DE2136796C2 - Process for the selective hydrogenation of a petroleum fraction boiling in the range of gasoline - Google Patents

Description

The invention relates to a process for the selective hydrogenation of a petroleum fraction which contains aromatic hydrocarbons, olefins, diolefins and sulfur compounds and boils in the range of gasoline Treatment of the petroleum fraction in three successive reaction stages with hydrogen, in which first reaction stage in the liquid phase in the presence of a hydrogenation catalyst which is a metal of the Group VIII contains, and in the second and third reaction stage in the gas phase in the presence of Catalysts is working.

There are numerous processes for the selective hydrogenation of petroleum fractions, in addition to an aromatic Fraction still contain diolefins, olefins and sulfur compounds. The aim of these procedures is one Elimination of the undesired compounds by hydrogenation of the diolefins and olefins and by Hydrodesulfurization so that ultimately the aromatic compounds in the batch can easily be separated off.

The catalytic one-step process, in which hydrogenation and desulphurization practically simultaneously carried out, were quickly abandoned because the temperature required to desulfurize the batch easily leads to the polymerization of the unstable compounds. The resins formed by this polymerization affect the convenience of carrying out the procedure.

DE-AS 11 92 773 describes a hydrogenation process for petroleum fractions boiling in the gasoline sector, which works in three stages, the first of which Stage in liquid phase and the second and the third Stage can be carried out in the gas phase. It is the catalyst in the first process stage is the same as the catalyst in the second process stage (nickel on alumina, aluminum oxide).

From DE-OS 18 04 769, DE-OS 1814 043 and US-PS 33 93 148 hydrogenation or desulfurization catalysts are known with a certain specific surface area Multi-stage catalytic processes (e.g. two or

ίο three stages), in which the hydrogenation and the Desulfurization of the batch is carried out in sequence, are also known. However, the methods proposed so far have disadvantages. You hydrogenate the olefins present in the batch by means of a

ι s classic hydrogenation catalyst, so it is difficult avoid hydrogenation of some of the aromatics in the batch. One conducts the procedure with the aim If the aromatics are refined, this hydrogenation leads to losses of over 10% of the end product tes. The classic hydrogenation catalysts are used ren in the first part of the process when the unstable compounds (like the diolefins) are not quite yet are hydrogenated, it is difficult to avoid the formation of polymeric compounds in the gas phase precipitate on the catalyst and lead to a rapid deactivation of the same.

In contrast, the invention is based on the object of avoiding these disadvantages. According to the invention, this object is achieved in a Method of the type mentioned above thereby solved that in the second reaction stage a catalyst made of molybdenum and / or tungsten, optionally with one or more Group VIII metal (s) deposited on a support, the one specific surface between 20 and 90 m ² per gram is used, and in the third reaction stage a catalyst consisting of molybdenum and / or tungsten is used, optionally with one or more metal (s) of Group VIII, deposited on a support having a specific surface area between 120 and 500 m ² per gram, with a volume ratio of between 200 and 4000 parts of hydrogen sulfide to one million parts of hydrogen in the second and third

Reaction stage is maintained.

Under a petroleum fraction boiling in the range of gasolines, is meant a fraction boiling from at least 80 wt .-% 30 to 220 ⁰ C. In such a procedure it is always interesting treat a batch rich in aromatics; the method can e.g. B. applied to such gasoline obtained by cracking (thermal, catalytic or steam cracking) of petroleum or gas oil receives.

The following are the reaction conditions for the inventive method described in more detail.

The first reaction stage is carried out in the liquid phase, i. H. at the exit of the first reaction stage there are always at least 50% by weight of the initial batch

bo ge liquid, while the rest of the fraction (provided they is present) was evaporated in the reaction stage. The evaporation is based on the fact that the hydrogenation reaction is strongly exothermic. The internal operation of the Reaction stage is between 50 and 200 ° C; preferential ^{wisely, it should not rise above 200 °} C. even at the exit of the stage if one wants to avoid excessive polymerization. The liquid charge is preferably at a temperature of 50 to 120 ⁰ C in the

Reaction stage introduced The pressure must be sufficient be large to keep the batch at least largely fluid; it is generally between 5 and 60 bar, preferably between 20 and 45 bar.

