Calorimetric Techniques Combined with Various Thermokinetic

Article pubs.acs.org/IECR

Calorimetric Techniques Combined with Various Thermokinetic Models to Evaluate Incompatible Hazard of tert-Butyl Peroxy-2-ethyl Hexanoate Mixed with Metal Ions Yun-Ting Tsai,† Mei-Li You,‡ Xin-Ming Qian,§ and Chi-Min Shu*,† †

Doctoral Program, Graduate School of Engineering Science and Technology, and Department of Safety, Health, and Environmental Engineering, National Yunlin University of Science and Technology (YunTech), Yunlin 64002, Taiwan, ROC ‡ Department of General Education Center, Chienkuo Technology University, Changhua 50094, Taiwan, ROC § State Key Laboratory of Explosion Science and Technology, Beijing Institute of Technology (BIT), Beijing 100081, China ABSTRACT: tert-Butyl peroxy-2-ethyl hexanoate (TBPO), an organic peroxide broadly used as initiator for polymerization of ethylene, styrene, methyl methacrylate, and acrylonitrile, has the characteristic of triggering a highly exothermic reaction. Mixing with a contaminant, such as metal ions, may result in a runaway reaction and acceleration decomposition under an abnormal situation. We investigated how Cu2+, Ni2+, and Fe2+ individually affected the thermal decomposition of TBPO. Our aim was to explore the thermal hazard of TBPO mixed with metal ions by calorimetric techniques combined with thermokinetic models. We employed nonisothermal and isothermal calorimeters to determine various thermokinetic and safety parameters, including exothermic onset temperature (To), peak temperature (Tp), final temperature (Tf), heat of decomposition (ΔHd), and maximum heat flow (Qmax) by differential scanning calorimetry (DSC) and thermal activity monitor III (TAM III). Moreover, the isothermal and nonisothermal kinetic models were applied to predict time to maximum rate under adiabatic conditions (TMRad), adiabatic temperature rise (ΔTad), time to conversion limit (TCL), control temperature (CT), emergency temperature (ET), and self-accelerating decomposition temperature (SADT). From the experimental results, Cu2+ could significantly affect TBPO to increase Qmax more than 2-fold as compared to the rest and T0 was advanced as well. Therefore, TBPO contamination by Cu2+ should be avoided during every stage of the manufacturing process.

1. INTRODUCTION

a low temperature environment and secured at operating conditions.6 When TBPO is mixed with metal ions, it may accelerate the reaction rate and increase heat flow. However, before this study, there has been scant open literature on the thermal hazard analysis of TBPO mixed with metal ions. The thermal hazard analysis was assessed initially by mixing hazard analysis software React95 before an experiment. This could obtain rough information about mixing hazard features of two or more substances, such as fire, explosion, or spillage of toxic gas. The results are listed in Table 1. According to the React95 results, metal ions may promote TBPO toward a more unsafe situation.7 Therefore, we explored the effects of TBPO mixed with metal ions, in order to reduce the opportunity as well as mitigate the impact of a thermal hazard accident. We evaluated thermal hazard and thermokinetic parameters, which include exothermic onset temperature (To), peak temperature (Tp), final temperature (Tf), and heat of decomposition (ΔHd) by differential scanning calorimetry (DSC) at heating rates of 1, 2, 4, and 8 °C/min in terms of 98 mass % TBPO individually mixed with 1 mass % CuCl2, FeCl2, and NiCl2. A liquid thermal explosion model was used with DSC data to predict important kinetic and safety parameters, including time

Organic peroxides (OPs) are prevailingly recognized by two characteristics, self-reaction and mixing hazard.1 This is because they have the oxygen-to-oxygen bond (O−O), two oxygen atoms joined together, which decompose readily to combine with other chemical substances and produce an enormous amount of heat. OPs under certain conditions are thermally unstable, so that a source of heat or external fire, thermal shock, and contamination of chemical substance can accelerate runaway decomposition to generate heat and increase pressure, causing process damage as well as causalities, not to mention the huge social impact.2−4 Many chemical substances, such as acids, alkalis, or metal ions, are commonly employed in the reaction of catalysis and neutralization for OPs. Using OPs under abnormal operating conditions, such as overdosing, overtemperature, or overpressure, may induce a runaway reaction and then follow-up explosion accidents. In Taiwan, many serious thermal hazards and explosions have occurred in the process industries, causing losses of human life and fortune. Therefore, we have to treat or use OPs cautiously. tert-Butyl peroxy-2-ethyl hexanoate (TBPO), an organic peroxide, is an initiator for polymerization of styrene in the range of temperature about 90 °C and is highly more active than BPO when the temperature of polymerization is raised in steps.5 This property of TBPO is liable to thermal sources, acids, alkalis, or metal ions. Therefore, it has to be stored under © XXXX American Chemical Society

Received: March 21, 2013 Revised: May 23, 2013 Accepted: May 24, 2013

A

dx.doi.org/10.1021/ie4009106 | Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

