BACKGROUND Styrene is a volatile organic compound used extensively worldwide. It is known to cause serious adverse effects on human health and the environment. The main limitation in the biological treatment of styrene is its low solubility. An alternative is the use of partitioning bioreactors (TPPB) which can improve mass transfer of styrene by addition of a hydrophobic non‐aqueous phase (NAP). This study explored silicone oil and an ionic liquid as NAPs in a TPPB to degrade styrene vapors using Pseudomonas putida S12. Lastly, the production of polyhydroxyalkanoates (PHA) was evaluated. RESULTS The NAPs were characterized in terms of biodegradability, toxicity and styrene partition coefficient (H). Results showed that styrene was 7.5 times more absorbed by the ionic liquid/aqueous phase mixture (H = 0.0035) than by the silicone oil/aqueous phase mixture (H = 0.0179) at 28 °C. Silicone oil and ionic liquid were non‐biodegradable by P. putida S12. However, the ionic liquid was inhibitory and toxic for P. putida S12 in contrast to silicone oil. Thus, the selected phase for the TPPB process was silicone oil. Silicone oil assays reached a 98% styrene removal efficiency faster (4 h) than the control (8 h). This finding was reflected in a faster production of the same amount of PHA in the presence of silicone oil. CONCLUSIONS The production of PHA was enhanced by the addition of silicone oil at 5% (v/v) in a TPPB batch process treating styrene vapors. © 2021 Society of Chemical Industry (SCI).