Search

The evolution of oxygen functional groups (OFGs) and the associated thermic effects upon heat treatment up to 800 °C were investigated experimentally as well as by theoretical calculations. A synthetic carbon with a carbonaceous structure close to that of natural chars, yet mineral-free, was derived from cellulose and oxidized by HNO

During the lifetime of coal and biomass particles in a reactor, severe changes in the carbonaceous structure occur. In the early stages of heat treatment, transformations at both the structural and...

A laminar drop tube reactor (DTR) was used to perform fast pyrolysis of walnut shells, a ligno-cellulosic biomass sample, in nitrogen and carbon dioxide atmospheres. The DTR reached the temperature of 1300 °C and the heating rate of 104–105 °C/s. Char samples collected at different residence times along the reactor were characterized by ultimate and proximate analysis and by SEM. Char combustion reactivity was then measured by non-isothermal thermogravimetric analysis (TGA) in air. The analyses show that at residence times of 66 ms pyrolysis in N2 is not complete, whereas it is complete in CO2. For residence times of 115 ms the differences between samples produced in N2 and CO2 atmospheres level off. The derivative thermogravimetric (DTG) curves of the char combustion show the existence of multiple peaks. Notably, early combustion peaks progressively fade in the chars collected at increasing reactor residence time, confirming the completion of pyrolysis. A kinetic model of char combustion is proposed which includes multiple parallel reactions.

Previous studies have shown that increased carbon dioxide concentrations upon heat up affects the products of coal pyrolysis and in particular that chars prepared under carbon dioxide rich atmospheres are less reactive than chars prepared in nitrogen, and consistently tars are more aromatic [1-4]. In the present work, this issue is investigated with reference to a biomass sample, namely walnut shells (WS), where the lignin component prevails over cellulose and hemicellulose. Preliminary experiments of thermal degradation have been carried out using a thermogravimetric (TG) apparatus, under constant heating rate conditions, in flows of either nitrogen or carbon dioxide. Derivative thermogravimetric (DTG) curves reveal the existence of multiple peaks, which are typically associated with the degradation of different lignocellulosic components. A multiple parallel reaction scheme has therefore been used to fit the experimental data and kinetic parameters have been obtained. Walnut shells were also pyrolyzed in a fixed bed reactor at 600 °C in either nitrogen or carbon dioxide so as to collect pyrolysis products in amounts sufficient for further analysis. Char and tar samples have been characterized using different techniques (e.g. GC-MS, elemental analyzer, TGA, SEM) revealing limited differences. Combustion rate of the chars has been measured by means of non-isothermal thermogravimetric experiments in air and again small differences have been observed between the samples prepared under carbon dioxide and nitrogen. It has been concluded that under the low heating rate conditions typical of the thermogravimetric apparatus and fixed bed reactor used in the work, the effect of carbon dioxide on liquid and solid products of biomass pyrolysis exist, but are less important than for coal. The work is complemented by a companion paper [5], which investigates the effect of carbon dioxide on biomass pyrolysis under high temperature and fast heating rate conditions typical of a drop tube reactor.

In a previous work [Heuer S et al. Fuel Process Technol 2016;150:41-9] a large production of a fluffy carbon-rich material was observed to accompany the char formed during the early stages of a medium rank (bituminous) coal pyrolysis carried out in a drop tube furnace, (1573 K, residence times < 130 ms). This peculiar material was found to be much more abundantly formed in CO2 than in N2 flow. SEM analysis showed that it contains a large portion of submicron soot-like particles mixed with particles of tenths of microns in size with the typical char morphology. The present work reports on the separation of the two differently sized fractions produced in CO2 and N2 flow and their subsequent analysis. The separation was performed dispersing the material in ethanol by ultrasonic mixing, followed by settling, and decanting to produce top and bottom products enriched in the fine and coarse particle fractions, respectively. The procedure was repeated several times and the size separation effectiveness was checked by SEM and laser granulometry sizing. Thermogravimetry, elemental and spectroscopic analysis were applied to the coarse and fine fractions to provide insights on their structural features. The fine soot particulate was almost ash- free suggesting that its formation occurs in the gas phase, as typically soot does, while the coarse fraction presented significant residues of coal inorganic matter typical of char. Both fine and coarse particulate resulted less reactive, and somewhat smaller in size, when produced in CO2 in comparison to N2/Ar pyrolysis conditions. Their lower reactivity is associated with higher aromaticity and structural order as well as with a lower presence of hydrogen and aliphatic functionalities.

