WO2007082785A1

WO2007082785A1 - Method for removal of fluorinated or chlorinated compounds from technical c4-hydrocarbon streams

Info

Publication number: WO2007082785A1
Application number: PCT/EP2007/050029
Authority: WO
Inventors: Phillip Hanefeld; Hans Peter Rath; Thomas Wettling
Original assignee: Basf Se
Priority date: 2006-01-13
Filing date: 2007-01-03
Publication date: 2007-07-26

Abstract

The invention relates to the removal of fluorinated or chlorinated compounds from technical C4-hydrocarbon streams, normally containing as main components 1-butene, 2-butene, isobutene and butane, for example raffinate-1, raffinate-1P or raffinate-2 streams, by means of bringing the technical C4-hydrocarbon stream into contact with inorganic adsorption agents, normally, aluminium oxides, aluminium halides, zirconium oxides, titanium oxides, calcium oxides, silicates, or zeolites.

Description

Process for removing fluorine- or chlorine-containing compounds from C4 hydrocarbon technical streams

description

The present invention relates to a process for the removal of fluorine- or chlorine-containing compounds from technical C4 hydrocarbon streams, in particular from those technical C4 hydrocarbon streams from which isobutene was partially or largely removed by polymerization reaction by means of a fluorine- or chlorine-containing catalyst.

The polymerization of isobutene, which can be used as pure isobutene or in the form of technical C4 hydrocarbon streams, to polyisobutenes is usually carried out as cationic polymerization using fluorine-containing catalysts such as boron trifluoride or boron trifluoride adducts such as boron trifluoride etherates or boron trifluoride alcoholates. In this case, polyisobutenes having a high content of terminal double bonds, so-called highly reactive polyisobutenes, are preferably produced. This technology is described, for example, in WO 94/20554, WO 96/40808, WO 99/31 151 and WO 99/64482. Alternatively, chlorine-containing catalysts for the polymerization of isobutene, for example, anhydrous aluminum chloride, can be used.

In the catalysis with boron trifluoride or boron trifluoride adducts, however, there is a side reaction to the addition of fluorine to the polyisobutene or to the formation of low and medium molecular fluorine-containing by-products such as tert-butyl fluoride, diisobutyl fluoride or triisobutyl fluoride, which contaminate the polyisobutene and the residual gas stream , If technical C4 hydrocarbon streams such as the so-called raffinate 1 are used as isobutene source, which in addition to isobutene contain relatively large amounts of linear butenes, in particular 1-butene, higher polyisobutyl fluorides are also observed. The latter are hardly removed from the polyisobutene formed and the residual gas stream and lead to a significant increase in the fluorine content. The same applies to chlorine-containing catalysts for the polymerization of isobutene.

German Application No. 10 2004 033988.0 discloses a process for the preparation of highly reactive polyisobutenes having a low fluorine content, in which special moderators are used in the polymerization or the liquid reaction mixture after completion of the polymerization in the presence of such a moderator with an inorganic adsorbent such as a zeolite or Alumina is brought into contact. In order to be able to supply the isobutene-depleted C4-hydrocarbon residual gas streams, which occur in addition to the polyisobutene, to industrial reuse or to be able to use them elsewhere in the value-added chain, a reduction in the fluorine or chlorine content is required. Here, maximum fluorine contents of 10 ppm by weight and maximum chlorine contents of 50 ppm by weight are desirable. This generally applies to reusable C4 hydrocarbon streams containing fluorochemical compounds. The fluorine- or chlorine-containing compounds, if they remain in the streams, can lead to severe corrosion problems in the plant components and later to problems of the quality of the products resulting at the end of a value-added chain, due to later release of hydrogen fluoride or hydrogen chloride.

The object of the present invention was therefore to provide a process for the removal of fluorine- or chlorine-containing compounds from technical C 4 hydrocarbon streams, in particular from those technical C 4 hydrocarbon streams from which isobutene has been partly or substantially removed by a polymerization reaction using a fluorine- or chlorine-containing catalyst, provide.

Accordingly, a process for the removal of fluorine- or chlorine-containing compounds from technical C4 hydrocarbon streams has been found, which is characterized in that one brings the technical C4 hydrocarbon stream with an inorganic adsorbent in contact.

