Note: Descriptions are shown in the official language in which they were submitted.
2l8o8~
Description
This invention relates to an apparatus for carrying out
chemical reactions between liquid or ga6eous and solid reac-
tants under the influence of ultra60und. The invention also
relates to the use of such apparatus.
Ultrasound is known to produce a number of mechanical, chemi-
cal and biological effects- For instance, by means of ultra-
sonic pulses soiled textiles or soiled metal articles can be
cleaned. Furthermore, due to high pressure diiferences pro-
duced on a minimum of spaCe, ultra80nic osCillations provide
for extremely fine mixing and grinding operations, the pro-
duction of extremely fine dispersions, the degassing of liq-
uids and melts, the coagul~tion of aerosols, the production
of alloys from otherwise non-alloyable metals, the dispersion
of immiscible liquids, and the atomization of liquids for the
production of aerosols. Finally, ultrasound destroys oxide
layers on aluminium, iron and copper. Meanwhile, a branch of
chemistry, the sonochemi5try, deals with the effects of ul-
trasound on chemical reactions. It was found that the main
effects of the sonochemical reactions preferably carried out
in liquid phase are based on cavitations, where actually high
temperatures and pressures in the micro-range are observed.
Organic molecules are, for instance, broken down under the
influence of ultrasound, polymers are depolymerized and mono-
mers are polymerized (acrylonitrile). Even the execution of
the Grignard reaction under the influence of ultrasound has
already been suggested, where by means of the ultrasound in
particular the reaction ra1~e is increased and the induction
period, i.e. the start of l:he reaction, is reduced.
Ultrasound is understood to be the sound whose frequency lies
above the human range of hearing, i . e . above about 20 kHz .
For the generation of ultrasound mechanical or electrical os-
cillators ( electroacoustical transducers ) are used . In par-
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ticular piezoelectrical oscillators are utilized, which are
made of quartz or a ceramic material. As regards mechanical
impact and energy, ultrasound is by far superior to ordinary
sound. In addition, ultrasound can easily be focussed. How-
ever, the medium for the transport of ultrasound plays an im-
portant role. Since the absorption of sound generally in-
creases with increasing frequency, the ultrasound is attenu-
ated at a f aster rate than ordinary sound on its way through
a medium. Since gases greatly attenuate the ultrasound, pro-
cesses taking place under the influence of ultrasound are
preferably carried out in liquid media. The absorption of the
ultrasound effects a local heating of the medium.
For the execution of chemical reactions on a technical scale,
the use of ultrasound has not yet gained acceptance, as on
the one hand only a small number of possible applications was
examined, and on the other hand the development of suitable
reactors has only started. It is therefore the object of the
invention to provide an apparatus for carrying out chemical
reactions between liquid or gaseous and solid reactants under
the influence of ultrasou~d, which is also applicable on a
technical scale, ensures a high operational safety, and sig-
ni~icantly increases in p~rticular the reaction rate.
The object underlying the invention is solved by creating an
apparatus comprising a funnel-shaped reaction space and a
subsequently disposed container, where the reaction space has
the shape of a truncated cone, on whose small basal surface
the ultrasonic source is arranged, and where adjacent the ul-
trasonic source at least one nozzle is provided, through
which the liquid and gaseous reactants are supplied to the
reaction space . Since the ef fect of ultrasound in the liquid
phase is better than in the gaseous phase, the liquid reac-
tants are either used as such or in the form of solutions. In
the form of solutions - possibly under pressure -, the
2180864
gaseous reactants reach the reaction spaCe, or are supplied
as such to the reaction space in the pre88urized condition.
In the reaction 8pace, there i8 thu8 in any ca6e present a
liquid phase, which po88ibly contain8 ga8 bubbles, and in
which the solid phase i8 su8pended in particular under the
influence of the ultra80und- Due to the effect of the ultra-
sound and the supply of the liquid and ga8eoUs reactants in
the vicinity of the ultrasonic source it is achieved that the
solid phase is properly di3tributed in the liquid phase and
always is in a vortical state. Moreover, on and adjacent the
ultrasonic source solids are not deposited, so that the ul-
trasound can unimpededly enter the reaction space. Due to the
inventive shape of the reaction space, in particular disad-
vantageous superpositions and cancellations of the sound
waves are avoided, which results in an optimum and uniform
tran~ ; on of energy to the reactants.
