1100
Ind. Eng. Chem. Res. 1991,30, 1100-1105
Kinetics of Dewaxing Neutral Oils over ZSM-5 Dennis J. O'Rear* and Brent K. Lok Chevron Research and Technology Company, Richmond, California 94802 Four neutral oils were dewaxed and the kinetics were measured by a little u ed global techniqu ! based on measurements a t constant extent of reaction. Over the range of commercial interest, eac: 1 oil behaved as if a single lumped species controlled the reaction. T h e activation energy for the four oils differed, suggesting that the properties of the kinetically important lumps also differed. nParaffins in the oils determine the yield of dewaxed product, but these species are very reactive and are completely converted under commercial conditions. Under commercial conditions, waxy nonn-paraffins appear to control the kinetics. Oils with high molecular weights contained more highly branched but waxy non-n-paraffins and had the lowest activation energies. In addition to providing insights to the fundamental nature of neutral oil dewaxing, this simple method can be extended with empirical correlations to relate temperature, throughput, and neutral oil properties with product pour point.
Introduction Processes for catalytic dewaxing of neutral oils have been commercialized by BP and Mobil and offered for license. (The BP process is now licensed by UOP.) Several zeolites can be used in this service. Researchers at Mobil and BP describe the use of ZSM-6 (Graven and Green, 1980) and platinum mordenite (Donaldson and Pout, 1972). The function of these zeolites is to selectively crack the undesirable wax species while not converting the valuable species that make up the remainder of the neutral oil. These processes selectively crack the wax by virtue of the small pores in the zeolites which preferentially admit and then convert the wax. In the 1984 Chevron commercialized ita own version of a selective catalytic neutral oil dewaxing process that is uniquely suited to hydrocracked neutral oils rather than the older style solvent refined neutral oils (Zakarian and Farrell, 1986). With commercial processes established there is a need to model the kinetics of these reactions. The goals of this effort are common to other modeling efforts: Develop reliable correlations that can relate operating conditions with the product specification (pour point). Normalize pilot and commercial plant data to assess catalyst fouling independent of changes in operating conditions and feedstock properties. Predict the process conditions needed for changes in feed rate or feed properties. Determine the activation energy of the reaction and whether the reaction is diffusion or reaction controlled. However, catalytic dewaxing of neutral oils presents a difficult challenge to a kinetic modeler. The usual method for modeling reactions uses three steps: identify individual species or lumps of species that control the product specification, follow their reactions, and relate their concentrations to the product specification. For neutral oil dewaxing, analytical techniques have not been found that can identify and adequately measure the controlling species. n-Paraffins in oil can be measured by gas chromatography, and wax can be separated from oil by physical methods. These methods work well to characterize waxy neutral feedstocks but do not work well on dewaxed products. Another problem to face in this analysis is that the relationships between the species that can be measured (n-paraffin)and the key specification (pour point) are very complex and difficult to generalize (Krishna et al., 1989). When a fundamental approach cannot be used, researchers will often try to use a global kinetic analysis based on reactant lumps, as typified by the pseudo-first-order analysis. This global approach requires the use of ques-
Table I. Properties of Hydrocracked Lube Feedstocks medium medium light neutral neutral heavy neutral no. 1 no. 2 neutral 80 95 100 135 pour point, O F viscosity at 100 OC, 3.71 6.79 5.63 10.52 cSt molecular weight 368 405 482 544 batch solvent dewaxing 5 10 10 10 dewaxed oil pour point, O F 25.3 9.28 14.4 wax content, wt 12.3 %
n-paraffins in wax, 90 '
71.3
56.3
42.3
24.0
tionable assumptions of both the order of reaction and the relationship between the reactant concentration and the product specification. As an alternative, this paper employs a different and little used global kinetics method that is based on measurements at a constant extent of reaction. It gives one key kinetic parameter, the activation energy, even for reactions of complex mixtures. It also does not require knowledge of the order of reaction or knowledge of an analytical relationship between the reactants and the product specification.
