WO2010069482A1

WO2010069482A1 - Process for preparing sulphur trioxide

Info

Publication number: WO2010069482A1
Application number: PCT/EP2009/008666
Authority: WO
Inventors: Ralph Schellen; Leslaw Mleczko; Verena Haverkamp; Evin Hizaler Hoffmann; Stephan Schubert
Original assignee: Bayer Technology Services Gmbh
Priority date: 2008-12-20
Filing date: 2009-12-04
Publication date: 2010-06-24
Also published as: DE102009025510A1

Abstract

The present invention relates to a process for preparing sulphur trioxide by catalytic gas-phase oxidation of sulphur dioxide by means of oxygen, in which the reaction is carried out under adiabatic conditions over from 5 to 40 catalyst beds connected in series.

Description

Process for the preparation of sulfur trioxide

The present invention relates to a process for the preparation of sulfur trioxide by catalytic gas phase oxidation of sulfur dioxide with oxygen, wherein the reaction is carried out on 4 to 40 catalyst beds connected in series under adiabatic conditions.

Sulfur trioxide is generally produced under catalytic influence of gaseous sulfur dioxide and gaseous oxygen vanadium catalysts in an exothermic, catalytic equilibrium reaction according to formula (I):

2 ^■ SO ₂ (g) + O ₂ (g) → 2 ^■ SO ₃ (g); ΔH = -196 kJ / mol (I)

The sulfur trioxide prepared by the reaction of formula (I) forms an essential precursor for, for example, the synthesis of sulfuric acid, which in turn is an essential basic chemical for many chemical processes. However, the sulfur trioxide can also be used directly for further conversion, for example with alcohols, so that alkyl sulfides are obtained from such processes, which are used as surfactants.

The removal and use of the heat of reaction is of great importance in carrying out the sulfur trioxide synthesis. An uncontrolled increase in temperature can lead to permanent damage to the particular catalyst used. On the other hand, at high temperatures, there is an unfavorable shift in the reaction equilibrium according to the formula (I) in the direction of the educts with a corresponding deterioration of the yield and / or of the conversion. However, a high purity of the product gas stream of sulfur trioxide is necessary in particular in a further use, for example, according to the surfactant preparation described above, so that a high conversion is necessary in such cases.

It is therefore advantageous to maintain the temperature of the catalyst bed controlled in the course of the process at a level which allows a quick turnover while minimizing the re-reactions and / or catalyst inactivation.

A process for the production of sulfur trioxide is disclosed in WO 2008 052 649 A1. Herein, a process gas mixture comprising sulfur dioxide and oxygen is reacted in a quasi-isothermal process to sulfur trioxide. The process is carried out in a tube contactor with the reaction zones in the tubes and fixed beds of catalyst material in these tubes. The catalyst materials may be vanadium pentoxides having promoters such as supported potassium or sodium salts. The method according to WO 2008 052 649 A1 is operated such that in the reaction zones a temperature of 640 ° C is not exceeded. This is on the one hand ensured by inlet temperatures of the process gases from 360 ⁰ C to 450 ⁰ C and on the other hand by intensive cooling of the reaction zones on the outer surfaces of the tubes.

The process disclosed in WO 2008 052 649 A1 is not adiabatic. Also, no spatially separate adiabatic reaction zones and heat exchange zones are disclosed.

A process in which no direct cooling of the reaction zones is provided is disclosed in DE 202 68 18 B2. Here, the process gases oxygen and sulfur dioxide are reacted in one embodiment in four series reaction zones to sulfur trioxide and subsequently fed to a gas scrubber, wherein a partial stream is returned to the four series reaction zones.

DE 202 68 18 B2 does not disclose the possibility of more than four reaction zones connected in series and also does not provide the possibility between these heat exchange zones.

The method according to DE 202 68 18 B2 is disadvantageous since an exact temperature control, in particular between the reaction zones, is not possible. Should be in an accident

Excess starting material to be introduced into the reaction zones, this leads to a strong

Temperature increase in at least one of the four reaction zones, which no longer means of a

Heat exchange zone can be collected for the subsequent reaction zone. The consequence is irreversible destruction of the catalyst in at least one of the reaction zones of the process. Next, the yield and the sales are unfavorable

Equilibrium position of the reaction according to formula (I) at such temperatures very disadvantageous.