Industrial & Engineering Chemistry Research

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°C/min. The test scope of temperature climbing was deliberately chosen from 30 to 300 °C.13 2.3. Thermal Activity Monitor III (TAM III). TAM III, an isothermal calorimeter, is used to obtain thermokinetic parameters for evaluating the thermal stability of substances. The maximum heating rate of TAM III is ±2 K/h, and the temperature range limit of TAM III is 15−150 °C. The sample is tested in a 4 mL glass container with an aluminum lid. In this study, we observed TBPO mixed with metal ions for thermal behavior under isothermal conditions at four temperatures (65, 70, 75, and 80 °C) and the mass ratio of TBPO mixed with metal ions was ca. 10:1.14 2.4. Simulations of Thermokinetic and Safety Parameters and Thermal Hazards of TBPO Mixed with Metal Ions. A liquid thermal explosion model was designed to evaluate thermal hazards of a substance of interest; it can simulate many important thermokinetic and safety parameters by adiabatic, liquid phase, or solid phase thermal explosion models. Because TBPO is liquid phase at room temperature, the liquid thermal explosion model was selected. The boundary condition set was according to three types of heat transfer models for simulation of the reactor. The “wall” and “e” were expressed as the temperature change between the surface of the reactor and the environment, where q is heat flow and n is unit outer normal on the boundary. We assessed thermal hazards of TBPO mixed with metal ions in 25, 400, 800, and 1600 kg, as typical commercial containers. The container’s radius, height, shell thickness, boundary conditions, and TBPO’s properties are listed in Table 2.15,16 1st type

Table 1. Evaluation of Chemical Reaction Hazard by React957 substances TBPO mixed with CuCl2

TBPO mixed with FeCl2

TBPO mixed with NiCl2

hazard analysis 1. Heat generation by chemical reaction may initiate explosion 2. Heat generation by chemical reaction may cause pressurization 3. Contact with substance liberates toxic gas and may cause pressurization 1. Explosive when mixed with oxidizing substances 2. Heat generated from chemical reaction may initiate explosion 3. May cause fire heat generation by chemical reaction and cause pressurization 1. Heat generated from chemical reaction may initiate explosion 2. Heat generation by chemical reaction may cause pressurization 3. Contact with substance liberates toxic gas and may cause pressurization

to maximum rate under adiabatic conditions (TMRad), adiabatic temperature rise (ΔTad), time to 10% conversion limit (TCL10%), control temperature (CT), emergency temperature (ET), and self-accelerating decomposition temperature (SADT). By simulation results, we could effectively decrease the number of experiments and human errors in the future.8 Finally, we directed a test program to evaluate the thermal runaway parameters of the chemical product, in order to neglect the requirements of large−scale runaway or explosive experiments. The method can be used in many different fields, including evaluation of chemical process risk, reactor container design, inherently safer process design, raw material safety during preparation, operations, disposed safety of storage and transportation, and thermal hazard characteristic assessment.9−12

T |wall = Te(t )

(1)

2nd type

q|wall = q(t )

2. EXPERIMENTAL SECTION 2.1. Samples. A 98 mass % tert-butyl peroxy-2-ethyl hexanoate (TBPO) colorless liquid was packed in a 100 mL plastic package. Since TBPO is thermally sensitive, it should be stored in a refrigerator below 4 °C and kept away from any external thermal source. As far as incompatible trials, metal ions, including CuCl2, FeCl2, and NiCl2, were used. The structure of TBPO is shown in Figure 1.

(2)

3rd type −λ

∂T ∂n

= U (Twall − Te) s

(3)

2.4.1. Application of Nonisothermal Kinetic Model to Determine Thermokinetic Parameters. The processes of chemical reaction, which are composed of several independent, parallel, and consecutive stages, are very sophisticated. In general, OPs have two fundamental reaction types: nth order and autocatalysis reactions. A one-stage reaction is a simple nth order reaction and a multistage reaction is a complex autocatalysis reaction. The typical kinetic model often is employed to evaluate the chemical reaction stages for a chemical engineering process. Simple one-stage is nth order reaction, as denoted in eq 4.17−21

Figure 1. Structure of TBPO.5,27

2.2. Differential Scanning Calorimetry (DSC). Nonisothermal experiments were tested by TA8000 system DSC821e. The test cell, a gold-plated high-pressure crucible, could sustain pressure and temperature of 150 bar and 720 °C, respectively. DSC could obtain a temperature versus heat flow diagram and various thermokinetic parameters from experimental data. The sample size of TBPO and TBPO mixed with metal ions acquired approximately 5−8 mg by each experiment. The heating rates of this study were selected as 1, 2, 4, and 8

r=

dC = −kC n dt

(4)

An nth order reaction is a relationship between reaction rate and concentration. From eq 4, the reaction rate is directly proportional to concentration. Therefore, the maximum rate appears in initial time, where r is reaction rate, k is reaction rate constant, and n is reaction order. Arrhenius equation can be expressed in eq 5. B



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Table 2. Size and Boundary Conditions for the 25, 400, 800, and 1600 kg Containers radius (m)

height (m)

thickness (m)

boundary conditions

U (W/m2 K)

λ (W/m K)

density (kg/m)

25

0.20

0.30

0.015

10/10/10

10

890

400

0.38

1.22

0.038

10/10/10

10

890

800

0.52

1.42

0.052

10/10/10

10

890

1600

0.65

1.74

0.065

top/third kind side/third kind bottom/third kind top/third kind side/third kind bottom/third kind top/third kind side/third kind bottom/third kind top/third kind side/third kind bottom/third kind

