Ind. Eng. Chem. Res. 1994,33, 285-291
285
PROCESS DESIGN AND CONTROL A Study on Resol-Type Phenol-Formaldehyde Runaway Reactions Enio Kumpinsky R&D Department, Ashland Chemical Co., P.O. Box 2219, Columbus, Ohio 43216
Resol polymerizations are very exothermic, and certain circumstances can lead them to uncontrollable self-heating. To prevent disasters, chemical reactors are usually equipped with emergency relief lines whose design is based on small-scale tests with the field formulation. A large number of such experiments were performed in the Reactive System Screening Tool (RSST) for resol polymerizations in this work,exploring the different facets of runaway reactions. The most significant finding in this study is the recognition that the small-scale test may yield erroneous results if the conditions are not carefully chosen. Introduction
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Phenolic resins are synthetic polymers whose building blocks include formaldehydeand phenol or, among others, alkyl-substituted phenols, furfural, and furfuryl alcohol. They have a large number of applications, wood composites, fiber bonding, laminates,foundry (resin-bonded sand), coatings, and adhesives,just to name a few. Acid-catalyzed phenol-formaldehyde resins are known as novolacs, which usually contain molar excess of phenol. Formaldehyde adds to the ortho- or para-position of phenol, forming methylene bridges. Base-catalyzed phenolics are called resols. They are usually polymerized with molar excess of formaldehyde, and the resins contain methylene and dimethylene ether bridges and methylol groups (Maciel et al., 1984). Figure 1 illustrates the fundamental resol reactions. Structure I is the methylolated phenol, formed by the addition of formaldehyde to phenol at the orthoand/or para-position. Structure I1 represents the portion of the polymer with a methylene bridge while structure I11 depicts a dimethylene ether bridge. Alkali-catalyzed reactions account for the largest percentage of phenolic resin production (Brode, 1982),and many occurrences of explosions or near misses with base-catalyzed systems have been reported in the literature (Waitkus and Griffiths, 1977;Gustin et al., 1993). The batch reactor for resol reactions and ita ancillary equipment such as an overhead reflux condenser are usually designed to handle the heat load under normal circumstances. However, these reactions can become uncontrollable under upset conditions, such as loss of cooling or agitation and fast addition of the delayed feed componentin a semibatchpolymerization. The emergency vent must be adequately sized to discharge the overwhelming reaction mass and safely relieve the pressure generated by the heat of reaction. Many exothermic reactions of industrial interest are deterred from running away by restraining them at an early stage. For example, it is well-known that chaingrowth polymerizations can be terminated by free-radical scavengers. Likewise, resol runaway reactions can be halted by acids, but it may be difficult to reach a neutralization point in a runaway situation since the pH can change during the reaction. Thus, venting through an emergencyline is of paramount importance for the safe handling of resol runaway reactions. Waitkus and Griffiths (1977)studied the venting of acid0888-5SS5/94/2633-0285$04.5QI0 0
OH
6
@-
+ CH,O-
CH,OH
I
1
L
J
I11
n/2
Figure 1. Schematic of resol reactions.
