Modular reactor

Abstract

Modular microreactors are provided composed of microreactor parts including a plate body which has, on one plate side, a groove-shaped depression in which a reactor tube is accommodated, and the reaction tube has connection ends on the outer sides of the plate body. Also disclosed are reaction tubes for turbulent mixing, kits for producing the reactors and the use thereof for commencing chemical reactions.

Claims

1. A microreactor part comprising: a plate body including opposing sides, one of said sides having .Iadd.an outer surface and .Iaddend.a depression .Iadd.formed in said outer surface, .Iaddend. a reaction tube in said depression .Iadd.and positioned completely below said outer surface.Iaddend., said reaction tube having connection ends located at an edge of the plate body, and being spaced from the plate body along an entire length of said reaction tube; and .[.an induction coil.]. .Iadd.a thermal transfer medium .Iaddend.in said depression between said reaction tube and said plate body.

2. The microreactor part according to claim 1, wherein the plate body is cuboid.

3. The microreactor part according to claim 1, wherein the plate body comprises at least two reaction tubes in the depression.

4. The microreactor part according to claim 3, further comprising at least one connection element connected to the connection ends and the edge of the plate body of the at least two reaction tubes, said at least one connection element having one of a fluid inlet and a fluid outlet.

5. The microreactor part according to claim 3, wherein the depression has a meander-shaped course and partition walls are provided between meander-shaped portions of the course, the partition walls being sealed together with the plate body, by a plate.

6. A reaction tube comprising: an inner diameter of up to 20 mm and a cross-sectional constriction as a mixing element, the cross-section being constricted on one side of the tube, preferably a round tube, by at least 15%, preferably at least 20%.

7. The reaction tube according to claim 5, characterised in that the cross-section of the tube is not enlarged compared to the constriction, preferably also 90 to the constriction, and the cross-section preferably forms a semi-circle at the constriction.

8. The reaction tube according to claim 5, which comprises a plurality of cross-sectional constrictions, the side of the cross-sectional constriction preferably changing in an alternating sequence, in particular the cross-sectional constrictions being spiralled or opposingly offset in the tube cross-section, and/or the cross-sectional constrictions preferably being straight, prismatic, cylindrical or spherical.

9. A microreactor comprising: at least two microreactor parts, each having a plate body which has .Iadd.an outer surface and .Iaddend.a depression .Iadd.formed in said outer surface .Iaddend.on one plate side; a reaction tube in said depression .Iadd.and positioned completely below said outer surface.Iaddend., said reaction tube being spaced from said plate body and including connection ends located at an edge of said plate body, wherein ends of said reaction tubes of the at least two microreactor parts are connected via a connection element; and .[.an induction coil.]. .Iadd.a thermal transfer medium .Iaddend.in said depression between said reaction tube and said plate body.

10. The microreactor according to claim 9, wherein said connection element comprises at least one of an inlet and an outlet for accommodating reaction fluid into or from the reaction tube, and an inlet or outlet for fluid into or from a channel of the depression.

11. A kit for producing a microreactor comprising; at least two microreactor parts having a plate body which each have .Iadd.an outer surface and .Iaddend.a depression .Iadd.formed in said outer surface .Iaddend.on one plate side of said plate body; a reaction tube in said depression .Iadd.and positioned completely below said outer surface.Iaddend., said reaction tube including connection ends located at an edge of the plate body; a connection element for connecting the reaction tubes of the microreactor parts; and .[.an induction coil.]. .Iadd.a thermal transfer medium .Iaddend.in said depression between said reaction tube and said plate body.

12. The microreactor part according to claim 1, wherein at least one of the connection ends comprises a fluid mixer, the fluid mixer being one of a flow breaker, a flow accelerator, a mixing jet or a projecting injection needle.

13. The microreactor part according to claim 4, wherein one of the fluid inlet or the fluid outlet of the at least one connection element comprises a fluid mixer, the fluid mixer being one of a flow breaker, a flow accelerator, a mixing jet or a projecting injection needle.

