The formation of isoprene and dl-limonene during waste tyre pyrolysis was investigated in terms of the effect of the heating rate (up to 100 °C/min). Ion current signals were used to track during pyrolysis the evolution of the predominant ions of isoprene (isoprene 67) and dl-limonene (limonene 93), by using a thermogravimetric analyser coupled with mass spectrometry (TGA/MS). The combined model-free and model-based kinetics were used to estimate the activation energy (Ea) for isoprene and dl-limonene formation at 131 and 115 kJ/mole, respectively, based on the Kissinger method. Reaction order (n) values were estimated at 1.2 and 1.1 for isoprene and dl-limonene, respectively. Better model fit (R2 = 0.998) of the experimental data to the Arrhenius equation for isoprene and dl-limonene, respectively, was observed when the Kissinger method was used compare to Friedman method. Although the Ea values for isoprene and dl-limonene were not significantly different, the combined three kinetic parameters (Ea, pre-exponential constant (A), and n) may be significantly different. Therefore, for dl-limonene formation selectivity over isoprene, the differences in the three kinetic parameters values for each compound model and heating rate on the reaction progress was significant. The reaction progress at peak isoprene and dl-limonene formation rate increased from 0.42 to 0.45 and more significantly from 0.35 to 0.44, respectively as the heating rate was increased from 15 to 100 °C, confirming that the preferred strategy to maximise dl-limonene production is rapid heating to the moderate final pyrolysis temperature.

This study investigates the effect the pyrolysis reactor and the condensing system type have on the tyre derived oil (TDO) and DL-limonene yield, as well as benzothiazole concentration in the TDO. All the experiments were performed at 475 degrees C and three technologies were investigated, fixed bed reactor (FBR), bubbling fluidised bed reactor (BFBR) and conical spouted bed reactor (CSBR), with the latter being the reactor that provided the highest TDO yield (58.2 wt.%). Furthermore, the CSBR enhances DL-limonene production due to its excellent features (low residence time of volatiles and high heat and mass transfer rates), which minimize secondary cracking reactions. Moreover, in order to maximize the TDO retention efficiency and selectively reduce the concentration of certain heteroaromatic species, two types of condensation systems were evaluated: tube-and-shell condenser (indirect contact) and quenching condenser (direct contact). The quenching condenser not only promoted the condensation efficiency for DL-limonene, but also reduced the concentration of benzothiazole in the collected TDO. Indeed, the direct contact between water (fed into the quencher) and the hot volatile stream favours the dissolution of some polar heteroaromatic species, thus reducing the nitrogen and sulphur content in the TDO and increasing the applicability of TDO as fuel.

Julius Caesar enjoyed a notable reputation for celeritas, as evidenced by literary references in the works of both contemporary and later ancient authors. Modern scholars furthermore argue that Caesar patently promoted his own military prowess, especially in his Bellum Gallicum. This paper therefore investigates Caesar’s representation of celeritas in the Gallic War commentaries by performing a comparative quantitative analysis of all explicit references to swiftness. The results show that celeritas was noticeably emphasised in the Bellum Gallicum, but also that these references do not surpass in number such references in, for example, Sallust’s contemporaneously written Iugurtha to such a large extent as has been previously claimed, based on the study of the cognate family of celer alone. Caesar did, however, have a distinct preference for using these cognates to indicate swiftness, probably thereby implicitly associating himself with celeritas.

Waste truck tyre valorization by fast pyrolysis has been performed in a conical spouted bed reactor in the 425-575 degrees C range. The tyre pyrolysis oil (TPO) yield was found to decrease with increasing temperature whilst the yield of gas increased. The effect of temperature on TPO properties has been studied in order to establish the best possible valorization route. FTIR and chromatographic analysis revealed the presence of some undesired compounds with sulphur, nitrogen or oxygen functionalities (benzotiatholes, nitriles and carboxylic acids amongst others) and an increase of TPO aromaticity with increasing temperature. The carbon and sulphur content and the heating value of the TPO increased with temperature. The simulated distillation showed that approximately 70% of the TPOs produced at 425 and 475 degrees C correspond to diesel range, whereas that TPO obtained at 575 degrees C is between diesel and gasoline range. The properties of the TPOs evidenced their potential to substitute conventional fuels. However, some of them need to be improved, i.e., by reduction of the sulphur, nitrogen and aromatic content. Additionally, the TPO obtained at 425 and 475 degrees C could be an important source of limonene and that at 575 degrees C of xylenes, although current removal methods present some limitations. (C) 2017 Elsevier Ltd. All rights reserved.