Experimental Section Four waxy neutral oils were prepared from predominantly Alaskan North Slope crude oil by hydrocracking at commercial conditions (Table I). Since these neutral oils were prepared by hydrocracking rather than solvent refining, the typical catalyst poisons (sulfur and nitrogen) were reduced to insignificant levels. Aromatics were also greatly reduced (Zakarian and Farrell, 1986). The dewaxing catalyst used in this study contained ZSM-5 in the hydrogen form as the active component. The reaction data were obtained in pilot plants operated in downflow mode under commercial H2 pressures and with commercial recycle gas rates. The catalyst temperature and the liquid hourly space velocity (LHSV) were varied, but the gas/ liquid ratio was constant to minimize hydrodynamic effects. This also permitted the LHSV to be directly related to the residence time in the reactor. With one exception, the catalyst did not foul during the course of these experiments. The one exception was a pilot plant upset during the run on the heavy neutral (HN), which was the last neutral oil studied. The catalyst lost an estimated 30 O F of activity, and the results from the latter portion of the run on this oil were corrected. The product pour points
0888-5885/91/2630-1100$02.50/0 0 1991 American Chemical Society
Ind. Eng. Chem. Res., Vol. 30,No. 6, 1991 1101
35-l
\
30h \
25 Pour Point, 4
Pour Polnt, OF
580 5BO 600 610 620 630 640 650 Temperature, O F
680
660
Figure 1. Dewaxing of light neutral over ZSM-5. Abscissa: pour point, OF. Ordinate: temperature, OF.
700
720 740 Temperature, O F
760
780
Figure 4. Dewaxing of heavy neutral over ZSM-5. Abscissa: pour point, O F . Ordinate: temperature, O F . 1.2
1
~ntrrcrpt= > ko = 4.2 x 104
1.0
Pour Polnt, OF
-0.2 -20
-
1
1.45
e -40 I 1 I 1 1 1 1 I 560 580 600 620 640 660 680 700 720 740 Temperature, O F
Figure 2. Dewaxinn of medium neutral no. 1over ZSM-5. Abscissa: pour point, O F . Ordinate: temperature, OF.
1.50
1.55 1.60 1000IT°K
1.65
1.70
Figure 5. Impact of wrong order of reaction on calculated activation energies. Second-order reaction, E, = 25 kcal/mol; ko = 2 X lo8. Abscissa: In (k). Ordinate: 1000/TK.
is the apparent activation energy. The term f(C) describes the order of reaction and, more generally, the relationship between the concentration and the rate. This equation can be integrated over time and the residence time related to the LHSV. Ordering terms and converting to log form gives
Pour Polnt, OF
I
1
I
l
l
I
560 580 600 620 640 660 680 700 720 740 Temperature,O F
Figure 3. Dewaxing of medium neutral no. 2 over ZSM-5. Abscissa: pour point, O F . Ordinate: temperature, O F .
were related to the catalyst temperature and the LHSV (Figures 1-4).
Kinetic Analysis The method of analysis used liere is an extension of published methods (Anderson, 1968; Bliznakov et al., 1970; Rajadhyaksha and Doraiswamy, 1976). To our knowledge, this method has seen little application. It involves making measurements at a constant extent of reaction, so it is convenient to call it by that name, or simply CER. To describe it, first consider the irreversible reaction of a single species whose concentration is C. The rate of disappearance of C is dC/dt = -ko exp(-E,/RT)f(C) (1) where ko is the preexponential of the rate constant and E,
Examination of this equation shows that whenever the extent of reaction is constant, the integral term is also constant. Thus, if a set of data is available in which the temperature and residence time are varied while a constant extent of reaction is maintained, the activation energy can be calculated. This approach also provides a way to measure the activation energy without first measuring or assuming the order of reaction. It is well-known that the traditional approach to measuring activation energies has a problem in that the results depend on the assumed order of reaction. This is illustrated in Figure 5 for a secondorder reaction that is interpreted as first order. The CER method gives the correct energy without assuming an order (Figure 6). To be of use to neutral oil dewaxing, an additional assumption has to be made that goes beyond previously published analyses: when the product specification (pour point in this case) is constant, the extent of reaction is constant. Another way of stating this is that reactions of the species which control the pour are similar and can be treated as one lunlp, and that there is a monotonic relationship between the concentration of that lump and the product specification. However, in this analysis, the explicit form of this relationship does not have to be assumed.
1102 Ind. Eng. Chem. Res., Vol. 30, No. 6, 1991 2.0
,
\
\
\
I
\
1.5 1.0 -
Ln (LHSV)
0.5-
Ln (LHSV)
0.0 -
-0.4-
-0.5 -
-0.6 -
1.3
1.4
1.5
1.6
1.7
1.8
rooo/T,gc Figure 6. Constant extent of reaction method for calculating activation energies without assuming an order of reaction: second-order reaction. Abscissa: In (LHSV). Ordinate: 1000/TK.
