1
Thermal hazards of a green antimicrobial peracetic acid combining DSC calorimeter with thermal
2 3 4
analysis equations
Yih-Wen Wang•Min-Siou Liao•Chi-Min Shu 5 6 7 Abstract Peracetic acid (PAA) is a widely used green antimicrobial agent of the environmental protection chemicals, which registered applications have expanded to include in sanitation at food processing and 8 9 pasteurizers in beverage plants, agricultural premises, wineries and breweries, as well as the disinfection of medical supplies, to prevent biofilm formation in pulp industries, and as a water purifier and disinfectant. The 10 11 thermal reactivity and hazard characteristics were evaluated for PAA solutions by calorimetry analysis methodology, where the thermal reaction and kinetic data were programed by differential scanning calorimetry 12 13 (DSC). The thermal stability screening test was able to determine the self-decomposition of PAA solutions, and to observe the initial exothermic temperature (T i ) and heat of decomposition (ΔH d ). The thermokinetic 14 15 parameters of PAA were also calculated according to the experimental data by temperature programming and thermal analysis model with Arrhenius equation. The purpose of this study was to elucidate the self-heating 16 17 exothermic excursions associated with the various PAA solutions via C++ programming language. Understanding the thermal decomposition hazard of PAA was beneficial to proactive safety protocol for the 18 19 20 21 22 industrial process, storage, as well as transportation. Keywords Peracetic acid (PAA)•Green antimicrobial agent•Calorimetry analysis methodology•Differential scanning calorimetry (DSC)•Thermal decomposition hazard 1

1 2 3 Y.
W. Wang () Department of Occupational Safety and Health, College of Public Health, China Medical University, 91, Hsueh-Shih Rd., Taichung 40402, Taiwan, ROC 4 5 6 e-mail: evenwang@mail.cmu.edu.tw M.-S. Liao•C.-M. Shu 7 Department of Safety, Health, and Environmental Engineering, YunTech, Douliou, Yunlin 64002, Taiwan, ROC 8 2

1
Introduction
2 3 Peracetic acid (PAA) is an important and widely used green antimicrobial agent of environmental protection 4 5 chemicals, which registered applications have expanded to include in sanitation at food processing and pasteurizers in wineries, beverage plants, agricultural premises, greenhouse facilities and equipment, as well as 6 7 the disinfection of medical supplies, to prevent biofilm formation in pulp industries, and as a water purifier and disinfectant [ 1 ]. Although PAA provides free radicals to execute epoxidation, their weak oxygen-oxygen single 8 9 bond is readily broken at a particular temperature interval, which could court a self-heating reaction and then generates unexpected heat to vaporize a significant amount of gas during thermal decomposition. If the heat 10 11 from the runaway reaction is not removed adequately and pressure increased, then a thermal explosion could result in the reactor or container. The thermally reactive nature of organic peroxides has both particular 12 13 oxidizing and combustible properties that necessitate taking safety measures and precautions into account [ 2 ]. Take two catastrophic accidents caused by PAA as typical examples. One was an explosion in the Alpha 14 15 Campholenine Aldehyde (ACA) plant in India due to the presence of foreign oxidizing material in the high density polyethylene (HDPE) barrel into which highly explosive PAA was decanted. Unfortunately, two 16 17 employees were injured [ 3 ]. The other incident involved mishandling of PAA and resulting in the death of one worker in a chemical plant in China [ 4 ]. 18 19 Organic peroxy acids are one of the most useful classes of organic peroxides because of the prevailing application of specific oxidation reactions in the chemical industry. Concentrated organic peroxy acids are 20 21 particularly unstable, reactive, and unpredictable explosive. The stability decreases with decreasing chain length of peroxy acids and the reactions proceed spontaneously in the direction of minimum Gibbs free energy, which 22 23 are considerably more stable and decompose slowly at lower, unperceivable temperature. For example, peracetic (CH 3 COOOH), perpropionic (C 2 H 5 COOOH), and perbutyric (C 3 H 7 COOOH) acids need to be stored at room 24 25 temperature. Nevertheless, performic acid (CHOOOH) may be stored at 0 to 5.0 °C without appreciable decomposition [ 5 ]. PAA is extremely corrosive and widely used peroxy acid, which is a powerful oxidant as 26 bleaching, disinfection, epoxidation of olefins, and so on. PAA is vastly applied because of excellent 3

