HBEA zeolites

Keywords hydroisomerization, n-hexadecane, platinum, HBEA zeolite, crystallite size... 

The hydroisomerization of heavy linear alkanes is of a great interest in petroleum industry. Indeed, the transformation of long chain n-alkanes into branched alkanes allows to improve the low temperature performances of diesel or lubricating oils [1-3]. On bifunctional Pt-exchanged zeolite catalysts, n-CK, transformed into monobranched isomers, multibranched isomers and cracking products [4], The HBEA zeolite based catalyst was more selective for isomerization than those containing MCM-22 or HZSM-5 zeolites [4], This was explained on one hand by a rapid diffusion of the reaction intermediates inside the large HBEA channels, and on the other hand by the very small crystallites size of this zeolite (0.02 pm). 

An increase in the crystallites size of the HBEA zeolite brings a neat increase in the activity of the corresponding Pt-exchanged catalyst for n-C.% transformation (Table 1). However, this increase in activity is accompanied by a significant deactivation of the catalyst 90% with the 10-15 pm crystallite size, 60% with the 1-1.5 pm crystallite size, while no deactivation is observed with the 0.02 pm crystallite size. 

Among the wide variety of organic reactions in which zeolites have been employed as catalysts, may be emphasized the transformations of aromatic hydrocarbons of importance in petrochemistry, and in the synthesis of intermediates for pharmaceutical or fragrance products.5 In particular, Friede 1-Crafts acylation and alkylation over zeolites have been widely used for the synthesis of fine chemicals.6 Insights into the mechanism of aromatic acylation over zeolites have been disclosed.7 The production of ethylbenzene from benzene and ethylene, catalyzed by HZSM-5 zeolite and developed by the Mobil-Badger Company, was the first commercialized industrial process for aromatic alkylation over zeolites.8 Other typical examples of zeolite-mediated Friedel-Crafts reactions are the regioselective formation of p-xylene by alkylation of toluene with methanol over HZSM-5,9 or the regioselective p-acylation of toluene with acetic anhydride over HBEA zeolites.10 In both transformations, the p-isomers are obtained in nearly quantitative yield. 

The location of 2-MN acetylation over HBEA zeolites was largely debated. Some authors claimed that the bulkier isomer (1-AMN) could be formed only on the external surface, and the linear one (2-AMN) both within the micropores and on the external surface, while other than that both isomers were essentially formed within the micropores. The second proposal seems to be more likely indeed, adsorption experiments showed that 1-AMN could enter the micropores of HBEA and even those of MFI, a medium-pore zeolite. ... 

Kinetic studies of the acetylation of several arylethers were carried out over HBEA zeolites. The main conclusion is that the rate and stability of the reactions are determined by the competition between reactant(s) and product(s) molecules for adsorption within the zeolite micropores. This competition shows that the autoinhibition of arene acetylation, that is, the inhibition by the acetylated products, and also by the very polar acetic acid product is generally observed. This effect is much more pronounced with hydrophobic substrates such as methyl and fluoro aromatics than with hydrophilic substrates because of the larger difference in polarities between substrate and product molecules. 

Marques, J.P., Gener, L, Lopes, J.M., Ramoa Ribeiro, F., and Guisnet, M. (2005) n-Heptane cracking on dealuminated HBEA zeolites. 

The location of 2-MN acetylation reactions over HBEA zeolites was widely debated. Some authors claim that the bulkier isomer 1-AMN can only be formed at the generally large external surface of BEA zeolite, the linear isomer 2-AMN both within the micropores and on the external surface 119,21,24,28,381 other authors state that both isomers are essentially formed within the micropores.[26,32,33,35] Both proposals can explain the increase in the selectivity to the bulky isomer (1-AMN) with decrease in the crystallite size/28 321 Indeed the smaller this size, the greater the external surface, hence the higher the rate of reactions on this surface, but also the shorter the micropore length and, consequently, the smaller the differences in the rates of desorption of the bulky and linear isomers. Both proposals can also explain the decrease in the selectivity for 1-AMN with the passivation or the poisoning of the external surface by bulky base molecules.[28] Additional arguments in favour of the formation of both isomers within the micropores are provided by ... 

