PL200221B1 - Method for obtaining olefines - Google Patents

Abstract

1. A method for obtaining C2-C5 olefins by oxidative dehydrogenation of C2-C5 paraffins, which comprises passing paraffin and oxygen or a gas containing oxygen through a bed of a molecular sieve catalyst at a temperature of 523 to 923K, characterized in that the catalyst comprises a microporous molecular sieve, which is a metal silicate with an MFI structure, in the crystal lattice of which a portion of silicon atoms, not exceeding 4%, is isomorphically substituted with manganese, cobalt and optionally iron atoms, wherein the molecular sieve also contains cations.

Description

The subject of the invention is a method for obtaining C2- _C5 olefins from C2- _C5 paraffins by oxidative dehydrogenation of paraffins in the presence of molecular sieves.

Methods for obtaining C2- _C5 olefins are known by oxidative dehydrogenation of C2- _C5 paraffins in the presence of catalysts. The oxidative dehydrogenation process involves simultaneously achieving equilibrium dehydrogenation of paraffins to olefins and burning the resulting hydrogen, which shifts the reaction equilibrium toward olefins. Various oxygen-containing gases, such as oxygen, air, carbon monoxide, carbon dioxide, and nitrous oxide, are used for the oxidative dehydrogenation of paraffins.

Known catalysts for the oxidative dehydrogenation of C2- _C5 paraffins are crystalline manganese phosphates modified with cations from the group including alkali metals, alkaline earth metals (except calcium), hydronium ion, organoammonium ions, silver, copper (II), zinc (II), nickel (II), mercury (II), cadmium (II) and their mixtures, and with metals from the group: aluminum, iron, gallium, tin, titanium, antimony, silver, zinc, copper, nickel, cadmium and their mixtures, aluminophosphate molecular sieves of the MeAPO-5 type with the AFI structure containing vanadium, cobalt and/or magnesium atoms in the crystal lattice, molecular sieves of the MCM-41 type containing chromium and vanadium.

Known catalysts for the oxidative dehydrogenation of C2-C5 paraffins are zeolites with structures of the MFI, BEA, FER, MOR, FAU type modified with cations of cadmium, barium, lithium, sodium, potassium, iron, gallium, zinc, silver, zeolites with the MFI structure containing platinum, tin or at least one metal from the group consisting of chromium, molybdenum, gallium, zinc, metals of group VIII of the periodic table of elements and at least one metal oxide from the group: bismuth, indium, antimony, zinc, thallium, lead, tellurium, titanium, optionally with the addition of elements of groups I, IIa, IIIb and carriers such as oxides of silicon, aluminum, zirconium, titanium, hafnium and mixtures of these oxides.

Known catalysts are also crystalline metallosilicates with the MFI structure, having isomorphically substituted silicon atoms in the crystal lattice with iron, gallium, boron, vanadium, titanium and zinc atoms.

Md. Azhar Uddin and co-authors, in J. of Catal., 150 (1994), 439-441, described the use of [Fe]-ZSM-5 as a catalyst for the oxidative dehydrogenation of propane and isobutane using oxygen diluted with helium as the oxidizing gas. At 723 K, propylene selectivities exceeding 65.8% were obtained, but the propane conversion was 2.2%. In the case of isobutane, the conversion was 1.6%, and the isobutylene selectivity was 39.6%. For the oxidative dehydrogenation of ethane, the same catalyst was used by L. Brabec and co-authors in Appl. Catal. A: General, 170 (1998), 105-116. Air was used as the oxidizing gas. Ethylene yields did not exceed 4.5%.

The method known from the work of Roman Bulanek et al., Appl. Catal. A: General 235 (2002), 181-191, is the oxidative dehydrogenation of ethane and propane in the presence of zeolites with MFI, BEA, FER, and MOR structures exchanged with cobalt cations, carried out at temperatures of 350-500°C. In the presence of these catalysts, a low paraffin conversion rate of several percent is achieved.

