Sustainable treatment of sewage sludge via plasma-electrolytic liquefaction for bio-friendly production of polyurethane foam.

Safe and green disposal or utilization of sewage sludge (SS) has attracted significant attention as SS is increasingly produced worldwide and emerges as an environmental burden if without proper treatment. In this study, efficient and sustainable treatment of SS was achieved using plasma-electrolytic liquefaction (PEL) with alkaline catalysts including sodium hydroxide (NaOH), sodium carbonate (Na2CO3), and sodium acetate (NaAc) and renewable solvents including polyethylene glycol (PEG) 200 and glycerol. Furthermore, the obtained bio-oil with abundant hydroxyl groups could partially replace polyols derived from fossil energy to synthesize bio-based polyurethane foams (BPUFs) for oil adsorption. The results showed that the Na2CO3 catalyst exhibited better performance and yielded bio-oil with a higher heating value (HHV) of 26.26 MJ/kg, very low nitrogen content (0.14%) and metal ions, and a nearly neutral pH of 7.41, under the optimized conditions. Compared with conventional oil bath liquefaction, PEL can significantly improve the liquefaction efficiency, promote the transfer of metal ions in SS to the solid residue (SR), and facilitate the transfer of nitrogen to the gas phase and SR, thereby upgrading the bio-oil to a certain extent. The BPUFs showed excellent oil adsorption capacity, reusability, and desorption and can play an important role in combating oil spills. The PEL method may provide a green avenue for SS valorization and the comprehensive utilization of the obtained products.

Mechanism and optimization for plasma electrolytic liquefaction of sawdust.

In this work, plasma electrolytic technology was successfully employed to achieve fast liquefaction of sawdust when polyethylene glycol 200 (PEG 200) and glycerol were used as liquefacient in the presence of the catalyst sulfuric acid. Results showed that H ions could heat the solution effectively during the plasma electrolytic liquefaction (PEL) process. The influence of some key parameters including liquefaction time, catalyst percentage, liquefacient/sawdust mass ratio, and PEG 200/glycerol molar ratio on the liquefaction yield were investigated. Based on the results of single factor experiments, response surface methodology (RSM) was applied to optimize the liquefaction process. Under the optimal conditions that is liquefaction time of 5.10min, catalyst percentage of 1.05%, liquefacient/sawdust mass ratio of 7.12/1 and PEG 200/glycerol molar ratio of 1.40/1, the liquefaction yield reached 99.48%. Hence, it could be concluded that PEL has good application potential for biomass fast liquefaction.

Fast liquefaction of bamboo shoot shell with liquid-phase microplasma assisted technology.

In this study, liquid-phase microplasma technology (LPMPT) was employed to facilitate the liquefaction of bamboo shoot shell (BSS) in polyethylene glycol 400 (PEG 400) and ethylene glycol (EG) mixture. Effects of liquefaction conditions such as liquefaction time, catalyst percentage, solvent/BSS mass ratio, PEG/EG volume ratio on liquefaction were investigated experimentally. The results showed that the introduction of LPMPT significantly shortened the liquefaction time to 3min without extra heating. The liquefaction yield reached 96.73% under the optimal conditions. The formation of massive reactive species and instantaneous heat accumulation both contributed to the rapid liquefaction of BSS. Thus, LPMPT could be considered as a simple and efficient method for the assistance of biomass fast liquefaction.

Liquefaction of bamboo shoot shell for the production of polyols.

Bamboo (Dendrocalamus latiflorus Munro) shoot shell (BSS) was liquefied in polyethylene glycol 400 (PEG400) and ethylene glycol (EG) catalyzed by sulfuric acid under atmospheric pressure. The effects of liquefaction conditions such as liquid-solid ratio, temperature, time, catalyst, solvents ratio, and material size on the liquefaction yield of BSS have been investigated. Methods including Elemental analysis, Thermogravimetric analysis, Fourier transform infrared spectroscopy, nuclear magnetic resonance and gas chromatography-mass spectrometry were selected to analyze the characteristics of products in three fractions: an aqueous fraction (AQ), an acetone-soluble fraction (AS) and a residue (RS), respectively. Results showed that the highest liquefaction percentage was 99.79% under the optimal conditions (liquid-solid ratio 6:1; temperature 150°C; reaction time 80min; raw size more than 40 mesh; catalyst mass percentage of solvent 4%; solvent volume ratio 3:1). Polyols could be obtained effectively by the liquefaction of BSS, an agricultural by-product.