Beta zeolite product selectivity

Running the Fisher indole synthesis on an unsymmetrical phenyl hydrazone gives a mixture of 2,3-disubstituted indoles. For example, reaction of the phenyl hydrazone, 34, with acid can give both 35 and 36 (Eqn. 22.26). Soluble acids and Amberlyst-15 give these two products in a 75 25 ratio at 100% conversion. With an H-M catalyst they are formed in a 65 35 ratio but over a dealuminated H-beta zeolite, the selectivity is reversed and 36 is produced in an 82% yield at 100% conversion.62 n was proposed that the preferential formation of 36 over the H-beta catalyst was the result of a restricted transition state selectivity. ... 

ITQ-21 presents excellent catalytic properties for the production of cumene, being more active and stable towards deactivation and presenting lower selectivity to NPB than a comparable beta zeolite. The benefits of ITQ-21 can be directly related to its open three-dimensional crystalline structure that favors diffusion of the products and minimizes undesired consecutive reactions. 

The catalytic activity of hierarchical and conventional Beta zeolites for acylation of 2-MN is displayed in Figure 2(a) The Beta (PHAPTMS) sample shows a superior catalytic activity than the conventional one, due to its enhanced textural properties. In this case, the bulky nature of both substrate and products may cause the existence of diffusional problems inside the zeolitic channels, which are attenuated in the modified Beta sample due to the presence of the hierarchical porosity. Regarding the product distribution (Figure 2(b)), two main products are observed and a third isomer, 8-A,2-MN isomer is produced just in minor amounts. Interestingly, the selectivity towards the desired isomer increases in the material obtained from silanized seeds, reaching values around 75%. Probably, the active sites located on the surface of the secondary porosity are able to catalyze also the formation of 6-A,2-MN by transacylation. However, this reaction is expected to be strongly hindered in the conventional Beta zeolite since it requires the participation of two bulky molecules as reactants. 

The 1-butene conversion and product distribution obtained at 25°C after 1 h of alkylation reaction of isobutane on JML-I50 and Beta catalysts are summarized in Table 6.1. The conversion (97%) with JML-I50 catalyst is higher than that (86%) with zeolite Beta. The primary products with the above catalysts are Cs compounds (59.9% with JML-I50 and 62% with Beta). The Cg products mainly consist of trimethylpentanes (TMPs), 58.7% for JML-I50 and 73% for zeolite Beta. The TMP/DMH (dimethylhexane) ratios are 13.5 for JLM-I50 and 4.1 for Beta, demonstrating that the selectivity of JML-I50 is higher than that of zeolite Beta. The yields of alkylate are 6.6 mL and 5.2 mL for JML-I50 and Beta zeolite, respectively. The weights of alkylate produced per weight of butene fed to the reactor are 1.13 and 0.95 for JML-I50 and zeolite Beta, respectively. 

Cumene is generated following a deprotonation step [85]. One of the undesired reactions is multiple alkylahon with propylene. Oligomerization of propylene is also undesired. Beta zeolite is a typical catalyst for this reaction. A series of Beta zeolites synthesized with Si/Af rahos ranging from 20 to 350 were evaluated for the alkylation of benzene with propylene at 423°K and 3 MPa in the presence of benzene alkene molar raho of 7.0. The benzene alkene molar ratio was kept high in order to minimize the undesired reactions. The selectivity to the mono-alkylate product was 92-93% in every case with the balance being the dialkylated product. The activity decreased with increase in Si/Al2 but the selectivity was independent of the Si/A12 ratio [86]. 

Product selectivity curves for gas-oil cracking on a Beta zeolite with a nominal Si/Al ratio of 10 and 27 are compared in Figures 8 and 9 with those for HY zeolites with framework Si/Al ratios of 7.7 and 35, respectively. 