The technical C4 hydrocarbon streams to be treated, which are usually gaseous under the customary physical boundary conditions, generally contain 1-butene, 2-butene, isobutene and butanes as essential constituents, with both cis- and butene-2-butene Trans-2-butene and mixtures thereof are to be understood. Butadienes and butynes may be present in small amounts in the streams, but have mostly been greatly depleted prior to their use by special treatment methods of the streams, for example distillation, selective hydrogenation or extractive distillation. For the purposes of the present invention, technical C4 hydrocarbon streams also include fluorine or chlorine-containing residual gas streams from polymerization reactions of isobutene which are operated with pure isobutene.

The technical C4 hydrocarbon streams to be treated are, based on their technical origin, in particular C4 raffinate streams such as raffinate 1, raffinate 1 P or raffinate 2, C4 cuts from isobutane dehydrogenation, C4 cuts from steam cultivators according to US Pat Butadiene extraction, C4 cuts from steam crackers after TeN hydrogenation (HC4) or C4 cuts from Fluid Catalyst Cracking (FCC). Such streams are largely exempt from contained 1, 3-butadiene, they contain in usually less than 1000 ppm by weight, preferably less than 200 ppm by weight of butadiene.

Typically, in a raffinate 1 stream, the content of 1-butene is 10 to 50% by weight, 2-butene is 10 to 40% by weight, isobutene is 30 to 50% by weight, and butanes 2 to 35% by weight.

Typically, in a raffinate 1 P stream, the content of 1-butene is 1 to 15% by weight, 2-butene is 15 to 50% by weight, isobutene is 35 to 60% by weight, and butanes 2 are to 40% by weight.

In a raffinate 2 stream, the content of 1-butene is typically 15 to 60% by weight, 2-butene 5 to 50% by weight, isobutene 0.5 to 10% by weight and butanes 5 to 45 wt .-%.

Typically, in a C4 cut from isobutane dehydrogenation, the content of 1-butene is less than 1 wt%, 2-butene is less than 1 wt%, isobutene is 20 to 70 wt%, and butanes From 30 to 80% by weight.

Typically, in a C4 cut from steam crackers after butadiene extraction, the content of 1-butene is 10 to 30 wt .-%, of 2-butene 10 to 30 wt .-%, of isobutene 30 to 50 wt .-% and butane 5 to 20 wt .-%.

Typically, in a partially hydrogenated C4 cut from the steam cracker (HC4 stream), the content of 1-butene is 15 to 60% by weight, 2-butene is 5 to 50% by weight, and isobutene is 10 to 45% by weight. % and butanes 5 to 45 wt .-%.

Typically, in a FCC stream, the content of 1-butene is 5 to 25% by weight, 2-butene 10 to 40% by weight, isobutene 10 to 30% by weight, and butanes 30 to 70% by weight. -%.

The fluorine-containing compounds to be removed by the process according to the invention may be inorganic compounds such as hydrogen fluoride or metal fluorides, for example sodium fluoride, or organic compounds such as the mono- and polyisobutyl fluorides already mentioned. Typical mono- or polyisobutyl fluorides can be represented by the following general formula:

n = 0 monoisobutenyl fluoride (= tert-butyl fluoride) n = 1 diisobutyl fluoride n = 2 triisobutyl fluoride n = 3 tetraisobutyl fluoride n = 4 pentaisobutyl fluoride

Corresponding chlorine-containing compounds to be removed by the process according to the invention are structured or built up analogously to this.

With the process according to the invention, such fluorine- or chlorine-containing compounds are completely or at least for the most part removed from technical C 4 hydrocarbon streams. The maximum fluorine content in the streams treated by the process according to the invention is significantly lower than before treatment and is usually 10 ppm by weight, in many cases it is even lower, for example at a maximum of 5 ppm by weight. The maximum chlorine content in the streams treated by the process according to the invention is also significantly lower than before treatment and is usually 50 ppm by weight, in many cases even lower, for example at a maximum of 20 ppm by weight.

In a preferred embodiment, the inventive method for the removal of fluorine- or chlorine-containing compounds is applied to such technical C4 hydrocarbon streams from which isobutene was partially or largely removed by polymerization reaction using a fluorine- or chlorine-containing catalyst. In this embodiment, the treated C4 hydrocarbon stream (after isobutene removal) is typically a raffinate 2 stream.

