NO821242L - PROCEDURE FOR THE PREPARATION OF I-ALKENES, SUITABLE CATALYST AND PROCEDURE FOR THEIR PREPARATION - Google Patents

Description

The invention relates to a method for producing i-alkenes by catalytic conversion of n-alkenes, a catalyst which is suitable for this conversion and a method for producing such a catalyst.

It is generally known that n-paraffins with, for example, 4-7 C atoms, using suitable Psure catalysts, can be converted in the temperature range from 100 to 250°C to the corresponding isomeric paraffins. Examples of this are numerous

in the petrochemical and mineral oil industry, isomerization processes are used to increase the octane number of light paraffinic petroleum fractions. Furthermore, it is known that, in contrast, olefins of the same carbon number do not resp. only under difficult conditions, for example at high temperatures and with poor yields, convert to the corresponding isoolefins. The experiments mentioned so far in the literature

for direct skeletal isomerization of, for example, n-butene to i-butene resp. of n-pentene to i-pentene on fixed catalysts is characterized by initially high conversions and selectivities which, after a short operating time, often after only a few hours, end and become significantly poor. The reduction in yields and selectivity is generally attributable to the loss of actively active catalyst surfaces or to the loss of active centers. This results in high degrees of coking, oligomer formation and cracking reactions.

Thus, US patent 3.5 31.54 2 describes a method for the production of i-butene from n-butene, in which a multi-stage A^O^ catalyst arranged in solid storage is used. According to US patent 3.66 3.45 3, the same conversion is also carried out in a fixed storage with a catalyst consisting of zirconium oxide and an Al-^O^/ZrOCl catalyst.

In US Patent 2,568. 964 also mentions the catalytic isomerization of olefinic carbons in a solid storage. It is mentioned that during the isomerization process carbon deposits occur on the catalyst material which reduces the activity and necessitates periodic regeneration of the catalyst. After the regeneration, the catalyst must regain its full activity, however at least the disadvantage remains that during the regeneration period the actual isomerization process must be interrupted.

Representative of other alkanes, butenes are used to mention the following compounds: In petrochemical plants or in refineries, distillate fractions containing n-butene often appear, possibly in a mixture with i-butene, i-butane and n-butane, so for example after separation of 1,3-butadiene from a C^ cut or by cracking wash distillates. The possibly present i-butene in such distillate fractions is converted above all in catalytic reactions, for example with methanol to methyl-tert-butyl ether, which is separated by distillation from the remaining C^-part, and can be used as a knock-number improver for Kgørebensin or as a solvent.

A further catalytic reaction of the isobutene in such mixtures is the oligomerization on acid catalysts to, for example, Cgj-C, 2~ e^ are C^g oligomers of isobutene, which can likewise be separated by distillation. In both cases, the residual product remains a mixture of n-butenes, n-butane and i-butane, which in most cases can only be added to a subordinate application purpose, for example heating gas.

There is therefore a desire to produce an i-butene-containing mixture from the n-butene/n-butane/i-butane mixture remaining from the above-mentioned reaction as a residual product by a catalytic conversion, which can again be added to reactions which, for example, are mentioned above.

A method for production has been found

of i-alkenes by catalytic conversion of n-alkenes, the method being characterized by a mixture containing at least one n-alkene, hydrogen and possibly inert gases at a temperature from 400 to 600°C and a residence time from 0.2 to 20 sec. is brought into contact with a specially activated A^O^ and/or SiC^ catalyst and which is doped with halogen compounds of elements from the third to fifth main group and second to eighth subgroup in the periodic system according to Mendelejew and/or halogen -hydrogen acids, as the special activation consists in that an aluminum hydroxide and# or aluminum oxide hydrate and/or silicic acid regel with a content of volatile ammonium salts is calcined to A^O^ before the doping while expelling volatile ammonium salts

and/or SiO 2 .

