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6287991 
Journal Article 
Methane adsorption as a calorie upgrading PSA in the SNG process 
Ishigaki, Y; Nishida, S; Otowa, T; Shiraki, A 
1989 
3 
A pressure swing adsorption (PSA) method for H2N2 removal is described in this paper. Results were achieved by selective adsorption of CH4 and other hydrocarbons from the products of our demonstration plant (550 Nm3 h−1) converting coke oven gas to substitute natural gas (SNG). High calorie gas (10 000 kcal Nm−3) was obtained from the pressure swing process between 0.26 and 4 kg cm−2 after adsorption at 7 kg cm−2. In the course of screening various adsorbents, a higher amount of methane adsorption, qCH4, was obtained for higher qN2. However, N2 content was relatively low for the adsorbent of high qCH4 due to the fact that the increase of qCH4 was larger than that of qN2. There were no such clear relations between qH2 and qCH4. N2 content in the product from the zeolite adsorbent was relatively high. Therefore, active carbon was preferable to zeolite in this case. Although there was no correlation between qCH4 and the total pore volume or BET surface area of the adsorbent, qCH4 strongly depended upon the number of very small pores, e.g. below 8 Å diameter. Such an ultra small pore was quantified by applying the Horvath-Kawazoe isotherm in the low region of N2 partial pressure between 0.00001 and 0.003 atm. As an application of this correlation, the optimal preparation conditions of the active carbon derived from coconut shell were established as temperature (900°C) versus time (20 min). This gave the highest performance of qCH4 as 24.9 ml per ml-Ad among tested adsorbents. 
methane adsorption; active carbon; micropores