Ind. Eng. Chem. Res. 2001, 40, 1125-1132
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Thermal Runaway Hazards of Cumene Hydroperoxide with Contaminants Yih-Wen Wang and Chi-Min Shu* Department of Environmental and Safety Engineering, National Yunlin University of Science and Technology, Touliu, Yunlin, Taiwan, R.O.C.
Yih-Shing Duh Jin-Teh Junior College of Medicine, Nurse and Management, Miaoli, Taiwan, R.O.C.
Chen-Shan Kao Center for Industrial Safety and Health Technology, Industrial Technology Research Institute, Hsinchu, Taiwan, R.O.C.
Cumene hydroperoxide (CHP) has been used in producing phenol and acetone by catalytic cleavage and as an initiator in polymerization. However, many severe fires and explosions have occurred because of its thermal instability and incompatibility. In fact, CHP has been given a hazard classification of flammable type or Class III by the National Fire Protection Association (NFPA). To date, however, its reactive and incompatible hazards have not yet been clearly identified. In this study, the thermal decomposition and runaway behaviors of CHP with about 1 wt % incompatibilities such as H2SO4, HCl, NaOH, KOH, Fe2O3, FeCl3, and Fe2(SO4)3 were analyzed by DSC thermal analysis and VSP2 adiabatic calorimetry. The thermokinetic data obtained via calorimetry, such as onset temperature, heat of decomposition, adiabatic temperature rise, and self-heat rate, were also compared with those of CHP in cumene. Hydroxide ion and ferric ion were found to be quite incompatible with CHP. The worst case of thermal runaway of CHP was observed when it was mixed with hydroxides (in the production or storage of CHP). The adiabatic self-heat rate of 15 wt % CHP was 9 °C min-1 in VSP2, which increased quite dramatically to a value of 100 °C min-1. This study reveals that thermal hazards of CHP influenced by incompatibilities should not be overlooked. The different thermokinetic data affected by the incompatibilities are the key issues for ERS (Emergency Relief System) design in CHP-related processes using DIERS technology. The decomposition pathway of CHP in various impurities was proposed by use of chromatography in product analyses. Introduction The very properties that make cumene hydroperoxide (CHP) valuable to industry require that such materials be handled and stored with caution. During transport, storage, or processing, any accidental mixing of industrial chemicals poses a potential energy hazard. This hazard is defined in terms of both the magnitude of release of heat or gas as a result of chemical incompatibility or “other chemical” reactivity and the potential formation of an explosive mixture that can subsequently be initiated by an appropriate stimulus (mechanical impact, thermal activation, or physical shock). Thermal runaway incidents caused by organic peroxides are recognized as being due to the peroxy group (-O-O-), which is intrinsically unstable and reactive. Cumene hydroperoxide (CHP) is an organic hydroperoxide. Because of the hydroxy group or the acidic hydrogen, the hydroperoxides are more reactive than other alkyl peroxides. Hydroperoxides such as hydrogen * Correspondence concerning this paper should be addressed to Dr. Chi-Min Shu, Department of Environmental and Safety Engineering, National Yunlin University of Science and Technology, 123 University Road, Section 3, Touliu, Yunlin, Taiwan 640, R.O.C. (
[email protected]).
