EP0210514B1 - Hydrogenation of olefinic hydrocarbons in t-alkyl-alkyl-ether-containing hydrocarbon fractions - Google Patents

Description

The present invention relates to a process for the hydrogenation of olefinic hydrocarbons which are in a mixture with tert-alkyl alkyl ethers and optionally other saturated aliphatic or aromatic hydrocarbons, the tert-alkyl alkyl ethers being largely retained.

To increase the octane number, tertiary alkyl alkyl ethers, the best known of which are methyl tertiary butyl ether (MTBE) and tertiary amyl methyl ether (TAME), can be added to the motor spirit. Such ethers are generally prepared by etherification of tertiary alkenes in gasoline cuts and other suitable starting materials with lower alkanols on acidic catalysts, such as cation exchangers, sulfuric acid and other acidic catalysts.

The resulting ether-containing reaction mixtures contain even larger amounts of olefinic hydrocarbons, which impair the quality of these mixtures as gasoline additives, especially if they are unleaded Gasoline should be added. A significant improvement in quality could be expected from a hydrogenating treatment of such ether-containing reaction mixtures, for example an increase in the engine octane number (MOZ), a decrease in sensitivity (= distance between MOZ and resarch octane number (ROZ)) and an improvement in their shelf life.

Numerous processes are known for the hydrogenation of olefins or olefin-containing hydrocarbon mixtures, in which various catalysts are used. These hydrogenation catalysts have, as the hydrogenation-active component, one or more elements of the 6th, 7th or 8th subgroup of the Periodic Table of the Elements in elementary or bound form, which can be doped with various additives, in order to achieve certain catalyst properties, such as prolonging the service life, resistance to certain ones To obtain catalyst poisons, increase selectivity or better regenerability. Such hydrogenation catalysts often contain the hydrogenation-active component on supports such as mordenites, zeolites, Al₂O₃ modifications, SiO₂ modifications and others. For the extensive hydrogenation of the olefins, reaction temperatures of 150-250 ° C. are generally used. For example, EP 49 803 discloses the hydrogenation of a pyrolysis gasoline fraction in which metals from subgroup VIII of the periodic table of the elements on zeolitic supports are used as catalysts. Because of their regular structure, zeolites have passages and pores with discrete diameters depending on the type; pore diameters of 3-12 Å are suitable for the process of EP 49 803. Zeolites are generally acidic in character.

On the other hand, it is known that tert-alkyl alkyl ethers on acidic catalysts, which include acidic cation exchangers and also mordenites, zeolites, various Al₂O₃ modifications, various SiO₂ modifications and others, already from 90 ° C reaction temperature in alkanols and tert. -Alkenes are split back. Furthermore, it is known that oligomeric tertiary alkenes can also be cleaved on acidic catalysts, for example those mentioned.

It is also known to free ethers from olefinic admixtures, for example ethers which have been prepared by hydration of olefins, by hydrogenation using catalysts of nickel or cobalt on acid-reacting SiO 2 (FR 1,560,586 in connection with DE-OS 16 67 194). This process has been described for the purification of diethyl ether and can be applied to other normal-chain ethers.

We have now found a process for the hydrogenation of olefinic hydrocarbons in mixtures with tert-alkyl-alkyl ethers and optionally other saturated aliphatic, naphthenic or aromatic hydrocarbons while largely maintaining the ethers, which is characterized in that a catalyst is used which is a hydrogenation-active Component on a catalyst carrier with a specific surface area of more than 50 m² / g and a pore diameter of predominantly <1000 nm has, the catalyst carrier being neutral or doped with (earth) alkali compounds.

Elements of the 6th, 7th or 8th subgroup of the Periodic Table of the Elements, such as molybdenum, rhenium, iron, cobalt, nickel or the platinum metals, are suitable as the hydrogenation-active component. The platinum metals, especially platinum and / or palladium, very particularly palladium, are used in a concentration of 1-50 g / l catalyst, especially 5-20 g / l catalyst. The other elements mentioned, in particular cobalt, nickel and / or molybdenum, very particularly nickel, are used in a concentration of the hydrogenation-active component, calculated as metal, of 200-800 g / l, in particular 300-700 g / l, of catalyst. The other metals mentioned which are not among the platinum metals can also be used in bound form.

Substances can be used as carrier material for the hydrogenation catalysts to be used according to the invention, the specific surface area of which is> 50 m² / g catalyst, but especially> 100 m² / g catalyst and the pore diameter of which is predominantly <1000 nm, but especially <200 nm.

