WO2018059888A1

WO2018059888A1 - Centrally cooled reactor

Info

Publication number: WO2018059888A1
Application number: PCT/EP2017/072307
Authority: WO
Inventors: Bjarke Thomas Dalslet; Jeremy Neil Burn
Original assignee: Haldor Topsøe A/S
Priority date: 2016-09-27
Filing date: 2017-09-06
Publication date: 2018-04-05
Also published as: DK201700031A1

Abstract

The present disclosure relates to a chemical reactor adapted to operate with exothermal processes by means of both at least one primary and at least one secondary cooling medium enclosure.

Description

Centrally cooled reactor

The invention relates to a fluid cooled chemical reactor comprising catalyst. More particular, the invention relates to a fluid cooled chemical reactor comprising catalyst for exothermal reactions, comprising not only a cooling medium enclosure around the reaction enclosure with catalyst, but also a cooling medium enclosure arranged centrally within the reaction enclosure.

In exothermal processes a fluid cooled reactor is often a relevant option since such a reactor can ensure optimum reaction conditions by providing a substantially constant cooling medium temperature. This is favorable where the process is limited by an exothermal reaction. The typical design of the reactor involves a cooling medium enclosure with pressurized cooling fluid such as water, oil or other cooling media with a boiling point appropriate for the cat^¬ alytic process. The pressure in the cooling medium enclo- sure controls the boiling temperature of the cooling me^¬ dium, which may act as a heat sink at substantially con^¬ stant temperature when operating at the boiling point, to the extent that liquid water is present in the reactor. Known art as disclosed in US5079267, describes a process for production of methanol from process gas produced by steam reforming hydrocarbon feedstock in a tube type reformer followed by removing substantially all CO₂ and ¾0 from the process gas, adjusting the ¾/CO molar ratio to about 2 when necessary, and feeding the adjusted process gas to a methanol synthesis reactor contacting a methanol forming catalyst not requiring CO₂ activation at about 200° to about 300°C to produce product gas comprising methanol, and recovering liquid methanol having purity greater than about 99.85% pure by cooling the product gas to a tempera^¬ ture below the boiling point of methanol and separating the liquid methanol from gaseous components of the product gas. In a preferred embodiment, process gas of ¾/CO molar ratio of about 2.0 to about 2.5 is passed through an annular thermal exchange volume between a centre plug and an inner tube followed by passing the gas in contact with a catalyst in a catalyst bed between the inner tube and an outer tube of a double tube reactor assembly promoting the direct re^¬ action of ¾ and CO to product methanol. An improved double tube reactor having a plurality of inner and outer tube as^¬ semblies each of the assemblies having a reaction annular volume between the inner tube and outer tube and a closed centre plug within the inner tube forming an annular thermal exchange volume between the centre plug and the inner tube . The cooling of the catalyst in the reactor is crucial for exothermal reactions. If the temperature is not optimal, it may reduce performance, the lifetime of the equipment and the lifetime of the catalyst. When the lifetime of the cat^¬ alyst is reduced, not only the cost for catalyst is in- creased, but also the down-time of the reactor. It is therefore a problem with heavy impact on the process prof^¬ itability and lifetime of the catalyst and equipment to en^¬ sure the optimum cooling and suitable operation temperature of the catalyst in the reaction enclosure of the chemical reactor. This problem is solved by the invention as de^¬ scribed in the following and according to the claims. The invention is an elegant and simple idea for a much more efficient heat exchange in a fluid cooled reactor comprising catalyst. The core of the idea is to insert a tube into the middle of the reactor to cool the outer side of the reac- tion enclosure as well as the inner side. In this way the maximum catalyst volume for a given system size of reactor is traded for either better cooling or larger reactor tubes . An embodiment of the invention comprises a chemical reactor for an exothermal reaction with at least one reaction enclosure. The reaction enclosure typically comprises a cata^¬ lyst and though the following disclosure explains the in^¬ vention with the basis in a single reaction disclosure, it is to be understood that the reactor may comprise a plural^¬ ity of similar reaction enclosures and that the invention may also cover a number of reactors i.e. in serial or par^¬ allel connection. To cope with the heat generated from the exothermal reac^¬ tion, the chemical reactor further comprises at least one primary cooling medium enclosure. The cooling medium may be either liquid or gaseous or a combination of both. The cooling medium enclosure is configured to hold the fluid cooling medium under pressure at its boiling point for the given fluid. It is to be understood that the boiling point and thus to some extent the operating temperature for the chemical process can be modified by controlling the pres^¬ sure and thus optimize the chemical process.