Most of the assumptions used this approach are the same as those involved in other methods: f ( C ) must not depend strongly on temperature, and all the temperature dependence can be accounted for in the Arrhenius expression. If a heterogeneous catalyst is used, the number of active sites should be constant for all measurement conditions. Poisons should be absent, or at most block only a fixed number of sites. While the absolute value of the residence time does not need to be known, its correlating variable (LHSV in this case) must be strictly proportional to it. The reaction should be not be limited by equilibrium. Other factors (reactants such as H2, etc.) should not affect the rate or be held constant. Heat- and mass-transfer effects are negligible. The reacting species that control the specification can be treated as one kinetic lump. The first five assumptions are believed to be valid, but the lest two might not be. Following the approach used by Rajadhyaksha and Doraiswamy, the validity of these assumptions is tested by plotting the data to see if they fall on a straight line (Figure 6). Diffusion limits are a real possibility for molecules as large as this. Data in the upper left of Figure 6 are obtained at high temperatures and short contact times, and the opposite is true for data the lower right. The high-temperature and short-contact-time region may result in the reaction becoming mass diffusion limited. If this is the case, the data will not fall on a straight line but will curve downward. Heat-transfer limits could also cause the data to deviate from the line-either upward (for an exothermic reaction) or downward (for an endothermic reaction). This approach is not foolproof. If all the data are influenced by diffusion limits, a straight line may be obtained, and heat-transfer limits might compensate for mass-transfer limits giving a straight line. Thus if the data fall on a straight line, there is some evidence that the reaction does not enter a diffusion limit, but it cannot be proven. This approach can also be used to see if the assumption of one kinetic lump is valid. If there are several species that control the product specification and they react by mechanisms that have different activation energies or orders of reactions, straight lines will not likely be found. To rigorously test all these assumptions may require that the data span a wide range, beyond that which can be obtained in pilot plants. Because these last two assumptions cannot be proven to be valid, the activation energies reported here should be considered as apparent activation energies. As described below, the results suggest that one of these two assumptions cannot be ruled out under all conditions. Separate studies found no effect of zeolite
1.55
1.80
1.65
1.70
1.75
lOOO/T,gc
Figure 7. Constant extent of reaction plot for dewaxifig light neutral. Abscissa: In (LHSV). Ordinate: 1000/TK.
Ln (LHSV)
1.55
1.60
1.65
1.70
1.75
1ooo/T,gc
Figure 8. Constant extent of reaction plot for dewaxing medium neutral no. 1. Abscissa: In (LHSV). Ordinate: 1000/TK.
Ln (LHSV)
a0.6
-
-0.8
1.55
I
1-60
I
1
1.65
1.70
1, '5
loooll;9( Figure 9. Constant extent of reaction plot for dewaxing medium neutral no. 2. Abscissa: In (LHSV). Ordinate: 1000/TK.
crystal size on activity, so diffusion effects are not believed to play a strong role. The most influential assumption is believed to be a change in the nature of the kinetically important lump. In summary, the activation energy is found by the CER method with three simple steps: Measure the conversion, extent of reaction, or product specification as a function of both temperature and residence time. Interpolate a set of data at constant extent of reaction, but at varying temperatures and residence times. Plot the CER data as In (LHSV) versus 1/T and measure the slope, which is -E,/R. Results CER plots for the four neutral oils were generated (Figures 7-10). For each oil, the data fall close to a straight line but not precisely on it. Also, the activation energy varies somewhat with the pour point (Figure 11).
Ind. Eng. Chem. Res., Vol. 30, No. 6, 1991 1103 0.2 46 -
0.1
40 -
0.0
35 -
-0.1
Actlvrtlon Enrrgy, KcriIMol
Ln (LHSV)
30 -
-0.2
-0.3 -0.4
-0.5 1.40
1.50
1.45
1.55
20 25 30 35 40 45 50 55 SO $5 70 75 POleOnt N-P8rrff/nE In tho w 8 X
1.60
lOOO/T, O K
Figure 10. Constant extent of reaction plot for dewaxing heavy neutral. Abscissa: In (LHSV). Ordinate: 1000/TK.