10/10/10

10

890

container (kg)

⎛ −E ⎞ k = k 0exp⎜ a ⎟ ⎝ RT ⎠

n ⎛ −Ea ⎞⎛ dCA Tf − T ⎞ ⎜ ⎟ −ra = = k 0exp ⎜1 − ⎟ ⎝ RT ⎠⎝ dt Tf − T0 ⎠

(5)

Where Ea is activation energy, R is gas constant, and T is absolute temperature. The nth order reaction equation and Arrhenius equation can be combined to receive the activation energy (Ea), and frequency factor (ko) of the nth order reaction, as shown in eq 6. ⎛ −E ⎞ dα = k 0exp⎜ a ⎟(1 − α)n ⎝ RT ⎠ dt

Here, ra is reaction rate, Ea is activation energy, k0 is frequency factor, R is gas constant, and n is reaction order. Because the heat of decomposition Q0 is dependent on reaction rate, the heat of decomposition Qt at time t is shown as eq 13. Q t = Q 0 × ( −ra)

Equation 14 is obtained by deriving eqs 12 and 13 then taking the natural logarithm. ⎛ ⎜ Qt ln⎜ ⎜ 1 − Tf − T Tf − T0 ⎝

(7)

Where α is conversion rate, z is autocatalysis constant, n1 and n2 are two different reaction stages. We can combine the autocatalysis reaction equation with the Arrhenius equation to acquire the Ea and ko of autocatalysis reaction, which can be written as eq 8. ⎛ −E ⎞ dα = k 0exp⎜ a ⎟(1 − α)n1 (α n2 + z) ⎝ RT ⎠ dt

(

1−

(8)

(10)

Equation 10 can be rearranged as eq 11. 1−α=1−

(Tf − T ) (Tf − T0)

(14)

(Tf − T ) ≈1−0=1 (Tf − T0) Ea RT

(15)

(16)

2.5. Process Safety Parameters Assessment. 2.5.1. Time to Maximum Rate under Adiabatic Conditions. TMRad is a useful tool to present the temperature scale and time scale for a decomposition reaction under adiabatic conditions when the cooling system has failed. Therefore, TMRad may be used to evaluate the possibility of causing a runaway reaction and determine the desired maximum temperature of synthesis reaction (MTSR) for the batch, semibatch, or continuous reactions. TMRad can be obtained from following models:22−25 When heat is generated in a batch reactor, the heat balance can be expressed as eq 17.

(9)

mCp(Tf − T ) mCp(Tf − T0)

)

ln(Q t ) = ln(Q 0k 0) −

Where Ea is activation energy, ko is frequency factor, R is gas constant, T is absolute temperature, n is reaction order. Additionally, α is degree of conversion which can be read in eq 10. α=

⎞ ⎟ Ea n ⎟ = ln(Q 0k 0) − RT ⎟ ⎠

Under isothermal conditions, the isothermal kinetic model is presented in eqs 15 and 16.

2.4.2. Application of Isothermal Kinetic Model to Determine Thermokinetic Parameters. Various kinetic models are derived based on the Arrhenius equation, as given in eq 9. ⎛ −E ⎞ dα = k 0exp⎜ a ⎟(1 − α)n ⎝ RT ⎠ dt

(13)

(6)

A complex multistage autocatalysis reaction is concerned can be expressed in eq 7. f (α) = (1 − α)n1 (α n2 + z)

(12)

(11)

• • • ΔQ Q in − Q out + Q r = Δt

Where α, m, Cp, T0, Tf, and T are conversional rate, sample mass, special heat, onset temperature, final temperature, and initial temperature, respectively. Equations 10 and 11 can be combined to derive eq 12.

(17)

According to eq 17, the heat balance of exothermic reaction for calorimetric tests can be given as eq 18. C


Industrial & Engineering Chemistry Research UA(Te − Ts) + Ms( −ΔHd) = MsCp,s

dTs + McCp,c dt

dα dt dTc dt

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position for organic peroxides. To understand the proper temperature and size for organic peroxides, we found a safety parameter to determine the optimum temperature and size of storage, transportation, and handling which is called SADT. SADT is the lowest ambient temperature at which overheat in the center of the commercial packaging exceeds 6 °C after a lapse of a 7-day period or less. This period is measured every once in a while when the packaging center temperature reaches 2 °C beneath the surrounding temperature. SADT is also used to understand the self-decomposition of TBPO. According to SADT as defined, we simulate the heat generating behavior of TBPO mixed with CuCl2 in various types of commercial containers under different boundary conditions by dynamic simulations. This is when the heat generation rate of TBPO mixed with CuCl2 can incur the lowest ambient temperature to raise ΔT = 6 °C on a temperature which is determined as SADT. The two-stage reaction models of the heat generation rate are displayed in eqs 26 and 27.27 nth order reaction

(18)

Where U, A, Te, Ts, Tc, Ms, Cp,s, and Cp,c are heat transfer coefficient, wetted surface area, environment temperature, sample temperature, test cell temperature, sample’s heat capacity, and test cell’s heat capacity, respectively. Equation 19 means that the sample and test cell were situated in a heat balance. dTc dT dT = s = dt dt dt

