CN101115697B

CN101115697B - Method for the production of propene from propane

Info

Publication number: CN101115697B
Application number: CN2006800040110A
Authority: CN
Inventors: S·克罗内; O·马赫哈默; G-P·申德勒; F·博格迈尔
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 2005-01-05
Filing date: 2006-01-04
Publication date: 2010-09-29
Anticipated expiration: 2026-01-04
Also published as: CN101115697A; DE102005000798A1

Abstract

Preparation of propene from propane comprises preparing a feed stream containing propane; feeding the feed stream to a dehydrogenation zone; cooling the obtained product gas stream; contating the cooled product gas stream with a selective inert absorption agent; optionally depressurizing the obtained propane charged absorption agent stream; and releasing a propene-containing gas stream. Preparation of propene from propane comprises: (i) preparing a feed stream containing propane; (ii) feeding the feed stream containing propane, optionally: steam and an oxygen-containing gas stream to a dehydrogenation zone and propane undergoes a dehydrogenation to give propene (where a product gas stream (b) containing propane, propene, methane, ethane, ethene, carbon monoxide, carbon dioxide, steam, and optionally hydrogen and oxygen, is obtained); (iii) cooling (b) and optionally compressing and steam separating, by condensation, to give a product gas stream (c) stripped of steam; (iv) contacting (c) with a selective inert absorption agent, which selectively absorbs propene in a first absorption zone, to give an essentially propane charged absorption agent stream (d1) and a gas stream (d2) containing propane, methane, ethane, ethene, carbon monoxide, carbon dioxide and hydrogen; (v) optionally depressurizing (d1), in a first desorption zone, to give an essentially propene-charged absorption agent stream (e1) and a gas stream (e2) (which is recycled into the first absorption zone), containing propene; and (vi) releasing a propene-containing gas stream (f1) from (d1) and (e1) in at least one second desorption zone by depressurization, heating and/or stripping of the absorption agent stream (d1) and (e1) with recycling of the selective absorption agent.

Description

Method for producing propylene from propane

The present invention relates to a process for the preparation of propylene from propane.

On an industrial scale, propylene is obtained by dehydrogenation of propane.

In a process known as UOP-oleflex, for the dehydrogenation of propane to formFor propylene, a gaseous feed stream comprising propane is preheated to 600-700 ℃ and hydrogenated over a catalyst comprising platinum on alumina in a moving bed dehydrogenation reactor to obtain a product gas stream comprising mainly propane, propylene and hydrogen. In addition, low-boiling hydrocarbons (methane, ethane, ethylene) formed by cracking and small amounts of high-boiling fractions (C) are also present in the product gas stream₄ ⁺Hydrocarbons). The product gas mixture is cooled and compressed in multiple stages. Then, C is condensed in a "cold box₂And C₃Hydrocarbons as well as high-boiling fractions are separated from the hydrogen and methane formed in the hydrogenation. Followed by removal of C in a first column by distillation₂Hydrocarbons and remaining methane, and C in a second distillation column₃The hydrocarbon stream is separated into a propylene fraction having a high purity and also contains C₄ ⁺A propane fraction of the hydrocarbons, thereby separating a liquid hydrocarbon condensate.

The disadvantage of this process is that the cold box condenses to form C₃The hydrocarbon is lost. Larger amount of C due to the large amount of hydrogen and phase equilibrium formed in dehydrogenation₃Hydrocarbons are also emitted with the hydrogen/methane off-gas unless condensation is carried out at very low temperatures. Thus, it is necessary to operate at temperatures from-20 ℃ to-60 ℃ to limit the C emitted with the hydrogen/methane off-gas stream₃The hydrocarbon is lost.

It is an object of the present invention to provide an improved process for the dehydrogenation of propane to propene.

The object is achieved by a process for the preparation of propene from propane, comprising the steps of:

A) providing a feed gas stream a comprising propane;

B) feeding a feed gas stream a comprising propane, if appropriate an oxygen-containing gas stream and if appropriate steam into a dehydrogenation zone and dehydrogenating propane to propene, obtaining a product gas stream b comprising propane, propene, methane, ethane, ethylene, carbon monoxide, carbon dioxide, steam, if appropriate hydrogen and if appropriate oxygen;

C) the product gas stream b is cooled, if appropriate compressed, and the vapors are removed by condensation to obtain a vapor-depleted product gas stream c;

D) the product gas stream c is contacted in a first absorption zone with a selective, inert absorbent capable of selectively absorbing propylene, to obtain an absorbent stream d1 loaded mainly with propylene and a gas stream d2 comprising propane, propylene, methane, ethane, ethylene, carbon monoxide, carbon dioxide, if appropriate hydrogen and if appropriate oxygen;

E) if appropriate, the absorbent stream d1 is decompressed to lower pressure in a first desorption zone, an absorbent stream e1 loaded mainly with propylene and a gas stream e2 comprising propylene are obtained and the gas stream e2 is recycled into the first absorption zone,

F) from the predominantly propylene-laden absorbent stream d1 or e1, a gaseous stream f1 comprising propylene is released and the selective absorbent is recovered by decompressing, heating and/or stripping the absorbent stream d1 or e1 in at least one second desorption zone.

In a first step a of the process, a feed gas stream comprising propane is provided. This stream generally comprises at least 80% by volume of propane, preferably 90% by volume of propane. In addition, the propane-containing feed gas stream a generally also comprises butanes (n-butane, isobutane). The basic composition of the propane-containing feed gas stream is described in DE-A10246119 and DE-A10245585. Typically, the propane-containing feed gas stream is obtained from Liquefied Petroleum Gas (LPG).

In process step B, the gaseous feed stream comprising propane is fed to a dehydrogenation zone and subjected to a conventional catalytic dehydrogenation. In this process step, propane is partially dehydrogenated in a dehydrogenation reactor over a dehydrogenation-active catalyst to provide propene. In addition, hydrogen and small amounts of methane, ethane, ethylene and C are obtained₄ ⁺Hydrocarbons (n-butane, isobutane, butenes, butadiene). In catalytic dehydrogenation of propaneAlso generally small amounts of carbon oxides (CO, CO) are obtained in the gaseous product mixture of (A)₂) Especially CO₂Steam and, if appropriate, inert gas. The dehydrogenated product gas stream generally comprises steam which has been added to the dehydrogenation gas mixture and/or formed during dehydrogenation in the presence of oxygen (oxidative or non-oxidative). When the dehydrogenation is carried out in the presence of oxygen, an inert gas (nitrogen) is introduced into the dehydrogenation zone under a stream of oxygen-containing gas, with the proviso that no pure oxygen is fed. In the case of feeding an oxygen-containing gas, the oxygen content thereof is generally at least 40% by volume, preferably at least 80% by volume, more preferably at least 90% by volume. In particular, commercially pure oxygen with an oxygen content of > 99% is fed in order to prevent an excessively high proportion of inert gas in the product gas mixture. In addition, unconverted propane is present in the product gas mixture.