Figure 12. Relationship between activation energy for lube dewaxing and character of wax. Abaciesa: activation energy, kcal/mol. Ordinate: percent n-paraffins in the wax. n-Paramnr
Fwad 0 1.21 LHSV H 1.71 LHSV A 0.70 Lnsv
35 Y N l , 34.2 KcallYol
85
n-Paraffln Control
Weld, Wt%
Actlvrtlon Enrrgy, 25 KcrlIMol
2oi
UN2. 16.2 KcallYol
,
Non.n-Paraffln Control
A
A
A *
Incroaalng Savorlty
70
c
&
-SO
I
I
-40
-20
I
HN, 11.2 KwllMol
I
I
20 40 Pour Point, O f 0
-
I I
SO
1
80
Figure 11. Variation in activation energy for lube dewaxing vs product pour point. Abscissa: activation energy, kcal/mol. Ordinate: pour point, OF.
It appears as if the kinetics for an individual neutral oil can be satisfactorily modeled as a single lump, provided the operating conditions do not vary too widely. This is the case for most commercial unite. In reality, the kinetically important lump is a series of species that are not precisely the same, and this shows up under extreme variations in conditions. While the product pour point has a small influence on the activation energy, the neutral oil type has a large influence (Figure 11). The influence of the neutral oil type on the activation energy can be attributed to a change in the chemical nature of the species that make up the kinetically important lump. Available analytical techniques can distinguish two type of waxes, n-paraffins and a general category of waxy non-n-paraffins. It appears reasonable to assume that the change in the chemical nature of the kinetically important lump is due to a change in the proportion of these two wax types. To study them, the wax in the oils was separated in a batch solvent process, and the percent n-paraffins in the wax was determined by GC. The remainder is the waxy non-n-paraffins. (Note that the measurement of the waxy non-n-paraffins is arbitrary, because it depends on the temperature used in the batch solvent process.) Following this reasoning, it appears that when the wax becomes more highly branched, the activation energy drops (Figure 12). (The error bars in this figure represent two standard deviations from the averages in Figure 11.) The shift in composition of the neutral oil wax is reasonable. As molecular weight increases, the melting point of slightly branched isoparaffins and n-alkylnaphthenes increases to the point that they are part of the wax. However, examination of other data shows that this correlation is fortuitous and overstates the role of the n-paraffm. A series of partially dewaxed medium neutrals
100
80
SO
40
20
0
D
Pour Polnt,°F
Figure 13. Relationship between lube pour point and lube yield for dewaxing medium neutral no. 2 over ZSM-5. Abscises: yield, w t %. Ordinate: pour point, OF. Table 11. Characterization of the Residual Wax in Partially Dewaxed Medium Neutral No. 2 pour point, O F 65 45 batch solvent dewaxing dewaxed oil pour point, O F 15 10 wax content, w t % 5.3 3.5 n-paraffins in wax, % 97 >98 n-paraffins non-n-paraffins 3 36
15
0 0.4 99 93
were prepared, and the residual wax in them was recovered and analyzed (Table 11). At all pour points, the nparaffins were converted to levels too low to measure. However, the non-n-paraffins were converted to varying levels. So, for the conditions of commercial interest, the reaction of n-paraffins is probably not responsible for controlling the reaction and setting the product pour point (Figure 13). They are, of course, very important for determining the yield of dewaxed oil. The n-paraffms appear to be very reactive and are generally completely converted. They might be responsible for controlling the pour point of light neutral and controlling the pour point of heavier stocks when the severity is much lower than commercial practice. Under commercial conditions, the most kinetically important species appear to be the non-n-paraffins. To explain the three anomalies (the slight nonlinearity of the CER plots, the shift in E, with pour point, and the shift in E, with neutral oil type) it is necessary to assume that the non-n-paraffins are a series of species that have different reactivities and activation energies. Those with the highest activation energy appear to be responsible for setting the pour point at low severity and with light stocks. Those with lower activation energy are responsible for setting the pour point a t high severity and with heavy stocks. It seems reasonable to propose that the species with high activation energies are slightly branched iso-
1104 Ind. Eng. Chem. Res., Vol. 30, No. 6, 1991 40
1
I
35
I
LN
30 -
U
750
1
I -
MN1
25 7
Predicted Rmperrturr
Ln (LHSV) t EaIRT 2 4 15
560 -60 -40 -20
0 20 40 60 Pour Point, OF
80
Figure 14. Development of an empirical relationship between product pour point, E,, LHSV, and T. Abscissa: In (LHSV) + EJRT. Ordinate: pour point, O F .