peroxide, cumene hydroperoxide, and tert-butyl hydroperoxide are extremely sensitive or reactive to acids, bases, metal ions, and other impurities. In fact, many fires or explosions have been caused by the runaway of CHP, because of its thermal instability or reactive incompatibility (Ho, 1998; Kletz, 1988). CHP is widely used as an initiator in polymerization, especially for the acrylontrile-butadiene-styrene (ABS) copolymer in Taiwan. It is also used in the production of phenol and acetone by catalytic cleavage. Numerous studies of induced hazards by organic peroxides have been performed worldwide. The United Nations has even suggested that an organic peroxide supplier must make a precise test of TSADT (temperature of self-accelerating decomposition temperature) in any specific commercial package (U. N., 1986; U. N., 1989). TNO in Netherlands has devoted considerable effort to the testing and classification of organic peroxides. CHP has been recognized as a flammable type or class III (fire hazard) by the NFPA (National Fire Protection Association) (NFPA 43B, 1986). The members of DIERS (Design Institute for Emergency Relief System) emphasize research on the characteristics of pressure relief for organic peroxides (Leung, 1989; Grolmes, 1998). The exothermic threshold temperature of many organic
10.1021/ie990900s CCC: $20.00 © 2001 American Chemical Society Published on Web 02/14/2001
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peroxides is usually around 50-120 °C. However, for some runaway incidents caused by CHP, the reaction or storage temperatures have even been as low as ambient temperature. The reactive and incompatible hazards of CHP have not been clearly identified until now, and more efforts are needed for the study of its properties. The reaction of CHP with a variety of incompatibilities is usually more complicated because of its complex reaction mechanism. Our previous reports verified the thermal hazard and kinetics on decomposition of CHP. On the basis of various tests from DSC, VSP2, and ARC, the reaction order of CHP decomposition was determined to be 0.5 (Duh, 1997; Duh, 1998). The emergency relief area of a safety relief valve or rupture disk of a reactor or storage tank is nearly proportional to the adiabatic self-heat rate at the blowdown conditions using DIERS methodology. Most thermal runaway reactions caused by organic peroxides will be accompanied by violent heat-releasing rates and thermal explosions. The maximum self-heat rate is larger than 100 K min-1 for many runaway reactions of organic peroxides. The self-heating rate or thermokinetics are affected by temperature, pH value, metal of containers, ions, and other impurities. The aim of this research was to verify incompatible characteristics and the products of CHP under runaway conditions. Both DSC and VSP2 techniques were used for thermal analyses in order to acquire thermal runaway data. Data such as initial exothermic temperature (T0), adiabatic time to maximum heat rate (TMRad), adiabatic temperature rise (∆Tad), and self-heat rate (dT/dt), were used for runaway hazard evaluation. Reaction products of CHP decomposition with impurities were proposed from the identification of some distinguishing decomposition products by chromatographic method. In summary, this study addresses the following objectives: determination of the inherent and relative instabilities of CHP mixed with impurities, identification and assessment of the effect of incompatibilities on CHP, and comparison of the relative hazard among various impurities. Experiment Samples. CHP of 80 wt %, as purchased directly from the supplier, was measured to determine both the density and concentration and then was stored in a 4 °C environment. Cumene purchased directly from Merck was used as the dilution solvent in the preparation of various CHP samples. Substances such as H2SO4, HCl, NaOH, KOH, FeCl3, and Fe2(SO4)3 were treated as incompatibilities. Contaminants that could be readily encountered in process or storage conditions were chosen to be from 0.1 to 0.5 wt % in both DSC and VSP2 experiments. CHP samples of 15 and 35 wt % diluted in cumene were used. Conditions of Incompatible Species. CHP might be contaminated in oxidation reactors for producing CHP, vessels for enriching CHP concentration, pipelines, storage tanks, or tank cars. The following upset situations are assumed: ferric oxide for simulating the effect of rust, ferric chloride and ferric sulfate for simulating the effect of ferric ion, hydrogen chloride solution and sulfuric acid for simulating the effect of acid or hydrogen ion, sodium chloride for simulating the
effect of chloride ion, and potassium hydroxide and sodium hydroxide for simulating the effect of an alkaline environment. Results from these process deviations can provide the basic data for identification of hazards, selection of the credible worst-case scenarios for process safety design, and even for case studies of thermal explosions caused by CHP. DSC (Differential Scanning Calorimetry). The dynamic screening and nonisothermal experiments were performed on a Mettler TA4000 system coupled with a DSC25 measuring cell that can withstand relatively high pressure (ca. 100 bar) (Mettler, 1993). The system was connected to an IBM-compatible PC with which data were evaluated and stored. Disposable highpressure crucibles (ME-26732) were used for acquiring thermograms and isothermal traces. Standard aluminum crucibles were used for heat capacity (CP) measurements. The average heat capacity of 35 wt % CHP solutions was determined to be 2.217 J g-1 K-1. The measuring method was verified by