(19)

We assumed that for the sample which is generating heat in a complete adiabatic environment the value of λ is equal to zero. The relationship with time and temperature in an adiabatic system can be rewritten by combining eqs 18 and 19. MsCp,s −ΔHd dα dT = dt McCp,s + MsCp,s Cp,s dt

dQ = Q∞k 0e−Ea / RT (1 − α) dt

(20)

In addition, the phi value (Φ) and ΔTad can read as eqs 20 and 21. Φ=

Autocatlysis reaction dQ = Q∞k 0e−Ea / RT (1 − α)(α + z) dt

MsCp,s + MsCp,s McCp,s

−ΔHd ΔTad = Cp,s

(21)

Where Q is heat production, Q is heat effect of a reaction, and z is autocatalysis factor. The illustration of CT and ET relies on SADT from safety and handling of organic peroxides of the National Fire Protection Association (NFPA). CT can ensure goods which are stored under a safety temperature that can avoid reaching the ET. Here, ET means that we have to start emergency procedures when the temperature of the goods reaches ET. CT and ET are given in eqs 28−33.11,28

(22)

(23)

Therefore, when the initial temperature and Φ are determined, the TMRad can be predicted by numerical integration of dT/dt. 2.5.2. Evaluation of TCL10%. TCL10% is the decomposition degree of substances under chemical and physical reactions. Therefore, TCL10% can be used to evaluate the thermal stability of substances during storage and transportation. TCL10% is determined by numerical methods from DSC experimental data and considered from two-stage reaction.26

dα = r2 = k 2α n21(1 − α)n22 dt

if SADT < 20 °C

(28)

CT = SADT − 15 °C

if SADT < 30 or 35 °C

(29)


if SADT < 40, 45, or 50 °C

ET = SADT − 10 °C

if SADT < 20 °C

(31)

ET = SADT − 10 °C

if SADT < 30 or 35 °C

(32)

ET = SADT − 5 °C

if SADT < 40, 45, or 50 °C

(33)

Note: there are no CT and ET when SADT is higher than 50 °C.11,26

(24)

Autocatalysis reaction −


(30)

nth order reaction dα − = r1 = k1(1 − α)n1 dt

(27)

∞

Then, eq 20 can be rearranged as eq 23. dT 1 dα = ΔTad dt Φ dt

(26)

3. RESULTS AND DISCUSSION A DSC experiment can observe quickly and conveniently the rudimentary thermal hazards and reaction behaviors for a reactive substance of interest. DSC was also used to exam incompatible hazards between two substances. Figure 2 shows the DSC tests for TBPO and TBPO mixed with CuCl2, FeCl2, or NiCl2 at a heating rate of 8 °C/min. We compared the exothermic reaction of TBPO and TBPO mixed with FeCl2 and NiCl2 and found no difference between them. However, when TBPO is mixed with CuCl2, the reaction process is not only earlier than pure TBPO, but also the maximum heat flow approximately rises 1.5-fold. In this case, three metal compounds all contain Cl− so that thermal decomposition of TBPO which is affected by Cl− which can be excluded.

(25)

Where ki (i = 0, 1, 2, 3) is reaction rate constant under isothermal conditions, n is reaction order of ith stage (i = 0, 1, 2, 3). TCL10% is employed for indicating the thermal stability of TBPO mixed with CuCl2 under storage and transportation conditions. 2.5.3. Liquid Thermal Explosion Simulation for Testing SADT, CT, and ET. When organic peroxides are undergoing a self-accelerating decomposition, it can release heat into the environment and may lead to an unexpected thermal hazard accident. However, both the temperature and size are the outstanding elements to affect the self-accelerating decomD



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Figure 2. DSC thermal curve of temperature versus heat flow for 98 mass % TBPO and TBPO mixed with 1 mass % CuCl2, NiCl2, and FeCl2 at 8 °C/min.

Figure 3. DSC thermal curves of heat flow versus temperature for 98 mass % TBPO mixed with 1 mass % CuCl2 at heating rates of 1, 2, 4, and 8 °C/min.

Therefore, it is confirmed that Cu2+ is an incompatible substance for TBPO. On the basis of above-mentioned phenomenon, if TBPO is mixed with Cu2+ during the product manufacturing process, storage, or transportation, it can quickly generate enormous heat in a shorter time than pure TBPO, causing fire, explosion, or releasing an amount of gas. Table 3 presents data of T0, Tp, Tf, and ΔHd from the DSC tests.