The propane dehydrogenation can in principle be carried out in any type of reactor known from the prior art. A review of the types of reactors suitable for the present invention can be found in "Catalytica

Studies Division，Oxidative Dehydrogenation and Alternative Dehydrogenation Process”(Study Number 4192 OD 1993，430 ferguson Drive，Mountain View，California，94043-5272，USA)。

The dehydrogenation can also be carried out in an oxidative or nonoxidative manner. The dehydrogenation can be carried out isothermally or adiabatically. The dehydrogenation can also be carried out catalytically in fixed-bed, moving-bed or fluidized-bed reactors.

The non-oxidative catalytic propane dehydrogenation is preferably carried out thermally. For this purpose, oxygen is additionally mixed with the reaction gas mixture of the propane dehydrogenation in at least one reaction zone and the hydrogen and/or hydrocarbons present in the reaction mixture are at least partially combusted, so that at least part of the heat required for the hydrogenation is generated in the reaction gas mixture in the at least one reaction zone.

In contrast to the oxidative process, a feature of the nonoxidative process is the at least intermediate formation of hydrogen, which is manifested in the presence of hydrogen in the dehydrogenated product gas. In oxidative dehydrogenation, no free hydrogen is found in the product gas of the dehydrogenation.

Suitable reactor types are fixed-bed tube reactors or tube bundle reactors. In these reactors, the catalyst (dehydrogenation catalyst and, if appropriate, special oxidation catalyst) is located as a fixed bed in the reaction tubes and in the tube bundles of reaction tubes. Conventional reaction tubes have an internal diameter of about 10-15 cm. A typical dehydrogenation tube bundle reactor contains about 300-1000 reaction tubes. The internal temperature of the reaction tube is generally varied within 300 ℃ to 1200 ℃, preferably 500 ℃ to 1000 ℃. The working pressure for propane or butane dehydrogenation by Phillips Petroleum co. is typically 0.5-8 bar, often 1-2 bar when low steam dilution is used, or 3-8 bar when high steam dilution is used (corresponding to the steam activated reforming process (STAR process) or the Linde process). Typical Gas Hourly Space Velocity (GHSV) is 500-^-1. The catalyst geometry may be, for example, spherical or cylindrical (hollow or solid).

The catalytic dehydrogenation of propane can also be carried out in a fluidized bed under heterogeneous catalysis according to the Snamprogetti/Yarsintez-FBD process. Suitably, the two fluidised beds are operated in parallel, one of which is normally in a regenerated state.

The working pressure is generally 1-2 bar and the dehydrogenation temperature is generally 550-600 ℃. The heat required for dehydrogenation can be introduced into the reaction system by preheating the dehydrogenation catalyst to the reaction temperature. The addition of an oxygen-containing auxiliary feed makes it possible to dispense with the preheater and to generate the required heat directly inside the reaction gas system by combustion of hydrogen and/or hydrocarbons in the presence of oxygen. If appropriate, an auxiliary feed comprising hydrogen can additionally be admixed.

The catalytic dehydrogenation of propane can also be carried out in a tray reactor. When the dehydrogenation is carried out autothermally by feeding an oxygen-containing gas stream, it is preferably carried out in a tray reactor. Such reactors contain one or more continuous catalyst beds. The number of catalyst beds may be from 1 to 20, advantageously from 1 to 6, preferably from 1 to 4, in particular from 1 to 3. The reaction gas preferably flows radially or axially through the catalyst bed. Typically, such tray reactors operate using a fixed catalyst bed. In the simplest case, the fixed catalyst bed is distributed axially in the shaft furnace reactor or in the annular gap of a concentric cylindrical grid. The shaft furnace reactor corresponds to one tray. Performing the dehydrogenation in a single shaft furnace reactor corresponds to one embodiment. In another preferred embodiment, the dehydrogenation reaction is carried out in a tray reactor with 3 catalyst beds.

In general, the amount of oxygen-containing gas added to the reaction gas mixture is chosen in the following manner: the heat required for the dehydrogenation of propane is generated by combustion of the hydrogen present in the reaction gas mixture and, if appropriate, of the hydrocarbons present in the reaction gas mixture and/or of the carbon present in the form of coke. In general, the total amount of oxygen provided is from 0.001 to 0.8mol/mol, preferably from 0.001 to 0.6mol/mol, more preferably from 0.02 to 0.5mol/mol, based on the total amount of propane. The oxygen may be provided in the form of pure oxygen or in the form of an oxygen-containing gas comprising an inert gas. However, in order to avoid high losses of propane and propylene in the treatment (see below), it is important that the oxygen-containing gas used is high in oxygen content and is at least 40% by volume, preferably at least 80% by volume, more preferably at least 90% by volume. A particularly preferred oxygen-containing gas is commercially pure oxygen having an oxygen content of about 99% by volume.

The hydrogen burnt for generating heat is the hydrogen produced in the catalytic dehydrogenation of propane and, if appropriate, additionally added as hydrogen-containing gas to the reaction gas mixture. The hydrogen is preferably present in such an amount that, after the oxygen has been fed in, H is present in the reaction gas mixture₂/O₂The molar ratio is immediately in the range from 1 to 10mol/mol, preferably from 2 to 5 mol/mol. In the multistage reactor, this requirement is adapted to each intermediate supply of oxygen-containing gas and, if appropriate, hydrogen-containing gas.

The hydrogen is catalytically combusted. The dehydrogenation catalysts used are generally also capable of catalyzing the combustion of hydrocarbons and the combustion of hydrogen and oxygen and, therefore, in principle do not need to be usedAdditional specific oxidation catalysts. In one embodiment, the operation is carried out in the presence of one or more oxidation catalysts capable of selectively catalyzing the combustion of hydrogen and oxygen in the presence of a hydrocarbon. Thus, these hydrocarbons are combusted with oxygen to produce CO, CO₂And water only to a minimum. The dehydrogenation catalyst and the oxidation catalyst are preferably present in different reaction zones.

