Catalytic Conversion of Free Fatty Acids to Bio-Based Aromatics: A Model Investigation Using Oleic Acid and an H-ZSM-5/Al₂O₃ Catalyst

Abstract

The catalytic conversion of oleic acid to aromatics (benzene, toluene, and xylenes, BTX) over a granular H-ZSM-5/Al2O3 catalyst (ϕ 1.2–1.8 mm, 10 g loading) was investigated in a continuous bench-scale fixed-bed reactor (10 g oleic acid h–1). A peak carbon yield of aromatics of 27.4% was obtained at a catalyst bed temperature of 550 °C and atmospheric pressure. BTX was the major aromatics formed (peak carbon yield was 22.7%), and a total BTX production of 1000 mg g–1 catalyst was achieved within a catalyst lifetime of 6.5 h for the fresh catalyst. The catalyst was deactivated due to severe coke deposition (ca. 22.1 wt % on the catalyst). The used catalyst was reactivated by an ex situ oxidative regeneration at 680 °C in air for 12 h. The regenerated catalyst was subsequently recycled, and in total, 7 cycles of reaction-regeneration were performed. A gradual decrease in the peak carbon yield of BTX was observed with reaction-regeneration cycles (e.g., to 16.3% for the catalyst regenerated for 6 times). However, the catalyst lifetime was remarkably prolonged (e.g., >24 h), leading to a significantly enhanced total BTX production (e.g., 3000 mg g–1 catalyst in 24 h). The fresh, used, and regenerated catalysts were characterized by N2 and Ar physisorption, XRD, HR-TEM-EDX, 27Al, and 29Si MAS ssNMR, NH3-TPD, TGA, and CHN elemental analysis. Negligible changes in textural properties, crystalline structure, and framework occurred after one reaction-regeneration cycle, except for a slight decrease in acidity. However, dealumination of the H-ZSM-5 framework was observed after 7 cycles of reaction-regeneration, leading to a decrease in microporosity, crystallinity, and acidity. Apparently, these changes are not detrimental for catalyst activity, and actually, the lifetime of the catalyst increases, rationalized by considering that coke formation rates are retarded when the acidity is reduced.

Catalytic Pyrolysis of Nonedible Oils for the Production of Renewable Aromatics Using Metal-Modified HZSM-5 Catalysts

“…It is difficult to compare these yields with the literature data as large differences in reaction conditions and reactor types are applied. However, the overall yields of aromatics in this study were in the range within or even higher than those reported for canola oil, coconut oil, palm oil residue, and wasted cooking oil (30–40%) . Compared to other oils, the catalytic pyrolysis of TO produced fewer aromatics, which may be attributed to its peculiar fatty acid with three conjugated double bonds.…”

“…However, the overall yields of aromatics in this study were in the range within or even higher than those reported for canola oil, coconut oil, palm oil residue, and wasted cooking oil (30–40%). 42 Compared to other oils, the catalytic pyrolysis of TO produced fewer aromatics, which may be attributed to its peculiar fatty acid with three conjugated double bonds. It is also found that the Zn-modified catalysts can enhance the liquid product and aromatics formation compared with the parent HZSM-5 catalyst (39.28–58.43 and 36.68–50.33%, respectively).…”

Catalytic conversion of glycerol and co-feeds (fatty acids, alcohols, and alkanes) to bio-based aromatics: remarkable and unprecedented synergetic effects on catalyst performance

“…Catalyst deactivation for zeolites used for the conversion of alcohols and organic acids is typically associated with rapid coke formation in the time frame of hours 6,36 . Catalyst regeneration by coke removal using oxidative methods has proven to be well possible 6,14,27 .…”

“…5. Irreversible catalyst deactivation is reflected by a decrease in the total BTX productivity after 2 reaction-regeneration cycles for glycerol 27 and after 3 reactionregeneration cycles for oleic acid conversion 36 (Fig. 5).…”

“…The latter is of particular interest as crude glycerol may contain considerable amounts of such free fatty acids. Previous studies have shown that fatty acids and vegetable oils are good feeds for bio-BTX production, examples are the use of oleic acid 36 and glycerol blended with canola oil. 37 In total, 13 different glycerol – co-feeds at different blending ratios were tested in this study using a technical H-ZSM-5/Al 2 O 3 catalyst 27,36 in a fixed bed reactor at times on stream (TOS) between 8.5–12 h. We particularly aimed to determine synergetic effects between glycerol and the co-feed on catalyst performance including peak BTX yields, catalyst productivity, and regenerability.…”