A further developed process variant is disclosed in DE 102 497 82 A1. In a process variant according to DE 102 497 82 A1, the process gas comprising sulfur dioxide and oxygen is first preheated in a first heat exchange zone and then converted to sulfur trioxide in a first reaction zone. Thereafter, the process gas is brought back into contact with the same heat exchange zone and introduced into another reaction zone. According to the disclosure of DE 102 497 82 A1, this happens at least twice in succession. The method according to DE 102 497 82 A1 is therefore also characterized in that on the one hand the process gas is brought into contact more than once with the same heat exchanger and it is further disclosed for this purpose that the heat exchangers and the reaction zones are in direct spatial contact with each other, which is even disclosed as advantageous.

It follows that the reaction zones can not be operated adiabatically by the direct contact between these and the aforementioned heat exchangers. An exact one Thus, temperature control is likewise not possible with the method according to DE 102 497 82 A1, as well as according to the method of the aforementioned WO 2008 052 649 A1, so that at least in partial regions of the reaction zones of DE 102 497 82 A1 significant non-flowing temperature gradients, to be expected with the aforementioned negative consequences on sales and yield. In this context, the necessity of intermediate washing of the process gases in the context of the process according to DE 102 497 82 A1 naturally appears to be necessary in order to prevent unfavorable conversions / yields. However, the necessity of intermediate washing is disadvantageous as such because it requires a further energy-intensive thermodynamic separation step if the sulfur trioxide is to be recovered from the intermediate wash product. In addition, this is expensive in terms of apparatus.

EP 1 251 951 (B1) discloses a device and the possibility of carrying out chemical reactions in the device, wherein the device is characterized by a cascade of reaction zones in contact with one another and heat exchanger devices which are arranged in a composite with one another. The method to be carried out here is thus characterized by the contact of the various reaction zones with a respective heat exchanger device in the form of a cascade. There is no disclosure as to the usability of the apparatus and method for the synthesis of sulfur trioxide from gaseous oxygen and sulfur dioxide. Thus, it remains unclear how, starting from the disclosure of EP 1 251 951 (B1), such a reaction should be carried out by means of the device and the method carried out therein.

Further, for the sake of uniformity, it is to be understood that the method disclosed in EP 1 251 951 (B1) is carried out in a device the same as or similar to the disclosure regarding the device. As a result, by the large-area contact of the heat exchange zones with the reaction zones according to the disclosure, a significant amount of heat is transferred by heat conduction between the reaction zones and the adjacent heat exchange zones. The disclosure with regard to the oscillating temperature profile can therefore only be understood as meaning that the temperature peaks ascertained here would be stronger if this contact did not exist. Another indication of this is the exponential increase in the disclosed temperature profiles between the individual temperature peaks. These indicate that there is some heat sink of appreciable but limited capacity in each reaction zone which can reduce the temperature rise in it. It can never be ruled out that a certain dissipation of heat (eg by radiation) takes place; however, with a reduction in the possible removal of heat from the reaction zone, a linear or, in its gradient, degressive Indicate temperature course, since at higher temperatures, the equilibrium of exothermic reactions on the side of the starting materials shifts and thus reduce the reaction rate and with it the generated heat of reaction. Thus, EP 1 251 951 (B1) discloses multi-stage processes in cascades of reaction zones from which heat in an undefined amount is removed by heat conduction. Accordingly, the disclosed method is disadvantageous in that accurate temperature control of the process gases of the reaction is not possible.

It would therefore be advantageous to provide a method that can be carried out in simple reaction devices and that allows for accurate, simple temperature control so that it allows high conversions with the highest possible purity of the product. Such simple reaction devices would be easily scaled up and are inexpensive and robust in all sizes.

For the catalytic gas phase oxidation of sulfur dioxide with oxygen to sulfur trioxide, as has just been described, neither suitable reactors have yet been described, nor are suitable processes disclosed that permit this.

