JP2560056B2 - Method for selective hydrogenation of acetylenes - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improved process for removing alkynes from a liquid hydrocarbon stream while minimizing the loss of the conjugated dienes present therein. In particular, the invention relates to the selective hydrogenation of alkynes present in the 1,3-butadiene-enriched C ₄ cut from steam crackers used primarily for the production of synthetic rubber.

Polymerization of 1,3-butadiene to produce synthetic rubber is an important industrial process, producing tens of millions of tons annually. A large proportion of typical feedstocks used are 1,3
It contains butadiene and butenes, but they also contain a sufficient amount of alkynes (so-called acetylenes), mainly vinylacetylene. Since acetylenes act as catalyst poisons in the polymerization, they have to be removed as completely as possible. Therefore, 1,3
It is common to selectively hydrogenate acetylenic compounds while avoiding or limiting the loss of butadiene.

The selection conditions for the process are high, as other reactions must be avoided or prevented as far as possible. Of course for those reactions 1,
It includes not only hydrogenation of 3-butadiene and butenes but also polymerization reactions that reduce catalyst life. Regeneration of catalysts is possible, but their frequency is economically important, they induce modification of the catalyst and indeed mechanical destruction of the catalyst particles, resulting in a relatively high pressure drop in the bed.

SiO ₂ / Al ₂ O ₃ copper on a support at a high temperature - vapor selective hydrogenation over a nickel catalyst has been known for a long time. However, such methods are becoming increasingly obsolete because the catalysts often have to be replaced or regenerated, and the loss of 1,3-butadiene and the residual acetylene concentration are currently believed to be very important. .

U.S. Pat. No. 4,493,906 discloses a catalyst for the removal of acetylenes from a liquid hydrocarbon stream, which catalyst is essentially a well-defined gamma alumina (35% by weight).
Up to (can contain alpha-alumina) composed of finely divided Cu metal dispersed on. The gamma-alumina used has a surface area of 68-350 m ² / g, 40-98% of the pores have a pore diameter of 4-12 nm and 2-25% are 100-1000 n.
Pore diameters between m. The carrier is of high purity and silicon is S
It is less than 0.15% by weight as iO ₂ and Na is <0.15 as Na ₂ O. The catalyst of US Pat. No. 4,493,906 is claimed to leave 0 ppm of acetylene when used at about 68 ° C. and at LHSV (liquid hourly space velocity) below 1. However, the corresponding cycle life is
It is only 51/2 days, and after 6 days, about 100 ppm of acetylenes are detected in the effluent. Of course, higher LHSV
Values will further reduce cycle life or incomplete removal of acetylenes.

Other types of catalysts are based on palladium. Palladium is the most active and selective metal of Group VIII metals for acetylenic hydrogenation. However, Hydrocarbon Processing
Processing), March 1985, it is known in the art to encounter two types of operational difficulties, as explicitly disclosed in page 52: Even at moderate conversions of alkynes. Loss of 1,3-butadiene is observed, and loss of palladium often reduces catalyst life.

Over time, the severity of steam cracking has increased and C ₄ feed cuts have been found to contain increasing concentrations of alkynes up to 1 wt% or higher.
On the other hand, the conditions regarding the concentration of acetylenes in the effluent from selective hydrogenation are becoming increasingly severe. Accordingly, there is a need in the art for improved methods for removing alkynes from a liquid hydrocarbon stream while minimizing the loss of the conjugated dienes present therein.

The process of the present invention for the selective hydrogenation of alkynes present in a 1,3-butadiene-enriched C ₄ cut over a palladium-based catalyst comprises (i) 1,3- A butadiene-rich C ₄ cut is prepared, (ii) the cut is passed over the catalyst bed in trickle mode in the presence of hydrogen, and (iii) residual hydrogen is separated from the rest of the effluent from step (ii). And (iv) recovering the feedstock rich in 1,3-butadiene.

Palladium-based catalysts that can be used in the method of the present invention are known in the art. A particularly preferred catalyst consists of activated palladium metal deposited on a high purity alumina support.

