RU2528830C1 - Method of producing ethylene - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to a method of producing ethylene via oxidative dehydrogenation of ethane in a gaseous mixture of oxygen and ethane at high temperature in the presence of a mixed oxide catalyst of the composition Mo_1.0V_0.37Te_0.17Nb_0.12O₃ in a flow reactor. The reactor further includes a selective carbon monoxide oxidation catalyst, which is gold or rhodium on a titanium dioxide support, with the following ratio of components, wt %: gold 0.05-0.3, rhodium 0.5-1.0 and titanium dioxide - the balance, wherein the mixed oxide catalyst is located at the gaseous material inlet, and the selective carbon monoxide oxidation catalyst is located further downstream of the gas stream and the catalysts are taken in volume ratio of 80-90 and 20-10, respectively.

EFFECT: use of the disclosed method enables to achieve high conversion of oxygen, which facilitates further separation of ethylene from the reaction mixture and also makes reaction gaseous mixtures less explosive; the proposed volume ratio of catalysts loaded into the reactor enables to combine two reactions in a single process to obtain ethylene with a minimum amount of undesirable impurities.

4 cl, 4 ex, 1 tbl

Description

The invention relates to a technology for processing hydrocarbon feedstocks, in particular, to a method for producing ethylene from ethane, ethane-containing gases of thermal and catalytic cracking, the use of a combined two-layer catalyst allows to achieve increased oxygen conversion, which facilitates the further evolution of ethylene from the reaction mixture, and also makes reaction gas mixtures are less explosive.

Catalytic oxidative dehydrogenation of ethane (ODE) as an available gaseous hydrocarbon feed is the most efficient way to produce ethylene for several reasons. Unlike non-oxidative dehydrogenation, the catalytic process is carried out at lower temperatures. By-products of the reaction are carbon monoxide and dioxide. In oxidative dehydrogenation of ethane, deactivation of catalysts due to coking is minimal due to the presence of oxygen in the initial reaction mixture. At the same time, during the ODE reaction, the oxygen conversion on all known catalysts is incomplete, which significantly complicates the further evolution of ethylene from the reaction gases.

The most effective is the method of oxidative dehydrogenation of light paraffins, namely ethane, using catalysts consisting of a mixture of molybdenum, vanadium and transition metal oxides (E.M. Thorsteinson et al., "The Oxidative Dehydrogenation of Ethane over Catalyst Containing Mixed oxide of Molybdenum and Vanadium, "J. Catalysis, 1978, v. 52, p. 116). However, this method does not allow to obtain the target products with high yield and selectivity.

US Pat. Nos. 4,524,236 and 4,899,003 describe the ODE method, where already in the range of moderate temperatures of 375-400 ° C on mixed oxide catalysts of the composition V-Mo-Nb-Sb-O _x ethane conversion reached 70% with ethylene selectivity 71-73 % However, these parameters were achieved only at very low volumetric flow rates of the gas mixture (up to 720 h ^-1 ).

International patent application WO 03/064035 describes a method for the oxidative dehydrogenation of ethane on mixed oxide catalysts of the composition Mo-V-Te-Nb-O _x , which provide a high 50-70% ethane conversion at moderate temperatures of 360-420 ° C. However, in the proposed method, increased selectivity for ethylene (up to 95%) is achieved only with a low conversion of ethane (up to 38%).

A common drawback of the known ODE methods is that the oxygen conversion does not exceed 90%, which complicates its further separation from C ₂₊ hydrocarbons, including from ethylene, and also makes reaction gas mixtures explosive.

Closest to the present invention is RF patent No. 2358958, which describes a method for producing ethylene by oxidative dehydrogenation of ethane, in which a gas mixture containing oxygen and ethane in a ratio of 1: 2.5 to 1: 3.5 is supplied at a pressure of 1 atm with a bulk velocity of 500-30000 h ^-1 into a flow reactor with a stationary layer of a heterogeneous catalyst based on oxides or mixed oxides of transition metals selected from the group consisting of Mo, V, Te, Nb, heated to 380-420 ° C. EFFECT: increased productivity of the oxidative dehydrogenation process while maintaining high ethane conversion and selectivity for C ₂ hydrocarbons.

