JP2013082691A - Method and device for producing propylene oxide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and a device for producing propylene oxide, which reduce the generation of byproducts to the minimum.SOLUTION: The device for producing propylene oxide from propylene includes: a reaction container having a reaction tube supported by an upper tube plate and a lower tube plate; a separation grid separating the reaction container to an upper stream area and a lower stream area; a system, which is the upper stream cooling system for supplying the cooling medium to the upper stream area, removing the medium from the upper stream area and recirculating the medium into the upper stream area, to enable the discharge of a part of a cooling medium from an upper stream cooling system as vapor; and a system, which is the lower stream cooling system for supplying the cooling medium to the lower stream area, removing the medium from the lower stream area and then recirculating the medium into the lower stream area, to enable additional cooling medium further to be added to a lower stream cooling system. The separation grid makes the cooling medium flow from the lower stream area to the upper stream area substantially.

Description

  The present invention relates to a method and an apparatus for producing propylene oxide.

Propylene oxide can be produced, for example, by catalytic gas phase oxidation of propylene in the presence of a metal catalyst. The reaction is an exothermic reaction, and the reaction vessel is typically composed of a number of reaction tubes filled with a metal catalyst, and the cooling medium flows outside the reaction tube to remove reaction heat and thereby control the reaction temperature.
Reaction vessel designs for ethylene oxide production have been developed to improve the quality of ethylene oxide by reducing the formation of by-products. US3147084 describes a reaction vessel that is divided laterally into an upstream reaction zone and a downstream cooling zone by means of a tube plate. Although a small amount of fluid is allowed to ooze between the two regions, the heat exchange fluid is circulated separately in the two independent regions. US 5292904 describes a reactor which is divided laterally into a reaction zone and a cooling zone by means of a partition plate. Hot water used as a heat exchange fluid in the cooling zone is supplied to the gas-liquid separation tank, and the hot water is returned from the tank to the reaction zone.
EP 821678 describes a method using a single compartment reaction vessel in which some or all of the heat exchange fluid is introduced at the downstream end of the reaction vessel at a temperature that is at least 20 ° C. lower than the temperature when it is removed from the reaction vessel. ing. EP 1358441 describes a conventional tubular reactor that combines a heat exchanger that is integral with the discharge head of the tubular reactor.
US4203906 describes a reaction vessel that is divided into two heat transfer zones by a perforated shield plate. The heat exchange fluid can flow between the heat transfer zones through the perforated shield plate and further maintain the temperature difference between the two zones. There is no substantial movement of the heat transfer medium between the two regions.
EP0911313 discloses a reaction vessel that is divided into an upper space and a lower space by a partition plate and in which a heat medium circulates substantially independently in the upper space and the lower space. Thereby, the temperature of the catalyst layer of the reaction tube is controlled.

  Patent Document 1 describes a method and an apparatus for producing ethylene oxide.

WO2010 / 081906

  The subject of this invention is providing the manufacturing method and manufacturing apparatus of a propylene oxide from the propylene which minimized the production | generation of a by-product. Furthermore, it is desirable to provide an apparatus that is simple and cost effective and that allows for energy efficient process operation.

As a result of studies to solve the above problems, the present invention shown below has been completed.
[1] An apparatus for producing propylene oxide from propylene,
A reaction vessel having a reaction tube held by an upper tube plate and a lower tube plate;
A separation grid that divides the reaction vessel into an upstream region and a downstream region;
An upstream region cooling system that supplies the cooling medium to the upstream region, removes it from the upstream region, and recirculates it to the upstream region, wherein a part of the cooling medium can be discharged as steam from the upstream region cooling system;
A downstream zone cooling system that supplies cooling medium to the downstream zone, removes it from the downstream zone, and recirculates it to the downstream zone, wherein an additional cooling medium can be added to the downstream zone cooling system;
The separation grid allows the cooling medium to substantially flow from the downstream area to the upstream area.

[2] A method for producing propylene oxide from propylene,
a) supplying propylene and oxygen to a reaction tube, the reaction tube being held by an upper tube plate and a lower tube plate of the reaction vessel, which divides the reaction vessel into an upstream region and a downstream region A process having a separation grid;
b) supplying a cooling medium from the upstream area cooling system to the upstream area, removing the cooling medium from the upstream area to the upstream area cooling system, and discharging a part of the cooling medium as steam from the upstream area cooling system;
c) supplying a cooling medium from the downstream area cooling system to the downstream area, removing the cooling medium from the downstream area to the downstream area cooling system, and adding an additional cooling medium to the downstream area cooling system;
A method wherein the cooling medium substantially flows from the downstream zone to the upstream zone through the separation grid.

