1956
Ind. Eng. Chem. Res. 1987,26, 1956-1960
Polymerization of Gaseous Benzyl Alcohol. 1. Study of Si02/A1203Catalysts and Reaction Conditions Martin Olazar,* Javier Bilbao, Andrgs T. Aguayo, and Arturo Romero Departamento de Qulmica TZcnica, Universidad del Pais Vasco, 48080 Bilbao, Spain
The process of obtaining polybenzyls by polycondensation of the gaseous benzyl alcohol on SiOz/Alz03 acidic catalysts prepared with different physical properties and surface acidity has been studied. An experimental study of the effect of the operating conditions has been carried out. The operating conditions studied were gas-solid contact regime, temperature, monomer concentration, catalyst particle size, gas linear velocity, and catalyst dilution with inerts. By use of the results of this study, the values of those conditions under which a subsequent kinetic study is advisable have been delineated. It is concluded that the kinetic study of the polymerization must lead to the calculation of the kinetics of the three steps separately: initiation, developed polymerization, and deactivation. The formation of polybenzyls was first studied by Haas et al. (1955), who demonstrated the tendency of benzyl alcohol to polymerize in the presence of Friedel-Crafts catalysts. In later publications, polymerization studies carried out with several monomers in the liquid phase are shown. The main purpose of these subsequent studies was to obtain linear polybenzyls with high molecular weights (Valentine and Winter, 1956; Lefebre, 1963; Kennedy and Isaacson, 1966; Montaudo et al., 1970; I o n and Tudorache, 1971; Lenz et al., 1974; Kuo and Lenz, 1976; Geller et al., 1977a,b; Pinkus and Lin, 1979). In spite of the number of works published, the existing information about structure, properties, and applications of those polymers is very poor. The high thermal stability that the above-mentioned authors have observed up to the 300-450 "C range is remarkable. The glass transition is between 55 and 80 "C. The number-average molecular weights vary between 1000 and 2500. Nomiya et al. (1980, 1984) have verified the polycondensation of benzyl alcohol to polybenzyl via carbonium ion mechanism generated by the Bronsted acidity of the Kegging-type heteropolyacids such as H4[SiMI2O4,-,]and H~[PM1@401(M = Mo, W). Polybenzyls deposited on a solid catalyst in the gaseous benzyl alcohol dehydrogenation were detected by Jodra et al. (1974) on Cu/asbestos catalyst bed in the temperature range between 250 and 310 "C. Later the same authors (Jodra et al., 1975,1976)studied the effect of catalyst composition (Cu content and Cr203presence) and preparation conditions on the polymer deposition rate. Later, (Gonzalez-Velasco, 1979; Romero et al., 1979, 1980) the presence of polybenzyls has been found on Cu/Si02 catalysts in the same reaction of benzyl alcohol dehydrogenation. It has been determined that the polymerization in the above-mentioned works is a secondary process by dehydration of the alcohol. This reaction takes place in parallel with the main reaction of dehydrogenation and where the polymer formed was studied because it was the precursor of the coke that deactivated the catalyst. In this paper, the process of obtaining polybenzyls directly by gaseous benzyl alcohol dehydration on acidic solid catalysts has been studied. The purpose was to obtain results that would provide conclusions concerning the most suitable catalyst, the reaction system and the conditions to carry out the necessary experiments for a subsequent kinetic study. As the literature about polymerization with solid catalysts is very poor, the guidance we had "a priori" was not very useful. Because of that, we followed the accepted experimental methods in contact catalysis, although it required us to make suitable changes to the 0888-5885/87/2626-1956$01.50/0
Table I. Preparation Method of the Catalysts VARIABLES
STEPS
Na251Oj I~SCL
?
t -
I
1
PRECIPITATION
PY
89-92
Tenperature Ro,e
20 o c l1-5,1-35 I 50 O C [ 11-5, I1 - 3 5 I
3 , 5 cm3H2SO~ 3 N min
2ressure
760 mm HS
T e m p e r a t k r e 30 OC F l n a l humidity 0 9 3 q +O/g
1
IMPREGhATION
1
5O h j 1-5. :I- 5 1 ! 1-35 :1-35
% Al2!50~!3
35
Terrperature
110
Time
OC
61 h
Temperature Rate Time
gel
553'C
9OC/min
2 h
CAT 1-35 sressure
2000 K S / C P ?
Tlme 5 m i n Mould diameter
5 mm
operational techniques and conditions.
