Studies on para-selectivity and yield enhancement in zeolite catalyzed toluene nitration.

Sreedhar, I. ; Reddy, K. Suresh Kumar ; Ramakrishna, M. 等

INTRODUCTION

Mononitration of toluene to provide a mixture of ortho, meta, and para-nitrotoluenes is an important process for producing an array of downstream organic intermediates with a good industrial potential (Elvers et al., 1991). Conventionally, nitration is carried out by treating toluene with nitrating acid viz., nitric and sulphuric acid mixture in water. The latter protonates the former to generate nitronium ions which are the actual nitrating species. It also acts as water binder and heat sink for exothennicity. The nitration occurs in aqueous phase in which aromatic compound solubility is very low. The organic phase acts as the aromatic compound reservoir. The major drawback of this process is the need to regenerate large amounts of spent acid, which is highly expensive, environmentally polluting, and energy intensive (Evans et al.,1996) . Recent advances in heterogeneous catalysis have helped to substitute sulphuric acid with a range of solid acids, which can be regenerated by simple heat treatment. Also, the shape selectivity feature can be introduced favouring the formation of para-nitrotoluene, which is the most desired of the three isomers. However, one of the main concerns in this process is the inhibiting effect of water formed in the reaction. The use of zeolites (Akolar et a1.,1995; Malysheva et a1.,1995; Germain et al., 1996) and their partially dealuminated (Bertia et al., 1995) or cationic-exchanged (Smith, 1989), tributylamine modified (Nagy et al., 1994) and Fe, B, and Ti substituted versions (Salakhutdinov et al., 1993), sulphonated ion exchange polystyrene resins (Wright et al., 1965), perfluorinated sulphonic acid (Olah et al., 1978), clay supported metal nitrates (Laszlo and Vondormea1, 1988; Delaude et al., 1993), [Fe.sup.3+] on K10 Montmorillonite (Choudary et al., 1994), modified silica (Smith, 1989), modified silica-alumina, and supported acid (Kameo et al., 1974; Schubert and Wunder, 1978; Suzuki et al., 1987; Riego et al., 1996) versions have been reported. Conventional nitrating agents like nitric acid alone or in combination with acetic anhydride, mixed acids, nitrogendioxide (Radoslaw and Smallridge, 2001), acyl nitrates (benzoyl and acetyl), and alkyl nitrates continue to engage the attention of some researchers (Olah et al., 1989) which resulted in achieving improved para-selectivity (defined as the molar ratio of para- and ortho-nitrotoluenes) although their commercial viability is questionable. Their vulnerability to process hazards has also limited their application (Smith et al., 1998) .

In the present investigation, solid acid catalyzed nitration of toluene is carried out in batch and semi-batch modes of operation with and without continuous withdrawal of water formed during the reaction and the effect of process parameters viz., morphology of toluene-nitric acid dispersion, speed of agitation, temperature, catalyst/toluene and toluene/nitric acid ratios, dosing rate of reactants, boil-up rate (BR), and micro reaction environment and its influence on lattice aluminum transformation in catalyst are studied to achieve significant selectivity and yield enhancement of para-nitrotoluene.

EXPERIMENTAL

Materials and Methods

Toluene (99%, commercial grade) and nitric acid (40 mole %, Merck) are used for preparing various feed compositions. The various catalysts used for the experimental study viz., H-Beta zeolite (Si[O.sub.2]/[Al.sub.2][O.sub.3] = 30), H-Beta zeolite (Si[O.sub.2]/[Al.sub.2][O.sub.3] = 22), HZSM-5 (80), HZSM-5 (480) are procured from Sud-Chemie India Ltd. The catalysts in powder form are calcined at 450[degrees]C for 6 h before using in the nitration reactions.