1 non-chlorine bleaching ability in global pulp and paper industry, and commonly used as disinfection in 2 3 wastewater treatment for its excellent virucidal, sporicidal, and fungicidal effectiveness [ 6 ]. In addition, PAA at lower agent concentrations is used to disinfect in medical categories, food-processing and beverages, etc., and 4 5 grades with higher concentrations up to 40 mass percent are exclusively used for oxidation reactions. PAA is a green chemical and non-persistent in the environment while it breaks down to CO 2 and H 2 O, which are no toxic 6 7 byproducts with its use. A reviewed of the literature shows most researches of PAA were focused principally on synthesis, hydrolysis, and applications, whereas fewer studies have delved into its thermal decomposition 8 9 hazards [ 7 ].
The safety-related scope of organic peroxides regarding preparation, use, storage, transportation, and disposal has been concerned because of theirs considerable instability during shipment or storing for 10 11 extended periods of time. Therefore, thermal hazardous identification for manufactures and users is a crucial task [ 8 , 9 ]. However, industrial grade PAA is used mostly as an epoxidation agent, and the general concentration 12 13 is higher than 40 mass%. It is necessary to understand the thermal hazards, corrosive, and incompatible properties for PAA solutions and their safe handling regulations [ 10 ]. 14 15 In our previous studies, calorimetric instruments, including differential scanning calorimetry (DSC), vent sizing package 2 (VSP2), and thermal analysis methods, have been applied to test the thermal decomposition 16 17 and runaway reaction of the energetic chemicals [ 8 , 9 ]. Our aim was to evaluate the thermal hazard of self-reactive decomposition of PAA solutions by using calorimetric methodology. DSC was used to obtain the 18 19 essential thermokinetic parameters for thermal decomposition of PAA solutions, and the thermal analysis data were implemented by the thermal reaction analytical equations. Through these experiments, the results could be 20 21 applied as proactive safety protocol for the manufacturing process of PAA plant. 4

1
Experimental and methods
2 3 Materials 4 5 In theory, peroxy acids are readily synthesized by acid catalyzed reaction. It is performed using of sulfuric acid 6 7 (H 2 SO 4 ) or combining transition metal catalysts with PAA to enhance rapid conversion. There are two methods for producing PAA, of which one is by the mixing acetic acid and acid-catalyzed reaction of hydrogen peroxide 8 with H 2 SO 4 as a catalyst, as shown in Eq. 1 [ 6 ]. 9 CH 3 COOH  H 2 O 2    CH 3 COOOH  H 2 O (1) 10 This method has been applied for years; because of the acetic anhydride-hydrogen peroxide an exothermic 11 12 reaction is difficult to govern in the formation of diacetyl peroxide, which has explosive hazards [ 10, 11 ]. Therefore, it should deliberately choose the acetic acid-hydrogen peroxide reaction to synthesize PAA solution 13 14 in which the heat of formation is about 6.40 kJ mol –1 , and employ distillation to remove H 2 SO 4 . An equimolar mixture of acetic acid and hydrogen peroxide containing 1 mass% H 2 SO 4 is allowed to stand at 15 °C for 12 15 16 hours, a solution containing 50 mass% PAA is obtained [ 5 , 12 ]. In addition, the issue of pollution and remaining acetic acid handling for PAA process were effectively reduced. Special care should be taken with regard to 17 18 contamination and instabitity by highly explosive acetic peroxide [ 13 ]. PAA is a clear, colorless liquid with no foaming capability. It has a strong pungent acetic acid odor (acetic 19 20 acid is the principal component of vinegar) and has an acidic pH of less than 2. In addition, 30, 35, 40, and 45 mass% PAA solutions with H 2 O as solvent were prepared for experimental samples. Peracetic acid is probably 21 22 the most important and widely used peroxy acids. The melting points of PAA (–56 °C) in organic solvents is an important aspect for their use as oxidents and whose boiling point (110 °C) is lower than other acids. All of 23 24 these samples were stored at 4 °C. The physical and chemical characteristics of PAA are recommended in Table 1 [ 14 , 15 ]. 25 5

