GB2460514A

GB2460514A - An epoxidation reactor and process for the production of an olefin oxide

Info

Publication number: GB2460514A
Application number: GB0908295A
Authority: GB
Inventors: Wayne Errol Evans; Marek Matusz
Original assignee: Shell Internationale Research Maatschappij BV
Current assignee: Shell Internationale Research Maatschappij BV
Priority date: 2008-05-15
Filing date: 2009-05-14
Publication date: 2009-12-09
Also published as: GB0908295D0

Abstract

An epoxidation reactor system 17 is disclosed which comprises one or more purification zones 32 comprising a spent epoxidation catalyst 35; and a reaction zone 26 comprising a fresh epoxidation catalyst 36, which reaction zone is positioned downstream from the one or more purification zones. The catalyst may comprise silver, and may further be doped with one of rhenium, molybdenum, tungsten, chromium, nitrate- or nitrite-forming compounds. Also disclosed is a process for the production of an olefin oxide; and a process for preparing a 1,2-diol, a 1,2-diol ether, a 1,2-carbonate, or an alkanolamine using the reactor system.

Description

A REACTOR SYSTEM AND A PROCESS FOR THE PRODUCTION OF AN

OLEFIN OXIDE, A 1,2-DIOL, A 1,2-DIOL ETHER, A 1,2-CARBONATE, OR AN

ALKANOLAMINE

Field of the Invention:

The invention relates to a reactor system and a process for the production of an olefin oxide, a 1,2-diol, a I,2-diol ether, a 1,2-carbonate, or an alkanolamine.

Baclcground of the Invention: Industrial-scale preparations of olefins yield impure olefins. Typically, the olefins are subjected to a purification process to reduce the impurities. However, low levels of impurities still remain in the olefins and can act as catalyst poisons in a subsequent epoxidation process, adversely affecting the performance of the catalyst. Of particular concern are trace sulfur impurities that may be present in the reaction feed. In the production of olefin oxides, such as ethylene oxide, silver-based catalysts are used to convert ethylene and oxygen into ethylene oxide. These silver-based catalysts are especially susceptible to sulfur poisoning even at sulfur quantities on the order of parts per billion levels. The catalyst poisoning impacts the catalyst performance, in particular the selectivity or activity, and shortens the length of time the catalyst can remain in the reactor before having to exchange the poisoned catalyst with fresh catalyst.

Typical sulfur impurities include, but are not limited to, dihydrogen sulfide, carbonyl sulfide, mercaptans, and organic sulfides. Mercaptans and organic sulfides, especially organic sulfides, are particularly difficult sulfur impurities to remove from the feed components.

Additional impurities may include, acetylene, carbon monoxide, phosphorous, arsenic, selenium, and halogens. Impurities may also be present in the additional reaction feed components such as the recycle gas, the saturated hydrocarbons, the inert gases, etc. The olefin, such as ethylene, may be derived from several sources including, but not limited to, petroleum processing streams such as those generated by a thermal cracker, a catalytic cracker, a hydrocracker or a reformer, natural gas fractions, naphtha and organic oxygenates such as alcohols.

US 4921681 describes the use of an inert solid in the upper portion of the reactor tubes in a shell-and-tube reactor. The inert solid is used to facilitate heat transfer between the feed gas and the steam exiting the shell side of the reactor. However, placing an inert material upstream from the catalyst does not significantly reduce the amount of impurities present in the reaction feed which can poison the catalyst.

Thus, not withstanding the improvements already achieved, there exists a desire for a reactor system and reaction process that further improves the performance of the catalyst, in particular the duration of time the catalyst remains in the reactor before exchanging with a fresh catalyst.

Summary of the Invention

The present invention provides an epoxidation reactor system comprising one or more purification zones containing a spent epoxidation catalyst; and a reaction zone comprising a fresh epoxidation catalyst, which reaction zone is positioned downstream from the one or more purification zones.

The invention also provides a process for the production of an olefin oxide comprising: contacting one or more feed components containing one or more impurities with a spent epoxidation catalyst to reduce the quantity of the one or more impurities in the feed components; and -subsequently contacting the feed components, and optionally one or more additional feed components, with a fresh epoxidation catalyst to yield an olefin oxide.

Further, the invention provides a process of preparing a 1,2-diol, a 1,2-diol ether, a 1,2-carbonate, or an alkanolamine comprising preparing an olefin oxide by the process according to this invention, and converting the olefin oxide into the I,2-diol, the I,2-diol ether, the 1,2-carbonate, or the alkanolamine.

Brief Description of the Drawings

Figure 1 is a schematic view of a reactor system according to an embodiment of the invention which has the spent epoxidation catalyst positioned inside the reactor tubes.

Figure 2 is a schematic view of a reactor system according to an embodiment of the invention which has the spent epoxidation catalyst positioned inside the reactor vessel and upstream from the reactor tubes.

Figure 3 is a schematic view of a reactor system according to an embodiment of the invention which has the spent epoxidation catalyst in a vessel separate from the reactor vessel and upstream from the reactor vessel.

Figure 4 shows the volume percent of ethylene oxide ("%EO") as a function of time (hours), for Example 1 and Example 2, described hereinafter.

Detailed Description of the Invention

In accordance with this invention, it has been found that placing a spent epoxidation catalyst upstream from the fresh epoxidation catalyst is beneficial for removing impurities from one or more of the reaction feed components. By removing impurities from the feed components, the performance of the catalyst is improved, in particular the selectivity, activity and duration of time the catalyst remains in the reactor vessel before exchanging it with a fresh catalyst is improved.

The terms "substantially vertical" and "substantially horizontal", as used herein, are understood to include minor deviations from true vertical or horizontal positions relative to the central longitudinal axis of the reactor vessel, in particular the terms are meant to include variations ranging from 0 to 20 degrees from true vertical or horizontal positions.

True vertical is aligned along the central longitudinal axis of the reactor vessel. True horizontal is aligned perpendicular to the central longitudinal axis of the reactor vessel.

The term "substantially parallel", as used herein, is understood to include minor deviations from a true parallel position relative to the central longitudinal axis of the reactor vessel, in particular the term is meant to include variations ranging from 0 to 20 degrees from a true parallel position relative to the central longitudinal axis of the reactor vessel.