The mixture used in the method according to the invention contains an n-alkene, for example with 4-8, preferably 4-5, particularly preferably 4 C atoms and an end-placed or internally-placed double bond. In the case of butene, it can therefore be both n-butene-1, n-butene-2 or a mixture of absolutely arbitrary composition of these two. Other n-alkenes that can be used according to the invention are, for example: n-pentene-1, n-pentene-2, n-hexene-1, n-hexene-2, n-hexene-3, n-heptene-1, -2 or - 3, as well as n-octene-1, -2, -3 or -4. However, these n-alkenes or one of them can also be

followed by other hydrocarbons. These hydrocarbons are primarily those with the same number of C atoms in the case of butenes, for example n-butane and i-butane. Likewise, the n-alkenes that can be used according to the invention can already contain smaller amounts of i-alkene next to the substances mentioned. Such mixtures arise from the material and process composition desired in a petrochemical plant, for example after removal of other valuable substances such as . aromatics, i-alkenes or diolefins, as it should be shown by means of (^-hydrocarbons by means of the following example: After the separation of butadiene from a C^-mixture produced from the thermal cracking according to one of the known methods remains i-butene-containing C^-mixture, an i-butene-containing C^-mixture of the following composition remains: 35-45% by weight i-butene, 30-50% by weight n-butene, 8-15% by weight n-butane and 4-6% by weight i-butane. After removal of the isobutene, for example by catalytic reaction with methanol to methyl tert-butyl ether or by reaction of the isobutene to an oligomer, a residual C^-hydrocarbon mixture with approximately the following composition: 0-2% by weight i-butene, 60-80% by weight n-butene, 10-30% by weight n-butane and 5-10% by weight i-butane The remaining C^ mixture can be used according to the invention.

Also smaller content, for example up to 10% by weight each time of not pure separated amounts of the neighboring C 3 hydrocarbon fraction and the Cj- hydrocarbon fraction in the case of n-butenes or the other possible neighboring fractions in the case of alkenes with more than 4 C atoms is uncritical for progress

the method according to the invention.

The mixture used in the method according to the invention is further characterized by its hydrogen content. This hydrogen is usually added to en-alkenes or a mixture containing these before entering the reactor filled with the catalyst. In addition, an amount of from 0.01 to 15 parts by volume, preferably 0.1 to 10 parts by volume, particularly preferably 0.5 to 5 parts by volume of hydrogen per 1 volume part total amount of hydrocarbons in the product used. In the event that the hydrocarbon mixture to be used, which contains the n-alkene, from a upstream refining process already contains hydrogen in the aforementioned order of magnitude, the addition of further hydrogen can of course be dispensed with.

Pure or technical hydrogen can be added as hydrogen. Technical hydrogen can, for example, contain smaller amounts of hydrocarbons such as methane or ethane, or inert gases such as nitrogen, carbon dioxide or noble gases. The content of such substances in technical hydrogen is calculated on the amount of hydrogen used, however, otherwise it is completely uncritical^. For example, 0.1 to 20% by volume should be mentioned as the content of such substances in technical hydrogen. Also the hydrogen, which is separated from the mixture formed in the method according to the invention, can again be used as an admixture to the input product.

For the mixture to be used according to the invention and which contains at least one n-alkene and hydrogen,

inert gases such as water vapour, nitrogen, carbon dioxide or argon can also be added. Such inert substances have already been partially mentioned as possible byproducts of technical hydrogen. Preferred among these inert substances is the addition of water vapour. Such inert substances can be added in a wide range of variations, for example 1-50% by volume, preferably 5-30% by volume, referred to the overall mixture of n-alkenes, hydrogen and the aforementioned hydrocarbons as secondary compounds.

For activity improvement of the catalyst can

halogenated hydrocarbons such as e.g. carbon tetrachloride, chloroform, chlorinated ethane, dichloropropane, fluorine-

chloroethane and the like to the reaction product. Quantities of discontinuously 0.1-1% and continuously 1-100 ppm are used, referred to the total mixture used.

The method according to the invention is carried out at a temperature of 400 to 600°C, preferably 420 to 520°C and at a pressure of 0.5 to 10 bar, preferably 1 to 3 bar.

In the method according to the invention is set

a residence time from 0.2 to 20, preferably from 1 to 10, especially from 2 to 6 seconds. For this, an amount of catalysts is used which corresponds to an amount of from 180 to 18,000, preferably from 360 to 3,600, particularly preferably from 600 to 1,800 volume parts per hour completed mixing per volume fraction catalyst.

The aforementioned residence time of the fed mixture to be reacted on the catalyst means a gas/space velocity (GHSV = Gas Hourly Space Velocity) of approx. 180 to 18,000, preferably 360 to 3,600, particularly preferred 600 to 1,800 parts by volume of gas mixture per volume fraction of catalyst storage per hour.

