My preferred route, and what I have done in the lab many times, is hydrothermal liquefaction. If you take the biomass up to supercritical or near supercritical temperatures, you get liquids. Exactly which liquids you get is critically dependent on how you do it, including the rate of heating. Ideally you want to do it in a continuous reactor, which is essentially a heated tube, but this requires some engineering skill. Depending on the biomass you can make petrol, diesel and aviation fuel. all meeting excellent specifications. This works on the lab scale, but again to take it furether you need engineering. Of course, it is possible. In Germany during WW II the Bergius process made millions of tonnes of fuel from lignite.

I would second Ian's answer - only to add that most biofuels inherently become liquid (or gas depending on process selectivity) upon heating - even if it is far below supercritical.

Biofuel is by definition a VOC - heat it up, it brings its own liquid.

Unless you are talking about digestion (fermentation) - then just use water.

Unless yeast likes acetone? MEK? Hexane? (that's a joke).