Benzene reduction in a fuels refinery: An unconventional approach

The benzene content of motor-gasoline is regulated by fuel specifications that are becoming increasingly stringent. Acid catalyzed alkylation of benzene by olefins in commonly found refinery units was explored as a low cost benzene reduction strategy. Cofeeding benzene to aliphatic alkylation, etherification, and olefin oligomerization processes were evaluated. Benzene can be alkylated in a sulfuric acid-based aliphatic alkylation unit at 5 degrees C, but significant disruption of the aliphatic alkylation reaction occurs if the feed contains more than 3% benzene. No benzene alkylation was found during reaction at 90 degrees C in an acidic resin based etherification process, since the alcohol is the proton carrier. When the same process was operated as an olefin oligomerization process (no alcohol in feed), alkylation proceeded. Benzene was also successfully alkylated during H-ZSM-5 based oligomerization (180-280 degrees C, 4 MPa), but the pore constrained geometry of the zeolite resulted in < 5 % alkylation selectivity with a hexene feed. Catalysts with a more open pore structure should rather be considered for the industrial application of benzene alkylation in an oligomerization process. Alkylation of benzene by cofeeding it to a solid phosphoric acid catalyzed oligomerization process (220 degrees C, 3.8 MPa, and benzene to olefin ratio in the range 1:6 - 6:1) was successful.