The nature and mechanisms of synergistic effects observed during the co-pyrolysis of cellulose and low density polyethylene (LDPE), two major components in municipal solid wastes, were investigated at milligram and gram-scales. Pyrolysis of a mixture of LDPE and cellulose increased the yield of the liquid product, with an 83% increase in the energy recovery, compared to a mixture of the liquid products from pyrolysis of the individual components. Further experiments distinguished the synergistic effects during devolatilization and condensation, respectively. Synergism during devolatilization was investigated by mixing cellulose char (prepared at 400 degrees C) with LDPE, and resulted in an increase in liquid yield, indicating an interaction between char and LDPE to promote liquid production. Solid-gas and/or gas-gas interactions occurred, where in the former the char acted as a catalyst rather than a reactant. For synergistic effects during the condensation process, LDPE was pyrolysed and the hot volatiles were condensed while the liquid products of cellulose pyrolysis were present in the condensation system, which also increased the liquid yield. Gas-gas and/or gas-liquid interactions occurred during condensation which enhanced the formation of the liquid phase. Moreover, the sum of the synergisms during devolatilization and condensation was similar to the overall synergistic effects observed during co-pyrolysis of the mixture, confirming the contribution of both to the overall positive synergistic effect on the liquid yield.

The flash pyrolysis of waste truck-tyres was studied in a conical spouted bed reactor (CSBR) operating in continuous regime. The influence of temperature on product distribution was analysed in the 425-575 degrees C range. A detailed characterization of the pyrolysis products was carried out in order to assess their most feasible application. Moreover, special attention was paid to the sulphur distribution among the products. The analysis of gaseous products was carried out using a micro-GC and the tyre pyrolysis oil (TPO) by means of GC-FID using peak areas for quantification, with GC/MS for identification and elemental analysis. Finally, the char was subjected to elemental analysis and surface characterization. According to the results, 475 degrees C is an appropriate temperature for the pyrolysis of waste tyres, given that it ensures total devolatilisation of tyre rubber and a high TPO yield, 58.2 wt.%. Moreover, the quality of the oil is optimum at this temperature, especially in terms of high concentrations of valuable chemicals, such as limonene. An increase in temperature to 575 degrees C reduced the TPO yield to 53.9 wt.% and substantially changed its chemical composition by increasing the aromatic content. However, the quality of the recovered char was improved at high temperatures. (C) 2017 Elsevier Ltd. All rights reserved.

Two techniques for cooling and condensing of the hot volatiles to produce tyre derived oil (TDO) from a waste tyre pyrolysis reactor were compared, i.e., conventional tube-and-shell heat exchanger type condensation, and quenching condensation by direct contact between the hot volatiles and quenching water. Exchanging the tube-and-shell condenser with direct quenching condensation increased the total TDO yield. Additionally, application of the quenching condenser increased the D- and L-isomers of limonene (DL-limonene) yield from 7.6 to 7.9 wt.%, while the benzothiazole concentration (a sulphurous and nitrogenous compound) in the TDO was decreased by 60%. The optimal operating conditions for quenching condensation were a quenching water volume of 2.1 L (a 50:1 weight of water to weight of tyre crumb ratio) and a spraying flow rate of 0.96 L/min. Additionally, the quenching condenser unit worked as a gas cleaner by wetting and trapping soot and fine solids from the non-condensable gases. (C) 2017 Elsevier B.V. All rights reserved.

The effect of pyrolysis temperature and heating rate on limonene production during waste tyre pyrolysis was investigated using gram-scale (fixed-bed) and microgram-scale (TGA) pyrolysis reactors. The investigation was carried out with final pyrolysis temperatures between 350 and 550 degrees C and heating rates in the range of 5-25 degrees C/min. Only the effect of the pyrolysis temperature was significant on the tyre derived oil (TDO) yield, while the effects of both pyrolysis temperature and heating rate were significant on the chemical composition of the TDO, i.e., limonene yield. In the gram-scale reactor, a maximum limonene yield was obtained at a pyrolysis temperature of 475 degrees C and a heating rate of 20 degrees C/min, with a value of 7.62 wt.% (based on the steel- and fabric-free tyre) or 22 wt.% (based on, the polyisoprene content of the tyre). DTG curves showed that increasing the heating rate led to (1) a decrease in secondary degradation reactions, and (2) an increased temperature at the maximum depolymerisation rate. At the same heating rate, MS ion current signals showed that limonene formation occurred at slightly higher temperatures compared to isoprene formation, indicating a slight higher activation energy for the former reaction. Since a higher activation energy indicates a stronger temperature dependency for a reaction, it implies, in combination with the observation of higher temperatures at maximum limonene production rate in the MS ion current signal, an improvement of the selectivity of polyisoprene depolymerisation towards limonene. (C) 2016 Elsevier B.V. All rights reserved.