According to this embodiment, the primary cooling medium enclosure at least partly encompasses said reaction enclo^¬ sure and the reaction enclosure comprises an outer surface configured to be in thermal contact with the cooling me^¬ dium. Hence, at least a part of the outer surface of the reaction enclosure is in thermal contact with the cooling medium to provide heat exchange between the reaction enclo^¬ sure and the cooling medium. The reaction enclosure comprises a reaction enclosure inlet and a reaction enclosure outlet to provide for a stream of process fluid through the reaction enclosure where it may react with the catalyst within the reaction enclosure. Furthermore, the primary cooling medium enclosure comprises a cooling medium inlet and a cooling medium outlet to facilitate a flow of cooling medium through the cooling medium enclosure for removal of the heat exchanged from the reaction to the cooling medium, to keep a constant operating temperature.

According to the invention, the reactor further comprises a secondary cooling medium enclosure which is in fluid con- tact with the at least one primary cooling medium enclo^¬ sure. Thus, the cooling medium flows through both the primary and the secondary cooling medium enclosure when passing from the cooling medium inlet to the cooling medium outlet, which ensures a relative simple construction of the reactor even though there is both a primary and a secondary cooling medium enclosure. The reaction enclosure at least partly encompasses the secondary cooling medium enclosure. This increases the heat exchange potential of the reactor considerably, since the reaction enclosure has both an outer and an inner surface in contact with the cooling me^¬ dium. A larger amount of heat can be transferred from the reaction enclosure, but also the temperature in the reac^¬ tion enclosure can be kept much more even, with lower temperature difference within the reaction enclosure than if only an outer surface of the reaction enclosure is in con- tact with cooling medium. This is crucial for the lifetime of the catalyst within the reaction enclosure.

In a further embodiment of the invention, the secondary cooling medium enclosure is centrally arranged along the center line of the reactor to provide the best heat ex^¬ change with the reaction enclosure. The secondary cooling medium enclosure may be cylindrically shaped and comprises a first cooling medium connection to the primary cooling medium enclosure in its lower end and a second cooling me- dium connection to the primary cooling medium enclosure in its upper end of the secondary cooling medium enclosure, thus providing an optimum flow of cooling medium relative to the shape of the secondary cooling medium enclosure. In an embodiment of the invention, the primary cooling medium enclosure comprises a cylindrical inner wall. This in^¬ ner wall is at least partially in thermal contact with the reaction enclosure to provide an optimum balance between construction strength, material consumption, external di- mensions and heat exchange of the reactor. However accord^¬ ing to the invention, other shapes of cooling medium enclosures and reaction enclosure may be chosen if beneficial for instance for production of the equipment. In a further embodiment, all of the components, the primary cooling medium enclosure, the reaction enclosure and the secondary cooling medium enclosure are arranged concentric. Thus, the secondary cooling medium enclosure is arranged in the middle of the reactor along the center line and can have a cylindrical shape; the reaction enclosure is ar^¬ ranged around the secondary cooling medium enclosure for instance in a doughnut shape when seen in a cross sectional view and the primary cooling medium enclosure is arranged around the reaction enclosure for instance also in a dough^¬ nut shape to create a large heat exchange area relative to the reaction enclosure volume. As mentioned, the reactor may operate with both gas and liquid or both as a cooling medium. In one embodiment the cooling medium is oil and the cooling medium enclosures are adapted to operate with oil.

In a further embodiment of the invention, the reaction en- closure is adapted to operate with a formaldehyde catalyst within the reaction enclosure. The present invention is es^¬ pecially advantageous for this application, since this re^¬ action is highly exothermal and requires efficient heat ex^¬ change to remove the excess heat generated.

In a further embodiment of the invention, the total cooling area between the reaction enclosure and the primary and secondary cooling medium enclosure is between one and four times larger than the volume in the reaction enclosure. And in yet a further embodiment of the invention the total cooling area between the reaction enclosure and the primary and secondary cooling medium enclosure is between one and two times larger than the volume in the reaction enclosure. In a further embodiment of the invention, the outer diame^¬ ter of the reaction enclosure is larger than one and less than three times larger than the outer diameter of the secondary cooling medium enclosure. In yet a further embodiment of the invention, the outer diameter of the reaction enclosure is larger than one and less than two times larger than the outer diameter of the secondary cooling medium enclosure .