Anisole and veratrole acetylation with AA were carried out over three large pore zeolites HFAU, HBEA and HMOR and one average pore size zeolite HMFI.[3] With both substrates, the initial rates as well as the maximum yield were found lower over the monodimensional MOR zeolite and with MFI, which was explained by diffusion limitations. Anisole acetylation was shown to be quicker and the maximum yield higher over HBEA than over HFAU, whereas the reverse was found with veratrole acetylation.[3,4] Such behaviour could be explained from the relative sizes of the acetylation intermediates and of the micropores (transition shape selectivity).[3] Whereas HFAU and HBEA zeolites with similar Si/Al ratios have practically the same activity for 2-MN acetylation, HMFI is practically inactive. Furthermore, HBEA is more active than HFAU for 1-AMN isomerization. 

MN acetylation is most likely related to the high polarity and bulkiness of the products with limitations in the reaction rate by product desorption. Dealumination would have a positive effect on the acetylation rate because of the decrease in the zeolite hydrophilicity and of the increase in the rate of diffusion of the bulky products owing to elimination of extra-framework A1 species. Curiously, in anisole acetylation, the Si/Al ratio of the HBEA zeolite had practically no effect on the reaction rate. However it is worth noting that most of the tested samples had Si/Al ratios between 11 and 30. Like for 2-MN acetylation,[28,32] the performance of HBEA zeolites in anisole acetylation depends on their crystallite size.[17] This was shown by comparing the activities of samples with large size (0.1-0.4 pm) and of a nanosize sample (0.01-0.02 pm) prepared within the pores of a carbon black matrix. The superior performance of the nanosize sample was ascribed to a decrease in diffusional constraints limiting the desorption of the bulky and polar p-methoxyacetophenone product from the BEA micropores. 

Table 3.8 Influence of the reaction temperature on the gas phase Fries rearrangement of phenyl acetate over a HBEA zeolite. Values of conversion obtained after 1 and 10 h reaction (Xi, Xio) and of selectivity and yield to hydroxyacetophenones after lh reaction...

In the Fries rearrangement of PA, high yield and selectivity for o-HAP can be obtained with large pore zeolites such as HFAU, HBEA and average pore zeolites such as HMFI. HBEA zeolite modified by ion exchange with cerium[77] and especially a commercial HMFI made of primary crystallites and agglomerates joined by finely dispersed alumina[78] were claimed to be particularly stable and selective for the formation of o-HAP. 

Figure 3.8 Liquid phase transformation of phenyl acetate (2.2 mol l-1 in sulfolane solvent) at 433 K. (a) Yield in o-hydroxyacetophenone, o-HAP ( ) and p-hydroxyacetophenone, p-HAP (X) versus reaction time, (b) Effect of the addition of phenol (P) on the p-HAP yield. [P] =0 mol l-1 (x) and [P] =0.6 mol l-1 ( ). Reprinted from Catalysis Letters, Vol. 41, Jayat et al., Solvent effects in liquid phase Fries rearrangement of phenyl acetate using a HBEA zeolite, pp. 181-187, copyright (1996), Kluwer Academic Publishers, with kind permission of Springer Science and Business Media...

A kinetic study of PA transformation was carried out in a batch reactor over a HBEA zeolite[82] in the presence of nonpolar (dodecane) and very polar (sulfolane) solvents. The solvent polarity has a negative effect on the initial reaction rate, but a positive effect on the catalyst stability and selectivity for p-HAP (Table 3.7). 

Advantage can be drawn from the positive effect of phenol on PA transformation into p-HAP to improve the yield and selectivity of p-HAP production.[82 84] Thus, with a HBEA zeolite the yield and selectivity for p-HAP passes from ca. 5 and 28 % respectively with cumene solvent to 24 and 60% with phenol as a solvent .[84] Again sulfolane was shown to have a very positive effect on the selectivity for p-HAP and limits the catalyst deactivation. To explain these observations as well as the effect of P and PA concentrations on the reaction rates, it was proposed that sulfolane plays two independent roles in phenol acylation solvation of acylium ion intermediates and competition with P and PA for adsorption on the acid sites.1831... 

