De-alumination

A fourth option is to apply high silica zeolites (de-aluminated mordenite, US-Y or beta) to cope with the HBr formed. 

Consider, for instance, the interaction of the alumina-free silica framework of de-aluminated faujasite with water in the liquid phase. Per mol Si02, 1.3 mol H2O can be occluded. The heat of evaporation of water is 36 kJ/mol and the heat of adsorption -30 kJ/mol, so per mol Si02 there is an energy cost of 20 kJ. 

Of interest with respect to this hypothesis is the significant difference in heat of paraffin adsorption between the medium-pore zeolite silicalite and large-pore, de—aluminated faujasite. The heat of paraffin adsorption is much smaller in the case of the de-aluminated faujasite, which has so far had to be prepared by an indirect route, than for silicalite, which can be synthesized direct in the presence of an organic molecule. The difference, which increases with chain length, is of the order of 5 kJ/mol per CH2 unit, and may be ascribed to the optimum fit of hydrocarbon and channel in the case of the medium-pore zeolite (H, 12). ... 

The results indicate that both NH4,TMA-fl and NH.,K-L are de-aluminated upon fluorination. Strong supporting evidence comes from framework I. R. data where the shifts in band position to higher wave numbers are as much as 20 cm-1. However, there is no evidence of structure stabilization. Also McBain water adsorption data give no indication of surface hydrophobicity. Therefore, it is likely that structure defects are formed in these two zeolites as a result of dealumination and cause low thermal stability. 

DDM A process for making cumene from propylene and benzene by alkylation followed by transalkylation over a de-aluminated mordenite catalyst. Operated since 1992 by Dow Chemicals at Terneuzen, The Netherlands. 

Heats of immersion in water have been determined for a number of outgassed porous crystals enriched by ion exchange in various cations (zeolites X, Y, A, chabazite, and synthetic ferrierite), and for clinoptilolite and mordenite in their Na-forms, decationated, and in various stages of de-alumination. Finally, heats of immersion were determined in NaX, NaY, NaA, and (Ca,Na) chabazite in which the crystals initially contained various known loadings of zeolitic water. From the results, the influence of the exchange cations upon integal heats of sorption of water, AH, and other derived heats have been evaluated and discussed. 

In the ensuing discussion we deal exclusively with hydrophobic (de-aluminated) zeolites. In these zeolites nearly all Al3+ ions have been substituted by Si ions, so that the stoichiometries of these solids are close to those of pure silica, Si02. The diameters of the pores in the framework are typically of the order of 5A, up to 7.sA (zeolite Y). (Recently, wider pore hydrophobic "zeolites" have been synthesised. These are discussed later in this chapter for now we restrict our attention to the "classical" zeolites.)... 

The catalyst for the alkylation is ZSM-5 in the form. This zeolite is prepared using the tetrapropylammonium ion as the template. After the synthesis the template is removed by calcination. Several other zeolites, H-Y, H-MCM-22, and H-Beta are industrially applied for the ethylation and isopropylation of benzene. Also a highly de-aluminated H-mordenite has been reported to be an excellent alkylation catalyst. 

Finally, Olsson and Rollman found that mordenite de-aluminated to Si02/ AI2O3 = 100 gave X-ray data which clearly demonstrated non-uniform lattice shrinkage. This has been taken as evidence that there are three types of A1 site in the mordenite lattice. 

The hydrocracking and isomerization of hexane over de-aluminated mordenites were investigated with detailed product analyses. The hydroisomerization and hydrocracking of pentane over various exchanged mordenite catalysts were studied by Gray and Cobb. The cracked products consisted of relatively more propane and butanes over the smallest cation form (Be-mordenite) and relatively more methane for the largest cation form (Ba-mordenite), indicating a selectivity effect. The catalysts used in commercial processes for the hydroisomerization... 

De-aluminated mordenites were claimedto give more active and stable catalysts for toluene disproportionation than conventional H-mordenite. Becker, Karge, and StreubeP studied the alkylation of benzene with ethene and propene over an H-mordenite catalyst. Shape-selective catalysis was found because only ethylbenzene, w-diethylbenzene, p-diethylbenzene, cumene, p-di-isopropylbenzene, and m-di-isopropylbenzene were detected in the products neither o-diethylbenzenes nor higher alkylated products were found. The results are in agreement with earlier transalkylations over H-mordenite. Catalyst aging was caused by olefin polymerization. The selectivity of Be-mordenite... 

A wide range of reactions of polar compounds was claimed to be catalysed by zeolites of high Si02/Al203 ratio, such as de-aluminated mordenite and HZSM-5. The liquid-phase dehydration of t-butanol catalysed by H-mordenite was studied by Ignace and Gates.Reaction took place within the pore structure and was hindered by the difficulty of transport of reactant, product, and diluent molecules. Barrer and Oei found that ethylvinyl, n-butylvinyl, and isobutylvinyl ethers all react readily over H-mordenite near room temperature... 

HL but less selective for pyrrolidine. Other partially exchanged HL zeolites were both less active and less selective than HL itself but de-aluminated HL had enhanced activity and selectivity. The high selectivity for ring transformation was attributed to transition-state shape-selective catalysis in the straight channels of L zeolite. 

Crystalline de-aluminated zeolitic SiC>2 made by acid extraction of clinoptilolite. 

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