Tubular reactor for heterogeneous reactions

A reactor for accelerating heterogeneous reactions and affording an increased yield rate per unit of time and space comprises a cylindrical reactor tube containing in its interior a piston having relatively flat profiling in its skirt in the form of annular ribs and grooves therebetween, inlet conduits leading into the interior of the reaction tube through the bottom clousre thereof, which may also be introduced from above and extend axially through the piston, an outlet tube is provided in the region of the top closure of the reaction tube, the piston is being connected via a piston rod with a vibrator imparting axial oscillatory movement of the piston, these oscillations generating turbulences in the annular piston grooves which effect a thorough mixing of the reaction participants without causing any noteworthy re-mixing of the resulting reaction products with the starting components.

BACKGROUND OF THE INVENTION 
This invention relates in a first aspect to a tubular reactor, and more 
particularly to such reactor comprising a reactor tube having two open 
tube ends, inlet means for the substances to be processed, at one of these 
tube ends, and at least one outlet for the product to be obtained at the 
other tube end, inset means in the reactor tube being axially displaceable 
therein, as well as drive means for an axial to-and-fro displacement of 
the inset means relative to the reactor tube. 
In a second aspect, the invention relates to the use of the aforesaid 
reactor for continuously performing heterogeneous reactions therein. 
However, the reactor is also suitable for performing heterogeneous 
reactions the heat exchange of which is to be accelerated. 
In a third aspect, the invention relates to a novel process for 
continuously performing a heterogeneous reaction. 
In former times chemical reactions were carried out in apparatus which was 
specially designed for a specific reaction. In the beginning of this 
century factors influencing chemical reactions such as the influence of 
flow, mixing, distribution of sojourn times and the transfer of substances 
and of heat were more generally investigated. The concept of chemical 
reaction techniques originated only in the mid-Fifties. The field of 
reactor development is therefore a relatively young one and, 
correspondingly, comprises many problems to be solved. 
A particular problem, hitherto unsolved in a satisfactory manner in the 
field of reaction techniques, is the control of heterogeneous reactions. 
Particularly in those cases in which a re-mixing of reactants and reaction 
products has a negative influence on the alternate outcome of the process, 
e.g. on a possible subsequent reaction step, and which require a thorough 
mixing in order to accelerate the reaction, the selection of a suitable 
reaction apparatus becomes difficult. Hereinafter, a few known reactor 
types shall be briefly discussed. 
As a first reactor type a vessel equipped with a stirrer is well-known. 
This apparatus comprises a vessel in the interior of which the stirring 
elements, e.g., rotating propellers or vane elements are lodged. With the 
aid of stirrer-equipped vessels, it is possible to attain an excellent 
degree of mixing. As, however, the starting components as well as the 
resulting final product are present in the same vessel and are being 
continuously mixed with each other, a re-mixing thereof is unavoidable, as 
it is inherent in the technical system. 
A further frequently used type of reactor is the tubular reactor which 
comprises a cylindrical tube into which the starting components are 
introduced at one end thereof. Due to the continuous flow of additional 
material into the tube, the starting components are pushed through the 
tube while reacting with each other during their travel through the tube, 
while the resulting end products leave the tube at the other end thereof. 
As the flow of subsequent components pushes those already in the tube 
ahead of them, remixing is relatively minor. On the other hand, due to the 
laminar flow of the substances through the tube, mixing of the same is not 
particularly satisfactory. Moreover, tubes of great length may be required 
in order to guarantee the necessary sojourn times for completing the 
reaction. 
A combination of a tubular reactor and stirrer-equipped vessel is provided 
by subdividing the tubular reactor into several chambers, each of which is 
designed as a stirrer-equipped vessel, and which are arranged as a series 
of cascades, wherein the components do not remain stationary in the 
stirrer-equipped chambers during mixing, but flow through the same. 
However, this combination suffers from several drawbacks. Centrifugal 
forces generated by the stirrer element cause a sedimentation of 
particles. Furthermore, the angular velocity of the stirrer element is not 
the same at all points, but is smallest near the driving shaft of the 
stirrer so that no uniform mixing can be attained. As a further drawback 
the component parts of the reactor are difficult to clean. 