Experimental Set-Up and Procedure

The experimental set-up consists of a four-necked Borosil-glass reactor of 1 L capacity (diameter, 108 mm and height, 178 mm) fitted with a glass stirrer with teflon blade and reflux condenser with decanter leg to remove water as and when formed. For semi-batch experiments, a syringe pump is used to dose nitric acid at specified rates. The experiments in the glass reactor are performed under batch and semi-batch modes with azeotropic water removal as shown in Figure 1 under reflux conditions (120[degrees]C) at atmospheric pressure.

Suitably designed experimental runs have been conducted on Mettler Toledo RC1 Reaction Calorimeter to determine the thermal parameters viz., heat of reaction, overall heat transfer coefficient, specific heat, and others.

Analytical

The product samples from the organic phase are quickly quenched in an ice bath and analyzed using a gas chromatograph (GC 17A Shimadzu) with a column packed with Apizon-L (3 m length, 3.2 mm diameter). The samples of 2 mL are taken at desired intervals using sampling syringe from the reaction mixture. They are then filtered and thoroughly washed with water till they get neutralized. This organic sample is then injected into the GC for analysis. The conditions employed are FID Temp =220[degrees]C, injection port temperature = 220[degrees]C. The column temperature is maintained at 135[degrees]C for 24 min and then heated up to 190[degrees]C at the rate of 12.5[degrees]C/ min and retained for 5 min. Carrier gas (nitrogen) flow rate has been fixed at 50 mL/min. The scanning electron microscopic analysis of the catalyst samples for changes in Si/Al ratio is done using Hitachi S-520 instrument. The solid state MAS-NMR analysis has been done by employing Varian (PALO ALTO, CA (USA); UNITY INOVA model) with a frequency of 400 MHz. [Al.sub.2][(S[O.sub.4]).sub.3], 6[H.sub.2]O is used as a standard for [sup.27]Al.

[FIGURE 1 OMITTED]

RESULTS AND DISCUSSION Thermal Parameters

The thermal parameters are estimated using Mettler Toledo RC1 Reaction Calorimeter (Table 1). Batch experiments are conducted using 3.2 moles of toluene, 0.6 moles of nitric acid, and 20 g of catalyst at 50[degrees] for 2 h with an agitation speed of 100 rpm. The heat of reaction of catalytic nitration of toluene determined experimentally is found to be close to the reported value (Chen and Wu, 1996) of 120 KJ/mol.

Effect of Catalyst Characteristics

H-Beta and ZSM-5 type zeolites were employed by Vassena et al. (1999) and Dagade et al. (2002) for vapour phase toluene nitration. The catalytic activity is ascribed to their Bronsted acidity whereas the improved para-selectivity to their pore size and shape. Haouas et al. (2000) ascribed the para-selectivity of H-Beta to the lattice aluminum transformations during the reaction. Choudhary et al. (2000) employed solid acid catalysts for liquid phase nitration of toluene with 30-70 mole % nitric acid with azeotropic removal of water. In the present work, H-Beta and HZSM-5 catalysts are employed for liquid phase nitration. The role of Si[O.sub.2]/[A1.sub.2][O.sub.3] ratio (hereinafter called S/A) of catalyst on the product distribution is broadly assessed. Figure 2 shows the conversion and para-selectivity achieved by using four catalyst samples with different S/ A ratios in the batch nitration experiments conducted under reflux. It shows H-Beta zeolite with S/A of 22 has provided relatively better conversions and para-selectivity. It is interesting that the same catalyst was reported to be highly para-selective in liquid phase nitration with acetyl nitrate (Smith et al., 1996) and in vapour phase nitration of toluene (Dagade et al., 2002) and fluorobenzene (Germain et al., 1996) and reactive distillation of toluene (Choudhary et al., 2000). Vassena et al. (1999) reported that classical transition state selectivity cannot be the sole cause for the enhanced selectivity. Haouas et al. (2000) ascribed the flexible lattice aluminum in zeolite beta is responsible for the phenomenon. The lower para-selectivity of HZSM-5 may be due to its hydrophobic pores that resist the diffusion of aqueous nitric acid resulting in fewer acidic sites available to generate required nitronium ions.

