On Fractioning the Tire Pyrolysis Oil in a Pilot-Scale Distillation Plant under Industrially Relevant Conditions.

Tire pyrolysis oil (TPO) is one of the most interesting products derived from the pyrolysis of end-of-life tires. Among others, it contains valuable chemicals, such as benzene, toluene, ethylbenzene, and xylene (BTEX), as well as limonene. In order to recover these chemicals, a pilot-scale distillation plant has been designed, erected, and operated using TPO derived from an industrial-scale pyrolysis plant. The distillation facility consists of a packed column (20 kg/h) and is within the fifth technological readiness level. This work describes for the first time the fractioning of the TPO in a continuous operational mode under industrially relevant conditions. For this purpose, different reboiler temperatures (250-290 °C) and reflux ratios (up to 2.4) were preliminarily assessed on the yields and properties of the resulting products: light fraction (LF) and heavy fraction (HF). Thus, the distillation plant is capable of producing 27.0-36.7 and 63.3-73.0 wt % of LF and HF, respectively. The highest BTEX concentration in the LF (55.2 wt %) was found using a reboiler temperature of 250 °C and a reflux ratio of 2.4. Contrarily, the highest limonene concentration (4.9 wt %) in the LF was obtained at 290 °C in the reboiler without reflux. In this sense, the lower the reboiler temperature, the higher the BTEX, and the lower the limonene concentration in the LF. The main results herein obtained serve to gain key insights to operate packed distillation columns using complex and promising hydrocarbons as TPO in order to recover valuable products. In addition, this work provides significant information for optimizing the recovery efficiencies of both BTEX and limonene, as well as their potential applications including that for the resulting HF.

The role of temperature profile during the pyrolysis of end-of-life-tyres in an industrially relevant conditions auger plant.

Pyrolysis is a chemical recycling process of interest as a means to achieve a sustainable circular economy for end-of-life tyres (ELTs). In the pyrolysis process, ELTs are converted into tyre pyrolysis gas (TPG), tyre pyrolysis oil (TPO) and raw recovered carbon black (RRCB). This work investigates for the first time the effect of different temperature profiles by using a single-auger pyrolysis reactor in an industrially relevant scale (TRL-5). Since the development of this process at this representative scale is quite limited and the temperature profile has not been previously studied, the results achieved in this work can provide a useful database for the development of this process at industrial scale. For this purpose, two different sources of ELTs, commercial truck tyres (CTTs) and passenger car tyres (PCTs), were used. Accordingly, the experimental campaign was conducted using two different incremental temperature profiles (425-550-775 °C and 600-700-800 °C) based on those that can be replicated in an industrial-scale auger pyrolysis plant. For the sake of comparison, two isothermal heating conditions (500-500-500 °C and 600-600-600 °C) were also tested. The results confirmed the remarkable influence of temperature profile on both the distribution and properties of products. The 425-550-775 °C temperature profile was found to enhance limonene production, which is associated with the minimisation of secondary reactions in the first heating zone of the reactor. Additionally, there were very low carbonaceous deposits found in the RRCB because of the high severity of devolatilisation conditions in the third heating zone of the reactor. On the other hand, when the temperature profile was raised, the production of single-ring aromatics, particularly benzene, toluene, ethylbenzene and xylenes (BTEX) significantly increased in the TPO at the expense of limonene. Thus, from this strategy, it is possible to tune the properties of the products depending on the requirements of the application in a single step, getting closer for circular economy in the ELT recycling domain.

Incorporating the recovered carbon black produced in an industrial-scale waste tire pyrolysis plant into a natural rubber formulation.