Zeolite Beta has also been studied for isobutane/butene alkylation (65, 66), but it was less selective to the desired TMP than USY, suggesting some diffusional limitations for these highly branched products at the relatively low reaction temperatures used. In fact, an increase of activity was observed when decreasing the crystal size of the Beta zeolite (66). As for USY zeolites, the activity, selectivity and deactivation rate of Beta zeolite were influenced by the presence of EFAL species (67). Medium pore zeolites, such as ZSM-5 and ZSM-11 were also found active for alkylation, but at temperatures above 100°C (68, 69). Moreover, the product obtained on ZSM-5 and ZSM-11 contained more light compounds (C5-C7), and the Os fraction was almost free of trimethylpentanes, indicating serious pore restrictions for the formation of the desired alkylation products. 

It is clear that (3-picoline formation is a higher order reaction than pyridine formation, since the reactions involve 5 and 4 molecules respectively. Since a lower order reaction is favored in a more shape-selective environment, pyridine production is highest on ZSM-5 zeolites. Alternatively, one might try to maximize the fraction of (3-isomers in the picoline products. With a H-Beta zeolite, more than 98% of the picolines consist of (3-picoline, which highly simplifies the product purification (12) ... 

The influence of temperature has been investigated within the range from 25 °C to 80 °C. The optimum temperature for alpha-pinene methoxylation has been found at 40 °C at a reaction time of 5 h. At this temperature, the highest selectivity obtained over beta zeolite is about 54% at 92% conversion. A temperature above 40 °C gives significant reduction in selectivity due to occurrence of consecutive reactions or decomposition of l-methyl-4-[alpha-methoxy-isopropyl]-l -cyclohexene and other side reactions at even shorter reaction times. A lower temperature causes a drop of the alpha-pinene conversion. However, this can be compensated by a longer reaction time (59). The dependencies of temperature and reaction time are consistent with the above observations for limonene methoxylation. However selectivities up to 98% are obtained for limonene methoxylation, whereas the highest selectivity achieved for methoxylation of alpha-pinene amounts to 54%. On account of the above mentioned additional formation of various bicyclic addition products, the selectivities for all methoxy compounds increase to about 80%. This indicates that for the production of l-methyl-4-[alpha-methoxy-isopropyl]-l-cyclohexene beta zeolite is more selective for the addition of methanol to limonene than to alpha-pinene. The activity of the catalyst, however, is nearly the same for both reactions. 

TS-2 was shown to be almost indistinguishable from TS-1, as predicted by similarity of structures and active sites [46]. Ti-Beta zeolites, with and without A1 in the structure, were less effective than TS-1. The yields based on hydrogen peroxide, just above 60%, were typical of rather modest catalysts. Apparently, product selectivity was influenced by the A1 content. The relatively hydrophilic Ti,Al- 3 produced catechol and hydroquinone in nearly equimolar amounts [50]. The Al-free Ti-p showed a higher catechol selectivity, with an ortho/para ratio of 2 [47]. In both cases, the greater spaciousness of pores favoured ortho hydroxylation. For a useful comparison, the orthojpara ratio on medium-pore TS-1 was 0.77 under analogous conditions. 

In the alkylation of benzene with long-chain a-olefins (Ce, Cg, C12, etc ), the large-pore zeolites mordenite, beta-zeolite, and ZSM-12 favor the less bulky 2-phenyl isomers. HY and rare-earth-Y produce a mixture of other -alkylbenzene isomCTS. Shiqie selectivity is attributed here to both product- and restricted transition state type selectivities [76]. 

The catalytic test reaction, the acylation of 2-methox)maphthalene (2MN), distinguishes between the inner and outer surfaces by means of product selectivity. Absorption experiments under the same reaction conditions show that the linear ketone product 2-acetyl-6-methoxynaphthalene (2AC) can pass through the 12-ring channels of beta whereas the other product l-acetyl-2-methoxynaphthalene (lAC) is too bulky to enter into any zeolite except Y. Once formed, lAC is unstable in the presence of acids and can deacylate to give the starting material (see reaction scheme 1). Since 1 AC can only form outside the micropore space of zeolite beta, the yield can be used as a measure of the catalytic activity on the external surface, although high yields can be expected because the 1-position is the most favoured for electrophilic attack. 