[FIGURE 2 OMITTED]

The Morphological Effects of Toluene--Nitric Acid Dispersions

Phase inversions in liquid-liquid dispersions containing polar and non-polar liquids like HN[O.sub.3]--toluene can provide interesting options for nitration reaction. It is surprising that the effect of their dispersion morphology on conversions and para-selectivity of toluene nitration did not receive much attention in the reported studies on toluene nitration.

[FIGURE 3 OMITTED]

Quinn and Sigloh (1963) and Selker and Sleicher (1965) found liquid properties, geometry of impeller and reaction vessel, speed of agitation, and mode of initiation of dispersion as important factors for achieving stable liquid--liquid dispersions. The latter reported the existence of an ambivalent region in which either component can remain stably dispersed. Kumar (1996) proposed a validated model to address the coalescence phenomenon in liquid-liquid dispersions. Norato et al. (1998) studied the role of physical and operating parameters on the phase inversion. In a recent study, Leslie et al. (2002) reported a simple tool based on interfacial energy minimization for predicting the limits of ambivalent region of phase inversion process.

In the present work, an attempt has been made to study the role of morphology of toluene--nitric acid dispersions on conversion and para-selectivity in liquid phase nitration. Employing the correlations reported earlier, three regimes viz., toluene dispersed in nitric acid, ambivalent, and nitric acid dispersed in toluene have been delineated. Batch nitration experiments have been conducted under reflux conditions covering a wide range of toluene volume fractions (0.1 to 0.95) to generate the conversion and para-selectivity data covering all the three regions as shown in Figure 3.

The following observations can be made:

* Conversion of limiting reactant exceeds 80% in case of toluene dispersed in nitric acid ("a" region; toluene volume fraction < 0.3).

* A maximum of 60% conversion of limiting reactant is achieved when nitric acid is dispersed in toluene ("b" region; toluene volume fraction > 0.7).

* The conversion of the limiting reactant dropped to a minimum value (35%) and increased again in ambivalent region ("c" region).

* The morphology of toluene-nitric acid dispersions has very marginal effect on para-selectivity, which remained in the range of 0.7-0.8.

Interestingly, Hanson and Ismail (1975, 1976) found that mass transfer resistances are more important at high sulphuric acid concentrations whereas the conversion at low sulphuric acid concentrations is kinetically controlled in conventional two-phase nitration processes.

Agitation Effects

Apart from promoting a good contact between the phases for enhanced mass transfer rate, the agitation has stabilization effect on liquid--liquid--solid dispersions. Inversion hold up of intensely agitated liquid--liquid systems was studied by Deshpande and Kumar (2003). In the present work, the agitation effect was studied separately in (a) toluene dispersed in nitric acid and (b) nitric acid dispersed in toluene as the continuous phase. Experiments have been conducted in batch mode with finely powdered catalyst and water removal under reflux conditions at four different stirrer speeds (Table 2). While the radial and longitudinal velocity components created by the agitation have been reported to make positive contribution to the mixing action, the tangential component contributes to the vortex formation, which tends to outwardly throw the catalyst particles by centrifugal action contributing to their concentration rather than distribution. The tip velocity "u" and impeller Reynolds number "[N.sub.ReI]" and Weber numbers ([W.sub.eI]) have been evaluated at four agitation speeds employing Olney--Carlson methodology (Perry and Chilton, 1984) and are presented in Table 2. The vortex depths at various agitation speeds have been calculated employing the correlations proposed by Rieger et al. (1979) for mixed unbaffled vessels. It has been found that there is a steep increase in the vortex formation at rpm >200. The influence of agitation speed on conversions can now be explained more effectively in (a) and (b) dispersions. The intensity of agitation has no influence on conversion of limiting reactant as well as on para-selectivity in dispersion "a." However, in dispersion "b," agitation speed, vortex depth, and turbulence have significant effect on conversion of limiting reactant. The best limiting reactant conversion is obtained at a stirrer speed of 200 rpm for the given geometric configuration of vessel and propeller agitator employed in this work. Impeller Reynolds number beyond 20 000 and vortex depth beyond 2 cm have negative influence on conversion of limiting reactant.

