Process for the production of metal soaps

A process for the production of a solid metal soap of the formula EQU M(R--COO)(R"--COO) in which M is at least one metal from the group of Ca, Mg, Cd, Ba, Zn, and Pb; and R and R' are C.sub.8 -C.sub.34 hydrocarbon radicals, by direct synthesis from at least one fatty acid with metal oxides and/or metal hydroxides which comprises maintaining a reaction zone containing a liquid phase comprising fatty acid under reduced pressure, passing a portion of the liquid phase to an external premixing zone, introducing a solid metal oxide and/or metal hydroxide into the liquid phase in the premixing zone, passing the mixture to the reaction zone through an intensive mixing zone, and continuously removing water of neutralization formed by the reaction.

FIELD OF THE INVENTION 
This invention relates to a process for the production of solid, neutral or 
basic metal soaps by a controlled solid/liquid reaction of liquid fatty 
acids with solid metal oxides and/or metal hydroxides in an external 
premixing zone under reduced pressure and to the use of the metal salts as 
a stabilizer and/or lubricant mixture in the processing of plastics. 
BACKGROUND OF THE INVENTION 
It is known that metal soaps are produced either by the melt process, in 
which the molten fatty acid is reacted with metal oxides, hydroxides 
and/or suitable metal salts, or by the precipitation process in which 
their sodium soaps are subjected to double decomposition with 
water-soluble salts of the corresponding metals. The precipitation process 
generally gives very clean and voluminous products which can be processed 
at temperatures below 100.degree. C. However, filtration and drying costs 
make it much more expensive than the melt process. 
Stabilizers produced by the melt process are satisfactory in purity and 
color for many industrial applications, for example as stabilizers in the 
processing of plastics. For example, the lead, barium and cadmium 
compounds have been successfully used in practice as such stabilizers. 
However, these substances have a highly toxic effect, particularly when 
they are present in powder form. Dust emission, particularly during 
processing, is a particular hazard to manufacturers of powder-form 
stabilizers because the powder-form metal soaps are taken up by the 
respiratory system and are able to develop their toxic effect therein. 
RELATED ART 
For these reasons, melt processes are described in DE-PS 15 44 697 and 
DE-PS 17 94 429 which, to prevent dust emission, claim a 
stabilizer/lubricant combination consisting of a mixture--combined in the 
melt--of a purely organic component suitable as lubricant, for example an 
ester of wax acids and higher aliphatic alcohols, paraffins or fatty 
alcohols, a suitable metal soap, a long-chain aliphatic carboxylic acid or 
basic lead salts of inorganic or organic acids. DE-PS 15 45 697 in 
particular describes a process for the production of these dust-free 
stabilizer/lubricant combinations, in which the toxic, insoluble dust-form 
stabilizers are dispersed in melts of the lubricants or in molten mixtures 
of stabilizers and lubricants and are converted into the solid state 
either on a flake-forming roller or by simple discharge into pans. The 
powder-form toxic stabilizers are completely enveloped in the non-toxic 
lubricants by this process. They are present in solid form and are 
completely dust-free because the lubricants naturally have considerably 
better adhesion than the powder-form stabilizers. 
In addition, EP-A 163 395 and GB-A 2,113,521 describe processes for the 
production of animals feeds in which liquid or molten fatty acids are 
reacted with calcium oxide or calcium hydroxide in the presence of 
proteins and carbohydrates. However, these processes are very expensive on 
equipment because the reaction mixture, which evidently does not react off 
completely, has to be spread out on an endless belt or the like for 
after-reaction and drying. The calcium soaps obtained in this process 
would appear to be difficult to convert into free-flowing particles 
without the additives mentioned above, such as proteins or carbohydrates. 
Finally, applicants' DE-OS 38 06 192 describes a process for the production 
of powder-form basic metal soaps, in which powder-form fatty acids are 
reacted with powder-form metal oxides or metal oxide mixtures in the 
presence of water or an acid as catalyst at temperatures from ambient 
temperature to 100.degree. C., optionally under reduced pressure, the 
reaction mixture having to be present throughout the reaction in the form 
of discrete free-flowing particles. 
Now, the problem addressed by the present invention was to provide an 
improved process for the production of powder-form, neutral or basic metal 
soaps which would provide for dust-free, environmentally safe introduction 
of the solid metal oxide or metal hydroxide into the fatty acid melt in 
the form of a controlled solid/liquid reaction without the addition of a 
catalyst. Another problem addressed by the present invention was to 
provide a process for working up the liquid metal soaps which would enable 
the water of neutralization formed to be readily removed under process 
conditions via a suitable condensation unit. 