When the reaction is carried out in more than one multiple stages, the oxidation catalyst may be present in only one reaction zone, more than one reaction zone, or all of the reaction zones.

It is preferred to place the catalyst capable of selectively catalysing the combustion of the hydrocarbon at a point where the partial pressure of oxygen is higher than at other points in the reactor, particularly close to the point where the oxygen-containing gas is fed. The oxygen-containing gas and/or the hydrogen-containing gas may be fed from one or more points of the reactor.

In a preferred embodiment of the process according to the invention, there is an intermediate feed point for the oxygen-containing gas and the hydrogen-containing gas upstream of each tray of the tray reactor. In another embodiment of the process of the present invention, the oxygen-containing gas and the hydrogen-containing gas are fed upstream of each tray other than the first tray. In one embodiment, there is a layer of a special oxidation catalyst downstream of each feed point, followed by a layer of dehydrogenation catalyst. In another embodiment, no special oxidation catalyst is present. The dehydrogenation temperature is generally 400 ℃ and 1100 ℃ and the pressure in the last catalyst bed of the tray reactor is generally from 0.2 to 15 bar, preferably from 1 to 10 bar, more preferably from 1 to 5 bar. GHSV is generally 500-2000h^-1And at high load operation, even up to 100000h^-1Preferably 4000-^-1。

Preferred catalysts capable of selectively catalysing the combustion of hydrogen include oxides and/or phosphates selected from the group consisting of oxides and/or phosphates of germanium, tin, lead, arsenic, antimony and bismuth. Other preferred catalysts capable of selectively catalyzing the combustion of hydrogen include noble metals of transition group VIII and/or group I of the periodic table of elements.

The dehydrogenation catalysts used generally have a support and an active composition. The support is usually composed of a refractory oxide or a mixed oxide. The dehydrogenation catalyst preferably comprises as support a metal oxide selected from the group consisting of: zirconium dioxide, zinc oxide, aluminum oxide, silicon dioxide, titanium dioxide, magnesium oxide, lanthanum oxide, cerium oxide and mixtures thereof. The mixture may be a physical mixture or a chemical mixture such as magnesium aluminum oxide or zinc aluminum oxide mixed oxide. Preferred supports are zirconium dioxide and/or silicon dioxide, particularly preferably mixtures of zirconium dioxide and silicon dioxide.

Suitable catalyst geometries are extrudates, stars, rings, saddles, spheres, foams and monoliths having a reference dimension of 1 to 100 mm.

The active composition of the dehydrogenation catalyst generally comprises one or more elements of transition group VIII of the periodic table of the elements, preferably platinum and/or palladium, more preferably platinum. Furthermore, the dehydrogenation catalyst may comprise one or more elements of main groups I and/or II of the periodic table of the elements, preferably potassium and/or cesium. The dehydrogenation catalyst may further comprise one or more elements of transition group III of the periodic table of elements, including lanthanides and actinides, preferably lanthanum and/or cerium. Finally, the dehydrogenation catalyst may comprise one or more elements of main groups III and/or IV of the periodic table of the elements, preferably one or more elements selected from the group consisting of boron, gallium, silicon, germanium, tin and lead, more preferably tin.

In a preferred embodiment, the dehydrogenation catalyst comprises at least one transition group VIII element, at least one main group I and/or II element, at least one main group HI and/or IV element and at least one transition group III element including the lanthanides and actinides.

All dehydrogenation catalysts disclosed, for example, by WO99/46039, US4,788,371, EP-A705136, WO99/29420, US5,220,091, US5,430,220, US5,877,369, EP 0117146, DE-A19937106, DE-A19937105 and DE-A19937107 can be used in accordance with the invention. Particularly preferred catalysts for the autothermal dehydrogenation of propane described above are those described in DE-A19937107 examples 1, 2, 3 and 4.

The autothermal dehydrogenation of propane is preferably carried out in the presence of steam. The added steam acts as a heat carrier and supports the vaporization of organic deposits on the catalyst, which resists carbonization of the catalyst and extends the service time of the catalyst. This converts the organic deposits into carbon monoxide, carbon dioxide and, if appropriate, water. Dilution with steam shifts the equilibrium towards the dehydrogenation product.

The dehydrogenation catalyst can be regenerated in a manner known per se. For example, steam may be added to the reaction gas mixture or from time to time an oxygen-containing gas may be passed through the catalyst bed at elevated temperature and the deposited carbon burnt off. After regeneration, the catalyst is, if appropriate, reduced with a hydrogen-containing gas.

The product gas stream b can be divided into two substreams, with one substream being recirculated to the autothermal dehydrogenation in accordance with the cycle gas mode described in DE-A10211275 and DE-A10028582.

The propane dehydrogenation can be carried out in an oxydehydrogenation mode. The oxidative dehydrogenation of propane can be carried out in a homogeneous oxidative dehydrogenation or in a heterogeneously catalyzed oxidative dehydrogenation.

When the propane dehydrogenation in the process of the invention is characterized by a homogeneous oxidative dehydrogenation, it can in principle be carried out as described in the following documents: U.S. Pat. No. 3,798,28, CN-A1,105,352, applied Catalysis, 70(2), 1991, pp 175-187, Catalysis Today 13, 1992, pp 673-678 and prior application DE-A19622331.

The temperature of the homogeneous oxidative dehydrogenation is generally 300-700 ℃, preferably 400-600 ℃, and more preferably 400-500 ℃. The pressure may be from 0.5 to 100 bar or from 1 to 50 bar. The pressure is often from 1 to 20 bar, in particular from 1 to 10 bar.

Under the oxidative dehydrogenation conditions, the residence time of the reaction gas mixture is generally from 0.1 or 0.5 seconds to 20 seconds, preferably from 0.1 or 0.5 seconds to 5 seconds. The reactors used may be, for example, tube furnaces or tube bundle reactors, for example countercurrent tube furnaces with exhaust gas as heat carrier, or tube bundle reactors with salt melt as heat carrier.