1 Differential scanning calorimetry (DSC) 2 3 According to National Fire Protection Association (NFPA code 704) [15] , DSC is considered to be the available 4 5 screening test for assessing thermal hazards of reactive chemicals. DSC was performed by using a Mettler DSC821 e in the temperature range of 30 to 300 °C at specific heating rate of 0.5 to 8.0 °C min -1 . Only 4–5 mg of 6 7 sample was added in the crucible and sealed. DSC curves and chemical kinetic data were obtained by using DSC thermoanalytical software.
The dynamic temperature-programmed screening of DSC was used to measure 8 9 the heat of reaction/decomposition (ΔH), initial exothermic temperature (T i ) and various thermokinetic data. 10 11 Thermal self-reaction analytical equations 12 13 Oxidation reaction of peroxy acids could be rapid and energetic. When the oxidant is supplied within the molecule itself, then the resulting self-reaction mechanisms are generally decomposition reactions. Hence by 14 15 calculating the oxygen balance of peroxy acids is an effective mean of predicting the reactivity of the energetic chemicals [16] . The calculating equation to determine the oxygen balance (OB) in mass percent for a chemical 16 17 having the composition C i H j N k O n is: OB = −1600(2i+j/2−n) mass% molecular mass (2) The molecular formula for PAA is C 2 H 4 O 3 . It is not in its stable oxidant state and the decomposition of PAA is 18 19 20 as follows, C 2 H 4 O 3  1.5O
2 2 CO 2  2H 2 O (3) 21 Accordingly, the OB can be determined meaningfully. Substituting the numbers 2, 4, and 3 for the variables i, j, 22 23 24 25 and n in Eq. 3 and using the a molecular mass 76.06 gives, OB = −1600(2·2+4/2−3) 76.06
= −63.1 mass% The Chemical Thermodynamic and Energy Release Program (CHETAH) code, developed by the American Society for Testing and Materials (ASTM), indicates the explosion hazard criteria with respect to OB 26 that between −120 mass% and +80 mass% have high explosion potential. Comparing of this OB value of −63.1 6

1 mass% to the CHETAH criteria indicates it is in the high category with respect to self-reactive potential make 2 3 the decomposition of PAA more energetic. Because of the sensitivity of the reaction rate towards temperature, and therefore of the enthalpy of the 4 5 6 7 8 9 10 reaction is important to define a criterion as an indicator of this effect. The thermal reaction number, B-value, defined as follows [ 17 ]:
B

E
a 
T
ad
RT
2 (4) B is a measure of the violence of a thermal explosion. The number value of B is within the range 1–50, which is a ratio of the adiabatic temperature rise (ΔT ad ). In the theory of thermal explosion with heat loss the temperature difference (R T 0
2 ) E
a –1 will appear as the critical temperature rise for the occurrence of a thermal explosion. It is influenced by the temperature dependence of the rate of reaction as well as the adiabatic temperature rise. 11 12 The calculation of the exothermic chemical reaction was used by simplified analytical equations combined with the classical Arrhenius equation to reproduce the required thermokinetic data by DSC trails and to match 13 14 the variability of the self-heating rate which could evaluate the exothermic reaction and thermal hazard of PAA solutions in the industrial processes. Therefore, using calorimetric methodology to classify thermal hazards of 15 16 the industrial reactive chemicals is an alternative study. The simplified analytical equations related to thermal runaway reactions to programme scanning curves from calorimetry methodology were proposed [ 9 , 16 , 18 ]. The 17 18 simplified analytical equations may be calculated to obtain the self-heating rate by taking reaction order, heat of decomposition, Arrhenius frequency factor, and apparent activation energy, etc. into account. Zhao et al. in 19 20 recent reports have shown that the spontaneous decomposition of PAA under an acid condition was an observed second-order reaction with respect to PAA concentration [ 6 , 19 ]. The nth-order reaction with a single reactant 21 22 was used for verification of our approaches [ 18 , 20 ]. For an exothermic reaction, the enthalpy from the reaction will result in a temperature rise, which, in turn, represented the rate of reaction as shown in Eqs. 5 to 6. 23 24 25 Reacent
d
C 
dt

k
C n Products (5) (6) The concentration of the reactant could be approximately related to the variation of the temperature in the 7

