synthesis kinetics of zeolite a

Ind . Eng. Chem. Res. 1990, 29, 749-754 749

Synthesis Kinetics of Zeolite A

Hsin C. Hu a n d Ting Y. Lee* Department of Chemical Engineering, National Tsing Hua University, Hsinchu, Taiwan 30043, ROC

Zeolite A was synthesized by a hydrothermal process at three temperatures: 50,70, and 90 "C. The nucleation and crystallization curves for these syntheses were obtained. The concentration change in the liquid phase during the synthesis was followed a t close intervals and analyzed by ICP-AES. The synthesized amorphous and crystal phases were examined, characterized, and identified by XRD, NMR, and SEM. The kinetics of nucleation and crystallization were correlated t o the initial concentrations and temperature. The correlations of nucleation and crystallization rates were in good agreement with observations. The activation energies of the nucleation and crystallization, obtained from experiments, are 15.0 and 10.9 kcal/mol, respectively. Moreover, the possible reaction path and mechanism were proposed and discussed.

For the part 20 years, zeolites have been prominently employed in many fields, such as adsorption, separation, catalytic cracking, isomerization reactions, etc. The uni- form pore size and the specific adsorption characteristics of zeolites are the main reasons for the development of adsorptive separation and catalytic reaction processes.

In spite of the energetic and the intense research efforts on zeolite synthesis (Breck, 1974), the mechanism of zeolite synthesis remains ambiguous. Two postulations have been proposed for the synthesis mechanism: the solution-phase mass-transport mechanism (Culfaz and Sand, 1973; Barer, 1982; Roozeboom et al., 1983; Dutta and Shieh, 19861, and the solid-phase transformation mechanism (McNicol et al., 1972, 1973; Polak and Cichocki, 1973). The former postulated that the crystallization was achieved by the de- position of the structure species on the crystals and that the amorphous aluminosilicate was dissolved and rear- ranged to form these species continuously and migrated in the solution phase to the nearby crystal surface. The latter, on the other hand, emphasized the direct transformation of zeolite crystal from the amorphous gel phase. Because it is difficult to study the transient reaction mixture as a whole and observe the changes of species coexisting in the mixture precisely during the entire synthesis, both mechanisms might be explained by the experimental results. The solution-phase mass-transport mechanism is easy to understand due to its similarity to the traditional crystallization theory and receives much support from investigation of the Raman spectrum of the liquid phase (Roozeboom et al., 1983; Dutta and Shieh, 1986). The solid-phase transformation mechanism is rather difficult to observe. Some studies (Derouane et al., 1981; Gabelica et al., 1983) even pointed out that both mechanisms are important, depending on the SiOz source and the gel formulation. Nevertheless, more convincing evidence for either postulated mechanism is needed to illuminate the physical phenomenon.

Some reports (Ciric, 1968; Kerr, 1966) on the kinetics of zeolite A synthesis found that an induced period of nucleation was immediately followed by a stage of fast crystal growth. This was claimed to be an autocatalytic reaction. Zhdanov (1971) had a detailed review and discussion on this subject and proposed a simple equation for crystallization. Meise and Schwochow (1973) considered that the nucleation and the crystallization were represented separately by two equations, and they derived another equation that correlated the normalized mass of the crystal with time. Kacirek and Lechert (1975, 1977) sug- gested a polynomial equation relating the mole fraction

* To whom correspondence should be addressed.

0888-5885/90/ 2629-0749$02.5Q/O

of zeolite crystal to the reaction time. However, the crystallization activation energy of zeolite A was not reported. All of the above correlations described the time dependence of the crystal mass. Unfortunately, the de- pendences of the rates of nucleation and crystallization on the reactant concentrations as well as the effect of temperature have not been correlated. Moreover, the parameters in their equations need some physical justification. In this paper, the rates of nucleation and crystallization of zeolite A as a function of the reactant concentrations and temperature are investigated. The possible synthesis mechanism of zeolite A is postulated and substantially verified by the 29Si NMR analysis of the solid phase and by the direct measurements of the transient concentrations of Na, Si, and A1 in the solution phase.