.Iadd.14. The microreactor part according to claim 1, wherein said thermal transfer medium is in said depression between said reaction tube and said plate body along an entire length of said reaction tube. .Iaddend.

.Iadd.15. The microreactor according to claim 9, wherein said thermal transfer medium is in said depression between said reaction tube and said plate body along an entire length of said reaction tube. .Iaddend.

.Iadd.16. The kit according to claim 11, wherein said thermal transfer medium is in said depression between said reaction tube and said plate body along an entire length of said reaction tube. .Iaddend.

Description

(1) The present invention will further be explained in greater detail by the figures and examples below, but is not limited to these.

(2) In the drawings:

(3) FIG. 1 is a three-dimensional view of an assembled microreactor formed of a plurality of microreactor parts which are linked by connection elements;

(4) FIG. 2 shows a side view of the reactor;

(5) FIG. 3 shows a section through the front view of the reactor through various connection plug elements;

(6) FIG. 4 shows a cross-section through the reactor in which the individual depressions are visible with the reaction tubes;

(7) FIG. 5a shows a plan view of a microreactor part in which the depressions and reaction tubes are shown on a plate side;

(8) FIG. 5b shows an alternative plan view of a microreactor part;

(9) FIG. 6 shows a section through the connection of a reaction tube to a connection element in side view;

(10) FIGS. 7a, b and c show reaction tubes with cross-sectional reductions and cross-sectional enlargements;

(11) FIG. 8 shows a one-sided cross-sectional constriction of a reaction tube;

(12) FIG. 9 shows a section through a connection element in plan view, this connection element comprising an additional fluid inlet or fluid outlet;

(13) FIG. 10 shows a connection part comprising a mixing lance with a plurality of holes which project into the reaction tube;

(14) FIG. 11 a) shows a connection plug element, b) shows a connection plug element comprising an additional fluid inlet or outlet, and c) shows a connecting block with no tube connector comprising two inlets or outlets for adjacent reaction tubes;

(15) FIG. 12 shows a front and side view of the microreactor which is arranged on a transport or assembly mount;

(16) FIG. 13 shows a front view of a microreactor with a specific connection assembly of individual reaction tubes, the numbers given being based on positions to which reference is made in examples 2 and 3; and

(17) FIG. 14 shows a perforated disk as a mixing element for use in a mixing jet which comprises mixing lances of different length, a) cross-sectional view, b) sectional side view;

(18) FIG. 15 shows different tube shapes and tube cross-sectional shapes, in particular (a) circular, (b) segment of a circle, (c) square, (d) rectangular, (e) rectangular, (f) octagonal. FIG. 15g shows a shaped tube with a circular inner cross-section and a rectangular outer cross-section in a separable embodiment.

(19) FIG. 16 shows different tube shapes which can be laid in a microreactor part, in particular (a) winding, (b) serpentine, (c) jagged, (d) saw-tooth, (e) angled or (f) rectangular tube bend shapes.

(20) FIG. 17 shows a reaction tube (2) with a wound spiral (1) for inductive heating of the tube.

EXAMPLES

Example 1

Description of the Assembly

(21) The microreactor is characterised by a modular construction, whereby parameters such as residence time, etc. can be adapted to the different reactions.

(22) A modular plate or a microreactor part 1 consists of a plate body in which the reaction tubes 21 are guided in depressions 22. The reaction tubes 21 are stabilised by U-shaped mounts 24 in the depressions 22. The tubes are supplied with the reaction media on the front side. The depressions in the plate body 1 act as a guide for the cooling or heating liquid in order to adjust the temperatures required for the reaction. The microreactor is designed as a heat exchanger and the cooling or heating processes can be carried out in co-current flow and also in counterflow. The supply 9, 10 for the heating media is carried out on the left- and right-hand side of the plate body. The connections may be designed in such a way that the holes are at the highest point of the depression and can therefore allow any air to escape. The tube connectors 20 are attached to the front side and can be positioned in a flexible manner. The tube length can be specifically adapted to the reaction by using tube clamps 8. The tube clamps 8 also act as connections between the individual modules.

