CS206291B1 - Method of making the alcenes by the catalytic dehydrogenase of alcanes - Google Patents

Description

(54) Process for producing alkenes by catalytic dehydrogenation of alkanes i

The present invention relates to a process for producing alkenes by catalytic dehydrogenation of alkane hydrocarbons having from 2 to 25 carbon atoms per molecule.

The method of dehydrogenation of alkane hydrocarbons to monofilaments of the same chain length is covered by the Czechoslovak patent no. 144 7S8. Dehydrogenation takes place on catalysts containing four- to five-component combinations of aluminum, chromium, thorium, cesium, potassium and zirconium. ·

Czechoslovak Patint no. 161,635 protects the process of dehydrogenation of alkane hydrocarbons with catalysts comprising a system of oxides or metals of chromium and platinum in combination with the oxide of aluminum, arsenic, selenium, manganese and beryllium.

Three- to eight-component combinations of aluminum, chromium, tellurium, selenium, antimony, crime, manganese and vanadium, or four to nine-component combinations of these oxides with one of the alkali metals, preferably cesium oxide, are the object of the invention of the alkanes U.S. Patent No. 5,632,516; 144 788.

Combination of 85 to 94.5% by weight, preferably 90 to 92% by weight, of alumina with 0.5 to 6% by weight of platinum and platinum oxides and with alkali metal oxides in an amount of 5 to 9% by weight, preferably 6 to 7% by weight, is protected as a dehydrogenation catalyst of alkanes in the Czechoslovak copyright certificate

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δ. 151 661.

A catalyst system consisting of chromium oxides and / or metals, platinum, in a ratio of 1 part platinum> 0.2 to 6 parts chromium, with or without antimony, tin, selenium, manganese, beryllium and alkali metal, is used for dehydrogenation alkanes according to the Czechoslovak author's certificate no. 161 633.

U.S. Pat. 3,345,427 covering the dehydrogenation of alkanes Cg - C ₀ to catalysts consisting of oxides of aluminum, nickel, molybdenum, and alkali metal.

U.S. Pat. No. 3,310,599 discloses the dehydrogenation of alkanes using noble metal catalysts, in particular platinum, as well as the use of casting and selenium or their compounds deposited on alumina.

DOS č. 2 118 155 chromium catalysts for the dehydrogenation of alkanes consisting of aluminum, rhenium, wolfram or molybdenum oxides.

U.S. Pat. No. 3,742,078 describes a process for producing n-olefins from n-paraffins containing 4 to 30 carbon atoms per molecule in the presence of a catalyst system consisting of aluminum oxides, platinum group elements, germanium and casting.

In accordance with the present invention, alkane hydrocarbons containing from 2 to 25, preferably from 6 to 18, carbon atoms per molecule are used as starting material. Hydrocarbons or hydrocarbon-containing fractions having a chain length of 2 to 8 carbons can be hydrogenated individually.

Catalyst assemblies with relatively high activity and selectivity of the alkane dehydrogenation reaction contain inorganic refractories in an amount of 75 to 98.9 parts by weight, 0.1 to 6 parts by weight of platinum group elements, 0.1 to 20 parts by weight of rare earth elements.

As inorganic refractories, the individual metal oxides and carbonates of the second group of the Periodic Table of Elements are beryllium, magnesium, calcium, strontium, barium and zinc or any mixture thereof. These refractory inorganic materials are preferably combined with titanium and aluminum oxides, with oxides, carbonates and nitrates and with alkali metal oxides and carbonates. Their amount in the catalyst system ranges from 75 to 98.9 parts by weight. Inorganic refractory materials can be prepared from natural raw materials or by synthetic routes.

Rare earth elements are an important component of catalyst systems with high activity and selectivity of the alkane dehydrogenation reaction. These are incorporated into the catalyst system in the form of oxides, sulfides, halides, carbonates and sulfates or in the form of a mixture thereof and in the form of a metal, a mixture or metal alloys.

The catalytic activity and selectivity of the catalyst system are positively influenced by lanthanides, especially those having only partially filled 4 orbitals and a subgroup of scandium (Sc, Y, La) belonging to the electron conductivity semiconductor. Rare earth elements actively form catalyst systems when present in them in an amount of 0.1 to 20 parts by weight, preferably in an amount of 2 to 8 parts by weight.

elements of the platinum group, Pt, Ir, Ku, Os, Rh, preferably platinum and iridium having only partially filled 4d and 5d orbitals and Pd can be present in the catalyst system either as metal, metal alloys, oxides, chlorides, carbonyl, complex compounds and hydrides. The platinum elements or compounds form the active catalyst composition either as chemical individuals or mixtures thereof. They are active in amounts of from 0.1 to 6% by weight.

The catalyst system can be prepared either by coupling the annealed refractory carrier with rare earth solutions and platinum group elements, or by precipitation of all three components, or by mixing and subsequent forming.

The hydrogenation of the alkane hydrocarbons on the catalyst system according to the invention takes place in the presence of hydrogen, a diluent gas or any mixture thereof.

Nitrogen, noble gases, methane and water vapor can be used as diluent gas. The idole ratio of diluent gas to alkanes in the reaction zone may range from 1 to 30 moles; 1. Increasing the molar ratio of diluent to alkanes makes it possible to increase the conversion to alkenes in one pass of the alkanes over the catalyst while maintaining a relatively high selectivity.

