DE2728218C2 - Process for the isomerization of 1-butene to 2-butene - Google Patents

Description

The invention relates to a process for the isomerization of 1-butene to 2-butene.

Various chemical processes, e.g. cracking of various petroleum fractions, produce C4 fractions containing a significant amount of 1-butene. However, for certain uses it is preferred to obtain a higher content of 2-butene. Accordingly, it is an object of the present invention to isomerize 1-butene to 2-butene.

Butadiene is also present in certain batches. It is therefore advantageous to separate it by any known means, for example by distillation or extraction with a polar solvent. Nevertheless, after this treatment, a considerable amount of residual butadiene and traces of the polar extraction solvent are present, traces which are sufficient to gradually poison the catalyst. A second aim of the present invention is to carry out simultaneously the hydrogenation of the residual butadiene and the isomerization of 1-butene to 2-butene without appreciably deactivating the catalyst.

It is known to carry out these reactions by contacting 1-butene or a mixture of 1-butene and butadiene (which may contain other hydrocarbons, e.g. butane, isobutane, 2-butene and isobutene) with a palladium catalyst on alumina in a hydrogen atmosphere.

• - Überschüssige Hydrierung, die zu merklichen Verlusten an Olefinen führt;
  - Polymerisation von stark ungesättigten Kohlenwasserstoffen, die zu einer Desaktivierung des Katalysators führt.

Various difficulties have arisen, as described in US Patent 35 31 545:

• - Excess hydrogenation leading to significant losses of olefins;
  - Polymerization of highly unsaturated hydrocarbons, which leads to deactivation of the catalyst.

US Pat. No. 3,531,545 proposes to overcome these difficulties by adding sulphur compounds to the hydrocarbon feedstock. To do this, it is necessary to operate at elevated temperatures between 135° and 260°C, preferably between 163° and 190°C; at these elevated temperatures, the thermodynamic equilibrium in the conversion of 1-butene to 2-butene is unfavourable. Moreover, at these temperatures, as observed, for example, in US Pat. No. 3,772,400, the isobutene polymerises, thereby reducing the selectivity of the isomerisation reaction. Finally, in the presence of sulphur, it is usually necessary to use an increased amount of hydrogen and to remove the sulphur at the end of the operation.

In "Chemical Abstracts", Vol. 78, No. 97, 104 (1973), a process for the isomerization of 1-butene to 2-butene is described in which a palladium-alumina catalyst is pretreated in a first stage with hydrogen containing 1% hydrogen sulfide at 200°C for 5 hours. A C₄ fraction containing 1-butene and 2-butene with 5 mol% hydrogen and 150 ppm hydrogen sulfide is passed over this catalyst at 50°C and 35 atm, whereby a high yield of 2-butene is obtained.

The state of the art processes therefore have the disadvantages of side reactions (hydrogenation), polymerization of the monomers and deactivation of the catalyst as well as sensitivity to butadiene admixtures.

In contrast, the present invention is based on the object of providing a process for the isomerization of 1-butene to 2-butene, which operates with high yield, low losses due to polymerization or the like and with long catalyst service lives (little impairment of catalyst activity).

This object is achieved by the method characterized in the patent claims.

The present invention eliminates the disadvantages of the known processes. It makes it possible to isomerize 1-butene at lower temperatures than was possible with the known processes, thus obtaining a dramatically higher conversion to 2-butene. The reaction rate is increased, even at these relatively low temperatures. The hydrogenation of the olefins to saturated hydrocarbons is negligible. The sensitivity of the catalyst to poisons is reduced in relation to the use of noble metals without the pretreatment according to the invention. Finally, the polymerization reactions are prevented.

• - Butadien
  - 2-Buten (cis und/oder trans)
  - Isobuten
  - Butan und Isobutan

As described above, 1-butene can be used alone or in a mixture with one or more hydrocarbons, in particular one or more of the following hydrocarbons:

• - Butadien
  - 2-butene (cis and/or trans)
  - Isobuten
  - Butane and isobutane

If butadiene is present, it is hydrogenated to butene, which is an advantage of the present inventive process.

The presence in the feed of compounds capable of deactivating or selecting the catalyst, such as sulphur or nitrogen compounds, is undesirable; in fact, as described above, in the presence of such compounds it is necessary to operate at elevated temperatures, that is to say under conditions unfavourable to isomerisation. Accordingly, it is preferable that the feed contains less than 5 ppm in moles of sulphur or nitrogen, preferably less than 1 ppm in moles of sulphur or nitrogen (ppm=parts per million).