In accordance with a further a8pect of the invention the re-
action space has a cone angle ~ of 7 to 35 , a volume of 0 . 5
to 100 1, and a ratio between maximum diameter and height of
0 .1 to 1. 7 . These features advantageously lead to the forma-
tion of planar sound waves, a good intensity distribution in
the reaction space, and the usability of the apparatuS both
on a semi-technical and on a technical scale. Even with a
volume of 100 1, there are not observed macroscopically local
overheatings or local fluctuations of the concentratiOn of
the reactants in the reaction space, so that there are no
safety problems. In accordance with the invention, a reaction
space with a volume of 0.5 to 10 1 is particularly useful, as
it can also be operated with great safety over an extended
period .
In accordance with a further aspect of the invention the re-
action space and/or the container have a cooling jacket. Via
the cooling jacket heat is d ssipated in exothermal reac-
218086~
.
tions, and in endothermal reactions heat is supplied, so that
the optimum reaction temperature can saf ely be maintained .
The ultrasonic source used in the inventive apparatus com-
prises an electroacoustical tran8ducer and a sound amplifier,
where as electroacoustical transduc~r a piezoelectrical
transducer i9 used, and as sound amplifier a sonotrode or a
horn is used. By means of 'the sonotrode or the horn it is
achieved that the ultrason ic source emits the ultrasound al-
most uniformly over the sound inlet diameter.
In accordance with a further aspect of the invention the ul-
trasonic source emits sound wave8 with a frequency of 20 kHz
to 10 MHz almost uniformly into the reaction space and gener-
ates an ultrasonic intensi-ty of 0.1 to 1000 W/cm . The maxi-
mum value of the ultrasonic intensity of 0.1 to 1000 W/cm2 is
reached at the 60und-emitting surface of the sonotrode or the
horn. With these features the reaction rate is increased con-
siderably without the reactor getting out of control; there
will in particular not be an uncontrolled evolution of heat
in the reaction space.
In accordance with the invention it was found to be particu-
larly advantageous that the reaction products present in the
liquid phase are transferred from the upper part of the reac-
tion space to the container, and the solid reactants are sup-
plied to the upper part of the reaction space. The container
is dimensioned such that it provides for a long enough secon-
dary reaction time and acts as buffer. The container is ad-
vantageously designed as stirred vessel. The cooperation of
reaction space and container in particular provides for the
continuous execution of the chemical reactions by circulating
the liquid phase.
It is furthermore possible to select the material of the in-
ner wall of the reaction space such that the sound field for
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the intended reaction is advantageously influenced; acousti-
cally hard materials promo~te the formation of plane waves,
and acoustically soft materials promote the formation of
spherical waves.
To avoid that coarser particles of the solid reactants are
transferred to the container, it is expedient in accordance
with the invention to provide a f ilter element between reac-
tion space and container. With this feature it is ensured
that the major part of the reaction work is effected in the
reaction space, and in the container merely the secondary re-
action takes place.
In accordance with the invention it is finally provided that
through the nozzles disposed adjacent the ultrasonic source
an inert gas is introduced into the reaction space in addi-
tion to the liquid and gaseous reactants. In this way, the
cavitation ef fects of the ultrasound are supported and the
vortical state of the solid reactants is improved.
In accordance with the invention it is particularly advanta-
geous to use the apparatus for the execution of organometal-
lic reactions, in particular the Grignard reaction.
The Grignard reaction
R -- X + Mg ----> R -- Mg - X
R = alkyl or aryl residue; X = Cl, Br, J
is generally carried out in an ether as solvent. On a techni-
cal scale, problems occur in the execution of the Grignard
reaction because the reaction rate is comparatively low, and
the reaction does frequently not start as desired. Under the
inf luence of ultrasound the reaction rate can be increased
and the induction period can be reduced, which is particu-
larly advantageous in the execution of the Grignard reaction
_ . .. . ... . . _ _ _ _
218086~
on a technical scale. It was found that the Grignard reaction
can be mastered particularly well on a technical scale, when
it is carried out in the apparatus in accordance with the in-
vention. Moreover, due to the increase of the reaction rate
and the reduction of the induction period, a continuOus op-
eration, which is extremely economic, is also possible on a
technical scale in the apparatu8 in accordance with the in-
vention. The apparatus in accordance with the invention can
advantageously also be u8ed for the generation of alkyl and
aryl compounds of lithium.
The subject-matter of the invention will subsequently be ex-
plained in detail with reference to the drawing, a calcula-;
tion program, and an embodiment. The drawing shows a sche-
matic representation of the apparatus in accordance with the
invention .