checking the heat capacity temperature function of aluminum oxide (RAl2O3 single crystal) with the data provided by the National Bureau of Standards (NBS). For better thermal equilibrium purposes, the scanning rate chosen for the temperature-programmed ramp was determined to be 4 K min-1. VSP2 (Vent Sizing Package2). A PC-controlled adiabatic calorimeter system, the Vent Sizing Package 2 (VSP2) manufactured by FAI (FAI, 1997), was used to measure thermokinetic and thermal hazard data such as temperature and pressure traces with respect to time. The low heat capacity of the cell ensures that essentially all of the reaction heat released remains within the test sample. Thermokinetics and pressure behavior in the test cell can therefore be extrapolated directly to the industrial scale because of the low thermal inertia of about 1.05-1.20. Three types of test cell made of stainless steel 316 for closed testing, top venting, or bottom dumping are available. Detailed information on the performance of the VSP calorimeter can be found in the literature (Leung, 1986; Leung, 1989). Basic design data for emergency relief systems can be obtained from the VSP2 calorimeter and related DIERS methodology. Basically, two-phase flow patterns such as churn-turbulent, homogeneous equilibrium, or other flows can be determined from top venting experiments using the VSP2. Chromatographic Studies. The decomposition experiments were carried out in the ampules under an isothermal oven temperature of 130 °C after complete decomposition. The decomposition products were identified by HPLC by using a UV-970 detector employing a C18 column (150 mm × 4 mm internal diameter). The eluting solvent was a mixture of acetonitrile and water (3:7) at a flow rate of 1.0 mL min-1. The detection was carried out at a wavelength of 254 nm. Results and Discussion Reactive hazards of CHP are essentially related to temperature and concentration; reactive hazards due to incompatible impurities are unexpected. For hazard analysis, nonisothermal calorimetry was performed to measure the characteristics of the exothermic decomposition of CHP influenced by incompatibilities using programmed heating or adiabatic heating.
Ind. Eng. Chem. Res., Vol. 40, No. 4, 2001 1127
Figure 1. Thermal decomposition comparison of CHP with various incompatibilities by DSC test.
Thermal Analysis. The onset temperature and heat of decomposition of CHP with a specific impurity can be acquired easily by using DSC programmed scanning. Figure 1 shows typical heat flow curves versus temperature for the thermal decomposition of a 35 wt % CHP/ cumene solution with hydrogen chloride (H+), sodium hydroxide (OH-), and ferric chloride (Fe3+). Thermal decomposition hazards of CHP with different impurities can be characterized using a nonisothermal method to probe the detailed exothermic reactions spanned in the temperature scale. Physical data of heat of decomposition, initially exothermic onset temperature, peak power, and curves of thermograms are suitable for exhibiting the strength of reactivity on CHP with impurities. The heat of CHP thermal decomposition with various impurities was measured and is in good agreement with values for purely thermal decomposition. In particular, more than 25% additional heat was detected by thermograms in the mixtures of CHP with either alkaline impurities or ferric chloride. These experiments illustrated that thermal decomposition of CHP with various impurities should be different from the thermal decomposition of pure CHP in cumene. Thermograms induced by sodium hydroxide or potassium hydroxide on CHP decompositions were almost the same, which means the hydroxide ion played the same role in the incompatibility effect. The peaks on the thermograms indicate that CHP reacting with hydroxide ion will result in the worst exothermic hazard in the case of inadvertent mixing with other substances. Two peaks and the highest heat of decomposition of CHP reacting with hydroxide ion show a complicated reaction mechanism and thermal hazard that need further study. Data on thermal analyses are listed in Table 1. Physical data including heat of decomposition, peak power, and curves of thermograms are suitable for exhibiting the strength of reactivity on CHP with impurities. When mixed with the alkaline impurities or ferric chloride, CHP will be more hazardous and unstable because of lower exothermic behavior, higher peak power at lower
Table 1. Heat of Decomposition and Initial Exothermic Temperature of Cumene Hydroperoxide with Incompatibilities Thermal Analysis sample 35 wt % CHP (mg) 6.15
thermogram data incompatibility substance H2SO4
4.33
weight (mg)
scanning rate (°C min-1)
onset temp (°C)
∆H (J g-1)
-
4
135
607.3
1.05
4
90
667.3
0.74
4
90
715.7
0.81
4
60
768.7
1.05
4
60
781.3
1.13
4
100
613.6
0.81
4
40
695.7
1.44
4
80
707.6
0.58
4
80
580.9
(0.5 M) HCl 4.68 4.78
4.74
(1 M) NaOH (1 M) KOH (1 M) NaCl
5.17 (1 M) FeCl3 5.20 (1 M) Fe2SO4 4.96 (0.5 M) Fe2O3 5.29 (solid)
temperature, higher heat of decomposition, and so on. Ferric ion in ferric sulfate and chloride ion in hydrogen chloride did not affect the onset temperature and the heat of decomposition in any obvious manner. However, the exothermic temperature and the heat of decomposition were strongly changed in the DSC thermograms. It is interesting that the onset point of the mixture with ferric chloride measured in DSC is as low as 40 °C. Runaway Hazard Evaluation in Adiabatic Experiments. Because of the corrosive property of chlo-
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Figure 2. Self-heat rate versus temperature for thermal decomposition of 15 wt % CHP.
