Decomposition of methyl ethyl ketone peroxide and mixtures with sulfuric acid

Journal of Loss Prevention in the Process Industries 17 (2004) 23–28www.elsevier.com/locate/jlp

Decomposition of methyl ethyl ketone peroxide and mixtures withsulfuric acid�

Xinrui Li a,∗, Hiroshi Kosekia, Yusaku Iwataa, Yun-Soo Mokb

a National Research Institute of Fire and Disaster (NRIFD), 14-1 Nakahara 3-Chome, Mitaka-shi, Tokyo 181-8633, Japanb Pukyong National University, South Korea

Abstract

The fact that an explosion starts at a lower ambient temperature when methyl ethyl ketone peroxide (MEKPO) is not sufficientlyneutralized, is demonstrated with a highly sensitive small-scale calorimeter (C80D). The data indicate that MEKPO might undergoacid and redox decompositions in addition to thermal decomposition in the accidental scenario. Meanwhile, experimental resultsof modified closed pressure vessel tests (MCPVT) suggest that the decomposition is much more active for MEKPO in the presenceof sulfuric acid. Under such conditions, the maximum pressures and the maximum rates of pressure rise are significantly higherthan those of pure MEKPO. 2003 Elsevier Ltd. All rights reserved.

Keywords: Methyl ethyl ketone peroxide; Thermal decomposition; Redox decomposition; Acid decomposition; Heat flux calorimeter; Modifiedclosed pressure vessel tests

1. Introduction

Methyl ethyl ketone peroxide (MEKPO, Permek H )is widely used as a curing agent of unsaturated polymerresin to mold products. The variety of peroxides(monomeric, dimeric, trimeric, or polymeric) which canbe produced from the interaction of a given ketone andhydrogen peroxide are very wide, and the proportion ofproducts in the reaction mixture depends on the reactionconditions as well as on the structure of ketone(Bretherick, 1987). Many of the products appear tocoexist in equilibrium, and several structure types areexplosive and sensitive to varying degrees to heat andshock. MEKPO is normally produced in the phlegmat-izer (dimethyl phtalate, DMP) with acid as a catalyst. Inthe addition, the product with a concentration up to 10%active oxygen is neutralized, and then is brought to thedesired concentration by further dilution with phtalate.Subsequently, a drying procedure is executed in one ofthe production steps. Finally, before packaging, the pro-

� This paper was originally presented at the Fourth InternationalSymposium on Hazards, Prevention and Mitigation of IndustrialExplosions, 21–25 October 2002, Bourges, France.

∗ Corresponding author. Tel./fax:+81-422-44-8392.E-mail address: [email protected] (X. Li).

0950-4230/$ - see front matter 2003 Elsevier Ltd. All rights reserved.doi:10.1016/j.jlp.2003.08.003

duct is stored in temporary storage vessels, which aremade of stainless steel or polyethylene.

Among organic peroxides, the accidents caused byMEKPO were ranked as the most frequent level(Yoshida, 1987; Fukuyama, 1981; Haba, 2002). On 24August 2000, a serious explosion occurred at a factoryin Korea where MEKPO was manufactured. The processof production was that ketone dissolved in DMP wasmixed with H2O2 in the presence of sulfuric acid(H2SO4) as a catalyst. The next step was the neutralizingtreatment with calcium carbonate in order to removeH2SO4 from the product. Finally the gelation and fil-tration process followed before packaging. Factory per-sonnel had left the factory two days before the accidentdue to the founding holidays of the factory. When theoperation at the plant started again after the product hadbeen left in the vessel for more than 60 h, an explosionoccurred and destroyed the entire factory. Six workerswere killed and 19 injured. A number of possible causesof the fire were considered, it was assumed from reportsof authorities that the final product had been kept formore than 60 h in vessels at about 30°C prior to thepackaging step. The product might not have been suf-ficiently neutralized. As a result, the product in the pres-ence of H2SO4 at the summer ambient temperature mightbecome unstable and decomposed and heat accumulation

24 X. Li et al. / Journal of Loss Prevention in the Process Industries 17 (2004) 23–28

from the reaction might result in a serious explosion. Inorder to confirm this scenario, a Setaram C80D calor-imeter was used and the thermal characteristics ofMEKPO and its mixtures with sulfuric acid were exam-ined. A mini autoclave, modified closed pressure vesseltester (MCPVT), was used to measure the decompositionintensity under confinement.

2. Properties of MEKPO

MEKPO is ordinarily a mixture of several isomersincluding three main chemical structures (Nicholas &Golubovic, 1959), such as:

All isomers contain the bivalent –O–O– linkage, andthe molecules and their anions are powerful nucleo-philes. Radicals, which are generated from decompo-sition of peroxides and are capable of spontaneousdecomposition with an initiation reaction, can be acti-vated by heat, or existence of metal, metal ions, or acid.The followings are three main types of decomposition(Hiatt, 1971). All reactions are vigorously exothermic.