In the method according to the invention, the conversion of alkenes to i-alkenes is achieved, preferably from n-butenes in i-butene to close to the setting of the thermodynamic equilibrium. This equilibrium lies at the butenes between 400 and 500°C at approx. 36-40% by weight for those cases where the pure system of n- and i-butenes is considered. This equilibrium is often not achieved by a single contact of the mixture to be used according to the invention with the catalyst used according to the invention. In a special process variant, however, the product stream leaving the catalyst storage can be divided, with only a part being immediately added to the processing, while the other part, together with the starting hydrocarbon mixture, is again run over the catalyst storage. This division of the product flow for return can be varied within wide limits, for example between the ratios 1:9 to 9:1, worked up or returned material. A high degree of recovery thereby means a lower performance referred to a constant catalyst quantity and constant other reaction conditions, however, entails a desired shift of the component spectrum in favor of the i-alkene, for example of the i-butene to close to the thermodynamic equilibrium. A decision for the height of the return rate will, with other process parameters constant, depend above all on the composition of the available starting hydrocarbon mixture. With the catalyst according to the invention, however, a generally high recovery rate can be disregarded. However, this can be optimized by simple preliminary tests.

Of the above-mentioned typical C^ extraction, which remains after removal of the i-butene in one of the aforementioned processes and which has the following composition: 0-2% by weight di-butene, 60-80% by weight n-butene, 10 -30% by weight n-butane and 5-10% by weight i-butane, for example according to the invention a hydrocarbon mixture of the following composition can be obtained: approx. 2 5% by weight i-butene, approx. 41% by weight n-butene, approx. 2 5% by weight n-butane/i-butane, approx. 1% by weight C3~hydrocarbons and approx. 8 wt% Cg and higher hydrocarbons. This reaction product can, for example, be added directly to a new reaction for the production of methyl tert-butyl ether, of oligomers of isobutene or an extraction of the isobutene with selective solvents or with sulfuric acid. The residual gas remaining after separation of the i-butene can then be used again in the method according to the invention.

The method further relates to a catalyst, with which the method according to the invention with conversion of n-alkenes to i-alkenes is carried out. This catalyst consists of a specially activated Al 2 O 3 and/or SiO 2 , which is doped with 0.1 to 20% by weight, referred to the amount of Al-^O^ and/or SiO 2 of halogen compounds of the elements from the third to fifth main groups of the second and eighth subgroup in the periodic system according to Mendelejew and/or halogen hydrogen acids, as the special activation consists in that an aluminum hydroxide and/or aluminum oxide hydrate and/or silicic acid gel with a content of volatile ammonium salts is calcined before the doping while expelling the volatile ammonium salts to Al^O^ and /or SiO 2 .

As halogen compounds from the aforementioned elements k, for example, the following should be mentioned: aluminum fluoride, aluminum chloride, aluminum bromide, boron fluoride, boron chloride, titanyl chloride, germanium chloride, germanium fluoride, stannous chloride, arsenic chloride, arsenic fluoride, antimony fluoride, antimony chloride, antimony bromide, bismuth chloride, bismuth chloride, zinc chloride, zinc bromide, cadmium fluoride, cadmium chloride , lanthanum fluoride, lanthanum chloride, lanthanum bromide, vanadyl chloride, tungsten oxychloride, iron fluoride, iron chloride, iron bromide, cobalt chloride, nickel chloride.

Halohydrogen acids can also be used both alone and in connection with the above-mentioned halogen compounds as doping, for example hydrogen fluoride, hydrogen chloride, hydrogen bromine, hydrogen iodo or mixtures thereof.

The mentioned halogen compounds and halogen hydrogen acids can be used as well as single compounds as well as mixtures of several of them for doping.

Preferred as halogen compound and/or halogen hydrogen should be mentioned: aluminum chloride, boron fluoride, antimony-(III) fluoride, vanadyl chloride, titanyl chloride, bis-mutyl chloride, hydrogen chloride and hydrogen bromine. Particularly preferred should be mentioned: boron fluoride, antimony-(III) fluoride,

and hydrogen chloride. Particularly preferred is hydrogen chloride.

These halogen compounds and/or halogen hydrogen acids are used for doping in an amount from 0.1 to 20% by weight, preferably 0.5 to 15% by weight, particularly preferably 1 to 10% by weight, referred to the weight of A^O^ and/or SiO 2 .