The propane/oxygen ratio in the starting mixture used can be from 0.5: 1 to 40: 1. The molar ratio of propane to molecular oxygen in the starting mixture is preferably < 6: 1, more preferably < 5: 1. In general, the above molar ratio should be ≥ 1: 1, for example ≥ 2: 1. The starting mixture may also comprise other substantially inert components, such as H₂O、CO₂、CO、N₂Noble gases and/or propylene. Propylene may be contained in C from refining₃In the distillation section. It is advantageous to oxidatively dehydrogenate propane homogeneously to propene with a minimum ratio of reaction space surface area to reaction space volume, since the homogeneous oxidative dehydrogenation of propane can proceed by a free-radical mechanism and the reaction space surfaces generally act as free-radical scavengers. Particularly advantageous surface materials are alumina, quartz glass, borosilicate, stainless steel and aluminum.

When the first reaction stage of the process of the invention is characterized by heterogeneously catalyzed oxidative dehydrogenation, this can in principle be carried out as described in the following documents: US-A4,788,371, CN-A1,073,893, Catalysis Letters 23(1994) 103-: general, 100(1993)111-130, J.of Catalysis 148, 56-67(1994), V.Cort. Cort. barber. na nd S.vic. Bell Lo n (eds.), New definition in Selective expression II, 1994, Elsevier Science B.V., p.305-313, 3^rdWorld convergence on oxidation Catalysis r.k.grasselli, s.t.oyama, a.m.gaffney and j.e.lyons (eds.), 1997, Elseviser Science b.v., page 375 and below. In particular, all the oxidative dehydrogenation catalysts specified in the above documents can be used. In relation to the above-mentioned publicationThe statements made apply equally to:

a) otsuka, K; uragami, Y; komatsu, t.; hatano, m., Natural GasConversion, stud.surf.sci.caral; holmen a.; jens, k.j.; kolboe, s., edit; elsevier Science: amsterdam, 1991; volume 61, page 15;

b) seshan, k.; swaan, h.m.; smits, rh.h.; van Ommen, J.G.; ross, J.R.H., New Developments in Selective Oxidation; stud.surf.sci.catal.; centi.g.; trifir oa, f, editing; EIsevier Science: amsterdam 1990; volume 55, page 505;

c) smits, r.h.h.; seshan, k.; ross, J.R.H., New development in selective Oxidation by Heterogeneous Catalysis; stud.surf.sci.catal; ruiz, P.; delmon, b., edit; EIsevier Science: amsterdam, 1992 a; volume 72, page 221;

d)Smits，R.H.H.；Seshan，K.；Ross，J.R.H.Proceedings，Symposiumon Catalytic Selective Oxidation，Washington DC；American ChemicalSociety：Washington.DC，1992b；1121；

e)Mazzocchia.，C.；Aboumrad，C.；Daigne，C.；Tempesti，E.；Herrmann，JM.；Thomas，G.CataL Lett.1991，10，181；

f)Bellusi，G.；Conti，G.；Perathonar，S.；Trifiro，F.Proceedings，Symposium on Catalytic Selective Oxidation，Washington，DC；AmericanChemical Society：Washington，DC，1991；P 1242；

g) ind, Eng, chem, Res, 1996, 35, 2137-

h)Symposium on Heterogeneous Hydrocarbon Oxidation Presentedbefore the Division of Petroleum Chemistry，Inc.211th National Meeting，American Chemical Society New Orleans，LA.March 24-29.1996。

Particularly suitable oxidative dehydrogenation catalysts are the multimetal oxide compositions or catalysts A from DE-A19753817, and very particularly advantageous as the multimetal oxides or catalysts A specified as preferred. In other words, suitable reactive compositions are, in particular, multimetal oxides of the formula I,

M¹ _aMo_1-bM² _bO_x(I)

wherein,

M¹co, Ni, Mg, Zn, Mn and/or Cu,

M²w, V, Te, Nb, P, Cr, Fe, Sb, Ce, Sn and/or La,

a＝0.5-1.5

b is 0 to 0.5, and

x is a number determined by the valence and frequency of the elements in formula I other than oxygen.

Other multimetal oxides suitable for use as oxidative dehydrogenation catalysts are described in detail below:

suitable Mo-V-Te/Sb-Nb-O multimetal oxide catalysts are disclosed in EP-A0318295, EP-A0529853, EP-A0603838, EP-A0608836, EP-A0608838, EP-A0895809, EP-A0962253, EP-A1192987, DE-A19835247, DE-A10051419 and DE-A10119933.

Suitable Mo-V-Nb-O multimetal oxide catalysts are described in particular in E.M.Thorsteins, T.P.Wilson, F.G.Young, P.H.Kasei, Journal of Catalysis52(1978), p.116. sub.132 and U.S. Pat. No. 4,250,346 and EP-A0294845.

Suitable Ni-X-O multimetal oxide catalysts are described in WO00/48971, where X ═ Ti, Ta, Nb, Co, Hf, W, Y, Zn, Zr, Al.

In principle, a suitable active composition can be obtained in a simple manner by obtaining a very homogeneous, good quality from its suitable component source compoundsA finely divided dry mixture corresponding to the stoichiometry is selected and calcined at 450-1000 ℃. Calcination may be carried out under an inert gas or an oxidizing atmosphere, such as air (a mixture of inert gas and oxygen), and also under a reducing atmosphere (such as inert gas, oxygen, and NH)₃CO and/or H₂Mixtures of (a) and (b). Suitable source compounds for the components of the multimetal active composition include oxides and/or those compounds that can be converted to oxides by heating, at least in the presence of oxygen. In addition to oxides, suitable starting compounds of this type are, in particular, halides, nitrates, oxalates, citrates, acetates, carbonates, complex amine salts, ammonium salts and/or hydroxides.

The multimetal oxide compositions can be used in the process of the invention in powder form or in the form of shaped bodies to a certain catalyst geometry, and the shaped bodies can be formed before or after the final calcination. Suitable unsupported catalyst geometries are, for example, solid cylinders or hollow cylinders having an outer diameter and length of from 2 to 10 mm. In the case of hollow cylinders, a suitable wall thickness is 1-3 mm. Suitable hollow cylinders have geometric dimensions of, for example, 7mm by 4mm or 5mm by 3mm by 2mm or 5mm by 2mm (length by outer diameter by inner diameter in each case). The unsupported catalyst may of course also have a spherical geometry, in which case the spheres may have a diameter of from 2 to 10 mm.