BRIEF DESCRIPTION OF THE INVENTION 
The technical solution to the problem addressed by the present invention is 
based on the concept of removing parts of the fluid phase of the fatty 
acid mixture initially introduced from the contents of the reactor under 
process conditions and delivering them to a premixing zone into which the 
solid metal oxide and/or hydroxide is introduced. In this premixing zone, 
a mixture is formed from the circulated liquid phase and the solid phase 
introduced and is adjusted in its consistency so that the mixture may 
function as a so-called "living seal". By establishing suitable reaction 
conditions for the solid reactants to be introduced into the interior of 
the reactor kept under reduced pressure, the pressure inside the reactor 
can be reliably controlled with regard to foaming. After the solid has 
been introduced, the reaction space of the premixing zone can be closed by 
suitable mechanical elements so that outside air cannot be admitted into 
the reaction system. 
Accordingly, the present invention relates to a process for the production 
of solid, neutral or basic metal soaps corresponding to the following 
general formula 
EQU M (R--COO)(R.sup.1 --COO) 
in which M represent one or more metal cations from the group consisting of 
Ca, Mg, Cd, Ba, Zn and Pb and R and R.sup.1 may be the same or different 
and represent C.sub.8-34 hydrocarbon radicals, by direct synthesis from a 
corresponding fatty acid or fatty acid mixture with metal oxides and/or 
metal hydroxides, characterized in that a stream of the liquid phase of a 
fatty acid or fatty acid mixture kept under reduced pressure in the 
reactor is run off into an external premixing zone and contacted therein 
with a solid metal oxide and/or metal hydroxide in a solid/liquid 
reaction, the reaction product formed is returned to the reactor via a 
following intensive mixer and the water of neutralization formed is 
continuously removed from the reactor via the gas phase. 
The advantages of the process according to the invention lie on the one 
hand in the exact dust-free and, hence, environmentally safe introduction 
of the metal oxides or metal hydroxides into the fatty acid melt, so that 
the reactor capacity can be better utilized through relatively low 
foaming, and on the other hand in the fact that, in contrast to the prior 
art, there is no need to add a catalyst. Another advantage of the process 
according to the invention is that the metal soaps returned to the reactor 
do not have to be subjected to a time-consuming after-reaction because the 
neutralization reaction has already taken place completely in the external 
reaction loop.

DETAILED DESCRIPTION OF THE INVENTION 
In one preferred embodiment of the invention, the liquid/solid reaction 
according to the invention is carried out in such a way that the external 
premixing zone before the intensive mixer is in direct pressure 
equalization with the reduced pressure prevailing inside the reactor and 
at the same time--via the feed system for the solids--with the ambient 
pressure and the consistency of the paste-form mixture formed in the 
premixing zone is selected so that the mixture serves as a sealing 
compound for pressure equalization. 
According to the invention, the melt of the fatty acid or fatty acid 
mixture is run off into the external premixing zone under a reduced 
internal reactor pressure of approximately 100 to 900 mbar and preferably 
200 to 800 mbar, the internal pressure in the premixing zone having to be 
reduced to take the fall in pressure into consideration. In the premixing 
zone, the fatty acid melt is contacted under reduced pressure--optionally 
several times--with at least stoichiometric quantities of metal oxide 
and/or metal hydroxide in a solid/liquid reaction. 
Accordingly, a considerable difference in pressure prevails between the 
interior of the reactor and the atmospheric pressure. The mixture serving 
as a "living seal" in the premixing zone therefore has to be adjusted in 
its consistency so that, under the particular conditions prevailing, it is 
able to act as an actual sealing element against penetration of the far 
higher external pressure into the interior of the reactor. This threat to 
the desired pressure equalization is not the only burden on the paste-form 
sealing compound. To prepare the mixture, the liquid component has to be 
introduced into the premixing zone under a limited elevated pressure. If 
the liquid pressures are too high, parts of the liquid phase are in danger 
of breaking through the powder-form metal oxide and/or metal hydroxide 
introduced--preferably continuously--from "outside". Accordingly, this is 
a second source of danger to the desired trouble-free, preferably 
continuous section of the process where the solid reactants are introduced 
into the reactor under time control. 