Al^ O^ and/or SiO 2 for the catalyst according to the invention is especially activated before the doping with the aforementioned halogen compounds. This special activation consists in the fact that during the production of not yet doped Al^O^ and/or SiO2, a volatile ammonium salt which was absorptively bound in the aluminum hydroxide and/or aluminum oxide hydrate and/or is expelled from aluminum hydroxide and/or aluminum oxide hydrate and/or silicic acid by calcination or the silicic acid rule, thereby producing a particularly active structure of the calcined A^O^ and/or Si02> The structure of A^O^ and/or SiC^ and its doping is therefore closely linked to the manufacturing method for this catalyst. A^O^ and SiO2 can be used individually or as a mixture. Of A^O-j<og/>or SiC^to be doped, A^O^ is preferred. Correspondingly, the special activation of aluminum hydroxide and/or aluminum oxide hydrate is preferred.

The invention therefore also relates to a method for the production of a special activated A^O^- and/or SiO2-catalyst doped with halogen compounds, the method being characterized in that aluminum hydroxide and/or aluminum oxide hydrate and/or silica gel are treated with an excess solution of volatile ammonium salts to absorb these salts, the thus treated aluminum hydroxide and/or aluminum oxide hydrate and/or silica gel is separated from the remaining solution of these salts, dried at 60-200°C and calcined at 400-800°C

during expulsion of the volatile ammonium salts and during the formation of A^O^ and/or SiO2 and then doped with 0.1 to 20% by weight referred to the amount of A^O^ and/or SiO2 of halogen compounds of the elements from the third to fifth main group and other to the eighth subgroup of the periodic table and/or halogen hydrogen acids.

As a volatile ammonium salt, for example, a salt of ammonia or a lower primary, secondary or tertiary aliphatic amine such as methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine or triethylamine should be mentioned here. Salts of ammonia are preferably used. As anions, inorganic or organic anions such as fluoride, chloride, bromide, iodide, nitrate, sulfate, phosphate, carbonate, hydrogen carbonate, hydrogen sulfate, hydrogen phosphate, acetate, propionate, formate, oxalate or benzoate should be mentioned. Salts of inorganic acids are preferably used, particularly preferred are easily volatile inorganic acids, such as fluoride, chloride, bromide, iodide or nitrate. Ammonium nitrate is used in a particularly preferred way.

Such volatile ammonium salt has, for example, in an approx. 5 to 20% solution in a suitable solvent such as water, methanol or ethanol, preferably water, to aluminum hydroxide and/or aluminum oxide hydrate and/or the silicic acid regel and brought into contact with it while stirring approx. half an hour to 6 hours to complete as much absorption as possible by the aluminum compound and/or silicic acid rule. The absorptively bound amount of ammonium salt amounts to approx. 10-70% by weight, referred to the dried aluminum hydroxide and/or aluminum oxide hydrate and/or the silica gel.

In connection with this, aluminum hydroxide and/or aluminum oxide hydrate and/or silicic acid gel with absorptively bound ammonium salt are separated from the excess solution, for example by filtration or centrifugation, and dried at a temperature from 60 to 200°C, preferably 100 to 160°C, possibly under application of vacuum. The dried material is then calcined at 400 to 800°C, preferably 500 to 650°C, driving out the volatile ammonium salts and forming A^O^ and/or SiC^. Drying and calcination can conveniently be carried out in a circulation furnace which can be supplied with air as well as with nitrogen, argon or CC^.

In a special method variant for the case that the substance to be doped and specially activated for the catalyst is A^O-^, the starting point is not a separately prepared aluminum hydroxide and/or aluminum oxide hydrate, but from a freshly precipitated aluminum hydroxide. Nothing specially added is used as volatile ammonium salt, but the salt formed from the aqueous ammonia used as precipitant and the anion of the aluminum salt used is taken. For example, aluminum chloride, aluminum bromide or aluminum nitrate are combined with concentrated or diluted aqueous ammonia at 0-90°C, preferably at room temperature, and the aluminum hydroxide thus formed is left for some time, for example 0.5 to 6 hours, in contact with the precipitation solution which contains the ammonium chloride, ammonium bromide or ammonium nitrate formed. The aluminum hydroxide thereby absorptively binds this ammonium salt present, it is then filtered off or centrifuged off and supplied without a washing process at once to the above-mentioned drying and subsequent calcination.

