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

Abstract

ACCEPTED MANUSCRIPT When citing this work, please refer to the final version published in "Biomass and Bioenergy" (Elsevier), which is available through the following bibliographic details:M.S. Haider, D. Castello, L.A. Rosendahl, Two-stage catalytic hydrotreatment of highly nitrogenous biocrude from continuous hydrothermal liquefaction: A rational design of the stabilization stage.Abstract: Effective catalytic hydrotreatment of highly nitrogenous biocrudes derived from the hydrothermal liquefaction (HTL) of primary sewage sludge and microalga Spirulina biomass was explored. A critical issue is the lack of thermal stability of raw HTL biocrudes at the severe conditions (~400 °C) required for hydrodenitrogenation. This fact suggests the need for a two-stage approach, involving a first low-temperature stabilization stage followed by another one operated at higher temperature. In this study, DSC was successfully used to indicate the thermal stability of both biocrudes. During hydrotreating, it was observed that complete deoxygenation was already achieved in the first stage at 350 °C, with limited coke formation.Moreover, after second stage up to 92% denitrogenation associated with the higher hydrogen consumption (39.9 g kg -1 for Spirulina and 36.9 g kg -1 for sewage sludge) was obtained for both biocrudes. Consequently, comparable oil yields but significantly less coke yields were recorded during two-stage upgrading (1.0% for Spirulina and 0.7% for sewage sludge), compared to direct processing at 400 °C (9.1% for Spirulina and 3.4% for sewage sludge). In addition, the properties of the upgraded oils were enhanced by increasing the temperature in the first stage (310 °C, 330 °C and 350 °C respectively). Finally, the results indicated that remarkable drop-in fuel properties were obtained, with respect to heteroatom (O and N) removal, HHV, and H/C ratio during the two-stage hydrotreatment. Two-stage hydrotreating is therefore proposed as a successful approach for the upgrading of HTL biocrudes with high nitrogen content.

An In-Depth Process Model for Fuel Production via Hydrothermal Liquefaction and Catalytic Hydrotreating

“…The heavy diesel fraction still contains a considerable amount while vacuum gas oil (VGO) and residue fractions only play a minor role. These results are somewhat different to those reported in literature [50,51]. The gasoline fraction is almost half of the herein reported amount, while the VGO and residue fraction contain significantly more upgraded biocrude.…”

“…The high amount of aromatics in the upgraded biocrude of wheat straw originates to a major extent from the high amount of carbohydrates and to a minor extent from the lignin present in the feedstock. Generally, these results are in good agreement with literature [49][50][51]. For batch-hydrotreating experiments, Haider et al [51] and Castello et al [50] both report amounts of n-paraffins of over 50% for microalgae, which is also reflected by the model.…”

“…Generally, these results are in good agreement with literature [49][50][51]. For batch-hydrotreating experiments, Haider et al [51] and Castello et al [50] both report amounts of n-paraffins of over 50% for microalgae, which is also reflected by the model. Aromatics, O-containing compounds as well as cyclic-and isoparaffins are in the range of 5% to 10%.…”

“…In the model, the amounts of O-containing and N-containing compounds are inverted, while the amounts of cyclic-paraffins and aromatics are slightly overestimated compared to these literature results. In the case of sewage sludge, both Haider et al [51] and Castello et al [50] report amounts of n-paraffins of over 80%. Aromatics, cyclic-and iso-paraffins are below 5%, while O-containing compounds might be slightly over 5%.…”

“…Based on the results of the boiling point distribution curves, fractions for different fuel cuts can be obtained, as listed in Table 7. The fuel cuts were chosen according to Haider et al and Castello et al [50,51]. For Spirulina the gasoline fraction is most prominent, followed by the light diesel and jet fuel fraction, also containing more than 20 wt%.…”