Table 4. DSC Thermal Curve of Temperature versus Heat Flow for 98 mass % TBPO and TBPO Mixed with 1 mass % CuCl2 at 1, 2, 4, and 8 °C/min

Table 3. Calorimetric Data from the Dynamic Heating Experiments of 98 mass % TBPO and TBPO mixed with 1 mass % CuCl2, FeCl2, and NiCl2 for the Total Peak of the Reaction by DSC sample TBPO TBPO + 1 mass % CuCl2 TBPO + 1 mass % FeCl2 TBPO + 1 mass % NiCl2

mass (mg)

T0 (°C)

Tp (°C)

Tf (°C)

ΔHd (J/g)

5.2 5.0 + 1.3

104.2 111.2

131.5 126.4

151.0 137.1

902.8 888.0

5.2 + 1.5

104.6

132.3

154.6

916.0

5.2 + 1.3

105.2

133.1

154.6

952.4

Figure 3 shows the heat flow versus temperature curve of TBPO mixed with CuCl2 at heating rates of 1, 2, 4, and 8 °C/ min. We performed the DSC experiment three times to calculate the average values as given in Table 4. T0 and ΔHd of TBPO mixed with CuCl2 are ca. 110 °C and 871 J/g, respectively. In accordance with experimental results, Table 4 indicates an excellent relationship. When the heating rate was increased, T0 and Tf were delayed and exothermic peak height was increased. The phenomenon corresponded completely to normal DSC test results. Subsequently, the numerical simulation method was used to curve fit the thermal decomposition graph of TBPO mixed with CuCl2 under different heating rates. Heating rates of 4 and 8 °C/min were deliberately chosen to calculate the thermokinetic parameters by thermokinetic equations. From Figures 4−11, there are heat production and heat production rate versus time of DSC results by experiments and simulations. A two-stage reaction is an autocatalytic reaction combined with nth order, and a one-stage reaction is a simple nth order reaction. Figures 4 and 5 demonstrate the curve fitting compared with simulation and experimental results

β (°C/min)

T0 (°C)

Tp (°C)

Tf (°C)

ΔHd (J/g)

1 2 4 8

84.8 89.4 99.2 111.2

94.5 102.9 113.2 126.4

106.3 114.2 124.0 137.1

707.4 771.3 872.0 888.0

Figure 4. 98 mass % TBPO mixed with 1 mass % CuCl2 heat production versus time curves of two-stage reaction with DSC nonisothermal tests at heating rate of 4 °C/min by experiment and simulation.

of heat production versus time of TBPO mixed with CuCl2 with two heating rates of 4 and 8 °C/min by DSC test. The first stage reaction of TBPO mixed with CuCl2 generated heat of 822.4 and 905.3 kJ/kg, and the maximum heat generation happened after 22 and 13 min under heating rates of 4 and 8 °C/min, respectively. The second stage reaction from start to finish was likely to first stage, and the heat generation was 50.9 and 44.4 kJ/kg under heating rates of 4 and 8 °C/min, respectively. Figures 6 and 7 diagram heat production rate E



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Figure 7. 98 mass % TBPO mixed with 1 mass % CuCl2 heat production rate versus time curves of two-stage reaction with DSC nonisothermal test at heating rate of 8 °C/min by experiment and simulation.

Figure 5. 98 mass % TBPO mixed with 1 mass % CuCl2 heat production versus time curves of two-stage reaction with DSC nonisothermal tests at heating rate of 8 °C/min by experiment and simulation.

Figure 6. 98 mass % TBPO mixed with CuCl2 heat production rate versus time curves of two-stage reaction with DSC nonisothermal tests at hearing rate of 4 °C/min by experiment and simulation.

Figure 8. 98 mass % TBPO mixed with 1 mass % CuCl2 heat production versus time curves of one-stage reaction with DSC nonisothermal test at heating rate of 4 °C/min by experiment and simulation.

versus time for thermal decomposition of TBPO mixed with CuCl2, and show that the result is similar to Figures 4 and 5. As a result, if the heating rate is higher, the maximum heat generation could advance. Thus, if the TBPO manufacturing process is contaminated by Cu2+ and the heating rate is controlled under an incorrect operation, it may accelerate heat generation of TBPO, leading to the development of a violent runaway reaction. Figures 8−11 show heat production and heat production rate versus time of one-stage simulated for TBPO mixed with CuCl2 under heating rates of 4 and 8 °C/min. According to Figures 8 and 9, this is so even if they all have great curve fitting for heat production versus time of TBPO mixed with CuCl2. However, the heat production rate versus time curve of TBPO mixed with CuCl2 has a part which is inferior from 20 to 30 min and 14 to 15 min in Figures 10 and 11, respectively. Therefore, a two-stage reaction is matching better than a one-stage nth order reaction. Additionally, we can observe the calculation results, which are reasonable by twostage reaction because Ea and A are too large in calculation

results by the nth order equation. Therefore, TBPO mixed with CuCl2 can be proven to be a two-stage reaction. The thermokinetic parameters are presented in Table 5 by twostage reaction and one-stage reaction. Figure 12 demonstrates the TAM III thermal curves of heat flow versus time for TBPO mixed with CuCl2 at 65, 70, 75, and 80 °C. We can employ the TAM III experimental results combined with the isothermal condition model for estimating Ea of TBPO mixed with CuCl2. Because the isothermal kinetic model does not consider reaction order, Ea can be calculated easily and faster than nonisothermal kinetic model. In Figure 13, the plot of the ln Qmax versus 1/T graph was used to determine the slope, which is Ea, and the value of Ea for TBPO mixed with CuCl2 under isothermal conditions is approximately 124 kJ/mol. We compared the simulation results with literature values, revealing the Ea of TBPO and TBPO mixed with CuCl2 has not a remarkable difference between each other under isothermal conditions.29 F



