RU2612305C1 - Method for oxidative conversion of ethane into ethylene - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method comprises feeding ethane to a dehydrogenation reactor, where it contacts with a dehydrogenation catalyst based on metals oxides, the catalytic dehydrogenation of ethane at increased temperature, the separation of the reaction products from the recovered catalyst, feeding the recovered catalyst after separation from the reaction products into the oxidation reactor, the oxidation of the recovered catalyst with atmospheric oxygen at increased temperature in a fluidized bed, which is created by transport nitrogen in the oxidation reactor, the separation of gas mixtures containing exhaust air and transport nitrogen from the regenerated oxidized catalyst, and its returning to the dehydrogenation reactor. Said catalyst is represented by vanadium pentoxide on γ-Al₂O_3, or a mixed oxide of metals Mo-Te-Nb-V on γ-Al₂O₃, or chromium oxide (III) on γ-Al₂O₃ or a mixed oxide of metals V-Mo onγ-Al₂O₃, or a mixed oxide of metals Ni-Mo on γ-Al₂O₃; the catalyst circulation multiplicity defined as the ratio of the mass of the catalyst to the mass of the raw material fed into the reactor is 10÷15, the catalytic ethane dehydrogenation is carried out at a temperature of 500-700°C, the gas flow conveying the oxidized regenerated catalyst and containing exhaust air and transport nitrogen is removed from the system as technical nitrogen.

EFFECT: using the proposed method allows to provide explosion and fire safety of the ethane conversion to ethylene and the sufficient ethane conversion, the process stability, to increase selectivity as per ethylene, to obtain technical nitrogen together with the ethylene without using special devices for air separation.

3 cl, 1 dwg, 2 tbl, 14 ex

Description

The invention relates to methods for producing ethylene from ethane by catalytic oxidative conversion with a separate supply of raw materials and an oxidizing agent and the simultaneous production of technical nitrogen from the air and can be used in the chemical and petrochemical industries.

Currently, much attention is paid to the development of processes for the catalytic conversion of ethane and propane to the corresponding olefins. The catalytic conversion of ethane to ethylene is reversible; therefore, the yield of conversion products is limited by thermodynamic equilibrium, and relatively high temperatures (up to 700 ° C) are required to produce ethylene. The conversion of hydrocarbons at such temperatures is accompanied by thermal cracking, which reduces the selectivity of the process and leads to the necessity of carrying out the process at a sufficiently low conversion of ethane to maintain high selectivity for ethylene (80-95%). Intensive coke formation on the surface of the catalysts during the reaction leads to a decrease in the activity and selectivity of the catalysts and necessitates oxidative regeneration, and the regeneration and recovery time of the catalyst often exceeds the useful life.

These disadvantages are eliminated when used in the process of an oxidizing agent. The use of an oxidizing agent in the conversion of lower alkanes to olefins has several advantages: increasing the yield of the product, lowering the reaction temperature due to its exothermicity, increasing the useful life of the catalyst due to the possible burning of coke during the reaction. However, this path also causes a number of technological problems:

- high energy and capital intensity of the process: the implementation of the oxidative conversion of ethane to ethylene using oxygen as an oxidizing agent requires additional capital costs for the release of oxygen from the air and the organization of explosion-proof production, and when using air as an oxidizing agent, the reaction products include ballast nitrogen, which requires additional costs for its allocation;

- the explosiveness of the ethane-oxygen mixture.

In this regard, the most appropriate technology is the oxidative conversion of ethane to ethylene with a separate supply of raw materials and an oxidizing agent, which ensures the explosion safety of the process.

In known methods for the conversion of ethane to ethylene with a separate supply of raw materials and an oxidizing agent, it is usually carried out using:

- reactors of a special design with separate tubes or channels for supplying raw materials and an oxidizing agent, which requires capital expenditures for the conversion of existing reactors and solves the explosion safety problem only partially - at the stage of supplying raw materials and an oxidizing agent, while ethane and an oxygen-containing gas are directly mixed in the reaction zone, and does not solve the problem of isolating ballast nitrogen from reaction products;

- pulsed alternate supply of raw materials and oxidizing agent, which reduces the productivity and stability of the process due to the inability to ensure its continuity;

- membranes, the use of which makes the process more expensive, and also disrupts its continuity due to the need to regularly clean the membranes from coke and other impurities that have settled on it, as well as restore their activity.