Further reactors have been described, for instance, in the French patent 
publication No. 2,321,513, the German patent publication No. 1,125,175, 
and the U.S. Pat. Nos. 3,716,590 and 4,268,437. These known reactors are 
badly suited or completely unsuitable for carrying out heterogeneous 
reactions. 
OBJECTS AND SUMMARY OF THE INVENTION 
In its first aspect, the invention sets out to solve the task of providing, 
according to the principal object of the invention, a cylindrical reactor 
which 
(a) is of relatively short length, 
(b) affords an acceleration of the reaction to be performed therein, in 
comparison with known reactors, thanks to intensive mixing of the reaction 
components, while 
(c) being free, to the highest possible extent, from re-mixing of reaction 
products and starting components, and 
(d) being easy to clean. 
As mentioned before, it is another object to provide a reactor according to 
the invention satisfying the abovedefined objects, which is adapted for 
continuously performing heterogeneous reactions such as, in particular, 
the diazotization of amino compounds which are insoluble in an aqueous 
medium, such as 4-aminoazobenzene. When a diazotization reaction does not 
occur sufficiently rapidly, there will occur an undesirable decomposition 
of the nitrate accompanied by the development of gases. In order to 
accelerate heterogeneous reactions, it has hitherto been the custom to 
grind the reaction participant which is insoluble in the reaction medium, 
superfinely, and/or to add surface-active agents to the reaction medium, 
and/or to add organic solvents. It is a further object of the invention to 
largely or to completely avoid such additional measures. 
In its second and third aspects, the invention sets out to solve the task 
of accelerating heterogeneous reactions by attaining the objects of 
(a) achieving a better, more thorough mixing of the reaction components and 
thereby an improved exchange of material, 
(b) without the occurrence of substantial re-mixing, thereby 
(c) avoiding undesirable secondary reactions, and 
(d) thereby increasing the yield. 
The objects of the first invention aspects are attained in accordance with 
the invention, in a reactor of the initially described type, in which the 
inset means consist essentially of a piston or plunger having in its 
piston skirt circumferential grooves whose depth t is less than about half 
the maximal radius of the piston taken in a plane radially to the 
longitudinal piston axis. 
Preferred embodiments of the reactor according to the invention have at 
least one of the following features: 
(1) the distance g between the piston skirt and the internal wall surface 
of the reactor tube amounts to about 0.5 to 3 times the depth t of the 
circumferential grooves; 
(2) the width b of the circumferential grooves amounts to 0.2 to 2 times 
the depth t of the circumferential grooves, and is preferably from about 
half to the same as the said depth t between adjacent annular ribs of the 
piston; 
(3) the distance a of adjacent circumferential grooves from each other is 
about 0.5 to 2 times the width b of the circumferential grooves (i.e., a 
is the axial height of each rib); 
(4) the circumferential grooves have a substantially rectangular cross 
section, and preferably so have the ribs; 
(5) at least one inlet is extended through the piston and the lower piston 
end is provided with an inlet valve; 
(6) the lower piston end is designed at least partly as a static mixer; 
(7) the frequency of the oscillation of the piston amounts to from 0.1 
cycles to one kilocycle, and the oscillation stroke (amplitude) amounts to 
from 0.1 to 30 mm; 
(8) the gap between the piston and the tube amounts to 0.05 to 5 times the 
oscillation stroke; 
(9) the width of the circumferential grooves amounts to 0.05 to 5 times the 
oscillation stroke of the piston; 
(10) the distance between adjacent circumferential grooves amounts to 0.05 
to 5 times the oscillation stroke; and/or 
(11) the distance between the piston end and the adjacent reactor tube 
bottom corresponds to the width of the circumferential grooves, and at 
least to the oscillation stroke of the piston. 