The reaction enclosure comprises a catalytically active ma^¬ terial in at least 50% to 80% of its volume in an embodi- ment of the invention and in a further embodiment; the chemical reactor of the invention is adapted to operate at a temperature of 250°C to 500°C.

Features of the invention

1. A chemical reactor for an exothermal reaction comprising at least one reaction enclosure and at least one primary cooling medium enclosure configured to hold a fluid cooling medium under pressure at the boiling point of said cooling medium, the cooling medium enclosure at least partly encom^¬ passes said reaction enclosure, said reaction enclosure comprises an outer surface configured to be in thermal con^¬ tact with the cooling medium, said reaction enclosure comprises a reaction enclosure inlet and a reaction enclosure outlet and said cooling medium enclosure comprises a cool^¬ ing medium inlet and a cooling medium outlet, wherein said reactor further comprises a secondary cooling medium enclosure which is in fluid contact with the at least one pri^¬ mary cooling medium enclosure, the reaction enclosure at least partly encompasses said secondary cooling medium en^¬ closure . 2. A chemical reactor according to feature 1, wherein said secondary cooling medium enclosure is centrally arranged along the center line of the chemical reactor. 3. A chemical reactor according to any of the preceding features, wherein said secondary cooling medium enclosure is cylindrical and comprises a first cooling medium connec^¬ tion to the primary cooling medium enclosure in the lower end of the secondary cooling medium enclosure and a second cooling medium connection to the primary cooling medium enclosure in the upper end of the secondary cooling medium enclosure .

4. A chemical reactor according to any of the preceding features, where the primary cooling medium enclosure com^¬ prises a cylindrical inner wall.

5. A chemical reactor according to any of the preceding features, where the primary cooling medium enclosure, the reaction enclosure and the secondary cooling medium enclosure are arranged concentric.

6. A chemical reactor according to any of the preceding features, wherein the cooling medium enclosures are adapted to operate with oil as cooling medium.

7. A chemical reactor according to any of the preceding features, wherein the reaction enclosure is adapted to op^¬ erate with a formaldehyde catalyst.

8. A chemical reactor according to any of the preceding features, wherein the cooling area, A_COOL to reaction vol^¬ ume, VREACTION ratio is: 4 nr¹ > A_COOL / V_REACTION > 1 m^"1.

9. A chemical reactor according to any of the preceding features, wherein the cooling area, A_COOL to reaction vol^¬ ume, VREACTION ratio is: 2 nr¹ > A_COOL / V_REACTION > 1 m^"1.

10. A chemical reactor according to any of the preceding features, wherein the ratio between the outer diameter of the reaction enclosure, D_REACTION and the outer diameter of the secondary cooling medium enclosure, D_COOL2 is: 3 > D_REAC-

TION / DcoOL2 > 1 ·

11. A chemical reactor according to any of the preceding features, wherein the ratio between the outer diameter of the reaction enclosure, D_REACTION and the outer diameter of the secondary cooling medium enclosure, D_COOL2 is: 2 > D_REAC-

TION / DcoOL2 > 1 · 12. A chemical reactor according to any of the preceding features, further comprising a catalytically active mate^¬ rial inside at least 50% or 80% of the volume of the reac^¬ tion enclosure. 13. A chemical reactor according to any of the preceding features adapted to operate at a temperature of 250 °C to 500°C.

Brief description of the drawings

Embodiments of the present invention are explained by way of example and with reference to the accompanying drawings. It is to be noted that the appended drawings illustrate only examples of embodiments of this invention and they are therefore not to be considered limiting of its scope, for the invention may admit to other effective embodiments.

Fig. 1 shows a cross sectional side view of a centrally cooled reactor according to an embodiment of the invention,

Fig. 2 shows a cross sectional top view of a cooled reactor as known in the art related to the invention, and

Figs. 3 and 4 show a cross sectional top view of a cen^¬ trally cooled reactor according to two embodiments of the invention .