ABSTRACTDevulcanization processes have potential to increase the economic value of ground tire rubber (GTR) derived from waste tires, although the chemistry of the devulcanization process is still poorly understood. This article presents a method, based on sol extraction and swelling measurements, for quantifying the selectivity for crosslink scission over main chain scission, and applies it to extrusion‐based mechanical and mechanochemical devulcanization processes at various operating conditions. The mechanochemical devulcanization process, using diphenyl disulfide and process oil, resulted in a higher selectivity for crosslink scission than the mechanical devulcanization process. Furthermore, it was shown that the process oil, along with lower reaction temperature, in the mechanochemical devulcanization process was responsible for the increased selectivity, rather than the presence of diphenyl disulfide. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43932.

The rubber composition of three different waste tyre crumbs has been predicted using a kinetics model for tyre devolatilisation. The kinetics are based on a sophisticated mechanism which includes two consecutive devolatilisation reactions for the rubbers and a single intermediate condensed product. Activation energies are obtained using model-free kinetics and are subsequently incorporated as fixed values in model-based kinetics. The model has been validated with binary and ternary mixtures of three predominant tyre rubbers (natural polyisoprene, butadiene and styrene-butadiene rubber) and subsequently applied for three waste tyre crumbs consisting of different ratios of passenger car and truck tyres. It turned out that the model is capable of predicting the natural polyisoprene content very accurately. Due to the similarity of butadiene and styrene-butadiene rubber, discriminating quantitatively between these two rubbers is notoriously difficult. The present model is however capable of correctly indicating increasing styrene contents in tyre crumbs. (C) 2015 Elsevier B.V. All rights reserved.

The present review concerns the production of dipentene (dl-limonene) from the pyrolysis of waste tires and is divided into three parts, which discuss (1) the mechanism of dipentene formation from polyisoprene, (2) the reported dipentene yields from experimental studies and (3) the separation and purification of dipentene from a tire-derived oil. Dipentene is formed via an intramolecular cyclization reaction of the allylic radicals formed by random scission of the β bonds with respect to the double bonds in the polyisoprene chains. Dimerization of two isoprene molecules to form dipentene seems unlikely under pyrolytic conditions. Especially at higher temperatures, the formed dipentene transforms further into either isoprene or aromatic compounds, the latter possibly via a diallyl diradical. Both the pyrolysis operating conditions and the tire type and brand have significant influence on the dipentene yield. Among these, the pyrolysis temperature is the most important variable, with temperatures between 400 and 500 °C resulting in maximum dipentene yields. Vacuum pyrolysis and basic additives have been propounded as a means of further improving this yield, but additional results are required to confirm this conclusively. Based on the presently available information in the literature, at least 2.5 wt% of a steel-free tire can be converted to dipentene. Finally, the literature has shown that it is not a trivial exercise to obtain a highly concentrated dipentene fraction of sufficient quality from the tire-derived oil. In particular, the removal of sulfur-containing compounds and the separation of dipentene from 1,2,3-trimethylbenzene, m- and p-cymene and indane are challenges that need to be addressed in the future.

The presented derivative thermogravimetric and mass spectral data, obtained simultaneously for the pyrolysis of three different tyre rubbers, corroborate the assumption that the devolatilisation of a tyre rubber proceeds via two consecutive zones of weight loss and that these zones are characterised by different products and thus different reactions. The spectral data of the depolymerisation products moreover confirm that depolymerisation occurs exclusively (in case of polyisoprene rubber) or predominantly (in case of the polybutadiene rubbers) during primary devolatilisation.

It is known that both acids and salts have a positive catalytic effect on the dehydration of pentoses to form furfural, a potentially attractive platform chemical. In this study the effects of the combined usage of an organic acid, instead of stronger mineral acids, and a saline catalyst is investigated. In order to assess these effects, the kinetics of pentose dehydration to furfural are studied using oxalic acid as the primary catalyst and NaCl or seawater as the secondary saline catalyst. The interactions between these two types of catalysts are complex and are, therefore, also assessed thermodynamically. The addition of salts lowers the activity coefficient of the hydronium ions, but simultaneously favours the dissociation of the organic acid. It turned out that these two effects are of similar magnitude, resulting in a fairly constant hydronium ion activity. Because nonetheless higher furfural yields are obtained using the salts as a secondary catalyst, it is concluded that the salts influence the pentose dehydration mechanism directly. The final furfural yields obtained using oxalic acid as the primary catalyst were only slightly lower than those for similar experiments using HCl. The most distinctive difference between the two acids is the lower reaction rate (and thus longer reaction times) when using oxalic acid. Finally, it was observed that if no acidic catalyst is used, the salts tend to catalyse a loss reaction, which is suppressed when an acid is present.