At this stage the liquid feed is brought into contact with a hydrogenation catalyst Metal of group VIII of the periodic table contains e.g. B. nickel, cobalt, palladium or platinum. Nickel is that preferred metal. The metals used are preferably applied in metal form; they can on Supports deposited and used in a test bed or in a fluidized bed. One can also use it as a suspension, e.g. B. Raney nickel or cobalt In a preferred embodiment of the invention, a supported catalyst is used and a fixed bed. The catalyst support consists of the usual support materials, e.g. B. aluminum oxide, silicon oxide or mixtures thereof, magnesium oxide, clay or zeolite. It is preferable to choose a carrier that is slightly acidic (aluminum oxide or Silicon oxide). You can get the natural acidic surface of the support by adding alkali or Neutralize alkaline earth oxides. The supported catalysts usually contain 5 to 50% by weight of the active Metal. The space velocity (WH), i.e. the amount of batch introduced per liter Catalyst and per hour can vary between 0.5 and 5, depending on the activity of the catalyst and depending on the content of unsaturated compounds in the batch. One can see the amount of in the Reaction stage introduced hydrogen vary so that the molar ratio of hydrogen to the Hydrocarbons between 0.1 and 1 is.

At the exit of the first reaction stage, a substantial amount of the charge is still in the liquid State; this part is evaporated in the usual way, avoiding the formation of resin; z. B. one evaporates only 90 to 99% of the liquid

The gaseous charge now enters the second reaction stage at a temperature of preferably -to 230 to 300 ^° C. The charge is now brought into contact with hydrogen in the presence of a supported catalyst. This catalyst contains molybdenum and / or tungsten, optionally with one or more metal ( en) of group VIII (e.g. cobalt or nickel or their mixtures) can be used. The active elements of the catalyst are deposited on a support which must have a particularly small surface area; this surface is between 20 and 90 m ² / g. Suitable supports are: aluminum oxide, silicon oxide, magnesium oxide and titanium oxide. It is preferred to use practically neutral supports, ie those with a weak acidity of the surface (it is indicated below what is meant by a weak acidity of the support). The temperature at the beginning of the reaction stage is between 230 and 360 ^c C; in order to avoid too great a temperature increase (because of the exothermic hydrogenation reaction), it is possible to introduce at least one point in the middle of the catalyst bed a fraction of the charge which originates from the first stage or was circulated. The pressure inside the zone fluctuates between 25 and 60 bar. The amount of hydrogen introduced is preferably such that the molar ratio of hydrogen to b5 olefins is between 5 and 15 and that the partial pressure of the hydrogen at the level of the catalytic bed is 8 to 30 bar. The rate of increase in space is preferably between 4 and 20, the volume of the charge being measured in liquid form.

In a preferred embodiment, the pairs molybdenum-cobalt, molybdenum-nickel, tungsten-cobalt, tungsten-nickel, are selected as the catalyst. The above catalysts can also be in oxidized form be used; however, they are preferably used in the sulfided form. Sulphidation of the Catalyst in the reactor is achieved that a volume ratio of hydrogen sulfide to Maintains hydrogen between 200 and 4000 ppm. For this purpose, one can use the in the gas mixture of the third stage (where the desulfurization of the batch is terminated) hydrogen sulfide present in the Use circuit.

If the catalyst consists only of molybdenum or tungsten, the proportion of active is Elements preferably 6 to 40 percent by weight of the metal (expressed as oxide).

If the catalyst contains at least two metals, the amount is preferably 4 to 25% by weight Molybdenum or tungsten (as oxide) and 2 to 15% by weight of Group VIII metal (as oxide).

The gas stream which leaves the second stage is preferably ^{fed into the third reaction zone at a temperature of 300 to 350 0} C, where it is brought into contact with a catalyst which contains molybdenum and / or tungsten, optionally with one or more metal ( en) of group VIII.

The good metal components as in the second stage are preferred. The metal or metals are deposited on a support which must have a sufficiently large specific surface; the specific surface area is 120 to 500 m ² / g. Eta-aluminum oxide or silicon oxide-aluminum oxide can be selected as the carrier. It is preferable to use slightly acidic carriers (compare the definition given below). The reaction temperature within the third zone is between 300 and 390 ⁰ C; the total pressure fluctuates, for example, between 10 and 60 bar, preferably between 30 and 50 bar. The space flow rate is preferably between 0.5 and 5 liters per liter of catalyst per hour, the volume of the charge being measured in the liquid state. The hydrogen is introduced in such a way that the partial pressure at the level of the catalytic bed is preferably between 8 and 25 bar and the molar ratio of hydrogen to the olefins is between 5 and 15.