From the reservoir 1 the liquid or gasePux reactants, which
are possibly dissolved in a solVent, are supplied in the form
20 of a liquid phase via line 2 and a plurality of nozzles 2a,
2b to the reaction space 3. From the reservoir 20 an inert
gas is additionally metered via line 21 into line 2. The noz-
zles 2a, 2b are provided in the bottom 4 of the reaction
space 3 and are disposed in the vicinity of the ultrasonic
source. The bottom 4 is formed by the small basal surface of
the reaction space 3, which has the shape of a truncated
cone. The ultrasonic source disposed in the bottom 4 consists
of the electroacoUstical tran8ducer 6 and the sonotrode 5 and
emits almost uniform ultrasonic waves into the reaction space
30 3. From the reservoir 7 t~le comminuted solid reactants are
introduced into the upper part of the reaction space 3 via
line 8. The reaction temperature is adjusted in the reaction
space 3 via the cooling jacket 9 as well as the temperature
measuring device 10.
2I~08~4
Both the solid reactants and the reactants present in the
liquid and/or gaseous pha8~e and the inert gas are introduced
continuously into the reaction 8pace 3- By means of the gas
or liquid jet, which is generated by the nozzles 2a, 2b, and
by means of the ultra80und emitted by the ultrasonic source
an optimum mixing of the reactant8 is achieved in the reac-
tion space 3, where the solid reactants are in the vortical
state and are not deposited on the bottom 4 or on the ultra-
sonic source 5, 6. The liquid phaBe, which also contains the
reaction products, i8 continuou81y discharged from the upper
part of the reaction space 3 via line 11 into the stirred
vessel 13, in which a stirrer 14 is provided. The stirred
vessel 13 is equipped with a cooling jacket lS, by means of
which the reaction temperature is also maintained in the
stirred vessel 13. The gas liberated in the stirred vessel 13
~ inert gas and unreacted gaseous reactants ) is discharged via
line 22 and, possibly after a treatment, recirculated to the
reaction space 3, which is not repre8ented in the drawing. In
line 11 a filter element 16 is provided, which retains the
solid particles from the liquid phase supplied to the stirred
vessel 13.
Via line 17, part of the liquid phase is continuously with-
drawn from the stirred vessel 13. A partial stream thereof is
returned to the reaction space 3 through the pump 12 as well
as the lines 18 and 2, so as to convert the reactants still
pre~ent in the liquid phase. A second partial stream flows
through line 19 for product recovery.
The height, the cone angle 1', the maximum diameter, the ratio
between maximum diameter and height, and the volume of the
reaction space 3 as well as the diameter, the frequency and
the ultrasonic intensity of the ultrasonic source 5, 6 are in
particular dependent on the reaction rate of the chemical re-
action, the absorption behaviour of the multi-phase content
of the reaction space wit~l respect to the sound waves, the
218G864
.~
design of the sonotrode 5 and the performance characteristics
of the electroacoustical tran8ducer 6- The 8election of the
ultrasonic source and the design of the reactiOn space 3 will
be made depending on the respective application of the i,uven-
tive apparatus by utilizin.g a calculation program based on
Webster's differential equ.ation, which is generally used for
the calculation of sound funnels- The dimensioning of the
stirred vessel 13 is effected such that it ensures a suffi-
cient secondary reaction E'erid and has sufficient buffer ca-
pacity. To avoid secondary reactions care should, however, be
taken that the volume of the stirred vessel 13 is not chosen
too large.
Subsequently, the calculation program used for designing the
reaction 6pace 3 will be explained- Webster's differential
equation reads as follows:
~r J~n~r ~1 ~r (~)
~xL d~ t~
For the case of a conical funnel the equation for the vari-
able cross-sectional area of the funnel reads as follows:
,~ ( x I = ~
and the above-stated differentia1 equation is transferred to:
- t k (~ C ~)
clx~ 8
218~86~
with the wave number:
k= ~
c = speed of sound in the reaction mixture;
o~ = angular frequency of the oscillations;
The solutions of these differential equations for the pres-
sure and the speed of sound read as follows:
Xx I e,~r(~ Yr ( 'kX) (~J
and
2~ yLX ) - ~ c ` ,~ . e~(r ( ~ c.i t ~ ` ~Xr ~~ ~k x~ '('I ~ ~ kX ) ( S
Accordingly, the radiation impedance for the conical funnel
at the coordinate o~ the piston-type source is equal to:
--f~ T~x~ ;kxI ~)
~r VT lxl ) ,1 ~-kxr
For the emission of energy as compression wave the imaginary
part must disappear, i.e. the real part of the radiation im-
pedance ZR~ the radiation resistance R~.~, must become large.
