MXPA98007197A - Selective hydrogenation of diens in currents reform - Google Patents

Abstract

In the process for the selective hydrogenation of the dienes in feed streams containing dienes, a feed stream containing dienes, a feed stream containing dienes is hydrogenated on a precipitated catalyst containing nickel from 40 to 100 ° C, a pressure from 3 to 20 bar and a VEHP (space velocity per hour weighted) from 1 to 10 kg / (1xh) in the presence of hydrogen

Description

SELECTIVE HYDROGENATION OF DIENS IN RENDERED CURRENTS The present invention relates to a process for the selective hydrogenation of dienes, in particular of dienes in reformed streams (feed streams) over a precipitated catalyst with a nickel content. In addition, the present invention relates to a process for preparing high purity aromatics or mixtures of aromatics. The reformed produced by catalytic reforming of naphtha represents a very important source of aromatics to isolate pure aromatics. The important constituents of the reforming stream are aromatic compounds such as benzine, toluene xylene and ethyl benzene. The boiling range of the hydrocarbon mixture between 60 and 1 ° C. In addition to saturated hydrocarbons and aromatics, untreated reformed streams contain other constituents such as olefins and diolefins. To further process them to obtain pure aromatics, a series of distillation, extraction and extractive distillation steps have been used up to now. If high purity is required, the diene compounds which are difficult to separate by means of the aforementioned physical processes have to be removed from the pure aromatic traction. According to Ullmann 's Encyclopedia of Industrial Chemistry, 5th ed., Vol. A3, page 490, Verlag Chemie, this is also done by treating pure aromatics on an active alumina: by passing them through the fixed bed, the • d-iene compounds are selectively adsorbed. The disadvantages of this process are the high solids consumption and the need to dispose of the alumina contaminated with the hydrocarbon compounds, disadvantages that become increasingly important in view of the stricter environmental controls. An alternative process comprises the selective hydrogenation of the traces of the unsaturated compounds. FR-A-2 720 754 describes, in the case of pyrolysis gasoline, selectively hydrogenating the dienes on an impregnated palladium catalyst at approximately 150 ° C and approximately 15 bar. An object of the present invention is to provide a process for the selective hydrogenation of »diene = in which: - a highly effective hydrogenation of the dienes occurs - the aromatics are not essentially hydrogenated - - a stable, inexpensive catalyst is used. - the process can be automatically controlled in a simple and effective way, and - the process can be carried out in a simple way in existing plants and refineries.

We have found that this goal is achieved by a process for the selective hydrogenation of dienes in feed streams containing dienes, which consists of hydrogenating a feed stream containing dienes, on a precipitated catalyst with a nickel content of 40 to 100 ° C, a pressure of 3 to 20 bar and a VEHP from 1 to 10 g / (lxh) in the presence of free hydrogen. In accordance with the present invention it has been found that nickel-containing precipitated catalysts which are known per se from EP-A 0 672 452 allow highly effective selective hydrogenation of dienes, with the hydrogenation used by this catalyst being carried out with Reformed space velocities are very high on the catalyst and under low pressure and low temperature conditions. By using the process of the present invention it is possible, during operation under conditions of pressure and low temperatures and high reforming efficiency, to feed the hydrogen into the hydrogenation reactor in such a way that the fed amount is regulated as a function of the dienes that are going to be hydrogenated.

Precipitated nickel catalyst Precipitated nickel catalysts used in accordance with the present invention are described in EP-A 0 672 452. These catalysts consist essentially of 65 to 80 'nickel, calculated as nickel oxide from 10 to 25. silicon, calculated as silicon dioxide, from 2 to 10% zirconium, calculated as zirconium oxide and from 0 to 10% aluminum, calculated as aluminum oxide, with the proviso that the sum of the dioxide and oxide contents of aluminum is at least 15 '? (percentages in percent by weight, based on the total mass of catalyst). These are prepared by the addition of an aqueous acid solution of nickel, zirconium and, if desired, aluminum salts to a basic aqueous solution of silicon and, if desired, aluminum compounds, the pH being reduced to at least 6.5, and subsequently adjusted from 7 to 8 by adding another basic solution, isolating the solid precipitated here, drying, forming and calcining. The catalysts which are used according to the present invention preferably contain from 70 to 78% nickel, from 10% to 20% silicon, from 3% to 7% zirconium and from 2% to 10% aluminum. Preference is given to the use of catalysts containing only nickel as the catalytically active metal. In particular, catalysts that are free of palladium can be used. In addition to the specified oxides, the catalysts may contain promoters in amounts up to 10%. These are compounds such as CuO, Ti0, MgO, CaO, ZnO and However, preference is given to catalysts that do not contain promoters. The catalysts that are applied in the present invention are prepared by starting from aqueous acid solutions of nickel, zirconium and, if desired, aluminum salts. Suitable salts are organic and inorganic salts such as acetates, sulfates, carbonates, but preferably nitrates of the specified metals. The total content of the metal salts is, in general, from 30 to 40% by weight. Since the final precipitation of the metals from the solution is almost quantitative, the concentration of the individual components in the solution will depend only on the content of this component in the catalyst to be prepared. The aqueous solution is adjusted to pH below 2 by the addition of mineral acid, preferably nitric acid. This solution, suitably stirred with a vortex, is introduced into a basic aqueous solution containing silicon compounds and, if desired, aluminum compounds. This solution contains, for example, alkali metal hydroxide or preferably sodium carbonate, generally in amounts of 15 to 40% by weight, based on the solution. The pH in general is above 10.

