In this work, the catalytic synthesis of alkylketenes over functionalized silica monoliths at short contact times was extended to high molecular weight products such as decylketene, hexadecylketene and 7-hexadecenylketene. The reactor was coupled with a derivatization system with methanol to obtain the corresponding esters in high yields, allowing the ketene identification. It was found that it is possible to maintain the activity that the silica catalyst has shown for the synthesis of low molecular weight ketenes, in the temperature range between 700 and 830 K, obtaining selectivities in the order of 75-90% for the decylketene and the hexadecylketene, and near to 43% for 7-hexadecenylketene. The results showed that the control of contact time is a valid strategy to increase the yield in the catalytic synthesis of high molecular weight ketenes. (C) 2008 Published by Elsevier B.V.