That by the simultaneous calcination and expulsion

A^O^ or SiO2 formed by volatile ammonium salts is then present in a special active form which can then be doped with the above-mentioned amounts of the above-mentioned halogen compounds. To this end, Al 2 O 3 and/or SiO 2 brought into contact with the halogen compound dissolved in a suitable solvent is brought to a grain size of from 0.01 to 20 mm 0, and then calcined again. As a solvent for the mentioned halogen compounds and/or hydrohalic acids, water is used in the vast majority of cases. In the event that hydrolysis-sensitive halogen compounds are to be used, to withdraw this hydrolysis, an addition of the corresponding halogen hydrogen

acid to the water. In the case of water-sensitive halogen compounds, a polar solvent, such as acetone or acetonitrile, can also be used. For uniform doping of Al 2 O 3 and/or SiO 2 , it is appropriate to use such a volume of the solution of the solvent and the mentioned halogen compound, which roughly corresponds to the pore volume of Al 2 O 3 and/or SiO 2 determined by a suitable method. For this, for example, an amount of from 80 to 300, preferably 100 to 200% by volume of solution, referred to the pore volume of A12C>2 and/or SiO2, should be mentioned.

The doped catalyst is then calcined in

about. 1 to 10, preferably 2 to 8 hours at approx. 400 to 600°C, preferably 420 to 500°C. It is then ground to a grain size of 0.05 to 10 mm and is then ready for use.

It was found that the doped Al 2 O 3 and/or SiO 2 catalyst can be regenerated to its original activity by heating from 400 to 800°C, preferably 550 to 650°C, after a longer period of use and/or reduced conversion activity. This regeneration is carried out in an oxygen-containing atmosphere which is next to oxygen as well

may contain inert gases such as nitrogen, water vapor or other gases such as noble gases, CO or C02 with the addition of halogenated hydrocarbons such as carbon tetrachloride, chloroform, chlorinated ethanes, dichloropropane, fluorochloroethane and the like.

The pressure in the regeneration reactor is not essential for the invention and can fluctuate within wide limits, for example from 0.5 to 20 bar, preferably 1 to 10 bar, particularly preferably 2-5 bar. The catalyst to be regenerated is left for 0.01 to 10, preferably 0.1 to 5, particularly preferably 0.2 to 3 hours under these conditions. The mentioned halogenated hydrocarbons are used when discontinuously conducting the regeneration process in an amount of, for example, 0.1 to 1% and when continuously conducting the regeneration process in an amount from 1 to 100 ppm, referred to the total amount used, consisting of catalyst and regeneration atmosphere.

The ratio between the catalyst to be regenerated and the said medium as regeneration atmosphere can fluctuate within wide limits. For the regeneration, for example, 200-5000 liters of this atmosphere can be mentioned per kilo of catalyst to be regenerated. The oxygen content of the regeneration atmosphere is, for example, 5 to 50% by volume C, air is preferably used.

It may be appropriate for the regeneration step once again to carry out a doping with halogen compounds as stated above. However, this repeated doping is not necessary in many cases.

The regenerated catalyst is then again fully usable for the isomerization reaction.

In the method according to the invention, the catalyst can be used in fixed storage as well as in moving catalyst storage. For example, a fluidized bed or a flow bed should be mentioned as moving catalyst storage. Preference is hereby given to the use of the catalyst in moving catalyst storage, particularly preferred in flow storage.

In fig. 1 shows, for example, a diagram for the possible execution of the method according to the invention: 1 here means supply of the n-alkene-containing hydrocarbon stream,

2 means supply of hydrogen,

3 means a mixing and dosing device,

4 means one preheater,

5 means the reactor with the catalyst to be used according to the invention. This can be arranged in the reactor, as well as a fixed catalyst and also as a moving catalyst, preferably as a moving catalyst, 6 means a circulation pump, through which part of the reaction product taken out at the top of 5 is fed back into the lower part of 5, 7 means a cooler for the hot reaction products, which are then taken away for further processing or processing.

It is known that many reactions proceed in solid storage with high yields and good selectivity. To let

the reaction of n-alkanes to i-alkanes, especially of n-butenes to i-butene proceeds with sufficient speed, the isomerization must be carried out at high temperature, for example between 400 and 600°C and at low pressure. Corresponding to the chosen reaction conditions, the yield, for example, of i-butene is thermodynamically limited from this isomerization process so that the methods known in the literature, especially when using fixed storage, aim for the highest possible yield and selectivity. Hereby, the above-mentioned disadvantages are deliberately taken for granted, i.e. in the case of rapid activity and selectivity losses of the catalyst due to the unwanted coking reaction, oligomer formation and cracking reaction.