A complex multi-zone method is known for converting C2-C4 alkanes to the corresponding alkenes, including ethane to ethylene, including the exothermic conversion of alkanes to alkenes by oxidative dehydrogenation in the exothermic reaction zone in the presence of oxygen and a catalyst and feeding products from this zone to the endothermic reaction zone, where part unconverted alkanes are endothermally dehydrated in the presence of CO ₂ and catalyst. The oxidative dehydrogenation catalyst contains at least one catalyst composition selected from: A) a catalyst containing one or more noble metals selected from Pt, Pd, Rh, Ir and Ru; C) a catalyst containing one or more metal oxides selected from Li, Mo, W, V, Nb, Sb, Sn, Ga, Zr, Mg, Mn, Ni, Co, Ce and rare-earth metals, and contains a monolith support, such as pieces of metal or metal oxide, foam, cellular structure, including alumina. Examples of catalysts include WNb / Si / O _x and V ₂ O ₅ / Al ₂ O ₃ on cordierite. Oxygen-containing gas is supplied to the exothermic reaction zone separately from alkane C2-C4 (see, application US 2008/177117 A, publ. 24.07.2008, class IPC C07C 5/333).

Thanks to the use of effective catalysts and a two-stage process, complete oxygen conversion and an increase in the yield of olefins are achieved. However, in this method, the safety problem is solved only at the stage of supplying the raw materials and oxidizing agent to the reactor. In the exothermic zone, the oxygen-containing gas and ethane are directly mixed, which leads to the risk of the formation of an explosive mixture. In addition, when not expensive purified oxygen, but air, is used as an oxidizing agent, the raw material mixture contains up to 85% nitrogen, which is then removed with the reaction products and must be separated from them.

Closest to the claimed invention is a method for producing ethylene from ethane by oxidative conversion with separate supply of saturated hydrocarbon and oxygen at elevated pressures. Mixed compounds based on non-stoichiometric rare earth oxycarbonate are preferably used as catalysts, but oxides or other reducible compounds Sn, Pb, Bi, Tl, Cd, Mn, Sb, Ge, In, Ru, Pr, Ce, Fe, Tb can also be used. , Cr, Mo, Re, W, V. In the redox mode, lower alkanes and oxygen are not directly mixed. The active phase of the catalyst on an oxygen substrate is subjected to cyclic oxidation and reduction reactions, so that the catalyst alternately contacts the oxidizing agent and lower alkane. Lower alkanes react with bound oxygen and reduce the catalyst. Since lower alkanes do not come into contact with gaseous oxygen, homogeneous oxidation is suppressed and the safety of alkane conversion is significantly increased. Dehydrogenation of ethane and oxidation of the catalyst is carried out in two different reactors, which ensures the continuity of the process and the ability to carry out each of its stages under optimal conditions. After dehydrogenation, the reduced catalyst is fed to an oxidation reactor using a transport (purge) inert gas stream such as nitrogen. After oxidation, the catalyst is separated from the air and returned to the dehydrogenation reactor. Suitable reactors may be fluidized bed reactors. The exhaust air is subjected to multi-stage cooling and expansion, using its energy, and then discarded. The conversion of lower alkanes is usually not more than 40%, but can reach 80% (see, WO 02/24614 A1, publ. March 28, 2002, class IPC C07C 11/02, C07C 2/84, C07C 5/48, C07C 7/152).

In the known method, atmospheric oxygen is not completely consumed in the process — about 15-30% of the oxygen remains not converted. Reuse only the heat of the heated exhaust air. The exhaust air itself, depleted of oxygen after oxidation of the catalyst and containing contaminants, is not used in the future, emitting it as exhaust gas. In addition, the olefin selectivity is low - the molar ratio of olefin to alkane by-product is 1: 1 - 2.5: 1 with a total selectivity of 40-70%.

From the prior art it is unknown the simultaneous production of ethylene and technical nitrogen in the process of oxidative conversion of ethane.