Position numbers

01. Chemical reactor

02. Reaction enclosure

03. Primary cooling medium enclosure

04. Reaction enclosure outer surface

05. Secondary cooling medium enclosure

06. First cooling medium connection

07. Second cooling medium connection

08. Cylindrical inner wall of the primary cooling me^¬ dium enclosure

09. Cooling medium

10. Catalyst An embodiment of the invention is shown in Fig. 1 where the chemical reactor 01 is seen in a cross sectional side view. Within the reactor is a reaction enclosure 02 which serves to hold a catalyst 10 (not shown in details) . When process fluid is provided to the reaction enclosure at proper con^¬ ditions such as temperature and pressure, the catalyst en^¬ hances the chemical reaction in the reaction chamber. The process fluid enters the reaction enclosure through a reac^¬ tion enclosure inlet (not shown) and exits through a reac^¬ tion enclosure outlet (not shown) .

The reactor according to invention is well suited for exo- thermal reactions because cooling of the reaction enclosure is optimized. A primary cooling medium enclosure 03 encompasses or at least partly encompasses the reaction enclo^¬ sure. The cylindrical inner wall of the primary cooling me^¬ dium enclosure 08 is also the reaction enclosure outer sur- face 04. Hence, the reaction enclosure is in thermal con^¬ tact with the cooling medium 09 comprised in the primary cooling medium enclosure to provide an efficient heat ex^¬ change between the reaction enclosure and the primary cool^¬ ing medium enclosure. The cooling medium enters the primary cooling medium enclosure via a cooling medium inlet (not shown) and exits the cooling medium enclosure via a cooling medium outlet (not shown) .

According to the invention and as shown in Fig. 1, the chemical reactor further comprises a secondary cooling medium enclosure 05. In the embodiment shown, the secondary cooling medium enclosure is centrally arranged in the reac^¬ tor and centrally in the reaction enclosure, such that the reaction enclosure encompasses or at least partly encom- passes the secondary cooling medium enclosure. This has, among others, the advantages that the largest distance from a catalyst within the reaction enclosure to a cooling surface is reduced and that the reduction of the effective re^¬ action enclosure volume to allow for the secondary cooling medium enclosure is minimal. As shown in Fig. 1, the sec- ondary cooling medium enclosure is provided with cooling medium from the primary cooling medium enclosure via a first cooling medium connection 06 which in this embodiment is arranged in the lower end of the secondary cooling me^¬ dium enclosure. The cooling medium flows through the sec- ondary cooling medium enclosure in thermal contact with the reaction enclosure, providing central cooling by means of heat exchange to the reaction enclosure. The cooling medium then exits the secondary cooling medium enclosure back to the primary cooling medium enclosure via a second cooling medium connection 07. Thus, according to this embodiment of the invention, the construction of the reactor is kept simple with the necessity of only one external cooling medium inlet and one external cooling medium outlet. The reactor is adapted to operate with a cooling medium under pressure. This involves selection of appropriate mate^¬ rial, design of the shapes and material thickness among other parameters as known in the art. In an embodiment the cooling medium may be oil. In Fig. 1 a typical operation situation is shown where the cooling medium is boiling, bubbles of gas phase of the cooling medium is shown. As mentioned, the operating temperature may be controlled by varying the pressure of the cooling medium and by selecting a cooling medium with an appropriate boiling temperature. The ability of keeping a constant operation temperature in the reactor according to the invention is improved by the feature of the secondary cooling medium enclosure. Furthermore, the ability to operate with a two-phase cooling me^¬ dium enhances the stability of the operation temperature, since the phase shift from liquid to gas requires a surplus of energy in addition to the energy required to raise the temperature. Thus, the reactor according to the invention is well suited for even strongly exothermal reactions, such as reactions with a formaldehyde catalyst. The difference between the invention according to the claims and the known art is clearer when comparing the known art chemical reactor as shown in a top cross sec^¬ tional view in Fig 2. and the chemical reactors according to embodiments of the invention as shown in Fig. 3 and Fig. 4. The known art reactor according to Fig. 2 has a cooling medium enclosure encompassing a reaction enclosure, whereas the reactor according to the invention shown in Fig. 3 and Fig. 4 further comprises a secondary cooling medium enclosure in different relative sizes. In Fig. 3, the size of the secondary cooling medium enclosure is larger relative to the reaction enclosure than in Fig. 4, which means that the cooling area relative to the reaction volume of the re^¬ actor according to the embodiment shown in Fig. 3 is larger than in the embodiment shown in Fig. 4. The trade-off which must be calculated is the cost of equipment and operation relative to the process output. This may vary according to the process in question, process parameters and catalyst type etc. Thus the embodiments shown in Fig. 3 and Fig. 4, as well as further embodiments not shown in the Figures but described according to the claims, may each be the best choice in different situations. Furthermore, the design and shape of the reaction and cooling medium enclosures may vary as best suited for a specific situation. Example . A study has been made in which a center cooling tube was added to each reactor tube in an FK formaldehyde catalyst reactor, connected it to the main cooling bath. Modelling shows that this lowers the temperature and the radial tem^¬ perature spread in the reactor tubes. This leads to an in- crease in the catalyst lifetime by a factor of 3 while keeping the same yield.