A further disadvantage for a technical application of the isomerization in a fixed storage reaction is the continuously changing product composition and the necessary switching from one catalyst storage to the next to enable a regeneration period.

It is therefore a particular advantage that by using the above-mentioned catalyst, the skeletal isomerization of n-alkenes to i-alkenes can be achieved with high yield and outstanding selectivity without the listed disadvantages, when the isomerization is carried out in a moving catalyst storage.

Of particular advantage here is the process variant where the catalyst is completely or partially replaced with new and/or regenerated catalyst without interrupting the process.

lysator.

To this end, the catalyst present in the process is removed from the reactor to the extent that a new and/or regenerated catalyst is introduced into the reactor. The elimination of the catalyst found in the process and replacement by new and/or regenerated catalyst can further take place in portions or continuously. For portionwise removal and replacement of the catalyst, for example, the catalyst present in the process can be completely or partially removed from the reactor by simultaneous replacement of a new catalyst, after which the isomerization reaction is then continued without catalyst exchange until, after a suitable time, a renewed discharge of replacement of the catalyst will be carried out. Work with continuous draining and replacement of the catalyst is preferred. In general, one can proceed in such a way that the total amount of catalyst is completely exchanged each time and has been replaced discontinuously or continuously from the moved catalyst storage during a period of from 5 days to 30 days, preferably 7 to 20 days. In the case of continuous exchange and replacement, this corresponds, for example, to approx. 1-0.01% of the total quantity of the catalyst filling per hour.

The regeneration process itself can be carried out both discontinuously and continuously. A preferred embodiment is the combination of the continuous discharge and replacement of the catalyst from the moving catalyst storage with a continuous regeneration of this catalyst in a special regeneration reactor separated before the isomerization reaction.

Of course, according to the invention, it is possible to introduce completely new catalyst in the moved catalyst storage of the isomerization reaction instead of the discarded catalyst. In a preferred way, however, the regenerated catalyst is returned. New catalyst is usually only necessary to replace minor catalyst losses, for example as flying dust.

The use of the method according to the invention of moving catalyst storage and the separately possible catalyst regeneration without process interruption enables during an unlimited operating time and under control of the resp. from the regeneration to the returned amount of catalyst" to produce a uniformly composed reaction product with uniform yields of i-alkene and constant operating conditions. It is therefore not necessary, according to the state of the art, to accept changing product composition and switching on and off of different reaction systems Thus, with a fixed storage method, in order to achieve a result roughly comparable to the fluidized bed method, after such short intervals of time that each time after 12 and 24 hours the coked catalyst had to be burned off and regenerated. In addition to the difficulties with alternating and interrupted method management due to the resulting fluctuating product composition, any burning of coke on the catalyst means a strain on this catalyst, which with frequent use has a negative effect on the catalyst's activity and lifetime. Furthermore, according to the invention, by constantly maintaining the isomerization process, it is possible to replace the catalyst contaminated with others and doping, refreshing and replacing catalyst quantities destroyed by wear or to offset minor loss of activity when fresh catalyst is introduced. All mentioned operations with the catalyst take place outside the isomerisation reactor and therefore do not lead to contamination of the substances to be isomerised.

Fig. 2 shows a possible embodiment of the isomerization reaction using the catalyst in moving catalyst storage and continuous regeneration of the catalyst. Hereby, 1) to 7) have the same meaning as in fig. 1.

In addition, 8) means a regeneration reactor and 9) the supply of the above-mentioned substances necessary for the regeneration atmosphere.

Fig. 2 shows an example of the execution of the method according to the invention when, in a preferred manner, catalyst is continuously withdrawn from the moving catalyst storage in the reactor 5, continuously fed into the regeneration catalyst 8 and continuously fed back from this regeneration catalyst into the moving catalyst layer in the reactor 5.

In contrast to previously mentioned attempts at skeletal isomerization of olefins, the method according to the invention can be carried out at high residence times of the catalyst with high activity and high selectivity without coke deposition and without oligomer formation with a high yield of i-alkenes. The high catalyst service life can be further improved by the mentioned regeneration precautions so that the method according to the invention can also be carried out very economically. It is surprising that the presence of volatile ammonium salts at the beginning of the calcination of the not yet doped aluminum hydroxide and/or aluminum oxide hydrate and/or silica gel, and which are expelled during the formation of A1203 and/or SiO2, gives A1203 and/or SiO2 such advantageous properties that the other precautionary measures according to the invention such as doping and admixture of hydrogen to the n-alkene-containing starting products unfold their full effect.

