An improved frequency-response apparatus was used to study the diffusion of ethane in silicalite as a function of bed-depth of the zeolite. The diffusion coefficients obtained were much smaller than those found using pulsed field gradient NMR. The diffusivity of ethane was 3.0 x 10-5cm2/s at 323K. When the silicalite crystals were widely distributed throughout a glass-wool plug, the diffusion coefficient was much higher and in good agreement with the NMR value. The diffusion of propane and butane was also studied using this zero bed-depth method, giving values of 6.0 x 10-6 and 5.4 x 10-7cm2/s, respectively, at 323K. The activation energy for butane diffusion was 21.5kJ/mol.

Diffusion of Hydrocarbons in Silicalite Using a Frequency-Response Method. N.G.Van-Den-Begin, L.V.C.Rees: Studies in Surface Science and Catalysis, 1989, 49, 915–24

 

Table 36

Diffusion in Silicalite-1

 

Diffusant

Technique

T(K)

D(m2/s)

C3H8

zero-length column

363

3.3 x 10-12

C3H8

pulsed field gradient

363

3.5 x 10-11

C3H8

zero-length column

333

1.4 x 10-12

C3H8

pulsed field gradient

333

3.4 x 10-11

C3H8

zero-length column

303

4.0 x 10-13

C3H8

pulsed field gradient

303

1.8 x 10-11

n-C4H10

zero-length column

363

2.2 x 10-12

n-C4H10

pulsed field gradient

363

3.6 x 10-11

n-C4H10

zero-length column

333

7.0 x 10-13

n-C4H10

pulsed field gradient

333

3.0 x 10-11

n-C4H10

zero-length column

303

4.0 x 10-13

n-C4H10

pulsed field gradient

303

1.4 x 10-11

i-C4H10

zero-length column

363

9.0 x 10-13

i-C4H10

pulsed field gradient

363

2.0 x 10-12

i-C4H10

zero-length column

333

3.0 x 10-13

i-C4H10

pulsed field gradient

333

2.0 x 10-12