The objective of the invention is, while ensuring the explosion and fire safety of the conversion of ethane to ethylene, to increase the selectivity for ethylene, to ensure process stability and the most complete utilization of air used as an oxidizing agent. The latter is ensured by the almost complete conversion of atmospheric oxygen, after which the exhaust air is removed as technical nitrogen, which can then be returned to the cycle or used as an additional commercial product along with ethylene. In this way, production nitrogen is also provided without costly air separation. The stability of the process is ensured by using a reactor-regenerator system using a microspherical catalyst, similar to the catalytic cracking technology of vacuum gas oil, which is widely used in oil refineries around the world [V. Kapustin Chemistry and oil refining technology / M., Chemistry, 2013].

The problem is solved in that in a method for the oxidative conversion of ethane to ethylene, comprising supplying ethane to a dehydrogenation reactor, where it is in contact with a metal oxide-based dehydrogenation catalyst, catalytic dehydrogenation of ethane at elevated temperature, separating the reaction products from the reduced catalyst, feeding the reduced catalyst after separation from reaction products into the oxidation reactor, oxidation of the reduced catalyst with atmospheric oxygen at an elevated temperature in pseudo izhennom layer which creates transport nitrogen in an oxidation reactor, separation of gas mixtures containing exhaust air and the transport of nitrogen from the regenerated oxidized catalyst and return it to the dehydrogenation reactor, as said catalyst is a vanadium pentoxide on γ-Al ₂ O ₃ or a mixed metal oxide Mo-Te-Nb-V on γ-Al ₂ O ₃ , or chromium (III) oxide on γ-Al ₂ O ₃ , or mixed metal oxide V-Mo on γ-Al ₂ O ₃ , or mixed metal oxide Ni-Mo on γ-Al ₂ O ₃ , the ratio of the circulation of the catalyst, defined as the ratio the mass of the catalyst to the mass of the feed to the reactor is 10-45, the catalytic dehydrogenation of ethane is carried out at a temperature of 500-700 ° C, the gas stream transporting the regenerated oxidized catalyst and containing exhaust air and transport nitrogen is removed from the system as technical nitrogen.

The multiplicity of circulation is defined as the ratio of the mass of the catalyst to the mass of raw materials supplied to the reactor [Khadzhiev S.N. Cracking of oil fractions on zeolite-containing catalysts / M.: Chemistry, 1982].

The oxidation of the reduced catalyst is carried out at a temperature of 500-700 ° C.

Part of the extracted technical nitrogen can be returned to the cycle as transport nitrogen.

The short contact time of the feedstock and catalyst, which corresponds to a catalyst circulation of 10-45, contributes to the process in the through flow mode, which ensures high ethane conversion and at the same time high ethylene selectivity. The through flow mode is described, in particular, in the book of S. Khadzhiev. Cracking of oil fractions on zeolite-containing catalysts / M .: Chemistry, 1982. A further increase in the catalyst circulation rate is undesirable, since it leads to increased catalyst attrition and wear of the reactor equipment, as well as a decrease in ethylene selectivity associated with an excess of lattice oxygen in the catalyst composition into the reactor at high multiples of catalyst circulation.

In FIG. 1 is a schematic diagram of the process of oxidative conversion of ethane to ethylene with a separate supply of raw materials and an oxidizing agent.

Vanadium pentoxide on γ-Al ₂ O _{3 is} obtained by impregnating γ-Al ₂ O _{3 with a} vanadium pentoxide precursor (for example, a solution of vanadium acetylacetonate in toluene), followed by drying and calcination. A mixed Mo-Te-Nb-V oxide on a γ-Al ₂ O ₃ support is obtained by impregnating the support with a reaction mixture of ammonium molybdotellurate, vanadyl sulfate and niobium oxalate taking into account moisture absorption, followed by drying and calcination. The Cr ₂ O ₃ / Al ₂ O ₃ catalyst is prepared by spray-drying a suspension obtained from aluminum hydroxide, chromium (III) oxide and water, followed by heat treatment. The V-Mo / γ-Al ₂ O ₃ catalyst is obtained by impregnating γ-Al ₂ O _{3 with a} precursor of vanadium pentoxide (for example, a solution of vanadium acetylacetonate in toluene), followed by drying and calcination and further application of (NH ₄ ) ₆ Mo ₇ O ₂₄ ⋅ 4H ₂ O in an alkaline medium according to the moisture absorption of the carrier, followed by drying and calcination. The Ni-Mo / γ-Al ₂ O ₃ catalyst is obtained by applying (NH ₄ ) ₆ Mo ₇ O ₂₄ ⋅ 4H ₂ O in an alkaline medium by moisture absorption of the support on γ-Al ₂ O ₃ , followed by drying and calcining and further applying a nitrate solution nickel, followed by drying and calcination.