catalyzed reactions using kinetic and thermochemical principles, and the authors made some recommendations to improve safety in the phenolic industry. Gustin et al. (1993) demonstrated the usefulness of experimental methods to investigate resol runaway reactions using a typical industrial composition. In this work we did a process safety analysis by studying the various parameters that are relevant to resol runaway reactions, such aq pressure, vapor inerting, formaldehyde/phenolmolar ratio, amount and type of catalyst, effect of methanol, and comparison between formaldehyde and paraformaldehyde. Experimental Equipment and Procedures The experiments of this work used the guidelines provided by the Design Institute for Emergency Relief Systems (DIERS) of the American Institute of Chemical Engineers (AIChE) (Fisher et al., 1992). The experimental apparatus of this study is called Reactive System Screening Tool (RSST), as described by Creed and Fauske (1990). Essentially, it consists of a spherical glass test cell with total volume of 14 mL, working volume of 10 mL, and low
1994 American Chemical Society
286
Ind. Eng. Chem. Res., Vol. 33, No. 2, 1994
thermal mass, equipped with a tiny magnetic stirring bar. It has a neck with diameter of 6 mm, through which the thermocouple is inserted and the runaway products can escape. The dual bottom external heater used in these experiments is held around the test cell by means of a tape belt, and this assembly is wrapped in aluminum foil. It is then insulated and mounted on a metal sheath. The reaction mass is charged and the unit is placed inside a 350-mL containment vessel, which can be pressurized to the desired setpoint, measured by a transducer. The containment vessel is secured and placed on a magnetic stirrer with strong coupling, inside a vented hood. The unit is pressurized and the experiment is initiated by computer control. The reaction mass is heated at 2 "C/ min until the temperature rise can sustain itself, typically 40-60 OC for resol polymerizations, at which point the heating rate is switched to 0.25 OCImin. The phenol-formaldehyde reactions of this study are of the vapor type: there is no significant gas generation due to chemical decomposition and the pressure increases with temperature mostly as a result of methanol and water vaporization. Upon cooling, the methanol and water condense and the pressure returns to the original setpoint with only small deviations. The water is originated from formulation and condensation reactions. According to eq 1 of Creed and Fauske (1990), the emergency vent crosssection area for vapor-type reactions is given by A = 1.5 X 1 0 - 5 m ~ T ' ~ / ( F where ~ P , ) A is the area in square meters, mR is the mass of reactants in the field-scale vessel in kilograms, T'T is the self-heating rate at the tempering condition in degrees Celsius per minute, and P, is the relief set pressure in absolute pounds per square inch. FF is a flow reduction factor which depends on the emergency vent diameter and equivalent length. Reactant mass and flow reduction factor are production and design requisites and are beyond the scope of this work. Regarding self-heating rates, two variables are used in this work: T'Mand T'T. T'Mis the maximum self-heating rate attained at a given runaway reaction test (point D in Figure 2). T'T is the self-heating condition used to determine vent sizes, and it is obtained as follows. First, a test is run with the containment vessel at P, to determine the tempering point, that is, the temperature at which the self-heating rate reaches a maximum at the relief set pressure. Then, a second test is run at a high pressure, which is used to determine T'T. T'T is the self-heating rate of the high-pressure test at the tempering point of the low-pressure test. Inerting was required for oxygen-freeexperiments. The containment vessel was pressurized with nitrogen to 3 MPa and slowly released. This operation was repeated and the containment vessel was then pressurized to the desired setpoint with nitrogen.
A Typical Resol Runaway Reaction Figure 2 illustrates a resol runaway reaction. It is an Arrhenius plot of self-heating rate versus temperature. This test was run with a starting pressure of 170 kPa. A mixture of the following raw materials was used (weight basis): phenol, 46.7 % ; 91 % paraformaldehyde, 28.7 ?6 ; deionized water, 21.1 %; methanol, 2%; 50% sodium hydroxide solution, 1.5%. The formaldehyde to phenol molar ratio was 1.75. The experiment began at 21.9 "C (A) with a heating rate of 2 "C/min until the reaction mass reached 55.0 "C (B).Then the heating rate was switched to 0.25 OC/min. The actual heating rate dropped as the temperature reached 58.2 "C (C). From then on, the selfheating rate increased steadily to the tempering point of
T
12.5
34.5
3.5
("C) 60.1
90.4
3.0
126.8
2.5
1 / T (1000/K)
Figure 2. Self-heating rate for a resol with formaldehyde to phenol molar ratio of 1.75.
10
0
1
2
3
4
P (MPa) Figure 3. Starting pressure and oxygen effects on T Mfor a resol with formaldehyde to phenol molar ratio of 1.52, using a 50% formaldehyde solution.