A method known from the work of K. Nowińska and co-authors, Appl. Catal. A: General 243 (2003), 225-236, involves oxidative dehydrogenation of propane in the presence of ZSM-5 zeolites with Si/Al ratios ranging from 14 to 100, modified with Fe ³⁺ , Mn ²⁺ , and Co ²⁺ cations. In the presence of these zeolites, at temperatures of 300-400°C and using molecular oxygen, optionally diluted with an inert gas, very low propylene selectivities of a few percent are obtained - the main products of the oxidative dehydrogenation reaction are carbon dioxide and oxygen derivatives of propane. Selectivities to propylene greater than 60% are obtained using nitrous oxide as the oxygen source.

Depending on the catalyst used, oxidative dehydrogenation of C ₂ -C ₅ paraffins is carried out at temperatures ranging from approximately 250 to approximately 800°C. In known methods, olefin selectivity exceeding 40% has been achieved only at low paraffin conversion rates of a few percent. Increasing the paraffin conversion rate significantly reduces olefin selectivity.

It has surprisingly turned out that the method according to the invention can be used to increase the selectivity and degree of conversion in the process of oxidative dehydrogenation of _C2 - _C5 paraffins to C2-C5 olefins using a catalyst containing microporous molecular sieves, which are metallosilicates with an MFI type structure, with isomorphically substituted manganese, cobalt and optionally iron atoms in place of silicon atoms in the crystal lattice.

PL 200 221 B1

This method consists in passing C2- _C5 paraffins and oxygen or an oxygen-containing gas, at a temperature of 523 to 973K, through a catalyst bed containing a microporous molecular sieve, which is a metallosilicate with an MFI type structure, in the crystal lattice of which a part of silicon atoms, not exceeding 4%, is isomorphously substituted with manganese, cobalt and optionally iron atoms, wherein the crystal lattice of the molecular sieve also contains cations.

The catalyst used in the method according to the invention may contain cations from the group of manganese, cobalt, iron, magnesium, zinc, lithium, sodium, potassium, rubidium, cesium, barium, cadmium, calcium, beryllium, copper, hydrogen cations in the crystal lattice of the molecular sieve.

The catalysts of the processes carried out according to the invention may contain a mixture of metal silicate molecular sieves with an MFI type structure.

The catalysts used in the process for obtaining C2-C5 olefins by oxidative dehydrogenation of C2-C5 paraffins according to the invention are microporous metallosilicate molecular sieves with an MFI structure deposited on a support, crystallized on a support, pressed, or formed using compounds of elements from groups IIa, IIIa, IV, and V of the periodic table, such as oxides, carbonates, silicates, phosphates, aluminosilicates, aluminophosphates, aluminosiliconphosphates, silicophosphates, and/or with activated carbon. The molecular sieve can also be deposited on monolithic or metallic shapes.

C2-C5 olefins are obtained by oxidative dehydrogenation of C2-C5 paraffins by the method according to the invention while maintaining the molar ratio of paraffins to oxygen as in known methods - from about 1:10 to about 10:0.1.

The oxidative dehydrogenation of olefins according to the invention involves catalytic dehydrogenation of C2-C5 paraffins, combustion of the resulting hydrogen to produce water, and combustion of some of the dehydrogenation products, possibly cracking, to produce carbon monoxide and carbon dioxide. While combustion of some of the carbon products reduces the process efficiency, it also prevents catalyst coking. Depending on the composition of the reaction gases and the process conditions, olefin selectivity of up to 90% is achieved. Trace amounts of organic oxygen-containing compounds are detected in the products, and the catalysts are subject to very little coking.

The method according to the invention for obtaining C2-C5 olefins by oxidative dehydrogenation of C2-C5s paraffins is illustrated by examples.

Examples I-IV

Catalysts were placed in heated, tubular, flow-through reactors. The catalysts were metallosilicates with an MFI structure, with cobalt, manganese, and additional iron atoms isomorphously substituted in the crystal lattice for silicon atoms. The catalyst compositions were characterized by the Si/Me mole ratios in the dehydrated molecular sieves (Me = Co, Mn, Fe) and the cation content expressed in weight percent. After dehydrating the catalysts at 523-923K and flushing the air contained in the catalyst pores with an inert gas, gas mixtures containing paraffin, nitrogen, and oxygen in various molar ratios were passed through the catalysts. The process temperatures and reactant flow rates were varied. The obtained results regarding the degree of paraffin conversion and the selectivity of olefin production are summarized in Table 1.