The term "spent epoxidation catalyst", as used herein, is understood to refer to an epoxidation catalyst which has produced more olefin oxide than the fresh epoxidation catalyst in the reaction zone. In some embodiments, the spent epoxidation catalyst has produced at least I kT/m3, preferably at least 1.6 kTfm3, in particular at least 2 kT/m3.

Frequently, the spent epoxidation catalyst has aged sufficiently to cause the selectivity to be reduced by at least 2.5 mole-% and/or the activity to be raised by at least 15 °C, wherein selectivity and activity are defined hereinafter.

The term "fresh epoxidation catalyst", as used herein, means an epoxidation catalyst immediately after its preparation or rejuvenation, or an epoxidation catalyst which, in the course of operation, has produced less olefin oxide than the spent epoxidation catalyst.

As used herein, the temperature of the fresh and spent catalyst bed is deemed to be the weight average temperature of the catalyst particles in the packed bed.

The reactor vessel of the present invention may contain one or more open-ended reactor tubes. Preferably, the reactor vessel may contain a plurality of reactor tubes. The reactor tubes may be any size. Suitably, a reactor tube may have an internal diameter of at least 5 mm (millimeters), in particular at least 10mm. Suitably, a reactor tube may have an internal diameter in the range of from 15 to 80 mm, more preferably from 20 to 75 mm, and most preferably from 25 to 70 mm. Suitably, a reactor tube may have a length of at least 1 m (meter), in particular at least 5 m. Suitably, a reactor tube may have a length of at most 50 m, in particular at most 30 m. A reactor tube may preferably have a length in the range of from 5 to 20 m, more preferably from 10 to 15 m.

Preferably, the reactor vessel is a shell-and-tube heat exchanger containing a plurality of reactor tubes. The shell-and-tube heat exchanger may contain from 1000 to 20000 reactor tubes, in particular from 2500 to 15000 reactor tubes.

The plurality of reactor tubes are positioned substantially parallel to the central longitudinal axis of the reactor vessel and are surrounded by a shell adapted to receive a heat exchange fluid (i.e., the shell side of the shell-and-tube heat exchanger). The heat exchange fluid in the heat exchange chamber may be any fluid suitable for heat transfer, for example water or an organic material suitable for heat exchange. The organic material may include oil or kerosene. The upper ends of the one or more reactor tubes are connected to a substantially horizontal upper tube plate and are in fluid communication with the one or more inlets to the reactor vessel, and the lower ends of the one or more reactor tubes are connected to a substantially horizontal lower tube plate and are in fluid communication with the one or more outlets to the reactor vessel (i.e., the tube side of the shell-and-tube heat exchanger). The reactor vessel contains a reaction zone containing a packed bed of fresh epoxidation catalyst positioned inside the one or more reactor tubes.

The reactor system also comprises a purification zone containing a packed bed of spent epoxidation catalyst positioned upstream from the reaction zone containing the fresh epoxidation catalyst.

In an embodiment, the fresh and/or spent catalyst beds may contain particles other than catalyst particles. In this embodiment, a major portion of the catalyst bed comprises catalyst particles. By a "major portion" it is meant that the ratio of the weight of the catalyst particles to the weight ofll the particles contained in the catalyst bed is at least 0.50, in particular at least 0.8, preferably at least 0.85, more preferably at least 0.9.

Particles which may be contained in the catalyst beds other than the catalyst particles are, for example, inert particles; however, it is preferred that such other particles are not present in the catalyst beds. The fresh epoxidation catalyst bed is supported in the one or more reactor tubes by a catalyst support means arranged in the lower ends of the reactor tubes.

The support means may include a screen or a spring.

Reference is made to FIG. 1, which is a schematic view of an embodiment of the present invention relating to a reactor system (17). The reactor system (17) comprises a shell-and-tube heat exchanger reactor vessel having a substantially vertical vessel (18) and a plurality of open-ended reactor tubes (19) positioned substantially parallel to the central longitudinal axis (20) of the reactor vessel (18). The upper ends (21) of the reactor tubes (19) are connected to a substantially horizontal upper tube plate (22) and the lower ends (23) of the reactor tubes (19) are connected to a substantially horizontal lower tube plate (24). The upper tube plate (22) and the lower tube plate (24) are supported by the inner wall of the reactor vessel (18). The plurality of reactor tubes (19) contain a purification zone (25) containing a packed bed of spent epoxidation catalyst (35) and a reaction zone (26) containing a packed bed of a fresh epoxidation catalyst (36) positioned downstream from thepurificationzone (25). The purification zone (25) contains spent epoxidation catalyst particles (35), described hereinbefore. The reaction zone (26) contains fresh epoxidation catalyst particles (36), described hereinbefore. The fresh epoxidation catalyst particles (36) in the reaction zone (26) are supported in the reactor tubes (19) by a catalyst support means (not shown) arranged in the lower ends (23) of the reactor tubes (19).

Components of the reaction feed (33), such as the olefin, enter the reactor vessel (18) via one or more inlets such as inlet (27) which are in fluid communication with the upper ends (21) of the reactor tubes (19). The reaction product (34) exits the reactor vessel (18) via one or more outlets such as outlet (28) which are in fluid communication with the lower ends (23) of the reactor tubes (19). The heat exchange fluid enters the heat exchange chamber (29) via one or more inlets such as inlet (30) and exits via one or more outlets such as outlet (31). The heat exchange chamber (29) may be provided with baffles (not shown) to guide the heat exchange fluid through the heat exchange chamber (29).

The packed bed of spent epoxidation catalyst (35) in the purification zone (25) may have a bed height of at least 0.25 % of the length of the reactor tube (19), in particular at least 0.5 %, more in particular at least I %, most in particular at least 2 % of the length of * 30 the reactor tube (19). The packed bed of spent epoxidation catalyst (35) in the purification zone (25) may have a bed height of at most 20 % of the length of the reactor tube (19), in * particular at most 15 %, more in particular at most 10 %, most in particular at most 5 % of the length of the reactor tube (19). In this embodiment, the total epoxidatiori reactor feed is contacted with the spent epoxidation catalyst. When using a highly selective epoxidation catalyst containing rhenium, tungsten, molybdenum, chromium, or nitrate-or nitrite-forming compounds as the fresh epoxidation catalyst, it is preferred to use a spent highly selective epoxidation catalyst when the spent epoxidation catalyst is located within the epoxidation reactor vessel.

