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

• Published in: The Science of the total environment 2022-05, Vol.820, p.153348-153348, Article 153348
• Main Authors: Leng, Songqi, Jiao, Huiting, Liu, Tonggui, Pan, Wei, Chen, Jiefeng, Chen, Jie, Huang, Huajun, Peng, Haoyi, Wu, Zhibin, Leng, Lijian, Zhou, Wenguang
• Format: Article
• Language: English
• Subjects: Aqueous phase recirculation; Bio-oil; Biofuels - analysis; Biomass; Chlorella; Co-liquefaction; Glycine max; Hydrothermal liquefaction; Microalgae; Straw; Temperature; Water - chemistry
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2022.153348

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. [Display omitted] •The combination of aqueous phase recirculation with co-liquefaction was investigated.•The increased co-liquefaction bio-crude yield was stable during recirculation.•Recirculation increased algal bio-crude yield and co-liquefied hydrochar yield.•The amines were the main reason for the increased yield and N content of bio-crude.•The fuel properties of co-liquefied bio-crude were improved by reusing aqueous phase.