Note: Descriptions are shown in the official language in which they were submitted.
~ ~ 3 ~
28414/lOOOU
PROCESS AND DEVICE FOR T~E CONTINUOUS
PRODIJC TION OF PEROXYCARBOXYLIC AClDS
BAC~GRO~ OF T~E I~WENTION
S A. Field Of The Inventior~
The invention relates to a process for the continuous an~d
controlled production of peroxycarboxylic acids, in particular, peroxyacetic
acid, and to a device for carrying out this process.
B. Background
Peroxycarboxylic acids are used in the laboratory and on an
industrial scale for the production of epoxides according to the so-called
Prilezhaev reaction (compare Trahaowsky, Oxidation in Organic Chemistry,
Part C, p. 211 to 252, New York, Academic Press, 1978~ and for the
hydroxylation, the Baeyer Villiger oxidation and special oxidation processes.
15 In addition, peroxycarboxylic acids a~e being increasingly used in the chemical
and allied industries, e.g., in the food industry, the phannacelltical industry
and the paper industry andl as a disinfectant in wa~er ~reatment.
In these branches of industry, there is a continuously increasing
demand for disin~ectants for sterilizing production facilities. Disinfectants
2() used ~or this pulpose include sodium hypochlorite, chlorine dioxide,
halogenat~d carboxylic acids, aldehydes, quaten ary ammonium compounds,
hydrogen peroxide and peroxycarboxylic acids, in particular peroxyacetic acid,
(peracetic acid).
Hydrogen peroxide and the peroxycarboxylic acids, such as
25 peroxyacetic acid, are not thermally stable and can undergo violent
~ ~ 2~3~
decomposition reaclions when subjected to excess heating or in the presence of
contaminants, as a result of which serious problems arise during transportation
and storage. Because peroxyacetic acid explodesl e.g., in the form of organic
solutions of >50 percent by volume ("vol. %") and of aqueous solutions of ~ ;
:>70 vol. %, it is frequently prepared in the presence of acid in si~u, i.e., ~ :~
from acetic acid and ~22 .
However, handling low molecular peroxycarboxylic acids such
as peroxyacetic acid causes problems to the user because these substances have
a pungent odor and the vapors have a strongly corrosive effect on the eyes, the
skin and the mucous membranes.
Ihe commercial quality peroxycarboxylic acids, such as
peroxyacetic acid, which are usually used for disinfection purposes, consist of
the so-called equilibrium peroxycarboxylic acids. The concentration of
peroxycarboxylic acid in these disinfectants is usually between S and 15% by
weight. In a peroxyacetic acid equilibrium concentrate, th~ concentrate
contains the components hydrogen peroxide, acetic acid, peroxyacetic acid,
water, acid catalyst and stabilizers, wherein the components hydrogen
peroxide, acetic acid, peroxyacetic acid and water are in a chemical
equilibrium according to the following equation:
[cat.3 ~T
CH3$:~001H ~ H202 ~ CH3COOOH + H20 ~3
acetic hydrogen per2cetic water
acid peroxide acid
- I'he content oî peroxyace~ic acid in equilibrium conse~uently
depends on the concentration of ~he reactants, acetic acid and hydrogen
.. .~
peroxide, as well as on the temperature. Adjusting the equilibrium is done by
acid catalysis.
From EP-A-0269 345, a process and a device is known ~or
dilu~ing a reaction product, in particular a peroxyacid, for the production of adisinfection solution. According to EP-A-0269 345, a reaction is carried out
between two or more reactants in a reactor, and the reaction product is diluted.The concentration of the reaction product after dilution is monitored with an
eiectrochemical sensor and the dilution of the reactioa product is controlled
according to the values indicated by this sensor. In addition to re~uiring
dilution of the resultant peroxyacid, the reactor of EP-A-0269 345 is not
equipped with a device for heating the reaction mixture. Consequently, the
reactor in EP-A-0269 345 cannot quickly and colltinuollsly provide a peroxy
carboxylic aci~l by carrying out the process at ~m elevated ternperature for a
more rapid adjustment of the equilibrium. For this reason, the present day
requirements, such as those arising in connection with the production of
pe~xyacetic acid, e.g., in large industrial operations in the food industry,
could not be satisfied to a satisfactory degree by the process of EP-A-0269
345.