The technical C4 hydrocarbon streams largely freed from fluorine- or chlorine-containing compounds by the process of the invention are suitable for a wide variety of industrial applications. In the event that from the technical

C4 hydrocarbon stream isobutene was partially or largely removed by polymerization reaction using a fluorine- or chlorine-containing catalyst, the current largely freed from fluorine- or chlorine-containing compounds according to the invention is preferably attributed to the polymerization reaction of isobutene.

A further technical possibility for the use of the process of the invention of fluorine- or chlorine-containing compounds substantially freed technical C4 hydrocarbon streams is the production of isooctene by dimerization reaction. Isooctene is suitable, for example, as an additive for petrol for octane number improvement. Furthermore, isooctene serves as starting material for the oxo synthesis of nonanols, which in turn can be a basis for the production of plasticizers or surfactants. Another technical application for the process according to the invention of fluorine or chlorine-containing compounds largely freed technical C4 hydrocarbon streams, especially those with high 1-butene content, is the preparation of pentanols and / or pentanals by oxo synthesis (hydroformylation). mylierung). For example, pentanals such as n-valeraldehyde can subsequently be converted by Aldolkondensation and subsequent hydrogenation to 2-propylheptanol, which in turn can be a basis for the production of plasticizers or surfactants.

Another technical application for the process of the invention of fluorine or chlorine-containing compounds largely freed technical C4 hydrocarbon streams is the return of these streams as a raw material in the steam cracker.

The said polymerization of the isobutene by means of a fluorine- or chlorine-containing catalyst, in particular a boron trifluoride-containing catalyst, is carried out by methods known to the person skilled in the art. The polyisobutene produced usually has a number average molecular weight of 400 to 50,000 and a content of vinylidene groups of more than 50 mol%.

The term "vinylidene group content" refers to the percentage of polyisobutene molecules having a vinylidene group based on the number of all olefinically unsaturated polyisobutene molecules in a sample. It can be determined by ¹ H-NMR and / or ¹³ C-NMR spectroscopy, as is known in the art. The content of methylidene groups is more than 50 mol%, preferably at least 60 mol%, particularly preferably at least 75 mol%.

The polyisobutene thus obtained has a number-average molecular weight M _{n of} from 400 to 50,000, preferably from 500 to 5,000, in particular from 700 to 2,500. The dispersity (D = Mw / Mn) is typically less than 2.5, preferably less than 2.0, and more preferably less than 1.8.

In the polymerization of isobutene with fluorine-containing catalysts such as boron trifluoride hydrogen cyanide, cyanides or nitriles can be included, which control the reactivity of the boron trifluoride catalyst and therefore can be referred to as "moderators". In contrast to other measures for controlling the catalyst activity, such. As lowering the temperature, these moderators allow high isobutene sales, whereby the formation of undesired Isobutenoligomerer and fluorinated compounds is pushed back. Suitable moderators in the polymerization of the isobutene are hydrogen cyanide (hydrocyanic acid) or organic nitriles of the general formula R-CN, where R is alkyl, alkenyl, alkynyl, alkaryl or aralkyl having preferably up to 12 carbon atoms. Preferably, the moderator is selected from acetonitrile, propionitrile, acrylonitrile and benzonitrile.

In addition, inorganic cyanides, in particular alkali metal and / or alkaline earth metal cyanides, such as sodium cyanide or potassium cyanide are also suitable. The cyanides may conveniently be applied to inert insoluble carriers which are suspended in the reaction mixture.

The moderator is generally added to the reaction mixture in an amount of 1 to 25 mol%, preferably 5 to 15 mol%, based on the boron trifluoride.

Due to the high viscosity of the polyisobutenes produced, the polymerization of the isobutene is generally carried out in the presence of a diluent. For this purpose, such diluents or mixtures are suitable, which are inert to the reagents used. Suitable diluents are saturated or unsaturated aliphatic, cycloaliphatic and aromatic hydrocarbons, for example saturated hydrocarbons such as butane, pentane, hexane, heptane, octane, isooctane, cyclopentane, cyclohexane, methylcyclohexane, toluene or ethylbenzene; halogenated hydrocarbons such as methyl chloride, dichloromethane or trichloromethane and mixtures of the abovementioned compounds. When C4 hydrocarbon feedstreams are used as feedstock, the hydrocarbons other than isobutene can play the role of an inert diluent. Isobutene itself can also be used as diluent if the polymerization is operated only to a partial conversion. Preferably, the diluents are freed prior to their use of impurities such as water, carboxylic acids or mineral acids, for example by adsorption on solid adsorbents such as activated carbon, molecular sieves or ion exchangers.