Figure 5. Self-heat rate versus temperature for thermal decomposition of 15 wt % CHP reacted with Fe2(SO4)3.
Figure 3. Self-heat rate versus temperature for thermal decomposition of 15 wt % CHP reacted with H2SO4.
Figure 6. Self-heat rate versus temperature for thermal decomposition of 35 wt % CHP.
Figure 4. Self-heat rate versus temperature for thermal decomposition of 15 wt % CHP reacted with NaOH.
Figure 7. Self-heat rate versus temperature for thermal decomposition of 35 wt % CHP reacted with H2SO4.
ride ion along the weld of the test cell, only the adiabatic data influenced by sulfuric acid, ferric sulfate, and sodium hydroxide were obtained. Other sets of adiabatic data influenced by five additives were obtained by using spherical test bombs equipped with ARC. Data from the VSP2 test cells (112 mL) and spherical bombs (24 mL) were consistent with each other. The characteristic curves of self-heat versus reciprocal temperature for CHP reacting with impurities were recorded from Figures 2-11. VSP2 experimental data are summarized in Tables 2 and 3. Data from the test
cell and the spherical bomb revealed that the onset temperature was lower than that of pure CHP in the mixtures with about 1 wt % of impurity. CHP will transform into an unstable intermediate when there is an unexpected mixing with incompatibilities. Aside from the qualititative similarity detected in DSC, these exothermic behaviors are much more quantitative in VSP2. The effects of acids or ferric sulfate are quite similar to each other in final temperature, self-heat rate, and onset temperature. These data were even very close to those of pure CHP except that the onset temperatures
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Figure 8. Self-heat rate versus temperature for thermal decomposition of 35 wt % CHP reacted with HCl.
Figure 10. Self-heat rate versus temperature for thermal decomposition of 35 wt % CHP reacted with Fe2(SO4)3.
Figure 9. Self-heat rate versus temperature for thermal decomposition of 35 wt % CHP reacted with NaOH.
Figure 11. Self-heat rate versus temperature for thermal decomposition of 35 wt % CHP reacted with FeCl3.
were different. The importance of ferric chloride to the lower exothermic temperature, final temperature, and lowest self-heat rate were determined. The self-heat rate, highest final temperature, largest final pressure, and largest pressure-rising rate were unusually high
for mixtures of CHP and sodium hydroxide. These reveal that the decomposition pathways initiated by these additives are significantly different or that there are nonequal branching ratios in the decomposition mechanism. This issue needs to be investigated more deeply.
Table 2. VSP2 Experimental Data of Incompatibilities on 15 wt % CHPa Pmax (psig)
final weight (g)
(dP/dt)max (psig min-1)
(dT/dt)0 (°C min-1)
(dT/dt)max (°C min-1)
sample
φ
T0 (°C)
Tmax (°C)
15% CHP (50 g) 15% CHP (50 g) + H2SO4 (0.5 M, 2.5 g) 15% CHP (50 g) + NaOH (1 M, 2.5 g) 15% CHP (50 g) + Fe2(SO4)3 (0.5 M, 2.5 g)
1.20 1.20
115.11 94.96
223.91 209.03
353.73 326.21
48.50 50.32
40 8
0.10 0.10
9 3
1.20
75.00
365.17
837.37
50.50
600
0.10
100
1.20
100.02
179.42
216.32
49.25
6
0.10
a
1.6
By test cell.