Leaching of Active Constituents from Catalyst

Though high conversions of toluene could be achieved in laboratory nitration at its low volume fractions ("a" region), the stability of the catalyst need to be investigated since nitric acid, in high concentrations, has been reported to remove extra framework aluminum species from the zeolite catalysts (Bertia et al., 1995). Vassena et al. (2000) also observed the occurrence of catalyst dealumination in continuous nitrations due to the leaching effect of nitric acid. An attempt is, therefore, made in this work to study this aspect adequately.

Due to practical difficulty in handling toluene nitration at very low toluene fractions, the catalyst performance is evaluated at two volume fractions A and B (Figure 3) at which the conversion level of limiting reactant is same in a batch nitration. It is interesting to note from Table 3, that H-Beta catalyst employed in this work, has undergone very significant level of dealumination and loss of structural strength within 4 h of reaction at lower toluene volume fraction A ([V.sub.T] = 0.42). On the other hand, no appreciable dealumination has been noted at higher toluene volume fraction B ([V.sub.T] = 0.9). To establish the effect of catalyst dealumination on para-selectivity, semi-batch nitration is carried out in a laboratory reactor employing a nitric acid dosing rate of 30 mL/h for a specific duration to maintain toluene volume fraction as at A and other conditions as specified in Table 3. The dealuminated catalyst is regenerated and recycled two times and in each cycle, toluene conversion and selectivity are measured. It is found that the para-selectivity has dropped by 25% in first recycle and by 40% in second recycle. This might be due to the increase in the pore size as a resultant of the reduced number of bronsted acid sites with dealumination (Choudhary et al., 2000) favouring the formation of ortho-isomer, which requires more space. These results show that toluene dispersed in nitric acid is not a viable option. Nitric acid dispersed in toluene as a continuous phase is, therefore, the most preferred option for achieving consistent catalyst activity for toluene nitration.

Nitration without Catalyst

Smith and Fry (1989) observed sluggish nitration in case of benzoyl nitrate in tetrachloromethane (4% yield in 10 d) without any catalyst. They, however, obtained an unusual product distribution of o, m, p at 55, 35, 10%, respectively. Vassena et al. (2000) reported 2% conversion when no catalyst was employed. They ascribed it to the self-protonation equilibrium limitations of nitric acid. In the present work, a conversion of 27.4% has been obtained under reflux conditions (110[degrees]C) with no unusual isomer distribution.

Effect of Catalyst/Toluene Ratio

H-Beta zeolite (S/A, 30) catalyst in different proportions with toluene has been employed in batch nitration experiments under reflux for 3 h. The results in Table 4 show that the recommended ratio of catalyst to toluene is around 4.5 beyond which no improvement in conversion or para-selectivity could be realized.

The Dynamics of Water Removal

Olah et al. (1978) reported that nitration of alkyl benzene in the presence of Nafion-H catalyst slows down with time due to [H.sub.2]O molecule produced in the reaction. It dilutes nitric acid and demands excess of the same. By refluxing the reaction mixture and azeotropically distilling off [H.sub.2]O-aromatic mixture until no remaining HN[O.sub.3] could be detected, they obtained nitrotoluene yields upto 80 % with a product distribution of o, m, p at 56, 4, 40. They found that [H.sub.2]O molecules get strongly adsorbed on the catalyst acid sites leading to mediating effect on its acidity. The other secondary effects is the loss of HN[O.sub.3] on account of (a) ternary azeotrope formation with water and aromatic compound and (b) decomposition into nitrous gases at the reaction conditions. Both of these have to be minimized.

Continuous removal of water formed during the nitration from the acidic sites of the catalyst has been a challenge for sulphuric acid free nitration processes. The literature reports four alternatives for water removal viz., (a) vapour phase processing (Vassena et al., 1999; Dagade et al., 2002), (b) chemical trapping, (c) inert gas passage, and (d) azeotropic distillation (Olah et al., 1978). The first three options have, so far, not found commercial viability whereas the azeotropic distillation has better chances of succeeding. In the present work, the effect of water on toluene nitration has been studied with and without reflux to study the BR effect on the product distribution.