The isomerization temperature is usually between 50 and 140°C, preferably between 65 and 120°C and especially between 70 and 110°C. The lower the temperature, the more favorable the thermodynamic equilibrium is to obtain an increased amount of 2-butene.

The pressure can be selected within a wide range, for example from about 1 to 50 bar gauge (atm), preferably from 5 to 30 bar gauge (atm). The best results are obtained when 1-butene is kept, at least for the most part, in the liquid phase and preferably practically all of it in the liquid phase. The pressure can be exerted by means of hydrogen or a mixture of hydrogen and an inert gas. The flow rate of 1-butene is usually 1 to 50 l, preferably 5 to 20 l (in the liquid state) per liter of catalyst per hour. The hydrogen is usually used at a flow rate of 0.1 to 15 moles per hundred, preferably 1 to 10 moles per hundred, relative to the 1-butene or the mixture of 1-butene and butadiene.

The catalyst contains 0.01 to 2 weight percent palladium on alumina.

According to the invention, the catalyst is first treated with hydrogen sulphide and hydrogen and then, before being used as a catalyst, with hydrogen alone. However, it is not necessary for the catalytic metal to be in the reduced state when used in this treatment; it is also possible to work with the catalyst containing the noble metal in a bound state, for example as an oxide. An excess of hydrogen sulphide is used, i.e. at least two moles (gram atoms) of sulphur and, for example, 5 to 100 moles or more (gram atoms) of sulphur per mole (gram atoms) of noble metal. Its partial pressure is, for example, 0.01 to 10 bar (atmospheres).

According to a preferred procedure, the hydrogen sulphide is allowed to flow until it is no longer retained by the catalyst. The temperature during this treatment is usually from 50 to 400°C, preferably from 80 to 130°C.

The time for treatment with the sulphur compound is not critical, provided that the desired amount of sulphur is delivered to the catalyst. The usual time for this treatment is between 5 minutes and 6 hours.

The second step of treating the catalyst according to the process of the invention is treating the presulphurised catalyst with hydrogen as described above.

Although the limiting conditions for this treatment are not yet fully known, it appears that the best results are obtained when operating at 110 to 250°C, preferably 120 to 160°C. The contact time is usually 10 minutes to 10 hours. The hydrogen pressure is, for example, 0.1 to 10 bar (atmospheres) or more.

It is preferable to avoid treatment with hydrogen which is too severe or too long; in fact, if the treatment is too ruthless, the catalyst will acquire an excess of hydrogenation activity which can harm the selectivity of the isomerization. The following examples show the particularly favorable conditions when using this treatment.

The following examples illustrate the invention.

Examples example 1 (Production of the catalyst)

80 g of a catalyst containing 0.5% by weight of palladium are deposited on alumina in a fixed bed at a temperature of 100°C under a hydrogen atmosphere [1 bar (atmosphere)]. At the same temperature and pressure, 80 litres of hydrogen containing 2% by volume of hydrogen sulphide are passed over the catalyst for two hours. The temperature is then raised to 130°C and the hydrogen is passed under 1 bar (atmosphere) for 6 hours at a rate of 40 litres per hour. The catalyst is then ready for further use.

Example 2

• - 1-Buten: 10,9%
  - 2-Buten: 87%
  - n-Butan: 2,1%

Hydrogen with a mixture of 99.66% 1-butene and 0.34% n-butane is allowed to flow over 20 cm³ of the catalyst thus obtained at a temperature of 80°C under an overpressure of 25 bar (atm). The flow rate of hydrocarbons (VVH) is 5 volumes per volume of catalyst per hour, the flow rate of Hydrogen 1 litre per litre of catalyst per hour. An effluent is obtained whose volumetric analysis is given below:

• - 1-Butene: 10.9%
  - 2-Butene: 87%
  - n-Butane: 2.1%

Example 3

Example 2 is repeated with the batch whose analysis is given in Table I. The temperature is 100°C, the overpressure 25 bar (atm), the VVH 10, 20 and 40 respectively and the hydrogen flow rate 2.4 and 8 litres per litre of catalyst per hour respectively; the results are given in Table I. Table I &udf53;vu10&udf54;&udf53;vz15&udf54;

Example 4

Example 2 is repeated with the batch rich in isobutene and butadiene, the composition of which is given in Table II.