Table 3. VSP2 Experimental Data of Contaminants on 35 wt % CHPa
sample
φ
T0 (°C)
35% CHP (16 g) 35% CHP + H2SO4 (0.5 M, 1 g) 35% CHP + HCl (1 M, 1 g) 35% CHP + NaOH (1 M, 1 g) 35% CHP + Fe2(SO4)3 (0.5 M, 1 g) CHP35%+FeCl3(1M,1 g)
1.45 1.45 1.45 1.45 1.45 1.45
140.93 121.01 131.15 120.29 140.79 115.08
a
By spherical bomb.
Tmax (°C)
Pmax (psig)
final weight (g)
(dP/dt)max (psig min-1)
(dT/dt)0 (°C min-1)
(dT/dt)max (°C min-1)
248.72 241.42 259.64 256.17 250.77 202.31
683.01 567.86 947.58 990.06 806.61 615.90
15.12 14.89 15.12 13.94 15.10 14.56
800 700 100 >1,000 1,000 200
0.70 0.45 0.15 1.00 0.80 0.15
108 100 150 500 200 40
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Chromatographic Analysis of the Products after Decomposition. The detection of decomposition products of CHP with differential incompatibilities at the isothermal temperature of 130 °C proved the presence of R-methylstyrene, acetonphenol, 2-phenyl-2-propanol, and phenol, which were clearly identified by HPLC. These final products can be regarded as direct evidence for proposing the decomposition mechanism of CHP with different incompatibilities. The varieties of incompatible decomposition products of CHP are shown in Table 4. Most of the products are the same but occur in different ratios. This indicates that the decomposition mechanisms are similar; however, the branching ratios are unequal in elementary reactions of the mechanisms. Thus, the overall reaction rate, vapor-liquid equilibrium, and thermodynamics are destined to be different. Proposed Decomposition Mechanism Homolytic Decomposition. The thermal decomposition of organic hydroperoxides has been studied thoroughly in various organic solvents (Hiatt, 1968; Howard, 1982; Furimsky, 1980; Coeley, 1982; Shopova, 1994). It has been verified that the solvents are involved in the mechanisms of thermal decomposition. Most of the organic peroxides decomposed via complicated pathways that are called free-radical “induced decomposition” (Hiatt, 1964; Hiatt, 1968). Some interesting phenomena concerning the active hydrogen atom at the R-position or -OH induced hydrogen bonding were proposed in the explanation of the typical kinetics of decomposition (Duh, 1998; Shopova, 1994). IR spectrometry verified that the hydroperoxide might form dimers in some solvents even at 70 °C. The thermal decomposition of CHP was proposed, and it followed the suggested mechanisms (Duh, 1998; Hiatt, 1964; Hiatt, 1968).
2C6H5C(CH3)2OOH T [C6H5C(CH3)2OOH]2 C6H5C(CH3)2OOH f C6H5C(CH3)2O• + •OH
Table 4. Analysis of Thermal Decomposition of CHP with Incompatibilities by HPLCa CHP + CHP + CHP + CHP + CHP + CHP H2SO4 HCl NaOH FeCl3 Fe2(SO4)3 phenol acetonphenone 2-phenyl2-propanol a-methylstyrene
Y Y Y
Y Y Y
Y Y Y
Y Y Y
Y Y Y
Y Y Y
N
N
N
Y
Y
N
a
Note: Y indicates that specific substance had been detected by HPLC. N indicates that specific substance did not appear.