The catalysts of the third stage can be used in their oxidized form, whereby one can use both can use a single metal as well as a metal pair. A sulfated catalyst is preferred used. A sulfidation of the catalyst is achieved by having a volume ratio of Maintains hydrogen sulfide to hydrogen between 200 and 4000 ppm. The catalyst from one single metal (molybdenum or tungsten) preferably contains 5 to 35% of the metal (as oxide).

If the catalyst consists of at least one metal pair of the type mentioned above, the amount is of molybdenum or tungsten (as oxide) preferably between 5 to 30 wt .-% and that of the metals of Group VIII (as oxide) preferably between 1 and 6%.

The weight of the metals is given as oxide.

The acidity of the carrier used in the various process stages can be due to the heat of adsorption of ammonia on the carrier a pressure of 0.00013 mbar can be measured. the Adsorptionswärmezl // is calculated as follows:

AH =

Free law t e heat (in calories per gram of support) Amount of ammonia adsorbed (in millimoles of NH ₃ per gram of carrier)

These two measurements are made by microgravimetry and by differential thermal analysis carried out at the temperature at which the catalyst is used.

A carrier is considered practically neutral or weak

referred to as acidic when ΔΗ is less than 0.04 (catalyst carrier of the second stage). A carrier is said to be slightly acidic if 4 // is between 0.04 and 0.1 (catalyst carrier of the third stage).

example 1

A batch of gasoline from the steam cracking is used with the following composition:

Paraffins and naphthenes 27% by volume Monoolefine 8.6% by volume Diolefins and cycloolefins 10.4% by volume Aromatics and alkenyl aromatics 54% by volume Total sulfur 160 ppm

The reaction conditions are as follows:

Catalyst: cobalt

1st stage

Temperature at the inlet of the reactor Temperature at the exit of the reactor

80 ° C 180 ° C

The catalyst consists of nickel, which is deposited on aluminum oxide (12.5% nickel as Oxide).

pressure

Molar ratio hydrogen /

Hydrocarbons

30 bar 2

0.3

2nd stage

Temperature at the beginning of the reactor 280 ° C Temperature at the exit of the reactor 320 ° C Total pressure 43 bar Partial pressure of hydrogen 15 bar Volume ratio of sulphurous water substance / hydrogen '000 ppm Hydrogen / olefins molar ratio 10 V / V / H 6th

molybdenum

5.7% by weight, as CoO (0.076 mol of the oxide per 100 g of the catalyst) 5.7% by weight, as MoO ₃ (0.040 mol of the oxide per 100 g of the catalyst).

There are thus 0.116 mol of metal oxide per 100 g of the catalyst deposited on the aluminum oxide support with a specific surface area of 70 m ² / g. This catalyst is sulfided by pretreatment with a mixture of hydrogen sulfide and hydrogen

The acidity test of the carrier gives ad // = 0.03.

3rd stage

Initial temperature 320 ° C Starting temperature 340 ° C Total pressure 43 bar Partial pressure of hydrogen 14 bar V / V / H 1 Volume ratio Hydrogen sulfide / hydrogen 1200 ppm Catalyst: cobalt 2.2 wt%, as CoO molybdenum 12.2% by weight, as MoO ₃

The catalyst is located on an aluminum

carrier with a specific surface area of 300 m ² / g and an H of 0.07. This catalyst is through prior treatment with hydrogen sulfide /

Sulfided hydrogen. The characteristics of the batch

before and after the treatment are in Table I with the corresponding result of a comparative example compiled.

Comparative Example 1A

The same charge as in Example 1 is subjected to a three-stage hydrogenation treatment: The first stage is identical to that described in Example 1, but a cobalt-molybdenum catalyst with a content of 2.2% by weight is used in the second stage. % CoO and 12.2% by weight MoO ₃ , which are deposited on the same aluminum oxide as in Example 1 (30OmVg). This

Platinum catalyst on alumina (1 wt% platinum); b5 catalyst is as previously described in Example 1

the aluminum oxide used has a very large specific surface area (220 m ² / g) and the catalyst is used in the metal form. Sulphided in the third stage. The properties of the batch and the end product are shown in Table I below.