As catalysts boron trifluoride complex catalysts are preferred. This is understood to mean catalysts of boron trifluoride and at least one cocatalyst. Suitable cocatalysts are usually oxygen-containing compounds. The catalyst preferably has the composition:

wherein L ^{1 is} water, a halogenated hydrocarbon, a primary C ¹ to C 8 alkanol, a C ³ to C 8 secondary alkanol, a phenol and / or a tertiary butyl ether,

L ^{2 represents} at least one aldehyde and / or one ketone,

L ^{3 is} an ether other than a tert-butyl ether having at least 5 carbon atoms, a secondary alkanol having at least 6 carbon atoms, a primary alkanol having at least 6 carbon atoms and / or a tertiary alkanol,

The ratio b: a lies in the range from 0.9 to 3.0, preferably 1, 1 to 2.5,

The ratio c: a lies in the range from 0 to 0.5, preferably 0 to 0.3,

The ratio d: a is in the range from 0 to 1.0, preferably 0.1 to 1, in particular 0.1 to 0.6.

The starters L ¹ are compounds with an abstractable hydrogen atom without significant steric hindrance. They are called "starters" because their active hydrogen atom is incorporated at the beginning of the growing polyisobutene chain. In addition, tert-butyl ethers such as tert-butyl methyl ether, which readily form a tert-butyl cation, phenols such as phenol or cresols, or halogenated hydrocarbons such as dichloromethane or trichloromethane are suitable. As L ¹ , for example, water, methanol, ethanol, 2-propanol and / or 1-propanol are suitable. Of these, methanol is most preferred.

Aldehydes and / or ketones, which usually comprise one to 20, preferably 2 to 10, carbon atoms and in which preferably other functional groups than the carbonyl group are absent, may also be used as regulator L ² . As L ² , for example, formaldehyde, acetaldehyde, propionaldehyde, n-butyraldehyde, isobutyraldehyde, acetone, methyl ethyl ketone and diethyl ketone are suitable. Acetone is the most preferred.

The solubilizers L ³ have a solubilizing effect and increase the solubility of the catalyst complex in the feedstock. These are ethers which are other than tert-butyl ethers and have at least 5 carbon atoms or long-chain and / or sterically hindered alcohols which provide shielding against the access of isobutene molecules. It is preferable to use dialkyl ethers having 5 to 20 carbon atoms, a secondary alkanol having 6 to 20 carbon atoms, a primary alkanol having 6 to 20 carbon atoms, and / or a tertiary C ₄ to C 20 alkanol. If primary alkanols are used, these preferably have a β-branch, ie, a branch on the adjacent carbon atom to the carbon atom bearing the hydroxyl group. Suitable representatives are, for example, di-n-butyl ether, di-n-hexyl ether, dioctyl ether, 2-ethylhexanol, 2-propylheptanol, the oxo alcohols of di-, tri- and tetramerpropylene and di- and trimerbutene, linear 1 - Alcohols (which are available, for example, by the Alfol® process), if they are liquid under reaction conditions, such as n-hexanol or n-octanol, and selected tert-butanol. Of these, 2-ethylhexanol is most preferred.

The BF3 concentration in the reactor is generally in the range of 0.005 to 1 wt .-%, based on the liquid reaction phase, in particular in the range of 0.01 to 0.7 wt .-% and especially in the range of 0.02 to 0.5% by weight.

The boron trifluoride complexes can be preformed in separate reactors prior to their use in the process according to the invention, stored after their formation and metered into the polymerization apparatus as required.

Another preferred variant is that the boron trifluoride complexes are generated in situ in the polymerization apparatus or an inlet. In this procedure, the particular cocatalyst is optionally fed together with a solvent into the polymerization apparatus or the feed and dispersed boron trifluoride in the required amount in this mixture of the reactants. Here, the boron trifluoride and the cocatalyst to the boron trifluoride complex to. Instead of an additional solvent, the reaction mixture of unreacted isobutene and polyisobutene may function as a solvent in the in situ generation of the boron trifluoride catalyst complex.