Experiment Section I. Reagents. Reagent-grade sodium metasilicate, so-

dium aluminate, and sodium hydroxide were used throughout this work. Sodium metasilicate, purchased from Hayashi Pure Chemical Industries, Ltd., Osaka, Ja- pan, contains 0.3811 mol of SO2, 0.1483 mol of Na20, and 3.7744 mol of H,O per 100 g of the reagent. Sodium aluminate, purchased from Wako Pure Chemical Industries, Ltd., Osaka, Japan, contains 0.2987 mol of A1203, 0.2596 mol of Na20, and 2.9687 mol of H 2 0 per 100 g of the reagent. Sodium hydroxide, purchased from Riedel-de Haen, West Germany, contains 1.2313 mol of NazO and 1.3144 mol of H20 per 100 g of the reagent.

11. Synthesis Procedure. The sodium aluminate was first dissolved in the deionized water to which the required amount of sodium hydroxide had been added. The sodium metasilicate was dissolved in additional deionized water in another glass flask. Both clear solutions were set aside overnight to ensure complete dissolution. A white and viscous aluminosilicate gel was formed instantly once the sodium metasilicate solution was poured into the sodium aluminate solution. The flask was shaken vigorously for approximately 5 min. Subsequently the mixture was di- vided into portions of 35 mL, sealed in 50-mL poly- propylene tubes, and placed in a thermostated water bath. Generally, 10-12 gel portions were prepared for each batch composition. All reactions were conducted under static conditions, and the temperature was maintained to an accuracy of *0.1 "C of the settings. Samples were taken out from the bath at the desired time intervals and were centrifuged and separated into solution and solid phases. The solid phase was washed with neutral deionized water repeatedly until the pH of the wash liquid was close to 10, separated out again, dried at 300 "C for 3 h, and ground into powder.

C 1990 American Chemical Society

750 Ind. Eng. Chem. Res., Vol. 29. No. 5 , 1990

I I

me I m i r l

Figure 3. Effect of NapO on crystallization.

- jF 2- 2 - 7" 1. i

c e s r e e

Figure 1. Typical X-ray diffractograph of zeolite A (2Na20-2Si- 02-AIp03-200H,O)

' ) ^ r e m -

Figure 2. Effect of H,O on crystallization.

111. Analysis. The concentrations of Na, Si, and A1 in the solution phase were measured by a Shimadzu GVM-1000P inductively coupled plasma atomic emission spectrometer (ICP-AES). The X-ray diffraction analysis of the solid samples was conducted on a Shimadzu XD-5 X-ray powder diffractometer, using Cu K a radiation. The '%i NMR spectra were obtained a t 39.73 MHz on a Bruker MSL-200 NMR spectrometer and were based on the technique of magic-angle sample spinning. The SEM pictures were taken from a Hitachi S-570 scanning electron microscope.

Results and Discussion The X-ray diffraction spectrum of zeolite A showed the

standard peaks between 28 = 5" and 60". A typical X-ray diffraction spectrum of zeolite A is shown in Figure 1. The total area of the 12 significant peaks having strong signal intensities between 28 = 5" and 40" was calculated for each solid sample so that the errors induced by the different growth rates of the different crystal planes could be min- imized and the obtained values would be adequate to represent the overall crystallinity. The crystallinity per- centage is defined as the ratio of the total peak area of the sample to the reference sample that has the largest value. The reference sample was synthesized from the composition of 4Na20-2Si02-A1z03-200Hz0. The X-ray diffraction spectrum of the reference sample is shown in Figure 1, and its crystallinity is set to be 100% zeolite A.

The compositions chosen for the synthesis experiments of zeolite A are shown in Table I. In general, the composition of a zeolite could be represented as xNa20- ySi02-tA1203-~H20. Changing the values of x , y, z , and w would give different reactant concentrations and reac-

T i 7 ? e , m - Figure 4. Effect of SiO, on crystallization

? ,me ' rmr

Figure 5. Effect of A1,0, on crystallization.

Figure 6. Temperature effect on crystallization of 2Na20-2Si02- A1,0,-160H,O.

tant ratios. If all the compositions listed in Table I are plotted in a trianglar diagram with NazO, SiOz, and A1203 as the three vertices, they will be located inside the area for zeolite A synthesis reported by Kostinko (1983).

