International
Journal for t
he Brewing and beverage industry
2/15 | April | Volume 33 | NUREMBERG | www.brauweltinternational.com
Chlorine dioxide solutions in the
beverage industry
BRAUWELT international | Knowledge | Cleaning and disinfection
Chlorine dioxide solutions
in the beverage industry
Corrosive | Use of chlorine dioxide for disinfection of drinking,
process and industrial water, for bottle disinfection and for disinfection of plants and plant components has been common practice in
beverage production for decades. However, the oxidising disinfectant causes corrosion on metal surfaces. The corrosion behaviour of
austenitic chromium-nickel steel 1.4301 (304SS, V2 A) at different concentrations of chlorine dioxide has been investigated in the
Dr. Küke GmbH laboratory, Wedemark. A chlorine dioxide solution
containing hydrochloric acid and a pH neutral one was used.
Results of the investigations
as well as a comparison of the two processes
used in Hofbrauhaus Wolters, Brunswick,
are presented below. The standard process
for producing pH neutral chlorine dioxide solutions described in DIN EN 12671
“Chemicals used for treatment of water
intended for human consumption – Chlorine dioxide generated in situ” is an alternative to classic chloride dioxide solutions
containing hydrochloric acid. Using the
sodium peroxodisulphate/chlorite process,
3 g of CIO2/d in 1 l containers up to 3000 g
of CIO2/d in 1000 l containers can be made
available as packed material. When the process is run continuously, it is currently possible to produce 20.8 g of CIO2/h.
lCorrosion tests
As in breweries, concentrations of 3 mg of
CIO2/l [1] are used to some extent for killing off beer spoilers and up to 6 mg CIO2/l
for making up for depletion e.g. caused by
conveyor belt lubricants or up to 30 mg
of CIO2/l [2] for acid CIP, it is particularly
interesting to make a comparison of available solutions in terms of corrosivity. This
makes it possible to estimate the life of
plants that are disinfected with chlorine
dioxide. Figure 1 shows the test arrangement for corrosion testing according to
DIN 50905.
750 ml of chlorine dioxide solution are
placed in a triple-neck round bottom flask
and the test specimen is suspended on a
glass hook and immersed 1 cm below the
liquid surface. The solution is stirred. A reflux condenser prevents vaporisation of the
aqueous part of the solution. Each test is
carried out at a temperature of 25 °C.
After the tests, the test specimens are
freed from corrosion products using a soft
brush, washed with water and ethanol and
dried with acetone. A total of four tests,
each lasting for 120 hours, were carried out
(fig. 2 and 3). Table 1 summarises the data
resulting from the tests and figures 4 and 5
present them graphically.
reflux condenser
H2O
glass rod with hook
thermometer
triple-neck
round-boom
flask
ClO2 soluon
test specimen
srring bar
Authors: Maximilian Küke, Dr. Küke GmbH,
Wedemark; Tanja Frickmann, Head of Laboratory Hofbrauhaus Wolters GmbH, Brunswick;
Dr. Fritz Küke, Managing Director, Dr. Küke
GmbH, Wedemark; Germany
2 Brauwelt international | 2015/II
Fig. 1 Test arrangement in accordance with DIN 50905
Cleaning and disinfection | Knowledge | BRAUWELT international
lUse in the brewery
Operational safety in a brewery makes it
mandatory that the generator produces the
required quantity of chlorine dioxide for
several dosage points reliably and failurefree. In order to cover fluctuating chlorine
dioxide withdrawals and operational standstill times e.g. at weekends, the chlorine dioxide should ideally be storable for a certain
period.
The unit should also be user friendly and
prevent mistaking the chemicals used for
production of chlorine dioxide and connecting them incorrectly to the plant. The unit
should also produce a chlorine dioxide solution that, as far as possible, does not contain
any, or hardly any, excess chloride. In addition, it should not change or hardly change
the pH value of the water to which chloride
dioxide is added. This is necessary so that
materials and equipment that, in most instances, are made of 1.4301 stainless steel
and come into contact with chloride dioxide
are not damaged by corrosion to any appreciable extent.
The chlorine dioxide solution has to be
produced in a commercially viable manner. A small surcharge has to be accepted in
some measure in favour of higher safety at
work and lower corrosivity.
lComparison of processes
Chlorine dioxide solution for several dosage points can be produced in one unit with
both the hydrochloric acid/chlorite and the
sodium peroxodisulphate/chlorite process.