Such substances can be, for example, neutral aluminum silicates, diatomaceous earth, Al₂O₃, coal, etc. if they meet the above conditions. Kieselguhr and Al₂O₃ are particularly suitable.

Furthermore, carrier materials such as SiO₂ or acidic aluminum silicates are suitable if they are doped with alkali or alkaline earth compounds. The concentration of alkali or alkaline earth compounds is 0.01-1, preferably 0.02-0.2 equivalents of alkali / alkaline earth metal per liter of catalyst in question. The above-mentioned neutral carriers can also be given such a doping.

The hydrogenation according to the invention is possible both in the trickle phase and in the liquid or gaseous phase and is generally carried out at a temperature of 50-200 ° C., preferably 80-180 ° C., particularly preferably 100-150 ° C.

The hydrogen partial pressure is generally set at 1-100 bar, preferably 2-40 bar, particularly preferably 5-30 bar.

Pure hydrogen, technical hydrogen or hydrogen-containing residual gas present in petrochemical plants can be used as hydrogen. The hydrogen content is 70-100%, in many cases also about 80 to about 90%. The impurities present in technical hydrogen and in hydrogen-containing residual gases are, for example, nitrogen, methane or ethane. The amount of hydrogen is adjusted in the process according to the invention so that the degree of remaining unsaturation corresponds to the desired value. To achieve the remaining degree of unsaturation, the reaction temperature and / or the residence time in the hydrogenation reactor are also used in a manner known to the person skilled in the art; it is often possible to work with an excess of hydrogen which is removed after the hydrogenation reaction or is operated as a cycle gas. The remaining degree of unsaturation is measured by the bromine number in g Br₂ / 100 g hydrocarbon mixture. Bromine numbers over 50, even over According to the invention, 70 g Br₂ / 100 g hydrocarbon mixture can be pressed over all conceivable intermediate values down to values of less than 5, even down to <0.01 g Br₂ / 100 g hydrocarbon mixture. The content of tert-alkyl alkyl ether is obtained. Preservation means, for example, the maintenance of at least 90% of the original ether content, in many cases more than 96% of the ether.

The catalyst load in the process according to the invention is 1-5 l of the material used per l catalyst and hour for working in the liquid and trickle phases. For working in the gas phase, the catalyst load is 2-3 l / l catalyst and hour.

The heat of reaction generated can be dissipated by cooling the reactor or by the sensible heat of the reaction product. To avoid temperature peaks, the feed can be diluted by returning some of the hydrogenated product to the feed.

Suitable starting materials for the process according to the invention are those which contain tert-alkyl alkyl ethers in addition to olefinic, paraffinic, naphthenic or aromatic hydrocarbons and, if appropriate, minor amounts of diolefins. Such mixtures are obtained, for example, when gasoline cuts, for example from a steam cracker, a fluid catalyst cracker (FCC) or from dehydrogenation plants are reacted with lower alkanols. Particularly suitable gasoline cuts are those which, due to their C number range, are suitable for suitable for later use in petrol. Examples of such tertiary alkyl alkyl ethers in such mixtures are those derived from tertiary C₄-C₄ alkenes and C₁-C₄ alcohols. In particular, the ethers of the tertiary C₄-C Alk alkenes with methanol, in particular those of the tertiary C₅-C₆ alkenes with methanol.

After carrying out the process according to the invention, excess hydrogen is optionally separated off with accompanying substances such as methane, ethane or nitrogen and other low boilers as residual gas.

The hydrogenation product according to the invention which is present after the removal of a residual gas can be used as a gasoline additive.

Of course, the hydrogenation mixture obtainable according to the invention can also be separated in such a way that a gasoline cut without a tert-alkyl alkyl ether is obtained in a distillation column, from which the residual gas still has to be removed, a pure ether, for example TAME, is obtained as a side stream and Small amounts of higher boilers, such as higher ethers and oligomers, remain in the swamp.

Examples

The present invention is illustrated by the following examples. Conventional hydrogenation apparatuses are used here (FIGS. 1, 2 and 3). The experimental setup was basically the same for the hydrogenations; the only difference was the direction of flow through the hydrogenation reactor, which was set from bottom to top in the case of liquid phase hydrogenation and from top to bottom in the cases of gas phase and trickle phase hydrogenation.