(23) The microreactor can be provided, for example, for the reaction of a plurality of reactants in a plurality of stages, for example:

(24) 1. heating the reactants to a reaction temperature (first module)

(25) 2. reacting the reactants (second to fourth module)

(26) 3. diluting the solution and stopping the reaction (fifth module)

(27) The individual reaction tube portions or microreactor parts represent separate modules.

(28) Modules 1-4 are located in a functional plane since they operate at the same temperature level. The fifth module does not directly adjoin the fourth module if there is a different temperature level. It can be spatially separated by a spacer 3 and insulation plate 2.

(29) For example the specific embodiment of a reactor according to FIG. 1 shows the construction of individual microreactor parts 1 or modules which, for example, can be separated by cover modules 2 and an insulation body 3. The individual microreactor parts and plate insulation bodies are retained by fixing clips 4 which are fixed by connecting rods 5 and locking clamps 6. A foot in the form of a fork-lift attachment 7 is located beneath the reactor. The individual microreactor parts are connected by connection elements (plate connectors) 8. Individual reaction tubes inside a plate body are connected, for example, by tube connection elements in the form of connecting blocks 20. The individual plates may comprise cooling medium inflows or outflows 9 or heating medium inflows or outflows 10. These cooling or heating media are guided through the plates in the depressions 22 as a heat transfer medium.

(30) The microreactor can have a plurality of reaction media inlets and outlets, such as an inlet for a fluid A 11, inlet for a fluid B 12, an outlet for a mixture A/B 13, an inlet for a reaction fluid C 14, a supply for the reaction mixture A/B 15 in a further plate; alternatively an outlet for a mixture A/B/C (in this case: free connection end 16), a supply for the mixture A/B/C 17 in a further plate, a supply for the reaction medium D 18 and a product discharge 19.

(31) FIG. 2 shows a schematic side view of this reactor with six different plate bodies 1, illustrated in section C (FIG. 3) and B (FIG. 4).

(32) FIG. 3 shows the section through different connection elements for connecting the tubes of the plates (tube connector) 20. The individual plates are connected by plate connectors 8.

(33) In accordance with FIG. 4 a cross-section through a reactor formed of five different plates is shown and graphically shows how the reaction tubes 21 are embedded in the groove-shaped depressions 22. The individual plates can be sealed by seals 23.

(34) As can be seen from FIG. 5a, the individual tubes can be fixed in the depressions by mounts 24. In order to fix the individual plates by the connecting rods 5, notches 25 are provided for the fixing of said connecting rods. FIG. 5b additionally shows a feed/discharge point 11 of the module, an inlet point 12, an discharge point 13, a mixing inlet 13b and a feed/outlet point 11b of the module. A thermal transfer medium supply 22b or thermal transfer medium discharge 22a is additionally illustrated.

(35) FIG. 6 shows a cross-section in side view through a connection element as it is attached to a plate body 1. In this instance a connection piece of the tube 21 was provided which could lead in depth to a further tube. The connection element is in this instance illustrated as a connecting block 26 which comprises a tube 27 which projects into the reaction tube of the plate 21. This tube 27 is sealed by a distribution element 30. Holes are provided in the distribution element 30 such that fluids can be supplied to the reactor from different directions (angles). The individual connection points are sealed by seals 28, 29 which can be designed as a tension seal 28 or pressure seal 29.

(36) FIG. 7a shows a reaction tube 21 with cross-sectional reductions 31 and cross-sectional enlargements 32. These are preferably spaced by regular spacings a, for example 50 mm; FIG. 7b shows a reaction tube with round or spherical cross-sectional constrictions; and FIG. 7c shows a reaction tube with round cross-sectional enlargements and oblique cross-sectional constrictions at an inclined angle to the cross-section of the reaction tube.