cumene. It was not affected by the cation of potassium or sodium that came from the alkaline solution. The first step of the decomposition mechanism involves an attack by the alkaline component, as suggested by the study of Shashin et al. (Shashin, 1983; Shashin, 1987). Namely, in this interaction of NaOH with CHP in cumene, salts were formed in an irreversible reaction that resulted in the formation of ion pairs in the system. The reaction mechanism can be illustrated as follows:
NaOH + C6H5C(CH3)2OOH f C6H5C (CH3)2OO-Na+ + H2O C6H5C(CH3)2OOH f C6H5C(CH3)2O• + •OH C6H5C(CH3)2OO- + C6H5C(CH3)2H f C6H5C (CH3)2• + C6H5C(CH3)2O• + OHC6H5C(CH3)2O• f C6H5COCH3 + •CH3 C6H5C(CH3)2H + •CH3 f CH4 + C6H5C(CH3)2• C6H5C(CH3)2O• + C6H5C(CH3)2H f C6H5C (CH3)2• + C6H5C(CH3)2OH
C6H5C(CH3)2O• f C6H5COCH3 + •CH3 C6H5C(CH3)2H + •CH3 f CH4 + C6H5C(CH3)2• C6H5C(CH3)2H + •OH f H2O + C6H5C(CH3)2• C6H5C(CH3)2O• + C6H5C(CH3)2H f C6H5C (CH3)2OH + C6H5C(CH3)2• C6H5C(CH3)2O• + •OH f C6H5OH + CH3COCH3 C6H5C(CH3)2• + •OH f C6H5CH3CdCH2 + H2O 2C6H5C(CH3)2• f [C6H5C(CH3)2]2 Alkaline Decomposition. From the data on thermal analysis and adiabatic runaway behaviors, we concluded that the decomposition of CHP influenced by the addition of NaOH was completely different from the characteristics of thermal decomposition of CHP in
C6H5C(CH3)2O• + •OH f C6H5OH + CH3COCH3 C6H5C(CH3)2• + •OH f C6H5CH3CdCH2 + H2O 2C6H5C(CH3)2• f [C6H5C(CH3)2]2 Acidic Decomposition. In the presence of inorganic acids, most of the CHP decomposes into acetone and phenol. In commercial processes, sulfuric acid is commonly used. The reactions are undertaken at a temperature between 60 and 90 °C with a reaction time ranging from 24 to 90 min. Other inorganic acids also act as an alternative for acidic cleavage, such as hydrochloric acid, sulfur dioxide, and perchloric acid. The overall reaction is
CHP + acid f phenol + acetone + others At a higher temperature, the side products of dimethylphenyl carbinol, methyl styrene, cumyl phenyl, and
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tar were discovered (Fleming, 1976; Chen, 1967). The mechanism of catalytic cleavage by acid was proposed according to the previous studies (Kharasch, 1950) and modified in this study.
C6H5C(CH3)2OOH + A f [C6H5C(CH3)2O] + + AOH[C6H5C(CH3)2O]+ f [C6H5O(CH3)2C]+
decomposition or acid-catalyzed reaction.
Fe3+ + C6H5C(CH3)2OOH f Fe2+ + C6H5C(CH3)2OO• + H+ C6H5C(CH3)2OO• + C6H5C(CH3)2H f C6H5C(CH3)2OOH + C6H5C(CH3)2• C6H5C(CH3)2OOH + H+ f [C6H5C(CH3)2O]+ + H2O [C6H5C(CH3)2O]+ f [C6H5O(CH3)2C]+
+
C6H5C(CH3)2OOH + [C6H5O(CH3)2C] f [C6H5C(CH3)2O]+ + (CH3)2CO + C6H5OH
C6H5C(CH3)2OOH + [C6H5O(CH3)2C]+ f [C6H5C(CH3)2O]+ + (CH3)2CO + C6H5OH
C6H5C(CH3)2OOH f C6H5C(CH3)2O• + •OH
C6H5C(CH3)2OOH f C6H5C(CH3)2O• + •OH
C6H5C(CH3)2O• + C6H5C(CH3)2H f C6H5C(CH3)2• + C6H5C(CH3)2OH
C6H5C(CH3)2• + •OH f C6H5CH3CdCH2 + H2O
C6H5C(CH3)2• + •OH f C6H5CH3CdCH2 + H2O +
C6H5C(CH3)2OH + A f C6H5C(CH3)2 + B + H2O C6H5C(CH3)2+ + B f C6H5(CH3)CdCH2 + A 2C6H5C(CH3)2OOH f 2C6H5C(CH3)2O• + H2O2 C6H5C(CH3)2+ + H2O2 + B f C6H5C(CH3)2OOH + A
C6H5C(CH3)2+ + C6H5(CH3)2CdCH2 + B f dimer + A Note that, in the first equation above, A is an acid, and B is its conjugate base (B + H+ f A). Also, in the last of the preceding reactions, dimer of R-methylstyrene is equivalent to (2,4-diphenyl-4-methyl-2-pentene) in IUPAC nomenclature. Ion-Induced Decomposition. The mechanisms involving metal-catalyzed decomposition were proposed by Hiatt et al. (Hiatt, 1968). The products and rate law suggested the radical-induced decomposition initiated by the interactions between the metal ions and hydroperoxide.
