DE2016614A1 - Exothermic oxidation in catalytic reactor - Google Patents

Abstract

Cylindrical reactor for the partial vapour phase catalytic oxidation of organic cpds. has solid catalyst chips (2-4 mm) charged into radially segmented beds interspaced by plate heat exchange elements of similar form and a typical surface or 10-100 m2/m3 reactor bed volume. The process is applicable to reactions with oxygen, releasing over 40 Kcal/mole; typical residence times of 0.1-15 secs. and linear bed velocities of 2-200 cm/s. are used. It is used, e.g. for propylene oxidation. The distribution of gas over the catalyst is uniform, and poisoning of the catalyst through side reactions is avoided so that it has a long-life.

Description

Apparatus and method for passing through exothermic catalytic Oxidation reactions Oxidation reactions that take place in the gas phase on solid catalysts proceed with strong heat development and in which the desired products Represent partial oxidation products, such as the oxidation of butenes and butadiene to acetic acid or maleic acid, from isobutylene to methacrolein, from Propylene to acrolein and acrylic acid, from methanol to formaldehyde, from o-xylene to Phthalic anhydride and the ammoxidation of propylene or o-xylene to acrylonitrile or phthalonitrile, must be driven through under isothermal conditions if possible to avoid side reactions or over-oxidation as a result of excessive heating to avoid the catalyst.

There are three known reactor and process principles: The isothermal Fluidized bed, the quasi-isothermal reaction tube and the metal mesh. The before and Disadvantages of the process principles mentioned have been described variously. In the fluidized bed reactor, although a uniform temperature is within the Catalyst layer largely reached because of the large spread of the residence time however, the fluidized bed is often less selective. The usability of the axial flow tubes through which there are also limits. The speed of response and thus the amount of heat developed per unit of time is at the entrance to the catalyst layer the highest; it decreases with the catalyst layer in accordance with the decreasing concentration the reactant more or less from. To local overheating in the first To avoid catalyst zones and thus over-oxidation, the heat transfer between the catalyst bed and the cooling medium must be achieved be done quickly enough.

Measures to increase the speed of this heat transfer consist in the fact that the cooling surface per unit volume of catalyst, for example by choosing smaller pipe diameters for tube furnaces or smaller ones Plate spacing in plate contact furnaces and increased by changing the profile of the pipes or by evaporative cooling of the tubes using moving heat transfer media with high thermal conductivity or heat transfer coefficients, the heat transfer resistance or by increasing the linear gas velocity of the reaction gases with unchanged To reduce the volume of the heat transfer resistance on the inside of the pipe tried (= extension of the pipes).

The reduction of the pipe diameter is limited by that the ratio of grain diameter to pipe diameter is at least 1: 5 to 1: 8 must be to have a relatively uniform residence time over the pipe cross-section to reach. Since the catalyst has a grain size of less than 3 - 4 mm only in the form of grit can be used, which in the usual technical dump heights of 200 up to 300 cm due to lower abrasion resistance and less favorable aerodynamic properties Dimensions leads to high pressure losses, pipe diameters also represent cost reasons of 15 mm is the lowest limit used in practice. The dumping height of the catalyst and thus the linear velocity for a given volume loading the upper limit of the reaction gases is limited by the pressure loss. Dumping heights of over 250 - 300 cm or linear speeds of over 1.5 - 2 m / sec are therefore barely used. Since with an increase in the linear gas velocity, the pressure loss increases quadratically, is corresponding to the pressure dependence of the reaction rate the ratio of heat development at the beginning and end of the layer with increasing linear velocity less favorable.

A general disadvantage of tube ovens or plate ovens with parallel arranged plates is that the pipe diameter or

The distance between the plates must be adjusted to the heat development at the entrance to the shift got to; the rest of the catalyst layer is oversized with regard to the heat exchange surface.