117.0 "C (D), at the absolute pressure of 193 kPa. At this pressure water boils at 119 "C, so the tempering point of 117 "C is consistent with the vapor pressure of saturated steam. Upon cooling,the pressure returned to the original setting, which confirms that this resol system is of the vapor type. Experimental Results and Discussion Figure 3 shows the effects of background pressure and oxygen content on the maximum self-heating rate T'Mfor a resol with the following composition: phenol, 49.0%; 50 % formaldehyde solution in water, 47.5 5% ; methanol, 2.0 % ; 50 % sodium hydroxide solution, 1.5% Note that each symbol in Figure 3 represents one experiment. Some surprising features were observed in this plot. As one would anticipate, the maximum self-heating rate is higher at elevated background pressures. This is a vapor system that is tempered by heat loss from the generation of vapors, so the higher the pressure, the higher the boiling point of water and the higher the tempering point. However, the three curves exhibit an unexpected pattern. They show a maximum for T'Mat about 1.5 MPa and a minimum at approximately 2.2 MPa. Another maximum in the T'M versus P curve was observed for all cases, but those with oxygen present had a much stronger exotherm. No runaway reaction occurred for nitrogen atmosphere at 2.8 MPa, as if there was a ceiling pressure. Due to equipment limitations, it was not possible to carry out experiments with background pressures above 3.2 MPa. However,
.
Ind. Eng. Chem. Res., Vol. 33, No. 2, 1994 287
A
91% paraformaldehyde
0
10 0
1
2
3
4
0
P (MPa)
0
Figure 4. Effect of starting pressure on T M for a resol with formaldehyde to phenol molar ratio of 1.52 using formaldehyde solution and paraformaldehyde (nitrogen atmosphere).
50% f o r m a l d e h y d e 1
2
3
4
P (MPa)
Figure 6. Pressure effect on !PTfor the experimental conditions of Figure 3 (nitrogen atmosphere).
.-
E
\ 0
e - I
IA
50% f o r m a l d e h y d e 91% poraformaldehyde
1 0 50% formaldehvde
I
"
0
1
2
3
4
P (MPa)
Figure 7. Pressure effect on YTfor experimental conditions of Figure 4 (2.55 mol % of 02).
zation, 17.7-22.7 kcal/g-mol (Leung et al., 1986). However, the dissolution of formaldehyde in water is exothermic, 15 kcal/g-mol (Haddeland, 19671,which compensates for the heat of depolymerization. Even though the choice of liquid formaldehyde or solid paraformaldehyde has an effect on the maximum self-heating rates, the experiments of this work demonstrate that the peak temperatures are the same for both forms of formaldehyde. The study of the maximum self-heating rate asa function of pressure is useful to appreciate the intricacies of this system, but another criterion is used for the calculation of vent size. According to DIERS technology, a minimum of two runs are required to determine the self-heating rate to be used in vent size calculations, a8 described in the Experimental Equipment and Procedures section. One run is made at the relief set pressure of the vessel to determine the tempering point. The other run is carried out at a higher pressure. The self-heating rate of the highpressure test measured a t the tempering point of the low pressure test (T'T)is used for vent design. Ideally, the value of T'T should not vary too much at high pressures, such as 2 MPa and above, since the boiling of water is inhibited. However, Figures 6 and 7 show that T'T exhibits a complex behavior of maxima and minima. This finding is of paramount importance for emergency vent design since an improper choice of background pressure could lead to an undersized vent. Notice the additional minimum and maximum in Figure 7 due to the presence of oxygen when compared with Figure 6 (inert atmosphere).
h
40
0
e 200
?.- t
t
ar i
i
3
01 VI
1 P
a
20 A
0
"
0
~
30
~
60
0 9c
'
time (min)
Figure 8. Temperature and absolute pressure versus time for a resol polymerization.