Experiment description:

The starting material for all experiments described below was a C₅-C₆ hydrocarbon fraction from a pre-hydrogenated pyrolysis gasoline which had been subjected to etherification with methanol and consequently contained tert-amyl methyl ether (TAME) and tert-hexyl methyl ether. This feed material had the following characteristic compositional characteristics:

The experimental apparatus (FIG. 1: hydrogenation in the trickle phase, FIG. 2: gas-phase hydrogenation and FIG. 3: hydrogenation in the liquid phase) were composed as the following units:
The feed material was transported from a graduated insert vessel (1) by means of a piston pump (2) via the preheater (3) into the hydrogenation reactor (4). This consisted of a thermostatted double jacket with the following dimensions: inner diameter 25 mm and length 750 mm. The hydrogenation catalyst (250 ml) was arranged as a fixed bed and was enclosed up and down by a pack of ceramic balls (each 50 mm long). The hydrogen (7) (about 80 vol .-% H₂, about 20 vol .-% CH₄) was added to the feed before the preheater (3). The hydrogenated product reached the separator (6) via the cooler (5). The amount of exhaust gas (8) (predominantly H₂ and CH₄) was 200 Nl / h.

Deviating from this description, in experiments with redilution of the feed material, the feed material with hydrogenated product was blended in a ratio of 2 parts feed material to 1 part hydrogenated product.

In the gas phase hydrogenation, a circuit line (9) was additionally used to recirculate part of the H₂ residual gas (8) obtained in the separator (6) to the fresh hydrogen (7). In this variant, the preheater (3) was also used as an evaporator and the cooler (5) was also used as a condenser. During the hydrogenation in the liquid phase, the hydrogenation reactor (4) was flown from below. Valves and measuring and control devices known to the person skilled in the art are not shown in FIGS. 1, 2 and 3.

Test conditions:

The following reaction conditions were set for all catalysts used in the liquid and trickle phase hydrogenation:

In the case of gas phase hydrogenation, the reaction pressure was adjusted to 2 bar at 100 ° C reactor temperature and to 5 bar at 150 ° C reactor temperature. The amount of circulating gas in the gas phase hydrogenation was 500 Nl / h.

Test results:

The mode of action of the hydrogenation was assessed for the reactor temperatures of 100 and 150 ° C. after the hydrogenation of the alkenes in the feed material by the bromine number and the TAME content. The catalysts used for the hydrogenation are listed in Table 1. The results for the particular hydrogenation depending on the catalysts listed in Table 1 are summarized in Table 2.

Claims (9)

1. Process for the hydrogenation of olefinic hydrocarbons in mixtures with tert.-alkyl alkyl ethers and, if appropriate, other saturated aliphatic, naphthenic or aromatic hydrocarbons, with substantial preservation of the ethers, characterized in that a catalyst which has an active component for hydrogenation on a catalyst support having a specific surface area of more than 50 m²/g and a pore diameter of, in the main, < 1,000 nm is used, the catalyst support being neutral or doped with alkali or alkaline earth metal compounds.
2. Process according to Claim 1, characterized in that the active component for hydrogenation is at least one noble metal of the 8th subgroup of the periodic system of the elements, particularly platinum and/or palladium, and in that the concentration of noble metal is 1-50 g/l of catalyst, in particular 5-20 g/l of catalyst.
3. Process according to Claim 1, characterized in that the active component for hydrogenation is cobalt, nickel, molybdenum or mixtures thereof in elementary or combined form, and in that the concentration of the active components for hydrogenation, calculated as metal, is 200-800 g/l, especially 300-700 g/l, of catalyst.
4. Process according to Claim 1-3, characterized in that aluminium silicates, kieselguhrs, charcoal or Al₂O₃, especially kieselguhr and Al₂O₃, are used as the support material, the specific surface area thereof being > 50 m²/g of catalyst and the pore diameter thereof being < 1,000 nm.
5. Process according to Claim 1-4, characterized in that the specific surface area of the catalyst support is > 100 m²/g.
6. Process according to Claim 1-5, characterized in that the pore diameter of the catalyst support is, in the main, < 200 nm.
7. Process according to Claim 1-6, characterized in that the support material or the catalyst is doped with alkali or alkaline earth metal compounds, the concentration being 0.01-1 equivalent of alkali/alkaline earth metal per litre of catalyst.
8. Process according to Claim 1-7, characterized in that the hydrogenation is carried out at a reaction temperature of 50-200°C, especially at 80-180°C, and under an H₂ partial pressure of 1-100 bar, especially 2-40 bar.
9. Process according to Claim 1-8, characterized in that the feed material used is hydrocarbon mixtures containing the methyl ether of isobutene and/or of tert.-amylenes and/or of tert.-hexenes, in particular pyrolysis gasoline fractions containing methyl ethers of tert.-amylenes and/or of tert.-hexenes.

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