It is the object of the present invention to avoid the
disadvantages and problems detailed above which are connected with the
production, treatment and use of peroxycarboxylic acids, in palticular the
pungent odor and thF risk of irritation and corrosion of the eyes, the skin and
the mucous membranes of the operatives and to make a process and a device
a~vailable by means of which a rapid adjus~ment of the reaction equilibrium and
consequently a satisfactory continuous execution of the process is possible.
2 ~
SUI~L~RY OF THE IIYVENTION
The object of the present invention is achieved by way of a
continuous process and a device for the production of peroxycarboxylic acids,
and in parlicular, peroxyacetic acid, in which the peroxyca~boxylic acid is
S produced in a closed facility, only when directly re~uired and in the desired
quantity. Direct contact wi~h personnel is avoided during the manufacture of
the peroxycarboxylic a~ids and during their use, e.g., as a disinfectant.
In particular, the continuous process of the present invention
comprises the step of: converting a carboxylic acid with hydrogen peroxide in
10 an aqueous medium in the presence of a catalyst, at a temperature of 40 to
60C. The process of the present invention is characterized in that the
hydrogen peroxide and the carboxylic acid are continuously passing into the
retention reactor, and after the reaction equilibrium has been adjusted, the
peroxycarboxylic acid that is formed is continuously withdrawn from the
15 retention reactor.
The present invention is also dire ted to a device for carrying ut
the continuous process of the present invention. ~he device of the present
invention comprises a retention reactor for holding tbe reaction medium; a
heating element capable of heating the reaction me~ium to 40 to 60C; and
20 two feedlines, wherein each of the ~eedlines is equipped with a returll valve
and a metering punnp capable of substantially continuously pumping a reaction
component from its storage vessel into the feedline and into the retention
reactor.
21316~
IBÆF DESCRIPTION OF THE FIGURES -
FIGURE I is a graph plot of " % peroxyacid" (y axis) versus
"reaction time" hl minutes (x axis) as a function of three different
temperatures. The three temperatures reflect the effect of temperature on the
S time required to achieve reaction equilibrium.
FIGURE 2 is a diagrammatic representation of one embodiment
of a device of the present invention ~or continuously producing the
peroxycarboxylic acid.
, ~, .,
. " ~.
~ 2~3~
I:2ETAILED DESCRIPTIOIY OF TH!E I~WENTION
The present invention has two aspects. In its first aspect, the
invention is directed to a continuous process for producing a peroxycarboxylic
acid. The process of the present invention comprises the step of converting a
5 carboxylic acid with hydrogen peroxide in an aqueous reaction medium in the
presence of a catalyst at a temperature of 40 to 60C. l~e process of the
present invention is characterized in that the hydrogen peroxide and the
carboxylic acid are continuously passing into the reaction chamber, and after
the reaction equilibrium has been achieved, ~he peroxycarboxylic acid thus
10 formed is continuously withdrawn from the retention reactor.
The effect of the reaction temperature on the reaction
equilibrium and the results obtained are showrl in the following Figure 1. The
measured values are based on a mixture of 14 7% hyclrogerl peroxide, 37.5%
acetic acid, û.S% stabilizer, 11.25% suiphuric acid and 36.05% water. Figure
15 I shows that by heating the reaction mixture to approximately 50C, the
reactiorl equilibrium, i.e., the optimum concentration of desired peroxyacetic
acid, is achieved after only approximately thirty minutes. At room
temperature or lower temperatures (e.g., at 5C in an unheated room in ~:
winter), the equilibriurn is reached much later, narne1y a~ter a period which is
20 too long ~or a contimlous process in order to satis~y the requirement of
peroxyacetic acid, Çor exarnple, for disinfecting purposes in a modem clean~ng
facility ~e.g., a bonle cleaning facility in the beverage industry) or ~n a
pros~uction ~acility (e.g., tank disinfection in breweries).
The subject matter of the invention is a process for the
25 continuous production of peroxycarboxylic acids by converting a ca~oxylic
acid with hydrogen peroxide in an aqueous medium in the presence of a
3 ~
catalyst. charact~r~ed in that the conversion is carried out at a temperature in
the range of ~0 to 60C and further characterized in that the peroxycarboxylic
aid so produced does not require dilution.