The objects of the second and third aspects of the invention are attained 
by using the reactor according to the first invention aspect for 
continuously performing heterogeneous reactions, and by a process for 
carrying out such a heterogeneous reaction continuously, which comprise, 
in accordance with the invention 
(a) introducing simultaneously and continuously into the lower end of a 
reactor apparatus or system, which comprises a substantially vertically 
disposed reaction tube or zone, at least one suspension, each such 
suspension being introduced containing a reaction participant being 
insoluble in the reaction medium, and at least one solution, each such 
solution containing a reaction participant being soluble in the reaction 
medium; 
(b) effecting periodic linear up-and-down movements of piston means having 
relatively flat circumferential grooves in the skirt thereof and being 
lodged in said reaction tube or zone, thereby thoroughly mixing and 
conveying upwardly through said tube or zone that at least one suspension 
and that at least one solution, while avoiding any substantial re-mixing 
of volume units having different sojourn times in the reaction tube or 
zone; and 
(c) removing the resulting mixture containing the reaction product from the 
upper end of the reaction tube or zone. 
The resulting mixture is then worked up in a manner known per se in order 
to isolate the reaction product. Preferably, the reaction product is 
soluble in the reaction medium. 
More in particular, the reactor according to the invention is used for 
continuous diazotization of an amino compound being insoluble in an 
aqueous medium, and comprises introducing simultaneously and continuously 
into the lower end of the reactor tube an aqueous suspension of the amino 
compound, an aqueous nitrite solution and an aqueous solution of 
hydrochloric acid, and removing from the upper end of the reaction tube a 
solution of a diazonium compound being soluble in the reaction medium. 
Thus, an aqueous sodium nitrite solution can be added to a suspension of 
4-aminoazobenzene containing preferably a surfactant, and the resulting 
nitrite-containing suspension can be introduced simultaneously with a 
hydrochloric acid solution into the lower end of the reaction tube. 
In a preferred mode of carrying out the process according to the third 
invention aspect, an aqueous suspension of an amino component being 
insoluble in aqueous media is diazotized with an aqueous nitrite solution 
and an aqueous hydrochloric acid solution in the reaction zone, and 
removing from the upper end of the latter a solution of the resulting 
diazonium compound in the aqueous reaction medium. Thus, an aqueous sodium 
nitrite solution can be added to a suspension of 4-aminoazobenzene in 
water, containing preferably a surfactant, and the resulting mixture can 
be introduced simultaneously with a hydrochloric acid solution into the 
lower end of the reaction tube. 
The foregoing as well as other objects and advantages of the present 
invention and the particular aspects thereof will become apparent by 
reference to the following detailed description thereof with reference to 
the accompanying drawings which illustrate, by way of example, preferred 
embodiments of installations according to the invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS SHOWN IN THE DRAWINGS 
The reactor embodiment shown in FIG. 1 consists essentially of a 
cylindrical tube 1 whose lower end is provided with a closure member 8 and 
whose upper end is provided with a top closure or lid member 9. The 
reactor tube 1 is made preferably of glass and contains in its interior an 
elongated piston 2 having a profiled circumferential sidewall the profile 
of which consists of radially extending flange-like ribs 2a with annular 
interspaces 2b between each pair of adjacent ribs. 
The piston 2 is connected by means of a linkage system 7 with a vibrator 6 
or a similar suitable device for generating oscillations of the piston 2 
along its longitudinal axis. Inlet tubes 3, 4 and 5 serve to convey 
substances to be reacted with each other into the interior of the reactor 
tube 1 in the vicinity of the closure member 8 at the lower tube end. 
Of these inlet tubes, the tube 5 extends through a part of the linkage 
system 7 and axially downwardly through the piston 2 to open at the lower 
end 10 thereof. This lower piston end 10 can be designed as a static mixer 
and is provided with one or several openings 10a through which reactant 
substances can be supplied to the interior of the reaction tube. The two 
inlet tubes 3 and 4 also lead through the closure member 8 into the lower 
end of the reaction tube 1, while the reaction product and byproducts of 
the reaction can leave the reactor tube 1 by way of an outlet tube 11 
which is connected to the upper region of the tube in the vicinity of the 
top closure 9. 
Measuring points can be provided in several regions of the reactor tube 1 
in order to be able to survey and check the kinetics of the reaction. 
