Shape selectivity in Y-zeolites

Yield of aromatics from naphthenics upon catalytic cracking

“…15 It can be seen in the comparison with cyclohexane in Figure 2 that in the proposed configuration of cis-decalin, the second six-atom ring is built on an equatorial bond and an axial bond in the first ring, 16 this bond suffering van der Waals repulsion through 1,3 diaxial interactions. In the case of transdecalin, the second ring is constructed on two equatorial bonds in the first ring.…”

“…For example, Lai and Song 13 and Kubicka et al, 14 who studied the conversion of decalin over different zeolites at lower temperatures, from 473 to 573 K, reported similar results on pure Y zeolite. A study performed by Mostad et al 15 with a wider temperature range (603 to 733 K) over various zeolites, showed that if the reactant was cis-, trans-or a mixture of both isomers over Y zeolite at 603 or 665 K, the only product was trans-decalin and concluded that cis-decalin stereoisomerizes into trans-decalin; at 733 K they found that cis-decalin appeared in the products from trans-decalin conversion, but, more interestingly, they determined that the rate of cis-to trans-isomerization was about 6 to 10 times faster than the trans-to cis-isomerization. Moreover, and considering that the products from the conversion of both pure isomers were the same, they determined that the conversion of cis-decalin into other products was 10 5 times faster than that of trans-decalin.…”

“…In the case of transdecalin, the second ring is constructed on two equatorial bonds in the first ring. However, Y zeolite cavities are large enough to accommodate these molecules similarly, 15 and no significant restrictions to diffusion are to be expected in the zeolite structure.…”

Influence of reaction temperature and crystallite size on HBEA zeolite deactivation by coke

“…Furthermore, the effect of reaction temperature on the deactivation by coke was mainly reported with very reactive compounds such as olefins [9,21,22] or alkylaromatics [10,[23][24][25] because at low temperature (<250 8C) there is generally no coke formation from paraffins or satured naphthenes which cannot be transformed into more reactive compounds (essentially olefins). However, over strong acid catalysts paraffins [26][27][28] and naphthenes [29][30][31][32][33][34][35] can be cracked and coke produced even at low temperature. That was the reason why in this paper, the transformation of methylcyclohexane was investigated over an acidic HBEA zeolite at 250, 350 and 450 8C.…”

Formation of aromatics in heavy gasoline and light LCO ends in FCC

“…However, a number of publications showed that the conversion of decalin on Y zeolite is not subjected to diffusion restrictions. In that sense, Mostad et al [33] compared ZSM-5, offretite, mordenite, different Y zeolites and an amorphous silica-alumina, while Corma et al [32] reported to ZSM-5, MCM-22, ITQ-2, USY, beta, and MCM-41. Al-Sabawi and de Lasa [34] also compared the performance of Y zeolite with different crystal sizes to conclude that pore diffusion resistance would not affect the overall rate of conversion, in consistency with previous observations by Sousa-Aguiar et al [35].…”