Reaction Conditions Study Catalysts. Several catalysts of silica-alumina prepared in the laboratory with different physical properties and different surface acidity have been tried. To prepare the silica-alumina gels, the silicg gel impregnation method was chosen. This method, as has been demonstrated in previous works (Corella et al., 1981; Romero et al., 1982,19831, is appropriate for obtaining catalysts with different physical properties and different acidic strength levels by controlling the preparation conditions. The catalysts prepared in this way have good kinetic behavior in alcohol dehydration reactions (Aguayo et al., 1984a,b; Bilbao et al., 1985). In Table I, the steps followed in the preparation of the silica-alumina pellets named 1-5, 1-35, 11-5, 11-35, and 11-35 are shown. The surface acidity measurements were carried out by Benesi's method (1956, 1957) using neutral red (pK +6.8), methyl red (pK +4.8), p(dimethy1amino)azobenzene (pK +3.3), and p-aminoazobenzene (pK +2.8) as indicators. The A1203content was measured by three conventional methods: treatment with HF, atomic absorption spectrophotometry, and titration of A12(S04)3solution before 0
1987 American Chemical Society
Ind. Eng. Chem. Res., Vol. 26, No. 10, 1987 1957 Table 11. Properties of the Catalysts" Sf, V!, pr, pa, particle size, catalyst m /g cm /g g/cm3 g/cm3 mm Physical Properties 1-5 356 0.64 2.30 0.93 +0.32 to -0.50 1-35 286 0.56 2.37 1.02 +0.32 to -0.50 1-35 pellet 216 1.06 2.56 0.69 4.3 X 4.3 cylinders 0.36 2.25 1.24 +0.32 to -0.50 11-5 297 2.29 1.30 +0.32 to -0.50 225 0.33 11-35 acidity, mg of n-butylamine/ g of catalyst catalyst ALO, DK +6.8 DK +4.8 DK +3.3 DK +2.8 Chemical Properties 16.5 13.5 29 22 1-5 6.2 48 26 23 1-35 12.3 35 18 11 10.5 1-35 pellet 12.3 26.5 10.5 9 18 13.5 11-5 5.3 34.5 25 20 18.5 11-35 10.1 OS, = surface area, V,, = pore volume, particle density.
pr
= solid density,
pa
p'g151
t jminj
Figure 1. Polymer deposited vs. time for the different catalysts.
=
and after the impregnation. The three methods yielded the same value. The physical properties of the catalysts (surface area, pore volume, and pore volume distribution) have been calculated by N2 adsorption-desorption isotherms. The real and apparent densities were by Hg pycnometry. In Table 11, properties of the catalysts that were studied are summarized.
Reaction Equipment The reaction equipment is similar to that used in other previous works (Jodra et al., 1974,1975,1976; Romero et al., 1981), and it consists of a continuous feed and benzyl alcohol measuring system, a preheater, a reactor of 16-mm inside diameter made of Pyrex glass, and condensation and reaction product measuring apparatus. The analysis of the liquid reaction products was done by using a Perkin-Elmer Sigma 3 gas chromatograph. The conditions were as follows: column, 2.5% SE 30, Chromosorb GAW-DMCS; Tinjector, 250 OC; T,,,,,190 OC; Tdetector, 250 "C; carrier gas flow, 30 cms/min. The more remarkable reaction characteristics that conditioned its experimental development are the following: highly exothermic (because of this, high rate conditions must be avoided in order to control the reaction); the polymer deposits which outwardly covered the catalyst particles. These characteristics make a fluidized bed reactor advisable as contact system. In fact, when we operate with a fixed bed, the catalyst particles fuse together and to the reactor walls. This way, there is a bad distribution of the gas reactant and consequently axial and radial temperature gradients. In the fluidized bed, after proper dilution of the catalyst with an inert solid (silica gel of the same particle size as the catalyst utilized), an acceptable isothermicity is obtained. After a theoretical and experimental hydrodynamic study, 40 cm/s was determined to be the most suitable feed gas velocity because with this velocity the regime of the solid is very nearly perfectly mixed. Comparison of the Catalysts. The experiments were carried out in a fluidized bed with the granulated catalysts (I-5,I-35,II-5, and 11-35) and in a fixed bed with the 1-35 pellet. The conditions were temperature, 270 "C; partial pressure of benzyl alcohol in the feed (diluted with N2), 0.4 atm; and space time, 0.4 g of catalyst.h/mol. In Figure 1, the obtained results have been plotted as deposited polymer mass vs. reaction time.