A significant disadvantage of the proposed method is that even with a stoichiometric lack of oxygen in a mixture with ethane (O ₂ : C ₂ H ₆ in the range from 1: 2.5 to 1: 3.5) and a maximum temperature (420 ° C), oxygen conversion in a number of examples it did not exceed 90%, and its content in the reaction gas in some cases exceeds 4% vol. In addition, a by-product of carbon monoxide (up to 2% vol.) Is present in the reaction gas. The presence of these impurities (O ₂ and CO) in the reaction gas significantly complicates the further isolation of the target reaction product, ethylene, since the kinetic diameters of these molecules are similar, and also makes the reaction mixtures toxic and explosive.

The objective of the present invention is to improve the method of producing ethylene, which provides almost complete conversion of oxygen, which simplifies the selection of the target reaction product - ethylene, and also makes the process safer.

The goal is achieved by the method of producing ethylene by oxidative dehydrogenation of ethane in a gas mixture of oxygen and ethane at elevated temperature in the presence of a mixed oxide catalyst of the composition Mo _1.0 V _0.37 Te _0.17 Nb _0.12 O ₃ in a flow reactor, the distinguishing feature of which is that the reactor additionally contains a selective a carbon monoxide oxidation catalyst, which is gold and rhodium on a support — titanium dioxide in the following ratio of components, wt.%: gold 0.05-0.3, rhodium 0.5-1.0 and dioxide Titan - the rest, wherein the mixed oxide catalyst is located on the raw gas inlet, and selective oxidation of carbon monoxide catalyst located downstream of the gas stream and wherein the catalysts are taken in a volume ratio equal to 80-90 and 20-10, respectively.

The process is carried out at a temperature of 380-420 ° C, atmospheric pressure and a volumetric feed rate of gas raw materials in the range of 500-30000 h ^-1 , and the mixture is oxygen: ethane, taken in a ratio of 1: 2.5-3.5, respectively.

It should be noted that when using the proposed method, the yield and selectivity for C ₂ hydrocarbons, including ethylene, practically do not decrease, and a significant decrease in the concentration of oxygen in the reaction gases at the outlet of the reactor is achieved as a result of the fact that at the outlet of the ODE catalyst layer a selective carbon monoxide oxidation catalyst is located, which is present in the reaction gas as a by-product.

The traditional mixed oxide Mo _1.0 V _0.37 Te _0.17 Nb _0.12 O ₃ the ODE reaction catalyst is prepared by one of the known methods, for example, by sequentially mixing aqueous solutions of molybdenum tellurate, vanadium sulfate and niobium oxalate, with the addition of an aqueous solution of vanadium sulfate to the molybdenum tellurate solution, after stirring, a suspension is obtained, a solution of niobium oxalate is introduced into it, the resulting mixture is further intensively stirred for 10 minutes, kept in an autoclave at 175 ° C for 50 hours and after filtration and washing of the product pour at 600 ° C in a stream of inert gas.

The procedure for preparing the Au + Rh / TiO ₂ catalyst for the selective oxidation of carbon monoxide includes the steps of deposition and fixing of the rhodium precursor on the surface of titanium oxide, and reduction of the precursor particles to nanoparticles of rhodium metal. Gold is applied to rhodium particles by adding a solution of a gold compound to a reduced sample of rhodium on titanium oxide in the mother liquor or in water under a hydrogen-containing atmosphere.

The objective of the present invention is to improve the method of oxidative conversion of ethane to produce ethylene in the ethane-ethylene fraction with a significantly lower residual oxygen content and carbon monoxide formed during the ODE reaction, which facilitates the subsequent separation of the reaction gas into components. The problem is solved using a two-component (two-layer) catalyst, characterized in that the oxidative dehydrogenation of ethane with the formation of ethylene, oxide and carbon dioxide proceeds on the first (frontal) catalyst layer, consisting of a mixed Mo _1.0 V _0.37 Te _0.17 Nb _0.12 O ₃ oxide , and then on the second (in the direction of movement of raw material gas) catalyst layer Au + Rh / TiO ₂ unreacted oxygen at the same temperature selectively react with those present in the reaction mixture with carbon monoxide to form CO _2, thus without watching etsya any oxidation of ethane and ethylene. An essential feature of the present invention is also the proposed volume ratio of the catalysts loaded into the reactor, which made it possible to combine two reactions in one process to produce ethylene with a minimum amount of undesirable impurities.