The liquid phase benzoylation reactions over HBEA zeolite catalyst were operated under nitrogen to minimize the hydrolysis of acylating agent in a magnetically stirred glass reactor equipped with a condenser and a dropping funnel. 

SELECTIVE SYNTHESIS OF 2-ACETYL-6-METHOXYNAPHTHALENE OVER HBEA ZEOLITE... 

This paper deals with the selective synthesis of 2-acetyl-6-methoxynaphthalene, precursor of Naproxen, over zeolite catalysts and especially over HBEA zeolites. As has been previously observed3 8, acetylation of 2-methoxynaphthalene occurs preferentially at the kinetically controlled 1-position with formation of l-acetyI-2-methoxynaphthalene (I). The desired isomer, 2-acetyl-6-methoxynaphthalene (II) and the minor isomer, l-acetyl-7-methoxynaphthalene (HI), are the other primary products. However, it will be shown that in presence of 2MN, isomerization of I can occur allowing a selective production of II, the desired product the effect of the operating conditions (solvent, temperature) and of the acidity and porosity of the zeolite catalyst will be presented. 

Acetylation of 2-methoxynaphthalene (2MN) with acetic anhydride (AA) was carried out in a batch reactor over a HBEA zeolite with a framework Si/Al ratio of 15 (HBEA 15). The standard operating conditions were the following temperature of 120°C, 500mg of catalyst previously activated at 500°C overnight under dry air flow, solution containing 35 mmol of 2MN (C2MN = 3,43mol l 1), 7 mmol of AA (Caa = 0,68 mol.I 1) and 4 cm3 of nitrobenzene. 

Figure 1 Acetylation of 2-methoxynaphthalene with acetic anhydride over a HBEA zeolite (Si/Al = 15). Total yield in acetylmethoxynaphthalene (I + II + III) and yields in isomers 1 II and III versus reaction time,...

Selective Synthesis of 2-Acetyl-6-methoxynaphthalene over HBEA Zeolite... 

The effect of solvent polarity on the activity and selectivity of the HBEA zeolite was examined on the acetylation of 2MN with acetic anhydride as well as on the transacylation of 2MN with isomer I. The reactions were carried out in solvents of various polarities under the following conditions temperature of 120°C, 500mg of HBEA and 35mmol of 2MN (3,43 mol.l 1), 7mmol of AA (O Smol.l 1) and 4 cm3 of solvent (sulfolane, nitrobenzene, 1,2-dichlorobenzene or 1-methylnaphthalene) for acylation and 20 mmol of 2MN (4 mol.l 1), 4 mmol of I (1 mol.l 1) in 3,3 cm3 of solvent for transacylation. The Et parameter defined by Dimroth et alu was used for characterizing the solvent polarity. 

The acetylation of 2MN was carried out under the standard conditions over a series of HBEA zeolites resulting from dealumination of a commercial sample with a framework Si/Al ratio of 15, by treatment with chlorhydric acid15 or with ammonium hexafluorosilicate16 The initial reaction rate passes through a maximum for a number of A1 atoms per unit cell between 2 and 3 (i.e. for a framework Si/Al ratio between 20 and 40) and this whatever the mode of dealumination. An important remark is that on these dealuminated zeolites, the number of acidic Lewis sites is very low compared to the non dealuminated sample. This confirms that acidic Lewis sites do not participate in acetylation of 2MN16. 

Over HBEA zeolites, acetylation of 2-methoxynaphthalene with acetic anhydride leads mainly to l-acetyl-2-methoxynaphthalene. However, the desired product, i.e. 2-acetyl-6-methoxynaphthalene, precursor of Naproxen is obtained at long reaction time by an intermolecular irreversible isomerization process. A very selective production of II (83%) can be obtained by acetylation of 2-methoxynaphthalene over a commercial HBEA zeolite (Si/Al = 15) at 170°C, with nitrobenzene as a solvent. With dealuminated HBEA samples (framework Si/Al ratio between 20 and 40), better results could be expected. Furthermore, preliminary experiments showed that this selective synthesis of 2-methoxynaphthalene can be carried out in a flow reactor system. 