r 181
Figure 2. Pore volume distribution of the 1-35 catalyst when it is unused and after reactions for 3 and 9 min.
With the most active catalyst, the one named 1-35, the instantaneous conversion at minute 3 is 0.85 (g of polymer/min)/(g of alcohol/min). This high conversion obtained with such a low value of the space time as the one used lead us to consider the irreversibility of the reaction. In fact, at 270 "C with a space time of 4 g of catalyst.h/mol which, is obtained by increasing the catalyst weight and maintaining a fixed molar flow of feeding alcohol, an average conversion of 0.95 is obtained during the early instants of the reaction which, seems to prove the irreversibility of the reaction. If we try to relate the activity order observed in Figure 1 to the physical properties and surface acidity of the catalysts detailed in Table 11, the activity order is different from the one that could be established for the total acidity (pK +6.8) or for the strong acidity (pK +3.3). The activity order does not correspond either to the one that can be related to the surface area or the pore volume. These results ratify the conclusions of previous papers (Aguayo, 1981; Aguayo et al., 1984a,b) where it was found that the activity of the amorphous silica-aluminas in the dehydration of the alcohols (1-butanol and 2-ethylhexanol) is conditioned by the different levels of surface acidity as well as by the surface area and the pore volume. On the other hand, the selectivity of all the catalysts is very high. As a byproduct, benzaldehyde is obtained, but the quantity of this in the product stream is less than 1% by weight as compared to nonreacted benzyl alcohol in the worst case. PolymerizationSteps. The polymer is formed initially
1958 Ind. Eng. Chem. Res., Vol. 26, No. 10, 1987
\
-
-4- t -
--
-
T IOC)
t
Figure 3. Steps in the polymer evolution with time.
in the porous structure of the catalyst. In Figure 2, the pore volume distribution of the 1-35 catalyst is plotted when it is unused and after reactions for 3 and 9 min under the conditions mentioned previously. The data of Figure 2, which have been measured from the N2 adsorptiondesorption isotherms, show that in a few minutes the polymer fills most of the micro- and mesopores of the catalyst. As reaction occurs, the polymer formed in the porous structure of the catalyst is moved toward the outside by the new chains of polymer recently desorbed from the acidic centers of the catalyst, which are free for adsorption of monomers or a new growing polymer chain. Consequently, the catalyst particles increase outwardly with polymer. For the various catalysts and operation conditions tested, the polymer deposition with time describes a curve such as the one shown in Figure 3. For short times the polymerization goes through an initiation period where the reaction rate increases exponentially with time; it then reaches a maximum value and goes on to decrease progressively. The initiation period corresponds to the time that is needed to form the polymerization active compounds and consequently to reach steady state. The fact that after the initiation period the polymerization rate decreases can be attributed to the catalyst deactivation and not to the diffusion impediment due to the external polymer deposition. Observation with a magnifying glass of the polymer that covers outwardly the catalyst particles allows us to appreciate that the morphology is similar to the one of the polyethylene for which the structural grain model has been established (Yermakov et al., 1970). The size of these micrograins is between 0.1 and 0.5 mm, noticing that all become smaller as the average radius of the catalyst pores becomes smaller. Anyway, with this structure and with the values of the reaction rate observed, small values for Thiele's modulus of diffusion across the structure of the micrograins of polymer are calculated, so that the reaction is not limited in the experimental conditions by the diffusion across the polymer layer outside the catalyst particles. The deactivation has its cause in the partial blocking of the internal porous structure of the catalyst by the polymer that remains occluded in micropores of difficult exit and which is degraded toward structures of high molecular weight and high C/H ratio (Bilbao et al., 1985). This cause of the decrease of the polymerization rate has been proved by experiments since, by removing the polymer that covers outwardly the catalyst used, the activity that had the fresh catalyst is not recuperated. In order to recuperate this activity, a regeneration treatment that
Figure 4. Polymer deposited vs. temperature for two catalysts. 7
7
5L
.-
i
3c
'i
/ P&;01 m I
Figure 5. Polymer deposited vs. partial pressure of the benzyl alcohol in the feed for two catalysts.