1. Thermal decomposition: MEKPO undergoes complexdecomposition involving four general types of homo-lytic reaction such as unimolecular homolysis, mol-ecularly assisted homolysis, free-radical abstractionand free-radical displacement on O–O bond. Gener-ally, the decomposition of MEKPO gives less uni-molecular homolysis and much molecularly assistedhomolysis, and readily yields alcohols, aldehydes,ketones, carboxylic acids and so on.

2. Redox decomposition: Redox refers to the oxidation–reduction decomposition with metal or metal ion con-taminations.

3. Acid decomposition: MEKPO undergoes acid-cata-lyzed heterolysis as follows.

MEKPO is classified as Division 5.2 of the UN rec-ommendation (United Nations, 1995) thermally unstablesubstance, which may undergo exothermic self-acceler-ating decomposition. Results of pressure vessel test(PVT) based on the Japanese Fire Services Law showsthat a rupture disk is broken for MEKPO (55%) (NOF,1996) with an orifice plate of 1.0 mm diameter. Theflashpoint of MEKPO is 82 °C (Seta closed-cup test) and

the self -accelerating decomposition temperature(SADT) using heat accumulation storage test is 65 °C.In a differential scanning calorimeter (DSC, heating rate:5 K/min), the onset temperature of decomposition isnearly 112 °C with an enthalpy near 1.65 kJ/g (Ujikawa,Tamamura, & Kojima, 1998).

3. Experimental

A Setaram C80D heat flux calorimeter was used toinvestigate the characteristics of the decomposition ofMEKPO. The structure and operation of the C80Dresembles that of the differential scanning calorimeter(DSC). But there are significant differences. The samplesize may be up to 103 greater than that normally usedin a DSC. This factor as well as extremely slow thermalscanning rates as low as 0.01 K/min allows more accur-ate simulation of the self reaction or the self heatingdecomposition. The considerable thermal stability of theC80D contributes to a much higher sensitivity than thatof the DSC or an accelerating rate calorimeter (ARC)(Sun, Li, & Hasegawa, 2001). In the experiments,MEKPO with a purity of 55% in DMP was suppliedby Nippon Oil & Fats Co. Ltd. Exothermal reactions ofMEKPO with and without sulfuric acid were measuredwith the C80D. Samples were mixed by stirring, and testsamples of 500 mg were placed in an air or nitrogenatmosphere and then heated at the rate of 0.1 K/min inthe C80D. A glass cell was comparably used in order toinvestigate the possible redox catalysis from the stainlesssteel cell, whose components were Z2CND17-12(316L) alloy.

MCPVT tests were conducted to evaluate thermalexplosion hazards of MEKPO under confinement. In atest, a 1 g sample was placed into a 6 ml glass cup,which was then positioned in the pressure vessel. A rup-ture disc to protect the cell from overpressure wassecured tightly by a flange bolt. The test vessel was thenput into an electric oven with a heating rate controlledat 10 K/min. Temperature and pressure were detectedby sensors, with a sampling rate of 200 Hz (Peng &Hasegawa, 1995).

4. Results and discussion

4.1. Effect of atmosphere

Generally, it is preferable to measure decompositionbehavior in an inert atmosphere, such as N2. But in thecase of MEKPO–H2SO4 mixtures, there is a significantweight loss in vacuum before filling the test cell withN2. For example, 15% weight reduction was measuredfor MEKPO–1% H2SO4 and MEKPO–3% H2SO4 afterfilling with N2. This loss may result from some volatile

25X. Li et al. / Journal of Loss Prevention in the Process Industries 17 (2004) 23–28

Fig. 1. Decomposition in N2 using C80D.

Fig. 2. Decomposition in air using C80D.

products in vacuum from a preliminary reaction of themixture and could have an unfavorable influence on thedecomposition measurement of the mixture and lead tofalse results. Tests in air can avoid such situation andshow actual conditions. As shown in Figs. 1 and 2 andTable 1, under both atmospheres, the decompositions ofMEKPO are seen as multi peaks, which correspond to

Table 1Decomposition results using C80Da

Sample Atmosphere Onset temperature (°C) Peak temperature (°C) Enthalpy (J/g)

MEKPO N2 77.6 102.2 1646.2MEKPO–1% H2SO4 N2 44.9 64.9 786.0MEKPO–3% H2SO4 N2 31.7 49.8 860.8MEKPO Air 69.6 89.1 1813.5MEKPO–1% H2SO4 Air 51.9 72.4 1552.5MEKPO–3% H2SO4 Air 38.4 66.0 1528.0MEKPO–5% H2SO4 Air 30.3 41.7 1423.9

a Sample amount: 500 mg; heating rate: 0.1 K/min.

those of isomers, e.g., the decomposition of monomertakes place firstly, then followed by the decompositionof larger molecules, such as dimer and trimer. Theresults are in agreement with what has been studied byUjikawa et al. (1998). All decompositions of isomerswere catalyzed in the presence of H2SO4.