The results for the crystallinity versus reaction time are shown in Figures 2-6. The nucleation rate is taken as the reciprocal of the time at which crystals start to take shape,

Ind. Eng. Chem. Res., Vol. 29, No. 5 , 1990 751

Table I. Compositions Used in the Synthesis of Zeolite A"

A0 1 A02 A03 A05 A04 A02 A09 A02 A08 A10 A02 A12

2 2 1 160 2 2 1 200 2 2 1 240 4 2 1 200 3 2 1 200 2 2 1 200 2 2.5 1 200 2 2 1 200 2 1.5 1 200 2 2 1.3 200 2 2 1 200 2 2 0.8 200

0.6944 0.5556 0.4630 1.1111 0.8333 0.5556 0.5556 0.5556 0.5556 0.5556 0.5556 0.5556

0.6944 0.5556 0.4630 0.5556 0.5556 0.5556 0.6944 0.5556 0.4167 0.5556 0.5556 0.5556

composition Concentration, mol/kg of H 2 0 ratio Na Si A1 W Na Si A1 W, wt 90 Si/Al Na/Si W/Na

0.3472 89.28 2.0 1 .o 80.0 0.2778 0.2315 0.2778 0.2778 0.2778 0.2778 0.2778 0.2778 0.3704 0.2778 0.2222

91.24 92.59 88.46 89.83 91.24 90.55 91.24 91.94 90.46 91.24 91.71

2.0 2.0 2.0 2.0 2.0 2.5 2.0 1.5 1.5 2.0 2.5

1.0 1.0 2.0 1.5 1.0 0.8 1.0 1.3 1.0 1.0 1.0

100.0 120.0 50.0 66.7

100.0 100.0 100.0 100.0 100.0 100.0 100.0

"Na: Na20. Si: SOz . AI: A120,. W: H 2 0

and the rate of crystallization is taken as the slope at the corresponding half-maximum crystallinity on the crystallization curve (Culfaz and Sand, 1973; Huang et al., 1986). It is difficult to pinpoint the exact time of transition from nucleation to crystallization; therefore, in order to obtain the nucleation time correctly, sufficient data points are essential.

In Figure 2, it is shown that the rates of nucleation and crystallization decrease as the HzO concentration increases. In Figure 3, the significant effect of Na,O concentration in increasing the rates of nucleation and crystallization is shown. The S O z , shown in Figure 4, in contrast to the effect of NazO, exerts no appreciable change on the rate of nucleation and has only a small effect on the rate of crystallization. As shown in Figure 5 , the rate of crystallization and nucleation decreased moderately and slightly respectively as the AlZ0, concentration was low- ered. The reaction temperature, as shown in Figure 6, is the most important factor affecting the synthesis of zeolite A. There is a drastic decrease in both the rate of nucleation and the rate of crystallization with decreasing temperature.

Kostinko (1983) stated that the relatively important effects of the three ratios HzO/NazO, NazO/Si02, and SiOZ/Alz0, on the reaction time of crystallization are as follows: HzO/Na20 > Na20/SiOz > SiOz/AlZO3. In fact, the ratio of HzO/NazO determines the high and low concentration of the gel if the other two ratios are kept constant; hence, it may be the most important factor besides temperature. The same result has been reported elsewhere (Meise and Schwochow, 1973). However, they explained that the phenomenon was due to the alkalinity variation, rather than the overall changes in concentration.

Some interesting results of this study have been obtained in the solution phase during synthesis. The solution portions centrifugated from the samples are all equal to each other in the induction period, but the expelled solution portion increases progressively with the crystallinity of the solid phase during the crystallization. This quali- tative observation implies that the solution must be released from the gel mixture during the crystallization. Analysis of the samples of the solution phase during the crystallization reveals further that the concnetrations of Na, Si, and A1 remain almost constant. This result indicates that the composition of the released material is in- deed very similar to the initial composition of the aluminosilicate gel. Since the transient solution concentration is almost constant in the synthesis of zeolite A, either during the nucleation or in the crystallization stage, the initial concentrations could be used in the correlation.

The ?!3i NMR spectra of the solid phase obtained from the composition 2Na~0-2Si02-A1203-20H20 in the period