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Table 5. Thermokinetic Parameter Evaluation under DSC Tests by Nonisothermal Kinetic Simulation at 4 and 8 °C/ min β (°C/min)

4

kinetics

nth order

autocatalysis + nth order

nth order

autocatalysis + nth order

66.2668 227.1724 1.2015

36.8361 132.2481 1.0160

60.0000 212.1129 1.1983

20.6702 79.3302 1.1887

N/A

0.4679

N/A

1.1909

N/A

0.0112

N/A

0.0381

872.6796

822.3825

905.2941

860.9776

N/A N/A N/A

20.5913 83.3733 0.8067

N/A N/A N/A

40.9142 153.6034 1.0256

N/A

50.8507

N/A

44.3829

first stage ln(k0) Ea (kJ/mol) reaction order (n1)/auto reaction order (n2) autocatalytic constant (z) ΔHd (kJ/kg) second stage ln(k0) Ea (kJ/mol) reaction order (n1)/auto ΔHd (kJ/kg)

Figure 9. 98 mass % TBPO mixed with 1 mass % CuCl2 heat production versus time curves of one-stage reaction with DSC nonisothermal test at heating rate of 8 °C/min by experiment and simulation.

Figure 10. 98 mass % TBPO mixed with 1 mass % CuCl2 heat production rate versus time curves of one-stage reaction with DSC nonisothermal test at heating rate of 4 °C/min by experiment and simulation.

8

Figure 12. TAM III thermal curves of heat flow versus time for 98 mass % TBPO mixed with 1 mass % CuCl2 decomposition at 65, 70, 75, and 80 °C.

Figure 11. 98 mass % TBPO mixed with 1 mass % CuCl2 heat production rate versus time curves of one-stage reaction with DSC nonisothermal test at heating rate of 8 °C/min by experiment and simulation.

Figure 13. Determination of Ea of 98 mass % TBPO mixed with 1 mass % CuCl2 by isothermal kinetic model under isothermal conditions.

G



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Thermokinetic parameters provide reliable information to evaluate the thermal hazard for TBPO contaminated by Cu2+. This study utilized isothermal and nonisothermal kinetic models to compare with simulation and experimental results, presenting excellent curve fitting and R2 values. Therefore, the data set can be effectively and precisely applied for further study. Figure 14 displays ΔTad and TMRad for TBPO mixed with metal ions. The calculation of ΔTad and TMRad should be

Figure 15. 98 mass % TBPO mixed with 1 mass % CuCl2 of TCL10% was achieved with two-stage reaction kinetics simulation.

Table 6. Comparison of the Values from the Literature and the Liquid Thermal Hazard Simulation for the SADT, CT, and ET under DSC Nonisothermal Conditions at 4 °C/min in the 25, 400, 800, and 1600 kg Containers samples TBPO

Figure 14. Evaluation of TMRad and ΔTad for 98 mass % TBPO mixed with 1 mass % CuCl2 under adiabatic conditions.

TBPO + CuCl2

dependent on the Φ of the reactor or test cell, and ΔHd and Cp of the sample. In completely adiabatic situations, the Φ of the reactor or test cell is approximately equal to 1, and the average ΔHd with four heating rates and Cp of TBPO mixed with CuCl2 are 809.7 kJ/mol and 1800.0 J/g K, respectively. If a chemical process is contaminated with Cu2+ under an operating temperature of 90 °C, the values of ΔTad and TMRad are 558.0 °C and 5.1 min based on the above conditions. According to the simulation results, when the chemical process is contaminated by Cu2+, a violent and uncontrolled runaway reaction maybe occur rapidly, resulting in an unexpected fire and/or explosion. To evaluate thermal stability, the characteristic of conversion degree at certain constant temperature, which is necessarily determined, can ensure a material’s quality and safety during storage or transportation. Figure 15 presents the TCL10% of TBPO mixed with CuCl2. TCL10% is less than three days at 20 °C. According to literature results, TCL10% of pure TBPO is approximately 175 days at 20 °C.19 Therefore, when TBPO is mixed with CuCl2, it may tend to an extreme thermally unstable situation. To promote safety and lengthen the life cycle for TBPO, TBPO should be stored in a low temperature environment below 20 °C and avoid contacting or being used in cupriferous vessel or equipment. Additionally, we investigated TBPO mixed with CuCl2 thermal stability in the 25, 400, 800, and 1600 kg commercial containers by SADT, ET, and CT. According to the calculation results, the thermal stability of the 25 kg container is greater than that of the 400 kg container, which clearly indicates the bigger container can readily cause an incompatible hazard by Cu2+. Table 6 shows literature and simulation results at 4 °C/ min, which reveals that SADT, ET, and CT are lower than the

mass in container

SADT (°C)

CT (°C)

ET (°C)

25 400 25 400 800 1600

46 40 45 39 37 35

31 25 30 24 22 20

41 35 40 34 32 25

literature results. On the basis of the above-reasons, Cu2+ can indeed accelerate self-heating decomposition and increase heat accumulation for TBPO. Therefore, when TBPO is manufactured, stored, or transported, we have to avoid TBPO being contaminated by Cu2+.28,30−33