consists in burning the carbonaceous matter deposited inside the catalyst is required. Temperature. Below 250 OC it was not advisable to operate due to condensation and flow problems in the feeding alcohol. The upper limit of the temperature is 310 "C; above this the alcohol is cracked appreciably. In this range of temperatures, the experiments were carried out in a fluidized bed with the 1-35catalyst and in a fixed bed with the 1-35 pellet catalyst. The conditions were partial pressure of feeding alcohol (diluted with NJ, 0.2 atm; space time of 1-35, 0.4 g of catalyst.h/mol; space time of 1-35 pellet, 0.2 g of catalyst-h/mol; gas linear velocity of 1-35, 40 cm/s; g p linear velocity of 1-35 pellet, 20 cm/s; reaction time, 5 min. In Figure 4, results of deposited polymer weight have been plotted. The results are different for both catalysts, whereas for 1-35 increasing the temperature caused the deposited polymer amount to decrease; for the 1-35pellet the reverse is true. The results of Figure 4 could be explained if the polymerization kinetics follows a complex relation with temperature, as corresponds to Langmuir-Hinshelwood's kinetic model, in which the numerator as well as the denominator vary exponentially with temperature. Concentration. For the 1-35 catalyst at 270 "C and above 0.7 atm of feeding alcohol partial pressure, the reaction is uncontrollable due to its high exothermicity and to the high value of reaction rate in those conditions. For the 1-35 pellet, the partial pressure limit of alcohol in feed is 1 atm. Experiments have been carried out under several partial pressures of feeding alcohol with the following conditions: temperature, 270 "C; space time of 1-35, 0.4 g of catalyst.h/mol; space time of 1-35 pellet, 0.2 g of catalyst-h/mol; gas linear velocity of 1-35, 40 cm/s; gas linear velocity of 1-35 pellet, 20 cm/s; reaction time, 2 min. The results are shown in Figure 5 where it can be seen that for both catalysts the deposition increases more than proportionally
Ind. Eng. Chem. Res., Vol. 26, No. 10, 1987 1959 with the partial pressure of feeding alcohol.
corresponds to a (C,H,), formula.
