Cryogenic air separation processes are widely used for the large-scale production of nitrogen and oxygen. The most widely used design for this process involves two distillation columns operating at different pressures. This work focuses on the selection of suitable cryogenic air separation process by evaluating seven alternative designs of the two-column air separation process based on detailed exergy analysis. The feed conditions (500 tons/h, and 50% relative humidity of air), product purities (99 mole% for both nitrogen and oxygen), and operational conditions (pressures of both distillation columns) are kept same in all designs. The two cryogenic distillation columns in each configuration are heat-integrated to eliminate the need for external utilities. Steady-state simulation results are used to calculate the exergy efficiency (%) of each equipment as well as its contribution toward the overall exergy destruction rate (kW) of the process. The results show that the compression section is a major source of exergy destruction, followed by the low-pressure column, and the multi-stream heat exchanger. A Petlyuk-like configuration, labeled as C1, provides the lowest exergy destruction rate.

The utilization of agricultural biomass for the synthesis of carbonaceous adsorbents is an active research topic because of a wide range of precursors and good adsorption properties of the resulting adsorbent materials. Rubber-seed shell (RSS) is a suitable precursor for the synthesis of activated carbon (AC) due to its naturally high carbon content. In addition, it is available in large quantities due to the growing rubber plantations in Malaysia. In this work, activated carbon is produced via chemical activation of RSS for CO₂ adsorption. A two-step and a modified three-step activation method using K₂CO₃ as an activating agent are used for the preparation of RSS-derived AC. AC samples prepared by both techniques are compared based on structural properties and CO₂ adsorption capacity to identify the more effective synthesis method. Carbon content increased from 48.40 wt.% in the untreated RSS to >77 wt.% in prepared AC samples, indicating successful activation. BET surface area for AC2 and AC3 was 474.7 m²/g and 683.4 m²/g, respectively. The highest CO₂ adsorption capacity of 60.06 mg/g at 25 °C was obtained for AC3. Overall, AC produced by the three-step activation has superior structural properties and CO₂ adsorption performance.