1 2 3 exothermic system [ 21 ]. C C 0  (
T
f 
T

T
ad ) 
T
ad 
T
f 
T
i 4 (7) (8) For normal thermal decomposition reaction, where k is an Arrhenius rate constant, x is the fraction degree 5 6 of conversion evaluated from the DSC curve and heat of decomposition reaction can therefore be calculated form Eqs. 9 and 10. 7 8 9 10 
H d
 
T ad mc p x x
 ( (  
H
 
H
d ) ) 
mc
p (
T
f 
T mc
p 
T
ad ) (9) (10) The E a for the decomposition could be calculated by applying Arrhenius kinetic model, which can be described 11 12 13 by Eq. 11.
k

A
exp[ 
E
a
RT
] (11) From Arrhenius equation it is evident that a plot of the natural logarithm of the peak power output measured in various DSC dynamic scanning rate (β) against T –1 the reciprocal of the absolute temperature at which they were 14 15 carried out should give a straight line with a slope of –E a R –1 . Thus the apparent activation energy can be determined. The ASTM Standard E698 kinetic parameters were evaluated by using five different heating rates 16 17 18 19 20 21 22 by DSC dynamic scanning experiments. E a and A could be calculated by ASTM E698 [ 22 ], as in the following Eqs. 12 to 14:
E a
 ( 2.303
D R
)[
d
logβ ]
d
(
T
1 )
D

d
ln[  (
x
)]
dx

d
ln(
x
 2 )  1
x
 1
e

x
]
dx A
 (
E
a
RT β 2
)exp(
E
a
RT
) (12) (13) (14) The self-heating rate was determined by DSC data and physical properties. The strongly exothermic 23 nth-order reaction with the greatest period of self-heating can be proposed the analytical equations as follows: dC  dt
dx

dt k
( 1 
x
)
n
(15) 8

1 2
dT dt
  ( 
H mc
p d )
d
x
dt
  ( 
H
d
mc
p )
k
( 1 
x
) n (16) 9

1
Results and discussion
2 3 Thermal decomposition of PAA 4 5 Peroxy acids typically form free radicals upon decomposition. The free radical formation could induce further 6 7 decomposition by autocatalysis or heats, and thus a runaway reaction might exist with thermal accumulation. The peroxy bonds (–O–O–) in peroxides are easily cleaved by thermal sources, such as heat or light, and shock. 8 9 The gas-phase decomposition kinetics of peroxy acids, such as performic acid, peracetic acid, and perbutyl acid, afford a peroxy bond energy of 138.0 kJ mol –1 at 130–240 °C [ 13 ]. Generally, the peroxy acids proceed by two 10 reaction mechanisms of thermal decomposition: 11 22 R 1 COOOH   R 1 OH  CO 2 CH 3 COOOH  CH 3 COO    HO 12 13 R 1 COOOH  R 1 CO 2 H  1 2 O 2 (18) The spontaneous decomposition of various peroxy acids showed that the rate of a peracid (RCOOH) was 14 15 nth-order with respect to the concentration of peracid anion (ROO−). However, the spontaneous decomposition of PAA under an acid condition was an observed second-order reaction with respect to PAA concentration in the 16 raising reaction rate [ 5, 6, 19 ].
The reaction is shown as follows: 17 18 CH 3 COOOH CH 3 COOH  1 2 O 2 (19) Free radical decomposition of peroxy acids in solvent solution is hemolytic cleavage of the peroxy bond 19 20 as the initial step. The relative reactivity of radicals with PAA is correlated with the ionization potentials. Heating of PAA above 80 °C starts the peroxy bond homolysis to yield radicals according to the following 21 reactions [ 13 ]: (17) (20) 23 CH 3 COO  CH 3   CO 2 (21) 24 CH 3   CH 3 COOOH  CH 3 OH  CH 3 COO  10 (22)