Batch nitrations have been conducted at a constant atmospheric pressure and three different temperatures including the reflux temperature (110[degrees]C). It is observed (Table 5) that conversions are maximum at reflux temperature since the inhibiting effect of water on the catalyst activity is minimal due to its speedier removal.

Experiments have also been conducted employing 19 mole % and 40 mole % nitric acid at 65[degrees]C maintaining the same nitric acid content in each case. There is practically no conversion in case of 19 mole % nitric acid whereas 15.93% conversion has been achieved with 40 mole % nitric acid.

The BR variation effect on toluene conversion and selectivity has been studied under reflux conditions in semi-batch mode. The intensity of BR is measured in terms of the difference between the oil bath ([t.sub.b]) and the reaction mixture ([t.sub.r],) temperatures. The results are presented in Figure 4. The nitric acid is dosed at 30 mL/h for 3 h employing 2.2 moles of toluene and 10 g of H-Beta catalyst (S/A, 30). The results show that at a BR as represented by [t.sub.r] - [t.sub.b], 20, high toluene conversion is achievable. The drop in conversion at higher BRs is due to the offset of water removal by greater loss of nitric acid. The effect of BR on para-selectivity is, however, minimal.

Enhancement of Para-Selectivity

Above investigations on batch nitration have not provided any definite directions for enhancement of para-selectivity. In this section, the influence of semi-batch mode of nitration on isomer distribution has been explored since it provides additional degrees of freedom to the process optimization through control of critical reactant quantity and its concentration at the desired levels. Past literature on product distribution in toluene nitration has shown that the relative reactivity of o, m, p isomers of nitrotoluene is proportional to the electron availability at the active sites of the catalyst and the relative probability of their collision with a nitronium ion (Haouas et al., 2000). In case of mixed acid nitration, the sulphuric acid concentration was found to have noticeable influence on o and p isomer formation. Considering this aspect, an attempt has been made in this work to examine the effect of semi-batch mode of operation on o, m, and p isomer distribution in general and para-selectivity in particular.

The toluene nitration is carried out under reflux conditions in a semi-batch reactor in which overall toluene to nitric acid, catalyst to nitric acid ratio, and other process parameters have been maintained at prefixed values. The nitric acid, which is the limiting reactant, is fed continuously by using a syringe pump. The experiment is terminated after dosing the required amount of acid.

Catalyst Role in Para-Selectivity Enhancement

To establish the role of catalyst on para-selectivity enhancement, semi-batch nitration is carried out with and without catalyst at a nitric acid dosing rate of 30 mL/h. The results are presented in Table 6. Batch nitration of toluene has been carried out employing the same amount of nitric acid and toluene (toluene= 235 mL; nitric acid (70%) =135 mL;10 g catalyst; 3 h reaction under reflux) that has been used for the semi-batch nitration experiment with 30 mL/h acid dosing rate for 3.5 h. A conversion of 31 % w.r.t. nitric acid and para-selectivity of 0.68 has been achieved. These results establish that in catalytic nitration in semi-batch mode,

(i) Para-selectivity has nearly doubled.

(ii) Significant reduction in formation of m isomer as well as other products.

(iii) A slight improvement in overall conversion of toluene.

(iv) Non-catalytic and catalytic nitrations are likely to proceed in parallel mode and the observed conversion and selectivity are attributed to their combined effect.

[FIGURE 4 OMITTED]

Effect of Nitric Acid Dosing Rate on Para-Selectivity

Three dosing rates, as given in Table 7, have been employed. The dosing process is continued in each case for sufficient time to get a proper picture of para-selectivity variation. For the first time, para-selectivity of 1.5 has been achieved in this work.

