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- A thermogravimetric study of HDPE conversion under a reductive atmospherePublication . Costa, Cátia S.; MUÑOZ, MARTA; Ribeiro, M. Rosário; Silva, JoãoThe plastic waste has suffered a dramatic increase and has become one of the biggest environmental problems nowadays. The chemical transformation of plastics by catalytic cracking under hydrogen atmosphere (hydrocracking) is one of the viable solutions to this problem since it can convert plastic residues into petrochemicals and fuels. In this work a thermogravimetric study of high-density polyethylene (HDPE) conversion under hydrogen atmosphere and in the presence of catalysts with different textural and chemical features is presented. The effect of distinct micro (H-ZSM-5, H-FER and H-MOR) and mesoporous (SBA-15 and MCM-41) catalysts is studied, both in terms of energy requirements and products distribution. Moreover, the effects of sample preparation method, catalyst amount, Si/Al ratio and incorporation of a metallic function (Ni and Pt) are also analyzed. The results show that when MCM-41 and SBA-15 mesoporous silicas are added to HDPE no significant changes are observed in terms of the degradation profile. On the contrary, the use of microporous materials decreases significantly the onset of HDPE degradation temperature. The accessibility and acidic content of the materials proved to be the most important factors influencing the HDPE degradation profiles. Moreover, the introduction of a metal function results in a further shift to lower degradation temperatures and favors the liquid products distribution, promoting the formation of gasoline and diesel.
- Induction heating in nanoparticle impregnated zeolitePublication . Morales Casero, Irene; MUÑOZ, MARTA; Costa, Catia S.; Alonso, Jose Maria; Silva, João M.; Multigner, Marta; Quijorna, Mario; Ribeiro, M. Rosário; De La Presa, PatriciaThe ultra-stable Y (H-USY) zeolite is used as catalyst for the conversion of plastic feedstocks into high added value products through catalytic cracking technologies. However, the energy requirements associated with these processes are still high. On the other hand, induction heating by magnetic nanoparticles has been exploited for different applications such as cancer treatment by magnetic hyperthermia, improving of water electrolysis and many other heterogeneous catalytic processes. In this work, the heating efficiency of gamma-Fe2O3 nanoparticle impregnated zeolites is investigated in order to determine the potential application of this system in catalytic reactions promoted by acid catalyst centers under inductive heating. The gamma-Fe2O3 nanoparticle impregnated zeolite has been investigated by X-ray diffraction, electron microscopy, ammonia temperature program desorption (NH3-TPD), H-2 absorption, thermogravimetry and dc and ac-magnetometry. It is observed that the diffusion of the magnetic nanoparticles in the pores of the zeolite is possible due to a combined micro and mesoporous structure and, even when fixed in a solid matrix, they are capable of releasing heat as efficiently as in a colloidal suspension. This opens up the possibility of exploring the application at higher temperatures.
- H-USY and H-ZSM-5 zeolites as catalysts for HDPE conversion under a hydrogen reductive atmospherePublication . Costa, Cátia S.; MUÑOZ, MARTA; Ribeiro, M. Rosário; Silva, João MThe rapid increase in the consumption of plastic caused by the abrupt growth in living standards had a noticeable effect on the plastic waste generated. Consequently, a significant number of solutions have been proposed to address this issue, with catalytic cracking under H-2 atmosphere being one of the most promising ones. In this study, the catalytic conversion of HDPE under a reductive atmosphere was evaluated by thermogravimetric analysis using large and medium pore zeolites (H-USY and H-ZSM-5, respectively) with distinct Si/Al ratios as catalytic systems. The effect of adding a metallic source to zeolites was also analyzed in this work. Results show that high temperatures are required to convert HDPE (433-480 degrees C). However, the energy requirements can be reduced by adding a zeolite catalyst to the process. In this case, the H-USY zeolite was the most efficient catalytic system for HDPE degradation, allowing for a reduction of around 169 degrees C to the onset degradation temperature. The accessibility of this large pore zeolite, together with its acidic character, seems to have a determining role on the reaction. The addition of a Ni metallic source to H-USY and H-ZSM-5 led to further reduction on energy inputs. Moreover, the liquid product distribution for H-USY was shifted to lighter fractions.