1 2 3 The reaction is followed by rapid loss of non-condensable gas, carbon dioxide, from the acyl peroxy radical which continues the chain reaction by abstraction of hydroxyl radical (HO  ) from another molecule of peroxy acid to form relatively stable alcohol and acyl peroxy radical. The gases from the decomposition of PAA 4 5 were the flammable substances to initial fire and explosion hazards. 6 7 Thermal analysis of PAA by DSC 8 9 The PAA solutions at various concentrations were analyzed under dynamic program at a heating rate of 4.0 °C min –1 by DSC trails. Figure 1 displays the thermal decomposition of PAA solutions with the exothermal peaks, 10 11 whether the concentrations of PAA solutions were high or not. The T i1 of PAA solutions at 30, 35, 40, 45, and 50 mass% were 41.2, 40.0, 39.7, 38.6, and 38.1 °C, respectively. The reproduced experimental results showed that 12 13 the T i1 were raised when the concentrations of PAA solutions were reduced. The initial exothermal temperature (T i1 ) of the first peak for various PAA solutions initiated at about 40.0 ± 2.0 °C, at which the thermal-induced 14 15 period of PAA solutions could be self-reacting at higher room temperature or ambient thermal sources. The second peak for T i2 is initiated between 80 and 100 °C and released unexpected enthalpy with out of normal 16 17 temperature control in the process operating or storage conditions. The second peak indicates obvious exothermic reaction, which was increasing with the concentrations of PAA. The PAA solutions by DSC dynamic 18 19 program trails were listed in Table 2 . Comparing with our previous studies of organic peroxides, PAA solution is more dangerous than other commercial peroxides in terms of earlier initial exothermal temperature and higher 20 21 22 23 enthalpy, as presented in Table 3 [ 8 , 9 , 23 – 26 ].
The heat of decomposition of 50 mass% PAA solutions had the highest enthalpy, reaching ca. 1,500 J g –1 . From DSC trials, the heat of decomposition of various PAA solutions was proportioned to its concentration. Furthermore, the pH value of PAA detected by the digital pH meter is lower which has the containers or piping 24 25 lines corrective hazard and as potential sources of incompatible element in the plant [ 5 ]. The thermal decomposition of PAA solutions is complicated because it consisted of PAA, acetic acid, and H 2 O 2 . In addition, 26 PAA in solutions may be consumed by the spontaneous decomposition in Eqs. 20–22, and the hydrolysis 11

1 reaction of PAA is in the following equation [ 6, 19 ]. 2 3 4 CH 3 COOOH  H 2 O CH 3 COOH  H 2 O 2 (23) In aqueous solution, hydrolysis of PAA is relatively slow, whereas, as in the presence of heat sources, it could in the presence of heat sources, it could rapidly decompose and release prominent heat, as indicated the 5 6 enthalpy change. Nevertheless, the effect of concentration of PAA solutions was obviously in terms of heat of decomposition. PAA will be spontaneously reactive on heating at ca. 40.0 °C or above. PAA and 7 8 methyl-ethyl-ketone peroxide (MEKPO) were considered thermal instability of theirs heat of decomposition larger than 3,000 J/g which a minimum theoretical value is generally accepted as a criterion for detonation 9 10 properties [ 5 ]. Materials with low SADT may even need to be stored in freezers, with backup refrigeration capability. Recommended practices for low-temperature storage of organic peroxides are given in NFPA [ 15 ]. 11 12 In this study, understanding the exothermic temperature of PAA could provide the process safety protocol during normal chemical plant operation.
13 14 Self-heating rate of PAA by thermal analytical equations 15 16 DSC was used to estimate the thermokinetic parameters of PAA, as presented in Table 3 . When the heating rate 17 18 19 20 was accelerated, the apparent onset temperature (T i ) was initiated later. For instance, the heating rate was chosen by the pre-set experiments and compared 0.5 °C min –1 with 8.0 °C min –1 . T i was detected ca. 31.0 and 45.0 °C, respectively. The exothermic peak of PAA generated heat and increased sharply because the heating rate (8 °C min –1 ) supplied higher energy to the reaction. Then, these curves had exothermal reactions of information over 21 22 the temperature of experimental design from Figure 2 , which shows that the detected T i of PAA was ca. 30.0 °C. The value of T
i
was low, even close to room temperature (between ca. 25.0 and 35.0 °C). If the ambient 23 24 25 temperature at which PAA is stored is close to T i , PAA could kick off a risky runaway or explosion. Consequently, the influence of temperature upon PAA is obvious. The data could show the appearances of PAA at various heating rates, 0.5, 1.0, 2.0, 4.0, and 8.0 °C min –1 , as given in Table 4 . As far as thermodynamic 12