According to an appropriate embodiment of the process
5 accordin~, to the invention, the hydrogen peroxide and the carbo~ylic
acid/catalyst mixture are passed continuously to a retention reactor for
receiving the reaction mixture in two separate feedlines and the
peroxycarboxylic acid formed is continuous!y withdrawn from the retention
reactor after adjusting the reaction equilibrium.
The hydrogen peroxide used according to the process is
preferably a hydrogen peroxide with a concentration of 30 to 50% by weight.
As catalyst, any common catalyst known as suitable for the
produc~ion of peroxycarboxylic acids by conver!ing a carboxylic acid with
hydrogen peroxide can be used. Catalysts used according to the invention are
prefe~bly mineral acids such as phosphoric acid or nitric acid and in
particular, sulphuric acid. Hydrochloric acid is not suitable for use as mineral
acid because it can easily lead to decomposition reactions. Basically, however,
any organic (e.g., phosphonic acid) or inorganic acid can be used as catalyst
provided that it is stable vis-a-vis the oxidizing medium and does not promote
2û the decomposition of the active oxygen carrier.
The conve~sion is camed out at a temperature in the region of
40 to 6ûC, and preferably a~ a temperature of approxirnately S0 to 60C.
The concentration of the peroxycarboxylic acid in the reac~ior
medium can be varied within a wide range. Preferably, the concentration is
10 to 30%; more preferably, 10 to 25% by weight; and most preferably, 13 to
15% by weight.
~:~3~6~
In general, the reaction temperature is in the region of 40 to
60, particularly, in the region of 50 to 55C. Typically, the reaction is
carried out at a temperature of approximately 50C.
If temperatures above 60C are used, the decomposition of the
S peroxycarboxylic acids is accelerated in an undesirable manner. If a
~emperatuse of less than 40C is used, the reaction equilibrium is reached after
a time which is unsuitably long for a continuous execution of the process.
In the process of the present invention, the carboxylic acid used
is preferably a C~ - C6 carboxylic acid or an oligocarboxylic acid, and in
10 particular, ~ormic acid or acetic acid.
According to a preferred embodiment of the process of the
invention, ~he peroxycarboxylic acid (e.g., peroxyacRtic acid~ that is
withdrawn from the retention reactor is passed directly to the application, e.g.,
directly to a line to be disinfected or to a bottle cleaning plant in the beverage
15 industry or directly to a production facility to be disinfected e.g., the
fermentation, storage and pressure tanks in a breweryt or directly to any other
disinfectant circuit. In this way, contact with the peroxycarboxylic acid ,
harTnful to heal~h or its vapors and the associated problems such as irritation
and corTosion of the eyes, the mucous membranes and the skin can be avoided
20 by controllin~ the process lcontrolling ~he quantities of peroxycarboxylic acid
conc~ntJate produced) and by using a closed circui~ up to the intended
application, e.g., up to the plant or line to be disin~ected.
By controlling the reaction temperature according to the present
i~i~tention, it is also possible to achieve the reaction equilibrillm in a time
25 sufficiently brielF for a con~im30us easily controllable execution of the process,
e.g., in approximately thirty minutes as a result of wSIich the process is easy to
~ ~ 3 ~
~ontrol and it is thus possible to adjust the quantities produced according to the
process to the requirement concerned, and to consequently avoid funher
treatment of the peroxycarboxylic acids hannful to health connected with
intennediate storage.
S In its second aspect, the subject matter of the present invention
also includes a device which is suitable for the continuous production of
peroxycarboxylic acid according to the process of the invention and comprises:
a retention reactor for receiving the reaction medium, the retention reactor
being equipped with a heating device and two supply lines equipped with
return valves, which lines are each equipped with a metering pump for
supplying the reaction components from the storage vessel to the supply lines
and into the retention reactor.
The volume of the retention reactor depends mainly on the
perforrnance required (e.g., the output of peroxycarboxylic acid concentrate
per hour). Heating of the reaction mLxture can take place by way of internal
heating, e.g., in the fonn of an elec~nc heating coil, or by external heating, ~-~
e.g., in the fonn of a hollow jacket surrounding the reactor through which a
heating liquid or steam is passed. If the reactor consists of a material with a
low thermal conductivi~y, e.g., of a material resistant to the components of thereaction mi%ture, such as a polymer, heating talces place preferably via an
internal heating unit.