The above results indicate that a factor other than catalyst shape selectivity may be responsible for achieving para-selectivity. Haouas et al. (2000) proposal of flexible lattice aluminum transformation in zeolite as responsible for enhancing the para-selectivity looks highly credible. They achieved change in aluminum coordination in the solid from tetrahedral to octahedral form by employing 72 mole % HN[O.sub.3],1:1 molar ratio of toluene and HN[O.sub.3] and effective water removal by acetic anhydride. It is interesting that the reaction mixture as obtained by employing a nitric acid dosing rate of 30 mL/h after 3 h in semi-batch nitration broadly satisfy the above conditions. The catalyst sample was subjected to solid-state NMR spectroscopy. The [sup.27]Al MAS-NMR spectra of the parent H-Beta zeolite showed two signals centred at 54.0 ppm (tetrahedrally coordinated aluminum) and 0.0 ppm (octahedrally coordinated aluminum). It is observed that the intensity of the signal corresponding to the octahedral aluminum has increased after the reaction indicating the transformation of framework aluminum from tetrahedral into octahedral configuration resulting in enhanced para-selectivity (Figure 5).

A micro-level analysis of the above process leads to following:

(i) Process optimization to achieve higher para-selectivity has to centre around creating a favourable microenvironment around the catalyst particle.

(ii) Nitration rate has to be properly controlled through water removal to maintain high HN[O.sub.3] concentration (>85 %) conducive for high para-selectivity.

(iii) The lower the non-catalytic reaction, the better for achieving high para-selectivity.

Reactive Distillation Prospects

The above results establish the desirability of employing reactive distillation concept for toluene nitration to achieve higher levels of conversion and selectivity since it may help effective removal of water from the reaction front and maintenance of appropriate nitric acid concentration locally. The solid acid catalyst can be packed in the distillation column and a liquid-liquid separator can be introduced to recycle toluene after separation from water formed during the reaction. A configuration which will help parallel nitration-water separation processes will have number of positive effects including enhanced mass transfer as well as reaction rates. The chemical reaction and inter- and intra-diffusion steps will drive each other in a proactive fashion. Incorporation of distillation column to the reactor will ensure spatial continuity along the axial direction. Both reaction and distillation take place in every slice of reactive distillation section. Preliminary experiments have shown its viability.

[FIGURE 5 OMITTED]

CONCLUSION

The liquid phase toluene nitration employing H-Beta catalyst has been studied primarily to assess the sensitivity of various parameters related to catalyst, process, and reactor operation. The conversion and para-selectivity could be significantly enhanced by a proper reactor operation mode selection, nitric acid--toluene dispersion morphology, agitator speed, reactant--catalyst ratio, water removal methodology, and suitably tailoring the microenvironment around the catalyst particle to achieve a favourable lattice aluminum configuration.

ACKNOWLEDGEMENT

The authors are thankful to the Director, Indian Institute of Chemical Technology, Hyderabad, India for having provided necessary support and facilities to carry out this research.

NOMENCLATURE

A heat exchange area ([m.sup.2])
BR boil-up rate ([degrees]C)
[C.sub.p] specific heat of reaction mass (J/Kg x K)
[N.sub.ReI] impeller Reynolds number
[t.sub.r] reaction mixture temperature ([degrees]C)
[t.sub.b] oil bath temperature ([degrees]C)
u tip velocity of impeller blade (m/s)
U overall heat transfer coefficient (W/[m.sup.2]K)
[We.sub.I] impeller Weber number
[V.sub.T] volume fraction of toluene
N agitation speed (rpm)
[X.sub.A] percent conversion w.r.t. nitric acid
[X.sub.B] percent conversion w.r.t. toluene
S/A silica/alumina ratio

Manuscript received November 16, 2006; revised manuscript received April 22, 2007; accepted for publication June 24, 2007.

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Vassena, D., A. Kogelbauer and R. Prins, "Potential Routes for the Nitration of Toluene and Nitrotoluene with Solid Acids," Catal. Today 60, 275-287 (2000).