The invention is illustrated by the following examples.

Example 1

The preparation of the catalyst is the reaction of oxidative dehydrogenation of ethane.

As the catalyst for the ODE reaction, Mo _1.0 V _0.37 Te _0.17 Nb _0.12 O ₃ powder is used, prepared according to the RF patent No. 2358958, which we selected for the prototype.

The mixed oxide Mo-V-Te-Nb-O _n catalyst, which is active in the oxidative dehydrogenation of ethane to ethylene, was obtained by hydrothermal synthesis: 6.4 g of ammonium molybdotellurate was suspended in 21.3 g of water at 80 ° C. A solution of 2.4 g of vanadyl sulfate in 10 ml of water is added to the resulting suspension, then a solution of 2.3 g of niobium oxalate in 10 ml of water is added to the resulting mixture. The mixture is stirred for 10 minutes and transferred to a stainless steel autoclave with an inner liner of Teflon® (tetrafluoroethylene). The air in the autoclave is replaced with an inert gas, the autoclave is sealed and heated to 175 ° C. The autoclave is maintained at a predetermined temperature for 48 hours and then cooled to room temperature. The solid precipitate formed in the autoclave as a result of hydrothermal synthesis is filtered off, washed with distilled water until the wash water becomes discolored and dried at 80 ° C. Next, the precipitate is calcined in a stream of inert gas at 600 ° C for 2 hours (heating rate from room temperature is 2 ° C / min). The obtained powder of the ODE catalyst according to chemical analysis has the following composition Mo _1.0 V _0.37 Te _0.17 Nb _0.12 O ₃ .

Preparation of a catalyst for the selective oxidation of carbon monoxide.

The rhodium salt RhCl ₃ · 3H ₂ O (0.069 g) is dissolved in 200 ml of distilled water at room temperature. To the resulting solution, 5.4 g of titanium oxide powder are added in one portion. With vigorous stirring, a 1 M Na ₂ CO ₃ solution was added dropwise to pH = 6.7. The concentration of rhodium in the resulting solution is 1.3 mmol L ^-1 . The suspension is kept for 12 hours at 20 ° C, maintaining the pH by adding 1 M Na ₂ CO ₃ solution. The suspension is heated to 95 ° C and incubated for another 1 hour. After that, the flask with the suspension was purged with hydrogen with stirring for 2 hours at 95 ° C, then cooled to room temperature and continued to stir for another 1 hour to saturate rhodium with hydrogen. With stirring turned on, without depressurization of the system, a 0.24 M HAuCl ₄ solution (0.38 ml) was added to the flask and stirring was continued for 1 hour. The resulting suspension is filtered, the precipitate is washed on the filter with water and dried in an oven at 60 ° C.

The composition of the resulting catalyst is 0.3% Au + 0.5% Rh / TiO ₂ .

Then, 1 ml of 0.3% Au + 0.5% Rh / TiO ₂ catalyst was loaded into the lower reactor layer, and then 9 ml of Mo _1.0 V _0.37 Te _0.17 Nb _0.12 O ₃ catalyst were added to the top. The ratio of the layers of 2 catalysts (in vol.%) Was 10 and 90, respectively.

Example 2

The catalysts were prepared according to example 1, except that in the preparation of the catalyst for selective oxidation of carbon monoxide, the weight of the rhodium salt was 0.138 g, 0.24 M HAuCl ₄ solution (0.065 ml) was added, and the pH was maintained with 1 M NaOH solution.

The composition of the obtained catalyst is 0.05% Au + 1% Rh / TiO ₂ .

In addition, at the stage of reactor loading, the ratio of the layers of 2 catalysts (in vol.%) Was 20 and 80, respectively.

Examples 3-4.

The catalysts obtained in examples No. 1 and 2 are tested in the method of producing ethylene proposed in the present invention (table).