[3] The apparatus according to [1] or the method according to [2], wherein the open area of the separation grid is 0.5% to 8% of the cross-sectional area of the reaction vessel.
[4] The apparatus according to [1] or [3], wherein the upstream region is 50% to 95% of the volume of the reaction vessel, and the downstream region is 5% to 50% of the volume of the reaction vessel, or [2] Or the method of [3] description.
[5] The apparatus according to [1], [3] or [4], or the method according to any one of [2] to [4], wherein the cooling medium is water.
[6] The apparatus according to any one of [1], [3] to [5], or the method according to any one of [2] to [5], wherein the upstream cooling system has a steam drum.
[7] The apparatus according to any one of [1], [3] to [6], or any one of [2] to [6], wherein the cooling medium in the downstream cooling system is used for heat exchange. Method.
[8] The apparatus according to any one of [1], [3] to [7], or the method according to any one of [2] to [7], wherein the downstream cooling system includes a trim cooler and a pump.
[9] The apparatus according to any one of [1], [3] to [8], or any one of [2] to [8], wherein the reaction tube includes all the catalyst beds in the upstream region. Or the method described.
[10] The apparatus or method according to [9], wherein the reaction tube is substantially free of catalyst in the downstream region.
[11] The apparatus or method according to [9] or [10], wherein the catalyst bed contains a metal catalyst.
[12] The apparatus or method according to [11], wherein the metal catalyst is a catalyst containing (a) copper oxide and (b) ruthenium oxide.

In the prior art system in which the heat exchange fluid circulates separately within two separate regions separated by the divider tube plate, it is possible to maintain a large temperature difference between the two regions. This temperature difference has the advantage that the temperature in the downstream region can be significantly lower than that in the upstream region, the production of by-products can be reduced, and the quality of propylene oxide can be improved. However, a reaction vessel having a partition plate is expensive, and the use and production of the partition plate are mechanically complicated. In the production apparatus and production method of the present invention, the inventors maintain a large temperature difference between the upstream region and the downstream region even if the reaction vessel has a simple separation grid instead of a fixed tube plate. Found that you can. By controlling the cooling system so that the cooling medium substantially flows through the separation grid from the downstream region to the upstream region, little or no cooling medium flows from the higher temperature upstream region to the lower temperature downstream region. The difference can be maintained.
Therefore, the production method and production apparatus of the present invention can provide high-quality propylene oxide containing almost no by-products.

It is a schematic diagram which shows the manufacturing apparatus which concerns on this invention.

Examples of the method for catalytic vapor phase oxidation of propylene to which the present invention can be applied include a production method in which propylene and oxygen are reacted in the presence of a metal catalyst containing a metal oxide or the like. For the production method of reacting propylene and oxygen in the presence of such a metal catalyst, for example, WO2011 / 075458, WO2011 / 0754559, WO2012 / 005822, WO2012 / 005823, WO2012 / 005824, WO2012 / 005825, WO2012 / 005831, WO2012 / 005832, WO2012 / 005835, WO2012 / 005837, WO2012 / 009054, WO2012 / 009059, WO2012 / 009058, WO2012 / 009053, WO2012 / 009057, WO2012 / 009055, WO2012 / 009055, WO2012 / 009055 and the like. As the catalyst used in the production method, the following (a), (b), (c), (d), (e), (f), (g), (h), (i), (j), ( and a catalyst containing at least two selected from the group consisting of k), (l), (m), (n), (o), (p) and (q).
(A) copper oxide (b) ruthenium oxide (c) manganese oxide (d) nickel oxide (e) osmium oxide (f) germanium oxide (g) chromium oxide (h) thallium oxide (i ) Tin oxide (j) bismuth oxide (k) antimony oxide (l) rhenium oxide (m) cobalt oxide (n) osmium oxide (o) lanthanoid oxide (p) tungsten oxide (q) alkali Metal component or alkaline earth metal component, preferably a catalyst containing (a) copper oxide and (b) ruthenium oxide, more preferably (a) copper oxide, (b) ruthenium oxide and (q) A catalyst containing an alkali metal component or an alkaline earth metal component.