(37) FIG. 8 shows a cross-section through a cross-sectional constriction with an inner diameter i (for example 5 mm), an outer diameter a (for example 6 mm) and the cross-sectional constriction b (for example 1.51 mm). Of course, other measurements may also be provided for a cross-sectional constriction.

(38) In FIG. 9 a connection element 20 is shown which connects tubes 21. In addition, an inlet or outlet point 34 is provided here. The tubes 21 and the inlet point 34 lead via mixing jets 33, which are designed as perforated disks, into a common channel and into an inlet point in a tube 35 arranged beside.

(39) In accordance with FIG. 10 an inlet point 40 is shown where an injection lance 43 is shown above an inlet tube 41 above a connecting block element 37, which injection lance is closed by a centring piece 43b and leads into the tube 21 through different holes. Owing to the use of a plurality of holes, admitted fluid is guided continuously into the tube 21 at different points. The tube 21 leads directly into a further connection tube 42. The depressions 22 with the thermal transfer medium can be connected via a connection point 36 to adjacent tubes and the medium can be imported or exported. The tube 21 is fixed by a bushing 39 and a screw nut 38.

(40) FIG. 11 shows three different plug elements a), b), c), one of which is designed as a simple plug connection a) between the tubes 21. In accordance with the embodiment b), a fluid inlet or outlet point is additionally located in the plug element 20. In accordance with FIG. 11 embodiment c) the plug element 20b is not designed as a connection element, but as an inlet or outlet for two adjacent tubes.

(41) FIG. 12 shows a front and side view of the microreactor illustrated in FIG. 1.

(42) FIG. 13 shows a front view of a specifically connected microreactor with illustrated positions 1-70. In this figure, in accordance with position 1 a fluid inlet of a fluid A is shown (11 in FIG. 1). In accordance with position 2 fluid B is supplied. The tube in position 3 heats the fluid A/B mixture. Position 4 shows the A/B offtake. Position 5 shows the reaction medium C inlet. Positions 6-12 show tubes for heating fluid C. The first module from beneath thus heats A/B and C in parallel. From position 12 to position 12 fluid C is guided into the second module. In position 14 the fluid A/B mixture is supplied to the second module. The tubes of positions 15-49 are used for the chemical reaction of A/B/C. In position 50 fluid D is supplied. The tubes in positions 51-59 are used for the reaction or to terminate a reaction, provided fluid D is a reaction terminator, and for temperature control. Position 60 shows the product run-off. In accordance with positions 61-68 a heating medium is supplied or removed and in accordance with positions 68 and 70 a cooling medium is supplied or removed.

(43) FIG. 14 shows mixing lances in the form of four different injection needles which project through a mixing jet which is in the form of a perforated disk. Different mixing areas can be controlled by the staggered offset of the injection needles at different distances (b1, b2, b3).

Example 2

Operation

(44) Feed

(45) For a reaction of a microreactor connected in accordance with FIG. 13 the necessary chemicals are fed via pumps to the feed points or mixing points provided in the first module, where they are then introduced into the microreactor.

(46) Feed Points:

(47) fluid A position 1

(48) fluid B position 2 (mixing point)

(49) fluid C position 5

(50) fluid D position 50 (mixing point)

(51) The cooling/heating medium is fed by means of pumps and the medium enters on the longitudinal side through a inch Swagelok screw connection and exits on the opposite side (pos. 61-70). The modules 1-4 are supplied via a common feed line for the heating liquid since the modules are operated in the same temperature range. The liquid is fed in the fifth module via a separate line if the temperature level is different.

(52) Mixing

(53) The reactants are mixed in a counterflow mixer in which the reactants impact one another at considerably increased speeds. The increase in speed is achieved by small mixing plates. The mixed reactants are fed back into the reaction tube through a further small mixing plate.

(54) Mixing Points are Located at the Following Positions:

(55) mixing point 1 position 2

(56) mixing point 2 position 14

(57) mixing point 3 position 50

(58) Reaction

(59) The reaction is started at position 14, fluid C being added at this position to the fluid A/B mixture by a counterflow mixer. The necessary residence time can be adjusted by the number of tubes and modules.