The amount of palladium in the catalyst containing the high purity alumina support is preferably 0.1-0.35% by weight, more preferably about 0.2% by weight,
Is. Advantageously, the alumina is of high purity and the concentration of heavy metals other than Pd is below 0.05% by weight.

The surface area of the catalyst is preferably 50-110 m ² / g, more preferably 6
It is 5-95 m ² / g. The pore volume is preferably 0.5-0.6 cm ³ / g. The catalyst is preferably spherical with a size of 2-4 mm.

It has already been stated that the acidity of the alumina influences the undesired oligomeric reactions, so that it is preferred that the gamma-alumina is a common eta-alumina. However, this is not necessary in the process according to the invention, since this concerns only the long-term stability, not the activity of the new or regenerated catalyst. Other types of alumina, such as Q-type alumina as disclosed in Japanese Patent Application JP-58017835, can also be used.

So-called stabilized or promoted catalysts based on palladium are known, for example the palladium-gold supported catalysts disclosed in European Patent EP-89,252. However, the activity of these catalysts is generally lower than that of palladium-based catalysts. Without wishing to be bound by theory, this can be explained by the poor homogenous distribution of the metals on the support, the reason for which was adjusted at the low loading levels used for industrial precious metal catalysts. This is because it is almost impossible to obtain a supported bimetal catalyst. In practice, the support must be suitable for proper metal-metal interaction and a well-dispersed bimetallic species must be obtained and then maintained. The use of stabilizing or promoting catalysts in the process of the present invention is optional and therefore its use will depend on activity and long term stability conditions.

The activation, start-up and regeneration processes for palladium-based catalysts are known in the art. Activation consists of (i) purging oxygen using nitrogen, and (ii) passing hydrogen under atmospheric pressure with gradual heating to a level of about 90 ° C and then cooling. The start-up process consists of slowly increasing the hydrogen pressure, then increasing the feed and hydrogen flow rates, and finally increasing the temperature. The regeneration step is conducted by passing steam under atmospheric pressure while gradually raising the temperature to about 400 ° C., then continuing passing steam at atmospheric pressure at a temperature of about 400 ° C. for about 2 hours, after which 5 , Gradually adding up to 6 mol% of air. During the regeneration process, the catalyst temperature is about 500 ℃
Should not be exceeded. Regeneration is complete when the CO ₂ content at the outlet is low enough.

Prior art and catalyst manufacturers have found that liquid 1,3-butadiene-rich C ₄ using palladium-based catalysts.
The following typical process conditions are recommended for the selective hydrogenation of vinyl and ethylacetylene in the cut: -Temperature: 15-20 ° C (inlet) -Pressure: 0.5 MPa (5 bar)- LHSV:. 30l / l h mole ratio of ^-1 -H ₂ / alkynes: 2: 1.

Typical results obtained using these conditions are: -Raw material: 1,3-butadiene 50% by volume ethyl acetylene 0.2% by volume vinyl acetylene 1.2% by volume Remaining butenes-Purified effluent: 500 ppm total Alkynes 3% butadiene loss.

-Cycle life: 8-10 months.

Applicants have unexpectedly found that known palladium-based catalysts are more selective when used in the trickle mode than when used in the homogeneous liquid phase. As used herein, the term "increased selectivity" means that for a given feed, a lesser amount of 1,3-butadiene is lost for a given level of alkyne hydrogenation. The term "trickle mode" as used herein is defined as operating under temperature and pressure conditions such that the feedstock passes over the catalyst in a mixed gas-liquid phase. Since the hydrogenation reaction is exothermic, it is generally convenient to feed the raw materials in liquid form under conditions very close to gas-liquid equilibrium.

The reactor can be either an isothermal reactor or an adiabatic reactor. In the latter case, the heat released by the hydrogenation reaction is compensated by the partial vaporization of the liquid phase. Therefore, in the case of an adiabatic reactor, it is necessary to have sufficient feedstock in the liquid phase at the inlet to absorb all the heat released by the hydrogenation reaction, and also to have part of the feedstock in liquid form in the reactor. Injection along the axis is highly desirable.

