Issue 3, 2014

Hydrothermal catalytic processing of saturated and unsaturated fatty acids to hydrocarbons with glycerol for in situ hydrogen production

Abstract

Lipids are a promising feedstock to produce renewable hydrocarbon fuels and H2via catalytic hydrothermal processing. Upon exposure to hydrothermal media (e.g., 300 °C, 8–11 MPa), lipids rapidly hydrolyze to produce saturated and unsaturated free fatty acids in varying ratios, depending on the feedstock, as well as glycerol. This report demonstrates the potential of Pt–Re/C for the hydrothermal conversion of saturated and unsaturated fatty acids to hydrocarbons, using glycerol reforming for in situ H2 production to meet process demands. Experiments showed that deoxygenation of stearic acid, a model saturated fatty acid, was significantly enhanced with Pt–Re/C under a reducing atmosphere compared to Pt/C. The coupled hydrogenation and deoxygenation (HYD–DOX) of oleic aid, a model unsaturated fatty acid, was also moderately enhanced under an inert atmosphere using glycerol for in situ H2 production, with DOX as the rate-limiting step. Characterization of Pt–Re/C showed that Re had a significant effect on CO : H uptake ratio (2.2) compared to commercial Pt/C (1.3), with the metals dispersed as small crystallites (∼3–4 nm) throughout carbon support. Experiments revealed that the initial system H2 headspace loading <3.45 MPa greatly enhances fatty acid DOX kinetics via decarboxylation/decarbonylation without net H2 consumption. At higher initial H2 loadings (≥3.45 MPa), fatty acid reduction was also observed as a minor DOX pathway. Experiments also showed that oleic acid HYD–DOX and glycerol reforming are affected by initial glycerol concentration and catalyst loading. Under optimized process conditions, complete HYD–DOX of oleic acid to heptadecane was achieved within 2 h with a net-zero H2 consumption using a 1 : 3 glycerol-to-fatty acid ratio (i.e., the native ratio in triacylglycerides). X-ray photoelectron spectroscopy showed that H2 in the reactor headspace results in lower oxidation states of Pt and Re, suggesting a possible mechanism for enhanced DOX kinetics. This approach holds promise for overcoming the high external H2 demands of conventional lipid hydrotreatment processes.

Graphical abstract: Hydrothermal catalytic processing of saturated and unsaturated fatty acids to hydrocarbons with glycerol for in situ hydrogen production

Article information

Article type
Paper
Submitted
31 Aug 2013
Accepted
19 Dec 2013
First published
03 Jan 2014

Green Chem., 2014,16, 1507-1520

Hydrothermal catalytic processing of saturated and unsaturated fatty acids to hydrocarbons with glycerol for in situ hydrogen production

D. R. Vardon, B. K. Sharma, H. Jaramillo, D. Kim, J. K. Choe, P. N. Ciesielski and T. J. Strathmann, Green Chem., 2014, 16, 1507 DOI: 10.1039/C3GC41798K

To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page.

If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given.

If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page.

Read more about how to correctly acknowledge RSC content.

Social activity

Spotlight

Advertisements