(60) Dilution

(61) Owing to the addition of fluid D at position 50 the reaction is terminated by dilution and temperature change. The two flows are again mixed in a counterflow mixer.

(62) Product Discharge

(63) The product is discharged at position 60 at a temperature of approx. 40 C.

(64) The apparatus should only be opened after the prior emptying of the reaction chambers and of the cooling circuit. In order to open the apparatus the locking clamps are released and the fixing rods are unscrewed therewith. The fixing rods and fixing clips can then be removed from the reactor. The reactor can now be opened by removing the individual modules.

(65) For assembly the reactor modules are to be placed accurately on top of one another again and it should be checked that the modules are arranged in a flush and tight manner.

(66) The fixing rods, fixing clips and locking clamps are then attached to the reactor and the fixing rods are biased by means of the locking clamp and the lock is then reversed.

Example 3

Operating Values

(67) Specific flow rates and pressure ratios will be given by way of example in the following example with reference to the parameter values of Table 1 below. The microreactor designed in accordance with the invention was equipped with reaction tubes of diameter (2) and operated with the corresponding mass flow rates (1). The specific surface/volume ratio (3) was calculated on the basis of the reactor design and geometry.

(68) TABLE-US-00001 TABLE 1 Parameters 1 Flow rate [kg/h] 0.1 1 8 2 Tube inner diameter [mm] 1 3 5.00 3 Surface/volume [m.sup.2/m.sup.3] 4000 1333.33 800.00 Empty tube speed [m/s] 4 Fluid A 0.40 0.44 1.27 5 Fluid B 0.03 0.04 0.11 6 Mixture 1 0.43 0.48 1.38 7 Fluid C 0.29 0.32 0.93 8 Mixture 2 0.72 0.80 2.31 9 Fluid D 0.35 0.39 1.13 10 Product 1.07 1.19 3.44 Speed ratio at nozzle [v2/v1] 11 Fluid A 4.50 12 Fluid B 75.00 13 Mixture 1 4.50 14 Fluid C 7.20 15 Mixture 2 4.50 16 Fluid D 7.20 17 Product 4.50 Volume flow/surface [l/hm.sup.2] 18 Fluid A 257 771 1286 19 Mixture 1 280 841 1402 20 Fluid C 38 113 189 21 Mixture 2 29 88 147 22 Product 140 419 699 Reynolds number 23 Fluid A 1326 4421 21221 24 Mixture 1 88 293 1407 25 Fluid C 265 884 4244 26 Mixture 2 221 735 3529 27 Product 414 1381 6629 Total pressure loss [bar] 33.0 4.1 13.73 28 Pressure loss [%] 29 Fluid A 0 1 2 30 Mixture 1 4 4 4 31 Fluid C 3 3 3 32 Mixture 2 70 69 68 33 Product 23 23 23 34 Nusselt number 35 Fluid A 1.5 22.8 0 36 Mixture 1 25.0 33.6 44.84 37 Fluid C 5.9 6.2 37.44 38 Mixture 2 16.5 17.3 50.17 39 Product 12.1 14.1 89.86

(69) The fluid A was added to the microreactor at position 1 by means of pressure pumps and transported further to position 2 (mixing point) at an empty tube speed v1 (4) in the first reaction tubes.

(70) Before mixing fluid A with fluid B, fluid A was fed via a mixing jet in order to adapt the flow speed.

(71) The values of the speed ratio v2/v1 set by the mixing jet were as given under (11). In position 2 (mixing point) fluid b was supplied at an empty tube speed (5). In order to increase the first empty tube speed fluid B was also fed via a mixing jet. The speed ratio v2/v1 adjusted by the mixing jet assumed values as given under (12). The mixture 1 obtained was transported further at an empty tube speed (6) via connection pieces and was fed via a mixing jet in order to increase the fluid speed. The value of the speed ratio v2/v1 set by the mixing jet was as given under (13).