4. CONCLUSIONS Isothermal and nonisothermal thermokinetic models are applied for understanding the thermal hazard of TBPO mixed with Cu2+. Upon the basis of simulation results, TBPO mixed with Cu2+ is inferred to be a complex two-stage reaction. Cu2+ is an incompatible ion for TBPO, which can significantly raise the thermal hazard when TBPO is used or manufactured. Therefore, we have to choose vessels with appropriate material of construction or avoid the pipeline from being rusty. We can combine with thermal calorimetric technology and thermokinetic model to obtain SADT, ΔTad, TMRad, TCL10%, CT, and ET and apply them to the practical process. The thermal analysis technology is used in incompatible hazard investigation, and it is fast, precise, and highly sensitive, which intensifies the theoretical foundation for the substance’s thermal stability. Conventional thermal analysis has significant disadvantages, such as large-scale experiments, environmental pollution, or long-term research planning. Therefore, we have discovered an effective alternative method to improve process design and to provide safer storage management and use information for organic peroxides with incompatibles, here TBPO. H



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5. OUTLOOK Other kinetic evaluation tools, such as advance kinetic and technology solutions (AKTS), thermal safety software (TSS), and calorimeters, such as vent sizing package 2 (VSP2), accelerating rate calorimeter (ARC), reaction calorimeter (RC1), or C80, will be applied to obtain more thermal stability and safety parameters for future studies on TBPO.

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Article

REFERENCES

(1) Lu, K. T.; Chen, T. C.; Hu, K. H. Investigation of the decomposition reaction and dust explosion characteristics of crystalline benzoyl peroxides. J. Hazard. Mater. 2010, 161, 246−256. (2) Luo, K. M.; Chang, J. G.; Lin, S. H.; Chang, C. T.; Yeh, T. F.; Hu, K. H.; Kao, C. S. The criterion of critical runaway and stable temperatures in cumene hydroperoxide reaction. J. Loss Prev. Process Ind. 2001, 14, 229−239. (3) Fisher, H. G.; Goetz, D. D. Determination of self−accelerating decomposition temperatures for self−reactive substances. J. Loss Prev. Process Ind. 1993, 6, 183−194. (4) Tseng, J. M.; Shu, C. M. Isothermal kinetic evaluation of methyl ethyl ketone peroxide mixed with acetone by TAM III tests. Thermochim. Acta 2010, 45, 507−508. (5) Product Data Sheets for TRIGONOX 21S; AkzoNobel Polymer Chemicals: Amsterdam, The Netherlands, 2013. (6) Hou, H. Y.; Duh, Y. S.; Lin, W. H.; Shu, C. M. Reactive incompatibility of cumene hydroperoxide mixed with alkaline solutions. J. Therm. Anal. Calorim. 2006, 85, 145−150. (7) Chemical Reactivity Worksheet; Office of Response and Restoration: New Castle, DE, 2013. (8) User Manual; AKTS Advanced Thermal Analysis Software: Siders, Valais, Switzerland, 2013. (9) Yu, Y.; Song, P.; Jin, C.; Fu, S.; Wu, L. Q.; Ye, J. Catalytic effects of nickel (cobalt or zinc) acetates on thermal and flammability properties of polypropylene-modified lignin composites. Ind. Eng. Chem. Res. 2012, 51, 12367−12374. (10) Duh, Y. S.; Wu, X. H.; Kao, C. S. Hazard ratings for organic peroxides. Process Saf. Prog. 2008, 27, 89−99. (11) Organic Peroxide Formulations and Storage Class Definitions, NFPA 400; National Fire Protection Association: Anaheim, CA, 2013. (12) Lin, C. P.; Chang, C. P.; Chou, Y. C.; Shu, C. M. Modeling solid thermal explosion containment on reactor HNIW and HMX. J. Hazard. Mater. 2010, 176, 549−558. (13) Operating Instructions; STARe Software with Solaris Operating System; Mettler Toledo: Switzerland, 2004. (14) TAM III Brochure; TA Instrument: New Castle, DE, 2013. (15) Lin, C. P.; Chang, Y. M.; Tseng, J. M.; Shu, C. M. Comparisons of nth-order kinetic algorithms and kinetic model simulation on HMX by DSC tests. J. Therm. Anal. Calorim. 2010, 100, 607−614. (16) Thermal Safety Software (TSS); Cheminform Saint-Petersburg (CISP) Ltd., St Petersburg: Russia, 2013. (17) You, M. L.; Shu, C. M. Further explanations of lauroyl peroxide runaway reaction by DSC tests and simulations. J. Therm. Anal. Calorim. 2011, 103, 411−412. (18) Singh, A.; Chavda, A.; Nandula, S.; Jasra, R. V.; Maiti, M. Kinetic study on stereospecific polymerization of 1,3-butadiene using a nickel based catalyst system in environmentally friendly solvent. Ind. Eng. Chem. Res. 2012, 51, 11066−11071. (19) Lin, C. P.; Tseng, J. M. Green technology for improving process manufacturing design and storage management of organic peroxide. Chem. Eng. J. 2012, 180, 284−292. (20) Tseng, J. M.; You, M. Y.; Chen, S. L.; Hwang, W. T.; Gupta, J. P.; Shu, C. M. Runaway effects of nitric acid on methyl ethyl ketone peroxide by TAM III tests. J. Therm. Anal. Calorim. 2009, 96, 789− 793. (21) Lin, C. P.; Tseng, J. M.; Chang, Y. M.; Liu, S. H.; Cheng, Y .C.; Shu, C. M. Modeling liquid thermal explosion reactor containing tert− butyl peroxybenzoate. J. Therm. Anal. Calorim. 2010, 102, 587−595. (22) Roduit, B.; Folly, P.; Sarbach, A.; Berger, B.; Brogli, F.; Mascarello, F.; Schwaninger, M.; Glarner, T.; Irle, E.; Tobler, F.; Wiss, J.; Luginbühl, M.; Williams, C.; Reuse, P.; Stoessel, F. Estimation of time to maximum rate under adiabatic conditions (TMRad) using kinetic parameters derived from DSC-investigation of thermal behavior of 3-methyl-4-nitrophenol. Chem. Propel. Polym. Mater. 2011, 1, 84−93. (23) Stoessel, F. Planning protection measures against runaway reactions using criticality classes. Process Saf. Environ. 2009, 87, 105− 112.