The polymerization of isobutene is preferably carried out in a continuous process. Measures for the continuous polymerization of isobutene in the presence of boron trifluoride-containing catalysts in inert organic solvents to give polyisobutene are known per se. In a continuous process, part of the reaction mixture formed in the polymerization reactor is continuously discharged. An amount of feedstocks corresponding to the discharge is continuously supplied to the polymerization reactor and mixed with a circulating amount. The ratio of circulating amount to feed quantity is generally in the range from 1000: 1 to 1: 1, preferably in the range from 500: 1 to 5: 1 and in particular in the range from 20: 1 to 100: 1 v / v. The average residence time of the isobutene to be polymerized in the polymerization reactor, which is determined by reaction volume and feed quantity, can be from 5 seconds to several hours. Residence times of 1 to 30 minutes, in particular 2 to 20 minutes, are preferred.

The polymerization is generally carried out at a temperature in the range of -60 ° C to + 40 ° C, preferably less than 0 ° C, more preferably in the range of -5 ° C to -40 ° C and especially in the range of -10 ° C to -30 ° C. The heat of polymerization is dissipated by means of a cooling device accordingly. This can be operated, for example, with liquid ammonia as a coolant. Another way to dissipate the heat of polymerization is the boiling-cooling. In this case, the heat released is removed by evaporation of the isobutene and / or other volatile constituents of the isobutene feedstock or the optionally volatile solvent.

The isobutene is polymerized in the reactors customary for continuous polymerization, such as stirred kettles, tube, shell and loop reactors, loop reactors, ie. H. Pipe (bundle) reactors with recirculation and turbulent flow or internals such as static mixers, d. H. with Rührkesselcharakteristik, are preferred. In low-viscosity reaction mixtures, loop reactors with tube cross-sections which lead to turbulent flow are particularly favorable; on the other hand, in the case of highly viscous reaction mixtures, larger tube cross sections with static mixing elements are more favorable.

Preferably, the polymerization of the isobutene is carried out in at least two successive reactors, of which at least the first reactor is remixed in some areas, wherein one doses at least in the second and / or further reactor one or more of the above moderators. In particular, a first subset of the moderator (s) is metered into the first reactor and at least one further subset is metered into the second or further reactor. The proportion of the metered in the first reactor subset of the total amount of moderators is preferably 40 to 90%.

In the first reactor, the isobutene supplied is generally polymerized to a partial conversion of up to 95%, preferably 50 to 90%, particularly preferably 70 to 90%, based on the isobutene introduced into the first reactor. The discharge from the first reactor is preferably passed without further work-up into the second reactor or from a preceding to the subsequent reactor. Here, the further polymerization takes place without the addition of fresh isobutene.

The residence time of the reaction mixture in the first reactor is usually 5 to 60 minutes when adjusting an isobutene conversion of 50 to 90%, but may be shorter or longer, depending on whether a very active or less active catalyst is used. In the second reactor, a residence time of from 1 to 180, preferably from 2 to 120 minutes is generally set. In general, isobutene conversion is set in the last reactor so that the total conversion of the isobutene is 90 to 99.5%. The concentration of isobutene in the liquid reaction phase in the main reactor is generally in the range of 0.2 to 50 wt .-%, preferably in the range of 0.5 to 20 wt .-% and in particular in the range of 1 to 10 wt. -%, based on the liquid reaction phase. In the preparation of polyisobutenes with number-average molecular weights M _n in the range from 500 to 5000, it is preferable to work at an isobutene concentration in the range from 1 to 20% by weight and in particular in the range from 1 to 5% by weight. In the preparation of polyisobutenes having a number average molecular weight M _n of more than 5000, preference is given to working at an isobutene concentration in the range from 4 to 50% by weight. In particular, in the first reactor an isobutene concentration of 3% by weight does not fall below.

When leaving the last reactor, the reaction mixture usually contains 2 wt .-% or less isobutene. Preferably, an isobutene concentration of 0.5 wt .-% does not fall below.

Preferably, in the polymerization of the isobutene, at least in the main reactor, under isothermal conditions, i. the temperature of the liquid reaction mixture in the polymerization reactor has a steady state value and does not change or only slightly during operation of the reactor. If desired, the polymerization in the second reactor may be at a lower polymerization temperature than in the first reactor; it then usually requires further activation by addition of, for example, fresh boron trifluoride or a regulator, such as an aldehyde or ketone, z. Acetone. However, it is preferred to operate the second or further reactor at a slightly higher temperature to complete the isobutene conversion by thermal activation. Since the polymerization is exothermic, one can operate the second or further reactor under substantially adiabatic conditions, d. H. the reactor is not actively cooled or heated, and the heat of polymerization is taken up by the reaction mixture.