The pulverulent active composition which has not been calcined or a pulverulent precursor composition thereof can of course also be shaped by application to a preformed inert catalyst support. The layer thickness of the powder composition applied to the support is suitably selected in the range of 50-500mm, preferably 150-250 mm. Suitable support materials include conventional porous or non-porous aluminas, silicas, thorias, zirconias, silicon carbides or silicates such as magnesium or aluminium silicates. The support may have a regular or irregular shape, preferably a regular shaped support with a significant surface roughness, such as a sphere, a hollow cylinder or a saddle with dimensions in the range of 1-100 mm. Use is suitably made of substantially nonporous, roughly spherical talc supports having a diameter of from 1 to 8mm, preferably from 4 to 5 mm.

The reaction temperature of the heterogeneous catalytic oxidative dehydrogenation of propane is usually 300-600 ℃, and the typical temperature is 350-500 ℃. The pressure is from 0.2 to 15 bar, preferably from 1 to 10 bar, for example from 1 to 5 bar. Pressures above 1 bar, for example 1.5 to 10 bar, have been found to be particularly advantageous. Typically, the heterogeneously catalyzed oxidative dehydrogenation of propane is carried out over a fixed catalyst bed. The latter are suitably located within the tubes of tube bundle reactors, as described, for example, in EP-A700893 and EP-A700714 and the references therein. The mean residence time of the reaction gas mixture in the catalyst bed is generally from 0.5 to 20 seconds. According to the invention, the ratio of propane to oxygen in the starting reaction gas mixture to be used for the heterogeneously catalyzed oxidative dehydrogenation of propane can be from 0.5: 1 to 40: 1. Advantageously, the molar ratio of propane to molecular oxygen in the starting gas mixture is 6: 1 or less, preferably 5: 1 or less. In general, the above ratio may be ≧ 1: 1, e.g., 2: 1. The starting gas mixture may further comprise a substantially inert component such as H₂O、CO₂、CO、N₂Noble gases and/or propylene. In addition, a small amount of C may be contained₁、C₂And C₄A hydrocarbon.

The product gas stream b is generally at a pressure of from 0.2 to 15 bar, preferably from 1 to 10 bar, more preferably from 1 to 5 bar, and has a temperature of from 300 ℃ and 700 ℃ when it leaves the dehydrogenation zone.

In the propane dehydrogenation process, a gas mixture is obtained which generally has the following composition: 10-80% by volume of propane, 5-50% by volume of propylene, 0-20% by volume of methane, ethane, ethylene and C₄ ⁺Hydrocarbons, 0-30 vol.% carbon oxides, 0-70 vol.% steam and 0-25 vol.% hydrogen, and 0-50 vol.% inert gas.

In the preferred autothermal propane dehydrogenation, a gas mixture is obtained which generally has the following composition: 10-80% by volume of propane, 5-50% by volume of propylene, 0-20% by volume of methane, ethane, ethylene and C₄ ⁺Hydrocarbons, 0.1-30 vol.% carbon oxides, 1-70 vol.% steam and 0.1-25 vol.% hydrogen, and 0-30 vol.% inert gas.

In process step C, water is first removed from product gas stream b. The removal of water is effected by condensation, cooling and, if appropriate, compression of the product gas stream b and can be effected in one or more cooling and, if appropriate, compression stages. For this purpose, the product gas stream b is generally cooled to from 20 to 80 ℃ and preferably from 40 to 65 ℃. In addition, the product gas stream may be compressed to a pressure of typically 2 to 40 bar, preferably 5 to 20 bar, more preferably 10 to 20 bar.

In one embodiment of the process according to the invention the product gas stream b is passed through a set of heat exchangers and is thus first cooled to a temperature of from 50 to 200 c, followed by further cooling with water in a quench tower to a temperature of from 40 to 80 c, for example 55 c. This condenses out not only a major amount of the steam but also part C present in the product gas stream b₄ ⁺Hydrocarbons, especially C₅ ⁺A hydrocarbon. Suitable heat exchangers are, for example, direct heat exchangers and counterflow heat exchangers, such as gas-gas counterflow heat exchangers, and air coolers.

A product gas stream c depleted in steam is obtained. The product generally still contains 0 to 10% by volume of steam. For substantially complete removal of water from the product gas stream c, drying using molecular sieves or membranes may be provided when a special solvent is used in step D).

In process step D), the product gas stream C is contacted in a first absorption zone with a selected inert solvent which selectively absorbs propylene to obtain a load C₃A hydrocarbon, essentially propylene absorbent stream d1, and a gas stream d2 comprising propane, methane, ethane, ethylene, carbon monoxide, carbon dioxide and hydrogen. Propylene may also be present in small amounts in the gaseous stream d 2.

Carbon dioxide can be removed from the product gas stream c by means of gas scrubbing before carrying out process step D), obtaining a product gas stream c depleted in carbon dioxide. Carbon dioxide gas purification can be carried out by a separate combustion step, in which carbon monoxide is selectively oxidized to carbon dioxide.

To remove CO₂The purification liquid used is generally a sodium hydroxide solution, a potassium hydroxide solution or an alkanolamine solution; preferably, a solution of activated N-methyldiethanolamine is used. Typically, the product gas stream c is compressed to a pressure of 5-25 bar by compression in one or more steps before gas purification is carried out.

The resulting carbon dioxide depleted product gas stream d has CO₂The content is generally < 100ppm, preferably < 10 ppm.

The absorption can be carried out simply by passing stream c through an absorbent. However, it can also be carried out in a column. It can be carried out in a concurrent, countercurrent or cross-current manner. Suitable absorption columns are, for example, tray columns having bubble cap trays, valve trays and/or filter trays, columns having structured packings, for example fibrous packings or columns having a specific surface area of 100-1000m²/m³Sheet metal fillings, e.g.

250Y, and columns with random packing, for example with metal, plastic or ceramic balls, rings or saddles as random packing. However, trickle and spray towers, graphite block absorbents, surface absorbents such as thick film and thin film absorbents, and bubble towers with and without internals can also be used.

The absorption column preferably has an absorption section and a rectification section. The absorbent is generally introduced overhead and stream c is generally introduced in the middle or upper half of the column. In order to increase the degree of enrichment of propylene in the solvent by means of rectification, heat can be introduced into the bottom of the column. Alternatively, a stripping gas stream, for example consisting of nitrogen, air, steam or propylene, preferably consisting of propylene, can be fed to the bottom of the column. A portion of the overhead product may be condensed and reintroduced overhead in reflux to limit solvent loss.