To rule out interruptions of the type just mentioned, a preferred 
embodiment of the process according to the invention is characterized in 
that the premixing zone is also operated under reduced pressure. However, 
the reduced pressures prevailing therein are higher by comparison with the 
reduced pressure prevailing inside the reactor. The pressure in the 
premixing zone is preferably kept at around 400 to 900 mbar and, more 
preferably, at around 750 to 850 mbar. This pressure range is established 
by adapted control of the streams of liquid and solid material to the 
premixing zone and their discharge into the interior of the reactor. 
Selected mass ratios of the streams of liquid and solid reactants have 
proved to be advantageous for forming the mixture acting as a living seal 
in the premixing zone. The preferred mass ratios of the liquid phase 
(m.sub.1) to the solid reactants (m.sub.2) are in the range from about 
20:1 to 100:1. Mass ratios of m.sub.1 to m.sub.2 of approximately 30:1 to 
80:1 have proved to be particularly suitable. 
In applicants' above-cited earlier application DE-OS 38 06 192, it is 
pointed out that the particles should be present in discrete free-flowing 
form during the reaction. Accordingly, it is proposed (the teaching of the 
present invention in its preferred embodiment also makes use of this) to 
subject the mixture of active substances initially formed to fine 
dispersion under the effect of suitable technical mixing elements. 
So-called inline mixers, for example operating on the stator/rotor 
principle, have proved to be particularly suitable for this purpose. More 
particularly, that unit of the reactor installation which is affected by 
the process according to the invention is designed, for example, as 
follows: 
A premixing zone is provided separate from the main reaction zone, but in 
direct pressure communication with the main reaction zone. The dry, 
preferably powder-form, solid reactant is delivered to the premixing zone, 
preferably by a screw conveyor. At the same time, liquid phase in 
admixture with the solid reactant introduced is added to the premixing 
zone from the interior of the reactor through a circulation pipe so that 
the mixture acts as a living seal in the premixing zone (particularly in 
the region of the stated mass ratios of liquid phase to solid phase). From 
the premixing zone, the paste follows the pressure gradient towards the 
interior of the reactor and enters the intensive mixer, i.e. for example 
the following inline mixer, which it then leaves to enter the interior of 
the reactor. The rate at which the material passes through the premixing 
zone can be controlled virtually as required under these conditions and 
optimally adapted to the course of the reaction inside the reactor. The 
solid reactants may be added in batches and/or continuously. 
After the solid reactants have been introduced, the interior of the reactor 
is closed off from its surroundings. This can be done, for example, by a 
separating element provided in the premixing zone which separates the 
premixing zone and the screw conveyor for the solid material from one 
another. During introduction of the solid reactants, the separating 
element is opened. After the total quantity of solid reactants required 
has been added, it is closed again. 
In one particularly preferred embodiment of the invention, the solid metal 
oxide or metal hydroxide is introduced into the fatty acid melt by means 
of an inline mixer which meters the fatty acid mixture at a rate of 
approximately 1 to 20 m.sup.3 per hour and the solids at a rate of 50 kg 
to 500 kg per hour and preferably 100 to 300 kg/h. In order to guarantee 
maximum transport capacity of the inline mixer, the pressure of the 
installation has to be varied so that the fatty acid melt does not flow 
back into the space of the screw conveyor for the solid material. 
According to the invention, the solid metal oxide and/or metal hydroxide 
are introduced into the fatty acid melt in such a way that the particle 
size of the agglomerate formed is below 10 .mu.m and the acid values of 
the metal soaps formed are between 0.1 and 30 and preferably between 0.5 
and 10. 
Any fatty acids of natural or synthetic origin containing 8 to 34 carbon 
atoms can be converted into the desired powder-form, neutral or basic 
metal soaps by the process according to the invention, saturated fatty 
acids preferably being used. The process according to the invention may be 
used with particular advantage for reacting technical mixtures of natural 
saturated fatty acids containing 12 to 22 carbon atoms, with the proviso 
that the melting point of the fatty acids is below 200.degree. C. and 
preferably below 150.degree. C. Typical examples of such fatty acids are 
palmitic acid, stearic acid, behenic acid and montanic acids and also 
technical mixtures rich in the fatty acids mentioned. 
According to the invention, oxides and/or hydroxides of calcium, magnesium, 
cadmium, barium, zinc and/or lead known to the expert may be used as the 
metal oxides or metal hydroxides. According to the invention, calcium 
hydroxide, magnesium oxide and/or zinc oxide is/are preferably used. In 
principle, other salts of the above-mentioned metal ions, such as for 
example the carbonates, acetates, stearates, or other metal soaps may of 
course also used in the process according to the invention. 
