Mulitube falling-film reactor for the continuous sulfonation and sulfation of fluid-state organic substances by reaction with gaseous sulphuric anhydride (SO.sub.3), has each tubular element non-permanently fixed to the plates and has a nozzle (10) fitted in a sleeve (20) integral with a reaction tube (23). The nozzle (10) can slide within the sleeve (20) and may be placed at different heights with respect to the latter, forming with the end-piece (14) a cylindrical crown opening (18) of fixed width and variable height. Such arrangement permits to control the delivery of the fluid to be sulfonated. The opposite end of each tube (23) fits into a double-plate seal system.

FIELD OF THE INVENTION 
This invention refers to a multitube falling-film reactor, utilizable in 
particular for the continuous sulfonation and the sulfation of fluid-state 
organic substances by reaction with gaseous sulphuric anhydride 
(SO.sub.3). 
Reactors of this type are well known in the art and are available on the 
market. They are essentially constituted by a nest of tubes wherein the 
tubes are permanently fixed to at least one plate. 
The organic substance and the SO.sub.3, opportunely diluted with air at a 
concentration of about 4%, are fed from above within the tubes, while a 
cooling fluid, generally water, is provided externally to the tubes to 
absorb the heat of the reaction (exothermic). In order to obtain high 
yields and a sulfonated or sulfated product of good quality, reaction must 
take place uniformly in each tube of the reactor. 
To obtain this result, the reagents should be distributed homogeneously and 
constantly in each tube of the reactor. However, while for SO.sub.3 this 
uniform distribution takes place spontaneously, as this reagent is fed at 
a constant pressure in the gaseous phase, for the organic substance, on 
the contrary, a control system must be provided in the various tubes in 
order to obtain the necessary distribution uniformity. At present, various 
control systems are utilized, all of which have a distributor on top of 
each tube provided with a slit or orifice whose section can be 
mechanically adjustable in various ways. 
These systems permit a poorly precise control of the delivery. Actually, 
minor variations in the passage sections suffice to produce rather high 
delivery variations, which prevent the organic substance from reaching an 
optimum distribution uniformity in all the tubes. Besides, the known 
reactors show another drawback which adds to the above mentioned 
inconvenience. In fact, they are produced with tubes that are permanently 
fixed to the plates and therefore they cannot be easily removed, should 
they break. As a consequence, maintenance operations are needed which are 
rather wearisome and lengthy, to have the reactor repaired. 
Now, the applicant has devised the multitube falling-film reactor subject 
of this invention, utilizable in particular for sulfonation and sulfation 
reactions, which permits to eliminate all the above mentioned drawbacks of 
the known reactors of the known types. 
SUMMARY OF THE INVENTION 
An object of this invention is therefore a reactor comprising: 
a) a very simple and precise control system of the delivery of the 
fluid-state organic composition to be sulfonated or sulfated, based on the 
formation, on top of each tube, of a cylindrical crown opening placed 
between a concentric nozzle and sleeve unit. The internal nozzle can slide 
within the external sleeve, integral with a reaction tube and may be 
placed at various heights. Such arrangement permits to have fixed width 
and variable height openings, which allow for variations in the charge 
loss in the splits, such as to produce flow variations, utilizable to 
control and make uniform the fluid flow in the various tubes of the 
reactor. The precision and accuracy of this control system ensue from the 
fact that even minor delivery variations--allowing for very exact and 
easily reproducible calibrations--can be obtained through rather high and 
easily controllable vertical shifts of the nozzle; 
b) nest of tubes non permanently fixed to the plates, but blocked to the 
latter by means of systems with flanges, ring nuts and seals. Such tubes 
can be easily taken out and may be replaced in a very short time; 
c) adoption on the reactor outlet side (lower side) of a double plate seal 
system, which permits to avoid, in case of loss from the first plate, any 
infiltration of cooling water into the reaction fluid, which would cause 
its pollution and the onset of corrosion phenomena downstream of the 
reactor.

With reference to the above drawings, the reactor is represented, by way of 
example, by a single tubular element. 
A top cap, bounds a chamber 1 of distribution of the gaseous SO.sub.3 in 
the various tubes, placed upon a first top plate 2. Nozzles 10 fit in 
special holes of said plate, said nozzles having each an edge 11, utilized 
to fix the nozzle to said plate by means of screws 12 and gaskets 19. Each 
nozzle 10 comprises a lower part 13 having a toothed-wheel-shaped radial 
section and a lower end-piece 14. 
Such lower part 13 fits into a sleeve 20, which, in its turn, fits into a 
special hole provided in a second top plate 4, to which it is fixed along 
edge 21 by means of screws 22 and gaskets 29. At both ends of said sleeve 
20, projecting under plate 4, a reaction tube 23 is connected. This 
connection is made in such a way as to cause the internal wall of said 
tube 23 to be flush with the internal wall of said sleeve 20. 
A chamber 3 of distribution of the fluid to be sulfonated or sulfated is 
placed between the first top plate 2 and the second top plate 4. From this 
chamber, the fluid flows in the longitudinal channels 15 provided in the 
lower part 13 of nozzle 10, collects in a cavity 16 and then flows down 
from a cylindrical crown-shaped opening 18 provided between the inner wall 
of the lower part of sleeve 20 and the external wall of end-piece 14 of 
nozzle 10, forming a film that flows down along the internal wall of tube 
23 and that reacts with SO.sub.3 which moves in concurrent. 
The width of each circular crown of each opening 18 is fixed and calibrated 
in function of the fluid to be fed. 
Generally, it has a constant value in all tubes, comprised between 0.15 and 
0.50 mm, and preferably between 0.25 and 0.35 mm. On the contrary, the 
height of each opening 18 can be changed by raising or lowering nozzle 10, 
so as to obtain charge losses through said opening, and, therefore, 
variations in the delivery of fluid fed to reaction tube 23. Such an 
arrangement permits to calibrate, with the utmost precision and accuracy, 
the fluid delivery into the various tubes of the reactor, making the 
distribution uniform in each tube and making up in this way for the flow 
differences which would create in the tubes, due to unavoidable, however 
minor, width differences in the various openings 18. In practice, such 
calibration operation is made by utilizing varying thickness strips 51, 
calibrated to thickness differences of 0.01-2.0 mm, which are fitted 
between the edge of each nozzle 10 and gasket 19, until a uniform fluid 
flow is obtained in all tubes. 
The lower end of each tube 23 is fitted in a double plate system. In fact, 
the reactor comprises a first lower plate 6 and a second lower plate 8, 
both of them having non permanently fixed through-tubes. On each tube 23, 
the seal is provided respectively by braid-gaskets 33 and 43, which are 
set against tube 23 by ring nuts 31 and 41, when these latter are screwed, 
through threads 32 and 42 to said plates. Such double plate system 
prevents any possible infiltration of the pressurized cooling water in 
zone 5--provided on the outside of the tubes--from ending up in the 
reaction substance, giving rise in this way to the aforementioned 
problems. 
This infiltration would cause the cooling water to collect in fact in the 
air gap at atmospheric pressure in zone 7 on the reactor outside, between 
the two plates 6 and 8. 
The reactor according to the above described invention permits an easy and 
rapid taking out of any tube, if a change should be needed. 
While the invention has been described with reference to a specific 
embodiment, many alternatives and changes may be obviously made by the 
experts in the light of the above description. Hence the invention 
embraces all the alternatives and changes which fall within the spirit and 
protection scope of the following claims.