Passing the reaction components (e.g., hydrogen peroxide and
acetic acid) from the storage vessel into the supply lines and into the retention
se~ctor ~akes place via metering pumps with flow controls. The suction
"lances" into the S~otage vessel ate eqoipped with "empty" indieatots.
~ ~ - 2 ~
- 10 -
In the device and process of the present invention, the hydrogen
peroxide is stor~d separately from the carboxylic acid component.
Preferably, the device according to the invention is equipped
with a pressure sensor situated at the outlet of the retention reactor.
S Appropriately, this pressure sensor is coupled with a device which douses the
device automatically w;th water once a maximum pressure has been exceeded.
In this way, it is possible to guarantee a high level of operational safety
because the device can be doused automatically with water via the pressure
sensor and the facility coupled with it if a pressure limit is exceeded which can
iO be caused e.g., by an unexpected decomposition reaction.
Appropriately, the device is also equipped with a mechanical
pressure relief valve by way of which a decrease in pressure in the reactor can
take place even ~n the case of a power failure.
For proper and simple maintenallce of the facility, it is
appropriate to equip the device with a ventlng valve and a discharge valve for
ventin~ and/or draining respectively and with a valve for dousing with water.
The discharge of the peroxycarboxylic acid ejectecl by ~he water douse via the
discharge valve takes place appropriately via a neutralization vessel colmected
to the device.
According to a par~icularly appropriate embodimeot, tbe device
is equipped with suitable facilities for directly metering tihe peroxycarboxylicacid withdrawn from the retention reactor to the site of application. In this
way, it is possible by a suitable controi of the process, i.e., of the output ofperoxycarboxylic acid concentrate per hour and direct dispatch to the site of
application (e.g., bottle cleaning facilities to be disin~cted with
peroxycarboxylic acid in the beverage industry, production f~ilities, e.g.,
211 3~ 6~
fennentation stordge and pressure tanks in breweries etc.) to avoid any
intermediate storage and disect contact between the peroxycarboxylic acid that
is hannful to health and the operating personnel. lFor this reason, the
peroxycarboxylic acid concentrate is usually metered directly, e.g., into the
5 lines to be disinfected or into a disinfection circuit, the metering operation
being controlled via the controls of the process for the production of the
peroxycarboxylic acids (output of peroxycarboxylic acid concentrate per hour)
coupled with electrochemical sensors.
In the device according to the invention, at least those parts
10 coming into contact with the starting or the end products (carboxylic acid,
hydrogen peroxide" mineMI acid catalyst, peroxycarboxylic acid) consist of
materials resistant to corrosion vis-a-vis these substances. Such materials are
e.g., polymers, in particular polyvinylidene fluoride (PVDF) and/or
polytetrafluoroethylene ~PDFE), glass or corrosion-resistant steel and/or non-
15 fierrous metal, if necess~ry additionally provided with a corrosion-resistant
coating by a suitable passivating measure, such as are hlown to the art.
The retention reactor, particularly, if i~ is equipped with interna~
heating, is provided with a heat insulating jacket, e.g., a hollow jacket filled,
if necessasy, with thennal insulating material, or a coating of a thermally
20 insulating material. The heating of the retention reactor can appropriately be
controlled in an infinitely variable manner. A standard heat exchanger or
retentiorl reactor known and suitable for this purpose can be used, it being
possible ~or the retention reactor to be subdivided into a temperature-controlled
he~ting section and a thennally insulated residence section.
~5 It is also within the scope of the device of the present invention
that the electronic control, regula~ion and overflow control ~acility be provided
2~L3~6~
by way of a member selected from the group consisting of a memory-
progfammable control, a single-board microcomputer, ~ microcomputer
development system, a personal computer havin~ digital and analog input and
output boards and discreet electronic or electromechanical circuits, and a
S combination ~hereof.