A simple implementation of the invention as described in the foregoing is to connect the inner cooling tube (the secondary cooling medium enclosure) to the oil bath in the primary cooling medium enclosure.

In the table, the parameters for three basic cases, a) to c) was calculated and normalized to the standard case, a) where no internal cooling tube is present in the reaction enclosure .

D_CAT is the diameter of the catalyst tube (reaction enclo- sure) and D_COOL is the diameter of the inner cooling tube

(secondary cooling medium enclosure) . n_tUbe s is the number of tubes that can be fit in a reactor covering a given area

(normalized to 1 for case a) ) . V_CAT per tube is the catalyst which can fit into a single tube. V_{t o}tai CAT = V_{CAT pe r} tube ritu_bes is the total catalyst which can fit into all the tubes. ΓΜΑΧ is the maximum distance between a catalyst par^¬ ticle and a cooling wall. As can be seen, case a) naturally allows more catalyst into the reactor vessel. The difference to case b) and c) is large however.

It is also seen that case b) only requires the loading of a quarter of the cubes of case a) . Case c) only requires 1/9 the tubes of case a) . Fewer tubes to load gives a time sav^¬ ing during reload of the cat tubes.

It is further seen that case b) has only half the maximum distance from a catalyst particle to a cooling wall, r^_¾x than case a) This is true for all cases where 0 < D_CAT ^~ DCOOL < 2. 1/r_MAx is used as a proxy for the heat exchange efficiency between the oil bath in the cooling medium enclosures and the catalyst. This leads to the conclusion that case b) has a much better heat exchange than case a) .

A better heat exchange means that the radial temperature profile is more flat which entails large advantages:

• Heating of the catalyst in the top of the reactor is much faster and the reaction starts quicker.

• If a maximum temperature is a condition (for selectivity or lifetime reasons) the oil bath temperature can be increased which leads to much more reaction activity of the coldest parts of the catalyst near the re- actor walls. This is a large catalyst volume which suddenly becomes important and this should more than compensate for lower V_totai CAT in case b) . • If a certain conversion rate is a condition, the maximum temperature of the reactor can be significantly reduced compared to case a) and consequently a much longer lifetime and higher selectivity is achievable. · If the bottom connection tube (first cooling medium connection) is raised to the middle of the reactor, it is possible to cool the bottom part of the reactor less than the top, which would ensure higher tempera^¬ ture and thus higher activity in the bottom for a given oil temperature.

Thus the advantages of the invention are plural: faster cat loading, better process control, and better yield to men^¬ tion some.

In a GIPS (GENRAD) study the cases a) to c) are studied more detailed.

Case a) :

Flow (10000 tubes) : 814 kmol/h.

Temperature: 265°C.

Inner diameter Cat tube. 22 mm.

Outer diameter Cat tube: 26 mm. Case b) , same flow as for case a), only ¼ of the tubes: Flow (2500 tubes) : 814 kmol/h.

Temperature 265°C.

Inner diameter cooling tube: 22 mm.

Outer diameter cooling tube: 26 mm.

Inner diameter Cat tube: 48 mm.

Outer diameter Cat tube: 52 mm. Case c) , same flow as for case a), only 1/9 of the tubes:

Flow (1111 tubes) : 814 kmol/h.

Temperature 265°C.

Inner diameter Cat tube. 22 mm.

Outer diameter Cat tube: 26 mm.

Inner diameter Cat tube: 74 mm.

Outer diameter Cat tube: 78 mm.

In the table above, the yield and selectivities of the standard operation points for case a) to c) are tabulated. There is a slight yield increase when using case b) rather than case a) . This is primarily due to a larger C¾0 selec^¬ tivity, as the conversion is somewhat lower in case b) than in case a) .

Contour plots of the temperatures in the three standard cases show that case a) has a hotspot above 390°C at the reactor center line. In case b) , the catalyst is cooled from both its inner and outer periphery and does not have hot spot, but a maximum temperature around 350 °C.