Experience has shown that an advantageous frequency of the oscillations 
ranges from 0.1 cycle to 1 kilocycle. As a basis for the dimensioning of 
the reactor, there can be used the oscillation stroke of the piston 2 
which can vary, depending on the embodiment used, from 0.1 mm to about 30 
mm. The width g of the gap between the interior wall of the reactor tube 1 
and the external cylinder of the piston 2 whose diameter d is equal to the 
rib diameter taken in a plane radial to the piston axis, preferably 
amounts to from 0.05 times to 5 times the oscillation stroke of the piston 
2. The thickness of the flange-shaped ribs 2a, i.e. the height a of each 
rib in axial direction, preferably amounts to from about 0.05 times to 5 
times the oscillatory stroke, and the distance between adjacent ribs, b, 
i.e. the axial width of each groove 2b between them, preferably is in the 
same range of dimensions, i.e. from about 0.05 times to 5 times the 
oscillatory stroke. The distance e between the lower piston end 10 and the 
reactor bottom closure member 8 is preferably of the same size as the 
width of the circumferential grooves but must, of course, be at least 
large enough to permit unobstructed oscillations of the piston. 
The reactor functions in the following manner: 
The reactant components which enter the reaction tube 1 in the lower region 
thereof flow upwardly through the tube, and the resulting reaction 
products with or without residual starting components leave the upper 
region of the reaction tube 1 through the outlet tube 11. The periodic 
longitudinal oscillation of the piston 2 cause the formation of 
turbulences of flow of the substances in the interspaces 2b between the 
ribs 2a of the piston 2. These turbulences produce an intensive mixing of 
the starting components. Moreover, these turbulences have a cleaning 
effect in the interspaces 2b, so that no intermediary or final reaction 
products will be retained therein and be re-mixed with upwardly flowing 
starting components. These cleaning properties are particularly important 
in the case of heterogeneous reactions whose reaction velocity is directly 
proportional with the thoroughness of mixing of the starting components. 
In FIG. 2 there are shown two reactor tubes 1 and 1' connected in series, 
i.e., in cascade arrangement. The outlet pipe line 11 of the first reactor 
tube 1 leads in this arrangement to the closure 8' at the lower end of the 
second reactor tube 1' and the reaction mixture introduced through the 
pipe line 11 into the reactor tube 1' passes upward through the latter and 
leaves the reactor tube 1' through the outlet tube 12 at the upper end of 
the reactor tube 1'. The other parts of the reactor tube 1' being 
designated by 2', 6', 7', 9' and 10' are identical with the 
correspondingly designated parts of the reactor tube 1. With the aid of 
such cascade arrangements, the effective length of the reaction tube can 
be multiplied as desired. 
In FIG. 3 there is shown an embodiment of the reactor according to the 
invention which is particularly suited for carrying out diazotizations 
therein. The outlet pipeline 11 is connected in this embodiment with a 
pressure relief vessel 13 having the configuration of an upright 
cylindrical tubular element which is provided at its lower end with an 
outlet 14. The pipeline 11 extends axially upwardly in the interior of the 
vessel 13 and opens in the vicinity of the closed upper end of the same. 
The entire reactor is provided with a number of measuring points 15, 15' 
and 15" of the reactor tube 1 and 17 and 18 at the top region and the 
bottom region, respectively, of the pressure relief tube 13, whereby the 
reaction kinetics can be traced. 
In FIG. 4, there is shown an embodiment of the reactor according to the 
invention in an apparatus for the diazotization of 4-aminoazobenzene. Two 
mearuring cylinders 19 and 20 having each a capacity of 500 milliliteres 
are connected via the conduits 3 and 4, respectively, with the closure 8 
at the lower end of the reactor tube 1 containing the oscillatory piston 
2. A hose squeezing-stroke pump 23, for instance of the ISMATEC MV-GE type 
sold by the company ISMATEC SA, in CH-4000 Basel, Switzerland, with 
multiple seizure, is interposed in the path of the two conduits 3 and 4. 