The question then is What pressure should be chosen to determine the self-heating rate at the tempering point? The information in Figures 6 and 7 might lead us to propose that only one test be necessary for calculations, that is, at the set pressure of the relief device, since the self-heating rate was the highest for this condition. That is not always the case, however, since other resol compositions may not act as in Figures 6 and 7 from quantitative and even qualitative viewpoints. Indeed, a composition having 29.4% phenol, 19.6% furfuryl alcohol, 26.1 % paraformaldehyde (91%),21.4% deionized water, and 1.5% NaOH (50%) showed a very different behavior. First, no runaway condition was detected for pressures above 2.0 MPa. Second, T'T at 1.5MPa was 20% higher than the maximum self-heating rate at 0.1 MPa, which is just the opposite of the results shown in Figures 6 and 7. Hence, there is no clear answer to the question posed above. Since T'T is pressure dependent, the choice of test pressure cannot be arbitrary. A reasonable approach is to run the highpressure test at the maximum allowable pressure of the vessel, as suggested by Creed and Fauske (1990). This unexpected pressure effect on a liquid reaction is further corroborated by the runaway reaction of Figure 8. The composition studied was the following: phenol, 38% ; furfuryl alcohol, 30 % ;91 % paraformaldehyde, 31% ;50 % sodium hydroxide solution, 1% . The experiment was started at 27.5 "C (A) with an absolute pressure of 2.88 MPa and heating rate of 1.5 "C/min. At 65 "C (B)the RSST heating rate was reset to near 0 "C/min. At 77 "C (C)the actual temperature rate of rise was almost zero. It is well-known that resols can show reactivity even below 38 "C (Gustin et al., 19931, so the reaction suppression is obvious. At 78 "C (D) the pressure was 2.96 MPa. The containment vessel was partially vented and the pressure was lowered to 2.19 MPa (E). Immediately the self-heating rate increased to 1.4 "C/min. At 92 "C (F) the containment vessel was partially vented again and the pressure lowered to 1.50 MPa. The runaway reaction started at once, reaching a maximum self-heating rate of 680 "C/min at 215 "C and a maximum temperature of 259 "C (G) at a pressure of 1.82 MPa. A t 121 "C (H) the experiment was terminated. In a second experiment with the same composition and background pressure of 1.50 MPa, the runaway reaction began at 50 "C and reached the maximum self-heating rate of 715 "C/min at 200 "C in 41 min (compare with 80 min for the first test). The maximum temperature reached was 230 "C (contrast with 259 "C above) because less heat was provided in the beginning of the test. Note that at 77 "C the self-heating rates of the first and second experiments were respectively near 0 "C/ min and 4 "C/min.
~
v' ~
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10
1 .o
1.5
2.0
2.5
R Figure 9. Effect of formaldehyde-phenol molar ratio and oxygen on the self-heating rate of a resol. Composition at R = 1.52 is the same as in Figures 3-6, using 91 % paraformaldehyde.
/
;=lot
i
0 3 4 5 R Figure 10. Effect of formaldehyde-phenol molar ratio on the selfheating rate of a resol in nitrogen atmosphere. 1
2
A variable of utmost importance in resol technology regarding end-use properties and runaway potential is the formaldehyde to phenol molar ratio (R). The following extreme compositions were used for Figure 9. A t R = 1.0, the composition was phenol, 55.2 % ; 91 % paraformaldehyde, 19.3% ; methanol, 2.0% ; deionized water, 22.0%; and 50% sodium hydroxide solution, 1.5%. At R = 2.5, the composition was phenol, 40.5% ; 91 % paraformaldehyde, 35.5 % ; methanol, 2.0% ; deionized water, 20.5 7% ; and 50% sodium hydroxide solution, 1.5%. Figure 9 clearly shows for this composition that T'Mincreases with R and then levels off or goes down. It also indicates that oxygen, on average, makes this reaction slightly more exothermic, based on the third-degree polynomial regression represented by the solid and dashed lines of Figure 9. A different composition was studied in a broader range of R (Figure lo), as follows. A t R = 1.0, the composition was phenol, 36.95 % ; 91 % paraformaldehyde, 12.96%; deionized water, 45.09 % ; and 50 % NaOH, 5 % . At R = 5.0, the composition was phenol, 18.78%; 91% paraformaldehyde, 32.93% ; deionized water, 43.29% ; and 50% NaOH, 5%. These experiments confirm that there is a maximum for a certain formaldehyde to phenol molar ratio. In Figure 11it is shown that T'Mexhibits a maximum for agiven amount of sodium hydroxide solution. The extreme compositions for these tests were the following. At N = 0.010, the composition was phenol, 25.91% ;91% paraformaldehyde, 27.28%; deionized water, 45.81%; and 50% sodium hydroxide solution, 1.00%. At N = 0.099, the composition was phenol, 23.65%;91 % paraformaldehyde,
~
Ind. Eng. Chem. Res., Vol. 33, No. 2, 1994 289 30
7
T ("C) 127 10 .
97
112 .
.
.
.
.
.
.
.
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28
29
30
1 / T (1000/K)
Figure 11. Effect of amount of sodium hydroxideon the self-heating rate of the resol of Figure 8 having R = 3.