Crys t a I 1 I n I ? y = 53 77 % - 3 9 . 6 7 % -

i

t:135 min - ?=125 min

~~~

t.115 min - -

-40 - 80 -120 -160 PPm

Figure 7. 29Si NMR spectra of the solid phases of 2Na20-2Si02- A1203-200H20 in the stage of crystallization.

of crystal growth are shown in Figure 7. A sharp peak exists a t the chemical shift of -89 ppm at high crystallinity, while a much weaker intensity of the peak at -89 ppm and a broad shoulder are detected for the samples with lower crystallinity. The differences in the 29Si NMR spectra between the amorphous and the crystalline sodium aluminosilicate are very pronounced. The chemical shift peak at -89 ppm was verified to be a single, unique peak if the Si/Al ratio in the crystal of zeolite A was equal to unity and should be assigned to the Si atom surrounded by four A1 atoms (Melchior et al., 1982; Klinowski et al., 1981; Bennett et al., 1983; Jarman et al., 1983). The shoulder occurring at a chemical shift lower than -85 ppm and the weaker signal of the sample at low crystallinity in this study, as shown in Figure 7 , indicate that the Si atom might be surrounded by four weakly bonded A1 atoms in the framework of zeolite A precursor (Lippmaa et al., 1980; Engelhardt e t al., 1983). Due to the existence of the

752 Ind. Eng. Chem. Res., Vol. 29, No. 5, 1990 - ( MONO or POLY 1

ALUMINATE ANIONS SOLUTION

( 1 1 i n i t i a l s t a t e

AMORPHOUS GEL AMORPHOUS GEL

k SUPERSATURATED -) SUPERSATURATED

SOLUTION

k SOLUTION

EMBRYO & NUCLEI

( 2 1 nucleat ion s t o g e

CRYSTALS

( 3 ) c r y s t a l l i z a t ~ o n stage

Figure 8. Reaction path of zeolite A synthesis.

Table 11. Results of Model" Regression of R. coeff t t,b

a -0.8880 -5.2528 -3.169 b -1.0476 -5.6477 -3.169 C -2.8840 -15.0528 -3.169 -En/R -7.5743 -40.1596 -3.169 In A, 30.5219 F 500.5 (>F, = 5.999

"R, = k,(Si02/A1203)a(Na20/Si02)b(H20/Na20)c. bThe critical values of t and F are that for the 99% confidence level.

Table 111. Results of Model" Regression of R, coeff t t,b

a' -2.2512 -4.3368 -2.228 b' -1.7255 -3.0297 -2.228 e' -2.9892 -5.0812 -2.228 -E,/R -5.4903 -9.4808 -2.228 In A, 30.7372 F 36.5 (>F, = 3.48b)

" R, = k,(Si02/A1203)"'(Na20/Si02)b'(HzO/Na20)c'. values of t and F are that for the 95% confidence level.

substantial amorphous part in the low-crystallinity solid samples, the environment surrounding the Si atom is likely to be more disordered and highly contaminated than those in the samples with higher crystallinity. Therefore, ir- regular shoulders in the low-field shift of NMR are detected.

I. Kinetics of the Synthesis. The reaction path of the synthesis of zeolite A may be postulated as Figure 8. Since zeolite crystallization is postulated to be autocatalytic in nature (Zhdanov, 1971; Barrer, 19821, nucleation may be coupled with crystal growth but will be terminated eventually. For simplicity, however, the correlations of nucleation and crystallization rates to the initial concentrations and temperature were considered separatly. The rate equations for nucleation and crystallization, if represented by a power law, may be written as

R, = k,(Si02/A1z03)u(Na20/Si02)6(H20/Na20)c

R, = k,(Si0z/A1203)a'(Na20/Si02)b'(H20/Na20)C' where R, and k, are the rate and the rate constant for nucleation and R, and k, are the corresponding quantities for crystallization. Taking the logarithm on both sides of the equation gives the linear multivariable form whose coefficients are the kinetic parameters -E,/R (or -E,/R), a (or u' ) , b (or b'), and c (or c'). These kinetic parameters can be obtained by a multiple regression analysis, using the data obtained from Figures 2-6. The results of the

The critical

Experimental Rn ( 1 /min 1 x 100

Figure 9. Comparison of nucleation rate.

1 I I 1 1 2 3 4

Experimental Rc ( % /m ln l

Figure 10. Comparison of crystallization rate.

regression, listed in Table I1 for R, and Table I11 for R,, yield the following rate equations: R, = k,(Si02/A1203)-0~seao x

R, = k,(Si02/A1203)-2.2512 x

where

(Na20/Si02)-1~0476(H20/Na20)-2~8840

(Na20 / Si02)-1.7255( HzO / Na20)-2.9892

(-15.0 t;l/mol

(-10.9 t;i/mol 1 1

k, = 1.801 X 1013 exp

k, = 2.233 X 1013 exp

Table I1 lists the regression results of the reactant ratio dependency of the nucleation rate. The significantly large F value of the analysis of variance for the regression of the model indicated that the nucleation rates correlated to the reactant ratios are physically meaningful. Figure 9 shows the comparison between the experimental data and the model predictions. Table I11 lists the regression results of the reactant ratio dependency of the crystallization rate. Although the F value is not as large as that for the nucleation rate case, it is still large enough to ensure the significance of the correlation. Figure 10 shows the comparison of the experimental data with the model predictions and indicates good agreement. The t values of the regression coefficients in the model imply the statistical significance and relative importance of these coefficients.