In a preferred design the volume of the reactor tube 1 may be of 33 
milliliters. The linkage system 7 comprises a piston rod which is 
connected with the upper end of the piston 2 as well as with a 
commercially available vibrator 6 adapted for generating oscillations of 
the piston 2 along the longitudinal piston axis. The frequency of the 
oscillation of the vibrator 6 amounts, for instance, to 50 or 60 cycles, 
and the amplitude of the oscillation can be freely adjusted within the 
range from 0 to 3 mm. An outlet pipeline 11 leads from the upper region of 
the reactor tube 1 into the lower end of a pressure relief vessel 13 and 
opens in the upper region thereof. A vent valve 24 is provided in the top 
wall of the vessel 13, and a discharge pipe 14 leads from the lower region 
of the vessel 13 to a suction filter, e.g. a porcelain funnel 25. 
In the embodiment of the piston 2 shown in FIG. 5 which is otherwise 
similar to the piston shown in the embodiment in FIG. 1, the branch of the 
inlet tube 5 which extends axially downwardly through the piston 2 
protrudes with its lower end from the bottom end of the piston 2 and can 
be closed with a stopper member 16 which is detachable and can either 
close off the lower end of tube 5 or it can be provided with orifices. In 
both cases this stopper member can be designed as a static mixer. 
A preferred design of the reactor in this and the other embodiments shown 
in FIGS. 1 to 4 comprises a metal tube having a wall thickness of 5 mm. 
The piston consists of a tubular body of synthetic resin material, 
preferably Teflon (tetraperfluoroethylene) into the outer cylindrical wall 
of which a number of circular grooves 2b has been cut. The length 1 of the 
piston in a preferred configuration amounts to 300 mm, the diameter d of 
the transverse cross sectional area amounts to 12 mm, the circumferential 
end wall of each rib 2a, which is left standing between the grooves 2b, 
has a height a, in axial direction, of 3 mm, and the distance b between 
two adjacent ribs 2a also amounts to 3 mm. The depth of each groove 2b in 
a plane radial to the longitudinal piston axis is 2.5 mm. The internal 
width w of the reactor tube 1 amounts to 14 mm, so that the distance 
between the outer wall of the piston 2 and the internal wall of the 
reactor tube 1 amounts to one mm on each side. 
FIG. 6 shows in axial sectional view on a scale of 1:1 a preferred 
embodiment of the reactor according to the invention. The lower part of 
this reactor corresponds largely with the lower reactor half shown in FIG. 
7; however, the piston 110 in the upper reactor half of FIG. 6 differs by 
its broader ribs 111 and its wider interspaces between them from the 
narrower ribs and interspaces of the piston 110 in the lower reactor half 
shown in FIG. 7. 
The reactor tube 100 in the embodiment of FIG. 6 is made preferably of 
glass and is mounted in its upper end region in two parallel flanges 101 
and 102 which are made preferably of metal. An O-ring 103 and a flat 
sealing member 104 afford the necessary sealing and the elastic movability 
of the glass and metal parts relative to each other in the joints between 
them. The two flanges 101 and 102 are secured together by means of screw 
bolts 105, tension springs 106 and tightening nuts 107. 
The upper flange 102 constitutes a cover lid for the reactor tube 100 by 
having a downwardly projecting disc part which fits sealingly into the 
open upper end of the tube 100, and contains an outlet duct 108 for the 
discharge of reaction products which has an entry orifice in the underside 
of the said disc part and an exit opening in the circumferential sidewall 
102a thereof. The lower end of a vibrator rod 109 extends through a 
central opening of this flange into the upper region of the interior of 
the hollow piston 110. 
This hollow piston 110 is housed axially in the interior of the reactor 
tube 100 and consists essentially of a piston shell having a cylindrical 
internal wall surface and a profiled external surface, an upper piston lid 
112 (FIG. 6) and a lower piston lid 113 (FIG. 7) closing off the hollow 
interior of the piston shell, and an axially extending connecting rod 114 
which secures the two lids 112 and 113 together with bias. The upper end 
of the connecting rod 114 wears an external threading which is screwed 
into the internal threading of a bushing 115 which is in turn screwed onto 
the external threading of an extension member 116 of the vibrator rod 109. 
This extension member 116 traverses with a tight seal a central opening in 
the upper piston lid 112 and is secured in the lid 112 by means of lock 
nuts 117, whereby the axial upward and downward movements of the vibrator 
rod 109 are transmitted via the upper piston lid 112 to the piston 110. 