Figure 12. Rate constant versus temperature for the reaction of Figure 7, run under air with R = 2.5.
24.83%; deionized water, 41.62%; and 50% sodium hydroxide solution, 9.90%. The room temperature viscosity of the runaway product increased with the weight fraction of sodium hydroxide (N), being a thin liquid at N = 0.010and a solid at N = 0.099. This rise in viscosity indicates that cross-linking reactions become more important at higher alkali concentrations. The kinetics of phenol-formaldehyde reactions can be studied on the basis of lumping techniques (Booth et al., 1980). Even though resols are typically produced with R between 1 and 3 with a number of competing reactions, these authors were able to justify the assumption of equimolar reactant concentration when studying the kinetics of runaway reactions. They considered only that part of the reaction where the rate constant is sufficiently high to generate a runaway reaction, i.e., the condensation reaction of the methylol group with phenol. Intermediate methylolation reactions were ignored. Compositions with higher formaldehyde to phenol molar ratios behave as bimolecular systems too, since the excess formaldehyde also reacts with phenol due to the polyfunctionality of the latter. With the explanation by Booth et al. (19801, we can use the formulation of Townsend and Tou (1980) for the examination of adiabatic exothermic reactions. The rate constant at any temperature is given by (see Nomenclature)
determined that resols follow an apparent second-order reaction rate. However, their results are valid at 70 OC, a condition under which cross-linking reactions are not significant. Figure 12 shows that higher order kinetics can be assumed at lower temperatures: for this particular composition ko and kl are straight lines up to about 80 "C. Different catalysts were studied. For the paraformaldehyde composition of Figures 4 through 7, it was found at 0.17 MPa that T'Mwas 30.9 "C/min. Using the same formulation but with an identical number of moles of other bases, lithium hydroxide yielded a T'Mof 19.2 "C/min and potassium hydroxide 25.5 OC/min. Therefore, among the bases of common alkali metals, sodium hydroxide would require the largest vent size, followed by KOH and LiOH. The only base of alkaline-earth metals tested was calcium hydroxide, and its maximum self-heating rate was 45.4 OC/min. Triethylamine had a peak exotherm of 21.6 "C/ min. Methanol, which represents only 2 % of the composition in the experiments of Figures 4-7, was removed from the formulation and replaced with water. The value of T'M was 37.3 "C/min, an increase of 20.7 5%. This shows that the inadvertent failure to add methanol to a batch could lead to vessel overpressure. Another experiment with 4 % methanol exhibited a maximum self-heating rate of only 21.5 OC/min. On a weight basis, isopropyl alcohol is less effective than methanol in its ability to curtail heat release rates. With isopropyl alcohol T'Mwas 33.1 "C/min, an increase of 7.1 % over the reaction containing methanol. A run was made with a molar equivalent of o-cresol in lieu of phenol and T'Mwas 21.3 "C/min (compare with 30.9 "C/min for phenol). Finally, it is desired to compare our experimental results with the information in the literature. For the composition of Figure 3, the adiabatic temperature rise (ATA)for the high-pressure tests above 2 MPa was 195 "C (from 40 to 235 "C), the specific heat (C,) was estimated at 0.68 cal/(g "C) based on the initial composition, the thermal inertia of the test cell (@),as defined by Leung et al. (19861, was 1.04, the mass of limiting reactant (m)was 2.375 g was 10.0g. From (formaldehyde), and the total mass (mt) eq 4 of Leung et al. (1986) we obtain