Suitable silicon compounds are liquid sodium silicate, which is preferred, and also SiO. The silicon content of the solution is for convenience from 0.5 to 4% by weight. In addition, the solution may, if desired, contain aluminum compounds in the form of oxidic solids, although it is preferred to add aluminum salts alone to the acid solution. The addition of the acid solution to the basic solution is generally carried out at 30 to 100 ° C, preferably at 60 to 80 ° C. In general, it is carried out for a period from 0.5 to 4 hours. A sufficient amount of the acid solution is added so that the pH drops to at least 6.5, thus precipitating the insoluble compounds. Preference is given to a range from 4.0 to 6.5, particularly preferably from 5.5 to 6.5. The lower pH values are possible, but they do not provide a visible advantage for the catalysts thus prepared. In general, this pH is maintained for 1 to 60 minutes, depending on the amount of the solutions that are used, then it is adjusted from 7 to 8 by adding more basic solution and precipitation of the metal compounds. this pH. If catalysts containing promoters are used, it is advantageous to add soluble metal salts as precursors for the promoters to one of the described solutions to co-precipitate these metals and further to process the product of the precipitation thus obtained. However, the promoters can also be added as solids to the precipitation solution. ~ The precipitated product is isolated, for example, by filtration. In general, this is followed by a washing step during which, in particular, any of the alkali metal ions and the nitrate ions entrained during the precipitation are washed. Subsequently, the solid thus obtained is dried, for which purpose it may be used, for example a drying oven or a spray dryer depending on the amount of material to be dried. In general, the drying temperature is from 100 to 200 ° C. If desired, the aforementioned promoters can be mixed in the solid before the next step of the process. The dried product is then preferably calcined, generally from 300 to 700 ° C, preferably from 320 to 450 ° C, for a period of 0.5 to 8 hours. For use in accordance with the present invention, the calcined solid is formed to produce bodies formed, for example, by extrusion to give the extrudate or by rattling. For this purpose, the peptizing agents, such as nitric acid or formic acid, are added to the calcined solid in amounts in general from 0.1 to 10 or by weight, based on the solid to be formed. For tabletting, for example graphite can be used. The shaped bodies thus obtained are generally calcined from 300 to 700 ° C, preferably 350 to 500 ° C, for 1 to 8 hours.

Hydrogenation process The process parameters that are used according to the present invention and the preferred process parameters are shown in the following table.