Wright, O. L., J. Teipel and D. Thoennes, "The Nitration of Toluene by Means of Nitric Acid and an Ion Exchange Resin," J. Org. Chem. 30,1301-1303 (1965).

I. Sreedhar, (1) K. Suresh Kumar Reddy, (2) M. Ramakrishna, (2) S. J. Kulkarni (3) and K.V. Raghavan (4) *

(1.) Department of Chemical Engineering, Birla Institute of Technology and Science, Pilani 333031, India

(2.) Chemical Engineering Division, Indian Institute of Chemical Technology, Hyderabad 500007, India

(3.) Catalysis Division, Indian Institute of Chemical Technology, Hyderabad 500007, India

(4.) Recruitment and Assessment Centre, Defence Research and Development Organisation, Delhi 110054, India

* Author to whom correspondence may be addressed.

E-mail address: [email protected]

([dagger]) IICT Communication No. 061018

Can. J. Chem. Eng. 86:219-227, 2008

DOI 10.1002/cjce.20016

Table 1. Estimation of thermal data

U(W/[m.sup.2]K) A ([m.sup.2]) [C.sub.p] Heat of reaction
 (j/Kg x K) (Kj/mol)

180 0.021 1960 125

Table 2. Contrastina effects of agitation screed on nitric
acid-toluene dispersions

N u Vortex depth [N.sub.Re,I] [We.sub.I]
(rpm) (m/s) (cm)

 a b a b a b

100 0.39 0.52 0.55 9380 11270 46 28
200 0.78 2.06 2.15 18750 22540 182 112
400 1.58 7.80 8.00 37500 45080 730 450
600 2.37 17.00 17.40 56250 67620 1640 1010

N u Percent Conv of Para/ortho
(rpm) (m/s) limiting reactant ratio

 a b a b

100 0.39 85.00 21.40 0.65 0.63
200 0.78 85.00 47.20 0.65 0.50
400 1.58 85.00 38.50 0.62 0.68
600 2.37 85.00 24.10 0.67 0.68

a: Toluene/nitric acid (molar ratio) = 0.85:3.66; catalyst
(zeolite H-Beta S/A, 30) =10 g; temperature under reflux =
120[degrees]C, limiting reactant: toluene.

b: Toluene/nitric acid (molar ratio) = 2.2:1.4; catalyst
(zeolite H-Beta S/A, 30) =10 g; temperature under reflux =
120[degrees]C; limiting reactant: nitric acid; batch
experiments with azeotropic water removal.

Table 3. Dealumination of catalyst

Element Fresh Catalyst in Catalyst in
 catalyst excess toluene excess nitric acid *
 ([V.sub.T] = 0.9) ([V.sub.T] = 0.42)

O 61.43 64.14 62.13
AI 2.86 2.80 1.15
Si 35.72 33.06 36.72
Total 100.00 100.00 100.00

Semi-batch experiments under reflux; toluene =1.2 moles; nitric
acid dosing rate = 30 mL/h, temperature = 120[degrees]C; catalyst
(H-Beta zeolite S/A, 22) =10 g; * : ambivalent region.

Table 4. Effect of catalyst to toluene ratio

Catalyst/ Percent ONT MNT PNT Others Para/
Tol(g/mol) Tol ortho
 conversion ratio

Nil 27.4 16.90 1.00 7.08 2.46 0.42
2.26 34.9 22.05 1.75 8.57 2.50 0.39
4.50 38.5 23.19 1.49 11.70 2.17 0.50
6.80 38.2 22.92 1.47 11.67 2.14 0.51
9.10 38.4 23.12 1.48 11.69 2.11 0.51

Toluene/nitric acid (molar ratio) = 2.2:1.4; agitation speed =
200 rpm; temperature under reflux =120[degrees]C; time = 3 h;
batch experiments with azeotropic water removal; ONT:
ortho-nitrotoluene; MNT: meta-nitrotoluene; PNT: para-nitrotoluene.