Propylene and oxygen are supplied to a reaction vessel having a reaction tube held by an upper tube plate and a lower tube plate. Oxygen is supplied as oxygen or air, but is preferably supplied as oxygen. A ballast gas such as methane is preferably provided to react at high oxygen levels without causing a combustible mixture. Additives such as organochlorine compounds described in WO2012 / 102918 may be added to control catalyst performance. Propylene, oxygen, ballast gas and additives are preferably added to the recycle gas from the propylene oxide absorber and fed to the propylene oxide reaction vessel.
The reaction vessel has 1000 to 20000 reaction tubes, preferably 2500 to 15000 reaction tubes. The reaction tube preferably has a height of 5m to 20m, more preferably a height of 10m to 15m, preferably an inner diameter of 15m to 80mm, more preferably an inner diameter of 20mm to 75mm, most preferably 25mm to 70mm. Has an inner diameter. The reaction tube is preferably substantially vertical, preferably no more than 5 ° from vertical.
The upper end of the reaction tube is connected to the upper tube plate and is in fluid communication with one or more inlets to the reaction vessel. The lower end of the reaction tube is connected to the lower tube plate and is in fluid communication with one or more outlets to the reaction vessel. The upper tube sheet and the lower tube sheet are preferably horizontal, and preferably 3 ° or less from the horizontal.

The reaction tube has a catalyst bed. The particles that may be contained in the catalyst bed other than the catalyst particles are, for example, inert particles. Preferably, the catalyst bed is supported on the reaction tube by catalyst support means arranged at the lower end of the reaction tube. The support means may include a net and a spring.
The reaction tube also includes a bed of particles of one or more different inert materials for the purpose of heating the feed stream as needed or for cooling the reaction product. Also, a rod-shaped metal insert may be used in place of the inert material floor. A description of such an insert is described in US Pat. No. 7,132,555.

The separation grid divides the reaction vessel into an upstream region and a downstream region so that the cooling medium substantially flows from the downstream region to the upstream region. The separation grid is a plate having a through hole through which the reaction tube can pass. Although the reaction tube and the separation grid can be contacted, the reaction tube is not connected (eg, welded) to the separation grid. Thus, a part of the reaction tube can be in the upstream region and another part of the same reaction tube can be in the downstream region.
When the reaction tube is mounted in the reaction vessel so as to pass through the holes of the separation grid, the separation grid has an open area where the cooling medium can pass through the separation grid. The holes in the separation grid are larger than the outer diameter of the reaction tube, and the reaction tube easily passes through the through hole (typical tolerances are 0.2 mm to 3 mm). The gap between the reaction tube and the separation grid provides part or all of the open area of the separation grid. In addition, there may be additional holes in the separation grid through which the reaction tubes do not pass, thereby providing part of the open area of the separation grid. Preferably, the open area of the separation grid is 0.5% to 8% of the cross-sectional area of the reaction vessel, more preferably 1% to 5%, and most preferably 1% to 3%. It is difficult to achieve a smaller open area due to manufacturing tolerances when drilling holes in the separation grid so that the reaction tubes pass during assembly. If the open area is made larger, a large amount of cooling medium flows from the upstream area to the downstream area, the downstream area is heated, and the production of by-products is increased, so that a larger open area is not preferable.

The separation grid is preferably metal, more preferably made from a single sheet of metal. The most preferred metal is carbon steel. The thickness of the separation grid is preferably 100 mm or less, more preferably 5 mm to 50 mm, and most preferably 10 mm to 30 mm.
The separation grid is preferably suspended by a vertical bar from the upper tube sheet. Preferably, the rod also supports a conventional tube support grid, which is in a fixed position to ensure tube position, typically every 1.5 m to 2.5 m. A conventional tube support grid is a plate having a through hole through which a reaction tube can pass and further having a hole for passing steam and water. The difference between a conventional tube support grid and a separation grid is that the separation grid is designed to limit the flow of fluid through the grid, whereas the conventional tube support grid is much larger than the grid. It is designed to allow fluid flow. The open area of the tube support grid is usually 20-30% of the cross-sectional area of the reaction vessel.
There is preferably a small gap, for example 1 mm to 5 mm, between the outer periphery of the separation grid and the shell of the reaction vessel. This is to enable the installation of the reaction vessel and to cope with the difference in thermal expansion.
The separation grid divides the reaction vessel into an upstream region and a downstream region. Separation in the vertical direction is preferable because cooling efficiency can be improved and the flow state and temperature of the cooling medium in the downstream region can be achieved. However, the separation grid is preferably divided into an upstream region occupying 50% to 95% of the reaction vessel volume and a downstream region occupying 5% to 50% of the reaction vessel volume. More preferably, the upstream region occupies 70% to 90% of the reaction vessel volume, and the downstream region occupies 10% to 30% of the reaction vessel volume.