Selective Synthesis of 2-Acetyl-6-methoxynaphthalene over HBEA Zeolite 145 E. Fromentin, J.-M. Coustard and M. Guisnet... 

However, as shown in Figure 14.4, over an HBEA zeolite with a Si/Al ratio of 15 (HBEA15), acetylation is followed by secondary reactions of isomer I isomerization into II and into l-acetyl-7-methoxynaphthalene (III) and deacylation. Therefore, the transformation of the 2MN/AA mixture on HBEA15 can be proposed to occur mainly through the following successive scheme (25) ... 

Tables 14.1 and 14.2 show the dramatic improvement brought by the substitution of the old technology with AICI3 catalyst and acetylchloride as acylating agent in a batch reactor by the new technology with a HBEA zeolite catalyst, acetic anhydride as acylating agent in a fixed bed reactor (12). The fixed bed reactor process constitutes a major break-through in anisole acetylation.

Obviously, it is very desirable to substitute these modes of benzylic ether preparation by an heterogeneous catalysis process. Clays (50) and resins (51, 52) which were the first solid acid catalysts used have given low or moderate yields. The first experiments with zeolites were carried out by Rhodia (53, 54) on the etherification of vanillic alcohol (A) in a batch reactor over a HBEA zeolite with a Si/Al ratio of 12.5 ... 

To estimate the effect of reaction time on activity and selectivity of HBEA (12.5), this zeolite was recovered by filtration after 5 hours reaction and reused several times under the same operating conditions batch reactor, 80°C, 7.5 g of vanillic alcohol and 35 g of ethanol. Only a small decrease in conversion was observed from 98% to 88%, 86% and 84%, the selectivity remaining close to 100%. Furthermore, the activity is completely recovered after calcination under air flow for 5 hours. The slow deactivation of the HBEA zeolite is most likely due to a partial blockage of the access to the active sites by heavy secondary products ( coke ). 

Phenols react with deactivated carbonyl compounds such as chloral (2,2,2-trichloroethanal) in the presence of different dealuminated protonic zeolites (Y-EAU, MOR, MFI and BEA) to give the corresponding carbinols. A high para-selectivity was achieved using HBEA zeolite (Si A1 = 12.5) (equation 18). ... 

Acetylation of 2-methoxynaphthalene by acetic anhydride over HBEA zeolite gives l-acetyl-2-methoxynaphthalene, 2-acetyl-6-methoxynaphthalene and a small amount of l-acetyl-7-methoxynaphthalene (equation 45) . The l-acetyl-2-methoxynaphthalene rearranges to the other isomers under longer contact times, probably involving both intermolecular transacylation and intramolecular rearrangements (equation 46). 

Rhodia has manufactured, selectively, acetoveratrole by acetylation of veratrole with acetic anhydride catalyzed by HBEA zeolite in the same process using fixed bed reactor technology. In this case, the best heterogeneous catalyst for acylation of veratrole is the HY zeolite. 

Acylation of aromatics over a HBEA Zeolite. Effect of solvent and of acylating agent. 

A kinetic study of the acylation of phenol with phenyl acetate was carried out in liquid phase at 160°C over HBEA zeolite samples, sulfolane or dodecane being used as solvents. The initial rates of hydroxyacetophenone (HAP) production were similar in both solvents. However the catalyst deactivation was faster in dodecane, most likely because of the faster formation of heavy reaction products such as bisphenol A derivatives. Moreover, sulfolane had a very positive effect on p-HAP formation and a negative one on o-HAP formation. To explain these observations as well as the influence of phenol and phenyl acetate concentrations on the rates of 0- and p-HAP formation it is proposed that sulfolane plays two independent roles in phenol acylation solvation of acylium ions intermediates and competition with phenyl acetate and phenol for adsorption on the acid sites. Donor substituents of phenyl acetate have a positive effect on the rate of anisole acylation, provided however there are no diffusion limitations in the zeolite pores. 

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