Benzene Reduction in a Fuels Refinery: An Unconventional Approach

Abstract

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 °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 °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 °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 °C, 3.8 MPa, and benzene to olefin ratio in the range 1:6-6:1) was successful.

Refining Technology Selection

“…This serves as an introduction to the chapters that describe selected conversion processes important to high-temperature Fischer-Tropsch (HTFT) and low-temperature Fischer-Tropsch (LTFT) refining in more detail (Chapters [17][18][19][20][21][22][23]. This serves as an introduction to the chapters that describe selected conversion processes important to high-temperature Fischer-Tropsch (HTFT) and low-temperature Fischer-Tropsch (LTFT) refining in more detail (Chapters [17][18][19][20][21][22][23].…”

“…This is a very important hydrotreating function in Fischer-Tropsch refining (Section 16.2.1). The HDA of benzene is one way of dealing with refinery benzene, but is not preferred when alternatives exist [22,23]. The polynuclear aromatic content of LTFT and HTFT material is well below diesel fuel specifications (Table 15.4), and deep HDA to remove such compounds is not important in Fischer-Tropsch refining.…”

Catalysis in the Refining of Fischer–Tropsch Syncrude

“…Of the technologies for refinery benzene reduction, benzene alkylation has the advantage that it retains the octane value of benzene in the final motor gasoline. 30,31 There are various commercial processes for the acid-catalysed alkylation of benzene with either ethylene or propylene. The catalysts most often used are solid phosphoric acid (SPA) and zeolite-type materials such as H-ZSM-5 (Mobil-Badger), H-MCM-22 (Mobil-Ratheon/Mobil-Badger), HY-zeolite (CDTech) and modified H-Beta-zeolite (Enichem).…”

Oligomerization

“…Straight-run Fischer-Tropsch syncrude is lean in isobutene, and isobutene dimerization should typically be considered in conjunction with another refining technology that produces isobutene, such as skeletal isomerization (Chapter 18) or catalytic cracking (Chapter 21). 10) Refinery benzene reduction can be accomplished by co-feeding the benzene with alkenes to an appropriate acid-catalyzed refinery process, of which oligomerization has been shown to be the most suitable [15]. This technology is well matched to Fischer-Tropsch syncrude, because it does not require isobutene.…”