In this embodiment, when the spent epoxidation catalyst is positioned within the reactor tubes near the reactor tube inlet instead of an inert material, as disclosed in US- 4921681, an improvement in the process is obtained. In particular, the spent epoxidation catalyst reduces impurities in the reaction feed while preheating the feed. The inert material simply preheats the reaction feed without removing impurities that might damage the fresh epoxidation catalyst bed. An additional unexpected advantage of this embodiment is that impurities, such as sulfur -containing species, can be reduced in the feed without requiring any additional equipment such as an auxiliary vessel or pipe to remove the impurities. Also, the spent epoxidation catalyst can be more cost effective than other materials placed in the reactor tubes.

FIG. 2 is a schematic view of an embodiment of the present invention relating to a reactor system (17). The reactor system (17) comprises a shell-and-tube heat exchanger reactor vessel (18) similar to FIG. 1 except that the purification zone (32) containing a packed bed of spent epoxidation catalyst (35) is positioned upstream from the reactor tubes (19). In this embodiment, the total epoxidation reactor feed is contacted with the spent epoxidation catalyst. An unexpected advantage of this embodiment is that impurities, such as sulfur-containing species, can be reduced in the feed without requiring any additional equipment such as an auxiliary vessel or pipe to remove the impurities. In this embodiment, the packed bed of spent epoxidation catalyst (35) in the purification zone (32) may have a bed height of at least 0.05 m, in particular at least 0.075 m, more in particular at least 0.1 m, most in particular at least 0.15 m. Suitably, the packed bed of spent epoxidation catalyst (35) in the purification zone (32) may have a bed height of at most 2 m, in particular at most I m, more in particular at most 0.5 m. In this embodiment, when using a highly selective epoxidation catalyst containing rhenium, tungsten, molybdenum, chromium, or nitrate-or nitrite-forming compounds as the fresh epoxidation catalyst, it is preferred to use a spent highly selective epoxidation catalyst.

Reference is made to FIG. 3, which is a schematic view of a reactor system (17) comprising a shell-and-tube heat exchanger reactor vessel having a substantially vertical vessel (18) similar to FIG. I. The plurality of reactor tubes (19) contain a reaction zone (26) containing a fresh epoxidation catalyst (36). The fresh epoxidation catalyst (36) is supported in the reactor tubes (19) by a catalyst support means (not shown) arranged in the lower ends (23) of the reactor tubes (19).

The reactor system (17) comprises a purification zone (37) contained inside a separate purification vessel (38) positioned upstream of and separate from the reactor vessel (18). The purification zone (37) contains a spent epoxidation catalyst (35). One or more feed components to be treated (39) enter the separate purification vessel (38) through inlet (40), and the treated feed components (41) exit the separate purification vessel (38) through outlet (42). The treated feed components subsequently enter the reactor vessel (18) along with any additional feed components (43) as feed (33) through inlet (27).

In this embodiment, a purification zone may comprise one or more separate purification vessels containing a packed bed of the spent epoxidation catalyst. The packed bedof the spent epoxidation cataIyst may be of any suitable height. One or more -purification zones may be used in series with the reactor vessel and are located upstream from the reactor vessel. Suitably, purification zones may be located in the olefin feed line, the diluent hydrocarbon feed line, the oxygen feed line, the inert gas feed line, and/or the recycle gas loop. When a purification zone contains two or more purification vessels, the purification vessels may be arranged in parallel with associated switching means to allow the process to be switched between purification vessels, thus maintaining a continuous operation of the process. Suitable switching means that can be used in this embodiment are known to the skilled person.

Suitably, the temperature of the spent epoxidation catalyst bed in the purification zone may be at least 25 °C, in particular at least 70 °C, more in particular at least 140 °C, most in particular at least 160 °C. The temperature of the spent epoxidation catalyst bed may be at most 300 °C, in particular at most 290 °C, more in particular at most 280 °C.

Suitably, the temperature of the spent epoxidation catalyst bed in the purification zone when positioned within the reactor tubes may be at least 140 °C, in particular at least °C, more in particular at least 160 °C. The temperature of the spent epoxidation catalyst bed may be at most 300 °C, in particular at most 290°C, more in particular at most 280 °C. The temperature of the spent epoxidation catalyst bed may be in the range of from to 300 °C, preferably from 180 to 285 °C, most preferably from 210 to 270 °C.

Suitably, the temperature of the spent epoxidation catalyst bed in the purification zone when positioned within the reactor vessel and upstream from the reactor tubes may be at least 120 °C, in particular at least 130 °C, more in particular at least 140 °C. The temperature of the spent epoxidation catalyst bed may be at most 200 °C, in particular at most 190 °C, more in particular at most 180 °C. The temperature of the spent epoxidation catalyst bed may be in the range of from 120 to 200 °C, preferably from 130 to 190 °C, most preferably from 140 to 180 °C.

Suitably, the temperature of the spent epoxidation catalyst bed in the purification zone when positioned within a separate purification vessel located upstream from the reactor vessel may be at least 25 °C, in particular at least 60 °C, more in particular at least °C. The temperature of the spent epoxidation catalyst bed may be at most 200 °C, in particular at most 190 °C, more in particular at most 180 °C. The temperature of the spent epoxidation catalyst bed may be in the range of from 50 to 200 °C, preferably from 60 to :. .190 °C, most preferably from 70 to 180 °C. -. Suitably, the reaction temperature of the fresh epoxidation catalyst bed may be at least 150 °C, in particular at least 180 °C, more in particular at least 220 °C. The temperature of the fresh epoxidation catalyst bed may be at most 325 °C, in particular at most 300 °C. The temperature of the fresh epoxidation catalyst bed may be in the range of from 180 to 325 °C, preferably from 200 to 300 °C.

The catalyst typically used for the epoxidation of an olefin is a catalyst comprising silver deposited on a carrier. The size and shape of the catalyst is not critical to the invention and may be in the form of chunks, pieces, cylinders, rings, spheres, wagon wheels, tablets, and the like of a size suitable for employment in a fixed bed shell-and-tube heat exchanger reactor vessel, for example from 2 mm to 20 mm.