Another disadvantage of the types of furnace mentioned is that the Gas inlet temperature is fixed, so that the height and position of the temperature peak at Beginning of the shift and the optimal axial temperature distribution when the catalyst activity decreases in the course of the operating time only about the temperature of the surrounding Cooling medium can be adjusted. Because the activity at the location of the temperature peak is stronger is damaged, the temperature peak migrates to the exit of the shift in the course of the exposure time and becomes flatter; the decline in sales is caused by an increase in the bath temperature If an attempt is made to compensate, the undamaged catalyst sections are also used raised to a temperature level that is less favorable for them and, as a result, the continued or accelerated total oxidation of the desired intermediate products. The effects force often to the reaction at low, for example well below the lower Carry out explosive limits lying substrate concentrations, whereby the theoretically achievable tent yields are undercut and various disadvantages the high air dilution, such as high pressure loss, making it difficult to separate the condensable fractions from the exhaust gas must be accepted.

It was therefore necessary to have a device that avoids the disadvantages indicated for carrying out exothermic catalytic reactions.

The solution to the problem consists in a cylindrical reactor for Carrying out partial catalytic oxidation reactions of gaseous organic Connections to solid catalysts, each with a nozzle for the inlet of the reaction gas mixture and the exit of the reaction products and with a Device for heating and cooling the reaction space filled with catalyst is provided, which is designed so that mutually reactive gaseous substances flow through the catalyst layer radially, the cylindrical reactor having a Cross-section ', in the center of which there is a circular gas supply (1) is located around which an in-circular ring sectors (2 and 3) divided inner annulus is arranged, which in turn is surrounded by a further outer annular space (4) -is, the circular ring sectors of the inner annular space alternating as with catalyst to be filled reaction chambers (2) with radial gas supply '(1) from the center to outer as a collector for the ': resulting reaction products formed annulus- (4) - and than with the heating and Cooler related heat exchangers (3), in which the cooling medium passes the reactor perpendicular to the radial direction of flow the reaction gases is guided, are formed.

In the figure 1 is a schematic example in cross section Embodiment of the device according to the invention shown and is the radial guide of the gases drawn schematically through the catalyst sectors.

The gas mixture to be converted generally enters the central gas supply (1) and flows radially through a perforated plate or wire mesh into the catalytic converter filled ancient ring sectors (2). The converted gas mixture is in the annulus (4) collected and discharged at (5). The sectors (3) are plate heat exchangers, through which is pumped in the axial direction of the cooling liquid. If necessary, plate heat exchangers can be used be installed with plane-parallel walls.

The heat of reaction absorbed by the cooling medium is transferred via heat exchangers, which can be located in the central annulus (1) or outside the reactor, released again.

The ratio of the through the partition walls between the annulus sectors formed cooling surfaces (6) to the volume of the reaction spaces to be filled with catalyst (2) behaves like 10 m2 / m3 to 200 m22 / m3, preferably the ratio is 30 m2 / m3 to 100 m / m3. The distance between the cooling plates at the gas inlet is between 7 mm and 40 mm, preferably 10 mm to 25 mm.

This arrangement has the particular advantage that the main flow resistance at the entrance to the catalyst sectors (2), so that in all catalyst sectors uniform gas supply is guaranteed.

In addition, the special spatial arrangement of the catalytic converter the heat exchange surfaces are adapted to the course of the reaction in the form of circular ring sectors. Sales and thus the heat of reaction is at the entrance to the catalyst sectors largest, namely where the distance between the cooling surfaces is smallest and thus the cooling effect is greatest.

This will damage the catalytic converter from overheating and side reactions as well as over-oxidation are prevented and at the same time the service life is prevented of the catalytic converter is extended considerably.

For the design of the radial flow furnace there is a ratio outer diameter to height of 1: 1 to 1: 3 advantageous.

The diameter of the central gas supply is expedient (1) for the radial dimensioning of the annular space from Eühl and catalyst sectors like 1 : 1 to 1: 4 and for the radial dimensioning of the outer annular space (4) as 1: 0.01 up to 1: 0.5.

Filler nozzles are provided to fill the catalyst chambers. It It can be advantageous that the catalyst sectors which are continuous from top to bottom are divided into floors, perforated floors are advantageously used, a uniform Allow corrugation of sectors with catalyst.

A molten salt made of KN03, NaNO3, NaNO2; Water; Diphenyl or others suitable for evaporative cooling or heat dissipation Liquids.

The usual materials are used as building material.