Example 1

100 g (A1(N03)3. 9H20 is dissolved in 500 ml of distilled water and precipitated with 60 ml of concentrated aqueous ammonia over two hours. The precipitated aluminum hydroxide is stirred for another two hours, filtered off and dried for 24 hours at 150°C. The dry mass is then heated for one hour under nitrogen at 600°C. A solution of 0.75 g of SbF3 in 10 ml of distilled water is applied to this thus prepared Al2O3 support and dried for 2 hours at 150°C and then calcined at 450°C in 4-5 hours. The thus produced catalyst is then brought to the necessary grain size by crushing and fractional screening.

Example 2

For implementation, it is used in fig. 1 schematically shown apparatus. Over the dosing device 3, a gaseous mixture of butene-1 (1) and hydrogen (2) in a volume ratio of 1:1;5 is run over the preheater 4 into the reactor 5. Part of the reaction product is returned via circuit gas pump 6 to the reactor 5 in a degree that the volume ratio between applied amount and circuit gas amount amounts to 1:1.

As a catalyst, one according to e.g. 1 prepared, however, with 9.1% by weight of BiOCl doped alumina. The reaction temperature was 480°C, the pressure 1 bar, the gas space velocity GHSV (Gas hourly space velocity) 1,500h corresponding to an average residence time of 2.4 seconds. The liquid reaction product discharged behind the cooler 7 had the following composition:

Example 3

Corresponding to Ex. 2 is run in an apparatus according to fig. 1 a gaseous mixture of a hydrocarbon stream 1 consisting of 0.5% by weight i-butene, 76% by weight n-butene and 2 3.5% by weight butanes with hydrogen 2 in a volume ratio of 1:1.5 over the preheater 4 into the reactor 5. A catalyst according to Ex. 1 prepared, at least with 1.5% by weight of BF^doped alumina. The circuit ratio was 1:1, the reaction temperature 4 50°C and the gas space velocity GHSV

1,500 h \ corresponding to an average residence time of 2.4 seconds. The liquid reaction product discharged behind the cooler 7 has the following composition:

Examples 4-6

A commercially available filter roll grade 13 corresponding to US patent 3,663,453 as well as one according to Ex. 1 produced A^O^

was brought to the same grain size by crushing and sieving doped with 9.1% by weight ZrOCl2. 8H20 and used as a catalyst. Furthermore, an Al^^ according to Ex. 1 but without doping for comparison.

Corresponding to Ex. 2, a gaseous C2 stream with hydrogen in the ratio 1:1.5 was passed over the preheater into the reactor. The ratio between circuit gas and material used was 1:1, the reaction temperature 480°C and the gas space velocity GHSV 1,500 h corresponding to an average residence time of 2.4 seconds. The liquid reaction product discharged behind the cooler had the following composition:

The catalyst in experiment 4 coked after approx. 1 hour and thereby showed a strong drop in activity and a strong destruction of the initial i-butene value, while experiment 6 was stopped after 72 hours without a visible change in activity and yield values.

Example 7

Corresponding to Ex. 2 and 3 are run in an apparatus according to fig. 1 a gaseous mixture of a hydrocarbon stream 1 consisting of 1% by weight i-butene, 75% by weight n-butene and 24% by weight butane with hydrogen 2 in a volume ratio of 1:1.5 over preheater 4 into the reactor 5. As a catalyst, used a according to Ex. 1 prepared - however with 15% by weight of hydrogen chloride doped aluminum oxide. The circuit ratio was 1:1, the reaction temperature 450°C and the gas space velocity GHSV 1,500h corresponding to an average residence time of 2.4 seconds. The liquid reaction product discharged behind the cooler 7 has the following composition:

Example 8 (comparison)

In this example, the apparatus as in fig. 1 operated with arrangement of the catalyst in fixed catalyst storage. As a catalyst, an according to e.g. 1

however, produced with 15% by weight of hydrogen chloride doped with aluminum oxide. A gaseous mixture of a hydrocarbon stream 1, consisting of 0.5% by weight of i-butene, 71% by weight of n-butenes, 28% by weight of butanes and 0.5% by weight of other components is mixed with hydrogen 2 in a volume ratio of 1:1.5 and is run over preheater 4 into the fixed storage reactor 5. The reaction temperature is 450°C, GHSV 1,500 h"<1> and circuit ratio 1:1 (volume/volume).