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors are indebted to the donors of the National Science Council (NSC) in Taiwan under the contract number NSC-992221-E-224-029-MY3 for financial support and to Dr. Arcady A. Kossoy for technical assistance for this study.

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LIST OF SYMBOLS AND ACRONYMS A = wetted surface area, m2 Cp = heat capacity, J/g K Cp,c = sample’s heat capacity, J/g K Cp,s = test cell’s heat capacity, J/g K CT = control temperature, °C Ea = activation energy, kJ/mol ET = emergency temperature, °C k0 = frequency factor, m3/mol s ki = reaction rate constant at isothermal temperature, mol/L s, i = 0, 1, 2, 3 Ms = sample mass, mg MTSR = maximum temperature of synthesis reaction, °C n = unit outer normal on the boundary, dimensionless ni = reaction order of ith stage, dimensionless Q = heat generation, J/g Q∞ i = heat effect of a reaction, J/kg Qmax = maximum heat flow, W/g SADT = self-accelerating decomposition temperature, °C T = absolute temperature, K T0 = exothermic onset temperature, °C Tc = test cell temperature, °C TCL10% = time to 10% conversion limit, day Te = ambient temperature, °C Tf = final temperature, °C Tiso = isothermal temperature, °C TMRad = time to maximum rate under adiabatic conditions, min TP = peak temperature, °C Ts = sample temperature, °C Twell = temperature on the wall, °C U = heat transfer coefficient, W/m2 K t = time, s z = autocatalytic constant, dimensionless

Greek Symbols

αi = degree of conversion, dimensionless β = heating rate, °C/min ρ = density, kg/m3 λ = thermal conductivity, W/m K Φ = thermal inertia, dimensionless ΔHd = heat of decomposition, J/g ΔTad = adiabatic temperature rise, °C I



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(24) Stoessel, F. Thermal Safety of Chemical Processes; Wiley-VCH: Weiheim, Germany and New York, 2008; p 374. (25) Steinbach, J. Safety Assessment for Chemical Processes; WileyVCH: Weiheim, Germany and New York, 1999; p 305. (26) Kossoy, A.; Benin, A.; Akhmetshin, Y. An advanced approach to reactivity rating. J. Hazard. Mater. 2005, 118, 9−17. (27) Fauske, H. K. Gassy System Vent Sizing the Role of Two-phase Flow; Process Safety News; Fauske and Associates: Burr Ridge, IL, 2011; Vol 18, p 3. (28) Kossoy, A. A.; Sheinman, I. Y. Comparative analysis of the methods for SADT determination. J. Hazard. Mater. 2006, 118, 626− 638. (29) Tsai, L. C.; Tsai, Y. T.; Lin, C. P.; Liu, S. L.; Wu, T. C.; Shu, C. M. Isothermal versus non-isothermal calorimetric technique to evaluate thermokinetic parameters and thermal hazard of tert-Butyl peroxy-2-ethyl hexanoate. J. Therm. Anal. Calorim. 2012, 109, 1291− 1296. (30) Organic Peroxide Initiators; AkzoNobel Polymer Chemicals: Amsterdam, The Netherlands, 2013. (31) Malow, M.; Wehrstedt, K. D. Prediction of the self−accelerating decomposition temperature (SADT) for liquid organic peroxides from differential scanning calorimetry (DSC) measurements. J. Hazard. Mater. 2005, 120, 21−24. (32) Jia, H.; Zhao, X. H.; Jin, F. Y.; Pu, W. F.; Li, Y .M.; Li, K. X.; Li, J. M. New insights into the gelation behavior of polyethyleneimine cross-linking partially hydrolyzed polyacrylamide gels. Ind. Eng. Chem. Res. 2012, 51, 12155−12166. (33) Tseng, J. M.; Lin, C. P. Green thermal analysis technology for evaluating the thermal hazard of di-tert-butyl peroxide. Ind. Eng. Chem. Res. 2011, 50, 9487−9494.

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