Examples V-VII

Metallosilicates with an MFI structure, with cobalt and manganese atoms isomorphously substituted in the crystal lattice for silicon atoms, were formed into extrudates using the following binders: alumina, silica, and aluminum phosphate. The molecular sieve contents in the catalysts were 55, 53, and 51% by weight, respectively. The extrudates were placed in heated tubular flow reactors. After dehydrating the catalysts at 523-923K and flushing the air contained in the catalyst pores with an inert gas, gas mixtures containing n-butane, nitrogen, and oxygen in molar ratios of 1/0.7/24 were passed through the extrudates. The volumetric ^{hourly rate} of the catalyst ( ^VHSV ) was ^20,000 h' ¹ . ^{At 750 K} the n-butane ^conversion rates were 30.0, 25.7 and 35.3%, respectively, and the selectivity of butene production was 60, 54 and 69%.

Example IX

A catalyst containing 15% by weight of metallosilicate K-[CoMn]-MFI deposited on a support with the following composition: Al2O3 - 67.5%, _SiO2 - 25.7%, _Na2O - 1.2%, BaO 0.3%, MgO - 5.3% by weight was placed in a tubular reactor. After dehydration of the catalyst at a temperature of 523-973K and washing out the air contained in the catalyst pores with an inert gas, a mixture of

PL 200 221 B1 gas mixture containing propane, nitrogen, oxygen in molar ratios 1/0.1/80 at a temperature of 973K, at VHSV = 10000 h ¹ . 20% propane conversion was achieved, and the selectivity of propylene production was 92%.

T a b l e 1

By- Catalyst Si/Me Conclude- Paraffin Temper- Ratio VHSV Reacted Selective lay thisness rata parish wain para- olefi- cation process na:O2:N2 fins ny mol/mol % wt. K mol/mol/mol h ^-1 % % And [CoMn]-MFI Co-75 Na-1.04 Ethane 923 1/1/50 20000 19.0 70.0 Mn-73 Propane 28.0 60.7 n-butane 50.2 65.1 Isobutane 55.0 63.1 n H-[CoFeMn]-MFI Co-220 Na-0.06 Ethane 873 1/0,1/32 10000 20.5 90.0 Fe-85 Propane 26.4 87.5 Mn-187 n-butane 26.2 89.1 Isobutane 36.0 88.2 m K-[CoMn]-MFI Co-74 K-2.25 Propane 773 1/2/10 5000 40.0 66.5 Mn-72 n-butane 54.5 63.8 Isobutane 45.8 62.2 IV Zn-[Co,Fe,Mn]-MFI Co-215 Zn-1.8 n-butane 573 1/10/5 1000 21.0 50.2 Fe-87 Isobutane 21.5 51.5 Mn-190 n-pentane 25.0 50.0

Patent claims

Claims (3)

Patent claims 1. Method for obtaining olefins C ₂ 2C ₅ for oxidative dehydrogenation of paraffins C ₂ 2C ₅ consisting in passing, at a temperature of 523 to 923K, paraffin and oxygen or oxygen-containing gas through a catalyst bed with a molecular sieve structure, characterized by the use of a catalyst containing in its composition a microporous molecular sieve, which is a metallosilicate of the MFI type structure, in the crystal lattice of which a part of silicon atoms, not exceeding 4%, is isomorphically substituted with manganese, cobalt and possibly iron atoms, and the molecular sieve also contains cations. 2. Way to wedtLigzasfrz. A method according to claim 1, characterized in that the carallzarot is composed of manganese, cobalt, iron, magnesium, zinc, lithium, sodium, potassium, rubidium, cesium, barium, cadmium, calcium, beryllium, copper and hydrogen cations. 3. The method according to claim 1 A method according to claim 1, characterized in that the carallzarot is composed of a mixture of metallosilicate molecular sieves of the MFI type structure. Publishing Department of the Polish Patent Office