The carrier may be based on a wide range of materials. Such materials may be natural or artificial inorganic materials and they may include refractory materials, silicon carbide, clays, zeolites, charcoal, and alkaline earth metal carbonates, for example calcium carbonate. Preferred are refractory materials, such as alumina, magnesia, zirconia, silica, and mixtures thereof. The most preferred material is a-alumina. Typically, the carrier comprises at least 85 %w, more typically at least 90 %w, in particular at least 95 %w a-alumina, frequently up to 99.9 %w a-alumina, . relative to the weight of the carrier. Other components of the a-alumina carrier may comprise, for example, silica, titania, zirconia, alkali metal components, for example sodium and/or potassium components, and/or alkaline earth metal components, for example calcium and/or magnesium components, The surface area of the carrier may suitably be at least 0.1 m2/g, preferably at least 0.3 m2Ig, more preferably at least 0.5 m2/g, and in particular at least 0.6 m2/g, relative to the weight of the carrier; and the surface area may suitably be at most 10 m2/g, preferably at most 6 m2/g, and in particular at most 4 m2Ig, relative to the weight of the carrier.

Surface area" as used herein is understood to relate to the surface area as determined by the B.E.T. (Brunauer, Emmett and Teller) method as described in Journal of the American Chemical Society 60 (1938) pp. 309-3 16. High surface area carriers, in particular when they are alpha alumina carriers optionally comprising in addition silica, alkali metal and/or alkaline earth metal components, provide improved performance and stability of operation.

The water absorption of the carrier may suitably be at least 0.2 g/g, preferably at least 0.25 g/g, more preferably at least 0.3 gig, most preferably at least 0.35 gIg; and the water absorption may suitably be at most 0.85 g/g,-preferably at most 0.7 gIg, more preferably at most 0.65 gIg, most preferably at most 0.6 g/g. The water absorption of the carrier may be in the range of from 0.2 to 0.85 g/g, preferably in the range of from 0.25 to 0.7 gig, more preferably from 0.3 to 0.65 gig, most preferably from 0.3 to 0.6 gig. A higher water absorption may be in favor in view of a more efficient deposition of the metal and promoters, if any, on the carrier by impregnation. However, at a higher water absorption, the carrier, or the catalyst made therefrom, may have lower crush strength. As used herein, water absorption is deemed to have been measured in accordance with ASTM C20, and water absorption is expressed as the weight of the water that can be absorbed into the pores of the carrier, relative to the weight of the carrier.

The preparation of the catalyst comprising silver is known in the art and the known methods are applicable to the preparation of the shaped catalyst particles which may be used in the practice of this invention. Methods of depositing silver on the carrier include impregnating the carrier with a silver compound containing cationic silver and/or complexed silver and performing a reduction to form metallic silver particles. For further description of such methods, reference may be made to US-A- 5380697, US-A-5739075, EP-A-266015, and US-B-6368998, which methods are incorporated herein by reference. Suitably, silver dispersions, for example silver sols, may be used to deposit silver on the carrier.

The reduction of cationic silver to metallic silver may be accomplished during a step in which the catalyst is dried, so that the reduction as such does not require a separate process step. This may be the case if the silver containing impregnation solution comprises a reducing agent, for example, an oxalate, a lactate or formaldehyde.

Appreciable catalytic activity may be obtained by employing a silver content of the catalyst of at least 10 g/kg, relative to the weight of the catalyst. Preferably, the catalyst comprises silver in a quantity of from 50 to 500 g/kg, more preferably from to 400 gfkg, for example 105 g/kg, or 120 g/kg, or 190 gfkg, or 250 glkg, or 350 g/kg, on the same basis. As used herein, unless otherwise specified, the weight of the catalyst is deemed to be the total weight of the catalyst including the weight of the carrier and catalytic components.

The catalyst for use in this invention may comprise a promoter component which comprises an element selected from-rhenium, tungsten, molybdenum, chromium, nitrate-or nitrite-forming compounds, and combinations thereof. Preferably the promoter component comprises, as an element, rhenium. The form in which the promoter component may be deposited onto the carrier is not material to the invention.

Rhenium, molybdenum, tungsten, chromium or the nitrate-or nitrite-forming compound may suitably be provided as an oxyanion, for example, as a perrhenate, molybdate, tungstate, or nitrate, in salt or acid form.

The promoter component may typically be present in a quantity of at least 0.1 mmole/kg, more typically at least 0.5 mmole/kg, in particular at least 1 mmole/kg, more in particular at least 1.5 mmole/kg, calculated as the total quantity of the element (that is rhenium, tungsten, molybdenum and/or chromium) relative to the weight of the catalyst. The promoter component may be present in a quantity of at most mmole/kg, preferably at most 10 mrnolefkg, calculated as the total quantity of the element relative to the weight of the catalyst.

When the catalyst comprises rhenium, as the promoter component, the catalyst may preferably comprise a rhenium co-promoter, as a further component deposited on the carrier. Suitably, the rhenium co-promoter may be selected from components comprising an element selected from tungsten, chromium, molybdenum, sulfur, phosphorus, boron, and combinations thereof. Preferably, the rhenium co-promoter is selected from tungsten, chromium, molybdenum, sulfur, and combinations thereof. It is particularly preferred that the rhenium co-promoter comprises, as an element, tungsten and/or sulfur.

The rhenium co-promoter may typically be present in a total quantity of at least 0.1 mmolefkg, more typically at least 0.25 niniolefkg, and preferably at least 0.5 mmolefkg, calculated as the element (i.e. the total of tungsten, chromium, molybdenum, sulfur, phosphorus and/or boron), relative to the weight of the catalyst.

The rhenium co-promoter may be present in a total quantity of at most 40 mmolefkg, preferably at most 10 mmole/kg, more preferably at most 5 mmolelkg, on the same basis. The form in which the rhenium co-promoter may be deposited on the carrier is not material to the invention. For example, it may suitably be provided as an oxide or as an oxyanion, for example, as a sulfate, borate or molybdate, in salt or acid form.

The catalyst preferably comprises silver, the promoter component, and a component comprising a further element, deposited on the carrier. Eligible further elemefits may be selected from the-group of nitrogen, fluorine, alkali metals, alkaline earth metals, titanium, hafnium, zirconium, vanadium, thallium, thorium, tantalum, niobium, gallium and germanium and combinations thereof. Preferably the alkali metals are selected from lithium, potassium, rubidium and cesium. Most preferably the alkali metal is lithium, potassium and/or cesium. Preferably the alkaline earth metals are selected from calcium, magnesium and barium. Typically, the further element is present in the catalyst in a total quantity of from 0.01 to 500 mmolelkg, more typically from 0.05 to 100 mmolefkg, calculated as the element, relative to the weight of the catalyst. The further elements may be provided in any form. For example, salts of an alkali metal or an alkaline earth metal are suitable. For example, lithium compounds may be lithium hydroxide or lithium nitrate.

