Direct upgrading of biogas produced by anaerobic digestion: preliminary results at laboratory scale

The present study investigated, at laboratory scale, the possibility of achieving biogas upgrading with a single step of treatment, namely without involving any pre- or post-treatment or multiple stage recirculation. In this respect, three commercial molecular sieves (i.e., Honeywell 13X, 4A, and 5A) have been tested according two different configurations in series (4A/13X and 4A/5A) in 25/75 v/v relative amounts. A control trap containing only the 4A molecular sieve using the same amount of the in series configurations has also been used. Real biogas feed directly from the production reactors at atmosphere pressure has been used in the experiments. 4A sample resulted highly efficient in biogas upgrading (CO2 retention rate of 42.4 gCO2/kg, equivalent to 0.96 mmolCO2/g) but its activity was limited to 18 days while by increasing the material amount and combining different types of molecular sieves in series, performance increased. The possibility to regenerate and reuse the sieves was also proven although preliminary.