H-beta zeolite proved to be an active and selective catalyst for alkylation of benzene with propene. In situ spectroscopic methods were applied to follow the formation and the evolution of surface intermediates and products,. It was found that when benzene is taken alone on the zeolite surface, its adsorption is reversible up to 473 K. On the contrary propene undergoes to several transformations even at 295 K. Isopropylbenzene behaves as propene, giving the same intermediates and products by decomposition at higher temperatures. Isopropyl cations formed upon chemisorption of propene on Broensted acid sites are the key intermediates for the alkylation reaction and are responsible for the faster deactivation via unsaturated caibenium ions formation. 

A similar shape selective effect was observed in the liquid phase. Those catalysts with the smaller pore and channel openings were more selective for para-nitrotoluene. However, in the liquid phase, no induction period was observed. Rather, all catalysts exhibited significant deactivation throughout time on stream and after 5 hrs. little of the original activity remained. As shown in Fig. 3, the para selectivity was found to decrease with time on stream. This would indicate that deactivation occurs within the pore channels effectively reducing the preferential capacity of the catalyst to generate the para isomer. The decrease in para selectivity was not evident on Beta zeolite, which has larger pores and may allow for a more uniform production of... 

By 1992, UOP had selected the most promising catalyst, based on beta zeolite, for cumene production and then began to optimize a liquid phase based process design around this new catalyst. The result of this work led to the commercialization of the UOP Q-Max process and the QZ-2000 catalyst in 1996. More recently in 2001, UOP commercialized a new alkylation catalyst, QZ-2001, which offers improved stability and operation as low as 2B/P molar feed... 

Because new high-acfivify befa zeolife cafalysfs such as QZ-2000 catalyst are such strong acids, they can be used at lower reaction temperatures than SPA catalyst or other relatively lower-activity zeolites such as MCM-22 catalyst. The lower reaction temperature in turn reduces the olefin oligomerization reaction rate, which is relatively high for SPA catalyst. The result is that beta zeolite catalysts tend to have higher selectivity to cumene and lower selectivity to both nonaromatics that distill with cumene (such as olefins, which are analyzed as Bromine Index, and saturates) and heavy by-products. For example, although butyl-benzene is typically produced from traces of butylene... 

Beta zeolite catalyst is also an extremely effective catalyst for the transalkylation of DIPB to produce cumene. Because of the high activity of beta zeolite, transalkylation promoted by beta zeolite can take place at very low temperature to achieve high conversion and minimum side products such as heavy aromatics and additional -propylbenzene as highlighted in Fig. 6. Virtually no tri-isopropyl benzene is produced in the beta system owing to the shape selectivity of the three-dimensional beta zeolite structure, which inhibits compounds heavier than DIPB from forming. 

Beta zeolite catalyst can be optimized to nearly eliminate all undesirable side reactions in the production of cumene. The improvement in beta zeolite catalyst quality has occurred to the point that any significant impurities in the cumene product are governed largely by trace impurities in the feeds. The selectivity of the catalyst typically reduces by-products to a level resulting in production of ultrahigh cumene product purities up to 99.97 wt%. At this level, the only significant byproduct is n-propylbenzene with the catalyst producing essentially no EB, butylbenzene, or cymene beyond precursors in the feed. Fig. 7 shows the reactions of some common feedstock impurities that produce these cumene impurities. 

Taking advantage of the in situ regeneration capability, the customer opted to regenerate the catalyst three times during this period. The results show the remarkable resilience of the beta zeolite catalyst to the stresses of regeneration with virtually no loss in monoalkylate selectivity or cumene product quality as a result of repeated regenerations. 

In addition to the effect on the product selectivity, it is seen in Table 3 that, for a given synthetic method, the activity (1-hexene and H202 conversion) as well as the selectivity of H202 increases as the A1 content of the zeolite decreases. These results show that the A1 content of zeolite Ti-Beta is one of the most important factors in determining its activity and selectivity in oxidation reactions, and the benefits that the new methods of synthesizing Ti-Beta with low A1 content can provide. 

---