Belén Lobato

Distillation of granulated scrap tires in a pilot plant

This paper reports the pyrolytic treatment of granulated scrap tires (GST) in a pilot distillation unit at moderate temperature (550°C) and atmospheric pressure, to produce oil, char and gas products. Tire-derived oil is a complex mixture of organic C(5)-C(24) compounds, including a very large proportion of aromatic compounds. This oil has a high gross calorific value (∼ 43 MJ kg(-1)) and N and S contents of 0.4% and 0.6%, respectively, falling within the specifications of certain heating fuels. The distillation gas is composed of hydrocarbons; methane and n-butane are the most abundant, investing the distillation gas with a very high gross calorific value (∼ 68 MJ Nm(-3)). This gas is transformed into electric power by a co-generation turbine. The distillation char is mostly made of carbon but with significant inorganic impurities (∼ 12 wt%). The quality of the solid residue of the process is comparable to that of some commercial chars. The quantity of residual solids, and the qualities of the gas, liquid and solid fractions, are similar to those obtained by conventional pyrolytic treatments of waste tires. However, the simplicity of the proposed technology and its low investment costs make it a very attractive alternative.

Reduced graphite oxide in supercapacitor electrodes.

The current energy needs have put the focus on highly efficient energy storage systems such as supercapacitors. At present, much attention focuses on graphene-like materials as promising supercapacitor electrodes. Here we show that reduced graphite oxide offers a very interesting potential. Materials obtained by oxidation of natural graphite and subsequent sonication and reduction by hydrazine achieve specific capacitances as high as 170 F/g in H2SO4 and 84F/g in (C2H5)4NBF4/acetonitrile. Although the particle size of the raw graphite has no significant effect on the physico-chemical characteristics of the reduced materials, that exfoliated from smaller particles (<75 μm) result more advantageous for the release of the stored electrical energy. This effect is particularly evident in the aqueous electrolyte. Graphene-like materials may suffer from a drop in their specific surface area upon fabrication of electrodes with features of the existing commercial devices. This should be taken into account for a reliable interpretation of their performance in supercapacitors.

Gasification of the char derived from distillation of granulated scrap tyres

This work reports the effect of pressure on the steam/oxygen gasification at 1000°C of the char derived from low temperature-pressure distillation of granulated scrap tyres (GST). The study was based on the analysis of gas production, carbon conversion, cold gas efficiency and the high heating value (HHV) of the product. For comparison, similar analyses were carried out for the gasification of coals with different rank. In spite of the relatively high ash (≈12 wt.%) and sulphur (≈3 wt.%) contents, the char produced in GST distillation can be regarded as a reasonable solid fuel with a calorific value of 34MJkg(-1). The combustion properties of the char (E(A)≈50 kJ mol(-1)), its temperature of self-heating (≈264°C), ignition temperature (≈459°C) and burn-out temperature (≈676°C) were found to be similar to those of a semi-anthracite. It is observed that the yield, H(2) and CO contents and HHV of the syngas produced from char gasification increase with pressure. At 0.1 MPa, 4.6 Nm(3)kg(char)(-1) of syngas was produced, containing 28%v/v of H(2) and CO and with a HHV around 3.7 MJ Nm(-3). At 1.5 MPa, the syngas yield achieved 4.9N m(3)kg(char)(-1) with 30%v/v of H(2)-CO and HHV of 4.1 MJ Nm(-3). Carbon conversion significantly increased from 87% at 0.1 MPa to 98% at 1.5 MPa. It is shown that the char derived from distillation of granulated scrap tyres can be further gasified to render a gas of considerable heating value, especially when gasification proceeds at high pressure.

Large-scale conversion of helical-ribbon carbon nanofibers to a variety of graphene-related materials

Helical-ribbon carbon nanofibers produced on an industrial scale were successfully converted in highly functionalized graphene nanoplatelets by using a slight modification of the Hummers oxidation method. The duration of the oxidative process severely affected the interlayer spacing in the resulting nanoplatelets and, consequently, they showed very different exfoliation behavior. Therefore, it was possible to obtain a variety of graphene-related products through their ultrasonication or thermal treatments such as exfoliation-reduction by flash-pyrolysis in air at temperatures between 400 and 1000 °C or standard activation with CO2 at 800 °C. Detailed comparison of the functionalized carbon nanoplatelets, graphene oxides, reduced graphene oxides and activated carbon nanoplatelets reveals the wide spectrum of their properties with specific surface areas in the range of 4–500 m2 g−1, oxygen content from 38 to 5 wt% and different structural ordering. This study also underlines the impact of the structural, textural and chemical changes experienced by the carbon nanofibers along the various processes on the performance as supercapacitor electrodes. This preliminary study, based on cyclic voltammetry in 2 M H2SO4 aqueous electrolyte, is a summary of the strengths and weaknesses of the different graphene-related materials for this application. The helical-ribbon carbon nanofibers displayed only 10 F g−1, the capacitance of the functionalized graphene nanoplatelets greatly rose to 104 F g−1 with clear contributions from pseudocapacitance. Values around 100–120 F g−1 were found for the graphene oxides and activated graphene nanoplatelets although a marked resistive character is detected. Flash-pyrolysis at 1000 °C leads to lower capacitance (79 F g−1) but much quicker charge propagation. Among all these materials, the lower-cost functionalized graphene nanoplatelets displayed the better behavior for aqueous supercapacitors.