ABI Research forecasts autonomous parking technology revenues to grow by 29.5% CAGR within next decade
2017 Chrysler Pacifica minivan EPA-rated at 28 mpg highway, 22 mpg combined; stop/start and PHEV still to come

New highly selective catalytic process for conversion of vegetable oils to diesel-range alkanes under mild conditions

A team led by researchers from the University of Oxford has developed a simple but highly selective catalytic process for the direct hydrodeoxygenation of vegetable oils (triglycerides) into diesel-range alkanes under mild conditions over a Pd/NbOPO4 catalyst. As reported in their paper in the RSC journal Chemical Communications The mass yields of diesel-range alkanes from palm oil and soybean oil can approach to quantitative values.

A number of approaches are being developed and commercialized to convert vegetable oils into diesel fuels. The current primary commercial pathway is the production of first-generation biodiesel—the transesterification of triglycerides with methanol to form fatty acid methyl ester (FAME), with glycerol as the by-product.

FAME has several drawbacks, including high viscosity and poor calorific value, while the by-product glycerol has low commercial demand and is creating environmental problems.

Another alternative is the catalytic cracking of triglycerides over zeolites such as HZSM-5 to produce gasoline- and diesel-range fuel. This approach has low selectivity, however.

The hydrotreating of triglycerides at high temperature over supported metal sulfide catalysts such as NiMo and CoMo sulfide is selective and existing infrastructure and application experience from the petroleum industry can be used. However, the leaching of sulfur from the sulfide catalysts is an issue at high temperature—;leading inevitably to product contamination and catalyst deactivation.

An alternative approach—decarboxylation and/or decarbonylation of carboxylic acids at high temperature over non-sulfide catalysts—shows low activities towards triglycerides conversion.

Hydrodeoxygenation of triglycerides over metal supported on acidic zeolites (H-beta, H-ZSM-5) as bi-functional catalysts produces diesel-range alkanes as high-grade transportation fuels. However, rapid carbon deposition in the zeolitic cavity leads to catalyst deactivation. A Nb2O5-modified Pd/SiO2 has been reported to be active for the total hydrodeoxygenation of fatty acid and triglycerides, but the detailed mechanism remains to be studied.

Herein, we report that a simple methodology for the direct hydrodeoxygenation of vegetable oils over Pd/NbOPO4 catalyst under mild conditions (180 ˚C, 30 bar). Total conversions with near quantitative yields for alkane formation from triglycerides can be obtained over this efficient catalyst. The low reaction temperature preserves C-C bond cleavage, giving >96% corresponding n-alkane selectivity from fatty acid and propane from glycerol moieties.

Catalyst characterization suggests that the glassy nature of NbOPO4 phase can loss its lattice oxygen in H2 readily at mild temperature to expose strong Lewis acid Nb5+ sites hence generating oxygen deficient phase with a high propensity for the adsorption of [O] from triglyceride. In combination with active hydrogen spilled from Pd surface, a highly efficient cooperative catalysis for direct hydrodeoxygenation reaction of triglyceride can be achieved.

—Tsang et al.

Resources

  • E. Tsang, Q. Xia, X. Zhuang, M. M. Li, Y. Peng, G. Liu, T. Wu, Y. L. Soo, X. Gong and Y. Wang (2016) “Cooperative Catalysis for Direct Hydrodeoxygenation of Vegetable Oils into Diesel-range Alkanes over Pd/NbOPO4Chem. Commun. doi: 10.1039/C5CC10419J

Comments

Alain

Very nice, but palm oil is the worst source for fuel immaginable. Compared to that, coal is much more responsible.

SJC

It does not have to be only palm oil any triglyceride will do.

ai_vin

Conversion of vegetable oils to diesel-range alkanes is needed for most road-going diesels because they have been tuned to run on what we now call diesel fuel. But when Rudolf Diesel invented his engine it ran on straight vegetable oils. Even today there are applications where we could use unconverted vegetable oils, like in shipping. Marine diesels are designed to run on cr@p, literally the bottom of the barrel stuff from the refinery. They could even run on the waste glycerol from this process.

SJC

Neste renewable diesel is a bio synthetic that can run 100%.

Engineer-Poet

If you're going to hydrodeoxygenate stuff and you've got glycerine, turn it into propane.  There's no sense in spending the fixed carbon on anything less energetic.

Back to converting fatty acids to alkanes, I would still like to see an accounting of the size of the resource.  IIRC the consumption of vegetable oils in the USA is on the order of 2 billion gallons per year, perhaps 7% of diesel consumption.  "Waste" vegetable oils have other uses such as animal feed.  It doesn't seem likely that there's very much potential fuel without getting into issues of source-shifting elsewhere and the consequent indirect land-use changes.

ai_vin

If you're going to hydrodeoxygenate stuff and you've got glycerine, turn it into propane. There's no sense in spending the fixed carbon on anything less energetic.

Good point. In fact, when producing biogas and exporting it to the natural gas grid, the Wobbe index and heating value does not match the existing natural gas, even after upgrading, (particularly in regions where natural gas has a high calorific value such as Sweden) so propane has to be added. It would be better if this was bio-propane rather than fossil propane.

The comments to this entry are closed.