Table 1

properties Kinhcil Batch example Example I Λ lindprindukl Ii nil product Paraffins + naphthenes % VoI 27 47 52 Monoolefins - 8.6 0 0 Diolefins + cycloolefins - 10.4 0 0 Aromatics + alkenyl aromatics - 54 53 48 specific weight g / cm ¹ 0.793 0.785 0.778 Bromine number gBrj / lOOg 66 1 1 M. A. V. mgM: i / g 74 0 0 Resins present mg / 100 ml 30th 2 2 Resins potentially mg / 100 ml 7740 3 3.2 Total sulfur ppm 20th 4th 4th

The bromine number was determined according to ASTMD 1159-61. MAV means maleic anhydride value; the determination was carried out with the help of the »UOP method 326-58«. The tests used to determine the resins present and potential are ASTM D 2 ^r i 381-61 and ASTM D 873.

From the table it can be seen (bromine number and M.A.V.) that the hydrogenation of the olefins in both Procedure is practically identical; however, the composition of the products obtained is different the. In Example 1, the loss of aromatics in the hydrogenation is limited to one unit during in comparative example 1A, the loss is 6.

In comparison to the known method, the method according to the invention thus provides a product with! 5 an aromatic content that is around 10% higher.

Comparative Example 1B

The same batch as in Example 1 is subjected to a three-stage hydrogenation, using the same reaction conditions and the same catalysts; however, the aluminum oxide used in the second stage (Co-Mo catalyst) has a very large specific surface area (220 m ² / g). The product obtained contains 51 vol ⁰ Zb aromatics and 4 alkenylaromatics (compared with 53% in Example 1).

Comparative example IC

A three-stage hydrogenation is carried out with the same batch as in Example 1, the same being used Reaction conditions and the same catalysts used; however, the volume ratio is of Hydrogen sulfide to hydrogen in the second stage reaction is equal to 100 parts per million. That The product obtained contains 51.5% by volume of aromatics and alkenyl aromatics, furthermore 100 mg / 100 ml of resins, while in Example 1 the product contained only 2 mg / 100 ml of resins.

Example 2

The same batch is used as in the previous examples; the process differs from Example 1 only in the use of a sulphided molybdenum catalyst (MOS2) in the second stage, which is deposited on an aluminum oxide support with a specific surface area of 70 m ² / g. (This catalyst contains 16.6 wt% molybdenum, as MoO ₃ , i.e. 0.116 moles of the oxide.)

The following values are obtained:

composition Sobriety Batch product Paraffins + naphthenes % VnI. 17th 45.4 Monoolefins - 3.6 1.1 Diolefins + cycloolefins - 10.4 - Aromatics + alkenyl aromatics - 54 53.5 specific weight g / cm ³ 0.793 0.7855 Bromine number gBr, / 100g 66 1.8 M. A. V. mg M.A./g 74 0 Resins present mg / 100 ml 30th 2 Resins potentially mg / 100 ml 7740 3 Total sulfur ppm 20th 5

When comparing these results with those of Example 1, it is found that the method with a Molybdenum catalyst in the second stage is excellent; albeit eliminating the undesirable Compounds (olefins and sulfur) is somewhat less complete, the aromatics yield is better (Loss only 0.5 units).

Claims (1)

Claim: Process for the selective hydrogenation of a petroleum fraction, which contains aromatic hydrocarbons, olefins, diolefins and sulfur compounds and boils in the range of gasoline, by treating the petroleum fraction in three successive reaction stages with hydrogen, wherein in the first reaction stage in the liquid phase in the presence of a hydrogenation catalyst, which a Contains metal of group VIII, and in the second and third reaction stage in the gas phase in the presence of catalysts, characterized in that in the second reaction stage a catalyst made of molybdenum and / or tungsten, optionally with one or more metals) of group VIII , which are deposited on a support having a specific surface area between 20 and 90 m ^z per gram, is used, and in the third reaction stage a catalyst consisting of molybdenum and / or tungsten is used, optionally with one or more metal ( en) of group VIII, which are deposited on a carrier having a specific surface area between 120 and 50Om ² per gram, a volume ratio of between 200 and 4000 parts of hydrogen sulfide to one million parts of hydrogen being maintained in the second and third reaction stage.