Abstract: The invention relates to a method to reduce the formation of high molecular weight compounds and catalyst coking in the production of renewable diesel. Renewable diesel is produced using hydrogenation, decarboxylation, decarbonylation, and/or hydrodeoxygenation of renewable feedstocks such as animal and/or plant fats, oils, and/or greases (FOG). By first reacting the most reactive species in the FOG in an initial reaction zone prior to the main reaction zone, maximum reaction temperatures and side reactions that lead to the formation of high molecular weight compounds are reduced. This reduces catalyst coking (extends catalyst life) and improves product quality.