The resulting catalysts are a microspherical powder with an average particle size of 120 microns.

Raw materials - ethane - are fed to the lower part of the dehydrogenation reactor (1), which is a vertical cylindrical apparatus, where it is in contact with the catalyst. The multiplicity of the circulation of the catalyst is 10 ÷ 15.

An ethane dehydrogenation reaction is carried out in the reactor to produce ethylene at an optimum temperature of 600 ° C:

with simultaneous recovery of the catalyst.

The mixture of reaction products containing ethylene, reaction by-products (methane, water, CO and CO ₂ ), and spent (recovered) catalyst from the dehydrogenation reactor are fed to the separator of the dehydrogenation reactor (2) for separation. After separation from the catalyst, reaction products containing ethylene are removed from the unit. The spent catalyst enters the oxidation reactor (3), which also serves air and transport nitrogen to create a fluidized bed and transport. The spent catalyst in the oxidation reactor is saturated with lattice oxygen by contact with hot air, which leads not only to oxidation, but also to the removal of coke deposits from the catalyst surface. The oxidation of the catalyst occurs at a temperature of 600 ÷ 650 ° C in a fluidized bed, which is supported by the flow of air and nitrogen. The resulting gas mixture carrying the regenerated catalyst from the oxidation reactor is separated in the separator of the oxidation reactor (4) from the catalyst. The catalyst is transported through a transport line to a dehydrogenation reactor (1), and a gas containing mainly nitrogen is removed from the system as technical nitrogen. Since all the incoming oxygen in the air is used in the process of oxidation of the catalyst, a stream of industrial nitrogen leaves the unit. Its purity is further increased due to the fact that the transport stream that enters the oxidation reactor and mixes with air in it is nitrogen.

Process nitrogen can be recycled as a transport stream (not shown).

The implementation of the invention is confirmed by the following examples.

Example 1

Use a catalyst containing 10% V ₂ O ₅ / Al ₂ O ₃ . The catalyst is an orange microspherical powder. The characteristics of the catalyst are shown in table 1 (sample 1).

The dehydrogenation is carried out at a temperature of 600 ° C and the catalyst circulation rate determining the oxygen to ethane ratio of 10. The reaction products together with the catalyst enter the dehydrogenation reactor separator and are discharged as a product. Spent (recovered) catalyst is sent to the oxidation reactor. The spent catalyst is oxidized with air at 600 ° C in a fluidized bed. From there, a gas mixture containing exhaust air — a gas mainly containing nitrogen and transport nitrogen — together with the catalyst, enters the separator of the oxidation reactor. The regenerated catalyst is returned to the dehydrogenation reactor and the second product, technical nitrogen, is removed.

The results of the process are presented in table 2.

Example 2

The ethane conversion is carried out analogously to example 1, but using a catalyst containing 20% V ₂ O ₅ / Al ₂ O ₃ . The catalyst is an orange microspherical powder with an average particle size of 120 microns. The characteristics of the catalyst are shown in table 1 (sample 2).

The results of the process are presented in table 2. The conversion of ethane to 20% V ₂ O ₅ / Al ₂ O ₃ oxide-metal system is slightly higher compared to a 10% V ₂ O ₅ / Al ₂ O ₃ sample, under the same experimental conditions, with selectivity decreases, apparently due to the intensification of oxidation reactions with increasing lattice oxygen content in the catalyst.

Example 3

The ethane conversion is carried out analogously to example 1, but using a catalyst containing a mixed oxide of 10% Mo-Te-Nb-V / Al ₂ O ₃ . The characteristics of the catalyst are shown in table 1 (sample 3).

The results of the process are presented in table 2. The experimental data indicate the effectiveness of the mixed oxide Mo-Te-Nb-V as a selective catalyst for the conversion of ethane to ethylene: selectivity for C ₂ H ₄ reaches 92%.

Example 4 (comparative).