Characteristics of the Polymer The polymer removed from the catalyst mechanically is a yellow powder at room temperature whose tonality is different depending on the reaction conditions, specially on temperature and on benzyl alcohol concentration fed at the reactor. If the temperature is increased in the 250-310 "C range and the partial pressure between 0.02 and 1atm, the polymer coloration becomes dark and it is ocher at the most extreme conditions. Solvent testing has been carried out with a dual purpose: firstly, to extract and remove the polymer from the catalyst instead of by mechanical separation and, secondly, to apply analysis techniques to the soluble fractions of the polymer. Polymer disintegrators, which can be used to remove the polymer from the catalyst with good results but that dissolve only an insignificant quantity of polymer, are as follows: benzene, nitrobenzene, crotonaldehyde, 1,2,3,4tetrahydronaphthalene, pyridine, and ether-phenol-nhexane. The polymer dissolves partially in chloroform, chlorobenzene, dichloroethane, and dichloromethane. Among these, the last two are the better solvents of the ones tested. As dichloromethane has a density intermediate between the polymer and the catalyst, the insoluble fraction of the polymer can be separated by flotation, leaving the catalyst and the silica at the bottom of the decantation funnel. The fraction of the gross polymer obtained in the reaction that is dissolved in dichloromethane varies with the reaction conditions, specifically reaction time, temperature, and benzyl alcohol concentration fed at the reactor. From the solubility results of polymer obtained with the 1-35 catalyst, the maximum solubility corresponds to the polymer obtained at the lowest temperature of the range, 250 "C, under the lowest partial pressure of benzyl alcohol of those used, 0.02 atm, and with a reaction time as short as 0.5 min. Under these conditions, 30% of the polymer is dissolved. The soluble fraction of the polymer, after evaporating the dichloromethane, is a viscous brown material. The insoluble fraction is a firm white solid if the solution with dichloromethane is done completely. A systematic IR structure analysis of polybenzyls was carried out by Fourier transform IR spectroscopy in a Nicolet MX-1, which has conducted us to results similar to those described by Haas et al. (1955) and Kuo and Lenz (1976) for polybenzyls obtained by benzyl alcohol polycondensation in the liquid phase. In the same way, our results of lH NMR conduct us to the same conclusions as the studies of Kuo and Lenz (1977) and Tsonis and Hasan (1983), which established that the structure is not linear para substituted but branching. This fact may be attributed to the nature of the polybenzyl chain, which as it grows generates more potential sites for attack by the reactive electrophilic species, the resulting polymer having a highly multisubstituted branch structure. For the different catalysts, reaction conditions, and solvents, molecular weights in the 400-4000 range have been obtained for the dissolved fractions by using vapor pressure osmometry. These results seem to indicate that the catalyst and reaction conditions do have an effect on the magnitude of the soluble fraction, but this fraction has a similar molecular weight, within the mentioned range. The carbon and hydrogen contents (in weight %) are as follows: gross polymer, C = 93.73, H = 6.34; soluble fraction in dichloromethane, C = 93.21, H = 6.63; insoluble fraction, C = 93.78, H = 6.28. These results indicate a similar composition of the three analyzed samples which
Conclusions The high activity of acidic catalysts such as the amorphous silica-aluminas used in this work has been shown in the polymerization of benzyl alcohol, via dehydration, to obtain polybenzyls. The catalysts used yield a much higher production than those pointed out in the previous literature, concerning the process of obtaining polybenzyls as a secondary product in the benzyl alcohol dehydrogenation. It has been shown that the activity of the catalysts used depends as much on their physical properties as on their total surface acidity and acidic strength distribution. If the surface area, the pore volume, and the different acidic strength levels are increased, polymer formation rate increases as well. From the analysis carried out, it is concluded that the fraction of soluble polymer depends on the reaction conditions: temperature, alcohol concentration in feed, and reaction time. For all the catalysts and reaction conditions studied, the evolution of polymer amount deposited with time goes through an initiation period where the polymerization rate is increasing exponentially with time. The polymerization rate reaches a maximum and subsequently, due to catalyst deactivation, it decreases progressively. I t is concluded that the kinetic study of the polymerization must lead to the calculation of the kinetics of the following steps separately: initiation, developed polymerization, and deactivation. The utilization of 1-35silica/alumina is proposed for the future kinetic study due to the results obtained in this work. The regime of fluidized bed is the most suitable and the reaction conditions must be temperature, 250-310 "C; partial pressure of the feeding alcohol, up to 0.7 atm; gas linear velocity, 40 cm/s; catalyst particle size, +0.32 to -0.50 mm; and catalyst dilution (with silica gel), 10% by weight. Nomenclature P = polymer weight, g PAo= partial pressure of benzyl alcohol at reactor inlet, atm T = temperature, "C t = time, min t d = reaction time from the initiation period, min ti = initiation period, min Registry No. A1,03, 1344-28-1;Si02,7631-86-9; CBH5CH,0H (homopolymer), 27134-46-9. Literature Cited Aguayo, A. T. Ph.D. Thesis, Pais Vasco University, 1981. Aguayo, A. T.; Romero, A,; Bilbao, J. An. Quim. 1984a, 80, 429. Aguayo, A. T.; Arandes, J. M.; Romero, A.; Bilbao, J. An. Quim. 1984b,80,435. Benesi, H. A. J. Am. Chem. SOC.1956, 78,5490. Benesi, H. A. J. Am. Chem. SOC. 1957,61, 970. Bilbao, J.; Aguayo, A. T.; Arandes, J. M. Znd. Eng. Chem. Prod. Res. Deu. 1985,24,531. Corella, J.; Bilbao, J.; Aznar, Rn. P. Afinidad 1981,38, 518. Geller, B. A.; Khaskin, I. G.; Mullik, I. Y . J. Appl. Chem. USSR 1977a,50,1525. Geller, B. A.; Khaskin, I. G.; Mullik, I. Y. Zh. Priklad. Khim. 1977b, 50, 1588.
