Waste tire valorization by pyrolysisproduction and application of the products

Resumen

Pyrolysis seems to be more attractive in comparison with other thermochemical processes to tackle the waste tire (WT) disposal problem because of its minor environmental impact and the recovery of liquid and solid materials of high added-value. However, the practical applicability of these products has been rather limited. Finding practical uses for these products represents a major challenge that may be addressed from realistic, robust and practical processes. This means (i) performing long-term experiments by using a pilot and scalable plant for demonstrating the technical feasibility of the WT pyrolysis process, (ii) proving realistic alternatives to incorporate the pyrolysis products into current markets, and (iii) exploring the production of secondary products of high potential such as syngas. In order to achieve these goals, a continuous auger reactor at pilot scale has been used to demonstrate the process stability and reproducibility in terms of the product yields and their properties, in a long-term experimental campaign accounted by 100 hours of operation. The temperature reaction was 550 °C and the yields to solid, liquid and gas were 40.5 ± 0.3, 42.6 ± 0.1 and 16.9 ± 0.3 wt.% respectively. Similarly, some of their main properties remained practically invariable along the experimental campaign and significant technical problems were not evidenced. With the obtained results a mass and energy balances for an industrial-scale plant (5000 ton/y of WT) were solved and a possible energy integration of the process to achieve an autonomous system was proposed. Likewise, the pyrolytic products obtained were characterized and used in realistic alternatives. The current dependence on fossil fuels and their rapid depletion, together with the disposal problem of the WTs, makes quite attractive to research the use the liquid fraction as a counterpart of diesel fuel and the solid fraction as substitute of virgin carbon black. For this, it was performed a complete characterization as fuel of the liquid fraction, herein named TPL (tire pyrolysis liquid), and its blends with commercial diesel fuel (D). The most critical properties of TPL compared to D were density, cold filter plugging point (CFPP), calculated cetane index (CCI), water content, total acid number (TAN) and sooting tendency. Similarly, sulfur content was also critical. In this sense, blending strategies between TPL and D, may help to reduce these limitations, and for this reason, TPL could represent a feasible alternative as counterpart of diesel fuel as long as it is blended in low concentrations. For example, a 5 vol.% of TPL and 95 vol.% of D keep some of these properties within the range set in the European standard EN 590 (CFPP, water content and TAN). Although, other aspects such as density and sulfur content did not fulfill the limits established in the standard, the practical use of this blend in diesel engines can be considered as a realistic application and also crucial not only to show the trend of both emissions and engine performance (and thus to estimate the potential usage of TPL) but also to reveal the scope of some upgrading process for the TPL. In this way, 5TPL was fueled in an automotive diesel engine under stationary and transient conditions. Although some regulated and unregulated emissions were worst than those found using diesel fuel, for example smoke opacity, particle matter and total hydrocarbons (THC), the experimental campaign proved the feasibility for using TPL blended with diesel fuel without any constructive modification in the engine. The low-volatile fraction and the sulfur content are the major issues that should be faced to upgrade the TPL. Furthermore, the solid fraction, herein named CBp (pyrolytic carbon black), was submitted to a demineralization process and used in rubber formulations. The mineral matter presence in CBp represents an inert load and consequently does not contribute to its reinforcement properties. After demineralization, the ash content in CBp was reduced in 67 % by using a commercial and cheap reagent such HCl. This treatment also led to the introduction of some acidic functional groups onto the surface of the new CBp which enhanced the CBp properties as a reinforcement filler for rubber compounding. The mechanical properties of the rubber vulcanizes did not show a significant detriment when the upgraded CBp was used as a filler. In fact some mechanical properties were improved and hence it can be used for rubber formulation. Finally, the volatiles released in the WT pyrolysis were characterized in order to find out the maximum limit on syngas composition when they are submitted to an air¿steam partial oxidation process. The stoichiometric equilibrium model showed that equivalence ratios (ERs) lower than 0.4 leads to interesting performance parameters and attractive syngas concentrations for power generation through internal combustion engines. This thermodynamic analysis provides essential data on the optimization of syngas production from volatiles released in WT pyrolysis prior to run any test. Thus, this thesis pretends being considered as an important contribution for strengthening and encouraging the WT pyrolysis process as an attractive alternative for its recycling.