The influence of temperature on the decomposition kinetics of peracetic acid in solutions

THE INFLUENCE OF TEMPERATURE ON THE DECOMPOSITION KINETICS OF PERACETIC ACID IN SOLUTIONS

L.Kunigk, D.R.Gomes, F.Forte, K.P.Vidal, L.F.Gomes and P.F.Sousa

Escola de Engenharia Mauá,,Departamento de Engenharia Química e de Alimentos,

Praça Mauá 01, CEP 09580-900, Phone: [phone], Fax: [phone],

São Caetano do Sul - SP, Brazil

E mail: [e-mail]

(Received: February 10, 2000 ; Accepted: April 10, 2001)

Abstract - Peracetic acid is a powerful sanitizer that has only recently been introduced in the Brazilian food industry. The main disadvantage of this sanitizer is its decomposition rate. The main purpose of this paper is to present results obtained in experiments carried out to study the decomposition kinetics of peracetic acid in aqueous solutions at 25, 35, 40 and 45 °C. The decompositon of peracetic acid is a first-order reaction. The decomposition rate constants are between 1.71x10^-3 h ^-1 for 25 °C and 9.64x10^-3 h^-1 for 45 °C. The decomposition rate constant is affected by temperature according to the Arrhenius equation, and the activation energy for the decomposition of peracetic acid in aqueous solutions prepared from the commercial formulation used in this work is 66.20 kJ/mol.

Keywords: peracetic acid,decomposition kinetics, temperature, pH, concentration.

INTRODUCTION

Peracetic acid is a powerful sanitizer that has only recently been introduced in the Brazilian food industry. Commercial formulations of this sanitizer contain mixtures of acetic acid, hydrogen peroxide, water and peracetic acid as shown by the following chemical equation:

CH₃ COOH + H₂O₂«CH₃COOH + H₂O

Tensoactive agents may be added to the peracetic acid sanitizer formulations to improve product penetration into cracks and crevices on equipment surfaces and stabilizers may be added to increase the product shelf life.

Peracetic acid has many advantages when compared to sodium hypochlorite, the most commonly used sanitizer in Brazil. One of the many advantages of peracetic acid is that its decomposition produces only acetic acid and oxygen and therefore affects neither the final product nor the waste treatment process. It may be used over a wide temperature spectrum (0 to 40°C) (Leaper, 1984), in the CIP (clean in place) process since it does not produce foam, and in a medium saturated with carbon dioxide (Jurado, 1993). Peracetic acid may also be used with hard water, and proteins do not affect its efficiency when no catalase is present. To date no microbial resistance to this type of sanitizer has been observed, and a concentration as low as 40 mg/L is effective in the destruction of some microorganims typically found on food industry surfaces. It is efficient at pH values from 3.0 to 7.5 (Block, 1991; Lenahan, 1992; Jurado, 1993) unlike chlorine compounds, which below a pH value of 6.0 release chlorine gas and above 8.0 quickly lose their efficiency. Commonly used concentrations of peracetic acid have varied between 50 and 750 mg/L. This sanitizer is compatible with stainless steel, glass, Teflon®, Viton®, silicon and some types of rubber, but it is incompatible with alkalis, rust, iron, copper and nickel. Rusty metal causes a rapid breakdown of bulk peracetic acid. When Fe³⁺ is introduced into 25 °C bulk solution, the rate of oxygen generation from the reaction is increased. For instance, a 15% solution of peracetic acid released 7.0 mL of oxygen/L.h. When 10mg of Fe₂O₃/L were added to this solution, the rate at which oxygen was released became 14 mL/L.h (Jurado, 1993).

Greenspan et al., (1955) observed that peracetic acid solutions are less stable than solutions of hydrogen peroxide. At room temperature, 40% solutions of peracetic acid lost between 1 and 2% of their active ingredient per month while 30 to 90% solutions of hydrogen peroxide lost only 1% of their active agent per year. Also, at room temperature, diluted solutions of peracetic acid (1%) lost half of their sanitation power within 6 days. The shelf life of solutions of peracetic acid, is improved when they are stored at temperatures below 30 °C, preferably in their original containers.