Figure 2 contains a diagrammatic representation of one
embodiment of a device according to the invenCion. The present invention will
now be explained in further detail on the basis of the device illustrated in
Figure 2 without being limited thereto in terms of its scope. The embodimen~
10 illustrated in Figure 2 is a device for the execution of the process according to
the invention for the continuous production peroxycarboxylic acid by
converting a carboxylic acid with hydrogen peroxide in the presence of a
catalyst, the device comprising a retention reactor I for receiving the reaction
medium. The retention reactor is equipped wilLh an el~ctrical internal heater
15 10 which is controlled in an infinitely variable marmer. The retention reactor
is connected with ~wo feedlines 2,2 equipped with re~um valves 9,9, each line
being equipped with a metering pump 3,3 for respectively supplying the
reaction components (components I and 2) from the storage vessels 11, 12 to
lines 2,2. The retention reactor is provided with a thermal insulation jacket
20 13. At the reactor outlet, there is a pressure sensor 4 (not illustrated) as an
excess pressure control; this is connected to a magnetic valve 17 which opens
when a pressure limit is exceeded, as a result of which the device is
automatically doused with water. The device is also equipped with a
n1echanical pressure relief valve 20 which is capable of e~fecting a decrease in
25 pressure in the reactor even in the c2se of a power fai~ure (e.g., failure of the
mains powsr supply). The device is also equipped with a venting valve 5 and
a discharge valve 6 for v~nting or discharging. It is additionally equipped with
a neutralization vessel 7 via which the discharge of the peroxycarboxylic acid
ejected by the water douse via the pressure relief valve 20 or discharged via
the discharge valve 6 takes place. The neutrali~ation vessel has the form of an
S overflow vessel. Metering of the peroxycarboxylic acid takes place in line
with the user's requirements by controlling the magnetic valve 14 and the
metering pumps 3,3 which suck the components from containers 11, 12 via
suction iances with filling level sensors 15, 15. The storage vessels 11 and 12
are designed according to an ernbodiment used as an example as containers ~ ~.
10 with an 800 liter capacity and according to another ernbodiment provided as an
example as drums with a 200 liter capacity. A~ magnetic valve 17 and a ball
return valve 18 are connected downstream of the water connection. Between
the metering pumps 3,3 and the retum valves 9,9, there is a device (19,19) for
flow control.
The device illustrated in Pigure 2 was used to carry out the ;~
process according to the invention with a reactor output of 44 g peroxyacetic
acid per hour or 2.76 kg of a 15% peroxyacetic acid concentrate forrned
continuously by the reactor within one hour. The temperature of the heating
section was approximately 50C as a result of which an equilibrium mixture
20 was obtained within approximately 30 minutes with an approximaiely 15%
peroxyacetic acid. rhe reactor volume was only I.5 Iiters, however, this was
sufficient for the reactor perfonnance of 400 g peroxyacetic acid per hour
indicated.
- By increasing the temperature andlor the concentlatioll of the
25 reactants further, it is possible to achieve a further acceleration of the reaction
~ ~ 3 ~
- 14 -
(shortest time to reach the equilibrium reaction mixhlre) an~d, if necessary, a
filrther reduction of the reactor volume.
By utilizing the process and device according to the invention,
it is thus possible, clepending on the selection and the concentration of the
5 cornponents and the choice of the reaction temperature, to continuously
produce aqueous concentrates of peroxycarboxylic acids having the same or - -
different concentrations as added to satisfy any demand. In this way, it is .
possible to continuously satisfy the requirement for peroxycarboxylic acids,
particularly, peroxyacetic acid as disinfectant m the chemical industry and
10 allied branches of industry, e.g., in the food industry, the paper industry and
in particular, in beverage operations and breweries. In average operations,
such as mineral water wells and breweries, peroxyacetic acid is used as a
disinfectant for sterilizing the rinsing areas of the bottle cleaning facilities.
These facilities res~uire a continuous, uni~olm dosage of approximately 10-20
15 mg peroxyacetic acid per Liter fresh water supplied. In the bottle cleaning
facilities of the usual size, approximately 10-20m3 fresh water are consumed
per hour. On ~his basis, a maximum requirement of 400 g peroxyacetic acid
per hour can be calculated which, as indicated above, can be easily provided
in a controlled manner by way of the process according to the invention and
20 the device according to the inven~ion in a closed circuit which is safe even for
the operating personnel, while avoiding intermediate stolage.