The pressure is 15 bar (atm), the temperature 80°C, the VVH 10 and the hydrogen flow rate 3 litres per litre of catalyst per hour. Table II &udf53;vu10&udf54;&udf53;vz16&udf54;

Example 5 (Comparison example)

A catalyst containing 0.5% by weight of palladium reduced to alumina is used. A charge whose composition is given in Table III and to which 100 parts per million by weight of hydrogen sulphide has been added is passed over this catalyst, which is placed in a fixed bed.

• Temperatur: 80°C
  Druck: 25 bar (kg/cm²)
  VVH: 5
  Durchsatz an Wasserstoff: 40 Liter pro Stunde und pro Liter Katalysator

The conditions are as follows:

• Temperature: 80°C
  Pressure: 25 bar (kg/cm²)
  VVH: 5
  Hydrogen throughput: 40 liters per hour and per liter of catalyst

After 48 hours, the effluent is analyzed and it is found that the isomerization is practically zero.

This example shows that isomerization does not occur at 80°C in the presence of hydrogen sulfide.

Example 6 (Comparison example)

The experiment of Example 5 is carried out in the same manner, except that the addition of hydrogen sulphide is omitted.

The effluent is analyzed after 48 hours. The analysis, which is given in Table III, shows that the degree of isomerization is low, which is due to the presence of sulfur previously fixed by the catalyst (Example 5).

Example 7

The catalyst obtained according to Example 6 is treated with hydrogen at 135°C under atmospheric pressure, the hydrogen flow rate being 400 liters/hour/liter of catalyst.

After 6 hours of this treatment, the isomerization step is carried out under the conditions of Example 6, i.e. at 80°C, 25 bar (kg/cm²), VVH=5 and 40 litres of H₂/hour/litre of catalyst (in the absence of hydrogen sulphide).

After 48 hours, the product is analyzed as shown in Table III. Table III &udf53;vu10&udf54;&udf53;vz13&udf54;

Example 8

80 g of a catalyst containing 0.5% by weight of palladium on alumina in a fixed bed are used at a temperature of 200°C under a flow of hydrogen gas at a pressure of 1 atmosphere, the hydrogen gas containing 1% by volume of H₂S, at a flow rate of 40 litres per hour and for a period of 5 hours. After this first treatment stage, the temperature is reduced to 130°C and then pure hydrogen is passed through under 1 atmosphere for 6 hours at a flow rate of 40 litres per hour.

After this second treatment stage, the catalyst is ready for use. It is then used in the hydrogenation of a C4 hydrocarbon feedstock whose composition is given in Table IV. The operating conditions are the same as in Example 3, the VVH value is 10. The results obtained are given in Table IV.

Example 9 (Comparison example)

80 g of the same catalyst as that of Example 8 are treated, but only the first stage of treatment is carried out. The catalyst thus treated is then tested under the same conditions as those of the previous example. The results obtained are shown in Table IV for comparison purposes. Table IV &udf53;vu10&udf54;&udf53;vz14&udf54;&udf53;vu10&udf54;

It can be seen that the treatment of the catalyst carried out according to the present invention alone makes it possible to obtain a virtually complete conversion of butadiene, as well as a significant transformation of 1-butene. It can be seen that, on the other hand, omitting the second stage of treatment leads to a much less active catalyst: the residual butadiene is 280 ppm and the 1-butene content is 39.58%, which indicates a very weak isomerization with an identical material balance (~100%) between Examples 8 and 9.

Claims (3)

1. A process for the isomerization of 1-butene to 2-butene by contacting a hydrocarbon feed containing 1-butene in the presence of hydrogen at a temperature of 50 to 140°C with a catalyst containing 0.01 to 2% by weight of palladium on alumina and which has been pretreated with hydrogen and hydrogen sulphide at an elevated temperature, characterized in that the pretreatment is carried out in two stages, wherein the catalyst
(a) in the first stage with hydrogen sulphide diluted with hydrogen at a temperature of 50 to 400°C and b) subsequently treated with hydrogen at a temperature of 110 to 250°C.
2. Process according to claim 1, characterized in that a hydrocarbon feed is used which contains butadiene in addition to 1-butene. 3. A process according to claim 1 or 2, characterized in that a hydrocarbon feed containing less than 5 ppm in moles of sulfur or nitrogen is used.