This paper presents the experimental results obtained after incorporating the recovered Carbon Black (rCB) produced in an industrial-scale waste tire pyrolysis plant into a Natural Rubber (NR) formulation. The purpose of this study is to increase the technical knowledge on the use of rCB as a sustainable raw material in the rubber industry. The rCB and virgin Carbon Black (vCB) (ref. N550) under study were characterized using elemental and proximate analyses, X-Ray Fluorescence (XRF), Fourier Transform Infrared (FTIR) spectroscopy, and Scanning Electron Microscopy (SEM) were used, and different measures, including the Brunauer-Emmett-Teller (BET) surface area (SBET), particle size distribution (PSD), specific gravity, and pH, were estimated. The effect of rCB incorporation on the rheological, thermal, structural, and mechanical properties of the NR composites was assessed and compared to those obtained with vCB alone. The NR composites were prepared using different loads of vCB (20, 30, 40, and 50 phr), which was also replaced with rCB at different proportions (0, 50, and 100%). According to the characterization results, rCB offers lower reinforcement properties than vCB, which is attributable to its higher volatile matter and ash contents, higher apparent PSD, lower presence of acidic functional groups, and lower SBET. Despite this, interesting performances can be achieved when rCB is partially incorporated into the formulations or by increasing its load in the composites. For instance, when 50% of vCB was replaced with rCB, the values of the aforementioned properties were found to be between those obtained with the NR composites prepared with vCB and rCB. In addition, when increasing the rCB loading, some properties matched the behavior exhibited by vCB alone, thus compensating for the low reinforcement properties of rCB. These results are expected to provide an important impetus to move towards circular economy strategies having very positive impacts from the sustainable perspective.

Waste tire valorization by intermediate pyrolysis using a continuous twin-auger reactor: Operational features.

Pyrolysis can be regarded as a roadmap towards a circular and sustainable economy for waste tires (WT). This work investigates the operational characteristics of a novel twin-auger reactor to transform WT by intermediate pyrolysis into tire pyrolysis oil (TPO), recovery carbon black (rCB), and tire pyrolysis gas (TPG). The influence of four operating parameters: reactor temperature (X1), WT mass flow rate (X2), solid residence time (X3) and N2 volumetric flow rate (X4), was assessed in order to maximize the TPO yield (Y1), while keeping the rCB one (Y2) as low as possible. The experimental campaign was conducted based on central composite design (CCD). The analysis of variance (ANOVA) showed that X1 and X2 exhibit the highest statistical influence. An optimization of both responses resulted in TPO, rCB, and TPG yields of 45, 40 and 15 wt%, respectively, when the pyrolyzer is operated at 475 °C, 1.16 kg/h, 3.5 min and 300 mL/min. At these conditions, the resulting TPO showed contents of C, H, S, N and O around 88.2, 9.7, 1.3, 0.7 and <0.1 wt%, respectively, along with a heating value of 42.02 MJ/kg. The rCB is comprised of moisture, volatile matter, fixed carbon, and ash around 2.5, 3.7, 75.5, and 18.3 wt%, respectively; while the TPG was mainly composed of H2 (23.7 vol%) and CH4 (28.2 vol%). Overall, these results suggest that twin-auger pyrolyzers are well suited for valorizing WT by intermediate pyrolysis.

Pyrolysis kinetics of biomass wastes using isoconversional methods and the distributed activation energy model.

In this work, a thermogravimetric analyser was used to assess the pyrolysis kinetics of pineapple, orange and mango peel wastes and agro-industrial by-products, rice husk and pine wood. Five isoconversional methods (KAS, FWO, Starink, Vyazovkin and Friedman) and one model-fitting method (DAEM) accurately fitted the experimental data at three heating rates (5, 10 and 20 °C/min) between 10% and 90% conversion. These methods agree with the trends shown by the activation energy (Ea) distribution calculated, with fluctuations between 150 and 550 kJ/mol. The fluctuations of Ea in the whole range of conversion, in addition to a higher number of relevant reactions obtained by DAEM for fruit peel samples compared to agro-industrial samples, are associated with a higher extractive content in the peels. Kinetic parameters fitted by DAEM were successfully verified at the highest heating rate studied.

Carbon black recovery from waste tire pyrolysis by demineralization: Production and application in rubber compounding.

