Unveiling drastic influence of cross-interactions in hydrothermal carbonization of spirulina with cellulose, lignin or poplar on nature of hydrochar and activated carbon.

Spirulina platensis contains abundant nitrogen-containing organics, which might react with derivatives of cellulose/lignin during hydrothermal carbonization (HTC), probably affecting yield, property of hydrochar, and pore development in activation of hydrochar. This was investigated herein by conducting co-HTC of spirulina platensis with cellulose, lignin, and sawdust at 260 °C and subsequent activation of the resulting hydrochars with K2C2O4 at 800 °C. The results showed that cross-condensation of spirulina platensis-derived proteins with cellulose/lignin-derived ketones and phenolics did take place in the co-HTC, forming more π-conjugated heavier organics, retaining more nitrogen species in hydrochar, reducing yields of hydrochar, making the hydrochar more aromatic and increasing the thermal stability and resistivity towards activation. This enhanced the yield of activated carbon (AC) by 7 %-20 % and significantly increased specific surface area of the AC from activation of hydrochar of spirulina platensis + lignin to 2074.5 m2/g (859.3 m2/g from spirulina platensis only and 1170.1 m2/g from lignin only). Furthermore, more mesopores from activation of hydrochar of spirulina platensis + cellulose (47 %) and more micropores from activation of hydrochar of spirulina + sawdust (93 %) was generated. The AC from spirulina platensis + lignin with the developed pore structures generated sufficient sites for adsorption of tetracycline from aqueous phase and minimized steric hindrance for mass transfer with the abundant mesopores (43 %).

Pyrolysis of furfural residues: Property and applications of the biochar.

Furfural residue (FR) is a solid waste generated during the production of furfural from corn cobs. The chemical energy and material potential of FR can be potentially recovered via pyrolysis. In this study, the pyrolysis of FR at the temperature ranging from 350 to 650 °C at the varied heating rate was investigated, aiming to understand the characteristics of the pyrolysis products. The results indicate that the organic components of FR tend to be cracked to form biochar and gases as the dominate products, due to the high ash content of FR. The FR-derived bio-oil also contained abundant organics derived from cellulose and lignin. Increasing pyrolysis temperature favored formation of the organics with fused ring structures. Lower heating rate in pyrolysis also formed biochar with higher thermal stability and higher fixed carbon content by enhancing the extent of deoxygenation. Additionally, the transformation of -OH via dehydration, -C-H into = C-H via dehydrogenation, and the cracking of CO during carbonization of biochar in the pyrolysis were also observed during pyrolysis of FR. Activation of the FR-derived biochar generated abundant micropores and mesopores, rendering the activated carbon with superior specific capacitance as electrodes of electrocapacitors (329 Fg-1) and the excellent adsorption efficiency of phosphate (up to 98.81%).

Activation of waste paper: Influence of varied chemical agents on product properties.

Waste paper (WP) is rich in cellulose, which can be activated to produce porous carbon, bio-oil, and combustible gases. During chemical activation of WP, the use of varied chemical agents not only generates activated carbon of distinct pore structure but also bio-oil/gases of different property. In this study, the activation of WP with varied chemical agents was conducted. The distinct characteristics of activated carbon and also bio-oil/gases were correlated with the different nature of the used chemical agents. The results indicated that H3PO4 and ZnCl2 catalyzed polymerization reactions for producing more bio-oil while less gases owing to their Brønsted and Lewis acidic sites. K2C2O4 showed high activity for cracking/gasification reactions, forming bio-oil with higher abundance of organics with smaller π-conjugated structures. In addition, ZnCl2 could create a very coarse porous structure with abundant macropores via destroying fiber structure in WP and promoting the growth of graphitic crystals. In comparison, K2C2O4 hindered the aromatization and facilitated the formation of amorphous activated carbon. K2C2O4 and ZnCl2 were much more effective than H3PO4 for creating micropores and mesopores from WP, the derived activated carbon showed superior performances as the electrode of supercapacitor and adsorbent for adsorption of oxytetracycline from aqueous solution. In addition, K2C2O4 as activating agent showed lower environmental impact than ZnCl2 in terms of energy consumption, environmental pollution and the greenhouse effect.