The pyrolytic devolatilisation behaviour of four rubbers, which are predominantly used in tyre manufacturing, has been studied using combined model-free and model-based kinetics. Natural rubber, synthetic polyisoprene, butadiene and styrene-butadiene rubbers were investigated experimentally using a TGA-DTA instrument. For all of these rubbers two distinct zones of weight loss (here termed as devolatilisation reactions) were observed, i.e., primary depolymerisation/condensation and secondary (consecutive) degradation of the condensed product. Moreover, the DTG and DTA results indicated that the two butadiene rubbers started to boil around 450 degrees C. Next, fixed values of the activation energy, derived from two different isoconversional methods, were implemented as fixed values in a model-based kinetic procedure. The values of the apparent activation energies for the rubber devolatilisation reactions were between 200 and 440 kJ mol(-1). This kinetic strategy resulted in a decrease of the degrees of freedom of the model-based multivariate nonlinear regression procedure. Therefore, the estimated kinetic parameters are less dependent on the initial guesses. Furthermore, the interdependence of the two consecutive devolatilisation reactions has also been successfully incorporated in the model, further improving the regression. This combined kinetic approach resulted in very accurate predictions of the experimental data. (C) 2014 Elsevier B.V. All rights reserved.

Furfural promises to be a very important product of the lignocellulosic feedstock biorefinery. In this study the kinetics of both xylose and arabinose dehydration toward furfural is investigated in a dilute acidic medium under three different salt conditions. These comprise no salts, a 500 mM NaCl solution, and seawater. The results demonstrate that the salts catalyze all disappearance reactions of the pentoses, both toward furfural and toward loss products. Especially at higher temperatures, the increase in the reaction rate toward furfural is larger than toward loss products. The values of the reaction rate constants at different salt conditions and temperatures indicate that different ions catalyze specific (temperature dependent) reactions in the dehydration mechanism of a pentose. Furthermore, the increase in the reaction rates is more pronounced with the combined salts naturally present in seawater compared to only NaCl, even at the same salinity and ionic strength. It is shown in additional experiments with no acid added that the observed salt effects are independent of the acidic environment. Furthermore, the effects of the salts are larger for the dehydration of xylose compared to arabinose. Moreover, for all temperatures the molar furfural yield was improved by the addition of the salts. Finally, it is shown that the salts inhibit furfural loss reactions toward formic acid. The presented results further contribute to the understanding of the effects of saline catalysis on the mechanism of pentose dehydration.

It is known that lower furfural yields are obtained for the dehydration of biomass resources compared to pure pentoses. In order to study this discrepancy, the dehydration of xylose (0.05 mol L-1) in complex saccharide solutions using homogeneous catalysts is investigated. Firstly, kinetic results are presented for the dehydration of both xylose and arabinose in separate experiments. In the second part, experimental results of the dehydration of xylose in complex saccharide solutions are compared with these kinetic models. It is observed that pentoses disappear similarly in complex saccharide solutions as they do separately. Furfural, however, is degrading faster in more complex saccharide solutions. Both the presence of pentose and hexose degradation products enhances furfural degradation, however, the effect of the latter was larger. These observations partly explain the lower furfural yields observed for the dehydration of actual biomass resources. (C) 2014 Elsevier Ltd. All rights reserved.

In this paper both the mechanistic and kinetic aspects of furfural formation from pentoses in aqueous acidic media have been reviewed. Based on the reviewed literature, a comprehensive reaction mechanism has been proposed consisting of more than one route, all starting from acyclic xylose, and involving alternately 1,2-enolization, β-elimination or isomerization via 1,2-hydride shift as key steps. Those studies that employ combined acid–base catalysts, soluble halide salts and trivalent cations in aqueous solutions appear to be most promising. Next, a detailed overview is presented of the results of kinetic studies on furfural formation from pentoses and furfural disappearance in aqueous acidic media. Although these results span over a very wide range of both experimental conditions and different kinetic models employed, an attempt has been made to present the published kinetic data in such a manner that it allows a global comparison. Since even in those cases where the reaction conditions seemed to be comparable, the reported kinetic constants often agree merely in the order of magnitude, thus, the validity of most of the data presented here is restricted to the specific conditions as used by each author. Additionally, a very concise overview is included of research on direct furfural production from lignocellulosic materials. In conclusion, the intricate set of reactions accompanying furfural formation from pentoses, although appearing well established in some aspects, is yet to be fully unraveled, especially with regard to the complex set of side and loss reactions seemingly involving largely unknown reaction intermediates. Such uncertainties are reflected in the contradictory kinetic models exploited and kinetic data presented in the literature, which still prevent a common and coherent interpretation.

•Degradation of pure furfural in an acidic and saline solution is accurately modeled both using first- and second-order kinetics.•Furfural is degrading significantly faster when glucose is present in the reaction mixture.•The influence of glucose on furfural degradation is best incorporated by addition of a second-order reaction.•A Diels–Alder reaction is propounded for the second-order degradation of furfural.