The activation energies of the nucleation and crystallization are 15.0 and 10.9 kcal/mol, respectively. Culfaz and Sand (1973) synthesized zeolite A in the temperature

Ind. Eng. Chem. Res., Vol. 29, No. 5, 1990 753

be more feasible physically in the solution instead of in the gel phase. Although the evidence is not strong enough to rule out completely the direct transformation from the gel into crystals, yet if this were true, the activation energy of crystallization would be expected to be much larger than 10 kcal/mol. The concentration of the solution may be expected to decrease during the process due to the mi- gration of nutrients to the gel phase instead of the other way around as proposed in this study.

Conclusion From the experimental data, the nucleation and crys-

tallization rates were estimated and correlated to the initial reactant ratios under the synthesis conditions used in this study. The rate equations are statistically significant, and the predicted rate results are fairly good. The supersaturated solution is always a t equilibrium; hence, its concentration is invariant. The dissolution rate is faster than either the nucleation rate or the crystallization rate. Consequently, the lumped rate constants, k, and k,, are most likely the rate-controlling parameters for nucleation and crystallization, respectively. The moderate activation energies, of 15.0 and 10.9 kcal/mol for nucleation and crystallization, respectively, might be construed as substantial evidence of the presence of mass transfer in the synthesis of zeolite A. The reaction path and mechanism are postulated and substantiated by the NMR study and the observations of no appreciable changes in transient concentrations.

range 60-90 "C with the composition 2.5Na20-1.7Si02- A1,0,-150H20 and reported activation energies of 12 kcal/mol for nucleation and 19 kcal/mol for crystallization. The former is slightly lower, while the latter is much higher than ours. Breck and Flanigen (1968) and Zhdanov (1971) obtained 11 and 10.5 kcal/mol for the activation energy of crystallization of zeolite A, respectively; these values are very close to ours.

11. Mechanism of the Reaction. The mechanism of zeolite A formation might be discussed as shown in Figure 8. As soon as the sodium silicate and sodium aluminate solutions were mixed together, two phases were produced, the amorphous gel and the supersaturated solution phase. I t is very likely that they were coexistent and in equilibrium with each other. The silicates and aluminates are arranged around the sodium cations under the influence of ionic forces. From this time on, it can be called the aging or nucleation period until a third phase of the crystal embryos or nuclei slowly emerges from the solution phase.

Gradually, these ions align in an orderly fashion and center on the hydrated sodium ions. I t is speculated that the nutrients required for the formation of the nuclei are supplied from the supersaturated solution, which in turn is furnished by the dissolution of the amorphous gel. Also, it is postulated that the dissolution rate is much faster than the formation rate of the nuclei, k,; hence, the equilibrium between the amorphous gel and the supersaturated solution is always established. Eventually, the alignment as- sumes the regular form corresponding to an aluminate tetrahedron surrounded by four silicate tetrahedrons and vice versa. This is the nucleus, a precursor of the crystal. At this stage, the solid-state 29Si NMR spectrum shows a peak at -89 ppm as indicated in the 2.3% crystallinity spectrum in Figure 7 . It should be noted that the signal at this time is rather weak, and the scanning time for this spectrum was approximately 20 h as compared to about 20 min of scanning time for the high-crystallinity samples. Furthermore, there are broad shoulders on both sides of the peak, which are mainly caused by overlapping of in- dividual peaks with slightly different chemical shift values due to small differences in the structural arrangements of the SiOz tetrahedra in the gel skeleton, and indicates a certain disordering around the Si atoms, where atoms might be loosely or weakly bounded to.

Once the nuclei are formed, the consumption rate of the nutrients in the solution is shifted to the crystal growth and becomes the rate of crystallization. In the meantime, the formation of nuclei is terminated. I t is postulated that the rate of dissolution of gel is much faster than the rate of crystallization, and the equilibrium between the amorphous gel and the solution is still maintained. The conditions in the solution phase remain steady simply by the transfer of the building species from the amorphous gel to the surfaces of crystal. During this period, the gel gradually disappears while the size as well as the number of crystals increase, until the gel is exhausted and the growth is terminated.