1 reaction is concerned, E a was altered with continuous excursions. Then, the standard method, ASTM E698, was 2 3 4 5 6 7 tested. Figure 3 depicts the relationship between the logarithm of heating rates and the reciprocal of absolute temperature. The slopes of the line and E a were, in turn, in direct proportion to each other. From ASTM E698, E a of PAA was computed and the value was 66.15 kJ mol –1 . Swern [ 5 ] and Zhao et al [ 6, 19 ] proposed the reaction order for spontaneous of PAA under an acid condition was second-order reaction and the value of
E
a was 70.20 kJ mol –1 . Analytical equations related self-heating reactions to programmed scanning curves from DSC trails were proposed [ 27 ]. 8 9 The calculations of self-heating rate from mainly exothermic curve of the DSC, thermodynamic data, and physical properties were operated by C++ programming language from Eqs. 5 to 14, as listed in Tables 5 and 6 .
10 11 The time to maximum rate (TMR) and simulated degree of conversion versus temperature curves of PAA by thermal reaction analytical equations are given in Figures 4 to 7 . From the exothermic behaviors of PAA based 12 13 on the observations of DSC dynamic thermal scanning it was well recognized that self-heating rate of the runaway reaction increased exponentially with temperatures and concentrations in Figure 8 . The results of the 14 15 16 experiment agreed with those obtained by thermal analytic equations, for which the analytic solution for the self-heating reaction was formulated, and its accuracy technique was proposed to study thermal decomposition [ 18 ]. By multiplying the term E a (RT 2 ) –1 withΔT ad obtained a criterion. Figure 9 displays the thermal reaction 17 numbers calculated in Eq. 2 for an initial exothermal temperature of 40 °C as a function of PAA adiabatic 18 19 temperature rise. The parameters of PAA such as the apparent activation energy and frequency factor were 66.15 kJ mol –1 and 9.20E8 s –1 , respectively. The higher E a , the more sensitive to temperature the reaction rate 20 21 will be. The reactions with B-value above 5 are difficult to dictate in batch reactors because of highly sensitivity to temperature [ 17, 20 ]. This figure shows that a ΔT ad of 60 °C or above, corresponding to a B-value of 5, 22 23 makes a thermal explosion possible. The results presented here reveal that the hazards of PAA solutions cause violent thermal decomposition above 50 °C in a runaway reaction or in case of fire, and we must pay attention to 24 25 safer use of this kind of organic peroxy acid. Peracetic acid is a strong oxidant and disinfectant with a broad spectrum antimicrobial. The United 26 Nations Recommendations on the Transport of Dangerous Goods (UN TDGs) [ 28 ], by contrast, uses a heat of 13

1 reaction/decomposition of 300.0 J g –1 as the criterion for determining a self-reactive substance and the need for 2 3 obtaining a SADT for shipment purposes. PAA may spontaneously decompose at room temperature and will explode violently on rapid heating to about 50 to 100 °C [ 5 ]. Its SADT passed at 50.0 °C by UN TDGs 4 5 recommendations [ 26 ]. The decomposition can be initiated by heat, contact with impurities, friction, or impact. The rate of decomposition increases with temperature and varies with its concentation. Decomposition may 6 7 result in the evolution of flammable gases or vapors. The report described 41–43 mass% PAA with water was classified as organic peroxide D, E, and F according to chapter 2.15 via Globally Harmonized System of 8 9 Classification and Labelling of Chemicals (GHS) [ 29 ]. It also revealed that the SADT of 41 mass% PAA in 20 m 3 insulated tank was 40.0 °C by adiabatic storage test (AST). PAA is generally considered to be an economic 10 11 and environmentally friendly organic peroxy acid for the industrial application in non-conventional bleaching sequences like totally chlorine free. Its oxidation potential is larger than that of chlorine or chlorine dioxide.
12 13 Owing to its bactericidal, virucidal, fungicidal, and sporicidal effectiveness as demonstrated in industrial applications, the use of PAA as a disinfectant for wastewater treatment process has been drawing more attention 14 15 in environmental protection. On the other hand, the use of PAA is its high cost, which is partly due to limited commercial production capacity. PAA has an acidic pH of less than 2, in case of spills or leaks should be 16 17 covered with weak reducing agents, such as sodium thiosulfate, and neutralized the residue with a dilute solution of sodium carbonate. The incompatible such as oxidizing agents, reducing agents, organic materials, 18 19 metals, acids, alkalis should be avoided because they can cause decomposition so rapid as to cause ignition and produce fires. Special care should be taken with regard to contamination by highly explosive potential [ 13, 15, 20 21 30 ]. PAA combines the active oxygen characteristics of a peroxide within an acetic acid molecule and belongs to the Class II of organic peroxides that burn very rapidly and that present a severe reactivity hazard by NFPA 22 23 recommendations [ 15 ]. Which molecular structure contains peroxide radicals (–OO) that are a source of oxygen. The peroxide radical also promotes instability and combustion. Our experimental data demonstrate 24 25 PAA are high-energy-state compounds and need to recognize theirs thermal instability [ 1, 2, 30 ]. 14

