DE1518584B - Process for the catalytic isomerization of butenes - Google Patents

Description

The invention relates to a process for the catalytic isomerization of butenes at increased Temperature, both the conversion of isobutene to n-butenes and the conversion of n-butenes in isobutene.

The method of the parent patent application for the catalytic isomerization of butenes at elevated temperature is characterized in that the isomerization at a temperature in the range of 250 to 55O ⁰ C, optionally in the presence of a diluent gas, in the presence of 0.5 to 1.5 percent by weight of one, preferably 0.7 to 1.4 percent by weight of fluorine-containing aluminum oxide carried out as a catalyst, which by fluorination of an aluminum oxide which has a reversible benzene adsorption of at least 2 micromoles of benzene per gram, measured at a benzene partial pressure of 0.11 mm Hg and a temperature of 190 ⁰ C, with a fluorine compound of the general formula

20 Y

Y-X-F

in which X is carbon or sulfur and Y is fluorine or hydrogen, or with ammonium fluoride, Hydrogen fluoride or ammonium hydrogen fluoride, preferably by means of an aqueous slurry Solution of an amount of calculated according to the required amount of fluorine in the finished catalyst Ammonium fluoride, hydrogen fluoride or ammonium hydrogen fluoride, drying the sludge produced and subsequent calcining.

Such catalysts show a high degree of selectivity for the isomerization of butenes. Outside the stated limits, fluorinated aluminas are proportionate to the desired reaction inactive or not selective and lead to a high proportion of by-products.

The further development of the process for the catalytic isomerization of butenes at elevated temperature consists in the fact that the reaction is carried out in the presence of hydrogen as the diluent gas performs. This procedure increases the life of the catalyst and its productivity increased considerably.

The use of reversible benzene adsorption to assess the suitability of various aluminum oxides for use in the low-temperature isomerization of C ₄ and higher paraffinic hydrocarbons is described in British Patent 1,042,885.

Reversible Behzol adsorption is a measure of acidity; low values indicate low acidity. The measurement of the benzene adsorption of an aluminum oxide consists in contacting the aluminum oxide with benzene vapors at a low partial pressure and a fixed temperature and measuring the amount of vapor adsorbed and desorbed. The amount of benzene adsorbed can change with the test conditions used, in particular with the partial pressure of the benzene vapor and the temperature. It is therefore necessary to standardize the conditions and for the purpose of the present invention the partial pressure used is 0.11 mm Hg and the temperature 190 ⁰ C.

A description of a suitable method for measuring benzene adsorption and an apparatus for this can be found in an essay by R. C. P i tkethly and G. A. G o b 1 e with the title: »The Adsorption of Benzene on Supported Platinum Catalysts ", published in" Actes du Deuxieme Congres International de Catalyse ", Paris, 1960, Vol. 2, p. 1851. Adsorption at low partial pressures is normally Attributing chemosorption with a relatively small contribution to physical adsorption, and the device for measuring it has three main parts, viz

(a) a device for introducing steam,

(b) a holder for the solid to be examined,

(c) a steam indicator.

The apparatus for introducing steam has a source of carrier gas, e.g. B. for nitrogen or hydrogen, a container for the material to be adsorbed and a valve which allows either the gas alone or gas that contains very small amounts of the substance to be adsorbed, passed over the solid will. The holder, which contains the catalyst or catalyst carrier, can be used in a wide temperature range be kept at constant temperature. Gas passed over the catalyst then leaves via the sampling valve after the vapor indicator, which is a hydrogen flame ionization detector can be. The indicator system can have gas chromatographic columns if the relative speeds the adsorption of various substances should be determined or if a reaction is taking place the test conditions are likely and the composition of the reaction product must be determined target. This is not likely to be true of the present invention.

By having a gas stream, which contains the substance to be adsorbed, over the catalyst or the catalyst base to be tested directs and the difference between that of the catalyst or the amount of substance added to the catalyst base and the amount that goes according to the indicator, measures the amount of substance adsorbed after a small correction for the dead space in the system to be determined. If the material flow is then interrupted and the gas alone over the catalyst is passed, the amount of substance can also be determined which can be desorbed. the amount desorbed is known as the reversible adsorption; the difference between the adsorbed and amount desorbed is known as the irreversible adsorption.

The carrier gas for the benzene vapors should be inert to aluminum oxide and is preferred Nitrogen.

The aluminum oxides to be tested are expediently given a standard pretreatment in order to bring them into a standardized chemical and physical state and in order to eliminate any effects which, for example, could be a result of different water contents. A prolonged heating in an inert atmosphere is preferred, for example 1- to 75stündiges heating between 100 and 800 ⁰ C in dry nitrogen. A particularly preferred pretreatment is heating for 16 hours at 470 ° C. in dry nitrogen.

Aluminum oxides suitable for use in the present invention have a reversible benzene

adsorption of at least 2 μΜοΙ benzene per gram Aluminum oxide under the specified measuring conditions. Preferably the reversible adsorption is benzene at least 3.5 μΜοΙ per gram. Fluorinated alumina catalysts based on of aluminum oxides, which have reversible benzene adsorptions of less than 2 μΜοΙ per gram have proven to be relatively inactive catalysts for the mutual conversion of butenes proven.

