Catalytic Hydrotreatment of Microalgae Biocrude from Continuous Hydrothermal Liquefaction: Heteroatom Removal and Their Distribution in Distillation Cuts

Abstract

To obtain drop-in fuel properties from 3rd generation biomass, we herein report the catalytic hydrotreatment of microalgae biocrude, produced from hydrothermal liquefaction (HTL) of Spirulina. Our contribution focuses on the effect of temperature, initial H2 pressure, and residence time on the removal of heteroatoms (O and N) in a batch hydrotreating setup. In contrast to common experimental protocols for hydrotreating at batch scale, we devised a set of two-level factorial experiments and studied the most influential parameters affecting the removal of heteroatoms. It was found that up to 350 °C, the degree of deoxygenation (de-O) is mainly driven by temperature, whereas the degree of denitrogenation (de-N) also relies on initial H2 pressure and temperature-pressure interaction. Based on this, complete deoxygenation was obtained at mild operating conditions (350 °C), reaching a concurrent 47% denitrogenation. Moreover, three optimized experiments are reported with 100% removal of oxygen. In addition, the analysis by GC-MS and Sim-Dis gives insight to the fuel quality. The distribution of heteroatom N in lower (<340 °C) and higher (>340 °C) fractional cuts is studied by a fractional distillation unit following ASTM D-1160. Final results show that 63–68% of nitrogen is concentrated in higher fractional cuts.

Feedstock-Dependent Phosphate Recovery in a Pilot-Scale Hydrothermal Liquefaction Bio-Crude Production

“…Table 1 illustrates the difference between PSS and SPR in terms of composition. The ash content, which reflected the inorganic matter of SPR (5.8 wt%), was similar to those reported by other studies [22,38,44,45] and significantly lower than the ash content of PSS (19.3 wt%). Its value in the literature ranged from 7.5 wt% [14,15] to over 30 wt% [46,47].…”

Two-stage catalytic hydrotreatment of highly nitrogenous biocrude from continuous hydrothermal liquefaction: A rational design of the stabilization stage

“…On the other hand, results from elemental analysis ( Table 2) clearly show that nitrogen is still present in all samples. This corroborates the conclusion that the remaining nitrogen-containing compounds are actually found in the higher boiling point fractions, which are not enough volatile to be analyzed through GC-MS [19]. The absence of nitrogencontaining compounds from the volatile fraction of the upgraded oils, corresponding to range from which gasoline, jet-fuel and diesel are derived, represents a point in favor of their utilization for drop-in fuels production.…”

“…The overall results obtained from two-stage processing were compared with those of single-stage direct hydrotreatment, conducted at severe conditions (400 °C). A detailed list of test runs is reported in Table 1, where, both reaction time (4 h) and initial H 2 pressure (8 MPa) are kept constant, based on the findings from previous work by Haider et al [19].…”

“…The relation between denitrogenation and hydrogenation can be better understood by means of a modified van Krevelen plot in terms of H/C and N/C atomic ratios [19,48]. From Figure 5, it is clear that temperature has a significant effect on both nitrogen removal and the reduction of the aromatic content (especially in Spirulina).…”

Catalytic upgrading of hydrothermal liquefaction biocrudes: Different challenges for different feedstocks

“…It can be hypothesized that such compounds are mostly present in higher boiling point fractions, thus not being detectable via GC-MS. This assumption has been recently proved by our group for algal biocrudes [34], but its validity to sewage sludge still needs to be confirmed. The severity of the hydrotreating conditions has a strong impact in selecting the upgrading pathways.…”