Although overall there is a decrease in N content, the extent to which this takes place is opposite to that of O depending on the reaction condition. For instance at 30 s RT for all temperatures, the O removal is noticed to improve but the amount of denitrogenation decreases. This trait is generally observed at all reaction conditions. The elemental N content tends to reach a stable concentration level after which there is no change in its wt.% thus, elucidating that nitrogen containing compounds are stable under hydrothermal conditions. Faeth et al. (2013) and Garcia Alba et al. (2011) had a similar trend in their HTL biocrude and it Ramelteon is understood that the change is procured by increasing temperature. Hence, this work demonstrates that denitrogenation can be achieved rapidly (in seconds) eliminating the need for more severe reaction conditions.
The van Krevelen plot, originally introduced to represent a graphical relationship between C, H and O ratio in coal processing is used to show the O:C, H:C and N:C atomic ratio of the produced biocrude. As seen from plot Fig. 3a and b, basal body is obvious that there is O and N removal after fast (HTL) of microalgae. The biocrudes produced in this study are concentrated approximately around H:C ratio of 1.6 and an O:C ratio of 0.15. There is a slight increase in deoxygenation at longer RT, but when compared to previous batch reactor HTL study (Patel and Hellgardt, 2013), it is deduced that longer operating time does not significantly improve aforementioned ratios. Based on current HTL studies, algal biocrude produced in this investigation contains the lowest O:C ratio using a continuous flow reactor at short contact time. Biocrude produced in this investigation contains marginally lower O than that from the pilot scale HTL study by Jazrawi et al. (2013).