In the inert section of the reaction enclosure, case a) and case b) heat up equally fast. While case b) has better heat exchange suggesting it should heat up faster, this is off^¬ set by the larger gas flow and thus larger heat capacity per catalyst volume. Case c) has worse heat exchange than both case a) and case b) and only heats up slowly. Case a) has a strong hot spot with a temperature of 400°C at the center line and a temperature of 356°C at the reac^¬ tor perimeter. Case b) has a less expressed hot spot with a temperature of 359°C and 340°C.

While the yields of case a) and case b) are comparable, an important factor is also the lifetime of the catalyst. The FK catalyst primarily ages due to Mo volatization in the hot spot. The volatization rate increases by a factor of 10 per 100 K, meaning that the 40 K lower maximum temperature in case b) should cause the catalyst lifetime to increase by a factor 3. The reference conditions were designed for the best performance of case a) . They have not been adapted to case b) , which means that case b) can be further opti^¬ mized.

The comparatively narrower temperature spread for case b) should allow for an increase of the temperature in the hot spot to get a higher conversion. This can be done by in^¬ creasing the FK concentration in the diluted part of the reaction enclosure, or by increasing the oil bath tempera^¬ ture. The overall conclusion is that the hot spot tempera^¬ ture can be reduced without decreasing neither the conver- sion nor the yield. This suggests an estimated lifetime in^¬ crease of the catalyst by at least a factor 3 as compared to known art reactors .

Claims

1. A chemical reactor for an exothermal reaction comprising at least one reaction enclosure and at least one primary cooling medium enclosure configured to hold a fluid cooling medium under pressure at the boiling point of said cooling medium, the cooling medium enclosure at least partly encompasses said reaction enclosure, said reaction enclosure comprises an outer surface configured to be in thermal con- tact with the cooling medium, said reaction enclosure comprises a reaction enclosure inlet and a reaction enclosure outlet and said cooling medium enclosure comprises a cool^¬ ing medium inlet and a cooling medium outlet, wherein said reactor further comprises a secondary cooling medium enclo- sure which is in fluid contact with the at least one pri^¬ mary cooling medium enclosure, the reaction enclosure at least partly encompasses said secondary cooling medium en^¬ closure .

2. A chemical reactor according to claim 1, wherein said secondary cooling medium enclosure is centrally arranged along the center line of the chemical reactor.

3. A chemical reactor according to any of the preceding claims, wherein said secondary cooling medium enclosure is cylindrical and comprises a first cooling medium connection to the primary cooling medium enclosure in the lower end of the secondary cooling medium enclosure and a second cooling medium connection to the primary cooling medium enclosure in the upper end of the secondary cooling medium enclosure.

4. A chemical reactor according to any of the preceding claims, where the primary cooling medium enclosure com^¬ prises a cylindrical inner wall.

5. A chemical reactor according to any of the preceding claims, where the primary cooling medium enclosure, the re^¬ action enclosure and the secondary cooling medium enclosure are arranged concentric.

6. A chemical reactor according to any of the preceding claims, wherein the cooling medium enclosures are adapted to operate with oil as cooling medium.

7. A chemical reactor according to any of the preceding claims, wherein the reaction enclosure is adapted to oper- ate with a formaldehyde catalyst.

8. A chemical reactor according to any of the preceding claims, wherein the cooling area, A_COOL to reaction volume, VREACTION ratio is: 4 nr¹ > A_COOL / V_REACTION > 1 m^"1.

9. A chemical reactor according to any of the preceding claims, wherein the cooling area, A_COOL to reaction volume, VREACTION ratio is: 2 nr¹ > A_COOL / V_REACTION > 1 m^"1.

10. A chemical reactor according to any of the preceding claims, wherein the ratio between the outer diameter of the reaction enclosure, D_REACTION and the outer diameter of the secondary cooling medium enclosure, D_COOL2 is: 3 > D_REACTION /

11. A chemical reactor according to any of the preceding claims, wherein the ratio between the outer diameter of the reaction enclosure, D_REACT ION and the outer diameter of the secondary cooling medium enclosure, D_COOL2 is: 2 > D_REACT ION /

12. A chemical reactor according to any of the preceding claims, further comprising a catalytically active material inside at least 50% or 80% of the volume of the reaction enclosure .

13. A chemical reactor according to any of the preceding claims adapted to operate at a temperature of 250 °C to 500°C.