8024
Ind. Eng. Chem. Res. 2006, 45, 8024-8028
Hydration of Dicyclopentadiene in the Presence of Cation Exchange Resin Sandip Talwalkar,† Pramod Kumbhar,‡ and Sanjay Mahajani*,† Department of Chemical Engineering, Indian Institute of Technology Bombay, Powai, 400076 Mumbai, India, and R & D DiVision, Schenectady Herdillia Ltd., Mumbai, India
In the present work the hydration of dicyclopentadiene (DCPD) has been studied in the presence of cation exchange resin catalyst. Ion exchange resin Amberlyst-15 was found to offer the best performance with more than 95% selectivity toward cydecanol and conversion as high as 15%. The literature suggests that the zeolites are more active than ion exchange resin catalysts for such reactions. However, this is one of those few liquid phase hydrations for which ion exchange resins offer much better performance in terms of both rate and selectivity toward alcohol. An important finding of our earlier study on this reaction is that the properties of the ion exchange resin catalyst are modified during the course of reaction, which helps in improving the reaction kinetics. In the present work, the kinetic studies have been discussed in detail and issues such as catalyst reusability and reasons for the rate enhancement have been addressed. 1. Introduction Cydecanol, the hydrated product of dicyclopentadiene, is an unsaturated bicyclic alcohol with applications in the manufacture of hydrocarbon resins and polyesters. It is also a potentially important chemical in the flavor and fragrance industry. It is an interesting monomer, in that the functionality of the double bond in combination with a hydroxyl group has many synthesis opportunities.1 Generally it is prepared by liquid or vapor phase hydration of DCPD in the presence of acid catalyst as shown in Figure 1.2 The syntheses of cydecanol with conventional acidic catalysts such as sulfuric acid,3 niobic acid,4 ion exchange resin, and metal oxides4 have been reported in the literature. Sulfuric acid, being a homogeneous acid, poses problems due to corrosion, disposal, and handling. Nafion is active but expensive. Niobic acid and metal oxides need special pretreatment, and the performance of these catalysts is sensitive to the pretreatment conditions.4 However, the information available is not exhaustive and is insufficient for the design of a commercial reactor. There is a lack of exhaustive information in the open literature regarding this important reaction. The main limitation of liquid phase reaction is the extremely poor miscibility of the two reactants, water and DCPD. The solubility of DCPD in water at 298 K is less than 0.024 v/v %.5 Due to this, the reaction rates are substantially low and extremely active catalysts are required to obtain a significant conversion level. One alterative to enhance the rate of reaction is to introduce a cosolvent.6,7 However, this approach of addition of an external component introduces extra process steps and increases the process cost. The reactions in biphasic (liquidliquid mode) conditions are relatively clean but need active catalysts to compensate for the rate depletion caused by the lower solubility of olefins in water. The use of zeolite catalysts such as ZSM-5 and β-zeolites has been successfully investigated in the past for such reactions.8 These catalysts are reported to have offered significant rates compared to the relatively mild ion exchange resins. In our earlier work on this reaction with cation exchange resin, Amberlyst-15 catalyst showed some interesting features.9 It was * To whom correspondence should be addressed. Tel.: +91-2225767246. Fax: +91-22-25726895. E-mail:
[email protected]. † IIT Bombay. ‡ Schenectady Herdillia Ltd.
Figure 1. Reaction scheme for hydration of DCPD.
demonstrated that the catalyst can be effectively used in solid (catalyst)-liquid-liquid mode, and it was observed that the catalyst surface undergoes modification during the course of the reaction and in turn enhances the reaction rate without compromising on selectivity. The present work aims to investigate the kinetic behavior of the system and develop a model, which may be used to design a commercial reactor. 2. Experimental Section 2.1. Materials. Dicyclopentadiene (90% pure) was obtained from Lancaster Ltd. U.K. Rohm and Haas, France, supplied Amberlyst-15, and it was used without any prior treatment. 2.2. Apparatus and Procedure. The batch reactions were conducted in a liquid-liquid-solid mode. A glass stirred reactor of 160 mL capacity, equipped with an online temperature and agitation speed measuring facility, was used for this purpose. The reactor was inserted in an oil bath used to maintain the required reaction temperature. The desired quantities of catalyst and reactants were charged to the reactor, and the reaction mixture was heated to the desired temperature with slow stirring. As the reaction temperature was reached, the speed of agitation was increased up to the desired level and the corresponding time was considered the zero reaction time. The samples of both phases, organic and aqueous, were withdrawn at different time intervals to study the concentration change of reactants and products with respect to time. The reproducibility of the few representative experiments was checked by repeating the experiment three times, and the deviation from mean with error bars is given in section 3.6, Effect of Temperature. 2.3. Catalyst Characterization. The fresh and reused catalysts were characterized for surface area, ion exchange capacity, and wettability. The surface area of the catalyst was determined by nitrogen adsorption technique using the microflow BET technique (Smart Instruments Co. Ltd., India). The concentration of active sites is determined by the procedure given in the literature.10 A 1% NaCl solution was passed through the bed of the catalyst, and hydrochloric acid eluted was determined by titration with standard sodium hydroxide solution.