Table 5. Temperature effect on product distribution

Temperature Percent ONT MNT PNT Others Para-
([degrees]C) Tol selectivity
 conversion

45 11.4 6.12 0.80 4.00 0.48 0.65
65 14.9 7.91 1.22 4.66 1.10 0.59
Reflux 38.5 23.19 1.49 11.70 2.17 0.50
 (110)
Reflux 45.7 22.96 2.40 17.90 2.44 0.78
 (110) *

Toluene/nitric acid (molar ratio) = 2.2:1.4; catalyst (zeolite
H-Beta S/A, 30) = 10 g; agitation speed = 200 rpm; time = 3 h;
batch experiments with azeotropic water removal; * : catalyst
(zeolite H-Beta S/A, 22).

Table 6. Effect of nitric acid dosing rate in semi-batch nitration
of toluene

Non-catalytic nitration

Dosing [X.sub.A] [X.sub.B] Para/ 0 m P Others
time, h (%) (%) ortho

1.5 (0.16) 40 * 12.7 0.59 16.4 1.22 9.7 1.7
3.5 (0.31) 25.7 * 19.3 0.64 20.1 2.0 13.0 2.5
6.0 (0.43) 41.3 ** 32.2 0.60 33.0 3.4 21.9 2.7

Catalytic nitration

Dosing [X.sub.A] [X.sub.B] Para/ 0 m P Others
time, h ortho

1 (0.11) 59.8 * 18.5 0.93 8.97 0.7 8.3 0.5
2 (0.22) 41.1 * 23.2 1.25 9.3 0.8 11.7 1.4
4.5 (0.37) 27.7 * 33.0 1.50 11.8 1.2 17.6 2.2

Nitric acid (40 mole %) dosed; figures in parantheses: toluene
volume fraction; toluene = 235 mL; *: limiting reactant, nitric
acid; * *: limiting reactant, toluene; [X.sub.A] = percent
conversion w.r.t. nitric acid; [X.sub.B] = percent conversion
w.r.t. toluene

Table 7. Effect of nitric acid dosinq rate-time interactions

Acid dosing Reaction [X.sub.A] [X.sub.B] ONT MNT
rate (mL/h) time (h)

15 1 57.0 9.0 5.3 0.2
 2 38.8 12.2 7.2 0.3
 2.5 33.4 14.6 8.3 0.4
30 1 59.8 18.5 9.0 0.7
 2 41.1 23.2 9.3 0.8
 4.5 27.7 33.0 11.8 1.2
 6 25.7 38.6 13.9 1.5
60 1 40.2 22.5 11.7 0.6
 2 37.9 40.7 20.1 1.8
 4.5 48.0 55.0 27.4 2.3

Acid dosing Reaction PNT Others PNT/ONT
rate (mL/h) time (h)

15 1 3.0 0.4 0.57
 2 4.2 0.5 0.58
 2.5 5.1 0.8 0.61
30 1 8.3 0.5 0.93
 2 11.7 1.4 1.25
 4.5 17.6 2.2 1.50
 6 20.8 2.4 1.50
60 1 9.7 0.5 0.83
 2 17.7 1.1 0.88
 4.5 23.9 1.4 0.87

Acid dosing Reaction Percent [H.sub.2]O Remaining
rate (mL/h) time (h) HN[O.sub.3] removed/ toluene:
 in aq phase [H.sub.2]O HN[O.sub.3]
 formed g/g (wt)

15 1 63 1.88 27
 2 69 2.78 13
 2.5 69 2.78 10
30 1 74 2.44 13
 2 81.7 1.44 6
 4.5 84.6 5.88 2
 6 78.4 3.70 0.6
60 1 71.1 2.02 4
 2 55.5 3.85 1.7
 4.5 70.6 3.57 0.5

Toluene = 2.2 moles; catalyst (H-Beta S/A, 22)=10 g; agitation
speed =200 rpm; temperature = 130[degrees]C; [X.sub.A]: percent
conversion w.r.t. HN[O.sup.3] limiting reactant; [X.sub.B]:
percent conversion of toluene (GC)