No information was found on the decomposition kinetics of peracetic acid. The main purpose of this paper is to present results obtained in experiments carried out to study the decomposition kinetics of peracetic acid in aqueous solutions at 25, 35, 40 and 45 ^oC.

MATERIAL AND METHODS

A commercial formulation of a peracetic acid sanitizer containing 5% peracetic acid and 20% hydrogen peroxide was used in the experiments. The above product was diluted with distilled water in order to obtain concentrations of peracetic acid equal to about 240 mg/L and 280 mg/L. The solutions were then maintained at constant temperatures (25, 35, 40 and 45 ^oC) and the concentrations of peracetic acid were measured at regular intervals. The concentrations of peracetic acid were measured using the iodimetric methodology proposed by ECOLAB (1997), but the concentrations of sodium permanganate and sodium thiosulphate used were of 0.02 and 0.01 N, respectively.

RESULTS AND DISCUSSION

Figure 1 shows the results obtained in our experiments. Each point shown in Figure 1 is the average of three to five measurements; the corresponding standard deviations are also represented. It can be observed that the concentration of peracetic acid decreases with time. Increasing the temperature caused decomposition to occur more quickly. At 45 °C the concentration was halved in 72 hours, but at 25 °C the loss in 240 hours was of only 33%. Therefore, temperature has an important role in the shelf life of solutions of acid peracetic.

Equations (1) to (4) were proposed to correlate concentration (C) and time (2) with a confidence level of 95%. Equations (1) to (4) represent the curves in Figure 1:

The percentage differences between the values of C calculated with equations (1) to (4) and the corresponding experimental values of C varied from 0.0 to 13.4% (average, 4.2%; standard deviation, 3.7%).

We may then conclude that the decomposition of peracetic acid is a first-order reaction. Table 1 shows the influence of temperature on the specific decomposition rate constants (k).

Figure 2 shows that equation (5) may be proposed to correlate k and T. The percentage differences between the values of k calculated with equation (5) and the corresponding experimental values of k varied from 3.9 to 9.9% (average, 6.8%; standard deviation, 2.9%). Figure 2 also shows that the Arrhenius law was obeyed.

Equation (5) permits calculation of the activation energy for the decomposition of peracetic acid in aqueous solutions prepared from the commercial formulation used in this work, which is 66.20 kJ/mol (15.81 kcal/mol). With this value, it is possible to compare the efficiency of two different stabilizers if the concentration of the compounds present in the sanitizer formulation are kept constant.

CONCLUSIONS

When the concentration is around 250 mg/L, the decompositon of peracetic acid, is a first-order reaction, and the corresponding rate constant is affected by temperature according to the Arrhenius equation. The activation energy of the decomposition of peracetic acid in aqueous solutions prepared from the commercial formulation used in this work is 66.20 kJ/mol.

ACKNOWLEDGEMENTS

This work was supported by Instituto Mauá de Tecnologia. The authors would like to thank Dr. Walter Borzani and Prof. Lyrio Sartorio for their helpful comments.

NOMENCLATURE

C Concentration of peracetic acid, mg/L K decomposition rate constant, h^-1 t temperature, °C T temperature, K 2 time, minutes

• Block, S.S., Disinfection, Sterilization, and Preservation, pp.167-181. Fourth edition, Lea & Febiger, Philadelphia, (1991).
• Ecolab Inc., P3 - Oxônia^® Ativo. Technical Information (1997).
• Greenspan et al. (1955) apud Block, S.S., Disinfection, Sterilization, and Preservation. Fourth edition, Lea & Febiger, Philadelphia (1991).
• Jurado, J., The Stability of Disinfectants Used in Brewery CIP, MBAA Technical Quarterly (Madison), 30, 58-63 (1993).
• Leaper, S., Influence of Temperature on the Synergistic Sporicidal Effect of Peracetic Acid plus Hydrogen Peroxide on Bacillus subtillis SA 22 (NCA 72-52), Food Microbiology (London), 1,199-203 (1984).
• Lenahan, R.J., Peroxyacetic Acid: The New Generation Sanitizer, MBAA Technical Quarterly (Madison), 29, 53-56 (1992).

Publication Dates

• Publication in this collection
  02 Aug 2001
• Date of issue
  June 2001

History

• Received
  10 Feb 2000
• Accepted
  10 Apr 2001