AIST Researchers Devise Catalysts To Boost Yield of Renewable Diesel from Hydrotreatment of Jatropha Oil
|Effect of different catalysts with jat/cat weight ratio = 10. The platinum-rhenium catalyst showed the highest conversion, along with high selectivity for C18. Credit: ACS, Murata et al. Click to enlarge.|
Researchers at Japan’s National Institute of Advanced Industrial Science and Technology (AIST) have devised rhenium-modified catalysts that significantly increase the yield of diesel-type alkanes (C15-C18) from the hydrotreatment of jatropha oil under conditions of higher jatropha-to-catalyst weight ratios. A paper on their work was published online 10 March in the ACS journal Energy & Fuels.
The direct hydrotreatment of triglycerides (i.e., vegetable oils) to produce renewable, drop-in hydrocarbon molecules for use in liquid fuels can be performed using existing technology in petroleum refineries, where hydrotreatment is used, among other applications, to remove sulfur from petroleum feedstocks. Applied to triglycerides, hydrotreatment can produce straight chain alkanes ranging from n-C15-C18. The products have a high cetane number (above 98), compared to a petroleum diesel cetane number of around 50.
Murata et al. first explored the catalytic performance of platinum on a variety of supports for the hydrotreating of jatropha oil. They found that at temperature as low as 543 K (270 °C), a platinum catalyst on a zeolite support (Pt/H-ZSM-5) achieved approximately 100% conversion into hydrocarbons, with selectivity to C15-C18 hydrocarbons of 79.0%. This was run with a jatropha-catalyst weight ratio of 1; practical commercial production would require a higher ratio (i.e., more jatropha).
However, they found that catalytic activity into hydrocarbons was greatly affected by the jatropha oil/catalyst weight ratio (abbreviated as jat/cat ratio). At the jat/cat weight ratios of 2 and 10, the conversions into hydrocarbons were only 21.6% and 14.2%, with the C15-C18 alkane yields falling to 13.5 and 2.7%.
In these cases, white solid products of hydrogenated triglycerides were detected, ascertained by GC analysis. This indicates that at a high jat/cat ratio, unsaturated triglycerides would only convert to saturated structure without any decarboxylation, decarbonylation, and hydrodeoxygenation. Thus, from a practical point of view, a modified catalyst active even at the jat/cat weight ratios of 10 has to be explored.
—Murata et al.
To improve the Pt/H-ZSM-5 catalyst, the researchers prepared rhenium-modified catalysts; Pt-Re-based catalysts are known to be effective for naptha reforming and other processes. At 20 wt % Re, the conversion into hydrocarbons was found to be constant at ~80% at any jat/cat ratio employed, with high selectivity for C18. They also found that Pd-modified Re/H-ZSM-5 catalysts are excellent candidates for triglyceride conversion as well.
Rhenium-modified Pt/H-ZSM-5 catalysts were found to be much more effective for hydrotreating jatropha oil even at a high jat/cat ratio of 10, and 80% conversion and 70% C18 selectivity were achieved. The reaction pathway involves hydrogenation of the C=C bonds of the these triglycerides followed by mainly C15-C18 alkane production through hydrodeoxygenation with decarbonylation and decarboxylation.
—Murata et al.
Kazuhisa Murata, Yanyong Liu, Megumu Inaba and Isao Takahara (2010) Production of Synthetic Diesel by Hydrotreatment of Jatropha Oils Using Pt-Re/H-ZSM-5 Catalyst. Energy Fuels, Article ASAP doi: 10.1021/ef901607t