The catalysts used in the process according to the invention should have a fluorine content of 0.5 up to 1.5 percent by weight. Although catalysts containing less than 0.5 weight percent fluorine are active to a certain extent, they have a very short lifespan, while those which contain more than 1.5 weight percent fluorine, too high levels of cracked and polymeric Products lead to the disadvantage of the desired butene isomers. Preferably the The amount of fluorine present in the catalyst is 0.7 to 1.4 percent by weight.

The catalysts used in the process according to the invention can be used in various ways getting produced. The aluminum oxide can be fluorinated by adding hydrogen fluoride, ammonium fluoride or ammonium hydrogen fluoride or an organic fluorine compound of the general formula

Y_X_F

(where X is carbon or sulfur and each Y is fluorine or hydrogen) is used. the Compounds of the general formula are carbon tetrafluoride, fluoroform, methylene fluoride and the corresponding sulfur compounds. Carbon tetrafluoride is preferred. Is carbon tetrafluoride an extremely stable compound and prima facie is not an obvious choice for the production of fluorine-containing Catalysts. Nevertheless, it has been found suitable and has certain advantages over it some other fluorinating compounds. For example, it is non-corrosive compared to hydrogen fluoride, easier to handle, convenient to use in the vapor phase and less inclined to that To damage aluminum oxide. Compared to alkyl fluorides, which contain a higher number of carbon atoms, for example tertiary butyl fluoride, it is less likely to have carbon or hydrocarbon deposits on the catalysts generated during fluorination.

Preferably, non-reducing conditions are used when the alumina has a organic fluorine compound is brought into contact. A common method of touching consists in a stream of steam either alone or in admixture with an inert gas, for example Nitrogen, or in a mixture with an oxygen-containing gas, for example air, via the Aluminum oxide is passed.

When the above organic fluorine compounds are used for the fluorination of the aluminum oxides, are generally temperatures in the range 200 to 500 ⁰ C, in particular 300 to 35O ⁰ C applied. In general, higher temperatures are used with shorter contact times, and vice versa. However, it has been found that when the catalysts for use in the present invention are prepared using the above organic fluorine compounds, it is often difficult to control the amount of fluorine taken up by the oxide. Catalysts with fluctuating fluorine contents can thus be obtained if the aluminum oxide is exposed to the organic fluorinating agent under identical fluorinating conditions. In order to prepare the catalysts in a reproducible manner, it is preferred to use the method described in British Patent 1,065,009 in which the alumina is first exposed to water vapor at room temperature, then partially dehydrated before exposure to the fluorinating agent. Using this method, catalysts with essentially the same fluorine content can be made in a reproducible manner.

However, it has been found that the problem of reproducibility practically does not exist when the aluminum oxide is fluorinated with ammonium fluoride. Therefore the catalysts are used preferably used in the present invention by fluorinating the alumina with ammonium fluoride manufactured.

The alumina is slurried with an aqueous solution of ammonium fluoride, the amount of ammonium fluoride used being calculated to give the required amount of fluorine, ie 0.5 to 1.5 percent by weight, in the finished catalyst. The slurry is then dried, for example at about 110 ^° C., and calcined for example at 450 ^° C. in a stream of nitrogen for a period of, for example, about 3 hours.

As mentioned above, the process according to the invention can be applied both to the conversion of n-butenes into isobutene and to the conversion of isobutene into n-butenes. Therefore, the feed to the process any Butenisomeres or a mixture of isomers may include, provided that the mixture is not the / reaction conditions corresponding equilibrium mixture.

The process is carried out at elevated temperature, and in general, temperatures are used in the range 250 to 55O ⁰ C. Pressures can be sub-atmospheric, atmospheric, or super-atmospheric, and the gas hourly space velocity (GHSV) of the feed can be in the range of 100 to 10,000 depending on the temperature.

The butene feed is brought into contact with the catalyst in the presence of hydrogen, wherein the molar ratio of starting material to hydrogen is preferably in the range 0.05 to 10. For example, a ratio of about 2 is appropriate. The method according to the invention is carried out by the following example explains in more detail.

A butene feed containing 96.0 weight percent butenes containing hydrogen in the Feed to hydrogen molar ratio of 2: 1 was diluted over a catalyst fluorinated aluminum oxide with a content of 1 weight percent fluorine. The aluminum oxide had a reversible benzene adsorption of

17.6 μΜοΙ benzene per gram of alumina, measured at a benzene partial of 0.11 mm Hg and a temperature of 190 ⁰ C after pre-treatment, which consisted of a 16-hour heating at 470 ° C in dry nitrogen. The temperature was 450 ⁰ C, and the total gas hourly space velocity (GHSV) was 1500 v / v.

The half-life of the catalyst, taken as the point where the percentage of isobutene had fallen in the Gesamtbutenen in the gaseous product to half of its equilibrium value at 450 ⁰ C, that of 39 to 19.5 ° / o> was 69 hours, and the Half-life isobutene productivity was 36.1 grams of isobutene per milliliter of catalyst.

For comparison, the above experiment was exactly repeated with the. Difference that. Nitrogen as Diluent gas was used in place of hydrogen. In this case the half-life was des Catalyst only 30 hours, and the isobutene half-life was only 18.5 g isobutene per Milliliters of catalyst. .

Claims (1)

Claim: ίο Further training of the process for catalytic table isomerization of butenes at elevated temperature according to patent application P 15 18 580.-5-42, characterized in that the reaction is carried out in the presence of hydrogen performs as a diluent gas.