paraffins and the species with low energies are more highly branched isoparaffins or n-alkylnaphthenes. Diffusion limits are a ready explanation of why the conversion of waxy non-n-paraffins shows anomalies (nonlinearity of the CER plots, decrease in E , with severity, and decrease in Ea with molecular weight). With this explanation, as the severity of the reaction increases, the reaction should shift to the conversion of the remaining more highly branched species. Because of their size, they would be expected to have greater diffusion limits and lower values of E,. Likewise as higher molecular weight stocks are processed, the wax should be more highly branched, which again should have greater diffusion limits and lower values of E,. However, experiments performed with different size crystals did not show an expected increase in activity with small crystals consistent with diffusion limits. Another explanation should also be considered: the more highly branched hydrocarbons have an intrinsically lower activation energies and their reaction is not significantly limited by diffusion. The data in this paper cannot discriminate between these explanations, and this area is worthy of additional study. This has practical significance. If the reaction is diffusion limited, smaller crystals will be of value. However, if the reaction is limited by intrinsic kinetics, increased activity could be obtained by increasing the number of active sites. Once the activation energy is known, eq 2 can be used to calculate the change in temeperature needed to respond to a change in LHSV, but only at a constant pour point. To be of greater use, a relationship must be found that relates LHSV, temperature, pour point, and feedstock properties. The first step in this process is to find an empirical correlation G(pour) that relates the product pour point to temperature and LHSV. Rewriting eq 2 gives In (LHSV) + E,/RT = In
ko
-
600
640
680
720
760
100
= G(pour) (3) dC/f (C)
For each data point, the left-hand side of this expression was evaluated by using the average value of E, for that neutral oil, and the result was plotted versus the product pour point (Figure 14). The data fall on a series of straight lines, so G(pour) is simply a linear expression. For this data, the slopes are indistinguishably different, so only the average is used. However, the intercepts differ between neutral oils. With two constants (E, and the intercept) eq 3 can be used to relate the two key process variables (temperature and LHSV) with the product pour point. When these measured constants are used to interpret the starting data set, a satisfactory agreement is fomd (Figure 15). So for a given neutral oil, plant operating guidelines
ObSeN8d Rmperature, OF
Figure 15. Comparison of observed and predicted lube dewaxing temperatures with measured values. Values for E, and kinetic intercept from measurements. Abscissa: predicted temperature, O F . Ordinate: observed temperature, O F .
800
1
t
A
Prrdlctrd 650 600 5 5 0 E , 560
600
,
I
640
I
I
680
, ,R2 =, 0.78 , 720
1
760
ObSeNed Temperature, OF
Figure 16. Comparison of observed and predicted lube dewaxing temperatures with correlated values. Values for E, and kinetic intercept based on the wax n-paraffin content. Abscissa: predicted temperature, O F . Ordinate: observed temperature, O F .
can be generated quickly. An example of a guideline is a prediction of the shift in pour point with catalyst temperature which is generated by differentiating eq 3, d(pour point) = - - 1 E, (4) dT B R12 where B is the slope from Figure 14 and T is to be expressed in kelvin. A greater challenge is to predict operating temperatures on the basis of neutral oil properties alone. To evaluate this approach, the activation energies and kinetic intercept terms in G(pour) were correlated with the neutral oil's wax properties (Figures 12 and 14). The equations that relate these variables are In (LHSV) + E&-paraffins)/RT(K) = A(E,) + 0.0224(pour, O F ) (5) where E,(n-paraffins) = 701('% n-paraffins) - 8040 A@,) = 0.861 (E,) - 1.33 When predictions are made on the basis of these neutral oil properties, the accuracy for fitting the data set is not as good, but it is satisfactory for laboratory purposes when a guess at initial operating temperatures is needed (Figure 16). Summary For most neutral oils dewaxed at typical product pour points, n-paraffins are completely converted over ZSM-5 and are not responsible for controlling the kinetics of the
Ind. Eng. Chem. Res. 1991,30, 1105-1110
Of
Const.n! Extent Re8CtlOn Method Fundrmrntsl
Pure Correlrtlons
1105
The constant extent of reaction method should not be overlooked in other modeling studies. I t has a unique advantage of measuring the activation energy without assuming an order of reaction. Like the pseudo-fiiborder method, the constant extent of reaction method is a useful bridge between correlations and fundamental studies (Figure 17). Literature Cited
-
Low Modal Sophlrtlc~tlon-Hlah Hlgh
h8CtlOn Complaxlty LOW
Figuru 17. Constant extent of reaction method helps extend range of kinetic analyses.
reaction. The kinetics appear to be controlled by the types of waxy non-n-paraffins. For a given neutral oil operated under commercial conditions, the kinetics can be satisfactorily modeled by a single kinetic lump. For widely varying conditions, the differences between the individual species'that make up the kinetic lump will be important. The activation energy decreases as the molecular weight of the neutral oil increases, presumably due to the inclusion of highly branched species in the kinetically important lump of waxy non-n-paraffins. Empirical correlations could be used to extend the constant extent of reaction method and predict operating temperatures from neutral oil properties, product pour point, and throughput.
