Understanding the Upgrading of Sewage Sludge-Derived Hydrothermal Liquefaction Biocrude via Advanced Characterization

Abstract

Hydrothermal liquefaction (HTL) can thermochemically transform sewage sludge into a biocrude with high energy content, high chemical complexity, and high O and N content. The development of an efficient upgrading process for such complex feedstocks necessitates detailed knowledge of the molecular composition and the specific heteroatom-containing compounds to understand and optimize the hydrotreating reactions. In this study, we present the upgrading of sewage sludge-derived HTL biocrude via a two-stage hydrotreatment process and perform advanced chemical characterization of the feedstock, intermediate, and final upgraded products with gas chromatography–mass spectrometry (GC–MS) and Fourier transform ion cyclotron resonance mass spectrometry (FTICR–MS). We show that hydrotreatment significantly improves the quality of the oil, primarily succeeding in cracking the heavy molecules and removing the sulfur- and oxygen-containing components. FTICR–MS analysis shows that the HTL biocrude has a high concentration of fatty acid amides that readily lose their oxygen and nitrogen during hydrotreating and are converted into saturated hydrocarbons, whereas the aromatic O x N y compounds are converted into N1 and N2 classes, which are more resistant to hydrotreating. We also demonstrate that the upgraded HTL oil can be successfully blended with intermediate refinery streams, such as vacuum gas oil (VGO), for further co-processing to in-spec fuels in conventional processes. This provides an alternative route to introduce renewable carbon in existing fossil-based refineries.

Lignite and Biomass Waste Hydrothermal Liquefaction Crude Upgrading by Hydrotreatment

“…Similar product compositions of heavy compounds were observed by Jarvis et al and Heracleous et al when analyzing sewage sludge HTL crude oils via FT-ICRMS. 3,15 The significant presence of aromatic-N and aromatic-N + O compounds in HTL crudes is characteristic of the Maillard reaction between amino acids and carbohydrates of the feedstock, which are known to condense and produce highly reactive amines and ammonia and are also responsible for the transformation of fatty acids into the observed fatty amides. 28 Despite the different origins, the two sewage sludge samples showed close compositions with the main difference being a higher occurrence of aromatic-N, such as with indoles and amides in Sewage S. 2.…”

“…An alternative approach is to upgrade the HTL crude oils in two stages. The first stage, which was performed under milder conditions ( T ≈ 250 °C), aims to stabilize the crude oil, that is, eliminate highly reactive compounds, for example, aldehydes, sugars, and so on, and the second stage focuses on eliminating heteroatoms. , The effectiveness in the removal of heteroatoms either via one-stage or two-stage hydrotreatment will significantly depend on the used catalyst and, most importantly, on the nature of the compounds in the crude oil, which is tied to the HTL feedstock. Consequently, different crude oils will require different degrees of hydrotreatment severity to reach fuel specifications.…”

Direct and Two-Stage Hydrothermal Liquefaction of Chicken Manure: Impact of Reaction Parameters on Biocrude Oil Upgradation

“…Bio-oil product quality and yield depend on reaction conditions (temperature and reaction time), feedstock characteristics, and presence of a catalyst. − HTL bio-oil upgrading in conventional refineries to substitute fossil crude is hindered by its higher N and O contents. O and N are naturally present in the original feedstock and depending on the operating conditions can be transferred to bio-oil during HTL. ,, This decreases the bio-oil heating value and increases hydrogen consumption during the hydrotreating step to remove O and N. − HTC at low temperatures can partition N into the aqueous phase (AP) while retaining C in the solid hydrochar. ,, On the one hand, N in the APespecially in its inorganic form, e.g., NH 3 –N, NO 2 –N, and NO 3 –N– can be recovered as a fertilizer. , On the other hand, the C-rich hydrochar can be used as a feedstock in a subsequent HTL step to produce a bio-oil with lower N content.…”

Zirconia-Supported Pt, Pd, Rh, Ru, and Ni Catalysts in the Hydrotreatment of Fatty Amides and Amines

“…Renewable fuels enable mitigating CO 2 emissions of heavy-duty transport sectors and the aviation industry. Significant efforts have consequently been dedicated to research on the hydrotreatment of bio-based feedstocks to renewable fuels, with a focus on hydrodeoxygenation (HDO), due to the significant oxygen content of biomass. − Some renewable feedstocks, such as animal fats and biocrudes obtained via hydrothermal liquefaction (HTL) of algae and sewage sludge, contain nitrogen in addition to oxygen. − Reducing the nitrogen content of such feedstocks via hydrodenitrogenation (HDN) is important, in parallel with HDO, as nitrogen-containing compounds are known to poison catalysts in the downstream processing units and negatively impact the fuel stability . While a complete oxygen removal can be obtained in the hydrotreatment of HTL biocrudes, HDN has been found to be more challenging, with the nitrogen removal often ranging between 50 and 80%. − There is, thus, a need to develop catalysts that are active for both HDO and HDN.…”