Preferred amounts of the components of the catalysts are, when calculated as the element, relative to the weight of the catalyst: -silver from 10 to 500 glkg, -rhenium from 0.01 to 50 mmolefkg, if present, -the further element or elements, if present, each from 0.1 to 500 mmolefkg, and, -the rhenium co-promoter from 0.1 to 30 mmole/kg, if present.

As used herein, the quantity of alkali metal present in the catalyst is deemed to be the quantity insofar as it can be extracted from the catalyst with de-ionized water at 100 °C.

The extraction method involves extracting a 10-gram sample of the catalyst three times by heating it in 20 ml portions of de-ionized water for 5 minutes at 100 °C and determining in the combined extracts the relevant metals by using a known method, for example atomic absorption spectroscopy.

As used herein, the quantity of alkaline earth metal present in the catalyst is deemed to be the quantity insofar as it can be extracted from the catalyst with 10 %w nitric acid in de-ionized water at 100 °C. The extraction method involves extracting a 10-gram sample of the catalyst by boiling it with a 100 ml portion of 10 %w nitric acid for 30 minutes (1 atm., i.e. 101.3 kPa) and determining in the combined extracts the relevant metals by using a known method, for example atomic absorption spectroscopy. Reference is made to US-A-5801259, which is incorporated herein by reference.

Although the present epoxidation process may be carried out in many ways, it is preferred to carry it out as a gas phase process, i.e. a process in which one or more components of the reaction feed are first contacted in the gas phase with the spent epoxidation catalyst to yield a-treated feed, and subsequently the treated gaseous feed is --.

optionally combined with additional feed components and then contacted with the fresh epoxidation catalyst to yield a reaction product comprising an olefin oxide. The term "reaction product", as used herein, is understood to refer to the fluid exiting from the outlet of the reactor vessel. Generally the process is carried out as a continuous process.

The reaction feed comprises one or more feed components. The feed components include an olefin and oxygen. In addition to the olefin and oxygen, the feed components may further comprise a saturated hydrocarbon as a dilution gas. The feed components may further comprise a reaction modifier, an inert dilution gas, and a recycle gas stream. One or more of the feed components are contacted with the spent epoxidation catalyst, preferably the olefin, saturated hydrocarbon, and the recycle gas, more preferably the olefin andlor the recycle gas.

The olefiri for use in the epoxidation process may include any olefin, such as an aromatic olefin, for example styrene, or a di-olefin, whether conjugated or not, for example I,9-decadiene or I,3-butadiene. Preferably, the olefin may be a monoolefin, for example 2-butene or isobutene. More preferably, the olefin may be a mono-cx-olefin, for example 1-butene or propylene. The most preferred olefin is ethylene. Suitably, mixtures of olefins may be used. -The olefin may be obtained from several sources including, but not limited to, petroleum processing streams such as-those generated by a thermal cracker, a catalytic cracker, a hydrocracker or a reformer, natural gas fractions, naphtha, and organic oxygenates such as alcohols. The alcohols are typically derived from the fermentation of various biomaterials including, but not limited to, sugar cane, syrup, beet juice, molasses, and other starch-based materials. An olefin, such as ethylene, derived from an alcohol prepared via a fermentation process can be a particularly troublesome source of sulfur impurities.

The quantity of olefin present in the reaction feed may be selected within a wide range. Typically, the quantity of olefin present in the reaction feed may be at most mole-%, relative to the total reaction feed. Preferably, it may be in the range of from 0.5 to 70 mole-%, in particular from 1 to 60 mole-%, more in particular from 15 to 40 mole-%, on the same basis.

The reaction feed may also comprise a saturated hydrocarbon. The saturated hydrocarbon may be selected from methane, ethane, propane, butane, pentane, hexane, heptane octane, nonane, decane, undecane,.dodecane and mixtures..hereof. In particular, the saturated hydrocarbon may be selected from methane, ethane, propane, and mixtures thereof, preferably methane. Saturated hydrocarbons are common dilution gases in an epoxidation process and can be a significant source of impurities in the feed, in particular sulfur impurities.

Saturated hydrocarbons, in particular methane, ethane and mixtures thereof, more in particular methane, may be present in a quantity of at most 80 mole-%, relative to the total reaction feed, in particular at most 75 mole-%, more in particular at most 65 mole-%, on the same basis. The saturated hydrocarbons may be present in a quantity of at least 1 mole-%, preferable at least 10 mole-%, more preferably at least 30 mole-%, most preferably at least 40 mole-%, on the same basis. Saturated hydrocarbons may be added to the reaction feed in order to increase the oxygen flammability limit.

The present epoxidation process may be air-based or oxygen-based, see "Kirk-Othmer Encyclopedia of Chemical Technology", 3" edition, Volume 9, 1980, pp. 445-447.

In the air-based process, air or air enriched with oxygen is employed as the source of the oxidizing agent while in the oxygen-based processes high-purity (at least 95 mole-%) oxygen or very high purity (at least 99.5 mole-%) oxygen is employed as the source of the oxidizing agent. Reference may be made to US-6040467, incorporated by reference, for further description of oxygen-based processes. Presently most epoxidation plants are oxygen-based and this is a preferred embodiment of the present invention.

The quantity of oxygen present in the reaction feed may be selected within a wide range. However, in practice, oxygen is generally applied in a quantity which avoids the flammable regime. Oxygen may be present in a quantity of at least 0.5 mole-%, relative to the total reaction feed, in particular at least I mole-%, more in particular at least 2 mole-%, most in particular at least 5 mole-%, relative to the total reaction feed. Oxygen may be present in a quantity of at most 25 mole-%, relative to the total reaction feed, in particular at most 20 mole-%, more in particular at most 15 mole-%, most in particular at most 12 mole-%, relative to the total reaction feed.

In order to remain outside the flammable regime, the quantity of oxygen in the reaction feed may be lowered as the quantity of the olefin is increased. The actual safe operating ranges depend, along with the reaction feed composition, also on the reaction conditions such as the reaction temperature and the pressure.