The discharged from the polymerization reaction mixture still contains active catalyst. As a result, the polyisobutene formed in the polymerization reactor may be adversely affected in terms of molecular weight, molecular weight distribution and end group content. Therefore, in order to prevent further reaction, the polymerization is usually stopped by deactivating the catalyst. The deactivation can be effected, for example, by adding water, alcohols, acetonitrile, ammonia or aqueous solutions of mineral bases or by introducing the discharge into one of the abovementioned media. Preferably, the deactivation with water, which is preferably carried out at temperatures in the range of 1 to 60 ° C (water temperature). At lower temperatures, termination is recommended by the addition of acetonitrile; the deactivated discharge can be suitably used for pre-cooling of the inlet, z. B. in a countercurrent heat exchanger. The boron trifluoride complex catalysts can also be largely separated from the effluent and recycled to the polymerization reaction. The separation and recycling of the catalyst from the discharge of the polymerization reaction is known from WO 99/31 151, to which reference is made in its entirety. To separate the catalyst from the discharge is preferably used sparingly soluble boron trifluoride complex catalysts and / or the reaction mixture to temperatures of, for example, 5 to 30 Kelvin below reactor temperature, preferably 10 to 20 Kelvin below reactor temperature, from. In the separation of the catalyst from the reactor effluent, it is recommended that the isobutene concentration in the discharge to values below 2 wt .-%, preferably 1 wt .-% and in particular below 0.5 wt .-%, based on the discharge, lower.

The catalyst precipitates in the form of finely divided droplets which, as a rule, rapidly change into a coherent phase. The complex droplets or the coherent phase have a significantly higher density than the polymer solution. As a rule, they can therefore be separated from the polymer-rich, catalyst-poor product phase with the aid of separators, separators or other collecting containers. The thereby separated polymer-rich product phase is generally homogeneous and contains only small amounts of soluble catalyst components. These are deactivated in the manner described above, preferably with water.

In order to further reduce the fluorine or chlorine content in the polyisobutene, it is expedient to bring the reaction mixture into contact with an inorganic adsorbent after the end of the polymerization, which is explained in more detail below. The reaction mixture may, prior to adsorbent treatment, be subjected to various other treatments, e.g. B. a laundry for catalyst deactivation / removal and / or removal of volatile components.

The inorganic adsorbents to be used in the context of the present invention for the removal of fluorine- or chlorine-containing compounds from technical C 4 hydrocarbon streams are in principle the same, which can also be used to reduce the fluorine or chlorine content in the polyisobutene.

The mode of action of the inorganic adsorbent is obviously largely based on an adsorptive splitting of the fluorine- or chlorine-containing compounds and binding of the fluorine- or chlorine-containing fragments on its surface. The inorganic adsorbent could therefore also be referred to as a "nip contact".

This inorganic adsorbent generally comprises oxides and salts such as halogenides, in particular chlorides, sulfates, phosphates, carbonates or nitrates of silicon, aluminum, zirconium, calcium and / or titanium, which can have various dopings. In most cases, aluminum oxides, aluminum halides, zirconium ox- de, titanium oxides, calcium oxides, silicates, zeolites or mixtures thereof. Preferably, one works with alumina, zeolites and combinations thereof. The alumina used can in particular with a base, for. Example, an alkali or alkaline earth metal hydroxide or an alkali or alkaline earth metal cyanide, be doped.

The inorganic adsorbent may have an acidic, a neutral or a basic character. Particularly well-suited inorganic adsorbents are those which have on their surface in addition to acidic or weakly acidic regions also basic or weakly basic ranges; The latter are able to covalently bind split-off hydrogen fluoride or hydrogen chloride. Efficient removal of the hydrogen fluoride or hydrogen chloride in particular prevents the undesired acid-catalyzed structural isomerization of 1-butene to 2-butene.

In a preferred embodiment, the inorganic adsorbent comprises an aluminum oxide. Aluminum oxides are known as adsorbents for gases, liquids and solids, especially in chromatographic processes and methods. Acid, neutral or basic aluminum oxides can be used for the process according to the invention for the removal of fluorine- or chlorine-containing compounds, in particular basic aluminas are suitable for this purpose. Acidic aluminas usually have a pH of from 3 to 6, typically about 4. Neutral aluminum oxides usually have a pH of 6 to 8, typically of about 7, on. Basic aluminum oxides usually have a pH of 8 to 1 1, typically of about 9.5, on.