10.1021/ie060470n CCC: $33.50 © 2006 American Chemical Society Published on Web 11/01/2006
Ind. Eng. Chem. Res., Vol. 45, No. 24, 2006 8025
The contact angles were determined by using the Washburn method (GBX, Model DS, France), which uses a tensiometric method for measuring contact angles. The instrument is operated in two steps: in the first step the cell constant is determined by using a wetting liquid (hexane or heptane); i.e., contact angle ) 0°. In the second step the contact angle of the solid with the test liquid (in this case water) is measured by measuring the amount of liquid that rises in the cell in which the solid is placed. Then the contact angle is calculated by applying the Washburn equation:11
m2 CFLγL cos θ ) t ηL
(1)
where m is the mass of liquid that rises in the capillary cell in time, t. FL, ηL, and γL are the liquid density, viscosity, and surface tension, respectively. C is the cell constant, and θ is the contact angle to be determined. 2.4. Analysis. The reactants and products were analyzed using a gas chromatograph (GC-MAK-911) equipped with a flame ionization detector (FID). A 30 m long capillary column, BP-1 (SGE, Australia), was used to separate the different components in the reaction mixture using toluene as an external standard. The GC oven was operated under isothermal condition at 453 K. The various components in the reaction mixture were characterized either by authentic sample and/or by gas chromatography-mass spectrometry (GC-MS). The higher products, which were not eluted in the GC, were calculated by difference in moles of DCPD reacted and moles of alcohol formed. The loss of DCPD to products other than alcohol was less than 5% in all experiments. Each sample was injected three times, and the maximum standard deviation, in the GC analysis, was less than 3.8%. 3. Results and Discussion 3.1. General Course of the Reaction. As mentioned earlier, we define the zero reaction time as the time at which the desired temperature is obtained. Hence, in all the kinetic runs, we see the small extent of reaction that occurred until the desired temperature was attained (Figure 2a). The extent of reaction during this heating period was found to be relatively higher at high catalyst loading. Typically, 96-98% of the total cydecanol formed exists in the organic phase for the organic to aqueous phase ratio of 0.89 (v/v). The formation of the other side products is negligible in the temperature range of interest. The extent of oligomerization increases with an increase in temperature. However, at lower temperatures (363 K) and in the range of conversion studied, the oligomerization is insignificant. This may be attributed to the large amount of water present in the reaction mixture. One may notice two distinct regions in the batch kinetics as shown in Figure 2a, and there is a significant decline in the rate of the reaction after about 25 min. Such behavior was realized consistently for all the kinetic runs performed under different conditions. Interestingly, the rate of the reaction in region 2 remains constant until one obtains nearquantitative conversion. This aspect is discussed in more detail in section 3.10, Kinetic Modeling. 3.2. Mass Transfer Effects. The reaction was performed over a wide range of speed of agitation, and it was found that the kinetics is independent of agitation beyond 600 rpm (Figure 2b). All the runs were conducted at 1300 rpm to ensure no external mass transfer resistance across both solid-liquid and liquid-liquid interfaces. However, as shown in Figure 2c, it was observed that while the intraparticle diffusion effect is
Figure 2. (a) General course of DCPD hydration. Catalyst Amberlyst15 temperature 363 K; initial aqueous:organic phase ratio 0.89 v/v; catalyst loading 0.40 w/w aqueous phase. (b) Effect of stirrer speed. Catalyst Amberlyst-15; temperature 363 K; initial aqueous:organic phase ratio 0.89 v/v; catalyst loading 0.40 w/w aqueous phase. (c) Effect of catalyst size. Catalyst Amberlyst-15; temperature 363 K; initial aqueous:organic phase ratio 0.89 v/v; catalyst loading 0.40 w/w aqueous phase.