It is therefore an object to provide a method for catalytic gas phase oxidation of sulfur dioxide and oxygen to sulfur trioxide, which can be carried out under accurate temperature control in a simple reaction apparatus and thereby high conversions at high purities of the product allowed, the heat of reaction, for example, to set an advantageous temperature level can be used for the reaction or steam generation.

It has surprisingly been found that a heterogeneously catalyzed process for the preparation of sulfur trioxide in the gas phase, which is characterized in that it comprises a conversion of sulfur dioxide with oxygen to sulfur trioxide in 5 to 40 successive reaction zones under adiabatic conditions in the presence of heterogeneous catalysts and At least the emerging from a reaction zone process gas is then passed through at least one of these reaction zone downstream heat exchange zone, this task is able to solve.

Sulfur dioxide in the context of the present invention refers to a process gas which is introduced into the process according to the invention and which essentially comprises sulfur dioxide.

Essentially, in the context of the present invention, a proportion of more than 90% by weight. Oxygen, in the context of the present invention, denotes a process gas which is introduced into the process according to the invention and which essentially comprises oxygen.

In addition to the essential components of the process gases oxygen and sulfur dioxide, these can also include secondary components. Non-exhaustive examples of minor components that may be included in the process gases include nitrogen, carbon dioxide, argon, other noble gases, and water vapor.

In general, in connection with the present invention, process gases are understood as gas mixtures which comprise oxygen and / or sulfur dioxide and / or sulfur trioxide and / or secondary components. Essentially, however, process gases include oxygen and / or sulfur dioxide and / or sulfur trioxide.

According to the invention, carrying out the process under adiabatic conditions essentially means that the reaction zone is neither actively supplied with heat nor heat withdrawn from the outside. It is well known that complete isolation against heat transfer or removal is possible only by complete evacuation, excluding the possibility of heat transfer by radiation. Therefore, in the context of the present invention, adiabat means that no heat supply or removal measures are taken.

In an alternative embodiment of the method according to the invention, however, e.g. by isolation by means of well-known isolation means, e.g. Polystyrene insulating materials, or by sufficiently large distances to heat sinks or heat sources, wherein the insulating agent is air, a heat transfer can be reduced.

An advantage of the adiabatic driving method according to the invention of the 5 to 40 reaction zones connected in series with respect to a non-adiabatic mode of operation is that no means for heat removal must be provided in the reaction zones, which entails a considerable simplification of the construction. This results in particular simplifications in the manufacture of the reactor and in the scalability of the process and an increase in reaction conversions. In addition, the heat generated in the course of the exothermic reaction may be utilized in a controlled manner in the single reaction zone to increase the conversion by allowing the process gases and reaction zone to increase in temperature to near equilibrium limitation as the reaction zone passes through.

Another advantage of the method according to the invention is the possibility of very accurate temperature control by the close staggering of adiabatic reaction zones. It can thus be adjusted in that reaction zone advantageous in the reaction progress temperature. The catalysts used in the process according to the invention are usually catalysts which consist of a material which, in addition to its catalytic activity for the reaction of the formula (I), is characterized by sufficient stability under the conditions of the process and by a high specific surface area. Catalyst materials characterized by such stability under the conditions of the process are, for example, vanadium pentoxide, platinum and / or uranium oxide.

Preference is given to uranium oxide.

Specific surface area in the context of the present invention refers to the area of the catalyst material that can be reached by the process gases, based on the mass of catalyst material used.

A high specific surface area is a specific surface area of at least 10 m ² / g, preferably of at least 20 m ² / g.

The catalysts of the invention are each in the reaction zones and can be used in all known forms, e.g. Fixed bed or fluidized bed, are present.

Preference is given to the appearance of the fixed bed.

The fixed bed arrangement comprises a catalyst bed in the true sense, d. H. loose, supported or unsupported catalyst in any form and in the form of suitable packings. The term catalyst bed as used herein also encompasses contiguous areas of suitable packages on a support material or structured catalyst supports. These would be e.g. to be coated ceramic honeycomb carrier with comparatively high geometric surfaces or corrugated layers of metal wire mesh on which, for example, catalyst granules is immobilized. As a special form of packing, in the context of the present invention, the presence of the catalyst in monolithic form is considered.

