The effect of chain-length, chain-branching and polarity of sorbate molecule on diffusion in H-ZSM-5 zeolite was investigated by studying the sorption of liquid normal C2-C8 alcohols (isobutanol, tertiary-butanol, n-butylamine, n-hexane, isooctane) at 274 to 338K (tables 64 and 65), using the volumetric sorption method. Chain branching and increasing chain length caused a large decrease in the diffusivity and a large increase in the activation energy for diffusion. For sorbates with a given molecular critical size, chain length and similar molecular weight, the diffusion was strongly affected by the polarity of the sorbate; the diffusion of non-polar sorbate was found to be much faster. For polar sorbates, the diffusion depended not only upon the polarity of sorbate molecules but also upon their interactions with the acid sites and/or cations in the zeolite.

Diffusion of Straight- and Branched-Chain Liquid Compounds in H-ZSM 5 Zeolite. V.R.Choudhary, V.S.Nayak, A.S.Mamman: Industrial and Engineering Chemistry Research, 1992, 31[2], 624-8

 

Table 64

Diffusion of Alcohols in H-ZSM-5

 

Alcohol

Temperature(K)

D(cm2/s)

ethanol

274

3.00 x 10-9

n-butanol

274

2.50 x 10-10

n-butanol

293

3.80 x 10-10

n-butanol

308

6.00 x 10-10

isobutanol

274

2.50 x 10-12

isobutanol

293

5.40 x 10-12

isobutanol

308

7.50 x 10-12

tertiary butanol

308

1.00 x 10-12

n-pentanol

274

2.60 x 10-11

n-pentanol

293

5.44 x 10-11

n-pentanol

308

7.91 x 10-11

n-hexanol

274

6.80 x 10-12

n-hexanol

293

1.95 x 10-11

n-hexanol

308

2.72 x 10-11

n-heptanol

274

1.60 x 10-12

n-heptanol

293

4.40 x 10-12

n-heptanol

308

8.20 x 10-12

n-octanol

308

4.20 x 10-12

continued

 

 

Table 64 (continued)

Diffusion of Alcohols in H-ZSM-5

 

Alcohol

Temperature(K)

D(cm2/s)

n-octanol

308

4.2 x 10-12

n-octanol

323

1.22 x 10-11

n-butylamine

274

1.49 x 10-11

n-butylamine

293

3.35 x 10-11

n-hexane

293

1.00 x 10-9