All the bio-oils were produced either in batch or continuous microwave assisted pyrolysis (MAP) processes at the University of Minnesota (Figure 1). About 250 g samples were put in a 1000 mL quartz flask, which in turn was placed inside the microwave cavity (Panasonic NN-SD797S). The power level was set at 8 (the output power is about 1000 W). After the sample was microwaved for around 12 minutes, the volatile pyrolyzates were condensed with cool water at temperature of around 4-5 °C. The fraction collected from bottles connected to the bottom of the condensers was termed as the bio-oil. The condensates adhering to the interior wall of the tubes were then washed with ethanol and concentrated at 80°C using a vacuum rotovap (Buchi R-141, Flawil, Switzerland) to a near constant weight, and the concentrate was added to the bio-oil.

As mentioned earlier aspen, canola, and corn cob were the feedstocks selected for the bio-oil production. Aspen pellets were used for the production of bio-oil in a batch MAP process. Canola compost pellets were also used in a batch MAP process. All corn cobs were ground to less than 1 cm in size before MAP. Corn cob 1 and corn cob 2 bio-oils were produced using a continuous MAP, where heavy fractions of the bio-oil were not collected. Corn cob 3 bio-oil was produced using a batch MAP, where heavy fractions of the bio-oil were collected. Corn cob 4 was the bio-oil produced in a batch MAP of corn cob pretreated with 4% sulfuric acid; the bio-oil contained more water and furfural than other bio-oil samples. Fig. 2 shows bio-oils from different feedstocks produced through MAP. Heavy fractions of

the bio-oils were collected for all batch processes. The bio-oil separated into two phases: about top one-third of the bio-oil was in oily phase and the bottom two-thirds were in aqueous phase. The oily phase is a relatively stable, light emulsion containing water soluble chemicals and light oily components; whereas the aqueous phase is a large molecule oily mixture characterized by high viscosity and water insolubles (Yang et al., 2010). The aqueous phase yield varied between batch (aspen and canola >60%) and continuous (corn cobs 10-20%) production. The aqueous phase yield of corn cobs were in agreement with corn stover (Yang et al., 2010).