Reducing the molar ratio of diluent to alkanes results in an increase in alkene formation per unit weight of catalyst per unit time.

Experimentally, it has been found that, in order to maintain the relatively high conversion and selectivity of the dehydrogenation reaction, it is advantageous to increase the molar ratio of diluent to alkanes in proportion to their relative molecular weight increase.

In accordance with the laws of thermodynamics, it is necessary to dehydrogenate alkanes at the higher the temperature, the lower their relative molecular weight. Ethane is catalytically dehydrogenated at 700 ° C, pentane at 550 ° C to 600 ° C, tetradecane to eicosan at 420 ° C to

500 ° C, the alkane fraction containing 23 to 25 carbon atoms per molecule is dehydrogenated at 320 ° C to 400 ° C.

The total pressure in the catalyst bed is maintained between 0.1 and 10 bar. From the thermodynamic point of view, the hydrocarbon partial pressure is decisive for the conversion of alkanes to alkenes. The total pressure is selected by the molar ratio of alkanes to diluent.

The amount of liquid alkane fed per catalyst volume per hour may vary between 5 and 50. With increasing volumetric rate, the productivity of the catalyst calculated on the alkenes formed increases over a given interval.

The advantage of producing the alkenes of the present invention is the high selectivity and productivity of the catalyst bed. The catalyst system is capable of accelerating the dehydrogenation reaction in very short dehydrogenation cycles between court regenerations of 5 to 60 minutes, as well as in very long dehydrogenation cycles of 1 to 500 hours. The catalyst system can be periodically regenerated without degradation of its dehydrogenation activity and selectivity after hundreds to thousands of oxidative regenerations.

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In the dehydrogenation of C8 and high alkanes there is only a relatively very low aromatic formation on this catalyst system.

The following non-limiting examples illustrate the invention.

Example 1

Isopentane diluted with a nitrogen mixture was charged to a reactor packed with a catalyst system consisting of magnesium, zinc and titanium oxides of 85% by weight, cerium rare earth and lanthanum and yttrium oxides of 14.8 parts by weight and platinum at 0.2% by weight. and water vapor at a molar ratio of 1: 5 at a total pressure of 0.1 MPa at a volumetric rate of 400 liters of isopentane gas per liter of catalyst system per hour. A temperature of 595 ° C was maintained in the reactor over the entire height of the catalyst.

The product coming out of the catalyst bed was cooled to 20 ° C. Analysis of the dehydrogenate showed the conversion of isopentane to the sum of isopentenes and isoprene, 39% by weight and the selectivity of the dehydrogenation reaction to 90% by weight.

Example 2

Normal tetradecane preheated to 440 ° C was charged to a reactor filled with a catalyst containing 91% by weight of heat-resistant materials such as magnesium oxide, alumina and beryllium oxide, 8% by weight of rare earth oxides, namely mixtures of cerium, samarium and prazodymium oxides. 1% by weight of platinum and iridium oxides, at a flow rate of 50 liters of liquid n-tetradecane per liter of catalyst per hour, at a catalyst bed temperature of 450 ° C, at a total reactor pressure of 0.3 MPa, and diluted 1: 8 with hydrogen. The dehydrogenation mixture was cooled to 20 ° C. Analysis of the liquefied product showed the conversion of n-tetradecane to tetradecenes at 10.5 wt% and the selectivity of the dehydrogenation *.

Reaction 97% by weight.

Example 3

75% w / w catalyst, magnesium oxide, barium oxide, barium oxide, 19% w / w rare earth elements, and 6% w / w platinum, platinum and palladium metals are fed to a reactor containing 23 to 25 carbon atoms per molecule at a flow rate of 15 liters of liquid hydrocarbons per liter of catalyst per hour, at 360 ° C, diluted 1:30 with hydrogen at 0.6 MPa. The dehydrogenation mixture was cooled to 60 ° C. Analysis of the liquid part revealed a conversion of paraffins to alkenes of 14% by weight and a selectivity of 92% by weight.

Claims (2)

OBJECT OF THE INVENTION A process for the production of alkenes by catalytic dehydrogenation of alkanes of 2 to 25 carbon atoms in a molecule, characterized in that the alkane hydrocarbon or mixture of alkane hydrocarbons is diluted with an inert gas or hydrogen or a mixture thereof to a molar ratio of gas to hydrocarbon of 1 to 30; 1, is then contacted with a catalyst system comprising 75 to 98.9 parts by weight of inorganic refractories based on elements of the second group of the Periodic Table of the Elements, in the form of individual substances or mixtures thereof, 0.1 to 6 parts by weight of metals, oxides, carbonates, sulfides, hydrides of the platinum group elements, 0.1 to 20 parts by weight of rare earth elements and scandalized elements at a temperature of 320 ° C to 700 ° C, at a total pressure in the dehydrogenation reactor of 0.1 to 1.0 MPa and rates of 5 to 50 volumes of liquid hydrocarbon per catalyst volume per hour. 2. The process according to claim 1, wherein the catalyst system preferably contains 0.1 to 20 parts by weight of lanthanide oxides.