8026
Ind. Eng. Chem. Res., Vol. 45, No. 24, 2006
Figure 3. Effect of mode of addition of reactants on DCPD hydration. Catalyst Amberlyst-15; temperature 363 K; initial aqueous:organic phase ratio 0.89 v/v; catalyst loading 0.40 w/w aqueous phase.
negligible in region 1, the same is substantial in region 2. It was observed during the subsequent kinetic analysis that the rate of reaction in region 2 is insensitive to almost all the operating parameters, and activation energy for this region is almost zero. Thus, there is considerable intraparticle diffusion resistance in region 2. However, using catalysts at the smaller size is less preferred due to difficulties in the industrial operations; therefore, the kinetic analysis is performed with the commercially available size. 3.3. Mode of the Reaction. Since DCPD is immiscible in water, the reaction takes place in triphasic solid-liquid-liquid mode. An interesting observation was made while studying the kinetic runs. If the catalyst is soaked in water followed by addition of DCPD (mode 2), the reaction in the initial period is much slower than when the reactor is first charged with catalyst and DCPD followed by water (mode 1) (see Figure 3). Because of the presence of water, DCPD oligomerization is much slower. However, when the catalyst is first exposed to DCPD, it is conjectured that the instantaneous oligomerization takes place and the presence of oligomers on the catalyst surface makes it hydrophobic. This hydrophobicity, in our opinion, is responsible for the enhanced rate and conversion. This hypothesis is supported by the fact that when the catalyst from mode 2 is reused with the fresh reactants, the initial reaction rate observed is higher than when the fresh catalyst is used under similar conditions. This effect is discussed in detail in section 3.7, Catalyst Reusability. All the runs in the present work, unless otherwise mentioned, have been performed in mode 1. 3.4. Effect of Catalyst Loading. The reactions were performed over a wide range of catalyst loading (0.10-0.40 w/w aqueous phase), and as expected, it was observed that the rate of reaction increases with the catalyst loading. Figure 4 shows the plot of conversion vs time at different catalyst loadings. The initial rate of reaction increases linearly with an increase in catalyst loading. Again, as mentioned before, two distinct regions in the batch kinetics are clearly evident. As expected, the rates in both regions appear to be a function of catalyst loading. 3.5. Effect of Aqueous Phase Holdup. The volume ratio of aqueous phase to organic phase was varied over the range 0.432.33 under otherwise similar values of catalyst loadings, total reaction volume, and reaction temperature. Figure 5 shows the
Figure 4. Effect of catalyst loading on DCPD hydration. Catalyst Amberlyst-15; temperature 363 K; initial aqueous:organic phase ratio 0.89 v/v. Catalyst loading is with respect to the aqueous phase, in w/w aqueous phase.
Figure 5. Effect of initial aqueous to organic phase ratio on DCPD hydration. Catalyst Amberlyst-15; temperature 363 K; catalyst loading 0.40 w/w aqueous phase. Initial aqueous:organic phase ratio in v/v.
influence of aqueous phase holdup on DCPD conversion. It was observed that the rate of reaction increases with an increase in aqueous to organic phase ratio. This effect is difficult to explain at this stage, and only a detailed investigation on the catalysis will throw light on this observation. However, it should be noted that the rate in region 2 is almost independent of the phase ratio. 3.6. Effect of Temperature. The extractive (liquid-liquid) reactions are highly influenced by temperature as both intrinsic rate constants and distribution coefficients are strong functions of temperature. DCPD hydration was studied over the temperature range of 346-368 K. Figure 6 shows the effect of temperature and standard deviation in the experimental data on the conversion vs time plot under otherwise similar conditions. The rate increases significantly with an increase in temperature. The rate in region 2 is less sensitive to the change in temperature. At high temperature (373 K), it was observed that the reaction mixture acquires a dark brownish color due to the formation of oligomers of DCPD. Hence, all the reactions were conducted at 363 K. It was also observed that, with an increase in the reaction temperature, the color of the used catalyst changes from
Ind. Eng. Chem. Res., Vol. 45, No. 24, 2006 8027
Figure 6. Effect of temperature on DCPD hydration. Catalyst Amberlyst15; Catalyst loading 0.40 w/w aqueous phase; initial aqueous:organic phase ratio 0.89 v/v. Temperatures in K.
