Two-column relay simulated moving-bed process for gas-phase separations

- A 2-column relay-SMB process was implemented for binary gas-phase separation.
- The separation of an isothermal binary trace system was studied.
- The process was designed to obtain 99% of purity in both extract and raffinate.
- Performance at low feed throughput similar to 4-zone SMB and Varicol configurations.

A new two-column, relay, simulated moving-bed (2-column R-SMB) process has been designed and implemented experimentally for the first time for gas-phase separation. Contrary to classical SMB configurations, in a R-SMB process the stream exiting a column is never partially withdrawn from the system, i.e., it is not divided into an outlet stream and a stream that is redirected to another column; instead, the stream exiting a column is handled in a relay mode: at any instant of the cycle the stream is either fully collected as product/waste or completely diverted to another column. In the present work the R-SMB concept is applied to the simplest case of separation of an isothermal, binary trace gas mixture. The separation of carbon dioxide (CO2)/methane (CH4) mixtures using nitrogen (N2) as carrier gas is evaluated as a proof-of-concept. The process is designed and optimized by model-based computer simulation and the obtained results are validated experimentally at laboratory-scale using a newly designed two-column SMB unit. The optimized 2-column R-SMB process produces extract and raffinate products both with 99%-purity (in an eluent free basis). The 2-column R-SMB performance is compared with the classical four-zone SMB and VARICOL-type configurations, and it is shown that at low feed throughput the process performances are coincident.

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