• Energy Research
• 2021-2025close

The present study investigates the influence of pressure on the products of fast pyrolysis of a lignocellulosic biomass (Walnut Shells).

Fluorescent carbon was produced from fast pyrolysis of lignocellulosic biomass in a modified wire-mesh reactor named heated strip reactor (HSR). The metal grid, usually employed as a sample holder in a wire-mesh reactor, is replaced in the HSR by a pyrolytic graphite foil. HSR can achieve temperatures up to 2073 K with a high heating rate (104 K/s). The volatiles produced by the HSR pyrolysis of a lignocellulosic biomass sample were immediately quenched in the surrounding low temperature environment, so avoiding the occurrence of secondary reactions of the volatiles. Volatiles were condensed in form of a tar-like material on a pyrex glass bridge located above HSR, whereas the residue solid (char and soot) remained on the strip. The tar-like material recovered and separated with different solvents in fractions of various characteristics showed blue and/or green fluorescence typical of fluorescent carbon dots (CDs). It was thus shown that fast pyrolysis of carbon resources as biomasses, can be employed as one-step approach to synthesize different classes of carbon materials, assimilable to CDs. The different CDs could be separated and isolated choosing appropriate organic solvents and constitute very promising materials for applications in photonics, electro-optics, chemical sensing, and other material science areas.

Heavy fractions of petroleum have for long time been bypassed in favour of lighter fractions. Nowadays, in the framework of the “circular economy”, there is a growing interest in residual petroleum heavy fractions. The present work briefly reviews the use and characterization at laboratory scale of some low valuable solid or semi-solid products of the oil refinery industry: asphaltenes (bitumen/asphalt), pet-coke and pitch for use as fuels. The use of solid and semi-solid refinery residues, in particular, of coke as a coal substitute in thermochemical processes and of pitch and asphaltenes as material precursors, requires careful analysis, and an understanding of their structure at the molecular level is mandatory for the development of processing technology. Techniques for the characterization of typical petroleum heavy fractions such as pitches, asphaltenes and cokes are reviewed. An experimental protocol for investigating at the laboratory scale the thermochemical conversion behavior of solid and semi-solid refinery wastes is proposed.

The present work focuses on the quality of char and primary tar produced from fast pyrolysis in N2 and CO2 of lignocellulosic biomasses: walnut shells (lignin-rich), straw (hemicellulose-rich) and pinewood (cellulose-rich). Heat treatments are carried out in a heated strip reactor (HSR) at 1573 and 2073 K for 3 s, with a heating rate of 104 K/s. The equipment allows for quenching the volatiles as soon as they are emitted. Chars are analyzed by thermogravimetric analysis in air. Results are compared with the products obtained from raw lignin, pure cellulose and pure hemicellulose. Cellulose and hemicellulose tars are dominated by anhydrous monosaccharides, which are scarce in straw tar and abundant in walnut shells tar. Polycyclic aromatic hydrocarbons PAHs are present in the primary products, in particular for walnut shells. The most reactive char is the one obtained from straw and the least reactive is the walnut shells char. Severe heat treatment and a CO2 atmosphere generate additional char components with higher and lower reactivity. The more reactive char component may arise from cross-linking reactions involving the monosaccharides (for which the result decreased in tar), whereas the less reactive component arises from thermal annealing and graphitization. Thus, the pyrolytic behavior of biomasses cannot be reconstructed with a mere addition of the lignin/cellulose/hemicellulose contribution, taking into account their content in the biomass.