4.2. Effect of H2SO4

In testing with the C80D, the concentration of H2SO4

has a significant influence on the decomposition ofMEKPO, particularly in the air, as shown in Table 1.The measured onset temperatures, which are defined asthe intersection point between the tangent of the heatflow versus time curve and the baseline, were 69.6 °C,51.9 °C, 38.4 °C, and 30.3 °C for MEKPO, MEKPO–1%H2SO4, MEKPO–3% H2SO4, and MEKPO–5% H2SO4,

respectively. The highest temperatures of the exothermicpeaks were 89.1 °C, 72.4 °C, 66.0 °C, and 41.7 °C forthese samples, respectively. The measured heat gener-ation for MEKPO (1813.5 J/g) was larger than those ofthe MEKPO–H2SO4 mixtures, for which the averagemeasured enthalpy was 1500 J/g. In addition, the firstpeak of the decomposition curves appeared at lower tem-peratures for the mixtures, but the peak widths weregreater than that of pure MEKPO. The reason is thatduring the preparation of sample of MEKPO–H2SO4, apreliminary reaction had occurred at ambient tempera-ture and part of heat evolvement from the reaction couldnot be captured by the measurement in the C80D.

But it still indicates by the data in the C80D that theonset temperatures dropped to 38.4 °C and 30.3 °C forMEKPO–3% H2SO4 and MEKPO–5% H2SO4, whichimplies that the explosion in Korea might start at about30 °C in case small amount of H2SO4 existed inMEKPO.

4.3. Effect of aging

Fig. 3 displays the experimental results using the samesample of MEKPO–5% H2SO4 which was kept for vari-ous periods of storage in a glass bottle (volume: 20 ml).


Fig. 3. MEKPO-5% H2SO4 decomposition for samples storing differ-ent periods at 20(±2) °C.

These data demonstrate that active components existedin the mixture, and during storage at ambient tempera-ture, the mixture spontaneously decomposed. As a resultthe heat flow peak in the sample stored for 5 days wasbroader than that in the fresh sample, and there was noexothermal peak at all at lower temperature after 20days. The sound of gas release was heard when eachsample bottle was opened. These behaviors could implya hazard that when MEKPO meets H2SO4, some activecomponents form and lead to an unstable system evenin ambient condition.

4.4. Effect of mixing process

It is interesting to further study the active componentsinvolved in the decomposition of the mixture. When themixture was prepared, its temperature increased andemitting of mist was observed, especially during quickaddition of sulfuric acid into the MEKPO sample. Some-times this operation also caused a small explosion. Whena small drop of H2SO4 was added to the wall of a samplemixing bottle and touched the MEKPO solution, a mistarose from the solution and white needle-shaped crystalswere observed immediately because of the condensationof the crystal on the wall of the bottle. These crystals areassumed to be a trimer or even larger MEKPO polymericmolecule, which are solids at the ambient temperature(Nicholas & Golubovic, 1959). This observation indi-cates that during the mixing process, larger molecularisomers, which are more explosive, are easily separatedfrom the solution, and if they accumulate in some localposition, a more violent explosion might be caused. Herethis aspect was ascertained in air by the addition of sulf-uric acid without stirring. The effect of direct additioncan be seen in Fig. 4 that there appeared more vigorousexothermal peaks at the beginning of the reaction nearthe ambient temperature for all mixtures of MEKPOwith H2SO4, and all of the MEKPO isomer decompo-

Fig. 4. Decomposition in the direct addition.

sitions are accelerated in the presence of acid (Ujikawaet al., 1998). As described in Section 2, decompositionof a monomer was most likely activated by acid inaddition to its thermal decomposition, leading toexothermal behavior at lower temperatures. At the sametime, it is often thought that the violence of thermaldecomposition decreases with increasing chain length ofthe sample materials, however in the case of MEKPOand other most organic peroxides, larger molecule caninclude higher concentrations of active oxygen and ismore explosive (Ujikawa et al., 1998). As the reactionis easily initiated by monomer and solid trimer is pro-gressively crystallized from the solution, a second viol-ent decomposition caused by trimer may be induced,which is clearly seen especially in MEKPO–5% H2SO4

in Fig. 4.