The reactor described is particularly suitable for implementation of partial catalytic oxidations of gaseous organic compounds on solid catalyst in gas mixtures containing molar oxygen which the released heat of reaction is more than 40 toal / mol, using of concentrations of the gaseous organic compounds at or above the lower explosion limit, with the mean Verwailzeiten of the reaction gas mixture be between 0.1 and 15 seconds and at Passing the catalyst layer a linear gas velocity of the reaction gas mixture between 200 cm / sec and 2 cm / sec is observed.

Partial catalytic oxidations which run exothermically in the gas phase organic compounds with molecular oxygen, possibly water vapor and optionally gas mixtures containing ammonia and inert gases, such as oxidations of saturated or unsaturated hydrocarbons and aromatics, aliphatic and aromatic alcohols or aldehydes, can advantageously be used in the described Radial flow furnace with high space-time yields per unit volume of catalyst, while avoiding side reactions and at the same time having a long service life of the catalyst carry out.

The gas is supplied through the central pipe (1). Possibly the incoming reaction gas mixture is heated to the required temperature, by having huber heat exchangers, which in a particularly advantageous embodiment are in connection with the coolant circulation, is conducted. The heat exchange or the heating of the reaction gases to the required reaction temperature can take place in the central gas supply space or outside the reaction. The smaller In general, the higher the linear velocity, the higher the gas must be preheated, in order to obtain the same conversion under otherwise identical operating conditions.

The procedure is effective both at lower substrate concentrations as well as relatively high concentrations above the lower explosion limit carried out and for oxidation reactions, in which one reaction product of more than 40 Kcal / mol is released, is suitable.

The optimum for a desired catalytic oxidation reaction Residence times, which are usually between 0.1 and 15 seconds, are thereby adhered to that depending on the radially flowed through layer thickness of the Catalyst maintained a certain linear gas velocity of the reaction gas will The volume flow is below the linear gas velocity of the reaction gas, calculated under normal conditions, based on the flow Cross-sectional area of the reaction space, understood. The linear gas velocity influences the course of the reaction in the reactor, especially in the area of high reaction rates, i.e. at high substrate concentrations above the lower explosion limit. With with increasing linear speed, the pressure loss increases quadratically and thus the heat development corresponding to the pressure dependence of the rate of oxidation in the entry layer. In addition, if the linear speeds are too high, the development of heat become too big in the hot spot and the reactor tends to "run away" more than at low linear speeds. Therefore, a certain linear velocity should are not exceeded in the catalytic converter 0 The concept of linear velocities not too high in ver, -relatively short catalyst layers with given residence times can be realized advantageously in radial flow furnaces. If the linear speed is too low in the laminar flow area there is a uniform flow through the catalyst layer not guaranteed due to increased channel formation. In addition, is a significant one The advantage is that if there is a short, radial flow through the catalyst layer, the printer is lustful is reduced. This makes the use of smaller catalyst holes of 1 up to 6 diameters that give higher performance are now possible.

The radial flow furnace is preferably suitable for oxidation reactions with high sales with a single pass and with heat tones greater than 60 tcal / mole and with one radial.

flow through catalyst layer from 100 cm to 200 cm at middle Residence times of preferably 1 to 10 seconds at a linear speed between 150 sec and 3 cm / sec is maintained. In doing so, catalyst granules are used with an average diameter of 2 to 4 mm are preferably used.

The method according to the invention can be based on, for example the catalytic oxidation of unsaturated C3 and C4 hydrocarbons such as propylene, n- and isobutenes, butadiene or mixtures of these compounds and also alkyl-substituted ones aromatic. Hydrocarbons, such as toluene, o- or p-xylene, or those containing oxygen Compounds such as alcohols, e.g. B. methanol, or aldehydes, e.g. B. acrolein apply.

In particular, the process for the catalytic oxidation of Propylene to acrolein and acrylic acid and in the presence of ammonia to acrylonitrile in the gas phase with atmospheric oxygen or to acetic acid in addition to maleic acid or for the catalytic oxidation of o-xylene to phthalic anhydride and in the presence from ammonia to phthalonitrile or for the catalytic oxidation of methanol to formaldehyde or the oxidation of butenes and butadiene or mixtures thereof suitable for acetic acid or maleic acid.