The use of biomass templating materials with a cheap production method as an enhanced sorbent for CO2 uptake has been proposed recently. However, the attrition and fragmentation behaviour of this type of material, which is a vital parameter for calcium looping sorbents, has not yet been investigated in detail. In this work the fragmentation behaviour of biomass-templated sorbents is investigated. Three types of materials were prepared using a mechanical pelletiser: 1. lime and cement (LC); 2. lime and flour (LF); and 3. lime, cement and flour (LCF). These samples were heat treated in a pressurised heated strip reactor (PHSR) and in a bubbling fluidised bed (BFB) and changes in particle size distribution were measured to assess fragmentation. Results indicated that the addition of biomass enhances the propensity to undergo fragmentation. Upon heat treatment in the PHSR the particle size of LC was not modified significantly; on the contrary the mean particle diameter of LF decreased from 520 mu m to 116 mu m and that of LCF from 524 mu m to 290 mu m. Fragmentation tests in the BFB confirmed the trend: 67% of the particles of LF fragmented, against 53% of LCF and 18% of LC samples. The addition of cement to the LF samples partially counteracts this performance degradation with respect to attrition. However, calcium aluminate pellets (LC) showed the lowest rate of fragmentation amongst all of the samples tested. (C) 2016 Published by Elsevier Ltd.

In the present work fast pyrolysis of coal in N2 and CO2 atmospheres was studied in a drop tube reactor (DTR) and in a heated strip reactor (HSR). In the DTR the volatiles generated by coal pyrolysis were entrained in a hot gas stream and were collected at the reactor outlet by tar traps. In the HSR, the volatiles were ejected from the hot coal particles into a cool environment and the condensable species, including primary tar, deposited and/or condensed on a glass bridge located above the heated strip. The composition of tars produced in the two reactors was compared to study the role of gas tar reactions in soot inception, and reference compounds for each class of tar species produced were identified. In the DTR the formation and growth of polycyclic aromatic hydrocarbons (PAH) were found higher than in the HSR. Soot formation occurred only in the DTR, being negligible in the HSR. It was concluded that the hot gas environment of the DTR favours secondary tar reactions, formation of PAH and eventually soot, while in the HSR this path was prevented due to prompt cooling down of volatiles. The presence of large concentration of CO2 in the pyrolysis atmospheres further promoted formation of heavy PAH and soot in the DTR, but not in the HSR, where the cooler environment limits soot-CO2 reactions in the gas phase.

The paper explores the primary products from fast pyrolysis of biomass components: Lignin, Cellulose and Hemicellulose (Xylan). A heated strip reactor is employed at temperatures of 1573 K and 2073 K with N2 and CO2 atmospheres. Volatiles quench immediately after volatilization on a cold pyrex bridge, while char remains on the heated strip for 3 s. Tar, soot and char are collected and subject to chemical treatments and analyses, including gas chromatography-mass spectrometry and Size Exclusion Chromatography, Thermogravimetric analysis, Raman spectroscopy and Scanning Electron Microscopy. Fast pyrolysis of Lignin produces “Light tar” (soluble in acetone) and “Heavy tar” (soluble in NMP), char, a minor fraction of soot. The “Light tar” contains Vanillin, which can be considered the main primary depolymerization product, but also aliphatics and PAHs. Higher temperature enhances “Heavy tar” and graphitization of the char. Cellulose at 1573 K produces only “Light tar”, largely made of Levoglucosan, as the result of depolymerization. At higher temperature the tar becomes heavier. Hemicellulose has a peculiar behavior: it produces a “Light tar” which is chemically similar to that of Cellulose and, at high temperature also “Heavy tar”. Hemicellulose pyrolysis results also in the production of an atypical solid residue: swollen ad spongy at lower temperature, bright and glassy at higher temperature. CO2 affects the pyrolysis products, particularly those of Lignin, promoting tar cracking and oxygenation already at the stage of primary pyrolysis and hindering thermal annealing and structural ordering of the solid carbonaceous structure.

The title compound, bis(4-butyloxyacetophenon)azine, exhibits a rich phase behavior. It has two different crystal phases and one liquid crystal phase before transition to the isotropic liquid phase. The liquid crystalline phase is nematic. All the phase transitions of the compound are reversible. In particular, the solid–solid transition at 83 °C is single-crystal-to-single-crystal as proven by optical and electron microscopy and X-ray diffraction analysis and it shows a remarkable degree of reversibility; single crystals can undergo several cycles of transition between the two phases without any damage. The crystal phase stable at lower temperature has been fully characterized by single crystal X-ray analysis. It shows an arrangement of the molecules in layers in the plane (a, b), with the layers piled up along c without interdigitation of the alkyl tails of molecules belonging to consecutive layers. The crystal phase stable at higher temperature is disordered.