Abstract
While commercial hydrodeoxygenation (HDO) processes convert fats, oils, and grease (FOG) to fuel-like hydrocarbons, alternative processes based on decarboxylation/decarbonylation (deCOx) continue to attract interest. In this contribution, the activity of 20% Ni-5% Cu/Al2O3 in the deCOx of waste free fatty acid (FFA)-based feeds—including brown grease (BG) and an FFA feed obtained by steam stripping a biodiesel feedstock—was investigated, along with the structure-activity relationships responsible for Ni promotion by Cu and the structural evolution of catalysts during use and regeneration. In eight-hour experiments, near quantitative conversion of the aforementioned feeds to diesel-like hydrocarbons was achieved. Moreover, yields of diesel-like hydrocarbons in excess of 80% were obtained at all reaction times during a BG upgrading experiment lasting 100 h, after which the catalyst was successfully regenerated in situ and found to display improved performance during a second 100 h cycle. Insights into this improved performance were obtained through characterization of the fresh and spent catalyst, which indicated that metal particle sintering, alloying of Ni with Cu, and particle enrichment with Cu occur during reaction and/or catalyst regeneration.
Highlights
Due to the interest in renewable fuels resulting from environmental and sustainability concerns and the high fuel demand of the transportation sector, biofuel production requires multiple feed sources
This is concerning since the majority of waste streams in general—and brown grease (BG) in particular—predominately consist of fatty acids
The composition of the free fatty acid (FFA) feed obtained by steam stripping a biodiesel feedstock—as determined by simulated distillation GC-MS—is shown in Appendix A within Table A1
Summary
Due to the interest in renewable fuels resulting from environmental and sustainability concerns and the high fuel demand of the transportation sector, biofuel production requires multiple feed sources. Alternative processes are needed to valorize BG and other fatty acid-based feeds, including the FFA waste streams of the biodiesel industry. The catalytic deoxygenation of some FOG waste streams to fuel-like hydrocarbons has been reported [11,12,13,14], mostly over noble metal catalysts whose cost can be industrially prohibitive. Most realistic feeds employed in deoxygenation studies are mostly triglycerides, which is significant since carboxylic acids are less active towards deoxygenation than esters [15] This is concerning since the majority of waste streams in general—and BG in particular—predominately consist of fatty acids. Catalysts considered for this process must be able to convert FFA feeds if they are to avoid the feed-related limitations of biodiesel production Another complication of waste streams is the high degree of unsaturation that can exist. Knowledge, this represents the first report in which non-sulfided Ni catalysts have been tested under the aforementioned conditions and allowed to reach steady state, as well as the first assessment of catalyst stability and amenability to online regeneration
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