water in liquid state. Recently, the application of SCW for biomass and carbohydrate hydrolysis has demonstrated its potential in the production of useful compounds. One advantage of using SCW
is that at higher temperature, water dissociates into hydrogen and hydroxide ions, which makes it an effective catalyst for hydrolysis or biodegradation reactions. This property has also played a great role in increasing the extractable neutral lipids from activated sludge for biodiesel preparation.
In our previous work, a two-step biodiesel production process has been introduced by using subcritical water pretreatment of Yarrowia lipolytica Po1g biomass followed by acid catalyzed transesterification of the neutral lipids. The study showed that subcritical water pretreatment
of the biomass showed a two-fold increment in the extractable amount of neutral lipids which led to an increase in the amount of fatty acid methyl esters (FAMEs). However, this two-step process needed prior pretreatment of biomass and acid catalysis, which is costly and environmentally unfriendly. Therefore, in another previous work of ours, a novel method was proposed for biodiesel production from refined soybean oil without the need of conventional catalyst such as potassium hydroxide and sulfuric acid. It was found that in the presence of a very small amount of water (~5% based on soybean weight), biodiesel can be produced by reacting methanol with refined soybean oil under subcritical condition and high biodiesel conversion (96.4%) had been achieved in a reasonable short time.
In the present work, a single step, catalyst free and in situ method was introduced for FAME synthesis from yeast biomass using water and methanol under subcritical conditions. To the best of our knowledge, there is no report on the study of FAME preparation from Yarrowia lipolytica Po1g biomass using subcritical water and methanol in situ. The objective of this work was to investigate the possibility of acid or base free FAME production from wet Y. lipolytica Po1g biomass (moisture content ~80%) using methanol under subcritical condition without prior biomass pretreatment. The effects of process variables on FAME yield were systematically investigated.