(72) Fluid C was fed at position 5 of the reactor at an empty tube speed (7) for temperature control and was fed to mixing point 2 (position 14) for intensive mixing of the fluid mixture 1 (formed of fluid A and fluid B). In order to increase the first empty tube speed, fluid C was also fed via a mixing jet. The value of the speed ratio v2/v1 set by the mixing jet was as given under (14). The fluid mixture 2 obtained was transported further at an empty tube speed (8) and was fed via a mixing jet in order to increase the fluid speed. The value of the speed ratio v2/v1 set by the mixing jet was as given under (15). After a precisely set residence time with temperature control the mixture 2 obtained was removed from the reactor positions arranged before position 50 once the reaction had taken place and was supplied to mixing point 3 (position 50). Fluid D was supplied to mixing point 3 at position 50 of the reactor at an empty tube speed (9) for intensive mixing of the fluid mixture 2 (formed of fluid A and fluid B and fluid C). In order to increase the first empty tube speed (9) fluid D was also fed via a mixing jet. The value of the speed ratio v2/v1 set by the mixing jet was as given under (16). The product fluid obtained was transported further at an empty tube speed (10) and was fed via a mixing jet in order to increase the fluid speed. The value of the speed ratio v2/v1 set by the mixing jet was as given under (16). The product obtained was fed via a further mixing jet for speed adjustment (17), was removed from the last reactor position after a precisely set residence time with temperature control or heat removal, and was supplied for further processing.

(73) The process parameters of volume flow/surface of the individual fluids, mixtures and products are illustrated, by way of example, by (18-22).

(74) The Reynolds numbers resulting from the tube flows and illustrated by (23-25) lie in the range of 80 to 22,000.

(75) The total pressure loss over the reactor area varies within a range of 4 to 33 bar as a function of the flow rate, the individual pressure losses of the fluids and mixtures which contribute to the total pressure loss possibly representing 1 to 70% of the total pressure loss.

(76) The Nusselt numbers calculated by thermal transfer processes lie within the range of 1-200 depending on the fluid and mixture as well as the product.

Example 4

Production of Nitrotoluene

(77) Pure toluene (boiling point 111 C., density=0.87 g/ml) is present in the microreactor (toluene storage container). Stabilised nitric acid (conc. nitric acid 65 wt. %, density=1.40 g/ml) and sulphuric acid (conc. sulphuric acid 95-98 wt. %, density=1.84 g/ml) are provided in separate buffer containers for the production of nitrating acid.

(78) The reaction to form nitrotoluene itself is carried out in the microreactor according to the invention, the starting materials being fed into the microreactor from the provided storage containers by means of nitrogen overpressure via individual feed lines.

(79) The reaction process for producing nitrotoluene is carried out in the microreactor, which is constructed in a modular manner as shown in FIG. 1 and basically comprises two zones: a reaction zone and a downstream residence time and cooling (temperature control) zone.

(80) The temperature of the reaction zone of the microreactor is controlled in such a way that reactants guided through the reaction tubes are kept at approx. 5-10 C.

(81) This preferably occurs by indirect heat removal controlled from the outer side of the tube by applying a cooling liquid (cooling oils or another heat transfer medium) to the reaction tubes.

(82) In the downstream residence time and process cooling zone the reaction mixture can be temperature-controlled or cooled to approx. 2 C.-6 C.

(83) Reaction Control:

(84) The mixture of toluene and the production of the nitrating acid (nitric acid and sulphuric acid) are carried out in the cold temperature-controlled microreactor part.

(85) The reaction portion of the microreactor for production of the nitrating acid is to be designed in terms of process technology in such a way that the temperature of the nitrating acid does not exceed 5 C. In a separate microreactor portion concentrated nitric acid is thus first mixed with concentrated sulphuric acid via a jet injection and mixing system, as shown in FIGS. 6, 10 and 9, and is immediately cooled in the tubes (FIG. 9, pos. 35) during the mixing process.

