• Energy Research

Large-scale commercialization of drop-in biofuel technologies requires a deeper understanding of the molecular structure of biocrude oils and their compatibility with fossil crudes in terms of molecular interactions that govern miscibility. For the first time, the compatibility of hydrothermal liquefaction (HTL) derived biocrude obtained from pinewood with straight-run gas oil (SRGO) was comprehensively investigated by theoretical prediction using Hansen double sphere plots and experimental confirmation from miscibility studies to achieve a biofeed compatible for coprocessing at refineries. The Hansen solubility parameters (HSPs) for biocrude, biocrude components (residue and light and heavy distillate fractions), and SRGO were determined by plotting a three-dimensional Hansen solubility sphere plot based on the experimental solubility data obtained on their solubility studies in 38 different solvents. The compatibility of HTL biocrude oil with SRGO was verified from the solubility distance (Ra) and relative energy difference (RED) values obtained from the center of their Hansen spheres and difference in HSPs, respectively, in a Hansen double sphere solubility plot. The experimental data obtained on miscibility studies confirmed that pyridine, cyclohexanone, and a pyridine-cyclohexanone solvent mixture (1:1) occupy a well-defined Hansen space and show fitting to HSPs of the biocrude-SRGO blend, improve the overall compatibility of the blending mixture, and display a maximum miscibility of 72%. To correlate the compatibility with the molecular structure, the compatibility of light, heavy, and residual fractions obtained by fractional distillation of HTL biocrude (pinewood) was also evaluated with SRGO using the Hansen double sphere plot, and a close agreement with differential scanning calorimetry (DSC) results as well as the experimental data on miscibility studies was verified. Furthermore, the comprehensive estimation of the detailed composition and chemical nature of biocrude and light, heavy, and residual fractions by the means of elemental (CHN/O), GC-MS, and GC × GC analysis was also presented. Additionally, the correlation between compatibility and interactions within chemical functionalities of blend components was established by analyzing the contribution of aromatic, aliphatic, and oxygen containing functional groups to the miscibility using quantitative 13C NMR spectroscopy. The present study reports a mixing strategy to assess the compatibility of biocrudes, heavy distillate fractions, asphaltenes, residues, and polymers with existing petroleum infrastructure for the cost-effective biorefinery process to balance economic and environmental considerations.

Aqueous phase recirculation increased the bio-crude yield and energy recovery along with promoting the production of N-heterocyclic compounds that lead to harsher required hydrotreating conditions.

Hydrothermal liquefaction (HTL) of biomass is establishing itself as one of the leading technologies for the conversion of virtually any type of biomass feedstock into drop-in biofuels and renewable materials. Several catalysis strategies have been proposed for this process to increase the yields of the product (biocrude) and/or to obtain a product with better properties in light of the final use. A number of different studies are available in the literature nowadays, where different catalysts are utilized within HTL including both homogeneous and heterogeneous approaches. Additionally, catalysis plays a major role in the upgrading of HTL biocrude into final products, in which field significant developments have been observed in recent times. This review has the ambition to summarize the different available information to draw an updated overall picture of catalysis applied to HTL. The different catalysis strategies are reviewed, highlighting the specific effect of each kind of catalyst on the yields and properties of the HTL products, by comparing them with the non-catalyzed case. This allows for drawing quantitative conclusions on the actual effectiveness of each catalyst, in relation to the different biomass processed. Additionally, the pros and cons of each different catalysis approach are discussed critically, identifying new challenges and future directions of research.

Hydrothermal liquefaction (HTL) is an emerging technology for bio-crude production but faces challenges in determining the optimal temperature for feedstocks depending on the process mode. In this study, three feedstocks—wood, microalgae spirulina (Algae Sp.), and hydrolysis lignin were tested for sub-supercritical HTL at 350 and 400 °C through six batch-scale experiments. An alkali catalyst (K2CO3) was used with wood and hydrolysis lignin, while e (Algae Sp.) was liquefied without catalyst. Further, two experiments were conducted on wood in a Continuous Stirred Tank Reactor (CSTR) at 350 and 400 °C which provided a batch versus continuous comparison. Results showed Algae Sp. had higher bio-crude yields, followed by wood and lignin. The subcritical temperature of 350 °C yielded more biocrude from all feedstocks than the supercritical range. At 400 °C, a significant change occurred in lignin, with the maximum percentage of solids. Additionally, the supercritical state gave higher values for Higher Heating Values (HHVs) and a greater amount of volatile matter in bio-crude. Gas Chromatography and Mass Spectrometry (GCMS) analysis revealed that phenols dominated the composition of bio-crude derived from wood and hydrolysis lignin, whereas Algae Sp. bio-crude exhibited higher percentages of N-heterocycles and amides. The aqueous phase analysis showed a Total Organic Carbon (TOC) range from 7 to 22 g/L, with Algae Sp. displaying a higher Total Nitrogen (TN) content, ranging from 11 to 13 g/L. The pH levels of all samples were consistently within the alkaline range, except for Wood Cont. 350. In a broader perspective, the subcritical temperature range proved to be advantageous for enhancing bio-crude yield, while the supercritical state improved the quality of the bio-crude.

This study focuses on the valorization of the organic fraction of municipal solid waste (biopulp) by hydrothermal liquefaction. Thereby, homogeneous alkali catalysts (KOH, NaOH, K2CO3, and Na2CO3) and a residual aqueous phase recirculation methodology were mutually employed to enhance the bio-crude yield and energy efficiency of a sub-critical hydrothermal conversion (350 °C, 15–20 Mpa, 15 min). Interestingly, single recirculation of the concentrated aqueous phase positively increased the bio-crude yield in all cases, while the higher heating value (HHV) of the bio-crudes slightly dropped. Compared to the non-catalytic experiment, K2CO3 and Na2CO3 effectively increased the bio-crude yield by 14 and 7.3%, respectively. However, KOH and NaOH showed a negative variation in the bio-crude yield. The highest bio-crude yield (37.5 wt.%) and energy recovery (ER) (59.4%) were achieved when K2CO3 and concentrated aqueous phase recirculation were simultaneously applied to the process. The inorganics distribution results obtained by ICP reveal the tendency of the alkali elements to settle into the aqueous phase, which, if recovered, can potentially boost the circularity of the HTL process. Therefore, wise selection of the alkali catalyst along with aqueous phase recirculation assists hydrothermal liquefaction in green biofuel production and environmentally friendly valorization of biopulp.

Sewage sludge from wastewater treatment plants (WWTPs) represents a source of feedstock for hydrothermal liquefaction (HTL), which in turn offers a sustainable alternative to valorize this societal waste.

The in situ generated supramolecular ensemble (2:Cu2O) of Cu2O NPs and aggregates of PBI derivative 2 exhibited excellent photocatalytic efficiency in the Suzuki–Miyaura and Suzuki type cross-coupling reactions under mild and eco-friendly conditions.