However, we have observed that Amberlyst-15 and Indion-130 are the best among all catalysts, with selectivity toward cydecanol more than 95% at the conversion on the order of 4%. The side products obtained with ZSM-5 and zeolite-β were significant under the conditions studied with conversion of DCPD on the order of 7% and 10% and selectivity toward cydecanol being 4% and 5%, respectively. Thus, in our opinion this is one of those few liquid phase olefin hydrations for which ion exchange resins offer much better performance in terms of both rate and selectivity toward the alcohol. 3.9. Catalyst Characterization. Our assumption of increase in hydrophobicity of the catalyst is supported by the contact angle measurement of catalyst with usage. The results show that the contact angle and hence hydrophobicity of the catalyst increases with usage. The results are summarized in Table 1. As expected, the surface area and the available concentration of the active sites reduce after every reuse. On the other hand, it is remarkable that there is no adverse effect of this change on the reaction kinetics. 3.10. Kinetic Modeling. It is difficult to develop a rigorous kinetic model for this reacting system as the catalyst is modified during the course of the reaction and exact mechanism of the same is not yet well understood. However, based on the results obtained in these studies, a working kinetic rate equation, useful for reactor design, has been proposed here. As mentioned before, the course of reaction may be divided into two different regions. In the initial period (region 1) the apparent kinetics can be given by
r ) Mcatk° ′ exp
Figure 7. Catalyst reusability for DCPD. Catalyst Amberlyst-15; temperature 363 K; initial aqueous:organic phase ratio 2.38 v/v; catalyst loading 0.14 w/w aqueous phase; typical batch time 4.5 h.9
light brown to dark blackish brown possibly due to the formation of higher oligomers. 3.7. Catalyst Reusability. It is a well-known fact that the reactions associated with olefins encounter the problems of catalyst deactivation due to formation of dimers, oligomers, and carbonaceous material.12 The kinetics for the used catalyst is compared with that for the fresh catalyst in Figure 7. The rate of reaction was found to increase after every reuse for a few intial runs of typical batch time of 4.5 h, and then it remained constant.9 As discussed earlier, the color of the reused catalyst was found to be dark brown. In our earlier work,9 we have observed that, with reuse, the hydrophobicity of the catalyst increased, and if the used catalyst is placed in the two-phase mixture, it slowly migrates from the aqueous phase toward the organic phase. ESEM pictures of fresh and used catalysts clearly show that the there is a uniform coating on the used catalyst as discussed in our earlier work.9 3.8. Comparison of Different Catalysts. Our previous experience8,13,14 and the literature15 suggest that zeolites perform better than ion exchange resin catalyst for many hydrations.
(-E° RT )
(2)
where r is the rate of reaction in s-1 and Mcat is mass of catalyst in kg. The estimated values of k° ′ and E° are 6.035 × 107 kg-1 s-1 and 74.12 kJ mol-1, respectively. In about 25 min of the batch time the reaction changes its course. It is conjectured that the catalyst undergoes changes in this period. The oligomerization reaction, which is responsible for the coating of the catalyst surface, takes place predominantly in the first 25 min. The kinetics thereafter can be simply given by a zero-order reaction with an apparent rate constant of 2.735 × 10-2 min-1 mol‚L-1 for a commercially available Amberlyst15 with a particle size of 600-800 µm. The activation energy for this region of kinetics is close to zero as the rate was found to be a weak function of temperature. It can be seen from Figure 2c that the rate in region 2, which is otherwise insensitive to the changes in other parameters, is a strong function of particle size. This leads us to the conclusion that in region 1 the reaction is controlled by intrinsic kinetics whereas, due to surface and pore structure modification in the catalyst, intraparticle diffusion plays an important role in region 2. An independent analysis on pore size distribution also shows a decline in the average pore size, which supports the above inference.9 The comparison between modeled and measured fractional conversion of DCPD for different temperatures and catalyst loadings is shown in Figures 8 and 9. The model predictions are in good agreement with the experimental values in region 1. However, the model slightly underpredicts the rate in region 2. 4. Conclusions Hydration of DCPD has been studied in the presence of a cation exchange resin. The batch reaction kinetics of this reaction may be divided into two regions: the initial region in which
8028
Ind. Eng. Chem. Res., Vol. 45, No. 24, 2006
Table 1. Properties of Fresh and Used Catalyst9 property m2/g
surface area, contact angle, deg concentration of active sites, mequiv/g
fresh
after 2 runs
after 4 runs
after 10 runs
34.85 0 4.2
29.98 68.2 3.60
18.46 89.9 2.82
15.43 90.0 2.35
this system due to the complex phenomenon of surface modification.