If a fixed-bed arrangement of the catalyst is used, the catalyst is preferably present in beds of particles with average particle sizes of 1 to 20 mm, preferably 2 to 15 mm, particularly preferably 5 to 10 mm.

Beds of such particles are advantageous because the particles have a high outer surface of the catalyst material compared to the process gases oxygen and sulfur dioxide due to their size and thus a high conversion rate can be achieved. Thus, the mass transport limitation of the reaction by diffusion can be kept low. At the same time, however, the particles are not yet so small that they lead to disproportionately high pressure losses Flow through the fixed bed comes. The ranges of the particle sizes given in the preferred embodiment of the process, comprising a reaction in a fixed bed, are thus an optimum between the achievable conversion from the reaction according to formula (I) and the pressure drop produced when carrying out the process. Pressure loss is coupled in a direct manner with the necessary energy in the form of compressor performance, so that a disproportionate increase in the same would result in an inefficient operation of the method.

Also preferably, the catalyst is in a fixed bed arrangement in monolithic form. Particularly preferred in a fixed bed arrangement is a monolithic catalyst consisting of uranium oxide at least on its surface.

In a preferred embodiment of the process according to the invention, the conversion takes place at from 5 to 30, more preferably from 5 to 20 reaction zones connected in series.

In a preferred further embodiment of the process, after each reaction zone is at least one, preferably exactly one heat exchange zone, through which the process gas leaving the reaction zone is passed.

The reaction zones can either be arranged in a reactor or arranged divided into several reactors. The arrangement of the reaction zones in a reactor leads to a reduction in the number of apparatuses used.

The individual reaction zones and heat exchange zones can also be arranged together in a reactor or in any combination of reaction zones with heat exchange zones in several reactors.

If reaction zones and heat exchange zones are present in a reactor, then in an alternative embodiment of the invention there is a heat insulation zone between them, in order to be able to support the adiabatic operation of the reaction zone.

In addition, each of the series-connected reaction zones can be replaced or supplemented independently of one another by one or more reaction zones connected in parallel. The use of reaction zones connected in parallel allows in particular their replacement or supplementation during ongoing continuous operation of the process.

Parallel and successive reaction zones may in particular also be combined with one another. However, the process according to the invention particularly preferably has exclusively reaction zones connected in series. The reactors preferably used in the process according to the invention can consist of simple containers with one or more reaction zones, as described, for example, in Ulimann's Encyclopedia of Industrial Chemistry (Fifth, Completely Revised Edition, VoI B4, pages 95-104, pages 210-216), wherein in each case between the individual reaction zones and / or heat exchange zones heat insulation zones can be additionally provided.

In an alternative embodiment of the method, there is thus at least one heat-insulating zone between a reaction zone and a heat exchange zone. Preferably, there is a heat isolation zone around each reaction zone.

The catalysts or the fixed beds thereof are mounted in a manner known per se on or between gas-permeable walls comprising the reaction zone of the reactor. Particularly in the case of thin fixed beds, technical devices for uniform gas distribution can be provided in the flow direction in front of the catalyst beds. These can be perforated plates or other internals that cause a uniform entry of the process gas into the fixed bed by generating a small but uniform pressure loss.

In a particular embodiment of the process according to the invention, a ratio of oxygen, based on the molar mass flow of sulfur dioxide, before entry into the reaction zone is preferably between 0.7 and 1.2, preferably between 0.8 and 1, particularly preferably from 0.8 to 0 , 9 used.

By increasing the ratio of oxygen to sulfur dioxide, on the one hand, the reaction can be accelerated and thus the space-time yield (produced amount of sulfur trioxide per

Mass of catalyst material) are increased, on the other hand, the equilibrium of the reaction is positively shifted in the direction of the product (sulfur trioxide). This can reduce the sales of the

Educt sulfur dioxide be increased. On the other hand, an excessive excess leads to an excessive increase in temperature at least in the first reaction zone, so that the equilibrium is disadvantageously shifted here.