Suitable selective solvents which selectively absorb propylene are, for example, N-methylpyrrolidone (NMP), NMP/water mixtures containing up to 20% by weight of water, m-cresol, acetic acid, methylpyrazine, dibromomethane, Dimethylformamide (DMF), propylene carbonate, N-methylmorpholine, ethylene carbonate, formamide, malononitrile, gamma-butyrolactone, nitrobenzene, dimethyl sulfoxide (DMSO), sulfolane, pyrrole, lactic acid, acrylic acid, 2-chloropropionic acid, triallyl trimellitate, tris (2-ethylhexyl) trimellitate, dimethyl phthalate, dimethyl succinate, 3-chloropropionic acid, morpholine, acetonitrile, 1-butyl-3-methylimidazolinium octylsulfate, ethylmethylimidazolinium tosylate, dimethylaniline, adiponitrile and formic acid.

Preferred selective absorbents are NMP, NMP/water mixtures containing up to 20% by weight of water, acetonitrile, and acetonitrile mixtures with acetonitrile contents of > 50% by weight, organic solvents and/or water, and dimethylaniline.

The absorption step D) is generally carried out at a pressure of from 2 to 40 bar, preferably from 5 to 20 bar, more preferably from 10 to 20 bar. In addition to propylene, propane is also absorbed to some extent by the selective absorber. In addition, small amounts of ethylene and butenes were also absorbed.

In an optional step E), absorbent stream d1 is decompressed to a lower pressure in a first absorption zone to obtain an absorbent stream E1 essentially loaded with propylene and a gas stream E2 comprising mainly propylene and still a small amount of propane, and gas stream E2 is recycled into the first absorption zone, preferably as purge gas into the rectifying section of the absorption column.

For this purpose, the absorbent stream D1 is depressurized from the pressure corresponding to the absorption stage D) to a pressure of generally from 1 to 20 bar, preferably from 1 to 10 bar. Decompression may be performed in a plurality of stages, typically up to 5 stages, for example 2 stages. The loaded absorbent stream may be additionally heated.

A gas stream e2 is obtained which comprises propylene and which typically comprises from 0 to 5% by volume of propane, from 50 to 99% by volume of propylene and from 0 to 15% by volume of other gaseous components such as steam, ethylene and carbon oxides, and from 0 to 50% by volume of solvent. This stream is recycled into the absorption zone. The recycle gas stream e2 is preferably fed in the lower half of the absorption column, for example at the level of the 1 st to 10 th theoretical plates. In one embodiment, the gas stream comprising propene obtained in the desorption step E) is fed as stripping gas to the bottom of the absorption column. As a result of the recycle propylene stream, propane dissolved in the absorbent is stripped away and the degree of enrichment of propylene in the absorbent is thus increased.

In step F), from the predominantly propylene-laden absorbent stream d1 or e1, a gaseous stream F1 comprising propylene is released and the selective absorbent is recovered by decompressing, heating and/or stripping the absorbent stream d1 or e1 in at least one (second) desorption zone. If appropriate, may contain C₄ ⁺A portion of this absorbent stream of hydrocarbons is discharged, treated and recycled, or otherwise discarded.

In order to desorb the gas dissolved in the absorbent, it is heated and/or decompressed to a lower pressure. Alternatively, desorption may also be carried out by stripping, typically with steam, or a combination of depressurization, heating and stripping in one or more process steps.

The gas stream f1 which comprises propylene and has been released by desorption typically comprises at least 98 vol% propylene, preferably at least 99 vol% propylene, more preferably at least 99.5 vol% propylene, based on the hydrocarbon content. In addition, it may also contain 0 to 2% by volume of propane and small amounts of low-boiling hydrocarbons such as methane and ethylene, but usually not more than 0.5% by volume, preferably not more than 0.2% by volume. When the desorption is carried out by steam stripping, the gas stream f1 also comprises steam, typically in an amount of at most 50% by volume, based on the total amount of the gas stream.

When propylene is desorbed in step F by stripping with steam, steam is usually subsequently removed from the gas stream F1. This removal can be effected by condensation, by cooling and, if appropriate, compression of the gas stream f 1. The removal can be carried out in one or more cooling and, if appropriate, compression steps.

For this purpose, the gas stream f1 is generally cooled to a temperature of from 0 to 80 ℃ and preferably from 10 to 65 ℃. Alternatively, the product gas stream may be compressed to a pressure of, for example, 2 to 50 bar. Drying with molecular sieves may be provided for substantially complete removal of water from gas stream f 1. The drying can also be carried out by absorption, membrane separation, rectification or other drying methods known in the art.

In order to achieve a particularly high propylene content of the gas stream F1, it is preferred that part of the gas stream F1 comprising propylene and obtained in step F) is recycled to the absorption zone. The proportion of the recycle gas stream is generally from 0 to 25%, preferably 0.10%, of gas stream f 1. Typically, at least part of the propane present in gas stream d2 is recycled to the dehydrogenation zone.

In one embodiment of the process of the invention, the propane-containing gas stream d2 is at least partly recycled directly to the dehydrogenation zone, and a side stream (purge gas stream) is typically removed from gas stream d2 to discharge inert gases, hydrogen and carbon oxides. The purge gas stream may be incinerated. However, a sub-stream of gas stream d2 may be directly recycled to the dehydrogenation zone, and propane may be removed from the other sub-stream by absorption and desorption and recycled to the dehydrogenation zone.

In another preferred embodiment of the process according to the invention, at least part of the gas stream D2 which comprises propane and is obtained in step D) is contacted with a high-boiling absorbent in a further step G), followed by desorption of the gas dissolved in the absorbent to obtain a recycle stream G1 which consists essentially of propane and an offgas stream G2 comprising methane, ethane, ethylene, carbon monoxide, carbon dioxide and hydrogen. A recycle stream consisting essentially of propane is recycled to the first dehydrogenation zone.

For this purpose, in the absorption stage, the gas stream d2 is contacted with an inert absorbent to separate propane and small amounts of C₂The hydrocarbons are absorbed in an inert absorbent and a propane-loaded absorbent and an off-gas comprising the remaining gas components are obtained. In practice, these remaining components are carbon oxides, hydrogen,Inert gas, C₂Hydrocarbons and methane. In the desorption phase, propane is released again from the absorbent.