Pyrolysis offers the possibility to convert waste tires into liquid and gaseous fractions as well as a carbon-rich solid (CBp), which contains the original carbon black (CB) and the inorganic compounds used in tire manufacture. Whilst both liquid and gaseous fractions can be valorized without further processing, there is a general consensus that CBp needs to be improved before it can be considered a commercial product, seriously penalizing the pyrolysis process profitability. In this work, the CBp produced in a continuous pyrolysis process was demineralized (chemical leaching) with the aim of recovering the CB trapped into the CBp and thus, producing a standardized CB product for commercial purposes. The demineralization process was conducted by using cheap and common reagents (HCl and NaOH). In this sense, the acid treatment removed most of the mineral matter contained in the CBp and concentration was the main parameter controlling the demineralization process. An ash content of 4.9 wt% was obtained by using 60 min of soaking time, 60 °C of temperature, 10 mL/g of reagent/CBp ratio and HCl 4 M. The demineralized CBp (dCBp) showed a carbon content of 92.9 wt%, while the FRX analysis indicated that SiO2 is the major component into the ash. The BET surface area was 76.3 m2/g, and textural characterizations (SEM/EDX and TEM) revealed that dCBp is composed by primary particles lower than 100 nm. Although dCBp showed a low structure, the surface chemistry was rich in surface acidic groups. Finally, dCBp was used in Styrene Butadiene Rubber (SBR) compounding, probing its technical feasibility as substitute of commercial CB N550.

Demonstration of the waste tire pyrolysis process on pilot scale in a continuous auger reactor.

This work shows the technical feasibility for valorizing waste tires by pyrolysis using a pilot scale facility with a nominal capacity of 150 kWth. A continuous auger reactor was operated to perform thirteen independent experiments that conducted to the processing of more than 500 kg of shredded waste tires in 100 h of operation. The reaction temperature was 550°C and the pressure was 1 bar in all the runs. Under these conditions, yields to solid, liquid and gas were 40.5 ± 0.3, 42.6 ± 0.1 and 16.9 ± 0.3 wt.% respectively. Ultimate and proximate analyses as well as heating value analysis were conducted for both the solid and liquid fraction. pH, water content, total acid number (TAN), viscosity and density were also assessed for the liquid and compared to the specifications of marine fuels (standard ISO 8217). Gas chromatography was used to calculate the composition of the gaseous fraction. It was observed that all these properties remained practically invariable along the experiments without any significant technical problem. In addition, the reaction enthalpy necessary to perform the waste tire pyrolysis process (907.1 ± 40.0 kJ/kg) was determined from the combustion and formation enthalpies of waste tire and conversion products. Finally, a mass balance closure was performed showing an excellent reliability of the data obtained from the experimental campaign.

Production of activated carbon by waste tire thermochemical degradation with CO2.

The thermochemical degradation of waste tires in a CO(2) atmosphere without previous treatment of devolatilization (pyrolysis) in order to obtain activated carbons with good textural properties such as surface area and porosity was studied. The operating variables studied were CO(2) flow rate (50 and 150 mL/min), temperature (800 and 900 degrees C) and reaction time (1, 1.5, 2, 2.5 and 3h). Results show a considerable effect of the temperature and the reaction time in the porosity development. Kinetic measurements showed that the reactions involved in the thermochemical degradation of waste tire with CO(2), are similar to those developed in the pyrolysis process carried out under N(2) atmosphere and temperatures below 760 degrees C, for particles sizes of 500 microm and heating rate of 5 degrees C/min. For temperatures higher than 760 degrees C the CO(2) starts to oxidize the remaining carbon black. Activated carbon with a 414-m(2)/g surface area at 900 degrees C of temperature, 150 mL/min of CO(2) volumetric flow and 180 min of reaction time was obtained. In this work it is considering the no reactivity of CO(2) for devolatilization of the tires (up to 760 degrees C), and also the partial oxidation of residual char at high temperature for activation (>760 degrees C). It is confirmed that there are two consecutive stages (devolatilization and activation) developed from the same process.