The maximum possible value is equal to p c, and the ratio:
218~86~
,~
h ~ T ~l (kXT ~
A I J~ ( K X, ~ ) ~
should approach one. With a given wave number k for the me-
dium, the coordinate XT of the piston-type source in the ~Eun-
nel should be calculated such that a predetermined value i6
reached. ~or the piston-type source in the free medium with
the same amplitude, half the piston diameter should be in-
serted in equation (7) inEtead of the coordinate ~T/ so that
the transmitted sound energy is constantly decreasing with
very small values of k dT/2. Together with the diameter of
the piston-type source dT the opening angle of the funnel can
then be determined to be:
~/ u r ~ f a '` ( x ) ( ~))
The coordinate ~L of the reactor output should be chosen such
that its maximum diameter dL is larger than the wave length
in the medium. A reflection of the wave is thus prevented,
and an unimpeded propagation into the f urther reaction space
is made possible:
X ~ q)
ta.l( r)
A reflection and thus the formation of a standing wave field
can be controlled by adjusting the filling level of the reac-
tion space. By making use of the funnel geometry the emitted
acoustic performance can be increased as against the perform-
21~86~
ance of the piston-type source oscillating in the free me-
dium. The radiation resistance of the used piston-type source
in the free medium is equal to:
~,
(k ~ 9 (/¦o
S -1 ~ ( K 1
~ I
As technically realizable dimensions of a production reactor
the folLowing assumptions 3rust be made:
1. Maximum diameter of the sonotrode: dT = 30 mm
2. Wave numbers of the operating media k = ~o/c
The smallest value is given at a frequency of 20 kHz and
water with c = 1500 m/s. Organic solvents generally have
a value of c < 1000 m/s, so that wave numbers between
0 .1257 1/mm 2 k 2 0 . 0838 1/mm can occur.
3. Efficiencies (according to equation 10):
They lie between 90 and 99%, so that the product k xT
is between 10 2 k XT 2 3.
4. Maximum diameter dL: I~ is larger than the wave length in
the medium. This condition is satisfied in any case, when
the maximum diameter i~ larger than the wave length in
water at 20 kHz, as in organic liquids smaller wave
lengths are measured, ~uch as dL 2 75 mm.
With these general conditions, the geometrical limit cases
can be determined for the different wave numbers. When de-
signing the reaction space 3, there should, however, also be
made considerations as to process technology.
218Q~
Example:
In the following, the apparatus in accordance with the inven-
tion and its use for the execution of a Grignard reaction
will be explained in detail- For carrying out a Grignard re-
action, which takes place in tetrahydrofuran, uses 2-chloro-
butane as liquid reactant and magnesium with a particle sizr~
of 1. 8 to 1. 4 mm as solid reactant, a reaction space is cre-
ated by mean6 of the calculation program, which has a cone
angle ~ of 7, a height of 200 mm, a volume of 0.5 l, a maxi-
mum diameter of 80 mm, a ratio between maximum diameter and
height of 0.4, and a bottom diameter of 30 mm. The ultrasonic
source comprises an electroacoustical transducer, which emits
an ultrasound with a frequency of 20 kHz and an intensity of
20 W/cm2. The sonotrode of the ultrasonic source has a diame-
ter of 13 mm. The Grignard reaction is carried out at a tem-
perature of 23 C and an excess pressure of 0 .1 MPa. 2 . 2
ml/min of a 1-molar 2-chlorobutane solution in tetrahydrofu-
ran are supplied continuously to the reaction space. Subse-
quent to the reaction space, a stirred vessel having a volume
of 3 l is provided. The reaction space contains 10 g magne-
sium .
It was noted that the speed of the Grignard reaction is in-
creased by 300 % under the influence of ultrasound. Hence it
follows that when using said reaction in a continuous plant,
the same conversion can be achieved in a third of the time
otherwise required. It was also found that under the influ-
ence of ultrasound at 5 C the Grignard reaction takes place
at the same speed as the Grignard reaction without ultrasound
at a reaction temperature of 23OC. Hence it follows that the
secondary reactions under the inf luence of the ultrasound can
be restrained due to the possible reduction of the reaction
temperature. 12
