In Ex. 15.8, Henry’s constant for adsorption k, identified as the intercept on a plot of n∕P vs. n, was found from a polynomial curve-fit of n∕P vs. n. An alternative procedure is based on a plot of ln(P∕n) vs. n. Suppose that the adsorbate equation of state is a power series in n: z = 1 + Bn + Cn² + . . . . Show how from a plot (or a polynomial curve-fit) of ln(P∕n) vs. n one can extract values of k and B.

 Ex. 15.8

Nakahara et al.¹¹ report data for ethylene adsorbed on a carbon molecular sieve ( A = 650 m² ·g⁻¹) at 50°C. The data, shown as filled circles in Fig. 15.7, consist of pairs of values (P, n), where P is the equilibrium gas pressure in kPa and n is moles of adsorbate per kg of adsorbent. Trends shown by the data are typical for physical adsorption on a heterogeneous adsorbent at low-to-moderate surface coverage. Use these data to illustrate numerically the concepts developed for pure-gas adsorption.

Fig. 15.7

Transcribed Image Text:

1.5 1.0 0.5 10 20 30 40 P/kPa Figure 15.7: Adsorption isotherm for ethylene on a carbon molecular sieve at 50°C. Legend: • experimental data; – • -.-• Henry's law;. Toth equation; --- Langmuir equation n→ 0. -1 n/mol-kg