Hydrothermal Co-Liquefaction of Lignite and Lignocellulosic Biomass with the Addition of Formic Acid: Study on Product Distribution, Characteristics, and Synergistic Effects

Advances in machine learning for high value-added applications of lignocellulosic biomass

Lignocellulose can be converted into biofuel or functional materials to achieve high value-added utilization. Biomass utilization process is complex and multi-dimensional. This paper focuses on the biomass conversion reaction conditions, the preparation of biomass-based functional materials, the combination of biomass conversion and traditional wet chemistry, molecular simulation and process simulation. This paper analyzes the mechanism, advantages and disadvantages of important machine learning (ML) methods. The application examples of ML in different aspects of high value utilization of lignocellulose are summarized in detail. The challenges and future prospects of ML in this field are analyzed.

Co-liquefaction of Chlorella and soybean straw for production of bio-crude: Effects of reusing aqueous phase as the reaction medium

Co-liquefaction was combined with hydrothermal liquefaction (HTL) aqueous phase (AP) recirculation to improve the practicality of HTL process. The Chlorella powder (CL), soybean straw (SS), and their mixture (CS) with ratio 1:1 were processed at 300 °C for 20 min, and the AP was recirculated four times. The yield of CS bio-crude was increased (from 24.28% to 31.83%) by co-liquefaction, but remained stable during AP recirculation. By contrast, the yields were increased for CL bio-crude (from 32.40% to 41.19%), SS hydrochar (from 19.55% to 30.88%), and CS hydrochar (from 9.42% to 14.76%) by recirculation. The elemental analysis, chemical composition analysis, functionality analysis, thermogravimetric analysis, and verification experiments (HTL with model AP components) show the N-containing compounds (e.g., amines) in AP were converted into amides (acylation) for CL bio-crude, into N-heterocycles (Maillard reactions) for CS hydrochar, and into Mannich bases for SS hydrochar, which contributed to the increased yield and N content (from 7.27% to 8.82% for CL bio-crude). Furthermore, the O content of CS bio-crude was decreased (from 15.31% to 12.52%) by recirculation, resulted from the conversion of N-heterocyclic ketones into pyrazine derivates. The decreased O content and comprehensive combustibility index (from 0.306 to 0.177) of CS bio-crude indicate the great potential of this craft combination.

Bio-Crude Production Improvement during Hydrothermal Liquefaction of Biopulp by Simultaneous Application of Alkali Catalysts and Aqueous Phase Recirculation

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.

Physicochemical Characterisation and the Prospects of Biofuel Production from Rubberwood Sawdust and Sewage Sludge

This study aims to evaluate the physicochemical properties of rubberwood sawdust (RWS) and sewage sludge (SS) for producing biofuel or liquid products via pyrolysis and co-pyrolysis. The chemical and thermal properties of both samples were observed to have superior bioenergy production capabilities. RWS and SS had significantly different physicochemical properties, such as particle-size distribution, bulk density, ultimate and proximate analysis, lignocellulose composition, thermal-degradation behaviour, and major and minor elements. The composition of extractives was found to only marginally affect the end product. Carbon and hydrogen content, the two main elements for biofuel enhancement, were found to correlate with the organic components of both RWS (48.49, 7.15 wt.%) and SS (32.29, 4.06 wt.%). SS had a higher elemental composition of iron, calcium, and potassium than RWS. Both samples had a higher heating value of 13.98 to 21.01 MJ/kg and a lower heating value of 11.65 to 17.66 MJ/kg, a lesser energy potential than that of fossil fuels. The findings from these blends are relatively moderate due to the related lignocellulosic potential composition. The novel contribution of this research was to optimize the use of local waste materials as a new raw material for biofuel production that could serve as a sustainable fuel source.