The construction of the lower reactor half in the embodiment, the upper 
half of which is shown in FIG. 6, corresponds, with the above-mentioned 
exception of the piston configuration, to that shown in FIG. 7. In this 
lower half the lower end of the reactor tube 100 is mounted firmly in 
position by means of the two flanges 120 and 121, while an O-ring 122 and 
a flat sealing member 123 are provided in a corresponding manner to afford 
the necessary elasticity of the joint between the reactor tube 100 and the 
two flanges, and the required tight seal. The lower flange 121 supports a 
base plate 124 which in turn bears an internal reactor tube bottom part 
125 which is fit sealingly into the lower end of the reactor tube 100. The 
two bottom elements 124 and 125 are provided with channels 126 and 127 
which are only partly visible in FIG. 7 and serve for the supply and 
withdrawal of material to and from the interior of the reactor tube 100. 
Furthermore, a temperature measuring device 128 extends through the two 
bottom elements 124 and 125 and has a detecting tip 129 protruding into 
the interior of the reactor. The internal bottom part 125 is attached to 
the lower end of the connecting rod 114 in the bottom region of the 
reactor tube interior by means of a fastening screw 130. 
FIGS. 6 and 7 being on a scale of 1:1 illustrate the dimensions of two 
different profiles of the external piston wall being constituted by 
annular ribs 111. In FIG. 6, the thickness of the ribs 111 in axial 
direction is larger, in FIG. 7 it is smaller. For especially favorable 
results, the following relationship should be observed between the depth t 
of the grooves between adjacent ribs 111, the thickness a of the ribs 111, 
i.e. the axial length of the circumferential sidewall of each of them, the 
width b of the grooves between each pair of adjacent ribs taken in axial 
direction, the maximal piston diameter d, and the spacing g between the 
cylinder defined by the circumferential sidewalls of the ribs 111 and the 
internal wall surface of the reactor tube 100, the sum of d+2 g being 
equal to the internal width w of the reactor tube 100, and should not be 
exceeded or fallen short of in practice: 
t=t 
g=from 0.5xt to 3xt 
b=from 0.2xt to 2xt, preferably 0.5xt to 1.0xt 
a=from 0.5xb to 2xb 
d approximately 4xt. 
By observing these ranges of dimensions there is achieved an optimal mixing 
of the reaction components without causing a re-mixing, worth mentioning, 
of reaction products with starting components. 
In the example carrying out the process according to the invention in 
practice, given below, parts by weight have the same relationship to parts 
by volumes as have grams to milliliters. 
EXAMPLE 
One half part by weight of a wetting agent consisting of the condensation 
product obtained from p-tertiary-octylphenol and ethylene oxide in a molar 
ratio of 1:8 is dissolved in 200 parts of water. 
To the resulting solution there are added 100.2 parts by weight of ground 
4-aminobenzene of technical grade (98.3% pure) and 125 parts by volume of 
4-normal aqueous sodium nitrite solution to afford a molar ratio of 
4-aminobenzene and sodium nitrite of 1:1. Water is added to the resulting 
suspension to make a total of 500 parts by volume and the whole is 
homogenized with the aid of a vibromixer. 
One hundred twenty two parts by weight of hydrochloric acid having a HCl 
content of 33% by weight are made up to a total of 500 parts by volume by 
adding 390 parts of water. The HCl-amount present in the resulting 
solution and the 4-aminobenzene amount of the above-described suspension 
are in a molar ratio of 2.2:1.0. 
The above suspension and the hydrochloric acid solution are fed 
continuously by way of the lines 3 and 4 by means of the squeezing-stroke 
pump simultaneously into a reactor according to the invention as shown in 
FIGS. 3 or 4. The reaction is carried out quasi-adiabatically at room 
temperature (20.degree. C.). The resulting reaction mixture is discharged 
via the exit line 14 and directly filtered off. By adjusting the sojourn 
times in the reactor to from 20 to 60 seconds, a yield rate of 98 to 99% 
by weight was obtained. No development of gas was observed. A throughput 
rate of from one to 3 moles per hour was achieved.