Mn+ + C6H5C(CH3)2OOH f (n+1)+
M
+ C6H5C(CH3)2O• + OH
C6H5C(CH3)2O• + C6H5C(CH3)2H f C6H5C(CH3)2• + C6H5C(CH3)2OH
-
M(n+1)+ + C6H5C(CH3)2OOH f Mn+ + C6H5C(CH3)2OO• + H+ The decomposition of CHP induced by ferric ion can be expressed using a similar series of equations. The generated hydrogen ion or peroxy radical initiates the decomposition in a manner similar to the thermal
From these proposed mechanisms and the studies in the literature (Shashin, 1983; Shashin, 1987; Fleming, 1976;Chen, 1967; Kharasch, 1950; Hiatt, 1968; Casemier, 1973), it is clear that the major decomposed products of CHP are similar because of the same pathways for the mechanisms. However, the rates of the ratedetermining steps and the branching ratios of elementary reactions are totally different. Thus, different overall reactions and related thermokinetics of CHP mixed with contaminants were determined in both DSC and VSP2 experiments. By comparing the exothermic onset temperature and the self-heat rate for the VSP2 tests, the incompatible hazard and reaction rate of CHP contaminated with impurities were suggested as follows. The labile or unstable sequences are
C6H5C(CH3)2OO• (Fe3+) > C6H5C(CH3)2OO- (alkaline) > C6H5C(CH3)2O+ (H+) > C6H5C(CH3)2O• (thermal) and the hazard ratings are
C6H5C(CH3)2OO- (alkaline) > C6H5C(CH3)2O+ (H+) > C6H5C(CH3)2O• (thermal) > C6H5C(CH3)2OO• (Fe3+) Conclusion Clearly, CHP materials must be handled and stored with caution, as any accidental mixing of industrial chemicals poses a potential energy hazard during transport, storage, or processing. This hazard is defined in terms of both the magnitude of release of heat or gas as a result of chemical incompatibility or “other chemical” reactivity and the potential formation of an explosive mixture that can subsequently be initiated by an appropriate stimulus (mechanical impact, thermal activation, or physical shock). This study addresses a systematic approach to the effect of incompatibilities on thermal runaway hazard of CHP. Chromatography,
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DSC, and VSP2 methodologies are promising techniques for generating the data for the study of incompatibilities.
(13) Leung, J. C.; Greed, M. J.; Fisher, H. G. Round-Robin Vent Sizing Package Results; International Symposium on Runaway Reactions, Cambridge, MA, March 1989, March; pp 264-280.
Acknowledgment
(14) Hiatt, R.; Milland, T.; Mayo, F. R. Homolytic Decompositions of Hydroperoxides. I. Summary and Implications for Autoxidation. J. Org. Chem. 1968, 33, 1416.
The authors thank the Ministry of Economic Affairs of the R.O.C. and the National Science Council of the R.O.C. for financial support of this study under Contracts 88-EC-2-A-17-0233 and NSC 87-CPC-E-224-001.
(15) Howard, J. A.; Chenier, J. H. B.; Yamada, T. Can. J. Chem. 1982, 60, 2566. (16) Furimsky, E.; Howard, J. A.; Sewyn, J. Can. J. Chem. 1980, 58, 677.
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Received for review December 14, 1999 Revised manuscript received June 22, 2000 Accepted June 29, 2000 IE990900S