In a further particularly preferred embodiment of the process the inlet temperature of the material entering the first reaction zone process gas of 380 to 45O ⁰ C, preferably of 400 to 450 ⁰ C.

In yet another particularly preferred embodiment of the process, the absolute pressure at the inlet of the first reaction zone is between 1.1 and 1.5 bar. In a further particularly preferred embodiment of the process, the residence time of the process gas in a reaction zone is between 0.1 and 100 s, preferably between 0.5 and 50 s, particularly preferably between 1 and 10 s.

The sulfur dioxide and the oxygen are preferably fed only before the first reaction zone. This has the advantage that the entire process gas for the absorption and removal of the

Reaction heat can be used in all reaction zones. In addition, by such a

Procedure, the space-time yield can be increased, or the necessary

Catalyst mass can be reduced. However, it is also possible to meter in sulfur dioxide and / or oxygen into the process gas as required before one or more of the reaction zones following the first reaction zone. About the supply of gas between the

Reaction zones can be controlled in addition to the temperature profile in the reaction zone.

In a preferred further development of the process, the process gas leaving the last reaction zone is at least partially reused by being introduced into one of the reaction zones. Most preferably, only the portion of the sulfur dioxide is reused by being introduced into the first reaction zone.

This further development is advantageous because the process gas at the outset of the last reaction zone essentially comprises only sulfur dioxide and sulfur trioxide and thus a further conversion of the sulfur dioxide with oxygen to sulfur trioxide can be achieved via reuse.

In a particularly preferred embodiment of the inventive method, the process gas is cooled after at least one of the reaction zones used, more preferably after each of the catalyst beds used. For this purpose, the process gas is passed after exiting a reaction zone through one or more of the above-mentioned heat exchange zones, which are located behind the respective reaction zones. These may be used as heat exchange zones in the form of heat exchangers known to those skilled in the art, e.g. Tube bundle, plate, Ringnut-, spiral, finned tube, microstructured heat exchanger be executed. Preference is given to microstructured heat exchangers.

In the context of the present invention, microstructured means that the heat exchanger for the purpose of heat transfer comprises fluid-carrying channels, which are characterized in that they have a hydraulic diameter between 50 μm and 5 mm. The hydraulic diameter is calculated as four times the flow cross-sectional area of the fluid-conducting channel divided by the circumference of the channel. In a particular embodiment of the method, steam is generated during cooling of the process gas in the heat exchange zones by the heat exchanger.

Within this further embodiment, it is preferable in the heat exchangers, which include the heat exchange zones, to carry out evaporation on the side of the cooling medium, preferably partial evaporation.

Partial evaporation referred to in the context of the present invention, an evaporation in which a gas / liquid mixture of a substance is used as a cooling medium and in which there is still a gas / liquid mixture of a substance after heat transfer in the heat exchanger.

The carrying out of evaporation is particularly advantageous because in this way the achievable heat transfer coefficient from / to the process gases to / from the cooling / heating media becomes particularly high and thus an efficient cooling can be achieved.

Performing a partial evaporation is particularly advantageous because the absorption / release of heat by the cooling medium thereby no longer results in a temperature change of the cooling medium, but only the gas / liquid balance is shifted. This has the consequence that over the entire heat exchange zone, the process gas is cooled to a constant temperature. This in turn safely prevents the occurrence of temperature profiles in the flow of process gases, thereby improving control over the reaction temperatures in the reaction zones and, in particular, preventing the formation of local overheating by temperature profiles.

In an alternative embodiment, instead of evaporation / partial evaporation, a mixing zone may also be provided upstream of the inlet of a reaction zone in order to standardize the temperature profiles, if appropriate during the cooling, in the flow of the process gases by mixing transversely to the main flow direction.

In a further preferred embodiment of the process, the successively geschalieteii reaction zones are operated at increasing or decreasing from reaction zone to reaction zone average temperature. This means that within a sequence of reaction zones, the temperature can be both increased and decreased from reaction zone to reaction zone. Thus, it may be particularly advantageous to allow the average temperature to first increase from reaction zone to reaction zone to increase the conversion and then to allow the average temperature in the following last reaction zone to decrease again to shift the equilibrium. This can be done, for example, by controlling the be set between the reaction zone connected heat exchange zones. Further options for setting the average temperature are described below.