Gonzalez-Velasco, J. R. Ph.D. Thesis, Pais Vasco University, 1979. Haas, H. C.; Livingston, D. I.; Saunders, M. J. Polym. Sci. 1955,15, 503. Iovu, M.;Tudorache, E. Die. Makromol. Chem. 1971,147, 101. Jodra, L. G.; Romero, A.; Katime, I.; Corella, J. An. Quim. 1974,70, 10.
Jodra, L. J.; Corella, J.; Romero, A. Sp. Pat. 416940, 1975. Jodra, L. G.; Corella, J.; Romero, A. An. Quim.1976, 72,823. Kennedy, J. P.; Isaacson, R. B. J . Mucromol. Chem. 1966,1 , 541.
1960
Ind. Eng. Chem. Res. 1987, 26, 1960-1965
Kuo, J.; Lenz, R. W. J . Polym. Sci., Polym. Chem. Educ. 1976, 14, 2749. Kuo, J.;Lenz, R. W. J . Polym. Sci., Polym. Chem. Ed. 1977,15, 119. Lefebre, G. Rev. Inst. Fr. Pet. Ann. Combust. Liq. 1963, 18, 1192. Lenz, R. W.; Luderwald, I.; Montaudo, G.; Przybylski, M.; Rinsdorf, H. Makromol. Chem. 1974, 175, 2441. Montaudo, G.; Bottino, F.; Caccamese, S.; Finocchiaro, P.; Bruno, G. J . Polym. Sei. 1970, 8, 2475. Nomiya, K.; Ueno, T.; Miwa, M. Bull. Chem. Soc. Jpn. 1980,53,827. Nomiya, K.; Makoto, M.; Yoshio, S. Polyhedron 1984, 3, 381. Pinkus, A. G.; W. H. J. Macromol. Sei. Chem. 1979, A13(1), 133. Romero, A.: Bilbao. J.: Gonzalez-Velasco, J. R. Afinidad 1979. 36. 472.
Romero, A.; Bilbao, J.; Gonzalez-Velasco, J. R. Afinidad 1980,37, 21. Romero, A.; Bilbao, J.; Gonzalez-Veslasco, J. R. Ind. Eng. Chem. Process Des. Dev. 1981, 20, 570. Romero, A.; Bilbao, J.; Aguayo, A. T. An. Quim. 1982, 78, 365. Romero, A.; Bilbao, J.; Aguayo, A. T. An. Quim. 1983, 79, 393. Tsonis, C. P.; Hasan, M. U. Polymer 1983, 24, 707. Valentine, L.; Winter, R. W. J. Am. Chem. Soc. 1956, 78, 4767. Yermakov, Yu. I.; Mikhalchenko, V. G.; Beskov, V. S.; Grabovski, Yu. P.; Emirova, I. V. Plast. Massy 1970, 9, 7.
