Optimization and analysis of a VPSA process for N2/CH4 separation

One-Step Preparation of Activated Carbon for Coal Bed Methane Separation/Storage and Its Methane Adsorption Characteristics

Different coals were used as raw material for the preparation of carbonization precursors and coal-based activated carbons. The physicochemical structure and adsorption performance of the samples were tested. Results show that the carbonization and activation process greatly changed the molecular structure of raw coal, and a large number of organic functional groups disappeared. The carbonization process has enriched the pore structure of coal by thermal ablation, and it has a pore expansion effect on all the pores in coal, while the activation process is more conducive to micropore generation. The calculated mean isosteric heat of adsorption showed that the activated carbon needs to release more heat in the adsorption process as the same equilibrium pressure increased due to the adsorption capacity of the prepared activated carbon being far more than that of the raw coal. Adsorption processes of activated carbons are more sensitive to temperature changes, providing a certain guiding significance for the temperature swing adsorption and pressure swing adsorption.

Efficient screening of novel adsorbents for coalbed methane recovery

Many adsorbents with outstanding methane (CH₄)/nitrogen (N₂) separation performance are reported recently. Some may have the potential for coalbed methane (CBM) recovery to resolve the current energy crisis. However, no systematic assessment method for evaluating these adsorbents is available. This study was performed for efficient comparison and assessment of 47 novel adsorbents that are suitable for CBM recovery and to guide further adsorbent development with a three-step simulation-based method. First, the adsorbents of interest were prescreened based on the CH₄/N₂ adsorption selectivity predicted from the ideal adsorption solution theory and a composite parameter S that incorporates both adsorption selectivity and working capacity. Then, the top 10 adsorbents from the prescreening step were tested in a simulated vacuum pressure swing adsorption process. The process performance of the adsorbents was evaluated by comparing their product purity, recovery and productivity at two base conditions. It was observed that Cu-MOF and NAPC-3-6 exhibited the highest product purity and OAC-1 showed the highest product recovery and productivity at the two base cases. The process performance indicators of various adsorbents were also correlated with their adsorption selectivities and capacities to investigate how these adsorption characteristics would affect the process performance. We find that the working capacities of the adsorbents are highly related with the product recovery while the adsorption selectivities are more related with the product purity. Finally, a process optimization study was performed employing the three adsorbents that exhibited the best performance in the previous evaluation. The objective of the optimization is to minimize the energy consumption of the process while meeting specified product purity (95% or 98%) and recovery rate (90%). The decision variables include the evacuation pressure, feed flow rate and adsorption pressure. The sensitivity of each variable was also examined through a parametric study. The optimization results indicate that the adsorbent selection will depend on the production scale and purity requirement. OAC-1 is the best candidate for a large scale CH₄ production with a regular purity grade while NAPC-3-6 is a better choice for a small scale CH₄ production with high purity requirement.

Adsorption separation of CO from syngas with CuCl@AC adsorbent by a VPSA process

In this work, activated carbon (AC) supported CuCl (CuCl@AC) prepared with CuCl₂ as precursor is investigated for CO separation from the synthesis gas mixture. Firstly, the CuCl@AC adsorbents are investigated for their CO reversible adsorption capacity at an operation temperature of 303 K. And a vacuum pressure swing adsorption (VPSA) process of CO separation from syngas utilizing the prepared CuCl@AC adsorbent is investigated at ambient temperature and 0.79 MPa through a dynamic optimization with Aspen Adsorption software. The integrated model is closer to a realistic PSA process, making the results of the simulation and optimization more convincing. The adsorption result reveals that the obtained CuCl@AC adsorbent with the copper loading of 7 mmol g⁻¹ AC achieves a high reversible CO adsorption capacity and adsorption selectivity. The simulation result shows that, under optimal conditions, the CO product with the purity of 98.1 vol% can be separated from the syngas with the CO concentration of 32.3 vol% utilizing the prepared CuCl@AC adsorbent, and the recovery of CO is 92.9%.

High purity CO was obtained from syngas with low CO concentration utilizing CuCl@AC adsorbent by VPSA process at ambient temperature.