Both units allow storing of chlorine dioxide that is stable over a certain time period
Fig. 3
Test specimens IV
(chlorine dioxide
solution containing hydrochloric acid) and V (pH neutral chlorine dioxide solution) after an
Source: Dr. Küke GmbH
exposure time of 120 h in chlorine dioxide solution about 50 ppm
12
10
mass loss [%]
l
Requirements from an
industrial viewpoint
Fig. 2
Test specimens I
(chlorine dioxide
solution containing hydrochloric acid) and II (pH neutral chlorine dioxide solution) after an
Source: Dr. Küke GmbH
exposure time of 120 h in chlorine dioxide solution about 1000 ppm
8
6
4
2
0
hydrochloric acid/chlorite
DK-DOX persulfate chlorite
Fig. 4 Mass loss in tests 1 and 2
0,03
0,025
mass loss [%]
Most equipment and parts in Hofbrauhaus
Wolters GmbH in Brunswick are made of
1.4301 stainless steel. Since the autumn of
2013, DK-DOX® chlorine dioxide has been
used. This is produced using the DK-KONT®
chlorine dioxide generator in line with the
sodium peroxodisulphate/ sodium chlorite process of the same name [3, 4], it can
also be produced decentrally at the pasteuriser as container material in the form of a
manually made-up two component system.
As Brauhaus uses both the known hydrochloric acid/chlorite process as well as the
peroxodisulphate chlorite process, a direct
comparison of the two systems under industrial conditions is possible.
0,02
0,015
0,01
0,005
0
hydrochloric acid/chlorite
DK-DOX persulfate chlorite
Fig. 5 Mass loss in tests 3 and 4
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BRAUWELT international | Knowledge | Cleaning and disinfection
Summary of data tests 1-4
Test no.
pH
1
2
3
4
1.4
6.3
2.2
6.7
Concentration [mg ClO2/l]
920
914
51
51
Mass loss [%]
11.1
0.28
0.029
0.00001
Table 1
with shorter stoppage times before restarting without any problems.
The chlorine dioxide solution produced
by the sodium peroxodisulphate/chlorite
process has a stability of up to 30 days as a
function of ambient temperature. It is thus
stable for a longer period than the chlorine
dioxide solution produced with the process
using an excess of hydrochloric acid.
For the hydrochloric acid/chlorite
process, 9 percent hydrochloric acid and
7.5 percent sodium chlorite are used, both
are available as liquids. In the Dr. Küke GmbH process, sodium peroxodisulphate is in
the form of a solid and sodium chlorite in
the form of a liquid.
For water with a low total hardness and
buffer capacity, dosage of chlorine dioxide
produced with the hydrochloric acid/chlorite process and thus with a substantial
excess of hydrochloric acid lowers the pH
value. In the application described here,
the environment of the filler is sprayed with
1.5 ppm chlorine dioxide solution. A pH less
than four was measured in the raw water
used, having a total hardness of 4° German
hardness. Together with the chloride present, this causes considerable corrosion on
the equipment coming into contact with the
solution, such as the buffer tank for spray
water.
As the pH of the water to which chlorine
dioxide is added is not influenced and as
hardly any chloride is present in the sodium
peroxodisulphate/chlorite process, corrosion is a comparatively minor problem at the
same chloride dioxide concentration.
At Hofbrauhaus Wolters, dosage of
chlorine dioxide prepared with the sodium
peroxodisulphate/chlorite process takes
place in the area of conveyor belt lubrication.
Dosage of chlorine dioxide is such that
1.5 ppm are supplied to the nozzle holders
for conveyor belt lubrication. This is the
same concentration as is used for permanent spraying of the filler environment.
This is the reasons why the effects of the two
different chlorine dioxide solutions can be
compared.
l
Fig. 6 Slime-forming bacteria in the cooling tower of the pasteuriser
Photo: Hofbrauhaus Wolters
Fig. 7 Cooling tower of the pasteuriser operated with DK-DOX®
Photo: Hofbrauhaus Wolters
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Comparison of economics
of the two processes
At today’s prices for hydrochloric acid and
sodium chlorite, preparation of chlorine dioxide using the hydrochloric acid/chlorite
process costs about 6 Eurocent/g of chlorine
dioxide. Based on 250 production days and
requirements of 500 g of chlorine dioxide/
day, the chemicals cost about 7500 EUR/
annum.
Costs for the chemicals for operating the
sodium peroxodisulphate/chlorite unit,
producing the same amount of chlorine dioxide, amount to about 8000 EUR/annum.
The additional costs for this plant are about
500 EUR/annum or about 2 EUR/production day. These additional costs have to be
balanced off against higher safety at work
and lower corrosivity from a commercial
point of view.