In the aging period, it seems that the transport of species and the formation of nuclei are equally important. Con- sequently, the deterministic step lies in the transition zone kinetics and mass transfer and is supported by the experimentally obtained activation energy of nucleation, approximately 15 kcal/mol. In the crystallization stage, it is more likely that the interfacial mass transfer between the solution and the crystal surface is the controlling step. This is supported by the observed activation energy of crystallization, approximately 10 kcal/mol. I t is worth- while to know that the ordering arrangement of ions might

Acknowledgment

We thank Professor Ali Culfaz of The Middle East Technical University, Ankara, Turkey, and Professor K. C. Chao of our university for their advice on the zeolite synthesis. We also acknowledge the financial assistance from National Science Council of ROC under Grant NSC76-0208-M007-81.

Nomenclature a, b, c = exponents in rate equations A , = preexponential factor of k, A , = preexponential factor of k, E, = activation energy of crystallization E, = activation energy of nucleation k , = rate constant of crystallization k , = rate constant of nucleation R = gas constant R, = crystallization rate R, = nucleation rate T = temperature

Registry No. Sodium metasilicate, 6834-92-0; sodium aluminate, 1302-42-7; sodium hydroxide, 1310-73-2.

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Kacirek, H.; Lechert, H. Kinetic Studies of the Growth of Zeolites of the Faujasite and N-A Type. In Moieculur Sieve I J ; Katzer, J. R., Ed.; ACS Symposium Series 40; American Chemical Society: Washington, DC, 1977; p 244.

Kerr, G. T. Chemistry of Crystalline Aluminosilicates. 1. Factors Affecting the Formation of Zeolite A. J . Ph.xs. Chent. 1966, 70 (41. 1017.

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Received for revieu May 30, 1989 Accepted December 26, 1989

Kinetics of the Catalytic Hydrogenation of 2,4-Dinitrotoluene. 1. Experiments, Reaction Scheme, and Catalyst Activity

Henk J. Janssen,f Arjen J. Kruithof,l Gerard J. Steghuis,§ and K. Roe1 Westerterp* Chemical Reaction hngineering Laboratories, F a t u l t j of Chemical Engineering, I'niuersitJ of T r c ~ n t ~ , P I ) Box 217, 7850@ A E Enrchede, The Nethrrlandb

There is a great need for quantitative data of a complex reaction network that can be used to evaluate reactor performance and selectivity in heterogeneous reactors. To this end, the chemistry and the kinetics of the catalytic hydrogenation of 2,4-dinitrotoluene over a 5% P d / C catalyst in methanol have been studied in a batch slurry reactor a t isothermal and isobaric conditions, in the temperature range 308-357 K and a t hydrogen pressures ranging up to 4 MPa. The relevant reacting species have been characterized and analyzed quantitatively. A reaction scheme is proposed with two parallel pathways and three stable intermediates. During a short induction period a t the initial stage of the reaction, a rapid deactivation of the catalyst has been observed. It has been shown experimentally that exposure of the catalyst to oxygen and hydrogen plays an important role in this effect. For the five identified main reactions, the quantitative kinetic data will be given in another article.

In our laboratories we investigate, among other reactor types, the possible use for the fine chemicals industry of a continuous stirred three-phase slurry reactor for catalytic hydrogenations with high heat effects and selectivity problems. As in industrial practice where optimal selectivity gains more and more interest, there is a growing desire for model reactions to test reactor performance at temperatures and pressures in conventional process equipment. Some studies have been published on complex three-phase reaction systems (Kohler and Richarz, 1986; Chaudhari et ai., 1987), but regretfully kinetic data on

_______ * Author to whom correspondence should be addressed. 'Present address: DSM Research B.V , Process Technolog\

Present address. Andeno B.V., Venlo, T h e Netherland3 Present address: Akzo Engineering, Arnhem. The Netherland5

Department, PT-CP, Geleen, T h e Netherland-.

complex three-phase hydrogenation systems with high heat effects are not readily available. After considering several hydrogenation reactions, we have decided upon the catalytic hydrogenation of 2.4,6-trinitrotoluene and of 2,4-dinitrotoluene (2,4-DNT) in methanol using 5% palladium on active carbon (Pd/C) as a catalyst to be used as model reactions to test the performance of our reactors.

In the present article we focus on the hydrogenation of 2.4-DNT. The overall reaction equation is

CH3

NO,

2 4 - DNT

NH2

2,4 - DAT

A& = -1200 MJ kmol-' ( 1 )

synthesis kinetics of zeolite a

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