The aluminum oxides mentioned generally have pore volumes of 0.5 to 1.5 ml / g, typically of about 0.9 ml / g, usually inner surfaces of 70 to 250 m ² / g, typically of about 150 m ² / g, and usually particle sizes in the range of 30 to 300 microns, typically from 60 to 150 microns.

In a further preferred embodiment, the inorganic adsorbent comprises a zeolite having mean pore sizes of at least 3 Å, in particular from 5 to 15 Å. The mean pore size is determined by the crystal structure of the zeolite and z. B. are determined from X-ray structure data. In zeolites with smaller average pore sizes, the fluorine-containing compounds to be removed can diffuse poorly and are therefore inadequately adsorbed or split. Preferably, the zeolites used are substantially free of acid.

Preferred zeolites are selected from zeolite A, zeolite L, zeolite X and zeolite Y. Sodium zeolite A or sodium zeolite A, in which the sodium ions are wholly or partially replaced by magnesium and / or calcium ions, is particularly preferred. One Another particularly preferred zeolite is zeolite 10 A, which already shows a high absorptive cleavage performance at comparatively low temperatures.

In the zeolite treatment, the fluorine- or chlorine-containing compounds to be removed are presumably cleaved and the fluorine- or chlorine-containing cleavage products, such as hydrogen fluoride or hydrogen chloride, are adsorbed on the zeolite or chemically bound by the cations contained therein. In order to prevent undesired activation and / or structural change of the zeolite, it is possible, the hydrogen fluoride or hydrogen chloride by addition of an acid scavenger, z. B: an amine or a nitrile, to bind.

The inorganic adsorbent is conveniently activated prior to use by heating it usually under reduced pressure to a temperature of at least 150 ° C.

In a preferred embodiment, the technical C 4 -hydrocarbon stream is dried to a residual water content of 5 ppm by weight, in particular 3 ppm by weight, before it is brought into contact with the inorganic adsorbent. For this purpose, the gas stream is preferably brought into contact with a zeolite having an average pore size of 4 Å or less, usually at a temperature of less than 40 ° C., eg. At 5 to 35 ° C.

In a further preferred embodiment, therefore, the technical C ₄ hydrocarbon stream is introduced successively with (i) a first zeolite having an average pore size of 4 Å or less, preferably at a temperature of 5 to 35 ° C., and (ii) a second Zeolite having an average pore size of 5 to 15 Å or an alumina, preferably at a temperature of 60 to 180 ° C, in contact.

The contacting of the C4 hydrocarbon streams with the inorganic adsorbent (and also with a zeolite used for drying) can be carried out by any conceivable discontinuous or continuous process. The usually gaseous technical C 4 hydrocarbon streams are usually passed over the inorganic absorption medium in the form of a solid, the absorbent being essentially fixed in its position in the apparatus or installation. Preferably, the adsorbent is in a fixed bed or in a loose bed disposed in an adsorption column through which the gas stream is passed. The adsorption column is preferably arranged vertically and is flowed through by the gas flow in the direction of gravity or preferably against the force of gravity. It is also possible to use a plurality of adsorption columns connected in series. The contacting of the technical C4 hydrocarbon streams with the inorganic adsorbent to remove the fluorine- or chlorine-containing compounds is generally carried out at temperatures of 5 to 240 ° C, preferably 30 to 200 ° C, especially 40 to 150 ° C. The technical C4 hydrocarbon streams are usually adjusted in this contact to a pressure of 1 to 100 bar, in particular 1, 1 to 50 bar, especially 2 to 30 bar. In the described temperature and pressure conditions, the usually present in gaseous technical C4 hydrocarbon streams may also be liquefied in exceptional cases. The residence time, ie the time during which the gas stream is in contact with the adsorbent, is typically 10 to 100 minutes.

The following examples are intended to illustrate the present invention without limiting it.

example 1

In a adsorption column with a capacity of 3 m ³ , a raffinate 1 stream (1-butene: 15 wt .-%, 2-butene: 12 wt .-%, isobutene: 40 wt .-%, isobutane: 9 wt. %, n-butane: 24% by weight) with a fluorine content of 56 ppm by weight during a residence time of 30 minutes at 12 bar and 80 ° C. with commercially available basic aluminum oxide (pH 9.5, pore volume about 0, 9 ml / g, inner surface approx. 150 m ² / g, particle size 60 to 150 μm) brought into contact in bulk. Through the treatment, the fluorine content of the raffinate 1 stream could be reduced to 3 ppm by weight.