Received for review September 27, 1985 Revised manuscriDt received Februarv 19. 1987 Accepted June 24, 1987
Polymerization of Gaseous Benzyl Alcohol, 2. Kinetic Study of the Polymerization and of the Deactivation for a Si02/A1203Catalyst Javier Bilbao,* Martin Olazar, Jose M. Arandes, and Arturo Romero Departamento de Quimica Tgcnica, Uniuersidad del Pais Vasco, 48080 Bilbao, Spain
Langmuir-Hinshelwood's mechanism has been proposed for benzyl alcohol polymerization in the gas phase on an acidic catalyst of SiO2/AI2O3. Although the existence of these mechanisms in polymerization reactions on solid catalysts has already been defended, there was not a solid experimental base for their validity. T h e kinetic equation deduced for the proposed mechanism is eq 20. In order to calculate the kinetic constants of this equation, experiments were carried out in an isotherm fluidized bed, in the 250-310 " C range. The different length experiments are discontinuous for the catalyst and continuous for the gas, and the method of data analysis has been based on the calculation of the initiation period length and of the polymerization maximum rate, for different values of partial pressure of benzyl alcohol fed at the reactor. The deactivation kinetics has been studied. The equation obtained a t 270 " C is an expression of first order with respect to catalyst activity and to partial pressure of benzyl alcohol. In the first part of this work (Olazar et al., 1987), the high activity of amorphous Si02/A1,03 catalysts was determined in the process of obtaining polybenzyls from gaseous benzyl alcohol, via dehydration. In the same way, the mentioned work, the most suitable operating conditions were determined. After the effect of the temperature and monomer concentration on the polymerization rate is studied, the results obtained do not seem to correspond to a simple kinetic expression bid to a kinetic equation in which the numerator as well rls the denominator vary with temperature as it corresponds to a polymerization mechanism of the type proposed by Langmuir (1921) and Hinshelwood (1940) for contact catalysis. The Langmuir-Hinshelwood theory has allowed the development of mechanistic kinetic equations which are universally accepted as adequate for contact catalysis in reactions with hydrocarbons. In view of that, polymerization theories on solid catalysts (Clark and Bailey, 1963a,b;Guyot and Daniel, 1963; Guyot, 1964; Clark, 1970) based on the usual scheme of contact catalysis on active sites have been developed, that is to say, with three steps in the polymerization mechanism: adsorption, reaction, and desorption. However, there is poor experimental evidence about the validity of these mechanisms. In this work, Langmuir-Hinshelwood's mechanisms have been postulated for the polymerization, having obtained the corresponding kinetic equations whose validity will be proved by experimental data. With regard to the lack of methodology of data analysis when obtaining the kinetic equation in reactions as the one studied here, in this work the usual procedures for contact catalysis have been ap0888-5885/87/2626-1960$01.50/0
Table I. Catalyst Properties s, m2/g Vp, cm3/g pryg/cm3 Par g/cm3 Physical Properties 286 0.56 2.37 1.02 activity, mg of n-butylaminelg of catalyst %A1203 pK +6.8 pK +4.8 pK +3.3 pK +2.8 Chemical Properties 12.3 48 35 26 23
plied, even though difficulties appear due to the particular characteristics of the process, as the existence of an initiation period. Another difficulty of this process is the rapid deactivation of the catalyst. The deactivation kinetics has been studied, as this knowledge is necessary for the design of a reactor that provides the continuous production of polybenzyls on a large scale. Catalyst and Reaction Conditions
The catalyst used, named 1-35, is a gel of Si02/A1203 prepared and characterized in our laboratory in accordance with the methods detailed in the first part of this work (Olazar et al., 1987). In Table I, physical properties and surface acidity of the catalyst are summarized. The experiments were carried out in reaction equipment with continuous monomer feed under atmospheric pressure (Olazar et al., 1987) in a glass reactor of 16-mm inside diameter in a fluidized bed regime. The working conditions are as follows: temperature, 250, 270, 290, 310 "C; space time, 0.4 g of catalyst.h/mol; partial pressures of benzyl alcohol at inlet (diluted with N,),0.02, 0.06, 0.12, 1987 American Chemical Society