A reaction modifier may be present in the reaction feed for increasing the selectively, suppressing the undesirable oxidation of olefin or olefin oxide to carbon dioxide and water, relative to the desired formation of olefin oxide. Many organic compounds, especially organic halides and organic nitrogen compounds, may be employed as the reaction modifiers. Nitrogen oxides, organic nitro compounds such as nitromethane, nitroethane, and nitropropane, hydrazine, hydroxylamine or ammonia may be employed as well. It is frequently considered that under the operating conditions of olefin epoxidation the nitrogen containing reaction modifiers are precursors of nitrates or nitrites, i.e. they are so-called nitrate-or nitrite-forming compounds (cf. e.g. EP-A-3642 and US-A-4822900, which are incorporated herein by reference).

Organic halides are the preferred reaction modifiers, in particular organic bromides, and more in particular organic chlorides. Preferred organic halides are chlorohydrocarbons or bromohydrocarbons. More preferably they are selected from the group of methyl chloride, ethyl chloride, ethylene dichloride, ethylene dibromide, vinyl chloride or a mixture thereof. Most preferred reaction modifiers are ethyl chloride and ethylene dichioride.

Suitable nitrogen oxides are of the general formula NO wherein x is in the range of from I to 2.5, and include for example NO, N203, N204, and N205. Suitable organic nitrogen compounds are riitro compounds, nitroso compounds, amines, nitrates and nitrites, for example nitromethane, 1-nitropropane or 2-nit.ropropane. In preferred embodiments, nitrate-or nitrite-forming compounds, e.g. nitrogen oxides and/or organic nitrogen compounds, are used together with an organic halide, in particular an organic chloride.

The reaction modifiers are generally effective when used in small quantities in the reaction feed, for example at most 0.1 mole-%, relative to the total reaction feed, for example from 0.OlxlO4 to 0.01 mole-%. In particular when the olefin is ethylene, it is preferred that the reaction modifier is present in the reaction feed in a quantity of from 0.1x10 to 5O0x10 mole-%, in particular from 0.2x10 to 200x10 mole-%, relative to the total reaction feed.

A recycle gas stream may be used as a reaction feed component in the epoxidation process. The reaction product comprises the olefin oxide, unreacted olefin, unreacted oxygen, and optionally, reaction modifiers, saturated hydrocarbons, inert gases, and other reaction by-products such as carbon dioxide and water. The reaction product is passed through one or more separation systems, such as an olefin oxide absorber and a carbon dioxide absorber, so the unreacted olefin and oxygen as well as other components such as the dilution gases and reaction modifier may be recycled to the reactor system. The recycle gas loop comprises interconnecting pipework between the olefiri oxide absorber and the epoxidation reactor vessel and optionally includes a carbon dioxide absorber, heat exchangers, compressors, and water removal vessels in the recycle gas loop.

Carbon dioxide is a by-product in the epdxidation process. However, carbon dioxide generally has an adverse effect on the catalyst activity. Typically, a quantity of carbon dioxide in the reaction feed in excess of 25 mole-%, in particular in excess of 10 mole-%, relative to the total reaction feed, is avoided. A quantity of carbon dioxide of less than 3 mole-%, preferably less than 2 mole-%, more preferably less than I mole-%, relative to the total reaction feed, may be employed. Under commercial operations, a quantity of carbon dioxide of at least 0.1 mole-%, in particular at least 0.2 mole-%, relative to the total reaction feed, may be present in the reaction feed.

Inert dilution gases, for example nitrogen, helium or argon, may be present in the reaction feed in a quantity of from 30 to 90 mole-%, typically from 40 to 80 mole-%, relative to the total reaction feed.

It is unexpected that the spent epoxidation catalyst can reduce the amount of impurities, especially sulfur. impurities, in the reaction feed components. Sulfur impurities may include, but are not limited to, dihydrogen sulfide, carbonyl sulfide, mercaptans, organic sulfides, and combinations thereof. The mercaptans may include methanethiol or ethanethiol. The organic sulfides may include aromatic sulfides or alkyl sulfides, such as dimethylsullide. Mercaptans and organic sulfides, in particular organic sulfides, are particularly difficult sulfur impurities to remove from a feed. After contact with the spent epoxidation catalyst bed, the treated feed may contain at most 70 %w of the total quantity of sulfur impurities present in the untreated feed, preferably at most 35%w, more preferably at most 10 %w, on the same basis.

The epoxidation process is preferably carried out at a reactor inlet pressure in the range of from 1000 to 3500 kPa. "GHSV" or Gas Hourly Space Velocity is the unit volume of gas at normal temperature and pressure (0°C, 1 atm, i.e. 101.3 kPa) passing over one unit volume of packed catalyst per hour. Preferably, when the epoxidation process is a gas phase process involving a packed catalyst bed, the GHSV is in the range of from 1500 to 10000 Nl/(l.h). Preferably, the process is carried out at a work rate in the range of from 0.5 to 10 kmole olefin oxide produced per m3 of catalyst per hour, in particular 0.7 to 8 km_ole olefin oxide produced perm3 of catalyst per hour, for example 5 kmole olefin oxide produced per m3 of catalyst per hour. As used herein, the work rate is the amount of the olefin oxide produced per unit volume of catalyst per hour and the selectivity is the molar quantity of the olefin oxide formed relative to the molar quantity of the olefin converted. As used herein, the activity is a measurement of the temperature required to achieve a particular ethylene oxide production level. The lower the temperature, the better the activity.

The olefin oxide produced in the epoxidation process may be converted into a 1,2-diol, a I,2-diol ether, a 1,2-carbonate, or an alkanolamine. As this invention leads to a more attractive process for the production of the olefin oxide, it concurrently leads to a more attractive process which comprises producing the olefin oxide in accordance with the invention and the subsequent use of the obtained olefin oxide in the manufacture of the 1,2-diol, I,2-diol ether, 1,2-carbonate, and/or alkanolarnine.