In accordance with one aspect of the invention, a sufficient proportion of the feedstock, preferably up to about 20%, is injected in the liquid state at one or several places in the catalyst bed in the adiabatic reactor, preferably about halfway. To do. While not wishing to be bound by theory, Applicants believe that these injections will likely work to keep the trickle mode conditions in the adiabatic reactor constant.

Given that the gas phase is partly caused by the vaporization of the feedstock, the trickle mode is generally operated in a co-current mode. Although it is possible to operate in upflow mode, the Applicant has found that it is highly preferred to operate in downflow mode.

Hydrogen can be injected with the raw materials. However, it has also been found highly desirable to distribute a portion of the hydrogen injection along the axis of the reactor, for example at one or several points approximately half way through the catalyst bed. According to one embodiment of the invention, up to 30%, preferably up to about 15%, of the total hydrogen stream is injected at one or several points in the adiabatic reactor at approximately half of the catalyst bed. While not wishing to be bound by theory, Applicants believe that these injections will likely work to keep the trickle mode conditions in the adiabatic reactor constant.

At 100% hydrogen flow, the total pressure should be 0.4-0.9 MPa, most preferably 0.6-0.8 MPa. Thus, when refinery hydrogen is used in the process of the present invention, the refinery hydrogen will generally contain about 75% hydrogen and about 25% methane, and the total pressure will preferably be that. Must be slightly higher.

In order to maintain the desired trickle mode operation, the reaction temperature (ie the inlet temperature when using an adiabatic reactor) is adjusted as a function of the total pressure. Within the preferred range, higher pressure and temperature values tend to give the catalyst greater activity.

The LHSV used can be readily determined by one of ordinary skill in the art, taking into account the specifications for residual acetylenes (and / or loss of 1,3-butadiene in the case of a 1,3-butadiene-enriched C ₄ cut). Can be decided For example, LHSVs generally lower than 10 for almost complete hydrogenation of alkynes at a 1% concentration level in 1,3-butadiene enriched C ₄ cuts using palladium-based catalysts. The corresponding loss of 1,3-butadiene is about 8% or more, which results in a lower loss of 1,3-butadiene by using a higher LHSV but complete hydrogenation of alkynes. May disappear.

The hydrogen / alkynes molar ratio is generally 2: 1-20: 1, preferably 4: 1-10: 1, most preferably about 6: 1.

C ₄ feedstock such that can be used in the methods of the present invention are generally normally consist of a mixture of gaseous hydrocarbons: 1,3-butadiene 30-55%, typically 40-50%, to 2% 1,2-butadiene, typically about 0.2% - alkynes (up primarily 5%, ethyl and vinyl typically acetylene to 1.5%) -C ₃ hydrocarbons and traces of heavy oil such - butane Up to 10%, typically up to 5% -butenes The remaining feedstocks are generally obtained from steam crackers. However, it is contemplated that other sources or sources derived from other sources, such as propylene-rich sources containing methylacetylene as an impurity, do not depart from the scope of the invention.

The invention will now be illustrated by the following examples, which are not intended to be limiting.

Example 1 a. Preparation of catalyst A selected alumina support was used with a diameter of 2-4 mm and 0.72 g.
Spherical with a bulk density of / cm ³ .

The support was contacted with a solution of palladium acetylacetonate in benzene. The carrier: solution weight ratio was 10:16. The Pd weight concentration in the solution was 1350 ppmw before contacting the solution with the support and 100 ppmw after 8 hours of soaking.

The soaked carrier was passed over and dried at 120 ° C. for 6 hours under a stream of air. It was then heated to 300 ° C. in a tube furnace under a stream of air for the first 2 hours and then after purging with nitrogen and for a further 2 hours under a stream of hydrogen.

After cooling, the catalyst contained 0.2% by weight of palladium.

b. Catalyst Activation and Startup The catalyst was flushed with nitrogen for 1 hour at a space velocity of 333 l / l.hr. Hydrogen under atmospheric pressure was then passed over the catalyst at a space velocity of 200 l / l.h, the catalyst was heated to 66 ° C for 0.5 hours, then to 93 ° C for 2 hours and finally cooled to 20 ° C.