1
Conclusions
2 3 By their chemical nature of peroxyacides, the peroxygen bond is a powerful oxidizer. Aqueous PAA appears to 4 5 present no hazard from toxicity as disinfectants and sterilants. However, concentrated PAA solution must be treated with caution as is the case with any strong oxidant. The thermally reactive characteristics of PAA were 6 7 validated to be dangerous combining with calorimetry methodology and thermal analytical equations. These preliminary data suggest that thermal analysis may provide an alternative method for PAA. The programming 8 9 languages aided experimental data by calorimeter provide thermodynamic and coordinative analysis. According to the thermal hazards data of the temperature evaluation in our studies, the alternative choices are to design the 10 11 safe process operation condition, the type and material of storage tank or transportation truck, fire protection on temperature control and pressure relief system in order to avoid industrial accidents. The conclusions are drawn 12 13 as follows: (1) Peroxyacids should be stored in a cool, well-ventilated area which room temperature below 30 °C to 14 15 16 17 prevent self-decomposition runaway reaction, and in the storage containers provided with relief systems and suitable fire extinguishing equipment. Extremely lower initial exothermic temperature than other organic peroxides and high heat of decomposition should be cautiously taken the safe recognition of PAA into account. 18 19 (2) The demonstration of PAA solutions was unstable at or near room temperature with its higher concentrations, such as 40, 45, and 50 mass%. The results proved that the hazard level of PAA solutions 20 21 22 23 above 40 mass% was conspicuously higher than lower concentration of PAA solutions. The apparent onset temperature could be initiated above 30.0 °C with higher concentrations. If the self-sustaining decomposition of PAA solutions above 40 mass% is initiated at lower temperature, their thermal hazards should be gingerly concerned in preparation, manufacturing process, storage, transportation, and disposal. 24 25 26 (3) As the storage temperature exceeds the apparent onset temperature, an exothermic reaction of PAA will inevitably ensue. TMR of PAA is shortened in 3 to 6 hours interval. PAA resulted in the highest risk of thermal and self-reactive hazards which will undergo thermal explosion in case of self-heating conditions 15

1 2 or external fire.
16

1
Acknowledgements
2 3 The authors are grateful to Chang Chun Plastics Co., Ltd. and National Science Council of Taiwan, ROC (NSC 4 5 100–2622–E–224–003–CC2), for financial support of this study. 17

1 2
Nomenclature
A
Frequency factor (s –1 )
B
Thermal reaction number (dimensionless) C C 0
c
p
D E
a
k
m n The concentration of the reactant The initial concentration of the reactant Specific heat at constant pressure (k kg –1 °C –1 ) Activation energy correction coefficient, dimensionless Apparent activation energy (kJ mol –1 ) Reaction rate constant (dimensionless) Q R
R 1
T Mass of reactant (g) Order of reaction (dimensionless) Heat flow (W g –1 ) Ideal gas constant (8.314 J mol –1 °C –1 )
T
i
T
f
t x
dT dt –1 Carbon chain Temperature (°C) Apparent onset temperature (°C) Final temperature (°C) Time (sec) Degree of conversion, 0 to 1 (dimensionless) Temperature derivative with respect to time (°C min –1 )
Greek letters
β
Heating rate (K min –1 ) △H △H d Heat of decomposition (J g –1 ) Heat of decomposition at a particular temperature (J g –1 ) ΔT ad The adiabatic temperature rise (°C) 18

1 2 3 4
References
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