The conversion into the I,2-diol or the I,2-diol ether may comprise, for example, reacting the olefin oxide with water, suitably using an acidic or a basic catalyst. For example, for making predominantly the I,2-diol and less 1,2-diol ether, the olefin oxide may be reacted with a ten fold molar excess of water., in a liquid phase reaction in presence of an acid catalyst, e.g. 0.5-1.0 %w sulfuric acid, based on the total reaction mixture, at 50- °C at 1 bar absolute, or in a gas phase reaction at 130-240 °C and 20-40 bar absolute, preferably in the absence of a catalyst. The presence of such a large quantity of water may favor the selective formation of 1,2-diol and may function as a sink for the reaction exotherm, helping control the reaction temperature. If the proportion of water is lowered, the proportion of I,2-diol ethers in the reaction mixture is increased. The I,2-diol ethers thus produced may be a di-ether, tn-ether, tetra-ether or a subsequent ether. Alternative 1,2-diol ethers may be prepared by converting the olefin oxide with an alcohol, in particular a primary alcohol, such as methanol or ethanol, by replacing at least a portion of the water by the alcohol.

The olefin oxide may be converted into the corresponding 1,2-carbonate by reacting it with carbon dioxide. If desired, a 1,2-diol may be prepared by subsequently reacting the 1,2.-carbonate with water or an alcohol to form the 1,2-diol. For applicable methods, reference is made to US-6080897, which is incorporated herein by reference.

The conversion of the olefin oxide into the alkanolamine may comprise, for example, reacting the olefin oxide with ammonia. Anhydrous ammonia is typically used to favor the production of monoalkanolamine. For methods applicable in the conversion of - the olefin oxide into the alkanolamine, reference may be made to, for example US-A- 4845296, which is incorporated herein by reference.

The I,2-diol and the 1,2-diol ether may be used in a large variety of industrial applications, for example in the fields of food, beverages, tobacco, cosmetics, thermoplastic polymers, curable resin systems, detergents, heat transfer systems, etc. The 1,2-carbonates may be used as a diluent, in particular as a solvent. The alkanolamine may be used, for example, in the treating ("sweetening") of natural gas.

Unless specified otherwise, the low-molecular weight organic compounds mentioned herein, for example the olefins, I,2-diols, I,2-diol ethers, 1,2-carbonates, alkanolamines, and reaction modifiers, have typically at most 40 carbon atoms, more typically at most 20 carbon atoms, in particular at most-10 carbon atoms, more in particular at most 6 carbon atoms. As defined herein, ranges for numbers of carbon atoms (i.e. carbon number) include the numbers specified for the limits of the ranges.

Having generally described the invention, a further understanding may be obtained by reference to the following examples, which are provided for purposes of illustration only and are not intended to be limiting unless otherwise specified.

EXAMPLES:

Example 1

Into a U-shaped stainless steel tube having an internal diameter of 3/16" was placed 4.2g of crushed (14-20 mesh) epoxidation Catalyst A comprising silver, rhenium, tungsten, lithium and cesium which was freshly prepared. On top of the fresh epoxidation catalyst bed was placed 1 g of crushed (14-20 mesh) "spent" Catalyst A which had produced 1.7 kilotons of cumulative olefin oxide production per cubic meter of the catalyst. Crushed catalyst material was held in place by means of glass wool plugs. The tube was placed into a liquid Wood's metal bath to provide temperature control, and affixed to a system to provide 281 cc/mm of flowing gas mixture composed of 30.0 %v ethylene + 8.0 %v oxygen + 5.0 %v carbon dioxide + 2.5 ppmv ethyl chloride + balance nitrogen. The feed stream was periodically diverted directly to a gas chromatograph to allow the quantitative analysis of the feed stream. Performance was stabilized at a temperature of 260°C, and held at 260°C for the duration of the expeiiment. After the performance of the fresh Catalyst A was stabilized, where we defined "time = zero", the catalyst achieved an EO production of 3.16 %v in the product stream.

After the fresh Catalyst A was stabilized (at "time zero"), a 9.0 cc/mm flow of stock dihydrogen sulfide in balance nitrogen was introduced into the feed stream, while 9.0 cc/mm of nitrogen flow was subtracted from the feed stream. This resulted in a flow of 2.0 ppmv (parts per million by volume) dihydrogen sulfide into the stainless steel tube. Such a flow of dihydrogen sulfide represents a substantial excess as compared with dihydrogen sulfide concentrations typically experienced in ethylene oxide operation. Thus, this experimental design represents an accelerated test as compared with typical ethylene oxide production.

Performance of the catalyst was monitored for forty hours. During that interval, ethylene oxide production declined from 3.16 %v to 2.68 %v, which represents a relative production change of -15%.

Example 2. Comparative Example.

Experiment 2 was conducted in exactly the same manner as was Experiment 1, except that an equal volume (0.86 g) of crushed alpha-alumina was used instead of I g of "spent" Catalyst A in a purification zone. -. -Performance of the catalyst was monitored for forty hours. During that interval, ethylene oxide production declined from 3.12 %v tb 2.42 %v, which represents a relative production change of -22%.

Figure 4 is a plot of the data from Example I and Example 2 showing the ethylene oxide production (%EO) decline over time (hours). As can be seen from the data, utilizing a spent epoxidation catalyst in a purification zone upstream from a fresh epoxidation catalyst results in an improvement in the duration of time the epoxidation catalyst in the reaction zone can remain in the reactor before having to exchange it for new catalyst.