The inert absorbent used in the absorption stage is generally a high-boiling, nonpolar solvent in which the propane to be removed has a significantly higher solubility than the remaining gas components. Absorption can be carried out by simply passing stream d2 through the absorbent. However, it can also be carried out in a column or in a rotating absorber. It may be operated in a co-current, counter-current or cross-current manner. Suitable absorption columns are, for example, tray columns having bubble cap trays, centrifuge trays and/or filter trays, columns having structured packings, for example fibrous packings or columns having a specific surface area of 100-²/m³Sheet metal fillings, e.g. Mellapak

250Y, and a column with random packing. It is also possible to use trickle and spray towers, graphite block absorbents, surface absorbents such as thick film and thin film absorbents, and also rotating towers, disc scrubbers, cross-spray scrubbers, rotating scrubbers and bubble towers with and without internals.

Suitable absorbents are relatively nonpolar organic solvents, for example aliphatic C₄-C₁₈Olefins, naphthas or aromatic hydrocarbons such as middle oil fractions from the distillation of paraffins, or ethers having bulky radicals or mixtures of these solvents, to which polar solvents such as dimethyl-1, 2-phthalate may be added. Suitable absorbents are also benzoic acid and phthalic acid with straight-chain C₁-C₁₈Esters of alkanols, for example n-butyl benzoate, methyl benzoate, ethyl benzoate, dimethyl phthalate, diethyl phthalate, and heat carrier oils such as biphenyl and diphenyl ethers, their chloro derivatives, and triarylolefins. Suitable absorbents are mixtures of biphenyl and Diphenyl ether, preferably mixtures of azeotropic composition, e.g. commercially available Diphenyl

. Frequently, such solvent mixtures contain from 0.1 to 25% by weight of dimethyl phthalate. Suitable absorbents are also butane, pentane, hexane, heptane, octane, nonane, decane, undecane, dodecane, tridecane, tetradecane, pentadecane, hexadecane, heptadecane and octadecane, or fractions obtained from refinery streams and comprising linear olefins as main component.

To desorb propane, the loaded absorbent is heated and/or depressurized to a lower pressure. Alternatively, desorption may also be carried out by stripping, typically with steam or an oxygen-containing gas, or by a combination of one or more process steps of depressurization, heating and stripping. For example, desorption may be carried out in two stages, the second desorption stage being carried out at a lower pressure than the first stage, and the desorption gas of the first stage being recirculated to the absorption stage. The absorbent regenerated in the desorption stage is recycled to the absorption stage.

In one embodiment, the desorption step is carried out by decompressing and/or heating the loaded absorbent. In other process variants, stripping is additionally carried out with steam. In other embodiments, stripping is additionally carried out with an oxygen-containing gas. The stripping gas may be used in an amount corresponding to the amount of oxygen required for autothermal dehydrogenation.

Alternatively, in process step G), carbon dioxide can be removed from the gas stream d2 or a side stream thereof by gas scrubbing to obtain a carbon dioxide-depleted recycle stream G1. Carbon dioxide gas purification may be carried out by a separate incineration stage, in which carbon monoxide is selectively oxidized to carbon dioxide.

To remove CO₂As the purification liquid, a sodium hydroxide solution, a potassium hydroxide solution or an alkanolamine solution is usually used; preferably, a solution of activated N-methyldiethanolamine is used. Typically, the product gas stream c is compressed to a pressure of from 5 to 25 bar by one or more stages of compression before gas purification is carried out. Can obtain CO₂The carbon dioxide-depleted recycle stream g1 is generally present in an amount of < 100ppm, preferably < 10 ppm.

If appropriate, hydrogen can be removed from gas stream d2 by membrane separation or pressure swing absorption.

In order to remove the hydrogen present in the exhaust gas stream, the exhaust gas stream may, if appropriate after cooling, be passed through a membrane, which is generally tubular in shape and is only permeable to molecular hydrogen, for example in a direct heat exchanger. The molecular hydrogen thus removed can, if desired, be used at least partially for dehydrogenation or fed to other utilities, for example to generate electrical energy in a fuel cell. Alternatively, the exhaust gas stream may be incinerated.

The invention will be further illustrated by the following examples.

Examples

The embodiment of the invention shown in the figure is simulated by calculation. The process parameters are assumed as follows.

The capacity of a 320kt/a propylene plant at 8000 hours run time was assumed.

Fresh propane typically contains 2 wt.% butane, in addition to 98 wt.% propane. The butane content can be depleted to 0.01% by weight in a C3/C4 splitter column having 40 theoretical plates at an operating pressure of 10 bar and a reflux ratio of 0.41. Hereinafter, the propane content is assumed to be 100% for the fresh propane stream 1.

Fresh propane stream 1 is combined with

recycle streams

21 and 22 to provide feed propane stream 2. The feed propane stream 2 is preheated to 400 c and enters the dehydrogenation zone 24 at a pressure of about 3 bar and undergoes autothermal dehydrogenation. The pure oxygen stream 3 and the steam stream 4 are additionally fed to a dehydrogenation zone 24. The conversion of dehydrogenation was 35.3% based on propane; the selectivity for propylene formation was 95.5%. In addition, 0.8% of cracked products (ethane and ethylene) and 3.7% of carbon oxides were formed by total combustion. The water concentration in the outlet gas of the dehydrogenation zone was 21% by weight; the residual oxygen content in the outlet gas was 0 wt.%; the outlet temperature of the product gas mixture was 595 ℃.