In a preferred embodiment of the present invention, the reaction tube contains the entire catalyst bed in the upstream zone, and the reaction tube contains inert materials such as inert particles and reaction vessel inserts in the downstream zone. The inert material in the downstream zone improves heat transfer from the reaction product gas to the cooling medium, thereby reducing the production of by-products in the downstream zone. The reaction tube preferably has a bed of inert material upstream of the catalyst bed in the upstream zone. With this configuration, heat transfer from the cooling medium to the raw material supply gas is improved in the upstream region.
Thus, in one embodiment, the reaction tube can be substantially free of catalyst in the downstream zone. The term “substantially free of catalyst” means that a portion in the downstream region of the reaction tube does not include a catalyst bed, but a small amount of catalyst, for example, a catalyst that moves on the gas stream from the catalyst bed in the upstream region to the downstream region is included. But it means good. In a further embodiment, the reaction tube can be completely free of catalyst in the downstream zone.

The upstream cooling system supplies a cooling medium to the upstream area and removes the cooling medium from the upstream area. In the upstream cooling system, a part of the cooling medium is discharged as steam before the cooling medium is recirculated to the upstream area. The downstream area cooling system supplies a cooling medium to the downstream area and takes in the cooling medium from the downstream area. In the downstream cooling system, additional cooling medium is added before the cooling medium is recirculated to the downstream area. An additional cooling medium is added to the downstream area, and the cooling medium is discharged from the upstream area as vapor so that the open area present in the separation grid flows through the separation grid. The cooling medium can substantially flow from the upstream region to the upstream region.
The cooling medium for the upstream cooling system and the downstream cooling system is essentially the same material as the cooling medium flowing from the downstream area to the upstream area. The cooling medium is a cooling medium that can be discharged as steam. The cooling medium may be a hydrocarbon or a mixture of hydrocarbons such as n-octane, n-nonane, kerosene, ISOPAR®, MOBILTHERM® or Dowsum®, but preferably The cooling medium is an aqueous material, most preferably water.
The cooling medium is preferably supplied as a liquid to the downstream zone cooling system and discharged as vapor from the upstream zone cooling system. Preferably, the supply rate and the discharge rate are the same or equivalent so that the amount of the cooling medium in the system is substantially constant. The supply rate of the cooling medium is determined according to the amount of cooling required at least partially. There is a temperature difference between the product and the reactant, and the heat of reaction is removed along with the product, but most of the heat of reaction produced is removed by the cooling medium.

In one embodiment of the invention, the additional cooling medium is supplied to the upstream cooling system, preferably as a liquid. In this embodiment, the sum of the cooling medium supply rates to the upstream cooling system and the downstream cooling system is preferably the same as or equivalent to the cooling medium discharge rate from the upstream cooling system. Even if the cooling medium is supplied to the upstream area cooling system, the cooling medium is discharged from the upstream area cooling system, so that the substantial flow of the cooling medium from the downstream area to the upstream area can be ensured. Adding the cooling medium to the two locations (downstream cooling system and upstream cooling system) provides additional flexibility to control the flow of the cooling medium through the separation grid.
The reaction for producing propylene oxide by reacting propylene and oxygen is an exothermic reaction. Furthermore, there is also a side reaction with extremely high heat generation in which propylene and propylene oxide are burned to produce carbon dioxide and water. In the present invention, most of the reaction occurs in the upstream region of the reaction vessel, and therefore it is necessary to remove the heat of reaction in the upstream region to ensure that the reaction proceeds at the desired temperature and with the desired selectivity. It also ensures that the production of by-products such as aldehydes is minimized by rapidly cooling the products of the oxidation reaction. Therefore, it is necessary to cool the downstream area of the reaction vessel. It is desirable to maintain a temperature difference between the cooling medium in the downstream zone and the cooling medium in the upstream zone. The temperature of the cooling medium in the downstream region is preferably at least 5 ° C., more preferably at least 10 ° C., even more preferably at least 20 ° C., most preferably at least 30 ° C. or less than the temperature of the cooling medium in the upstream region. It is. The temperature in the downstream zone is preferably between 120 ° C and 275 ° C, more preferably between 160 ° C and 230 ° C, and most preferably between 170 ° C and 210 ° C. The temperature in the upstream region is preferably between 150 ° C and 350 ° C, more preferably between 200 ° C and 300 ° C, and most preferably between 220 ° C and 300 ° C.

