The novel dehydration/hydrogenation technique developed by Huber, et al. produces unbranched alkane chains.   In this technique, a sugar is modified by condensing an organic molecule on it and removing the oxygen molecules associated with the carbohydrate.   The chain length can be controlled by varying the type of starting sugar (a sugar with 5 or 6 carbons) used and the size of the molecule condensed onto the sugar.   The pathways below demonstrate how to construct alkanes of 9, 12, and 15 carbons.   Analogous pathways with a 5 carbon feedstock sugar produce alkanes of 8, 11, and 14 carbons.   The alkanes in this process retain 90% of the energy in the feedstock carbohydrate 1, making this process energy efficient.   The longer alkane chains could be used as diesel fuel.  

Huber, G.W., Chheda, J.N., Barrett, C.J., Dumesic, J.A., 2005, Science 308, 1446-1450.