Example The reaction is carried out in an oven, which is shown schematically in Figure 2 is shown, carried out with a net capacity of 0.6 l. The cooling plate distance is 10 mm at the gas inlet and 20 mm at the gas outlet. The linear gas velocity with a feed of 60 liters of technical grade propylene per liter of catalyst per hour 730 1 air / l, h rind 41 l / l, h water vapor at the entrance to the layer 7 cm / sec, am Exit from the layer 3.5 cm / sec. With a catalyst layer of 23.7 cm that of a dwell time of 4.3 sec when the steam-gas mixture is preheated at 220.degree. C. and a bath temperature of 355.degree. C., acrolein yields of 65 up to 70 mole percent with a water vapor concentration down to 5 mole percent. The catalyst, consisting of oxides of molybdenum, tungsten and tellurium, takes place in the form of 3 mm pills used as chippings with a grain size of 1 to 3 mm, so the propylene load can be increased by 30% without the acrolein yield demonstrably decreases. The pressure loss is significantly lower with 30 mm of mercury than that in a comparable 25 mm tube filled with 0.6 to 1 liter of catalyst pills (60 to 130 mm mercury).

For example, if the reaction takes place under the same conditions carried out in a cylindrical tube, the heat exchange area corresponding to an inner diameter of 20 (25) mm is comparable to the mean heat exchange surface per unit volume of catalyst in Example 1, at a layer height of 1.91 (2.04) m and corresponding linear gas velocities of 43.5 (58) cm / sec Acrolein yields of 60 to 65 (50 to 55) mole percent are obtained. At one layer height of 2.86 (3.06) m and corresponding linear speeds of 65.2 (87) cm / sec due to excessively high hot spot temperatures and subsequent catalyst disintegration no measurement can be carried out.

Claims (8)

Claims 1. Cylindrical reactor for partial catalytic oxidation reactions of gaseous organic compounds on solid catalysts, each with one Nozzle for the inlet of the reaction gas mixture and the outlet of the reaction products as well as with a device for heating and cooling the filled with catalyst Reaction space is provided, which is designed so that reacting with each other gaseous substances can flow radially through the catalyst layer, characterized in that that the cylindrical reactor has a cross section, in the center of which a circular gas supply (1) is located, around which a circular ring sectors (2 and 3) divided inner annulus is arranged, which in turn of a further outer annular space (4) is surrounded, the circular ring sectors of the inner Annular space alternating as reaction spaces (2) to be filled with catalyst with radial Gas feed (1) from the center to the outside as a collector for the reaction products formed formed annular space (4) and as in connection with the heating and cooling device standing heat exchanger (3), in which the cooling medium flows through the reactor perpendicular to the radial flow direction of the reaction gases is performed, are formed. 2. Cylindrical reactor according to claim 1, characterized in that that the ratio of the through the partition walls between the circular ring sectors (6) the volume of the reaction spaces to be filled with the catalyst (2) behaves like 10 m2 / m3 to 200 m2 / m3. 3. Cylindrical reactor according to claim 1 and 2, characterized in that that the ratio of the through the partition walls between the circular ring sectors formed cooling surfaces to the volume of the reaction spaces to be filled with catalyst (2) behaves like 30 m2 / m3 to 100 m2 / m3. 4. Cylindrical reactor according to claim 1 to 3, characterized in 2, that the EUhlplatte distance at the gas inlet between 7 mm and 40 mm, preferably 10 mm and 25 mm. 5. Process for the partial catalytic oxidation of gaseous organic compounds on solid catalysts in molecular oxygen-containing Gas mixtures in which the heat of reaction released is more than 40 Kcal / mol, using concentrations of the gaseous organic compounds or above the lower explosion limit, the mean residence times of the Reaction gas mixture between 0.1 and 15 seconds, characterized in that that the oxidation is carried out in a cylindrical reactor according to claims 1 to 4 and a linear gas velocity of the reaction gas mixture as it passes through the catalyst layer between 200 cm / sec and 2 cm / sec. 6. The method according to claim 5, characterized in that at one radial flow through catalyst layer from 100 cm to 200 cm and at middle Residence times from 1 to 10 seconds a linear gas velocity between 150 cm / sec and 3 cm / sec is observed. 7. The method according to claim 5 and 6, characterized in that one Catalyst grains with an average diameter of 2 to 4 mm are used. 8. The method according to claim 5 to 7, characterized in that one propylene is used as the gaseous organic compound to be oxidized. Sign. L e r s e i t e