The hydrogen flow was then increased at a temperature of 26 ° C. for 35 minutes at 333 l / l.h. Next, change the hydrogen pressure from atmospheric pressure to 0.61 MPa (6.2 kg / c
m ² ) slowly and held for 45 minutes. Next, increase the flow rates of the raw material and hydrogen to the nominal 1/4 and hold for 50 minutes,
It was raised to half its nominal value, held for 15 minutes, and finally raised to the nominal value, raising the temperature to 57 ° C at a heating rate of 10 ° C / hour.

. c selective hydrogenation operating conditions of alkynes was as follows: -. inlet temperature 57.5 ° C. - Pressure (gauge) 0 / 61MPs (6.2kg / cm 2) - feed LHSV 14.2 L / l at - hydrogen : Raw material molar ratio 1: 20-adiabatic reactor operated in downflow mode.

The composition of the feedstock and the composition of the treated effluent after 24 and 44 hours was as follows: Example 2 The procedure described in Example 1 is followed, using a feedstock having a composition similar to that of Example 1 and containing 7140-7768 ppmw vinyl acetylene and 1680-1882 ppmw ethyl acetylene. It was operated continuously for 438 hours from the start. The operating conditions were the same as in Example 1.

After 438 hours of continuous operation, the following composition was measured: Example 3 The selective hydrogenation experiment of Example 1 was repeated with feedstocks having slightly different compositions. All experimental conditions were the same except those noted in Table 1.

This example shows that hydrogenation was most selective when using the process of the invention, i.e. 1,3 for a constant pressure at temperatures such that hydrogenation is carried out in trickle mode.
-The amount of butadiene lost and the residual acetylene concentration was minimal.

Example 4 Example 1 using the same raw materials used in Example 3
Was repeated (all experimental conditions were the same except as noted in Table 2).

This example shows that at pressures such that the hydrogenation is carried out in trickle mode, the selectivity is improved for a constant temperature.

Example 5 The experiment of Example 4 was repeated at lower temperatures. Experimental data are shown in Table 3.

Example 6 The selective hydrogenation experiment of Example 1 was repeated using two slightly different feedstocks shown in Table 4 at different LHSV values (all except those noted in Table 4). The experimental conditions were the same).

This example shows that under otherwise similar conditions, the lower LHSV gave a lower residual concentration of vinyl and ethylacetylenes at the expense of higher loss of 1,3-butadiene.

Example 7 Two selective hydrogenations were carried out in the same reactor with the same feed, but with the reactor being (i) upflow mode and (i)
i) Operated in a downflow mode (from the data in Table 4). All experimental conditions were the same except as noted in Table 5.

Example 8 The selective hydrogenation experiment of Example 1 was repeated with a C ₄ feed containing a significant amount of methylacetylene (MAC) (all experiments except those noted in Table 6). The conditions were the same).

This example shows that hydrogenation was selective for all acetylenes.

Example 9 The selective hydrogenation experiment of Example 1 was repeated using materials of similar composition (all experimental conditions were the same except as noted in Table 7).

This example shows that a small amount of feed and hydrogen injection in about half of the catalyst bed is advantageous in the process of the invention.

Example 10 a. Preparation of catalyst A palladium catalyst was prepared as described in Example 1a. It was then contacted with an aqueous solution of HAuCl ₄ . The carrier: solution weight ratio was 10:18. The Au concentration in the solution was 120 ppmw before contacting the solution with the support and below 10 ppmw after 3 hours of soaking.

The impregnated catalyst was passed, dried, calcined and reduced as described in Example 1. After cooling, the catalyst is washed with normal aqueous NH ₄ OH solution until chloride ions can no longer be detected in the solution, then rinsed with water and 120
It was dried at ° C for 1 hour. The resulting catalyst contained 0.2% by weight palladium and 0.02% by weight gold.

b. Catalyst Activation and Start-up The process used in Example 1 was used for Pd-Au catalyst activation and start-up.

c. Selective hydrogenation of alkynes Operating conditions and results are shown in Table 8.

This example demonstrates that Pd-Au catalysts can remove acetylenes to 30 ppmm or less, but they are indicated by the relatively high loss of 1,3-butadiene observed with Pd-Au catalysts. So it has less selectivity than Pd catalysts.

