. Example 4

The procedure is as in Example 3, except that the exposure time is 120 seconds. Example 5

The procedure is as in Examples 1 to 4 except that argon is used as the plasma-forming gas. Compared to other examples, the equilibrium degree of conversion is achieved at 4x lower spatial time values.

Claims (1)

The following Examples illustrate the invention. EXAMPLE In the fluidization reactor, prepare a catalyst e.g. 5% w / w WO ₃ / SiO ₂ . Set the flow rate N ₂ to 3.10 “ ⁴ m ³ . s ^_1 and create a 10 MHz discharge over the fluidized HF layer. The column pressure is 60 Pa and the neutral gas temperature is 103 ° C at 460 W. After 30 seconds of exposure, the catalyst is placed in a reactor in which it is activated in the alkene stream until constant activity is achieved. The equilibrium degree of conversion is achieved at 5x lower spatial time values. Example 2 The procedure is as in Example 1, except that the exposure time is 120 seconds. EXAMPLE 1 a d 3 The procedure is as in Example 1, except that the RF generator power input is 800 W and the neutral gas temperature is 150 degrees Celsius. Example 1 4 The procedure is as in Example 3, except that the exposure time is 120 seconds. Example 5 The procedure is as in Examples 1-4, except that argon is used as the plasma forming gas. Compared to the other examples, the equilibrium degree of conversion is achieved at 4x lower spatial time values. SUBJECT A process for the plasma activation of tungsten or molybdenum oxide catalysts on a silica gel support for the disproportionation of alkenes, characterized in that the catalyst is treated with a low temperature nitrogen or argon plasma of a high frequency discharge of 10-15 MHz, preferably 12 MHz in a fluidized bed pressure of 100 Pa, flow rate 2 to 3.5.10 ^-4 m. ^s1 and a neutral plasma particle temperature of 75-150 ° C for 30-120 seconds, preferably 40 sec.