We assume that k , has a classical Arrhenius form, and in a plot of log k , versus 1/T we can expect to obtain a straight line if the reaction order is properly chosen (Townsend and Tou, 1980). Figure 12 exemplifies the use of the above equation. It was obtained from the compositions of Figure 9 with R = 2: phenol, 44.4%; 91% paraformaldehyde, 31.1% ; methanol, 2.0% ; deionized water, 21.0%;50%sodium hydroxide solution, 1.5%.The containment vessel was pressurized with air. A curve resulted for n = 1while for n = 0 the output was a straight line. The calculations indicate that the order of reaction for this formulation quickly approaches zero with an increase in R . The following pairs of (R,n)were obtained for the compositions of Figure 9, regardless of the presence of oxygen in the vapor space: (1.00,1.7); (1.25,0.4); (1.52,0.2);(1.75,O.l). Above R = 1.75 n was found to be 0. This can be explained by the fact that phenol active sites are saturated faster when more formaldehyde is present, leading to zero-order kinetics. Kim et al. (1990)
"c)X 10.0 g X 30.03 g/g-mol 2.375 g X loo0 cal/kcal
- 195 "C X 1.04 X 0.68 cal/(g
This gives a heat of reaction (exothermic) of 17.4 kcal/ g-mol of formaldehyde. Leung et al. (1986) specified
290 Ind. Eng. Chem. Res., Vol. 33, No. 2, 1994
4.1-5.0 kcal/g-mol for the addition (methylolation) reactions and 17.7-22.7 kcal/g-mol for the combined (methylolation + polymerization) reactions. Since the methylol group is unstable in a runaway reaction (Boothet al., 1980), the 17.4 kcal/g-mol figure is consistent with complete polymerization. Gustin et al. (1993) worked with differential thermal analysis and isothermal calorimetry to determine the heat of reaction for a typical industrial composition, having 35.67 % phenol, 21.59 % formaldehyde, 1.79% caustic soda, 5.84% methanol, and 35.11% water. The formaldehyde to phenol molar ratio is 1.897. Even though their formulation is different from the one used in this work, it can be used for comparison purposes, to illustrate the consistency of results. Gustin et al. (1993) determined a heat of reaction equivalent to 17.96 kcall g-mol of formaldehyde by differential thermal analysis and 16.97 kcal/g-mol of formaldehyde by isothermal calorimetry. Hence, our result is consistent with the findings of these authors. Conclusions This study was designed to identify some intricacies of resol reactions during out-of-control polymerization. Among the most significant findings of this work is the wide variability of the self-heating rates T'T and T'Mwith pressure. This makes the choice of experimental conditions difficult. It might be appropriate to run the highpressure test at the maximum allowable pressure of the vessel to simulate more realistic conditions. Another important result is the comparison of self-heating rates of reactions with and without methanol. If there is even the slight possibility that formulation methanol might be excluded from a plant-scale polymerization, some laboratory tests should be run with no methanol to develop a worse-casescenario. Other variables should be tested such as excessive catalyst and/or formaldehyde charges to determine their impact on vent sizing. Under some worsecase conditions, an impractical vent size may be required. In these cases, the data would serve to highlight the need for sufficient controls and procedures to prevent the conditions from occurring. Acknowledgment The author is indebted to John E. Corn, Warren L. Robbins, Robert J. Schafer, Jay F. Schnaith, and G. Fred Watts for carefully reviewing the manuscript and for making valuable additions to the text, to Charmaine R. Burgin for running some of the experiments, and to Young D. Kim for many discussions on the chemistry of phenolformaldehyde reactions. Nomenclature
M = weight fraction of added methanol to the reactive mixture MF= weight fractionof methanol in the formaldehydesolution (0 for paraformaldehyde solids) n = order of the resol reaction assuming lumped kinetics N = weight fraction of 50% sodium hydroxide solution in a given composition P = starting absolute test pressure at 25 "C, MPa P, = relief set pressure of the field-scale vessel R = formaldehyde to phenol molar ratio T = temperature, "C Tf = final (peak) temperature, "C To = temperature at which the exotherm begins, "C T' = self-heating rate, "C/min T'T = self-heating rate measured at the tempering point