Example 2

In a adsorption column with a capacity of 3 m ³ was a raffinate 2 stream (1-butene: 47 wt .-%, 2-butene: 18 wt .-%, isobutene: 3 wt .-%, isobutane: 9 wt. %, n-butane: 23% by weight) with a fluorine content of 22 ppm by weight during a residence time of 30 minutes at 12 bar and 50 ° C. with commercially available basic aluminum oxide (pH 9.5, pore volume about 0, 9 ml / g, inner surface approx. 150 m ² / g, particle size 60 to 150 μm) brought into contact in bulk. The treatment reduced the fluorine content of the raffinate 1 stream to 4 ppm by weight.

Example 3

In a adsorption column with a capacity of 3 m ³ was a raffinate 2 stream (1-butene: 47 wt .-%, 2-butene: 18 wt .-%, isobutene: 3 wt .-%, isobutane: 9 wt. -%, n-butane: 23 wt .-%) with a fluorine content of 20 ppm by weight during a residence time of 30 min at 12 bar and 80 ° C with commercially available basic 0.9 ml / g, inner surface approx. 150 m ² / g, particle size 60 to 150 μm) in bulk. The treatment reduced the fluorine content of the Raffinate 1 stream to less than 1 ppm by weight.

Example 4

In a adsorption column with a capacity of 3 m ³ was a raffinate 2 stream (1-butene: 47 wt .-%, 2-butene: 18 wt .-%, isobutene: 3 wt .-%, isobutane: 9 wt. %, n-butane: 23% by weight) with a fluorine content of 22 ppm by weight during a residence time of 60 minutes at 12 bar and 50 ° C. with commercially available basic aluminum oxide (pH 9.5, pore volume approx. 9 ml / g, inner surface approx. 150 m ² / g, particle size 60 to 150 μm) brought into contact in bulk. The treatment reduced the fluorine content of the Raffinate 1 stream to less than 1 ppm by weight.

Claims

claims

1. A process for the removal of fluorine- or chlorine-containing compounds from technical C4 hydrocarbon streams, characterized in that brings the technical C4 hydrocarbon stream with an inorganic adsorbent in contact.

2. The method of claim 1 for the removal of fluorine- or chlorine-containing compounds from technical C4 hydrocarbon streams containing as essential constituents 1-butene, 2-butene, isobutene and butane.

3. The method of claim 1 or 2 for the removal of fluorine- or chlorine-containing compounds from C4-raffinate streams, C4 cuts from the isobutane dehydrogenation, C4 cuts from steam crackers after the butadiene extraction, C4 cuts from steam crackers after Partial hydrogenation (HC4) or

C4 sections from Fluid Catalyst Cracking (FCC).

4. The method according to claims 1 to 3 for the removal of fluorine- or chlorine-containing compounds from technical C4 hydrocarbon streams from which isobutene was partially or largely removed by polymerization reaction using a fluorine- or chlorine-containing catalyst.

5. The method according to claim 4 for the removal of fluorine- or chlorine-containing compounds from technical C4 hydrocarbon streams, characterized in that the resulting largely freed from fluorine- or chlorine-containing compounds stream leads back into the polymerization reaction of isobutene.

6. Process according to claims 1 to 5 for the removal of fluorine- or chlorine-containing compounds from technical C4 hydrocarbon streams, characterized in that, as the inorganic adsorbent, aluminum oxides,

Aluminum halides, zirconium oxides, titanium oxides, calcium oxides, silicates, zeolites or mixtures thereof.

7. Process according to claims 1 to 6 for the removal of fluorine- or chlorine-containing compounds from technical C4 hydrocarbon streams, characterized in that the technical C4 hydrocarbon stream before contacting with the inorganic adsorbent to a residual water content of 5 wt. -ppm dries.

8. Process according to claims 1 to 7 for the removal of fluorine- or chlorine-containing compounds from technical C4 hydrocarbon streams, characterized in that brings the technical C4 hydrocarbon stream with an inorganic adsorbent at temperatures of 5 to 240 ° C in contact.