The liquid reaction product discharged behind the cooler 7 shows the following composition during the duration of the reaction:

Example 9

In this example, an apparatus was operated which in fig. 2 with arrangement of the catalyst in a fluidized bed.

A catalyst according to Ex. 1, however, prepared with 15% by weight of hydrogen chloride doped aluminum oxide. A hydrocarbon stream 1 consisting of 0.5% by weight of i-butene,

76% by weight of n-butenes and 2 3.5% by weight of butanes are reacted in the mixture with a hydrogen flow 2 in a ratio of 1:1.5. The circuit ratio between the vented and returned reaction gas amount is 1:1/the reaction temperature 450°C and the gas space velocity GHSV 1.50 0 h . The catalyst is discharged from the reactor 5 and continuously regenerated in the reactor 8 with air 9 and returned to the fluidized bed reactor 5. The reaction product withdrawn from behind the cooler 7 had the following composition during the duration of the reaction:

Claims (10)

1. Process for the production of i-alkenes by catalytic conversion of n-alkenes, characterized in that a mixture containing at least one n-alkene, hydrogen and possibly inert gases at a temperature from 400 to 600°C and a residence time from 0.2 to 5 0 sec. is brought into contact with specially activated and with halogen compounds of elements from the third to fifth main group and second to eighth subgroup in the periodic table according to Mendelejew and/or halogen-hydrogen acid-doped Al^^ - and/or Sx©2 -catalyst, as the special activation consists in that an aluminum hydroxide and/or aluminum oxide hydrate and/or silicic acid regel with a content of volatile ammonium salts is calcined before the doping while expelling the volatile ammonium salts to A^O^ and/or SiO 2 . 2. Method according to claim 1, characterized in that the mixture is brought into contact with a specially activated Al 2 0 3 and/or SiO 2 ~ catalyst already used in this method and doped with said halogen compounds, which has been regenerated at a temperature from 400 to 80 0°C in an oxygen-containing atmosphere which may also contain inert gases with the addition of halogenated hydrocarbons 3. Method according to claims 1 and 2, characterized in that the catalyst is used as moving catalyst storage and, if necessary, the catalyst is replaced without interrupting the process in whole or in part by new and/or regenerated catalyst. 4. Method according to claims 1-3, characterized in that the catalyst is arranged in a fluidized bed. 5. Method according to claims 1-4, characterized in that the catalyst is arranged in a flow storage. 6. Method according to claims 1-5. characterized in that partial quantities are discharged from the moving catalyst storage, regenerated and returned to the moving catalyst storage. 7. Method according to claims 1-6, characterized in that sluicing, regeneration and back-sluicing take place continuously. ; 8. Catalyst consisting of a specially activated Al 2 °3 and/or SiO 2 , which is doped with 0.1 to 20% by weight referred to the amount of Al 2 0 3 and/or SiO 2 of halogen compounds of elements from the third to fifth main group and second to eighth subgroup of the periodic table according to Mendelejew and/or halogen hydrogen acids, the special activation consisting in that an aluminum hydroxide and/or aluminum oxide hydrate and/or silicic acid regel with a content of volatile ammonium salts is calcined before the doping while expelling volatile ammonium salts to A12C>3 and/or SiO2 . 9. Process for the production of a special activated and with halogen compound doped A12 03~ and/or Si02 -catalyst, characterized in that an aluminum hydroxide and/or aluminum oxide hydrate and/or silica gel is treated with an excess solution of volatile ammonium salts to absorb these salts , thus treated aluminum hydroxide and/or aluminum oxide hydrate and/or silicic acid regel is separated from the remaining solution of these salts, dried at 60-200°C and calcined at 400 to 800°C while expelling volatile ammonium salts and with the formation of Al2O3 and/or SiO2 and then doped with 0.1 to 20% by weight, referred to the amount of A^O^ and/or SiO2 of halogen compounds of elements with from third to fifth main group and second to eighth subgroup of the periodic system according to Mendelejew and/or halogen hydrogen acids. 10. Method according to claim 9, characterized in that the volatile ammonium salt is chosen which consists of the cation of the ammonia used for precipitation and the anion of the soluble aluminum salt used for the production of aluminum hydroxide, this aluminum salt being assimilated into the newly precipitated aluminum hydroxide by absorptive co-precipitation.