The outlet gas was cooled to 55 ℃ at 2.5 bar and water was condensed out until a saturated vapour pressure was reached. The product gas mixture is then compressed in two stages in a two-stage compressor 25 with intermediate cooling. From 2.5 bar to 6 bar in the first compression stage and from 5.9 bar to 15.3 bar in the second stage. After the first compression stage, the gas mixture was cooled to 55 ℃ and after the second compression stage to 30 ℃. When the compression is complete, a condensate stream 7 is obtained which consists mainly of water. The compressed and cooled gas stream 6 is contacted with a water/NMP mixture 17 as absorbent in an absorption column 26 at a pressure of 15 bar. The absorbent 17 is introduced from the top of the column. The propylene-loaded stream 8 discharged from the bottom of the absorber 26 contains only a small amount of propane, so that propane/propylene separation can be dispensed with during further processing. Propane-containing stream 9 discharged overhead from absorber 26 can be partially recycled as stream 21 to dehydrogenation zone 24. The remaining substream 10 is contacted with Tetradecane (TDC) as an absorbent in an absorption/desorption unit 13. The remaining residual gas stream 23 comprises mainly hydrogen and carbon oxides. The desorption provides a gas stream 22 comprising primarily propane and is recycled to the dehydrogenation zone 24. The bottom discharge stream 8 consisting of the propylene-laden absorbent is depressurized in a first desorption stage 27 to a pressure of 6 bar. On completion of the aforesaid treatment, a gas stream 11 comprising mainly propylene is released and recycled to the absorption column 26. The propylene loaded absorbent is fed as stream 12 to a desorber 28. In the desorption column 28, propylene is desorbed by decompression to 1.2 bar, heating of the bottom and stripping with steam 14 at a high pressure of 16 bar, obtaining a stream 13 consisting of regenerated absorbent and a stream 15 consisting of propylene and steam. Regenerated absorbent 13 is replenished with fresh absorbent 16 and recycled to absorber 26. The stream discharged via the top of the column is compressed in 15 stages to 15 bar and simultaneously cooled to 40 ℃. When the treatment is complete, water is condensed out and discharged from the process as waste water stream 18 and a substantially water-free pure propylene stream 19 is obtained. The vapor depleted pure propylene stream 20 is recycled to the absorber column.

The composition of the stream is reproduced in parts by mass according to the following table.

Claims

1. A process for producing propylene from propane comprising the steps of:

A) providing a feed gas stream a comprising propane;

B) a feed gas stream a comprising propane, if appropriate steam and if appropriate an oxygen-containing gas stream is fed to a dehydrogenation zone and propane is dehydrogenated to propene, a product gas stream b comprising the following components being obtained: propane, propylene, methane, ethane, ethylene, carbon monoxide, carbon dioxide, steam, if appropriate hydrogen and if appropriate oxygen;

D) the product gas stream c is contacted in a first absorption zone with a selective inert absorbent capable of selectively absorbing propylene, obtaining an absorbent stream d1 loaded mainly with propylene and a gas stream d2 comprising propane, propylene, methane, ethane, ethylene, carbon monoxide, carbon dioxide, if appropriate hydrogen and if appropriate oxygen;

E) if appropriate, the absorbent stream d1 is decompressed in a first desorption zone to obtain a predominantly propylene-laden absorbent stream e1 and a gaseous stream e2 comprising propylene, and the gaseous stream e2 is recycled into the first absorption zone,

F) from the predominantly propylene-laden absorbent stream d1 or e1, a gaseous stream f1 comprising propylene is released by decompressing, heating and/or stripping the absorbent stream d1 or e1 in at least one second desorption zone and the selective absorbent is recovered.

2. The process as claimed in claim 1, wherein the dehydrogenation in step B) is carried out as an oxidative or nonoxidative dehydrogenation.

3. The process as claimed in claim 1, wherein the dehydrogenation in step B) is carried out adiabatically or isothermally.

4. The process of claim 1, wherein the dehydrogenation in step B) is carried out in a fixed bed reactor, a moving bed reactor or a fluidized bed reactor.

5. The process of claim 1 wherein an oxygen-containing gas stream is fed in step B), said oxygen-containing gas stream comprising at least 90% by volume of oxygen.

6. The process as claimed in claim 5, wherein the dehydrogenation is carried out as autothermal dehydrogenation.

7. The process according to claim 1, wherein a portion of the gaseous stream F1 comprising propylene and obtained in step F) is recycled to the absorption zone.

8. The process according to claim 1, wherein the selective absorber used in step D) is selected from NMP, NMP/water mixtures containing up to 20% by weight of water, m-cresol, acetic acid, methylpyrazine, dibromomethane, DMF, propylene carbonate, N-methylmorpholine, ethylene carbonate, formamide, malononitrile, γ -butyrolactone, nitrobenzene, DMSO, sulfolane, pyrrole, lactic acid, acrylic acid, 2-chloropropionic acid, triallyl trimellitate, tris (2-ethylhexyl) trimellitate, dimethyl phthalate, dimethyl succinate, 3-chloropropionic acid, morpholine, acetonitrile, 1-butyl-3-methylimidazolinium octylsulfate, ethylmethylimidazolinium tosylate, adiponitrile, dimethylaniline and formic acid.

9. The process as claimed in claim 1, wherein the absorption zone in step D) is an absorption column having an absorption section and a rectification section, and heat and/or stripping gas is fed to the bottom of the column.

10. The process according to claim 9, wherein the gas stream comprising propene obtained in the desorption step E) is fed as stripping gas to the bottom of the absorption column.

11. The process of claim 1, wherein the stripping is carried out with steam in step F).

12. The process according to claim 11, wherein steam is condensed out by one or more stages of cooling and compression and removed as water from the gas stream F1 comprising propylene and steam and obtained in step F), or removed by absorption, rectification and/or membrane separation.

13. The process according to claim 1, wherein the off-gas stream D2 comprising propane and obtained in step D) is at least partly recycled to the dehydrogenation zone.

14. The process as claimed in claim 1, wherein at least part of the gas stream D2 which comprises propane and is obtained in step D) is contacted in a further step G) with a high-boiling absorbent, the gas dissolved in the absorbent is subsequently desorbed, a recycle stream G1 consisting essentially of propane and an offgas stream G2 comprising methane, ethane, ethylene, carbon monoxide, carbon dioxide and hydrogen are obtained, and the recycle stream G1 consisting essentially of propane is recycled to the dehydrogenation zone, wherein the high-boiling absorbent used in step G) is selected from the group consisting of C₄-C₁₈Olefins, naphtha or middle oil fractions from the distillation of paraffins.

15. The process as claimed in claim 14, wherein the gas dissolved in the absorbent is desorbed by stripping with steam in step G).

16. The process as claimed in claim 1, wherein in a further step G) carbon dioxide is removed by gas scrubbing at least from a side stream of the gas stream D2 comprising propane obtained in step D), obtaining a recycle stream G1 which is low in carbon dioxide and which is recycled to the dehydrogenation zone.