Anderson, R. B. Experimental Methods in Catalytic Research; Academic Press: New York, 1968; p 34. Bliznakov, G.; Bakardjiev, I.; Peshev, 0. New Approach In Treating Kinetic Data. J. Catal. 1970, 16,148-156. Donaldson, R.; Pout, C. R. The Application of a Catalytic Dewaxing Process to The Production of Lubricating Oil Base Stock. Presented before the Division of Petroleum Chemistry, American Chemical Society, New York Meeting, August 1972. Graven, R. G.; Green, J. R. Presented at the Congress of the Australia Institute of Petroleum: Sydney, Australia, September 1980. Krishna, R.; Joshi, G. C.; Purohit, K. M.; Agrawal, P. S.; Bhattacharjee, V.; Bhatacharjee, S. Correlation of Pour Point of Gas Oil and Vacuum Gas Oil Fractions With Compositional Parameters. Energy Fuels 1989, 3, 15-20. Rajadhyaksha, R. A.; Doraiswamy, L. K. Falsification of Kinetic Parameters by Transport Limitations and Its Role in Discerning The Controlling Regime. Catal. Reu.-Sci. Eng. 1976, 13, 209-258. Zakarian, J. A.; Farrell, T. R. Lube Facility Makes High-Quality Lube Oil From Low-Quality Feed. Oil Gas J. 1986, May 19.
Received for review June 19, 1990 Accepted December 11,1990
Kinetics for the Reaction between Chlorine and Basic Hydrogen Peroxide Gabriel Ruiz-Ibanez and Orville C. Sandall* Department of Chemical & Nuclear Engineering, University of California, Santa Barbara, Santa Barbara, California 93106 The objective of this research was to study the kinetics of the liquid-phase reaction between chlorine and basic hydrogen peroxide (BHP). This reaction is being used to produce singlet delta oxygen for the oxygen-iodine laser. The purpose was to determine the relevant kinetic rate constant of what appears t o be the rate-limiting step in the mechanism proposed in the literature. The experimental approach consisted of the measurement of the rate of absorption of Clz by a liquid B H P solution. Gas absorption measurements of ClZin B H P in a laminar liquid jet absorber were carried out over the temperature range 1.8-8.9 "C to determine the rate constant of this reaction. The system was operated in the second-order regime of gas absorption due to the relatively high value of the reaction rate constant and because of the instability of B H P a t high hydroxide concentrations. The results for the second-order rate constant can be correlated by k (L/(g mo1.s)) = 6.477 X 1020 exp(-9872/T (K)). Introduction Production of singlet delta oxygen [02(lAg)] has shown increasing interest due to its use in the chemical oxygeniodine laser (COIL). Singlet delta oxygen is an excited state of molecular oxygen that has approximately 22.5 kcal/mol more energy than ordinary ground-state oxygen (Demyanovich and Lynn, 1987; Held et al., 1978). In the COIL, singlet delta oxygen transfers its energy to atomic iodine which lases as its atoms release energy. The performance of a COIL depends on the ability to produce 02('Ag) generated from its singlet oxygen generator (Takehisa et al., 1987). The chemical reaction between chlorine and basic hydrogen peroxide (BHP) is the most common reaction used
for the production of singlet oxygen. The stoichiometry of this reaction is as follows: 2KOH + H202+ C12 2KC1+ 2H20 + O,('A,) (1)
-
In the design and modeling of singlet oxygen generators it is important to understand the kinetics of this reaction.
A plausible mechanism for the reaction, as proposed by Hurst and Goldberg (1980) and Storch et al. (1983),is given as follows. First, BHP is prepared in typical concentrations by mixing 6 M KOH and 90% (wt) hydrogen peroxide; the solution reaches equilibrium according to H202 + OH- H2O + HOO(2)
-
Typically an excess of hydrogen peroxide is used and the
0888-588519112630-1105$02.50/0 0 1991 American Chemical Society
