Single-Component Sorption/Diffusion of Cyclic Compounds from Their Bulk Liquid Phase in H-ZSM-5 Zeolite

Abstract

Single-component sorption/diffusion of cyclohexane, pyridine, benzene, toluene, aniline, ethylbenzene, xylene isomers, n-propyl-and isopropylbenzenes, and mesitylene in H-ZSM-5 (Si/Al ) 39.7) zeolite from their bulk liquid phase at 273-338 K has been measured volumetrically. The diffusivity and activation energy for the diffusion are found to be strongly influenced by the side groups attached to the benzene nucleus, polarity, critical molecular size, and configuration of sorbate molecules. However, the influence of configuration and/or flexibility (i.e., compressibility to the zeolite channel diameter) plays a vital role in controlling/deciding the penetration (or entry) and configurational diffusion (after penetration) of sorbate molecules in the zeolite channels. The influence of critical size and configuration of sorbate molecules, on their entry in the zeolite channel and also their configurational diffusion after sorption, can be explained by the shuttlecock-shuttlebox model for sorption/diffusion of bulky molecules in medium-pore zeolites. The influence is explained by taking into consideration the orientations in different conformations and compressibility in the movement in different directions of the sorbate molecules.

Xylene Isomerization in the Liquid Phase Using Large‐Pore Zeolites

“…On the other hand, in medium-pore zeolites, the size of the molecule outweighs the dipole moment, making MX the slowest isomer inside the channels [47]. The critical sizes of OX, MX, and PX are 0.73, 0.74, and 0.67 nm [28]. According to Č ejka and Wichterlová [37], zeolites with lower acidity can provide higher activity under specific reaction conditions, as it was seen in this work.…”

“…fusion of molecules with higher dipole moment is more hindered due to stronger adsorption on highly acidic catalysts [28,43,45]. The dipole moments for OX, MX, and PX are 0.62, 0.36, and 0.00 D, respectively [46]; this might explain the lower diffusivity of OX in large-pore zeolites.…”

“…A successful example is the production of ethylbenzene through alkylation of benzene; in the gas phase, the reaction was performed over ZSM-5, but due to diffusion problems, mediumpore zeolites were not suitable in the liquid phase [1,27]. Diffusion in the liquid phase is slower than in the gas phase; the molecule requires energy equivalent to its latent heat to enter into the channels and the degree of freedom for appropriate orientation is less due to its lower entropy [28]. Large-pore zeolites, such as Y and Beta, were used instead, with the latter being more selective.…”

Catalytic cracking of bio-oils improved by the formation of mesopores by means of Y zeolite desilication

“…The knowledge of the critical diameter of a given molecule [35] could assist this discussion; however, this property is known only for a few oxygenated molecules [7]. Table 4 shows the selectivity of some bulky phenolic and aromatic ethers for the various catalysts at Cat/Oil 3.5, at which the highest oxygenated yields were observed (see Figure 1).…”

Separation of p-xylene from binary xylene mixture over silicalite-1 membrane: Experimental and modeling studies

“…MFI-type zeolite membranes, ZSM-5 and silicalite-1 with the uniform dimensions of circular (0.54 Â 0.56 nm 2 ) and elliptical pores (0.51 Â 0.54 nm 2 ) (Choudhary et al, 1997), are capable to separate close-boiling point xylene isomers, which are currently separated by energy intensive technology such as cryogenic crystallization or selective adsorption process Parex. Although highly selective separations of xylene isomers could be achieved based on molecular sieving effect, it is reported in the literature that p-xylene adsorbs selectively on MFI zeolite membrane compared to its isomers and its permeation behavior is controlled by an adsorption-diffusion mechanism (Gu et al, 2006;Lai and Tsapatsis, 2004;Tarditi et al, 2006aTarditi et al, , 2006bTarditi et al, , 2008Xomeritakis et al, 2001).…”