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Graphical abstract Highlights • Insights on pitch structure for guiding the production of tailored carbon materials. • Correlation of pitch properties with their source. • Match of several techniques for coal-tar and petroleum pitches characterization. • Comparison of coal-tar and petroleum pitches characteristics and composition. Abstract The structural properties and composition of pitches are particularly important for the optimization of pitch processing to high-value products and practical application. Because of their complexity, pitch analysis requires both chemical and spectroscopic tools, as those applied in the present work to coal and petroleum-derived pitch samples. In particular, a large variety of methods, including chromatography, elemental analysis, thermogravimetry, mass spectrometry, UV–Visible and FTIR spectroscopy, was applied for evidencing the different characteristics of commercial solid pitch derived from petroleum and coal. The interrelation among some pitch properties was investigated by analyzing petroleum and coal-derived pitches having different softening points and volatility. It was observed that properties as the softening point and the coking yield are mainly related to the pitch volatility rather than on the pitch source (coal or petroleum), whereas some other features as the solubility and the oxidation reactivity of coke produced appeared correlated with the source characteristics. [ABSTRACT FROM AUTHOR]

Optical features of fluorescent components of pyrogenic carbons as flame-formed carbon particulate matter (PM) were studied by setting up a facile and fast method (SEC-Abs/Fluo) based on size exclusion chromatography (SEC) coupled with UV–Visible absorption and fluorescence spectrometers as detectors. The SEC-Abs/Fluo method simultaneously allowed the molecular weight (MW) separation and identification of blue- and green-fluorescent PM components exhibiting size and spectroscopic features typical of carbon dots (CDs). The SEC-Abs/Fluo method allowed the online determination of quantum yield (QY) and optical band gap of fluorescent components also in strongly-scattering carbon suspensions so avoiding tedious pretreatment of carbon samples. From the detailed separation and analysis of blue- and green-fluorescent PM components along with two commercial pitches, aromatic species having MW > 1000 u and band gap <1–1.5 eV resulted to be scarcely or no fluorescent indicating these are the MW and band gap thresholds for fluorescence emission. Indeed, a sharp QY decrease was for the first time noticed in a narrower band gap (1–1.5 eV) range, where carriers can more easily tunnel to defects of the carbon network reducing fluorescence emission. The exponential increase of QY as the band gap rises was found with a more regular trend for the MW-segregated components in comparison to the bulk samples. The method can support and guide the choice of the optimal operating conditions to maximize CD formation and their purification from not-fluorescing components and can also be helpful in disentangling CD fluorescence attribution. [Display omitted] • Novel method for separation and spectroscopic analysis of carbon fluorescent components. • Individuation of fluorescent components with online quantum yield and band gap evaluation. • Direct optical characterization of fluorescent components in strongly-scattering suspensions. • ArOmatic species with MW > 1000 u and band gap<1–1.5 eV are no or poorly fluorescent. [ABSTRACT FROM AUTHOR]

Abstract The paper explores changes in reactivity and chemico-physical characteristics of char and tar produced by severe heat treatment of lignite in both inert atmospheres and CO 2 rich atmospheres. The role of mineral matter, in particular metal oxides, in catalysing chemical and physical transformations is also addressed. A Rhenish Lignite from the Garzweiler mine was studied and compared with: a) mineral-free synthetic carbon (HTC), obtained from cellulose; b) a synthetic carbon doped with iron oxide (Fe 2 O 3). A heated strip reactor (HSR) was employed at temperatures of 1300 and 1800 °C in N 2 and CO 2 atmospheres. Liquid and solid products (tar and char) were analysed and compared. Tar composition was evaluated by extraction and gas chromatography-mass spectrometry, whereas the solid carbonaceous material produced by pyrolysis, mainly composed of char, was characterized regarding its thermal behaviour by thermogravimetric analysis and its structure by Raman spectroscopy and scanning electron microscopy. Results show that iron oxide exerts a catalytic influence on both pyrolysis and char oxidation. Upon severe heat treatment, it reduces char reactivity promoting graphitization and structural ordering. The overall effect on char reactivity is therefore not easy to predict. [ABSTRACT FROM AUTHOR]

In oxycombustion and gasification processes coal pyrolysis occurs in CO 2 -rich atmospheres. The present work investigates the effect of such conditions on the quantity and quality of the submicronic carbon particulate produced. Pyrolysis experiments were carried out in either N 2 or CO 2 atmospheres in a laminar drop tube reactor, with wall temperatures of 1573 K, heating rates of 10 4 –10 5 K/s and residence times below 130 ms, so as to reproduce pyrolysis conditions comparable to those of pulverized coal-fired boilers. The carbon particulate sampled in the reactor was found to have bimodal distribution in the micronic and submicronic ranges. A method based on solvent extraction was applied to carbon particulate for separating the two modes and determining the relative mass contribution of micronic and submicronic fractions. In CO 2 atmosphere the amount of submicronic fraction of carbon particulate, referred to as soot, was found to be up to four times as much as upon N 2 experiments. Beside the larger formation of soot, relevant differences in terms of combustion reactivity, size distribution and chemical structure of the residual carbon particulate produced in CO 2 environment in respect to N 2 environment were observed by means of a large array of techniques including thermogravimetry, microscopy (SEM+EDX), FT-IR, UV–visible and Raman spectroscopy along with XRD and XPS techniques. [ABSTRACT FROM AUTHOR]

• Data on chemical composition of primary tar are mandatory for understanding pyrolysis. • Secondary reactions of tar are a source of PAH which in turn can be soot precursors. • Soot formation is highly limited when primary tar is immediately quenched. • The limitation of secondary tar reactions reduces soot emissions with health benefits. In the present work fast pyrolysis of coal in N 2 and CO 2 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 CO 2 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-CO 2 reactions in the gas phase. [ABSTRACT FROM AUTHOR]