In one preferred embodiment of the invention, diluents adapted to the metal 
soaps are added to regulate viscosity, particularly where fatty acids 
having a melting point above 100.degree. to 150.degree. C. are used. 
Suitable diluents are, for example, paraffins having a melting point of 
20.degree. to 150.degree. C. and preferably to 100.degree. C., esters of 
wax acids and higher aliphatic alcohols preferably containing 12 to 22 
carbon atoms, spermaceti or suitable fatty acids. The diluents according 
to the invention may be mixed with the starting fatty acids in a ratio by 
weight of 1:10 to 10:1 and preferably 1:2 to 2:1, depending on the metal 
soap, this ratio by weight being determined by the pumpability of the 
reactor contents. 
To ensure continuous operation of the feeder, it has proved to be advisable 
for the purposes of the invention to provide the screw with an 
anti-adhesive coating. This coating is intended to prevent adhesion or 
bridge formation of the metal oxide or metal hydroxide on the screw 
conveyor. 
The process according to the invention is further optimized by the use of 
spray cooling in the condensation system. The superheated steam from the 
neutralization reactor is cooled in the condensation system via an 
injection nozzle operated with cold process water. Under the effect of 
this spray cooling, the danger of incrustations being formed in the 
condensation system is almost completely eliminated and adjustment of the 
installation pressure remains freely selectable. 
The present invention relates to the use of the neutral or basic metal 
soaps produced by the process according to the invention as stabilizer 
and/or lubricant mixtures in the processing of plastics and as a feed 
additive for dairy cows. 
The invention is illustrated by the following Examples. 
EXAMPLES 
Example 1 
In a 2.5 m.sup.3 reaction vessel equipped with a four-stage MIG stirrer 
with a base-mounted stirring element and a condensation system, 468 kg 
technical stearic acid were initially introduced with the bottom outlet 
valve closed and the jacket heating system was switched on. At a 
temperature of approximately 70.degree. C., 411 kg glycerol distearate 
were introduced and the reaction mixture was heated with stirring to 
150.degree. C. At the same time, the installation pressure was reduced to 
550 mbar. After the bottom outlet valve had been opened, the circulation 
pump of the external reaction loop and the inline mixer were switched on. 
By switching on the metering screw and opening the sealing element, 63 kg 
calcium hydroxide were introduced into the premixing zone over a period of 
45 minutes. The transport capacity of the inline mixer was adjusted in 
such a way that, on the one hand, no excessive foaming was caused by the 
return of the metal soap via the inline mixer to the reaction vessel and, 
on the other hand, no fatty acid flowed back into the metering screw. 
After the solid had been introduced, the installation pressure was reduced 
to around 30 mbar and the water of neutralization was continuously removed 
via the condensation system. The end point of the reaction (approx. 1 
hour) was determined by continuous sampling and determination of the acid 
value (required acid value: 5 to 10). The installation pressure was then 
returned to normal pressure with nitrogen and the liquid reaction mixture 
was made up in the usual way, for example by prilling. The melting point 
of the metal soap formed was approximately 95.degree. C. for a yield of 
99%. 
Example 2 
2800 kg technical stearic acid were introduced into and heated to around 
95.degree. C. in a 10 m.sup.3 reaction vessel equipped in the same way as 
described in Example 1. 2100 kg of a paraffin wax (melting point: 
&lt;80.degree. C.) were then introduced over a period of 1 hour with the 
proviso that a temperature of 85.degree. C. was not exceeded. After the 
reaction temperature had been increased to 150.degree. C., the 
installation pressure was lowered to 550 mbar and the external reaction 
loop was brought into operation via the circulation pump and the inline 
mixer. 160 kg zinc oxide were then introduced into the inline mixer by the 
metering screw over a period of 45 minutes. Without any interval, 213 kg 
calcium hydroxide were introduced in the same way over a period of 35 
minutes without any change in the reduced pressure of the system as a 
whole. After the solid had been introduced, the installation pressure was 
reduced to around 30 mbar and the water of neutralization was continuously 
removed through the condensation system. The end point of the reaction 
(approx. 1 hour) was determined by continuous sampling and determination 
of the acid value (required acid value: 5 to 10). The installation 
pressure was then increased to normal pressure with nitrogen and the 
liquid reaction mixture was made up in the usual way, for example by 
prilling. The melting point of the metal soap formed was approximately 
100.degree. C. for a yield of 99%.