Acknowledgment We thank Richard Wall of CXI (Texmark), USA, for supplying a sample of cydecanol. Literature Cited (1) Texmark, a Division of Chemical Exchange Industries, Inc. (CXI) Home Page. www.texmark.com/press-cydecanol.html (accessed Dec 2005). (2) Okazaki, S.; Kasano, K.; Kenji, U. Catalyst for dicyclopentadine hydration reaction. Japanese Patent 1,099,648, 1989. (3) Sasaki, A.; Saito, T.; Kikuchi, N. Production of tricyclo (5, 2, 1, 02.6)-3-decen-8(or 9)-ol. Japanese Patent 6,320,8542, 1988. Figure 8. Comparison between measured and modeled values for different temperatures. (]) 346 K; (O) 355 K; (4) 363 K; other conditions same as Figure 2a.
(4) Okazaki, S.; Harada, H. Vapor-phase hydration of dicyclopentadine catalyzed by niobic acid. Chem. Lett. 1988, 8, 1313. (5) UNEP Chemicals’ Programme Home Page, www.chem.unep.ch/irptc/ slids/OECDSIDS/66636.pdf (accessed June 2005). (6) Chakrabarti, A.; Sharma, M. M. Ion-exchange resin catalyzed hydration of R-methylstyrene and etherification of R-methylstyrene with methanol. React. Polym. 1992, 18, 117. (7) Panneman, H. J.; Beenackers, A. A. C. M. Effect on the hydration of cyclohexene catalyzed by strong ion exchange resins I: Solubility of cyclohexene in aqueous sulfolane mixture. Ind. Eng. Chem. Res. 1992, 31, 1226; Effect on the hydration of cyclohexene catalyzed by strong ion exchange resins II: Effect of sulfolane on reaction kinetics. Ind. Eng. Chem. Res. 1992, 31, 1426; Effect on the hydration of cyclohexene catalyzed by strong ion exchange resins III: Effect of sulfolane on equilibrium conversion. Ind. Eng. Chem. Res. 1992, 31, 1433. (8) Zhang, H.; Mahajani, S. M.; Sharma, M.; Sridhar, T. Hydration of cyclohexene with solid acid catalysts. Chem. Eng. Sci. 2002, 66, 316. (9) Talwalkar, S.; Kumbhar, P.; Mahajani, S. In situ coating on cation exchange resin catalyst, Amberlyst-15, and its impact on the hydration of dicyclopentadiene. Catal. Commun. 2006, 7, 717.
Figure 9. Comparison between measured and modeled values for different catalyst loadings. (]) 0.10 w/w aqueous phase; (O) 0.25 w/w aqueous phase; (4) 0.40 w/w aqueous phase; other conditions same as Figure 2a.
kinetics is sensitive to the change in parameters such as temperature, phase ratio, and catalyst loading and the second region in which rate becomes insensitive to almost all the parameters except catalyst loading and the particle size. The catalyst is modified during the course of reaction and offers improved kinetics. The reaction is zero order at longer reaction time and also insensitive to the change in temperature. Further investigations on catalysis are necessary to further capture this effect in a kinetic model. Manipulation of the catalyst hydrophobicity/hydrophilicity through variation in Si/Al to improve catalysis is common for inorganic catalysts like zeolites; however, ion exchange resins have not been studied well in this direction and this work provides important input in this regard. A working kinetic model is given which gives good agreement with observed values in the initial period. It is difficult to develop a rigorous kinetic model at this stage for
(10) Malshe, V. C.; Sujatha, E. S. Regeneration and reuse of cationexchange resin catalyst used in alkylation of phenol. React. Funct. Polym. 1997, 35, 159. (11) User manual for powder wettability, GBX Instrument. (12) Ishada, H. Liquid phase hydration of cyclohexene with zeolites. Catal. SurV. Jpn. 1997, 1, 241. (13) Mahajani, S. M.; Sharma, M. M.; Sridhar, T. Extractive hydration of n-butene with solid acid catalysts in the liquid phase and under supercritical conditions. Chem. Eng. Sci. 2001, 56, 5625. (14) Mahajani, S. M.; Sharma, M. M.; Sridhar, T. Direct hydration of propylene in liquid phase and under supercritical conditions in the presence of solid acid catalysts. Chem. Eng. Sci. 2002, 57, 4877. (15) Venuto, P. B. Organic catalysis over zeolites: A perspective on reaction paths within micropores. Microporous Mater. 1994, 2, 296.
ReceiVed for reView April 14, 2006 ReVised manuscript receiVed August 14, 2006 Accepted September 16, 2006 IE060470N