Parameters of the hydrogenation process Space velocity by weighted hour Feed streams Preferred feed streams used in the process of the present invention contain from about 15 to about 90% by weight aromatics and up to about 5000 ppm by weight of dienes. The most preferred feed streams are the reforming streams. In a particularly preferred embodiment of the process according to the present invention, the hydrogen is fed into the hydrogenation step in a controlled manner so that the amount of hydrogen fed is approximately that necessary to hydrogenate the dies. The control at this point of preference is carried out so that from 1 to 1.3 mol, preferably from 1 to 1.2 mol, particularly about 1.2 mol of hydrogen, is fed per mol of the diene structure in the feed stream. Preference is given to carry out the process using a catalyst containing from 6 5 to 80% by weight of nickel, from 10 to 25% by weight of silicon, from 2 to 10% by weight of zirconium, from 0 to 10% by weight of aluminum, all components calculated as oxides and percentages by weight, based on the total mass of the catalyst , with the proviso that the sum of the contents of silicon oxide and aluminum oxide is at least 15%. Further, it is preferred, in accordance with the present invention that the hydrogenated product be separated in an extractive distillation step in a mixture of aromatic hydrocarbons and a mixture of non-aromatic hydrocarbons. Finally, it is foreseen and preferred according to the present invention that the aromatics content of the mixture to be hydrogenated is increased before the selective hydrogenation by means of one or more steps of distillation, extraction and / or extractive distillation Upstream. Surprisingly, the nickel-containing precipitated catalysts described also show a high selectivity in the hydrogenation of the dienes in a mixture of aromatic-rich hydrocarbons when the process is configured such that the catalyst is subjected to a high feed stream, especially a stream of reforming current at pressure and low temperature and the hydrogen is fed to the reactor in such a way that its quantity is controlled as a function of the diene to be hydrogenated. The use of the hydrogenation step according to the present invention is particularly useful in combination with an extractive distillation downstream of the hydrogenated product to isolate them. valuable aromatics. It is already known that mixtures of aromatic hydrocarbons can be obtained selectively from the aromatic / non-aromatic hydrocarbon mixtures by extractive distillation, where the organic solvent used consists of a polar liquid of high boiling point (Ullmann's Encyclopedia of Industrial Chemistry , 5th Ed., Vol. A3, page 490, Verlag Chemie). DE-A 20 40 025 describes the fact that N-substituted morpholines are particularly suitable as a selective solvent. The selective solvent for the extractive distillation step is NEM (N-formylmorpholine).

Accordingly, the compounds that are formed in the selective hydrogenation of the reforming stream can be separated in a very simple manner from the mixture of aromatic hydrocarbons during the extractive distillation step. If the hydrogenation conditions are too drastic (for example, conditions at the end of the process) or the catalyst is too active, it is possible that the aromatics are hydrogenated. The naphthas thus formed in the same way are removed from the aromatic mixture during the extractive distillation step, so that high purity is guaranteed without further treatment with alumina. The practical utility of the process of the present invention is demonstrated by the following example. The initial hydrocarbon mixture used was a fraction of the benzene-rich reformate. The purity with respect to the present diene compounds was tested by means of the wash color test according to ASTM-D-848. The experimental reactor was operated in a descending flow mode according to the following conditions: - temperature: T = 60 ° C - pressure: PH ^ = 10 bar - yield: VEHP = 6 kg / (LCat xh) - gas discharge: 1.7 standard l / kg * As described in EP-A 0 672 452 with the following composition N 75% by weight Si 15"by weight Al 5% by weight ZR 5% by weight (all as oxides) This example shows that the die compounds present in the reformate are selectively hydrogenated by the use of the precipitated catalyst with a nickel content according to the present invention, which results, for example, in the value of the improved wash color test without a high loss of the aromatics.

Claims (7)

1. A process for the selective hydrogenation of dienes in feed streams containing dienes, which consists of hydrogenating this feed stream containing dienes, on a precipitated catalyst containing nickel from 40 to 100 ° C, a pressure of 3 to 20 bar and a VEHP from 1 to 10 kg / (lxh) in the presence of free hydrogen.

2. The process as recited in claim 1, wherein from 50 to 80 ° C, a pressure of 5 to 12 bar and a VEHP from 3 to 7 kg / (lxh).

3. The process as recited in claim 1 or 2, wherein the feed stream contains from 15 to 90% by weight of aromatics and up to 5000 ppm by weight of dienes.

4. The process as recited in any of claims 1 to 3, wherein the hydrogen is fed into the hydrogenation step in such a way that the amount is controlled as a function of the dienes to be hydrogenated, being particularly 1 to 1.3 mol, preferably 1 to 1.2 mol, particularly about 1.2 mol of hydrogen per mol of the diene structure in the feed stream. The process as mentioned in any of claims 1 to 4, wherein the catalyst contains from 65 to 80% nickel, from 10 to 25% silicon, from 2 to 10% zirconium, from 0 to 10% aluminum, all components calculated as oxides and weight percentages based on the total mass of the catalyst, provided that the sum of the content of silicon dioxide and aluminum oxide is at least 15%. 6. The process as recited in claim 1 or 2, wherein the hydrogenated product is separated into an extractive distillation step in a mixture of aromatic hydrocarbons and a mixture of non-aromatic hydrocarbons. The process as recited in claim 1 or 2, wherein the aromatics content of the feed stream is increased before selective hydrogenation by means of one or more steps of distillation, extraction and / or extractive distillation upstream . In the process for the hydrogenation of the dienes in feed streams containing dienes, a feed stream containing dienes is hydrogenated on a precipitated catalyst containing nickel from 40 to 100 ° C, a pressure of 3 to 20 bar and a VEHP (weighted hourly space velocity) from 1 to 10 kg / (lxh) in the presence of free hydrogen.