The ethane conversion is carried out analogously to example 3, but the dehydrogenation temperature is 450 ° C.

The results of the process are presented in table 2. A decrease in the reaction temperature to 450 ° C leads to a decrease in the conversion of ethane to 5 wt. %

Example 5

The ethane conversion is carried out analogously to example 3, but the dehydrogenation temperature is 700 ° C.

The results of the process are presented in table 2. An increase in the reaction temperature leads to an increase in ethane conversion with a certain decrease in the selectivity of ethylene formation.

Example 6

Carry out the conversion of ethane as in example 3, but the multiplicity of circulation of the catalyst is 15.

The results of the process are presented in table 2.

Example 7

The ethane conversion is carried out analogously to example 3, but the temperature of the oxidation reactor is 500 ° C.

The results of the process are presented in table 2.

Example 8

The ethane conversion is carried out analogously to example 3, but the temperature of the oxidation reactor is 700 ° C.

The results of the process are presented in table 2.

Example 9

Carry out the conversion of ethane analogously to example 3, but the multiplicity of circulation of the catalyst is 12.

The results of the process are presented in table 2.

Example 10

The ethane conversion is carried out analogously to example 1, but using a catalyst containing mixed 4% Cr ₂ O ₃ / Al ₂ O ₃ . The characteristics of the catalyst are shown in table 1 (sample 4).

The results of the process are presented in table 2.

Example 11

The ethane conversion is carried out analogously to example 1, but using a catalyst containing 10% V ₂ O ₅ + 4,5% MoO ₃ / Al ₂ O ₃ . The characteristics of the catalyst are shown in table 1 (sample 5).

The results of the process are presented in table 2.

Example 12

The ethane conversion is carried out analogously to example 1, but using a catalyst containing 10% V ₂ O ₅ + 7.5% MoO ₃ / Al ₂ O ₃ . The characteristics of the catalyst are shown in table 1 (sample 6).

The results of the process are presented in table 2.

Example 13

The ethane conversion is carried out analogously to example 1, but using a catalyst containing 10% V ₂ About ₅ + 10.5% MoO ₃ / Al ₂ O ₃ . The characteristics of the catalyst are shown in table 1 (sample 7).

The results of the process are presented in table 2.

Example 14

The ethane conversion is carried out analogously to example 1, but using a catalyst containing 4% MO + 4.3% MoO ₃ / Al ₂ O ₃ . The characteristics of the catalyst are shown in table 1 (sample 8).

The results of the process are presented in table 2.

As can be seen from the table. 2, in all cases of the invention, both ethylene and technical nitrogen are obtained with an impurity content of 0.7-0.9% by volume.

Claims (3)

1. The method of oxidative conversion of ethane to ethylene, comprising feeding ethane to a dehydrogenation reactor, where it is contacted with a metal oxide-based dehydrogenation catalyst, catalytic dehydrogenation of ethane at elevated temperature, separating the reaction products from the reduced catalyst, feeding the reduced catalyst after separation from the reaction products in oxidation reactor, oxidation of the reduced catalyst with atmospheric oxygen at an elevated temperature in the fluidized bed created by transp ortho nitrogen in the oxidation reactor, separating the mixture of gases containing exhaust air and transport nitrogen from the regenerated oxidized catalyst and returning it to the dehydrogenation reactor, characterized in that the catalyst is used vanadium pentoxide on γ-Al ₂ O ₃ , or a mixed oxide Mo-Te-Nb-V metals on γ-Al ₂ O ₃ , or chromium (III) oxide on γ-Al ₂ O ₃ , or mixed V-Mo metal oxide on γ-Al ₂ O ₃ , or mixed metal oxide Ni -Mo on γ-Al ₂ O ₃ , the ratio of the circulation of the catalyst, defined as the mass ratio of the catalyst and the mass of feed to the reactor is 10-15, the catalytic dehydrogenation of ethane is carried out at a temperature of 500-700 ° C, the gas stream transporting the regenerated oxidized catalyst and containing exhaust air and transport nitrogen is removed from the system as technical nitrogen. 2. The method according to p. 1, characterized in that the oxidation of the reduced catalyst is carried out at a temperature of 500-700 ° C. 3. The method according to p. 1, characterized in that part of the extracted technical nitrogen is returned to the cycle as transport nitrogen.

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