4.5. Effect of test cell material

Fig. 5 and Table 2 show the effect of an inner glasscup on the behavior of MEKPO decomposition. Com-

Fig. 5. Decomposition in glass cell.

27X. Li et al. / Journal of Loss Prevention in the Process Industries 17 (2004) 23–28

pared with the result in a stainless steel cell, decompo-sition in a glass cell appears at a much higher tempera-ture, implying that MEKPO may undergo the redoxdecomposition in stainless steel cell. The material of thestainless test cell in C80D was Z2CND17-12 (316L), analloy which is generally inert to many substances beingtested, while no record on what kind of stainless steelmaterial used in the Korean plant was found. It indicatesthe fact that in the Korean plant, if the product was keptin the stainless steel reactor (batch process in two stain-less steel creators of 2500 mm in height and 1400 mmin diameter) for a long time, not only acid decompositionin the presence of H2SO4 and thermal decomposition,but also redox decomposition might contribute to anintense explosion.

4.6. Evaluation of the decomposition hazard

Table 3 and Fig. 6 display the results of MCPVT testsperformed for MEKPO and the four mixtures with sulf-uric acid from 1% to 5%. The MCPVT, which was pro-posed to provide screening tests compared to the UNseries E tests (Watanabe, Matsunaga, Wada, Tamura, &Yoshida, 1990), was used to determine the sensitivenessof substances to the effect of intense heat under definedconfinement. Generally speaking, the maximum pressureand the maximum rate of pressure rise can be consideredas primary criteria for classifying decompositionbehavior of organic peroxides under confinement. Itimplies that, the maximum pressure of MEKPO–5%H2SO4 was twice as much as that of MEKPO, 3.3 MPa,and the maximum rate of pressure rise was 10 times asmuch as MEKPO (18.9 MPa/s). The onset temperatureof decomposition, at which point (dP/dt) is the highest,also decreased from 166 °C for MEKPO to 83 °C forMEKPO–5% H2SO4. With an increase of the sulfuric

Table 2Decomposition in glass cell using C80D

Sample Atmosphere Onset temperature (°C) Peak temperature (°C) Enthalpy (J/g)

MEKPO Air 111.9 117.9 1649.0MEKPO–1% H2SO4 Air 69.2 82.9 1918.4MEKPO–3% H2SO4 Air 47.3 76.2 1680.6MEKPO–5% H2SO4 Air 36.6 95.2 1638.7

Table 3Decomposition in MCPVT

Sample Pmax (MPa) (dP/dt)max (MPa/s) Onset temperature (°C) Peak temperature (°C)

MEKPO 3.3 18.9 166.2 261.1MEKPO– 1% H2SO4 3.0 66.3 130.6 230.3MEKPO– 3% H2SO4 4.3 102.2 91.0 261.9MEKPO– 5% H2SO4 6.7 189.6 83.0 216.2

Fig. 6. Temperature, pressure and (dP/dt) behaviors in the MCPVT.(a) Pressure and temperature (b) (dP/dt) calculated from pressure data.

acid concentration, the maximum pressure and the rateof pressure rise increased, and the onset temperaturedecreased, indicating that the presence of sulfuric acidin MEKPO caused a much more violent decomposition.


5. Conclusion

The study provided information regarding the influ-ence of acid on the decomposition of MEKPO. The datafrom the C80D showed that MEKPO stability in thepresence of 1% to 5% H2SO4 decreased dramatically andits onset temperatures approached to the ambient tem-perature with increasing H2SO4 concentration. Mean-while both acid and redox decomposition occurred bythe addition of acid impurity and in a stainless steel con-tainment. Results from the MCPVT tests suggested thatthe decomposition was much more active for MEKPOwith significantly larger values of the maximum press-ures and the maximum rates of pressure rise in the pres-ence of sulfuric acid.

It was demonstrated that under conditions of higheracidity, the facts that not only the low molecular weightisomer decompositions were accelerated in addition tothermal decomposition, but also more explosive cyclicMEKPO with higher concentration of active oxygen(trimer or polymer) was separated from the solution,potentially build up the degree of hazard. Therefore, thisresearch suggests a cause of the Korean accident in2000, which may have resulted from residual H2SO4 inthe MEKPO storage vessel.

Acknowledgements

The authors wish to express their great thanks to I.Kutsuzawa in Nippon Oil & Fats Co., Ltd, for supplyingthe information on MEKPO and to Drs W. J. Rogers and

S. Mannan of the Mary Kay O’Connor Process SafetyCenter, Texas A&M University, USA, for their instruc-tions and comments.

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Decomposition of methyl ethyl ketone peroxide and mixtures with sulfuric acid