A mixture of ethane and oxygen, containing oxygen and ethane in a ratio of 1: 2.5-3.5, was fed at atmospheric pressure into a flow reactor (quartz tube D = 20 mm) with a stationary catalyst bed with a bulk velocity of 500-30000 h ^-1 . The loading of the two-layer catalyst was 10 ml; in this case, a Mo _1.0 V _0.37 Te _0.17 Nb _0.12 O ₃ layer was placed at the inlet of the gas feedstock, followed by an Au + Rh / TiO ₂ layer along the gas stream.

The process of oxidative dehydrogenation of ethane was carried out in the temperature range of 380-420 ° C. The temperature of the catalyst layer in the reactor was measured using a thermocouple placed in a quartz glass directly in the middle of the catalyst layer.

The temperature in the catalyst bed was measured using a thermocouple placed in a quartz cup mounted in the reactor (coaxially in the center of the quartz reactor). At the outlet of the reactor, there was a trap cooled to 0 ° C to collect the resulting water. The gas at the outlet of the reactor (in% vol.) Was analyzed on a Model 3700 chromatograph using a fixed volume loop on a 3 m HayeSep-Q packed column (СО ₂ , С ₂ Н ₄ , С ₂ Н ₆ ), and gases (O ₂ , CO) were analyzed on a 2 m 5A molecular sieve column using a katharometer detector in isothermal mode at 50 ° C.

The table shows the conditions for the ODE reaction, the composition of the reaction gas at the outlet of the reactor, and oxygen conversion.

Table Example No. T, ° C The ratio of O ₂ : C ₂ H ₆ in raw materials Volumetric speed, h ^-1 The composition of the reaction gas vol.% The conversion of O ₂ % O ₂ C ₂ H ₄ C ₂ H ₆ CO CO ₂ Total 3 380 * 1: 2.5 500 3.31 36.33 58.04 1.74 0.58 100.0 91.2 380 1: 2.5 500 0.06 37.55 59,99 0.10 2,31 100.0 99.85 420 1: 3,5 500 0.01 48.81 49.20 0.04 1.94 100.0 99.95 four 420 * 1: 3,5 30000 4.19 28.05 65.15 1.95 0.65 100.0 85.1 420 1: 3,5 30000 0.06 29.26 67.96 0.14 2,58 100.0 99.8 * - experiments were carried out without using an additional lower layer of Au + Rh / TiO ₂ catalyst.

A comparison of the process indicators obtained by the prototype and the present invention shows (see table) that in the presence of an additional lower layer of Au + Rh / TiO ₂ catalyst, oxygen conversion in some cases increases by more than 10% (see example 4 ), while in the reaction mixture at the outlet of the reactor there is a significant (2-3% vol.) decrease in the concentration of undesirable oxygen and carbon monoxide. It should be noted that along with this in the reaction gas there is a certain (about 1 vol.%) Increase in the concentration of the target product, ethylene.

The technical result obtained by the implementation of the present invention is to achieve a higher oxygen conversion in the proposed process, as well as a significant reduction in the concentration of carbon monoxide in the reaction gas, which facilitates the further separation of the target product, ethylene, from the reaction gas mixture.

Claims (4)

1. The method of producing ethylene by oxidative dehydrogenation of ethane in a gas mixture of oxygen and ethane at elevated temperature in the presence of a mixed oxide catalyst of the composition Mo _1.0 V _0.37 Te _0.17 Nb _0.12 O ₃ in a flow reactor, characterized in that the reactor further comprises a selective carbon monoxide oxidation catalyst , which is gold and rhodium on a carrier - titanium dioxide in the following ratio of components, wt.%: gold 0.05-0.3, rhodium 0.5-1.0 and titanium dioxide - the rest, and the mixed oxide catalyst is located dix inlet feed gas and the carbon monoxide selective oxidation catalyst located downstream of the gas stream and wherein the catalysts are taken in a volume ratio equal to 80-90 and 20-10, respectively. 2. The method according to claim 1, characterized in that the gas mixture is taken in a volume ratio of oxygen: ethane 1: 2.5-3.5, respectively. 3. The method according to claim 1, characterized in that the process is carried out at a temperature of 380-420 ° C and atmospheric pressure. 4. The method according to claim 1, characterized in that the process is carried out at a volumetric feed rate in the range of 500-30000 h ^-1 .