In the upstream cooling system, a part of the cooling medium is discharged as steam. In a preferred embodiment of the invention where the cooling medium is water, a portion of the cooling medium is discharged as water vapor. Cooling in the upstream zone is at least partly achieved by evaporation of the cooling medium in the upstream zone, part of the cooling medium discharged from the upstream zone is in the form of vapor and part is in the form of liquid. A part of the cooling medium is discharged from the upstream cooling system as steam. Most preferably, a steam drum is present in the upstream cooling system. The steam is separated from the water / steam mixture entering the steam drum and the steam is discharged from the steam drum. Water is recycled to the upstream area. Preferably, the cooling liquid is introduced from the upstream cooling system into the upstream area along the circumference of the reactor via one or more cooling medium injection porous dispersion tubes or nozzles. Preferably, the cooling medium is introduced into the upstream zone at the bottom of the upstream zone (near the separation grid) and removed from the upstream zone near the top of the reaction vessel.
In embodiments of the invention in which additional cooling medium is supplied to the upstream cooling system, it is preferred to supply additional water to the steam drum. The vapor drum preferably has a liquid volume control system so that additional water is added when the liquid falls below a set level.

  In the downstream area cooling system, the cooling medium is supplied at a temperature equal to or lower than the temperature of the cooling medium in the upstream area. The reaction heat is removed by continuously supplying a cooling medium at a lower temperature. In addition to supplying the cooling medium, heat removal is also achieved by preferably exchanging heat in the cooling medium of the downstream cooling system. The heat exchange is most preferably performed by a trim cooler in the downstream cooling system. If a trim cooler is used, it is desirable that the temperature of the cooling medium removed from the downstream zone be sufficiently high that steam can be generated using the trim cooler or the process steam can be heated. Preferably, the cooling medium in the downstream area does not evaporate and the cooling medium in the downstream area and the downstream cooling system exists as a liquid. In order to circulate the cooling medium, a cooling medium circulation pump is preferably present in the downstream cooling system. Preferably, the cooling liquid is introduced from the downstream cooling system into the downstream area along the circumference of the reactor via one or more cooling medium injection porous dispersion tubes or nozzles. Preferably, the cooling medium is introduced near the bottom of the reaction vessel from the downstream zone and removed from the downstream zone at the top of the downstream zone (near the separation grid). For smaller systems, it is sufficient to introduce a cooling medium around the reaction vessel, but for larger systems, use a radial distribution tube with improved cooling medium distribution across all of the reaction tubes. It is preferable to do.

EXAMPLES Examples will be described below to describe the present invention in more detail. However, this example does not limit the scope of the present invention.
FIG. 1 shows a preferred embodiment of the production apparatus of the present invention. The reaction tube (2) is connected to the upper tube plate and the lower tube plate and installed in the reaction vessel (1). A separation grid (3) is arranged in the reaction vessel (1) so as to divide the reaction vessel (1) into an upstream region (4) and a downstream region (5). The upstream cooling system (7) includes a steam drum (9), and the downstream cooling system (11) includes a trim cooler (13) and a cooling medium circulation pump (15).
Propylene and oxygen are supplied to the upper part of the reaction tube (2) in the reaction vessel (1), and react under an exothermic reaction to produce propylene oxide. This reaction proceeds mainly in the reaction tube in the upstream region (4), and a large amount of heat is generated in the upstream region (4). While the reaction product passes through the reaction tube (2) in the downstream zone (5), it is desirable to cool the reaction product rapidly in order to reduce the formation of by-products.