Claims

CLAIMS1 An epoxidation reactor system comprising: -one or more purification zones comprising a spent epoxidation catalyst; and -a reaction zone comprising a fresh epoxidation catalyst, which reaction zone is positioned downstream from the one or more purification zones.
2. The reactor system as claimed in claim 1, wherein the epoxidation reactor vessel is a shell-and-tube heat exchanger comprising a plurality of reactor tubes positioned substantially parallel to the central longitudinal axis of the vessel; wherein the upper ends are connected to a substantially horizontal upper tube plate and the lower ends are connected to a substantially horizontal lower tube plate; and wherein the reaction zone contains the fresh epoxidation catalyst in the form of a packed bed positioned within the reactor tubes.
3. The reactor system as claimed in claim 1 or 2, wherein the epoxidation reactor vessel comprises a quantity of reactor tubes in the range of from 1000 to 20000, in particular from 2500 to 15000.
4. The reactor system as claimed in claim I or any of claims 2-3, wherein the spent epoxidation catalyst has produced a cumulative alkylene oxide production of at least 1 kTfm3 of the catalyst.
5. The reactor system as claimed in claim I or any of claims 2-3, wherein the spent epoxidation catalyst has produced a cumulative alkylene oxide production of at least 1.6 kT/m3 of the catalyst.
6. The reactor system as claimed in claim 2 or any of claims 3-5, wherein a purification zone is located within the reactor tubes.
7. The reactor system as claimed in claim 6, wherein the spent catalyst in the purification zone is in the form of a packed bed having a bed height of at least 0.25 % of the length of the reactor tube, in particular at least I % of the length of the reactor tube.
8. The reactor system as claimed in claim 6 or claim 7, wherein the spent epoxidation catalyst in the purification zone is in the form of a packed bed having a bed height of at most 20 % of the length of the reactor tube, in particular at most 10 % of the length of the reactor tube.
9. The reactor system as claimed in claim 2 or any of claims 3-8, wherein a purification zone is located in the epoxidation reactor vessel positioned upstream from the reactor tubes.
10. The reactor system as claimed in claim 9, wherein the spent epoxidation catalyst in the purification zone is in the form of a packed bed having a bed height of at least 0.05 meters, in particular at least 0.1 meters.
Ii. The reactor system as claimed in claim 9 or claim 10, wherein the spent epoxidation catalyst in the purification zone is in the form of a packed bed having a bed height of at most 2 meters, in particular at most 0.5 meters.
12. The reactor system as claimed in claim I or any of claims 2-5, wherein one or more purification zones comprise one or more separate purification vessels located upstream from the reaction zone.
13. The reactor system as claimed in claim 12, wherein at least one of the purification zones is located in a recycle gas loop connecting a gas outlet from an olefin oxide absorber to an inlet to an epoxidation reactor vessel, optionally including a carbon dioxide absorber and/or a water removal vessel.
14. The reactor system as claimed in claim 12 or claim 13, wherein at least one of the purification zones is located in an olefin feed. 0
15. The reactor system as claimed in claim 12 or any of claims 13-14, wherein at least one of the purification zones is located in a saturated hydrocarbon feed.
16. The reactor system as claimed in claim 1 or any of claims 2-15, wherein the spent epoxidation catalyst comprises silver.
17. The reactor system as claimed in claim I or any of claims 2-16, wherein the fresh epoxidation catalyst comprises silver.
18. The reactor system as claimed in claim 16, wherein silver is present in a quantity in the range of from 50 to 500 glkg, relative to the weight of the catalyst, in particular from 100 to 400 g/kg, relative to the weight of the catalyst.
19. The reactor system as claimed in claim 17, wherein silver is present in a quantity in the range of from 50 to 500 glkg, relative to the weight of the catalyst, in particular from 100 to 400 gfkg, relative to the weight of the catalyst.
20. The reactor system as claimed in claim 16 or 17, wherein the catalyst further comprises one or more selectivity enhancing dopants selected from the group consisting of rhenium, molybdenum, tungsten, chromium, nitrate-or nitrite-forming compounds, and combinations thereof.
21. A process for the production of an olefin oxide comprising: -contacting one or more feed components containing one or more impurities with a spent epoxidation catalyst to reduce the quantity of the one or more impurities in the feed components; and -subsequently contacting the feed components, and optionally one or more additional feed components, with a fresh epoxidation catalyst to yield an olefin oxide.
22. The process as claimed in claim 21, wherein the one or more impurities comprise one or more sulfur-containing impurities selected from dihydrogen sulfide, carbonyl sulfide, mercaptans, and organic sulfides.
23. The process as claimed in claim 21 or claim 22, wherein the feed components are contacted with the spent epoxidation catalyst at a temperature of at least 25 °C, in particular at a temperature in the range of from 25 to 300 °C, more in particular at a temperature in the range of from 70 to 280 DC.
24. The process as claimed in claim 21 or claim 22, wherein the feed components are contacted with the spent epoxidation catalyst positioned in an epoxidation reactor vessel within a plurality of reactor tubes additionally containing the fresh epoxidation catalyst.
25. The process as claimed in claim 24, wherein the feed components are contacted with the spent epoxidation catalyst at a temperature of at least 140 °C, in particular at least 160 °C, more in particular in the range f from 150 to 300 °C.
26. The process as claimed in claim 21 or claim 22, wherein the feed components are contacted with the spent epoxidation catalyst positioned in an epoxidation reactor vessel upstream from a plurality of reactor tubes containing the fresh epoxidation catalyst.
27. The process as claimed in claim 26, wherein the feed components are contacted with the spent epoxidatiori catalyst at a temperature of at least 120 °C, in particular at least 140 °C, more in particular in the range of from 120 to 200 °C.
28. The process as claimed in claim 21 or claim 22, wherein the feed components are contacted with the spent epoxidation catalyst positioned within one or more separate purification zones comprising one or more separate purification vessels containing the spent epoxidation catalyst; and wherein the feed components are subsequently contacted with the fresh epoxidation catalyst in a reaction zone located in an epoxidation reactor vessel having a plurality of reactor tubes containing the fresh epoxidation catalyst.
29. The process as claimed in claim 28, wherein the feed components are contacted with the spent epoxidation catalyst at a temperature of at least 25 °C, in particular at least 70 °C, more in particular in the range of from 60 to 200 °C.
30. The process as claimed in claim 21 or any of claims 22-29, wherein the one or more feed components contacted with the spent epoxidation catalyst comprise an olefin, in particular ethylene.
31. The process as claimed in claim 21 or any of claims 22-30, wherein the one or more feed components contacted with the spent epoxidation catalyst comprise a saturated hydrocarbon, in particular methane.
32. The process.as claimed iQclaim 21 or any of claims 22-31, wherein the one or more feed components contacted with the spent epoxidation catalyst comprise a recycle gas stream.
33. The process as claimed in claim 21 or any of claims 22-32, wherein one or more additional feed components comprising oxygen are contacted with the fresh epoxidation catalyst.
34. The process as claimed in claim 21 or any of claims 22-32, wherein the one or more feed components contacted with the spent epoxidation catalyst comprise an olefin, oxygen, a saturated hydrocarbon, a reaction modifier, and a recycle gas.
35. A process for preparing a l,2-diol, a 1,2-diol ether, a 1,2-carbonate, or an alkanolamine comprising converting an olefin oxide into the 1,2-diol, the 1,2-diol ether, the 1,2-carbonate, or the alkanolamine wherein the olefin oxide has been prepared by the process as claimed in claim 21 or any of claims 22-34.