Example 11 Catalytic GILDLER G-68-G (United Catalysts, Lewisville, Kentucky:
A commercially available palladium-based catalyst sold as Sched Hemiy, Munich, Germany) was used.
It had the following properties within the scope of the invention according to the manufacturer's instructions: -Palladium: 0.2 +/- 0.02% by weight on alumina-Particles: 2-4 mm diameter spheres-Bulk density: 0.7 kg / l-Surface area: 65-95 m ² g-Pore volume: 0.5-0.6 ml / g Activation and start-up was carried out as described in Example 1.

The operating conditions for the selective hydrogenation were as follows: - an adiabatic reactor is operated in downflow mode - inlet temperature: 57.7 ° C. - ^{Pressure: 0.61MPa (6.24kg / cm 2)} - feed LHSV: 14.3 l / l.h-hydrogen: feed molar ratio: 0.050 The feed and treated effluent had the following composition: Preferred embodiments of the present invention provide improved methods for removing alkynes from hydrocarbon streams and methods for removing alkynes from hydrocarbon streams to 30 ppm or less.

The preferred embodiment of the present invention also provides a method of removing alkynes from a hydrocarbon stream such that catalyst life is greatly increased.

The preferred embodiment of the present invention further provides an improved method for removing alkynes from a hydrocarbon stream while minimizing the loss of other components therein.

A preferred embodiment of the present invention is also the selective hydrogenation of the alkynes present in the 1,3-butadiene-enriched C ₄ cut from a steam cracker mainly used for the production of synthetic rubber. It also provides a method.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Raymond M. Kahen, Bee 1040, Belgium B-1040 Briyutsell Abeny Yuko Mandan Rotaire 21 (72) Inventor, Jyatsk F. Grotyans Bee-3061, Lef Dael Neh, Belgium Risestain Wake 39

Claims (16)

(57) [Claims] 1. A method for selectively hydrogenating alkynes present in a 1,4-butadiene-rich C ₄ cut over a palladium-based catalyst, comprising: (i) 1,3- A butadiene-rich C ₄ cut is prepared, (ii) the cut is passed over the catalyst bed in trickle mode in the presence of hydrogen, and (iii) residual hydrogen is separated from the rest of the effluent from step (ii). And (iv) recovering a feedstock rich in 1,3-butadiene. 2. The method according to claim 1, wherein the molar ratio of hydrogen: alkyne is 2: 1-20: 1. 3. The method according to claim 2, wherein the molar ratio of hydrogen: alkyne is 4: 1-10: 1. 4. The hydrogen: alkynes molar ratio is 6: 1.
The method according to claim 3. 5. A pressure range of 0.4-0.9 MPa in step (ii) when a 100% hydrogen stream is used.
The method of any one of the preceding clauses. 6. The pressure in step (ii) is 0.6 MPa-0.8 MPa.
The method according to claim 5, wherein 7. A process according to claim 1, wherein step (ii) is carried out in an adiabatic reactor. 8. A method according to claim 1, wherein a sufficient proportion of the raw material is injected in liquid form along the catalyst bed at one or several points.
~ The method according to any one of items 7 to 7. 9. A process as claimed in any one of the preceding claims, in which about 20% of the raw material is injected in liquid form at one or several points in approximately half of the catalyst bed. 10. Up to 30% of the total hydrogen stream 1 along the catalyst bed
Injecting at one or several points, claims 1 to 9
The method of any one of the preceding clauses. 11. Up to 15% of the total hydrogen stream 1 along the catalyst bed
The method according to claim 10, wherein the injection is performed at one or several points. 12. A process according to claim 1, wherein step (ii) is operated in a downflow mode. 13. A process according to claim 1, in which the catalyst contains 0.1-0.35% by weight of active palladium metal deposited on high-purity alumina. 14. The method of claim 13 wherein the catalyst contains about 0.2% by weight active palladium metal. 15. The method according to claim 13 or 14, wherein the catalyst is stabilized by the use of a bimetallic catalyst. 16. The method of claim 15 wherein the catalyst is made from a platinum-gold alloy deposited on high purity alumina.