Water is supplied (14) to the downstream cooling system (11). Water flows through the downstream cooling system (11) by the cooling medium circulation pump (15) and is supplied to the downstream zone (5) (16). When water is removed from the downstream zone (5) rather than when it is fed to the downstream zone (5) (16) because the water contacts the reaction tube (2) in the downstream zone (5) and absorbs heat (12) ) Is hotter. In the downstream cooling system (11), the trim cooler (13) removes heat from the water before being re-supplied to the downstream zone (5).
In the upstream zone (4), water comes into contact with the reaction tube (2) and is heated. The amount of reaction heat is present to the extent that water evaporates in the upstream zone (4). The mixture of water vapor and liquid water is recovered from the upstream zone (4) to the upstream zone cooling system (7) (6) and supplied to the steam drum (9). Steam is discharged (10) from the steam drum (9). Water is circulated and supplied to the upstream area (4) (8).
Water is supplied to the downstream cooling system (11) (14), and water vapor is discharged from the steam drum (9) in the upstream cooling system (7) (10). Thus, water substantially flows from the downstream area (5) to the upstream area (4) through the separation grid (3). Little or no cooling medium flows from the hotter upstream zone (4) to the cooler downstream zone (5), and the temperature difference between the two zones is maintained.

  The production method and production apparatus of the present invention can provide high quality propylene oxide containing almost no by-products.

1: reaction vessel 2: reaction tube 3: separation grid 4: upstream region 5: downstream region 7: upstream region cooling system 9: steam drum 11: downstream region cooling system 13: trim cooler 15: cooling medium circulation pump

Claims (12)

An apparatus for producing propylene oxide from propylene,
A reaction vessel having a reaction tube held by an upper tube plate and a lower tube plate;
A separation grid that divides the reaction vessel into an upstream region and a downstream region;
An upstream region cooling system that supplies the cooling medium to the upstream region, removes it from the upstream region, and recirculates it to the upstream region, wherein a part of the cooling medium can be discharged as steam from the upstream region cooling system;
A downstream zone cooling system that supplies cooling medium to the downstream zone, removes it from the downstream zone, and recirculates it to the downstream zone, wherein an additional cooling medium can be added to the downstream zone cooling system;
The separation grid allows the cooling medium to substantially flow from the downstream area to the upstream area. A method for producing propylene oxide from propylene, comprising:
a) supplying propylene and oxygen to a reaction tube, the reaction tube being held by an upper tube plate and a lower tube plate of the reaction vessel, which divides the reaction vessel into an upstream region and a downstream region A process having a separation grid;
b) supplying a cooling medium from the upstream area cooling system to the upstream area, removing the cooling medium from the upstream area to the upstream area cooling system, and discharging a part of the cooling medium as steam from the upstream area cooling system;
c) supplying a cooling medium from the downstream area cooling system to the downstream area, removing the cooling medium from the downstream area to the downstream area cooling system, and adding an additional cooling medium to the downstream area cooling system;
A method wherein the cooling medium substantially flows from the downstream zone to the upstream zone through the separation grid.   The apparatus of claim 1 or the method of claim 2, wherein the open area of the separation grid is 0.5% to 8% of the cross-sectional area of the reaction vessel.   The apparatus according to claim 1 or 3, or the method according to claim 2 or 3, wherein the upstream zone is 50% to 95% of the volume of the reaction vessel and the downstream zone is 5% to 50% of the volume of the reaction vessel. .   The apparatus according to claim 1, 3 or 4, or the method according to claim 2, wherein the cooling medium is water.   The apparatus according to any one of claims 1 to 3, or the method according to any one of claims 2 to 5, wherein a steam drum is provided in the upstream cooling system.   The apparatus according to any one of claims 1 and 3 to 6, or the method according to any one of claims 2 to 6, wherein the cooling medium of the downstream cooling system is subjected to heat exchange.   8. A device according to any one of claims 1, 3 to 7, or a method according to any one of claims 2 to 7, wherein there is a trim cooler and a pump in the downstream cooling system.   9. An apparatus according to any one of claims 1, 3 to 8, or a process according to any one of claims 2 to 8, wherein the reaction tube contains and contains all of the catalyst bed in the upstream zone.   10. An apparatus or method according to claim 9, wherein the reaction tube is substantially free of catalyst in the downstream zone.   The apparatus or method of claim 9 or 10, wherein the catalyst bed comprises a metal catalyst.   12. The apparatus or method according to claim 11, wherein the metal catalyst is a catalyst containing (a) copper oxide and (b) ruthenium oxide.

Images