Use of chlorine dioxide is lower in an industrial environment than in the sample
calculation. The capacity of the plant is currently being modified so that another dos-
Cleaning and disinfection | Knowledge | BRAUWELT international
age point can be operated. In addition to the
two existing dosage points for mixing to the
cold water of the bottle washer and for conveyor belt lubrication, a third dosage point
for permanent spraying of the filler environment will be operated as a result of the
positive experiences. This third dosage point
will also be supplied by the sodium peroxodisulphate/chlorite plant. To do so, the existing hydrochloric acid/chlorite unit will be
decommissioned.
lAnother application
Chlorine dioxide can also be used for the
cooling water loop of the pasteuriser. Prior
to using chlorine dioxide, a biocide based
on chlorine methylisothiazolinone compounds was added to the pasteuriser water.
As sugar-containing beverages pasteurised
in the unit contribute to high nutrient val-
ues, biological contamination is comparatively high.
The lamellae of the cooling tower are
made of plastic material so hot caustic
solution cannot be used for clarification.
Cold cleaning procedures did not yield the
required result. Especially during the summer months, biofilm formation could not be
prevented. Slime-forming bacteria settled
along the lamellae, this can be clearly seen
in figure 6.
Conversion to chlorine dioxide took
place in the autumn of 2013. DK-DOX®
has been used since. In contrast to disinfection in the filler environment, this comes
as a ready-to-use solution in a container.
Within a number of weeks, increased discharge of biofilm was observed in the cooling tower before the lamellae in the whole
cooling tower were uniformly cleared. This
is shown in figure 7, the photo was taken in
the spring of 2014.
n
lLiterature
1.http://www.dk-dox-brau.de/fileadmin/
head/110802_Desinfektionsmitteltest.
pdf
2.Piklaps, H. M.: „Experimentelle Studien
zur Bier- und Schankanlagenhygiene“,
term paper 1, Staatsexamen für das Lehramt an berufsbildenden Schulen, University Hannover, 2006.
3. Küke, F.: „Die Erzeugung von Chlordioxid
für den menschlichen Gebrauch“, Vom
Wasser, Wiley-VCH, Weinheim, 2005,
103 (4), pp. 18-22.
4.Küke, F.: „Preiswerte Chlordioxiderzeugung für den Einsatz zur Oberflächendesinfektion in CIP Anlagen“, BRAUWELT, Nr. 17, 1997, pp. 651-652.
In summary – comparison of processes
In Germany, the use of chlorine dioxide in the food industry is limited to disinfection agents and processes approved in the German
Drinking Water Regulation 2001.
Two processes for preparation of chlorine dioxide are currently used in breweries:
1. sodium chlorite hydrochloric acid process
5 NaClO2 + 4 HCl ➝ 4 ClO2 + 5 NaCl + 2 H2O
2. sodium chlorite/sodium peroxodisulphate process
2 NaClO2 + Na2S2O8 ➝ 2 ClO2 + 2 Na2SO4
Sodium chlorite HCL process
Sodium chlorite – Na2S2O8 process
DK-DOX®, DK-KONT® processes
Theoretically 80 per cent conversion of sodium chlorite to chlorine
dioxide.
Theoretically 100 per cent conversion of sodium chlorite to chlorine
dioxide.
Preparation of chlorine dioxide solutions with about 20 g of ClO2/l with
300 per cent hyperstoichiometric excess of hydrochloric acid.
Preparation of chlorine dioxide solutions without dilution of 2 - 3 g/l with
1000 per cent hyperstoichiometric excess of hydrochloric acid.
Preparation of chlorine dioxide solutions between 0 and 5 g/l according
to reaction equation (2).
Half-life of chlorine dioxide solutions with about 20 g of ClO2/l 6 - 12 h
depending on ambient temperature. Stability of chlorine dioxide solutions with 2-3 ClO2/l with 1000 per cent excess of hydrochloric acid about
2 weeks. Chlorate formation: “Disinfection gaps” possible.
Chlorine dioxide solutions are storable for one month with chlorine dioxide losses < 10 per cent p.m.; no disinfection gaps.
Chlorine dioxide solutions prepared have pH values between –1 and 0.6,
contain high amounts of chloride and, immediately after preparation,
contain free chlorine (Cl2).
Chlorine dioxide solutions prepared have pH values between 6 and 7,
contain very low amounts of chloride and, immediately after preparation,
do not contain free chlorine (neither HOCl nor NaOCl).
Mixing up suction lances for the liquid sodium chlorite and hydrochloric
acid reagents may result in severe accidents due to uncontrolled escape
of chlorine dioxide and thus to operators being endangered.
No mix-up of connections or hazardous situations can arise. The liquid
sodium chlorite reagent goes into the reactor using a suction lance and
a pump, the solid sodium peroxodisulphate reagent goes into the reactor
with the dilution water flowing through a cartridge.
Two dosing pumps for accurate dosing of identical volumes of hydrochloric acid (9 %) and sodium chlorite (7.5 %) are required in reactor.
A simple peristaltic pump for dosing a 10 % chlorite solution. Readymade salt in cartridge is dissolved in dilution water. Control using level
sensors.
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