The thickness of the flow-through reaction zones can be chosen to be the same or different and results according to laws generally known in the art from the residence time described above and the process gas quantities enforced in the process. The mass flows of product gas (sulfur trioxide) which can be carried out according to the invention with the method, from which the amounts of process gas to be employed, are usually between 0.01 and 60 t / h, preferably between 0.01 and 50 t / h, particularly preferably between 0, 03 and 40 t / h.

The maximum outlet temperature of the process gas from the reaction zones is usually in a range from 380 ^° C. to 650 ^° C., preferably from 400 ^° C. to 600 ^° C., more preferably from 420 ^° C. to 600 ^° C.

The control of the temperature in the reaction zones is preferably carried out by at least one of the following measures: dimensioning of the adiabatic reaction zone, control of heat dissipation between the reaction zones, addition of gas between the reaction zones, molar ratio of the reactants / excess sulfur dioxide used and / or oxygen, additive of inert gases, in particular nitrogen before and / or between the reaction zones.

The composition of the catalysts in the reaction zones according to the invention may be identical or different. In a preferred embodiment, the same catalysts are used in each reaction zone. However, it is also advantageous to use different catalysts in the individual reaction zones. Thus, especially in the first reaction zone, when the concentration of the reaction educts is still high, a less active catalyst can be used and in the further reaction zones the activity of the catalyst can be increased from reaction zone to reaction zone. The control of the catalyst activity can also be carried out by dilution with inert materials or carrier material. Also advantageous is the use of a catalyst in the first and / or second reaction zone, which is particularly stable against deactivation at the temperatures of the process in these reaction zones.

With the inventive method disclosed here, as well as its preferred further developments, a conversion of the sulfur dioxide from 95% to 99.9999%, in preferred embodiments from 99 to 99.9999% and in particularly preferred embodiments from 99.99% to 99.9999% be achieved. The inventive method is thus characterized by high space-time yields, combined with a reduction of the apparatus sizes and a simplification of the apparatus or reactors. This surprisingly high space-time yield is made possible by the interaction of the inventive and preferred embodiments of the new method. In particular, the interaction of staggered, adiabatic reaction zones with interposed heat exchange zones and the defined residence times allows precise control of the process and the resulting high space-time yields.

The present invention will now be described in more detail by way of examples and with the aid of drawings, without, however, restricting them to them.

1 shows temperature profile (T) and course of the conversion (U) of SO ₂ over the individual reaction zones (S) and heat exchange zones according to Example 1.

2 shows temperature profile (T) and course of the conversion (U) of SO ₂ over the individual reaction zones (S) and heat exchange zones according to Example 2.

Examples:

Example 1:

In this example, the process gas flows over a total of 7 fixed catalyst beds of vanadium (V) oxide, ie through 7 reaction zones. Each after a reaction zone is a heat exchange zone in which the process gas is cooled before it enters the next reaction zone. The process gases used at the beginning of the first reaction zone are pure sulfur dioxide and air in a ratio of 1: 1. The absolute inlet pressure of the process gases directly in front of the first reaction zone is 1.3 bar. The activity of the catalyst used is adjusted so that it substantially increases in the course of the reaction zones. With the exception of the third reaction zone, where it decreases again compared to the second reaction zone. That the catalyst of the first fixed catalyst bed is diluted with an inert material (quartz glass) to a concentration of 10% by weight. The exact relative catalyst activities are given in Table 1 with. There is no replenishment of gas before the individual catalyst stages.

Table 1: Catalyst activity in the reaction zones according to Example 1

The results are shown in FIG. Here, the individual reaction zones are listed on the x-axis, so that a spatial course of developments in the process is visible. The temperature of the process gas is indicated on the left y-axis. The temperature profile over the individual reaction zones is shown as a thick, solid line; the temperature curve to be obtained in the best case at infinitesimal small reaction zones is shown as a thin dashed line. Is on the right y-axis the total sales of sulfur dioxide indicated. The course of the conversion over the individual reaction zones is shown as a thick dashed line.