(86) Owing to the further mixing of the reactants (nitrating acid and toluene) the nitrating reaction is started in the tubes with the cross-sectional reductions according to the invention as shown in FIGS. 7a, 7b and 8.

(87) The nitrating reaction itself under the action of continuous mixing and energy supply and removal, the mixing of the reactants upstream of the reaction and the residence and termination of the reaction downstream of the reaction can also be carried out in microreactors with cross-sectional shapes as illustrated in FIGS. 15a-g and 16a-f.

(88) The cooling or temperature control of the microreactor reaction zone is expediently designed in such a way that the reaction product does not exceed a temperature of 5-10 C. At excessively high reaction temperatures NO.sub.2 development commences and must be prevented. The temperature of the reaction is controlled (heat removal/supply) as shown in FIG. 1 via the connections at pos. 9 and 10.

(89) The toluene fed into the microreactor (FIG. 1, pos. 11) reacts with the nitrating acid added to the microreactor (nitric acid and sulphuric acid) in the capillary and reaction tubes, as shown in FIG. 5a, to form a nitrogen mixture 2-nitrotoluene (ortho-nitrotoluene), 3-nitrotoluene (meta-nitrotoluene), 4-nitrotoluene (para-nitrotoluene), 2,4 dinitrotoluene and water.

(90) As is known from the literature, the actual nitrating agent (NO.sub.2.sup.+ is formed from nitric acid in the presence of sulphuric acid. The isomeric 2-nitrotoluene (Rmpp Chemie Lexikon, Thieme publishers Stuttgart; 10.sup.th edition; 1996) is also produced as a side reaction.

(91) The aromatic nitrotoluenes are characterised by substituents, a methyl group and a nitro group on the benzene ring. The different positioning of the substituents produces a mixture formed of three structural isomers. The structural isomers are produced as a mixture during the nitration of toluene. The amount of 3-nitrotoluene is low, however, as a result of the digesting properties of the methyl group. It is known from the literature that during the electrophilic aromatic substitution of toluene with nitric acid the inductive effect of the methyl group is decisive for the management of the secondary substituent. Approx. 65% 2-nitrotoluene (ortho-nitrotoluene), approx. 30% 4-nitrotoluene (para-nitrotoluene) and 5% 3-nitrotoluene (meta-nitrotoluene) are produced as primary products (Beyer/Walter: Lehrbuch der Organischen Chemie, 19.sup.th edition, S. Hirzel publishers, Stuttgart 1981).

(92) ##STR00001##

(93) Once the reactants have been passed through the reaction path of the microreactor constructed in a modular manner (FIG. 1), the mixture is cooled in the following, coupled region (FIG. 13, pos. 69 to 70) of the microreactor via the connection (FIG. 1 pos. 9). Sometimes the reaction can be stopped by adding water (FIG. 1, pos. 18), thus possibly affecting the conversion rate. Once the reaction in the microreactor has ended or has been stopped selectively, the acidically reacting reaction mixture can be continuously removed (FIG. 1, pos. 19), isolated and purified.

(94) The neutralisation may take place externally in batches in an associated apparatus, or else via a continuously operating static mixer which may also be part of the microreactor system.

(95) Once the reaction mixture has been removed, it is mixed with cold water (+2 C.) and with cyclohexane (boiling point 80 C., density=0.78 g/ml) and is shaken. The organic phase is alternately washed with cold water and saturated sodium-hydrogen carbonate solution. After treatment with sodium hydrogen carbonate it is washed again with cold water and dried over sodium sulphate before it is subjected to a filtration step and the solvent is distilled off, for example on a rotary evaporator. The oily residue can be distilled further, such that the desired product can be removed in the boiling range between 100 and 130 C. The crystallized distillate can be crystallized as required and recrystallized in methyl alcohol to obtain 4-nitrotoluene (para-nitrotoluene) as yield. The solid distillation residue can be recrystallized from ethyl alcohol and the yield of 2,4 dinitrotoluene can be determined. The reaction yield of 2-nitrotoluene (orthonitrotoluene) cannot be given by incomplete product separation.