of the low pressure test, "C/min T'M = maximum self-heating rate, "C/min AT* = adiabatic temperature rise, T f - To,"C X = weight fraction of pure formaldehydein the formaldehyde solution or in the paraformaldehyde solids Greek Symbols I . ~ F= molecular weight of formaldehyde, 30.03 g/gmol 4 = weight fraction of phenol in the reaction mixture = thermal inertia (a value of 1.04 means that (1.04 - 1)X 100/1.04= 3.8% of the reaction heat given off goes into the test cell) Appendix. Resol Composition Calculation When the formaldehyde to phenol molar ratio is changed, it is imperative to maintain the initial water content constant for the comparison between experimental results to be meaningful. The molar ratio is given by
R=-94'11F or F = 0.31914R
(AI) 30.034 where 94.11 and 30.03 are the formula weights of phenol and formaldehyde, respectively. The total initial water in the composition is then HT=H+
+
X
The unknowns in eq A2 are H a n d 4, and the 0.5 factor can be changed if catalyst concentrations other than 50% are used. Adding all weight fractions,
F +M 4 + 5~
+ N + H = (1+ 0.3191R ~ )+
4
M + N + H = l (A3) Again, the two unknowns are H and 4. Combining eqs A2 and A3 we obtain 4:
A = cross-section area of the emergency vent line C, = specific heat at constant volume F = weight fraction of pure formaldehyde in the reaction
mixture FF = flow reduction factor H = weight fraction of added deionized water in the reactive mixture HT = total weight fraction of initial water in the reaction mixture AHr = heat of reaction k, = exotherm rate constant (initial concentration term included) for reaction of order n, s-1 m = mass of limiting reactant correspondingto zero conversion mR = mass of reactant in the field-scale vessel mt = total mass of reacting mixture
1-x-M, F + 0.50N = H X 1-x-MF 0.31914R + 0.50N (A2)
4=
1-(H,+M+0.5N) 1+ (1+ MF/X)0.3191R
(A4)
To define the entire composition, we go back to eqs A1 and A2 to calculate F and H . Literature Cited Booth, A. D.; Karmarkar, M.; Knight, K., Potter, R. C. L. Design of Emergency Venting System for Phenolic Resin Reactors, Part 1. Inst. Chem. Eng. 1980,58,75-79. Brode, L. G. Phenolic Resins. In Kirk-Othmer Encyclopedia of Chemical Technology; John Wiley: New York, 1982; Vol. 17, pp 384-416.
Creed M. J.; Fauske, H. K. An Easy, Inexpensive Approach to the DIERS Procedure. Chem. Eng. B o g . 1990, March, 45-49.
Ind. Eng. Chem. Res., Vol. 33, No. 2,1994 291 Fisher, G. H.; Forrest, H. S.; Grossel, S. S., Huff, J. E., Muller, A. R.; Noronha, J. A.; Shaw,D. A.; Tilley,B. J. Emergency Relief System Design Using DIERS Technology; AIChE New York, 1992. Gerberich, H. R.; Stautzenberger, A. L.; Hopkins, W. C. Formaldehyde. In Kirk-Othmer Encyclopedia of Chemical Technology; John Wiley: New York, 1982;Vol 11, p 247. Gustin, J.-L.; Fillion, J; TrBand, G; El Biyaali, K. The Phenol + Formaldehyde Runaway Reaction. Vent Sizing for Reactor Protection. J. Loss Preu. Process Ind. 1993,6 (2),103-113. Haddeland, George E. Formaldehyde.A ProcessEconomicsProgram by the Stanford Research Institute. Menlo Park, CA, February 1967. Report 23. Kim, M. G.;Amos, L. W.; Barnes E. E. Study of the Reaction Rates and Structures of a Phenol-FormaldehydeResol Resin by Carbon13 NMR and Gel Permeation Chromatography. Ind. Eng. Chem. Res. 1990,29,2032-2037. Leung,J. C.;Fauske,H. K.; Fisher, H. G. ThermalRunaway Reactions in a Low Thermal Inertia Apparatus. Thermochim. Acta 1986, 104,13-29.
Maciel, G. E.; Chuang, I.; Gollob, L. Solid State l3C NMR Study of Resol-TypePhenol-Formaldehyde Resins. Macromolecules 1984, 17,1081-1087. Townsend, D. I.; Tou, J. C. Thermal Hazard Evaluation by an AcceleratingRate Calorimeter. Thermochim. Acta 1980,37,1-30. Waitkus, P. A.; Griffiths, G. R. Explosion Venting of Phenolic Reactors-Towards Understanding Optimum Explosion Vent Diameters. Saf.HealthPlast., Natl. Tech. Conf.,SOC.Plast. Eng. 1977,181-186.
Received for review August 3, 1993 Revised manuscript received October 18, 1993 Accepted October 26,1993@ e Abstract published in Advance ACS Abstracts, January 1, 1994.