It can be seen that the inlet temperature of the process gas before the first reaction zone is about 400 ° C. Due to the exothermic reaction to SO ₃ under adiabatic conditions, the temperature in the first reaction zone rises to about 580 ⁰ C, before the process gas is cooled back to about 400 ° C in the downstream heat exchange zone .. The sequence of heating and cooling continues ,

A conversion of 99.9% of the sulfur dioxide used at the beginning of the first reaction zone, calculated from the remaining mass output of the last reaction zone, is obtained.

Example 2:

In this example, the process gas flows through a total of 5 packed catalyst beds of vanadium (V) oxide through 5 reaction zones. Each after a reaction zone is a heat exchange zone in which the process gas is cooled before it enters the next reaction zone. The process gases used at the beginning of the first reaction zone are pure sulfur dioxide and air in a ratio of 88% by volume of air and 12% by volume of sulfur dioxide. The absolute inlet pressure of the process gases is equal to that of Example 1. The activity of the catalyst used is adjusted so that it increases in the course of the reaction zones. That the catalyst of the first fixed catalyst bed is diluted with an inert material (quartz glass) to a concentration of 28% by weight. The exact relative catalyst activities are shown in Table 2. There is no replenishment of gas before the individual catalyst stages.

Table 2: Catalyst activity of the reaction zones according to Example 2

The results are shown in FIG. Here, the individual reaction zones are listed on the x-axis, so that a spatial course of developments in the process becomes visible. The temperature of the process gas is indicated on the left y-axis. The temperature profile over the individual reaction zones is shown as a thick, solid line; the temperature curve to be obtained in the best case at infinitesimal small reaction zones is shown as a thin dashed line. The total conversion of sulfur dioxide is indicated on the right-hand y-axis. The course of the conversion over the individual reaction zones is shown as a thick dashed line.

It can be seen that the inlet temperature of the process gas before the first reaction zone is again about 400 ° C. Due to the exothermic reaction to SO ₃ under adiabatic conditions, the temperature in the first reaction zone rises to about 500 ° C, before the process gas is cooled back to about 400 ° C in the downstream heat exchange zone. The sequence of heating and cooling continues, but over the reaction zones, the inlet temperatures of the process gases increase.

Claims

claims

1. A process for the preparation of sulfur trioxide in the gas phase, characterized in that it comprises a conversion of sulfur dioxide with oxygen to sulfur trioxide in 5 to 40 successive reaction zones under adiabatic conditions in the presence of heterogeneous catalysts and wherein at least the emerging from a reaction zone process gas then by at least one of these reaction zone downstream heat exchange zone is passed.

2. The method according to claim 1, characterized in that the conversion takes place in 5 to 30, preferably 5 to 20 successive reaction zones.

3. The method according to claim 1 or claim 2, characterized in that the

Input temperature of the entering into the first reaction zone process gas from 380 to 450 ⁰ C, preferably from 400 to 450 ⁰ C.

4. The method according to claim 1 to 3, characterized in that the absolute pressure at the entrance of the first reaction zone is between 1.1 and 1.5 bar.

5. The method according to any one of the preceding claims, characterized in that the

Residence time of the process gas in all reaction zones together between 0.1 and 100 s, preferably between 0.5 and 50 s, more preferably between 1 and 10 s.

6. The method according to any one of the preceding claims, characterized in that the catalysts are present in a fixed bed arrangement.

7. The method according to any one of the preceding claims, characterized in that the

Catalysts are present as monoliths.

8. The method according to claim 6, characterized in that the catalysts are present in beds of particles having average particle sizes of 1 to 10 mm, preferably 2 to 7 mm, particularly preferably 3 to 5 mm.

9. The method according to any one of the preceding claims, characterized in that after each reaction zone at least one, preferably a heat exchange zone is located, through which the process gas is passed.

10. The method according to any one of the preceding claims, characterized in that there is at least one heat insulation zone between a reaction zone and a heat exchange zone.

11. The method according to claim 10, characterized in that there is a heat insulation zone around each reaction zone.